JPH0610220B2 - Super absorbent resin manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a highly water-absorbent resin having a large particle size, which is excellent in properties such as water absorption capacity, water absorption speed, tackiness, and gel strength. Since the superabsorbent resin produced by the present invention is excellent in the above-mentioned characteristics, it can be used as a sanitary material (paper diaper, sanitary napkin), a water retaining material for agricultural and horticultural soil, and the like.

[Prior Art and Problems] Water-absorbent resins are used as sanitary products, sanitary materials such as paper diapers, and as water retention materials for agricultural and horticultural purposes, as well as in various applications such as sludge coagulation and oil dehydration. , A useful synthetic resin for which new uses are being developed. These resins are hydrolyzates of tempun-acrylonitrile graft polymer (Japanese Patent Publication No. 53-46199, Japanese Patent Publication No. 55-4820), and modified cellulose (Japanese Patent Publication No. 50-80376). Sodium polyacrylate by turbidity method (Japanese Patent Publication No. 46-3
No. 0710, JP-A-56-26909) Sodium polyacrylate obtained by an aqueous solution polymerization method (adiabatic polymerization, thin film polymerization) (JP-A-55-133413) Crosslinked water-soluble polymer (JP-B-43 -23462) Starch-sodium acrylate 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, low water absorption speed even if water absorption capacity is high, and poor dispersibility in water.

After absorbing water, the gel becomes sticky, and when considering hygiene materials, there is concern about the effect on the skin.

The air permeability is poor due to the aggregation of resin particles in a water-swelling state, and there is a risk that the roots will rot when considering a water retaining material for soil.

Further, as a method for increasing the water absorption rate of the water absorbent resin and increasing the gel strength after water absorption, there are methods of simultaneous crosslinking and postcrosslinking using a crosslinking agent. But with these methods,
Although it has a water absorption rate, the water absorption ability is lowered, or the water absorption and swelling state causes aggregation between the resin particles, resulting in poor air permeability.

In recent years, as a method for overcoming the above-mentioned drawbacks of the water-absorbent resin, a method of synthesizing a bead-shaped resin having a large particle diameter by using an appropriate dispersant in inverse layer suspension polymerization has been proposed.

For example, Japanese Patent Application Laid-Open No. 57-158209 discloses a method of using a cellulose ester or a cellulose ether as a dispersant, but it has a drawback of blocking during drying or sticking to a dryer wall. Further, JP-A-57-94011 and JP-A-57-9
In 8512, a carboxy-containing polymer is used as a dispersant, but it is difficult to stably perform reverse phase suspension polymerization, and there is a risk that the polymer will be integrated during the polymerization. In addition, JP-A-61-403
In 09, a styrene-dimethylaminoethyl methacrylate copolymer is used as a dispersant, but it has a drawback that it is difficult to dissolve in n-hexane, the generated water-absorbent resin is hard to adapt to water, and the water-absorption rate is slow. .

[Means for Solving Problems] As a result of intensive studies conducted by the present inventors to improve the conventional drawbacks, the inventors have excellent properties such as water absorption capacity, water absorption speed, tackiness, and gel strength, and have a large particle size. We have found that a super absorbent polymer can be manufactured safely and have completed it.

According to the present invention, acrylic acid and an aqueous solution of an alkali metal salt thereof are dispersed in an aliphatic hydrocarbon solvent, and in a method for producing a highly water-absorbent resin by reverse phase suspension polymerization in the absence of a cross-linking agent, dispersion. As an agent, (A) acrylic acid or methacrylic acid alkyl ester, 40 to 95% by weight of a monomer having an alkyl group having 8 or more carbon atoms, (B) 5 to 40% by weight of acrylic acid or methacrylic acid hydroxyalkyl ester monomer %, (C) Methacrylic acid alkyl ester, monomer whose alkyl group has 4 or less carbon atoms and / or vinyl acetate 0-4
There is provided a method for producing a highly water-absorbent resin, which comprises using a copolymer having 0% by weight as a constituent component.

As the acrylic acid or methacrylic acid alkyl ester as the component (A), it is sufficient that the alkyl group has 8 or more carbon atoms, and commercially available and easily available monomers include 2-ethylhexyl acrylate and 2-ethylhexyl methacrylate. , Lauryl acrylate, lauryl methacrylate, tridecyl acrylate, tridecyl methacrylate, lauryl acrylate, tridecyl mixed ester, stearyl acrylate, stearyl methacrylate.

When the component (A) is selected, it is convenient that the glass transition point is as high as possible because beads are less likely to be blocked when the dispersant is synthesized by the aqueous suspension polymerization. Table 1 shows the glass transition points of the respective monomers.

For example, 2-ethylhexyl methacrylate, lauryl acrylate, lauryl acrylate, tridecyl mixed ester, tridecyl acrylate, stearyl acrylate,
Stearyl methacrylate and the like.

