CN110088147B

CN110088147B - Polyvinyl alcohol resin, dispersant, and dispersant for suspension polymerization

Info

Publication number: CN110088147B
Application number: CN201780078464.6A
Authority: CN
Inventors: 村松雄介; 山内芳仁; 万代修作
Original assignee: Mitsubishi Chemical Corp
Current assignee: Mitsubishi Chemical Corp
Priority date: 2016-12-21
Filing date: 2017-12-21
Publication date: 2023-10-24
Anticipated expiration: 2037-12-21
Also published as: CN110088147A; WO2018117246A1; TW201835119A; JP2023052330A; JPWO2018117246A1

Abstract

The present application provides a polyvinyl alcohol resin capable of suppressing coloring, and also provides a dispersing agent using the polyvinyl alcohol resin and a dispersing agent for suspension polymerization used in the production of polyvinyl chloride. The absorbance (X) at 320nm in the ultraviolet absorption spectrum when a 0.1 wt.% aqueous solution is produced is 0.1 or more, and the content of fine powder having a particle diameter of 500 μm or less in the polyvinyl alcohol resin of the present application is 60 wt.% or less.

Description

Polyvinyl alcohol resin, dispersant, and dispersant for suspension polymerization

Technical Field

The present application relates to a polyvinyl alcohol resin, and more particularly, to a polyvinyl alcohol resin, a dispersant, and a dispersant for suspension polymerization, which are suitable as a dispersant for suspension polymerization of a vinyl compound in the production of polyvinyl chloride.

Background

Polyvinyl alcohol resins (hereinafter, sometimes simply referred to as "PVA") are obtained by saponifying polymers obtained by polymerizing vinyl ester monomers such as vinyl acetate. The PVA-based resin is usually dehydrated by heat treatment, and has a structure having a double bond in a main chain, and the PVA-based resin having the above structure is used for a dispersion stabilizer for suspension, a water-retaining material, and the like when the PVA-based resin is used for producing polyvinyl chloride. It is also known that strength can be improved by heat-treating a film or a fiber using a PVA-based resin.

The double bond in the PVA-based resin can be confirmed by ultraviolet absorption spectrum of a 0.1 wt% aqueous solution. The peak around 215nm is attributed to [ -CO-CH=CH ]]The peak around 280nm is attributed to [ -CO- (CH=CH) ₂ -]The peak around 320nm is attributed to [ -CO- (CH=CH) ₃ -]Is a structure of (a).

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 resin has been proposed which has a carbonyl group in a molecule and contains a salt or hydroxide of a metal having a valence of 2 to 3 (for example, refer to patent document 1). Further, a PVA-based polymer has been proposed in which the absorbance (a) at 280nm based on an ultraviolet absorption spectrum of an aqueous solution having a concentration of 0.1 wt% is more than 0.1, the absorbance (b) at 320nm based on an ultraviolet absorption spectrum of the same aqueous solution is 0.03 or more, the absorbance (b)/absorbance (a) is less than 0.3, and the block character (block character) of the residual acetic acid group is 0.4 or more (for example, see patent document 2).

However, in order to obtain the PVA-based resins described in patent documents 1 and 2, a heat treatment at about 150 ℃ for 5 to 6 hours is necessary, and there is a problem that the production cost becomes high. In addition, there is a problem that there is a possibility that undissolved substances are generated and the randomness of the residual fatty acid ester group such as an acetoxy group is not increased because there are many opportunities to contact with oxygen in the production process.

In order to solve the above problems, for example, patent document 3 proposes a PVA-based resin having a carbonyl group in a molecule and a residual fatty acid ester group having a block character of 0.5 or more, wherein an absorbance at 215nm, 280nm, and 320nm of a 0.1 wt% aqueous solution of the polyvinyl alcohol resin based on an ultraviolet absorption spectrum is 0.1 or more and a ratio of absorbance at 320nm to absorbance at 280nm is 0.3 or more.

Prior art literature

Patent literature

Patent document 1: japanese patent application laid-open No. 08-269112

Patent document 2: japanese patent laid-open No. 08-283313

Patent document 3: japanese patent application laid-open No. 2004-250695

Disclosure of Invention

Problems to be solved by the application

However, the conventional PVA-based resin has the following problems: the resin obtained is colored, and when it is used as a dispersant for suspension polymerization in the production of polyvinyl chloride, the resin is colored in polyvinyl chloride.

In order to suppress coloring of a suspension polymer (for example, polyvinyl chloride) in order to improve physical properties required in recent years, it is required to suppress coloring of a PVA-based resin used as a dispersant for suspension polymerization.

Accordingly, an object of the present application is to provide a PVA-based resin capable of suppressing coloring, and to provide a dispersing agent using the PVA-based resin and a dispersing agent for suspension polymerization used in producing polyvinyl chloride.

