JP4647262B2 - Painting method - Google Patents

Description

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

As a method for coating a member such as a panel made of metal or resin constituting an automobile body, it is widely known that first, undercoating is performed by electrodeposition coating, then intermediate coating is performed, followed by overcoating for finishing. 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 top coating with water-based paint, after intermediate coating with water-based paint, color base coating is performed with a colored water-based paint in a wet state, and further, clear coating is performed in a wet state, followed by baking. Bake-type coating methods are being studied from the viewpoint of improving production efficiency.
In this 3-coat 1-bake method, for example, in each coating process, the coating is applied in a wet state (wet-on-wet), so that the intermediate layer and the base layer, or the base layer and the clear layer are coated. In order to prevent mixed layers between the intermediate coating process and the base coating process, and between the base coating process and the clear coating process, respectively, Heating (preheating) has been proposed.

For example, in the intermediate coating process, a water-based first colored paint is applied, and the coating film is preheated to adjust the coating film viscosity to 1 × 10 ⁶ mPa · sec (20 ° C., share rate 0.1 sec ⁻¹ ) or more. Then, in the base coating process, the aqueous second colored paint is applied, preheated or air blown to reduce the water content of the aqueous second colored paint to 10% by weight or less, and in the clear coating process, further clear paint is applied. It is proposed to paint (for example, refer to Patent Document 1).
Japanese Patent Laid-Open No. 2004-870

However, automobile body members include, for example, members such as door panels and engine compartments. In the case of door panels and the like, not only the appearance from the outside of the vehicle but also the appearance from the inside of the vehicle is important. It is necessary to paint both sides.
However, in each coating process of the above-described coating method, if the outer surface is painted after the inner surface of the door panel is painted, the water-based paint applied to the inner surface is dust (paint liquid) when the inner surface is painted. Droplets) which scatter on the outer surface and adhere to the outer surface. When the outer surface is painted, the adhered dust does not become the same as the water-based paint that is applied to the outer surface, and remains in a granular form as it is. As a result, there is a problem that an appearance defect is caused on the outer surface.

Further, in the engine room or the like, the appearance from the outside of the vehicle, that is, the appearance of the outer side is important, while the appearance of the inner side is not so important. Furthermore, even on the same inner surface, there are places where the appearance requirement level is high and low.
Accordingly, an object of the present invention is to provide a painting method capable of efficiently painting a member constituting an automobile body using a water-based paint, and reducing the appearance defect of the outer surface of the member. Is to provide.

In order to achieve the above object, the present invention provides a method for coating a member constituting an automobile body, comprising: an intermediate coating step in which the member is intermediate-coated with a water-based paint; and a solid concentration of the intermediate member in the wet state. Comprises a base coating process for base coating with 20 to 50% by weight of a water-based paint, a clear coating process for clear coating of the base-coated wet state member, and a baking process for baking the clear-coated member. in the base coating step, an inner coating step of coating the inner surface of the member, and an outer coating step of coating the outer surface of the member, the bell coating method, bell speed 25000～35000Min ^-1, shaving air The film thickness after baking is 1 under the coating conditions of a pressure of 1.0 to 2.0 kg / cm ² , a gun distance of 20 to 30 cm and a discharge amount of 150 to 350 mL. Within 20 minutes after performing the inner coating step so as to be 0 to 100 μm , bell rotation speed is 25000 to 35000 min ⁻¹ , shaving air pressure is 1.0 to 2.0 kg / cm ² , gun, distance 20 to 30 cm, in coating conditions of the discharge amount 150～350ML, the film thickness after baking has a feature to implement the outer coating step such that 10 to 100 [mu] m.

  According to this method, in the base coating process, the outer coating process is performed within 20 minutes after the inner coating process is performed. Then, when painting the inner surface, even if the water-based paint that is painted on the inner surface becomes dust (paint droplets) and scatters on the outer surface and adheres to the outer surface, the inner coating process is performed. Since the time until the start of the outer coating process is short afterwards, the moisture in the dust adhering to the outer surface is less likely to be absorbed into the intermediate-coated water-based paint or evaporated into the atmosphere. In the meantime, a water-based paint is applied to the outer surface. Therefore, the dust adhering to the outer surface can be applied to the water-based paint applied to the outer surface.

  As a result, in the base painting process, it is possible to efficiently coat the inner and outer surfaces of the member by a simple method that only manages the time from the execution of the inner coating process to the start of the outer coating process. However, it is possible to effectively prevent the outer surface from being uneven, and to reduce the appearance defect of the outer surface. In particular, in this method, it is possible to prevent the outer surface from being uneven in the base coating step, so that the outer surface finished by the subsequent clear coating can have an excellent smoothness.

Further, the present invention is a method for coating a member constituting an automobile body, wherein the member is intermediate-coated with an aqueous paint having a solid content concentration of 20 to 60% by weight , and the intermediate-coated wet state is applied. A base coating process for base-painting a member with a water-based paint, a clear coating process for clear-coating the base-painted wet member, and a baking process for baking the clear-coated member, An inner coating process for coating the inner surface of the member and an outer coating process for coating the outer surface of the member, and by a bell coating method, a bell rotation speed of 20000-30000 min ⁻¹ and a shaving air pressure of 0.5-1. .5kg / cm ^2, cancer distance 20 to 30 cm, in coating conditions of the discharge amount 150～350ML, the film thickness after baking, so that the 10~100μm After performing the inner coating step, within 10 minutes, the bell coating method, bell speed 20000～30000Min ^-1, shaving air pressure 0.5~1.5kg / cm ^2, cancer distance 20 to 30 cm, the discharge amount It includes a coating method in which the outer coating step is performed so that the film thickness after baking is 10 to 100 μm under a coating condition of 150 to 350 mL .

  According to this method, in the intermediate coating process, the outer coating process is performed within 10 minutes after the inner coating process is performed. Then, when painting the inner surface, even if the water-based paint that is painted on the inner surface becomes dust (paint droplets) and scatters on the outer surface and adheres to the outer surface, the inner coating process is performed. Since the time until the start of the execution of the outer coating process is short after that, the water-based paint is applied to the outer surface while the moisture in the dust adhering to the outer surface is less likely to evaporate into the atmosphere. Therefore, the dust adhering to the outer surface can be applied to the water-based paint applied to the outer surface.

As a result, in the intermediate coating process, it is possible to efficiently coat the inner and outer surfaces of the member by a simple method that only manages the time from the execution of the inner coating process to the start of the outer coating process. And it can prevent effectively that an unevenness | corrugation arises in an outer surface, and can reduce the external appearance defect of an outer surface .

Also, in the above coating method, between the base coating process and the intercoat step, first preheating step of preheating the intermediate been said member is provided, wherein the clear coating and the base coating step It is preferable that a second preheating step of preheating the base-coated member is provided between the steps.

By providing the first preheating step, it is possible to prevent a mixed layer between the wet paint film that has been intermediately coated and the water-based paint to be base-coated. In addition, by providing the second preheating step, it is possible to prevent a mixed layer between the base-coated wet coating and the clear coating .

Further, the present invention is a method for coating a member constituting a vehicle body, comprising: a coating step for coating the member with a water-based paint; and a baking step for baking the painted member, the coating step comprising: A solid coating process for solid-coating the member with a water-based paint having a solid content concentration of 20 to 70% by weight, the solid coating process including an inner coating process for coating the inner surface of the member, and an outer surface of the member An outer coating process for coating the surface, and by a bell coating method, a bell rotation speed of 20000 to 30000 min ⁻¹ , a shaving air pressure of 0.5 to 1.5 kg / cm ² , a gun distance of 20 to 30 cm, and a discharge amount of 200 to 400 mL. After performing the inner coating process so that the film thickness after baking is 10 to 100 μm under the coating conditions, the bell rotation is performed by the bell coating method within 20 minutes. Degrees 20000～30000Min ^-1, shaving air pressure 0.5~1.5kg / cm ^2, cancer distance 20 to 30 cm, in coating conditions of the discharge amount 200～400ML, the film thickness after baking, so that the 10~100μm Includes a coating method for performing the outer coating process .

  According to this method, in the coating process, the outer coating process is performed within 20 minutes after the inner coating process is performed. Then, when painting the inner surface, even if the water-based paint that is painted on the inner surface becomes dust (paint droplets) and scatters on the outer surface and adheres to the outer surface, the inner coating process is performed. Since the time until the start of the execution of the outer coating process is short after that, the water-based paint is applied to the outer surface while the moisture in the dust adhering to the outer surface is less likely to evaporate into the atmosphere. Therefore, the dust adhering to the outer surface can be applied to the water-based paint applied to the outer surface.

As a result, in the painting process, it is possible to efficiently coat the inner and outer surfaces of the member by a simple method that only manages the time from the implementation of the inner painting process to the start of the outer painting process. And it can prevent effectively that an unevenness | corrugation arises in an outer surface, and can reduce the external appearance defect of an outer surface. In particular, in this method, it is possible to prevent the outer surface from being uneven in the coating process, so that the appearance of the outer surface that is subsequently baked can be made to have an excellent smoothness.
In addition, a solid coating can realize a one-coating, one-bake coating method, which enables efficient coating.
Further, the present invention is a method for coating a member constituting an automobile body, comprising: a coating process for coating the member with a water-based paint; and a baking process for baking the painted member, wherein the coating process includes: An intermediate coating step in which a member is intermediate-coated with a water-based paint having a solid content concentration of 20 to 60% by weight, and a solid coating in which the wet-coated member is solid-coated with a water-based paint having a solid content concentration of 20 to 70% by weight. The intermediate coating step and the solid coating step include an inner coating step for coating the inner side surface of the member and an outer coating step for coating the outer side surface of the member. In the intermediate coating step, By bell coating method, bell rotation speed 20000-30000 min ⁻¹ , shaving air pressure 0.5-1.5 kg / cm ² , gun distance 20-30 cm, discharge amount 150-3 Under the coating conditions of 50 mL, after carrying out the inner coating process so that the film thickness after baking is 10 to 100 μm, within 10 minutes, the bell rotation speed is set to 20000 to 30000 min ⁻¹ , shaving air. Under the coating conditions of a pressure of 0.5 to 1.5 kg / cm ² , a gun distance of 20 to 30 cm, and a discharge amount of 150 to 350 mL, the outer coating process is performed so that the film thickness after baking becomes 10 to 100 μm, In the solid coating process, by the bell coating method, the bell rotation speed is 20000 to 30000 min ⁻¹ , the shaving air pressure is 0.5 to 1.5 kg / cm ² , the gun distance is 20 to 30 cm, and the discharge amount is 200 to 400 mL. After performing the inner coating process so that the film thickness after baking is 10 to 100 μm, the bell coating method is used within 20 minutes. , Bell speed 20000～30000Min ^-1, shaving air pressure 0.5~1.5kg / cm ^2, cancer distance 20 to 30 cm, in coating conditions discharge amount 200～400ML, film thickness after baking, 10 to 100 [mu] m A coating method for carrying out the outer coating process so that
According to this method, after the inner coating process is performed in the coating process, the outer coating process is performed within 10 minutes in the intermediate coating process and within 20 minutes in the solid coating process. Then, when painting the inner surface, even if the water-based paint that is painted on the inner surface becomes dust (paint droplets) and scatters on the outer surface and adheres to the outer surface, the inner coating process is performed. Since the time until the start of the execution of the outer coating process is short after that, the water-based paint is applied to the outer surface while the moisture in the dust adhering to the outer surface is less likely to evaporate into the atmosphere. Therefore, the dust adhering to the outer surface can be applied to the water-based paint applied to the outer surface.
As a result, in the painting process, it is possible to efficiently coat the inner and outer surfaces of the member by a simple method that only manages the time from the implementation of the inner painting process to the start of the outer painting process. And it can prevent effectively that an unevenness | corrugation arises in an outer surface, and can reduce the external appearance defect of an outer surface. In particular, in this method, it is possible to prevent the outer surface from being uneven in the coating process, so that the appearance of the outer surface that is subsequently baked can be made to have an excellent smoothness.
In addition, by applying a solid coating after the intermediate coating, a two-coating, one-bake coating method can be realized, and the coating can be performed efficiently.

