JP2017226781A - Vinyl alcohol-based polymer aqueous solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vinyl alcohol-based polymer aqueous solution capable of producing a high viscosity aqueous emulsion having excellent dispersion stability and having high viscosity.SOLUTION: Provided is a vinyl alcohol-based polymer aqueous solution comprising: a vinyl alcohol-based polymer (A); and a polyoxyalkylene alkyl ether inorganic acid ester salt (B), in which the vinyl alcohol-based polymer (A) being the saponified matter of a copolymer comprising: an unsaturated carboxylic acid-based monomer (a1) unit and a vinyl ester-based monomer(a2) unit, where the ratio of the weight average molecular weight (Mw(A)) to the number average molecular weight (Mn(A)) of the vinyl alcohol-based polymer (A), (Mw(A)//Mn(A)) is 3.0 to 8.0, the ratio of the weight average molecular weight (Mw(A')) to the number average molecular weight (Mn(A')) of the vinyl alcohol-based polymer (A') obtained by treating the vinyl alcohol-based polymer (A) at 40°C for 1 hr in a sodium hydroxide solution, (Mw(A')/Mn(A')) is 2.0 to below 3.0, and the polyoxyalkylene alkyl ether inorganic acid ester salt (B) is included in 1 to 50 pts.mass to 100 pts.mass of the vinyl alcohol-based polymer (A).SELECTED DRAWING: None

Description

  The present invention relates to an aqueous vinyl alcohol polymer solution and an emulsion using the same.

Vinyl alcohol polymers (hereinafter sometimes abbreviated as “PVA”) are known as water-soluble synthetic polymers and are used in various applications. In particular, since PVA has a hydrophobic group and a hydrophilic group and exhibits excellent surface activity, it is useful as a dispersion stabilizer for vinyl ester monomers such as vinyl acetate. Widely used in various fields such as adhesives for paper, woodworking, plastics, various binders for impregnated paper and non-woven products, admixtures, jointing materials, paints, paper processing, textile processing, etc. Yes.

  When PVA is used as a dispersion stabilizer for an aqueous emulsion, it may be used for the purpose of increasing the viscosity of the aqueous emulsion in addition to imparting dispersion stability of the emulsion. For example, it is generally known to use PVA having a high degree of polymerization for the purpose of increasing the viscosity of the emulsion. However, there is a limit to the types of PVA that can be obtained in order to achieve high viscosity using PVA with a high degree of polymerization. In addition, when an emulsion is prepared using a large amount of PVA for increasing the viscosity, there is a problem that the water resistance of the film prepared using the emulsion is lowered.

  Patent Document 1 discloses an aqueous emulsion using a vinyl alcohol polymer having a specific molecular weight distribution as a technique capable of increasing the viscosity of an aqueous emulsion and the strength of a film formed from the aqueous emulsion as compared with the prior art. ing. However, the obtained viscosity has a limit, and an aqueous emulsion having a higher viscosity has been demanded in the market. Moreover, in patent document 1, the solid content density | concentration of aqueous emulsion is about 35%, and the aqueous emulsion which has a higher viscosity with low solid content concentration was not obtained.

International Publication No. 2015/037683

  The present invention has been made based on the circumstances as described above, and an object thereof is to provide a vinyl alcohol polymer aqueous solution that is excellent in dispersion stability and can produce a high-viscosity aqueous emulsion. To do. Furthermore, it aims at providing the vinyl alcohol polymer aqueous solution in which the obtained aqueous emulsion has high thixotropic property.

  As a result of intensive studies to solve the above problems, the inventors of the present invention have found that a copolymer having an unsaturated carboxylic acid monomer (a1) unit and a vinyl ester monomer (a2) unit. Containing a vinyl alcohol polymer (A) which is a compound and a polyoxyalkylene alkyl ether inorganic acid ester salt (B), and a weight average with respect to the number average molecular weight (Mn (A)) of the vinyl alcohol polymer (A) The ratio of molecular weight (Mw (A)) (Mw (A) / Mn (A)) is 3.0 or more and 8.0 or less, and the vinyl alcohol polymer (A) is 40 ° C. in a sodium hydroxide solution. The ratio of the weight average molecular weight (Mw (A ′)) to the number average molecular weight (Mn (A ′)) of the vinyl alcohol polymer (A ′) obtained by treatment with 1 hour (Mw (A ′) / Mn ( A ')) is 2.0 or more Less than 0.0, and a vinyl alcohol polymer aqueous solution containing 1 to 50 parts by mass of the polyoxyalkylene alkyl ether inorganic acid ester salt (B) with respect to 100 parts by mass of the vinyl alcohol polymer (A). By producing an aqueous emulsion, it has been found that an aqueous emulsion having excellent dispersion stability and a higher viscosity than before can be obtained, and further research has been conducted based on this finding, and the present invention has been completed. It was.

That is, the present invention
Containing a vinyl alcohol polymer (A) and a polyoxyalkylene alkyl ether inorganic acid ester salt (B),
The vinyl alcohol polymer (A) is a saponified product of a copolymer having an unsaturated carboxylic acid monomer (a1) unit and a vinyl ester monomer (a2) unit,
The ratio (Mw (A) / Mn (A)) of the weight average molecular weight (Mw (A)) to the number average molecular weight (Mn (A)) of the vinyl alcohol polymer (A) is 3.0 or more and 8.0. The number average molecular weight (Mn (A ′)) of the vinyl alcohol polymer (A ′) obtained by treating the vinyl alcohol polymer (A) in a sodium hydroxide solution at 40 ° C. for 1 hour. The ratio (Mw (A ′) / Mn (A ′)) of the weight average molecular weight (Mw (A ′)) to is 2.0 or more and less than 3.0,
Provided is an aqueous vinyl alcohol polymer solution containing 1 to 50 parts by mass of a polyoxyalkylene alkyl ether inorganic acid ester salt (B) with respect to 100 parts by mass of a vinyl alcohol polymer (A).

  The present invention also provides an aqueous emulsion containing the vinyl alcohol polymer aqueous solution.

  The vinyl alcohol polymer (A) is obtained by polymerizing a copolymer of an unsaturated carboxylic acid monomer (a1) and a vinyl ester monomer (a2), followed by saponification and heat treatment. It is. By heat-treating the vinyl alcohol polymer (A), the carboxyl group and the hydroxyl group can be ester-bonded to form a branched structure as a whole, so that even better dispersibility can be exhibited during emulsion polymerization. The viscosity of the resulting aqueous emulsion is further improved.

