Aqueous dispersion, aqueous coating material, and plastic molded product having coating film of said aqueous coating material

Abstract

Provided is an aqueous dispersion that contains an aqueous medium (B) and an acrylic polymer (A) including, as essential raw materials, an alkyl (meth)acrylate (a1) that has an alkyl group having one or two carbon atoms, an isobornyl (meth)acrylate (a2), an unsaturated monomer (a3) having a hydroxyl group, and an unsaturated monomer (a4) having an acid radical. The aqueous dispersion is characterized in that, in monomer raw materials of the acrylic polymer (A), the amount of the alkyl (meth)acrylate (a1) is 20-50 mass%, the amount of the isobornyl (meth)acrylate (a2) is 20-60 mass%, the amount of the unsaturated monomer (a3) is 2-15 mass%, and the amount of the unsaturated monomer (a4) is 2-5 mass%. The aqueous dispersion has excellent storage stability and provides a coating film having excellent appearance, base material adhesiveness, hot water resistance, ethanol resistance, and sunscreen resistance. Thus, the aqueous dispersion is suitably used for an aqueous coating material and a plastic molded product having a coating film of the coating material.

Description

Aqueous dispersion, water-based paint, and plastic molded article having a coating film of the water-based paint

[0001] The present invention relates to an aqueous dispersion, a water-based paint, and a plastic molded article having a coating film of the water-based paint.

[0002] Plastic paints are paints that are applied to plastic surfaces to impart decorativeness and functionality in order to improve the commercial value of plastic molded products such as mobile phones, home appliances, office equipment, etc. Specifically, by applying plastic paints, it is possible to impart a multicolor finish, appearance, and texture not previously available on the surface of plastic molded products, and in terms of functionality, it is possible to impart resistance to wear, discoloration, sebum, high gloss, high weather resistance, electrical insulation, and other resistance properties.

[0003] Most of the paints currently used for plastics are solvent-based paints whose medium is composed of organic solvents, and since these paints release large amounts of organic solvents when they dry, they are not necessarily environmentally friendly. As a countermeasure to this, efforts are being made to make paints water-based by using water-based resins.

[0004] However, among water-based resins, water-based plastic paints using aqueous emulsions obtained by emulsion polymerization are inferior to solvent-based paints in terms of wettability and penetration into the surface of plastic molded products, and have problems with adhesion to plastic materials and resistance to hot water adhesion and hot water whitening due to the resin being in emulsion form.Furthermore, when plastic paints made from emulsions are applied to plastic surfaces, there are problems such as inferior gloss and vividness of the painted surface compared to solvent-based paints.

[0005] Against this background, a self-emulsifying aqueous resin composition that does not use an emulsifier has been developed (see, for example, Patent Document 1). This aqueous resin composition is obtained by dispersing in an aqueous medium a polymer having a glass transition temperature of 60°C or higher, which is obtained by solution polymerization of a mixture of unsaturated monomers containing, as essential components, a cycloalkyl(meth)acrylate, an unsaturated monomer having a carboxyl group, and an unsaturated monomer having a hydroxyl group. However, the composition has a problem of insufficient storage stability.

[0006] International Publication No. 2012 / 169395

[0007] The problem to be solved by the present invention is to provide an aqueous dispersion, an aqueous paint, and a plastic molded article having a coating film of the paint, which are excellent in storage stability, appearance, substrate adhesion, warm water resistance, ethanol resistance, and sunscreen resistance.

[0008] As a result of extensive research aimed at solving the above problems, the present inventors have found that an aqueous dispersion containing an acrylic polymer having a specific weight-average molecular weight and containing specific monomers as essential raw materials, and an aqueous medium, can give a coating film that is excellent in storage stability, appearance, substrate adhesion, warm water resistance, ethanol resistance, and sunscreen resistance, and have been completed based on this finding.

[0009] That is, the present invention relates to an aqueous dispersion containing an acrylic polymer (A) having, as essential raw materials, an alkyl(meth)acrylate (a1) having an alkyl group having 1 or 2 carbon atoms, isobornyl(meth)acrylate (a2), an unsaturated monomer (a3) ​​having a hydroxyl group, and an unsaturated monomer (a4) having an acid group, and an aqueous medium (B), wherein the alkyl(meth)acrylate (a1) is contained in the raw monomer materials for the acrylic polymer (A) at 20 to 50 mass%, the isobornyl(meth)acrylate (a2) is contained in 20 to 60 mass%, the unsaturated monomer (a3) ​​is contained in 2 to 15 mass%, and the unsaturated monomer (a4) is contained in 2 to 5 mass%, the weight average molecular weight of the acrylic polymer (A) is 1,000 to 40,000, and the glass transition temperature of the acrylic polymer (A) is 60 to 90°C.

