JPH05105839A - Topcoating composition - Google Patents

Abstract

PURPOSE:To provide a topcoating compsn. which gives a topcoating film excellent in water repellency and weather resistance for long. CONSTITUTION:A fluorocopolymer consisting of fluoroolefin units having no chlorine atom, isobutylene units, vinyl pivalate units, and hydroxyalkyl vinyl ether units, a melamine resin, and a blocked acid catalyst are compounded as the main components to give a topcoating compsn.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating composition for a topcoat, and more particularly to a coating composition suitable for a topcoat for the exterior of automobiles and the like.

[0002]

2. Description of the Related Art Topcoats for coating automobiles are required to retain weather resistance and water repellency for a long period of time regardless of whether they are metallic or solid color, and various proposals have been made.

For example, Japanese Patent Application Laid-Open No. 63-59373 describes a coating composition for providing a top coat for metallic coating, the composition containing a fluoroolefin unit and having a hydroxyl group and a carboxyl group. It is composed of a specific fluorine-containing copolymer and a melamine resin.

Further, in JP-A-2-283747, a specific fluorine-containing copolymer containing fluoroolefin, cyclohexyl vinyl ether, alkyl vinyl ether and hydroxyalkyl vinyl ether as essential units, a complete alkyl group type melamine resin and a blocked melamine resin are described. A coating composition for a topcoat comprising an acid catalyst is disclosed.

The deterioration of weather resistance after long-term use is due to the fact that suspended matter such as dust and dirt in the air adheres to the coating film, and further the chlorotrifluoroethylene unit described in the examples of the above publications is added. In the case of the fluororesin containing, it is considered that the coating film is deteriorated by ultraviolet rays.

Although the above-mentioned known coating compositions are certainly improved in water repellency and durability as compared with the previous coating compositions, their long-term weather resistance is still unsatisfactory.

[0007]

DISCLOSURE OF THE INVENTION The present invention provides a coating composition for a top coat, which does not deteriorate in water repellency and weather resistance for a longer period of time.

[0008]

That is, the present invention provides a fluorinated copolymer, a melamine resin, and a block containing a chlorine-free fluoroolefin unit, an isobutylene unit, a vinyl pivalate unit, and a hydroxyalkyl vinyl ether unit. TECHNICAL FIELD The present invention relates to a coating composition for a top coat, which contains a modified acid catalyst as a main component.

[0009]

Examples The fluorine-containing copolymer (A) in the present invention has a chlorine atom-free fluoroolefin unit, an isobutylene unit, a vinyl pivalate unit and a hydroxyalkyl vinyl ether unit as essential structural units, A coating film having a glass transition temperature and capable of maintaining excellent water repellency for a long time is provided.

Examples of fluoroolefins containing no chlorine atom include tetrafluoroethylene, trifluoroethylene, pentafluoropropylene, and hexafluoropropylene. Particularly, the solubility in an organic solvent, the compatibility with a curing agent, and the coating property. Tetrafluoroethylene is preferable from the viewpoint of film physical properties, copolymerizability, and the like. Fluoroolefin unit content is 20-80 mol%, preferably 30-60 mol%
If it is too large, the solvent solubility is poor, and if it is too small, problems occur in weather resistance, water repellency, and stain resistance.

The content of the isobutylene unit is 5 to 60 mol%, preferably 10 to 45 mol%. If it is too large, the solvent solubility is poor, and if it is too small, stain resistance becomes poor.

The content of vinyl pivalate is 3 to 45 mol%, preferably 5 to 30 mol%. If it is too large, the acid resistance is poor, and if it is too small, the compatibility with the melamine resin becomes poor.

Examples of hydroxyalkyl vinyl ethers include 2-hydroxyethyl vinyl ether, 3-hydroxypropyl vinyl ether, 2-hydroxypropyl vinyl ether, 2-hydroxy-2-methylpropyl vinyl ether, 4-hydroxybutyl vinyl ether and 4-hydroxybutyl vinyl ether.
Hydroxy-2-methylbutyl vinyl ether, 5-hydroxypentyl vinyl ether, 6-hydroxyhexyl vinyl ether, 2-hydroxyethyl allyl ether, 4-
Examples thereof include hydroxybutyl allyl ether. The content is 5 to 60 mol%, preferably 5 to 40 mol%. If the content is too large, gelation is likely to occur, the storage stability is poor, and the resulting coating film becomes brittle. If it is too small, the curability becomes insufficient.

In addition, other monomers can be copolymerized as long as the long-term durability which is the effect of the present invention is not impaired. The content ratio of other monomers is up to 30 mol%.

The copolymerization can be carried out by a conventionally known method, the obtained copolymer has a number average molecular weight of 3000 to 20000, preferably 5000 to 15000, and has a glass transition point of 0.
-80 degreeC, Preferably it is 20-50 degreeC.

The top coat coating composition of the present invention comprises such a fluorine-containing copolymer, a melamine resin and a blocked acid catalyst as main components.

