JP4762792B2 - Paint for automobile outer plate and coating method thereof - Google Patents

Description

  The present invention is characterized in that a top coat is simultaneously applied on both members on the surface of an automobile outer plate composed of a metal member and a plastic member attached thereto, and the plastic member is baked and dried at a temperature at which the plastic member is not thermally deformed. The present invention relates to a coating method for an automobile outer plate and a coating composition used therefor.

A metal member such as a steel plate and a plastic member such as a plastic bumper are often used together in the outer plate portion of an automobile body. In addition, in order to measure the vehicle body, attempts have been made to replace the entire steel plate or a part thereof with plastic.
When coating and baking a composite member in which such a metal member and a plastic member are integrally combined, heat resistance may be insufficient depending on the type of the plastic member. Since the appearance quality is deteriorated due to foaming of the film, there is a problem that the intended composite member cannot be prepared.
Therefore, it is generally performed that the metal member and the plastic member are separately coated with a paint and the coating film is baked and cured. As a top coating material for an automobile body steel plate portion, a coating material that is normally cured by baking at around 140 ° C. for 20 to 30 minutes is used. As a plastic member such as FRP, a two-component urethane paint that can be dried at room temperature or at a low temperature of 100 ° C. or lower is generally used.
Conventionally, for example, a colored paint (A) containing a hydroxyl group-containing resin, a melamine resin, and a color pigment is applied to a metal member, and the colored paint (A) is applied to a plastic member. A technique for applying a colored paint (B) in which a polyisocyanate compound is blended with A) has been proposed (see, for example, Patent Document 1).

JP 2001-334207 A

As described above, in the conventional coating method, since it is necessary to separately coat the metal member and the plastic member, there are problems such as complicated steps and extra steps.
The paint for plastic parts uses an isocyanate compound as a curing agent, which can be cured at a low temperature, but the finished quality is slightly inferior to that using a melamine resin, and handling is complicated due to the two-component paint. It becomes. In addition, since the metal member and the plastic member are separately coated and baked and dried, when the members are combined, there may be a difference in the color of the coating film. Therefore, there is a demand for integral painting of a metal member and a plastic member in painting an automobile body.

  In order to solve the above problems, the present invention applies a coating composition such as a top coating that cures at a low temperature to the surface of an automobile outer plate comprising a metal member and a plastic member attached thereto, and the plastic. It is characterized in that the manufactured member is baked and dried sequentially at a low temperature that is not thermally deformed.

Hereinafter, the present invention will be described in detail.
The present invention is suitably applied to an automobile outer plate in which a metal member such as a body, which is an outer plate portion of an automobile body, and a plastic member such as a bumper attached thereto are integrally combined. For example, when applying to an automobile outer plate in which a steel plate part and a plastic part are integrally attached, by converting a part of the steel plate part of a heavy duty commercial vehicle outer plate steel plate part and the steel plate part into plastic, It is very advantageous.
In addition, it is preferable to apply a primer coating such as an electrodeposition coating to a metal member of an automobile body such as a body in advance in order to impart rust prevention.

The metal member is obtained by processing a normal steel plate for automobiles, a metal such as stainless steel or aluminum, and an alloy.
Examples of the plastic member include a plastic body part, a bumper, an engine hood, a lid, a fender, a door, and a rear gate. Generally, plastic materials include FRP mainly composed of polyester resin and epoxy resin, polyolefin, polyurethane, polycarbonate, polyphenylene oxide, polyamide, ABS, and polymer alloys thereof. A polyester resin having excellent strength and strength is preferred. The polyester resin may be either a saturated polyester resin or an unsaturated polyester resin, or may be used in combination.
These plastic members are preferably made of a material that is not thermally deformed at the baking temperature of the paint (110 ° C. or lower).

The paint of the present invention is applied to an automobile outer plate. Examples of automobiles include passenger cars, buses, and trucks. Among them, commercial vehicles such as buses and trucks are preferable.
The top coating used in the present invention comprises 20 to 50% by weight of a polyester resin, 5 to 25% by weight of an imino group-type melamine resin, and 0.01 to 2% by weight of an acid catalyst, and is 110 ° C. or less, preferably It is a paint that is baked and cured at 110 to 100 ° C. (usually, it is difficult to form an excellent cured coating unless it is 120 ° C. or higher).

As the polyester resin used in the top coating, various polyester resins can be used without particular limitation. Such polyester resins include, for example, polybasic acid components such as phthalic anhydride, isophthalic acid and its hydride, succinic acid, trimellitic acid, ethylene glycol, propylene glycol, trimethylolpropane, neopentyl glycol, etc. It is obtained by condensation polymerization of the polyol component. It includes those modified with naturally-derived fatty acids or synthetic fatty acids. The acid value of the polyester resin is, for example, 5 to 20 KOH mg / g, preferably 6 to 12 KOH mg / g.
The polyester resin referred to here includes oilless alkyd resins modified with a small amount of fatty acids, alkyd resins modified with synthetic fatty acids, and the like in addition to common oil-free alkyd resins. The oilless alkyd resin mentioned here refers to an alkyd resin having an oil length of 15 or less, and is a kind of polyester resin. In addition, rosin, a polyester resin modified with epoxy, acrylic, silicon, fluorine, or the like can also be used.

