JP2005089492A - Polyvinyl alcohol particle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a PVA particle with high hydrophilicity useful for a paper coating agent, etc., and its manufacturing method. <P>SOLUTION: A crosslinked polyvinyl alcohol particle having an average particle size of 10-1,000 nm is provided. The method for manufacturing the polyvinyl alcohol particle, in which a monomer component containing a vinyl ester monomer and a crosslinking agent is polymerized in an emulsified state and then hydrolyzed, is provided. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to hydrophilic polyvinyl alcohol-based particles and a method for producing the same.

  As a method for producing hydrophilic gel particles, a method in which a hydrophilic monomer and a crosslinking agent are polymerized by a technique such as precipitation polymerization or reverse phase suspension polymerization is generally known. For example, it is widely known that gel particles having a high water absorption can be obtained by a reverse phase suspension polymerization method of an ionic monomer such as acrylic acid in the presence of a small amount of a crosslinking agent. However, the gel particles obtained by these methods all have a large particle size of several tens of μm or more, and hydrophilic microgels having high water absorption in a small particle size region (several μm or less) have been obtained. Absent. Kawaguchi et al. Have reported that a crosslinked microgel having a particle size of about several μm can be obtained by precipitation polymerization of acrylamides in the presence of a high concentration of a crosslinking agent (Non-patent Document 1). However, in this method, particles of about several μm can be prepared, but a high concentration of a crosslinking agent must be used for synthesizing fine particles. This is because in the fine particle generation process in precipitation polymerization, when the monomer and the crosslinking agent are polymerized in the presence of the polymerization initiator, the nucleus is precipitated, and the polymerization proceeds while the monomer and the crosslinking agent are distributed from the solvent to the nucleus. This is because, due to the hydrophilicity of the monomer itself and the solubility in the solvent, the cohesive force is insufficient under the conditions of using a small amount of the crosslinking agent, and the shape as fine particles cannot be achieved. Thus, when a high concentration crosslinking agent is used, the resulting microgel has a strong influence on the chemical structure of the crosslinking agent, and if the crosslinking degree is too high, the gel water retention is poor.

On the other hand, polyvinyl alcohol (hereinafter abbreviated as PVA), which is one of typical water-soluble polymers, has been industrially produced as a granulated product having an average particle size of 200 to 1000 μm, and has excellent film forming properties and strength. Therefore, it has been widely used in various applications such as paper coating agents (clear coating agents, pigment coating agents), paper modifiers, yarn glues, paper and wood adhesives. Normally, PVA is used in the form of an aqueous solution. However, in the coating under high shear conditions, there is a problem that the viscosity increases and the quality of the coating film decreases. In order to solve this problem, Various studies have been made to reduce the particle size of PVA. As a method for producing a small particle size PVA, a method of mechanically pulverizing general-purpose PVA (Patent Document 1), a dimethyl sulfoxide spray droplet (average particle size of 1 to several mm) or an oily dispersion of a dimethyl sulfoxide solution as a poor solvent Method of adding and solidifying and precipitating (Patent Document 2, Patent Document 3), Method of saponifying a non-aqueous dispersion of polyvinyl ester having an average particle size of 0.05 to 50 μm obtained by dispersion polymerization using a surfactant (Patent) Reference 4) is an example. However, any of the PVA-based particles obtained by these methods is soluble in water or warm water, and does not have an essentially crosslinked structure.
Polym.J., 23, 955 (1991) JP-A-2-225506 Japanese Patent Laid-Open No. 5-98023 Japanese Patent Laid-Open No. 5-98024 British Patent No. 1,199,651

  An object of the present invention is to provide a highly hydrophilic PVA-based particle useful for paper coating agents and the like, and a method for producing the same.

  Unlike the fine particle production methods such as suspension polymerization and precipitation polymerization, the present inventors focused on the emulsion polymerization method to obtain a smaller particle size, and emulsion polymerized monomer components including a vinyl ester monomer and a crosslinking agent. The present inventors have found that PVA-based particles having high hydrophilicity can be obtained by hydrolyzing the resulting polyvinyl ester-based emulsion particles.

  That is, the present invention provides a polyvinyl alcohol-based particle having an average particle diameter of 10 to 1000 nm, which is hydrolyzed after emulsion polymerization of a crosslinked polyvinyl alcohol-based particle and a monomer component containing a vinyl ester monomer and a crosslinking agent. Provide law.

