JPS62135553A - Water-absorbing polymer composition - Google Patents

Abstract

PURPOSE:To provide the titled compsn. which has a high capacity of absorbing solutions contg. salts. and a high initial water absorption rate and does not form undissolved lump, consisting of a specified water-absorbing polymer and crystalline cellulose. CONSTITUTION:An alpha,beta-unsaturated carboxylic acid or its metal salt [e.g., sodium (meth)acrylate] is subjected to reversed phase suspension polymerization with not more than 20wt% other copolymerizable monomer (e.g., acrylamide) in an high, petroleum hydrocarbon solvent having a b.p. of 30-200 deg.C (e.g., n-butane) in the presence of a surfactant having an HLB of 0.8 or above (e.g., polyoxyethylene alkyl ether), a polymn. initiator (e.g., ammonium persulfate), a crosslinking agent (e.g., N,N-methylenebisamide), etc., to obtain a water- absorbing polymer (A) having carboxyl groups and/or carboxylate groups in the molecule. 0.3-80pts.wt. crystalline cellulose (B) having an average particle size of 40-120mu, represented by the formula, is sprinkled over 100pts.wt. component A.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a body fluid absorbent for sanitary napkins, disposable diapers, etc.
The present invention relates to a water-absorbing polymer composition with improved water-absorbing properties, which has a wide range of uses such as soil water-retaining agents, seed coating agents, water-stopping agents, and dew-preventing agents.

[Conventional technology]

Various water-absorbing polymers have been known so far. For example, hydrolyzed products of starch-acrylonitrile graft polymers, neutralized products of starch-acrylic acid graft polymers, saponified products of vinyl acetate-acrylic acid ester copolymers, hydrolyzed products of acrylonitrile copolymers or acrylamide copolymers. or crosslinked products thereof, self-crosslinking sodium polyacrylate prepared by reverse-phase uEt polymerization, and the like. It is well known that when these water-absorbing polymers come into contact with water or an aqueous solution containing salt, they absorb water and swell.

However, generally, at the initial stage of contact with water or an aqueous solution containing a salt, the above-mentioned polymer is in a sticky state, that is, only the surface layer of the polymer particles absorbs water and becomes gel-like.
A phenomenon occurs that prevents water from penetrating into the interior, reducing the rate of water absorption. Therefore, when a water-absorbing polymer comes into contact with a large amount of water at once, there is a problem that the water-absorbing function of the water-absorbing polymer cannot be fully demonstrated. Therefore, various proposals have been made to solve this problem. For example, a method has been used in which a water-soluble organic solvent such as ethyl alcohol, propylene glycol, or glycerin is added to and mixed with a water-absorbing polymer, but with this method, the mixture becomes sticky and is inconvenient to handle. There is a drawback.

In addition, using a nonionic surfactant as a dispersant, α
In a method for manufacturing a hydrogel by reverse-phase suspension polymerization of β-unsaturated carboxylic acid monomers and their alkali metal salts, after the polymerization rate reaches 40% or more or after the completion of polymerization, inorganic substances insoluble in water are A method of manufacturing a hydrogel powder that can be easily implanted by adding powder has been proposed (Japanese Patent Application Laid-open No. 8711/1983). However, the material produced by this method is a fusion of polymer particles with each other.
Although this can be prevented, the water absorption rate at the initial stage of water absorption is still insufficient.

[Problem that the invention seeks to solve]

Therefore, an object of the present invention is to provide a water-absorbing poly7-composition that has a high water absorption capacity, particularly for solutions containing various salts, does not become sticky, and has a particularly high initial water absorption rate. .

[Failure to solve the problem]

The present invention is based on the finding that the above problems can be effectively solved by combining crystalline cellulose with a water-absorbing polymer having carboxyl groups and/or carboxylate groups in the molecule.

That is, the present invention particularly provides a water-absorbing polymer composition containing a water-absorbing polymer having a carboxyl group and/or a carboxylate group in the molecule and crystalline cellulose.

