JP6955313B2 - Multi-color finish painting method and manufacturing method of painted products - Google Patents

Description

The present invention relates to a multicolor finish coating method and a method for producing a coating, which are more than two-tone coating, which is optimal for coating a relatively large object to be coated such as a railroad vehicle, a bus, a truck, a construction machine, or an industrial equipment.

Conventionally, a thermosetting resin containing a hydroxyl group such as a hydroxyl group-containing acrylic resin, a cross-linking agent such as a melamine resin and / or a polyisocyanate compound, and a pigment as a coating composition used for painting an automobile body such as a passenger car. Paint compositions are widely used. However, usually, in the coating process, a heating / drying temperature of about 140 ° C. is required when the melamine resin is used as the cross-linking agent, and a heating / drying temperature of about 80 ° C. is required even when the polyisocyanate compound is used as the cross-linking agent (). Patent Document 1, Patent Document 2).

Large car bodies or parts such as railroad cars, trucks, buses, construction machinery or industrial equipment have a larger coating area than automobile car bodies such as passenger cars as objects to be coated, and inevitably the drying furnace becomes large and huge. In addition to requiring capital investment, it may not be possible to secure a sufficient and uniform heating and drying temperature for the entire object to be coated. In addition, since the object to be coated is large, it takes time to cool it when it is placed in a drying oven. At present, when applying two-tone or more multicolored coatings, a drying process is required for each color for about one day in order to ensure sufficient finish, and the drying process requires a great deal of man-hours. In particular, when multicolor coating is applied to a large area object such as a railroad vehicle, if it is not dried after each color coating, tape marks, adhesive residue, and color mixture will occur on the masking tape coating film, resulting in a finished product. The sex is not good. Therefore, as described above, not only the man-hours are required, but also the finish and stain resistance are dissatisfied due to the step difference at the color boundary and the difference in film thickness.

Further, in recent years, in the painting process of such a large vehicle, it has been desired to improve the productivity by reducing the man-hours, but in order to improve the finish, the drying process of each color is indispensable.

Japanese Unexamined Patent Publication No. 1-203085 Japanese Unexamined Patent Publication No. 8-332448

The present invention has been made in view of the above circumstances, and it is possible to reduce the work process including the drying process and shorten the time when multicolor coating is applied to a large-area object to be coated such as a railroad vehicle. In addition, it is an object of the present invention to provide a multicolor finish coating method and a method for producing a coated material, which are extremely excellent in finishability.

Under such circumstances, as a result of diligent research, the present inventors applied a base coating composition and a top coating composition containing a specific amount of a cellulose derivative, and then applied a top clear coating composition and dried the entire surface. By doing so, it was found that the above problems can be solved.

The present invention provides the methods shown in the following sections:
(Aspect 1.) On a large-area object to be coated,
(1) A process of applying a base coating composition to form a base coating film,
(2) A step of partially coating a topcoat coating composition of a different color on the base coating film at least once to form a topcoat coating film.
(3) Next, it is a multicolor finish coating method including a step of applying a top clear coating composition on the entire surface and drying it to form a clear coating film.
Both the base coating composition and the top coating composition contain a cellulose derivative (a), a hydroxyl group-containing resin (b) and a pigment (c), and the content of the cellulose derivative (a) is a component. A multicolor finish coating method, which is in the range of 5 to 75 parts by mass with respect to a total of 100 parts by mass of the solid content of (a) and the component (b).

(Aspect 2.) The multicolor finish coating method according to Aspect 1, wherein the top clear coating composition is a urethane curable coating composition.

(Aspect 3.) The multicolor finish coating method according to Aspect 1 or 2, wherein the base coating composition and the topcoat coating composition are one-component coating compositions that do not contain a cross-linking agent.

(Aspect 4.) In the step (1), the base coating composition is coated so that the dry film thickness of the base coating film is 5 to 30 μm, and in the step (2), the dry film of the top coat coating film is applied. The multicolor finish coating method according to any one of aspects 1 to 3, wherein the topcoat coating composition is coated so that the thickness is 5 to 30 μm.

(Aspect 5.) The multicolor finish coating method according to any one of aspects 1 to 4, wherein the object to be coated is a railroad vehicle.

(Aspect 6.) A method for producing a coated material having a coating film coated in two tones or more in multiple colors by using the multicolor finish coating method according to any one of aspects 1 to 5.

According to the multicolor finish coating method of the present invention (hereinafter, may be abbreviated as "the present method"), even if the object to be coated has a relatively large area, the process including the drying time in the coating process can be shortened. It is possible to obtain a coating film having excellent finish and adhesion and a coating material having the coating film. According to the present invention, multicolor coating is possible and the finish is excellent without requiring heat drying in all the steps.

Since the drying process, which used to take man-hours for each color, can be shortened or reduced, it is possible to paint multiple colors in a day, and the work process until completion can be significantly reduced and productivity is improved. In addition, although the work process can be shortened, poor finish and stain resistance due to the difference in film thickness (less likely to cause dirt accumulation due to the difference in film thickness) are improved, coating film defects are less likely to occur, and the total film thickness is small. Therefore, it can be expected to be effective in reducing carbon dioxide emissions and costs, reducing the weight, and improving safety.

1 to 5 are flowcharts for explaining the flow of the coating method according to the embodiment of the invention.
It is a flowchart for demonstrating the flow of the coating method which concerns on one Embodiment of this invention. It is a flowchart for demonstrating the flow of the coating method which concerns on one Embodiment of this invention. It is a flowchart for demonstrating the flow of the coating method which concerns on one Embodiment of this invention. It is a flowchart for demonstrating the flow of the coating method which concerns on one conventional Embodiment. It is a flowchart for demonstrating the flow of the coating method which concerns on one conventional Embodiment.

<Multicolor finish painting method>
The multicolor finish coating method of the present invention
On a large area to be coated
(1) A process of applying a base coating composition to form a base coating film,
(2) A step of partially coating a topcoat coating composition of a different color on the base coating film at least once to form a topcoat coating film.
(3) Next, a multicolor finish coating method including a step of applying a top clear coating composition over the entire surface and drying to form a clear coating film, wherein the cellulose derivative in the base coating composition and the top coating composition (3). It is characterized in that the content of a) is within a specific range.

<Object to be coated>
The object to be coated to which this method is applied is a material having a large coating area, and the shape and the like are not particularly limited. Even if this is the case, it is an object to be coated with a coating area in which the material reaching temperature is less than 60 ° C. (for example, the set temperature is less than 80 ° C.).

For example, construction machinery / large vehicles, industrial equipment, blades for wind power generators, aircraft and the like can be mentioned, and more specifically, railroad vehicles, buses, truck bodies and their parts and the like can be mentioned.
Railway vehicles are particularly preferable. Further, the object to be coated may have an old coating film.

