JPH09302138A - Super water absorbent resin composition - Google Patents

Abstract

(57) Abstract: A highly water-absorbent resin having excellent water absorption performance even in the presence of an aqueous solution or water containing a radical-generating species such as L-ascorbic acid or a salt thereof and a transition metal ion such as iron or copper. The present invention provides a highly water-absorbent resin composition, which is stable without being decomposed / deteriorated, and has excellent gel strength and liquid permeability after swelling. A superabsorbent resin composition of the present invention comprises a superabsorbent resin, an anatase crystal form, and an average particle size of 0.
Titanium dioxide having a specific surface area of 1 μm or less and a specific surface area of 50 m ² / g or more measured by the Brunauer-Emmett-Taylor method is contained.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention is excellent in water absorption performance,
The present invention relates to a highly water-absorbent resin composition which does not decompose / degrade even in a water-containing state in which it absorbs an aqueous liquid or body fluid such as urine, menstrual blood or sweat, and has excellent gel strength and liquid permeability after swelling. .

[0002]

2. Description of the Related Art In the field of hygiene products, superabsorbent resins are used in absorbent products such as disposable diapers (disposable diapers) for infants, adults or incontinent persons or sanitary napkins for women. It is used as a water-absorbing substance in articles, and is used as a water retention agent in the agricultural and horticultural fields, and is widely used as a coagulant for sludge, an anti-condensation agent or a water stopping agent in the civil engineering business field. Have been. The water-soluble polymer (crosslinked product) constituting the superabsorbent resin has a molecular weight that decreases with time and deteriorates in the presence of radicals such as hydrogen peroxide and L-ascorbic acid or a salt thereof. It is known that there is a problem. In particular, when the superabsorbent resin is used in absorbent articles such as disposable diapers and sanitary napkins, urine, menstrual blood, sweat, and other body fluids also contain L-ascorbic acid or salts thereof. The superabsorbent resin in the disposable diaper or sanitary napkin that has absorbed the water decomposes and degrades over time due to radical species generated from L-ascorbic acid or a salt thereof. Is a particularly serious problem.

[0003] The decomposition reaction of a water-soluble polymer by the above-mentioned radical-generating species is in a state of absorbing an aqueous liquid or a bodily fluid such as urine, blood or sweat (hereinafter referred to as a "water-containing state").
Under the air atmosphere, especially in the presence of iron or copper.
This is remarkable under a water-containing state in which a transition metal ion capable of taking an oxidation number of more than one species coexists. The reason for this is, for example, J. Am. Ch.
em. Soc., 89, 4176 (1967) and Carbohydrate Research,
As shown in 4, 63 (1967), a small amount of transition metal ions such as iron and copper serves as a catalyst to remarkably promote the decomposition reaction (radical generation reaction) of hydrogen peroxide or L-ascorbic acid or a salt thereof. That's because. Such a transition metal ion may be added intentionally or as a third component under the condition that a superabsorbent resin and a radical generating species such as hydrogen peroxide or L-ascorbic acid or a salt thereof coexist, Other than such a case, for example, it is known to have sufficient catalytic ability to decompose the polymer chain of the water-soluble polymer that constitutes the superabsorbent polymer over time [eg, Free Radical
Research Communications, 1, 349 (1986)].

[0004] Techniques for suppressing the decomposition / deterioration of the superabsorbent resin include: 1) sealing the superabsorbent resin under reduced pressure or under a nitrogen atmosphere to prevent contact with air (particularly oxygen); Avoid, 2) Use highly purified water and raw materials to prevent metal ions from being mixed into the superabsorbent resin. 3) Add antioxidant or reducing agent to the superabsorbent resin. 4) adding a protein or enzyme to the superabsorbent resin; 5) adding citric acid, (poly) phosphoric acid or a salt thereof, ethylenediaminetetraacetic acid (EDTA) or a salt thereof to the superabsorbent resin, A method of adding a metal chelating agent is known. However, the above methods 1) and 2) are often impossible in practice depending on the purpose of use of the superabsorbent resin. In addition, the method of adding an existing additive such as the above 3), 4) and 5) suppresses the decomposition / deterioration of the superabsorbent resin, but its effect is not always sufficient. In order to achieve the effect, it is often necessary to add the above-mentioned additive in a large amount, or to use an additive having a very strong effect. Under such circumstances, there is a problem that the original physical properties and functions of the superabsorbent resin are significantly impaired, and depending on the additive, there may be a case in which an odor may be generated, or the stability may be poor. In some cases, unfavorable hygiene situations can occur.

