JP3474307B2 - Dispersion stabilizer for suspension polymerization of vinyl compounds - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dispersion stabilizer for suspension polymerization of vinyl compounds. More specifically, the present invention relates to a dispersion stabilizer for suspension polymerization of a vinyl compound such as vinyl chloride, which has an excellent defoaming effect. [0002] When a vinyl polymer such as a vinyl chloride resin is produced industrially, a vinyl compound such as vinyl chloride is dispersed in an aqueous medium in the presence of a dispersion stabilizer. Suspension polymerization in which polymerization is performed using an oil-soluble catalyst is widely performed. In general, factors that control the quality of the vinyl polymer include a polymerization rate, a water-monomer ratio, a polymerization temperature, a type and amount of a catalyst, a type of a polymerization tank, a stirring speed, and a type of a dispersion stabilizer. In particular, the effect of the type of dispersion stabilizer is very large. [0003] The performance required of a dispersion stabilizer for suspension polymerization of vinyl compounds is that the obtained vinyl polymer particles have the function of sharpening the particle size distribution as much as possible, and the plasticizer absorption rate is greatly increased. Each polymer particle is made porous to facilitate processability, facilitate the removal of monomers such as vinyl chloride remaining in the polymer particles, and prevent the formation of fish eyes and the like in molded products. And a function of forming polymer particles having a large filling specific gravity. Conventionally, as a dispersion stabilizer for suspension polymerization of a vinyl compound, a cellulose derivative such as methylcellulose or carboxymethylcellulose or partially saponified polyvinyl alcohol has been used alone or in combination. However,
The conventional dispersion stabilizer has a problem that it does not satisfy the above-mentioned requirements. [0004] Suspension polymerization of vinyl compounds such as vinyl chloride is usually carried out in a batch system, and an aqueous medium, a dispersion stabilizer, a polymerization initiator, a vinyl compound and the like are charged into a polymerization vessel, and further required. A general method is to add an additive and then raise the temperature to cause a polymerization reaction. Recently, it has been required to shorten the time required for one batch of polymerization in order to improve productivity. In suspension polymerization of vinyl compounds, a reflux condenser or the like is installed to increase the efficiency of removing heat of polymerization. In addition, a method of shortening the heating time by a method of charging an aqueous medium heated in advance (hot charging method) is used. However, when a conventional dispersion stabilizer for suspension polymerization of a vinyl compound is used, the foaming during the polymerization is severe, so that the effective volume in the polymerization vessel is reduced and the productivity is reduced. The use of a polymerization reactor has a fatal drawback in that the temperature cannot be controlled, and the use of the hot charge method results in a decrease in the porosity of the vinyl polymer particles. On the other hand, when an antifoaming agent or the like is added to prevent foaming, there is a problem that the thermal stability of the resulting vinyl polymer particles is reduced. Poval (publisher: Polymer Publishing Association, 198
4) [Publication (a)] discloses, as a dispersion stabilizer for suspension polymerization of vinyl chloride, polyvinyl alcohol having a polymerization degree of 2,000 and a saponification degree of 80 mol%, and a polymerization degree of 700 to 80.
0, a polyvinyl alcohol having a saponification degree of 70 mol% is described. However, the dispersion stabilizers described in the publicly known document (a) have a drawback that satisfactory performance cannot be obtained with respect to the above requirements and foamability during polymerization is severe. Japanese Patent Publication No. 5-88251 [Publication (b)]
Has an average degree of polymerization of 500 or more, a ratio of the weight average degree of polymerization to the number average degree of polymerization of 3.0 or less, has a carbonyl group in the molecule, and has a vinylene group adjacent thereto,
280 nm by UV absorption spectrum of 0.1% aqueous solution
And the absorbance at 320 nm are 0.3 or more and 0.1, respectively.
A dispersion stabilizer for suspension polymerization of a vinyl compound comprising polyvinyl alcohol having a ratio of absorbance at 320 nm to 280 nm of at least 5 and at least 0.30 is described.