Specific examples of the material of the object to be coated include, for example, steel plate, zinc plating, stainless steel, aluminum and the like as the metal material, and for example, polyethylene resin, polypropylene resin and acrylonitrile-butadiene-styrene as the plastic material. Examples thereof include resins such as (ABS) resin, polyamide resin, acrylic resin, vinylidene chloride resin, polycarbonate resin, polyurethane resin and epoxy resin, and various plastic materials such as FRP. Further, a composite of these metal materials and plastic materials can also be mentioned as an object to be coated. Depending on these materials, polishing treatment, degreasing treatment, surface treatment, putty composition, primer surfacer and the like may be appropriately applied to prepare the base.

<Step (1) Step of forming the base coating film>
Base coating composition The base coating composition used in this method is formed to impart weather resistance, corrosion resistance, rust prevention, chipping resistance, etc. to the object to be coated, and the base coating composition is coated. It can be obtained by forming a base coating film.

The base coating composition used in this method contains a cellulose derivative (a), a hydroxyl group-containing resin (b) and a pigment (c), and the content of the cellulose derivative (a) is the component (a) and It is characterized by containing 5 to 75 parts by mass with respect to a total of 100 parts by mass of the solid content of the component (b).

(A) Cellulose derivative The cellulose derivative (a) is a compound containing cellulose as a constituent unit, and is, for example, an esterified product of cellulose obtained by esterifying a hydroxyl group of cellulose with an acid such as fatty acid or nitrate, or an esterified product of the cellulose. Examples thereof include a cellulose-modified copolymer obtained by reacting a polymerizable unsaturated group-containing cellulose esterified product obtained by introducing a polymerizable unsaturated group with another polymerizable unsaturated monomer.

Examples of the esterified product of cellulose include nitrocellulose, cellulose acetate butyrate, cellulose acetate, cellulose acetate propionate and the like. Of these, cellulose acetate butyrate can be preferably used.

Cellulose acetate butyrate (hereinafter sometimes abbreviated as CAB) is obtained by further butyl esterifying a partial acetylated product of cellulose, and specifically, for example, specifically, for example, "CAB-381-". 0.5 ”,“ CAB-381-0.1 ”,“ CAB-381-2.0 ”,“ CAB-381-20 ”,“ CAB-551-0.2 ”,“ CAB-551-0. 01 ”,“ CAB-553-0.4 ”,“ CAB-531-1 ”,“ CAB-500-5 ”,“ CAB-321-0.1 ”,“ Solus2100 ”,“ Solus2300 ”(above, USA) Commercial products such as (trade name) manufactured by Eastman Chemical Co., Ltd. can be exemplified, and these can be used alone or in combination of two or more.

The number average molecular weight of cellulose acetate butyrate is preferably in the range of 1,000 to 100,000, particularly 3,000 or more and less than 50,000 from the viewpoint of dryness, finish and polishability.

The content of the cellulose derivative (a) is in the range of 5 to 75 parts by mass with respect to 100 parts by mass of the total solid content of the cellulose derivative (a) and the hydroxyl group-containing resin (b) described later, and the surface is dried. From the viewpoint of the balance between the properties and the finish, the range of 15 to 70 parts by mass is preferable, and the range of 20 to 60 parts by mass is more preferable.

(B) Hydroxide-containing resin The hydroxyl group-containing resin (b) is not particularly limited as long as it contains a hydroxyl group, and examples thereof include an alkyd resin, a polyester resin, and an acrylic resin. It is preferable to contain a hydroxyl group-containing polyester resin (b-1) from the viewpoint of penetration, adhesion and finish of the crosslinked component from the clear coat, and further from the viewpoint of weather resistance and scratch resistance of the coating film. It is preferable to contain a hydroxyl group-containing acrylic resin (b-2).

(B-1) Hydroxy Group-Containing Polyester Resin The hydroxyl group-containing polyester resin (b-1) can be obtained by reacting a conventionally known polybasic acid with a polyhydric alcohol. Examples of the polybasic acid include adipic acid, succinic acid, isophthalic acid, terephthalic acid, phthalic acid anhydride, maleic anhydride, trimellitic acid, hexahydrophthalic anhydride, sodium 5-sulfoisophthalate, and the like. Examples thereof include ethylene glycol, propylene glycol, glycerin, trimethylolpropane, neopentyl glycol, 1,6-hexanediol, pentaerythritol, sorbitol and the like. Further, if necessary, fatty acids such as dehydrated castor oil fatty acid, flaxseed oil fatty acid, soybean oil fatty acid, and tall oil fatty acid, monobasic acid such as benzoic acid, and fats and oils can be used as copolymerization components.

The glass transition temperature (Tg) of the hydroxyl group-containing polyester resin (b-1) is −70 to 0 from the viewpoint of improving the drying property and the penetration property, adhesion and finish property of the cross-linked component from the top clear coat described later. The temperature is in the range of −65 to −10 ° C.

The weight average molecular weight of the hydroxyl group-containing polyester resin (b-1) is 1,000 to 30,000, preferably 3,000 to 25,000, from the viewpoint of improving the physical properties of the coating film and the solid content at the time of coating and finishing. It is within the range.

The hydroxyl value of the hydroxyl group-containing polyester resin (b-1) can be appropriately set within the range of 20 to 200 mgKOH / g, preferably 30 to 170 mgKOH / g, from the viewpoint of curability and finish of the coating film.

When the hydroxyl group-containing polyester resin (b-1) is contained in the hydroxyl group-containing resin (b) to be blended, the content of the hydroxyl group-containing polyester resin (b-1) is such that the hydroxyl group-containing polyester resin (b-1) is compatible with both surface dryness and finish. -1) / Other hydroxyl group-containing resin = 5/95 to 95/5, preferably 15/85 to 60/40, which can be appropriately set.

(B-2) Hydroxide-containing Acrylic Resin The hydroxyl group-containing acrylic resin (b-2) is, for example, a hydroxyl group-containing polymerizable unsaturated monomer and another polymerizable unsaturated monomer copolymerizable with the hydroxyl group-containing polymerizable unsaturated monomer. Can be produced by copolymerizing.

Examples of the hydroxyl group-containing polymerizable unsaturated monomer include 2-hydroxyethyl (meth) acrylicate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, and 4-hydroxybutyl (meth) acrylate. Monoesterates of (meth) acrylic acid and dihydric alcohols having 2 to 8 carbon atoms; ε-caprolactone modified products of these monoesterates; N-hydroxymethyl (meth) acrylamide; allyl alcohols; Examples thereof include (meth) acrylates having a polyoxyethylene chain as a hydroxyl group, and these can be used alone or in combination of two or more.