[0005] Mixing or dispersing a metal chelating agent in a superabsorbent resin is disclosed in JP-A-56-89838,
JP-A-59-230046 and JP-A-1-27
No. 5661, for example, EDTA,
It has been clarified that the use of sodium tripolyphosphate or the like does not lower the water absorption performance even in the case of water containing salts and ions. However, according to the study of the present inventors, when EDTA or sodium tripolyphosphate is used, hydrogen peroxide or a radical-generating species such as L-ascorbic acid or a salt thereof is present in an aqueous solution or in the presence of moisture. Has no significant effect on the stabilization of the superabsorbent resin.

[0006] In addition to the above-mentioned stability with time in a water-containing state (stability with time of the gel), the performance of the superabsorbent resin is not limited to water absorption capacity (water absorption), water absorption rate, and gel strength after swelling. Physical properties such as liquid permeability are important. However, these physical properties are often performances that conflict with each other,
It is very difficult to balance them, and this is one of the issues in developing a superabsorbent resin. For example, generally, there is a problem that, when an attempt is made to increase the water absorption capacity, the gel strength after swelling, the liquid permeability, etc., decrease.

[0007] In order to improve these problems, various methods have been proposed in recent years. For example, Japanese Patent Publication No. 60-18
No. 690 and Japanese Patent Publication No. 61-48521,
A method of forming a highly crosslinked density layer on the surface layer of a superabsorbent resin has been proposed. In addition, Japanese Patent Publication No. 5-19563, Japanese Patent Application Laid-Open No. 61- 211305, and Japanese Patent Application Laid-Open
JP-A-64006 and JP-A-62-36411 disclose a method of grafting a highly water-absorbing resin containing a carboxyl group and / or a carboxylate group with a silane coupling agent. In Japanese Patent Application Laid-Open Publication No. H11-264, a method of treating with alkoxytitanium is proposed. Further, an aqueous solution of a compound that easily reacts with a functional group such as a carboxylate group contained in the superabsorbent resin, for example,
A method is known in which an aqueous solution of a polyvalent metal salt, polyglycidyl ether, polyisocyanate or the like is sprayed on a superabsorbent resin and heated to form a highly crosslinked density layer on the surface layer of the superabsorbent resin. However, even these methods were insufficient to achieve both high water absorption performance such as water absorption capacity and stability over time of the gel after swelling.

Further, as one of methods for achieving both the gel strength after swelling and the stability over time of the gel, JP-A-6-306 discloses
In JP-A-202, there is described an example in which a mixed type or amorphous high-purity particulate titania having a crystal structure of rutile type and anatase type is added to a superabsorbent polymer.
However, when examined by the present inventors, in particular, a polymer having a high water absorption had a level at which the stability over time of the gel was insufficient.

Therefore, an object of the present invention is that it has excellent water absorption performance and has high water absorption even in the presence of an aqueous solution or water containing a radical-generating species such as L-ascorbic acid or a salt thereof and a transition metal ion such as iron or copper. A highly water-absorbent resin composition in which a water-soluble resin is stably present without being decomposed / deteriorated, and which has excellent gel strength and liquid permeability after swelling.

[0010]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that a superabsorbent resin composition containing a superabsorbent resin and a specific titanium dioxide can achieve the above object. I found out.

