JPH0472918B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of Industrial Application) The present invention relates to an electrodeposition coating method, and more specifically, the present invention relates to an electrodeposition coating method, and more particularly, the present invention relates to a method for electrocoating a conductive article, which has no coating defects such as pinholes, has excellent adhesion to a substrate, and has a thick electrodeposition coating. The present invention relates to an electrodeposition coating method that can form . (Prior art) Electrodeposition coating is widely used for aluminum building materials, automobile bodies and parts, home appliances, office equipment, etc. because it can impart excellent coating appearance and film performance to conductive articles with a single coating. There is. However, the resulting electrodeposition coating film is generally thin and insufficient to exhibit its anticorrosion function, and an electrodeposition coating method that can provide a higher film thickness is desired. Examples of methods for increasing the electrodeposition coating include (1)
Method of heating and baking without washing with water after electrodeposition coating, (2)
A method of further painting with a water-based paint after electrodeposition painting has been proposed. However, all of these conventional methods have a problem in that the film thickness that can be obtained is limited, and the film thickness cannot be freely controlled. On the other hand, a method in which anodized aluminum is treated with an organosilicon compound and then electrocoated in a thermosetting resin paint (Japanese Patent Publication No. 52-30945)
It has been known. This method adds a process of treatment with an organosilicon compound between the anodizing process and the electrodeposition process in order to eliminate problems during electrodeposition due to acid roots remaining in the micropores of the anodic oxide film. However, after this intermediate treatment, the electrodeposition coating is applied after washing with water, and the thickness of the electrodeposition coating obtained is at most 20 μm.
It was difficult to form a thicker electrodeposited coating film. (Problems to be Solved by the Invention) The purpose of the present invention is to eliminate the drawbacks of the conventional method,
It is an object of the present invention to provide an electrodeposition coating method which allows the thickness of the coating to be freely controlled and enables the formation of an electrodeposition coating with a high thickness that cannot be obtained by conventional methods. (Means for Solving the Problem) As a result of repeated research focusing on the pre-process of electrodeposition coating, the present inventors have found that, before electrodeposition coating, a conductive substance is added to a primer composition made of a specific alkoxysilane compound. The present invention was completed based on the knowledge that if a coating layer is formed using the method described above, an electrodeposited coating film with a high thickness can be obtained by subsequent electrodeposition coating. Moreover, this primer layer can be electrodeposited even though it is heated and dried, and a thick electrodeposited film can be formed, which is a totally innovative method that would be unimaginable under conventional wisdom. To outline the present invention, when electrocoating a conductive article, the article is coated with
After surface treatment with a primer composition consisting of A. an organic alkoxysilane compound having an amino group and B. an organic alkoxysilane compound having a glycidyl group and having a molar ratio of A component/B component of 0.42 to 1.37, and drying, This is an electrodeposition coating method characterized by performing electrodeposition coating. To explain the present invention in more detail, the organic alkoxysilane used as the primer is as follows:
A. Organic alkoxysilane having an amino group and
B. Characterized by the combined use of an organic alkoxysilane having a glycidyl group. This is because component A and component B of the primer exhibit a strong adhesive force to the conductive article due to a synergistic effect. A. As the organic alkoxysilane compound having an amino group, N-(2-aminoethyl)
3-aminopropylmethyldimethoxysilane, N
-(2-aminoethyl)3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, etc. can be used. In addition, as the organic alkoxysilane compound having a glycidyl group as component B, specifically, 3-
Glycidoxypropyltriethoxysilane, 3-
Glycidoxypropyltrimethoxysilane, 3-
glycidoxypropylmethyldimethoxysilane,
2-(3.4-epoxycyclohexyl)ethyltrimethoxysilane and the like can be used. In the present invention, it is possible to use it in combination with other types of organic alkoxysilanes, but no particular effect is observed. By forming this primer coating layer, which is a feature of the present invention, it promotes the formation of a homogeneous and pinhole-free coating film during electrodeposition coating, and improves throwing power and
High coulomb yield, and electrodeposition coating thickness of several μm
This makes it possible to arbitrarily control the thickness from m to several hundred μm. In the present invention, a composition of two types of organic alkoxysilanes, A and B components, is used as a primer, and the blending ratio is A component/B component (molar ratio).
A range of 0.42 to 1.37 is appropriate. This blending ratio
