JPH10324995A - Method for preventing cissing of electrodeposited coating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the defect cissing of electrodeposited coating films by the pollutant carried over from a coating pretreatment stage and to enable the finishing of the good coating films. SOLUTION: The following stages (a) to (d) are successively executed; (a) a stage for subjecting a material to be deposited to a degreasing treatment, washing and chemical conversion treatment, (b) a stage for subjecting the material to at least one time of a washing treatment by clean water, (c) a stage for subjecting the material to the washing treatment with pure water by immersing the material into a pure water immersing vessel having a surface velocity of flow of >=0.2 m/sec and (d) a stage for forming the electrodeposited coating films. A surfactant is preferably added at 0.5 to 500 ppm to the immersing vessel in the stage (c).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing cissing of an electrodeposition coating film, and in particular, to prevent the occurrence of coating defects caused by residual adhesion of oil and oil droplets, and to provide excellent coating appearance and coating performance. It relates to an electrodeposition coating method for obtaining.

[0002]

2. Description of the Related Art An electrodeposition coating method is a method in which a coating film is deposited on the surface of an object to be coated through a process such as electrophoresis by applying a voltage. Depending on the method of applying a voltage and the type of coating material, it is generally classified into a cationic electrodeposition coating method and an anionic electrodeposition coating method. For example, a cationic electrodeposition coating method is mainly used for coating an automobile body. In addition, electrodeposition coating, including the steps before and after electrodeposition coating, usually includes various steps of degreasing, washing with water, surface adjustment if necessary, chemical conversion treatment, washing with water, drying, electrodeposition coating, washing with water, and baking. It is performed sequentially.

[0003] However, in the conventional process, coating film defects such as cissing and pinholes may occur.

[0004] In order to remove contaminants on the surface of a metal object in advance, a method of finishing electrodeposition coating disclosed in Japanese Patent Application Laid-Open No. 57-92196 is required. It has been proposed to perform a wiping process on the surface of a metal workpiece prior to electrodeposition coating.

Japanese Unexamined Patent Publication No. 60-21384 discloses a "method of drying a car body after a chemical conversion treatment".
Preheating and heating while maintaining the surface of the body parts wet,
Next, a method of ventilation drying the body parts at high temperature was proposed,
Japanese Patent Application Laid-Open No. 60-33396 proposes a method for drying a car body after a chemical conversion treatment, in which a final spraying treatment in the water washing treatment is performed using hot water or saturated steam, and then directly dried with hot air in a drying oven. ing. Both methods,
In this method, the surface temperature of the vehicle body component is preheated to a certain temperature in a wet state, and the surface is dried at once by hot air drying, so that a coating defect due to residual water can be prevented without drying unevenness.

[0006] The "cation electrodeposition coating method" disclosed in JP-A-61-190098 includes a degreasing treatment, a chemical conversion treatment,
And after passing through a pre-coating step of washing and drying, the pH is adjusted to 5.8 to 8.2 in order to remove foreign substances on the surface of the object to be coated.
In addition, a method has been proposed in which deionized water having a specific conductivity of 10 μS / cm or less is sprayed onto the object to be coated, for example, at 100 ml / m ² , followed by cationic electrodeposition.

Japanese Unexamined Patent Publication (Kokai) No. 63-134697 discloses a "pretreatment method for cationic electrodeposition coating". In order to prevent cratering after electrodeposition coating on a galvanized steel sheet which is liable to be cratered, the method is described in Japanese Patent Application Laid-Open No. 63-134697. A method has been proposed in which a cationic thermosetting water-soluble resin solution is applied to a steel sheet without energization before coating, dried without curing the coating, and further subjected to cationic electrodeposition coating on the steel sheet.

[0008] Japanese Patent Application Laid-Open No. 64-25995 discloses an "electrodeposition coating method". In conducting an electrodeposition coating of a conductive article, a fluorine-based surfactant having a perfluorocarbon group before the electrodeposition coating is applied. 0.001 to 5.0% by weight of the agent
There has been proposed a method of performing a surface conditioning treatment (for example, immersion or spraying for 30 seconds to 5 minutes) with an aqueous liquid and then performing electrodeposition coating.

