JP2015147843A - Dispersant for emulsion polymerization and use thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dispersant for emulsion polymerization excellent in water dispersibility and polymerization stability of organic particles.SOLUTION: There is provided a dispersant for emulsion polymerization having a saponification degree of 50 to 99.99 mol%, a viscosity average polymerization degree of 200 to 5000 and the content of alkali metal salt of carboxylic acid of 0.5 mass% or less in terms of mass of alkali metal, and a peak top molecular weight measured by a differential refractive index detector (A) and the peak top molecular weight measured by absorbancy detector (measurement wavelength of 280 nm) (B) when the polyvinyl alcohol heated for 3 hours at 120°C is subjected to a gel permeation chromatography measurement satisfying following formula (1): (A-B)/A<0.75 and an absorbance of the peak top molecular weight (B) of 0.25×10to 3.00×10.

Description

  The present invention relates to a dispersant for emulsion polymerization containing a specific polyvinyl alcohol. The present invention also relates to an aqueous emulsion containing the specific polyvinyl alcohol. The present invention further relates to an adhesive comprising the above aqueous emulsion.

  Conventionally, polyvinyl alcohol (hereinafter sometimes abbreviated as “PVA”) has been widely used as a dispersant for emulsion polymerization of ethylenically unsaturated monomers, particularly vinyl ester monomers typified by vinyl acetate. Yes. Aqueous emulsions obtained using a dispersion agent for emulsion polymerization containing PVA are used in a wide range of applications such as various adhesives, binders, admixtures, paints and fiber processing agents.

  While such an aqueous emulsion has been heavily used in the above-mentioned applications, conventionally, there have been problems in polymerization stability during emulsion polymerization and water resistance of a film obtained from the aqueous emulsion. Various attempts have been made to solve such problems. For example, for the purpose of improving the polymerization stability of an ethylenically unsaturated monomer, it has been proposed to use a modified PVA having a specific hydroxyalkyl group in the side chain as a dispersant for emulsion polymerization (see Patent Document 1). ). Furthermore, it has been proposed to use carboxyl group-modified PVA (see Patent Document 2) or sulfonic acid-modified PVA (see Patent Document 3) as a dispersant for emulsion polymerization for the purpose of improving the water resistance of a film made of an emulsion. .

  However, in the case of using the dispersant for emulsion polymerization described in Patent Documents 1 to 3, none of them satisfied the polymerization stability and the water resistance of the film at the same time. Furthermore, the inventors have newly found that the water dispersibility of organic particles (dispersibility of ethylenically unsaturated monomers) is also important as an effect of the dispersant for emulsion polymerization. Patent Documents 1 to 3 do not describe any such effects, and are obtained by using an emulsion polymerization dispersant excellent in water dispersibility and polymerization stability of organic particles, and the emulsion polymerization dispersant. There is a need for emulsions that are excellent in water resistance of the film.

JP 08-325310 A JP 09-241466 A Japanese Patent Laid-Open No. 10-060015

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a dispersion agent for emulsion polymerization that is excellent in water dispersibility and polymerization stability of organic particles. Another object of the present invention is to provide an aqueous emulsion excellent in the water resistance of the film.

  As a result of intensive studies to solve the above problems, the present inventors have found that the dispersion agent for emulsion polymerization containing PVA satisfying specific requirements is excellent in water dispersibility and polymerization stability of organic particles, And it discovered that the water resistance of the film | membrane of an aqueous emulsion was excellent, and came to complete this invention.

That is, the object of the present invention is that the degree of saponification is 50 to 99.99 mol%, the viscosity average degree of polymerization is 200 to 5000, and the content of alkali metal salt of carboxylic acid is 0.5% by mass or less in terms of the mass of alkali metal. A dispersion agent for emulsion polymerization containing polyvinyl alcohol,
The peak top molecular weight (A) measured with a differential refractive index detector when the polyvinyl alcohol heated at 120 ° C. for 3 hours was measured by gel permeation chromatography (hereinafter sometimes abbreviated as GPC), The peak top molecular weight (B) measured with an absorptiometric detector (measurement wavelength: 280 nm) is expressed by the following formula (1)
(AB) / A <0.75 (1)
And a dispersant for emulsion polymerization having an absorbance at a peak top molecular weight (B) of 0.25 × 10 ^{−3 to} 3.00 × 10 ⁻³ is achieved.

  An aqueous emulsion obtained by emulsion polymerization of an ethylenically unsaturated monomer in the presence of the dispersant is a preferred embodiment of the present invention.

Further, the object of the present invention is that the degree of saponification is 50 to 99.99 mol%, the viscosity average degree of polymerization is 200 to 5000, and the content of alkali metal salt of carboxylic acid is 0.5% by mass or less in terms of the mass of alkali metal. An aqueous emulsion comprising a dispersant comprising polyvinyl alcohol and a dispersoid comprising a polymer comprising ethylenically unsaturated monomer units,
When the polyvinyl alcohol heated at 120 ° C. for 3 hours is measured by GPC, the peak top molecular weight (A) measured with a differential refractive index detector and the peak top measured with an absorptiometric detector (measurement wavelength 280 nm) The molecular weight (B) is the following formula (1)
(AB) / A <0.75 (1)
And an aqueous emulsion having an absorbance at a peak top molecular weight (B) of 0.25 × 10 ^{−3 to} 3.00 × 10 ⁻³ is also achieved.

However, in the GPC measurement,
Mobile phase: 20 mmol / l sodium trifluoroacetate-containing hexafluoroisopropanol (hereinafter, hexafluoroisopropanol may be abbreviated as HFIP.)
Sample injection volume: 1.00 mg / ml solution 100 μl
Column: “GPC HFIP-806M” manufactured by Showa Denko KK
Column temperature: 40 ° C
Flow rate: 1 ml / min Absorbance detector cell length: 10 mm
It is.

  In the GPC measurement, it is also preferable that the ratio Mw / Mn of the weight average molecular weight Mw to the number average molecular weight Mn of the PVA obtained by a differential refractive index detector is 2.2 to 6.0.

  An adhesive comprising the aqueous emulsion is also a preferred embodiment of the present invention.

  The dispersant for emulsion polymerization of the present invention is excellent in water dispersibility and polymerization stability of organic particles. The aqueous emulsion of the present invention is excellent in the water resistance of the film. Therefore, the aqueous emulsion is suitably used for various adhesives, binders, admixtures, paints and fiber processing agents.

In the PVA of Example 1, the relationship between the molecular weight and the value measured by the differential refractive index detector (RI), and the relationship between the molecular weight and the absorbance measured by the absorptiometric detector (UV) (measurement wavelength 280 nm). It is the graph which showed.

[Dispersant for emulsion polymerization]
The PVA contained in the dispersant for emulsion polymerization of the present invention has a saponification degree of 50 to 99.99 mol%, a viscosity average polymerization degree of 200 to 5000, and the content of alkali metal salt of carboxylic acid is converted to mass of alkali metal. The peak top molecular weight (A) measured with a differential refractive index detector when the PVA heated at 120 ° C. for 3 hours was measured by GPC, and the absorptiometry. The peak top molecular weight (B) measured by a detector (measurement wavelength: 280 nm) is expressed by the following formula (1)
(AB) / A <0.75 (1)
And the absorbance at the peak top molecular weight (B) is 0.25 × 10 ^{−3 to} 3.00 × 10 ⁻³ .

However, in the GPC measurement,
Mobile phase: HFIP containing 20 mmol / l sodium trifluoroacetate
Sample injection volume: 1.00 mg / ml solution 100 μl
Column: “GPC HFIP-806M” manufactured by Showa Denko KK
Column temperature: 40 ° C
Flow rate: 1 ml / min Absorbance detector cell length: 10 mm
It is.

  In the GPC measurement in the present invention, a GPC apparatus having a differential refractive index detector and an absorptiometric detector and capable of performing measurement by these detectors at the same time is used. The absorptiometric detector needs to be capable of measuring absorbance at a wavelength of 280 nm. A cell having a cell length (optical path length) of 10 mm is used as the cell of the detection unit of the absorptiometer. The absorptiometric detector may measure the absorption of ultraviolet light having a specific wavelength, or may measure the absorption of ultraviolet light having a specific range of wavelengths. The signal intensity by the differential refractive index detector is approximately proportional to the PVA concentration (mg / ml). On the other hand, PVA detected by the absorptiometric detector is only one having absorption at a predetermined wavelength. By the GPC measurement, the concentration and absorbance at a predetermined wavelength can be measured for each molecular weight component of PVA.

  HFIP containing 20 mmol / l sodium trifluoroacetate is used as a solvent and a mobile phase used for dissolving PVA measured in the GPC measurement. HFIP can dissolve PVA and polymethyl methacrylate (hereinafter abbreviated as PMMA). Further, by adding sodium trifluoroacetate, the adsorption of PVA to the column filler is prevented. The flow rate in the GPC measurement is 1 ml / min, and the column temperature is 40 ° C.

  In the GPC measurement, monodisperse PMMA is used as a standard. Several types of reference PMMA having different molecular weights are measured, and a calibration curve is created from the GPC elution capacity and the molecular weight of the reference PMMA. In the present invention, a calibration curve created using the detector is used for measurement by the differential refractive index detector, and a calibration curve created using the detector is used for measurement by the absorptiometric detector. Using these calibration curves, the GPC elution volume is converted into the molecular weight, and the peak top molecular weight (A) and the peak top molecular weight (B) are determined.