Solution for solving the problem

The present inventors have intensively studied to solve the above problems, and as a result, found that: the amount of fine powder in the resin is related to the coloring of the PVA based resin, and the present application has been completed.

Specifically, the gist of the present application is the following (1) to (5).

(1) A polyvinyl alcohol resin having an absorbance (X) of 0.1 or more at 320nm in the ultraviolet absorption spectrum when prepared as a 0.1 wt.% aqueous solution, wherein the polyvinyl alcohol resin has a fine powder particle size of 500 [ mu ] m or less and a content of 60 wt.% or less.

(2) The polyvinyl alcohol resin according to the item (1), wherein the ratio (X/Y) of the absorbance (X) at 320nm to the absorbance (Y) at 280nm in the ultraviolet absorption spectrum when the polyvinyl alcohol resin is prepared as a 0.1% by weight aqueous solution is 0.3 or more.

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

(4) A dispersant comprising the polyvinyl alcohol resin according to any one of the above (1) to (3).

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

ADVANTAGEOUS EFFECTS OF INVENTION

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

Detailed Description

The polyvinyl alcohol resin of the present application will be described in detail below.

[ polyvinyl alcohol resin ]

The polyvinyl alcohol resin (PVA resin) of the present application is a heat-treated PVA resin which has been heat-treated, and has an absorbance (X) of 0.1 or more at 320nm in an ultraviolet absorption spectrum when it is prepared into a 0.1 wt.% aqueous solution, and the content of fine powder having a particle diameter of 500 [ mu ] m or less is 60 wt.% or less. According to the studies by the present inventors, it has been found that a PVA-based resin having a fine powder of 500 μm or less tends to be easily colored by heat, and the coloring of the PVA-based resin of the present application can be suppressed by controlling the content of the fine powder to 60 wt% or less.

Generally, PVA-based resins are resins obtained by saponifying a vinyl ester homopolymer or a copolymer of a vinyl ester and another monomer with an alkali catalyst or the like. The PVA-based resin of the present application can be obtained as follows: the PVA-based resin obtained by the saponification is subjected to heat treatment to cause dehydration or a deacetylation reaction, thereby obtaining the PVA-based resin.

The saponification degree of the PVA based resin of the present application is the same as that of the PVA based resin before heat treatment. The saponification degree (measured in accordance with JIS K6726) 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%. In the PVA-based resin of the present application, since an acetic acid group (hydrophobic group) is present in addition to a hydroxyl group (hydrophilic group) in a molecule, the PVA-based resin has a surface active property and can be uniformly dispersed in a dispersion medium. When the saponification degree is too low, the water dispersibility tends to be lowered, and therefore, the saponification degree is preferably 60 mol% or more.

The average degree of polymerization of the PVA based resin of the present application is the same as that of the PVA based resin before heat treatment. The average degree of polymerization is preferably 100 to 4000, more preferably 200 to 3000, particularly preferably 300 to 1000. When the average polymerization degree is too low, the surface activity tends to be low, and when the dispersion agent is used as a dispersing agent for suspension polymerization of vinyl chloride, aggregation tends to be caused during suspension polymerization. Conversely, when the average polymerization degree is too high, the viscosity of the aqueous PVA-based resin solution increases, and the handleability decreases.

The average polymerization degree can be measured in accordance with JIS K6726.

When the PVA resin of the present application is used in the form of a 0.1% by weight aqueous solution, the absorbance (X) at 320nm in the ultraviolet absorption spectrum is 0.1 or more. When the ultraviolet absorbance at 320nm of the 0.1 wt% aqueous solution of the PVA-based resin is less than 0.1, the formation of double bonds is small, and therefore, the surface activity tends to be lowered. The ultraviolet absorbance at 320nm of the 0.1 wt% aqueous solution of the PVA-based resin is preferably 0.2 or more, and the upper limit is not particularly limited, but is about 1.5 from the standpoint of manufacturing possibility.

The ultraviolet absorbance at a wavelength other than 320nm is preferably not more than. Specifically, the ultraviolet absorbance at 215nm is preferably 0.1 or more, more preferably 0.3 or more, and the upper limit is about 2. The ultraviolet absorbance at 280nm is preferably 0.1 or more, more preferably 0.3 or more, and the upper limit is about 2. When the absorbance is too low, the formation of double bonds is small, and therefore, the surface activity tends to be low, and when the absorbance is too high, the production possibility tends to be low.

The absorption at 215nm of the ultraviolet absorption spectrum was attributed to the structure of-CO-CH=CH-in the PVA-based resin, and the absorption at 280nm was attributed to-CO- (ch=ch) in PVA-based resin ₂ -structure, absorption at 320nm is ascribed to-CO- (ch=ch) in PVA-based resin ₃ -a structure.

