JP2008280546A - Electrodeposition coating method and electrodeposition coating system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrodeposition coating method which can effectively reuse the cleaning water that has been used for washing in a secondary washing means in an electrodeposition coating process. <P>SOLUTION: The electrodeposition coating method comprises: a film-forming step of forming an electrodeposition coating film of a lead-free cationic electrodeposition paint composition on the surface of an article to be coated; a primary washing step of washing the obtained painted article; a secondary washing step of washing the painted article that has been cleaned in the primary washing step by using washing water; and a final washing step of washing the painted article that has been cleaned in the secondary washing step. The washing water used in the secondary washing step contains an organic solvent of 0.1 to 3.0 wt.%. <P>COPYRIGHT: (C)2009,JPO&INPIT

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 microorganisms 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 microorganisms is reduced, and the water-based components used in the electrodeposition coating system are rotted 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 to 35 ° C., so that it is in an environment where microorganisms are easy to propagate. The problem of the decay of the water component and the propagation of microorganisms 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 microbial 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, this treatment method uses an antibacterial or bactericidal agent that suppresses or kills the growth of bacteria that consume acid, such as silver ions, copper ions, aldehydes, phenolic compounds, and chlorine compounds. However, this is different from the present invention.

  In the pamphlet of WO96 / 07775 (Patent Document 2), which is an application by the present applicant, the pH of the waste liquid is always kept at 6.4 or less in the treatment method of the waste liquid discharged from the final washing tank in the cationic electrodeposition coating process. A method for treating the final washing waste liquid by filtering the waste liquid is described. In addition, in Japanese Patent Application Laid-Open No. 10-183396 (Patent Document 3), which is an application by the present applicant, the waste liquid discharged from the final washing tank in the cationic electrodeposition coating process is separated by a semipermeable membrane, and the obtained filter is obtained. A method for treating the waste water from the final washing tank, characterized in that water is deionized. By these methods, it becomes possible to effectively use the waste liquid in the final washing tank. However, when using a lead-free electrodeposition coating composition and a low-volatile component-containing electrodeposition coating composition that are environmentally friendly, even if the above treatment method is used, the waste water from the final washing tank is effectively used. Sometimes it becomes difficult. Therefore, in the case of using such an electrodeposition coating composition, it has become necessary to further examine the method for treating the final washing tank.

  Japanese Patent Application Laid-Open No. 2006-299380 (Patent Document 4), which is an application by the present applicant, discloses an electrodeposition coating using flush water containing an isothiazolone-based antibacterial agent as flush water used in the second washing step in electrodeposition coating. A method is described. This method is also different from the present invention in that a specific antibacterial agent is used.

JP 2003-200162 A WO96 / 07775 Japanese Patent Laid-Open No. 10-183396 JP 2006-299380 A

  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;
An electrodeposition coating method comprising:
The water-washing water used in the second water-washing step contains an organic solvent in an amount of 0.1 to 3.0% by weight,
This achieves the above object.

  The organic solvent contained in the washing water used in the second washing step is an alcohol solvent having 1 to 8 carbon atoms, an ethylene glycol monoalkyl ether solvent having 3 to 8 carbon atoms or an ethylene glycol having 4 to 8 carbon atoms. A monoalkyl ether ester solvent is preferred.

  The solid content concentration of the washing water used in the second washing step is preferably 1.0% by weight or less.

  The lead-free cationic electrodeposition coating composition is preferably a lead-free cationic electrodeposition coating composition having an organic solvent amount of 1.0% by weight or less and a coating solid content concentration of 20% by weight or less.

The present invention also provides
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 used in the second washing step also provides an electrodeposition coating system having an organic solvent amount of 0.1 to 3.0% by weight.

