JP7433853B2 - Formation method of multi-layer coating and multi-layer coating - Google Patents

Description

The present invention relates to a method for forming a multilayer coating film in which a first color layer and a second color layer are provided adjacent to each other on an intermediate coating layer, and a multilayer coating film.

Conventionally, in order to form a multilayer coating on an object to be coated such as an automobile body, intermediate coating, color coating, and clear coating are applied to the electrocoated body using a wet-on-wet method and then cured. is commonly practiced.

When different colors are applied to each predetermined area, such as two-tone coloring, for example, the first color paint is applied to some areas on the intermediate coating layer applied on the electrodeposited film. After applying appropriate masking, a second color paint is applied to the area adjacent to the first color paint layer on the intermediate paint paint layer to form a paint layer. ing.

In such a painting process, when applying the first color onto the intermediate coating, dust of the first color paint adheres to the area on the intermediate coating where the second color paint is applied. Therefore, the dust of the first color paint on the intermediate paint was hidden by coating with the second color paint.
However, if the dust of the first color paint is simply coated with the second color paint, slight color differences will be visible from the outside of the multilayer paint film obtained by curing the applied layer. Since the dust of the first color paint is sometimes visible, further improvement of the hiding property is being considered.

For example, in Patent Document 1, a white paint with high hiding power containing aluminum powder and titanium oxide white pigment is used, and a first color such as black can be seen through by a three-coat one-bake method (3C1B). A method has been proposed for forming a multilayer white coating film by preventing this.

Further, as shown in FIG. 3, a first color paint is applied on the intermediate coating layer 12 applied to the base layer 11 consisting of an electrodeposition coating film to form a first color coating layer 23, and after drying. , by applying the second color paint twice on the dust 17 of the first color paint, a thick second color coating layer 24 made of the second color paint is provided and dried, and the paint further has mica etc. dispersed therein. The coating layer 25 and the coating layer 26 of the clear paint are laminated and heated and dried to form a concealing layer 15 and a clear layer 16, thereby preventing the dust 17 of the first color paint from being visible from the outside. A method of forming a multilayer coating film 30 has also been implemented.

Japanese Patent Application Publication No. 11-226498

However, in the method shown in Fig. 3, in a multi-layer coating film in which a first color layer and a second color layer are provided adjacent to each other on an intermediate coating layer, dust of the first color paint can be reliably concealed, resulting in an excellent result. In order to form a multilayer coating film with good appearance quality, the second color layer made of the second color paint must be formed sufficiently thick.
For this reason, for example, it is difficult to form a thick coating layer at once, so there are problems such as increasing the number of coatings, drying and curing, etc., which increases the cost of coating and requires time and effort. there were.

SUMMARY OF THE INVENTION Accordingly, the present invention aims to easily obtain a multilayer coating film with excellent appearance quality, without being visible through the second color layer even if dust of the first color paint adheres to the intermediate coating layer. One object of the present invention is to provide a method for forming a multi-layer coating film that allows for the formation of a multi-layer coating film, and also to provide a multi-layer coating film with excellent appearance quality in which the dust of the first color paint is not visible through the second color layer. for other purposes.

The method for forming a multilayer coating film of the present invention which achieves the above object is to apply a first color layer, which is a cured first color coating layer, and a second color layer, which is a first color coating layer, on an intermediate coat layer, which is a cured intermediate coating layer. In a method for forming a multilayer coating film in which a colored coating layer and a second colored layer are provided adjacent to each other, the surface tension of the first color coating in the applied state is adjusted to form an intermediate coating layer. The surface tension is adjusted to be lower than the surface tension of the intermediate coating in the applied state, and the intermediate coating is applied on the intermediate coating layer in a wet state in which the dust of the first color paint can sink. A first color paint is applied to a part of the paint to form a first color paint layer, and the dust of the first color paint adhering to the area adjacent to the first color paint layer on the intermediate paint layer is removed. In this method, the intermediate coating layer is sunk deeper than the first color coating layer, and the second color paint is applied to the area to form the second color coating layer.

In the method for forming a multilayer coating film of the present invention, the coating viscosity of the intermediate coating layer is set to 100 Pa.S or more and 1200 Pa.S or less at the time of coating the first color coating layer, and the coating viscosity of the first color coating layer is It is preferable that the coating viscosity is 3.5 Pa·S or more and 10.3 Pa·S or less.
In addition, in the method for forming a multilayer coating film of the present invention, it is preferable that the surface tension of the first color paint is lower than the surface tension of the intermediate coat, and further, the curing start temperature of the first color paint is set to the temperature at which the intermediate coat starts curing. It is best to keep it above the temperature.

