JPH055910B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to an electrodeposition coating method, and more specifically, the present invention suppresses abnormal electrodeposition due to deterioration of the chemical conversion treatment state or the deterioration of the electrodeposition coating liquid in the electrodeposition coating pretreatment of conductive articles, and provides excellent This invention relates to an electrodeposition coating method that provides good coating appearance and coating performance. (Prior Art) Electrodeposition coating is widely practiced in many fields because it can impart excellent coating appearance and coating performance to conductive articles with a single coating. On the other hand, conductive articles are generally subjected to chemical conversion treatment for the purpose of improving corrosion resistance, improving adhesion with the coating film, etc., when performing electrodeposition coating. However, this chemical conversion treatment is insufficient,
Appearance abnormalities such as skin roughness, pinholes, and unevenness often occur in electrodeposition coatings due to continuous electrodeposition coating on conductive articles or changes in the composition of the electrodeposition coating solution due to changes in the solution itself over time. It will be done. As a way to eliminate such appearance abnormalities,
This problem can be solved to some extent by adding surfactants to the electrodeposition coating solution, controlling the chemical conversion treatment solution and electrodeposition coating solution, and strengthening the management of each processing condition, but it is still insufficient and needs improvement. It is requested. (Problems to be Solved by the Present Invention) The purpose of the present invention is to suppress the occurrence of appearance abnormalities in the conventional method, and to prepare the surface of conductive articles using a specific pretreatment liquid before electrodeposition coating. The present invention provides an electrodeposition coating method for performing treatment. (Means for Solving the Problems) To summarize the present invention, when electrocoating a conductive article, the article is coated with a fluorosurfactant containing a perfluorocarbon group before the electrocoating. This is an electrodeposition coating method characterized by performing electrodeposition coating after surface conditioning treatment with an aqueous liquid. As a result of intensive studies in order to eliminate the occurrence of appearance abnormalities in the conventional electrodeposition coating, the present inventors added surfactants known in the prior art, particularly fluorine-based surfactants, to the electrodeposition coating liquid. It was found that even when mixed, a thick film tends to be unable to be formed due to re-dissolution of the coating film during washing with water or re-dissolution of the coating film during electrodeposition coating. In addition, defects such as water marks and pinholes caused by the paint film being repelled during washing were also observed. However, when a conductive article is subjected to surface conditioning treatment in advance with an aqueous solution containing the fluorine-based surfactant shown below, a surprising effect occurs that suppresses appearance abnormalities, although the theoretical reason is not clear. Based on this knowledge, the present invention was completed. To explain the present invention in more detail, the fluorosurfactant having a perfluorocarbon group to be blended in the surface conditioning treatment liquid has a carbon atom number of 3 to 12.
Any type of anionic, nonionic, cationic, or anionic-cationic amphoteric type can be used. To give specific examples, examples of the anionic fluorine-based surfactant that can be used include perfluoroalkyl carboxylates, perfluoroalkyl sulfone hydrochloric acids, and perfluoroalkyl phosphates. In addition, as nonionic fluorine-based surfactants,
For example, perfluoroalkyl ethylene oxide adducts, perfluoroalkyl oligomers, etc. can be used. Next, as the cationic fluorine-based surfactant, for example, perfluoroalkyl quaternary ammonium salts can be used. In addition, as the anionic-cationic amphoteric fluorine surfactant, for example, perfluoroalkylbetaine and the like can be used. In the present invention, it is particularly preferable to use an anionic fluorine-containing surfactant and a nonionic fluorine-containing surfactant because they are uniformly adsorbed onto the surface of the conductive article and have an excellent effect of suppressing appearance abnormalities. The surface conditioning treatment liquid used in the present invention contains 0.001 to 5.0% by weight of the fluorine-based surfactant, preferably
It is used by adding it to water to a concentration of 0.005 to 3.0% by weight. If the amount added is less than 0.001% by weight, it is not preferable because treatment unevenness tends to occur on the surface of the conductive article and the desired effect of the present invention cannot be obtained. On the other hand, if it exceeds 5% by weight, the electrical resistance of the treated conductive article increases, coating unevenness tends to occur during electrodeposition coating, and the throwing power during electrodeposition coating decreases, which is not preferable. The surface conditioning treatment liquid of the present invention can be easily prepared by placing a fluorine-containing surfactant and deionized water into a container separately or simultaneously and stirring and mixing them. In the present invention, when a hydrophilic solvent such as isopropyl alcohol, butyl cellosolve, or ethyl cellosolve is added to and mixed with the treatment liquid, favorable results can be obtained, such as improved wettability for conductive articles, prevention of foaming, and improvement in treatment efficiency. . This hydrophilic solvent is contained in the treatment liquid in an amount of 0.5 to 20% by weight, preferably 1 to 10% by weight.
It is added in a range of % by weight. In the electrodeposition coating method of the present invention, after immersing a conductive article that has been subjected to a chemical conversion treatment in the surface conditioning treatment liquid,
This is done by ordinary electrodeposition coating. The surface conditioning treatment is achieved by immersing the conductive article in a surface conditioning treatment solution whose temperature ranges from room temperature to 50° C. for 30 seconds to 5 minutes, or by spraying the article. After the surface conditioning treatment, the conductive article is immersed in an electrodeposition coating liquid and used as an anode, and a cathode is provided.
Electrodeposition coating is performed by applying direct current at a voltage of 10 to 300 volts for 10 seconds to 5 minutes. After the electrodeposition coating is completed, remove the item from the liquid,
Thoroughly drain the liquid and bake the coating film by washing with water or without washing by heating and drying at 100 to 300°C for 10 to 60 minutes. The electrodeposition coating liquid used in the present invention contains a polycarboxylic acid resin and an amino resin as film-forming components. Examples of the polycarboxylic acid resin include saturated or unsaturated alkyd resins, oil modified products thereof, and carboxyl groups. One or a mixture of two or more of acrylic resins, vinyl resins, fluororesins, etc., having at least a portion of the carboxyl groups neutralized with organic amines or ammonia and permeated with water or diluted to form an emulsion. It is. As the amino resin, melanin resin, urea resin, benzoguanamine resin, acetoguanamine resin, etc. can be used. The conductive article that can be used in the present invention is not limited in shape, size, material, etc., as long as it has conductivity, and examples include iron, copper, aluminum, magnesium, titanium, etc., or alloys thereof,
Further examples include plastics with a metal plating layer formed on the surface. These conductive articles are usually subjected to chemical conversion treatment before electrodeposition coating, but types of chemical conversion treatment include various phosphate treatments,
Chromate treatment, boehmite treatment, anodic oxidation treatment, etc. are suitable. (Examples) In order to explain the present invention more specifically, Examples are shown below, but the present invention is not limited to these Examples. In addition, the number of parts in the examples means parts by weight unless otherwise specified. Example 1 In a container, put 940 parts of deionized water, 30 parts of anionic fluorine-based surfactant (perfluoroalkyl carboxylate, trade name: Unidyne DS101, manufactured by Daikin), and 30 parts of isopropyl alcohol, and stir thoroughly to coat the surface. An adjusted treatment solution was prepared. An aluminum plate that had been anodized according to a conventional method was immersed in this surface conditioning treatment solution for 1 minute, and then immersed as an anode in an allyl-melamine anionic electrodeposition coating with a resin solid content of 8% by weight. Electrodeposition coating was applied by applying a direct current of 180 volts to the stainless steel plate for 2 minutes. Next, the aluminum plate was pulled out of the liquid, washed with water, and heated to 180°C.
It was heated and dried at ℃ for 30 minutes. In this way, electrodeposition coating was carried out continuously without adjusting the solid content of the electrodeposition coating liquid. The acrylic-melanin anionic electrodeposition coating liquid contains 5 parts of methacrylic acid, 15 parts of 2-hydroxyethyl methacrylate, and 40 parts of butyl acrylate.
A copolymer obtained by reacting 1 part, 40 parts of styrene, and 80 parts of secondary butanol was neutralized with diethylamine, 30 parts of hexamethoxymethylolmelamine was added, and the copolymer was diluted to 8% by weight with deionized water. . Comparative Example 1 Electrodeposition coating was performed in the same manner as in Example 1, except that the surface conditioning treatment was not performed and water washing was performed. Examples 2 to 6 and Comparative Examples 2 to 5 Electrodeposition coating was performed in the same manner as in Example 1, except that the composition of the surface conditioning treatment liquid was changed to the contents shown in Table 1. The appearance, film thickness, and film performance of the electrodeposition coatings obtained in the following Examples and Comparative Examples were as shown in Table 2.

