JPH0673656B2 - Method of forming coating film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a method for forming a coating film, which can be applied to, for example, all dark color system coating colors of automobile top coatings.

[Prior Art] Conventionally, in 2 coat 1 bake solid coating, etc., a cloudy clear system is used, and in 1 coat solid, by appropriately selecting a pigment, the depth of deep dark colors and the sharpness of colors have been achieved. ing. Further, in the case of a black coating film, the jet black property is improved by appropriately selecting a pigment or using a dispersion technique in 2-coat 1-bake solid coating or 1-coat solid coating.

By the way, it is known to use a clear coating as a top coat for protecting a metallic coating or a solid coating, as described in JP-B-58-44430. It is also known to use a clear coat as an intermediate layer in a coating system as described in JP-A-53-108134. However, the above clear coat paints and coating systems were considered to only serve the function of protecting the base coat.

[Problems to be solved by the invention]

As described above, in the prior art, it is not possible to obtain a sufficient color depth or even color by the turbid clear method of the two-color one-bake solid coating of the dark color system or the pigment selection in the one-coat solid coating. Regarding black coating, there is a problem that even if a pigment having a high jetness is selected, the jetness of the pigment is not realized in the coating film.

Therefore, it is an object of the present invention to provide a method for forming a coating film that eliminates the above-mentioned problems of the prior art and can provide the depth of color and the sharpness of the color of a coating film of a dark color system.

[Means for Solving the Problems]

According to the present invention, the above-mentioned object is to cover a dark-colored base coat having a lightness and saturation of the Munsell value shown in FIG. 1 in a region A with a transparent clear coat layer having a refractive index of 1.51 or less. Will be solved by.

[Specific Description of the Means and Its Action]

In general, the coating system for automobiles is composed of electrodeposition paint and intermediate paint.
~ 2 layers of top coat paint.

Electrodeposition paints are well-known conventional paints for automobiles, such as anion type and cation type, and intermediate coatings are generally polyester resins composed of polyhydric alcohol and polybasic acid, and oils thereof. Is a alkyd resin modified by 1. or an acrylic resin made of acrylic acid or the like and a cross-linking agent such as melamine resin or blocked isocyanate as a vehicle, and a rust preventive pigment, a chipping resistant pigment and other materials are appropriately mixed therein.

The dark-colored base coat used in the present invention is shown in FIG. 1 in the drawing showing the relationship between the lightness (V) and the saturation (C) of the Munsell value, in the area A (one-hatched area and both-hatched areas in FIG. 1). Region), preferably region B (first
It can be manufactured by adding an inorganic pigment such as vehicle color pigment, carbon black, titanium oxide, metal flake pigment, coating mica, white mica, etc. and other additives so that it falls within both hatched areas in the figure. It can be painted with the paint of Lightness and saturation
If the amount is out of the above range, the object of the present invention tends to be insufficiently achieved even if a transparent clear coat having a low refractive index (hereinafter referred to as a clear coat) is applied. As described above, the method of the present invention is particularly effective for dark colors such as black, blue and red, and is not so effective for light colors.

In the present invention, as the resin used as a vehicle for the dark-colored base coat coating material and the refractive index of 1.51 or more and less than 1.535 medium-refractive-index clear coating material, an acrylic resin, a polyester resin, which has been generally used conventionally, Examples include alkyd resins.

The acrylic resin that can be used in the present invention is
For example, it can be produced by polymerizing the following monomers by a conventional method.

(1) Ethylenic monomers having a hydroxyl group such as hydroxylmethyl (meth) acrylate, hydroxylethyl (meth) acrylate, hydroxylpropyl (meth) acrylate, hydroxylbutyl (meth) acrylate, and N-methylolacrylamine. (2) (meth) acrylic acid, crotonic acid, itaconic acid,
Ethylenic monomers having carboxyl groups such as fumaric acid and maleic acid, (3) methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl acrylate, n-propyl acrylate, acrylic N-butyl acid,
An ethylenic monomer copolymerizable with the above-mentioned monomers (1) and (2) such as isobutyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, (meth) acrylic acid alkyl ester of acrylic acid n-dodecyl acid, In addition, (meth) acrylonitrile, styrene and the like are used.

