JP4676165B2 - Water-based coating composition and multilayer coating film forming method - Google Patents

Description

  The present invention relates to an aqueous coating composition that is excellent in chipping resistance, finish, and the like, has a low solvent amount and a high solid content concentration, and a method for forming a multilayer coating film using the aqueous coating composition.

  In recent years, there has been a great interest in environmental issues on a global scale, but the automobile industry is also actively working on environmental improvement in the production process. The automobile manufacturing process has problems such as global warming, industrial waste, and volatile organic solvent (VOC) emissions, and most of the VOC is generated from the painting process. Has become an urgent need.

The outer plate part of an automobile body is usually coated with a multilayer coating film composed of a primer coating film, an intermediate coating film and a top coating film with a cationic electrodeposition coating for the purpose of providing corrosion protection and aesthetics.
From the viewpoint of VOC reduction, water-based coatings are also being promoted in intermediate coatings and top coatings.

  In addition, automobile coatings are also required to have excellent damage resistance (referred to as “chipping resistance”) due to running stone splashes, etc. Plays an important role.

  So far, as an aqueous intermediate coating material excellent in chipping resistance, for example, an aqueous intermediate coating composition characterized by containing a specific talc and a silane coupling agent has been proposed (for example, Patent Document 1). ).

  However, the level of chipping resistance of the coating film obtained from the aqueous intermediate coating composition is insufficient.

  In addition, as a method of forming a chipping-resistant coating film using a water-based paint that can cope with VOC reduction, a water-based chipping primer and a melamine curable polyester-based water-based intermediate paint are applied wet-on-wet. A method for forming a chipping-resistant composite coating film characterized by curing at the same time has also been proposed (for example, Patent Document 2).

  However, the coating film forming method involves repeatedly applying a chipping primer and a water-based intermediate coating, and includes a chipping primer, and thus has a problem in terms of shortening the coating process.

Japanese Patent Laid-Open No. 2003-253211 JP-A-11-33478

  An object of the present invention is an aqueous coating composition that is excellent in chipping resistance, finish, and the like, and that can achieve a low solvent amount and a high solid content concentration, and a coating process for an aqueous intermediate coating and top coating It is to find a method for forming a multilayer coating film that enables shortening of the film.

  As a result of intensive studies, the present inventors have found that an anionic urethane resin emulsion (A) having a particle size of less than 100 nm, an acid value of 20 to 50 mgKOH / g, and a number average molecular weight of 5,000 or more. ) And an anionic urethane resin (B) having a number average molecular weight of less than 5,000 and a linear molecular structure as an essential component, the above-mentioned problems are solved. The present inventors have found that this can be done and have completed the present invention.

That is, the present invention provides: An anionic urethane resin emulsion (A) having a particle size of less than 100 nm, an acid value of 20 to 50 mgKOH / g, and a number average molecular weight of 5,000 or more, and a number average molecular weight of less than 5,000, and An aqueous coating composition characterized by containing an anionic urethane resin (B) having a linear molecular structure as an essential component;
2. Item 2. The aqueous coating composition according to Item 1, further comprising a hydroxyl group-containing resin (C), a crosslinking agent (D), and a pigment (E).
3. The aqueous coating composition according to Item 1 or 2, further comprising a polyolefin emulsion (F),
4). Item 1 to 3 in which the total solid weight of the anionic urethane resin emulsion (A) and the anionic urethane resin (B) is 1 to 80 parts by weight with respect to 100 parts by weight of the total resin solids in the paint. The water-based paint composition according to any one of
5. Process 1: Water-based paint of any one of claim | item 1 thru | or 4 without apply | coating a chipping primer on the electrodeposition coating film formed on electrodeposition coating on a metal coating or a metal coating Applying the composition to form an uncured coating or baking and drying the coating to form a cured coating, and Step 2: to the uncured coating or cured coating obtained in Step 1, A method for forming a multi-layer coating film comprising a step of coating one or more layers of a top coating to form a top coating film and baking and curing;
It is related to.

  The water-based coating composition of the present invention has a number average particle size of less than 100 nm, an acid value of 20 to 50 mgKOH / g, and a number average molecular weight of 5,000 or more and an anionic urethane resin emulsion (A). Since the anionic urethane resin (B) having a molecular weight of less than 5,000 and a linear molecular structure is an essential component, it has a low solvent amount and a high solid content concentration. In addition, it is possible to obtain a coating film having excellent finish and chipping resistance. In addition, after applying the aqueous coating composition of the present invention, by applying the top coating without curing, it is possible to shorten the process in the multilayer coating film forming step of the intermediate coating and the top coating Play.

  Hereinafter, the aqueous coating composition and the multilayer coating film forming method of the present invention will be described in detail.

  The aqueous coating composition of the present invention comprises an anionic urethane resin emulsion (A) and an anionic urethane resin (B) as essential components.

Anionic urethane resin emulsion (A)
The anionic urethane resin emulsion (A) in the present invention is an anionic urethane resin emulsion having a particle diameter of less than 100 nm, an acid value of 20 to 50 mgKOH / g, and a number average molecular weight of 5,000 or more. .

  In order to obtain an anionic urethane resin emulsion in the present invention, an isocyanate-terminated prepolymer is first synthesized by reacting a polyisocyanate with a polyol and an active hydrogen group-containing compound having an anionic group by a conventional method.

  The polyisocyanate is not particularly limited, and is usually used for the production of polyurethane and the like, for example, aliphatic polyisocyanate, alicyclic polyisocyanate, araliphatic polyisocyanate, aromatic polyisocyanate, and these polyisocyanates. And derivatives thereof.

  Examples of the aliphatic polyisocyanate include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, 1,2-butylene diisocyanate, 2,3-butylene diisocyanate, 1,3- Aliphatic diisocyanates such as butylene diisocyanate, 2,4,4- or 2,2,4-trimethylhexamethylene diisocyanate, 2,6-diisocyanatomethylcaproate, such as lysine ester triisocyanate, 1,4,8- Triisocyanatooctane, 1,6,11-triisocyanatoundecane, 1,8-diisocyanato-4-isocyanatomethyloctane, 1,3,6-triisocyanatohexane, 2 5,7 and aliphatic triisocyanates such as trimethyl-1,8-diisocyanato-5-isocyanatomethyl octane and the like.

  Examples of the alicyclic polyisocyanate include 1,3-cyclopentene diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (common name: Isophorone diisocyanate), 4,4'-methylenebis (cyclohexyl isocyanate), methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 1,3- or 1,4-bis (isocyanatomethyl) cyclohexane ( Common name: hydrogenated xylylene diisocyanate) or mixtures thereof, alicyclic diisocyanates such as norbornane diisocyanate, for example 1,3,5-triisocyanatocyclohexane, 1, , 5-trimethylisocyanatocyclohexane, 2- (3-isocyanatopropyl) -2,5-di (isocyanatomethyl) -bicyclo (2.2.1) heptane, 2- (3-isocyanatopropyl) -2 , 6-Di (isocyanatomethyl) -bicyclo (2.2.1) heptane, 3- (3-isocyanatopropyl) -2,5-di (isocyanatomethyl) -bicyclo (2.2.1) heptane 5- (2-isocyanatoethyl) -2-isocyanatomethyl-3- (3-isocyanatopropyl) -bicyclo (2.2.1) heptane, 6- (2-isocyanatoethyl) -2-isocyanate Natomethyl-3- (3-isocyanatopropyl) -bicyclo (2.2.1) heptane, 5- (2-isocyanatoethyl) -2-isocyanatomethyl-2- (3-isocyana Propyl) -bicyclo (2.2.1) -heptane, 6- (2-isocyanatoethyl) -2-isocyanatomethyl-2- (3-isocyanatopropyl) -bicyclo (2.2.1) heptane, etc. And alicyclic triisocyanate.

  Examples of the araliphatic polyisocyanate include 1,3- or 1,4-xylylene diisocyanate or a mixture thereof, ω, ω′-diisocyanato-1,4-diethylbenzene, 1,3- or 1,4-bis ( 1-isocyanato-1-methylethyl) benzene (common name: tetramethylxylylene diisocyanate) or an aromatic aliphatic diisocyanate such as a mixture thereof, for example, an araliphatic triisocyanate such as 1,3,5-triisocyanatomethylbenzene Etc.

  Examples of the aromatic polyisocyanate include m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4′-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, 2,4′- or 4,4′-diphenylmethane diisocyanate or a mixture thereof. 2,4- or 2,6-tolylene diisocyanate or mixtures thereof, aromatic diisocyanates such as 4,4′-toluidine diisocyanate, 4,4′-diphenyl ether diisocyanate, for example, triphenylmethane-4,4 ′, 4 Aromatic triisocyanates such as '' '-triisocyanate, 1,3,5-triisocyanatobenzene, 2,4,6-triisocyanatotoluene, such as 4,4'-diphenylmethane-2,2', 5 , 5'- Or the like can be mentioned aromatic tetracarboxylic isocyanates such as tiger isocyanate.

  Examples of the polyisocyanate derivative include the above-mentioned polyisocyanate dimer, trimer, biuret, allophanate, carbodiimide, uretdione, oxadiazine trione, polymethylene polyphenyl polyisocyanate (crude MDI, polymeric MDI), and crude TDI. Can give.

  These polyisocyanates may be used alone or in combination of two or more. Of these polyisocyanates, aliphatic diisocyanates and alicyclic diisocyanates are preferable.

  The polyol is not particularly limited, and a compound usually used for production of polyurethane or the like and having two or more hydroxyl groups in one molecule can be used. Specific examples include polyether polyol, polyester polyol, polycarbonate polyol, polybutadiene polyol, hydrogenated polybutadiene polyol, and the like. More specifically, examples of the polyether polyol include polypropylene glycol, poly (ethylene / propylene) glycol, polytetramethylene glycol, and poly (ethylene / tetramethylene) glycol.

