JPH0841381A - Water-base undercoat composition - Google Patents

Abstract

PURPOSE:To obtain a chipping-resistant water-base undercoat compsn. which forms a coating film excellent in adhesion to a substrate and in vibration- damping and soundproofing properties without causing cracks due to shrinkage even when dried at normal temp. by compounding specific ingredients. CONSTITUTION:This compsn. substantially comprises a water-dispersible urethane resin, a water-dispersible acrylic resin having a microgel structure cross- linked within particles, and an inorg. filler. The amts. (solid base) of the acrylic resin and the filler compounded are pref. 10-100 pts.wt. and 50-300 pts.wt., respectively, based on 100 pts.wt. the urethane resin. A urethane resin which forms a film having a 100% modulus of 3-150kg/cm<2> is pref. And the acrylic resin pref. has a Tg of -30 to -40 deg.C and a cross-link density so adjusted that the lower the Tg, the higher the cross-link density, and vice versa.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water-based undercoat composition applied to the underside of automobiles and the like. More specifically, the present invention is a water-based undercoat composition for coating automobile steel sheets such as galvanized steel sheets and electrodeposition coated steel sheets,
The present invention relates to a chipping-resistant undercoat composition for automobiles, which has strong adhesion to an adherend without causing shrinkage cracks even when dried at room temperature regardless of the presence or absence of a baking step during film formation. The undercoat composition according to the present invention also has appropriate flexibility, protects the body from the impact of flying stones from the road surface during running, and prevents the occurrence of rust due to chipping. Further, the present invention relates to an undercoat composition for automobiles, which can impart vibration damping properties to a steel sheet that has been applied and can form a film that exhibits a soundproofing effect and is flexible and has good adhesion.

[0002]

2. Description of the Related Art In recent years, the automobile industry has been facing global environmental problems, resource conservation, and higher functionality. When recycling organic solvents or structures discharged in the painting process such as paints, etc. It is required to review the raw materials including the generated environmental pollutants. In particular, the problem of environmental pollution due to combustion of organic chlorine compounds has come to be highlighted.

Conventionally, a polyvinyl chloride plastisol composition has been frequently used as an undercoat material for the purpose of preventing rust and chipping of the bottom surface of automobiles and the like. This is due to the development of adhesion improvers of polyamide type and blocked isocyanate type to improve the adhesion between galvanized steel sheet, cationic electrodeposition steel sheet and polyvinyl chloride plastisol. It has improved dramatically. However, the polyvinyl chloride resin contained in the conventional undercoat material is a cause of environmental pollution because a large amount of chlorine gas is generated by incineration at the time of disposal of the vehicle. Further, it is also desired to improve the working environment of the line when these are installed, and to lower the temperature and shorten the baking process due to energy saving requirements. Therefore, dechlorination of undercoat materials is being promoted, and various alternative coating materials have been proposed to replace the polyvinyl chloride undercoat materials as described below.

Among them, an aqueous coating composition which emits a small amount of solvent is drawing attention, but such a composition has problems in adhesion to an adherend, water resistance, chipping resistance and blister resistance. However, under the present circumstances, it is extremely difficult to develop a chipping-resistant coating material having both of these. As a coating material that solves these problems, a water-soluble resin, a water-dispersible resin, and an acrylic-modified butadiene-based polymer having a glass transition temperature (Tg) of -10 ° C or less, which has good chipping resistance and high protection A rust coating composition can be mentioned (JP-A-4-142375).

Further, there can be mentioned an aqueous coating composition comprising fine particles of a core-shell structure having a different Tg from a water-soluble resin (having a double structure consisting of a core having a high Tg and a shell having a low Tg). (JP-A-59-136361).

Further, a water-dispersible alkyd resin blended with an acrylic copolymer emulsion (Japanese Patent Publication No. 62-
No. 31748), a method of enhancing the rust preventive property of a coating film by using a water-soluble or water-dispersible resin has been proposed.

