JP5705056B2 - Method for producing polyvinyl alcohol polymer particles - Google Patents

Description

  The present invention relates to a method for producing polyvinyl alcohol (hereinafter also referred to as PVA) polymer particles.

  The PVA polymer is usually produced by polymerizing a vinyl ester monomer to obtain a polyvinyl ester polymer, which is saponified under alkaline conditions. Such polymerization is generally solution polymerization using alcohol as a solvent, and is usually carried out industrially by boiling point polymerization using methanol. The reason for using methanol is to remove the heat of polymerization of the vinyl ester monomer by using latent heat generated by evaporation of methanol, and the boiling point of methanol is suitable as the polymerization temperature. The methanol solution of the polyvinyl ester polymer thus obtained, after removing the unreacted monomer, was added with an alkali catalyst such as sodium hydroxide and saponified to become a methanol solution of the PVA polymer, and then dried. Removes methanol.

  However, the PVA polymer has a high affinity with alcohol because it has a large number of hydroxyl groups, and it is difficult to completely remove methanol by drying. On the other hand, drying at a high temperature or for a long time causes the PVA polymer to thermally deteriorate. This is not preferable. Therefore, 1 to 5% by weight of methanol remains in a normal PVA polymer, and it has been difficult to apply it to uses in which methanol is a problem, such as foods, cosmetics, and medicines.

  In order to solve this problem, as a method of removing the organic solvent in the PVA resin powder, for example, a method of replacing the organic solvent in the PVA resin powder and the water in the water-containing gas in a tower-type apparatus has been proposed. (Patent Document 1).

  However, although the method of Patent Document 1 is excellent in reducing the content of the organic solvent, there is room for improvement in terms of removing methanol in the PVA resin powder.

JP-A-9-302024

  The present invention has been made in view of the above circumstances, and its purpose is to remove more methanol in the PVA polymer particles than the conventional method while suppressing thermal deterioration of the PVA polymer particles. is there.

The present inventors efficiently remove the methanol content remaining in the polymer particles by washing the PVA polymer particles obtained by polymerization and saponification in a methanol-containing solvent with ethanol. It was learned that it can be reduced, and the present invention has been completed. The reason why the alcohol in the particles can be efficiently reduced is presumed to be that ethanol easily penetrates into the PVA polymer particles and easily replaces the methanol present in the particles.

That is, the present invention comprises a step of polymerizing a monomer containing at least a vinyl ester monomer in a solvent containing methanol and then saponifying to prepare polyvinyl alcohol polymer particles, and the particles are mainly composed of ethanol. And a step of washing with a washing liquid.

  According to the present invention, since the methanol in the PVA polymer particles can be removed more than the conventional method while suppressing the thermal deterioration of the PVA polymer, the use in which methanol is a problem, for example, It becomes possible to apply the PVA polymer particles to uses such as foods, cosmetics, and medicines.

  Hereinafter, although the manufacturing method of the PVA polymer particle of this invention is demonstrated in detail, these show an example of a desirable embodiment. The production method of the present invention includes a step of obtaining PVA polymer particles and a step of washing the particles with a washing liquid. First, the process for obtaining PVA polymer particles will be described.

[Preparation process of PVA polymer particles]
As PVA used for the PVA polymer particles in the present invention, polyvinyl alcohol obtained by polymerizing a vinyl ester monomer and then saponifying is used. Vinyl ester monomers include vinyl formate, vinyl acetate, vinyl trifluoroacetate, vinyl propionate, vinyl butyrate, vinyl caprate, vinyl laurate, vinyl versatate, vinyl palmitate, vinyl stearate, etc. However, vinyl acetate is suitable for practical use.

  In the present invention, modified polyvinyl alcohol can be used. Examples of the modified polyvinyl alcohol include a saponification product of a copolymer obtained by copolymerizing a vinyl ester monomer and a monomer containing an ethylenically unsaturated monomer copolymerizable therewith, and a post-modified polyvinyl alcohol. .

