JP2013155287A - Method for producing aqueous copolymer emulsion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an emulsion excellent in stability, inhibiting generation of aggregates even by easy-to-use reaction apparatus without using a special agitation device or the like, when producing an aqueous copolymer emulsion by emulsion polymerization.SOLUTION: A method for producing an aqueous copolymer emulsion is characterized by performing polymerization while extracting a reflux return liquid, condensed in a condenser during polymerization, out of the reaction vessel. As a method for extracting the condensed liquid out of the reaction vessel, the condensed liquid can be discharged out of the reaction vessel by trapping the condensed liquid once if a condenser attached with a Dean-Stark trap is used, for example. The condensed liquid may be returned once into a pre-emulsion and added to the reaction vessel after re-emulsified.

Description

  The present invention relates to a method for producing an aqueous copolymer emulsion. More specifically, the present invention relates to a method for producing an aqueous copolymer emulsion that is less flocculated and has good filterability in emulsion polymerization containing a highly volatile raw material monomer.

  An aqueous copolymer emulsion (hereinafter sometimes simply referred to as an emulsion) obtained by copolymerizing monomers such as (meth) acrylic acid esters by an emulsion polymerization method is a paint, a binder, and (pressure sensitive) It is widely used industrially as an adhesive. However, in the emulsion polymerization, an emulsion having an average particle diameter of about 30 nm to 2 μm can be obtained. However, depending on the polymerization conditions and the like, aggregates of emulsion particles are generated during the polymerization reaction. There is a case. When the amount of the agglomerates is large, various product defects such as a decrease in gloss as a coating agent, occurrence of streaks on the coated surface, and clogging of the spray nozzles may be caused. Moreover, also in the filtration process for filtering out the generated aggregate, clogging or the like occurs, resulting in a decrease in productivity. For this reason, various methods such as the selection of polymerization conditions such as the timing of addition of monomers, the addition method, and the selection of surfactants have been proposed for the purpose of suppressing the generation of aggregates in emulsions obtained by emulsion polymerization. Has been.

  Patent Document 1 proposes a method for producing a polymer latex in which emulsion polymerization is performed while repeating the forward and reverse rotations of the stirring blade. Further, Patent Document 2 discloses a method for producing a polymer emulsion excellent in polymerization stability with little generation of fine aggregates by using a polymerization tank equipped with a specific stirring blade. Furthermore, Patent Document 3 discloses that polymerization is carried out in the presence of a specific amount of a naphthalenesulfonic acid formaldehyde condensate or a salt thereof and an anionic surfactant to suppress fine aggregates.

JP 2006-274180 A JP-A-8-165304 JP 2004-352895 A

  However, the methods described in Patent Documents 1 and 2 are not versatile because they require the introduction of a special stirring device and stirring blade. Furthermore, the method described in Patent Document 1 includes a problem that the load on the stirrer is large. Moreover, in patent document 3, since the naphthalenesulfonic acid formaldehyde condensate or its salt was used, there existed a problem that formaldehyde derived from this was contained in a product emulsion.

On the other hand, during the polymerization reaction, a part of the unreacted monomer present in the reaction system is volatilized and then condensed in the condenser to return to the reactor as a reflux liquid. In ordinary emulsion polymerization, the raw material monomer is subjected to a polymerization reaction in the form of an aqueous dispersion of a monomer called a pre-emulsion obtained by mixing and stirring with water, an emulsifier and the like, thereby stabilizing the polymerization. Figured. However, the condensed reflux liquid returning to the reactor as described above is a monomer itself, and in such a case, aggregates are easily generated in the system. Further, since the condensed reflux liquid does not contain a polymerization inhibitor, a polymer may be generated in the condenser or in the reflux return pipe, which may cause agglomerates.
Here, monomers having a relatively low boiling point such as methyl acrylate and ethyl acrylate are likely to volatilize during the polymerization, so that the amount returned to the reactor as a condensed reflux liquid increases. For this reason, when these monomers are contained in the raw material monomer, the problem of the generation of aggregates due to the condensed reflux liquid tends to occur.
However, in the prior art, no attention has been paid to the aggregate derived from the condensed reflux liquid, and no suppression measures are found.

As described above, the method for suppressing the generation of aggregates derived from the condensed reflux liquid in emulsion polymerization and stably producing an emulsion is not yet satisfactory, and improvement is desired.
An object of the present invention is to provide a method for producing an emulsion having excellent stability in which generation of aggregates is suppressed even with a simple reaction apparatus without using a special stirring apparatus or the like during emulsion polymerization. is there.

