TWI834601B - Polyvinyl alcohol resin, dispersant and dispersant for suspension polymerization - Google Patents

Abstract

An object of the present invention is to provide a polyvinyl alcohol-based resin with suppressed coloration, a dispersant using the polyvinyl alcohol-based resin, and a dispersant for suspension polymerization used in the production of polyvinyl chloride. When the polyvinyl alcohol resin of the present invention is made into a 0.1% by weight aqueous solution, the absorbance (X) at 320 nm in the ultraviolet absorption spectrum is 0.1 or more, and the content of fine powder with a particle size of 500 μm or less is 60% by weight or less.

Description

Polyvinyl alcohol resin, dispersant and dispersant for suspension polymerization

The present invention relates to polyvinyl alcohol-based resins, and more specifically, to polyvinyl alcohol-based resins suitable as dispersants used when suspension polymerization of vinyl compounds in the production of polyvinyl chloride, dispersants, and suspension polymerization. Use dispersants.

Polyvinyl alcohol-based resin (hereinafter, "polyvinyl alcohol" may be abbreviated as "PVA") is obtained by saponifying a polymer obtained by polymerizing vinyl ester-based monomers such as vinyl acetate. PVA-based resins are usually dehydrated by heat treatment to form a structure with double bonds in the main chain. PVA-based resins with this structure are used as suspension dispersion stabilizers and water-retaining materials in the production of polyvinyl chloride. Furthermore, it is also known that the strength of films and fibers made of PVA-based resin can be improved by subjecting them to heat treatment.

The double bonds in the above-mentioned PVA resin can be confirmed especially by using the ultraviolet absorption spectrum of the 0.1% by weight aqueous solution. The peak near 215nm belongs to the structure of [-CO-CH=CH-], the peak near 280nm belongs to the structure of [-CO-(CH=CH) ₂ -], and the peak near 320nm belongs to the structure of [- The structure of CO-(CH=CH) ₃ -].

On the other hand, as a dispersant for suspension polymerization in the production of polyvinyl chloride, various heat-treated PVA-based resins have been studied.

For example, a polyvinyl alcohol-based resin containing a salt or hydroxide of a divalent to trivalent metal having a carbonyl group in the molecule has been proposed (see, for example, Patent Document 1.). In addition, someone has proposed a PVA-based polymer whose absorbance (a) at 280 nm measured by the ultraviolet absorption spectrum of an aqueous solution with a concentration of 0.1% by weight is greater than 0.1, and the absorbance (b) measured at 320 nm by the ultraviolet absorption spectrum of the aqueous solution is more than 0.03. , the absorbance (b)/absorbance (a) is less than 0.3, and the block character of the remaining acetate group is 0.4 or more (for example, refer to Patent Document 2).

However, in order to obtain the PVA-based resin described in Patent Documents 1 and 2, heat treatment is required at approximately 150°C for 5 to 6 hours, which raises the problem of increased manufacturing costs. In addition, there are many opportunities for contact with oxygen during the production process, and insoluble matter may be generated, and there is a problem that the randomness of residual fatty acid ester groups such as acetyloxy groups is not improved.

In order to solve the above problems, for example, Patent Document 3 proposes a polyvinyl alcohol-based resin that has a carbonyl group in the molecule and has a block character value (block character) of the remaining fatty acid ester group of 0.5 or more, which is 0.1 for the polyvinyl alcohol resin. The absorbances at 215nm, 280nm, and 320nm measured by the ultraviolet absorption spectrum of the aqueous solution by weight are all above 0.1, and the ratio of the absorbance at 320nm/the absorbance at 280nm is above 0.3.

[Prior technical literature]

[Patent Literature]

[Patent Document 1] Japanese Patent Application Publication No. 08-269112

[Patent Document 2] Japanese Patent Application Publication No. 08-283313

[Patent Document 3] Japanese Patent Application Publication No. 2004-250695

However, with conventional PVA-based resins, the obtained resin is colored. Even when used as a dispersant for suspension polymerization in the production of polyvinyl chloride, there is a problem that polyvinyl chloride is colored.

Due to the increase in required physical properties in recent years, in order to suppress the coloring of suspension polymers (for example, polyvinyl chloride), it is desired to suppress the coloring of PVA-based resins used as dispersants for suspension polymerization.

An object of the present invention is to provide a PVA-based resin with suppressed coloration, a dispersant using the PVA-based resin, and a dispersant for suspension polymerization used in the production of polyvinyl chloride.

In order to solve the above-mentioned problems, the inventors of the present case conducted diligent research and found that the coloring of PVA-based resin is related to the amount of fine powder in the resin, and completed the present invention.

That is, the gist of the present invention is the following (1) to (5).

(1) A polyvinyl alcohol-based resin whose absorbance (X) at 320 nm in the ultraviolet absorption spectrum is 0.1 or more when made into a 0.1% by weight aqueous solution, and the content of fine powder with a particle size of 500 μm or less is 60% by weight or less.

