JPH10324997A - 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 (f) are successively executed; (a) a stage for subjecting a material to be deposited to a degreasing 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 a chemical conversion treatment, (d) a stage for subjecting the material to at least one time of the washing treatment by the clean water, (e) a stage for subjecting the material to the washing treatment with immersion by pure water or by spraying thereof and (f) a stage for forming the electrodeposited coating films. In such a case, the oil-components coexisting in the immersion vessel or storage tank of the clean water or the immersion vessel or storage tank of the pure water are recovered by an oil adsorption belt 1 in at least one stage of (b), (d) or (e).

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 performing a degreasing treatment on the object to be coated, a step of (b) performing a water washing treatment with at least one time of clean water, a step of performing (c) a chemical conversion treatment, and a method of performing (d) at least one time of washing with clean water. (E) immersing or spraying with pure water for washing, (f) forming an electrodeposition coating film, and sequentially performing the above-described steps (a) to (f). In at least one of the above steps (b), (d) and (e), there is provided a method for preventing cissing provided with an oil collecting means using an oil adsorption belt for an oil component mixed in the washing water.

Further, the oil recovery means is provided in at least one of the steps (d) and (e).

Therefore, in the washing step (b), (d) or (e), only oil can be recovered from the washing water containing oil, so that repelling of the electrodeposition coating film can be prevented and washing can be performed. The drainage of water becomes easy, and in some cases, the water after collecting the oil can be reused. As a result, running costs can be significantly reduced.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The method for preventing cissing of an electrodeposition coating film of the present invention is a method which sequentially goes through the following steps (a) to (f). That is, (a) a step of performing a degreasing treatment on an object to be coated;
(B) a step of performing at least one water-washing treatment with tap water; (c) a step of performing a chemical conversion treatment;
(E) rinsing with pure water or spraying with spraying,
(F) a step of forming an electrodeposition coating film, and the above (a) to
In the step of sequentially passing through the step (f), the above (b),
This is a method for preventing cissing comprising an oil recovery means using an oil adsorption belt for an oil component mixed in the washing water in at least one step of (d) or (e).

Further, in the method for preventing cissing of the electrodeposition coating film according to the present invention, the above oil recovery means is further provided in at least one of the steps (d) and (e).

Hereinafter, each step will be described.

(A) degreasing treatment of the object to be coated, (b) washing with water,
(C) Step of performing a chemical conversion treatment : Any of degreasing, water washing, and chemical conversion treatments on the coated object may be used as long as the method is generally performed. For example, hot water washing → spray degreasing → Immersion degreasing treatment → first washing treatment → second washing treatment →
The treatment may be a treatment that proceeds from a surface conditioning treatment to an immersion chemical conversion 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.

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

(E) by dipping or spraying with pure water
Step of performing a water washing treatment : The pure water preferably has a pH of 5 to 7. The conductivity of pure water is 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, when the conductivity of pure water exceeds 5 μS / cm, there is a disadvantage that the contained impurities cause contamination of the electrodeposition coating film.

The spray pressure in the case of spray water washing is 0.2 kg / cm ² or more, preferably 0.5 kg / cm ^2.
/ Cm ² or more. In addition, the surface flow velocity in the case of immersion is
0.05 m / sec. Above, preferably 0.1 m / sec
c. That is all.

(F) 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 oil recovery means used in the method for preventing cissing of the electrodeposition coating film according to the present invention will be described with reference to FIGS.

FIG. 1 shows a first embodiment of the oil recovery means used in the cissing prevention method according to the present invention. The configuration of the oil recovery means is as follows. That is,
In the case where at least one of the washing steps (b), (d) and (e) is a immersion washing treatment, the washing water 5 containing oil contained in the washing tank 4 which is an immersion tank is mixed. Show. The endless belt-shaped oil adsorption belt 1 is stretched around a roller serving as the rotating unit 3 and a roller serving as the driving unit 2 such that a part thereof is immersed in the washing water 5 in the washing tank 4. A scraper 6 is disposed near the drive unit 2, and the scraper 6 scrapes off the oil adhering to the oil adsorption belt 1, and stores the oil as a recovered oil 7 in an oil recovery tank 8.

