JPH03126778A - Coating composition - Google Patents

Abstract

PURPOSE:To provide the title composition for topcoating of 1-coat-1-bake type for automotive use, excellent in coating workability, capable of giving coating films of good finish appearance, water resistance, hardness, recoat adhesivity, flexural resistance etc., comprising a specific polyester resin and a melamine resin at specified proportion. CONSTITUTION:The objective composition comprising (A) a polyester resin <-30 in acid value, 30-200 in hydroxyl value, 33-39 dyne/cm in surface tension and 5-45 deg.C in softening point (e.g. a reaction product of a polyol component, e.g. ethylene glycol and a polybasic acid, e.g. pelargonic acid) and (B) a melamine resin at the weight ratio A/B=(60:40)-(90:10).

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention provides a novel coating composition, and more specifically, the present invention provides a novel coating composition for automobiles that has excellent coating performance and good appearance and paint workability. This invention relates to a l-coat l-bake type top coating composition.

[Conventional technology] In recent years, the quality and functionality of automotive paints has been rapidly increasing.For example, cationic electrodeposition paints used as undercoats have significantly improved rust prevention and chipping resistance, and The transition to membranes is progressing. In addition, intermediate coating,
Topcoat paints are becoming more solid and water-based, and high-quality one-coat bake-type paints are also required for topcoat paints.

However, although conventional l-coat one-bake top coat paints for automobiles have excellent film performance such as economy and durability,
Appearance and painting workability were not necessarily satisfactory. For example, a thermosetting high solids coating composition containing a specific polyester resin, melamine resin, aliphatic or aromatic sulfonic acid or its amine salt, and a solvent can be used as a one-coat one-bake top coating for automobiles. has been disclosed (Special Publication No. 17903/1983)
Although this product has excellent coating performance, when painting on an automobile painting line, it can cause undesirable situations in the painting process, such as spot-like dents, so-called splashing and dripping, caused by poor paint application. However, it has the disadvantage that the surface of the coating film is difficult to become smooth, resulting in poor appearance.

[Problems to be Solved by the Invention] The present invention overcomes the drawbacks of the conventional l-coat l-bake type top coating paint for automobiles, has excellent coating film performance,
L-coat 1 for automobiles with good appearance and paint workability
This was made for the purpose of providing a bake-type top coating composition.

[Means for Solving the Problems] The present inventors have developed a method for automobiles having the above-mentioned preferable properties.
As a result of intensive research aimed at developing a coat l bake-type top coating composition, it was discovered that this purpose could be distantly achieved with a coating composition containing a specific polyester resin and melamine resin in a predetermined ratio. The present invention was completed based on this finding.

That is, the present invention provides (A) an acid value of less than 30, a hydroxyl value of 3
0-200, a surface tension of 33-39 dyne/cm and a softening point of 5-45°C, and (B) a melamine resin in a weight ratio of 60:40 to 90:10. A composition is provided.

The present invention will be explained in detail below.

In the composition of the present invention, a polyester resin is used as component (A), and this polyester resin has an acid value of less than 30, a hydroxyl value of 30 to 200, and a surface tension of 33-
39 dyne/cm and a softening point of 5-45°C.

When the acid value is 30 or more, the hydrophilicity of the resin becomes too high and the coating film becomes inferior in water resistance and flexibility. Further, if the hydroxyl value is less than 30, the coating film will have poor water resistance, and if it exceeds 200, the hydrophilicity of the resin will become too high, and the water resistance and flexibility of the coating film will tend to be poor.

On the other hand, if the surface tension is less than 33 dyne/cm, the adhesion between the coating films will be poor upon re-examination;
If it exceeds m, there is a tendency for flickering to occur during painting. Furthermore, if the softening point is less than 5°C, the hardness of the coating film will be too low and its water resistance will be poor, while if it exceeds 45°C, the coating film will have reduced flexibility and will be more likely to crack due to impact or the like.

