Process of producing vinyl acetate polymer

Abstract: The present invention provides a process of producing a vinyl acetate polymer by homopolymerization of a vinyl acetate monomer or copolymerization of a vinyl acetate monomer and another copolymerizable comonomer, wherein a polymerization initiator is an organic peroxide having a half life at 60°C of 10 to 110 minutes, and a polymerization liquid contains at least one carboxylic acid or its salt, said carboxylic acid being selected from the group consisting of a hydroxycarboxylic acid and a polycarboxylic acid. According to the process of producing a vinyl acetate polymer of the present invention, the amount of soluble matters is decreased in a waste liquid generated by saponification of the vinyl acetate polymer, the amount of insoluble matters is decreased in a solvent for preparing a solution of the vinyl alcohol polymer obtained by saponification of the vinyl acetate polymer, the transparency of the solution of the vinyl alcohol polymer obtained by saponification of the vinyl acetate polymer is improved, and the odor of the vinyl alcohol polymer obtained by saponification of the vinyl acetate polymer is decreased.

Description: The present invention relates to a process of producing a vinyl acetate polymer (hereinafter referred to as "PVAc", which includes a copolymer) by homopolymerization of a vinyl acetate monomer (hereinafter referred to as "VAc") or copolymerization of VAc and another comonomer copolymerizable with VAc. Hitherto, a solution polymerization, a bulk polymerization, a suspension polymerization, an emulsion polymerization and the like are known as a process of polymerizing VAc. A persulfate salt such as potassium persulfate, an azo compound such as azobisisobutyronitrile and an organic peroxide such as benzoyl peroxide are typically used as a polymerization initiator for the polymerization. PVAc obtained by the polymerization of VAc is converted by saponification to polyvinyl alcohol (hereinafter referred to as "PVA", which includes a copolymer) which is industrially useful. Japanese Patent Kokai Publication No. Heisei 4-213302 (hereinafter referred to as "known item A") discloses a specified organic peroxide which is used as a polymerization initiator. Japanese Patent Kokai Publication No. Showa 58-222102 (hereinafter referred to as "known item B") discloses that saponification of a copolymer obtained by copolymerizing ethylene and VAc by using a radical initiator having a half life at 60°C of at most 2 hours and a polymerization solvent of methanol or tert-butyl alcohol gives a film having excellent surface properties. Japanese Patent Kokoku Publication No. Showa 37-10590 (hereinafter referred to as "known item C") discloses that saponification of PVAc obtained by solution-polymerizing VAc in the presence of a specified organic acid or its salt gives PVA having excellent whiteness. Japanese Patent Kokoku Publication No. Showa 36-16446 (hereinafter referred to as "known item D") discloses that saponification of PVAc obtained by solution-polymerizing VAc in the presence of a specified organic acid reduces the decrease of the degree of polymerization of PVA. However, when PVAc produced by the conventional polymerization process disclosed in the known items A-D is saponified, the waste liquid generated by saponification contains a large amount of soluble matters so that there have been caused problems such as environmental pollution, clogging of a filter in treatment of waste liquid and increase of treatment cost. Frequently, PVA is usually dissolved in a solvent such as water and is used in the form of a solution. However, PVA obtained by the conventional process may cause the problems that the insoluble matters in a solvent such as water are increased and that the transparency of the solution is decreased when an aqueous solution is used. In addition, PVA obtained by using the persulfate salt, the azo compound or the organic peroxide as the polymerization initiator may cause the problem that odor is evolved, for example, when PVA is heated. The object of the present invention is to provide a process of producing PVAc which gives the following effects; the amount of soluble matters is decreased in a waste liquid generated by saponification of PVAc, the amount of insoluble matters is decreased in a solvent for preparing a solution of PVA obtained by saponification of PVAc, the transparency of the solution of PVA obtained by saponification of PVAc is improved, and the odor of PVA obtained by saponification of PVAc is decreased. The present invention relates to a process of producing a vinyl acetate polymer by homopolymerization of a vinyl acetate monomer