JP5078131B2 - Absorbent composite with ultrafast absorption capability - Google Patents

Description

  The present invention relates to an absorbent composite using a water absorbent resin having a specific shape. More specifically, the present invention relates to an absorptive composite that has both the performance of absorbing body fluid at high speed and the performance of high absorption power while being thin. This water-absorbent composite can be suitably used in various applications including sanitary materials such as paper diapers, sanitary napkins, and incontinence pads.

  In recent years, a water-absorbing resin that gels by absorbing a large amount of water has been developed as a kind of synthetic polymer, and is widely used in the field of sanitary materials such as disposable diapers and sanitary napkins, agriculture and forestry, and civil engineering. Yes. Examples of such a water-absorbing resin include a crosslinked polyacrylic acid partially neutralized product (see, for example, Patent Document 1), a hydrolyzate of starch-acrylonitrile graft polymer (see, for example, Patent Document 2), and starch-acrylic acid graft weight. Neutralized product of polymer (for example, see Patent Document 3), saponified product of vinyl acetate-acrylic acid ester copolymer (for example, see Patent Document 4), hydrolyzate of acrylonitrile copolymer or acrylamide copolymer (for example, Patent Document) Many are known. The properties that these water-absorbent resins should have include conventionally a high water absorption ratio and excellent absorption rate when in contact with aqueous liquids such as body fluids, liquid permeability, gel strength of swollen gels, and groups containing aqueous liquids. A suction amount for sucking water from the material is required.

  In recent years, the demand for disposable diapers for the elderly has been increasing with the increase in the average lifespan. Furthermore, in recent years, there has been a growing demand for thinner and lighter sanitary materials due to design problems, distribution problems, and dust problems. In order to cope with this, as a method generally used in the current sanitary material, there is a method in which the water-absorbing resin supporting carrier in the sanitary material such as fiber is reduced and a large amount of the water-absorbing resin is used. Hygienic materials with a low ratio of hydrophilic fibers and an increased water-absorbing resin are preferable from the standpoint of simply storing liquids. The problem is that the performance of the system is degraded. That is, there is a problem that a large amount of water-absorbing resin becomes a soft gel by water absorption, which causes a phenomenon of so-called gel blocking that greatly hinders liquid diffusion. For this reason, the water-absorbing resin used preferably has a high gel strength in order to prevent gel blocking. However, in general, a water-absorbing resin having a high gel strength has a low water retention because the number of cross-linking points between polymer chains increases. Therefore, a large amount of water-absorbing resin is used in such an absorbent body in order to supplement the water retention capacity.

  In addition, as a means for reducing fibers and preventing gel blocking that occurs when a large amount of water-absorbent resin is used, a method using two types of water-absorbent resins having different water absorption performances (see, for example, Patent Document 6), and cationic property. A method using a composition containing an ion-exchange hydrogel-forming polymer and an anionic ion-exchange hydrogel-forming polymer (see, for example, Patent Document 7), a method using a water-absorbent resin having a high surface crosslinking density (see, for example, Patent Document 8) )), A method of foaming and extruding a mixture of a water-absorbent resin and a thermoplastic resin (see, for example, Patent Document 9) has been proposed, but in either case, two types of resins are used, It is necessary to use special resins such as anionic ion exchange hydrogel-forming polymers, and as a result, resins with low water retention must be mixed. Because, there is a need to introduce a large amount of resin as the water-absorbing agent.

  These problems and methods for fixing a water-absorbent resin to a support carrier have also been studied. For example, a method of embossing the absorber, a method of including a thermoplastic binder fiber in an absorber composed of a water-absorbent resin and a hydrophilic fiber, and heat-sealing the absorber, a synthetic resin having a high recovery rate from strain A method of heat-sealing an absorbent body by containing it in an absorbent body composed of a water-absorbent resin and a hydrophilic fiber (see, for example, Patent Document 10 and Patent Document 11), and the surface of a water-absorbent resin having an anionic group is cationic. A method of coating a polymer and adhering and fixing particles through swelling (for example, see Patent Document 12 and Patent Document 13), a method of fixing a water-absorbent resin and a hydrophilic fiber using an emulsion binder, A method of fixing a water-absorbent resin to a substrate using a hot melt adhesive (for example, see Patent Document 14 and Patent Document 15). It is possible to use a resin with a relatively low degree of cross-linking with high water retention capacity in these methods, and it is possible to reduce the amount of resin used, but as a result, the water absorption speed as an absorber is reduced and the weight is reduced. In the thin state, there is a problem that leakage occurs when body fluid is introduced.

  In order to eliminate leakage at the time of body fluid injection with a light and thin absorbent body, it is necessary that the body fluid in contact with the water-absorbing resin is instantaneously absorbed into the resin and the water retention capacity of the resin is high. As a water-absorbing resin having a high water absorption rate, a water-absorbing resin having a particle size of several tens of microns, which is solidified with a water-absorbing resin to have a particle diameter of several hundred microns is used. In order to fix this resin without using a bulky material such as pulp, there are methods of fixing it to a cloth with an adhesive or putting it in a bag. However, if an adhesive is used, the particle surface is covered with a hydrophobic adhesive, resulting in a decrease in liquid permeability, resulting in a decrease in speed. When you put it in a bag, you need a certain amount of water-absorbing resin to absorb a large amount of liquid, but if you use a large-capacity bag to accommodate this, there will be a problem of bias, and many bags will be prepared As a result, the thickness will eventually increase. After all, it can be said that the amount of body fluid input that can be used as an absorbent body that does not leak with the amount of water-absorbing resin that can be fixed by the bag structure is about 15 cc.

Thus, when a large amount of body fluid is introduced, an absorbent body that can prevent leakage in a state where the bulk of pulp or the like is not used in a large amount has not been obtained so far.
JP 55-84304 A Japanese Patent Publication No.49-43395 Japanese Patent Laid-Open No. 51-125468 JP-A-52-14689 Japanese Patent Publication No.53-15959 JP 2001-252307 A International Publication No. 98/037149 Pamphlet Japanese Patent Laid-Open No. 06-057010 International Publication No. 01/64153 Pamphlet JP-A-10-118114 JP-A-10-118115 JP-A-5-31362 JP-A-6-370 JP 2000-238161 A Japanese National Patent Publication No. 10-510447

  The objective of this invention is providing the absorber which is lightweight and thin and can prevent a leak.

  As a result of intensive studies to achieve the above object, the inventors of the present invention are particularly excellent in liquid capturing ability by adhering a resin having a relatively low bulk specific gravity to a substrate with a predetermined structure. The present inventors have found that an absorbent body can be obtained, and have completed the present invention.

That is, the present invention includes the following [1] to [9].
[1] An absorptive composite comprising a base material and a particulate water-absorbing resin bonded to each other and satisfying the following conditions.
(1) The bulk specific gravity of the resin is 0.65 or less.
(2) The bending resistance change rate is 60% or less.
(3) At least one substrate is composed of hydrophilic fibers.
(4) 50% or more of the water absorbent resin is directly bonded to the base material.
(5) The residual monomer in the water absorbent resin is 200 ppm or less.
(6) The ratio of the water absorbent resin weight to the total weight of the absorbent composite is 50 to 99%.
(7) The surface of the water absorbent resin has a nonionic surfactant of HLB7 or higher.
[2] The hollow granular water-absorbing resin having a space in the resin, wherein the thickness of the hollow granular water-absorbing resin film is 1 to 30 μm. Absorbable complex.
[3] The absorbent composite according to [1] or [2], wherein the water absorbent resin has an average particle diameter of 5 to 1000 μm.
[4] The absorbent composite as described in [ 2 ] to [3], wherein the content of carboxyl group-containing units in the polymer molecular chain of the hollow granular water-absorbent resin is 50 mol% or more.
[5] The absorbent composite as described in any one of [ 2 ] to [4], wherein 50% or more of the carboxyl group-containing units in the polymer molecular chain of the hollow granular water-absorbent resin is a neutralized salt.
[6] The absorbent composite as described in any one of [5] , which is a 10 to 80 mol% ammonium salt among carboxyl group neutralized salt units in the polymer molecular chain of the hollow granular water-absorbent resin.
[7] A method for producing an absorbent composite comprising a base material and a particulate water-absorbent resin bonded together, wherein the following conditions are satisfied: The manufacturing method of an absorptive composite body including the process of spin-drying | dehydrating in the state which made the base material and the water absorbing resin particle contact after making a base material absorb water.
(1) The bulk specific gravity of the resin is 0.65 or less.
(2) The bending resistance change rate is 60% or less.
(3) At least one substrate is composed of hydrophilic fibers.
(4) 50% or more of the water absorbent resin is directly bonded to the base material.
(5) The residual monomer in the water absorbent resin is 200 ppm or less.
(6) The ratio of the water-absorbing resin weight to the total weight of the absorbent composite is 50 to 99%.
(7) The surface of the water absorbent resin has a nonionic surfactant of HLB7 or higher.
[8] The method for producing an absorbent composite according to [8], wherein the resin is an aggregate of particles and includes a step of applying a load to the resin before dehydration drying.
[9] The method for producing an absorbent composite according to [7] or [8], further comprising a step of lowering the stiffness of the absorbent after drying.

  Since the absorbent composite of the present invention has a high water absorption rate and high water retention, when used as an absorbent layer of a lightweight and thin absorber, a large amount of pulp or the like can be used without using a large amount of material. Even if the bodily fluids are added all at once, the absorber does not leak.

The present invention will be described in detail below.
1. Structure / Performance of the Composite of the Present Invention In the present invention, a structure obtained by bonding a water-absorbent resin and a substrate is called an absorbent composite. Resin does not change position and has excellent shape stability. Therefore, the base material can maintain the sheet shape.
The absorbent composite can be reduced in weight and thickness by not using a large amount of bulky material such as pulp for fixing the resin. It is preferable to mix the absorbent composite with short fibers such as pulp and other sheet-like materials to adjust the performance as an absorber. The feature of the absorbent composite of the present invention is that the hardness of the absorbent is lowered after a water-absorbing resin having a bulk specific gravity of 0.65 or less is adhered to a hydrophilic substrate. In general, a resin with a low specific gravity and a large surface area has a very fast initial water absorption rate, but if the particle surface is over a certain size, the particle surface becomes soft and the liquid flow into the interior becomes poor when the particle surface contains water. A blocking phenomenon occurs in this case, and a sufficient speed cannot be obtained. By adhering to a hydrophilic base material, the influence of intra-particle blocking was reduced by passing the liquid from the fiber to the inside of the resin, and ultrahigh-speed absorption became possible. Moreover, when the composite_body | complex became too hard compared with the base material, it discovered that an absorption rate fell remarkably. This is because when the composite is hard, the resin adheres to each other when the base material and the resin are adhered, and the resin adheres to each other, so that the liquid permeability between the resins decreases or the hydrophilicity that should work as a liquid passage This is considered to be due to the deterioration of the fibers and the impediment to liquid passage to the resin. High-speed absorption became possible by softening the hardness of the composite by physical or chemical methods.

  The resin may have a specific bulk density or less, that is, it may have a certain surface area, but is a hollow granule having a space inside, and a specific structure in which the resin has a thickness of 1 to 30 μm. It is preferable to have. This resin is particularly excellent in water retention and absorption rate. Moreover, it is possible to quickly get a dry feeling by absorbing the liquid at high speed. In order to adjust various performances of the absorber, a resin having a bulk specific gravity of 0.65 or more can be used in combination, but at least 30 wt% of the total water-absorbing resin used from the viewpoint of speed. Has a specific structure, more preferably 50 wt% or more, still more preferably 70% or more, and most preferably 90 wt% or more. It is preferable that the average bulk specific gravity of all the water-absorbent resins is 0.65 or less. It is preferable to use a resin having a hollow structure of 30 wt% or more of the total water-absorbing resin, more preferably 50 wt% or more, still more preferably 70% or more, and most preferably 90 wt% or more.

  It is not necessary for all the water-absorbing resins to be fixed, but in order to prevent performance degradation due to extreme bias, the non-fixed water-absorbing resin is 50% or less of the total water-absorbing resin weight. Preferably, it is preferably 30% or less, more preferably 10% or less, and most preferably 5% or less.

In the present invention, since the substrate is in the form of a sheet, one substrate has a front surface, a back surface, and two planes. In this invention, it is preferable that the average basic weight of the water absorbing resin with respect to the plane of a base material is 10-150 g / m < ² >. If a large amount of resin is arranged on one plane too much, blocking problems may occur at the time of water absorption, and the water absorption speed may be lowered, which is not preferable. In order to require higher absorption capacity and speed, when increasing the amount of water-absorbing resin used, use a plurality of absorbent composites or increase the number of base materials, It can be handled by increasing the number. In the absorbent composite of the present invention, the water absorbent resin layer adhered to the plane of the substrate is referred to as a water absorbent resin layer. When n base materials are used, it is possible to have n-1 to n + 1 water-absorbing resin layers.

  It is preferable that the water absorbent resin is bonded to the base material because the water absorbent resin can be prevented from moving during transportation or liquid absorption. The bonding method is not particularly limited, but a method that does not use an adhesive is preferable, and it is more preferable to bond in a form in which a part of the fibers of the base material is incorporated in the water-absorbent resin. It is preferable that 50% by weight or more of the water-absorbing resin in the bonded water-absorbing resin is bonded in a form in which a part of the fiber is taken into the water-absorbing resin, more preferably 70% by weight or more. Preferably, 90% by weight or more, most preferably 95% by weight or more of the water-absorbing resin is bonded in this form. If an adhesive is not used, it is preferable because it is not subjected to swelling regulation during liquid absorption. It is preferable that a part of the fibers are bonded in a form incorporated in the water-absorbent resin because the liquid can be fed into the water-absorbent resin through the fibers and the absorption speed is improved.

  Among various performances, there is a demand for a low residual monomer amount that is regulated in the voluntary standards for water-absorbing resins of the Japan Sanitary Materials Industry Association. The residual monomer of the resin in the absorbent composite of the present invention is preferably 200 ppm or less, more preferably 100 ppm or less, and even more preferably 50 ppm or less. This is a value that is difficult to achieve by a polymerization method on a resin base material used in a general base material-resin direct bonding method. It is preferable to polymerize a resin to be used in advance and use a resin having a predetermined low residual monomer state as a resin for the composite. It is preferable to use as the water-absorbent resin a resin that has been polymerized in an aqueous solution and the resulting mass is granulated in a process including a crushing process, or a particle aggregate that has been polymerized in advance by a reverse phase suspension polymerization method. .

The bendability of the absorbent composite of the present invention is preferably soft. When it is too hard, the absorption rate is lowered, and it is not preferable in terms of texture. The hardness of an absorptive composite can be expressed as a rate of change in stiffness compared to the hardness of the composite and the hardness of the substrate. Specifically, the bending resistance of the base material and the composite is measured by the bending resistance D method (Heart Loop method) described in JIS standard L1096, compared, and determined by the following equation.
(formula)
Flexural change rate = (base stiffness-composite stiffness) * 100 / base stiffness When multiple substrates are used, the stiffness of the substrate in a state where multiple substrates are stacked Measure softness. When the particle size and distribution of the particles are different between the front and the back, the values are different, but in the present invention, the harder, that is, the smaller value is regarded as the bending resistance. The bending resistance change rate is preferably 60% or less, more preferably 50% or less, still more preferably 40% or less, still more preferably 30% or less, and even more preferably 20% or less. Most preferred. From the viewpoint of texture, the stiffness of the composite is preferably 3 cm or more, more preferably 4 cm or more, still more preferably 5 cm or more, and most preferably 6 cm or more. When manufacturing the absorbent composite, it is also preferable to adjust the conditions so that the bending resistance does not become hard, and it is also preferable to soften the hardened composite later. The means for softening is not particularly limited, and for example, a softening agent is used or physical force is applied.

