Resin composition containing a modified polyvinyl alcohol-based polymer, method for producing the resin composition, dispersion stabilizer for suspension polymerization, and method for producing a vinyl-based resin

Abstract

Provided is a resin composition that contains a modified polyvinyl alcohol polymer useful as a dispersion stabilizer suitable for obtaining resin particles having minute and highly uniform particle sizes, few coarsened particles, and a high bulk specific gravity when suspension-polymerization of a vinyl compound such as vinyl chloride is carried out. The resin composition contains, in a main chain, a modified polyvinyl alcohol polymer having the structural unit shown in general formula (I) and a homopolymer of polyvinyl alcohol. The mass percentage of the homopolymer of polyvinyl alcohol in a total of 100 mass% of the modified polyvinyl alcohol polymer and the homopolymer of polyvinyl alcohol is 0 to 5 mass%. (In the formula, X and Y represent a lower alkyl group having 1 to 12 carbon atoms, a hydrogen atom, or a metal atom, and may be the same or different. Z represents the number of repeating units and is an integer from 0 to 3.)

Description

Technical Field

[0001] The present invention relates to a resin composition containing a modified polyvinyl alcohol-based polymer and a method for producing the same. The present invention also relates to a dispersion stabilizer for suspension polymerization, particularly a dispersion stabilizer suitable for suspension polymerization of vinyl-based compounds, especially vinyl chloride.

Background Art

[0002] When suspension polymerizing a vinyl chloride monomer or a mixture of a vinyl chloride monomer and a monomer copolymerizable therewith, it is essential to use various dispersion stabilizers, and dispersion stabilizers such as polyvinyl alcohol and methylol cellulose are used. Among them, polyvinyl alcohol (PVA) has excellent properties and is generally the most widely used. For example, as a dispersion stabilizer for suspension polymerization of vinyl-based compounds, a carbonyl group derived from an aldehyde is introduced at the terminal of a polyvinyl alcohol-based polymer, and an unsaturated double bond is introduced by undergoing a dehydration reaction or a deacetic acid reaction during saponification (see, for example, Patent Document 1), or a method of introducing an unsaturated double bond derived from a specific monomer into the main chain of a vinyl alcohol-based polymer molecule has been proposed (see, for example, Patent Documents 2 to 3). Patent Document 2 describes that in a modified PVA into which an unsaturated double bond is introduced, the content of unmodified PVA is preferably 25% by mass or less, and in the examples, the content of unmodified PVA was in the range of 10 to 45%.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] These methods are not sufficient to fully accommodate various types of polymerization tanks, such as large-scale polymerization tanks that have been used in recent years. That is, vinyl resin particles with non-uniform particle sizes are obtained, resulting in increased scale adhesion; vinyl resin particles with strong dispersing power but poor protective colloid properties and coarsening are obtained, leading to a decrease in processability; vinyl resin particles with poor dispersing power and low plasticizer absorbency are obtained; or problems such as low bulk specific gravity occur even with fine vinyl resin particles. Therefore, it has been insufficient to stably obtain vinyl resin particles that stably satisfy the required performance from users.

[0005] Therefore, in one embodiment, an object of the present invention is to provide a resin composition containing a modified polyvinyl alcohol-based polymer useful as a dispersion stabilizer suitable for obtaining resin particles that are fine, have high particle size uniformity, few coarsened particles, and a high bulk specific gravity when suspension-polymerizing vinyl-based compounds such as vinyl chloride.

Means for Solving the Problems

[0006] As a result of intensive research to solve the above problems, the present inventors have found that a resin composition containing a modified polyvinyl alcohol-based polymer having a dicarboxylic acid monomer unit and a conjugated double bond in the main chain of polyvinyl alcohol and a homopolymer of polyvinyl alcohol, wherein the mass ratio of the homopolymer of polyvinyl alcohol in the total 100% by mass of the modified polyvinyl alcohol-based polymer and the homopolymer of polyvinyl alcohol is 5% by mass or less, is effective to use.

[0007] Patent Document 2 describes that in a modified PVA into which an unsaturated double bond is introduced, the content of unmodified PVA is preferably 25% by mass or less. However, in Patent Document 2, the content of unmodified PVA is 10% by mass even in the example with the lowest content of unmodified PVA. Patent Document 2 does not describe either a method for setting the content of unmodified PVA to 5% by mass or less and the advantageous effects as a dispersion stabilizer obtained thereby.

[0008] In one aspect, the present invention is a resin composition containing a modified polyvinyl alcohol-based polymer having a structural unit represented by the general formula (I) in the main chain and a homopolymer of polyvinyl alcohol, wherein the mass ratio of the homopolymer of polyvinyl alcohol in the total 100% by mass of the modified polyvinyl alcohol-based polymer and the homopolymer of polyvinyl alcohol is 0 to 5% by mass.

Chemical formula

[0009] In one embodiment of the resin composition according to the present invention, the UV absorbance (Abs) at a wavelength of 280 nm and an optical path length of 10 mm in a 0.2% by mass aqueous solution is 0.1 or more and 5.0 or less.

[0010] In another embodiment of the resin composition according to the present invention, the UV absorbance (Abs) at a wavelength of 325 nm and an optical path length of 10 mm in a 0.2% by mass aqueous solution is 0.01 or more and 1.0 or less.

[0011] In still another embodiment of the resin composition according to the present invention, the saponification degree of the resin composition is 65 to 99.9 mol%.

[0012] In still another embodiment of the resin composition according to the present invention, the resin composition contains 0.1 to 5.0 mol% of a dicarboxylic acid monomer unit.

[0013] In another aspect, the present invention relates to a method for producing a resin composition according to the present invention, which includes a step of copolymerizing a vinyl ester monomer and an unsaturated monomer that induces a dicarboxylic acid monomer unit represented by the general formula (I) to obtain a modified vinyl ester polymer, and a step of saponifying the obtained modified vinyl ester polymer, and includes intermittently or continuously adding a dicarboxylic acid monomer until the polymerization rate reaches 90% or more with respect to the final polymerization rate of the modified vinyl ester polymer.

[0014] In yet another aspect, the present invention relates to a dispersion stabilizer for suspension polymerization containing the resin composition according to the present invention.

[0015] In yet another aspect, the present invention relates to a method for producing a vinyl resin, which includes dispersing a vinyl compound monomer or a mixture of a vinyl compound monomer and a monomer copolymerizable therewith in water using the dispersion stabilizer for suspension polymerization and performing suspension polymerization.

Advantages of the Invention

[0016] When suspension polymerization of a vinyl compound is carried out using the dispersion stabilizer for suspension polymerization of the present invention, resin particles with less formation of coarse particles and high particle size uniformity can be obtained. Since the formation of coarse particles is less, blocking during polymerization is suppressed, and since particles with high particle size uniformity are obtained, scale adhesion is reduced. Also, a resin with a high bulk specific gravity can be obtained, improving productivity during resin processing. Thus, the dispersion stabilizer for suspension polymerization of the present invention can possess required performances that were difficult to achieve with the prior art.

Embodiments for Carrying Out the Invention

[0017] In one embodiment, the dispersion stabilizer for suspension polymerization of the present invention is a resin composition containing a modified polyvinyl alcohol-based polymer (modified PVA) having a structural unit represented by the following general formula (I), that is, a structural unit in which a carbon chain having a conjugated double bond is linked to a dicarboxylic acid monomer unit, in the main chain of polyvinyl alcohol, and a homopolymer of polyvinyl alcohol (unmodified PVA), and the mass ratio of the homopolymer of polyvinyl alcohol in the total 100% by mass of the modified polyvinyl alcohol-based polymer and the homopolymer of polyvinyl alcohol is 0 to 5% by mass.

