JP2002126626A - Method for forming multilayered coating film, multilayered coating film and water-based intermediate coating material composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming a multilayered coating film by which a multilayered coating film having shock resistance, particularly chipping resistance comparable to a conventional three-coating film can be formed in a three-wet one-bake coating method to reduce the coating process, cost and load on the environment. SOLUTION: The method for forming a multilayered coating film includes a process (1) to apply a water-based intermediate coating material to form an unhardened intermediate coating film on the objective body to be coated where an electrodeposition coating film is preliminarily formed, a process (2) to apply a water-based base coating material on the intermediate coating film to form an unhardened base coating film, a process (3) to apply a clear coating material thereon to form an unhardened clear coating film, and a process (4) to heat and harden the intermediate coating film, base coating film and clear coating film at a time to obtain a multilayered coating film. The water-based intermediate coating material contains elastomers.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of applying an aqueous intermediate coating, an aqueous base coating, and a clear coating on a workpiece on which an electrodeposition coating film has been formed by wet-on-wet, and performing heat curing at a time. The present invention relates to a method for forming a multilayer coating film using a three-wet coating system, and more particularly, to a method for forming a multilayer coating film capable of obtaining a multilayer coating film having excellent chipping resistance, and a method for forming a multilayer coating film. Multilayer coatings,
In addition, the present invention relates to an aqueous intermediate coating composition that can be suitably used in the method for forming a multilayer coating film.

[0002]

2. Description of the Related Art In recent years, in the field of paints, especially in the field of automotive coatings, resource saving, cost saving and environmental burden (VOC and HOC) have been observed.
(APs etc.) In order to solve the problem of reduction, there is a strong demand for shortening the coating process. That is, in the conventional automobile coating finishing procedure, the electrodeposition coating, the intermediate coating, and the topcoat have been performed by a three-coat three-bake coating method in which the coating is baked after each coating. After baking the electrodeposition coating film, the three coating processes of intermediate coating, base coating and clear coating are performed on the wet coating on a wet basis, and a three-wet coating system for baking these wet coating films collectively is performed. It is required to reduce the number of baking steps and to maintain coating performance equivalent to that of a three-coat film obtained by a conventional three-coat three-bake coating method.

Among the above-mentioned coating film performances, with respect to the impact resistance, particularly the so-called chipping resistance due to the collision of obstacles such as pebbles against a running automobile body, the conventional three-coat, three-bake coating method requires chipping resistance. Although the chipping resistance could be ensured by providing a special intermediate coating film having a property, the conventional intermediate coating material used in the above-described three-wet coating system was adapted to the obtained coating film, It cannot be used because inferior appearance such as inversion occurs and the appearance is inferior, and the coating film obtained by the three-wet coating system has a drawback that the impact resistance and the chipping resistance are low.

Japanese Patent Application Laid-Open No. 62-65765 discloses that a resin layer (so-called chipping-resistant primer layer) having an ability to absorb impact on a coating film is formed during the formation of a multilayer film, especially between an electrodeposition coating film and an intermediate coating film. Is disclosed. However, further incorporation of such a step into the painting process of an automobile body does not meet the market needs for the above-mentioned step saving and cost saving.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a three-wet, one-bake coating method aiming at shortening the coating process, reducing costs and reducing environmental impact, and has excellent impact resistance comparable to conventional three-coat films, especially An object of the present invention is to provide a method for forming a multilayer coating film capable of forming a multilayer coating film having chipping resistance.

[0006]

According to the present invention, there is provided a step (1) of forming an uncured intermediate coating film by applying an aqueous intermediate coating material on an object on which an electrodeposition coating film is formed. A step (2) of applying an aqueous base paint to form an uncured base coat on the intermediate coat, and further applying a clear paint thereon to form an uncured clear coat. Step (3),
And a method of forming a multilayer coating film including a step (4) of simultaneously heating and curing the intermediate coating film, the base coating film, and the clear coating film to obtain a multilayer coating film, wherein the aqueous intermediate coating material is And a method for forming a multilayer coating film comprising an elastomer.

