JP2018083856A - Production method of aqueous dispersion of(meth)acrylic copolymer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To combine an improvement of adhesive strength due to formation of a crosslinking structure of a (meth)acrylic copolymer adhesive produced with a partially saponified polyvinyl acetate emulsifier and an improvement in the viscosity stability.SOLUTION: When a monomer mixture containing at least an aromatic vinyl monomer and a (meth)acrylic acid ester-based monomer is emulsion polymerized with a radical polymerization initiator under the presence of a partially-saponified polyvinyl acetate-based dispersant, the ratio of monomers having an active hydrogen-containing group in the monomer mixture is set to 2% by weight or lower, at the stage where a predetermined polymerization reaction temperature is reached, the monomer mixture is emulsified with a dispersion stabilizer and water and added into a reaction vessel as an emulsified dispersion.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing an aqueous dispersion of a (meth) acrylic copolymer.

It is known that (meth) acrylic copolymers such as styrene-acrylic polymers are used as wood adhesives (Patent Document 1, etc.). Various improvements of adhesive strength, pot life and the like have been studied for the adhesive made of this (meth) acrylic copolymer.
In the present specification, “(meth) acryl” means “acryl and / or methacryl”.

  As a method for increasing the adhesive strength, a method using a monomer having a functional group such as a hydroxyl group or a carboxyl group is known. In addition, a method using partially saponified polyvinyl acetate as an emulsifier in the production of a (meth) acrylic copolymer has also been proposed (Patent Documents 2, 3, etc.).

Japanese Patent No. 4067756 JP 2004-3000294 A Japanese Patent No. 5599146

However, in each of the above patent documents, emulsion polymerization is started in a state where at least a part of the partially saponified polyvinyl acetate as a dispersion stabilizer is charged in the reaction vessel.
At this time, the monomer component may be graft-polymerized onto the partially saponified polyvinyl acetate. For this reason, in the case of using a curing agent in the obtained polymer aqueous dispersion and using it for adhesives, etc. The viscosity tends to change with time, and the pot life tends to decrease.

  Therefore, the present invention improves the adhesive strength by forming a crosslinked structure when a (meth) acrylic copolymer produced using partially saponified polyvinyl acetate as an emulsifier is used as an adhesive, and contains a curing agent. The purpose is to achieve both improvement in viscosity stability later, that is, improvement in usable time (pot life).

The gist of the present invention resides in the following [1] to [9].
[1] A monomer mixture containing at least an aromatic vinyl monomer and a (meth) acrylic acid ester monomer in the presence of a dispersion stabilizer mainly composed of partially saponified polyvinyl acetate, In emulsion polymerization using a radical polymerization initiator, the ratio of the monomer having an active hydrogen-containing group in the monomer mixture is 2% by weight or less, and the liquid temperature in the reaction vessel in which the emulsion polymerization is performed is predetermined. When the polymerization reaction temperature is reached, at least a part of the monomer mixture is added into the reaction vessel as an emulsified dispersion emulsified using the dispersion stabilizer and water (meta ) A process for producing an acrylic copolymer aqueous dispersion.

[2] The aqueous (meth) acrylic copolymer dispersion according to [1], wherein the alcohol residue of the (meth) acrylic acid ester monomer has 1 to 12 carbon atoms. Manufacturing method.
[3] The method for producing an aqueous dispersion of a (meth) acrylic copolymer according to [1] or [2], wherein the monomer mixture further contains a vinyl ester monomer.
[4] The (meth) acrylic copolymer of any one of [1] to [3], wherein the ratio of the monomer having an active hydrogen-containing group in the monomer mixture is 1% by weight or less. A method for producing a combined aqueous dispersion.
[5] The aromatic vinyl monomer is at least one selected from the group consisting of styrene, vinyltoluene, and hydroxystyrene, according to any one of [1] to [4] A method for producing an aqueous dispersion of a (meth) acrylic copolymer.

[6] The viscosity average molecular weight of the partially saponified polyvinyl acetate is 3 to 50 mpa · s in a 4% aqueous solution (20 ° C.), [1] to [5], (Meth) acrylic copolymer aqueous dispersion manufacturing method.
[7] The (meth) acrylic copolymer according to any one of [1] to [6], wherein the saponification degree of the partially saponified polyvinyl acetate is 70 mol% to 90 mol%. A method for producing an aqueous polymer dispersion.
[8] The (meth) acrylic copolymer according to any one of [1] to [7], wherein the monomer mixture is added into the reaction vessel continuously or sequentially. A method for producing an aqueous dispersion.

