JP2006002216A - Washing water to ultrafiltration equipment for cation electrodeposition coating material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a simple and effective washing water as washing water to ultrafilter used for the reutilization of a cation electrodeposition coating material. <P>SOLUTION: The washing water to ultrafiltration equipment for a cation electrodeposition coating material is used when the ultrafiltration equipment for filtering the cation electrodeposition coating material is washed, and comprises a neutralizing acid for the cation electrodeposition coating material and a metal chelating agent. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to washing water used for ultrafiltration treatment of a cationic electrodeposition coating bath in a cationic electrodeposition coating system. In particular, the present invention relates to washing water for an ultrafiltration device for cationic electrodeposition paints.

  Cars and many metal products are painted to improve rust prevention and appearance. In that case, a cationic electrodeposition coating is generally applied as a primer coating. Cationic electrodeposition coating is a method of coating with a water-based paint containing a cationic resin composition, and is widely used as an undercoating method for conductive objects to be coated including automobile bodies due to its high rust prevention property.

  In the cationic electrodeposition coating, as shown in FIG. 1, the coating material 1 is deposited on the surface of the coating object 1 by immersing the coating object 1 in the cationic electrodeposition bath 2 and applying a voltage. Generally, the coating material of the electrodeposition bath 2 is sent to a filter 4 through a pump 3 to separate coarse solids. Thereafter, it is sent to an ultrafilter (UF) 5 for processing, and the filtrate is used as washing water in a washing bath, and the solid content is sent again to the electrodeposition bath 2 because it contains pigments and active components of the electrodeposition bath. Reused.

  Ultrafilters used for filtration of electrodeposition baths are clogged when used, so they have been washed with an acid used as a neutralizing acid for cationic electrodeposition paints, such as water containing acetic acid or lactic acid. . When used for a long period of time, inorganic salts that cannot be removed by washing with these weak acids accumulate in the ultrafilter. Nitric acid, one of the strong acids, is sometimes used to clog the ultrafilter. Excluded.

  However, when nitric acid, which is such a strong acid, is used, the clogging of the ultrafilter can be easily removed. However, since it is a strong acid, the ultrafilter may be damaged. . Therefore, there has been a demand for a method of cleaning the ultrafilter by a simple method without damaging the ultrafilter.

  In particular, in recent years, lead-free cationic electrodeposition coatings have been adopted, and lead ions in the electrodeposition bath have become extremely low at 100 ppm or less. However, lead impurities from other routes are present in the electrodeposition bath. When the amount of lead is large, phosphoric acid, which was used in the chemical conversion treatment performed in the pretreatment process of electrodeposition coating, is brought into the electrodeposition bath, and this phosphoric acid reacts with lead and immediately becomes lead phosphate. Since it was insolubilized and easily removed by a normal filter (filter 4 in FIG. 1), it rarely reached the ultrafilter. However, since lead-free cationic electrodeposition coatings have been used as described above, the amount of lead ions is reduced, so that it does not immediately insolubilize with phosphoric acid and slowly crystallizes over a long period of time. As a result, it is recognized that it cannot be removed by a normal filter and reaches the ultrafilter, which causes clogging.

  In JP-A-60-204898 (Patent Document 1), as described above, ultrafiltration that performs both treatment with an organic acid such as acetic acid and lactic acid and treatment with a strong inorganic acid such as hydrochloric acid and nitric acid. The method of recovery of the vessel is described. Of course, this method has a sufficient cleaning ability and is excellent. However, as described above, if a strong acid such as nitric acid or hydrochloric acid is used, the ultrafilter itself may be damaged.

  Japanese Patent Application Laid-Open No. 9-75685 (Patent Document 2) similarly describes a method for recovering the function of an ultrafilter by backwashing the filtrate by backflowing and then backwashing with pure water. ing. This method is cleaning by a physical method, but what is still not removed is deposited.

Japanese Patent Laid-Open No. 60-204898 JP-A-9-75685

  An object of the present invention is to provide cleaning water that does not damage an electrodeposition filter without using a strong acid such as nitric acid.

  That is, the present invention is a washing water used when washing an ultrafiltration device for filtering a cationic electrodeposition paint, and the washing water contains a neutralizing acid and a metal chelating agent for the cationic electrodeposition paint. Provided is a washing water for an ultrafiltration device for cationic electrodeposition paints.