In the present application, the ratio (X/Y: 320nm/280 nm) of the absorbance (X) at 320nm to the absorbance (Y) at 280nm in the ultraviolet absorption spectrum when the PVA resin of the present application is prepared as a 0.1% by weight aqueous solution is preferably 0.3 or more, more preferably 0.4 or more, still more preferably 0.5 or more. When the absorbance ratio is too small, the surface activity tends to be low and the suspension polymerization stability tends to be low when the dispersion agent is used as a dispersing agent for suspension polymerization of vinyl chloride. The upper limit is not particularly limited, but is about 3 from the viewpoint of productivity.

The absorbance can be measured as follows: the absorbance of a 0.1 wt% aqueous solution of the PVA based resin was measured at wavelengths of 215nm, 280nm, and 320nm using an ultraviolet-visible near-infrared spectrophotometer (for example, "V-560" (trade name) manufactured by Japanese Specification Co., ltd.). The measurement was performed using a sample container (cuvette) having a thickness of 1 cm.

The content of fine powder having a particle size of 500 μm or less in the PVA-based resin of the present application is 60 wt% or less, preferably 50 wt% or less, more preferably 35 wt% or less, particularly preferably 20 wt% or less, and most preferably no fine powder having a particle size of 500 μm or less (i.e., 0 wt%). When the content of fine powder (resin particles) having a particle diameter of 500 μm or less is too large, the PVA-based resin tends to be colored, and a PVA-based resin having a good appearance tends not to be obtained, and when used as a dispersing agent for suspension polymerization of vinyl chloride, the vinyl chloride resin tends to be colored.

The content of the fine powder having a particle diameter of 500 μm or less can be determined, for example, as follows: the mixture was sieved with a sieve having a nominal pore size of 500 μm (JIS Z8801-1:2000 "Standard sieve"), and the ratio of the fine powder passing through the sieve to the total weight of the PVA based resin was calculated.

In the present application, the Yellow Index (YI) value of the aqueous solution when the PVA based resin of the present application is made into a 1.0% by weight aqueous solution is preferably 33 or less, more preferably 31 or less, still more preferably 30 or less, particularly preferably 28 or less. The PVA-based resin having a small YI value is a PVA-based resin capable of suppressing coloring. The lower limit value is preferably 0.

The YI value can be measured by using, for example, a colorimeter "CM-3600A" (trade name) manufactured by Konica Minolta, inc.

The block character of the PVA-based resin of the present application (an index indicating the blockiness of the vinyl alcohol unit and the vinyl ester unit of the PVA-based resin) is preferably 0.5 or more, more preferably 0.55 or more. If the block character is too low, the foam suppressing effect tends to be low in suspension polymerization of vinyl compounds such as vinyl chloride. The upper limit is not particularly limited, but is 0.9 or less in terms of the possibility of producing the PVA-based resin.

The block characteristics (. Eta.) can be measured as follows.

By using ¹³ Determination of PVA-based resin by C-NMR (3- (trimethylsilyl) -2, 3-d was used) ₄ Sodium (3- (trimethylyl) propionic acid) salt 2, 3-d ₄ acid sodium salt) as an internal standard), an absorption of [ (OH, OH) dyad=43.5 to 46ppm, an absorption of (OH, OR) dyad=41 to 43.5ppm, an absorption of (OR, OR) dyad=38 to 40.5ppm, wherein R represents an acetyl group (CH), based on a methylene carbon moiety visible in a range of 38 to 49ppm ₃ CO-), more specifically, a value calculated from the following equation.

〔η〕＝(OH，OR)/2(OH)(OR)

(wherein, (OH, OR), (OH), (OR) are calculated as mole fractions, (OH) is, in addition, by ¹³ The saponification degree (mole fraction) calculated by the integral ratio of C-NMR (OR) represents the mole fraction of the acetoxy group at this time. )

In the PVA-based resin of the present application, at least 1 of a salt and a hydroxide of a metal having a valence of 2 to 3 is preferably contained. The heat treatment is effectively performed by containing at least 1 of a salt and a hydroxide of a metal having a valence of 2 to 3.

Examples of the metal having a valence of 2 to 3 include magnesium, calcium, zinc, and aluminum.

Specific examples of the salts or hydroxides of these metals include magnesium acetate tetrahydrate, calcium acetate, calcium propionate, magnesium butyrate, magnesium carbonate, magnesium hydroxide, zinc acetate, and aluminum hydroxide, and 1 kind of the metal salts or hydroxides may be used alone or 2 or more kinds of the metal salts or hydroxides may be used in combination. Among them, magnesium acetate tetrahydrate and calcium acetate are preferable in terms of easy industrial handling by dissolving in water and/or methanol.