Examples of other polymerizable unsaturated monomers copolymerizable with the hydroxyl group-containing polymerizable unsaturated monomer include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, and 2-ethylhexyl (meth) acrylate. Alkyl ester of acrylic acid or methacrylic acid such as lauryl (meth) acrylate, isobornyl (meth) acrylate; (meth) acrylic acid, styrene, vinyl toluene, vinyl acetate, (meth) acrylonitrile, (meth) acrylamide, glycidyl (meth) ) Acrylate, dimethylaminoethyl (meth) acrylate, (meth) acryloyloxyethylammonium chloride, t-butylacrylamide sulfonic acid, Na salt of sulfoethyl methacrylate, K salt and ammonium salt, Na salt of styrene sulfonic acid, K salt and Acrylate salt and the like can be mentioned.

The weight average molecular weight of the hydroxyl group-containing acrylic resin (b-2) is 1,000 to 100,000, preferably 3,000 to 80, from the viewpoint of improving the physical properties of the coating film and the solid content at the time of coating and the finish. It is within the range of 000.

The hydroxyl value of the hydroxyl group-containing acrylic resin (b-2) is in the range of 20 to 200 mgKOH / g, preferably 30 to 170 mgKOH / g, from the viewpoint of curability and finish of the coating film.

The glass transition temperature (Tg) of the hydroxyl group-containing acrylic resin (b-2) is 0 to 90 ° C., preferably 20 from the viewpoint of the physical properties (particularly scratch resistance) of the obtained coating film and the adhesion to the object to be coated. It is in the range of ° C. to 80 ° C.

In the present specification, the weight average molecular weight (Mw) and the number average molecular weight (Mn) are measured by a gel permeation chromatograph (gel permeation chromatograph: GPC) using a standard polystyrene calibration curve. Is.

"HLC-8120GPC" (trade name, manufactured by Tosoh Corporation) is used as the gel permeation chromatograph, and one "TSKgel G4000HXL", two "TSKgel G3000HXL", and one "TSKgel G2000HXL" are used as columns. A total of 4 books (trade names, all manufactured by Tosoh Corporation) are used, a differential refractometer is used as a detector, mobile phase: tetrahydrofuran, measurement temperature: 40 ° C., flow velocity: 1 mL / min. Can be measured with.

The "glass transition temperature" is a static glass transition temperature. For example, a differential scanning calorimeter "DSC-50Q type" (manufactured by Shimadzu Corporation, trade name) is used to take a sample in a measuring cup and vacuum suction. After completely removing the solvent, the calorific value change was measured in the range of -100 ° C to + 100 ° C at a heating rate of 3 ° C / min, and the first baseline change point on the low temperature side was the static glass transition temperature. And said.

When the hydroxyl group-containing acrylic resin (b-2) is contained in the hydroxyl group-containing resin (b) to be blended, the content of the hydroxyl group-containing acrylic resin (b-2) is such that the hydroxyl group-containing acrylic resin (b) is compatible with both surface dryness and finish. -2) / Other hydroxyl group-containing resin = 5/95 to 95/5, preferably 15/85 to 60/40, which can be appropriately set.

The content of the hydroxyl group-containing resin (b) is 25 to 95 parts by mass with respect to 100 parts by mass of the total solid content of the component (a) and the component (b) described later, and is in the range of 30 to 85 parts by mass. Is preferable, and the range of 40 to 80 parts by mass is more preferable.

(C) Pigments Examples of the pigment (c) used in the base coating composition applied to this method include bright pigments, coloring pigments, extender pigments and the like known in the coating field. The pigment can be used alone or in combination of two or more.

Typical examples of the bright pigment include metal flake powder such as aluminum, paste, pearl powder, graphite, bright pigment such as MIO, and the like. Examples of the metal flake powder include aluminum flakes, nickel flakes, copper flakes, stainless steel flakes, brass flakes and chrome flakes, and examples of the pearl powder include pearl mica and colored pearl mica.

Color pigments include, for example, titanium oxide, zinc flower, carbon black, graphite, iron oxide, molybdenum red, Prussian blue, cobalt blue, azo pigments, phthalocyanine pigments, quinacridone pigments, isoindolin pigments, slene pigments, etc. Examples thereof include perylene-based pigments, dioxazine-based pigments, and diketopyrrolopyrrole-based pigments.

Examples of the extender pigment include clay, kaolin, barium sulfate, barium carbonate, calcium carbonate, talc, silica, alumina white and the like.

These pigment components may be added directly to the coating composition, or may be mixed with a dispersant or a dispersion resin to disperse the pigment components to form a paste, and then blended into the coating material. Known dispersants, dispersion resins, and dispersion methods can be used.

The solid content of the pigment (c) can be appropriately adjusted according to the type of pigment. For example, with respect to 100 parts by mass of the total solid content of the cellulose derivative (a) and the hydroxyl group-containing resin (b). , 1 to 250 parts by mass is preferable, and a range of 15 to 200 parts by mass is more preferable.

When the pigment (c) contains a coloring pigment, it can be a color-based coating composition.

In the present invention, the color-based coating composition can be applied to adjust the brightness and hue of the object to be coated to form a color-based coating film.

In this method, by using a color-based coating film, the difference in color tone and texture is reduced even if the film thickness changes when the topcoat coating composition described later is applied, or it is conspicuous when the coating film surface is damaged. It may be difficult, which is preferable.

The color-based coating composition in this method can be blended with a white pigment as a coloring pigment. Examples of the white pigment include titanium oxide, and the titanium oxide pigment is widely used as a white pigment because of its high refractive index. There are rutile type and anatase type depending on the crystal form, and any of them may be used in the present invention, but the rutile type can be used from the viewpoint of weather resistance. Further, for the purpose of improving dispersibility and weather resistance, those whose surface is treated with an inorganic compound such as silica, zirconium or aluminum may be used. From the viewpoint of the hiding power of the coating film, it is preferable to use one having an average particle size in the range of 100 to 400 nm, and more preferably one in the range of 200 to 300 nm. This average particle system is an average particle diameter measured by observation with an electron microscope.

From the viewpoint of the hiding property of the coating film and the balance between the finish property and the drying property, the content of the white pigment is further 70 to 70 to 100 parts by mass with respect to 100 parts by mass of the total solid content of the cellulose derivative (a) and the hydroxyl group-containing resin (b). It is preferably in the range of 200 parts by mass, preferably 100 to 195 parts by mass, particularly 135 to 185 parts by mass.

In the present invention, when a coloring pigment other than the titanium oxide pigment is blended in the color-based coating composition, the content thereof is 100 parts by mass of the hydroxyl group-containing resin solid content contained in the coating composition from the viewpoint of the brightness of the multi-layer coating film. It is preferably in the range of 0.01 to 30 parts by mass, and more preferably in the range of 0.05 to 25 parts by mass.

The solid content of the base coating composition can be appropriately adjusted within the range of 3 to 70% by mass, particularly 4 to 60% by mass, from the viewpoint of spray coating suitability and finishability.

In particular, when the base coating composition contains a bright pigment and / or a white pigment, the solid content at the time of coating is 3 to 30% by mass and 4 to 20% by mass of the organic solvent. By diluting with and coating with, the design of the formed coating film (particularly the residue) may be improved, which is preferable. The organic solvent used for dilution is not particularly limited, and an organic solvent for ordinary paints can be used.