  The neutralizing acid for the cationic electrodeposition coating used in the washing water is generally an organic acid such as formic acid, acetic acid, lactic acid or sulfamic acid.

The chelating agents include EDTA (ethylenediaminetetraacetic acid), NTA (nitrilotriacetic acid), HEDTA (hydroxyethylethylenediaminetriacetic acid), HEDP (hydroxyethylidene diphosphate), NTMP (nitrilotris (methylenephosphoric acid)), PBTC ( Phosphonobutanetricarboxylic acid) and a mixture of two or more thereof.
The present invention also provides a method for cleaning an ultrafiltration device using the above-described cleaning water.

  According to the present invention, clogging of the ultrafiltration device can be effectively and prevented for a long time. Moreover, there is almost no damage of the electrodeposition apparatus by this washing water. In addition, the cleaning method of the ultrafiltration apparatus using the cleaning water is an effective method that is easy to handle and can be easily implemented without requiring a large preparation.

  The present invention will be described in more detail with reference to the drawings. FIG. 1 is a schematic diagram showing the location of the ultrafiltration apparatus of the present invention. FIG. 2 is a schematic diagram for explaining a cleaning method using the cleaning water of the present invention.

  A part of the electrodeposition bath 2 is sent to a general filter 4 by a pump 3. Unlike the ultrafiltration device 5 for microfiltration, this filter 4 is generally for removing coarse solids. In the electrodeposition coating bath, there is a possibility that a large amount of solids, metal pieces, etc. may be mixed from the outside, and these are removed by this filter 4.

  The size of the solid removed by the filter 4 is 50 μm or more, preferably 25 μm or more.

  The electrodeposition paint from which such a large solid material has been removed is further sent to an ultrafiltration device 5 (denoted as UF in FIG. 1). The ultrafiltration device is a precise filtration device, and the heating residue is separated into a filtrate of about 0.5 to 0.7% by weight and a solid content excluding the filtrate. The solid content contains pigments and those necessary for electrodeposition paints and is returned to the electrodeposition bath. The filtrate is an aqueous solution containing about 0.5 to 0.7% by weight of a heating residue containing a water-soluble solvent, a neutralizing acid, a metal ion, a low-molecular resin, and the like. In general, this is sent to a washing tank to be used for washing an electrodeposited object.

  If the ultrafilter is used for a certain period of time, there is a possibility of clogging, so this device is removed and washing with washing water is performed. Further, as shown in FIG. 2, the cleaning water may be circulated using the pump 9 by closing the electrodeposition bath side and opening the cleaning storage tank 8 side by valves 6 and 7.

  In this invention, it is invention of the washing water used for the washing | cleaning. As the washing water, pure water is mainly used, but in the present invention, it contains the neutralizing acid and the chelating agent used in the electrodeposition paint. The respective amount is 2 to 30% by weight, preferably 5 to 20% by weight of the neutralizing acid. A chelating agent is 0.02 to 3 weight%, More preferably, it is 0.1 to 2 weight%. If the neutralized acid is less than 2% by weight, the ability to remove organic deposits is low. On the other hand, if it is more than 30% by weight, the acid cleaning ability is saturated and the working environment is deteriorated by the acid vapor. When the chelating agent is less than 0.02% by weight, the cleaning is not sufficiently performed, and accumulation of impurities that cannot be removed by several uses occurs. Even if it exceeds 3% by weight, there is no significant change in the cleaning effect, which is wasted.

  About 5 to 10% by weight of butyl cellosolve (ethylene glycol monobutyl ether) may be added to the cleaning liquid as a solvent. The solvent can remove organic substances more effectively.

  The neutralizing acid used for the electrodeposition coating is generally a neutralizing acid used for the cationic electrodeposition coating, and examples thereof include formic acid, acetic acid, lactic acid, sulfamic acid, and mixtures thereof.

  The chelating agent may be one generally known to those skilled in the art as a metal chelating agent, such as EDTA (ethylenediaminetetraacetic acid), NTA (nitrilotriacetic acid), HEDTA (hydroxyethylethylenediaminetriacetic acid), HEDP (hydroxyl). It is selected from the group consisting of ethylidene diphosphate), NTMP (nitrilotris (methylene phosphate)), PBTC (phosphonobutane tricarboxylic acid) and mixtures of two or more thereof. Salts of these chelating agents such as sodium salts and ammonium salts can be used equally. Of course, it is not limited to these. These chelating agents can be dissolved and removed by chelating a metal component present in the ultrafilter.