However, the dispersion stabilizer described in the known document (b) has a problem that the foaming property in the polymerization vessel is severe. SUMMARY OF THE INVENTION An object of the present invention is to provide a conventional general suspension polymerization method for vinyl compounds, in which an aqueous medium at room temperature is charged into a polymerization vessel (cold charge method) and In addition to the method of controlling the polymerization temperature using the jacket or coil inside the polymerization vessel, the defoaming inside the polymerization vessel is also possible in the method using a polymerization vessel with a condenser, the hot charge method and the hot charge method using a polymerization vessel with a condenser. An object of the present invention is to provide a dispersion stabilizer which is extremely excellent in effect and simultaneously satisfies the above-mentioned requirements. The inventors of the present invention have conducted intensive studies in order to solve the above-mentioned problems. As a result, the absorbance (a) at 280 nm of the aqueous solution of 0.1% by weight in the ultraviolet absorption spectrum was determined. 0. 25 or more , and the absorbance (b) at 320 nm of the aqueous solution at an ultraviolet absorption spectrum of 0.03 or more, and the ratio of absorbance (b) / absorbance (a) to 0. 2 or less and the residual acetate group block character is 0.4
The present inventors have found a dispersion stabilizer for suspension polymerization of a vinyl compound comprising a polyvinyl alcohol-based polymer as described above, and have completed the present invention. The present invention will be described in more detail. The preferred range of the degree of saponification of the polyvinyl alcohol-based polymer of the present invention is 60 to 88 mol%, more preferably 65 to 75 mol%, even more preferably 68 to 74 mol%. The preferred range of the viscosity average degree of polymerization (hereinafter abbreviated as average degree of polymerization) of the polyvinyl alcohol polymer is 5
00 to 1500, more preferably 600 to 1200, and still more preferably 680 to 900. The polyvinyl alcohol-based polymer of the present invention has an absorbance (a) at 280 nm of a 0.1% by weight aqueous solution in an ultraviolet absorption spectrum of 0.25 or more . The absorbance (b) at 320 nm of the aqueous solution at an ultraviolet absorption spectrum thereof is 0.03 or more, and preferably 0.05 to 0.2. Absorbance (b) / absorbance (a) is 0.2
It is as follows . The block character of the residual acetic acid group of the polyvinyl alcohol polymer of the present invention is 0.4 or more, preferably 0.43 or more, more preferably 0.5 or more. Here, regarding the block character of the residual acetic acid group, Povar (publisher: Polymer Publishing Association, 1984) and Macromolecules, 10, 532 (19)
77) details the measurement method and the like. The method for producing the polyvinyl alcohol-based polymer of the present invention is not particularly limited. However, when a vinyl ester monomer is subjected to radical polymerization, a compound having a carbonyl group in the molecule such as acetaldehyde or butyl aldehyde may be used. A simple and efficient method is to saponify the vinyl ester polymer by treating the resulting polymer with an alkali such as sodium hydroxide or ammonia, or an acid such as hydrochloric acid or paratoluenesulfonic acid. The method for making the residual acetic acid group block character of the polyvinyl alcohol-based polymer of the present invention 0.4 or more can be obtained by saponifying the raw material polyvinyl ester. Even when the raw material polyvinyl ester is subjected to alkali saponification, it can be obtained by heat-treating the obtained polyvinyl alcohol-based polymer. In this case, before heat-treating the obtained polyvinyl alcohol-based polymer, the polyvinyl alcohol-based polymer is washed with an organic solvent such as acetone, methanol, and methyl acetate, and the content of a salt such as sodium acetate is reduced by the polyvinyl alcohol-based polymer. A method of performing heat treatment after reducing the content to 0.7% by weight or less, preferably 0.5% by weight or less with respect to the coalescence is suitable. Examples of the vinyl ester for radical polymerization of the vinyl ester monomer include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl versatate, vinyl caproate, vinyl caprylate, Examples include vinyl caprylate, vinyl laurate, vinyl palmitate, vinyl stearate, and vinyl oleate. In the polyvinyl alcohol-based polymer used in the present invention, an ionic group such as an ammonium group, a carboxyl group or a sulfone group, a nonionic group or a (long chain) alkyl group may be introduced in an amount of 10 mol% or less. In this case, the degree of saponification is determined from the vinyl ester group and the vinyl alcohol group, and does not include the introduced ionic group or the like. Although the polyvinyl alcohol-based polymer (A) of the present invention exhibits excellent performance when used alone as a dispersion stabilizer, the polyvinyl ester-based polymer (B) having a saponification degree of less than 60 mol% is In the combination system of the above, the weight ratio (A) / (B) of the component (A) and the component (B) is 40/6.
