WO2011010538A1 - Water-based primer coating composition and method for forming multilayer coating film - Google Patents

Abstract

Provided is a water-based primer coating composition characterized by comprising (A) a urethane resin emulsion which is prepared using (a1) a polyisocyanate component and (a2) a polyol component as raw materials and which has an acid value of 6 to 18mgKOH/g and a weight-average molecular weight of 50000 or more and (B) an oligomer which has a water tolerance of at least 10 and a number-average molecular weight of 200 to 1500. In the water-based primer coating composition, the component (a1) contains an alicyclic diisocyanate; the component (a2) contains (a2-1) a polyester polyol and/or polytetramethylene glycol and (a2-2) a diol that contains an anionic group; and when the component (a2-1) is polytetramethylene glycol, the component (A) has a weight-average molecular weight of 200000 or less. Also provided is a method for forming a multilayer coating film using the primer coating composition.

Description

Water-based primer coating composition and multilayer coating film forming method

The present invention relates to an aqueous primer coating composition excellent in chipping resistance, finish, etc., and excellent in wet-on-wet coating suitability with an aqueous intermediate coating, and a method for forming a multilayer coating film using the aqueous primer coating composition .

In recent years, there has been great interest in environmental issues on a global scale, but the automobile industry is also actively promoting 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 of an automobile body is usually covered with a multilayer coating consisting of a primer coating, an intermediate coating, and a top coating with a cationic electrodeposition coating for the purpose of providing corrosion protection and aesthetics. From this point of view, 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 stone splashes during traveling.

In order to impart this chipping resistance, a chipping primer coating film is formed between the primer coating film and the intermediate coating film by the cationic electrodeposition coating. The chipping primer coating film is formed by a chipping primer coating. Usually, in the application of this chipping primer coating, the chipping primer coating is applied onto the undercoat film made of a heat-cured cationic electrodeposition coating or the like, and the intermediate coating is applied wet-on-wet without being heated and cured. .

In recent years, chipping primer coatings and intermediate coatings have been made water-based due to the demand for water-based coatings. The above wet-on-wet coating process involves wet-on-wetting between water-based coatings of water-based chipping primer coatings and water-based intermediate coatings. There is a case where a problem arises in that the finished appearance becomes poor due to the coating, and the two coatings (multilayer coating film before curing with both coatings) are mixed.

Chipping primer paint is a body coated with an undercoating film such as cationic electrodeposition paint. The tip of the hood of the car body where the paint film is damaged by the stone splash during traveling, the underbody of a tire house, etc. Since the portion is partially coated, there is a portion that is painted in a dust shape and does not completely form a film. As described above, it is necessary to satisfy a good finished appearance even in a portion where the chipping primer coating is applied in the form of dust.

For example, Patent Document 1 discloses an aqueous copolymer resin mainly composed of ethylene and an ethylenically unsaturated monomer having a carboxyl group, having a specific amount of carboxyl groups, An automotive chipping-resistant aqueous coating composition is disclosed, which is a composition obtained by mixing an ethylene copolymer resin partially bonded to the main chain and an aqueous polyurethane resin at a specific blending ratio. .

Patent Document 2 discloses a method for forming a chipping-resistant composite coating film, in which a chipping-resistant primer has an aqueous dispersion of an ethylene copolymer containing a specific monomer, a water-based urethane resin, and a specific boiling point of the paint weight. Disclosed is a method comprising a water-miscible organic solvent having a temperature higher than a specific temperature and not higher than the baking temperature of the paint, or a melamine resin in a specific ratio of the weight of the paint, and the intermediate coating is a melamine-curable polyester-based water-based paint. ing.

However, in any of the above, the wet-on-wet coating suitability of the water-based chipping primer coating and the water-based intermediate coating is insufficient, so that a good finished appearance cannot be obtained. Further, the finished appearance of the dust part of the chipping primer coating was also insufficient.

Japanese Patent No. 2920026 JP-A-11-33478

An object of the present invention is to provide an aqueous primer coating composition excellent in chipping resistance, finished appearance and the like, and excellent in wet-on-wet coating suitability with an aqueous intermediate coating, and a method for forming a multilayer coating film.

As a result of intensive studies, the present inventors have found that an anionic group-containing diol and at least one selected from the group consisting of a polyisocyanate component containing alicyclic diisocyanate as an essential component, polyester polyol and polytetramethylene glycol And a urethane resin emulsion (A) having a specific range of acid value and weight average molecular weight, and an oligomer having a specific range of water tolerance and number average molecular weight (B) According to the water-based primer coating composition containing the present invention, it has been found that the above problems can be solved, and the present invention has been completed.

That is, the present invention provides the following items:
Item 1. A urethane resin emulsion (A) having an acid value of 6 to 18 mg KOH / g and a weight average molecular weight of 50,000 or more and a water tolerance of 10 produced using the polyisocyanate component (a1) and the polyol component (a2) as raw materials. The oligomer (B) having a number average molecular weight of 200 to 1500
A water-based primer coating composition comprising:
The polyisocyanate component (a1) contains an alicyclic diisocyanate,
The polyol component (a2) contains at least one (a2-1) selected from the group consisting of polyester polyol and polytetramethylene glycol, and an anionic group-containing diol (a2-2), and the (a2 -1) When the component is made of polytetramethylene glycol, the weight average molecular weight of the urethane resin emulsion (A) is 200,000 or less.
Water-based primer coating composition.

Item 2. The oligomer (B) is represented by the following general formula (1)

[Wherein, R ¹ and R ² are the same or different and each represents a hydrocarbon group having 4 to 18 carbon atoms.
R ³ is the same or different and represents an alkylene group having 2 to 4 carbon atoms.
m represents an integer of 3 to 25. ]
Item 2. The aqueous primer coating composition according to Item 1, which is a diester compound represented by the formula:

Item 3. Item 3. The aqueous primer coating composition according to Item 1 or 2, further comprising a blocked polyisocyanate curing agent.

Item 4. Item 4. The aqueous primer coating composition according to any one of Items 1 to 3, further comprising a urethane associative thickener.

Item 5. 5. Apply a water-based primer coating composition according to any one of Items 1 to 4 on an object to be coated to form a primer coating, and then apply a water-based colored coating on the uncured primer coating. Forming a colored coating film, and simultaneously curing the formed primer coating film and the colored coating film.

Item 6. An electrodeposition paint is applied on the object to be coated, and the primer coating film is formed by applying the water-based primer coating composition according to any one of Items 1 to 4 on the uncured primer coating film. A method for forming a multilayer coating film comprising: coating an aqueous intermediate coating composition to form an intermediate coating film, and applying one or more top coating compositions after curing or without curing.

Item 7. An article coated with the aqueous primer coating composition according to any one of items 1 to 4.

Item 8. An article coated by the method for forming a multilayer coating film according to Item 5.

Since the water-based primer coating composition of the present invention contains a urethane resin emulsion having an alicyclic diisocyanate as a polyisocyanate component and a polyester polyol and / or polytetramethylene glycol as a polyol component, it is particularly resistant to chipping. A coating film having excellent properties can be obtained. In addition, since the urethane resin emulsion has a specific weight average molecular weight and a relatively low acid value, it is possible to obtain a coating film excellent in wet-on-wet suitability with an aqueous intermediate coating material and excellent in finished appearance. Furthermore, since it has the water tolerance of a specific range and the oligomer of a number average molecular weight, the coating film excellent in the finishing external appearance can be obtained also in the dust part of an aqueous primer coating film.

As described above, according to the aqueous primer coating composition and the multilayer coating film forming method of the present invention, it is possible to obtain an effect that a multilayer coating film having excellent chipping resistance and excellent finished appearance can be obtained.

Hereinafter, the water-based primer coating composition and the multilayer coating film forming method of the present invention will be described in detail.

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

Urethane resin emulsion (A)
The urethane resin emulsion (A) in the present invention is
Polyisocyanate component (a1) containing alicyclic diisocyanate as an essential component, and at least one of polyester polyol and polytetramethylene glycol (a2-1) and an anionic group-containing diol (a2-2) as essential components Polyol component (a2)
It is a urethane resin emulsion obtained from the component containing.

In order to obtain the urethane resin emulsion in the present invention, for example, first, by a conventional method, a polyisocyanate component (a1) containing an alicyclic diisocyanate as an essential component, a polyester polyol and / or a polytetramethylene glycol (a2-1). An isocyanate-terminated prepolymer is synthesized by reacting a polyol component (a2) having an anionic group-containing diol (a2-2) as an essential component.