  Polyester polyols include those obtained by polycondensation of low molecular weight diols and dibasic acids, and polyester polyols obtained by ring-opening reaction of lactone compounds using low molecular weight diols as initiators. , Ethylene glycol, propanediol, 1,4-butylene glycol, 1,3-butylene glycol, 1,2-butylene glycol, 1,6-hexanediol, neopentyl glycol, alkane (C7 to C22) diol, diethylene glycol, tri Ethylene glycol, propylene glycol, dipropylene glycol, cyclohexanedimethanol, alkane-1,2-diol (C17-C20), hydrogenated bisphenol A, 1,4-dihydroxy-2-butene, 2,6-dimethyl-1- Octene-3, - diol, bishydroxyethoxybenzene, xylene glycol, include low molecular weight diols such as bis-hydroxy ethylene terephthalate, adipic acid as the dibasic acid, azelaic acid, sebacic acid, isophthalic acid, and terephthalic acid. A low molecular diol and a dibasic acid are each used individually or in combination of 2 or more types. In the latter case, examples of the lactone compound include ε-caprolactone and poly β-methyl-δ-valerolactone.

  Examples of the polycarbonate polyol include mixed diol polycarbonate polyols such as 3-methyl-1,5-pentanediol / 1,6-hexanediol polycarbonate polyol.

  Other polyols include silicone polyols and castor oil-based polyols. In addition to the polyol, if necessary, the low molecular weight diol, glycerin, 2-methyl-2-hydroxymethyl-1,3-propanediol, 2,4-dihydroxy-3-hydroxymethylpentane, 1,2, Low molecular weight triols such as 6-hexanetriol, trimethylolpropane, 2,2-bis (hydroxymethyl) -3-butanol, and other aliphatic triols (C8-24), or tetramethylolmethane, D-sorbitol, xylitol It is also possible to use a low molecular weight polyol having four or more hydroxyl groups, such as D-mannitol and D-mannitol.

  The said low molecular weight polyol may be used independently and may be used together 2 or more types. Of these low molecular weight polyols, those having a number average molecular weight of 62 to 500 are preferred, and low molecular weight diols and low molecular weight triols can be suitably used.

  The above polyols can be used alone or in combination. The number average molecular weight of the polyol (measured by gel permeation chromatography and determined in terms of polystyrene. The same applies to the molecular weight measurement method hereinafter) is 500 to 5,000 from the viewpoint of coating film performance, dispersion stability, and the like. Is more preferable, and 500 to 3,000 is more preferable.

  The active hydrogen group-containing compound having an anionic group has an anionic group such as a betaine structure-containing group such as a carboxyl group, a sulfonyl group, a phosphate group, or a sulfobetaine, and can react with an isocyanate group. For example, it is a compound containing an active hydrogen group such as a hydroxyl group or an amino group.

  By incorporating the compound into the urethane resin skeleton, hydrophilicity can be imparted to the urethane resin, and the urethane resin can be dispersed in water.

  Although it does not restrict | limit especially as an active hydrogen group containing compound which has such an anionic group, The compound which has one anionic group and has two or more active hydrogen groups is mentioned. More specifically, examples of the active hydrogen group-containing compound having a carboxyl group include 2,2-dimethylol acetic acid, 2,2-dimethylol lactic acid, 2,2-dimethylol propionic acid, and 2,2-dimethylol butanoic acid. Dihydroxyl carboxylic acids such as dimethylol heptanoic acid, dimethylol nonanoic acid, 2,2-dimethylol butyric acid, 2,2-dimethylol valeric acid, such as 1-carboxy-1,5-pentylenediamine, dihydroxybenzoic acid, Examples thereof include diaminocarboxylic acids such as 3,5-diaminobenzoic acid, lysine and arginine, and half ester compounds of polyoxypropylene triol with maleic anhydride and phthalic anhydride.

  Examples of the active hydrogen group-containing compound having a sulfonyl group include N, N-bis (2-hydroxyethyl) -2-aminoethanesulfonic acid, 1,3-phenylenediamine-4,6-disulfonic acid, and diaminobutane. Examples include sulfonic acid, 3,6-diamino-2-toluenesulfonic acid, and 2,4-diamino-5-toluenesulfonic acid.

  Examples of the active hydrogen group-containing compound having a phosphate group include 2,3-dihydroxypropylphenyl phosphate.

  Examples of the active hydrogen group-containing compound having a betaine structure-containing group include a sulfobetaine group-containing compound obtained by reaction of a tertiary amine such as N-methyldiethanolamine with 1,3-propane sultone.

  Furthermore, the alkylene oxide modified body obtained by adding alkylene oxides, such as ethylene oxide and a propylene oxide, to the active hydrogen group containing compound which has these anionic groups can also be mentioned.

  These active hydrogen group-containing compounds having an anionic group may be used alone or in combination of two or more. Of these active hydrogen group-containing compounds having an anionic group, an active hydrogen group-containing compound having a carboxyl group can be suitably used.

  Moreover, in the synthesis | combination of an isocyanate terminal prepolymer, it is also possible to use low molecular weight polyamine together. Examples of the low molecular weight polyamine include ethylenediamine, propylenediamine, hexamethylenediamine, hydrazine, 1,2-diaminoethane, 1,2-diaminopropane, 1,3-diaminopentane, 1,6-diaminohexane, diaminotoluene, Low molecular weight diamines such as bis- (4-aminophenyl) methane and bis- (4-amino-3-chlorophenyl) methane, and diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, 2,2′- Examples thereof include low molecular weight amines having three or more amino groups such as diaminodiethylamine.

  The said low molecular weight polyamine may be used independently and may be used together 2 or more types. Of these low molecular weight polyamines, those having a number average molecular weight of 62 to 500 can be suitably used.

  The synthesis of the isocyanate-terminated prepolymer can be carried out by a known method. Specifically, for example, the above-mentioned polyisocyanate, polyol, and active hydrogen group-containing compound having an anionic group are converted into active hydrogen groups (hydroxyl groups). And an amino group) in an equivalent ratio of isocyanate group to (isocyanate group / active hydrogen group), preferably in a ratio of 1.1 to 10, and by a known polymerization method such as bulk polymerization or solution polymerization. What is necessary is just to make it react.

  In bulk polymerization, for example, a polyisocyanate is stirred under a nitrogen stream, and a polyol, an active hydrogen group-containing compound having an anionic group, and a low molecular weight polyol and / or a low molecular weight polyamine as necessary are added thereto. The reaction may be performed at a reaction temperature of 75 to 85 ° C. for about several hours.

  In solution polymerization, polyisocyanate, polyol, an active hydrogen group-containing compound having an anionic group, and, if necessary, a low molecular weight polyol and / or a low molecular weight polyamine are added to an organic solvent at a reaction temperature of 20 to 80 ° C. It is sufficient to react for about an hour. As the organic solvent, a low-boiling solvent that is inert with respect to an isocyanate group, is rich in hydrophilicity, and can be easily removed can be used. Examples thereof include acetone, methyl ethyl ketone, ethyl acetate, and tetrahydrofuran. In the present invention, solution polymerization that allows easier adjustment of reactivity and viscosity is preferably used.

  Further, in the above reaction, for example, a known urethanization catalyst such as an amine-based, tin-based, or lead-based catalyst may be used, and an unreacted monomer of polyisocyanate is obtained from the resulting isocyanate-terminated prepolymer. For example, you may remove using well-known removal means, such as distillation and extraction.

  Furthermore, in the synthesis of this isocyanate-terminated prepolymer, for example, trimethylamine, triethylamine, tri-n-propylamine, tributylamine, monoethanolamine, diethanolamine, triethanolamine, triethylenediamine, dimethylaminoethanol before or after the reaction. Neutralizing so that anionic groups form salts by adding amines such as alkali metal hydroxides such as potassium hydroxide and sodium hydroxide, and other neutralizing agents such as ammonia. Is preferred. The amount of such neutralizing agent added is, for example, preferably 0.4 to 1.2 equivalents, and more preferably 0.6 to 1.0 equivalents per equivalent of anionic group.

  The isocyanate group content in the isocyanate-terminated prepolymer is preferably in the range of 0.2 to 4.5% by weight, more preferably 0.5 to 3.0% by weight.

  And the anionic urethane resin emulsion which is (A) component in this invention can be synthesize | combined by making the said isocyanate terminal prepolymer obtained then react with a chain extender in water. Thus, an anionic urethane resin emulsion in which the isocyanate-terminated prepolymer is chain-extended by the chain extender and dispersed in water can be obtained.

  The chain extender has two or more active hydrogens capable of reacting with the terminal isocyanate group of the urethane prepolymer in the molecule, and reacts with the terminal of the urethane prepolymer to form a high molecular weight urethane resin.

  As the chain extender, known ones can be used, and examples thereof include polyamines and amino alcohols.

  The polyamine is not particularly limited as long as it is a compound having two or more amino groups. For example, ethylenediamine, 1,3-propanediamine, 1,4-butanediamine, 1,6-hexamethylenediamine, 1 , 4-cyclohexanediamine, 3-aminomethyl-3,5,5-trimethylcyclohexylamine, piperazine, 2,5-dimethylpiperazine, isophoronediamine, 4,4'-cyclohexylmethanediamine, norbornanediamine, hydrazine, diethylenetriamine, tri Examples thereof include ethylene triamine, 1,3-bis (aminomethyl) cyclohexane, xylylenediamine and the like.

  Examples of amino alcohols include hydroxyethyl hydrazine, hydroxyethyl diethylene triamine, N- (2-aminoethyl) ethanolamine, 3-aminopropanediol, and the like.

  The chain extenders may be used alone or in combination of two or more.

  The polyamines may be in a form masked as a compound such as ketimine, ketazine, or amine salt.

  In order to react the isocyanate-terminated prepolymer and the chain extender in water, for example, first, water is added to the isocyanate-terminated prepolymer and the isocyanate-terminated prepolymer is dispersed in water, and then the chain extension is performed. An agent may be blended and the isocyanate-terminated prepolymer may be subjected to a chain extension reaction with a chain extender.

