JPH04246483A - Coating composition - Google Patents

Abstract

PURPOSE:To improve the balance between acid resistance and scratch resistance by compounding a specific resin, an alkyl-etherified melamine resin, a blocked polyisocyanate, and an organotin compd. CONSTITUTION:A polyhydric alcohol is reacted with a polycarboxylic acid (anhydride) to give a hydroxylated polyester resin having a number-average mol.wt. of 300-5000, a hydoxyl value of 50-300, and an acid value of 3-50. Separately, an aldehyde is condensed with melamine and the condensate is at least partially etherified with a 1-4C alcohol to give an alkyl-etherified melamine resin having a number-average mol.wt. of 400-1200. A hydroxylated acrylic resin having a number-average mol.wt. of 1800-10,000, a hydroxyl value of 60-150, and an acid value of 5-20 and/or said hydroxylated polyester resin. the melamine resin, a nonyellowing blocked polyisocyanate, and an organotin compd. are compounded to give a coating compsn.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to coatings for metals, particularly automotive topcoat compositions. In particular, it relates to paints that are highly resistant to acid rain and scratches while using general resins that are excellent in terms of economy and workability.

0002

[Prior Art] Recently, acid rain has become a condition that deteriorates top coats for automobiles, and the appearance of acrylic resin paints and polyester resin paints, which have been most commonly used as top coats, has been affected by stains, discoloration, etc. This may lead to a defective state and further progress to destruction of the coating film. On the other hand, silicone resin-based, fluororesin-based, and polyurethane resin-based paints that are highly resistant to acid rain are expensive and have drawbacks such as difficulty in painting workability.

[0003] In JP-A-61-143472, Tg is 0.
For thermosetting acrylic resins having a hydroxyl value of 20 to 130 and an acid value of 6 to 40 at temperatures below 1-158079 describes that a blocked polyisocyanate can be used in combination with an acrylic copolymer of a specific structural formula and an alkyl etherified melamine resin as a clear coat paint that is applied over a base coat paint containing a colorant. Just by being there,
It does not describe the effects associated with combined use.

[0004] In JP-A-60-67515, a hydroxyl value containing ε-caprolactone modified vinyl monomer is 20.
~200 acrylic copolymers and polyester resins are described as being heat-cured with aminoadehyde resins and/or isocyanates as crosslinking agents, but there is no description of the effects of using melamine resins and isocyanates together. This is a technology for resin systems that use polyester resin.

[0005] In JP-A-59-36112, Tg50°C
When the following acrylic copolymers contain active hydroxyl groups or active amide groups, a crosslinking agent consisting of a polyfunctional isocyanate, aminoadehyde resin, etc., or a mixture thereof can be used. It does not describe the accompanying effects. The acid resistance level of the prior art is not sufficient to meet the objective of the present invention.

[0006]

[Problems to be Solved by the Invention] As a composition that overcomes the above-mentioned drawbacks, JP-A-2-242867 discloses a composition containing a hydroxyl group-containing resin, an amino resin, and a blocked polyisocyanate compound as main components, and a hydroxyl group-containing resin and each crosslinking agent. It is described that the reaction initiation temperature is specified, a hydroxyl group-containing resin and an amino resin are reacted as an effect, and a blocked polyisocyanate compound is used as an auxiliary crosslinking agent. In this composition, acid resistance is still not sufficient due to unreacted hydroxyl groups and melamine caused by the reaction between the hydroxyl group-containing resin and the crosslinking agent. Furthermore, in order to react with blocked isocyanate whose starting temperature is higher than that of normal melamine, baking at a higher temperature than conventionally is required. Therefore, in the present invention, blocked isocyanate is not used as an auxiliary crosslinking agent, but is used as a main crosslinking agent together with melamine resin, and by reacting almost simultaneously with the crosslinking compound, a well-balanced paint having excellent acid resistance and scratch resistance is provided. It is to be.

[0007]

[Means for Solving the Problems] The present invention provides a hydroxyl group-containing acrylic resin and/or a hydroxyl group-containing polyester resin.
By adding a crosslinking agent consisting of an alkyl etherified miramin resin, a non-yellowing polyfunctional block isocyanate, and an organic tin-based compound, a coating composition that satisfies the above properties in a well-balanced manner is used to prevent acid rain and scratches, which are becoming worse. There is a particular thing.

The present invention will be explained in detail below. (A) Hydroxyl group-containing acrylic resin and/or hydroxyl group-containing polyester resin The hydroxyl group-containing acrylic resin and/or polyester resin used in the present invention need only have two or more hydroxyl groups in the molecule. The hydroxyl group-containing acrylic resin used in the present invention preferably has a number average molecular weight of 1,800 to 10,000, a hydroxyl value of 60 to 150, and an acid value of 5 to 20. For example, the following monomers can be polymerized by a conventional method.

