JPS644831B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to a coating finishing method that provides a coating film appearance with excellent metallic luster. As one of the painting methods, painting finishes using solvent-free powder paints have recently been rapidly developing for the reason of pollution prevention. However, when finishing with only powder paint mixed with metal powder or colored pigments, due to poor orientation of the metal powder in the paint film, etc.
It is extremely difficult to achieve the same level of gloss and sharpness as conventional solvent-based metallic coatings (referring to appearance performance such as visual gloss and metallic luster), and the smoothness of the coating film, so it is still not practical. has not been standardized. Therefore, a so-called two-coat, one-bake finishing method is being considered, in which a conventional solvent-based metallic paint is applied, then a thermosetting transparent powder paint is applied, and the coating is baked to harden. (JP 54-4934, JP 54-25943) However,
This method reduces gloss sharpness, poor smoothness,
(Referring to defects such as rough skin, pinholes and craters caused by foaming.) This caused practical problems.
The method of JP-A-56-26567 improves these. However, recently, while the vehicle is running, pebbles, gravel, frozen snow, etc. fly and collide with the underside of the vehicle, abrading or destroying the paint film, exposing the metal surface of the base material, and causing corrosion. It has become a problem that the service life of the vehicle is significantly reduced. Such a phenomenon of destruction of the paint film is called chipping, and since it cannot be solved by the above-mentioned conventional methods, a paint film that is resistant to chipping has been desired. An object of the present invention is to improve the deterioration in gloss and image clarity and smoothness caused by the two-coat, one-bake method as described above, and to provide a coating film with good chipping resistance. That is, the present invention comprises: (a) 3 to 30% by weight of N-alkoxymethyl (meth)acrylamide; and (b) 3 to 30% by weight of a vinyl monomer having a hydroxyl group.
20% by weight (c) Vinyl monomer with carboxyl group 0.5
~5% by weight (d) Other vinyl monomers copolymerizable with these 45
Number average molecular weight obtained by copolymerizing ~93.5% by weight with ~5000 ~
30,000 thermosetting vinyl copolymer (a), a pigment (c) that gives a metallic coating appearance, and an organic acid (b). This is a metallic coating finishing method characterized by first coating an object with an undercoat, then topcoating with a thermosetting transparent powder coating (B) (hereinafter abbreviated as top coat coating), and then baking. In the present invention, (a) N-alkoxymethyl (meth)acrylamide has an alkoxy group having a linear or branched alkyl group having 1 to 8 carbon atoms, and an example thereof is N-methoxymethyl (meth)acrylamide. Examples include acrylamide, N-butoxymethyl (meth)acrylamide, N-propoxymethyl (meth)acrylamide, and N-ethoxymethyl (meth)acrylamide. In addition,
In this specification, expressions such as "(meth)acrylic, (meth)acrylo" and the like mean "acrylic and/or methacrylic, acrylo and/or methacrylo", etc., respectively. N-alkoxymethyl (meth)acrylamide is contained in the copolymer (a) as a raw material composition in an amount of 3 to 30% by weight, preferably 10 to 30% by weight, and more preferably 15% by weight.
~25% by weight is required, and if it is less than 3% by weight, the crosslinking density of the baked coating will not be sufficient and the desired performance (water resistance, chemical resistance, gloss sharpness, and chipping resistance) will not be achieved. Moreover, if the raw material composition contains more than 30% by weight of N-alkoxymethyl (meth)acrylamide, the gloss and sharpness of the baked coating film will be poor. The (b)vinyl monomer having a hydroxyl group in the present invention is a vinyl monomer having one or more hydroxyl groups in the molecule, and typically includes, for example, 2-hydroxyethyl (meth)acrylate, 3-hydroxyethyl (meth)acrylate, Examples include hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, di(2-hydroxyethyl) fumarate, and the like. 1 or 2 with hydroxyl group
More than one type of vinyl monomer is required in the raw material composition of (a) in an amount of 3 to 20% by weight, preferably 5 to 20% by weight, more preferably 7 to 15% by weight, and if it is less than 3% by weight, The gloss and clarity of the baked paint film is poor, and
When the amount is more than 20% by weight, the gloss and clarity of the baked coating film is poor, and the desired performance (water resistance) is also poor. The (c) vinyl monomer having a carboxyl group in the present invention is a vinyl monomer having one or more carboxyl groups, such as (meth)acrylic acid, itaconic acid, maleic acid, and the like. One or more vinyl monomers having a carboxyl group have a content of 0.5 as the raw material composition of (a).
