JPH0117411B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a water absorbing agent. More specifically, the present invention relates to a water-absorbing agent that highly absorbs an aqueous substance when it comes into contact with an aqueous substance, and has high water retention even under pressure. (Prior Art) Attempts have been made to use water-absorbing resins as a constituent material in sanitary cotton, disposable diapers, and other sanitary materials that absorb body fluids. Examples of such water-absorbing resins include hydrolysates of starch-acrylonitrile graft polymers (Japanese Patent Publication No. 49-197-
43395), neutralized product of starch-acrylic acid graft polymer (JP-A-51-125468), vinyl acetate-
Saponified product of acrylic acid ester copolymer (JP-A-Sho
52-14689), hydrolysates of acrylonitrile copolymers or acrylamide copolymers (Tokukosho
53-15959), or crosslinked products thereof, self-crosslinking sodium polyacrylate obtained by reverse phase suspension polymerization (JP-A No. 53-46389), crosslinked products of partially neutralized polyacrylic acid (Japanese Unexamined Patent Publication No. 55-84304) is known. (Problems to be Solved by the Invention) However, all of these conventional water-absorbing resins have a fatal defect in that their water absorption speed is slower than that of cotton-like pulp or paper. For this reason, for example, when a conventional water-absorbing resin is incorporated into a disposable diaper, the amount of water absorbed by the disposable diaper is low for a while after urine is excreted, so the urine comes into contact with the skin, causing discomfort.
The current situation is that it takes time for the skin to become dry. Therefore, various attempts have been made to increase the water absorption rate. For example, in order to increase the surface area, attempts have been made to reduce the particle size, to form granules, or to form flakes. However, in general, when the particle size of a water-absorbing resin is made small, it becomes so-called "mamako" when it comes into contact with urine, and the water absorption rate becomes slower. When a water-absorbing resin is molded into granules, the granules themselves become a "mako", which causes the water absorption rate to slow down. In addition, when the water-absorbing resin is made into flakes, the water absorption rate is considerably improved, but it is still insufficient.Moreover, there are restrictions from the process perspective in order to make the water-absorbing resin into flakes, so the equilibrium water absorption amount is small. There is. Furthermore, since flakes are inevitably bulky, large facilities are required for transportation and storage, which is not economical. The present invention solves the above-mentioned problems of conventionally known water-absorbing resins,
The purpose is to provide a water absorbing agent that has a high water absorption rate and a high water retention property even under pressure. (Means and effects for solving the problems) As a result of intensive research to solve the above problems, the inventors of the present invention have mixed and heat-treated water-absorbing resin powder with polyhydric alcohol and a specific compound. The present invention was completed by discovering that the water-absorbing agent obtained by the method solves the problems of conventional water-absorbing resins. That is, the water-absorbing agent of the present invention includes a water-absorbing resin powder having a carboxyl group, a polyhydric alcohol (A), and one selected from the group consisting of water and a hydrophilic organic solvent.
The species or two or more compounds (B) and 0.001 to 10 of the polyhydric alcohol (A) per 100 parts by weight of the water-absorbing resin powder.
parts by weight and compound (B) in a ratio of 0.01 to 8 parts by weight, and heated at a temperature of 90°C or higher to react the water-absorbing resin powder and the polyhydric alcohol, thereby reducing the amount of water near the surface of the water-absorbing resin powder. It is obtained by crosslinking molecular chains. The water-absorbing resin used in the present invention needs to have a carboxyl group. Examples of such water-absorbing resins include hydrolysates of starch-acrylonitrile graft polymers, partially neutralized starch-acrylic acid graft polymers, saponified products of vinyl acetate-acrylic acid ester copolymers, and acrylonitrile copolymers. Alternatively, one or more of a hydrolyzate of an acrylamide copolymer, a crosslinked product thereof, a partially neutralized polyacrylic acid, a crosslinked partially neutralized polyacrylic acid, etc. can be used. Among these, it is desirable to have a crosslinked structure, but those without a crosslinked structure can also be used. Among such water-absorbing resins, preferred in the present invention include, for example, the water-absorbing resins shown in the following sections. 100 parts by weight of an acrylate monomer consisting of 1 to 50 mol% of acrylic acid and 50 to 99 mol% of an alkali metal salt of acrylic acid and 0 to 5 parts of a crosslinkable monomer
An alkali metal acrylate salt-based polymer obtained by heating and drying a gel-like hydrous polymer formed by copolymerizing part by weight with an aqueous solution at a monomer concentration of 20% by weight or more. Acrylic acid and/or a water-soluble radical polymerization initiator and optionally a crosslinkable monomer in an alicyclic and/or aliphatic hydrocarbon solvent.
or an aqueous solution of alkali metal acrylate.
