JP4696516B2 - Pre-treatment method for electrodeposition coating - Google Patents

Description

  The present invention relates to a surface treatment method for electrodeposition coating of automobile bodies and parts, and more particularly to a pretreatment method capable of preventing muscle rust and electrodeposition secondary sagging after forming a chemical conversion film.

  The pre-electrodeposition treatment process for automobile bodies consists of steps such as degreasing, water washing, surface conditioning, chemical conversion treatment, water washing, pure water washing and draining and drying, followed by electrodeposition coating, water washing and baking drying. A coating film is formed (Patent Document 1).

  In such a pretreatment step, the chemical conversion treatment liquid adhering to the body surface is removed by a water washing step using clean water and a pure water washing step using pure water after the chemical conversion treatment, but if this water washing is insufficient, The pretreatment liquid remains in the narrow part and the outer plate part such as the panel mating surface of the body, and rust is generated because the pretreatment liquid is acidic. Therefore, it is necessary to perform washing with water and pure water sufficiently so that the pretreatment liquid does not remain, and there is a problem that a large amount of clean water and pure water are consumed.

  Further, when the body is left for a long time after washing with water and pure water, the pretreatment liquid adhering to the body is dried and concentrated, and this is dried to cause streak rust (hereinafter referred to as muscle rust). ). Therefore, it is necessary to design between the pretreatment process and the electrodeposition process as quickly as possible, but in order to prevent the occurrence of such rust, the line after electrodeposition coating stopped. Sometimes it was necessary to install a storage line to temporarily evacuate the body after preprocessing. Installation of storage lines for emergencies has become a bottleneck in process design because it requires not only equipment costs but also a large space.

Furthermore, if the pretreatment liquid remains in the narrow part of the body, it is concentrated in the baking process after electrodeposition coating to become strongly acidic water, which erodes the undried electrodeposition coating film and causes secondary sagging. There was also.
Japanese Patent Laid-Open No. 10-46393

An object of this invention is to provide the pre-processing method which can prevent the muscle rust and electrodeposition secondary sagging after forming a chemical conversion film.
In order to achieve the above object, according to the present invention, there is provided a pretreatment method prior to an electrodeposition coating process for forming an electrodeposition coating film on the surface of an object to be coated, wherein a chemical conversion film is formed on the surface of the object to be coated. There is provided a pretreatment method for electrodeposition coating, comprising: a chemical conversion treatment step to be formed; and an alkaline water washing step for washing the object to be coated using an alkaline aqueous solution mainly composed of alkaline electrolyzed water. .

In the present invention, after the chemical conversion treatment step, the coated object is washed with an alkaline aqueous solution mainly composed of alkaline electrolyzed water. Therefore, even if the coated material is left for a long time before the electrodeposition coating process, Residual water is not concentrated on the acidic side, and generation of rust such as muscle rust can be prevented.

In addition, since the article to be coated is washed with an alkaline aqueous solution mainly composed of alkaline electrolyzed water after the chemical conversion treatment step, the electrodeposition is performed before the electrodeposition coating is energized by the alkaline aqueous solution remaining in the narrow part of the article to be coated. A coating film is deposited, which can prevent an excessive electrodeposition coating liquid from penetrating into a narrow portion or the like. As a result, secondary sagging that occurs after electrodeposition baking can be prevented.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a process diagram showing an embodiment of a process from an automobile body coating line (pretreatment to electrodeposition coating / baking) using the electrodeposition coating pretreatment method according to the present invention, and FIG. It is a figure which shows roughly the pre-processing apparatus from a surface treatment process of-to a draining drying process.

  As shown in FIG. 1, the pretreatment line of this example is composed of a degreasing process 1, a water washing process 2, a surface conditioning process 3, a chemical conversion treatment process 4, a water washing process 5, an alkaline water washing process 6, and a draining and drying process 7. After this, an electrodeposition coating process 8, a water washing process 9, and a baking process 10 are provided.

