Method for painting vehicle bodies

Abstract

The present application is a method for painting a vehicle body. A method for painting a vehicle body that can fully cure the paint by baking at a low temperature is provided. A method for painting a vehicle body, wherein the vehicle body is a vehicle body that has been electroplated, the method sequentially comprising: a step of applying a first base paint on the outer surface of the vehicle body to form a first base layer; a step of applying a mixture of a second base paint and a first curing agent on the inner surface of the vehicle body to form an inner second base layer; a step of applying the second base paint on the unbaked first base layer to form an outer second base layer; a step of applying a clear paint on the inner second base layer and the outer second base layer to form a clear layer; and a step of baking the first base layer, the inner second base layer, the outer second base layer, and the clear layer to cure them.

Description

Technical Field

[0001] The present invention relates to a method of painting a vehicle body. Background Art

[0002] Patent Document 1 describes a method for painting automobile bodies for reducing CO2 emissions, achieving energy savings, and achieving a good appearance. In this method, a first base coating is applied to the exterior surface of an electrodeposition-coated automobile body without applying a midcoat. A second base coating is then applied to the interior surface of the automobile body. The second base coating is then applied wet-on-wet to the exterior surface of the automobile body. A clear coating is then applied wet-on-wet to the automobile body. The applied coatings are then simultaneously baked and cured. The curing temperature of the second base coating is higher than that of the first base coating.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2015-009222 Summary of the Invention

[0006] To further reduce CO2 emissions and energy consumption during vehicle manufacturing, it is desirable to cure the coating by baking at a lower temperature. However, since the temperature of the inner surface of a vehicle body is generally lower than that of the outer surface during baking, the method described in Patent Document 1, using a low baking temperature, may result in insufficient curing of the second base coating applied to the inner surface of the vehicle body.

[0007] Therefore, a method for painting a vehicle body is provided, which enables the paint to be sufficiently cured by baking at a low temperature.

[0008] As aspects of the present disclosure, the following aspects can be cited.

[0009] [1] A method for coating a vehicle body, wherein the vehicle body is an electrodeposition-coated vehicle body, the method comprising:

[0010] a step of applying a first base coating on the outer surface of the vehicle body to form a first base layer;

[0011] A step of applying a mixture of a second base paint and a first curing agent on the inner surface of the vehicle body to form an inner second base layer;

[0012] The step of applying the second base coating on the unbaked first base layer to form an outer second base layer;

[0013] a step of applying a clear coating material on the inner second base layer and the outer second base layer to form a clear layer; and

[0014] The first base layer, the inner second base layer, the outer second base layer, and the transparent layer are baked to be cured.

[0015] [2] The method according to method 1,

[0016] In the step of baking the first base layer, the inner second base layer, the outer second base layer, and the transparent layer, a curing temperature of the inner second base layer is lower than a curing temperature of the outer second base layer.

[0017] [3] The method according to embodiment 1 or 2,

[0018] In the step of baking the first base layer, the inner second base layer, the outer second base layer, and the transparent layer, a curing temperature of the inner second base layer is lower than a curing temperature of the first base layer.

[0019] [4] The method according to any one of aspects 1 to 3,

[0020] The clear coating contains a second curing agent,

[0021] The second curing agent diffuses into the inner second foundation layer and the outer second foundation layer.

[0022] [5] The method according to any one of aspects 1 to 4,

[0023] The first base coating contains a third curing agent,

[0024] The third curing agent diffuses into the outer second base layer.

[0025] [6] The method according to any one of aspects 1 to 5,

[0026] The inner second base layer has a portion not covered by the transparent layer.

[0027] [7] The method according to any one of aspects 1 to 6,

[0028] In the step of applying the second base coating material on the first base layer, the first base layer is not preheated.

[0029] According to the method of the present invention, the coating material can be sufficiently cured by baking at a low temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1Flowchart showing a method according to an embodiment.

[0031] Figure 2 This is a schematic cross-sectional view of a vehicle body painted by the method according to the embodiment.