Dispersed in the presence of a surfactant with HLB8-12,
A water-absorbing resin obtained by suspension polymerization. A saponified product of a copolymer of vinyl ester and ethylenically unsaturated carboxylic acid or its derivative. By polymerizing starch and/or cellulose, monomers having carboxyl groups or producing carboxyl groups by hydrolysis, and optionally crosslinkable monomers in an aqueous medium, and optionally further hydrolyzing. The obtained water absorbent resin. A maleic anhydride copolymer made of maleic anhydride and at least one monomer selected from the group consisting of α-olefins and vinyl compounds is reacted with an alkaline substance, and if necessary, the resulting reaction product is A water-absorbing resin obtained by reacting polyvalent epoxy compounds. The amount of carboxyl groups contained in the water-absorbing resin is not particularly limited, but it is preferable that the amount of carboxyl groups is 0.01 equivalent or more per 100 g of the water-absorbing resin. Taking partially neutralized polyacrylic acid as an example, the proportion of unneutralized portion is preferably 1 to 50 mol%. There are no particular restrictions on the shape of the water-absorbing resin powder used in the present invention, and examples include a spherical shape obtained by reverse-phase suspension polymerization, a scaly shape obtained by drum drying, and an amorphous shape obtained by crushing a resin lump. Either is fine. Polyhydric alcohol (A) used in the present invention
must have two or more hydroxyl groups per molecule. Among such polyhydric alcohols, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, polyglycerin, propylene glycol, diethanolamine, triethanolamine, polyoxypropylene, oxyethylene oxypropylene block copolymer, sorbitan fatty acid ester, One or more selected from the group consisting of polyoxyethylene sorbitan fatty acid ester, trimethylolpropane, pentaerythritol, and sorbitol are preferred. The amount of polyhydric alcohol (A) used in the present invention is from 0.001 to 100 parts by weight of water-absorbing resin powder.
The proportion ranges from 10 parts by weight, preferably from 0.01 to 5 parts by weight. If the amount is within this range, a water absorbing agent with a high water absorption rate can be obtained. However, if the amount exceeds 10 parts by weight, it is not only uneconomical, but also the amount of water absorbed decreases because the proportion of the water-absorbing resin decreases. vice versa
If the amount is less than 0.001 part by weight, no improvement in water absorption rate will be observed even if the heat treatment takes a long time. The compound (B) used in the present invention is one or more selected from the group consisting of water and a hydrophilic organic solvent, and the compound (B) is one or more selected from the group consisting of water and a hydrophilic organic solvent, and the compound (B) is one or more compounds selected from the group consisting of water and a hydrophilic organic solvent. It has the effect of promoting uniform dispersion and penetration near the surface. As the hydrophilic organic solvent that can constitute compound (B), polyhydric alcohol (A)
Any material that mixes uniformly with the water-absorbing resin and does not affect the performance of the water-absorbing resin may be used. Such substances include, for example, methyl alcohol, ethyl alcohol,
Lower alcohols such as n-propyl alcohol, iso-propyl alcohol, n-butyl alcohol, iso-butyl alcohol, and t-butyl alcohol; Ketones such as acetone; Ethers such as dioxane and tetrahydrofuran; N,N-dimethylformamide and sulfoxides such as dimethyl sulfoxide. Among the compounds (B), water alone or an aqueous compound in which part of the water is replaced with a hydrophilic organic solvent is preferable from the viewpoint of economy and avoidance of fire and pollution problems. The optimum amount of compound (B) used in the present invention varies depending on the type and particle size of the water-absorbing resin powder, but it is based on 100 parts by weight of the water-absorbing resin powder.