When the ratio is 0 to 95/5, better performance is exhibited. The degree of saponification of the polyvinyl ester polymer (B) is less than 60 mol%, preferably from 20 to 55 mol%, more preferably from 25 to 45 mol%. The weight ratio (A) / (B) of component (A) and component (B) is 40/6
0/95/5, more preferably 50 / 50-90 / 10, and even more preferably 60 / 40-80 / 20. When the weight ratio (A) / (B) of the component (A) and the component (B) is more than 95/5, the porosity improvement effect may not be obtained, and when the weight ratio is less than 40/60, the porosity may not be improved. Stability may be lost. The degree of polymerization of the polyvinyl ester polymer (B) is not particularly limited.
00 or less, more preferably 100 to 550,
200-400 is even more preferred. The polyvinyl ester polymer (B) may be water-insoluble or water-dispersible, and may have self-emulsifiability by introducing an ionic group or the like. In the present invention, a form in which the polyvinyl ester-based polymer (B) is used in combination as the dispersion aid with the dispersion stabilizer of the polyvinyl alcohol-based polymer of the present invention is also referred to as a dispersant stabilizer. The method for producing the polyvinyl ester polymer (B) is not particularly limited, and conventionally known ones are suitably used. For example, a polyvinyl ester polymer having an ionic group in a side chain described in JP-A-1-95103,
WO 91/15518, a polyvinyl ester polymer having an ionic group at the terminal, and a known polyvinyl ester polymer having a nonionic group or a (long chain) alkyl group of 10 mol% or less are preferably used. Next, a method for producing a vinyl polymer by suspension polymerization of a vinyl compound using the dispersion stabilizer of the present invention will be described. The temperature of the aqueous medium used in the method for producing a vinyl polymer is not particularly limited, and cold water of about 20 ° C. and hot water of 90 ° C. or more are suitably used. The medium constituting this heated aqueous medium is, in addition to pure water,
An aqueous medium containing various additive components or an aqueous medium containing another organic solvent can be used. Further, the supply amount when the heated aqueous medium is charged into the polymerization reaction system may be an amount that can sufficiently heat the polymerization reaction system. Further, in order to enhance the heat removal efficiency, a polymerization vessel equipped with a reflux condenser is also preferably used. In the method for producing a vinyl-based polymer, the amount of the dispersion stabilizer is not particularly limited, but is usually 5 parts by weight or less based on 100 parts by weight of the vinyl-based compound, and is preferably from 0.01 to
1 part by weight is preferred, and 0.02 to 0.2 part by weight is even more preferred. The dispersion stabilizer of the present invention may be used alone, but a saponification degree of 65 to 98 which is usually used when suspension-polymerizing a vinyl compound such as vinyl chloride in an aqueous medium.
Mol% of polyvinyl alcohol, water-soluble cellulose ethers such as methylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, water-soluble polymers such as gelatin, sorbitan monolaurate, sorbitan triolate, glycerin tristearate, ethylene oxide propylene oxide block An oil-soluble emulsifier such as a copolymer, a water-soluble emulsifier such as polyoxyethylene sorbitan monolaurate, polyoxyethylene glycerin oleate, and sodium laurate may be used in combination. The amount added is not particularly limited, but is preferably 0.01 to 1.0 part by weight per 100 parts by weight of a vinyl compound such as vinyl chloride. Other various additives can be added as needed. Examples of the various additives include polymerization degree regulators such as acetaldehyde, butyraldehyde, trichloroethylene, perchloroethylene, and mercaptans, and polymerization inhibitors such as phenol compounds, sulfur compounds, and N-oxide compounds. It is also optional to add a pH adjuster, a scale inhibitor, a crosslinking agent, and the like, and a plurality of the above additives may be used in combination.
On the other hand, the polymerization initiator may be any of those conventionally used for the polymerization of vinyl compounds such as vinyl chloride. Examples thereof include diisopropyl peroxydicarbonate and di-2-carbonate.