  The blending of water is carried out while stirring the isocyanate-terminated prepolymer at a blending amount capable of dispersing the isocyanate-terminated prepolymer, for example, 20 to 500 parts by weight with respect to 100 parts by weight of the isocyanate-terminated prepolymer. On the other hand, it is preferable to add it slowly, whereby an isocyanate-terminated prepolymer aqueous dispersion in which the isocyanate-terminated prepolymer is dispersed in water can be prepared.

  Next, in the blending of the chain extender, the equivalent ratio of the isocyanate group of the isocyanate-terminated prepolymer to the active hydrogen group of the chain extender (isocyanate group / active hydrogen group) is, for example, a ratio of 0.8 to 1.2. In such a blending amount, the aqueous solution of the isocyanate-terminated prepolymer may be dripped quickly (while the reaction between the isocyanate group of the isocyanate-terminated prepolymer and water does not proceed) while stirring the aqueous dispersion of the isocyanate-terminated prepolymer. The dropping of the chain extender is preferably performed at a temperature of 30 ° C. or less. After the dropping is completed, the reaction may be completed at room temperature, for example, while stirring. By such a chain extension reaction, the isocyanate-terminated prepolymer is chain extended by a chain extender, and an anionic urethane resin emulsion can be obtained.

  The organic solvent in the anionic urethane resin emulsion can be removed by heating at an appropriate temperature under reduced pressure, for example, after the completion of the reaction, as necessary.

  Moreover, in order to improve stability, surfactant can be mix | blended in the anionic urethane resin emulsion in the range which does not inhibit water resistance.

  The surfactant is not particularly limited. For example, anionic surfactants such as fatty acid salts, alkyl sulfate esters, alkylbenzene sulfonates, alkyl naphthalene sulfonates, alkyl sulfosuccinates, and polyoxyethylene alkyl sulfate esters. Agents such as polyoxyethylene alkyl ethers, polyoxyalkylene alkyl ethers, polyoxyethylene derivatives, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, glycerin fatty acid esters, polyoxyethylene alkylamines, alkyls Nonionic surfactants such as alkanolamides such as alkylamine salts, quaternary ammonium salts, alkylbetaines, amine oxides and the like. On systems and amphoteric ionic surface active agents and the like. These surfactants may be used alone or in combination of two or more. In addition, when a surfactant having an ionic functional group is blended in such a surfactant, the stability of the polyurethane resin in water may decrease due to the interaction with the anionic group in the polyurethane resin. Therefore, a nonionic surfactant that does not contain an ionic functional group is preferably used.

  When the surfactant is blended, the ratio is not particularly limited, but is, for example, 0.01 to 10 parts by weight, preferably 0.1 to 5 parts by weight with respect to 100 parts by weight of the polyurethane resin. When the proportion of the surfactant is less than this, the effect of blending the surfactant may not be exhibited, and when it is more than this, the water resistance may be lowered.

  The blending timing of the surfactant is not particularly limited, and may be blended, for example, in an isocyanate-terminated prepolymer before being dispersed in water, or may be blended after completion of the chain extension reaction, or a solution In the case of polymerization, it may be blended after the removal of the organic solvent, and further, it may be blended in a plurality of times at an appropriate stage.

  In the present invention, it is essential that the particle diameter of the anionic urethane resin emulsion (A) is less than 100 nm, the acid value is in the range of 20 to 50 mgKOH / g, and the number average molecular weight is 5,000 or more. The particle diameter can be adjusted to an arbitrary particle diameter mainly by adjusting the acid value of the anionic urethane resin. From the viewpoint of finish, a particularly preferred particle size is in the range of 30 to 90 nm, and a particularly preferred acid value is in the range of 25 to 45 mgKOH / g.

  The particle size is largely governed mainly by the acid value, but it is also affected by the molecular weight and the hydroxyl value. Therefore, the adjustment of the particle size is adjusted to the desired particle size by adjusting the molecular weight and the hydroxyl group together with the acid value. can do.

  The particle size was measured with a COULTER N4 type submicron particle analyzer (manufactured by Nikka Kisha Co., Ltd.).

Anionic urethane resin (B)
The anionic urethane resin (B) used in the present invention is an anionic urethane resin characterized in that the number average molecular weight is less than 5,000 and the molecular structure is linear, and the polyisocyanate, polyol and It can be synthesized by reacting an active hydrogen group-containing compound having an anionic group. In order to obtain a straight chain, it is necessary to select and use bifunctional ones for the above three components. This is because when a trifunctional or higher functional group is included, a branched structure is formed and a linear structure cannot be obtained.

  As the polyisocyanate, for example, bifunctional ones can be used among those mentioned for the isocyanate-terminated prepolymer of the anionic urethane resin emulsion (A), and these can be used alone or in combination. .

  As the polyol, for example, bifunctional ones can be used among those mentioned for the isocyanate-terminated prepolymer of the anionic urethane resin emulsion (A), and these can be used alone or in combination.

  The active hydrogen group-containing compound having an anionic group has an anionic group such as a carboxyl group or a sulfonyl group, and can react with an isocyanate group, for example, an active hydrogen group such as a hydroxyl group or an amino group. For example, among those listed above for the isocyanate-terminated prepolymer of the anionic urethane resin emulsion (A), 2,2-dimethylolacetic acid, 2,2-dimethylollactic acid, 2,2-dimethylolpropion Compounds having two active hydrogen groups in one molecule such as acid and 2,2-dimethylolbutanoic acid can be used, and these can be used alone or in combination.

  The synthesis of the anionic urethane resin (B) can be performed by a known method. Specifically, for example, the above-mentioned bifunctional polyisocyanate, bifunctional polyol, and an active hydrogen group having an anionic group are contained. The compound (having two active hydrogen groups in one molecule) is more than 1 in the equivalent ratio (active hydrogen group / isocyanate group) of active hydrogen groups (hydroxyl group and amino group) to isocyanate groups, preferably What is necessary is just to mix | blend in the ratio of 1.1 / 1-2/1, and just to make it react by well-known polymerization methods, such as bulk polymerization and solution polymerization.

  In bulk polymerization, for example, a polyisocyanate is stirred under a nitrogen stream, and an active hydrogen group-containing compound having a polyol and an anionic group is added thereto and reacted at a reaction temperature of 75 to 85 ° C. for several hours. Just do it.

  In solution polymerization, a polyisocyanate, a polyol, and an active hydrogen group-containing compound having an anionic group may be added to an organic solvent and reacted at a reaction temperature of 20 to 80 ° C. for several hours. As the organic solvent, there can be used a low boiling point solvent which is inactive with respect to the isocyanate group, is highly hydrophilic, and can be easily removed, such as acetone, methyl ethyl ketone, ethyl acetate, tetrahydrofuran and the like. In the present invention, solution polymerization that allows easier adjustment of reactivity and viscosity is preferably used.

  Moreover, in the said reaction, you may use well-known urethanation catalysts, such as an amine type, a tin type, and a lead type, as needed.

  In the present invention, it is an essential requirement that the number average molecular weight of the anionic urethane resin (B) is less than 5,000. The number average molecular weight can be adjusted to an arbitrary number average molecular weight mainly by adjusting the molecular weight of the polyol, the ratio of the polyol and the isocyanate, and the like. A particularly preferred number average molecular weight is in the range of 500 to 2,500 from the viewpoint of the solid content concentration of the paint.

  The acid value of the anionic urethane resin (B) is preferably in the range of 5 to 50 mgKOH / g, particularly 8 to 30 mgKOH / g, from the viewpoints of viscosity and dispersion stability with respect to water. The hydroxyl value of the anionic urethane resin (B) is preferably in the range of 10 to 50 mgKOH / g, particularly 15 to 40 mgKOH / g, from the viewpoint of curability and the like.

  The ratio of the anionic urethane resin emulsion (A) and the anionic urethane resin (B) in the aqueous coating composition of the present invention is as follows. The anionic urethane resin (B) is preferably in the range of 90/10 to 50/50.

  The total solid weight of the anionic urethane resin emulsion (A) and the anionic urethane resin (B) in the aqueous coating composition of the present invention is the total of all solid resin contents in the coating from the viewpoint of finish and chipping resistance. The amount is preferably 1 to 80 parts by weight, particularly 5 to 50 parts by weight with respect to 100 parts by weight.

  In producing the aqueous coating composition of the present invention, the anionic urethane resin (B) neutralized with a neutralizing agent in advance (after diluting with deionized water as necessary) It is preferable from the viewpoint of improving the stability of the paint that the procedure of gradually blending the anionic urethane resin emulsion (A) therein is taken.

  Examples of the neutralizing agent include hydroxides of alkali metals or alkaline earth metals such as sodium hydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide, barium hydroxide; ammonia; ethylamine, propylamine, butylamine , Primary amines such as benzylamine, monoethanolamine, neopentanolamine, 2-aminopropanol, 3-aminopropanol; diethylamine, diethanolamine, di-n- or diisopropanolamine, N-methylethanolamine, N- Secondary monoamines such as ethylethanolamine; tertiary monoamines such as dimethylethanolamine, trimethylamine, triethylamine, triisopropylamine, methyldiethanolamine, dimethylaminoethanol; Rentoriamin, hydroxyethylaminoethylamine, ethylamino ethylamine, it may be mentioned polyamines such as methylamino propylamine.

  In addition to the anionic urethane resin emulsion (A) and the anionic urethane resin (B), which are essential components, the aqueous coating composition of the present invention further contains a hydroxyl group-containing resin (C), a crosslinking agent (D) and A pigment (E) and a polyolefin emulsion (F) can be contained.

Hydroxyl-containing resin (C)
The kind of the hydroxyl group-containing resin is not particularly limited, and examples thereof include an acrylic resin, a polyester resin, a urethane-modified polyester resin, and an epoxy resin.

  In the present invention, among these, acrylic resins and polyester resins are preferably used. Hereinafter, these resins will be described in detail.

It is an acrylic resin that can be synthesized according to a conventional method by copolymerizing an acrylic resin radically polymerizable monomer. Those synthesized by solution polymerization can be suitably used. As the organic solvent used for the reaction, it is preferable to use, for example, a hydrophilic organic solvent such as propylene glycol ether or dipropylene glycol ether. From the viewpoint of water dispersibility, the acrylic resin preferably has an acid group such as a carboxyl group.

