JP2002254024A - Forming method for paint film and paint film and paint composition object obtained by this method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a forming method for paint film and a paint film and a paint composition object for middle coat paint which can accomplish high appearance such as improvement of skin of middle coat paint without leaving a mark of masking material on a sash black. SOLUTION: A forming method for paint film which comprises the steps of forming middle coat paint film, by applying middle coat paint to coated object, (II) forming sash black paint film by applying sash black on the middle coat paint film, and (III) forming laminating paint film by heating and hardening the middle coat paint film and the sash black paint film. The middle coat paint features that a hard paint film, which is obtained by heating non-hardened paint film for 30 minutes by 140 deg.C, has the minimal value (E') of dynamic elastic modulas, measured under the condition which sets frequency as 11 Hz and the velocity of rising temperature as 2 deg.C/min, is 1.00×10<8> -5.00×10<8> dyne/cm<2> .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a coating film, and more particularly, to a method for forming a coating film on a sash portion of an automobile. Composition.

[0002]

2. Description of the Related Art A car body outer panel including a sash (a frame of a window glass of a door) is usually formed by coating an electrodeposition coating on the entire body, applying an intermediate coating, and curing the coating. After applying a black paint (sash black) only on the sash part by wet-on-wet method without heating, the resulting coating film is cured by heating, and then a top coat paint is applied to the outer plate except for the sash part and heated. Has been cured. In this coating process, in order to prevent the topcoat paint from adhering to the sash part, after applying sash black and heating and curing, applying masking by coating only the sash part with aluminum foil, etc. After coating and heat-curing, a step of removing the masking material is performed.

Japanese Patent Application Laid-Open No. 62-149765 discloses an acrylic resin having 45 to 30% by weight of melamine, with the aim of improving the overall finish level of automobile coating by finishing the sash portion at the same level as other portions. Wet-on-wet coating on a polyester-based coating characterized by containing 5 to 20% by weight of resin, 0.5 to 5% by weight of pigment and 49.5 to 45% by weight of solvent Acrylic / melamine resin coatings suitable for coating are disclosed.

[0004] Further, in order to prevent the reversal of the coating film, the adjustment of the surface tension of the intermediate coating paint and the sash top coating, which was once required, is made almost unnecessary. For the purpose of developing a coating method which does not cause the residual appearance and does not deteriorate the finished appearance even at the place filled with a sealing agent or the like, Japanese Patent Application Laid-Open No.
No. 827 discloses a coating method in which a colored top coat is applied to the surface of an uncured intermediate coat and then heated to cure both coats. A coating method characterized by imparting thixotropic properties is disclosed.

[0005] However, the sash black from which the masking material has been removed after the top coat has been applied and cured by heating is a masking material such as a wrinkled aluminum foil which is considered to be obtained by contact with the sash black. There was a problem that marks such as wrinkles remained and the appearance was reduced.

[0006]

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to leave no trace of a masking material on sash black.
Another object of the present invention is to provide a coating film forming method capable of achieving a high appearance such as improvement of skin of the intermediate coating film, a coating film obtained by this method, and a coating composition for an intermediate coating material.

[0007]

SUMMARY OF THE INVENTION The present inventor has found that it is desirable to ensure the heat flow property of the intermediate coating in order to improve the appearance of the intermediate coating by improving the skin. The cured coating film obtained by increasing the hardness tends to have a high softness, and the problem that the trace of the masking material remains on the sash black is likely to occur, but this phenomenon is a coating film that is usually measured at room temperature. It does not depend on pencil hardness. The present inventor further believes that, in the coating film forming step of the sash portion, depending on the physical properties of the coating film when applying a top coat and heating and curing, it is possible to prevent the adhesion of the masking material traces, specifically, The minimum value (E ') of the dynamic elastic modulus of the cured coating film measured under predetermined measurement conditions is 1.
In the case of using an intermediate coating having a density of 00 × 10 ^{8 to} 5.00 × 10 ⁸ dyne / cm ² , it has been found that both prevention of adhesion of a masking material trace and enhancement of the appearance of the intermediate coating can be achieved. Thus, the present invention has been completed.

More specifically, the present invention provides a step (I) of applying an intermediate coating to an object to be coated to form an intermediate coating, and applying sash black on the intermediate coating to form a sash. A coating film forming method comprising: a step (II) of forming a black coating film; and a step (III) of heating and curing the intermediate coating film and the sash black coating film to obtain a laminated coating film. Intermediate coating is performed by heating the uncured coating obtained by applying the above intermediate coating at 140 ° C. for 30 minutes to a cured coating having a frequency of 11 Hz and a heating rate of 2 ° C./min. Minimum value (E ') of the dynamic elastic modulus measured under the following conditions: 1.00 × 10 ^{8 to} 5.00 × 10
This is a method for forming a coating film, characterized in that the thickness is ⁸ dyne / cm ² . The minimum value (E ') of the dynamic elastic modulus is 1.2
It is preferably 0 × 10 ^{8 to} 2.50 × 10 ⁸ dyne / cm ² .