2. About adhesion In the present invention, the adhesion between the base material and the water absorbent resin means that the water absorbent resin is fixed to the base material, and the positional relationship between the base material and the water absorbent resin does not substantially change. Represent. In the present invention, holding one side of the absorbent composite by hand, shaking in the direction of the side in a state where the plane direction of the composite is vertical, swinging for 1 minute at a speed of one reciprocation per second with a width of 20 cm, Assume that particles that are not detached are adhered. The detached particles are considered to be mixed in the absorbent complex and are not included in the absorbent complex. There is no problem even if the absorbent composite is mixed with an unbonded water-absorbing resin that is detached in this test, but the unbonded water-absorbing resin is 50% of the weight of the absorbent composite. Or less, more preferably 30% or less, still more preferably 10% or less, and most preferably 1% or less. If the positional relationship between the base material and the water-absorbent resin does not change, the performance of the absorbent composite does not change due to transportation before use or the like, which is preferable from the viewpoint of repeated liquid absorption.

  In the present invention, there are no particular restrictions on the form of adhesion to the entire water-absorbent resin, but it is preferable that 50% or more of the water-absorbent resin is directly adhered to the substrate. Adhesion by an adhesive, adhesion by chemical bonding between a substrate and a water absorbent resin, adhesion by physical interaction, adhesion in a form in which fibers are contained in the water absorbent resin, or the like may be used. Examples of the adhesive include thermoplastic fibers and polymers, emulsion binders, and hot melt adhesives. Use of an adhesive is not preferable because swelling regulation by the adhesive usually works and the absorption rate and the amount of absorption decrease. However, in the present invention, since a thin resin is used, the ratio of the portion that comes into contact with the adhesive is small, so that it is difficult to be subject to swelling regulation. If a large amount of adhesive is used, the influence of swelling regulation may occur. Therefore, it is preferable that 50% by weight or more of the water-absorbing resin used is in a form in which the substrate and the resin are in direct contact. More preferably 75% or more, still more preferably 95% or more, and most preferably 99% or more is directly adhered. Here, “directly bonded” refers to bonding without using a base material such as an adhesive, water absorbent resin particles, or components other than these components. However, in the case where an adhesive is used together to such an extent that swelling control does not occur, it is included in direct adhesion. The ratio of the particles that are directly bonded can be determined by measuring the amount of water-absorbing resin particles that are still bonded after the absorbent composite is immersed in a solvent that dissolves the adhesive for 1 hour.

The direct bonding method is not particularly limited, and may be adhesion by chemical bonding between the substrate and the water-absorbent resin particles, adhesion by physical interaction, adhesion in a form in which fibers are contained in the water-absorbent resin, or the like.
Among these, adhesion in a form in which fibers are contained in the water absorbent resin is preferable. Specifically, it is preferable that 50% by weight or more of all water-absorbing resin particles are bonded in a form in which fibers are taken into the water-absorbing resin. Preferably, 60% by weight or more, more preferably 70% by weight or more, and still more preferably 90% by weight or more of particles are adhered in this form.

  The form in which the fibers are contained in the water absorbent resin represents a state in which the fibers in the substrate are present in the water absorbent resin matrix. The shape and length of the fibers that enter are not particularly limited. When bonded in this form, water can be taken into the water-absorbent resin through the fiber, so that excellent performance is exhibited in terms of absorption amount and absorption speed. It can be confirmed with an electron microscope whether or not the fibers are bonded in the form of entering the water-absorbent resin. Any 30 adhered particles can be extracted, peeled off, and observed with an electron microscope to determine the ratio.

  The resin may be bonded to only one side of the substrate, or may be bonded to both sides of the substrate. Since the amount of particles that can be arranged on one plane is limited, when a faster absorption rate and a larger amount of absorption are required, and it is necessary to increase the amount of resin to be used, it is preferable to arrange them on both sides. Further, when it is desired to increase the amount of resin to be used, it is preferable to use a plurality of absorbent composites in order to increase the resin layer. When processing becomes complicated by using multiple absorbent composites, it is possible to integrate multiple absorbent composites with an adhesive. The liquid permeability between the absorbent composites may be deteriorated depending on the agent. In this case, it can be improved by bonding the substrates to each other through one resin layer. That is, when the number of base materials is an arbitrary number n, it is preferable to use an integral absorbent composite having n−1 to n + 1 resin layers. In the case of using a plurality of substrates, it is not necessary that all the substrates are hydrophilic fibers, and they can be used properly according to the purpose. When it is desired to prevent leakage to the outside, it is preferable to use a hydrophobic substrate on the outermost side. However, from the viewpoint of ensuring liquid permeability between resin layers, one resin layer is preferably in contact with at least one hydrophilic substrate, and more preferably is in contact with two hydrophilic substrates.

  The higher the value of the number of hydrophilic substrates / the number of water-absorbing resin layers, the greater the contribution of the hydrophilic substrate to the resin layer, so the absorption rate can be increased efficiently. The value of the number of hydrophilic substrates / the number of water-absorbing resin layers is preferably 1.3 or more, more preferably 1.5 or more, and most preferably 2.

The surface of the absorbent composite in the present invention refers to a flat surface that is exposed to the outside. All absorbent composites have two surfaces. The resin present on the surface may be detached when a force is applied after swelling. For this reason, in applications where desorption is not preferred, it is preferable to limit the amount of resin on the surface. By reducing the amount of resin per plane, the base material area for one particle increases, so that the adhesive strength can be increased. The smaller the amount of resin on the surface of the absorbent composite, the better. Specifically, it is preferable that an average basis weight of 0~20g / ^{m 2,} more preferably 0 to 10 g / ^{m 2,} more preferably from 0~5g / ^{m 2,} 0~1g / M ² is most preferred.

3. About average basis weight of resin The average basis weight in the present invention is defined as the weight per unit area of the water-absorbent resin in one plane. The weight of the water-absorbent resin is measured with all particles removed. The average basis weight is preferably 10 to 150 g / ^{m 2,} more preferably from 30~130g / ^{m 2,} more preferably from 40 to 120 g / ^{m 2,} in 50~110g / ^{m 2} More preferably, it is most preferably 60 to 90 g / m ² . If the basis weight of the resin is too small, it is difficult to completely transfer the liquid in the substrate to the resin, which may cause the liquid to return. If the basis weight of the resin is too large, the amount of the resin that is not in contact with the base fiber increases, which may be affected by blocking. When a larger amount of resin is required, it can be handled by increasing the plane. Also in this case, it is preferable that the amount of resin in the plane between the base materials satisfies the above range.

4). Water-absorbent resin The water-absorbent resin of the present invention preferably has a bulk specific gravity of 0.65 or less. This resin may be any resin, but is preferably a high-speed absorption resin having an absorption time of 10 seconds or less in the vortex method.

  First, the absorbent resin that constitutes the absorbent resin particles in the present invention will be described. As the absorbent resin, only one kind of resin may be used, or a plurality of resins may be mixed and used. It is preferable that the same kind of absorbent resin is used for the same absorbent resin layer from the viewpoint of ease of production.

  In the present invention, the absorbent resin preferably has a residual monomer concentration of 200 ppm or less with respect to the weight of the absorbent resin, more preferably 100 ppm or less, still more preferably 50 ppm or less, and most preferably 10 ppm or less. When there are many residual monomers, there are many elution components at the time of liquid absorption, and it is not preferable in terms of performance.

  Residual monomer can be reduced by heat treatment at the time of production or after completion of the absorbent composite to complete the polymerization, but the residual monomer concentration of the absorbent resin before contact with the substrate may be 5% or less. Preferably, it is 1% or less, more preferably 0.1% or less, and most preferably 0.05% or less. If an absorbent resin with a large amount of residual monomer is used as a starting material, it is difficult to complete the polymerization reaction of the residual monomer at the time of producing the composite, and a large amount of residual monomer tends to remain in the end, which is not preferable. Further, depending on the reaction method, the texture of the substrate may be impaired, which is not preferable.

  For this reason, in the present invention, the absorbent resin is produced by an aqueous solution polymerization method, and then formed into an amorphous particle by a production method including a crushing step and / or a reverse phase suspension polymerization method. It is preferable to use prepared particles.

  The amount of residual monomer can be quantified using the following method.

  The absorbent resin is added to 0.9% physiological saline of 250 times the weight of the resin, extracted for about 6 hours with stirring at room temperature, and then filtered. The filtrate is quantified using a liquid chromatography method.

  In the present invention, the type of the absorbent resin is not particularly limited, and any absorbent resin may be used. It is preferably an absorbent resin having an acid group in the side chain, and more preferably a resin having a carboxylic acid group in the side chain. 50% or more of the acid groups are preferably neutralized in the form of a salt, and more preferably 50% or more of the acid groups are neutralized in the form of an ammonium salt. Such an absorbent resin is preferably used in at least one layer, and more preferably used in all layers. Absorbent resins having acid groups in the side chains are preferred because electrostatic repulsion between acid groups occurs during liquid absorption and the absorption rate is increased. It is preferable that the acid group is neutralized because the liquid is absorbed into the absorbent resin by osmotic pressure. When neutralized in the form of an ammonium salt, the ammonium salt is preferable because of its high affinity for water and an increased amount of absorption. Ammonium salts are preferred because the absorption rate is unlikely to decrease even when particles having an average particle size of 300 μm or more are used.

  Next, a hollow resin having a specific structure, which is particularly preferable when used in the present invention, will be described. By devising a specific form, it is possible to obtain a water-absorbing resin having a high balance between the absorption rate and the water-holding power, which is impossible with conventional water-absorbing resins.

  Usually, in order to increase the water absorption rate, it is considered necessary to improve the specific surface area of the resin. As the method, use of fine water-absorbing resin having a smaller particle diameter can be mentioned. However, since a water-absorbing resin having a particle size of several hundred μm is usually used, it is impossible to use a water-absorbing resin having a particle size of several μm to several tens of μm as it is. And having been used as having a particle size of several hundred μm. As a result, the fine particles taken into the interior of the aggregate cannot be brought into direct contact with the body fluid and the resin surface is far away from the ideal high specific surface area resin. Therefore, as a high specific surface area water-absorbing resin close to the ideal, as a result of diligent investigation on the idea of improving the probability that the resin layer can be in direct contact with body fluids, a space formed inside the thin layer is formed. We have succeeded in producing a water-absorbing resin.

  The shape of the hollow resin of the present invention is not particularly limited. It may have a nearly spherical structure as produced by reverse phase suspension polymerization or spray polymerization, or it may be a pulverized product produced by crushing a mass of water-absorbing resin produced by aqueous solution polymerization. An irregular structure may be used. Also, it may be in the form of a dice, a triangular pyramid, or a cone. Of course, the resin produced in a shape close to a sphere at the time of polymerization may have a structure in which the resin is deformed and broken in the post-treatment process. In order to improve the performance of the high speed and high water holding capacity, it is preferable to make the thickness of the resin layer homogeneous within a predetermined range. It is easy to be close to the inside and is a preferable shape. Moreover, the hollow does not need to be completely encased in the resin film, and a hole that comes into contact with external air may be provided. When the hole is open, the hollow interior can be used as the contact area with the body fluid, which is a preferable structure. Further, depending on the size of the hole, the body fluid that has entered the hollow interior is captured, and the absorption capacity is improved, which is a preferable structure.

  Here, there are two types of holes, a hole that can be formed when the liquid inside comes off during drying and a hole that breaks during crushing. The holes that break when pulverized include holes that are formed when the primary particles are broken as they are, and holes that are formed when the film of the bonded portion sticks to one of the particles when the bonded primary particles separate.

  The hollow resin in the present invention is in the form of particles and has a space inside thereof, and as a result, the hollow resin and the resin film surrounding the hollow portion are formed. About the thickness of the resin film of this invention, it is preferable that it is 1-30 micrometers. The thinner the thickness, the shorter the absorption response time at the time of contact with the body fluid, and as a result, the absorption speed is improved. However, when the thickness is less than 1 μm, there is a problem in strength for maintaining the hollow structure. . Moreover, when the thickness is 30 μm or more, the absorption rate may decrease. In order to achieve both the strength for maintaining the structure and the absorption rate, the thickness of the resin film is preferably in the range of 5 to 25 μm, more preferably 6 to 18 μm. The thickness of the resin film can be confirmed by observing with an electron microscope after the hollow resin is physically broken by grinding or the like. Specifically, the resin is copied with an electron microscope, 20 resins whose thickness can be observed are taken out arbitrarily, and the average value is taken as the thickness of the resin film.

  When the resin film becomes thin, most of the ammonium salt is liberated as ammonia during the heat treatment in the post-treatment step. In that case, a non-volatile alkali metal such as Na, K or the like is contained in the carboxyl group neutralized salt-containing unit. It is preferable to contain -80 mol%.

  The hollow water-absorbent resin of the present invention preferably has a bulk specific gravity of a certain value or less. This means that even when the thickness of the resin film is within a predetermined range, if the bulk specific gravity is high, the particle size of the hollow water-absorbent resin is extremely small, and the hollow water-absorbent resin can be used. This is because, when agglomerated to increase the particle size, the hollow water-absorbent resin incorporated in the agglomerated particles is difficult to contact with the body fluid, and the absorption rate may be significantly reduced. It is preferable that the bulk specific gravity is as small as possible because the specific surface area becomes large. On the other hand, when the bulk specific gravity is too small, the thickness of the resin layer becomes thinner than 1 μm, so that the resin becomes fragile and may be difficult to use in the absorbent body. A preferred range for the bulk specific gravity of the resin is 0.65 or less, more preferably 0.60 or less, and even more preferably 0.55 or less. The term “bulk specific gravity” as used herein means that the water-absorbent resin in a dry state is classified into a certain particle size and filled into a container of a predetermined volume at a room temperature so as to be in a dense state. A value obtained by measuring the weight of the resin in a fine state including the gap and dividing by the volume is defined as the bulk specific gravity.

  The hollow water-absorbent resin of the present invention can be used in the form of primary particles or aggregates thereof. If the particle diameter is 50 μm or more, it can be used as it is, but if the particle diameter is small, it can be aggregated and used by about several hundred μm. In order to increase the strength of the resin, it is preferable to use a hollow water-absorbent resin obtained by agglomerating particles having a small particle diameter, but if the particle diameter is too small, the hollow inside of the aggregated particles taken into the aggregated particles is preferred. Since the body fluid is not in direct contact with the water-absorbent resin and the absorption rate is lowered, it is not preferable. Therefore, the average particle diameter of a preferable hollow water-absorbent resin is 5 to 1000 μm as primary particles, more preferably 10 to 500 μm, and most preferably 30 to 200 μm.

  Here, the average particle diameter is taken with an electron microscope and 20 resins whose particle diameter can be observed are taken out arbitrarily, and the average value is defined as the average particle diameter.

  The hollow water-absorbing resin of the present invention has a high absorption rate and a high water-holding power due to its structure, and is not particularly concerned with the chemical composition of the water-absorbing resin, but has a higher absorption rate and a high water-holding property. Is preferably used.

  As a specific example of the water absorbent resin, a water absorbent resin having an acid group in the side chain is preferable, and a resin having a carboxyl group in the side chain is more preferable. In particular, it is preferable that the content of the carboxyl group-containing unit in the polymer molecular chain of the water-absorbent resin is 50 mol% or more.

  Further, 50% or more of the carboxyl group-containing units are preferably neutralized salts, and more preferably 70% or more are neutralized salts. It is preferable that the salt is partially neutralized with at least one salt containing ammonia. From the viewpoint of water absorption performance, 10 to 80 mol% of the carboxyl group neutralized salt units in the polymer molecular chain are preferably ammonium salts, and more preferably 30 to 70 mol% are ammonium salts.

  In addition, the ratio of the ammonium salt in a water absorbing resin can be calculated by calculating | requiring the total amount of nitrogen atoms in a water absorbing resin. The total amount of nitrogen atoms in the water absorbent resin can be determined by the Kjeldahl method. The alkali metal content can be measured using a metal quantitative analysis method such as atomic absorption or ICP.

