JP2015163659A - Stabilizer for emulsion polymerization - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stabilizer for emulsion polymerization exhibiting excellent dispersibility during an emulsion polymerization, capable of providing high viscosity aqueous emulsion and further excellent in strength of coating formed from the aqueous emulsion.SOLUTION: There is provided a stabilizer for emulsion polymerization containing a vinyl alcohol-based polymer (A), a ratio of a weight average molecular weight (Mw(A)) to a number average molecular weight (Mn(A)) of the vinyl alcohol-based polymer (A), (Mw(A)/Mn(A)), is 3 to 8, and the ratio of the weight average molecular weight (Mw(B)) to the number average molecular weight (Mn(B)) of a vinyl alcohol-based polymer (B) obtained by treatment of the vinyl alcohol-based polymer (A) in a sodium hydroxide solution at 40°C for 1 hour, (Mw(B)/Mn(N)), is 2 or more and less than 3.

Description

  The present invention relates to a stabilizer for emulsion polymerization.

  Vinyl alcohol polymers (hereinafter sometimes abbreviated as “PVA”) are known as water-soluble synthetic polymers and are used in various applications. In particular, PVA has a hydrophobic group and a hydrophilic group, and exhibits excellent surface activity. Therefore, PVA is useful as a protective colloid for emulsion polymerization of vinyl ester monomers such as vinyl acetate. Aqueous emulsions obtained using polymerization stabilizers are various adhesives for paper, woodwork, plastics, various binders for impregnated paper and non-woven products, admixtures, jointing materials, paints, paper Widely used in fields such as processing and textile processing.

  Such a stabilizer for PVA-containing emulsion polymerization is required to be excellent in so-called dispersion stability, which suppresses aggregation of the emulsion during emulsion polymerization in order to adjust the viscosity of the aqueous emulsion according to the purpose of use. Moreover, when using an aqueous emulsion as an adhesive agent, the aqueous emulsion obtained using the emulsion polymerization stabilizer is required to have a high viscosity. Furthermore, when using an aqueous emulsion for a binder, a coating material, etc., the intensity | strength of the film | membrane formed from an aqueous emulsion is requested | required.

  In order to meet the above-mentioned requirements, a technique has been developed in which modified PVA copolymerized with ethylene or modified PVA introduced with a functional group such as a silyl group is used as a protective colloid for emulsion polymerization (see Patent Document 1 and Patent Document 2). ). By using such modified PVA, the stability of the film obtained from the aqueous emulsion composition is improved.

  However, the conventional stabilizer for emulsion polymerization does not sufficiently satisfy all of the dispersibility during emulsion polymerization, the viscosity of the aqueous emulsion obtained, and the strength of the film formed from the aqueous emulsion.

Japanese Patent Laid-Open No. 08-259659 JP 2007-23148 A

  The present invention has been made based on the circumstances as described above, exhibits excellent dispersibility during emulsion polymerization, and can obtain a high-viscosity aqueous emulsion, and further provides a film formed from the aqueous emulsion. An object is to provide a stabilizer for emulsion polymerization having excellent strength.

  The invention made in order to solve the above problems is a stabilizer for emulsion polymerization containing a vinyl alcohol polymer (A), wherein the vinyl alcohol polymer (A) has a number average molecular weight (Mn (A)). ) (Mw (A) / Mn (A)) is 3 or more and 8 or less, and the vinyl alcohol polymer (A) is 40 ° C. in a sodium hydroxide solution. The ratio (Mw (B) / Mn (B)) of the weight average molecular weight (Mw (B)) to the number average molecular weight (Mn (B)) of the vinyl alcohol polymer (B) obtained by treating with 1 hour It is a stabilizer for emulsion polymerization that is 2 or more and less than 3.

  The emulsion polymerization stabilizer is a ratio (Mw (A) / Mn (Mw (A) / Mn (M)) of the weight average molecular weight (Mw (A)) to the number average molecular weight (Mn (A)) of the vinyl alcohol polymer (A) contained therein. A)) and the above-mentioned vinyl alcohol polymer (A) are subjected to alkali treatment under specific conditions, and the weight average molecular weight (Mw (Mw (M) (B)) of the vinyl alcohol polymer (B) obtained by alkali treatment. B)) ratio (Mw (B) / Mn (B)) within the above range can exhibit excellent dispersibility at the time of emulsion polymerization and can provide a highly viscous aqueous emulsion. The film formed from is excellent in strength.

