JP2007014852A - Electrostatic coating method of resin molding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrostatic coating method of a resin molding which enables a coating of high quality at low costs also to the resin molding having a complicated shape. <P>SOLUTION: The electrostatic coating method of the resin molding comprises a conductive agent-coating process of coating a back side 1b of a bumper 1 with a conductive agent 4 which gives the bumper 1 an energization nature, a water washing process of removing the wrap-around conductive agent 4 adhered to a front face 1a side, and an electrostatic coating process of electrostatically coating the front surface 1a in a state that the bumper 1 is grounded. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electrostatic coating method for resin molded products such as automobile bumpers.

  The resin molded product has a high surface resistivity and is a so-called insulator. For this reason, when electrostatic coating is performed on a resin molded product, it is necessary to provide conductivity to the surface to be coated (the surface of the resin molded product).

Therefore, conventionally, after applying a conductive primer on the surface of a resin molded product to form a conductive film to make it conductive, color and clear are applied by electrostatic coating. (See Patent Document 1).
In addition, by applying a conductive backing jig to the back surface of the resin molded product, the surface (the surface to be coated) was coated with color, etc. by electrostatic coating while ensuring the electrical conductivity of the surface (surface to be coated). (See Patent Document 2).
JP-A-6-25563 (paragraph numbers 0021 to 0023, FIG. 1) Japanese Patent Laid-Open No. 8-80458 (paragraph numbers 0010 to 0014, FIG. 1)

  However, in the method of applying the conductive primer to the surface (surface) to be coated, the viscosity of the conductive primer is generally high, and in order to ensure good electrical conductivity, if the conductive primer is applied thickly, In some cases, the conductive primer sags and the surface of the conductive film becomes uneven. And, when the color and clear are painted by electrostatic coating method on the conductive film whose surface is uneven in this way, pinholes and blisters (multiple miniature projections) are generated on the surface after coating, There was a case. Further, since the conductive primer contains VOC (volatile organic compound), there is a problem that the influence on the environment is concerned.

  In recent years, since the emphasis is placed on the design, the shape of the resin molded product is becoming more complex, and it is difficult to contact the backing jig following the back surface of the resin molded product having such a complicated shape. For this reason, the imperfect backing causes a disturbance in the distribution of electric lines of force between the backing jig formed during electrostatic coating and the counter electrode, and spots are generated on the surface of the resin molded product after painting. Or the coating thickness may not be uniform, resulting in poor coating. Furthermore, if a backing jig is produced for each resin molded product, the cost increases, which is not practical.

  Then, this invention makes it a subject to provide the electrostatic coating method of the resin molded product which can perform high-quality coating at low cost also to the resin molded product of a complicated shape.

  As means for solving the above-mentioned problem, the invention according to claim 1 includes: a conductive agent application step of applying a conductive agent that imparts conductivity to the resin molded product on the back surface of the resin molded product; and the resin molded product. And an electrostatic coating process for electrostatically coating the surface of the resin molded product in a grounded state.

  Here, the “conductive agent for imparting electrical conductivity to the resin molded product” is applied not only to the case where the conductive agent itself contains a conductive material (for example, conductive powder described later) and has conductivity, but also to the resin molded product. Therefore, it contains a surfactant that promotes the formation of a conductive film with water and imparts electrical conductivity to the resin molded product.

According to such an electrostatic coating method for a resin molded product, the surface can be electrostatically coated in a grounded state after applying electrical conductivity to the back surface to make the resin molded product have electrical conductivity.
Here, for example, even if the conductive agent hangs down, since it is on the back side of the resin molded product, the surface coating is not affected, and high-quality coating can be performed. Moreover, even if it is a complicated resin molded product, it can apply | coat an electrically conductive agent easily and at low cost using the existing apparatus. As a result, the distribution of electric lines of force formed during electrostatic coating is not disturbed, and the surface after coating is free from spotted patterns, enabling high-quality coating.

  In the invention according to claim 2, between the conductive agent application step and the electrostatic coating step, the conductive agent applied in the conductive agent application step wraps around the surface side and adheres to the surface. The method for electrostatic coating a resin molded article according to claim 1, further comprising a removing step of removing the conductive agent.