Further, Japanese Patent Application Laid-Open Nos. Hei 5-331592, Hei 6-33299, and Hei 6-93500 propose respective devices for removing foreign matter adhering to an object to be coated. Also, JP-A-7-113197 and JP-A-8-170194 disclose that before the electrodeposition coating, water remaining on the surface of the object is removed by spraying an electrodeposition coating solution or the like. An apparatus has been proposed.

[0010]

However, as described in JP-A-57-92196, when the surface of a metal workpiece is subjected to wiping treatment prior to electrodeposition coating, it remains in a portion where wiping is difficult. The presence of oil, oil droplets, and foreign matter may cause deterioration in the appearance of the coating.

The drying methods described in JP-A-60-21384 and JP-A-60-33396 can remove residual water, but cannot completely remove foreign matter by ordinary spraying. In such a case, the coating appearance may be deteriorated.

Further, as described in JP-A-61-190098, for example, 100 ml of deionized water is applied to an object to be coated.
Even when spraying at / m ² , there is a case where foreign matter cannot be completely removed due to insufficient pressure, and in such a case, the appearance of the coating is deteriorated.

Further, as described in JP-A-63-134697, a complicated process of applying a cationic thermosetting water-soluble resin solution to a steel sheet before electrodeposition coating and drying without curing the steel sheet is required. There was a problem that it was necessary.

Further, as described in JP-A-64-25995, a fluorine-containing surfactant having a perfluorocarbon group of 0.001 to 5.0 before the electrodeposition coating of the object to be coated.
When the surface conditioning treatment (for example, immersion or spraying for 30 seconds to 5 minutes) is performed with the aqueous solution by weight, bubbles are formed because the concentration of the surfactant is relatively high, and the bubbles attached to the object to be coated are removed by another means. There was a problem that had to be.

The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to prevent the occurrence of coating film defects caused by residual adhesion of oil and oil droplets, and to provide an excellent coating appearance and coating film. An object of the present invention is to provide a method for preventing cissing of an electrodeposition coating film in order to obtain performance.

[0016]

In order to achieve the above-mentioned object, a method for preventing cissing of an electrodeposition coating film according to the present invention comprises the steps of (a)
A step of subjecting the object to degreasing, water washing, and chemical conversion;
(B) a step of performing at least one water-washing treatment with tap water, and (c) a surface flow rate of the immersion tank of 0.2 m / sec. A step of immersing in the pure water tank described above and performing a water washing treatment with pure water, a step (d) of forming an electrodeposition coating film, and the steps (a) to (d)
This is a method of sequentially performing the step (d).

Further, the method for preventing cissing of the electrodeposition coating film is as follows.
The surfactant is added to the immersion tank in the step (c) in an amount of 0.5 to
This is a method of adding 500 ppm.

In the step (c), the surface flow rate is 0.2
m / sec. Since the substrate is immersed in the above-described pure water tank and subjected to a water-washing treatment with pure water, foreign substances on the surface of the object to be coated can be almost completely removed. Accordingly, defects (cissing) of the electrodeposition coating due to contaminants brought in from the coating pretreatment step are prevented, and the appearance of the coating is improved as compared with the related art. In the conventional treatment step, the steps are configured in the order of chemical conversion treatment, water washing, and electrodeposition coating. However, according to the present invention, the foreign matter is removed simply by providing the pure water immersion tank in the conventional treatment step. Therefore, it is possible to minimize the number of additional facilities for improvement. Further, pure water in the immersion tank does not need to be heated as in the conventional case. For this reason, there are few incidental facilities and it is excellent in economy.