[0018] [Chemical formula] (In the formula, X and Y represent a lower alkyl group having 1 to 12 carbon atoms, a hydrogen atom or a metal atom, and may be the same or different. Z represents the number of repeating units and is an integer of 0 to 3.)

[0019] The unsaturated monomer that induces the dicarboxylic acid monomer unit in the general formula (I) is not particularly limited, but dimethyl maleate, monomethyl maleate, diethyl maleate, monoethyl maleate, dipropyl maleate, monopropyl maleate, dibutyl maleate, monobutyl maleate, dipentyl maleate, monopentyl maleate, dihexyl maleate, monohexyl maleate, dioctyl maleate, monooctyl maleate, dimethyl fumarate, monomethyl fumarate, diethyl fumarate, monoethyl fumarate, dibutyl fumarate, monobutyl fumarate, dipentyl fumarate, monopentyl fumarate, dihexyl fumarate, monohexyl fumarate, diheptyl fumarate, monoheptyl fumarate, dioctyl fumarate, monooctyl fumarate, maleic acid, maleic anhydride, fumaric acid, etc. can be mentioned.

[0020] In the general formula (I), Z is preferably 0 to 3, more preferably 1 to 3, and even more preferably 1 to 2.

[0021] In the resin composition according to the present invention, it is preferable that the content of the modified polyvinyl alcohol-based polymer (modified PVA) having a structural unit represented by the following general formula (I) in the main chain of polyvinyl alcohol is high. Specifically, the mass ratio of the modified polyvinyl alcohol-based polymer in the total 100% by mass of the modified polyvinyl alcohol-based polymer and the homopolymer of polyvinyl alcohol (also referred to as "modified PVA content") is preferably 95% by mass or more, more preferably 96% by mass or more, still more preferably 97% by mass or more, and even more preferably 98% by mass or more.

[0022] In the resin composition according to the present invention, the homopolymer of polyvinyl alcohol, that is, the unmodified polyvinyl alcohol (unmodified PVA) containing neither the structural unit represented by the general formula (I) nor the structural unit derived from other copolymerizable monomers is an impurity, and it is desirable that its content is low. Specifically, the mass ratio of the homopolymer in the total 100% by mass of the modified polyvinyl alcohol-based polymer and the homopolymer of polyvinyl alcohol (also referred to as "homopolymer content") is preferably 5% by mass or less, more preferably 4% by mass or less, still more preferably 3% by mass or less. Polyvinyl alcohol includes both completely saponified polyvinyl alcohol obtained by completely saponifying a vinyl ester-based polymer and partially saponified polyvinyl alcohol in which vinyl ester units remain. When the above homopolymer content exceeds 5% by mass, the amount of components with low protective colloid properties increases, so that the number of coarsened particles of the vinyl-based resin may increase. In addition, there is no particular limitation on the lower limit of the above homopolymer content, and it may be 0% by mass, but from the viewpoint of purification cost, it is typically 0.1% by mass or more, more typically 0.3% by mass or more. When the resin composition according to the present invention contains the above homopolymer, the resin composition is a mixture of a modified polyvinyl alcohol-based polymer having a structural unit represented by the general formula (I) and a homopolymer of polyvinyl alcohol.

[0023] In the resin composition according to the present invention, the mass ratio of the homopolymer of the modified polyvinyl alcohol-based polymer and the polyvinyl alcohol in a total of 100% by mass is measured by the following procedure. After completely saponifying the resin composition to a saponification degree of 99.95 mol% or more, it is thoroughly washed with methanol to prepare a resin composition for analysis. The prepared resin composition for analysis is dissolved in pure water and measured by HPLC (high performance liquid chromatography). Based on the peak area ratio of the obtained HPLC results, the homopolymer content in a total of 100% by mass of the modified polyvinyl alcohol-based polymer and the homopolymer of the polyvinyl alcohol is calculated. For example, when HPLC is measured under the following conditions or equivalent conditions, the modified polyvinyl alcohol-based polymer has a peak detected at 3.5 to 7.0 minutes, and the homopolymer has a peak detected at 7.5 to 10.0 minutes. Therefore, the mass ratio of the homopolymer is calculated from these peak area ratios. Specifically, the ratio (%) of the peak area at 7.5 to 10.0 minutes to the total of the peak area at 3.5 to 7.0 minutes and the peak area at 7.5 to 10.0 minutes is taken as the mass ratio (mass%) of the homopolymer in a total of 100% by mass of the modified polyvinyl alcohol-based polymer and the homopolymer of the polyvinyl alcohol. Also, the ratio (%) of the peak area at 3.5 to 7.0 minutes to the total of the peak area at 3.5 to 7.0 minutes and the peak area at 7.5 to 10.0 minutes is taken as the mass ratio (mass%) of the modified polyvinyl alcohol-based polymer in a total of 100% by mass of the modified polyvinyl alcohol-based polymer and the homopolymer of the polyvinyl alcohol. <HPLC Measurement Conditions> Column: MCI (registered trademark) GEL CK08EH (manufactured by Mitsubishi Chemical Corporation) Eluent: Pure water Mobile phase flow rate: 0.6 ml / min Temperature: 40°C Injection concentration: 0.01 wt% Injection volume: 20 μL Detector: RI

[0024] In one embodiment, the resin composition according to the present invention has a total mass ratio of the modified polyvinyl alcohol polymer and the homopolymer of polyvinyl alcohol of 90% by mass or more, typically 95% by mass or more, and more typically 98% by mass or more. In this specification, the total mass ratio (also referred to as "total content of modified PVA and unmodified PVA in the resin composition") is defined as the ratio (%) of the sum of the peak areas at 3.5 to 7.0 minutes and 7.5 to 10.0 minutes to the sum of the peak areas at 0 to 20 minutes during the measurement by HPLC described above.

[0025] The resin composition according to the present invention preferably has a UV absorbance (Abs) at a wavelength of 280 nm of 0.2% by mass aqueous solution measured using a quartz cell with an optical path length of 10 mm of 0.1 or more and 5.0 or less. The UV absorbance (Abs) is more preferably 0.3 or more and 3.0 or less, and still more preferably 0.5 or more and 2.0. The UV absorption at this wavelength of 280 nm corresponds to a conjugated double bond chain (Z = 1). When the UV absorbance (Abs) is less than 0.1, the carbon-carbon double bond is insufficient, and the protective colloid property deteriorates. As a result, it is difficult to obtain a vinyl resin having an appropriate particle size. Further, when the UV absorbance (Abs) exceeds 5.0, coloring becomes remarkable, and when used as a dispersant, it may affect the coloring of the obtained vinyl resin. Also, it may become chemically unstable, and the viscosity of the aqueous solution may increase or gelation may occur.

[0026] The resin composition according to the present invention preferably has a UV absorbance (Abs) at a wavelength of 325 nm of an aqueous solution of 0.2% by mass measured using a quartz cell with an optical path length of 10 mm of 0.01 or more and 1.0 or less. The UV absorbance (Abs) at a wavelength of 325 nm is more preferably 0.03 or more and 0.5 or less, and even more preferably 0.05 or more and 0.25 or less. This UV absorption at a wavelength of 325 nm corresponds to a triple chain of conjugated double bonds (Z = 2). When this UV absorbance (Abs) is less than 0.01, the carbon-carbon double bonds are insufficient, and the protective colloid property deteriorates, resulting in difficulty in obtaining a vinyl-based resin having an appropriate particle size. Further, when this UV absorbance (Abs) exceeds 1.0, coloring becomes prominent, and when used as a dispersant, it may affect the coloring of the obtained vinyl-based resin. Further, it may become chemically unstable, and the viscosity of the aqueous solution may increase or gelation may occur.