  Prior to the GPC measurement, the PVA is heated at 120 ° C. for 3 hours. In the present invention, PVA is heated by the following method. After casting an aqueous solution in which the PVA powder is dissolved, the PVA film is obtained by drying at 20 ° C. and 65% RH. The thickness of the PVA film is 30 to 75 μm, and preferably 40 to 60 μm. In order to clearly reflect the difference in hue of the sample after heat drying in the difference in ultraviolet absorption, the film is heated at 120 ° C. for 3 hours using a hot air dryer. From the viewpoint of suppressing heat treatment errors between samples, a gear oven is preferable as the hot air dryer.

  The heated PVA is dissolved in the solvent described above to obtain a measurement sample. The concentration of PVA in the measurement sample is 1.00 mg / ml, and the injection volume is 100 μl. However, when the degree of viscosity polymerization of PVA exceeds 2400, the excluded volume increases, and therefore, there are cases where the PVA concentration cannot be measured with good reproducibility at 1.00 mg / ml. In that case, an appropriately diluted sample (injection amount 100 μl) is used. Absorbance is proportional to the concentration of PVA. Therefore, the absorbance when the PVA concentration is 1.00 mg / ml is determined using the diluted sample concentration and the actually measured absorbance.

  FIG. 1 shows the relationship between the molecular weight obtained by GPC measurement of PVA and the value measured by the differential refractive index detector, and the molecular weight and the absorptiometric detector (measurement wavelength). It is the graph which showed the relationship with the light absorbency measured by 280 nm. The GPC measurement in the present invention will be further described with reference to FIG. In FIG. 1, RI is a chromatogram obtained by plotting the value measured by the differential refractive index detector against the molecular weight (horizontal axis) of PVA converted from the elution volume. In the present invention, the molecular weight at the peak position in the chromatogram is defined as peak top molecular weight (A). When there are a plurality of peaks in the chromatogram, the molecular weight at the peak position where the peak height is the highest is the peak top molecular weight (A).

  In FIG. 1, UV is a chromatogram obtained by plotting the absorbance measured by an absorptiometric detector (measurement wavelength: 280 nm) against the molecular weight (horizontal axis) of PVA converted from the elution volume. In the present invention, the molecular weight at the peak position in the chromatogram is defined as peak top molecular weight (B). When there are a plurality of peaks in the chromatogram, the molecular weight at the peak position where the peak height is the highest is the peak top molecular weight (B).

The PVA has a peak top molecular weight (A) measured with a differential refractive index detector and a peak top molecular weight (B) measured with an absorptiometric detector (measurement wavelength 280 nm) when GPC measurement is performed by the method described above. ) Satisfies the following formula (1).
(AB) / A <0.75 (1)

  The peak top molecular weight (A) is a value serving as an index of the molecular weight of PVA. On the other hand, the peak top molecular weight (B) is derived from a component present in PVA and having absorption at 280 nm. Usually, since the peak top molecular weight (A) is larger than the peak top molecular weight (B), (AB) / A becomes a positive value. If the peak top molecular weight (B) increases, (AB) / A decreases, and if the peak top molecular weight (B) decreases, (AB) / A increases. That is, when (A−B) / A is large, it means that there are many components that absorb ultraviolet rays having a wavelength of 280 nm among the low molecular weight components in PVA.

  When (A-B) / A is 0.75 or more, as described above, the component that absorbs ultraviolet light having a wavelength of 280 nm increases in the low molecular weight component. In this case, it is impossible to balance the polymerization stability and the effect of improving the water dispersibility of the organic particles. (AB) / A is preferably less than 0.70, more preferably less than 0.65.

The PVA needs to have an absorbance at a peak top molecular weight (B) of 0.25 × 10 ^{−3 to} 3.00 × 10 ⁻³ when GPC is measured by the method described above. When the absorbance is less than 0.25 × 10 ⁻³ , the effect of improving the water dispersibility of the organic particles is lowered. Moreover, the water resistance of the film obtained from the aqueous emulsion obtained using the PVA is lowered. On the other hand, when the absorbance exceeds 3.00 × 10 ⁻³ , the polymerization stability becomes insufficient. The absorbance is preferably 0.50 × 10 ^{−3 to} 2.80 × 10 ^{−3, and} more preferably 0.75 × 10 ^{−3 to} 2.50 × 10 ⁻³ .

  Further, in the PVA, the ratio Mw / Mn of the weight average molecular weight Mw to the number average molecular weight Mn of the polyvinyl alcohol obtained by a differential refractive index detector in the GPC measurement is 2.2 to 6.0. preferable. Mw and Mn are determined from the chromatogram obtained by plotting the values measured by the differential refractive index detector with respect to the molecular weight of PVA described above. Mw and Mn in the present invention are values in terms of PMMA.

  In general, Mn is an average molecular weight that is strongly influenced by a low molecular weight component, and Mw is an average molecular weight that is strongly influenced by a high molecular weight component. Mw / Mn is generally used as an index of molecular weight distribution of a polymer. When Mw / Mn is small, it indicates that the polymer has a small proportion of low molecular weight component, and when Mw / Mn is large, it indicates that the polymer has a large proportion of low molecular weight component.

  Therefore, in this invention, when Mw / Mn is less than 2.2, it shows that the ratio of a low molecular weight component is small in PVA. When Mw / Mn is less than 2.2, the effect of improving the water dispersibility of the organic particles may be reduced. It is more preferable that Mw / Mn is 2.3 or more. On the other hand, when Mw / Mn exceeds 6.0, it shows that the ratio of a low molecular weight component is large in PVA. When Mw / Mn exceeds 6.0, the polymerization stability may be insufficient. Mw / Mn is more preferably 3.5 or less, and further preferably 3.0 or less. From these things, it is thought that the low molecular-weight component in PVA has affected the effect which improves superposition | polymerization stability and the water dispersibility of an organic particle.

The viscosity average degree of polymerization of the PVA is measured according to JIS-K6726. That is, after re-saponifying and purifying PVA to a saponification degree of 99.5 mol% or more, it can be obtained from the intrinsic viscosity [η] (l / g) measured in water at 30 ° C. by the following equation.
P = ([η] × 10000 / 8.29) ^{(1 / 0.62)}

  The PVA has a viscosity average polymerization degree of 200 to 5,000. When the viscosity average polymerization degree is less than 200, practical strength cannot be obtained. Therefore, the strength of the film made of an aqueous emulsion obtained using the dispersant for emulsion polymerization of the present invention is insufficient. On the other hand, when the degree of viscosity polymerization exceeds 5000, the viscosity of the aqueous emulsion obtained using the dispersant for emulsion polymerization of the invention becomes too high, and handling becomes difficult. The viscosity average degree of polymerization is preferably 250 to 4500, more preferably 300 to 4000, and still more preferably 400 to 3500.

  The degree of saponification of the PVA is measured according to JIS-K6726. The saponification degree of the PVA is 50 to 99.99 mol%. When the degree of saponification is less than 50 mol%, the water solubility of PVA is significantly reduced. On the other hand, when the degree of saponification exceeds 99.99 mol%, PVA cannot be produced stably. The saponification degree of the PVA is preferably 60 to 99.8 mol%, more preferably 70 to 99.7 mol%, and still more preferably 80 to 99.6 mol%.

  The PVA contains an alkali metal salt of a carboxylic acid, and its content is 0.5% by mass or less, preferably 0.37% by mass or less, more preferably 0.28% by mass in terms of the mass of the alkali metal. Hereinafter, it is more preferably 0.23% by mass or less. When the content of the alkali metal salt of the carboxylic acid exceeds 0.5% by mass, the polymerization stability of the ethylenically unsaturated monomer becomes insufficient.

  In the present invention, the content of alkali metal salt of carboxylic acid (in terms of alkali metal mass) is determined by alkali metal ions obtained by ashing PVA with a platinum crucible and then measuring the resulting ash content by ICP emission analysis. It can be determined from the quantity.

  Examples of the alkali metal salt of carboxylic acid include those obtained by neutralizing an alkali catalyst used in a saponification step described later, for example, sodium hydroxide, potassium hydroxide, sodium methylate, etc. with carboxylic acid, and a polymerization step described later. As an inhibitor added to stop radical polymerization, the carboxylic acid added for the purpose of inhibiting the alcoholysis of the vinyl ester monomer such as vinyl acetate used in the saponification process is neutralized. When a carboxylic acid having a conjugated double bond is used, those obtained by neutralizing the carboxylic acid in the saponification step, or those intentionally added are included. Specific examples include sodium acetate, potassium acetate, sodium propionate, potassium propionate, sodium glycerate, potassium glycerate, sodium malate, potassium malate, sodium citrate, potassium citrate, sodium lactate, potassium lactate, tartaric acid Sodium, potassium tartrate, sodium salicylate, potassium salicylate, sodium malonate, potassium malonate, sodium succinate, potassium succinate, sodium maleate, potassium maleate, sodium phthalate, potassium phthalate, sodium oxalate, potassium oxalate , Sodium glutarate, potassium glutarate, sodium abietic acid, potassium abietic acid, sodium sorbate, potassium sorbate, 2,4,6-octatri Sodium -1-carboxylate, potassium 2,4,6-octatriene-1-carboxylate, sodium eleostearate, potassium eleostearate, sodium 2,4,6,8-decatetraene-1-carboxylate 2,4,6,8-decatetraene-1-carboxylate, sodium retinoate, potassium retinoate and the like, but are not limited thereto.

  Examples of the vinyl ester monomer used for the production of the PVA include vinyl formate, vinyl acetate, vinyl propionate, vinyl valelate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, and versa. Examples thereof include vinyl tick acid, and vinyl acetate is particularly preferable.

