JP2005097468A - Method for producing aqueous emulsion containing ethylene-vinyl ester copolymer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing an aqueous emulsion containing an ethylene-vinyl ester copolymer, with reduced discoloration, enabling a persulfate to be used as an oxidizing agent even in the case of using an erythorbic acid compound and/or ascorbic acid compound as reducing agent for a redox polymerization initiator and a transition metal salt. <P>SOLUTION: The method for producing the aqueous emulsion containing the ethylene-vinyl ester copolymer comprises using the erythorbic acid compound and/or ascorbic acid compound as the reducing agent for the redox polymerization initiator in the presence of the transition metal salt and using the persulfate as the oxidizing agent for the redox polymerization initiator and also mixing hydrogen peroxide into the system during and/or after the polymerization reaction. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing an aqueous emulsion containing a copolymer obtained by emulsion polymerization of ethylene and vinyl esters such as vinyl acetate.

Conventionally, aqueous emulsions containing copolymers obtained by emulsion polymerization of ethylene and vinyl esters such as vinyl acetate have been widely used for various adhesives, binders and the like.
Recently, the present inventor has proposed a new method for producing an aqueous emulsion in which formalin, which is the main cause of sick house syndrome, does not occur from the obtained aqueous emulsion (Patent Document 1). Specifically, in the presence of a transition metal salt, emulsion polymerization is performed using erythorbic acid and / or ascorbic acid as a reducing agent for a redox polymerization initiator and hydrogen peroxide as an oxidizing agent for a redox polymerization initiator. Is the method. Further, the same document reports that the aqueous emulsion obtained is colored when sodium persulfate is used instead of hydrogen peroxide as an oxidizing agent.

JP 2001-163910 A (Claims)

By the way, when a persulfate such as sodium persulfate or ammonium persulfate is used as a polymerization initiator, a functional group derived from the persulfate (persulfate group) reacts with the end of the ethylene-vinyl ester copolymer, Since the copolymer is more stably present in the aqueous medium, it has been desired to use a persulfate as an oxidizing agent for emulsion polymerization. However, from Patent Document 1, there was a concern that the resulting aqueous emulsion would be colored.
The object of the present invention is to use persulfate as an oxidizing agent even when erythorbic acid and / or ascorbic acid is used as a reducing agent of a redox polymerization initiator in the presence of a transition metal salt, and coloring. It is to provide a method for producing an aqueous emulsion containing a reduced ethylene-vinyl ester copolymer.

  The present invention uses an erythorbic acid and / or ascorbic acid as a reducing agent for a redox polymerization initiator in the presence of a transition metal salt in the production of an aqueous emulsion containing an ethylene-vinyl ester copolymer. A method for producing an aqueous emulsion containing an ethylene-vinyl ester copolymer, wherein persulfate is used as an oxidant for a polymerization initiator, and hydrogen peroxide is further mixed during and / or after the polymerization reaction It is.

In the presence of a transition metal salt, as a reducing agent of a redox polymerization initiator, as an oxidizing agent, even if it is a method for producing an aqueous emulsion containing an ethylene-vinyl ester copolymer using erythorbic acid and / or ascorbic acid as a reducing agent A persulfate can be used, and an aqueous emulsion with reduced coloring can be obtained.
And the obtained aqueous | water-based emulsion can exist stably in an aqueous medium further. Moreover, since the manufacturing method of this invention is excellent in reactivity, it contains the copolymer using the monomer containing the olefinic double bond different from vinyl esters, such as (meth) acrylic acid, for example. It is suitably used for the production of an aqueous emulsion.

Hereinafter, the present invention will be described in detail.
The present invention is a method for producing an aqueous emulsion containing an ethylene-vinyl ester copolymer obtained by emulsion polymerization of ethylene and vinyl esters.
Here, examples of vinyl esters include vinyl acetate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl laurate, vinyl isononanoate, vinyl versatate, and the like. Of these, vinyl acetate and vinyl versatate are preferable, and vinyl acetate is particularly preferable.

The ethylene-vinyl ester copolymer usually contains about 5 to 70 parts by weight, preferably 10 to 60 parts by weight of a structural unit derived from ethylene with respect to 100 parts by weight of the copolymer. It is a copolymer containing about 30 to 95 parts by weight, preferably about 40 to 90 parts by weight, of a structural unit derived from a kind.
The aqueous emulsion (A) in which the structural unit derived from ethylene is 35 parts by weight or more with respect to 100 parts by weight of the ethylene-vinyl acetate copolymer is obtained by the method described in JP-A-2002-322216. Can do.