The above intermediate coating composition has an acid value of 5 to 20 mg KO.
H / g, hydroxyl value 50 to 150 and number average molecular weight 150
A polyester resin (1) having an aromatic acid monomer content of 50% by weight or more based on the total weight of the acid monomer component, and an acid value of 1 to 10 mgKOH / g, a hydroxyl value of 50 to 150 and a number average molecular weight of 1,000. ~ 300
Polyester resin (2), wherein the content of the aliphatic acid monomer is 60% by weight or more based on the total weight of the acid monomer component
Wherein the polyester resin (1)
Is 30 to 70% by weight based on the total solid content of the polyester resin (1) and the polyester resin (2).
Is preferred. It is preferable that the object to be coated has an electrodeposition coating film formed by applying an electrodeposition paint in advance.

[0010] The present invention also provides a coating film formed by the above coating film forming method. The present invention further provides a coating composition used for an intermediate coating, which is applied to an object to be coated to form a coating film, and sash black is applied on the coating film. Is applied to a cured coating film obtained by heating the uncured coating film obtained by applying the above-mentioned intermediate coating paint at 140 ° C. for 30 minutes, at a frequency of 11 Hz and a heating rate of 2 ° C./min. The minimum value (E ') of the dynamic elastic modulus measured in 1. is 1.
A coating composition characterized in that 00 is a ^{× 10 8 ~5.00 × 10 8 dyne} / cm 2. Hereinafter, the present invention will be described in detail.

The method of forming a coating film according to the present invention comprises the steps of: (I) applying an intermediate coating material to an object to be coated to form an intermediate coating film;
Apply sash black on the intermediate coating film,
The method includes a step (II) of forming a sash black coating film and a step (III) of heating and curing the intermediate coating film and the sash black coating film to obtain a laminated coating film.

The above-mentioned intermediate coating composition is obtained by heating an uncured intermediate coating film formed on a test plate by heating at 140 ° C. for 30 minutes to a frequency of 11 Hz.
The measured minimum value of the dynamic elastic modulus under conditions of a heating rate and 2 ° C. / min (E ') is 1.00 × 10 ⁸ ~5.00 × 1
0 ⁸ dyne / cm ² .

The minimum value (E ') of the dynamic elastic modulus is 1.0
If it is less than 0 × 10 ⁸ dyne / cm ² , the softness of the obtained coating film becomes too high, leaving a trace of the masking material,
If it exceeds 5.00 × 10 ⁸ dyne / cm ² , the resulting coating film will have too high a hardness, resulting in reduced adhesiveness and chipping resistance, as well as reduced sharpness during adhesion of dust and the like.
^{Preferably, 1.20 × 10 8 ~2.50 × 10} 8 dy
ne / cm ² . In the present invention, the minimum value (E ') of the dynamic elastic modulus was measured by a Leo Vibron DDV-II type (manufactured by Toyo Baldwin).

As a sample for the above measurement, an uncured coating film formed by applying the intermediate coating composition to a test plate at 140 ° C.
For 30 minutes. The heating time is a so-called pass, which is a time from the start of heating to the end of heating, and a so-called keep indicating a time maintained at 140 ° C. is 18 minutes.

The heating conditions for obtaining the above-mentioned sample are within the range of heating conditions usually applied for curing an uncured intermediate coating film formed on a sash portion of an automobile, as described later. Therefore, using the coating film obtained under the above-mentioned heating conditions as a sample, the intermediate coating material is set so that the minimum value (E ') of the dynamic elastic modulus obtained by measuring while increasing the temperature as described above is within a specific range. Is to focus on the viscoelasticity, particularly elasticity, of the cured coating film of the sash portion when a top coat is applied and heated in automotive coating.
By focusing on the physical properties of the coating film of the sash portion at the time of heating, and by limiting the minimum value (E ') of the dynamic elastic modulus to within the above range, the adhesion of the masking material trace to the sash black can be reduced. Can be reduced.

The above intermediate coating preferably contains a polyester resin (1) and a polyester resin (2). The polyester resin containing the polyester resin (1) and the polyester resin (2) is generally
It can be produced by polycondensing an acid monomer component, which is a polycarboxylic acid and / or an acid anhydride, and a polyhydric alcohol as essential components.

The polyester resin (1) has an acid value of 5-
20 mgKOH / g, hydroxyl value 50-150 and number average molecular weight 1500-4000, and aromatic acid monomer is 50% by weight or more based on the total weight of the acid monomer component. The polyester resin (1) has rigidity. By blending the polyester resin (1) with the above-mentioned intermediate coating material, the resulting coating film has increased hardness and is less likely to leave traces of a masking material.

