JP2002038103A - Intermediate coating composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an intermediate coating composition capable of providing an excellent finishing appearance in a 3-coat-1-bake method or 2-coat-1-bake method of coating the intermediate coating material, further coating a final coating material by a wet-on-wet method, and simultaneously baking and hardening the intermediate coating material and the final coating material when coating an automobile body or the like. SOLUTION: This intermediate coating composition contains (a) 10-70 wt.% hydroxy-containing resin, (b) 10-70 wt.% hardening agent reactable with the hydroxy group and (c) 18-50 wt.% nonaqueous dispersion resin expressed in terms of solid component, based on the total amount of solid resin components, and further contains a pigment. The intermediate coating composition is characterized in that the volume shrinkage when the composition is hardened at 140 deg.C for 30 min after coating is <=45%.

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 used for an automobile body or the like, and more particularly, to an intermediate coating composition applied to an automobile body or the like and a wet-on-wet method applied thereon. The present invention relates to an intermediate coating composition suitable for a so-called three-coat one-bake method or two-coat one-bake method in which a top coat, that is, a base paint and a clear paint or a solid paint are applied and baked and cured at one time.

[0002]

2. Description of the Related Art Automobile bodies and the like are subjected to a chemical conversion treatment using zinc phosphate or the like as a coating base on the surface of a steel sheet to be coated, and then to a base coat, a middle coat and a top coat, to form a double coat. A layer coating is formed. Of these, the coating process is usually performed by applying an undercoat by electrodeposition coating, baking and curing to form an undercoat film, applying an intermediate coating film thereon, baking and curing to form an intermediate coating film. ,
The top coat is applied, and the undercoat, intermediate coat and top coat are baked and hardened separately after each coating.

When a base paint and a clear paint are used as a top coat, an intermediate paint is applied, baked and cured, and then the base paint and the clear paint are wet-coated.
It is performed by a so-called three-coat two-bake method, in which the coating is applied by an on-wet method and then baked and cured at a time. In addition, even when a solid paint is used as the top coat, when the clear paint is applied on the solid paint, the same 3 coat 2 bake method is used as above, and when the clear paint is not used,
This is performed by a so-called two-coat two-bake method in which baking and curing are performed separately after each coating.

[0004] The three-coat two-bake method or the two-coat two-bake method has a problem that the total cost is high because the coating step is long and the energy consumption is large. JP-B-59-33033 discloses a metallic coating method in which an undercoat is applied by electrodeposition coating, baking is performed, then an intermediate coating and a metallic coating are applied and baking is performed at the same time. However, when this method is carried out using a conventional intermediate coating, three coats 2 in which the intermediate coating is applied and then baked and hardened once are applied.
There has been a problem that the finished appearance is inferior to the bake method or the two-coat two-bake method.

[0005] JP-A-10-5680 discloses an intermediate coating and / or a metallic base coating, or an intermediate coating and / or a solid coating.
Using the one to which the cross-linkable polymer fine particles (microgel) is added, apply the intermediate coating, and apply the top coating, that is, the metallic base coating and the clear coating, or the solid coating by the wet-on-wet method. A method of simultaneously baking and curing an intermediate coating and a top coating is described. These crosslinkable polymer fine particles (microgels) are added for the purpose of preventing each paint from being mixed at the interface of the coating to make the interface unclear, and have high sharpness and gloss. The appearance of the coating is obtained.

However, this method can provide a sufficient coating appearance when painting a small area and a portion that is not conspicuous, such as when a part of an automobile body is painted with a different color. When all the outer plates were coated by this method, the finished appearance was insufficient.

By the way, non-aqueous dispersion resin (N
AD) has been used for metallic coating of equipment, automobiles, etc. because of its low pollution, resource saving, and excellent coating workability and durability due to its flow characteristics. JP-A-57-177068 discloses a non-aqueous dispersible resin coating composition containing dispersed particles obtained by graft-polymerizing a monomer component in the presence of an acrylic copolymer. According to this, a coating film having excellent surface hardness and impact resistance can be obtained by dispersing the dispersed particles in the coating film even after curing to form a non-uniform structure.

[0008]

SUMMARY OF THE INVENTION The present invention relates to a method of applying an intermediate coating when coating an automobile body or the like, and applying a top coating by a wet-on-wet method, that is, a base coating and a clear coating, or a solid coating. A method of applying a base paint and simultaneously baking and curing the intermediate coat and the top coat to obtain an excellent or better finished appearance as compared with the conventional three-coat two-bake method or two-coat two-bake method It is an object of the present invention to provide an intermediate coating composition which can be used.