or copolymerization of a vinyl acetate monomer and another copolymerizable comonomer, wherein a polymerization initiator is an organic peroxide having a half life at 60°C of 10 to 110 minutes, and a polymerization liquid contains at least one carboxylic acid or its salt, said carboxylic acid being selected from the group consisting of a hydroxycarboxylic acid and a polycarboxylic acid, provided that the addition of a polyvinyl alcohol having a saponification degree of 95 mol% or more is excluded. The disclaimer is formulated in view of JP-A-51-11888. The monomer used in the present invention includes VAc, and another comonomer copolymerizable with VAc. It is preferable to decrease the amount of the copolymerizable comonomer and it is particularly preferable to use VAc alone. Specific examples of the comonomer copolymerizable with VAc are nonionic monomers, for example, olefins such as ethylene and propylene,hydroxyolefins such as 7-octen-1-ol, (meth)acrylate esters such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, allyl compounds such as allyl acetate and allyl chloride, (meth)acrylonitrile, and vinyltrimethoxysilane; anionic monomers such as itaconic acid, maleic acid, maleic anhydride, (meth)acrylic acid, fumaric acid, crotonic acid and (meth)allylsulfonic acid; and cationic monomers such as 3-(meth)acrylamido-propyltrimethylammonium chloride. The degree of polymerization of the PVAc obtained by the present invention is preferably from 50 to 30,000, more preferably from 100 to 20,000, particularly from 200 to 5,000. The degree of polymerization referred to in the present invention means a viscosity-average degree of polymerization of PVA obtained by saponification of PVAc. A fully saponified product and a partially saponified product are obtained from PVAc obtained by the present invention. The degree of saponification of PVA is preferably at least 60 mol%, more preferably from 70 to 99.9 mol%. The polymerization initiator used in the present invention is an organic peroxide having a half life at 60°C of 10 minutes to 110 minutes. The half life of the organic peroxide is preferably from 15 minutes to 100 minutes, more preferably from 20 minutes to 80 minutes. Specific examples of the organic peroxide are isobutyl peroxide (IBP), di-isopropyl peroxydicarbonate (IPPDC), di-allyl peroxydicarbonate (APDC), di-n-propyl peroxydicarbonate (NPPDC), di-myristyl peroxydicarbonate (MSPDC), di(2-ethoxyethyl) peroxydicarbonate (EEPDC), di(2-ethylhexyl) peroxydicarbonate (EHPDC) and di(methoxyisopropyl) peroxydicarbonate (MIPPDC). Among them, the peroxydicarbonates are particularly preferable. Hereinafter, a name of the organic peroxide is indicated by the above abbreviation in parenthesis. A method of using the organic peroxide is preferably a method of diluting the organic peroxide with a suitable solvent and supplying it to a polymerization vessel in view of the prevention of activation decrease of the organic peroxide, and the establishment of polymerization stability and handling safety. Specific examples of the solvent for dilution are lower aliphatic alcohols such as methanol, aliphatic hydrocarbons such as isoparaffin, aromatic compounds such as dimethyl phthalate, and mixtures thereof. In the case of IBP, IPPDC, APDC, EEPDC, EHPDC and the like, an aliphatic hydrocarbon such as isoparaffin is preferable. In the case of NPPDC, MSPDC, MIPPDC, EHPDC and the like, a lower aliphatic alcohol such as methanol is preferable. The supply amount of the organic peroxide is preferably from 1 x 10-3 to 1 x 10 -7 mol, more preferably from 5 x 10 -4 to 1 x 10 -6 mol, per 1 mol of the monomer (the total amount of the monomers in the case of the copolymer). If the supply amount of the organic peroxides is larger than the above upper limit, there may be the possibility that insoluble matters in the solvent for PVA are increased and that odor of PVA is increased. If the supply amount of the organic peroxide is smaller than the above lower limit, there may be the possibility that the fluctuation of a polymerization conversion is increased so that a stable continuous production is difficult to conduct. Specific examples of the hydroxycarboxylic acids and polycarboxylic acids used in the present invention are glycolic acid, lactic acid, glyceric acid, malic acid, tartaric acid, citric acid, salicylic acid, malonic acid, succinic acid, maleic acid, phthalic acid, oxalic acid, glutaric acid and the like. Among them, the saturated aliphatic hydroxycarboxylic acids are preferable and the saturated aliphatic hydroxypolycarboxylic acids are particularly preferable. The above carboxylic acid may be in the form of a salt, which may be an alkaline metal