JP2006299380A - Electrodeposition coating method and electrodeposition coating system - Google Patents

Abstract

［式中、Ｒは低級アルキル基であり、Ｘは水素原子またはハロゲン原子である。］
で示される抗菌剤を含む、電着塗装方法。
【選択図】 図１
PROBLEM TO BE SOLVED: To provide an electrodeposition coating method capable of effectively reusing washing water after being used for washing with a secondary washing means in electrodeposition painting.
An electrodeposition coating film forming step of forming an electrodeposition coating film of a lead-free cationic electrodeposition coating composition on a surface of an object to be coated; a first water washing step of washing the obtained coating material with water; An electrodeposition coating method comprising: a second water washing step of washing the paint washed by the water washing step with water; and a final water washing step of washing the paint washed by the second water washing step. The washing water of the second washing means is represented by the following formula:
[Chemical 1]

[Wherein, R represents a lower alkyl group, and X represents a hydrogen atom or a halogen atom. ]
An electrodeposition coating method comprising an antibacterial agent indicated by.
[Selection] Figure 1

Description

  The present invention relates to an electrodeposition coating method and an electrodeposition coating system. In particular, the present invention relates to an electrodeposition coating method and an electrodeposition coating system capable of effectively reusing washing water after being used for washing in a secondary water washing means in cationic electrodeposition coating.

  Electrodeposition coating is widely used in the coating field, particularly in the automobile field, because of its ease of coating management and high economic efficiency. Furthermore, the cationic electrodeposition coating composition is widely used not only in the automobile field but also in a wide range of fields such as building materials, general metal products, electrical products, and industrial machines.

  An electrodeposition coating system used for such electrodeposition coating generally includes an electrodeposition tank for forming an electrodeposition coating film on the surface of an object to be coated, and an electrodeposition coating composition that remains excessively in the obtained coating object. It has a means to wash off. And generally as a means to wash off the electrodeposition coating composition etc. which remain | survives excessively in the obtained coating material, a primary water washing means and a secondary water washing means are contained. The first water washing means is a means for washing off excess paint composition and the like physically adhered on the paint, and collecting paint components to replenish the electrodeposition tank. The secondary rinsing means is means for performing final cleaning using rinsing water such as ion exchange water, pure water or industrial water. In this secondary water washing means, a small amount of paint components that could not be washed out by the first water washing means and ions mixed in the paint composition are washed away. The coated material thus obtained is then finally washed with ion-exchange water or reverse osmosis membrane filtered water, and baked to cure the electrodeposition coating and obtain a cured electrodeposition coating. It will be. In the present specification, “electrodeposition coating film” means an uncured coating film before baking and curing, and “cured electrodeposition coating film” means a coating film after baking and curing.

  By the way, a large amount of water is required in the secondary water washing means that is finish washing. In particular, when the object to be coated is a large object such as an automobile body, water of 200 L / min or more is required as flush water. Further, since the washing water after used for washing, which is generated by this final washing, contains paint components and the like, it is not preferable to discharge it to the outside as it is. Therefore, also in this secondary washing means, the washing water after being used for the resulting washing is collected and filtered, and the filtered water is circulated and used as washing water, and the concentrate is returned to the electrodeposition tank, Some methods of re-use as paint have been put to practical use.

  On the other hand, due to the recent increase in environmental awareness, lead ions that adversely affect the environment are required to be used in a reduced amount. In advanced countries and the like, the amount of harmful air pollutants (HAPs) used has been regulated. Under such circumstances, there is a need for an attempt to reduce the amount of lead ions and organic solvents contained in the electrodeposition coating composition while maintaining the electrodeposition coating performance.

  These lead ions and organic solvents are generally highly toxic to living organisms. On the other hand, it has a bactericidal and antibacterial action that suppresses the growth of bacteria due to its high toxicity to organisms. Therefore, by reducing the content of these lead ions and organic solvents contained in the electrodeposition coating composition, the sterilization and antibacterial action against bacteria is lowered, and the water-based components used in the electrodeposition coating system are spoiled and altered. The problem of occurring has arisen. The electrodeposition coating composition is a water-based coating, contains a biodegradable acid, and is circulated in a closed system while being heated to 25-35 ° C., so that it is in an environment where bacteria can easily propagate. The problem of the decay of the water component and the propagation of bacteria is the same not only in the electrodeposition tank but also in the secondary washing means. In other words, the use of a lead-free electrodeposition coating composition that is less toxic to living organisms and has a low organic solvent content tends to cause spoilage of water-based components and bacterial growth in the electrodeposition coating system. .

  In JP 2003-200162 A (Patent Document 1), waste water discharged from a final water washing tank in a cationic electrodeposition coating process is applied to a membrane filtration device, separated into a filtrate and a concentrate, and the filtrate is used as washing water for circulation. In addition, in the method of returning the concentrated liquid to the electrodeposition main tank and recovering and reusing it as a paint, an antibacterial agent and / or a bactericidal agent are continuously or intermittently added to waste water and / or filtrate. A method for treating wastewater is described. However, the purpose of this treatment method is to reduce the influence on the membrane filtration device through which the wastewater passes due to the increase in pH of the wastewater due to bacterial metabolism. In addition, the antibacterial and bactericidal agents used in this treatment method are those that can inhibit the growth of bacteria that consume acid, such as silver ions, copper ions, aldehydes, phenolic compounds, and chlorine compounds, and can kill bacteria. It says that anything is acceptable. As described above, Japanese Patent Application Laid-Open No. 2003-200162 does not clearly indicate the difference in suitability and effect depending on the type of antibacterial agent in an actual electrodeposition coating system.