In the composition of the present invention, the polyester resin used as component (A) is not particularly limited as long as it satisfies the above conditions. Such a polyester resin can be produced by a known esterification reaction by combining a polyol component, which is a usual raw material constituting it, with a polybasic acid or its acid anhydride, and a fatty acid used as necessary. can.

Examples of the polyol component include ethylene glycol, propylene glycol, diethylene glycol, butylene glycol, neopentyl glycol, hexanediol, 2,2-dimethylpentanediol-1,3
, hydrogenated bisphenol A1 hexylene glycol, glycerin, trimethylolethane, trimethylolpropane, 1.2.6-hexanediol, trimethylolcyclohexane, pentaerythritol, sorbitol,
Examples include dimethylol and dipentaerythritol. In addition to these, tris(2-hydroxyethyl)incyanuride), 2,2-dimethyl-3-
Hydroxypropatol, 2,2-dimethyl-3-hydroquine propionate, and the like can also be used. These polyol components may be used alone or in combination of two or more.

Examples of fatty acids include pelargonic acid, octylic acid, nonanoic acid, lauric acid, stearic acid, and soybean oil.
Examples include fatty acids obtained from coconut oil, safflower oil, cottonseed oil, bran oil, castor oil, dehydrated castor oil, tung oil, linseed oil, tall oil, and the like. One type of these fatty acids may be used, or two or more types may be used in combination.

Furthermore, examples of polybasic acids and their acid anhydrides include phthalic anhydride, isophthalic acid, terephthalic acid, tetrahydro-7-talic anhydride, maleic anhydride, 7-malic acid, succinic acid,
Examples include glutaric acid, adipic acid, trimethyladipic acid, cepatic acid, dimethylolpropionic acid, trimellitic anhydride, butanetetracarboxylic acid, and the like. These polybasic acids and their acid anhydrides may be used alone or in combination of two or more.

There are no particular restrictions on the method for producing the polyester resin, and methods conventionally used in the production of alkyd resins, such as melt condensation, azeotropic condensation, or a combination thereof, can be used.

In the composition of the present invention, a melamine resin is used as component (B). There are no particular limitations on the melamine resin, and for example, a methylolated amino compound obtained by reacting melamine with formaldehyde and etherified with an alcohol such as methanol, gropanol, butatol, etc. can be used.

In the composition of the present invention, the polyester resin as the component (A) and the melamine resin as the component (B) may be used alone or in combination of two or more, and (A) The ratio of component (B) to component (B) needs to be selected within a weight ratio of 60:40 to 90:10.

If the amount of the polyester resin used as component (A) is less than the above range, the coating film will be less flexible and more likely to crack due to impact, etc. If it is more than the above range, the coating film will have reduced hardness and water resistance. becomes inferior.

The coating composition of the present invention may contain a suitable solvent in addition to the components (A) and (B). The solvent is not particularly limited as long as it can dissolve each component, and any solvent can be selected from those commonly used in conventional coating compositions.

Examples of such solvents include aromatic hydrocarbons, aliphatic hydrocarbons, alicyclic hydrocarbons, alcohols, esters, ethers, ketones, and specifically toluene,
xylene, methylnaphthalene, naphtha, mineral spirit, methanol, ethanol, isopropanol, n
-7'tanol, ethyl acetate, butyl acetate, glycol monoethyl ether, glycol monobutyl ether,
Examples include glycol monomethyl ether acetate-1-, glycol monoethyl ether acetate, methyl ethyl ketone, and methyl isobutyl ketone. These solvents may be used alone or in combination of two or more.