[0007]

By the way, the performance required for the undercoat material for automobiles is chipping resistance, vibration damping, and soundproofing. In order to satisfy these requirements, the physical properties of the film are good and the damping is good. It is necessary to have a film hardness with excellent properties and to apply it to a thick film. However,
Since the coating material using the above water-dispersible resin has a large latent heat of vaporization of water, when it is applied to a conventional high temperature baking construction line such as vinyl chloride plastisol, problems such as swelling occur.

When a film is formed by drying at room temperature without passing through a baking process, shrinkage or cracking occurs due to the volume reduction due to the drying characteristic of the water-dispersible resin, and the residual internal stress causes the adhesiveness to the substrate. There was a defect such as lack of. In order to solve these drawbacks, the methods described below are generally adopted, but not all performances are satisfied, and improvements are still required. For example, in order to prevent swelling during baking, there are methods such as high solidification of the paint and the use of a heat-sensitive gelling agent, but this method makes the paint highly viscous, making spray painting difficult and When the paint is stored at a high temperature as described above, there are drawbacks such as impairing the storage stability.

In order to prevent shrinkage and cracking during setting or drying at room temperature, the Tg of the polymer is lowered or a plasticizer such as a film-forming agent or a film-forming auxiliary is added to obtain the minimum film-forming temperature (MFT). However, this method causes swelling during baking, softening of the coating to deteriorate chipping resistance, deterioration of vibration damping and soundproofing, and the like. The present invention was devised in order to solve the problems of the prior art, the object of the present invention, regardless of the presence or absence of a baking step during film formation, even when dried at room temperature without causing shrinkage cracks It is an object of the present invention to provide a chipping-resistant water-based undercoat composition having strong adhesion to a body and excellent in vibration damping and soundproofing.

[0010]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to achieve the above object, and as a result, completed the present invention. That is, the present invention is a water-dispersible urethane resin, a water-dispersible acrylic resin having an intraparticle crosslinked microgel structure,
And an aqueous undercoat composition which is substantially composed of an inorganic filler.

The water-based undercoat composition of the present invention contains 10 to 100 parts by weight (solid content) of the water-dispersible acrylic resin and 50 to 50 parts by weight of the inorganic filler with respect to 100 parts by weight (solid content) of the water-dispersible urethane resin. A blending amount of 300 parts by weight (solid content) is preferable, and the water-based undercoat composition having such a blending ratio has no coating defect such as shrinkage crack under the film forming conditions of baking or drying at room temperature, and has excellent chipping resistance. It has a sound-proof property, a vibration-damping property, and a sound-proof property.

The water-dispersible urethane resin used in the present invention preferably has a relatively soft resin film and has anti-repulsive elasticity, and it is blended with the water-dispersible acrylic resin used in the present invention to fuse them. Basically, it is necessary to soften the film hardness of the water-dispersible acrylic resin and give it anti-resilient elasticity.

The water-dispersible acrylic resin used in the present invention has a crosslinked structure. Water-dispersible acrylic resin Tg
The appropriate range varies depending on the modulus value of the water-dispersible urethane resin used, but those in the range of -30 ° C to + 40 ° C, preferably -5 ° C to + 30 ° C are excellent in preventing shrinkage cracks during normal temperature drying. . The crosslink density of the water-dispersible acrylic resin differs depending on the resin Tg. It is preferable that the lower the Tg, the higher the crosslink density, and the higher the Tg, the lower the crosslink density.

The method of microgelation by intraparticle crosslinking is as follows.
Radical-polymerizable unsaturated group-containing monomer and its 1
A monomer having two or more molecules in the molecule may be copolymerized, or a radical-polymerizable unsaturated monomer having a functional group capable of reacting with each other may be copolymerized, and a cross-linking reaction may occur after or during the polymerization process. You may let me.