The polyester resin (1) preferably has an acid value of 8 to 15 mg KOH / g and a hydroxyl value of 80 to 12
0 and / or a number average molecular weight of 2,000 to 3,500.
If the acid value and / or hydroxyl value is less than the lower limit, the curability of the coating film may decrease, and if it exceeds the upper limit, the water resistance of the coating film may decrease. If the number average molecular weight is less than the lower limit, the curability of the coating film may decrease, and if it exceeds the upper limit, the appearance of the coating film may decrease.

The aromatic acid monomer for the polyester resin (1) refers to a polycarboxylic acid and / or acid anhydride containing an aromatic ring in the molecule, for example, phthalic acid, phthalic anhydride, Menlitic acid, trimellitic anhydride, pyromellitic acid, pyromellitic anhydride, isophthalic acid, terephthalic acid, and the like can be mentioned. Among them, from the viewpoint of imparting rigidity to the obtained polyester resin (1),
Isophthalic acid is preferred. The above polyester resin (1)
Can be a monomer containing an aromatic ring in the molecule as a polyhydric alcohol component.

In the polyester resin (1), the amount of the aromatic acid monomer is preferably 70 to 90% by weight based on the total weight of the acid monomer component. The content based on the total weight of the acid monomer component of the aromatic acid monomer,
If it is less than the lower limit, the rigidity of the obtained polyester resin (1) becomes insufficient, and the coating film obtained by blending the polyester resin becomes high in softness, which may leave traces of the masking material.

As the acid monomer component forming the polyester resin (1), an acid monomer other than the aromatic acid monomer may be used in combination with the aromatic acid monomer. Examples of the acid monomer include an aliphatic acid monomer. The aliphatic acid monomer,
It refers to a polycarboxylic acid and / or carboxylic anhydride containing no aromatic ring in the molecule, and usually contains a saturated or unsaturated cyclic or linear aliphatic hydrocarbon group. The aliphatic acid monomer is not particularly limited, for example, saturated or unsaturated such as tetrahydrophthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic acid, hexahydrophthalic anhydride, methyltetrahydrophthalic acid, methyltetrahydrophthalic anhydride, etc. Cyclic structure-containing polycarboxylic acid and / or acid anhydride; maleic acid, maleic anhydride, fumaric acid, itaconic acid, adipic acid, azelaic acid, sebacic acid, succinic acid, succinic anhydride, dodecenylsuccinic acid, dodecenylsuccinic anhydride Examples include polycarboxylic acids and / or acid anhydrides containing a saturated or unsaturated chain structure such as an acid.

The polyester resin (2) has an acid value of 1 to 1.
It has a hydroxyl value of 50 to 150 and a number average molecular weight of 1,000 to 3,000, a fatty acid monomer content of 60% by weight or more based on the total weight of the acid monomer component. The polyester resin (2) is softer than the polyester resin (1) described above, and provides an appropriate flow property to the intermediate coating composition containing the polyester resin (1), and prevents the resulting coating film from being roughened, and has a high appearance. To contribute.

The polyester resin (2) preferably has an acid value of 5 to 9 mgKOH / g and a hydroxyl value of 80 to 120.
And / or a number average molecular weight of 1500 to 2000. The reason why the acid value, the hydroxyl value and the number average molecular weight of the polyester resin (2) are within the above-mentioned ranges is the same as that described for the polyester resin (1).

The aliphatic acid monomer forming the polyester resin (2) is the above-mentioned polyester resin (1)
In these examples, adipic acid is preferred from the viewpoint of imparting flexibility to the obtained polyester resin (2).

In the polyester resin (2), the aliphatic acid monomer is preferably at least 70% by weight based on the total weight of the acid monomer component. If the content of the aliphatic acid monomer is less than the lower limit, the softness of the obtained polyester resin (2) is too low, and the flowability of the intermediate coating obtained by blending with the above-mentioned polyester resin (1). And the appearance of the coating film may be poor.

As the acid monomer component forming the polyester resin (2), an acid monomer other than the above-mentioned aliphatic acid monomer may be used in combination with the above-mentioned aliphatic acid monomer. Examples of the acid monomer include aromatic acid monomers as described in the polyester resin (1).

In the intermediate coating, the polyester resin (1) preferably accounts for 30 to 70% by weight of the total solid content of the polyester resin (1) and the polyester resin (2). If the amount is less than 30% by weight, the resulting coating film may have too high a softness to leave traces of the masking material. If the amount exceeds 70% by weight, too much resin having rigidity and a relatively large number average molecular weight is excessive. And the flowability of the intermediate coating material may be deteriorated, and the appearance may be reduced. Preferably, it is 40 to 60% by weight.

The intermediate coating composition may contain another polyester resin in combination with the polyester resin (1) and the polyester resin (2).
As the acid monomer component used for producing the other polyester resin, various acid monomer components described for the polyester resin (1) can be used.