The water-absorbing polymer that is the subject of the present invention has a carboxyl group and/or a carboxylate group in its molecule, and among these, α, β-unsaturated carboxylic acid and/or its Preferably, it is produced by polymerizing a salt. Specifically, the monomers include, for example, acrylic acid, methacrylic acid,
A homopolymer using maleic acid, itaconic acid, crotonic acid, fumaric acid or a salt thereof, a copolymer of two or more of these monomers, or a copolymer of these and other copolymerizable components. Examples of salts include alkali metal salts such as lithium, potassium, and sodium, alkaline earth metal salts such as calcium, and organic bases such as ammonium.Other copolymerizable components include acrylamide, vinyl acetate, starch, etc. is exemplified.

The content of other copolymerizable components is preferably 20% by weight or less (hereinafter referred to as %) based on the total monomers. Among the above monomers, acrylic acid, methacrylic acid, and alkali metal salts thereof are preferred, particularly acrylic acid and alkali metal salts thereof are 10/90 to 50151, preferably 20/80 to 30.
It is preferable to use a mixture in the range of /70 (molar ratio).

The concentration of acrylic acid and metal salts thereof is preferably 35% or more, preferably 40% or more.

Among the metal salts of acrylic acid, sodium salts are preferred from the viewpoint of safety, since sodium polyacrylate is approved as a food additive. In addition to the above monomers, monomers that use acrylamide or acrylonitrile and are saponified after polymerization to become water-absorbing polymers having carboxyl groups or carboxylate groups in the molecule are also targeted.

Therefore, the water-absorbing resins that are the subject of the present invention include, for example, saponified starch-acrylonitrile copolymers, starch-acrylic acid graft copolymers and their salts, saponified starch-acrylamide copolymers, and polyvinyl alcohol-acrylic acid. Copolymer and its vinyl chloride ester unsaturated carboxylic acid copolymer saponified product, acrylic acid or
Polymers of its salts, saponified products of acrylonitrile polymers, etc. can be mentioned. These also include those crosslinked using a crosslinking agent and self-crosslinking types.

The present invention is characterized in that the water-absorbing polymer described above is combined with crystalline cellulose. Cellulose is known as a main component of the cell membranes of plants such as wood, cotton, and hemp, but its structure consists of crystalline regions in which molecules are arranged relatively regularly and in parallel; It consists of a non-crystalline region with a disordered structure. Among cellulose grains with such a structure, particularly highly purified purified bulbs are selected, and after being hydrolyzed with mineral acid under certain conditions to wash and remove the amorphous region, the base frame, IY'M
The crystalline cellulose obtained by drying the cellulose is finely powdered and of extremely high purity.

This crystalline cellulose is a white powder of secondary aggregates of fine crystals, and when it is strongly submerged in water, the particles loosen, forming a network gel of rod-shaped crystals several microns in length. The chemical structure of crystalline cellulose is as follows, and the basic molecule is C6H1oO6. This crystalline cellulose is harmless to the human body; it is not easily contaminated by microorganisms such as mold and bacteria; it is chemically inert; it is white, tasteless and odorless; it has a high bulk density and many voids; It has excellent properties such as high water retention capacity.

The crystalline cellulose mentioned above is Asahi Kasei's "Avicel".
It is easily available as (product name). In the present invention, various grades of the above-mentioned "Avicel" are used as crystalline cellulose, such as P) (series 101.102.301, MO
6, M2S, M25, FD-101, RC series N
Both 81.591NF and 501 can be used. Also, regarding the particle size, the average particle size is approximately 6μ and 40μ.
Although various particles such as 120μ and 120μ can be used, those having an average particle size of 40 to 120μ are preferable.

In the present invention, crystalline cellulose can be combined with the water-absorbing polymer in any proportion, but it is preferable that the amount of crystalline cellulose is 0.3 to 80 parts by weight per 100 parts by weight of the water-absorbing raw polymer. More preferably, the amount is 1 to 50 parts by weight.

If the amount is within this range, the larger the amount used, the more the water absorption rate will be increased without causing a lumpy state. On the other hand, if the amount is as small as 0,3-fold jTt 71, when the combination method is swollen in ion-exchanged water, lumps will be formed and the initial absorption rate will be insufficient.

