JP2008189963A - Electrodeposition coating method and shortening the washing process or reducing the amount of washing water used - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for shortening a rinsing step or reducing a water resource, in a cation electrodeposition coating process. <P>SOLUTION: In the cation electrodeposition coating process comprising an electrodeposition coating step of immersing an article to be coated in a cation electrodeposition paint and applying voltage to the article, and a rinsing step of rinsing the article having been coated in the electrodeposition coating step, the method for shortening the rinsing step or reducing the water resource includes employing a low solid content type of the cation electrodeposition paint, and also removing at least one part of the undeposited paint by swinging the article and/or changing the angle of the article before rinsing the article taken out from the electrodeposition bath. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a cationic electrodeposition coating method and a method of shortening the washing step of the cationic electrodeposition coating method or reducing the amount of washing water used. In particular, the water washing process in cationic electrodeposition coating is carried out by reducing the number of steps or reducing the amount of water for water washing. It relates to a method for reducing the amount.

  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.

  As shown in FIG. 1, an electrodeposition coating system used for such an electrodeposition coating is an electrodeposition bath 10 for forming an electrodeposition coating on the surface of an object to be coated, and an excessive amount remaining in the obtained paint. Means for washing off the electrodeposition coating composition, etc., that is, the first water washing step A and the second water washing step B are included. The first water washing step is a means for washing away excess paint composition and the like physically adhered on the paint, and collecting paint components to replenish the electrodeposition bath. The secondary rinsing step is a means for performing final cleaning using rinsing water such as ion exchange water, pure water, or industrial water. In the first rinsing step, the rinsing step is performed using the ultrafiltrate obtained by ultrafiltration of the electrodeposition paint as the rinsing water, and usually in the three rinsing booths of the first rinsing booth 1 to the third rinsing booth 3. Water washing is performed. In the second washing step, ion exchange water, pure water or industrial water is a step in which a small amount of paint components and ions mixed in the paint composition that could not be washed out by the first washing means are washed out. Washing is performed at the three booths of the fourth flushing booth 4, the fifth flushing booth 5, and the pure water flushing booth 6. The coated material thus obtained is baked to cure the electrodeposition coating film, and a cured electrodeposition coating film is obtained.

  As is apparent from FIG. 1, the electrodeposition coating and the subsequent water washing process are arranged in a great number of processes and require a large area in terms of space. In addition, a large amount of water or ultrafiltrate (water is the main component) is required in the washing step, and the amount of water used is enormous when painting large objects such as automobiles. Since the washing water produced by the washing step contains paint components and the like, it is not preferable to discharge the washing water as it is. Therefore, it is necessary to perform some kind of processing and discharge, and this processing also takes time and cost. Shortening the water washing process or reducing the amount of water used is expected to have significant effects such as saving equipment and space, and saving water resources, but so far, the water washing process in cationic electrodeposition coating methods. There are almost no patent documents for the purpose of shortening the amount of water or reducing the amount of water resources used.

  In Japanese Patent Application Laid-Open No. 2001-214300 (Patent Document 1), in cation electrodeposition coating, when surface treatment is performed on an object to be coated and then immersed in a cation electrodeposition tank for electrodeposition coating, water is applied several times after the surface treatment. A cationic electrodeposition coating method is disclosed in which a conventional drying furnace is omitted by spraying the mist. In this method, the omission of the drying furnace after the surface treatment has been achieved, and the shortening of the water washing step after the cationic electrodeposition coating has not been studied.

In Japanese Patent Application Laid-Open No. 9-241891 (Patent Document 2), a cationic electrodeposition coating is applied to an object to be coated, followed by washing with water, followed by simple drying, further applying a powder coating material, and heating and curing the whole. A method is disclosed. This method simultaneously cures the cationic electrodeposition coating film and the powder coating film coating to reduce the baking and curing process once. However, shortening the water washing process after cationic electrodeposition coating has been studied. Not.
JP 2001-214300 A Japanese Patent Laid-Open No. 9-241891

  An object of this invention is to shorten the water washing process in the cationic electrodeposition coating method which has not been examined until now, or to reduce water resources.

  The inventors have changed the cationic electrodeposition paint to a low solid content type and changed the rocking and / or angle before washing the object to be washed from the electrodeposition bath to at least part of the undeposited paint. As a result, the water washing process was greatly improved, and it was found that the water washing process could be shortened or the amount of water resources used could be reduced, thereby achieving the present invention.