  The combination of the carboxyl group of the vinyl alcohol polymer (A) and the structure of the inorganic acid salt of the alkyl ether group of the polyoxyalkylene alkyl ether inorganic acid ester salt (B) results in a solid content concentration of less than 25% by mass. Even if it exists, while the viscosity of an emulsion improves further, the dispersibility at the time of emulsion polymerization also improves.

  By using the aqueous solution of the vinyl alcohol polymer of the present invention, for example, an aqueous emulsion having excellent dispersion stability and high viscosity can be provided. Moreover, the aqueous emulsion obtained using the vinyl alcohol polymer aqueous solution of the present invention has high thixotropic properties. Furthermore, the aqueous emulsion of the present invention can have a high viscosity even when the solid content concentration is less than 25% by mass. Accordingly, the aqueous emulsion of the present invention is suitably used for various adhesives, paints, fiber processing agents, paper processing agents, inorganic binders, cement admixtures, mortar primers, and the like.

<Vinyl alcohol polymer aqueous solution>
The aqueous vinyl alcohol polymer solution of the present invention comprises a vinyl alcohol polymer (A) (hereinafter sometimes abbreviated as “PVA (A)”), a polyoxyalkylene alkyl ether inorganic acid ester salt (B). Containing
The vinyl alcohol polymer (A) is an unsaturated carboxylic acid monomer (a1) unit (hereinafter, the unsaturated carboxylic acid monomer (a1) is abbreviated as “monomer (a1)”. And a saponified product of a copolymer having a vinyl ester monomer (a2) unit,
The ratio (Mw (A) / Mn (A)) of the weight average molecular weight (Mw (A)) to the number average molecular weight (Mn (A)) of the vinyl alcohol polymer (A) is 3.0 or more and 8.0. The number average molecular weight (Mn (A ′)) of the vinyl alcohol polymer (A ′) obtained by treating the vinyl alcohol polymer (A) in a sodium hydroxide solution at 40 ° C. for 1 hour. The ratio (Mw (A ′) / Mn (A ′)) of the weight average molecular weight (Mw (A ′)) to is 2.0 or more and less than 3.0,
1-100 mass parts of polyoxyalkylene alkyl ether inorganic acid ester salt (B) is contained with respect to 100 mass parts of vinyl alcohol-type polymer (A).

  In the present specification, the upper limit value and the lower limit value of the numerical ranges (content of each component, values calculated from each component, characteristics, etc.) can be appropriately combined.

[PVA (A)]
As PVA (A) in the aqueous vinyl alcohol polymer solution of the present invention, a copolymer having an unsaturated carboxylic acid monomer (a1) unit and a vinyl ester monomer (a2) unit was obtained by polymerization. Thereafter, the copolymer is obtained by saponification.

  The unsaturated carboxylic acid monomer (a1) is not particularly limited as long as it is a monomer having a carboxylic acid or a salt thereof or an acid anhydride thereof, and examples thereof include maleic acid, maleic acid monomethyl ester, and maleic acid. Dimethyl acid, monoethyl maleate, diethyl maleate, maleic anhydride, citraconic acid, monomethyl citraconic acid, dimethyl citraconic acid, diethyl citraconic acid, citraconic anhydride, fumaric acid, monomethyl fumarate, dimethyl fumarate, monoethyl fumarate, fumarate Examples include diethyl acid, itaconic acid, monomethyl itaconate, dimethyl itaconate, monoethyl itaconate, diethyl itaconate, itaconic anhydride, acrylic acid, methyl acrylate, ethyl acrylate, methacrylic acid, methyl methacrylate, and ethyl methacrylate. Be

  Among these monomers, monomethyl maleate, monomethyl citraconic acid, monomethyl itaconate, methyl acrylate, and methyl methacrylate are preferable, and monomethyl maleate, methyl acrylate, and methyl methacrylate are more preferable.

  The vinyl ester monomer (a2) is not particularly limited, and examples thereof include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl versatate, vinyl caproate, and caprylic acid. Examples thereof include vinyl, vinyl laurate, vinyl palmitate, vinyl stearate, vinyl oleate, vinyl benzoate and the like. Among these, vinyl acetate is preferable from the economical viewpoint.

  As a minimum of the content rate of the monomer (a1) unit in PVA (A), 0.02 mol% is preferable based on the number-of-moles of all the monomer units which comprise PVA (A), 0.05 mol % Is more preferable, and 0.1 mol% is more preferable. On the other hand, the upper limit of the content of the monomer (a1) unit in PVA (A) is preferably 5.0 mol% based on the number of moles of all monomer units constituting PVA (A), preferably 2 0.0 mol% is more preferable, and 1.0 mol% is more preferable. When the content is at least the above lower limit, the viscosity of the aqueous emulsion obtained and the water resistance of the film formed from the aqueous emulsion are further improved. On the other hand, when the content is less than or equal to the above upper limit, dispersibility during the emulsion polymerization is further improved.

The content rate of a monomer (a1) unit can be calculated | required from < ¹ > H-NMR of the vinyl ester polymer which is a precursor of PVA (A). For example, when monomethyl maleate is used as the monomer (a1), the content is obtained by the following procedure. That is, after reprecipitation and purification of the vinyl ester polymer with n-hexane / acetone 3 times or more sufficiently, drying is performed under reduced pressure at 50 ° C. for 2 days to prepare a sample for analysis. This sample is dissolved in CDCl ₃ and measured at room temperature using ¹ H-NMR of 500 MHz (“GX-500” manufactured by JEOL Ltd.). In the vinyl ester polymer, a peak α (4.7 to 5.2 ppm) derived from the methine structure of the vinyl ester unit and a peak β (3 derived from the methyl group of the methyl ester portion of the monomer (a1) unit) 6 to 3.8 ppm), the content S of the monomer (a1) unit can be calculated using the following formula.
S (mol%) = {(number of protons of β / 3) / (number of protons of α + (number of protons of β / 3))} × 100

  PVA (A) has a ratio of weight average molecular weight (Mw (A)) to number average molecular weight (Mn (A)) (Mw (A) / Mn (A)) of 3.0 or more and 8.0 or less. The lower limit of the ratio is preferably 3.2 from the viewpoint of further improving the viscosity of the resulting aqueous emulsion, more preferably 3.4, still more preferably 3.6, and the upper limit of the ratio is 6 0.0 is preferable, and 5.0 is more preferable.