  Here, “lead-free” means that it contains substantially no lead, and means that it does not contain lead in such an amount as to adversely affect 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 without adversely affecting the appearance of the electrodeposition coating composition and the cured electrodeposition coating film. This also has advantages in terms of running costs and wastewater 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;
A second water washing means 8 for washing the paint washed by the first water washing means using water for washing;
Secondary washing tanks 9 and 9 ′ for collecting the washing water after being used for washing with the second washing means 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, secondary water washing means 8 is described as the secondary water washing means. The secondary water washing means 8 uses filtered water from the washing water after being used for washing as washing water. However, the second water washing means 8 is limited to such a mode. Instead, the washing can be performed by newly introducing washing water from the outside as washing water in the secondary 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; secondary water washing tanks 9 and 9 '; the washing water used for washing the secondary water washing tanks 9 and 9' is converted into a concentrated liquid containing paint components and filtered water. The filter 19 to be separated; and the means 17 for introducing the 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. And in this invention, the flush water used for this secondary flush system contains the specific amount of organic solvent, It is characterized by the above-mentioned.

  In the cationic electrodeposition coating, the article 15 attached to the conveyor 14 is continuously conveyed. 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 conveyed to the first water rinsing tank 13. Here, for example, by immersing the coating object 16 in the primary rinsing tank 13 by the primary rinsing means 3 such as a shower nozzle, the coating material 16 and the rinsing water come into contact with each other. The painted object 16 is washed with water (first washing process). In FIG. 1, three primary flush tanks 13 are drawn, but the number of primary flush tanks 13 is not limited to three, and the size and shape of the object to be coated. Depending on the number of primary water rinsing tanks 13 can be varied. 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 such as an RO (reverse osmosis) membrane, a UF (ultrafiltration) membrane or an MF (precision osmosis) membrane is preferably used, and a UF (ultrafiltration) membrane is used. Is particularly preferred. The UF membrane is excellent in processing capacity per unit time and further in filtering capacity, and the balance between the two is taken. Moreover, you may provide a pre filter (not shown) before a 1st filter as needed. By providing the pre-filter before the first filter, it becomes possible to remove foreign matters contained in the washing water in advance before separation by the first filter, thereby further improving the processing capability of the first filter. More preferred.

  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 primary flushing tank 13, the filter 5, the primary flushing means 3, and a system that connects them and circulates flushed water is referred to as a primary flushing 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 coating 16 is immersed in the washing water in the secondary washing tank 9, and is washed with the washing water by the secondary washing means 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 generated by the washing with the washing water and used after the washing is recovered 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”). As the filter used for the second filter, it is preferable to use a semipermeable membrane such as an RO (reverse osmosis) membrane, a UF (ultrafiltration) membrane or an MF (fine osmosis) membrane, and a UF (ultrafiltration) membrane is used. Is particularly preferred. The UF membrane is excellent in processing capacity per unit time and further in filtering capacity, and the balance between the two is taken. If necessary, a prefilter (not shown) may be provided before the second filter. By providing a pre-filter (not shown) in front of the second filter, it is possible to remove foreign matters contained in the washing water in advance before separation by the second filter, and thereby processing by the second filter. The ability can be further improved, which is more preferable.

  The filtered water of the second filter is introduced into the secondary water washing means 8 through the line 17 as flush 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. The washing water of the secondary washing means may use the filtered water of the second filter, may use a mixture of filtered water and pure water, or may use pure water alone. In FIG. 1, the second water washing means 8 is illustrated as an example in which the coated object 16 is washed using the filtered water filtered by the filter 19. However, as described above, in the present invention, this is the case. However, the present invention is not limited to such an embodiment. For example, in the secondary water washing means 8, in the water washing just before the final water washing means, washing may be performed using water washed from the outside.

  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 spray in the second washing means 8. It means the washing water used for etc.

  Secondary washing means 8; secondary washing tanks 9 and 9 '; a filter 19 for separating the washing waste liquid of the secondary washing tank 9 into a concentrated liquid containing paint components and filtered water; A route for circulating the washing water, for example, a route 17 for introducing the filtered water into the secondary washing means as washing water, etc. is collectively referred to as a secondary washing system 12. 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 primary water washing tank 13, the secondary water washing means 8, and the secondary water washing tanks 9 and 9 ′ are all forms of water washing means using a shower nozzle. However, as a means for bringing the coating material 16 into contact with the rinsing water, it is possible to immerse the coating material in the primary rinsing tank 13 and the secondary rinsing tank 9, or to wash with water or flow water. Means can also be used. Furthermore, these means can be combined.