In the room temperature dry type water-based undercoat material, when an attempt is made to form a cured film by interparticle cross-linking with a water-soluble resin or a water-dispersible resin capable of reacting with each other,
On the contrary, the residual internal stress increases during the drying process of the coating, which promotes shrinkage cracking, which is not preferable.

The water-dispersible urethane resin used in the present invention has a resin film strength of 3 Kg / c at a 100% modulus value.
It is preferably m ^{2 to} 150 Kg / cm ² , and commercially available products can be used as long as they are within the range. For example, Aizerax S-1020 (100% modulus, 6Kg
/ Cm ² ), S-1040 (100% modulus, 15
Kg / cm ² ), S-2020 (100% modulus,
^{20Kg / cm 2), S-} 5050L (100% ^{modulus, 16Kg / cm 2), S} -1085C (100%
Modulus, 15 kg / cm ² ) (trade name, Hodogaya Chemical Co., Ltd.), Hydran HW-111 (1
00% modulus, 32 Kg / cm ² ), HW-301
(100% modulus, 15 kg / cm ² ), Bondic 1612 NSC (100% modulus, 15 kg / cm ²
cm ² ) (these are trade names, manufactured by Dainippon Ink and Chemicals, Inc.). Even if the resin film strength exceeds 150 kg / cm ² , the resin film strength of the entire urethane resin can be set within the above range by mixing and using two or more kinds. In addition, as shown in the synthesis examples below, the ionic group such as a carboxyl group is introduced into the side chain or the terminal of the polyurethane resin polymer, and a part of the polyol having a hydrophilic group such as ethylene oxide is used. It is also possible to use a self-emulsifying urethane resin dispersed and synthesized in water. These water dispersible urethane resins may be used alone or in 2
You may mix | blend what mixed the kind or more.

The blending ratio of the water-dispersible urethane resin and the water-dispersible acrylic resin used in the present invention is 10 to 10 of acrylic resin based on 100 parts by weight of urethane resin in terms of resin solid content.
Particularly good coating physical properties can be obtained in the range of 0 parts by weight, preferably 30 to 100 parts by weight. If the water-dispersible acrylic resin exceeds 100, the adhesion of the coating film to the adherend becomes insufficient due to shrinkage, cracks, etc., and if it is less than 10, the adhesion and water resistance of the coating film are poor and chipping resistance. Inferior to.

The water-dispersible acrylic resin used in the present invention can be synthesized by a known method, and two or more kinds of resins can be mixed and used. In particular, the water-dispersible acrylic resin of the present invention has a monomer containing a radically polymerizable unsaturated group, a monomer having two or more polymerizable unsaturated groups in the molecule, or a functional group capable of reacting with each other. It is a copolymer with a polymerizable unsaturated monomer. As the unsaturated monomer capable of radically polymerizing on the water-dispersible acrylic resin, methyl (meth) acrylate, ethyl (meth) acrylate,
Acrylates and methacrylates such as propyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, isodecyl (meth) acrylate, and lauryl (meth) acrylate can be used. In addition, styrene, α-methylstyrene, (meth) acrylonitrile, vinyltoluene, vinyl acetate and the like are also mentioned as the copolymerization component. These are not limited to the ones listed here, but one or two of them may be used.
It is possible to mix and use one or more species.

Examples of the monomer having two or more polymerizable unsaturated groups in the molecule used in the present invention include divinylbenzene, ethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate and diethylene glycol di (meth). Examples thereof include acrylate, 1,6 hexanediol diacrylate, N, N'-methylenebisacrylamide, trimethylolpropane (meth) acrylate, trivinylbenzene, oligoester (meth) acrylate, diallyl phthalate and the like. These are not limited to those listed here, and one kind or two or more kinds of them can be blended and used.