  JP 2003-138202 A (Patent Document 2) neutralizes an aqueous medium, a binder resin containing a cationic epoxy resin and a blocked isocyanate curing agent, or a cationic epoxy resin dispersed or dissolved in an aqueous medium. In the antibacterial lead-free cationic electrodeposition coating composition containing a neutralizing acid, an organic solvent, and an antibacterial agent, the volatile organic content is 2% by weight or less, and the antibacterial agent is an isothiazolone compound Antibacterial lead-free cationic electrodeposition coating compositions are described. In the present invention, the cationic electrodeposition coating composition contains an antibacterial agent. On the other hand, in this invention, the antibacterial agent is contained in the flush water of the secondary flush means. The cationic electrodeposition coating composition and the washing water of the secondary washing means differ greatly in the concentration of solids contained therein, etc., and the type of microorganisms that propagate and the amount of propagation thereof also differ greatly. Therefore, the invention described in Japanese Patent Application Laid-Open No. 2003-138202 is different from the present invention.

  Moreover, in invention described in patent document 2, when a cationic electrodeposition coating composition contains the said antibacterial agent, a part of the coating composition flows in into a 1st water washing tank. Thereby, the antibacterial agent and the organic solvent contained in this coating composition also flow into the first washing tank. In the first washing tank, the growth of microorganisms and the like is suppressed by the antibacterial action of these inflow components. Therefore, no significant growth of microorganisms was observed in the first washing tank. However, even when the electrodeposition coating composition containing the antibacterial agent as described above is used for electrodeposition coating, it is necessary to take some measures since the growth of microorganisms and the like has been confirmed in the second washing tank. It turned out to be. In addition, in this specification, the confirmation experiment about the proliferation amount of the microorganisms in these primary water washing tanks and secondary water washing tanks is also performed. These confirmation experiments will be described later as reference examples.

  JP-A-2-29468 (Patent Document 3) is characterized by containing 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one. Cationic electrodeposition coating compositions are described. This invention also includes an antibacterial agent in the electrodeposition coating composition, and is different from the present application.

JP 2003-200162 A JP 2003-138202 A JP-A-2-29468

  The present invention solves the above-mentioned conventional problems, and an object of the present invention is to effectively reuse the wash water after it has been used for the second water washing means in electrodeposition coating. The object is to provide an electrodeposition coating method and an electrodeposition coating system.

The present invention
An electrodeposition coating film forming step of forming an electrodeposition coating film of a lead-free cationic electrodeposition coating composition on the surface of the object to be coated;
A first water-washing step of washing the obtained paint with water; and a second water-washing step of washing the paint washed with the first water-washing process with water; and a second water-washing step. A final water washing step of washing the painted material with water;
An electrodeposition coating method comprising:
The washing water used in the second washing step is represented by the following formula (I):

[Wherein, R represents a lower alkyl group, and X represents a hydrogen atom or a halogen atom. ]
The electrodeposition coating method containing the antibacterial agent shown by this is provided, and the said objective is achieved by this.

  The concentration of the antibacterial agent is preferably 0.1 to 5 ppm with respect to the washing water.

  The electrodeposition coating composition contained in the electrodeposition tank is preferably a lead-free cationic electrodeposition coating composition having an organic solvent content of 2% by weight or less.

The present invention also provides an electrodeposition coating system. The electrodeposition coating system has the following configuration:
An electrodeposition tank for forming an electrodeposition coating film of a lead-free cationic electrodeposition coating composition on the surface of the object to be coated;
A first water-washing means for washing the obtained coated product with water;
Secondary washing means for washing the paint washed by the first washing means using washing water;
A secondary rinsing tank for recovering the rinsing water after being used for rinsing of the secondary rinsing means;
A filter for separating the wash water after being used for washing in the second water washing tank into a concentrated liquid containing paint components and filtered water;
Means for introducing the filtered water as washing water for the second water washing means; and final water washing means for washing the paint washed by the second water washing means;
An electrodeposition coating system comprising:
An electrodeposition coating system in which the washing water of the second washing means contains an antibacterial agent represented by the above formula (I) is mentioned.

  “Lead-free” as used herein means that it contains substantially no lead, and means that it does not contain lead in an amount that adversely affects the environment. Specifically, it means that the lead compound concentration in the electrodeposition bath does not contain lead in an amount exceeding 50 ppm, preferably 20 ppm.

  When an electrodeposition coating composition that is less toxic to the environment and living organisms, such as a lead-free cationic electrodeposition coating composition, is used for electrodeposition coating by the electrodeposition coating method and electrodeposition coating system of the present invention. Even so, it is possible to more favorably circulate and use the washing water in the secondary washing means and to form a cured electrodeposition coating film having a good coating film appearance. According to the present invention, the washing water in the secondary washing means can be circulated and reused, which is desirable from the viewpoint of running cost and waste water treatment.

Electrodeposition coating method and electrodeposition coating system The electrodeposition coating method of the present invention comprises:
An electrodeposition coating film forming step of forming an electrodeposition coating film of a lead-free cationic electrodeposition coating composition on the surface of the object to be coated;
A first water-washing step of washing the obtained coating with water;
A second water-washing step in which the paint washed in the first water-washing step is washed with water, and a final water-washing step in which the paint washed in the second water-washing step is washed in water;
Is included.

The configuration of the electrodeposition coating system used in the electrodeposition coating method of the present invention will be described using the electrodeposition coating system schematically shown in FIG. As an example of an electrodeposition coating system,
An electrodeposition tank 2 for forming an electrodeposition coating on the surface of the article 15;
Primary water washing means 3 for washing the obtained coating 16 with water;
Secondary water washing means 8 and 8 'for washing the paint washed by the first water washing means using water for washing;
Secondary water washing tanks 9 and 9 ′ for collecting the washing water after being used for washing of the second water washing means 8 and 8 ′;
A filter 19 for separating the washing water after being used for washing of the second water washing tanks 9 and 9 'into a concentrated liquid containing paint components and filtered water;
Means 17 for introducing the filtered water as washing water for the second washing means; and final washing means 25 for washing the paint washed by the second washing means;
And an electrodeposition coating system. In FIG. 1, as the second washing means, the second washing means 8 that uses the filtered water by the washing water after being used for washing as washing water, and the washing water is newly introduced from the outside. Although both the secondary water washing means 8 'to perform are described, it is not limited to such an aspect, Only filtered water can also be used as the washing water in a secondary water washing means. In addition, this electrodeposition coating system may further include a primary water rinsing tank 13 for collecting the washing water after being used for the water washing of the primary water washing means 3.