Next, the polyester resin can be produced from a polyhydric alcohol and a polybasic acid, as is well known. Examples of the polyhydric alcohol that can be used in the present invention include ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, neopentyl glycol, 1,2-, 1,8-, 2,3- , 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol,
Hydrogenated bisphenol A, hydroxyalkylated bisphenol A, 1,4-cyclohexanedimethanol, 2,2-dimethyl-3-hydroxypropyl-2,2-dimethyl-3
-Hydroxypropionate (BASHPN), 2,2,4-trimethyl 1,3F Trade name-Pentanediol, N, N-bis-
(2-hydroxyethyl) dimethylhydantoin, polytetramethylene ether glycol, polycaprolactone polyol, glycerin, sorbitol, annitol, trimethylolethane, trimethylolpropane,
One or more polyhydric alcohols such as trimethylolbutane, hexanetriol, pentaerythritol, dipentaerythritol, and tris- (hydroxyethyl) isocyanate can be appropriately combined and used.

On the other hand, examples of the polybasic acid used in the present invention include phthalic acid, phthalic anhydride, tetrahydrophthalic acid,
Tetrahydrophthalic anhydride, hexahydrophthalic acid, hexahydrophthalic anhydride, methyltetrahydrophthalic acid, methyltetrahydrophthalic anhydride, hymic acid anhydride, trimellitic acid, trimellitic anhydride, pyromellitic acid, pyromellitic anhydride, isophthalic acid , Terephthalic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, adipic acid, azelaic acid, sebacic acid, succinic acid, succinic anhydride, lactic acid, dodecenylsuccinic acid, dodecenylsuccinic anhydride, cyclohexane-1,4-dicarboxylic acid One or more polybasic acids such as acids and endo acids can be used in combination.

If necessary, oil or fat or fatty acid may be added to these polyester resins up to about 30% to impart flexibility to the resin.

Crosslinking of the acrylic, polyester and alkyd resins is, for example, an alkoxymethylmelamine resin in which an alkoxy group such as an n-butylated melamine resin and an isobutylated melamine resin has a methoxy group, an ethoxy group, an n-butoxy group and an i-butoxy group. Alternatively, a crosslinking agent such as benzoguanamine resin is used. These resins are usually obtained by subjecting an amino compound such as melamine and benzoguanamine to an addition reaction or an addition condensation reaction of an aldehyde such as formaldehyde and paraformaldehyde to obtain a compound having 1 carbon atom.
It can be obtained by etherification with a monohydric alcohol of ~ 4.

When these melamine resins are used as a cross-linking agent for polyester resins, it is preferable to add 60 to 80% of polyester resin and 40 to 20% of amino resin.

As the cross-linking agent component of the acrylic resin, an amino resin, particularly a melamine resin or a blocked isocyanate can be used. The ratio (weight ratio) of the acrylic resin or polyester resin / melamine resin or blocked isocyanate, which is a thermosetting resin, is preferably 9/1 to 6/4,
More preferably, it is 8/2 to 7/3.

In the method of the present invention, the most important thing is that the refractive index is 1.51 or less, preferably 5 μm or more, on the dark base coat.
By forming a film thickness of m or more, it is of course possible to protect the deeply colored base coat, and further to add the sharpness and depth of color of the base coat. Resins that give clear coats having a refractive index of 1.51 or less, and particularly clear coats having a refractive index of 1.480 or less, include polyester resins, alkyd resins, acrylic resins, and fluorine-containing resins, similar to the vehicle of the medium refractive index clear coat. As components constituting these resins, those having a large amount of aliphatic groups and fluorine are generally low in refractive index. From the above viewpoint, the vehicle having a low refractive index can be manufactured by adjusting the raw materials.

