JP2013170211A - Method of producing polymeric emulsion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing a polymeric emulsion, by which a coating film that can be formed at a low temperature and has excellent water resistance can be obtained.SOLUTION: A method of producing a polymeric emulsion includes the following steps 1 to 3. Step 1: An ethylenically unsaturated monomer mixture (a1) is emulsified and polymerized. Step 2: A monomer mixture (a2) containing an acid group-containing ethylenically unsaturated monomer is added to the polymer dispersion liquid obtained in the step 1, and emulsified and polymerized. Step 3: the polymer dispersion liquid obtained in the step 2 is neutralized by holding the liquid at 40°C or higher and lower than the boiling point of the polymer dispersion liquid, for 20 minutes or longer.

Description

  The present invention relates to a method for producing a polymer emulsion capable of forming a film at a low temperature and obtaining a coating film excellent in water resistance.

In recent years, in the paint field, conversion from a solvent-based paint using an organic solvent as a medium to an aqueous paint using water as a dispersion medium has been attempted in consideration of the global environment and the painting work environment.

  For example, Patent Document 1 discloses emulsion polymerization of a vinyl monomer mixture in an aqueous dispersion of a copolymer obtained by radical copolymerization of a vinyl monomer mixture containing an acid group-containing vinyl monomer. A method for producing an emulsion having excellent transparency is described.

  In Patent Document 2, an anionic surfactant and a nonionic surfactant are used in combination, and the monomer mixture (a) is emulsion-polymerized to form a polymer. There is described a method for producing an emulsion having improved water resistance and mud crack resistance, in which an ethylenically unsaturated monomer mixture (b) having a different composition is added and emulsion polymerization is performed.

JP 2003-268299 A JP 2010-138256 A

  However, in the method described in Patent Document 1, a monomer mixture containing an acid group-containing ethylenically unsaturated monomer is polymerized, and after performing a neutralization step, a vinyl monomer mixture is further added and polymerized. However, in this method, in order to obtain a stable dispersed state or dissolved state after neutralization, the amount of the acid group-containing vinyl monomer increases, and the water resistance tends to be insufficient.

  Moreover, in the method of patent document 2, when the thing containing an acid group containing ethylenically unsaturated monomer is used as the said monomer mixture (b), since the neutralization process is not optimized, low temperature The film-forming property and water resistance of the film tend to be insufficient.

  An object of the present invention is to provide a method for producing a polymer emulsion capable of forming a coating film having excellent film formability and water resistance at a low temperature.

The gist of the present invention resides in a method for producing a polymer emulsion by performing the following steps 1 to 3.
Step 1: A step of emulsion polymerization of the ethylenically unsaturated monomer mixture (a1).
Step 2: A step of emulsion polymerization by adding a monomer mixture (a2) containing an acid group-containing ethylenically unsaturated monomer to the dispersion of the polymer obtained in Step 1.
Step 3: A step of neutralizing the dispersion of the polymer obtained in Step 2 above at 40 ° C. or more and less than the boiling point of the dispersion of the polymer for 20 minutes or more.

  According to the present invention, it is possible to produce a polymer emulsion capable of forming a film at a low temperature and obtaining a coating film excellent in water resistance.

[Step 1]
Step 1 of the present invention is a step of emulsion polymerization of the ethylenically unsaturated monomer mixture (a1).

  The ethylenically unsaturated monomer contained in the ethylenically unsaturated monomer mixture (a1) only needs to be radically polymerizable, and examples thereof include the following monomers.