  PVA (A ′) is obtained by treating the above PVA (A) in a sodium hydroxide solution at 40 ° C. for 1 hour. As this treatment, the method of complete saponification described in the column of the average degree of polymerization in JIS K 6726 (1994) can be adopted, and specifically, it is obtained as follows. That is, about 10 g of PVA (A) is weighed into a common Erlenmeyer flask, 200 mL of methanol is added, and then 12.5 mol / L sodium hydroxide solution is added when the saponification degree of PVA (A) is 97 mol% or more. If the saponification degree of PVA (A) is less than 97 mol%, add 10 mL, stir and heat in a water bath at 40 ° C. for 1 hour, then add phenolphthalein as an indicator and observe an alkaline reaction. It can be obtained by washing with methanol until it disappears, removing sodium hydroxide, and finally transferring to a watch glass and drying at 105 ° C. for 1 hour until methanol is exhausted.

  In the PVA (A ′), the ratio of the weight average molecular weight (Mw (A ′)) to the number average molecular weight (Mn (A ′)) (Mw (A ′) / Mn (A ′)) is 2.0 or more and 3 Less than 0.0. The lower limit of the ratio is preferably 2.1, more preferably 2.2, and the upper limit of the ratio is preferably 2.9 and more preferably 2.8.

  The PVA (A) of the present invention is such that (Mw (A) / Mn (A)) and (Mw (A ′) / Mn (A ′)) are in the above range, and PVA (A) is a vinyl alcohol unit. It is thought that the hydroxyl group derived from the carboxylic acid group derived from the monomer (a1) unit undergoes an esterification reaction, whereby the PVA chains are bonded to each other to form a branched structure. And it is thought that it becomes what was excellent in the dispersibility of an emulsion by this branched structure.

In addition, the number average molecular weight (Mn) and the weight average molecular weight (Mw) in the above PVA (A) and PVA (A ′) are gel permeation using hexafluoroisopropanol as a mobile phase and a differential refractive index detector. It can obtain | require as a polymethylmethacrylate conversion value by a chromatography (GPC) measurement, As a more concrete method, the following can be employ | adopted.
GPC column: two “GMH _HR (S)” manufactured by Tosoh Corporation Mobile phase: hexafluoroisopropanol Flow rate: 0.2 mL / min Sample concentration: 0.100 wt / vol%
Sample injection volume: 10 μL
Detector: Differential refractive index detector Standard material: Polymethacrylic acid (for example, “EasiVial PMMA 4 mL tri-pack” manufactured by Agilent Technologies)

  It is preferable to add a salt such as sodium trifluoroacetate to hexafluoroisopropanol used as the mobile phase in order to suppress the adsorption of the sample to the GPC column filler. The concentration of the salt is usually 1 mmol / L to 100 mmol / L, preferably 5 mmol / L to 50 mmol / L.

  The ratio of the weight average molecular weight (Mw) of PVA (A) to the weight average molecular weight (Mw) of PVA (A ′) is not particularly limited, but the lower limit is 1 .4 is preferred and 1.5 is more preferred. On the other hand, the upper limit of the ratio (Mw (A) / Mw (A ′)) is preferably 3.0, and more preferably 2.5. When the ratio (Mw (A) / Mw (A ′)) is not less than the above lower limit, the viscosity of the obtained aqueous emulsion is further improved. On the other hand, when the ratio (Mw (A) / Mw (A ′)) is not more than the upper limit, the dispersion stability of the emulsion is further improved.

  Further, PVA (A) is a monomer (a3) unit other than the vinyl alcohol unit, the monomer (a1) unit, and the vinyl ester monomer (a2) unit, as long as the gist of the present invention is not impaired. May be included. Examples of the other monomer (a3) include α-olefins such as ethylene, propylene, n-butene, and isobutylene; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, vinyl ethers such as i-butyl vinyl ether, t-butyl vinyl ether, 2,3-diacetoxy-1-vinyloxypropane; vinyl cyanides such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride and vinyl fluoride Vinylidene halides such as vinylidene chloride and vinylidene fluoride; allyl compounds such as allyl acetate, 2,3-diacetoxy-1-allyloxypropane and allyl chloride; vinylsilyl compounds such as vinyltrimethoxysilane; isopropyl acetate Alkylsulfonyl and the like. The content of the other monomer (a3) unit in PVA (A) can be, for example, 15 mol% or less based on the number of moles of all monomer units constituting PVA (A). .

  The order of arrangement of the vinyl alcohol unit, the monomer (a1) unit, the vinyl ester monomer (a2) unit and the other monomer (a3) unit in PVA (A) is not particularly limited, and is random, block Any of these may be used alternately.

The primary structure of PVA (A) can be quantified by ¹ H-NMR. CDCl ₃ may be used as a solvent for ¹ H-NMR measurement.

  The degree of saponification of PVA (A) (the mole fraction of hydroxyl groups relative to the total of hydroxyl groups and ester bonds in PVA (A)) is measured according to JIS K 6726 (1994). As a minimum of saponification degree, 20 mol% is preferable, 60 mol% is more preferable, 70 mol% is further more preferable, 80 mol% is especially preferable, and 87 mol% is the most preferable. When the degree of saponification of PVA (A) is not less than the above lower limit, the dispersibility of the stabilizer for emulsion polymerization at the time of emulsion polymerization, the viscosity of the resulting aqueous emulsion, and the strength of the film formed from the aqueous emulsion are further improved. .

  As an upper limit of the viscosity average degree of polymerization of PVA (A), 6,000 is preferable and 5,000 is more preferable. On the other hand, as a minimum of the viscosity average degree of polymerization of PVA (A), 100 is preferred, 500 is more preferred, and 1,000 is still more preferred. When the viscosity average polymerization degree of PVA (A) is not less than the above lower limit, the viscosity of the aqueous emulsion obtained and the strength of the film formed from the aqueous emulsion are further improved. On the other hand, when the viscosity average polymerization degree of PVA (A) is not more than the above upper limit, the productivity of PVA (A) is improved, and PVA (A) can be produced at a lower cost.