[0032] Description of Reference Numerals

[0033] 10: Vehicle body; 12: Outer surface of the vehicle body; 14: Inner surface of the vehicle body; 30: First base layer; 50: Inner second base layer; 52: Covered portion; 54: Uncovered portion; 70: Outer second base layer; 90: Transparent layer. DETAILED DESCRIPTION

[0034] The embodiments will be described below with reference to the accompanying drawings as appropriate. In the drawings referenced in the following description, identical components or components having identical functions are denoted by identical reference numerals, and duplicate descriptions may be omitted. For ease of explanation, the dimensions, ratios, and shapes of various components in the drawings are exaggerated and may differ from their actual dimensions, ratios, and shapes.

[0035] In this application, "comprising" and "containing" mean that additional components may be included, including "consisting essentially of" and "consisting of." "Consisting essentially of" means that additional components that do not substantially cause adverse effects may be included. "Consisting of" means that only the listed materials are included, but the inclusion of unavoidable impurities is not excluded.

[0036] In addition, in the present application, “on” includes both “directly on” and “indirectly on” unless otherwise specified in the context.

[0037] The method of coating a vehicle body coated with electrodeposition coating (hereinafter referred to as "vehicle body") according to the embodiment is as follows: Figure 1 、 2 As shown, the process sequentially includes: step S1 of applying a first base coating 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 coating 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 coating 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 coating 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. Note that the preheating step S4 is not essential and is an optional step. Figure 2 This is a schematic cross-sectional view of a vehicle body painted by the method according to the embodiment.

[0038] (1) Step S1 of applying the first base coating

[0039] First, a vehicle body 10 is prepared. The vehicle body 10 is manufactured by, for example, subjecting a substrate made of a metal such as iron to electrodeposition coating. Electrodeposition coating can be either cationic electrodeposition coating or anionic electrodeposition coating. Cationic electrodeposition coating is generally used in vehicle manufacturing.

[0040] The vehicle body 10 may be a body of an automobile, a scooter, a bicycle, a truck, etc. The automobile body may include a roof, doors, a hood, a bumper, etc. The vehicle body 10 has an outer surface 12 facing the outside environment when assembled into a vehicle, and an inner surface 14 opposite to the outer surface 12.

[0041] The first base coating material is applied to the outer surface 12 of the vehicle body 10 to form the first base layer 30. The first base coating material can be applied by any method.

[0042] The first base coating can be a water-based coating, for example, a water-based emulsion coating. The first base coating can contain a resin and a pigment. Examples of resins include acrylic resins, polyesters, and polyurethanes. Examples of pigments include titanium oxide, carbon, inorganic body pigments, talc, aluminum, organic coloring pigments, and mica. Examples of inorganic body pigments include barium sulfate, calcium carbonate, and kaolin. The first base coating can also further contain a curing agent (hereinafter referred to as the "third curing agent"). Examples of the third curing agent include isocyanates and carbodiimides. The third curing agent can diffuse into the outer second base layer 70 formed in step S3 described later. The first base coating can further contain additives as needed.

[0043] The first base layer 30 is not baked, and preferably not preheated, until step S3, described below. In this application, baking means heating the layer under conditions that allow the coating material of the layer to cure. Preheating means actively heating the layer to dry it under conditions that do not allow the coating material of the layer to cure. Natural drying is not included in preheating.

[0044] (2) Step S2 of applying a mixture of a second base paint and a first curing agent

[0045] Next, a mixture of a second base paint and a first curing agent (hereinafter appropriately referred to as "second base mixture") is applied to the inner surface 14 of the vehicle body 10 to form the inner second base layer 50. The second base mixture can be applied by any method.

[0046] The second base coating is responsible for developing the color. The second base coating can be a water-based coating. The second base coating can contain a resin and a pigment. Examples of resins include acrylic resins, polyesters, and polyurethanes. Examples of pigments include aluminum, organic coloring pigments, titanium oxide, carbon, and mica. The second base coating can further contain additives as needed.

