JPH0130920B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for improving the adhesion of a transparent or translucent anionic electrodeposition coating, for example, on the surface of a metal-plated article. Conventionally, metal plating has been widely applied not only to articles made of metals such as iron, copper, brass, cupronickel, zinc, and aluminum, but also to articles made of synthetic resin for anticorrosion, corrosion resistance, or decorative purposes. Ta. However, if the plating metal is nickel (Ni) or a nickel alloy, it will turn black in a very short time in an atmosphere containing sulfur oxides (SOx), and it will also turn black in an extremely short period of time in an atmosphere containing sulfur oxides (SOx), and can also be easily exposed to sweat and moisture originating from the human body. However, it loses its brightness or changes color. If the plating metal is a noble metal such as gold, silver, rhodium, etc., there will be no chemical changes or discoloration as described above, but since the valence of each metal is expensive, thick plating cannot be applied. It is economically difficult and requires an extremely thin plating layer. As a result, the plating layer wears out during use, and the purpose of plating, such as anticorrosion, as described above, cannot be achieved. Furthermore, in terms of appearance, the metallic luster specific to the type of metal used for plating is often respected, and milder metallic luster or other colors are often required. For this purpose, attempts have been made to coat the surface of the metal plating layer with a transparent or translucent paint. As such a coating method, a dipping method or a spraying method is generally used. Even with these painting methods, if the outer shape of the plated item to be coated is simple, the coating can be applied relatively uniformly, but if the outer shape is complex, even the spray method will not coat the plated object. Also, so-called sagging and caribulation are likely to occur, and it is difficult to obtain a uniform coating film. Furthermore, these methods usually have problems with environmental hygiene due to the organic solvents in the paint, such as thinner, and the painting process itself requires special skills such as adjusting the paint viscosity. Painting efficiency is also low. Moreover, the above-mentioned coating on the surface of a plated article has some fundamental drawbacks. This means that the adhesion between the plating layer and the coating film is poor, and the coating film is likely to peel off. Normally, the surface of the plating layer applied to the surface of the product is extremely smooth, so it is difficult to mechanically adhere to the coating film, and the metal of the plating layer may be susceptible to oxidation or passivation. It is known that there is a change over time, which causes poor adhesion with the paint film. In addition, in all conventional cases, the plating process and painting process are necessarily separate and separate processes, so oil and dust contaminate the surface of the plating layer, which can lead to poor adhesion. There is. Methods for improving the adhesion between the surface of the plating layer and the coating film are described in Japanese Patent Publication No. 49-25537 and Japanese Patent Publication No. 43-2768.
No. 53-19981, No. 44417-47, and No. 35697-57. According to this, a chromate treatment using chromic acid, a salt thereof, a dichromate, or the like and an electrolytic chromic acid treatment are performed on the surface of an article that has been plated or the like. However, with these conventional techniques, the adhesion of the paint film is insufficient. For example, when painting eyeglass frames, sweat can penetrate into the paint film, cause rust, and cause the paint film to peel off. I couldn't solve the problem. Furthermore, since coating is carried out by dipping or spraying, it is difficult to obtain a uniform coating, and the problem of spoiling the aesthetic appearance of the metallic luster on the surface of the article remains unsolved. Additionally, chemically treated coatings (including chromate coatings)
A method of forming a coating film by electrodeposition on the above is disclosed in Japanese Patent Publication No. 48-29379.
However, although this method may provide a certain degree of adhesion, it is not possible to make the surface condition transparent and uniform, and the problem of spoiling the aesthetic appearance of the metallic luster on the surface of the article remains unsolved. . The present invention relates to a method for improving the adhesion of an anionic electrodeposition film in which anionic electrodeposition coating is applied as a final finish to an article having at least a metal layer on the surface. The electrolytic bath is a water-soluble one with a pH of 0 to 8 containing 0.01 to 1 g of catalyst, a bath temperature of 20 to 60°C, and a current density of 0.5.
Cathodic electrolysis is performed for 0.5 to 5 minutes under electrolytic conditions of ~5 A/ ^dm2 , the electrolytic catalyst is a water-soluble substance having sulfate ions or carboxylic acid ions in the presence of ammonium, and the cathodic electrolysis is performed This is a method for improving the adhesion of anionic electrodeposition coatings, which is characterized by applying anionic electrodeposition coating to form a transparent or semitransparent coating film after the metal plating process. This can be directly connected to the anion electrodeposition coating process via this cathode electrolysis. The article that is applied to the present invention and has at least a metal layer on its surface is an article that has been usually subjected to a plating treatment, and can be plated by any method such as electrolytic plating, electroless plating, or melt plating. This includes items that have been sold.