Here, in the present specification, the solid content content of the coating composition means that about 2.0 g of a sample is collected in an aluminum foil cup having a diameter of about 5 cm, and the residue (g) after heating at 105 ° C. for 3 hours is measured. It is a value calculated by.

When the base coating composition applied to this method contains a titanium oxide pigment as the pigment (c), if the pigment concentration is relatively high and the solid content content at the time of coating is low, the coating film hiding property is excellent. Moreover, it is particularly preferable because it has a good balance between finish and dryness.
Other Ingredients The base coating composition applied to the present invention may further contain organic polymer fine particles, an ultraviolet absorber, a light stabilizer, an antioxidant, a surface conditioner, a pigment dispersant, a curing catalyst and the like, if necessary. Additives for paints and film-forming resins other than the above-mentioned components (a) and (b) can be blended.

Examples of the film-forming resin other than the component (b) include a cross-linking agent such as a polyisocyanate compound, but the cross-linking agent may not be contained from the viewpoint of drying property and finish property. As a result, a one-component coating composition can be obtained.

Further, it is preferable that the base coating composition contains a copolymer containing a phosphoric acid group because it may promote the penetration of the cross-linking agent component from the top clear coating composition described later. When a copolymer containing a phosphoric acid group is contained, 0.2 to 10 parts by mass is preferable with respect to 100 parts by mass in total of the total film-forming resin in the coating composition. Here, the total film-forming resin in the coating composition is a copolymer containing the cellulose derivative (a), the hydroxyl group-containing resin (b), and a cross-linking agent and a phosphoric acid group when the cross-linking agent is contained. Is.

Coating method As a coating method when coating the base coating composition, for example, it can be coated by a known means such as spray coating, roller coating, brush coating, and sink coating. The number of coatings is not particularly limited, and the coating may be repeated once or a plurality of times.

When the base coating composition is applied a plurality of times, the base coating composition may be applied again with an undried coating film, but specifically, it is preferable to apply the base coating composition in a state of being dry to the touch or higher. In the present specification, the dry state to the touch refers to the dry state defined in JIS K 5600-1-1, and is such that the paint does not adhere to the finger by lightly touching it with a finger.

The solid content of the coating film obtained at this time is preferably 50% by mass or more, 70% by mass or more, and particularly preferably 80% by mass or more. The solid content of the obtained coating film can be calculated by weighing the mass change before and after drying.

In the present specification, the cured coating film or the dried coating film is a cured and dried state defined in JIS K 5600-1-1, that is, the center of the coated surface is strongly sandwiched between the thumb and the index finger to form the coated surface. The coating film is in a state where no dents due to fingerprints are formed, the movement of the coating film is not felt, and the center of the coated surface is rapidly and repeatedly rubbed with the fingertip to leave no scratches on the coated surface. On the other hand, the undried coating film is a state in which the coating film has not reached the above-mentioned cured-dried state, and also includes a touch-dried state and a semi-cured-dried state defined in JIS K 5600-1-1.

Dry film thickness The dry film thickness of the base coating film varies depending on the condition of the object to be coated and the type of coloring pigment, but is preferably in the range of 5 to 30 μm per color from the viewpoint of the balance between dryness and finish. The range of 8 to 25 μm is more preferable, and the range of 10 to 25 μm is particularly preferable.

After coating the base coating composition, drying is not essential, but for example, it may be left at room temperature, and air blow (air drying) may be performed if necessary. In normal temperature drying, for example, by leaving it in an environment of normal temperature (5 to 45 ° C.), the volatile components in the coating film gradually volatilize to form a film, and a dry coating film can be obtained.

The relative humidity (hereinafter sometimes abbreviated as RH) at the time of painting is preferably 70% or less, particularly 60% or less. The drying time for normal temperature drying varies depending on the drying film thickness, but can be within 24 hours.

When air drying is used in combination, for example, it can be carried out by blowing air heated to room temperature or a temperature of about 25 ° C. to about 80 ° C. for about 30 seconds to 15 minutes on the coated surface of the object to be coated. Further, in a normal temperature environment, a circulator or the like may be installed and ventilation may be performed for 5 to 120 minutes, preferably 10 to 100 minutes.

Depending on the coating environment and the like, there is no particular problem even if it is heat-dried or forced-dried, but room temperature drying is preferable from the viewpoint of shortening the drying process and finishing. As a supposed heating source, sunlight may be used. The painting environment may be indoors or outdoors.

<Step (2) Step of forming the topcoat coating film>
Topcoat paint composition The topcoat paint composition used in this method is formed to impart designability, chipping resistance, etc. to the object to be coated, and is formed on the base coating film formed in the step (1). It can be obtained by partially coating a topcoat coating composition having a color different from that of the base coating film at least once to form a topcoat coating film.

The portion to be painted on the object to be coated is not particularly limited, and may include, for example, a two-tone pattern, a line color pattern of two or more colors, a striped pattern, a pattern having a complicated shape such as character writing. The two-tone or higher of the present method can include, for example, those painted in two or more colors so as to have these patterns. Masking may be used when a part thereof is painted separately.

The masking material is not particularly limited, and conventionally known masking materials can be used. As the masking material, for example, a commercially available tape or the like can be used. By painting with masking tape, a color boundary with the unpainted part is created, and the design is excellent.

The time until masking application applied to this method varies depending on the coating amount of the base coating composition and the like, but from the viewpoint of the balance of finishability, the dry film thickness is within the range of 5 to 30 μm and is relative. When the humidity is 70% or less, it can be done for 24 hours or less, and specifically, the masking tape can be attached in 30 minutes to 120 minutes. In this method, even if masking is performed in an undried state, if the coating film is dry to the touch, the finish is not impaired by tape marks or the like, and the design is very excellent.

The topcoat coating composition used in this method contains a cellulose derivative (a), a hydroxyl group-containing resin (b) and a pigment (c), and the content of the cellulose derivative (a) is the component (a) and It is characterized by containing 5 to 75 parts by mass with respect to a total of 100 parts by mass of the solid content of the component (b).

As the cellulose derivative (a), the hydroxyl group-containing resin (b) and the pigment (c), those listed in the section of the base coating composition can be used. In particular, from the viewpoint of designability, it is preferable that the topcoat coating composition is a colored coating composition containing a coloring pigment as a pigment. The coloring pigment is not particularly limited, and can be appropriately selected from the viewpoint of visibility and design.

As the specific coloring pigment, those listed in the item of the pigment (c) can be used.

The solid content of the pigment component can be appropriately adjusted according to the type of pigment. For example, 10 parts by mass of the total solid content of the cellulose derivative (a) and the hydroxyl group-containing resin (b) is 10 parts by mass. The range of ~ 250 parts by mass is preferable, and the range of 15 to 200 parts by mass is more preferable.

