JPH0113490B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing hydrogels, which are polymeric materials that have the ability to absorb and retain large amounts of water. More specifically, it is an object of the present invention to provide an economical and simple method for producing granular or spherical hydrogel without special pulverization treatment. In recent years, as the use of hydrophilic polymer materials in the medical industry, food industry, and manufacturing fields has progressed, hydrogels that are insoluble in water and have hydrophilic or water-absorbing properties are being used as separation and purification materials such as various membranes and liquid chromatography carriers. It has come to be used for enzymes, immobilized carriers, culture media for microorganisms and plants, medical materials such as contact lenses and suture coverings, and various other uses that utilize water absorption and water retention. Among these applications, hydrogels used particularly in application fields that utilize water absorption or water retention are desired to have the ability to absorb as much water as possible in a short period of time upon contact with water. Methods for producing such hydrogels include crosslinking water-soluble polymeric substances such as polyethylene oxide, polyacrylic acid, polyvinylpyrrolidone, sulfonated polystyrene, and sodium polyacrylate using a crosslinking agent; A method of substituting with a lipophilic group to make it water-insoluble, a method of polymerizing an alkali metal acrylic acid salt and self-crosslinking, etc. have been proposed. However, in the above method, when the polymerization is carried out by a reversed-phase suspension polymerization method, when the hydrogel produced by the polymerization is separated from the organic solvent, the hydrogel sticks and solidifies into a lump. Not available in granular form. As a result, it is necessary to mechanically pulverize, which complicates the operation, and in addition, there are disadvantages such as a decrease in productivity and yield. As a method to improve these drawbacks, a powder-formable powder is obtained by polymerizing an aqueous solution of alkali metal acrylate in a petroleum-based aliphatic hydrocarbon solvent in the presence of a sorbitan fatty acid ester dispersant with HLB3 to HLB6. A method for producing a self-crosslinking alkali metal acrylate polymer has been proposed.
(Japanese Patent Application Laid-open No. 53-46389). In addition, the present applicant also filed α,
In a method for producing a hydrogel in which a β-unsaturated carboxylic acid monomer or/and its alkali metal salt is produced by a water-in-oil reverse phase suspension polymerization method,
A method using a hydrocarbon oil or/and fat with a specific melting point as an anti-blocking agent was proposed. However, in any of the above methods, no adhesion or aggregation is observed in the step of separating and recovering the granular hydrogel from the organic solvent, and it is possible to separate it as a clean granular hydrogel, but in the step of drying the separated granular hydrogel, adhesion, It has the disadvantage that aggregation cannot be completely prevented. In view of the above-mentioned circumstances, the present inventors conducted intensive studies on a method for producing a highly absorbent hydrogel that is granular or spherical and has sufficient gel strength. We have discovered that when a specific surfactant is present during separation, granular hydrogels can be directly produced without adhesion between hydrogel particles during the drying process.
The present invention has now been completed. That is, the present invention provides a method for producing a hydrogel in which an α,β-unsaturated carboxylic acid monomer or/and its alkali metal salt is produced by a water-in-oil type reverse-phase suspension polymerization method.
The present invention provides a method for producing a granular or spherical hydrogel characterized by using a nonionic surfactant with an HLB of 2.8 or less. In carrying out the method of the present invention, the anti-blocking agent is the fusion of the granular hydrogels that occurs when the granular hydrogels produced by polymerization are separated and recovered from the organic solvent in which they are dispersed or precipitated, and then dried. This substantially or completely eliminates the phenomenon of adhesion. In particular, according to the method of the present invention, when granular hydrogel is separated from an organic solvent, the dried product can be recovered as granular hydrogel by crushing even if it is in a sticky or agglomerated state. The use of such an anti-blocking agent has the advantage that the granular hydrogel produced by polymerization can be recovered without fusion. Therefore, the conventional operation of pulverizing after collection is not required, which is extremely economical. The anti-blocking agent used in carrying out the method of the present invention is a nonionic surfactant with an HLB of 2.8 or less. If the HLB is greater than 2.8, the hydrogel obtained in the step of drying the hydrogel separated from the solvent will be This results in a fused state, which is not preferable. A nonionic surfactant having an HLB of 2.5 to 0.3 is preferably used. More preferred are those that are oily at room temperature. Specifically, sorbitan triolate, sorbitan restearate, sorbitan tetrastearate, glycerol monooleate, glycerol monostearate, propylene glycol monostearate, or mixtures thereof can be suitably used. Among these, sorbitan triolate, sorbitan tristearate, glycerol monooleate, and glycerol monostearate are particularly preferably used. The HLB referred to here is a numerical value determined based on the theory of hydrophilic-lipophilic balance in surfactants proposed by W. C. Griffin [J.Soc. .Cosmetic
Chemists (Journal of Society Cosmetic Chemists) 1 , 311 (1949)]. The antiblocking agent is added to the dispersion or slurry after polymerization. The amount of anti-blocking agent added is generally 0.05% by weight or more, preferably 0.1 to 50% by weight based on the hydrogel.