[0010] The aqueous dispersion of the present invention can give a coating film that has excellent storage stability, appearance, substrate adhesion, warm water resistance, ethanol resistance, and sunscreen resistance, and therefore can be suitably used as a coating material for coating various articles such as the interior and exterior of various vehicles such as automobiles and railway cars, housings of electronic devices such as mobile phones, smartphones, tablet terminals, personal computers, digital cameras, and game consoles, housings of home appliances such as televisions, refrigerators, washing machines, and air conditioners, furniture, toys, interior decor, and 3D molded products.

[0011] The aqueous dispersion of the present invention contains an acrylic polymer (A) whose essential raw materials are an alkyl(meth)acrylate (a1) having an alkyl group having 1 or 2 carbon atoms, isobornyl(meth)acrylate (a2), an unsaturated monomer (a3) ​​having a hydroxyl group, and an unsaturated monomer (a4) having an acid group, and an aqueous medium (B). In the monomer raw materials of the acrylic polymer (A), the alkyl(meth)acrylate (a1) accounts for 20 to 50 mass%, the isobornyl(meth)acrylate (a2) accounts for 20 to 60 mass%, the unsaturated monomer (a3) ​​accounts for 2 to 15 mass%, and the unsaturated monomer (a4) accounts for 2 to 5 mass%, the weight average molecular weight of the acrylic polymer (A) is 1,000 to 40,000, and the glass transition temperature of the acrylic polymer (A) is 60 to 90°C.

[0012] First, the acrylic polymer (A) will be described. The acrylic polymer (A) can be obtained by copolymerizing an alkyl(meth)acrylate (a1) having an alkyl group with 1 or 2 carbon atoms, isobornyl(meth)acrylate (a2), an unsaturated monomer having a hydroxyl group (a3), an unsaturated monomer having a carboxyl group (a4), and, if necessary, other unsaturated monomers (a5).

[0013] In the present invention, the term "(meth)acrylate" refers to either or both of methacrylate and acrylate.

[0014] Examples of the alkyl (meth)acrylate (a1) having an alkyl group with 1 or 2 carbon atoms include methyl methacrylate, methyl acrylate, ethyl methacrylate, and ethyl acrylate, and among these, methyl methacrylate is preferred because the resulting coating film has better sunscreen resistance. These alkyl (meth)acrylates (a1) can be used alone or in combination of two or more.

[0015] Examples of the hydroxyl group-containing monomer (a3) ​​include 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxy-n-butyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxy-n-butyl (meth)acrylate, 3-hydroxy-n-butyl (meth)acrylate, 1,4-cyclohexanedimethanol mono(meth)acrylate, glycerin mono(meth)acrylate, polyoxyethylene mono(meth)acrylate, polyoxypropylene mono(meth)acrylate, polyoxybutylene mono(meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 2-(meth)acryloyloxyethyl-2-hydroxyethyl phthalate, polycaprolactone-modified hydroxyethyl mono(meth)acrylate, etc. Among these, 2-hydroxyethyl (meth)acrylate is preferred because the resulting coating film has better sunscreen resistance. These unsaturated monomers (a3) ​​can be used alone or in combination of two or more.

[0016] Examples of the carboxyl group-containing unsaturated monomer (a4) include unsaturated monocarboxylic acids such as (meth)acrylic acid, crotonic acid, β-carboxyethyl (meth)acrylate, ω-carboxy-polycaprolactone mono(meth)acrylate, 2-(meth)acryloyloxyethyl succinate, and 2-(meth)acryloyloxyethyl hexahydrophthalic acid; unsaturated dicarboxylic acids such as maleic acid, fumaric acid, and itaconic acid, and half esters of these unsaturated dicarboxylic acids. Among these, (meth)acrylic acid is preferred because the resulting coating film has excellent sunscreen resistance. Furthermore, these unsaturated monomers (a4) can be used alone or in combination of two or more.

[0017] The other unsaturated monomer (a5) is an unsaturated monomer other than the alkyl(meth)acrylate (a1), the isobornyl(meth)acrylate (a2), the unsaturated monomer (a3), and the unsaturated monomer (a4), and examples thereof include n-propyl(meth)acrylate, isopropyl(meth)acrylate, n-butyl(meth)acrylate, isobutyl(meth)acrylate, t-butyl(meth)acrylate, n-pentyl(meth)acrylate, n-hexyl(meth)acrylate, n-heptyl(meth)acrylate, n-octyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, cyclohexyl(meth)acrylate, nonyl(meth)acrylate, decyl(meth)acrylate, dodecyl(meth)acrylate, trimethylsilyl(meth)acrylate, methyl ... Examples of suitable acrylates include decyl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, behenyl (meth)acrylate, 4-tert-butylcyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate, benzyl (meth)acrylate, acrylamide, N,N-dimethyl (meth)acrylamide, (meth)acrylonitrile, 3-(meth)acryloyloxypropyltrimethoxysilane, N,N-dimethylaminoethyl (meth)acrylate, 2-(meth)acryloyloxyethyl acid phosphate, glycidyl (meth)acrylate, vinyl acetate, styrene, α-methylstyrene, p-methylstyrene, p-methoxystyrene, and diacrylate compounds such as ethylene glycol diacrylate. Among these, alkyl (meth)acrylates having an alkyl group having 3 to 20 carbon atoms and styrene are preferred because they provide a coating film with superior sunscreen resistance. These unsaturated monomers (a5) can be used alone or in combination of two or more.

