JP2006274413A - Method and system for electrodeposition coating - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrodeposition coating method and electrodeposition coating system by which the occurrence of the trace of electrodeposition sag is prevented and a hard electrodeposition coating film having excellent coating film appearance can be obtained. <P>SOLUTION: The electrodeposition coating method includes an electrodeposition coating film forming process for forming the electrodeposition coating film on the surface of object to be coated; a primary washing process of washing a resultant coating object; a secondary washing process of washing the coating object washed by the first washing process by using washing water; and a final washing process of washing the coating object washed by the secondary washing process. The washing water used in the secondary washing process includes an acetylene-based surfactant expressed by formula (1). <P>COPYRIGHT: (C)2007,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 obtaining a cured electrodeposition coating film having an excellent coating film appearance with suppressed generation of electrodeposition sagging traces.

  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.

  In cationic electrodeposition coating, first, an object to be coated is immersed as a cathode in the cationic electrodeposition paint, and a voltage is applied to form an electrodeposition coating film on the object to be coated. In the electrodeposition coating film thus obtained, water, solvent, undeposited coating composition and the like remain attached. Further, these surplus materials also enter and remain in the uneven portions of the article to be coated or the clearance (a slight gap) of the joint portion. In order to remove such surplus, the electrodeposition coating process generally rinses off the electrodeposition coating process for forming an electrodeposition coating film on the surface of the object to be coated, and the coating composition remaining on the resulting coating. Process.

  In general, the first washing step and the second washing step are included as a step of washing off the coating composition remaining on the coated product. The first water washing step is a step of washing away the residue physically attached on the coated object. The secondary water washing step is a step of performing final washing using washing water such as ion exchange water, pure water or industrial water. In the second water washing step, paint components that could not be washed out in the first water washing step, ions mixed in the coating composition, and the like 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.

  In the electrodeposition coating process, although the water washing process is performed many times as described above, it is still difficult to completely remove the surplus remaining in the coating. As a method for removing surplus materials remaining in the coated product, a method in which water washing means is performed in multiple stages can be mentioned. However, increasing the number of washing steps is limited from the viewpoint of work efficiency. On the other hand, when the removal of the surplus remaining in the clearance of the object to be coated is incomplete, when the electrodeposition coating film is baked to obtain a cured electrodeposition coating film, a sagging mark or a tamar mark is formed on the coating film surface. Will occur. This sagging trace is sometimes referred to as “secondary sagging”. Generation | occurrence | production of such a sagging trace etc. will damage the external appearance of a coating film greatly. In addition, when a coating film is formed by further applying a paint on such a sagging trace, there is a problem that pinholes are likely to be generated in the circumferential portion such as these traces.

  By the way, in the recent electrodeposition coating, there is a demand for an electrodeposition coating composition having excellent electrodeposition coating efficiency and more excellent throwing power. Here, throwing power refers to the property that a coating film is sequentially formed on an unattached portion of an object to be coated. By electrodeposition coating using an electrodeposition coating composition with excellent throwing power, an electrodeposition coating film having a more uniform film thickness can be formed even when the object to be coated has a complicated shape. There is an advantage that can be. However, because the throwing power of the electrodeposition coating composition is excellent, the amount of the electrodeposition coating composition that deposits in the clearance of the joint increases, which causes secondary sagging and the like, and the cured electrodeposition coating film It has become clear that there is a problem that the appearance of the coating film deteriorates.

Japanese Patent Laid-Open No. 2002-241994 (Patent Document 1) discloses a polyethylene oxide having an HLB of 10 to 16 and a hydrophilic group having a high molecular weight in a washing bath liquid in a washing step of washing an electrodeposition-coated article with water. A water-washing method in electrodeposition coating of one coat coating characterized by containing a nonionic surfactant as an adduct in a concentration of 50 to 200 ppm is described. However, this method is different from the present invention in that a nonionic surfactant is contained in a washing bath used for washing performed immediately after electrodeposition coating. In addition, the method of the present invention is not limited with respect to the HLB of the nonionic surfactant, and can be washed even when the surfactant concentration is less than 50 ppm. Also in these points, this invention and this invention differ.

