WO2018117246A1 - Polyvinyl alcohol-based resin, dispersing agent, and dispersing agent for suspension polymerization - Google Patents

Abstract

The purpose of the invention is to: provide a polyvinyl alcohol-based resin in which coloring is suppressed; and provide a dispersing agent and a dispersing agent for suspension polymerization used upon manufacturing polyvinyl chloride, the dispersing agents using said polyvinyl alcohol-based resin. The absorbance (X) at 320 nm in an ultraviolet absorption spectrum when this polyvinyl alcohol-based resin is made into a 0.1 wt% aqueous solution is 0.1 or greater; and the content of fines having particle diameters of 500 µm or less is 60 wt% or less.

Description

Polyvinyl alcohol resin, dispersant, and dispersant for suspension polymerization

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

A polyvinyl alcohol resin (hereinafter, “polyvinyl alcohol” may be abbreviated as “PVA”) is obtained by saponifying a polymer obtained by polymerizing a vinyl ester monomer such as vinyl acetate. The PVA resin is usually dehydrated by heat treatment and has a structure having a double bond in the main chain. The PVA resin having such a structure is a dispersion stabilizer for suspension during the production of polyvinyl chloride. It is used for applications such as water retention materials. It is also known that the strength can be improved by heat-treating a film or fiber made of PVA resin.

The double bond in the PVA-based resin can be confirmed particularly by an ultraviolet absorption spectrum of a 0.1% by weight aqueous solution. The peak near 215 nm belongs to the structure of [—CO—CH═CH—], the peak near 280 nm belongs to the structure of [—CO— (CH═CH) ₂ —], and the peak near 320 nm is [− It belongs to the structure of CO— (CH═CH) ₃ —].

On the other hand, various heat-treated PVA-based resins have been studied as a dispersant for suspension polymerization when producing polyvinyl chloride.
For example, a polyvinyl alcohol-based resin having a carbonyl group in the molecule and containing a divalent or trivalent metal salt or hydroxide has been proposed (see, for example, Patent Document 1). Further, the absorbance (a) at 280 nm according to the ultraviolet absorption spectrum of the 0.1 wt% aqueous solution is greater than 0.1, and the absorbance (b) at 320 nm according to the ultraviolet absorption spectrum of the aqueous solution is 0.03 or more, A PVA polymer having an absorbance (b) / absorbance (a) of less than 0.3 and a residual acetate group block character of 0.4 or more has been proposed (see, for example, Patent Document 2).

However, in order to obtain the PVA resins described in Patent Documents 1 and 2, it is necessary to perform a heat treatment at about 150 ° C. for 5 to 6 hours, resulting in a problem that the production cost is increased. In addition, in the production process, there are many opportunities to come into contact with oxygen, which may cause insoluble matter, and there is a problem that the randomness of residual fatty acid ester groups such as acetoxy groups does not increase.

In order to solve the above problem, for example, in Patent Document 3, a polyvinyl alcohol resin having a carbonyl group in the molecule and a block character of a residual fatty acid ester group of 0.5 or more, which is a polyvinyl alcohol resin A PVA resin is proposed in which the absorbance at 215 nm, 280 nm, and 320 nm is 0.1 or more and the ratio of absorbance at 320 nm / absorbance at 280 nm is 0.3 or more according to the ultraviolet absorption spectrum of 0.1 wt% aqueous solution of Has been.

Japanese Unexamined Patent Publication No. 08-269112 Japanese Unexamined Patent Publication No. 08-283313 Japanese Unexamined Patent Publication No. 2004-250695

However, the conventional PVA-based resin has a problem that coloring occurs in the obtained resin, and as a result, coloring occurs in polyvinyl chloride when used as a suspension polymerization dispersant during the production of polyvinyl chloride. Met.
Due to the recent increase in required physical properties, in order to suppress the coloring of the suspension polymer (for example, polyvinyl chloride), it is required to suppress the coloring of the PVA resin used as the dispersant for suspension polymerization.

Then, this invention makes it a subject to provide the PVA-type resin by which coloring was suppressed, and the dispersing agent using this PVA-type resin, and the dispersing agent for suspension polymerization used at the time of polyvinyl chloride manufacture. .

As a result of intensive studies to solve the above problems, the present inventors have found that the amount of fine powder in the resin is related to the coloring of the PVA resin, and have completed the present invention.