Examples of the polyisocyanate component (a1) include alicyclic diisocyanates as essential components and other polyisocyanates.

Examples of the alicyclic diisocyanate include isophorone diisocyanate, dicyclohexylmethane-4,4′-diisocyanate, trans-1,4-cyclohexyl diisocyanate, and norbornene diisocyanate.

Among these, as the alicyclic diisocyanate, isophorone diisocyanate and dicyclohexylmethane-4,4'-diisocyanate are particularly preferable from the viewpoint of improving the organic solvent swelling resistance of the resulting coating film.

From the viewpoint of chipping resistance, the content of the alicyclic diisocyanate in the polyisocyanate component (a1) is preferably 50 to 100% by mass, and preferably 70 to 100% by mass with respect to the total amount of the polyisocyanate component (a1). More preferably.

Other polyisocyanates include diisocyanates other than alicyclic diisocyanates and polyisocyanates having three or more isocyanate groups in one molecule.

Diisocyanates other than alicyclic diisocyanates include tolylene diisocyanate, diphenylmethane-4,4′-diisocyanate, p-phenylene diisocyanate, xylylene diisocyanate, 1,5-naphthylene diisocyanate, 3,3′-dimethyldiphenyl-4, Aromatic diisocyanates such as 4'-diisocyanate, dianisidine diisocyanate, tetramethylxylylene diisocyanate; 1,6-hexamethylene diisocyanate, 2,2,4 and / or (2,4,4) -trimethylhexamethylene diisocyanate, lysine Aliphatic diisocyanates such as diisocyanates are mentioned.

Examples of polyisocyanates having three or more isocyanate groups in one molecule include, for example, isocyanurate trimers, burette trimers, trimethylolpropane adducts of the above-mentioned diisocyanates; triphenylmethane triisocyanate, 1- Examples thereof include trifunctional or higher functional isocyanates such as methylbenzole-2,4,6-triisocyanate and dimethyltriphenylmethanetetraisocyanate. These isocyanate compounds are in the form of modified products such as carbodiimide modification, isocyanurate modification, biuret modification and the like. May be used.

These polyisocyanates may be used alone or in combination of two or more.

Examples of the polyol component (a2) include polyester polyol and / or polytetramethylene glycol (a2-1), an anionic group-containing diol (a2-2), and other polyols, which are essential components.

Examples of the polyester polyol include those obtained by polycondensation of a low molecular weight diol and a dibasic acid, and those obtained by a ring-opening reaction of a lactone compound using a low molecular weight diol as an initiator.

In the former case, the low molecular weight diol includes ethylene glycol, propanediol, 1,4-butylene glycol, 1,3-butylene glycol, 1,2-butylene glycol, 1,6-hexanediol, 3-methyl-1, 5-pentanediol, neopentyl glycol, alkane (C7 to C22) diol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, cyclohexanedimethanol, alkane-1,2-diol (C17 to C20), hydrogenated bisphenol A, low molecular weight diene such as 1,4-dihydroxy-2-butene, 2,6-dimethyl-1-octene-3,8-diol, bishydroxyethoxybenzene, xylene glycol, bis-2-hydroxyethylene terephthalate It can be mentioned Lumpur.

Of these, linear diols having 4 or more carbon atoms such as 1,4-butylene glycol and 1,6-hexanediol can be suitably used from the viewpoint of chipping resistance of the resulting coating film.

Examples of the dibasic acid include adipic acid, azelaic acid, sebacic acid, isophthalic acid, terephthalic acid and the like.

Among the above, from the viewpoint of chipping resistance of the resulting coating film, linear dibasic acids having 4 or more carbon atoms in the alkylene group such as adipic acid and azelaic acid can be preferably used.

The low molecular diol and the dibasic acid can be used alone or in combination of two or more.

In the latter case, examples of the lactone compound include ε-caprolactone and poly β-methyl-δ-valerolactone.

Polytetramethylene glycol is usually a compound synthesized by ring-opening polymerization of tetrahydrofuran, and those having a molecular weight of 500 to 3000, particularly 500 to 2000 can be suitably used.

The total amount of the polyester polyol and / or polytetramethylene glycol (a2-1) is 50 to 100 of the total amount of the polyol component excluding the anionic group-containing diol (a2-2) from the viewpoint of chipping resistance and finished appearance. The mass is preferably 70% by mass, particularly 70 to 100% by mass.

An anionic group-containing diol is a compound used to introduce an anionic group into a urethane resin. Examples of the anionic group-containing diol include diol compounds having 1 to 2, preferably 1 anionic group. By incorporating the anionic group-containing diol into the urethane resin skeleton, hydrophilicity can be imparted to the urethane resin, and the urethane resin can be dispersed in water.

Examples of the anionic group include a carboxyl group, a sulfonic acid group, a phosphonic acid group, and a boric acid group. From the viewpoint of dispersibility in water and ease of introduction into a urethane resin, a carboxyl group and a sulfonic acid group are preferable.

Examples of the carboxyl group-containing diol include 2,2-dimethylolacetic acid, 2,2-dimethylollactic acid, 2,2-dimethylolpropionic acid, 2,2-dimethylolbutanoic acid, dimethylolheptanoic acid, and dimethylolnonanoic acid. 2,2-dimethylolbutyric acid, 2,2-dimethylolvaleric acid, dihydroxycarboxylic acids such as dihydroxybenzoic acid, and half ester compounds of polyoxypropylenetriol with maleic anhydride and phthalic anhydride.

Examples of the sulfonic acid group-containing diol include 1,4-butanediol-2-sulfonic acid.

The anionic group-containing diol can be used alone or in combination of two or more.

Other polyols include polyether polyols other than polytetramethylene glycol, polycarbonate polyols, polybutadiene polyols, hydrogenated polybutadiene polyols, and the like.

Examples of polyether polyols other than polytetramethylene glycol include polypropylene glycol, poly (ethylene / propylene) glycol, poly (ethylene / tetramethylene) glycol, and the like.

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 above polyol, if necessary, 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 in combination.

The above low molecular weight polyols can be used alone or in combination of two or more. Further, these low molecular weight polyols preferably have a number average molecular weight of 62 to 500, and low molecular weight diols, low molecular weight triols and the like can be suitably used.

The above polyol components can be used alone or in combination of two or more. The number average molecular weight of the polyol (measured by gel permeation chromatography and determined in terms of polystyrene. The molecular weight measurement method is the same hereinafter) is 500 to 5000, particularly 500 to 3 in terms of coating film performance, dispersion stability, etc. Within the range of 1,000.

In the synthesis of the isocyanate-terminated prepolymer, if necessary, a low molecular weight polyamine can be used in combination. 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, bis- (4-amino-3-chlorophenyl) methane, and diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, 2,2'-diamino Examples thereof include a low molecular weight amine having 3 or more amino groups such as diethylamine.

The above low molecular weight polyamines can be used alone or in combination of two or more. Among 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 performed by a known method. Specifically, for example, the above-mentioned polyisocyanate component (a1) and polyol component (a2) exceed 1 in the equivalent ratio of isocyanate groups to isocyanate groups (isocyanate groups / active hydrogen groups) with respect to active hydrogen groups (hydroxyl groups, amino groups, etc.). It can be blended in a proportion, preferably 1.05 to 2.0, and can be carried out by a known polymerization method such as bulk polymerization or solution polymerization.

In bulk polymerization, for example, a polyisocyanate is stirred under a nitrogen stream, and a polyol and, if necessary, a low molecular weight polyol and / or a low molecular weight polyamine are added to the reaction mixture at a reaction temperature of 75 to 85 ° C. for about several hours. It can be performed by reacting.

Solution polymerization can be carried out by adding polyisocyanate, polyol and, if necessary, low molecular weight polyol and / or low molecular weight polyamine to an organic solvent and reacting at a reaction temperature of 20 to 80 ° C. for several hours. As the organic solvent, it is possible to use a low boiling point solvent that is inert with respect to the isocyanate group, is hydrophilic, and can be easily removed. Specific examples include acetone, methyl ethyl ketone, ethyl acetate, tetrahydrofuran and the like. In the present invention, solution polymerization in which the reactivity and viscosity can be easily adjusted 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 can be used as necessary. Moreover, the unreacted monomer of polyisocyanate can also be removed from the resulting isocyanate-terminated prepolymer using a known removal means such as distillation or extraction.