Types of plating metals include Ni, Au, Zn, Cr,
In addition to single metals such as Sn-Cu, Sn-Ni-Cu,
Also includes alloys such as Ni-Co and Sn-Co. Materials for articles to which such plating is applied include, in addition to metals, synthetic resins imparted with electrical conductivity and synthetic resins whose surfaces are imparted with electrical conductivity. Examples of such synthetic resins include composite resins such as ABS resins, polyolefin resins such as polypropylene, and polyamide resins such as nylon. The object of the present invention is to apply a transparent or semi-transparent coating that maintains the beauty of the metallic luster caused by the plating and has excellent adhesion to articles that have been subjected to such plating treatment and have at least a metal layer on the surface. This is to form a film. The aqueous solution containing hexavalent chromium ions, which is the electrolytic bath used in the present invention, contains 5 to 100 g of Cr ⁶⁺ and has a pH of
0 to 8 aqueous solution containing an electrolytic catalyst of 0.1 to 1
The content is within the range of g/g. This electrocatalyst is a water-soluble substance containing sulfate ions or carboxylic acid ions in the presence of ammonium. Chromic acid or its salts as a source of Cr6 ⁺ , such as potassium chromate, ammonium chromate,
Sodium chromate, ammonium dichromate,
Examples include sodium dichromate and potassium dichromate. When using such an electrolytic bath to cathodically electrolyze an article having at least a metal layer on the surface, the article is immersed in the bath while attached to the attachment device in the usual manner, and the article is cathode-electrolyzed. It is electrolyzed as Electrolysis conditions include bath temperature of 20 to 60°C and current density.
Dk0.5-5A/ ^dm2 for 0.5-5 minutes. At the anode,
Commonly used stainless steel carbon and lead-tin alloys are used. If the current density is less than 0.5 A/dm ² , a colorless and transparent chromate film containing hexavalent chromium will not be sufficiently formed. Furthermore, if the current density exceeds 5 A/dm ² , the chromate film becomes uneven and the aesthetic appearance of the metallic luster formed on the surface is impaired. Furthermore, if the electrolysis time is 0.5 minutes or less, the thickness of the chromate film formed will be too small, resulting in low resistance to organic solvents and the like. Furthermore, if electrolysis is carried out for an electrolysis time exceeding 5 minutes, the chromate film formed will be uneven, and as described above, the aesthetic appearance due to metal plating will be impaired. Further, if electrolysis is performed in an aqueous solution with a pH higher than 8, the adhesion to the coating film formed by anionic electrodeposition coating described later will be reduced. When using sulfate ions as an electrocatalyst,
Since the surface of the article is colored yellow by the sulfate ions, it is necessary to use ammonium in combination to alleviate this coloring. This ammonium is
The above-mentioned source of Cr ⁺ ₆ may be one in which ammonium salt is used, or ammonium sulfate or the like may be used. Furthermore, a water-soluble article having carboxylic acid ions may be included as an electrolytic catalyst. Such an electrocatalyst is 0.01 to 1 g/
If it is included in the aqueous solution constituting the electrolytic bath, a good coating film can be formed when performing anion electrodeposition coating, which will be described later. As described above, when cathodic electrolysis is performed, a colorless transparent or translucent chromate film containing hexavalent chromium is formed on the surface of the plating layer of the article.
This chromate film acts as a binder with the anionic electrodeposition coating that is applied next. According to the method of the present invention, anionic electrodeposition of a water-based paint is applied onto such a chromate film. As such water-based paints, commercially available paints containing acrylic resins, phenol-aldehyde initial condensates, etherified melamine resins, amine-neutralized alkyd resins, etc. as vehicles can be used as they are. The electrodeposition conditions are not particularly different from those of conventional anionic electrodeposition coating methods. After electrodeposition, a coating film curing treatment is applied in a conventional manner, for example at 160 to 200° C., thereby completing the coating on the surface of the plated article according to the present invention. The reason for performing anion coating in the present invention is as follows.