  The PVA is produced by polymerizing a vinyl ester monomer in the presence of a thiol compound such as 2-mercaptoethanol, n-dodecyl mercaptan, mercaptoacetic acid, 3-mercaptopropionic acid, and saponifying the resulting polyvinyl ester. You can also. By this method, PVA in which a functional group derived from a thiol compound is introduced at the terminal is obtained.

  Examples of the method for polymerizing the vinyl ester monomer include known methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. Among the methods, a bulk polymerization method performed without a solvent or a solution polymerization method performed using a solvent such as alcohol is usually employed. In terms of enhancing the effect of the present invention, a solution polymerization method in which polymerization is performed together with a lower alcohol is preferable. The lower alcohol is not particularly limited, but an alcohol having 3 or less carbon atoms such as methanol, ethanol, propanol and isopropanol is preferable, and methanol is usually used. When performing the polymerization reaction by the bulk polymerization method or the solution polymerization method, either a batch method or a continuous method can be used. Examples of the initiator used for the polymerization reaction include 2,2′-azobisisobutyronitrile, 2,2′-azobis (2,4-dimethyl-valeronitrile), 2,2′-azobis (4-methoxy). -2,4-dimethylvaleronitrile) and other azo initiators; organic peroxide initiators such as benzoyl peroxide and n-propyl peroxycarbonate, and the like, as long as they do not impair the effects of the present invention. Can be mentioned. Among these, organic peroxide initiators having a half-life at 60 ° C. of 10 to 110 minutes are preferable, and it is particularly preferable to use peroxydicarbonate. Although there is no restriction | limiting in particular about the polymerization temperature at the time of performing a polymerization reaction, The range of 5 to 200 degreeC is suitable.

  When the vinyl ester monomer is radically polymerized, a copolymerizable monomer can be copolymerized as necessary as long as the effects of the present invention are not impaired. Such monomers include α-olefins such as ethylene, propylene, 1-butene, isobutene, 1-hexene; carboxylic acids such as fumaric acid, maleic acid, itaconic acid, maleic anhydride, itaconic anhydride or the like Derivatives; acrylic acid or salts or esters thereof; methacrylic acid or salts or esters thereof; acrylamide derivatives such as acrylamide, N-methylacrylamide, N-ethylacrylamide; methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, etc. Methacrylamide derivatives; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether; ethylene glycol vinyl ether, 1,3-propa Hydroxy group-containing vinyl ethers such as diol vinyl ether and 1,4-butanediol vinyl ether; allyl ethers such as allyl acetate, propyl allyl ether, butyl allyl ether, and hexyl allyl ether; monomers having an oxyalkylene group; isopropenyl acetate, 3 -Buten-1-ol, 4-penten-1-ol, 5-hexen-1-ol, 7-octen-1-ol, 9-decene-1-ol, 3-methyl-3-buten-1-ol Hydroxy group-containing α-olefin such as ethylene sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid, monomers having a sulfonic acid group such as 2-acrylamido-2-methylpropane sulfonic acid; vinyloxyethyltrimethylammonium chloride, Vinyloxybutyl trimethyl Ammonium chloride, vinyloxyethyldimethylamine, vinyloxymethyldiethylamine, N-acrylamidomethyltrimethylammonium chloride, N-acrylamidoethyltrimethylammonium chloride, N-acrylamidodimethylamine, allyltrimethylammonium chloride, methallyltrimethylammonium chloride, dimethylallylamine, Monomers having a cationic group such as allylethylamine; vinyltrimethoxysilane, vinylmethyldimethoxysilane, vinyldimethylmethoxysilane, vinyltriethoxysilane, vinylmethyldiethoxysilane, vinyldimethylethoxysilane, 3- (meth) acrylamide- Propyltrimethoxysilane, 3- (meth) acrylamide-propyltriet Such monomers include having a silyl group such Shishiran. The amount of the monomer that can be copolymerized with these vinyl ester monomers varies depending on the purpose and use of the monomer, but is usually based on all monomers used for copolymerization. Is 20 mol% or less, preferably 10 mol% or less.

  PVA is obtained by saponifying the polyvinyl ester obtained by the above-mentioned method in an alcohol solvent.

  As the catalyst for the saponification reaction of the polyvinyl ester, an alkaline substance is usually used. Examples thereof include alkali metal hydroxides such as potassium hydroxide and sodium hydroxide, and alkali metal alkoxides such as sodium methoxide. The amount of the alkaline substance used is preferably within a range of 0.002 to 0.2 in a molar ratio based on the vinyl ester monomer unit of the polyvinyl ester, and within a range of 0.004 to 0.1. It is particularly preferred. The saponification catalyst may be added all at once in the early stage of the saponification reaction, or a part thereof may be added in the early stage of the saponification reaction, and the rest may be added and added during the saponification reaction.

  Examples of the solvent that can be used for the saponification reaction include methanol, methyl acetate, dimethyl sulfoxide, diethyl sulfoxide, dimethylformamide, and the like. Of these solvents, methanol is preferably used. At this time, the moisture content of methanol is preferably adjusted to 0.001 to 1% by mass, more preferably 0.003 to 0.9% by mass, and particularly preferably 0.005 to 0.8% by mass.

  The saponification reaction is preferably performed at a temperature of 5 to 80 ° C, more preferably 20 to 70 ° C. The saponification reaction is preferably performed for 5 minutes to 10 hours, more preferably for 10 minutes to 5 hours. The saponification reaction can be performed by either a batch method or a continuous method. After completion of the saponification reaction, the remaining catalyst may be neutralized as necessary. Usable neutralizing agents include organic acids such as acetic acid and lactic acid, and ester compounds such as methyl acetate.

  The alkaline substance containing an alkali metal added during the saponification reaction is usually neutralized by an ester such as methyl acetate generated by the progress of the saponification reaction, or neutralized by a carboxylic acid such as acetic acid added after the reaction. At this time, an alkali metal salt of a carboxylic acid such as sodium acetate is formed. As described above, the content of the alkali metal salt of the carboxylic acid in the PVA needs to be 0.5% by mass or less. In order to obtain such PVA, the PVA may be washed after saponification.

  Examples of the cleaning liquid used in this case include a lower alcohol such as methanol, a solution composed of 100 parts by weight of the lower alcohol and 20 parts by weight or less of water, and a solution composed of the lower alcohol and an ester such as methyl acetate produced in the saponification step. It is done. The content of the ester in the solution composed of the lower alcohol and the ester is not particularly limited, but is preferably 1000 parts by mass or less with respect to 100 parts by mass of the lower alcohol. The addition amount of the cleaning liquid is preferably 100 parts by mass to 10000 parts by mass, more preferably 150 parts by mass to 5000 parts by mass, and more preferably 200 parts by mass with respect to 100 parts by mass of the gel obtained by saponification and PVA swollen with alcohol. -1000 mass parts is still more preferable. When the addition amount of the cleaning liquid is less than 100 parts by mass, the alkali metal salt amount of the carboxylic acid may exceed the above range. On the other hand, when the addition amount of the cleaning liquid exceeds 10,000 parts by mass, the improvement of the cleaning effect by increasing the addition amount cannot be expected. The washing method is not particularly limited. For example, a step of adding a gel (PVA) and a washing solution into a tank, stirring or standing at 5 to 100 ° C. for about 5 to 180 minutes, and then removing the solution. Is a batch system in which the content of the alkali metal salt of the carboxylic acid is repeated within a predetermined range. Further, there is a continuous method in which PVA is continuously added from the top of the column at the same temperature and for the same time as the batch method, and a lower alcohol is continuously added from the bottom of the column, and the two are brought into contact with each other.

  In preparing the PVA, examples of the method for adjusting the absorbance at the peak top molecular weight (A), the peak top molecular weight (B), and the peak top molecular weight (B) so as to satisfy the above-described conditions include the following methods. It is done.

  A) A vinyl ester monomer from which a radical polymerization inhibitor contained in the raw vinyl ester monomer has been removed in advance is used for the polymerization.

  B) A vinyl ester monomer having a total content of impurities contained in the raw material vinyl ester monomer of preferably 1 to 1200 ppm, more preferably 3 to 1100 ppm, and still more preferably 5 to 1000 ppm is used for radical polymerization. Impurities include aldehydes such as acetaldehyde, crotonaldehyde, and acrolein; acetaldehyde such as acetaldehyde dimethyl acetal, crotonaldehyde dimethyl acetal, and acrolein dimethyl acetal obtained by acetalizing the aldehyde with a solvent alcohol; ketones such as acetone; methyl acetate and ethyl acetate And esters.

  C) In order to suppress the alcoholysis and hydrolysis of the monomer by alcohol and a small amount of water in a series of steps of radical polymerization of the raw material vinyl ester monomer in an alcohol solvent and collecting and reusing unreacted monomer, Organic acids, specifically hydroxycarboxylic acids such as glycolic acid, glyceric acid, malic acid, citric acid, lactic acid, tartaric acid, salicylic acid; malonic acid, succinic acid, maleic acid, phthalic acid, oxalic acid, glutaric acid, etc. A carboxylic acid or the like is added to suppress the generation of aldehydes such as acetaldehyde generated by decomposition as much as possible. The addition amount of the organic acid is preferably 1 to 500 ppm, more preferably 3 to 300 ppm, and still more preferably 5 to 100 ppm with respect to the raw material vinyl ester monomer.

  D) As a solvent used for polymerization, a solvent having a total content of impurities of preferably 1 to 1200 ppm, more preferably 3 to 1100 ppm, and still more preferably 5 to 1000 ppm. Examples of the impurities contained in the solvent include those described above as the impurities contained in the raw material vinyl ester monomer.