  Here, the content of the composition of the cationic electrodeposition paint will be described. The cationic electrodeposition paint includes a cationic epoxy resin, a curing agent and a pigment.

Cationic Epoxy Resin The cationic epoxy resin used in the present invention includes an amine-modified epoxy resin. The cationic epoxy resin may be a known resin described in JP-A Nos. 54-4978 and 56-34186.

  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).

  An oxazolidone ring-containing epoxy resin as described in the formula of the Japanese Patent Application Laid-Open No. 5-306327, paragraph 0004, Chemical Formula 3, 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 this oxazolidone ring-containing epoxy resin are described, for example, in paragraphs 0012 to 0047 of JP-A No. 2000-128959.

  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.

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

Curing Agent The polyisocyanate used in the curing agent of the present invention 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 weight, preferably 40 to 70% by weight of the total solid content of the electrodeposition coating composition. The

The pigment electrodeposition coating composition generally contains a pigment as a colorant. The electrodeposition coating composition of the present invention also contains a commonly used pigment. Examples of such pigments include colored pigments such as titanium white, carbon black and bengara, extender pigments such as kaolin, talc, aluminum silicate, calcium carbonate, mica, clay and silica, zinc phosphate, iron phosphate, Rust preventive pigments such as aluminum phosphate, calcium phosphate, zinc phosphite, zinc cyanide, zinc oxide, aluminum tripolyphosphate, zinc molybdate, aluminum molybdate, calcium molybdate and aluminum phosphomolybdate, aluminum phosphomolybdate Etc.

  The pigment is generally contained in the electrodeposition coating composition in an amount occupying 1 to 35% by weight, preferably 15 to 30% by weight of 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 advance in an aqueous medium at a high concentration to form a paste. This is because the pigment is in a powder form, and it is difficult to disperse in a single step in a low concentration uniform state used in the electrodeposition coating composition. Such a paste is generally called a pigment dispersion paste.

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

Electrodeposition Coating Composition The cationic electrodeposition coating composition used in the present invention is prepared by dispersing a cationic epoxy resin, a curing agent, a neutralizing agent and a pigment dispersion paste in an aqueous medium containing a neutralizing agent. .

  Specifically, a predetermined amount of the above-described cationic epoxy resin and a curing agent are mixed in advance and uniformly mixed, and then the mixture is dispersed in an aqueous medium containing a neutralizing agent to obtain a cationic epoxy resin. An emulsion (hereinafter referred to as “main emulsion”) of a mixture of a curing agent and a curing agent is obtained.

  Next, a predetermined amount of the main emulsion, pigment dispersion paste and ion-exchanged water are blended and mixed to obtain the cationic electrodeposition coating composition of the present invention.

  However, the method for producing the emulsion of the cationic epoxy resin and the curing agent is not limited to the above method. For example, the above components may be separately emulsified or after all the above components are mixed. It may be emulsified.

  The amount of the curing agent may be an amount sufficient to react with an active hydrogen-containing functional group such as an amino group or a hydroxyl group in the cationic epoxy resin during heat curing to give a good cured coating film. Generally, the weight ratio of the cationic epoxy resin to the curing agent is 90/10 to 50/50, preferably 80/20 to 65/35.

  The pigment dispersion paste is blended so that the pigment is 1 to 35% based on the total resin solid weight in the cationic electrodeposition coating.

  The cationic electrodeposition coating composition used in the present invention can contain a tin compound such as dibutyltin dilaurate and dibutyltin oxide, and a usual urethane cleavage catalyst. The addition amount is preferably 0.1 to 5.0% by weight of the block polyisocyanate curing agent.

  In addition, the cationic electrodeposition coating composition used in the present invention may contain conventional coating additives such as a water-miscible organic solvent, a surfactant, an antioxidant, and an ultraviolet absorber.

  The invention is explained in more detail by means of examples. The present invention should not be construed as being limited to these examples.

Examples 1-4 and Comparative Examples 1-2
An aqueous solution containing lead ions and phosphate ions that could cause clogging was prepared, and a chelating agent was added thereto to observe that precipitation was suppressed.

In 1 liter of an aqueous solution adjusted to pH 6 with acetic acid, lead ion (Pb ²⁺ ) was adjusted to a concentration of 60 ppm in the form of lead acetate, and phosphate ion (PO ₄ ³⁺ ) was adjusted to a concentration of 20 ppm in the form of sodium dihydrogen phosphate. . Separately, an aqueous chelating agent solution (EDTA-2Na aqueous solution 0.01 mol / L; 3,400 ppm) was prepared, and this chelating agent aqueous solution was added to the above aqueous solution containing lead ions and phosphate ions in the amounts shown in Table 1 (implementation). 20 ml for Example 1, 10 ml for Example 2, 4 ml for Example 3, and 2 ml for Example 4), and the state of the aqueous solution was visually observed. The results are shown in Table 1.

  As Comparative Example 1, a sample in which no aqueous chelating agent solution was added was also visually observed. The results are shown in Table 1. Further, as Comparative Example 2, visual observation was similarly performed for the case where 70% by weight acetic acid water was added in an amount of 10 ml instead of the chelating agent. The results are shown in Table 1.

  As is clear from the above examples, it can be seen that the precipitate formed in the aqueous solution containing lead ions and phosphate ions is dissolved by adding a chelating agent. On the other hand, Comparative Example 1 does not contain a chelating agent and naturally precipitates. In Comparative Example 2, it can be seen that the precipitate does not dissolve even when acetic acid, which is the neutralizing acid of the electrodeposition paint, is added at a high concentration. As a result, by adding a chelating agent to normal washing water (an aqueous solution containing a neutralized acid for electrodeposition paints), the precipitate (lead phosphate) was re-dissolved, and the ultrafilter It can be understood that the cleaning is sufficiently performed.

Example 5 and Comparative Example 3
The actual soiled ultrafilter (Polytex ED-500HK, membrane area 5 m ² ) was washed with washing water having the following composition.
Ingredient Example 5 Comparative Example 3
(Parts by weight) (parts by weight)
EDTA-2Na 0.1 0
Acetic acid 10.0 10.0
Butyl cellosolve 5.0 5.0
Pure water 84.5 85.0
100.0 100.0

  Washing was carried out at room temperature for 24 hours, and then rinsed with pure water. In the circulation washing, 10 liters (L) of the washing water was prepared, and this was circulated through the ultrafilter at a rate of 20 L / min with a pump. The experimental apparatus used is shown in FIG. The cleaning effect of the ultrafilter was evaluated. The washing effect was judged by the amount of filtrate collected before and after washing. The results are shown in Table 2.

  As a result, it was found that the cleaning of the ultrafilter is particularly effective with the cleaning water containing the chelating agent (Example 5), but the cleaning effect cannot be expected when the cleaning water does not include the chelating agent ( Comparative Example 3).

FIG. 1 is a schematic diagram showing the location of the ultrafiltration apparatus of the present invention. FIG. 2 is a schematic diagram for explaining a cleaning method using the cleaning water of the present invention. FIG. 3 is a schematic view showing an experimental apparatus used in an example of the cleaning method of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Coating object 2 ... Electrodeposition bath 3 ... Pump 4 ... Filter 5 ... Ultra filter 6 ... Valve 7 ... Valve 8 ... Washing water storage Tank 9 ... Pump

Claims (4)

  Washing water used when washing an ultrafiltration device for filtering cationic electrodeposition paint, characterized in that the washing water contains a neutralizing acid and a metal chelating agent for cationic electrodeposition paint Washing water for ultrafiltration equipment for cationic electrodeposition paints.   The washing water according to claim 1, wherein the neutralizing acid is formic acid, acetic acid, lactic acid or sulfamic acid.   Chelating agents include EDTA (ethylenediaminetetraacetic acid), NTA (nitrilotriacetic acid), HEDTA (hydroxyethylethylenediaminetriacetic acid), HEDP (hydroxyethylidene diphosphate), NTMP (nitrilotris (methylenephosphoric acid)), PBTC (phosphine). 2. Washing water according to claim 1 selected from the group consisting of phonobutanetricarboxylic acid) and mixtures of two or more thereof. The washing | cleaning method of the ultrafiltration apparatus which wash | cleans the ultrafiltration apparatus for filtering a cationic electrodeposition coating material using the washing water in any one of Claims 1-3.

Images