The proportion ranges from 0.01 to 8 parts by weight, preferably from 0.1 to 6 parts by weight. If the amount of compound (B) exceeds 8 parts by weight, not only will the heat treatment take a long time, but it will also penetrate into the center of the water-absorbing resin powder particles together with the polyhydric alcohol (A). The crosslinking reaction caused by A) will proceed to the center, reducing the performance of the water-absorbing resin. Furthermore, depending on the type of compound (B) used, it may form lumps when mixed with the water-absorbing resin powder. It becomes easy to form and the mixture becomes uneven. On the other hand, when the amount of compound (B) is as small as less than 0.01 part by weight, no effect of adding compound (B) is observed. In the present invention, in order to mix the polyhydric alcohol (A) and the compound (B) with the water-absorbent resin powder, the mixture of the polyhydric alcohol (A) and the compound (B) is sprayed or dropped onto the water-absorbent resin powder. -Commonly mixed. The mixer used for mixing is preferably one with a large mixing power in order to mix uniformly, but ordinary mixers and mixers can be used. For example, a cylindrical mixer, a double cone mixer, a V-type mixer, a ribbon mixer, a screw mixer, a fluidized mixer, a rotating disc mixer, an air flow mixer,
These include double-arm type machine, internal mixer, Muller type machine, roll mixer, screw type extruder, etc. To heat the mixture obtained by mixing polyhydric alcohol (A) and compound (B) with water-absorbing resin powder,
A normal dryer or heating furnace can be used. Examples include a groove type agitation dryer, a rotary dryer, a disc dryer, a water dryer, a fluidized bed dryer, a flash dryer, an infrared dryer, and the like. Heat treatment temperature is 90℃ or higher,
Preferably it is in the range of 150 to 250°C. At a low temperature of less than 90°C, it is not only uneconomical because the heat treatment takes a long time, but depending on the type and amount of polyhydric alcohol (A) used, crosslinking may not be sufficient to achieve the effects of the present invention. The reaction may not proceed. When the heat treatment temperature is set in the range of 150 to 250°C, the crosslinking reaction can be carried out in a short time to achieve the effects of the present invention without worrying about coloring or deterioration of the water-absorbing resin. At higher temperatures, depending on the type of water-absorbing resin, thermal deterioration may occur, so care must be taken. (Effects of the Invention) The water-absorbing agent of the present invention thus obtained has various advantages over conventionally known water-absorbing resins. That is, the water-absorbing agent of the present invention can be produced using an industrially simple process in which a water-absorbing resin powder is mixed with a polyhydric alcohol (A) and the compound (B) and heated to effectively react the polyhydric alcohol (A). Furthermore, compared to conventionally known water-absorbing resins, it not only has a high water-absorbing rate without becoming bulky, but surprisingly, it also has a high water absorption rate under pressure. It also has a large water retention capacity. The water absorbing agent of the present invention can be used as an absorbent for disposable diapers, sanitary cotton, etc., and can also be used in a wide range of applications, such as coagulating sludge, preventing condensation on building materials, and as a water retention agent or desiccant for agriculture and horticulture. . EXAMPLES Hereinafter, the present invention will be explained in detail with reference to Examples, but the scope of the present invention is not limited only to these Examples. In the examples, unless otherwise specified, % means % by weight and parts means parts by weight, respectively. Example 1 4000 parts of a 43% aqueous solution of acrylate monomers consisting of 74.95 mol% sodium acrylate, 25 mol% acrylic acid and 0.05 mol% trimethylolpropane triacrylate was mixed with ammonium persulfate.
Using 0.6 parts and 0.2 parts of sodium hydrogen sulfite, standing polymerization was carried out at 55 to 80°C in a nitrogen atmosphere to obtain a gel-like hydropolymer. This gel-like hydrous polymer was dried in a hot air dryer at 180° C., then ground in a hammer-type grinder, and sieved through a 28-mesh wire mesh to obtain a 28-mesh product (powder A). 100 parts of powder A, 2 parts of glycerin, 2 parts of water, and 2 parts of ethyl alcohol were mixed with a paddle mixer, and the resulting mixture was continuously heat-treated with a paddle dryer. The average residence time of this paddle dryer was 20 minutes. The material temperature at the outlet was 190°C. In this way, water absorbing agent (1) was obtained. The absorption capacity of the obtained powder A and water absorbing agent (1) and the presence or absence of mamaco formation were evaluated as follows. Place 0.2 g of the obtained powder A or water absorbing agent (1) evenly into a non-woven tea bag bag (40 mm x 150 mm), immerse it in 0.9% saline, and measure the weight after 1 minute and 10 minutes. did. Using the absorbed weight of only the tea bag as a blank, the absorption capacity of the water absorbing agent was calculated according to the following formula. Absorption capacity = Weight after absorption (g) - Blank (g) / Weight of water absorbing agent (g) In addition, to check the presence or absence of mamako formation, place a small amount of powder A or water absorbing agent (1 ) was conducted by observing the state when it was dropped. The results are shown in Table 1. Compared to powder A, water absorbing agent (1)
has significantly improved water absorption speed. Comparative Example 1 100 parts of the powder A obtained in Example 1 was mixed with 2 parts of glycerin using a paddle mixer, and the resulting mixture was heat-treated using a paddle dryer in the same manner as in Example 1 to prepare a comparative water absorbing agent. I got (1). The obtained comparative water absorbing agent (1) was evaluated in the same manner as in Example 1. The results are shown in Table 1. Comparative water absorbing agent (1) has significantly improved water absorption speed compared to powder A, but
The water absorption rate was inferior to that of water absorbing agent (1). Example 2 100 parts of the powder A obtained in Example 1 was mixed with 2 parts of sorbitan monostearate and 4 parts of water in a double-arm type.
