A METHOD OF FORMING A TRANSPARENT LAMINATE

Abstract: A method is provided of forming a transparent laminate using a wet-on-wet process in which a transparent acryl­ ic polymer paint A and a transparent fluorine-containing polymer paint B having the following formula are applied on a conventional finish coating: wherein X is a fluorine atom or chlorine atom, and R₁, R₂, R₃ and R₄ are at least one of hydrogen atom, hydroxyalkyl group, or carboxyalkyl group. The method produces a protective laminate consisting of a paint A layer to improve adhesion and a paint B layer to improve weatherability on the conventional finish coatings.

Description: This invention relates to a method of forming a transparent paint film having good adhesion to a conventional finish coating. Finish paint films applied on surfaces, such as automobile bodies and facing components, show undesirable signs of deterioration including discoloration, fading, and blistering following long years of weathering. Although the deterioration of conventional finish coatings is effectively prevented by waxing or other means, such maintenance increases the user's work load. To counter such inconvenience, several proposals have been made to improve weatherability by forming a fluoride resin paint on a finish coat. The Japanese Patent Kokai 61/197074 describes an automobile finish coating in which a clear paint, mainly composed of a fluoride polymer having the formula (I), is applied on a solid color finish coat using a wet-on-wet process, wherein X is a fluorine atom or a chlorine atom, and R is a hydroxyalkyl group or carboxyalkyl group. The Japanese Patent Kokai 63/59373 proposes a method of providing a metallic finish to paint by applying a clear top coat on a metallic base coat. The top coat consists of mainly fluorine-containing polymer (A) and a cross-linking agent, soluble in organic solvents. The fluorine-containing polymer (A) incorporates fluoroolefin, hydroxyl, and carboxyl groups, and has an average molecular weight of 3000-20000 and 1-40% wt. fluorine atoms. These conventional methods to form protective layers have been viewed as a way to further improve weatherability, such as resistance to discoloration and weathering, but these methods have a problem of adhesion. The object of this invention is to provide a method of forming a transparent laminate including a fluororesin on a conventional finish coating with good adhesion. The method of this invention is characterized by the formation of transparent multi-layers on a conventional finish coating using a wet-on-wet process with a transparent paint A composed of an acrylic copolymer resin and a transparent paint B based on a fluorine-containing polymer having the following formula: wherein X is a fluorine or chlorine atom, and R₁, R₂, R₃ and R₄ are at least one of hydrogen atom, hydroxyalkyl group, or carboxyalkyl group. The conventional finish coatings are formed by a common solid color paint or metallic color paint such as acrylic/melamine resin, polyester/melamine resin, and alkyd/melamine resin. The transparent paint A, which is mainly composed of an acrylic copolymer resin, incorporates functional monomers as components of the copolymer, including acidic type, such as acrylic acids and methacrylic acids; hydroxyl type, such as acrylic acid hydroxyethyl, methacrylic acid hydroxyethyl, and methacrylic acid hydroxypropyl; amide type, such as acrylamide and methacrylamide; or glycidyl type, such as acrylic acid glycidyl and methacrylic acid glycidyl. Such monomers have 5000-30000 of number average molecular weight, preferably 10000-20000, and 30-100 of hydroxyl value per gram solid content, preferably 45-80, and 5-20 of acid value, preferably 8-15. Acrylic copolymer used in the transparent paint A is cured by baking using a crosslinking agent such as alkyletherified melamine. The copolymer may be blended with dyes, organic tinting pigments, or inorganic fillers such as silica particles or barium sulphate at a blending ratio of 5% or less which does not degrade the transparency of the transparent paint A. The blending ratio of the above-described acrylic copolymer to melamine resin ranges from 90/10 to 70/30 by weight (solid ratio). The fluorine-containing polymer which substantially constitutes the transparent paint B is composed such that it has a number average molecular weight of 3000-20000, a hydroxyl value per gram solid content of 45-110, an acid value per gram solid content of 5-12, and has the following formula: wherein X is a fluorine or chlorine atom, and R₁, R₂, R₃ and R₄ are at least one of fluorine atom, hydrogen atom, hydroxyalkyl group, or carboxyalkyl group. The crosslinking agents which may be used to cure the fluorine-containing polymer include amino resins, such as metylolated or alkyletherified