  A water-absorbent resin having an acid group in the side chain is preferable because an electrostatic repulsion between acid groups occurs during absorption of a body fluid and the absorption speed increases. In addition, it is preferable that the acid group is neutralized because body fluid is absorbed into the water-absorbent resin by osmotic pressure. When neutralized in the form of an ammonium salt, the ammonium salt is preferable because of its high affinity for water and an increased amount of absorption. Examples of the water-absorbing resin include a crosslinked polyacrylic acid partially neutralized product (see, for example, JP-A-55-84304) and a hydrolyzate of starch-acrylonitrile graft polymer (see, for example, JP-B-49-43395). ), Neutralized starch-acrylic acid graft polymer (see, for example, JP-A No. 51-125468), saponified vinyl acetate-acrylic acid ester copolymer (see, for example, JP-A-52-14689) There are many known hydrolysates of acrylonitrile copolymer or acrylamide copolymer (see, for example, Japanese Patent Publication No. 53-15959), polyglutamate (see, for example, Japanese Patent Application Laid-Open No. 2003-192794). From the viewpoint of water absorption performance, cost, etc., a polymer having a carboxylic acid group which is usually used for hygiene materials is preferred.

  As the monomer used for the polymerization of the water-absorbing resin mainly composed of a polymer having a carboxylic acid group, those having an unsaturated bond are usually used. Examples include (meth) acrylic acid, ethacrylic acid, itaconic acid, maleic acid, crotonic acid, fumaric acid, sorbic acid, cinnamic acid, their anhydrides, and neutralized salts of unsaturated carboxylic acid monomers. However, a neutralized salt of (meth) acrylic acid is preferably used. The type of the neutralized salt is preferably an alkali metal salt such as lithium, sodium or potassium, or a nitrogen-containing basic substance such as ammonia.

  In polyacrylic acid having a neutralized salt of acrylic acid as a main component of the monomer, the repeating unit in the polymer molecular chain is preferably 50 mol% or more of carboxyl group-containing units. More preferably, it is 80 mol% or more, and most preferably 90 mol% or more. If the carboxyl group-containing unit in the repeating unit is 50 mol% or less, a decrease in water absorption performance is observed, which is not preferable.

  Other monomers may be copolymerized, and unsaturated monomers that may be copolymerized include (meth) acrylic acid, ethacrylic acid, itaconic acid, maleic acid, crotonic acid, sorbic acid, cinnamic acid, Their anhydrides, vinyl sulfonic acid, allyl sulfonic acid, styrene sulfonic acid, vinyl toluene sulfonic acid, 2- (meth) acrylamide-2-methylpropane sulfonic acid, 2- (meth) acryloylethane sulfonic acid, 2- ( Anionic unsaturated monomers such as (meth) acryloylpropane sulfonic acid, 2-hydroxylethyl acryloyl phosphate, 2-hydroxylethyl methacryloyl phosphate, phenyl-2-acryloyloxyethyl phosphate, vinyl phosphate, and salts thereof, acrylamide , Methacrylamide, N-eth (Meth) acrylamide, Nn-propyl (meth) acrylamide, N-isopropyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate Nonionic hydrophilic group-containing unsaturated monomers such as methoxypolyethylene glycol (meth) acrylate, polyethylene glycol mono (meth) acrylate, N-vinylpyrrolidone, N-acryloylpiperidine, N-acryloylpyrrolidine, and methyl You may use the hydrophilic monomer which forms a water absorbing resin by hydrolysis of the functional group after superposition | polymerization like (meth) acrylate, ethyl (meth) acrylate, vinyl acetate. Examples of the hydrophobic monomer that can be used in combination include styrene, vinyl chloride, butadiene, isobutene, ethylene, propylene, stearyl (meth) acrylate, lauryl (meth) acrylate, and the like. More than one type can be added. Alternatively, the polymer may be cross-linked to form a water-absorbing resin. As a crosslinking method, a method of copolymerization in the presence of a polymerizable crosslinking agent in a monomer, a method of crosslinking using a crosslinking agent that reacts with a carboxylic acid, and a resin is crosslinked by irradiating an electron beam or radiation. Methods and the like. Among these methods, a method using a polymerizable crosslinking agent and a method using a crosslinking agent that reacts with a carboxylic acid are preferable because the degree of crosslinking can be controlled accurately. Since the degree of cross-linking is a factor that greatly affects the various performances of the water-absorbent resin, when it is desired to precisely adjust the performance of the water-absorbent resin, it is possible to use a polymerizable cross-linking agent and a cross-linking agent that reacts with carboxylic acid in combination preferable.

  As the polymerizable crosslinking agent, one having two or more unsaturated bonds in one molecule can be used. For example, diethylene glycol diacrylate, N, N′-methylenebisacrylamide, polyethylene glycol diacrylate, polypropylene glycol diacrylate, trimethylolpropane diallyl ether, allyl glycidyl ether, pentaerythritol triallyl ether, pentaerythritol diacrylate monostearate, bisphenol Examples include diacrylate, isocyanuric acid diacrylate, tetraallyloxyethane, diallyloxyacetate, and the like. Two or more of these crosslinking agents may be used.

Examples of crosslinking agents that react with carboxylic acids include glycidyl ether compounds such as ethylene glycol diglycidyl ether, trimethylolpropane triglycidyl ether, (poly) glycerin polyglycidyl ether, diglycerin polyglycidyl ether, and propylene glycol diglycidyl ether; ) Polyhydric alcohols such as glycerin, (poly) ethylene glycol, propylene glycol, 1,3-propanediol, polyoxyethylene glycol, triethylene glycol, tetraethylene glycol, diethanolamine, triethanolamine; ethylenediamine, diethylenediamine, polyethylene Polyvalent amines such as imine and hexamethylenediamine; polyvalent amines such as zinc, calcium, magnesium and aluminum These crosslinking agents can be mentioned such emissions may be used two or more.
Moreover, you may superpose | polymerize by adding a foaming agent, a chain transfer agent, surfactant, a chelating agent, etc. other than the said monofunctional unsaturated monomer and an internal crosslinking agent as needed.

  The polymerization method of the monomer having an unsaturated bond is not particularly limited, and generally used methods such as aqueous solution polymerization, reverse phase suspension polymerization, reverse phase emulsion polymerization, spray polymerization, and belt polymerization can be applied. The polymerization initiation method is not particularly limited, and polymerization with a radical polymerization initiator, polymerization by irradiation with radiation, electron beam, or ultraviolet polymerization with a photosensitizer can be performed. Examples of the initiator used for such radical polymerization include persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate; hydrogen peroxide; cumene hydroperoxide, t-butyl hydroperoxide, and organic acids such as peracetic acid. Well-known initiators, such as an oxide, are mentioned. When an oxidizing radical polymerization initiator is used, a reducing agent such as L-ascorbic acid or Rongalite may be used in combination.

  It is preferable to perform a deoxygenation operation in the monomer solution in advance before the start of polymerization of the water absorbent resin. As a specific method, there is a method of removing dissolved oxygen by bubbling with an inert gas such as nitrogen or helium for a sufficient time. In addition, it is preferable that the atmosphere in the reactor is replaced with an inert gas such as nitrogen or helium. The inside of the reactor during polymerization may be any one of reduced pressure, normal pressure, and increased pressure. The polymerization start temperature is usually preferably in the range of 0 to 100 ° C. More preferably, it is the range of 20-70 degreeC. When the polymerization start temperature is too high, the polymerization by heat starts before the initiator is added, which is not preferable. On the other hand, if the starting temperature is too low, it takes too much time to start the polymerization, which is not preferable in terms of production efficiency. The temperature in the reactor during the polymerization may be left to the end, or the temperature may be controlled by cooling or heating from the outside. The temperature rising rate and the maximum temperature during the polymerization are not particularly problematic, and there is no problem even if the maximum temperature exceeds 100 ° C. The maximum temperature during the polymerization is usually 20 to 140 ° C, preferably 40 to 120 ° C, more preferably 50 to 100 ° C. The concentration of the monomer solution is preferably 10 to 80%, and most preferably 30 to 70%. If the concentration of the monomer solution is too high, the reaction tends to run away, which is not preferable. If the concentration is too low, the reaction takes too much time, and the subsequent drying process is also burdened. The polymerization time is not particularly limited, but is preferably set around the time when the heat generation from the reaction solution stops. Since there are heating processes such as a drying process and a post-crosslinking process as a post-process after the polymerization, the polymerization may be terminated before the heat generation from the reaction solution stops. Further, after completion of heat generation, it may be heated and kept for several hours.

  When the polymer obtained after the polymerization is a hydrogel, drying is performed. Although this drying method is not particularly limited, generally used methods such as azeotropic dehydration, fluidized drying, hot air drying, and vacuum drying can be applied, and hot air drying and vacuum drying are particularly preferable. Moreover, when the polymerization resin before drying can be made into a spray state, the drying method called spray drying is also possible. Although it does not specifically limit as a moisture content in resin, 30 mass% or less is preferable, and it is still more preferable to dry to 10 mass% or less. Drying may be performed with any form of hydrous gel, but it is preferable in terms of drying efficiency to dry after coarsely crushing to increase the surface area. The drying temperature is preferably in the range of 70 to 180 ° C, particularly preferably 90 to 150 ° C.

The particle diameter of the dried polymer resin body is adjusted by operations such as pulverization and classification as required.
Then, you may heat-process the dry resin adjusted to the predetermined particle diameter for post-crosslinking. The method of this heat treatment is not particularly limited, but it is preferable to coexist with a crosslinking agent that reacts with the carboxyl group to be used. The addition method of the crosslinking agent that reacts with the carboxyl group is not particularly limited, and may be added before polymerization or may be added to the particles before the heat treatment. When put in the particles before the heat treatment, it is preferable to dissolve them in a hydrophilic solvent such as water, alcohols, ethers, etc., and to disperse them uniformly on the particle surfaces. Although the temperature of heat processing is not specifically limited, Preferably it is the range of 90-250 degreeC. More preferably, it is 120-200 degreeC, Most preferably, it is 150-180 degreeC. The heat treatment may be performed continuously in the same apparatus after completion of drying, or may be a step independent of the drying step. For the heat treatment, a generally widely used apparatus such as a normal dryer or a heating furnace can be used. For example, a groove type mixed dryer, a rotary dryer, a disk dryer, a fluidized bed dryer, an airflow type dryer. And an infrared dryer.

  In the water-absorbing resin thus obtained, if necessary, deodorants, fragrances, various inorganic powders, foaming agents, pigments, dyes, antibacterial agents, hydrophilic short fibers, plasticizers, adhesives, surfactants, Fertilizers, oxidizing agents, reducing agents, chelating agents, antioxidants, heat stabilizers, UV absorbers, light stabilizers, water, salts, etc. may be added.

  Examples of the inorganic powder include fine particles of various inorganic compounds that are inert to water and hydrophilic organic solvents, fine particles of clay mineral, and the like. In particular, the inorganic powder preferably has an appropriate affinity for water and is insoluble or hardly soluble in water, such as metal oxides such as silicon dioxide and titanium oxide, natural zeolite, synthetic zeolite, etc. Examples thereof include silicic acid (salt), kaolin, talc, clay, bentonite and the like. Although the usage-amount of inorganic powder is not specifically limited, Usually, it is 0.001-10 weight part with respect to 100 weight part of water absorbing resin, Preferably it is 0.01-5 weight part. There is no restriction | limiting in particular in the mixing method of water absorbing resin and inorganic powder, It performs by general methods, such as a dry blend method and a wet mixing method.

  Moreover, it is a very preferable method to apply a water-permeable agent to the produced resin so that the body fluid diffuses at high speed on the surface of the water-absorbent resin. The method of applying the water permeable agent is not particularly limited, and is a method of spraying and drying the water permeable agent or a solution in which the water permeable agent is dissolved, a method of impregnating the resin in the water permeable agent or a solution in which the water permeable agent is dissolved and drying the resin. It is a preferable method that the water-permeable resin surface area of the water-absorbent resin surface can be easily improved.

The water-permeable agent is not particularly limited as long as it has high hydrophilicity and can adhere to the surface of the water-absorbent resin. Usually, as a water-permeable agent, a low molecular weight hydrophilic compound, hydrophilic polymer resin, etc. are mentioned. Specifically, polyoxyethylene nonylphenol ether, polyoxyethylene lauryl ether, polyoxyethylene oleyl ether, polyoxyethylene fatty acid esters, Dow Chemical Company has been manufactured by Voranol (Voranol ^TM) 2070, Voranol 2100, Voranol 3100 polyol TRITON ^™ X-100 Surfactant (available from Rohm & Haas), Tergitol ^™ 15-5-9, Ethoxylated Surfactant (available from Union Carbide), Polyethylene Glycol, Kao Emulgen LS-106, Emulgen LS-110, Emulgen LS-114, Emulgen MS-1110, Emulgen 11 Nonionic surfactants such as 8S-70, Emulgen 1135S-70, Emulgen 1150S-70, Rheodor TW-O106V, Rhedol TW-O120V, and durable hydrophilizing agents for polyolefin fibers described in Japanese Patent No. 3057521 Agents, anionic surfactants such as dodecylbenzene sulfonate, alkyl sulfate ester salts, alkyl phosphate ester salts, polyoxyethylene alkyl sulfate esters, amphoteric surfactants such as lauryl dimethyl betaine, cocoamidopropyl dimethyl betaine, JP-A-1-148879 And silicone-based hydrophilic treatment agents described in JP-A-10-53955. Of these, nonionic surfactants and silicone surfactants having an HLB value of 7 or more are particularly preferred because they exhibit high water permeability.

  The solvent used when the water-permeable agent is applied in a solution state is not particularly limited, but is preferably a solvent that dissolves the water-permeable agent and is easy to evaporate and remove after application. For example, it is most preferable to use a hydrophilic liquid. preferable. Specifically, ketones such as acetone and methyl ethyl ketone, nitriles such as acetonitrile and propionitrile, amides such as dimethylformamide and N, N-dimethylacetamide, ethyl acetate and acetic acid Esters typified by methyl, methyl propionate, etc., ethers typified by tetrahydrofuran, diethyl ether, methyl ethyl ether, etc., typified by methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, cyclohexanol, etc. Polyalcohols typified by monoalcohols, ethylene glycol, propylene glycol, polyethylene glycol, propylene glycol, glycerin, 1,2-cyclohexanediol, 1,6-hexanediol, etc. Class, also like water. Among these, those having a boiling point of 100 ° C. or less at normal pressure are preferably used from the viewpoint of solvent drying after application of the water-permeable agent. In view of process safety, water and ethanol are preferably used, and water is most preferable.

  Next, the simplest representative method for producing a hollow resin is shown.

  As a method for producing the hollow resin of the present invention, a reverse phase suspension polymerization method in which an aqueous monomer solution containing an unsaturated carboxylate is suspended in an organic solvent and polymerized is used as a preferred method. The type of the reactor is not particularly limited, and either a batch type or a continuous type may be used. For example, a continuous apparatus such as a loop reactor or a batch-type stirring layer generally used widely can be used.

  As an example of a specific polymerization method of the hollow resin, first, an aqueous solution of an unsaturated carboxylate and an organic solvent (hereinafter referred to as organic solvent 1) are used as a surfactant (hereinafter referred to as surfactant 1). Mix in the presence to create an emulsion in which oil droplets are stably present in the aqueous solution. Thereafter, this aqueous emulsion and an organic solvent (referred to as organic solvent 2) are mixed in the presence of a surfactant (surfactant 2). A simple method is a method in which an aqueous emulsion is stably present as water droplets in the organic solvent 2 and polymerized in that state.

  As a method for forming a hollow state, it is preferable to produce particles containing a substance that can be removed by evaporation after polymerization, and then evaporate and remove the substance to form a hollow state.