  The vinyl alcohol polymer (A) is obtained by polymerizing a vinyl ester monomer in the presence of the monomer (a), followed by saponification and heat treatment. ) Is a carboxylic acid having an unsaturated double bond, an alkyl ester of a carboxylic acid having an unsaturated double bond, an acid anhydride of a carboxylic acid having an unsaturated double bond, a carboxylic acid having an unsaturated double bond. It may be at least one selected from the group consisting of a salt and a silyl compound having an unsaturated double bond. The vinyl alcohol polymer (A) is obtained by using a vinyl ester polymer obtained by polymerizing a vinyl ester monomer in the presence of the monomer (a). The vinyl alcohol polymer (A) has a hydrophilic carboxyl group or silyl group derived from the monomer (a). Thereby, the hydrophilic property of the stabilizer for emulsion polymerization containing a vinyl alcohol polymer (A) improves, As a result, the dispersibility at the time of emulsion polymerization improves more. In addition, since the carboxyl group or silyl group and the hydroxyl group can be ester-bonded by heat treatment to form a branched structure as a whole, the emulsion polymerization stabilizer has further improved dispersibility during emulsion polymerization. The viscosity of the resulting aqueous emulsion and the strength of the film formed from this aqueous emulsion are further improved.

  The emulsion polymerization stabilizer may further contain water. By containing water in this way, the vinyl alcohol polymer (A) is dispersed or dissolved in water, and as a result, the stabilizer for emulsion polymerization makes it easier and more reliable for emulsion polymerization of vinyl ester monomers. It can be carried out.

  As described above, the stabilizer for emulsion polymerization of the present invention exhibits excellent dispersibility during emulsion polymerization, can provide a high-viscosity aqueous emulsion, and a film formed from the aqueous emulsion has excellent strength. . Therefore, the aqueous emulsion obtained using the emulsion polymerization stabilizer is suitably used for various adhesives, paints, fiber processing agents, paper processing agents, inorganic binders, cement admixtures, mortar primers, and the like.

<Stabilizer for emulsion polymerization>
The emulsion polymerization stabilizer is a vinyl alcohol polymer (A) containing a vinyl alcohol unit (—CH ₂ —CHOH—) (hereinafter, the vinyl alcohol polymer may be abbreviated as “PVA”). contains. Moreover, it is preferable to contain water further and you may contain other components, such as surfactant other than PVA (A), in the range which does not prevent the effect of this invention. By using the stabilizer for emulsion polymerization, an aqueous emulsion can be obtained from the ethylenically unsaturated monomer.

[PVA (A)]
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 or more and 8 or less. The lower limit of the ratio is preferably 3.2, more preferably 3.4, further preferably 3.6, and the upper limit of the ratio is preferably 6 and more preferably 5.

  PVA (B) is obtained by treating the 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 average degree of polymerization in JIS-K6726 can be employed, and specifically, it can be 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.

  The PVA (B) has a ratio of the weight average molecular weight (Mw (B)) to the number average molecular weight (Mn (B)) (Mw (B) / Mn (B)) of 2 or more and less than 3. 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) contained in the emulsion polymerization stabilizer of the present invention is such that (Mw (A) / Mn (A)) and (Mw (B) / Mn (B)) are in the above range, so that PVA (A) is considered that the PVA chains are bonded to each other to form a branched structure. And it is thought by this branched structure that the stabilizer for emulsion polymerization containing PVA (A) becomes the thing excellent in the dispersibility at the time of emulsion polymerization.

The number average molecular weight (Mn) and the weight average molecular weight (Mw) in the above PVA (A) and PVA (B) are determined by gel permeation chromatography using hexafluoroisopropanol as a mobile phase and a differential refractive index detector. It can obtain | require as a polymethylmethacrylate conversion value by a graphic (GPC) measurement, As a more concrete method, the following can be employ | adopted.
GPC column: 2 “GHH _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 the PVA (A) to the weight average molecular weight (Mw) of the PVA (B) (Mw (A) / Mw (B)) is not particularly limited. Is preferable, and 1.5 is more preferable. On the other hand, the upper limit of the ratio (Mw (A) / Mw (B)) is preferably 3.0, and more preferably 2.5. When the ratio (Mw (A) / Mw (B)) is equal to or higher than the lower limit, the viscosity of the obtained aqueous emulsion is further improved. On the other hand, when the ratio (Mw (A) / Mw (B)) is equal to or lower than the upper limit, the dispersibility during emulsion polymerization of the emulsion polymerization stabilizer is further improved.