The multilayer coating film of the present invention that achieves the above-mentioned other objects is a multilayer coating film formed by the method for forming a multilayer coating film as described above.

According to the method for forming a multilayer coating film of the present invention, when forming a first color coating layer by applying the first paint to a part of the intermediate coating layer, the first color coating layer is formed on the intermediate coating layer. The dust of the first color paint adhering to the area adjacent to the first color paint layer is allowed to sink into the inner side of the intermediate coat layer than the first color paint layer, and then the second color paint is applied to the adjacent area. to form a second color coating layer.
Therefore, even if dust of the first color paint adheres to the area adjacent to the first color coating layer, the dust does not protrude significantly onto the intermediate coating layer. As a result, even if a second color paint is applied on the intermediate coating layer to form a second color paint layer, the thickness of the second color paint layer becomes thinner locally due to the dust of the first color paint. This can be prevented.

Therefore, even if the thickness of the entire second color coating layer is formed to be thin, sufficient hiding performance can be ensured in the entire second color layer obtained by curing the second color coating layer. As a result, when viewed from the outside, dust of the first color paint is not seen through the second color layer, making it possible to easily form a multilayer coating film with excellent appearance quality.

In the method for forming a multilayer coating film of the present invention, in particular, by adjusting the solid content concentration of the intermediate coating layer at the time of coating and the solid content concentration of the first color coating layer at the time of coating, respectively, to a predetermined range, The dust of the first color paint is transferred to the intermediate coating layer while suppressing the first color coating layer from sinking into the intermediate coating layer and mixing of the first color coating layer and the intermediate coating coating layer. It is possible to sink the first color coating layer, and the smoothness of the surface of the first color coating layer can be ensured. Therefore, a multilayer coating film with excellent appearance quality can be formed more reliably.

In the method for forming a multilayer coating film of the present invention, the surface tension of the first color paint and the surface tension of the intermediate coating paint are adjusted to a predetermined relationship, so that the first color coating layer sinks into the intermediate coating layer. This can prevent the first color coating layer from mixing with the intermediate coating layer.

Furthermore, in the method for forming a multilayer coating film of the present invention, by setting the curing start temperature of the first color paint and the curing start temperature of the intermediate coat paint in a predetermined relative relationship, the intermediate coat layer and the first color paint When the attached layer and the second color coating layer are cured, the first color coating layer has fluidity and starts curing later than the intermediate coating layer when the intermediate coating layer starts curing. Therefore, a stable first color layer can be formed on the intermediate coating layer, and the appearance of the resulting multilayer coating film can be improved.

Further, according to the multi-layer coating film of the present invention, the dust of the first color paint constituting the first color layer is deposited on the intermediate coat layer in the area corresponding to the second color layer, on the inner side than the first color layer. It exists in a submerged state. Therefore, even if there is dust of the first color paint in the intermediate coat layer in the area corresponding to the second color layer, the dust does not protrude significantly from the surface of the intermediate coat layer, and the dust does not protrude from the surface of the intermediate coat layer in the area corresponding to the second color layer. It is possible to reduce the unevenness at the interface of the coating layer.

As a result, variations in the thickness of the second color layer on the intermediate coating layer are less likely to occur, and even if the second color layer is thin, sufficient hiding performance can be ensured in the entire second layer. As a result, when the multi-layer paint film is viewed from the outside, the dust of the first color paint will not be visible through the second color layer, ensuring the excellent appearance quality of the multi-layer paint film. .

FIG. 2 is a partially enlarged sectional view of a multilayer coating film in an embodiment of the present invention. (a) to (e) show the process of forming a multilayer coating film in an embodiment of the present invention. FIG. 2 is a partially enlarged sectional view showing an example of a conventional multilayer coating film.

Hereinafter, a multilayer coating film and a method for forming the same in an embodiment of the present invention will be described in detail.
The multi-layer coating film 10 is a laminated film as shown in FIG. The layers 14 are provided adjacent to each other. In this embodiment, the first color layer 13 has a black color, and the second color layer 14 has a white color. The second color layer 14 is a color base, and a hiding layer 15 containing and dispersing mica and a clear layer 16 are laminated on the second color layer 14 .

