JPS6117918B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for removing microbial damage occurring in an electrodeposition coating solution in an electrodeposition coating method. In places where closed systems have been adopted during the electrodeposition coating process due to stricter water quality regulations, various product defects have occurred, which are presumed to be caused by the growth of microorganisms within the system. An example of such an electrodeposition coating method will be explained based on FIG. 1. In FIG. 1, 1 is an electrodeposition pretreatment cleaning device, 2 is an electrodeposition bath, and 3
4 is a filter, 4 is a post-treatment cleaning tank, 5 is industrial water or tap water piping, 6, 7, and 8 are piping for circulating the electrodeposition coating solution, and 9 is a conveyance path for the object to be coated. The object to be coated is first cleaned in the pre-treatment cleaning device 1, and the pipe 5
Pre-cleaned with degreased and ion-exchanged industrial water or tap water. Thereafter, the object to be coated is sent to an electrodeposition bath 2, where a paint of an electrodeposition coating liquid is electrodeposited. Further thereafter, the object to be coated is treated in a post-treatment cleaning tank 4 and then sent to a baking furnace.
The electrodeposition coating liquid not only serves as a paint supply source in the electrodeposition bath 2, but also after being filtered by a filter 3, most of it is returned to the electrodeposition bath 2, but a portion is sent to a post-treatment cleaning tank. 4, where it plays the role of a cleaning liquid, and then returned to the electrodeposition bath 2 for circulation use. Conventionally, as a countermeasure against microbial damage occurring during the electrodeposition coating process as described above, a method has been adopted in which a disinfectant is directly administered into the electrodeposition bath 2. Furthermore, many organic compound-based fungicides were used. However, such a method is uneconomical because the disinfectant is directly administered to the electrodeposition bath, resulting in a large amount of disinfectant to be administered. Furthermore, as the disinfectant is repeatedly administered, it accumulates in the electrodeposition bath, resulting in a decrease in current efficiency and poor electrodeposition. In order to eliminate the drawbacks of the conventional methods as described above, the inventor of this invention has decided to set a disinfectant injection point other than the electrodeposition bath, and to find a non-residual disinfectant. In order to solve these problems, we first investigated the growth locations of microorganisms, types of microorganisms, and growth rates in the electrodeposition coating process. The results are shown in Tables 1 and 2 below.

[Table] From the results shown in Table 1, it was found that the places where microorganisms proliferate are the electrodeposition bath and the post-treatment cleaning tank, and particularly remarkable microbial growth was observed in the post-treatment cleaning tank.

[Table] Table 2 above is a survey of the evolution of microorganisms in the electrodeposition coating solution, and it is said that in the electrodeposition coating solution, there are far fewer bacteria that grow over time than bacteria that die over time. I gained knowledge. From the above results, the microbial growth process during the electrodeposition coating process is inferred as follows. The microorganisms that cause painting failure are dead sterilized cells accumulated in the electrodeposition bath and viable bacteria (No. 6 and No. 12 in Table 2) that have flowed into the bath. The places where microorganisms grow are the electrodeposition bath and the post-treatment cleaning tank, and a wider variety of microorganisms grow in the post-treatment cleaning tank.
Most of the microorganisms grown in the post-treatment cleaning tank (excluding No. 6 and No. 12 in Table 2) are killed in the electrodeposition bath.
The conditions for growth of microorganisms in the electrodeposition bath and post-treatment cleaning bath are satisfied over time (months). Based on the above results, the areas where fungicides should be administered are:
It is appropriate to use a location that eliminates the conditions for microbial growth in the post-treatment cleaning tank, which is the main place for microbial growth, and a location where the disinfectant can be administered effectively. That is, it is appropriate to administer it to the post-treatment cleaning liquid flowing through the circulation system from the filter 3 to the post-treatment cleaning tank 4 in FIG. Furthermore, the following Table 3 shows the sterilizing effect of ozone, which is a sterilizing agent with strong sterilizing power and no residual properties, and is administered to the post-treatment cleaning liquid.