That is, the gist of the present invention is the following (1) to (5).
(1) Polyvinyl alcohol type having an absorbance (X) at 320 nm in an ultraviolet absorption spectrum of 0.1 wt% aqueous solution of 0.1 or more and a fine powder content of particle diameter of 500 μm or less of 60 wt% or less. resin.
(2) In the above (1), the ratio (X / Y) of the absorbance (X) at 320 nm to the absorbance (Y) at 280 nm in the ultraviolet absorption spectrum in the case of 0.1 wt% aqueous solution is 0.3 or more. The polyvinyl alcohol-type resin of description.
(3) The polyvinyl alcohol-type resin as described in said (1) or (2) whose saponification degree is 60 mol% or more.
(4) A dispersant comprising the polyvinyl alcohol resin according to any one of (1) to (3).
(5) A suspension polymerization dispersant comprising the polyvinyl alcohol resin according to any one of (1) to (3).

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

Hereinafter, the polyvinyl alcohol resin of the present invention will be described in detail.

[Polyvinyl alcohol 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 a heat treatment, and has an absorbance (X) at 320 nm in an ultraviolet absorption spectrum of 0.1 wt% aqueous solution. 0.1 or more and the content of fine powder having a particle diameter of 500 μm or less is 60% by weight or less. According to the study by the present inventors, it becomes clear that the PVA resin forming fine powder of 500 μm or less tends to be colored by heat, and the PVA resin of the present invention has a fine powder content of 60% by weight or less. The coloring can be suppressed by controlling.

Generally, a PVA-based resin is a resin obtained by saponifying a vinyl ester homopolymer or a copolymer of vinyl ester and another monomer using an alkali catalyst or the like. The PVA resin of the present invention can be obtained by heat-treating the PVA resin obtained by this saponification to cause dehydration or deacetic acid reaction.

The saponification degree of the PVA resin of the present invention is the same as the saponification degree of the PVA resin before the heat treatment. The saponification degree (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%. Since the PVA resin of the present invention has an acetic acid group (hydrophobic group) in addition to a hydroxyl group (hydrophilicity) in the molecule, it has a surface activity and can be uniformly dispersed in the dispersion medium. If the degree of saponification is too low, the water dispersibility tends to be lowered. Therefore, the degree of saponification is preferably 60 mol% or more.

The average degree of polymerization of the PVA resin of the present invention is the same as the average degree of polymerization of the PVA resin before heat treatment. The average degree of polymerization is preferably 100 to 4000, more preferably 200 to 3000, and particularly preferably 300 to 1000. If the average degree of polymerization is too low, the surface activity tends to be low, and when used as a dispersant for vinyl chloride suspension polymerization, aggregation tends to occur during suspension polymerization. On the other hand, when the average degree of polymerization is too high, the viscosity of the aqueous PVA-based resin solution is increased, and the handling property is decreased.
The average degree of polymerization can be measured according to JIS K 6726.

The absorbance (X) at 320 nm in the ultraviolet absorption spectrum when the PVA resin of the present invention is a 0.1 wt% aqueous solution is 0.1 or more. If the UV absorbance at 320 nm of a 0.1 wt% aqueous solution of PVA-based resin is less than 0.1, the generation of double bonds is small, and the surface activity tends to decrease. The ultraviolet absorbance at 320 nm of a 0.1 wt% aqueous solution of PVA resin is preferably 0.2 or more, and the upper limit is not particularly limited, but is about 1.5 from the viewpoint of manufacturability.

In addition, the ultraviolet absorbance at other wavelengths other than 320 nm 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. The ultraviolet absorbance at 280 nm is preferably 0.1 or more, more preferably 0.3 or more, and the upper limit is about 2. If these absorbances are too low, the production of double bonds is small, so that the surface activity tends to decrease, and if it is too high, the manufacturability tends to decrease.

The absorption at 215 nm in the ultraviolet absorption spectrum is attributed to the structure of —CO—CH═CH— in the PVA resin, and the absorption at 280 nm is —CO— (CH═CH) ₂ in the PVA resin. The absorption at 320 nm is attributed to the structure of —CO— (CH═CH) ₃ — in the PVA resin.

In the present invention, the ratio of the absorbance (X) at 320 nm to the absorbance (Y) at 280 nm (X / Y: 320 nm / 280 nm) in the ultraviolet absorption spectrum when the PVA resin of the present invention is a 0.1 wt% aqueous solution. ) Is preferably 0.3 or more, more preferably 0.4 or more, and 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 surface activity tends to be low and suspension polymerization stability tends to be reduced. The upper limit is not particularly limited, but is about 3 from the viewpoint of productivity.