The content of the salt and/or hydroxide of the metal having a valence of 2 to 3 in the PVA based resin of the present application is preferably 30 to 300. Mu. Mol/g, more preferably 40 to 200. Mu. Mol/g, relative to the PVA based resin. When the content is too small, the amount of vinylidene formed decreases, whereas when it is too large, the PVA-based resin tends to be colored or decomposed.

The method for containing the salt and/or hydroxide of the metal having a valence of 2 to 3 is not limited, and the above-mentioned compound may be directly added to paste before saponification, slurry after saponification, or the like, and the following method is preferable: preferably, the aqueous dispersion is dissolved in an alcohol such as methanol, ethanol, propanol, or water, and added to the saponified PVA slurry in the form of a solution having a concentration of about 3 to 15% by weight, and then the aqueous dispersion is distributed to the PVA based resin.

[ method for producing polyvinyl alcohol resin ]

As described above, the absorbance (X) at 320nm in the ultraviolet absorption spectrum when the PVA resin of the present application is prepared as a 0.1% by weight aqueous solution is 0.1 or more. In order to set the absorbance (X) at 320nm to 0.1 or more, the following methods are exemplified: a resin in which a conjugated double bond is introduced into a PVA based resin having a carbonyl group in the molecule is used, and the resin is further subjected to a heat treatment to cause dehydration or a deacetic acid reaction.

First, a method of introducing carbonyl groups into the molecule of the PVA-based resin will be described. Examples of the method include the following methods (i) to (iv).

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

in the method (ii), when the vinyl ester monomer is polymerized, the polymerization is carried out in the coexistence of a carbonyl group-containing chain transfer agent such as aldehydes and ketones, and the obtained polymer is saponified;

a method (iii) wherein a vinyl ester monomer is polymerized in the presence of 1-methoxy-vinyl acetate or the like, and the resulting polymer is saponified;

in the method (iv), air is blown to polymerize the vinyl ester monomer during polymerization, the resulting polymer is saponified,

among them, the method (ii) is preferable from the viewpoint of industrially easily recovering the solvent.

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

Examples of the vinyl ester monomer as a starting material include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl caprate, vinyl laurate, vinyl palmitate, vinyl stearate, and other linear or branched saturated fatty acid vinyl esters. From the practical point of view, vinyl acetate is preferable, and in general, vinyl acetate may be used alone or in combination with a fatty acid vinyl ester compound other than vinyl acetate.

In polymerizing vinyl ester monomers, any known polymerization method can be used without particular limitation, and generally, solution polymerization using an alcohol having 1 to 3 carbon atoms such as methanol, ethanol or isopropanol as a solvent is carried out. Of course, bulk polymerization, emulsion polymerization, suspension polymerization may be carried out.

In the above solution polymerization, the vinyl ester monomer may be fed in any manner such as batch feeding and simultaneous feeding. The polymerization reaction is carried out using a known radical polymerization catalyst such as azobisisobutyronitrile, acetyl peroxide, benzoyl peroxide, lauroyl peroxide, azobisidimet valeronitrile, azobisisobutyronitrile and the like. The polymerization temperature is selected from the range of 40 to about the boiling point.

Examples of the chain transfer agent used in the method (ii) include acetaldehyde, propionaldehyde, butyraldehyde, and benzaldehyde, and examples of the ketones include acetone, methyl ethyl ketone, hexanone, and cyclohexanone, and 1 or 2 or more of them may be used alone or in combination.

Among them, aldehydes are preferably used, and acetaldehyde is particularly preferred, from the viewpoint that the structure after polymerization is similar to that of the final product.

The amount of the chain transfer agent added varies slightly depending on the chain transfer constant of the chain transfer agent to be added, the polymerization degree of the target PVA-based resin, and the like, and is usually preferably 0.1 to 5% by weight, more preferably 0.5 to 3% by weight, relative to the vinyl ester-based monomer. The chain transfer agent may be initially charged at the same time, or may be charged at the time of polymerization. The molecular weight distribution of the PVA-based resin can be controlled by adding a chain transfer agent by an arbitrary method.

