JP2013107970A - Method for producing aqueous resin dispersion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an aqueous resin dispersion excellent in stability, even upon a large scale production, without viscosity increase in an emulsion and generation of a large amount of aggregates etc. when producing a polymer having a large amount of carboxyl groups useful for an alkali-soluble thickener etc. by emulsion polymerization.SOLUTION: A preemulsion is prepared by adding a liquid monomer mixture prepared in advance in an another container to an emulsifier aqueous solution and stirring the resulting material, and emulsion polymerization is carried out. Preferably, a preemulsion-preparing process and/or an emulsifier aqueous solution-preparing process is carried out within a temperature range of polymerization starting temperature±20°C.

Description

  The present invention relates to a method for producing a carboxyl group-containing aqueous resin dispersion suitably used for applications such as a thickener, and more specifically, a carboxyl group having high stability during production and suppressing the occurrence of aggregates and the like. The present invention relates to a method for producing a contained aqueous resin dispersion.

  Emulsions containing polymers with a high amount of carboxyl groups introduced have been widely used as alkali-soluble thickeners since the polymers are dissolved or swollen by adding alkali to form a highly viscous liquid. . This type of thickener is required to have excellent solubility when an alkali is added and a high viscosity after neutralization. Here, in general, a polymer having a high carboxyl group introduction amount is good in solubility when an alkali is added, and the viscosity after neutralization is high when the thickener polymer has a high molecular weight.

Such a polymer is generally produced by emulsion polymerization from the viewpoint of easily obtaining a polymer having a high molecular weight. However, in the case of emulsion polymerization of a monomer mixture containing a highly hydrophilic monomer such as a carboxyl group-containing monomer, the rate of polymerization reaction not only in the polymer particles but also in the continuous phase (aqueous phase) increases. However, there is a problem that the viscosity of the obtained emulsion is increased and a large amount of aggregates are generated.
For the above problems, there are cases where measures are taken to increase the stability of emulsion particles by increasing the amount of emulsifier used during polymerization, but the emulsifier remains in the final product such as a coating film. In some cases, problems such as water resistance and transparency of the coating film may occur. Also, foaming may be a problem during handling. In addition, there are cases where measures are taken on the polymerization conditions such as lowering the solid content during polymerization, but this is not preferable from the viewpoint of productivity.

  Under such a background, in Patent Document 1, when a highly hydrophilic alkali-soluble polymer aqueous dispersion is produced, a specific amount of a strong acid group-containing polymerizable monomer is added to the initial polymerization step of emulsion polymerization. It is disclosed that manufacturing stability is improved. In Patent Document 2, in addition to Patent Document 1, the use of a specific amount of chain transfer agent in the initial polymerization step increases the amount of water-soluble polymer that acts as a protective colloid, resulting in stability during emulsion polymerization. The effect is improved.

JP 2002-161103 A JP 2002-332303 A

  However, the methods described in Patent Documents 1 and 2 both have a strong acid group-containing monomer such as sulfonic acid as an essential component, and do not use a strong acid group-containing monomer as the monomer. Was not applicable. In addition, when an aqueous dispersion of a polymer into which a strong acid group has been introduced is added to another emulsion, aggregates may be generated by a shock due to the addition. Further, in Patent Document 2, since a considerable amount of chain transfer agent is used, it is not suitable for obtaining a polymer having a high molecular weight such as a thickener, and the range to be used is limited. .

  Furthermore, the inventors of the present invention, when producing an emulsion containing a polymer containing a large amount of carboxyl groups, can be stably produced on a small scale, but a large amount of agglomerates are generated depending on the lot during actual production. I encountered an unexpected problem that I could not secure enough sex.

As described above, the method for stably producing an emulsion containing a polymer having a high carboxyl group introduction amount is not yet satisfactory and improvements are desired.
The object of the present invention is to produce a polymer having a high carboxyl group introduction amount by emulsion polymerization, without causing thickening of emulsion obtained or large amount of aggregate generation even in large scale production, It is to provide a production method having excellent stability.

  As a result of intensive investigations in view of the above problems, the present inventors have surprisingly found that when preparing a pre-emulsion, a monomer mixture prepared in advance in a separate container is added to the emulsifier aqueous solution and stirred, thereby stabilizing the polymerization. The present invention has been completed.

