JPS59208096A - Low temperature curing method of anion electrodeposition coating film - Google Patents

Abstract

PURPOSE:To form a coating film at a low temp. on an article consisting essentially of a resin by dipping the metal-plated resin article subjected to anion electrodeposition coating in an aq. soln. contg. an org. solvent, acid, surface active agent and metallic salt then subjecting the article to a heating treatment. CONSTITUTION:An anion electrodeposition coating film is deposited on a metal- plated thermoplastic resin article. The article is dipped for about 15sec - several min at about 10-50 deg.C in an aq. soln. for pretreatment contg. 5-90% org. solvent, 5-90% acid, 1-15% surface active agent and 0.1-1% metallic salt. The article is then pulled up and is washed and the washed article is subjected to a heating treatment for at least 30min at about 75 deg.C to cure the coating film. The coating film can be cured at a low temp. by the above-mentioned method and therefore the anion electrodeposition coating is made possible for the plated product consisting essentially of a thermoplastic resin susceptible to thermal deformation.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming an anionic electrodeposited 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 applications due to their advantages of having both the luster of plated metals and the high mechanical strength of raw metals, but they are also used in consumer products such as electric refrigerators, electric ranges, and electric fans. For use as switches, handles, panels, etc. in electrical appliances, office equipment such as electronic calculators, communication equipment such as television receivers, audio equipment such as tape recorders, electric sound generators, etc. There are some issues with the feel and the cold shine.

In order to reduce the coldness of the luster, recently, instead of the conventional mainstream chrome plating, binary alloys such as tin-plating, tin-copper-zinc, nickel-cobalt-tungsten, tin-nickel-copper, etc. are being used. Ternary alloy plating is heavily used.

Even with such alloy plating, since metal is metal, it is desired that it still have a cool luster, and if it has a warm luster. In addition, other difficulties with this type of alloy plating are as follows:
This means that it has poorer corrosion resistance than chrome plating.

Not only is it corroded by sweat and sulfur dioxide gas, but fingerprints also tend to remain in the form of stains, which is a type of corrosion.

Recently, a transparent or semi-transparent paint is often applied to the upper surface of the plated 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 buffing or spray painting, it is difficult to obtain a coating film with a uniform thickness, and sagging and fogging are likely to occur.As a result, fine irregularities such as honing, hair lines, and spin may be formed on the surface of the product. If it is, it is difficult to accurately reproduce the unevenness.

Therefore, when accurate reproduction is required, 'CdC coating, which is easy to reproduce, has come to be applied.

Exposure electrodeposition coating uses a water-based paint or a water-dispersible paint, and conducts electrolysis using the object to be coated (in this case, a metal plated product) as the @ electrode or cathode, thereby forming a coating film. It is a coating method that heats and cures the coating film, converting it into a tough cured coating. The reasons why the electrodeposition coating method is commonly used are: (1) The thickness of the deposited coating can be controlled freely by simply adjusting the voltage.

(2) Since it has excellent throwing power, it is possible to apply a coating with a uniform thickness over fine details such as irregularities on the article.

(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 irregularities of the article are fine and complex. In addition, there is an advantage that the article can be made into a lightweight product, and it is also easy to impart conductivity to the resin, so the surface thereof is plated with various metals, as in the case of metal articles. In this case, as with metal-plated products, problems such as unnecessary metallic luster on the plated surface and susceptibility to corrosion are naturally involved. Therefore, as with plated metal articles, the above-mentioned drawbacks should be able to be improved by applying anionic paint to the plated surface by electrodeposition.
As mentioned above, this is not actually done.

The reason for this is, as is well known, that thermoplastic resin articles have extremely low deformation temperatures; for example, the most widely used ABS resin articles have a deformation temperature of only about 90°C.

However, as mentioned above, anionic electrodeposition requires a step of curing the resulting coating film, which is called curing or baking at 160 to 200°C.
A heat treatment of 0 to 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 electrolyte in the same manner as the metal article. Not only can you enjoy the advantages of coating, but you can also enjoy the advantages unique to resins, such as light weight, low cost, and ease of molding.

The present invention has been made from such a viewpoint,
A metal-plated thermoplastic resin product coated with an anionic electrodeposited film is immersed in a pretreatment solution as described later, pulled up, and heated at around 75°C for at least 30 minutes after washing. That is.

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 no different from the coating film described above as a conventional method. As a reminder, the anionic electrodeposition paint used in the present invention mainly uses water-soluble or water-dispersible resins selected from acrylic-melamine resins, epoxy-melamine resins, alkyd-melamine resins, etc. As an ingredient,
Examples include those containing some solvent and neutralizing agent.

For electrodeposition coating, the above paint is adjusted to a solid content concentration of about 5 to 30% in the electrolytic coating, and the coated object is used as an anode, and a carbon plate or stainless steel plate S is used as an anode.
Using US 304 as a counter electrode, current is applied at a voltage of 10 to 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. This pretreatment liquid is specifically an organic solvent of 5 to 90%
%, organic or inorganic acid 5-90%, surfactant 1-1
It is an aqueous solution containing 5% and 0.1 to 1% of metal salts.