  A conventionally well-known thing can be used as a radically polymerizable monomer, For example, a hydroxyl-containing radically polymerizable monomer, a carboxyl group-containing radically polymerizable monomer, and another radically polymerizable monomer can be used.

  Examples of the hydroxyl group-containing radical polymerizable monomer include 2-hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, and ε-caprolactone-modified tetrahydrofur. Furyl (meth) acrylate, ε-caprolactone-modified hydroxyethyl (meth) acrylate, polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, 2-hydroxy- Examples thereof include 3-butoxypropyl (meth) acrylate and monohydroxyethyl (meth) acrylate phthalate.

  Examples of the carboxyl group-containing radical polymerizable monomer include acrylic acid and methacrylic acid.

  Examples of other radical polymerizable monomers include styrene, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, and cyclohexyl (meth) acrylate. , Cyclohexenyl (meth) acrylate, phenoxyethyl (meth) acrylate, phenoxypolyethylene glycol (meth) acrylate, dicyclopentenyl (meth) acrylate, dicyclopentenyloxyethyl (meth) acrylate, isobornyl (meth) acrylate, benzyl (meth) ) Acrylate, Aronix M110 (manufactured by Toagosei Co., Ltd.), N-methylol (meth) acrylamide, N-butoxy (meth) acrylamide, acryloyl morroli , Dimethylaminoethyl (meth) acrylate, N- vinyl-2-pyrrolidone, .gamma. such acryloxypropyl trimethoxysilane can be exemplified.

  In the above, “(meth) acrylate” means “acrylate or methacrylate”.

  The weight average molecular weight of the acrylic resin is suitably in the range of 1,000 to 200,000, preferably 2,000 to 100,000, from the viewpoints of weather resistance and finish. The hydroxyl value of the acrylic resin is 10 to 250 mgKOH / g, preferably 30 to 150 mgKOH / g. The acid value of the acrylic resin is 3 to 150 mgKOH / g, preferably 5 to 70 mgKOH / g.

Polyester resin The polyester resin suitably used in the present invention can be synthesized by an esterification reaction of a polybasic acid and a polyhydric alcohol according to a conventional method according to a known method. From the viewpoint of water dispersibility, the polyester resin preferably has an acid group such as a carboxyl group.

  A polybasic acid is a compound having two or more carboxyl groups in one molecule. For example, phthalic acid, isophthalic acid, terephthalic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, naphthalenedicarboxylic acid, 4,4 -Diphenyldicarboxylic acid, diphenylmethane-4,4'-dicarboxylic acid, het acid, maleic acid, fumaric acid, itaconic acid, trimellitic acid, pyromellitic acid, cyclohexane-1,3-dicarboxylic acid, cyclohexane-1,4- Examples thereof include dicarboxylic acid, hexahydrophthalic acid, hexahydroisophthalic acid, hexahydroterephthalic acid, tetrahydrophthalic acid, hexahydrotrimellitic acid, methylhexahydrophthalic acid, and anhydrides thereof.

Polyhydric alcohol is a compound having two or more hydroxyl groups in one molecule, for example,
Ethylene glycol, propylene glycol, diethylene glycol, trimethylene glycol, tetraethylene glycol, triethylene glycol, dipropylene glycol, 1,4-butanediol, 1,3-butanediol, 2,3-butanediol, 1,2-butane Diol, 3-methyl-1,2-butanediol, 1,2-pentanediol, 1,5-pentanediol, 1,4-pentanediol, 2,4-pentanediol, 2,3-dimethyltrimethylene glycol, Tetramethylene glycol, 3-methyl-4,5-pentanediol, 2,2,4-trimethyl-1,3-pentanediol, 1,6-hexanediol, 1,5-hexanediol, 1,4-hexanediol 2,5-hexanediol, neopenty Glycols such as glycol and hydroxypivalic acid neopentyl glycol ester, polylactone diols obtained by adding lactones such as ε-caprolactone to these glycols, polyester diols such as bis (hydroxyethyl) terephthalate, 1,3-cyclohexane Dimethanol, 1,4-cyclohexanedimethanol, tricyclodecane dimethanol, hydrogenated bisphenol A, hydrogenated bisphenol F, spiroglycol, dihydroxymethyltricyclodecane, glycerin, trimethylolpropane, trimethylolethane, diglycerin, tri Examples include glycerin, 1,2,6-hexanetriol, pentaerythritol, dipentaerythritol, dipentaerythritol, sorbitol, mannitol, etc. be able to.

In addition, as the polyester resin, sesame oil fatty acid, coconut oil fatty acid, safflower oil fatty acid, soybean oil fatty acid, sesame oil fatty acid, eno oil fatty acid, hemp oil fatty acid, tall oil fatty acid, dehydrated castor oil fatty acid, etc. (half) A fatty acid-modified polyester resin modified with a dry oil fatty acid or the like can also be used. It is generally suitable that the modified amount of these fatty acids is 30% by weight or less in terms of oil length. The polyester resin may be one obtained by reacting a part of a monobasic acid such as benzoic acid, or a compound having one epoxy group in one molecule, for example, Cardura E-10 (manufactured by Japan Epoxy Resin Co., Ltd.). ) Etc. may be reacted.
From the viewpoint of water dispersibility, for example, after esterification reaction of the polybasic acid and polyhydric alcohol to introduce an acid group into the polyester resin, a polybasic acid such as trimellitic acid or trimellitic anhydride is further added. And those obtained by reacting these anhydrides can be preferably used.

  The weight average molecular weight of the polyester resin is suitably in the range of 1,000 to 200,000, preferably 2,000 to 100,000, from the viewpoints of weather resistance and finish. The hydroxyl value of the polyester resin is suitably in the range of 10 to 250 mgKOH / g, preferably 30 to 150 mgKOH / g, from the viewpoint of finish properties and the like. The acid value of the polyester resin is 5-100 mgKOH / g, preferably 10-60 mgKOH / g.

Cross-linking agent (D)
The crosslinking agent (D) of the present invention is not particularly limited. For example, the following blocked polyisocyanate curing agent (d ₁ ), water-dispersible blocked polyisocyanate curing agent (d ₂ ), melamine Resin (d ₃ ) can be preferably used.

Blocked polyisocyanate curing agent (d ₁ ): A blocked polyisocyanate curing agent obtained by blocking the isocyanate group of a polyisocyanate compound having two or more free isocyanate groups in a molecule with a blocking agent.

Examples of the polyisocyanate compound in the blocked polyisocyanate curing agent (d ₁ ) include aliphatic polyisocyanates such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, dimer acid diisocyanate, and lysine diisocyanate; and burettes of these polyisocyanates. Type adduct, isocyanurate cycloadduct; isophorone diisocyanate, 4,4′-methylenebis (cyclohexyl isocyanate), methylcyclohexane-2,4- (or-2,6-) diisocyanate, 1,3- (or 1,4 -) Di (isocyanatomethyl) cyclohexane, 1,4-cyclohexane diisocyanate, 1,3-cyclopentane diisocyanate, 1,2-cyclohexane diisocyanate Any alicyclic diisocyanates; and burette-type adducts, isocyanurate cycloadducts of these polyisocyanates; xylylene diisocyanate, metaxylylene diisocyanate, tetramethyl xylylene diisocyanate, tolylene diisocyanate, 4,4'-diphenylmethane Diisocyanate, 1,5-naphthalene diisocyanate, 1,4-naphthalene diisocyanate, 4,4′-toluidine diisocyanate, 4,4′-diphenyl ether diisocyanate, (m- or p-) phenylene diisocyanate, 4,4′-biphenylene diisocyanate, 3,3′-dimethyl-4,4′-biphenylene diisocyanate, bis (4-isocyanatophenyl) sulfone, isopropylidenebis (4-phenylisocyanate) ) And other polyisocyanate burette type adducts, isocyanurate cycloadducts; triphenylmethane-4,4 ′, 4 ″ -triisocyanate, 1,3,5-triisocyanate Polyisocyanate having 3 or more isocyanate groups in one molecule such as natobenzene, 2,4,6-triisocyanatotoluene, 4,4′-dimethyldiphenylmethane-2,2 ′, 5,5′-tetraisocyanate And burette type adducts, isocyanurate cycloadducts of these polyisocyanates; ethylene glycol, propylene glycol, 1,4-butylene glycol, dimethylolpropionic acid, polyalkylene glycol, trimethylolpropane, hexanetriol, etc. Hydroxyl of polyol And urethanated adducts obtained by reacting a polyisocyanate compound in an excess ratio with isocyanate groups; and burette-type adducts and isocyanurate ring adducts of these polyisocyanates.

  The blocking agent blocks a free isocyanate group and can easily react with a hydroxyl group when heated to 100 ° C. or higher, preferably 130 ° C. or higher. Examples of such blocking agents include phenols such as phenol, cresol, xylenol, nitrophenol, ethylphenol, hydroxydiphenyl, butylphenol, isopropylphenol, nonylphenol, octylphenol, and methyl hydroxybenzoate; ε-caprolactam, δ-valerolactam, γ -Lactams such as butyrolactam and β-propiolactam; aliphatic alcohols such as methanol, ethanol, propyl alcohol, butyl alcohol, amyl alcohol, lauryl alcohol; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether , Diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, Ethers such as propylene glycol monomethyl ether and methoxymethanol; benzyl alcohol; glycolic acid; glycolic acid esters such as methyl glycolate, ethyl glycolate and butyl glycolate; lactic acid esters such as lactic acid, methyl lactate, ethyl lactate and butyl lactate; Alcohols such as methylol urea, methylol melamine, diacetone alcohol, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate; oximes such as formamide oxime, acetamide oxime, acetoxime, methyl ethyl ketoxime, diacetyl monooxime, benzophenone oxime, cyclohexane oxime System: dimethyl malonate, diethyl malonate, ethyl acetoacetate, methyl acetoacetate, acetylacetone, etc. Active methylene series; mercaptans such as butyl mercaptan, t-butyl mercaptan, hexyl mercaptan, t-dodecyl mercaptan, 2-mercaptobenzothiazole, thiophenol, methylthiophenol, ethylthiophenol; acetanilide, acetaniside, acetolide, acrylamide, methacryl Acid amides such as amides, acetic acid amides, stearic acid amides, benzamides; imides such as succinic acid imides, phthalic acid imides, maleic acid imides; Amines such as butylamine, dibutylamine and butylphenylamine; imidazoles such as imidazole and 2-ethylimidazole System; pyrazole system such as 3,5-dimethylpyrazole; urea system such as urea, thiourea, ethylene urea, ethylene thiourea, diphenyl urea; carbamate ester system such as phenyl N-phenylcarbamate; ethyleneimine, propyleneimine, etc. Examples thereof include sulphite systems such as sodium bisulfite and potassium bisulfite.