[0018] The content of the alkyl (meth)acrylate (a1) in the unsaturated monomer raw material of the acrylic polymer (A) is 20 to 50 mass %, but 25 to 45 mass % is preferred because this further improves the balance of storage stability, water resistance, and sunscreen resistance.

[0019] The content of the isobornyl (meth)acrylate (a2) in the unsaturated monomer raw material of the acrylic polymer (A) is 20 to 60 mass %, but 30 to 50 mass % is preferred because this further improves the balance of storage stability, water resistance, solvent resistance, and sunscreen resistance.

[0020] The content of the unsaturated monomer (a3) ​​in the unsaturated monomer raw material of the acrylic polymer (A) is 2 to 15% by mass, and is preferably 8 to 12% by mass because this further improves adhesion to plastic substrates.

[0021] The content of the unsaturated monomer (a4) in the unsaturated monomer raw material for the acrylic polymer (A) is 2 to 5 mass %, and 2 to 4 mass % is preferred because this further improves the balance between water resistance and sunscreen resistance.

[0022] The content of the unsaturated monomer (a5) in the unsaturated monomer raw material of the acrylic polymer (A) is preferably 5 to 20% by mass, since this further improves the adhesion to plastic substrates.

[0023] The hydroxyl value of the acrylic polymer (A) is preferably from 8.5 to 65 mgKOH / g, more preferably from 35 to 55 mgKOH / g, in order to further improve the balance between solvent resistance and sunscreen resistance.

[0024] The acid value of the acrylic polymer (A) is preferably from 15 to 40 mgKOH / g, more preferably from 15 to 25 mgKOH / g, since this further improves the balance between water resistance and sunscreen resistance.

[0025] In the present invention, the acid value and hydroxyl value of the acrylic polymer are calculated from the composition of the monomers that are the raw materials.

[0026] The weight average molecular weight of the acrylic polymer (A) is 1,000 to 40,000, and is preferably 15,000 to 35,000, as this further improves the balance between solvent resistance and sunscreen resistance.

[0027] The average molecular weight in the present invention is a value calculated in terms of polystyrene based on measurements by gel permeation chromatography (hereinafter abbreviated as "GPC").

[0028] The glass transition temperature of the acrylic polymer (A) is 60 to 90° C., and is preferably 70 to 90° C., since this further improves water resistance, solvent resistance, and sunscreen resistance.

[0029] In the present invention, the glass transition temperature is calculated according to the FOX formula: 1 / Tg=W1 / Tg1+W2 / Tg2+... (Tg: glass transition temperature to be determined, W1: weight fraction of component 1, Tg1: glass transition temperature of homopolymer of component 1). The glass transition temperature values ​​of the homopolymers of each component are those described in "Adhesive Technology Handbook" published by Nikkan Kogyo Shimbun or "Polymer Handbook" published by Wiley-Interscience.

[0030] The acrylic polymer (A) can be produced by various methods, including, for example, a method in which an unsaturated monomer raw material is polymerized in an organic solvent using a polymerization initiator.

[0031] Examples of the organic solvent include aromatic hydrocarbon compounds such as toluene and xylene; alicyclic hydrocarbon compounds such as cyclohexane, methylcyclohexane, and ethylcyclohexane; ketone compounds such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; ester compounds such as ethyl acetate, n-butyl acetate, isobutyl acetate, and propylene glycol monomethyl ether acetate; alcohol compounds such as n-butanol, isopropyl alcohol, and cyclohexanol; glycol compounds such as ethylene glycol monobutyl ether, propylene glycol monomethyl ether, and diethylene glycol dimethyl ether; and aliphatic hydrocarbon compounds such as heptane, hexane, octane, and mineral turpentine. Among these, water-miscible organic solvents are preferred because they can be used as the aqueous medium (B) without further modification. These organic solvents can be used alone or in combination of two or more.