As functional groups having mutual reactivity, a carboxyl group and a methylol group, an epoxy group, an aziridine group, an oxazoline group, an amide group and a methylol group, a methylol group and an epoxy group and self-condensation thereof, a hydroxyl group and a methylol group, There are carbonyl group, hydrazine group, silanol group and the like, and as the polymerizable unsaturated monomer having these functional groups, (meth) acrylic acid, crotonic acid, maleic acid, itaconic acid, (meth) acrylamide, N-
Methylol (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth)
Acrylate, glycidyl (meth) acrylate, 2-
Examples include (1-aziridyl) ethyl methacrylate, acrolein, 2-acetoacetoxypropyl methacrylate, vinyltrimethoxysilane and the like.

The water-dispersible acrylic resin in the present invention can be synthesized by emulsion polymerization and can be carried out by a method well known to those skilled in the art. The polymerization temperature varies depending on the monomers used and the polymerization initiator, but is usually in the range of 30 ° C to 90 ° C.

As the emulsifier that can be used in the emulsion polymerization of the water-dispersible acrylic resin, any of anionic, cationic and nonionic surfactants can be used, but it is necessary to select it depending on the ionicity of the polyurethane resin used in combination. . Further, in order to improve the water resistance of the coating film, a reactive emulsifier having an aryl group or a radically polymerizable unsaturated group can be used. Latemul S- as a reactive emulsifier
120A, S-180A (trade name, manufactured by Kao Corporation),
Aqualon HS-10, RN-20, New Frontier A-229E (trade name, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.),
Eleminor JS-2 (manufactured by Sanyo Chemical Industry Co., Ltd.) and the like can be mentioned.

As the polymerization initiator, general ones such as water-soluble ones such as potassium persulfate, ammonium persulfate, sodium persulfate, hydrogen peroxide, water-soluble azoamide compounds and the like can be mentioned. Isobutyl peroxide, t-butyl peroxide, as a type of polymerization initiator soluble in a radically polymerizable unsaturated monomer,
Examples thereof include octanoyl peroxide, decanoyl peroxide, lauroyl peroxide, benzoyl peroxide, azobisisobutyronitrile and azobiscyanovaleric acid. It is also possible to add a reducing agent to these and carry out the polymerization operation at a low temperature.

Regarding the operation of microgelation, the method of forming a crosslinked structure with monomers having reactivity with each other, and the reaction which requires a crosslinking catalyst, it is dissolved in the monomer or added to the aqueous phase after polymerization to crosslink. Let

Calcium carbonate is generally used as the inorganic filler used in the aqueous undercoat composition of the present invention, but kaolin, diatomaceous earth, talc and the like can also be used. For the purpose of weight reduction, various organic and inorganic balloons and fibrin-based fillers can be used.
If the blending amount of these fillers is too small, the adhesiveness is poor, and the water resistance is poor, and if the blending amount is too large, the physical properties are affected, and the occurrence of cracks during construction is affected. Will be a big factor.

Other optional additives are thickeners. To apply the prepared coating liquid to a constant film thickness without dripping, a viscosity of about 10,000 cps and thixotropy are required. In the organic system, hydroxyethyl cellulose,
Carboxymethyl cellulose, water-soluble polysaccharides, polyacrylic acid salts, associative thickeners, etc., and as an inorganic system, anhydrous silica (for example, Aerosil # 200, manufactured by Nippon Aerosil Co., Ltd.), bentonite, synthetic mica, metal soap, etc. Can be used. Further, as a method of improving the drying property of the undercoat material coated with such a high film thickness, for example, polyvinyl methyl ether, polypropylene glycol, a siloxane oxyalkylene copolymer, an alkylphenol alkylene oxide, an aliphatic alcohol alkylene oxide is additionally used. It is also effective to add a heat-sensitive gelling agent such as an adduct, a propylene oxide-ethylene oxide copolymer, an inorganic salt, etc. within a range that does not impair the storage stability. In addition, a surfactant, a polymer surfactant, a water-soluble polymer compound or the like can be used as the wetting and dispersing agent.