  E) When the vinyl ester monomer is radically polymerized, the ratio of the solvent to the vinyl ester monomer is increased.

  F) An organic peroxide is used as a radical polymerization initiator used for radical polymerization of a vinyl ester monomer. Organic peroxides include acetyl peroxide, isobutyl peroxide, diisopropyl peroxycarbonate, diallyl peroxydicarbonate, di-n-propyl peroxydicarbonate, dimyristyl peroxydicarbonate, and di (2-ethoxyethyl) peroxide. Examples include oxydicarbonate, di (2-ethylhexyl) peroxydicarbonate, di (methoxyisopropyl) peroxydicarbonate, and di (4-tert-butylcyclohexyl) peroxydicarbonate. It is preferable to use peroxydicarbonate with a period of 10 to 110 minutes.

  G) When an inhibitor is added after radical polymerization of the vinyl ester monomer to suppress polymerization, an inhibitor of 5 molar equivalents or less is added to the remaining undecomposed radical polymerization initiator. Examples of the inhibitor include a compound having a conjugated double bond having a molecular weight of 1000 or less and a compound that stabilizes a radical and inhibits a polymerization reaction. Specifically, isoprene, 2,3-dimethyl-1,3-butadiene, 2,3-diethyl-1,3-butadiene, 2-t-butyl-1,3-butadiene, 1,3-pentadiene, 2 , 3-dimethyl-1,3-pentadiene, 2,4-dimethyl-1,3-pentadiene, 3,4-dimethyl-1,3-pentadiene, 3-ethyl-1,3-pentadiene, 2-methyl-1 , 3-pentadiene, 3-methyl-1,3-pentadiene, 4-methyl-1,3-pentadiene, 1,3-hexadiene, 2,4-hexadiene, 2,5-dimethyl-2,4-hexadiene, , 3-octadiene, 1,3-cyclopentadiene, 1,3-cyclohexadiene, 1-methoxy-1,3-butadiene, 2-methoxy-1,3-butadiene, 1-ethoxy-1,3- Tadiene, 2-ethoxy-1,3-butadiene, 2-nitro-1,3-butadiene, chloroprene, 1-chloro-1,3-butadiene, 1-bromo-1,3-butadiene, 2-bromo-1, Conjugated dienes composed of a conjugated structure of two carbon-carbon double bonds such as 3-butadiene, fulvene, tropone, osymene, ferrandrene, myrcene, farnesene, semblene, sorbic acid, sorbic acid ester, sorbic acid salt, and abietic acid; 1,3,5-hexatriene, 2,4,6-octatriene-1-carboxylic acid, eleostearic acid, tung oil, conjugated triene having a conjugated structure of three carbon-carbon double bonds such as cholecalciferol Carbons such as cyclooctatetraene, 2,4,6,8-decatetraene-1-carboxylic acid, retinol, retinoic acid, etc. Polyenes such as conjugated polyene consisting Motoni double bond of four or more conjugated structure. Any one having a plurality of stereoisomers such as 1,3-pentadiene, myrcene, and farnesene may be used. Furthermore, p-benzoquinone, hydroquinone, hydroquinone monomethyl ether, 2-phenyl-1-propene, 2-phenyl-1-butene, 2,4-diphenyl-4-methyl-1-pentene, 3,5-diphenyl-5 Methyl-2-heptene, 2,4,6-triphenyl-4,6-dimethyl-1-heptene, 3,5,7-triphenyl-5-ethyl-7-methyl-2-nonene, 1,3- Diphenyl-1-butene, 2,4-diphenyl-4-methyl-2-pentene, 3,5-diphenyl-5-methyl-3-heptene, 1,3,5-triphenyl-1-hexene, 2,4 , 6-triphenyl-4,6-dimethyl-2-heptene, 3,5,7-triphenyl-5-ethyl-7-methyl-3-nonene, 1-phenyl-1,3-butadiene, 1,4 - Aromatic compounds such as Eniru 1,3-butadiene.

  H) An alcohol solution of polyvinyl ester from which the remaining vinyl ester monomer is removed as much as possible is used for the saponification reaction. Preferably, the residual monomer removal rate is 99% or more, more preferably 99.5% or more, still more preferably 99.8% or more.

  A desired PVA can be obtained by appropriately combining A) to H). The PVA thus obtained is less colored by heating and is excellent in the effect of improving the water dispersibility of organic particles and inorganic particles.

  The dispersant for emulsion polymerization of the present invention is an ethylenically unsaturated monomer, among which an olefin monomer, a vinyl ester monomer, a (meth) acrylic acid ester monomer, an acrylamide monomer, It can be used as a dispersant for emulsion polymerization of at least one monomer selected from a styrene monomer, a diene monomer, and a halogen vinyl monomer. The dispersant for emulsion polymerization of the present invention can also be used as a dispersant for aqueous emulsions.

[Aqueous emulsion]
The aqueous emulsion of the present invention is an aqueous emulsion containing a dispersant containing the PVA and a dispersoid composed of a polymer containing an ethylenically unsaturated monomer unit. Here, the polymer of the ethylenically unsaturated monomer may be a copolymer composed of two or more monomers.

  Examples of a method for obtaining the aqueous emulsion of the present invention include a method (1) a method in which an ethylenically unsaturated monomer is emulsion-polymerized in the presence of a dispersant containing the PVA. The aqueous emulsion thus obtained is excellent in water resistance of the film.

As the ethylenically unsaturated monomer,
Olefins such as ethylene, propylene and isobutylene;
Halogenated olefins such as vinyl chloride, vinyl fluoride, vinylidene chloride, vinylidene fluoride;
Vinyl esters such as vinyl formate, vinyl acetate, vinyl propionate, vinyl versatate;
Acrylic acid ester such as acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, 2-hydroxyethyl acrylate, methyl methacrylate, ethyl methacrylate, methacrylic acid Methacrylic acid esters such as butyl, 2-ethylhexyl methacrylate, dodecyl methacrylate, 2-hydroxyethyl methacrylate;
Acrylamide such as dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate and quaternized compounds thereof, acrylamide, methacrylamide, N-methylolacrylamide, N, N-dimethylacrylamide, acrylamide-2-methylpropanesulfonic acid and its sodium salt System monomers;
Styrene monomers such as styrene, α-methylstyrene, p-styrenesulfonic acid and sodium salts and potassium salts thereof;
Diene monomers such as butadiene, isoprene and chloroprene;
In addition, N-vinylpyrrolidone etc. are mentioned, These are used for superposition | polymerization individually or in mixture of 2 or more types. Among the ethylenically unsaturated monomers, vinyl esters, (meth) acrylic acid esters, styrene and diene monomers are preferable. In emulsion polymerization, it is preferable to use the above vinyl ester alone, to use ethylene and vinyl ester in combination, and to use vinyl ester and (meth) acrylic acid ester in combination. When using together vinyl ester and another monomer, it is preferable that vinyl ester is 51 mass% or more.

  In the method (1), when the emulsion polymerization dispersant is charged into the polymerization system, there is no particular limitation on the charging method and addition method. Examples thereof include a method of initially adding an emulsion polymerization dispersant into the polymerization system and a method of adding it continuously during the polymerization. Among these, from the viewpoint of increasing the graft ratio of PVA to the emulsion dispersoid, a method of initially adding a dispersant for emulsion polymerization into the polymerization system in an initial batch is preferable.

  The amount of the dispersant for emulsion polymerization used in the emulsion polymerization is preferably 0.2 to 40 parts by mass, more preferably 0.3 to 20 parts by mass with respect to 100 parts by mass of the ethylenically unsaturated monomer. More preferably, it is 0.5 to 15 parts by mass. When the amount of the dispersant for emulsion polymerization of the present invention is less than 0.2 parts by mass, the dispersoid particles of the aqueous emulsion may be aggregated or the polymerization stability may be lowered. In addition, when the amount of the dispersant for emulsion polymerization of the present invention exceeds 40 parts by mass, the viscosity of the polymerization system may become too high, and the polymerization cannot proceed uniformly, or the polymerization heat In some cases, the heat removal is insufficient.

In the emulsion polymerization using the above-mentioned dispersant for emulsion polymerization, a water-soluble single initiator or a water-soluble redox initiator usually used for emulsion polymerization is applied as the polymerization initiator. For example, hydrogen peroxide, persulfate (potassium, sodium or ammonium salt) etc. are mentioned as a single initiator. Examples of the redox initiator include a combination of a peroxide and a metal ion, and a combination of a peroxide, a metal ion, and a reducing substance. Examples of the peroxide include hydrogen peroxide, cumene hydroxy peroxide, hydroxy peroxide such as t-butyl hydroxy peroxide, persulfate (potassium, sodium or ammonium salt), t-butyl peracetate, peracid ester ( T-butyl perbenzoate). Examples of the metal ions include metal ions that can undergo one-electron transfer such as Fe ²⁺ , Cr ²⁺ , V ²⁺ , Co ²⁺ , Ti ³⁺ , and Cu ⁺ . Examples of the reducing substance include Rongalite and 1-ethyl-ascorbic acid.

  The dispersion medium in the emulsion polymerization is preferably an aqueous medium containing water as a main component. The aqueous medium containing water as a main component may contain water and a water-soluble organic solvent (alcohols, ketones, etc.) soluble in an arbitrary ratio. Here, “an aqueous medium mainly composed of water” is a dispersion medium containing 50% by mass or more of water. From the viewpoint of cost and environmental load, the dispersion medium is preferably an aqueous medium containing 90% by mass or more of water, and more preferably water.

