JP4570430B2 - Coating method - Google Patents

Description

  The present invention relates to a base material having an inner plate portion and an outer plate portion, particularly to a method for forming a coating film on an automobile body.

  As shown in FIG. 1, different coatings are applied to the outer plate 2 such as the bonnet and the roof and the inner plate 4 such as the engine room, the door opening, and the interior. The The inner plate does not have to have sufficient weather resistance as the outer plate, so a special paint for the inner plate is applied, and the outer plate has excellent design and weather resistance. The paint film is painted.

  The substrate as described above may be coated so as to have a schematic cross section as shown in FIG. That is, the base material 10 having an inner plate portion and an outer plate portion is composed of an article 9 and an electrodeposition coating film 8, and an intermediate coating film 11 is formed on the outer plate portion with an intermediate coating, An inner plate solid color coating film 12 is formed by applying a solid color paint exclusively for the inner plate to the inner plate portion. After that, a solid color coating film 13 is formed on the outer plate portion with the outer plate solid color paint.

  When the coating method shown in Fig. 2 is used, the inner plate-specific solid color paint to be applied to the inner plate part is also partially applied to the outer plate part, resulting in overlapping parts, and the spraying during inner plate coating is intermediate coating. It will be scattered on the film 11. The same occurs when the outer plate portion is coated with the solid color paint, but the problematic part is the inner plate paint portion formed between the intermediate coating and the outer plate portion solid color coating film 13 or its paint splash ( (Also referred to as dust) 12 'is the part to be applied.

  Recently, when the paint is applied, heat curing is not performed (also referred to as wet-on-wet coating), and heat curing is performed with two or three layers stacked (two-coat one-bake or three-coat).・ It is also called “one-bake method”). This has the merit of omitting the drying and heating steps and reducing energy. On the other hand, since each layer is formed in a wet state, there is a risk of interaction between the layers, which needs to be overcome.

  In the case of taking a coating form as shown in FIG. 2, the paint on the inner plate part is a paint having a large amount of pigment and a high viscosity because it is necessary to conceal the undercoat film in a single layer. Then, in order to obtain a good appearance, it is not always such a paint. When the paint on the inner plate adheres to the flat surface of the intermediate coating film 11 as spray droplets, the solvent is volatilized until the spray is applied from the spray nozzle, and the intermediate coating film 11 is in a very high concentration state. Stick on top. This state is represented as 12 'in FIG. On top of that, the solid color coating film 13 of the outer plate portion is formed. However, if the intermediate coating film 11 and the solid color coating film 13 are heated and cured at one time while leaving the solid color coating film 12 for the inner plate or the spray splash 12 'portion thereof, the surface of the cured coating film may be blurred or A film defect with unevenness called glossy appears.

Patent Document 1 (Japanese Patent Application Laid-Open No. 11-181356) recognizes problems such as blurring that occur when a paint for inner plate coating is applied before the outer plate is coated by overcoating. We are considering the composition from the viewpoint of composition.
Japanese Patent Laid-Open No. 11-181356

  The present invention provides a coating method in which such coating film defects do not appear on the surface.

This invention is providing the coating-film formation method without the said fault. That is, the present invention applies an intermediate coating (A) to an outer plate portion on an electrodeposition-coated substrate having an inner plate portion and an outer plate portion, and the inner plate portion has a solid color coating ( B) is applied, and then the outer plate part is coated with the solid color paint (C) for the outer plate. The respective coatings are applied in a wet-on-wet manner without curing, and the wet coatings are baked and cured at one time. A method of forming a coating film,
The coating viscosity of the intermediate coating (A), the solid color coating (B) for the inner plate, and the solid color coating (C) for the outer plate is the same as that of the intermediate coating (A) and the solid coating (B) for the inner plate. And the solid color paint (C) for the outer plate, and the pigment concentration (PWC) of the solid color paint (B) for the inner plate and the solid color paint (C) for the outer plate is the solid for the inner plate. The color paint (B) and the solid color paint (C) for the outer plate become lower in order,
Furthermore, the intermediate coating (A) is obtained by polycondensation of an acid component containing 80 mol% or more of isophthalic acid and a polyhydric alcohol, and has a glass transition point (Tg) of 40 to 80 ° C. 40-56% by weight of urethane-modified polyester resin (a) having a number average molecular weight of 1500-3000 obtained by reacting a resin with an aliphatic diisocyanate compound;
Melamine resin (b) 10 to 30% by weight;
Isocyanate compound (c) 15 to 30% by weight obtained by blocking hexamethylene diisocyanate and an isocyanate compound obtained by reacting with hexamethylene diisocyanate and a compound reactive therewith with a compound having an active methylene group;
Non-aqueous dispersion resin (d) having a core-shell structure (d) 4 to 15% by weight (the amount of (a) to (d) is based on the weight of the solid content of the paint resin); and the major axis is 1 to 10 μm, 0.4-2 parts by weight of a flat pigment (e) having an average particle size of 2-6 μm (the solid content of the coating resin is 100 parts by weight);
The coating film formation method characterized by containing is provided. Incidentally, the coating viscosity may be a paint adhering to an object to be coated after the paint is ejected from a painting nozzle of a coating machine such as a spray and flies as a coating particle, that is, continuous or discontinuous, It refers to the viscosity of the paint after adhering to the coating.

  Although not limited by any particular theory, the present inventors have found that in the coating film forming method, the surface is blurred, that is, the coating film is defective. It is thought that this is caused by the overlapping layers of the solid color paint dedicated to the inner plate formed between the two or the paint dust scattered during paint painting. In particular, the solid color paint exclusively for the inner plate requires high concealment, so the pigment content is high and the solvent content is low so that a thick film can be applied. It was considered that the difference in the solvent content with the color paint caused a swelling and shrinkage phenomenon in the formed laminated coating film. Accordingly, the inventors pay attention to the coating viscosity, and the coating viscosity has a certain gradient, that is, the intermediate coating (A), the solid color coating for the inner plate (B), and the solid color coating for the outer plate (C). By eliminating the coating viscosity of the intermediate coating> solid color coating for the inner plate> solid color coating for the outer plate, and limiting the composition of the intermediate coating, the poor appearance of the coating is eliminated. I found that I can do it. In addition, the pigment concentration (PWC) is also related to the coating film defect, and it is necessary to set the pigment concentration such that the inner plate-dedicated solid color paint> the outer plate solid color paint.

  According to the present invention, even if a large amount of solid color paint dedicated to the inner plate is scattered on the outer plate portion, an excellent coating film is formed on the cured coating film that does not have a poor appearance.