  That is, the present invention relates to a cation comprising an electrodeposition coating step in which a coating is immersed in a cationic electrodeposition coating and a voltage is applied, and a water washing step in which the coated coating obtained in the electrodeposition coating step is washed with water. In the electrodeposition coating method, at least a part of the undeposited paint is obtained by using a low solid content type as the cationic electrodeposition paint and changing the swing and / or the angle before washing the object to be washed from the electrodeposition bath. A cationic electrodeposition coating method characterized by shortening the washing step or reducing the amount of washing water used is eliminated.

  In the present invention, when the electrodeposition-coated object obtained by immersing the object in the cationic electrodeposition paint and applying a voltage is washed with water, the cationic electrodeposition paint is made into a low solid content type, And before washing the object to be washed from the electrodeposition bath, the washing process after electrodeposition coating can be shortened by removing at least a part of the undeposited paint by changing the swing and / or angle, or washing water Provide a way to reduce the usage of.

  Preferably, the water washing step includes a primary water washing step of washing with an ultrafiltrate of a cationic electrodeposition paint, and a secondary water washing in which final washing is performed using water such as ion exchange water, pure water, or industrial water. Process.

  The cationic electrodeposition coating material may have a solid content of 10 to 18% by weight, and may have a lower solid content of 0.5 to 9.0% by weight.

  In the cationic electrodeposition coating method of the present invention, the cationic electrodeposition coating material is changed to a low solid content type, and the oscillating and / or angle is changed before the object to be coated is washed with water from the electrodeposition bath. By removing at least a part of the water washing process, the water washing process can be shortened and the amount of water used can be reduced.If the process is shortened, space and equipment are reduced. This leads to savings and reduction of wastewater treatment. Shortening the process and reducing the amount of water used can also be combined, and in this case both effects can be expected.

Cationic electrodeposition coating method and method for shortening the washing step after electrodeposition coating In the cationic electrodeposition coating method of the present invention, an electrodeposition coating step in which a voltage is applied by immersing an object to be coated in a cationic electrodeposition coating, In a cationic electrodeposition coating method comprising a water washing step in which a coated object obtained in the electrodeposition process is washed with water, a low solid content type of cationic electrodeposition paint is used, and the object is washed with water from the electrodeposition bath. It is characterized in that at least part of the undeposited paint is removed by shaking and / or changing the angle before. Further, in the method of shortening the washing step after electrodeposition coating of the present invention or reducing the amount of washing water used, electrodeposition obtained by immersing the object to be coated in a cationic electrodeposition paint and applying a voltage. When washing the coated object to be washed with water, the cation electrodeposition paint is made into a low solid content type, and before the object to be coated is washed from the electrodeposition bath, the undeposited paint is changed. It is characterized by removing at least a part of.

  The present invention will be described with reference to FIG. FIG. 1 is a diagram schematically showing an electrodeposition coating method, particularly an electrodeposition bath and a subsequent water washing step. As described above, FIG. 1 illustrates a conventional example, but the process itself can also be used to explain the present invention.

  In FIG. 1, the object to be coated having the shape of a car body moves from the electrodeposition bath 10 to the second water washing step B through the first water washing step A and then flows to another step. In the first water washing step A, the liquid component (mainly water) stored in the ultrafiltrate 12 collected from the electrodeposition bath 10 through the ultrafilter 11 is sent from a pump (not shown). Use as flush water. In the second washing step B, ion exchange water, pure water, industrial water, or the like is introduced from the water source 14 and used as washing water. The object on which the electrodeposition coating is performed in the electrodeposition bath 10 moves to the first water washing booth 1 in the first water washing step A, and then passes through the second water washing booth 2 to the third water washing booth 3. Moving. In each booth, as shown in FIG. 1, flush water may be washed by spraying, but it is not limited to this method. A method of immersing in a washing bath as shown in the fourth washing booth 4 may be used, or other methods, for example, a method of passing an object through a water stream may be used. In the first rinsing step A, the rinsing water (ultrafiltrate) is used in the first rinsing booth 1 from the third rinsing booth 3 through the second rinsing booth 2 in the reverse of the flow of the object to be coated. The washing water containing a large amount is returned to the electrodeposition bath 10 and reused.