  Examples of the copolymerizable ethylenically unsaturated monomer include olefins such as ethylene, propylene, isobutylene, α-octene, α-dodecene, α-octadecene, acrylic acid, methacrylic acid, crotonic acid, maleic acid, Unsaturated acids such as maleic anhydride and itaconic acid, salts or mono- or dialkyl esters thereof, nitriles such as acrylonitrile and methacrylonitrile, amides such as acrylamide and methacrylamide, ethylene sulfonic acid, allyl sulfonic acid, methallyl sulfone Olefin sulfonic acids such as acids or their salts, alkyl vinyl ethers, N-acrylamidomethyltrimethylammonium chloride, allyltrimethylammonium chloride, dimethylallyl vinyl ketone, N-vinyl pyrrolidone, chloride Nyl, vinylidene chloride, polyoxyethylene (meth) allyl ether, polyoxyalkylene (meth) allyl ether such as polyoxypropylene (meth) allyl ether, polyoxyethylene (meth) acrylate, polyoxypropylene (meth) acrylate, etc. Polyoxyalkylene (meth) acrylamides such as polyoxyalkylene (meth) acrylate, polyoxyethylene (meth) acrylamide, polyoxypropylene (meth) acrylamide, polyoxyethylene (1- (meth) acrylamide-1,1-dimethylpropyl) ) Ester, polyoxyethylene vinyl ether, polyoxypropylene vinyl ether, polyoxyethylene allylamine, polyoxypropylene allylamine, polyoxyethylene vinylamine Polyoxypropylene vinyl amine.

  Examples of the post-modification method include those obtained by converting polyvinyl alcohol into acetoacetate ester, acetalization, urethanization, etherification, grafting, and phosphate esterification.

  As the polymerization method, solution polymerization in which a monomer is polymerized in a solvent containing methanol is employed. The polymerization reaction is performed using a known radical polymerization catalyst such as azobisisobutyronitrile, acetyl peroxide, benzoyl peroxide, lauroyl peroxide, or various known low-temperature active catalysts. The reaction temperature is selected from the range of about 35 ° C. to the boiling point.

  The resulting polymer is then saponified either continuously or batchwise. In the saponification, either alkali saponification or acid saponification can be employed, but industrially, the copolymer is dissolved in alcohol and carried out in the presence of an alkali catalyst. Examples of the alcohol include methanol, ethanol, butanol and the like. The concentration of the polymer in the alcohol is selected from the range of 20 to 60% by weight. If necessary, about 0.3 to 10% by weight of water may be added. Furthermore, various esters such as methyl acetate and various solvents such as benzene, hexane and DMSO (dimethyl sulfoxide) are added. You may do it.

  Specific examples of the saponification catalyst include alkali catalysts such as alkali metal hydroxides and alcoholates such as sodium hydroxide, potassium hydroxide, sodium methylate, sodium ethylate, potassium methylate, and the like. The amount of is preferably 1 to 100 mmol equivalent to the monomer.

  It is preferable to dry the obtained PVA polymer particles with hot air or the like in a continuous or batch manner, and to remove a solvent such as methanol to some extent before a washing step described later. The methanol content contained in the dried PVA polymer particles is usually 1 to 10% by weight, particularly 1.5 to 5% by weight, and particularly preferably 2 to 4% by weight.

  The average degree of polymerization in the PVA polymer particles is usually 500 to 4000, preferably 1000 to 3000, particularly 1500 to 2500. If the average degree of polymerization is too high, the particles tend to become large due to drying and pulverization, and the cleaning efficiency tends to decrease, requiring a high temperature and long time cleaning. If the average degree of polymerization is too low, the particles become smaller due to drying and pulverization, and the efficiency of solid-liquid separation after washing tends to deteriorate. The average degree of polymerization can be determined according to the method for calculating the average degree of polymerization described in JISK6726.

  The degree of saponification in the PVA polymer particles is usually from 70 to 100 mol%, particularly preferably from 80 to 99 mol%, particularly preferably from 85 to 98 mol%. If the degree of saponification is too high, the cleaning liquid tends to hardly penetrate into the particles, and the cleaning efficiency tends to decrease, requiring high temperature and long time cleaning. When the saponification degree is too low, the PVA polymer particles are expanded by the cleaning liquid, and the solid-liquid separation property tends to be lowered. The saponification degree can be determined according to the saponification degree calculation method described in JIS K6726.