The polyhydric alcohol used for producing the polyester resin (1), the polyester resin (2) and the other polyester resin is not particularly limited, and examples thereof include ethylene glycol, diethylene glycol, polyethylene glycol, and propylene. Glycol, dipropylene glycol, polypropylene glycol, neopentyl glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,5-pentanediol, 1, 6-hexanediol, 1,4-cyclohexanediol, 2,2-dimethyl-3-hydroxypropyl-2,2-dimethyl-3-hydroxypropionate, 2,2,4-trimethyl-1,3-pentanediol , Polytetramethy Emissions ether glycol, polycaprolactone polyol, glycerin, sorbitol, An'nitoru, trimethylol ethane, trimethylol propane, trimethylol butane, hexanetriol,
Examples include pentaerythritol and dipentaerythritol.

When producing the polyester resin (1), the polyester resin (2) and the other polyester resin, other reactive components other than the above-mentioned polycarboxylic acid and / or acid anhydride and polyhydric alcohol are used. As
It may contain a monocarboxylic acid, a hydroxycarboxylic acid or the like. It may also contain a drying oil, an anti-drying oil and their fatty acids. In addition, for example, a monoepoxide compound such as Cardura E (manufactured by Shell Chemical Co., Ltd.) or a lactone can be contained. The lactone is capable of forming a graft chain by ring-opening addition of a polyhydric carboxylic acid and a polyhydric alcohol to polyesters,
For example, β-propiolaclone, dimethylpropiolactone, butyllactone, γ-valerolactone, ε-caprolactone, γ-caprolactone, γ-caprylolactone, crotlactone, δ-valerolactone, δ-caprolactone, and the like. However, ε-caprolactone is particularly preferred. When producing the polyester resin (1), the polyester resin (2) and the other polyester resin, the above polycarboxylic acid and / or acid anhydride, polyhydric alcohol, other lactones, etc. They may be used alone or in combination of two or more.

The total amount of the polyester resin (1), the polyester resin (2) and, if necessary, the other polyester resin is 20 to 80 in the solid content of the coating composition.
It is preferable to mix them in a ratio of weight%. If the amount is less than 20% by weight, the coating film-forming property is deteriorated, and the adhesion to sash black is poor. If the amount is more than 80% by weight, poor curing occurs, and the concealability of the base is insufficient. More preferably, it is 30 to 60% by weight.

The intermediate coating composition may contain another base resin in combination with the polyester resin as a film-forming resin. Examples thereof include acrylic resins and alkyd resins. Species or two or more can be used.

The intermediate coating composition generally contains a curing agent as a film-forming resin in combination with the polyester resin and the other base resin. The curing agent is not particularly limited and, for example, a curing agent generally used in combination with a polyester resin can be used, for example, a melamine resin,
Examples include amino resins such as urea resins, and blocked isocyanate resins. The curing agent is preferably a melamine resin such as butylated melamine, methyl / butylated melamine, and fully alkylated methylated melamine from the viewpoint of pigment dispersibility and workability, and methyl / butylated melamine from the viewpoint of coating film appearance. Is more preferred. It is preferable that the melamine resin has an average of 1.0 to 3.0 imino groups per melamine nucleus in terms of coating film appearance, coating film curability, chipping resistance, and the like. More preferably, such a melamine resin is a methyl / butylated melamine. One or more of the above curing agents can be used.

The above-mentioned curing agent is based on the total amount of resin solids.
It is contained in an amount of 10 to 50% by weight in solid content. If the amount is less than 10% by weight, the curing may be insufficient, and the physical properties of the coating film may be poor. If it exceeds 50% by weight, not only the effect corresponding to the compounding amount cannot be obtained, but also the finished appearance of the coating film deteriorates. Preferably, it is 20 to 45% by weight.

The melamine resin and other amino resins are
Usually, an acid catalyst can be used in combination. The acid catalyst is not particularly limited, and examples thereof include paratoluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, and dinonylnaphthalenedisulfonic acid.

The above intermediate coating usually contains a pigment. The pigment is not particularly limited, and includes, for example, those commonly used in paints, for example, azochelate pigments, insoluble azo pigments, condensed azo pigments, benzimidazolone pigments, diketopyrrolopyrrole pigments Organic color pigments such as phthalocyanine pigments, indigo pigments, perinone pigments, perylene pigments, dioxane pigments, quinacridone pigments, isoindolinone pigments, metal complex pigments, etc .; graphite, yellow iron oxide, red iron oxide, carbon black,
Inorganic coloring pigments such as titanium dioxide and graphite; extenders such as calcium carbonate, barium sulfate, kaolin, aluminum silicate (clay) and talc; aluminum phosphomolybdate;
Rust preventing pigments such as lead silicate, lead sulfate, zinc chromate, strontium chromate, and the like are included. As the above-mentioned pigment, a standard gray intermediate paint containing carbon black and titanium dioxide as main pigments can be used, or the lightness or hue can be matched with that of the top coat.

