JPH02270996A - Electrodeposition coating method - Google Patents

Abstract

PURPOSE:To form a coated film having the excellent smoothness and edge covering property of a coated film by temporarily stopping energization at the time of depositing the coated film on an object to be coated by using a cation electrodeposition paint and executing the energization between the object to coated and a counter electrode. CONSTITUTION:The cation electrodeposition paint is diluted with deionized water or the like so as to attain about 5 to 40wt.% concn. of solid content and further the pH thereof is adjusted within an about 5.5 to 9.0 range. The temp. thereof is controlled to about 15 to 35 deg.C. The object to be coated is immersed into this electrodeposition bath and about 50 to 400V voltage is impressed to this object as a cathode and a counter electrode to execute the electrodeposition coating for about 1 to 5 minutes. The impressed voltage is stopped for about 10 to 180 seconds and thereafter, the electrodeposition coating is executed again for about 1 to 5 minutes with about 50 to 400V impressed voltage to form the coated film to about 20 to 30mu as a dry film thickness. This electrodeposition coated object is cleaned with deionized water, etc., and is baked and cured at about 100 to 180 deg.C, by which the coated film having the excellent smoothness and edge covering property is obtd.

Description

[Detailed Description of the Invention] The present invention is an electrodeposition coating method that has particularly excellent smoothness and forms a thick coating film even on edges such as corners and protrusions. Regarding.

Ai Todanka lid electrodeposition coating has excellent throwing power and uniformity of film thickness, and is widely used as an undercoat for automobile bodies. However, the deposited coating film by IF coating is Due to the effects of gas generation during electrodeposition and the high solids content (low amount of solvent), it generally has the disadvantage of lacking smoothness.

As a method for improving this smoothness, it has been proposed to cause the electrodeposited coating to melt and flow during baking to harden the coating. In particular, cationic electrodeposition paints generally have extremely low molten coating viscosity, and as a result, the smoothness is improved by the above method, but on the other hand, the coating film tends to melt and flow, so that most of the cured coating film is not deposited on the edges. If the rust is not formed at all or is not formed at all, this results in a defect in which the rust prevention properties of that part are extremely poor.

Conventionally, in order to improve the rust prevention properties of the edges where the sun shines, for example, rust-proof steel plates have been used or anti-corrosion paint has been applied to the edges with a roller or spacing. However, the cost is high and the number of steps is large.Also, in order to improve the rust prevention properties of the edges, it is necessary to incorporate a large amount of pigment into the electrodeposition paint or reduce the amount of plastic components. Although many attempts have been made, smoothness and film formation properties on the edges are not compatible.
There is a strong demand for the development of a durable electrodeposition paint that fully satisfies both of these properties.

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When electricity is applied between the object to be painted and the counter electrode to deposit a coating film on the object, when the electricity is temporarily stopped,
It was discovered that a coating film with excellent coating film smoothness and edge coverage can be formed, and the present invention was completed.

That is, in the present invention, an object to be coated is immersed in a cationic electrocoating paint bath, the object to be coated is used as a cathode, and a voltage is applied between it and a counter electrode to conduct electricity to form an electrodeposition coating film on the object to be coated. The present invention relates to an electro-11 coating method characterized in that electricity supply is temporarily stopped during deposition.

The cationic electrodeposition paint used in the electrodeposition coating method of the present invention is a well-known paint containing a resin having a water-dissociable cationic group as a vehicle component.

Examples of the water-dissociable cationic group include primary to tertiary ammonium salts, quaternary ammonium salts, and tertiary sulfonium salts.

Further, as the resin having a water-dissociable cationic group, specifically, as an epoxy resin, for example, an addition of polyepoxide and a primary mono- and polyamine, a secondary polyamine, or a mixed primary and secondary polyamine. Adducts of polyepoxides with secondary mono- and polyamines having ketiminated primary amine groups (see, e.g., U.S. Pat. No. 4,017.
438): polyepoxide and ketiminated 1
A reaction product obtained by etherification with a hydroxy compound having an amino group (e.g., JP-A-59-4-3013)
(see Japanese Patent Laid-Open No. 61-293273): cationic vinyl copolymers (see, for example, Japanese Patent Application Laid-Open No. 61-293273);
As an acrylic resin, for example, a polymer containing a tertiary amino group-containing monomer (for example, NN dimethylamine ethyl methacrylate, etc.) as an essential component: an acrylic resin having an epoxy group; Adducts with polyamines: There are polymers that contain sulfonium salt-containing monomers as an essential component, and examples of polybutadiene resins include adducts between maleated polybutadiene and polyamines: adducts between epoxidized polybutadiene and polyamines, etc. can be mentioned. These resins contain active hydrogen groups (e.g. OH, NH, N
H, etc.). Specific examples of amino resins and polyisocyanate compounds include amine resins such as melamine resins, urea resins, and benzoguanamine resins; examples of polyisocyanate compounds include:
Examples include those obtained by reacting aromatic, aliphatic, alicyclic, etc. compounds with compounds such as cabrolactums, oximes, phenols, alcohols, etc. in such a manner that no free incyanate group remains. can. The above-mentioned polyisocyanate compound can be used by mixing with a resin having a water-dissociable cationic group, but isocyanate which is blocked in the resin by partially reacting the polyisocyanate compound with the resin It is also possible to introduce groups.