  Alkyl (meth) acrylates having an alkyl group having 1 to 18 carbon atoms: methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, i-propyl (meth) acrylate, n-butyl (meth) ) Acrylate, i-butyl (meth) acrylate, sec-butyl (meth) acrylate, t-butyl (meth) acrylate, n-amyl (meth) acrylate, i-amyl (meth) acrylate, n-hexyl (meth) acrylate 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, and the like. Cycloalkyl (meth) acrylates: cyclohexyl (meth) acrylate, t-butylcyclohexyl (meth) acrylate, and the like. Hydroxyl group-containing radical polymerizable monomers: 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, glycerol mono ( (Meth) acrylate and the like. Polyoxyalkylene group-containing (meth) acrylates: hydroxypolyethylene oxide mono (meth) acrylate, hydroxypolypropyleneoxide mono (meth) acrylate, hydroxy (polyethyleneoxide-polypropyleneoxide) mono (meth) acrylate, hydroxy (polyethyleneoxide-propyleneoxide) ) Mono (meth) acrylate, hydroxy (polyethylene oxide-polytetramethylene oxide) mono (meth) acrylate, hydroxy (polyethylene oxide-tetramethylene oxide) mono (meth) acrylate, hydroxy (polypropylene oxide-polytetramethylene oxide) mono ( (Meth) acrylate, hydroxy (polypropylene oxide-tetramethylene oxide) mono (meth) acrylate Rate, methoxypolyethylene oxide mono (meth) acrylate, lauroxypolyethylene oxide mono (meth) acrylate, stearoxypolyethylene oxide mono (meth) acrylate, allyloxypolyethylene oxide mono (meth) acrylate, nonylphenoxypolyethylene oxide mono (meth) acrylate Nonylphenoxy polypropylene oxide mono (meth) acrylate, octoxy (polyethylene oxide-polypropylene oxide) mono (meth) acrylate, nonylphenoxy (polyethylene oxide-propylene oxide) mono (meth) acrylate, and the like. Hydroxycycloalkyl (meth) acrylates: p-hydroxycyclohexyl (meth) acrylate and the like. Lactone-modified hydroxyl group-containing radical polymerizable monomers. Aminoalkyl (meth) acrylates: 2-aminoethyl (meth) acrylate, 2-dimethylaminoethyl (meth) acrylate, 2-aminopropyl (meth) acrylate, 2-butylaminoethyl (meth) acrylate, and the like. Amide group-containing polymerizable monomer: (meth) acrylamide, N-methylolacrylamide, N-butoxymethyl (meth) acrylamide and the like. Multifunctional (meth) acrylates: ethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, butylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, and the like. Metal-containing radical polymerizable monomers: zinc diacrylate, zinc dimethacrylate, and the like. UV-resistant (meth) acrylates: 2- (2′-hydroxy-5 ′-(meth) acryloxyethylphenyl) -2H-benzotriazole, 1- (meth) acryloyl-4-hydroxy-2,2, 6,6-tetramethylpiperidine, 1- (meth) acryloyl-4-methoxy-2,2,6,6-tetramethylpiperidine, 1- (meth) acryloyl-4-amino-4-cyano-2,2, 6,6-tetramethylpiperidine and the like. Other (meth) acrylic monomers: dimethylaminoethyl (meth) acrylate methyl chloride salt, allyl (meth) acrylate, glycidyl (meth) acrylate, (meth) acrylonitrile, phenyl (meth) acrylate, benzyl (meth) acrylate , Isobornyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, methoxyethyl (meth) acrylate, ethoxyethyl (meth) acrylate, and the like. Carbonyl group-containing monomers based on aldehyde groups or keto groups: acrolein, diacetone acrylamide, formyl styrene, vinyl methyl ketone, vinyl ethyl ketone, vinyl isobutyl ketone, pivalin aldehyde, diacetone (meth) acrylate, acetonitrile acrylate, acetoacetoxyethyl (Meth) acrylate and the like. Aromatic vinyl monomers: styrene, methylstyrene, chlorostyrene, methoxystyrene, etc. Conjugated diene monomers: 1,3-butadiene, isoprene, 2-chloro-1,3-butadiene and the like. Other vinyl monomers: vinyl acetate, vinyl chloride, ethylene, vinyl propionate, etc. A silicone polymer having a graft crossing agent described later. Oxirane group-containing radical polymerizable monomer: glycidyl (meth) acrylate and the like. Self-crosslinkable functional group-containing radical polymerizable monomer: alkylol or alkoxy of ethylenically unsaturated amide such as N-methylol (meth) acrylamide, N-butoxymethyl (meth) acrylamide, N-methoxymethyl (meth) acrylamide Alkyl compounds and the like.

  Among alkyl (meth) acrylates having an alkyl group having 1 to 18 carbon atoms, it preferably contains a hydrophobic monomer such as an alkyl (meth) acrylate having an alkyl group having 4 or more carbon atoms. When the total amount of the unsaturated unsaturated monomer mixture (a1) is 100% by mass, it is preferably contained by 60% by mass or more. If it is 60 mass% or more, the water resistance of a coating film will improve.