The above-mentioned intermediate coating composition may further contain, if necessary, conventionally known additives such as a viscosity control agent, an anti-bake agent, an ultraviolet absorber, a hindered amine light stabilizer, an antioxidant, and an organic solvent. Adjusters, leveling agents, pigment dispersants, plasticizers, defoamers, diluting solvents and the like can be added. Examples of the viscosity control agent include swelling dispersions of fatty acid amides, amides such as amide-based fatty acids, and phosphates of long-chain polyaminoamides; polyethylene-based ones such as colloidal swelling dispersions of polyethylene oxide;
Organic bentonites such as organic acid smectite clay and montmorillonite; inorganic pigments such as aluminum silicate and barium sulfate; flat pigments which exhibit viscosity depending on the shape of the pigment;
Crosslinked resin particles and the like can be mentioned.

The above-mentioned intermediate coating composition contains the above-mentioned polyester resin (1), polyester resin (2) and, if necessary, other film-forming resins and curing agents, as well as pigments and other components, kneaders, rolls and the like. Can be obtained by a method known to those skilled in the art such as kneading and dispersing.

The intermediate coating obtained in this manner is applied to an object to be coated in the above-mentioned step (I) to form an intermediate coating film. The object to be coated is not particularly limited and includes, for example, metals, plastics, foams and the like. Of these, metals, especially castings are advantageously used, but cationic electrodeposition can be applied if necessary. Metal products are particularly preferably used. The metal product is not particularly limited, and examples thereof include simple metals such as iron, copper, aluminum, tin, and zinc, and alloys and castings containing the simple metals. It is particularly preferable that the metal product has been subjected to a chemical conversion treatment with a phosphate, a chromate or the like in advance.
INDUSTRIAL APPLICABILITY The coating film forming method of the present invention is used for a sash portion of an automobile outer panel such as a passenger car, a truck, and a bus.

An electrodeposition coating is applied on the metal product which has been subjected to the chemical conversion treatment as described above to form an electrodeposition coating film, thereby imparting corrosion resistance and rust prevention to the object to be coated. In terms of
preferable. As the electrodeposition paint, a cationic or anion type electrodeposition paint can be used, but a cationic electrodeposition paint is preferable because it gives a laminated coating film having excellent corrosion resistance. In general, the electrodeposition paint is coated by connecting a cathode (cathode electrode) terminal to a conductive base material to be coated, a bath temperature of the electrodeposition paint is 15 to 35 ° C., and a load voltage is 100 to 40.
Electrodeposition coating can be performed under the condition of 0V.
The uncured electrodeposition film obtained by applying the above electrodeposition paint,
Generally, 140-200 ° C., preferably 160-1
Heat at 80 ° C. for 10 to 30 minutes to cure and form an electrodeposition coating.

The edge of the sash of the automobile is usually coated with a sealer on the electrodeposition coating. The sealer is not particularly limited, and examples thereof include vinyl chloride-based and silicon-based sealers commonly used for the edge portion. The above-mentioned sealer is usually not particularly limited as a coating method, and is heated, for example, at 90 to 100 ° C. for 5 to 15 minutes.

The above-mentioned intermediate coat is then applied to the object having the chemical conversion film, electrodeposition coating film or sealer formed thereon as required to form an uncured intermediate coat film. When the intermediate coating film is formed, defects of the object to be coated, electrodeposition coating film and sealer are concealed, the surface smoothness after applying sash black is secured and the appearance is improved, and the impact resistance is also improved It is easy to impart physical properties of the coating film such as chipping resistance. The method for applying the intermediate coating is not particularly limited, and includes, for example, an air electrostatic spray so-called “react gun”;
It can be carried out by using a rotary atomizing type electrostatic coating machine called “μ) bell”, “micro (μ) bell”, “metabell” or the like.

On the uncured intermediate coating film, sash black is applied by the above-mentioned step (II) to form a sash black coating film. The sash black is usually colored black and may be glossy black, but is generally a matte black paint. The sash black is not particularly limited, and for example, a paint that is usually used as a sash black can be used, and examples thereof include a film-forming resin, a curing agent, a pigment and other additives. .

The sash black film-forming resin is not particularly restricted but includes, for example, acrylic resins, polyester resins, alkyd resins, epoxy resins, urethane resins and the like, and these are amino resins and / or blocked isocyanate resins. Used in combination with a curing agent such as A combination of an acrylic resin and / or a polyester resin and a melamine resin is preferred from the viewpoint of pigment dispersibility and workability.