Adjustment of coating viscosity In the case of the present invention, the intermediate coating has a coating viscosity of 70 to 300 Pa · s, preferably 100 to 300 Pa · s, more preferably 150 to 250 Pa · s. The coating viscosity of the paint is 20 to 200 Pa · s, preferably 50 to 180 Pa · s, more preferably 80 to 150 Pa · s. The coating viscosity of the solid color paint for the outer plate is 5 to 100 Pa · s, preferably 10 to 80 Pa · s, more preferably 15 to 50 Pa · s.

  Furthermore, the difference in coating viscosity between the intermediate coating and the solid color coating for the inner plate is 30 Pa · s or more, preferably 30 to 100 Pa · s, more preferably 50 to 100 Pa · s. Is expensive. Furthermore, the difference in the coating viscosity between the solid color paint exclusively for the inner plate and the solid color paint for the outer plate is 50 Pa · s or more, preferably 50 to 100 Pa · s, more preferably 70 to 100 Pa · s. In this case, naturally, the coating viscosity of the solid color paint exclusively for the inner plate is increased.

  If the coating viscosity is not in the order of the above coating viscosities, or if the respective coating viscosities are out of the predetermined range, the viscosity increase of only a part of the coating is promoted during curing, and surface defects become conspicuous.

  As described above, various methods can be considered for controlling the coating viscosity of the paint. The coating viscosity can also be controlled by changing the combination of the blended raw materials in each paint. The simplest method for controlling the coating viscosity is to select a solvent for dilution to be blended in the paint.

The coating viscosity is applied on a tin plate with a coating gun from a certain distance, and the paint is scraped off from the painted plate within 1 minute, and is stored in a sealed state. The viscosity (Pa · s) at a shear rate of 0.1 S ⁻¹ was measured for the stored paint within one hour with a viscosity measuring device (Solid Meter MR-300 / Rheology).

  The coating viscosity can be controlled by the solid content at the time of coating. The solid content at the time of coating can be controlled by the amount of solvent remaining at the time of coating, but by using appropriate amounts of medium-boiling solvent and high-boiling solvent, the evaporation rate can be adjusted, and the remaining amount is also It can be adjusted to an appropriate solid content during coating to obtain a target coating viscosity. This is because, for example, when a solvent having a high boiling point is selected, a solvent having a low boiling point has a strong tendency to volatilize, but a solvent having a high boiling point does not volatilize and remains in the paint. That is, when the amount of the remaining solvent is a constant amount, the applied viscosity can be controlled to be constant. Therefore, a method of controlling the solvent is easier and more general and preferable.

  The high boiling point solvent is an organic solvent having a boiling point exceeding 190 ° C., and it is considered that the solvent component is hardly volatilized from the inside of the coating grain and is applied while remaining as it is discharged from the coating machine as coating grain. . On the other hand, it is considered that the degree of volatilization of an organic solvent having a boiling point of 190 ° C. or less can be controlled depending on the coating environment and coating conditions (discharge amount, atomization pressure, etc.). When the paint is diluted to the coating viscosity, the solid content at the time of coating can be controlled by the mixing balance of the high boiling point solvent and the medium boiling point solvent. In addition, it is thought that the low boiling point solvent whose boiling point is less than 130 degreeC volatilizes most when a coating material atomizes.

  In addition, the type of residual solvent contributes to the solubility of dust, and by adding more polar solvents such as ester and alcohol to the solid color paint for the outer plate, the solubility in the inner plate paint dust is increased, so that the dust is reduced. Dissolves and can prevent unevenness.

  Furthermore, the solid color paint exclusively for the inner plate has a high pigment concentration (PWC) and adheres in a high concentration state as dust. Therefore, by reducing the PWC of the solid color paint for the outer plate, the resin content is increased, and by giving the solid color paint for the outer plate the solubility to the inner plate paint dust, the dust can be dissolved and unevenness can be prevented. it can. Also, the coating viscosity can be lowered by lowering the PWC.

  Each paint contains 8 to 35% by weight of a medium boiling point solvent having a boiling point of 130 to 190 ° C. with respect to the total weight of the diluted paint when diluted to the coating viscosity. If the content of the medium boiling point solvent exceeds the upper limit, a decrease in coating viscosity may cause familiarity or a mixed layer at the interface with other coating layers, resulting in appearance defects such as sagging. Below the lower limit, appearance defects may occur due to an increase in coating viscosity. Preferably it is 9 to 28% by weight.

Specific examples of the medium boiling solvent having a boiling point of 130 to 190 ° C. include ethylene glycol monoethyl ether acetate (commonly known as “celloace”, boiling point 156 ° C.), propylene glycol monomethyl ether acetate (commonly known as “PMAC”, boiling point 146 ° C), propylene glycol monoethyl ether acetate (common name “PEAC”, boiling point 158 ° C.), oxohexyl acetate (common name “OHA”, boiling point 170 ° C.), methyl methoxybutyl acetate (common name “Solfit acetate”, boiling point 188 ° C.) , Ester solvents such as methoxybutyl acetate (common name “Metace”, boiling point 173 ° C.), ethyl ethoxypropionate (common name “EEP”, boiling point 169 ° C.);
Aromatic solvents such as xylene (boiling point 144 ° C.), mineral spirits (boiling point 140-180 ° C.);
Methyl methoxybutanol (commonly known as “Solfit”, boiling point 174 ° C.), ethoxypropanol (commonly known as “EP”, boiling point 132 ° C.), ethylene glycol isopropyl ether (boiling point 141 ° C.), ethylene glycol t-butyl ether (boiling point 152 ° C.), Ethylene glycol monoethyl ether (common name “Ethicello”, boiling point 136 ° C.), ethylene glycol monobutyl ether (common name “Buticello”, boiling point 171 ° C.), methylmethoxybutanol (common name “Solfit”, boiling point 174 ° C.), methoxybutanol (common name) Ether solvents such as “Metobuta” (boiling point 160 ° C.), propylene glycol monobutyl ether (boiling point 170 ° C.);
Swazol 310 (Exxon, boiling point 153-177 ° C, trade name), Shellsol 70 (Showa Shell, boiling point 143-164 ° C, trade name), Shellsol 71 (Showa Shell, boiling point 165-192 ° C) , Trade name), Shellsol D40 (Showa Shell, boiling point 151-188 ° C, trade name), Shellsol A (Showa Shell, boiling point 160-182 ° C, trade name), S-100 (Esso) Examples thereof include aliphatic solvents such as a solvent, a boiling point of 158 to 177 ° C., a trade name), and S-150 (a solvent manufactured by Esso Corporation, a boiling point of 185 to 211 ° C., a trade name).

  Among the above-described medium-boiling solvents, it is preferable that the ether solvent and the aliphatic solvent are contained in an amount of 10 to 25% by weight based on the total weight of the diluted paint because the coating viscosity is controlled within an appropriate range. Furthermore, the coating film excellent in the external appearance can be formed by using an ether solvent and an aliphatic solvent in the range of 3/2 to 1/3.