The objects to be coated are various members formed into flat or three-dimensional shapes from various metal base materials such as steel, stainless steel, and aluminum, and various plastic base materials, such as vehicle bodies such as automobiles and motorcycles, and electrical products. The exterior body, etc. This embodiment mainly uses an example in which the object to be painted is an automobile body formed by forming and joining steel plates into a three-dimensional shape.

The base layer 11 of the multilayer coating film 10 may be the surface of the object to be painted, or may be a primer layer obtained by subjecting the surface of the object to various types of surface treatments. In this embodiment, the surface of the object to be coated is formed of an electrodeposition coating film.

In this multi-layer coating film 10, dust 17 of the first color paint generated when forming the first color layer 13 is present in the intermediate coat layer 12 in a region corresponding to the second color layer 14, and the intermediate coat layer The first color layer 13 is disposed inside the first color layer 12 so as to be sunk deeper than the first color layer 13 . The second color layer 14 is formed by laminating the intermediate coating layer 12 in which the dust 17 of the first color paint has sunk.

According to such a multi-layer coating film 10, since the dust 17 of the first color paint exists in a state of being sunk inside the intermediate coating layer 12, the intermediate coating layer in the area corresponding to the second color layer 14 Even if dust 17 of the first color paint is present in the intermediate coating layer 12, the dust 17 does not protrude significantly from the surface of the intermediate coating layer 12, and the interface of the intermediate coating layer 12 is formed flat.

Therefore, even when the second color layer 14 is formed on the intermediate coating layer 12, there is less variation in the thickness, and the second color layer 14 does not become locally excessively thin in areas where the dust 17 is present. Sufficient hiding performance can be ensured in the entire second color layer 14. As a result, even if the second color layer 14 is not provided thickly, it is possible to prevent the dust 17 of the first color paint from being visually recognized through the second color layer 14, and excellent appearance quality can be achieved.

In the present embodiment, in order to form such a multilayer coating film 10, the process shown in FIGS. 2(a) to 2(e) is performed under a coating atmosphere formed by maintaining the inside of a closed space under predetermined conditions. It can be formed by sequentially laminating each coating material in a wet-on-wet manner and curing it by appropriately heating and drying it. The method for forming it will be explained below.

A base layer 11 made of an electrodeposition coating film is previously formed on the object to be coated in a hardened state. The object to be coated is placed under a coating atmosphere, and a medium is applied to the base layer 11 of the object to be coated, as shown in FIG. A coating material is applied, and a wet intermediate coating layer 22 is formed by evaporating volatile components in a coating atmosphere.

As the intermediate paint, a known paint containing a resin component and a curing agent dispersed in an organic solvent is used. If necessary, various additives such as a viscosity-imparting agent, a flow regulator, a pigment dispersant, and the like may be added to the intermediate coating material. Examples of the resin component include acrylic resin, polyester resin, alkyd resin, epoxy resin, and polyurethane resin, and specifically, acrylic resin or polyester resin having a carboxyl group is used. Examples of the curing agent include melamine resin and block polyisocyanate. Furthermore, various pigments may be contained depending on the paint color.

Examples of organic solvents include aromatic solvents such as xylene; aliphatic solvents such as mineral spirits; ethyl acetate, butyl acetate, propyl propionate, butyl propionate, 1-methoxy-2-propyl acetate, 2 - Ester solvents such as ethoxyethyl propionate, 3-methoxybutyl acetate, ethylene glycol ethyl ether acetate, and propylene glycol methyl ether acetate; Ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, and methyl amyl ketone; isopropanol, n -Alcoholic solvents such as butanol, isobutanol, and 2-ethylhexanol can be mentioned.

By applying such an intermediate coating paint onto the base layer 11, an intermediate coating layer 22 having a thickness of, for example, 10 to 40 μm is formed. In this embodiment, the intermediate coating layer 22 is formed in a wet state without being subjected to heat drying alone. At this time, the intermediate coating layer 22 is formed such that the solid content concentration, viscosity, etc. are within a desired range, and the details will be described later.

Next, as shown in FIG. 2(b), a first color paint is applied to a part of the intermediate coating layer 22 using an appropriate coating means such as an air spray or an electrostatic coating machine. The first color coating layer 23 is formed by evaporating volatile components in a coating atmosphere. The first color paint is prepared by blending a film-forming resin component, a curing agent, a pigment, a solvent, and various additive components added as necessary.