Examples of organic solvents used for and\ 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. One or more mixed acids such as sulfuric acid, nitric acid, hydrofluoric acid, acetic acid, acetic acid, citric acid, tartaric acid, malic acid, and maleic acid can be mentioned, and surfactants include anionic and nonionic surfactants. One type of activator or a mixture of two or more activators, and as a metal salt, Snp
Typical examples include Pb + Za + Co, Mg + Ni, and a mixture of one or more of inorganic salts or organic salts.

It was something that was given to me. However, in terms of types, metal salts are those that crosslink and harden the vehicle of water-based paints, surfactants are those that promote this action, and acids are those that have the effect of accelerating the hardening of the paint film. Some of these are well known.

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 immersing in the pre-treatment liquid, of course, take it out and
After washing with clean water and drying, heat at around 75°C, especially from 70°C.
Heat at 80° C. for 30 minutes or more, thereby curing the electrodeposited coating. Drying can be performed as part of this heating. Generally, if the heating temperature is 70°C or lower, it is difficult to obtain a sufficient coating surface gloss, and if the heating temperature is 80°C or higher, there is a risk of deformation of the article. 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 completed and the baking process is completed.

If the time is less than about 30 minutes, the gloss of the coated surface and the coating performance will be poor. Therefore, in consideration of work efficiency, the appropriate heating time is about 60 to 120 minutes.

Example 1 Knob for electrical equipment made of grade ABS resin with Ni plating as usual (diameter 30cm x height 'l Qrsa
An anionic water-soluble acrylic-melamine resin paint was applied by anionic electrodeposition to the bottomed inner cylinder (of the cylinder) using a conventional method.

That is, the electrodeposition conditions were: vehicle concentration 15%, 30 volts,
It is 1 minute.

This product was immersed in a pretreatment liquid having the following composition.

Buta/-ru・・・・・・・・・・・・・・・・・・ 3
0% citric acid ・・・・・・−・・・−・・・・・・・・・・・・
・・20% alkyl sulfosuccinate・・・・
・1% fubartose sulfate・・・・・・・・・・・・・・・・
--- After immersing the sample at 0.3% at 25.degree. C. for 1 minute, it was taken out and washed with water, followed by a hardening treatment of heating at 80.degree. C. for 6.theta. minutes.

The physical properties of the resulting coating film are as listed in Table 1.

Example 2 The knob is the same as Example 1, but the plated metal is Ni.
An article that is SQL was used. The electrodeposition paint used was an anionic water-soluble epoxy-melamine resin paint. This was prepared in the usual manner at a vehicle concentration of 20% and an electrolytic voltage of 5.
OV for 2 minutes, and then immersed in a pretreatment liquid having the following composition.

Butyl cellosolve・・・・−・・・・・・・・・・・・・・・
・10% saccharic acid・・・・・・・・・・・・・・・・・・・
−・・・・・・・・・・・・・・・・・・・・50
% polyoxyethylene nonylphenol ether -・-
−−−・・−−−−−−・−・−・・・・・・・−・・
3% cobalt naphthenate 0.2% immersion conditions are 25°C for 2 minutes.

It was immersed, pulled up, 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 is polyacetal and the plating metal is SN-C.
There is gold 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.

Then, add this material to a pretreatment solution with the following composition at 25°C.
immersed in water for 1 minute.

Ethanol ・・・・・・・・・・・・−・・・・・・・
60% sulfuric acid・・・・・・・・・・・・・・・・・・
−・・・・・・・・・ 10% Sodium laurylbenzenesulfonate・・・・・・・・・・・・・・・・・・
・・・-3% lead succinate・・・・・・・・・・・・・・・・・・
・・・・・・・・・After pulling it out from 0.1% liquid, 70
A heat curing treatment was performed for 120 minutes at "C".The properties of the resulting coating film are as listed in Table 1.

In Table 1, Comparative Examples 1 to 3 are also listed, 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.

Wipe the painted surface with your hands using gauze impregnated with ethanol 2 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: A fingerprint is applied by pressing a finger against the painted surface, and the degree of discoloration is observed after 60 days have passed.

Sulfur dioxide gas test: The test item was exposed to 1% sodium thiosulfite 3
A mixed aqueous solution of 20 ml and 80 ml of 061N sulfuric acid.
1 in a desiccator and left at room temperature for 20 hours, then observe the state of discoloration.

Table 1 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. The benefits of this coating can now be enjoyed immediately.

Applicant: Shimizu Shoji Co., Ltd. Agent: Patent attorney Mibuya Doishima (1 other person) =5′;

Claims (1)

[Claims] A metal-plated thermoplastic resin article coated with an anionic electrodeposited film is treated with a pretreatment liquid of 5 to 90% organic solvent and 5 to 9% acid.
Anion electrodeposition characterized by immersion in an aqueous solution containing 0.0% surfactant, 1-15% surfactant, and 0.1-1% metal salt, pulling it up, washing, and heating at around 75°C for at least 30 minutes. Low-temperature curing method for coatings.