JPS6224149B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for forming a coating film that can be used in applications requiring a high quality appearance, such as automobile topcoat paints. Powder coatings are solvent-free, which is good for preventing pollution, and it is possible to apply a thick coating of approximately 50 μm or more in one coat, and it is easy to collect uncoated powder coatings, reducing paint loss. Being economical, etc.
Due to its various advantages, its usage is rapidly expanding. However, when powder coatings are used as enamels, especially as metallic enamels for automotive top coats, that is, when metal powders or metal powders and colored pigments are mixed into the resin composition for powder coatings, metal powders and powders are mixed. Due to the difference in the amount of charge with paint resins and the poor orientation of metal powder in the paint film due to the high melt viscosity of powder paints, electrostatic spray painting does not produce the same amount of metallic paint as conventional solvent-based metallic paints. It is very difficult to get a feel for it, and it has not yet been put to practical use. Apart from this, powder enamel, including when used as a solid base, requires an extremely laborious process to change the color, which also poses many problems. To solve these problems, the enamel base is currently coated with a normal thermosetting solvent-based paint (base coat paint) containing colored pigments or metal powder and colored pigments, and then a transparent thermosetting powder is applied. Various studies have been conducted on a two-coat, one-bake finishing method in which a paint (clear coat paint) is coated with dry-on wet and then heated and cured. However, when ordinary thermosetting solvent-based paints are used as base coat paints, abnormalities in the paint film that are thought to be caused by residual solvent and thermosetting reaction by-products in the paint film, such as underarms, skin irritation, etc. Metallic unevenness has occurred, and we are struggling to find countermeasures. Furthermore, when these systems are applied to automobile painting lines, the quality of the finish during repair becomes a problem. In other words, a solvent-based base coat paint is applied, a powder clear coat paint is applied on top of that, and if there are any defects when baked, the solvent-based base coat paint is applied again, and then the powder clear coat paint is applied. It is necessary to bake, but at this time, the solvent-based base coat paint is soaked into the powder clear coat, which tends to cause skin irritation, so a base coat paint with a particularly good finish is required. In addition, in relation to automobile painting lines, the clear coat paint that is applied on top of the solvent-based base coat paint during repair can be either a conventional solvent-based clear coat paint or a thermosetting powder paint. In the case of solvent-based clear coat paints, it is necessary to bake at 140 to 150°C for about 20 to 30 minutes, and in the case of thermosetting powder paints, it is necessary to bake at 160 to 170°C for 20 to 30 minutes. It is necessary to bake for about 30 minutes. Therefore, whether a powder clear coat or a solvent-based clear coat paint is used as a base coat paint for this purpose, it is necessary to form a coating film with good performance. As a result of intensive studies to solve these problems, the present inventors found that 60 to 99 parts by weight of a carboxylic acid amide copolymer having the composition specified in the claims, 1 to 20 parts by weight of cellulose acetate butyrate resin, When a solvent-based paint containing 0 to 20 parts by weight of a colored pigment or a metal powder and a colored pigment is applied to an object to be coated, a transparent thermosetting powder coating is applied to the coated surface. 160-170
℃ for 20 to 30 minutes, or when applying a normal thermosetting solvent-based clear coat paint to the painted surface and heating and curing at 140 to 150℃ for 20 to 30 minutes, the above-mentioned The present invention was completed by discovering that a coating film free from underarms, skin irritation, etc. and having good performance can be formed. It is preferable to use acrylamide or methacrylamide as the α,β monoethylenically unsaturated carboxylic acid amide, which is a raw material for the carboxylic acid amide copolymer used in the present invention, but there are also other options such as itaconic acid diamide, α- Ethylacrylamide, crotonic acid amide, fumaric acid diamide, maleic acid diamide, and other α,β-ethylenically unsaturated carboxylic acid amides containing up to about 10 carbon atoms may be utilized. The amount of unsaturated carboxylic acid amide used is preferably 2 to 20% by weight, preferably 5 to 15% by weight, based on the carboxylic acid amide copolymer. If it is less than 2% by weight, curing will be insufficient and the solvent resistance will be unsatisfactory, and if it is more than 20% by weight, wrinkles will easily occur and the flexibility of the coating will be insufficient, which is undesirable. α、β
When a monoethylenically unsaturated carboxylic acid amide is used, the carboxylic acid used in the present invention can be modified by modifying the carboxylic acid amide component in the resulting copolymer with an aldehyde and further etherifying it at least partially. An amide copolymer is obtained. Etherification is carried out using alcohols.