As the resin component, various resins used as resin components for paints are used. For example, it is at least one selected from acrylic resin, vinyl resin, polyester resin, alkyd resin, urethane resin, etc., and has a hydroxyl group, a carboxyl group, a silicon-containing group, an epoxy group, and a blocked functional group. Examples include resins having good isocyanate groups.

Examples of the curing agent include melamine resins, urea resins, optionally blocked polyisocyanate compounds, carboxyl group-containing compounds, and epoxy group-containing compounds that react with the functional groups in the resin component.

Examples of pigments include carbon black, acetylene black, lamp black, bone black, graphite, iron black oxide (triiron tetroxide), titanium black oxide, copper manganese black, copper chrome black, cobalt black, cyanine black, and aniline black. Black pigments; blue pigments such as phthalocyanine, indanthrone, and indigo; red pigments such as azo, diketopyrrolopyrrole, perylene, perinone, and iron oxide. In this embodiment, black pigment is used.

Examples of the solvent include aromatic solvents such as xylene; aliphatic solvents such as mineral spirits; ethyl acetate, butyl acetate, propyl propionate, butyl propionate, 1-methoxy-2-propyl acetate, 2- Ester solvents such as ethoxyethyl propionate, 3-methoxybutyl acetate, ethylene glycol ethyl ether acetate, and propylene glycol methyl ether acetate; Ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, and methyl amyl ketone; isopropanol, n- Examples include alcohol solvents such as butanol, isobutanol, and 2-ethylhexanol.

If necessary, various additives such as a viscosity imparting agent, a flow regulator, a light stabilizer, an ultraviolet absorber, an extender, and a pigment dispersant may be added to the first color paint.

In this embodiment, by applying such a first color paint onto the intermediate coating layer 22, the first color coating layer 23 having a thickness of 10 to 40 μm is applied to a predetermined area on the intermediate coating layer 22. Form into an area.

When the first color paint is applied to a predetermined area on the intermediate coating layer 22 to form the first color coating layer 23, the scattered dust 17 of the first color paint is deposited on the intermediate coating layer 22. It also adheres to the adjacent area adjacent to the first color coating layer 23 .
In the present invention, the dust 17 of the first color paint adhering to the intermediate coating layer 22 is caused to sink into the inner side of the intermediate coating layer 22, as shown in FIG. 2(c). Here, while maintaining the first color coating layer 23 on the intermediate coating layer 22 without sinking as much as possible, the dust 17 of the first color paint is transferred to the intermediate coating layer 22 from the first color coating layer 23. Let it sink into the inside of 22.

Here, sinking the first color paint dust 17 deeper into the intermediate coat layer 22 than the first color paint layer 23 means that at least a portion of the first color paint dust 17, preferably All of them are arranged closer to the object to be coated than the interface between the first color coating layer 23 and the intermediate coating layer 22. Preferably, more dust 17 of the first color paint adhering to the intermediate coating layer 22 in the area corresponding to the second color coating layer 24 is disposed inside the intermediate coating layer 22, so that the intermediate coating layer 24 is The surface of the coating layer 22 is preferably formed to be smooth.

In order to make the paint sink deeper into the intermediate coat layer 22 than the first color paint layer 23, if the paint is allowed to sink by leaving it in a coating atmosphere or in the atmosphere, leave it until the desired sink state is reached. You can. In this embodiment, in order to maintain the first color coating layer 23 on the intermediate coating layer 22 and allowing the dust 17 of the first color paint to sink, the solid content of the intermediate coating layer 22 at the time of coating is It is preferable to apply the first color paint on the intermediate coat layer 22 with the concentration and the solid content concentration of the first color layer 23 at the time of coating being adjusted to fall within a predetermined range.

This solid content concentration at the time of application refers to the mass of the applied layer formed after the paint is applied to the object to be coated and left uncured under controlled temperature and humidity conditions such as in a paint booth after curing. is the proportion of the mass of

This solid content concentration at the time of application can be adjusted by, for example, the selection of the components and solvent of each paint, the dilution rate with the solvent, the application conditions of each paint, the temperature and humidity of the paint booth, the time since application, etc.

Regarding such solid content concentration at the time of coating, in this embodiment, the solid content concentration of the intermediate coating layer 22 at the time of coating is set to 85 wt% or more and 90 wt% or less, and the solid content concentration at the time of coating of the first color coating layer 23 is set to 85 wt% or more and 90 wt% or less. It is preferable that the solid content concentration is 65 wt% or more and 75 wt% or less. More preferably, the solid content concentration of the intermediate coating layer 22 at the time of coating is 85.5 wt% or more and 88.5 wt% or less, and the solid content concentration of the first color coating layer 23 is 65 wt% or more. Make it 75wt% or less.