[0027] From the viewpoint of increasing water solubility and facilitating handling, the saponification degree of the resin composition of the present invention is preferably 65 mol% or more, more preferably 68 mol% or more, and even more preferably 70 mol% or more. Further, the saponification degree of the resin composition of the present invention is preferably 99.9 mol% or less, more preferably 90 mol% or less, and even more preferably 80 mol% or less in order to increase the porosity of the particles obtained when suspension polymerizing vinyl-based compounds and enhance the plasticizer absorbability.

[0028] The saponification degree of the resin composition of the present invention is measured in accordance with JIS K6726:1994. That is, it can be determined by quantifying the residual acetic acid groups (mol%) in the sample with sodium hydroxide and subtracting from 100.

[0029] The dicarboxylic acid monomer unit of the resin composition of the present invention is preferably 0.1 to 5.0 mol%, more preferably 0.3 to 3.0 mol%, and still more preferably 0.5 to 2.0 mol%. When it is less than 0.1 mol%, the conjugated double bond portion (-C=CH-(CH=CH)z-) linked to the dicarboxylic acid monomer unit decreases, and as a result, it is difficult to obtain a vinyl resin having an appropriate particle size. In addition, a vinyl resin having a low bulk density is obtained. Further, when it exceeds 5.0 mol%, the physical properties change greatly due to a change in pH, so the protective colloid property during suspension polymerization of the vinyl compound may decrease, or it may become chemically unstable and insolubilize or gel.

[0030] The content of the dicarboxylic acid monomer unit of the resin composition of the present invention is substantially equal to the ratio (mol%) of the number of moles of the dicarboxylic acid monomer to the total number of moles of the monomer units constituting the modified polyvinyl alcohol-based polymer and the homopolymer of polyvinyl alcohol. The method for determining the content of the dicarboxylic acid monomer unit is not particularly limited and can be determined by an acid value or the like, but it is convenient to determine it by carbon NMR ( 13 13C-NMR). Specifically, after completely saponifying the resin composition to a saponification degree of 99.95 mol% or more, it is thoroughly washed with methanol to prepare a resin composition for analysis. The prepared resin composition for analysis is dissolved in heavy water, and a few drops of an aqueous NaOH solution are further added to adjust the pH to 14, and then measured at 80 °C 13 13C-NMR is measured. Based on the integral value of the peak of the methylene group (25 to 50 ppm) of the resin composition of the obtained spectrum, it is calculated from the peak of 178 to 185 ppm which is the carbon atom of the carboxyl group. For example, if the integral value of the methylene group of the resin composition is b and the integral value of the carbon atom of the carboxyl group is a, the content of the dicarboxylic acid monomer unit is calculated as (a / 2) / (a / 2 + b) × 100 (mol%). For example, when a = 2 and b = 99, it is calculated as 1.0 mol%.

[0031] The viscosity-average degree of polymerization of the resin composition of the present invention is preferably 400 or more, more preferably 500 or more, in order to enhance the dispersion stability during suspension polymerization of the vinyl resin. Further, the viscosity-average degree of polymerization is preferably 4000 or less, more preferably 3000 or less, even more preferably 2000 or less, and even more preferably 1500 or less, so as not to reduce the dispersing power.

[0032] The viscosity-average degree of polymerization is measured in accordance with JIS K6726:1994. That is, after completely saponifying and purifying the resin composition, it is determined from the intrinsic viscosity [η] measured in dimethyl sulfoxide (DMSO) at 30°C.

[0033] The production method of the resin composition according to the present invention is not particularly limited, but a production method including a step of copolymerizing a vinyl ester monomer represented by vinyl acetate and an unsaturated monomer that induces a dicarboxylic acid monomer unit represented by the general formula (I) to obtain a modified vinyl ester polymer, and a step of saponifying the obtained modified vinyl ester polymer is easy and economical, and is preferably used. Examples of the vinyl ester monomer include vinyl acetate, vinyl formate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, and vinyl versatate. The unsaturated monomer that induces the dicarboxylic acid monomer unit represented by the general formula (I) is as described above.

[0034] Monomers copolymerizable with vinyl ester monomers, such as unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, or alkyl esters of these unsaturated monocarboxylic acids, unsaturated dicarboxylic acids such as fumaric acid, itaconic acid, or alkyl esters of these unsaturated dicarboxylic acids, nitriles or amides such as acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, olefin sulfonic acids such as ethylene sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid, or salts thereof, vinyl ethers, vinyl ketones, α-olefins, vinyl halides, vinylidene halides, etc. can be copolymerized alone or in combination. The mixing ratio of the copolymerizable monomers is preferably 10 mol% or less, more preferably 5 mol% or less, based on the total number of moles of the vinyl ester monomer and the unsaturated monomer that induces the structural unit represented by the general formula (I).

[0035] The method for introducing a dicarboxylic acid monomer unit and a structural unit containing a conjugated double bond as shown in the general formula (I) is not particularly limited, but includes (i) a modified vinyl ester polymer obtained by polymerizing a vinyl ester monomer in the presence of a chain transfer agent such as an aldehyde or ketone containing a carbonyl group, or (ii) a method of introducing a conjugated double bond into the main chain of polyvinyl alcohol by causing a dehydration reaction or a deacetic acid reaction in a drying step after saponifying a modified vinyl ester polymer obtained by copolymerizing a vinyl ester monomer and an unsaturated monomer that induces a dicarboxylic acid monomer unit. In order to further develop the conjugated double bond by the drying step, it is preferable to perform drying while heating at 90°C or higher for 1 hour or more, preferably 100°C or higher for 1 hour or more, more preferably 120°C or higher for 2 hours or more. Although there is no particular upper limit set for the heating temperature during drying, from the viewpoint of preventing gelation, it is desirable to perform drying while heating to 180°C or lower, preferably 160°C or lower, more preferably 150°C or lower. Therefore, when introducing a conjugated double bond by the drying step, the heating conditions are preferably, for example, 90 to 180°C for 1 to 5 hours, more preferably 100 to 160°C for 1 to 5 hours.

[0036] As the polymerization method adopted for producing the resin composition according to the present invention, any of batch polymerization, semi-batch polymerization, continuous polymerization, and semi-continuous polymerization may be used. As the polymerization method, any method can be adopted from known methods such as bulk polymerization method, solution polymerization method, suspension polymerization method, emulsion polymerization method, etc. Among them, instead of the suspension polymerization method and the emulsion polymerization method that require controlling the polymerization particle size, the solution polymerization method of performing polymerization in the presence of an alcohol-based solvent or the bulk polymerization method of performing polymerization without using a solvent is preferably adopted. As the alcohol-based solvent used in the solution polymerization method, methanol, ethanol, isopropanol, etc. can be used, but it is not limited thereto. These solvents may be used alone or in combination of two or more kinds.

[0037] The polymerization temperature when obtaining the resin composition of the present invention is not particularly limited, but it is preferably 0°C or higher and 200°C or lower, and more preferably 30°C or higher and 150°C or lower. When the temperature for copolymerization is lower than 0°C, it is not preferable because a sufficient polymerization rate cannot be obtained. Also, when the temperature for polymerization is higher than 200°C, it is difficult to obtain the target modified polyvinyl alcohol-based polymer. Examples of the method for controlling the temperature adopted during copolymerization to be 0°C or higher and 200°C or lower include a method of controlling by an external jacket using an appropriate heat medium such as water.

[0038] The polymerization initiator used when obtaining the resin composition of the present invention is not particularly limited, but azo compounds such as azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile, azobis(4-methoxy-2,4-dimethylvaleronitrile), azobisdimethylvaleronitrile, azobismethoxyvaleronitrile, peroxides such as acetyl peroxide, benzoyl peroxide, lauroyl peroxide, acetylcyclohexylsulfonyl peroxide, 2,4,4-trimethylpentyl-2-peroxy phenoxyacetate, percarbonate compounds such as diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, diethoxyethyl peroxydicarbonate, perester compounds such as t-butyl peroxyneodecanoate, α-cumyl peroxyneodecanoate, etc. can be used alone or in combination of two or more. Further, for the purpose of making the polymerization rate constant, it is preferable to add the polymerization initiator intermittently or continuously. Making the polymerization rate constant contributes to a decrease in the mass ratio of the homopolymer of the polyvinyl alcohol in the resin composition.