  According to the present invention, it is possible to obtain PVA-based particles having a high hydrophilicity with an average particle size of several μm or less when swollen with water.

  The PVA-based particles of the present invention are crosslinked particles having an average particle size of 10 to 1000 nm, preferably 50 to 800 nm.

  The average particle size of the PVA-based particles of the present invention is essentially the same as the average particle size in ethanol of the polyvinyl ester emulsion before hydrolysis described below.

  The PVA-based particles of the present invention swell with water and become a gel having a crosslinked structure with an average particle size of several μm or less. In addition, the average particle diameter of a gel can be measured by the method described in the following Example.

  The PVA-based particles of the present invention can be produced by the following steps 1 and 2.

Step 1: Step of obtaining a polyvinyl ester emulsion by emulsion polymerization of a monomer component containing a vinyl ester monomer and a crosslinking agent Step 2: Step of hydrolyzing the polyvinyl ester emulsion obtained in Step 1 to obtain PVA particles The process will be described below.

  Examples of the vinyl ester monomer used in Step 1 include esters of vinyl alcohol and fatty acids having 1 to 6 carbon atoms. Vinyl acetate, vinyl propionate, vinyl butyrate and the like are preferable, and vinyl acetate is more preferable.

  The cross-linking agent used in step 1 is not particularly limited as long as it is involved in the copolymerization reaction with the vinyl ester monomer and forms a cross-linked structure, but is a cross-linkable unsaturated having at least two vinyl groups in the molecule. Monomers are preferred. Examples of the crosslinkable unsaturated monomer include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, dipropylene glycol di (meth) acrylate, Polypropylene glycol di (meth) acrylate, 1,2-butylene glycol di (meth) acrylate, 1,3-butylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, glycerin di (meth) acrylate, glycerin tri (Meth) acrylates, (meth) acrylic esters of polyhydric alcohols such as trimethylolpropane tri (meth) acrylate and pentaerythritol tetra (meth) acrylate N-methylallylacrylamide, N-vinylacrylamide, N, N'-methylenebis (meth) acrylamide, acrylamides such as bisacrylamideacetic acid, divinyl compounds such as divinylbenzene, divinyl ether, divinylethyleneurea, diallyl phthalate, diallyl malate , Diallylamine, triallylamine, triallyl ammonium salt, allyl etherified product of pentaerythritol, allyl etherified product of sucrose having at least two allyl ether units in the molecule, vinyl (meth) acrylate, allyl ( And (meth) acrylates of unsaturated alcohols such as (meth) acrylate and 2-hydroxy-3- (meth) acryloyloxypropyl (meth) acrylate. Among these, ethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, and divinylbenzene are preferable.

  In the present specification, (meth) acrylate, (meth) acryl and (meth) acryloyl mean acrylate or methacrylate, acrylic or methacryl, acryloyl or methacryloyl, respectively.

  If the proportion of the crosslinking agent in the monomer component used in step 1 is too small, the degree of crosslinking of the resulting polymer will be too small, and it will dissolve in water at the stage of the hydrolysis reaction performed in the next step 2. Even if the insoluble component can be extracted, the high hydrophilicity cannot be maintained, and if it is too much, the high hydrophilicity is lost. -5.0 wt% is preferable, and 0.002-1.0 wt% is particularly preferable.