  Secondary water washing means 8 and 8 '; secondary water washing tanks 9 and 9'; the washing water used for washing the secondary water washing tanks 9 and 9 'is concentrated and filtered with a paint component. The filter 19 that separates into water; and the means 17 that introduces filtered water into the secondary washing means as washing water are collectively referred to as a secondary washing system 12. This secondary water washing system is a water washing system used for advanced washing provided independently of the first water washing means immediately after electrodeposition coating. The flush water is collected and circulated in the secondary flush system. The secondary water washing system preferably has means 20 for introducing the concentrate of the filter 19 into the electrodeposition tank. In the present invention, the washing water used for the secondary washing means contains a specific antibacterial agent.

  In the cationic electrodeposition coating, the article 15 attached to the conveyor 14 is continuously flowed. The object 15 is immersed in the electrodeposition coating composition in the electrodeposition tank 2 to form an electrodeposition coating film (electrodeposition coating film forming step). Here, an electrodeposition coating film is formed on the surface of the object to be coated 15 to form the coated object 16.

  In general, the coated object 16 on which the electrodeposition coating film is formed is carried to the washing tank 13. Here, for example, the first washing unit 3 such as a shower nozzle brings the coating 16 into contact with the washing water, thereby washing the painting 16 with water (first washing step). Further, in FIG. 1, three washing tanks 13 are depicted, but the number of washing tanks 13 is not limited to three, and depending on the size and shape of the object to be coated, The number of tanks 13 can be changed. Further, if necessary, before the object to be coated is immersed in the electrodeposition coating composition in the electrodeposition tank 2, before the object 15 is coated, for example, by means of water to be coated such as a shower nozzle. Washing may be performed.

  The washing water after being used for washing in the first water washing means 3 flows in a countercurrent direction with respect to the article 15 and the article 16 to be coated, and through the recovery path 4, an overflow tank adjacent to the electrodeposition tank 2. 1 recovered. The coating composition containing the washing water after being used for washing with water, which is contained in the overflow tank 1, is concentrated by the filter 5 (hereinafter also referred to as “first filter”), the concentrated liquid containing the paint components, filtered water, Can be separated. As the filter used for the first filter, a semipermeable membrane is preferably used, and a UF (ultrafiltration) membrane is particularly preferably used. The UF membrane is excellent in processing capacity per unit time and further in filtering capacity, and the balance between the two is taken.

  The concentrated liquid concentrated by the filter 5 may be introduced into the overflow tank 1 or the electrodeposition tank 2 through the line 6, for example. In FIG. 1, the example which introduce | transduces a concentrate into the overflow tank 1 by the line 6 is shown. The filtered water is introduced into the first water washing means 3 and can be reused as washing water.

  The washing tank 13, the filter 5, the first washing means 3, and a system that connects them and circulates washing water is referred to as a first washing system 11.

  The painted product 16 that has been washed with water is further subjected to secondary washing with water. The coated object 16 is subsequently carried to the secondary water rinsing tank 9. Here, for example, the coated object 16 is immersed in the washing water in the secondary washing tank 9, and washed with the washing water by the secondary washing means 8 and 8 'such as a shower nozzle or a spray. (Second water washing step). Examples of the washing water used in the secondary washing step include ion exchange water, pure water, city water, and industrial water. Then, the wash water that has been used for washing, which is generated by washing with this washing water, is collected in the secondary washing tanks 9 and 9 '. The washing water after being used for this washing with water is separated into a concentrated liquid containing paint components and filtered water by a filter 19 (hereinafter also referred to as “second filter”). Then, this filtered water is introduced into the secondary water washing means 8 through the line 17 as washing water. The concentrated liquid is introduced into the electrodeposition tank 2 or the overflow tank 1 through a line 20, for example. In FIG. 1, the example which introduce | transduces a concentrate into the electrodeposition tank 2 by the line 20 is shown. As washing water, if necessary, filtered water and pure water may be used in combination. In FIG. 1, the secondary water washing means 8 wash | cleans the coating material 16 using the filtered water filtered by the filter 19, and secondary water washing means 8 'uses the washing water introduce | transduced from the outside. Although the aspect which wash | cleans the coating material 16 is shown as an illustration, as above-mentioned, in this invention, it is not limited to such an aspect.

  In the present specification, “washing water used in the second washing step” refers to the washing water used in the dipping washing in the second washing tanks 9 and 9 ′, and the second washing means 8 and 8. It means washing water used for spraying etc.

  Secondary water washing means 8 and 8 '; secondary water washing tanks 9 and 9'; a filter 19 for separating the washing waste liquid of the secondary water washing tank 9 into a concentrated liquid containing paint components and filtered water; and these Are connected together to circulate the flush water, for example, the path 17 for introducing the filtered water as the flush water to the secondary flush means, and so on. In FIG. 1, three rinsing tanks (9 and 9 ′) in the secondary rinsing system 12 are depicted, but the number of rinsing tanks is not limited to three, Depending on the size and shape, the number of flush tanks can be varied.

  The final washed item 25 is subjected to final washing by the final washing unit 25 (final washing step). Examples of the washing water used in the final washing include ion exchange water, pure water, or reverse osmosis membrane filtered water (RO water). The washing water after used for washing by this final washing is collected in the secondary washing tank 9 'of the secondary washing system. As another aspect, a water tank may be provided that collects only the washing water after being used for washing by this final washing. The washing water collected in the secondary washing tank 9 ′ and used for washing may be collected in the secondary washing tank 9 through the collecting path 24. The final water washing means 25 is referred to as a final water washing system 21.