[0032] Examples of the polymerization initiator include ketone peroxide compounds such as cyclohexanone peroxide, 3,3,5-trimethylcyclohexanone peroxide, and methylcyclohexanone peroxide; 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(tert-butylperoxy)cyclohexane, n-butyl-4,4-bis(tert-butylperoxy)valerate, and 2,2-bis(4,4-ditert-butylperoxycyclohexyl)propane. Peroxyketal compounds such as 2,2-bis(4,4-ditert-amylperoxycyclohexyl)propane, 2,2-bis(4,4-ditert-hexylperoxycyclohexyl)propane, 2,2-bis(4,4-ditert-octylperoxycyclohexyl)propane, and 2,2-bis(4,4-dicumylperoxycyclohexyl)propane; hydroperoxide compounds such as cumene hydroperoxide and 2,5-dimethylhexane-2,5-dihydroperoxide; 1,3-bis(tert dialkyl peroxide compounds such as 2,5-dimethyl-2,5-di(tert-butylperoxy-m-isopropyl)benzene, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, diisopropylbenzene peroxide, tert-butylcumyl peroxide, and di-tert-butyl peroxide; diacyl peroxide compounds such as decanoyl peroxide, lauroyl peroxide, benzoyl peroxide, and 2,4-dichlorobenzoyl peroxide; bis(tert-butylcyclohexyl)peroxydicarbonyl peroxycarbonate compounds such as tert-butylperoxy-2-ethylhexanoate, tert-amylperoxy-2-ethylhexanoate, tert-butylperoxybenzoate, and peroxyester compounds such as 2,5-dimethyl-2,5-di(benzoylperoxy)hexane; and azo compounds such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methyl)butyronitrile, and 1,1'-azobis(cyclohexane-1-carbonitrile). These polymerization initiators can be used alone or in combination of two or more.

[0033] The aqueous medium (B) may be water, a hydrophilic organic solvent, or a mixture thereof. The hydrophilic organic solvent is preferably a water-miscible organic solvent that is miscible with water without separating, and more preferably an organic solvent having a solubility in water (the number of grams of organic solvent that dissolves in 100 g of water) of 3 g or more at 25° C. Examples of these water-miscible organic solvents include alcohol-based solvents such as methanol, ethanol, propanol, butanol, 1,3-butylene glycol-3-monomethyl ether (generic name: 3-methoxybutanol), and 3-methyl-3-methoxybutanol (product name: Solfit, manufactured by Kuraray Co., Ltd.); ketone-based solvents such as acetone and methyl ethyl ketone; and glycol ether-based solvents such as ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, ethylene glycol monoethyl ether, ethylene glycol diethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol dimethyl ether, diethylene glycol monoethyl ether, diethylene glycol diethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol dimethyl ether, propylene glycol monomethyl ether, propylene glycol dimethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, and dipropylene glycol dimethyl ether. These aqueous media (B) can be used alone or in combination of two or more.

[0034] The aqueous dispersion of the present invention is preferably one in which the acrylic polymer (A) is dispersed in the aqueous medium (B), and examples of a method for dispersing the acrylic polymer (A) in the aqueous medium (B) include a phase inversion emulsification method.

[0035] Examples of the phase inversion emulsification method include a method in which a basic compound is added to the acrylic polymer (A) to neutralize some or all of the acid groups in the acrylic polymer (A), and then water is added to disperse the acrylic polymer in water.

[0036] Examples of the basic compound include organic amines such as monoalkanolamines (e.g., methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, butylamine, dibutylamine, tributylamine, N,N-dimethylethanolamine, and 2-aminoethanol), diethanolamine, diisopropanolamine, and dibutanolamine; inorganic basic compounds (e.g., ammonia, sodium hydroxide, and potassium hydroxide); and quaternary ammonium hydroxides (e.g., tetramethylammonium hydroxide, tetra-n-butylammonium hydroxide, and trimethylbenzylammonium hydroxide). Among these, organic amines and ammonia (or aqueous ammonia) are preferred. These basic compounds can be used alone or in combination of two or more.

[0037] The amount of the basic compound used is preferably an amount such that the neutralization rate of the acid groups in the acrylic polymer (A) falls within the range of 50 to 100%, since this further improves the dispersibility and storage stability of the aqueous dispersion.

[0038] As each of the above-mentioned raw materials used in the aqueous dispersion of the present invention, biomass raw materials can also be used.

[0039] The average particle size of the particles formed by the acrylic polymer (A) in the aqueous dispersion of the present invention is preferably 50 to 200 nm, since this further improves the coating film appearance and adhesion to plastic substrates. Here, the average particle size in the present invention refers to a value measured by a method for determining particle size distribution based on the measurement principle of detecting dynamic scattered light from particles.

[0040] A curing agent can be added to the aqueous dispersion of the present invention when the coating material is formulated. Examples of the curing agent include polyisocyanate compounds, amino resins, epoxy compounds, oxazoline compounds, and carbodiimide compounds, with polyisocyanate compounds being preferred. These curing agents can be used alone or in combination of two or more.