The imino group-type melamine resin used in the top coating is a resin obtained by further alkylating a product obtained by condensing melamine and formaldehyde, and is a condensation product partially containing an imino group. . The imino group-type melamine resin is excellent in the finished quality of the coating film (glossy, skin, etc.) and has excellent reactivity at low temperatures when combined with an acid catalyst.
The acid catalyst used in the top coating composition of the present invention is a catalyst formulated to constitute a top coating composition suitable for low temperature baking. This acid catalyst accelerates the curing reaction of the coating film when the top coat is baked.

  Examples of the acid catalyst used in the present invention include p-toluenesulfonic acid, sulfonic acid compounds such as dodecylbenzenesulfonic acid, cumenesulfonic acid, dinonylnaphthalene monosulfonic acid, dinonylnaphthalenedisulfonic acid, and trimethyl phosphate. Preferable examples include alkyl phosphates such as triethyl phosphate, monobutyl phosphate, dibutyl phosphate, tributyl phosphate and trioctyl phosphate, phosphoric acid, formic acid, acetic acid and hydrochloric acid. In the present invention, in particular, p-toluenesulfonic acid, cumenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalene monosulfonic acid, dinonylnaphthalenedisulfonic acid, and alkylphosphorus are used so that they can be baked and cured at a low temperature of 110 ° C. or lower. A mixture of acid catalysts containing three or more compounds selected from the group consisting of acids is preferred. However, these acid catalysts may be partially or completely neutralized with basic compounds such as amines.

The top coat used in the present invention is 20 to 50% by mass of polyester resin, preferably 22 to 40% by mass, 5 to 25% by mass of imino group-type melamine resin, preferably 8 to 16% by mass, and 0. 01 to 2% by mass, preferably 0.3 to 1.2% by mass.
When the polyester resin is less than 20% by mass relative to the mass of the top coat, the appearance of the coating film tends to deteriorate. On the other hand, when the amount of the polyester resin exceeds 50% by mass, problems such as concealment of the coating film and difficulty in producing hardness are likely to occur, which is not preferable.
When the imino group type melamine resin is less than 5% by mass with respect to the mass of the top coat, the coating film is hardly cured. On the other hand, when the imino group type melamine resin exceeds 25% by mass, the hardness of the coating film is too high and it is difficult to obtain sufficient flexibility.

  When the acid catalyst is less than 0.01% by mass with respect to the weight of the top coat, the coating film is hardly cured. On the other hand, when the acid catalyst exceeds 2% by mass, the storage stability of the paint is lowered, the curing reaction of the paint film is excessively advanced, the gloss of the paint film is lowered, the water resistance is lowered, and the like.

In addition to the resin component and catalyst described above, the top coating composition of the present invention includes a solvent and, if necessary, pigments such as colored pigments and extender pigments, a rheology control agent, a pigment dispersant, a surface conditioner, light Various additives such as a stabilizer, an ultraviolet absorber, and an electrostatic assistant can be blended.
Examples of the solvent include alcohols such as methanol, ethanol, propanol, isopropanol, and butanol, esters such as ethyl acetate and butyl acetate, alcohol ethers such as ethylene glycol monoethyl ether and ethylene glycol monobutyl ether, acetone, and methyl ethyl ketone. Ketones, various organic solvents for paints such as toluene, xylene, and aromatic hydrocarbon mixed solvents, or mixtures thereof can be used. The blending amount is 0 to 80% by mass, preferably 20 to 60% by mass in the paint.
Examples of the pigment include inorganic color pigments such as titanium dioxide, carbon black, ocher, bengara, bismuth vanadate, chrome lead, molybdate orange, ultramarine, and complex oxide fired pigment. The organic coloring pigments include compounds such as phthalocyanines, azo compounds, quinacridone, perylene, perinone, isoindolinone, isoindoline, dioxazine, anthraquinone, quinophthalone, diketopyrrolopyrrole, and various metal complexes. Barium sulfate, calcium carbonate, bentonite, silica, lithopone and the like can be used as extender pigments for paints. The blending amount is suitably 1.5 to 50% by mass depending on the coating color in the top coat.
Furthermore, you may add various additives, such as a pigment dispersant, a ultraviolet absorber, a light stabilizer, a rheology control agent, an electrostatic adjuvant, and a surface conditioning agent, as needed.