In this way, by setting the solid content concentration of the intermediate coating layer 22 and the first color coating layer 23 within the above range, the coating viscosity of the intermediate coating layer 22 can be set to 100 Pa·s or more and 1200 Pa.・It can be set to not more than s, and more preferably, not less than 120 Pa·s and not more than 900 Pa·s. Moreover, the coating viscosity of the first color coating layer 23 can be set to 3.5 Pa·s or more and 10.3 Pa·s or less, more preferably 5 Pa·s or more and 7 Pa·s or less.

If the solid content concentration and coating viscosity of the above-mentioned intermediate coating layer 22 are excessively low, when the first color coating layer 23 is applied, the intermediate coating layer 22 and the first color coating As a result, it is difficult to form a smooth surface of the first color layer 13 in the multilayer coating film 10 obtained, and it is difficult to ensure quality such as skin and gloss.
On the other hand, if the solid content concentration or coating viscosity of the intermediate coating layer 22 during coating is excessively high, the first color paint may adhere to the intermediate coating layer 22 in the area corresponding to the second color coating layer 24. This makes it difficult for the dust 17 to sink into the inner side of the intermediate coating layer 22.

Furthermore, if the solid content concentration or coating viscosity of the first color coating layer 23 is excessively low, when the first color coating layer 23 is coated, the intermediate coating layer 22 and the first color coating layer 23 may It is easy to mix with the single color coating layer 23 and form a mixed layer, making it difficult to form a smooth surface of the first color layer 13 in the resulting multilayer coating 10, making it difficult to ensure quality such as skin and gloss. It becomes difficult.
On the other hand, if the solid content concentration or coating viscosity of the first coating layer 23 during coating is excessively high, the first color paint adheres to the intermediate coating layer 22 in the area corresponding to the second color coating layer 24. This makes it difficult for the dust 17 to sink into the inner side of the intermediate coating layer 22.

In this embodiment, in order to maintain the first color coating layer 23 on the intermediate coating layer 22 and causing the dust 17 of the first color paint to sink into the inner side of the intermediate coating layer 22, the intermediate coating is applied. In addition to adjusting the solid content concentration of the coating layer 22 and the first color coating layer 23 at the time of coating, it is also necessary to adjust the surface tension of the first color paint and the surface tension of the intermediate coating paint to a predetermined relationship. good. The surface tension of the first color paint and the surface tension of the intermediate paint can be adjusted by, for example, adding a surface conditioner such as polysiloxane or adjusting the amount added.

Specifically, it is preferable that the surface tension in the applied state of the first color paint be equal to or lower than the surface tension in the applied state of the intermediate paint. By doing so, it is possible to prevent the first color coating layer 23 from sinking into the intermediate coating layer 22 and mixing the first color coating layer 23 and the intermediate coating layer 22, and to obtain a complex The first color layer 13 of the layer coating can be made smoother and the appearance quality can be improved.

Furthermore, in this embodiment, in order to sink the intermediate coating layer 22 into the inner side of the intermediate coating layer 22 than the first color coating layer 23, the intermediate coating layer 22 and the first color coating layer 23 are solid during coating. In addition to adjusting the respective concentrations, it is also preferable to set the relative relationship between the curing start temperature of the first color paint and the curing start temperature of the intermediate paint.
The curing start temperature of these paints can be measured, for example, from changes in viscosity with respect to temperature changes.

Specifically, it is preferable that the curing start temperature of the first color paint is equal to or higher than the curing start temperature of the intermediate paint. In this way, when the intermediate coating layer 22, the first color coating layer 23, and the second color coating layer 24 are cured, the first color coating layer 22 starts curing. Since the layer 23 has fluidity and the first color coating layer 23 starts curing later than the intermediate coating layer 22, a smooth first color layer 13 is formed on the intermediate coating layer 12. obtain.

In this embodiment, while maintaining the first color coating layer 23 on the intermediate coating layer 22 in this manner, the dust 17 of the first color paint is applied to the intermediate coating layer 23 rather than the first color coating layer 23. After sinking into the inner side of the layer 22, the intermediate coating layer 22 and the first color coating layer 23 are heated and dried. The intermediate coating layer 12 and the first color layer 13 are formed by curing. As a result, the dust 17 of the first color paint existing in the area adjacent to the first color layer 13 sinks into the interior of the intermediate coat layer 12 and hardens, and the area corresponding to the second color layer 14 becomes smooth. A surface is formed.