  Furthermore, it is preferable in terms of gloss and water resistance of the coating film to contain a cyclic monomer such as an aromatic vinyl monomer or cycloalkyl (meth) acrylate that is hydrophobic and has a high refractive index. These monomers preferably contain 20% by mass or more when the total amount of the ethylenically unsaturated monomer mixture (a1) is 100% by mass. If it is 20 mass% or more, the glossiness of the coating film is exhibited and the water resistance is improved.

  In addition, the acid group-containing ethylenically unsaturated monomer contained in the monomer mixture (a1) is 0.3% by mass or more, 1% in the monomer mixture (a1) from the viewpoint of improving water resistance. It is preferably 8% by mass or less.

  Examples of the acid group-containing ethylenically unsaturated monomer include (meth) acrylic acid, itaconic acid, citraconic acid, maleic acid, monomethyl maleate, monobutyl maleate, monomethyl itaconate, monobutyl itaconate, vinylbenzoic acid, Oxalic acid monohydroxyethyl (meth) acrylate, tetrahydrophthalic acid monohydroxyethyl (meth) acrylate, tetrahydrophthalic acid monohydroxypropyl (meth) acrylate, 5-methyl-1,2-cyclohexanedicarboxylic acid monohydroxyethyl (meth) acrylate , Monohydroxyethyl (meth) acrylate phthalate, monohydroxypropyl (meth) acrylate phthalate, monohydroxyethyl (meth) acrylate maleate, hydroxypropyl maleate (meth) acrylate Relate, tetrahydrophthalic acid mono-hydroxybutyl (meth) acrylate. These may be used individually by 1 type and may be used in combination of 2 or more type.

  The polymerization in Step 1 can be performed by a known emulsion polymerization. In the emulsion polymerization, for example, a known method in which an ethylenically unsaturated monomer mixture is supplied into a polymerization system in the presence of a surfactant and polymerized with a polymerization initiator can be used. Further, a soap-free polymerization method or a seed polymerization method may be used, and the polymerization may be performed in two or more stages.

  As the initiator, known initiators for radical polymerization can be used. For example, persulfates such as potassium persulfate, sodium persulfate, ammonium persulfate, azobisisobutyronitrile, 2,2′-azobis (2-methylbutyrate). Nitrile), 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile), 2-phenylazo-4-methoxy-2, Oil-soluble azo compounds such as 4-dimethylvaleronitrile, 2,2′-azobis {2-methyl-N- [1,1-bis (hydroxymethyl) -2-hydroxyethyl] propionamide}, 2,2 ′ -Azobis {2-methyl-N- [2- (1-hydroxyethyl)] propionamide}, 2,2'-azobis {2-methyl-N- [2- (1-hydroxy) Til)] propionamide}, 2,2′-azobis [2- (5-methyl-2-imidazolin-2-yl) propane] and its salts, 2,2′-azobis [2- (2-imidazoline-2) -Yl) propane] and its salts, 2,2′-azobis [2- (3,4,5,6-tetrahydropyrimidin-2-yl) propane] and its salts, 2,2′-azobis (1-imino -1-pyrrolidino-2-methylpropane) and salts thereof, 2,2′-azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl] propane} and salts thereof, 2,2 Water-soluble azo compounds such as' -azobis (2-methylpropionamidine) and salts thereof, 2,2'-azobis [N- (2-carboxyethyl) -2-methylpropionamidine] and salts thereof, And organic peroxides such as benzoyl oxide, cumene hydroperoxide, t-butyl hydroperoxide, t-butyl peroxy-2-ethylhexanoate, and t-butyl peroxyisobutyrate. These initiators can be used alone or as a mixture of two or more.

  In the case where the polymerization rate is accelerated and the polymerization at a low temperature of 70 ° C. or lower is performed, for example, 2,2′-azobis [2- (2-imidazoline-2-2] having a 10-hour half-life temperature of 70 ° C. or lower is used. Yl) propane], and water-soluble azo compounds such as salts thereof, or reducing agents such as sodium bisulfite, ferrous sulfate, ascorbate, and longalite can be used in combination with a radical polymerization initiator.

  The addition amount of the radical polymerization initiator is usually in the range of 0.01 to 10 parts by mass with respect to the total amount of the monomer, but 0.05 to 5 in view of the progress of polymerization and control of the reaction. A range of parts by mass is preferred.