  In the electrodeposition coating method of the present invention, the washing water used in the secondary washing means contains 0.1 to 3.0% by weight of an organic solvent. By using such washing water in the secondary washing means, it becomes possible to circulate and use the washing water well in the secondary washing means.

  The organic solvent contained in the washing water used in the second washing step is preferably an alcohol solvent, an ethylene glycol monoalkyl ether solvent or an ethylene glycol monoalkyl ether ester solvent. By containing these organic solvents, the activity of microorganisms can be suppressed.

The alcohol solvent used as the organic solvent contained in the washing water used in the second water washing step is more preferably an alcohol solvent having 1 to 8 carbon atoms. Examples of such alcohol solvents include isopropyl alcohol, methanol, ethanol, propanol, butanol and the like.
The ethylene glycol monoalkyl ether solvent is more preferably an ethylene glycol monoalkyl ether solvent having 3 to 8 carbon atoms. Examples of such ethylene glycol monoalkyl ether solvents include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, and ethylene glycol monobutyl ether.
The ethylene glycol monoalkyl ether ester solvent is more preferably an ethylene glycol monoalkyl ether ester solvent having 4 to 8 carbon atoms. Examples of such ethylene glycol monoalkyl ether ester solvents include ethylene glycol monomethyl ether acetate and ethylene glycol monoethyl ether acetate.
In addition, only 1 type may be sufficient as these organic solvents contained in flush water, and 2 or more types may be sufficient as them.

  Among the above organic solvents, ethylene glycol monoalkyl ether solvents having 3 to 8 carbon atoms such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, and ethylene glycol monobutyl ether are more preferably used.

  In the present invention, the washing water used in the second washing step contains 0.1 to 3.0% by weight of an organic solvent. The amount of the organic solvent is more preferably 0.2 to 2.0% by weight. When the amount of the organic solvent contained in the washing water exceeds 3.0% by weight, the electrodeposition coating film may be dissolved when the article to be coated is immersed in the washing water. Moreover, when the amount of the organic solvent contained in the washing water is less than 0.1% by weight, the activity of microorganisms may not be suppressed.

  The method for adding the organic solvent to the washing water is not particularly limited. For example, the organic solvent may be added as appropriate when the washing water is introduced into the secondary washing system, or the organic solvent may be added to the washing water contained in the secondary washing tank. And you may add by methods other than these.

  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. And when the washing water decays, the slime adheres to the inner wall surface or pipe of the washing tank, and the paint component accompanying it, and the filter, prefilter or nozzle clogging due to the occurrence of such slime, Furthermore, poor coating due to adhesion of aggregates due to rot on the coated material 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. Moreover, since the amount of 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. However, the secondary water washing means is a washing step close to the final stage before baking and curing, and it is desirable that the amount of contaminants contained in the washing water is as small as possible. If the bactericidal additive is added as it is to the washing water of the secondary washing means, the bactericidal agent remains on the surface of the electrodeposited coating film, which may cause deterioration of the coating film appearance after baking and curing.

  Moreover, the concentrate of the washing water after being used for washing in the secondary washing means can be introduced into the electrodeposition tank as a paint component. In this case, components contained in the washing water used in the secondary washing means are also introduced into the electrodeposition tank. Therefore, by adding the bactericidal additive to the washing water, the bactericidal additive is mixed into the electrodeposition coating composition, thereby changing the electrical conductivity of the coating composition, gas pinning, throwing power There may be a disadvantage that it adversely affects

  On the other hand, in the present invention, organic solvents commonly used in electrodeposition coating compositions such as alcohol solvents, ethylene glycol monoalkyl ether solvents and ethylene glycol monoalkyl ether ester solvents are used. . Therefore, even if these organic solvents are mixed in the electrodeposition coating composition, no problem occurs. According to the present invention, it is possible to prevent the rinsing water from decaying without adversely affecting the coating film appearance of the electrodeposition coating composition and the cured electrodeposition coating film.