As the acrylic acid or methacrylic acid hydroxyalkyl ester as the component (B), commercially available and easily available monomers are 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate; methacrylic acid 2 -Hydroxypropyl and the like can be mentioned. The monomer as the component (C) is a methacrylic acid alkyl ester having a high glass transition point and an affinity for an aliphatic hydrocarbon solvent and having an alkyl group having 4 or less carbon atoms, or vinyl acetate. Examples thereof include methyl acidate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, vinyl acetate and the like. Preferably, methyl methacrylate, ethyl methacrylate and isobutyl methacrylate are suitable.

The copolymers of these components (A), (B), and (C) are safe as a dispersant for water-absorbent resins for sanitary materials when considering monomers, and can be used at all.

(A), (B), the composition ratio of the (C) component, dispersion solubility in an aliphatic hydrocarbon solvent, colloidal dispersibility of polymerization, physical properties of the water-absorbent resin, such as water absorption capacity, water absorption speed, stickiness, Gel strengthening,
It has a great influence on the particle size.

Usually, the component (A) is 40 to 95% by weight, the component (B) is 5 to 40% by weight, the component (C) is 0 to 40% by weight, and more preferably the component (A) is 45 to 70% by weight and the component (B) is 5-25% by weight,
20 to 40% by weight of component (C) is suitable. (A) component is 40
If it is less than 5% by weight, decomposition solubility in a solvent is lowered, and if it exceeds 95% by weight, the component (B) is relatively less than 5% by weight and colloid dispersibility becomes poor. It will be difficult to continue. The larger the amount is in the range of 45 to 95% by weight, the better the dispersion and solubility in the solvent, the slower the water absorption rate of the water-absorbent resin, and the less stickiness tends to be. When the content of the component (B) is less than 5% by weight, the colloidal dispersibility becomes poor as described above, and when it exceeds 40% by weight, the dispersibility in a solvent decreases, and it is difficult to continue the reverse phase suspension polymerization. Become. 5
In the range of up to 40% by weight, the higher the amount, the better the colloidal dispersibility of polymerization and the higher the water absorption rate of the water absorbent resin,
It tends to become sticky and the grain size becomes finer. When the amount of the component (C) exceeds 40% by weight, the ratio of the component (A) is relatively decreased and the solubility in the solvent is deteriorated. The more it is in the range of 0 to 40% by weight, the higher the gel strength of the water absorbent resin.

The copolymer used as the dispersant in the present invention is synthesized by an aqueous suspension polymerization method. In solution polymerization, the solvent remains,
A low molecular weight polymer may be inferior in function as a dispersant. As an example of an aqueous suspension polymerization method, a partially saponified polyvinyl alcohol is dissolved in ion-exchanged water by heating, and after nitrogen substitution, (A), (B), and (C) component monomers are azo or A solution in which a peroxide-based polymerization initiator is dissolved is added dropwise and dispersed, and the mixture is heated and maintained to complete the polymerization. After cooling, the solid matter is washed with water and dried under reduced pressure to obtain a bead-like polymer, that is, a dispersant.

The dispersant obtained by the above method is dispersed and dissolved in an aliphatic hydrocarbon solvent for reverse phase suspension polymerization. The amount of the dispersant is 0.5 to 20% by weight with respect to acrylic acid and its alkali metal salt monomer,
It is preferably used in the range of 1.0 to 10% by weight. If the amount of the dispersant is less than 0.5% by weight, the colloidal dispersibility of polymerization becomes unstable, and if it exceeds 20% by weight, the particle size becomes too fine, which is economically disadvantageous. Further, as a dispersant, a conventionally known nonionic surfactant such as sorbitan fatty acid ester may 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 alkaline acid monomer with an aqueous solution of sodium hydroxide, potassium hydroxide or the like. The degree of neutralization is preferably 60 to 85% in consideration of water absorption capacity and safety. The monomer concentration in the aqueous solution is 35 to 75% by weight, preferably 40 to 70% by weight.

In the present invention, acrylic acid and an unsaturated monomer capable of copolymerizing with acrylic acid alkali metal salt monomer may be copolymerized within the range of producing the water absorbent resin.

When reverse phase suspension polymerization of acrylic acid and an aqueous solution of an alkali metal thereof in the present invention, the polymerization initiator is a self-crosslinking type that does not use a crosslinking agent monomer, and therefore water-soluble such as potassium persulfate and ammonium persulfate. Persulfate and hydrogen peroxide are preferred. The amount of the polymerization initiator used is 0.1 to 2.0 with respect to the monomer.
%, Preferably 0.2 to 1.0% by weight.