  Furthermore, each coating material used in the present invention, when diluted to the coating viscosity, in addition to the above-mentioned medium boiling ester solvent, other solvents such as a high boiling solvent and a low boiling solvent within the total weight of the solvent that becomes a volatile component Can be contained. These solvents are used to make the coating viscosity less susceptible to the coating environment.

  As said high boiling point solvent, it is a solvent whose boiling point exceeds 190 degreeC, and contains 1 to 8 weight% with respect to the diluted paint total weight. If the content of the high-boiling solvent exceeds the upper limit, a decrease in coating viscosity may cause familiarity or a mixed layer at the interface with other coating layers, resulting in appearance defects such as sagging. Below the lower limit, appearance defects may occur due to an increase in coating viscosity. Preferably it is 1.5-7 weight%.

Specifically, ethylene glycol monobutyl ether acetate (boiling point 191 ° C.), diethylene glycol monoethyl ether acetate (common name “carbitol acetate”, boiling point 217 ° C.), diethylene glycol monobutyl ether acetate (common name “butyl carbitol acetate”, boiling point 246 ° C. ) And other ester solvents;
Ketones such as isophorone (boiling point 215 ° C.);
Examples include ether solvents such as ethylene glycol monohexyl ether (boiling point 208 ° C.), ethylene glycol 2-ethylhexyl ether (boiling point 225 ° C.), diethylene glycol monomethyl ether (boiling point 194 ° C.), and diethylene glycol monoethyl ether (boiling point 203 ° C.).

  Among the high-boiling solvents described above, it is preferable in terms of appearance that the ester solvent is contained in an amount of 1.5 to 5% by weight.

Other low-boiling solvents that can be used are those having a boiling point lower than 130 ° C., specifically, ethyl acetate (boiling point 77 ° C.), butyl acetate (boiling point 126 ° C.), isobutyl acetate (boiling point 118). Ester solvents other than those described above;
Ether solvents such as propylene glycol monomethyl ether (common name “methoxypropanol”, boiling point 120 ° C.), ethylene glycol monomethyl ether (common name “methicello”, boiling point 124 ° C.);
Alcohol solvents such as methanol (boiling point 65 ° C.), butanol (boiling point 117 ° C.), ethanol (boiling point 78 ° C.), propyl alcohol (boiling point 97 ° C.);
Ketone solvents such as acetone (boiling point 56 ° C.), methyl ethyl ketone (boiling point 80 ° C.), methyl isobutyl ketone (boiling point 118 ° C.);
n aliphatic solvents such as hexane (boiling point 69 ° C.), heptane (boiling point 98 ° C.), cyclohexane (boiling point 81 ° C.);
Aromatic solvents such as toluene (boiling point 111 ° C.) can be used.

  The total amount of the dilution solvent is preferably 25 to 55% by weight based on the total amount of the diluted paint. When the total amount of the diluted solvent is out of the above range, the coating workability is deteriorated. Preferably it is 30 to 50% by weight.

Coating material The coating material used for the base material coating is mainly a car body of an automobile, but is not limited thereto, and is a metal such as iron, copper, aluminum, tin, zinc, or an alloy containing these metals. , Glass, plastics, foams and castings. When using a metal base material, it is preferable that it is previously subjected to chemical conversion treatment with phosphate, chromate or the like.

  An electrodeposition coating film is formed on the object to be coated to constitute a substrate. The electrodeposition coating film is formed by cationic and anionic electrodeposition coatings, and cationic electrodeposition coatings that are excellent in anticorrosion properties are common.

Intermediate Coating Film In the coating film forming method of the present invention, an intermediate coating film is used for forming the intermediate coating film.

  The intermediate coating contains a urethane-modified polyester resin (a), a melamine resin (b), a blocked isocyanate compound (c), a non-aqueous dispersion resin (d) having a core-shell structure, and a flat pigment (e). The intermediate coating can further contain various organic and inorganic color pigments and extender pigments.

  Examples of the urethane-modified polyester resin (a) include those having a number average molecular weight of 1500 to 3000 obtained by reacting a hydroxyl group-containing polyester resin with an aliphatic diisocyanate compound.

  Further, the content of the urethane-modified polyester resin (a) is 40 to 56% by weight based on the weight of the solid content of the coating resin. When the content is less than 40% by weight, chipping resistance is insufficient, and when the content is more than 56% by weight, the coating film hardness is lowered. Preferably it is 43 to 50% by weight.

  The urethane-modified polyester resin (a) has a number average molecular weight of 1500 to 3000. Preferably it is 1700-2500. If it is less than 1500, workability and curability are not sufficient, and if it exceeds 3000, the non-volatile content at the time of coating becomes too low, and workability becomes worse. In the present specification, the molecular weight is determined by a GPC method using a styrene polymer as a standard.

  The urethane-modified polyester resin preferably has a hydroxyl value of 30 to 180, more preferably 40 to 160. When the upper limit is exceeded, the water resistance of the coating film decreases, and when the lower limit is exceeded, the curability of the coating film decreases. Moreover, it is preferable that it has an acid value of 3-30 mgKOH / g, More preferably, it is 5-25 mgKOH / g. When the upper limit is exceeded, the water resistance of the coating film decreases, and when the lower limit is exceeded, the curability of the coating film decreases.

  In general, a polyester resin can be produced by polycondensation of an acid component such as a polyvalent carboxylic acid and / or an acid anhydride with a polyhydric alcohol. Isophthalic acid is contained in the component in an amount of 80 mol% or more based on the total number of moles of the acid component. If the amount of isophthalic acid in the acid component is less than 80 mol%, the glass transition point (Tg) of the hydroxyl group-containing polyester resin becomes too low.

  The hydroxyl group-containing polyester resin has a glass transition point (Tg) of 40 to 80 ° C, preferably 45 to 75 ° C. When the glass transition point (Tg) is below the lower limit, the coating film hardness is lowered, and when it exceeds the upper limit, the chipping resistance is lowered.

  The polyvalent carboxylic acid and / or acid anhydride other than the above isophthalic acid is not particularly limited. For example, phthalic acid, phthalic anhydride, tetrahydrophthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic acid, hexahydrophthalic anhydride, Methyltetrahydrophthalic acid, methyltetrahydrophthalic anhydride, hymic anhydride, trimellitic acid, trimellitic anhydride, pyromellitic acid, pyromellitic anhydride, terephthalic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, adipine Acid, azelaic acid, sebacic acid, succinic acid, succinic anhydride, dodecenyl succinic acid, dodecenyl succinic anhydride and the like.

