JP2975068B2 - Cathodic electrodeposition coating method - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a cationic electrodeposition coating method, and more particularly, to a cationic electrodeposition coating method capable of suppressing the formation of holes in a coating film due to the occurrence of sparks at the time of coating film deposition. The present invention relates to an electrodeposition coating method.

(Conventional technology and problems to be solved) Electrodeposition coating is applied to members having a bag structure, such as automobiles and electric appliances, in comparison with air spray coating or electrostatic spray coating of an organic solvent type paint. It is widely used because it has a characteristic that it has good roundness and a coating film having a relatively uniform thickness is easily obtained. Also, recently, cationic electrodeposition coating can form a coating film with superior rust resistance compared to anion electrodeposition coating. Is being replaced by cationic electrodeposition coating.

In general, cationic electrodeposition coating is carried out by applying an electrodeposition paint containing an amine-added epoxy resin and a cross-linking agent, for example, a blocked isocyanate compound as a vehicle component, as a coating bath to the object to be coated, and using the counter electrode as an anode to conduct electricity. A method of forming a cross-linked cured coating by forming a deposited coating thereon and then heating the deposited coating is performed.

In cationic electrodeposition coating, as a main vehicle component, a high-molecular-weight, hard solid epoxy resin is generally used to form a coating film with excellent rust prevention properties.
It is difficult for the deposited coating film formed to perform sufficient thermal flow of the coating film during heat curing, and defects during deposition of the electrodeposited coating film tend to remain even after the coating film is cured.

In recent years, for the purpose of improving the anti-corrosion performance of automobile outer panels, plated steel sheets such as galvanized steel sheets and iron-zinc alloy-plated steel sheets have been used as objects to be coated, in addition to conventional cold-rolled steel sheets. When a voltage is applied to these coated steel sheets for cationic electrodeposition coating, sparks cause many holes (hereinafter referred to as "craters") in the deposited coating film, and these defects remain even after the electrodeposition coating film is cured. In addition to lowering the rust resistance, there is a problem that a glossy coating film having excellent smoothness cannot be obtained even when the intermediate coating and the top coating are applied on the electrodeposition coating film. The likelihood of crater generation varies depending on the type of the object to be coated. Generally, cold-rolled steel sheets have less craters, and craters increase more in the order of cold-rolled steel sheets <galvanized steel sheets <iron-zinc alloyed coated steel sheets. .

Crater generation occurs at the same applied voltage for the same time,
In the case of performing electrodeposition, generally, the smaller the thickness of the obtained electrodeposited film, the larger the number. When the electrodeposition film thickness is smaller than the expected film thickness, a predetermined film thickness can be obtained by increasing the applied voltage, but craters are more likely to be generated by increasing the applied voltage. In general, when an electrodeposition paint bath immediately after production is compared with an electrodeposition paint bath after storage of the same, that is, an aged electrodeposition paint bath, the aged one is less likely to have a film thickness, and the occurrence of craters tends to increase. is there.

In order to solve the problem of crater generation during electrodeposition coating, (1) addition of a high-boiling alcohol-based or cellosolve-based organic solvent, (2) use of a low molecular weight epoxy resin as a base resin, (3) polyalkylene Glycol compounds,
Methods such as addition of an acrylic soft resin were studied. However, the method (1) has a problem that the bath stability such as emulsion stability and retention over time is not sufficient, and the wastewater treatment amount in a coating line increases. The method (3) has a problem that the throwing power and the rust prevention property are deteriorated, and the method (3) is not sufficiently effective in suppressing the occurrence of craters, and the interlayer adhesion between the obtained electrodeposition coating film and the obtained coating film. There is a problem that the properties and rust prevention are also insufficient.

(Means for Solving the Problems) Therefore, the present inventor did not reduce the electrodeposition bath stability, rust prevention, throwing power, interlayer adhesion with the upper coating film, and increased the amount of wastewater treatment. The problem of the occurrence of craters at the time of depositing the coating film of electrodeposition coating without causing the problem of
As a result of intensive studies for obtaining an electrodeposition coating film having no defects and excellent smoothness, the present inventors have found that the above object can be achieved by adding a benzoin-based compound, and reached the present invention.

That is, the present invention provides a method for cationically electrodepositing a cationic electrodeposition paint containing an amine-added epoxy resin and a cross-linking agent as a resin component using the article to be coated as a cathode, wherein the resin solid content in the cationic electrodeposition paint is 100%. An object of the present invention is to provide a cationic electrodeposition coating method characterized by comprising 0.5 to 10 parts by weight of benzoin and / or an alkyl ether compound of benzoin having 1 to 10 carbon atoms per part by weight.