  In the emulsion polymerization, other protective colloids such as polyacrylic acid or polymethacrylic acid and salts thereof; polyvinyl alkyl ethers; vinyl acetate and acrylic acid, methacrylic acid or maleic anhydride are used as long as the effects of the present invention are not impaired. Polymers and saponified products thereof; lower alkyl vinyl ether-maleic anhydride copolymer; cellulose derivatives such as alkyl cellulose, hydroxyalkyl cellulose, alkylhydroxyalkyl cellulose, and carboxymethyl cellulose; starch derivatives such as alkyl starch, carboxymethyl starch, and oxidized starch It is also effective to add desired characteristics to the emulsion by adding gum arabic, tragacanth gum, polyalkylene glycol or the like during or after polymerization. In addition, it is possible to use a liquid regulator, monovalent or polyhydric alcohol, plasticizer, antifoaming agent and the like conventionally used in emulsion polymerization in combination with or after polymerization. There is no problem as long as it does not impair the effect.

  In emulsion polymerization, it can be used in combination with a surfactant as long as the effects of the present invention are not impaired. Examples of the surfactant include conventionally known anionic surfactants, cationic surfactants, nonionic surfactants, amphoteric surfactants, polymer surfactants, and the like. Two or more kinds may be used in combination. The addition amount in the case of using a surfactant in combination is not particularly limited as long as it does not impair the effects of the present invention, but is preferably 10000 parts by mass or less with respect to 100 parts by mass of the emulsion polymerization dispersant of the present invention. Is 2000 parts by mass or less, more preferably 100 parts by mass or less. If it exceeds 10,000 parts by mass, the characteristics (moderate radical reactivity) of the present invention may be inhibited.

  As the method for obtaining the aqueous emulsion of the present invention, the method (2) is a method in which an ethylenically unsaturated monomer is emulsion-polymerized to obtain an aqueous emulsion, and then the dispersant containing the PVA is added to the aqueous emulsion. It can also be mentioned. Thus, the aqueous emulsion of this invention obtained by adding the dispersing agent containing the said PVA to an aqueous emulsion is excellent in the water resistance of a film | membrane. Moreover, the stability and thickening of an aqueous emulsion can be improved more by adding the dispersing agent containing the said PVA to an aqueous emulsion.

  Examples of the method for adding the dispersant containing PVA to the aqueous emulsion include a method of adding an aqueous solution obtained by dissolving the dispersant in a solvent such as water to the aqueous emulsion. At this time, the aqueous solution is added while stirring the aqueous emulsion at room temperature. Moreover, the method of adding the dispersing agent containing the said PVA as it is can also be mentioned. When the dispersant containing PVA is a powder, the powder is added while stirring the aqueous emulsion, and the mixture is heated to 50 to 85 ° C. The amount of the dispersant added is usually 1 to 40% by mass, preferably 2 to 30% by mass, based on the solid content of the aqueous emulsion obtained by emulsion polymerization of an ethylenically unsaturated monomer.

  In the emulsion polymerization in the above method (2), the ethylenically unsaturated monomer described above can be used. As the dispersion medium used when the ethylenically unsaturated monomer is emulsion-polymerized, those described above can be used. In the emulsion polymerization of the ethylenically unsaturated monomer, the above-mentioned dispersant for emulsion polymerization containing PVA may be used, or a conventionally known dispersant for emulsion polymerization containing PVA may be used.

  The solid content of the aqueous emulsion of the present invention obtained by the above methods (1) and (2) is not particularly limited, and is usually 30 to 60% by mass.

  The dispersant for emulsion polymerization of the present invention is excellent in water dispersibility and polymerization stability of organic particles. Therefore, the aqueous emulsion obtained by emulsion polymerization using the dispersant for emulsion polymerization is grafted onto the emulsion dispersoid of PVA in comparison with the aqueous emulsion obtained by emulsion polymerization using conventionally known PVA as a dispersant. Since the rate is high, the water resistance of the film obtained from the aqueous emulsion is excellent.

  Even if an ethylenically unsaturated monomer is emulsion-polymerized to obtain an aqueous emulsion, and the PVA is added to the aqueous emulsion, an aqueous emulsion having excellent water resistance of the film can be obtained.

  The aqueous emulsion of the present invention makes use of this feature for various uses, for example, flash panels, laminated timber, wood board, plywood processing, plywood secondary processing (kneading), general woodwork, paper tube, bag making, etc. It can be suitably used for binders for impregnated paper products; admixtures such as mortar; paints;

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. In the following examples and comparative examples, “parts” and “%” are based on mass unless otherwise specified. “Polymerization degree” means “viscosity average polymerization degree”.

[Polymerization degree and saponification degree of PVA]
The degree of polymerization and saponification of PVA were determined by the method described in JIS-K6726.

[Measurement of sodium acetate content]
The sodium acetate content (in terms of sodium) of PVA is determined by measuring the amount of sodium in the obtained ash using Jarrel Ash ICP emission analyzer “IRIS AP” after ashing PVA. It was.

[GPC measurement of PVA]
(Sample preparation)
After heating at 95 ° C. for 1 hour to dissolve PVA in water, it was cooled to room temperature to obtain a 2% aqueous solution of PVA. The obtained aqueous solution was cast on a polyethylene terephthalate film (20 cm × 20 cm) and dried for 1 week under the conditions of 20 ° C. and 65% RH to obtain a PVA film having a thickness of 50 μm. The obtained film was fixed with a clip to a stainless steel metal frame (20 cm × 20 cm, 1 cm wide metal frame) and heat-treated in a gear oven at 120 ° C. for 3 hours.

(measuring device)
GPC measurement was performed using “GPCmax” manufactured by VISCOTECH. As a differential refractive index detector, “TDA305” manufactured by VISCOTECH was used. “UV Detector 2600” manufactured by VISCOTECH was used as an ultraviolet-visible absorption detector. The optical path length of the detection cell of the absorptiometric detector is 10 mm. “GPC HFIP-806M” manufactured by Showa Denko KK was used for the GPC column. Moreover, OmniSEC (Version 4.7.0.406) attached to the apparatus was used as analysis software.

(Measurement condition)
A sample was collected from the vicinity of the center of the PVA film after heat treatment obtained by the above method. The sample was dissolved in HFIP containing 20 mmol / liter of sodium trifluoroacetate to prepare a 1.00 mg / ml solution of PVA. The solution was filtered through a 0.45 μm polytetrafluoroethylene filter and used for measurement.

  As the mobile phase, HFIP containing 20 mmol / l sodium trifluoroacetate was used. The mobile phase flow rate was 1.0 ml / min. The sample injection amount was 100 μl, and measurement was performed at a GPC column temperature of 40 ° C.

In addition, the sample in which the viscosity average polymerization degree of PVA exceeded 2400 performed GPC measurement using the sample (100 microliters) diluted suitably. The absorbance at a sample concentration of 1.00 mg / ml was calculated from the measured value according to the following formula. α (mg / ml) is the concentration of the diluted sample.

Absorbance at a sample concentration of 1.00 mg / ml = (1.00 / α) × measured value of absorbance

(Create a calibration curve)
As a standard, PMMA (peak top molecular weight: 1944000, 790000, 467400, 271400, 144000, 79250, 35300, 13300, 7100, 1960, 1020, 690) manufactured by Agilent Technologies was measured, and a differential refractive index detector and absorbance were measured. A calibration curve for converting the elution volume into the PMMA molecular weight was prepared for each detector. The analytical software was used to create each calibration curve.
In this measurement, a column in a state where the peaks of standard samples having both molecular weights of 1944000 and 271400 can be separated in the PMMA measurement is used.

[Synthesis of polyvinyl acetate]
PVAc-1
A 6 L separable flask equipped with a stirrer, thermometer, nitrogen introduction tube, and reflux tube was deoxygenated in advance, and vinyl acetate monomer (VAM) 2555 g containing 500 ppm acetaldehyde (AA) and 50 ppm acetaldehyde dimethyl acetal (DMA). 945 g of methanol (MeOH) containing 50 ppm of acetaldehyde dimethyl acetal and an acetaldehyde content of less than 1 ppm; 1% methanol solution of tartaric acid in an amount of 20 ppm of tartaric acid in the vinyl acetate monomer was charged. While blowing nitrogen into the flask, the temperature inside the flask was adjusted to 60 ° C. In addition, -10 degreeC ethylene glycol / water solution was circulated through the reflux pipe. A 0.55% by mass methanol solution of di-n-propyl peroxydicarbonate was prepared, and 18.6 mL was added to the flask to initiate polymerization. The amount of di-n-propyl peroxydicarbonate added at this time was 0.081 g. A methanol solution of di-n-propyl peroxydicarbonate was sequentially added at a rate of 20.9 mL / hour until the completion of polymerization. During the polymerization, the temperature in the flask was kept at 60 ° C. Four hours after the start of polymerization, when the solid content concentration of the polymerization solution reached 25.1%, 0.0141 g of sorbic acid (3% of di-n-propyl peroxydicarbonate remaining undecomposed in the polymerization solution) was obtained. After adding 1200 g of contained methanol (corresponding to a molar equivalent), the polymerization solution was cooled to stop the polymerization. When the polymerization was stopped, the polymerization rate of the vinyl acetate monomer was 35.0%. After the polymerization solution was cooled to room temperature, the inside of the flask was depressurized using a water aspirator to distill off the vinyl acetate monomer and methanol, thereby precipitating polyvinyl acetate. 3000 g of methanol was added to the precipitated polyvinyl acetate, and the polyvinyl acetate was dissolved while heating at 30 ° C., and then the inside of the flask was decompressed again using a water aspirator to distill off the vinyl acetate monomer and methanol. Thus, polyvinyl acetate was precipitated. The operation of dissolving polyvinyl acetate in methanol and then precipitating it was further repeated twice. Methanol was added to the precipitated polyvinyl acetate to obtain a 40% by mass methanol solution of polyvinyl acetate (PVAc-1) with a vinyl acetate monomer removal rate of 99.8%.