The present inventors have found that in the case of the conventional three-coat two-bake method or two-coat two-bake method in which baking and curing are performed after the application of an intermediate coating, the base material has high concealing properties, The surface roughening of the electrodeposition coating film formed by the above does not have much effect on the coating film coated with the top coating after coating and curing the intermediate coating, but the baking and curing is performed after applying the intermediate coating. In the case of a three-coat one-bake method or a two-coat one-bake method in which a top coat is applied by a wet-on-wet method and baked and cured at the same time, the base coat concealing property is low and the electrodeposition formed by the electrodeposition paint It was found that roughening of the surface of the coating film greatly affected the final finished appearance, and that the appearance of wrinkled skin was exhibited. In order to improve the concealing property of the undercoating with respect to the electrodeposition coating film, it is necessary to use (1) a solvent contained in the topcoating material when the topcoating material is applied by a wet-on-wet method after applying the intermediate coating material. (2) In the process of baking and curing the intermediate coating and the top coating, the solvent evaporates and the volume of the coating decreases, but this volume shrinkage is reduced. (3) In the process of baking and curing the intermediate coating and the top coating, the viscosity initially decreases as the temperature rises, and when the curing starts, the viscosity starts to increase, but the minimum viscosity in this baking process is reduced. It is thought that it is important that the coating film has flowability even if the volume shrinks, and as a component of the intermediate coating, the non-aqueous dispersion resin Found that the inclusion of (NAD), and completed the present invention.

[0010]

According to the present invention, a hydroxyl group-containing resin (a) of 10 to 7 is used as a solid content ratio based on the total resin solid content.
0% by mass, curing agent (b) 10-70 which can react with a hydroxyl group
% By mass and non-aqueous dispersion resin (c) 18 to 50
An intermediate coating composition comprising a pigment and a pigment, and having a volume shrinkage of 45% or less when cured at 140 ° C. for 30 minutes after coating. It is a coating composition.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The intermediate coating composition of the present invention contains a hydroxyl group-containing resin (a). The hydroxyl group-containing resin (a) means a resin containing a hydroxyl group and soluble in a medium used for the intermediate coating composition, and examples thereof include an acrylic resin and / or a polyester resin. It is preferable to use an acrylic resin because it can be designed to have a high SP value. As the polyester resin, a resin composed of a polyol and a polycarboxylic acid or an anhydride thereof can be used.

The hydroxyl group-containing resin (a) has a hydroxyl value of 5
0-250, acid value 1-50 mgKOH / g, SP value 9.
What is 5-12 is preferable. Hydroxyl value, acid value and S
If the P value exceeds the upper limit of these ranges, the water resistance of the coating film decreases. If the hydroxyl value and the acid value are less than the lower limits, the curability of the paint will be reduced, and if the SP value is less than the lower limits, the paint will be compatible with the base paint. The hydroxyl group-containing resin (a) has a number average molecular weight of 1,000 to 1,000.
0, but preferably 1100 to 5000, more preferably 1200 to 3000. By using the above range, the intermediate coating composition of the present invention can be made into a high solid type, so that volume shrinkage when baked and cured is reduced, and the finished appearance of the coating film is improved. Can be.

In the present specification, the SP value is called a solubility parameter and indicates a measure of solubility. The SP value was written by SUH and CLARKE.
J. Polymer Science, A-1, 5th
Volume, pages 1671 to 1681 (1967). That is, at a measurement temperature of 20 ° C.,
As a sample, 0.5 g of a resin was weighed into a 100 mL beaker, and 10 mL of a good solvent was added using a whole pipette.
Dissolve with a magnetic stirrer. Dioxane and acetone are used as good solvents, and n
-Use hexane and ion-exchanged water. The turbid point measurement is 50
The poor solvent was added dropwise using a mL burette, and the point at which turbidity occurred was taken as the amount of addition. The SP value δ of the resin can be calculated by the following equation. δ = (V _ml ^1/2 δ _ml + V _mh ^1/2 δ _mh ) / (V _ml ^1/2 + V
^{_{mh 1/2) V m = V 1}} V 2 / (φ 1 V 2 + φ 2 V 1) δ m = φ 1 δ 1 + φ 2 δ 2 V i: solvent molecular volume (mL / mol) φ _i: turbidity point Δ _i : SP value of solvent ml: low SP value poor solvent mixture system MH: high SP value poor solvent mixture system

The hydroxyl group-containing resin (a) is contained in an amount of 10 to 70% by mass in terms of solid content based on the total amount of resin solid content. When the amount is less than 10% by mass, the obtained coating film becomes brittle or the appearance of the coating film is deteriorated, so that the basic performance of the coating film is inferior. If it exceeds 70% by mass, the blending ratio of the non-aqueous dispersion resin (c) is reduced, and as a result, the finished appearance of the coating film is reduced. Preferably, it is 10 to 50% by mass, more preferably 20 to 50% by mass.

The intermediate coating composition of the present invention contains a curing agent (b) capable of reacting with a hydroxyl group. The curing agent (b) is not particularly limited, and includes, for example, a melamine resin and / or a blocked isocyanate resin. The curing agent (b) is contained in a solid content of 10 to 70% by mass based on the total resin solid content. If the amount is less than 10% by mass, curing may be insufficient, and the physical properties of the coating film may be poor. If it exceeds 70% by mass, it is uneconomical and the finished appearance of the coating film deteriorates. Preferably, 20
５０50% by mass. The combination of the hydroxyl group-containing resin (a) and the curing agent (b) capable of reacting with a hydroxyl group is not particularly limited, but from the viewpoint of pigment dispersibility and workability, an acrylic resin and / or a polyester resin is combined with a melamine resin. Is preferred.

