JPS6356512A - Production of resin having high water absorption property - Google Patents

Abstract

PURPOSE:To obtain the titled resin having large particle diameters, water absorption ability, water absorption rate, gel strength, etc., by dispersing an aqueous solution containing acrylic acid and an alkali metallic salt thereof into an aliphatic hydrocarbon by the use of a specific dispersant and subjecting the dispersion to reverse-phase suspension polymerization. CONSTITUTION:First, a copolymer consisting of (A) 40-95wt% (meth)acrylic acid alkyl ester monomer containing >=8C alkyl group, (B) 5-40wt% (meth) acrylic acid hydroxyalkyl monomer and (C) 0-40wt% unsaturated monomer copolymerizable with the compositions A and B is used as dispersant. By the dispersant, an aqueous solution containing acrylic acid and an alkali metallic salt thereof is dispersed into an aliphatic hydrocarbon solvent (preferably n- hexane, etc.) and subjected to reverse-phase suspension polymerization in the presence of a crosslinking agent to give the aimed resin. Lauryl acrylate is preferable as the component A and 2-hydroxyethyl acrylate, etc., are used as the component B.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a method for producing a super absorbent resin having excellent properties such as water absorption capacity, water absorption rate, stickiness, and gel strength, and having a large particle size. Since the superabsorbent resin produced by the method has excellent properties as described above, it can be used for sanitary materials (disposable diapers, sanitary napkins), water retaining materials for agricultural and horticultural soils, and the like.

[Conventional technology and problems] Water-absorbing resins are used for various purposes such as sanitary products, sanitary materials such as disposable diapers, water-retaining materials used in agriculture and horticulture, coagulation of sludge, and dehydration of oils. It is a useful synthetic resin for which new uses are being developed. These resins are: ■ Hydrolyzate of starch-acronitrile graft polymer (Japanese Patent Publication No. 53-46199, Japanese Patent Application Laid-Open No. 55-4820); ■ Modified cellulose (Japanese Patent Publication No. 50-80378); Sodium polyacrylate produced by reverse phase suspension method
No. 4-30710, Japanese Unexamined Patent Publication No. 58-28909)■
Sodium polyacrylate obtained by aqueous solution polymerization method (adiabatic polymerization, thin film polymerization) (JP-A-55-133413) ■ Cross-linked product of water-soluble polymer (JP-A-43-234G2) (φ Starch-acrylic acid Soda graft polymer (Japanese Patent Publication No. 53-48199) and the like are known.

[Problems to be Solved by the Invention] However, the above method has the following problems.

■ It has drawbacks such as insufficient water absorption capacity, and even if the water absorption capacity is high, the water absorption rate is slow and the dispersibility in water is poor.

■ Gel becomes sticky after water absorption, considering sanitary materials.
There are concerns about its effect on the skin.

■ Air permeability is poor due to agglomeration of resin particles in a swollen state after absorbing water, and when considered as a water retaining material for soil, there is a risk of root rot.

Further, as a method of increasing the water absorption rate of the water absorbent resin and increasing the gel strength after water absorption, there is a method of simultaneous crosslinking or post crosslinking using a crosslinking agent. However, these methods
Although the water absorption rate increases, the water absorption capacity decreases, and the resin particles in a swollen state after absorbing water coagulate with each other, resulting in poor air permeability.

In recent years, as a method to overcome the above-mentioned drawbacks of water-absorbing resins, a method has been proposed in which bead-shaped resins with large particle diameters are synthesized by inverse phase suspension polymerization using a suitable dispersant.

For example, JP-A-57-158209 discloses a method using cellulose ester or cellulose ether as a dispersant, but this method has the disadvantage of blocking during drying and adhesion to the dryer wall. Also, JP-A-57-940
11. In JP-A-57-98512, a carboxy-containing polymer is used as a dispersant, but it is difficult to carry out stable reverse phase suspension polymerization, and there is a risk that the polymers may be integrated during the polymerization. Furthermore, in JP-A-Sho Ei+-40309, a styrene-dimethylaminoethyl methacrylate copolymer is used as a dispersant, but it is difficult to dissolve in n-hexane, and the resulting water-absorbing resin is difficult to mix with water, resulting in a slow water absorption rate. It has its drawbacks.