Conventionally known pigments can be used as the sash black pigment. Examples of the sash black pigment include carbon black, iron oxide, silica fine powder which is also a matting agent, and the like. It is preferably from 5 to 45% by weight based on the weight of the solid content of sash black. If the amount is less than 5% by weight, a suitable black or luster as an automobile sash black cannot be obtained. If the amount exceeds 45% by weight, the resulting coating film lacks smoothness and tends to cause poor appearance such as rough skin. is there. More preferably, 10 to 35
% By weight. In the sash black, if desired, various pigments described as pigments that can be contained in the above-mentioned intermediate coating material and additives can be used in combination.

The total solid content of the sash black at the time of coating is preferably 20 to 70% by weight. If the amount is less than 20% by weight, the viscosity is too low, resulting in poor appearance such as inversion, conformity, and unevenness. If the amount is more than 70% by weight, the viscosity may be too high and the coating film appearance may be deteriorated. Preferably, it is 30 to 60% by weight. The method for producing the sash black is not particularly limited, and for example, a method known to those skilled in the art as described for the above-mentioned intermediate coating can be used. The method of applying the sash black is not particularly limited, but usually, an air spray, a hand spray, a REA gun coating machine or the like is used. The sash black is usually applied on a wet-on-wet basis without curing the above-mentioned intermediate coating film.

The intermediate coating film obtained in the above step (I) and the sash black coating film obtained in the above step (II) are cured by heating in the above step (III) to obtain a laminated coating film. The heat curing can be performed under general baking conditions, for example, at 120 to 160 ° C., whereby a cured coating film having a high crosslinking density can be obtained. If it is lower than 120 ° C., the curing is not sufficient, and if it exceeds 160 ° C., the coating film may be hard and brittle. Preferably, it is 130 to 150 ° C. The curing time varies depending on the curing temperature.
~ 30 minutes is appropriate.

When the above-mentioned sash black is applied on a wet-on-wet basis without curing the intermediate coating film, the uncured intermediate coating film obtained in the step (I) and the above The uncured sash black coating film obtained in the step (II) is simultaneously heated and cured in the step (III) to obtain a laminated coating film. In this case, for the uncured intermediate coating film,
Before applying the sash black, a preheating step of drying the coating film in advance by leaving it at room temperature for a certain period of time or by heating it at, for example, 60 to less than 100 ° C. for 2 to 10 minutes can be performed.

The dry film thickness of each of the above-obtained coating films thus obtained varies depending on the application, but each of the intermediate coating film is 10 to 60 μm and the sash black is 10 to 50 μm.
m. Exceeding these upper limits may result in poor image clarity or inconveniences such as unevenness and sagging at the time of coating. Below the lower limits, unevenness of the base may not be concealed and the film may break.

An object to be coated having a coating film obtained in this manner is usually further coated with a top coating material, and heated to cure the obtained top coating film. In order to prevent the top coat from adhering, the sash portion of the automobile is subjected to masking such as coating with a masking material before the top coat is applied. The masking material is not particularly limited, and examples thereof include an aluminum foil and a tape, and an aluminum foil is preferable. It is not particularly limited as the top coating, for example,
A base paint or a clear paint composed of a film-forming resin, a curing agent, and if necessary, a pigment or other additives is used. There is no particular limitation on the heating conditions for the top coat, and for example, the heating conditions described for the above-mentioned step (III) can be used.

After heating the above top coat, the above-mentioned masking material is removed, and if necessary, washed with water. According to the coating film forming method of the present invention, on the sash black surface from which the masking material has been removed, a trace of wrinkles or the like of the masking material that has been conventionally adhered does not remain, and a high-appearance coating film without rough skin can be obtained. .

As described above, the coating film forming method of the present invention
The minimum value (E ') of the dynamic elastic modulus of the cured coating film measured under predetermined measurement conditions is from 1.00 × 10 ^{8 to} 5.00 ×.
Since the intermediate coating of 10 ⁸ dyne / cm ² is used, a masking material such as an aluminum foil is coated on the above-mentioned intermediate coating and the coating film obtained by applying and curing the sash black, and then the top coating is applied. After applying and heating and curing, when removing the masking material, not only does not cause defects such as traces of contact of the masking material having wrinkles on the surface of the sash black, and also the skin of the intermediate coating film Higher appearance such as improvement can also be achieved.

The mechanism by which the coating film forming method of the present invention exhibits such advantageous effects is not clear, but is considered as follows. That is, at the time of heating the top coat, the conventional coat of the sash portion is too soft, so it is assumed that the masking material traces have adhered, whereas in the present invention, within the above specific range. Since the intermediate coating having the minimum value (E ') of the dynamic modulus of elasticity is used, the coating of the sash portion can maintain the hardness when the top coating is heated, and can reduce the influence of the masking material in contact. Conceivable. Therefore, the coating composition for an intermediate coating preferably used in the method for forming a coating film and the above method of the present invention is suitably used for a sash portion of an automobile outer panel.