  In Japanese Patent Application Laid-Open No. 2001-121074 (Patent Document 2), powder coating is performed, followed by preliminary heating, and then a cationic thermosetting electrodeposition coating is electrodeposited on an unpainted portion and washed with water. Treated with an aqueous treatment liquid obtained by dissolving or dispersing a surfactant and / or an aqueous organic solvent in a range of 0.1% by weight and a surface tension measured at 25 ° C. of 30 dyne / cm to 60 dyne / cm, A coating method characterized by comprising a step of heating and thermosetting is described. However, in this method, the surfactant and / or the aqueous organic solvent is in the range of 0.001% by weight to 5.0% by weight based on the aqueous treatment liquid, and the aqueous treatment liquid contains a large amount of surfactants. It is included. Further, when the embodiment of the present invention is confirmed, the amount of the surfactant contained in the aqueous treatment liquid is 0.01 to 0.1% by weight, that is, 100 ppm to 1000 ppm, and a larger amount of the surfactant is compared with the present invention. It is included. When a large amount of surfactant is contained in the aqueous treatment liquid for washing and washing, problems such as foaming of the aqueous treatment liquid or poor coating appearance due to the surfactant remaining on the coating film surface may occur. .

  Japanese Patent Laid-Open No. 10-317191 (Patent Document 3) discloses a step of electrodepositing a cationic electrodeposition coating on the surface of a substrate; a step of washing the surface of the electrodeposition coating with water and drying; a surface of the electrodeposition coating Is treated with an aqueous solution containing a surfactant having a surface tension of 30 to 35 dyn / cm; and a method of drying and curing the electrodeposited film is described. However, this method is different from the present invention in that it aims to provide a surface treatment method for an electrodeposited coating film that does not leave unevenness in water washing on the surface of the electrodeposited coating film and water marks.

  Japanese Patent Application Laid-Open No. 10-046393 (Patent Document 4) discloses a pre-electrodeposition treatment method for an automobile body before entering an electrodeposition coating, and after performing a film forming treatment, washing with water and pure water washing, Further, there is described a method for pre-electrodeposition treatment of an automobile body, characterized by comprising a cleaning liquid treatment step for cleaning with pure water containing a cleaning liquid containing 5 to 1000 ppm of a nonionic surfactant. This method is different from the present invention in that it is a treatment after the film forming treatment that is performed before entering the electrodeposition coating.

Japanese Patent Laid-Open No. 2002-241994 JP 2001-121074 A Japanese Patent Laid-Open No. 10-317191 Japanese Patent Laid-Open No. 10-046393

  The present invention solves the above-mentioned conventional problems, and its object is to perform electrodeposition in which generation of electrodeposition sagging traces is suppressed and a cured electrodeposition coating film having an excellent coating film appearance can be obtained. It is to provide a coating method and an electrodeposition coating system.

The present invention
An electrodeposition coating film forming step for forming an electrodeposition coating film on the surface of the object;
A first water-washing step of washing the obtained coating with water;
A second water-washing step of washing the paint washed by the first water-washing step using washing water; and a final water-washing step of washing the paint-washed material washed by the second water washing step;
An electrodeposition coating method comprising:
The washing water used in the second washing step is represented by the following formula (I):

[Wherein, R ¹ and R ⁴ are each independently a linear or branched alkyl group having 1 to 7 carbon atoms, a cyclic alkyl group having 3 to 7 carbon atoms, or an aryl group having 5 to 7 carbon atoms. Yes,
R ² and R ³ are each independently a hydrogen atom, a methyl group or an ethyl group,
R ⁵ is a C ₂ -C ₄ alkylene oxide,
p is an integer of 0-15, and q is an integer of 0-15. ]
The electrodeposition coating method containing the acetylene type surfactant shown by these is provided, and the said objective is achieved by this.

  The concentration of the acetylene surfactant is more preferably 3 to 80 ppm with respect to the washing water.

The acetylene surfactant is
An acetylene surfactant, and a nonionic surfactant,
More preferably, it is contained in the washing water as a surfactant composition containing.

As one aspect of the present invention, an electrodeposition coating composition contained in the electrodeposition tank is
A cation having a film resistance of 900 to 2000 kΩ · cm ² electrodeposited to a thickness of 20 μm with respect to the object to be coated, and a conductivity of the electrodeposition coating composition of 1200 to 2000 μS / cm The case where it is an electrodeposition coating composition is mentioned.

  The present invention also provides an electrodeposition coating film obtained by the above electrodeposition coating method.

The present invention also provides
An electrodeposition tank for forming an electrodeposition coating on the surface of the object;
A first water-washing means for washing the obtained coated product with water;
A second water washing means for washing the paint washed by the first water washing means using washing water; and a final water washing means for washing the paint washed by the second water washing means;
An electrodeposition coating system comprising:
There is also provided an electrodeposition coating system in which the washing water used in the secondary washing means contains an acetylene surfactant represented by the above formula (I).