Furthermore, in the synthesis of this isocyanate-terminated prepolymer, before or after the reaction, for example, trimethylamine, triethylamine, tri-n-propylamine, tributylamine, monoethanolamine, diethanolamine, triethanolamine, triethylenediamine, dimethylaminoethanol. An amine compound such as, for example, an alkali metal hydroxide such as potassium hydroxide or sodium hydroxide, or other neutralizing agents such as ammonia may be added to neutralize the anionic group to form a salt. preferable.

The amine compound is particularly preferably a compound having a relatively high boiling point (170 ° C. or higher) from the viewpoint of the finished appearance. Examples of such amines include alkanolamines such as diisopropylethanolamine (boiling point 190 ° C.), dibutylethanolamine (boiling point 229 ° C.), and methyldiethanolamine (boiling point 247 ° C.).

The amount of such a neutralizing agent added is, for example, preferably 0.4 to 1.2 equivalents, 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 mass, more preferably 0.5 to 3.0% by mass.

Then, the urethane resin emulsion as the component (A) in the present invention can be synthesized by reacting the obtained isocyanate-terminated prepolymer with a chain extender in water. As a result, a 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 in the molecule that can react with the terminal isocyanate group of the urethane prepolymer, and reacts with the terminal of the urethane prepolymer to generate a high molecular weight urethane resin.

As the chain extender, known ones can be used, and examples thereof include polyamine compounds, amino alcohol compounds, diol compounds and the like.

The polyamine compound 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, , 4-cyclohexanediamine, 3-aminomethyl-3,5,5-trimethylcyclohexylamine, piperazine, 2,5-dimethylpiperazine, isophoronediamine, 4,4'-cyclohexylmethanediamine, norbornanediamine, hydrazine, diethylenetriamine, tri Mention may be made of ethylenetriamine, 1,3-bis (aminomethyl) cyclohexane, xylylenediamine and the like.

Examples of amino alcohol compounds include hydroxyethyl hydrazine, hydroxyethyl diethylenetriamine, N- (2-aminoethyl) ethanolamine, 3-aminopropanediol, and the like.

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

Further, the polyamine compound 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, the isocyanate-terminated prepolymer is dispersed in water, and then the chain extender is added. What is necessary is just to mix | blend and to carry out chain extension reaction of an isocyanate terminal prepolymer 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 4.5. With such a blending amount, it can be carried out by rapidly dropping the isocyanate-terminated prepolymer aqueous dispersion while stirring (so that the reaction between the isocyanate group of the isocyanate-terminated prepolymer and water does not proceed). 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 a urethane resin emulsion can be obtained.

In addition, the organic solvent in the urethane resin emulsion can be removed by heating under an appropriate temperature condition under reduced pressure, for example, after the completion of the above reaction, if necessary.

In addition, a surfactant can be blended in the urethane resin emulsion in a range not impairing water resistance in order to improve stability.

The surfactant is not particularly limited, and examples thereof include anionic surfactants such as fatty acid salts, alkyl sulfate esters, alkylbenzene sulfonates, alkyl naphthalene sulfonates, alkyl sulfosuccinates, polyoxyethylene alkyl sulfates, and the like. For example, polyoxyethylene alkyl ether, polyoxyalkylene alkyl ether, polyoxyethylene compound, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, glycerin fatty acid ester, polyoxyethylene alkylamine, alkyl alkanol Nonionic surfactants such as amides, for example, cations such as alkylamine salts, quaternary ammonium salts, alkylbetaines, amine oxides, etc. And it can be exemplified amphoteric surfactants.

These surfactants can 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, in such a case, a nonionic surfactant containing no ionic functional group can be preferably used.

The amount of the surfactant used is not particularly limited. For example, it is preferably 0.01 to 10 parts by mass, more preferably 0.1 to 5 parts by mass with respect to 100 parts by mass of the polyurethane resin. When the amount of the surfactant used is less than 0.01 parts by mass, the effect of blending the surfactant may not be exhibited. When the amount exceeds 10 parts by mass, the water resistance of the coating film may be reduced. is there.

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 can be blended in a plurality of times at an appropriate stage.

The acid value of the urethane resin emulsion (A) is 6 to 18 mgKOH / g, preferably 7 to 18 mgKOH / g, more preferably 7 to 16 mgKOH / g, from the viewpoint of the finished appearance and water resistance of the coating film. If the acid value is less than 6 mgKOH / g, the stability of the urethane resin emulsion may be poor, and if it exceeds 18 mgKOH / g, the finished appearance of the coating film may be poor.

In the present invention, the acid value was measured according to JISK-5601-2-1 (1999). Specifically, titration was performed with a potassium hydroxide solution using phenolphthalein as an indicator, and calculation was performed according to the following formula.
Acid value (mgKOH / g) = 56.1 × V × C / m
V: titration volume (ml), C: concentration of titrant (mol / l), m: weight of solid content of sample (g)

The hydroxyl value of the urethane resin emulsion (A) is preferably 0 to 10 mgKOH / g, particularly preferably 0 to 5 mgKOH / g, from the viewpoint of coating film performance.

In the present invention, the hydroxyl value was measured according to JISK-0070 (1992). Specifically, 5 ml of acetylating reagent (acetic anhydride pyridine solution adjusted to 100 ml by adding pyridine to 25 g of acetic anhydride) was added to the sample and heated in a glycerin bath, followed by potassium hydroxide solution Was titrated with phenolphthalein as an indicator, and calculated according to the following formula.
Hydroxyl value (mgKOH / g) = [V × 56.1 × C / m] + D
V: titration (ml), C: titrant concentration (mol / l), m: solid weight of sample (g), D: acid value of sample (mgKOH / g)

The weight average molecular weight of the urethane resin emulsion (A) is 50000 or more, preferably 60000 or more from the viewpoint of chipping resistance and finished appearance. If the weight average molecular weight is less than 50,000, chipping resistance may be poor.

Here, when the component (a2-1) (at least one selected from the group consisting of polyester polyol and polytetramethylene glycol) is made of polytetramethylene glycol, the weight average molecular weight of the urethane resin emulsion (A) is 200000 or less, preferably 180000 or less, more preferably 150,000 or less.

By setting the weight average molecular weight of the urethane resin emulsion (A) in the above range, a coating film having excellent chipping resistance and finished appearance can be obtained.

In the present invention, the weight average molecular weight is a value obtained by converting a weight average molecular weight measured with a gel permeation chromatograph (“HLC8120GPC” manufactured by Tosoh Corporation) based on the weight average molecular weight of polystyrene. Columns are “TSKgel G-4000H × L”, “TSKgel G-3000H × L”, “TSKgel G-2500H × L”, “TSKgel G-2000H × L” (all manufactured by Tosoh Corporation, trade names) ), Mobile phase: tetrahydrofuran, measurement temperature: 40 ° C., flow rate: 1 cc / min, detector: RI. The number average molecular weight is also a value measured under the same conditions as described above. The number average molecular weight is also a value measured under the same conditions as described above.

The average particle diameter of the urethane resin emulsion (A) is usually 250 nm or less, preferably in the range of 50 to 200 nm, from the viewpoint of film forming properties and stability. When the average particle diameter exceeds 250 nm, the stability of the urethane resin emulsion may be poor.

The adjustment of the average particle diameter can be performed mainly by adjusting the acid value of the urethane resin. Although the average particle size is largely governed mainly by the acid value, it is also affected by the molecular weight, hydroxyl value and neutralizing agent. Therefore, the adjustment of the average particle size is combined with the acid value and the molecular weight, hydroxyl group and neutralizing agent. A desired particle size can be obtained by adjusting the kind and the addition amount.

The measurement of the average particle diameter was performed with a COULTER N4 type submicron particle analyzer (manufactured by Nikka Kisha Co., Ltd.).

Oligomer (B)
The oligomer (B) in the present invention is an oligomer having a water tolerance of 10 or more and a weight average molecular weight of 200 to 1500.

The oligomer (B) has a water tolerance of 10 or more, preferably 20 or more, more preferably 50 or more, and a number average molecular weight of 200 from the viewpoint of improving the finished appearance of the chipping primer dust coating part of the multilayer coating film. Those in the range of ˜1500, preferably 300 to 1000, more preferably 400 to 1000 are used.

Specific examples include polyalkylene glycols such as polyethylene glycol and polypropylene glycol, etherified products thereof, diester compounds represented by the following formula (1), and the like.