(2) The polyvinyl alcohol-based resin of (1), wherein the ratio (X/Y) of the absorbance (X) at 320 nm to the absorbance (Y) at 280 nm in the ultraviolet absorption spectrum when it is made into a 0.1% by weight aqueous solution is above 0.3.

(3) The polyvinyl alcohol-based resin according to (1) or (2), wherein the degree of saponification is 60 mol% or more.

(4) A dispersant composed of the polyvinyl alcohol-based resin according to any one of (1) to (3).

(5) A dispersant for suspension polymerization consisting of the polyvinyl alcohol-based resin according to any one of (1) to (3).

According to the present invention, a PVA-based resin with little coloration and good appearance can be obtained. Therefore, when a PVA-based resin is used as a dispersant for suspension polymerization, coloring of the obtained polymer can be suppressed.

The polyvinyl alcohol-based resin of the present invention will be described in detail below.

[Polyvinyl alcohol-based resin]

The polyvinyl alcohol-based resin (PVA-based resin) of the present invention is a heat-treated PVA-based resin that has been subjected to heat treatment. When it is made into a 0.1% by weight aqueous solution, the absorbance (X) at 320 nm in the ultraviolet absorption spectrum is 0.1 or more, and the particle size is The content of fine powder below 500 μm is below 60% by weight. According to the research of the inventors of the present case, it was found that PVA-based resin in the form of fine powder of 500 μm or less tends to be easily colored by heat. The PVA-based resin of the present invention can suppress this coloring by controlling the content of fine powder to 60% by weight or less. .

Generally speaking, PVA-based resin is a resin obtained by saponifying a vinyl ester homopolymer or a copolymer of vinyl ester and other monomers using an alkali catalyst or the like. The PVA-based resin of the present invention is obtained by subjecting the PVA-based resin obtained by saponification to heat treatment and causing dehydration or deacetylation reaction.

The saponification degree of the PVA-based resin of the present invention is the same as the saponification degree of the PVA-based resin before heat treatment. The degree of saponification (measured in accordance with JIS K 6726.) is preferably 60 mol% or more, more preferably 65 to 98 mol%, still more preferably 67 to 90 mol%, particularly preferably 69 to 88 mol%. . The PVA-based resin of the present invention has an acetate group (hydrophobic group) in the molecule in addition to the hydroxyl group (hydrophilicity), so it has interfacial activation energy and can be uniformly dispersed in the dispersion medium. If the saponification degree is too low, the water dispersibility tends to decrease, so the saponification degree is preferably 60 mol% or more.

The average degree of polymerization of the PVA-based resin of the present invention is the same as the average degree of polymerization of the PVA-based resin before heat treatment. The average degree of polymerization is preferably 100 to 4000, more preferably 200 to 3000, even more preferably 300 to 1000. If the average degree of polymerization is too low, the interfacial activation energy will tend to decrease, and when used as a dispersant for vinyl chloride suspension polymerization, aggregation will easily occur during suspension polymerization. On the other hand, if the average polymerization is too high, the viscosity of the PVA-based resin aqueous solution will increase and the operability will decrease.

In addition, the average degree of polymerization can be measured in accordance with JIS K 6726.

When the PVA-based resin of the present invention is made into a 0.1% by weight aqueous solution, the absorbance (X) at 320 nm in the ultraviolet absorption spectrum is 0.1 or more. If the ultraviolet absorbance at 320 nm of the 0.1% by weight aqueous solution of PVA resin is less than 0.1, the formation of double bonds will be small, so the interfacial activation energy will tend to decrease. The ultraviolet absorbance at 320 nm of the 0.1% by weight aqueous solution of the PVA resin is preferably 0.2 or more. The upper limit is not particularly limited, but from the viewpoint of manufacturability, it is about 1.5.

In addition, the ultraviolet absorbance at wavelengths other than 320nm is preferably as follows. Specifically, the ultraviolet absorbance at 215 nm is preferably 0.1 or more, more preferably 0.3 or more, and the upper limit is about 2. 280nm purple The external absorbance is ideally 0.1 or more, more preferably 0.3 or more, and the upper limit is about 2. If the absorbance is too low, the formation of double bonds will be small, so the interfacial activation energy will tend to decrease. If it is too high, the manufacturability will tend to decrease.

In addition, the absorption at 215nm in the ultraviolet absorption spectrum belongs to the -CO-CH=CH- structure in PVA resin, and the absorption at 280nm belongs to the -CO-(CH=CH) ₂ - structure in PVA resin. , the absorption at 320nm is attributed to the -CO-(CH=CH) ₃ - structure in PVA resin.

Furthermore, in the present invention, when the PVA-based resin of the present invention is made into a 0.1% by weight aqueous solution, the ratio of the absorbance (X) at 320 nm to the absorbance (Y) at 280 nm in the ultraviolet absorption spectrum (X/Y: 320nm/280nm) It is preferably 0.3 or more, more preferably 0.4 or more, still more preferably 0.5 or more. If the absorbance ratio is too small, when used as a dispersant for vinyl chloride suspension polymerization, the interfacial activation energy will be reduced and the suspension polymerization stability will tend to decrease. The upper limit is not particularly limited, but from the viewpoint of productivity, it is about 3.