Next, as shown in FIG. 2(d), after masking the area corresponding to the first color coating layer 23, a first color coating layer 23 is applied to an adjacent area on the intermediate coating layer 12 adjacent to the first color coating layer 23. A two-color paint is applied using an appropriate coating means such as an air spray, an airless spray, or an electrostatic coating machine, and volatile components are evaporated in a coating atmosphere to form a second color coating layer 24. In this way, the second color paint is applied to a predetermined area on the intermediate coat layer 22, including the area where the dust 17 of the first color paint has sunk, to provide the second color paint layer 24.

As the second color paint in the present invention, those exemplified as the first color paint can be used similarly. In that case, except for using different pigments, it is possible to use the same coating film-forming resin components, curing agents, solvents, various additive components, etc. as in the first color paint.

The second color coating layer 24 formed on the intermediate coating layer 12 by applying such a second color paint may be heated and dried; however, in this embodiment, in order to simplify the process, the second color coating layer 24 is heated and dried. The process proceeds to the next step of forming the concealing layer 15 in a wet state without curing.

Next, as shown in FIG. 2(e), a known mica-containing paint is applied to the area corresponding to the second color paint layer 24 to form a mica-containing paint layer 25 for forming the concealing layer 15. Stack. This mica-containing paint contains a film-forming resin component that is compatible with the second color paint, a curing agent, a solvent, various additive components, etc. It contains various types of mica and is uniformly dispersed. Any known paint can be used.

Thereafter, by applying a clear paint to a region corresponding to the second color paint layer 24, a clear paint layer 26 is laminated on the mica-containing paint paint layer 25. Known clear paints can be used as appropriate, such as acrylic resins, polyester resins, alkyd resins, urethane resins, and epoxy resins, crosslinking agents such as block polyisocyanates, melamine resins, and urea resins, and other additives. You may use the paint which dissolved or dispersed in the organic solvent.

In this embodiment, the second color coating layer 24, the coating layer 25 of the mica-containing coating material, and the coating layer 26 of the clear coating material are applied to the remaining area of the intermediate coating layer 12 excluding the first color layer 13. By heating and drying the laminated state, these layers are cured, and a second color layer 14, a concealing layer 15, and a clear layer 16 are formed on the intermediate coating layer 12.

In this embodiment, by doing so, the first color layer 13, which has the first color coating layer 23 cured, and the second color coating layer 12, which has the first color coating layer 23 cured, are placed on the intermediate coating layer 12, which has the intermediate coating layer 22 cured. A multilayer coating film 10 can be formed in which the second color layer 14 is formed by hardening the adhesive layer 24 and is provided adjacent to each other.

According to the method for forming the multilayer coating film 10 as described above, when forming the first color coating layer 23 by applying the first paint to a part of the intermediate coating layer 22, the intermediate coating The dust 17 of the first color paint adhering to the area adjacent to the first color paint layer 23 on the layer 22 is allowed to sink into the inner side of the intermediate paint layer 22 from the first color paint layer 23, and then A second color coating layer 24 is formed by applying a second color paint to the adjacent area.

Therefore, even if the dust 17 of the first color paint adheres to the area adjacent to the first color coating layer 23, the dust 17 does not protrude significantly onto the intermediate coating layer 22. As a result, even if the second color coating layer 24 is formed by coating the second color coating layer 22 on the intermediate coating layer 22, the thickness of the second color coating layer 24 is reduced due to the dust 17 of the first color coating material. Local thinning can be prevented.

As a result, even if the entire thickness of the second color coating layer 24 is formed to be thin, the entire second color layer 14 obtained by hardening the second color coating layer 24 can ensure sufficient hiding performance, and it is possible to ensure that the second color coating layer 24 can be visually recognized from the outside. At this time, the dust 17 of the first color paint is not visible through the second color layer 14, and a multilayer coating film 10 with excellent appearance quality can be easily formed.

Furthermore, in the method for forming the multilayer coating film 10 of the present embodiment, the second color coating layer 24 is formed after the intermediate coating layer 22 and the first color coating layer 23 are cured. Mixing of the first color coating layer 23 and the second color coating layer 24 can be prevented, and a clear boundary between the first color layer 13 and the second color layer 14 can be formed.