  According to such an electrostatic coating method for a resin molded product, by removing the conductive agent adhering to the surface of the resin molded product in the removing step, the primer formed by electrostatic coating and the resin molded product Adhesion can be ensured and blistering can be prevented.

  The invention according to claim 3 is the electrostatic coating method for a resin molded product according to claim 1 or 2, wherein the conductive agent is water-soluble.

  According to the electrostatic coating method of such a resin molded product, since the conductive agent is water-soluble and does not contain VOC, it can be in a state friendly to the operator.

  ADVANTAGE OF THE INVENTION According to this invention, the electrostatic coating method of the resin molded product which can perform high quality coating at low cost also to the resin molded product of a complicated shape can be provided.

Hereinafter, an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a process diagram of an electrostatic coating method for a resin molded article according to the present embodiment, wherein (a) is a conductive agent coating process, (b) is a degreasing process, (c) is a water washing process, and (d) is a washing process. The surface adjustment step, (e) shows the drying step, and (f) shows the electrostatic coating step.
Here, the case where the resin molded product to be painted is a bumper of an automobile that is an injection molded product of polypropylene is exemplified.

  As shown in FIG. 1, the electrostatic coating method for a resin molded product according to the present embodiment includes a conductive agent coating process, a degreasing process, a water washing process (removing process), a surface adjustment process, a drying process, a static process. And the electropainting process.

<Conducting agent application process>
The conductive agent application process will be described.
As shown in FIG. 1 (a), a resin bumper 1 (resin molded product) is placed on a conveying jig 3 on a conveying carriage 2 with the surface 1a, which is the surface to be coated, facing upward. Then, it is transported to a painting factory by a transport conveyor (not shown). Next, a water-soluble conductive agent 4 is spray-coated with a spray gun 5 on the entire back surface 1 b of the conveyed bumper 1, and the entire back surface 1 b is covered with a conductive film 6.
The bolt holes formed in the bumper 1 are masked before the conductive agent 4 is applied.

[Conductive agent]
The conductive agent 4 is an agent for forming a conductive film 6 having conductivity after coating, and making the bumper 1 conductive. Such conductive agent 4, the electrically conductive powder (carbon, graphite, silver, copper, nickel, etc.), or quaternary ammonium salts (e.g., tetrabutylammonium hydrogensulfate (TBAHS: Tetrabutylammonium hydorogensulfate, [CH 3 ( CH ₂ ) ₃ ] ₄ N (HSO ₄ )), potassium titanate, borate, etc. are dissolved or dispersed in an aqueous solvent (for example, water), that is, the conductive agent 4 is water-soluble. Since it does not contain VOC, it can be in a state that is easy on the operator, and as such a conductive agent 4, for example, “Surf Power PL-500” manufactured by Nippon Paint Co., Ltd. is used. You can also.
In addition, such a conductive agent 4 is dissolved or dispersed in a surfactant such as lauryltrimethylammonium chloride (CH ₃ (CH ₂ ) ₁₁ N (CH ₃ ) ₃ Cl, CAS112-00-5). A conductive surfactant can also be used.

Thus, by applying the conductive agent 4 to the back surface 1b of the bumper 1 to form the conductive film 6, the surface specific resistance value of the bumper 1 is lowered, and the bumper 1 can be provided with stable electrical conductivity. Further, since the conductive film 6 is formed so as to cover the entire back surface 1b, the surface specific resistance value does not vary on the front surface 1a side, and the distribution of electric lines of force is not disturbed in the electrostatic coating process described later. , Primer, color, and clear can be suitably electrostatically coated. That is, after electrostatic coating, the surface does not have a spotted pattern, and high-quality coating can be performed.
Further, when the conductive agent 4 is dripped when the conductive agent 4 is applied thickly to apply the conductive agent 4 to the back surface 1b, the front surface 1a side is not affected at all. Therefore, no blister occurs after electrostatic coating.
Furthermore, since the conductive agent 4 is applied by the spray gun 5, even if there are ribs or protrusions on the back surface 1b, it can be easily handled.