Ethylhexyl peroxydicarbonate, percarbonate compounds such as diethoxyethyl peroxydicarbonate, t-butyl peroxyneodecanate, α-
Perester compounds such as cumylperoxyneodecanate and t-butylperoxyneodecanate, acetylcyclohexylsulfonyl peroxide, 2,4,4-
Peroxides such as trimethylpentyl-2-peroxyphenoxyacetate, 2,2'-azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile,
Examples include azo compounds such as azobis (4-methoxy-2,4-dimethylvaleronitrile) and the like, and further, potassium persulfate, ammonium persulfate, hydrogen peroxide and the like can be used in combination. Examples of the vinyl compound which can be subjected to suspension polymerization using the dispersion stabilizer of the present invention include, in addition to vinyl chloride alone, a monomer mixture mainly composed of vinyl chloride (50 wt. % Or more), and examples of the comonomer copolymerized with vinyl chloride include vinyl esters such as vinyl acetate and vinyl propionate, and (meth) acrylic acid such as methyl (meth) acrylate and ethyl (meth) acrylate. Examples include esters, olefins such as ethylene and propylene, maleic anhydride, acrylonitrile, itaconic acid, styrene, vinylidene chloride, vinyl ether, and other monomers copolymerizable with vinyl chloride. Further, the dispersion stabilizer of the present invention can be used for homopolymerization or copolymerization of the above vinyl compound containing no vinyl chloride. In the suspension polymerization using the dispersion stabilizer of the present invention, the charge ratio of each component, the polymerization temperature, etc. may be determined according to the conditions conventionally used in suspension polymerization of vinyl compounds such as vinyl chloride. Good.
The order and ratio of the vinyl compound, the polymerization initiator, the dispersion stabilizer, the heated aqueous medium, and other additives are not limited at all. In addition, a method in which warm water is used and the vinyl compound is heated before the vinyl compound is charged into the polymerization vessel is also preferably used. EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the present invention. In the following examples, “%” and “parts” are “% by weight” unless otherwise specified.
And "parts by weight". Production Example [Polyvinyl alcohol polymer] 5235 parts of vinyl acetate (hereinafter abbreviated as VAc), 380 parts of methanol and 115 parts of acetaldehyde were placed in a reaction vessel, and the inside was sufficiently purged with nitrogen. When the internal temperature reached 60 ° C., 20 parts of a methanol solution containing 1 part of 2,2′-azobisisobutyronitrile previously substituted with nitrogen was added. The polymerization rate after 5 hours was 60.7%. After 5 hours, the vessel was cooled, and the operation of purging the remaining VAc and the like under reduced pressure together with methanol to the outside of the system was performed while adding methanol to obtain a methanol solution of polyvinyl ester (hereinafter abbreviated as PVAc) (concentration: 55). %). A part of this methanol solution was taken, and the PVAc concentration was 30%, the water content was 2%, and [NaOH] /
Performed saponified with [VAc] = 0.05 (molar ratio), after which the polyvinyl alcohol obtained (PVA) was purified by sock scan rate washing with methanol, was 99.2 mol% as measured degree of saponification. The intrinsic viscosity was measured at 30 ° C. in water, and the average degree of polymerization was calculated to be 780.
Met. Next, take a part of the above methanol solution, water,
Methanol and methyl acetate were added and [NaOH] / [VA
c] = 0.02 (molar ratio), a methanol solution of NaOH was added, the PVAc concentration was 20%, and the water content was 1
% And methyl acetate 30% at 40 ° C.
Five minutes after the addition of the alkali, the system gelled, so the mixture was pulverized with a mixer, a mixed solution of methyl acetate / water = 8/2 was added in the same amount as the saponification system, and the mixture was heated to 60 ° C. and the reaction was continued for another hour. . Thereafter, the saponified product (PVA) was filtered and dried at 60 ° C. in a hot air drier to obtain PVA. The resulting PVA, was purified by performing a sock scan rate washing with methanol for 10 hours. Isokinetic electrophoresis (isotacophoresis)
Was determined to be 0.48%. Thereafter, heat treatment was performed in a hot-air dryer at 150 ° C. in an air atmosphere for 4 hours. The measured degree of saponification was 72 mol%. The absorbance at 280 nm and 320 nm of the 0.1% aqueous solution in the ultraviolet absorption spectrum was 0.4
5, 0.08. The residual acetic acid group block character measured by ¹³ C- NMR was 0.46.