Cationic electrodeposition paint used in the method of the present invention is a cationic resin known as a resin for cationic electrodeposition paint, an amine-added epoxy resin and a blocked isocyanate,
It is obtained by neutralizing and dispersing a vehicle component containing a crosslinking agent such as an amino resin in water.

Examples of amine-added epoxy resins include (i) adducts of polyepoxides with primary mono- and polyamines, secondary mono- and polyamines or mixed primary and secondary polyamines (see, for example, US Pat. No. 3,984,299); (ii) polyepoxides And a secondary mono- having a ketiminated primary amino group.
And adducts with polyamines (eg, US Pat. No. 4,017,43)
And (iii) a reaction product obtained by etherification of a polyepoxide with a ketiminated hydroxy compound having a primary amino group (for example, see JP-A-59-43013).

The polyepoxide used for producing the above amine-added epoxy resin has an epoxy group Is a compound having two or more in one molecule, generally at least 200, preferably 400 to 4000, more preferably 800
Those having a number average molecular weight in the range of 20002000 are suitable, and particularly those obtained by reacting a polyphenyl compound with epichlorohydrin are preferred. Examples of the polyphenol compound that can be used for forming the polyepoxide include, for example, bis (4-hydroxyphenyl) -2,2-
Propane, 4,4'-dihydroxybenzophenone, bis (4-hydroxyphenyl) -1,1-ethane, bis (4
-Hydroxyphenyl) -1,1-isobutane, bis (4
-Hydroxy-tert-butyl-phenyl) -2,2-propane, bis (2-hydroxynaphthyl) methane, 1,5-
Dihydroxynaphthalene, bis (2,4-dihydroxyphenyl) methane, tetra (4-hydroxyphenyl)-
1,1,2,2-ethane, 4,4'-dihydroxydiphenyl sulfone, phenol novolak, cresol novolak and the like.

The polyepoxide is a polyol, a polyether polyol, a polyester polyol, a polyamined amine,
It may be partially reacted with a polycarboxylic acid, a polyisocyanate compound, or the like, or may be one obtained by graft polymerization of ε-caprolactone, an acrylic monomer, or the like.

The cationic electrodeposition coating composition of the present invention may further contain, if necessary, ordinary paint additives, for example, coloring pigments, for example, titanium white, carbon black, red iron, graphite, etc .; extender pigments, for example, talc, calcium carbonate , Mica, clay, silica, etc .; rust preventive pigments, for example, chromium pigments such as strontium chromate and zinc chromate, lead pigments such as basic lead silicate, lead chromate, etc .; including repelling inhibitors, aqueous solvents, curing catalysts, etc. It can also be done.

In the method of the present invention, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin n are exemplified as benzoin and / or an alkyl etherified product of benzoin having 1 to 10 carbon atoms (hereinafter abbreviated as “benzoin derivative”). -Propyl ether, benzoin isopropyl ether, benzoin n-
Butyl ether, benzoin isobutyl ether, benzoin n-hexyl ether, benzoin n-octyl ether and the like. Of these, benzoin and benzoin alkyl ether compounds having 1 to 4 carbon atoms are particularly preferred. The benzoin derivative is blended in a proportion of 0.5 to 10 parts by weight, preferably 1 to 3 parts by weight, based on 100 parts by weight of the resin solid content in the cationic electrodeposition paint to be used. The effect of suppressing the generation is not sufficient.On the other hand, even if used in an amount exceeding 10 parts by weight, the effect of suppressing the crater generation is hardly further increased, it is not economical, and the stability of the electrodeposition paint is rather deteriorated. is there.

The benzoin derivatives can be used alone or as a mixture of two or more, and the benzoin derivatives are compounded when (1) the pigment of the electrodeposition paint is dispersed. (2) It is blended with the emulsion resin dispersion for electrodeposition paint at normal temperature or under heating. (3) Compounded at the time of synthesizing the amine-added epoxy resin. (4) There is a method of blending at the time of preparing an electrodeposition paint or an electrodeposition paint bath, and any of the blending methods does not affect the effect of suppressing crater generation and may be determined as appropriate.

In the present invention, the surface of the object is subjected to cationic electrodeposition in a cationic electrodeposition coating bath containing the above benzoin derivative. Cationic electrodeposition is performed according to a method known per se, and generally has a solid content of about 5 to 40% by weight,
The electrodeposition bath is preferably diluted with deionized water so as to have a concentration of 15 to 25% by weight, and further adjusted to a pH within the range of 5.5 to 8.0, usually adjusted to a bath temperature of 15 to 35 ° C and applied voltage. 100-400
The coating can be performed as a cathode under the condition of V.