Moreover, in this coating method, it is preferable that a preheating step for preheating the intermediate coated member is provided between the intermediate coating step and the solid coating step.
By providing the preheating step, it is possible to prevent a mixed layer between the wet coated film that has been intermediately coated and the water-based paint to be solid-coated.

  According to the coating method of the present invention, a member constituting an automobile body can be efficiently painted using a water-based paint, and the appearance defect of the outer surface of the member can be reduced.

FIG. 1 is a process diagram showing a coating process for carrying out a coating method by a three-coat one-bake method, which is an embodiment of the coating method of the present invention. Moreover, FIG. 2 is sectional drawing which shows one Embodiment of the coating film painted by the coating method shown in FIG. With the 3-coat 1-bake coating method, efficient coating can be realized.
This coating method is used for coating a member constituting an automobile body such as a door panel, and first, a member primed by electrodeposition coating is first subjected to intermediate coating in the intermediate coating booth 1 (intermediate coating step).

The intermediate coating booth 1 is provided on the inner intermediate coating booth 2 for coating the inner side surface (for example, door panel inner) of the member and on the downstream side of the inner intermediate coating booth 2 (the downstream side in the conveying direction of the members, the same applies hereinafter). And an outer intermediate coating booth 3 for coating an outer surface (for example, a door panel outer) of a member to be arranged.
The water-based paint used for the intermediate coating is not particularly limited, but a water-based or water-dispersible coating containing a water-soluble or water-dispersible resin component, a curing agent and a pigment is used.

  Examples of the resin component include a hydrophilic group (for example, a carboxyl group, a hydroxyl group, a methylol group, an amino group, a sulfonic acid group, and a polyoxyethylene bond) and a functional group that reacts with a curing agent (for example, a hydroxyl group). , Known aqueous resins such as acrylic resins, polyester resins, alkyd resins, epoxy resins and polyurethane resins. Preferably, an acrylic resin or a polyester resin having a carboxyl group is 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.
It does not restrict | limit especially as a hardening | curing agent, For example, a melamine resin, block polyisocyanate, etc. are mentioned. 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

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.
Moreover, it does not restrict | limit especially as a pigment, A normal coloring pigment and a metallic pigment are mentioned. Examples of the color pigment include titanium dioxide, zinc oxide, basic lead sulfate, calcium leadate, zinc phosphate, aluminum phosphate, zinc molybdate, calcium molybdate, bitumen, ultramarine blue, cobalt blue, copper phthalocyanine blue, indium Dunslon Blue, Yellow Lead, Synthetic Yellow Iron Oxide, Transparent Bengal (Yellow), Bismuth Vanadate, Titanium Yellow, Zinc Yellow (Zinc Yellow), Strontium Chromate, Cyanamide Lead, Monoazo Yellow, Monoazo Yellow, Disazo, Monoazo Yellow, Iso Indolinone yellow, metal complex salt azo yellow, quinophthalone yellow, isoindoline yellow, benzimidazolone yellow, red bean, transparent red bean (red), red lead, monoazo red, monoazo red, unsubstituted quinacridone red, azo lake (Mn salt) Quinacridone magenta, ansanthrone orange, dianslaquinonyl red, perylene maroon, quinacridone magenta, perylene red, diketopyrrolopyrrole chromium vermilion, basic lead chromate, chromium oxide, chlorinated phthalocyanine green, brominated phthalocyanine green, Examples include pyrazolone orange, benzimidazolone orange, dioxazine violet, and perylene violet. Examples of metallic pigments include aluminum powder, flaky aluminum oxide, pearl mica, and flaky mica. These pigments can be used alone or in combination of two or more.

The blending ratio of the pigment is usually 120 parts by weight or less, preferably 20 to 100 parts by weight with respect to 100 parts by weight of the resin component.
Further, the intermediate water-based paint preferably contains a dissociation catalyst for the blocking agent and 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-ethylhexinate and zinc octylate. Examples of the acid catalyst include phosphoric acid-based and sulfonic acid-based acid catalysts.

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.
In addition, in the intermediate coating water-based paint, if necessary, a light interference pigment, an extender pigment, a dispersant, an anti-settling agent, an organic solvent, a reaction accelerator (such as an organic tin compound), an antifoaming agent, a thickener, Known additives such as a rust preventive, an ultraviolet absorber, and a surface conditioner can be appropriately blended.

The intercoat aqueous paint, the components of the blended by known methods with water, by water-soluble or water dispersing a resin component, a solid content concentration of that 20 to 60 wt%, preferably, It is prepared to be 35 to 60% by weight.
Further, the coating method of the intercoat aqueous paints, bell coating method is used, the coating conditions are, bell speed 20000～30000Min ^-1, shaving air pressure 0.5~1.5kg / cm ^2, gun distance 20 -30 cm, discharge amount 150-350 mL.

Moreover, the coating film thickness of a middle coating water-based paint is 10-100 micrometers as a film thickness after baking, Preferably, it is 13-35 micrometers.
In this coating method, in the intermediate coating booth 1, first, the inner side surface (for example, door panel inner) of the member is coated by the above-described method in the inner intermediate coating booth 2 (inner coating process), and then the outer intermediate coating. In the painting booth 3, the outer surface of the member (for example, the door panel outer) is painted in the same manner as described above (outer painting step). Then, first, after coating the inner surface of the member in the inner intermediate coating booth 2, and then coating the outer surface of the member in the outer intermediate coating booth 3, the inner surface is coated on the inner surface when the inner surface is painted. On the other hand, the intermediate water-based paint applied to the outer surface is scattered as dust (paint droplets) and adheres to the outer surface. Painted.

Therefore, in this coating method, the time from the end of the coating of the inner surface of the member in the inner intermediate coating booth 2 to the start of the outer surface of the member in the outer intermediate coating booth 3 is within 10 minutes, preferably The process is controlled so that it is within 5 minutes, more preferably within 3 minutes.
By managing the process in this way, the time from the end of painting the inner surface to the start of painting the outer surface is short, so the moisture in the dust adhering to the outer surface is absorbed by the primed coating, or While it is unlikely to evaporate into the atmosphere, an intermediate water-based paint is applied to the outer surface. That is, the intermediate water-based paint is applied to the outer surface before the viscosity of the dust adhering to the outer surface (solid content concentration of dust) increases. Then, the dust adhering to the outer surface is compatible with and absorbed by the intermediate water-based paint applied to the outer surface, so that it can be adapted to the intermediate water-based paint applied to the outer surface.

As a result, in the intermediate coating process, it is possible to efficiently coat the inner surface and the outer surface of the member by a simple method that only manages the process from the end of the inner surface coating to the start of the outer surface coating. And it can prevent effectively that an unevenness | corrugation arises in an outer surface, and can reduce the external appearance defect of an outer surface.
Moreover, the water evaporation possible amount (difference in absolute humidity with respect to the saturated water vapor amount) in the intermediate coating booth 1 (including the inner intermediate coating booth 2 and the outer intermediate coating booth 3) is 2 to 11 g / kg, preferably 3 to 3. Control to 6 g / kg. If the amount of water evaporation in the intermediate coating booth 1 is lower than 2 g / kg, sagging may occur at the time of coating, and if it is higher than 11 g / kg, the finished appearance may be deteriorated.

In addition, the temperature in the intermediate coating booth 1 (including the inner intermediate coating booth 2 and the outer intermediate coating booth 3) is controlled to 20 to 30 ° C., for example.
In this coating method, the intermediate-coated member is preheated in the first hot air drying furnace 4 (first preheating step).
The first hot air drying furnace 4 includes a first hot air zone 5, a second hot air zone 6 disposed downstream of the first hot air zone 5, and a first cooling zone disposed downstream of the second hot air zone 6. 7.

  In the first hot air drying furnace 4, the intermediately coated member is first preheated in the first hot air zone 5 (upstream preheating step). In the first hot air zone 5, the member is preheated by hot air. The preheating conditions include, for example, a hot air blowing temperature of 45 to 100 ° C., preferably 65 ° C. to 90 ° C., a hot air blowing speed of 0.3 to 10.0 m / s, The wind speed on the coated surface (the surface of the member) is 1 to 3 m / s, the distance from the hot air outlet to the coated surface is 20 to 50 cm, and the preheating time is 0.5 to 1 .5 minutes. The hot air blowing temperature in the first hot air zone 5 is set lower than the hot air blowing temperature in the second hot air zone 6 described below.

  When the blowing temperature of hot air is lower than 45 ° C., the solid content concentration of the intermediate water-based paint may be low, resulting in a mixed layer or armpit. On the other hand, when the temperature is higher than 100 ° C., the solid content concentration of the intermediate water-based paint may increase rapidly and the fluidity of the coating film may decrease. On the other hand, if the blowing speed of the hot air is lower than 0.3 m / s, the solid content concentration of the intermediate water-based paint may be low, resulting in a mixed layer or armpit. Moreover, when higher than 10.0 m / s, only the surface dries, the fluidity | liquidity of a coating film may fall or it may cause a crack.

Note that the temperature and humidity in the first hot air zone 5 are controlled to, for example, a temperature of 20 to 30 ° C. and a water evaporable amount of 10 to 25 g / kg.
The member preheated in the first hot air zone 5 is then preheated in the second hot air zone 6 (downstream preheating step). In the second hot air zone 6, the member is preheated by hot air. The preheating conditions include, for example, a hot air blowing temperature of 45 to 100 ° C., preferably 70 to 100 ° C., a hot air blowing speed of 0.3 to 10.0 m / s, The wind speed on the coating surface (the surface of the member) is 1 to 3 m / s, the distance from the hot air blowing port to the coating surface is 20 to 50 cm, and the preheating time is 0.5 to 1. 5 minutes. The hot air blowing temperature in the second hot air zone 6 is set higher than the hot air blowing temperature in the first hot air zone 5.

  When the blowing temperature of hot air is lower than 45 ° C., the solid content concentration of the intermediate water-based paint may be low, resulting in a mixed layer or armpit. On the other hand, when the temperature is higher than 100 ° C., energy consumption for blowing hot air increases. On the other hand, if the blowing speed of the hot air is lower than 0.3 m / s, the solid content concentration of the intermediate water-based paint may be low, resulting in a mixed layer or armpit. Moreover, when higher than 10.0 m / s, only the surface dries, the fluidity | liquidity of a coating film may fall or it may cause a crack.

The temperature and humidity in the second hot air zone 6 are controlled to, for example, a temperature of 20 to 30 ° C. and a water evaporation rate of 10 to 25 g / kg.
Then, the member preheated in the second hot air zone 6 is then cooled in the first cooling zone 7 (cooling step). In the first cooling zone 7, the member is cooled by cold air. The cooling conditions are, for example, a cold air blowing temperature of 15 to 23 ° C., a cold air blowing speed of 10 m / s or less, and a distance from the cold air blowing port to the coating surface of 20 to 50 cm. Yes, the cooling time is 0.5 to 1.3 minutes. In such cooling, the temperature of the member is preferably cooled to 45 ° C. or lower, more preferably 40 ° C. or lower.