In the above step (c), by adding a surfactant, foreign substances adhering to the surface of the substrate can be easily removed. The concentration of the surfactant in the immersion tank of the present invention is determined by the above-mentioned JP-A-64-2599.
No. 5, the surfactant concentration becomes 1/2 to 1/100, the foaming property is reduced, and accordingly, the foam does not adhere to the surface of the article to be treated. Therefore, the object to be coated can be transferred to the immediate electrodeposition coating process, and the processing efficiency up to the electrodeposition coating can be improved.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The method for preventing cissing of an electrodeposition coating film according to the present invention is a method which sequentially carries out the following steps (a) to (d). That is, (a) a step of performing a degreasing treatment, washing with water, and a chemical conversion treatment on an object to be coated; (b) a step of performing at least one washing treatment with tap water; and (c) a surface flow rate of 0.2 m / sec.
c. The above steps of immersing in a pure water immersion tank and performing a water washing treatment with pure water and (d) a step of forming an electrodeposition coating film are sequentially performed.

Hereinafter, each step will be described.

(A) Degreasing treatment, washing with water, chemical conversion treatment
Step of applying : Any method may be used as long as all of the processes of degreasing, rinsing, and chemical conversion are generally performed. For example, hot water washing → spray degreasing → immersion degreasing →
It may be a treatment through first rinsing treatment → second rinsing treatment → surface conditioning treatment → immersion chemical treatment.

The degreasing agent used in the degreasing treatment is not particularly limited as long as it is a generally used alkaline degreasing agent.

As the chemical conversion treating agent used in the chemical conversion treatment, for example, a zinc phosphate treating agent, an iron phosphate treating agent and the like can be used.

(B) At least one washing with tap water
Step of applying treatment: As the water washing treatment, either spray water washing or immersion water washing may be performed.

(C) When the surface flow velocity is 0.2 m / sec. that's all
Immersed in pure water immersion tank and rinsed with pure water
Step : The pure water preferably has a pH of 5 to 7. Further, the conductivity of pure water is preferably 5 μS / cm or less.

When the pH of pure water is less than 5, there is a disadvantage that a phosphate film may be partially dissolved,
On the other hand, if the pH exceeds 7, there is a disadvantage that contamination due to the alkali component contained in the pure water occurs.

Further, if the conductivity of pure water exceeds 5 μS / cm, there is a disadvantage that impurities contained therein cause contamination of the electrodeposition paint.

The surface velocity of the immersion tank is 0.2 m / s.
ec. It is preferable that it is above. Surface velocity is 0.2m
/ Sec. If less than, deposits are not sufficiently removed,
There is a disadvantage that repelling of the electrodeposition coating film occurs.

(D) Step of forming an electrodeposition coating film: The electrodeposition coating material used in the present invention may be an anionic resin type, a cationic type resin type, or a water-soluble type. Or a dispersion type, and any of conventional types can be used. For example, (1) α, β-ethylenically unsaturated dibasic acid or an anhydride adduct thereof of a liquid rubber such as drying oil or polybutadiene, a resin having an epoxidized resin as a main skeleton, and a modified derivative thereof, such as (2) those having a fatty acid ester of a resinous polyol as a main skeleton and modified derivatives thereof, such as a maleated oil resin, a maleated polybutadiene resin, and an amine-modified epoxidized polybutadiene resin, such as an epoxy resin and an esterified resin; Examples include those having an alkyd resin as a main skeleton, and (4) those having an acrylic resin as a main skeleton.

In order to dissolve or disperse the electrodeposition resin in water, an acidic resin is used with a base such as ammonia, amine or inorganic alkali, and a basic resin is used with acetic acid, lactic acid, boric acid or phosphoric acid. And the like. Further, in addition to the above components, conventional additives such as a crosslinking agent such as a melamine resin and a blocked polyisocyanate, a pigment, a solvent, and a surfactant are appropriately blended.

In the case of an anionic resin-based coating, the electrodeposition coating is applied by a usual method of providing an anode with an object to be coated as a positive electrode and performing electrodeposition, and in the case of a cationic resin-based coating, This is performed by reversing the electrodes when the resin paint is used. The electrodeposition coating film is usually provided so that the film thickness after baking is 5 to 50 μm. Further, the bath temperature of the electrodeposition paint is preferably 20 to 40 ° C. Further, the applied voltage is preferably from 50 to 500V.