The absorbance is 0.1 weight of PVA resin at wavelengths of 215 nm, 280 nm, and 320 nm using an ultraviolet-visible near-infrared spectrophotometer (for example, “V-560” (trade name) manufactured by JASCO Corporation). The absorbance of the aqueous solution can be measured. Note that the measurement is performed using a sample container (cell) having a thickness of 1 cm.

In the PVA resin of the present invention, the content of fine powder having a particle diameter of 500 μm or less is 60% by weight or less, preferably 50% by weight or less, more preferably 35% by weight or less, and particularly preferably 20% by weight or less. Most preferably, no fine powder having a particle diameter of 500 μm or less is contained (that is, 0% by weight). If the content of fine powder (resin particles) having a particle diameter of 500 μm or less is too large, the PVA resin tends to be colored, and a PVA resin having a good appearance cannot be obtained. Even when used as a dispersant, the vinyl chloride resin tends to be colored.

The content of fine powder having a particle size of 500 μm or less is, for example, sieved with a sieve having a nominal aperture of 500 μm (JIS Z8801-1: 2000 “standard sieve”) and passed through the sieve with respect to the total weight of the PVA resin. It can be determined by calculating the proportion of fine powder.

In the present invention, the yellow index (YI) value of the aqueous solution when the PVA resin of the present invention is 1.0% by weight is preferably 33 or less, more preferably 31 or less, and still more preferably 30. Hereinafter, it is particularly preferably 28 or less. A PVA resin having a small YI value is a PVA resin with suppressed coloring. The lower limit is preferably 0.
The YI value can be measured using, for example, a colorimeter “CM-3600A” (trade name) manufactured by Konica Minolta, Inc.

The block character of the PVA resin of the present invention (an index representing the block property of vinyl alcohol units and vinyl ester units of the PVA resin) is preferably 0.5 or more, more preferably 0.55 or more. If the block character is too low, the foaming suppression effect during suspension polymerization of vinyl compounds such as vinyl chloride tends to be low. Although there is no upper limit in particular, it is 0.9 or less from the viewpoint of manufacturability of PVA resin.

The block character (η) can be measured as follows.
PVA-based resin was measured by ¹³ C-NMR (3- (trimethylsilyl) -2,2,3,3-d ₄ -propionic acid sodium salt (3- (trimethylsilyl) propionic-2,2,3 , 3-d ₄ acid sodium salt), absorption based on the methylene carbon moiety found in the range of 38-49 ppm [(OH, OH) dyad absorption = 43.5-46 ppm, (OH, OR) dyad absorption = 41 to 43.5 ppm, (OR, OR) dyad absorption = 38 to 40.5 ppm, where R represents an acetyl group (CH ₃ CO-)]. 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 terms of mole fraction. (OH) is the degree of saponification calculated by the integration ratio of ¹³ C-NMR. (Mole fraction), (OR) indicates the mole fraction of the acetoxy group at that time.)

The PVA 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 a divalent to trivalent metal salt and a hydroxide, heat treatment is efficiently performed.

Examples of the bivalent to trivalent metal include magnesium, calcium, zinc, and aluminum.
Specific examples of these metal salts or hydroxides include magnesium acetate tetrahydrate, calcium acetate, calcium propionate, magnesium butyrate, magnesium carbonate, magnesium hydroxide, zinc acetate, aluminum hydroxide and the like. 1 type may be used independently and may be used in combination of 2 or more type. Among these, magnesium acetate tetrahydrate and calcium acetate are preferable in that they are dissolved in water and / or methanol and are industrially easy to handle.

The content of the divalent to trivalent metal salt and / or hydroxide in the PVA resin of the present invention is preferably 30 to 300 μmol / g, more preferably 40 to 200 μmol / g. If the content is too small, the amount of vinylene groups produced decreases, and conversely if too large, the PVA resin tends to be colored or decomposed.

The method for containing the divalent or trivalent metal salt and / or hydroxide is not limited, and the above compound may be added directly to the paste before saponification or the slurry after saponification, but preferably methanol. It is preferable to dissolve in alcohol such as ethanol or propanol, or water and add it to the PVA slurry after saponification in the form of a solution having a concentration of about 3 to 15% by weight and distribute it to the PVA resin.