The intermediate water-based paint applied to the inner and outer surfaces of the member by the preliminary heating in the first hot air drying furnace 4 is a wet coating film, that is, the intermediate coating layer 21 (see FIG. 2). Form.
In addition, the elution rate (water elution rate) with respect to water of the coating film of the intermediate water-based paint forming the intermediate coating layer 21 is adjusted to 55% by weight or less. If the water elution rate of the coating film of the intermediate coating is 55% by weight or less, a mixed layer between the intermediate coating layer 21 and the base layer 22 can be prevented. In addition, in order to prepare so that a water elution rate may be 55 weight% or less, it is suitable to add a urethane emulsion etc. in an intermediate-coat water-based coating material, for example. Further, in the first hot air zone 5, after heating for 1.3 minutes with 75 ° C. hot air so that the wind speed of the surface of the member becomes 0.5 to 2.0 m / s, the second hot air zone 6 is entered. In addition, it is also preferable to heat the mixture with hot air at 80 ° C. for 1.3 minutes.

In addition, the water elution rate of the coating film of the intermediate coating material can be measured as follows, for example. That is,
Operation 1:
(1) An intermediate water-based paint is applied to an aluminum foil with a thickness of 25 μm, and this is approximately the same temperature as the heating temperature (hot air blowing temperature) in the primary preheating step in the drying furnace (for example, 5 at 80 ° C. Minutes). Then, after cooling this to room temperature in a desiccator, the total weight Wb of the aluminum foil and the intermediate coating water-based paint is measured.
(2) The preheated aluminum foil and intermediate coating are further heated at substantially the same temperature as the baking temperature (eg, 140 ° C. for 60 minutes), and then allowed to cool to room temperature in a desiccator. Thereafter, the total weight Wc of the aluminum foil and the intermediate water-based paint is measured.
(3) The weight Wa of the aluminum foil used above is measured.
Operation 2:
(1) An intermediate water-based paint is applied to an aluminum foil with a thickness of 25 μm, and this is approximately the same temperature as the heating temperature (hot air blowing temperature) in the primary preheating step in the drying furnace (for example, 5 at 80 ° C. Minutes). Then, after cooling this to room temperature in a desiccator, the total weight Wd of the aluminum foil and the intermediate coating water-based paint is measured.
(2) The preheated aluminum foil and intermediate coating are immersed in pure water or deionized water at 30 ° C. for a predetermined time (for example, 60 minutes). After taking out, it is heated at a temperature almost the same as the baking temperature (for example, 140 ° C. for 60 minutes). To do.
(3) The weight Wf of the aluminum foil used above is measured.
Calculation:
(1) The solid content weight after preheating is calculated from the following formula.

Solid weight after preheating A = (Wd−Wf) (Wc−Wa) / (Wb−Wa)
(2) The water elution weight is calculated from the following formula.
Water elution weight B = (Wd−Wf) (Wc−Wa) / (Wb−Wa) − (We−Wf)
(3) The water elution rate is calculated from the following formula.
Water elution rate = water elution weight B / preheated solid content weight A × 100 (%)
In such preheating in the first hot air drying furnace 4, first, in the first hot air zone 5, the member is preheated at a lower temperature, and then in the second hot air zone 6, the member is heated to a higher temperature. Is preheated. Therefore, in the first hot air zone 5, the fluidity of the coated intermediate coating is ensured, and after the coating film having a uniform thickness is formed, the base layer 22 (next formed in the second hot air zone 6 ( It is possible to form a coating film capable of preventing the occurrence of mixed layers and cracks with the case of FIG. As a result, the intermediate coating water-based paint can be efficiently preheated, and good properties can be imparted to the preheated coating film.

Next, in this coating method, base coating is performed in the base coating booth 8 (base coating process).
The base painting booth 8 includes an inner base painting booth 9 for painting the inner side surface (for example, door panel inner) of the member and an outer side surface (for example, door panel outer) of the member disposed on the downstream side of the inner base painting booth 9. And an outer base painting booth 10 for painting.

  The water-based paint used for the base coating is not particularly limited, and is composed of the same components as the intermediate-coat water-based paint, and a base water-based paint containing a water-soluble or water-dispersible resin component, a curing agent and a pigment 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 having a carboxyl group or a hydroxyl group, a crosslinking agent such as a block polyisocyanate, a melamine resin, or a urea resin, a pigment, and other It can be prepared by dissolving or dispersing the additive in water.

  For example, if a metallic pigment such as aluminum powder, flaky aluminum oxide, pearl mica, or flaky mica is used as the pigment, a metallic or pearly coating film can be formed. The pigment content in the base water-based paint is such that the coating film formed by the base coating has transparency and the color of the intermediate coating layer 21 can be visually recognized through the coating film. The

The base aqueous paint is prepared so that the solid content concentration thereof is 20 to 50% by weight, preferably 25 to 45% by weight.
The base water-based paint is prepared so that the contact angle with respect to the intermediate coating layer 21 is 40 ° or more, preferably 55 ° or more. If the contact angle with respect to the intermediate coating layer 21 of the base aqueous paint is 40 ° or more, a mixed layer between the intermediate coating layer 21 and the base layer 22 (see FIG. 2) can be prevented. In order to prepare the contact angle to be 40 ° or more, for example, it is preferable to add a surface conditioner or the like. Further, in the first hot air zone 5, after heating for 1.3 minutes with 75 ° C. hot air so that the wind speed of the surface of the member becomes 0.5 to 2.0 m / s, the second hot air zone 6 is entered. In addition, it is also preferable to heat the mixture with hot air at 80 ° C. for 1.3 minutes.

In addition, a contact angle can be calculated | required by dripping a base aqueous coating material on the surface of the intermediate coating layer 21, and measuring the inclination angle of the droplet with a commercially available contact angle meter.
Further, the method for coating a base aqueous paint, bell coating method is used, the coating conditions are, bell speed 25000～35000Min ^-1, shaving air pressure 1.0~2.0kg / cm ^2, gun distance 20 -30 cm, discharge amount 150-350 mL.

Further, the coating thickness of the base aqueous paint, the film thickness after baking, 1 0～100Myuemu, preferably from 10 to 25 [mu] m.
In this painting method, first, in the base painting booth 8, after the inner side surface (for example, door panel inner) of the member is painted by the above-described method in the inner base painting booth 9 (inner painting step), then, the outer side. In the base painting booth 10, the outer side surface (for example, door panel outer) of the member is painted by the same method as described above (outer painting step). Thus, after first painting the inner surface of the member in the inner base painting booth 9, and then painting the outer surface of the member in the outer base painting booth 10, when the inner surface is painted, On the other hand, the base water-based paint to be painted is scattered as dust (paint droplets) on the outer surface and adheres to the outer surface. Painted.

Therefore, in this coating method, the period from the end of the coating of the inner surface of the member in the inner base coating booth 9 to the start of the coating of the outer surface of the member in the outer base coating booth 10 is within 20 minutes, preferably The process is controlled to be within 15 minutes, more preferably within 10 minutes.
By managing the process in this way, since the time from the end of painting the inner surface to the start of painting the outer surface is short, moisture in the dust adhering to the outer surface is absorbed by the wet intermediate coating layer 21, Alternatively, the base water-based paint is applied to the outer surface while it hardly evaporates into the atmosphere. That is, the base water-based paint is applied to the outer surface before the viscosity of dust adhering to the outer surface (solid content concentration of dust) increases. As a result, the dust adhering to the outer surface is compatible with and absorbed by the base aqueous paint applied to the outer surface, so that it can be adapted to the base aqueous paint applied to the outer surface.

As a result, in the base painting process, it is possible to efficiently coat the inner and outer surfaces of a member by a simple method that only manages the process from the end of painting of the inner surface to the start of painting of the outer surface. However, it is possible to effectively prevent the outer surface from being uneven, and to reduce the appearance defect of the outer surface.
Further, the water evaporable amount (difference in absolute humidity with respect to the saturated water vapor amount) in the base coating booth 8 (including the inner base coating booth 9 and the outer base coating booth 10) is 2 to 11 g / kg, preferably 3 Manage to ~ 6 g / kg. If the amount of water vapor that can be evaporated in the base coating booth 8 is lower than 2 g / kg, sagging may occur at the time of coating, and if it is higher than 11 g / kg, the finished appearance may be deteriorated.

In addition, the temperature in the base coating booth 8 (including the inner base coating booth 9 and the outer base coating booth 10) is controlled to, for example, 20 to 30 ° C.
In this coating method, the base-coated member is preheated in the second hot air drying furnace 11 (second preheating step).
The second hot air drying furnace 11 includes a third hot air zone 12, a fourth hot air zone 13 disposed downstream of the third hot air zone 12, and a second cooling zone disposed downstream of the second hot air zone 6. 14.

  In the second hot air drying furnace 11, the base-coated member is first preheated in the third hot air zone 12 (upstream preheating step). In the third hot air zone 12, the member is preheated with hot air. The preheating conditions include, for example, a hot air blowing temperature of 45 to 100 ° C., preferably 65 to 90 ° C., a hot air blowing speed of 0.3 to 10.0 m / s, The wind speed on the coating surface (the surface of the member) is 1 to 3 m / s, the distance from the hot air outlet to the coating surface is 20 to 50 cm, and the preheating time is 0.5 to 1. 5 minutes. The hot air blowing temperature in the third hot air zone 12 is set lower than the hot air blowing temperature in the fourth hot air zone 13 described below.

  When the hot air blowing temperature is lower than 45 ° C., the solid content concentration of the base water-based paint is low, which may result in mixed layers or cracks. On the other hand, when the temperature is higher than 100 ° C., the solid content concentration of the base water-based paint may rapidly increase and the fluidity of the coating film may be lowered. On the other hand, if the blowing speed of hot air is lower than 0.3 m / s, the solid content concentration of the base water-based paint may be low, resulting in a mixed layer or armpit. Moreover, when higher than 10.0 m / s, only the surface dries, the fluidity | liquidity of a coating film may fall or it may cause a crack.

The temperature and humidity in the third hot air zone 12 are controlled to, for example, a temperature of 20 to 30 ° C. and a water evaporation rate of 10 to 25 g / kg.
The member preheated in the third hot air zone 12 is then preheated in the fourth hot air zone 13 (downstream preheating step). In the fourth hot air zone 13, the member is preheated by hot air. The preheating conditions include, for example, a hot air blowing temperature of 45 to 100 ° C., preferably 70 to 100 ° C., a hot air blowing speed of 0.3 to 10.0 m / s, The wind speed on the coating surface (the surface of the member) is 1 to 3 m / s, the distance from the hot air blowing port to the coating surface is 20 to 50 cm, and the preheating time is 0.5 to 1. 5 minutes. The hot air blowing temperature in the fourth hot air zone 13 is set higher than the hot air blowing temperature in the third hot air zone 12.

  When the hot air blowing temperature is lower than 45 ° C., the solid content concentration of the base water-based paint is low, which may result in mixed layers or cracks. On the other hand, when the temperature is higher than 100 ° C., energy consumption for blowing hot air increases. On the other hand, if the blowing speed of hot air is lower than 0.3 m / s, the solid content concentration of the base water-based paint may be low, resulting in a mixed layer or armpit. Moreover, when higher than 10.0 m / s, only the surface dries, the fluidity | liquidity of a coating film may fall or it may cause a crack.

The temperature and humidity in the fourth hot air zone 13 are controlled to, for example, a temperature of 20 to 30 ° C. and a water evaporable amount of 10 to 25 g / kg.
The member preheated in the fourth hot air zone 13 is then cooled in the second cooling zone 14 (cooling step). In the fourth cooling zone 14, the member is cooled by cold air. The cooling conditions are, for example, a cold air blowing temperature of 15 to 23 ° C., a cold air blowing speed of 10 m / s or less, and a distance from the cold air blowing port to the coating surface of 20 to 50 cm. Yes, the cooling time is 0.5 to 1.3 minutes. In such cooling, the temperature of the member is preferably cooled to 45 ° C. or lower, more preferably 40 ° C. or lower.