In the method for forming the multilayer coating film 10 of the present embodiment, the solid content concentration of the intermediate coating layer 22 and the solid content concentration of the first color coating layer 23 are adjusted to predetermined ranges. There is. Therefore, while suppressing the first color coating layer from sinking into the intermediate coating layer and mixing the first color coating layer and the intermediate coating layer, the dust of the first color paint is transferred to the intermediate coating coating. It can be made to sink into the layer, and the smoothness of the surface of the first color coating layer can be ensured.

In the method for forming the multilayer coating film 10 of this embodiment, the surface tension of the first color paint and the surface tension of the intermediate paint are adjusted to have a predetermined relationship. Therefore, it is possible to prevent the first color coating layer from sinking into the intermediate coating layer and mixing the first color coating layer and the intermediate coating layer.

Furthermore, in the method for forming the multilayer coating film 10 of this embodiment, the curing start temperature of the first color paint and the curing start temperature of the intermediate paint are set in a predetermined relative relationship. Therefore, when the intermediate coating layer 22, the first color coating layer 23, and the second color coating layer 24 are cured, at the time when the intermediate coating layer 22 starts curing, the first color coating layer 23 is Since it has fluidity and starts curing later than the intermediate coating layer 22, a stable first color layer 13 can be formed on the intermediate coating layer 12, and the appearance of the resulting multilayer coating film 10 is improved. can.

Note that the above embodiments can be modified as appropriate within the scope of the present invention.
In the above embodiment, an example in which the hiding layer 15 is laminated on the second color layer 14 has been described, but this is not particularly limited. It is also possible to configure the multilayer coating film 10 without providing it.
Further, in the above embodiment, a two-tone multilayer coating film is formed, which is composed of the first color layer 13 and the layer in which the hiding layer 15 and the clear layer 16 are stacked on the second color layer 14. The present invention can be applied even when forming a multi-color multilayer coating film provided with.

Examples and comparative examples of the present invention will be described below.
[Example 1]
An intermediate coating layer 22 is formed by applying an intermediate coating to a flat test piece that has been electrocoated using a spray nozzle, and black is applied to some areas on the intermediate coating layer 22 of the test piece. The first color paint was applied using a spray nozzle to form a first color coating layer 23 having a thickness of 30 μm.

The intermediate coating was a uniform mixture of a polyester resin melamine curing resin intermediate coating and 40 wt % of an organic solvent. The intermediate coating composition contained 40 wt% titanium oxide and 0.05 wt% carbon black as pigment components. Here, wt% is the ratio to the solid content excluding the organic solvent.
The organic solvent used was a mixture of 10 wt% ethyl acetate, 5 wt% butyl acetate, 5 wt% methanol, 5 wt% butanol, 10 wt% xylene, and 5 wt% Solvent #150 (manufactured by Sankyo Kagaku Co., Ltd.). Here, wt% is the ratio to the entire coating composition.

Regarding the intermediate coating layer 22 formed by applying this intermediate coating paint, the solid content concentration at the time of application of the first color paint was measured and found to be 86 wt%. The coating viscosity was measured using a cone plate viscometer (manufactured by Brookfield) and was found to be 550 Pa·s.

Further, the surface tension of this intermediate coating layer 22 was 28.8 dyn/cm when measured using a contact angle meter DMo-501 (manufactured by Kyowa Interface Science).

Further, the curing start temperature of this intermediate coating layer 22 was measured using a rigid pendulum type physical property tester (RPT-3000W manufactured by A&D) and found to be 113°C.

On the other hand, as the black first color paint applied on the intermediate coating layer 22, a paint composition of an acrylic acid epoxy curing resin paint and an organic solvent were uniformly mixed. The first color coating composition contained 3 wt % of carbon black as a pigment component.
As an organic solvent, a mixture of 7 wt% butyl acetate, 13 wt% butanol, 7 wt% ethyl-3-ethoxyprobionate, and 18 wt% Solvent #100 (manufactured by Sankyo Kagaku Co., Ltd.) was used.

When the first color coating layer 23 formed by applying the black first color paint was measured in the same manner as the intermediate coating layer 22, the solid content concentration at the time of coating was 70 wt%. Moreover, when the coating viscosity was measured, it was 6.1 Pa·s.
The surface tension was 28.6 dyn/cm, which was lower than the surface tension of the intermediate coating.
Furthermore, the curing start temperature was 117°C, which was higher than the curing start temperature of the intermediate coating.