As the fluorine-containing resin, for example, JP-A-57-34107 (JP-B-60-21686) discloses a room temperature-curable fluorine-containing copolymer. According to this publication, fluoroolefin and cyclohexyl vinyl ether are disclosed. By using a copolymer containing a specific amount of an alkyl vinyl ether and a hydroxyalkyl vinyl ether as essential components, the curability of the resin is significantly improved, and it is possible to cure the resin in a short time by using a general-purpose curing agent such as melamine. It is described that not only this is possible, but also the use of isocyanate gives a weather-resistant coating film which can be cured at room temperature and which is rich in gloss and excellent in solvent resistance.

Further, JP-A-59-197471 describes a thermosetting resin composition for coatings containing a fluorine-containing copolymer, and in this publication, a fluorine-containing copolymer containing a hydroxyl group and acrylic acid or By using a thermosetting resin composition for coating material comprising a copolymer mixture of a copolymer of an alkyl ester of methacrylic acid and another acrylic monomer and a curing agent having a functional group that reacts with a hydroxyl group, water resistance can be improved. It is disclosed that solid color paints, metallic paints, clear paints and the like having excellent properties, solvent resistance and weather resistance can be obtained.

Further, Japanese Patent Application Laid-Open No. 61-46283 discloses a coating composition containing a fluorine-containing copolymer. According to this publication, fluoroolefin, cyclohexyl vinyl ether, alkyl vinyl ether, hydroxyalkyl vinyl ether and other copolymers are disclosed. And a fluorine-containing copolymer obtained by polymerizing the above in a specific ratio.

By the way, according to the study by the present inventors, the refractive index is 1.535.
It has been found that the above clear coat forming the high refractive index layer does not meet the object of the present invention. As a resin for forming such a high refractive index clear coat, for example, similar to the medium refractive index clear coat vehicle as described above,
There are polyester resins, alkyd resins, acrylic resins and fluorine-containing resins. In general, as a component constituting these resins, those having a high concentration of aromatic groups and higher groups have a high refractive index, and from this point, it is possible to manufacture a vehicle having a low refractive index by adjusting the raw materials. it can.

The clear coat used in the present invention is, for example, a clear coat for automobile top coating, and 2 coats 1 bake,
2 coat 2 bake, 3 coat 2 bake, multi-layer clear coat, etc. are included. When a clear film having a different refractive index constitutes a multi-layer system, interference fringes tend to occur when the film thickness is thinner, but when the thickness is 5 μm or more, the interference fringes do not occur. As described above, the bending ratio of the clear coat is classified as follows in the present invention.

High Refractive Index (H) 1.535 Medium Refractive Index (M) 1.505 Low Refractive Index (L) 1.480 In addition, the preferred combinations for improving the performance of the base by using two or more layers of clear coat of each refractive index are as follows. is there.

[Operation] In the method for forming a coating film according to the present invention, when the clear refractive index is increased, the reflectance on the surface is increased, and the light reflected from the surface increases whitish color to increase the depth of color and even color. , Jet blackness is lost. Further, by clear-coating a low-refractive-index clear film, the reflectance on the surface becomes smaller and the light reflected from the surface is reduced, so that the depth of color, the dullness of the color, and the jetness are improved more than ever.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples.
It goes without saying that the technical scope of the present invention is not limited to these examples, and in the following description, "parts" and "%" are based on weight unless otherwise specified.

Preparation of dark-colored base coat (1) Preparation of polyester resin Phthalic anhydride 21.05 parts, isophthalic acid 23.61 parts, trimethylolpropane 16.80 parts, neopentyl glycol 6.21
Part, ethylene glycol 3.83 parts, coconut oil 18.44 parts, and Cardura E 10.59 parts were condensed to give a polyester resin having xylol added to give a solid content of 60%.

(2) Preparation of coating material The following pigments were dispersed in this resin with a sand grind mill (melamine resin (Uban 20-SE-60 manufactured by Mitsui Toatsu Co., Ltd.)).
And were mixed to produce the following paint.