  In terms of ease of production of the hollow resin, examples of the unsaturated carboxylate used include ammonium salts, sodium salts, potassium salts, and lithium salts. Preferably ammonium and sodium salts, most preferred are ammonium salts. Depending on the purpose, it may be possible to partially or completely substitute another salt such as sodium salt or potassium salt after creating a resin in a hollow state using a monomer mainly composed of an ammonium salt as an unsaturated carboxylate. I do not care.

  The unsaturated ammonium carboxylate may partially contain an unsaturated carboxylic acid amide. An unsaturated amide refers to a compound containing both an unsaturated bond and a functional group represented by the general formula RCONH- (wherein R is an arbitrary organic group such as an alkyl group or an aryl group) in the molecule. Examples of such a compound include cinnamamide, acrylamide, methacrylamide, and the like, acrylamide and methacrylamide are preferable, and acrylamide is more preferable.

  The most preferable unsaturated ammonium carboxylate as the unsaturated carboxylate may be one produced by any method. For example, a. A method of subjecting an unsaturated nitrile and / or an unsaturated amide to a hydrolysis reaction by a microorganism; b. The method of neutralizing unsaturated carboxylic acid with ammonia is mentioned. Next, each specific manufacturing method will be described.

a. Method for Hydrolyzing Unsaturated Nitrile and / or Unsaturated Amide An unsaturated nitrile to be subjected to a hydrolysis reaction by a microorganism refers to a compound containing both an unsaturated bond and a cyan group in the molecule. Moreover, you may contain many unsaturated bonds and cyan groups, respectively. Unsaturated bonds are those containing double bonds (ethylene bonds) or triple bonds (acetylene bonds) between carbon atoms. Examples of such compounds include acrylonitrile, methacrylonitrile, crotonnitrile, and cinnamic acid. A nitrile etc. are mentioned. Of these, acrylonitrile and methacrylonitrile are preferable, and acrylonitrile is more preferable. Further, the unsaturated amide subjected to hydrolysis reaction by microorganisms includes both an unsaturated bond and a functional group represented by the general formula RCONH- (where R is an arbitrary organic group such as an alkyl group or an aryl group) in the molecule. It refers to the compound that contains it. Examples of such compounds include cinnamamide, acrylamide, and methacrylamide, with acrylamide and methacrylamide being preferred, and acrylamide being particularly preferred.

  The conditions for hydrolysis of unsaturated nitrile and / or unsaturated amide by microorganisms are not particularly limited, but microorganisms capable of producing an aqueous solution of unsaturated ammonium carboxylate having a concentration of 20% by weight or more are preferable. As such a microorganism, it is preferable to use at least one selected from the group consisting of Acinetobacter, Alkagenes, Corynebacterium, Rhodococcus, and Gordona. Among the microorganisms, microorganisms belonging to the genus Acinetobacter are more preferable, and among these microorganisms, the microorganism is Acinetobacter sp. AK226 strain (FERM BP-08590) or Acinetobacter sp. Most preferably, it is AK227 strain (FERM BP-08591). Acinetobacter sp. AK226 strain (FERM BP-08590) and Acinetobacter sp. The microbiological properties of the AK227 strain (FERM BP-08591) are as shown in Table 1.

Table 1 continued

The aqueous solution of unsaturated ammonium carboxylate produced by this microorganism hydrolysis method has a very small amount of impurities such as dimers and / or hydrates of unsaturated carboxylic acid, and therefore the production method is a preferred method. . Specific examples of impurities include, in the case of acrylic acid, β-acryloyloxypropionic acid which is a dimer of acrylic acid, β-hydroxypropionic acid which is a hydrate of acrylic acid, and salts thereof. It is done.
b. Method for neutralizing unsaturated carboxylic acid with ammonia As the unsaturated carboxylic acid used in the method for neutralizing unsaturated carboxylic acid with ammonia, the same unsaturated carboxylic acid as described above is used.

  This unsaturated carboxylic acid may be produced by any method. When such an unsaturated carboxylic acid contains a large amount of impurities, it is preferable to purify and reduce the impurities. The impurity here refers to a compound that can be decomposed to become a monomer component. For example, hydrated unsaturated bonds, oligomers, and acrylic acid include β-hydroxypropionic acid and β-acryloyloxypropionic acid. The purification method may be any method as long as the amount of impurities can be reduced to a specified amount or less, and the means is not particularly limited, and is generally used as a specific purification method such as distillation. You may carry out by the method. The amount of impurities is preferably reduced to 1000 ppm or less, more preferably 500 ppm or less, still more preferably 300 ppm or less, and most preferably 100 ppm or less. If the amount of impurities is large, the resulting water-absorbent resin has a large amount of residual monomer, and the residual monomer increases in the subsequent manufacturing process. Further, various physical properties of the polymer may be insufficient, which is not preferable.

  The neutralization method is not particularly limited, and ammonia water or ammonia gas may be used. Moreover, you may neutralize on the conditions through which the neutralization rate of unsaturated carboxylic acid passes the state exceeding 100 mol% at least for one time in the neutralization process. In the neutralization step, the temperature is preferably maintained at 0 to 50 ° C. by cooling. If the temperature rises too much, β-hydroxypropionic acid and oligomers are generated, which is not preferable. Therefore, the temperature during neutralization is more preferably 0 to 30 ° C. or less.

  The amount of the unsaturated ammonium carboxylate monomer used is in the range of 50 to 100 mol% with respect to the total molar amount of the unsaturated carboxylic acid and its salt. From the viewpoint of In order to improve the absorption capacity of the produced water-absorbent resin, the content of unsaturated ammonium carboxylate is preferably high, and is preferably in the range of 80 to 100 mol%, more preferably 95 to 100. %. At this time, the amount of the alkali metal salt used as the unsaturated carboxylate other than the ammonium salt is the total molar amount of the unsaturated carboxylic acid and the salt thereof (which includes the unsaturated ammonium carboxylate and the unsaturated carboxylate alkali metal salt). It is preferably in the range of 0 to 45 mol% with respect to the total molar amount of each unsaturated carboxylic acid. In order to improve the absorption capacity of the produced water-absorbing resin, the content of unsaturated carboxylic acid alkali metal salt is preferably low, more preferably in the range of 0 to 20 mol%. More preferably, it is 0 to 10%.

  Next, the concentration of the unsaturated ammonium carboxylate monomer to be used for polymerization in the aqueous solution is not particularly limited. However, when it is desired to stably produce the hollow resin, it is preferably carried out at a relatively high concentration. The concentration of the polymerizable monomer in the aqueous solution is preferably 20% by weight or more, more preferably 40% by weight or more, and most preferably 60% by weight or more. The practical upper limit of the concentration is the solubility of the polymerizable monomer in water under the polymerization conditions. The substantial upper limit mentioned here means that even if some of the monomers are not dissolved and exist in the aqueous solution as solids, the solids in the aqueous solution are consumed after the dissolved monomers are consumed by the polymerization reaction. The insoluble solid content that can be dissolved in the polymer and polymerized is also the upper limit of solubility when considered as a dissolved component.

The crosslinking agent capable of reacting with the polymerizable crosslinking agent and / or the carboxylic acid group is not particularly limited, but it is preferable to add it to the aqueous solution of the polymerizable monomer.
As a result, the polymerization initiator may be added at any stage as long as it is introduced so as to dissolve as uniformly as possible in the unsaturated carboxylate aqueous solution. For example, before an unsaturated carboxylate aqueous solution is mixed with the organic solvent 1, an emulsion solution composed of the unsaturated carboxylate aqueous solution and the organic solvent 1 is introduced at any time before being mixed with the organic solvent 2. A method is mentioned.

  The organic solvent 1 is not particularly limited as long as oil droplets can be generated in the presence of the surfactant 1 in the unsaturated carboxylate aqueous solution. Usually, the process solvent is preferably a solvent having a small latent heat of vaporization, good separability from water, and hardly chemically reacting with the surfactant. Specifically, a hydrocarbon solvent is mentioned as a preferable solvent. An aliphatic hydrocarbon solvent is more preferable, and a saturated aliphatic hydrocarbon solvent is more preferable. The saturated aliphatic hydrocarbon solvent may have a linear structure, a branched structure, or a cyclic structure. Of course, it may be a compound having a plurality of structures of a linear structure, a branched structure, and a cyclic structure in one molecule. Specific examples of the saturated aliphatic hydrocarbon solvent include saturated aliphatic hydrocarbon solvents having a cyclic structure such as cyclopentane, cyclohexane, methylcyclopentane, methylcyclohexane, and cyclooctane; n-pentane, n-hexane, n -Saturated aliphatic hydrocarbons having a chain structure such as heptane, n-octane, ligroin and the like. Of these, cyclopentane, cyclohexane, cyclooctane, n-pentane, and n-hexane are preferable, and cyclohexane is more preferable, in view of the stability of the resulting emulsion and various physical properties such as the boiling point and specific gravity of the solvent.

  Surfactant 1 can be used to stably disperse organic solvent 1 as an oil droplet in a stirred or stationary state in an aqueous monomer solution containing an unsaturated carboxylate as a main component and does not inhibit the polymerization reaction. There is no particular limitation. Specific examples of the surfactant 1 that can be used include an anionic surfactant, a nonionic surfactant, a cationic surfactant, and an amphoteric surfactant. Of these, the surfactant 1 is preferably a nonionic surfactant, and the nonionic surfactant is preferably polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene oleyl. Ether, polyoxyethylene alkyl ether, polyoxyethylene octidodecyl ether, polyoxyethylene alkylene alkyl ether, polyoxyethylene polyoxypropylene glycol, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan Monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitant Polyoxyethylene derivatives such as oleate, polyoxyethylene sorbitan triisostearate, sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan tristearate, sorbitan monooleate, sorbitan monolaurate, sorbitan sesquioxide Examples include sorbitan fatty acid esters such as oleate, polyoxyethylene sorbitol fatty acid ester such as polyoxyethylene sorbitol tetraoleate, glycerin fatty acid ester such as glycerol monostearate, and sucrose fatty acid ester. In order to improve the stability of the suspended or emulsified state, it is preferable to use a nonionic surfactant having an HLB value of 4 to 14, more preferably an HLB value of 7 to 13. Is. Moreover, the thing which does not exist below 30 degreeC of a cloud point is preferable, More preferably, a cloud point does not exist. The addition amount of the surfactant 1 is 10% by weight or less with respect to the weight of the organic solvent 1, usually 0.05 to 8% by weight, and preferably 0.1 to 5% by weight.

  If the organic solvent 2 is an organic solvent that is stirred and mixed with an equal amount of water and then separated into two layers as a stationary state and does not significantly inhibit the radical polymerization reaction of the raw material monomer, the type, amount, and constituent atoms of the functional group There is no need to be particularly limited with respect to the above. Usually, as the process solvent, a solvent having a small latent heat of vaporization, good separability from water, and difficult to chemically react with the surfactant 1 and the surfactant 2 is preferably used. Specifically, a hydrocarbon solvent is mentioned as a preferable solvent. More preferred are aliphatic hydrocarbon solvents, and more preferred are saturated aliphatic hydrocarbon solvents. The saturated aliphatic hydrocarbon solvent may have a linear structure, a branched structure, or a cyclic structure. Of course, a compound having a plurality of structures of a linear structure, a branched structure, and a cyclic structure in one molecule may be used. Specific examples of the saturated aliphatic hydrocarbon solvent include saturated aliphatic hydrocarbon solvents having a cyclic structure such as cyclopentane, cyclohexane, methylcyclopentane, methylcyclohexane, and cyclooctane; n-pentane, n-hexane, n -Saturated aliphatic hydrocarbons having a chain structure such as heptane, n-octane, ligroin and the like.

  Of these, cyclopentane, cyclohexane, cyclooctane, n-pentane, and n-hexane are preferable, and cyclohexane is more preferable because of the stability of the resulting emulsion and various physical properties such as the boiling point and specific gravity of the solvent.

  Surfactant 2 can stabilize a suspension or emulsion of an aqueous monomer solution containing organic solvent 1 as oil droplets in a suspended or emulsified state in organic solvent 2 under stirring or standing conditions. If it is a thing, it will not specifically limit. Specific examples of the surfactant 2 that can be used include an anionic surfactant, a nonionic surfactant, a cationic surfactant, and an amphoteric surfactant. Among these, as the surfactant 2, the unsaturated carboxylate used as a raw material monomer is ionic, and it is difficult for changes in performance due to ion exchange or the like to occur. Therefore, a nonionic surfactant is used. Is preferred. As the nonionic surfactant, those having an HLB value in the range of 4 to 12 are preferably used because they exhibit high stability when suspended or emulsified. In addition, when it is desired to generate a relatively large aqueous phase droplet, it is preferable to use a nonionic surfactant having an HLB value in the range of 5 to 10. Examples of nonionic surfactants having an HLB value of 4 to 12 include sorbitol fatty acid ester, sorbitol fatty acid ester ether, sorbitan fatty acid ester, and sorbitan fatty acid ester ether. Of these, sorbitan fatty acid ester type and sorbitan fatty acid ester ether type are preferable. Moreover, as an example of a nonionic surfactant having an HLB value of 5 to 10, sorbitan monostearate, sorbitan monolaurate or oxyethylene sorbitan monostearate ether is preferable. More preferred is sorbitan monostearate.

  The HLB value in the present invention is the HLB value of Griffin described in the introduction of a new surfactant published by Sanyo Chemical Industries, Ltd. The formula for calculating the HLB value is defined as follows.

Nonionic surfactant HLB = (molecular weight of hydrophilic group portion / molecular weight of surfactant) × 20
The amount of the surfactant used is suitably in the range of 0.1 to 15% by weight, preferably 0.2 to 5% by weight, based on the monomer. The amount of surfactant used is not particularly limited as long as a stable emulsion state can be maintained, but a stable emulsion state cannot be maintained even if the amount of surfactant used is too small. Even if it is used in an amount of 15% by weight or more, good results associated therewith cannot be obtained.

The polymerization reaction temperature is not particularly limited, but is preferably adjusted according to the temperature dependency of the radical generation rate of the polymerization initiator used. Since the suspension state and the emulsified state due to the change in the viscosity of the polymer during polymerization and the temperature change associated with the heat of polymerization may become unstable, the polymerization starts at a relatively low temperature of 70 ° C. or less at the initial stage of polymerization. After proceeding, it is preferable to raise the temperature to 70 ° C. or higher to complete the polymerization.
When the particle size is small after completion of the polymerization, the particles may be aggregated to have an average particle size of 100 μm or more. Examples of the agglomeration method include a method in which the third component is added and the surfactant 2 is peeled off from the particle surface to adhere the particles, and a method in which the solvent is distilled off in a situation where the particles are in contact with each other and the particles are adhered to each other. It is done.

  As a method for peeling off and aggregating the surfactant 2 from the particle surface, it is preferable to mix the emulsion solution after polymerization and an organic solvent exhibiting solubility in water, and the mixing method is not particularly limited. For example, a water-soluble solvent may be added to the emulsion, an emulsion may be added to the water-soluble solvent, or the emulsion and the water-soluble solvent may be charged into the reaction vessel at the same time. A simple production method is a method of adding a water-soluble solvent to the emulsion solution after polymerization, and a method of adding a water-soluble solvent to the stirred emulsion solution is a preferred method.

  By mixing the emulsion and the water-soluble solvent, the stabilizing effect of the surfactant holding the emulsion is disrupted and the particles are aggregated. In order to disrupt the stabilizing effect of the surfactant, the water solubility of the mixed water-soluble solvent needs to be 1% by weight or more, preferably 5% by weight or more, more preferably 10% by weight. That's it.