The base aqueous coating material applied to the inner side surface and the outer side surface of the member by such preheating in the second hot air drying furnace 11 forms a wet coating film, that is, the base layer 22.
In such preheating in the second hot air drying furnace 11, first, in the third hot air zone 12, the member is preheated at a lower temperature, and then in the fourth hot air zone 13, the member is preliminarily heated at a higher temperature. Heated. Therefore, in the third hot air zone 12, the fluidity of the coated base aqueous paint is ensured, and after the coating film having a uniform thickness is formed, the clear layer 23 ( It is possible to form a coating film capable of preventing the occurrence of mixed layers and cracks with the case of FIG. As a result, the base aqueous paint can be efficiently preheated, and good properties can be imparted to the preheated coating film.

Next, in this painting method, clear painting is performed in the clear painting booth 15 (clear painting process).
The clear painting booth 15 includes an inner clear painting booth 16 for painting the inner side surface (for example, door panel inner) of the member, and an outer side surface (for example, door panel outer) of the member disposed on the downstream side of the inner clear painting booth 16. And an outer clear painting booth 17 for painting.

  The paint used for clear coating is not particularly limited, and a known clear paint is used. For example, resin components such as acrylic resin, polyester resin, alkyd resin, urethane resin, and epoxy resin, crosslinking agents such as block polyisocyanate, melamine resin, and urea resin, and other additives are dissolved in an organic solvent or water. Alternatively, it can be prepared by dispersing.

In addition, the clear paint can contain a base color pigment or a metallic pigment as long as it does not impair transparency, and can further contain extender pigments, ultraviolet absorbers and the like as appropriate.
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. 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 painting method, first, in the clear painting booth 15, after painting the inner side surface (for example, the door panel inner) of the member by the above-described method in the inner clear painting booth 16, then in the outer clear painting booth 17. Similarly, the outer surface (for example, door panel outer) of the member is painted by the above-described method.

In this coating method, the clear-coated member is baked in the baking furnace 18 (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 about 160 ° C., and the baking time is about 20 to 40 minutes.
As a result, as shown in FIG. 2, a coating film in which the intermediate coating layer 21, the base layer 22 and the clear layer 23 are laminated on the undercoat layer 20 is formed.

As described above, the three-layer coating film formed in this way is prevented from having irregularities on the outer surface in each of the intermediate coating layer 21, the base layer 22 and the clear layer 23. It has a good appearance.
In the above description, in the intermediate coating booth 1 and the base coating booth 8, first, the inner surface of the member (for example, door panel inner) is painted, and then the outer surface of the member (for example, door panel outer) is painted. For example, in the intermediate coating booth 1 and the base coating booth 8, as shown in the process diagram shown in FIG. 3, first, the outer side surface (for example, door panel outer) of the member is coated, and then the inner side surface (for example, door panel) of the member. Inner) may be painted.

That is, in FIG. 3, although it is not one embodiment of the coating method of the present invention, the intermediate coating booth 1 includes an outer intermediate coating booth 3 for coating the outer side surface (for example, door panel outer) of the member, and an outer intermediate coating booth. 3 is provided with an inner intermediate coating booth 2 for coating an inner surface (for example, door panel inner) of a member disposed on the downstream side. The base painting booth 8 includes an outer base painting booth 10 for painting an outer side surface of the member (for example, a door panel outer), and an inner side surface (for example, a door panel) of a member disposed on the downstream side of the outer base painting booth 10. And an inner base painting booth 9 for painting the inner).

In FIG. 3, the same components as those described above are denoted by the same reference numerals as those described above, and the description thereof is omitted.
In this coating method, first, in the intermediate coating booth 1, after coating the outer side surface (for example, the door panel outer) of the member by the above-described method in the outer intermediate coating booth 3, the inner intermediate coating booth. 2, the inner side surface (for example, door panel inner) of the member is painted by the above-described method (inner coating process).

  In this way, after coating the outer surface of the member in the outer intermediate coating booth 3, when the inner surface of the member is painted in the inner intermediate coating booth 2, the intermediate coating is applied to the outer surface when the outer surface is painted. The water-based paint is scattered as dust (paint droplets) on the inner surface and adheres to the inner surface. However, since the outer surface is not required to be as strict as the outer surface, the intermediate water-based paint can be applied to the inner surface without any harmful effects.

As a result, in the intermediate coating process, it is efficient by a simple method that only manages the order of the coating of the outer surface of the member in the outer intermediate coating booth 3 and the coating of the inner surface of the member in the inner intermediate coating booth 2. In addition, it is possible to effectively coat the inner surface and the outer surface of the member, and to effectively prevent the outer surface from being uneven, and to reduce the appearance defect of the outer surface.
Further, in this painting method, after the outer side surface (for example, door panel outer) of the member is painted in the base coating booth 8 by the above-described method in the outer base coating booth 10 (outer coating step), In the base painting booth 9, the inner surface (for example, door panel inner) of the member is painted by the above-described method (inner painting process).

  In this way, after the outer surface of the member is first painted in the outer base painting booth 10, and then the outer surface of the member is painted in the inner base painting booth 9, when the outer surface is painted, The base water-based paint to be painted is scattered as dust (paint droplets) on the inner surface and adheres to the inner surface. However, since the outer surface is not required to be as strict as the outer surface, the base water-based paint can be applied to the inner surface without any harmful effects.

  As a result, in the base coating process, the efficiency is improved by a simple method that only manages the order of the coating of the outer surface of the member at the outer base coating booth 10 and the coating of the inner surface of the member at the inner base coating booth 9. In particular, it is possible to effectively coat the inner side surface and the outer side surface of the member, while effectively preventing the outer side surface from being uneven, and to reduce the appearance defect of the outer side surface.

  3, in both the intermediate coating booth 1 and the base coating booth 8, first, the outer side surface (for example, door panel outer) of the member is painted, and then the inner side surface (for example, door panel inner) of the member. In the booth of either the intermediate coating booth 1 or the base coating booth 8, first, after coating the outer surface of the member (for example, the door panel outer), as shown in the process diagram of FIG. After painting the inner surface of the member (for example, door panel inner), and in the other booth, as shown in the process diagram of FIG. The outer surface of the member (for example, the door panel outer) may be painted.

  Further, when the member is an engine roof panel or the like, the appearance from the outside of the vehicle, that is, the appearance of the outer side is important, while the appearance of the inner side is not so important. In the intermediate coating booth 1 and the base coating booth 8, as shown in the process diagram of FIG. 4, the inner side surface (for example, engine roof panel inner) of the member is not painted, and the outer side surface (for example, engine roof) of the member is coated. Only the panel outer) may be painted.

That is, in FIG. 4, although it is not one embodiment of the coating method of the present invention, the intermediate coating booth 1 includes only the outer intermediate coating booth 3 for coating the outer surface of the member (for example, the engine roof panel outer). Yes. The base painting booth 8 includes only the outer base painting booth 10 for painting the outer surface of the member (for example, the engine roof panel outer).
In FIG. 4, the same components as those described above are denoted by the same reference numerals as those described above, and the description thereof is omitted.

In this coating method, in the intermediate coating booth 1, only the outer side surface (for example, the engine roof panel outer) of the member is coated in the outer intermediate coating booth 3 by the method described above.
Further, in this painting method, in the base painting booth 8, only the outer side surface (for example, the engine roof panel outer) of the member is painted in the outer base painting booth 10 by the method described above.

  In this method, as a member to which this method is applied, a member that does not require the inner surface appearance as much as the outer surface appearance, such as an engine roof panel, is selected. Even if the water-based paint to be applied is scattered as dust (paint droplets) on the inner surface and adheres to the inner surface, the inner surface is not required to have the same appearance as the outer surface. It can be finished by clear painting.

As a result, while the process of coating the inner side surface of the member in the intermediate coating process can be omitted, it is possible to effectively prevent the outer surface from being uneven, and to reduce the appearance defect of the outer side surface.
In the above description, with reference to FIGS. 1 to 4, the coating method by the 3-coat 1-bake method has been described as one embodiment of the coating method of the present invention. Next, another coating method of the present invention is described. As an embodiment, a coating method by a 2-coat 1-bake method and a 1-coat 1-bake method in solid coating in which the clear coating process is omitted will be described. Efficient coating can be realized by the 2-coat 1-bake method or the 1-coat 1-bake method.

FIG. 5 is a process diagram showing a painting process for carrying out a painting method by a 2-coat 1-bake method. Moreover, FIG. 6 is sectional drawing which shows one Embodiment of the coating film painted by the coating method shown in FIG.
The coating method by the two-coat one-bake method is used for painting a member constituting an automobile body such as a door panel. First, a member primed by electrodeposition coating is first baked, and then first in the intermediate coating booth 24. Apply (intermediate coating process).

The intermediate coating booth 24 is provided on the inner intermediate coating booth 25 for coating the inner side surface of the member (for example, the door panel inner) and on the downstream side of the inner intermediate coating booth 25 (the downstream side in the conveying direction of the members, the same applies hereinafter). And an outer intermediate coating booth 26 for coating an outer surface (for example, a door panel outer) of a member to be arranged.
The water-based paint used for the intermediate coating is not particularly limited, and the same water-based paint as that used in the above-described coating method by the 3-coat 1-bake method is used. In addition, the coating method of the intermediate water-based paint is the same as the coating method used in the above-described coating method by the 3-coat 1-bake method. Further, the coating film thickness of the intermediate water-based paint is, for example, 10 to 100 μm, preferably 13 to 35 μm as the film thickness after baking.

  In this coating method, the inner coating booth 24 first coats the inner surface (for example, the door panel inner) of the member by the above-described method in the inner coating booth 25 (inner coating process), and then the outer coating. In the painting booth 26, the outer side surface (for example, door panel outer) of the member is painted in the same manner as described above (outer painting step). In this way, first, after coating the inner surface of the member in the inner intermediate coating booth 25, and then coating the outer surface of the member in the outer intermediate coating booth 26, when the inner surface is painted, On the other hand, the intermediate water-based paint applied to the outer surface is scattered as dust (paint droplets) and adheres to the outer surface. Painted.

Therefore, in this coating method, the time from the end of the coating of the inner surface of the member in the inner intermediate coating booth 25 to the start of the coating of the outer surface of the member in the outer intermediate coating booth 26 is within 10 minutes, preferably The process is controlled so that it is within 5 minutes, more preferably within 3 minutes.
By managing the process in this way, the time from the end of painting the inner surface to the start of painting the outer surface is short, so the moisture in the dust adhering to the outer surface is absorbed by the primed coating, or While it is unlikely to evaporate into the atmosphere, an intermediate water-based paint is applied to the outer surface. That is, the intermediate water-based paint is applied to the outer surface before the viscosity of the dust adhering to the outer surface (solid content concentration of dust) increases. Then, the dust adhering to the outer surface is compatible with and absorbed by the intermediate water-based paint applied to the outer surface, so that it can be adapted to the intermediate water-based paint applied to the outer surface.

As a result, in the intermediate coating process, it is possible to efficiently coat the inner surface and the outer surface of the member by a simple method that only manages the process from the end of the inner surface coating to the start of the outer surface coating. And it can prevent effectively that an unevenness | corrugation arises in an outer surface, and can reduce the external appearance defect of an outer surface.
Further, the water evaporable amount (difference in absolute humidity with respect to the saturated water vapor amount) in the intermediate coating booth 24 (including the inner intermediate coating booth 25 and the outer intermediate coating booth 26) is 2 to 11 g / kg, preferably 3 to 3. Control to 6 g / kg. If the water evaporation possible amount in the intermediate coating booth 24 is lower than 2 g / kg, sagging may occur at the time of coating, and if it is higher than 11 g / kg, the finished appearance may be deteriorated.

The temperature in the intermediate coating booth 24 (including the inner intermediate coating booth 25 and the outer intermediate coating booth 26) is controlled to, for example, 20 to 30 ° C.
In this coating method, the intermediately coated member is preheated in the first hot air drying furnace 27 (preheating step).
The first hot air drying furnace 27 includes a first hot air zone 28, a second hot air zone 29 disposed downstream of the first hot air zone 28, and a first cooling zone disposed downstream of the second hot air zone 29. 30.