The viscosity average degree of polymerization (P) of PVA (A) is measured according to JIS K 6726 (1994). That is, after the PVA (A) is completely saponified and purified, the intrinsic viscosity of the PVA (A) containing the monomer (a1) unit in a 30 ° C. aqueous sodium chloride solution (0.5 mol / L) [ η] (unit: liter / g) is measured, and for PVA (A) not containing the monomer (a1) unit, the intrinsic viscosity [η] (unit: liter / g) is measured in an aqueous solution at 30 ° C. . From this intrinsic viscosity [η], the viscosity average degree of polymerization (P) of PVA (A) is obtained by the following formula.
P = ([η] × 10 ⁴ /8.29) ^{(1 / 0.62)}

  Moreover, since PVA (A ′) is obtained by treating PVA (A) in a sodium hydroxide solution at 40 ° C. for 1 hour, the viscosity average degree of polymerization of PVA (A ′) is PVA (A). The viscosity average polymerization degree is substantially the same value.

<Method for producing PVA (A)>
Although it does not specifically limit as a manufacturing method of PVA (A), For example, the process (henceforth a "polymerization process") which superposes | polymerizes a monomer (a1) and a vinyl ester type monomer (a2), this, And a step of saponifying the vinyl ester polymer obtained by the polymerization step (hereinafter also referred to as “saponification step”). In addition, it is preferable to further include a step of heating the vinyl ester polymer or the saponified PVA (hereinafter also referred to as “heating step”).

[Polymerization process]
In this step, the monomer (a1) and the vinyl ester monomer (a2) are polymerized to synthesize a vinyl ester polymer. As the polymerization method, any of batch polymerization, semi-batch polymerization, continuous polymerization, and semi-continuous polymerization may be used. As the polymerization method, any known method such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, or an emulsion polymerization method can be employed. Among these, a bulk polymerization method or a solution polymerization method in which polymerization proceeds in a solvent-free or solvent such as alcohol is usually employed. In order to obtain a vinyl ester polymer having a high degree of polymerization, one of the options is to employ an emulsion polymerization method. The solvent for the solution polymerization method is not particularly limited, and examples thereof include alcohol. The alcohol used as the solvent for the solution polymerization method is, for example, a lower alcohol such as methanol, ethanol, or n-propanol. A solvent may be used individually by 1 type, or may use 2 or more types together. The amount of solvent used in the polymerization system may be selected in consideration of the chain transfer of the solvent according to the degree of polymerization of the target PVA (A). For example, when the solvent is methanol, it is included in the solvent and the polymerization system. The mass ratio with respect to the total monomer {= (solvent) / (total monomer)} is preferably in the range of 0.01 to 10, and more preferably in the range of 0.05 to 3.

  The polymerization initiator used for such polymerization may be appropriately selected from known polymerization initiators such as azo-based initiators, peroxide-based initiators, redox-based initiators and the like according to the polymerization method. Examples of the azo initiator include 2,2′-azobisisobutyronitrile, 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobis (4-methoxy-2, 4-dimethylvaleronitrile) and the like. Examples of the peroxide initiator include percarbonate compounds such as diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, and diethoxyethyl peroxydicarbonate; t-butyl peroxyneodecanate, α -Perester compounds such as cumylperoxyneodecanate and t-butylperoxydecanate; acetyl peroxide; acetylcyclohexylsulfonyl peroxide; 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate . The initiator may be combined with potassium persulfate, ammonium persulfate, hydrogen peroxide, or the like. Examples of the redox initiator include a combination of the above peroxide initiator and a reducing agent such as sodium hydrogen sulfite, sodium hydrogen carbonate, tartaric acid, L-ascorbic acid, Rongalite and the like.

  The amount of the polymerization initiator used varies depending on the polymerization catalyst and the like and cannot be determined unconditionally, but may be appropriately selected according to the polymerization rate. For example, when 2,2′-azobisisobutyronitrile or acetyl peroxide is used as the polymerization initiator, 0.01 to 0.2 mol% is preferable with respect to the vinyl ester monomer (a2). 02 to 0.15 mol% is more preferable.

  As a minimum of temperature in a polymerization process, 0 ° C is preferred and 30 ° C is more preferred. As an upper limit of polymerization temperature, 200 degreeC is preferable and 140 degreeC is more preferable. When the polymerization temperature is equal to or higher than the above lower limit, the polymerization rate is improved. On the other hand, when the polymerization temperature is not more than the above upper limit, it becomes easy to keep the content of the monomer (a1) unit in the PVA (A) at an appropriate ratio. As a method of controlling the polymerization temperature within the above range, for example, by controlling the polymerization rate, a method of balancing the heat generated by the polymerization and the heat radiation from the surface of the reactor, or using an appropriate heating medium is used. A method of controlling with an external jacket is preferable, but the latter method is preferable from the viewpoint of safety.

  The polymerization may be carried out in the presence of a chain transfer agent as long as the gist of the present invention is not impaired. Examples of chain transfer agents include aldehydes such as acetaldehyde and propionaldehyde; ketones such as acetone and methyl ethyl ketone; mercaptans such as 2-hydroxyethanethiol; halogenated hydrocarbons such as trichloroethylene and perchloroethylene; sodium phosphinate Examples thereof include phosphinic acid salts such as monohydrate. Of these, aldehydes and ketones are preferred. The amount of chain transfer agent added to the polymerization system can be determined according to the chain transfer coefficient of the chain transfer agent to be added, the degree of polymerization of the target PVA (A), etc., and is generally a vinyl ester monomer. (A2) 0.1-10 mass parts is preferable with respect to 100 mass parts.

  In addition, when the said superposition | polymerization is performed under high temperature, coloring etc. of PVA (A) resulting from decomposition | disassembly of a vinyl ester type monomer (a2) may be seen. In this case, a method of adding about 1 to 100 ppm of an antioxidant such as tartaric acid to the polymerization system with respect to the vinyl ester monomer (a2) for the purpose of preventing coloring.

[Saponification process]
In this step, the vinyl ester polymer obtained in the polymerization step is saponified. By saponifying this polymer, the vinyl ester unit in the polymer is converted into a vinyl alcohol unit.

  Although it does not restrict | limit especially as reaction used for the saponification of a vinyl ester polymer, The well-known alcoholic decomposition reaction or hydrolysis reaction performed in the state which the said polymer melt | dissolved in the solvent is employable.

  Examples of the solvent used for saponification include lower alcohols such as methanol and ethanol; esters such as methyl acetate and ethyl acetate; ketones such as acetone and methyl ethyl ketone; aromatic hydrocarbons such as benzene and toluene. These solvents may be used alone or in combination of two or more. Among these, methanol and a mixed solution of methanol and methyl acetate are preferable.

  Examples of the catalyst used for saponification include alkali catalysts such as alkali metal hydroxides (potassium hydroxide, sodium hydroxide, etc.), sodium alkoxides (sodium methoxide, etc.); acids such as p-toluenesulfonic acid and mineral acids. A catalyst etc. are mentioned. Among these, it is preferable to use sodium hydroxide because it is simple.