[0041] Examples of the polyisocyanate compound include aromatic diisocyanate compounds such as tolylene diisocyanate, diphenylmethane diisocyanate, m-xylylene diisocyanate, and m-phenylenebis(dimethylmethylene)diisocyanate; and aliphatic or alicyclic diisocyanate compounds such as hexamethylene diisocyanate, lysine diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, 2-methyl-1,3-diisocyanatocyclohexane, 2-methyl-1,5-diisocyanatocyclohexane, 4,4'-dicyclohexylmethane diisocyanate, and isophorone diisocyanate.

[0042] Examples of the polyisocyanate compound that can be used include prepolymers having an isocyanate group obtained by subjecting the above diisocyanate compounds to an addition reaction with a polyhydric alcohol; compounds having an isocyanurate ring obtained by cyclotrimerizing the above diisocyanate compounds; polyisocyanate compounds having a urea bond or a biuret bond obtained by reacting the above diisocyanate compounds with water; homopolymers of acrylic monomers having an isocyanate group, such as 2-isocyanatoethyl (meth)acrylate, 3-isopropenyl-α,α-dimethylbenzyl isocyanate, and (meth)acryloyl isocyanate; and copolymers having an isocyanate group obtained by copolymerizing the above acrylic monomers having an isocyanate group with monomers such as other acrylic monomers, vinyl ester compounds, vinyl ether compounds, aromatic vinyl monomers, and fluoroolefins.

[0043] The polyisocyanate compound is preferably a water-dispersible polyisocyanate obtained by modifying the above-mentioned polyisocyanate compound, because when blended with the water dispersion of the present invention, it has excellent stability and curability and a high degree of freedom in terms of pot life.

[0044] The polyisocyanate compounds can be used alone or in combination of two or more kinds.

[0045] The amount of the polyisocyanate compound blended is preferably 0.5 to 2.0, more preferably 0.8 to 1.5, in terms of the equivalent ratio (NCO / OH) of the isocyanate groups in the polyisocyanate compound to the hydroxyl groups in the acrylic polymer (A), because a coating film with high strength can be obtained.

[0046] The urethanization reaction can be carried out in the presence of a urethanization catalyst to promote the reaction. Examples of the urethanization catalyst include amine compounds such as triethylamine, organotin compounds such as dibutyltin dioctate, dibutyltin dilaurate, dioctyltin dilaurate, octyltin trilaurate, dioctyltin dineodecanoate, dibutyltin diacetate, dioctyltin diacetate, and tin dioctylate, and organometallic compounds such as zinc octylate (zinc 2-ethylhexanoate).

[0047] The aqueous coating material of the present invention may contain additives other than those mentioned above, such as antifoaming agents, viscosity modifiers, light stabilizers, weather stabilizers, heat stabilizers, ultraviolet absorbers, antioxidants, leveling agents, pigment dispersants, thickeners, etc. Pigments such as titanium oxide, calcium carbonate, aluminum powder, copper powder, mica powder, iron oxide, carbon black, phthalocyanine blue, toluidine red, perylene, quinacridone, and benzidine yellow may also be used.

[0048] Examples of methods for applying the aqueous coating material of the present invention include spraying, applicators, bar coaters, gravure coaters, roll coaters, comma coaters, knife coaters, air knife coaters, curtain coaters, kiss coaters, shower coaters, wheeler coaters, spin coaters, dipping, screen printing, etc. After application, methods for forming a coating film include drying at room temperature to 120°C.

[0049] There are no particular limitations on the articles that can be coated with the aqueous coating material of the present invention, but because it has better adhesion to plastic substrates, preferred examples include the interior and exterior of various vehicles such as automobiles and railway cars, housings for electronic devices such as mobile phones, smartphones, tablet devices, personal computers, digital cameras and game consoles, housings for home appliances such as televisions, refrigerators, washing machines and air conditioners, furniture, interior decoration, and plastic molded articles such as 3D molded products.

[0050] The present invention will be described in more detail below with reference to specific examples. The average particle size was measured using a Nanotrac UPA-EX150 manufactured by Nikkiso Co., Ltd. The average molecular weight was measured under the following GPC measurement conditions.

[0051] [GPC Measurement Conditions] Measurement apparatus: High-speed GPC apparatus ("HLC-8220GPC" manufactured by Tosoh Corporation) Column: The following columns manufactured by Tosoh Corporation were used, connected in series: "TSKgel G5000" (7.8 mm I.D. x 30 cm) x 1 "TSKgel G4000" (7.8 mm I.D. x 30 cm) x 1 "TSKgel G3000" (7.8 mm I.D. x 30 cm) x 1 "TSKgel G2000" (7.8 mm I.D. x 30 cm) x 1 Detector: RI (differential refractometer) Column temperature: 40°C Eluent: tetrahydrofuran (THF) Flow rate: 1.0 mL / min Injection volume: 100 μL (tetrahydrofuran solution with a sample concentration of 4 mg / mL) Standard sample: A calibration curve was prepared using the following monodisperse polystyrene.