Blocked polyisocyanate curing agent imparted with water dispersibility (d ₂ ): In order to reduce the amount of solvent (lower VOC), it is better to reduce the amount of organic solvent than the crosslinking agent (D), and to improve the coating performance. A blocked polyisocyanate curing agent obtained by imparting water dispersibility to the blocked polyisocyanate curing agent (d ₁ ) can be used as long as it is not lowered.

The blocked polyisocyanate curing agent (d ₂ ) imparted with water dispersibility is a water dispersion obtained by blocking the isocyanate group of the polyisocyanate with a blocking agent and hydroxymonocarboxylic acids and neutralizing the carboxyl group of the hydroxymonocarboxylic acids. It is a blocked polyisocyanate compound imparted with properties.

As the polyisocyanate compound, polyisocyanate compounds similar to those exemplified for the blocked polyisocyanate curing agent (d ₁ ) can be used. Among them, preferred examples include hexamethylene diisocyanate (HMDI) and hexamethylene diisocyanate. Mention may be made of derivatives of (HMDI), isophorone diisocyanate (IPDI), and derivatives of isophorone diisocyanate (IPDI).

In order to produce the water-dispersible blocked polyisocyanate curing agent (d ₂ ), the isocyanate group of the polyisocyanate compound is blocked with a blocking agent and reacted with hydroxymonocarboxylic acids. It is made to react so that an isocyanate group may be added to the hydroxyl group of hydroxymonocarboxylic acids.

As the blocking agent, the same blocking agent as exemplified for the blocked polyisocyanate curing agent (d ₁ ) can be used. Examples of hydroxy monocarboxylic acids include 2-hydroxyacetic acid, 3-hydroxypropanoic acid, 12-hydroxy-9-octadecanoic acid (ricinoleic acid), 3-hydroxy-2,2-dimethylpropanoic acid (hydroxypivalic acid), Examples thereof include dimethylolpropionic acid (DMPA), among which 3-hydroxy-2,2-dimethylpropanoic acid (hydroxypivalic acid) is preferable. The solvent used for the reaction is preferably non-reactive with isocyanate groups, and examples include ketones such as acetone and methyl ethyl ketone, esters such as ethyl acetate, and solvents such as N-methylpyrrolidone (NMP). be able to.

Melamine resin (d ₃ ): Examples of the melamine resin (d ₃ ) include methylolated amino resins obtained by reaction of melamine and aldehyde. Examples of the aldehyde include formaldehyde, paraformaldehyde, acetaldehyde, benzaldehyde and the like. Moreover, what methylated the methylol group of this methylolated amino resin partially or entirely with monoalcohol can also be used. Examples of the monoalcohol used for etherification include methyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol, n-butyl alcohol, i-butyl alcohol, 2-ethylbutanol, 2-ethylhexanol and the like. be able to.

As the melamine resin (d ₃ ), in particular, an average of 3 or more methylol groups of methylol groups per triazine nucleus and a part of the methoxy group were substituted with a monoalcohol having 2 or more carbon atoms. A melamine resin that has an imino group and has an average degree of condensation of about 2 or less and a mononuclear ratio of about 50% by weight or more can be preferably used.

Pigment (E)
The pigment (E) of the present invention is not particularly limited, and examples thereof include titanium oxide, zinc white, carbon black, phthalocyanine blue, Prussian blue, cobalt blue, azo pigment, phthalocyanine pigment, quinacridone pigment, and isoindoline pigment. Color pigments such as selenium pigments and perylene pigments; extender pigments such as talc, clay, kaolin, barita, barium sulfate, barium carbonate, calcium carbonate, silica, alumina white; mica coated with aluminum powder, mica powder, titanium oxide Metallic pigments such as powder can be suitably used.

  The blending amount of the pigment is generally in the range of 0 to 250 parts by weight, particularly 3 to 150 parts by weight per 100 parts by weight of the total resin solids in the paint.

  The coating composition of the present invention can be applied to a plastic material. However, in the case of use, it is necessary to use a polyolefin emulsion in order to impart adhesion to the plastic material. preferable.

Polyolefin emulsion (F)
The polyolefin emulsion (F) used in the present invention is not particularly limited, but for example, a dispersion of an olefin monomer copolymer in water can be suitably used.
The olefin monomer is not particularly limited, and specific examples thereof include, for example, ethylene, propylene, 1-butene, 3-methyl-1-butene, 4-methyl-1-pentene, 3- Α-olefins such as methyl-1-pentene, 1-heptene, 1-hexene, 1-decene, 1-dodecene; conjugated dienes such as butadiene, ethylidene norbornene, dicyclopentadiene, 1,5-hexadiene, nonconjugated dienes, etc. These monomers can be used alone or in combination of two or more.

  In the copolymer of the olefin monomer, a monomer other than the olefin monomer can be used in combination without any particular limitation as long as it is a monomer copolymerizable with the olefin monomer. Specific examples include vinyl acetate, vinyl alcohol, and the like. One or more of these monomers can be used.

  Specific examples of the copolymer of the olefinic monomer include, for example, low density polyethylene, high density polyethylene, polypropylene, poly 1-butene, poly 3-methyl-1-butene, poly 4-methyl-1- Pentene, poly-3-methyl-1-pentene, or ethylene / propylene copolymer, ethylene / 1-butene copolymer, propylene / 1-butene copolymer, representative of propylene / 1-butene / ethylene copolymer Ethylene, propylene, 1-butene, 3-methyl-1-butene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-heptene, 1-hexene, 1-decene, 1-dodecene, etc. Α-olefin homopolymers, random or block copolymers thereof, ethylene / butadiene copolymers, ethylene Copolymer of α-olefin and conjugated diene or non-conjugated diene represented by lidene norbornene copolymer, ethylene / propylene / butadiene terpolymer, ethylene / propylene / dicyclopentadiene terpolymer A conjugated diene or a non-conjugated diene and two or more α-olefins represented by a coalescence, ethylene / propylene / ethylidene norbornene terpolymer, ethylene / propylene / 1,5-hexadiene terpolymer, etc. Examples thereof include a copolymer, or a copolymer of an olefin resin such as an ethylene / vinyl acetate copolymer and an ethylene / vinyl alcohol copolymer and another thermoplastic monomer.

  In the polyolefin emulsion (F), in particular, in order to improve water dispersion stability, resin particles (F-1) containing an olefin copolymer and an acrylic copolymer in the same particle can be used. . The structure is not particularly limited, and examples thereof include a core / shell structure, a composite structure, a localized structure, a daruma-like structure, a saddle-like structure, a raspberry-like structure, a multi-particle composite structure, and an IPN structure. .

  The resin particles (F-1) can be produced, for example, by polymerizing an acrylic monomer in the presence of an emulsion in which olefin polymer particles are dispersed in water. An acrylic polymer is formed on the surface of particles in the coalescence or in the particles.

  The acrylic monomer is not particularly limited, and specific examples include (meth) acrylic acid esters, particularly alkyl esters having 1 to 12 carbon atoms. For example, methyl acrylate, acrylic Ethyl acetate, n-butyl acrylate, i-butyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, methacrylic acid 2 -Ethylhexyl, lauryl methacrylate, etc .; aromatic monomers such as styrene, α-methylstyrene; hydroxyalkyl acrylates such as hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate; acrylic acid, METAKU Carboxylic group-containing monomers such as phosphoric acid, crotonic acid, itaconic acid, fumaric acid, maleic acid; and other monomers such as acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, glycidyl methacrylate, These 1 type, or 2 or more types can be used.

  When a carboxyl group-containing monomer is used as the acrylic monomer, the amount used is preferably an amount not exceeding 5% by weight based on the total total weight of the acrylic monomers.

  The weight ratio of the olefin polymer to the acrylic polymer is 95 to 10% by weight of the olefin polymer and 5 to 90% of the acrylic polymer based on the total weight of the olefin polymer and the acrylic polymer. % By weight, preferably 95 to 30% by weight of olefin polymer, 5 to 70% by weight of acrylic polymer, more preferably 95 to 40% by weight of olefin polymer and 5% of acrylic polymer. Within the range of ˜60% by weight.

  If the olefin polymer is less than 10% by weight, the characteristics of the olefin are not expressed, and for example, the adhesion to a nonpolar substrate tends to be lowered. On the other hand, when the olefin polymer is 95% by weight or more, the characteristics of the acrylic polymer are not exhibited, and for example, the adhesion to a polar substrate tends to be lowered.

  As the initiator used for the polymerization reaction of the acrylic monomer, any initiator generally used for emulsion polymerization can be used. Hydrogen peroxide; ammonium persulfate, potassium persulfate, sodium persulfate and the like can be used. Sulfates; Organic peroxides such as cumene hydroperoxide, t-butyl hydroperoxide, benzoyl peroxide, t-butylperoxy-2-ethylhexanoate, t-butylperoxybenzoate, lauroyl peroxide; azo Redox by combining azo compounds such as bisisobutyronitrile; or metal ions such as iron ions and reducing agents such as sodium sulfoxylate, formaldehyde, sodium pyrosulfite, sodium hydrogen sulfite, L-ascorbic acid, Rongalite, etc. Initiators, etc. It can be used one or two or more kinds of al. Specific examples of the initiator preferably used include those having a water solubility of 0 to 10%, more preferably 0 to 5%, and most preferably 0 to 3%.