[0054]

The present invention will now be described in detail with reference to specific examples.
However, the present invention is limited by the following examples.
Not something. Parts and% are parts by weight and% by weight, respectively.
MeansSynthesis Example 1 Synthesis of polyester resin (1)  Thermometer, stirrer, cooling pipe, nitrogen inlet pipe, water separator and
85 parts of isophthalic acid and adipic acid
15 parts, 25 parts of neopentyl glycol (NPG),
Limethylolpropane (TMP) 25 parts, 1,6-hexyl
29 parts of sundiol (1,6HD), dibutyltin oxa
Charge 0.02 parts of the solution and heat it to 210 ° C.
I did. However, it takes 3 hours from 160 ° C to 210 ° C.
At a constant rate. The condensed water generated is system
Distilled out. Keep warm when it reaches 210 ° C
One hour later, 20 parts of xylene was refluxed into the reaction vessel.
Add slowly and switch to condensation in the presence of solvent to continue the reaction.
I did. Resin acid value reaches 8.5mgKOH / g (solid content)
Then, it was cooled to 100 ° C. Xylene 85
And a number average molecular weight of 3000, an acid value of 10 mg KOH
/ G (solid content), hydroxyl value 100 mgKOH / g (solid
Varnish with 60% non-volatile content containing polyester resin
I got

[0055]Synthesis Example 2 Synthesis of polyester resin (2)  Thermometer, stirrer, cooling pipe, nitrogen inlet pipe, water separator and
80 parts of adipic acid and hexahydro
20 parts of phthalic acid, neopentyl glycol (NPG) 4
0 parts, Trimethylolpropane (TMP) 37 parts, Jib
0.02 parts of chill tin oxide is charged and heated to 210 ° C.
Temperature. However, from 160 ° C to 210 ° C
Was heated at a constant heating rate over 3 hours. Generate
The condensed water was distilled out of the system. When it reaches 210 ° C
After keeping the temperature for 1 hour, xy
Slowly add 20 parts of ren, cut into condensation in the presence of solvent
The replacement reaction was continued. Resin acid value is 8.5mgKOH / g
When the solid content was reached, the mixture was cooled to 100 ° C. Change
To the mixture were added 32 parts of xylene, number average molecular weight 1800, acid value
8 mg KOH / g (solid content), hydroxyl value 100 mg KO
Non-volatile content 7 containing H / g (solid content) polyester resin
5% varnish was obtained.

[0056]Example 1  30 parts of the polyester resin (1) obtained in Synthesis Example 1 and
24 parts of the polyester resin (2) obtained in Synthesis Example 2
39 parts of ren, titanium oxide as pigment (R-650, Sakai Chemical
40 parts, Gaku Kogyo Co., Ltd., barium sulfate (BF-20, Sakai Chemical)
9 parts by Gaku Kogyo Co., Ltd. and carbon black (MA-10)
0.5, manufactured by Mitsubishi Chemical Corporation) and premixed.
Later, remove the glass bead medium in the paint conditioner.
In addition, the mixture was mixed and dispersed at room temperature for 1 hour,
A pigment-dispersed paste with a 60% emission was obtained. The above pigment dispersion
140 parts of methyl / butyl melamine resin
Mel-254, manufactured by Mitsui Cytec Co., Ltd.)
Along with Mitsui Chemicals' Resix Mix RL-4
0.1 part was blended to obtain a coating composition.

On a 0.8 mm-thick phosphoric acid-treated steel plate, a cationic electrodeposition paint (Powertop U-5 manufactured by Nippon Paint Co., Ltd.) was applied.
0) is applied to a dry film thickness of about 25 μm,
Bake at 0 ° C. for 30 minutes. Next, the intermediate coating material obtained by diluting the coating composition obtained above with a thinner (toluene / S-150 / butyl acetate = 40/40/20 manufactured by Exxon Co., Ltd.) is adjusted to a dry film thickness of about 40 μm. Was coated with an air spray gun, and sash black (OP-30 Black, manufactured by Nippon Paint Co., Ltd.) was thinned (by weight, ethyl acetate / Exxon S-150 = 70).
/ 30), and coated with an air spray gun so that the dry film thickness becomes about 25 μm. After setting for 7 to 10 minutes, the mixture was heated in a pass at 140 ° C. for 30 minutes to obtain a cured coating film. The coated plate is covered with an aluminum foil and adhered to the surface of the coating film, and then heated in a pass at 140 ° C. for 30 minutes. After cooling, the aluminum foil is removed, and the exposed coating film is used as a coating film (A).

(Evaluation) Evaluation was made according to the following criteria, and the results are shown in Table 1. 1. The minimum value of the dynamic elastic modulus (E ') The diluted intermediate coat is applied to a polypropylene plate as a test plate under the above conditions and heated.
It was measured by DV-II type (manufactured by Toyo Baldwin).