The resulting mixture was heated using a paddle dryer in the same manner as in Example 1 to form a water-absorbing agent.
I got (2). The obtained water absorbing agent (2) was evaluated in the same manner as in Example 1. The results are shown in Table 1. Example 3 100 parts of the powder A obtained in Example 1 was mixed with 2 parts of sorbitan monostearate and 4 parts of ethyl alcohol using a double-arm mixer, and the resulting mixture was mixed with a paddle in the same manner as in Example 1. A water absorbing agent (3) was obtained by heat treatment using a dryer. The obtained water absorbing agent (3) was evaluated in the same manner as in Example 1. Results first
Shown in the table. Comparative Example 2 Polymerization, drying, and pulverization were carried out in the same manner as in Example 1, except that 2 parts of glycerin was added to the aqueous acrylate monomer solution. A portion of the resulting powder that had passed through 28 meshes (powder B) was taken, placed on a stainless steel plate, and heat-treated in a hot air dryer at 200° C. for 15 minutes to obtain a comparative water-absorbing agent (2). The obtained powder B and comparative water absorbing agent (2) were evaluated in the same manner as in Example 1. The results are shown in Table 1. Comparative Example 3 100 parts of the powder A obtained in Example 1 was mixed with 2 parts of glycerin, 10 parts of water, and 10 parts of ethyl alcohol using a paddle mixer, and the resulting mixture was heated using a paddle dryer in the same manner as in Example 1. A comparative water absorbing agent (3) was obtained by heat treatment. Obtained comparative water absorbing agent (3)
Evaluation was made in the same manner as in Example 1. The results are shown in Table 1. Example 4 100 parts of the powder A obtained in Example 1 was mixed with 2 parts of glycerin, 2 parts of water, and 2 parts of ethyl alcohol using a paddle mixer, and the resulting mixture was continuously heat-treated using a paddle dryer. . The average residence time of this paddle dryer was 180 minutes.
The material temperature at the outlet was 120°C. In this way, a water absorbing agent (4) was obtained. The obtained water absorbing agent (4) was evaluated in the same manner as in Example 1. The results are shown in Table 1. Comparative Example 4 100 parts of the powder A obtained in Example 1 was mixed with 2 parts of glycerin, 2 parts of water, and 2 parts of ethyl alcohol using a paddle mixer, and the resulting mixture was continuously heated using a paddle dryer. did. The average residence time of this paddle dryer was 180 minutes. The material temperature at the outlet was 60°C. In this way, a comparative water absorbing agent (4) was obtained. The obtained comparative water absorbing agent (4) was evaluated in the same manner as in Example 1. The results are shown in Table 1. Example 5 50 parts of corn starch, 200 parts of water, and 1000 parts of methanol were placed in a reaction vessel equipped with a stirring bar, a nitrogen blowing tube, and a thermometer, stirred at 50°C for 1 hour under a nitrogen stream, and then cooled to 30°C. 25 parts acrylic acid, 75 parts sodium acrylate,
Add 0.5 parts of methylene bisacrylamide, 0.1 parts of ammonium persulfate as a polymerization catalyst and 0.1 parts of sodium bisulfite as a promoter,
After reacting at 60°C for 4 hours, a white suspension was obtained. The powder obtained by filtering this white suspension was mixed with water.
Washed with a mixed solution of methyl alcohol (water to methyl alcohol weight ratio: 2:10), dried under reduced pressure at 60°C for 3 hours, crushed, and further sieved through a 28-mesh wire mesh to remove the material passing through the 28-mesh (powder). C) was obtained. 100 parts of powder C, 5 parts of glycerin and 5 parts of water were mixed in a turbulizer (manufactured by Hosokawa Micron Co., Ltd.), and the resulting mixture was dried at 180°C in a Japanese dryer.