The present invention has been made based on the above findings, and is a super absorbent polymer, anatase type in crystal form, an average particle size of 0.1 μm or less, and a Brunauer-Emmett-Taylor method (Brunauer- Emett-Teller method; BET
The present invention provides a highly water-absorbent resin composition containing titanium dioxide having a specific surface area of 50 m ² / g or more as measured by the method).

The superabsorbent resin composition of the present invention is used in combination with a cosmetic or food additive containing a radical-generating species such as L-ascorbic acid or a salt thereof, depending on the type of superabsorbent resin used. It is effectively used in some cases and as an absorbent substance in hygiene products. In particular, the highly water-absorbent resin composition of the present invention is suitably used as a water-absorbing substance in sanitary articles.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the superabsorbent resin composition of the present invention will be described in detail. The super absorbent polymer used in the present invention is not particularly limited, and examples thereof include polyacrylate cross-linked products, poly (vinyl alcohol / acrylate) copolymers (cross-linked products), starch-acryl. Acid graft copolymer (crosslinked) and polyvinyl alcohol-polymaleic anhydride graft copolymer (crosslinked) partially crosslinked polymer compound having a carboxyl group or a salt thereof, or carboxymethylcellulose salt crosslinked product And partially cross-linked polysaccharides and the like. Among them, from the viewpoint of water absorption performance, it is preferable to use a crosslinked polyacrylate or a starch-acrylate graft copolymer (crosslinked product), and particularly preferable to use a crosslinked polyacrylate. The super absorbent polymers may be used alone or in combination of two or more kinds.

The "salt" constituting the various superabsorbent resins exemplified as the superabsorbent resin is, for example,
Alkali metal salts (sodium salt, potassium salt, lithium salt, etc.), alkaline earth metal salts (calcium salt, magnesium salt, barium salt, etc.), ammonium salts (quaternary ammonium salt, quaternary alkyl ammonium salt, etc.), etc. Is mentioned. Here, the degree of neutralization of the superabsorbent resin is preferably 0.01 to 100%, more preferably 1 to 99%, and particularly preferably 40 to 100, based on the number of moles of acid groups in the superabsorbent resin. ~ 95%. In the present invention,
The term “degree of neutralization” refers to the ratio (based on moles) of the acid groups in the superabsorbent resin that constitute the salt, that is, (moles of the acid groups constituting the salt) / ( The total number of moles of free acid groups that can form a salt and acid groups that form a salt) × 10
It means 0 (%).

The titanium dioxide used in the present invention has an anatase crystal form and an average particle size of 0.1 μm or less, preferably 0.05 μm or less, more preferably 0.03 μm.
m or less and a specific surface area measured by the Brunauer-Emmett-Taylor method (hereinafter, "BET specific surface area")
That) is 50m ² / g or more, preferably 100m ² /
g or more, more preferably 200 m ² / g or more. In the composition of the present invention, 10 parts by weight or less, preferably 5 parts by weight or less, of titanium dioxide having a rutile crystal form, relative to 100 parts by weight of titanium dioxide having a crystal form of anatase. May be included.

When any one of the crystal form, average particle size and BET specific surface area of titanium dioxide does not satisfy the above conditions, radical-generating species such as L-ascorbic acid or a salt thereof and iron or copper. It is impossible to satisfy all of the stability, gel strength, liquid permeability, etc. of the gel in the presence of an aqueous solution or water containing transition metal ions such as.

The content of the titanium dioxide is 0.01 to 10 parts by weight, based on 100 parts by weight of the super absorbent polymer.
Preferably 0.05 to 5 parts by weight, more preferably 0.1.
３3 parts by weight. If the content is less than 0.01 parts by weight, the gel stability, gel strength, and liquid permeability are all insufficient, and even if it exceeds 10 parts by weight, the improvement of the effect is small,
It is preferable to be within the above range. In the present invention,
The “highly water-absorbent resin” used as the standard for the content means a resin in a dry state which does not absorb water.