Further, since the production method of the present invention is excellent in reactivity, the copolymer further contains an olefinic double bond in addition to the structural unit derived from ethylene and the structural unit derived from vinyl esters. When about 50 parts by weight or less of monomer is contained, this is a preferred production method.
Here, the monomer containing an olefinic double bond is a monomer containing an olefinic double bond different from vinyl esters, for example, a vinyl compound not containing an ester group, α, β -Unsaturated carboxylic acids, acrylamides, allyl group-containing compounds, diene compounds, and the like.
Examples of the vinyl compound not containing an ester group include vinyl chloride, vinyl bromide, styrene, vinyl sulfonate, and the like.
Examples of α, β-unsaturated carboxylic acids include 2-ethylhexyl (meth) acrylate, n-butyl (meth) acrylate, ethyl (meth) acrylate, methyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, (Meth) acrylic acid esters such as glycidyl (meth) acrylate; α, β-unsaturated carboxylic acids such as (meth) acrylic acid, crotonic acid, maleic acid and itaconic acid; salts of α, β-unsaturated carboxylic acids; Maleic acid ester, crotonic acid ester, itaconic acid ester and the like can be mentioned.
Examples of acrylamides include triallyl cyanurate, triallyl isocyanurate, and diallyl phthalate. Examples of allyl group-containing compounds include allyl sulfonate, triallyl cyanurate, triallyl isocyanurate, and diallyl phthalate. Is mentioned.
Examples of the diene compound include butadiene, isoprene, chloroprene and the like.
As the monomer containing an olefinic double bond, among them, α, β-unsaturated carboxylic acids and vinyl compounds not containing an ester group are preferable, and in particular, (meth) acrylic acid ester, (meth) acrylic acid, Styrene is preferred.

Examples of the transition metal salt used in the present invention include chlorides such as iron, copper, cobalt, titanium, nickel, chromium, zinc, manganese, vanadium, molybdenum, cerium, sulfates, and the like. Of these, ferrous chloride, ferrous sulfate, copper sulfate and the like are preferably used. The transition metal salt is usually used in an amount of about 0.001 to 0.05 parts by weight with respect to 1 part by weight of erythorbic acid and / or ascorbic acid. The amount of 0.001 part by weight or more is preferable because emulsion polymerization tends to be promoted, and the amount of 0.05 part by weight or less is preferable because coloring of the produced aqueous emulsion (B) tends to be reduced.
Here, with respect to 1 part by weight of erythorbic acid and / or ascorbic acid, 0.01 part by weight means 0.01 part by weight for only 1 part by weight of erythorbic acid, and 0.01 part by weight for only 1 part by weight of ascorbic acid In addition, it means any one of 0.01 parts by weight with respect to 1 part by weight in total of erythorbic acids and ascorbic acids. Hereinafter, the above expressions mean the same thing.

The reducing agent of the redox polymerization initiator used in the present invention is erythorbic acid and / or ascorbic acid.
Examples of the reducing agent include alkali metal salts such as sodium salts and potassium salts in addition to erythorbic acid and ascorbic acid. Of these, sodium salts are preferable, and sodium erythorbate is particularly preferably used.

  The erythorbic acid and / or ascorbic acid is usually used in an amount of 0.02 to 1 part by weight based on 100 parts by weight of the vinyl ester. When the amount is 0.02 part by weight or more, the reaction tends to be promoted. When the amount is 1 part by weight or less, the produced emulsion is colored, or the obtained emulsion is coated and dried. Since there exists a tendency which an intensity | strength, water resistance, etc. improve, it is preferable.

  The oxidizing agent of the redox polymerization initiator used in the present invention is a persulfate such as sodium persulfate or ammonium persulfate. The persulfate is used in an amount of about 0.5 to 10 mol times, preferably 1 to 5 mol times, more preferably 1 to 3 mol times per mol of erythorbic acid and / or ascorbic acid. Since it tends to improve the storage stability of the emulsion when it is 0.5 mol times or more, the strength and water resistance of the film obtained by coating and drying the emulsion obtained when it is 10 mol times or less The heat resistant colorability tends to be improved.