If it is less than 0.42, the adhesion to the electrodeposition coating and conductive article is insufficient, while if it is greater than 1.37, the film forming properties of the primer coating are poor, and the primer coating will be removed during the next electrodeposition coating. This is not preferable because layer lifting tends to occur. Primers used in the present invention are prepared as follows. Into a container, charge a specified amount of component A, an organic alkoxysilane compound having an amino group, and component B, an organic alkoxysilane compound having a glycidyl group, and continue stirring while controlling the temperature at 5 to 60°C until no heat is generated. and exit. On this occasion,
Hydrophilic organic solvents, such as ethyl alcohol, n
- One or more types of propyl alcohol, isopropyl alcohol, n-butyl alcohol, etc. can be added in any proportion, but it is necessary to select a suitable blending amount for forming the primer coating layer. Various coating methods such as dip coating, spray coating, electrostatic coating, electrodeposition coating, and brush coating can be applied to coat the conductive article with the primer prepared in this manner. The solid content of the primer varies depending on the coating method, but is generally 1 to 50% by weight, preferably 5 to 50% by weight.
It is used after adjusting to 30% by weight. The thickness of the coating film formed on the surface of the conductive article by primer treatment is 1 μm to 30 μm, preferably 2 μm to 20 μm, particularly preferably 3 μm to 10 μm in dry film thickness.
m is appropriate. This is because if the primer coating film thickness is less than 1 μm, it is difficult to form a thick electrodeposited film, which is the objective of the present invention, and on the other hand, if it is thicker than 30 μm, it is difficult to form an electrodeposited film uniformly. This is because trends can be seen. For conductive articles coated with a primer, this
The coating layer is dried at a temperature of ~200°C, preferably 10-150°C. The conductive article on which the primer coating layer has been formed in this manner is then subjected to electrodeposition coating. Various commonly used methods such as anionic electrodeposition, cationic electrodeposition, and alternating current electrodeposition can be applied to the electrodeposition coating. In electrodeposition coating, a conductive article with a primer coating layer formed thereon is immersed in an electrodeposition coating solution, connected to an anode or a cathode, provided with a counter electrode, and heated at a voltage of 10 to 300 volts for 10 minutes.
This is achieved by applying electricity for seconds to 10 minutes. After the electrodeposition coating is completed, remove the item from the liquid, drain the liquid thoroughly, and wash it with water or do not wash it with water.
Heat and dry at 300℃ for 10 to 60 minutes to bake the coating. In the case of anionic electrodeposition, the electrodeposition coating liquid used in the present invention uses a polycarboxylic acid resin having carboxyl groups in the resin skeleton as a base, and coats this with a crosslinking resin and, if necessary, a modifying resin. As a film-forming component, for example, polycarboxylic acid resins include one or more of saturated or unsaturated alkyd resins, oil modified products thereof, acrylic resins having carboxyl groups, vinyl resins, fluorine resins, etc. A mixture of the following, at least a portion of the carboxyl group is neutralized with an organic amine or ammonia, and the mixture is diluted with water to form a clear or emulsified state. As the crosslinking resin, amino resins such as melamine resin, urea resin, benzoguanamine resin, and acetoguanamine resin can be used. In addition, anionic resins such as polyester and polybutadiene can be used. In the case of cationic electrodeposition, a cationic resin is used as a base, which is a polyamine resin that has an amino group in the resin skeleton, and a crosslinking resin and, if necessary, a modifying resin are used together to form a coating film. For example, polyamine resins are made by adding amino groups as functional groups to epoxy resins, vinyl, acrylic resins, polybutadiene resins, urethane resins, etc., and neutralizing them with low molecular acids to make them water-soluble. It is dissolved or dispersed in As the crosslinking agent, isocyanate, resin into which blocked isocyanate, etc. can be used. The conductive article that can be used in the present invention is not limited to any shape, size, material, etc., as long as it has conductivity, and includes, for example, iron, copper, aluminum, magnesium, titanium, etc., or alloys thereof. Examples include plastics with a metal plating layer formed on the surface. These conductive articles are usually subjected to chemical conversion treatment before electrocoating, but suitable chemical conversion treatments include various phosphate treatments, chromate treatments, boehmite treatments, anodization treatments, etc. It is. (Examples) In order to explain the present invention more specifically, Examples are shown below, but the present invention is not limited to these Examples. [Preparation of Primer 1] N-
(2-Aminoethyl) 111.1g of 3-aminopropyltrimethoxysilane, 236.3g of 3-glycidoxypropyltrimethoxysilane, and 1389.6g of isopropyl alcohol were charged, and while keeping the temperature at 30℃.
Stirring was performed for 240 minutes. Then, it was cooled to room temperature, and Primer 1 was prepared. [Preparation of Primers 2 to 14] In the method for preparing Primer 1, except that the type and amount of organic alkoxysilane and the type and amount of hydrophilic solvent were changed to those shown in Table 1.
Primers 2-14 were prepared using the same method.

