JPH06145253A - Production of resin having high water absorption property - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a highly absorbent resin having a high water absorption property, a reduced water-soluble content, and an excellent gel stability over time. [Structure] In producing an acrylic superabsorbent resin by polymerizing a water-soluble unsaturated monomer containing (meth) acrylic acid and a water-soluble salt of (meth) acrylic acid as main components in the presence of a crosslinking agent, 0.001-0.1 parts by weight of hypophosphorous acid and / or its salt and 0.05-2 parts by weight of urea compound are made to coexist with 100 parts by weight of the water-soluble unsaturated monomer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a highly water-absorbent resin in which water-soluble components are reduced while maintaining high water-absorbing performance.

[0002]

2. Description of the Related Art Starch is a resin that absorbs a large amount of water.
Acrylonitrile graft polymer partial hydrolyzate, polyacrylic acid partially neutralized salt, polyethylene oxide type,
Super water-absorbent resins such as polyacrylonitrile-based, polyvinyl alcohol-based, and cross-linked systems thereof are known. Among these, a partially neutralized polyacrylic acid salt obtained by copolymerizing (meth) acrylic acid and a water-soluble (meth) acrylic acid salt in the presence of a crosslinking agent is particularly useful.

The highly water-absorbent resin is useful as a body fluid absorbent for absorbing body fluids and preventing leakage in sanitary and hygiene products, and also as a soil water retention agent, seed coating agent, water blocking agent and thickener. It is used for anti-condensation agent, sludge coagulant, desiccant, humidity control agent, etc. This powder is
It is required that Mamako phenomenon does not occur when it comes into contact with water or body fluid, and that it has a high absorption rate and absorption capacity for water and body fluid, and that it has high gel strength when swollen by absorbing water and body fluid. However, in order to improve the absorption capacity, it is necessary to reduce the crosslink density of the partially neutralized polyacrylic acid salt. However, when the crosslink density of the partially neutralized polyacrylic acid salt is decreased, the gel strength is decreased and the uncrosslinked component is increased, resulting in the elution of water-soluble components. When used in, it causes stickiness and it is difficult to balance all these physical properties.

In order to improve the physical properties of the partially neutralized polyacrylic acid salt, a method in which a water-soluble chain transfer agent is allowed to coexist during polymerization (USP4698404, JP-A-2-255804), and a hypophosphorous acid compound is allowed to coexist during polymerization. Method (JP-A-2-300210), method of allowing water-absorbent resin powder to coexist during polymerization (JP-A-3-52903), and method of reducing residual monomer in the absorbent resin by using a radical scavenger after polymerization. Although Japanese Patent Laid-Open No. 4-120111 and Japanese Patent Laid-Open No. 4-120112 are proposed, none of these methods is a solution to the problem of the present application.

[0005]

That is, in the method in which a water-soluble chain transfer agent is allowed to coexist during polymerization, the water-absorbing ability is improved, but the elution of water-soluble components cannot be reduced and is still insufficient. Similarly, it is difficult to reduce the elution of water-soluble components even by the method in which a hypophosphorous acid compound is allowed to coexist during polymerization. Further, although the water-soluble content is reduced by the method of allowing the water-absorbent resin powder to coexist during the polymerization, there is still room for improvement in the water-absorbing ability. Furthermore, a method of reducing the residual monomer in the absorbent resin by using a radical scavenger after the polymerization is studied by the present inventors.
Although the gel condition immediately after absorption is good, over time (for example, at room temperature for 6 hours or more), the gel is decomposed and the stringing phenomenon is observed by observing the fingers, and it is considered that there is still room for improvement.

[0006]

Therefore, the present inventors have
As a result of earnest studies to solve the above problems, as a result, (meth) acrylic acid and a water-soluble unsaturated monomer containing (meth) acrylic acid water-soluble salt as a main component are polymerized in the presence of a crosslinking agent. In producing the acrylic super absorbent polymer, hypophosphorous acid and / or 100 parts by weight of the water-soluble unsaturated monomer are used.
Or 0.001 to 0.1 part by weight of a salt thereof and a urea compound of 0.
By carrying out the polymerization in the presence of 05 to 2 parts by weight, a highly absorbent resin having a high water absorption property, a reduced water-soluble content, and an excellent gel stability over time can be obtained. We have found this and completed the present invention. The present invention will be described in detail below.

The (meth) acrylic acid and the water-soluble unsaturated monomer whose main component is the water-soluble salt of (meth) acrylic acid of the present invention include (meth) acrylic acid which is sodium hydroxide, potassium hydroxide, carbonic acid. Alkali metal hydroxides such as sodium and potassium carbonate, ammonium hydroxide, or those partially neutralized with amines as the main component, mainly consisting of a mixture of (meth) acrylic acid and a water-soluble salt of (meth) acrylic acid. It is a monomer used as a component.