The vinyl ester monomer may be used alone, or a modified PVA resin obtained by copolymerizing a monomer polymerizable with the vinyl ester monomer may be used as needed. Examples of the monomer include: monomers having vinyl groups and epoxy groups such as glycidyl (meth) acrylate, glycidyl (meth) allyl ether, 3, 4-epoxycyclohexyl (meth) acrylate, and allyl glycidyl ether; monomers having 2 or more allyl groups such as triallyloxyene, diallyl maleate, triallylcyanurate, triallylisocyanurate, tetraallyloxyethane, diallyl phthalate, triallylcyanurate, triallylisocyanurate and the like; allyl ester monomers such as allyl acetate, vinyl acetoacetate, allyl acetoacetate, and allyl diacetoacetate; acetoacetoxy alkyl (meth) acrylates such as acetoacetoxy ethyl (meth) acrylate and acetoacetoxy propyl (meth) acrylate; acetoacetoxyalkyl crotonates such as acetoacetoxyethyl crotonate and acetoacetoxypropyl crotonate; 2-cyanoacetoacetoxyethyl (meth) acrylate; divinylbenzene; alkylene glycol (meth) acrylates such as ethylene glycol di (meth) acrylate, 1, 2-propylene glycol di (meth) acrylate, 1, 3-propylene glycol di (meth) acrylate, 1, 4-butanediol di (meth) acrylate, 1, 6-hexanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, and the like; trimethylolpropane tri (meth) acrylate; allyl (meth) acrylate; hydroxyalkyl (meth) acrylates such as 2-hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, and 4-hydroxybutyl (meth) acrylate (the alkyl moiety is a C1-C10 alkyl group, preferably a C1-C6 alkyl group); nitrile monomers such as (meth) acrylonitrile; styrene monomers such as styrene and α -methylstyrene; olefins such as ethylene, propylene, 1-butene, and isobutylene; halogenated olefins such as vinyl chloride, vinylidene chloride, vinyl fluoride, and vinylidene fluoride; olefin monomers such as vinylsulfonic acid; diene monomers such as 1, 3-butadiene, 2-methylbutadiene, 1,3 or 2, 3-dimethyl-1, 3-butadiene, 2-chloro-1, 3-butadiene; hydroxy-containing alpha-olefins such as 3-buten-1-ol, 4-penten-1-ol, 5-hexene-1, 2-diol, glycerol monoallyl ether, and derivatives such as acylate; hydroxymethylvinylidene diacetates such as 1, 3-diacetoxy-2-methylenepropane, 1, 3-dipropyloxy-2-methylenepropane, and 1, 3-dibutyloxy-2-methylenepropane; unsaturated acids such as itaconic acid, maleic acid, and acrylic acid, and salts and mono-and dialkyl esters thereof; nitriles such as acrylonitrile, amides such as methacrylamide and diacetone acrylamide, compounds such as vinylsulfonic acid, allylsulfonic acid, methallylsulfonic acid, and olefinsulfonic acid such as AMPS, or salts thereof, and vinyl alkyl dialkoxysilanes such as vinyltriethoxysilane, vinyltrimethoxysilane, vinyltripropoxysilane, vinyltributoxysilane, vinylmethyldimethoxysilane, and vinylmethyldiethoxysilane; gamma- (meth) acryloxypropyl trialkoxysilane such as gamma- (meth) acryloxypropyl trimethoxysilane and gamma- (meth) acryloxypropyl triethoxysilane; gamma- (meth) acryloxypropyl alkyl dialkoxysilane such as gamma- (meth) acryloxypropyl methyl dimethoxy silane and gamma- (meth) acryloxypropyl methyl diethoxy silane; vinyl tri (beta-methoxyethoxy) silane, hydroxymethyl vinylidene diacetate. Specific examples of the hydroxymethylvinylidene diacetate include 1, 3-diacetoxy-2-methylenepropane, 1, 3-dipropyloxy-2-methylenepropane, and 1, 3-dibutyloxy-2-methylenepropane.

Examples of the compound include 3, 4-dihydroxy-1-butene, 3, 4-diacyloxy-1-butene, 3-acyloxy-4-hydroxy-1-butene, 4-acyloxy-3-hydroxy-1-butene, 3, 4-diacyloxy-2-methyl-1-butene, 4, 5-dihydroxy-1-pentene, 4, 5-diacyloxy-1-pentene, 4, 5-dihydroxy-3-methyl-1-pentene, 4, 5-diacyloxy-3-methyl-1-pentene, 5, 6-dihydroxy-1-hexene, 5, 6-diacyloxy-1-hexene, monoallyl ether, 2, 3-diacetoxy-1-allyloxypropane, 2-acetoxy-1-allyloxy-3-hydroxypropane, 3-acetoxy-1-allyloxy-2-hydroxypropane, glycerol monovinyl ether, glycerol monoisopropenyl ether, ethylene carbonate, 2-dimethyl-4-dioxolane, and the like. These monomers may be used singly or in combination of 2 or more.

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

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 the polymerization is saponified, and a carbonyl group is introduced into the molecule.