[Method for producing polyvinyl alcohol resin]
As described above, the PVA resin of the present invention has an absorbance (X) at 320 nm in an ultraviolet absorption spectrum of 0.1 wt% aqueous solution of 0.1 or more. In order to increase the absorbance (X) at 320 nm to 0.1 or more, for example, a resin in which a conjugated double bond is introduced into a PVA resin having a carbonyl group in the molecule is used, and the resin is further heat-treated to perform dehydration or A method for causing a deacetic acid reaction is mentioned.

First, a method for introducing a carbonyl group into the molecule of the PVA resin will be described. Examples of such methods include the following methods (i) to (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) vinyl ester monomer (Iii) A method in which polymerization is performed in the presence of a chain transfer agent containing a carbonyl group such as aldehydes and ketones, and the resulting polymer is saponified (iii) such as 1-methoxy-vinyl acetate Method of polymerizing vinyl ester monomer in the coexistence and saponifying the obtained polymer (iv) Air is blown during polymerization of vinyl ester monomer, and the resulting polymer is saponified Among these, the method (ii) is preferred from the viewpoint of industrially easy solvent recovery.

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

Examples of vinyl ester monomers that are starting materials include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl caprate, vinyl laurate, vinyl palmitate, vinyl stearate, and other straight or branched chains. And the like saturated fatty acid vinyl ester. From a practical viewpoint, vinyl acetate is preferable, and usually vinyl acetate is used alone or in combination with a fatty acid vinyl ester compound other than vinyl acetate.

There are no particular limitations on the polymerization of the vinyl ester monomer, and any known polymerization method can be used. Usually, solution polymerization using an alcohol having 1 to 3 carbon atoms such as methanol, ethanol or isopropyl alcohol as a solvent is used. To be implemented. Of course, bulk polymerization, emulsion polymerization, and suspension polymerization are also possible.
In such solution polymerization, the vinyl ester monomer may be charged by any means such as divided charging or batch charging. The polymerization reaction is carried out using a known radical polymerization catalyst such as azobisisobutyronitrile, acetyl peroxide, benzoyl peroxide, lauroyl peroxide, azobisdimethylvaleronitrile, azobismethoxyvaleronitrile and the like. The polymerization reaction temperature is selected from the range of 40 ° C. to about the boiling point.

Examples of the chain transfer agent used in the method (ii) include aldehydes such as acetaldehyde, propionaldehyde, butyraldehyde, and benzaldehyde. Examples of ketones include acetone, methyl ethyl ketone, hexanone, and cyclohexanone. These may be used, and one kind may be used alone, or two or more kinds may be used in combination.
Among them, aldehydes are preferably used, and acetaldehyde is particularly preferable in that the structure after polymerization is similar to the final product.

The amount of chain transfer agent to be added varies slightly depending on the chain transfer constant of the chain transfer agent to be added and the degree of polymerization of the target PVA resin, but is usually 0.1 to 5 weights relative to the vinyl ester monomer. %, More preferably 0.5 to 3% by weight. The chain transfer agent may be charged in the initial batch or in the polymerization reaction. The molecular weight distribution of the PVA resin can be controlled by charging the chain transfer agent by an arbitrary method.

