阅读说明：本技术 悬浮聚合用分散稳定剂 (Dispersion stabilizer for suspension polymerization ) 是由 新居真辅 于 2019-03-19 设计创作，主要内容包括：本发明提供甲醇含量得以降低、进而不溶于水溶液的成分量得以降低的乙烯基化合物的悬浮聚合用分散稳定剂。本发明涉及乙烯基化合物的悬浮聚合用分散稳定剂,其含有改性乙烯醇系聚合物,所述改性乙烯醇系聚合物中的来自烯属不饱和二羧酸的衍生物(A)的结构单元的含量(X)为0.05摩尔%以上且2.0摩尔%以下,皂化度为65.0摩尔%以上且90.0摩尔%以下,利用顶空气相色谱法进行测定时的甲醇含量为0.01质量%以上且小于3.0质量%,并且,在90℃下不溶于浓度5质量%的水溶液的成分量为0.1ppm以上且小于2000ppm。(The invention provides a dispersion stabilizer for suspension polymerization of a vinyl compound, which has a reduced methanol content and a reduced amount of components insoluble in an aqueous solution. The present invention relates to a dispersion stabilizer for suspension polymerization of a vinyl compound, which contains a modified vinyl alcohol polymer having a content (X) of a structural unit derived from an ethylenically unsaturated dicarboxylic acid derivative (a) of 0.05 to 2.0 mol%, a degree of saponification of 65.0 to 90.0 mol%, a methanol content of 0.01 to less than 3.0 mass% as measured by headspace gas chromatography, and a component content of 0.1 to less than 2000ppm which is insoluble in an aqueous solution having a concentration of 5 mass% at 90 ℃.)

1. A dispersion stabilizer for suspension polymerization of a vinyl compound, which comprises a modified vinyl alcohol polymer having a content (X) of a structural unit derived from an ethylenically unsaturated dicarboxylic acid derivative (A) of 0.05 to 2.0 mol%, a degree of saponification of 65.0 to 90.0 mol%, a methanol content of 0.01 to less than 3.0 mass% as measured by headspace gas chromatography, and a content of a component insoluble in an aqueous solution having a concentration of 5 mass% at 90 ℃ of 0.1 to less than 2000 ppm.

2. The dispersion stabilizer for suspension polymerization according to claim 1, wherein the derivative (A) of an ethylenically unsaturated dicarboxylic acid is a monoester, a diester or an anhydride of an ethylenically unsaturated dicarboxylic acid.

3. The dispersion stabilizer for suspension polymerization according to claim 1 or 2, wherein the derivative (a) of an ethylenically unsaturated dicarboxylic acid comprises monoalkyl maleate, dialkyl maleate, maleic anhydride, monoalkyl fumarate or dialkyl fumarate.

4. The dispersion stabilizer for suspension polymerization according to any one of claims 1 to 3, wherein at least a part of the structural units derived from the derivative (A) of an ethylenically unsaturated dicarboxylic acid is a structural unit represented by the following formula (I), and the values of the content (X) of the structural units derived from the derivative (A) of an ethylenically unsaturated dicarboxylic acid and the content (Y) of the structural units represented by the formula (I) satisfy the following formula (Q):

[ solution 1]

In the formula (I), R¹Is a hydrogen atom or a linear or branched alkyl group having 1 to 8 carbon atoms, R²A metal atom, a hydrogen atom, or a linear or branched alkyl group having 1 to 8 carbon atoms,

0.05≤Y/X<0.98 (Q)。

5. the dispersion stabilizer for suspension polymerization according to any one of claims 1 to 4, wherein the modified vinyl alcohol polymer has a saponification degree of 68.0 mol% or more and 80.0 mol% or less.

6. The dispersion stabilizer for suspension polymerization according to any one of claims 1 to 5, wherein the amount of the component insoluble in an aqueous solution having a concentration of 5% by mass at 90 ℃ is 0.1ppm or more and less than 500 ppm.

7. The dispersion stabilizer for suspension polymerization according to any one of claims 1 to 6, wherein the amount of a sieve having a mesh size of 1.00mm penetrating through the modified vinyl alcohol polymer is 95% by mass or more of the whole.

8. The dispersion stabilizer for suspension polymerization according to any one of claims 1 to 7, wherein the amount of the sieve having a mesh size of 500 μm penetrating through the modified vinyl alcohol polymer is 30% by mass or more of the whole.

9. A method for producing a vinyl polymer, comprising: a process for suspension polymerization of a vinyl compound in the presence of the dispersion stabilizer for suspension polymerization according to any one of claims 1 to 8.

Technical Field

The present invention relates to a dispersion stabilizer for suspension polymerization of a vinyl compound containing a specific modified vinyl alcohol polymer.

Background

A polyvinyl alcohol (hereinafter, abbreviated as "PVA") is known as a water-soluble synthetic polymer, and is used as a raw material of a synthetic fiber vinylon, and is widely used for applications such as paper processing, fiber processing, adhesives, stabilizers for emulsion polymerization and suspension polymerization, binders for inorganic substances, and films.

In particular, PVA containing a group derived from a carboxylic acid or a derivative thereof is used as a sizing agent for acidic paper containing aluminum sulfate by utilizing the reactivity of the carboxylic acid; and a water-resistant coating film obtained by combining with a crosslinking agent. Further, the water solubility of carboxylic acids and derivatives thereof is industrially useful as packaging films for agricultural chemicals, washing detergents, and industrial chemicals, and is widely used.