The present invention is suitable for coating the above-mentioned top coat paint on an automobile outer plate in which a plastic member is integrally combined with a part of an automobile metal member. It is desirable to preliminarily apply primer coating such as electrodeposition coating and intermediate coating to the metal body portion in order to impart rust prevention. Further, the surface of the plastic member may be subjected to surface treatment such as etching or primer coating in order to provide adhesion with the paint.
In the present invention, a top coat is applied to the surface of an automobile outer plate, and the plastic member is baked and dried at a temperature that does not cause problems such as deterioration in physical strength, thermal deformation, and foaming. The baking temperature is the substrate surface temperature, preferably 110 to 100 ° C., and the baking time is, for example, 10 to 40 minutes, preferably 20 to 30 minutes.
When the baking temperature of the coating film is lower than 100 ° C., for example, the coating film is not sufficiently cured. On the other hand, when the temperature exceeds 110 ° C., the coating film is cured, but problems such as a decrease in physical strength of the plastic member, thermal deformation, foaming and the like are likely to occur.
The coating method of the present invention is not particularly limited as long as it is a coating method applied to an automobile body such as air spray, airless spray, electrostatic coating, and the like, and various coating methods can be applied.
The film thickness of the top coating is a dry film thickness, for example, 15 to 60 μm, preferably 25 to 50 μm.
EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, these Examples do not limit the scope of the present invention at all.
In the examples, “parts” and “%” are based on mass unless otherwise specified.

<Preparation of top coat>
In the formulation shown in Table 1, each component such as resin, acid catalyst, pigment, and additive is mixed, stirred and kneaded, and finally an acid catalyst is added and mixed to Preparation Examples 1 to 5 and Reference Preparation Example 1 A top coat of ~ 2 was prepared. In addition, the liquid thing was described as solid content.

Table 1

Table 1 (continued)

(Note 1: Synthetic fatty acid alkyd resin (Dainippon Paint, IN-45K-70, non-volatile content 70%, oil length 45, acid value 8.5 KOHmg / g)
(Note 2: Oilless alkyd resin (Dai Nippon Paint, CIH11-65, 65% non-volatile content, oil length 11, acid value 10.2 KOHmg / g)
(Note 3: Polyester resin (Dai Nippon Paint, HI33E-65, 65% non-volatile content, acid value 7.5 KOHmg / g)
(Note 4: Melamine resin A (manufactured by Mitsui Toatsu, Yuban 225, nonvolatile content 60%, low temperature curing type, normal butylated melamine resin)
(Note 5: Imino group type melamine resin B (Mitsui Cytec, Cymel 207, non-volatile content 75%, low temperature curing type, imino group type alkylated melamine resin)
(Note 6: Melamine resin C (Mitsui Toatsu, Uban 128, nonvolatile content 60%, medium temperature curing type, normal butylated melamine resin)

(Note 7: Titanium oxide pigment (rutile titanium oxide pigment)
(Note 8: Dispersant (copolymer containing acid group)
(Note 9: Surface conditioner (mixture of vinyl polymer and modified silicon compound)
(Note 10: Rheology control agent (urea polymer)
(Note 11: UV absorber (benzotriazole type / hindered amine type = 2/1 mixture)
(Note 12: Acid catalyst A (manufactured by Teika Co., Ltd., monobutyl phosphate)
(Note 13: Acid catalyst B (Taika Corporation, p-toluenesulfonic acid)

(Note 14: Acid catalyst C (manufactured by Teika), cumene sulfonic acid)
(Note 15: Acid catalyst D (manufactured by Teika Co., Ltd., dodecylbenzenesulfonic acid)
(Note 16: Acrytan Super 3000 White (Dainippon Paint, acrylic polyisocyanate 2-pack enamel)

<Test plate>
A test plate (manufactured by Nippon Test Panel Co., Ltd.) obtained by applying cationic electrodeposition coating to a dull steel plate (0.8 mm × 70 mm × 150 mm) in a predetermined process was used as a metal member. Hereinafter, it is referred to as an electrodeposited steel sheet.
An unsaturated polyester FRP plate (manufactured by Chubu Kogyo Co., Ltd.) coated with a vinyl ester gel coat was cut into 1 mm × 70 mm × 150 mm to obtain a plastic member. Hereinafter, it is referred to as an FRP plate.

<Preparation of test plate>
The surfaces of the electrodeposited steel plate and the FRP plate were wiped with gauze containing petroleum benzine for degreasing. The electrodeposited steel plate and the FRP plate were integrally combined to form an outer plate test plate.
This was spray-coated with an intermediate coating diluted to a viscosity suitable for coating (Daikon Paint, Delicon intermediate coating SF110 white: polyester / melamine-based coating) to a thickness of 30 to 35 μm (dry film thickness), temperature 110 ° C. And baked and dried for 20 minutes, and then cooled to room temperature.
Next, the top coating material prepared as described above was diluted to a viscosity suitable for coating, and spray coating was performed at 35 to 40 μm (dry film thickness), and the coating materials of Examples 1 to 5 were compared at a temperature of 110 ° C. for 20 minutes. The paint of No. 1 was baked and dried at 120 ° C. for 20 minutes, the paint of Comparative Example 2 at 140 ° C. for 20 minutes, and the paint of Comparative Example 3 at 80 ° C. for 30 minutes, and then cooled to room temperature to prepare a test plate. .
Evaluation of the coating film of the coating material produced above was performed as follows.