It is said that If the amount added is less than 0.05% by weight, the anti-adhesive effect will be slight, and although there is no particular restriction on adding a large amount, it is not economical, so the amount is generally up to about 10% by weight based on the produced hydrogel. In the process of separating hydrogels from organic solvents by using the above-mentioned nonionic surfactant with a specific HLB as an anti-blocking agent, what appears to be sticky or agglomerated at first glance can be removed through the next drying process. The advantage is achieved that it can be recovered afterwards as a granular hydrogel or by disintegration as a granular hydrogel. In the well-known Japanese Patent Application Laid-open No. 53-46389, it is stated that if a surfactant has an HLB of less than 3 during polymerization, it will not become smooth particles that are easy to handle, but this is due to the separation process and drying. It is not recognized by the inventors of the known literature that granular hydrogels can be obtained by doing so. Furthermore, in carrying out the method of the present invention, in addition to the above-mentioned anti-blocking agent, a hydrocarbon oil or/and fat is added to prevent adhesion and aggregation of the hydrogel in the step of separating the hydrogel from the organic solvent, and to prevent the hydrogel from drying from the separation step. It is more effective to facilitate handling of the hydrogel during processing. By using such a combined anti-blocking agent, a remarkable effect is exhibited in that a more effective anti-blocking agent can be achieved even in the drying process. The hydrocarbon oil or/and oil has a boiling point higher than the drying temperature of the hydrogel recovery system, preferably 50°C or more higher than the drying temperature, and a melting point lower than the separation operation temperature of the hydrogel and solvent, preferably 20°C higher than the separation operation temperature. A hydrocarbon oil or/and fat or oil having a melting point as low as 250° C. or higher, preferably a hydrocarbon oil or/and fat having a boiling point of 250° C. or higher and a melting point of 30° C. or lower is used. Specifically, liquid paraffin, cottonseed oil, soybean oil,
Examples include rapeseed oil, coconut oil, liquid wax, salad oil, tempura oil, hetu, lato, and the like. The anti-blocking agent made of hydrocarbon oil or/and fat may be applied to the polymerization system or to the dispersion or slurry after the polymerization, but it is more preferable to add it to the dispersion or slurry after the polymerization. More suitable. Further, the amount of the anti-blocking agent made of hydrocarbon oil and/or oil or fat added is generally 0.05% by weight or more, preferably 0.1 to 10% by weight, based on the hydrogel. The method of the present invention is applied to the following hydrogel manufacturing method. The α,β-unsaturated carboxylic acid monomers and/or their alkali metal salt monomers used in the method of the present invention include acrylic acid, methacrylic acid, itaconic acid, crotonic acid, maleic acid, fumaric acid and their ammonium salts, alkali metal Examples include salt monomers. Among these, acrylic acid, methacrylic acid, and alkali metal salt monomers thereof can be mentioned as those which can be used particularly preferably. Alkali metals include sodium, potassium,
Examples include calcium and barium. Of course, other ethylenically unsaturated monomers can also be copolymerized within the scope of the purpose of producing the hydrogel. The organic solvent used as the polymerization medium is n
- Known organic solvents such as aliphatic hydrocarbons such as hexane, n-heptane and cyclohexane, and aromatic hydrocarbons such as benzene, toluene and xylene can be used. The method of the present invention can be applied to a system in which polymerization is carried out in the presence or absence of a crosslinking agent in a reverse phase suspension polymerization method. Hydrogels made with crosslinking agents have improved mechanical strength, but generally have reduced water absorption. On the other hand, self-crosslinking hydrogels produced without the use of crosslinking agents are characterized by high water absorption. The polymerization method is appropriately selected depending on the intended use of the hydrogel. When polymerizing in the presence of a crosslinking agent, any crosslinking agent that can be copolymerized with the α,β-unsaturated acid monomer and/or its alkali metal salt monomer may be used, such as ethylene glycol. , di- or tri(meth)acrylic acid esters of polyols such as propylene glycol, trimethylolpropane, glycerin, polyoxyethylene glycol, and polyoxypropylene glycol, and combinations of the above polyols and unsaturated acids such as maleic acid and fumaric acid. unsaturated polyesters obtained by reacting polyepoxide with (meth)acrylic acid; bisacrylamides such as N,N-methylenebisacrylamide; Di(meth)acrylic acid carbamyl esters obtained by reacting polyisocyanates such as diisocyanate and hexamethylene diisocyanate with hydroxyethyl (meth)acrylate, allylated starch, allylated cellulose, diallyl phthalate, N,N ',N''-trialyl isocyanurate, divinylbenzene, etc. The crosslinking agent is generally used in a proportion of 0.001 to 1% by weight, preferably 0.01 to 0.5% by weight, but the proportion of the crosslinking agent is 0.001% by weight. When the amount is less than 1% by weight, the strength of the resulting hydrogel decreases, while when it exceeds 1% by weight, the water absorption amount of the hydrogel decreases to 50% or less.During polymerization, α,β-unsaturated carboxylic acid monomer and The concentration of / or the alkali metal salt thereof in the organic solvent is generally in the range of 5 to 50% by weight, and the water/organic solvent (weight ratio) is generally in the range of 0 to 50% by weight.