Further, a film-forming agent, a film-forming auxiliary agent or the like can also be used in order to auxiliary adjust the surface of the dry coating film and prevent cracks and small cracks. For this, it is common to use alcohol, alcohol ethers or the like. In addition, an antifreezing agent for emulsion, an antiseptic / antifungal bactericidal agent, an anticorrosive agent and the like may be added.

The water-based undercoat composition of the present invention is applied to an adherend so that the thickness of the dry coating film is 300 to 1000 μm. The undercoat material for automobiles has been conventionally coated by a spray method, and it is preferable to coat the water-based undercoat composition of the present invention with an airless spray coating machine. However, in this case, the thickness of the dry coating film of the water-based undercoat composition is partly 3000 μm.
May reach. The heating and drying conditions for the water-based undercoat composition of the present invention applied to an adherend are 10 to 3 at room temperature.
After setting for 0 minutes, it is preferable to preheat at least 90 ° C. for 10 minutes and heat-dry at 130 to 140 ° C. for 20 to 30 minutes.

[0029]

Since the water-based undercoat composition according to the present invention is composed of a water-dispersible urethane resin, a water-dispersible acrylic resin having a crosslinked microgel structure, and an inorganic filler, it is set during normal temperature drying and baking drying. In this case, a good film having no shrinkage cracks and a high swelling limit at the time of baking can be obtained, and good film forming properties can be obtained by both the ordinary temperature drying method and the baking drying method.

It is considered that this is because the internal cross-linking of the water-dispersible acrylic resin acts in the direction of alleviating the internal stress generated during the dry fusion process of the emulsion resin. Therefore, even at the time of drying at room temperature, it can be easily and firmly adhered to a metal surface or a metal coated surface, particularly to a thick film electrodeposition coated steel sheet surface which is difficult to adhere (adhesive strength cannot be obtained).

The water-based undercoat composition of the present invention is easy to handle like conventional vinyl chloride plastisols, has good storage stability, and does not show an extreme increase in viscosity even after long-term storage. Further, it is not colored not only by drying at room temperature but also by heat treatment at the time of processing or after coating, and the discoloration does not occur even when the topcoat paint is thinly applied.

As described above, even when it is applied to the current automobile manufacturing line or the like, it has a feature that it can be replaced without any improvement to the conventional coating and baking / drying equipment. When used as a post-installation (room temperature drying) type, it also leads to energy saving.

[0033]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited thereto. The test method in the test example will be described later. In addition, the content and% are weight unless otherwise specified.

[Synthesis of Water-Dispersible Acrylic Resin] Synthesis Example 1 380.0 parts of ion-exchanged water, Solvalite S-80 (trade name, anionic surfactant manufactured by Kyoeisha Chemical Co., Ltd.)
1.0 part, Latemur S-180A (trade name, reactive emulsifier manufactured by Kao Co., Ltd.) 7.0 parts were weighed in a 1-liter 4-necked flask equipped with a stirrer, a thermometer, a nitrogen introducing tube, and a condenser, It heated at 75 degreeC-80 degreeC under nitrogen stream. Next, 1/5 weight of the following monomer mixed solution and 2,
Polymerization started by dissolving 1.0 part of 2'-azobis [2 methyl-N- (2-hydroxyethyl) -propionamide] (trade name, VA-086 manufactured by Wako Pure Chemical Industries, Ltd.) in 50 parts of ion-exchanged water. Add 1/5 weight of the solution to 75
Initial polymerization was carried out at ℃ for 1 hour. Then, the remaining monomer mixture and the polymerization initiator aqueous solution were dropped into the flask over 4 hours. After the dropping was completed, the mixture was aged at the same temperature for 2 hours. Methyl methacrylate 170.0 parts N-butyl acrylate 220.0 parts 2-Hydroxypropyl methacrylate 20.0 parts 1,6 Hexanediol diacrylate 5.0 parts Methacrylic acid 10.0 parts ─────────── ──────────────────── Total 425.0 parts Solid content of the water-dispersible acrylic resin thus obtained is 5
1.2% and Tg were -1.3 degreeC.

