KR960008111B1 - Process for producing absorption resin having a high absorptivity - Google Patents

Abstract

The method includes the steps of; (1) keeping water content of the polymer, obtained by polymerizing carboxyl or carboxylic monomer partially, below 25 wt% by azeotropic distillaltion in lipophilic solvent; (2) dehydrating by azeotropic distillation after the addition of the solution of hydrophilic bridging agent; (3) removing lipophilic solvent, adding hydrophilic solvent and hydrophilic bridging agent, reacting it at above the boiling point of the solvent; (4) drying after removing the solvent by filtration.

Description

Manufacturing method of super absorbent polymer having superabsorbent force

The present invention relates to a method for producing a super absorbent polymer.

In particular, the present invention relates to a method for producing a superabsorbent polymer having superabsorbent force by special crosslinking.

Absorbent materials include natural materials such as sponges, pulp and paper, and synthetic materials made by partially neutralizing materials with hydrophilic groups such as -OH, -NH ₂ , -COOH, and the like. In the past, natural materials such as sponges, pulp and paper have been widely used as sanitary and agricultural materials. However, since they have a mechanism of sucking water by a physical method, they have a low absorption capacity, and there is a problem that most of the absorbed water escapes even with a slight pressure on them. In order to solve this problem, synthetic materials having a mechanism of sucking water by physical and chemical methods have been required. -Acrylate graft copolymers and the like. The synthetic materials thus made are mainly used in the sanitary field such as diapers and hygienic napkin, and civil engineering and horticultural fields. In addition, it is used in various fields such as flocculation of sediment, dehydration in oil and prevention of dew condensation of building materials.

Among them, the largest use of the super absorbent polymer is in the field of hygienic materials. Until now, the properties of super absorbent polymers used in the field of hygienic materials have been developed with the focus on high absorption rate and high absorption capacity in deionized water and brine, and most of the patents are related to manufacturing methods for improving them. Examples are US Pat. Nos. 4, 497, 930 and US Pat. Nos. 4, 541, 871. However, in the field of hygienic materials and disposable absorbent products, the secretion of the discharge from the pulp is absorbed by the pump first, and then the absorbent resin is absorbed from the pulp, that is, the suction force and the absorbed force to maintain the soft state after absorption. Water retention, ie gel strength is of utmost importance.

U.S. Patent No. 4, 497.930 discloses that water may be removed by azeotropic distillation so that 10 to 40% by weight of water, based on the polymer after polymerization, is present in the polymer and then reacted with the carboxyl and carboxylate groups in a lipophilic solvent. Using a crosslinking agent having at least two reactors at 0.01 to 5% by weight based on the polymer and refluxing at 40 to 150 ° C., but this method can only dissolve the crosslinking agent together with the crosslinking agent. Since only water is used, the amount of water added together with the crosslinking agent is so small that a small amount of the crosslinking agent penetrates into the polymer surface only, and the crosslinking agent does not penetrate into the polymer, so that the absorbency and absorption rate are high and the suction force and gel strength are significantly reduced. Difficult to do

In addition, US Pat. No. 4,541,871 discloses that water is removed by azeotropic distillation or water is added to a dry polymer (water content of 2.5% by weight or less) in order to ensure that the water content in the polymer is 0.01 to 1.3 parts by weight after polymerization. However, a method of crosslinking reaction is described by adding 0.005 to 5% by weight of a crosslinking agent based on the polymer in 0.1-50 parts by weight of a nonpolar solvent based on the polymer, but this method also adds only the crosslinking agent or changes the water content in the polymer. When the solvent is added by adding an appropriate amount of water (5.6 to 75.6% by weight based on the polymer) to remove the solvent, only 0.5 parts by weight or less of water is removed based on the amount of water added. .

Therefore, these conventional patent resins are difficult to use as sanitary materials because they have a high absorption capacity and absorption rate, but a significant drop in suction force and gel strength. Therefore, in the field of sanitary materials, there is a great demand for improving the ability to suck water through pulp (absorption force) and the gel state (gel strength) after absorbing water, and these are the most important problems in practical application.

In the present invention, in order to solve the above problems, a method of producing a superabsorbent polymer having a superabsorbing force by special crosslinking has been completed.

That is, the present invention (1) partially neutralized a carboxyl group or a carboxylate group-containing monomer or polymer, followed by azeotropic distillation of the polymer obtained in a lipophilic solvent to reduce the water content of the polymer to 25% by weight or less based on the polymer. Maintaining step, (2) adding an aqueous solution of a hydrophilic crosslinking agent and then dehydrating by azeotropic distillation, (3) removing the lipophilic solvent, adding a solution mixed with a hydrophilic solvent and a hydrophilic crosslinking agent, and reacting at a solvent boiling point or higher. It relates to a method for producing a superabsorbent polymer having a superabsorbing force by special crosslinking, comprising the step, and (4) removing the solvent by filtration and drying.