The present invention is also a method for preventing the occurrence of electrodeposition sagging marks when forming a cured electrodeposition coating film,
This cured electrodeposition coating film has the following steps:
An electrodeposition coating film forming step for forming an electrodeposition coating film on the surface of the object;
A first water-washing step of washing the obtained coating with water;
A second water washing step of washing the paint washed by the first water washing step with washing water;
A final water washing step of washing the paint washed by the second water washing step; and a baking step of baking and curing the final water washed paint;
And the washing water used in the second water washing step includes an acetylenic surfactant represented by the above formula (I).

  By the electrodeposition coating method of the present invention, the occurrence of secondary sagging in electrodeposition coating can be effectively prevented. The electrodeposition coating method of the present invention is a secondary that can occur when electrodepositing an object having a complicated shape without adding a new cleaning process, that is, using an existing electrodeposition coating system. The occurrence of sagging can be effectively prevented. By the electrodeposition coating method of the present invention, a cured electrodeposition coating film having an excellent coating film appearance can be obtained.

Electrodeposition coating method and electrodeposition coating system The electrodeposition coating method of the present invention comprises:
An electrodeposition coating film forming step for forming an electrodeposition coating film on the surface of the object;
A first water-washing step of washing the obtained coating with water;
A second water-washing step of washing the paint washed by the first water-washing step using washing water; and a final water-washing step of washing the paint-washed material washed by the second water washing step;
Is included.

The electrodeposition coating method of the present invention will be described using an electrodeposition coating system schematically shown in FIG. The electrodeposition coating system shown in FIG.
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;
Second water washing means 8 and 8 'for washing the paint washed by the first water washing means using washing water; and final water washing means 25 for washing the paint washed by the second water washing means;
It has. The electrodeposition coating system has a primary washing tank 13 for collecting the washing waste liquid of the first washing means 3, and secondary washing tanks 9 and 9 'for collecting the washing waste liquid of the second washing means 8. You may do it. In general, the washing water used in the secondary water washing means is often circulated and used in the secondary water washing means by performing filtration or the like.

  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 coating 16 and the cleaning water come into contact with each other by the primary washing means 3 such as a shower nozzle or by immersing the coating 16 in the washing water in the washing tank 13. The product 16 is washed with water (first water washing step). In addition, the water washing tank 13, the filter 5, the paint water washing means 3, and the path | route which connects these and circulates washing water are collectively called the 1st water washing system 11. FIG. In FIG. 1, three flushing tanks 13 of the primary flushing system 11 are depicted, but the number of flushing tanks 13 is not limited to three, and the size and shape of the object to be coated are not limited. Depending on it, the number of the washing tanks 13 can be changed.

  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 washing water by the secondary washing means 8 and 8 'such as a shower nozzle or spray. (Second water washing step). Examples of the washing water used in the second water washing step include ion exchange water, pure water, and industrial water. 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, it is not limited to such an aspect.

  In the present specification, “washing water used in the secondary water washing step” refers to the washing water used in the immersion water washing tanks 9 and 9 ′ and the secondary water washing means 8 and 8. It means washing water used for spray 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 cleaning water, for example, the path 17 for introducing the filtered water as the cleaning water into the secondary rinsing 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 water washing include ion exchange water, pure water, and reverse osmosis membrane filtered water (RO water). The waste liquid from the final water washing is collected in the secondary water washing tank 9 'of the secondary water washing system. As another embodiment, a water tank for collecting only the waste liquid from the final water washing may be provided. The washing waste liquid collected in the secondary washing tank 9 ′ may be collected in the secondary washing tank 9 through a path 24 for collecting the washing waste liquid. The final water washing means 25 is referred to as a final water washing system 21.

  The washing waste liquid in the first water washing means 3 may flow in the countercurrent direction with respect to the article 15 and the painting object 16, and may be collected in the overflow tank 1 adjacent to the electrodeposition tank via the collection path 4. The coating composition containing the wash water contained in the overflow tank 1 can be separated into a concentrated liquid containing the paint component and filtered water by the filter 5. 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 primary water washing means 3 and can be reused as washing water.

  Moreover, it is preferable that the washing waste liquid generated by the washing in the second washing step is recovered into the second washing tank 9. This washing waste liquid is preferably separated by the filter 19 into a concentrated liquid containing paint components and filtered water. The filtered water may be introduced into the secondary water washing means 8 as washing water through the line 17. The concentrated liquid may be introduced into the electrodeposition tank 2 or the overflow tank 1 through the 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.