  In addition, it is not necessary to add the said organic solvent about the washing water in a 1st water washing means. The reason is that the amount of the electrodeposition coating composition mixed in the first water washing means is larger than that in the second water washing means, and the activity of microorganisms is suppressed by the mixture of the electrodeposition coating composition. It is done.

  In this invention, it is preferable that the solid content density | concentration of the washing water used for a 2nd washing process is 1.0 weight% or less. According to the experimental results to be described later, when the solid content concentration of the rinsing water used in the secondary rinsing step exceeds 1.0% by weight, there may be a problem that the activity of the microorganisms cannot be effectively suppressed. confirmed. The reason why such a problem may occur when the solid content concentration of the washing water exceeds 1.0% by weight is that the present inventors are solid in the balance between the amount of the organic solvent contained in the washing water and the solid content concentration. We believe that the concentration of the component becomes too high, which may result in failure to effectively suppress microbial activity.

Electrodeposition Coating Composition In the electrodeposition coating method of the present invention, any commonly used electrodeposition coating composition can be used. However, it is more toxic to the environment and living organisms, such as lead-free cationic electrodeposition coating compositions having an organic solvent content of 1.0% by weight or less, and further 0.1 to 1.0% by weight. Even in the case of using an electrodeposition coating composition that is low, that is, there is a possibility that microorganisms may propagate in the washing water for electrodeposition coating, the organic solvent is contained in the washing water, so that in the second washing A cured electrodeposition coating film that can be recycled without rinsing the washing water and has a good coating film appearance is obtained. Examples of the electrodeposition coating composition include an amine-modified epoxy resin, a curing agent, and, if necessary, a pigment and an additive. Hereinafter, each component will be described.

As the amine-modified epoxy resin, an amine-modified epoxy resin generally used in an electrodeposition coating composition can be used without particular limitation. As the amine-modified epoxy resin, an amine-modified epoxy resin known to those skilled in the art and a commercially available epoxy resin obtained by amine modification can be used.

  A preferred amine-modified epoxy resin is an amine-modified epoxy resin obtained by modifying an oxirane ring in the resin skeleton with an organic amine compound. In general, an amine-modified epoxy resin is produced by opening a ring of an oxirane ring in a starting material resin molecule with a primary amine, a secondary amine, a tertiary amine, and / or an amine such as an acid salt thereof. A typical example of the starting material resin is a polyphenol polyglycidyl ether type epoxy resin which is a reaction product of a polycyclic phenol compound such as bisphenol A, bisphenol F, bisphenol S, phenol novolak, cresol novolak and epichlorohydrin. Examples of other starting material resins include oxazolidone ring-containing epoxy resins described in JP-A-5-306327 and known. These epoxy resins are obtained by a reaction between a diisocyanate compound or a bisurethane compound obtained by blocking an NCO group of a diisocyanate compound with a lower alcohol such as methanol or ethanol, and epichlorohydrin.

  The starting material resin is used by extending the chain with a bifunctional polyester polyol, polyether polyol, bisphenol, dibasic carboxylic acid or the like, if necessary, before the oxirane ring-opening reaction with amines. be able to.

  In addition, prior to the oxirane ring-opening reaction with amines, 2-ethylhexanol, nonylphenol, ethylene glycol mono- acrylate for some oxirane rings for the purpose of adjusting molecular weight or amine equivalent, improving heat flow, etc. Monohydroxy compounds such as 2-ethylhexyl ether, ethylene glycol mono-n-butyl ether, propylene glycol mono-2-ethylhexyl ether can be added and used.