【table】

[Preparation of electrodeposition coating liquid ED-1]

In a four-neck flask equipped with a stirrer, thermometer, nitrogen inlet, and reflux condenser, add 30 g of isopropyl alcohol, 20 g of ethylene glycol monobutyl ether, and 2 tert-butyl peroxy.
- Add 1.0 g of ethylhexanoate and raise the temperature to 80°C while stirring. Methyl methacrylate 41.0
g, n-butyl methacrylate 20.0g, 2-ethylhexyl acrylate 20.0g, methacrylic acid 3.0g,
2-hydroxyethyl methacrylate 16.0g, n-
A mixture of 0.3 g of dodecyl mercaptan was added dropwise into the flask over 180 minutes, and stirring was continued for an additional 120 minutes.
Then ethylene glycol monobutyl ether
A mixture of 5.0 g of tert-butyl-2-ethylhexanoate and 0.1 g of tert-butyl-2-ethylhexanoate was added into the flask three times every 60 minutes, and stirring was continued for an additional 120 minutes, followed by cooling to room temperature. Add to this 2.8g of triethylamine
After adding and stirring thoroughly, add deionized water 663.9
g was added to prepare an electrodeposition coating solution (ED-1).
The resulting electrodeposition coating liquid had a resin solid content of 12% by weight and an acid value of 20.0 mgKOH. [Preparation of electrodeposition coating liquid ED-2] 1900 parts of bisphenol A type epoxy resin (trade name Epicote 1004, manufactured by Ciel Chemical Co., Ltd.) having an epoxy equivalent of 950 was dissolved in 1012 parts of butyl cellosolve, and 124 parts of diethylamine was dissolved. After dropwise addition at 80 to 100°C, the mixture is maintained at 120°C for 2 hours to obtain an epoxy resin-amine adduct having an amine value of 47. Next, 1000 parts of a dimer acid type polyamide resin with an amine value of 100 (trade name Persamide 460, manufactured by Henkel Hakusui Co., Ltd.) was dissolved in 429 parts of methyl isobutyl ketone, heated to reflux at 130 to 150°C, and the produced water was distilled off. to convert the unterminated amino group into ketimine. This material is kept at 15°C for about 3 hours, and after water has stopped distilling off, it is cooled to 60°C. Next, this product was added to the epoxy resin-amine adduct, heated to 100°C, maintained for 1 hour, and then cooled to room temperature to obtain an epoxy resin-amine-polyamide adduct resin having a solid content of 68% and an amine value of 65. Add 1.5 parts of acetic acid to 100 parts of this resin to neutralize it. Next, 4-4′ dicyclohexylmethane diisocyanate
7.3 parts and bis(4-hydroxyphenyl)-2,2
- Dissolve 7.9 parts of propane in 7.6 parts of methyl isobutyl ketone, add 1 drop of dibutyltin dilaurate, react at 120°C for 12 hours, and then cool to room temperature to synthesize curing resin B. The thus obtained neutralized epoxy resin-amine-polyamide addition resin A (101.5 parts) and curing resin B solution (22.8 parts) have an epoxy equivalent of 200 and a viscosity of 25°C.
Add 20 parts of 700 poise epoxidized polybutadiene (trade name E-1000, manufactured by Nippon Petrochemicals Co., Ltd.), and while stirring thoroughly, add 272 parts of deionized water to give a solid content of 20% and pH 6.2. Electrodeposition coating liquid (ED-2)
was prepared. Example 1 An aluminum plate that had been anodized according to a conventional method was immersed in Primer 1 for 2 minutes, and then heated to 30°C.
When dried by heating for 60 minutes, a primer layer with a thickness of 3 μm was formed. Next, this was immersed in an electrodeposition coating solution (ED-1) heated to 30℃, connected to the anode, and a direct current was applied between it and the counter electrode stainless steel plate at a voltage of 160 volts for 3 minutes to complete the electrodeposition coating. was applied.
Next, the aluminum plate was pulled out of the liquid, washed with water, and then heated and dried at 180°C for 30 minutes. As a result, a uniform electrodeposition coating film with a film thickness of 50 μm was formed. When this coating film was subjected to a pinhole test and an impact resistance test, no pinholes were found, and no abnormalities in the coating film were observed. However, the pinhole test was conducted using a pinhole detector (trade name: TRC-200B manufactured by Sanko Electronics Laboratory) and charged with 1 Kv. Moreover, the impact resistance test was conducted based on the method of JIGK-6902. Examples 2 to 7 and Comparative Examples 1 to 5 Electrodeposition coating was performed in the same manner as in Example 1, except that the type of primer and heating drying conditions were changed as shown in Table 2. As a result, the electrodeposition coating films shown in Table 2 were formed. Example 8 An iron plate treated with zinc phosphate according to a conventional method was immersed in Primer 1 for 2 minutes and then heated and dried at 30° C. for 60 minutes to form a primer layer with a thickness of 3 μm. Next, this was immersed in an electrodeposition coating solution (ED-2) heated to 30°C and connected to the cathode.
3 with a voltage of 200 volts between the opposite stainless steel plate.
Electrodeposition coating was applied by applying direct current for one minute. Then,
The iron plate was pulled out of the liquid, washed with water, and then heated and dried at 140°C for 30 minutes. As a result, a uniform electrodeposition coating film with a film thickness of 45 μm was formed. When this coating film was subjected to a pinhole test in the same manner as in the examples, no pinholes were observed. Examples 9 to 12 and Comparative Examples 6 to 9 Electrodeposition coating was performed in the same manner as in Example 2, except that the type of primer and heating drying conditions were changed as shown in Table 3. As a result, the electrodeposition coating films shown in Table 2 were formed. Comparative Examples 10 to 11 Electrodeposition coating was performed in the same manner as in Examples 1 and 8 except that the primer treatment was not performed. As a result, electrodeposited coatings shown in Tables 2 and 3 were formed.