  Although it does not specifically limit as temperature which performs saponification, 20 to 60 degreeC is preferable. When a gel-like product precipitates as saponification progresses, it is preferable to pulverize the product and further promote saponification. Then, saponification is complete | finished by neutralizing the obtained solution, and it can wash | clean and dry and can obtain a vinyl alcohol-type polymer. As a saponification method, not only the method mentioned above but a well-known method is employable.

[Heating process]
In this step, the vinyl ester polymer or the saponified PVA is heated. Specifically, the vinyl ester polymer is heated by heating simultaneously with the saponification step, or the PVA obtained after the saponification step is heated. PVA (A) in which a branched structure is formed by this heating can be easily obtained, and the dispersibility of the stabilizer for emulsion polymerization at the time of emulsion polymerization and the viscosity of the resulting aqueous emulsion are further improved. The heat treatment is preferably performed in an air or nitrogen atmosphere. Moreover, it is preferable that a heating process is performed with respect to PVA after saponification.

  As a minimum of heating temperature in a heating process, 90 ° C is more preferred, 100 ° C is more preferred, and 110 ° C is still more preferred. As an upper limit of the said heating temperature, 150 degreeC is preferable and 130 degreeC is more preferable. The lower limit of the heating time in the heating step is preferably 30 minutes, more preferably 1 hour, and even more preferably 2 hours. The upper limit of the heating time is preferably 10 hours, more preferably 7 hours, and even more preferably 5 hours. By setting the heating temperature and the heating time within the above ranges, PVA (A) satisfying the provisions of the present invention can be easily obtained, and the dispersibility of the stabilizer for emulsion polymerization during emulsion polymerization can be obtained. The viscosity of the is further improved.

[Polyoxyalkylene alkyl ether inorganic acid ester salt (B)]
The vinyl alcohol polymer aqueous solution of the present invention and the aqueous emulsion using the same contain a polyoxyalkylene alkyl ether inorganic acid ester salt (B). By preparing an aqueous solution in which the polyoxyalkylene alkyl ether inorganic acid ester salt (B) is dissolved in water and using it in emulsion polymerization, an aqueous emulsion having higher viscosity and excellent stability can be obtained. The polyoxyalkylene alkyl ether inorganic acid ester salt (B) is an anionic surfactant. The alkyl group of the polyoxyalkylene alkyl ether inorganic acid ester salt (B) preferably has 8 to 22 carbon atoms, more preferably 9 to 20 carbon atoms, and still more preferably 10 to 18 carbon atoms. As the polyoxyalkylene alkyl ether inorganic acid ester salt (B), polyoxyethylene alkyl ether (hereinafter referred to as POE alkyl ether) inorganic acid ester salt (B1) is preferable. A polyoxyalkylene alkyl ether inorganic acid ester salt (B) may be used individually by 1 type, and may use 2 or more types together.

  Examples of inorganic acids that form esters with polyoxyalkylene alkyl ethers include sulfuric acid, phosphoric acid, nitric acid, and carbonic acid, with sulfuric acid being preferred. An inorganic acid may be used individually by 1 type, and may use 2 or more types together.

  As the POE alkyl ether inorganic acid ester salt (B1), the POE alkyl ether sulfate ester salt (b1) is preferable. Examples of the salt include alkali metal salts and ammonium salts.

The POE alkyl ether sulfate ester salt (b1) is represented by the following formula (1):
R ¹ —O— (EO) _n —SO ₃ M (1)
(In the formula, R ¹ represents an alkyl group having 8 to 22 carbon atoms, EO represents a polyoxyethylene group (CH ₂ CH ₂ O), n represents an average added mole number of the polyoxyethylene group, and n represents 1 to 30 and M represents an alkali metal or ammonium.)
It is a compound represented by these.

Examples of the alkyl group having 8 to 22 carbon atoms of R ¹ include octyl group, nonyl group, decyl group, undecyl group, dodecyl group (lauryl group), myristyl group, tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group , Octadecyl group, nonadecyl group, eicosyl group, heneicosyl group, docosyl group and the like.

The number of carbon atoms of R ^1, preferably from 9 to 20, more preferably from 10 to 18, more preferably 10 to 16.

  As for n of Formula (1), 2-8 are preferable, 2-5 are more preferable, and 2-4 are more preferable. Examples of the alkali metal of M include lithium, sodium, potassium, rubidium and cesium, and sodium is preferable.

As the POE alkyl ether sulfate ester salt (b1), in the formula (1), a compound in which R ¹ represents an alkyl group of 10 to 18, n is 2 to 5, and M is an alkali metal or ammonium is preferable. In the formula (1), a compound in which R ¹ represents an alkyl group of 10 to 16, n is 2 to 4, and M is sodium or ammonium is more preferable.

  Examples of the polyoxyalkylene alkyl ether inorganic acid ester salt (B) include sodium polyoxyethylene lauryl ether sulfate, sodium polyoxyethylene tridecyl ether sulfate, sodium polyoxyethylene myristyl ether sulfate, sodium polyoxyethylene pentadecyl ether sulfate And polyoxyethylene lauryl ether ammonium sulfate. Of these, sodium polyoxyethylene lauryl ether sulfate and ammonium polyoxyethylene lauryl ether sulfate are preferred from the viewpoints of polymerization stability during emulsion production and high viscosity expression.

  A commercial item can be used for polyoxyalkylene alkyl ether inorganic acid ester salt (B). Examples of commercially available products include Arscope DA-330 S (polyoxyethylene alkyl ether sodium sulfate (12,13 carbon atoms of alkyl group, average number of added moles of EO group: 3), manufactured by Toho Chemical Industry Co., Ltd.); Polyoxyethylene alkyl ether phosphate ester salt such as Plysurf A208F (Daiichi Kogyo Seiyaku Co., Ltd.); Polyoxyethylene alkyl ether sodium acetate such as Neo Haitenol ECL-45 (Daiichi Kogyo Seiyaku Co., Ltd.); Tenols LA-10, LA-12, LA-16 and other polyoxyethylene lauryl ether ammonium sulfate (Daiichi Kogyo Seiyaku Co., Ltd.); Hytenol 227L, 325L polyoxyethylene lauryl ether sodium sulfate (Daiichi Kogyo Seiyaku Co. Company made); Emar 170J (Polyoki) Sodium ethylene lauryl ether sulfate (average added mole number of EO group: 1)), Emar 270J (sodium polyoxyethylene lauryl ether sulfate (average added mole number of EO group: 2)), Emar 20C (polyoxyethylene lauryl ether) Sodium sulfate (average added mole number of EO group: 3), Emar E-27C (sodium polyoxyethylene lauryl ether sulfate (average added mole number of EO group: 2)), Emar 327 (sodium polyoxyethylene lauryl ether sulfate (EO) Examples include Emar series (manufactured by Kao Corporation) such as the average number of added moles of group: 3).

