JP4752191B2 - Process for producing purified aqueous emulsion - Google Patents

Description

  The present invention relates to a method for producing an aqueous emulsion containing a vinyl acetate polymer. More specifically, the present invention relates to a method for producing a purified aqueous emulsion containing a vinyl acetate polymer such as vinyl acetate homopolymer, ethylene-vinyl acetate copolymer, ethylene-vinyl acetate-vinyl chloride copolymer.

Aqueous emulsions containing vinyl acetate polymers such as vinyl acetate homopolymer, ethylene-vinyl acetate copolymer, ethylene-vinyl acetate-vinyl chloride copolymer are used for various adhesives for paper, woodworking and plastics. It is widely used in the fields of various binders, admixtures, jointing materials, paints, paper processing and textile processing, wallpaper, etc. for agents, for impregnated paper and non-woven products. An aqueous emulsion containing a vinyl acetate polymer is produced by emulsion polymerization of a raw material monomer such as vinyl acetate.
The aqueous emulsion contains aldehydes such as acetaldehyde derived from vinyl acetate and vinyl acetate during emulsion polymerization, and the cured product obtained by drying the aqueous emulsion is colored when heated. was there.
As a method for producing an aqueous emulsion that gives a cured product with reduced coloration, for example, hydrogen peroxide and tartaric acid are used as an initiator for emulsion polymerization, an iron compound is added, and emulsion polymerization is performed at pH 3 to 5, and then hydropolymerization is performed. Patent Documents 1 and 2 disclose methods of adding peroxides and tartaric acid. It has been reported at the same time that the aqueous emulsion obtained by this method has a reduced content of vinyl acetate and aldehydes, and the cured product provided by the aqueous emulsion does not color when left at 100 ° C. for 10 minutes. Yes.
By the way, as an emulsion polymerization, the present inventors devised a method for producing hydrogen peroxide as an oxidizing agent and using erythorbic acid and / or ascorbic acid as a reducing agent, and the aqueous emulsion obtained by the method contains formalin. Moreover, it was reported that coloring was reduced even when the aqueous emulsion was heated at 90 ° C. (Patent Document 3).

JP 2003-82006 A (Claim 1) JP 2003-277411 A (Claim 1) JP 2001-163910 A (Claim 1)

The present inventor emulsified in order to further reduce vinyl acetate and aldehydes in the aqueous emulsion obtained in Patent Document 3, and to not color the cured product obtained from the aqueous emulsion even when left at a high temperature of 200 ° C. After the polymerization was completed, hydroperoxides and tartaric acid were further added to produce an aqueous emulsion. Vinyl acetate and acetaldehyde contained in the resulting aqueous emulsion were reduced, but a cured product of the aqueous emulsion. Is left to stand at 200 ° C., it becomes colored in 1 minute, and it becomes clear that it is colored more than a cured product of an aqueous emulsion to which hydroperoxides and tartaric acid are not added, that is, an aqueous emulsion obtained by Patent Document 3. It was.
It is an object of the present invention to reduce the content of vinyl acetate and aldehydes in an aqueous emulsion containing a vinyl acetate polymer, and to give a cured product that is hardly colored even when left at 200 ° C. It is to provide a method for producing a purified aqueous emulsion.

  The present invention is characterized in that a crude product of an aqueous emulsion containing a vinyl acetate polymer is obtained by emulsion polymerization, and then the crude product is stirred at a reduced pressure of 0.04 MPa or less and 45 to 65 ° C. A method for producing a purified aqueous emulsion.

  The purified aqueous emulsion containing the vinyl acetate polymer obtained by the production method of the present invention is reduced in vinyl acetate and aldehydes, and the cured product of the purified aqueous emulsion is allowed to stand at 200 ° C. Even so, coloring is significantly reduced.

Hereinafter, the present invention will be described in detail.
The vinyl acetate polymer contained in the aqueous emulsion used in the present invention is a polymer having a structural unit derived from vinyl acetate as an essential component, and further derived from a monomer copolymerizable with vinyl acetate. A structural unit may be contained.