  Moreover, it is preferable that 0.1-10 mass parts of surfactant is included with respect to a total of 100 mass parts of monomer mixture (a1) and monomer mixture (a2). When the surfactant is present in an amount of 0.1 part by mass or more, the storage stability of the aqueous coating material is improved, and the stability during polymerization is also improved. In addition, by setting the surfactant to 10 parts by mass or less, it is possible to maintain stability at the time of coating and blending, stability over time, and the like without impairing water resistance. A more preferable blending amount is 0.5 to 8 parts by mass.

  Examples of the surfactant include various known anionic, cationic or nonionic surfactants, and polymer emulsifiers. A reactive emulsifier having an ethylenically unsaturated bond in the surfactant component can also be used.

[Step 2]
In the step 2 of the present invention, the monomer mixture (a2) containing an acid group-containing ethylenically unsaturated monomer is added to the dispersion of the polymer obtained in the step 1, and emulsion polymerization is performed.

  By adding the monomer mixture (a2) containing an acid group-containing ethylenically unsaturated monomer to the dispersion liquid of the polymer obtained in step 1, the acid group is localized on the surface of the emulsion particles by emulsion polymerization. Therefore, the film formability at a low temperature is improved without lowering the water resistance.

  Examples of the acid group-containing ethylenically unsaturated monomer include (meth) acrylic acid, itaconic acid, citraconic acid, maleic acid, monomethyl maleate, monobutyl maleate, monomethyl itaconate, monobutyl itaconate, vinylbenzoic acid, Oxalic acid monohydroxyethyl (meth) acrylate, tetrahydrophthalic acid monohydroxyethyl (meth) acrylate, tetrahydrophthalic acid monohydroxypropyl (meth) acrylate, 5-methyl-1,2-cyclohexanedicarboxylic acid monohydroxyethyl (meth) acrylate , Monohydroxyethyl (meth) acrylate phthalate, monohydroxypropyl (meth) acrylate phthalate, monohydroxyethyl (meth) acrylate maleate, hydroxypropyl maleate (meth) acrylate Relate, tetrahydrophthalic acid mono-hydroxybutyl (meth) acrylate. These may be used individually by 1 type and may be used in combination of 2 or more type. Of these, methacrylic acid and acrylic acid are preferable in terms of water resistance and weather resistance.

  Examples of the monomer other than the acid group-containing ethylenically unsaturated monomer contained in the monomer mixture (a2) include the ethylenically unsaturated monomer exemplified in the ethylenically unsaturated monomer mixture (a1) in Step 1. A mer can be used.

  The acid group-containing ethylenically unsaturated monomer contained in the monomer mixture (a2) is 0.3% by mass of the total amount of the monomer mixture (a1) and the monomer mixture (a2). The content is preferably 1.8% by mass or less, more preferably 0.5% by mass or more and 1.5% by mass or less, and still more preferably 0.8% by mass or more and 1.2% by mass or less.

  When it is 0.3% by mass or more, the film formability at low temperature is good, and when it is 1.8% by mass or less, the water resistance is good.

  Furthermore, the mass ratio of the monomer mixture (a1) and the monomer mixture (a2) is preferably 40/60 to 70/30. If the monomer mixture (a1) is 40% by mass or more, the film formability at low temperatures and the elongation of the coating film at low temperatures are good, and if it is 70% by mass or less, the stain resistance and tackiness are good. It becomes good.

  The glass transition temperature (hereinafter referred to as Tg) obtained by the Fox formula of the polymer obtained by polymerizing the monomer mixture (a1) is preferably −20 ° C. or higher and 10 ° C. or lower. If the Tg is −20 ° C. or higher, the stain resistance and tackiness are good, and if it is 10 ° C. or lower, the film formability at low temperatures and the elongation of the coating film at low temperatures are good.

  Furthermore, Tg of the polymer obtained by polymerizing the monomer mixture (a2) is preferably 60 ° C. or higher and 90 ° C. or lower. When the Tg is 60 ° C. or higher, the stain resistance and tackiness are good, and when it is 90 ° C. or lower, the film formability at a low temperature and the elongation of the coating film at a low temperature are good.