[9] The glass transition temperature (Tg) calculated from the FOX formula of the obtained (meth) acrylic copolymer is from −10 ° C. to 30 ° C. [1] to [8] ] The manufacturing method of the (meth) acrylic-type copolymer aqueous dispersion liquid of any one of.

  In the present invention, when the temperature of the liquid in the reaction vessel reaches a predetermined polymerization reaction temperature, that is, when the chain growth of the polymer continuously occurs due to decomposition of the radical polymerization initiator, By adding at least a part of the mixture into the reaction vessel as an emulsified dispersion emulsified using a dispersion stabilizer mainly composed of partially saponified polyvinyl acetate and water, the partially saponified poly which is an emulsifying dispersant is added. Grafting of the above monomer component onto vinyl acetate can be suppressed, and the grafting rate can be reduced. Thereby, it became possible to improve the viscosity stability after compounding the curing agent and lengthen the pot life.

  In addition, the copolymer comprising the aromatic vinyl monomer and the (meth) acrylic monomer obtained by the production method of the present invention as main raw material components is less susceptible to a change in viscosity over time and is sufficient. Since it exhibits excellent adhesive strength and excellent shear strength, it exhibits good performance as an adhesive during and after construction.

The present invention will be described in detail below.
The method for producing an aqueous dispersion of a (meth) acrylic copolymer according to the present invention comprises a monomer mixture containing at least an aromatic vinyl monomer and a (meth) acrylic acid ester monomer. (Meth) acrylic copolymer aqueous solution by using a specific monomer addition method when emulsion polymerization is performed using a radical polymerization initiator in the presence of a dispersion stabilizer mainly composed of a modified polyvinyl acetate. A method for producing a dispersion.

  The aromatic vinyl monomer is a vinyl compound having an aromatic ring, and examples thereof include styrene, vinyl toluene, and hydroxystyrene.

  The (meth) acrylic acid ester monomer means an ester compound of (meth) acrylic acid, and examples thereof include (meth) acrylic acid alkyl ester and (meth) acrylic acid alkoxyalkyl ester. Even if it uses, the mixture of those 2 or more types may be used.

  Examples of the (meth) acrylic acid alkyl ester include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, (meth ) Cyclohexyl acrylate, benzyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, isobornyl (meth) acrylate, and the like.

  As said (meth) acrylic-acid alkoxyalkyl ester, (meth) acrylic-acid 2-methoxyethyl, (meth) acrylic-acid 2-ethoxyethyl, (meth) acrylic-acid 2-butoxyethyl, etc. are mention | raise | lifted.

  1-12 are preferable and, as for the carbon atom number of the alcohol residue of said (meth) acrylic acid ester type monomer, 1-8 are more preferable. When the number of carbon atoms is larger than 12, it is difficult to obtain a stable emulsified dispersion and easy to separate when emulsifying with a dispersion stabilizer mainly composed of partially saponified polyvinyl acetate and water. May occur.

  The above monomer mixture may further contain a vinyl ester monomer. Examples of the vinyl ester monomer include vinyl acetate, vinyl propionate, and vinyl butyrate.

  Further, a vinyl halide compound, a polyfunctional unsaturated monomer, other unsaturated monomers, and the like may be contained. Examples of the vinyl halide compound include vinyl chloride, vinylidene chloride, vinyl bromide, and vinyl fluoride. Examples of the polyfunctional unsaturated monomer include divinylbenzene, divinylnaphthalene, and derivatives thereof. Examples include aromatic divinyl compounds, polyallyl carboxylic acid allyl esters such as diallyl phthalate and triallyl isocyanurate. Furthermore, examples of the other unsaturated monomer include N, N-divinylaniline, divinyl ether, divinyl sulfide, divinyl sulfone, and compounds having three or more vinyl groups.