[0007] The present invention is also a multilayer coating film formed by the above-mentioned method for forming a multilayer coating film. The present invention is also an aqueous intermediate coating composition, characterized in that it contains an elastomer. Hereinafter, the present invention will be described in more detail.

In the method for forming a multilayer coating film of the present invention, a step (1) of applying an aqueous intermediate coating material on an object to be coated with an electrodeposition coating film to form an uncured intermediate coating film; A step (2) of applying an aqueous base paint to form an uncured base coat on the intermediate coat, and further applying a clear paint thereon to form an uncured clear coat. Step (3) and Step (4) of simultaneously heating and curing the intermediate coating film, the base coating film and the clear coating film to obtain a multilayer coating film.

[0009]Process (1)  In the method for forming a multilayer coating film of the present invention, the step (1)
Is an aqueous intermediate coating on the object on which the electrodeposition coating is formed.
Paint to form an uncured intermediate coating film.
You.

[0010]Waterborne intermediate coating  The water-based intermediate coating composition contains an elastomer.
You. By obtaining the above elastomer,
Gives flexibility to the paint film, and has impact resistance and chipping resistance
Performance can be improved.

The elastomer preferably has a designed glass transition temperature of -110 to 10 ° C. 10 ℃
If it exceeds, the resulting coating film is inferior in flexibility and impact resistance, and if it is lower than -110 ° C, it is actually difficult to prepare it. More preferably, it is -100 to -10C.
The above-mentioned design glass transition temperature can be obtained by calculation from the blending amount of the raw materials at the time of producing the above-mentioned elastomer.

The above elastomer is not particularly limited. For example, a homopolymer of a conjugated diene monomer such as butadiene, isoprene and chloroprene, or a conjugated diene monomer and ethylene, propylene, ethylidene, norbornene, dicyclone Pentadiene, 1,4-hexadiene, vinyl acetate, vinyl chloride, styrene, acrylonitrile, isobutylene, (meth) acrylic acid (ester)
Random or block copolymers with monomers such as
Polyurethane thermoplastic elastomer synthesized by polyaddition reaction of diisocyanate and diol; synthesized by transesterification reaction and polycondensation reaction using dimethyl terephthalate, 1,4-butanediol, poly (tetramethylene) glycol as raw materials Polyester-based thermoplastic elastomer; a polyamide-based thermoplastic elastomer synthesized from a lactam, a dicarboxylic acid, or a polyether diol as a raw material by a transesterification and polycondensation reaction, and the like.

The above elastomer may contain a reactive group such as a hydroxyl group, an amino group, a vinyl group, a carboxyl group, a urethane group, a urea group, or a polar group in the middle and / or at the end of the molecular structure. The reactive group and the polar group, when preparing the elastomer, copolymerize a monomer component containing a monomer having a reactive group and a polar group, or to the elastomer obtained by copolymerization On the other hand, it can be introduced by a known method.

When the elastomer is an oligomer (liquid rubber) having a number-average molecular weight of less than 10,000, it has high tackiness and low impact resistance as it is. It is necessary to cause a curing reaction to occur during the formation of a coating film. In this case, the hydroxyl number is 2
It is preferable to contain a hydroxyl group so as to be in the range of 0 to 200. If the hydroxyl value is less than 20, poor curing of the coating film is caused, and rubber properties such as sufficient elongation are not exhibited. 2
If it exceeds 00, as a result of excess hydroxyl groups remaining in the coating film after curing, the water resistance may decrease. Furthermore, as a result of an increase in the hardness of the cured coating film, a sufficient elongation cannot be achieved.

When the above elastomer has a high molecular weight having a number average molecular weight of 10,000 or more, it is necessary to carry out a curing reaction particularly in the formation of a coating film if the elastomer has low tackiness without curing and shows sufficient impact resistance. There is no. In the case above,
It is not necessary to provide a reactive group and a polar group in the resin structure in advance.