  As PVA (A), what is obtained by saponifying a vinyl ester polymer can be used. Although PVA (A) may consist only of a vinyl alcohol unit, it is preferable that the unit derived from a monomer (a) is further included.

  The vinyl ester monomer used for the production of the vinyl ester polymer is not particularly limited. For example, vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, versatic acid Examples thereof include vinyl, vinyl caproate, vinyl caprylate, vinyl laurate, vinyl palmitate, vinyl stearate, vinyl oleate, and vinyl benzoate. Among these, vinyl acetate is preferable from the economical viewpoint.

  The monomer (a) includes a carboxylic acid having an unsaturated double bond, an alkyl ester of the carboxylic acid, an acid anhydride of the carboxylic acid, a salt of the carboxylic acid, and a silyl compound having an unsaturated double bond. At least one monomer selected from the group consisting of:

  Examples of the carboxylic acid having an unsaturated double bond, an alkyl ester of the carboxylic acid, an acid anhydride of the carboxylic acid, and a salt of the carboxylic acid include maleic acid, maleic acid monomethyl ester, maleic acid dimethyl ester, Maleic acid monoethyl ester, maleic acid diethyl ester, maleic anhydride, citraconic acid, citraconic acid monomethyl ester, citraconic acid dimethyl ester, citraconic acid diethyl ester, citraconic anhydride, fumaric acid, fumaric acid monomethyl ester, fumaric acid dimethyl ester, Fumaric acid monoethyl ester, fumaric acid diethyl ester, itaconic acid, itaconic acid monomethyl ester, itaconic acid dimethyl ester, itaconic acid monoethyl ester, itaconic acid diethyl ester, itaconic anhydride Acrylate, methyl acrylate, ethyl acrylate, methacrylic acid, methyl methacrylate, and ethyl methacrylate.

  Examples of the silyl compound having an unsaturated double bond include compounds having an unsaturated double bond and a trialkoxysilyl group such as trialkoxysilane such as vinyltrimethoxysilane and vinyltriethoxysilane. .

  Among these monomers (a), maleic acid monomethyl ester, citraconic acid monomethyl ester, itaconic acid monomethyl ester, methyl acrylate, methyl methacrylate, vinyltrimethoxysilane are preferred, maleic acid monomethyl ester, methyl acrylate, More preferred are methyl methacrylate and vinyltrimethoxysilane.

  As a minimum of the content rate of the unit derived from the monomer (a) in PVA (A), 0.02 mol% is preferable based on the number-of-moles of all the monomer units which comprise PVA (A), 0 0.05 mol% is more preferable, and 0.1 mol% is more preferable. On the other hand, the upper limit of the content of units derived from the monomer (a) in PVA (A) is preferably 5 mol% based on the number of moles of all monomer units constituting PVA (A), 2 mol% is more preferable and 1 mol% is further more preferable. When the content is at least 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 content is less than or equal to the above upper limit, the dispersibility of the emulsion polymerization stabilizer during emulsion polymerization is further improved.

Content of units derived from monomer (a) can be determined from the ^{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 (a), the content is determined 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 derived from the methine structure of a vinyl ester unit (4.7 to 5.2 ppm) and a peak derived from a methyl group of a methyl ester portion of a unit derived from the monomer (a) From β (3.6 to 3.8 ppm), the content S of the unit derived from the monomer (a) 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

  Moreover, PVA (A) may contain the unit derived from other monomers other than the unit derived from a vinyl alcohol unit and a monomer (a) in the range which does not impair the meaning of this invention. Examples of the unit derived from the other monomer 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, and n-butyl vinyl ether. Vinyl ethers such as i-butyl vinyl ether, t-butyl vinyl ether and 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; It includes units derived from such a propenyl. The content rate of the unit derived from the said other monomer in PVA (A) can be 15 mol% or less based on the number-of-moles of all the monomer units which comprise PVA (A), for example. .

  There is no particular limitation on the order of arrangement of the vinyl alcohol unit, the unit derived from the monomer (a) and the unit derived from the other monomer in PVA (A), which may be random, block, or alternating. Good.