  The blending ratio of the monomer mixture, that is, the content of the aromatic vinyl monomer and the (meth) acrylic acid ester monomer in 100 parts by weight of the monomer mixture, The weight is preferably 10 parts by weight or more, more preferably 20 parts by weight or more. When the amount is less than 10 parts by weight, there may be a problem that boiling resistance is lowered. On the other hand, the upper limit of the content of the aromatic vinyl monomer is preferably 80 parts by weight, and more preferably 70 parts by weight. When the amount is more than 80 parts by weight, there may be a problem that the normal strength is lowered.

  When the dispersion stabilizer is dispersed in water, a water-soluble organic solvent such as methanol or ethanol, or an aqueous dispersion medium that is a mixture of these, the emulsified state is changed. In the present invention, a dispersion stabilizer mainly composed of partially saponified polyvinyl acetate is used. By using partially saponified polyvinyl acetate as the main component, as described later, by dropping it into a reaction vessel under predetermined conditions, the viscosity stability after blending the curing agent is improved and the pot life during use is lengthened. You can demonstrate the feature of doing.

  The viscosity average molecular weight of the partially saponified polyvinyl acetate is preferably 3 mpa · s or more, preferably 3.5 mpa · s or more in a 4% aqueous solution (20 ° C.). If it is less than 3 mpa · s, the average molecular weight of the dispersion stabilizer is lowered, so that the protective power is lowered and it is difficult to obtain a uniform emulsified dispersion. On the other hand, the upper limit of the viscosity average molecular weight is preferably 50 mpa · s, and preferably 30 mpa · s. If it is greater than 50 mpa · s, the average molecular weight of the dispersion stabilizer becomes too high, and the viscosity of the emulsified dispersion becomes high, which may make it difficult to handle.

  The saponification degree of the partially saponified polyvinyl acetate is preferably 70 mol% or more, and preferably 80 mol% or more. If it is lower than 70 mol%, the solubility in water will be extremely low, and a good dispersion may not be obtained. On the other hand, the upper limit of the degree of saponification is preferably 90 mol%, and preferably 88 mol%. If it is higher than 90 mol%, it may be difficult to emulsify and disperse an aromatic vinyl monomer having high hydrophobicity such as styrene.

As the dispersion stabilizer, in addition to partially saponified polyvinyl acetate, oil-soluble partially saponified polyvinyl acetate having a low polymerization degree and low saponification degree and a general-purpose low molecular surfactant can be used as an auxiliary. .
When such a dispersion stabilizer is used in combination, the partially saponified polyvinyl acetate used as the main agent in the mixture is preferably contained in an amount of 70% by weight or more, and more preferably 85% by weight or more. If the amount is less than 70% by weight, it may be difficult to sufficiently exert the effect of the present invention by using predetermined partially saponified polyvinyl acetate as the main agent.

  As said radical polymerization initiator, the polymerization initiator used by normal radical emulsion polymerization can be used without specifically limiting. Examples of polymerization initiators include persulfates such as ammonium persulfate, potassium persulfate, sodium persulfate, 2,2′-azobisisobutyronitrile, 2,2′-azobis (2,4-dimethylvaleronitrile). ) And other radical polymerization initiators such as hydrogen peroxide, hydroperoxides such as t-butyl hydroperoxide, peroxides such as benzoyl peroxide, lauroyl peroxide, and the like. Or a mixture of two or more of them may be used. These radical polymerization initiators can be used as a redox polymerization initiator in combination with a reducing agent such as sodium sulfite, sodium hydrogen sulfite, sodium thiosulfate, tartaric acid, L-ascorbic acid.

  The polymerization temperature of the emulsion polymerization can be adjusted according to the type and usage of the polymerization initiator and the target molecular weight of the copolymer to be produced, but is usually about 40 to 100 ° C., and the reaction time is usually about 2 to 16 hours. preferable.

(Production of aqueous dispersion of (meth) acrylic copolymer)
Next, a method for producing an aqueous (meth) acrylic copolymer dispersion (hereinafter sometimes simply referred to as “emulsion”) will be described.
First, an aqueous dispersion in which a part of the aqueous medium or the monomer mixture is dispersed in the aqueous medium and a dispersion stabilizer that does not contain partially saponified polyvinyl acetate is charged into a reaction vessel that performs emulsion polymerization. . Further, a part of the radical polymerization initiator is charged.