In addition, pigments such as inorganic pigments, organic pigments, and extender pigments can be added to the composition of the present invention, if necessary. Examples of the inorganic pigments include white pigments such as titanium dioxide, zinc white, and white lead, black pigments such as carbon black, acetylene black, and graphite, red pigments such as vermilion, cadmium red, antimony vermilion, and red red, and navy blue. , blue pigments such as ultramarine blue and cobalt blue, chromium oxide green, yellowish green,
Examples include green pigments such as chrome green, zinc wire, and edge green pigments, and iron oxide pigments having various tones. Examples of organic pigments include azo pigments, phthalocyanine pigments,
Thread-based, quinacridone-based, dioxazine-based, and isoindolinone-based organic pigments are included, and extender pigments include, for example, chalk, precipitated calcium carbonate, dung, pallite powder, precipitated barium sulfate, clay, talc, and silica powder. , diatomaceous earth, alumina, and ceracola.

Furthermore, the composition of the present invention may optionally include additive components commonly used in conventional paint m acids, such as curing accelerators, antifoaming agents, thickeners, anti-settling agents, anti-sagging agents, and anti-color separation agents. Agents, pigment dispersants, leveling agents, anti-skinning agents, anti-scratch agents, anti-mold agents, ultraviolet absorbers, antioxidants, antistatic agents, etc. may be added within the range that does not impair the purpose of the present invention. can.

There are no particular limitations on the method for preparing the composition of the present invention, and conventional methods can be used. For example, the above-mentioned (A) component, (B) component and various additive components used as necessary may be mixed in a roll mill, a corn mill, a 7-rutstone mill,
It can be prepared by thoroughly and homogeneously mixing using a speed drying mill, ball mill, sand grind mill, crow mill, attritor, desilver, etc.

There are no particular limitations on the method of applying the coating composition of the present invention, including methods conventionally used for applying topcoat paints,
For example, an appropriate method can be selected from among methods such as air spray painting, airless spray painting, roll coater painting, brush painting, and tampon painting.

[Example] Next, the present invention will be explained in more detail with reference to Examples.
The present invention is not limited in any way by these examples.

The properties and coating performance of the polyester resin were determined according to the following method.

(1) Surface tension of polyester resin A solution prepared by adding 50 parts by weight of pyrrolidone to 50 parts by weight of a polyester resin reaction mixture (solid content 100% by weight) was measured using a Deitzmeter (manufactured by BYK-Hemi, trade name). The surface tension was measured using

(2) Softening point of polyester resin The softening point of the polyester resin reaction mixture (solid content 100% by weight) was measured using a thermal analyzer (manufactured by Shimadzu Corporation, Model DT-30).

1 (3) Finished appearance of the coating film The finished appearance of the coating film was evaluated using an image clarity measuring device (HA-I CM, trade name) manufactured by Suga Test Instruments Co., Ltd. The higher the value, the better the finished appearance of the coating film.

(4) Water resistance test piece of paint film was immersed in warm water at 40°C for 240 hours, and the presence or absence of abnormalities in appearance such as swelling and shrinkage of the paint film was examined.

(5) Pencil hardness of coating film Determined according to JIS K-54006, 14 pencil scratch test.

(6) Recoat film adhesion (recoat adhesion) test piece:
After applying the same prototype paint and baking it at 140°C for 30 minutes, a cross cut was made and a peel test was performed using Sellotape.

(7) Flexing resistance of paint film In accordance with LRS K-54006, 16 bending resistance test, the surface of the paint film was examined by bending it 180 degrees along a 10 mm diameter 2 iron rod with the paint surface facing up. .

Production Example 1 Production of Polyester Resin A-1 In a reactor equipped with a stirrer, a thermometer, and a water separator, 35.0 parts by weight of isophthalic acid, 7.1 parts by weight of adipic acid, and 20.0 parts by weight of isononanoic acid were added.
Parts by weight, 28.6 parts by weight of trimethylolpropane, and 963 parts by weight of neopentyl glycol were charged and heated, and the temperature was gradually raised to 160 to 230°C over 3 hours while stirring, and then 230°C for 1 hour. 3 parts by weight of xylene was added, water was distilled off by azeotropy with xylene at 230'O to proceed with the reaction, and when the acid value reached 9, the reaction was terminated by cooling. The reaction mixture was diluted with xylene 41.3
parts by weight, and diluted with 17.7 parts by weight of n-butanol. The obtained polyester resin A-1 solution had a solid content of 60.3
% by weight, Gardner viscosity P.