Examples of the aliphatic hydrocarbon solvent for reverse phase suspension polymerization in the present invention include n-pentane, n-hexane, n-heptane and n.
Examples thereof include aliphatic hydrocarbons such as octane, and alicyclic hydrocarbons such as cyclohexane, methylcyclohexane, and decalin, with preference given to n-hexane, n-heptane, and cyclohexane.

The polymer obtained by the reverse phase suspension polymerization in the present invention is recovered as a bead-shaped water absorbent resin by distilling most of the water by azeotropic dehydration as it is after the completion of the polymerization and further drying under reduced pressure. However, the method is not limited to these.

[Effects of the Invention] The water-absorbent resin obtained by reverse-phase suspension polymerization using the dispersant of the present invention has high water-absorbing ability, fast water-absorption rate, low stickiness, and high gel strength. Most suitable for sanitary materials. In addition, it is a bead-like polymer with a particle size of around 200 μm, has low hygroscopicity, and has a bulk specific gravity.
Since it is 0.9 to 1.1, handling of the powder becomes easy at the time of manufacturing the water absorbent resin and at the time of making the water absorbent sheet. Further, during reverse phase suspension polymerization, there is almost no adhesion of the polymer to the polymerization kettle, so the maintenance of the polymerization kettle can be reduced and the operation can be performed safely.

Example Next, the method of the present invention will be specifically described by way of examples, but the present invention is not limited to these examples.

Water-absorbent resins obtained in Examples and Comparative Examples, by the following operations, water absorption capacity, water absorption speed, tackiness after water absorption, gel strength,
The average particle size was measured.

Water absorption capacity 1) In the case of the water absorption capacity of ion-exchanged water, 0.5 g of the dried polymer is dispersed in 1 ion-exchanged water, left standing for one day and one night, and then swelled polymer weight (W ) Was measured and this value was divided by the initial dry polymer weight (W ₀ ). In other words, the ion-exchanged water absorption capacity (g /
g) = W / W ₀ .

2) In case of water absorption of artificial urine, 0.2 g of dried polymer is dispersed in 40 g of artificial urine, and after standing for 30 minutes, the weight of swollen polymer (W) obtained by passing through a 100 mesh wire net is measured. Is the value obtained by dividing this value by the initial dry polymer weight (W ₀ ). That is, the artificial urine water absorption capacity (g / g) = W / W ₀ .

Artificial urine composition (g / 100 ml) Urea 2.0 g, NaCl 0.82 g, MgSO ₄ 0.0553 g, CaCl ₂ 0.064 g Water absorption rate Stirring method. Ion-exchanged water 50c in a 100cc beaker
c was added, 0.5 g of the dried polymer was added while stirring with a magnetic stirrer, and the time from the addition of all the water until the fluidity of the water disappeared.

Stickiness after absorption of water 4.0 g of artificial urine was added to 0.10 g of dry polymer, and the mixture was allowed to stand for 30 minutes.
2.0g of gel was written on circular qualitative paper (No.2, 11cm diameter) 5.
Spread in a circle with a diameter of 0 cm. After standing for 3 minutes, the gel was removed, the weight (W) of the paper was measured, and the weight of the paper (W ₀ ) weighed in advance was subtracted to obtain the weight of the artificial urine attached to the gel.

Gel strength 1) Wet back 8.0 g of artificial urine was added to 0.20 g of dry polymer and allowed to stand for 30 minutes.
Remove the attached artificial urine with paper and remove the circular qualitative paper (No.2,11c
Spread in the circle with a diameter of 3.0 cm written above. Sandwich it with two pieces of top and bottom with the same quality paper, aluminum plate (15 cm
X 15 cm, 153 g), place an aluminum plate of the same shape, and place a 750 g weight. After standing for 3 minutes, the gel was removed, the weight (W) of the paper was measured, and the weight of the paper (W ₀ ) weighed in advance was subtracted to obtain the weight of the artificial urine absorbed in the paper.

2) Gel Spread Area After the wet back measurement, the gel spread area (Scm ² ) of the circular paper on which the gel was placed was calculated.

Average particle size The particle size was measured by the centrifugal sedimentation method using an automatic particle size distribution analyzer CAPA-300 manufactured by Horiba Ltd., and the area-based median value was used as the average particle size.

Synthesis Example 1 A 500 ml separable flask equipped with a stirrer, a reflux condenser, a dropping funnel, a thermometer and a nitrogen gas inlet tube was charged with ion-exchanged water 1
Charge 50 g, add 0.2 g of partially saponified polyvinyl alcohol (GH-23 manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) as a dispersant,
After heating and dissolving, the atmosphere was replaced with nitrogen.

