JPS581095A - Cation electrodeposition coating method - Google Patents

Abstract

PURPOSE:To reduce a cost while maintaining a requested quality, by specifying a temperature of a coating bath, concentration of an organic solvent, voltage and conduction time, and drying a coated substance which was subjected to electrodeposition coating under condition specified above, and forming a film of specific thickness. CONSTITUTION:A substance to be coated 3 hung from a conveyor 1 is de-fatted in advance by a de-fatting agent spraying device 6, is soaked in a de-fatting agent of a tank, is de-fatted, and is rinsed by water spraying devices 8a, 8b, a water tank 14, and water spraying devices 16a, 16b and 19. Subsequently, the substance to be coated 3 is soaked in an electrodeposition coating material bath of a cation electrodeposition tank 25 at a bath temperature 22-27 deg.C, the substance to be coated 3, and a pair of poles on both sides in the tank 25 are set to the negative side and the positive side, respectively, and an electric power supply is turned on for 2.5-4min, applying the voltage of 180-250V. As a result, on the surface of the substance to be coated 3, a coating film whose dry film thickness is 4-13mum is formed. In this case, concentration of an organic solvent in a coating material to be used is 4-5%. The substance to be coated which was subjected to water-cut in an overflow tank 26 is rinsed, and is baked and dried by a furnace 39.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cationic electrodeposition coating method, particularly to a cationic electrodeposition coating method for forming a thin film coating.

Heavy cloth painting uses electrophoresis using the fact that paint molecules are stationary or negatively charged in water-based paint or water.
& It is a method of depositing paint on the painted object, and since the corrosion resistance of the applied paint film is destroyed, automatic tlj @ L type and M1 products, electric refrigerators, electric washing machines, etc.] l industry products. It is widely used as a guise.

There are two types of electrodeposition coating methods: anionic and cationic. Hitherto, the anionic coating method has been mainly used because the paint is inexpensive and has relatively good coverage. However, the cationic electrodeposition coating method has the drawback that metals or chemical conversion coatings may be leached from the object to be coated, and therefore, the cationic electrodeposition coating method has recently been used. That is, according to this method, there are advantages in that the adhesion of the coating film to the object to be coated is good and the corrosion resistance of the resulting coating film is superior to that of anionic electrodeposition coating films.

In addition, in cationic electrodeposition coating, the coating has good adhesion, so a thick coating can be formed on the entire surface of the object to be coated, and corrosion resistance is further improved.

In the past, the corrosion resistance of the objects to be coated was greatly improved, but some objects did not require any corrosion resistance, resulting in excessive quality. For this reason, it may be possible to reduce the thickness of the coating film to reduce costs while maintaining the quality of the object to be coated, but in addition, in cationic electrodeposition coating, the paint coverage is good, so
It has been thought that it is difficult to form a thin film.

In order to reduce costs while maintaining the required quality, the inventors of the present invention did not follow the path of conventional cationic electrodeposition coating, but repeated research, experimentation, and development of the present invention. It happened.

In the present invention, the object to be coated is coated in a cationic electrodeposition paint bath with a paint bath temperature of 22 to 27C, an organic bath agent, and a viscosity of 4 to 5%.
Applying the voltage of
This is a cationic electrodeposition coating method characterized by forming a coating film of 13 μm.

Hereinafter, the present invention will be explained with reference to the drawings. 6. FIG. 1 is a diagram showing an embodiment of the present invention.

That is, in the present invention, as shown in FIG. 1, the object to be coated 3 suspended from the overhead conveyor 1 by the coating bunker'-2 passes through the booth °x'' opening 4, and then is transferred to the tank 5 in the preliminary degreasing step A. A degreasing agent whose main components are an alkali such as sodium phosphate, sodium carbonate, or sodium lyate, a surfactant, and a surface conditioner is sprayed from the degreaser spraying device 6 for 30 to 90 seconds, e.g. The object to be coated is preliminarily degreased by spraying for 60 seconds.In this preliminary degreasing step A, the degreasing power and spray pressure of the alkaline degreaser mainly removes press processing oil, dust, etc. adhering to the surface of the object to be coated. is removed.