  The polyhydric alcohol is not particularly limited, and examples thereof include ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, neopentyl glycol, 1,2-butanediol, and 1,3-butanediol. 1,4-butanediol, 2,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanediol, 2,2-dimethyl-3-hydroxypropyl-2,2 -Dimethyl-3-hydroxypropionate, 2,2,4-trimethyl-1,3-pentanediol, polytetramethylene ether glycol, polycaprolactone polyol, glycerin, sorbitol, annitol, trimethylolethane Trimethylol propane, trimethylol butane, hexanetriol, pentaerythritol, dipentaerythritol and the like.

  As other reaction components other than the polyvalent carboxylic acid and / or acid anhydride and the polyhydric alcohol component, monocarboxylic acid, hydroxycarboxylic acid, lactone and the like may be contained. Moreover, you may contain drying oil, anti-drying oil, and those fatty acids. Specific examples include monoepoxide compounds such as Cardura E (manufactured by Shell Chemical Co.) and lactones. The lactones can be subjected to ring-opening addition to polyvalent carboxylic acid and polyhydric alcohol polyesters to form a graft chain. For example, β-propiolaclone, dimethylpropiolactone, butyllactone, γ- Examples include valerolactone, ε-caprolactone, γ-caprolactone, γ-caprolactone, crotolactone, δ-valerolactone, and δ-caprolactone, among which ε-caprolactone is most preferable.

  Specific examples of the aliphatic diisocyanate compound include hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, cyclohexane-1,4-diisocyanate, dicyclohexylmethane-4,4-diisocyanate, and methylcyclohexane diisocyanate. Of these, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, and their burettes, isocyanurates, and adducts are preferably used from the viewpoint of chipping resistance and weather resistance.

  The melamine resin (b) is 10 to 30% by weight based on the solid content weight of the coating resin. When the content is less than 10% by weight, the curability becomes insufficient, and when the content exceeds 30% by weight, the cured film becomes too hard and brittle. Preferably, it is 15 to 25% by weight.

  The melamine resin is not particularly limited, and a methylated melamine resin, a butylated melamine resin, or a methyl / butyl mixed melamine resin can be used. For example, “Cymel-303”, “Cymel 254”, “Uban 128”, “Uban 20N60” commercially available from Mitsui Cytec Co., Ltd., “Summar Series” commercially available from Sumitomo Chemical Co., Ltd., and the like. .

  The blocked isocyanate compound (c) is obtained by adding a compound having an active methylene group to a multimer such as hexamethylene diisocyanate or its nurate, and the blocking agent is dissociated by heating to generate an isocyanate group. And those that react with the functional groups in the urethane-modified polyester resin and cure. Examples of the compound having an active methylene group include active methylene compounds such as acetylacetone, ethyl acetoacetate, and ethyl malonate.

  The content of the blocked isocyanate compound is 15 to 30% by weight based on the solid weight of the coating resin. More preferably, it is 17 to 25% by weight. Outside the above range, curing is insufficient.

  Specific examples include active methylene type blocked isocyanate “Duranate MF-K60X” manufactured by Asahi Kasei Corporation.

  The non-aqueous dispersion resin (d) having the core-shell structure is a non-crosslinked resin that is insoluble in this mixed solution by copolymerizing a polymerizable monomer in a mixed solution of a dispersion stabilizing resin and an organic solvent. It can be prepared as particles. The monomer to be copolymerized in the presence of the dispersion stable resin in order to obtain non-crosslinked resin particles is not particularly limited as long as it is a radical polymerizable unsaturated monomer.

  However, in order to synthesize the dispersion-stable resin and the non-aqueous dispersion, it is preferable to use a polymerizable monomer having a functional group. This is because the non-aqueous dispersion having a functional group can form a three-dimensionally crosslinked coating film by reacting with the post-curing agent together with the dispersion-stabilized resin containing the functional group.

  The content of the non-aqueous dispersion resin (d) is 4 to 15% by weight based on the solid content of the coating resin. When the content is less than 4% by weight, the overall coating film appearance is insufficient, and when the content is more than 15% by weight, chipping resistance is deteriorated. Preferably, it is 5 to 12% by weight.

  The dispersion stable resin is not particularly limited as long as it can stably synthesize a non-aqueous dispersion in an organic solvent. Specifically, the hydroxyl value is 10 to 250, preferably 20 to 180, the acid value is 0 to 100 mgKOH / g, preferably 0 to 50 mgKOH / g, and the number average molecular weight is 800 to 100,000, preferably 1000 to 20000. It is preferable to use acrylic resin, polyester resin, polyether resin, polycarbonate resin, polyurethane resin, or the like. If the upper limit is exceeded, the handling property of the resin is lowered, and the handling of the non-aqueous dispersion itself is also lowered. If the lower limit is not reached, the resin may be detached or the stability of the particles may be reduced when the coating film is formed.

  The method for synthesizing the dispersion stabilizing resin is not particularly limited, and preferred examples include a method obtained by radical polymerization in the presence of a radical polymerization initiator and a method obtained by a condensation reaction or an addition reaction. Furthermore, the monomer used to obtain the dispersion-stable resin can be appropriately selected according to the properties of the resin, but has a polymerizable monomer used to synthesize a non-aqueous dispersion described later. It is preferable to use those having a functional group such as a hydroxyl group and an acid group, and if necessary, those having a functional group such as a glycidyl group and an isocyanate group may be used.

  Further, the constituent ratio of the dispersion stabilizing resin and the polymerizable monomer can be arbitrarily selected according to the purpose. For example, the dispersion stabilizing resin is 3 to 80% by weight based on the total weight of the two components. 5 to 60% by weight, the polymerizable monomer is preferably 97 to 20% by weight, and particularly preferably 95 to 40% by weight. Furthermore, the total concentration of the dispersion stabilizing resin and the polymerizable monomer in the organic solvent is preferably 30 to 80% by weight, particularly 40 to 60% by weight, based on the total weight.

The non-aqueous dispersion can be obtained by polymerizing a radical polymerizable monomer in the presence of a dispersion stable resin. The non-aqueous dispersion has a hydroxyl value of 50 to 400, preferably 100 to 300, an acid value of 0 to 200 mgKOH / g, preferably 0 to ₅₀ mgKOH / g, and an average particle size (D ₅₀ ) of 0. A thickness of 05 to 10 μm, preferably 0.1 to 2 μm is preferable. If the lower limit is exceeded, the particle shape cannot be maintained, and if the upper limit is exceeded, the stability when dispersed in the paint is reduced.

  Typical examples of the polymerizable monomer having a functional group used for synthesizing the non-aqueous dispersion are as follows. Examples of those having a hydroxyl group include hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, hydroxymethyl methacrylate, allyl alcohol, hydroxyethyl (meth) methacrylate and ε- Examples include adducts with caprolactone.

  On the other hand, what has an acidic group includes a polymerizable monomer having a carboxyl group, a sulfonic acid group or the like. Examples of those having a carboxyl group include (meth) acrylic acid, crotonic acid, ethacrylic acid, propylacrylic acid, isopropylacrylic acid, itaconic acid, maleic anhydride, fumaric acid and the like. Examples of the polymerizable monomer having a sulfonic acid group include t-butylacrylamide sulfonic acid. When using the polymerizable monomer which has an acidic group, it is preferable that a part of acidic group is a carboxyl group.

