JP6467220B2 - Painting method - Google Patents

Description

  The present invention relates to a coating method, and more particularly, to a method for coating a member constituting an automobile body.

  As a method of coating members such as panels made of metal or resin that make up an automobile body, it is widely known to first apply an undercoat by electrodeposition (only for metal parts), then apply an intermediate coat and then overcoat the finish. ing. Also, in the top coating process, it is widespread that a base paint is first applied with a colored paint and then a clear paint is applied with a clear paint. In such a coating method, in recent years, from the viewpoint of reducing the environmental load, as a coating for intermediate coating and overcoating, a conventionally used organic solvent-based coating is shifted to a water-based coating (water-based coating). That is going on. In such intermediate coating and overcoating with a water-based coating, for example, in each coating process, since the coating is applied in a wet state (wet-on-wet), it is applied between the intermediate coating layer and the base layer, or In order to prevent mixed layers between the base layer and the clear layer, and to prevent bumping of residual moisture in the baking process, between the intermediate coating process and the base coating process, and between the base coating process and the clear coating process. Have been proposed to preheat each of them (for example, see Patent Document 1).

JP 2006-61799 A

  In the case of manufacturing an automobile body using sheet metal, painting is performed integrally. However, with the adoption of resin parts, the same paint is often applied in a separate coating process for each part. At this time, a phenomenon that a difference in color tone between parts after baking occurred. Therefore, the inventors have intensively studied and found that the difference in color tone is that when a clear layer is applied on the base layer, a mixed layer occurs between the base layer and the clear layer, and the pigment in the base layer It turned out that the movement of the distribution was caused and the movement of this pigment was different depending on the parts to be painted. Then, it was found that how the pigment moves depends on the solid content rate (NV) of the base layer when the clear layer is applied. For example, when using a water-based base paint, there is generally a preheating process after spraying the base paint. However, depending on the part size, plate thickness, mounting position, preheating equipment specifications, the solid content of the base layer after preheating depends on the part. (E.g., between body and resin parts). If it does so, a difference will arise in the color tone after baking because of the difference in pigment distribution by the mixed layer which arises in the case of clear layer application.

  The difference in color tone after baking is, for example, that the same surface is small and the horizontal dividing line is inconspicuous between a general bumper and a fender, but the same surface is large in a resin outer plate that is widened for weight reduction, and Between panels (members) are vertical secant lines, so they are easily noticeable, and the appearance is likely to be markedly poor.

  The present invention solves the above-mentioned problems, and provides a coating method that can easily and inexpensively match the coating color after the baking process when a steel plate member and a resin member are included as constituent members. The purpose is to provide.

In order to achieve the above object, a coating method of the present invention is a method of coating a member constituting an automobile body including a steel plate member and a resin member,
The steel plate member and the resin member are L ^* a ^* b ^* tables calculated from reflectance measured at a reflection angle of 45 degrees using a spectrocolorimeter after the same paint is applied in a separate coating process. On each member on which a primer coating film having an L ^* value in the range of 70 to 80 in the color system is formed, the proportion of yellow pigment in all pigments is 50 mass% or more, and the proportion of white pigment is 30 mass%. A base coating step of applying the above-described yellow water-based solid base paint to form a base paint film having a b ^* value in the range of 60 to 70 in the L ^* a ^* b ^* color system, and the base paint film The yellow water-based solid used in the base coating process is further provided with a clear coating process in which each of the formed members is preheated and then painted with a clear paint, and a baking process in which each of the clear-coated members is baked. base Fee includes a viscosity modifier and a hydrophilic solvent, wherein the viscosity modifier is a viscosity modifier selected from alkali swelling type viscosity modifiers and associative thickener type viscosity modifier, wherein the hydrophilic solvent is ethylene glycol monomethyl ether, ethylene glycol a solvent selected from mono -tert- butyl ether and ethylene glycol monobutyl ether, by adjusting at least one of content and content of the hydrophilic solvent of the viscosity modifier, between each member after the baking step It includes a toning step for toning so that the paint colors match.