The mixing ratio of (meth) acrylic acid and the water-soluble salt of (meth) acrylic acid, in other words, the degree of partial neutralization is
60 to 90 mol% of the total (meth) acrylic acid is preferable.
That is, the mixture is polymerized in a ratio of (meth) acrylic acid / (meth) acrylic acid water-soluble salt in the range of 40/60 to 10/90 (molar ratio). The above ratio is 40/6
When it exceeds 0, the water absorption capacity and water absorption rate are inferior, and there is a problem that the product exhibits acidity. On the other hand, when it is less than 10/90, the water absorption capacity and water absorption rate decrease, and the product has alkalinity, which is a practical problem. May occur.

The hypophosphorous acid or its salt used in the present invention includes hypophosphorous acid, sodium hypophosphite,
Examples thereof include water-soluble salts such as potassium hypophosphite, ammonium hypophosphite and amine hypophosphite, and at least one of them is used. Among them, sodium hypophosphite and potassium hypophosphite are preferably used from the viewpoint of easy handling. Further, examples of the urea compound used in the present invention include urea, thiourea, ethylene urea, ethylene thiourea, guanidine salt and the like.
More than one seed is used. Among them, thiourea and urea are preferably used.

The coexisting amount of the above hypophosphorous acid and / or its salt is 100 parts by weight of the total amount of the above water-soluble unsaturated monomer, that is, (meth) acrylic acid and (meth) acrylic acid water-soluble salt. And 0.001 to 0.1 part by weight, preferably 0.005 to 0.05 part by weight. Hypophosphorous acid and /
Alternatively, if the amount of the salt is less than the above range, high absorbency cannot be obtained, while if it is more than the above range, the soluble content becomes too large. In addition, the coexisting amount of the urea compound is 0.05 based on 100 parts by weight of the total amount of the water-soluble unsaturated monomer, that is, (meth) acrylic acid and the water-soluble salt of (meth) acrylic acid.
˜2 parts by weight, preferably 0.05 to 1 part by weight. When the amount of the urea compound is less than the above range, it becomes difficult to obtain high absorbency, while when the amount of the urea compound is more than the above range, the amount of water-soluble component becomes high although the absorbency becomes high.

Furthermore, the coexistence ratio of the above hypophosphorous acid and / or its salt and the urea compound cannot be generally stated depending on the purpose of use, but it is 1 by weight ratio of the hypophosphorous acid and / or its salt / urea compound. / 1-1 / 20, preferably 1 / 5-1 / 10. In applications such as sanitary products such as paper diapers and sanitary products, the coexisting amount of the hypophosphorous acid and / or its salt and the urea compound is 0.005 to 100 parts by weight of the water-soluble unsaturated monomer. About 0.05 parts by weight and about 0.05 to 1.0 parts by weight are sufficient.
It is preferable that the amount is about 05 to 0.1 parts by weight and 0.5 to 2 parts by weight. The method for adding the hypophosphite and the urea compound is not particularly limited as long as they coexist at the time of polymerization, but it is added in advance to the partially neutralized solution of the water-soluble unsaturated monomer, and the polymerization is performed. Is preferable from the viewpoint of homogenizing the polymer.

In carrying out the polymerization, any known method can be adopted, such as aqueous solution polymerization (static polymerization), emulsion polymerization (reverse phase emulsion polymerization), suspension polymerization (reverse phase suspension polymerization) and the like. Can be mentioned. In the present invention, any of the above-mentioned polymerization methods can be adopted, but in order to obtain a resin having a high water absorption and a low water-soluble content, which is an object of the present invention, a reverse phase whose polymerization temperature is easily controlled is used. The suspension polymerization method is particularly preferred. Hereinafter, the polymerization method will be described more specifically. In carrying out reverse phase suspension polymerization, an aqueous solution containing a cross-linking agent such as (meth) acrylic acid, a water-soluble salt of (meth) acrylic acid and a polyfunctional vinyl monomer is dispersed in an organic solvent that is insoluble in water to generate radicals. Polymerization is performed in the presence of a polymerization initiator.

At this time, it is also possible to stabilize the polymerization by coexisting with a known dispersion stabilizer or surfactant. Examples of the organic solvent include alicyclic hydrocarbons such as cyclohexane and cyclopentane, aliphatic hydrocarbons such as n-pentane, n-hexane, n-heptane and ligroin, and aromatic hydrocarbons such as benzene, toluene and xylene. To be done. Judging from the boiling point, melting point, price, and industrial availability of the solvent, n-hexane and cyclohexane are the most practical. The polymerization temperature is 50 to 90 ° C., and the polymerization time is 0.5 to
5 hours is appropriate. After completion of the polymerization, the desired superabsorbent resin can be obtained by filtering the produced particles, washing and drying according to a conventional method.