In the present invention, as long as the water-absorbing polymer and the crystalline cellulose coexist during water absorption, their coexistence state is not critical, but it is preferable that the water-absorbing polymer and the crystalline cellulose are intricately intertwined. Specifically, it is preferable to use a form in which a water-absorbing polymer exists around crystalline cellulose particles. In such a form, for example, crystalline cellulose is added to an aqueous alkali metal solution of an acrylic acid monomer containing a water-soluble radical polymerization initiator and a crosslinking agent at the time of polymerization of a monomer for forming a water-absorbing polymer, and then dispersed. After that, it is easily produced by suspension polymerization, solution polymerization, or suspension polymerization by dropping an aqueous monomer solution into a system in which a crystalline polymer is dispersed in hexane, and then dried and smoked using a conventional method. can be manufactured. In addition, as another form, it is also preferable to use a form in which a water-absorbing polymer is sprinkled with crystalline cellulose. Such a form can be easily produced by adding crystalline cellulose during or after the polymerization of the monomer for forming the water-absorbing polymer, or after drying. The method of adding crystalline cellulose after completion of polymerization is to add it directly to the hexane slurry containing the water-absorbing polymer, or to dehydrate the water contained in the water-absorbing polymer with alcohol such as methanol, ethanol, isopropanol, etc. Examples include a method in which crystalline cellulose is added after that, and a method in which crystalline cellulose is added after further azeotropic dehydration.

Various polymerization methods such as solution polymerization, emulsion polymerization, and reversed-phase suspension polymerization can be employed as the polymerization method of the water-absorbing polymer-forming monomer for producing the water-absorbing polymer of the present invention, including aqueous solution polymerization, It is preferable to carry out reverse phase suspension polymerization. Next, preferred examples of solvents, emulsifiers, polymerization initiators, crosslinking agents, etc. in reverse-phase suspension polymerization will be given.

The solvent used is an aliphatic petroleum hydrocarbon, preferably one having a boiling point in the range of 30 to 200°C.

Specifically, normal hexane, cyclohexane, normal hexane, ligroin, etc. can be mentioned. Particularly preferred are normal hexane and cyclohexane. Furthermore, the amount of solvent is preferably in the range of 1 to 5 times the weight of the monomer.

Emulsifiers, dispersants, various surfactants can be used, but
8 or more is preferred. For example, polyoxyethylene alkyl ether, sorbitan fatty acid ester, oxyethylene oxypropylene block copolymer, sucrose fatty acid ester, etc. can be used as a nonionic surfactant having an HLB of 7 or more, and sorbitan having an HLB of 3 to 6. Fatty acid esters such as sorbitan monostearate can be used. Furthermore, nonionic surfactants having an HLB of 2.5 or less can also be used. Specific examples include sorbitan triolate, sorbitan tristearate, chrycerol monooleate, propylene glycol monostearate, and mixtures thereof. Furthermore, cellulose esters or cellulose ethers that are soluble in the dispersion medium such as cyclohexane at the polymerization temperature (40° C. or higher) can also be used.

Examples of such cellulose esters or cellulose ethers include cellulose acetate, cellulose butyrate, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate phthalate, ethyl cellulose, and ethyl hydroxyethyl cellulose.

The amount used is 0 per 100 weight of acrylate single fingers.
．． The amount is preferably in the range of 0.01 to 10 parts by weight.

Polymerization initiator All water-soluble radical polymerization initiators used in ordinary emulsion polymerization can be used, and examples include water-soluble peroxides such as potassium persulfate, ammonium persulfate, and hydrogen peroxide. These may be combined with reducing substances such as sulfites or amines to form a redox initiator.

Ammonium persulfate is preferred.

The amount of polymerization initiator used is 0.01 to 1 per monomer.
%.

A crosslinking agent is preferably one that has good copolymerizability with the acrylate monomer and can form a crosslinked structure efficiently. Such crosslinkable monomers include ethylene glycol diacrylate,
Ethylene glycol dimethacrylate, diethylene glycol diacrylate, diethylene glycol dimethacrylate, triethylene glycol diacrylate,
Triethylene glycol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol triacrylate, pentaerythritol trimethacrylate), N,N'-methylenebisacrylamide, triallyl isocyanurate, pentaerythritol dimethacrylate Examples include one type or a mixture of two or more types selected from methacrylates and the like. Among these, preferably N, N
'-methylenebisacrylamide.

The amount of the crosslinking monomer used is preferably 0.001 to 5% based on the monomer for forming the water-absorbing polymer.