The film thickness of the electrodeposition coating that can be formed using the coating composition of the present invention is not particularly limited, but is generally 10 to 60 μm, preferably 20 to 40 μm based on the cured coating film. Appropriate. Also, the bake hardening temperature of the coating film is generally
Suitably baking at 100-200 ° C., preferably 150-180 ° C., for a time period of about 10-30 minutes.

The substrate to be coated may be any substrate having a conductive surface, such as iron, aluminum, copper, zinc, a substrate having a surface such as a metal such as tin or an alloy of these metals, and the like. Specifically, cold-rolled steel sheet, aluminum sheet,
Aluminum profile, copper plate, galvanized steel plate, tin plate,
Substrates such as an iron-zinc alloy-plated steel sheet and a zinc-aluminum alloy-plated steel sheet. These substrates have chromate treatment, iron phosphate treatment, zinc phosphate treatment,
It may or may not be subjected to surface treatment such as boehmite treatment or alumite treatment.

Among these base materials, conventionally, the occurrence of craters is also suppressed in plated steel sheets, such as iron-zinc alloyed plated steel sheets, in which the occurrence of craters was particularly large, and the effect of suppressing the occurrence of craters in these plated steel sheets is remarkable. .

(Actions and Effects) Although it is not clear why the method of the present invention suppresses the occurrence of craters during the deposition of an electrodeposition coating film, the present inventors have found that the adhesion of the precipitated emulsion resin particles to the blend of the benzoin derivative It is thought that the crater is prevented from being generated because the strength is improved and the strength of the deposited coating film is increased.

By the method of the present invention, electrodeposition bath stability, rust prevention, throwing power, without lowering the interlayer adhesion with the upper coating film, and without causing problems such as an increase in the amount of wastewater treatment, electrodeposition It is possible to suppress the occurrence of craters at the time of coating film deposition of the coating, and to form an electrodeposited coating film having no defects and excellent smoothness even on an iron-zinc alloy plated steel sheet.

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.

Example 1 Kansai Paint Elecron No.9400 Clear (solid content 3
Using 278 parts of 6%, thermosetting aqueous epoxy polyamino resin-blocked isocyanate-based cationic electrodeposition coating resin, an electrodeposition coating composition was prepared according to the formulation shown in Table 1. The benzoin derivative was blended when the pigment was dispersed. This electrodeposition coating composition was diluted with a diluting solvent to a solid content of 18%, and the coated object (iron-zinc alloy-plated steel sheet) was treated with the coated object as a cathode so as to have a dry film thickness of 30 μm. After performing electrodeposition coating under the conditions of 3 minutes, baking was performed at 170 ° C. for 30 minutes, and a test was performed. The test results are shown in Table 2.

Examples 2 to 6 and Comparative Examples 1 to 3 For Examples 2 to 6 and Comparative Examples 1 to 3, electrodeposition coating was performed in the same manner as in Example 1. The coating composition is shown in Table 1 and the test results are shown in Table 2.

 The tests in Table 2 followed the following method.

Crater resistance: The baked coated plate was visually evaluated according to the following criteria.

○: crater does not occur at all ○ ^-: crater slightly occurred ×: craters remarkably occurs coated surface smoothness was evaluated by the following criteria by visually for baking coated plate.

○: good ○ ^- : almost good △: slightly bad ×: bad

Continuation of the front page (72) Inventor Hidehiko Haneishi 4-171-1, Higashi-Hachiman, Hiratsuka-shi, Kanagawa Examiner, Kansai Paint Co., Ltd. Akihiro Kitamura (56) References JP-A-63-89578 (JP, A) JP-A Sho 61-246399 (JP, A) JP-A-59-43013 (JP, A) JP-A-4-502170 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C25D 13/10 C09D 5/44

Claims (2)

(57) [Claims] In a method of cationically electrodepositing a cationic electrodeposition paint containing an amine-added epoxy resin and a crosslinking agent as a resin component using the object to be coated as a cathode, the resin solid content in the cationic electrodeposition paint is 100%. A cationic electrodeposition coating method comprising adding 0.5 to 10 parts by weight of benzoin and / or an alkyl etherified product of benzoin having 1 to 10 carbon atoms with respect to parts by weight. 2. The cationic electrodeposition coating method according to claim 1, wherein the object to be coated is an iron-zinc alloy plated steel sheet.