The present invention will be described in detail as follows.

The carboxyl or carboxylate group-containing monomers and polymers used in the present invention may be monomers such as acrylic acid, methacrylic acid and the like, and polymers grafted acrylic acid to starch, cellulose, agarose, chitin, and the like, or acrylic acid or methacrylic acid. May be a polymer copolymerized with maleic acid acrylamide, 2-acrylamide-2-methylpropyl sulfonic acid, 2-hydroxy methacrylate and the like in an appropriate ratio.

An alkali metal hydroxide, preferably sodium hydroxide, may be used for neutralizing the monomer or polymer.

As for neutralization degree of acrylic acid, 50-100 mol% is suitable, and 60-80 mol% is preferable. If the degree of neutralization is less than 50 mol%, the salt concentration is small and the charge density to the water is small, so that the penetration pressure is appropriately generated and the desired high absorbency cannot be obtained. In addition, the monomer or polymer may be used in an aqueous solution of 20 to 70%, preferably 40 to 60%.

In these polymerizations, a reverse phase suspension polymerization method is used, and as the lipophilic solvent used, an aliphatic or aromatic hydrocarbon having a boiling point of 30 to 200 ° C, for example, n-hexane, n-heptane, benzene, xylene, toluene, cyclo Pentane, cyclohexane, and the like, with cyclohexane being preferred. As for the usage-amount of a solvent at the time of superposition | polymerization, 0.1-50 weight part is preferable with respect to 1 weight part of monomers, and 0.5-30 weight part is more preferable.

At the time of polymerization, sorbitan monolaurate having an HLB (lipophilic balance) value of 8 to 12, preferably Rotosugar ester S-970 (HLB value = 9.0), may be used as a dispersant. As the polymerization initiator, a water-soluble radical polymerization initiator such as ammonium persulfate, potassium persulfate and hydrogen peroxide, preferably potassium persulfate, may be used alone or in combination of two or more thereof.

The polymer is dehydrated during or after polymerization by azeotropic distillation. The content of water in the polymer should be adjusted to 25% by weight or less based on the polymer to exhibit the effect to be obtained in the present invention, and beyond this range, the water absorption is drastically reduced.

The crosslinking agent is preferably hydrophilic or water soluble and has two or more epoxy groups capable of reacting with a carboxyl group or carboxylate. Examples are ethylene glycol diglycidyl ether, glycerol polyglycidyl ether, trimethylol propane polyglycidyl ether and sorbitol polyglycidyl ether and the like, with ethylene glycol diglycidyl ether being preferred. The amount of crosslinking agent used depends on the type of crosslinking agent used and the polymer, but is usually 0.005 to 1.0% by weight based on the polymer. When the amount of the crosslinking agent is 0.005% by weight or less, there is no crosslinking effect inside the particles, and when the amount of the crosslinking agent is 1.0% by weight or more, the crosslinking density inside the particles is too large, so that the water absorption capacity is drastically reduced.

The amount of water used with the crosslinking agent is suitably 7.0 to 25.0% by weight based on the polymer in order to obtain a superabsorbent polymer having excellent suction and gel strength. If the amount of water to be added is 7.0% by weight or less, the absorption capacity is increased, but the suction power and gel strength are sharply decreased, and when the amount of water is more than 25.0% by weight, the absorption capacity is sharply decreased. In order to obtain a superabsorbent polymer having good suction power and gel strength and adequate absorbency, water at least 60% by weight of the amount of water added during the crosslinking reaction should be removed. When water is removed at 60% by weight or less, it is difficult to obtain a desired absorbent resin because the suction force and the absorbency are drastically reduced.

As described above, the polymer obtained by partially neutralizing the carboxyl group or carboxylate-containing monomer or polymer and polymerizing is azeotropically distilled in a lipophilic solvent so that the water in the polymer is 25% by weight or less based on the polymer and then a small amount of hydrophilicity. When an aqueous solution in which a crosslinking agent is dissolved in an appropriate amount of water is added, a small amount of crosslinking agent is present in the polymer since water penetrates into the polymer and the crosslinking agent also penetrates. Subsequently, when the reaction is carried out at the boiling point of the solvent so that an appropriate amount of water is removed, the degree of crosslinking is properly maintained within the polymer.