The solid content of the topcoat coating composition is preferably in the range of 3 to 50% by mass and 4 to 45% by mass from the viewpoint of spray coating suitability and finishability.

In particular, when the topcoat coating composition contains a bright pigment and / or a white pigment, it is diluted with an organic solvent until the solid content is 3 to 30% by mass and 4 to 20% by mass. The design of the formed coating film may be improved by coating the film. The organic solvent used for dilution is not particularly limited, and an organic solvent for ordinary paints can be used.

Other Ingredients The topcoat coating composition applied to the present invention may further contain organic polymer fine particles, ultraviolet absorbers, light stabilizers, antioxidants, surface conditioners, pigment dispersants, curing catalysts and the like, if necessary. Additives for paints and film-forming resins other than the above-mentioned components (a) and (b) can be blended.

Examples of the film-forming resin other than the component (b) include a cross-linking agent such as a polyisocyanate compound, but the cross-linking agent may not be contained from the viewpoint of drying property and finish property. As a result, a one-component coating composition can be obtained.

Further, it is preferable that the topcoat coating composition contains a copolymer containing a phosphoric acid group because it may promote the penetration of the cross-linking agent component from the top clear coating composition described later. When a copolymer containing a phosphoric acid group is contained, 0.2 to 10 parts by mass is preferable with respect to 100 parts by mass in total of the total film-forming resin in the coating composition. Here, the total film-forming resin in the topcoat coating composition includes the cellulose derivative (a), the hydroxyl group-containing resin (b), and the copolymer containing the cross-linking agent and the phosphoric acid group when the cross-linking agent is contained. That is.

Coating method As a coating method when coating the topcoat coating composition, for example, it can be coated by a known means such as spray coating, roller coating, brush coating, and sink coating. The number of coatings is not particularly limited, and the coating may be repeated once or a plurality of times. That is, this step (2) may be repeated a plurality of times. At the time of recoating, it may be further applied on the base coating film, the top coating film, or both.

The topcoat coating composition may be overcoated with an undried coating film, and specifically, it is preferably overcoated in a state of being dry to the touch or higher. The dry state to the touch refers to the dry state defined in JIS K 5600-1-1, and is such that the paint does not adhere to the finger by lightly touching it with a finger. The solid content of the obtained coating film at this time is preferably about 50% by mass or more, 70% by mass or more, and particularly preferably about 80% by mass or more. The solid content of the obtained coating film can be calculated by weighing the mass change before and after drying.

Dry film thickness The dry film thickness of the topcoat film varies depending on the condition of the object to be coated and the type of coloring pigment, but is preferably in the range of 5 to 30 μm per color from the viewpoint of the balance between dryness and finish. The range of 8 to 25 μm is more preferable, and the range of 10 to 25 μm is particularly preferable.

After the topcoat coating composition is applied, drying is not essential, but for example, it may be left at room temperature, and air blow (air drying) may be performed if necessary. In normal temperature drying, for example, by leaving it in an environment of normal temperature (5 to 45 ° C.), the volatile components in the coating film gradually volatilize to form a film, and a dry coating film can be obtained.

The relative humidity (hereinafter sometimes abbreviated as RH) at the time of painting is preferably 70% or less, particularly 60% or less. The drying time for normal temperature drying varies depending on the drying film thickness, but can be within 24 hours.

When air drying is used in combination, for example, it can be carried out by blowing air heated to room temperature or a temperature of about 25 ° C. to about 80 ° C. for about 30 seconds to 15 minutes on the coated surface of the object to be coated. Further, in a normal temperature environment, a circulator or the like may be installed and ventilation may be performed for 5 to 120 minutes, preferably 10 to 100 minutes.

Depending on the coating environment and the like, there is no particular problem even if it is heat-dried or forced-dried, but room temperature drying is preferable from the viewpoint of shortening the drying process and finishing. As a supposed heating source, sunlight may be used. The painting environment may be indoors or outdoors.

<Step (3) Step of forming a top clear coating film>
In this method, a coating film is sequentially formed by the steps (1) and (2) described above, and then the top clear coating composition is repeatedly applied to the front surface to form a clear coating film.

Top clear paint composition The top clear paint composition used in the method of the present invention is a top clear used as the top layer (top coat), and is, for example, an acrylic resin or a fluororesin having a crosslinkable functional group such as a hydroxyl group (block). ) A curable paint containing a cross-linking agent such as polyisocyanate or a melamine resin as a main component, or a lacquer paint containing a cellulose acetate butyrate-modified acrylic resin as a main component can be preferably used. By using a top coat in this method, designability, finishability and stain resistance are improved. In particular, when a urethane curable coating composition is used as the top clear coating composition, a part of the isocyanate component permeates from the clear coating film into the top coating film and the base coat coating film, and the cellulose derivative (a) used in the base coat. And, it is suitable because it can react with the hydroxyl group of the hydroxyl group-containing resin (b) to form an adhesive and tough film in the base coat paint or the top coat paint without using a cross-linking agent component.

Further, the top clear paint composition can be blended with paint additives such as polymer fine particles, a curing catalyst, an ultraviolet absorber, an antioxidant, a surface conditioner, and an antifoaming agent, if necessary. The coating film made of the top clear coating composition is suitable in the range of 10 to 100 μm in dry film thickness.

As a coating method of the top clear coating composition, for example, it can be coated by a known means such as spray coating, roller coating, brush coating, and sink coating. The number of coatings is not particularly limited, and the coating may be repeated once or a plurality of times.

The drying method may be either heat drying or room temperature drying, and setting and / or air blowing (air drying) may be performed as necessary. As a drying method, heat drying or forced drying is more preferable because curing can be promoted and the drying time can be shortened.

In the case of heat drying, for example, a coating film can be obtained by drying in an environment of 30 to 80 ° C., preferably 35 to 70 ° C., particularly 40 to 60 ° C. for 5 to 120 minutes, preferably 10 to 100 minutes. can. The heat source may be sunlight.

The contents of the coating method according to the embodiment of the invention will be described with reference to the drawings. In the present embodiment, the contents will be described below by taking as an example the case where the outer surface of the body of a railway or the like is coated with line color.

FIG. 1 is a flowchart for explaining a flow of a coating method according to an embodiment of the invention.

As shown in the figure, this coating method is performed on an object to be coated, which has been subjected to substrate adjustment as necessary.
(S1) A step of applying a base coating composition to form a base coating film,
(S2) A step of partially coating a topcoat coating composition of a different color on the base coating film at least once to form a topcoat coating film.
(S3) Next, the step of applying the top clear paint composition over the entire surface and drying it is included.
If necessary, after forming the base coating film, (S12) a step of masking a part of the base coating film layer with a masking sheet and (S23) a step of removing the masking may be provided.