The saponification can be carried out by a known method, and is usually carried out by dissolving the vinyl ester polymer in an alcohol in the presence of a base catalyst or an acid catalyst. Examples of the alcohol include alcohols having 1 to 6 carbon atoms such as methanol, ethanol and butanol.

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

As the base catalyst, for example, it is possible to use: alkali catalysts such as hydroxides and alkoxides of alkali metals such as sodium hydroxide, potassium hydroxide, sodium methoxide, sodium ethoxide and potassium methoxide. As the acid catalyst, for example, it is possible to use: hydrochloric acid, sulfuric acid and other inorganic acid aqueous solution, p-toluenesulfonic acid and other organic acid. The amount of the catalyst to be used is preferably 1 to 100 milliequivalents, more preferably 1 to 40 milliequivalents, and still more preferably 1 to 20 milliequivalents, relative to the vinyl ester monomer. When the amount of the catalyst is too small, it tends to be difficult to carry out saponification up to the target saponification degree, and even when the amount of the catalyst is too large, there is no increase in the saponification reactivity, which is not preferable.

The reaction temperature at the time of saponification is not particularly limited, and is usually desirably selected from the range of preferably 10 to 70 ℃, more preferably 20 to 50 ℃.

The reaction time for the saponification may be appropriately adjusted depending on the method of the saponification, and in the case of batch saponification, for example, the saponification reaction is usually carried out over 2 to 3 hours.

In the present application, the resulting PVA-based resin is post-modified, whereby a modified PVA-based resin can be produced. Examples of the method for producing the modified PVA resin include methods for acetoacetating, acetalizing, urethanizing, etherifying, grafting, phosphonating, and oxyalkylating the PVA resin.

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

The temperature of the heat treatment is generally preferably in the range of 120 to 180 ℃, more preferably 140 to 155 ℃. When the temperature of the heat treatment is too low, it tends to be difficult to obtain a desired vinylidene content (double bond), whereas when it is too high, decomposition by the heat treatment tends to occur easily.

The time of the heat treatment is usually preferably 0.5 to 5 hours, more preferably 1.5 to 4 hours. When the time of the heat treatment is too short, the amount of vinylidene formed tends to decrease, whereas when it is too long, the PVA-based resin tends to be colored and insoluble components to water are formed.

The heat treatment may be performed by using any device, for example, a stirring device such as a nodavizer or a conical dryer, which heats and stirs the content.

The heat treatment is preferably performed under an oxygen atmosphere having an oxygen concentration of 20 vol% or less, more preferably under an oxygen atmosphere having an oxygen concentration of 3 to 12 vol%. When the oxygen concentration is too high, coloring of the PVA-based resin occurs and the PVA-based resin tends to become insoluble.

In the heat treatment, the metal salt shown above is contained in the PVA-based resin obtained by a known method, and the carbonyl group content of the PVA-based resin before the heat treatment is preferably 0.03 to 2.5 mol%, more preferably 0.05 to 2 mol%, in order to generate a sufficient amount of vinylidene group required to obtain good surface activity.

The content of the fine powder was adjusted so that 60% by weight or less of the fine powder having a particle diameter of 500 μm or less was contained in the PVA-based resin after heat treatment obtained as described above. The content of fine powder of 500 μm or less in the PVA-based resin after heat treatment is preferably 50 wt% or less, more preferably 35 wt% or less, particularly preferably 20 wt% or less, and most preferably no fine powder having a particle diameter of 500 μm or less (i.e., 0 wt%) at all. Since the smaller the particle size of the PVA-based resin, the stronger the coloration by heat treatment tends to be, the coloring of the PVA-based resin can be suppressed by setting the content of fine powder having a particle size of 500 μm or less to 60 wt% or less.

In order to adjust the content of fine powder having a particle diameter of 500 μm or less, examples include: a method of sieving with a sieve having a nominal pore diameter of 500 μm (JIS Z8801-1:2000 "Standard sieve"); and a method of reducing stirring power or stirring time in the step of stirring such as saponification and drying.

[ use ]

The PVA-based resin of the present application obtained as described above can suppress coloring, and therefore, is excellent in color tone and can be suitably used for various applications. Examples of the use of the PVA-based resin of the present application include the following.

(1) Molded article-related: fibers, films, sheets, pipes, catheters, leakproof films, temporary fixing films, water-soluble laces, water-soluble fibers and the like.

(2) Adhesive correlation: adhesives for wood, paper, aluminum foil, plastics, etc., adhesives, rewetting agents, adhesives for nonwoven fabrics, adhesives for various building materials such as gypsum boards and fiber boards, adhesives for various powder granulation, additives for cement and mortar, hot melt adhesives, pressure sensitive adhesives, fixing agents for anionic paints, etc.