In the degreasing process B, the main ingredients are degreasing m 7 , alkali J, W such as sodium carbonate, sodium carbonate, sodium silicate, and sodium hydroxide, a surfactant, and a surface conditioner blended as necessary. The degreasing process is carried out by immersing the product in a degreasing agent at a liquid temperature of 5° C. to 75° C. for 9° C. to 180 seconds, for example, about 120 seconds. In this degreasing process IB, the degreasing power of the alkaline degreaser and the flow of the liquid due to stirring are used to remove the inner surface of the board (for example, in the case of a bag-like object, the inner surface [
Press processing oil, dust, etc. adhering to lO) are removed, and the entire surface of the object to be coated is etched to increase the adhesion of the cationic electrodeposited coating described later.

The object to be coated which has been degreased in this way is then washed with water pli 9a in the first washing step C.
Water for pears is sprayed from the water spray device 8a at room temperature 9 for 20 to 40 seconds, for example, for about 30 minutes, and then washed, and then the second pear water step C
', water for commercial use at room temperature supplied from water $14 is sprayed from the water spray device 8b to 20 to 40 matsu, for example, 30 matsu at room temperature.
The water is sprayed for seconds to wash, and then in the third water washing step I', 4'l of water is added! M] Supplied from 5a 'a 116 Clean by immersing in industrial water in the water tank 14 for 20 to 40 seconds, for example about 30 seconds, at room temperature. The object to be coated which has been washed with water in this way is further sprayed with 1-1 commercial water, which is supplied from the water supply pipe +6c in the fourth washing machine J', for 20 to 40 seconds at room temperature from the water spraying device 16a. After cleaning by spraying for about 30 seconds, in the circulating pure water washing process J', water is supplied from the water tank 15b where the washing water was stored in Q (Step 11') to the fogging device 16.
Clean by circulating spray with a split vortex from b. In this case, a small amount of acetic acid, fugobionic acid, formic acid, etc., for example, acetic acid, may be added to the hot water. Further, in the fresh pure water washing process, pure water or ion-exchanged water is supplied from the water supply pipe 17 and then sprayed at room temperature from the water spray device 19 for washing. The first to fourth washing steps are a combination of water spraying and dipping, and are used to sequentially dilute and remove excess alkali, floating oil, etc. attached to the surface of the object to be coated. In the method, a second washing step C' and a fourth washing step J' are added to prevent the alkaline degreasing agent from being brought into the cationic electrodeposition tank. In addition, in the circulating pure water washing process J' and the fresh pure water washing process, the extremely small amount of miscellaneous ions still remaining on the surface of the object to be coated is replaced with pure water to prevent the miscellaneous ions from being carried into the electrodeposition bath. It is something to do. In this case, if a small amount of weak acid is added to the circulating pure water, the alkaline miscellaneous ions can be neutralized and removed, resulting in even better results.

The object 3 to be coated which has been washed with water does not require any special water-drying treatment or forced air cooling treatment, and is then subjected to cationic electrodeposition coating either as is or after these treatments are performed as necessary. That is, in the cationic electrodeposition step N, the object to be coated 3 suspended from the coating carrier 2 is continuously transferred by the overhead conveyor 1 into the cationic electrodeposition paint bath of the electrodeposition tank 25 at a bath temperature of -22 to 27C1, for example. 25°±】C, near> −: −/f ItoniHII;F
h t: u”tli A negative voltage is applied to the bunker 2 and the object to be coated 3 by a current collector (not shown) attached to the burner nozzle 2, and a positive voltage is applied to the counter electrodes (not shown) attached to both sides of the yam 25. voltage of 180 to 250■, for example about 200
By applying electricity for 2.5 to 4 minutes, for example, about 3 minutes while applying V, the positively charged paint migrates toward the negatively charged object, and a film thickness ( A coating film with a dry film thickness standard (the same applies below) of 4 to 13 μm is formed. In this case, the organic solvent concentration in the paint used is 4 to 5%.
The number of stirring (1 hour pump discharge (tons)/total number of tons of paint in the electrodeposition tank) is 4 to 30 times/hour, and even if it is a bag-like object, the film thickness on the back side is It becomes 3 μm or more.