  As a result of intensive studies in view of the above problems, the present inventors have found that the generation of aggregates is dramatically suppressed by extracting the reflux liquid condensed in the condenser during the polymerization to the outside of the reactor. Was completed.

The present invention is as follows.
[1] A method for producing an aqueous copolymer emulsion obtained by an emulsion polymerization method, wherein the polymerization is carried out while withdrawing the reflux liquid condensed by a condenser during the polymerization out of the reaction vessel. Production method.
[2] The above emulsion polymerization, wherein the emulsion polymerization is an emulsion polymerization of a monomer mixture containing 5 to 100% by mass of an alkyl (meth) acrylate having an alkyl group having 1 or 2 carbon atoms [ [1] A process for producing an aqueous copolymer emulsion as described in [1].
[3] The method for producing an aqueous copolymer emulsion as described in [1] or [2] above, wherein the reflux liquid is returned to the pre-emulsion, emulsified again, and then added to the reactor.
[4] The method for producing an aqueous copolymer emulsion according to any one of the above [1] to [3], wherein the polymerization temperature in the emulsion polymerization is 60 to 100 ° C.

  According to the method for producing an aqueous copolymer emulsion of the present invention, a single amount having a low boiling point such as methyl acrylate or ethyl acrylate is produced without causing a problem that a large amount of aggregates are generated during the production of the emulsion. It can also be stably produced in emulsion polymerization in which the body is contained as a raw material monomer.

The present invention relates to a method for stably producing an emulsion by suppressing the generation of aggregates derived from a condensed reflux liquid of raw material monomers when an aqueous copolymer emulsion is obtained by emulsion polymerization.
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, an aqueous copolymer emulsion is obtained by emulsion polymerization of a monomer mixture containing various ethylenic unsaturations such as acrylic, vinyl acetate and styrene.
As the ethylenically unsaturated monomer, (meth) acrylic acid alkyl ester, unsaturated carboxylic acid, unsaturated acid anhydride, (meth) acrylic acid hydroxyalkyl ester, aromatic vinyl compound, nitrogen-containing unsaturated compound, Examples thereof include unsaturated sulfonic acids, unsaturated amides, and esters of (meth) acrylic acid containing a polyalkylene oxide skeleton. These may be used alone or in combination of two or more.

  Since each said monomer has volatility, when a reaction liquid is heated at the time of superposition | polymerization, a part of raw material monomer may volatilize. Usually, the monomer component volatilized during the polymerization is condensed by a condenser such as a condenser and returned to the reaction liquid as a reflux liquid. In general, in emulsion polymerization, polymerization is performed in a state where the raw material monomer and the produced polymer are dispersed and stabilized by an emulsifier or the like. However, the monomer returned to the reactor as the condensed reflux liquid is not emulsified with an emulsifier or the like, but is charged into the reaction liquid as the monomer itself, so the amount of the monomer reflux liquid is large. In some cases, a large amount of aggregates and the like are likely to be generated due to insufficient polymerization stability. According to the production method of the present invention, the generation of such aggregates can be effectively suppressed.

As said (meth) acrylic-acid alkylester, what an alkyl group is a C1-C18 hydrocarbon group is preferable, for example, (meth) acrylic acid methyl, (meth) acrylic acid ethyl, (meth) acrylic N-propyl acid, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, sec-butyl (meth) acrylate, tert-butyl (meth) acrylate, (meth) acrylic N-hexyl acid, n-octyl (meth) acrylate, isooctyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-nonyl (meth) acrylate, isononyl (meth) acrylate, (meth) acrylic Decyl acid, dodecyl (meth) acrylate, stearyl (meth) acrylate, octa (meth) acrylate Sil, (meth) acrylate, cyclohexyl (meth) acrylate, phenyl include benzyl (meth) acrylate and the like. These can be used alone or in combination of two or more. As said (meth) acrylic-acid alkylester, that whose carbon number of an alkyl group is 1-12 is more preferable from viewpoints, such as polymerizability and availability.
The content ratio of the (meth) acrylic acid alkyl ester is appropriately adjusted depending on the application to which it is applied, and is preferably 5 to 100% by mass when the total of the ethylenically unsaturated monomer mixture is 100% by mass.

Among the above (meth) acrylic acid alkyl esters, when the (meth) acrylic acid alkyl ester having an alkyl group having 1 or 2 carbon atoms is included as a monomer component, the effect of the present invention is more remarkably exhibited.
Since the (meth) acrylic acid alkyl ester having an alkyl group having 1 or 2 carbon atoms is a compound having a relatively low boiling point, it has a characteristic that the monomer is easily volatilized during the above-described polymerization. The present invention is more effective in such a case.