  Examples of monomers copolymerizable with vinyl acetate include ethylene; propylene; vinyl esters other than vinyl acetate, such as vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl laurate, vinyl isononanoate, vinyl versatate, and the like. Vinyl halides such as vinyl chloride and vinyl bromide; aromatic vinyl such as styrene; 2-ethylhexyl (meth) acrylate, n-butyl (meth) acrylate, ethyl (meth) acrylate, methyl (meth) acrylate, 2 -Α, β-unsaturated carboxylic acid esters such as hydroxyethyl (meth) acrylate, glycidyl (meth) acrylate, maleic acid ester, crotonic acid ester, itaconic acid ester; (meth) acrylic acid, crotonic acid, maleic acid, itaconic Α, β-unsaturation such as acid Carboxylic acid; acrylamide, N- methylol acrylamide, acrylamide, such as N- butoxymethyl acrylamide; acid allyl, vinyl sulfonic acid, triallyl cyanurate, triallyl isocyanurate, diallyl phthalate.

  Among these, polymers having structural units derived from vinyl acetate and ethylene as essential components (hereinafter sometimes referred to as ethylene / vinyl acetate copolymers) are preferably used, and in particular, structures derived from vinyl acetate and ethylene. A polymer consisting only of units is preferred.

In the production method of the present invention, first, a crude product of an aqueous emulsion is prepared by emulsion polymerization in an aqueous solution containing the monomer and an emulsifier. When the vinyl acetate copolymer contains a structural unit derived from a gaseous monomer such as ethylene, an aqueous solution containing an emulsifier and a liquid monomer such as vinyl acetate is used under a high pressure, etc. What is necessary is just to superpose | polymerize, making a gaseous monomer contact.
Examples of the emulsifier include protective colloids such as partially saponified polyvinyl alcohol, fully saponified polyvinyl alcohol, hydroxyethyl cellulose, methyl cellulose, and 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 salt, alkyl sulfosuccinate salt, alkyl diphenyl ether disulfonate salt, polyoxyethylene Anionic surfactants such as alkyl sulfates and polyoxyethylene alkyl phosphates It is below.
As the emulsifier, an emulsifier containing a protective colloid is preferably used, and partially saponified polyvinyl alcohol and completely saponified polyvinyl alcohol are particularly preferable.

Emulsion polymerization usually involves oxidizing agents such as hydrogen peroxide, ammonium persulfate, sodium persulfate, t-butyl hydroperoxide, sodium aldehyde bisulfite (commonly referred to as Rongalite), tartaric acid and / or its salts, ascorbic acids, erythorbic acids A redox catalyst in combination with a reducing agent such as is used. For the redox catalyst, a method in which a salt of a transition metal is further added is recommended.
Here, examples of the transition metal salt include chlorides such as iron, copper, cobalt, titanium, nickel, chromium, zinc, manganese, vanadium, molybdenum, and cerium, and sulfates. Of these, ferrous chloride, ferrous sulfate, copper sulfate and the like are preferably used.

  As a specific emulsion polymerization method, hydrogen peroxide as an oxidizing agent and sodium aldehyde bisulfite as a reducing agent are described in JP-A-2-289640. Ammonium persulfate as an oxidizing agent and aldehyde as a reducing agent The case of using sodium bisulfite is described in Japanese Patent Publication No. 58-8409. The case where hydrogen peroxide is used as an oxidizing agent, tartaric acid and / or a salt thereof as a reducing agent, and a salt is further used as a transition metal is described in Patent Documents 1 and 2, and hydrogen peroxide as an oxidizing agent and ascorbine as a reducing agent. Patent Document 3 describes a case where acids and / or erythorbic acids are used and a salt is used as a transition metal. Among them, a method using a redox catalyst of hydrogen peroxide-ascorbic acid and / or erythorbic acid, hydrogen peroxide-tartaric acid and / or a salt thereof is preferable because formalin is not generated from the obtained aqueous emulsion. -A method using a redox catalyst of ascorbic acid and / or erythorbic acid and a salt as a transition metal is preferable because coloring tends to be further reduced.