Heat treatment was performed for 30 minutes to obtain a water absorbing agent (5). The material temperature at the time of removal was 178°C. The obtained powder C and water absorbing agent (5) were evaluated in the same manner as in Example 1. The results are shown in Table 1. Example 6 0.5 parts of benzoyl peroxide was added as a polymerization initiator to a mixture consisting of 60 parts of vinyl acetate and 40 parts of methyl acrylate, and this was dispersed in 30 parts of water containing 3 parts of partially saponified polyvinyl alcohol and 10 parts of common salt. After suspension polymerization at 65℃ for 6 hours,
A copolymer was obtained by filtering and drying. The obtained copolymer was saponified, washed, and dried, then ground and classified to obtain powder D that passed through a 28-mesh wire gauze. Add 2 parts of trimethylolpropane and 5 parts of acetone to 100 parts of powder D, and heat the jacket with a heat medium.
The mixture was placed in a ribbon blender heated to 230°C and mixed and heat treated to obtain a water absorbing agent (6). The temperature of the material at the time of removal was 186°C. Obtained powder D
and Water absorbing agent (6) were evaluated in the same manner as in Example 1. The results are shown in Table 1. Example 7 300 parts of n-hexane was placed in a reactor, and 0.7 part of sorbitan monostearate was dissolved therein. Next, in this, 30 parts of acrylic acid was dissolved in 40 parts of water, and then
The mixture was neutralized with 12.5 parts of caustic soda, and an aqueous monomer solution obtained by dissolving 0.05 part of potassium persulfate was added to disperse the mixture. Polymerization was carried out under a nitrogen stream at 65° C. for 5 hours. After the polymerization was completed, the mixture was dried under reduced pressure and pulverized to obtain powder E that passed through a 28-mesh wire gauze. 100 parts of powder E, 3 parts of polyethylene glycol 400, 2 parts of ethyl alcohol and 4 parts of dioxane
1 part and mixing was carried out using a V-type mixer. The resulting mixture was thinly placed on a belt conveyor and passed through an infrared dryer for heat treatment to obtain a water absorbing agent (7). The average heating time was 10 minutes, and the material temperature at the dryer outlet was 193°C. The obtained powder E and water absorbing agent (7) were evaluated in the same manner as in Example 1. The results are shown in Table 1. Example 8 Powder A and water absorbing agent obtained in Example 1
(1) and Comparative Water Absorbing Agent (1) and Comparative Water Absorbing Agent (3) obtained in Comparative Example 1 and Comparative Example 3. and a waterproof film weighing 72 g). Add 100 c.c. of 0.9% saline solution to each of these disposable diapers, leave them at room temperature for 10 minutes, then fold 10 paper towels measuring 23 cm x 23 cm in half and place them over the diapers, and then place a 10 kg weight on top of them. After leaving it for 1 minute, the amount of saline solution returned to the paper towel was measured. The results are shown in Table 2.

【table】

[Table] △: Hard to become a mamako.
×: Mamako is formed.

[Table] As is clear from the results shown in Table 1, the water absorbing agent of the present invention does not become sticky and has a high water absorption rate. Furthermore, as is clear from the results shown in Table 2, the water absorbing agent of the present invention has high water retention even under pressure.

Claims (1)

[Claims] 1. A water-absorbing resin powder having a carboxyl group,
Polyhydric alcohol (A) and one or more compounds (B) selected from the group consisting of water and a hydrophilic organic solvent are added to 100 parts by weight of water-absorbing resin powder. 0.001-10 parts by weight and compound (B)
By mixing at a ratio of 0.01 to 8 parts by weight and heating at a temperature of 90°C or higher, the water-absorbing resin powder and polyhydric alcohol are reacted, and the molecular chains near the surface of the water-absorbing resin powder are crosslinked. The resulting water absorbent. 2 The water-absorbing resin having a carboxyl group contains 1 to 50 mol% of acrylic acid and an alkali metal salt of acrylic acid.
Acrylate monomer consisting of 50 to 99 mol%
100 parts by weight and 0 to 5 parts by weight of a crosslinkable monomer,
Claim 1 which is an acrylic acid alkali metal salt-based polymer obtained by heating and drying a gel-like hydrous polymer formed by copolymerizing an aqueous solution with a monomer concentration of 20% by weight or more. Water absorbing agent.