  In the first hot air drying furnace 27, the intermediately coated member is first preheated in the first hot air zone 28 (upstream preheating step). In the first hot air zone 28, the member is preheated by hot air. The preheating conditions include, for example, a hot air blowing temperature of 45 to 100 ° C., preferably 65 ° C. to 90 ° C., a hot air blowing speed of 0.3 to 10.0 m / s, The wind speed on the coated surface (the surface of the member) is 1 to 3 m / s, the distance from the hot air outlet to the coated surface is 20 to 50 cm, and the preheating time is 0.5 to 1 .5 minutes. The hot air blowing temperature in the first hot air zone 28 is set lower than the hot air blowing temperature in the second hot air zone 29 described below.

  When the blowing temperature of hot air is lower than 45 ° C., the solid content concentration of the intermediate water-based paint may be low, resulting in a mixed layer or armpit. On the other hand, when the temperature is higher than 100 ° C., the solid content concentration of the intermediate water-based paint may increase rapidly and the fluidity of the coating film may decrease. On the other hand, if the blowing speed of the hot air is lower than 0.3 m / s, the solid content concentration of the intermediate water-based paint may be low, resulting in a mixed layer or armpit. Moreover, when higher than 10.0 m / s, only the surface dries, the fluidity | liquidity of a coating film may fall or it may cause a crack.

The temperature and humidity in the first hot air zone 28 are controlled to, for example, a temperature of 20 to 30 ° C. and a water evaporation rate of 10 to 25 g / kg.
The member preheated in the first hot air zone 28 is then preheated in the second hot air zone 29 (downstream preheating step). In the second hot air zone 29, the member is preheated by hot air. The preheating conditions include, for example, a hot air blowing temperature of 45 to 100 ° C., preferably 70 to 100 ° C., a hot air blowing speed of 0.3 to 10.0 m / s, The wind speed on the coating surface (the surface of the member) is 1 to 3 m / s, the distance from the hot air blowing port to the coating surface is 20 to 50 cm, and the preheating time is 0.5 to 1. 5 minutes. The hot air blowing temperature in the second hot air zone 29 is set higher than the hot air blowing temperature in the first hot air zone 28.

  When the blowing temperature of hot air is lower than 45 ° C., the solid content concentration of the intermediate water-based paint may be low, resulting in a mixed layer or armpit. On the other hand, when the temperature is higher than 100 ° C., energy consumption for blowing hot air increases. On the other hand, if the blowing speed of the hot air is lower than 0.3 m / s, the solid content concentration of the intermediate water-based paint may be low, resulting in a mixed layer or armpit. Moreover, when higher than 10.0 m / s, only the surface dries, the fluidity | liquidity of a coating film may fall or it may cause a crack.

The temperature and humidity in the second hot air zone 29 are controlled to, for example, a temperature of 20 to 30 ° C. and a water evaporable amount of 10 to 25 g / kg.
The member preheated in the second hot air zone 29 is then cooled in the first cooling zone 30 (cooling step). In the first cooling zone 30, the member is cooled by cold air. The cooling conditions are, for example, a cold air blowing temperature of 15 to 23 ° C., a cold air blowing speed of 10 m / s or less, and a distance from the cold air blowing port to the coating surface of 20 to 50 cm. Yes, the cooling time is 0.5 to 1.3 minutes. In such cooling, the temperature of the member is preferably cooled to 45 ° C. or lower, more preferably 40 ° C. or lower.

The intermediate water-based paint applied to the inner and outer surfaces of the member by the preheating in the first hot air drying furnace 27 is a wet coating film, that is, the intermediate coating layer 41 (see FIG. 6). Form.
In such preheating in the first hot air drying furnace 27, first, in the first hot air zone 28, the member is preheated at a lower temperature, and then in the second hot air zone 29, the member is heated to a higher temperature. Is preheated. Therefore, in the first hot air zone 28, the fluidity of the applied intermediate water-based paint is ensured, and after the coating film having a uniform thickness is formed, the solid layer 42 ( It is possible to form a coating film that can prevent the occurrence of mixed layers and cracks with FIG. As a result, the intermediate coating water-based paint can be efficiently preheated, and good properties can be imparted to the preheated coating film.

Next, in this coating method, solid coating is performed in the solid coating booth 31 (solid coating process).
The solid painting booth 31 includes an inner solid painting booth 32 for painting the inner side surface (for example, door panel inner) of the member, and an outer side surface (for example, door panel outer) of the member disposed on the downstream side of the inner solid painting booth 32. And an outer solid painting booth 33 for painting.

The water-based paint used for solid coating is not particularly limited, but a solid water-based paint containing a water-soluble or water-dispersible resin component, a curing agent and a pigment is used.
Examples of the resin component include a hydrophilic group (for example, a carboxyl group, a hydroxyl group, a methylol group, an amino group, a sulfonic acid group, and a polyoxyethylene bond) and a functional group that reacts with a curing agent (for example, a hydroxyl group). , Known aqueous resins such as acrylic resins, polyester resins, alkyd resins, epoxy resins and polyurethane resins. Preferably, an acrylic resin or a polyester resin having a carboxyl group is 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.
It does not restrict | limit especially as a hardening | curing agent, For example, a melamine resin, block polyisocyanate, etc. are mentioned. 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

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.
Moreover, it does not restrict | limit especially as a pigment, A normal coloring pigment and a metallic pigment are mentioned. Examples of the color pigment include titanium dioxide, zinc oxide, basic lead sulfate, calcium leadate, zinc phosphate, aluminum phosphate, zinc molybdate, calcium molybdate, bitumen, ultramarine blue, cobalt blue, copper phthalocyanine blue, indium Dunslon Blue, Yellow Lead, Synthetic Yellow Iron Oxide, Transparent Bengal (Yellow), Bismuth Vanadate, Titanium Yellow, Zinc Yellow (Zinc Yellow), Strontium Chromate, Cyanamide Lead, Monoazo Yellow, Monoazo Yellow, Disazo, Monoazo Yellow, Iso Indolinone yellow, metal complex salt azo yellow, quinophthalone yellow, isoindoline yellow, benzimidazolone yellow, red bean, transparent red bean (red), red lead, monoazo red, monoazo red, unsubstituted quinacridone red, azo lake (Mn salt) Quinacridone magenta, ansanthrone orange, dianslaquinonyl red, perylene maroon, quinacridone magenta, perylene red, diketopyrrolopyrrole chromium vermilion, basic lead chromate, chromium oxide, chlorinated phthalocyanine green, brominated phthalocyanine green, Examples include pyrazolone orange, benzimidazolone orange, dioxazine violet, and perylene violet. Examples of metallic pigments include aluminum powder, flaky aluminum oxide, pearl mica, and flaky mica. These pigments can be used alone or in combination of two or more.

The blending ratio of the pigment is usually 120 parts by weight or less, preferably 20 to 100 parts by weight with respect to 100 parts by weight of the resin component.
The solid water-based paint 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-ethylhexinate and zinc octylate. Examples of the acid catalyst include phosphoric acid-based and sulfonic acid-based acid catalysts.

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.
In addition, the solid water-based paint includes a light interference pigment, an extender pigment, a dispersant, an anti-settling agent, an organic solvent, a reaction accelerator (for example, an organic tin compound), an antifoaming agent, a thickener, Known additives such as a rust preventive, an ultraviolet absorber, and a surface conditioner can be appropriately blended.

The solid aqueous paints, the components of the blended by known methods with water, by water-soluble or water dispersing a resin component, a solid content concentration of that 20 to 70 wt%, preferably, It is prepared to be 35 to 60% by weight.
Further, the method for coating a solid aqueous paints, bell coating method is used, the coating conditions are, bell speed 20000～30000Min ^-1, shaving air pressure 0.5~1.5kg / cm ^2, gun distance 20 -30 cm, discharge amount 200-400 mL.

Moreover, the coating film thickness of the solid water-based paint is 10 to 100 μm, preferably 20 to 40 μm as the film thickness after baking.
In this painting method, in the solid painting booth 31, first, the inner side of the member (for example, the door panel inner) is painted by the above-described method in the inner solid painting booth 32 (inner painting process), and then the outer side. In the solid coating booth 33, the outer surface (for example, door panel outer) of the member is painted by the same method as described above (outer coating step). In this way, first, after coating the inner surface of the member in the inner solid painting booth 32, and then painting the outer surface of the member in the outer solid painting booth 33, when the inner surface is painted, On the other hand, the water-based paint to be applied is scattered as dust (paint droplets) on the outside surface and adheres to the outside surface, and the solid water-based paint is applied to the outside surface from the adhered dust. Is done.

Therefore, in this coating method, the time from the end of painting of the inner surface of the member in the inner solid painting booth 32 to the start of painting of the outer surface of the member in the outer solid painting booth 33 is within 20 minutes, preferably The process is controlled to be within 15 minutes, more preferably within 10 minutes.
If the process is managed in this way, the time from the end of painting the inner side to the start of painting on the outer side is short, so moisture in the dust adhering to the outer side is absorbed by the primed coating, or Solid water-based paint is applied to the outer surface while it does not easily evaporate into the atmosphere. That is, the solid water-based paint is applied to the outer surface before the viscosity of the dust attached to the outer surface (solid content concentration of dust) increases. As a result, the dust adhering to the outer surface is compatible with the solid water-based paint applied to the outer surface and absorbed, so that it can be adapted to the solid water-based paint applied to the outer surface.

As a result, in the solid painting process, the inner and outer surfaces of the member can be efficiently painted by a simple method that only manages the time from the end of painting the inner surface to the start of painting the outer surface. However, it is possible to effectively prevent the outer surface from being uneven, and to reduce the appearance defect of the outer surface.
Further, the water evaporable amount (difference in absolute humidity with respect to the saturated water vapor amount) in the solid coating booth 31 (the inner solid coating booth 32 and the outer solid coating booth 33) is 2 to 11 g / kg, preferably 3 to 6 g / kg. Manage to kg. If the amount of water that can be evaporated in the solid coating booth 31 is lower than 2 g / kg, sagging may occur at the time of coating, and if it is higher than 11 g / kg, the finished appearance may be deteriorated.

In addition, the temperature in the solid coating booth 31 (the inner solid coating booth 32 and the outer solid coating booth 33) is controlled to 20 to 30 ° C., for example.
In this coating method, the solid-coated member is preheated in the second hot air drying furnace 34 (preheating step).
The second hot air drying furnace 34 includes a third hot air zone 35, a fourth hot air zone 36 disposed downstream of the third hot air zone 35, and a second cooling zone disposed downstream of the fourth hot air zone 36. 37.

  In the second hot air drying furnace 34, the solid-coated member is first preheated in the third hot air zone 35 (upstream preheating step). In the third hot air zone 35, the member is preheated by hot air. The preheating conditions include, for example, a hot air blowing temperature of 45 to 100 ° C., preferably 65 to 90 ° C., a hot air blowing speed of 0.3 to 10.0 m / s, The wind speed on the coating surface (the surface of the member) is 1 to 3 m / s, the distance from the hot air outlet to the coating surface is 20 to 50 cm, and the preheating time is 0.5 to 1. 5 minutes. The hot air blowing temperature in the third hot air zone 35 is set lower than the hot air blowing temperature in the fourth hot air zone 36 described below.

  When the blowing temperature of hot air is lower than 45 ° C., the solid content concentration of the solid water-based paint may be low and cause cracking. On the other hand, when the temperature is higher than 100 ° C., the solid content concentration of the solid water-based paint may rapidly increase, and the fluidity of the coating film may decrease. On the other hand, if the blowing speed of the hot air is lower than 0.3 m / s, the solid content concentration of the solid water-based paint may be low, which may cause a crack. Moreover, when higher than 10.0 m / s, only the surface dries, the fluidity | liquidity of a coating film may fall or it may cause a crack.