The absorbance can be measured using a UV-visible-near-infrared spectrophotometer (for example, "V-560" (trade name) manufactured by JASCO Corporation) at wavelengths of 215 nm, 280 nm, and 320 nm for a 0.1% by weight aqueous solution of PVA resin. Absorbance. In addition, a sample container (colorimetric tube) with a thickness of 1 cm was used for measurement.

In the PVA-based resin of the present invention, the content of fine powder with a particle size of 500 μm or less is 60% by weight or less, preferably 50% by weight or less, more preferably 35% by weight or less, even more preferably 20% by weight or less, and contains no particle size. Micron powder below 500 μm (that is, 0% by weight) is most ideal. Micropowder (resin) with a particle size of 500 μm or less If the content of PVA-based resin is too high, the PVA-based resin will be colored, and a PVA-based resin with good appearance will tend not to be obtained. Even when used as a dispersant for vinyl chloride suspension polymerization, the vinyl chloride resin will tend to be colored.

In addition, the content of fine powder with a particle diameter of 500 μm or less can be calculated by sieving it through a sieve with a nominal mesh opening of 500 μm (JIS Z8801-1: 2000 "standard sieve"), and calculating the total weight of the fine powder that has passed the sieve relative to the PVA-based resin. to find the ratio.

In the present invention, when the PVA-based resin of the present invention is made into a 1.0% by weight aqueous solution, the yellow index (YI) value of the aqueous solution is preferably 33 or less, preferably 31 or less, still more preferably 30 or less. , especially preferably below 28. A PVA-based resin with a small YI value is a PVA-based resin in which coloring is suppressed. The lower limit value is preferably 0.

In addition, the YI value can be measured using a colorimeter "CM-3600A" (trade name) manufactured by Konica Minolta Co., Ltd., for example.

The block characteristic value of the PVA resin of the present invention (an index expressing the blocking properties of the vinyl alcohol unit and the vinyl ester unit of the PVA resin) is preferably 0.5 or more, more preferably 0.55 or more. If the block characteristic value is too low, the foaming inhibitory effect during suspension polymerization of vinyl compounds such as vinyl chloride tends to be reduced. There is no particular upper limit, but from the viewpoint of the manufacturability of the PVA-based resin, it is 0.9 or less.

In addition, the block characteristic value (?) can be measured in the following manner.

For PVA-based resin, measured by ¹³ C-NMR (3-(trimethylsilyl)-2,2,3,3-d ₄ -propionic acid sodium salt (3-(trimethylsilyl)propionic-2) was used as the internal standard material ,2,3,3-d ₄ acid sodium salt), from the absorption based on the methylene carbon moiety observed in the range of 38~49ppm [(OH,OH)dyad absorption = 43.5~46ppm, (OH, The absorption of OR)dyad = 41~43.5ppm, the absorption of (OR,OR)dyad = 38~40.5ppm, but R represents the absorption intensity ratio of acetyl group (CH ₃ CO-)]. More specifically, It is a value calculated from the following formula.

〔η〕=(OH,OR)/2(OH)(OR)

(However, (OH, OR), (OH), and (OR) are all calculated in molar fraction. Also, (OH) is the degree of saponification (molar fraction) calculated from the integral ratio of ¹³ C-NMR, (OR) ) represents the molar fraction of acetyloxy group at this time.)

The PVA-based resin of the present invention preferably contains at least one of a divalent to trivalent metal salt and a hydroxide. By containing at least one of salts and hydroxides of divalent to trivalent metals, efficient heat treatment can be performed.

Metals with 2~3 valence, such as magnesium, calcium, zinc, aluminum, etc.

Specific examples of salts or hydroxides of these metals, such as magnesium acetate tetrahydrate, calcium acetate, calcium propionate, magnesium butyrate, magnesium carbonate, magnesium hydroxide, zinc acetate, aluminum hydroxide, etc., can be used alone. 1 type, or 2 or more types can be used in combination. Among these, magnesium acetate tetrahydrate and calcium acetate are preferred from the viewpoint of being soluble in water, methanol, etc. and being easily handled industrially.

The content of divalent to trivalent metal salts and/or hydroxides in the PVA-based resin of the present invention is preferably 30-300 μmol/g, and more preferably 40-200 μmol/g relative to the PVA-based resin. If the content is too small, the amount of vinyl vinyl group produced will be low, whereas if it is too high, the PVA resin will tend to be discolored and decomposed.

The method of containing salts and/or hydroxides of divalent to trivalent metals is not limited. The above compounds can be added directly to the paste before saponification, the slurry after saponification, etc., but it is preferably dissolved in methanol, ethanol, or propylene. A method in which alcohol, such as alcohol, or water is added to the saponified PVA slurry in the form of a solution with a concentration of about 3 to 15% by weight, and is distributed to the PVA-based resin.