The intermediate coating composition of the present invention contains a non-aqueous dispersion resin (c). The non-aqueous dispersion resin (c) has a core with a high SP value and a low S
It consists of a shell part with a P value. High S core
Since it has a P value, it is insoluble in the solvent in the paint, so that the swelling ratio due to the solvent can be reduced, and furthermore, the color return caused by delicate mixing with the base coating film can be prevented. Can be. The shell part with low SP value is
It acts as a dispersion stabilizer. Further, since the non-aqueous dispersion resin (c) is a non-crosslinked particle, the minimum viscosity during baking can be reduced. Also, the particles themselves can be cross-linked by the curing agent (b) capable of reacting with the above-mentioned hydroxyl group. In this case, the particles can be used as a coating film forming component, so that the amount of the particles can be increased. Therefore, the non-aqueous dispersion resin (c) has a large undercoat concealing property of the electrodeposition coating film, can suppress the occurrence of unpleasant skin, and can provide a coating film appearance with high sharpness and gloss.

JP-A-10-5680 discloses the addition of crosslinkable polymer microparticles (microgels) to an intermediate coating composition, which is added as a viscosity-imparting agent and blends between layers. To prevent inversion and inversion,
The purpose of the present invention is to obtain a coating film having high sharpness and gloss. However, since the particles themselves are crosslinked and cannot be a coating film forming component, the addition amount is limited to 15% by mass or less, and as a result, the ratio contributing to the reduction of the swelling ratio due to the solvent is reduced. It was small.

Non-aqueous dispersion resin (c) of the present invention
Also acts as a viscosity-imparting agent, prevents conformation or inversion between layers, and provides a coating film with high sharpness and gloss. Furthermore, this is a non-crosslinked particle having a core portion with a high SP value, and can be added in a high amount, so that not only the ratio contributing to the reduction of the swelling ratio due to the solvent is large, but also the intermediate coating. The crosslinkable polymer fine particles (the above-described crosslinkable polymer fine particles ( Microgel).

The non-aqueous dispersion resin (c) is
The SP value is 11 to 14, and the S value of the core portion and the shell portion is
It is preferable that the difference between the P values is 0.5 to 3. If the difference in SP value is less than 0.5, the non-volatile content of the paint cannot be reduced, and the coating will dissolve and swell, and the viscosity control effect of the core portion will be low. , And furthermore, the film becomes compatible with the base paint, and a coating film having an excellent finished appearance cannot be obtained. If the SP value difference exceeds 3, dispersion may become unstable, separation may occur, or the intermediate coating and the base coating may be mixed to cause inversion or cracking. Preferably, the difference in SP value is 1-3. The relationship between the SP value of the hydroxyl group-containing resin (a) and the SP value of the non-aqueous dispersion resin (c) is such that the compatibility with the base paint can be suppressed. Is preferably higher.

The non-aqueous dispersion resin (c) has a hydroxyl value of 100 to 400, preferably 130 to 400.
300. If it is less than 100, the curability of the coating material will decrease, and if it exceeds 400, the water resistance may decrease. The acid value is from 0 to 200 mgKOH / g, preferably from 0 to 50 mgKOH / g. 200mgK
If it exceeds OH / g, the water resistance of the coating film decreases. Average particle size (D _50), 0.05 to 5 [mu] m, preferably 0.05 to 1 [mu] m. If it is less than 0.05 μm, the non-volatile content of the coating material is reduced, and if it exceeds 5 μm, the effect of controlling the viscosity is poor and the appearance is poor. The Tg of the dispersion stable resin is preferably 30 ° C. or lower. If it exceeds 30 ° C., the appearance of the coating film is inferior and the chipping resistance is reduced.

The non-aqueous dispersion resin (c) is
By polymerizing a polymerizable monomer in a mixture of a dispersion stable resin and an organic solvent, non-crosslinked resin particles insoluble in this mixture can be prepared. The dispersion-stable resin constitutes the shell part, and the copolymerized polymerizable monomer constitutes the core part.

As the polymerizable monomer, a monomer having a functional group is preferable. The monomer having a functional group can form a three-dimensionally cross-linked coating film by reacting the obtained non-aqueous dispersion resin with the curing agent (b) capable of reacting with the hydroxyl group. Representative examples of the polymerizable monomer having the above functional group are as follows. As those having a hydroxyl group, for example, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate,
Examples thereof include hydroxybutyl (meth) acrylate, hydroxymethyl (meth) acrylate, allyl alcohol, and adducts of hydroxyethyl (meth) acrylate with ε-caprolactone.

On the other hand, those having an acid group include those having a carboxyl group, a sulfonic acid group and the like. Examples of those having a carboxyl group include (meth) acrylic acid, crotonic acid, ethacrylic acid, propyl Acrylic acid, isopropyl acrylic acid, itaconic acid, maleic anhydride, fumaric acid and the like can be mentioned. Examples of those having a sulfonic acid group include t-butylacrylamide sulfonic acid. When a polymerizable monomer having an acid group is used, a part of the acid group is preferably a carboxyl group. Further, a glycidyl group-containing unsaturated monomer such as glycidyl (meth) acrylate, m-isopropenyl-
Isocyanate group-containing unsaturated monomers such as α, α-dimethylbenzyl isocyanate and isocyanatoethyl acrylate are also included.