In this carboxylic acid amide copolymer, one hydrogen atom of the amide group has the formula (However, in the formula, R represents a hydrogen atom when formaldehyde is used, an alkyl group when other aliphatic aldehydes are used, and R ₁ is a group obtained by removing the hydroxyl group from the alcohol used for etherification, In other words, it is necessary to be substituted with a group (for example, an organic group such as an alkyl or aryl group), and if the etherification is insufficient, problems with storage stability tend to occur. The alcohol used for etherification is preferably butanol or isobutanol, but methanol, ethanol, propanol,
Monohydric alcohols such as pentanol and other alkanols containing up to about 8 carbon atoms can be used. An alternative method of preparing the preferred carboxylic acid amide copolymers for this invention is to carry out the copolymerization using an amide modified with an aldehyde such as an alkylol amide instead of using an unsaturated carboxylic acid amide, and then using an amide modified with an aldehyde such as an alkylolamide. There is also a method of copolymerizing using an N-alkoxyalkyl substituted amide from the beginning.
N-alkoxyalkyl-substituted amides have the structural formula (wherein R ₂ is an aliphatic hydrocarbon group containing 2 to 6 carbon atoms and having a single terminal polymerizable α,β-ethylenically unsaturated group, and R ₃ is an aliphatic hydrocarbon group containing 1 to 8 carbon atoms. It is a lower alkyl group containing an atom. A specific example of the N-alkoxyalkyl substituted amide is N-methoxymethyl (meth)
Acrylamide, N-ethoxyethyl (meth)acrylamide, N-butoxymethyl (meth)acrylamide, N-isobutoxymethyl (meth)acrylamide, etc. are used in an amount of 4 to 40% by weight in the carboxylic acid amide copolymer. , preferably 10 to 30% by weight. Examples of α,β unsaturated carboxylic acids having one or more carboxyl groups include acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, and their monoalkyl esters, α-methyleneglutaric acid, and aconitic acid. , atropic acid and acid anhydride and α,β
Examples include adducts with hydroxyalkyl unsaturated carboxylates, and the amount used is 0.5 to 10% by weight, preferably 1 to 7% by weight. These acids not only play an important role as crosslinking reaction catalysts for carboxylic acid amide copolymers, but the acids themselves act as crosslinking reaction groups, and also have great effects on affinity with pigments and adhesive strength. do. If the amount of α,β unsaturated carboxylic acid used is less than 0.5% by weight, the above effects will be insufficient, and if it is more than 10% by weight, the viscosity of the resulting carboxylic acid amide copolymer will increase, and This is not preferable because performance such as water resistance deteriorates. The unsaturated polyester resin used in the present invention is obtained by subjecting a polyhydric alcohol and a polyhydric carboxylic acid to a heating reaction. This unsaturated polyester resin has carboxyl groups, epoxy groups, and It is desirable to use 0.5 to 5% by weight of an ethylenically unsaturated compound having a group, a hydroxyl group, or an amide group. Examples of polyhydric alcohols that can be used include ethylene glycol, diethylene glycol, neopentyl glycol, 1,6-hexanediol,
1,3-butylene glycol, 1,4-butylene glycol, bis(hydroxyethyl) terephthalate, hydrogenated bisphenol A, trimethylolpropane, trimethylolethane, glycerin,
Examples of polyhydric carboxylic acids include phthalic anhydride, isophthalic acid, terephthalic acid, trimellitic anhydride, tetrahydrophthalic acid, adipic acid, sebacic acid, azelaic acid, and fumaric acid. Examples of the acid include maleic acid, benzoic acid, tert-butylbenzoic acid, versatic acid, and the like. These unsaturated polyester resins improve pigment dispersibility, atomization during coating, low-temperature curing properties, etc. of solvent paints containing the carboxylic acid amide copolymer of the present invention as a main component, and provide paint films with good finished appearance. The weight average molecular weight is preferably about 2,000 to 50,000, and the amount used is preferably from 5 to 30% by weight. If the amount is less than 5% by weight, the above effect will be insufficient, and if it exceeds 30% by weight, the water resistance and weather resistance of the resulting coating film will deteriorate, which is not preferable. Other copolymerizable unsaturated monomers used in the present invention include (meth)acrylic