The above-mentioned elastomer can be stably present in the above-mentioned aqueous intermediate coating by using a water-dispersed one or a water-soluble one.

As a method of dispersing in water, for example, a dispersing agent such as a dispersing resin or a surfactant may be separately applied and emulsified and dispersed in an aqueous medium. Or, after introducing a functional group such as a reactive group and a polar group into the elastomer,
It can be carried out as it is or in a form capable of self-emulsifying and dispersing in an aqueous medium with a neutralizing agent.

When the functional group is a cationic group such as an amine, the neutralizing agent may be an inorganic acid such as hydrochloric acid, nitric acid or phosphoric acid; formic acid, acetic acid, lactic acid, sulfamic acid, acetylglycinic acid or the like. Organic acids. On the other hand, when the functional group is an anionic group such as a carboxyl group, an inorganic base such as ammonia; methylamine;
Organics such as primary, secondary or tertiary amines such as dimethylamine, triethylamine, monoethanolamine, diethanolamine, N-methylethanolamine, triethylamine, N, N-dimethylethanolamine, morpholine and piperazine Bases can be mentioned. As the dispersing resin and the surfactant, those conventionally used as dispersing agents can be used.

The above-mentioned aqueous intermediate coating composition may contain, in addition to the above-mentioned elastomer, other film-forming resins in order to adjust the physical properties of the resulting coating film. The other film-forming resin is not particularly limited, for example, acrylic resin, polyester resin, alkyd resin,
Epoxy resins, urethane resins and the like can be mentioned. Acrylic resins and / or polyester resins are preferred from the viewpoint of pigment dispersibility and workability.

The above other film-forming resins preferably have an acid value of solid content of 20 to 100 mgKOH / g. If it is less than 20 mgKOH / g, poor curing of the coating film may be caused. If it exceeds 100 mgKOH / g,
The resulting coating film has poor water resistance. Preferably, 30 to 80
mg KOH / g.

The other film-forming resins preferably have a hydroxyl value in the range of 30 to 150. If it is less than 30, poor curing of the coating film is caused, and if it exceeds 150,
As a result of excessive hydroxyl groups remaining in the coating film after curing, the water resistance may decrease.

Further, the number average molecular weight is from 1,000 to 3,000.
A range of 0 is preferred. If it is less than 1,000, physical properties such as solvent resistance of the cured coating film are inferior. If it exceeds 30,000, the viscosity of the resin solution is high, so that not only is it difficult to handle the obtained resin in operation such as emulsification and dispersion, but also the film appearance of the obtained intermediate coating film may be significantly reduced. . Preferably, it is 2000 to 20000.

The above-mentioned elastomer and other film-forming resins may be used alone, but two or more kinds may be used in order to balance the performance of the film. .

The above-mentioned aqueous intermediate coating composition usually contains a curing agent when it is necessary to cure the above-mentioned elastomer at the time of forming a coating film or when using the above-mentioned other film-forming resins. The curing agent is not particularly limited, and examples thereof include an amino resin and / or a blocked isocyanate resin. Melamine resins are preferred from the viewpoint of pigment dispersibility and workability.

The content of the elastomer with respect to the resin solid content in the aqueous intermediate coating composition is 20 to 1 based on the solid content.
It is preferably 00% by weight. If the amount is less than 20% by weight, the flexibility and chipping resistance of the obtained coating film are reduced. More preferably, it is 30 to 100% by weight. The resin solid content is the total solid content of the elastomer, the other film-forming resin and the curing agent that are added as desired.