  The object to be coated that has undergone the first water washing step A is subjected to water washing with ion exchange water, pure water, industrial water, or the like, instead of the ultrafiltrate in the second water washing step B. In the second water washing step B, the object to be coated moves from the fourth water washing booth 4 to the final pure water washing booth 6 through the fifth water washing booth 5. On the contrary, the washing water moves from the pure water washing booth 6 to the fourth washing booth 4. In the example of FIG. 1, the fourth flush booth 4 has a method of immersing an object in a flush bath, but is not limited to this method. Moreover, although the other flush booths 5 and 6 are also spray type, it is not limited to the method, What kind of flush system may be taken. In the example of FIG. 1, a pipe 20 for supplying water from the water source 14 to the pure water flush booth 6 and a pipe 21 for supplying water to the fourth flush booth 4 are described, but the present invention is not limited to this method. The washing water may be supplied by any method. Further, although the flush water used in the fourth flush booth 4 is drained 13 through the pipe 22, it is not limited to this method, and it can be reused as flush water through filtration or the like depending on circumstances. is there. In addition, the waste water 13 is not directly discarded, and the waste water is naturally treated so as to meet various environmental standards.

  According to the present invention, the cationic electrodeposition paint used in the electrodeposition bath 10 is changed to a low solid content type, and the rocking and / or the angle is changed before the object to be coated is washed from the electrodeposition bath. By removing at least a portion of the undeposited paint, the washing step is shortened, the amount of washing water used is reduced, or a mixture of both is achieved. The aspect of reducing the amount of water to be used is to reduce the amount of water used in the water washing step of FIG. 1 (that is, either or both of the first water washing step A and the second water washing step B). Reduce the amount of flush water used per unit. This saves water resources for the entire washing process and saves resources and improves environmental compatibility. The amount of water used is reduced within 50% by weight, preferably 10-50% by weight, more preferably 30-50% by weight of the current amount used. Reductions of more than 50% by weight may be possible, but defects in the paint film become noticeable.

  The shortening of the water washing step is performed by reducing one or more booths in the water washing step shown in FIG. 1 or shortening the water washing distance by using one or more water washing booths. In any method, the distance of the entire washing process is shortened, which leads to shortening of the washing space and consequently shortening of the electrodeposition coating process. Moreover, shortening the water washing process shortens the water washing time, and also shortens the time of the entire electrodeposition process. Furthermore, since the shortening of the washing process also reduces the use of flush water used in the shortened portion, the amount of flush water used is naturally reduced.

  In the present invention, as described above, the cationic electrodeposition coating material needs to be a low solid content type. The low solid content type means that the solid content of the cationic electrodeposition paint is 10 to 18% by weight, preferably 14 to 18% by weight. In conventional cationic electrodeposition coatings, the solid content is usually about 15 to 22% by weight. Therefore, in the present invention, it is necessary to use a low solid content type having a lower solid content than the conventional one. In order to make the cationic electrodeposition coating material have a low solid content, the amount of the inorganic pigment is reduced. When the pigment is reduced, the concealability tends to be deteriorated. Therefore, it can be achieved by reducing the pigment to such an extent that the concealability is not adversely affected or by eliminating the concealability by another method. In addition to the solid content of 10 to 18% by weight, cationic electrocoating paints having a low solid content type have recently been investigated in addition to those having a solid content of 10 to 18% by weight. ing. The present invention can also be used for such a lower solid content cationic electrodeposition coating.

  There is no particular limitation on the method of changing the swing and / or angle before washing the object to be coated from the electrodeposition bath. Oscillation can be interpreted widely, and means that the object is actively shaken by some force and changes the posture of the object. For example, if the line for moving the conveying means for moving the object to be coated comes out of the electrodeposition bath and is not linear before reaching the washing tank, it becomes zigzag or wavy. Swings sideways. As a result of such shaking, the angle of the object to be coated changes, and undeposited electrodeposition paint flows out in a state where it is trapped in a bag-like portion or gap of the object to be coated.

  Recently, a transport facility that can change the angle of an object to be coated in an automobile painting line has been proposed. As an example of such a conveying means, JP-A-2005-335945 can be cited. Japanese Patent Application Laid-Open No. 2005-335945 discloses a suspension support device, an elevating means for moving the suspension support device up and down, and an attitude for operating the suspension support device to adjust the posture of the object to be conveyed (coating object). An apparatus having an adjustment device is disclosed. By using such a conveying means, by using a means for adjusting the posture of the object to be coated, the position of the object to be coated is changed before reaching the washing tank from the electrodeposition bath. What exists in a state where the paint is trapped in the bag-like portion or gap of the object to be coated flows out. FIG. 2 schematically shows an apparatus used for this. In FIG. 2, 31 is a suspension support device, 32 is an elevating means, 33 is a posture adjusting device, and 34 is a transported body.

  Although the angle to change the posture is not particularly limited, it can be said that the greater the change from the posture in the electrodeposition bath, the more easily the undeposited electrodeposition paint flows out, but depending on the time to reach the device and the washing tank, etc. It changes a lot. In some cases, if the object to be coated can be rotated up to a maximum of 90 ° from the posture in the painted state, the undeposited electrodeposition paint is more likely to flow out.