Synthesis Example 2 400.0 parts of ion-exchanged water and 1.0 part of nonylphenol EO 6 mol adduct were weighed in a 1-liter 4-necked flask equipped with a stirrer, a thermometer, a nitrogen introducing tube, and a water diverter. It heated at 50 degreeC-55 degreeC under nitrogen stream. Next, 1/5 weight of a mixed solution prepared by dissolving 8.0 parts of Aqualon HS-10 and 0.5 part of triphenylphosphine in the following monomers, 30.0 parts of a 5% aqueous solution of potassium persulfate, and 5 parts of sodium metasulfite. % Aqueous solution (7.5 parts) was added to carry out initial polymerization at 50 ° C. for 1 hour. Then, at the same temperature, the remaining monomer mixed solution and polymerization initiator aqueous solution
It dripped over time. After completion of the dropping, the temperature was raised to 80 ° C., and the mixture was aged at the same temperature for 3 hours to carry out a crosslinking reaction. Methyl methacrylate 225.0 parts N-butyl acrylate 100.0 parts 2-Ethylhexyl acrylate 50.0 parts 2-Hydroxypropyl methacrylate 20.0 parts Methacrylic acid 20.0 parts Glycidyl methacrylate 10.0 parts ─────── ─────────────────────── Total 425.0 parts The water-dispersible acrylic resin thus obtained has a solid content of 5
0.2% and Tg were 16.8 degreeC.

Synthesis Examples 3 to 7 and Comparative Synthesis Examples 1 to 3 Synthesis Examples 3 and 4 follow the method of Synthesis Example 1, and Synthesis Examples 5 to 7 and Comparative Synthesis Examples 1 to 3 follow the method of Synthesis Example 2. Emulsion polymerization was performed at a monomer mixing ratio of 1 to obtain water-dispersible acrylic resins.

[0037]

[Table 1]

[Synthesis of Water-Dispersible Urethane Resin] Synthesis Example 8 294 parts of polycarbonate diol (molecular weight 1958) was placed in a four-necked flask equipped with a stirrer, a thermometer, a nitrogen inlet tube, and a condenser, and stirred. It dehydrated by heating at 120 ° C. under reduced pressure (−220 mmHg). Next, the temperature inside the flask was lowered to 70 ° C., 600 parts of methyl ethyl ketone, 52 parts of diphenylmethane diisocyanate, and 0.06 part of dibutyltin dilaurate were charged under a nitrogen stream and reacted at 70 ° C. to 75 ° C. for 3 hours and 30 minutes. Next, the internal temperature was lowered to 40 ° C., and then dimethylolpropionic acid 7.
8 parts was added and the mixture was reacted at 70 ° C to 75 ° C for 4 hours. Then, 7.7 parts of polyoxyethylene polyoxypropylene block polymer (oxyethylene chain content 8%, propylene glycol molecular weight 3200) was added and reacted at the same temperature for 3 hours to obtain a highly viscous transparent resin liquid. Further, 42 parts of Noniolite NS-50 (trade name, nonionic surfactant manufactured by Kyoeisha Chemical Co., Ltd.) was added to the reaction solution at 70 ° C.
The mixture was stirred at 75 ° C for 30 minutes to obtain a transparent viscous solution. While lowering the temperature of the reaction solution to 55 ° C and stirring it well,
340 parts of deionized water at 0 ° C. was gradually added to obtain a milky white dispersion liquid. Finally, this is decompressed (-220mmH
Methyl ethyl ketone was distilled off while stirring in g) at 55 ° C. for 4 hours. Thus, 598 g of a milky white water-dispersible urethane resin having a solid content of 50% was obtained. The 100% modulus value of the dried resin film of this product was 5.0 Kg / cm ² .