The diester compound is

[Wherein, R ¹ and R ² are the same or different and each represents a hydrocarbon group having 4 to 18 carbon atoms.
R ³ represents an alkylene group having 2 to 4 carbon atoms.
m represents an integer of 3 to 25. ]
It is a diester compound represented by these.
As described above, in general formula (1), R ³ may be the same or different. That is, m oxyalkylene units (R ³ —O) may be the same as or different from each other.

Among these, from the viewpoint of the sharpness of the coating film obtained, the coating film appearance, and the water resistance, R ¹ and R ² in the general formula (1) have 4 to 18 carbon atoms, preferably 5 to 11 carbon atoms. More preferably, it is preferably an alkyl group having 5 to 9 carbon atoms, particularly preferably 6 to 8 carbon atoms. Among them, the alkyl group is a linear or branched alkyl group, particularly preferably a branched one. It is preferable that it is an alkyl group. In particular, R ¹ and R ² in the general formula (1) are particularly preferably branched alkyl groups having 6 to 8 carbon atoms. When R ¹ and R ² are branched alkyl groups, a coating film having excellent sharpness can be formed even when the paint is applied after being stored for a relatively long period of time.

The diester compound can be obtained, for example, by esterifying a polyoxyalkylene glycol having two terminal hydroxyl groups and a monocarboxylic acid having a hydrocarbon group having 4 to 18 carbon atoms.

Examples of the polyoxyalkylene glycol include polyethylene glycol, polypropylene glycol, a copolymer of polyethylene and propylene glycol, and polybutylene glycol. Among them, it is particularly preferable to use polyethylene glycol. These polyoxyalkylene glycols generally have a weight average molecular weight of 100 to 1,200, preferably 150 to 600, and more preferably 200 to 400.

Examples of the monocarboxylic acid having a hydrocarbon group having 4 to 18 carbon atoms include pentanoic acid, hexanoic acid, 2-ethylbutanoic acid, 3-methylpentanoic acid, benzoic acid, cyclohexanecarboxylic acid, heptanoic acid, -Ethylpentanoic acid, 3-ethylpentanoic acid, octanoic acid, 2-ethylhexanoic acid, 4-ethylhexanoic acid, nonanoic acid, 2-ethylheptanoic acid, decanoic acid, 2-ethyloctanoic acid, 4-ethyloctanoic acid, Examples include dodecanoic acid, hexadecanoic acid, and octadecanoic acid.

Among them, hexanoic acid, heptanoic acid, 2-ethylpentanoic acid, 3-ethylpentanoic acid, octanoic acid, 2-ethylhexanoic acid, 4-ethylhexanoic acid, nonanoic acid, 2-ethylheptanoic acid, decanoic acid, 2- Monocarboxylic acids having an alkyl group having 5 to 9 carbon atoms such as ethyloctanoic acid and 4-ethyloctanoic acid, preferably heptanoic acid, 2-ethylpentanoic acid, 3-ethylpentanoic acid, octanoic acid, 2-ethylhexane Monocarboxylic acids having an alkyl group having 6 to 8 carbon atoms such as acid, 4-ethylhexanoic acid, nonanoic acid, 2-ethylheptanoic acid, more preferably 2-ethylpentanoic acid, 3-ethylpentanoic acid, 2-ethylpentanoic acid, Use of monocarboxylic acids having a branched alkyl group having 6 to 8 carbon atoms such as ethylhexanoic acid, 4-ethylhexanoic acid, 2-ethylheptanoic acid, etc. Rukoto is preferred.

The diesterification reaction between the polyoxyalkylene glycol and the monocarboxylic acid having a hydrocarbon group having 4 to 18 carbon atoms can be carried out by a method known per se. Monocarboxylic acids having 18 hydrocarbon groups can be used alone or in combination of two or more. The molecular weight of the obtained diester compound is preferably in the range of 320 to 1,400, preferably 450 to 1,000, more preferably 500 to 800, and particularly preferably 500 to 700. *

Among the oligomers, polyoxypropylene glyceryl ether and the diester compound represented by the formula (1) are preferably used.

Examples of commercially available products include polyoxypropylene glyceryl ether commercially available products such as GP400, GP600, and GP1000 (manufactured by Sanyo Kasei Co., Ltd.), and other diester compounds represented by the above formula (1) such as W-262 (DIC). Can be mentioned.

For the oligomer, water tolerance is a parameter indicating the affinity of the oligomer for water, and is a value determined by the following measurement.

The water tolerance of the oligomer was measured by the following method. Take 5.0 g of sample (oligomer) in a 200 ml beaker with a diameter of 5 cm and dilute with 50 ml of acetone. The sample solution is set to 20 ° C., a newspaper printed with No. 4 (13.75 points) type is placed under the bottom of the beaker, and deionized water is added dropwise while stirring with a magnetic stirrer. At this time, water tolerance is defined as the maximum dripping amount (ml) of deionized water at the limit at which the No. 4 type of newspaper placed under the bottom of the beaker can be seen through from the top of the beaker. Here, the above test is performed with a panel with visual acuity of 1.0 or more away from the newspaper by about 0.3 m. In addition, the fact that No. 4 type is “illegible” means that the solution becomes cloudy and the characters cannot be seen. Therefore, as long as the character is visible, it is determined that it can be read.

The larger the water tolerance value, the more hydrophilic the oligomer.

The ratio of the urethane resin emulsion (A) and the oligomer (B) in the aqueous primer coating composition of the present invention is urethane as a solid content with respect to the total resin solid content in the coating composition from the viewpoint of finish properties and the like. The resin emulsion (A) is preferably 50 to 97% by mass, more preferably 60 to 90% by mass, and the oligomer (B) is preferably 3 to 15% by mass, more preferably 3 to 12% by mass.

In producing the aqueous primer coating composition of the present invention, from the viewpoint of improving the stability of the coating, it is possible to gradually mix the oligomer (B) while stirring the urethane resin emulsion (A). preferable.

The aqueous primer coating composition of the present invention is preferably neutralized with a neutralizing agent from the viewpoint of storage stability.

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

In addition to the urethane resin emulsion (A) and the oligomer (B), which are essential components, the water-based primer coating composition of the present invention further contains other resins (C), a crosslinking agent (D) and a pigment (E) as necessary. Can be contained.

Other resins (C)
Examples of other resins include acrylic resins, polyester resins, urethane-modified polyester resins, and epoxy resins.

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

Acrylic resin In the present invention, examples of the acrylic resin include an acrylic resin that can be synthesized in accordance with a conventional method by copolymerizing a radical 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.

As the radical polymerizable monomer, conventionally known monomers can be used. For example, a hydroxyl group-containing radical polymerizable monomer, a carboxyl group-containing radical polymerizable monomer, and other radical polymerizable monomers 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 morro Emissions, dimethylaminoethyl (meth) acrylate, N- vinyl-2-pyrrolidone, can be mentioned γ- acryloxypropyltrimethoxysilane trimethoxysilane or the like.

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

The weight average molecular weight of the acrylic resin is in the range of 1,000 to 200,000, preferably 2000 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 A 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.

The 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-butanediol, 3-methyl-1,2-butanediol, 1,2-pentanediol, 1,5-pentane Diol, 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- Glycol compounds such as xanthdiol, 1,4-hexanediol, 2,5-hexanediol, neopentyl glycol, and hydroxypivalic acid neopentyl glycol ester, and polylactones obtained by adding a lactone compound such as ε-caprolactone to these glycol compounds Polyester diol compounds such as diol, bis (hydroxyethyl) terephthalate, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, tricyclodecane dimethanol, hydrogenated bisphenol A, hydrogenated bisphenol F, spiroglycol, dihydroxy Methyltricyclodecane, glycerin, trimethylolpropane, trimethylolethane, diglycerin, triglycerin, 1,2,6-hexanetriol, pentaerythritol And dipentaerythritol, dipentaerythritol, sorbitol, mannitol and the like.

In addition, as the polyester resin, (semi) drying oil such as 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. A fatty acid-modified polyester resin modified with a 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, such as 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 in the range of 1,000 to 200,000, preferably 2000 to 100,000, from the viewpoint 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. The acid value of the polyester resin is 5 to 100 mgKOH / g, preferably 10 to 60 mgKOH / g.