[0039] When obtaining the resin composition of the present invention, it is also possible to polymerize by charging all of the vinyl ester monomer, dicarboxylic acid monomer, and other copolymerizable monomers at the initial stage of polymerization. However, in order to make the mass ratio of the homopolymer 5% by mass or less, first, 1 to 30% by mass, preferably 5 to 20% by mass of the total addition amount of the dicarboxylic acid monomer is added to the reaction vessel, and the remaining dicarboxylic acid monomer is added intermittently or continuously from the initial stage of polymerization (the stage where the polymerization rate is 0 to 1% with respect to the final polymerization rate). Further, in order to make the mass ratio of the homopolymer 5% or less, the intermittent or continuous addition of the dicarboxylic acid monomer is preferably continued until the polymerization rate reaches 90% or more with respect to the final polymerization rate, more preferably continued until the polymerization rate reaches 93% or more with respect to the final polymerization rate, and even more preferably continued until the polymerization rate reaches 95% or more with respect to the final polymerization rate.

[0040] The final polymerization rate when obtaining the resin composition of the present invention is preferably 30% by mass to 97% by mass, more preferably 50% by mass to 94% by mass, and still more preferably 70% by mass to 93% by mass. When the final polymerization rate is less than 30%, it is necessary to discard or recover and purify the unreacted raw materials, which is not economically efficient. When the final polymerization rate exceeds 97% by mass, a branched structure is likely to be generated in the modified vinyl ester polymer, and the particle size of the vinyl resin may increase.

[0041] The polymerization rate is determined by measuring 5.0 g of the polymerization solution, drying it at 150°C for 30 minutes to volatilize the unreacted monomer and solvent, obtaining the concentration of the polymerization solution from the mass of the dried solid, calculating the mass of the polymer polymerized at that time from the concentration of the polymerization solution, and calculating the polymerization rate from the ratio of the polymer to the total charged amount of the monomer.

[0042] In addition, when the polymerization is carried out at a high temperature, coloring of polyvinyl alcohol due to decomposition of the vinyl ester monomer may be observed. In that case, it is possible to add an antioxidant such as citric acid in an amount of 1 ppm or more and 100 ppm or less (based on the mass of the vinyl ester monomer) to the polymerization system for the purpose of preventing coloring.

[0043] The saponification method for producing the resin composition of the present invention is not particularly limited, and it is preferable to use alcohols as both a solvent and a reactant for the modified vinyl ester polymer obtained by the method described above according to a conventional method. Examples of the alcohol include methanol, ethanol, and butanol. The concentration of the modified vinyl ester polymer in the alcohol can be selected from the range of 20 to 50% by mass. As the alkali catalyst, alkali metal hydroxides and alcoholates such as sodium hydroxide, potassium hydroxide, sodium methylate, sodium ethylate, and potassium methylate can be used. As the acid catalyst, inorganic acid aqueous solutions such as hydrochloric acid and sulfuric acid, and organic acids such as p-toluenesulfonic acid can be used. The amount of these catalysts used is preferably 1 to 100 milliequivalents based on the vinyl ester monomer. The saponification temperature is not particularly limited, but is usually in the range of 10 to 70°C, preferably selected from the range of 30 to 50°C. The reaction is usually carried out over 0.5 to 3 hours.

[0044] The dispersion stabilizer for suspension polymerization of the present invention may be the resin composition of the present invention alone, or may contain, within a range not impairing the gist of the present invention, the modified polyvinyl alcohol polymer having a structural unit represented by the general formula (I) in the main chain, a polyvinyl alcohol polymer other than the homopolymer of polyvinyl alcohol, and various other additives. Examples of the additives include polymerization regulators such as aldehydes, halogenated hydrocarbons, and mercaptans; polymerization inhibitors such as phenolic compounds, sulfur compounds, and N-oxide compounds; pH adjusters; crosslinking agents; preservatives; antifungal agents, antiblocking agents; and antifoaming agents. From the viewpoint of significantly exhibiting the effects of the present invention, the dispersion stabilizer for suspension polymerization of the present invention preferably contains 10% by mass or more of the modified polyvinyl alcohol polymer, more preferably 30% by mass or more, and still more preferably 70% by mass or more.

[0045] The dispersion stabilizer for suspension polymerization of the present invention can be particularly preferably used for suspension polymerization of vinyl compounds. Therefore, according to another aspect of the present invention, there is provided a method for producing a vinyl resin, which includes dispersing a vinyl compound monomer or a mixture of a vinyl compound monomer and a monomer copolymerizable therewith in water using the dispersion stabilizer for suspension polymerization and performing suspension polymerization.

[0046] Examples of the vinyl compound include vinyl halides such as vinyl chloride; vinyl esters such as vinyl acetate and vinyl propionate; acrylic acid, methacrylic acid, esters and salts thereof; maleic acid, fumaric acid, esters and anhydrides thereof; styrene, acrylonitrile, vinylidene chloride, vinyl ether and the like. Among these, the dispersion stabilizer for suspension polymerization according to an embodiment of the present invention is particularly preferably used when vinyl chloride is suspended and polymerized alone or together with a monomer copolymerizable with vinyl chloride. Examples of the monomer copolymerizable with vinyl chloride include vinyl esters such as vinyl acetate and vinyl propionate; (meth)acrylic acid esters such as methyl (meth)acrylate and ethyl (meth)acrylate; α-olefins such as ethylene and propylene; unsaturated dicarboxylic acids such as maleic anhydride and itaconic acid; acrylonitrile, styrene, vinylidene chloride, vinyl ether and the like.

[0047] The dispersion stabilizer for suspension polymerization of the present invention can be used alone or in combination with other stabilizers such as cellulose derivatives and surfactants.

[0048] By using the dispersion stabilizer for suspension polymerization of the present invention, a vinyl chloride resin having a high bulk specific gravity of resin particles, a uniform particle size distribution and excellent physical properties can be obtained. Hereinafter, examples of the polymerization method of vinyl compounds will be given and specifically described, but the present invention is not limited thereto.

[0049] When producing vinyl resin particles such as vinyl chloride resin particles, 0.01% to 0.3% by mass, preferably 0.04% to 0.15% by mass, of the above-mentioned dispersion stabilizer for suspension polymerization is added to the vinyl compound monomer. Also, the ratio of the vinyl compound to water can be vinyl compound: water = 1: 0.9 to 1: 3 by mass ratio, preferably vinyl compound: water = 1: 1 to 1: 1.5.

[0050] The polymerization initiator may be one conventionally used for the polymerization of vinyl compounds, and examples thereof include percarbonate compounds such as diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, and diethoxyethyl peroxydicarbonate, perester compounds such as t-butyl peroxyneodecanoate and α-cumyl peroxyneodecanoate, peroxides such as acetylcyclohexylsulfonyl peroxide and 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate, azo compounds such as azobis-2,4-dimethylvaleronitrile and azobis(4-methoxy-2,4-dimethylvaleronitrile), and furthermore, potassium persulfate, ammonium persulfate, hydrogen peroxide, etc. can be used alone or in combination.

[0051] Furthermore, it is optional to add a polymerization regulator, a chain transfer agent, a gelation improver, an antistatic agent, a pH adjuster, etc. that are appropriately used for the polymerization of vinyl compounds.

[0052] The charging ratio of each component, the polymerization temperature, etc. when carrying out the polymerization of vinyl compounds may be determined according to the conditions conventionally used in the suspension polymerization of vinyl compounds, and there is no particular reason for limitation.