  Generally, when an initiator having a water solubility of more than 10% is used, it becomes difficult to form an acrylic copolymer in the olefin polymer particles. The amount of initiator used is usually 0.1 to 5% by weight based on the total amount of monomers. If necessary, mercaptans such as t-dodecyl mercaptan and n-dodecyl mercaptan, allyl sulfonic acid, methallyl sulfonic acid and allyl compounds such as soda salts thereof can be used as molecular weight regulators. is there.

  In order to improve the stability of the particles when the acrylic monomer is polymerized in the presence of the olefin emulsion, it is possible to use a surfactant used in usual emulsion polymerization.

  Specific examples of such surfactants include, for example, anionic surfactants, nonionic surfactants, cationic surfactants, other reactive surfactants, and the like, one or more of these. Can be used in combination. Nonionic surfactants include polyoxyethylene lauryl ether, polyoxyethylene octyl phenyl ether, polyoxyethylene oleyl phenyl ether, polyoxyethylene nonyl phenyl ether, oxyethylene / oxypropylene block copolymer, tert-octylphenoxyethyl poly Examples include ethoxyethanol, nonylphenoxyethyl polyethoxyethanol, and the like.

  Anionic surfactants include sodium dodecylbenzenesulfonate, sodium lauryl sulfate, sodium alkyldiphenyl ether disulfonate, sodium alkylnaphthalenesulfonate, sodium dialkylsulfosuccinate, sodium stearate, potassium oleate, sodium dioctylsulfosuccinate, poly Sodium oxyethylene alkyl ether sulfate, sodium polyoxyethylene alkyl ether sulfate, sodium polyoxyethylene alkyl phenyl ether sodium dialkyl sulfosuccinate, sodium stearate, sodium oleate, sodium tert-octylphenoxyethoxypolyethoxyethyl sulfate It is done. Examples of the cationic surfactant include lauryltrimethylammonium chloride and stearyltrimethylammonium chloride.

  The amount of the surfactant used is not particularly limited, but if the amount used is increased, particles composed only of acrylic monomers are generated, so it is difficult to generate an acrylic polymer in the olefin polymer particles. Tend to be. The amount of the surfactant used is usually 0.02 to 5% by weight based on the total weight of the acrylic monomer. The above-mentioned various monomers are added all at once, divided or continuously, and added at a temperature of 0 to 100 ° C., practically 30 to 90 ° C. in the presence of the initiator. Is polymerized.

  The average particle diameter of such resin particles (F-1) is in the range of 10 nm to 5 μm, preferably 10 nm to 1 μm, and more preferably 10 nm to 800 nm.

  The added amount of the polyolefin emulsion (F) is 3 to 40 parts by weight, preferably 5 to 30 parts by weight with respect to 100 parts by weight of the total resin solids in the paint, and chipping resistance and paint stability. Suitable from the aspect of sex.

  If necessary, the aqueous coating composition of the present invention further includes a dispersant, an anti-settling agent, an organic solvent, a catalyst for promoting urethanization reaction (for example, an organic tin compound), and a crosslinking reaction between a hydroxyl group and a melamine resin. A catalyst (for example, an acid catalyst), an antifoaming agent, a thickening agent, an ultraviolet absorber, a surface conditioner, and the like can be appropriately used.

  The aqueous coating composition of the present invention can be applied by a conventionally known method, for example, air spray, airless spray, electrostatic coating, brush coating, etc. Therefore, the range of 3 to 100 μm, particularly 5 to 60 μm is preferable, and the coating film can be cured by heating at 120 to 170 ° C., particularly 130 to 160 ° C. for 10 to 40 minutes.

  Since the aqueous coating composition of the present invention can provide a coating film excellent in finish performance and chipping resistance and other coating performance, it is suitable for use as, for example, an automotive intermediate coating or top coating. .

  In particular, overcoating is applied either on or after the intermediate coating is applied to the object to which an undercoating such as electrodeposition coating is applied on the outer plate of the automobile body. It can be suitably used as an intermediate coating material in a multilayer coating film.

  Hereinafter, the multilayer coating film forming method using the aqueous coating composition of the present invention will be described in detail.

Multilayer coating film forming method The multilayer coating film forming method of the present invention is a step 1: coating a chipping primer on a metal coating or an electrodeposition coating formed by electrodeposition coating on a metal coating. Without applying the aqueous coating composition according to any one of claims 1 to 4, forming an uncured coating film or baking and drying the coating film to form a cured coating film, and a process 2: A multi-layer coating film forming method including a step of coating the uncured coating film or the cured coating film obtained in Step 1 with one or more layers of a top coating to form a top coating film and baking and curing.

  Although it does not specifically limit as a to-be-coated object, For example, it is preferable that it is a vehicle body of various vehicles, such as a motor vehicle, a two-wheeled vehicle, a container. In addition, cold rolled steel sheets, galvanized steel sheets, zinc alloy plated steel sheets, stainless steel sheets, tin plated steel sheets, etc., metal substrates such as aluminum plates, aluminum alloy plates, etc .; Good.

  Moreover, as a to-be-coated object, surface treatments, such as a phosphate process, a chromate process, a complex oxide process, may be given to the metal surface of the said vehicle body or a metal base material. Furthermore, as the object to be coated, an undercoat film and / or an intermediate coat film such as various electrodeposition paints may be formed on the vehicle body, metal base material, or the like.

  In step 1, the aqueous coating composition of the present invention is applied without applying a chipping primer on the object to be coated, thereby forming an uncured coating film or baking and drying the coating film to form a cured coating film. It is a process. It is possible to omit the baking step by performing the next step 2 while it is uncured. In this case, it is necessary to accelerate the evaporation of the solvent in the coating film before proceeding to step 2. You may perform preheating for about 1 to 10 minutes at the temperature of about -90 degreeC.

  The coating film thickness in step 1 is 3 to 100 μm, preferably 5 to 60 μm, based on the cured film thickness. Moreover, the conditions at the time of baking hardening are a baking temperature of 120-170 degreeC, Preferably it is 130-160 degreeC, and a baking time is 5 to 60 minutes, Preferably it is 10 to 40 minutes.

  Step 2 is a step in which one or more top coats are formed on the uncured coating or cured coating obtained in Step 1 to form a top coating and bake and cure.

  The top coating is not particularly limited, and for example, those usually used in automobile painting can be used. For example, one coat of organic solvent or water containing a thermosetting resin composition and a pigment. One-baking colored top coating can be mentioned. Examples of the thermosetting resin composition used for the colored top coating include base resins such as acrylic resins having a crosslinkable functional group such as hydroxyl groups, polyester resins and urethane resins, melamine resins, and (block) polyisocyanate compounds. Examples thereof include a composition comprising a crosslinking agent, an acid / epoxy crosslinking coating composition mainly composed of an acid group-containing resin and an epoxy group-containing resin. Moreover, as a pigment, a color pigment, a luster pigment, an extender pigment, etc. can be used. Furthermore, if necessary, extender pigments, anti-settling agents, ultraviolet absorbers, and the like can be appropriately contained.

  Further, as the top coating material, a two-coat one-bake specification or a three-coat one-bake specification made of a colored base paint and a clear paint, which are commonly used, can be used.

  As the colored base paint, for example, the same ones as those mentioned for the 1-coat 1-bake colored top coat can be used.

  The clear paint is an organic solvent-based or water-based clear paint having a thermosetting resin composition as a main component. As the thermosetting resin composition, for example, a resin used for a colored top coat of 1 coat and 1 bake specification. The same composition can be used.

  The top coating can be applied by a method known per se, for example, electrostatic coating, airless spraying, air spraying, etc., after adjusting to an appropriate coating viscosity with an organic solvent and / or water. Based on the cured coating, the colored top coat is in the range of about 25-50 μm, especially 30-45 μm, the colored base paint is in the range of about 10 μm-25 μm, especially 15-20 μm, and the clear paint is about 25-50 μm, in particular A range of 30 μm to 45 μm is suitable.

  Moreover, in order to accelerate | stimulate evaporation of the solvent in a coating film similarly to the said process 1, after pre-coating each said top-coat paint, it preheats for about 1 to 10 minutes at the temperature of about 40-90 degreeC as needed. Also good.

  Baking and curing can be carried out at a temperature of 100 to 180 ° C., preferably 120 to 170 ° C., for 5 to 60 minutes, preferably 10 to 40 minutes to cure the coating film obtained.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. The present invention is not limited to the following examples. Hereinafter, “part” and “%” are both based on weight, and the film thickness of the coating film is based on the cured coating film.
(Example)
Production of anionic urethane resin emulsion (A)
(Production Example 1) 100 parts by weight of polytetramethylene glycol having a production number average molecular weight of 2,000 of (A-1) was dehydrated under vacuum at 110 ° C, and after dehydration, cooled to 60 ° C. Then, 16.8 parts by weight of hexamethylene diisocyanate, 22.2 parts by weight of isophorone diisocyanate, 14.8 parts by weight of 2,2-dimethylolbutanoic acid and 152.2 parts by weight of acetone were added in order, and the temperature was adjusted to 50 to 55 ° C. The reaction was continued with stirring until the reaction rate reached 98% or more.

  Thereafter, 10.0 parts by weight of triethylamine was added to obtain an acetone solution of an isocyanate-terminated prepolymer.