The vinyl ester monomer may be used alone, but if necessary, a modified PVA resin obtained by copolymerizing a vinyl ester monomer and a polymerizable monomer may be used. Examples of such monomers include monomers having a vinyl group and an epoxy group such as glycidyl (meth) acrylate, glycidyl (meth) allyl ether, 3,4-epoxycyclohexyl (meth) acrylate, allyl glycidyl ether; Monomers having two or more allyl groups such as allyloxyethylene, diallyl maleate, triallyl cyanurate, triallyl isocyanurate, tetraallyloxyethane, diallyl phthalate, triallyl cyanurate, triallyl isocyanurate; allyl acetate Allyl ester monomers such as vinyl acetoacetate, allyl acetoacetate and allyl acetoacetate; acetoacetoxy such as acetoacetoxyethyl (meth) acrylate and acetoacetoxypropyl (meth) acrylate Alkyl (meth) acrylates; acetoacetoxyalkyl crotonates such as acetoacetoxyethyl crotonate and acetoacetoxypropyl crotonate; 2-cyanoacetoacetoxyethyl (meth) acrylate; divinylbenzene; 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 ( Alkylene glycol (meth) acrylate such as (meth) acrylate; trimethylolpropane tri (meth) acrylate; allyl (meth) acrylate; 2-hydroxyethyl (meth) acrylate, Hydroxyalkyl (meth) acrylates such as droxypropyl (meth) acrylate and 4-hydroxybutyl (meth) acrylate (the alkyl moiety is a C1-C10 alkyl group, preferably a C1-C6 alkyl group); (meth) acrylonitrile, etc. Styrene monomers such as styrene and α-methylstyrene; olefins such as ethylene, propylene, 1-butene and isobutene; halogens such as vinyl chloride, vinylidene chloride, vinyl fluoride and vinylidene fluoride Olefinic monomers; olefinic monomers such as ethylene sulfonic acid; butadiene-1,3,2-methylbutadiene, 1,3 or 2,3-dimethylbutadiene-1,3, 2-chlorobutadiene-1,3, etc. Diene monomer; 3-buten-1-ol, 4-penten-1-ol Hydroxy group-containing α-olefins such as 5-hexene-1,2-diol and glycerin monoallyl ether, and derivatives such as acylated products thereof; 1,3-diacetoxy-2-methylenepropane, 1,3-dipropionyloxy -2-hydroxymethylvinylidene diacetates such as 2-methylenepropane and 1,3-dibutyronyloxy-2-methylenepropane; unsaturated acids such as itaconic acid, maleic acid and acrylic acid, salts or mono- or dialkyl esters thereof; Nitriles such as acrylonitrile, amides such as methacrylamide and diacetone acrylamide, olefin sulfonic acids such as ethylene sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid, and AMPS or salts thereof, vinyl triethoxysilane, vinyl tri Methoxysila Vinylalkyldialkoxysilanes such as vinyl tripropoxysilane, vinyltributoxysilane, vinylmethyldimethoxysilane, vinylmethyldiethoxysilane; γ- (meth) acryloxypropyltrimethoxysilane, γ- (meth) acryloxypropyl Γ- (meth) acryloxypropyltrialkoxysilane such as triethoxysilane; γ- (meth) acryloxy such as γ- (meth) acryloxypropylmethyldimethoxysilane, γ- (meth) acryloxypropylmethyldiethoxysilane Examples thereof include propylalkyl dialkoxysilane; vinyl tris (β-methoxyethoxy) silane, and hydroxymethylvinylidene diacetate. Specific examples of hydroxymethylvinylidene diacetate include 1,3-diacetoxy-2-methylenepropane, 1,3-dipropionyloxy-2-methylenepropane, and 1,3-dibutyronyloxy-2-methylenepropane. Etc.
In addition, 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-diasiloxy-1-pentene, 4,5-dihydroxy-3-methyl-1-pentene, 4,5-diasiloxy- 3-methyl-1-pentene, 5,6-dihydroxy-1-hexene, 5,6-diasiloxy-1-hexene, glycerin monoallyl ether, 2,3-diacetoxy-1-allyloxypropane, 2-acetoxy-1 -Allyloxy-3-hydroxypropane, 3-acetoxy-1-allyloxy-2-hydroxypropane, glycerol monovinyl ether Le, glycerol mono isopropenyl ether, vinyl ethylene carbonate, compounds having a diol such as 2,2-dimethyl-4-vinyl-1,3-dioxolane. These monomers may be used alone or in combination of two or more.

Note that “(meth) acrylate” means “acrylate and / or methacrylate”, and the same applies to “(meth) allyl” and “(meth) acrylo”.

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

The vinyl ester polymer obtained by the above polymerization is saponified and a carbonyl group is introduced into the molecule.
Saponification can be carried out by a known method, and is usually carried out in the presence of an alkali catalyst or an acid catalyst after dissolving a vinyl ester polymer in alcohol. 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 alkali catalyst, for example, an alkali catalyst such as an alkali metal hydroxide or alcoholate such as sodium hydroxide, potassium hydroxide, sodium methylate, sodium ethylate or potassium methylate can be used. As the acid catalyst, for example, an inorganic acid aqueous solution such as hydrochloric acid or sulfuric acid, or an organic acid such as p-toluenesulfonic acid can be used. The amount of the catalyst used is preferably 1 to 100 mmol equivalent, more preferably 1 to 40 mmol equivalent, still more preferably 1 to 20 mmol equivalent, relative to the vinyl ester monomer. If the amount of catalyst used is too small, it tends to be difficult to proceed with saponification to the desired degree of saponification, and if the amount of catalyst used is too large, no improvement in saponification reactivity is observed. Therefore, it is not preferable.