-5% by weight, preferably 1-4% by weight, more preferably 1-3% by weight, and if it is less than 0.5% by weight, the desired performance (water resistance, chemical resistance) will be poor. When the amount is more than 5% by weight, the gloss and sharpness of the baked coating film is poor. Very typical examples of (d) other copolymerizable vinyl monomers in the present invention include linear or branched hydrocarbon groups having 1 to 13 carbon atoms as alkyl groups, specifically methyl groups, (Meth)acrylic acid alkyl esters having ethyl, propyl, butyl, 2-ethylhexyl, isodecyl, cyclohexyl, lauryl, etc. groups are often used.
Further examples include styrene and its derivatives, (meth)acrylonitrile, glycidyl or β-methylglycidyl (meth)acrylate. In order to obtain the thermosetting vinyl copolymer (a) referred to in the present invention, the above (a) N-alkoxymethyl (meth)acrylamide, (b) a vinyl monomer having a hydroxyl group, and (c) a carboxyl group are used. The obtained vinyl monomer and (d) the vinyl monomer copolymerizable with these are added by a conventional method to a chain transfer agent, a polymerization initiator, etc., as necessary, and the number average molecular weight is determined by a solution polymerization method. is heated and polymerized to obtain a thermosetting vinyl copolymer having a molecular weight of 5,000 to 30,000. The polymerization temperature at this time is preferably about 60°C to 150°C, and typically the polymerization is carried out at a temperature depending on the monomer, polymerization solvent, polymerization initiator, and other conditions. However, in the present invention, thermosetting vinyl copolymer (a)
The polymerization method, the mixing order of monomers, the polymerization order, etc. are not limited at all. The thermosetting vinyl copolymer (a) in the present invention is
When the number average molecular weight is less than 5000, the gloss clarity (especially metallic gloss) of the baked coating film is poor.
When the number average molecular weight is greater than 30,000, the coating workability during spray coating (poor atomization, uneven spraying, etc.) is poor, and it cannot be used in the present invention. Examples of polymerization solvents used in solution polymerization to obtain the copolymer (a) of the present invention include ethyl acetate,
Solvents such as acetate esters such as butyl acetate, aromatics such as toluol and xylol, alcohols such as ethanol, propanol and butanol, ketones such as acetone and methyl ethyl ketone, and cellosolves such as methyl cellosolve and butyl cellosolve, either alone or in combination. and use it. As the chain transfer agent, for example, mercaptans such as n-dodecylmercaptan, tertiarydodecylmercaptan, and 2-mercaptoethanol are used as necessary. Examples of the polymerization initiator include common radical catalysts, such as diazo compounds such as azobisisobutylnitrile, and peroxides such as benzoyl peroxide and cumene hydroperoxide. The organic acid (b) in the present invention refers to an acid excluding carbonic acid in which carbon atoms are bonded within the molecule. For example, very typical examples include acetic acid, lactic acid, succinic acid, oxalic acid, maleic acid, decanedicarboxylic acid, (meth)
Carboxylic acids such as acrylic acid, sulfonic acids such as para-toluenesulfonic acid, dodecylbenzenesulfonic acid, and dinonylnaphthalenedisulfonic acid, and organic alkyl phosphate ester compounds such as dimethyl phosphoric acid, dibutyl phosphoric acid, dimethyl pyrophosphoric acid, and dibutyl pyrophosphoric acid. Can be mentioned. Among these organic acids, sulfonic acids, especially sulfonic acids with 6 or more carbon atoms, especially 10
The above are particularly desirable. The blending ratio of these organic acids (b) is 0.01 parts by weight or more and 5 parts by weight or less, more preferably 1 to 4 parts, and especially 1 to 3 parts per 100 parts by weight of the thermosetting vinyl copolymer (a). is preferred. organic acid
When (b) is less than 0.01 part by weight, the chipping resistance of the cured coating film is poor. If the amount is more than 5 parts by weight, the water resistance of the cured coating film will be poor. Pigment (c) giving a metallic coating appearance in the present invention
refers to those normally used in this field, such as aluminum powder (non-leafing type,