  The polymerization degree was measured using a part of the methanol solution of PVAc-1 obtained. To a methanol solution of PVAc-1, a 10% methanol solution of sodium hydroxide was added so that the molar ratio of sodium hydroxide to vinyl acetate units in polyvinyl acetate was 0.1. When the gelled product was formed, the gel was pulverized and subjected to Soxhlet extraction with methanol for 3 days. The obtained polyvinyl alcohol was dried and subjected to viscosity average polymerization degree measurement. The degree of polymerization of PVAc-1 was 1700.

PVAc-2 to PVAc-20
Polyvinyl acetate (PVAc-2 to PVAc-20) was obtained by the same method as PVAc-1, except that the conditions described in Table 1 were changed. In Table 1, “ND” means less than 1 ppm. The polymerization degree of each obtained polyvinyl acetate was calculated | required similarly to PVAc-1. The results are shown in Table 1.

Example 1
(Synthesis of PAV)
PVA-1
Mole of sodium hydroxide relative to vinyl acetate monomer units in methanol and polyvinyl acetate so that the total solid concentration (saponification concentration) is 30% by mass with respect to a 40% by mass methanol solution of PVAc-1. An 8% methanol solution of sodium hydroxide was added with stirring so that the ratio was 0.020, and the saponification reaction was started at 40 ° C. The gel is pulverized when the gelated product is generated as the saponification reaction proceeds, and the crushed gel is transferred to a container at 40 ° C. When 60 minutes have elapsed from the start of the saponification reaction, methanol / methyl acetate / water ( 25/70/5 mass ratio) solution and neutralized. The obtained swollen gel was centrifuged, and methanol twice as much as the swollen gel was added, immersed, left for 30 minutes, and then centrifuged four times, 60 ° C. for 1 hour, 100 It dried at 2 degreeC for 2 hours, and PVA-1 was obtained.

  The degree of polymerization of the obtained PVA-1 was 1700, the degree of saponification was 99.1 mol%, and the sodium acetate content was 0.7% (0.20% by mass in terms of sodium). These physical property data are also shown in Table 2.

Gel permeation measurement of the obtained PVA-1 was performed. FIG. 1 is a graph showing the relationship between the molecular weight and the value measured by the differential refractive index detector, and the relationship between the molecular weight and the absorbance measured by the absorptiometric detector (measurement wavelength 280 nm). The molecular weight at this time is one converted from the elution volume using a calibration curve (PMMA equivalent molecular weight). The peak top molecular weight (A) measured with the differential refractive index detector obtained from FIG. 1 was 100,000, and the peak top molecular weight (B) measured with the absorptiometric detector (280 nm) was 53,000. It was. The obtained value is expressed by the following formula (AB) / A
The value obtained by substituting for was 0.47. The absorbance at the peak top molecular weight (B) was 1.30 × 10 ⁻³ . These results are also shown in Table 2.

  A 3 L separable flask equipped with a stirrer, reflux tube, dropping funnel, thermometer and nitrogen introduction tube was charged with 900 parts by mass of ion-exchanged water and 78 parts by mass of PVA-1, heated to 95 ° C. and dissolved for 1 hour. And cooled. The obtained PVA aqueous solution was heated to 60 ° C. with stirring while purging with nitrogen, and 13.2 parts by mass of a 10% by mass aqueous solution of tartaric acid and 9 parts by mass of 5% by mass hydrogen peroxide (based on vinyl acetate monomer) (0.015 times as a ratio) was added all at once, 78 parts by mass of vinyl acetate monomer was added, initial emulsion polymerization was started, and after 30 minutes, the completion of initial emulsion polymerization was confirmed.

  A part of the sample was collected at the end of the initial emulsion polymerization, diluted with water about 100 times, and then the initial emulsion particle size was determined using an electrophoretic light scattering photometer (ELS-800, manufactured by Otsuka Electronics Co., Ltd.). It was measured. This was used as an index of water dispersibility of the monomer (organic particles).

  After the initial emulsion polymerization, 2.7 parts by weight of a 10% by weight aqueous solution of tartaric acid and 9 parts by weight of 5% by weight hydrogen peroxide were added all at once, and 702 parts by weight of vinyl acetate monomer was continuously added from the dropping funnel over 2 hours. The emulsion polymerization was carried out.

  After completion of the addition, the obtained emulsion was cooled to room temperature and filtered using a 60 mesh stainless steel wire mesh to obtain an emulsion having a solid content concentration of 48.2% by mass. Here, the amount of filtration residue of 60 mesh was used as an index of polymerization stability.

The obtained emulsion was cast on a polyethylene terephthalate film at 20 ° C. and 65% RH, and dried for one week to obtain a film having a thickness of 450 μm. A part of the film was collected and dried at 105 ° C. for 2 hours, and the solid content mass% (i) of the film was measured from the mass change before and after drying. Separately from this, it cut out from the said 450 micrometer film to the magnitude | size of 10 cm x 10 cm, and measured mass (ii). And mass (ii ') in the cut-out film was calculated | required by multiplying mass (ii) by solid content mass% (i) as shown in following formula (3). The cut-out film was immersed in warm water at 90 ° C. for 30 minutes, cooled to room temperature, and centrifuged at 20000 rotation for 30 minutes with a centrifuge (manufactured by Hitachi Koki Co., Ltd .; SCR-20B). The obtained solid was collected and dried at 105 ° C. for 2 hours, and the mass (iii) of the solid was measured. And the elution rate (%) was computed by following formula (4), and it was set as the water resistance parameter | index of the membrane | film | coat.
Film mass correction before immersion: (ii ′) = (ii) × (i) / 100 (3)
Elution rate (%) = {[(ii ′) − (iii)] / (ii ′)} × 100 (4)

[Emulsion evaluation]
The obtained emulsion was evaluated for water dispersibility of organic particles, polymerization stability and water resistance of the film according to the following indicators. The results are shown in Table 2.

(Water dispersibility of organic particles)
A: Less than 300 nm B: 300 nm or more and less than 350 nm C: 350 nm or more and less than 400 nm D: 400 nm or more and less than 450 nm E: 450 nm or more The smaller the particle size, the better the water dispersibility. When the water dispersibility of the organic particles was evaluated according to the above criteria, the evaluation was “A”.

(Polymerization stability)
A: 60 mesh filtration residue was not seen.
B: A 60-mesh filtration residue was slightly observed.
C: Coarse particles were observed, and there were many 60 mesh filtration residues.
D: There were many coarse grains and the polymerization did not proceed sufficiently.
The smaller the 60 mesh filtration residue, the better the polymerization stability. When the polymerization stability was evaluated based on the above criteria, the evaluation was “A”.

(Water resistance of the film)
A: Less than 55% B: 55% or more and less than 60% C: 60% or more and less than 65% D: 65% or more and less than 70% E: 70% or more The smaller the elution rate (%), the better the water resistance of the film. Indicates that When the durability of the film was evaluated based on the above criteria, the evaluation was “A”.

Examples 2-8, Comparative Examples 1-5
Except for changing to the conditions shown in Table 2, each PVA was synthesized in the same manner as in Example 1, and an emulsion was prepared using the PVA as a dispersant for emulsion polymerization. Table 2 shows the physical property data of the obtained PVA. Gel permeation measurement was carried out in the same manner as in Example 1. The results are shown in Table 2. The obtained emulsion was evaluated in the same manner as in Example 1 for water dispersibility of organic particles, polymerization stability, and water resistance of the film. The results are shown in Table 2.

Table 2 shows the evaluation of fully saponified PVA having a degree of polymerization of 1700 and emulsions obtained using the PVA as a dispersant for emulsion polymerization. When the values obtained by gel permeation chromatography satisfy the conditions defined in the present invention (Examples 1 to 8), the water dispersibility of the organic particles, the polymerization stability, and the water resistance of the film were all excellent. On the other hand, when the absorbance at the peak top molecular weight (B) measured with an absorptiometric detector (measurement wavelength: 280 nm) is less than 0.25 × 10 ⁻³ (Comparative Examples 1 and 3), and further the peak top molecular weight (A ) And peak top molecular weight (B) also did not satisfy the above formula (1) (Comparative Example 3), the water dispersibility of the organic particles and the water resistance of the film were inferior. When the absorbance at the peak top molecular weight (B) exceeded 3.00 × 10 ⁻³ (Comparative Examples 2 and 4), the polymerization stability was particularly poor. When the content of sodium acetate (in terms of sodium) exceeds 0.5% by mass (Comparative Example 5), the polymerization of the vinyl acetate monomer does not proceed sufficiently, and a film can be produced using the obtained emulsion. could not.

Example 9, Comparative Examples 6-8
Except having changed into the conditions shown in Table 3, each PVA was synthesize | combined similarly to Example 1, and emulsion was produced using each PVA. Table 3 shows the physical property data of the obtained PVA. Gel permeation measurement was carried out in the same manner as in Example 1. The results are shown in Table 3. The obtained emulsion was evaluated in the same manner as in Example 1 for water dispersibility of organic particles, polymerization stability, and water resistance of the film. The results are shown in Table 3.