salt, an alkaline earth metal salt, an ammonium salt and the like. In the case of the polycarboxylic acid, the salt may be one in which a part of the carboxyl groups are salified or one in which all of the carboxyl groups are salified. However, a carboxylic acid with no salt (namely, a free carboxylic acid) is particularly preferable in the present invention. The supply amount of the carboxylic acid is preferably from 1 ppm to 500 ppm, more preferably from 3 ppm to 300 ppm, most preferably from 5 ppm to 200 ppm, based on the weight of VAc. A method of supplying the carboxylic acid includes a method of supplying the carboxylic acid alone to a polymerization vessel, a method of supplying a solution of the carboxylic acid to a polymerization vessel, a method of previously adding the carboxylic acid to the monomer such as vinyl acetate before polymerization, a method of supplying the carboxylic acid together with the polymerization initiator to a polymerization vessel, and a combination of the above methods. A batch polymerization process gives a good effect of the present invention, but a continuous polymerization process, particularly a continuous solution polymerization process exhibits the best effect. The present invention will be illustrated in detail by the following Examples. In the following Examples, "%" stands for "% by weight", unless specified. A method of measuring the half life of a polymerization initiator: A solution of a polymerization initiator having the concentration of 0.05 to 0.1 mol/liter (mol/L) is prepared by using a solvent inert to the polymerization initiator such as benzene and poured into a glass tube. The atmosphere of the tube is replaced with a nitrogen gas and the tube is immersed in a temperature-controlled bath adjusted to 60°C. After a given time, the concentration of the polymerization initiator is measured by a known method. The time at which the concentration of the polymerization initiator is a half of the initial concentration is determined as half life from passing of time and the polymerization initiator concentration. A known method is suitably adopted as a quantitative analysis of the polymerization initiator. For example, the following method can be exemplified as the quantitative analysis of the polymerization initiator. A quantitative analysis of an organic peroxide: In a flask, 30 milliliters (mL) of isopropyl alcohol, 2 mL of glacial acetic acid and 2 mL of a saturated solution of potassium iodide, based on about 0.5 g of a sample (an organic peroxide) are charged in this order, and then the weighed sample (organic peroxide) is charged. A reflux condenser is attached to the flask and then the mixture is gently boiled on a hot plate for 3 minutes. Immediately after the reflux condenser is removed from the flask, sodium thiosulfate is titrated till the disappearance of color of iodine and the amount of the organic peroxide is calculated from the titration amount thereof. The effect of the present invention was evaluated according to the following methods. (1) Soluble matters in waste liquid generated by saponification A waste liquid generated by saponification of PVAc is evaporated to dryness at a temperature of 100°C and the weight of the residue is measured. The weight of the residue is converted to percentage per unit weight of PVA obtained by saponification of PVAc. (2) Insoluble matters in solvent for PVA PVA is added to a solvent to give a concentration of 10 % and a dissolution operation is conducted at 90°C for one hour. The resultant solution is filtered with a metal net of 250 mesh, and the weight of insoluble matters left on the net is measured. The weight of the insoluble matters is converted to ppm per unit weight of PVA. When PVA is water-soluble, water is used as solvent. When PVA is water-insoluble or poorly water-soluble, a good solvent (for example, dimethylsulfoxide, water/isopropyl alcohol mixture solvent) is suitably selected. (3) Transparency of PVA solution Transparency of the PVA solution having a concentration of 10 % which is obtained in the above item (2) is measured at a temperature of 20°C by a D-type photoelectric tube colorimeter manufactured by Shimadzu Corp. (4) Odor of PVA PVA (20 grams) is charged in a glass test tube (internal diameter: 4 cm, height: 11 cm). The tube is sealed and heated in a water bath at 95°C for 3 hours. Immediately after the tube is cooled to 20°C and opened, the strength of odor evolved in the tube is sensually evaluated. The evaluation results are indicated by the following symbols: ○ ○ : Very weak odor and excellent ○ : Weak odor and good Δ : Strong odor and poor X : Very strong odor and very poor Example 1 VAc was