Examples

[0053] Hereinafter, the present invention will be described in more detail with reference to examples. (Example 1) 1410 g of vinyl acetate, 700 g of methanol, 1.8 g of dimethyl maleate as a modifying species (dicarboxylic acid monomer), and 0.1 g of di-2-ethylhexyl peroxydicarbonate were charged into a polymerization kettle. The system was purged with nitrogen for 30 minutes, and then the temperature increase was started. When the liquid temperature reached 60 °C, continuous addition of vinyl acetate, dimethyl maleate, and di-2-ethylhexyl peroxydicarbonate was started, and polymerization was carried out. Specifically, 440 g of vinyl acetate was continuously added at a rate of 38.3 g per hour over 11.5 hours, 16.7 g of dimethyl maleate was continuously added at a rate of 1.45 g per hour over 11.5 hours, and simultaneously, 2.0 g of di-2-ethylhexyl peroxydicarbonate was continuously added at a rate of 0.2 g per hour over 10 hours to carry out the polymerization. After 12 hours had elapsed since the liquid temperature reached 60 °C, it was cooled to stop the polymerization. Table 1 shows the polymerization rate at the end of the continuous addition of the dicarboxylic acid monomer at this time, the final polymerization rate, and the polymerization rate at the end of the continuous addition of the dicarboxylic acid monomer relative to the final polymerization rate. Next, unreacted vinyl acetate was removed by a conventional method. A methanol solution of sodium hydroxide was added to the obtained polymer by a conventional method, and saponification was carried out at 40 °C for 1 hour. Then, neutralization treatment was performed, and drying was carried out at 110 °C for 2 hours to obtain PVA1.

[0054] <Characteristics Evaluation of Modified PVA> The modification rate (content per unit of dicarboxylic acid monomer), saponification degree, modified PVA content, homopolymer content, total content of modified PVA and unmodified PVA in the resin composition, and viscosity-average degree of polymerization of the obtained PVA1 were measured by the above-described analytical methods. The results are shown in Table 1.

[0055] A 0.2 mass% aqueous solution of PVA1 was placed in a sample cell (quartz cell) with an optical path length of 10 mm, and the UV absorbance of the 0.2 mass% aqueous solution of PVA1 at wavelengths of 280 nm and 325 nm was measured using an ultraviolet-visible-near-infrared spectrophotometer (Spectrophotometer UV1800 manufactured by Shimadzu Corporation). The results are shown in Table 1. Here, the absorption at a wavelength of 280 nm represents a conjugated double bond chain (in the general formula (I), Z = 1), and the absorption at 325 nm represents a conjugated double bond chain (in the general formula (I), Z = 2).

[0056] <Suspension polymerization of vinyl chloride> Into a 30 L stainless steel autoclave equipped with a stirrer, 10 kg of water at 30 °C under stirring, 5.6 g of PVA1 as a dispersion stabilizer, 4.6 g of t-butyl peroxyneodecanoate as a polymerization initiator, and 1 g of α-cumyl peroxyneodecanoate were charged. After degassing the autoclave under vacuum, 7 kg of vinyl chloride monomer was added, and polymerization was carried out at 53 °C for 4 hours. In this suspension polymerization, the ratio of the vinyl chloride monomer to water was increased, and polymerization was carried out at a low temperature to create conditions under which the particles of the vinyl chloride resin were likely to coarsen.

[0057] <Evaluation of vinyl chloride resin> The average particle size, the ratio of particles of 250 μm or more, and the bulk specific gravity of the obtained vinyl chloride resin were evaluated by the following methods.

[0058] The measurement of the average particle size was carried out in accordance with JIS Z8815:1994 using sieves of 60 mesh (aperture 250 μm), 80 mesh (aperture 180 μm), 100 mesh (aperture 150 μm), 150 mesh (aperture 106 μm), and 200 mesh (aperture 75 μm) to determine the average particle size, which is the particle size (D50) at a cumulative frequency of 50% (mass basis), and the mass ratio of particles of 250 μm or more.

[0059] The bulk specific gravity was measured in accordance with JIS K6720-2:1999.

[0060] After taking out the polymer slurry from the autoclave, the scale adhesion state in the reactor was visually observed, and the degree of scale adhesion was evaluated according to the following criteria. A: There is almost no scale adhesion in the autoclave. B: More than 100 g of scale adheres to the stirrer and the inner wall in the autoclave, but it can be easily removed by washing with water. C: A large amount of scale of more than 100 g that is difficult to remove by washing with water adheres to the stirrer and the inner wall in the autoclave.

[0061] (Example 2) 1410 g of vinyl acetate, 700 g of methanol, 3.1 g of dimethyl maleate as a modifying species (dicarboxylic acid monomer), and 0.1 g of di-2-ethylhexyl peroxydicarbonate were charged into a polymerization kettle, the system was purged with nitrogen for 30 minutes, and the temperature increase was started. When the liquid temperature reached 60°C, the continuous addition of vinyl acetate, dimethyl maleate, and di-2-ethylhexyl peroxydicarbonate was started, and polymerization was carried out. Specifically, 440 g of vinyl acetate was continuously added at a rate of 38.3 g per hour over 11.5 hours, 27.9 g of dimethyl maleate was continuously added at a rate of 2.43 g per hour over 11.5 hours, and at the same time, 2.4 g of di-2-ethylhexyl peroxydicarbonate was continuously added at a rate of 0.24 g per hour over 10 hours to carry out polymerization. After 12 hours had elapsed since the liquid temperature reached 60°C, it was cooled to stop the polymerization. Next, unreacted vinyl acetate was removed by a conventional method, a methanol solution of sodium hydroxide was added to the obtained polymer by a conventional method, saponification was carried out at 40°C for 1 hour, then neutralization treatment was carried out, and drying was carried out at 110°C for 2 hours to obtain PVA2. The modification rate, saponification degree, modified PVA content, homopolymer content, total content of modified PVA and unmodified PVA in the resin composition, viscosity average degree of polymerization, and UV absorbance of the obtained PVA2 were measured in the same manner as in Example 1. In addition, suspension polymerization of vinyl chloride was carried out under the same conditions as in Example 1 except that PVA2 was used, and the physical properties of the obtained vinyl chloride resin were measured. The results are shown in Table 1.

[0062] (Example 3) 1410 g of vinyl acetate, 700 g of methanol, 3.1 g of dimethyl maleate as a modifying species (dicarboxylic acid monomer), and 0.1 g of di-2-ethylhexyl peroxydicarbonate were charged into a polymerization kettle. The system was purged with nitrogen for 30 minutes, and then the temperature was raised. When the liquid temperature reached 60°C, continuous addition of vinyl acetate, dimethyl maleate, and di-2-ethylhexyl peroxydicarbonate was started, and polymerization was carried out. Specifically, 440 g of vinyl acetate was continuously added at a rate of 40.0 g per hour over 11 hours, 27.9 g of dimethyl maleate was continuously added at a rate of 2.54 g per hour over 11 hours, and simultaneously, 2.4 g of di-2-ethylhexyl peroxydicarbonate was continuously added at a rate of 0.24 g per hour over 10 hours to conduct the polymerization. After 12 hours had elapsed since the liquid temperature reached 60°C, cooling was carried out to stop the polymerization. Next, unreacted vinyl acetate was removed by a conventional method, and a methanol solution of sodium hydroxide was added to the obtained polymer by a conventional method. Saponification was carried out at 40°C for 1 hour, followed by neutralization treatment, and drying was carried out at 110°C for 2 hours to obtain PVA3. The modification rate, saponification degree, modified PVA content, homopolymer content, total content of modified PVA and unmodified PVA in the resin composition, viscosity average degree of polymerization, and UV absorbance of the obtained PVA3 were measured by the same method as in Example 1. Also, suspension polymerization of vinyl chloride was carried out under the same conditions as in Example 1 except that PVA3 was used, and the physical properties of the obtained vinyl chloride resin were measured. The results are shown in Table 1.

