JP2002285081A - Intermediate-coat composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an intermediate-coat composition and its film-forming method ensuring the superiority of a film appearance and chipping resistance in a wet-on-wet coating method for the intermediate coat and a top coat. SOLUTION: The intermediate-coat composition contains a resin composition having a hydroxy group (a) of 10-70 wt.% containing a polyoxylalkylene glycol, a curing agent curable with the hydroxy group (b) of 10-70 wt.% a film-forming resin composition having a nonaqueous dispersion resin (c) of 18-50 wt.% and a pigment, and the solid content ratio of the polyoxyalkylene glycol contained in the resin composition having the hydroxy group (a) toward a resin containing the other hydroxy group is 5/95-50/50. The polyoxyalkylene glycol is a polytetramethylene-ether glycol and the number-average molecular weight of 650-2,000 is preferable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an intermediate coating composition for coating an automobile body, and more particularly to an intermediate coating composition and a coating film suitable for a wet-on-wet coating method of an intermediate coating and a top coating. It relates to a forming method.

[0002]

2. Description of the Related Art In recent years, particularly in the field of automobile coating, resource saving, energy saving and environmental burden (VOC and HA) have been observed.
Ps) In order to solve the problem of reduction, there is a strong demand for shortening the coating process. In response to such demands, conventionally, automobile coating has been performed by a three-coat three-bake coating method in which an intermediate coating and a top coating consisting of a base coating and a clear coating are heat-cured after each coating on the electrodeposition coating film. Although it has been done, intermediate coating,
In addition, a three-coat one-bake coating method in which a top coat consisting of a base coat and a clear coat is performed by a wet-on-wet coat method, and then heated and cured at a time has been attempted.

[0003] By the way, the coating film obtained by the conventional three-coat three-bake coating method has such a function because of the resistance of the coating film to collision of obstacles such as pebbles on the vehicle body during traveling, that is, the so-called chipping resistance. It can be ensured by using an intermediate coating having the same. In addition, due to stress relaxation due to dispersion between the layers, damage to the coating film could be minimized. However, this intermediate coating cannot be applied because the coating obtained when used in the three-coat one-bake coating method suffers from blemishes and the appearance is deteriorated. In addition, in the three-coat one-bake coating method, since each layer is integrated and behaves as if it were a single layer, stress relaxation between the layers cannot be expected, and it is very difficult to achieve both a coating film appearance and chipping resistance. Was.

[0004]

SUMMARY OF THE INVENTION The present invention provides a method for wet-on-wet application of an intermediate coating and a top coating, which provides an intermediate coating composition having excellent coating film appearance and chipping resistance. It is the purpose.

[0005]

According to the present invention, there is provided a resin composition (a) containing 10 to 70% by weight of a hydroxyl group-containing resin containing polyoxyalkylene glycol, based on the total solid content of the resin composition.
In an intermediate coating composition containing a film-forming resin composition and a pigment containing 10 to 70% by weight of a curing agent (b) capable of hardening with a hydroxyl group and 18 to 50% by weight of a non-aqueous dispersion resin (c). The weight ratio of the solid content of the polyoxyalkylene glycol and the other hydroxyl group-containing resin contained in the hydroxyl group-containing resin composition (a) is 5/95 to 50/50.
It is an intermediate coating composition characterized by the following. Here, the polyoxyalkylene glycol is a polytetramethylene ether glycol, and preferably has a number average molecular weight of 650 to 2,000.

The content of the pigment is preferably 10 to 70% by weight based on the total weight of the solid content of the film-forming resin and the pigment. Furthermore, the volume shrinkage when heating at 140 ° C. for 30 minutes after applying the coating composition is preferably 45% or less.

Further, the present invention comprises a step (1) of forming an uncured intermediate coating film by applying an intermediate coating material on an object on which an electrodeposition coating film is formed, and the step (1). A step (2) of applying an overcoat paint on the obtained uncured intermediate coating film to form an uncured topcoat film, the uncured intermediate coating film obtained in the above step (1), A method for forming a coating film including a step (3) of simultaneously heating and curing an uncured topcoat film obtained in the step (2) to obtain a coating film, wherein the intermediate coating material is the intermediate coating material. A method for forming a coating film, which is a composition.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The film-forming resin composition contained in the intermediate coating composition of the present invention contains a hydroxyl group-containing resin composition (a). The above hydroxyl-containing resin composition (a)
Is 10 to 70% by weight based on the total solid content of the film-forming resin contained in the coating composition. When the content is less than 10% by weight, the obtained coating film becomes brittle or the appearance of the coating film and various properties of the coating film are deteriorated. When the content is more than 70% by weight, other components are reduced and thus obtained. The appearance of the coating may be reduced. Preferably it is 10 to 50% by weight, more preferably 20 to 50% by weight.

The hydroxyl group-containing resin composition (a) is composed of a polyoxyalkylene glycol and another hydroxyl group-containing resin, and is soluble in an organic solvent used for an intermediate coating composition. The above polyoxyalkylene glycol is HO- (RO) _n -H (wherein, R represents 2 to 2 carbon atoms)
6 alkyl group, n can be represented by 5 to 50), _{specifically, HO- (CH 2 CH 2 CH} 2 CH 2 O) n -
And polytetramethylene ether glycol represented by H (where n is 5 to 50). The polytetramethylene ether glycol preferably has a number average molecular weight of 650 to 3000,
More preferably, it is 50 to 2,000. When the number average molecular weight is less than 650, the curability of the coating film may be insufficient, and when it exceeds 3000, the chipping resistance of the obtained coating film may be reduced. If the ratio is outside the above range, the volume shrinkage of the coating film due to heating after coating may increase, and the appearance of the coating film may be deteriorated.