  Examples of amines that can be used for opening an oxirane ring and introducing an amino group include butylamine, octylamine, diethylamine, dibutylamine, methylbutylamine, monoethanolamine, diethanolamine, N-methylethanolamine , N-ethylethanolamine, triethylamine, N, N-dimethylbenzylamine, primary amines such as N, N-dimethylethanolamine, secondary amines or tertiary amines and / or their acid salts. Further, ketimine block primary amino group-containing secondary amine such as aminoethylethanolamine methyl isobutyl ketimine, diethylenetriamine diketimine can also be used. These amines must be reacted with at least an equivalent amount relative to the oxirane ring in order to open all the oxirane rings.

  The number average molecular weight of the amine-modified epoxy resin is preferably in the range of 1,500 to 5,000, more preferably in the range of 1,600 to 3,000. When the number average molecular weight is less than 1,500, physical properties such as solvent resistance and corrosion resistance of the cured coating film may be inferior. If it exceeds 5,000, the viscosity of the resin solution may be difficult to control and synthesis may be difficult, and handling such as emulsification and dispersion of the resulting resin may be difficult to handle. Furthermore, because of its high viscosity, the flowability during heating and curing is poor, and the appearance of the coating film may be impaired.

  The amine-modified epoxy resin is preferably molecularly designed so that the hydroxyl value is in the range of 50 to 250 mmol / 100 g. If the hydroxyl value is less than 50 mmol / 100 g, poor curing of the coating is caused. On the other hand, if it exceeds 250 mmol / 100 g, excessive hydroxyl groups remain in the coating film after curing, and as a result, the water resistance may decrease.

  The amine-modified epoxy resin is preferably molecularly designed so that the amine value is in the range of 40 to 150 mmol / 100 g. If the amine value is less than 40 mmol / 100 g, the emulsification dispersion failure in the aqueous medium due to the acid treatment described in detail below will be caused. Conversely, if the amine value exceeds 150 mmol / 100 g, excess amino groups will remain in the coating film after curing. The water resistance may decrease.

The block polyisocyanate curing agent cationic electrodeposition coating composition contains a block polyisocyanate curing agent obtained by blocking polyisocyanate with a blocking agent. Here, the polyisocyanate means 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); and the like. 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 the block polyisocyanate curing agent.

  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. Blocking agents include lactam-based blocking agents such as ε-caprolactam, δ-valerolactam, γ-butyrolactam, and β-propiolactam, and formaldoxime, acetoaldoxime, acetoxime, methyl ethyl ketoxime, diacetyl monooxime, cyclohexane oxime An oxime blocking agent such as is preferably used.

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-dispersed 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 together with a pigment dispersion resin in an aqueous medium. As the pigment dispersion resin, 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 dispersion resin 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 resin for pigment dispersion 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 mill is used until the particle size of the pigment in the mixture reaches a predetermined uniform particle size. The pigment dispersion paste is obtained by dispersing using a normal dispersing device such as the above.

Preparation of an electrodeposition coating composition An electrodeposition coating composition is prepared by dispersing an amine-modified epoxy resin, a curing agent, and a pigment dispersion paste in an aqueous medium. Further, the aqueous medium usually contains a neutralizing agent in order to improve the dispersibility of the amine-modified 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 that which 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 amine-modified epoxy resin during curing to give a good cured coating film. Generally, it is generally 90/10 to 50/50, preferably 80/20 to 65/35, expressed as a solid mass ratio of the amine-modified 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. The amount is preferably 0.1 to 5% by mass of the block polyisocyanate compound. Since the cationic electrodeposition coating composition used in the present invention is lead-free, it is preferable to use those catalysts that do not substantially contain lead.

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

  The electrodeposition coating composition used in the present invention may be a lead-free cationic electrodeposition coating composition having an organic solvent amount of 1.0% by weight or less and a coating solid content concentration of 20% by weight or less. In the present invention, even in the case of using a lead-free cationic electrodeposition coating composition that has a low load on the environment or the like and is likely to rot the washing water in the electrodeposition coating system, the rinsing water is rotted. Can be effectively prevented.