Other polymerizable monomers include, for example,
Methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate,
T-butyl (meth) acrylate, isobutyl (meth) acrylate, 2-ethylhexyl (meth) acrylate,
(Meth) alkyl acrylates such as n-octyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate and tridecyl methacrylate; acrylic acid or methacrylic acid ester monomers having an oil fatty acid and an oxirane structure (E.g., an addition reaction product of stearic acid and glycidyl methacrylate); an addition reaction product of an oxirane compound containing an alkyl group having at least C ₃ and acrylic acid or methacrylic acid; styrene, α-methylstyrene, o- Methyl styrene, m-methyl styrene, p-methyl styrene, pt-butyl styrene; benzyl (meth) acrylate; itaconic acid ester (dimethyl itaconate); maleic acid ester (dimethyl maleate); fumaric acid ester (Dimethyl fumarate, etc.); Acrylonitrile, methacrylonitrile; methyl isopropenyl ketone; vinyl acetate; veoba monomer (trade name, manufactured by Shell Chemical Co., Ltd.), vinyl propionate, vinyl pivalate, vinyl propionate; ethylene, propylene, butadiene, N, N-dimethylaminoethyl Acrylate, N, N-dimethylaminoethyl methacrylate, acrylamide, vinylpyridine and the like can be mentioned. The above-mentioned polymerizable monomers can be used alone or in combination of two or more of those having a functional group and other monomers.

The above polymerizable monomer is preferably copolymerized in the presence of a radical polymerization initiator. Examples of the radical polymerization initiator include azo initiators such as 2,2'-azobisisobutyronitrile and 2,2'-azobis (2,4-dimethylvaleronitrile); benzoyl peroxide, lauryl peroxide And a peroxide-based initiator such as t-butyl peroctoate. The amount of these initiators to be used is preferably 0.2 to 10 parts by mass, more preferably 0.5 to 5 parts by mass per 100 parts by mass of the total of the polymerizable monomers. In general, the polymerization reaction in an organic solvent containing a dispersion-stable resin is preferably performed in a temperature range of about 60 to 160 ° C. for about 1 to 15 hours.

The dispersion-stable resin to be present when the above-mentioned polymerizable monomer is copolymerized is not particularly limited as long as it can stably synthesize a non-aqueous dispersion resin in an organic solvent. Specifically, the hydroxyl value is 10 to 25.
0, preferably 20 to 180. If it is less than 10, the curability, adhesion, stability and the like will be reduced, and if it exceeds 250, the dispersion will be unstable. Acid value is 0-100mgK
OH / g, preferably 0 to 50 mgKOH / g.
If it exceeds 100 mgKOH / g, the water resistance of the coating film decreases. The number average molecular weight is 2000 to 1
0000 is preferred. If it is less than 2,000, dispersion becomes unstable, and if it exceeds 10,000, the non-volatile content of the coating material decreases.

The method for producing the dispersion-stable resin is not particularly limited, and examples thereof include a method obtained by radical polymerization in the presence of a radical polymerizable initiator, a method obtained by a condensation reaction and an addition reaction, and the like. As the dispersion stable resin, an acrylic resin, a polyester resin, a polyether resin, a polycarbonate resin, a polyurethane resin, or the like can be used. The monomer used to obtain the dispersion-stable resin can be appropriately selected according to the properties of the resin, but has a functional group such as a hydroxyl group or an acid group used in the polymerizable monomer. It is preferable to use a monomer, and if necessary, a monomer having a functional group such as a glycidyl group or an isocyanate group may be used. The monomer having a functional group can form a three-dimensionally cross-linked coating film by reacting the obtained non-aqueous dispersion resin with the curing agent (b).

The monomer used to obtain the above-mentioned dispersion-stable resin preferably has 10 to 50% by mass of a monomer having a side chain having 10 or more carbon atoms based on the total amount of the monomer. If the content is less than 10% by mass, conformity with the base paint occurs. If it exceeds 50% by mass, separation may occur in the intermediate coating, or the intermediate coating and the base coating may be mixed to cause inversion or cracking.

Further, it is preferable that the above monomer has a hydrophilic group in an amount of 20 to 50% by mass based on the total amount of the polymerizable monomer. If the amount is less than 20% by mass, the curability, adhesion and stability may be poor. If it exceeds 50% by mass, the dispersibility may be unstable. Examples of the hydrophilic group include a hydroxyl group, a carboxyl group, an amide group, and an ether group.

The ratio of the above-mentioned dispersion stabilizer to the above-mentioned polymerizable monomer can be arbitrarily selected depending on the intended purpose.
-80 mass%, preferably 5-60 mass%, and the polymerizable monomer is 97-20 mass%, preferably 95-40 mass%. Further, the total concentration of the dispersion stabilizer and the polymerizable monomer in the organic solvent is 30 to 80% by mass, preferably 40 to 60% by mass based on the total mass.

The non-aqueous dispersion resin (c) thus obtained contains 18 to 50% by mass of the solid content based on the total solid content of the resin. If the amount is less than 18% by mass or more than 50% by mass, the appearance of the obtained coating film deteriorates. Preferably, it is 23 to 45% by mass.