The reaction temperature for carrying out the saponification is not particularly limited, but is usually preferably 10 to 70 ° C, more preferably 20 to 50 ° C.

The reaction time for saponification may be appropriately adjusted according to the saponification treatment method. For example, in the case of batch saponification, the saponification reaction is usually performed for 2 to 3 hours.

In the present invention, a modified PVA resin may be produced by post-modifying the obtained PVA resin. Examples of the method for producing the modified PVA-based resin include a method in which the PVA-based resin is acetoacetate esterified, acetalized, urethanized, etherified, grafted, phosphoric esterified, and oxyalkylenated.

The obtained PVA resin undergoes a heat treatment to cause dehydration or deacetic acid reaction to generate a conjugated double bond, and the PVA resin of the present invention is obtained.

The temperature of the heat treatment is usually preferably in the range of 120 to 180 ° C, more preferably 140 to 155 ° C. If the temperature of the heat treatment is too low, the desired vinylene group amount (double bond) tends to be difficult to obtain, and conversely if too high, decomposition due to the heat treatment tends to occur.

The heat treatment time is usually preferably 0.5 to 5 hours, more preferably 1.5 to 4 hours. If the heat treatment time is too short, the amount of vinylene groups produced tends to decrease. Conversely, if it is too long, there is a tendency to cause coloring of the PVA-based resin and generation of insoluble matter in water.

Any apparatus may be used for the heat treatment, for example, a stirring apparatus that stirs the contents while heating, such as a nauter mixer or a conical dryer.

Further, the heat treatment is preferably performed in an oxygen atmosphere having an oxygen concentration of 20% by volume or less, and more preferably in an oxygen atmosphere of 3 to 12% by volume. If the oxygen concentration is too high, the PVA resin tends to be colored or cause insolubilization.

In this heat treatment, a PVA resin obtained by a known method containing the metal salt shown above can be used, but a sufficient amount of vinylene groups is added to obtain a good surface activity. In order to make it form, the content of carbonyl groups in the PVA resin before heat treatment is preferably 0.03 to 2.5 mol%, more preferably 0.05 to 2 mol%.

The PVA-based resin after the heat treatment obtained as described above adjusts the content of the fine powder so that the fine powder having a particle diameter of 500 μm or less is contained by 60% by weight or less. The content of fine powder of 500 μm or less in the PVA-based resin after the heat treatment is preferably 50% by weight or less, more preferably 35% by weight or less, particularly preferably 20% by weight or less, and a particle diameter of 500 μm or less. Most preferably, no fines are contained (ie 0% by weight). Since the PVA resin tends to be colored more strongly by heat treatment as the particle size is smaller, coloring of the PVA resin can be suppressed by setting the content of fine powder having a particle size of 500 μm or less to 60% by weight or less. .

In order to adjust the content of fine powder having a particle diameter of 500 μm or less, for example, in a method of sieving with a sieve having a nominal aperture of 500 μm (JIS Z8801-1: 2000 “standard sieve”), a step of stirring such as saponification or drying And a method of reducing the stirring power or shortening the stirring time.

[Usage]
The PVA resin of the present invention obtained as described above is excellent in hue because coloring is suppressed, and can be suitably used for various applications. Examples of the use of the PVA resin of the present invention include the following.
(1) Molded items: fibers, films, sheets, pipes, tubes, leak-proof membranes, temporary coatings, chemical laces, water-soluble fibers, etc.
(2) Adhesive-related: Adhesives such as wood, paper, aluminum foil and plastic, adhesives, rehumidifiers, binders for nonwoven fabrics, binders for various building materials such as gypsum board and fiberboard, binders for various types of powder granulation , Cement and mortar additives, hot melt adhesives, pressure sensitive adhesives, anionic paint fixing agents, etc.
(3) Coating agents: Paper clear coating agent, paper pigment coating agent, paper internal sizing agent, textile product sizing agent, warp glue, fiber processing agent, leather finishing agent, paint, anti-fogging agent, Metal corrosion inhibitor, galvanizing brightener, antistatic agent, conductive agent, provisional paint, etc.
(4) Hydrophobic resin blending agent: hydrophobic resin antistatic agent, hydrophilicity-imparting agent, composite fiber, film and other additives for molded articles.
(5) Dispersant-related: Dispersant for developer of coating solution for thermosensitive coloring layer, pigment dispersion stabilizer such as paint, ink, water color, adhesive, vinyl chloride, vinylidene chloride, styrene, (meth) acrylate Dispersion stabilizers for suspension polymerization of various vinyl compounds such as vinyl acetate.
(6) Emulsion dispersion stabilizers: various acrylic monomers, ethylenically unsaturated compounds, emulsifiers for emulsion polymerization of butadiene compounds, hydrophobic resins such as polyolefins and polyester resins, post-emulsifiers such as epoxy resins, paraffin and bitumen.
(7) Thickener-related: Various aqueous solutions and emulsions, thickeners for oil drilling fluids, etc.
(8) Coagulant relation: coagulant of suspension in water and dissolved substance, drainage of pulp, slurry, etc.
(9) Exchange resin, etc .: ion exchange resin, chelate exchange resin, ion exchange membrane, etc.
(10) Others: soil improver, photosensitizer, photosensitive resist resin, and the like.
Among the above, the PVA 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 particularly as a dispersion stabilizer for suspension polymerization of vinyl chloride compounds. Useful.