In the emulsion polymerization, the conversion rate of vinyl acetate is usually reacted to about 95% or more. If it is 95% or more, the stirring time after emulsion polymerization described later tends to be reduced, which is preferable.
Here, the conversion rate of vinyl acetate is calculated by the following formula.
(Conversion rate) = [1-{(Remaining amount of vinyl acetate) / (Amount of vinyl acetate used)}] × 100
(In the formula, the residual amount of vinyl acetate is the amount (weight) of vinyl acetate contained in the aqueous emulsion after completion of emulsion polymerization, and the amount of vinyl acetate used is the amount of vinyl acetate used in emulsion polymerization. Represents.)
In order to improve the conversion rate in emulsion polymerization, further addition of the redox catalyst after the conversion rate reaches 95% or more may cause the aqueous emulsion to be colored, or the storage stability such as viscosity and pH may be deteriorated. It is not preferable.

  After obtaining an aqueous emulsion containing an ethylene / vinyl acetate copolymer obtained by emulsion polymerization, vinyl acetate and other vinyl esters, and (meth) acrylic acid esters such as methyl (meth) acrylate An aqueous emulsion containing a seed polymer obtained by emulsion polymerization of vinyl halide such as vinyl chloride or aromatic vinyl such as styrene may be used as a crude product.

  As an aqueous emulsion containing a vinyl acetate polymer used as a crude product, a commercially available aqueous emulsion may be used as it is. As an aqueous emulsion of a vinyl acetate homopolymer, for example, Shinko Bond series (( Oshika Co., Ltd.), Bond CH series (registered trademark, manufactured by Konishi Co., Ltd.), Polyzol series (registered trademark, manufactured by Showa Polymer Co., Ltd.); ethylene-vinyl acetate copolymer-containing aqueous emulsion For example, Sumikaflex series (registered trademark, manufactured by Sumitomo Chemical Co., Ltd.), Airflex series (registered trademark, manufactured by Air and Products), Panflex series (registered trademark, manufactured by Kuraray Co., Ltd.), Denka EVA tex series (Registered trademark, manufactured by Denki Kagaku Kogyo Co., Ltd.), Polysol EVA series (Registered) Trademark, manufactured by Showa Polymer Co., Ltd.).

The production method of the present invention is a method for producing a purified aqueous emulsion by stirring the crude product thus obtained at a reduced pressure of 0.04 MPa (300 mmHg) or less at 45 to 65 ° C.
If the degree of vacuum is low, vinyl acetate and aldehydes are distilled off even if the temperature is low, and coloring is also reduced, but water is remarkably distilled off from the aqueous emulsion. Therefore, preferably 0.016 to 0.04 MPa ( 120-300 mmHg).

  In order to sufficiently reduce vinyl acetate and aldehydes in the purified aqueous emulsion, when the degree of vacuum is stirred at a reduced pressure of about 0.016 to 0.027 MPa (about 120 to 200 mmHg), When the aqueous emulsion is stirred at a temperature of about 45 to 55 ° C. and is at a relatively high degree of vacuum such as about 0.027 to 0.04 MPa (about 200 to 300 mmHg), the aqueous emulsion is usually about 55 to 65 ° C. At a temperature of

The stirring time varies depending on the shape and capacity of the stirring tank, the type, amount, viscosity, and remaining amount of vinyl acetate of the aqueous emulsion containing the vinyl acetate polymer. For example, if the laboratory level is about 1 L, If it is stirred for 5 to 60 minutes, vinyl acetate and aldehydes tend to be distilled off sufficiently. In the case of an industrial stirring tank of about 1 to 10 m ³ , if it is stirred for about 30 to 90 minutes, it is sufficiently vinyl acetate. And aldehydes tend to be reduced.

The stirring blades only need to be able to stir, and examples thereof include anchor blades, fiddler blades, paddle blades, and twin star blades.
As for the stirring state, it is preferable because the gas-liquid interface is renewed if vigorously stirred, but since an aqueous emulsion may adhere to the upper part of the stirring tank, there is no problem in manufacturing from the manufacturing conditions such as the stirring tank. In addition, the stirring state may be determined as appropriate.