leafing type), bronze powder, copper powder, mica powder, etc. When used, it is generally used in the form of fine scales or flakes in an amount of 2 to 15% by weight based on the solid content of the paint. The base coat paint (A) according to the present invention includes the above (a),
It is obtained by mixing (b) and (c), but in addition to the pigment (c) that gives a metallic appearance, it also contains colorants and additives such as inorganic pigments, organic pigments, and oil-soluble dyes used in ordinary paints. (e.g. dispersion aid, coating surface conditioner) etc. (a),
It can also be used in combination with (b) and (c). The thermosetting vinyl copolymer (a) referred to in the present invention can usually be used without a curing agent, but if necessary, for example, methylated melamine formaldehyde resin, butylated melamine formaldehyde resin or other known known resins may be used. It is also possible to mix and use aminoplast resins as long as the gloss and clarity of the coating film is not impaired. The top coat paint (B) used in the present invention has a thermosetting resin powder (containing a crosslinking agent and a curing agent as necessary) as a main component, and various additives and
It is also a powder coating containing some coloring agents. Any thermosetting powder coating that provides a transparent coating after curing may be used, but specifically, from the viewpoint of coating film properties and weather resistance, well-known thermosetting acrylic resins and thermosetting polyester resins are mainly used. Preferably, the paint is a component. Among these resins, for example, the top coat paint (B) using a thermosetting acrylic resin is specifically explained using a functional monomer such as glycidyl (meth)acrylate, β-methylglycidyl, and/or acrylic glycidyl. (or β-
Using a well-known general vinyl monomer such as methylglycidyl) ether, alkyl (meth)acrylate or hydroxyalkyl ester as a non-functional monomer, and styrene, a glass transition temperature of 50°C was obtained by a known copolymerization method. A vinyl copolymer at ~80°C is produced, a hardening agent component such as a polyhydric carboxylic acid is mixed therein, a coating surface conditioner, an anti-repellent agent, etc. are added, and the process is carried out using a known powder coating manufacturing method. It is manufactured by Next, the coating finishing method of the present invention will be explained using a typical example. First, the base coat paint (A) of the present invention is diluted with a predetermined diluting solvent and generally has a viscosity of 10 to 100 cps/25
℃, and apply this to the object to be coated with a primer such as cationic electrodeposition paint or anionic electrodeposition paint by air spray or electrostatic coating so that the dry film thickness is 10 to 40μ. Undercoat. Next, after leaving it at room temperature for about 1 to 30 minutes, apply the top coat paint (B), and the film thickness after baking will be 30 to 30 minutes, except for (A).
Apply electrostatic coating to a thickness of 150μ, set it at room temperature or relatively low temperature for about 0 to 30 minutes, and then bake at 150℃ to 220℃ for 10 to 45 minutes to cure the top coat and base coat paints at the same time. , to obtain a metallic finish coating with excellent gloss and clarity. Next, the present invention will be specifically explained with reference to Examples and Comparative Examples. % and parts in the examples indicate weight % and parts by weight unless otherwise specified. Example 1 (1) Production of base coat paint (A); 80 parts of xylene and 20 parts of butanol were charged into a four-necked flask equipped with a stirrer, a reflux condenser, and a thermometer. As components of (d), 10 parts of styrene, 32 parts of methyl methacrylate
15 parts of butyl acrylate, 15 parts of 2-ethylhexyl acrylate, 15 parts of N-butoxymethylacrylamide as component (a), and 15 parts of N-butoxymethylacrylamide as component (b).
10 parts of 2-hydroxyethyl methacrylate,
As component (c), a mixed monomer of 3 parts of methacrylic acid and 1.5 parts of benzoyl peroxide were added, and the reaction was allowed to proceed for 4 hours by maintaining the temperature at 85°C to 90°C with stirring, and then adding benzoyl peroxide every 2 hours. 0.2 parts were added at a time and the reaction was carried out for a total of 8 hours. The obtained acrylic resin, which is the copolymer (a) of the present invention, has a solid content of 50% and a number average molecular weight of 15,000.