The temperature and humidity in the third hot air zone 35 are controlled to, for example, a temperature of 20 to 30 ° C. and a water evaporable amount of 10 to 25 g / kg.
The member preheated in the third hot air zone 35 is then preheated in the fourth hot air zone 36 (downstream preheating step). In the fourth hot air zone 36, the member is preheated by hot air. The preheating conditions include, for example, a hot air blowing temperature of 45 to 100 ° C., preferably 70 to 100 ° C., a hot air blowing speed of 0.3 to 10.0 m / s, The wind speed on the coating surface (the surface of the member) is 1 to 3 m / s, the distance from the hot air blowing port to the coating surface is 20 to 50 cm, and the preheating time is 0.5 to 1. 5 minutes. The hot air blowing temperature in the fourth hot air zone 36 is set higher than the hot air blowing temperature in the third hot air zone 35.

  When the blowing temperature of hot air is lower than 45 ° C., the solid content concentration of the solid water-based paint may be low and cause cracking. On the other hand, when the temperature is higher than 100 ° C., energy consumption for blowing hot air increases. On the other hand, if the blowing speed of the hot air is lower than 0.3 m / s, the solid content concentration of the solid water-based paint may be low, which may cause a crack. Moreover, when higher than 10.0 m / s, only the surface dries, the fluidity | liquidity of a coating film may fall or it may cause a crack.

The temperature and humidity in the fourth hot air zone 36 are controlled to, for example, a temperature of 20 to 30 ° C. and a water evaporation rate of 10 to 23 g / kg.
The member preheated in the fourth hot air zone 36 is then cooled in the second cooling zone 37. In the second cooling zone 37, the member is cooled by cold air (cooling step). The cooling conditions are, for example, a cold air blowing temperature of 15 to 23 ° C., a cold air blowing speed of 10 m / s or less, and a distance from the cold air blowing port to the coating surface of 20 to 50 cm. Yes, the cooling time is 0.5 to 1.3 minutes. In such cooling, the temperature of the member is preferably cooled to 45 ° C. or lower, more preferably 40 ° C. or lower.

The solid water-based paint coated on the inner and outer surfaces of the member by such preheating in the hot air drying furnace 34 forms a wet solid layer 42 (see FIG. 6).
In such preheating in the second hot air drying furnace 34, first, in the third hot air zone 35, the member is preheated at a lower temperature, and then in the fourth hot air zone 36, the member is preliminarily heated at a higher temperature. Heated. Therefore, in the third hot air zone 35, the fluidity of the painted solid water-based paint is ensured, and after the coating film having a uniform thickness is formed, the occurrence of cracks in the fourth hot air zone 36 can be prevented. A coating film can be formed. As a result, the solid water-based paint can be efficiently preheated, and good properties can be imparted to the preheated coating film.

In this coating method, the solid-coated member is baked in the baking furnace 38 (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., and the baking time is about 20 to 40 minutes.
As a result, as shown in FIG. 6, a coating film in which the solid layer 42 is laminated on the intermediate coating layer 41 is formed.

The coating film formed of the intermediate coating layer 41 and the solid layer 42 thus formed has a good appearance because it is prevented from having irregularities on the outer surface.
In the above description, in the intermediate coating booth 24 and the solid coating booth 31, first, the inner surface of the member (for example, door panel inner) is painted, and then the outer surface of the member (for example, door panel outer) is painted. For example, in the intermediate coating booth 24 and the solid coating booth 31, as shown in the process diagram shown in FIG. 7, first, the outer side surface (for example, door panel outer) of the member is coated, and then the inner side surface (for example, the door panel) Inner) may be painted.

That is, in FIG. 7, although it is not one embodiment of the coating method of the present invention, the intermediate coating booth 24 includes an outer intermediate coating booth 26 for coating the outer surface of the member (eg, door panel outer), and an outer intermediate coating booth. And an inner intermediate coating booth 25 for coating the inner side surface (for example, door panel inner) of a member disposed on the downstream side of H.26. The solid painting booth 31 includes an outer solid painting booth 33 for painting an outer side surface (for example, a door panel outer) of a member, and an inner side surface (for example, a door panel) of a member disposed on the downstream side of the outer solid painting booth 33. And an inner solid painting booth 32 for painting the inner).

In FIG. 7, the same components as those described above are denoted by the same reference numerals as those described above, and the description thereof is omitted.
In this coating method, first, in the intermediate coating booth 24, after the outer surface (for example, door panel outer) of the member is coated by the above-described method in the outer intermediate coating booth 26 (outer coating step), the inner intermediate coating booth. In 25, the inner side surface (for example, door panel inner) of the member is coated by the above-described method (inner coating process).

  In this way, when the outer side surface of the member is painted at the outer intermediate coating booth 26 and then the inner surface of the member is painted at the inner intermediate coating booth 25, the intermediate coating is applied to the outer surface when the outer surface is painted. The water-based paint is scattered as dust (paint droplets) on the inner surface and adheres to the inner surface. However, since the outer surface is not required to be as strict as the outer surface, the intermediate water-based paint can be applied to the inner surface without any harmful effects.

As a result, in the intermediate coating process, it is efficient by a simple method that only manages the order of the coating of the outer surface of the member in the outer intermediate coating booth 26 and the inner surface of the member in the inner intermediate coating booth 25. In addition, it is possible to effectively coat the inner surface and the outer surface of the member, and to effectively prevent the outer surface from being uneven, and to reduce the appearance defect of the outer surface.
Further, in this coating method, after the outer surface (for example, door panel outer) of the member is first painted in the solid coating booth 31 by the above-described method in the outer solid coating booth 33 (outer coating step), In the solid painting booth 32, the inner side surface (for example, door panel inner) of the member is painted by the above-described method (inner painting process).

  As described above, after the outer surface of the member is first painted in the outer solid painting booth 33, and then the outer surface of the member is painted in the inner solid painting booth 32, the outer surface is coated with respect to the outer surface. The solid water-based paint to be painted is scattered as dust (paint droplets) on the inner surface and adheres to the inner surface. However, since the outer surface is not required to be as strict as the outer surface, the solid water-based paint can be applied to the inner surface without any harmful effects.

  As a result, in the solid coating process, the efficiency is improved by a simple method that only manages the order of the coating of the outer surface of the member at the outer solid coating booth 33 and the coating of the inner surface of the member at the inner solid coating booth 32. In particular, it is possible to effectively coat the inner side surface and the outer side surface of the member, while effectively preventing the outer side surface from being uneven, and to reduce the appearance defect of the outer side surface.

  In the process diagram shown in FIG. 7, in both the intermediate coating booth 24 and the solid coating booth 31, first, the outer side surface (for example, door panel outer) of the member is coated, and then the inner side surface (for example, door panel inner) of the member. In the booth of either the intermediate coating booth 24 or the solid coating booth 31, as shown in the process diagram of FIG. 7, first, the outer surface of the member (for example, the door panel outer) is first coated, After painting the inner surface of the member (for example, door panel inner), and in the other booth, as shown in the process diagram shown in FIG. 5, first the inner surface of the member (for example, door panel inner) is painted, and then The outer surface of the member (for example, the door panel outer) may be painted.

FIG. 8 is a process diagram showing a coating process for carrying out a coating method by a 1-coat 1-bake method. Moreover, FIG. 9 is sectional drawing which shows one Embodiment of the coating film coated by the coating method shown in FIG.
The coating method by the 1-coat 1-bake method is used to paint members constituting the automobile body such as a door panel. First, after the members primed by electrodeposition coating are baked, first, in the solid coating booth 31 Solid painting (solid painting process).

In the same manner as described above, the solid coating booth 31 has an inner solid coating booth 32 for coating the inner side surface (for example, door panel inner) of the member, and an outer side surface of the member disposed on the downstream side of the inner solid coating booth 32. And an outer solid painting booth 33 for painting (for example, door panel outer).
As the water-based paint used for solid coating, the above-mentioned solid water-based paint is used. In addition, the above-described coating method is also used as a method for applying the solid water-based paint.

  In this painting method, first, in the solid painting booth 31, after painting the inner side surface (for example, door panel inner) of the member by the above-described method in the inner solid painting booth 32 (inside painting step), In the solid coating booth 33, the outer surface (for example, door panel outer) of the member is painted by the same method as described above (outer coating step). In this way, first, after coating the inner surface of the member in the inner solid painting booth 32, and then painting the outer surface of the member in the outer solid painting booth 33, when the inner surface is painted, On the other hand, the water-based paint to be applied becomes dust (paint droplets) and scatters on the outside surface, adheres to the outside surface, and the solid water-based paint is applied to the outside surface from the adhered dust. Is done.

Therefore, in this coating method, the time from the end of painting of the inner surface of the member in the inner solid painting booth 32 to the start of painting of the outer surface of the member in the outer solid painting booth 33 is within 20 minutes, preferably The process is controlled to be within 15 minutes, more preferably within 10 minutes.
If the process is managed in this way, the time from the end of painting the inner side to the start of painting on the outer side is short, so moisture in the dust adhering to the outer side is absorbed by the primed coating, or Solid water-based paint is applied to the outer surface while it does not easily evaporate into the atmosphere. That is, the solid water-based paint is applied to the outer surface before the viscosity of the dust attached to the outer surface (solid content concentration of dust) increases. As a result, the dust adhering to the outer surface is compatible with the solid water-based paint applied to the outer surface and absorbed, so that it can be adapted to the solid water-based paint applied to the outer surface.

As a result, in the solid painting process, the inner and outer surfaces of the member can be efficiently painted by a simple method that only manages the time from the end of painting the inner surface to the start of painting the outer surface. However, it is possible to effectively prevent the outer surface from being uneven, and to reduce the appearance defect of the outer surface.
Further, the amount of water evaporable in the solid coating booth 31 (the inner solid coating booth 32 and the outer solid coating booth 33) (difference in absolute humidity with respect to the saturated water vapor amount) is 2 to 11 g / kg, preferably as described above. 3-6 g / kg. If the amount of water that can be evaporated in the solid coating booth 31 is lower than 2 g / kg, sagging may occur at the time of coating, and if it is higher than 11 g / kg, the finished appearance may be deteriorated.

In addition, the temperature in the solid coating booth 31 (the inner solid coating booth 32 and the outer solid coating booth 33) is controlled to 20 to 30 ° C., for example.
In this coating method, the solid-coated member is preheated in the second hot air drying furnace 34 in the same manner as described above (preheating step).
The second hot air drying furnace 34 includes a third hot air zone 35, a fourth hot air zone 36 disposed downstream of the third hot air zone 35, and a second cooling zone disposed downstream of the fourth hot air zone 36. 37.

  In the second hot air drying furnace 34, the solid-coated member is first preheated in the third hot air zone 35 (upstream preheating step). In the third hot air zone 35, the member is preheated by hot air. The preheating conditions include, for example, a hot air blowing temperature of 45 to 100 ° C., preferably 65 to 90 ° C., a hot air blowing speed of 0.3 to 10.0 m / s, The wind speed on the coating surface (the surface of the member) is 1 to 3 m / s, the distance from the hot air outlet to the coating surface is 20 to 50 cm, and the preheating time is 0.5 to 1. 5 minutes. The hot air blowing temperature in the third hot air zone 35 is set lower than the hot air blowing temperature in the fourth hot air zone 36 described below.

  When the blowing temperature of hot air is lower than 45 ° C., the solid content concentration of the solid water-based paint may be low and cause cracking. On the other hand, when the temperature is higher than 100 ° C., the solid content concentration of the solid water-based paint may rapidly increase, and the fluidity of the coating film may decrease. On the other hand, if the blowing speed of the hot air is lower than 0.3 m / s, the solid content concentration of the solid water-based paint may be low, which may cause a crack. Moreover, when higher than 10.0 m / s, only the surface dries, the fluidity | liquidity of a coating film may fall or it may cause a crack.