When the first color coating layer 23 was formed in a part of the area on the intermediate coating layer 22 in this way, the first color paint scattered during coating was found in areas other than the first color coating layer 23. A large amount of dust 17 consisting of
After the coating was completed, the cross section of the coating layer was observed under magnification of 500 times using a microscope, and it was confirmed that a large amount of these dust particles 17 had sunk into the interior of the intermediate coating layer 22. At this time, the first color coating layer 23 was kept flat on the intermediate coating layer 22.

Thereafter, with the first color coating layer 23 formed on the intermediate coating layer 22, the test piece is heated and dried in a drying oven at 140° C. for 30 minutes to cure each layer, thereby applying the intermediate coating. Layer 12 and first color layer 13 were formed.

Next, using the heat-cured test piece, the first color layer 13 is masked and coated, and the remaining area is coated with a white second color paint using a spray nozzle. A coating layer 24 was formed on the intermediate coating layer 22. This white second color paint was used by uniformly mixing 60 wt % of a paint composition of a polyester resin melamine curing paint and 40 wt % of an organic solvent.

The second color coating composition contained 50 wt% titanium oxide and 0.03 wt% carbon black as pigment components. Here, wt% is the ratio to the solid content excluding the organic solvent.

Thereafter, the test piece is heated and dried under the same conditions as described above to cure the second color coating layer 24, so that the second color layer 14 is applied to the area adjacent to the first color layer 13 on the intermediate coating layer 12. was formed. When the obtained test piece was visually confirmed, it was found that in the area of the second color layer 14, the dust 17 of the first color paint that had adhered in large quantities to the intermediate coating layer 22 during application of the first color paint was not visible at all. There wasn't.

[Comparative example 1]
When applying the first color paint, the coating viscosity of the intermediate coating layer 22 is set to 2000 Pa·s, and the dust of the first color paint adhering to the intermediate coating layer 22 is appropriately removed from the intermediate coating layer 22. A multilayer coating film was formed in the same manner as in Example 1 except that the coating was not allowed to sink into the interior.
As a result, in Comparative Example 1, although the second color layer 14 was formed to the same thickness by the same method as in Example 1, when the obtained test piece was visually observed from the outer surface side under natural light, it was found that the first color layer 14 The shape of paint dust 17 was visually recognized.

10 Multilayer coating film 11 Base layer 12 Intermediate coating layer 13 First color layer 14 Second color layer 15 Hiding layer 16 Clear layer 17 Dust 22 Intermediate coating layer 23 First color coating layer 24 Second color coating layer 25 Application layer of mica-containing paint 26 Application layer of clear paint

Claims (5)

On the intermediate coating layer in which the intermediate coating layer is cured, a first color layer in which the first color coating layer is cured and a second color layer in which the second color coating layer is cured are placed adjacent to each other. In the method for forming a multilayer coating film provided,
Adjusting the surface tension of the first color paint in the applied state to be lower than the surface tension in the applied state of the intermediate coating that forms the intermediate coating layer ,
Applying the first color paint to a part of the intermediate coat layer in a wet state in which the intermediate coat layer can sink the dust of the first color paint to coat the first color. forms an adhesion layer,
The dust of the first color paint adhering to the area adjacent to the first color paint layer on the intermediate paint layer is settled to the inner side of the intermediate paint layer from the first color paint layer. Let me put it in,
A method for forming a multilayer coating film, comprising applying a second color paint to the area to form the second color coating layer. The coating viscosity of the intermediate coating layer is 100 Pa·S or more and 1200 Pa·S or less when applying the first color coating layer, and the coating viscosity of the first color coating layer is 3.5 Pa·S or more. The method for forming a multilayer coating film according to claim 1, wherein the pressure is 10.3 Pa·S or less. The method for forming a multilayer coating film according to claim 1 or 2, wherein the curing start temperature of the first color paint is set to be equal to or higher than the curing start temperature of the intermediate coating paint. A solid content concentration of the intermediate coating layer at the time of coating is 85 wt% or more and 90 wt% or less, and a solid content concentration of the first color coating layer is 65 wt% or more and 75 wt% or less. 4. The method for forming a multilayer coating film according to any one of 1 to 3 . A multilayer coating film formed by the method for forming a multilayer coating film according to any one of claims 1 to 4.

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