Cross-linking agent (D)
As the crosslinking agent (D), for example, the following blocked polyisocyanate curing agent (d ₁ ), water-dispersible blocked polyisocyanate curing agent (d ₂ ), and melamine resin (d ₃ ) can be used. Among the above, from the viewpoint of finished appearance and chipping resistance, the blocked polyisocyanate curing agent (d ₁ ) and the water-dispersible blocked polyisocyanate curing agent (d ₂ ) can be preferably used.

Blocked polyisocyanate curing agent (d ₁ ): a curing agent obtained by blocking an 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 polyisocyanate compounds 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 Alicyclic diisocyanate compounds such as these; and burette-type adducts and isocyanurate cycloadducts of these polyisocyanates; xylylene diisocyanate, metaxylylene diisocyanate, tetramethylxylylene 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) Aromatic polyisocyanate compounds, such as poly (isocyanates); and burette-type adducts, isocyanurate cycloadducts of these polyisocyanates; triphenylmethane-4,4 ′, 4 ″ -triisocyanate, 1,3,5- 3 or more isocyanate groups in one molecule such as triisocyanatobenzene, 2,4,6-triisocyanatotoluene, 4,4′-dimethyldiphenylmethane-2,2 ′, 5,5′-tetraisocyanate Polyisocyanate compounds; and burette-type adducts, isocyanurate cycloadducts of these polyisocyanates; ethylene glycol, propylene glycol, 1,4-butylene glycol, dimethylolpropionic acid, polyalkylene glycol, trimethylolpropane, hexanetriol Polyol water etc. Examples thereof include urethanated adducts obtained by reacting polyisocyanate compounds with an excess ratio of isocyanate groups to acid groups; and burette-type adducts and isocyanurate ring adducts of these polyisocyanates.

Among the above, from the viewpoint of chipping resistance and finished appearance, aliphatic polyisocyanate compounds, burette type adducts and isocyanurate ring adducts of these polyisocyanates can be preferably used.

The blocking agent blocks a free isocyanate group and can easily react with a hydroxyl group when heated to, for example, 100 ° C. or higher, preferably 130 ° C. or higher. Examples of such blocking agents include phenolic blocking agents such as phenol, cresol, xylenol, nitrophenol, ethylphenol, hydroxydiphenyl, butylphenol, isopropylphenol, nonylphenol, octylphenol, and hydroxymethyl benzoate; ε-caprolactam, δ-valerolactam Lactam blocking agents such as γ-butyrolactam and β-propiolactam; aliphatic alcohol blocking agents 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 Ether-based blocking agents such as rumonoethyl ether, propylene glycol monomethyl ether and methoxymethanol; benzyl alcohol; glycolic acid; glycolic acid esters such as methyl glycolate, ethyl glycolate and butyl glycolate; lactic acid, methyl lactate, ethyl lactate and lactic acid Lactic acid esters such as butyl; alcohol blocking agents such as methylol urea, methylol melamine, diacetone alcohol, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate; formamide oxime, acetamide oxime, acetoxime, methyl ethyl ketoxime, diacetyl monooxime, Oxime-based blocking agents such as benzophenone oxime and cyclohexane oxime; dimethyl malonate, diethyl malonate, acetoacetate Active methylene blocking agents such as chill, methyl acetoacetate and acetylacetone; mercaptans such as butyl mercaptan, t-butyl mercaptan, hexyl mercaptan, t-dodecyl mercaptan, 2-mercaptobenzothiazole, thiophenol, methylthiophenol and ethylthiophenol Block agents; acid amide block agents such as acetanilide, acetanisid, acetolide, acrylamide, methacrylamide, acetic acid amide, stearamide, and benzamide; imide block agents such as succinimide, phthalimide, and maleimide; diphenylamine, Phenylnaphthylamine, xylidine, N-phenylxylidine, carbazole, aniline, naphthylamine, butylamine, dibutylamine, butylphenol Amine blocking agents such as ruamine; Imidazole blocking agents such as imidazole and 2-ethylimidazole; Pyrazole blocking agents such as 3,5-dimethylpyrazole; Ureas such as urea, thiourea, ethylene urea, ethylene thiourea and diphenyl urea Blocking agents; carbamate ester blocking agents such as phenyl N-phenylcarbamate; imine blocking agents such as ethyleneimine and propyleneimine; and sulfites such as sodium bisulfite and potassium bisulfite. .

Of the above, from the viewpoint of finished appearance, pyrazole-based and oxime-based blocking agents can be suitably used.

Blocked polyisocyanate curing agent imparted with water dispersibility (d ₂ ): A blocked polyisocyanate curing agent imparted with water dispersibility to the blocked polyisocyanate curing agent (d ₁ ) within a range not deteriorating the coating film performance. Can be used.

The blocked polyisocyanate curing agent (d ₂ ) imparted with water dispersibility is obtained by blocking the isocyanate group of the polyisocyanate with a blocking agent and a hydroxy monocarboxylic acid compound, and neutralizing the carboxyl group of the hydroxy monocarboxylic acid compound. It is a blocked polyisocyanate compound imparted with water dispersibility.

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).

Examples of the polyisocyanate derivative include, for example, the dimer, trimer, biuret, allophanate, uretdione, uretoimine, isocyanurate, oxadiazine trione, polymethylene polyphenyl polyisocyanate (crude MDI, polymeric MDI) and the polyisocyanate compound described above. Examples include Crude TDI.

In order to produce a water-dispersible blocked polyisocyanate curing agent (d ₂ ), the isocyanate group of the polyisocyanate compound is blocked with a blocking agent and reacted with a hydroxymonocarboxylic acid compound. The isocyanate group is reacted so as to be added to the hydroxyl group of the hydroxymonocarboxylic acid compound.

As the blocking agent, the same blocking agent as exemplified for the blocked polyisocyanate curing agent (d ₁ ) can be used. Examples of the hydroxy monocarboxylic acid compound include 2-hydroxyacetic acid, 3-hydroxypropanoic acid, 12-hydroxy-9-octadecanoic acid (ricinoleic acid), 3-hydroxy-2,2-dimethylpropanoic acid (hydroxypivalic acid). And dimethylolpropionic acid (DMPA), among which 3-hydroxy-2,2-dimethylpropanoic acid (hydroxypivalic acid) is preferred. The solvent used in the reaction is preferably non-reactive with isocyanate groups, and examples thereof include ketone compounds such as acetone and methyl ethyl ketone, ester compounds 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 a methylolated amino resin obtained by a reaction between melamine and an 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 monoalcohols 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, a melamine resin having an average of 3 or more methylol groups per one triazine nucleus and methyletherified, further having an imino group, and having an average condensation degree of about 2 or less. Hydrophilic melamine in which the proportion of the nuclei is about 50% by weight or more, and a part of the methoxy group of the melamine resin in which 3 or more methylol groups are averaged as a methyl ether per triazine nucleus is a mono-carbon having 2 or more carbon atoms. A melamine resin substituted with an alcohol, which further has an imino group and has an average condensation degree of about 2 or less and a mononuclear ratio of about 50% by weight or more, can be suitably used.

Pigment (E)
Examples of the pigment (E) include colored pigments such as titanium oxide, zinc white, carbon black, phthalocyanine blue, Prussian blue, cobalt blue, azo pigment, phthalocyanine pigment, quinacridone pigment, isoindoline pigment, selenium pigment, and perylene pigment. Extender pigments such as talc, clay, kaolin, barita, barium sulfate, barium carbonate, calcium carbonate, silica, and alumina white 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.

In the water-based primer coating composition of the present invention, a thickener, a dispersant, an anti-settling agent, an organic solvent, a catalyst, an antifoaming agent, an ultraviolet absorber, a surface conditioner and the like are appropriately used as necessary. be able to.

Examples of the thickener include inorganic thickeners such as silicate, metal silicate, montmorillonite, colloidal alumina; copolymer of (meth) acrylic acid and (meth) acrylic ester, poly Polyacrylic acid thickeners such as sodium acrylate; one molecule has a hydrophilic part and a hydrophobic part, and in an aqueous medium, the hydrophobic part adsorbs to the surface of pigment or emulsion particles in the paint. Or an associative thickener that effectively exhibits a thickening action by the hydrophobic parts being associated with each other; a fibrous thickener such as carboxymethylcellulose, methylcellulose, hydroxyethylcellulose; casein, sodium caseinate, Protein thickeners such as ammonium caseinate; Alginate thickeners such as sodium alginate; Polyvinyl alcohol, Polyvinylpyrrolide , Polyvinyl thickeners such as polyvinyl benzyl ether copolymer; polyether thickeners such as pluronic polyether, polyether dialkyl ester, polyether dialkyl ether, polyether epoxy modified product; vinyl methyl ether-maleic anhydride Examples thereof include a maleic anhydride copolymer thickener such as a partial ester of a copolymer; a polyamide thickener such as a polyamideamine salt. These thickeners can be used alone or in combination of two or more.