acid esters having an alkyl group having 1 to 18 carbon atoms, styrene and vinyl aromatics such as α-methylstyrene, and vinyltoluene. α, such as organic nitriles such as acrylonitrile and methacrylonitrile, vinyl esters of organic acids such as vinyl acetate and vinyl propionate, 2-hydroxyethyl (meth)acrylate and 2-hydroxypropyl (meth)acrylate, β-unsaturated hydroxyalkyl carboxylates, unsaturated monomers with a glycidyl group such as glycidyl (meth)acrylate, esters of fumaric acid or maleic acid such as diethyl fumarate, dibutyl fumarate, diisopropyl maleate, itacon Examples include itaconate esters such as diethyl acid and dibutyl itaconate. It is desirable that these unsaturated monomers be appropriately selected in consideration of the coating workability and coating film performance of a solvent-based coating material containing a carboxylic acid amide copolymer as a main component. The carboxylic acid amide copolymer of the present invention can be obtained by copolymerizing monomers in an organic solvent in the presence of a vinyl polymerization initiator. The solvent-based paint of the present invention uses 1 to 20 parts by weight of cellulose acetate butyrate resin per 100 parts by weight of the solid content of the solvent-based paint. Used to form a coating film. If the amount used is less than 1 part by weight, no effect can be expected, and if it is more than 20 parts by weight, costs increase and performance such as water resistance becomes unsatisfactory. As this cellulose acetate butyrate resin, those having various characteristic values can be used, but those having a degree of butylation of 30% or more are usually suitable. Eastman is a product that meets these conditions.
There are "EAB-381" and "EAB-551" manufactured by Kodak, among which EAB-551-02 is particularly suitable.
Note that although the solvent-based paint containing a carboxylic acid amide copolymer as a main component used in the present invention is originally a self-crosslinking type, it is also possible to use an amino resin in combination. However, in this case, it is preferable to use one that takes into account the prevention of underarm and skin irritation. Specific examples of these amino resins include methylated melamine resin, butylated melamine resin, isobutylated melamine resin, and JP-A-Sho.
54-4934. These amino resins are used to improve low temperature curability. The amount used is desirably 20 parts by weight or less based on 100 parts by weight of resin solid content of the solvent-based paint from the viewpoint of underarm and skin irritation. Coloring pigments or metal powder and coloring pigments are added to carboxylic acid amide copolymer, cellulose acetate butyrate resin, and optionally amino resin to make a base coat paint, which is then painted on the electrodeposition primer that is the object to be coated. By applying a 2-coat, 1-bake finish by applying a transparent thermosetting powder coating and baking at 160-170℃ for 20-30 minutes, it has an excellent appearance with no coating defects such as underarms or skin roughness, and Forms a coating film with good adhesion to the object to be coated. Also, when a normal solvent-based acrylic-melamine cross-linked clear paint was applied instead of a transparent thermosetting powder paint and baked at 140-150°C for 20-30 minutes, the paint film had good appearance and performance. form. Various types of powder coatings that are widely used can be used as transparent thermosetting powder coatings used as clear coat coatings with a two-coat and one-bake finish, but the main purpose of the present invention is the top coating of automobiles. For use in acrylic powder coatings, for example, vinyl monomers with glycidyl or hydroxyl groups as functional monomers (meth)
An appropriate amount of polyhydric carboxylic acid or blocked isocyanate as a curing agent component is added to an acrylic copolymer resin using glycidyl acrylate, hydroxyethyl (meth)acrylate, alkyl acrylate, alkyl methacrylate, styrene, etc. as non-functional monomers. Acrylic powder coatings containing appropriate amounts of coating surface conditioners, anti-repellent agents, etc. are particularly preferred, but polyester powder coatings can also be used. In the following production examples and examples, "parts" indicate "parts by weight." Production Example 1 Production of unsaturated polyester resin A 1080 parts of isophthalic acid and 467 parts of adipic acid were placed in a reaction vessel equipped with a stirrer, a thermometer, and a nitrogen gas blowing tube.