The superabsorbent resin composition of the present invention may contain water in addition to the superabsorbent resin and the titanium dioxide. In this case, the superabsorbent resin may be a water-containing polymer in a state containing water, or the composition of the present invention may be in a state of a water-containing gel. Here, when the superabsorbent resin composition of the present invention contains water, its water content may be any ratio within the range of the saturated water absorption.

Further, the highly water-absorbent resin composition of the present invention comprises
If necessary, various additives such as a water-soluble organic solvent, a surfactant, a salt, a stabilizer, a chelating agent, an antioxidant, a reducing agent, and / or a preservative can be added.

Examples of the method for adjusting the superabsorbent resin composition of the present invention include the following methods 1 to 4 and the like. 1. A method of mixing the super absorbent polymer and the titanium dioxide in a dry state. 2. A method in which the titanium dioxide is mixed with the water-absorbent superabsorbent resin and, if necessary, dried. 3. A method of adding the above titanium dioxide in the state of an aqueous dispersion (or in the state of a sol) to the above water-absorbing or water-absorbing superabsorbent resin, and drying if necessary. 4. A method of adding at the time of producing the above superabsorbent resin (for example, dispersing in a monomer, adding after polymerization, etc.).

The superabsorbent resin composition of the present invention is not particularly limited in its water absorption amount, but the retention amount measured by the following [method of measuring retention amount by centrifugal dehydration method] is 35 g / g or more, particularly It is preferably 38 g / g or more.

In general, when the water-absorbent resin composition has a high water absorption amount, for example, when it is used in a paper diaper, the amount of resin per paper diaper can be small, which contributes to thinning the paper diaper and reducing the cost. it can. However, when the water absorption increases, the stability of the gel over time, gel strength,
A resin having a high water absorption is difficult to use for a disposable diaper because the performance such as liquid permeability is reduced. On the other hand, the super-water-absorbent resin composition of the present invention has a relatively high water absorption, in which the holding amount is 35 g / g or more. is there.

As described above, the highly water-absorbent resin composition of the present invention is particularly useful as a water-absorbent substance in hygiene products such as absorbent articles such as paper diapers and sanitary napkins. Such an absorbent article is provided with a water-permeable top sheet, a water-impermeable back sheet, and an absorber interposed between the top sheet and the back sheet. As such an absorber, fluff pulp obtained by crushing wood pulp can be used. The superabsorbent resin composition of the present invention is used in combination with the flap pulp, and in this case, it may be used in combination with the fluff pulp, or may be present in a layer only in a specific portion of the fluff pulp. You may. As the above-mentioned absorber, as another embodiment, a heat-treated mixture of a thermoplastic resin, fluff pulp and the superabsorbent resin composition of the present invention can be used.

Further, as described above, in the body fluid such as urine, L-
Since ascorbic acid or a salt thereof is contained, the superabsorbent resin in the conventionally known superabsorbent resin composition deteriorates due to such a substance in the absorbent article that has absorbed body fluid. On the other hand, when the superabsorbent resin composition of the present invention used as an absorbent substance in an absorbent article is used, deterioration of the superabsorbent resin is suppressed.

Moreover, the superabsorbent resin composition of the present invention is
Since it has high gel strength and liquid permeability after swelling, it can be preferably used for absorbent articles such as paper diapers and sanitary napkins.

Further, the highly water-absorbent resin composition of the present invention comprises
Since the above titanium dioxide also has a deodorizing action, it is also useful for applications requiring a deodorizing effect.

[0027]

The present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. In addition, "%" in the following Examples and Comparative Examples represents "% by weight" unless otherwise specified.

First, the test methods used in Examples and Comparative Examples are shown below. [Measurement of Retention Amount by Centrifugal Dehydration Method] After swelling 1 g of the superabsorbent resin composition with 150 ml of physiological saline (0.9% NaCl solution, manufactured by Otsuka Pharmaceutical Co., Ltd.) for 30 minutes, put in a nonwoven bag and centrifuged The mixture was dehydrated at 143 G for 10 minutes using a machine, and the total weight (total weight) after the dehydration was measured. Then, the retention amount after centrifugal dehydration was measured according to the formula (1) shown in the following [Equation 1].