  In the case of performing electrodeposition coating using an electrodeposition coating composition, the object to be coated is preferably a conductor that has been subjected to surface treatment such as zinc phosphate treatment by dipping or spraying 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 typically about 10 amps / m ² to 160 amperes / m ^2, 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 occurrence 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 to examine microorganisms contained in each aqueous component. Microorganisms were examined using a bacterial checker for each aqueous component of the collected electrodeposition coating system. In addition, the amount of organic solvent and solid content contained in each aqueous component were also measured. The obtained results are shown in Table 1 below. The criteria for microbial testing are as follows.
○: No generation of bacteria is confirmed Δ: Generation of bacteria of 10 ⁴ or less is confirmed Δ ×: Generation of bacteria of 10 ⁶ or less is confirmed ×: Generation of bacteria exceeding 10 ⁶ is confirmed

  In the present specification, the content of the organic solvent in the washing water was measured using gasography. Moreover, the measurement of the solid content in the washing water in this specification was performed by determining the percentage of the mass of the residue after heating when 10 ml of the washing water was heated at 105 ° C. for 3 hours with respect to the original mass.

As the electrodeposition coating composition, a lead-free cationic electrodeposition coating composition (Power Nix 1020, manufactured by Nippon Paint Co., Ltd., paint solid content 20.0% by weight) having an organic solvent content of 0.93% by weight is used. It was. The cationic electrodeposition coating composition used was 200 m ³ , the amount of washing water used in the first washing system was 55 L / min, and the amount of washing water used in the second washing system was 50 L / min. .

^＊１：図１において第１次水洗槽１３と示されるうち、第２次水洗システムの直前に位置する水洗槽から採取
^＊２：図１において第２次水洗槽９’と示される水洗槽から採取
^＊３：図１においてライン１７を通過する濾過水を採取
^＊４：図１においてライン２０を通過する濃縮液を採取
^＊５：図１において最終水洗手段２５を通過する水洗水を採取

^{* 1} : Collected from the flush tank located immediately before the secondary flush system among the primary flush tank 13 shown in FIG.
^{* 2} : Collected from the washing tank shown as the second washing tank 9 'in FIG.
^{* 3} : Collect filtered water passing through line 17 in FIG.
^{* 4} : Collect the concentrated solution that passes through the line 20 in FIG.
^{* 5} : Collecting water that passes through the final water washing means 25 in FIG.

  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 washing system, a large amount of microorganisms are present in the washing water of the second washing system. It is understood that it is included. From the results of this reference experiment, it is considered that the washing water of the second washing system has a low organic solvent content, and thus contains a large amount of microorganisms. The reason why a large amount of microorganisms is contained in the concentrate obtained by the second filter is that the organic solvent content in this concentrate is high, but the paint solids concentration is also very high. It is thought that the activity of microorganisms became more active. And from this result, it is possible to confirm the necessity to establish means for preventing the rinsing of the rinsing water used in the secondary rinsing system.

Example 1
In the electrodeposition coating system shown in FIG. 1, a lead-free cationic electrodeposition coating composition (Power Nix 1020, manufactured by Nippon Paint Co., Ltd.) having an organic solvent content of 0.93% by weight was used as the electrodeposition coating composition. . A pre-filter (not shown) was installed before the second filter. The cationic electrodeposition coating composition used was 250 m ³ , the amount of washing water used in the first washing system was 55 L / min, and the amount of washing water used in the second washing system was 50 L / min.

Next, ethylene glycol monoethyl ether was added to the washing water in the secondary washing tank 9 ′ in FIG. 1 in such an amount that the content in the washing water was 0.13% by weight.
Thereafter, the electrodeposition coating system was operated for 1 hour.

At the time when 1 hour has passed since the start of the microbe inspection electrodeposition coating system, the water in the second water washing tank in the second water washing system is designated as the second water washing tank (9 ') in FIG. It was collected from the tank. Microbial tests similar to those in the reference example were performed on the collected washing water.