Used within the range of 50/100 to 50. The amount of polymerization catalyst used is generally the same as that of the monomer.
It is used in a range of 0.001 to 1% by weight, preferably 0.01 to 0.1% by weight. Since polymerization is carried out in the aqueous phase in reverse-phase suspension polymerization, suitable polymerization catalysts such as potassium persulfate, ammonium persulfate, hydrogen peroxide, or these together with sodium bisulfite, sodium thiosulfate, sodium pyrosulfite, Rongarit, etc. A water-soluble catalyst is used in combination with a reducing agent. The polymerization reaction is generally carried out at a temperature of 40 to 100°C with stirring, and at a wide range of pressures from reduced pressure to increased pressure. As the dispersion stabilizer and surfactant used in the polymerization, known ones can be used. Preferred dispersion stabilizers and surfactants include carboxyl group-containing polymers having affinity for organic solvents, basic nitrogen-containing polymers, and
Examples include nonionic surfactants with an HLB of 3 to 9. Specifically, as the carboxyl group-containing polymer, any carboxyl group-containing polymer that has an affinity for organic solvents can be used, but usually a monomer having a carboxyl group and an ethylenically unsaturated polymer are used. Copolymers with monomers, polymers obtained by reacting monomers or copolymers of ethylenically unsaturated monomers with monomers having a carboxyl group, monomers or copolymers of ethylenically unsaturated monomers Graft copolymers obtained by graft-polymerizing a monomer having a carboxyl group to a polymer, modified products thereof, and the like are used. As the basic nitrogen-containing polymer, any basic nitrogen-containing polymer that has an affinity for organic solvents can be used, but usually monomers having basic nitrogen and ethylenically unsaturated monomers are used. copolymers with basic nitrogen-containing monomers, monopolymers or copolymers of ethylenically unsaturated monomers, monopolymers or copolymers of ethylenically unsaturated monomers, monomers or copolymers of ethylenically unsaturated monomers; Graft copolymers obtained by graft-polymerizing a monomer having basic nitrogen onto a polymer, modified products thereof, and the like are used. Nonionic surfactants with an HLB of 3 to 9 include sorbitan fatty acid esters such as sorbitan monostearate, sorbitan monooleate, sorbitan monolaurate, and sorbitan monopalmitate; glycerin fatty acid esters such as glycerin monostearate;
Examples include sucrose fatty acid esters such as sucrose distearate and sucrose tristearate, and mixtures thereof. The amount of these dispersants and surfactants used is generally 0.01 to 20% by weight based on the monomers charged. The polymerization reaction product is separated into hydrogel and organic solvent by known means such as sedimentation, filtration, and centrifugation. Separation operations are generally carried out at temperatures between 10 and 100°C. The separated hydrogel is then dried by known means such as a groove dryer, a shelf-type vacuum dryer, a vacuum dryer with an agitator, a rotary dryer, a fluidized bed dryer, a flash dryer, a plate dryer, etc. . Although the drying temperature varies depending on the type of organic solvent used in the polymerization, it is generally carried out at a temperature of 20 to 150°C. Thus, according to the method of the present invention in which an anti-blocking agent is added during polymerization or after polymerization, the hydrogel obtained by drying does not stick or coagulate into lumps, and there is no need for steps such as mechanical crushing. Particulate hydrogels can be produced using The hydrogel produced by the method of the present invention detailed above generally has an average particle diameter of about 20 to
It is possible to produce hydrogels with arbitrarily controlled thickness in the range of 3000μ without the need for pulverization. The granular hydrogel produced by the method of the present invention has sufficient gel strength and excellent water absorption ability. The method of the present invention will be explained in more detail with reference to Examples below, but the present invention is not limited thereto. In the examples, the water absorption rate of the hydrogel was expressed as water absorption rate (g/g)=(weight of water-absorbing hydrogel)/(weight of dry hydrogel). The average particle size was determined by the sieving method. Furthermore, the strength of the hydrogel was expressed as the crushing strength of the saturated water-absorbing hydrogel particles as hydrogel strength = (crushing load)/π (saturated hydrogel radius) ² . An ethylene-propylene-diene monomer copolymer (hereinafter abbreviated as EPDM) was obtained by grafting methacrylic acid and ethyl methacrylate into the flask of Example 1-5.