  The content of the polyoxyalkylene alkyl ether inorganic acid ester salt (B) in the aqueous vinyl alcohol polymer solution of the present invention is 0.005 to the total 100 parts by mass of the vinyl alcohol polymer (A) and water. 1.0 mass part is preferable, 0.010-0.90 mass part is more preferable, and 0.10-0.80 mass part is still more preferable. The compounding ratio of the vinyl alcohol polymer (A) and the polyoxyalkylene alkyl ether inorganic acid ester salt (B) is determined by the polymerization stability and target viscosity of the emulsion. For example, the vinyl alcohol polymer (A) It is essential to contain 1 to 50 parts by mass of the polyoxyalkylene alkyl ether inorganic acid ester salt (B) with respect to 100 parts by mass, preferably 3 to 40 parts by mass, and more preferably 5 to 30 parts by mass. When the amount is less than 1 part by mass, the effect of improving the polymerization stability and viscosity is insufficient. When the amount is more than 50 parts by mass, the water resistance is insufficient.

  The concentration of the vinyl alcohol polymer aqueous solution containing the vinyl alcohol polymer (A), polyoxyalkylene alkyl ether inorganic acid ester salt (B) and water is controlled within a range that does not hinder emulsion polymerization. For example, 0.1 to 40% by mass is preferable, 0.2 to 30% by mass is more preferable, and 0.5 to 20% by mass is further preferable. When the concentration of the aqueous solution is within the above range, a highly viscous aqueous emulsion can be easily obtained.

  As a solvent of the aqueous vinyl alcohol polymer solution of the present invention, the main component is water, but if necessary, lower alcohols such as methanol and ethanol; esters such as methyl acetate and ethyl acetate; acetone, methyl ethyl ketone and the like Ketones; ethers such as dimethyl ether may be added. Moreover, you may add the solvent generally known to mix with water, such as a dimethylsulfoxide and a dimethylformamide. These organic solvents may be used individually by 1 type, and may use 2 or more types together.

  The present invention includes various surfactants other than the vinyl alcohol polymer other than the vinyl alcohol polymer (A) and the polyoxyalkylene alkyl ether inorganic acid salt (B) as long as the effects are not impaired. You may add.

  Examples of the other surfactants include anionic surfactants such as alkylnaphthalene sulfonate and dialkylsulfosuccinic acid; cationic surfactants such as alkylamine salt and lauryltrimethylammonium chloride; polyoxyethylene alkyl ether, poly Nonionic surfactants such as oxyethylene alkyl phenyl ether and sorbitan fatty acid ester; amphoteric surfactants such as alkyl betaine and amine oxide; polymer surfactants such as hydroxyethyl cellulose and the like.

  The aqueous vinyl alcohol polymer solution of the present invention can be used as a stabilizer dispersant for emulsion polymerization. That is, the aqueous vinyl alcohol polymer solution of the present invention can be subjected to emulsion polymerization in a form dispersed or dissolved in water. As a result, emulsion polymerization of the vinyl ester monomer can be performed more easily and reliably. As an upper limit of water content of vinyl alcohol polymer aqueous solution, 99.5 mass% is preferable and 99 mass% is more preferable. On the other hand, as a minimum of content of the above-mentioned water, 70 mass% is preferred and 75 mass% is more preferred. If the water content exceeds the above upper limit, the emulsion polymerization reaction may not occur sufficiently. On the other hand, when the water content is less than the above lower limit, the dispersion or dissolution of PVA (A) may be insufficient.

<Aqueous emulsion>
The aqueous emulsion is suitably used for various adhesives, paints, fiber processing agents, paper processing agents, inorganic binders, cement admixtures, mortar primers, and the like. As a method for producing the aqueous emulsion, an ethylenically unsaturated monomer is added temporarily or continuously in the presence of a polymerization initiator in the aqueous vinyl alcohol polymer solution of the present invention which is a stabilizer for emulsion polymerization. The method of emulsion polymerization is mentioned. Moreover, the method of adding continuously the ethylenically unsaturated monomer emulsified using the said stabilizer for emulsion polymerization to a polymerization reaction system is also employable. Although the usage-amount of the said stabilizer for emulsion polymerization is not specifically limited, 1-30 mass parts is preferable with respect to 100 mass parts of ethylenically unsaturated monomers, and 2-20 mass parts is more preferable.

  Further, when the emulsion polymerization stabilizer is used for emulsion polymerization, the emulsion polymerization stabilizer containing another vinyl alcohol polymer (C) (hereinafter sometimes abbreviated as “PVA (C)”). Can be used in combination. The PVA (C) is preferably PVA having a saponification degree of 70 mol% or more and a polymerization degree of 300 to 4500, a saponification degree of 80 to 99 mol%, and a polymerization degree of 500 to 3500. Some PVA is more preferred. The measuring method of a saponification degree and a polymerization degree is the same method as what was demonstrated by PVA (A).

  Moreover, PVA (C) may be given water resistance by introducing an ethylene group, an acetoacetyl group, or the like. The weight ratio of the addition amount of PVA (A) and the addition amount of PVA (C) in the stabilizer for emulsion polymerization in the case of using together the stabilizer for emulsion polymerization containing PVA (C) (the PVA (A) / PVA (C)) varies depending on the type of emulsion polymerization stabilizer used and the like, and thus cannot be defined uniformly, but is preferably in the range of 95/5 to 5/95, particularly 90/10 to 10 /. 90 is preferred. These stabilizers for emulsion polymerization may be charged all at the beginning of emulsion polymerization, or may be charged in the middle of emulsion polymerization.