[Production method of polyvinyl alcohol-based resin]

As mentioned above, the PVA-based resin of the present invention has an absorbance (X) of 320 nm in the ultraviolet absorption spectrum of 0.1 or more when it is made into a 0.1% by weight aqueous solution. In order to make the absorbance (X) at 320 nm 0.1 or more, for example, a PVA-based resin having a carbonyl group in the molecule with a conjugated double bond introduced into the resin is used, and then the resin is heat-treated to cause dehydration or deacetylation reaction.

First, the method of introducing a carbonyl group into the molecule of PVA-based resin is explained. This method, for example: the following methods (i)~(iv).

(i) A method of polymerizing a vinyl ester monomer, saponifying the obtained polymer, and oxidizing the obtained PVA resin with an oxidizing agent such as hydrogen peroxide.

(ii) When polymerizing vinyl ester monomers, the polymerization is carried out in the presence of chain transfer agents containing carbonyl groups such as aldehydes and ketones, and the resulting polymer is saponified.

(iii) A method of polymerizing a vinyl ester monomer in the presence of 1-methoxy-vinyl acetate, etc., and saponifying the obtained polymer

(iv) A method of polymerizing vinyl ester monomers by blowing air into them and saponifying the resulting polymer.

Among them, the method (ii) above is preferred in terms of industrialization and ease of solvent recovery.

Hereinafter, the method for producing the PVA-based resin of the present invention will be described, taking the method (ii) above as an example. In the method (ii), the PVA-based resin of the present invention is obtained according to the method shown in the following scheme. Moreover, in the scheme, Ac represents an acetyl group.

Vinyl ester monomers that are starting materials, such as: vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl decanoate, vinyl laurate, vinyl palmitate, vinyl stearate And other linear or branched saturated fatty acid vinyl esters, etc. From a practical point of view, vinyl acetate is more preferred, and vinyl acetate is usually used alone or in combination with a fatty acid vinyl ester compound other than vinyl acetate.

When polymerizing vinyl ester monomers, there are no particular restrictions and any known polymerization method can be used. Usually, solution polymerization is performed using an alcohol with 1 to 3 carbon atoms such as methanol, ethanol, or isopropyl alcohol as a solvent. Of course, block polymerization, emulsion polymerization, and suspension polymerization can also be performed.

In this solution polymerization, any method of feeding the vinyl ester monomer, such as split feeding or one-time feeding, can be used. The polymerization reaction uses well-known free radical polymerization such as azobisisobutyronitrile, acetyl peroxide, benzyl peroxide, lauryl peroxide, azobisdimethylvaleronitrile, and azobismethoxyvaleronitrile. Catalyst proceeds. In addition, the polymerization reaction temperature is selected from the range of about 40° C. to the boiling point.

As for the chain transfer agent used in the method (ii), aldehydes include acetaldehyde, propionaldehyde, butyraldehyde, benzaldehyde, etc., and ketones include acetone, methyl ethyl ketone, hexanone, cyclohexanone, etc., One of these may be used alone, or two or more types may be used in combination.

Among them, considering that the structure after polymerization is similar to the final product, it is better to use aldehydes, especially acetaldehyde.

The amount of chain transfer agent added varies slightly depending on the chain transfer constant of the added chain transfer agent, the degree of polymerization of the intended PVA resin, etc. It is usually 0.1 to 5% by weight relative to the vinyl ester monomer. % is preferred, and 0.5 to 3% by weight is more preferred. In addition, the chain transfer agent can be fed in one time at the beginning or during the polymerization reaction. The chain transfer agent can be fed by any method to control the molecular weight distribution of PVA resin.