The hydroxyl value of the polytetramethylene ether glycol is not particularly limited, but is generally 40 to 200. Further, the acid value of the polytetramethylene ether glycol is not particularly limited, but is 1 or less. Commercially available polytetramethylene ether glycols include PT
Examples include PTMG series (manufactured by Mitsubishi Chemical Corporation) such as MG1000 and PTMG2000.

The other hydroxyl group-containing resin is other than polytetramethylene ether glycol, and examples thereof include an acrylic resin and / or a polyester resin. The acrylic resin is not particularly limited, and can be obtained by polymerizing a hydroxyl group-containing unsaturated monomer and other monomers by a conventional method using a radical polymerization initiator or the like, if necessary. Specific examples of the hydroxyl group-containing unsaturated monomer include 2-hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, hydroxymethyl (meth) acrylate, and allyl alcohol. And adducts of hydroxyethyl (meth) acrylate with ε-caprolactone.

Examples of the other monomers include carboxylic acid group-containing unsaturated monomers such as (meth) acrylic acid, crotonic acid, itaconic acid, maleic anhydride and fumaric acid; t-butylacrylamide sulfone Sulfonic acid group-containing unsaturated monomers such as acids; epoxy group-containing unsaturated monomers such as glycidyl (meth) acrylate; methyl (meth) acrylate, ethyl (meth) acrylate;
N-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, Lauryl methacrylate, phenyl acrylate, isobornyl (meth) acrylate, cyclohexyl methacrylate, t-butylcyclohexyl (meth) acrylate, dicyclopentadienyl (meth) acrylate, dihydrodicyclopentadi (meth) acrylate (Meth) acrylic acid esters such as enyl; (meth) acrylamide, N-methylol (meth) acrylamide, N-butoxymethyl (meth)
Acrylamide, N, N-dimethyl (meth) acrylamide, N, N-dibutyl (meth) acrylamide, N,
N-dioctyl (meth) acrylamide, N-monobutyl (meth) acrylamide, N-monooctyl (meth)
Polymerizable amide compounds such as acrylamide, 2,4-dihydroxy-4′-vinylbenzophenone, N- (2-hydroxyethyl) acrylamide, N- (2-hydroxyethyl) methacrylamide; styrene, α-methylstyrene, vinyl ketone, polymerizable aromatic compounds such as t-butylstyrene, parachlorostyrene and vinylnaphthalene; polymerizable nitriles such as acrylonitrile and methacrylonitrile; vinyl esters such as ethylene and propylene;
Α-olefins such as vinyl acetate and vinyl propionate;
Examples thereof include dienes such as butadiene and isoprene.

As the above radical initiator, for example,
Azo initiators such as 2,2'-azobisisobutylnitrile and 2,2'-azobis (2,4-dimethylvaleronitrile); peroxides such as benzoyl peroxide, lauryl peroxide and t-butylperoxyoctoate Oxide-based initiators and the like can be mentioned.

The polyester resin can be obtained by polymerizing an acid component and an alcohol component by a conventional method using a catalyst such as an organic tin compound, if necessary. As the acid component, specifically, phthalic anhydride, isophthalic acid, terephthalic acid, succinic anhydride, adipic acid, azelaic acid, sebacic acid, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, maleic anhydride, fumaric acid And polybasic acids such as itaconic acid and trimellitic anhydride. Examples of the alcohol component include ethylene glycol, propylene glycol, 1,6-hexanediol, diethylene glycol, neopentyl glycol, hydrogenated bisphenol A, trimethylolpropane, pentaerythritol, and dipentaerythritol. Of polyhydric alcohols.

The other hydroxyl group-containing resin preferably has a number average molecular weight of 1,000 to 10,000.
More preferably, the number is from 1,000 to 5,000,
More preferably, it is 3000. When the number average molecular weight is less than 1,000, the curability of the coating film may decrease, and when it exceeds 10,000, the chipping resistance of the obtained coating film may decrease. Outside the above range, the volume shrinkage of the coating film when heated after coating may increase, and the appearance of the coating film may be reduced.

The hydroxyl value of the other hydroxyl group-containing resin is not particularly limited, but is generally 50 to 250. When the hydroxyl value is less than 50, the curability of the coating film decreases, and when it exceeds 250, the water resistance of the obtained coating film decreases. The acid value of the other hydroxyl group-containing resin is not particularly limited, but is generally 1 to 50. When the acid value is less than 1, the curability of the coating film decreases, and
If it exceeds 50, the water resistance of the resulting coating film may be reduced.

Further, the solubility parameter of the other hydroxyl group-containing resin is preferably from 9.5 to 12.
When the solubility parameter is less than 9.5, the intermediate coating composition of the present invention and the top coating composition are wet-on-coated.
When applied by the wet coating method, bleeding occurs with the top coat, and when it exceeds 12, the water resistance of the obtained coating film may be reduced.

As used herein, the solubility parameter is:
SUH, CLARK is a measure of the degree of solubility.
E. J. Polymer Science, A-1,
5, pp. 1671-1681 (1967), which is well known to those skilled in the art, and by calculation from solubility parameters of monomers as raw materials. The other hydroxyl group-containing resin contained in the hydroxyl group-containing resin composition (a) of the present invention contains an acrylic resin because the resin for securing adhesion to the overcoat film can be made highly polar. Is preferred.

The weight ratio of the solid content of the polyoxyalkylene glycol and the other hydroxyl group-containing resin contained in the hydroxyl group-containing resin composition (a) is from 5/95 to 50/50.
50. When the weight ratio is less than 5/95, the chipping resistance of the obtained coating film is reduced, and when it is more than 50/50, various properties of the coating film may be reduced. Preferably it is 5/95-25/75.