The surface tension of this resin is 36,1 dyne/cm,
The softening point was 36°C. The results are shown in Table 1.

Production examples 2 to 17 Polyester resins A-2 to A-10,
Production of B-1-B-7 Polyester resins A-2 to A-10, B-1 to B-
7 was manufactured. The results are shown in Table 1.

Examples 1 to 12, Comparative Examples 1 to 9 Coating compositions were prepared by processing each component of the type and amount shown in Table 2 in a sand mill for 1 hour to sufficiently homogeneously disperse it.

The obtained coating composition was mixed with an aromatic solvent (Tsurpets #1
00. The viscosity was adjusted to 25 seconds (Ford cup #4, temperature 20° C.) using a mixed solvent of 70 parts by weight (manufactured by Esso, trade name) and 30 parts by weight of n-butyl alcohol.

Next, a steel plate treated with zinc phosphate [manufactured by Nippon Bar Riki Rising Co., Ltd., trade name, Bonderite #3004] was used.
A cationic electrodeposition paint [manufactured by Nippon Oil & Fats Co., Ltd., trade name, Aqua #4100] was applied to a dry film thickness of 20 μm, baked at 165°C for 30 minutes, and an intermediate coat [
Nippon Oil & Fats Co., Ltd., trade name, Hiebiko No. 1] was applied to a dry film thickness of 30l1m and heated at 140°C.
The test plate was baked at 140°0 for 30 minutes, and the coating N [acid whose viscosity was adjusted as described above] was air-sprayed to a dry coating thickness of 30 μm. .

The physical properties of the coating film were determined for the test piece thus prepared. The results are shown in Tables 2 and 3.

As is clear from Tables 2 and 3, the coating film obtained from the coating composition of the present invention has good appearance, water resistance, pencil hardness,
Excellent in both recoat adhesion and bending resistance.

On the other hand, Comparative Example 1, in which the polyester resin has a softening point of less than 5°C, has poor water resistance and pencil hardness;
Comparative Example 2 where the temperature exceeds 5°C has poor bending resistance. Further, Comparative Example 3 in which the surface tension of the polyester resin exceeds 39 dyne/cm is inferior in coating film appearance, and Comparative Example 4 in which the surface tension of the polyester resin is less than 33 dyne/cm is inferior in recoat adhesion.

In addition, Comparative Example 5, in which the amount of polyester resin used is less than 60% by weight with respect to the total amount of Polyester resin and melamine resin, has poor bending resistance, and Comparative Example 6, in which the amount of polyester resin used is more than 90% by weight, is poor in water resistance. and inferior to pencil hardness.

On the other hand, Comparative Example 7 in which the acid value of the polyester resin exceeds 30
and Comparative Example 8 in which the number of hydroxyl groups exceeds 200 is inferior in water resistance and bending resistance. Furthermore, Comparative Example 9 in which the polyester resin had a hydroxyl value of less than 30 had poor water resistance.

(The following is a blank space) 6- [Effects of the Invention] The coating composition of the present invention contains a specific polyester resin and a melamine resin in a predetermined ratio, has excellent coating workability, and is free from repelling and dripping. It does not cause defects on the surface of the paint film, has a good finished appearance, and
It can provide a coating film with excellent coating properties such as water resistance, hardness, recoat adhesion, and bending resistance, and is suitably used as a one-coat, one-bake type top coating for automobiles.

Claims (1)

[Claims] 1 (A) a polyester resin with an acid value of less than 30, a hydroxyl value of 30 to 200, a surface tension of 33 to 39 dyne/cm, and a softening point of 5 to 45°C, and (B) a melamine resin in a weight ratio of 6
A coating composition comprising the following components in a ratio of 0:40 to 90:10.