The vinyl ester monomer can be used alone, but if necessary, a modified PVA resin obtained by copolymerizing a monomer polymerizable with the vinyl ester monomer can also be used. The monomer, for example: (meth)glycidyl acrylate, Monomers with vinyl and epoxy groups such as epoxypropyl (meth)allyl ether, 3,4-epoxycyclohexyl (meth)acrylate, and allyl glycidyl ether; triallyl oxide Ethylene, diallyl maleate, triallyl cyanurate, triallyl isocyanurate, tetraallyloxyethane, diallyl phthalate, triallyl cyanurate, Triallyl isocyanurate and other monomers with more than 2 allyl groups; allyl esters such as allyl acetate, vinyl acetate, allyl acetate, and allyl diacetate. Monomers; (meth)acetyl acetyloxyethyl acrylate, (meth)acetyl acetyloxypropyl acrylate and other acetyl acetyloxyalkyl acrylates; acetyl ethyl crotonic acid Acetyl acetyloxyalkyl crotonic acid, acetyl acetyloxypropyl crotonic acid, etc.; 2-cyanoacetyl acetyloxyethyl (meth)acrylate; divinylbenzene ; Ethylene glycol di(meth)acrylate, 1,2-propanediol di(meth)acrylate, 1,3-propanediol di(meth)acrylate, 1,4-propanediol di(meth)acrylate Alkylene glycol (meth)acrylates such as butanediol ester, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, etc.; trimethylolpropane (meth)acrylate; allyl (meth)acrylate; 2-hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, etc. (methyl )Hydroxyalkyl acrylate (the alkyl part is C1~C10 alkyl, preferably C1~C6 alkyl); (meth)acrylonitrile and other nitrile monomers; styrene, α-methylstyrene and other styrenes Monomers; olefins such as ethylene, propylene, 1-butene, isobutylene; halogenated olefins such as vinyl chloride, vinylidene chloride, fluorinated ethylene, fluorinated vinylene; olefin monomers such as ethylene sulfonic acid; butadiene- 1,3, 2-methylbutadiene, 1,3 or 2,3-dimethylbutadiene-1,3, 2-chloroprene-1,3 and other diene monomers; 3- Buten-1-ol, 4-penten-1-ol, 5-hexene-1,2-diol, glycerol monoallyl ether and other hydroxyl-containing α-olefins, and their acyl compounds and other derivatives ; 1,3-Diethyloxy-2-methylenepropane, 1,3-dipropyloxy-2-methylenepropane, 1,3-dibutyloxy-2-methylene Hydroxymethylethylene diacetates such as propane; unsaturated acids such as itaconic acid, maleic acid, acrylic acid, their salts or mono- or dialkyl esters; nitriles such as acrylonitrile, methacrylamide, diacetone propylene Amides such as amide, vinyl sulfonic acid, allyl sulfonic acid, methylallylsulfonic acid, AMPS and other olefin sulfonic acids or their salts and other compounds, Vinyltriethoxysilane, vinyltrimethoxysilane, vinyltripropoxysilane, vinyltributoxysilane, vinylmethyldimethoxysilane, vinylmethyldiethoxysilane etc. Vinyl alkyl dialkoxysilane; γ-(meth)acryloxypropyltrimethoxysilane, γ-(meth)acryloxypropyltriethoxysilane, etc. (Methyl)acryloxypropyltrialkoxysilane; γ-(meth)acryloxypropylmethyldimethoxysilane, γ-(meth)acryloxypropylmethyldiethyl Oxysilane and other γ-(meth)acryloxypropylalkyl dialkoxysilane; vinyl silane (β-methoxyethoxy)silane, hydroxymethylvinylidene diacetate. Specific examples of hydroxymethylethylene diacetate include 1,3-diethyloxy-2-methylenepropane, 1,3-dipropyloxy-2-methylenepropane, 1 , 3-dibutyloxy-2-methylenepropane, etc.

Also, 3,4-dihydroxy-1-butene, 3,4-dihydroxy-1-butene, 3-hydroxy-4-hydroxy-1-butene, 4-hydroxy-3 -Hydroxy-1-butene, 3,4-diyloxy-2-methyl-1-butene, 4,5-dihydroxy-1-pentene, 4,5-diyloxy-1- Pentene, 4,5-dihydroxy-3-methyl-1-pentene, 4,5-dihydroxy-3-methyl-1-pentene, 5,6-dihydroxy-1-hexene , 5,6-diethyloxy-1-hexene, glycerol monoallyl ether, 2,3-diethyloxy-1-allyloxypropane, 2-ethyloxy-1-allyl Oxy-3-hydroxypropane, 3-acetyloxy-1-allyloxy-2-hydroxypropane, glyceryl monovinyl ether, glyceryl monoisopropylene ether, vinyl ethyl carbonate, 2,2-di Compounds containing diols such as methyl-4-vinyl-1,3-dioxolane (2,2-dimethyl-4-vinyl-1,3-dioxolane), etc. These monomers can be used individually or in combination of 2 or more types.

Moreover, "(meth)acrylate" means "acrylate and/or methacrylate", and the same applies to "(meth)allyl" and "(meth)acrylyl".

The content of the monomer polymerizable with the vinyl ester monomer is preferably 20 mol% or less, more preferably 10 mol% or less.

The vinyl ester polymer obtained by polymerization is saponified and a carbonyl group is introduced into the molecule.

Saponification can be carried out by a known method. Usually, the vinyl ester polymer is dissolved in alcohol and carried out in the presence of an alkali catalyst or an acid catalyst. Alcohols, such as methanol, ethanol, butanol and other alcohols with 1 to 6 carbon atoms.

The concentration of the vinyl ester polymer in the alcohol is selected from the range of 20 to 50% by weight in consideration of the dissolution rate.

Alkali catalysts such as alkali metal hydroxides and alkoxides such as sodium hydroxide, potassium hydroxide, sodium methoxide, sodium ethoxide, and potassium methoxide can be used. Examples of the acid catalyst include inorganic acid aqueous solutions such as hydrochloric acid and sulfuric acid, and organic acids such as p-toluenesulfonic acid. The usage amount of the catalyst is preferably 1 to 100 mmol equivalents relative to the vinyl ester monomer, more preferably 1 to 40 mmol equivalents, and more preferably 1 to 20 mmol equivalents. If the amount of the catalyst used is too small, saponification will tend to be difficult to achieve the desired degree of saponification. If the amount of the catalyst used is too large, the reactivity of saponification cannot be further improved, so it is not preferable.