Table 3 shows evaluation of fully saponified PVA having a polymerization degree of 300 and a polymerization degree of 150, and emulsions obtained using the PVA as a dispersant for emulsion polymerization. When the value obtained by the gel permeation chromatography satisfies the conditions specified in the present invention (Example 9), the water dispersibility of the organic particles, the polymerization stability, and the water resistance of the film were all excellent. On the other hand, when the absorbance at the peak top molecular weight (B) measured with an absorptiometric detector (measurement wavelength: 280 nm) is less than 0.25 × 10 ⁻³ (Comparative Example 6), the water dispersibility of organic particles and The water resistance of the film was poor. When the absorbance at the peak top molecular weight (B) exceeded 3.00 × 10 ⁻³ (Comparative Example 7), the polymerization stability and the water resistance of the film were inferior. When the degree of polymerization was less than 200 (Comparative Example 8), the polymerization stability and the water resistance of the film were inferior.

Example 10, Comparative Example 9 and Comparative Example 10
Except having changed into the conditions shown in Table 4, each PVA was synthesize | combined like Example 1, and emulsion was produced using each said PVA. Table 4 shows the physical property data of the obtained PVA. Gel permeation measurement was carried out in the same manner as in Example 1. The results are shown in Table 4. The obtained emulsion was evaluated in the same manner as in Example 1 for water dispersibility of organic particles, polymerization stability, and water resistance of the film. The results are shown in Table 4.

Table 4 shows the evaluation of fully saponified PVA having a polymerization degree of 500 and emulsions obtained using the PVA as a dispersant for emulsion polymerization. When the value obtained by the gel permeation chromatography satisfies the conditions specified in the present invention (Example 10), the water dispersibility of the organic particles, the polymerization stability, and the water resistance of the film were all excellent. On the other hand, when the absorbance at the peak top molecular weight (B) measured with an absorptiometric detector (measurement wavelength: 280 nm) is less than 0.25 × 10 ⁻³ (Comparative Example 9), the water dispersibility of organic particles and The water resistance of the film was poor. When the absorbance at the peak top molecular weight (B) exceeded 3.00 × 10 ⁻³ (Comparative Example 10), the polymerization stability and the water resistance of the film were inferior.

Example 11, Comparative Example 11 and Comparative Example 12
Except having changed into the conditions shown in Table 5, each PVA was synthesize | combined like Example 1, and emulsion was produced using this each PVA. Table 5 shows the physical property data of the obtained PVA. Gel permeation measurement was carried out in the same manner as in Example 1. The results are shown in Table 5. The obtained emulsion was evaluated in the same manner as in Example 1 for water dispersibility of organic particles, polymerization stability, and water resistance of the film. The results are shown in Table 5.

Table 5 shows the evaluation of fully saponified PVA having a polymerization degree of 2400 and emulsions obtained using the PVA as a dispersant for emulsion polymerization. When the values obtained by gel permeation chromatography measurement satisfy the conditions defined in the present invention (Example 11), the water dispersibility of the organic particles, the polymerization stability, and the water resistance of the film were all excellent. On the other hand, the absorbance at the peak top molecular weight (B) measured by an absorptiometric detector (measurement wavelength: 280 nm) is less than 0.25 × 10 ⁻³ , and the peak top molecular weight (A) and the peak top molecular weight (B) are as described above. When the formula (1) was not satisfied (Comparative Example 11), the water dispersibility of the organic particles and the water resistance of the film were inferior. When the absorbance at the peak top molecular weight (B) exceeded 3.00 × 10 ⁻³ (Comparative Example 12), the polymerization stability and the water resistance of the film were inferior.

Example 12, Comparative Examples 13-15
Except for changing to the conditions shown in Table 6, each PVA was synthesized in the same manner as in Example 1, and an emulsion was prepared using each PVA. Table 6 shows the physical property data of the obtained PVA. Gel permeation measurement was carried out in the same manner as in Example 1. The results are shown in Table 6. The obtained emulsion was evaluated in the same manner as in Example 1 for water dispersibility of organic particles, polymerization stability, and water resistance of the film. The results are shown in Table 6.

Table 6 shows the evaluation of fully saponified PVA having a polymerization degree of 3600 and a polymerization degree of 5500, and emulsions obtained using the PVA as a dispersant for emulsion polymerization. When the values obtained by gel permeation chromatography measurement satisfy the conditions defined in the present invention (Example 12), the water dispersibility of the organic particles, the polymerization stability, and the water resistance of the film were all excellent. On the other hand, the absorbance at the peak top molecular weight (B) measured with an absorptiometric detector (measurement wavelength 280 nm) is less than 0.25 × 10 ⁻³ , and the peak top molecular weight (A) and the peak top molecular weight (B) are also described above. When the formula (1) was not satisfied (Comparative Example 13), the water dispersibility of the organic particles and the water resistance of the film were inferior. When the absorbance at the peak top molecular weight (B) exceeded 3.00 × 10 ⁻³ (Comparative Example 14), the polymerization stability and the water resistance of the film were inferior. When the degree of polymerization exceeded 5000 (Comparative Example 15), the water dispersibility of the organic particles and the water resistance of the film were inferior.

Examples 13 to 19, Comparative Example 16 to Comparative Example 19
Except having changed into the conditions shown in Table 7, each PVA was synthesize | combined similarly to Example 1, and emulsion was produced using each PVA. Table 7 shows the physical property data of the obtained PVA. Gel permeation measurement was carried out in the same manner as in Example 1. The results are shown in Table 7. The emulsion was evaluated in the same manner as in Example 1 except that the water dispersibility of the organic particles and the index of the water resistance of the film were changed as shown below. The results are shown in Table 7.

[Emulsion evaluation]
(Water dispersibility of organic particles)
A: Less than 200 nm B: 200 nm or more and less than 220 nm C: 220 nm or more and less than 240 nm D: 240 nm or more and less than 260 nm E: 260 nm or more

(Water resistance of the film)
A: Less than 45% B: 45% or more and less than 50% C: 50% or more and less than 55% D: 55% or more and less than 60% E: 60% or more

Table 7 shows the evaluation of partially saponified PVA having a degree of polymerization of 1700 (degree of saponification of about 88 mol%). When the values obtained by gel permeation chromatography measurement satisfy the conditions defined in the present invention (Examples 13 to 19), the water dispersibility of the organic particles, the polymerization stability, and the water resistance of the film were all excellent. On the other hand, when the absorbance at the peak top molecular weight (B) measured with an absorptiometric detector (measurement wavelength: 280 nm) is less than 0.25 × 10 ⁻³ (Comparative Examples 16 and 18), the peak top molecular weight (A ) And peak top molecular weight (B) also did not satisfy the above formula (1) (Comparative Example 18), the water dispersibility of the organic particles and the water resistance of the film were inferior. When the absorbance at the peak top molecular weight (B) exceeded 3.00 × 10 ⁻³ (Comparative Examples 17 and 19), the polymerization stability and the water resistance of the film were inferior.

Example 20, Comparative Examples 20 and 21
Except having changed into the conditions shown in Table 8, each PVA was synthesize | combined similarly to Example 1, and emulsion was produced using each PVA. Table 8 shows the physical property data of the obtained PVA. Gel permeation measurement was carried out in the same manner as in Example 1. The results are shown in Table 8. The obtained emulsion was evaluated in the same manner as in Example 13 for water dispersibility of organic particles, polymerization stability, and water resistance of the film. The results are shown in Table 8.

Example 21
The total solid concentration (saponification concentration) is 40% by mass relative to a 55% by mass methanol solution of polyvinyl acetate in PVAc-3, and the molar ratio of sodium hydroxide to vinyl acetate monomer units in the polyvinyl acetate is Methanol and an 8% methanol solution of sodium hydroxide were added with stirring so that the concentration became 0.005, and the saponification reaction was started at 40 ° C. In addition, saponification reaction was performed by adding distilled water so that the moisture content in the system container at this time was 1.2%. One hour after adding the methanol solution of sodium hydroxide, 0.8 mol equivalent of 1% aqueous acetic acid and a large amount of distilled water were added to stop the saponification reaction. The obtained solution was transferred to a dryer, dried at 65 ° C. for 12 hours, and then dried at 100 ° C. for 2 hours to obtain PVA. An emulsion was prepared using the obtained PVA in the same manner as in Example 1.

  The degree of polymerization of the obtained PVA was 300, the degree of saponification was 60.2 mol%, and the sodium acetate content was 1.3%. Table 8 shows the physical property data of the obtained PVA. Gel permeation measurement was carried out in the same manner as in Example 1. The results are shown in Table 8. The obtained emulsion was evaluated in the same manner as in Example 13 for water dispersibility of organic particles, polymerization stability, and water resistance of the film. The results are shown in Table 8.

Comparative Example 22
The total solid concentration (saponification concentration) is 40% by mass relative to a 55% by mass methanol solution of polyvinyl acetate in PVAc-3, and the molar ratio of sodium hydroxide to vinyl acetate monomer units in the polyvinyl acetate is Methanol and an 8% methanol solution of sodium hydroxide were added with stirring so that the concentration became 0.005, and the saponification reaction was started at 40 ° C. Note that saponification reaction was performed by adding distilled water so that the water content in the system was 3.0%. One hour after adding the methanol solution of sodium hydroxide, 0.8 mol equivalent of 1% aqueous acetic acid and a large amount of distilled water were added to stop the saponification reaction. The obtained solution was transferred to a dryer, dried at 65 ° C. for 12 hours, and then dried at 100 ° C. for 2 hours to obtain a comparative PVA.

  The degree of polymerization of the obtained PVA was 300, the degree of saponification was 45.3 mol%, and the sodium acetate content was 1.2%. Since the obtained PVA was insoluble in water, a film for GPC measurement could not be prepared, and GPC measurement and PVA evaluation could not be performed. Moreover, the emulsion was not able to be produced by the same method as Example 1, and the evaluation of the emulsion could not be performed.