14 g (carboxy group content = 6.6 mol%) was dissolved in 2 mols of n-hexane and added. Meanwhile, after mixing 270 ml of water, 200 g of acrylic acid and 90 g of sodium hydroxide, 150 mg of potassium persulfate was added.
and N,N'-methylene-bis-(acrylamide)
30 mg was added to prepare an aqueous sodium acrylate solution. This aqueous sodium acrylate solution was added dropwise into the flask in step 5 while stirring at 300 rpm, and polymerized at 60°C for 3 hours. After polymerization, add the type and amount of anti-blocking agent shown in Table 1, and heat at 60℃ for 30 minutes.
Stir for a minute. Thereafter, the polymerization reaction product was centrifuged at 30°C to separate the hydrogel. The separated hydrogel was dried under reduced pressure at 80°C for 10 hours in a vacuum dryer equipped with a stirrer. Table 1 shows the state of the hydrogel particles during the drying process. In Experiment No. 1-1, the obtained hydrogel had an average particle size of 210 μm, a water absorption rate of 600 g/g, and a gel strength of 800 g/cm ² .

[Table] Example 2 An anti-blocking agent of the type and amount shown in Table 2 was added to the dispersion obtained by polymerization according to the method of Example 1.
Stirred at ℃ for 1 hour. After that, the anti-blocking agent-added dispersion was centrifuged at 30°C to separate the hydrogel, and then the separated hydrogel was dried at 80°C for 10 minutes in a vacuum dryer with a stirrer.
Dry under reduced pressure for an hour. Table 2 shows the state of the hydrogel particles during the separation process and drying process.

【table】

[Table] Example 3 Sorbitan monostearate in 10 flasks
28 g and 40 g of cottonseed oil were dissolved in 4 cyclohexane and added. Meanwhile, 540ml of water, 400g of acrylic acid
After mixing 180 g of sodium hydroxide, 300 mg of potassium persulfate and 60 mg of N,N'-methylene-bis-(acrylamide) were added to prepare an aqueous sodium acrylate solution. This aqueous sodium acrylate solution was added dropwise to the flask No. 10 above while stirring at 200 rpm, and polymerized at 50° C. for 6 hours under reduced pressure of 300 Torr. After polymerization, the solvent is removed by decantation.
After removal, sorbitan tristearate 40
After adding 1.5 g of water and stirring gently, the hydrogel was separated from the polymerization reaction product at room temperature using a suction filter. A granular hydrogel was obtained. The obtained hydrogel was dried at 80°C for 10 hours using a shelf vacuum dryer. The state of the hydrogel particles during the drying process showed no adhesion or agglomeration. The characteristics of the obtained hydrogel are an average particle size of 45μ, a water absorption rate of 400g/g, and a hydrogel strength of 250g/g.
It was warm in ^cm2 .

Claims (1)

[Claims] 1 α,β-unsaturated carboxylic acid monomer or/
In the method for producing hydrogels in which alkali metal salts and their alkali metal salts are produced by a water-in-oil type reverse-phase suspension polymerization method, it is recommended that a nonionic surfactant with an HLB of 2.8 or less be added as an anti-blocking agent after the completion of polymerization. Characteristic hydrogel manufacturing method.