There is no particular restriction on the reaction temperature during saponification. Generally, 10 to 70°C is ideal, and more preferably, the reaction temperature is selected from the range of 20 to 50°C.

The reaction time during saponification can be adjusted appropriately according to the saponification treatment method. For example, when implementing batch saponification, the saponification reaction usually takes 2 to 3 hours.

In the present invention, the modified PVA-based resin can also be produced by post-modifying the obtained PVA-based resin. Methods for producing modified PVA resins, such as acetoacetation, acetalization, urethanization, etherification, grafting, phosphate esterification, and oxyalkylation of PVA resins wait.

The obtained PVA-based resin is subjected to heat treatment to cause dehydration or deacetylation reaction and generate conjugated double bonds, thereby obtaining the PVA-based resin of the present invention.

The temperature of heat treatment is usually preferably in the range of 120~180℃, and more preferably 140~155℃. If the temperature of this heat treatment is too low, it will tend to become difficult to obtain the desired vinyl vinyl content (double bond). On the other hand, if the temperature is too high, it will tend to be easily decomposed due to heat treatment.

The heat treatment time is usually 0.5 to 5 hours, more preferably 1.5 to 4 hours. If the heat treatment time is too short, the amount of vinyl vinyl group produced will tend to decrease. On the other hand, if it is too long, it will tend to cause coloration of the PVA-based resin and the formation of water-insoluble components.

The heat treatment can be performed using any device, for example, a stirring device that stirs while heating the contents, such as a Nauta mixer or a cone dryer.

In addition, the heat treatment is preferably carried out in an oxygen environment with an oxygen concentration of 20% by volume or less, and more preferably in an oxygen environment with an oxygen concentration of 3 to 12% by volume. If the oxygen concentration is too high, it will tend to cause coloring or insolubilization of the PVA-based resin.

In this heat treatment, a PVA-based resin obtained by a known method containing the metal salt shown above can be used. However, in order to obtain good interfacial activation energy and to generate a sufficient amount of vinyl vinyl groups, the carbonyl group of the PVA-based resin before heat treatment is The content is preferably 0.03~2.5 mol%, more preferably 0.05~2 mol%.

In the heat-treated PVA-based resin obtained as described above, the content of the fine powder is adjusted so that the content of the fine powder having a particle size of 500 μm or less is 60% by weight or less. The content of micropowders with a diameter of less than 500 μm in the heat-treated PVA resin is preferably less than 50% by weight, more preferably less than 35% by weight, especially less than 20% by weight, and does not contain any micropowder with a particle size of less than 500 μm (also That is, 0% by weight) is optimal. The smaller the particle size of PVA-based resin, the stronger the tendency for coloring due to heat treatment. By setting the content of fine powder with a particle size of 500 μm or less to 60% by weight or less, the coloring of PVA-based resin can be suppressed.

In order to adjust the content of fine powder with a particle size of 500 μm or less, for example, sieving through a sieve with a nominal mesh opening of 500 μm (JIS Z8801-1: 2000 "standard sieve"), or during the stirring steps of saponification, drying, etc., reduce Stirring power, or methods to shorten stirring time, etc.

[use]

The PVA-based resin of the present invention obtained in the above manner is suppressed in coloring and therefore has an excellent hue and is suitable for use in various applications. Examples of uses of the PVA-based resin of the present invention are as follows.

(1) Related molded products: fibers, films, sheets, pipelines, tubes, leak-proof films, temporary films, chemical laces, water-soluble fibers, etc.

(2) Adhesive related: adhesives for wood, paper, aluminum foil, plastic, etc., adhesives, rewetting agents, adhesives for non-woven fabrics, adhesives for various building materials such as gypsum board, fiberboard, etc., adhesives for various powder granulations , additives for cement and stucco, hot-melt adhesives, pressure-sensitive adhesives, anionic paint fixing agents, etc.

(3) Coating agent related: transparent coating agent for paper, pigment coating agent for paper, sizing agent for paper, sizing agent for fiber products, warp paste, fiber processing agent, leather processing agent, coating, anti-corrosion agent Atomizer, metal anti-corrosion agent, gloss agent for zinc plating, antistatic agent, conductive agent, temporary coating, etc.

(4) Relevant blending agents for hydrophobic resins: antistatic agents for hydrophobic resins, hydrophilicity imparting agents, additives for molded products such as composite fibers and films, etc.

(5) Dispersant related: dispersants for color developers of coating liquids for thermochromic layers, pigment dispersion stabilizers such as paints, inks, watercolors, and adhesives, vinyl chloride, vinylidene chloride, styrene, (methane dispersion stabilizer for suspension polymerization of various vinyl compounds such as acrylate, vinyl acetate, etc.