  One or more water-soluble solvents having a solubility in water of 1% by weight or more may be added, but two or more water-soluble solvents are preferably used. More preferably, two or more types of water-soluble solvents containing a polyhydric alcohol are used. It is preferable that the polyhydric alcohol containing two or more alcohol groups is contained in the water-soluble solvent to be added because the effect of reducing the water-soluble component generated in the aggregation step is high. In the case of using a plurality of kinds of alcohols, the timing of addition is not particularly limited, and may be added simultaneously or independently. Examples of water-soluble solvents having a solubility in water of 1% by weight or more include ketones typified by acetone and methyl ethyl ketone, nitriles typified by acetonitrile and propionitrile, dimethylformamide, N, N- Amides typified by dimethylacetamide, etc., esters typified by ethyl acetate, methyl acetate, methyl propionate, etc., ethers typified by tetrahydrofuran, diethyl ether, methyl ethyl ether, etc., methyl alcohol, ethyl alcohol, n -Monoalcohols represented by propyl alcohol, isopropyl alcohol, cyclohexanol, etc., ethylene glycol, propylene glycol, polyethylene glycol, propylene glycol, glycerin, 1,2-cyclohexanediol, 1, - polyhydric alcohols typified hexanediol, and the like. Among them, it is preferable to use a water-soluble solvent in which monoalcohols and polyhydric alcohols are combined. As monoalcohols, methyl alcohol, ethyl alcohol, and isopropyl alcohol are used, and as polyhydric alcohols, propion glycol, glycerin. , Ethylene glycol is preferably used in combination, and a combination of ethyl alcohol and glycerin or a combination of isopropyl alcohol and glycerin is most preferred.

  The addition amount of the water-soluble solvent is not particularly limited, and it is preferable to adjust the aggregate to have a desired particle size, for example, 0.1 to 20% by weight, more preferably based on the solid content in the emulsion Is 1 to 10% by weight.

The temperature at the time of addition is not particularly limited as long as the emulsion is maintained. For example, it may be carried out as it is at the polymerization temperature, or may be added after heating. Or you may cool to room temperature vicinity and may carry out.
After passing through the coagulation step, a step of reducing the moisture content of the gel by azeotropic dehydration with a solvent may be passed, and the conditions are not particularly limited, such as pressure and temperature.

  The particle size of the aggregate can be controlled by the amount of the water-soluble solvent to be added and the magnitude of the stirring power, and an arbitrary particle size can be obtained. In the present invention, the aggregate particle size is not particularly limited. However, in hygienic material applications where water-absorbent resins are most used, dust particles are not used when the particle size is small. Those with extremely large diameters are not used due to the slow water absorption rate. Considering the above, the particle size of the aggregate is preferably 100 to 5000 μm, and particularly preferably 100 to 1500 μm.

  Use of a step of keeping the emulsion at 40 ° C. or higher after forming the aggregate and fusing the particles together is effective in increasing the bond strength of the aggregate. The reason why the heat treatment is effective is not clear, but it is presumed that the free polymer chains of the particles in contact with each other or their segments diffuse to each other and so-called self-adhesion proceeds. In order to promote interdiffusion of polymer chains, it is preferable to heat to a temperature equal to or higher than the glass transition temperature of the agglomerated hydrogel. The glass transition temperature of the gel varies depending on the moisture content, neutralization rate, and type of neutralized salt of the gel, but the heating temperature is preferably 40 to 200 ° C, more preferably 60 to 180 ° C, and even more preferably 60 to 150 ° C. The heating time is preferably 1 to 120 minutes. There is no particular limitation as long as the gel can be sufficiently melted at both the heating temperature and the heating time and the performance of the product is not deteriorated. In order to increase the heating temperature, it is effective to pressurize the inside of the polymerization apparatus, and a solvent different from that used during polymerization may be used. Further, the bond strength of the aggregated particles is not particularly limited, but it is preferably high strength in consideration of handling the produced resin.

  As a method for separating and recovering the particle aggregate and the solvent after the aggregation step, a generally used solid-liquid separation method can be used. For example, filtration separation, separation by centrifugation, removal of solvent by heating, and the like can be mentioned, but any method may be used.

  The method for drying the particle aggregate gel is not particularly limited, and usually vacuum drying or hot air drying is used. The drying temperature is preferably in the range of 70 ° C to 180 ° C, more preferably 90 to 140 ° C. If the drying temperature is too low, it takes too much time for drying, which is not economical, and if it is too high, the water-absorbing resin is decomposed, resulting in a decrease in water absorption performance. The drying step is not particularly limited as long as it does not cause these problems, and the temperature may be raised in multiple stages or may be dried at a constant temperature.

  When an ammonium salt is used as the water-absorbing resin, after the above-mentioned drying, a heat treatment step is performed on the water-absorbing resin as shown in JP-A-2005-200630 to release ammonia, and the ammonia neutralization rate is increased. It can be controlled to an arbitrary ratio. At this time, the release of ammonia occurs from the surface of the resin, so that there is a difference in the neutralization rate between the inside of the water absorbent resin aggregate and the vicinity of the surface. It is also possible to control the neutralization rate by adding a non-volatile alkali metal such as lithium, sodium or potassium to the portion where the neutralization rate is reduced due to the release of ammonia. At the same time, it is possible to reduce the water-soluble content by reacting the polyhydric alcohol added during the agglomeration process with the functional groups in the low-molecular-weight polymer that becomes the water-soluble component, thereby increasing the molecular weight of the low-molecular polymer. Thereby, the gel blocking phenomenon at the time of resin water absorption can be reduced. This heat treatment process may be performed in a state where the water-absorbent resin after drying is coexisted with the nonwoven fabric or pulp, such as contact, adhesion, adhesion, or the like, or may be performed alone. The heat treatment is preferably performed in the range of 100 to 250 ° C, more preferably 130 to 200 ° C. Further, from the viewpoint of the distribution structure of the neutralization rate in the water-absorbent resin body and the water absorption performance, the heating temperature is preferably 10 to 150 ° C. higher than the drying temperature, more preferably 30 to 100 ° C. higher. Is to be done. The heating time is preferably 0.5 minutes to 5 hours, more preferably 2 to 60 minutes, and further preferably 3 to 15 minutes. The heating temperature and time are not particularly limited as long as the performance of the water absorbent resin does not deteriorate. The atmosphere of the heat treatment step is not particularly limited, but it is preferably performed in an inert gas atmosphere such as nitrogen so that unnecessary reaction does not occur.

  It is also possible to perform so-called surface cross-linking treatment by impregnating a dried water-absorbing resin with a compound containing two or more functional groups capable of reacting with a carboxyl group and causing a cross-linking reaction by heat treatment. Is within.

  The hollow resin of the present invention has the effect that the resin layer is thin, i.e., the response speed when contacting with body fluids is significantly improved, and the effect of the high specific surface area of the resin, i.e., the probability of direct contact with body fluids. The absorption speed becomes high due to the two effects of the improvement effect, and the water retention capacity is high due to the ability to capture water in the resin hollow portion.

  In the present invention, it is possible to produce a water-absorbing resin having an absorption rate measured by a vortex method (details of measurement methods below) of 10 seconds or less and a water retention capacity (details of measurement methods below) of more than 25 g / g. Become. Furthermore, the hollow water-absorbent resin of the present invention can be combined with the resin by carrying out the heat treatment step, which is the final step, in contact with the cellulosic fibers in a water-containing state, and further increase the absorption rate. It is a resin that enables high water retention.

(Salt concentration near the surface)
The absorbent resin particles before adhering onto the substrate preferably have a salt concentration in the vicinity of the surface (hereinafter referred to as “surface salt concentration”) of 50 mol% or more, more preferably 60 mol% or more, and more Preferably it is 70 mol%, and most preferably 80 mol% or more. If the surface salt concentration before bonding onto the substrate is too low, the adhesion of the particles may be reduced, which is not preferable.

  The surface salt concentration of the absorbent resin particles in the absorbent composite after the final adhesion to the substrate is not particularly limited, but the higher the salt concentration, the more preferable from the viewpoint of water absorption rate. From the viewpoint of water absorption magnification, the total salt concentration is preferably 40 to 99%, more preferably 50 to 90%, and still more preferably 60 to 80%. In order to bring the overall salt concentration into a specific range and increase the surface salt concentration, it is conceivable to coat the surface with salt. The vicinity of the surface means an outer layer portion having a thickness of about 1 μm in the depth direction from the surface. The adjustment of the surface salt concentration may be performed in a resin state or may be performed after forming a composite.

  If the salt concentration has a gradient in the particles, it can be said that it is preferable from the viewpoint of absorption speed because a suction force due to a difference in osmotic pressure works. That is, only the surface portion has a high salt concentration, a gradient structure with a low salt concentration inside and a high salt concentration inside. Such a structure can be obtained by coating a resin neutralized with an ammonium salt with a salt after lowering the outer salt concentration by heat treatment. The coating at this time is preferably performed with an alkali metal or the like different from the ammonium salt. Coating can be performed by spraying an aqueous solution of sodium hydroxide, potassium hydroxide, lithium hydroxide or the like evenly on the resin.

  Absorbent resin usually consists of acid groups such as carboxyl groups and sulfonic acid groups and neutralized salts thereof, basic groups such as amino groups and neutralized salts thereof, etc. What is the surface salt concentration of absorbent resin particles? The ratio of the neutralized group of the surface part of an absorptive resin particle is represented. In the present invention, the salt concentration in the vicinity of the surface of the resin particle is determined by measuring by a microscopic ATR method which is one of infrared absorption analysis methods. In this ATR method, structural information having a surface layer depth of 1 μm is usually obtained, so that the neutralization rate of the resin particle surface can be directly measured by the microscopic ATR method. The internal portion is measured by a micro ATR method after cleaving the resin by using an ultramicrotome (ULTRACUT N manufactured by Reichert) to expose the central portion. As a measuring device, FTS-575 manufactured by Bio-Rad is used.

Hereinafter, a polyacrylic acid-based absorbent resin will be described as an example. As an indicator for defining the composition ratio of carboxylic acid and carboxylate, 1,695 cm ^-1 (carboxylate νC = 0 Baseline 1774~1616cm ^-1) and 1558cm ^{-1 -} peak of (carboxylate νCOO baseline 1616~1500cm ^-1) An area ratio (1695/1558 cm ⁻¹ ) was calculated, and separately prepared by measuring and preparing 10 mol%, 30 mol%, 50 mol%, 70 mol%, 90 mol%, 100 mol% partially neutralized polyacrylic acid neutralized with ammonia as a standard sample The composition ratio is obtained from the line.

(Surface strength)
Next, the absorbent resin particles before adhering onto the substrate preferably have a surface strength of 0.1 to 5.5N, more preferably 0.1 to 5N, and even more preferably 0.2 to 4N. Most preferably, it is 0.2-3N. The surface strength is a parameter representing the ease of deformation of the particle surface. When absorbent resin particles that have been swollen after absorbing at a specific magnification are put in a container and a load is applied, the gel moves and deforms so as to fill the gaps in the absorbent resin particles that have been filled in the container. I will do it. Since the surface strength is an elastic modulus when the absorbed resin particles that have been absorbed reach an actual volume, it means the magnitude of interaction between gel particles and the ease of surface deformation. A high surface strength indicates that the absorbent resin particles are not easily deformed. That it is hard to deform | transform will mean that an absorbent resin particle will absorb and swell, whereas it will have a strong negative force, and will thereby reduce the absorption capacity. Further, if the surface is not easily deformed, the adhesion surface between the resin and the substrate becomes small, and the particles are likely to be detached from the composite, which is not preferable. The surface strength of the absorbent resin particles of the present invention is determined as follows.
Equipment: Shimadzu Autograph AG-1
Sample: 0.10 g of absorptive resin particles were precisely weighed and uniformly placed in the bottom of a cylindrical container having an inner diameter of 20.5 mm and a height of 50 mm, with a nylon sheet having a pore diameter of 75 μm attached to the bottom surface. A 50φ petri dish was prepared, 0.90 g of physiological saline was added, and the cylindrical container containing the absorbent resin particles was left to stand for absorption swelling for 1 hour.
Measurement: A 1 kN load cell was used, and a cylindrical shaft having a diameter of 19.7 mm was attached. The measurement range is set to 0.2 kN, and is set so that the load cell is lowered at a constant speed of 0.6 mm / min according to the height at which no load is applied to the load cell. The pressure applied to the load cell was recorded over time. Here, the surface strength represents the load (N) when the actual volume is reached. The actual volume of the absorbent resin particles was calculated using the specific gravity of physiological saline 1.010 g / cm ³ and the specific gravity of the absorbent resin particles.

(Evaluation of water absorbent resin)
Next, evaluation of the water absorbent resin performance will be described.

  If 1 g of water-absorbing resin exhibits the ability to capture 60 g or more of physiological saline in 1 second, it can be used as a “thin and lightweight absorber” that does not leak very thinly. However, the current vortex method is a method in which 2 g of water-absorbing resin is introduced into 50 g of physiological saline stirred at a predetermined speed, and the time until the liquid surface becomes flat immediately after the addition (the time when the vortex disappears) is measured. In this method, the water-absorbing resin is only uniformly diffused in the physiological saline and takes 3 to 4 seconds. This is 8.3 g / sec · g-water-absorbing resin even at the highest calculation speed, and the absorption rate of the water-absorbing resin having a rate substantially equal to or higher than 10 g / sec · g-water-absorbing resin cannot be measured. . Accordingly, it has become possible to measure the absorption rate of a water-absorbing resin having a rate equal to or higher than 60 g / sec · g-water-absorbing resin by the following method as a new method for measuring the absorption rate.

  As a new measurement method, first, a predetermined amount of resin is sandwiched between cloths of a predetermined size, and physiological saline is dropped to the center of the cloth for a predetermined time. At that time, the time from the start of the physiological saline dropping until the physiological saline leaks from the end of the cloth is measured. As a result of measuring the water absorption rate of the resin by this measurement method, it was confirmed that the resin of the present invention has a performance higher than that of 60 g / sec · g-water absorbent resin.

(Measurement method of absorption rate by sandwiching between sheets)
Cut rayon spun lace 25 g / ^{m 2} basis weight of (Kuo made paper) Vertical 15cm, a rectangular horizontal 10 cm. Between two cut rayon spunlaces, 0.75 g of water-absorbing resin is dispersed as evenly as possible to prepare an absorbent body. A weir is provided in the longitudinal direction of the absorbent body so that the physiological saline does not leak in the lateral direction of the absorbent body, and the physiological saline leaking in the lateral direction is allowed to run in the longitudinal direction. (See FIG. 1) 0.9% physiological saline adjusted to 25 ° C. is dropped at a rate of 5 g / sec from a height of 1.5 cm onto the center of the absorber. When the liquid leaks outside from the longitudinal edge of the absorbent body, the dropping of the physiological saline is finished. The amount of saline solution (g) finally dropped is measured. The dropping time (seconds) is a value obtained by dividing the dropped saline amount by 5 g / sec. According to (Formula 1), the absorption speed of the sheet sandwiching method is calculated.
(Formula 1)
Absorption rate of sheet sandwiching method (g / sec · g-water absorbent resin) = 5 (g / sec) / {0.75 g × 1 (sec) / drop time (sec)}
Moreover, in the water absorption magnification measurement test of the T-bag method (details of the measurement method are described below), the water-absorbent resin exhibits a performance of 35 g / g or more. Usually, a water-absorbing resin having a water absorption rate of 60 g / sec · g-water absorbing resin or more, a water holding power of 25 g / g or more, and an absorption ratio of 35 g / g or more has not been confirmed. In the present invention, the thickness of the resin layer is set to 30 μm or less, and the response speed when the resin is in contact with the liquid is increased to enable ultra-high-speed absorption of body fluid. Further, since the resin has a hollow space inside the resin in addition to the resin portion, the water can be retained, so that high water retention can be achieved.
(T-bag method absorption capacity measurement test)
The absorption capacity of the water-absorbent resin of the present invention is an amount capable of freely swelling and absorbing 0.9% physiological saline in a state where no load is applied to the water-absorbent resin. The absorption capacity of the water absorbent resin is measured by the following method.