As an example of the embodiment of the present invention, a partially saponified polyvinyl alcohol, a semi-completely saponified polyvinyl alcohol or the like is used as an emulsifier in a pressure-resistant reaction vessel, and vinyl ester, if necessary, a single unit containing an olefinic double bond. After adding a monomer, transition metal salt, etc. and raising the temperature to about 40 to 70 ° C., the reaction system is purged with ethylene to remove oxygen, and ethylene is introduced to a predetermined pressure of about 1 to 7 MPa. Thereafter, there is a method in which an aqueous solution of persulfate as an oxidant component and an aqueous solution of erythorbic acid and / or ascorbic acid as a reducing agent component are sequentially mixed to carry out emulsion polymerization, and then hydrogen peroxide is mixed.
In the present invention, it is the latter stage of emulsion polymerization in which the concentration of unreacted vinyl esters is as low as several percent, and a small amount of organic peroxide may be added before dropwise addition of hydrogen peroxide. Vinyl esters can be reduced to several thousand ppm or less in a relatively short time. Examples of the organic peroxide include tertiary butyl perbenzoate, dilauryl peroxide, benzoyl peroxide, and tertiary butyl hydroperoxide. When an organic peroxide is used, it is usually used in an amount of about 0.0001 to 0.005 parts by weight per 1 part by weight of the vinyl ester.

Hydrogen peroxide is mixed in order to reduce the coloring of the resulting aqueous emulsion. The amount of hydrogen peroxide used is about 0.9 to 10 moles, preferably 1 to 5 moles relative to the reducing agent component. Is double. Here, since it tends to suppress coloring of the emulsion obtained when it is 0.9 mol times or more, the performance of the emulsion obtained when it is 10 mol times or less, for example, strength when used as a film, It is preferable because water resistance and the like tend to be improved.
As illustrated above, hydrogen peroxide may be mixed after emulsion polymerization, or hydrogen peroxide may be mixed during emulsion polymerization. When hydrogen peroxide is mixed during emulsion polymerization, a larger amount than the reducing agent used for polymerization is usually mixed.

As the emulsifier, in addition to the partially saponified polyvinyl alcohol and semi-completely saponified polyvinyl alcohol, for example, protective colloid such as hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, polyoxyethylene alkyl ether, polyoxyethylene alkyl phenol ether, polyoxyethylene poly Nonionic surfactants such as oxypropylene block copolymer, polyoxyethylene fatty acid ester, polyoxyethylene sorbitan fatty acid ester, alkyl sulfate ester salt, alkylbenzene sulfonate, alkyl sulfosuccinate, alkyl diphenyl ether disulfonate, polyoxyethylene Using anionic surfactants such as alkyl sulfates and polyoxyethylene alkyl phosphates It is possible.
Two or more different emulsifiers may be used in combination as the emulsifier.

As the emulsifier, partially saponified polyvinyl alcohol and quasi-completely saponified polyvinyl alcohol are preferable. A) is preferred because it tends to stabilize. Here, the viscosity average polymerization degree of partially saponified polyvinyl alcohol and semi-completely saponified polyvinyl alcohol is usually about 100 to 8000, and preferably about 300 to 3000.
When the use amount of the emulsifier is described for the quasi-completely saponified polyvinyl alcohol, the emulsifier is usually about 2 to 15 parts by weight, preferably 3 to 10 parts by weight with respect to 100 parts by weight of the vinyl ester and the emulsifier to be used. Degree. It is preferable that the amount of the emulsifier used is in the range of 2 to 15 parts by weight because the film-forming property at low temperature tends to be improved.

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. Parts and% in the examples mean weight basis unless otherwise specified.

As for the non-volatile content, about 1 g of an aqueous emulsion is accurately collected on a pre-dried aluminum board, precisely weighed, then placed in a constant temperature dryer at 105 ° C. and dried for 2 hours, and the obtained dryness for the collected aqueous emulsion is obtained. It calculated | required in the weight ratio (%) of the thing.
The viscosity was measured using a BL viscometer at 25 ° C. and 60 rpm.