  As long as the effects of the present invention are not impaired in Step 1, other monomers that can be copolymerized therewith can be used as the monomer component in addition to the vinyl ester monomer and the crosslinking agent. Other monomers include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl ( (Meth) acrylate, n-pentyl (meth) acrylate, neopentyl (meth) acrylate, cyclopentyl (meth) acrylate, n-hexyl (meth) acrylate, cyclohexyl (meth) acrylate, n-octyl (meth) acrylate, isooctyl (meth) Acrylate, 2-ethylhexyl (meth) acrylate, n-decyl (meth) acrylate, isodecyl (meth) acrylate, lauryl (meth) acrylate, tridecyl (meth) acrylate, stearyl (meth) Acrylate, isostearyl (meth) acrylate, behenyl (meth) acrylate, phenyl (meth) acrylate, toluyl (meth) acrylate, xylyl (meth) acrylate, benzyl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, 2- Butoxyethyl (meth) acrylate, 2-phenoxy (meth) acrylate, 2-methoxypropyl (meth) acrylate, 3-methoxypropyl (meth) acrylate, 2-ethoxypropyl (meth) acrylate, 3-ethoxypropyl (meth) acrylate Anionic groups such as (meth) acrylic acid derivatives such as 2-acrylamido-2-methylpropanesulfonic acid, sodium styrenesulfonate, (meth) acrylic acid, 2-sulfoethyl (meth) acrylate Monomer, N- (3-sulfopropyl) -N- (meth) acryloyloxyethyl-N, N-dimethylammonium betaine, N- (3-sulfopropyl) -N- (meth) acryloylamidopropyl-N, N -Dimethylammonium betaine, N-carboxymethyl-N- (meth) acryloylamidopropyl-N, N-dimethylammonium betaine, N-carboxymethyl-N- (meth) acryloyloxyethyl-N, N-dimethylammonium betaine, etc. Examples include betaines.

  The proportion of these other monomers is preferably 50% by weight or less, more preferably 30% by weight or less, based on the total amount of monomers.

  In Step 1, as a polymerization method of the monomer component, an emulsion polymerization method is used from the viewpoint of obtaining small particle size particles having high hydrophilicity (average particle size of particles swollen with water is several μm or less). When the suspension polymerization method is used, a particle size of several tens of μm or more can be obtained. When the precipitation polymerization method is used, a particle size of about several μm can be obtained, but the crosslinking agent is used at a high concentration. It is not preferable because it can be created only when it is made.

  The emulsifier required for carrying out the emulsion polymerization is preferably a nonionic surfactant, and preferably has an HLB of 16 to 19, particularly 16.5 to 18.8. As such a nonionic surfactant, a polyalkylene having an alkyl chain or alkenyl chain having 8 to 18 carbon atoms, preferably 10 to 18 carbon atoms, and an average ethylene oxide addition mole number of 20 to 70, preferably 30 to 60. Examples thereof include oxyethylene alkyl ether and polyoxyethylene alkenyl ether. The nonionic surfactant is preferably used in a proportion of 0.1 to 5% by weight, more preferably 0.2 to 3% by weight, based on the total amount of monomers.

  Moreover, it is preferable to use a dispersing agent when performing emulsion polymerization. By using a dispersing agent, it is possible to prepare a dispersion of PVA-based particles having excellent dispersibility by stabilizing the particles during emulsion polymerization and the subsequent hydrolysis reaction. Moreover, at the time of emulsion polymerization, a part of used dispersing agent forms a chemical bond with the polyvinyl ester obtained by emulsion polymerization, and is fix | immobilized. As such a dispersant, any of a nonionic polymer compound and an ionic polymer compound can be used, and a nonionic polymer compound is preferable. Examples of nonionic polymer compounds include polyvinyl alcohol, polyvinyl pyrrolidone, modified starch, and water-soluble cellulose derivatives. The dispersant is preferably used in the range of 0.1 to 10% by weight based on the total amount of monomers.

  During emulsion polymerization, hydrolysis may occur due to the influence of acid and alkali in the system. Acids such as acetic acid generated during emulsion polymerization gradually make the pH of the polymerization system acidic, so that sodium carbonate, sodium bicarbonate, sodium orthophosphate, monobasic sodium phosphate, sodium chloride, sodium sulfate are used as buffers. When inorganic salts such as these are used, adverse effects on polymerization behavior due to pH fluctuations can be avoided. The ratio of the buffering agent used here is preferably 2% by weight or less, more preferably 0.1 to 1% by weight, based on the total amount of monomers.

  As the polymerization initiator at the time of emulsion polymerization, a conventionally known polymerization initiator that is soluble in a dispersion medium is used, and a water-soluble azo initiator such as 2,2′-azobis (2-amidinopropane), persulfuric acid. Examples include water-soluble peroxide initiators such as potassium and ammonium persulfate, and water-soluble redox initiators such as hydrogen peroxide / ferrous salt, persulfate / acidic sodium sulfite, and the like. The amount of the polymerization initiator used is preferably in the range of 0.01 to 5% by weight based on the total amount of monomers.