  The glass transition temperature obtained from the Fox calculation formula is calculated by the following formula (1). As the glass transition temperature of the i-component homopolymer, standard analysis values described in “Polymer Handbook, J. Brandrup, Interscience, 1989” edited by Polymer Society of Japan were used. Table 1 shows literature values of Tg of typical homopolymers.

[Equation 1]
Tg: Glass transition temperature of copolymer (° C)
Tgi: Glass transition temperature of homopolymer of i component (° C.)
Wi: mass ratio of i component, ΣWi = 1

The polymerization in step 2 can be performed by known emulsion polymerization as in step 1.
[Step 3]
In step 3, the polymer dispersion obtained in step 2 is neutralized by holding at 40 ° C. or more and less than the boiling point of the polymer dispersion for 20 minutes or more.

  When the neutralization temperature is less than 40 ° C., the resulting coating film has insufficient water resistance, and when the temperature is higher than the boiling point of the polymer dispersion, the emulsion form cannot be stably maintained.

  Moreover, the water resistance of the coating film obtained becomes favorable because the holding time at the time of neutralizing shall be 20 minutes or more. In addition, the holding time is preferably 110 minutes or less from the viewpoint of film formability at a low temperature.

  From the viewpoint of the film formability at low temperature and the water resistance of the coating film, the neutralization temperature is preferably 45 ° C. or more and 65 ° C. or less, and the holding time is more preferably 40 minutes or more and 110 minutes or less.

  Examples of basic compounds used for neutralization include ammonia, triethylamine, propylamine, dibutylamine, amylamine, 1-aminooctane, 2-dimethylaminoethanol, ethylaminoethanol, 2-diethylaminoethanol, 1-amino-2- Propanol, 2-amino-1-propanol, 2-amino-2-methyl-1-propanol, 3-amino-1-propanol, 1-dimethylamino-2-propanol, 3-dimethylamino-1-propanol, 2- Examples include propylaminoethanol, ethoxypropylamine, aminobenzyl alcohol, morpholine, sodium hydroxide, and potassium hydroxide. Among these, a low-boiling basic compound having a low possibility of remaining in the coating film is preferable, and ammonia is preferable.

  As for the addition amount of the basic compound, it is preferable to add 0.5 to 1.2 molar equivalents of the basic compound with respect to the acid group of the acid group-containing ethylenically unsaturated monomer (a3). If it is 0.5 molar equivalent or more, the film formability and water resistance at low temperature are good, and if it is 1.2 molar equivalent or less, the ammonia odor during drying of the coating film is small and the workability is good. From the viewpoint of water resistance, 0.8 molar equivalent or more is more preferable.

  Further, the degree of neutralization obtained by the following formula (2) is preferably 45% or more from the viewpoint of storage stability of the emulsion, and more preferably 80% or more from the viewpoint of water resistance.

[Equation 2]
Degree of neutralization (%) = [Surface acid value (w) / Whole particle acid value (wa)] × 100 Formula (2)
The surface acid value (w) is an acid value measured using water that does not dissolve particles as a solvent, and the whole particle acid value (wa) is measured using a mixture of acetone: water = 8: 2 as a solvent. Acid value.

  Moreover, the average particle diameter by the cumulant analysis of the polymer emulsion of the present invention is preferably 100 nm or more and 140 nm or less. If it is 100 nm or more, the viscosity of the emulsion will not be too high, and if it is 140 nm or less, the transparency of the coating film will be good.

  The mass average molecular weight of the polymer emulsion of the present invention measured by gel permeation chromatography (GPC) is preferably 50,000 to 5,000,000. 100,000 or more are preferable from the viewpoint of durability of the coating film, and less than 4 million are preferable from the viewpoint of film formability.

[Coating composition containing polymer emulsion]
The polymer emulsion of the present invention comprises various pigments, antifoaming agents, pigment dispersants, leveling agents, anti-sagging agents, matting agents, ultraviolet absorbers, antioxidants, heat resistance improvers, slips as paint compositions. Various additives such as a preservative, preservative, and film-forming aid may be included, and may be used in a mixture with other emulsion resins, water-soluble resins, viscosity control agents, melamines and other curing agents.

  In particular, it is possible to add 5 to 50% by weight of a film-forming aid that has plasticity and softening properties to the copolymer component to the polymer. From the point of view, it is preferable.