(1) Ethylene having a hydroxyl group such as hydroxylmethyl (meth)acrylate, hydroxylethyl (meth)acrylate, hydroxylpropyl (meth)acrylate, hydroxylbutyl (meth)acrylate, N-methylolacrylamine, etc. monomer, (2
) Ethylene monomers having a carboxyl group such as (meth)acrylic acid, crotonic acid, itaconic acid, fumaric acid, maleic acid, (3) methyl (meth)acrylate, ethyl (meth)acrylate, (meth)acrylic acid propyl,
Butyl acrylate, n-propyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-acrylate
Ethylenic monomers copolymerizable with the monomers (1) and (2), such as (meth)acrylic acid alkyl esters such as ethylhexyl, n-octyl acrylate, and n-dodecyl acrylate, as well as (meth)acrylonitrile, styrene, etc. is used.

[0010] When the number average molecular weight is less than 1,800,
Due to lack of crosslinking, sufficient coating film quality could not be obtained, resulting in
If it exceeds 0, the viscosity increases and there is a tendency that an appearance with excellent smoothness cannot be obtained. A more preferable range is 2,0
00 to 8,000. If the hydroxyl value is less than 60, the adhesion and curing properties tend to decrease;
If it exceeds this amount, the water resistance and acid resistance tend to decrease due to the remaining hydroxyl groups. A more preferable range is 80-120. If the acid value is less than 5, it will not cure sufficiently, and if it exceeds 20, the stability of the paint during storage will be poor, or the paint will harden too quickly, leading to a tendency for the appearance of the paint film to lack smoothness. A more preferable range is 8-15.

The hydroxyl group-containing polyester resin used in the present invention preferably has a number average molecular weight of 300 to 5,000, a hydroxyl value of 50 to 300, and an acid value of 3 to 50. It is an ester reaction product of polyhydric alcohol and polybasic acid or its anhydride, and has a hydroxyl group in the molecule. Polyhydric alcohols that can be used to produce the polyester resin of the present invention include ethylene glycol, propylene glycol, butylene glycol, 1,6-hexanediol, diethylene glycol, dipropylene glycol, neopentyl glycol, triethylene glycol,
Examples include glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, and dipentaerythritol. Examples of polybasic acids or their anhydrides include phthalic acid, phthalic anhydride, isophthalic acid, terephthalic acid,
Succinic acid, succinic anhydride, adipic acid, azelaic acid,
Sebacic acid, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, maleic anhydride, fumaric acid, itaconic acid, trimellitic anhydride, etc. can be used.

The polyester resin used in the present invention is prepared by reacting the hydroxyl group of the polyhydric alcohol with the carboxyl group of the polybasic acid or its anhydride in a molar ratio of 1.2 to 1.8. It has a residual hydroxyl group in the molecule. If the number average molecular weight is less than 300, there will be insufficient crosslinking in the coating film, and sufficient coating quality will not be obtained.On the other hand, if it exceeds 5,000, the viscosity of the coating will increase, and the appearance with excellent smoothness will not be obtained. There is a tendency not to get it. A more preferable number average molecular weight range is 500 to 4,000. Regarding the hydroxyl value, when it is less than 50, the adhesion of the coating film tends to decrease, and the curability of the coating material also tends to decrease. On the other hand, if it exceeds 300, water resistance and acid resistance tend to decrease due to the remaining hydroxyl groups. A more preferable range of hydroxyl value is 70 to 280. If the acid value of the polyester resin is less than 3, the paint film will not cure sufficiently, and if it exceeds 50, the stability of the paint during storage will deteriorate.
Curing may occur too quickly and the appearance (smoothness) of the coating film tends to deteriorate. A more preferable range is 5-20. Furthermore, if a material modified with urethane or the like is used, the scratch resistance from car washes or the like will be improved.

(B) Alkyl etherified melamine resin The alkyl etherified melamine resin used in the present invention includes, for example, methylated melamine resin, n-butylated melamine resin, isobutylated melamine resin, etc., in which the alkoxy group is a methoxy group or an ethoxy group. , n-butoxy group, i-butoxy group, and alkoxymethylmelamine resin. These resins are usually obtained by subjecting melamine to an addition reaction or addition condensation reaction of an aldehyde such as formaldehyde or paraformaldehyde, and then at least partially etherifying it with a monohydric alcohol having 1 to 4 carbon atoms.