Therefore, if the film thickness on the back surface is 3 μm or more, sufficient corrosion resistance can be obtained.

The object to be coated from which the paint has been removed on the overflow cypress 26 is washed in the fifth washing step O by spraying room temperature washing river water supplied from the water 4*'27a from the water spray device 28. , in the sixth water washing process O', the water tank 27"b supplied from the water tank 29 in the seventh water washing process P'
Clean by immersing it in room temperature cleaning water. Further, in the seventh water washing step P', washing is performed by spraying the washing water supplied from the water tank 31 in the p liquid washing step Q from the water spray device 30. Next, in the tear washing process Q, washing is performed by spraying ultrafiltrate at normal temperature supplied from the ultrafiltration device 33 from the Kyoto spray device W32. In addition, 34 is a filter, 35 is a heat exchanger, 36 is a P liquid tank, and 27b
is a water tank and P is a pump. In the 5th to 7th and tear washing steps, excess paint physically attached to the object to be coated by methods other than electrodeposition is washed away by spraying and dipping using ultralacrimal fluid, and the washing water is supplied to the conduit 40. , a part of the overflow is guided to the overflow tank 26 and transferred to the ultra-high-water flow device 33.
It is then filtered and recovered.

The object 3 coated with cationic electrodeposition in this way is
Next, in the baking drying process R, the baking drying oven 39 is a direct-fired hot air circulation type baking drying furnace 39 in which hot air is supplied through the air supply port 37 and exhausted from the exhaust port 38, and the air is heated at 170 to 190 U s, for example, about 18-5CT20. Baking drying is performed for ~40 minutes, for example about 30 minutes, to obtain a desired product. This baking and drying process heats and hardens the film-forming resin such as epoxy resin, which is the main component of the paint.

The method of this embodiment does not require the chemical conversion coating treatment step as described above, or may be added if necessary.

Next, the method of the present invention will be explained in more detail by giving specific examples.

Specific Example A transverse link S of a passenger car as shown in FIGS. 2 and 3 was coated with a force-on electrodeposition method such as a tsuki.

In the coating apparatus shown in FIG. 2, the transverse link S is used as the object to be coated 3, and a degreasing agent (Lidrin 5D-250 manufactured by Nippon Paint Co., Ltd.) with a liquid temperature of about 65 C is supplied from the tank 5 in the preliminary resin step A. Degreaser @ fog device 6
Approximately 608 minutes! After preliminary degreasing by misting, in the degreasing step B, the alkaline degreaser (
A degreasing treatment was performed by immersing the sample in Ridrin 5D-250) at a liquid temperature of about 650 for 120 seconds.

Next, the object to be coated is placed in a water tank 2a in a first water washing step C.
After spraying the industrial water supplied from the water spray device 8a for about 30 seconds at room temperature, the water m is
The industrial water at room temperature supplied from the water tank 14 is sprayed from the water spray device 8b for about 30 seconds at room temperature, and then in the third water washing step ■', the industrial water at room temperature at about 30 Washing was performed by dipping for a second. Furthermore, in the fourth water washing step J', industrial/industrial water is sprayed from the water spray device @16a for about 30 seconds at room temperature for washing, and then in the circulating pure water washing step J', the washing water from the water tank 15b is sprayed into the water spray device, Cleaning was carried out by circulating mist at room temperature from No. 16b. Then, in a fresh pure water washing step, ion-exchanged water was sprayed at room temperature from the water spray device 18 for washing.