  Water is used as the solvent during the emulsion polymerization, but an appropriate amount of a hydrophilic solvent may be used when a component that is hardly soluble in water is used as the monomer.

  In the polymerization reaction of the present invention, it is preferable to start the polymerization by substituting the reaction system with an inert gas such as nitrogen as necessary, and at room temperature or by heating. The polymerization reaction is performed under stirring, and it is particularly preferable to uniformly stir the entire system. Moreover, the addition method of each component required in performing a polymerization reaction may add all the components simultaneously, and may make it react, The container which prepared components other than a vinyl ester monomer, a crosslinking agent, and another monomer Alternatively, these monomer components may be gradually added. A vinyl ester monomer, a crosslinking agent, and other monomers may be added all at once or individually. The reaction temperature during emulsion polymerization is 40 to 120 ° C., preferably 50 to 90 ° C., and the pH is preferably 3 to 9, preferably 4 to 8.

  The polyvinyl ester emulsion obtained in step 1 is subsequently subjected to the hydrolysis reaction in step 2 to saponify the polyvinyl ester.

  The solid content concentration in carrying out the hydrolysis reaction is preferably 10% by weight or less, and more preferably 5% by weight or less, in order to suppress aggregation and particle coarsening during saponification.

  Examples of the catalyst used in the hydrolysis reaction include alkali catalysts and acid catalysts, and conventionally known catalysts can be used. Examples of the alkali catalyst include sodium hydroxide, potassium hydroxide, ammonia, sodium methylate, and the like, and the acid catalyst includes sulfuric acid, hydrochloric acid, p-toluenesulfonic acid, and the like. The alkali used in the hydrolysis reaction is partially neutralized by the influence of an acid such as acetic acid generated as a result of the hydrolysis reaction, so an excess amount is used with respect to the vinyl ester component constituting the polyvinyl ester, and all monomers. It is preferable to use in the range of 100 to 300 mol% with respect to the amount.

  As the solvent used for the hydrolysis reaction, ion exchange water is preferable in order to avoid complicated operations such as solvent substitution, but alcohol solvents such as methanol, ethanol, n-propanol, isopropanol, and n-butanol are appropriately used. As long as it is a poor solvent for the precipitated PVA-based particles, aprotic polar solvents such as dimethyl sulfoxide and dimethylformamide, aromatic solvents such as benzene, toluene and chlorobenzene, tetrahydrofuran, dioxane and the like Ether solvents, ester solvents such as methyl acetate and ethyl acetate, and ketone solvents such as acetone and methyl ethyl ketone may be added.

  During the hydrolysis reaction, a solvent-soluble dispersant may be added to the system, and the above-mentioned surfactants and polymer type dispersants that can be used in Step 1 can be used. .

  The temperature of the hydrolysis reaction is preferably 10 ° C. or higher, more preferably 50 ° C. or higher from the viewpoint of the saponification rate. Moreover, 150 degrees C or less is preferable and 100 degrees C or less is more preferable.

  The PVA-based particles after the hydrolysis reaction can be separated from the liquid phase reaction medium by methods such as decantation, liquid separation operation, and centrifugation to remove coexisting alkalis, acids such as acetic acid and coexisting impurities. .

  The saponification degree of the PVA-based particles is not particularly limited, but is preferably 50% or more, more preferably 80% or more from the viewpoint of maintaining a high water content. The degree of saponification can be analyzed by various methods. When gas chromatography (hereinafter abbreviated as GC) is used, the amount of acid such as acetic acid present in the hydrolysis reaction solution can be easily measured. The degree of saponification inside can be calculated.

  The particle diameter of the gel of the PVA-based particles of the present invention is preferably 0.2 to 10 μm, and more preferably 1 to 10 μm, in pH 7 ion-exchanged water.

  The PVA-based particles obtained by the present invention have a small particle size and high hydrophilicity, and are preferably used for various applications such as paper coating agents, paper modifiers, yarn glues, paper and wood adhesives. It is done.

  In the following examples, “%” and “parts” mean “% by weight” and “parts by weight”, respectively, unless otherwise specified. The physical property values in the examples were measured by the following methods.

<Average particle size of polyvinyl ester emulsion>
The emulsion was dispersed in ethanol and measured at 20 ° C. using an electrophoretic light scattering photometer (manufactured by Otsuka Electronics Co., Ltd., model ELS-8000).