  When a part of the monomer mixture is charged into the reaction vessel, the charged amount is preferably 10% by weight or less of the whole monomer mixture, and preferably 5% by weight or less. When the amount is more than 10% by weight, there may be a problem that the generation of aggregates becomes remarkable or the viscosity of the obtained emulsion becomes high. In addition, it is not essential to charge the monomer mixture in the reaction vessel in advance, and the lower limit of the charged amount is 0% by weight.

  In addition, when a part of the radical polymerization initiator is charged into the reaction vessel, the charging amount is preferably 50% by weight or less, and preferably 30% by weight or less of the whole radical polymerization initiator. If it is more than 50% by weight, the reaction controllability may deteriorate. In addition, it is not essential to charge the radical polymerization initiator in the reaction vessel in advance, and the lower limit of the charged amount is 0% by weight.

Next, when the reaction vessel is heated to reach a predetermined polymerization reaction temperature, at least a part of the monomer mixture, that is, the whole of the monomer mixture or the remainder excluding the amount charged in the reaction vessel is It is added into the reaction vessel as an emulsified dispersion emulsified using a dispersion stabilizer mainly composed of partially saponified polyvinyl acetate and water. Further, at least a part of the radical polymerization initiator, that is, the rest of the radical polymerization initiator other than the whole charged in the reaction vessel is added to the reaction vessel.
Examples of the addition method to the reaction vessel include a method of continuously adding to the reaction vessel and a method of sequentially adding to the reaction vessel or a batch addition method. It is preferable to add continuously from the viewpoint of the properties and uniformity of the obtained copolymer.

  The above-mentioned “predetermined polymerization reaction temperature” refers to the stage where the liquid temperature in the reaction vessel reaches the temperature at which the polymerization reaction occurs, that is, the chain growth of the polymer is continuously caused by the decomposition of the radical polymerization initiator. This is the temperature at which you get up. Specifically, the temperature is determined by the decomposition temperature of the radical polymerization initiator and the molecular weight of the desired polymer.

  According to this method, the partially saponified polyvinyl acetate, which is the main component of the dispersion stabilizer, is added together with the monomer mixture in a state where the radical polymerization initiator is decomposed to generate radicals. Radical polymerization of the monomer mixture occurs preferentially, and graft polymerization to partially saponified polyvinyl acetate hardly occurs, and as a result, grafting to partially saponified polyvinyl acetate can be suppressed.

  When the (meth) acrylic copolymer produced by the above method contains a large number of active hydrogen-containing groups such as carboxyl groups and hydroxyl groups, for example, a crosslinking reaction by mixing two liquids when a curing agent such as isocyanate is blended May gradually progress and viscosity stability may deteriorate. The ratio of the monomer having an active hydrogen-containing group is 2% by weight or less, preferably 1% by weight or less, particularly preferably 0.5% by weight or less.

  Such active hydrogen-containing monomers include carboxyl group-containing monomers such as (meth) acrylic acid, itaconic acid, crotonic acid, maleic acid and monoesters thereof, fumaric acid and monoesters thereof, and hydroxyethyl ( Examples thereof include hydroxyl group-containing monomers such as (meth) acrylate, 2-hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, ethylene glycol mono (meth) acrylate, and polyethylene glycol mono (meth) acrylate.

The glass transition temperature (Tg) of the (meth) acrylic copolymer produced by the above method is
It should be −10 ° C. or higher, preferably 0 ° C. or higher. When it is lower than −10 ° C., there may be a problem that the normal adhesive strength of the copolymer after curing is lowered. On the other hand, the upper limit of the glass transition temperature is preferably 30 ° C, and preferably 15 ° C. When the temperature is higher than 30 ° C., it is difficult to obtain a uniform coating film when used in a cold district or the like, and adhesion failure may occur.