29 parts of maleic anhydride, 536 parts of trimethylolpropane, 832 parts of neopentyl glycol, and 0.3 parts of hydroquinone, and while blowing nitrogen, 220 parts of
The reaction was carried out at ℃ until the acid value reached 9. After the reaction vessel is cooled, it is diluted with a mixed solvent consisting of n-butanol/butyl acetate/xylene=20/10/70 (weight ratio) so that the solid content becomes 50%. The unsaturated polyester resin A thus obtained was a transparent viscous liquid with an acid value of 4.5. Production Example 2 Production of unsaturated polyester resin B In a reaction vessel similar to Production Example 1, 1112 parts of isophthalic acid, 482 parts of adipic acid, and 26 parts of itaconic acid were added.
1, 728 parts of neopentyl glycol, 90 parts of 1,4-butanediol, 536 parts of trimethylolpropane, and 0.6 parts of hydroquinone, and the mixture was reacted while blowing nitrogen until the acid value reached 10. After the reaction vessel is cooled, it is diluted with a mixed solvent consisting of n-butanol/butyl acetate/xylene=20/10/70 (weight ratio) so that the solid content becomes 50%. The polyester resin B thus obtained was a transparent viscous liquid with an oxidation level of 5. Production Example 3 Production of unsaturated carboxylic acid amide copolymer A 25 parts of n-butanol and 65 parts of xylene were placed in a reaction vessel equipped with a stirrer, thermometer, cooler and decanter.
parts, acrylamide 10 parts, methyl methacrylate 30 parts
1 part, 20 parts of unsaturated polyester resin A, 2.5 parts of methacrylic acid, 47.5 parts of ethyl acrylate, 1.5 parts of t-dodecyl mercaptan, and 1 part of cumene hydroperoxide, and the temperature was raised to 100°C in 1 hour.
Thereafter, it was kept at 100°C for 8 hours. Next, 20 parts of butylformcel and 0.4 parts of maleic anhydride were added, and the mixture was refluxed for 4 hours, and the water was removed from the decanter. The thus obtained carboxylic acid amide copolymer A is a transparent viscous liquid.
The solid content was 50.5% and the acid value was 7.7. Production Example 4 Production of Carboxylic Acid Amide Copolymer B 25 parts of n-butanol and 60 parts of xylene are charged into a reaction vessel equipped with a stirrer, a thermometer, a dropping funnel, and a condenser, and the temperature is raised to 100°C. Next, N-methoxymethyl methacrylamide was added to the reaction vessel.
20 parts, 2 parts of acrylic acid, 20 parts of methyl methacrylate
A mixture consisting of 30 parts of unsaturated polyester resin B, 38 parts of ethyl acrylate, 10 parts of n-butyl acrylate, and 1 part of benzoyl peroxide was added over 4 hours, and after the addition was completed, benzoyl peroxide was added every hour. Add 0.2 parts three times and keep at 100°C for 5 hours. The thus obtained carboxylic acid amide copolymer B was a transparent viscous liquid with a solid content of 50.7% and an acid value of 8.8. Production Example 5 Production of thermosetting acrylic powder coating A 20 parts of methyl methacrylate, 20 parts of n-butyl methacrylate, 30 parts of styrene, 5 parts of n-butyl acrylate, 5 parts of 2-hydroxyethyl acrylate, methacrylic acid The weight average molecular weight obtained by copolymerizing a mixed monomer consisting of 20 parts of glycidyl is 1.