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 molar fraction of hydroxyl groups relative to the total of hydroxyl groups and ester bonds in PVA (A)) is measured according to JIS-K6726. 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 polymerization degree of PVA (A), 5,000 is preferable and 4,000 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-K6726. That is, after PVA (A) is completely saponified and purified, PVA (A) containing units derived from monomer (a) is about 30 ° C. in a sodium chloride aqueous solution (0.5 mol / L). Intrinsic viscosity [η] (unit: deciliter / g) was measured, and for PVA (A) not containing the unit derived from monomer (a), the intrinsic viscosity [η] (unit: deciliter) in an aqueous solution at 30 ° C. / G) is measured. From this intrinsic viscosity [η], the viscosity average degree of polymerization (P) of PVA (A) is obtained by the following formula.
P = ([η] × 10 ³ /8.29) ^{(1 / 0.62)}

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

  The stabilizer for emulsion polymerization preferably contains water in addition to PVA (A). Moreover, as another component which the said stabilizer for emulsion polymerization may contain, a solvent, surfactant, etc. are mentioned, for example.

  When the stabilizer for emulsion polymerization contains water, the PVA (A) can be subjected to emulsion polymerization in a form dispersed or dissolved in water. As a result, the emulsion polymerization stabilizer can carry out the emulsion polymerization of the vinyl ester monomer more easily and reliably. The upper limit of the water content in the emulsion polymerization stabilizer is preferably 99.5% by mass, more preferably 99% by mass. 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.

  Examples of the solvent 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.

  Examples of the surfactant include anionic surfactants such as alkylnaphthalene sulfonate and dialkylsulfosuccinic acid; cationic surfactants such as alkylamine salt and lauryltrimethylammonium chloride; polyoxyethylene alkyl ether and polyoxyethylene Nonionic surfactants such as alkylphenyl ethers and sorbitan fatty acid esters; amphoteric surfactants such as alkylbetaines and amine oxides; vinyl alcohol polymers other than PVA (A), polymer surfactants such as hydroxyethyl cellulose, etc. Can be mentioned.

<Method for producing stabilizer for emulsion polymerization>
The method for producing the emulsion polymerization stabilizer is not particularly limited. For example, a step of polymerizing a monomer containing a vinyl ester monomer (hereinafter, also referred to as “polymerization step”) is obtained by this polymerization step. A step of saponifying the obtained vinyl ester polymer (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, a monomer containing a vinyl ester monomer is polymerized to synthesize a vinyl ester polymer. As described above, the monomer containing the vinyl ester monomer includes only the vinyl ester monomer, and as described above, the vinyl ester monomer, the monomer (a) and / or Or it may contain either the said other monomer.

  As a polymerization method of the monomer containing the vinyl ester monomer, 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. What is necessary is just to select from the range of 0.01-10, preferably the range of 0.05-3 by mass ratio {= (solvent) / (total monomer)} with respect to all the monomers.

The polymerization initiator used for such polymerization may be appropriately selected from known polymerization initiators such as azo initiators, peroxide initiators, redox 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, or longalite.
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, and 0.02 to 0 More preferred is 15 mol%.

  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, for example, even when the monomer (a) is used, the content of units derived from the monomer (a) in the PVA (A) is kept at an appropriate ratio. It becomes easy. 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 polymerization and the heat radiation from the surface of the reactor, or using an appropriate heat 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. 0.1-10 mass parts is preferable with respect to 100 mass parts.

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

[Saponification process]
In this step, the vinyl ester polymer 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, the viscosity of the resulting aqueous emulsion, and the film formed from the aqueous emulsion Strength is 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, 70 ° C is preferred and 90 ° C is 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 film and the strength of the film formed from the aqueous emulsion are further improved.

  The stabilizer for emulsion polymerization can be produced by appropriately mixing the PVA (A) obtained by the above production method and an optional component.

<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. Examples of the method for producing the aqueous emulsion include a method of emulsion polymerization by adding an ethylenically unsaturated monomer temporarily or continuously in the presence of a polymerization initiator in an aqueous solution of the emulsion polymerization stabilizer. 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.

  Furthermore, when using the said stabilizer for emulsion polymerization for emulsion polymerization, the stabilizer for emulsion polymerization containing the other polyvinyl alcohol-type polymer (C) can be used together. The PVA (C) is preferably a PVA having a saponification degree of 70 mol% or more and a polymerization degree of 300 to 4500, more preferably a saponification degree of 80 to 99 mol% and a polymerization degree of 500 to 3500.