The intermediate coating composition of the present invention comprises the above-mentioned hydroxyl group-containing resin (a), a curing agent (b) capable of reacting with a hydroxyl group, and a non-aqueous dispersion resin (c), and further contains a pigment. Things. The pigment is preferably contained in an amount of 10 to 70% by mass based on the total amount of the pigment and the solid content of the resin. In the present invention, the resin solid content means the total amount of the solid content of the hydroxyl group-containing resin (a), the curing agent (b) capable of reacting with the hydroxyl group, and the non-aqueous dispersion resin (c). When the content is less than 10% by mass, the obtained intermediate coating composition cannot be made into a high solid system, and the volume shrinkage becomes large when baked and cured,
The finished appearance may be poor. If it exceeds 70% by mass, the appearance of the coating film is deteriorated because the amount of the pigment is too large.

The above-mentioned pigments are not particularly limited, and include those used in conventional intermediate coating compositions, such as azochelate pigments, insoluble azo pigments, condensed azo pigments, phthalocyanine pigments, indigo pigments, and the like. Organic coloring pigments such as perinone pigments, perylene pigments, dioxane pigments, quinacridone pigments, isoindolinone pigments, metal complex pigments; inorganic colorings such as graphite, yellow iron oxide, red iron oxide, carbon black, and titanium dioxide Pigments and the like. Further, extenders such as calcium carbonate, barium sulfate, clay and talc; and flat pigments such as aluminum powder and mica powder may be used in combination. As the above pigment, a standard gray intermediate paint having carbon black and titanium dioxide as main pigments can be used, or a so-called color combining a set gray or various color pigments combining lightness or hue with an overcoat paint. Intermediate paints can also be used.

The intermediate coating composition of the present invention may contain conventionally known additives, for example, a viscosity controlling agent, an anti-bake agent, a diluting solvent and the like. As the viscosity control agent,
Polyamides such as swelling dispersions of fatty acid amides, amide fatty acids, and phosphates of long-chain polyaminoamides; polyethylenes such as colloidal swelling dispersions of polyethylene oxide; organic acids such as smectite clay and montmorillonite Bentonite-based inorganic pigments such as aluminum silicate and barium sulfate; flat pigments which exhibit viscosity depending on the shape of the pigment;

The above intermediate coating composition is prepared by mixing a hydroxyl group-containing resin (a), a curing agent (b) reactive with hydroxyl groups, a non-aqueous dispersion resin (c), and a pigment or other components with a kneader or a roll. And the like, and kneading and dispersing can be performed by a method known to those skilled in the art. The nonvolatile content of the intermediate coating composition thus obtained is preferably 40 to 70% by mass at the time of application. 40% by mass
When the amount is less than the above range, the amount of the solvent is too large, so that a high solid type intermediate coating composition cannot be obtained, and the volume shrinkage ratio becomes large, so that the finished appearance of the coating film may be poor.
If it exceeds 70% by mass, the viscosity is too high, so that the appearance of the coating film may be poor or the workability may be low. More preferably, it is 45 to 60% by mass.

After coating, the intermediate coating composition of the present invention can
The volume shrinkage when cured at 40 ° C. for 30 minutes is 45
% Or less. If it exceeds 45%, the base coat concealing property of the electrodeposition coating film is inferior, so that a coating film having a good finished appearance cannot be obtained. Preferably, it is at most 40%. In the present invention, the volume shrinkage when cured at 140 ° C. for 30 minutes can be obtained by the following equation. Volume shrinkage (%) = {(100-coating NV) / solvent specific gravity} / [{(100-coating NV) / solvent specific gravity} + (coating NV / dry coating specific gravity)} × 100 (wherein The weight of the coated object before coating is W1, the weight of the coated object after coating is W2, and the weight after drying at 140 ° C. for 30 minutes is W3. (%) = (W3-W1) / (W2-W1) × 1
Represents the value of the non-volatile content obtained by 00. 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 intermediate coating composition of the present invention can be used for various substrates, for example, metals, glass, plastics, foams and the like, and can be suitably used particularly for metal products which can be subjected to cationic electrodeposition coating. As the metal product, for example,
Iron, copper, aluminum, tin, zinc, etc .; and 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 have been previously subjected to a chemical conversion treatment with a phosphate, a chromate, or the like.

When the intermediate coating composition of the present invention is applied to an automobile body or the like, the base coating is applied to an electrodeposition-coated object by a wet-on-wet method, and then a clear coating is applied. 3 coats for baking and curing intermediate paint, base paint and clear paint simultaneously
It can be suitably used in the bake method. When the top coating is a solid coating, the intermediate coating composition of the present invention is applied to the electrodeposition-coated substrate, and then the wet coating is applied.
The intermediate coating composition of the present invention is applied to an object to be coated by applying a solid coating in an on-wet method, and simultaneously baking and curing the intermediate coating and the solid coating. After applying, wet on
It can be suitably used in a three-coat one-bake method in which a solid paint and a clear paint are sequentially applied by a wet method, and the intermediate paint, the solid paint and the clear paint are simultaneously baked and cured.