Electrodeposition coating composition In the cationic electrodeposition coating method of the present invention, the commonly used cationic electrodeposition coating composition includes a cationic epoxy resin, a curing agent, and optionally a pigment or an additive. It is done. 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.

  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); 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 curing agents.

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

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

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

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

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

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

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

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

Pigment-dispersed paste When a pigment is used as a component of an electrodeposition paint, generally the pigment is dispersed in an aqueous medium at a high concentration in advance together with a resin called a pigment-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 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. Further, 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 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 cationic epoxy resin during curing to give a good cured coating film. In general, it is generally in the range of 90/10 to 50/50, preferably 80/20 to 65/35, expressed as a solid mass ratio of the cationic epoxy resin to the curing agent.

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

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

  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.

Example 1
The pretreated article (car body) was immersed in a low solid content type cationic electrodeposition paint (manufactured by Nippon Paint Co., Ltd .; solid content 12% by weight), and electrodeposition coating was performed at 150 V for 3 minutes. . The obtained coated object was slowly changed from the painted state to 90 ° once and then returned to the original state, and then washed with pure water. The amount of pure water used was 100 liters until sufficient water washing for the next heat curing step was performed. The amount of water used was the average value when 10 objects were washed with water. The reason why pure water was used for washing was that the amount used was quantitatively understood. In practice, as shown in FIG. 1, an ultrafiltrate or the like is used.

Comparative Example 1
The object to be coated by electrodeposition in the same manner as in Example 1 was washed with pure water without swinging or changing the angle as usual. The amount of pure water used was 250 liters until sufficient water washing was performed for the next heat curing step. As in Example 1, the amount of water used was an average value when 10 water was washed.

  As is clear from the above examples and comparative examples, it can be seen that the amount of water (pure water) required for water washing is clearly small in Example 1.

It is a figure which shows typically an electrodeposition coating method, especially an electrodeposition bath and the subsequent water-washing process. It is a figure which shows typically an example of the apparatus used in order to rock | fluctuate a to-be-coated article, or to change an angle.

Explanation of symbols

A ... First water washing step A
B ... Secondary water washing process B
1 ... The first washing booth,
2 ... 2nd flush booth 3 ... 3rd flush booth,
4 ... Fourth washing booth,
5 ... Fifth flush booth,
6 ... Pure water flush booth,
10 ... Electrodeposition bath,
11 ... Ultrafiltration device,
12 ... ultrafiltrate,
13 ... Waste water,
14 ... Water source
20, 21, 22, ... piping,
31 ... Suspension support device,
32 ... Lifting means,
33 ... Posture adjustment device 34 ... Conveyed body.

Claims (8)

  In a cationic electrodeposition coating method comprising an electrodeposition coating step of immersing a coating object in a cationic electrodeposition coating and applying a voltage, and a water washing step of washing the coated object obtained by the electrodeposition coating step, By using a low solid content type as the cationic electrodeposition paint and removing at least a part of the undeposited paint by changing the rocking and / or angle before washing the object from the electrodeposition bath with water, Cationic electrodeposition coating method characterized by shortening the process or reducing the amount of washing water used.   The water washing step includes a primary water washing step in which water is washed with an ultrafiltrate of a cationic electrodeposition paint, and a secondary water washing step in which final washing is performed using water such as ion exchange water, pure water, or industrial water. The method of cationic electrodeposition coating according to claim 1.   The cationic electrodeposition coating method according to claim 1, wherein the cationic electrodeposition coating material has a solid content of 10 to 18% by weight.   The cationic electrodeposition coating method according to claim 1, wherein the cationic electrodeposition coating material has a solid content of 0.5 to 9.0% by weight.   When the electrodeposition-coated object obtained by immersing the object in the cationic electrodeposition paint and applying a voltage is washed with water, the cationic electrodeposition paint is made into a low solid content type and the object to be coated is Shorten the water washing process after electrodeposition coating or reduce the amount of water used for washing by removing at least part of the undeposited paint by changing the swing and / or angle before washing from the electrodeposition bath. how to.   The water washing step includes a primary water washing step in which water is washed with an ultrafiltrate of a cationic electrodeposition paint, and a secondary water washing step in which final washing is performed using water such as ion exchange water, pure water, or industrial water. The method of claim 3 comprising:   The method according to claim 5, wherein the cationic electrodeposition paint has a solid content of 10 to 18% by weight.   The method according to claim 5, wherein the cationic electrodeposition coating material has a solid content of 0.5 to 9.0% by weight.

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