The film-forming resin composition contained in the intermediate coating composition of the present invention contains a hydroxyl group and a curable curing agent (b). The content of the curing agent (b) is 10 to 7 based on the total solid content of the film-forming resin.
0% by weight. When the content is less than 10% by weight, the curability of the coating film becomes insufficient, and when it exceeds 70% by weight, the obtained coating film becomes brittle and the physical properties of the coating film may be deteriorated. Preferably it is 20 to 50% by weight.

The curing agent (b) is not particularly restricted but includes, for example, a melamine resin and / or a (blocked) polyisocyanate compound. From the viewpoint, it is preferable that the melamine resin or a combination of the melamine resin and the blocked polyisocyanate compound is used.

Further, the film-forming resin composition contained in the intermediate coating composition of the present invention contains a non-aqueous dispersion resin (c). The content of the non-aqueous dispersion resin (c) is 18 to 50% by weight based on the total solid content of the film-forming resin. When the content is out of the above range, the appearance of the coating film is deteriorated. Preferably it is 23 to 45% by weight. Specific examples of such a non-aqueous dispersion resin (c) include those composed of a dispersion stable resin soluble in an organic solvent and particles insoluble in the organic solvent. By doing so, the swelling ratio due to the organic solvent in the coating material can be reduced, and color return due to delicate mixing with the overcoat film can be prevented.

The non-aqueous dispersion resin (c) has a hydroxyl value of 10
It is preferably from 0 to 400, and more preferably from 130 to 300. When the hydroxyl value is less than 100, the curability of the coating film is reduced, and when it exceeds 400, the water resistance of the obtained coating film may be reduced. Further, the acid value is preferably 200 or less, more preferably 50 or less. If the acid value exceeds 200, the water resistance of the resulting coating film may be reduced.

Such a non-aqueous dispersion resin (c) is, for example, a resin solution obtained by dissolving a dispersion-stable resin in an organic solvent, and is soluble before polymerization but particles formed after polymerization are insoluble. It can be obtained by polymerizing a monomer mixture composed of the following monomers by a conventional method using a radical polymerization initiator.

The dispersion-stable resin for obtaining the non-aqueous dispersion resin (c) is not particularly limited, and examples thereof include an acrylic resin, a polyester resin, a polyether resin, a polycarbonate resin and a polyurethane resin. These can be obtained by a conventional method from raw materials composed of monomers well known by those skilled in the art.
The dispersion-stable resin preferably has a hydroxyl group, an acid group, and the like from the viewpoint of crosslinkability with the curing agent (b),
Further, it may have an epoxy group, an isocyanate group or the like as needed.

The raw material preferably contains 10 to 50% by weight of a monomer having a side chain having 10 or more carbon atoms. If the content is less than 10% by weight, bleeding with the base paint may occur. Also, 50
If the content is more than 10% by weight, the inside of the coating material may become uneven. Further, the raw material preferably contains 20 to 50% by weight of a monomer having a hydrophilic group such as a hydroxyl group, a carboxylic acid group, an amide group, and an ether group. If the content is less than 20% by weight, curability, stability, and adhesion to the layer immediately above may be reduced. Also,
If it exceeds 50% by weight, the dispersibility may be reduced.

The number average molecular weight of the dispersion stable resin is 200
It is preferably from 0 to 10,000. When the number average molecular weight is less than 2,000, the dispersibility decreases, and
If it exceeds 00, the amount of the organic solvent contained in the paint at the time of application may be large.

The dispersion stable resin has a hydroxyl value of 10
Preferably it is ~ 250. When the hydroxyl value is less than 10, the curability of the coating film is reduced, and when it exceeds 250, the dispersibility may be reduced. The acid value is 10
It is preferably less than 0, more preferably less than 50. If the acid value exceeds 100, the water resistance of the resulting coating film may be reduced.

Further, the glass transition temperature of the above-mentioned dispersion stable resin is not particularly limited, and is preferably, for example, 30 ° C. or lower. When the temperature exceeds 30 ° C., the appearance of the coating film may be reduced, and the chipping resistance may be reduced. The organic solvent is not particularly limited and includes, for example, well-known organic solvents such as aliphatic hydrocarbon solvents, aromatic hydrocarbons, petroleum-based mixed solvents, alcohol-based solvents, ether-based solvents, ketone-based solvents, and ester-based solvents. Can be mentioned. These may be used alone or in combination of two or more.

The non-aqueous dispersion resin (c) is soluble in the above-mentioned organic solvent in which the above-mentioned dispersion-stable resin is dissolved in the above-mentioned organic solvent before polymerization, but the particles formed after the polymerization become insoluble. A monomer mixture of various monomers can be polymerized by a conventional method using a radical polymerization initiator.

Such monomers are not particularly limited, and specific examples include the hydroxyl-containing unsaturated monomers and other monomers described above for the other hydroxyl-containing resins.

The solubility parameter of the monomer mixture is preferably from 11 to 14. If the solubility parameter is less than 11, the obtained particles may be dissolved in the organic solvent and particles may not be obtained.
When it exceeds, particles may not be obtained substantially.

The value of (solubility parameter of the monomer mixture)-(solubility parameter of the dispersion-stable resin) is preferably 0.5 to 3. The above value is 0.5
When the amount is less than the above, dispersion stability in the paint is reduced, and interface control becomes difficult, and when the overcoat is applied by a wet-on-wet method, bleeding with the overcoat may occur. On the other hand, if it exceeds 3, the dispersibility may be reduced in the paint and the coating may be separated. Preferably, the above values are 1-3.

The value of (solubility parameter of the above-mentioned monomer mixture)-(solubility parameter of other hydroxyl-containing resin contained in the above-mentioned hydroxyl-containing resin composition (a)) is not particularly limited. It is preferable that the value be a positive number from the viewpoint of preventing bleeding.