melamine resin and urea resin; polyisocyanates, such as hexamethylene diisocyanate, isophorondiisocyanate, xylylenediisocyanate, tolylenediisocyanate, and lysinediisocyanate; polyisocyanate compounds having more than one free isocyanate group within one molecule, which are formed by adding a polyhydric alcohol to one of the above polyisocyanates, and blocked polyisocyanate compounds which are formed by a blocked polyisocyanate compound with a hydroxyl group-containing compound. The blending ratio of fluorine-containing polymer to amino resin is preferably in the range of 100:25-70 parts by weight. The blending ratio of polyisocyanate compound to the fluorine-containing polymer is preferably in the range of 0.3-1.5 as the mole ratio of isocyanate group/hydroxyl group. The blended composition is dissolved in an adequate organic solvent at a concentration of 20-50% to prepare the clear paint B. Adequate organic solvents include acetone, methylethylketone, methylisobutylketone, ethylacetate, butylacetate, Cellosolve acetate, tetrahydrofuran, methanol, ethanol, butanol, toluene, xylene, dimethylsulfoxide, dimethylformamide, and dimethylacetamide. The transparent laminate of this invention is formed on the conventional finish coatings by successively depositing the transparent paint A composed of the above-described acrylic copolymer and the transparent paint B composed of the fluorine-containing polymer using a wet-on-wet process, and by curing simultaneously these transparent multi layers. The transparent paint A is uniformly painted on the conventional finish coatings at a thickness of 5-20 microns (solid film base) using a conventional method. after Approximately 2-4 minutes flash off solvents of the transparent paint film A, the transparent paint B is applied. The transparent paint B is applied at a thickness of 20-40 microns using a conventional method on the transparent paint film A, which has not yet dried. After setting for approximately 10 minutes, the films are baked. The standard conditions of baking are within 30 minutes at 140°C. The transparent laminate formed by the above-described procedure is structured such that the transparent paint B of the fluorine-containing polymer is layed on the conventional finish coating via the transparent paint A of acrylic copolymer resin with a wet-on-wet process. Since the transparent paint A gives improved adhesion and the transparent paint B gives improved weatherability and good dirt resistance, the laminate offers extremely stable protective performance for many years. Examples The invention is described in more detail in the following examples. Fluororesins were produced by the autoclave reaction of the compositions listed in Table 1 at 65°C for 10 hours. Example products of fluororesin 1 2 Chloro-tri-fluoroethylene 53 53 Cyclohexylvinylether 15 16 Ethylvinylether 12 13 Hydroxybutylvinylether 20 18 Xylene 142 111 Ethanol 40 32 K₂CO₃ 4.2 3.6 AIBN 0.36 0.31 The example fluororesin products 1 and 2 were reacted with 1.43 weight parts and 0.9 weight parts of succinic anhydride per 100 weight parts of the solid resin, respectively, at 150°C for 1 hour to obtain the modified fluororesins. The hydroxyl value, acid value, and number average molecular weight of each obtained modified fluororesin are listed in Table 2. Example product of modified fluororesin 1 2 Hydroxyl value 90 80 Acid value 8 5 Number average molecular weight 6000 9000 The obtained modified fluororesin products 1 and 2 were substituted with xylene to produce the modified fluororesin varnish 1 and 2, having 50% of solid content, respectively. 100 weight parts of the obtained modified fluororesin varnish 1 was mixed with 20.8 weight parts of modified alkylether melamine resin (Uban 205E-60, made by Mitsui Toatsu Chemicals, Inc.), 10 weight parts of solvesso 100 (made by Exxon Chemical Co.), and 0.2 weight parts of Modaflow (made by Monsanto Co.) under conventional (process) to prepare paint samples of the transparent paint B-1, which would be used in example 1. Example 1 On a conventional finish coating (2 coat, 1 bake type metallic coatings) consisting of a metallic base coat of an acrylic/melamine resin type (SP-M-80 silver, made by Nippon Paint Co.) and a clear coat of acrylic/melamine resin type (SP-O-80 clear, made by Nippon Paint Co.), the acrylic paint (SP-M-80 clear, made by Nippon Paint Co.) was applied as the transparent paint A, and the fluorine-containing melamine curable top transparent paint was applied as the clear paint B-1. Baking conditions, film thickness, and the evaluation of adhesion, appearance, and sanding marks are listed in Table 3. Example 2 On the same conventional finish coating as Example 1, the acrylic resin type clear paint (SP-M-80 clear, made by Nippon Paint Co.) as the transparent paint