Commercially available products can be used as the polyacrylic acid thickener. Commercially available product names include, for example, “Primal ASE-60”, “Primal TT-615”, “Primal RM-5” manufactured by Rohm and Haas, “SN thickener 613”, “SN thickener 618” manufactured by San Nopco. ”,“ SN thickener 630 ”,“ SN thickener 634 ”,“ SN thickener 636 ”, and the like. A commercial product can be used as the associative thickener. Examples of commercially available product names include “UH-420”, “UH-450”, “UH-462”, “UH-472”, “UH-540”, “UH-752”, “ UH-756VF, UH-814N, Rohm and Haas “Primal RM-8W”, “Primal RM-825”, “Primal RM-2020NPR”, “Primal RM-12W”, “Primal SCT-275” "SN thickener 612", "SN thickener 621N", "SN thickener 625N", "SN thickener 627N", "SN thickener 660T", etc. manufactured by San Nopco.

As the above thickener, it is preferable to use a polyacrylic acid-based thickener and / or an associative thickener, more preferably an associative thickener, having a hydrophobic group at the terminal, and a molecular chain It is more preferable to use a urethane associative thickener containing a urethane bond therein. A commercially available product can be used as the urethane associative thickener. Examples of commercially available product names include “UH-420”, “UH-462”, “UH-472”, “UH-540”, “UH-752”, “UH-756VF”, “ “UH-814N”, “SN thickener 612”, “SN thickener 621N”, “SN thickener 625N”, “SN thickener 627N”, “SN thickener 660T” manufactured by San Nopco, “TAFIGEL PUR60” manufactured by MUNZING CHEMIE GMBH, etc. Is mentioned.

Further, when the aqueous primer coating composition of the present invention contains the above thickener, the blending amount of the thickener is 0.01 to 10% by mass with respect to the total resin solid content in the coating composition. It is preferably 0.02 to 6% by mass, more preferably 0.03 to 4% by mass.

The aqueous primer 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., and the film thickness is a cured coating film. Is preferably in the range of 1 to 15 μm, especially 2 to 10 μm.

For coating, it is preferable to adjust the viscosity at 20 ° C. for 20 to 60 seconds, preferably 30 to 50 seconds using Ford Cup # 4. The solid content during coating is 20 to 50% by mass, preferably 30 to 40% by mass.

According to the aqueous primer coating composition of the present invention, it is possible to obtain a multilayer coating film excellent in finish performance and chipping resistance coating performance, so that it is suitable for use as, for example, an aqueous chipping primer coating for automobiles. ing.

Automotive chipping primer coating is generally a coating applied between an undercoat layer and an intermediate coating layer such as electrodeposition coating on the outer plate of an automobile body.

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

The multi-layer coating film forming method is not particularly limited, but is preferably the body of various vehicles such as automobiles, motorcycles, containers, and the like. 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.

Also, the object to be coated may be a metal surface such as a car body or a metal substrate that has been subjected to a surface treatment such as a phosphate treatment, a chromate treatment, or a complex oxide treatment. Furthermore, as the object to be coated, an undercoat film such as various electrodeposition paints may be formed on the vehicle body, the metal base material, or the like.

In one embodiment, the present invention applies a water-based primer coating composition of the present invention to form a primer coating, and a water-based coloring coating is applied onto the uncured primer coating thus formed. Provided is a multilayer coating film forming method characterized in that a film is formed and the formed primer coating and colored coating are simultaneously baked and dried.

It is preferable to apply the aqueous colored paint after adjusting the solid content of the coating film of the aqueous primer paint composition to 70% by mass or more, preferably 75% by mass or more.

When the aqueous colored paint is applied in a state where the solid content of the applied paint film of the aqueous primer paint composition is less than 70% by mass, the finished appearance of the obtained multilayer paint film may be deteriorated.

Adjustment of the solid content of the coating film of the aqueous primer coating composition is, for example, usually at room temperature to 100 ° C., preferably at room temperature to 60 ° C., for 1 to 10 minutes, preferably Can be carried out by air drying for about 2 to 5 minutes.

In accordance with this method, as the water-based colored paint applied to the coating surface of the water-based primer paint composition of the present invention, for example, a water-based colored paint such as a water-based intermediate coating usually used in automobile coating can be used. . Specifically, an aqueous colored paint having an acrylic resin and / or a polyester resin as a base resin and an amino resin and / or a block polyisocyanate compound as a crosslinking agent can be preferably used.

The mixing ratio of the base resin and the cross-linking agent is generally within the range of 50 to 90%, particularly 60 to 80% for the base resin, and 50 to 10%, particularly 40 to 20% for the cross-linking agent, based on the solid mass. preferable. Furthermore, a coloring pigment, an extender pigment, other additives for coating materials, etc. can be mix | blended with an aqueous coloring coating material as needed.

Application of the aqueous colored coating to the coating surface of the aqueous primer coating composition of the present invention can be carried out in the same manner as the aqueous primer coating composition, and the coating film thickness is generally about 20 to 20 based on the cured coating film. About 50 μm, particularly within the range of about 25 to about 40 μm is preferable. After coating with an aqueous colored coating, both the aqueous primer coating composition and the aqueous colored coating are applied at room temperature to 100 ° C., preferably from room temperature to Both coatings are air-dried at a temperature of about 60 ° C. for 1 to 10 minutes, preferably about 2 to 5 minutes, and heated at a temperature of about 110 to about 170 ° C., particularly about 120 to about 160 ° C. for 10 to 40 minutes. Can be cured.

Further, in another embodiment, the present invention is an uncured primer formed by coating an electrodeposition paint on an object to be coated, and applying a water-based primer coating composition of the present invention to form a primer coating film. Provided is a method for forming a multi-layer coating film, wherein an intermediate coating film is formed by coating an aqueous coating composition on a coating film, and one or more layers of the coating composition are applied after curing or without curing.

A top coating is usually applied to the surface of the cured or uncured aqueous intermediate coating. The top coat is intended to give cosmetics to the coated article. Use a normal top coat that forms a film with excellent clarity, smoothness, gloss, weather resistance, chemical resistance, etc. Can do.

Specifically, for example, acrylic resin / amino resin type, alkyd resin / amino resin type, polyester resin / amino resin type, carboxyl group-containing resin / epoxy group-containing resin type, etc. can be used. Examples of the form of the liquid paint include an organic solution type, a non-aqueous dispersion type, an aqueous solution type, and an aqueous dispersion type.

These top coats are classified into solid color paints containing colored pigments, metallic paints containing metallic pigments, clear paints containing no or little of these pigments, etc. A top coat film can be formed by a coating method, a two-coating method (two-coating one baking, two-coating two baking) or the like.

The top coat can be applied by adjusting to an appropriate coating viscosity with an organic solvent and / or water, followed by electrostatic coating, airless spraying, air spraying, or the like.

Specifically, for example, a solid color coating is applied to the surface of a cured or uncured aqueous intermediate coating with a cured coating so as to have a thickness of about 10 to about 40 μm, and 10 to 10 at a temperature of about 100 to about 160 ° C. Solid color finish by 1 coat method performed by heating for 40 minutes; Solid color paint or metallic paint is applied to the coated surface of cured or uncured water-based intermediate coating to a thickness of about 10 to about 30 μm with a cured coating film After coating or in an uncured state, a clear coating is applied with a cured coating film to a thickness of about 20 to about 60 μm and heated at a temperature of about 100 to about 160 ° C. for 10 to 40 minutes for 2 coats and 1 bake. Examples thereof include a solid color or metallic finishing method by a method (2C1B) or a two-coat two-bake method (2C2B).

According to this method, for example, by interposing a coating film of the aqueous primer coating composition of the present invention between an undercoat film such as an electrodeposition coating film and an intermediate coating film such as an aqueous intermediate coating, finally, The chipping resistance of the resulting multilayer coating film can be significantly improved.

In addition, in the wet-on-wet coating specification between water-based paints of a water-based primer paint composition and a water-based colored paint such as a water-based intermediate paint, a multilayer coating film excellent in finished appearance is obtained by suppressing mixing of both coating films. Can be 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. In the following, “part” and “%” are both based on mass, and the film thickness of the coating film is based on the cured coating film.