【table】

【table】

[Table] Examples 13 to 16 Electrodeposition coating was carried out in the same manner as in Example 1, except that the electrodeposition coating conditions were changed as shown in the table. As a result, electrodeposited coating films having the thickness shown in Table 4 were formed.

[Table] Examples 17 to 19 Electrodeposition coating was performed in the same manner as in Example 1 except that the primer coating treatment was changed to the contents shown in Table 5. As a result, the electrodeposition coating films shown in Table 5 were formed. However, the number of cycles is a numerical value in which one cycle is the formation of a dry coating layer by primer treatment.

[Table] Examples 20 to 21 Same method as in Example 1, except that the conductive article was replaced with anodized aluminum, an aluminum plate and a steel plate were used, and electrodeposition was applied at 100 volts for 2 minutes. Electrodeposition painting was performed. The aluminum plate was degreased and dried in a conventional manner, and the iron plate was treated in a conventional manner with zinc phosphate and dried. As a result, the aluminum plate has a film thickness of 40 μm,
A uniform electrodeposited coating film with a thickness of 38 μm was formed on the iron plate. When these coating films were subjected to a pinhole test and an impact resistance test, no pinholes were found, and no abnormalities were observed in the coating films. (Effects of the Invention) The electrodeposition coating method of the present invention has the excellent effect of being able to freely control the coating thickness and forming a pinhole-free electrodeposited coating with a high thickness in one coating. play.

Claims (1)

[Claims] 1. When electrocoating a conductive article, before electrocoating the article, prepare A component A/B consisting of A. an organic alkoxysilane compound having an amino group and B. an organic alkoxysilane compound having a glycidyl group.
1. A method for electrodeposition coating, which comprises treating a surface with a primer composition having a molar ratio of components of 0.42 to 1.37, drying the surface, and then performing electrodeposition coating.