The present invention is as follows.
1. A method for producing an aqueous resin dispersion obtained by emulsion polymerization of a monomer mixture containing 10 to 80% by mass of a carboxyl group-containing monomer in the presence of an emulsifier, wherein the emulsion polymerization comprises a pre-emulsion adjustment step and polymerization. Characterized in that, after the pre-emulsion is adjusted by adding and stirring the monomer mixture prepared in advance in a separate container in the pre-emulsion aqueous solution in the pre-emulsion adjustment step, the polymerization step is started. A method for producing an aqueous resin dispersion.
2. 2. The method for producing an aqueous resin dispersion according to 1 above, wherein the monomer mixture further contains 20 to 90% by mass of a (meth) acrylic acid ester having an alkyl group having 1 to 2 carbon atoms.
3. 3. The method for producing an aqueous resin dispersion as described in 1 or 2 above, wherein the pre-emulsion adjusting step is carried out at a temperature in the range of polymerization initiation temperature ± 20 ° C.
4). The said emulsifier contains a nonionic emulsifier, The manufacturing method of the aqueous resin dispersion in any one of said 1-3 characterized by the above-mentioned.
5. The aqueous resin dispersion obtained by the manufacturing method in any one of said 1-4.
6). 6. A thickener comprising the aqueous resin dispersion as described in 5 above.

  According to the method for producing an aqueous resin dispersion of the present invention, a polymer having a large amount of introduced carboxyl groups is stabilized by emulsion polymerization without causing problems such as thickening of the resulting emulsion and generation of a large amount of aggregates during production. Can be manufactured.

The present invention relates to a production method for obtaining a polymer having a large amount of carboxyl groups introduced by emulsion polymerization, which is useful for an alkali-soluble thickener and the like.
The present invention will be described in detail below. In the present specification, acrylic acid and / or methacrylic acid is represented as (meth) acrylic acid.

In the present invention, a carboxyl group-containing monomer is used as an essential component. When the carboxyl group-containing monomer is introduced into the polymer in a specific amount, the viscosity increases when it is neutralized and, for example, exhibits an effective function as a thickener.
Examples of the carboxyl group-containing monomer include unsaturated monocarboxylic acid monomers such as (meth) acrylic acid, crotonic acid, and isocrotonic acid and salts thereof; maleic acid, itaconic acid, mesaconic acid, fumaric acid, citracone Examples thereof include unsaturated dicarboxylic acid monomers such as acids, and salts and anhydrides thereof, and one or more of these can be used in combination.
Among these, use of (meth) acrylic acid is preferable from the viewpoint of good polymerizability and wide application range.

  The amount of the carboxyl group-containing monomer is required to be 10 to 80% by mass with respect to the total monomers. A preferable range is 20 to 75% by mass, and more preferably 30 to 70% by mass. If it is less than 10% by mass, the alkali solubility may not be sufficient. Further, there are cases where satisfactory thickening cannot be achieved when used as a thickener. On the other hand, when it exceeds 80 mass%, polymerization stability will fall remarkably.

In the present invention, other monomers are used in addition to the carboxyl group-containing monomer as long as alkali solubility and viscosity increase are not impaired.
Other monomers include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, (meth) Acrylic acid alkyl esters such as octyl acrylate, isooctyl (meth) acrylate, nonyl (meth) acrylate, isononyl (meth) acrylate, decyl (meth) acrylate and lauryl (meth) acrylate; (meth) acrylic acid Cyclopentyl, cyclohexyl (meth) acrylate, cyclooctyl (meth) acrylate, cyclononyl (meth) acrylate, isobornyl (meth) acrylate, alicyclic alkyl esters of (meth) acrylic acid; hydroxy (meth) acrylate Ethyl, hydroxypropyl (meth) acrylate, ( T) Hydroxybutyl acrylate, (meth) acrylic acid ω-hydroxypolyalkylene glycol and (meth) acrylic acid ω-hydroxypolycaprolactone-containing (meth) acrylic acid ester; styrene, α-methylstyrene, p-phenyl Aromatic vinyl monomers such as styrene and vinyltoluene; (meth) acrylonitrile, vinyl acetate, (meth) acrylamide and the like can be mentioned, and one or more of these can be used.

Among the other monomers, it is preferable to use a highly hydrophilic monomer from the viewpoint of ensuring alkali solubility, and specifically, it has 1 to 1 carbon atoms such as methyl (meth) acrylate and ethyl (meth) acrylate. The use of (meth) acrylic acid esters having 2 alkyl groups is preferred.
The usage-amount of another monomer is 20-90 mass% with respect to all the monomers. A preferable range is 25 to 80% by mass, and more preferably 30 to 70% by mass. When the amount is less than 20% by mass, the amount of the carboxyl group-containing monomer used is too large, so that the polymerization stability is remarkably lowered, and it cannot exist as an aqueous dispersion. On the other hand, when it exceeds 90 mass%, alkali solubility may not be enough. Moreover, when used as a thickener, there are cases where satisfactory thickening cannot be achieved.