(3) Coating agent correlation: transparent coating agents for paper, pigment coating agents for paper, internal sizing agents for paper, sizing agents for fiber products, silk pastes, fiber processing agents, leather processing agents, paints, antifogging agents, metal anticorrosive agents, gloss agents for galvanization, antistatic agents, conductive agents, temporary fixing paints, and the like.

(4) The hydrophobic resin is related to the blending agent: antistatic agents for hydrophobic resins, hydrophilicity imparting agents, additives for molded articles such as composite fibers and films, and the like.

(5) Dispersant-related: pigment dispersion stabilizers such as dispersants for color developers for coating liquids for heat-sensitive color-developing layers, paints, inks, aqueous colors, adhesives, and dispersion stabilizers for suspension polymerization of various vinyl compounds such as vinyl chloride, vinylidene chloride, styrene, (meth) acrylate, and vinyl acetate.

(6) Emulsion dispersion stabilizer correlation: various acrylic monomers, ethylenically unsaturated compounds, emulsifiers for emulsion polymerization of butadiene compounds, hydrophobic resins such as polyolefin and polyester resins, post-emulsifiers such as epoxy resins, paraffin wax and asphalt, and the like.

(7) Thickener-related: various aqueous solutions, emulsions, thickeners for petroleum drilling fluids, and the like.

(8) Flocculant correlation: flocculant for suspended matters and dissolved matters in water, water filtering property of paper pulp and slurry, etc.

(9) Exchange resin, etc.: ion exchange resins, chelating exchange resins, ion exchange membranes, and the like.

(10) Other: soil amendment, photosensitizer, photosensitive resist resin, etc.

Among the above, the PVA-based resin of the present application is 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 application is used as a dispersing agent, examples of the dispersion include polymerizable monomers and powders, and particularly, it is preferable to disperse the polymerizable monomers and use the dispersion as a dispersing agent for suspension polymerization.

Examples of the polymerizable monomer to be suspension polymerized include vinyl chloride, vinylidene halide, vinyl ether, vinyl acetate, vinyl benzoate, acrylic acid, methacrylic acid, maleic acid or anhydride thereof, ethylene, propylene, and styrene. Among them, it is suitable for homo-polymerization of vinyl chloride or copolymerization with a monomer copolymerizable with vinyl chloride.

[ dispersant for suspension polymerization ]

The PVA-based resin of the present application is used as a dispersant for suspension polymerization in the following description.

The amount of the PVA-based resin of the present application to be used may be appropriately adjusted depending on the monomer to be suspension-polymerized, and for example, in the case of suspension-polymerization of a vinyl chloride-based monomer, it is usually preferably 5 parts by weight or less, more preferably 0.01 to 1 part by weight, still more preferably 0.02 to 0.2 part by weight, based on 100 parts by weight of the vinyl chloride-based monomer. When the amount is too large, the PVA based resin which does not function as a dispersing agent tends to increase.

In the suspension polymerization, the PVA resins of the present application are usually added to water or a heated aqueous medium as a dispersing agent to disperse vinyl chloride monomers, and the polymerization is carried out in the presence of an oil-soluble catalyst.

As a method of adding the PVA-based resin, the PVA-based resin is directly added as a powder, and is added in a state of being dissolved in water, an organic solvent such as an alcohol, a ketone, or an ester, or a solution of a mixed solvent of these organic solvents and water, or in a state of being dispersed in a dispersion of the above-mentioned solvents.

The timing of addition may be at the same time as the initiation of polymerization or may be batchwise during polymerization.

As other additives, known stabilizers such as polymer substances may be used in combination. Examples of the polymer substance include PVA resins other than the PVA resin of the present application. Examples of the PVA-based resin include unmodified PVA and the modified PVA-based resin described above.

Examples of the polymerization auxiliary agent include various surfactants and inorganic dispersants, and the PVA-based resin of the present application may be used as a polymerization auxiliary agent.

The polymerization catalyst may be an oil-soluble catalyst, and for example, may be used: benzoyl peroxide, lauroyl peroxide, diisopropyl peroxydicarbonate, α '-azobisisobutyronitrile, α' -azobis-2, 4-dimethyl-valeronitrile, acetyl cyclohexylsulfonyl peroxide or mixtures thereof.

Examples

The present application will be described in further detail with reference to examples, but the present application is not limited to the examples provided below as long as the gist thereof is not exceeded. The "parts" and "%" are weight basis.