A water-absorbing resin 0.5 g is uniformly placed in a non-woven tea bag bag (60 × 40 mm) and immersed in 0.9% physiological saline at 23 ° C. After 60 minutes, the bag is taken out, the corner of the tea bag is fixed, suspended for 10 minutes in an oblique state, drained, and then weighed. The same operation is performed without using the water absorbent resin, and the weight is measured to obtain a blank. Absorption capacity is calculated according to (Equation 2). The measurement is performed three times, and the average value is taken as the absorption magnification.
(Formula 2)
Absorption capacity of water absorbent resin (g / g) = {(weight of tea bag after water absorption) − (weight of tea bag after water absorption) − (weight of water absorbent resin)} / (weight of water absorbent resin)
(Water retention test)
The T-bag containing the water-containing resin immediately after the T-bag method absorption ratio measurement test is put into a centrifuge, dehydrated at 250 G for 3 minutes, and the weight is measured. The same operation is performed without using the water absorbent resin, and the weight is measured to obtain a blank. The water retention capacity is calculated according to (Equation 3). The measurement is performed three times, and the average value is the water retention capacity.
(Formula 3)
Water retention capacity of water-absorbent resin (g / g) = {(weight of tea bag after water absorption and dewatered by centrifugal separator) − (weight of blank tea bag after water absorption) − (weight of water-absorbent resin)} / ( Weight of water absorbent resin)
(Measurement method of absorption rate by vortex method)
50 g of 0.9% physiological saline adjusted to 25 ° C. is measured in a 100 cc glass beaker. Put a 30 * 8mm rotor here, put it on a magnetic stirrer with a tachometer, and rotate it at 600 rpm. Check the rotation speed with a non-contact tachometer. 2.00 g of water-absorbing resin is weighed and put into a beaker. The absorption time is defined as the time after the water-absorbing resin is charged until the liquid surface becomes flat. The absorption rate is calculated according to (Equation 4).
(Formula 4)
Absorption rate of water-absorbent resin by vortex method (g / sec · g-water-absorbent resin) = 50 g / (2 g × absorption time (seconds))
The water-absorbing resin of the present invention is a resin having a very excellent balance of absorption capacity, water retention, and water absorption speed, and the resin may be used alone, but is used in combination with resins having different performances. This is also a preferred method.
(Bulk specific gravity measurement method)
The dried water-absorbent resin is charged into a 2 cc volumetric flask (allowable error + −0.015 cc) at room temperature for 2 cc so as to be finely packed. A value obtained by measuring the resin weight in a fine state including the gap and dividing by the volume of 2 cc is defined as the bulk specific gravity.

5. Regarding the particle diameter of the water absorbent resin in the composite The weight average particle diameter of the water absorbent resin particles used in the present invention is preferably 10 to 500 μm, more preferably 30 to 400 μm, still more preferably 50 to 300 μm, most preferably. Is 70-200 μm. If the average particle size is too small, it is not preferable in terms of water absorption performance. On the other hand, if it is too large, the absorption rate is inferior and the feel of the particles becomes conspicuous.

  In the present invention, the particle diameter of the water-absorbent resin particles is 32 μm, 38 μm, 45 μm, 53 μm, 63 μm, 75 μm, 90 μm, 106 μm, 125 μm, 150 μm, 180 μm, 212 μm, 250 μm, 300 μm, 355 μm, 425 μm, 500 μm. , 600 μm, 710 μm, 850 μm, 1000 μm, 1180 μm, 1400 μm, 1700 μm and 2500 μm. In the present invention, the particle diameter is an intermediate value between the opening of a sieve that can pass and the opening of a sieve that cannot pass. In addition, about what passed the 32 micrometers sieve, it is set to 16 micrometers, and about what remained on the 2500 micrometers sieve, it shall be 2700 micrometers. By this operation, 16 μm, 35 μm, 41.5 μm, 49 μm, 58 μm, 69 μm, 82.5 μm, 98 μm, 115.5 μm, 137.5 μm, 165 μm, 196 μm, 231 μm, 275 μm, 327.5 μm, 390 μm, 462.5 μm, The particle sizes are classified into 550 μm, 655 μm, 780 μm, 925 μm, 1090 μm, 1290 μm, 1550 μm, 1850 μm, 2100 μm and 2700 μm.

  The water-absorbent resin particles in the composite of the present invention preferably have 50% or less, more preferably 30% or less, and still more preferably 10% of the particles that cannot pass through a sieve having an opening of 500 μm. It is as follows. Particles that cannot pass through a 300 μm sieve are preferably 70% or less, more preferably 50% or less. Particles with an opening of 106 μm are preferably 50% or less, and more preferably 30% or less. Particles that pass through a 63 μm sieve are preferably 30% or less, and preferably 10% or less. When a large amount of particles that are too large are present, the tactile sensation of the particles becomes noticeable in the composite, which is not preferable. Particles that are too small are not a problem as long as they are completely adhered, but are not preferred because they are likely to scatter when they are not adhered.

6). About Base Material In the present invention, the base material refers to a material that can maintain a sheet shape.
(Material)
In the present invention, the substrate refers to a sheet. Any material may be used, but it is preferably hydrophilic and preferably paper and / or cloth. In the present invention, the hydrophilic substrate means a substrate having an absorption rate of 0.2 mg / second or more described later. Paper refers to paper in a broad sense defined by JISP0001, and cloth is a generic term for sheet-like fiber products defined by JISL0206. The cloth is classified into a woven fabric, a knitted fabric, a braided article, a lace, a net, and a non-woven fabric according to the means for forming the sheet. The fabric used in the present invention is preferably a woven fabric, a knitted fabric, or a non-woven fabric, and more preferably a non-woven fabric. Paper and / or cloth is preferred because of its excellent shape stability. Nonwoven fabric is defined by JIS L 0222.

The raw material for the substrate is not limited, and a plurality of combinations of substrates may be used. The base fiber includes both natural fiber and synthetic fiber, and a combination of a plurality of fibers may be used. The length of the fiber may be short fiber or long fiber. A treatment may be applied for strengthening or imparting hydrophilicity. Long fibers are preferred when diffusibility is desired. Short fibers are preferred from the viewpoint of capture power. In particular, since pulp has an excellent capturing power, a base material in which the pulp is cloth-like is preferable.
Of the hydrophilic substrates, cellulose-based substrates are particularly preferable. The cellulosic substrate in the present invention refers to a fabric and / or paper containing cellulose as a main raw material, and among these, a fabric and / or paper composed of cellulosic fibers, particularly a cellulose nonwoven fabric is preferred. Cellulose may be derivatized by treatment such as esterification or etherification. Moreover, what was mixed with the other fiber may be used. Examples of cellulose include natural fibers such as cotton and hemp, and regenerated fibers such as rayon, polynosic, lyocell, and cupra. As the fiber, a regenerated fiber is preferable, and a fiber obtained by regenerating a cotton seed which is an annual grass is more preferable.

(shape)
The shape of the substrate is not particularly limited, and the thickness per sheet is preferably 0.001 mm or more, more preferably 0.01 mm or more, further preferably 0.05 mm or more, and most preferably 0.1 mm. That's it. The basis weight per one substrate is preferably from 28~100g / ^{m 2,} more preferably from 35~80g / ^{m 2,} and still more preferably from 40 to 60 g / ^{m 2.} Those that are too thin are not preferred in terms of strength. The thicker the thickness, the larger the space for holding the resin, the less likely the contact between the resins occurs, and the greater the contact between the resin and the fiber, which is preferable from the viewpoint of absorption speed. In addition, the surface of the base material is more preferable than the smooth surface since the number of contact points between the resin and the base fiber increases as the number of irregularities increases. An excessively light one is not preferable because the amount of fiber that becomes a water passage is insufficient with respect to the water absorbent resin. When the resin is too heavy, the ratio of the fibers to the resin becomes too high, and if the resin cannot absorb the liquid in the fibers, it may cause reversal, which is not preferable.

In the case of using a plurality of base materials, it is preferable that at least one base material satisfies the aforementioned basis weight. When there are a plurality of resin layers, it is preferable that at least one base material satisfies the basis weight described above for each resin layer.
The number of the base material and the resin layer may be any number, but when the ratio of the total weight of the water-absorbing resin and the total weight of the base material is within a certain range, the balance between the absorption rate and the reversibility becomes particularly good. The ratio of the water absorbent resin to the substrate is preferably 35 to 300%, more preferably 42 to 250%, still more preferably 50 to 200%, and 60 to 140%. Most preferred.

(Tensile strength at break)
In the present invention, the tensile breaking strength after physiological saline is preferably 0.6 N / 20 mm or more, more preferably 0.6 to 5000 N / 20 mm, and further preferably 0.7 to 500 N / 20 mm. Yes, more preferably 0.85 to 100 N / 20 mm, and most preferably 1 to 100 N / 20 mm.

  In the present invention, the direction in which the intensity is maximum is the vertical direction, and the direction perpendicular to the vertical direction is the horizontal direction, but in the horizontal direction (that is, in both the vertical direction and the horizontal direction) preferable.

  In the present invention, the tensile strength at break after absorption of physiological saline by the substrate represents the tensile strength at break after absorption of physiological saline by the substrate. In sanitary materials, they may be used as they are without being replaced immediately after liquid absorption. Moreover, after liquid absorption, liquid absorption over several times may be calculated | required. If the use is continued after absorbing once, a load is applied in a state where moisture exists in the absorber. If the substrate breaks due to the load, the liquid permeability and liquid diffusibility are lowered, and the performance of the absorber is deteriorated. It can be said that a base material that maintains a high strength even after absorption of physiological saline is preferable in terms of durability of the absorbent body. Moreover, in the case of a process in which the base material contains water at the time of production, there may be a problem if the strength at the time of water inclusion is low. However, even if the strength is too high, there is virtually no difference in performance.

The tensile strength at break after absorption of physiological saline is determined as follows.
Sample: 15 cm × 2 cm rectangular base material (preparing several types by changing direction)
Equipment: Tensile tester (Shimadzu autograph)
Method: 700 g of 0.9% saline is taken in a 1 L beaker and the substrate is immersed for 10 minutes. The substrate is pulled up, left on a Kim towel for 1 minute, and a portion of 2.5 cm is set from both ends so that the distance is 10 cm, and the substrate is pulled until it breaks at a speed of 10 mm / min. The force at this time is recorded, and the maximum value is the strength N / 20 mm. If there is a direction, change the direction and measure several points.

(Absorption capacity)
In the present invention, the absorption rate of the base material is a value measured by measuring how many times the base material absorbs 0.9% physiological saline in 60 minutes, and is specifically as follows. Measure by method. The substrate is cut into a circle having a diameter of 59.5 mm, and the weight is recorded. Then, a wire is passed through the circumferential portion at a distance of 1 cm. 500 g or more of 23 ° C. physiological saline is prepared in a 1 L beaker, and the substrate is dipped in the physiological saline together with the wire. After 60 minutes, the substrate together with the wire is taken out from the physiological saline and suspended for 10 minutes so that the substrate does not come into contact with the other. Ten minutes later, the wire is removed and the total weight of the water-containing base material and the attached water is measured.

The absorption capacity of the base material is shown by the formula (7).
(Formula 7)
Absorption capacity of substrate (g / g) = weight after absorption (g) / weight before absorption (g)
In the present invention, the absorption capacity of the substrate is preferably from 6 g / g to 200 g / g, more preferably from 8 g / g to 100 g / g, still more preferably from 10 g / g to 50 g / g. Most preferably, it is 12 g / g or more and 30 g / g.

  In the absorbent composite, the fiber absorbs faster than the water-absorbent resin particles, so that the substrate absorbs in the early stage of absorption and the water-absorbent resin particles absorb in the later stage. A higher absorption rate of the substrate is preferable because an initial liquid absorption rate is increased. Usually, the absorption of the substrate is due to capillary action, and when a load is applied, the liquid may return or may cause stuffiness during use. Therefore, when the resin particles are bonded in the form of taking in the fibers of the base material, the water-absorbing resin absorbs the liquid from the base material. For this reason, it is unlikely that the liquid will return due to the load or stuffy during use.

(Absorption rate)
As an index representing the hydrophilicity and liquid permeability of the substrate, there is an absorption rate. In the present invention, the absorption rate of the substrate represents a rate at which the substrate having a width of 2 cm absorbs 0.9% physiological saline in the vertical direction.

  The absorption rate of the substrate is preferably 0.2 mg / second or more and 100 mg / second or less, more preferably 0.3 mg / second or more and 50 mg / second or less, further preferably 0.40 mg / second or more and 30 mg / second or less, Most preferably, it is 0.5 mg / second or more and 10 mg / second or less.

Specifically, the absorption rate of the substrate is measured as follows.
Sample: 10 cm × 2 cm rectangular substrate
For those with vertical and horizontal directions, change the direction and prepare two or more points: Electronic balance, Petri dish with a diameter of 90 mm Method: Place the petri dish on the electronic balance and suspend the substrate vertically from 10 cm above the petri dish. The petri dish is taken from the electronic balance, and 60 g of 0.9% physiological saline is weighed with another balance. Hold the lower part of the base material by hand and place the petri dish again on the electronic balance so as not to touch the physiological saline, and set the value of the balance to 0 point. The substrate is gently soaked in physiological saline, and the value of the electronic balance is recorded over time. The time (second) and the absolute value (mg) of the value of the electronic balance are plotted on a graph, and the slope (mg / second) between 120 seconds and 240 seconds is taken as the absorption rate. If the substrate has a direction, change the direction, measure several points, and take the fastest value as the absorption rate.

  It can be said that it is preferable that the substrate has directions with different absorption rates. When a direction exists in the substrate, the liquid permeability in a specific direction is excellent and the liquid is easily diffused in the specific direction, so that the balance of absorption in the absorber can be controlled.

(Longitudinal and transverse tensile elongation at break, strength ratio)
When a direction exists in the base material, strength and elongation change in each direction. As described above, in the present invention, the direction in which the intensity is maximum is the vertical direction, and the direction perpendicular thereto is the horizontal direction. The ratio between the tensile strength at break in the machine direction and the transverse direction is preferably 1.2: 1 or more, more preferably 1.5: 1 or more, still more preferably 2: 1 or more, and 10: 1 or less.

The ratio of the tensile elongation at break in the machine direction and the transverse direction is preferably 1: 1.2 or more, more preferably 1: 1.5 or more, still more preferably 1: 2 or more, and 1:10 or less. is there. The elongation and strength of the base material can be determined by conducting a tensile test in a dry state without being immersed in physiological saline in the same manner as the strength of the base material after absorption of physiological saline. The tensile test is performed until the base material breaks, and the force at the maximum strength is defined as the strength of the base material, and the distance stretched at that time is defined as the elongation.
(Contact angle)
The base material in the present invention is preferably a nonwoven fabric having a contact angle of 130 degrees or less.

  The contact angle in the present invention is defined as an angle formed after 10 seconds after contacting a substrate with a 44% ammonium polyacrylate aqueous solution having a viscosity of 74 cp at room temperature. The measurement is performed using a contact angle meter (CA-X150 type) manufactured by FACE (Kyowa Interface Science Co., Ltd.). The liquid is a Wako Pure Chemicals 44% ammonium polyacrylate aqueous solution (70 to 110 cp), which is used after adjusting the viscosity with water. Viscosity is measured using a rotating disk viscometer.

  The contact angle is preferably 130 degrees or less, more preferably 120 degrees or less, still more preferably 110 degrees or less, and most preferably 100 degrees or less. The smaller the contact angle, the higher the affinity between the base material and water, and the base material and the water-absorbent resin, which is preferable in terms of absorbability and adhesiveness.

7). Production method of absorbent composite The absorbent composite in the present invention is preferably produced by a production method including a step of adhering the water-absorbent resin particles to the substrate using the water-absorbent resin particles and the substrate as raw materials.