The temperature and humidity in the third hot air zone 35 are controlled to, for example, a temperature of 20 to 30 ° C. and a water evaporable amount of 10 to 25 g / kg.
The member preheated in the third hot air zone 35 is then preheated in the fourth hot air zone 36 (downstream preheating step). In the fourth hot air zone 36, the member is preheated by hot air. The preheating conditions include, for example, a hot air blowing temperature of 45 to 100 ° C., preferably 70 to 100 ° C., a hot air blowing speed of 0.3 to 10.0 m / s, The wind speed on the coating surface (the surface of the member) is 1 to 3 m / s, the distance from the hot air blowing port to the coating surface is 20 to 50 cm, and the preheating time is 0.5 to 1. 5 minutes. The hot air blowing temperature in the fourth hot air zone 36 is set higher than the hot air blowing temperature in the third hot air zone 35.

  When the blowing temperature of hot air is lower than 45 ° C., the solid content concentration of the solid water-based paint may be low and cause cracking. On the other hand, when the temperature is higher than 100 ° C., energy consumption for blowing hot air increases. On the other hand, if the blowing speed of the hot air is lower than 0.3 m / s, the solid content concentration of the solid water-based paint may be low, which may cause a crack. Moreover, when higher than 10.0 m / s, only the surface dries, the fluidity | liquidity of a coating film may fall or it may cause a crack.

The temperature and humidity in the fourth hot air zone 36 are controlled to, for example, a temperature of 20 to 30 ° C. and a water evaporation rate of 10 to 23 g / kg.
The member preheated in the fourth hot air zone 36 is then cooled in the second cooling zone 37. In the second cooling zone 37, the member is cooled by cold air (cooling step). The cooling conditions are, for example, a cold air blowing temperature of 15 to 23 ° C., a cold air blowing speed of 10 m / s or less, and a distance from the cold air blowing port to the coating surface of 20 to 50 cm. Yes, the cooling time is 0.5 to 1.3 minutes. In such cooling, the temperature of the member is preferably cooled to 45 ° C. or lower, more preferably 40 ° C. or lower.

The solid water-based paint applied to the inner and outer surfaces of the member by the preheating in the hot air drying furnace 34 forms a wet solid layer 42 (see FIG. 8).
In such preheating in the second hot air drying furnace 34, first, in the third hot air zone 35, the member is preheated at a lower temperature, and then in the fourth hot air zone 36, the member is preliminarily heated at a higher temperature. Heated. Therefore, in the third hot air zone 35, the fluidity of the painted solid water-based paint is ensured, and after the coating film having a uniform thickness is formed, the occurrence of cracks in the fourth hot air zone 36 can be prevented. A coating film can be formed. As a result, the solid water-based paint can be efficiently preheated, and good properties can be imparted to the preheated coating film.

In this coating method, the solid-coated member is baked in the baking furnace 38 (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 about 160 ° C., and the baking time is about 20 to 40 minutes.
As a result, as shown in FIG. 8, a coating film in which the solid layer 42 is laminated on the undercoat layer 40 is formed.

The coating film formed of the solid layer 42 thus formed has a good appearance because it is prevented from having irregularities on the outer surface.
In the above description, in the solid painting booth 31, first, the inner surface of the member (for example, the door panel inner) is painted, and then the outer surface of the member (for example, the door panel outer) is painted. As shown in the process diagram of FIG. 10, in the solid coating booth 31, first, the outer side surface (for example, door panel outer) of the member is painted, and then the inner side surface (for example, door panel inner) of the member may be painted. .

That is, in FIG. 10, although it is not one embodiment of the painting method of the present invention, the solid painting booth 31 includes an outer solid painting booth 33 for painting an outer surface of the member (for example, a door panel outer), and an outer solid painting. And an inner solid painting booth 32 for painting an inner surface (for example, door panel inner) of a member disposed on the downstream side of the booth 33.
In FIG. 10, the same components as those described above are denoted by the same reference numerals as those described above, and the description thereof is omitted.

In this painting method, in the solid painting booth 31, first, the outer solid painting booth 33 is coated on the outer surface (for example, door panel outer) of the member by the above-described method (outer painting step), and then the inner solid painting is performed. In the booth 32, the inner side surface (for example, door panel inner) of the member is painted by the above-described method (inner painting process).
In this way, after the outer surface of the member is painted in the outer solid painting booth 33 and then the inner surface of the member is painted in the inner solid painting booth 32, the solid that is painted on the outer surface when the outer surface is painted. The water-based paint is scattered as dust (paint droplets) on the inner surface and adheres to the inner surface. However, since the outer surface is not required to be as strict as the outer surface, the solid water-based paint can be applied to the inner surface without any harmful effects.

  As a result, in the solid coating process, the efficiency is improved by a simple method that only manages the order of the coating of the outer surface of the member at the outer solid coating booth 33 and the coating of the inner surface of the member at the inner solid coating booth 32. In particular, it is possible to effectively coat the inner side surface and the outer side surface of the member, while effectively preventing the outer side surface from being uneven, and to reduce the appearance defect of the outer side surface.

  In the above description, a door panel, an engine hood panel, and the like are illustrated as members of the automobile body. However, in the above description, the outer surface of the member is exposed in a state in which a lid member such as a door or a hood is closed. The inner surface of the member means a surface that is not exposed when the lid member is closed, but is exposed when the lid member is opened.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further more concretely, this invention is not limited to these Examples.
Painting example 1
In accordance with the process diagram shown in FIG. 1, a door panel previously primed by electrodeposition coating was applied as follows by a three-coat one-bake coating method.
(Inner coating process)
The water evaporation capacity in the intermediate coating booth 1 was controlled to 5 to 6 g / kg, and the temperature was controlled to 28 ° C.

First, in the inner coating booth 2 in the inner coating booth 1, the inner coating water-based paint shown below was applied to the door panel inner under the bell coating conditions shown below.
Bell coating conditions: Bell rotation speed 25000 min ⁻¹ , shaving air pressure 1 kg / cm ² , gun distance 25 cm, discharge amount 260 mL, film thickness after baking 20 μm
Intermediate water-based paint: WP-550D (manufactured by Kansai Paint)
Two minutes after the inner panel coating booth 2 finishes painting the inner panel coating booth 2, the outer panel coating booth 3 of the middle coating booth 1 applies the intermediate coating water-based coating with the same composition as above to the door panel under the same bell coating conditions. Painted on the outer.

(First preheating step)
The temperature in the 1st hot air zone 5 and the 2nd hot air zone 6 was controlled to 28 degreeC, and the water evaporation possible amount was controlled to 18 g / kg.
The intermediately coated door panel is preheated in the first hot air zone 5 under the following preheating conditions, and then preheated in the second hot air zone 6 under the following preheating conditions, and then the first cooling is performed. In zone 7, cooling was performed under the following conditions.

Preheating conditions for the first hot air zone 5: hot air blowing temperature 75 ° C., hot air blowing speed 10 m / s, hot air blowing speed 1 to 2 m / s, distance from hot air blowing outlet to coating surface 40-50 cm, preheating time 1.3 minutes Preheating conditions for second hot air zone 6: hot air blowing temperature 80 ° C., hot air blowing speed 10 m / s, wind speed 1-2 m / s on the hot air coated surface, 40 to 50 cm from the hot air outlet to the coating surface, preheating time 1.3 minutes Cooling conditions of the first cooling zone 7: cold air blowing temperature 20 to 23 ° C., cold air blowing speed 10 m / s, The distance from the outlet to the coated surface is 40 to 50 cm and the cooling time is 1.3 minutes. The water elution rate of the coating film of the intermediate coating material was 30%.
(Base painting process)
The amount of water evaporable in the base coating booth 8 was controlled to 5 to 6 g / kg, and the temperature was controlled to 28 ° C.

First, in the base coating booth 9 inside the base coating booth 8, the base coating water-based paint shown below was applied to the door panel inner under the bell coating conditions shown below.
Bell coating conditions: Bell rotation speed 30000 min ⁻¹ , shaving air pressure 1.5 kg / cm ² , gun distance 30 cm, discharge amount 200 mL, film thickness after baking 13 μm
Base aqueous paint composition: WBC-710D (manufactured by Kansai Paint) contact angle 63 °
Six minutes after the inner base painting booth 9 finishes painting the door panel inner, the outer base painting booth 10 of the base painting booth 8 applies the base water-based paint having the same composition as described above under the same bell painting conditions as described above. Painted on the door panel outer.

(Second preheating step)
The temperature in the third hot air zone 12 and the fourth hot air zone 13 was controlled to 28 ° C., and the water evaporable amount was controlled to 18 g / kg.
The base-coated door panel is preheated in the third hot air zone 12 under the following preheating conditions, and then preheated in the fourth hot air zone 13 under the following preheating conditions, and then the second cooling zone. No. 14 was cooled under the following conditions.

Preheating conditions for the third hot air zone 12: hot air blowing temperature 75 ° C., hot air blowing speed 10 m / s, wind speed 1-2 m / s on the hot air coating surface, distance from hot air blowing port to coating surface 40 to 50 cm, preheating time 1.3 minutes Preheating conditions for the fourth hot air zone 13: hot air blowing temperature 80 ° C., hot air blowing speed 10 m / s, wind speed 1-2 m / s on the hot air coating surface, The distance from the hot air blowing port to the coated surface is 40 to 50 cm, the preheating time is 1.3 minutes. Cooling conditions of the second cooling zone 14: cold air blowing temperature 20 to 23 ° C., cold air blowing speed 10 m / s, 40-50cm distance from the outlet to the coated surface, cooling time 1.3 minutes (clear coating process)
The water evaporable amount in the clear coating booth 15 was controlled to 5 to 6 g / kg, and the temperature was controlled to 28 ° C.

First, in the clear paint booth 16 inside the clear paint booth 15, the clear paint shown below was applied to the door panel inner under the bell paint conditions shown below.
Bell coating conditions: Bell rotation speed 30000 min ⁻¹ , shaving air pressure 1.5 kg / cm ² , gun distance 30 cm, discharge amount 300 mL, film thickness after baking 30 μm
Clear paint: DNC-K12 (manufactured by Kansai Paint)
Two minutes after the inner panel paint booth 16 finishes painting the inner clear paint booth 16, the outer paint paint booth 17 of the clear paint booth 15 applies the clear paint having the same composition as described above under the same bell painting conditions as above. Painted on the outer.

(Baking process)
In the baking furnace 18, baking was performed at a baking temperature of 140 ° C. and a baking holding time of 18 minutes.
The appearance of the door panel outer painted as described above was visually evaluated. The results are shown in Table 1.

Painting examples 2-8
In the intermediate coating process and the base coating process, paint the door panel under the same conditions as in Coating Example 1, except that the time from the end of the coating of the door panel inner to the start of the coating of the door panel outer is the time shown in Table 1. The appearance of the rear door panel outer was visually evaluated. The results are shown in Table 1.

In addition, the evaluation shown to the following Tables 1-8 is as follows.
○: Good ○ △: Almost good △: Normal ×: Poor

Painting example 9 (reference example)
According to the process diagram shown in FIG. 3, in the intermediate coating process, the door panel outer was painted at the outer intermediate coating booth 3, and 15 minutes after the coating was finished, the door panel inner was painted at the inner intermediate coating booth 2, and In the base painting process, the door panel outer was painted in the outer base painting booth 10, and 30 minutes after the painting was completed, the door panel inner was painted in the inner base painting booth 9. The door panel was painted under conditions, and the appearance of the door panel outer after painting was visually evaluated. The results are shown in Table 2.