[0052] (Monodisperse polystyrene) "TSKgel Standard Polystyrene A-500" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene A-1000" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene A-2500" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene A-5000" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene F-1" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene F-2" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene F-4" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene F-10" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene F-20" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene F-40" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene F-80" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene F-128" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene F-288" manufactured by Tosoh Corporation "TSKgel Standard Polystyrene F-550" manufactured by Tosoh Corporation

[0053] Example 1: Production of aqueous dispersion (1) A reaction vessel equipped with a reflux condenser, a stirrer, a thermometer, a dropping funnel, and a nitrogen inlet tube was charged with 295.0 parts by mass of diethylene glycol dimethyl ether, and stirring was started, followed by heating to 135° C. Under a nitrogen stream, an unsaturated monomer mixture (I) consisting of 19.6 parts by mass of methyl methacrylate, 28.0 parts by mass of isobornyl methacrylate, 8.4 parts by mass of 2-hydroxyethyl methacrylate, 8.8 parts by mass of n-butyl acrylate, and 3.5 parts by mass of styrene, 4.2 parts by mass of a polymerization initiator (1) (tert-butylperoxy-2-ethylhexanoate), and 60.0 parts by mass of diethylene glycol dimethyl ether were continuously added dropwise to the reaction vessel over 2.5 hours. Subsequently, 8.4 parts by mass of methyl methacrylate, 12.0 parts by mass of isobornyl methacrylate, 3.6 parts by mass of 2-hydroxyethyl methacrylate, 2.5 parts by mass of acrylic acid, 3.8 parts by mass of n-butyl acrylate, and 1.5 parts by mass of styrene were added dropwise to an unsaturated monomer mixture (II), a polymerization initiator (2) (tert-butylperoxy-2-ethylhexanoate), and 45.0 parts by mass of diethylene glycol dimethyl ether over 1.5 hours. After stirring at the same temperature for 1.5 hours, the mixture was cooled to 95 ° C., and 25.0 parts by mass of dimethylethanolamine was added. 1071.4 parts by mass of ion-exchanged water was added, and the mixture was dispersed in water to obtain an aqueous dispersion (1) with a nonvolatile content of 44.0% by mass. The acrylic polymer in this aqueous dispersion (1) had an acid value of 19.5 mg KOH / g and a solids hydroxyl value of 51.7 mg KOH / g.

[0054] (Example 2: Production of aqueous dispersion (2)) An aqueous dispersion (2) having a nonvolatile content of 44.0 mass% was obtained in the same manner as in Example 1, except that the unsaturated monomer mixtures (I) and (II) were changed as shown in Table 1 and the polymerization initiator (1) was changed to 8.4 parts by mass and the polymerization initiator (2) was changed to 3.6 parts by mass. The acrylic polymer in this aqueous dispersion (2) had an acid value of 19.5 mgKOH / g and a hydroxyl value of 43.1 mgKOH / g.

[0055] (Example 3: Production of aqueous dispersion (3)) An aqueous dispersion (3) having a nonvolatile content of 44.0 mass% was obtained in the same manner as in Example 1, except that the unsaturated monomer mixtures (I) and (II) were changed as shown in Table 1. The acrylic polymer in this aqueous dispersion (3) had an acid value of 19.5 mgKOH / g and a hydroxyl value of 43.1 mgKOH / g.

[0056] (Example 4: Production of aqueous dispersion (4)) An aqueous dispersion (4) having a nonvolatile content of 44.0 mass% was obtained in the same manner as in Example 1, except that the unsaturated monomer mixtures (I) and (II) were changed as shown in Table 1. The acrylic polymer in this aqueous dispersion (4) had an acid value of 27.2 mgKOH / g and a hydroxyl value of 43.1 mgKOH / g.

[0057] (Example 5: Production of aqueous dispersion (5)) An aqueous dispersion (5) having a nonvolatile content of 44.0 mass% was obtained in the same manner as in Example 1, except that the unsaturated monomer mixtures (I) and (II) were changed as shown in Table 1. The acrylic polymer in this aqueous dispersion (5) had an acid value of 19.5 mgKOH / g and a hydroxyl value of 43.1 mgKOH / g.