On the other hand, in advance, in an Erlenmeyer flask, lauryl acrylate and tridecyl mixed ester (LT manufactured by Osaka Organic Chemical Co., Ltd.
A) 30.0 g, hydroxyethyl methacrylate 7.5 g, and methyl methacrylate 12.5 g were dissolved by adding 1.0 g of azobisdimethylvaleronitrile, and the mixture was added dropwise to the above separable flask over 1 hour while bubbling a nitrogen gas stream. The mixture was kept at 65 ° C for 5 hours to terminate the reaction, and after cooling, the solid matter was filtered off, washed with water, and then dried under reduced pressure to obtain a beaded dispersant (1).
Got

Synthesis Example 2 22.5 g of lauryl acrylate / tridecyl mixed ester,
A beaded 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 45.0 g of lauryl acrylate / tridecyl mixed ester,
A beaded dispersant (3) was obtained in the same manner as in Synthesis Example 1 except that 5.0 g of hydroxyethyl methacrylate was used.

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

Synthesis Example 5 A beaded dispersant (5) was obtained in the same manner as in Synthesis Example 1 except that 35.0 g of 2-ethylhexyl methacrylate, 5.0 g of hydroxyethyl methacrylate and 10.0 g of methyl methacrylate were used.

Synthesis Example 6 A beaded 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 30 g, hydroxyethyl methacrylate 10.0 g,
A beaded dispersant (7) was obtained in the same manner as in Synthesis Example 1 except that 10.0 g of methyl methacrylate was used.

Example 1 n-hexane 36 was placed in a one-separable flask equipped with a stirrer, a reflux condenser, a dropping funnel, a thermometer and a nitrogen gas inlet tube.
0.7 g and 4.32 g of dispersant (1) were charged, the temperature was raised to 50 ° C to disperse and dissolve, and then the atmosphere was replaced with nitrogen.

On the other hand, in advance, in an Erlenmeyer flask, 72.0 g of acrylic acid
Sodium hydroxide dissolved in 103.6 g of deionized water 32.
Partially neutralized with 2 g, and potassium persulfate 0.24 g at room temperature
Was dissolved. This monomer aqueous solution was added dropwise to the above separable flask at a stirring speed of 300 rpm under bubbling with nitrogen gas flow for 1 hour, and after refluxing for 2 hours, 30% hydrogen peroxide solution 0.1% was added.
g was added and reflux was continued for 1 hour to complete the polymerization. Then, azeotropic dehydration was carried out, and the residue was dried under reduced pressure to obtain a white beaded copolymer. Also, there was almost no polymer deposit in the separable flask.

Examples 2 to 6 The procedure of Example 1 was repeated, except that the dispersants (2) to (6) obtained in Synthesis Examples 2 to 6 were used instead of the dispersant (1) of Example 1.
A white beaded copolymer was obtained. Also, there was almost no polymer deposit in the separable flask.

Example 7 The procedure of Example 1 was repeated using cyclohexane instead of n-hexane of Example 1, to obtain a white beaded copolymer. Also, there was almost no polymer deposit in the separable flask.

Comparative Example 1 The dispersant obtained in Synthesis Example 7 instead of the dispersant (1) of Example 1
When the same operation as in Example 1 was carried out using (7), the dispersant (7) was not dispersed and dissolved in n-hexane, and reverse phase suspension polymerization could not be carried out.

Comparative Example 2 The same procedure as in Example 1 was carried out using sorbitan monolaurate instead of the dispersant (2) in Example 1 to obtain a white powder copolymer. In addition, polymer deposits were found on the walls and agitating blades in the separable flask.

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

Continuation of the front page (56) Reference JP-A-57-98512 (JP, A) JP-A-54-54186 (JP, A) JP-A-57-94011 (JP, A) JP-A-57-98513 (JP , A)

Claims (3)

[Claims] 1. A method for producing a highly water-absorbent resin by dispersing acrylic acid and an aqueous solution of an alkali metal salt thereof in an aliphatic hydrocarbon solvent and carrying out reverse phase suspension polymerization in the absence of a cross-linking agent. As (A) acrylic acid or methacrylic acid alkyl ester, 40 to 95% by weight of a monomer having an alkyl group having 8 or more carbon atoms, (B) 5 to 40% by weight of acrylic acid or methacrylic acid hydroxyalkyl ester monomer , (C) a methacrylic acid alkyl ester in which the alkyl group has 4 or less carbon atoms and / or vinyl acetate 0 to
A method for producing a highly water-absorbent resin, which comprises using a copolymer having 40% by weight as a constituent component. 2. A dispersant is (A) lauryl acrylate, 45-70 wt% of tridecyl mixed ester, and (B) acrylic acid or methacrylic acid hydroxyethyl ester 5-5.
The production method according to claim 1, wherein the copolymer comprises 25% by weight of (C) methyl methacrylate or / and ethyl methacrylate, or / and 20 to 40% by weight of isobutyl methacrylate as a constituent component. 3. An aliphatic hydrocarbon solvent is n-hexane, n-
The production method according to claim 1, which is heptane or cyclohexane.