  In addition, glycidyl group-containing unsaturated monomers such as glycidyl (meth) acrylate and isocyanate group-containing unsaturated monomers such as m-isopropenyl-α, α-dimethylbenzyl isocyanate and isocyanatoethyl acrylate are functional. Examples thereof include a polymerizable monomer having a group.

Other polymerizable monomers include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, n-propyl (meth) acrylate, and n- (meth) acrylate. Butyl, t-butyl (meth) acrylate, isobutyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, (Meth) acrylic acid alkyl ester such as tridecyl methacrylate, addition reaction product of oil fatty acid and acrylic acid or methacrylic acid ester monomer having oxirane structure (for example, addition reaction product of stearic acid and glycidyl methacrylate), C ₃ or more Between an oxirane compound containing an alkyl group and acrylic acid or methacrylic acid Addition reaction product, styrene, α-methyl styrene, α-methyl styrene, m-methyl styrene, p-methyl styrene, pt-butyl styrene, benzyl (meth) acrylate, itaconic acid ester (such as dimethyl itaconate), Maleic acid esters (such as dimethyl maleate), fumaric acid esters (such as dimethyl fumarate), acrylonitrile, methacrylonitrile, methyl isopropenyl ketone, vinyl acetate, Veova monomer (made by Shell Chemical Co., Ltd., trade name), vinyl pro Examples thereof include polymerizable monomers such as pionate, vinyl pivalate, ethylene, propylene, butadiene, N, N-dimethylaminoethyl acrylate, N, N-dimethylaminoethyl methacrylate, acrylamide, and vinylpyridine.

  The polymerization reaction for obtaining the non-aqueous dispersion is preferably performed in the presence of a radical polymerization initiator. Examples of the radical polymerization initiator include azo initiators such as 2,2′-azobisisobutyronitrile and 2,2′-azobis (2,4-dimethylvaleronitrile), benzoyl peroxide, lauryl peroxide, Examples include t-butyl peroctoate. These initiators are used in an amount of 0.2 to 10 parts by weight, preferably 0.5 to 5 parts by weight per 100 parts by weight of the polymerizable monomers. In general, the polymerization reaction for obtaining a non-aqueous dispersion in an organic solvent containing a dispersion-stable resin is preferably performed in a temperature range of about 60 to 160 ° C. for about 1 to 15 hours.

  Further, the non-aqueous dispersion is different from the crosslinked polymer fine particles, and is a particle component in the paint, but has a characteristic that it does not form a particle structure in the coating film. That is, the non-aqueous dispersion is different from the crosslinked polymer fine particles in that there are no cross-linked sites in the particles, so that the particle shape changes during the baking process and can become a resin component.

  Furthermore, for example, resin particles called NAD (Non Aqueous Dispersion) used in the NAD paint described in Color Material, Vol. 48 (1975), pages 28 to 34 are also used. be able to.

  Examples of the flat pigment (e) include mica, alumina, talc and silica, but talc is preferably used from the viewpoint of chipping performance.

  The flat pigment preferably has a major axis of 1 to 10 μm and a number average particle size of 2 to 6 μm. If the major axis is outside the above range, the appearance of the coating film is inferior or sufficient chipping resistance is not achieved. If the number average particle size is outside the above range, the appearance of the coating film is inferior, and sufficient chipping resistance is present. It will not come out.

  The content of the flat pigment (e) is 0.4 to 2 parts by weight based on 100 parts by weight of the resin solid content in the paint. More preferably, it is 0.5 to 1.5 parts by weight. Outside of the above range, sufficient chipping performance cannot be obtained because adhesion to the base coating film is reduced.

  The resin that can be contained in addition to the above is not particularly limited, and examples thereof include an acrylic resin, a polyester resin, an alkyd resin, an epoxy resin, and the like. Can do.

  Examples of color pigments include organic azo chelate pigments, benzimidazolone pigments, diketopyrrolopyrrole pigments, insoluble azo pigments, condensed azo pigments, phthalocyanine pigments, indigo pigments, perinone pigments, and perylene pigments. , Dioxane pigments, quinacridone pigments, isoindolinone pigments, metal complex pigments, and the like. Inorganic pigments such as yellow lead, yellow iron oxide, bengara, carbon black, and titanium dioxide can be used. In addition, calcium carbonate, barium sulfate, aluminum powder, kaolin and the like can be used as extender pigments. The total pigment concentration (PWC) of the intermediate coating is preferably 30 to 55% by weight, and more preferably 35 to 50% by weight. When the upper limit is exceeded, the appearance is lowered, and when it is less than the lower limit, the concealability of the base coating film is lowered. It is particularly preferably 38 to 47% by weight.

  As a standard, a gray type having carbon black and titanium dioxide as main pigments is used. Furthermore, the thing which combined the hue with top coat and the thing which combined various coloring pigments can also be used.

  In addition, a viscosity control agent can be added to the intermediate coating material in order to prevent familiarity with the solid color coating film and to ensure coating workability. Viscosity control agents can generally include those exhibiting thixotropy, such as fatty acid amide swelling dispersions, amide fatty acids, polyamides such as long-chain polyaminoamide phosphates, colloidal swelling dispersion of oxidized polyethylene Such as polyethylene-based bodies, organic acid smectite clay, organic bentonite-based materials such as montmorillonite, inorganic pigments such as aluminum silicate and barium sulfate, flat pigments that develop viscosity depending on the shape of the pigment, crosslinked resin particles, etc. It can be mentioned as a viscosity control agent.

The total solid content at the time of application of the intermediate coating composition used in the present invention is 30 to 80% by weight, preferably 35 to 65% by weight. Outside this range, the paint stability is reduced. When the upper limit is exceeded, the viscosity is too high and the appearance of the coating film is lowered. When the viscosity is lower than the lower limit, the viscosity is too low and appearance defects such as familiarity and unevenness occur.
In the intermediate coating composition used in the present invention, additives usually added to the coating composition, for example, a surface conditioner, an antioxidant, an antifoaming agent, etc. may be blended in addition to the above components. These compounding amounts are within the range known to those skilled in the art.

  The method for producing the coating composition used in the present invention is not particularly limited, including those described later. For those skilled in the art such as kneading and dispersing a compound such as a pigment using a kneader or a roll, an SG mill or the like. All known methods can be used.

Solid color paint for inner plate and solid color paint for outer plate In the coating film forming method of the present invention, a coating film with a solid color paint is formed on both the inner plate part and the outer plate part. Solid color paint is applied exclusively. However, since there are many common ingredients in the solid color paint, they will be explained here simultaneously. The solid paint can contain a film-forming resin, a curing agent, various organic and inorganic color pigments, extender pigments, and the like. The solid paint generally has a monotone color tone by finishing the coating film with one coat.