  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. However, as a means for bringing the coated article 16 and the washing water into contact with each other, means such as the above-described immersion water washing and flow water washing can also be used. Further, these means can be used in combination.

  In the electrodeposition coating method of the present invention, the washing water used in the second washing step is represented by the following formula (I):

[Wherein, R ¹ and R ⁴ are each independently a linear or branched alkyl group having 1 to 7 carbon atoms, a cyclic alkyl group having 3 to 7 carbon atoms, or an aryl group having 5 to 7 carbon atoms. Yes,
R ² and R ³ are each independently a hydrogen atom, a methyl group or an ethyl group,
R ⁵ is a C ₂ -C ₄ alkylene oxide,
p is an integer of 0-15, and q is an integer of 0-15. ]
It contains the acetylene type surfactant shown by these. These acetylene surfactants may be used alone or in combination of two or more. In the present invention, the acetylene-based surfactant may be contained in the washing water used in the immersion washing in the secondary washing tank 9, and the washing used for spraying in the secondary washing means 8 and 8 '. May be included in the water. Furthermore, you may include in both of these.

A preferred example of the acetylene surfactant is an acetylene surfactant represented by the formula (I),
In the formula, R ¹ and R ⁴ are each independently a linear or branched alkyl group having 1 to 5 carbon atoms,
R ² and R ³ are each independently a methyl group or an ethyl group,
R ⁵ is a C ₂ -C ₄ alkylene oxide,
p is an integer from 0 to 15 and q is an integer from 0 to 15;
Surfactant is mentioned. These acetylene-based surfactants are preferred because they can exhibit the effect of preventing the occurrence of excellent electrodeposition sagging traces even when used in a very small amount.

  The acetylene-based surfactant may be contained in washing water as a surfactant composition containing an acetylene-based surfactant and another surfactant. Other surfactants are preferably nonionic surfactants, and examples include ether-type, ester-type, ether-ester-type, and alcohol-type surfactants. Specific surfactants include, for example, ethylene glycol, propylene glycol, dipropylene glycol, dipropylene glycol monomethyl ether, polyoxyethylene alkyl ether, polyoxyethylene nonylphenyl ether, polyalkoxyalkyl ether, 2-butoxyethanol and the like. Can be mentioned. When the acetylene surfactant is contained in the washing water as the surfactant composition, the weight ratio of the acetylene surfactant to the other surfactant is preferably 99: 1 to 50:50, More preferably, it is 95: 5-75: 25. By including the acetylene-based surfactant in the washing water as the surfactant composition, the dispersibility or solubility in water can be improved, and a stronger surfactant activity can be exhibited.

  The method for adding the acetylene surfactant to the washing water is not particularly limited. For example, the surfactant may be appropriately added when introducing the washing water into the secondary washing means, and the surfactant is added to the washing waste liquid contained in the secondary washing tank for collecting the washing water. May be added. And you may add by methods other than these.

  The concentration of the acetylene surfactant contained in the washing water can be changed depending on the type of the acetylene surfactant used. A preferable concentration of the acetylene surfactant is 3 to 80 ppm with respect to the washing water. This concentration is more preferably 7 to 40 ppm. Further, when the acetylene surfactant is contained in the washing water as a surfactant composition containing an acetylene surfactant and another surfactant, the preferred concentration of the surfactant composition is On the other hand, the case is 5 to 80 ppm. This concentration is more preferably 10 to 40 ppm.

  Thus, the acetylene-based surfactant represented by the above formula (I) has an advantage that it can exhibit the effect of preventing the occurrence of electrodeposition sagging traces even when used at a very low concentration.

  Surfactants are used as substances that change the surface tension of liquids. As a rough classification of the surfactant, there are an anionic surfactant, a cationic surfactant, a nonionic surfactant and an amphoteric surfactant. Among these, cationic surfactants, anionic surfactants and amphoteric surfactants tend to have an adverse effect on the coating performance, particularly corrosion resistance, in terms of their ionic performance. Therefore, the surfactant that can be used for the washing water in the secondary water washing step needs to be selected from nonionic surfactants.