The intermediate coating composition of the present invention is applied to a substrate to which electrodeposition has been applied and then baked and cured.
In the conventional three-coat two-bake method in which a base paint and a clear paint are applied and the base paint and the clear paint are simultaneously baked and cured, and in the two-coat two-bake method conventionally used in the case of a solid paint, good results are obtained. A coating film having an appearance can be obtained. However, the above 3
The effect of the present invention that the use of the coat 1 bake method or the 2-coat 1 bake method in the case of using a solid paint is excellent in the base layer concealing property and that a coated film with a good finished appearance can be obtained is remarkable. It is preferable to use these methods because they can be obtained.

Furthermore, the baking step of the intermediate coating can be omitted as compared with the conventional three-coat two-bake method and the conventional two-coat two-bake method for solid paints. Therefore, since the coating process can be shortened and energy consumption can be reduced, the total cost can be significantly reduced. Preferably, it is used in the one-bake method.

In the three-coat one-bake method and the two-coat one-bake method when a solid paint is used, it is preferable to use a high-solid base paint and a clear paint or a solid paint. The non-volatile content of the base paint and solid paint is 30 to 6 at the time of painting.
0% by mass, more preferably 40% by mass.
50% by mass. The nonvolatile content of the clear coating is preferably 40 to 70% by mass at the time of coating, and more preferably 45 to 60% by mass. Not only the intermediate coating, but also a base coating and a clear coating or a solid coating, using a high solid type coating, the total volume shrinkage when applied by a 3-coat 1-bake method or a 2-coat 1-bake method. Since the ratio can be reduced, a coating film having a very excellent finished appearance can be obtained. The coating method and the curing method using the intermediate coating composition of the present invention are not particularly limited, and
The base paint, clear paint, and solid paint used in combination therewith are not particularly limited, and those widely used conventionally can be used.

[0042]

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 Examples, "parts" represents parts by mass. Synthesis Example 1 Synthesis of Acrylic Resin 1 A container equipped with a stirrer, a temperature controller and a reflux condenser was charged with 82 parts of xylene, and then a solution having the following composition: 4.5 parts of methacrylic acid 26.0 parts of ethyl acrylate FM-1 64.5 parts (hydroxyl-containing monomer manufactured by Daicel Chemical Industries, Ltd.) MSD-100 5.0 parts (Methylstyrene dimer manufactured by Mitsui Toatsu Chemicals) 20 parts of azoisobutyronitrile 13.0 parts are added. The mixture was heated with stirring to increase the temperature. While refluxing, the remaining 93.0 of the mixed solution
Then, a solution consisting of 1.0 part of azoisobutyronitrile and 12 parts of xylene was added dropwise over 30 minutes. After the reaction solution was further stirred and refluxed for 1 hour, 63 parts of the solvent was distilled off under reduced pressure to terminate the reaction.
Acrylic resin varnish 1 having a solid content of 75% and a number average molecular weight of 2,000 was obtained.

Synthesis Example 2 Synthesis 2 of Acrylic Resin A container equipped with a stirrer, a temperature controller and a reflux condenser was charged with 300 parts of toluene and methyl isobutyl ketone (MIB).
K) 100 parts were charged and heated with stirring to raise the temperature. When the temperature rose to 105 ° C., a solution having the following composition was dropped at a constant speed over 3 hours while refluxing. Styrene 50.0 parts Methyl methacrylate 300.0 parts Ethyl methacrylate 79.0 parts Ethyl acrylate 444.0 parts 2-hydroxyethyl methacrylate 104.0 parts Methacrylic acid 23.0 parts Toluene 400.0 parts t-butyl 7.0 parts of peroxy-2-ethylhexanoate After aging for 30 minutes, a solution composed of 200 parts of toluene and 3 parts of t-butylperoxy-2-ethylhexanoate was dropped at a constant speed for 30 minutes. The reaction solution was further stirred and refluxed for 1 hour to increase the rate of change into a resin, and then the reaction was terminated to obtain an acrylic resin varnish 2 having a solid content of 50% and a number average molecular weight of 21,000.

Synthesis Example 3 Synthesis of Polyester Resin A reaction vessel equipped with a thermometer, a stirrer, a cooling pipe, a nitrogen inlet pipe, a water separator, and a rectification tower was charged with 258 hexahydrophthalic anhydride.
Parts, 184 parts of isophthalic acid, trimethylolpropane 2
13 parts, 180 parts of neopentyl glycol, 72 parts of neopentyl glycol hydroxypivalate, and 94 parts of Kadura E (glycidyl versatic acid ester manufactured by Shell Chemical Co., Ltd.) were charged and heated. After the raw materials have been melted and stirred, dibutyltin oxide 0.2
And stirring was started, and the temperature of the reaction tank was raised from 180 ° C. to 2
The temperature was raised to 20 ° C. over 3 hours while maintaining a constant rate of temperature increase. The generated condensed water was distilled out of the system. When the temperature reached 220 ° C., the temperature was maintained for 1 hour, and 17 parts of xylene was gradually added as a refluxing solvent in the reaction vessel to allow the condensation reaction to proceed in the presence of the solvent. When the resin acid value reaches 10.0,
After cooling to 150 ° C., 182 parts of Praxel M (ε-caprolactone, manufactured by Daicel Chemical Industries, Ltd.) were added dropwise, and the mixture was kept warm for 1 hour and then cooled to 100 ° C. Further, 264 parts of xylene was added, the solid content was 79%, the number average molecular weight was 1,400, and the acid value was 8.
0 (mgKOH / g) and a polyester resin solution having a hydroxyl value of 210 were obtained.