  Moreover, PVA (C) may be given water resistance by introducing an ethylene group or an acetoacetyl group. Weight ratio of the addition amount of the stabilizer for emulsion polymerization and the addition amount of the stabilizer for emulsion polymerization containing PVA (C) when the stabilizer for emulsion polymerization containing PVA (C) is used in combination (the emulsion polymerization) Stabilizer for emulsion / stabilizer for emulsion polymerization containing PVA (C)) varies depending on the type of stabilizer for emulsion polymerization used and the like, and cannot be defined uniformly, but 95/5 to 5/95. Is preferable, and 90/10 to 10/90 is particularly preferable. 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; vinyl formate , Vinyl ester monomers such as vinyl acetate, vinyl propionate, vinyl versatate; acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, acrylic acid Acrylic acid ester monomer such as 2-hydroxyethyl; Methacrylic acid ester monomer such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, 2-hydroxyethyl methacrylate Body; Acrylamide monomers such as dimethylaminoethyl silylate, 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-styrenesulfonic 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.

  Hereinafter, the present invention will be described in detail by way of examples and comparative examples. 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-K6726.

[Saponification degree]
The degree of saponification of each PVA (A) was determined by the method described in JIS-K6726.

[Modification rate]
The modification rate of each PVA (the content of units derived from the monomer (a) in the PVA (A)) is determined by using the vinyl ester polymer that is the precursor of the PVA (A), and the above ¹ H- It calculated | required by the method using NMR.

[Preparation of PVA (B)]
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 ( B) was prepared.

[Number average molecular weight (Mn) and weight average molecular weight (Mw) of PVA (A) and PVA (B)]
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: 2 Tosoh "GMH _HR (S)" 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 740 parts of vinyl acetate and 260 parts of methanol, and nitrogen was bubbled through the system for 30 minutes. Replaced. Further, monomethyl maleate was selected as monomer (a), and a methanol solution of monomethyl maleate (concentration 20%) was replaced with nitrogen by bubbling nitrogen gas. The temperature of the reactor was increased, and when the internal temperature reached 60 ° C., 0.25 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 monomer (a) added until the termination of polymerization was 0.9 part, and the solid content concentration at the termination of polymerization was 33.3%. Subsequently, unreacted monomers were removed while sometimes adding methanol under reduced pressure at 30 ° C. to obtain a methanol solution (concentration 35%) of a vinyl ester polymer. Next, 790.8 parts of a methanol solution of a vinyl ester polymer prepared by adding methanol to this methanol solution (200.0 parts of the polymer in the solution) was added to a 10% methanol solution of sodium hydroxide 9. Two parts were added and saponification was carried out at 40 ° C. (25% of the polymer concentration in the saponification solution, 0.01 molar ratio of sodium hydroxide to vinyl acetate units in the polymer). After adding a sodium hydroxide methanol solution, a gel was formed in about 15 minutes. This was pulverized with a pulverizer and further allowed to stand at 40 ° C. for 1 hour to proceed with saponification, and then 500 parts of methyl acetate. Was added to neutralize the remaining alkali. After confirming the completion of neutralization using a phenolphthalein indicator, the mixture was filtered to obtain a white solid. To this white solid, 2,000 parts of methanol was added, and the mixture was left to wash at room temperature for 3 hours. After repeating this washing | cleaning operation 3 times, the white solid obtained by carrying out centrifugation liquid removal was heat-processed at 120 degreeC with the dryer for 4.5 hours, and PVA (A) (PVA-1) was obtained. Table 2 shows the physical properties of PVA-1.

[Synthesis Examples 2 to 17] (Production of PVA-2 to PVA-17)
Polymerization conditions such as the amount of vinyl acetate and methanol charged, the type and amount of monomer (a) used during polymerization, the concentration of vinyl ester polymer during saponification, the molar ratio of sodium hydroxide to vinyl acetate units, etc. Various PVA (A) were produced by the same method as in Synthesis Example 1 except that the saponification conditions; and the heat treatment conditions were changed as shown in Table 1. Table 2 shows the physical properties of each PVA (A) and PVA (B) obtained therefrom. In Synthesis Example 13, after producing two types of PVA (A), PVA-13a and PVA-13b, two types of PVA are used so that 45 parts of PVA-13a and 55 parts of PVA-13b are included. (A) was mixed. Moreover, since PVA-10 and PVA-12 were not completely dissolved in hexafluoroisopropanol, Mn and Mw could not be measured.