Next, the operation of the device of the oil recovery means will be described with reference to FIG. In the washing tank 4, washing water 5 mixed with oil generated in the washing step is stored. On the other hand, the rotation of the drive unit 2 causes the oil suction belt 1 to rotate via the rotation unit 3. Generally, oil floats because it has a lower specific gravity than water. Therefore, when a part of the oil absorption belt 1 is immersed in the upper part of the washing tank 4, the oil absorption belt 1 comes into contact with the oil in the washing tank 4. Then, the oil adheres to the surface of the oil absorption belt 1, is carried upward, is scraped off by the scraper 6, and is collected by the oil recovery tank 8
Will be collected. Here, the oil adsorption belt 1 contacts not only the oil in the washing tank 4 but also water, but since only the oil is selectively adhered, it is possible to separate the oil and the water and collect only the oil. it can.

Accordingly, since only the oil is selectively recovered from the rinsing water 5 in the rinsing tank 4, it is possible to reuse the water after collecting the oil. Thereby, repelling of the electrodeposition coating film can be prevented, and the running cost can be significantly reduced.

The oil absorption belt 1 used in the present embodiment is, for example, a non-woven fabric or a woven fabric made of polypropylene fibers disclosed in "Apparatus for Separating and Recovering Oil from Sewage" in JP-A-48-17169. A non-oil-absorbing sheet having no water absorption may be used.
An oil recovery belt made of a fluororesin having a fluorine content of 40 to 76% by weight, which is disclosed in "Floating Oil Recovery Belt" of JP-A No. 8 may be used. As the fluororesin, for example, at least one monomer selected from ethylene tetrafluoride, ethylene trifluoride, ethylene trifluoride chloride, vinylidene fluoride, vinyl fluoride, propylene hexafluoride, and perfluoroalkyl vinyl ethers A thermoplastic fluororesin which is contained as a structural unit and has a sum of ratios of these monomers to the whole resin of 50% by weight or more is preferable. Furthermore, the thermoplastic fluororesin is used in oil recovery operation.
Flexural modulus at 23 ° C. is 10 to 1,000 MPa, and heat deformation temperature under a load of 4.6 kg / cm ² is 40 ° C.
It is preferable that it is above. The thermoplastic fluororesin composition has a critical surface tension of 18 to 30 dynes / cm.
Is preferred, and 18 to 25 dynes / cm is more preferred.
If the critical surface tension is too high, the selective adsorption of oil to water will be poor, and if it is too low, the affinity between the belt and the oil will be poor.

Next, a second embodiment of the oil recovery means used in the cissing prevention method according to the present invention is shown in FIG. Note that the same components as those of the device configuration of the oil recovery means of the first embodiment include:
The same reference numerals are given and the description is omitted.

As shown in FIG. 2, the apparatus configuration of the oil recovery means of this embodiment is such that at least one of the water washing steps (b), (d) or (e) employs a spraying process. Configuration. In order to wash an object to be coated with water, a riser 11 is provided on opposite sides of the washing chamber 14.
The sprayer 12 has a plurality of spray nozzles 12. Spray nozzle 12
Clean water or pure water sprayed and used for washing is stored in the washing tank 4 via the washing water return pipe 13. The oil floating on the upper layer of the washing tank 4 is recovered by the oil absorption belt 1, and the clean water or pure water from which the oil has been removed is sucked from the lower part of the washing tank 4 by the washing pump 9 and risers 11 through the pipe 10. Is transferred to

As a result, it is possible to selectively recover only the oil from the rinsing water 5 in the rinsing tank 4 and reuse the water after collecting the oil, thereby preventing cissing of the electrodeposition coating film.
Running costs can be significantly reduced.

Next, FIG. 3 shows a third embodiment of the oil recovery means used in the cissing prevention method according to the present invention. The first,
The same components as those of the device configuration of the oil recovery means of the second embodiment are denoted by the same reference numerals, and description thereof will be omitted.