  Nonionic surfactants include polyoxypropylene-polyoxyethylene (PO-EO) block copolymers, various higher alcohols, aromatic ethoxylate (EO) addition types, fatty acid ester types, fatty acid amides, and ethoxys thereof. Examples include rate (EO) addition type, polyglycerin fatty acid esters, silicone surfactants, and fluororesin-containing surfactants. Further, studies have been made to add higher alcohol ethoxylates and the like to the cationic electrodeposition coating composition.

  As the nonionic surfactant used for the washing water in the second water washing step, a nonionic surfactant that is easily dispersed in water, greatly reduces the surface tension, and has a low bubble property is preferable. Among the nonionic surfactants, for example, a silicone-based surfactant, a fluororesin-containing surfactant, and the like can greatly reduce the surface tension. However, when these surfactants remain on the surface of the cured electrodeposition coating film, there is a possibility that the adhesion between the intermediate coating, the top coating, the sealer, or the like applied thereon is impaired. For this reason, it is not preferable to use it in the secondary water washing step close to the final step of the electrodeposition coating system.

  In the present invention, an acetylene-based surfactant is used as the surfactant used in the washing water in the secondary water washing step. Although some acetylene surfactants do not have excellent water dispersibility, the surface tension can be greatly reduced with a small amount of use. It has an excellent advantage of not deteriorating.

  By the way, the following causes can be considered as a cause of the electrodeposition sagging trace (secondary sagging) occurring at the time of image sticking and curing in the coated product that has been washed with water after the electrodeposition coating film is formed and further washed with the second water. . The main cause is that an excessive amount of the electrodeposition coating composition enters into the clearance (slight gap) of the joint portion of the object to be coated when forming the electrodeposition coating film. The surplus electrodeposition coating composition cannot be completely washed by being blocked by the surrounding uncured electrodeposition coating film in a washing step or the like. On the other hand, the surrounding electrodeposition coating film is melted by heating at the time of baking and curing of the electrodeposition coating film, thereby reducing the volume of the coating film. And by this reduction | decrease of the coating-film volume, the surplus electrodeposition coating-material composition will flow out, and, thereby, an electrodeposition sagging trace (secondary sagging) will arise. Furthermore, the surface tension of the excess electrodeposition coating composition that has entered the clearance (slight gap) of the joint portion of the object to be coated is reduced by heating in the baking and curing of the electrodeposition coating film. Due to the decrease in the surface tension of the electrodeposition coating composition due to heating, an excessive amount of the electrodeposition coating composition flows out from the clearance portion, thereby generating an electrodeposition sagging trace (secondary sagging). It has become clear that the occurrence of this secondary sagging is more likely to occur when using an electrodeposition coating composition having excellent throwing power. The reason for this is that the throwing power of the electrodeposition coating composition is excellent, which increases the amount of the electrodeposition coating composition that precipitates in the clearance of the joint portion of the object to be coated. It may be difficult to completely clean the electrodeposition coating composition.

  In the electrodeposition coating method of the present invention, even when an electrodeposition coating composition having excellent throwing power is used for electrodeposition coating, washing water containing an acetylenic surfactant represented by the above formula (I) is used. By using it, it was possible to exhibit an excellent secondary sagging prevention effect. Furthermore, the electrodeposition coating method of the present invention can effectively prevent the occurrence of secondary sagging in the cured electrodeposition coating film without the generation of washing water bubbles and the like.

Electrodeposition Coating Composition In the electrodeposition coating method of the present invention, any commonly used electrodeposition coating composition can be used. However, the electrodeposition coating composition having excellent throwing power, for example, the film resistance of the electrodeposition coating film electrodeposited to a thickness of 20 μm on the object to be coated is 900 to 2000 kΩ · cm ² , and the electrodeposition coating composition Even when a cationic electrodeposition coating composition having an electrical conductivity of 1200 to 2000 μS / cm is used for electrodeposition coating, the acetylene surfactant is contained in the washing water. While preventing problems such as foaming, it is possible to prevent the occurrence of coating appearance defects such as electrodeposition sagging marks in the baking and curing process after electrodeposition coating. 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.

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 coating composition may contain conventional coating additives such as water-miscible organic solvents, surfactants, antioxidants, ultraviolet absorbers, and pigments.

The electrodeposition coating composition used in the electrodeposition coating method of the present invention preferably has a film resistance of 900 to 2000 kΩ · cm ² at a film thickness of 20 μm. In the electrodeposition coating method of the present invention, even when a high throwing power electrodeposition coating composition in which the film resistance of the electrodeposition coating is in such a range is used, an electrodeposition sagging trace or the like is generated. A cured electrodeposition coating film can be formed without any problem. Moreover, when the film resistance of an electrodeposition coating film exceeds 2000 kohm * cm < ² >, there exists a possibility that a coating-film external appearance may be inferior. The film resistance of the electrodeposition coating film is more preferably 900-1500 kΩ · cm ² .