Electrodeposition film elution test The sample on which the uncured electrodeposition film was formed was immersed in the collected washing water, and it was tested whether or not elution of the electrodeposition film occurred. The evaluation criteria are as follows.
○: Elution of the electrodeposition coating film is not confirmed even after immersion for 10 minutes or more. ×: Elution of the electrodeposition coating film is confirmed within 10 minutes.

System suitability test When the electrodeposition coating system was operated for 24 hours, the number of times the prefilter was replaced due to the occurrence of clogging of the prefilter provided before the secondary filter was counted.

Example 2
The same evaluation was performed as in Example 1 except that ethylene glycol monoethyl ether was added so that the content in the washing water was 0.22% by weight. The obtained results are shown in Table 2.

Example 3
The same evaluation was performed as in Example 1 except that ethylene glycol monoethyl ether was added so that the content in the washing water was 0.33% by weight. The obtained results are shown in Table 2.

Example 4
The same evaluation was performed as in Example 1 except that ethylene glycol monoethyl ether was added so that the content in the washing water was 0.43% by weight. The obtained results are shown in Table 2.

Example 5
The same evaluation was performed as in Example 1 except that ethylene glycol monoethyl ether was added so that the content in the washing water was 0.54% by weight. The obtained results are shown in Table 2.

Example 6
The same evaluation was performed as in Example 1 except that ethylene glycol monoethyl ether was added so that the content in washing water was 1.03% by weight. The obtained results are shown in Table 3.

Example 7
The same evaluation was performed as in Example 1 except that ethylene glycol monoethyl ether was added so that the content in the washing water was 2.03% by weight. The obtained results are shown in Table 3.

Example 8
The same evaluation was performed as in Example 1 except that ethylene glycol monoethyl ether was added so that the content in washing water was 2.54% by weight. The obtained results are shown in Table 3.

Comparative Example 1
The same evaluation was performed as in Example 1 except that ethylene glycol monoethyl ether was not added to the washing water. The obtained results are shown in Table 3.

Comparative Example 2
The same evaluation was performed as in Example 1 except that ethylene glycol monoethyl ether was added so that the content in the washing water was 3.03% by weight. The obtained results are shown in Table 3.

  As shown in the above Examples and Comparative Examples, it was confirmed that the activity of microorganisms was effectively suppressed when the washing water in the secondary washing system contained a specific amount of organic solvent. On the other hand, in the example in which the amount of the organic solvent in Comparative Example 1 is less than the specific amount, the activity of the microorganism remains active. Moreover, in the example in which the amount of the organic solvent in Comparative Example 2 is greater than the specific amount, it was confirmed that there was a problem that elution of the electrodeposition coating film occurred although the activity of microorganisms was suppressed.

  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 economic efficiency such as running cost, waste water to be treated is reduced, and the amount of lead compound used can be reduced.

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,
9 ... Secondary washing tank,
9 '... second water washing tank,
11 ... The first water washing system,
12 ... Secondary water washing system,
13 ... primary washing 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 (5)

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;
An electrodeposition coating method comprising:
The electrodeposition coating method in which the washing water used in the second washing step contains 0.1 to 3.0% by weight of an organic solvent.   The organic solvent contained in the washing water used in the second washing step is an alcohol solvent having 1 to 8 carbon atoms, an ethylene glycol monoalkyl ether solvent having 3 to 8 carbon atoms or an ethylene glycol having 4 to 8 carbon atoms. The electrodeposition coating method according to claim 1, which is a monoalkyl ether ester solvent.   The electrodeposition coating method of Claim 1 or 2 whose solid content concentration of the flush water used for the said 2nd flush process is 1.0 weight% or less.   The lead-free cationic electrodeposition coating composition is a lead-free cationic electrodeposition coating composition having an organic solvent amount of 1.0% by weight or less and a coating solid content concentration of 20% by weight or less. The electrodeposition coating method according to any one of the above. 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 used in the second washing step is an electrodeposition coating system in which the amount of organic solvent is 0.1 to 3.0% by weight.

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