It was hot. A base coat paint (A) was produced using this resin with the following formulation. Acrylic resin (a) with a solid content of 50% 200 parts para-toluene sulfonic acid ^* 1 part non-leafing aluminum powder ^** 10 parts* (diluted to 40% with isopropanol) ** (Product manufactured by Toyo Aluminum Co., Ltd.) 1109MA) and then add a mixed solvent consisting of 80 parts of xylene and 20 parts of butanol to it.
The viscosity was adjusted to 50 cps/25°C to obtain the base coat paint (A) of the present invention. (2) Manufacture of top coat paint (B); 15 parts of styrene, 48 parts of methyl methacrylate,
18 parts of n-butyl acrylate, 19 parts of glycidyl methacrylate, and 100 parts of toluene were placed in a four-necked flask equipped with a stirrer and a reflux condenser, and 1.5 parts of azobisisobutylnitrile was added thereto, followed by stirring. The contents were heated at a temperature of 85°C to 95°C. After maintaining this temperature for 4 hours, 1.5 parts of azobisisobutylnitrile was further added and the temperature was maintained for 4 hours to complete the copolymerization. Next, attach a cooling pipe so that the cooled and condensed solvent flows out of the flask, and
Stirring was continued while heating at 120°C to 140°C, and then the pressure inside the flask was reduced to about 200 mmHg and the external temperature was raised to 140°C to 170°C to almost completely remove residual toluene. After the copolymer thus obtained is allowed to cool and solidify, it is pulverized using a pulverizer to obtain acrylic resin powder. Using this, 100 parts of acrylic resin powder, 16 parts of decanedicarboxylic acid, and 1 part of coating surface conditioner (Regimics P, manufactured by Mitsui Toatsu Chemical Co., Ltd.) were mixed, and the mixture was heated to about 100 parts by heating roll. Melt and knead for 10 minutes at ℃, then cool down to 20~
The top coat paint (B) used in the present invention was produced by finely pulverizing it to a particle size of 100μ. (3) Paint finish: The base coat paint is applied on the surface-treated steel plate coated with an epoxy ester resin electrodeposited primer.
(A) was coated using an air spray gun so that the dry film thickness was 15 to 17μ. After leaving this at room temperature for 3 minutes, the top cord paint (B) was applied using an electrostatic spray coating machine to achieve a film thickness of 60 mm.
It was electrostatically coated to a thickness of ~70μ. After setting for 10 minutes, baking was performed at 170°C for 20 minutes in a hot air drying oven to harden both coatings and prepare test pieces. (4) Evaluation of test piece: The test piece thus prepared was visually evaluated for visual glossiness and metallic glossiness, which represent gloss selectivity. In addition, the specular reflectance at an incident angle of 60° was measured using a gloss meter, and the value expressed as a percentage was referred to as "60° gloss" and was used as an index to express glossiness and smoothness. The chipping resistance test was conducted in the following manner. Γ test equipment; gravelometer (Suga Test Instruments Co., Ltd.)
) ΓStone to be blown; Marble with a diameter of approximately 15-20m/m) Capacity of ΓStone to be blown; Approximately 500ml ΓBlowing air pressure; Approximately 4Kg/cm ² ΓTemperature during test; 20℃ Test piece Attach it to the test piece holding stand and weigh about 4Kg/
Approximately 500 ml of marble grains are fired onto the specimen with a blowing air pressure of ^cm2 . The depth and size of scratches caused on the paint film surface due to impact, as well as the remaining state of the paint film, etc., were visually observed and evaluated using the following criteria. 〇 (Good): No peeling of the coating film was observed, and the coating film had no scratches due to impact or only slight scratches were observed in some parts. △ (slightly poor); Some scratches due to impact were observed on the coating film. (In terms of quality, this level is acceptable.) × (Poor): The coating film on the impact area, including the impact area or its surroundings, has peeled off. In the humidity test, the test piece with the back and surroundings sealed is left in a humidity tester at 50°C and 100% RH for 500 hours, and the presence or absence of blisters is observed. Example 2 Using the acrylic resin (a) produced in Example 1,
A base coat paint (A) was prepared in the same manner as in Example 1 using the following formulation. Acrylic resin (a) of Example 1 190 parts Methylated melamine resin (manufactured by Mitsui Toatsu Chemical Co., Ltd., trade name Cymel 325) 6 parts Dodecylbenzenesulfonic acid 0.5 parts Non-leafing type aluminum powder (1109MA mentioned above)
10 parts 206.5 parts This mixed paint was diluted in the same manner as in Example 1 to obtain a base coat paint (A). Using this paint (A) and the top coat paint (B) produced in Example 1,
Test pieces were prepared and evaluated in the same manner as in Example 1. The evaluation results are shown in Table-3. Examples 3 to 5 The solid content was determined in the same manner as in Example 1 with the composition shown in Table 1.