  In addition, in FIG. 1, although a conveying apparatus, the electrode other member in an electrodeposition tank, a baking / drying furnace, etc. are not illustrated, these are not specifically limited, A well-known aspect, means, etc. are arbitrary. Can be used. In FIG. 1, the primary water washing means 3, the water washing tank 13, the secondary water washing means 8 and 8 ′, and the secondary water washing tanks 9 and 9 ′ are all forms of water washing means using a shower nozzle. As a means for bringing the paint 16 into contact with the washing water, a means such as immersion water immersing the paint in the water washing tank 13 and the secondary water washing tank 9 or a flow water washing is used. You can also. Furthermore, these means can be combined.

  In the electrodeposition coating method of the present invention, the washing water used for the secondary washing means is represented by the following formula (I):

[Wherein, R represents a lower alkyl group, and X represents a hydrogen atom or a halogen atom. ]
It is characterized by including the antibacterial agent shown by these. This antibacterial agent is generally sometimes referred to as an isothiazolone compound.

  In the antibacterial agent, R is more preferably an alkyl group having 1 to 6 carbon atoms, and further preferably an alkyl group having 1 to 3 carbon atoms. X is more preferably a hydrogen atom or a chlorine atom. The antibacterial agent represented by the formula (I) has a high antibacterial effect even in a small amount, and has an excellent effect that it does not adversely affect the appearance of the coating film even if it is included in the washing water used for the secondary washing means.

Preferable specific isothiazolone compounds include, for example, 5-chloro-2-methyl-4-isothiazolin-3-one (in formula (I), R = CH ₃ , X = Cl), 2-methyl-4-isothiazoline. 3- (in the formula _{(I), R = CH 3} , X = H) on the like.

  The method for adding the antibacterial agent to the washing water is not particularly limited. For example, the antibacterial agent may be added as appropriate when the washing water is introduced into the secondary water washing system, and the antibacterial agent is added to the washing water after being used for the water washing contained in the secondary water washing tank. May be. And you may add by methods other than these.

  The concentration of the antibacterial agent contained in the washing water can be changed depending on the type of the antibacterial agent used. A preferable concentration of the antibacterial agent is 0.1 to 5 ppm with respect to the washing water. As described above, the isothiazolone compound represented by the above formula (I) has an advantage that it can exhibit an excellent antibacterial action against washing water even at a very low concentration. In addition, the isothiazolone compound represented by the above formula (I) can exhibit an excellent antibacterial action against washing water even at a very low concentration, and thus is excellent in terms of economy such as cost.

  In the electrodeposition coating system, it is desirable to circulate and reuse the flush water from the viewpoint of running cost and wastewater treatment. However, with recent lead-free electrodeposition coating compositions and low organic solvent content, the problem of the rot of washed water being circulated is becoming serious. The term “water decay” as used herein refers to alteration of water accompanying the activity of microorganisms (bacteria, algae, etc.). Examples of such alteration of water include generation of slime scale due to accumulation of bacterial colonies or dead bodies such as bacteria and algae, and alteration due to changes in water properties, such as organic acids contained in water. And alterations caused by the digestion of bacteria. As the washing water rots, the slime adheres to the inner wall or pipe of the washing tub, and the paint components that accompany it, and the filter or nozzle is clogged due to the occurrence of such slime. A coating failure due to the agglomerates caused by adhering to the coating may occur.

  As one of the methods for preventing such rot of the washing water, there is a method in which the washing water after being used for washing is discharged to the outside, and newly introduced pure water or the like is used as the washing water. . However, this method is disadvantageous in terms of cost because it requires a large amount of water. In addition, since the amount of cleaning water (waste water) discharged becomes large, the cost of waste water treatment also increases. Furthermore, in this method, when the electrodeposition coating system is not in operation, the washing water contained in the tank is drained to clean the tank wall or piping, and then the electrodeposition coating system is operated. Must be refilled with flush water. Therefore, the management of the electrodeposition coating system becomes more complicated.

  In addition, the method of preventing decay of washing water by adding the bactericidal additive conventionally added to the aqueous coating composition to washing water is also considered. Examples of such additives include ethylene glycol monobutyl ether, ethylene glycol monoethyl ether, ethylene glycol, bactericidal organic solvents such as methanol and ethanol, bactericides such as formaldehyde, hydrogen peroxide, and silver nitrate, Ionic compounds such as salicylic acid are included.

  However, among these conventional bactericidal substances, hydrophilic organic solvents are inappropriate for realizing a low solvent in the coating line. Moreover, the effective amount of the bactericide conventionally used for the water-based paint is a concentration as high as exceeding 50 ppm, for example. On the other hand, the secondary washing means is a washing step close to the final stage before baking and hardening, and it is desirable that the contaminants contained in the washing water be as small as possible. When such a concentration of bactericidal agent is added to the washing water of the secondary washing means as it is, a large amount of the bactericidal agent remains on the surface of the electrodeposition coating film, resulting in a decrease in the appearance of the coating film after baking and curing. There is a risk and it is inappropriate.

  Similarly, when the ionic compound remains on the surface of the electrodeposition coating film, the appearance of the coating film after baking and curing is deteriorated. Furthermore, the paint component contained in the secondary water rinsing tank can be introduced into the electrodeposition tank after having been concentrated with a filter. When an ionic compound is used as a bactericidal agent, the ionic compound is also mixed into this concentrated liquid, and finally, the ionic compound is mixed into the electrodeposition coating composition. When an ionic compound is mixed into the electrodeposition coating composition, the electrical conductivity of the coating composition changes, and there is a disadvantage that the gas pinning property, throwing power, etc. are adversely affected.

  In the present invention, the isothiazolone compound represented by the formula (I) is included in the washing water used in the secondary washing step, thereby adversely affecting the coating film appearance of the electrodeposition coating composition and the cured electrodeposition coating film. This makes it possible to prevent the rinsing water from decaying. The present invention is an invention relating to the inclusion of the isothiazolone compound represented by the formula (I) in the washing water used in the second washing step, and even if the isothiazolone compound is included in the electrodeposition coating composition. In addition, the isothiazolone compound is not included in the washing water used in the first washing step. In the present invention, in the reference examples described later, there is little need to use an antibacterial agent in the washing water in the first washing step, and there is a high need to use an antibacterial agent in the washing water in the second washing step. I have found out. The present invention finds that the isothiazolone compound represented by the formula (I) is suitable as an antibacterial agent for use in washing water in the second washing step.