The carboxylic acid or a derivative thereof can be introduced into the PVA, for example, by copolymerizing a vinyl ester monomer with a monomer containing a carboxylic acid or a derivative thereof to obtain a vinyl ester copolymer, and then saponifying the vinyl ester copolymer. In order to efficiently introduce carboxylic acid, an ethylenically unsaturated dicarboxylic acid derivative having high reactivity and reacting with a vinyl ester monomer is used, and from the viewpoint of ease of industrial availability, maleic acid derivatives and fumaric acid derivatives are known. Among these, since ethylenically unsaturated dicarboxylic acids such as maleic acid and fumaric acid have poor solubility in vinyl ester monomers, monomers having improved solubility in vinyl ester monomers such as monoesters, diesters, and anhydrides of ethylenically unsaturated dicarboxylic acids are used in the solution polymerization method.

The PVA introduced with the carboxylic acid or the derivative thereof is usually produced by subjecting vinyl acetate to radical polymerization in a methanol solvent to obtain a methanol solution of a vinyl acetate polymer, and then adding an alkali catalyst to the methanol solution to saponify the methanol solution. Therefore, the solvent methanol is always left in the modified PVA obtained by drying. When such a polymer with methanol remaining therein is used as a coating agent, there is a problem that methanol is released into the atmosphere in the polymer dissolution step and the polymer solution coating step, and improvement is required from the viewpoint of working environment. To solve such a problem, the techniques of patent documents 1 to 3 have been proposed.

Patent documents 1 and 2 disclose techniques for efficiently removing organic volatile components by supplying a moisture-containing gas under drying to replace the organic volatile components in PVA with moisture. However, PVA containing a structural unit derived from a monoester, a diester or an anhydride of an ethylenically unsaturated dicarboxylic acid has high affinity and solubility with water, and when a gas containing water is supplied, the surfaces of PVA particles are dissolved, and the particles fuse with each other and are agglomerated during drying, and it is difficult to apply this technique because the process is not satisfactory.

Patent document 3 proposes a technique for effectively reducing the methanol content by washing PVA with a washing liquid mainly composed of an alcohol having 2 to 3 carbon atoms. However, the current situation is: since the alcohol having 2 to 3 carbon atoms and having a boiling point and a latent heat of vaporization higher than those of methanol is used, the amount of heat and time required in the drying step increase, and thus, there remains an industrial problem such as an increase in production cost.

Even if the drying technique as described above is not used, the methanol component can be removed by heating and drying at a high temperature for a long time in general, but the energy consumption is large and the industrial production efficiency is sacrificed. Further, in the PVA containing a structural unit derived from a derivative of an ethylenically unsaturated dicarboxylic acid (for example, a monoester, a diester, or an acid anhydride), as described in non-patent document 1, a crosslinking reaction between a structural unit derived from a monoester, a diester, or an acid anhydride and a hydroxyl group portion of PVA proceeds at a high temperature to produce a water-insoluble component, and when an aqueous solution is prepared and used as a coating agent, problems such as poor printability of the coated surface, roll fouling, and filter clogging may occur. Therefore, it is substantially difficult for this PVA to suppress the production of water-insoluble components while reducing the methanol content. Further, due to such properties, it is also difficult to apply the method of patent document 3, which requires a higher heat amount and longer drying time than usual.

Disclosure of Invention

Problems to be solved by the invention

An object of the present invention is to provide an industrially useful dispersion stabilizer for suspension polymerization, which contains a structural unit derived from an ethylenically unsaturated dicarboxylic acid derivative and has a reduced methanol content and a reduced amount of insoluble matter when dissolved in water.

Means for solving the problems

The present inventors have made intensive studies to solve the above problems, and as a result, have found that: the present inventors have found that a modified vinyl alcohol polymer having a residual methanol content of 0.01 mass% or more and less than 3.0 mass% and an insoluble matter content of 0.1ppm or more and less than 2000ppm when dissolved in water can be produced by improving particle size and washing conditions before drying even when a structural unit derived from an ethylenically unsaturated dicarboxylic acid derivative is introduced, and the present invention has been completed by a dispersion stabilizer for suspension polymerization containing a vinyl compound of the modified vinyl alcohol polymer.

That is, the present invention includes the following aspects.

[1] A dispersion stabilizer for suspension polymerization of a vinyl compound, which comprises a modified vinyl alcohol polymer having a content (X) of a structural unit derived from an ethylenically unsaturated dicarboxylic acid derivative (A) of 0.05 to 2.0 mol%, a degree of saponification of 65.0 to 90.0 mol%, a methanol content of 0.01 to less than 3.0 mass% as measured by headspace gas chromatography, and a content of a component insoluble in an aqueous solution having a concentration of 5 mass% at 90 ℃ of 0.1 to less than 2000 ppm.

[2] The dispersion stabilizer for suspension polymerization according to the above [1], wherein the derivative (A) of the ethylenically unsaturated dicarboxylic acid is a monoester, a diester or an anhydride of the ethylenically unsaturated dicarboxylic acid.

[3] The dispersion stabilizer for suspension polymerization according to the above [1] or [2], wherein the derivative (A) of the ethylenically unsaturated dicarboxylic acid comprises a monoalkyl maleate, a dialkyl maleate, maleic anhydride, a monoalkyl fumarate or a dialkyl fumarate.

[4] The dispersion stabilizer for suspension polymerization according to any one of the above [1] to [3], wherein at least a part of the structural units derived from the ethylenically unsaturated dicarboxylic acid derivative (A) are structural units represented by the following formula (I), and the values of the content (X) of the structural units derived from the ethylenically unsaturated dicarboxylic acid derivative (A) and the content (Y) of the structural units represented by the formula (I) satisfy the following formula (Q).