As for the number of work items, the painting process, the drying process, the masking work (pasting), the masking work (removal), the drying process (drying), and the drying process (cooling after heating and drying) are counted as one work item. In the case of 1, the number of work items is 9 excluding the substrate adjustment.

As described above, it is possible to obtain a coated material having a coating film coated in two tones or more by this method. The obtained coating film is a multi-layer coating film, and the total dry film thickness varies depending on the number of coating colors. The maximum total film thickness of the dry film thickness in the above case can be in the range of 15 to 160 μm, preferably in the range of 28 to 150 μm. In the multi-layer coating film obtained by this method, the base coating film and the top coating film are applied at least once or multiple times to form a clear coating film at the end, but the base coating film and the top coating film are partially formed with at least three layers and multiple colors. It becomes a multi-layer coating film that is painted separately.

Hereinafter, the present invention will be further described with reference to examples. Here, "part" and "%" mean "parts by mass" and "% by mass", respectively.

(Production Example 1) Paint composition No. B-1
Cellulose derivative No. 1 (Note 1) 45 parts, 50% hydroxyl group-containing acrylic resin (A-1) (Note 3) 50 parts (solid content 25 parts by mass), 70% hydroxyl group-containing polyester resin (E-1) (Note 4) 42 .9 parts (30 parts by mass of solid content), 167 parts of typake CR-93 (Note 5) as pigment P-1, and a mixed solvent consisting of xylene / butyl acetate = 50/50 were added, and the mixture was stirred with a disper for about 20 minutes. Base paint composition No. B-1 (white) was manufactured. At the time of coating, the same mixed solvent was used as a diluting solvent, and the solid content was adjusted to 15% by mass, and the drying property and the adhesiveness after drying of the obtained coating composition were evaluated and shown in Table 1.

(Production Examples 2 to 6 and Production Examples 7 to 11)
In Production Example 1, the base coating composition No. 1 was prepared in the same manner as in Production Example 1 except that the composition of each component was the composition shown in Table 1. B-2 to B-6 and topcoat coating composition No. T-1 to T-5 were manufactured. Each of the obtained coating compositions was diluted and adjusted so as to have the solid content at the time of coating shown in Table 1, and the drying property and the adhesiveness after drying were evaluated and shown in Table 1. The compounding composition in Table 1 is a solid content display.

The notes in the table are shown below.

(Note 1) Cellulose derivative No. 1: "CAB-381-0.5", trade name, manufactured by Eastman Chemical Company, cellulose acetate butyrate, number average molecular weight 30,000,
(Note 2) Cellulose derivative No. 2: Solid content 30% by mass, cellulose-modified copolymer (Production method of cellulose derivative No. 2: Production example: A reactor equipped with a thermometer, a stirrer, a reflux condenser and a dropping funnel is charged with the following components, and nitrogen gas is charged. It was heated in an atmosphere and heated to 110 ° C. over about 4 hours.
Butyl acetate 600 parts,
"CAB-381-0.5" (Note 1) 200 copies,
After the temperature was raised, it was confirmed that "CAB-381-0.5" (Note 1) was completely dissolved, then heating was stopped, and 133 parts of butyl acetate was distilled off under reduced pressure. The temperature inside the reactor was 87 ° C. While maintaining this temperature, 11.1 parts of a 90% butyl acetate solution of an isophorone diisocyanate and 2-hydroxyethyl acrylate equimolar addition reaction, 0.02 parts of pt-butyl catechol as a polymerization inhibitor, and urethane. 0.02 part of dibutyltin dilaurate as a conversion catalyst was put into a reactor and aged at 87 ° C. for 7 hours in dry air to obtain an unsaturated group-containing cellulose acetate butyrate solution. Next, the reaction temperature was raised to 115 ° C., and a mixed solution of the following polymerizable unsaturated monomer and polymerization initiator was added dropwise over 2 hours under a nitrogen atmosphere. Butyl acetate 130 parts Methyl methacrylate 58.2 parts t-butyl peroxy-2-ethylhexanoate 2 parts After completion of dropping, 0.5 part of t-butyl peroxy-2-ethylhexanoate and 20 parts of butyl acetate The mixed solution of (1) was added dropwise over 1 hour, and the mixture was aged at 115 ° C. for 1 hour in a nitrogen atmosphere. A cellulose-modified copolymer solution having a solid content of 30% was obtained.

(Note 3) Hydroxide-containing acrylic resin (A-1): solid content 50% by mass, hydroxyl value 92 mgKOH / g, acid value less than 1 mgKOH / g, glass transition temperature 42 ° C., weight average molecular weight 50,000.

(Note 4) Hydroxide-containing polyester resin (E-1): solid content 70% by mass, hydroxyl value 55 mgKOH / g, weight average molecular weight 20,000, glass transition temperature -60 ° C, DBR (dibasic acid ratio) 0.95.

(Note 5) Pigment P-1: Typake CR-93, trade name, manufactured by Ishihara Sangyo Co., Ltd., white pigment, titanium white, average particle size 280 nm,
(Note 6) Pigment P-2: Aluminum paste CR-9800RM, trade name, manufactured by Asahi Kasei Metals Co., Ltd., metallic pigment, aluminum paste, average particle size 7 μm, specific gravity 1.1, solvent Mineral spirit and solvent naphtha mixed solvent, solid Content content 42%,
(Note 7) Pigment P-3: Black pigment, carbon black, average particle size 0.01 μm
(Note 8) Pigment P-4: Red pigment, perylene red pigment,
(Note 9) Pigment P-5: Blue pigment, phthalocyanine pigment.

(Note 10) Polyisocyanate compound: Sumijoule N3300, trade name, manufactured by Sumika Corobestrourethane, isocyanurate of hexamethylene diisocyanate, solid content 100%.

Test item 1: Drying property A commercially available tin plate of 300 × 150 × 2.0 mm was coated with a commercially available lacquer primer surfacer (40 μm), dried at room temperature for 30 minutes, and then polished with # 400 water-resistant abrasive paper. Each of the coating compositions of Production Examples 1 to 11 was coated on the coated plate so as to have a dry film thickness of 20 ± 5 μm, and left at room temperature (23 ± 5 ° C., humidity 50 ± 10% RH) for 10 minutes. Then, a masking tape was attached to the surface of the coating film, left at room temperature for 1 hour, then the tape was peeled off, and the surface of the coating film was visually observed. After that, clear coating is applied by spraying so that the drying film thickness is 15 ± 5 μm, and it is heated and dried for 30 minutes in a drying oven set at 50 ° C (so that the maximum temperature at which the material reaches 45 ° C), assuming a large drying oven. I let you. The remaining tape marks on the test coating film were visually evaluated. The evaluation criteria are as follows.
⊚: Almost no tape marks can be seen when the tape is peeled off and after the clear coating film is formed.
◯: Tape marks remain when the tape is peeled off, but no tape marks are seen after the clear coating film is formed.
Δ: Tape marks remain on all the pasted parts, but the tape marks become slightly inconspicuous after the clear coating film is formed.
X: The tape marks of all the pasted parts remain strongly.

Test item 2: Adhesiveness (after dryness test)
The coating film on the test plate after the drying property test is cross-cut so as to reach the object to be coated, and the adhesive cellophane is applied to the coated surface. It was between the objects to be coated.
◯: No peeling,
Δ: Slight peeling,
X: There is remarkable peeling.

(Example 1)
A commercially available tin plate having a size of 300 × 150 × 2.0 mm was coated with a commercially available lacquer primer surfacer (40 μm) as a base adjustment, dried at room temperature for 30 minutes, and then polished with # 400 water-resistant abrasive paper. The base coating composition shown in Table 2 was spray-coated on the coated plate so as to have a dry film thickness of 15 μm, and left to stand for 30 minutes under the conditions of room temperature (air temperature 23 ° C., humidity 50% RH). Then, masking is performed with masking tape so as to form a line pattern, and the unmasked portion is spray-coated with the topcoat coating composition shown in Table 2 so as to have a dry film thickness of 15 μm, and the room temperature (temperature 23 ° C., humidity 50). It was left for 30 minutes under the condition of% RH). After leaving, the masking was removed, and the top clear paint composition No. As No. 1, "Retan PG2K Clear" (manufactured by Kansai Paint Co., Ltd., urethane curable coating composition) was spray-coated so as to have a dry film thickness of 15 μm. After that, the coated plate was placed in a drying oven at 50 ° C. (material reaching temperature 45 ° C.) assuming a large drying oven for 30 minutes and dried by heating to obtain a test plate.

FIG. 1 shows a schematic diagram of the work procedure of this embodiment. Table 2 shows the maximum total dry film thickness of the test plate, the total number of steps, the number of coating colors, and the time from coating to completion. The time required for cooling after heating and drying was set to 2 hours. In this case, the number of work items is 9.

(Example 2)
A commercially available tin plate having a size of 300 × 150 × 2.0 mm was coated with a commercially available lacquer primer surfacer (40 μm) as a base adjustment, dried at room temperature for 30 minutes, and then polished with # 400 water-resistant abrasive paper. The base coating composition (B-2) shown in Table 2 was spray-coated on the coated plate so as to have a dry film thickness of 15 μm on the entire surface, and under the conditions of room temperature (air temperature 23 ° C., humidity 50% RH), 30 I left it for a minute. After that, masking was performed with masking tape so as to form a line pattern, and the unmasked portion was spray-coated as the topcoat coating composition 1 shown in Table 2 (T-1: gray) so as to have a dry film thickness of 15 μm. , Room temperature (air temperature 23 ° C., humidity 50% RH), left for 30 minutes. After that, further masking is performed with masking tape so as to form another line pattern on the topcoat coating film 1, and the unmasked portion is partially further on the base coating film and the topcoat coating film 1. As the topcoat coating composition 2, (T-3: blue) was spray-coated so as to have a dry film thickness of 15 μm, and left for 15 minutes under the conditions of room temperature (temperature 23 ° C., humidity 50% RH). After leaving, the masking was removed, and the clear paint composition No. As No. 1, "Retan PG2K Clear" (manufactured by Kansai Paint Co., Ltd., urethane curable coating composition) was spray-coated so as to have a dry film thickness of 15 μm. After that, the coated plate was placed in a drying oven at 50 ° C. (material reaching temperature 45 ° C.) assuming a large drying oven for 30 minutes and dried by heating to obtain a test plate.

FIG. 2 shows a schematic diagram of the work procedure of this embodiment. Table 2 shows the maximum total dry film thickness of the test plate, the total number of steps, the number of coating colors, and the time from coating to completion. The time required for cooling after heating and drying was set to 2 hours. In this case, the number of work items is 12.

(Example 3)
A commercially available tin plate having a size of 300 × 150 × 2.0 mm was coated with a commercially available lacquer primer surfacer (40 μm) as a base adjustment, dried at room temperature for 30 minutes, and then polished with # 400 water-resistant abrasive paper. The base coating composition (B-1) shown in Table 2 was spray-coated on the coated plate so as to have a dry film thickness of 15 μm on the entire surface, and under the conditions of room temperature (air temperature 23 ° C., humidity 50% RH), 30 I left it for a minute. Then, masking is performed with masking tape, and the unmasked portion is spray-coated as the topcoat coating composition 1 shown in Table 2 (T-1: gray) so as to have a dry film thickness of 15 μm, and the room temperature (air temperature 23). It was left for 30 minutes under the conditions of ° C. and humidity 50% RH). Then, further masking is performed with masking tape, and the unmasked portion is partially over the base coating film and the topcoat coating film 1, and (T-2: red) is further applied as a topcoat coating composition 2 as a dry film. It was spray-coated to a thickness of 15 μm and left for 15 minutes under the conditions of room temperature (air temperature 23 ° C., humidity 50% RH). After that, masking is further performed with masking tape, and the unmasked portion is further partially coated on the multi-layer coating film in which the base coating film, the top coating film 1 and the top coating film 2 are laminated in this order. As the composition 3, (T-3: blue) was spray-coated so as to have a dry film thickness of 15 μm, and left to stand for 15 minutes under the conditions of room temperature (temperature 23 ° C., humidity 50% RH). After that, the masking was removed, and the clear paint composition No. As No. 1, "Retan PG2K Clear" (manufactured by Kansai Paint Co., Ltd., urethane curable coating composition) was spray-coated so as to have a dry film thickness of 15 μm. After that, the coated plate was placed in a drying oven at 50 ° C. (material reaching temperature 45 ° C.) assuming a large drying oven for 30 minutes and dried by heating to obtain a test plate.

FIG. 3 shows a schematic diagram of the work procedure of this embodiment. Table 2 shows the maximum total dry film thickness of the test plate, the total number of steps, the number of coating colors, and the time from coating to completion. The time required for cooling after heating and drying was set to 2 hours. In this case, the number of work items is 15.

(Examples 4 to 5, Comparative Examples 1 to 3)
In Example 1, a test plate was prepared in the same manner as in Example 1 except that the base coating composition, the top coating composition, the coating film thickness, the drying temperature and the time were as shown in Table 2. The work procedures of Examples 4 to 5, Comparative Examples 1 to 3 and Comparative Examples 5 to 6 are the same as those shown in FIG. The number of work items in this case is nine.

