JPS6233320B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for forming an anionic electrodeposition coating film on the surface of a metal-plated thermoplastic resin article at a low temperature. Metal-plated metal articles are used in a wide variety of fields due to their advantages of having both the luster of plated metals and the high mechanical strength of raw metals.
Switches, handles, When used as a panel, it has problems such as a cold feel and a cold shine. In order to reduce the coldness of the luster, recently, instead of the conventional mainstream chrome plating, binary alloys such as tin-copper, tin-copper-zinc, nickel-cobalt-tungsten, and tin-copper are being used. Plating of ternary alloys such as nickel-copper is increasingly being used.
Even with such alloy plating, since the metal is metal, it is desirable that it still have a cool luster, and preferably a warm luster. Another drawback of this type of alloy plating is that it has poorer corrosion resistance than chrome plating. Not only is it corroded by sweat and zinc acid gas, but fingerprints also tend to remain as stains, which is a kind of corrosion. Recently, transparent or translucent paint is often applied to the upper surface of the mating surface in order to improve the gloss or appearance mentioned above and to protect it from damage due to corrosion. If the painting is done by brushing or spray painting, it is difficult to obtain a coating film with a uniform thickness, and sagging and fogging are likely to occur.
When fine irregularities such as hair lines and spin are applied, it is difficult to accurately reproduce the irregularities. Therefore, when accurate reproduction is required, electrodeposited coatings that are easy to reproduce have come to be used. This electrodeposition coating film uses water-soluble or water-dispersible paint to coat the object (in this case, a metal-plated product).
This is a coating method in which electrolysis is carried out using a molten metal as an anode or a cathode, thereby forming a coating film, and then heating and curing the coating film to convert it into a tough cured coating film.
The reasons why the electrodeposition coating method is commonly used are: (1) The thickness of the deposited coating can be freely controlled simply by adjusting the voltage. (2) Since it has excellent throwing power, it is possible to apply thick coatings to fine details such as irregularities on objects. (3) Since it is a water-based paint, there are fewer considerations for disaster prevention such as fire. Examples include. However, although there is no difficulty in applying the electrodeposition coating method, which has such advantages, when the base material of the article is metal, it cannot be applied when the base material is thermoplastic resin (hereinafter also simply referred to as resin). has been considered inapplicable. The reason for this will be explained later. Thermoplastic resins (hereinafter simply referred to as resins), which have recently been widely used as base materials for articles, are significantly easier to mold than metals, even if the uneven shapes of the articles are minute and complex. In addition, it has the advantage of reducing the weight of the article, and it is also easy to impart conductivity to the resin, so the surface of the article is plated with various metals, just as in the case of metal articles. In this case, as with metal-plated products, there are of course disadvantages such as unnecessary metallic luster on the plated surface and susceptibility to corrosion. As with plated metal articles, the above-mentioned difficulties should be remedied by electrocoating an anionic paint on the plated surface, but as mentioned above, this is not actually possible. Not known. The reason for this is that thermoplastic resin articles are
Its deformation temperature is extremely low; for example, the most commonly used ABS resin product has a deformation temperature of only about 90°C. However, as mentioned above, anionic electrodeposition coating requires a process of curing the resulting coating film, which is called curing or baking.
Heat treatment at 160-200°C for 20-30 minutes is required. Of course, at this temperature, the article itself becomes deformed. This is the reason why anionic electrodeposition coating has not been applied to resin articles. If a means is found that allows the curing of the electrodeposited coating to be completed at a temperature lower than the heat distortion temperature of the resin article, then the metal-plated resin article will also be treated with anionic materials in the same way as the metal article. In addition to enjoying the advantages of electrodeposition coating, it should also be possible to enjoy the advantages unique to resins, such as light weight, low cost, and ease of molding. The present invention has been made from this point of view, and involves immersing a metal-plated thermoplastic resin product coated with an anionic electrodeposition coating in a pretreatment liquid as described later, and pulling it up. It is characterized by heating at around 75°C for at least 30 minutes after washing. An anionic electrodeposition coating film is, of course, a coating film formed on a metal-plated resin article by an anionic electrodeposition coating method, and is different from the coating film described above as a conventional method. No. As a reminder, the anionic electrodeposition material used in the present invention mainly consists of a water-soluble or water-dispersible resin selected from acrylic-melamine resins, epoxy-melamine resins, alkyd-melamine resins, etc. Examples include those containing some solvent and neutralizing agent. For electrodeposition coating, the solid content concentration of the above paint is adjusted to about 5 to 30% in the electrolytic bath, and the coated object is made of a glazed resin article as an anode and a carbon plate or stainless steel plate SUS304 is used as a counter electrode. As, 10~
Electricity is applied at a voltage of 200V, preferably 20 to 50V, for 30 seconds to 3 minutes. Thus, a spongy coating film with poor gloss is deposited on the plated surface of the article. In the present invention, this material is then immersed in a pretreatment liquid. Specifically, this pretreatment liquid includes 5 to 90% organic solvent, 5 to 90% organic or inorganic acid,
It is an aqueous solution containing 1-15% surfactant and 0.1-1% metal salt. Examples of organic solvents used here include one or a mixed solvent of two or more of methanol, ethanol, propyl alcohol, butanol, methyl cellosolve, ethyl cellosolve, acetone, and methyl ethyl ketone. ,