In the method for producing an aqueous resin dispersion according to the present invention, the polymer into which the carboxyl group is introduced is produced by emulsion polymerization. Here, the emulsion polymerization includes a pre-emulsion adjustment step and a polymerization step performed subsequently.
The pre-emulsion adjusting step is a step of obtaining an aqueous dispersion (pre-emulsion) of a monomer mixture by stirring and mixing water as a polymerization medium and an emulsifier and a monomer mixture. The pre-emulsion obtained here is supplied to a reactor together with an initiator and the like in a subsequent polymerization step, and polymerization is performed.

In the present invention, it is necessary to adjust the pre-emulsion by adding and stirring the monomer mixture prepared in advance in a separate container to the aqueous emulsifier solution in the pre-emulsion adjusting step. In ordinary emulsion polymerization, water, an emulsifier, raw material monomers, etc. are introduced into a tank for adjusting the pre-emulsion, taking into consideration workability and safety, and the pre-emulsion is adjusted by mixing with stirring. Is common. Here, when using a some monomer as a raw material, normally, it supplies separately to the tank for adjusting the said pre emulsion from a raw material container or a raw material tank.
In contrast, in the present invention, as described above, an aqueous emulsifier solution and a plurality of kinds of raw material monomers to be used are prepared in advance in separate containers, and then the pre-emulsion is prepared by mixing and stirring them. Thereby, the polymerization stability in the polymerization step in the next step is ensured.

The reason why the polymerization stability is improved by adjusting the pre-emulsion to the above method is not clear, but in the pre-emulsion, the proportion of raw material monomers distributed between the continuous phase (water phase) and the dispersed phase (oil phase) is stable. It is estimated that In particular, on a large scale where the capacity of the reactor exceeds 1 m ³ , conditions such as the charging time and charging interval of the raw material monomer are likely to vary, and the pre-emulsion thus produced is particularly hydrophilic. It is presumed that the proportion of the high monomer distributed to the continuous phase (aqueous phase) and the dispersed phase (oil phase) tends to vary. In the present invention, since the variation is reduced, it is considered that the polymerization stability is improved.

  Here, the amount of agglomerates is mentioned as one of the indexes for judging the polymerization stability. In this invention, as shown in the Example mentioned later, the amount of this aggregate is measured by filtering the obtained aqueous resin dispersion with a polynet etc. As shown in FIG. The aggregate amount is desirably 1000 ppm or less, and more desirably 500 ppm or less. If the amount of aggregate exceeds 1000 ppm, it takes time to filter the aggregate when filling the product. In some cases, the entire emulsion may be agglomerated and solidified.

  The pre-emulsion adjustment step is preferably performed at a temperature in the range of polymerization initiation temperature ± 20 ° C. By controlling the temperature within this range, the polymerization stability is further improved. The relationship between the pre-emulsion adjustment temperature and the polymerization stability is not clear, but by controlling the pre-emulsion adjustment temperature within the temperature range, the water phase / oil of the raw material monomer from the pre-emulsion adjustment step to the polymerization step It is estimated that the distribution to the phase is stabilized within a certain range.

  As the emulsifier used in the present invention, known emulsifiers used in usual emulsion polymerization can be used. For example, various emulsifiers such as an anionic emulsifier, a nonionic emulsifier, a cationic emulsifier, and a zwitterionic emulsifier can be used. As anionic emulsifiers, dialkyl sulfosuccinate, alkylbenzene sulfonate, alkyl sulfate, polyoxyethylene alkylphenyl ether sulfate, polyoxyethylene alkyl diphenyl ether sulfate, polyoxyethylene alkyl ether sulfate, alkyl diphenyl ether disulfonate And polymer emulsifiers. Nonionic emulsifiers include polyoxyethylene higher alcohol ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene alkyl diphenyl ethers, polyoxyethylene-polyoxypropylene block copolymers, acetylenic diol emulsifiers, sorbitan higher fatty acid esters. Polyoxyethylene sorbitan higher fatty acid esters, polyoxyethylene higher fatty acid esters, glycerin higher fatty acid esters, polycarboxylic acid-based polymer emulsifier, polyvinyl alcohol and the like. Examples of the cationic emulsifier include alkyl (amido) betaines and alkyldimitylamine oxides, and examples of the special emulsifier include a fluorine-based emulsifier and a silicone-based emulsifier. These emulsifiers may be used alone or in combination of two or more. Of these, the use of a nonionic emulsifier is preferred from the viewpoint of good stability of a pre-emulsion containing a highly hydrophilic monomer.