  The adhesion method is not particularly limited, and an adhesion method that satisfies the above-described conditions may be performed. Examples of the bonding method include a method in which a water-absorbing resin is entangled in a base material, a method using an adhesive, and the like. In this method, the water-absorbing resin and / or the base material is absorbed, and then the water-absorbing resin and the base material are in contact with each other and dehydrated. The amount of water is preferably 20 to 2000 parts by weight and more preferably 50 to 1000 parts by weight with respect to 100 parts by weight of the water absorbent resin particles. Adhesion by this method is preferable because it is not necessary to use an adhesive as an impurity. Moreover, since adhesion | attachment is carried out by this method, since a part of fiber will be taken in into a water absorbing resin, it is preferable at the point of an absorption rate or an absorption magnification. The larger the amount of water, the higher the adhesiveness and the better. However, too much water is inefficient because it takes too long to dry.

  Water may be absorbed by either the base material or the water-absorbing resin, but it is preferable that the base material absorb water. The water content of the base material when the base material is water-containing and then brought into contact with the water-absorbent resin particles is preferably in the range of 50 to 500% by weight. In order to improve the adhesiveness between the water-absorbent resin particles and the substrate, it is preferable that the water content is high, but if it is too high, it takes time to dry. Of course, if the water content is too low, there is a problem that the adhesion between the substrate and the resin is lowered. Therefore, the range of a preferable moisture content is 50 to 200% by weight, and more preferably 80 to 150% by weight. When using a plurality of base materials, it is preferable to hydrate all the base materials.

  As a water-containing method for adhesion, a method in which water for adhesion is included in the water-absorbent resin particles may be adopted, but in that case, the water-absorbent resin tends to stick to parts other than the base material. The water absorbent resin particles before contact are preferably dried to such an extent that they do not adhere to other substances or adhere to each other. In this case, the water content of the water-absorbent resin particles is preferably 1 to 50% by weight. More preferably, it is 5 to 30% by weight.

  Examples of the contact method include a method of spraying water-absorbing resin particles from above on a substrate, a method of spraying the water-absorbing resin together with air, and the like. A method in which the water-absorbent resin particles can be arranged so that there is less overlap is preferable from the viewpoint of adhesiveness. Furthermore, it is preferable that the method increases the entanglement between the base fiber and the resin because the absorption rate is improved. As a method of increasing the entanglement between the base fiber and the resin, there are a method of raising the base material and a method of applying a press to improve the adhesion between the base material and the resin after contact. When pressing is performed, the resin may adhere to a portion where the press machine and the resin are in contact with each other. Therefore, it is preferable that the contact portion is made of a material that does not easily adhere to the resin. The material that does not easily adhere is a hydrophobic material, and examples thereof include polyolefins and Teflon (registered trademark), and Teflon (registered trademark) is particularly preferable. A Teflon (registered trademark) sheet may be rubbed or coated. The most preferable method for preventing the adhesion of the resin is not to dispose the resin on the surface. In other words, one more base material than the resin layer is used, and the resin is completely sandwiched between the base materials.

  The water to be hydrated may contain impurities. Examples of the impurities include cations such as sodium ion, ammonium ion and iron ion, anions such as chlorine ion, water-soluble organic compounds such as acetone, alcohols, ethers and amines. In order to adjust the pH of the water-absorbent resin and / or the absorbent composite, an acidic or basic one may be used. In view of the contact between the water-absorbent resin and the substrate and the absorption capacity, it is preferable to use distilled water or ion-exchanged water free from these impurities alone.

  In addition, it is a preferable method to impart a function to the absorbent composite produced by dissolving and / or dispersing a substance having a function such as deodorization in water. Examples of deodorants that can be used here include organic and inorganic deodorants. When using a deodorant insoluble in water, it is preferable to use a dispersant or a surfactant as necessary. In addition, inorganic deodorants can be dispersed in water without using a dispersant by reducing the particle size to the nano level. It is preferred to use without.

  There is no particular limitation on the water-containing method. For example, a method of attaching to a water bath, a method of spraying water, a method of contacting with a water-containing body, a method of exposing to a humidified state and the like can be mentioned. Among these, the water spray method, which is industrially simple and easy to adjust the water content, is a preferred method. As the water spraying method, it is preferable to adopt a method in which the moisture content of the substrate such as cloth is uniform. If there is a large variation in the moisture content at each location on the base material, the amount of water absorbent resin particles that absorb water before contacting the water absorbent resin and before the dehydration drying process varies depending on the location. The accompanying foaming behavior is different, and the resin particle size in the absorbent composite after drying becomes inhomogeneous. An absorptive complex in which resin particles having a non-uniform particle size are arranged may deteriorate the texture.

  When the water absorbent resin is an aggregate of particles, it is preferable to apply a load to the resin so that a part of the aggregate is broken before dehydration drying. The load may be before moisture content, after moisture content, before contact with the cloth, or after contact. Considering the scattering of fragments, it is preferable to be after hydration, and preferably after contact with the cloth. Any method may be used for loading. In order to give the resin a sufficient speed, it is conceivable to increase the surface hardness of the resin. However, a resin having a high surface hardness has a drawback that it is difficult to adhere. Even if the surface hardness of the aggregated particles is high, there is a part with low hardness inside, so by applying a load and breaking a part of the aggregate, the part with low hardness is exposed sufficiently. It can be glued.

  Any method of dehydration may be used. Examples of the method include drying by heating, a method of spraying dry air or nitrogen, vacuum drying, freeze drying, azeotropic dehydration, fluidized drying, and microwave, and drying by heating is preferable. The heating condition is preferably 70 to 350 ° C. for 1 second to 1000 seconds, more preferably 100 to 340 ° C. for 1 second to 1000 seconds, and still more preferably 120 to 330 ° C. for 1 second to 1000 seconds. Most preferably, it is 150 to 300 ° C. for 1 to 1000 seconds. The higher the temperature, the shorter the drying time is. However, when the heating is performed for a long time at a high temperature, the absorption performance may be lowered depending on the type of the resin. Simultaneously with the drying, a surface treatment such as surface crosslinking may be performed. The dehydration may be performed at any time until the final product is obtained, but it is preferable to perform the dehydration promptly after hydration from the viewpoint of deterioration of the water absorbent resin.

  It is preferable to include a step of softening the flexibility of the absorbent composite after dehydration. This process improves the texture and absorption rate. Although the method is not particularly limited, there are a method of spraying a drug having an effect of softening a base material such as a softening agent, a method of softening by applying a physical force, and the like. A method of softening by physical force can be said to be a simple and preferable method. In order to apply a force to the composite, there are a method in which a small roll is used to flow the fabric at a steep angle, or an embossing roll is passed. It is preferable to apply a force so as to be soft in both the vertical and horizontal directions.

  Since an absorptive complex is a sheet form and a substrate is also a sheet form, it is preferred to manufacture a roll absorptive complex using a roll substrate. That is, the substrate that has flowed from the substrate roll is hydrated, a dried water-absorbing resin is disposed, dried, and then rolled again. Considering the slipperiness when spread on a roll, it is preferable that no resin is present on the surface. That is, it can be said that a production method in which two base rolls are prepared, resin is arranged on one base, and another base is stacked and dried simultaneously is preferable. At this time, it is preferable that the base material to be stacked later is also hydrated. Moreover, it is also preferable to press after overlapping. By increasing the number of base rolls and increasing the number of devices to place the resin, the number of resin layers and bases can be increased, but considering the thickness of the product roll and the ease of drying, the number of resin layers is limited to two. It is preferable that

8). Absorbent composite performance (absorption capacity)
In the present invention, the absorption capacity of the absorbent complex is the amount absorbed after 3 hours when 0.9% physiological saline is freely absorbed. Specifically, a circular absorptive composite absorbent body having a diameter of 59.5 mm is prepared, and measurement is performed using a method similar to the above-described absorption capacity of the substrate. However, when desorption occurs, the water-absorbent resin particles are collected by filtration, left to stand on the Kimwipe for 10 seconds or more, drained, and the weight is added for calculation. When water-absorbing resin particles that are not bonded are included, measurement is performed after removing the water-absorbent resin particles.

The absorption capacity of the absorbent composite is preferably 20 g / g or more, more preferably 30 g / g or more, and further preferably 40 g / g or more.
(Absorption per area)
The amount of absorption per area is important as an index of the absorption performance of the absorbent composite. The amount of absorption per area can be calculated according to (Equation 8) from the above measurement results.
(Formula 8)
Absorbed amount per area (g / cm ² ) = ((total weight after absorption (g) −weight of absorbent composite (g)) / area of absorbent composite (cm ² )
The greater the amount of absorption per area, the more preferably 0.1 g / cm ² or more, more preferably 0.3 g / cm ² or more, and even more preferably 0.6 g / cm ² or more.

(Absorption after 1 minute)
Absorption after 1 minute represents the initial liquid absorption rate. In hygiene material applications such as paper diapers, since it is required to absorb body fluid instantly, a larger absorption rate after 1 minute is preferable. The absorption capacity after 1 minute is determined according to (Equation 10). Specifically, it is measured by the following method. The absorbent composite is cut into a length of 2 cm and a width of 7 cm, and the weight is measured. Place 700 cc of physiological saline in a 1000 cc glass beaker. First, the weight of 80 cm long and 70 cm wide T-Bag is measured, water is absorbed for 1 minute in the state of only T-Bag, and then the weight is measured. By dividing this weight by the weight of T-Bag before water absorption, the absorption capacity after 1 minute of T-Bag is determined. The T-Bag of the same size is weighed and the absorbent complex is placed in the T-Bag. In order to quickly draw T-Bag from the liquid, prepare a clip with a string, attach it to the T-Bag, and immerse it quickly and carefully in the liquid so that the cloth does not break or get entangled. After 1 minute of soaking, quickly pull up with a string. Then remove the clip, centrifuge at 150 G for 3 minutes, and measure the weight. The absorption capacity after 1 minute is determined by subtracting the water absorption of T-Bag from the total weight and dividing by the weight of the absorbent composite before water absorption. The period from the lifting of the absorbent complex to the start of centrifugation is within 15 seconds.
(Formula 10)
Absorption rate after 1 minute (g-raw food / g) = (weight after centrifugation (g) -weight of T-Bag (g) * absorption rate after 1 minute of T-Bag) / weight of absorbent complex (G)

(Evaluation of absorbent composite)
(Evaluation of liquid capture ability and returnability of absorbent complex)
Install a sufficiently large wooden board on a horizontal laboratory table. The size of the absorbent composite is 26 cm in the longitudinal direction and 8 cm in the short direction. A top sheet part is cut out from the Unicharm Lifely Refreshing Pad 120cc and placed on the absorbent composite. As shown in FIG. 1, weirs are provided along the longitudinal direction of the absorbent composite so that the liquid does not flow in the lateral direction. 80 g of physiological saline warmed to 37 ° C. is weighed and added dropwise to the center of the absorbent composite over 10 seconds. The absorption time is defined as the time when the entire surface is felt dry when touched lightly so that no force is applied to the surface. The length at which the liquid spreads at that time is defined as the diffusion length. It can be said that the shorter the diffusion length, the higher the liquid capturing ability and the less likely it is to leak. The faster the absorption time, the faster the absorption rate. Ten minutes after the start of dropping, about 100 g of filter paper obtained by cutting Advantech No. 2 filter paper having a diameter of 150 mm into a square with a side of 10 cm is left below the drop. A 3.5 kg load is applied thereon. Remove the load 3 minutes after setting the load, measure the weight of the filter paper, and use the increased weight as the return amount. The smaller the return amount, the better the dry feeling.

9. About the usage method of an absorptive complex The usage as a component of a bodily fluid absorption article is mentioned as a preferable usage method of the absorptive complex of this invention. The case where it uses as a component of a bodily fluid absorption article below is demonstrated.
(Body fluid absorbent article)
The bodily fluid absorbent article of the present invention is a bodily fluid absorbent article composed of a liquid permeable sheet, a liquid impermeable sheet, and an absorbent composite interposed therebetween, and refers to all articles having the ability to absorb bodily fluids. The body fluid to be absorbed in the present invention is not particularly limited, and examples thereof include urine, menstrual blood, breast milk, and loose stool. The shape of the article is not particularly limited, but a pad shape, a tape type, a pants type, or the like is preferably used. Specific examples include diapers, sanitary napkins, urine pads, breast milk pads, and the like.

  When the absorbent composite of the present invention is combined with a liquid-permeable sheet and a liquid-impermeable sheet, a body fluid-absorbing article that is thin and lightweight and has a high absorption rate can be constituted. In addition, since the absorber does not easily shift or move in the body fluid absorbent article during use, the body fluid can be stably absorbed.

  In the present invention, the liquid-permeable sheet is a sheet shape, and any sheet may be used as long as it allows water to pass through when the sheet is sprayed with water, but a cloth as defined in JISL0206. It is preferable that Fabrics are classified into woven fabrics, knitted fabrics, braided fabrics, laces, nets, and non-woven fabrics according to the means for forming the sheet. However, the fabrics used in the liquid-permeable sheet of the present invention are preferably woven fabrics, knitted fabrics, and non-woven fabrics. preferable. In order to eliminate the moist feeling of the part in contact with the skin and make the touch comfortable, a sheet having a low water absorption capacity made of a polyolefin such as polyethylene and polypropylene is preferable. It is preferable that it is a polyolefin system which has been subjected to hydrophilization treatment.

  In the present invention, the liquid-impervious sheet may be any sheet as long as it has a sheet shape and does not transmit water. From the viewpoint of preventing dampness, a material having good air permeability is preferable.

  In the bodily fluid absorbent article of the present invention, there is no problem as long as there is at least an absorbent composite interposed between the liquid permeable sheet and the liquid impermeable sheet, but between the liquid permeable sheet and the absorbent composite, and / or Alternatively, other members may exist between the liquid-impermeable sheet and the absorbent composite. Further, other members may exist outside the liquid-permeable sheet and the liquid-impermeable sheet.

  Examples of the member used here include fibrous materials such as pulp, particulate materials such as a water-absorbing resin, and sheet materials such as tissue, cloth and paper. These members may be bonded to the absorbent composite of the present invention. As an adhesion method, it may be adhered using an adhesive, or may be directly adhered to the water absorbent resin particles in the absorbent composite of the present invention. In the body fluid absorbent article, in addition to the liquid permeable sheet, liquid impermeable sheet, and absorbent composite, for example, tape and rubber for fixing to the body, gathers for preventing side leakage, etc. It is preferable that there is.

  The shape of the bodily fluid absorbent article of the present invention may be a square, a perfect circle, a rectangle, an ellipse, a trapezoid, or an indefinite shape. In the case of a diaper, sanitary product, urine collection pad, etc., the shape of a rectangle or ellipse, or a shape that has a longitudinal direction and a transverse direction (direction perpendicular to the longitudinal direction) similar to that of a rectangle or ellipse. It is preferable because it can be attached together. There may be a part to be used for bonding the absorbent composite to other members.

  In addition, although there may be a marginal portion in which the water-absorbing resin does not exist in the absorbent composite, the basis weight of the water-absorbing resin in the absorbent composite is in a state where the portion is omitted, It is preferable that the preferable range of conditions for the absorbent composite is satisfied.

  The number of absorbent composites used may be one, or a plurality of sheets may be used. In order to construct a thin article, it is preferable to use only one sheet. It is preferable to use a plurality of sheets in order to construct an article having a higher absorbency. When using a plurality of sheets, they may be used in a stacked manner, or may be used side by side. Moreover, the thing of the completely same shape may be used, and the thing of a different shape may be used. In order to improve the absorption capacity without waste, it is preferable to use only the part where the body fluid is secreted, and when it is desired to prevent leakage, it is preferable to use the part that is likely to leak.

  The state of the absorbent composite in the body fluid absorbent article is not particularly limited, and the absorbent composite sheet may be in a fully stretched state, in a wrinkled state, or in a folded state.

  Specific examples and comparative examples of the present invention are shown below, but the present invention is not limited to the following examples.