[Step F to solve the problem] As a result of intensive research to improve the conventional drawbacks, the present inventors have developed a product with excellent properties such as water absorption capacity, water absorption rate, stickiness, and gel strength, and a large particle size. We have discovered that it is possible to safely produce a super absorbent resin with

According to the present invention, in a method for producing a superabsorbent resin by dispersing acrylic acid and an aqueous solution of its alkali metal salt in an aliphatic hydrocarbon solvent and carrying out reverse phase suspension polymerization in the absence of a crosslinking agent, As agents: (A) 40 to 95% by weight of an acrylic acid or methacrylic acid alkyl ester monomer having an alkyl group of 8 or more carbon atoms; (B) 5 to 40% by weight of an acrylic or methacrylic acid hydroxyalkyl ester i-mer; , (C) above (A),
There is provided a method for producing a superabsorbent resin characterized by using a copolymer having as a constituent component 0 to 40% by weight of a monochromatic monomer that can be copolymerized with (B).

The acrylic acid or methacrylic acid alkyl ester of component (A) may be used as long as the number of carbon atoms in the alkyl group is 8 or more. -Ethylhexyl, lauryl acrylate, lauryl methacrylate,
Examples include tridecyl acrylate, tridecyl methacrylate, lauryl acrylate, tridecyl mixed ester, stearyl acrylate, and stearyl methacrylate.

When selecting the component (A), the higher the glass transition point of each monomer is, the more convenient it is because blocking of beads is less likely to occur when synthesizing a dispersant by aqueous @WJ polymerization. It is shown in Table-1.

Examples include 2-ethylhegicyl methacrylate, lauryl acrylate, lauryl acrylate, tridecyl mixed ester, tridecyl acrylate, lauryl acrylate, stearyl methacrylate, and the like.

As the component (B), acrylic acid or methacrylic acid hydroxyalkyl ester, commercially available monomers such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate; -Hydroxypropyl, etc. Examples of the monomer of component (C) include methacrylic acid alkyl esters having a high glass transition point and affinity for aliphatic hydrocarbon solvents with an alkyl group having 4 or less carbon atoms, and vinyl acetate. For example, methyl methacrylate, ethyl methacrylate.

Isopropyl methacrylate, n-butyl methacrylate,
Examples include isobutyl methacrylate and vinyl butyrate. Preferably, methyl methacrylate, ethyl methacrylate, and isobutyl methacrylate are suitable.

The copolymer of these components (A), (B), and (C) is
Considering the monomer content, it is safe as a dispersant for water-absorbing resins used in sanitary materials, and there is no problem in using it.

The composition ratio of components (A), (B), and (C) is based on dispersion solubility in aliphatic hydrocarbon solvent, colloidal dispersibility of polymerization,
It has a great influence on the physical properties of the water absorbent resin, such as water absorption capacity, water absorption rate, stickiness, gel strength, and particle size.

Usually (A) component 40-95fff amount%, (B) component 5-5%
40i% by weight, component (C) 0 to 40% by weight, more preferably component (A) 45 to 70% by weight, component (B) 5 to 40% by weight.
Appropriate amounts are 25% by weight and component (C) from 20 to 40% by weight. When component (A) is less than 400% by weight, the dispersion solubility in the solvent decreases, and when it exceeds 95% by weight, it is relatively (B)
) If the content of the component is less than 5% by weight, colloidal dispersibility deteriorates, and in both cases it becomes difficult to continue reverse phase suspension polymerization.

In the range of 40 to 95% by weight, the higher the amount, the better the dispersion and solubility in the solvent, the slower the water absorption rate of the water absorbent resin, and the less sticky it tends to be. (B) component is 5% by weight
If it is less than 4, the colloidal dispersibility deteriorates as described above, and
If it exceeds 0% by weight, the dispersion solubility of the solvent and ＼ will decrease, making it difficult to continue the reverse phase suspension polymerization. In the range of 5 to 40% by weight, the higher the amount, the better the colloidal dispersibility of polymerization and the faster the water absorption rate of the water absorbent resin, but there is a tendency for stickiness to increase and particle size to become finer. (C) component is 4
When it exceeds 0% by weight, the proportion of component (A) decreases relatively and the dispersion solubility in the solvent deteriorates. In the range of 0 to 40% by weight, the gel strength of the water absorbent resin increases as the amount increases.