Examples of surfactants include one or more mixed acids such as sulfuric acid, nitric acid, hydrofluoric acid, acetic acid, formic acid, citric acid, tartaric acid, malic acid, and areic acid. Examples of surfactants include anionic and nonionic surfactants. Or a mixed activator of two or more types, furthermore, typical examples of metal salts include one or a mixed salt of two or more of inorganic salts or organic salts containing Sn, Pb, Zn, Co, Mg, and Ni. . The types and composition ratios of the constituent substances of the pretreatment liquid were found to be appropriate as a result of trial and error experiments conducted by the present inventors. However, in terms of types, metal salts are catalysts when the vehicle of water-based paint is crosslinked and cured, and organic solvents serve to swell the electrodeposition coating and make it easier for the catalyst to penetrate inside the coating. The surfactant is a substance that promotes its function, and the acid is a substance that is partly well known as having the effect of accelerating the hardening of the coating film. The conditions for immersing the plated article in such a pretreatment liquid are sufficient at room temperature, particularly at a temperature of about 10 to 50°C, for about 15 seconds to several minutes. After being immersed in the pre-treatment liquid, it is of course taken out, washed with clean water, dried, and then heated at around 75℃, especially 70 to 80℃ for 30 minutes or more, thereby curing the electrodeposited coating. . Drying can be performed as part of this heating. Normally, if the heating temperature is below 70℃, it is difficult to obtain sufficient gloss on the coating surface, and
At temperatures above ℃, there is a risk of deformation of the product. The heating time of at least 30 minutes is the time required for the vehicle to crosslink and cure; longer times are acceptable. Within 30 minutes, the so-called hardening reaction is almost complete and baking is complete. If the time is less than about 30 minutes, the gloss of the painted surface and the film performance will be poor. Therefore, in consideration of work efficiency, the appropriate heating time is about 60 to 120 minutes. Example 1 Anionic water-soluble acrylic-melamine resin paint was applied to a knob for electrical equipment made of nickel-plated ABS resin (diameter 30 mm x height 20 mm bottomed inner cylinder) as usual. Anion electrodeposition coating. That is, the electrodeposition conditions were a vehicle concentration of 15%, 30 volts, and 1 minute. This product was immersed in a pretreatment liquid having the following composition. Butanol: 30% Citric acid: 20% Alkyl sulfosuccinate: 1% Cobalt sulfate: 0.3% Immersed at 25℃ for 1 minute, then pulled out and washed with water, then heated to 80℃ for 60 minutes
A hardening process was performed by heating for 30 minutes. The physical properties of the resulting coating film are as listed in Table 1. Example 2 An article was used that had the same knob as in Example 1, but the plating metal was Ni-Sn. The electrodeposition paint used was an anionic water-soluble epoxy-melamine resin paint. This product was prepared in the usual manner, with vehicle concentration
20% and an electrolytic voltage of 50 V for 2 minutes, and then immersed in a pretreatment solution having the following composition. Butyl cellosolve......10% Succinic acid...50% Polyoxyethylene nonyl phenol ether
...3% Cobalt naphthenate ...0.2% Immersion conditions were 25°C for 2 minutes. After dipping, it was pulled out, washed, and heat-cured at 80°C for 50 minutes. The physical properties of the resulting coating film are as listed in Table 1. Example 3 The article used was a knob of the same size as in Example 1, but the base resin was polyacetal and the plating metal was Sn--Cu alloy. This material was coated with an anionic water-dispersible acrylic-melamine resin paint by anionic electrodeposition in a conventional manner. The electrodeposition conditions were a vehicle concentration of 15%, an electrolytic voltage of 20 V, and a current application time of 2 minutes. Next, add this material to a pretreatment solution with the following composition.
It was immersed for 1 minute at 25°C. Ethanol: 60% Sulfuric acid: 10% Sodium laurylbenzenesulfonate
...3% Lead sulfate 0.1% After being pulled out of the solution, it was heat-hardened at 70°C for 120 minutes. The properties of the obtained coating film are as listed in Table 1. Note that Comparative Examples 1 to 3 are also listed in Table 1, but these are those in which the immersion operation in the pretreatment liquid as in Examples 1 to 3 was not performed, and other electrodeposition or , heat curing was the same as that described in Examples 1 to 3. Moreover, the coating film performance test is as follows. Ethanol wiping: Wipe the painted surface by hand with gauze impregnated with pharmacopoeial ethanol and check the number of times the painted surface peels off. 20 times or more is considered a pass. Salt spray test: According to the regulations of JIS-H8617. Fingerprint stain test: Apply a fingerprint by pressing your finger against the painted surface, and observe the degree of discoloration after 60 days. Sulfur dioxide gas test: The test item was mixed with a mixed aqueous solution of 320ml of 1% sodium thiosulfite and 80ml of 0.1N sulfuric acid.
Place it in a desiccator containing 200ml and leave it at room temperature for 20 hours, then observe the state of discoloration.

【table】

[Table] Since the present invention is constructed as described above, it is possible to apply anion electrodeposition coating even to tight articles made of thermoplastic resin, which has conventionally been considered impossible due to thermal deformation caused by curing treatment. Because it has been made possible,
The advantages of the coating can now be enjoyed as is.

Claims (1)

[Claims] 1. A metal-plated thermoplastic resin article coated with an anionic electrodeposited film is heated with methanol, ethanol,
One or more mixed solvents of propyl alcohol, butanol, methyl cellosolve, ethyl cellosolve, acetone, methyl ethyl ketone
90%, hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, acetic acid, formic acid,
5-90% of one or more mixed acids of citric acid, tartaric acid, malic acid, and areic acid, 1-15% of one or more mixed surfactants of anionic and nonionic surfactants, Sn , Pb, Zn,
It is immersed in a pretreatment solution consisting of an aqueous solution containing 0.1 to 1% of one or more mixed salts of inorganic salts or organic salts containing Co, Mg, and Ni, and then pulled up after being washed for 70~
A low-temperature curing method for anionic electrodeposition coatings, characterized by heating at 80°C for at least 30 minutes.