Synthesis Example 4 Synthesis of Nonaqueous Dispersion Resin (a) Production of Dispersion-Stable Resin A container equipped with a stirrer, a temperature controller and a reflux condenser was charged with 90 parts of butyl acetate, and then a solution having the following composition: Methyl methacrylate 38.9 parts Stearyl methacrylate 38.8 parts 2-Hydroxyethyl acrylate 22.3 parts 20 parts of azoisobutyronitrile 5.0 parts were added, and the mixture was heated with stirring to increase the temperature. . At 110 ° C., the remaining 85 parts of the above mixed solution was added dropwise over 3 hours, and then a solution composed of 0.5 parts of azoisobutyronitrile and 10 parts of butyl acetate was added dropwise over 30 minutes. The reaction solution was further stirred and refluxed for 2 hours to increase the rate of conversion into a resin, and then the reaction was terminated to obtain an acrylic resin having a solid content of 50%, a number average molecular weight of 5,600 and an SP value of 9.5.

(B) Production of Nonaqueous Dispersion Resin 35 parts of butyl acetate is charged into a container equipped with a stirrer, a temperature controller and a cooler, and the acrylic resin 60 obtained in the above (a) production of dispersion stable resin is prepared. The department was charged. Next, a solution having the following composition: styrene 7.0 parts methacrylic acid 1.8 parts methyl methacrylate 12.0 parts ethyl acrylate 8.5 parts 2-hydroxyethyl acrylate 40.7 parts azoisobutyronitrile 1.4 parts Was added dropwise at 100 ° C. for 3 hours, and then a solution consisting of 0.1 part of azoisobutyronitrile and 1 part of butyl acetate was added to 30 parts of the solution.
In minutes. When the reaction solution was further stirred for 1 hour, an emulsion having a solid content of 60% and a particle size of 0.18 μm was obtained. This emulsion is diluted with butyl acetate,
A butyl acetate dispersion having a viscosity of 300 cps (25 ° C.) and a non-aqueous dispersion resin content of 40% by mass having a particle size of 0.18 μm was obtained. The Tg of this non-aqueous dispersion resin is
At 23 ° C., the hydroxyl value was 162. The SP value is 11.
The difference between the SP value of the shell portion and the SP value of the core portion, which was a dispersion-stable resin, was 2.3.

Embodiment 1Preparation of intermediate coating  The acrylic resin wafer obtained in Synthesis Example 1 was placed in a 2 L vessel.
328 parts of varnish 1 were put in, followed by CR-93 (Ishihara Sangyo
973 parts of Titanium Oxide, FW-200P (Degussa)
10 parts, and 159 parts of butyl acetate
And 82 parts of xylene. After that, the whole quality
The same amount of glass beads (product name GB503M, particle size 1.
6 mm) and dispersed for 3 hours with a desktop SG mill. The
The particle size at the end of dispersion with a lined gauge is 5 μm or less.
there were. Finally, about 10 minutes after adding 81.8 parts of xylene
Stir and filter the glass beads to make a pigment paste.
Was. The solid content ratio of the prepared paste is as shown in Table 2.
In this way, the resin, non-aqueous dispersion resin and hardener
Together, an intermediate coating was prepared.

[0048]Base paint and clear paint  As a base paint, SPM-13 having a nonvolatile content of 46%
00 black (Nippon Paint Co .; black base paint),
As a clear paint, MACO with a non-volatile content of 48%
-1330 (manufactured by Nippon Paint Co., Ltd.) was used.Dilution conditions  Each paint was diluted under the following conditions and painted. (Intermediate coating) Thinner: EEP (ethoxyethyl propionate) /
Xylene = 9/11 19 seconds / No. 4 Ford cup / 20 ° C (base paint) Thinner: EEP / S-100 (exxon aromatic resin)
(Hydrocarbon solvent) / ethyl acetate = 8/7/5 20 seconds / No. 4 Ford cup / 20 ° C (clear paint) Thinner: EEP / S-150 (Axon aromatic product)
(Hydrocarbon solvent) = 1/1 22 seconds / No. 4 Ford cup / 20 ℃

[0049]Painting method  Under the coating conditions shown in Table 1, an SPC dull steel plate (20 cm × 3
0cm x 0.8mm) Power Top V-20
Into Co., Ltd. cationic electrodeposition paint)
The electrodeposited cation-coated plate to the moving plate
Apply the intermediate coating while moving while attached, 10 minutes later
Apply base paint to the base, and base again after 2.5 minutes
Apply paint (two-stage painting), and then after 20 minutes, clear
Paint. Painted intermediate coating film, base coating film
And clear coating is baked and cured at 140 ° C for 30 minutes
I let it.

[0050]

[Table 1]

[0051]Appearance evaluation  The appearance of the painted plate is compared with Big Chemie Wave Ski
The evaluation was made based on the value of the SW of Jan. The results are shown in Table 2. Number
A smaller value indicates that a better result was obtained.