The above-mentioned waterborne intermediate coating usually contains a pigment. The water-based intermediate coating is preferably a color pigment from the viewpoint of improving weather resistance and securing concealment. In particular, titanium dioxide is more preferable since it is excellent in white color hiding properties and is inexpensive.
Examples of the pigment include, in addition to titanium dioxide, inorganic pigments such as iron oxide and carbon black according to the purpose of coating preparation; phthalocyanine blue, phthalocyanine green, carbazole violet, anthrapyrimidine yellow, flavanthrone yellow, isoindoline yellow, An appropriate amount of an organic pigment such as indanthrone blue, quinacridone violet and the like; and if necessary, an extender pigment such as clay, talc, kaolin, barium sulfate and the like can be blended.

As the above-mentioned pigment, a standard gray aqueous intermediate paint having carbon black and titanium dioxide as main pigments may be used, or a set gray or various color pigments having the same lightness or hue as the top coat paint may be used. A so-called color waterborne intermediate coating in combination can also be used.

The pigment preferably has a weight ratio (PWC) of 10 to 60% by weight of the total weight of the pigment and the resin solids in the aqueous intermediate coating composition. If it is less than 10% by weight, the concealing property may be reduced due to insufficient pigment. If the amount exceeds 60% by weight, the viscosity at the time of curing is increased due to an excessive amount of the pigment, whereby the flowability is reduced and the appearance of the coating film may be reduced. The above-mentioned pigment can be previously dispersed in a commonly used pigment dispersion resin, a pigment dispersion paste is prepared, and then an appropriate amount can be blended in preparing an aqueous intermediate coating composition.

The above-mentioned aqueous intermediate coating composition can be prepared by mixing the above-mentioned pigment-dispersed paste, the above-mentioned elastomer and a curing agent. Further, ultraviolet absorbers; antioxidants;
Additive components such as an antifoaming agent; a surface conditioner; and an anti-bake agent can be added.

[0030]Intermediate coating film formation method  The above-mentioned aqueous intermediate paint is a coating material on which the above-mentioned electrodeposition coating film is formed.
A coating is applied on the garment to form an uncured intermediate coat.
As the electrodeposition paint for forming the electrodeposition coating film, cationic
And anionic types can be used. Corrosion protection
From the point that a coating film excellent in
Are preferred.

The material for the electrodeposition coating is not particularly limited, and examples thereof include iron, copper, aluminum, tin, zinc and the like; alloys and castings containing these metals. Specific examples include automobile bodies and parts such as passenger cars, trucks, motorcycles, and buses. It is particularly preferable that these metals are subjected to a chemical conversion treatment with a phosphate, a chromate or the like before the electrodeposition coating is performed.

The method of applying the aqueous intermediate coating composition is not particularly limited, and includes, for example, an air electrostatic spray so-called “react gun”;
It can be carried out by using a rotary atomizing type electrostatic coating machine called “μ) bell”, “micro (μ) bell”, “metabell” or the like. Preferably, a method using a rotary atomization type electrostatic coating machine or the like is used.

The dry film thickness of the intermediate coating film varies depending on the application, but is preferably 5 to 50 μm. If the amount exceeds the upper limit, the sharpness may be reduced, or sagging may occur during coating or baking may occur. If the amount is below the lower limit, the appearance may be reduced.

In the present invention, to form an uncured coating film for the aqueous intermediate coating, the aqueous base coating, and the clear coating means that the intermediate coating, the base coating, and the clear coating are applied in a wet-on-wet order in this order. It means to do. In the present specification, uncured means
For example, the concept includes a state after performing preheating. As the above preheat, after coating, for example,
This is a step of leaving or heating at room temperature to less than 100 ° C. for 1 to 10 minutes. For the purpose of obtaining a good finished appearance, it is preferable to perform preheating after applying the aqueous intermediate coating and after applying the aqueous base coating.

[0035]Step (2)  The above step (2) is performed in the uncured state formed as described above.
A water-based base paint is applied on the intermediate coating film and is not cured
To form a base coating film.