  Examples of the film-forming aid include 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate and the like 2,2,4-trimethyl-1,3-pentanediol alkyl ethers; Monoethers such as (poly) ethylene glycol such as butyl ether or (poly) propylene glycol; Phthalic acid esters such as dibutyl phthalate; Carbitols such as diethylene glycol monoethyl ether, diethylene glycol monoethyl ether acetate, and diethylene glycol monobutyl ether Is mentioned. In particular, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate is preferable because of its excellent elasticity.

  These film-forming aids may be used alone or in combination of two or more.

  In order to form a coating film on the surface of various materials using the coating composition containing the polymer emulsion of the present invention, for example, spray coating method, roller coating method, bar coating method, air knife coating method, brush coating method, Various coating methods such as a dipping method can be appropriately selected, and a coating film sufficiently formed can be obtained by drying at room temperature or by heating to 40 to 200 ° C.

  In addition, after forming a coating film at room temperature or by drying at a low temperature of about 50 ° C., the coating between the emulsion particles is strengthened by heating above the glass transition temperature of the polymer to form a coating film with better weather resistance. You can also.

Hereinafter, the present invention will be described using examples. Evaluation methods and evaluation criteria in the examples are as follows.

(1) Degree of neutralization The surface acid value (w) and the whole particle acid value (wa) were measured and determined by the following formula (2).

[Equation 2]
Degree of neutralization (%) = [Surface acid value (w) / Whole particle acid value (wa)] × 100 Formula (2)
For the surface acid value (w), 2 g of the polymer emulsion was weighed (E) and diluted with 50 cc of water to prepare a measurement solution. Next, titration of 0.2 mol / l potassium hydroxide solution using an automatic acid value measuring device (automatic titrator AUTOTITRATOR COM-1600 manufactured by Hiranuma Sangyo Co., Ltd.) and titration of potassium hydroxide solution at the maximum potential difference displacement (K ) Using the following formula (3).

  The total particle acid value (wa) is the same as the measurement of the surface acid value (w) except that, in the surface acid value measurement method, the dilution solvent for preparing the measurement solution was changed to a mixed solvent of 10 cc of water / 40 cc of acetone. It was done by the method.

[Equation 3]
Surface acid value (w) (mg KOH / g) = [potassium hydroxide solution titration (K) × 56.1 × factor (F) × 0.2 / emulsion sample amount (E)] / [emulsion solid content (% ) × 0.01] Formula (3)
(2) The average particle size polymer emulsion by cumulant analysis is diluted with ion-exchanged water so as to have a solid content of 1%, and measured at room temperature using a particle size analyzer FPAR-1000 manufactured by Otsuka Electronics Co., Ltd. The average particle size is calculated by analysis.

(3) Minimum film forming temperature (MFT)
Using a MFT measuring device (Imoto Manufacturing Co., Ltd. Membrane Temperature Tester) with the temperature setting of the hot plate set to 0 ° C on the low temperature side and 50 ° C on the high temperature side, the polymer emulsion was coated on the hot plate with a 200 µm applicator It implemented according to the method of JISK6828 5.11.
MFT is preferably less than 20 ° C., more preferably less than 10 ° C., from the viewpoint of the appearance of the coating film.