[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, ion exchange water 350 g and PVA-1 12.6 g were charged and completely dissolved at 95 ° C. Next, this PVA aqueous solution was cooled and purged with nitrogen, and then 16.8 g of vinyl acetate was added while stirring at 200 rpm, and the temperature was raised to 60 ° C. Thereafter, 4.6 g of 5% hydrogen peroxide / 2.0 g of 20% tartaric acid was added to initiate a polymerization. After 15 minutes from the start of polymerization, 151.6 g of vinyl acetate was continuously added over 3 hours, and then 0.6 g of 5% hydrogen peroxide / 0.2 g of 20% tartaric acid was added to terminate the polymerization. A polyvinyl acetate emulsion having a partial concentration of 34.8% and a particle size of 2 μm was obtained.

[Examples 2 to 8 and Comparative Examples 1 to 9]
A polyvinyl acetate emulsion was produced in the same manner as in Example 1 except that the type of PVA (A) used was changed as shown in Table 3. The solid content concentrations in these polyvinyl acetate emulsions are shown in Table 3. In Comparative Examples 2 and 4, PVA-10 and PVA-12 were not completely dissolved in ion-exchanged water, and a polyvinyl acetate emulsion could not be obtained.

[Dispersibility during emulsion polymerization]
The obtained polyvinyl acetate emulsion was observed with a system microscope (OLYMPUS "BX-53"), and there was no aggregation or gelation and no filtration residue was observed. Although there was no filtration residue, it was evaluated as “B” when there was a slight filtration residue, “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.

[Film strength of polyvinyl acetate emulsion]
The polyvinyl acetate emulsions of Examples and Comparative Examples were cast on PET under an environment of a temperature of 20 ° C. and a relative humidity of 65% and dried for 7 days to obtain a dry film having a thickness of 500 μm. The film was punched into a width of 1 cm and a length of 6 cm, and a tensile test was performed using a precision universal testing machine (“Autograph AG-IS” manufactured by Shimadzu Corporation) at a pulling rate of 100 mm / min to determine the strength of the film. The evaluation results are also shown in Table 3.

  As Table 3 shows, it turns out that the stabilizer for emulsion polymerization of Examples 1-8 is excellent in the dispersibility at the time of emulsion polymerization. Moreover, it turns out that the polyvinyl acetate emulsion obtained in Examples 1-8 is highly viscous, and the film | membrane formed from these polyvinyl acetate emulsions is excellent in intensity | strength.

  On the other hand, the stabilizers for emulsion polymerization of Comparative Examples 1 to 9 are inferior in dispersibility during emulsion polymerization, and the viscosity of the obtained polyvinyl acetate emulsion and the strength of the film formed from the polyvinyl acetate emulsion are also insufficient. I understand that. In particular, PVA in Comparative Examples 2 and 4 could not be used as a stabilizer for emulsion polymerization.

  The stabilizer for emulsion polymerization of the present invention exhibits excellent dispersibility at the time of emulsion polymerization, and can obtain a high-viscosity aqueous emulsion, and a film formed from the aqueous emulsion is excellent in strength. Therefore, the aqueous emulsion obtained using the emulsion polymerization stabilizer is suitably used for various adhesives, paints, fiber processing agents, paper processing agents, inorganic binders, cement admixtures, mortar primers, and the like.

Claims (3)

A stabilizer for emulsion polymerization containing a vinyl alcohol polymer (A),
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 or more and 8 or less,
Weight average molecular weight (Mw) relative to the number average molecular weight (Mn (B)) of the vinyl alcohol polymer (B) obtained by treating the vinyl alcohol polymer (A) in a sodium hydroxide solution at 40 ° C. for 1 hour. (B)) ratio (Mw (B) / Mn (B)) is a stabilizer for emulsion polymerization having a value of 2 or more and less than 3. The vinyl alcohol polymer (A) is obtained by polymerizing a vinyl ester monomer in the presence of the monomer (a), followed by saponification and heat treatment,
The monomer (a) is a carboxylic acid having an unsaturated double bond, an alkyl ester of a carboxylic acid having an unsaturated double bond, an acid anhydride of a carboxylic acid having an unsaturated double bond, or an unsaturated double bond. The stabilizer for emulsion polymerization according to claim 1, which is at least one selected from the group consisting of a carboxylic acid salt having a bond and a silyl compound having an unsaturated double bond. The stabilizer for emulsion polymerization according to claim 1 or 2, further comprising water.