The radical polymerization initiator is not particularly limited, and specific examples thereof include those described above in connection with the hydroxyl group-containing resin composition (a). The amount is 0.2 to 10 parts by weight, preferably 0.5 to 5 parts by weight, per 100 parts by weight. The polymerization reaction in an organic solvent containing a dispersion-stable resin is generally performed at a temperature of about
It is preferably performed for 15 hours.

The average particle diameter of the particles contained in the non-aqueous dispersion resin (c) thus obtained is 0.05 to 5 μm.
And more preferably 0.05 to 1 μm. When the average particle size is less than 0.05 μm, the curability of the coating film is insufficient, and when it exceeds 5 μm, bleeding with the top coat may occur and the appearance of the coating film may be deteriorated.

The weight ratio of the solid content of the dispersion-stable resin to the monomer mixture in obtaining the non-aqueous dispersion resin (c) can be arbitrarily selected according to the purpose. / Monomer mixture is 3 / 97-80 /
It is preferably 20 and more preferably 5/95 to 60/40. The concentration by the total weight of the dispersion stable resin and the monomer mixture in the organic solvent is 30 to 80% by weight, preferably 40 to 6% by weight.
0% by weight. Further, the film-forming resin composition contained in the intermediate coating composition of the present invention may contain, for example, a resin component such as a pigment-dispersed resin in addition to the above components.

The intermediate coating composition of the present invention contains a pigment in addition to the above-mentioned film-forming resin composition. The content of the pigment is preferably 10 to 70% by weight based on the total weight of the solid content of the film-forming resin composition and the pigment. When the concentration is less than 10% by weight, volume shrinkage due to heating and curing after application is increased, and the appearance of the coating film may be deteriorated. 70% by weight
When it exceeds, there is a possibility that the amount of the pigment is too large and the appearance of the coating film is deteriorated.

The above-mentioned pigments are not particularly restricted but include, for example, azochelate pigments, insoluble azo pigments, condensed azo pigments, phthalocyanine pigments, indigo pigments, perinone pigments, perylene pigments, dioxane pigments, quinacridone pigments. Organic color pigments such as pigments, isoindolinone pigments, metal complex pigments; graphite, yellow iron oxide, red iron oxide,
Inorganic color pigments such as carbon black and titanium dioxide;
There may be mentioned extenders such as calcium carbonate, barium sulfate, clay and talc, and these may be of two or more types. By containing such a pigment, a standard gray intermediate paint, a set gray intermediate paint and a color intermediate paint having the same lightness or hue as the top coat can be obtained.

The intermediate coating composition of the present invention may further comprise a viscosity control agent, if necessary, in addition to the above-mentioned film-forming resin and pigment.
It may contain various additives such as an anti-bake agent, various organic solvents, and the like.

Examples of the viscosity controlling agent include swelling dispersions of fatty acid amides, amides such as amide-based fatty acids and phosphates of long-chain polyaminoamides; polyethylene-based materials such as colloidal swelling dispersions of polyethylene oxide. Organic bentonites such as smectite clay and montmorillonite; inorganic ones such as aluminum silicate and barium sulfate; and flat pigments which exhibit viscosity depending on their shapes.

The intermediate coating composition of the present invention can be obtained by a method well-known to those skilled in the art, such as kneading and dispersing the above components using a kneader, roll or the like. The intermediate coating composition thus obtained can be diluted with an organic solvent well-known to those skilled in the art at the time of application when necessary. The nonvolatile content of the intermediate coating composition at the time of the application is preferably 40 to 70% by weight. When the non-volatile content is less than 40% by weight, the amount of the solvent may increase, and the volume shrinkage of the obtained coating film may increase, and the appearance of the coating film may decrease. On the other hand, if it exceeds 70% by weight, the viscosity becomes too high, and the appearance of the coating film may be reduced, or the coating workability may be reduced. More preferably, it is 45 to 60% by weight.

The intermediate coating composition of the present invention preferably has a volumetric shrinkage of 45% or less when heated at 140 ° C. for 30 minutes after application. The volume shrinkage rate is 4
If it exceeds 5%, the base concealing property may decrease, and the appearance of the coating film may decrease. More preferably, it is 40% or less. In this specification, the volume shrinkage when heated at 140 ° C. for 30 minutes is represented by the following formula: volume shrinkage (%) = ｛(100−solid content of paint at the time of application)
/ Solvent specific gravity} / {(100-solid content of coating at the time of coating) / solvent ratio} + (solid content at coating / specific gravity of dried coating film) × 10
0 (where the solid content of the paint at the time of application is W1 as the weight of the work before coating, and W1 as the weight of the work after coating is applied.
2. When the weight of the object to be coated after heating at 140 ° C. for 30 minutes is W3, the solid content of the coating at the time of application (%) = (W3−W1) / (W2−
W1) × 100. The specific gravity of the solvent represents the specific gravity of the solvent contained in the intermediate coating composition. The specific gravity of the dried coating film is the specific gravity of the nonvolatile components in the paint, and is a value obtained by calculation from the specific gravity of each component and its ratio. ).

The method for forming a coating film according to the present invention comprises the steps of: (1) forming an uncured intermediate coating film by applying an intermediate coating material on an object on which an electrodeposition coating film has been formed; A step (2) of applying a top coat on the uncured intermediate coat film obtained in 1) to form an uncured top coat film, and the above step (1)
And a step (3) of heating and curing the uncured intermediate coating film obtained in step (1) and the uncured topcoat film obtained in step (2) at a time to obtain a coating film. And wherein the intermediate coating composition is the intermediate coating composition.