[0036]Water-based paint  In the present invention, the aqueous base paint is not particularly limited.
For example, film-forming resins, curing agents, pigments and others
Can be mentioned. The above coating
The formable resin is not particularly limited, for example, acrylic
Resin, polyester resin, alkyd resin, epoxy tree
Fats, urethane resins, etc., which are amino resins and
And / or hardener such as blocked isocyanate resin
Used together. In terms of pigment dispersibility and workability,
Krill resin and / or polyester resin and melamine resin
Is preferred.

The above-mentioned aqueous base paint can be used as a metallic base paint by adding a glittering pigment, or by blending a coloring pigment such as red, blue or black and / or an extender pigment without blending a glittering pigment. It can also be used as a solid base paint. The brilliant pigment is not particularly limited. For example, an uncolored or colored metallic brilliant such as a metal or an alloy and a mixture thereof, interference mica powder, colored mica powder, white mica powder, graphite or a colorless colored flat pigment And the like. A non-colored or colored metallic brilliant material such as a metal or an alloy, and a mixture thereof are preferable since a coating film having excellent dispersibility and high transparency can be formed. Specific examples of the metal include aluminum, aluminum oxide, copper, zinc, iron, nickel, and tin.

The shape of the glitter pigment is not particularly limited.
Further, it may be colored, but for example, has an average particle size (D ₅₀ ) of 2 to ₅₀ μm and a thickness of 0.1 to 5 μm
Is preferable. Average particle size 10-35μ
Those having a range of m are excellent in glitter and are more preferable. The pigment concentration (PWC) of the glitter pigment in the base paint is generally 23% by weight or less. When the content exceeds 23% by weight, the appearance of the coating film is deteriorated. Preferably, it is 0.01 to 20% by weight, more preferably 0.01 to 18% by weight.

As the pigments other than the above-mentioned brilliant pigments, the coloring pigments and extenders described in the above-mentioned aqueous intermediate coating composition can be used. As the pigment, a brilliant pigment,
One or a combination of two or more of the coloring pigment and the extender pigment can be used. The pigment concentration (PWC) in the base paint including the glitter pigment and all other pigments is generally 0.1 to 50% by weight,
Preferably it is 0.5 to 40% by weight, more preferably 1 to 30% by weight. If it exceeds 50% by weight, the appearance of the coating film will be reduced. Examples of the base paint include other additives to be used, and examples of the method of preparing the base paint include those exemplified for the aqueous intermediate paint.

[0040]Base coating film formation method  The base paint is the uncured material formed as described above.
Apply to form an uncured base coating on top of the coating
You. As the above coating method, apply an aqueous intermediate coating
The method exemplified at that time can be mentioned. Base coating
When applying paint to automobile bodies, etc.,
Multistage coating with air electrostatic spray
Coating, preferably in two stages, or air
Combine the electrostatic spray with the above-mentioned rotary atomizing type electrostatic coating machine.
It is preferable to carry out by a combined coating method.

The dry film thickness of the base coating film varies depending on the application, but is preferably from 5 to 35 μm. Exceeding the upper limit may result in poor clarity and / or inconveniences such as unevenness and flow during coating. Below the lower limit, color unevenness may occur.

[0042]Step (3)  In the step (3), the uncured base formed as described above is used.
Apply a clear paint on the uncoated
To form a coating film.Clear paint  The clear coating film contains a glitter pigment as a base paint.
Due to glitter pigments when using tallic base paint
Smoothes the unevenness and flicker of the base coating film.
It is also formed to protect the base coating.
You. There is no particular limitation on the clear paint, for example,
For example, from film-forming resins, curing agents and other additives.
Can be mentioned.

The above-mentioned film-forming resin is not particularly restricted but includes, for example, acrylic resins, polyester resins, epoxy resins, urethane resins, etc., which are combined with a curing agent such as an amino resin and / or a blocked isocyanate resin. Used. From the viewpoint of transparency or acid etching resistance, etc., a combination of an acrylic resin and / or a polyester resin and an amino resin, or a carboxylic acid.
It is preferable to use an acrylic resin and / or a polyester resin having an epoxy curing system.