  Examples of the ethylenically unsaturated monomer include olefin monomers such as ethylene, propylene, and isobutylene; halogenated olefin monomers such as vinyl chloride, vinyl fluoride, vinylidene chloride, and vinylidene fluoride; formic acid Vinyl ester monomers such as vinyl, vinyl acetate, vinyl propionate and vinyl versatate; acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, acrylic Acrylic acid ester monomers such as 2-hydroxyethyl acid; Methacrylic acid ester monomers such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, 2-hydroxyethyl methacrylate Mer; Acrylamide monomers such as dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, acrylamide, methacrylamide, N-methylolacrylamide, N, N-dimethylacrylamide, acrylamide-2-methylpropanesulfonic acid; styrene, α-methyl Examples thereof include styrene monomers such as styrene and p-styrene sulfonic acid; and diene monomers such as N-vinylpyrrolidone, butadiene, isoprene and chloroprene.

  As the ethylenically unsaturated monomer, among these, a vinyl ester monomer, a (meth) acrylic acid ester monomer, and a styrene monomer are preferable, and a vinyl ester monomer is more preferable. More preferred is vinyl acetate. The ethylenically unsaturated monomer may be used alone or in combination of two or more.

  Conventional additives such as fillers such as titanium oxide, organic solvents such as toluene, plasticizers such as dibutyl phthalate, and film-forming aids such as glycol ether may be added to the aqueous emulsion. Further, a so-called powder emulsion obtained by pulverizing an aqueous emulsion by spray drying or the like may be used. Such aqueous emulsions and powder emulsions are suitably used for a wide range of applications such as various adhesives, paints, fiber processing agents, paper processing agents, inorganic binders, cement admixtures, mortar primers and the like.

  The aqueous emulsion obtained using the aqueous vinyl alcohol polymer solution of the present invention preferably has a viscosity ratio (η2 rpm / η20 rpm) of 4.5 or more, more preferably 4.7 or more, and 4 .9 or more is more preferable, and 5.0 or more is particularly preferable. The measuring method of (eta) 2rpm and (eta) 20rpm is as the description in the Example mentioned later.

  EXAMPLES Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples at all, and many variations are within the technical idea of the present invention. This is possible by those with ordinary knowledge. In the following examples and comparative examples, “parts” and “%” are based on mass unless otherwise specified.

  About the physical property value of PVA of the following Example and comparative example, it measured in accordance with the following method.

[Degree of polymerization]
In each Example or Comparative Example, the viscosity average degree of polymerization of PVA (A) was determined by the method described in JIS K 6726 (1994).

[Saponification degree]
The degree of saponification of each PVA (A) was determined by the method described in JIS K 6726 (1994).

[Modification rate]
The modification rate of each PVA (the content of the monomer (a1) unit in PVA (A)) uses the above-mentioned ¹ H-NMR by using a vinyl ester polymer that is a precursor of PVA (A). Was determined by the method used.

[Preparation of PVA (A ′)]
About 10 g of PVA (A) was weighed into a common conical Erlenmeyer flask, 200 mL of methanol was added, 10 mL of 12.5 mol / L sodium hydroxide solution was added, stirred, and heated in a 40 ° C. water bath for 1 hour. Next, phenolphthalein is added as an indicator, washed with methanol until no alkaline reaction is observed to remove sodium hydroxide, and finally transferred to a watch glass and dried at 105 ° C. for 1 hour until no methanol is left, and PVA ( A ′) was prepared.

[Number average molecular weight (Mn) and weight average molecular weight (Mw) of PVA (A) and PVA (A ′)]
It calculated | required as a polymethylmethacrylate conversion value by the gel permeation chromatography (GPC) measurement using the differential refractive index detector, using hexafluoro isopropanol for a mobile phase. Specifically, the following conditions were adopted.
GPC column: Tosoh's “GMH _HR (S)” 2 mobile phase: hexafluoroisopropanol (contains sodium trifluoroacetate at a concentration of 20 mmol / L)
Flow rate: 0.2 mL / min Sample concentration: 0.100 wt / vol%
Sample injection volume: 10 μL
Detector: Differential refractive index detector Standard material: Polymethacrylic acid (for example, “EasiVial PMMA 4 mL tri-pack” manufactured by Agilent Technologies)

[Synthesis Example 1] (Production of PVA-1)
A reactor equipped with a stirrer, reflux condenser, nitrogen inlet, comonomer dropping port and polymerization initiator addition port was charged with 100 parts of vinyl acetate and 5.26 parts of methanol, and the system was maintained for 30 minutes while bubbling nitrogen. Was replaced with nitrogen. Further, a methanol solution of monomethyl maleate (concentration 2%) was purged with nitrogen by bubbling nitrogen gas. The temperature of the reactor was increased, and when the internal temperature reached 60 ° C., 0.00395 part of 2,2′-azobisisobutyronitrile (AIBN) was added to initiate polymerization. The methanol solution of monomethyl maleate was dropped into the reactor to polymerize at 60 ° C. for 3 hours while keeping the monomer composition ratio in the polymerization solution constant, and then cooled to stop the polymerization. The total amount of monomethyl maleate added up to the termination of polymerization was 0.106 parts, and the solid content concentration at the termination of polymerization was 22%. Subsequently, unreacted monomers were removed while sometimes adding methanol under reduced pressure at 30 ° C. to obtain a methanol solution (concentration 20%) of a vinyl ester polymer. Next, 100 parts of a methanol solution of vinyl ester polymer prepared by adding methanol to this methanol solution (200.0 parts of the polymer in the solution) was added to 5.1 parts of a 10% methanol solution of sodium hydroxide. And saponification was carried out at 40 ° C. (concentration of the polymer in the saponification solution was 25%, molar ratio of sodium hydroxide to vinyl acetate units in the polymer was 0.011). After adding a methanol solution of sodium hydroxide, a gel-like product was formed after a while. This was pulverized by a pulverizer, further left to stand at 40 ° C. and saponified for 1 hour, and then 500 parts of methyl acetate was added to the residue. To neutralize the alkali. After confirming the completion of neutralization using a phenolphthalein indicator, the mixture was filtered to obtain a white solid. Further, the obtained solid was washed three times with 500 parts of methanol. The white solid obtained by centrifugal drainage was heat-treated at 110 ° C. for 3 hours with a dryer to obtain PVA (A) (PVA-1). Table 2 shows the physical properties of PVA-1.

[Synthesis Examples 2 to 5] (Production of PVA-2 to PVA-5)
Polymerization conditions such as the amount of vinyl acetate and methanol added, the addition amount of monomethyl maleate used during polymerization, the concentration of vinyl ester polymer during saponification, and the saponification conditions such as the molar ratio of sodium hydroxide to vinyl acetate units; Various PVA (A) was manufactured by the same method as Synthesis Example 1 except that the heat treatment conditions were changed as shown in Table 1. Table 2 shows the physical properties of each PVA (A) and the PVA (A ′) obtained therefrom.