Next, the present invention will be described specifically by way of examples. The obtained aqueous emulsion was evaluated as follows.
(1) Residual vinyl acetate monomer Measurement was performed according to the method of JIS K 6828.
(2) Acetaldehyde content
5 g of the emulsion was collected in a 250 ml polypropylene bottle, sealed, heated in a 40 ° C. oven for 3 hours, and then measured using gas detector tubes (No. 92M and No. 92, Gastec Co., Ltd.).
(3) Film heat-resistant discoloration
After coating and drying the emulsion to a thickness of 0.5 mm on a PET film, it was heat-treated in a 200 ° C. oven for a predetermined time, and this heat-treated sample film was subjected to a yellowness test by a reflection method (JIS K7103) and a hunter whiteness meter The degree of yellowing (YI) was measured using (CM-8P type, Murakami Color Research Laboratory Co., Ltd.).

Example 1
<Production Example 1 of Crude Product>
In a pressure vessel, 170 parts by weight of water in advance, 190 parts by weight of vinyl acetate, polyvinyl alcohol “Poval 217” (manufactured by Kuraray Co., Ltd., saponification degree 88 mol%, average polymerization degree 1700), 2 parts by weight, “Poval 205” (manufactured by Kuraray Co., Ltd.) A solution in which 7 parts by weight of saponification degree 88 mol%, average polymerization degree 500), 7 parts by weight of ferrous sulfate heptahydrate and 0.4 parts by weight of acetic acid were dissolved was introduced. 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, 0.3 parts by weight of hydrogen peroxide and 0.6 parts by weight of sodium erythorbate were diluted with water and added dropwise over 4 hours. During the polymerization, the temperature in the reaction vessel was kept at 60 ° C. by controlling the temperature of the jacket, and stirred until the vinyl acetate concentration in the crude product was 2% by weight or less (conversion rate: 96%). A crude product was obtained.

<Production Example 1 of Purified Aqueous Emulsion>
Next, the crude product was stirred under reduced pressure at 60 ° C. to 0.02 MPa (150 mmHg) to remove ethylene gas, and then stirred for 60 minutes at the reduced pressure, and then taken out. A purified aqueous emulsion was obtained containing an ethylene-vinyl acetate copolymer with 18% by weight of structural units derived from ethylene and 82% by weight of structural units derived from vinyl acetate. The non-volatile content of the aqueous emulsion was 55% and the viscosity was 1200 mPa · s. Table 1 shows the results of the residual vinyl acetate monomer, the amount of acetaldehyde contained, and the film heat discoloration resistance of this emulsion.

(Example 2: Production Example 2 of Purified Aqueous Emulsion)
<Production Example 2 of Purified Aqueous Emulsion>
A crude product having a vinyl acetate concentration of 2% by weight or less (conversion rate of 96%) obtained in the same manner as in <Production Example 1 of Crude Product> was measured at 50 ° C. at a reduced pressure of 0.02 MPa (150 mmHg). A purified aqueous emulsion was obtained in the same manner as in Example 1 except for stirring for 60 minutes. The results are shown in Table 1.

(Example 3: Production Example 3 of Purified Aqueous Emulsion)
A crude product of an aqueous emulsion having a vinyl acetate concentration of 2% by weight or less (conversion rate of 96%) obtained in the same manner as in <Production Example 1 of Crude Product> was applied at a reduced pressure of 0.035 MPa (260 mmHg). A purified aqueous emulsion was obtained in the same manner as in Example 1 except that stirring was performed at 60 ° C. for 30 minutes. The results are shown in Table 1.

Example 4
<Production Example 2 of Crude Product>
In a pressure vessel, 130 parts by weight of water, 150 parts by weight of vinyl acetate, polyvinyl alcohol “Poval 217” (manufactured by Kuraray Co., Ltd., saponification degree 88 mol%, average polymerization degree 1700), 2 parts by weight, “Poval 205” (manufactured by Kuraray Co., Ltd.) A solution in which 10 parts by weight of saponification degree of 88 mol%, average polymerization degree of 500), 0.005 part by weight of ferrous sulfate heptahydrate and 0.4 part by weight of acetic acid were introduced. 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 with ethylene to 6.0 MPa. Next, 0.3 parts by weight of hydrogen peroxide and 0.8 parts by weight of sodium erythorbate were diluted with water and added dropwise over 7 hours. During the polymerization, the temperature in the reaction vessel was kept at 60 ° C. by controlling the temperature of the jacket, and the mixture was stirred until the vinyl acetate concentration in the crude product was 2% by weight or less to obtain a crude product of an aqueous emulsion.