Application example 10 (reference example)
Instead of the door panel, the engine roof panel is used as an object to be coated, and only the engine roof panel outer is painted in the outer intermediate coating booth 3 in the intermediate coating process according to the process diagram shown in FIG. The door panel was painted under the same conditions as in Coating Example 1 except that only the engine roof panel outer was painted at the booth 10, and the appearance of the coated door panel outer was visually evaluated. The results are shown in Table 2.

Painting examples 11-16
Table 3 shows hot air blowing temperatures and blowing speeds in the first hot air zone 5, the second hot air zone 6, the third hot air zone 12, and the fourth hot air zone 13 in the first preheating step and the second preheating step. The door panel was painted under the same conditions as in Coating Example 1 except that the temperature and speed were set, and the edge and finish of the door panel outer after intermediate coating and base coating were visually evaluated. The results are shown in Table 3.

Painting examples 17-20
In the intermediate coating booth 1 and the base coating booth 8, the door panel was painted under the same conditions as in Coating Example 1 except that the amount of water evaporation was the amount shown in Table 4, and the door panel after intermediate coating and after base coating The sagging and finish of the outer were visually evaluated. The results are shown in Table 4.

Painting example 21
According to the process diagram shown in FIG. 8, the door panel previously coated by electrodeposition coating was applied as follows by a one-coat one-bake coating method.
(Solid painting process)
The water evaporable amount in the solid coating booth 31 was controlled to 5 to 6 g / kg and the temperature was controlled to 28 ° C.

First, in the solid coating booth 32 inside the solid coating booth 31, a solid coating water-based paint having the composition shown below was applied to the door panel inner under the bell coating conditions shown below.
Bell coating conditions: Bell rotation speed 30000 min ⁻¹ , shaving air pressure 1.0 kg / cm ² , gun distance 25 cm, discharge amount 270 to 290 mL, film thickness after baking 30 μm
Solid paint water-based paint composition: WT-2000D (manufactured by Kansai Paint)
6 minutes after the coating of the door panel inner in the inner solid painting booth 32 is completed, the solid aqueous paint having the same composition as described above is applied at the outer solid painting booth 33 of the solid painting booth 31 under the same bell painting conditions as described above. Painted on the door panel outer.
(Preheating process)
The temperature in the third hot air zone 35 and the fourth hot air zone 36 was controlled to 28 ° C., and the water evaporable amount was controlled to 18 g / kg.

The solid-coated door panel is preheated in the third hot air zone 35 under the following preheating conditions, and then preheated in the fourth hot air zone 36 under the following preheating conditions, and then the second cooling zone. In 37, it cooled on the following conditions.
Preheating conditions for the third hot air zone 35: hot air blowing temperature of 75 ° C., hot air blowing speed of 4.0 m / s, hot air blowing speed of 1 to 2 m / s, from hot air blowing outlet to coated surface Distance of 40 to 50 cm, preheating time 1.3 minutes Preheating conditions of the fourth hot air zone 36: hot air blowing temperature 78 ° C., hot air blowing speed 10 m / s, wind speed on the coated surface of hot air 1-2 m / s s, distance from hot air blowing port to coated surface: 40-50 cm, preheating time: 1.3 minutes Cooling conditions of second cooling zone 37: cold air blowing temperature: 20-35 ° C., cold air blowing speed: 10 m / s, Distance from cold air outlet to coated surface 40-50cm, cooling time 1.3 minutes (baking process)
Baking was performed in a baking furnace 38 at a baking temperature of 140 ° C. and a baking holding time of 18 minutes.

The appearance of the door panel outer painted as described above was visually evaluated. The results are shown in Table 5.
Painting examples 22-24
In the solid painting process, the door panel was painted under the same conditions as in Example 21 except that the time from the end of painting the door panel inner to the start of painting the door panel outer was set to the time shown in Table 5, and the door panel after painting The outer appearance was visually evaluated. The results are shown in Table 5.

Painting example 25 (reference example)
According to the process diagram shown in FIG. 10, in the solid painting process, the door panel outer was painted at the outer solid painting booth 33, and 30 minutes after the painting was completed, the door panel inner was painted at the inner solid painting booth 32. The door panel was painted under the same conditions as in Coating Example 21, and the appearance of the door panel outer after coating was visually evaluated. The results are shown in Table 6.

Painting examples 26-30
In the preheating step, the door panel is painted under the same conditions as in Coating Example 21 except that the hot air blowing temperature and blowing speed in the third hot air zone 35 and the fourth hot air zone 36 are set to the temperatures and speeds shown in Table 7. The edge and finish of the door panel outer after the solid coating were visually evaluated. The results are shown in Table 7.

Painting examples 31-34
In the solid paint booth 31, the door panel was painted under the same conditions as in paint example 1 except that the amount of water evaporation was set to the amount shown in Table 8, and the sagging and finish of the door panel outer after solid painting was visually evaluated. did. The results are shown in Table 8.

It is process drawing which shows the coating process for enforcing the coating method by the 3 coat 1 baking system which is one Embodiment of the coating method of this invention. It is sectional drawing which shows one Embodiment of the coating film coated by the coating method shown in FIG. It is process drawing which shows the reference embodiment (The aspect which coats an inner surface after coating the outer surface of a member) of the coating process shown in FIG. It is process drawing which shows the reference embodiment (mode which abbreviate | omits the coating of the inner surface of a member) of the coating process shown in FIG. It is process drawing which shows the coating process for enforcing the coating method by a 2 coat 1 baking system. It is sectional drawing which shows one Embodiment of the coating film coated by the coating method shown in FIG. FIG. 6 is a process diagram illustrating a reference embodiment of the painting process illustrated in FIG. 5 (an aspect in which an inner surface is painted after an outer surface of a member is painted). It is process drawing which shows the coating process for enforcing the coating method by 1 coat 1 baking system. It is sectional drawing which shows one Embodiment of the coating film painted by the coating method shown in FIG. FIG. 9 is a process diagram illustrating a reference embodiment of the painting process illustrated in FIG. 8 (an aspect in which an inner surface is painted after an outer surface of a member is painted).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Intermediate coating booth 2 Inner intermediate coating booth 3 Outer intermediate coating booth 4 First hot-air drying oven 8 Base coating booth 9 Inner base coating booth 10 Outer base coating booth 11 Second hot-air drying oven 15 Clear coating booth 18 Baking oven 24 Intermediate coating booth 25 Inner intermediate coating Booth 26 Outer intermediate coating booth 27 First hot air drying furnace 31 Solid coating booth 32 Inner solid coating booth 33 Outer solid coating booth 34 Second hot air drying furnace 38 Baking furnace

Claims (6)

A method of painting a member constituting an automobile body,
An intermediate coating step in which the member is intermediate-coated with a water-based paint, a base coating step in which the member in the intermediate-coated wet state is base-coated with an aqueous paint having a solid content concentration of 20 to 50% by weight, and a base-coated wet state A clear coating process for clear coating the member, and a baking process for baking the clear-coated member,
The base coating process includes an inner coating process for coating the inner surface of the member, and an outer coating process for coating the outer surface of the member.
With the bell coating method, the film thickness after baking under the coating conditions of bell rotation speed 25000-35000 min ⁻¹ , shaving air pressure 1.0-2.0 kg / cm ² , gun distance 20-30 cm, discharge amount 150-350 mL. Within 20 minutes after performing the inner coating process to be 10-100 μm ,
With the bell coating method, the film thickness after baking under the coating conditions of bell rotation speed 25000-35000 min ⁻¹ , shaving air pressure 1.0-2.0 kg / cm ² , gun distance 20-30 cm, discharge amount 150-350 mL. The coating method is characterized in that the outer coating step is performed so as to be 10 to 100 μm . A method of painting a member constituting an automobile body,
An intermediate coating process in which the member is intermediate-coated with a water-based paint having a solid content concentration of 20 to 60% by weight; a base coating process in which the member in the intermediate-coated wet state is base-coated with an aqueous paint; and a base-coated wet state A clear coating process for clear coating the member, and a baking process for baking the clear-coated member,
The intermediate coating step includes an inner coating step of coating the inner surface of the member, and an outer coating step of coating the outer surface of the member.
According to the bell coating method, the film thickness after baking under the coating conditions of bell rotation speed 20000-30000 min ⁻¹ , shaving air pressure 0.5-1.5 kg / cm ² , gun distance 20-30 cm, discharge amount 150-350 mL. Within 10 minutes after performing the inner coating step to be 10-100 μm ,
According to the bell coating method, the film thickness after baking under the coating conditions of bell rotation speed 20000-30000 min ⁻¹ , shaving air pressure 0.5-1.5 kg / cm ² , gun distance 20-30 cm, discharge amount 150-350 mL. The coating method is characterized in that the outer coating step is performed so as to be 10 to 100 μm . Between the intermediate coating step and the base coating step, a first preheating step for preheating the intermediate coated member is provided,
Between the clear coating step and the base coating process, characterized in that the second preheating step of preheating the member that is the base coating is provided, the coating according to claim 1 or 2 Method. A method of painting a member constituting an automobile body,
A coating step of painting the member with a water-based paint, and a baking step of baking the painted member,
The coating process includes a solid coating process in which the member is solid-coated with an aqueous paint having a solid content concentration of 20 to 70% by weight;
The solid coating process includes an inner coating process for coating the inner surface of the member, and an outer coating process for coating the outer surface of the member.
According to the bell coating method, the film thickness after baking under the coating conditions of bell rotation speed 20000-30000 min ⁻¹ , shaving air pressure 0.5-1.5 kg / cm ² , gun distance 20-30 cm, discharge amount 200-400 mL. Within 20 minutes after performing the inner coating process to be 10-100 μm,
According to the bell coating method, the film thickness after baking under the coating conditions of bell rotation speed 20000-30000 min ⁻¹ , shaving air pressure 0.5-1.5 kg / cm ² , gun distance 20-30 cm, discharge amount 200-400 mL. The coating method is characterized in that the outer coating step is performed so as to be 10 to 100 μm. A method of painting a member constituting an automobile body,
  A coating process for coating the member with a water-based paint, and a baking process for baking the painted member;
  The coating step includes an intermediate coating step in which the member is intermediate-coated with an aqueous paint having a solid content concentration of 20 to 60% by weight, and an aqueous coating material having a solid content concentration of 20 to 70% by weight in the wet coated member. With a solid coating process to solid paint with,
  The intermediate coating step and the solid coating step include an inner coating step for coating the inner surface of the member, and an outer coating step for coating the outer surface of the member,
  In the intermediate coating step,
  Bell rotation speed of 20000-30000min by bell coating method ^-1 , Shaving air pressure 0.5-1.5kg / cm ² Within 10 minutes after performing the inner coating step so that the film thickness after baking is 10 to 100 μm under the coating conditions of a gun distance of 20 to 30 cm and a discharge amount of 150 to 350 mL,
  Bell rotation speed of 20000-30000min by bell coating method ^-1 , Shaving air pressure 0.5-1.5kg / cm ² The outer coating step is performed so that the film thickness after baking is 10 to 100 μm under the coating conditions of a gun distance of 20 to 30 cm and a discharge amount of 150 to 350 mL.
  In the solid painting process,
  Bell rotation speed of 20000-30000min by bell coating method ^-1 , Shaving air pressure 0.5-1.5kg / cm ² Within 20 minutes after performing the inner coating process so that the film thickness after baking is 10 to 100 μm under the coating conditions of a gun distance of 20 to 30 cm and a discharge amount of 200 to 400 mL,
  Bell rotation speed of 20000-30000min by bell coating method ^-1 , Shaving air pressure 0.5-1.5kg / cm ² A coating method, wherein the outer coating step is performed under a coating condition of a gun distance of 20 to 30 cm and a discharge amount of 200 to 400 mL so that the film thickness after baking is 10 to 100 μm. The coating method according to claim 5 , wherein a preheating step of preheating the intermediate-coated member is provided between the intermediate coating step and the solid coating step.

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