[Example 1]
(Emulsion polymerization of polyvinyl acetate)
In a 1 L glass polymerization vessel equipped with a reflux condenser, a dropping funnel, a thermometer, and a nitrogen inlet, 419.3 parts by mass of ion-exchanged water, 12 parts by mass of PVA-1 and 0.5 parts by mass of a surfactant. (Sodium polyoxyethylene lauryl sulfate: EMAL 20C, active ingredient 25% manufactured by Kao Corporation) was charged and completely dissolved at 95 ° C. to obtain an aqueous PVA solution. Next, the PVA aqueous solution was cooled and purged with nitrogen, and then heated to 80 ° C. while stirring at 200 rpm. Thereafter, 14.2 parts by mass of 1% ammonium persulfate and 4.0 parts by mass of 1% sodium hydrogen carbonate were added, and 128.6 parts by mass of vinyl acetate was continuously added dropwise over 3 hours. While watching the progress of emulsion polymerization, 15.9 parts by mass of 1% ammonium persulfate was added in three portions and the polymerization was terminated to obtain a polyvinyl acetate emulsion having a solid content of 23% by mass.

[Examples 2 to 6 and Comparative Examples 1 to 5]
A polyvinyl acetate emulsion was produced in the same manner as in Example 1 except that the vinyl alcohol polymer (A) and polyoxyalkylene alkyl ether inorganic acid ester salt (B) used above were changed as shown in Table 3. did.

[Dispersibility during emulsion polymerization]
The polyvinyl acetate emulsion obtained as described above was observed with a system microscope (OLYMPUS "BX-53"), and there was no aggregation or gelation and no filtration residue was observed. Or, although there was no gelation, it was evaluated as “B” when there was little filtration residue, and “C” when there was aggregation or gelation and there was much filtration residue. The evaluation results are also shown in Table 3. Note that the smaller the aggregation or gel and the smaller the filtration residue, the better the dispersibility during emulsion polymerization.

[Viscosity of polyvinyl acetate emulsion]
As a plasticizer, 5 parts by mass of dibutyl phthalate was added to and mixed with 100 parts by mass of the solid content of the polyvinyl acetate emulsions of Examples and Comparative Examples. About this mixture, using a BH type viscometer (“BII type viscometer” manufactured by Toki Sangyo Co., Ltd.), the viscosity under the condition of 30 ° C. and 2 rpm (η2 rpm) and the viscosity under the condition of 30 ° C. and 20 rpm (η20 rpm) It was measured. The evaluation results are also shown in Table 3.

  As shown in Table 3, it can be seen that the aqueous emulsions of Examples 1 to 6 are excellent in dispersibility during emulsion polymerization. In addition, the polyvinyl acetate emulsions obtained in Examples 1 to 6 were obtained because of the very high viscosity and the high viscosity ratio (2 rpm / 20 rpm) under the condition of 2 rpm and the viscosity of 20 rpm. It can be seen that the emulsion is excellent in thixotropy. Furthermore, it can be seen that the polyvinyl acetate emulsions obtained in Examples 1 to 6 have high viscosity even when the solid content concentration is less than 25% by mass.

  On the other hand, the aqueous emulsions of Comparative Examples 1 to 5 had insufficient dispersibility during emulsion polymerization, and Comparative Examples 4 and 5 were particularly insufficient. In Comparative Examples 1 to 3, an aqueous emulsion was obtained, but the viscosity and thixotropy of the emulsion were insufficient.

  The vinyl alcohol polymer aqueous solution of the present invention exhibits excellent dispersibility during emulsion polymerization and can provide a high-viscosity aqueous emulsion. Accordingly, the aqueous emulsion obtained using the aqueous solution is suitably used for various adhesives, paints, fiber processing agents, paper processing agents, inorganic binders, cement admixtures, mortar primers, and the like.

Claims (7)

Containing a vinyl alcohol polymer (A) and a polyoxyalkylene alkyl ether inorganic acid ester salt (B),
The vinyl alcohol polymer (A) is a saponified product of a copolymer having an unsaturated carboxylic acid monomer (a1) unit and a vinyl ester monomer (a2) unit,
The ratio (Mw (A) / Mn (A)) of the weight average molecular weight (Mw (A)) to the number average molecular weight (Mn (A)) of the vinyl alcohol polymer (A) is 3.0 or more and 8.0. The number average molecular weight (Mn (A ′)) of the vinyl alcohol polymer (A ′) obtained by treating the vinyl alcohol polymer (A) in a sodium hydroxide solution at 40 ° C. for 1 hour. The ratio (Mw (A ′) / Mn (A ′)) of the weight average molecular weight (Mw (A ′)) to is 2.0 or more and less than 3.0,
A vinyl alcohol polymer aqueous solution containing 1 to 50 parts by mass of the polyoxyalkylene alkyl ether inorganic acid ester salt (B) with respect to 100 parts by mass of the vinyl alcohol polymer (A).   The aqueous vinyl alcohol polymer solution according to claim 1, wherein the polyoxyalkylene alkyl ether inorganic acid ester salt (B) is a polyoxyethylene alkyl ether inorganic acid ester salt (B1).   The aqueous vinyl alcohol polymer solution according to claim 1 or 2, wherein the inorganic acid is at least one selected from the group consisting of sulfuric acid, phosphoric acid, nitric acid and carbonic acid.   The vinyl alcohol polymer aqueous solution according to any one of claims 1 to 3, wherein the polyoxyalkylene alkyl ether inorganic acid ester salt (B) is a polyoxyethylene alkyl ether sulfate ester salt (b1).   The vinyl alcohol polymer according to any one of claims 1 to 4, wherein the polyoxyalkylene alkyl ether inorganic acid ester salt (B) is polyoxyethylene alkyl ether sodium sulfate or polyoxyethylene alkyl ether ammonium sulfate. Aqueous solution.   The ratio (Mw (A) / Mw (A ′)) of the weight average molecular weight (Mw) of the vinyl alcohol polymer (A) to the weight average molecular weight (Mw) of the vinyl alcohol polymer (A ′) is 1. The aqueous vinyl alcohol polymer solution according to any one of claims 1 to 5, which is 4 or more and 3.0 or less.   An aqueous emulsion comprising the vinyl alcohol polymer aqueous solution according to any one of claims 1 to 6.