While stirring the acetone solution of the isocyanate-terminated prepolymer obtained above, 323 parts by weight of distilled water was slowly added thereto to obtain a milky white isocyanate-terminated prepolymer aqueous dispersion. Thereafter, 10.0 parts by weight of N- (2-aminoethyl) ethanolamine was quickly added dropwise to cause a chain extension reaction. In this chain extension reaction, the reaction temperature was adjusted to 30 ° C. or lower. Subsequently, stirring was continued at room temperature for 1 hour, and then acetone was removed at 40 to 50 ° C. under reduced pressure to obtain a solid content of 35% by weight, a viscosity of 1150 mPa · s / 25 ° C., a pH of 7.8, an acid value of 35 mgKOH / g, An anionic urethane resin emulsion (A-1) having an average particle diameter of 80 nm and a number average molecular weight of 100,000 was obtained.
(Production Example 2) Production of (A-2) 100 parts by weight of UH-CARB100 (manufactured by Ube Industries, polycarbonate diol, number average molecular weight 2,000) was dehydrated at 110 ° C. under vacuum, and after dehydration, up to 60 ° C. Cooled down. Then, 16.8 parts by weight of hexamethylene diisocyanate, 22.2 parts by weight of isophorone diisocyanate, 14.8 parts by weight of 2,2-dimethylolbutanoic acid and 152.2 parts by weight of acetone were added in order, and the temperature was adjusted to 50 to 55 ° C. The reaction was continued with stirring until the reaction rate reached 98% or more.

  Thereafter, 10.0 parts by weight of triethylamine was added to obtain an acetone solution of an isocyanate-terminated prepolymer.

While stirring the acetone solution of the isocyanate-terminated prepolymer obtained above, 323 parts by weight of distilled water was slowly added thereto to obtain a milky white isocyanate-terminated prepolymer aqueous dispersion. Thereafter, 10.0 parts by weight of N- (2-aminoethyl) ethanolamine was quickly added dropwise to cause a chain extension reaction. In this chain extension reaction, the reaction temperature was adjusted to 30 ° C. or lower. Subsequently, stirring was continued at room temperature for 1 hour, and then acetone was removed at 40-50 ° C. under reduced pressure to obtain a solid content of 35% by weight, a viscosity of 1000 mPa · s / 25 ° C., a pH of 7.8, an acid value of 35 mgKOH / g, An anionic urethane resin emulsion (A-2) having an average particle diameter of 80 nm and a number average molecular weight of 100,000 was obtained.
Production Example 3 100 parts by weight of polytetramethylene glycol having a production number average molecular weight of 2,000 of (A-3) was dehydrated under vacuum at 110 ° C., dehydrated, and then cooled to 60 ° C. Next, 10.5 parts by weight of hexamethylene diisocyanate, 13.9 parts by weight of isophorone diisocyanate, 5.2 parts by weight of 2,2-dimethylolbutanoic acid and 152.2 parts by weight of acetone were added in order, and the temperature was adjusted to 50 to 55 ° C. The reaction was continued with stirring until the reaction rate reached 98% or more.

  Thereafter, 3.5 parts by weight of triethylamine was added to obtain an acetone solution of an isocyanate-terminated prepolymer.

  While stirring the acetone solution of the isocyanate-terminated prepolymer obtained above, 262 parts by weight of distilled water was slowly added thereto to obtain a milky white isocyanate-terminated prepolymer aqueous dispersion. Thereafter, 8.0 parts by weight of N- (2-aminoethyl) ethanolamine was quickly added dropwise to cause a chain extension reaction. In this chain extension reaction, the reaction temperature was adjusted to 30 ° C. or lower. Subsequently, stirring was continued at room temperature for 1 hour, and then acetone was removed under reduced pressure at 40 to 50 ° C. to obtain a solid content of 35% by weight, a viscosity of 600 mPa · s / 25 ° C., a pH of 7.8, an acid value of 15 mgKOH / g, An anionic urethane resin emulsion (A-3) having an average particle diameter of 150 nm and a number average molecular weight of 100,000 was obtained.

Production of aqueous dispersion of anionic urethane resin (B)
(Production Example 4) 100 parts by weight of polytetramethylene glycol having a production number average molecular weight of 1,000 of (B-1) was dehydrated under vacuum at 110 ° C, and after dehydration, cooled to 60 ° C. Subsequently, 22.2 parts by weight of isophorone diisocyanate, 7.4 parts by weight of 2,2-dimethylolbutanoic acid and 140 parts by weight of acetone were added in order, and the reaction was continued while stirring while maintaining the temperature in the range of 50 to 55 ° C. The reaction was continued until the rate reached 98% or more.

  Thereafter, 4.7 parts by weight of triethylamine was added to obtain an acetone solution of a polyurethane resin.

While stirring the acetone solution of the polyurethane resin obtained above, 194.4 parts by weight of distilled water was slowly added thereto to obtain an aqueous dispersion of milky white polyurethane resin. Subsequently, by removing acetone at 40-50 ° C. under reduced pressure, the solid content is 40% by weight, the viscosity is 800 mPa · s / 25 ° C., the pH is 8.3, the number average molecular weight is 2,500, the acid value is 20 mgKOH / g, and the average particle size is An aqueous dispersion (B-1) of an anionic urethane resin having a thickness of 70 nm was obtained.
(Production Example 5) 100 parts by weight of polytetramethylene glycol having a production number average molecular weight of 2,000 of (B-2) was dehydrated under vacuum at 110 ° C, and after dehydration, cooled to 60 ° C. Subsequently, 32.7 parts by weight of isophorone diisocyanate, 7.3 parts by weight of 2,2-dimethylolbutanoic acid and 140 parts by weight of acetone were successively added, the temperature was kept in the range of 50 to 55 ° C., and the reaction was conducted while stirring. The reaction was continued until the rate reached 98% or more. Subsequently, 7.2 parts by weight of 2-amino-2-methyl-1-propanol was added to make the remaining isocyanate group disappear. Thereafter, 4.5 parts by weight of triethylamine was added to obtain an acetone solution of a polyurethane resin.

  While stirring the acetone solution of the polyurethane resin obtained above, 255.5 parts by weight of distilled water was slowly added thereto to obtain an aqueous dispersion of milky white polyurethane resin. Subsequently, by removing acetone at 40 to 50 ° C. under reduced pressure, the solid content is 35% by weight, the viscosity is 1,200 mPa · s / 25 ° C., the pH is 8.3, the number average molecular weight is 2,900, the acid value is 20 mgKOH / g, the average An aqueous dispersion (B-2) of an anionic urethane resin having a particle size of 70 nm was obtained.

(Production Example 6) 100 parts by weight of polytetramethylene glycol having a production number average molecular weight of 1,000 of (B-3) was dehydrated at 110 ° C under vacuum, and after dehydration, cooled to 60 ° C. Next, 33.3 parts by weight of isophorone diisocyanate, 7.4 parts by weight of 2,2-dimethylolbutanoic acid, 4.5 parts by weight of trimethylolpropane, and 140 parts by weight of acetone were added successively, and the temperature was adjusted to a range of 50 to 55 ° C. The reaction was continued while stirring until the reaction rate reached 98% or more. Thereafter, 4.5 parts by weight of triethylamine was added to obtain an acetone solution of a polyurethane resin.

  While stirring the acetone solution of the polyurethane resin obtained above, 224.5 parts by weight of distilled water was slowly added thereto to obtain an aqueous dispersion of milky white polyurethane resin. Next, by removing acetone at 40 to 50 ° C. under reduced pressure, the solid content is 40% by weight, the viscosity is 1500 mPa · s / 25 ° C., the pH is 8.3, the number average molecular weight is 2,500, the acid value is 20 mgKOH / g, the average An aqueous dispersion (B-3) of an anionic urethane resin having a particle size of 70 nm and a branched molecular structure was obtained.

Manufacture of polyester resin (C)
(Production Example 7) Production of (C-1) In a four-necked flask equipped with a heating device, a stirrer, a thermometer, a reflux condenser, and a water separator, 61.9 parts of 1,3-cyclohexanedicarboxylic acid, adipine The contents formed by charging 70.1 parts of acid, 62.8 parts of trimethylolpropane, 24.2 parts of neopentyl glycol, and 44.6 parts of 1,4-cyclohexanedimethanol from 160 ° C. to 230 ° C. for 3 hours Then, the condensed water generated by maintaining at 230 ° C. for 1 hour was distilled off using a rectifying column.

  Next, after adding 15.0 parts of trimellitic anhydride to the product, the solvent was removed, neutralized with N, N-dimethylethanolamine, dispersed in water, and a polyester resin having a solid content of 40%. (C-1) was obtained. The obtained polyester resin (C-1) had a hydroxyl value of 150 mgKOH / g, an acid value of 35 mgKOH / g, and a number average molecular weight of 2,000.

Production of polyolefin emulsion (F)
(Production Example 8) Production of (F-1) 100 parts of an ethylene / 1-butene copolymer, 10 parts of maleic anhydride-grafted polyethylene and 5 parts of oleic acid were put into a pressure kneader and heated at 140 ° C. for 30 minutes. Next, 20 parts of alkaline water in which potassium hydroxide necessary for neutralizing maleic anhydride-grafted polyethylene and all carboxylic acids of oleic acid was dissolved in 5 minutes using a pump connected to a kneader. Press-fitted.

  Thereafter, kneading was continued for 30 minutes, and then the kneader was cooled to 60 ° C. and the contents were taken out. The contents were a white solid. 10 parts of a white solid was poured into 10 parts of water, stirred with a turbine blade stirrer, and then filtered with a 100 mesh wire mesh. No residue was observed. The solid content of the obtained water dispersion was 50%.

  140 parts of the aqueous dispersion and 152 parts of deionized water were charged into a reaction vessel and heated to 80 ° C. under a nitrogen stream. Separately, an emulsified mixture obtained by emulsifying 15 parts of styrene, 15 parts of 2-ethylhexyl acrylate and 0.3 part of benzoyl peroxide in 12 parts of deionized water using 0.12 part of sodium dodecylbenzenesulfonate. This emulsion mixture was dropped into the reaction vessel in 3 hours, and then kept at the same temperature for 4 hours to complete the polymerization to obtain a polyolefin emulsion (F-1) having a solid content of 30%.

Manufacture of water-based paint composition

  50 parts of polyester resin (C-1) obtained in Production Example 7, 1 part of carbon MA100 (carbon black, manufactured by Mitsubishi Chemical Corporation), 70 parts of JR806 (titanium white, manufactured by Teika) and MICRO ACE S-3 (fine powder talc) (Manufactured by Nippon Talc Co., Ltd.) 10 parts were mixed and dispersed with a paint shaker for 30 minutes to obtain pigment dispersion paste 1.