The melamine resin functions as a curing agent, and is a completely alkyl group type melamine resin, a methylol group type melamine resin, an imino group type melamine resin, an iminomethylol group type melamine resin, a butylated melamine resin, a methylated melamine resin. Can be used widely. In this respect, the composition described in JP-A-2-283747 can be used only for the completely alkyl group type, but in the present invention, the kind of the melamine resin is not particularly limited. The blending ratio of the melamine resin is 20 to 60 parts, preferably 20 to 40 parts, relative to 100 parts of the fluorocopolymer (parts by weight, the same applies hereinafter). When the amount is more than the range, the weather resistance is lowered, and when the amount is less than the range, the crosslinking density is lowered and the resin becomes soft and easily soiled.

As a blocked acid catalyst, there is disclosed in
You can use the ones listed in 2-283747,
For example, carboxylic acids such as acetic acid, lactic acid, succinic acid, oxalic acid, and maleic acid; sulfonic acids such as dodecylbenzenesulfonic acid and dinonylnaphthalenedisulfonic acid; dimethylphosphoric acid, dibutylphosphoric acid, dimethylpyrophosphoric acid, dibutylpyrophosphoric acid Examples thereof include alkyl phosphates such as carboxylic acid and sulfonic acid blocked with a blocking agent such as triethanolamine, dodecylamine, dimethylamine and dibutylamine. The mixing ratio of the blocked acid catalyst is 0.2 to 6.0 parts, preferably 0.5 to 100 parts of the fluorocopolymer.
~ 3.0 copies. If it is too large, the coating film becomes brittle, and if it is too small, the curing reaction does not proceed smoothly.

In the present invention, other resins may be blended, if necessary. Examples include acrylic resin (SS-1080, SS-792, AR-2078, LR-620, all manufactured by Mitsubishi Rayon Co., Ltd.), acrylic silicone resin (Zemlac AM1532, YC3623. Fluorine-containing copolymer 10
Up to 50 copies for 0 copies. Further, other known additives for the top coat, for example, a leveling agent, a defoaming agent, an antioxidant, an ultraviolet absorber, a light stabilizer, an anti-sagging agent and the like may be appropriately blended. Further, mica, pearl pigment and the like may be dispersed.

The coating composition of the present invention is usually used in the form of being dissolved and dispersed in an organic solvent. Examples of the organic solvent include aliphatic solvents such as hexane and octane; aromatic solvents such as toluene and xylene; ester solvents such as ethyl acetate and butyl acetate; ketone solvents such as methyl ethyl ketone and methyl isobutyl ketone; methanol and Examples include alcohol solvents such as ethanol.

The coating composition may be prepared by dispersing and dissolving the above components in an organic solvent and adjusting the concentration of the solid content with the organic solvent so that the concentration is usually 40 to 70% by weight. Before application, adjust the viscosity in the range of 20 to 40 seconds (20 ° C) with a No. 4 Ford cup using an organic solvent, apply a coating method such as spray type or electrostatic spray coating, and use a conventionally known method. Set and bake. A suitable baking temperature is 120 to 160 ° C.

The coating composition of the present invention is used as a topcoat which is in contact with the outside world, and can be applied not only as a two-coat one-bake topcoat but also as an overcoat. As a method of forming a base coat or the like, the conventional method can be applied as it is.

Next, the coating composition for a top coat of the present invention will be explained based on production examples, examples and comparative examples, but the present invention is not limited to these examples.

Production Example 250 ml of butyl acetate was added to a 1000 ml stainless steel autoclave.
g, vinyl pivalate (VPi) 36.4 g, hydroxybutyl vinyl ether (HBVE) 65 g and isopropoxycarbonyl peroxide 4.0 g were charged, and the mixture was ice-cooled to 0 ° C. and then degassed under reduced pressure. G of tetrafluoroethylene (TFE) 171 g and isobutylene (IB) 47 g of this one, was heated to 40 ° C. under stirring, allowed to react for 8 hours, 10.0 kg internal pressure of the reactor from ^{17.2kg / cm 2 g / cm 2} G The reaction was stopped when the temperature had dropped to (polymerization yield 70.0% by weight). The obtained fluorine-containing copolymer was analyzed by ¹⁹ F-NMR, ¹ H-NMR and elemental analysis methods, and it was found that TFE 50 mol%, IB 19 mol% and VPi
It was a copolymer consisting of 10 mol% and HBVE 21 mol% and had a number average molecular weight (Mn) of 6000 as measured by GPC.

Example 1 The fluorocopolymer obtained in the production example was dissolved in butyl acetate to obtain a resin varnish having a concentration of 50% by weight. This varnish 100
Melamine resin shown in Table 1 as a curing agent was added to 20 parts, and 20 parts of an organic solvent (Solvesso 150 / butyl acetate (3/1 weight ratio)) and triethanolamine-blocked dodecylbenzenesulfonic acid were further added. A coating composition was prepared by thoroughly mixing 0.5 parts of Solvesso 150, an organic solvent manufactured by Esso.