As the above clear paint, a viscosity control agent is contained as an additive in order to apply the base paint described above in an uncured state after application, and to prevent break-in, inversion or sagging between layers. Is preferred. The amount of the viscosity control agent to be added is 0.01 to 10 parts by weight, preferably 0.1 to 100 parts by weight, based on 100 parts by weight of the resin solid content of the clear paint.
The amount is from 02 to 8 parts by weight, more preferably from 0.03 to 6 parts by weight. If the amount is more than 10 parts by weight, the appearance deteriorates. If the amount is less than 0.1 part by weight, the effect of controlling the viscosity cannot be obtained, which causes problems such as sagging.

The form of the clear paint may be any of an organic solvent type, an aqueous type (water-soluble, water-dispersible, emulsion), a non-aqueous-dispersion type, and a powder type. An adjusting agent or the like can be used.

[0046]Clear coating film forming method  The preparation method and coating method of the above clear paint are as follows.
It can be done according to the following method. Above clear coating
The dry film thickness varies depending on the application, but is 10 to 70 μm
It is. When the dry film thickness exceeds the upper limit, the sharpness deteriorates.
Troubles such as unevenness and flow during painting
Yes, if it is below the lower limit, the appearance may be reduced.

[0047]Step (4)  In the step (4), the intermediate coating film, the base
Heat-curing simultaneously the clear coating film and the clear coating film,
Obtain a multilayer coating. The temperature for heat curing is 1
Perform at 10 to 180 ° C, preferably 120 to 160 ° C
By doing so, it is possible to obtain a cured coating film with a high degree of crosslinking.
You. When the temperature exceeds 180 ° C., the coating film becomes hard and brittle,
If the temperature is lower than ℃, curing is not sufficient. Curing time depends on curing temperature
It changes more, but it takes 10-60 minutes at 120-160 ° C
Appropriate.

The thickness of the multilayer coating film obtained by the coating film forming method of the present invention is usually 30 to 300 μm, preferably 5 to 300 μm.
0 to 250 μm. If it exceeds 300 μm, the physical properties of the film such as a thermal cycle decrease, and if it is less than 30 μm, the strength of the film itself decreases.

The multilayer coating film obtained by the method for forming a multilayer coating film of the present invention can impart flexibility to the intermediate coating film because the intermediate coating material contains an elastomer.
Impact resistance and chipping resistance can be improved.
Furthermore, the three-wet one-bake coating method of the present invention makes it possible to reduce
Since the baking process of the intermediate coating can be omitted, a new coating system aiming at shortening the process, reducing the cost, reducing the energy consumption and reducing the environmental load can be constructed.

[0050]

EXAMPLES The present invention will be described in detail with reference to specific examples, but the present invention is not limited to the following examples. Parts and% mean parts by weight and% by weight, respectively.

Production Example 1 Production of Water-Soluble Polyester Resin 200.0 parts of isophthalic acid and 1 phthalic anhydride were placed in a reaction vessel.
79.0 parts, adipic acid 176.0 parts, trimethylolpropane 150.0 parts, neopentyl glycol 29
After 5.0 parts and 2 parts of dibutyltin oxide were charged and heated in a nitrogen stream to melt the raw materials, the temperature was gradually increased to 170 ° C. while mixing and stirring. Thereafter, dehydration transesterification was performed while the temperature was raised to 220 ° C. over a further 3 hours. When the acid value reached 10, the mixture was cooled to 150 ° C. Further, 114.0 parts of hexahydrophthalic acid was added and reacted for 1 hour to complete the reaction. Further, after cooling to 100 ° C., 112.0 parts of butyl cellosolve was added to obtain a polyester resin. The obtained polyester resin is
The solid content had an acid value of 50, a hydroxyl value of 65, and a number average molecular weight of 10,000 obtained by GPC (gel permeation chromatography). The obtained resin was cooled to 60 ° C., and 80.0 parts of dimethylethanolamine and ion-exchanged water were added to obtain a resin having a nonvolatile content of 50%.