As shown in FIG. 3, the apparatus configuration of the oil recovery means of the present embodiment is such that at least one of the washing steps (b), (d) or (e) employs a spraying process. Configuration. In the second embodiment, the washing tank 4 is one tank (see FIG. 2), but in the present embodiment, the washing tanks 4 and 4a are arranged in parallel in two tanks. Therefore, in the present embodiment, the washing tank 4 is connected via the washing water return pipe 13.
Of the washing water 5 stored in the washing tank 5a, the oil is collected by the oil adsorption belt 1, and then overflows and is stored in the washing tank 4a. Therefore, in the washing tank 4a, washing water with a small amount of oil that has not been adsorbed and collected in the washing tank 4 is stored. And the washing tank 4
The washing water sucked from the lower part of a by the washing pump 9 is transferred to the riser 11 via the pipe 10, and is again subjected to spray washing. Although FIG. 3 illustrates an example in which the tank 4a is a single tank, the amount of mixed oil can be further reduced by connecting a plurality of layers.

As a result, compared to the device of the second embodiment,
Further, the purified washing water can be reused. Therefore, repelling of the electrodeposition coating film can be prevented, the degree of reuse of the washing water can be increased, and the running cost can be further reduced.

Next, FIG. 4 shows a fourth embodiment of the oil recovery means used in the cissing prevention method according to the present invention. The first,
The same components as those of the device configuration of the oil recovery means of the second embodiment are denoted by the same reference numerals, and description thereof will be omitted.

As shown in FIG. 4, the apparatus configuration of the oil recovery means of the present embodiment is such that at least one of the washing steps (b), (d) or (e) employs a spraying process. Configuration. In the third embodiment, the washing tanks 4 and 4a are arranged in two tanks in parallel (see FIG. 3), but in the present embodiment, the washing water 5 from the washing water return pipe 13 is temporarily stored in the washing tank 4, and Is lifted upward, the floating oil is removed by scraping or the like, and the washing water 5 from which almost oil has been removed is transferred from the lower part of the washing tank 4 to the washing water treatment tank 15 which is not adjacent by the liquid sending pump 16. The oil is recovered by the oil adsorption belt 1 installed in the washing water treatment tank 15. Although not shown in the figure, the washing water treatment tank 15 may be adjacent to the washing tank 4.

Therefore, since the washing water 5 from which most of the oil has been removed in advance by the washing tank 4 is recovered by the oil absorption belt 1 in the washing tank 15, the degree of purification of the washing water 5 is improved and the oil absorption is improved. Since the degree of contamination of the belt 1 is also reduced, its life is prolonged. Although FIG. 4 shows an example in which the tank 4 is a single tank, the processing load of the washing water treatment tank 15 can be reduced by connecting a plurality of layers with the washing water treatment tank 15.

The washing water treatment tank 15 of the present embodiment
The washing water sucked by the washing pump 9 from the lower part of
It is transferred to the riser 11 via the pipe 10 and is again subjected to spray cleaning.

Therefore, compared with the apparatuses of the second and third embodiments, the further purified washing water can be reused.
Therefore, repelling of the electrodeposition coating film can be prevented, the degree of reuse of the washing water can be increased, and the running cost can be further reduced.

In the third and fourth embodiments, the spray method has been described as an example. However, if the immersion tank for washing is also used as the washing tank 4, the immersion method (dip method) can be used.
Can also be used.

[0050]

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

Examples 1-4 and Comparative Example 1 <Test method> (1) Degreasing: "Surf Cleaner SD-550" (manufactured by Nippon Paint Co., Ltd.) ↓ (2) Rinsing 1 (immersion) ↓ (3) Surface Adjustment: "Surffine 5N-8R" (Nippon Paint Co., Ltd.) ↓ (4) Chemical formation: "Surfdine SD-5000" (Nippon Paint Co., Ltd./Zinc phosphate) ↓ (5) Rinse 2 (immersion) ↓ (6) Rinse with pure water (immersion): pH 6, conductivity 3 μS / cm ↓ (7) Electrodeposition coating: "Power Top V-6" (Nippon Paint Co., Ltd., cationic electrodeposition paint) (dry film) Thickness: 20μ
m) ↓ (8) Rinsing ↓ (9) Baking: 160 ° C. for 10 minutes Test piece (cold-rolled steel sheet: size 30 cm × 30 cm ×) coated with rust preventive oil by the above steps (1) to (6)
0.8cm thick (manufactured by Nippon Test Panel Industries, Ltd.)
0 sheets were treated, and oil was mixed in each immersion tank of (2) water washing 1, (5) water washing 2, and (6) pure water washing. Next, in each of the steps (2), (5) and (6), using the above-mentioned oil-mixed clean water or oil-mixed pure water purified by an oil recovery unit described below using water. (Conditions shown in Table 1 below), test piece (cold rolled steel sheet: size 10 cm ×)
30 cm × 0.8 cm (manufactured by Nippon Test Panel Industry Co., Ltd.) were subjected to the process treatments (1) to (9).