  The amount of the emulsifier used is selected depending on the type and polymerization conditions, but is usually 0.01 to 20 parts by weight, preferably 0.05 to 15 parts by weight, more preferably 0, per 100 parts by weight of the monomer. .1 to 8 parts by mass. By using 0.01 mass part or more of an emulsifier, there exists a tendency for stability at the time of manufacture to be ensured and generation | occurrence | production of an aggregate etc. to be reduced. On the other hand, when the amount of the emulsifier used is 20 parts by mass or less, there are problems such as deterioration of water resistance and cloudiness of the coating film due to moisture absorption and water absorption of the emulsifier when the product containing the aqueous resin dispersion of the present invention is used. It tends to be suppressed.

  In addition, depending on the type of emulsifier, there are solid ones at room temperature and high viscosity ones, so that the emulsifier may be heated in advance for the purpose of improving handling during addition. In particular, nonionic emulsifiers with a high HLB are often solid at room temperature, and are often used after being heated and melted before use.

  The monomer concentration of the pre-emulsion adjusted in the present invention is preferably 50% by mass or less. If it exceeds 50% by mass, the polymerization stability may be reduced and aggregates may be generated.

  In the polymerization step, polymerization is performed according to a known emulsion polymerization method in the presence of a polymerization initiator using the pre-emulsion adjusted in the pre-emulsion adjustment step. The polymerization temperature is preferably 20 to 100 ° C, more preferably 30 to 80 ° C. By setting the polymerization temperature to 20 ° C. or higher, the polymerization can proceed stably. On the other hand, the polymerization temperature during emulsion polymerization does not substantially exceed 100 ° C.

As the polymerization initiator, known radical polymerization initiators such as peroxides and azo compounds can be used.
Examples of the peroxide include hydrogen peroxide; inorganic peroxides such as persulfates (sodium persulfate, ammonium persulfate, potassium persulfate, etc.); hydroperoxides (cumene hydroperoxide, paramentane hydroperoxide, tert -Butyl hydroperoxide, etc.), dialkyl peroxide (tert-butyl cumyl peroxide, dicumyl peroxide, etc.), diacyl peroxide, peroxy ester (tert-butyl peroxylaurate, tert-butyl peroxybenzoate, etc.) And organic peroxides such as benzoyl peroxide, lauroyl peroxide, peracetic acid and persuccinic acid. These can be used alone or in combination of two or more.
Examples of the azo compound include 2,2′-azobisisobutyronitrile, 2,2′-azobis (2,4-dimethylvaleronitrile), and 2,2′-azobis (2-methylbutyronitrile). 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile) and the like. These can be used alone or in combination of two or more.

  Although the usage-amount of a radical polymerization initiator is selected by the kind, superposition | polymerization conditions, etc., it is 0.01-10 mass parts normally with respect to 100 mass parts of said monomers.

It is also possible to employ a redox initiator containing the peroxide and reducing agent.
As a reducing agent, ascorbic acid, sodium ascorbate, sodium erythorbate, tartaric acid, citric acid, metal salt of formaldehyde sulfoxylate, sodium thiosulfate, sodium sulfite, sodium bisulfite, sodium metabisulfite, ferrous sulfate, Examples thereof include cuprous sulfate and ferric chloride, and one or more of these can be used in combination.

  The emulsion polymerization of the present invention is usually carried out in a reaction system heated in an aqueous medium with stirring and reflux cooling. Here, the addition method of raw material components, such as a pre-emulsion and an initiator, may be any of a batch addition method, a continuous addition method, and a divided addition method. In the case of the continuous addition method, the supply rate may be constant or indefinite. In addition, in the case of the divided addition method, the addition interval of the raw material components may be constant or indefinite. Here, when a polymer having a high molecular weight such as a thickener is desired, it is preferable to initially charge 50% by mass or more of the pre-emulsion.

  As the aqueous medium, water alone or a mixture of water and a water-soluble organic solvent (alcohol, ketone, ether, dimethyl sulfoxide, dimethylformamide, etc.) can be used. When this aqueous medium is a mixture, the content of water is usually 30% by mass or more when the aqueous medium is 100% by mass.