Production Example 2 Production of Colored Pigment Paste 1 50.0 parts of the polyester resin obtained in Production Example 1, 17.9 parts of ion-exchanged water, 34.5 parts of rutile titanium dioxide
Parts, 34.4 parts of barium sulfate, 6 parts of talc, and 0.1 part of carbon black, preliminarily mixed, added a glass bead medium in a paint conditioner, mixed and dispersed at room temperature for 1 hour, and colored with a particle size of 5 μm or less. Pigment paste 1 was obtained.

Production Example 3 Production of Colored Pigment Paste 2 9.4 parts of a commercially available pigment dispersant “Disperbyk 190” (manufactured by BYK Chemie), 36.8 parts of ion-exchanged water,
34.5 parts of rutile titanium dioxide, barium sulfate.
A colored pigment paste 2 having a particle size of 5 μm or less was obtained in the same manner as in Production Example 2 except that 4 parts, 6 parts of talc, and 0.1 part of carbon black were used.

Production Example 4 Preparation of aqueous base paint Dipropylene glycol methyl ether 2 was placed in a reaction vessel.
3.9 parts and propylene glycol methyl ether 1
6.1 parts were added and mixed and stirred in a nitrogen stream for 120 minutes.
The temperature was raised to ° C. Then, 54.5 parts of ethyl acrylate,
A mixed solution of 12.5 parts of methyl methacrylate, 14.7 parts of 2-hydroxyethyl acrylate, 10.0 parts of styrene, 8.5 parts of methacrylic acid and 10.0 parts of dipropylene glycol methyl ether, t-butyl peroxy -2-ethylhexanoate, 2.0 parts of an initiator solution
It was dropped into the reaction vessel in parallel over time. After completion of the dropping, aging was performed at the same temperature for 0.5 hour. Further, an initiator solution consisting of 5.0 parts of dipropylene glycol methyl ether and 0.3 parts of t-butylperoxy-2-ethylhexanoate was dropped into the reaction vessel over 0.5 hour. After completion of dropping, aging was performed at the same temperature for 1 hour. Then, the solvent is removed under reduced pressure (70 Torr) 110
After distilling off 16.1 parts of the solvent at ℃, dimethylethanolamine and ion-exchanged water were added to obtain a water-soluble acrylic resin having a nonvolatile content of 31%, an acid value of 56 mgKOH / g and a hydroxyl value of 70.

100.0 parts of the above water-soluble acrylic resin,
After premixing 28.9 parts of ion-exchanged water, 0.3 parts of dimethylaminoethanol, and 5.1 parts of Degussa Carbon FW-285 (manufactured by Degussa AG), a glass bead medium was added in a paint conditioner, and room temperature was added. For 1 hour to obtain a color pigment paste having a particle size of 5 μm or less.
134.3 parts of the coloring paste, 118.8 parts of a water-soluble acrylic resin, 29.1 parts of a melamine resin (Cymel 204, manufactured by Mitsui Cytec), and 161.
The aqueous base paint was prepared by blending to be 3 parts.

Example 1 (1) Preparation of aqueous intermediate paint As shown in Table 1, elastomer, colored pigment paste 1, water-soluble polyester resin and melamine resin of Production Example 1 (Cymel 235, manufactured by Mitsui Cytec Co., Ltd.) To prepare an aqueous intermediate coating composition. In Table 1, as the elastomer, Luck Star 3622A (manufactured by Dainippon Ink Co., Ltd .; nonvolatile content: 52.5% by weight; design glass transition temperature −3)
0 ° C.).