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[Table] Comparative Example 6 All except that 30 parts of an anionic fluorine-based surfactant (perfluoroalkyl carboxylate, trade name Unidyne DS101, manufactured by Daikin) was added to the electrodeposition coating solution used in Comparative Example 1. Electrodeposition coating was performed using the same method. As a result, the film thickness at the start of electrodeposition coating was 14μm.
When treated with 2 m ² , the film thickness decreased to 6 μm, water marks and pinholes were observed in the coating film, and the effect of adding the anionic fluorosurfactant was not achieved. Example 7 An iron plate was degreased, washed with water, treated with zinc phosphate (concentration: 4%, solution temperature: 50°C, immersed for 1 minute), and washed with water according to a conventional method, and then coated with a commercially available acrylic-melamine anion type electrode with 8% by weight of resin solids. It was immersed as an anode in a coating solution (product name: Honey Clean, manufactured by Honey Kasei Co., Ltd.), and a voltage of 100 volts was applied for 2 minutes between it and a stainless steel plate as the counter electrode, then it was pulled out of the solution, drained, and washed with water. After that, electrodeposition coating was performed continuously by heating and drying at 170°C for 30 minutes. However, the zinc phosphate treatment solution was not renewed, and the electrodeposition coating solution was controlled by replenishing resin solid content, ion exchange treatment, etc. As a result, as the zinc phosphate treatment solution deteriorated, appearance abnormalities such as unevenness and skin irritation were observed in the electrodeposition coating. At this point, as in Example 1, the iron plate treated with zinc phosphate was treated with a surface conditioning treatment liquid before electrocoating, and then electrocoating was performed, and the appearance abnormality was resolved and the beautiful painted appearance was achieved. I started to be able to do it. (Effects of the Invention) As explained above, the electrodeposition coating method of the present invention suppresses the effects of changes over time in chemical conversion treatment liquids and electrodeposition coating liquids, and provides excellent electrodeposition coating appearance and coating film performance over a long period of time. This has the effect that an electrodeposition coated article exhibiting the following properties can be obtained.

Claims (1)

[Claims] 1. When electrocoating a conductive article, the article is subjected to surface conditioning treatment with a 0.001 to 5.0% by weight aqueous liquid of a fluorine-based surfactant containing a perfluorocarbon group before the electrodeposition coating. An electrodeposition coating method characterized by: