How to paint a vehicle body

Abstract

To provide a method for coating a vehicle body capable of sufficiently curing a coating material with a baking at a low temperature.SOLUTION: A method for coating a vehicle body on which an electrodeposition coating has been performed includes, in the stated order: applying a first base coating material onto an outer surface of the vehicle body to form a first base layer; applying a mixture of a second base coating material and a first curing agent onto an inner surface of the vehicle body to form an inner second base layer; applying the second base coating material onto the first base layer that has not been baked, to form an outer second base layer; applying a clear coating material onto the inner second base layer and the outer second base layer to form a clear layer; and baking and curing the first base layer, the inner second base layer, the outer second base layer and the clear layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for painting a vehicle body. [Background technology]

[0002] Patent Document 1 describes a method for painting automobile bodies to achieve a good appearance while reducing CO2 emissions and saving energy. In this method, a first base paint is applied to the electrodeposition-coated exterior surface of an automobile body without applying an intermediate coat, a second base paint is then applied to the interior surface of the automobile body, the second base paint is then applied wet-on-wet to the exterior surface of the automobile body, a clear paint is then applied wet-on-wet to the automobile body, and the above applied paints are then baked and cured simultaneously. The curing temperature of the second base paint is higher than that of the first base paint. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-009222 Summary of the Invention [Problem to be solved by the invention]

[0004] To further reduce CO2 emissions and energy consumption during the vehicle manufacturing process, it is desirable to bake and cure the paint at a lower temperature. However, since the temperature of the inner surface of a vehicle body during baking is usually lower than that of the outer surface, applying a low baking temperature to the method described in Patent Document 1 may result in insufficient curing of the second base paint applied to the inner surface of the automobile body.

[0005] Therefore, a method for painting a vehicle body is provided that allows the paint to be sufficiently hardened by baking at a low temperature. [Means for solving the problem]

[0006] Aspects of the present disclosure include the following. [1] A method for painting an electrodeposition-coated vehicle body, comprising: Applying a first base paint to the outer surface of the vehicle body to form a first base layer; Applying a mixture of a second base paint and a first curing agent onto the inner surface of the vehicle body to form an inner second base layer; applying the second base paint onto the unbaked first base layer to form an outer second base layer; Applying a clear coating to the inner second base layer and the outer second base layer to form a clear layer; baking and curing the first base layer, the inner second base layer, the outer second base layer, and the clear layer; A method comprising, in this order: [2] The method of claim 1, wherein in the step of baking the first base layer, the inner second base layer, the outer second base layer, and the clear layer, the curing temperature of the inner second base layer is lower than the curing temperature of the outer second base layer. [3] A method according to aspect 1 or 2, wherein in the step of baking the first base layer, the inner second base layer, the outer second base layer, and the clear layer, the curing temperature of the inner second base layer is lower than the curing temperature of the first base layer. [4] The clear coating contains a second curing agent, Aspect 4. The method of any one of aspects 1-3, wherein the second curing agent diffuses into the inner second base layer and the outer second base layer. [5] the first base coating contains a third curing agent; Aspect 5. The method of any one of aspects 1-4, wherein the third curing agent diffuses into the outer second base layer. [6] Aspect 6. The method of any one of aspects 1 to 5, wherein the inner second base layer has a portion that is not covered by the clear layer. [7] Aspect 7. The method according to any one of Aspects 1 to 6, wherein in the step of applying the second base paint onto the first base layer, the first base layer has not been preheated. [Effects of the Invention]

[0007] The method of the present invention makes it possible to sufficiently cure the coating by baking at a low temperature. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a flow chart illustrating a method according to an embodiment. [Figure 2] FIG. 2 is a schematic cross-sectional view of a vehicle body painted by the method according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments will be described with reference to the drawings as appropriate. In the drawings referred to in the following description, the same components or components having similar functions are designated by the same reference numerals, and repeated explanations may be omitted. For convenience of explanation, the dimensional ratios and shapes of each part in the drawings may be exaggerated and may differ from the actual dimensional ratios and shapes.

[0010] As used herein, "comprising" and "containing" mean that additional components may be included, and encompass "consisting essentially of" and "consisting of." "Consisting essentially of" means that additional components may be included that do not have a substantial adverse effect. "Consisting of" means that the material contains only the listed materials, but does not exclude the inclusion of unavoidable impurities.