In addition to making the coating thickness uniform, the chromate film formed by the electrolysis described above elutes Cr ⁶⁺ by electrode reaction, and this Cr ⁶⁺ reacts with anions to insolubilize and precipitate. This is because the adhesion strength can be greatly increased. Therefore, the Cr eluted from the chromate film will also be distributed in the coating formed by anionic electrodeposition, resulting in a high adhesion strength that cannot be obtained with ordinary coating methods such as dipping or spraying. A coating film can be formed. Moreover, since such a phenomenon does not occur even in cationic electrodeposition coating, anionic electrodeposition coating must be performed in the present invention. As described above, according to the present invention, remarkable improvement in adhesion to the plating layer is observed even with the same water-based paint film. This adhesion test includes the following:
Five test methods A to E were adopted. A: Tape peeling...JIS K-5400 B: Acetone immersion...24 in acetone (reagent grade 1)
After soaking for an hour, peel off the tape (cross cut). C: Ethanol immersion...After 48 hours of immersion in ethanol (grade 1 reagent), tape peeling (cross cut). D: Cast test...according to JIS H8610 (48h). E: Erichsen...Using an Erichsen testing machine according to JIS B7729, tape was peeled off after extruding 6 mm. Example 1 A brass plate (7 x 15 x 0.3 cm) was attached to a fixing jig for electrolysis in the usual manner, and Ni plating was applied to a thickness of 5μ by the electrolysis method in the usual manner. Only the bath was changed and Au plating with a thickness of 0.1μ was applied on top of it. Without removing it from the attachment jig, cathodic electrolysis was performed in the following chromium ion electrolytic bath using this material as a cathode and 18-8 stainless steel as an anode. Chromium ion electrolytic bath Potassium dichromate...120g/Ammonium sulfate...0.5g/PH...4.3 Electrolytic condition bath Temperature...45℃ Current density (D _k )...3A/dm ² Electrolysis time...2 minutes Immediately after the above cathodic electrolysis is completed was taken out of the bath and rinsed in a washing tank while still attached to the anchoring device, and then anionic electrodeposition coating was applied while it was still attached to the same anchoring device. That is, it was suspended in an anionic thermosetting acrylic resin electrodeposition paint bath with a solid content of 12%, and this was used as an anode, and 18-8 stainless steel was used as a cathode, and a voltage of 100 V was applied.
Electricity was applied for 1 minute at a bath temperature of 25°C. After energization was completed, it was removed from the paint bath and then baked at 170°C for 20 minutes.
The test results of the adhesion of the obtained coating film are shown in Table 1 together with Comparative Example 1 in which chromium ion electrolytic bath electrolysis was not performed. Example 2 Iron plate (7×
15 x 0.3 cm), and cathode electrolysis was carried out in the same manner as in Example 1 in the following chromium ion electrolytic bath. Chromium ion electrolytic bath Potassium chromate...50g/Sodium acetate...1g/PH...8.0 Electrolytic condition bath Temperature...25°C Current density (D _k )...0.5A/dm ² Electrolysis time...After 5 minutes of energization, remove from the electrolytic bath Then, I washed it with water, and applied the following anionic electrodeposition coating while it was still attached to the same attachment tool. The paint and electrolytic conditions used for this coating were the same as in Example 1. The baking conditions after painting were also the same as in Example 1: 170°C, 20 minutes. The adhesion test results of the obtained coating film are listed in Table 1 together with Comparative Example 2 in which chromium ion electrolytic bath electrolysis was omitted.

[Table] As described above, according to the present invention, in a method of painting as a final finish on an article having a metal layer on at least the surface, uniform and extremely high adhesion can be achieved while maintaining the aesthetic appearance of the metallic luster on the surface. A transparent or semi-transparent coating film can be easily formed. Moreover, when forming the metal layer by plating,
The jig can be used to form the metal plating by cathodic electrolysis in an electrolytic bath using hexavalent chromium.
The surface treatment can be performed as a series of processes including the electrodeposition coating process or the baking process without further pulling up and removing it from the attachment jig. This makes it possible to significantly streamline the work process. Moreover, in this case, since the plated metal is not passivated or contaminated between the metal plating process and the electrodeposition coating process, the adhesion of the formed coating film is further improved.

Claims (1)

[Scope of Claims] 1. A method for improving the adhesion of an anionic electrodeposition film in which anionic electrodeposition coating is applied as a final finish to an article having at least a metal layer on the surface, comprising: An electrolytic bath is an aqueous solution with a pH of 0 to 8 containing 0.01 to 1 g of an electrolytic catalyst, a bath temperature of 20 to 60°C, and a current density of 0.5.
Cathodic electrolysis is performed for 0.5 to 5 minutes under electrolytic conditions of ~5 A/dm ² , the electrolytic catalyst is a water-soluble substance having sulfate ions or carboxylic acid ions in the presence of ammonium, and the cathodic electrolysis is performed under electrolytic conditions of ~5 A/dm2. 1. A method for improving the adhesion of an anionic electrodeposition coating film, which comprises applying anionic electrodeposition coating after coating to form a transparent or semitransparent coating film.