In the present ^{invention, L * a * b * L} * and ^{b *} values in the color system, using a spectrocolorimeter "CM512m3" (manufactured by Konica Minolta Holdings, Inc., trade name), a light receiving angle of 45 degrees ( This is a value calculated from the spectral reflectance measured at a reflection angle of 45 degrees with respect to the vertical direction with respect to the coated surface as 0 degrees.

  ADVANTAGE OF THE INVENTION According to this invention, the coating method which can match the coating color after the baking process in the case of including a steel plate member and a resin member as a structural member at low cost and easily can be provided.

FIG. 1 is a schematic process diagram showing a coating line in an embodiment of the coating method of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited or limited to the following examples.

  FIG. 1 is a schematic process diagram showing a coating line of an aqueous coating process which is an embodiment of the coating method of the present invention. The aqueous coating process includes a primer coating process, a base coating process, a clear coating process, and a baking process. And it has a preheating (preheating, PH) process after the primer application process and the base coating process. In FIG. 1, the coating line 10 includes a primer coating booth 11, a base coating booth 13, a clear coating booth 15, and a baking furnace 16. A first preheating booth 12 is provided between the primer coating booth 11 and the base coating booth 13, and a second preheating booth 14 is provided between the base coating booth 13 and the clear coating booth 15.

  When a member made of a metal steel plate is coated by the present aqueous coating process, a member on which an undercoat layer has been formed by electrodeposition coating (undercoating) by a known method is put into the coating line 10. Further, when the resin member is to be coated by the present aqueous coating process, it is directly put into the coating line 10. In this water-based coating process, first, the charged members are applied with a primer in the primer application booth 11 (primer application process).

In the present invention, the aqueous primer used for primer application is, for example, an aqueous primer containing a water-soluble or water-dispersible resin component (hydrophilic resin component) and a curing agent. The L ^* value in the L ^* a ^* b ^* color system calculated from the reflectance measured at a reflection angle of 45 degrees is used in the range of 70-80.

  The hydrophilic resin component includes a hydrophilic group (for example, a carboxyl group, a hydroxyl group, a methylol group, an amino group, a sulfonic acid group, a polyoxyethylene bond) and a functional group that reacts with a curing agent (for example, a hydroxyl group). For example, a known aqueous resin such as an acrylic resin, a polyester resin, an alkyd resin, an epoxy resin, or a polyurethane resin is used. Such resin components may be used alone or in combination. Of these resin components, an acrylic resin or polyester resin having a carboxyl group is preferably used. Depending on the type of hydrophilic group, such a resin component may be neutralized with a basic compound or acid to be water-solubilized or water-dispersed, or it may be water-solubilized as it is when it is polyoxyethylene-bonded. Or disperse in water.

  The curing agent is not particularly limited, and for example, melamine resin, block polyisocyanate and the like are used. More specifically, examples of the melamine resin include hydrophilic melamine, and more specific examples of the block polyisocyanate include an isocyanate group of the polyisocyanate such as oxime, phenol, alcohol, lactam, and mercaptan. Those blocked with a blocking agent such as Such curing agents may be used alone or in combination. The blending ratio of the curing agent is usually 60 parts by weight or less, preferably 20 to 50 parts by weight with respect to 100 parts by weight of the resin component.

  The aqueous primer preferably contains a blocking agent dissociation catalyst or an acid catalyst in order to promote the crosslinking reaction. The dissociation catalyst for the blocking agent is not particularly limited. For example, tin octylate, dibutyltin di (2-ethylhexanoate), dioctyltin di (2-ethylhexanote), dioctyltin diacetate, dibutyltin dilaurate , Organic metal compounds such as dibutyltin oxide, monobutyltin trioctate, lead 2-ethylhexanoate and zinc octylate are used. As the acid catalyst, for example, phosphoric acid-based or sulfonic acid-based acid catalysts are used. The mixing ratio of the catalyst is usually 0.005 to 5 parts by weight, preferably 0.01 to 3 parts by weight with respect to 100 parts by weight of the resin component.

The water-based primer is L ^* a ^* b ^* defined in JIS Z8781-4 (2013) calculated from the reflectance measured with a spectrophotometer at a reflection angle of 45 degrees for the primer coating ^. The L ^* value as the lightness in the color system must be in the range of 70-80. Due to the low hiding power of the base coat, it becomes difficult to obtain the desired color tone regardless of whether the L ^* value is out of the high side or the low side. In order to make the L ^* value of the coating film satisfy this condition, the water-based primer may contain, for example, a color pigment, an extender pigment, a dispersant, an anti-settling agent, an organic solvent, in addition to the above components. , Well-known additives such as reaction accelerators (eg, organic tin compounds), antifoaming agents, thickeners, rust inhibitors, ultraviolet absorbers, surface conditioners, and the like are appropriately blended.

And the said water-based primer mix | blends said each component with water by a well-known method, for example, the solid content density | concentration is 20-60 weight%, preferably by water-solubilizing or water-dispersing a resin component, It is prepared to be 35 to 60% by weight.

  The method for applying the water-based primer is not particularly limited, and for example, an air spray method, an airless spray method, an electrostatic coating method, or the like is used. More specifically, for example, a bell coating method is used.

  Moreover, the coating film thickness of the said water-based primer is 10-100 micrometers as a film thickness after baking, for example, Preferably, it is 13-35 micrometers.

  In addition, the temperature in the primer application booth 11 is managed at 20-30 degreeC, for example. In this coating method, the primer-coated member is preheated in the first preheating booth 12 (first preheating step).

  In the first preheating booth 12, the members are preheated with hot air. The preheating conditions are, for example, a hot air blowing temperature of 45 to 100 ° C., a hot air blowing speed of 0.3 to 10 m / s, and the wind speed on the coated surface of the hot air (the surface of the member) 1 to 3 m / s, the distance from the hot air outlet to the surface to be coated is 20 to 50 cm, and the preheating time is 0.5 to 5 minutes.

  In addition, the temperature and humidity in the 1st preheating booth 12 are managed by temperature 20-30 degreeC and the water evaporation possible amount 10-25 g / kg, for example. The first preheating booth 12 may be divided into one or more hot air zones and a cooling zone, heated in the hot air zone, and then cooled in the cooling zone. And the aqueous primer coated on the member by such preheating in the first preheating booth 12 forms a wet coating film (primer layer).

  Next, base coating is performed on the member on which the primer layer is formed (base coating process). In this coating method, base coating is performed at the base coating booth 13.

For the base coating, a yellow water-based solid base paint (water-based base paint) is used. This yellow aqueous solid base paint has a yellow pigment ratio of 50% by mass or more and a white pigment ratio of 30% by mass or more in the total pigment, and the L ^* a ^* b ^* color system of the coated film after painting. It is a coating material whose b ^* value in the range of 60-70. The yellow aqueous solid base paint contains a water-soluble or water-dispersible resin component (hydrophilic resin component) that forms a base coating film, a curing agent, a pigment, and a viscosity modifier. Examples of the hydrophilic resin component include those similar to the hydrophilic resin component contained in the above aqueous primer. For example, an acrylic resin, a polyester resin, an alkyd resin, a urethane resin, an epoxy having a carboxyl group or a hydroxyl group. It can be prepared by dissolving or dispersing a resin component such as resin, a crosslinking agent such as block polyisocyanate, melamine resin, and urea resin, a pigment, and other additives in water.

  As said hardening | curing agent, the hardening | curing agent contained in said aqueous primer is mention | raise | lifted, for example.

  The color pigment blended in the aqueous base paint has a yellow pigment ratio of 50% by mass or more and a white pigment ratio of 30% by mass or more in all pigments. Preferably, the ratio of the yellow pigment is in the range of 50 to 60% by mass, and the ratio of the white pigment is in the range of 30 to 40% by mass. Examples of the yellow pigment include synthetic yellow iron oxide, transparent brown (yellow), bismuth vanadate, titanium yellow, zinc yellow (monochrome), monoazo yellow, monoazo yellow, disazo, monoazo yellow, isoindolinone yellow, metal complex salt Examples include azo yellow, quinophthalone yellow, isoindoline yellow, and benzimidazolone yellow. Examples of the white pigment include titanium dioxide, zinc oxide, zinc phosphate, aluminum phosphate, zinc molybdate, and calcium molybdate. The coloring pigment component other than the yellow pigment and the white pigment is not particularly limited, and ordinary coloring pigments and metallic pigments are used.

  Examples of the coloring pigment include bitumen, ultramarine blue, cobalt blue, copper phthalocyanine blue, indanthrone blue, red rose, transparent red rose (red), monoazo red, monoazo red, unsubstituted quinacridone red, azo lake (Mn salt), and quinacridone. Magenta, Ansanthrone Orange, Dianthraquinonyl Red, Perylene Maroon, Quinacridone Magenta, Perylene Red, Diketopyrrolopyrrole Chrome Vermillion, Chlorinated Phthalocyanine Green, Brominated Phthalocyanine Green, Pyrazolone Orange, Benzimidazolone Orange, Dioxazine Violet And perylene violet. Examples of metallic pigments include aluminum powder, flaky aluminum oxide, pearl mica, and flaky mica.

  Examples of metallic pigments include aluminum powder, flaky aluminum oxide, pearl mica, and flaky mica. If such a metallic pigment is used, a metallic or pearly coating film can be formed.

As the viscosity modifier (RC agent), an alkali swelling type RC agents, associative thickening type RC agent Ru Agerare.

In order to prepare such an aqueous base paint, a hydrophilic resin component, a curing agent, a pigment and a viscosity modifier are blended together with water and a hydrophilic solvent and mixed by a known method. As a result, an aqueous base paint is prepared. As the hydrophilic solvent, e Chi glycol monomethyl ether, ethylene glycol monobutyl -tert- butyl ether, ethylene glycol monobutyl ether and the like. Content of the said hydrophilic solvent is 1-5 mass% with respect to resin solid content, Preferably it is 1-3 mass%.

  The blending ratio of the hydrophilic resin component is, for example, 50 to 85 mass%, preferably 60 to 80 mass%, based on the total solid content of the hydrophilic resin component and the curing agent.

Moreover, the mixture ratio of a hardening | curing agent is 15-50 mass% with respect to the solid content total amount of a hydrophilic resin component and a hardening | curing agent, for example, Preferably, it is 20-40 mass%.

Moreover, the mixture ratio of a pigment is 1-120 mass parts with respect to 100 mass parts of solid content total amount of a hydrophilic resin component and a hardening | curing agent, Preferably, it is 1-100 mass parts.

  Moreover, the mixture ratio of a viscosity modifier is 1-5 mass parts with respect to 100 mass parts of solid content of a hydrophilic resin component and a hardening | curing agent, for example, Preferably, it is 1-3 mass parts.

  Such an aqueous base paint has a solid content concentration of, for example, 25 to 45 mass%, preferably 30 to 40 mass%.

  The method for applying the aqueous base paint is not particularly limited, and for example, an air spray method, an airless spray method, an electrostatic coating method, or the like is used. More specifically, for example, a bell coating method is used.

  Moreover, the coating film thickness of a water-based base coating material is 10-100 micrometers as a film thickness after baking, for example, Preferably, it is 10-25 micrometers.

  In addition, the temperature in the base coating booth 13 is managed at 20-30 degreeC, for example. In this coating method, the base-coated member is preheated in the second preheating booth 14 (second preheating step). The aqueous base coating material applied to the member by preheating in the second preheating booth 14 forms a wet coating film (base layer).

  In the second preheating booth 14, the members are preheated with hot air. The preheating conditions are, for example, a hot air blowing temperature of 45 to 100 ° C., a hot air blowing speed of 0.3 to 10 m / s, and the wind speed on the coated surface of the hot air (the surface of the member) 1 to 3 m / s, the distance from the hot air outlet to the surface to be coated is 20 to 50 cm, and the preheating time is 0.5 to 5 minutes.

  The temperature and humidity in the second preheating booth 14 are controlled to, for example, a temperature of 20 to 30 ° C. and a water evaporation rate of 10 to 25 g / kg. The second preheating booth 14 may be divided into one or more hot air zones and a cooling zone, heated in the hot air zone, and then cooled in the cooling zone. The aqueous base coating material applied to the member by such preheating in the second preheating booth 14 forms a wet coating film, that is, a base coating film (base layer).

  Next, clear coating is performed on the member on which the base coating film is formed (clear coating process). In this painting method, clear painting is performed in the clear painting booth 15.

  The paint used for clear coating is not particularly limited, and a known clear paint is used. For example, a resin component such as an acrylic resin, a polyester resin, an alkyd resin, a urethane resin, or an epoxy resin, a cross-linking agent such as a block polyisocyanate, a melamine resin, or a urea resin, and other additives are dissolved or dispersed in an organic solvent. Can be prepared.

  In addition, the clear paint can appropriately contain an ultraviolet absorber or the like as long as it does not inhibit transparency. The clear paint is prepared such that the solid content concentration is, for example, 30 to 70% by weight, preferably 40 to 60% by weight.

  The method for applying the clear paint is not particularly limited, and for example, an air spray method, an airless spray method, an electrostatic coating method, or the like is used. Preferably, a bell coating method is used. Moreover, the coating film thickness of a clear coating is 10-60 micrometers as a film thickness after baking, for example, Preferably, it is 25-50 micrometers.

  In this coating method, the clear-coated member is baked in the baking furnace 16 (baking process). For the baking, for example, a known baking method such as hot air heating, infrared heating, high frequency heating or the like is used. The baking temperature is, for example, 80 to 170 ° C., preferably 120 to 160 ° C. for a steel plate member, and 50 to 130 ° C., preferably 70 to 120 ° C. for a resin member. The baking time is about 20 to 40 minutes.

  As a result, a coating film in which the base layer and the clear layer are laminated on the primer layer is formed.

  In the above process, clear coating is performed on the surface of the formed base layer. As described above, when a clear layer is applied on the base layer, a mixed layer may occur between the base layer and the clear layer. found. This mixed layer causes a movement in the pigment distribution in the base layer, and the difference in the movement causes a difference in the color tone of the parts after painting and baking. That is, when the base paint contains a plurality of types of pigments, yellow pigments and white pigments, a distribution depending on the pigment types may occur due to the mixed layer. This is thought to be due in part to differences in specific gravity between pigments and differences in affinity with solvents. When the distribution state of a plurality of pigments changes, the color tone may change to such an extent that it can be visually recognized. Therefore, in order to suppress the mixed layer, the inventors focused on increasing the viscosity of the surface portion of the base layer or promoting the drying of the surface portion. The color tone of the base layer can be stabilized by adjusting at least one of the content and the content of the hydrophilic solvent.

  On the other hand, the likelihood of the mixed layer depends on the solid content rate (NV) of the base layer at the time of applying the clear layer. When the solid content rate of the base layer is low, the mixed layer is likely to occur. It was found that when the rate is high, mixing is difficult to occur. Therefore, for example, when the color tone after the baking process is different for the two members, the solid content rate of the base layer at the time of applying the clear layer is measured and used for the member having the lower solid content rate (the one in which mixed layers tend to occur). By increasing the content of the viscosity modifier or decreasing the content of the hydrophilic solvent, the difference in color tone from the other member can be reduced. This is because by increasing the content of the viscosity modifier, the viscosity of the surface portion of the base layer is increased, or by decreasing the content of the hydrophilic solvent, drying of the surface portion is promoted and mixing is less likely to occur. This is thought to be due to this.

  The coating color after the baking process between a plurality of members using the water-based base paint as described above is compared, and the content and hydrophilicity of the viscosity modifier contained in the base paint used for the member determined to be toned By adjusting at least one of the solvent contents, the paint color after the baking process between the members can be easily achieved at low cost without preparing new paint or reviewing the conditions of each process in the coating line 10. , It can be matched to such an extent that the difference by visual recognition is not recognized.

  In addition, when adjusting the color tone between the members, if it is desired to match the paint color with the color tone before the color adjustment of the member on which the color adjustment is performed, the color adjustment may be further performed.

  The present invention can be applied to any member as a steel plate member and a resin member constituting an automobile body. In particular, since the same surface is large and the panel (member) is a vertical dividing line, the color tone is large. It can be suitably applied to a steel plate door member and a resin fender member, in which the difference between the two is easily recognized and the difference in paint color between the members is easily noticeable.

  As mentioned above, although the coating method by the aqueous coating process was demonstrated with reference to FIG. 1, this invention is not restricted to this, It can apply also to the coating method by the coating process using an organic-solvent type primer.

The organic solvent-based primer contains, for example, a resin component and a curing agent, and L ^* a ^* b ^* color system calculated from the reflectance measured at a reflection angle of 45 degrees using a spectrocolorimeter after the coating film is formed. The L ^* value in the range of 70-80 is used. Examples of the resin component include known resin components used for primers, such as acrylic resin, polyester resin, alkyd resin, epoxy resin, and polyurethane resin. Examples of the curing agent include known curing agents such as melamine resin and block polyisocyanate. Preferably, a melamine resin is mentioned.

In order to prepare an organic solvent-based primer, a resin component and a curing agent are blended together with an organic solvent and mixed by a known method. At this time, in order to make the L ^* value of the coating film satisfy the above condition, for example, a coloring pigment, an extender pigment, and other known additives are appropriately blended in addition to the above-described components. Thereby, an organic solvent-based primer is prepared.

  Examples of the organic solvent include hydrocarbon solvents such as xylene and toluene, alcohol solvents such as methyl alcohol and isopropyl alcohol, such as ethylene glycol, propylene glycol, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, and diethylene glycol monomethyl. Examples include ether alcohol solvents such as ether and diethylene glycol monobutyl ether, for example, ketone solvents such as methyl isobutyl ketone, cyclohexanone, and isophorone, and ester solvents such as ethylene glycol monoethyl ether acetate.

  These organic solvents can be used alone or in combination of two or more. The organic solvents are preferably used alone or in combination, and the boiling point thereof is adjusted to, for example, about 100 to 150 ° C.

  Even when an organic solvent-based primer is used, the water-based base coating material used in the base coating process and the clear coating used in the clear coating process should use the same paint as the water-based base paint and clear coating used in the above-mentioned water-based coating process. it can.

  Next, the present invention will be described based on examples and comparative examples, but the present invention is not limited to the following examples.

[Examples 1 to 6, Comparative Example 1]
In the examples and comparative examples, as a steel plate member (ED plate), a cationic electrodeposition paint “Electron 9900” was applied to the steel sheet by electrodeposition coating, and baked to form an electrodeposition coating film having a thickness of about 20 μm. What was formed was used. As the resin member (PP plate), a polypropylene plate “TSOP-6” was used. Each member was coated with the following primer, yellow water-based solid base paint and clear paint.

(Primer for steel plate members)
“WP555D-3” which is a primer containing an acrylic resin, a polyester resin, a urethane resin and a melamine resin as a resin component and a titanium oxide, iron oxide and carbon as a pigment was used. The coating viscosity (No. 4 Ford Cup, 20 ° C.) of this primer was 20 to 24 seconds. This primer coating film had an L ^* value of 76 in the L ^* a ^* b ^* color system calculated from the reflectance measured at a reflection angle of 45 degrees using a spectrocolorimetric system.

(Primer for resin parts)
“Ascalex 3800-1” which is a primer containing an olefin resin, a urethane resin and an acrylic resin as a resin component and containing titanium oxide, iron oxide and carbon as a pigment was used. The coating viscosity (No. 4 Ford Cup, 20 ° C.) of this primer was 45 to 55 seconds. This primer coating film had an L ^* value of 76 in the L ^* a ^* b ^* color system calculated from the reflectance measured at a reflection angle of 45 degrees using a spectrocolorimetric system.