Met. By appropriately changing the amount of VAc, methanol, acetaldehyde, or the like charged, or using an alkali or an acid as a saponification catalyst, and appropriately changing the temperature and time of the heat treatment in a hot-air dryer, a polyvinyl alcohol-based polymer as shown in Table 1 is obtained. Was prepared. [Polymerization of vinyl chloride] In a glass-lined autoclave equipped with a reflux condenser, 1 part of deionized water in which the dispersion stabilizer shown in Table 1 (Examples 1 to 7 and Comparative Examples 1 to 6 ) was dissolved, and 0.04 parts of a 70% toluene solution of diisopropyl peroxydicarbonate was charged, and the inside of the autoclave was moved to 50 mm.
After degassing until Hg to remove oxygen, 8
39 parts of 0 ° C. warm water and 30 parts of vinyl chloride monomer were simultaneously charged. The liquid level at the end of the charging was 60% above the bottom of the polymerization vessel, and the internal temperature was 50 ° C. Thereafter, the polymerization was continued while the internal temperature was kept at 50 ° C. At the start of polymerization, the pressure inside the autoclave is 7.0 kg / cm ² G
Was 4.0 kg / cm ² G 6 hours after the start of the polymerization.
At the time of, the polymerization was stopped, the unreacted vinyl chloride monomer was purged, the contents were taken out and dehydrated and dried. The performance of the obtained vinyl chloride resin was evaluated by the following method,
Table 2 shows the results. The polymerization yield of the vinyl chloride polymer was 85%, and the average degree of polymerization was 1,300. (1) In a planetary mixer connected to a plasticizer-absorbing plastograph,
400 g of the obtained vinyl chloride polymer powder was added, and 60 r
After preheating (4 minutes) to 88 ° C. while stirring at pm, 200 g of dioctyl phthalate was added thereto, and the time from the time of addition to the point of time when the torque decreased was defined as plasticizer absorbency (minutes). (2) CPA (Cold Plasticizer A)
bsorption: cold plasticizer absorption) ASTM-D3
The absorption amount of dioctyl phthalate at 23 ° C. was measured by the method described in 367-75. (3) Evaluation of foaming property At the end of polymerization, the foaming state in the polymerization vessel was visually observed,
Shown by the following symbols. ：: no foaming ：: foaming was observed from the bottom of the polymerization vessel to a height of 62 to 65%. Δ: Bubbles were observed up to a height of 66 to 70% from the bottom of the polymerization vessel. ：: Bubbles were observed up to a height of 90 to 100% from the bottom of the polymerization vessel. ×: Bubbles were observed up to a height of 100% from the bottom of the polymerization vessel, and bubbles were clogged in the reflux condenser. [Table 1] [Table 2] According to the dispersion stabilizer of the present invention, since the foaming behavior during polymerization is extremely small as compared with the conventional dispersion stabilizer, the effective volume in the polymerization vessel is increased and the productivity is improved. ,
Suspension polymerization using a polymerization vessel with a reflux condenser,
In suspension polymerization by the hot charge method or suspension polymerization by the hot charge method using a polymerization vessel with a reflux condenser, the temperature of the polymerization vessel can be easily controlled. When the dispersion stabilizer for suspension polymerization of the present invention is used, the obtained vinyl polymer particles have a large particle size, a sharp distribution, little scattering during handling,
In addition, it has good penetration into molding machines and the like, improves the porosity of vinyl-based polymer particles, has a high plasticizer absorption rate, and has a high filling specific gravity.

Claims (1)

(57) [Claims 1] The absorbance (a) at 280 nm of an aqueous solution having a concentration of 0.1% by weight in the ultraviolet absorption spectrum is 0.4%. 25 or more and 320 n according to an ultraviolet absorption spectrum of the aqueous solution.
m is 0.03 or more, and the absorbance (b)
/ Absorbance (a) is 0. A dispersion stabilizer for suspension polymerization of a vinyl compound comprising a polyvinyl alcohol polymer having a block character of 2 or less and a residual acetic acid group of 0.4 or more.