[ solution 1]

(in the formula, R¹Is a hydrogen atom or a linear or branched alkyl group having 1 to 8 carbon atoms, R²Is a metal atom, a hydrogen atom, or a linear or branched alkyl group having 1 to 8 carbon atoms. )

0.05≤Y/X<0.98 (Q)。

[5] The dispersion stabilizer for suspension polymerization according to any one of the above [1] to [4], wherein the modified vinyl alcohol polymer has a saponification degree of 68.0 mol% or more and 80.0 mol% or less.

[6] The dispersion stabilizer for suspension polymerization according to any one of the above [1] to [5], wherein the amount of the component insoluble in an aqueous solution having a concentration of 5 mass% at 90 ℃ is 0.1ppm or more and less than 500 ppm.

[7] The dispersion stabilizer for suspension polymerization according to any one of the above [1] to [6], wherein the amount of the sieve having a mesh opening of 1.00mm in the modified vinyl alcohol polymer is 95% by mass or more of the whole.

[8] The dispersion stabilizer for suspension polymerization according to any one of the above [1] to [7], wherein the amount of the sieve having a mesh opening of 500 μm in the modified vinyl alcohol polymer is 30% by mass or more of the whole.

[9] A method for producing a vinyl polymer, comprising: and (3) a step of suspension-polymerizing a vinyl compound in the presence of the dispersion stabilizer for suspension polymerization according to any one of the above [1] to [8 ].

ADVANTAGEOUS EFFECTS OF INVENTION

The dispersion stabilizer for suspension polymerization of the present invention is environmentally friendly because the content of methanol is reduced, and is reduced in the amount of components insoluble in an aqueous solution, so that the vinyl compound has excellent polymerization stability, the vinyl polymer obtained has a small amount of coarse particles, and fish eyes can be reduced even when the vinyl polymer obtained is formed into a sheet. In the present specification, the polymerization stability means: since the dispersion of the droplets containing the vinyl compound is good during polymerization, as a result, coarse granulation is suppressed, and particles of the vinyl polymer having a uniform diameter can be obtained.

Detailed Description

< Dispersion stabilizer for suspension polymerization of vinyl Compound >

The dispersion stabilizer for suspension polymerization of the present invention contains a modified vinyl alcohol polymer (hereinafter, may be abbreviated as "modified PVA") having a content (X) of a structural unit derived from an ethylenically unsaturated dicarboxylic acid derivative (a) of 0.05 to 2.0 mol%, a degree of saponification of 65.0 to 90.0 mol%, a methanol content of 0.01 to less than 3.0 mass% as measured by headspace gas chromatography, and a component content insoluble in an aqueous solution having a concentration of 5 mass% at 90 ℃ of 0.1 to less than 2000 ppm.

[ modified PVA ]

Importantly, the ethylenically unsaturated di-moieties in the modified PVAThe content (X) of the structural unit of the carboxylic acid derivative (a) is 0.05 mol% or more and 2.0 mol% or less, preferably 0.1 mol% or more and 1.5 mol% or less, and more preferably 0.5 mol% or more and 1.3 mol% or less. When the content (X) of the structural unit derived from the ethylenically unsaturated dicarboxylic acid derivative (a) is less than 0.05 mol%, the amount of the carboxylic acid to be introduced is small, and when the copolymer is used as a dispersion stabilizer for suspension polymerization of a vinyl compound, the proportion of coarse particles in the obtained vinyl polymer becomes large. When the content (X) exceeds 2.0 mol%, the water solubility of the modified PVA becomes too high, and therefore, when the modified PVA is used as a dispersion stabilizer for suspension polymerization of a vinyl compound, the surface active ability is lowered, and when the obtained vinyl polymer is formed into a sheet, fish eyes increase. The content (X) of the structural unit derived from the derivative (A) of an ethylenically unsaturated dicarboxylic acid can be determined by the method of preparing a vinyl ester copolymer before saponification ¹H-NMR analysis.

In the present specification, the upper limit and the lower limit of the numerical range (the content of each component, the value calculated from each component, each physical property, and the like) may be appropriately combined.

It is important that the saponification degree of the modified PVA is 65.0 mol% or more and 90.0 mol% or less, preferably 67.0 mol% or more and 83.0 mol% or less, more preferably 68.0 mol% or more and 80.0 mol% or less, and further preferably 70.0 mol% or more and 75.0 mol% or less. When the saponification degree is less than 65.0 mol%, the proportion of coarse particles in the obtained vinyl polymer becomes large when the dispersion stabilizer is used as a dispersion stabilizer for suspension polymerization of a vinyl compound. The degree of saponification of the modified PVA can be measured by the method described in JIS K6726: 1994.

The viscosity average polymerization degree (hereinafter also simply referred to as "polymerization degree") of the modified PVA is not particularly limited, but is preferably 100 to 2000, more preferably 200 to 1200, and still more preferably 500 to 1000. When the viscosity average degree of polymerization of the modified PVA is not less than the lower limit, the proportion of coarse particles in the obtained vinyl polymer is reduced when the modified PVA is used as a dispersion stabilizer for suspension polymerization of a vinyl compound. When the modified PVA is used as a dispersion stabilizer for suspension polymerization of a vinyl compound by setting the viscosity average degree of polymerization of the modified PVA to the upper limit or less, fish eyes are reduced when the resulting vinyl polymer is formed into a sheet. The degree of polymerization of the modified PVA can be measured by the method described in JIS K6726: 1994.