The cationic electrodeposition paint used in the electrodeposition coating method of the present invention includes:
If necessary, for example, coloring pigments, extender pigments, anti-rust pigments,
A curing accelerator, a wetting agent, and various additives can be added in commonly used amounts.

In the electrodeposition coating of the present invention, the above-mentioned cationic electrodeposition paint is generally coated with a solid content of about 5 to 40% by weight, preferably about 1% by weight.
Dilute with deionized water etc. to a concentration of 0 to 30% by weight,
Furthermore, the pH is about 5.5 to 9.0, preferably about 5.8 to
The paint adjusted to within the range of 7.0 was used as an electrodeposition bath, and the bath temperature was 1.
In the first step, the temperature was adjusted to 5 to 35°C, and the object to be coated was immersed in the bath, and a voltage of 50 to 400 cm was applied between the object to be coated and the counter electrode for about 1 to 5 minutes. After that, the applied voltage is stopped for about 10 to 180 seconds, preferably about 20 to 120 seconds, and the second stage electric IF is applied again at a voltage of about 50 to 400 cm for about 1 to 5 minutes. Painting is recommended.

The film thickness of the electrodeposition coating is usually about 15 to 35 F+, preferably about 20 to 30 P (dry film thickness).

N@ Painted objects are usually cleaned using deionized water, tap water, paint filtrate, reverse osmosis filtrate, or the like.

The electrodeposition coating film formed on the object to be coated is cured by baking at about 100 to about 180° C. after cleaning.

According to the Ti electrodeposition coating method according to the present invention, the corrosion resistance of the edges of the coated object, which has been a weak point of conventional electrodeposition coatings, is significantly improved, so it can be used in a wide range of industrial coating fields such as automobiles, electrical equipment, and prefabricated steel frames. It can be applied as an anti-corrosion coating method.

(Operation and Effects of the Invention) The coating film formed by the electrodeposition coating method of the present invention can be formed on the surface of the deposited coating film formed on the object to be coated, especially by stopping the applied voltage during electrodeposition coating for a certain period of time. Nearby relatively low molecular weight (soft) resin components are redissolved in the bath to form a coating layer with a low content of the low molecular weight resin components. This coating layer forms a multilayer coating that exists between the deposited coatings that are finally formed. When such a coating film is baked, the coating layer with a low content of low molecular weight resin components is difficult to melt and flow due to heat, so a coating film with excellent edge coverage is formed on the object to be coated. In addition, the coating layer near the surface of the object to be painted and the surface layer of the coating material melt and flow to form a coating film that has excellent adhesion to the object and is free from defects such as wrinkles and pinholes. do.

(Example) The present invention will be specifically described below with reference to Examples and Comparative Examples. "Parts" and "%" are "parts by weight" and "important %"
” means.

Example 1 A cationic electrolyte paint (paint 1) using a water-based epoxy polyamino resin equivalent to Nireclone No. 9000 manufactured by Kansai Paint Co., Ltd. was applied by electrodeposition under the conditions shown in Table 1, and after washing with water, it was heated at approximately 180°C. Baking in a dryer formed a cured coating. The test results for this coating film are shown in Table 3.

Paint 1 Medium 1 An epoxy polyamino resin with a resin base value of 80 is water-dispersed with acetic acid at a neutralization equivalent of 0.55.

Umbrella 2 Manufactured by Asahi Carbon Co., Ltd. Product name: “Carbon ASMJ*3”
Hydrous amorphous silicon dioxide pigment (oil absorption 300) manufactured by Fuji Devison Co., Ltd., trade name "Syroid 244" Example 2 Cation electricity using a water-based epoxy polyamino resin equivalent to Nireclone No. 9400 manufactured by Kansai Paint Company! A paint (paint 2) was applied by electrodeposition under the conditions shown in Table 2. After washing with water, baking was performed in an electric dryer at about 180° C. to form a cured coating film.

The test results for this coating film are shown in Table 3.

Paint 2 Comparative Example 1 Using paint 1 described in Example 1, electrocoating was performed under the same conditions as in Example 1 except that the voltage stop time in Table 1 was 0.5.3.00 seconds. A coating film was obtained by baking.

The test results for this coating film are shown in Table 3.

Comparative Example 2 Electrodeposition was performed using paint 2 described in Example 2 under the same conditions as described in Example 2 except that the voltage stop time in Table 2 was 0.5.300 seconds, and no baking occurred. A coating film was obtained.

The test results for this coating film are shown in Table 3.

*4 Electrodeposition coating surface smoothness Visually evaluate the finish of the electrodeposited surface.

○ Good ■ Good △ Slightly poor * Corrosion resistance at 545° joint: A SPC mild steel plate was processed at an angle of 45°, subjected to surface treatment Bonderite #3004, and then subjected to a predetermined electrodeposition coating and used for the test. The corrosion resistance test was based on JIS 22371 salt spray test. The test continued for up to 720 hours. 240 hours during the exam.

An intermediate check was performed for 480 hours to determine the presence or absence of spot pain.

Umbrella 6 general part corrosion resistance: Based on JIS 22371 salt spray test. Spotting and blistering of the paint film on the general area where there were no cuts were removed for 720 hours and 1500 hours.

Claims (1)

[Claims] 1. When the object to be painted is immersed in a cationic electrodeposition paint bath, the object to be painted is used as a cathode, and a voltage is applied between it and a counter electrode to conduct electricity to deposit an electrodeposition coating film on the object to be painted. An electrodeposition coating method characterized by temporarily stopping energization.