  The particle size of the PVA polymer particles is usually 40 to 6000 μm, particularly preferably 70 to 3000 μm, and particularly preferably 100 to 1700 μm. If the particle size is too large, the cleaning efficiency is lowered, and there is a tendency to require high temperature and long time cleaning. On the other hand, if the particle size is too small, the solid-liquid separation efficiency after washing tends to decrease. The particle size can be determined by particle size measurement using a vibration tap type measuring device.

[Washing process]
Next, the obtained PVA polymer particles are washed with a washing liquid. The washing liquid, washing liquid consisting mainly of d Tano Le is used. The cleaning liquid may further contain water, an alcohol having 4 or more carbon atoms, and a ketone (acetone, MEK, etc.). In particular, it is preferably a mixed washing solution of ethanol and water, and the water content is preferably 0.1 to 20% by weight, more preferably 0.1 to 15% by weight, particularly 1 to 10% by weight, especially 3 to 3%. 7% by weight is preferred. When there is too much content of water, there exists a tendency for a PVA polymer particle to melt | dissolve and to aggregate at the time of drying, and there exists a tendency for solid-liquid separability to fall.

  The cleaning method may be a continuous method (rotating cylindrical type, counter-current contact type, centrifugal sprinkling cleaning, etc.), but a batch method is usually adopted. Examples of the stirring method (apparatus) at the time of washing include a screw blade, a ribbon blender, and a kneader. The bath ratio (weight of cleaning solution / weight of PVA polymer particles) is usually from 1 to 30, particularly preferably from 2 to 20, particularly preferably from 3 to 10. If the bath ratio is too large, a large cleaning device is required, which tends to increase the cost. If the bath ratio is too small, the cleaning effect tends to decrease and the number of cleaning times tends to increase.

  The temperature at the time of washing is usually 20 to 80 ° C, particularly 30 to 70 ° C, particularly 35 to 65 ° C. If the temperature is too high, the volatilization amount of the cleaning liquid increases, and there is a tendency to require reflux equipment. If the temperature is too low, the methanol removal effect is reduced, and the bath ratio and the number of washings tend to increase. The washing time is usually 5 to 360 minutes, preferably 30 to 240 minutes, particularly preferably 60 to 90 minutes. If the cleaning time is too long, the production efficiency tends to decrease, and if the cleaning time is too short, the methanol removal effect tends to decrease. Moreover, the frequency | count of washing | cleaning is 1 to 5 times normally, Especially 1 to 3 times are preferable especially 1 to 2 times. If the number of washings is too large, the productivity tends to be poor and costs tend to increase. If the number of washings is too few, the methanol removal effect tends to be reduced.

[Drying process]
The washed PVA polymer particles are preferably dried. The drying temperature is usually from 50 to 150 ° C, particularly preferably from 70 to 130 ° C, particularly preferably from 80 to 110 ° C. If the drying temperature is too high, the PVA polymer particles tend to be thermally deteriorated. If the drying temperature is too low, the drying tends to take a long time. The drying time is usually 30 to 240 minutes, preferably 60 to 180 minutes, particularly preferably 90 to 150 minutes. If the drying time is too long, the PVA polymer particles tend to be thermally deteriorated, and if the drying time is too short, drying tends to be insufficient or high temperature drying is required. The degree of vacuum at the time of drying is usually 0 to 760 Toor, particularly preferably 0 to 500 Toor, particularly preferably 0 to 300 Toor.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further more concretely, this invention is not limited to a following example, unless the summary is exceeded. In the examples, “parts” and “%” mean weight basis unless otherwise specified.

[Example 1]
<Preparation of PVA polymer particles>
A reaction vessel equipped with a reflux condenser, a dropping funnel and a stirrer was charged with 750 parts of vinyl acetate and 117 parts of methanol, and 0.0043 mol% of acetyl peroxide (as opposed to the charged vinyl acetate) was added as a polymerization initiator and stirred. While increasing the temperature under a nitrogen stream, polymerization was started. When the polymerization rate of vinyl acetate reaches 68%, m-dinitrobenzene is added to complete the polymerization, and then unreacted vinyl acetate monomer is removed from the system by blowing methanol vapor. A methanol solution was obtained.