[0058] Comparative Example 1: Production of Water Dispersion (R1) Water dispersion (R1) having a nonvolatile content of 44.0 mass% was obtained in the same manner as in Example 1, except that the unsaturated monomer mixtures (I) and (II) were changed as shown in Table 1. The acrylic polymer in this water dispersion (R1) had a solid content acid value of 19.5 mgKOH / g and a solid content hydroxyl value of 64.7 mgKOH / g.

[0059] Comparative Example 2: Production of Water Dispersion (R2) Water dispersion (5) having a nonvolatile content of 44.0 mass% was obtained in the same manner as in Example 1, except that the unsaturated monomer mixtures (I) and (II) were changed as shown in Table 1. The acrylic polymer in this water dispersion (R2) had a solid content acid value of 19.5 mg KOH / g and a solid content hydroxyl value of 64.7 mg KOH / g.

[0060] Comparative Example 3: Production of Water Dispersion (R3) Water dispersion (R3) having a nonvolatile content of 44.0 mass% was obtained in the same manner as in Example 1, except that the unsaturated monomer mixtures (I) and (II) were changed as shown in Table 1. The acrylic polymer in this water dispersion (R3) had a solid content acid value of 19.5 mgKOH / g and a solid content hydroxyl value of 43.1 mgKOH / g.

[0061] Comparative Example 4: Production of Water Dispersion (R4) Water dispersion (R4) having a nonvolatile content of 44.0 mass% was obtained in the same manner as in Example 1, except that the unsaturated monomer mixtures (I) and (II) were changed as shown in Table 1. The acrylic polymer in this water dispersion (R4) had a solid content acid value of 19.5 mgKOH / g and a solid content hydroxyl value of 43.1 mgKOH / g.

[0062] [Evaluation of storage stability] The aqueous dispersion obtained above was allowed to stand at 40°C for one month, and the state of the aqueous dispersion was evaluated according to the following criteria: A: Neither separation nor precipitation was observed B: Separation and / or precipitation was observed

[0063] The monomer compositions, property values, and evaluation results of the acrylic polymers of the aqueous dispersions (1) to (5) and (R1) to (R4) obtained above are shown in Tables 1 and 2.

[0064]

[0065]

[0066] The abbreviations in the table are as follows: MMA: methyl methacrylate IBOMA: isobornyl methacrylate β-HEMA: 2-hydroxyethyl methacrylate nBA: n-butyl acrylate 2-EHMA: 2-ethylhexyl methacrylate St: styrene

[0067] (Example 6: Preparation and evaluation of aqueous coating material (1)) 80 parts by mass of the water dispersion (1) obtained above and 11.6 parts by mass of a curing agent ("Burnoc DNW-5500" manufactured by DIC Corporation, a water-dispersible polyisocyanate with a non-volatile content of 80% by mass) were mixed by stirring, and the mixture was diluted with ion-exchanged water to a viscosity of 15 seconds (23°C) measured using a "Viscosity Cup NK-2" manufactured by Anest Iwata Corporation, to prepare an aqueous coating material (1). Next, the following coating film evaluation was carried out using the obtained aqueous coating material (1).

[0068] (Examples 7 to 11: Preparation and evaluation of water-based paints (2) to (6)) Water-based paints (2) to (6) were prepared in the same manner as in Example 1, except that the formulations were changed as shown in Table 3, and then the coating films of each paint were evaluated.

[0069] (Comparative Examples 5 to 8: Preparation and Evaluation of Water-Based Paints (R1) to (R4)) Water-based paints (R1) to (R4) were prepared in the same manner as in Example 1, except that the formulation was changed as shown in Table 3, and then the coating film of each paint was evaluated.

[0070] [Preparation of coating film for evaluation] The water-based paint obtained above was applied to an ABS (acrylonitrile-butadiene-styrene copolymer) plate and a PC (polycarbonate) plate using a spray gun so that the dry film thickness was 25 μm. Then, the coating was subjected to a heat drying treatment at 80°C for 30 minutes in a dryer, and then aged at 23°C for 7 days to prepare a coating film for evaluation.

[0071] [Evaluation of Coating Appearance] The coating surface of the evaluation coating (ABS plate) obtained above was visually observed, and the coating appearance was evaluated according to the following criteria: A: Transparent, with no whitening, cracking, or foreign matter. B: Whitening, cracking, or foreign matter.