  The amount of the (meth) acrylic acid alkyl ester having an alkyl group having 1 or 2 carbon atoms is preferably in the range of 5 to 100% by mass, more preferably in the range of 8 to 100% by mass with respect to the total monomers. And most preferably in the range of 10 to 100% by mass. When the amount is less than 5% by mass, the effects of the present invention may not be sufficiently exhibited because the influence of the generation of aggregates due to the reflux liquid is small.

  Examples of the unsaturated carboxylic acid (carboxyl group-containing monomer) include (meth) acrylic acid, maleic acid, itaconic acid, fumaric acid and the like. These can be used singly or in combination of two or more, but (meth) acrylic acid is preferred in view of polymerizability and ease of handling.

  When the content of the unsaturated carboxylic acid is too large, there is a risk of gelation during polymerization in the polymerization of the aqueous medium, and when it is too small, the stability of the emulsion may not be sufficiently ensured. When the total of the ethylenically unsaturated monomer mixture is 100% by mass, 0.2 to 20% by mass is preferable, 0.5 to 10% by mass is more preferable, and 1.0 to 5% by mass is still more preferable.

  Examples of the (meth) acrylic acid hydroxyalkyl ester include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, and 2-hydroxybutyl (meth) acrylate. , (Meth) acrylic acid 3-hydroxybutyl, (meth) acrylic acid 4-hydroxybutyl and the like. These can be used alone or in combination of two or more.

  Examples of the aromatic vinyl compound include styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, vinyltoluene, β-methylstyrene, ethylstyrene, p-tert-butylstyrene, vinylxylene, vinylnaphthalene and the like. It is done. These can be used alone or in combination of two or more.

  Examples of the nitrogen-containing unsaturated compound include acrylonitrile, methacrylonitrile, vinyl pyridine, and N-vinyl pyrrolidone. These can be used alone or in combination of two or more.

  Unsaturated amides include (meth) acrylamide, N-methylol (meth) acrylamide, N-alkoxymethyl (meth) acrylamide (N-methoxymethyl (meth) acrylamide, N-ethoxymethyl (meth) acrylamide, N-isopropoxy Methyl (meth) acrylamide, N-butoxymethyl (meth) acrylamide, N-isobutoxymethyl (meth) acrylamide and the like. These can be used alone or in combination of two or more.

  Examples of the unsaturated acid anhydride include maleic anhydride and itaconic anhydride. These can be used alone or in combination of two or more.

  Examples of unsaturated sulfonic acids include allyl sulfonic acid, methallyl sulfonic acid, vinyl sulfonic acid, p-styrene sulfonic acid, acryloxybenzene sulfonic acid, methacryloxybenzene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, sulfone. Examples include ethyl acrylate. These can be used alone or in combination of two or more.

  Examples of esters of (meth) acrylic acid containing a polyalkylene oxide skeleton include polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, polybutylene glycol mono (meth) acrylate, and polyethylene glycol polypropylene glycol mono (meth) acrylate. , Polyethylene glycol polybutylene glycol mono (meth) acrylate, polypropylene glycol polybutylene glycol mono (meth) acrylate, polyethylene glycol polypropylene glycol polybutylene glycol mono (meth) acrylate, etc., polyalkylene glycol (the number of alkylene glycol units is 2 or more ) Mono (meth) acrylic acid ester; methoxypolyethylene glycol mono (me ) Acrylate, methoxypolypropylene glycol mono (meth) acrylate, methoxypolybutylene glycol mono (meth) acrylate, ethoxypolyethylene glycol mono (meth) acrylate, ethoxypolypropylene glycol mono (meth) acrylate, ethoxypolybutylene glycol mono (meth) acrylate, etc. And mono (meth) acrylic acid ester of alkoxy polyalkylene glycol. These can be used alone or in combination of two or more.

  In addition, vinyl ester monomers such as vinyl acetate and vinyl propionate, and vinyl ether monomers such as vinyl methyl ether, vinyl ethyl ether, vinyl isobutyl ether, and vinyl phenyl ether can be used.

The aqueous copolymer emulsion of the present invention may be cross-linked as necessary.
Crosslinking is performed by a crosslinking reaction between a polymer into which a reactive functional group such as a carboxyl group, a sulfonic acid group, a hydroxyl group, an amino group, and a carbonyl group is introduced and a crosslinking agent having a crosslinkable functional group. In addition, methylene bis (meth) acrylamide, ethylene bis (meth) acrylamide, ethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, divinylbenzene, etc. having two or more vinyl groups in one molecule Crosslinking is also possible by copolymerization of crosslinkable monomers, or by introducing monomers having self-crosslinkable functional groups such as methylol group-containing monomers and hydrolyzable silyl group-containing monomers. .