Manufacture example 1 of urethane resin emulsion (A)
73.5 parts of polytetramethylene glycol having a number average molecular weight of 2000 was dehydrated under vacuum at 110 ° C., and after dehydration, cooled to 60 ° C. Subsequently, 3.2 parts of 2-dimethylolpropanoic acid, 152.2 parts of acetone, and 23.3 parts of dicyclohexylmethane-4,4′-diisocyanate were added successively, and the temperature was maintained in the range of 50 to 55 ° C., While stirring, the reaction was continued until the reaction rate reached 98% or more.

Thereafter, 10.0 parts 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, 180 parts of distilled water was slowly added thereto to obtain a milky white isocyanate-terminated prepolymer aqueous dispersion. Thereafter, 0.6 part of methylethanolamine was quickly added dropwise. 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 mass, a viscosity of 500 mPa · s / 25 ° C., a pH of 7.8, an acid value of 14 mgKOH / g, A urethane resin emulsion (A-1) having an average particle diameter of 150 nm and a number average molecular weight of 100,000 was obtained.

Production Examples 2-14
Each urethane resin emulsion (A-2) to (A-14) was obtained by synthesizing in the same manner as in Production Example 1 with the composition shown in Table 1. Table 1 shows the special values of the obtained urethane resin emulsions.

In Table 1, (Note 1) to (Note 8) are as follows.
(Note 1) PTMG-2000; polytetramethylene glycol, molecular weight 2000, manufactured by Mitsubishi Chemical Corporation.
(Note 2) P-1010; polyester diol (component: adipic acid / methylpentanediol), manufactured by Kuraray Co., Ltd.
(Note 3) T-6001: Polycarbonate diol, manufactured by Asahi Kasei Corporation.
(Note 4) DMPA; dimethylolpropionic acid (Note 5) DMBA; dimethylolbutanoic acid (Note 6) H12MDI; dicyclohexylmethane-4,4′-diisocyanate (Note 7) IPDI; isophorone diisocyanate (Note 8) HMDI; Methylene diisocyanate

The urethane resin emulsions (A-9) to (A-14) in Production Examples 9 to 14 are for comparative examples.

Further, the urethane resin emulsion (A-10) of Production Example 10 had poor water dispersibility, and the average particle size could not be measured.

Production of urethane resin emulsion (A) (polyester polyol)
Production Example 15
364 parts of polyester polyol 1 (weight average molecular weight 2000, trade name Polylite OD-X-2610, manufactured by DIC) and 364 parts of polyester polyol 2 (weight average molecular weight 2000, trade name Polylite OD-X-2420, manufactured by DIC) The reaction vessel was charged and dehydrated at 110 ° C. under vacuum, and after dehydration, cooled to 60 ° C. Next, 32 parts of 2-dimethylolpropionic acid, 660 parts of methyl ethyl ketone, and 240 parts of dicyclohexylmethane-4,4′-diisocyanate were sequentially added, and the reaction rate was maintained while maintaining the temperature in the range of 70 to 75 ° C. Was reacted until it became 98% or more to obtain an isocyanate-terminated prepolymer solution.

The solution was cooled to 40 ° C. and neutralized by adding 21 parts of methyldiethanolamine, and then 2116 parts of distilled water was slowly added with sufficient stirring to obtain a milky white isocyanate-terminated prepolymer aqueous dispersion. Thereafter, 108.1 parts of diethylenetriamine 5% aqueous solution (5.2 parts of solid content) was quickly added dropwise. Next, stirring was continued at room temperature for 1 hour, and then methyl ethyl ketone was removed at 40 to 50 ° C. under reduced pressure to obtain a urethane resin emulsion having a solid content of 30% by mass, a pH of 7.8, an acid value of 13 mgKOH / g, and an average particle size of 170 nm. (A-15) was obtained.

Production Examples 16-24
Each urethane resin emulsion (A-16) to (A-24) was obtained by synthesizing in the same manner as in Production Example 15 with the composition shown in Table 2. Table 2 shows the special values of the obtained urethane resin emulsions. In addition, diethylenetriamine compounding quantity is shown by solid content mass.

The weight average molecular weights of the urethane resin emulsions (A-15) to (A-23) of Production Examples 15 to 23 are 50000 or more.

Further, the urethane resin emulsion (A-24) of Production Example 24 had poor water dispersibility, and the average particle size could not be measured.

Production and production example 25 of polyester resin
In a four-necked flask equipped with a heating device, a stirrer, a thermometer, a reflux condenser and a water separator, 61.9 parts 1,3-cyclohexanedicarboxylic acid, 70.1 parts adipic acid, 62.8 trimethylolpropane 1 part, 24.2 parts of neopentyl glycol and 44.6 parts of 1,4-cyclohexanedimethanol were heated from 160 ° C. to 230 ° C. over 3 hours. Condensed water generated by maintaining the time was distilled off using a rectifying column.

Next, after adding 15.0 parts of trimellitic anhydride to the product, the solvent is removed, neutralized with N, N-dimethylethanolamine, dispersed in water, and a polyester resin having a solid content of 40%. 1 was obtained. The obtained polyester resin 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 and production example 26 of acrylic resin
A reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, nitrogen inlet tube and dropping device was charged with 30 parts of propylene glycol monopropyl ether, heated to 85 ° C., 10 parts of styrene, 30 parts of methyl methacrylate, 15 parts of 2-ethylhexyl acrylate, 11.5 parts of n-butyl acrylate, 30 parts of hydroxyethyl acrylate, 3.5 parts of acrylic acid, 10 parts of propylene glycol monopropyl ether and 2,2′-azobis (2,4-dimethylvalero Nitrile) 2 parts of the mixture was added dropwise over 4 hours, and aged for 1 hour after completion of the addition. Thereafter, a mixture of 5 parts of propylene glycol monopropyl ether and 1 part of 2,2′-azobis (2,4-dimethylvaleronitrile) was added dropwise to the flask over 1 hour, followed by aging for 1 hour after completion of the addition. Further, 3.03 parts of 2- (dimethylamino) ethanol was added and deionized water was gradually added to obtain a solution of acrylic resin 1 having a solid content concentration of 40%. The resulting acrylic resin 1 had an acid value of 27 mgKOH / g, a hydroxyl value of 145 mgKOH / g, and a number average molecular weight of 5000.

Production Example 1 of water-based primer coating composition
Polyester resin 150 obtained in Production Example 25 (solid part 20 parts), carbon MA-100 (carbon black, manufactured by Mitsubishi Chemical Corporation) 4 parts, JR-806 (titanium white, manufactured by Teica) 56 parts, and talc PK 10 parts of —S (fine talc, manufactured by Nippon Talc Co., Ltd.) were mixed and dispersed with a paint shaker for 30 minutes to obtain pigment dispersion paste 1.

In 120 parts of the obtained pigment dispersion paste 1, 228 parts of urethane resin emulsion (A-1) obtained in Production Example 1 (80 parts of solid content), W-262 (oligomer, water tolerance 20, the following structural formula (1) In

R ¹ and R ² are both 2-ethylhexyl groups, R ³ is a methylene group, m is 6-7 diester compound, number average molecular weight 550, manufactured by DIC, 7.5 parts, Surfynol 104A (antifoam) Agent, Air Products Japan Co., Ltd.) 2 parts, BYK-349 (Surface Conditioner, BYK CHEMIE INTERNATIONAL GMBH) 1 part, Ethanol 45 parts and ADD-68N (Rheology Control Agent, Enomoto Kasei Co., Ltd.) 1 part The mixture was further stirred, and deionized water and dimethylethanolamine were added to obtain pH 8.2, Ford Cup No. 4 to 35 seconds to adjust the viscosity to 35 seconds, the aqueous primer coating composition no. 1 was obtained.

Examples 2 to 29 and Comparative Examples 1 to 12
By adjusting in the same manner as in Example 1 with the compositions shown in Tables 3 and 4 below, each water-based primer coating composition No. 2 to 41 were obtained. In the table, the amount of each component in the paint blending is the solid mass.

In addition, the water-based primer coating composition no. In Example 13, in the production of the pigment dispersion paste 1 in Example 1, instead of the polyester resin 1 obtained in Production Example 25, the pigment dispersion paste 2 produced using the acrylic resin 1 obtained in Production Example 26 was used. did.