(6) Related emulsification and dispersion stabilizers: emulsifiers for emulsion polymerization of various acrylic monomers, ethylenically unsaturated compounds, butadiene compounds, hydrophobic resins such as polyolefins and polyester resins, epoxy resins, paraffin wax, Post-emulsifier for bitumen, etc.

(7) Tackifier related: various aqueous solutions, emulsions, thickeners for petroleum excavation fluids, etc.

(8) Coagulant related: coagulant for suspended matter and dissolved matter in water, water filterability of wood pulp and slurry, etc.

(9) Exchange resin, etc. related: ion exchange resin, chelate exchange resin, ion exchange membrane, etc.

(10) Others: soil conditioner, photosensitive agent, photosensitive photoresist resin, etc.

Among the above, the PVA-based resin of the present invention is particularly useful as a dispersion stabilizer for suspension polymerization of various vinyl compounds such as vinyl acetate and vinyl chloride, and is particularly useful as a dispersion stabilizer for suspension polymerization of vinyl chloride-based compounds.

[Dispersant]

When the PVA-based resin of the present invention is used as a dispersant, examples of the dispersant include polymerizable monomers, powders, etc. In particular, it is preferable to disperse the polymerizable monomer and use it as a dispersant for suspension polymerization.

Polymerizable monomers that are subject to suspension polymerization, such as: vinyl chloride, vinylene halide, vinyl ether, vinyl acetate, vinyl benzoate, acrylic acid, methacrylic acid, maleic acid or its anhydride, ethylene, propylene, benzene Ethylene etc. Among them, it is suitable to be used in homopolymerization of vinyl chloride or copolymerization with monomers that can be copolymerized with vinyl chloride.

[Dispersant for suspension polymerization]

The use of the PVA-based resin of the present invention as a dispersant for suspension polymerization is described in detail below.

The usage amount of the PVA-based resin of the present invention can be appropriately adjusted according to the suspension polymerization monomer. For example, when used in the suspension polymerization of vinyl chloride-based monomer, it is usually suitable to use 5 parts by weight relative to 100 parts by weight of the vinyl chloride-based monomer. The following is preferred, 0.01 to 1 part by weight is more preferred, and 0.02 to 0.2 part by weight is more ideal. If the usage amount is too large, the amount of PVA-based resin that does not serve as a dispersant tends to increase.

When performing suspension polymerization, the PVA-based resin of the present invention is usually added to water or a heated water medium as a dispersant to disperse the vinyl chloride monomer, and then polymerize in the presence of an oil-soluble catalyst.

The method of adding PVA-based resin is to add it as a powder, a solution dissolved in water or an organic solvent such as alcohol, ketone, ester, or a mixed solvent of such an organic solvent and water, or a dispersion dispersed in the above solvent. .

As for the time point of addition, it can be added all at once at the beginning of the aggregation, or it can be added in divisions during the aggregation.

As for other additives, well-known stabilizers such as polymer substances may also be used together. Examples of the polymer material include PVA-based resins other than the PVA-based resin of the present invention. Examples of the PVA-based resin include unmodified PVA, the above-mentioned modified PVA-based resin, and the like.

Examples of the polymerization auxiliary include various surfactants and inorganic dispersants. The PVA-based resin of the present invention can also be used as the polymerization auxiliary.

The polymerization catalyst can be any oil-soluble catalyst. For example, benzoyl peroxide, lauryl peroxide, diisopropyl peroxydicarbonate, α,α'-azobisisobutyronitrile, α , α'-Azobis-2,4-dimethyl-valeronitrile, peroxyacetyl cyclohexyl sulfonyl group or mixtures thereof.

[Example]

The present invention will be described in more detail below using examples. However, the present invention is not limited to the following examples as long as the gist is not exceeded. In addition, "parts", "%", etc. are based on weight.

(Example 1)

<Manufacture of PVA resin>

100 parts of vinyl acetate, 1.2 parts of acetaldehyde, 4.7 parts of methanol and 0.0092% acetyl peroxide (APO) relative to vinyl acetate were fed into the polymerization tank and replaced with nitrogen. Then heat and polymerize at boiling point The polymerization was started and stopped when the polymerization rate reached 91.8% after about 5.7 hours of reaction time. Next, unpolymerized vinyl acetate was removed, and the obtained polymer was saponified with sodium hydroxide according to the usual method to prepare a PVA-based resin with a resin component of 12% (degree of polymerization 770, degree of saponification 71.7 mol%, and carbonyl content 0.16 Mol%) saponified slurry (solvent of methyl acetate/methanol = 8/2 (weight ratio)).

Then, a 10% methanol solution of magnesium acetate tetrahydrate as a metal compound was added to the PVA-based resin prepared above at a ratio of 350 g per 1 kg of PVA-based resin, and the mixture was stirred at 25° C. for 1 hour. Thereafter, the mixture was shaken in a Buchner funnel to obtain a PVA-based resin containing 177 μmol/g of magnesium acetate.