  Next, the methanol solution was further diluted with methanol, adjusted to a concentration of 33%, and charged into a kneader. While maintaining the solution temperature at 40 ° C., a 3.5% methanol solution of sodium hydroxide was added to the vinyl acetate structure in the polymer. Saponification was carried out at a rate of 2.0 mmol per 1 mol of unit. As the saponification progressed, the saponified product precipitated and became particulate, and then filtered, washed well with methanol and dried in a hot air dryer to prepare the desired PVA polymer particles.

  The degree of saponification determined according to JIS K 6726 of the obtained PVA polymer particles was 87.8 mol%, and the average degree of polymerization was 2200. Moreover, the average particle diameter calculated | required by the particle size measurement was 500 micrometers. The methanol content determined by gas chromatography was 2.91%.

<Washing of PVA polymer particles>
100 parts of the obtained PVA polymer particles were put into 500 parts of an ethanol / water mixture (washing liquid) with a water content of 6.2% heated to 40 ° C. (bath ratio 5), stirred for 60 minutes, and shaken off. After removing the cleaning liquid adhering to the particle surface, it was stirred and dried in a dryer under the conditions of 90 ° C., 0 Toor, and 120 minutes to obtain PVA polymer particles.

  The methanol content and ethanol content contained in the obtained PVA polymer particles were measured using gas chromatography. The results are shown in Table 1. The obtained PVA polymer particles did not show thermal degradation such as discoloration.

[Examples 2 to 4]
Cleaning was performed in the same manner as in Example 1 except that the water content of the ethanol / water mixture used as the cleaning liquid in Example 1 was as shown in Table 1 to obtain respective PVA polymer particles. In addition, as in Example 1, the methanol content and the ethanol content contained in these PVA polymer particles were measured, and the results are shown in Table 1. The obtained PVA polymer particles did not show thermal degradation such as discoloration.

[ Reference Example 1 ]
In Example 1, PVA polymer particles were obtained in the same manner as in Example 1 except that isopropanol was used instead of ethanol in the cleaning solution, the cleaning temperature was 70 ° C., and the cleaning time was 120 minutes. As in Example 1, the methanol content and ethanol content contained in the PVA polymer particles were measured, and the results are shown in Table 1. The obtained PVA polymer particles did not show thermal degradation such as discoloration.

[Comparative Example 1]
In Example 1, PVA polymer particles were obtained in the same manner as in Example 1 except that n-butanol was used instead of ethanol in the cleaning solution. As in Example 1, the methanol content and ethanol content contained in the PVA polymer particles were measured, and the results are shown in Table 1. The obtained PVA polymer particles did not show thermal degradation such as discoloration.

As shown in Table 1, in Examples 1 to 4 and Reference Example 1 , the methanol content in the PVA polymer particles can be reduced to about 1/8 to about 1/24 before washing, and n-butanol is reduced. It turns out that it becomes about 1/3 to about 1/8 of the methanol content when it is used and washed (Comparative Example 1). In addition, the methanol content decreases in the order of 0.1%, 12.2%, 3.1%, 6.2% in the water content of the ethanol washing liquid, and the water content in the alcohol is 0.1 to It can also be seen that 15%, in particular 1-10%, in particular 3-7%, is preferred.

  According to the method for producing polyvinyl alcohol polymer particles of the present invention, it is possible to obtain PVA polymer particles in which the content of methanol is lower than that of the conventional one. Therefore, the PVA polymer particles are used as foods and cosmetics. It can be used as a constituent material such as chemicals or a packaging material thereof. For example, it can be used as a binder in the production process of tablets and the like, a suspending agent contained in cosmetics, and a molding film molding material.

Claims (2)

A step of polymerizing a monomer containing at least a vinyl ester monomer in a solvent containing methanol and then saponifying to prepare particles of a polyvinyl alcohol polymer; and a step of washing the particles with a washing liquid mainly composed of ethanol ; The manufacturing method of the polyvinyl-alcohol-type polymer particle containing this. The method for producing polyvinyl alcohol polymer particles according to claim 1, wherein the cleaning liquid is a mixed cleaning liquid of ethanol and water, and the water content is 0.1 to 20% by weight.