In Tables 3 and 4, (Note 9) to (Note 13) are as follows.
(Note 9) GP-600; polyoxypropylene glyceryl ether, number average molecular weight of about 600, water tolerance 80 <, manufactured by Sanyo Chemical Industries.
(Note 10) Oligomer X; ethylene glycol trimer, water tolerance 80 <, molecular weight 150.
(Note 11) GP-3000: polyoxypropylene glyceryl ether, number average molecular weight of about 3000, water tolerance 15, manufactured by Sanyo Chemical Industries.
(Note 12) Polyisoasocyanate compound 1; an oxime block of hexamethylene diisocyanate trimer.
(Note 13) PUR60; TAFIGEL PUR60 Urethane associative thickener manufactured by MUNZING CHEMIE GMBH.

Preparation of test plates Aqueous primer coating composition Nos. Obtained in Examples 1 to 29 and Comparative Examples 1 to 12 were used. Using 1 to 41, test plates were prepared as follows and subjected to evaluation tests.

In addition, water-based primer coating composition No. Regarding 15 and 39, the test plate could not be produced because the paint stability was poor.

(Preparation of test article)
Cationic electrodeposition paint (trade name “Electron GT-10” manufactured by Kansai Paint Co., Ltd.) is applied to a cold-rolled steel sheet with Palbond # 3020 (manufactured by Nippon Parkerizing Co., Ltd., zinc phosphate treatment) so that the cured film thickness is 20 μm. It was coated and heated at 170 ° C. for 30 minutes to be cured to obtain a test article.

Example 30
Aqueous primer coating composition No. 1 prepared in Example 1 on the test object. 1 was applied with gradient coating (0 to 6 μm, standard film thickness of 4 μm for film forming part) so that the dust part and thin film part were also formed (hand gun coating, booth temperature 23 ° C., relative Humidity 63%). After preheating at 80 ° C. for 3 minutes, the Ford Cup No. A water-based intermediate coating WP-306T (manufactured by Kansai Paint Co., Ltd., polyester / melamine resin-based aqueous intermediate coating) adjusted to a viscosity of 45 seconds at 4 was applied to a film thickness of 30 μm (booth temperature 24 ° C., relative humidity 70 %). Then, it was left for 3 minutes, pre-heated at 80 ° C. for 3 minutes, and then heated at 150 ° C. for 30 minutes to obtain an intermediate coating test plate.

In addition, the obtained intermediate coating test plate was further coated with a water-based metallic base coat WBC-713T (manufactured by Kansai Paint Co., Ltd., acrylic / melamine resin-based water-based colored base coat paint) to a film thickness of 15 μm. After standing for 3 minutes and preheating at 80 ° C. for 3 minutes, an organic solvent type clear paint KINO # 1200TW (manufactured by Kansai Paint Co., Ltd., acid / epoxy curable acrylic resin type clear paint) is adjusted to a thickness of 35 μm. It was painted and allowed to stand for 7 minutes, and then heated at 140 ° C. for 30 minutes to cure both coating films together to obtain a top coat test plate.

Examples 31-58 and Comparative Examples 13-24
In Example 30, the aqueous primer coating composition No. obtained in Example 1 was used. 1 is an aqueous primer coating composition No. shown in Tables 3 and 4 above. Each test plate was produced in the same manner as in Example 30 except that any one of 2-41 was changed.

Evaluation Test Each test plate obtained in Examples 30 to 58 and Comparative Examples 13 to 24 was evaluated by the following test method. The evaluation results are shown in Tables 5 and 6 below.

Finished appearance of performance test results : Chipping primer unpainted part (coating surface is smooth, glossy, and finished appearance is good) for film-forming part and dust part of water-based primer coating composition of intermediate coating test board and top coating test board The difference in the finished appearance visually was evaluated according to the following criteria:
A: There is no difference in the finished appearance from the unpainted portion of the chipping primer, and it is extremely good;
B: No difference in finished appearance from the unpainted portion of the chipping primer, good;
C: The difference in the finished appearance from the unpainted portion of the chipping primer is slight, and the difference in the finished appearance is hardly felt;
D: There is a slight difference in the finished appearance from the uncoated part of the chipping primer, and the smoothness and / or gloss of the coated part of the chipping primer is slightly inferior;
E: The difference in the finished appearance from the uncoated portion of the chipping primer is large, and the smoothness and / or gloss of the coated portion of the chipping primer is greatly inferior.

Chipping resistance: A test plate is placed on the specimen holder of the Toishiishi tester (trade name “JA-400” manufactured by Suga Tester Co., Ltd.) for the film-forming part of the aqueous primer coating composition of the top coat test plate. Then, at −20 ° C., 50 g of granite crushed stone having a particle size of 7 was made to collide with the test plate at an angle of 45 degrees with compressed air of 0.392 MPa (4 kgf / cm ² ) from a position 30 cm away from the test plate. Thereafter, the obtained test plate was washed with water and dried, and a cloth adhesive tape (manufactured by Nichiban Co., Ltd.) was attached to the coated surface. Then, the tape was peeled off, and the degree of occurrence of scratches on the coating film was visually observed and evaluated:
A: The size of the scratch is small, and the electrodeposition surface and the base steel plate are not exposed;
C: Although the size of the scratch is small, the electrodeposition surface and / or the base steel plate are exposed;
E: The size of the scratches is quite large, and the base steel plate is also greatly exposed.

Water resistance: With respect to the film-forming portion and dust portion of the aqueous primer coating composition of the top coat test plate, the coating surface state after each test plate was immersed in deionized water at 40 ° C. for 240 hours was evaluated:
(Painted state)
A: No abnormality and good;
E: Glossy or white blur is observed.

Comprehensive evaluation: In the field of coating automobile bodies and the like to which the present invention belongs, it is required that the finished appearance, chipping resistance and water resistance of the obtained coating film are all excellent. Therefore, a comprehensive evaluation was performed according to the following criteria:
A: Finished appearance, chipping resistance, and water resistance of the film formation part and dust part of the film formation part and dust part of the intermediate coating test plate, and the film formation part and dust part of the top coating test plate are all A;
B: all the above items are A or B, and at least one is B;
C: the above items are all A, B or C, and at least one is C;
D: The above items are all A, B, C or D, and at least one is D.
E: The above items are all A, B, C, D or E, and at least one is E.

Claims (8)

1. Urethane resin emulsion (A) having an acid value of 6 to 18 mg KOH / g and a weight average molecular weight of 50,000 or more, and water tolerance, produced using polyisoasocyanate component (a1) and polyol component (a2) as raw materials Is an oligomer (B) having a number average molecular weight of 200 to 1500
   A water-based primer coating composition comprising:
   The polyisocyanate component (a1) contains an alicyclic diisocyanate,
   The polyol component (a2) contains at least one (a2-1) selected from the group consisting of polyester polyol and polytetramethylene glycol, and an anionic group-containing diol (a2-2), and the (a2 -1) When the component is made of polytetramethylene glycol, the weight average molecular weight of the urethane resin emulsion (A) is 200,000 or less.
   Water-based primer coating composition.
2. The oligomer (B) is represented by the following general formula (1)
   

   

   [Wherein, R ¹ and R ² are the same or different and each represents a hydrocarbon group having 4 to 18 carbon atoms.
   R ³ is the same or different and represents an alkylene group having 2 to 4 carbon atoms.
   m represents an integer of 3 to 25. ]
   The water-based primer coating composition according to claim 1, which is a diester compound represented by the formula:
3. The water-based primer coating composition according to claim 1, further comprising a blocked polyisocyanate curing agent.
4. The water-based primer coating composition according to claim 1, further comprising a urethane associative thickener.
5. A primer coating film is formed by coating the water-based primer coating composition according to claim 1 on an object to be coated, and a colored coating film is formed by applying an aqueous coloring coating on the uncured primer coating formed. A method for forming a multilayer coating film, wherein the primer coating film and the colored coating film formed are cured simultaneously.
6. An electrodeposition paint is applied on the object to be coated, a primer coating film is formed by applying the aqueous primer coating composition according to claim 1, and an aqueous intermediate coating composition is formed on the uncured primer coating film. A method for forming a multi-layer coating film, comprising: forming an intermediate coating film by coating, and applying one or more top coatings after curing or without curing.
7. An article coated with the aqueous primer coating composition according to claim 1.
8. Articles coated by the multilayer coating film forming method according to claim 5 or 6.