  In addition, since the pre-processing method which concerns on this example is the alkaline water washing process 6, it does not restrict | limit in particular about each process from the degreasing process 1-the water washing process 5 and the draining drying process 7-the baking process 10. The known manufacturing techniques (including manufacturing methods, direct / indirect materials, manufacturing apparatus / equipment, etc.) can be widely applied. Therefore, in adopting the pretreatment method of this example, from the degreasing process 1 to the water washing process 5 which is a pre-process of the alkaline water washing process 6 and the draining and drying process 7 to the baking process 10 which is a subsequent process of the alkaline water washing process 6. The existing coating line can be applied as it is for this process. That is, when remodeling an existing facility having a pure water washing step between the water washing step 5 and the draining and drying step 7, the effect of the present invention can be obtained only by changing the pure water washing step to the alkaline water washing step 6 according to this example. Can be fully exhibited.

  In the degreasing step 1, the automobile body is immersed in a degreasing tank filled with a strong alkaline type degreasing agent such as caustic soda and a surfactant held at about 40 to 60 ° C. for 2 to 3 minutes. And a step of removing dust.

    The water washing step 2 following the degreasing step 1 is a step of spraying normal temperature clean water onto the automobile body for about 20 seconds, for example, to wash the degreasing agent adhering to the body surface. This water washing step is performed in a plurality of stages, for example, twice (two steps) as necessary.

    In the surface conditioning step 3 following the water washing step 2, the automobile body is placed in a surface conditioning tank 31 (see FIG. 2) filled with a surface conditioning agent (for example, Surf Fine 5N-10 manufactured by Nippon Paint Co., Ltd.) held at room temperature. This is a step of immersing for about 20 seconds to form crystal nuclei for zinc phosphate crystals on the body surface.

    In the chemical conversion treatment step 4 following the surface conditioning step 3, the automobile body is immersed in a chemical conversion bath 41 (see FIG. 2) filled with a zinc phosphate-based chemical conversion treatment solution held at 40 to 50 ° C. for 2 to 3 minutes. This is a step of forming a zinc phosphate coating of about 3 to 10 μm (thickness after baking) on the body surface.

    The water washing step 5 following the chemical conversion treatment step 4 is a step of washing the chemical conversion treatment liquid adhering to the automobile body by spraying normal temperature clean water from the nozzle 51 (see FIG. 2) for about 20 seconds onto the automobile body. This water washing step 5 is performed in a plurality of stages, for example, 2 to 3 times as necessary. In FIG. 2, clean water used for washing is collected in the collection tank 52 and then sprayed from the nozzle 51.

  Further, in addition to or instead of spraying, a dip-type cleaning device that immerses the automobile body in a water tank filled with clean water at room temperature for about 20 seconds may be used. In addition, when the chemical conversion treatment liquid is used in a good state or a chemical conversion treatment liquid that does not cause a problem even if the chemical conversion treatment liquid remains, this cleaning step 5 is omitted, and the chemical conversion treatment step 4 is continued. The next alkaline water washing step 6 may be provided directly.

  In this example, the water-washing process using pure water is not provided after the water-washing process 5, but instead, an alkaline water-washing process 6 for washing the automobile body using an alkaline aqueous solution is provided. The surface of the automobile body that has undergone the chemical conversion treatment step 4 is acidic at a pH of around 4. However, by washing with an alkaline aqueous solution in this alkaline water washing step 6, the body surface changes from neutral to alkaline. Even if the body is left for a long time before the coating process 8, the generation of muscle rust can be suppressed. Also, the occurrence of secondary sagging can be suppressed.

    Examples of the alkaline aqueous solution used in the alkaline water washing step 6 include aqueous solutions containing ammonium hydroxide or an organic base and alkaline electrolyzed water, and particularly easy post-treatment (such as wastewater treatment) after washing with water. Alkaline electrolyzed water is most preferable as the alkaline aqueous solution according to this example because it has little influence on the chemical conversion film.

  The pH of the alkaline aqueous solution used in the alkaline water washing step 6 is preferably 8-12. If the pH is less than 8, the effect of the present invention is small, and if the pH exceeds 12, the chemical conversion film may be redissolved.