The copolymer used as a dispersant in the present invention is synthesized by an aqueous suspension polymerization method. In solution polymerization, solvent may remain,
Low molecular weight polymers may have poor functionality as a dispersant. To take an example of an aqueous suspension polymerization method, partially saponified polyvinyl alcohol is heated and dissolved in ion-exchanged water, and after nitrogen 222 conversion, azo-based or A solution containing a peroxide-based polymerization initiator is dropped and dispersed, and the temperature is maintained to complete the polymerization. After cooling, the solid matter is filtered, washed with water, and then dried under reduced pressure to obtain a bead-shaped polymer, that is, a dispersant.

The dispersant obtained by method 1 is dispersed and dissolved in the aliphatic hydrocarbon solvent in the reverse phase suspension polymerization. % by weight, preferably 1. If the amount of the 0 dispersant used in the range of 10% by weight of ON is less than 0.5% by weight, the colloidal dispersibility of the polymerization will become unstable, and if it exceeds 20% by weight, the particle size will become too small.

It is also economically disadvantageous. Further, as a dispersant, a conventionally known nonionic surfactant such as sorbitan fatty acid ester can be used in combination.

The aqueous solution of acrylic acid and its alkali metal salt used in the present invention is prepared by partially neutralizing an acrylic acid monomer with an aqueous solution of sodium hydroxide, potassium hydroxide, or the like. Neutralization degree is 60-85% considering water absorption capacity and safety.
is preferable, and the monomer concentration in the aqueous solution is preferably 35 to 75% by weight, preferably 40 to 70% by weight.

In the present invention, an unsaturated monomer that can be copolymerized with acrylic acid and an acrylic acid alkali metal salt monomer may be copolymerized within the scope of producing a water absorbent resin.

In the present invention, when acrylic acid and its aqueous alkali metal solution are subjected to reverse phase suspension polymerization, the polymerization initiator is a self-crosslinking type that does not use a crosslinking monomer, so water-soluble polymers such as potassium persulfate and ammonium persulfate are used as the polymerization initiator. Persulfates and hydrogen peroxide are preferable. The amount of polymerization initiator used is 0.1 to 0.1 to 0.0 per monomer.
2.0% by weight, preferably 0.2-1.0% by weight.

Examples of aliphatic hydrocarbon solvents for reverse phase suspension polymerization in the present invention include n-pentane, n-hexane, n-heptane, n-
Examples include aliphatic hydrocarbons such as -octane, alicyclic hydrocarbons such as cyclohexane, methylcyclohexane, and decalin, and preferably n-hexane, n-heptane, and cyclohexane.

In the polymer obtained by reverse-phase suspension polymerization in the present invention, most of the water is distilled off by azeotropic dehydration directly after the polymerization is completed, and the polymer is further filtered and dried under reduced pressure to be recovered as a bead-shaped water-absorbing resin. However, the method is not limited to these methods.

[Effects of the Invention] The water absorbent resin obtained by reverse-phase suspension polymerization using the dispersant of the present invention has high water absorption capacity, fast water absorption rate, low stickiness, and high gel strength, so it can be used for disposable diapers, etc. Ideal for sanitary materials.

In addition, it is a bead-shaped polymer with a particle size of around 200 mm, and has low hygroscopicity and a bulk specific gravity of 0.9 to 1.1. Easy to handle. Furthermore, during reverse phase suspension polymerization, there is almost no polymer adhesion to the polymerization pot, so maintenance of the polymerization pot can be reduced and operation can be performed safely.

[Example] Next, the method of the present invention will be specifically explained with reference to Examples, but the present invention is not limited to these Examples.

The water absorbent resins obtained in Examples and Comparative Examples were tested for water absorption capacity, water absorption rate, stickiness after water absorption, gel strength,
The average particle size was measured.

Water absorption capacity 1) In the case of water absorption capacity of ion-exchanged water, dry polymer 0.
Disperse 5g in lρ ion-exchanged water, leave it to stand for a day and night,
Swollen polymer weight obtained by filtration through 00 mesh wire mesh 1
(W) and convert this value into the initial dry polymer weight (W
o) is the value obtained by dividing by In other words, the water absorption capacity of ion-exchanged water (g/g) = W / W o.