Step (1) in the coating film forming method of the present invention
Is a step of forming the uncured intermediate coating film by applying the above-mentioned intermediate coating composition on the object on which the electrodeposition coating film has been formed. The object to be coated on which the electrodeposition coating film is formed is not particularly limited, and examples thereof include metals such as iron, copper, aluminum, tin, and zinc and alloys containing these, glass, plastics, and flat or molded articles such as foams. Although it can be mentioned, it is particularly preferable that the electrodeposition coating is possible. In particular,
Examples include automobile bodies such as passenger cars, trucks, buses, and motorcycles, and parts thereof. These objects to be coated are preferably subjected to a chemical conversion treatment with a phosphate, a chromate or the like before forming the electrodeposition coating film. As a method of forming an electrodeposition coating film on the object to be coated, specifically, a method of applying an electrodeposition coating material by electrodeposition and then heating and curing. The electrodeposition paint is not particularly limited, and examples thereof include a cationic electrodeposition paint and an anion electrodeposition paint which are well known by those skilled in the art.
It is preferably a cationic electrodeposition paint. The conditions for heat curing are not particularly limited, and can be appropriately set according to the type of the electrodeposition paint.

Specific examples of the method of applying the intermediate coating composition to the object to be coated include an air electrostatic spray coater and a rotary atomizing electrostatic coater. In addition, when performing the above-mentioned application in two or more stages,
The application method at each stage may be the same method or different methods. The coating thickness in the above step (1) is not particularly limited and can be set according to a desired use. Generally, regardless of the number of coating steps,
At the end of the step (1), the dry film thickness is 5 to 40.
μm is preferred. If the thickness is less than 5 μm, the base may not be able to be concealed.
If it exceeds 0 μm, there is a possibility that the effect corresponding to the film thickness cannot be obtained. Thus, an uncured intermediate coating film can be formed on the object to be coated.

Step (2) in the coating film forming method of the present invention
Is to form an uncured top coat by applying a top coat on the uncured intermediate coat obtained in the above step (1). This step (2) is roughly classified into a case where a solid color paint is used as the top coat (i) and a case where a base paint and a clear paint are used (ii).

(I) When a solid color paint is used When a solid color paint is used as the top coat, this step (2) is carried out on the uncured intermediate coat obtained in the step (1). An uncured solid color coating film, that is, a top coat film is formed by applying a solid color paint. The method for applying the solid color paint is not particularly limited, and specific examples include the method described in the above step (1). Further, the coating film thickness is not particularly limited, and is generally 5 to 40 μm. In this way, an uncured top coat consisting of a solid color coat can be formed.

The form of the solid color paint is not particularly limited, and examples thereof include an organic solvent type dissolved or dispersed in an organic solvent and an aqueous type dissolved or dispersed in water. Such solid color paints generally include a film-forming resin composition and a pigment. The film-forming resin composition contains, for example, an acrylic resin, a polyester resin, an alkyd resin, an epoxy resin, a urethane resin, and the like, and a melamine resin and a blocked polyisocyanate compound. In addition, from the viewpoint of pigment dispersibility and coating workability, a combination of an acrylic resin and / or a polyester resin and a melamine resin, or a combination of an acrylic resin and / or a polyester resin and a blocked poly It is preferable to use a combination with an isocyanate compound or a mixture thereof.

When the solid color paint is aqueous, the film-forming resin composition described in US Pat. Nos. 5,151,125 and 5,183,504 can be used as the film-forming resin composition. . In particular,
From the viewpoint of the appearance of the coating film, a combination of an acrylic resin having an acrylamide group, a hydroxyl group and an acid group described in US Pat. No. 5,183,504 and a melamine resin is preferable.

As the above-mentioned pigments, in addition to the pigments described in the above intermediate coating composition, interference mica powder, colored mica powder, metals or alloys such as aluminum, aluminum oxide, copper, zinc, iron, nickel, tin and the like. , White mica powder, graphite, or glass flakes and the like, and glitter mixtures thereof. The brilliant pigment has an average particle diameter of 2 to 50 μm, preferably a flaky pigment having a thickness of 0.1 to 5 μm, and more preferably a flake pigment having an average particle diameter of 10 to 35 μm. Excellent and preferred.

[0052] Two or more pigments may be contained in the solid color paint. When the solid color paint contains the brilliant pigment, the content is, in the total weight of the solid content and all the pigments of the film-forming resin composition,
0.01 to 30% by weight, preferably 0.01 to 30% by weight.
More preferably, it is で 25% by weight. Further, the content of all the pigments is preferably 1 to 50% by weight, and more preferably 0.5 to 40% by weight based on the total weight of the solid content of the film-forming resin composition and all the pigments. More preferably, it is more preferably 1 to 30% by weight.

As the solid color paint, in addition to the above components, if necessary, in addition to a viscosity control agent well known to those skilled in the art, a surface conditioner, an ultraviolet absorber, an antioxidant, a light stabilizer and the like. Various additives can be exemplified.
The solid color paint can be obtained by a method well-known to those skilled in the art, such as kneading and dispersing the above components using a kneader, roll, or the like.

The solid color paint thus obtained can be diluted with an organic solvent well-known to those skilled in the art at the time of application when necessary. The nonvolatile content of the solid color paint at the time of the above application is preferably 30 to 60% by weight. When the non-volatile content is less than 30% by weight, the amount of the solvent may be large, and the volume shrinkage of the obtained coating film may increase, and the appearance of the coating film may decrease. On the other hand, if it exceeds 60% by weight, the viscosity becomes too high, and the appearance of the coating film may be reduced, or the coating workability may be reduced.

(Ii) When a base paint and a clear paint are used When a base paint and a clear paint are used as the top coat, this step (2) comprises the following two steps.
First, an uncured base coat is formed by applying the base paint on the uncured intermediate coat obtained in the above step (1). The method for applying the base paint is not particularly limited, and specific examples include the method described in the above step (1). Further, the coating film thickness is not particularly limited, and is generally 5 to 35 μm. Thus, an uncured base coating film can be formed. The base paint is not particularly limited, and specific examples thereof include those similar to the solid color paint.