  Moreover, even if the alkaline water washing process 6 of this example is a dip system which immerses a motor vehicle body in the water tank 61 filled with alkaline aqueous solution as shown in FIG. 2, it is a spray system like the water washing process 5 mentioned above. Is not particularly limited. However, the dip type is desirable because it is easy to allow the alkaline aqueous solution to enter the panel mating surface of the body, but it is advantageous from the viewpoint of the equipment cost to use the method applied to the existing coating line.

  The washing time using the alkaline aqueous solution and the temperature of the alkaline aqueous solution are not particularly limited, but in this example, it is sufficient to attach the alkaline aqueous solution to the body surface. good.

  In the draining and drying step 7 following the alkaline water washing step 6, the automobile body is carried into the draining and drying furnace 71 and heated at 100 to 130 ° C. for 10 to 15 minutes. The draining and drying process 7 is not particularly limited, and a wide range of known manufacturing techniques (including a drying method, a drying apparatus / equipment, etc.) including a general manufacturing line can be widely applied. If electrodeposition coating is performed with the alkaline aqueous solution attached to the body, a local concentration difference occurs in the electrodeposition tank, resulting in uneven electrodeposition. This causes the alkaline aqueous solution on the body surface to evaporate in this draining and drying step 7. However, since this process is sufficient if it is evaporated, the draining and drying process 7 can be omitted depending on the state of attachment of the alkaline aqueous solution.

  The automobile body that has finished the draining and drying step 7 is made alkaline by the treatment with the alkaline aqueous solution, and there is no risk of rusting, so a storage line for temporary retraction is unnecessary.

    After performing the above pretreatment, an electrodeposition coating film is formed through each process of the electrodeposition coating process 8, the water washing process 9, and the baking drying process 10. These processes from electrodeposition coating 8 to baking drying 10 are not particularly limited, and are known manufacturing techniques (manufacturing methods, direct / indirect materials, manufacturing equipment / equipment, etc.) including general coating lines. Can be applied widely, so existing coating lines can be applied as they are.

    If an example of the process from the electrodeposition coating 8 to baking drying 10 is demonstrated, the motor vehicle body which finished the pre-processing will be conveyed to the electrodeposition coating process 8 as it is. This electrodeposition coating process 8 is for coating the entire front and back surfaces of the body steel plate for the purpose of rust prevention. The electrodeposition coating process (for example, blocked isocyanate-modified epoxy system) that provides high rust-preventing power is satisfied. Immerse the body in the tank. The electrodeposition paint is held at ± 1 ° C. in the electrodeposition tank so that the paint temperature is in the range of 25-30 ° C., for example, the coating time is 2-5 minutes, the voltage is 150-300V, the current is 2000A, etc. Cationic electrodeposition is performed under coating conditions.

    In the water washing step 9 following the electrodeposition coating step 8, normal water is sprayed for about 20 seconds to wash the filtrate of the automobile body, and the body is immersed in a water tank filled with water for about 20 seconds. Wash with water, and spray with normal temperature water for about 20 seconds. Thereby, the unreacted electrodeposition paint adhering to the electrodeposition coating film surface of the body is removed.

  In the baking process 10 following the water washing process 9, the electrodeposition coating film (wet state) of the body is baked at 150 to 170 ° C. for 15 to 30 minutes to form a dried electrodeposition coating film having a film thickness of 20 to 30 μm.

  The above is the outline of the process of this example from pretreatment to electrodeposition coating, but the point that the electrodeposition secondary sagging can be suppressed by the alkaline water washing process 6 using the alkaline aqueous solution of this example will be described.

  The electrodeposition secondary sagging means that the electrodeposition coating liquid remaining inside the steel sheet joint cannot be removed even by washing in the water washing step 9, and the body temperature reaches a high temperature of 100 ° C. or higher on the inlet side of the subsequent baking step 10. When this happens, it means a coating failure that bumps from the joint of the steel plates and hardens while corroding the uncured coating on the outer plate surface to cause irregularities on the coating surface. This electrodeposition secondary sagging defect impairs the appearance of the finished paint near the joint of the steel plates, and it takes a lot of man-hours to correct the appearance. For example, as shown in FIG. 3 (A), the connecting portion B between the side sill 50 and the center pillar 60 has a so-called side sill outer panel 51 and center pillar outer panel 61 as shown in FIG. It is a solid-contact structure, and the electrodeposition coating liquid that has entered the gap between the solid-contact surfaces D due to surface tension is sprayed in the baking furnace and flows down to the silouter. To do.