Then, in the heat treatment tank, after drying for 2 hours at 110°C in a nitrogen atmosphere, a gas of nitrogen: air = 1:1 (volume ratio) was flowed into the heat treatment tank at a speed of 100L/hr, keeping the oxygen concentration at 10% state, heat treatment at 145°C for 3 hours. The characteristics of the PVA-based resin after heat treatment are as follows.

Average degree of polymerization; 650 (measured in accordance with JIS K 6726), saponification degree; 72.0 mol% (measured in accordance with JIS 6726)), magnesium acetate content; 177 μmol/g (calculated from the amount of magnesium contained)

<Micropowder recovery steps>

Then, the obtained PVA-based resin was sieved using a 30-mesh sieve (mesh opening: 500 μm) to remove fine powder (resin particles) with a particle size of 500 μm or less, and PVA-based resin A (which only had a particle size larger than 500 μm) was obtained. Micropowder content: 0% by weight).

<Evaluation 1: Measurement of ultraviolet absorbance>

Prepare a 0.1% aqueous solution of PVA resin A. The absorbance of the 0.1% aqueous solution of PVA-based resin A was measured at wavelengths of 215 nm, 280 nm, and 320 nm using an ultraviolet, visible, and near-infrared spectrophotometer ("V-560" (trade name) manufactured by JASCO Corporation). Also, use a sample container (colorimetric tube) with a thickness of 1 cm.

Furthermore, the ratio (X/Y) of the absorbance (X) at 320 nm to the absorbance (Y) at 280 nm was calculated.

The results are shown in Table 1.

<Evaluation 2: Determination of yellow index (YI) value>

Prepare a 1.0% aqueous solution of PVA resin A. The YI value of this aqueous solution was measured using a colorimeter "CM-3600A" (trade name) manufactured by Konica Minolta Co., Ltd.

The results are shown in Table 1.

(Example 2)

PVA-based resin A obtained in Example 1 was mixed with fine powder having a particle size of 500 μm or less recovered in the recovery step of Example 1 so that the content of the entire resin became 31%, to obtain PVA-based resin B (fine powder amount: 31% by weight).

For the obtained PVA-based resin B, the ultraviolet absorbance, X/Y value, and YI value at each wavelength were measured in the same manner as in Example 1. The results are shown in Table 1.

(Example 3)

PVA-based resin A obtained in Example 1 was mixed with fine powder having a particle size of 500 μm or less recovered in the recovery step of Example 1 so that the content in the entire resin became 57%, to obtain PVA-based resin C (fine powder amount: 57% by weight).

For the obtained PVA-based resin C, the ultraviolet absorbance, X/Y value, and YI value at each wavelength were measured in the same manner as in Example 1. The results are shown in Table 1.

(Comparative example 1)

The fine powder recovery step in Example 1 was not performed. Otherwise, the same procedure as in Example 1 was performed to obtain PVA-based resin D. The content of micropowder with particle size below 500 μm is 78% by weight.

For the obtained PVA-based resin D, the ultraviolet absorbance, X/Y value, and YI value at each wavelength were measured in the same manner as in Example 1. The results are shown in Table 1.

From the results in Table 1, it can be seen that compared with Comparative Example 1, Examples 1 to 3 have smaller YI values and the coloring is suppressed. In particular, it is found that the smaller the content of fine powder with a particle size of 500 μm or less, the smaller the coloring of the PVA-based resin.

Furthermore, the ratio of the absorbance (X) at 320 nm to the absorbance (Y) at 280 nm measured by ultraviolet absorption spectrum of the 0.1% by weight aqueous solution of the PVA resin was high in all Examples 1 to 3, suggesting that it can be used as a dispersion for suspension polymerization. When the agent is used, the suspension polymerization stability remains good.

The present invention has been described in detail with reference to specific embodiments. However, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. This application is based on a Japanese patent application filed on December 21, 2016 (Special Application No. 2016-247686), the contents of which are incorporated herein by reference.

[Industrial Applicability]

The PVA-based resin of the present invention has double bonds and has little coloring. When used as various dispersants, it can also suppress coloring of the obtained polymer. In particular, it is useful as a dispersant for suspension polymerization of vinyl chloride monomers.

Claims (5)

A polyvinyl alcohol-based resin whose absorbance (X) at 320 nm in the ultraviolet absorption spectrum is 0.1 or more when made into a 0.1% by weight aqueous solution, and the ratio (X/Y) of the absorbance (X) at 320 nm to the absorbance (Y) at 280 nm ) is 0.3~0.568, and the content of fine powder with a particle size of less than 500 μm is less than 60% by weight. For example, in the polyvinyl alcohol-based resin of item 1 of the patent application, the content of fine powder with a particle size of 500 μm or less is 35% by weight or less. For example, the polyvinyl alcohol-based resin in item 1 or 2 of the patent application scope has a saponification degree of 60 mol% or more. A dispersant is composed of a polyvinyl alcohol-based resin as described in any one of claims 1 to 3 of the patent application. A dispersant for suspension polymerization is composed of a polyvinyl alcohol-based resin as described in any one of claims 1 to 3 of the patent application.