A, and then a top transparent paint film B-2 consisting of the modified fluororesin varnish 2 and a urethane isocyanate curing agent were applied with a wet-on-wet process. Baking conditions, film thickness and the evaluation of adhesion, appearance, and sanding marks are listed in Table 3. Example 3 The multi layer was formed using the same paint combination of the transparent paints A and B as that used in Example 1, except that the conventional finish coat was formed with the polyester/melamine resin solid color paint (Orga-G-65 white, made by Nippon Paint Co.). Baking conditions, film thickness and the evaluation of adhesion, appearance, and sanding marks are listed in Table 3. Reference Example 1 On the same conventional finish coatings as that used in Example 1, the transparent paint B of the same type used in Example 1 was directly formed (without transparent paint A). Baking conditions, film thickness and the evaluation of adhesion, appearance, and sanding marks are listed in Table 3. Reference Example 2 On the same type of finish coatings as that used in Example 3, the paint B of the same type as used in Example 3 was formed directly without transparent paint A. Baking conditions, film thickness and the evaluation of adhesion, appearance, and sanding marks are listed in Table 3. As Table 3 clearly illustrates, all examples of this invention, Examples 1 through 3, which formed the clear paint film of fluorine-containing polymer applied with a wet-on-wet process on the acrylic copolymer resin transparent paint film gave good results regarding adhesion, appearance, and sanding marks. On the contrary, reference examples 1 and 2, which had no acrylic copolymer transparent paint A film, showed poor adhesion and worse appearance and sanding marks than those in Examples 1 through 3. By using the method of this invention, a protective multi layer can be formed on the conventional finish coatings to give both a transparent layer which improves adhesion and a transparent top layer which has excellent weatherability. Consequently, all the problems which have been encountered in painting work are solved and stable transparent paint performance can be secured for many years without the need of troublesome maintenance, such as waxing the film surface.

Claims: A method for forming a transparent multilayer wherein first a transparent paint A comprising an acrylic copolymer incorporating functional monomers which have an average molecular weight of from 5,000 to 30,000, a hydroxyl value per gram of solid content of from 30 to 100, and an acid value of from 5 to 20 as components of the copolymer, and then a transparent paint B comprising a fluorine-containing polymer comprising the formula wherein X represents a fluorine or chlorine atom, and R₁, R₂, R₃ and R₄ each represents a hydrogen atom, hydroxyalkyl group, or carboxyalkyl group, and an organic solvent are applied on a conventional finish coating with a wet-on-wet process. A method for forming a transparent multilayer as in claim 1, wherein monomers incorporated to form the acrylic copolymer have an average molecular weight of from 10,000 to 20,000, a hydroxyl value per gram of solid content of from 45 to 80, and an acid value of from 8 to 15. A method for forming a transparent multilayer as in claim 1, wherein the fluorine-containing polymer has a number average molecular weight of from 3,000 to 20,000, a hydroxyl value per gram of solid content of from 45 to 110, and an acid value of from 5 to 12. A method for forming a transparent multilayer as in claim 3, wherein said fluorine containing polymer is cured with a cross linking agent. A method for forming a transparent multilayer as in claim 4, wherein said cross linking agent is a melamine resin and the blending ratio of fluorine-containing polymers to amino resin is in the range of 100:25-70 parts by weight. A method for forming a transparent multilayer as in claim 4, wherein said fluorine-containing polymer is cured with a polyisocyanate compound cross linking agent, and the blending ratio of polyisocyanate compound to the fluorine-containing polymer is in the range of from 0.3 to 1.5 (mol ratio of isocyanate group/hydroxyl group). A method for forming a transparent multilayer as in claim 1, wherein said transparent paint A is applied at a thickness of from 5 to 20 microns (dry thickness). A method for forming a transparent multilayer as in claim 1, wherein transparent paint B is applied at a thickness of from 20 to 40 microns (dry thickness) on transparent paint A.

Inventors: HANAOKA, MOTOYOSHI, KINOSHITA, MASAKATSU, KONSE, HIROAKI, SHIGENO, HARUHISA, YAMANAKA, MASAHIKO
Applicants: NIPPON PAINT CO., LTD., NISSAN MOTOR CO., LTD.
Application year: 1989
Main classification: C09D133
IPC codes: B05D7, B05D1, C08L61, C08G18, B05D5, C09D127