  In 131 parts of the pigment dispersion paste 1 obtained, 57 parts of the anionic urethane resin emulsion (A-1) obtained in Production Example 1 and an aqueous dispersion (B-1) of the anionic urethane resin obtained in Production Example 4 50 Part, polyester resin (C-1) 50 parts and Cymel 325 (Mitsui Cytec Co., Ltd., methylated melamine resin, solid content 80%) are mixed and stirred, and deionized water and dimethylethanolamine are further added. pH 8.5, Ford Cup No. 4 was adjusted to a viscosity of 40 seconds to obtain an aqueous coating composition 1.

  50 parts of Bihydrol PT241 (manufactured by Sumika Bayer Urethane Co., Ltd., urethane-modified polyester resin, solid content 40%), 1 part of carbon MA100, 70 parts of JR806 and 10 parts of MICRO ACE S-3 are mixed and dispersed with a paint shaker for 30 minutes. A pigment dispersion paste 2 was obtained.

  In 131 parts of the obtained pigment dispersion paste 2, 57 parts of the anionic urethane resin emulsion (A-2) obtained in Production Example 2, 50 parts of an anionic urethane resin aqueous dispersion (B-1), 50 parts of bihydrol PT241 And 25 parts of Cymel 325 were mixed and stirred. Further, deionized water and dimethylethanolamine were added, pH 8.5, Ford Cup No. 4 was adjusted to a viscosity of 40 seconds to obtain an aqueous coating composition 2.

  In 131 parts of the pigment dispersion paste 1 obtained in Example 1, 57 parts of the anionic urethane resin emulsion (A-1) obtained in Production Example 1 and the aqueous dispersion of the anionic urethane resin obtained in Production Example 5 (B -2) 57 parts, 50 parts of Bihydrol PT241 and 25 parts of Cymel 325 were mixed and stirred, and further, deionized water and dimethylethanolamine were added, pH 8.5, Ford Cup No. 4 was adjusted to a viscosity of 40 seconds to obtain an aqueous coating composition 3.

  In 131 parts of the pigment dispersion paste 1 obtained in Example 1, 86 parts of the anionic urethane resin emulsion (A-1) obtained in Production Example 1 and the aqueous dispersion of the anionic urethane resin obtained in Production Example 4 (B -1) 25 parts, 25 parts of Bihydrol PT241, 12.5 parts of Cymel 325 and 50 parts of Bihydur VPLS2310 (manufactured by Sumika Bayer Urethane Co., Ltd., blocked polyisocyanate curing agent imparted water dispersibility) were further stirred Add deionized water and dimethylethanolamine, pH 8.5, Ford Cup No. 4 was adjusted to a viscosity of 40 seconds to obtain an aqueous coating composition 4.

In 131 parts of the pigment dispersion paste 1 obtained in Example 1, 57 parts of the anionic urethane resin emulsion (A-2) obtained in Production Example 2 and the aqueous dispersion of the anionic urethane resin obtained in Production Example 5 (B -2) 57 parts, 25 parts of Cymel 325 and 67 parts of the polyolefin emulsion (F-1) obtained in Production Example 8 were mixed and stirred, and deionized water and dimethylethanolamine were further added, pH 8.5, Ford Cup No. 4 was adjusted to a viscosity of 40 seconds to obtain an aqueous coating composition 5.
(Comparative Example 1)
In 131 parts of the pigment dispersion paste 1 obtained in Example 1, 57 parts of the anionic urethane resin emulsion (A-3) obtained in Production Example 3 and the aqueous dispersion of the anionic urethane resin obtained in Production Example 6 (B -3) 50 parts, 50 parts of polyester resin (C-1) and 25 parts of Cymel 325 were mixed and stirred, and deionized water and dimethylethanolamine were further added to obtain a pH of 8.5, Ford Cup No. 4 was adjusted to a viscosity of 40 seconds to obtain an aqueous coating composition 6.
(Comparative Example 2)
In 131 parts of the pigment dispersion paste 1 obtained in Example 1, 114 parts of the anionic urethane resin emulsion (A-3) obtained in Production Example 3, 50 parts of the polyester resin (C-1) and 25 parts of Cymel 325 were mixed. The mixture was further stirred, and deionized water and dimethylethanolamine were added to adjust the pH to 8.5, Ford Cup No. 4 was adjusted to a viscosity of 40 seconds to obtain an aqueous coating composition 7.
(Comparative Example 3)
To 131 parts of pigment dispersion paste 1 obtained in Example 1, 125 parts of polyester resin (C-1), 25 parts of Cymel 325 and 25 parts of bihydrup VPLS2310 were mixed and stirred, and deionized water and dimethylethanolamine were further added. PH 8.5, Ford Cup No. 4 was adjusted to a viscosity of 40 seconds to obtain an aqueous coating composition 8.

Preparation of test plate (for coating performance test)
Using the water-based coating compositions obtained in Examples 1 to 5 and Comparative Examples 1 to 3, test plates were prepared as follows for each.
Cold-rolled steel sheet with Palbond # 3020 (Nihon Parkerizing Co., Ltd., zinc phosphate treatment) was electrocoated with ELECRON GT-10 (Kansai Paint Co., Ltd., cationic electrodeposition paint) and heated at 170 ° C for 30 minutes. Curing was performed to obtain a coating film having a thickness of 20 μm.
After coating aqueous coating compositions 1 to 8 (see Table 1 for coating composition) on the coating film and baking at 150 ° C. for 20 minutes, aqueous metallic base coat WBC710T (manufactured by Kansai Paint Co., Ltd.) Acrylic / melamine resin-based top-coated base coat paint) was applied to a film thickness of 15 μm, left at room temperature for 3 minutes, preheated at 80 ° C. for 3 minutes, and then an organic solvent-type clear paint (KINO #). 1200 TW, manufactured by Kansai Paint Co., Ltd., acid / epoxy curable acrylic resin-based clear paint) is applied to a film thickness of 35 μm and heated at 140 ° C. for 30 minutes to cure both coating films together. Got.

Performance test was performed on each of the test plates obtained. The performance test results are shown in Table 1. The paint formulation is also shown. In addition, in the table | surface, all the compounding quantities of each component in coating composition are solid content weight.

The test and evaluation methods are as follows.

  Paint solid content: About 2 g of paint was sampled into an aluminum foil cup having a diameter of about 5 cm, and the solid content weight concentration (%) was measured (solid content measurement condition: measured after drying at 110 ° C. for 1 hour).

VOC: paint solid content (by the above method), paint specific gravity (measured by a specific gravity cup method according to JIS K-5400 4.6.2), moisture content (automatic moisture measuring device KF-100, manufactured by Mitsubishi Chemical Corporation) Measured in advance, the VOC amount excluding water in the paint was calculated by the following formula (1).
Formula (1): VOC (g / l) = 1000 × specific gravity A × ((100−paint solid content) / 100)
(Specific gravity A: (Specific gravity of paint excluding water))
Paint stability: The condition after storing the paint at 40 ° C. for 10 days was examined.
○: Good without problems.
Δ: Increase in viscosity is observed.
X: The viscosity increase is remarkable.

  Finishability (smoothness): The appearance of each test plate was visually evaluated. “Horizontal” means that the test plate was set and heat-cured in a horizontal state at an angle of 0 ° with respect to the horizontal plane after painting, and “Vertical” means that the test plate was leveled after painting. In contrast, it represents that setting and heat-curing were performed in a vertical state at an angle of 90 °.

    ○: Smoothness, gloss and clearness are all good.

    Δ: Any of smoothness, gloss, and sharpness is slightly inferior.

    X: Smoothness, gloss, or sharpness is remarkably inferior.

  Water resistance: Evaluation was performed by conducting a coating surface state after immersing each test plate in deionized water at 40 ° C. for 240 hours and a 2 mm square gobang adhesion test. The coated surfaces of all the test plates were good without problems.

○: Remaining number of Gobang eyes 100/100 Δ: Remaining number of Gobang eyes 95 to 99/100 ×: Remaining number of Gobang eyes Less than 95/100 pieces Chipping resistance: Stepping stone testing machine JA-400 manufactured by Suga Test Instruments Co., Ltd. A test plate was placed on a specimen holder of a mold (chipping test device), and granulated crushed stones of granule No. 7 were sprayed onto the coating surface at −20 ° C. with compressed air of 0.392 MPa (4 kgf / cm ² ). The degree of occurrence of scratches on the coating film was observed and evaluated visually.

  ○: The size of the scratch is small, and the electrodeposition surface and the base steel plate are not exposed.

  (Triangle | delta): Although the magnitude | size of a crack is small, the electrodeposition surface and the base steel plate are exposed.

X: The size of the scratch is quite large, and the base steel plate is also greatly exposed.

Claims (5)

An anionic urethane resin emulsion (A) having a particle size of less than 100 nm, an acid value of 20 to 50 mgKOH / g, and a number average molecular weight of 5,000 or more, and a number average molecular weight of less than 5,000, and An aqueous paint composition comprising an anionic urethane resin (B) having a linear molecular structure as an essential component. Furthermore, the aqueous coating composition of Claim 1 containing a hydroxyl-containing resin (C), a crosslinking agent (D), and a pigment (E). The aqueous coating composition according to claim 1 or 2, further comprising a polyolefin emulsion (F). The solid content total weight of the anionic urethane resin emulsion (A) and the urethane resin (B) is 1 to 80 parts by weight with respect to 100 parts by weight of the total resin solids in the paint. The water-based paint composition according to claim 1. Step 1: The aqueous solution according to any one of claims 1 to 4, without applying a chipping primer on the metal coating or on the electrodeposition coating film formed by electrodeposition coating on the metal coating. Applying the coating composition to form an uncured coating film or baking and drying the coating film to form a cured coating film; and Step 2: to the uncured coating film or the cured coating film obtained in Step 1 A method for forming a multilayer coating film comprising a step of coating one or more top coating compositions to form a top coating film and baking and curing.