  In the pretreatment method of this example, the body is washed with an alkaline aqueous solution in the alkaline water washing step 6, and thus the alkaline aqueous solution infiltrates also into the steel sheet mating surface of the body by performing the alkaline water washing treatment by the dip method. . This alkaline aqueous solution remains on the mating surface of the steel sheet, but the electrodeposition coating film is deposited on the mating surface of the steel plate before energization of the electrodeposition coating using the weakly acidic paint by this alkaline aqueous solution, that is, when the body enters the electrodeposition bath. To do. Thereby, it can suppress that an excessive electrodeposition coating liquid penetrate | invades into a steel plate mating surface, As a result, the secondary sagging produced after electrodeposition baking can be prevented.

  The embodiment described above is described for facilitating the understanding of the present invention, and is not described for limiting the present invention. Therefore, each element disclosed in the above embodiment is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

It is process drawing which shows the pre-processing method which concerns on embodiment of this invention. It is a figure which shows roughly the pre-processing apparatus of the coating line principal part to which the pre-processing method which concerns on embodiment of this invention is applied. (A) is a perspective view which shows the motor vehicle body which is a to-be-coated object, (B) is an enlarged view of the B section. FIG. 4 is a schematic cross-sectional view taken along line CC in FIG. 3 (B). FIG. 5 is a diagram schematically showing a sagging trace after baking with a coating liquid flowing out from a steel plate joint portion (a center pillar and a side sill joint portion) on the vehicle body side, as viewed from the arrow E in FIG. 4.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Degreasing process 2 ... Water washing process 3 ... Surface adjustment process 4 ... Chemical conversion treatment process 5 ... Water washing process 6 ... Alkaline water washing process 7 ... Draining drying process 8 ... Electrodeposition coating process 9 ... Water washing process 10 ... Baking process

Claims (9)

A pretreatment method before an electrodeposition coating process for forming an electrodeposition coating on the surface of an object to be coated,
A chemical conversion treatment step for forming a chemical conversion film on the surface of the object to be coated;
An alkaline water washing step of washing the object to be coated using an alkaline aqueous solution mainly composed of alkaline electrolyzed water ;
A pretreatment method for electrodeposition coating, comprising:   The pretreatment method for electrodeposition coating according to claim 1, further comprising a water washing step of washing the object to be coated using clean water between the chemical conversion treatment step and the alkaline water washing step.   3. The pretreatment method for electrodeposition coating according to claim 1 or 2, further comprising a degreasing cleaning step of cleaning the object to be coated using a degreasing liquid before the chemical conversion treatment step.   The pretreatment method for electrodeposition coating according to any one of claims 1 to 3, further comprising a drying step of drying the object to be coated between the alkaline water washing step and the electrodeposition coating step. The pretreatment method for electrodeposition coating according to any one of claims 1 to 4 , wherein the pH of the alkaline aqueous solution is 8 to 12. The pretreatment method for electrodeposition coating according to any one of claims 1 to 5 , wherein the alkaline water washing step is performed by immersing the article to be coated in the alkaline aqueous solution. The electrodeposition coating process according to any one of claims 1 to 6 , wherein there is no step of washing the object to be coated with pure water between the chemical conversion treatment step and the electrodeposition coating step. Pre-processing method. The chemical conversion treatment step, the pretreatment method for electrodeposition coating according to any one of claims 1 to 7, characterized in that to form a conversion coating on the coating object surface with a zinc phosphate conversion treatment solution . The electrodeposition coating pretreatment according to any one of claims 1 to 8 , wherein the electrodeposition coating step forms an electrodeposition coating film on the surface of the object to be coated using a cationic electrodeposition coating. Method.

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