When the base paint is of an aqueous type, in order to further improve the appearance of the obtained coating film, it is left at room temperature for a certain period of time, called preheating, after application, or at a temperature of, for example, 110 ° C. or less. After heating and drying for 2 to 10 minutes, it is preferable to proceed to the next step.

Next, on the obtained uncured base coating film,
An uncured clear coating film is formed by applying a clear paint. The method for applying the clear paint is not particularly limited, and specific examples include the method described in the above step (1), and it is preferably a rotary atomization type electrostatic coating method. Further, the coating film thickness is not particularly limited, and is generally from 10 to 70 μm.

The form of the clear coating is not particularly limited, and various forms such as an organic solvent type dissolved or dispersed in an organic solvent, an aqueous type dissolved or dispersed in water, and a powder type can be used. Can be mentioned. Such a clear coating generally includes the film-forming resin composition described above for the solid color coating. In addition, from the viewpoint of transparency and acid etching resistance, a combination of an acrylic resin and / or a polyester resin and a melamine resin, an acrylic resin and / or a polyester resin and a blocked polyisocyanate compound are used as the coating film-forming resin composition. In combination with
It is preferable to use a mixture thereof, or an acrylic resin and / or a polyester resin having a carboxylic acid / epoxy curing system.

The clear paint may contain the pigment to the extent that transparency is not impaired. As the clear coating, in addition to the above components, if necessary, a viscosity control agent well-known by those skilled in the art, a surface conditioner, an ultraviolet absorber,
Various additives such as an antioxidant and a light stabilizer can be exemplified.

The above-mentioned clear paint can be obtained by a method well-known to those skilled in the art such as kneading and dispersing the above-mentioned components using a kneader, a roll or the like according to the form, and if necessary, a classification operation. .

When the form of the thus obtained clear paint is an organic solvent type or an aqueous type, it can be diluted with an organic solvent or water well-known by those skilled in the art as needed at the time of application. The non-volatile content of the clear coating at the time of the application is preferably 40 to 70% by weight. When the non-volatile content is less than 40% by weight, the amount of the solvent may increase, and the volume shrinkage of the obtained coating film may increase, and the appearance of the coating film may decrease. On the other hand, if it exceeds 70% by weight, the viscosity becomes too high, and the appearance of the coating film may be reduced, or the coating workability may be reduced. In this way, an uncured top coat consisting of an uncured base coat and a clear coat can be formed.

Step (3) in the coating film forming method of the present invention
Is a method in which the uncured intermediate coating film obtained in the step (1) and the uncured topcoat film obtained in the step (2) are heat-cured at a time to obtain a coating film. The heating conditions are not particularly limited, and can be appropriately set depending on the types of the intermediate coating material and the top coating material to be used, and are usually preferably 110 to 180 ° C, and more preferably 120 to 160 ° C. preferable.
When the heat curing temperature is lower than 110 ° C., the curing of the coating film may be insufficient, and when the temperature exceeds 180 ° C.,
The coating film becomes hard and brittle, and the physical properties may be reduced. The heat-curing time can be adjusted by the heat-curing temperature, but is preferably 10 to 60 minutes from an industrial viewpoint.

The total coating thus obtained is usually preferably from 30 to 300 μm, and more preferably from 50 to 2 μm.
It is preferably 50 μm. The total film thickness is 30
If it is less than μm, the strength of the coating film itself may decrease, and if it exceeds 300 μm, the heat resistance may decrease.

[0064]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. In the examples, "parts" represents parts by weight.

[0065]Production example 1 Production of acrylic resin 1 solution  Thermometer, stirrer, temperature controller, reflux condenser and nitrogen
In a reaction vessel equipped with an inlet tube, 300 parts of toluene and
Charge 100 parts of butyl isobutyl ketone and stir
The temperature was raised to 105 ° C. While refluxing, 50
Parts, 23.0 parts of methacrylic acid, ethyl methacrylate 7
9.0 parts, methyl methacrylate 300.0 parts, acrylic
444.0 parts of ethyl acrylate, 2-hydroxyethyl methacrylate
Chill 104.0 parts and t-butylperoxy-2-e
A monomer mixture comprising 7.0 parts of tyl hexanoate;
A solution obtained by mixing 400 parts of toluene is dropped over 3 hours.
After that, the mixture was kept for 30 minutes with stirring. Then, t-
Butyl peroxy-2-ethylhexanoate 3.0 parts
And a solution consisting of 200 parts of toluene over 30 minutes
It was dropped. While maintaining the reaction solution at 105 ° C., 1
After stirring and refluxing for an hour, the reaction was terminated and GPC (gel
Number average by measurement
Acrylic resin 1 having a particle size of 21000 and a solid content of 50% by weight
A solution was obtained.

[0066]Production Example 2 Production of acrylic resin 2 solution  Thermometer, stirrer, temperature controller, reflux condenser and nitrogen
In a reaction vessel equipped with an introduction tube, 82 parts of xylene was charged,
4.5 parts of methacrylic acid, 26.0 parts of ethyl acrylate,
Plaxel FM-1 (containing hydroxyl groups manufactured by Daicel Chemical Industries, Ltd.)
Monomer) 64.5 parts, α-methylstyrene dimer
5.0 parts, from 13.0 parts of azobisisobutyronitrile
20 parts of the resulting monomer mixture and stirring
Heat and raise temperature to 95 ° C. While refluxing
Drop the remaining 93.0 parts of the monomer mixture over 3 hours
And then add 1.0 part of azobisisobutyronitrile
Solution consisting of xylene and 12 parts of xylene is dropped over 30 minutes
did. The reaction solution was further stirred at 95 ° C for 1 hour.
After stirring and refluxing, 63 parts of the solvent was distilled off under reduced pressure to carry out the reaction.
And the number average molecular weight measured by GPC is 2
000, 75% by weight solid content acrylic resin 2 solution
Was.