After melt-mixing 90 parts of a solid copolymer resin, 10 parts of sebacic acid, and 1 part of Regimix L (manufactured by Mohawk Co., Ltd.) as a coating surface smoothing agent in an extruder, the mixture was cooled and pulverized and passed through a 200-mesh sieve. Powder particles were collected to produce acrylic powder coating A. Production Example 6 Production of thermosetting acrylic powder coating B Styrene 30 parts, methyl methacrylate 20 parts, ethyl acrylate 10 parts, n-butyl acrylate 20 parts,
65 parts of a solid copolymer resin with a weight average molecular weight of 12,000 obtained by copolymerizing a mixed monomer consisting of 25 parts of 2-hydroxyethyl methacrylate and 25 parts of adduct B-1870 (manufactured by Fueva) Acrylic powder coating B was produced by melting and mixing 35 parts of Modaflow (manufactured by Monsanto) and 1 part of Modaflow (manufactured by Monsanto) in an extruder, cooling and grinding, and collecting the powder particles that passed through a 200-mesh sieve. . Production Examples 7 and 8 Carboxylic acid amide copolymers E and F were produced in the same manner as in Production Example 3 with the following compositions.

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[Table] Example 1 Using the above-mentioned carboxylic acid amide copolymer A, a base coat paint A having the following formulation was prepared. Carboxylic acid amide copolymer A 54 parts *EAB-551-02 (15% cellosolve acetate solution) 20〃 ※※Albast #1109MA 8〃 ※※※Corofain Blue #720 2〃 *Cellulose acetate manufactured by Eastman Kodatsu Butyrate resin ※※Alpaste made by Toyo Aluminum Co., Ltd. ※※※Organic pigment made by Dainippon Ink Co., Ltd. Dilute the above paint with a mixed solvent of toluene/butyl acetate/Solbetsuso #150 = 50/40/10 (weight ratio). Prepared at FC#4 (25°C) for 13 seconds. The above base coat paint A was applied to a surface-treated steel plate (JISG 3310 steel plate subjected to zinc phosphate chemical conversion treatment) coated with an automotive cationic electrodeposition primer.
was applied to a dry film thickness of 20 μm, and then set for 5 minutes. Thermosetting acrylic powder paint A was applied to the wet paint film to a dry film thickness of 80 μm, and then heated at 170°C for 30 minutes. Bake for a minute. The coating film thus obtained had a very good finished appearance and good coating properties such as solvent resistance, water resistance, and weather resistance, and was useful as a top coating film for automobiles. . In addition, in order to evaluate the coating performance during low-temperature baking, we used Dianal HR-538, an ordinary acrylic-melamine crosslinked solvent-based resin, as a clear paint instead of a thermosetting acrylic powder paint.
(manufactured by Mitsubishi Rayon, 50% solid content) and Yuban 20SE (manufactured by Mitsui Toatsu, 60% solid content) as a melamine resin are blended so that the solid content ratio is acrylic/melamine = 70/30, and Supersol # is used as a thinner. FC #4 (25
The base coat paint of this example was applied with a clear paint diluted for 30 seconds at ℃) to a dry film thickness of 20μ, set for 3 minutes, and then wet-on-wet until the dry film thickness was 30μ. Paint as shown and bake at 140℃ for 30 minutes. The coating film thus obtained had good finished appearance, solvent resistance, and weather resistance, and was useful as a top coating film for automobiles. Example 2 Using carboxylic acid amide copolymer B, base coat paint B having the following formulation was prepared. Carboxylic acid amide copolymer B 57 parts EAB-55-02 (15% cellusolve acetate solution) 10〃 Alpaste #1109MA 10〃 The above base coat paint B was used in place of base coat paint A used in Example 1. Then, according to Example 1, an automobile top coating film was prepared. The coating film thus obtained was free from coating defects such as wrinkles, yellowing, and marked orange skin, and had good metallic feel and image clarity. In addition, in order to evaluate the performance at the time of repair, base coat paint B and thermosetting acrylic powder paint A were applied again to a part of the coated plate that had been baked with the above two coats.