The film resistance of the electrodeposition coating film can be adjusted by controlling the charge transfer medium amount and viscosity of the deposited film. Moreover, the film resistance value of an electrodeposition coating film is calculated | required by the following formula from the residual current value (A) of a coating film in the final coating voltage (V).
Membrane resistance value (FR) = V / A

  The electrodeposition coating composition used in the electrodeposition coating method of the present invention preferably has an electric conductivity of 1200 to 2000 μS / cm. In the electrodeposition coating method of the present invention, even when a high throwing power electrodeposition coating composition in which the conductivity of the electrodeposition coating composition is in such a range is used, an electrodeposition sagging trace is generated. A cured electrodeposition coating film can be formed without causing it to occur. On the other hand, if it exceeds 2000 μS / cm, the appearance of the coating film surface may be deteriorated. The conductivity can be measured using a commercially available conductivity meter.

  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 coating is baked at an elevated temperature in a conventional manner, for example, in a baking furnace, in a baking oven or with an infrared heat lamp. The baking temperature may vary but is usually about 140 ° C to 180 ° C. The coated material coated by the electrodeposition coating system 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.

Preparation of Electrodeposited Test Piece Cold-rolled steel sheet (JIS G3141, SPCC-SD) was treated with Surfdyne SD-5000 (manufactured by Nippon Paint Co., Ltd.) to obtain a zinc phosphate-treated cold-rolled steel sheet. As shown in FIG. 2, the obtained two cold-rolled steel plates were overlapped and fixed with a spacer interposed therebetween, thereby creating a test piece having a predetermined clearance. The clearance of the test piece was adjusted to 50 mm × 50 mm × 0.1 mm.

Example 1
A cationic electrodeposition coating composition (“PN-310”, manufactured by Nippon Paint Co., Ltd.) was placed in a 4 L stainless steel beaker. The prepared test piece is dipped so that all the parts that become clearances are immersed, the temperature is raised to 200 V in 30 seconds at a liquid temperature of 30 ° C., a voltage is applied while holding 200 V for 150 seconds, and electrodeposition is performed. A coating film was formed.

The test piece on which the electrodeposition coating film was formed was taken out from the electrodeposition coating composition. The test piece was washed weakly using a spray to wash away the undeposited electrodeposition coating composition adhering to the surface of the test piece.
Acetylene-based surfactant ("Orphine ^{(registered trademark)} EXP.4051F", active ingredient concentration: 50%, manufactured by Nissin Chemical Industry Co., Ltd.) was ^added to 4 L of ion-exchanged water (20 ° C) at 10 ppm, 20 ppm, and 40 ppm, respectively. (In this case, the contents of the active ingredients contained in the surfactant are 5 ppm, 10 ppm, and 20 ppm, respectively) to prepare washing water for the second water washing step. The test piece was immersed in the prepared washing water and allowed to stand for 1 minute. Then, the test piece was taken out from the washing water and allowed to stand for 10 minutes. The test piece thus coated was baked and dried at 170 ° C. for 20 minutes. The active ingredient contained in this acetylene surfactant is an EO adduct of 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol. The structural formula of this active ingredient is as shown below.

The cured electrodeposition coating film thus obtained was examined for the presence of electrodeposition sagging traces. The results are shown in Table 1. The evaluation criteria are as follows.
○: Good electrodeposition traces are not confirmed.
○ △: Slightly visible traces of electrodeposition.
Δ: Electrodeposition sagging remains.
Δ ×: A large amount of electrodeposition sagging is generated, and a slight rise can be confirmed in the sagging portion.
×: The amount of electrodeposition sagging is large, and the sagging portion is greatly raised.

Measurement of surface tension of washing water Acetylene-based surfactant ("Olfin ^{(registered trademark)} EXP.4051F", manufactured by Nissin Chemical Industry Co., Ltd.) was used so that the contents were 10 ppm, 20 ppm, 40 ppm and 80 ppm, respectively. And added to ion-exchanged water. The washing water thus obtained was adjusted to a liquid temperature of 20 ° C., and the surface tension was measured using Resurf (A & D Orientec). Table 2 shows the measured values. The measured values shown in Table 2 are shown in FIG.