(Yellow aqueous solid base paint)
As a resin component, “WBC713D-3”, which is a yellow aqueous solid base paint containing acrylic resin, polyester resin, urethane resin and melamine resin and containing synthetic yellow iron oxide, bismuth vanadate and titanium oxide as pigments, was used. PWC (pigment weight concentration) was synthetic yellow iron oxide / bismuth vanadate (yellow) / titanium oxide (white) = 33% / 33% / 33%. The coating viscosity (B-type viscometer, 20 ° C.) of this paint was 600 to 800 mPa · s. This base coating film had a b ^* value of 62 in the L ^* a ^* b ^* color system calculated from the reflectance measured at a reflection angle of 45 degrees using a spectrocolorimetric system. In Examples 1 to 6 and Comparative Example 1, steel sheet members and resins after clear coating were prepared using the yellow water-based solid base paints prepared by adjusting the amounts of the hydrophilic solvent and the viscosity modifier as shown in Table 1. The b ^* value of the paint color with the manufactured member was compared to evaluate the degree of coincidence of the paint color between the members.

(Clear paint for steel plate parts)
“DNC-K12-1”, which is an acid epoxy clear paint, was used. The coating viscosity (No. 4 Ford Cup, 20 ° C.) of this paint was 28 to 32 seconds.

(Clear paint for resin parts)
"Soflex 8538D" which is an acrylic / isocyanate two-component clear paint was used. The mixing ratio was main agent / curing agent / thinner = 100/42/42.

(Steel plate component painting process)
A primer “WP555D-3” for a steel plate member was applied to a steel plate member (after electrodeposition coating baking). After setting for 3 minutes, preheating at 75 ° C. for 3 minutes, and cooling for 3 minutes, a yellow-based aqueous solid base paint “WBC713D-” 3 ”, setting for 3 minutes, preheating at 75 ° C. for 3 minutes, cooling for 5 minutes, applying steel plate clear paint“ DNC-K12-1 ”, and after setting for 10 minutes, baking at 140 ° C. for 30 minutes. went.

(Resin component painting process)
Apply resin component primer “ASCALEX 3800-1” to the resin member, and after setting for 3 minutes, preheat 90 ° C. for 5 minutes and cooling for 3 minutes, apply yellow-based aqueous solid base paint “WBC713D-3”. After 3 minutes of setting, 3 minutes of preheating and cooling, a clear paint “SOFLEX 8538D” for resin parts was applied, and after 5 minutes of setting, baking was performed at 100 ° C. for 30 minutes. Here, the preheating after the application of the yellow aqueous solid base paint “WBC713D-3” was performed under two conditions of 75 ° C. for 3 minutes (condition 1) and 90 ° C. for 5 minutes (condition 2).

In Examples 1 to 6 and Comparative Example 1, the contents of the hydrophilic solvent and the viscosity modifier in the yellow aqueous solid base paint are as shown in Table 1. As a result of comparing b ^* values of the coating color of the steel plate member and the resin member after clear coating when using the yellow aqueous solid base paint having the composition of Examples 1 to 6 and Comparative Example 1, the finished LW evaluation The results and the water resistance evaluation results are shown in Table 1. Here, the finished LW is an index indicating the smoothness in the finished appearance. Comparative Example 1 is an example using a yellow aqueous solid base paint before adjusting the contents of the hydrophilic solvent and the viscosity modifier.

(Finished LW evaluation)
The finish of the coating film surface was evaluated using Wave Scan Plus (trade name, manufactured by BYK Gardner). Wavescan Plus irradiates the coating surface with laser light emitted from the measuring device and detects the intensity of the reflected light one by one using a detector, and can observe optical unevenness on the coating surface that is close to the naked eye by the intensity of the reflected light. . A long wave value (LW) and a short wave value (SW) are measured by wave scan plus. The Long Wave value is an index of the amplitude of the surface roughness having a wavelength of about 1.2 to 12 mm, and can evaluate the condition of the medium wave skin of the coated surface. The Short Wave value is an index of the amplitude of the surface roughness having a wavelength of about 0.3 to 1.2 mm, and the condition of the minute skin on the coated surface can be evaluated. The wave scan value is better as the numerical value is smaller. In general, the wave scan value is 20 or less for small cars and 10 or less for luxury cars. The finished LW was evaluated according to the following criteria.
◎: 15 or less ○: More than 15 and 20 or less