[Dispersant]
When the PVA resin of the present invention is used as a dispersant, examples of the dispersion include polymerizable monomers and powders. In particular, the polymerizable monomers are dispersed as a dispersant for suspension polymerization. It is preferable to use it.
Examples of the polymerizable monomer to be subjected to suspension polymerization include vinyl chloride, vinylidene halide, vinyl ether, vinyl acetate, vinyl benzoate, acrylic acid, methacrylic acid, maleic acid or anhydride thereof, ethylene, propylene, styrene, etc. Is mentioned. Among them, it is preferably used for vinyl chloride homopolymerization or copolymerization with a monomer copolymerizable with vinyl chloride.

[Dispersant for suspension polymerization]
The case where the PVA resin of the present invention is used as a dispersant for suspension polymerization is described in detail below.
The amount of the PVA-based resin of the present invention may be appropriately adjusted according to the monomer to be subjected to suspension polymerization. For example, when used for suspension polymerization of a vinyl chloride-based monomer, a vinyl chloride-based resin is usually used. The amount is preferably 5 parts by weight or less based on 100 parts by weight of the monomer, more preferably 0.01 to 1 part by weight, and still more preferably 0.02 to 0.2 part by weight. When there is too much this usage-amount, there exists a tendency for the PVA-type resin which does not act as a dispersing agent to increase.

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

As a method for adding the PVA-based resin, powder or water, an organic solvent such as alcohol, ketone, or ester, a solution dissolved in a mixed solvent of these organic solvent and water, or a dispersion dispersed in the above solvent Add in the state.
The timing of addition may be added all at the beginning of the polymerization or may be divided and added during the polymerization.

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

Examples of the polymerization aid include various surfactants or inorganic dispersants, and the PVA resin of the present invention can also be used as the polymerization aid.

The polymerization catalyst may be any oil-soluble catalyst. For example, benzoyl peroxide, lauroyl peroxide, diisopropyl peroxydicarbonate, α, α′-azobisisobutyronitrile, α, α′-azobis-2 1,4-dimethyl-valeronitrile, acetylcyclohexylsulfonyl peroxide or mixtures thereof are used.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist. “Parts”, “%” and the like 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) with respect to vinyl acetate were charged into the polymerization vessel and replaced with nitrogen. Thereafter, the mixture was heated to start polymerization at the boiling point, and the polymerization was stopped when the polymerization rate reached 91.8% after about 5.7 hours of reaction time. Next, unpolymerized vinyl acetate was removed, and the resulting polymer was saponified with sodium hydroxide by a conventional method to give a PVA resin having a resin content of 12% (polymerization degree 770, saponification degree 71.7 mol%, carbonyl group). A saponification slurry (a solvent of methyl acetate / methanol = 8/2 (weight ratio)) was prepared.
Next, a 10% methanol solution of magnesium acetate tetrahydrate as a metal compound was added to the PVA resin prepared above at a ratio of 350 g with respect to 1 kg of the PVA resin, and the mixture was stirred at 25 ° C. for 1 hour. Then, it was shaken off with Nutsche to obtain a PVA resin containing 177 μmol / g of magnesium acetate.
Next, after drying in a heat treatment can under a nitrogen atmosphere at 110 ° C. for 2 hours, a gas of nitrogen: air = 1: 1 (volume ratio) was flowed into the heat treatment can at a rate of 100 L / hr, and the oxygen concentration Was kept at 145 ° C. for 3 hours while maintaining 10%. The characteristics of the PVA resin after the heat treatment were as follows.
Average polymerization degree: 650 (measured according to JIS K 6726), saponification degree: 72.0 mol% (measured according to JIS 6726)), magnesium acetate content; 177 μmol / g (calculated from the contained magnesium content) )