Example 2
An electrodeposition coating film was formed in the same manner as in Example 1 using the prepared test piece. Add "Orphine ^{(registered trademark)} EXP. 4036" (manufactured by Nissin Chemical Industry Co., Ltd., active ingredient concentration: 80%) as an acetylene-based surfactant to 10 ppm, 20 ppm, and 40 ppm, respectively (in this case The contents of the active ingredients contained in the surfactant are 8 ppm, 16 ppm and 32 ppm, respectively.) Example 1 except that cleaning water was prepared and the test piece on which the electrodeposition coating film was formed was cleaned. And similar evaluations. The results are shown in Table 1, Table 2 and FIG. The active ingredient contained in the acetylene surfactant is an EO adduct of 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol.

Example 3
An electrodeposition coating film was formed in the same manner as in Example 1 using the prepared test piece. Add "Orphine ^{(registered trademark)} EXP.4001" (manufactured by Nissin Chemical Industry Co., Ltd., active ingredient concentration: 80%) as an acetylene-based surfactant so as to be 10 ppm, 20 ppm, and 40 ppm, respectively (in this case The contents of the active ingredients contained in the surfactant are 8 ppm, 16 ppm and 32 ppm, respectively.) Example 1 except that cleaning water was prepared and the test piece on which the electrodeposition coating film was formed was cleaned. And similar evaluations. The results are shown in Table 1, Table 2 and FIG. The active ingredient contained in the acetylene surfactant is an EO adduct of 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol.

Comparative Example 1
An electrodeposition coating film was formed in the same manner as in Example 1 using the prepared test piece. It was carried out in the same manner as in Example 1 except that the test piece on which the electrodeposition coating film was formed was washed with washing water containing no surfactant. The generation of the electrodeposition sagging trace of the test piece was evaluated in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 2
An electrodeposition coating film was formed in the same manner as in Example 1 using the prepared test piece. An electrodeposition coating film was formed using washing water containing Adecatol SO-120 (manufactured by Asahi Denka Kogyo Co., Ltd., HLB = 12.0) (higher alcohol ethoxylate surfactant) instead of the acetylene surfactant. The same procedure as in Example 1 was performed except that the test piece was washed. The occurrence of electrodeposition sagging traces on the test piece was evaluated in the same manner as in Example 1 (surfactant content was up to 1000 ppm). The results are shown in Table 1.

Comparative Example 3
An electrodeposition coating film was formed in the same manner as in Example 1 using the prepared test piece. An electrodeposition coating film was formed using washing water containing Adecatol SO-105 (manufactured by Asahi Denka Kogyo Co., Ltd., HLB = 10.5) (higher alcohol ethoxylate surfactant) instead of the acetylene surfactant. The same procedure as in Example 1 was performed except that the test piece was washed. The occurrence of electrodeposition sagging traces on the test piece was evaluated in the same manner as in Example 1 (surfactant content was up to 1000 ppm). The results are shown in Table 1.

Electrodeposition coating film resistance In the electrodeposition bath containing the cationic electrodeposition coating composition used in Examples and Comparative Examples, zinc phosphate-treated steel sheets (JIS G 3141 SPCC-SD, Surfdyne SD-2500 (Nippon Paint Co., Ltd.) The product was treated with the electrodeposition coating material (dimensions: 70 mm × 150 mm, thickness 0.7 mm). A voltage was applied to the steel sheet, the voltage was increased to 200 V over 30 seconds, and electrodeposition was performed for 150 seconds. The coating voltage with a coating thickness of 20 μm at a bath temperature of 30 ° C. and the residual current at the end of electrodeposition were measured to calculate the coating resistance value (kΩ · cm ² ). The coating film resistance was 960 kΩ · cm ² .

Electric conductivity of the electrodeposition coating composition The electric conductivity in this specification is a liquid temperature of 25 according to JIS K 0130 (general rules for measuring electric conductivity) using CM-30S manufactured by Toa Denpa Kogyo Co., Ltd. Measured at ° C. The electrical conductivity of the cationic electrodeposition coating composition used in Examples and Comparative Examples was 1630 μS / cm.

  As is clear from the results of Examples and Comparative Examples, the use of cleaning water containing an acetylenic surfactant in the secondary cleaning step generates electrodeposition sagging marks during baking and curing of the electrodeposition coating film. Can be effectively prevented. It can also be seen that the acetylene-based surfactant exhibits a significant effect even when used in a very small amount as compared with other nonionic surfactants.