The cross-linking agent is not particularly limited as long as it can undergo a cross-linking reaction with the reactive functional group. For example, it is selected from cross-linking agents such as epoxy, isocyanate, hydrazide, carbodiimide, oxazoline, and metal cross-linking agents. 1 type (s) or 2 or more types can be used.
Although the addition amount of a crosslinking agent is suitably adjusted with the intended use and performance, 0.05-10 mass parts is preferable with respect to 100 mass parts of polymers, and 0.1-5 mass parts is further more preferable.

The emulsion polymerization of the present invention includes a pre-emulsion adjusting step and a subsequent polymerization step.
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. There are no particular limitations on the equipment for stirring and mixing, and various types of emulsifiers such as stirring by a stirrer, various mixers such as a homomixer, colloid mill, high pressure emulsifier, and high pressure discharge type emulsifier can be used.
The obtained pre-emulsion is supplied to a reactor together with an initiator or the like in a subsequent polymerization step, and polymerization is performed. Thus, the polymerization stability is ensured by supplying the monomer to the reactor in the form of a pre-emulsion.

  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 temperature in the pre-emulsion adjustment step is preferably 60 ° C. or less, more preferably 50 ° C. or less, and further preferably 40 ° C. or less. When the temperature exceeds 60 ° C., the amount of volatilization of the low-boiling monomer and the like increases, which is not preferable. In addition, an uncontrollable polymerization reaction may occur, which is not preferable from the viewpoint of safety.

  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.

  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. As the reactor used in the process, those generally used in the polymerization reaction can be widely adopted, and various reactors such as a tank type, a tube type and a column type can be used. It is necessary to provide a condenser for condensing and recovering raw materials volatilized. Moreover, it is preferable that a stirring and mixing device such as a stirrer and / or a mixer and a heating and cooling device for controlling the polymerization temperature are provided.

In the present invention, it is necessary to proceed the polymerization reaction while extracting the reflux liquid containing the monomer condensed by the condenser out of the reaction vessel. Since the reflux liquid in which the volatilized monomer is condensed does not contain an emulsifier, when the reflux liquid is returned to the reaction liquid, aggregates are likely to be generated.
As a method for extracting the condensed reflux liquid out of the reaction vessel, for example, if a condenser equipped with a Dean-Stark trap is used, the reflux solution can be once taken out and discharged out of the reaction vessel.
In addition, in a condenser in an actual production facility, the volatile gas and the reflux liquid are generally separated by separate lines, so no special equipment is required, and the reflux liquid generated during the polymerization is removed from the return pipe to the outside of the reactor. It only has to be discharged.
The reflux liquid may be once returned to the pre-emulsion, emulsified again, and then added to the reactor. When the monomer is returned to the reaction system by this operation, the condensed monomer is added in an emulsified state, so that the polymerization stability is ensured.

  The polymerization temperature in the polymerization step is preferably 60 to 100 ° C, more preferably 60 to 95 ° C, and still more preferably 60 to 90 ° C. When the polymerization temperature is lower than 60 ° C., the progress of polymerization becomes unstable, and aggregates and the like may be generated. 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, the emulsion obtained in each example was measured and evaluated by the method 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

<Viscosity>
The liquid temperature of the emulsion was adjusted to 25 ° C., and the viscosity after 90 seconds at 12 rpm was measured using a B-type viscometer.

<PH>
The liquid temperature of the emulsion was adjusted to 25 ° C. and measured with a pH meter.

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

Example 1
<Pre-emulsion adjustment process>
To a reaction vessel equipped with a stirrer, a reflux condenser equipped with a Dean-Stark trap, a dropping tank, a nitrogen gas introduction tube and a thermometer, 3000 g of ion-exchanged water was charged.
In the dropping tank, 2900 g of ion-exchanged water, 310 g of polyoxyethylene nonylphenyl ether (EO addition 30 mol 65% aqueous solution, manufactured by Nippon Emulsifier Co., Ltd., trade name “New Coal 506 (65)”), acrylic acid (hereinafter “AA”) 110 g, methyl acrylate (hereinafter referred to as “MA”) 1540 g, and 2-ethylhexyl acrylate (hereinafter referred to as “HA”) 9350 g were added, and the pre-emulsion was prepared by stirring and mixing.
<Polymerization process>
After the reactor internal temperature was raised to 65 ° C. and stirred for 120 minutes while blowing nitrogen gas, the pre-emulsion was continuously added dropwise over 5.5 hours. At the same time, ammonium persulfate ( Hereinafter, emulsion polymerization was carried out by dropping 510 g of a 1% aqueous solution (referred to as “APS”) over 6 hours. After the completion of the APS addition, the mixture was further aged for 1 hour, and then 13.2 g of a 70% aqueous solution of t-butyl hydroperoxide and 17.6 g of sodium erythorbate were added to reduce the amount of unreacted monomers, thereby reducing the aqueous copolymer emulsion A1. Obtained. The obtained A1 had a solid content of 59.9%, a viscosity of 259 mPa · s, and a pH of 2.9. When the amount of aggregate was evaluated, a result of 58 ppm was obtained.