2) For the water absorption capacity of artificial urine, 0.2 g of dry polymer is
The swollen polymer (W) obtained by dispersing it in 0 g of artificial urine, leaving it for 30 minutes, and filtering it through a 100-mesh wire mesh was measured.
This value is obtained by dividing this value by the initial dry polymer weight 1 t (Wo).

In other words, human - ■ urine water absorption capacity (g/g) = W/Wo.

Artificial urine composition (g/100112) Urea 2.0g, NaCl! 0.82g, Mg5O
a O, 0553g.

CaCRz 0.084g Based on water absorption rate stirring method. 50 cc of ion-exchanged water was put into a 100 cc beaker, and 0.5 g of the dry polymer was added while stirring with a magnetic stirrer.The time from the introduction until all the water was absorbed and the water lost its fluidity was measured. .

4.0 g of artificial urine was added to 0.10 g of the sticky dry polymer after water absorption, and after leaving it for 30 minutes, 2.0 g of the gel was filtered onto circular qualitative filter paper (No. 2.11).
c+s diameter) Spread within the 5.0 cm diameter circle drawn above.

After leaving for 3 minutes, remove the gel, measure the weight (W) of the filter paper, and subtract the weight of the filter paper (WO) weighed in advance.

Gel strength 1) Add 8.0 g of artificial urine to 0.20 g of wet back dry polymer,
After standing for a minute, remove the adhered artificial urine with a filter paper and spread it in a circle with a diameter of 3.0 cm drawn on a circular qualitative filter paper (No. 2.11 cm diameter). Sandwich it between two pieces of paper of the same quality, one on top and one on top, and place it on an aluminum plate (15cm x 15cm, 153
g), place an aluminum plate of the same shape on top, and then
Place a 50g weight on it. After leaving it for 3 minutes, remove the gel.
The weight (W) of the filter paper was measured, and the weight of the artificial urine absorbed into the vJ paper was determined by subtracting the weight (W) of the paper, which had been weighed in advance.

2) Gel spreading area After the wet back measurement, the gel spreading area (S cm2) of the paper where the gel was placed was calculated.

Average particle size Automatic particle size distribution measuring device CAPA-30 manufactured by Horiba, Ltd.
0 using a centrifugal sedimentation method, and the area-based median value was taken as the average particle diameter.

Synthesis Example 1 A 500 tR separable flask equipped with a stirrer, a reflux condenser, a dropping funnel, a thermometer, and a nitrogen gas introduction tube was charged with 150 g of ion exchange water, and partially saponified polyvinyl alcohol (Nippon Gosei Kagaku Co., Ltd. GW) was added as a dispersant. -23) 0.
After adding 2 g and heating and dissolving, the mixture was replaced with nitrogen.

Meanwhile, in advance, lauryl acrylate and tridecyl mixed ester (LTA manufactured by Osaka Organic Chemical Co., Ltd.) was prepared in an Erlenmeyer flask.
) 30.0g, hydroxyethyl methacrylate 7.5
g, 1.0 g of azobisdimethylvaleronitrile was added to 12.5 g of methyl methacrylate, dissolved, and added dropwise to the above separable flask over 1 hour under a nitrogen stream/blow. Maintained at 65°C for 5 hours. and terminate the reaction,
After cooling, the solid matter was filtered, washed with water, and then dried under reduced pressure to obtain bead-shaped dispersant (1).

Synthesis Example 2 Lauryl acrylate, tridecyl mixed nistyl 22.5
A bead-shaped dispersant (2) was obtained in the same manner as in Synthesis Example 1 except that 10.0 g of hydroxyethyl methacrylate and 17.5 g of methyl methacrylate were used.

Synthesis Example 3 Lauryl acrylate, tridecyl mixed ester 45.0
g, Bead-shaped dispersant (3) was prepared in the same manner as in Synthesis Example 1 except for using 5.0 g of hydroxyethyl methacrylate.
I got it.

Synthesis Example 4 Lauryl acrylate, tridecyl mixed ester 30.0
A bead-shaped dispersant (4) was obtained in the same manner as in Synthesis Example 1 except that 7.5 g of hydroxyethyl methacrylate, 7.5 g of isobutyl methacrylate, and 12.5 g of isobutyl methacrylate were used.