(4) A polymer emulsion is coated on a water-resistant glass plate with a 150 μ applicator and dried at 60 ° C. for 4 hours to prepare a dry coating film. A black cloth for preventing light reflection is applied to the back surface of the prepared coating film, and the L value (L1) is measured using a color difference meter (Spectral Color Meter SE-2000, manufactured by Nippon Denshoku Co., Ltd.), and the whiteness standard before the test And Next, the coating film was immersed in ion-exchanged water at 50 ° C., the L value (L2) immediately after watering was measured after 12 hours, and ΔL obtained by subtracting L1 from L2 was calculated as the amount of change in whiteness.
[Judgment criteria for ΔL value]
Less than 4: Especially good water resistance Less than 6: Good water resistance Less than 7: Usable level 7 or more: Insufficient water resistance (Example 1)
In a 2-liter four-necked flask equipped with a thermometer, nitrogen gas introduction tube, stirring rod, dropping funnel, and cooling tube, 315 g of pure water and 11.2 g of SR-1025 (reactive emulsifier: manufactured by ADEKA Corporation) were added. Then, nitrogen gas was sufficiently passed through for 30 minutes to replace dissolved oxygen in pure water. After stopping nitrogen gas flow, the temperature was raised to 75 ° C. while stirring at 120 rpm. Here, 10.7 g of styrene, 2.9 g of methyl methacrylate, 3.2 g of t-butyl methacrylate, 18.2 g of 2-ethylhexyl acrylate (monomer mixture (a1-1)), SR-1025 (reactive emulsifier: ADEKA) Polymerization was carried out by adding 0.2 g of an emulsified dispersion obtained from 2.6 g and (13.9 g) pure water and ammonium persulfate dissolved in 7.0 g of pure water. Next, after confirming the polymerization exothermic peak, 1.5 g of ammonium persulfate dissolved in 35.0 g of pure water was added, and after 5 minutes 135.6 g of styrene, 36.3 g of methyl methacrylate, 40.9 g of t-butyl methacrylate, 2 -An emulsified dispersion obtained from 229.6 g of ethylhexyl acrylate (monomer mixture (a1-2)), SR-1025 (reactive emulsifier: manufactured by ADEKA) and 175.1 g of pure water for 2 hours The polymerization in step 1 was completed.

  After holding for 1 hour, styrene 65.8 g, methyl methacrylate 46.2 g, t-butyl methacrylate 67.9 g, 2-ethylhexyl acrylate 35.7 g, methacrylic acid 7 g (monomer mixture (a2)), SR- 1025 (Reactive emulsifier: ADEKA Co., Ltd.) 17.3 g and an emulsified dispersion obtained from 91 g of pure water were added dropwise over 2 hours to complete the polymerization in Step 2. After the completion of the dropping, 16.8 g of pure water was dropped to wash the emulsified dispersion liquid drop piping. Stirring was continued at 80 ° C. for 1 hour after the completion of dropping of pure water, and then 5.7 g of 28% aqueous ammonia solution was added and neutralized at 60 ° C. for 30 minutes to obtain an acid group-containing acrylic polymer emulsion. It was. The evaluation results of the resulting polymer emulsion are shown in Table 2.

St: styrene MMA: methyl methacrylate t-BMA: t-butyl methacrylate 2-EHA: 2-ethylhexyl acrylate MAA: methacrylic acid (Examples 2 to 6)
Examination was performed in the same manner as in Example 1 except that the neutralization conditions were changed as shown in Table 2. The evaluation results of the resulting polymer emulsion are shown in Table 2.

(Examples 7 and 8)
Except that the amount of the acid group-containing ethylenically unsaturated monomer and the neutralization conditions were changed as shown in Table 2, the examination was conducted in the same manner as in Example 1. The evaluation results of the resulting polymer emulsion are shown in Table 2.

(Comparative Examples 1 and 2)
Examination was performed in the same manner as in Example 1 except that the neutralization conditions were changed as shown in Table 2. The evaluation results of the resulting polymer emulsion are shown in Table 2.
In Comparative Example 1, the water resistance was insufficient because the retention time in neutralization was short.
In Comparative Example 2, the water resistance was insufficient due to the low neutralization temperature.

(Comparative Example 3)
The examination was performed under the same conditions as in Example 1 except that the neutralization temperature was 100 ° C.
Since the polymer dispersion boiled and polymer was ejected from the container, the investigation was stopped.

Claims (5)

A method for producing a polymer emulsion by performing the following steps 1 to 3.
Step 1: A step of emulsion polymerization of the ethylenically unsaturated monomer mixture (a1).
Step 2: A step of emulsion polymerization by adding a monomer mixture (a2) containing an acid group-containing ethylenically unsaturated monomer to the dispersion of the polymer obtained in Step 1.
Step 3: A step of neutralizing the dispersion of the polymer obtained in Step 2 above at 40 ° C. or more and less than the boiling point of the dispersion of the polymer for 20 minutes or more. The method for producing a polymer emulsion according to claim 1, wherein the polymer emulsion is neutralized at 45 ° C. or more and 65 ° C. or less in Step 3. The method for producing a polymer emulsion according to claim 1, wherein in Step 3, neutralization is carried out by maintaining for 40 minutes or more and 110 minutes or less. The polymer emulsion obtained by the method in any one of Claims 1-3. A coating composition comprising the polymer emulsion according to claim 4.