Production Example 1
Weigh 100 g of reagent acrylic acid (manufactured by Wako Pure Chemicals, reagent special grade) into a 200 ml flask and add dropwise 95.7 g of 25 wt% aqueous ammonia while stirring to keep the internal temperature below 30 ° C. 195.7 g of neutralized ammonium acrylate aqueous solution was produced. As a polymerization apparatus, the above-mentioned ammonium acrylate aqueous solution and 0.0173 g of N, N′-methylenebisacrylamide were charged in a 2 L separable flask equipped with a reflux condenser whose atmosphere was previously replaced with nitrogen, and dissolved sufficiently. -106 (Kao Co., Ltd., nonionic surfactant) 1.1 g and cyclohexane 22.15 g are added and stirred under a nitrogen flow to be suspended and oil droplets are stably present in the aqueous solution. An emulsion was prepared. At this time, the inside of the polymerization apparatus was controlled to 65 kPa, and oxygen in the apparatus was completely deaerated. Next, 4.44 g of the surfactant sorbitan monostearate was dissolved in 450 g of cyclohexane in a 500 ml flask, and oxygen deaeration in the solvent was sufficiently performed by nitrogen bubbling. Thereafter, 0.0925 g of ammonium persulfate was dissolved in 2 g of distilled water and added to the suspension in the polymerization apparatus. A cyclohexane solution that had been degassed with oxygen was added while thoroughly stirring the inside of the polymerization apparatus. After completion of the addition, the mixture was heated by an oil bath at 60 ° C. to initiate polymerization, and polymerization was carried out for 1 hour. Thereafter, the internal pressure of the polymerization apparatus was increased to normal pressure in a nitrogen atmosphere, the oil bath temperature was increased to 80 ° C., and polymerization was performed for 1 hour to obtain an emulsion containing a hydrous gel. Next, a mixed solution of 20.0 g of ethanol, 1.15 g of glycerin and 180 g of cyclohexane was slowly dropped into an emulsion solution maintained at 80 ° C., and the particles were aggregated so as to have an appropriate particle size. The aggregated particles were taken out, washed with cyclohexane, collected by filtration and vacuum dried at 100 ° C. At this time, cyclohexane inside the particles is removed by evaporation, resulting in a hollow state. The dried resin was pulverized and classified. The electron micrograph of the taken out resin is shown in FIG.

Production Example 2
The resin of Production Example 1 was heated at 150 ° C. for 10 minutes under a nitrogen atmosphere using an inert oven.

Production Example 3
Sodium hydroxide (0.482 g) was dissolved in distilled water (2.4 g), and ethanol (30 g) was added thereto. To this, 10 g of the resin of Production Example 2 was added and stirred for 5 minutes, followed by filtration. Ethanol was added for washing, and drying was performed at 30 ° C. using a vacuum dryer.

Production Example 4
After adding 10.14 g of distilled water to 100 g of reagent acrylic acid, 7.25 g of activated carbon (Shirakaba WH2C manufactured by Nippon Enviro Chemical Co., Ltd.) is added, and the mixture is stirred for 1 hour while cooling so as to keep the internal temperature at 30 ° C. or less. The inhibitor is removed by adsorption with activated carbon, and the aqueous acrylic acid solution is recovered by filtration. 105.6 g of this aqueous acrylic acid solution was weighed into a 200 ml flask, and 80.13 g of 28 wt% ammonia water was added dropwise while stirring so as to keep the internal temperature at 30 ° C. or lower. 185.7 g was produced.

As a polymerization apparatus, 450 g of cyclohexane and 1.11 g of sorbitan monostearate were added to a 2 L separable flask equipped with a reflux condenser whose interior was previously purged with nitrogen, and completely dissolved to prepare an oil phase. The oxygen in the apparatus was completely degassed. Next, 0.0025 g of N, N′-methylenebisacrylamide was added to the aqueous ammonium acrylate solution, dissolved sufficiently, and oxygen was deaerated sufficiently by nitrogen bubbling.
The cyclohexane in the polymerization apparatus is heated to 60 ° C. When the internal temperature reaches the set temperature, a solution prepared by dissolving 0.0920 g of ammonium persulfate in 2 g of distilled water in an aqueous solution of ammonium acrylate is added and stirred uniformly. Thereafter, an aqueous ammonium acrylate solution was introduced into the polymerization apparatus to start polymerization, and the state was maintained for 2 hours. Two hours after the start of charging, the pressure was released to normal pressure to obtain an emulsion containing a hydrous gel. Next, a mixed solution of 8.5 g of ethanol, 1.06 g of glycerin, and 90 g of cyclohexane was slowly dropped into the emulsion solution emulsion maintained at 80 ° C., and the particles were aggregated so as to have an appropriate particle size. The produced hydrogel was washed with cyclohexane, collected by filtration, and dried by vacuum drying at 100 ° C. The dried resin was pulverized and classified.

  An electron micrograph of the extracted resin is shown in FIG. As shown in FIG. 3, the resin particles obtained in Production Example 4 are not hollow unlike those shown in FIG.

Production Example 5
The water absorbent resin obtained in Production Example 4 is heated in an inert oven at 150 ° C. for 30 minutes in a nitrogen atmosphere. Next, 0.16 g of sodium hydroxide, 0.98 g of distilled water, and 0.18 g were dissolved in 6.63 g of ethanol, and this mixed solution was added to 3.01 g of the heat-treated resin and uniformly dispersed. Vacuum drying was performed at room temperature.

Production Example 6
In a 300 ml separable flask, 90 g of 40 wt% ammonium acrylate aqueous solution (100% neutralized), 0.0062 g of N, N′-methylenebisacrylamide, 72.00 g of cyclohexane, nonionic surfactant manufactured by Kao Corporation Add 1.1250 g of Emulgen LS-110. The flask is stirred at 400 rpm for 20 minutes using a magnetic stirrer while bathing in a water bath so that the liquid temperature is maintained at 30 ° C. The aqueous solution was deaerated by bubbling with nitrogen gas, and the reaction system was purged with nitrogen. Next, 0.86 g of 42 wt% glycerin aqueous solution was added with a syringe, and after stirring well, 0.0917 g of 30 wt% aqueous hydrogen peroxide dissolved in 1 g of water and 0.0830 g of Rongalite were added to initiate polymerization. The internal temperature starts from 30 ° C and rises to 80 ° C in 10 minutes from the start of the reaction. Then, it heats for 1 hour with a water bath so that internal temperature may be maintained at 70 degreeC. Thereafter, the gel is taken out from the Separa flask and roughly crushed and then dried at 100 ° C. using an inert oven in a nitrogen atmosphere. After drying, the mixture was pulverized with a homogenizer and sieved.
The mixture was heated at 130 ° C. for 30 minutes in an inert oven under a nitrogen atmosphere.

Production Example 7
In a 300 ml separable flask, 90 g of 40 wt% sodium acrylate aqueous solution (75% neutralized), 0.0062 g of N, N′-methylenebisacrylamide, 72.00 g of cyclohexane, nonionic surfactant manufactured by Kao Corporation Add 1.1250 g of Emulgen LS-110. The flask is stirred at 400 rpm for 20 minutes using a magnetic stirrer while bathing in a water bath so that the liquid temperature is maintained at 30 ° C. The aqueous solution was deaerated by bubbling with nitrogen gas, and the reaction system was purged with nitrogen. Next, 0.0917 g of a 30 wt% aqueous hydrogen peroxide solution and 0.0830 g of Rongalite each dissolved in 1 g of water are added to initiate polymerization. The internal temperature starts from 30 ° C and rises to 80 ° C in 10 minutes from the start of the reaction. Then, it heats for 1 hour with a water bath so that internal temperature may be maintained at 70 degreeC. Thereafter, the gel is taken out from the Separa flask and roughly crushed and then dried at 100 ° C. using an inert oven in a nitrogen atmosphere. After drying, the mixture was pulverized with a homogenizer and sieved.
A solution of 0.05 g of glycerin, 0.15 g of water and 1.5 of isopropyl alcohol was uniformly sprayed on 5 g of the resin of Production Example 8, and heated at 130 ° C. for 30 minutes in a nitrogen atmosphere using an inert oven.

106-300 micrometers resin was taken out out of resin of each manufacture example, and the measurement was performed.

In addition, the resin particles of Production Examples 1 to 3 are hollow, and the resin particles of Production Examples 4 to 7 are not hollow.

Example 1
A registered trademark of “Oji Kinocross KS-40” manufactured by Oji Kinocross Co., Ltd. was cut into rectangles of 30 cm and 20 cm. Water was sprayed on the cloth, and 3.8 g of the resin of Production Example 1 classified to 106 to 300 μm and 3.1 g of the resin classified to 300 to 600 μm were uniformly sprayed thereon. Another piece of cloth cut to the same size was prepared, sprayed with water with a spray, and overlaid on the resin surface that was sprayed earlier. Water was again sprayed thereon, and 3.8 g of the resin of Production Example 1 classified to 106 to 300 μm and 3.1 g of the resin classified to 300 to 600 μm were uniformly sprayed thereon. Another piece of cloth cut to the same size was prepared, sprayed with water, and overlaid on the resin surface. This was sandwiched between plastic plates and lightly loaded by hand and then taken out. A cylinder having a width of 20 cm, a diameter of 10 cm, and 5 kg was prepared, and the cylinder was rolled back and forth twice. Drying was performed at 150 ° C. for 15 minutes under a nitrogen atmosphere using an inert oven. The taken-out absorbent composite was applied to a cylinder having a diameter of 2 cm twice in the vertical and horizontal directions. This is Example 1.

Example 2
A composite was prepared in the same manner as in Example 1 except that the resin of Production Example 3 was used and the drying condition was 120 ° C. for 20 minutes. This is Example 2.

Example 3
A composite was produced in the same manner as in Example 1, except that the resin before heating in the inert oven of Production Example 6 was used and the drying condition was 130 ° C. for 40 minutes (the resin was heated on the cloth). did. This is Example 3.

Example 4
Of the resin after 100 ° C. drying, pulverization and classification in Production Example 7, 7.6 g of the resin classified to 106 to 300 μm and 6.2 g of the resin classified to 300 to 600 μm were weighed and mixed. To this, a solution of 0.138 g of glycerin, 0.414 g of water and 4.14 g of isopropyl alcohol was sprayed uniformly and dried at 80 ° C. using a vacuum dryer. A composite was produced using this resin in the same manner as in Example 3. This is Example 4.

Example 5
A composite was prepared in the same manner as in Example 1 except that no load was applied by a 5 kg cylinder during composite preparation.

Example 6
A composite was produced in the same manner as in Example 1 except that rayon spunlace (basis weight: 45 g / m ² ) manufactured by Kokuko Paper Co., Ltd. was used as the substrate. This is Example 6.

Example 7
The composite of Example 2 was immersed in a solution of 0.69 g of Emulgen LS-110 (manufactured by Kao Corporation, nonionic surfactant) and 40 g of ethanol. After air-drying while applying a nitrogen stream, it was dried at room temperature using a vacuum dryer. This is Example 7.

Comparative Example 1
A composite was produced in the same manner as in Example 2 except that the resin of Production Example 5 was used. This is referred to as Comparative Example 1.

Comparative Example 2
Using the “Oji Kinocross KS-40” registered trademark manufactured by Oji Kinocross Co., Ltd., a bag having the size of an absorber used for each test was prepared. For example, in the case of a diffusivity test, two cloths having a length of 24 cm and a width of 8 cm are prepared, and four sides are formed into a bag using an adhesive. The absorber was produced by putting resin so that it might become the same quantity as Example 1 among resin of manufacture example 3 here. Resin tends to be biased and not stable.

Comparative Example 3
Six pieces of “Spunbond Eltus” (registered trademark) manufactured by Asahi Kasei Fibers Co., Ltd., 20 g / m ² , cut into a length of 30 cm and a width of 20 cm, were prepared and stacked. Of the resin of Production Example 6, 7.6 g of 106 to 300 μm resin and 6.2 g of 300 to 600 μm resin were mixed. 2.76 g of this was uniformly sprayed between 6 nonwoven fabric layers. A composite was prepared by fusing with heat. This is referred to as Comparative Example 3.

Comparative Example 4
A rayon spun lace (basis weight 45 g / m ² ) manufactured by Kokuko Paper Co., Ltd. was cut into a 30 cm and 20 cm rectangle. On top of that, 3.8 g of the resin classified into 106 to 300 μm and 3.1 g of the resin classified into 300 to 600 μm of the resin of Production Example 7 were adhered uniformly using a spray type glue. Further spraying was performed on this, and another piece of cloth cut to the same size was adhered. The same operation was repeated, and the same composite as in Example 6 was produced except that all the resins were bonded with an adhesive. This is referred to as Comparative Example 4.

Comparative Example 5
A composite was produced in the same manner as in Example 4 except that no winding was performed after drying. This is referred to as Comparative Example 5.

Comparative Example 6
A composite was prepared in the same manner as in Example 1 except that the resin amount per resin layer was 1.7 g for those classified to 106 to 300 μm and 1.7 g for those classified to 300 to 600 μm. . This is referred to as Comparative Example 6.

  Although the invention has been described with reference to preferred embodiments, it is to be understood that modifications and changes can be made without departing from the principles and scope of the invention as will be readily appreciated by those skilled in the art. . Accordingly, such modifications can be implemented within the scope of the present invention.

  Since the absorbent composite of the present invention has a high water absorption rate and high water retention, it is lightweight and thin and exhibits high absorption capacity. Therefore, an absorber that does not leak even when a large amount of liquid is added at once can be used without using a large amount of bulky material such as pulp.

Device schematic diagram of the method of measuring the absorption speed of the sandwiching method between sheets Electron micrograph of hollow water-absorbent resin with space inside Electron micrograph of water-absorbent resin of spherical particle aggregate

Claims (9)

An absorbent composite comprising a base material and a particulate water-absorbent resin bonded to each other, wherein the following condition is satisfied.
(1) The bulk specific gravity of the resin is 0.65 or less.
(2) The bending resistance change rate is 60% or less.
(3) At least one substrate is composed of hydrophilic fibers.
(4) 50% or more of the water absorbent resin is directly bonded to the base material.
(5) The residual monomer in the water absorbent resin is 200 ppm or less.
(6) The ratio of the water-absorbing resin weight to the total weight of the absorbent composite is 50 to 99%.
(7) The surface of the water absorbent resin has a nonionic surfactant of HLB7 or higher. The water-absorbent resin is a hollow granular water-absorbent resin having a space inside, and the thickness of the film of the hollow granular water-absorbent resin is 1 to 30 µm. Absorbable complex. The absorbent composite according to claim 1 or 2, wherein the water-absorbent resin has an average particle size of 5 to 1000 µm. 4. The absorbent composite according to claim 2, wherein the content of carboxyl group-containing units in the polymer molecular chain of the hollow granular water-absorbent resin is 50 mol% or more. The absorbent composite according to any one of claims 2 to 4, wherein 50% or more of the carboxyl group-containing units in the polymer molecular chain of the hollow particulate water-absorbent resin is a neutralized salt. The absorptive complex according to claim 5 , which is 10 to 80 mol% ammonium salt among carboxyl group neutralized salt units in the polymer molecular chain of the hollow granular water-absorbent resin. A composite in which a base material and a particulate water-absorbing resin are bonded, wherein the method satisfies the following conditions: A method for producing an absorptive composite comprising a step of dehydrating and drying a substrate and water-absorbent resin particles in contact with each other after absorbing water.
(1) The bulk specific gravity of the resin is 0.65 or less.
(2) The bending resistance change rate is 60% or less.
(3) At least one substrate is composed of hydrophilic fibers.
(4) 50% or more of the water absorbent resin is directly bonded to the base material.
(5) The residual monomer in the water absorbent resin is 200 ppm or less.
(6) The ratio of the water-absorbing resin weight to the total weight of the absorbent composite is 50 to 99%.
(7) The surface of the water absorbent resin has a nonionic surfactant of HLB7 or higher. The method for producing an absorbent composite according to claim 7, wherein the resin is an aggregate of particles and includes a step of applying a load to the resin before dehydration drying. The method for producing an absorbent composite according to claim 7 or 8, further comprising a step of reducing the bending resistance of the absorbent after drying.