[0047] As examples of the first curing agent, isocyanates and carbodiimides can be cited. The second base mixture has a curing temperature lower than the curing temperature of the second base coating due to the action of the first curing agent. In addition, the second base mixture may also have a curing temperature lower than the curing temperature of the first base coating. In this application, the so-called "curing temperature" of the coating or mixture means: the temperature at which the viscosity of the coating or mixture stops decreasing and begins to rise during the increase in the temperature of the coating or mixture. The viscosity of the coating or mixture during the temperature increase is measured using a dynamic viscoelasticity measuring device.

[0048] The second base coating material and the first curing agent can be mixed using any method. For example, a bell-type coating apparatus can be used to mix and apply the second base coating material and the first curing agent. In a bell-type coating apparatus, the supply lines for the second base coating material and the first curing agent can merge at or near the bell cap.

[0049] (3) Step S3 of applying the second base coating

[0050] Next, a second base coating is applied to the first base layer 30 formed on the outer surface 12 of the vehicle body 10 to form an outer second base layer 70. At this time, as described above, the first base layer 30 is not baked, and preferably not preheated. This reduces CO2 emissions and energy consumption during the coating process. The second base coating can be applied using any method.

[0051] The second base paint used in step S3 is the same as the second base paint used in step S2, so detailed description thereof is omitted. The second base paint may have a curing temperature higher than that of the first base paint.

[0052] (4) Preheating step S4

[0053] Next, the first base layer 30, the inner second base layer 50, and the outer second base layer 70 may be preheated. The temperature, time, and other conditions for preheating are appropriately set according to the type and amount of the first base paint, second base paint, and first curing agent used.

[0054] (5) Step S5 of applying a clear coating

[0055] Next, a clear coating is applied to the inner second base layer 50 and the outer second base layer 70 to form a clear layer 90. The clear coating can be applied using any method. The outer second base layer 70 can be entirely covered with the clear layer 90. The inner second base layer 50 can have a covered portion 52 covered with the clear layer 90 and an uncovered portion 54 not covered with the clear layer 90 and exposed.

[0056] The transparent coating material can be a water-based or oil-based coating material. The transparent coating material can contain a resin and a pigment. Examples of the resin include acrylic resins, polyesters, and polyurethanes. The transparent coating material can further contain a curing agent (hereinafter referred to as the "second curing agent"). Examples of the second curing agent include isocyanates. The second curing agent can diffuse into the inner second base layer 50 and the outer second base layer 70. The transparent coating material can further contain additives, curing catalysts, etc. as needed. The transparent coating material can have a curing temperature higher than the curing temperature of the second base mixture used in step S2. In addition, the transparent coating material can also have a curing temperature higher than the curing temperature of the second base coating material.

[0057] (6) Baking step S6

[0058] 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 to cure. Baking can be performed using any heating method, such as hot air heating, infrared heating, or high-frequency heating. Baking conditions, such as the temperature and time, are appropriately set based on the type and amount of the first base coating, second base coating, first curing agent, and clear coating used.

[0059] The curing temperature of the outer second base layer 70 can be higher than that of the first base layer 30 and lower than that of the transparent layer 90. Thus, on the outer surface 12 of the vehicle body 10, the first base layer 30, the outer second base layer 70, and the transparent layer 90 are cured in this order. This allows these layers to have a high degree of smoothness after curing, resulting in a high-quality appearance. Furthermore, the outer second base layer 70 can contain the third curing agent supplied from the first base layer 30 and / or the second curing agent supplied from the transparent layer 90. This allows the outer second base layer 70 to have a curing temperature lower than that of the second base coating material.

[0060] The curing temperature of the inner second base layer 50 can be lower than that of the transparent layer 90. Thus, on the inner surface 14 of the vehicle body 10, the inner second base layer 50 and the transparent layer 90 are cured in this order, resulting in these layers having a high degree of smoothness after curing, thereby achieving a high-quality appearance. Furthermore, the covering portion 52 of the inner second base layer 50 can contain the second curing agent supplied from the transparent layer 90, thereby allowing the covering portion 52 of the inner second base layer 50 to have a curing temperature lower than that of the second base mixture. On the other hand, since no curing agent is supplied from other layers to the non-covered portion 54 of the inner second base layer 50, the non-covered portion 54 of the inner second base layer 50 can have a curing temperature equal to that of the second base mixture.