  The film-forming resin contained in the solid coating used in the coating film forming method of the present invention preferably has a number average molecular weight of 800 to 30000, more preferably 1000 to 25000. If it is smaller than 800, workability and curability are not sufficient, and if it exceeds 30000, the non-volatile content at the time of coating becomes too low, and the workability becomes worse. In the present specification, the molecular weight is determined by a GPC method using a styrene polymer as a standard.

  Furthermore, the coating film-forming resin preferably has a hydroxyl value of 20 to 180 mgKOH / g (solid content), preferably 30 to 160 mgKOH / g (solid content). When the upper limit is exceeded, the water resistance of the coating film decreases, and when the lower limit is exceeded, the curability of the coating film decreases. Moreover, it is preferable that it has an acid value of 2-30 mgKOH / g (solid content), More preferably, it is 3-25 mgKOH / g (solid content). When the upper limit is exceeded, the water resistance of the coating film decreases, and when the lower limit is exceeded, the curability of the coating film decreases.

  As said film-forming resin, an acrylic resin, a polyester resin, an alkyd resin, a polyether resin, a polyolefin resin, a urethane resin etc. can be mentioned as a preferable thing, It is using combining 1 type (s) or 2 or more types. it can. An acrylic resin or a polyester resin is preferably used from the viewpoint of coating performance such as weather resistance and water resistance.

  Preferred examples of the curing agent include amino resins, blocked isocyanate resins, epoxy compounds, aziridine compounds, carbodiimide compounds, and oxazoline compounds. An amino resin and / or a blocked isocyanate resin is generally used in view of various performances and costs of the obtained coating film.

  Content of the said hardening | curing agent is 20 to 100 weight% with respect to solid content of the said film-forming resin. If the content is less than 20% by weight, the curability is insufficient, and if it exceeds 100% by weight, the cured film becomes too hard and brittle. However, it is important that the pigment concentration (PWC) of the solid color paint for the outer plate is lower than the pigment concentration (PWC) of the solid color paint for the inner plate. This is because the appearance of the coating film deteriorates.

  Examples of the colored pigment include organic azo chelate pigments, insoluble azo pigments, condensed azo pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, phthalocyanine pigments, indigo pigments, perinone pigments, and perylene pigments. Examples thereof include pigments, dioxane pigments, quinacridone pigments, isoindolinone pigments, metal complex pigments, and inorganic pigments include yellow lead, yellow iron oxide, bengara, carbon black, titanium dioxide and the like. In addition, calcium carbonate, barium sulfate, clay, talc and the like can be used as extender pigments. Furthermore, you may add flat pigments, such as aluminum powder and mica powder, to such an extent that a glitteriness does not appear. Since the solid color paint dedicated to the inner plate needs a higher background concealing property, the difference from the solid color for the outer plate causes a difference in pigment selection or blending amount. The total pigment concentration (PWC) in the solid color paint exclusively for the inner plate is 35 to 65%, preferably 38% to 60%, and more preferably 43% to 55%. When the upper limit is exceeded, the appearance of the coating film deteriorates. Below the lower limit, the underlying coating film is not concealed. The total pigment concentration (PWC) in the solid color paint exclusively for the outer plate is 30 to 60%, preferably 35 to 55%. When the upper limit is exceeded, the appearance of the coating film is deteriorated, and when it is less than the lower limit, it becomes familiar with the base and the appearance is deteriorated. 38 to 50% is particularly preferable.

  In addition, a viscosity control agent can be added to the solid paint in order to ensure painting workability. As the viscosity control agent, those generally showing thixotropy can be used, for example, swelling dispersions of fatty acid amides, polyamides such as amide fatty acids, phosphates of long chain polyaminoamides, colloidal swelling dispersion of polyethylene oxide Polyethylene-based materials, organic acid smectite clays, organic bentonite-based materials such as montmorillonite, inorganic pigments such as aluminum silicate and barium sulfate, flat pigments that develop viscosity depending on the shape of the pigment, cross-linked or non-cross-linked Resin particles and the like can be mentioned as viscosity control agents.

  In the solid paint used in the present invention, in addition to the above components, additives usually added to the paint, for example, a surface conditioner, an antioxidant, an antifoaming agent and the like may be blended. These compounding amounts are within the range known to those skilled in the art.

  The total solid content at the time of coating of the solid paint used in the present invention is 10 to 60% by weight, preferably 15 to 50% by weight. When the upper limit and the lower limit are exceeded, the coating stability is lowered. If the upper limit is exceeded, the viscosity is too high and the appearance of the coating film is lowered. If the lower limit is not reached, the viscosity is too low and appearance defects such as familiarity and unevenness occur.

  The manufacturing method of the coating composition used in the present invention is not particularly limited, including those described later, and all known to those skilled in the art such as kneading and dispersing a compound such as a pigment using a kneader or a roll. The method can be used.

Coating film forming method In the coating film forming method of the present invention, an intermediate coating film is applied to the outer plate portion on the base material by an intermediate coating, and then a solid color dedicated to the inner plate is applied to the inner plate portion, and then to the outer plate portion. Apply solid color paint for skin. They are sequentially formed wet on wet.

  When the intermediate coating is applied to the substrate in the present invention, in order to enhance the appearance, it is applied by multi-stage coating by air electrostatic spray coating, preferably by two stages, or by air electrostatic spray coating, commonly known as The coating film can be formed by a coating method combined with a rotary atomizing electrostatic coating machine called “μμ (micro micro) bell”, “μ (micro) bell” or “metabell”.

  In the present invention, the film thickness of the dry coating film by the intermediate coating varies depending on the desired use, but in many cases, 10 to 60 μm is useful. If the upper limit is exceeded, sharpness may deteriorate, or defects such as unevenness or flow may occur during coating. If the lower limit is exceeded, the substrate cannot be concealed and film breakage occurs.

  Next, a solid color paint dedicated to the inner plate is applied to the inner plate portion. The inner plate part is painted in a complicated or difficult-to-reach area, so hand spray painting using a spray gun is convenient. A film thickness is 10-30 micrometers, and when it exceeds an upper limit, it has defects, such as a blurring with a sagging and a top coat, and when it is less than a lower limit, it has defects, such as a nonuniformity and a skin defect.

  In the coating film forming method of the present invention, a solid color paint for the outer plate is further applied wet-on-wet on the uncured intermediate coating film.

  The solid color paint for the outer plate in the method of the invention can be applied by air electrostatic spray coating or a rotary atomizing electrostatic coating machine such as Metabell, μμ Bell, μ Bell, etc., similar to the above intermediate coating. The dry film thickness of the coating film can be set to 10 to 50 μm, preferably 15 to 40 μm. If the film thickness exceeds 50 μm, the sharpness may deteriorate, or the coating film may be uneven or flow. None of these is preferable because a discontinuous state) may occur.