[0011] Furthermore, in this application, unless otherwise specified in the context, "on" encompasses both "directly on" and "indirectly on."

[0012] As shown in Figures 1 and 2, the method for painting an electrodeposition-coated vehicle body according to the embodiment (hereinafter, the electrodeposition-coated vehicle body will be simply referred to as the "vehicle body") includes, in this order, step S1 of applying a first base paint to the outer surface 12 of the vehicle body 10 to form a first base layer 30, step S2 of applying a mixture of a second base paint and a first curing agent to the inner surface 14 of the vehicle body 10 to form an inner second base layer 50, step S3 of applying a second base paint to the unbaked first base layer 30 to form an outer second base layer 70, step S4 of preheating the first base layer 30, the inner second base layer 50, and the outer second base layer 70, step S5 of applying a clear paint to the inner second base layer 50 and the outer second base layer 70 to form a clear layer 90, and step S6 of baking and curing the first base layer 30, the inner second base layer 50, the outer second base layer 70, and the clear layer 90. It should be noted that the preheating step S4 is not essential but is an optional step. Fig. 2 is a schematic cross-sectional view of a vehicle body painted by the method according to the embodiment.

[0013] (1) Step S1 of applying a first base paint First, a vehicle body 10 is prepared. The vehicle body 10 is manufactured by, for example, electrodeposition coating a substrate containing a metal such as iron. The electrodeposition coating may be either cationic electrodeposition coating or anionic electrodeposition coating. In vehicle manufacturing, cationic electrodeposition coating is generally used.

[0014] The vehicle body 10 may be the body of an automobile, a scooter, a bicycle, a cart, etc. The automobile body may include a roof, doors, an engine hood, a bumper, etc. The vehicle body 10 has an outer surface 12 that faces the external environment when installed in a vehicle, and an inner surface 14 that is the opposite surface of the outer surface 12.

[0015] A first base paint is applied to the outer surface 12 of the vehicle body 10 to form a first base layer 30. The first base paint may be applied by any method.

[0016] The first base paint may be a water-based paint, for example, a water-based emulsion paint. The first base paint may contain a resin and a pigment. Examples of the resin include acrylic resin, polyester, and polyurethane. Examples of the pigment include titanium oxide, carbon, inorganic filler pigment, talc, aluminum, organic color pigment, and mica. Examples of the inorganic filler pigment include barium sulfate, calcium carbonate, and kaolin. The first base paint may further contain a curing agent (hereinafter referred to as a "third curing agent"). Examples of the third curing agent include isocyanate and carbodiimide. The third curing agent may diffuse into the outer second base layer 70 formed in step S3, which will be described later. The first base paint may further contain additives as necessary.

[0017] The first base layer 30 is not baked, and preferably not preheated, until step S3, which will be described later. In this application, baking means heating a layer under conditions that harden the paint that makes up the layer. Preheating means actively heating and drying a layer under conditions that do not harden the paint that makes up the layer. Natural drying is not included in preheating.

[0018] (2) Step S2 of applying a mixture of the second base paint and the first hardener Next, a mixture of the second base paint and the first curing agent (hereinafter referred to as the "second base mixture") is applied to the inner surface 14 of the vehicle body 10 to form the inner second base layer 50. The application of the second base mixture may be carried out by any method.

[0019] The second base paint is responsible for the development of color. The second base paint may be a water-based paint. The second base paint may contain a resin and a pigment. Examples of the resin include acrylic resin, polyester, and polyurethane. Examples of the pigment include aluminum, organic color pigment, titanium oxide, carbon, and mica. The second base paint may further contain additives as needed.

[0020] Examples of the first curing agent include isocyanate and carbodiimide. Due to the action of the first curing agent, the second base mixture has a curing temperature lower than that of the second base paint. The second base mixture may also have a curing temperature lower than that of the first base paint. In this application, the "curing temperature" of a paint or mixture means the temperature at which the viscosity of the paint or mixture stops decreasing and begins to increase while the temperature of the paint or mixture is increasing. The viscosity of the paint or mixture while the temperature is increasing is measured using a dynamic viscoelasticity measuring device.