2. Crosslink density (n) From the measured value (E ') obtained in 1 above, the crosslink density (n) was calculated by the following equation. n (mol / L) = E '/ 3RT In the above formula, T and R are as follows. T: Absolute temperature (K) at the above measurement point; 273+
x ° C. R: gas constant; 8.3143 × 10 ⁻⁷ (erg / de
g. mol. )

3. Adhesion of aluminum foil traces The coating film (A) was visually observed and evaluated according to the following criteria. ○ There was no trace such as wrinkles of the aluminum foil. Δ: Some traces such as wrinkles of the aluminum foil were found. × There were many traces such as wrinkles of the aluminum foil. 4. Pencil hardness Regarding the coating film (A), JIS K 5400 8.4.
The pencil scratch value was determined according to 1.

[0061]Comparative Example 1  Without using the polyester resin (1) obtained in Synthesis Example 1,
Using 60 parts of the polyester resin (2) obtained in Example 2,
Except for preparing the feed composition,
Paint preparation, painting, and evaluation.

[0062]

[Table 1]

From Table 1, in Comparative Example 1 where the minimum value (E ') of the dynamic elastic modulus is not within the range of the present invention, traces of the aluminum foil remain, whereas the minimum value (E') In Example 1 where ') is within the scope of the present invention, it was found that no trace of the aluminum foil was left and the hardness of the coating film was higher than that of Comparative Example 1.

[0064]

Since the coating film forming method of the present invention has the above-described structure, a masking material such as an aluminum foil is coated on the coating film cured by applying the above-mentioned intermediate coating and sash black. After coating, after applying a top coat and curing by heating, when removing the masking material,
Not only does not cause a problem such as a trace of the wrinkles of the masking material remaining on the surface of the sash black and the like, but also a high appearance such as improvement of the skin of the intermediate coating film can be achieved. Therefore, the method for forming a coating film of the present invention, the coating film obtained by the above method, and the composition for an intermediate coating material of the present invention are suitably used for a sash portion of an automobile outer panel.

────────────────────────────────────────────────── ─── of the front page continued (51) Int.Cl. ⁷ identification mark FI theme Court Bu (reference) B05D 7/24 302 B05D 7/24 302V C09D 167/00 C09D 167/00 201/00 201/00 F -term ( 4D075 AE06 AE09 BB26Z BB93Z BB94Z BB99Z CA48 CB14 DA23 DA31 DB02 DC11 EA05 EA19 EB35 EB52 EB55 EB56 EB60 4J038 DD061 DD062 DD081 DD082 DD121 DD122 GA03 GA06 MA14 NA01 NA11 PA04 PA19 P

Claims (6)

[Claims] 1. A step (I) of applying an intermediate coating to an object to be coated to form an intermediate coating, wherein on the intermediate coating,
A step of forming a sash black coating film by applying sash black; and a step (III) of heating and curing the intermediate coating film and the sash black coating film to obtain a laminated coating film. A method for forming a film, wherein the intermediate coating is a cured coating obtained by heating an uncured coating obtained by applying the intermediate coating at 140 ° C. for 30 minutes, at a frequency of 11 Hz, and 2 ° C /
The minimum value (E ') of the dynamic elastic modulus measured under the condition of 1.00 × 10 ^{8 to} 5.00 × 10 ⁸ dyn
e / cm ² . 2. The minimum value (E ') of the dynamic elastic modulus is 1.2
^{0 × 10 8 ~2.50 × 10 8} dyne / cm 2 at a coating film forming method according to claim 1, wherein. 3. The intermediate coating composition has an acid value of 5 to 20 mg KOH.
/ G, hydroxyl value 50-150 and number average molecular weight 1500
A polyester resin (1) in which the aromatic acid monomer is 50% by weight or more based on the total weight of the acid monomer component, and an acid value of 1 to 10 mgKOH / g, a hydroxyl value of 50 to 150, and a number average molecular weight of 1,000. 3000
Wherein the polyester resin (1) contains the polyester resin (2) in which the aliphatic acid monomer is 60% by weight or more based on the total weight of the acid monomer component.
Is 30 to 70% by weight based on the total solid content of the polyester resin (1) and the polyester resin (2).
The method for forming a coating film according to claim 1 or 2, wherein 4. An object to be coated is coated with an electrodeposition paint in advance,
4. The method for forming a coating film according to claim 1, wherein the electrodeposition coating film is formed. 5. A coating film formed by the method for forming a coating film according to claim 1, 2, 3, or 4. 6. A coating composition used for an intermediate coating composition which is applied to an object to be coated to form a coating film and applies sash black on the coating film, wherein the intermediate coating material is The uncured coating film obtained by applying the intermediate coating material is heated at 140 ° C. for 30 minutes, and the cured coating film is obtained under the conditions of a frequency of 11 Hz and a heating rate of 2 ° C./min. The minimum value (E ′) of the measured dynamic elastic modulus is 1.
A coating composition having a composition of from 00 × 10 ^{8 to} 5.00 × 10 ⁸ dyne / cm ² .