The methanol content in the modified PVA is, from the viewpoint of reducing the environmental load when used as a dispersion stabilizer for suspension polymerization of a vinyl compound, 0.01 mass% or more and less than 3.0 mass%, preferably 0.01 mass% or more and less than 2.5 mass%, more preferably 0.01 mass% or more and less than 2.0 mass% in 500mg of the modified PVA as measured by headspace gas chromatography. When the content is less than 0.01% by mass, the production is substantially impossible.

The methanol content in the modified PVA was determined by the following method using headspace gas chromatography.

< preparation of Standard Curve >

Using isopropanol as an internal standard solution, 3 kinds of aqueous solutions having a known methanol content were prepared, and measured by using a gas chromatograph (GC-2010, shimadzu corporation) equipped with a headspace sampler (TurboMatrix HS40, manufactured by Parkin Elmer corporation), and a calibration curve was prepared.

< measurement of methanol content in modified PVA >

Distilled water was collected against the marked line of a 1000mL volumetric flask, and 0.1mL of isopropanol as an internal standard solution was added by a pipette and stirred well. This liquid was referred to as "solution". Subsequently, 500mg of the modified PVA was weighed into a vial for headspace gas chromatography measurement, a stirrer was put into the vial, and 10mL of the above-mentioned solution was measured by a full volume pipette and put into the vial. The vial was capped and screwed until locked, and then the vial was placed on a hot stirrer and the modified PVA was dissolved by heating. After it was visually confirmed that the modified PVA was completely dissolved, the methanol content in the modified PVA was determined from the calibration curve prepared as described above by a headspace gas chromatography measurement.

The amount of components insoluble in an aqueous solution having a concentration of 5% by mass at 90 ℃ (hereinafter also simply referred to as "the amount of components insoluble in an aqueous solution") in the modified PVA is 0.1ppm or more and less than 2000ppm, more preferably 0.1ppm or more and less than 1500ppm, still more preferably 0.1ppm or more and less than 1000ppm, and particularly preferably 0.1ppm or more and less than 500 ppm. When the amount is less than 0.1ppm, the production is substantially impossible. When the amount of the component insoluble in an aqueous solution is 2000ppm or more, when the modified PVA is used as a dispersion stabilizer for suspension polymerization of a vinyl compound, the proportion of coarse particles in the obtained vinyl polymer becomes large. In the present specification, ppm means mass ppm. In the present specification, the component amounts of the water-insoluble solution are: the mass ppm of particles (water-insoluble matter) remaining undissolved used for preparing the aqueous solution relative to the total amount of the modified PVA.

The amounts of the aforementioned components insoluble in water are determined by the following method. A500 mL flask equipped with a stirrer and a reflux condenser was prepared in a water bath set at 20 ℃, 285g of distilled water was poured, and stirring was started at 300 rpm. 15g of the modified PVA was weighed out, and the modified PVA was gradually charged into the flask. Immediately after the entire amount (15g) of the modified PVA was charged, it took about 30 minutes to raise the temperature of the water bath to 90 ℃. After the temperature reached 90 ℃, it took further 60 minutes to continue the dissolution while stirring at 300rpm, and then particles remaining undissolved (undissolved particles) were filtered by a metal filter having a mesh size of 63 μm. The filter was thoroughly washed with 90 ℃ warm water to remove the adhering solution, and then the filter was dried with a 120 ℃ heat dryer for 1 hour. The amount of the component insoluble in the aqueous solution is determined from the mass of the undissolved particles thus taken.

The ethylenically unsaturated dicarboxylic acid derivative (a) which is a base of the structural unit of the modified PVA used in the present invention is not particularly limited as long as the effects of the present invention are not impaired. As the derivative (A) of an ethylenically unsaturated dicarboxylic acid, a monoester, a diester or an anhydride of an ethylenically unsaturated dicarboxylic acid is preferred. Specific examples of the derivative (A) of the ethylenically unsaturated dicarboxylic acid include unsaturated dicarboxylic acid monoalkyl esters such as monomethyl maleate, monoethyl maleate, monomethyl fumarate, monoethyl fumarate, monomethyl citraconate, monoethyl citraconate, monomethyl mesaconate, monoethyl mesaconate, monomethyl itaconate, and monoethyl itaconate; unsaturated dicarboxylic acid dialkyl esters such as dimethyl maleate, diethyl maleate, dimethyl fumarate, diethyl fumarate, dimethyl citraconate, diethyl citraconate, dimethyl mesaconate, diethyl mesaconate, dimethyl itaconate, and diethyl itaconate; unsaturated dicarboxylic anhydrides such as maleic anhydride and citraconic anhydride. Among them, in view of easy industrial availability and reactivity with the vinyl ester monomer, monoalkyl maleate, dialkyl maleate, maleic anhydride, monoalkyl fumarate, and dialkyl fumarate are preferable, and monomethyl maleate and maleic anhydride are particularly preferable. The modified PVA may be one having a structural unit derived from at least 1 of the above-mentioned ethylenically unsaturated dicarboxylic acid derivatives (A), and 2 or more ethylenically unsaturated dicarboxylic acid derivatives (A) may be used in combination.

From the viewpoint of being able to suppress the amount of components insoluble in an aqueous solution, it is preferable that: at least a part of the structural units derived from the ethylenically unsaturated dicarboxylic acid derivative (a) are structural units represented by the following formula (I), and the content (X) (hereinafter also referred to as a modification amount (X)) of the structural units derived from the ethylenically unsaturated dicarboxylic acid derivative (a) and the content (Y) (hereinafter also referred to as a modification amount (Y)) of the structural units represented by the formula (I) satisfy the following formula (Q).