Moreover, in the said superposition | polymerization, a chain transfer agent can be used according to the use etc. of the polymer obtained.
As this chain transfer agent, a mercapto group-containing compound (ethanethiol, butanethiol, dodecanethiol, benzenethiol, toluenethiol, α-toluenethiol, phenethylmercaptan, mercaptoethanol, 3-mercaptopropanol, thioglycerin, thioglycolic acid, 2-mercaptopropionic acid, 3-mercaptopropionic acid, α-mercaptoisobutyric acid, methyl mercaptopropionate, ethyl mercaptopropionate, thioacetic acid, thiomalic acid, thiosalicylic acid, octyl mercaptan, n-dodecyl mercaptan, tert-dodecyl mercaptan, n-hexadecyl mercaptan, n-tetradecyl mercaptan, tert-tetradecyl mercaptan, etc.), xanthogen disulfide compounds (dimethyloxa) Tonogen disulfide, diethyl xanthogen disulfide, diisopropyl xanthogen disulfide, etc.), thiuram disulfide compounds (tetramethyl thiuram disulfide, tetraethyl thiuram disulfide, tetrabutyl thiuram disulfide, etc.), halogenated hydrocarbons (carbon tetrachloride, ethylene bromide, etc.), aromatic And hydrocarbon (pentaphenylethane, α-methylstyrene dimer, etc.). These can be used alone or in combination of two or more.

  In the aqueous resin dispersion of the present invention, various known additives can be added as long as the characteristics are not impaired. Examples of the additive include an antifoaming agent, an antiseptic agent, an antifungal agent, a pH adjuster, a dispersant, a deodorant, and a rheology control agent.

Hereinafter, the present invention will be specifically described based on examples. In the following description, “%” means mass%.
Moreover, solid content concentration, such as a polymer obtained in each case, was measured by the method as described below.

<Solid content>
About 1 g of the measurement sample was weighed (a), then the residue after drying for 45 minutes at 155 ° C. in a draft dryer was measured (b), and calculated from the following formula. A weighing bottle was used for the measurement. Other operations were in accordance with JIS K 0067-1992 (chemical product weight loss and residue test method).
Solid content (%) = (b / a) × 100

<Aggregate amount>
The aqueous resin dispersion is filtered through a 200-mesh polynet, the residue remaining on the polynet is dried, and the weight is measured.
Aggregate amount (%) = (residue amount after drying / weight of aqueous resin dispersion subjected to filtration) × 100

Example 1
<Pre-emulsion adjustment process>
A 3 m ³ reactor equipped with a stirrer, reflux condenser, nitrogen gas inlet tube and thermometer was charged with 1080 kg of ion-exchange water, 39 kg of Latemul E-118B (manufactured by Kao Corporation, anionic emulsifier), and Emulgen 1150S-60 (manufactured by Kao Corporation) ), 12 kg of nonionic emulsifier) was added, and the aqueous emulsifier solution was prepared by stirring and mixing. At this time, the liquid temperature was adjusted to 30 ° C. On the other hand, 192 kg of methacrylic acid (hereinafter referred to as “MAA”), 54 kg of ethyl acrylate (hereinafter referred to as “EA”), and 54 kg of methyl acrylate (hereinafter referred to as “MA”) are mixed well in a separate container. The body mixture was adjusted. Subsequently, this monomer mixture was added to the emulsifier aqueous solution, and the pre-emulsion was prepared by stirring and mixing while maintaining the liquid temperature at 30 ° C.
<Polymerization process>
The temperature inside the reactor was raised to 45 ° C. and stirred for 120 minutes while blowing nitrogen gas. Then, 6.6 kg of a 0.6% by mass ammonium persulfate aqueous solution was added, and after 5 minutes, 1.4% hydrosulfite. Polymerization was started by adding 3.0 kg of an aqueous sodium solution into the flask. After 40 minutes, the reactor internal temperature rose to 50 ° C., and the internal temperature reached its peak. After confirming the internal temperature peak, the temperature was raised to 60 ° C. and maintained for 45 minutes, and then at 55 ° C., 27 kg of 0.2% t-butyl hydroperoxide aqueous solution and 27 kg of 0.3% sodium erythorbate aqueous solution were added as post-added catalysts. Added.
When the obtained aqueous resin dispersion was cooled and filtered through a 200-mesh polynet, the amount of aggregate was as small as 100 ppm, and the polymerization could be performed stably.
Further, 19 g of the aqueous resin dispersion after filtration was diluted with 356 g of ion-exchanged water, and then adjusted to pH 7.5 by adding a 20% aqueous sodium hydroxide solution. The aqueous resin dispersion quickly solubilized into an aqueous solution. The aqueous solution was adjusted to 25 ° C., and the B-type viscosity at 12 rpm was measured. As a result, it was 5,200 mPa · s, and it was confirmed that a good viscosity increase was exhibited.