(2) Coating method Power top U-50 is applied to dull steel plate treated with zinc phosphate.
(Nippon Paint cationic electrodeposition paint)
A plate was formed by electrodeposition coating so as to have a thickness of 0 μm and baked at 160 ° C. for 30 minutes. The plate was coated with the above-mentioned intermediate paint by 20 μm by air spray coating, and dried at 80 ° C. for 5 minutes. Thereafter, the base paint of Production Example 4 was applied by 18 μm by air spray coating, and dried at 80 ° C. for 5 minutes. Further, MacFlow O-1801W Clear (clear paint made by Nippon Paint Co., Ltd.) is applied to the coated plate by air spraying to a thickness of 35 μm.
After painting, it was baked at 140 ° C. for 30 minutes.

(3) Evaluation of chipping resistance The sample holder of the stepping stone tester (manufactured by Suga Test Instruments Co., Ltd.)
The coated plate cooled to 0 ° C. was attached so that the angle of entry of the stone was 90 °, and 100 g of No. 7 crushed stone was injected at an air pressure of 3 kg / cm ² to cause the crushed stone to collide with the coated plate. At that time, the degree (number, size, destruction place) of peeling was evaluated on a five-point scale. The results are shown in Table 1. 1: peeling on the entire surface, peeling off from the substrate 2: peeling on the entire surface, no peeling off from the substrate 3: partly peeling, peeling off from the substrate 4: partly peeling No peeling from substrate 5: Almost no destruction

[0059]

[Table 1]

Examples 2 and 3 In the same manner as in Example 1 except that the aqueous intermediate coating composition was prepared according to the formulation shown in Table 1, a coated plate having a multilayer coating film formed thereon was evaluated. In addition, in Example 3, the coloring pigment paste 2 was used. The results are shown in Table 1.

Comparative Examples 1 and 2 A coated plate having a multi-layer coating film was prepared and evaluated in the same manner as in Example 1 except that the aqueous intermediate coating composition was prepared according to the formulation shown in Table 1. The results are shown in Table 1.

From the examples and comparative examples, it is clear that since the aqueous intermediate coating composition produced in this example contains an elastomer, a multilayer coating film having excellent chipping resistance can be formed.

[0063]

According to the method for forming a multilayer coating film of the present invention, since an aqueous intermediate coating material contains an elastomer, a so-called three-wet coating method in which an intermediate coating material, a base coating material, and a clear coating material are applied by wet-on-wet and simultaneously heat-cured. When coating is performed, a multilayer coating film having excellent chipping resistance can be obtained.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Chisato Yabushita 19-17 Ikedanakamachi, Neyagawa-shi, Osaka F-term in Nippon Paint Co., Ltd. (reference) 4D075 AE12 BB26Z CA03 CA04 CB06 DA06 DB02 DB05 DB06 DB07 DB08 DC12 DC13 EA06 EA07 EA10 EA43 EB12 EB13 EB14 EB15 EB19 EB20 EB22 EB32 EB33 EB35 EB36 EB38 EB39 EB45 4J038 CA021 CA031 CA041 CA061 CB031 CB091 CB111 CC041 CD021 CF021 CG141 MA03 GA03 MA08 GA03 MA03 GA08

Claims (5)

[Claims] 1. A step (1) of applying an aqueous intermediate coating composition on an object to be coated with an electrodeposition coating film to form an uncured intermediate coating film, Applying an aqueous base paint to form an uncured base coating film (2), further applying a clear paint thereon to form an uncured clear coating film, and (3) Intermediate coating film,
A method for forming a multilayer coating film including a step (4) of simultaneously heating and curing the base coating film and the clear coating film to obtain a multilayer coating film, wherein the aqueous intermediate coating material contains an elastomer. A method for forming a multilayer coating film. 2. The method according to claim 1, wherein the elastomer is water-dispersed or water-soluble. 3. The method according to claim 1, wherein the content of the elastomer relative to the solid content of the resin in the aqueous intermediate coating composition is 20 to 100% by weight based on the solid content. 4. A multilayer coating film formed by the method for forming a multilayer coating film according to claim 1, 2 or 3. 5. An aqueous intermediate coating composition comprising an elastomer.