<Appearance of coating film>
The coating film appearance of the coated plate prepared above was evaluated by measuring the 60 ° gloss value using a gloss meter as follows.
○… 92 or more Δ… less than 92 to 88 or more ×… less than 88

<Paper eye test>
After applying the intermediate coating, it was dried, and the surface of the coating film was polished with a rotating sander # 320, and then coated with a top coating, and then dried, and the surface of the coating was visually evaluated as follows.
〇… Sharp marks are not seen △… Slightly seen ×… Clearly seen

<Dust resistance>
Ten minutes after the top coating was applied, paint dust was applied from the surface, and the roughness of the coating film surface was visually evaluated as follows.
○… Good △… Slightly rough skin is seen ×… Clear skin rough is seen

<Coating hardness>
Using the coated plate prepared above, according to JIS K5600-5-4, the surface of the coating film was scratched using a Mitsubishi Hi-Uni pencil, and the hardness was evaluated as follows with the hardest pencil hardness at which the coating film was not damaged.
○… F or more △… HB
× ... B or less

<Solvent resistance>
Using the coated plate prepared above, the rubbing test was repeated 10 times with gauze where the surface of the coating film was moistened with xylene at room temperature, and then the state of the coating film surface was visually evaluated as follows.
○… No abnormality △… Slightly glossy ×… Completely glossy <Interlayer adhesion>
After the first coating with the same top coating and the baking at the specified temperature / time specified in the test plate preparation conditions was repeated four times, the second top coating was applied with the same coating on the test plate, and 1 at the specified temperature / time. Test plates were prepared by baking and drying. According to JIS K5600-5-6, the test plate was subjected to a 2 mm wide gobang eye adhesion test, and when the surface of the coating film was peeled off with cello tape (registered trademark), depending on the number of gobang eyes, the following: It was evaluated as follows.
○ ... 100/100
× ... 99/100 or less

  The results of evaluating the coating film according to the above-described coating film evaluation method are shown in Table 2 below.

Table 2

Table 2 (continued)

  According to the present invention, in the coating of an automobile body integrally having a steel plate portion and a plastic member, it is possible to simultaneously and simultaneously apply a top coat paint and bake drying on both surfaces of the steel plate portion and the plastic member. The coating film was excellent in finished appearance, hardness, solvent resistance, interlayer adhesion, and the like. Thus, even melamine resin type baking paints can be baked at a low temperature, and a coating film having a finished feeling superior to urethane resin type coatings can be obtained. At the same time, integrated members with different materials, such as steel plates and plastics, can be painted and baked and dried at the same time, which makes it possible to shorten the process and eliminate subtle color differences between the members. In the future, multicolor design painting will be possible, and it is expected to be applied to the painting of automobile bodies with excellent design.

Claims (7)

A method of painting a surface of an automobile outer plate in which a metal member and a plastic member are integrally combined,
A top coat containing 20-50% by mass of a polyester resin, 5-25% by mass of an imino group-type melamine resin, and 0.01-2% by mass of an acid catalyst and baked and cured at 110 ° C. or less is applied and baked at the temperature. A method of painting an automobile outer plate characterized by drying.   A compound wherein the acid catalyst in the top coating is selected from the group consisting of p-toluenesulfonic acid, cumenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalene monosulfonic acid, dinonylnaphthalenedisulfonic acid, and alkyl phosphate The method according to claim 1, which is a mixture containing three or more kinds.   The method according to claim 1 or 2, wherein the plastic member is a material that does not thermally deform at the baking temperature of the paint.   The method according to claim 1, wherein the plastic member is a polyester resin.   The method according to any one of claims 1 to 4, wherein the automobile skin is an automobile skin for a commercial vehicle. A coating composition for an automobile outer plate surface in which a metal member and a plastic member are integrally combined,
A coating composition comprising 20 to 50% by mass of a polyester resin, 5 to 25% by mass of an imino group-type melamine resin, and 0.01 to 2% by mass of an acid catalyst, and is baked and cured at 110 ° C. or less.   The acid catalyst contains three or more compounds selected from the group consisting of p-toluenesulfonic acid, cumenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalene monosulfonic acid, dinonylnaphthalenedisulfonic acid, and alkyl phosphate. The coating composition according to claim 6, which is a mixture.