(Example 1)
In a pressure-resistant container, 170 parts of water in advance 190 parts of vinyl acetate, polyvinyl alcohol “Poval 217” (manufactured by Kuraray Co., Ltd., saponification degree 88 mol%, average polymerization degree 1700), 2 parts “Poval 205” (manufactured by Kuraray Co., Ltd., degree of saponification) 88 mol%, average polymerization degree 500) 7 parts, ferrous sulfate heptahydrate 0.005 parts and acetic acid 0.4 parts were dissolved. Next, the inside of the pressure vessel was replaced with nitrogen gas, and the inside of the vessel was heated to 60 ° C. and then pressurized to 4.6 MPa with ethylene. Next, 0.7 parts of ammonium persulfate and 0.5 part of sodium erythorbate were diluted with water and added dropwise over 4 hours. During polymerization, the temperature in the reaction vessel was kept at 60 ° C. by controlling the temperature of the jacket, and after stirring until the vinyl acetate concentration in the reaction solution became 1% or less, unreacted ethylene gas was removed. Next, after 0.3 parts of hydrogen peroxide is diluted with water and added, the reaction product is taken out by sufficiently stirring to obtain an aqueous emulsion containing an ethylene-vinyl ester copolymer having a nonvolatile content of 55% and a viscosity of 1200 mPa · s. It was. With respect to 100 parts of the copolymer, 18 parts of a structural unit derived from ethylene and 82 parts of a structural unit derived from vinyl acetate.
This emulsion was coated on white fine paper at a thickness of 10 mil. (250 μm), dried in an oven at 90 ° C. for 5 minutes, and the resulting sample was obtained as a Hunter whiteness meter (CM-8P type, Co., Ltd.). The yellowing degree (YI) was measured using Murakami Color Research Laboratory. The results are shown in Table 1.

(Example 2)
The same procedure as in Example 1 was performed except that sodium erythorbate as a reducing agent in Example 1 was changed to sodium ascorbate. The amount of sodium ascorbate used was equimolar with sodium erythorbate. The results are shown in Table 1.

(Example 3)
In a pressure vessel, 70 parts of water, 10 parts of vinyl acetate, 0.2 parts of sodium vinyl sulfonate, 4 parts of nonionic surfactant “Emulgen 1135S-70” (HLB 17.9, manufactured by Kao Corporation), “Emulgen 1108” (HLB 13.5) 2 parts of Kao Corporation), 0.2 part of sodium persulfate, 0.002 part of ferrous sulfate heptahydrate and 0.1 part of acetic acid were introduced. Next, the inside of the pressure vessel was replaced with nitrogen gas, the inside of the vessel was heated to 50 ° C., and then pressurized to 4.0 MPa with ethylene. Next, 0.8 parts / h of 8% sodium persulfate aqueous solution and 1.3 parts / h of 2.0% sodium erythorbate aqueous solution were added to the pressure vessel to initiate polymerization. Subsequently, after confirming that the liquid temperature in the pressure vessel had risen, 7 parts of an aqueous solution in which 0.2 parts of sodium vinyl sulfonate was dissolved, and 90 parts of vinyl acetate were added over 4 hours. While maintaining the temperature at 50 ° C., ethylene was added for 3 hours so that the pressure was kept constant at 4.0 MPa, 8% sodium persulfate 3.5 parts / h as an oxidizing agent when 5 hours passed after the start of polymerization, and reduction The solution was added to a pressure vessel at a rate of 3 parts / h of 5% sodium erythorbate aqueous solution and stirred until the residual vinyl acetate monomer was less than 1% to remove unreacted ethylene gas. Next, 0.12 part of hydrogen peroxide was diluted with water and added, and the mixture was sufficiently stirred to take out the reaction product. An aqueous solution containing an ethylene-vinyl acetate-vinylsulfonic acid copolymer having a nonvolatile content of 56% and a viscosity of 310 mPa · s. An emulsion was obtained. With respect to 100 parts of the copolymer, they were 21.9 parts of structural units derived from ethylene, 77.8 parts of structural units derived from vinyl acetate, and 0.3 parts of structural units derived from vinyl sulfonic acid.