The glass transition temperature (Tg) can be experimentally measured with a differential scanning calorimeter (DSC) or dilatometer using a copolymer. In the present invention, the homopolymer of the constituent monomer is used. When the glass transition temperature is known, Tg calculated from the type and composition ratio using the Fox equation is used.
Specifically, the monomers constituting the copolymer are M1, M2, M3... Mn, and the glass transition temperatures of the homopolymers obtained from the respective monomers are Tg1, Tg2, Tg3,. When Tgn and the molar fraction of the structural unit derived from each monomer in the copolymer are m1, m2, m3... Mn, the glass transition temperature Tg of the copolymer is as follows: It can be calculated from the equation (1) (Fox equation) shown.
1 / Tg = m1 / Tg1 + m2 / Tg2 + m3 / Tg3 +... Mn / Tgn (1)

  In addition, when the (meth) acrylic copolymer produced by the above method is blended at the following prescribed blending ratio, the viscosity change with time is η0 as the viscosity immediately after blending, and η60 as the viscosity for 60 minutes after blending. (Η60 / η0) is preferably 0.5 or more, and more preferably 1 or more. If it is less than 0.5, there may be a problem that adhesive strength does not develop. The upper limit of (η60 / η0) is preferably 3, and 2 is preferable. When the ratio is larger than 3, the viscosity increases in a short time, that is, the pot life (pot life) is shortened, which may cause a problem that the coating cannot be performed during long-time operation or construction in the line.

By the way, the blending ratio is as follows: 42 parts by weight of (meth) acrylic copolymer (converted to solid content, hereinafter the same), 29 parts by weight of partially saponified polyvinyl acetate (polymerization degree 1700, saponification degree 87-89%) , And 29 parts by weight of calcium carbonate (average particle size 2.1 μm), and then 15 parts by weight of an isocyanate curing agent (MDI).
A specific method for evaluating the above “change in viscosity with time” will be described in detail in the Examples section.

EXAMPLES Hereinafter, although this invention is demonstrated in detail using an Example, this invention is not limited by a following example, unless the summary is exceeded. In the examples, “parts” and “%” are based on weight.
First, the raw materials used and the evaluation method will be described.

(raw materials)
[Monomer]
・ SM: Asahi Kasei Chemicals Co., Ltd .: Styrene monomer ・ BA: Mitsubishi Chemical Co., Ltd .: butyl acrylate ・ HEMA ... Mitsubishi Gas Chemical Co., Ltd .: Hydroxyethyl methacrylate ・ 4HBA ... Osaka Organic Chemical Industry Co., Ltd. : Acrylic acid 4-hydroxybutyl AA ... Mitsubishi Chemical Corporation: Acrylic acid

[Dispersion stabilizer]
PVA: partially saponified polyvinyl acetate, saponification degree: about 88, polymerization degree: 300
Anion (anionic surfactant): Sanyo Chemical Industries, Ltd .: Eleminol ES-70
Nonion (nonionic surfactant) ... Sanyo Chemical Industries, Ltd .: Nonipol 200,

[Radical polymerization initiator]
・ Ammonium persulfate: Wako Pure Chemical Industries, Ltd .: Reagent

[Others]
・ Sodium acetate: Nippon Synthetic Chemical Industry Co., Ltd.

(Evaluation method)
[(Meth) acrylic copolymer aqueous dispersion]
(1) Nonvolatile content Approximately 1 g of the polymer aqueous dispersion was precisely weighed, then dried in a hot air circulating dryer at 105 ° C. for 3 hours, then allowed to cool in a desiccator, and its weight was measured. Nonvolatile content was calculated.
Nonvolatile content (%) = (weight of sample after drying / weight of sample before drying) × 100
(2) Viscosity Using a Brookfield viscometer (manufactured by Tokimec Co., Ltd., type B viscometer, type BM), the viscosity was measured at a rotor rotational speed of 60 rpm and 23 ° C.

[Test method for wood (glulam) adhesive]
(1) Main agent blending The (meth) acrylic copolymer aqueous dispersion (emulsion) produced in the examples or comparative examples has a blending amount of (meth) acrylic copolymer of 42 parts by weight (in terms of solid content, The same applies hereinafter), and 29 parts by weight of partially saponified polyvinyl acetate (manufactured by Kuraray Co., Ltd .: PVA-217, degree of polymerization 1700, degree of saponification 87-89%) was added to this under stirring. And stirred for 15 minutes. Next, 29 parts by weight of calcium carbonate (manufactured by Nitto Flour Industry Co., Ltd .: NS-100, average particle size 2.1 μm) was added with stirring, and stirring was further performed for 15 minutes to prepare a main agent.