In carrying out the polymerization method as described above,
Polymerization initiators used include azonitriles such as azobisisobutyronitrile; t-butyl peroxide,
Alkyl peroxides such as cumene hydroperoxide; Dialkyl peroxides such as di-t-butyl peroxide; Acyl peroxides such as acetyl peroxide, lauroyl peroxide, stearoyl peroxide, benzoyl peroxide; t-butyl peroxyacetate , Peroxyesters such as t-butylperoxyisobutyrate and t-butylperoxypivalate; ketone peroxides such as methyl ethyl ketone peroxide and cyclohexanone peroxide, hydrogen peroxide, ammonium persulfate, potassium persulfate, cerium salts, etc. And a water-soluble substance is particularly preferable.

Further, it is practically preferable to add a surfactant to keep the system stable. Examples of such an active agent include polyoxyethylene alkyl ether, polyoxyethylene acyl ester, polyoxyethylene sorbitan fatty acid ester. , Sorbitan fatty acid ester, oxyethyleneoxypropylene block copolymer, sucrose fatty acid ester, higher alcohol sulfuric acid ester salt, alkylbenzene sulfonate, polyoxyethylene sulfate, or other nonionic surfactant or anionic surfactant Alternatively, they are used in combination.

The cross-linking agent used in combination is 0.00001 to the total amount of acrylic acid and water-soluble acrylic acid salt.
0.5 mol%, preferably 0.0001 to 0.1 mol%
Examples of such a crosslinking agent used include ethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol diacrylate, triethylene glycol methacrylate, trimethylolpropane triacrylate, trimethyloltrimethacrylate, pentaerythritol trimethacrylate. Polyfunctional vinyl compounds such as acrylate, pentaerythritol trimethacrylate, N, N'-methylenebisacrylamide, isocyanuric acid triallyl pentaerythritol diacrylate and pentaerythritol dimethacrylate, or (poly) ethylene glycol diglycidyl ether, (poly) glycerol Polyglycidyl ether, sorbitol polyglycidyl ether, Examples thereof include water-soluble or water-dispersible polyglycidyl compounds such as pentaerythritol polyglycidyl ether. Among them, N, N'-methylenebisacrylamide, ethylene glycol diglycidyl ether and the like are preferably used.

Industrially, the superabsorbent resin thus obtained is industrially dried and then subjected to a sizing step (crushing and sieving), and then packaged and shipped (transported). Needless to say, conventionally known so-called surface crosslinking may be performed after the above polymerization. The superabsorbent resin of the present invention is usually used in the form of powder or particles, but in some cases, it may be used in the form of a composite molded product with a film, sheet, fiber, paper or the like. In addition, the resin of the present invention is particularly useful as a body fluid absorbent that absorbs body fluids and excretions and prevents leakage in sanitary products and sanitary products. In addition, soil water retention agent, seed coating agent, water blocking agent,
Thickener, anti-condensation agent, dehydration agent, desiccant, humidity control agent, sludge
It can also be used as a coagulant for liquid wastes, heavy metal adsorbents, sustained-release agents for chemicals and fragrances, poultices, and cool agents.

[0018]

[Operation] Since the super absorbent polymer of the present invention is produced by polymerization in the presence of hypophosphorous acid and / or its salt and a urea compound, It is possible to obtain a highly absorbent resin which has a reduced soluble content and is excellent in gel stability over time.

[0019]

[Examples] Hereinafter, the present invention will be described specifically with reference to Examples. In the examples, "part" and "%" are based on weight unless otherwise specified. Example 1 A 2 liter separable flask equipped with a stirrer, a reflux condenser and a nitrogen gas inlet tube was charged with 500 ml of cyclohexane and 2.5 g of sorbitan monostearate, and nitrogen bubbling was performed for 30 minutes to dissolve dissolved air and the inside of the flask. Expelled the air of. Add acrylic acid 7 to another 1 liter beaker
After 0.0 g was charged, a solution of 30.7 g of sodium hydroxide having a purity of 95% in 90 g of water was stirred and gradually added dropwise under cooling to neutralize, and 17.5 g of acrylic acid and 68 of sodium acrylate were added. A mixed solution containing 0.5 g was obtained.

Next, 3.5% 1% ammonium persulfate aqueous solution
ml, 0.5% N, N'-methylenebisacrylamide aqueous solution 4.2 ml, sodium hypophosphite 0.0086
g and 0.086 g of urea were added and thoroughly mixed.
And it moved to the dropping funnel of 500 ml, and set it in the said separable flask. The separable flask was immersed in a bath and heated, and the contents of the beaker were added dropwise from a dropping funnel at 70 to 75 ° C over 1.5 hours while stirring.
After aging for 0 minutes, about 60% of the water in the system after polymerization was expelled by azeotropic distillation with cyclohexane. After cooling, the content was filtered through a wire mesh of 325 mesh, the content on the wire mesh was washed with warm cyclohexane, and then vacuum dried at 80 ° C.
As a result, a highly water-absorbent resin was obtained.