(Comparative Example 4)
A commercially available tin plate having a size of 300 × 150 × 2.0 mm was coated with a commercially available lacquer primer surfacer (40 μm) as a base adjustment, dried at room temperature for 30 minutes, and then polished with # 400 water-resistant abrasive paper. The base coating composition (B-5) shown in Table 2 is spray-coated on the coated plate so that the drying film thickness is 15 μm on the entire surface, and the temperature is 50 ° C. (material reaching temperature 45 ° C.) assuming a large drying furnace. It was placed in a drying oven for 60 minutes and dried by heating. Then, when it was cooled to room temperature, the coated plate was masked with masking tape, and the unmasked portion was used as the topcoat coating composition 1 shown in Table 2 (T-1: gray) to a dry film thickness of 15 μm. It was spray-painted so as to be so that it was placed in a drying oven at 50 ° C. (material reaching temperature 45 ° C.) assuming a large drying oven for 60 minutes and dried by heating. Then, when it was cooled to room temperature, the coated plate was further masked with masking tape, and the unmasked portion was partially applied to the base coating film and the topcoat coating film 1 as the topcoat coating composition 2. (T-3: blue) was spray-coated so as to have a drying film thickness of 15 μm, and placed in a drying oven at 50 ° C. (material reaching temperature 45 ° C.) assuming a large drying oven for 60 minutes to be heated and dried. When it was cooled to room temperature, the masking was removed, and the clear paint composition No. As No. 1, "Retan PG2K Clear" (manufactured by Kansai Paint Co., Ltd., urethane curable coating composition) was spray-coated so as to have a dry film thickness of 15 μm. After that, the coated plate was placed in a drying oven at 50 ° C. (material reaching temperature 45 ° C.) for 30 minutes, assuming a large drying oven, and dried by heating to obtain a test plate.

FIG. 4 shows a schematic diagram of the work procedure of this embodiment. Table 2 shows the maximum total dry film thickness of the test plate, the total number of steps, the number of coating colors, and the time from coating to completion. The time required for cooling after drying was set to 2 hours. In this case, the number of work items is 15.

(Comparative Examples 5 and 6)
In Example 1, a test plate was prepared in the same manner as in Example 1 except that the base coating composition, the top coating composition, the coating film thickness, the drying temperature and the time were as shown in Table 2. The work procedure of Comparative Examples 5 and 6 is the same as that shown in FIG. The number of work items in this case is nine.

(Comparative Example 7)
In Example 1, the test plate is the same as in Example 1 except that the base coating composition, the top coating composition, the coating film thickness, the drying temperature and the time are as shown in Table 2 and the working procedure is as shown in FIG. Was produced. As shown in FIG. 5 of the work procedure, the clear paint composition No. 1 is painted. FIG. 5 shows a schematic diagram of the work procedure. The number of work items in this case is 21. Maximum total dry film thickness of test plate, total number of processes (painting, masking application work, masking removal work, drying and drying (cooling) are counted as one work item), number of paint colors and from painting to completion The time is shown in Table 2.

Test item 3. Coating film appearance:
The appearance of the coating film (gloss, solder, design) of each test plate was visually observed and evaluated according to the following criteria.

Appearance of coating film (gloss)
◯: Good (uniform glossiness is observed)
Δ: Slightly defective (very slight uneven gloss is observed)
× Defective (uneven luster is observed).

Appearance of coating film (Hada):
The appearance of the coating film (retaining) of each test plate was visually evaluated according to the following criteria.
◯: Good (uniform and smooth)
△: Slightly defective (slightly yuzu skin is observed)
× Poor (prominent citron skin is observed).

Appearance of coating film (design)
The color boundary portion of each test plate was visually observed and evaluated according to the following criteria.
◯: Good (color boundaries are clear),
Δ: Slightly defective (color boundaries are slightly blurred)
X: Defective (color boundaries are not significantly clear).

Test item 4: Contamination resistance: Carbon adhesion test
A 10% by mass aqueous dispersion of a carbon pigment (FW-200, trade name, manufactured by Orion Engineer Carbons Co., Ltd.) was used as model contaminated water on the surface of the coating film of each test plate, and 2 g of the contaminated water was spot-dropped to 80. After baking at ° C. for 30 minutes and then lightly washing with water with a sponge, residual carbon was confirmed on the flat portion and the color boundary portion on each test plate.
◯: There is almost no difference in the residual rate of carbon between the flat part and the color boundary part, which is good.
X: Carbon remains at the color boundary and is defective.

S0: Object to be coated with base adjustment S1: Step of forming base coating film S2: Step of forming topcoat coating film on base coating film S3: Top clear coating composition is applied and dried to form a clear coating film. Step S1': Step of forming a base coating film for comparison S2': Step of forming a top coat coating film on the base coating film for comparison S3': A clear coating composition that is not the top is applied, dried and cleared. Film forming step S11: Painting step in S1 step S12: Drying step in S1 step S13: Masking work after forming the coating film in S1 S21: Painting step in S2 step S22: Drying step in S2 step S23: Masking work after forming the coating film of S2 S31: Painting step in the S3 process S32: Drying step in the S3 process S33: Cooling step in the S3 process S2 (1): Forming the first (first color) topcoat coating film Step S2 (2): Step of forming the second (second color) topcoat coating S2 (3): Step of forming the third (third color) topcoat S2 (1) 1: 1st (1) Painting step in S2 step of (color) S2 (1) 2: Drying step in S2 step of the first (first color) S2 (1) Masking work after forming the coating film of S2 in the first (first color) S2 (2) 1: Painting process during the second (second color) S2 process S2 (2) 2: Drying process during the second (second color) S2 process S2 (2) 3: Second (second color) Masking work after forming the coating film of S2 S2 (3) 1: Painting step during the third (third color) S2 step S2 (3) 2: Drying step S2 during the third (third color) S2 step ( 3) 3: Masking work after the third (third color) S2 coating film formation

Claims (6)

On a large area to be coated
(1) A process of applying a base coating composition to form a base coating film,
(2) A step of partially coating a topcoat coating composition of a different color on the base coating film at least once to form a topcoat coating film.
(3) Next, it is a multicolor finish coating method including a step of applying a top clear coating composition on the entire surface and drying it to form a clear coating film.
Both the base coating composition and the top coating composition contain a cellulose derivative (a), a hydroxyl group-containing resin (b) and a pigment (c), and the cellulose derivative (a) is a cellulose acetate butyrate. or a modified copolymer of cellulose acetate butyrate, content of that is in the range of from 5 to 75 parts by weight per 100 parts by weight of the solid content of the components (a) and (b) A multicolor finish painting method characterized by this. The multicolor finish coating method according to claim 1, wherein the top clear coating composition is a urethane curable coating composition. The multicolor finish coating method according to claim 1 or 2, wherein the base coating composition and the top coating composition are one-component coating compositions that do not contain a cross-linking agent. In the step (1), the base coating composition is coated so that the dry film thickness of the base coating film is 5 to 30 μm, and in the step (2), the dry film thickness of the top coat film is 5 to 30 μm. The multicolor finish coating method according to any one of claims 1 to 3, wherein the topcoat coating composition is coated so as to be. The multicolor finish coating method according to any one of claims 1 to 4, wherein the object to be coated is a railroad vehicle. A method for producing a coating material having a coating film coated in two tones or more in multiple colors by using the multicolor finish coating method according to any one of claims 1 to 5.

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