Examples 2-6
An aqueous resin dispersion was obtained in the same manner as in Example 1, except that the monomer composition and the temperature during pre-emulsion preparation were as described in Table 1.
The results of the aggregate amount evaluated in each example are shown in Table 1.

Comparative Example 1
The same operation as Example 1 was performed except having changed the pre-emulsion adjustment process in Example 1 as follows.
<Pre-emulsion adjustment process>
A 3 m ³ reactor equipped with a stirrer, reflux condenser, nitrogen gas inlet tube and thermometer was charged with 1080 kg of ion-exchanged water, 39 kg of Latemul E-118B, and 12 kg of Emulgen 1150S-60, and mixed with stirring to obtain an aqueous emulsifier solution. Adjusted. At this time, the liquid temperature was adjusted to 30 ° C. Subsequently, 192 kg of MAA, 54 kg of EA, and 54 kg of MA were sequentially added to this aqueous emulsifier solution, and the pre-emulsion was prepared by stirring and mixing while maintaining the liquid temperature at 30 ° C.

  When the aqueous resin dispersion obtained in Comparative Example 1 was cooled and filtered through a 200th polynet, the amount of aggregates was a large amount of 4500 ppm.

Comparative Examples 2-4
An aqueous resin dispersion was obtained by the same operation as in Comparative Example 1 except that the monomer composition and the temperature during pre-emulsion preparation were as described in Table 2.
Table 2 shows the results of the amount of aggregates evaluated in each example.

The adjustment method of the pre-emulsion in Table 1 and Table 2 is shown below.
A: The monomer mixture is prepared in a separate container and then added to the emulsifier aqueous solution, and mixed with stirring.

Details of the compounds used in Tables 1 and 2 are shown below.
MAA: Methacrylic acid MA: Methyl acrylate EA: Ethyl acrylate E-118B: Latemul E-118B (manufactured by Kao Corporation)
1150-S60: Emulgen 1150-S60 (manufactured by Kao Corporation)

  The aqueous resin dispersions obtained in Examples 1 to 6 had a small amount of aggregates, and were excellent in polymerization stability even when produced on a large scale. In addition, the neutralized solution of the resin dispersion showed a sufficiently high viscosity, indicating that it was useful as an alkali-soluble thickener.

  On the other hand, Comparative Examples 1 to 4 in which the pre-emulsion was prepared by sequentially adding each monomer to the emulsifier aqueous solution and stirring and mixing had a large amount of agglomerates, indicating that the polymerization stability was insufficient. . In particular, in Comparative Example 4 where no nonionic emulsifier was used, the amount of agglomerates was too large to pass through during filtration, and thus filtration was impossible.

  According to the present invention, an emulsion containing a polymer having a high carboxyl group introduction amount can be stably produced without generating a large amount of aggregates even on a large scale. The aqueous resin dispersion obtained by the present invention can be suitably used for applications such as an alkali-soluble thickener.

Claims (6)

  A method for producing an aqueous resin dispersion obtained by emulsion polymerization of a monomer mixture containing 10 to 80% by mass of a carboxyl group-containing monomer in the presence of an emulsifier, wherein the emulsion polymerization comprises a pre-emulsion adjustment step and polymerization. Characterized in that, after the pre-emulsion is adjusted by adding and stirring the monomer mixture prepared in advance in a separate container in the pre-emulsion aqueous solution in the pre-emulsion adjustment step, the polymerization step is started. A method for producing an aqueous resin dispersion.   The method for producing an aqueous resin dispersion according to claim 1, wherein the monomer mixture further comprises 20 to 90% by mass of a (meth) acrylic acid ester having an alkyl group having 1 to 2 carbon atoms.   The method for producing an aqueous resin dispersion according to claim 1 or 2, wherein the pre-emulsion adjusting step is performed at a temperature in the range of polymerization initiation temperature ± 20 ° C.   The said emulsifier contains a nonionic emulsifier, The manufacturing method of the aqueous resin dispersion in any one of Claims 1-3 characterized by the above-mentioned.   The aqueous resin dispersion obtained by the manufacturing method in any one of Claims 1-4.   A thickener comprising the aqueous resin dispersion according to claim 5.