Bake for 30 minutes at °C. As a result, a coating film was formed in which the finished appearance of the areas that were recoated and baked did not differ much from the areas that were not. Furthermore, the adhesion between these coating films was also good. Example 3 A coating film similar to that of Example 1 was prepared using thermosetting acrylic powder coating B instead of thermosetting acrylic powder coating A of Example 1. The coating film thus obtained had a good finished appearance as in Example 1. Example 4 Using carboxylic acid amide copolymer B, base coat paint C having the following formulation was prepared. Carboxylic acid amide copolymer B 56 parts EAB-551-02 5〃 (15% cellosolve acetate solution) *Sumimar M-504C 1.1 parts※※Titanium oxide R-820 2〃 *※※Irgazine Yellow 2GLT 4〃 *Sumitomo Chemical Methylated melamine resin (68% solution) manufactured by Ishihara Sangyo Co., Ltd. ※※Pigment manufactured by Ciba Geigy Co., Ltd. The above paint is converted into Cellosolve Acetate/Toluene
FC#4 with a mixed solvent consisting of 20/80 (weight ratio)
Dilute to 18 s at (25 °C). The base coat paint C was applied onto a surface-treated steel plate coated with the same electrodeposition primer as used in Example 1 so that the dry film thickness was 20 μm. After setting for 5 minutes, apply thermosetting acrylic powder paint A to a dry film thickness of 80 μm.
Baked at 170°C for 30 minutes. The coating film thus obtained had good finished appearance and sharpness, and was useful as a solid color coating film for automobiles. The base coat paint C had good pigment dispersibility and atomization during coating, and was a paint with good coating workability. Comparative Example 1 Instead of the base coat paint A of Example 1, an acrylic-melamine crosslinked base coat paint D having the following formulation was prepared. Dianal HR-560 (manufactured by Mitsubishi Rayon, 50% solids) 42 parts Yuban 20SE (60%) 15〃 Alpaste #1109MA 8〃 Corofain Blue #720 2〃 Next, apply the above base coat paint D in the same manner as in Example 1. After diluting, it was painted and baked in the same manner as in Example 1, and a 2-coat, 1-bake coating was created using thermosetting acrylic powder coating A as a clear. The coating film thus obtained had underarm and skin roughness, and its finished appearance was considerably inferior to that of the coating film obtained in Example 1. Comparative Examples 2 and 3 In the same manner as Comparative Example 1, the physical properties of the paint film were evaluated using a base paint with the following composition. In Comparative Example 2, the gloss (60 degree gloss) was low, and the gloss and metallic In addition, in Comparative Example 3, the coating performance such as solvent resistance and water resistance was poor, and the weather resistance was poor. It was hot.

[Table] In order to further clarify the effects obtained by the present invention, Table 1 summarizes the evaluation results of coating film performance obtained in each Example and Comparative Example.

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Claims (1)

[Scope of Claims] 1 A colored pigment or a metal powder and a colored pigment are blended with 60 to 99 parts by weight of a carboxylic acid amide copolymer, 1 to 20 parts by weight of a cellulose acetate butyrate resin, and 0 to 20 parts by weight of an amino resin. In a coating film forming method in which a solvent-based coating is applied to an object to be coated, a transparent thermosetting powder coating is then applied to the coated surface, and the coating is then cured by heating, the carboxylic acid amide copolymer used is (a) α, β monoethylenically unsaturated carboxylic acid amide 2 to 20% by weight, 1 or 2
0.5 to 10% by weight of an α,β unsaturated carboxylic acid having 1 or more carboxyl groups, 5 to 30% by weight of an unsaturated polyester resin, and 92.5 to 40% by weight of other copolymerizable unsaturated monomers. It is a copolymer obtained by (In the formula, R represents a hydrogen atom or an alkyl group, and R ₁ represents a hydrogen atom or an organic group.) or (b) (wherein R ₂ is an aliphatic hydrocarbon group containing 2 to 6 carbon atoms and having a single terminal polymerizable α,β-ethylenically unsaturated group; R ₃ is an aliphatic hydrocarbon group containing 2 to 6 carbon atoms and having a single terminal polymerizable α, β-ethylenically unsaturated group; 4 to 40% by weight of N-alkoxyalkyl-substituted amide (lower alkyl group containing a carbon atom), 0.5 to 10% of α,β unsaturated carboxylic acid having one or more carboxyl groups
A method characterized in that the copolymer is obtained by copolymerizing 5-30% by weight of an unsaturated polyester resin and 90.5-20% by weight of another copolymerizable unsaturated monomer.