[ solution 2]

(in the formula, R¹Is a hydrogen atom or a linear or branched alkyl group having 1 to 8 carbon atoms, R²Is a metal atom, a hydrogen atom, or a linear or branched alkyl group having 1 to 8 carbon atoms. )

0.05≤Y/X<0.98 (Q)。

When Y/X satisfies the range represented by the formula (Q), the modified PVA having a reduced amount of the aqueous solution-insoluble component can be industrially easily produced. The lower limit of Y/X is more preferably 0.06 or more. On the other hand, the upper limit of Y/X is more preferably 0.80 or less, still more preferably 0.60 or less, and particularly preferably 0.40 or less. The content (Y) of the structural unit represented by formula (I) means: the ratio of the number of moles of the structural unit of formula (I) to the total number of moles of the monomer units constituting the main chain of the modified PVA.

As R¹And R²Examples of the linear or branched alkyl group having 1 to 8 carbon atoms include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, 2-methylpropyl, tert-butyl, n-pentyl, isopentyl, sec-pentyl, neopentyl, tert-pentyl, 1-ethylpropyl, 1-dimethylpropyl, 1, 2-dimethylpropyl, n-hexyl, 1-methylpentyl, 2-methylpentyl, 3-methylpentyl, 4-methylpentyl (isohexyl), 1-ethylbutyl, 2-ethylbutyl, 1-dimethylbutyl, 1, 2-dimethylbutyl, 1, 3-dimethylbutyl, 1, 4-dimethylbutyl, 2-dimethylbutyl, 2, 3-dimethylbutyl, and the like, 3, 3-dimethylbutyl, 1-ethyl-2-methyl-propyl, 1, 2-trimethylpropyl, n-heptyl, 2-methylhexyl, n-octyl, isooctyl, tert-octyl, 2-ethylhexyl, 3-methylheptyl and the like. The alkyl group preferably has 1 to 6 carbon atoms, more preferably 1 to 4 carbon atoms, and still more preferably 1 to 3 carbon atoms.

As R²Examples of the metal atom include alkali metals such as sodium, potassium, rubidium and cesium; among alkaline earth metals such as calcium, barium, strontium and radium, alkali metals are preferable, and sodium is more preferable.

When the modified PVA is produced using the ethylenically unsaturated dicarboxylic acid derivative (a), it is known that a part of structural units derived from the ethylenically unsaturated dicarboxylic acid derivative (a) introduced after saponification forms a six-membered ring lactone structure represented by the formula (I). As described in non-patent document 1, the six-membered ring lactone structure represented by the above formula (I) is opened by heating and then forms a crosslinked body by an intermolecular esterification reaction, and therefore, the amount of the water-insoluble solution component of the modified PVA may increase. That is, if the content (Y) of the structural unit represented by the formula (I) is large relative to the content (X) of the structural unit derived from the ethylenically unsaturated dicarboxylic acid derivative (a) introduced, it means that the crosslinking reaction is suppressed. It can be considered that: the six-membered ring lactone structure of the formula (I) is determined by using deuterated dimethyl sulfoxide solvent¹Detected at 6.8 to 7.2ppm in the H-NMR spectrumAnd (5) measuring. In the modified PVA, the content (Y) of the structural unit represented by the formula (I) preferably satisfies the formula (Q) with respect to the content (X) of the structural unit derived from the ethylenically unsaturated dicarboxylic acid derivative (A) obtained from the vinyl ester-based copolymer before saponification, so that the amount of the component insoluble in an aqueous solution is less than 2000 ppm. When Y/X in the formula (Q) is 0.50, it means that half of all the structural units derived from the ethylenically unsaturated dicarboxylic acid derivative (A) to be introduced form the structural unit represented by the formula (I).

The particle diameter of the particles constituting the modified PVA is not particularly limited, but it is preferable that 95% by mass or more of the entire modified PVA passes through a sieve having a mesh opening of 1.00mm, more preferably a sieve having a mesh opening of 710. mu.m, and particularly preferably a sieve having a mesh opening of 500. mu.m. Here, the phrase "95% by mass or more of the modified PVA as a whole" means that: as the particle size distribution, for example, the particles passing through a sieve having a mesh opening of 1.00mm have a cumulative distribution of 95 mass% or more. When the amount of particles passing through a sieve having a mesh size of 1.00mm is less than 95% by mass, methanol incorporated in the modified PVA is less likely to volatilize, and the content of methanol exceeds 3.0% by mass, or the particles are large, so that drying unevenness occurs, and the amount of components insoluble in an aqueous solution increases. The modified PVA is not particularly limited, and the amount of the sieve having a mesh opening of 500 μm is preferably 30 mass% or more, more preferably 35 mass%, still more preferably 45 mass% or more, and particularly preferably 56 mass% or more of the entire modified PVA. Further, as for the particle diameter of the particles constituting the modified PVA, it is preferable that 99% by mass or more of the modified PVA passes through a sieve having a mesh opening of 1.00mm, and it is particularly preferable that 99% by mass or more of the modified PVA passes through a sieve having a mesh opening of 1.00mm and 56% by mass or more passes through a sieve having a mesh opening of 500. mu.m. The aforementioned sieve is based on JIS Z8801-1: 2006 nominal mesh W.

[ Process for producing modified PVA ]

Hereinafter, a method for producing the modified PVA used in the dispersion stabilizer for suspension polymerization of the present invention will be described in detail. The present invention is not limited to the embodiments described below.