(3) Preparation of coating film Cation electrodeposition (Power Coat U-500 manufactured by Nippon Paint Co., Ltd.) and an intermediate coating film (Nippon Paint Co., Ltd.) were applied to 0.8 × 90 × 300 mm zinc phosphate chemically treated dull steel sheet. ) Olga O
On a test piece subjected to (P-2 gray), a paint whose viscosity was adjusted as described below was applied so as to have a predetermined film thickness. This was set for 7 minutes at room temperature and then baked at 140 ° C. for 30 minutes to prepare a test piece.

(4) Coating method of base coat and clear Comparative Example 1: A base coat was painted and baked as it was.

Examples 1 and 2 and Comparative Examples 2 to 3: 2 coat 1 bake in which base is coated, clear is coated and baked as it is, and 2 coat and 2 bake in which base is coated and baked, and clear (1) is coated and baked. Both were performed but both gave the same results.
The thickness of each clear film was 20 μm.

Examples 3 to 5 and Comparative Examples 4 to 6: The base is coated, the clear (1) is coated as it is, and the clear (2) is coated thereon and baked. Both 3 coats 1 bake and 3 coats 2 bases of coating and baking the base, coating clear (1) and then clearing (2) and baking were carried out, but both obtained the same result. The film thickness of each clear is 20μ
It was m.

(Note) In the table below, A / C indicates that C is formed first and A is formed later.

Example 6 and Comparative Examples 7 to 9: Coating films were obtained by baking 3 coats of Example 3 and Comparative Examples 4 to 6 with 1 coat of clear coat (3).

Comparative Example 10: D = 3 μm A = 20 μm C = 20 μm The film thickness was changed to 4 coats and 3 baking to obtain a coating film.

Example 7: D = 6 μm A = 20 μm C = 20 μm Each film thickness was changed to obtain a coating film by 4 coats and 3 baking.

The results of Examples 1 and 2 and Comparative Examples 1 to 3 are shown in Table 1.

Next, Table 2 shows the results of Examples 3 to 7 and Comparative Examples 4 to 10 in which the clear film thickness was changed as follows.

(5) Evaluation method (according to JIS-K-5400 6.1) (i) Visual judgment of coating film ⊚ ... Extremely deep depth of color and even excellent jet blackness.

Good: The depth of color and even the color have good jet blackness.

Δ: The depth of the color is whitish and even the color is not very jet black.

×: There is no jet blackness even if the white blur is severe.

* ...... Interference fringes occur in the coating film, and the color cannot be determined. (Ii) Refractive index The free film can be peeled off and measured with the Abbe refractometer according to the prescribed method.

〔effect〕

As described above, according to the present invention, by using a low refractive index clear of a clear coat of a dark color paint for automobiles, it is possible to obtain a deeper color depth than before, a dull color, and a jet-black coating film. Can be done.

That is, by controlling the refractive index of the currently used dark color type paints for automobiles and paints for clear coating on the coating film to 1.510 or less, it is possible to obtain a dark color and a black color which cannot be obtained by the conventional clear coat. The depth and even the color of jets have improved jetness, and the appearance is better than ever.

[Brief description of drawings]

FIG. 1 is a drawing showing a region of a preferable dark color capable of producing a color depth and a sharpness in accordance with the method of the present invention, in terms of the relationship between lightness and saturation of the color, and regions A and B are, respectively, in the present invention, The preferred and particularly preferred regions are indicated.

Claims (2)

[Claims] 1. A dark-colored base coat having a lightness and saturation of the Munsell value shown in FIG. 1 in a region A has a refractive index of 1.51.
A method for forming a coating film, which comprises coating with the following transparent clear coat layer. 2. The total thickness of the transparent clear coat layer is 10 μm.
The method for forming a coating film according to claim 1, wherein the thickness of the transparent clear coat layer having a refractive index of 1.485 or less is 5 μm or more in total among the above clear coat layers.