Electrodeposition Coating Composition In the electrodeposition coating method of the present invention, any commonly used electrodeposition coating composition can be used. However, it is less toxic to the environment and organisms, such as lead-free cationic electrodeposition coating compositions having an organic solvent content of 2% by weight or less, and further 0.1 to 1.0% by weight That is, even when an electrodeposition coating composition in which bacteria or the like may propagate in the washing water is used for electrodeposition coating, the above-mentioned antibacterial agent is contained in the washing water. Thus, a cured electrodeposition coating film that can be recycled without being spoiled and has a good coating film appearance is obtained. Examples of the electrodeposition coating composition include a cationic epoxy resin, a curing agent, and, if necessary, a pigment or an additive. Hereinafter, each component will be described.

Cationic Epoxy Resin The cationic epoxy resin used in the present invention includes an amine-modified epoxy resin. Cationic epoxy resins typically open all of the epoxy rings of a bisphenol-type epoxy resin with an active hydrogen compound capable of introducing a cationic group, or some epoxy rings with other active hydrogen compounds. It is produced by opening the ring and opening the remaining epoxy ring with an active hydrogen compound capable of introducing a cationic group.

  A typical example of the bisphenol type epoxy resin is a bisphenol A type or bisphenol F type epoxy resin. As the former commercial product, there are Epicoat 828 (manufactured by Yuka Shell Epoxy Co., Epoxy Equivalent 180-190), Epicoat 1001 (Same, Epoxy Equivalent 450-500), Epicoat 1010 (Same, Epoxy Equivalent 3000-4000), etc. Examples of the latter commercially available product include Epicoat 807 (same as above, epoxy equivalent 170).

  The following formula described in JP-A-5-306327

[Wherein R represents a residue excluding the glycidyloxy group of the diglycidyl epoxy compound, R ′ represents a residue excluding the isocyanate group of the diisocyanate compound, and n represents a positive integer. An oxazolidone ring-containing epoxy resin represented by the above formula may be used as the cationic epoxy resin. This is because a coating film having excellent heat resistance and corrosion resistance can be obtained.

  As a method for introducing an oxazolidone ring into an epoxy resin, for example, a block polyisocyanate blocked with a lower alcohol such as methanol and a polyepoxide are heated and kept in the presence of a basic catalyst, and a by-product lower alcohol is introduced from the system. Obtained by distilling off.

  Particularly preferred epoxy resins are oxazolidone ring-containing epoxy resins. This is because a coating film having excellent heat resistance and corrosion resistance and further excellent impact resistance can be obtained.

  It is known that an epoxy resin containing an oxazolidone ring can be obtained by reacting a bifunctional epoxy resin with a diisocyanate blocked with a monoalcohol (ie, bisurethane). Specific examples and production methods of the oxazolidone ring-containing epoxy resin are described in, for example, paragraphs 0012 to 0047 of JP-A No. 2000-128959 and are publicly known.

  These epoxy resins may be modified with suitable resins such as polyester polyols, polyether polyols, and monofunctional alkylphenols. In addition, the epoxy resin can be chain-extended using a reaction between an epoxy group and a diol or dicarboxylic acid.

  These epoxy resins are ring-opened with an active hydrogen compound so that an amine equivalent of 0.3 to 4.0 meq / g is obtained after ring opening, and more preferably 5 to 50% of them are occupied by primary amino groups. It is desirable to do.

  Active hydrogen compounds that can introduce a cationic group include primary amines, secondary amines, tertiary amine acid salts, sulfides and acid mixtures. In order to prepare a primary, secondary or / and tertiary amino group-containing epoxy resin, an acid salt of a primary amine, secondary amine or tertiary amine is used as an active hydrogen compound capable of introducing a cationic group.

  Specific examples include butylamine, octylamine, diethylamine, dibutylamine, methylbutylamine, monoethanolamine, diethanolamine, N-methylethanolamine, triethylamine hydrochloride, N, N-dimethylethanolamine acetate, diethyl disulfide / acetic acid mixture, etc. In addition, there are secondary amines in which primary amines such as aminoethylethanolamine ketimine and diethylenetriamine diketimine are blocked. A plurality of amines may be used in combination.

Curing Agent The curing agent used in the present invention is preferably a blocked polyisocyanate obtained by blocking polyisocyanate with a blocking agent, where polyisocyanate refers to a compound having two or more isocyanate groups in one molecule. . The polyisocyanate may be, for example, any of aliphatic, alicyclic, aromatic and aromatic-aliphatic.

  Specific examples of polyisocyanates include aromatic diisocyanates such as tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), p-phenylene diisocyanate, and naphthalene diisocyanate; hexamethylene diisocyanate (HDI), 2,2,4- C3-C12 aliphatic diisocyanates such as trimethylhexane diisocyanate and lysine diisocyanate; 1,4-cyclohexane diisocyanate (CDI), isophorone diisocyanate (IPDI), 4,4′-dicyclohexylmethane diisocyanate (hydrogenated MDI) , Methylcyclohexane diisocyanate, isopropylidene dicyclohexyl-4,4'-diisocyanate, and 1,3-diisocyanatomethylcyclo Carbon such as xane (hydrogenated XDI), hydrogenated TDI, 2,5- or 2,6-bis (isocyanatomethyl) -bicyclo [2.2.1] heptane (also referred to as norbornane diisocyanate). Aliphatic diisocyanates having a number of 5 to 18; aliphatic diisocyanates having an aromatic ring such as xylylene diisocyanate (XDI) and tetramethylxylylene diisocyanate (TMXDI); modified products of these diisocyanates (urethanes, carbodiimides, Uretdione, uretoimine, burette and / or isocyanurate modified product); These may be used alone or in combination of two or more.