(2) Compounding of curing agent 15 parts by weight of isocyanate curing agent (MDI (diphenylmethane diisocyanate), manufactured by Sumitomo Chemical Co., Ltd .: Sumidur 44V-20 (trade name)) is mixed with 100 parts by weight of the above main agent. Stir for 1 minute.

(3) Viscosity change with time When the obtained (meth) acrylic copolymer aqueous dispersion was blended at the following blending ratio, the viscosity change with time was viscosity (η0) immediately after blending, 60 at 25 ° C. after blending. The viscosity (η60) when a minute elapsed was measured, and the viscosity change rate (η60 / η0) was calculated. The viscosity change ratio is
0.5 ≦ η60 / η0 ≦ 3
Those satisfying the conditions were evaluated as having good viscosity stability.
Viscosity was measured using a Brookfield viscometer (manufactured by Tokimec Co., Ltd., B type viscometer, type B8H, No. 6 rotor) at a rotor rotational speed of 10 rpm.
・ Combination ratio:
(Meth) acrylic copolymer / partially saponified polyvinyl acetate (polymerization degree 1700, saponification degree 87-89%) / calcium carbonate (average particle size 2.1 μm) / isocyanate curing agent (MDI) = 42 / 29/29/15 (weight ratio, solid content conversion).

(4) Foaming Immediately after the curing agent was blended (mixed for 1 minute), about 30 ml was transferred to a 100 ml sample bottle, and the height of the liquid level was measured.
Thereafter, it was left in an atmosphere at 25 ° C., and the height of the liquid level was measured after 15 minutes, 30 minutes and 60 minutes. And the expansion ratio was calculated | required using the following formula.
Foaming ratio (%) = liquid level height after a predetermined time / initial liquid level height × 100

(5) Initial adhesive strength Using a birch material (mass) specified in JISK6848-4, the above curing agent blended product was applied at a coating amount of 270 g / m ² , and the coated surfaces were bonded together to 8 kgf / It was clamped under a load of cm ^2. Then, the pressure was released after 10 minutes, 20 minutes, and 30 minutes, and the split adhesion strength was measured. The split adhesive strength was in accordance with JIS K6853.

(6) Shear strength The sample clamped in the same procedure as the above initial adhesive strength measurement was kept at 23 ° C. for 16 hours. Next, after decompression, the film was cured for 2 days, and then the following evaluation was performed.
1) Normal state: The compression shear strength was measured according to JIS K 6852 under the condition of 23 ° C.
2) Repeated boiling: After immersing the test piece in boiling water for 4 hours, it was dried at 60 ° C. for 20 hours and again immersed in boiling water for 4 hours. Then, after being immersed in room temperature water for 15 minutes or more, the compressive shear strength was measured according to JIS K6852 in a wet state.

(Examples 1 to 5, Comparative Examples 1 and 2)
[Pre-emulsion adjustment]
To the flask, 4.9 parts by weight of the dispersion stabilizer shown in Table 1 and 46 parts by weight of water were added and dissolved sufficiently at 80 ° C. for 1 hour, and then cooled to room temperature. Next, various monomers shown in Table 1 were added in the amounts shown in the same table, and the mixture was stirred and emulsified with a turbine blade for 30 minutes to prepare a pre-emulsion solution.
The obtained pre-emulsified liquid is referred to as “pre-EM” in Table 1. The dispersion stabilizer used in Comparative Example 1 is a mixture of 1 part by weight of an anion (anionic surfactant) and 0.2 part by weight of a nonion (nonionic surfactant).

[Production of aqueous synthetic resin emulsion]
Add 49 parts by weight of water and 1.0 part by weight of sodium acetate to a separable flask equipped with a paddle type stirring blade, reflux condenser, dropping funnel and thermometer, and raise the temperature in the flask to 80 ° C. while stirring at 150 rpm. Warm up. Subsequently, 2.8 parts by weight of 10% aqueous solution of ammonium persulfate was added to the flask, and then 148 parts by weight of the pre-emulsion prepared above and 4.7 parts by weight of 10% aqueous solution of ammonium persulfate were added from the dropping funnel for 4.5 hours. The polymerization reaction was carried out by dropping.
Subsequently, aging was performed at 80 ° C. for 2 hours, during which time 2.9 parts by weight of a 10% aqueous solution of ammonium persulfate was added in three portions to complete the reaction, cooled to room temperature, and (meth) acrylic copolymer aqueous solution A dispersion was obtained. Said each evaluation was performed about the obtained (meth) acrylic-type copolymer aqueous dispersion. The results are shown in Table 1.