[0063] (Example 4) 1410 g of vinyl acetate, 700 g of methanol, 4.3 g of dimethyl maleate as a modifying species (dicarboxylic acid monomer), and 0.15 g of di-2-ethylhexyl peroxydicarbonate were charged into a polymerization kettle. The system was purged with nitrogen for 30 minutes, and then the temperature increase was started. When the liquid temperature reached 60°C, continuous addition of vinyl acetate, dimethyl maleate, and di-2-ethylhexyl peroxydicarbonate was started, and polymerization was carried out. Specifically, 440 g of vinyl acetate was continuously added at a rate of 38.3 g per hour over 11.5 hours, 38.7 g of dimethyl maleate was continuously added at a rate of 3.37 g per hour over 11.5 hours, and simultaneously, 3.0 g of di-2-ethylhexyl peroxydicarbonate was continuously added at a rate of 0.3 g per hour over 10 hours to carry out the polymerization. After 12 hours had elapsed since the liquid temperature reached 60°C, it was cooled to stop the polymerization. Next, unreacted vinyl acetate was removed by a conventional method, and a methanol solution of sodium hydroxide was added to the obtained polymer by a conventional method, and saponification was carried out at 40°C for 1 hour. Then, neutralization treatment was performed, and drying was carried out at 110°C for 2 hours to obtain PVA4. The modification rate, saponification degree, modified PVA content, homopolymer content, total content of modified PVA and unmodified PVA in the resin composition, viscosity average degree of polymerization, and UV absorbance of the obtained PVA4 were measured in the same manner as in Example 1. Also, except for using PVA4, the physical properties of polyvinyl chloride obtained by suspension polymerization of vinyl chloride under the same conditions as in Example 1 were measured. The results are shown in Table 1.

[0064] (Example 5) 1410 g of vinyl acetate, 700 g of methanol, 5.6 g of dimethyl maleate as a modifying species (dicarboxylic acid monomer), and 0.2 g of di-2-ethylhexyl peroxydicarbonate were charged into a polymerization kettle. The system was purged with nitrogen for 30 minutes, and then the temperature increase was started. When the liquid temperature reached 60°C, the continuous addition of vinyl acetate, dimethyl maleate, and di-2-ethylhexyl peroxydicarbonate was started, and polymerization was carried out. Specifically, 440 g of vinyl acetate was continuously added at a rate of 38.3 g per hour over 11.5 hours, 50.1 g of dimethyl maleate was continuously added at a rate of 4.36 g per hour over 11.5 hours, and simultaneously, 3.6 g of di-2-ethylhexyl peroxydicarbonate was continuously added at a rate of 0.36 g per hour over 10 hours to conduct the polymerization. After 12 hours had elapsed since the liquid temperature reached 60°C, it was cooled to stop the polymerization. Next, unreacted vinyl acetate was removed by a conventional method, and a methanol solution of sodium hydroxide was added to the obtained polymer by a conventional method, and saponification was carried out at 40°C for 1 hour. Then, neutralization treatment was performed, and drying was carried out at 110°C for 2 hours to obtain PVA5. The modification rate, saponification degree, modified PVA content, homopolymer content, total content of modified PVA and unmodified PVA in the resin composition, viscosity average degree of polymerization, and UV absorbance of the obtained PVA5 were measured in the same manner as in Example 1. Also, suspension polymerization of vinyl chloride was carried out under the same conditions as in Example 1 except that PVA5 was used, and the physical properties of the obtained vinyl chloride resin were measured. The results are shown in Table 1.

[0065] (Example 6) 1410 g of vinyl acetate, 700 g of methanol, 7.4 g of dimethyl maleate as a modifying species (dicarboxylic acid monomer), and 0.25 g of di-2-ethylhexyl peroxydicarbonate were charged into a polymerization kettle. The system was purged with nitrogen for 30 minutes, and then the temperature increase was started. When the liquid temperature reached 60°C, the continuous addition of vinyl acetate, dimethyl maleate, and di-2-ethylhexyl peroxydicarbonate was started to carry out the polymerization. Specifically, 440 g of vinyl acetate was continuously added at a rate of 38.3 g per hour over 11.5 hours, 66.8 g of dimethyl maleate was continuously added at a rate of 5.81 g per hour over 11.5 hours, and simultaneously, 4.2 g of di-2-ethylhexyl peroxydicarbonate was continuously added at a rate of 0.42 g per hour over 10 hours to carry out the polymerization. After 12 hours had elapsed since the liquid temperature reached 60°C, it was cooled to stop the polymerization. Next, unreacted vinyl acetate was removed by a conventional method, and a methanol solution of sodium hydroxide was added to the obtained polymer by a conventional method, and saponification was carried out at 40°C for 1 hour. Then, a neutralization treatment was performed, and drying was carried out at 110°C for 2 hours to obtain PVA6. The modification rate, saponification degree, modified PVA content, homopolymer content, total content of modified PVA and unmodified PVA in the resin composition, viscosity average degree of polymerization, and UV absorbance of the obtained PVA6 were measured by the same method as in Example 1. Also, suspension polymerization of vinyl chloride was carried out under the same conditions as in Example 1 except that PVA6 was used, and the physical properties of the obtained vinyl chloride resin were measured. The results are shown in Table 1.

[0066] (Example 7) 1410 g of vinyl acetate, 700 g of methanol, 9.3 g of dimethyl maleate as a modifying species (dicarboxylic acid monomer), and 0.3 g of di-2-ethylhexyl peroxydicarbonate were charged into a polymerization kettle. The system was purged with nitrogen for 30 minutes, and then the temperature increase was started. When the liquid temperature reached 60°C, the continuous addition of vinyl acetate, dimethyl maleate, and di-2-ethylhexyl peroxydicarbonate was started, and polymerization was carried out. Specifically, 440 g of vinyl acetate was continuously added at a rate of 38.3 g per hour over 11.5 hours, 83.7 g of dimethyl maleate was continuously added at a rate of 7.28 g per hour over 11.5 hours, and simultaneously, 5.4 g of di-2-ethylhexyl peroxydicarbonate was continuously added at a rate of 0.54 g per hour over 10 hours to conduct the polymerization. After 12 hours had elapsed since the liquid temperature reached 60°C, it was cooled to stop the polymerization. Next, unreacted vinyl acetate was removed by a conventional method, and a methanol solution of sodium hydroxide was added to the obtained polymer by a conventional method, and saponification was carried out at 40°C for 1 hour. Then, a neutralization treatment was performed, and drying was carried out at 110°C for 2 hours to obtain PVA7. The modification rate, saponification degree, modified PVA content, homopolymer content, total content of modified PVA and unmodified PVA in the resin composition, viscosity average degree of polymerization, and UV absorbance of the obtained PVA7 were measured by the same method as in Example 1. Further, suspension polymerization of vinyl chloride was carried out under the same conditions as in Example 1 except that PVA7 was used, and the physical properties of the obtained vinyl chloride resin were measured. The results are shown in Table 1.