  Adducts or prepolymers obtained by reacting polyisocyanates with polyhydric alcohols such as ethylene glycol, propylene glycol, trimethylolpropane and hexanetriol at an NCO / OH ratio of 2 or more may also be used as curing agents.

  The polyisocyanate is preferably an aliphatic polyisocyanate or an alicyclic polyisocyanate. This is because the formed coating film is excellent in weather resistance.

  Preferred specific examples of the aliphatic polyisocyanate or alicyclic polyisocyanate include hexamethylene diisocyanate, hydrogenated TDI, hydrogenated MDI, hydrogenated XDI, IPDI, norbornane diisocyanate, dimer (biuret) and trimer thereof. (Isocyanurate) etc. are mentioned.

  The blocking agent is added to a polyisocyanate group and is stable at ordinary temperature, but can regenerate a free isocyanate group when heated to a temperature higher than the dissociation temperature.

  As a blocking agent, when low temperature curing (160 ° C. or lower) is desired, lactam blocking agents such as ε-caprolactam, δ-valerolactam, γ-butyrolactam and β-propiolactam, and formaldoxime, acetoald It is preferable to use an oxime blocking agent such as oxime, acetoxime, methyl ethyl ketoxime, diacetyl monooxime, and cyclohexane oxime.

  The binder containing the cationic epoxy resin and the curing agent is generally contained in the electrodeposition coating composition in an amount that occupies 25 to 85% by mass, preferably 40 to 70% by mass of the total solid content of the electrodeposition coating composition. The

Pigment The electrodeposition coating composition used in the present invention may contain a commonly used pigment. Examples of pigments that can be used include commonly used inorganic pigments, for example colored pigments such as titanium white, carbon black and bengara; extender pigments such as kaolin, talc, aluminum silicate, calcium carbonate, mica and clay; Zinc phosphate, iron phosphate, aluminum phosphate, calcium phosphate, zinc phosphite, zinc cyanide, zinc oxide, aluminum tripolyphosphate, zinc molybdate, aluminum molybdate, calcium molybdate and aluminum phosphomolybdate, phosphomolybdic acid Examples include rust preventive pigments such as aluminum zinc.

  The pigment is generally contained in the electrodeposition coating composition in an amount of 1 to 35% by mass, preferably 10 to 30% by mass, based on the total solid content of the electrodeposition coating composition.

  Since the electrodeposition coating composition of the present invention is lead-free, corrosion resistance imparting agents containing lead, for example, lead-based anticorrosive pigments such as basic lead silicate, basic lead sulfate, lead red, and cyanamide lead are used. It should not be used or should be used in such an amount that the lead ion concentration of the diluted paint (added to the electrodeposition bath) is 50 ppm or less. This is because a high lead ion concentration is harmful to the environment.

Pigment-dispersed paste When a pigment is used as a component of an electrodeposition paint, generally, the pigment is dispersed in an aqueous medium at a high concentration in advance together with a resin called a pigment-dispersing resin to form a paste. This is because the pigment is in a powder form, and it is difficult to disperse in a single step in a low concentration uniform state used in the electrodeposition coating composition. Such a paste is generally called a pigment dispersion paste.

  The pigment dispersion paste is prepared by dispersing a pigment in an aqueous medium together with a pigment dispersion resin varnish. As the pigment-dispersed resin varnish, a cationic polymer such as a cationic or nonionic low molecular weight surfactant or a modified epoxy resin having a quaternary ammonium group and / or a tertiary sulfonium group is generally used. As the aqueous medium, ion-exchanged water or water containing a small amount of alcohol is used. Generally, the pigment-dispersed resin varnish is used at a solid content ratio of 5 to 40 parts by mass, and the pigment is used at a solid content ratio of 10 to 30 parts by mass.

  After the pigment dispersion resin varnish and the pigment are mixed in an amount of 10 to 1000 parts by mass with respect to 100 parts by mass of the resin solid content, a ball mill or a sand grind is used until the pigment in the mixture has a predetermined uniform particle size. A pigment dispersion paste is obtained by dispersing using a normal dispersing device such as a mill.

Preparation of an electrodeposition coating composition An electrodeposition coating composition is prepared by dispersing a cationic epoxy resin, a curing agent, and a pigment dispersion paste in an aqueous medium. Moreover, the aqueous medium usually contains a neutralizing agent in order to improve the dispersibility of the cationic epoxy resin. Neutralizing agents are inorganic or organic acids such as hydrochloric acid, nitric acid, phosphoric acid, formic acid, acetic acid, lactic acid. The amount is an amount that achieves a neutralization rate of at least 20%, preferably 30-60%.

  The amount of curing agent is sufficient to react with active hydrogen-containing functional groups such as primary, secondary or / and tertiary amino groups and hydroxyl groups in the cationic epoxy resin during curing to give a good cured coating film. In general, it is generally in the range of 90/10 to 50/50, preferably 80/20 to 65/35, expressed as a solid mass ratio of the cationic epoxy resin to the curing agent.

  The electrodeposition paint can contain a tin compound such as dibutyltin dilaurate and dibutyltin oxide, and a usual urethane cleavage catalyst. Since what does not contain lead substantially is preferable, it is preferable that the quantity shall be 0.1-5 mass% of a block polyisocyanate compound.

  The electrodeposition paint can contain conventional paint additives such as water-miscible organic solvents, surfactants, antioxidants, UV absorbers, and pigments.

  The object to be coated in the case of performing electrodeposition coating using the electrodeposition coating composition is preferably a conductor that has been subjected to surface treatment such as zinc phosphate treatment by dipping, spraying method or the like in advance. It may be one that has not been processed. In addition, the conductor is not particularly limited as long as it can become a cathode in performing electrodeposition coating, and a metal substrate is preferable.

The conditions under which electrodeposition is performed are generally the same as those used for other types of electrodeposition coating. The applied voltage may vary greatly and may range from 1 volt to several hundred volts. The current density is usually about 10 amperes / m ^{2 to} 160 amperes / m ² and tends to decrease during electrodeposition.