  By the electrodeposition coating method of the present invention, the occurrence of secondary sagging in electrodeposition coating can be effectively prevented. The electrodeposition coating method of the present invention is a secondary that can occur when electrodepositing an object having a complicated shape without adding a new cleaning process, that is, using an existing electrodeposition coating system. The occurrence of sagging can be effectively prevented. By the electrodeposition coating method of the present invention, a cured electrodeposition coating film having an excellent coating film appearance can be obtained.

It is a schematic diagram which shows an example of the electrodeposition coating system of this invention. It is a schematic diagram which shows the preparation methods of an electrodeposition coating test piece. It is a graph which shows the surface tension of washing water.

Explanation of symbols

1 ... overflow tank,
2 ... Electrodeposition tank,
3 ... primary washing means,
4 ... Path for collecting waste water from 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 waste liquid,
25. Final washing means,
30: Electrodeposition coating system.

Claims (7)

An electrodeposition coating film forming step for forming an electrodeposition coating film on the surface of the object;
A first water-washing step of washing the obtained coating with water;
A second water-washing step of washing the paint washed by the first water-washing step using washing water; and a final water-washing step of washing the paint-washed material washed by the second water washing step;
An electrodeposition coating method comprising:
The washing water used in the second washing step is represented by the following formula (I):

[Wherein, R ¹ and R ⁴ are each independently a linear or branched alkyl group having 1 to 7 carbon atoms, a cyclic alkyl group having 3 to 7 carbon atoms, or an aryl group having 5 to 7 carbon atoms. Yes,
R ² and R ³ are each independently a hydrogen atom, a methyl group or an ethyl group,
R ⁵ is a C ₂ -C ₄ alkylene oxide,
p is an integer of 0-15, and q is an integer of 0-15. ]
An electrodeposition coating method comprising an acetylene surfactant represented by   The electrodeposition coating method according to claim 1, wherein the concentration of the acetylene-based surfactant is 3 to 80 ppm with respect to the washing water. The acetylene surfactant is
An acetylene surfactant, and a nonionic surfactant,
The electrodeposition coating method of Claim 1 or 2 contained in washing water as a surfactant composition containing. The electrodeposition coating composition contained in the electrodeposition tank,
A cation having a film resistance of 900 to 2000 kΩ · cm ² electrodeposited to a thickness of 20 μm with respect to the object to be coated, and a conductivity of the electrodeposition coating composition of 1200 to 2000 μS / cm The electrodeposition coating method according to claim 1, which is an electrodeposition coating composition.   The electrodeposition coating film obtained by the electrodeposition coating method in any one of Claims 1-4. An electrodeposition tank for forming an electrodeposition coating on the surface of the object;
A first water-washing means for washing the obtained coated product with water;
A second water washing means for washing the paint washed by the first water washing means using washing water; 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 for the secondary washing means is represented by the following formula (I):

[Wherein, R ¹ and R ⁴ are each independently a linear or branched alkyl group having 1 to 7 carbon atoms, a cyclic alkyl group having 3 to 7 carbon atoms, or an aryl group having 5 to 7 carbon atoms. Yes,
R ² and R ³ are each independently a hydrogen atom, a methyl group or an ethyl group,
R ⁵ is a C ₂ -C ₄ alkylene oxide,
p is an integer of 0-15, and q is an integer of 0-15. ]
An electrodeposition coating system comprising an acetylenic surfactant represented by A method for preventing the occurrence of electrodeposition sagging marks when forming a cured electrodeposition coating film,
The cured electrodeposition coating film has the following steps:
An electrodeposition coating film forming step for forming an electrodeposition coating film on the surface of the object;
A first water-washing step of washing the obtained coating with water;
A second water-washing step of washing the paint washed in the first water-washing step with washing water;
A final water-washing step of washing the paint washed by the second water-washing step; and a baking step of baking and curing the paint finally washed with water;
And the washing water used in the second washing step is represented by the following formula (I):

[Wherein, R ¹ and R ⁴ are each independently a linear or branched alkyl group having 1 to 7 carbon atoms, a cyclic alkyl group having 3 to 7 carbon atoms, or an aryl group having 5 to 7 carbon atoms. Yes,
R ² and R ³ are each independently a hydrogen atom, a methyl group or an ethyl group,
R ⁵ is a C ₂ -C ₄ alkylene oxide,
p is an integer of 0-15, and q is an integer of 0-15. ]
A method comprising an acetylenic surfactant represented by the formula:

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