<Fine powder recovery process>
Subsequently, the obtained PVA-based resin is sieved using a 30-mesh sieve (opening: 500 μm) to remove fine powder (resin particles) having a particle diameter of 500 μm or less, and only PVA having a particle diameter larger than 500 μm. System resin A (fine powder amount 0% by weight) was obtained.

<Evaluation 1: Measurement of UV absorbance>
A 0.1% aqueous solution of PVA-based resin A was prepared. Measure the absorbance of a 0.1% aqueous solution of PVA resin A at wavelengths of 215 nm, 280 nm, and 320 nm using an ultraviolet-visible near-infrared spectrophotometer (“V-560” (trade name) manufactured by JASCO Corporation). did. A sample container (cell) having a thickness of 1 cm was used.
Further, 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: Measurement of Yellow Index (YI) Value>
A 1.0% aqueous solution of PVA resin A was prepared. The YI value of the 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)
The PVA resin A obtained in Example 1 is mixed with fine powder having a particle diameter of 500 μm or less recovered in the recovery step of Example 1 so that the content is 31% in the entire resin, and PVA Resin B (31% by weight of fine powder) was obtained.
About the obtained PVA-type resin B, the ultraviolet light absorbency in each wavelength, X / Y value, and YI value were measured similarly to Example 1. FIG. The results are shown in Table 1.

(Example 3)
To the PVA resin A obtained in Example 1, the fine powder having a particle diameter of 500 μm or less recovered in the recovery step of Example 1 is mixed so that the content thereof becomes 57% in the entire resin, and PVA Resin C (fine powder amount 57% by weight) was obtained.
About the obtained PVA-type resin C, the ultraviolet light absorbency in each wavelength, X / Y value, and YI value were measured similarly to Example 1. FIG. The results are shown in Table 1.

(Comparative Example 1)
In Example 1, it carried out like Example 1 except not having performed a fine powder recovery process, and PVA system resin D was obtained. The content of fine powder having a particle diameter of 500 μm or less was 78% by weight.
About the obtained PVA-type resin D, the ultraviolet light absorbency in each wavelength, X / Y value, and YI value were measured similarly to Example 1. FIG. The results are shown in Table 1.

From the results in Table 1, it was found that Examples 1 to 3 had a smaller YI value than that of Comparative Example 1, and suppressed coloring. In particular, it was found that the smaller the content of fine powder having a particle diameter of 500 μm or less, the smaller the coloring of the PVA resin.
The ratio of the absorbance (X) at 320 nm to the absorbance (Y) at 280 nm according to the ultraviolet absorption spectrum in the 0.1 wt% aqueous solution of the PVA resin was high in all of Examples 1 to 3, and the dispersant for suspension polymerization When used as, it was suggested that the suspension polymerization stability was kept good.

Although the present invention has been described in detail and with reference to specific embodiments, 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 invention. This application is based on a Japanese patent application filed on December 21, 2016 (Japanese Patent Application No. 2016-247686), the contents of which are incorporated herein by reference.

Since the PVA resin of the present invention has a double bond and is less colored, the resulting polymer can be prevented from being colored when used as various dispersants. In particular, it is useful as a dispersant for suspension polymerization of vinyl chloride monomers.

Claims (5)

A polyvinyl alcohol resin having an absorbance (X) at 320 nm in an ultraviolet absorption spectrum of 0.1% by weight aqueous solution of 0.1 or more and a fine powder content of particle size of 500 μm or less of 60% by weight or less. 2. The polyvinyl alcohol system according to claim 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 in the case of 0.1 wt% aqueous solution is 0.3 or more. resin. The polyvinyl alcohol resin according to claim 1 or 2, wherein the saponification degree is 60 mol% or more. A dispersant comprising the polyvinyl alcohol resin according to any one of claims 1 to 3. A dispersant for suspension polymerization comprising the polyvinyl alcohol resin according to any one of claims 1 to 3.