  After electrodeposition by the electrodeposition coating method of the present invention, the electrodeposition coating film is baked at an elevated temperature in a usual manner, for example, in a baking furnace, a baking oven or an infrared heat lamp. The baking temperature may vary but is usually about 140 ° C to 180 ° C. The coated product coated by the electrodeposition coating method of the present invention is dried and baked after the final water washing to form a cured electrodeposition coating film, thereby completing the coating process.

  The following examples further illustrate the present invention, but the present invention is not limited thereto. In the examples, “parts” and “%” are based on weight unless otherwise specified.

Reference Example As a reference experiment, the number of microorganisms contained in each aqueous component of the electrodeposition coating system shown in FIG. 1 was examined. A test solution was collected from each part of the electrodeposition coating system actually in operation shown in FIG. 1, and the number of microorganisms contained in each aqueous component was measured. The number of microorganisms was measured according to the following procedure. First, a solution was prepared by diluting each aqueous component solution of the electrodeposition coating system to 10 n times using sterilized water, and 0.1 ml of each diluted solution was prepared in advance in a petri dish having a diameter of 90 mm. It was uniformly applied to the surface of a plate agar medium and cultured at 30 ° C. for 2 weeks (repetition number = 3). All the above operations were performed aseptically in a clean bench. After completion of the culture, the number of colonies formed on the agar plate (the mass formed by the growth of microorganisms) was counted, and the number of microorganisms in the stock solution was calculated from the dilution rate of the diluted solution applied to the petri dish. The obtained results are shown in Table 1 below.

As the electrodeposition coating composition, a lead-free cationic electrodeposition coating composition (Power Nix 310 Gray, manufactured by Nippon Paint Co., Ltd.) having an organic solvent content of 0.5% by weight was used. The cationic electrodeposition coating composition used was 200 m ³ , the amount of washing water used in the first water washing system was 40 L / min, and the amount of washing water used in the second water washing system was 120 L / min. .

  From this reference example, even if the electrodeposition coating conditions are such that microorganisms are not detected from the electrodeposition coating composition or the washing water of the first water washing means, the second water washing means is used for washing with water. It can be seen that the washing water contains a large amount of microorganisms. From this result, it is clear that it is necessary to establish means for preventing the decay of the washing water used in the secondary washing means.

  Moreover, as a result of identifying microorganisms that propagated in this washing wastewater, it was found that they were Burkholderia cepacias, Pseudomonas huttiensis, and the like.

Example 1
In this example, 5-chloro-2-methyl-4-isothiazolin-3-one (in formula (I), R = CH ₃ , X = Cl) was used as an antibacterial agent. In the electrodeposition coating system shown in FIG. 1, a lead-free cationic electrodeposition coating composition (Powernix 310 Gray, manufactured by Nippon Paint Co., Ltd.) having an organic solvent content of 0.5% by weight is used as the electrodeposition coating composition. It was. The cationic electrodeposition coating composition used was 200 m ³ , the amount of washing water used in the first washing system was 40 L / min, and the amount of washing water used in the second washing system was 80 L / min.

  The washing water of the secondary washing system was collected, and the antibacterial agent was added to the washing water so as to have concentrations of 0.1 ppm, 0.3 ppm, 1 ppm, 3 ppm, and 5 ppm, respectively. Using this as a test solution, the same treatment as the measurement method described in the above Reference Example was performed, and the number of microorganisms was measured. The obtained results are shown in Table 2.

Example 2
The same procedure as in Example 1 was conducted except that 2-methyl-4-isothiazolin-3-one (R = CH ₃ , X = H in formula (I)) was used as the antibacterial agent. The obtained results are shown in Table 2.

Comparative Example 1
Example except that 2-n-octyl-4-isothiazolin-3-one (in formula (I), R = n-C ₈ H ₁₇ (normal octyl), X = H) was used as the antibacterial agent. 1 was performed. The obtained results are shown in Table 2.

＊ｐＨの測定は、電着塗装システムを３０℃で４日間稼働させた後の洗浄水のｐＨを測定した。稼働前のｐＨは５．４であり、抗菌剤を加えない場合の洗浄水のｐＨは６．４である。

* The pH was measured by measuring the pH of the washing water after the electrodeposition coating system was operated at 30 ° C. for 4 days. The pH before operation is 5.4, and the pH of the washing water when no antibacterial agent is added is 6.4.

  As shown in the above Examples and Comparative Examples, by using the isothiazolone compound represented by the formula (I) for the washing water in the secondary washing system, the antibacterial action can be effectively achieved despite a very small amount of use. Can be demonstrated. Moreover, in Example 1, the increase in pH can also be suppressed effectively. In Example 2, although the increase in pH was not effectively suppressed, the antibacterial effect could be confirmed. On the other hand, in Comparative Example 1, no antibacterial effect due to the antibacterial agent was observed, and no pH increase inhibiting effect was observed.

Effect of antibacterial agent on electrodeposition coating formation In the electrodeposition coating system in which the cleaning liquid is filtered through a filter in the secondary cleaning system and the paint components are concentrated and reused, the antibacterial agent used in the secondary cleaning system is the paint. It migrates and accumulates in the composition. In this case, there is a possibility that the antibacterial agent may adversely affect the coating composition. Then, the evaluation test was done about the coating-film performance at the time of forming a cured electrodeposition coating film using the coating composition containing an antibacterial agent.