[0067]Production Example 3 Production of polyester resin solution  Thermometer, stirrer, temperature controller, reflux condenser, nitrogen introduction
A reaction vessel equipped with tubes and a fractionator
258 parts of phthalic acid, 184 parts of isophthalic acid, trimethylo
213 parts propane, neopentyl glycol 180
Part, neopentyl glycol es hydroxypivalate
Tellur 72 parts and Cardura E-10 (manufactured by Shell Chemical Company)
94 parts of glycidyl versatate)
And heated to 180 ° C. The above raw materials can be melted and stirred
After that, add 0.2 parts of dibutyltin oxide
Stirring was started and the reaction vessel was heated from 180 ° C to 220 ° C for 3 hours.
Generates heat over a period of time while maintaining a constant heating rate
The condensed water formed was distilled out of the system. After reaching 220 ° C
While stirring for 1 hour, and use xylene as a reflux solvent.
17 parts were gradually added to further advance the reaction. resin
When the acid value reaches 10, cool to 150 ° C and
Kusel M (E-caprolactone manufactured by Daicel Chemical Industries, Ltd.)
182 parts was added dropwise, and the mixture was kept for 1 hour while stirring, and then 1
Cooled to 00 ° C. Further, 264 parts of xylene was added.
And a number average molecular weight of 1400 by GPC measurement and a solid content of 7
9% by weight, hydroxyl value 210, acid value 8 polyester resin
A solution was obtained.

[0068]Production Example 4 Production of non-aqueous dispersion resin liquid  (A) Production of dispersion stable resin Thermometer, stirrer, temperature controller, reflux condenser, and nitrogen
Charge 90 parts of butyl acetate into a reaction vessel equipped with an inlet tube
38.9 parts of methyl methacrylate,
Allyl 38.8 parts, 2-hydroxyethyl acrylate 2
2.3 parts and 5.0 parts of azobisisobutyronitrile
The calculated solubility parameter is 9.5
Add 20 parts of a certain monomer mixture and stir
Heat and raise temperature to 80 ° C. While refluxing
The remaining 85.0 parts of the monomer mixture were added dropwise over 3 hours.
And then 0.5 parts of azobisisobutyronitrile
And a solution consisting of 10 parts of butyl acetate in drops over 30 minutes
I dropped it. 2 hours while keeping the reaction solution at 80 ° C.
After stirring and refluxing, the reaction was terminated and measured by GPC measurement.
A dispersion stable tree having a number average molecular weight of 5600 and a solid content of 50% by weight.
A fat solution was obtained.

(B) Production of Non-Aqueous Dispersion Resin 35 parts of butyl acetate and 60 parts of the obtained dispersion-stable resin were placed in a reaction vessel equipped with a thermometer, a stirrer, a temperature controller, a reflux condenser and a nitrogen inlet tube. It was charged and heated to 100 ° C. Further, 7.0 parts of styrene, 1.8 parts of methacrylic acid, 12.0 parts of methyl methacrylate, 8.5 parts of ethyl acrylate, and 2-hydroxyethyl acrylate 4
A monomer mixture having a solubility parameter of 11.8 calculated from 0.7 part and 1.4 parts of azobisisobutyronitrile was added dropwise over 3 hours, and then azobisisobutyronitrile was added. A solution consisting of 0.1 part and 1 part of butyl acetate was added dropwise over 30 minutes. After the reaction solution was further stirred for 1 hour, diluted with butyl acetate, the average particle diameter was 0.18 μm, the solid content was 40% by weight, and the
Viscosity at 300 ° C., glass transition temperature 23 ° C.
A non-aqueous dispersion resin solution having a hydroxyl value of 162 was obtained.

[0070]Example 1  To 328 parts of the polyester resin solution obtained in Production Example 3,
And CR-93 (Titanium dioxide manufactured by Ishihara Sangyo) 973
Part, FW-200P (Carbon black manufactured by Degussa) 1
0 parts, 159 parts of butyl acetate and 82 parts of xylene in order.
In addition, after premixing, 1552 parts of glass
And dispersed with a sand grinding mill for 3 hours.
When the particle size becomes 5 μm or less with a grind gauge
After the dispersion was completed and 81.8 parts of xylene was added, about 1
Stir for 0 minutes, remove glass beads by filtration and remove face
A paste was obtained. Against this pigment paste
In order to obtain the solid content weight ratio as shown in Table 1, each component
By blending, an intermediate coating composition was obtained.

The resulting intermediate coating composition was mixed with a mixture of ethyl ethoxypropionate / xylene = 9/11 at 20 ° C., using a Ford Cup No. 4 and diluted to 19 seconds. The solid content of the diluted intermediate coating composition was 51% by weight. 200 × 200 × 0.8mm S
After power-coating U-50 (Nippon Paint Co., Ltd. isocyanate-curable aminoepoxy resin-based cationic electrodeposition paint) on a PC dull steel plate so as to have a dry film thickness of 20 μm, it was cured by heating at 180 ° C. for 30 minutes. .

The thus-obtained object to be coated and an aluminum foil of 150 × 200 mm whose weight was measured in advance to measure the solid content at the time of application of the intermediate coating were mixed with the above-mentioned diluted medium. Apply the coating composition to a thickness of 21 μm.
Bell (Rotary atomizing electrostatic coating machine manufactured by ABB Randsburg)
And then left at room temperature for 10 minutes. Immediately after the application, the aluminum foil was quickly folded. Next, Super Luck M-1300 Black (melamine-curable acrylic resin-based organic solvent type base paint, Nippon Paint Co., Ltd., solid content: 46% by weight) was applied to the object on which the uncured intermediate coating film was formed at 15 μm. So that
Metallic Bell COPES-IV twice at 2.5 minute intervals
(ABB Industry Co., Ltd., rotary atomizing electrostatic coating machine for water-based paint) was applied to obtain an uncured base coating film, and then left at room temperature for 20 minutes. Then, Mac Flow O-133
0 (a carboxylic acid / epoxy-curable acrylic resin and a polyester resin-based organic solvent type clear paint, Nippon Paint Co., Ltd., 48 wt% solid content) is spray-coated to a dry film thickness of 40 μm, and then heated at 140 ° C. for 30 minutes. It was cured to obtain a coated plate on which a coating film was formed.