[0029]

[Equation 1]

[Measuring Method of Liquid Flow Rate] A measuring apparatus 10 shown in FIG. 1 (a burette made of a glass cylindrical tube having an inner diameter of 25.6 mm and a length of about 500 mm (cylindrical portion)) was added to a super absorbent polymer composition P0.5 g. And equilibrated swelling of the super absorbent polymer composition P with an excess of physiological saline, and adjusting the liquid level to 200 ml from the lower part with a cock to show the swollen super absorbent resin composition P as illustrated. Check that the water has settled sufficiently as shown in Fig. 2 and open the cock.
The time for passing between the marked line L (150 ml point from the bottom) and M (100 ml point from the bottom) of the book (50 cc of liquid) was measured, and the amount of liquid (ml) between the marked lines was measured ( m
in) and the flow rate (ml / min) was obtained.

[Evaluation Method of Time Stability of Gel After Swelling] 1 g of the super absorbent polymer composition was swollen with 45 g of physiological saline containing 0.05% L-ascorbic acid, and this was sealed in a screw tube. And left at 40 ° C. for 3 hours. The time stability of the gel after swelling was evaluated by observing the state of the gel after swelling at that time. In addition, the evaluation of the stability over time of the gel after swelling was carried out in four steps based on the criteria shown in the following [Table 1] for the fluidity, spinnability and shape retention of the gel.
In addition, in this evaluation, in the case of evaluation of ◎ and ○, it indicates that it is suitable as a water-absorbing substance used for sanitary napkins, disposable diapers, adult sheets, tampons, sanitary cotton and the like.

[0032]

[Table 1]

Next, a synthetic example of the super absorbent resin used in Examples and Comparative Examples will be shown. Synthesis Example 1 [Synthesis of Superabsorbent Resins (I) and (II)] 400 ml of cyclohexane and ethyl cellulose as a dispersant were placed in a 1000 ml four-necked flask equipped with a stirrer, a reflux condenser, a dropping funnel and a nitrogen gas introducing tube. (Hercules, trade name ethyl cellulose N-100)
0.625 g (0.5% relative to the produced polymer) was charged, nitrogen gas was blown in to expel dissolved oxygen, and the temperature was raised to 75 ° C. In a separate flask, 102.0 g of acrylic acid was diluted with 25.5 g of ion-exchanged water and neutralized with 140 g of a 30% sodium hydroxide aqueous solution while being cooled from the outside. Then potassium persulfate 0.2
A solution obtained by dissolving 04 g (0.2% of acrylic acid) in 7.5 g of water was added and dissolved, and then nitrogen gas was blown thereinto to remove oxygen remaining in the aqueous solution. The contents of the flask were added dropwise to the four-necked flask over 1 hour to polymerize. After completion of the polymerization, azeotropic dehydration was performed using a dehydration tube, and the water content of the superabsorbent resin was adjusted to 30 parts by weight based on 100 parts by weight of the superabsorbent resin. After that, as a cross-linking agent, polyglycerol polyglycidyl ether (manufactured by Nagase Kasei Co., Ltd.,
Product name Denacol EX-512) 0.04 g (0.04
% Acrylic acid) in 4 g of water was added,
The reaction was carried out at 5 to 80 ° C for 1 hour. After cooling, cyclohexane is removed by decantation, and a highly water-absorbent resin (hydrated material)
I got This is referred to as superabsorbent resin (I). Further, the super absorbent resin (I) is further added at 80 to 100 ° C. at 50 Torr.
And dried under reduced pressure. This is a super absorbent resin (II)
And