The method for preventing cissing of an electrodeposition coating film according to the present invention is characterized in that a surfactant is further added to the immersion tank in the step (c) in an amount of 0.5 to 500 ppm.

When the amount of the surfactant is less than 0.5 ppm, there is a disadvantage that the adhering oil is not sufficiently removed and repelling is caused on the electrodeposited coating film. There is an inconvenience that the appearance of the electrodeposited coating film and the performance of the coating film are poor due to the foaming of the film and the carry-in to the electrodeposition paint.

The surfactant used in the present invention may be any as long as it emulsifies the oil introduced from the degreasing and / or chemical conversion treatment step. Examples of the surfactant include a nonionic surfactant, a cationic surfactant, and an anionic surfactant. Both surfactants and amphoteric surfactants can be used. Nonionic surfactants and cationic surfactants are preferred for cationic electrodeposition coating, and nonionic surfactants and anionic surfactants are preferred for anionic electrodeposition coating.

<Nonionic surfactant> For example, polyethylene glycol type surfactants include higher alcohol ethylene oxide adducts, fatty acid ethylene oxide adducts, polyhydric alcohol fatty acid ester ethylene oxide adducts, higher alkylamine ethylene oxide adducts , A fatty acid amide ethylene oxide adduct, a polypropylene glycol ethylene oxide adduct, and the like. As the polyhydric alcohol type,
And sucrose fatty acid esters. Specific examples of surfactants that can be used include mainly the following.

(A) Polyethylene glycol type surfactant
Agents : (i) Higher alcohol ethylene oxide adducts: Examples of the general formula include those shown below, for example, polyoxyethylene alkylphenyl ether, polyoxyethylene alkyl ether, particularly polyoxyethylene nonylphenol ether, polyoxyethylene. Examples include octyl phenol ether, polyoxyethylene oleyl ether, polyoxyethylene lauryl ether, polyoxyethylene stearyl ether, and polyoxyethylene octyl ether.

[0038]

Embedded image Here, R: an alkyl group of C _{11 to} C ₁₈ R ₁ : an alkyl group of C _{7 to} C ₉ n: generally 8 to 15 As a product, “ADEKATOL LO series”, “ADEKATOL SO series” (above, Asahi Denka Co., Ltd.),
"Emulgen series" (manufactured by Kao Corporation), "Neugen ET series", "Neugen EA series" (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) and the like can be used.

(Ii) Aliphatic ethylene oxide adduct: The general formula is represented by the following chemical formula 2. Examples thereof include polyoxyethylene fatty acid esters, polyoxyethylene sorbitan fatty acid esters, and sorbitan fatty acid esters, and the use of polyoxyethylene oleate, sorbitan monourarate, and polyoxyethylene sorbitan monooleate is preferred.

[0040]

Embedded image Here, R: an alkyl group of C _{11 to} C ₁₄ n: generally 5 to 30 As products, “ADEKATOL OEG series” (manufactured by Asahi Denka Co., Ltd.) and “Emanon series” (Kao Corporation)
), "Neugen ES Series" (Daiichi Kogyo Pharmaceutical Co., Ltd.)
Manufactured) can be used.

(Iii) Polyhydric alcohol fatty acid ester ethylene oxide adduct: The following general formula is given.

[0042]

Embedded image Here, R: an alkyl group of C ₁₂ -C _18, including diesters other than the above.

Commercial products include "ADEKANOL NK series" (manufactured by Asahi Denka Co., Ltd.) and "LEODOL TW series"
Or "Reo Doll 400 Series" (Kao Corporation)
), "Solgen TW Series" (Daiichi Kogyo Pharmaceutical Co., Ltd.)
Manufactured) can be used.