In a world within this range, the larger the amount of crosslinkable monomer used, the higher the crosslinking density of the crosslinked polymer, which tends to increase the gel stress when the crosslinked polymer is swollen in ion-exchanged water. be.

However, if the amount exceeds 5%, the crosslinking density becomes too high and the thickening property and absorption capacity are reduced.

On the other hand, if the bond is less than 0.00196, the crosslinking density becomes too small, and the stress of the gel becomes small when the crosslinked polymer is swollen in ion-exchanged water. Furthermore, when it comes into contact with the liquid to be absorbed, it tends to become sticky or form a lump, resulting in a slow initial absorption rate.

According to the above reverse tenmoku suspension polymerization method, particles with a fine particle size can be obtained, and by blending crystalline cellulose with these dry particles, it is easy to obtain a product in the form of a water-absorbing polymer sprinkled with crystalline cellulose. Particularly preferred. In the present invention, particularly preferred are those made by adding crystalline cellulose at the beginning or during the polymerization of monomers, and those made by sprinkling crystalline cellulose onto dried water-absorbing polymer particles.

As mentioned above, the present invention is based on the combination of a water-absorbing polymer and crystalline cellulose, but it is unclear why such a combination would degrade the excellent water-absorbing properties. Even if an inorganic substance is added instead of a crystalline polymer, excellent results like those of the present invention can be obtained (
), it is presumed that this is due to the unique properties of crystalline cellulose, such as having many voids and water retention.

In the present invention, known additives such as perfumes, deodorizers, pigments, dyes, etc. can be added to the water-absorbing polymer '111'.

〔Effect of the invention〕

The water-absorbing polymer composition of the present invention is characterized by a high water-absorbing capacity, particularly for solutions containing a large amount of salts, and a high initial absorption rate without leaving a sticky state.

Therefore, it is effective to apply the water-absorbing polymer composition according to the present invention in the form of a sheet-like product that is sandwiched between two sheets of thin paper or the like and embossed to take advantage of the above-mentioned excellent water-absorbing properties. Such sheet products are advantageously used as water-absorbent sheets for sanitary napkins, disposable diapers, sheets for patients, and the like.

In addition, water retention agents for soil, water stop agents for civil engineering and construction, anti-condensation agents, sheep agents, poultices, suture coatings, aromatic bases, culture media for microorganisms, etc. are used in the fields of agriculture, civil engineering and construction, the medical industry, and food. Used in various industrial applications that utilize water absorption and water retention properties.

Next, the present invention will be explained with reference to Examples, but the present invention is not limited thereto.

〔Example〕

In Examples, water absorption amount and water absorption rate were measured as follows.

0 water absorption amount 6 x 8 cm tea bag with water absorbing polymer composition 0.
After crushing 3 g, soak in 0.9% saline (physiological saline) prepared in advance for 10 minutes. iL.

Ta. Next, the tea bag was taken out and allowed to drain for 1 minute, and the water absorption capacity was measured.

Water absorption capacity (g/g) = (Amount of water absorbed - blank)
/ Sample amount: 0 Water absorption degree: Water-absorbing polymer composition 1.
After weighing the Og, it was immersed vertically in 0 and 9% saline (artificial urine) that had been adjusted to the desired temperature, and the water absorption amount at each time was measured, and the water absorption capacity of the physiological saline and artificial urine was measured. The time required to reach 50% was determined.

The reason for vertical immersion is to increase the size of the polymer particle layer 17 to make it easier to get into a "stank state".

Example 1 500m equipped with a stirrer, reflux condenser, and nitrogen gas introduction pipe
1.24 ml of normal hexane in a four-piece removable flask
3m1! After adding and dissolving 3 g of sorbitan monostearate, nitrogen gas was blown into the solution to drive out dissolved oxygen. Acrylic acid 671.6 in a separate four-loaf flask
29 g of 96.1% caustic soda while cooling it with ice from the outside.
A solution of 5.1 g dissolved in 861.2 g of ion-exchanged water was added dropwise to neutralize 75% of the carboxyl groups. Then 4.33 g of ammonium persulfate and 0.0087 g of N,N'-methylenebisacrylamide were added.
g of ion-exchanged water, and then added to 174 g of the above neutralized acrylic acid and mixed. Next, 3.2 g of crystalline cellulose (Asahi Kasei Kogyo FF1) was added and nitrogen gas was blown into the solution. Oxygen was removed.