Synthesis Example 2 [Synthesis of Superabsorbent Resins (III) and (IV)] 25% of polyoxyethylene lauryl ether sulfate sodium salt (average ethylene oxide addition mole number = 2) was used instead of ethyl cellulose as a dispersant. 0.04 g to 0.06 g of polyglycerol polyglycidyl ether (manufactured by Nagase Kasei Co., Ltd., trade name Denacol EX-512) as a cross-linking agent using 1.5 g of an aqueous solution.
Except that the amount was increased, a superabsorbent resin (hydrate) was obtained in the same manner as in Synthesis Example 1. This is referred to as superabsorbent resin (III).
Further, a superabsorbent resin (III) is further added at 80 to 100 ° C for 5 minutes.
It was dried under a reduced pressure of heating of 0 Torr. This is referred to as superabsorbent resin (IV).

[Examples 1 to 10] Superabsorbent resin (I),
Put (II), (III) or (IV) (see [Table 2] below) in a double-arm kneader, add titanium dioxide of the grade and addition amount (relative to resin) shown in [Table 2] below, and sufficiently Mix with stirring. Here, when the super absorbent polymer (I) or (III) is used, after addition and mixing, it is further heated at 80 to 100 ° C. for 50 minutes.
It was dried under reduced pressure by heating Torr to obtain a super absorbent polymer composition. The obtained superabsorbent resin composition was evaluated (retained amount after centrifugal dehydration, liquid passing rate, and stability of swollen gel) according to the test method described above. In the evaluation, particles having a size of 850 μm or more were removed from the composition with a sieve.

[Comparative Examples 1 and 2] Superabsorbent resin (II) or (IV) (see Table 2 below) was used, and this was used as it was as a superabsorbent resin composition without adding titanium dioxide. In accordance with the above-mentioned test method, evaluation (retention amount after centrifugal dehydration, liquid passage rate and stability of swollen gel) was performed. In the evaluation, particles having a size of 850 μm or more were removed from the composition with a sieve.

[Comparative Examples 3 and 4] Superabsorbent resin (IV) and titanium dioxide other than the specific titanium dioxide according to the present invention (grades and addition amounts shown in Table 2 below) were used.
Superabsorbent resin compositions are obtained in the same manner as in Examples 1 to 10,
An evaluation was performed.

[0038]

[Table 2]

[0039]

Industrial Applicability The superabsorbent resin composition of the present invention is excellent in water-absorbing performance, and is an aqueous solution or water in which radical-generating species such as L-ascorbic acid or a salt thereof and transition metal ions such as iron and copper are present. Even under the condition, the highly water-absorbent resin is stably present without being decomposed / deteriorated and has excellent gel strength and liquid permeability after swelling. Further, the superabsorbent resin composition of the present invention, the titanium dioxide also has a deodorizing action,
It is also useful for applications where a deodorizing effect is required.

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] August 23, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Brief description of drawings

[Correction method] Added

[Correction contents]

[Brief description of drawings]

FIG. 1 is a schematic view showing a measuring device for measuring the flow rate of physiological saline used in Examples and Comparative Examples.

[Explanation of Codes] 10 Measuring Device for Flow Rate of Saline Solution W Saline solution P Superabsorbent resin composition M, L Marked line

Claims (5)

[Claims] 1. A highly water-absorbent resin, an anatase type crystal form, an average particle size of 0.1 μm or less, and a specific surface area of 50 m ² / g or more measured by the Brunauer-Emmett-Taylor method. A highly water-absorbent resin composition containing titanium. 2. The super absorbent polymer composition according to claim 1, wherein the average particle size is 0.05 μm or less and the specific surface area is 100 m ² / g or more. 3. The super absorbent polymer composition according to claim 1, wherein the average particle diameter is 0.03 μm or less and the specific surface area is 200 m ² / g or more. 4. The content of the titanium dioxide is 0.01 to 10 parts by weight with respect to 100 parts by weight of the super absorbent polymer, according to claim 1. Super absorbent polymer composition. 5. The superabsorbent resin according to any one of claims 1 to 4, wherein the amount retained after swelling with physiological saline for 30 minutes and centrifugal dehydration is 35 g / g or more. Composition.