These alkyl etherified melamine resins are synthesized by conventional methods, and those having a number average molecular weight of about 400 to 1,200 are preferably used. When the number average molecular weight is less than 400, the proportion of low molecular weight resin increases, resulting in an increase in volatile content, and 1,200
If it exceeds this, the solid content during coating will decrease and the appearance will also tend to deteriorate. A more preferable range is 600 to 1,000
It is. A conventional cured coating film in which a hydroxyl group-containing resin is cured only with an alkyl etherified melamine resin cannot ensure the level of acid resistance and scratch resistance that is the objective of the present invention.

(C) Non-yellowing polyfunctional block isocyanate The non-yellowing polyfunctional block isocyanate used in the present invention is aliphatic polyfunctional isocyanate such as non-yellowing hexamethylene diisocyanate (hereinafter referred to as HDI), and isophorone diisocyanate (hereinafter referred to as HDI). MD as alicyclic functional isocyanates such as IPDI) and other isocyanates.
Part of I, H12 MDI (hydrogenated MDI), etc. can be used, and partially blocked or (completely) blocked such that these are thermally dissociated are used. Blocking agents include acetone oxime, cyclohexanone oxime, acetophenone oxime, benzophenone oxime, and the like. Among the above, MEK oxime-blocked IPDI is most preferred.

(D) Organotin Compound The organotin compound used in the present invention is a salt of an organotin and a monocarboxylic acid. Examples of organic tin include methyl, butyl,
Alkyltins such as octyl are preferred, and di-alkyltins are more preferred. The most preferred organic tin is di-
n-butyltin is mentioned. Therefore, the preferred organotin monocarboxylic acid is di-n-butyltin dialiphatic monocarboxylic acid, and the aliphatic monocarboxylic acid is preferably laurylate, maleate, phthalate, etc., and more preferably laurylate, Maleate. The most preferred organotin compound is di-n-butyltin dilaurylate. Furthermore, by using di-n-butyltin dilaurylate and di-n-butyltin dimaleate together, the reactivity can be suppressed more than that of di-n-butyltin laurylate.

Conventional cured coating films made by curing hydroxyl group-containing resins only with isocyanate have good acid resistance, but cannot achieve the objectives of the present invention in terms of low-temperature curability, economical efficiency, painting workability, etc. . Note that it is also effective for the stability of the paint to mix the hydroxyl group-containing resin and the blocked isocyanate in advance.

When the hydroxyl group-containing resin is cured with the crosslinking agent, the preferred ratio is 50 to 20 parts by weight of the alkyl etherified melamine resin and the blocked isocyanate crosslinking agent to 50 to 80 parts by weight of the hydroxyl group-containing resin. . If the amount of crosslinking agent is less than 10 parts by weight, a sufficiently cured coating film will not be obtained, and if it exceeds 50 parts by weight, acid resistance will decrease if there is a large amount of alkyl etherified melamine resin, and non-yellowing polyfunctional block isocyanate may If the amount is too large, the strength of the coating film tends to be insufficient. A more preferable range is 45 to 25
Parts by weight. The present invention is characterized in that an alkyl etherified melamine resin (B) and a non-yellowing polyfunctional block isocyanate (C) are used in combination as a crosslinking agent, and an organic tin-based compound is also used in combination, and in particular (B)/( C) ratio is 50
/50 to 95/5 is preferable; if the alkyl etherified melamine resin is less than 50/50, curing is insufficient and gas hole properties are poor, and if it exceeds 95/5, acid resistance tends not to be sufficiently improved. . A more preferable range of alkyl etherified melamine resin/non-yellowing polyfunctional block isocyanate is 70/30 to 90/10.

[0019] The preferred addition amount of the organotin compound in the present invention is 0.1 to 0.5% based on the solid content of the hydroxyl group-containing acrylic and/or polyester resin and the crosslinking agent.
．． If it is less than 1%, the degree of curing and acid resistance will be insufficient, and if it exceeds 0.5%, the water resistance of the coating film will tend to be insufficient.