The modified PVA can be produced, for example, by a production method having the following steps: a step of copolymerizing a derivative (A) of an ethylenically unsaturated dicarboxylic acid with a vinyl ester monomer to obtain a vinyl ester copolymer; a saponification step of saponifying the obtained vinyl ester copolymer in a solvent using an alkali catalyst or an acid catalyst; a cleaning process and a drying process.

Examples of the vinyl ester monomer include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, and vinyl versatate, and vinyl acetate is particularly preferable.

Examples of the method for copolymerizing the ethylenically unsaturated dicarboxylic acid derivative (a) and the vinyl ester monomer include known methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. Among them, a bulk polymerization method performed in the absence of a solvent or a solution polymerization method performed using a solvent such as alcohol is generally used. From the viewpoint of improving the effect of the present invention, a solution polymerization method of polymerizing with a lower alcohol such as methanol is preferable. When the polymerization reaction is carried out by the bulk polymerization method or the solution polymerization method, the reaction system may be either a batch system or a continuous system.

The initiator used in the polymerization reaction is not particularly limited as long as it does not impair the effects of the present invention, and examples thereof include azo initiators such as 2,2 ' -azobisisobutyronitrile, 2 ' -azobis (2, 4-dimethylvaleronitrile), and 2,2 ' -azobis (4-methoxy-2, 4-dimethylvaleronitrile); and organic peroxide initiators such as benzoyl peroxide and n-propyl peroxycarbonate. The polymerization temperature in the polymerization reaction is not particularly limited, and may be in the range of 5 to 200 ℃ or 30 to 150 ℃.

When the ethylenically unsaturated dicarboxylic acid derivative (a) and the vinyl ester monomer are copolymerized, if necessary, other copolymerizable monomers other than the ethylenically unsaturated dicarboxylic acid derivative (a) and the vinyl ester monomer may be further copolymerized as long as the effect of the present invention is not impaired. Examples of such other monomers include α -olefins such as ethylene, propylene, 1-butene, isobutylene and 1-hexene; (meth) acrylamide derivatives such as (meth) acrylamide, N-methyl (meth) acrylamide, and N-ethyl (meth) acrylamide; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, and n-butyl vinyl ether; hydroxyl-containing vinyl ethers such as ethylene glycol vinyl ether, 1, 3-propylene glycol vinyl ether, and 1, 4-butylene glycol vinyl ether; allyl ethers such as propyl allyl ether, butyl allyl ether, and hexyl allyl ether; a monomer having an oxyalkylene group; hydroxyl group-containing α -olefins such as isopropenyl acetate, 3-buten-1-ol, 4-penten-1-ol, 5-hexen-1-ol, 7-octen-1-ol, 9-decen-1-ol, and 3-methyl-3-buten-1-ol; silyl group-containing monomers such as vinyltrimethoxysilane, vinylmethyldimethoxysilane, vinyldimethylmethoxysilane, vinyltriethoxysilane, vinylmethyldiethoxysilane, vinyldimethylethoxysilane, 3- (meth) acrylamido-propyltrimethoxysilane and 3- (meth) acrylamido-propyltriethoxysilane; n-vinylamide monomers such as N-vinylformamide, N-vinylacetamide, N-vinyl-2-pyrrolidone and N-vinyl-2-caprolactam. The amount of these other monomers to be used varies depending on the purpose of use, application, and the like, and is usually 10 mol% or less, preferably 5.0 mol% or less, more preferably 3.0 mol% or less, and still more preferably 2.0 mol% or less, based on the total monomers to be used for copolymerization. In the present specification, "(meth) acrylic" refers to a generic name of acrylic and methacrylic.

The modified PVA can be obtained by subjecting the vinyl ester copolymer obtained by the above-described method to a saponification step in a solvent, a washing step, and a drying step. The saponification conditions and the drying conditions for obtaining the modified PVA are not particularly limited, and it is preferable to set the water content of the saponification raw material solution, the temperature of the PVA resin at the time of drying, and the drying time to specific ranges from the viewpoint of reducing the methanol content in the modified PVA and suppressing the amount of components insoluble in an aqueous solution.

The saponification raw material solution can be prepared by further adding a small amount of water to the solution containing the vinyl ester copolymer and the solvent obtained in the copolymerization step. The amount of water to be added is preferably adjusted so that the water content of the obtained saponified raw material solution (also referred to as "system water content") exceeds 1.0 mass% and is less than 5.0 mass%. The water content is more preferably 1.5 to 4.0 mass%. When the water content is 1.0 mass% or less, the alkali catalyst is not easily deactivated, and functions as a catalyst for crosslinking, and the amount of the component insoluble in an aqueous solution increases in some cases during drying. On the other hand, when the water content is 5.0 mass% or more, the saponification reaction rate decreases or the modified PVA is easily soluble in water, and therefore, the modified PVA may be eluted into the saponification reaction solution to cause a problem in the production process.

Examples of the solvent usable for the saponification reaction include methanol, ethanol, isopropanol, methyl acetate, dimethyl sulfoxide, diethyl sulfoxide, and dimethylformamide. The solvent used is not particularly limited, and 1 kind may be used alone, or 2 or more kinds may be used in combination. Among these solvents, methanol or a mixed solvent of methanol and methyl acetate is preferably used.