Example 4
In a pressure vessel, 50 parts of water, 30 parts of vinyl acetate, nonionic surfactant “Emulgen 1135S-70” (HLB 17.9, manufactured by Kao Corporation) 1.5 parts, “Emulgen 1108” (HLB 13.5, manufactured by Kao Corporation) A solution in which 1.5 parts, 2 parts of sodium lauryl sulfate, 0.002 part of ferrous sulfate heptahydrate and 0.1 part of acetic acid were dissolved was introduced. Next, the inside of the pressure vessel was replaced with nitrogen gas, the inside of the vessel was heated to 50 ° C., and then pressurized to 5.0 MPa with ethylene. Next, 3.7 parts / h of 5% sodium persulfate aqueous solution and 1.9 parts / h of 5% sodium erythorbate aqueous solution were added to the pressure vessel to initiate polymerization. Subsequently, after confirming that the liquid temperature in the pressure vessel had risen, 20 parts of vinyl acetate and 50 parts of 2-ethylhexyl acrylate were added over 4 hours, while maintaining the liquid temperature in the container at 50 ° C. Then, ethylene was added for 3 hours so that the pressure was kept constant at 5.0 MPa, and when 6 hours had elapsed after the start of polymerization, 4.5 parts / h of 12% sodium persulfate as the oxidizing agent and 10% sodium erythorbate as the reducing agent The solution was added to the pressure vessel at a rate of 1 part / h of aqueous solution and stirred until the residual vinyl acetate monomer was less than 1% to remove unreacted ethylene gas. Next, after diluting 0.12 part of hydrogen peroxide with water and adding it well, the reaction product is taken out, and contains 52% non-volatile content and ethylene-vinyl acetate-2-ethylhexyl acrylate copolymer with a viscosity of 70 mPa · s. An aqueous emulsion was obtained. With respect to 100 parts of the copolymer, they were 18 parts of a structural unit derived from ethylene, 41 parts of a structural unit derived from vinyl acetate, and 41 parts of a structural unit derived from 2-ethylhexyl acrylate.

(Example 5)
The same operation as in Example 4 was performed except that the hydrogen peroxide added in Example 4 was 0.23 part. The results are shown in Table 1.

(Comparative Example 1)
The same procedure as in Example 1 was performed except that the aqueous hydrogen peroxide solution added in Example 1 was not added. The results are shown in Table 1.

(Comparative Example 2)
The same operation as in Example 2 was performed except that the aqueous hydrogen peroxide solution added in Example 2 was not added. The results are shown in Table 1.

(Comparative Example 3)
The same operation as in Example 3 was performed except that the aqueous hydrogen peroxide solution added in Example 3 was not added. The results are shown in Table 1.

(Comparative Example 4)
The same operation as in Example 4 was performed except that the added aqueous hydrogen peroxide solution added in Example 4 was not added. The results are shown in Table 1.

Since the aqueous emulsion obtained in the present invention is excellent in adhesiveness, it is for paper, woodwork, plastic, paper tube, packaging, (secondary) plywood, construction site / building factory, laminating, household Adhesives for paper, bookbinding and bag making; binders for paper coating, fibers, etc .; cement modifiers such as cement mortar admixtures and cement mortar joints; coating materials such as paint Used.
Further, a filler can be further added to the aqueous emulsion, and it can be used for materials in these fields, foamed wallpaper materials, and the like.
In addition, the aqueous emulsion can be spray-dried to be powdered, and can be used in the above-mentioned fields by adding water, stirring sufficiently, and redispersing.
Furthermore, the aqueous emulsion of the present invention is obtained by mixing with an aqueous emulsion containing, for example, an aqueous emulsion containing polyurethane, an aqueous emulsion containing an acrylic resin, or an aqueous emulsion containing an ethylene-vinyl ester copolymer. The resulting mixture can be used in the above fields.

Claims (4)

  In the production of an aqueous emulsion containing an ethylene-vinyl ester copolymer, erythorbic acid and / or ascorbic acid is used as a reducing agent for the redox polymerization initiator in the presence of a transition metal salt. A method for producing an aqueous emulsion containing an ethylene-vinyl ester copolymer, wherein persulfate is used as an oxidizing agent, and hydrogen peroxide is further mixed during and / or after the polymerization reaction.   The production method according to claim 1, wherein the amount of persulfate used is 0.5 to 10 mol per mol of erythorbic acid and / or ascorbic acid.   The production method according to claim 1 or 2, wherein the hydrogen peroxide is used in an amount of 0.9 to 10 moles per mole of erythorbic acid and / or ascorbic acid.   The amount of erythorbic acid and / or ascorbic acid used is 0.02 to 1 part by weight with respect to 100 parts by weight of the vinyl ester, and the amount of transition metal salt used is 1 part by weight of erythorbic acid and / or ascorbic acid. The production method according to claim 1, wherein the content is 0.001 to 0.05 parts by weight.