Thereafter, the object to be coated is subjected to a cationic electrodeposition process N using an epoxy cationic electrodeposition paint ([Power Top U-30J (manufactured by Nippon Paint Co., Ltd., solid content 19% fine wrinkles, organic solvent concentration 4-5%, l)] Electrodeposition coating was carried out by immersing the sample in H6,3) at 25±IC and applying a voltage of 200 µ while applying electricity for about 3 minutes. The number of times of stirring at this time was 6 times/hour.

Next, the object to be coated is washed in a fifth water washing step O by spraying room temperature washing water supplied from the water tank 27a from a water spray device, and then in a sixth water washing step O', the room temperature washing in the water tank 27b is carried out. It was cleaned by immersing it in water. Then, the seventh
In the washing step P', the washing water supplied from the water PII3 is sprayed from the water jet device 30 for washing, and then
1! In the water washing process Q, washing was carried out by spraying room-temperature ultra-P water from the water spray device 32, which was supplied from the ultra-high-quality air filter 33. Next, the object to be coated was baked and dried for about 30 minutes at a temperature of about 185 C in a baking drying process R to complete the coating.

The distribution state of the coating film thickness thus obtained is as shown in Table 1. In addition, each measurement site|part is as shown in FIGS. 2-3. In addition, in the above method, when the average coating film thickness on the surface
and 1000 hours of salt water @ polar (curve C) results in the fourth
As shown in the figure.

The distribution state of the coating film thickness thus obtained was as shown in Table 1. In addition, each measurement site|part was as shown in FIGS. 3-4.

As described above, in the cationic electrodeposition coating method according to the present invention, the object to be coated is coated at a pigment bath temperature of 22 to 27 r and an organic solvent concentration of 4.
~\% is in a cationic electrodeposition paint bath.

While applying a voltage of ~250■, energize for 2.5 to 4 minutes,
After washing with water and baking drying, the dry film thickness is 4 to 13 μm.
Since it is made of silicate acid, it is possible to reduce the thickness of the coating compared to conventional methods, and still ensure sufficient corrosion resistance, resulting in significant cost reductions while maintaining quality. I can measure things. Furthermore, since painting is performed at a lower voltage than in the past, there is less paint adhesion to the paint hanger, extending the cleaning cycle of the hanger.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an apparatus for carrying out the cationic electrodeposition coating method according to the present invention, FIG. 2 is a perspective view of a test piece using the method of the present invention, and FIG. 3 is a cross-sectional view of the test piece shown in FIG. It is a conceptual diagram,
Figure 4 shows the salt water of the coating film obtained by the method of the present invention.
It is a graph showing the relationship between paint film thickness and red rust occurrence commercial rights without testing. 1. Conveyor, 2. Bunker, 3. Object to be coated, 5. Tank, 6. Degreasing agent spraying device, 7. Degreasing tank, 8a. 8b, 16a, +6b, 19, 28, 30.3: l"・
Water spray device, 9'a', 14,, I 5 a,
15 b + 27a, 27 b, 2'9, 3
1. Water tank, 25. Cation electrodeposition tank, 2.5. Overflow cypress, 39. Baking drying oven, A. Preliminary degreasing step, B. Degreasing step, C.. First washing step, C'・Second
Washing Tamakashi, I'... 3rd washing process, J' 4th washing process, J" - Circulating pure water washing process, K'... Fresh pure water washing process, N
・Cationic electrodeposition step, 0.5th washing step, 0'...6th
Washing process, P'/7th washing process, Q/P liquid washing process, R
・Baking drying process. Watch applicant: Nissan Motor Vehicle Co., Ltd.] -: Industry Co., Ltd.

Claims (1)

[Claims] 1. Place the object to be coated in a fungal bath at a temperature of 22-27 C1 and an organic bath agent concentration of 4.
A dry film of 1 yen 4 to 13 μm is formed by applying electricity for 2.5 to 4 minutes while applying a voltage of 180 to 250 μm in a separate bath of ~5% cationic military sugar, washing with water, and then performing a baking drying process.
A cationic electrodeposition coating method characterized by forming a 7:l coating film.