(Comparative Examples 3 and 4) [Monomer dropping]
[Adjustment of monomer mixture]
Monomers were added to the flask in the types and amounts shown in Table 1, and stirred for 30 minutes with a turbine blade to prepare a monomer mixture.

[Production of aqueous synthetic resin emulsion]
Add 55 parts by weight of water and 4.9 parts by weight of a dispersion stabilizer to a separable flask equipped with a paddle type stirring blade, reflux condenser, dropping funnel, and thermometer, and stir at 80 ° C for 1 hour at 150 rpm. Then, 1.0 part by weight of sodium acetate was added. Subsequently, 2.8 parts by weight of a 10% aqueous solution of ammonium persulfate was added to the flask. Subsequently, 100 parts by weight of the monomer mixture prepared above and 4.7 parts by weight of a 10% aqueous solution of ammonium persulfate were added from the dropping funnel. The polymerization reaction was carried out dropwise over 5 hours.
Subsequently, aging was carried out at 80 ° C. for 2 hours, during which time 2.9 parts by weight of 10% aqueous solution of ammonium persulfate was added in three portions to complete the reaction, then cooled to room temperature, and (meth) acrylic copolymer A combined aqueous dispersion was obtained. Said each evaluation was performed about the obtained (meth) acrylic-type copolymer aqueous dispersion. The results are also shown in Table 1.
In Comparative Example 4, the initial polymerization is “Yes”. The emulsion polymerization was performed in the same manner as in Comparative Example 3 except that 1.5% by weight of the monomer mixture was added to the initial flask and the remaining 98.5% by weight was used as the dropping liquid. It means that.

Claims (9)

Starting radical polymerization of a monomer mixture containing at least an aromatic vinyl monomer and a (meth) acrylic acid ester monomer in the presence of a dispersion stabilizer mainly composed of partially saponified polyvinyl acetate In emulsion polymerization using an agent,
The ratio of the monomer having an active hydrogen-containing group in the monomer mixture is 2% by weight or less,
When the liquid temperature in the reaction vessel for carrying out the emulsion polymerization reaches a predetermined polymerization reaction temperature, at least a part of the monomer mixture is emulsified using the dispersion stabilizer and water as an emulsion dispersion. A method for producing an aqueous dispersion of a (meth) acrylic copolymer, which is added to a reaction vessel.   2. The method for producing an aqueous (meth) acrylic copolymer dispersion according to claim 1, wherein the alcohol residue of the (meth) acrylic acid ester monomer has 1 to 12 carbon atoms. .   The method for producing an aqueous (meth) acrylic copolymer dispersion according to claim 1 or 2, wherein the monomer mixture further contains a vinyl ester monomer.   The ratio of the monomer having an active hydrogen-containing group in the monomer mixture is 1% by weight or less. The (meth) acrylic copolymer aqueous dispersion according to any one of claims 1 to 3. Production method.   The (meth) acrylic system according to any one of claims 1 to 4, wherein the aromatic vinyl monomer is at least one selected from the group consisting of styrene, vinyltoluene and hydroxystyrene. A method for producing an aqueous copolymer dispersion.   The (meth) acryl according to any one of claims 1 to 5, wherein the partially saponified polyvinyl acetate has a viscosity average molecular weight of 3 to 50 mPa · s in a 4% aqueous solution (20 ° C). For producing a water-based copolymer aqueous dispersion.   The (meth) acrylic copolymer aqueous dispersion according to any one of claims 1 to 6, wherein the saponification degree of the partially saponified polyvinyl acetate is 70 mol% to 90 mol%. Manufacturing method.   The production of the aqueous (meth) acrylic copolymer dispersion according to any one of claims 1 to 7, wherein the monomer mixture is added continuously or sequentially into the reaction vessel. Method.   The glass transition temperature (Tg) calculated by the FOX formula of the obtained (meth) acrylic copolymer is -10 ° C or higher and 30 ° C or lower. The manufacturing method of the (meth) acrylic-type copolymer aqueous dispersion liquid of description to term.