<Degreasing process>
Next, the degreasing process will be described.
The degreasing step is a step of detaching oil and fat adhering to the surface 1 a of the bumper 1. In this embodiment, as shown in FIG. 1B, only the surface 1a of the bumper 1, for example, (a) an alkaline aqueous solution containing sodium carbonate and polyoxyethylene polynuclear phenol, (b) caustic alkali salt and white Degreasing treatment is carried out by spraying a degreasing agent comprising an alkaline aqueous solution containing kerosene or (c) an alkaline aqueous solution containing a polyethylene glycol-type nonionic active agent or the like into an alkali mainly composed of potassium salt. Do. As such a degreasing agent, for example, “Surf Cleaner PL-1000 series” manufactured by Nippon Paint Co., Ltd. can be used.

<Washing process>
Next, the water washing process (removal process) will be described.
The water washing step is a step of washing the surface 1a of the bumper 1 with water. In this embodiment, as shown in FIG.1 (c), washing water is sprayed only on the surface 1a of the bumper 1 with a shower nozzle (not shown), and water washing is performed.

Thus, by carrying out in the order of the conductive agent application step, degreasing step, and water washing step, in other words, by performing the water washing step (removal step) between the conductive agent application step and the electrostatic coating step, Even if the conductive agent 4 wraps around the surface 1a and adheres to the surface 1a in the conductive agent application step, the attached conductive agent 4 can be surely removed. Thereby, it is possible to reliably prevent the adhesion failure between the primer and the surface 1a due to the conductive agent 4 remaining on the surface 1a and the generation of blisters.
Moreover, the outflow of the conductive film 6 formed on the back surface 1b can be prevented by washing only the front surface 1a.

<Surface adjustment process>
Next, the surface adjustment process will be described.
The surface adjustment step is a step of roughening the surface 1a, which is the surface to be coated of the bumper 1, and improving the drainage drying property. In the present embodiment, for example, the surface 1a is roughened by spraying a surface conditioner mainly composed of polyoxyethylene higher alcohol on the surface 1a, and the drainage drying property is improved. Specifically, for example, “Surf Power PL-100” manufactured by Nippon Paint Co., Ltd. can be used as such a surface conditioner.
By roughening the surface 1a in this way, the adhesion between the primer coated on the surface 1a and the surface 1a can be enhanced in the electrostatic coating process described later.

<Drying process>
Next, the drying process will be described.
The drying step is a step of drying the bumper 1. In this embodiment, the bumper 1 is heated to a predetermined temperature (for example, 70 to 90 ° C.) by a draining and drying furnace (not shown) to dry the surface 1 a.

<Electrostatic coating process>
Next, the electrostatic coating process will be described.
A primer, color, and clear are sequentially electrostatically coated on the surface 1a of the bumper 1 by an electrostatic coating gun 7 such as a bell-type coating gun or an airless coating gun to form a coating film 8 having a three-layer structure. At this time, the bumper 1 is in a state of being grounded (grounded) via the conveyance jig 3 and the conveyance carriage 2.
Here, since the surface specific resistance value of the surface 1a is uniform, the distribution of electric lines of force formed between the counter electrode and the bumper is not disturbed, and the finely divided primer, color, and clear have the electric force described above. Since it rides on the line and proceeds to the surface 1a, a high-quality coating film 8 is formed. That is, the coating surface is prevented from becoming uneven after painting.

According to such an electrostatic coating method for a resin molded product according to the present embodiment, the following effects can be obtained.
Since the surface specific resistance value of the surface 1a of the bumper 1 is uniform, the primer, the color, and the clear can be finely divided by the electrostatic coating method to improve the coating efficiency.

  In order to apply the conductive agent 4 to the back surface 1b of the bumper 1 and remove the conductive agent 4 that has wrapped around the surface 1a in the water washing process, and then directly apply a primer or the like to the surface 1a of the bumper 1. The adhesion between the bumper 1 and the primer can be improved. Furthermore, blisters and the like do not occur due to sagging of the conductive agent 4 and waviness of the surface of the conductive film 6.