Next, the organic solvent is removed, and the internal crosslinked polymer is surface crosslinked. At this time, methanol or ethanol is used as the hydrophilic solvent, and methanol is more preferable. The amount of the hydrophilic solvent is suitably 1.7 to 2.7 parts by weight based on 1 part by weight of the polymer, and when used at 1.7 parts by weight or less, agglomeration occurs, and when used at 2.7 parts by weight or more, the crosslinking agent dissolved in the solvent may contact the polymer. There is little chance that there is less effect of crosslinking the polymer surface.

The crosslinking agent used for the surface crosslinking may be a hydrophilic crosslinking agent such as ethylene glycol diglycidyl ether used for internal crosslinking, and the amount of the crosslinking agent is 0.5 to 5.0% by weight based on the polymer. The amount of 0.5 wt% or less has almost no crosslinking effect, and the 5.0 wt% or more crosslinks too much, so that the water absorption is drastically reduced.

When a solution mixed with a hydrophilic solvent and a hydrophilic crosslinking agent is added to a polymer crosslinked beforehand, the hydrophilic solvent swells only on the polymer surface, and a large amount of the crosslinking agent in the hydrophilic solvent is present only on the polymer surface. Subsequently, when the polymer solution in this state is reacted at the boiling point or more of the solvent, a polymer having a low crosslinking degree inside the polymer and a high crosslinking degree at the surface is produced.

The polymer thus obtained can be recovered by filtration and drying, and the filtration and drying may employ a method which is generally well known.

Hereinafter, the present invention will be described in detail through examples.

In the embodiment, the suction force is a column method, and the absorbency is measured for the saline of 1, 2, 3. 4, and 5 minutes (ml / g) with respect to 1 g of the resin for physiological saline, and the absorbency (fold) is the absorbency. After weighing 1 g of resin in 1000 g of deionized water, the weight of the gel was measured by filtration through an 80 mesh sieve after 30 minutes. In addition, gel strength was evaluated by hand pressing the water absorbent resin saturated and swollen with deionized water according to the following four criteria.

◎: Hard to press well

○: Destroyed if pressed hard

△: simply destroyed

×: Sticky and destroyed with slight force

Example 1

Into a 500 ml four-necked round flask equipped with a stirrer, Dean stocker, condenser, pressure funnel and nitrogen injector, add 160 g of cyclohexane and 1.0 g of Rotosugar ester S-970 to remove oxygen from the flask Nitrogen gas was injected, and the bath temperature was raised to 75 ° C. 30.9 g of acrylic acid was added to another 200 ml flask, and 49.1 g of sodium hydroxide solution (9.2 g of sodium hydroxide) was slowly added while cooling to room temperature to prepare a sodium salt solution having a degree of neutralization of 60% and a monomer concentration of 45% by weight. To the sodium acrylate salt solution, a solution in which 0.1 g of potassium persulfate was dissolved in 3 g of distilled water was added and stirred well. Subsequently, the solution was injected into a flask containing 160 g of cyclohexane and 1.0 g of a dispersant (RotoSugar ester S-970) through a pressure-controlled funnel to react. After the polymer was formed, the bath temperature was raised to 90 ° C., and 38 g of water was removed by azeotropic distillation so that the water content of the polymer was 20% by weight, and then 0.2 g of ethylene glycol diglycidyl ether was dissolved in 3 g of water. The resulting aqueous solution was added and crosslinked. At this time, 5 g of water was removed using a Dean Stark apparatus during the reaction. After the reaction was completed, cyclohexane was removed, and a solution obtained by adding 0.3 g of ethylene glycol diglycidyl ether to 100 g of methanol was added again and reacted at 90 ° C. for 2 hours. After completion of the reaction, methanol was removed by filtration, and then the obtained polymer was dried to measure suction force, water absorption capacity, and gel strength. The results are shown in Table 1.

[Examples 2 to 4]

It carried out similarly to Example 1 except having changed the quantity of the water which melt | dissolved 0.2 g of ethylene glycol diglycidyl ether, and the quantity of the methanol used at the time of particle surface crosslinking as follows. The results are shown in Table 1.

Example 5

The same procedure as in Example 2 was carried out except that 0.5 g of ethylene glycol diglycidyl ether was used together with methanol when the particle surface was crosslinked. The results are shown in Table 1.

Example 6

The same procedure as in Example 2 was carried out except that 0.5 g of ethylene glycol diglycidyl ether was used together with water for crosslinking of the inner surface of the particles. The results are shown in Table 1.