[0052]Painted NV (Nonvolatile content) measurement method  Separate for intermediate coating, base coating and clear coating
And calculated according to the following method. Instrument: 5 cm × 1 aluminum foil whose mass (w1) was measured
Mask the one covered with a 0cm square holed paper
Attach to the iron plate with tape. Operation: Move this iron plate adjacent to the painted plate during the above painting
After attaching to the moving plate and applying paint, peel off the aluminum foil from the iron plate
You. NV measurement: Measure the mass (w2) of aluminum foil with paint
After the measurement, measure the mass (w3) after drying at 140 ° C. for 30 minutes.
I do. Calculation: The coating NV (%) is calculated from the following equation. Coating NV (%) = (w3-w1) / (w2-w1) × 1
Table 2 shows the obtained results.

[0053]Volume shrinkage calculation method  The volume shrinkage (%) is calculated according to the following equation. Volume shrinkage (%) = ｛(100-coated NV) / solvent ratio
Weight｝ / [｛(100-coating NV) / solvent specific gravity （+ (coating
NV / Dry coating specific gravity) x 100 Solvent specific gravity: From the solvent composition in the coating, the intermediate coating, clear
-The paint was 0.87 and the base paint was 0.86. Dry coating specific gravity: From each coating composition, intermediate coating 1.64,
Base paint 1.23 and clear paint 1.12. Total volume shrinkage (%) = Volume shrinkage of intermediate coating
X (dry film thickness of intermediate coating film / total dry film thickness) +
Volume shrinkage of base paint x (dry film thickness of base coating / toe
Dry film thickness) + volume shrinkage of clear paint x (clear
Table 2 shows the obtained results.

[0054]Solvent resistance test method  After applying the intermediate coating on a tin plate (20μm), 80 ℃
X 10 minutes to make a product with a raised NV,
Typical paint solvents S-150, Xylol, EE
Spot one drop of P, let stand for about 45 degrees after standing for 30 seconds
Condition was observed. ：: No change Δ: Swelling X: Dissolution The results obtained are shown in Table 2.

Examples 2 to 7 and Comparative Examples 1 to 3 The procedure of Example 1 was repeated except that the resin, the non-aqueous dispersion resin, and the curing agent were blended so that the solid content ratio was as shown in Table 2. Then, prepare and paint the intermediate coating,
Measurement and evaluation were performed. The results are shown in Table 2.

[0056]

[Table 2]

In Table 2, Cymel 254 is a methyl-butyl mixed melamine resin (manufactured by Mitsui Cytec), Uban 20N-60 is a butylated melamine resin (manufactured by Mitsui Cytec), and Sumidur BL3175 is hexamethylene diisocyanate (HMDI). ) Blocked isocyanate (Sumitomo Bayer Urethane Co.).

The intermediate paints of Examples 1 to 7 have a small volume shrinkage and excellent solvent resistance. Therefore, a base paint and a clear paint are applied thereon by a wet-on-wet method and baked and cured. In this case, the finished appearance was excellent. The intermediate coatings containing no non-aqueous dispersion resin of Comparative Examples 1 and 2 were inferior in solvent resistance, and were considered to be swollen by the solvent, and a good finished appearance was not obtained. . The intermediate coating composition of Comparative Example 3 had good solvent resistance, but had a low non-volatile content and a large volume shrinkage, so that a good finished appearance could not be obtained.

[0059]

By using the intermediate coating composition of the present invention, excellent results can be obtained when an automobile body or the like is painted by a three-coat one-bake method or, when a solid paint is used, by a two-coat one-bake method. The finished appearance can be obtained.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C09D 161/20 C09D 161/20 175/04 175/04 (72) Inventor Takuhiro Kakii South of Hiroshima City, Hiroshima Prefecture 1-30 Nihookicho, Ward Japan Paint Co., Ltd. (72) Inventor Hiroyuki Uemura 3-1 Fuchu-cho, Anaka-gun, Hiroshima Prefecture Mazda Co., Ltd. (72) Inventor Tsutomu Shigenaga 3rd Fuchu-cho, Aki-gun, Hiroshima Prefecture No. 1 Mazda Co., Ltd. F term (reference) 4D075 AE06 CA47 DA06 DB02 DC12 EB22 EB45 EB56 4J038 CE012 CG022 CG032 CG062 CG082 CG142 CG172 CH122 DA162 DG302 EA011 GA03 GA06 GA13 KA03 KA08 MA07 MA10 NA01 PA19

Claims (3)

[Claims] 1. A resin containing 10% to 70% by mass of a hydroxyl group-containing resin (a), 10% to 70% by mass of a curing agent capable of reacting with a hydroxyl group (b), and a non-aqueous dispersion resin c) an intermediate coating composition comprising 18 to 50% by mass and further containing a pigment,
The volume shrinkage when cured at 0 ° C. for 30 minutes is 45%
An intermediate coating composition comprising: 2. The pigment is contained in an amount of 10 to 70% by mass with respect to the total amount of the pigment and the solid content of the resin.
The intermediate coating composition according to the above. 3. The nonvolatile content at the time of coating is 40 to 70% by mass.
The intermediate coating composition according to claim 1 or 2, wherein