<Saponification degree of PVA particles>
0.1g of the fine particle dispersion is precisely weighed, and 1 drop of 6N hydrochloric acid is mixed with a Pasteur pipette to adjust the pH of the fine particle dispersion to 3 or less, and then included in the fine particle dispersion by GC measurement under the following conditions. The amount of acetic acid produced was quantified, and the degree of saponification was determined by the following formula.

Saponification degree (%) = (Measured amount of acetic acid / 100% theoretical amount of acetic acid for saponification) × 100
Here, the theoretical acetic acid amount of 100% saponification is represented by the following formula.

Theoretical amount of acetic acid for 100% saponification =
[Ratio of vinyl acetate in reaction solution × 0.1 / 86] × molecular weight of acetic acid 0.1: measured amount of fine particle dispersion 86: molecular weight of vinyl acetate / GC measurement conditions The amount of acetic acid was measured under the following conditions.

Equipment: HP6890 (manufactured by Hewlett-Packard Company)
Column: HP-FFAP 30 m × 0.53 mm × 0.1 μm (manufactured by Hewlett-Packard Company)
Inlet temperature: 170 ° C
Oven temperature: held at 80 ° C. for 1 minute, then heated up to 150 ° C. at 10 ° C./min. <PVA particle particle size>
The aqueous dispersion of PVA-based particles was visually observed with an optical microscope.

Example 1
In a five-necked flask, 10.0 parts of a nonionic surfactant (Emulgen 147 manufactured by Kao Corporation) and 350 parts of ion-exchanged water are uniformly dissolved at 90 ° C., then cooled to 60 ° C., and 10 parts of vinyl acetate 20.0 parts of polyvinyl alcohol (Nippon Synthetic Rubber Co., Ltd. Gohsenol GL-05) was added, and after the temperature was raised, it was completely dissolved at 80 ° C. Thereafter, an aqueous solution obtained by dissolving 200 parts of vinyl acetate and 0.01 part of divinylbenzene and 0.5 part of 2,2′-azobis (2-amidinopropane) hydrochloride in 20 parts of ion-exchanged water, The solution was individually dropped continuously into the reaction solution over 6 hours. After completion of dropping, the mixture was further aged for 2 hours. The reaction rate calculated from the solid content concentration of the obtained emulsion was 95.8%. The emulsion particles were dispersed in ethanol and the average particle size was measured and found to be 500 nm.

To the three-necked flask, 100 parts of the obtained emulsion and 100 parts of a 5N aqueous sodium hydroxide solution were added, and after the temperature was raised, the reaction was carried out at 80 ° C. for 10 hours. During this time, as the reaction progressed with heating, the solution was colored (yellow to orange). When the amount of acetic acid coexisting in the emulsion before and after the reaction was quantified and the degree of saponification was calculated, 11.8% before the reaction (acetic acid amount 2.3%), after the reaction 81.2% (acetic acid amount 15.6%) Met. Subsequently, for the purpose of removing impurities such as sodium hydroxide, acetic acid, and unreacted monomers present in large quantities in the system, ion exchange water is added to 100 g of emulsion and diluted 5 times, followed by centrifugation and separation. Washing was performed by repeating the operation of discarding the subsequent supernatant and adding fresh ion exchange water five times. The pH after washing was almost neutral, and the obtained particles were gel swollen with water. The particle diameter of the obtained gel swollen with water was, on average, about a few μm, although the particle size distribution due to partial aggregation was broadened by visual observation.

Claims (5)

  Cross-linked polyvinyl alcohol-based particles having an average particle size of 10 to 1000 nm.   The polyvinyl alcohol-type particle | grains of Claim 1 obtained by hydrolyzing, after emulsion-polymerizing the monomer component containing a vinyl ester monomer and a crosslinking agent.   The polyvinyl alcohol-based particles according to claim 2, wherein the vinyl ester monomer is vinyl acetate.   The polyvinyl alcohol-type particle | grains of Claim 2 or 3 whose ratio of a crosslinking agent is 0.002-5.0 weight% with respect to monomer whole quantity (except a crosslinking agent). A method for producing polyvinyl alcohol particles, wherein a monomer component containing a vinyl ester monomer and a crosslinking agent is subjected to emulsion polymerization and then hydrolyzed.