(E) Other ingredients that can be added Other raw materials that can be added to the coating composition of the present invention include the following raw materials that are commonly used in coatings. Aluminum foil, bronze foil, tin foil, gold foil, silver foil, copper foil, metallic titanium foil, stainless steel foil, nickel foil, chromium, cobalt sulfide, manganese sulfide, titanium sulfide, alloy foils of these, plastics with a particle size of 10 to 45μ A metallic foil-like pigment selected from foil-like phthalocyanine blue. Examples of inorganic transparent pigments include iron oxide, such as Cicotrans Red L2915D, Cicotrans Yellow L1915, and 1916 (all manufactured by BASF).
The organic transparent pigment is Chromophthal Red A2B (manufactured by Ciba Geigy), and the dye is dark colors such as red, blue, purple, black, brown, etc. For example, Orazole Black RL, Orazole Red B, Orazole Yellow 3R
(both manufactured by Ciba Geigy). Other pigments include titanium dioxide, Shanin Blue, Shanin Breen,
Colored pigments include quinacridone, indanthrone, isoindolinone, perylene, anthrabyrimidine, carbon black, benzimidazolone, yellow iron oxide, and red iron oxide. Furthermore, there are extender pigments such as calcium carbonate, magnesium carbonate, barium sulfate, silicic acid, silicate, aluminum hydrate, and calcium sulfate.

ethylene glycol monobutyl ether,
Alcohol solvents such as ethylene glycol monobutyl ether acetate, Solvesso 100, Solvesso 15
Hydrocarbon solvents such as 0, ether solvents such as carbitol acetate and butyl carbitol, high boiling point solvents such as ketone solvents such as isophorone, ester solvents such as ethyl acetate and butyl acetate, aromas such as toluene and xylene. Low-boiling point solvents such as family solvents, ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, and acetone, and alcohol solvents such as methanol, butanol, isopropanol, and ethylene glycol monomethyl ether can be adjusted as appropriate.

Other additive components include acid catalysts, benzophenol-based ultraviolet absorbers, phenol-based sulfide-based antioxidants, surface conditioners such as silicone and organic polymers, anti-sagging agents, and thickeners. etc. in paint from 0.1 to
Approximately 5% can be used. A combination of these is effective in improving paint performance and coating film performance, and is therefore preferred.

[0023] The coating composition of the present invention can be applied by applying an electrodeposition paint or an intermediate coating paint to metal parts in the same manner as in ordinary automobile painting.
After applying three coats and then using a paint containing the resin component vehicle of the paint composition of the present invention as a top coat, or after applying a top coat of a regular solid paint or three metallic materials, this book can be used as a clear paint to protect the top coat. The coating composition of the invention can be used. In this case, the coating film thickness, coating machine, coating conditions, etc. are the same as those for conventional automobile finish coating. When applying the coating composition of the present invention as a solid topcoat or a clear coating on top of the topcoat, it is preferable to use air spray or electrostatic coating, and the viscosity is 20 to 30 seconds/No. 4 Ford Cup (
20°C) has good workability and can be coated to a dry film thickness of 30 to 50 μm. In addition, the baking curing conditions are not much different from those when using melamine resin or isocyanate alone.
The temperature is 120-150°C for about 10-40 minutes.

[0024]

[Function] The coating composition of the present invention uses an alkyl etherified melamine resin, a non-yellowing polyfunctional block isocyanate, and an organotin compound together as a crosslinking agent, so the organotin compound prevents the dissociation of the block isocyanate from the melamine resin. In order to proceed simultaneously with the reaction with hydroxyl group-containing acrylic and/or polyester resin, composite crosslinking of hydroxyl groups, NCO groups, hydroxyl groups and imino groups in the alkyl etherified melamine resin is performed, and free melamine and free hydroxyl groups are crosslinked. The acid resistance is significantly improved, and as the hardness improves, the scratch resistance also improves. Furthermore, by specifying the dibutyltin dialiphatic monocarboxylic acid in the organotin compound, it became possible to further control the above reactivity.

[0025]

EXAMPLES The present invention will be explained in more detail with reference to the following specific examples. Thickness 0.8mm with zinc phosphate treatment
Cationic electrodeposition paint [Nippon Paint Co., Ltd.] was applied to the dull steel plate.
Power Top PU-50] has a dry coating thickness of approximately 25 cm.
Electrodeposition coating was performed so that the thickness was .mu.m. Next, an intermediate coating material [Olga P manufactured by Nippon Paint Co., Ltd.] was applied on the obtained electrodeposition coating film.
-41 Sealer] was air-sprayed to a dry coating thickness of approximately 40 μm, and baked at 140° C. for 30 minutes. After that, acrylic resin top coat base coat paint [
Nippon Paint Co., Ltd. Super Rack] was dried for approximately 2 coats.
It was coated to a thickness of 0 μm and set for 3 minutes. Next, a paint with a solid content composition shown in Table 1 was mixed with N.
o. 4Adjust the viscosity to 25 seconds with a Ford cup, apply with an electrostatic coating machine AutoREA (manufactured by Landsburg Gema) at an atomization pressure of 5 kg/cm2 so that the dry film thickness is approximately 40 μm, and after setting for approximately 7 minutes, Bake for 10 and 20 minutes at .degree. In Example 7 and Comparative Example 3, the top coat shown in Table 1 was applied on top of the intermediate coat to a dry film thickness of approximately 40 μm, and baked in the same manner as in the other Examples. . The numbers shown in Table 1 represent parts by weight.