Produce 50% copolymer (a), then copolymer (a)
Various organic acids were added in the amounts shown in Table 1 to 200 parts, a paint (A) was prepared in the same manner as in Example 1, and test pieces were prepared and evaluated. The evaluation results are shown in Table 3.

[Table] The meanings of the abbreviations in Table 1 and below are as follows: N-BuA N-butoxymethylacrylamide N-MeA N-methoxymethylacrylamide HEMA 2-hydroxyethyl methacrylate HPMA 2-hydroxypropyl methacrylate HEA 2 -Hydroxyethyl acrylate MAc Methacrylic acid AA Acrylic acid IA Itaconic acid MMA Methyl methacrylate EA Ethyl acrylate BA n-Butyl acrylate 2EHA 2-Ethylhexyl acrylate N-BMA n-Butyl methacrylate 2EHMA 2-Ethylhexyl methacrylate I-BMA Isobutyl Methacrylate St Styrene () Dinonylnaphthalenedisulfonic acid () 40% isopropanol solution of para-toluenesulfonic acid () Dodecylbenzenesulfonic acid Comparative example 1 Same as Example 1 using copolymer (a) of Example 1 The base coat paint was obtained using the same method. 50% solids acrylic resin (a) 200 parts non-leafing aluminum powder (1109MA above)
10 parts 210 parts Using this paint and the top coat paint (B) produced in Example 1, test pieces were prepared and evaluated in the same manner as in Example 1. The evaluation results are shown in Table-3. Comparative Example 2 In a four-necked flask in the same manner as in Example 1, 70 parts of xylol, 30 parts of butanol, and N-
BuA 35 parts, (B) component HEMA 15 parts, (C) component MAc 2 parts, (D) component MMA 30 parts, EA18
1.5 parts and further 1.5 parts of benzoyl peroxide were added and reacted to obtain an acrylic resin with a number average molecular weight of 13,000. Using this resin, a base coat paint was prepared in the same manner as in Example 1, and test pieces were prepared in the same manner as in Example 1. The evaluation results of the test pieces are shown in Table-3. Comparative Examples 3 to 5 In the same manner as in Comparative Example 1, copolymers outside the scope of the present invention were produced with the compositions shown in Table 2. A base coat paint was prepared using these resins in the same manner as in Example 1, and test pieces were prepared in the same manner as in Example 1. The evaluation results of the test pieces are shown in Table-
Shown in 3. In Comparative Examples 3 to 5, the crosslinking component (N-
Since the amount of (alkoxymethyl (meth)acrylamide) was small or zero, a curing agent was mixed and blended in the following formulation to prepare a base coat paint. Acrylic copolymer with solid content of Comparative Examples 3 to 5 with a solid content of 50%
160 parts Butylated melamine resin with solid content of 50% (manufactured by Mitsui Toatsu Chemical Co., Ltd., trade name Yuban 20SE) 40 parts Non-leafing aluminum powder (1109MA above)
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Claims (1)

[Scope of Claims] 1 (a) 3 to 30% by weight of N-alkoxymethyl (meth)acrylamide (b) Vinyl monomer having a hydroxyl group 3 to 30% by weight
20% by weight (c) Vinyl monomer with carboxyl group 0.5
~5% by weight (d) Other vinyl monomers copolymerizable with these 45
Number average molecular weight obtained by copolymerizing ~93.5% by weight with ~5000 ~
The object to be coated is primed with a liquid paint (A) containing a thermosetting vinyl copolymer (a) of 30,000%, an organic acid (b) and a pigment (c) giving a metallic coating appearance, and then heat cured. A metallic coating finishing method characterized by applying a transparent powder coating (B) and then baking it.