  The laminated coating film obtained as described above forms a coating film by so-called three-coat one-bake that is simultaneously cured.

  A cured coating film having a high degree of crosslinking can be obtained by setting the curing temperature for curing the laminated coating film to 100 to 180 ° C, preferably 130 to 160 ° C. If the upper limit is exceeded, the coating film becomes hard and brittle, and if it is less than the lower limit, curing is not sufficient. The curing time varies depending on the curing temperature, but 10 to 30 minutes is appropriate at 130 to 160 ° C. The curing time may be 10-60 minutes, preferably 15-50 minutes.

  The invention is explained in more detail by means of examples. The present invention is not limited to these examples. In the examples, parts and percentages are based on weight unless otherwise indicated.

Preparation of intermediate coating
Manufacture of urethane-modified polyester resin 440 parts of isophthalic acid, 20 parts of hexahydrophthalic acid, 40 parts of azelaic acid in a 2 L reaction vessel equipped with a nitrogen introducing tube, a stirrer, a temperature controller, a cooling tube equipped with a dropping funnel and a decanter Then, 300 parts of trimethylolpropane and 200 parts of neopentyl glycol were charged, and when the raw materials were dissolved and stirred by heating, 0.2 parts of dibutyltin oxide was added, stirring was started, and the reaction layer temperature was set at 180 ° C. The temperature was gradually raised to 220 ° C. over 3 hours. The resulting condensed water was distilled out of the system. When the temperature reached 220 ° C., the temperature was kept for 1 hour, 20 parts of xylene was gradually added into the reaction layer, and the condensation reaction was allowed to proceed in the presence of a solvent. When the resin acid value reached 10 mgKOH / g, it was cooled to 100 ° C., and 100 parts of hexamethylene diisocyanate was gradually added over 30 minutes. Furthermore, after maintaining for 1 hour, 200 parts of xylene and 200 parts of butyl acetate were added to obtain a urethane-modified polyester resin having a solid content of 70%, a number average molecular weight of 2000, an acid value of 8 mgKOH / g, a hydroxyl value of 120, and a resin Tg of 60 ° C.

Production of Non-Aqueous Dispersion (a) Production of Dispersion Stabilizing Resin 90 parts of butyl acetate was charged into a vessel equipped with a stirrer, a temperature controller, and a reflux condenser. Next, a mixed solution having the following monomer composition was prepared.

  20 parts of the monomer composition was added to the container and heated with stirring to raise the temperature. The remaining 85 parts of the above mixed solution was added dropwise at 110 ° C. over 3 hours, and then a solution consisting of 0.5 parts of azobisisobutyronitrile and 10 parts of butyl acetate was added dropwise over 30 minutes. The reaction solution was further stirred and refluxed for 2 hours to increase the rate of conversion to resin, and then the reaction was terminated to obtain an acrylic resin having a solid content of 50%, a number average molecular weight of 5600, and an SP value of 9.5.

(B) Production of non-aqueous dispersion A container equipped with a stirrer, a cooler, and a temperature controller was charged with 90 parts of butyl acetate and 60 parts of acrylic resin obtained in the production of (a) the dispersion-stable resin. Next, a mixed solution having the following monomer composition was prepared.

  The monomer composition was dropped into a container at 100 ° C. over 3 hours, and then a solution consisting of 0.1 part of azobisisobutyronitrile and 1 part of butyl acetate was dropped over 30 minutes. When the reaction solution was further stirred for 1 hour, an emulsion having a solid content of 60% and a particle size of 180 nm was obtained. This emulsion was diluted with butyl acetate to obtain a core-shell type butyl acetate dispersion having a viscosity of 300 mPa · s (25 ° C.) and a particle diameter of 180 nm and a non-aqueous dispersion content of 40% by weight. The non-aqueous dispersion resin had a Tg of 23 ° C. and a hydroxyl value of 162.

Preparation of intermediate coating material In 1 L vessel, 107 parts of urethane-modified polyester resin varnish obtained in the previous production example, 280 parts of CR-97 (Ishihara Sangyo Co., Ltd. titanium oxide), MA-100 (Carbon Black manufactured by Mitsubishi Chemical Corporation) Pigment) 13 parts, LMR-100 (Fuji talc scale scaly talc) 7 parts, butyl acetate 47 parts and xylene 47 parts were charged, and GB503M (particle diameter 1.6 mm glass beads) of the same amount as the charged weight was charged. The mixture was dispersed for 3 hours at room temperature using a tabletop SG mill to obtain a gray pigment paste. The particle size at the end of dispersion by a grind gauge was 5 μm or less. The glass beads were filtered to obtain a pigment paste. To this pigment paste, an intermediate coating was prepared so as to have the composition shown in Table 3.

Preparation of inner plate-dedicated paint A solid color paint dedicated to an inner plate was prepared from the components and formulations shown in Table 4 below.

  The above-mentioned pigment paste formulation was added with glass bead medium in a paint conditioner, and mixed and dispersed at room temperature for 2 hours to obtain a pigment dispersion paste having a nonvolatile content of 79%.

  The pigment dispersion paste was mixed with the resin varnish blended to obtain a solid color paint exclusively for the inner plate.

  A solid color paint for an outer plate was prepared using the composition shown in Table 5 below.

  The above pigment paste formulation was added with glass bead medium in a paint conditioner and mixed at room temperature for 2 hours to obtain a pigment dispersion paste having a nonvolatile content of 79%.

  A resin color varnish was further added to the pigment dispersion paste to obtain a solid color paint for an outer panel.

(1) Intermediate coating High-boiling solvent: Carbitol acetate is added in an amount of 1.5% by weight based on the weight of the paint. Medium-boiling solvent: ethoxypropanol / S-100 = 1/2 and low-boiling solvent: toluene / ethyl acetate / Methyl isobutyl ketone = 3/1/1 was mixed in half and No. Dilute to 20 seconds at 20 ° C. using 4 Ford cups. When the internal solvent composition of the obtained diluted paint was analyzed, it was 12% by weight of the medium boiling point solvent and 1.5% by weight of the high boiling point solvent. The total weight of volatile components in the diluted paint was 39% by weight. Further, among the medium boiling solvents, ether solvents and aliphatic solvents were ½.

(2) Inner plate paint High-boiling solvent: Carbitol acetate is added in an amount of 2.0% by weight based on the weight of the paint, medium-boiling solvent: ethoxypropanol / S-100 = 1/2, and low-boiling solvent: toluene / ethyl acetate. / Methyl isobutyl ketone = 3/1/1 and mixed to 1/1. Dilute to 20 seconds at 20 ° C. using a 4 Ford cup. When the internal solvent composition of the obtained diluted paint was analyzed, the medium boiling point solvent was 17% by weight and the high boiling point solvent was 2.0% by weight. The total weight of volatile components in the diluted paint was 40% by weight. Further, among the medium boiling solvents, ether solvents and aliphatic solvents were ½.