Example 2
<Pre-emulsion adjustment process>
Into a reaction vessel equipped with a stirrer, a reflux condenser equipped with a Dean-Stark trap, a dropping tank, a nitrogen gas introduction pipe and a thermometer, 330 g of ion-exchanged water was charged.
In the dropping tank, 500 g of ion-exchanged water, 25 g of a 30% aqueous solution of sodium lauryl sulfate (trade name “Emar 2F paste” manufactured by Kao Corporation), 300 g of ethyl acrylate (hereinafter referred to as “EA”), methacrylic acid (hereinafter referred to as “MAA”) The pre-emulsion was prepared by adding 200 g) and stirring and mixing.
<Polymerization process>
After the reactor internal temperature was raised to 90 ° C. and stirred for 120 minutes while blowing nitrogen gas, the pre-emulsion was continuously added dropwise over 2 hours, and at the same time, 50 g of 2% APS aqueous solution as a polymerization initiator was added. Emulsion polymerization was carried out by dropwise addition over 2 hours. After completion of dropping, the mixture was further aged at 80 ° C. for 1 hour to reduce the amount of unreacted monomers, thereby obtaining an aqueous copolymer emulsion A2. The obtained A2 had a solid content of 35.7%, a viscosity of 15 mPa · s, and a pH of 2.3. When the amount of aggregate was evaluated, a result of 250 ppm was obtained.

Comparative Example 1
An aqueous copolymer emulsion B1 was obtained in the same manner as in Example 1 except that the Dean Stark trap was not attached to the reflux condenser. During the polymerization, it was observed that the reflux liquid condensed in the condenser returned to the reactor. The obtained B1 had a solid content of 60.0%, a viscosity of 160 mPa · s, and a pH of 3.0. When the amount of aggregate was evaluated, a result of 1,100 ppm was obtained.

Comparative Example 2
An aqueous copolymer emulsion B2 was obtained by the same operation as in Example 2 except that the Dean Stark trap was not attached to the reflux condenser. During the polymerization, it was observed that the reflux liquid condensed in the condenser returned to the reactor. The obtained B2 had a solid content of 35.8%, a viscosity of 17 mPa · s, and a pH of 2.5. When the amount of aggregate was evaluated, a result of 2,000 ppm was obtained.

The aqueous copolymer emulsions obtained in Examples 1 and 2 had a small amount of aggregates and were excellent in polymerization stability. It was also confirmed that there was no problem with filterability.
On the other hand, Comparative Examples 1 and 2 in which the reflux liquid condensed in the condenser was returned to the reaction liquid had a large amount of aggregates, indicating that the polymerization stability was not sufficient.

  ADVANTAGE OF THE INVENTION According to this invention, in the case of emulsion polymerization of the raw material monomer containing a monomer with a low boiling point, the manufacturing method of the emulsion excellent in stability by which generation | occurrence | production of the aggregate was suppressed can be provided. The production method in the present invention is effective in stably producing an aqueous copolymer emulsion used for paints, binders, (pressure-sensitive) adhesives, and the like.

Claims (4)

  In the manufacturing method of the aqueous copolymer emulsion obtained by an emulsion polymerization method, it superposes | polymerizes, extracting the reflux liquid condensed with the capacitor | condenser during superposition | polymerization out of the reaction container, The manufacturing method of the aqueous copolymer emulsion characterized by the above-mentioned.   2. The emulsion polymerization according to claim 1, wherein the emulsion polymerization is an emulsion polymerization of a monomer mixture containing 5 to 100 mass% of a (meth) acrylic acid alkyl ester having an alkyl group having 1 or 2 carbon atoms. A method for producing an aqueous copolymer emulsion.   The method for producing an aqueous copolymer emulsion according to claim 1, wherein the reflux liquid is returned to the pre-emulsion, emulsified again, and then added to the reactor.   The method for producing an aqueous copolymer emulsion according to any one of claims 1 to 3, wherein a polymerization temperature in the emulsion polymerization is 60 to 100 ° C.