[0067] (Example 8) 1410 g of vinyl acetate, 700 g of methanol, 3.7 g of diethyl maleate as a modifying species (dicarboxylic acid monomer), and 0.1 g of di-2-ethylhexyl peroxydicarbonate were charged into a polymerization kettle. The system was purged with nitrogen for 30 minutes, and then the temperature increase was started. When the liquid temperature reached 60°C, the continuous addition of vinyl acetate, diethyl maleate, and di-2-ethylhexyl peroxydicarbonate was started, and polymerization was carried out. Specifically, 440 g of vinyl acetate was continuously added at a rate of 38.3 g per hour over 11.5 hours, 33.3 g of diethyl maleate was continuously added at a rate of 2.90 g per hour over 11.5 hours, and at the same time, 2.4 g of di-2-ethylhexyl peroxydicarbonate was continuously added at a rate of 0.24 g per hour over 10 hours to carry out the polymerization. After 12 hours had passed since the liquid temperature reached 60°C, it was cooled to stop the polymerization. Next, unreacted vinyl acetate was removed by a conventional method, and a methanol solution of sodium hydroxide was added to the obtained polymer by a conventional method, and saponification was carried out at 40°C for 1 hour. Then, neutralization treatment was performed, and drying was carried out at 110°C for 2 hours to obtain PVA8. The modification rate, saponification degree, modified PVA content, homopolymer content, total content of modified PVA and unmodified PVA in the resin composition, viscosity average degree of polymerization, and UV absorbance of the obtained PVA8 were measured by the same method as in Example 1. Also, suspension polymerization of vinyl chloride was carried out under the same conditions as in Example 1 except that PVA8 was used, and the physical properties of the obtained vinyl chloride resin were measured. The results are shown in Table 1.

[0068] (Comparative Example 1) 1410 g of vinyl acetate, 700 g of methanol, 1.8 g of dimethyl maleate as a modifying species (dicarboxylic acid monomer), and 0.1 g of di-2-ethylhexyl peroxydicarbonate were charged into a polymerization kettle, the system was purged with nitrogen for 30 minutes, and the temperature increase was started. When the liquid temperature reached 60°C, the continuous addition of vinyl acetate, dimethyl maleate, and di-2-ethylhexyl peroxydicarbonate was started, and polymerization was carried out. Specifically, 440 g of vinyl acetate was continuously added at a rate of 55.0 g per hour over 8 hours, 16.7 g of dimethyl maleate was continuously added at a rate of 2.09 g per hour over 8 hours, and at the same time, 2.0 g of di-2-ethylhexyl peroxydicarbonate was continuously added at a rate of 0.2 g per hour over 10 hours to carry out polymerization. After 12 hours had elapsed since the liquid temperature reached 60°C, it was cooled to stop the polymerization. Next, unreacted vinyl acetate was removed by a conventional method, a methanol solution of sodium hydroxide was added to the obtained polymer by a conventional method, saponification was carried out at 40°C for 1 hour, then neutralization treatment was carried out, and drying was carried out at 110°C for 2 hours to obtain PVA9. The modification rate, saponification degree, modified PVA content, homopolymer content, total content of modified PVA and unmodified PVA in the resin composition, viscosity average degree of polymerization, and UV absorbance of the obtained PVA9 were measured by the same method as in Example 1. Further, suspension polymerization of vinyl chloride was carried out under the same conditions as in Example 1 except that PVA9 was used, and the physical properties of the obtained vinyl chloride resin were measured. The results are shown in Table 2.

[0069] (Comparative Example 2) 1410 g of vinyl acetate, 700 g of methanol, 3.1 g of dimethyl maleate as a modifying species (dicarboxylic acid monomer), and 0.1 g of di-2-ethylhexyl peroxydicarbonate were charged into a polymerization kettle. The system was purged with nitrogen for 30 minutes, and then the temperature was raised. When the liquid temperature reached 60°C, continuous addition of vinyl acetate, dimethyl maleate, and di-2-ethylhexyl peroxydicarbonate was started, and polymerization was carried out. Specifically, 440 g of vinyl acetate was continuously added at a rate of 55.0 g per hour over 8 hours, 27.9 g of dimethyl maleate was continuously added at a rate of 3.49 g per hour over 8 hours, and simultaneously, 2.4 g of di-2-ethylhexyl peroxydicarbonate was continuously added at a rate of 0.24 g per hour over 10 hours to conduct the polymerization. After 12 hours from when the liquid temperature reached 60°C, cooling was carried out to stop the polymerization. Next, unreacted vinyl acetate was removed by a conventional method, and a methanol solution of sodium hydroxide was added to the obtained polymer by a conventional method, and saponification was carried out at 40°C for 1 hour. Then, neutralization treatment was performed, and drying was carried out at 110°C for 2 hours to obtain PVA10. The modification rate, saponification degree, modified PVA content, homopolymer content, total content of modified PVA and unmodified PVA in the resin composition, viscosity average degree of polymerization, and UV absorbance of the obtained PVA10 were measured by the same method as in Example 1. Also, suspension polymerization of vinyl chloride was carried out under the same conditions as in Example 1 except that PVA10 was used, and the physical properties of the obtained vinyl chloride resin were measured. The results are shown in Table 2.

[0070] (Comparative Example 3) 1850 g of vinyl acetate, 700 g of methanol, 31.0 g of dimethyl maleate as a modifying species (dicarboxylic acid monomer), and 0.1 g of di-2-ethylhexyl peroxydicarbonate were charged into a polymerization kettle. The system was purged with nitrogen for 30 minutes, and then the temperature increase was started. When the liquid temperature reached 60 °C, 2.4 g of di-2-ethylhexyl peroxydicarbonate was continuously added over 10 hours at a rate of 0.24 g per hour to carry out the polymerization. After 12 hours had elapsed since the liquid temperature reached 60 °C, the polymerization was stopped by cooling. Next, unreacted vinyl acetate was removed by a conventional method. To the obtained polymer, a methanol solution of sodium hydroxide was added by a conventional method under the same heating conditions as in Example 1, and saponification was carried out at 40 °C for 1 hour. Then, neutralization treatment was performed, and drying was carried out at 110 °C for 2 hours to obtain PVA11. The modification rate, saponification degree, modified PVA content, homopolymer content, total content of modified PVA and unmodified PVA in the resin composition, viscosity average degree of polymerization, and UV absorbance of the obtained PVA11 were measured by the same method as in Example 1. Also, suspension polymerization of vinyl chloride was carried out under the same conditions as in Example 1 except that PVA11 was used, and the physical properties of the obtained vinyl chloride resin were measured. The results are shown in Table 2.

[0071] (Comparative Example 4) 1410 g of vinyl acetate, 700 g of methanol, 4.3 g of dimethyl maleate as a modifying species (dicarboxylic acid monomer), and 0.2 g of di-2-ethylhexyl peroxydicarbonate were charged into a polymerization kettle. The system was purged with nitrogen for 30 minutes, and then the temperature increase was started. When the liquid temperature reached 60°C, the continuous addition of vinyl acetate, dimethyl maleate, and di-2-ethylhexyl peroxydicarbonate was started, and polymerization was carried out. Specifically, 440 g of vinyl acetate was continuously added at a rate of 55.0 g per hour over 8 hours, 38.7 g of dimethyl maleate was continuously added at a rate of 4.84 g per hour over 8 hours, and at the same time, 3.0 g of di-2-ethylhexyl peroxydicarbonate was continuously added at a rate of 0.3 g per hour over 10 hours to conduct the polymerization. After 12 hours had elapsed since the liquid temperature reached 60°C, it was cooled to stop the polymerization. Next, unreacted vinyl acetate was removed by a conventional method, and a methanol solution of sodium hydroxide was added to the obtained polymer by a conventional method under the same heating conditions as in Example 1, saponified at 40°C for 1 hour, then neutralized, and dried at 110°C for 2 hours to obtain PVA12. The modification rate, saponification degree, modified PVA content, homopolymer content, total content of modified PVA and unmodified PVA in the resin composition, viscosity average degree of polymerization, and UV absorbance of the obtained PVA12 were measured by the same method as in Example 1. Also, suspension polymerization of vinyl chloride was carried out under the same conditions as in Example 1 except that PVA12 was used, and the physical properties of the obtained vinyl chloride resin were measured. The results are shown in Table 2.