[0026]

[Table 1]

The following raw materials shown in Table 1 were used. *1 Manufactured by Mitsubishi Rayon Co., Ltd. Acrylic resin solid 60% Number average molecular weight 4,000 Hydroxyl value 95 Acid value 5-2
0 12*2 Made by Nippon Paint Co., Ltd. Acrylic resin solid 50% Number average molecular weight 8,000 Hydroxyl value 70 Acid value 5-2
0 20*3 A polyhydric alcohol consisting of neopentyl glycol, trimethylol, and hydroxypivalic acid neopentyl glycol ester was subjected to a condensation reaction with a polybasic acid containing a 6/4 ratio of hexahydrophthalic acid/isophthalic acid. A varnish (polyester resin) having an acid value of 9, a hydroxyl value of 110, and a number average molecular weight of 1,500 was used. *4 Butyl etherified melamine resin solid 60% manufactured by Mitsui Toatsu Chemical Co., Ltd. *5 Butyl etherified melamine resin solid 60% manufactured by Dainippon Ink and Chemicals Co., Ltd. *6 Blocked isocyanate (HDI) manufactured by Sumitomo Bayer Co., Ltd. *7 Blocked isocyanate (IPDI) manufactured by Sumitomo Bayer Ltd. *8 Isocyanate (H
DI) *9 Manufactured by Sankyoki Gosei Co., Ltd. (50% solution of di-n-butyltin dialiphatic monocarboxylate in xylene) *10
Di-n-butyltin dilaurate manufactured by Sankyoki Gosei Co., Ltd. As the coating solvent, Solvesso 150 manufactured by Exxon Chemical Co., Ltd. was used.

Evaluation and Evaluation Criteria (1) Acid resistance spot test is carried out by dropping approximately 0.5 ml of a 40% sulfuric acid solution onto a test piece, and after leaving it at 60°C for 15 minutes, the depth of corrosion of the coating film by the solution is determined by the Tokyo SURFC0M manufactured by Seimitsu Co., Ltd.
The surface roughness was measured using a two-dimensional surface roughness meter. The closer the value is to 0, the better. Unit Rmax. (μm) (2) Pencil hardness Measured in accordance with JIS K5400 8.4.2. (3) Approximately 1 c of scratch-resistant Kaneyo Co., Ltd. cleanser on a double layer of flannel
c and fixed it on the sliding head of a Gakushin friction fastness tester. After applying a load of 700 g and reciprocating the sliding head 10 times, the 20° gloss of the test part was measured and the gloss retention was calculated. (4) Water resistance test pieces were immersed in tap water at 40°C and left for 10 days. Thereafter, the state of the coating film on the test piece was observed. Evaluation was performed based on the following criteria. ○ ‥‥‥ No abnormality × ‥‥‥ ‥‥‥ A single liquid type of the coating exterior (skin, gloss, discoloration, crack, etc.) is recognized (5) One liquid type ○ ‥‥‥ 50 ° C, 120 hours of gel. Do not cause any damage or bumps. ×‥‥‥An abnormality occurs under the above conditions. (6) Workability ○‥‥‥Good (no sagging or wrinkles) △‥‥‥sagging,
Armpits may occur. ×‥‥‥Sag and armpits are likely to occur. (7) Low-temperature curing property: Excellent coating performance even when baked at a temperature 20°C lower (120°C) than standard. △‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ is good coating film performance even when baked at 20℃ lower temperature (120℃). (8) Economic efficiency: Both paint and coating equipment costs are low. △‥‥‥Paint and painting equipment costs are both medium. ×‥‥‥Both paint and painting equipment costs are high.

[0029]

Effects of the Invention The present invention avoids the drawbacks of workability that high-quality polyurethane paints have, and while ensuring ease of handling equivalent to conventional acrylic resin/melamine resin, the reaction between the main resin and the crosslinking agent is improved. By controlling the properties, acid resistance, scratch resistance, and low-temperature curability were improved, and a coating composition with excellent economic efficiency was completed.

Claims (1)

[Claims] 1. A coating composition comprising the following (A) to (D) as main components. (A) Hydroxyl group-containing acrylic resin and/or hydroxyl group-containing polyester resin (B) Alkyl etherified melamine resin (C) Non-yellowing polyfunctional block isocyanate (D) Organotin compound