Preparation of Test Specimen A zinc phosphate treatment was performed on a test piece made of a cold rolled steel sheet having a thickness of 0.8 mm and 70 mm × 150 mm. The zinc phosphate treatment can be performed using any known surface treatment system. The following paints (1) to (3) were prepared as paint compositions used in the test.
Paint (1) Electrodeposition paint composition containing no antibacterial agent (blank);
Paint (2) an electrodeposition paint composition containing 10 ppm of 2-methyl-4-isothiazolin-3-one in the paint composition; and paint (3) 5-chloro-2-methyl-4-isothiazolin-3-one An electrodeposition coating composition containing 10 ppm in the coating composition.
Using these coating compositions, a coating test having a cured electrodeposition coating film is performed by subjecting the test piece to electrodeposition coating under conditions to obtain a predetermined film thickness, washing with water, and then baking at 160 ° C. for 15 minutes. I got a piece. The following test was done using the obtained coating test piece.

Salt spray test Using the blade of a cutter knife, an X-shaped notch reaching the substrate was provided on the prepared coating test piece. The lengths of the two straight lines constituting the X character were each 100 mm. This test piece was subjected to a salt spray test apparatus defined in JIS Z2371. The test time was 480 hours when the film thickness was 10 μm, and 840 hours when the film thickness was 20 μm.

  Next, the presence or absence of abnormality on the entire surface of the test piece and the degree of rust generation from the X-shaped cut portion were inspected. The maximum value of the width of the blistering rust spouted from the cut part to the surface (measured in the direction of 90 degrees with respect to the cut line) was measured, and this half value was recorded as the rust width from the cut part. .

Salt water immersion test The prepared coating test piece was immersed in a 5% sodium chloride aqueous solution at a constant temperature of 50 ° C. and held for 480 hours. Next, a cellophane tape was affixed to the entire surface of the test piece to bring it into close contact with the coating film, and the tape was peeled off. When the adhesion between the substrate and the coating film was poor, the ratio of the peeling area to the coating area was determined by utilizing the fact that the coating film peeled off from the substrate and moved to the cellophane tape side. The peeled area ratio was measured with image analysis software.

Water resistance test The prepared coating specimen was immersed in a pure water bath maintained at 40 ° C. and held for 500 hours. Subsequently, the presence or absence of an abnormality in the appearance of the coating film was inspected. In addition, using the blade of a cutter knife, the test piece is provided with 11 cuts that are orthogonal to each other at intervals of 1 mm, reaching the substrate, and a 1 mm square narrow coating portion surrounded by the cuts (hereinafter referred to as a grid pattern). A total of 100 were prepared. A cellophane tape was affixed to the entire surface of the grid to bring it into close contact with the coating film, and the tape was peeled off. If the adhesion between the substrate and the coating is poor, use the fact that the coating is peeled off from the substrate and transferred to cellophane tape. The ratio of numbers was determined. In addition, when 1/2 or more of the area of one grid was peeled, it was considered that the whole grid was peeled.

  The evaluation test results obtained are shown in Table 3.

  As is clear from the results shown in Table 3, in both the salt spray test and the salt water immersion test, there was no noticeable difference between the respective coating compositions, and it was recognized that they were almost equivalent. The results of the water resistance test were all good (0/100). By this test, it was confirmed that the antibacterial agent used in the present invention does not adversely affect the formation of the electrodeposition coating film.

  Even when an electrodeposition coating composition having a lower toxicity to the environment and living organisms, such as a lead-free cationic electrodeposition coating composition, is used for electrodeposition coating by the electrodeposition coating method of the present invention. The cured washing electrode in the secondary washing means can be recycled and used more favorably and a cured electrodeposition coating film having a good coating film appearance can be formed. The electrodeposition coating system of the present invention is excellent in terms of environment because it is excellent in economics such as running cost, waste water to be treated is reduced, and the amount of organic solvent and lead compound can be reduced. It is.

It is a schematic diagram which shows an example of the electrodeposition coating system of this invention.

Explanation of symbols

1 ... overflow tank,
2 ... Electrodeposition tank,
3 ... primary washing means,
4 ... Path to collect the washing water after being used for washing,
5 ... Filter,
6 ... line,
7 ... line,
8 ... Secondary washing means,
8 '... secondary washing means,
9 ... Secondary washing tank,
9 '... second water washing tank,
11 ... The first water washing system,
12 ... Secondary water washing system,
13 ... Rinsing tank,
14 ... conveyor,
15 ...
16 ... painted material,
17 ... Line,
19 ... filter,
20 ... line,
21 ... Final water washing system,
24. Path for collecting washing water after being used for washing,
25. Final washing means,
30: Electrodeposition coating system.

Claims (4)

An electrodeposition coating film forming step of forming an electrodeposition coating film of a lead-free cationic electrodeposition coating composition on the surface of the object to be coated;
A first water-washing step of washing the obtained paint with water; and a second water-washing step of washing the paint washed with the first water-washing process with water; and a second water-washing step. A final water washing step of washing the painted material with water;
An electrodeposition coating method comprising:
The washing water used in the second washing step has the following formula:

[Wherein, R represents a lower alkyl group, and X represents a hydrogen atom or a halogen atom. ]
An electrodeposition coating method comprising an antibacterial agent indicated by.   The electrodeposition coating method of Claim 1 whose density | concentration of the said antibacterial agent is 0.1-5 ppm with respect to washing water.   The electrodeposition coating method according to claim 1 or 2, wherein the lead-free cationic electrodeposition coating composition is a lead-free cationic electrodeposition coating composition having an organic solvent content of 2% by weight or less. An electrodeposition tank for forming an electrodeposition coating film of a lead-free cationic electrodeposition coating composition on the surface of the object to be coated;
A first water-washing means for washing the obtained coated product with water;
Secondary washing means for washing the paint washed by the first washing means using washing water;
A secondary rinsing tank for recovering the rinsing water after being used for rinsing of the secondary rinsing means;
A filter for separating the wash water after being used for washing in the second water washing tank into a concentrated liquid containing paint components and filtered water;
Means for introducing the filtered water as washing water of the secondary washing means; and
A final water washing means for washing the paint washed by the second water washing means;
An electrodeposition coating system comprising:
The washing water of the second washing means has the following formula:

[Wherein, R represents a lower alkyl group, and X represents a hydrogen atom or a halogen atom. ]
An electrodeposition coating system containing the antibacterial agent indicated by.

Images