Comparative Example 1

In a 500 ml four-necked round flask equipped with a stirrer, Dean stark unit, condenser, pressure-controlled funnel and nitrogen injector, 160 g of cyclohexane and 1.0 g of Rotosugar ester S-970 were added to remove oxygen from the flask. Nitrogen gas was injected and the bath temperature was raised to 75 ° C. 30.9 g of acrylic acid was added to another 200 ml flask, and 49.1 g of sodium hydroxide solution (9.2 g of sodium hydroxide) was slowly added while cooling to room temperature to prepare a sodium salt solution having a degree of neutralization of 60% and a monomer concentration of 45% by weight. To this sodium acrylate salt solution, a solution in which 0.1 g of potassium persulfate was dissolved in 3 g of distilled water was added and stirred well. Subsequently, the solution was injected into a flask containing 160 g of cyclohexane and 1.0 g of a dispersant (RotoSugar ester S-970) through a funnel to adjust the pressure. When the polymer is formed, the bath temperature is raised to 90 ° C., and 38 g of water is removed by azeotropic distillation so that the water content in the polymer is 20% by weight. After cooling to room temperature, the polymer is filtered and dried to obtain suction, Absorption capacity and gel strength were measured. The results for this are also shown in Table 1.

Comparative Example 2

After the water was removed so that the water content in the polymer was 20% by weight, the same procedure as in Comparative Example 1 was carried out except that the mixture was refluxed for 2 hours by adding an aqueous solution of 0.2 g of ethylene glycol diglycidyl ether and 3 g of water. . The results are shown in Table 1.

Comparative Example 3

After the water was removed so that the water content in the polymer was 20% by weight, cyclohexane was removed and a solution of 0.3 g of ethylene glycol diglycidyl ether in 100 g of methanol was added and refluxed for 2 hours. The same was done. The results are shown in Table 1.

[Comparative Example 4]

The same procedure as in Example 1 was conducted except that the water content in the polymer was 45% by weight. The results are shown in Table 1.

[Comparative Example 5]

After the water was removed so that the water content in the polymer was 20% by weight, cyclohexane was removed, 100 g of methanol was added, and a solution of 0.3 g of ethylene glycol diglycidyl ether and 15 g of water was added to reflux for 2 hours. Was carried out in the same manner as in Comparative Example 1. The results are shown in Table 1.

As can be seen from the table, the suction force, the absorption amount and the gel-strength were found to be excellent by the following method.

(1) The content of water in the polymer after polymerization should be 25.0 wt% or less based on the polymer.

(2) The amount of water used for the primary crosslinking (crosslinking of the particles) in the lipophilic solvent is 7.0 to 25.0 wt% based on the polymer, and the amount of crosslinking agent used together is 0.005 to 1.0 wt% based on the polymer.

(3) Remove water by 0.6 parts by weight (60% by weight) or more based on the amount of water added using azeotropic distillation.

(4) Secondary crosslinking (particle surface crosslinking) on a mixture of 0.5 ~ 5.0 wt% crosslinking agent and hydrophilic solvent based on polymer in hydrophilic solvent.

Claims (5)

(1) The polymer obtained by partially neutralizing a carboxyl group or a carboxylate group-containing monomer or polymer with a neutralization degree of 50% or more and then azeotropically distilling in a lipophilic solvent is 25% by weight or less based on the polymer. (2) an aqueous solution of a hydrophilic crosslinker in which 0.005 to 1.0 wt% of a hydrophilic crosslinking agent is dissolved in 7.0 to 25.0 wt% of water based on a polymer in the reaction product of step (1). And azeotropic distillation to remove at least 60% by weight of water based on the amount of water added, (3) removing the lipophilic solvent used in step (1) from the reaction product of step (2), and After the addition of a solution of 1.7 to 2.7 parts by weight of the hydrophilic solvent and 0.5 to 5.0% by weight of the hydrophilic crosslinking agent based on the polymer based on 1 part by weight of the polymer, the boiling point of the solvent or more Standing the reaction step, and (4) a method of producing a super-absorbent resin, comprising the step of removing the solvent by filtration of the polymer solution obtained in the above step (3), dried to. The method of claim 1 wherein an alkali metal hydroxide is used for the partial neutralization. The method of claim 1, wherein the lipophilic solvent is n-hexane, n-heptane, benzene, xylene, toluene, cyclopentane or cyclohexane. The method of claim 1 wherein the crosslinker is ethylene glycol diglycidyl ether, glycerol polyglycidyl ether, trimethylol propane polyglycidyl ether or sorbitol polyglycidyl ether. The method of claim 1 wherein the hydrophilic solvent is methanol.