[Table] From the results in Table 3, ozone is removed from post-treatment cleaning solution 1.
It was found that a sufficient bactericidal effect could be obtained by administering 60mg per dose. Furthermore, the reaction between ozone and microorganisms is extremely fast, and excess ozone is also consumed by reacting with paint components present in the sample liquid. Also, the amount of reaction products between ozone and paint components is extremely small. Therefore, ozone has been found to be a suitable disinfectant against microorganisms that grow during electrocoating processes. This invention was completed based on the above-mentioned knowledge, and it circulates the electrodeposition coating liquid between the electrodeposition bath and the filter, and also directs a part of the electrodeposition coating liquid to the outlet of the filter. This electrodeposition coating method includes the steps of sending the electrocoating liquid from the electrocoating liquid to a post-treatment cleaning tank and returning it to the electrodeposition bath, and is characterized by injecting ozone into the electrodeposition coating liquid between the filter and the post-treatment cleaning tank. An embodiment of the present invention will be described below with reference to FIG. In Fig. 2, 10 is a three-way valve, 11 is a branch pipe for circulating electrodeposition coating liquid, 12 is an ozone reaction tower, 1
3 is an ozone generator, 14 is an aeration pipe, 15 is an exhaust ozone treatment device, and 16 is an exhaust pipe. In addition, the parts in FIG. 2 that are the same as or correspond to those in FIG. The electrodeposition coating liquid consisting of an aqueous solution of electrodeposition paint circulating between the electrodeposition bath 2 and the filter 3 is passed through the filter 3.
After removing some microorganisms and ozone consuming substances other than microorganisms, most of the ozone consuming substances are returned to the electrodeposition bath 2 from the outlet of the filter 3, and a part is sent to the post-treatment cleaning tank 4, and then It is sent to the electrodeposition bath 2. During the growth of microorganisms, the electrocoating liquid sent to the post-treatment cleaning tank 4 via the filter 3 is switched by operating the three-way valve 10 and introduced into the ozone reaction tower 12, where it is fed into the ozone generated by the ozone generator 13. is injected into the electrodeposition coating liquid from the aeration pipe 14,
After sterilizing the electrodeposition coating liquid in 2, the post-treatment cleaning tank 4
The electrodepositing bath 2 is sent to the electrodeposition bath 2, used for processing the object to be coated, and then returned to the electrodeposition bath 2. On the other hand, the gas after reacting with the electrodeposition coating liquid in the ozone reaction tower 12 is transferred to the exhaust ozone treatment device 15.
Excess ozone is removed and released into the atmosphere from the exhaust pipe 16. In the present invention, the ozone injection method may be performed by directly injecting the ozone-containing gas into the electrodeposition coating liquid in the circulating system, in addition to the bubble column shown in FIG. As explained above, according to the method for removing microbial disturbances of the present invention, the disinfectant injection point is installed in the circulation system leading to the post-treatment septic tank after passing through the filter,
Since ozone is used as a disinfectant, the following effects can be obtained. Since the disinfectant is not administered to the electrodeposition bath, the disinfectant does not accumulate in the electrodeposition bath and does not adversely affect the electrode reaction. Since the disinfectant is administered in a small amount of the electrodeposition coating solution after ozone consuming substances have been filtered out using a filter, the amount of ozone consumed can be reduced. Since the disinfectant is administered in the electrodeposition coating solution immediately before being sent to the post-treatment cleaning tank, which is the main site for microbial proliferation, microbial sterilization and proliferation prevention can be effectively achieved. Since ozone is used as a disinfectant, it has no residual properties and does not accumulate in the circulatory system. Ozone is generated by an ozone generator, the raw material is air, and it is easy to control. Since the ozone in the gas that has not reacted in the ozone reaction tower can be treated and discharged by the exhaust ozone treatment device, there is no fear of secondary pollution.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing an example of an electrodeposition coating process, and FIG. 2 is a system diagram showing an embodiment in which the present invention is applied to the electrodeposition coating process of FIG. 1...Pretreatment cleaning device, 2...Electrodeposition bath, 3...
... Filter, 4 ... Post-treatment cleaning tank, 10 ... Three-way valve, 12 ... Ozone reaction tower, 13 ... Ozone generator, 14 ... Diffuser, 15 ... Non-ozone treatment device, 16 ... Exhaust pipe. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1. Electrodeposition coating, which includes the process of circulating the electrodeposition coating liquid between the electrodeposition bath and the filter, and sending a part of this electrodeposition coating liquid from the filter outlet to the post-treatment cleaning tank and returning it to the electrodeposition bath. A method for removing microbial disturbances in an electrodeposition coating method, which is characterized by injecting ozone into an electrodeposition coating solution between a filter and a post-treatment cleaning tank.