(Iv) Higher alkylamine ethylene oxide adduct: As an example of the general formula, the following formula 4 can be mentioned.

[0045]

Embedded image Here, R: alkyl group n of C ₁₂ ~C _18, m: 0~20 polyoxyethylene alkyl amide

Embedded image Here, R: alkyl group n of C ₁₂ ~C _18, m: 0~20 The product, "A meat series" (Kao Corporation
Amiran Series) (Daiichi Kogyo Pharmaceutical Co., Ltd.)
Manufactured) can be used.

(V) Polypropylene glycol ethylene oxide adduct: The following general formula is given.

[0047]

Embedded image Here, n + m + m '= 20 to 80 n: about 15 to 50 As products, "Bluronic series", "Adecanol B series" (manufactured by Asahi Denka Co., Ltd.), "Emulgen PP"
Series "(manufactured by Kao Corporation)," Evan Series "(manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) and the like can be used.

(B) Polyhydric alcohol type : Fatty acid ester type of sucrose.

[0049]

Embedded image Here, R: alkyl group Product C ₁₂ -C _18, it can be used to "Span series", "Emulgen series" (manufactured by Kao Corporation) and the like.

<Cationic surfactant> Specific examples of the cationic surfactant which can be used in the present invention include:
Dialkoxyalkylamine salts as primary amine salts,
Disiloxyethyl stearylamine; and the secondary amine salt is N- (3-alkoxy-2-hydroxypropyl) monoalkylamine salt, monoalkylester ethylmonoalkylamine salt, alkylamidoethylmonoalkylamine salt. And the like. Examples of the tertiary amine salts include N- (3-alkoxy-2-hydroxypropyl) dialkylamine salts, monoalkylester ethyldialkylamine salts, and alkylamidoethyldialkylamine salts. Further, examples of the quaternary ammonium salt include N- (3-alkoxy-2-hydroxypropyl) trialkylammonium halide, monoalkylester ethyltrialkylamine salt, alkylamidoethyltrialkylamine salt, lauryltrimethylammonium chloride and the like. Can be Preferred of the above salts are salts having a halogen,
A preferred halogen is chlorine. Preferably, N
-(3-alkoxy-2-hydroxypropyl) trialkylammonium halide, N- (3-alkoxy-
2-Hydroxypropyl) dialkylamine halide and the like, more preferably these chlorides and the like are used. At least two or more of the alkoxy groups and alkyl groups of the above components have 10 or more carbon atoms.

Further, for example, triethanolamine monostearate, 2-heptadecenylhydroxyethylimidazoline, alkylbensene sulfonate, polyoxyethylene alkylphenyl ether sulfate, polyoxyethylene alkyl ether sulfate or a salt thereof (for example, sodium And alkali metals such as potassium, and amines such as ammonia, triethylamine and diisopropylamine. Particularly preferably,
Sodium dodecylbenzenesulfonate; sodium oxyethylene tridecyl ether sulfate; Also, an alkylamine salt quaternary ammonium salt or the like can be used.

<Anionic Surfactant> Examples of the anionic surfactant include fatty acid metal gypsum such as sodium oleate, sodium naphthenate, and sodium rosinate, sodium lauryl alcohol sulfate, lauryl ether sulfate, and alkylbenzene. Sodium sulfonate, furthermore, fatty acid salt, higher alcohol sulfate, alkylbenzene sulfonate, dialkyl sulfosuccinate, polyoxyethylene polyoxypropylene glycol ether sulfate, polycarboxylic acid polymer surfactant and the like can be used.

<Amphoteric Surfactant> As the amphoteric surfactant, for example, stearyl dimethyl betaine, methyl laurylaminopropionate and the like are used.

Further, other preferred embodiments of the present invention other than those described in the claims are shown below.

1. Pure water used in the immersion tank in step (c)
H preferably has a pH of 5 to 7, and the conductivity of pure water is preferably 5 μS / cm or less.

2. The surfactant used in the present invention is at least one of a nonionic surfactant, a cationic surfactant, an anionic surfactant, and an amphoteric surfactant.