As a base material, a dull steel sheet (70 × 150 × 0.8 mm) that has been subjected to a chemical conversion treatment with zinc phosphate is subjected to cationic electrodeposition coating (Nippon Paint Co., Ltd .: Power Top PU-100) to a dry film thickness of about Electrodeposition coating was performed so as to have a thickness of 25 μm. Then, an intermediate coating (Amillac No. 1000, manufactured by Kansai Paint Co., Ltd.) was coated on the obtained electrodeposition coating film so that the dry film thickness was about 40 μm, and baked at 140 ° C. for 30 minutes.

After that, an acrylic resin base coat (Kansai Paint Co., Ltd .: Magicron base coat No. 1000)
) Was applied to give a dry film thickness of about 20 μm, and the coating was set for 3 minutes.

Next, the coating composition was diluted with a mixed solvent of Solvesso 150 / butyl acetate (5/1), and the viscosity was adjusted to 20 seconds with Ford cup No. 4, and this was applied onto the metallic base coating film. A test coated plate was prepared by spray coating to a dry film thickness of about 40 μm and drying at 140 ° C. for 30 minutes.

With respect to the obtained test pieces, the glass transition temperature of the top coat, the change with time of water repellency and the acid resistance were examined in the following manner. The results are shown in Table 1.

(Measurement of the glass transition temperature of the topcoat coating film) Using a dynamic viscoelasticity apparatus, using RSAII (manufactured by Rheometric Co.), the frequency was measured at 62.8 Hz, from room temperature to 200 ° C. under the conditions of 5 ° C./min. , The maximum value of tan δ was defined as the glass transition temperature (° C.) of the coating film.

(Change with time of contact angle of water of top coat)
Super accelerated weather resistance tester Eye super UV tester SUV-W13
Using (SUV) (manufactured by Iwasaki Electric Co., Ltd.), an accelerated weather resistance test was performed under the following conditions. And before the start of the test
The water-resistant contact angle after 350 hours and 690 hours was measured by a CA-A type contact angle meter manufactured by Kyowa Interface Science Co., Ltd.

Operating conditions of SUV Light 11 hours 63 ° C relative humidity 70% Condensation 11 hours 30 ° C relative humidity 100% overhumid 1 hour 63 ° C relative humidity 85% Shower 1 time per hour (12 seconds) (acid resistance) 1 ml of 50% sulfuric acid aqueous solution was dropped on the test piece, and the temperature was 80 ° C.
After leaving it for 15 minutes, visually inspect the appearance of the coating film.

A: No change B: Swelling and slightly coloring C: Remarkably swelling and coloring Examples 2 to 6 A coating composition having the composition shown in Table 1 was prepared in the same manner as in Example 1, and the same as in Example 1. It was painted and the performance of the coating film was examined.

The results are shown in Table 1.

Comparative Examples 1 to 4 Examples 1 and 2 except that Lumiflon 900 (manufactured by Asahi Glass Co., Ltd.) containing chlorotrifluoroethylene, cyclohexyl vinyl ether and hydroxybutyl vinyl ether as essential components was used as the fluorine-containing copolymer. A coating composition was prepared in the same manner as in Example 5, coated on a substrate, and the obtained coating film performance was examined.

The results are shown in Table 1.

The components in Table 1 are as follows.

Fluorine-containing copolymer: obtained in the production example Comparative copolymer: Lumiflon 900 (manufactured by Asahi Glass Co., Ltd.) Comparative acrylic paint: Magicron 1026 clear (manufactured by Kansai Paint Co., Ltd .: acrylic melamine paint) ) Acrylic resin for blending: AR-2078 (manufactured by Mitsubishi Rayon Co., Ltd.) Melamine resin A: Cymel 303 (manufactured by Mitsui Cyanamid Co., Ltd .: fully alkyl group type melamine resin) Melamine resin B: Cymel 771 (Mitsui Cyanamid Co., Ltd.) Made: Methylol-based melamine resin) Melamine resin C: Uban 20SE60 (Mitsui Toatsu Co., Ltd .: Butylated melamine resin) Melamine resin D: Cymel 202 (Mitsui Cyanamid Co., Ltd .: Imino-methylol-based melamine) Resin) Acid catalyst: triethanolamine blocked dodecylbenzenesulfonic acid Organic solvent: Solvesso 150 / Butyl acetate (5/1 weight ratio) Leveling agent: BYK-320 (manufactured by Big Chem Co., Ltd.)

[0039]

[Table 1]

[0040]

The coating composition of the present invention provides a coating film excellent in properties such as water repellency, weather resistance and acid resistance over a long period of time, and is optimal as a coating composition for a top coat.

Claims (1)

[Claims] 1. A fluorine-containing copolymer containing a fluoroolefin unit containing no chlorine atom, an isobutylene unit, a vinyl pivalate unit and a hydroxyalkyl vinyl ether unit, a melamine resin, and a blocked acid catalyst as main components. Topcoat coating composition.