Example 1

< manufacturing of PVA-based resin >

100 parts of vinyl acetate, 1.2 parts of acetaldehyde, 4.7 parts of methanol and 0.0092% of Acetyl Peroxide (APO) relative to vinyl acetate were charged into a polymerization reactor, and the mixture was replaced with nitrogen. Thereafter, heating was performed to start polymerization at the boiling point, and polymerization was stopped at a point in time when the polymerization rate reached 91.8% after about 5.7 hours of the reaction time. Next, unpolymerized vinyl acetate was removed, and the resulting polymer was saponified with sodium hydroxide by a conventional method to prepare a saponified slurry (solvent of methyl acetate/methanol=8/2 (weight ratio)) of PVA-based resin (polymerization degree 770, saponification degree 71.7 mol%, carbonyl amount 0.16 mol%) having a resin component of 12%.

Next, to the PVA-based resin prepared in the above, a 10% methanol solution of magnesium acetate tetrahydrate as a metal compound was added in a proportion of 350g to 1kg of the PVA-based resin, and stirred at 25 ℃ for 1 hour. Thereafter, suction filtration was performed using a Buchner funnel to obtain a PVA based resin containing 177. Mu. Mol/g of magnesium acetate.

Next, after drying in a heat treatment kettle at 110 ℃ for 2 hours under a nitrogen atmosphere, nitrogen gas was: air = 1:1 (volume ratio) of gas was injected into the heat treatment vessel at a rate of 100L/hr, whereby heat treatment was performed at 145℃for 3 hours while maintaining the oxygen concentration at 10%. The properties of the PVA-based resin after heat treatment are as follows.

Average degree of polymerization; 650 (measured in accordance with JIS K6726), saponification degree; 72.0 mol% (measured in accordance with JIS 6726)), magnesium acetate content; 177 mu mol/g (calculated according to the magnesium content)

< procedure of recovering micropowder >

Next, the obtained PVA based resin was sieved through a 30-mesh sieve (pore size: 500 μm), and fine powder (resin particles) having a particle diameter of 500 μm or less was removed, whereby only PVA based resin A having a particle diameter of more than 500 μm (amount of fine powder 0 wt%) was obtained.

< evaluation 1: determination of ultraviolet absorbance

A0.1% aqueous solution of PVA based resin A was prepared. The absorbance of the 0.1% aqueous solution of PVA-based resin A at wavelengths of 215nm, 280nm, and 320nm was measured using an ultraviolet-visible near-infrared spectrophotometer (trade name "V-560", manufactured by Japanese Specification Co., ltd.). A sample container (cuvette) having a thickness of 1cm was used.

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

The results are shown in Table 1.

< evaluation 2: determination of Yellow Index (YI) value

A1.0% aqueous solution of PVA based resin A was prepared. YI value of the above aqueous solution was measured using a Konica Minolta, inc. colorimeter "CM-3600A" (trade name).

The results are shown in Table 1.

Example 2

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

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

Example 3

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

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

Comparative example 1

In example 1, PVA-based resin D was obtained in the same manner as in example 1, except that the fine powder recovery step was not performed. The content of the fine powder having a particle diameter of 500 μm or less was 78% by weight.

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

TABLE 1

As is clear from the results in Table 1, examples 1 to 3 have lower YI values than comparative example 1, and can suppress coloring. In particular, it is found that the smaller the content of fine powder having a particle diameter of 500 μm or less, the smaller the coloration of the PVA resin becomes.

Further, the ratio of absorbance (X) at 320nm to absorbance (Y) at 280nm in a 0.1 wt% aqueous solution of the PVA based resin based on the ultraviolet absorption spectrum was high in all of examples 1 to 3, suggesting that the suspension polymerization stability was well maintained when the PVA based resin was used as a dispersing agent for suspension polymerization.

While the application has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof. The present application is based on Japanese patent application 2016-247686 (Japanese patent application laid-open No. 2016-247686) filed on the year 2016, 12 and 21, the contents of which are incorporated herein by reference.

Industrial applicability

Since the PVA-based resin of the present application has a double bond and is less colored, coloring of the resulting polymer can be suppressed even when it is used as various dispersants. In particular, the dispersion is useful as a dispersing agent for suspension polymerization of vinyl chloride monomers.

Claims

1. A polyvinyl alcohol resin having an absorbance (X) of at least 0.1 at 320nm in the ultraviolet absorption spectrum when a 0.1 wt% aqueous solution is produced, and a ratio (X/Y) of the absorbance (X) of at least 320nm to the absorbance (Y) of at least 280nm in the ultraviolet absorption spectrum when a 0.1 wt% aqueous solution is produced, wherein the content of fine particles having a particle diameter of at most 500 [ mu ] m is at most 60 wt%.

2. The polyvinyl alcohol resin according to claim 1, having a saponification degree of 60 mol% or more.

3. A dispersant comprising the polyvinyl alcohol resin according to any one of claims 1 to 2.

4. A dispersant for suspension polymerization comprising the polyvinyl alcohol resin according to any one of claims 1 to 2.