Add this to the above four robotable flasks and disperse.
While introducing a slight amount of nitrogen gas, the internal temperature of the flask was maintained at 60 to 63° C. using a hot water bath, and stirring was continued for 3 hours to polymerize the monomer. When the stirring was stopped, the reaction system became a field type in which the swollen polymer particles easily sedimented and separated. After the reaction was completed, normal hexane was filtered off, and a portion of the remaining polymer was dried at 30 to 120°C under reduced pressure. The water-absorbing polymer composition was ground as a powder containing agglomerates that were easily powdered and triturated.

Example 2 A water-absorbing polymer composition was produced in the same manner as in Example 1, except that 1.92 g of crystalline cellulose was added after completion of polymerization.

Example 3 Crystalline cellulose was added to a dried water-absorbing polymer with 12,8
A water-absorbing polymer composition was produced in the same manner as in Example 1, except that g was added and the powder was mixed.

Example 4 A water-absorbing polymer composition was produced in the same manner as in Example 3, except that the amount of crystalline cellulose used was 19.2 g.

Example 5 37% sodium acrylate aqueous solution 956 g, 80% acrylic acid aqueous solution 11
3g, N,N' methylenebisacrylamide 0.4g
and 75.72 g of crystalline cellulose were added. The mixture was stirred at a rotational speed of about 5 rpm, heated to 40° C. under a nitrogen cloud atmosphere, and 50 g of a 10% ammonium persulfate aqueous solution was added to polymerize the monomer.

Heat is generated with the start of polymerization, reaching 82°C approximately 10 minutes after the start of polymerization.
reached. At the same time, the polymerized aqueous solution turned into a hydrogel, which was gradually divided into smaller pieces by stirring. After 90 minutes from the start, stirring was stopped, and the hydrogel polymer was taken out and dried at 30 to 120°C under reduced pressure. The obtained water-absorbing polymer composition was simply pulverized to obtain 1 fathom of powdered water-absorbing polymer composition.

Practical Example 6 A water-absorbing polymer composition was produced in the same manner as in Example 5, except that 18.92 g of crystalline cellulose was added to 8.4 g of dry-pulverized water-absorbing polymer 37 and the powder was mixed.

Example 7 A water-absorbing polymer composition was produced in the same manner as in Example 6, except that the amount of crystalline cellulose per liter was changed to i 13.52 g.

Example 8 A water-absorbing polymer composition was produced in the same manner as in Example 1, except that 3.2 g of crystalline cellulose was added to the recycled water-absorbing polymer and mixed into powder.

Example 9 A water-absorbing polymer composition was produced in the same manner as in Example 1, except that 3.2 g of crystalline cellulose was added after completion of polymerization.

Comparative Example A water-absorbing polymer was produced in the same manner as in Example 1 without using crystalline cellulose.

Table 1 summarizes the performance of the water-absorbing polymer compositions and water-absorbing polymers produced in Examples 1 to 9 and Comparative Examples.

Table 1 *Water absorption (as the weight of the raw polymer, water absorption I main polymer forming monomer (acrylic acid + acrylate)!
)n;jl of crystalline cellulose per g.

As is clear from the results in Table 1, it can be seen that the methods of Examples 1 to 9 are much superior in water absorption speed compared to the comparative examples that do not contain crystalline cells.

Claims (5)

[Claims] (1) A water-absorbing polymer composition characterized by containing a water-absorbing polymer having a carboxyl group and/or a carboxylate in the molecule and crystalline cellulose. (2) The composition according to claim (1), in which a water-absorbing polymer exists around crystalline cellulose particles. (3) The composition according to claim (1), which is in the form of a water-absorbing polymer sprinkled with crystalline cellulose. (4) The composition according to claim (1), wherein the amount of crystalline cellulose is in the range of 0.3 to 80 parts by weight per 100 parts by weight of the water-absorbing polymer. (5) The composition according to claim (1), wherein the water-absorbing polymer is formed using an α,β-unsaturated carboxylic acid and/or a salt thereof as a water-absorbing polymer forming monomer.