As a catalyst for the saponification reaction of the vinyl ester copolymer, an alkali catalyst is generally used. Examples of the alkali catalyst include hydroxides of alkali metals such as potassium hydroxide and sodium hydroxide; and alkali metal alkoxides such as sodium methoxide, preferably sodium hydroxide. The amount of the saponification catalyst is preferably 0.005 to 0.50, more preferably 0.008 to 0.40, and particularly preferably 0.01 to 0.30 in terms of a molar ratio to a vinyl ester monomer unit of the vinyl ester copolymer. The saponification catalyst may be added all at once at the initial stage of the saponification reaction, or a part of the saponification catalyst may be added at the initial stage of the saponification reaction, and the remaining amount may be added during the saponification reaction.

The temperature of the saponification reaction is preferably in the range of 5 to 80 ℃, and more preferably in the range of 20 to 70 ℃. The time for the saponification reaction is preferably 5 minutes to 10 hours, and more preferably 10 minutes to 5 hours. The saponification reaction may be carried out by either a batch method or a continuous method. In the case of using an alkali catalyst for the saponification reaction, the residual catalyst may be neutralized by adding an acid such as acetic acid or lactic acid as needed in order to stop the saponification reaction, but since the intermolecular crosslinking reaction of the modified PVA is likely to occur during drying due to the residual acid after neutralization, it is preferable not to perform neutralization by the addition of an acid in order to suppress the amount of the aqueous solution-insoluble component to less than 2000 ppm.

The saponification method is not particularly limited as long as it is a known method. Examples thereof include the following methods: (1) a method in which a solution of a vinyl ester copolymer having a concentration adjusted to more than 20% by mass is mixed with a saponification catalyst, and the obtained semisolid (gel-like material) or solid is pulverized by a pulverizer, thereby obtaining a modified PVA; (2) a method in which the concentration of the vinyl ester copolymer dissolved in a solvent containing methanol is controlled to less than 10% by mass, thereby suppressing the reaction solution from being in a gel state without fluidity as a whole, and the modified PVA is precipitated in the solvent to be obtained as fine particles dispersed in methanol; (3) and a method in which a saturated hydrocarbon solvent is added to emulsify the vinyl ester copolymer or saponify the vinyl ester copolymer in a suspension phase to obtain a modified PVA. In the above (1), the pulverizer is not particularly limited, and a known pulverizer or crusher can be used.

From the viewpoint of production, the method (1) or (2) which does not require a saturated hydrocarbon solvent is preferred, and the method (2) is more preferred from the viewpoint of reduction of the methanol content. In the production method (1), the concentration of the vinyl ester copolymer in the solution of the vinyl ester copolymer is preferably 21 mass% or more, and more preferably 25 mass% or more. Further, the production method (2) is preferable from the viewpoint of reducing the methanol content even when the subsequent washing step and drying step are performed less frequently than in the conventional method, and also making it possible to reduce the amount of components insoluble in an aqueous solution, which is industrially advantageous. In the above (2), the concentration of the vinyl ester-based copolymer and the partially saponified product thereof dissolved in the solvent containing methanol is preferably less than 8.0% by mass, more preferably less than 5.0% by mass, and still more preferably less than 4.0% by mass.

From the viewpoint of being able to make the methanol content in the obtained modified PVA less than 3.0 mass%, it is preferable to provide a step of washing the modified PVA after the saponification step as necessary. As the cleaning liquid, a solution containing a lower alcohol such as methanol as a main component and further containing water and/or an ester such as methyl acetate may be used. The cleaning liquid is preferably a solution containing methanol as a main component and methyl acetate. When methanol suitable for use in the copolymerization step of the vinyl ester copolymer and methyl acetate produced in the saponification step are used as the cleaning liquid, they can be reused in the step, and it is not necessary to prepare another solvent as the cleaning liquid, which is preferable from the economical aspect and the step aspect. In one embodiment, in the method of saponification reaction (1), since a part of the washing solvent is impregnated into the PVA during washing, and thus methanol contained in the PVA may be replaced, in order to set the methanol content in the modified PVA after drying to less than 3.0 mass%, the content of methyl acetate as the washing liquid is preferably 45 vol% or more, more preferably 60 vol% or more, and further preferably 70 vol% or more from the viewpoint of further reducing the amount of components insoluble in an aqueous solution of the obtained modified PVA.

After the saponification step or after the washing step, the polymer is dried to obtain a modified PVA. Specifically, hot air drying using a drum dryer is preferable, and the temperature of the modified PVA during drying is preferably more than 80 ℃ and less than 120 ℃, and more preferably 90 ℃ or more and less than 110 ℃. In addition, the drying time is preferably 2 to 10 hours, and more preferably 3 to 8 hours. By setting the conditions at the time of drying to the above ranges, the methanol content in the resulting modified PVA can be easily suppressed to less than 3.0 mass%, and the amount of components insoluble in an aqueous solution can be suppressed to less than 2000ppm, which is preferable.

[ other ingredients ]

The dispersion stabilizer for suspension polymerization of the present invention may contain various additives within a range not to impair the gist of the present invention. Examples of the additives include polymerization regulators such as aldehydes, halogenated hydrocarbons, and thiols; polymerization inhibitors such as phenol compounds, sulfur compounds and N-oxide compounds; a pH adjusting agent; a crosslinking agent; a preservative; a mold inhibitor; an anti-blocking agent; defoaming agents; a compatibilizer, and the like. The content of each additive in the dispersion stabilizer for suspension polymerization is preferably 10% by mass or less, more preferably 5% by mass or less, based on the whole dispersion stabilizer for suspension polymerization.

< Process for producing vinyl Polymer >

A suitable embodiment of the present invention includes a method for producing a vinyl polymer, which comprises: a step of suspension-polymerizing a vinyl compound in the presence of the dispersion stabilizer for suspension polymerization of the present invention. The production method can obtain a vinyl polymer in a granular form.