  The conductive agent 4 is sprayed on the back surface 1b of the bumper 1 to form the conductive film 6. Therefore, even if the shape of the bumper 1 (resin molded product) is complicated, it can be easily handled. Moreover, it can respond easily to the bumper 1 which is different for each vehicle type.

  As mentioned above, although preferred embodiment of this invention was described, this invention is not limited to the said embodiment, For example, it can change as follows in the range which does not deviate from the meaning of this invention.

In the conductive agent application step according to the above-described embodiment, the conductive agent 4 containing conductive powder, quaternary ammonium salt, potassium titanate, borate, etc. is applied. A surfactant such as monoalkylammonium chloride or dialkylammonium chloride may be applied to the back surface 1b.
In this case, after drying by a draining and drying furnace in the water washing step, the booth atmosphere in the electrostatic coating step (for example, booth temperature 25 ° C., humidity 70%) due to the moisture absorption effect of the surfactant applied to the back surface 1b of the bumper 1 Below, moisture is adsorbed on the back surface 1b of the bumper 1 to form a water film, and the bumper 1 is rapidly cooled by this water film. Thus, when the bumper 1 is rapidly cooled, the temperature of the air near the surface 1a of the bumper 1 is lowered, and fine water droplets adhere to the surface 1a. Then, the water droplets adhering to the front surface 1a become conductive with the water film on the back surface 1b, and are grounded via the transport jig 3 and the transport carriage 2, so that the bumper 1 (resin molded product) has electrical conductivity. Become.

  In the above-described embodiment, the conductive agent application process, the degreasing process, and the water washing process (removal process) are performed in this order. However, the conductive agent application process may be performed before the water washing process, for example, the degreasing process and the conductive agent application process. The order of the water washing step may be used.

In the degreasing process according to the above-described embodiment, the degreasing process is performed by spraying a degreasing agent on the surface 1a of the bumper 1. For example, (a) phosphoric acid or phosphate is a main component. Acid agents containing acid and polyethylene glycol type nonionic surfactants, (b) Octadecyltrimethylammonium chloride, CH ₃ (CH ₂ ) ₁₇ N (CH ₃ ) ₃ Cl, CAS-112-03- 8) Tetradecyldimethylbenzylammonium chloride, CH ₃ (CH ₂ ) ₁₃ N (CH ₃ ) ₂ (CH ₂ C ₆ H ₅ ) Cl, CAS139-08-2), Oxyethyltenedodecylamine, The surface 1a may be sprayed with a cationic agent such as C ₁₂ H ₂₅ NHCH ₂ CH ₂ OH) for degreasing treatment. Further, degreasing treatment may be performed by spraying high-temperature (50 to 70 ° C.) and high-pressure (300 to 500 KPa) jet flush water on the surface 1a.

  In the electrostatic coating process according to the above-described embodiment, the primer, the color, and the clear are sequentially electrostatically coated. For example, in the case of the bumper 1 having a desired color mixed with a pigment, only the clear is electrostatically coated. Also good.

It is process drawing of the electrostatic coating method of the resin molded product which concerns on this embodiment, (a) is a electrically conductive agent application | coating process, (b) is a degreasing process, (c) is a water washing process, (d) is a surface adjustment process, (E) shows a drying process and (f) shows an electrostatic coating process.

Explanation of symbols

1 Bumper (resin molded product)
1a surface 1b back surface 4 conductive agent 6 conductive film 8 coating film

Claims (3)

A conductive agent application step of applying a conductive agent that imparts electrical conductivity to the resin molded product on the back surface of the resin molded product;
In the state where the resin molded product is grounded, an electrostatic coating step of electrostatically coating the surface;
An electrostatic coating method for a resin molded product comprising: Between the conductive agent application step and the electrostatic coating step,
The removal step of removing the conductive agent that wraps around the surface side and adheres to the surface by applying the conductive agent in the conductive agent application step,
The method of electrostatic coating of a resin molded product according to claim 1, further comprising:   The method of electrostatic coating a resin molded product according to claim 1, wherein the conductive agent is water-soluble.

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