continuously polymerized in a 10 L polymerization vessel having a cooling coil in an internal part and equipped with a four-blade paddle stirrer by using di-isopropyl peroxydicarbonate (IPPDC) as a polymerization initiator and lactic acid as a hydroxycarboxylic acid, under the following conditions. Supply amount of VAc 1,000 g/hr Supply amount of a 0.04% solution of lactic acid in methanol 50 g/hr Supply amount of a 0.08% solution of IPPDC in methanol 50 g/hr Supply amount of methanol 150 g/hr Polymerization temperature 60°C Average residence time 5 hr Then, the obtained polymerization solution was fed to a middle portion of a purge column, methanol vapor was supplied to the bottom of said column and the unreacted VAc is purged from the top of said column to give a solution of PVAc in methanol. Sodium hydroxide was added to the obtained solution of PVAc in methanol. The solution was saponified at 40°C and dried at 120°C for 2 hours to give PVA having a degree of polymerization of 1,700 and a degree of saponification of 98.5 mol%. The evaluation results are shown in Table 1. Examples 2 to 11 and Comparative Examples 1 to 7 PVAc was obtained by polymerizing VAc in the same manner as in Example 1, except that a polymerization initiator and an acid shown in Table 1 or 2 were used. Then, a solution of PVAc in methanol was prepared and saponified to give PVA. The evaluation results are shown in Tables 1 and 2. Example No. Polymerization Initiator Acid Evaluation results Type Half life (min.) Soluble matters in waste liquid (%) Insoluble matters in solvent for PVA (ppm) Transparency of PVA solution (%) Odor 1 IPPDC 35 Lactic acid 0.2 40 96 ○ 2 MSPDC 52 Oxalic acid 0.3 50 97 ○ 3 IPPDC 35 Tartaric acid 0.1 30 98 ○○ 4 NPPDC 44 Citric acid 0.1 25 98 ○○ 5 NPPDC 44 Lactic acid 0.2 40 96 ○ 6 IPPDC 35 monosodium malate 0.3 55 96 ○ 7 EHPDC 51 Tartaric acid 0.1 30 98 ○○ 8 EEPDC 45 Oxalic acid 0.3 40 96 ○ 9 MIPPDC 45 Citric acid 0.1 35 98 ○○ 10 EHPDC 51 Monopotassium tartrate 0.3 45 96 ○ 11 EHPDC 51 Dipotassium tartrate 0.4 55 95 ○ Comparative Example No. Polymerization Initiator Acid Evaluation results Type Half life (min.) Soluble matters in waste liquid (%) Insoluble matters in solvent for PVA (ppm) Transparency of PVA solution (%) Odor 1 MSPDC 52 min. None 1.6 500 90 Δ 2 NPPDC 44 min. None 1.5 600 88 Δ 3 LP 13 hr. Oxalic acid 1.1 1,100 92 X 4 AIBN 32 hr. Tartaric acid 1.5 1,250 90 X 5 AP 32 hr. Citric acid 1.3 1,500 91 X 6 IPPDC 35 min. Acetic acid 1.5 750 89 X 7 EHPDC 51 min. Sulfuric acid 1.7 800 92 X (Explanation of abbreviations in Tables 1 and 2) MSPDC : Di-myristyl peroxydicarbonate IPPDC : Di-isopropyl peroxydicarbonate NPPDC : Di-n-propyl peroxydicarbonate EHPDC: Di(2-ethylhexyl) peroxydicarbonate EEPDC: Di(2-ethoxyethyl) peroxydicarbonate MIPPDC: Di(methoxyisopropyl) peroxydicarbonate LP: Lauroyl peroxide AIBN : Azobisisobutyronitrile AP: Acetyl peroxide According to the process of producing PVAc of the present invention, the amount of soluble matters is decreased in a waste liquid generated by saponification of PVAc, the amount of insoluble matters is decreased in a solvent for preparing the solution of PVA obtained by saponification of PVAc, the transparency of the solution of PVA obtained by saponification of PVAc is improved, and the odor of PVA obtained by saponification of PVAc is decreased.

Claims: A process of producing a vinyl acetate polymer by homopolymerization of a vinyl acetate monomer or copolymerization of a vinyl acetate monomer and another copolymerizable comonomer, wherein the polymerization initiator is an organic peroxide having a half life at 60°C of 10 to 110 minutes, and the polymerization liquid contains at least one carboxylic acid or its salt, said carboxylic acid being selected from the group consisting of a hydroxycarboxylic acid and a polycarboxylic acid, provided that the addition of a polyvinyl alcohol having a saponification degree of 95 mol% or more is excluded. The process of producing a vinyl acetate polymer according to claim 1, wherein the organic peroxide is a peroxydicarbonate. The process according to claim 1 or 2, wherein the supply amount of the organic peroxide is from 1x10 -3 to 1x10 -7 mol per mol of the monomer. The process of producing a vinyl acetate polymer according to claim 1 to 3, wherein the carboxylic acid compound is a hydroxypolycarboxylic acid. The process according to claim 1 to 4, wherein the supply amount of the carboxylic acid is from 1 ppm to 500 ppm based on the weight of VAc.

Inventors: TAKACHI HIROSHI, YOSHIMI KAZUYORI, TAKACHI, HIROSHI, YOSHIMI, KAZUYORI
Applicants: KURARAY CO, KURARAY CO., LTD.
Application year: 1997
Main classification: C08F18
IPC codes: C08F18, C08F2