[0061] The curing temperature of the inner second base layer 50 can be lower than the curing temperature of the outer second base layer 70. During the baking process, the temperature of the inner surface 14 of the vehicle body 10 is generally lower than the temperature of the outer surface 12. Taking this into consideration, in the conventional art where the curing temperature of the inner second base layer 50 and the curing temperature of the outer second base layer 70 are the same, it is necessary to set the baking temperature to be significantly higher than the curing temperature of the outer second base layer. This is because otherwise, the curing of the inner second base layer 50 becomes insufficient. However, in this embodiment, where the curing temperature of the inner second base layer 50 is lower than that of the outer second base layer 70, the inner second base layer 50 can be sufficiently cured even if the baking temperature is set lower than in the conventional art.

[0062] 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 further reducing the set temperature for baking.

[0063] Furthermore, in the present application, the curing temperature of each layer can be compared by using the curing temperature of the first base coating as the curing temperature of the first base layer 30, the curing temperature of the second base mixture as the curing temperature of the inner second base layer 50, the curing temperature of the second base coating as the curing temperature of the outer second base layer 70, and the curing temperature of the clear coating as the curing temperature of the transparent layer 90.

[0064] The coating method according to the above embodiment can be performed, for example, in an apparatus having: a zone for applying a first base coating to the outer surface 12 of the vehicle body 10 to form a first base layer 30; a zone for applying a second base mixture to the inner surface 14 of the vehicle body 10 to form an inner second base layer 50; a zone for applying a second base coating to the unbaked first base layer 30 to form an 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 coating to the inner second base layer 50 and the outer second base layer 70 to form a 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. These zones are sequentially arranged along the conveyance direction of the vehicle body 10. The vehicle body 10 can be conveyed sequentially to each zone.

[0065] In the above-mentioned equipment, the coating and mixture can be applied by robots or manually. In addition, the doors, hood, etc. can be opened and closed appropriately in each area. The doors can be opened and closed by robots or manually.

[0066] In the above-described apparatus, a setting zone may be further provided between the various 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 transparent layer 90 formed in the upstream zone can be made to flow, thereby improving smoothness. Furthermore, the quality of the first base layer 30, the inner second base layer 50, the outer second base layer 70, and / or the transparent layer 90 formed in the upstream zone can also be inspected in the setting zone.

[0067] The present invention is not limited to the above-described embodiment, and various design changes can be made without departing from the spirit of the present invention described in the claims.

Claims

1. A method for coating a vehicle body, wherein the vehicle body is an electrodeposition-coated vehicle body, the method comprising: a step of applying a first base coating material containing a third curing agent on the outer surface of the vehicle body to form a first base layer; A step of applying a mixture of a second base paint and a first curing agent on the inner surface of the vehicle body to form an inner second base layer; The step of applying the second base coating on the unbaked first base layer to form an outer second base layer; a step of coating a clear coating material containing a second curing agent on the inner second base layer and the outer second base layer to form a clear layer; and The first base layer, the inner second base layer, the outer second base layer and the transparent layer are baked to be cured. In the step of baking the first base layer, the inner second base layer, the outer second base layer and the transparent layer, the curing temperature of the inner second base layer is lower than the curing temperatures of the outer second base layer, the first base layer and the transparent layer, and the curing temperature of the outer second base layer is higher than the curing temperature of the first base layer and lower than the curing temperature of the transparent layer.

2. The method for painting a vehicle body according to claim 1, The second curing agent diffuses into the inner second foundation layer and the outer second foundation layer.

3. The method for painting a vehicle body according to claim 1 or 2, The third curing agent diffuses into the outer second base layer.

4. The method for painting a vehicle body according to claim 1 or 2, The inner second base layer has a portion not covered by the transparent layer.

5. The method for painting a vehicle body according to claim 1 or 2, In the step of applying the second base coating material on the first base layer, the first base layer is not preheated.

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