[0073]Examples 2-3 and Comparative Examples 1-2  Pigment paste so that the solid content weight ratio is as shown in Table 1.
Example 1 was prepared except that each component was blended after preparing
Prepare, dilute, and apply the intermediate coating composition in the same manner as
To obtain a coating film.

[0074]Evaluation test  Coatings in Examples 1-3 and Comparative Examples 1-2 and obtained
The following evaluation test was performed on the coated plate. The resulting knot
The results are shown in Table 1. <Volume shrinkage> Solvent specific gravity of the intermediate coating composition was 0.8
7. The dry coating specific gravity of the intermediate coating film is 1.64 and
30 minutes at 140 ° C with cured aluminum coating film
Each intermediate paint calculated from the weight change when heated for one minute
Using the paint solid content at the time of application of the composition, the following equation: Volume shrinkage (%) = ｛(100-paint solid content at application)
/ Solvent specific gravity｝ / ｛(100-paint solid content at the time of coating) / Solvent
Agent ratio {+ (solid content at coating / specific gravity of dried coating film)} × 10
0.

<Chip resistance>
After cooling to 0 ° C., this was mounted on a sample holder of a stepping stone tester (manufactured by Suga Test Instruments Co., Ltd.) so that the angle of approach of the stone was 90 °, and 100 g of No. 7 crushed stone was injected at an air pressure of 3 kg / cm ^2. Then, the crushed stone was caused to collide with the surface of the coating film of the coated plate. The degree of peeling of the coating film (number, size, peeling place) at that time was evaluated according to the following evaluation criteria. ：: Some peeling was found to some extent, and no peeling from the substrate was found. ×: Peeling from the substrate was found, or peeling was found on the entire surface.

<Coating Film Appearance> The appearance of the obtained coating film was visually evaluated. The evaluation criteria were as follows. (1) Najimi ○: Najimi is not seen and it is good ×: Najimi is seen (2) Smoothness ○: Good ×: Round is seen

[0077]

[Table 1]

As is clear from Table 1, Examples 1 to 3 containing a polyoxyalkylene glycol as the hydroxyl group-containing resin composition were able to achieve both the appearance of the coating film and the chipping resistance.

[0079]

The intermediate coating composition of the present invention contains a hydroxyl group-containing resin composition containing a predetermined amount of polyoxyalkylene glycol, a curing agent and a non-aqueous dispersion resin.
A coating film obtained by using the wet-on-wet coating method of the intermediate coating and the top coating using this is excellent in chipping resistance. This is considered that polyoxyalkylene glycol has a function of relieving external stress. In addition, since it has a hydroxyl group, the curability of the coating film in a predetermined amount is not impaired.

The appearance of the obtained coating film is also good.
This is presumably because the non-aqueous dispersion resin suppresses the swelling of the uncured intermediate coating film due to the solvent contained in the top coat. Further, since polyoxyalkylene glycol has many ether groups, it has high polarity, which is also considered to suppress swelling of the uncured intermediate coating film due to the solvent contained in the top coating material.

Since the intermediate coating of the present invention has a high coating solid content at the time of application, the load on the environment is small, and the formation of a coating film using a wet-on-wet coating method of the intermediate coating and the top coating. The method has a small environmental load and can greatly contribute to resource saving and energy saving.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4J038 CG002 CG141 CG142 CH121 CH122 CJ001 CJ002 DD041 DD042 DF021 DF022 DN012 GA03 KA08 MA07 MA13 MA14 PB07 PC02 PC03 PC08

Claims (6)

[Claims] 1. A hydroxyl group-containing resin composition containing polyoxyalkylene glycol (a) in an amount of 10 to 70% by weight and a hydroxyl group-curable curing agent (b) in an amount of 10 to 70% by weight, based on the total solid content of the resin composition. And non-aqueous dispersion resin (c)
A film-forming resin composition containing 18 to 50% by weight;
In the intermediate coating composition containing a pigment, the weight ratio of the solid content of the polyoxyalkylene glycol contained in the hydroxyl group-containing resin composition (a) to the other hydroxyl group-containing resin is 5/95 to 50/50. An intermediate coating composition, comprising: 2. The polyoxyalkylene glycol according to claim 1,
2. The polytetramethylene ether glycol according to claim 1,
The intermediate coating composition according to the above. 3. The polytetramethylene ether glycol has a number average molecular weight of 650 to 2,000.
The intermediate coating composition according to the above. 4. The content of the pigment is from 10 to 10% based on the total weight of the solid content of the film-forming resin composition and the pigment.
The intermediate coating composition according to any one of claims 1 to 3, which is 70% by weight. 5. The method according to claim 1, wherein after applying the coating composition, the coating composition is heated at 140 ° C. for 30 minutes to have a volume shrinkage of 45% or less. Coating composition. 6. A step (1) of applying an intermediate coating on an object to be coated on which an electrodeposition coating film is formed to form an uncured intermediate coating, and the uncoated intermediate coating obtained in the step (1). (2) forming an uncured top coat by applying a top coat on the cured middle coat, the uncured middle coat obtained in the step (1) and the step (2). A method for forming a coating film comprising a step (3) of heating and curing the uncured top coating film obtained at the same time to obtain a coating film, wherein the intermediate coating material is any one of claims 1 to 5. A method for forming a coating film, which is the intermediate coating composition according to any one of the first to third aspects.