(3) Outer plate paint High-boiling solvent: Carbitol acetate is added in an amount of 2.5% by weight based on the paint weight, medium-boiling solvent: ethoxypropanol / S-100 = 1/1, and low-boiling solvent: toluene / ethyl acetate. / Methyl isobutyl ketone = 3/1/1 and mixed to 1/1. Dilute to 20 seconds at 20 ° C. using a 4 Ford cup. Analysis of the internal solvent composition of the obtained diluted paint revealed that the medium boiling point solvent was 23% by weight and the high boiling point solvent was 2.5% by weight. The total weight of volatile components in the diluted paint was 39% by weight. Further, among the medium boiling solvents, the ether solvent and the aliphatic solvent were 1/1.

  By adjusting the paste amount and the resin amount, an intermediate coating material, a solid color coating material exclusively for the inner plate, and a solid color coating material for the outer plate were prepared by adjusting the coating viscosity and PWC. Using these, combination experiments of Examples 1 and 2 and Comparative Examples 1 to 4 were performed. Table 6 shows the coating viscosity, the pigment concentration, and the obtained results.

First, a dull steel plate (dimension: 8 × 30 cm) is prepared by electrodeposition coating a cationic electrodeposition paint (V-20) manufactured by Nippon Paint Co., Ltd. so as to have a dry film thickness of 20 μm. On this steel plate, using the coating materials of the above Examples and Comparative Examples, an intermediate coating material, a solid color coating material exclusively for the inner plate, and a solid color coating material for the outer plate were applied under the following coating conditions.
Each paint application condition booth temperature: 18 ℃
Humidity; 70%
Wind speed: 0.3 m / sec. Coating machine: Intermediate coating and outer coating are “μμ Bell” ABB Industries, Inc., rotary atomization type
Using an electrostatic coating machine, the coating amount is 24 in a state where electrostatic of −60 KV is applied.
The coating was performed at 0 mL / min and 200 mL / min. The inner plate paint is
The coating was performed using a Dar 100 (spray gun manufactured by Iwata Co., Ltd.).

Coating Viscosity After coating under the above coating conditions, the paint applied to the object was scraped off within 1 minute and stored in a sample bottle. The viscosity (Pa · s) at a shear rate of 0.1 S ⁻¹ was measured with a viscosity measuring device (Solid Meter MR-300 / Rheology) within 1 hour. The obtained values are shown in Table 6.

Coating method The diluted intermediate coating was applied under the above-mentioned conditions to the outer plate part at the lower part of the door of an automobile on which an electrodeposition coating film was formed in advance. Next, after providing an interval of 2 minutes, the inner plate paint diluted in advance was applied to the inner plate paint application site of the door opening / closing part using a spray gun.

  Further, a pre-diluted outer coating was applied under the above conditions at an interval of 13 minutes. After setting time of 10 minutes, baking was performed at 140 ° C. for 30 minutes. After cooling, the coating film appearance of the coating boundary portion between the inner plate paint and the outer plate paint and the coating dust application site of the inner plate paint was visually evaluated according to the following criteria.

Appearance criteria ○: Glossy feeling and smoothness equivalent to the part where no dust is attached Δ: Glossy feeling is inferior to the part where dust is not attached x: There is no glossy feeling and the paint film is rough due to dust The results are shown in Table 6.

The state after the steel plate including the water-resistant dust application site was immersed in deionized water having a water temperature of 40 ° C. for 10 days was visually observed.
Judgment criteria ○: No change Δ: Discolored ×: Blister is generated in the coating film. A blister is a bulge of a fine paint film that occurs after water resistance evaluation.

The figure which represents typically the inner-plate part and outer-plate part of a coating base material. The figure which represents typically the cross section of the coating film painted on the base material.

Explanation of symbols

2 ... outer plate,
4 ... inner plate part,
8 ... Electrodeposition coating,
9 ...
10 ... base material,
11 ... Intermediate coating film,
12 ... Solid color coating for inner plate,
13 ... Solid color coating for outer panel,
12 '... Solid color splash for inner plate.

Claims (3)

Apply an intermediate coating (A) to the outer plate on the electrodeposited substrate that has an inner plate and an outer plate, and apply a solid color paint (B) for the inner plate to the inner plate. After that, when applying the solid color paint (C) for the outer panel to the outer panel part, each coating film is applied by wet on wet without curing, and the wet coating film is baked and cured at once. There,
The coating viscosity of the intermediate coating (A), the solid color coating (B) for the inner plate, and the solid color coating (C) for the outer plate is the same as that of the intermediate coating (A) and the solid coating (B) for the inner plate. And the solid color paint (C) for the outer plate, and the pigment concentration (PWC) of the solid color paint (B) for the inner plate and the solid color paint (C) for the outer plate is the solid for the inner plate. The color paint (B) and the solid color paint (C) for the outer plate become lower in order,
Furthermore, the intermediate coating (A) is obtained by polycondensation of an acid component containing 80 mol% or more of isophthalic acid and a polyhydric alcohol, and has a glass transition point (Tg) of 40 to 80 ° C. 40-56% by weight of urethane-modified polyester resin (a) having a number average molecular weight of 1500-3000 obtained by reacting a resin with an aliphatic diisocyanate compound;
Melamine resin (b) 10 to 30% by weight;
Isocyanate compound (c) of 15 to 30% by weight obtained by blocking hexamethylene diisocyanate and an isocyanate compound obtained by reacting with hexamethylene diisocyanate and a compound reacting therewith with a compound having an active methylene group;
Non-aqueous dispersion resin (d) having a core-shell structure (d) 4 to 15% by weight (the amount of (a) to (d) is based on the weight of the solid content of the coating resin); and the major axis is 1 to 10 μm, 0.4-2 parts by weight of a flat pigment (e) having an average particle size of 2-6 μm (the solid content of the coating resin is 100 parts by weight);
A method of forming a coating film, comprising:   The coating viscosities of the intermediate coating (A), the solid color coating (B) for the inner plate and the solid color coating (C) for the outer plate are 70 to 300 Pa · s, 20 to 200 Pa · s and 5 to 100 Pa, respectively. The coating film forming method according to claim 1, wherein the coating film forming method is s. The difference in coating viscosity between the intermediate coating (A) and the solid color paint (B) for the inner plate is 30 Pa · s or more, and the solid color paint (B) for the inner plate and the solid color paint for the outer plate ( The coating film forming method according to claim 2, wherein the difference in coating viscosity from C) is 50 Pa · s or more.

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