Synthesis Example 5 Bead-shaped dispersant (5) was obtained by the same procedure as Synthesis Example 1 except for using 35.0 g of 2-ethylhexyl methacrylate, 5.0 g of hydroxyethyl methacrylate, and 10.0 g of methyl methacrylate. Ta.

Synthesis Example 6 A bead-shaped dispersant (6) was obtained in the same manner as in Synthesis Example 1 except that 30 g of stearyl methacrylate, 10.0 g of hydroxyethyl methacrylate, and 10.0 g of methyl methacrylate were used.

Synthesis Example 7 Styrene 30g, hydroxyethyl methacrylate 10.
The same procedure as in Synthesis Example 1 was performed except that 10.0 g of methyl methacrylate was used to obtain a bead-shaped dispersant (7).

Example 1 N-hexane 3 was placed in a separable flask equipped with a stirrer, a reflux condenser, a dropping funnel, a thermometer, and a nitrogen gas inlet tube.
Add 60.7 g and 4.32 g of dispersant (1) to 50
After the mixture was humidified to ℃ and dispersed and dissolved, it was replaced with nitrogen.

Meanwhile, 72% of acrylic acid was prepared in advance in an Erlenmeyer flask.
0 g was partially neutralized with 32.2 g of sodium hydroxide dissolved in 103.8 g of ion exchange water, and further 0.24 g of potassium persulfate was dissolved at room temperature. This heavy aqueous solution was added dropwise to the above separable flask at a stirring speed of 300 rpm over 1 hour under nitrogen bubbling, and after refluxing for 2 hours, 0.1 g of 30% hydrogen peroxide was added, and the mixture was further refluxed. The polymerization was continued for 1 hour to complete the polymerization. Thereafter, azeotropic dehydration was carried out, followed by filtration and drying under reduced pressure to obtain a white bead-like polymer. Furthermore, there was almost no polymer deposit inside the separable flask.

Examples 2 to 6 White beads were prepared in the same manner as in Example 1 except that dispersants (2) to (6) obtained in Synthesis Examples 2 to 6 were used instead of dispersant (1) in Example 1. A polymer was obtained.

Furthermore, there was almost no polymer deposit inside the separable flask.

Example 7 The same procedure as in Example 1 was performed except that cyclohexane was used in place of n-hexane in Example 1 to obtain a white bead-like polymer. Furthermore, there was almost no polymer deposit inside the separable flask.

Comparative Example 1 When the same procedure as in Example 1 was performed using the dispersant (7) obtained in Synthesis Example 7 instead of the dispersant (1) in Example 1, n
・-The dispersant (7) is not dispersed and dissolved in hexane, resulting in reverse phase suspension.
pA polymerization was not possible.

Comparative Example 2 A white powder polymer was obtained in the same manner as in Example 1 except that sorbitan monolaurate was used in place of the dispersant (2) in Example 1. In addition, polymer deposits were observed on the walls and the size of the stirrer inside the separable flask.

The evaluation results of Examples 1 to 7 and Comparative Example 2 are shown in Table 2.

Claims (3)

[Claims] (1) In a method for producing a superabsorbent resin by dispersing acrylic acid and its alkali metal salt aqueous solution in an aliphatic hydrocarbon solvent and carrying out reverse phase suspension polymerization in the absence of a crosslinking agent, as a dispersant ( A) 40 to 95% by weight of an acrylic acid or methacrylic acid alkyl ester monomer whose alkyl group has 8 or more carbon atoms, (B) 5 to 40% by weight of an acrylic acid or methacrylic acid hydroxyalkyl ester monomer, ( C) A method for producing a superabsorbent resin, characterized by using a copolymer containing 0 to 40% by weight of an unsaturated monomer copolymerizable with the above (A) and (B). (2) The dispersant is (A) lauryl acrylate, tridecyl mixed ester 45-70% by weight, (B) acrylic acid or methacrylic acid hydroxyethyl ester 5-25% by weight, (C) methyl methacrylate or/and methacrylic acid Ethyl or/and isobutyl methacrylate 2
The manufacturing method according to claim 1, which is a copolymer containing 0 to 40% by weight as a constituent component. (3) The production method according to claim 1, wherein the aliphatic hydrocarbon solvent is n-hexane, n-heptane, or cyclohexane.