Synthetic Example 9 Using the same reactor as in Synthetic Example 8 above, a propylene oxide adduct of trimethylolpropane (average molecular weight 3000, OH number 56.
1) 300 parts were charged and 100-1 at 1-10 mmHg
After dehydration under reduced pressure at 20 ° C., the temperature was lowered to 40 ° C., 52.2 parts of tolylene diisocyanate was added, and the mixture was reacted at 80 ° C. for 3 hours under a nitrogen stream to obtain a urethane prepolymer. 9 parts of dimethylolpropionic acid was reacted with this polymer at 85 to 95 ° C. for 5 hours under a nitrogen stream to obtain a urethane prepolymer having a carboxyl group. This prepolymer was maintained at 80 ° C. and emulsified into 360 parts of ion-exchanged water containing 18 parts of Noniolite NS-50 (trade name, same as above) while mixing with a homomixer to give a milky white powder having a solid content of about 50%. A water-dispersible urethane resin was obtained. The 100% modulus value of the dried resin film of this product was 4.0 Kg / cm ² .

Table 2 shows the characteristic values of the water-dispersible urethane resin obtained in the above synthesis example and the commercially available water-dispersible urethane resin used in this test.

[0041]

[Table 2]

[Manufacture of Water-based Undercoat Composition] Examples 1 to 10 and Comparative Examples 1 to 5 Water-dispersible resins, inorganic fillers and other additive components were placed in a kneader stirrer according to the formulations shown in Table-3. The mixture was kneaded at room temperature for 30 minutes and then defoamed under reduced pressure to prepare an aqueous undercoat composition. Further, the prepared water-based undercoat composition was coated with a doctor blade on a cationic electrodeposition steel sheet having a thickness of 0.8 mm to a dry film thickness of about 500 μm, and dried at room temperature and heat (after setting at room temperature for 10 minutes , 90 ° C for 10 minutes with a blow dryer → 130 ° C
X 20 minutes) to prepare a test plate.

[0043]

[Table 3]

The coating film performance evaluation methods for the compositions of Examples and Comparative Examples are shown below. The evaluation results of the examples are shown in Table-3.
It was shown to. Dry film thickness in the coating film performance evaluation method] Drying cationic electrodeposition steel plate tilted paint coating compositions such that 500～4000Myuemu, dried by heating under the above conditions, to confirm the blister limit thickness. Those with a film thickness of 3000 μm and no swelling are indicated by ◯, and those with swelling are indicated by X. Shrinkage and cracks The coating composition is gradient coated under the above film thickness conditions, and the presence or absence of shrinkage and cracks in the undercoat film formed by room temperature drying and heat drying under the above conditions is confirmed. Those with no shrinkage or cracks are indicated by a circle, and those with a crack are indicated by a cross. Adhesiveness The coating film dried under the above conditions is peeled off with a nail to check whether it is cohesive failure or interface failure. Cohesive failure is indicated by cf and interface failure is indicated by af. Anti-chipping property Test plate (film thickness 500 μm) prepared under the above conditions is 1.0
Cross-cut at mm intervals, and evaluate the integrated weight of the nut until the coating layer is broken and the base is exposed by the nut dropping method (M-4 nut weight measurement).

Claims (3)

[Claims] 1. A water-based undercoat composition comprising a water-dispersible urethane resin, a water-dispersible acrylic resin having a cross-linked intra-particle microgel structure, and an inorganic filler. 2. Water-dispersible acrylic resin is 10 to 1 to 100 parts by weight (solid content).
00 parts by weight (solid content), 50-300 inorganic filler
The water-based undercoat composition according to claim 1, which is a weight part (solid content). 3. A water-dispersible urethane resin, water-based undercoat composition according to claim 1 or 2 characterized in that it has a film strength in the range of 3Kg / cm ² ~150Kg / cm ² at 100% modulus value Stuff.