3. The surfactant used in the present invention is preferably a nonionic surfactant or a cationic surfactant in the case of cationic electrodeposition coating, and a nonionic surfactant or anionic surfactant in the case of anionic electrodeposition coating. preferable.

[0058]

Next, the present invention will be described in detail with reference to examples and comparative examples.

Examples 1 to 10 and Comparative Example 1 <Test Method> (1) Degreasing: "Surf Cleaner SD-550" (manufactured by Nippon Paint Co., Ltd.) ↓ (2) Rinsing (immersion), surface flow rate 0.1 m / S ↓ (3) Surface adjustment: “Surf Fine 5N-8R” (Nippon Paint Co., Ltd.) ↓ (4) Chemical formation: “Surf Dine SD-5000” (Nippon Paint Co., Ltd.) ↓ (5) Rinse : Spray, spray pressure 0.5 kg / cm ² ↓ (6) Rinse with pure water: immersion: pH 6, conductivity 3 μS / cm ↓ (7) Electrodeposition: “Power Top V-6 Gray” (Nippon Paint Co., Ltd.) ↓ (8) Baking: 170 ° C. for 20 minutes In the above steps (1) to (6), 100 pieces of 7 × 15 cm matte steel plate coated with rust-preventive oil were treated, and (6) ) Pure water with an oil concentration of 5 ppm in the pure water process The pure water was used as a test solution. Next, the above-mentioned steel plate, which is a test plate, is subjected to the above-described steps (1) to (5), and then (6)
The surface flow rate of the pure water immersion tank in the process is set as shown in Table 1 below, and the surface is further washed with pure water containing the amount of added surfactant under the conditions shown in Table 1, and the steps (7) to (8) are performed. After that, the repellency state of the electrodeposition coating film and the foaming property of the pure water immersion tank were evaluated.

<Evaluation Method> (1) Repelling: Visually evaluated.

◎: No repelling at all ○: Almost no repelling ×: With repelling (2) Foamability: Evaluated visually.

◎: no foaming ○: almost no foaming △: a little foaming ×: much foaming The results are shown in Table 1.

[0063]

[Table 1] Note) Nonionic surfactant: "Neugen EA-87" (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd .; polyoxyethylene allyl phenyl ether) Cationic surfactant: "Adecamine 4MAC-30"
(Asahi Denka Kogyo Co., Ltd .; quaternary ammonium salt monoalkyl) From these results, according to the method for preventing cissing of the electrodeposition coating film of the present invention, the cissing prevention is significantly improved as compared with the conventional method. It was found that there was no foaming in the pure water immersion tank.

[0064]

As described above, according to the method for preventing cissing of an electrodeposition coating film according to the present invention, cissing is prevented and the occurrence of coating film defects caused by residual adhesion of oil and oil droplets is prevented. And
Excellent coating appearance and coating film performance can be obtained. Also,
In the conventional processing step, the steps are configured in the order of chemical conversion treatment, water washing, and electrodeposition coating. However, according to the present invention, it is possible to remove foreign substances simply by providing a pure water immersion tank in the conventional processing step. Therefore, it is possible to minimize the number of additional facilities for improvement. Further, pure water in the immersion tank does not need to be heated as in the conventional case. Therefore, there are few incidental facilities,
Excellent economy.

Claims (2)

[Claims] (1) a step of performing a degreasing treatment, a washing with water and a chemical conversion treatment on an object to be coated; (b) a step of performing at least one washing with water; and (c) a surface flow rate of 0.2 m. / Sec. The above steps of immersing in a pure water immersion tank and performing a water washing treatment with pure water, (d) a step of forming an electrodeposition coating film, and the above steps (a) to (d) are sequentially performed. A method for preventing cissing of an electrodeposition coating film. 2. A method for preventing cissing of an electrodeposition coating film, which comprises adding 0.5 to 500 ppm of a surfactant to the immersion tank in the step (c) according to claim 1.