Table 8 shows the evaluation of partially saponified PVA having a polymerization degree of 300. When the values obtained by the gel permeation chromatography satisfy the conditions defined in the present invention (Examples 20 and 21), the water dispersibility of the organic particles, the polymerization stability, and the water resistance of the film were all excellent. On the other hand, when the absorbance at the peak top molecular weight (B) measured with an absorptiometric detector (measurement wavelength: 280 nm) is less than 0.25 × 10 ⁻³ (Comparative Example 20), the water resistance of the film is poor. It was. When the absorbance at the peak top molecular weight (B) exceeded 3.00 × 10 ⁻³ (Comparative Example 21), the polymerization stability and the water resistance of the film were inferior.

Example 22, Comparative Examples 23 and 24
Except having changed into the conditions shown in Table 9, each PVA was synthesize | combined similarly to Example 1, and emulsion was produced using this each PVA. Table 9 shows the physical property data of the obtained PVA. The obtained emulsion was evaluated in the same manner as in Example 13 for water dispersibility of organic particles, polymerization stability, and water resistance of the film. The results are shown in Table 9.

Table 9 shows evaluations of partially saponified PVA having a polymerization degree of 500 (saponification degree of about 88 mol%) and emulsions obtained using the PVA as a dispersant for emulsion polymerization. When the value obtained by the gel permeation chromatography satisfies the conditions defined in the present invention (Example 22), the water dispersibility of the organic particles, the polymerization stability, and the water resistance of the film were all excellent. On the other hand, when the absorbance at the peak top molecular weight (B) measured with an absorptiometer (measurement wavelength: 280 nm) is less than 0.25 × 10 ⁻³ (Comparative Example 23), the water dispersibility of the organic particles and The water resistance of the film was poor. When the absorbance at the peak top molecular weight (B) exceeded 3.00 × 10 ⁻³ (Comparative Example 24), the polymerization stability and the water resistance of the film were inferior.

Example 23, Comparative Examples 25 and 26
Except having changed into the conditions shown in Table 10, each PVA was synthesize | combined like Example 1, and emulsion was produced using this each PVA. Table 10 shows the physical property data of the obtained PVA. Gel permeation measurement was carried out in the same manner as in Example 1. The results are shown in Table 10. The obtained emulsion was evaluated in the same manner as in Example 13 for water dispersibility of organic particles, polymerization stability, and water resistance of the film. The results are shown in Table 10.

Table 10 shows evaluation of partially saponified PVA having a polymerization degree of 2400 (saponification degree of about 88 mol%) and emulsions obtained using the PVA as a dispersant for emulsion polymerization. When the value obtained by the gel permeation chromatography satisfies the conditions defined in the present invention (Example 23), the water dispersibility of the organic particles, the polymerization stability, and the water resistance of the film were all excellent. On the other hand, the absorbance at the peak top molecular weight (B) measured by an absorptiometric detector (measurement wavelength: 280 nm) is less than 0.25 × 10 ⁻³ , and the peak top molecular weight (A) and the peak top molecular weight (B) are as described above. When the formula (1) was not satisfied (Comparative Example 25), the water dispersibility of the organic particles and the water resistance of the film were inferior. When the absorbance at the peak top molecular weight (B) exceeded 3.00 × 10 ⁻³ (Comparative Example 26), the polymerization stability and the water resistance of the film were inferior.

Example 24, Comparative Examples 27 and 28
Except having changed into the conditions shown in Table 11, each PVA was synthesize | combined like Example 1, and emulsion was produced using this each PVA. Table 11 shows the physical property data of the obtained PVA. Gel permeation measurement was carried out in the same manner as in Example 1. The results are shown in Table 11. The obtained emulsion was evaluated in the same manner as in Example 13 for water dispersibility of organic particles, polymerization stability, and water resistance of the film. The results are shown in Table 11.

Table 11 shows evaluation of partially saponified PVA having a polymerization degree of 3600 (saponification degree of about 88 mol%) and emulsions obtained using the PVA as a dispersant for emulsion polymerization. When the value obtained by the gel permeation chromatography satisfies the conditions defined in the present invention (Example 24), the water dispersibility of the organic particles, the polymerization stability, and the water resistance of the film were all excellent. On the other hand, the absorbance at the peak top molecular weight (B) measured by an absorptiometric detector (measurement wavelength: 280 nm) is less than 0.25 × 10 ⁻³ , and the peak top molecular weight (A) and the peak top molecular weight (B) are as described above. When the formula (1) was not satisfied (Comparative Example 27), the water dispersibility of the organic particles and the water resistance of the film were inferior. When the absorbance at the peak top molecular weight (B) exceeded 3.00 × 10 ⁻³ (Comparative Example 28), the polymerization stability and the water resistance of the film were inferior.

Example 25
An emulsion was obtained in the same manner as in Example 1 except that a butadiene monomer was used instead of the vinyl acetate monomer. The obtained emulsion was evaluated in the same manner as in Example 1. The evaluation was “A” for all of the water dispersibility of the organic particles, the polymerization stability, and the water resistance of the film.

Example 26
A 3 L separable flask equipped with a stirrer, a reflux tube, a dropping funnel, a thermometer and a nitrogen introduction tube was charged with 900 parts by mass of ion-exchanged water and 78 parts by mass of PVA (“PVA205” manufactured by Kuraray Co., Ltd.), 95 ° C. The solution was heated to 1, dissolved for 1 hour and cooled. The obtained PVA aqueous solution was heated to 60 ° C. with stirring while purging with nitrogen, and 13.2 parts by mass of a 10% by mass aqueous solution of tartaric acid and 9 parts by mass of 5% by mass hydrogen peroxide (based on the vinyl acetate monomer) (0.015 times as a ratio) was added all at once, 78 parts by mass of vinyl acetate monomer was added, initial emulsion polymerization was started, and after 30 minutes, the completion of initial emulsion polymerization was confirmed.

  After the initial emulsion polymerization, 2.7 parts by weight of a 10% by weight aqueous solution of tartaric acid and 9 parts by weight of 5% by weight hydrogen peroxide were added all at once, and 702 parts by weight of vinyl acetate monomer was continuously added from the dropping funnel over 2 hours. The emulsion polymerization was carried out. After completion of the addition, 970 parts by mass of a 5% aqueous solution of PVA-1 was added to the obtained emulsion, followed by filtration using a 60 mesh stainless steel wire mesh. In this way, an emulsion to which PVA-1 was added was obtained. When the emulsion to which PVA-1 was added was evaluated in the same manner as in Example 1, the water resistance of the film was “B”.

  From the above results, it is clear that the emulsion polymerization dispersant of the present invention containing a specific PVA is excellent in water dispersibility and polymerization stability of organic particles and also in balance of performance. An aqueous emulsion obtained by emulsion polymerization using the dispersant for emulsion polymerization is excellent in water resistance of the film. Furthermore, even if an ethylenically unsaturated monomer is emulsion-polymerized to obtain an aqueous emulsion, and the specific PVA is added to the aqueous emulsion, an aqueous emulsion having excellent water resistance of the film can be obtained. Therefore, the aqueous emulsion is particularly preferably used for an adhesive or the like.

Claims (6)

Emulsification containing polyvinyl alcohol having a saponification degree of 50 to 99.99 mol%, a viscosity average polymerization degree of 200 to 5000, and a content of alkali metal salt of carboxylic acid of 0.5% by mass or less in terms of mass of alkali metal. A dispersing agent for polymerization,
When the polyvinyl alcohol heated at 120 ° C. for 3 hours is measured by gel permeation chromatography, the peak top molecular weight (A) measured by a differential refractive index detector and measured by an absorptiometric detector (measurement wavelength: 280 nm) The peak top molecular weight (B) is expressed by the following formula (1)
(AB) / A <0.75 (1)
And the absorbance at the peak top molecular weight (B) is 0.25 × 10 ^{−3 to} 3.00 × 10 ⁻³ .   The ratio Mw / Mn of the weight average molecular weight Mw to the number average molecular weight Mn of the polyvinyl alcohol determined by a differential refractive index detector in the gel permeation chromatography measurement is 2.2 to 6.0. The dispersant for emulsion polymerization as described.   An aqueous emulsion obtained by emulsion polymerization of an ethylenically unsaturated monomer in the presence of the dispersant according to claim 1. A dispersant comprising polyvinyl alcohol having a saponification degree of 50 to 99.99 mol%, a viscosity average polymerization degree of 200 to 5000, and an alkali metal salt content of carboxylic acid of 0.5% by mass or less in terms of the mass of the alkali metal. And an aqueous emulsion containing a dispersoid consisting of a polymer comprising ethylenically unsaturated monomer units,
When the polyvinyl alcohol heated at 120 ° C. for 3 hours is measured by gel permeation chromatography, the peak top molecular weight (A) measured by a differential refractive index detector and measured by an absorptiometric detector (measurement wavelength: 280 nm) The peak top molecular weight (B) is expressed by the following formula (1)
(AB) / A <0.75 (1)
An aqueous emulsion in which the absorbance at the peak top molecular weight (B) is 0.25 × 10 ^{−3 to} 3.00 × 10 ⁻³ .   The ratio Mw / Mn of the weight average molecular weight Mw to the number average molecular weight Mn of the polyvinyl alcohol obtained by a differential refractive index detector in the gel permeation chromatography measurement is 2.2 to 6.0. The aqueous emulsion as described.   An adhesive comprising the aqueous emulsion according to any one of claims 3 to 5.

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