Examples 2 to 8 In Example 1, the types and blending amounts of hypophosphorous acid and its salts and urea compounds were changed as shown in Table 1 to obtain superabsorbent resins. Comparative Examples 1 to 6 In the method of Example 1, the blending amounts of hypophosphite and urea compound were changed as shown in Table 1 to obtain superabsorbent polymers. In Comparative Example 1, the hypophosphite and the urea compound were not added. The following evaluations were performed on the superabsorbent polymers obtained in the above Examples and Comparative Examples.

(Saline absorption capacity) 0.2 g of super absorbent resin was put into a 100 ml beaker containing 60 g of 0.9% sodium chloride aqueous solution, and left at room temperature for 20 minutes,
Filter the swollen gel through wire mesh (200 mesh) for 20 minutes,
The weight of the swollen gel after draining was measured. The absorption capacity was calculated by the following formula. Absorption capacity (g / g) = swelling gel weight (g) /0.2
(G) (Water-soluble content) 300 ml containing 200 g of ion-exchanged water
Add 0.1 g of superabsorbent resin to the beaker, and mix at room temperature for 6
After standing for 0 minutes, swell the gel with a wire mesh (200 mesh).
After filtration for 0 minute, the obtained filtrate was concentrated to dryness at 100 ° C. and the residue was measured. The water-soluble content was determined by the following formula. Water-soluble content (%) = [concentrated dry solid residue (g) /0.1
(G)] × 100

(Gel stability) 25 g of 0.9% aqueous sodium chloride solution containing 1.0 ppm of Fe ²⁺ ions
1 g of highly water-absorbent resin was put into a 100 ml beaker containing the mixture, lightly stirred with a glass rod, and then left at room temperature for 6 hours. Then, the swollen gel was taken out, and the presence or absence of stringing of the gel was confirmed by touching with a finger. ○ −−− No string pulling × −−− String pulling is shown in Table 2.

[0024]

[Table 1] Hypophosphorous acid (salt) urea compound Hypophosphorous acid Sodium hypophosphite Potassium hypophosphite Thiourea Urea Example 1 --- 0.01 --- 0.1 --- 〃 2 --0 .01 −−−− 0.2 〃 3 −− 0.005 −− 0.2 0.2 −− 〃 4 −−−− 0.005 0.05 −− 〃 5 −−−− 0.05 05 1.0− − 〃 6 − − 0.025 0.025 − − 0.5 〃 7 0.001 − − − − 0.1 − − 〃 8 0.005 0.005 − − 0.1 − − Comparative Example 1 − − −−−−−−−− 〃 2 −− 0.01 −− −− −− 〃 3 −− −−−− 0.1 0.1 −− 〃 4 −− 0.01 −− 3.0 −− −−0.3−−0.1−− 〃6−−0.3−−3.0−− Note) Numerical values represent the addition parts by weight to 100 parts by weight of the water-soluble unsaturated monomer.

[0025]

[Table 2] Saline absorption capacity Water-soluble content Gel stability (g / g) (%) Example 1 85 13 ○ 〃 2 80 12 ○ 〃 3 85 12 ○ 〃 4 85 12 ○ 〃 5 105 17 ○ 〃 6 90 14 ○ 〃 7 90 14 ○ 〃 8 85 13 ○ Comparative Example 1 50 8 ○ 〃 2 63 18 × 〃 3 55 13 ○ 〃 4 68 19 × 〃 5 * 50 <× 〃 6 * 50 <× * Since the superabsorbent resin became a viscous substance and could not be filtered, it could not be measured.

[0026]

The method for producing a superabsorbent resin of the present invention has a superabsorbent property because it is produced by polymerizing in the presence of hypophosphorous acid and / or its salt and a urea compound. In addition, it reduces the water-soluble content, and can obtain a highly absorbent resin with excellent gel stability over time, which is extremely useful as a body fluid absorbent for sanitary products and sanitary products. It can be suitably used for various purposes such as agents.

Claims (2)

[Claims] 1. A highly water-absorbent acrylic resin is produced by polymerizing a water-soluble unsaturated monomer containing (meth) acrylic acid and a water-soluble salt of (meth) acrylic acid as main components in the presence of a crosslinking agent. At this time, 0.001 to 0.1 parts by weight of hypophosphorous acid and / or a salt thereof and 0.05 to 2 parts by weight of a urea compound coexist with 100 parts by weight of a water-soluble unsaturated monomer and polymerize. A method for producing a highly water-absorbent resin, comprising: 2. The method for producing a highly water-absorbent resin according to claim 1, wherein hypophosphorous acid and / or its salt and a urea compound are added to a water-soluble unsaturated monomer and polymerized.