<Production Example 4 of Aqueous Emulsion>
Next, the crude product was stirred under reduced pressure at 60 ° C. to 0.02 MPa (150 mmHg) to remove ethylene gas, and then stirred for 60 minutes at the reduced pressure, and then taken out. An aqueous emulsion containing an ethylene-vinyl acetate copolymer having 30% by weight of structural units derived from ethylene and 70% by weight of structural units derived from vinyl acetate was obtained. The non-volatile content of the aqueous emulsion was 55% and the viscosity was 1000 mPa · s. The emulsion was measured in the same manner as in Example 1, and the results are shown in Table 1.

(Comparative Example 1)
In the same manner as in Example 1, after stirring the vinyl acetate to 2% by weight or less (conversion rate of 96%) to obtain a crude product of an aqueous emulsion, the pressure was reduced to 25 ° C. and 0.02 MPa (150 mmHg) and cooled. The ethylene gas was removed. Subsequently, an aqueous solution obtained by diluting 0.1 part by weight of hydrogen peroxide and 0.1 part by weight of sodium erythorbate was added, and the mixture was stirred for 60 minutes to obtain a structural unit derived from ethylene and a structural unit derived from vinyl acetate. An aqueous emulsion containing 82% by weight of ethylene-vinyl acetate copolymer was obtained. The non-volatile content of the aqueous emulsion was 54.5% and the viscosity was 1100 mPa · s. Table 1 shows the results of the residual vinyl acetate monomer, the amount of acetaldehyde contained, and the film heat discoloration resistance of this emulsion.

(Comparative Example 2)
In the same manner as in Example 4, after stirring the vinyl acetate to 2% by weight or less (conversion rate of 96%) to obtain a crude product of an aqueous emulsion, the pressure was reduced to 25 ° C. and 0.02 MPa (150 mmHg), followed by cooling. The ethylene gas was removed. Subsequently, 0.25 parts by weight of hydrogen peroxide, 0.15 parts by weight of sodium erythorbate and 0.18 parts by weight of tertiary-butyl hydroperoxide were added, and the mixture was stirred for 60 minutes, and the structural unit derived from ethylene 30 An aqueous emulsion containing an ethylene-vinyl acetate copolymer having a weight unit of 70% by weight and a structural unit derived from vinyl acetate was obtained. The non-volatile content of the aqueous emulsion was 54.5% and the viscosity was 850 mPa · s. Table 1 shows the results of the residual vinyl acetate monomer, the amount of acetaldehyde contained, and the film heat discoloration resistance of this emulsion.

(Comparative Examples 3-4)
After removing ethylene gas from the crude product of the aqueous emulsion obtained in the same manner as in Example 4 under the degassing conditions described in Table 1, the catalyst amount described in Table 1 was further added in the same manner as in Comparative Example 2. The results are summarized in Table 1.

(Comparative Example 5)
The crude product of the aqueous emulsion obtained in the same manner as in Example 4 was decompressed and cooled to 25 ° C. and 0.02 MPa (150 mmHg) to remove ethylene gas, and then stirred for 60 minutes to take out the aqueous emulsion. The results are shown in Table 1.

  The cured product obtained by drying the purified aqueous emulsion obtained by the method of the present invention does not color even at high temperatures, and does not color for a long time at room temperature. It can be used for various adhesives for paper, woodworking and plastics, various binders for impregnated paper and non-woven products, admixtures, splicing materials, paints, paper processing and textile processing, wallpaper and the like.

Claims (1)

A crude product of an aqueous emulsion containing a polymer containing a structural unit derived from ethylene and a structural unit derived from vinyl acetate , hydrogen peroxide as an oxidizing agent, and erythorbic acid and / or ascorbic acid as a reducing agent And, after preparing by emulsion polymerization using a transition metal salt , the crude product is stirred at 45 to 65 ° C. for 5 to 90 minutes at a reduced pressure of 0.016 to 0.04 MPa. A method for producing a purified aqueous emulsion. However, hydrogen peroxide, sodium erythorbate and tertiary butyl hydroperoxide are not added after emulsion polymerization.