As shown in Table 1 below, in Examples 1 to 3, the immersion tanks of (2) water washing 1, (5) water washing 2, and (6) pure water washing were used. 1) An oil recovery device as shown in FIG. 1 was installed in both of the immersion tanks for washing 2 and (6) pure water washing.

Comparative Example 1 was carried out in the same manner as in Example 1 except that the oil recovery device installed in (2) Washing 1 of Example 1 was removed.

<Structure of oil recovery device> Oil absorption belt: width 10 cm × length 1 m, material: number of rotations of polypropylene fibrous belt: 30 rotations per minute Belt operating time: 10 minutes <Evaluation method> Repelling: burning The number of cissing of the later coating film was visually counted and evaluated according to the following criteria.

◎: No repelling number at all ○ ⁺ : 1-2 repelling numbers ○: 3 to 5 repelling numbers Δ ⁺ : 6 to 10 repelling numbers △: 11 to 20 repelling numbers ×: 21 or more repelling numbers Table 1 shows the results.

[0056]

[Table 1] From these results, it was found that the method for preventing cissing of the electrodeposition coating film of the present invention significantly improved cissing prevention compared to the conventional method.

[0057]

As described above, according to the method for preventing cissing of an electrodeposition coating film according to the present invention, cissing of the electrodeposition coating film is prevented by removing mixed oil with an oil recovery belt. The occurrence of film defects can be prevented, and excellent coating appearance and coating film performance can be obtained. Further, in the above-mentioned (b), (d) or (e) washing step, only oil can be recovered from wastewater mixed with oil by the oil recovery means. In some cases, it is possible to reuse the water after collecting the oil. This allows
Running costs can be significantly reduced. Therefore, it is excellent in economy.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an apparatus configuration of an oil adsorbing unit of a first embodiment used in a method for preventing cissing of an electrodeposition coating film according to the present invention.

FIG. 2 is a diagram illustrating a device configuration of an oil adsorbing unit according to a second embodiment used in the method for preventing cissing of an electrodeposition coating film according to the present invention.

FIG. 3 is a diagram illustrating a device configuration of an oil adsorbing unit according to a third embodiment used in the method for preventing cissing of an electrodeposition coating film according to the present invention.

FIG. 4 is a diagram illustrating a device configuration of an oil adsorbing unit of a fourth embodiment used in the method for preventing cissing of an electrodeposition coating film according to the present invention.

[Explanation of symbols]

1 oil absorption belt, 2 drive section, 3 rotating section, 4 washing tank, 5 washing water, 6 scraper, 7 collected oil, 8
Oil recovery tank.

Claims (2)

[Claims] (A) a step of performing a degreasing treatment on an object to be coated; (b) a step of performing at least one water-washing treatment with tap water; (c) a step of performing a chemical conversion treatment; (E) a step of performing a water-washing treatment with tap water, (e) a step of performing a water-washing treatment by immersion or spraying with pure water, and (f) a step of forming an electrodeposition coating film; In step f), at least one of the steps (b), (d) or (e)
What is claimed is: 1. A method for preventing cissing of an electrodeposited coating film, comprising an oil collecting means for collecting an oil mixed in washing water by an oil absorption belt. 2. A method for preventing cissing of an electrodeposition coating film, comprising the oil recovery means according to claim 1 in at least one of the steps (d) and (e).