Examples of a method for charging the dispersion stabilizer for suspension polymerization of the present invention containing a modified PVA into a polymerization tank include: (i) a method of preparing an aqueous solution and charging the aqueous solution into a polymerization vessel; (ii) a method of directly charging the powder, etc. From the viewpoint of uniformity in the polymerization vessel, the above-mentioned method (i) is preferred.

In the suspension polymerization of a vinyl compound, the amount (concentration) of the dispersion stabilizer for suspension polymerization of the present invention may be 1500ppm or less, 1000ppm or less, or 800ppm or less based on the vinyl compound. The ppm mentioned above means mass ppm.

Examples of the vinyl compound include vinyl halides such as vinyl chloride; vinyl esters such as vinyl acetate and vinyl propionate; (meth) acrylic acid, esters and salts thereof; maleic acid, fumaric acid, their esters and anhydrides; styrene, acrylonitrile, vinylidene chloride, vinyl ether, and the like. Among them, vinyl chloride is preferably used alone or in combination with vinyl chloride and 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) acrylates 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.

For suspension polymerization of vinyl compounds, oil-soluble or water-soluble polymerization initiators conventionally used for polymerization of vinyl chloride can be used. Examples of the oil-soluble polymerization initiator include percarbonate compounds such as diisopropyl peroxydicarbonate, di (2-ethylhexyl) peroxydicarbonate, and diethoxyethyl peroxydicarbonate; perester compounds such as t-butyl peroxyneodecanoate, t-butyl peroxypivalate, t-hexyl peroxypivalate and cumyl peroxyneodecanoate; peroxides such as acetylcyclohexylsulfonyl peroxide, 2,4, 4-trimethylpentyl-2-phenoxyacetic acid ester, 3,5, 5-trimethylhexanoyl peroxide, lauroyl peroxide and the like; azo compounds such as 2,2 ' -azobis (2, 4-dimethylvaleronitrile), 2 ' -azobis (isobutyronitrile), and 2,2 ' -azobis (4-methoxy-2, 4-dimethylvaleronitrile). Examples of the water-soluble polymerization initiator include potassium persulfate, ammonium persulfate, hydrogen peroxide, cumene hydroperoxide, and the like. These polymerization initiators may be used in an amount of 1 kind alone or in combination of 2 or more kinds.

In the suspension polymerization of the vinyl compound, the polymerization temperature is not particularly limited, and may be a low temperature of about 20 ℃ or a high temperature exceeding 90 ℃, and preferably about 40 to 70 ℃. Further, in order to improve the heat removal efficiency of the polymerization reaction system, a polymerizer equipped with a reflux condenser may be used.

The dispersion stabilizer for suspension polymerization of the present invention may be used alone in suspension polymerization of a vinyl compound, or may be used in combination with a water-soluble cellulose ether such as methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxyethyl methyl cellulose (HEMC), hydroxypropyl methyl cellulose (HPMC), or the like, as long as the gist of the present invention is not impaired; water-soluble polymers other than the aforementioned modified PVA, such as modified (e.g., modified based on a carboxylic acid or sulfonic acid plasma group) or unmodified polyvinyl alcohol, gelatin, and the like; oil-soluble emulsifiers such as sorbitan monolaurate, sorbitan trioleate, glycerin tristearate, ethylene oxide propylene oxide block copolymers and the like; and water-soluble emulsifiers such as polyoxyethylene sorbitan monolaurate, polyoxyethylene glyceryl oleate, and sodium laurate.

Examples of polyvinyl alcohols other than the modified PVA include saponified polyvinyl alcohol (S) having a saponification degree of less than 65 mol% and a viscosity average degree of polymerization of 50 to 750, and polyvinyl alcohol (T) having a saponification degree of 65 mol% or more and 99.5 mol% or less and a viscosity average degree of polymerization of 800 to 3500. The degree of saponification and the degree of viscosity-average polymerization can be measured in the same manner as in the case of the modified PVA. The polyvinyl alcohol (S) is preferably a polyvinyl alcohol having a saponification degree of 30 to 60 mol% and a viscosity average polymerization degree of 180 to 650. The polyvinyl alcohol (T) is preferably a polyvinyl alcohol having a saponification degree of 80 mol% or more and 99.5 mol% or less and a viscosity-average degree of polymerization of 1000 to 3200. The polyvinyl alcohol (S) and the polyvinyl alcohol (T) may be unmodified, or may be modified by introducing an ionic group such as a carboxylic acid or a sulfonic acid to impart self-emulsifiability. The mass ratio of the polyvinyl alcohol (S) used in combination with the modified PVA (modified PVA/polyvinyl alcohol (S)) is not particularly limited, and is preferably 95/5 to 20/80, and more preferably 90/10 to 30/70. The mass ratio of the polyvinyl alcohol (T) used in combination with the modified PVA (modified PVA/polyvinyl alcohol (T)) is not particularly limited, and is preferably 95/5 to 20/80, and more preferably 90/10 to 30/70. The modified PVA and the polyvinyl alcohol (S) and/or the polyvinyl alcohol (T) may be fed together at the initial stage of the suspension polymerization, or may be fed in several portions during the suspension polymerization.

The obtained vinyl polymer can be used for various molded article applications by appropriately blending a plasticizer and the like.

The present invention includes embodiments in which the above-described configurations are combined in various ways within the scope of the technical idea of the present invention while the effects of the present invention are exhibited.