(Water resistance evaluation)
The test plate is immersed in warm water of 40 ° C. for 240 hours, pulled up, dried at 20 ° C. for 1 to 2 hours, and then the multilayer coating film of the test plate is cut into a lattice shape with a cutter so as to reach the substrate, and the size is 2 mm × Make 100 2mm Gobang eyes. Subsequently, an adhesive cellophane tape was attached to the surface, and the remaining number of the Gobang eyes coating after the tape was rapidly peeled off at 20 ° C. was examined. The water resistance was evaluated according to the following criteria.
◎: 100 galvanic coatings remain, and no small chipping of the coating occurs at the cutting edge of the cutter. ○: 100 galvanic coatings remain, but the coating is small at the cutting edge of the cutter. Spots are generated. Δ: 90 to 99 goby-eyed paint films remain. ×: The remaining number of goby-eyed paint films is 89 or less.

As shown in Table 1, in Comparative Example 1, the b ^* value of the coating color with the steel plate member when the preheat after application of the yellow aqueous solid base paint on the resin member is 90 ° C. for 5 minutes (condition 2) Difference (Δb ^* ) increased to 2.53, and the difference in color tone became conspicuous. Here, “matching the paint colors between members” means that Δb ^* is within 1.0. In Examples 1 to 6, Δb ^* was within 1.0 in both conditions 1 and 2 in the resin member coating process, and the coating colors could be matched.

  In Example 3, the evaluation result of the finished LW was slightly inferior to the other examples. From this result, it can be seen that if the content of the hydrophilic solvent is too small, the coating colors can be matched, but the smoothness in the finished appearance is lowered, so that it cannot be made free (content 0).

  In Example 4, spotting was observed as a result of the water resistance evaluation. From this result, it can be seen that if the content of the viscosity modifier is excessively increased, the paint color can be matched, but the water resistance tends to deteriorate.

  As described above, in the coating of members constituting an automobile body including a steel plate member and a resin member, the content of the viscosity modifier and the content of the hydrophilic solvent contained in the yellow aqueous solid base paint are used as a toning process. It can be seen that by including the step of adjusting at least one of these, it is possible to match the coating colors between the members after the baking step.

DESCRIPTION OF SYMBOLS 10 ... Paint line 11 ... Primer application booth 12 ... First preheating booth 13 ... Base coating booth 14 ... Second preheating booth 15 ... Clear painting booth 16 ... Baking furnace

Claims (1)

A method of painting a member constituting an automobile body including a steel plate member and a resin member,
The steel plate member and the resin member are coated with the same paint in a separate coating process,
The primer coating film in which the L ^* value in the L ^* a ^* b ^* color system calculated from the reflectance measured at a reflection angle of 45 degrees using a spectrocolorimeter is in the range of 70 to 80 is formed. On each member, a yellow aqueous solid base paint having a yellow pigment ratio of 50% by mass or more and a white pigment ratio of 30% by mass or more in the total pigment is applied, and in the L ^* a ^* b ^* color system a base coating step for forming a base coating film having a b ^* value in the range of 60 to 70;
A clear painting step of painting with a clear paint after preheating each member on which the base coating film is formed;
A baking step of baking each member that has been painted clear,
Further, the yellowish water-based solid base paint used in the base coating step includes a viscosity modifier and a hydrophilic solvent, and the viscosity modifier is selected from an alkali swelling type viscosity modifier and an associated thickening type viscosity modifier. , and the said hydrophilic solvent is ethylene glycol monomethyl ether, a solvent selected from ethylene glycol monobutyl -tert- butyl ether and ethylene glycol monobutyl ether, at least one adjustment of the content and the content of the hydrophilic solvent of the viscosity modifier Then, the coating method characterized by including the toning process which performs toning so that the coating color between each said member after the said baking process may correspond.

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