[0021] The second base coating material and the first curing agent may be mixed by any method. For example, the second base coating material and the first curing agent may be mixed and applied using a bell-type applicator. In the bell-type applicator, the supply lines for the second base coating material and the first curing agent may converge at or near the bell cup.

[0022] (3) Step S3 of applying a second base paint Next, a second base paint is applied to the first base layer 30 formed on the outer surface 12 of the vehicle body 10 to form the outer second base layer 70. As described above, the first base layer 30 is not baked, and preferably not preheated. This reduces CO2 emissions and energy consumption in the painting process. The application of the second base paint may be performed by any method.

[0023] The second base paint used in step S3 is similar to the second base paint used in step S2, and therefore a detailed description thereof will be omitted. The second base paint may have a curing temperature higher than the curing temperature of the first base paint.

[0024] (4) Preheat step S4 Next, the first base layer 30, the inner second base layer 50, and the outer second base layer 70 may be preheated. The preheating conditions, such as temperature and time, are set appropriately depending on the types and amounts of the first base paint, second base paint, and first curing agent used.

[0025] (5) Step S5: Applying clear paint Next, a clear coating is applied onto the inner second base layer 50 and the outer second base layer 70 to form a clear layer 90. The application of the clear coating may be performed by any method. The outer second base layer 70 may be entirely covered with the clear layer 90. The inner second base layer 50 may have a covered portion 52 covered with the clear layer 90 and an uncovered portion 54 that is not covered by the clear layer 90 and is exposed.

[0026] The clear coating may be a water-based or oil-based coating. The clear coating may contain a resin and a pigment. Examples of resins include acrylic resin, polyester, and polyurethane. The clear coating may further contain a curing agent (hereinafter referred to as a "second curing agent"). An example of the second curing agent is isocyanate. The second curing agent may diffuse into the inner second base layer 50 and the outer second base layer 70. The clear coating may further contain additives, curing catalysts, etc., as necessary. The clear coating may have a curing temperature higher than the curing temperature of the second base mixture used in step S2. The clear coating may also have a curing temperature higher than the curing temperature of the second base coating.

[0027] (6) Baking step S6 Next, the first base layer 30, the inner second base layer 50, the outer second base layer 70, and the clear layer 90 are baked and cured. Baking can be performed by any heating means, such as hot air heating, infrared heating, or high-frequency heating. Baking conditions such as temperature and time are set appropriately depending on the types and amounts of the first base paint, second base paint, first curing agent, and clear paint used.

[0028] The curing temperature of the outer second base layer 70 may be higher than the curing temperature of the first base layer 30 but lower than the curing temperature of the clear layer 90. As a result, the first base layer 30, outer second base layer 70, and clear layer 90 are cured in this order on the outer surface 12 of the vehicle body 10, allowing these layers to have high smoothness after curing and resulting in high appearance quality. Furthermore, the outer second base layer 70 may contain the third curing agent supplied from the first base layer 30 and / or the second curing agent supplied from the clear layer 90. As a result, the outer second base layer 70 may have a curing temperature lower than the curing temperature of the second base paint.

[0029] The curing temperature of the inner second base layer 50 may be lower than the curing temperature of the clear layer 90. This allows the inner second base layer 50 and the clear layer 90 to cure in this order on the inner surface 14 of the vehicle body 10, resulting in high smoothness of these layers after curing and a high quality appearance. The coated portion 52 of the inner second base layer 50 may contain the second curing agent supplied from the clear layer 90, thereby allowing the coated portion 52 of the inner second base layer 50 to have a curing temperature lower than the curing temperature of the second base mixture. On the other hand, the uncoated portion 54 of the inner second base layer 50 does not receive a curing agent from another layer, so the uncoated portion 54 of the inner second base layer 50 may have a curing temperature similar to the curing temperature of the second base mixture.

[0030] The curing temperature of the inner second base layer 50 may be lower than the curing temperature of the outer second base layer 70. The temperature of the inner surface 14 of the vehicle body 10 during baking is typically lower than the temperature of the outer surface 12. Considering this, in the prior art, in which the curing temperature of the inner second base layer 50 is the same as the curing temperature of the outer second base layer 70, the set baking temperature had to be significantly higher than the set baking temperature of the outer second base layer. Otherwise, the inner second base layer 50 would not be sufficiently cured. However, in the present embodiment, in which the curing temperature of the inner second base layer 50 is lower than the set baking temperature of the outer second base layer 70, the inner second base layer 50 can be sufficiently cured.