[0072] (Comparative Example 5) 1410 g of vinyl acetate, 700 g of methanol, 18.5 g of dimethyl maleate as a modifying species (dicarboxylic acid monomer), and 0.5 g of di-2-ethylhexyl peroxydicarbonate were charged into a polymerization kettle. The system was purged with nitrogen for 30 minutes, and then the temperature was raised. When the liquid temperature reached 60°C, continuous addition of vinyl acetate, dimethyl maleate, and di-2-ethylhexyl peroxydicarbonate was started, and polymerization was carried out. Specifically, 440 g of vinyl acetate was continuously added at a rate of 55.0 g per hour over 8 hours, 167.1 g of dimethyl maleate was continuously added at a rate of 20.89 g per hour over 8 hours, and at the same time, 9.0 g of di-2-ethylhexyl peroxydicarbonate was continuously added at a rate of 0.9 g per hour over 10 hours to carry out polymerization. After 12 hours had elapsed since the liquid temperature reached 60°C, it was cooled to stop the polymerization. Next, unreacted vinyl acetate was removed by a conventional method, and a methanol solution of sodium hydroxide was added to the obtained polymer by a conventional method, and saponification was carried out at 40°C for 1 hour. Then, neutralization treatment was performed, and drying was carried out at 110°C for 2 hours to obtain PVA13. The modification rate, saponification degree, modified PVA content, homopolymer content, total content of modified PVA and unmodified PVA in the resin composition, viscosity average degree of polymerization, and UV absorbance of the obtained PVA13 were measured by the same method as in Example 1. Also, except for using PVA13, the physical properties of the vinyl chloride resin obtained by suspension polymerization of vinyl chloride under the same conditions as in Example 1 were measured. The results are shown in Table 2.

[0073] (Comparative Example 6) 1670 g of vinyl acetate, 1160 g of methanol, 2.5 g of dimethyl maleate as a modifying species (dicarboxylic acid monomer), and 2.0 g of azobisisobutyronitrile were charged into a polymerization kettle, the system was purged with nitrogen for 30 minutes, and the temperature increase was started. When the liquid temperature reached 60°C, the continuous addition of vinyl acetate, methanol, and dimethyl maleate was started, and polymerization was carried out. Specifically, 520 g of vinyl acetate was continuously added at a rate of 104 g per hour over 5 hours, 270 g of methanol was continuously added at a rate of 54 g per hour over 5 hours, and 23 g of dimethyl maleate was continuously added at a rate of 4.60 g per hour over 5 hours to carry out the polymerization. After 6 hours had elapsed since the liquid temperature reached 60°C, it was cooled to stop the polymerization. Next, unreacted vinyl acetate was removed by a conventional method, a methanol solution of sodium hydroxide was added to the obtained polymer by a conventional method, saponification was carried out at 40°C for 1 hour, then neutralization treatment was carried out, and drying was carried out at 110°C for 2 hours to obtain PVA14. The modification rate, saponification degree, modified PVA content, homopolymer content, total content of modified PVA and unmodified PVA in the resin composition, viscosity average degree of polymerization, and UV absorbance of the obtained PVA14 were measured by the same method as in Example 1. Further, suspension polymerization of vinyl chloride was carried out under the same conditions as in Example 1 except that PVA14 was used, and the physical properties of the obtained vinyl chloride resin were measured. The results are shown in Table 2.

[0074] (Comparative Example 7) 1410 g of vinyl acetate, 700 g of methanol, and 0.1 g of di-2-ethylhexyl peroxydicarbonate were charged into a polymerization kettle. The system was purged with nitrogen for 30 minutes, and then the temperature increase was started. When the liquid temperature reached 60 °C, the continuous addition of vinyl acetate and di-2-ethylhexyl peroxydicarbonate was started for polymerization. Specifically, 440 g of vinyl acetate was continuously added at a rate of 55.0 g per hour over 8 hours. At the same time, 1.8 g of di-2-ethylhexyl peroxydicarbonate was continuously added at a rate of 0.18 g per hour over 10 hours for polymerization. After 12 hours from when the liquid temperature reached 60 °C, it was cooled to stop the polymerization. Next, unreacted vinyl acetate was removed by a conventional method. To the obtained polymer, a sodium hydroxide methanol solution was added by a conventional method, saponified at 40 °C for 1 hour, then neutralized, and dried at 110 °C for 2 hours to obtain PVA15. The modification rate, saponification degree, modified PVA content, homopolymer content, total content of modified PVA and unmodified PVA in the resin composition, viscosity average degree of polymerization, and UV absorbance of the obtained PVA15 were measured by the same method as in Example 1. Also, suspension polymerization of vinyl chloride was carried out under the same conditions as in Example 1 except that PVA15 was used, and the physical properties of the obtained vinyl chloride resin were measured. The results are shown in Table 2.

[0075]

Table 1

[0076]

Table 2

[0077] In Comparative Examples 1 to 6, since the content of the homopolymer in the resin composition was high, the vinyl chloride resin particles became coarse, the amount of coarse particles was large, and there was a large amount of scale adhesion. In Comparative Example 7, since it did not contain a structure as shown in the general formula (I), the vinyl chloride resin particles became coarse, the amount of coarse particles was large, and there was a large amount of scale adhesion. On the other hand, when the resin compositions shown in Examples 1 to 8 were used, there was little formation of coarse particles in the vinyl chloride resin, particles with high particle size uniformity were obtained, the bulk specific gravity was also high, and the scale adhesion was also small. Therefore, the dispersion stabilizers (PVA1 to PVA8) according to Examples 1 to 8 are extremely industrially advantageous.

Claims

1. A resin composition containing a modified polyvinyl alcohol-based polymer having a structural unit represented by the general formula (I) in the main chain and a homopolymer of polyvinyl alcohol as an optional component, wherein the mass ratio of the homopolymer of polyvinyl alcohol in the total 100% by mass of the modified polyvinyl alcohol-based polymer and the homopolymer of polyvinyl alcohol is 0 to 5% by mass, and the saponification degree is 65 to 80 mol%, and a dispersion stabilizer for suspension polymerization containing the resin composition. 【Chemical 1】 (In the formula, X and Y represent a lower alkyl group having 1 to 12 carbon atoms, a hydrogen atom or a metal atom, and may be the same or different. Z represents the number of repeating units and is an integer of 0 to 3.)

2. The dispersion stabilizer for suspension polymerization according to claim 1, wherein the UV absorbance (Abs) at a wavelength of 280 nm and an optical path length of 10 mm in a 0.2% by mass aqueous solution is 0.1 or more and 5.0 or less.

3. The dispersion stabilizer for suspension polymerization according to claim 1 or 2, wherein the UV absorbance (Abs) at a wavelength of 325 nm and an optical path length of 10 mm in a 0.2% by mass aqueous solution is 0.01 or more and 1.0 or less.

4. The dispersion stabilizer for suspension polymerization according to any one of claims 1 to 3, wherein the saponification degree of the resin composition is 70 to 80 mol%.

5. The dispersion stabilizer for suspension polymerization according to any one of claims 1 to 4, wherein the resin composition contains 0.1 to 5.0 mol% of a dicarboxylic acid monomer unit.

6. A method for producing a dispersion stabilizer for suspension polymerization according to any one of claims 1 to 5, comprising copolymerizing a vinyl ester-based monomer and an unsaturated monomer that induces a dicarboxylic acid monomer unit represented by the general formula (I) to obtain a modified vinyl ester-based polymer, and saponifying the obtained modified vinyl ester-based polymer, and intermittently or continuously adding a dicarboxylic acid monomer until a polymerization rate of 90% or more is reached with respect to the final polymerization rate of the modified vinyl ester-based polymer.

7. A method for producing a vinyl-based resin, comprising dispersing a vinyl-based compound monomer or a mixture of a vinyl-based compound monomer and a monomer copolymerizable therewith in water and performing suspension polymerization using the dispersion stabilizer for suspension polymerization according to any one of claims 1 to 6.

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