[0072] [Evaluation of Adhesion to Substrate] The coating films for evaluation obtained above were subjected to a cross-cut test (1 mm, 100 squares, 4 directions) in accordance with JIS K 5600-5-6, and the coating films were visually observed to evaluate the adhesion to the substrate according to the following criteria. 5B is the best rating. 5B: No defects 4B: Defective areas within 5% 3B: Defective areas greater than 5% and less than 15% 2B: Defective areas greater than 15% and less than 35% 1B: Defective areas greater than 35% and less than 65% 0B: Defective areas greater than 65%

[0073] [Evaluation of Warm Water Resistance (Whitening)] The coating film (ABS plate) obtained above for evaluation was immersed in tap water heated to 50°C for 48 hours, and the coating film surface was visually observed and evaluated for warm water resistance (whitening) according to the following criteria: A: No whitening B: Whitening

[0074] [Evaluation of Warm Water Resistance (Adhesion)] The coating film for evaluation obtained above was immersed in tap water heated to 50°C for 36 hours, and a cross-cut test (1 mm, 100 squares, 4 directions) was performed in accordance with JIS K 5600-5-6. The coating film was visually observed and the warm water resistance (adhesion) was evaluated according to the following criteria. 5B is the best rating. 5B: No defects 4B: Defects within 5% 3B: Defects greater than 5% and less than 15% 2B: Defects greater than 15% and less than 35% 1B: Defects greater than 35% and less than 65% 0B: Defects greater than 65%

[0075] [Evaluation of Sunscreen Resistance] The coating film (ABS plate) for evaluation obtained above was cut to a size of 50 mm x 70 mm, and a sunscreen cream ("Coppertone Sports Ultra Sweatproof SPF30" manufactured by SSL Healthcare Japan Inc.) was uniformly applied to the coating film (0.5 g / 100 cm ２ ) and then dried at 55°C for 4 hours. After drying, the sunscreen cream was washed with a neutral detergent ("Cucute" manufactured by Kao Corporation), the coating film was visually inspected, and the sunscreen resistance was evaluated according to the following criteria: A: No marks left B: Marks left on part of the coating film C: Marks left on the entire coating film

[0076] [Evaluation of Ethanol Resistance] A felt (manufactured by Valqua Corporation, width 10 mm x height 10 mm x depth 40 mm) soaked in ethanol (95% or more, first-grade reagent) was pressed against the coating film (ABS plate) for evaluation obtained above, and a rubbing test was performed in which the felt was rubbed back and forth up to 500 times while applying a load of 1 kg. The state of the coating film after rubbing was visually observed, and the ethanol resistance was evaluated according to the following criteria depending on the number of times until the bare ABS substrate was visible. A: More than 500 times B: More than 250 times but not more than 500 times C: Not more than 250 times

[0077] The formulations and evaluation results of the water-based paints (1) to (6) and (R1) to (R4) obtained above are shown in Tables 3 and 4.

[0078]

[0079]

[0080] It was confirmed that the aqueous dispersions of Examples 1 to 5 had excellent storage stability, and the resulting coating films had excellent appearance, substrate adhesion, warm water resistance, ethanol resistance, and sunscreen resistance.

[0081] In Comparative Example 1, the glass transition temperature of the acrylic polymer exceeded the upper limit of the present invention, but it was confirmed that the appearance and substrate adhesion of the resulting coating film were insufficient.

[0082] Comparative Example 2 is an example in which the amount of alkyl (meth)acrylate (a1) having an alkyl group with 1 or 2 carbon atoms in the monomer raw material of the acrylic polymer is less than the lower limit of the present invention, and it was confirmed that the appearance, substrate adhesion and sunscreen resistance of the resulting coating film were insufficient.

[0083] Comparative Example 3 is an example in which the amount of isobornyl (meth)acrylate (a2) in the monomer raw material of the acrylic polymer was less than the lower limit of the present invention, but it was confirmed that the storage stability was insufficient and the appearance of the resulting coating film was unsatisfactory.

[0084] Comparative Example 4 is an example in which the amount of isobornyl (meth)acrylate (a2) in the monomer raw material of the acrylic polymer is greater than the upper limit of the present invention, and it was confirmed that the storage stability was insufficient and the sunscreen resistance of the resulting coating film was insufficient.

Claims

1. An aqueous dispersion containing an acrylic polymer (A) having as essential raw materials an alkyl (meth)acrylate (a1) having an alkyl group with 1 or 2 carbon atoms, isobornyl (meth)acrylate (a2), an unsaturated monomer having a hydroxyl group (a3), and an unsaturated monomer having an acid group (a4), and an aqueous medium (B), wherein the alkyl (meth)acrylate (a1) is 20 to 50 mass%, the isobornyl (meth)acrylate (a2) is 20 to 60 mass%, the unsaturated monomer (a3) ​​is 2 to 15 mass%, and the unsaturated monomer (a4) is 2 to 5 mass%, the weight average molecular weight of the acrylic polymer (A) is 1,000 to 40,000, and the glass transition temperature of the acrylic polymer (A) is 60 to 90°C.

2. The aqueous dispersion according to claim 1, wherein the average particle size of the particles formed from the acrylic polymer (A) is 50 to 200 nm.

3. A water-based paint containing the water dispersion according to claim 1 or 2.

4. A plastic molded product having a coating film of the water-based paint according to claim 3.

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