[0031] The curing temperature of the inner second base layer 50 is preferably lower than the curing temperature of the first base layer 30. This allows the inner second base layer 50 to be sufficiently cured while still using a lower baking temperature setting.

[0032] In this application, the curing temperature of the first base layer 30 is used as the curing temperature of the first base paint, the curing temperature of the second base mixture is used as the curing temperature of the inner second base layer 50, the curing temperature of the second base paint is used as the curing temperature of the outer second base layer 70, and the curing temperature of the clear paint is used as the curing temperature of the clear layer 90, and the curing temperature of each layer can be compared.

[0033] The painting method according to the above embodiment can be performed using equipment that includes, for example, a zone for applying a first base paint to the outer surface 12 of the vehicle body 10 to form the first base layer 30, a zone for applying a second base mixture to the inner surface 14 of the vehicle body 10 to form the inner second base layer 50, a zone for applying the second base paint to the unbaked first base layer 30 to form the outer second base layer 70, a zone for preheating the first base layer 30, the inner second base layer 50, and the outer second base layer 70, a zone for applying a clear paint to the inner second base layer 50 and the outer second base layer 70 to form the clear layer 90, and a zone for baking and curing the first base layer 30, the inner second base layer 50, the outer second base layer 70, and the clear layer 90, and these zones are arranged in this order along the conveyance direction of the vehicle body 10. The vehicle body 10 may be conveyed sequentially to each zone.

[0034] In the above-mentioned equipment, the application of the paint or mixture may be performed by a robot or manually. In addition, in each zone, doors, hoods, etc. may be opened and closed as appropriate. Doors may be opened and closed by a robot or manually.

[0035] The above-described equipment may further include a setting zone between each of the zones. In the setting zone, the first base layer 30, the inner second base layer 50, the outer second base layer 70, and / or the clear layer 90 formed in the upstream zone may be flowed to improve smoothness. The setting zone may also be used to verify the quality of the first base layer 30, the inner second base layer 50, the outer second base layer 70, and / or the clear layer 90 formed in the upstream zone.

[0036] The present invention is not limited to the above-described embodiment, and various design modifications can be made without departing from the spirit of the present invention as defined in the claims. [Explanation of symbols]

[0037] 10: vehicle body, 12: outer surface of vehicle body, 14: inner surface of vehicle body, 30: first base layer, 50: inner second base layer, 52: coated portion, 54: uncoated portion, 70: outer second base layer, 90: clear layer

Claims

1. A method for painting an electrodeposition-coated vehicle body, comprising: Applying a first base paint containing a third curing agent to the outer surface of the vehicle body to form a first base layer; Applying a second base mixture, which is a mixture of a second base paint and a first curing agent, onto the inner surface of the vehicle body to form an inner second base layer; applying the second base paint onto the unbaked first base layer to form an outer second base layer; Applying a clear coating containing a second curing agent on the inner second base layer and the outer second base layer to form a clear layer; baking and curing the first base layer, the inner second base layer, the outer second base layer, and the clear layer; in this order, In the step of baking the first base layer, the inner second base layer, the outer second base layer, and the clear layer, The outer second base layer contains the third curing agent supplied from the first base layer and the second curing agent supplied from the clear layer, and is cured at a temperature lower than the curing temperature of the second base paint; The method of claim 1, wherein the inner second base layer contains the second curing agent provided from the clear layer and cures at a temperature lower than the curing temperature of the second base mixture.

2. 2. The method of claim 1, wherein in the step of baking the first base layer, the inner second base layer, the outer second base layer, and the clear layer, the curing temperature of the inner second base layer is lower than the curing temperature of the outer second base layer.

3. 3. The method according to claim 1, wherein in the step of baking the first base layer, the inner second base layer, the outer second base layer, and the clear layer, the curing temperature of the inner second base layer is lower than the curing temperature of the first base layer.

4. The method of claim 1 or 2, wherein the inner second base layer has a portion that is not covered by the clear layer.

5. The method according to claim 1 or 2, wherein in the step of applying the second base paint onto the first base layer, the first base layer is not preheated.

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