JP2002294493A - Method for preventing electrodeposition coating apparatus from corrosion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for preventing an electrodeposition coating apparatus from corrosion without causing any problems in performance of the coating, and a composition of less corrosive electrodeposition paint. SOLUTION: The method for preventing a composing metal of a circulation way in the electrodeposition coating apparatus comprises adding molybdate ions of 5-500 ppm in the lead-free electrodeposition paint. The above method further comprises adding molybdate based pigment in the electrodeposition paint, which can supply molybdate ions through the elution. The composition of the cationic electrodeposition paint superior in a corrosion preventing property for the circulation way of the electrodeposition coating apparatus, which includes molybdate based pigment of 0.01-1.0 wt.% in the electrodeposition paint.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing corrosion of a paint circuit in lead-free cationic electrodeposition coating and a cationic electrodeposition paint composition which does not cause corrosion in the paint circuit.

[0002]

2. Description of the Related Art In electrodeposition coating, a foreign matter removing filter (generally, a wire mesh filter for removing coarse dust) is generally used to remove foreign matter generated in a coating liquid in an electrodeposition tank as the operation is continued. (Including a Knoe filter for removing fine dust). This circuit becomes corrosive to the inner surfaces of the piping, especially the welds, during prolonged use. In order to prevent this corrosion, the addition of a corrosion inhibitor was examined, but the corrosion could not be sufficiently prevented.

[0003]

An object of the present invention is to provide a method for protecting a metal constituting an electrodeposition paint circulation circuit from corrosion without causing problems such as repelling of a paint film, and a method for preventing corrosion of the electrodeposition paint circulation circuit. It is an object of the present invention to provide a lead-free electrodeposition coating composition having excellent properties.

[0004]

According to the present invention, molybdate ions are introduced into a lead-free cationic electrodeposition coating bath in an amount of 5 to 500 p.
The present invention relates to a method for preventing corrosion of metals constituting a circuit for circulating an electrodeposition paint, characterized in that the metal is added so as to be pm. In one embodiment, the present invention relates to the above-described corrosion prevention method, wherein molybdate ions are supplied by blending a molybdate-based pigment capable of eluting molybdate ions into an electrodeposition paint. In particular, the present invention relates to the above corrosion prevention method, wherein the metal constituting the electrodeposition paint circulation circuit is iron. The present invention also relates to a lead-free cationic electrodeposition coating composition containing a molybdic acid-based pigment in an amount of 0.01 to 1.0% by weight in the electrodeposition coating composition and having excellent anti-corrosion properties in an electrodeposition coating circuit. .

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, molybdate ions are added in an amount of 5 to 500 ppm in an electrodeposition coating bath in order to prevent corrosion of the electrodeposition coating circuit. Preferably, it is added so as to be 50 to 200 ppm. As for molybdate ion, a compound capable of eluting molybdate ion may be directly added to the electrodeposition coating bath. It is convenient to mix it in the coating composition. As the pigments capable of eluting molybdate ions, zinc molybdate-based rust preventive pigments, calcium molybdate-based rust preventive pigments, aluminum molybdate-based rust preventive pigments, and the like can be used. Specifically, "SHE
R-WHITE 101 ed plus "(trade name, manufactured by Sherwin Williams KK)," SHER-W
HITE 501 "(manufactured by Sherwin Williams KK; trade name) and the like. These pigments are contained in the electrodeposition coating composition in an amount of 0.01 to 1% by weight, preferably 0.01% by weight.
It is blended in the range of 5 to 0.3% by weight.

[0006] In the present invention, the electrodeposition paint circulation circuit refers to a coating liquid which is introduced to the outside of the electrodeposition tank in order to remove foreign substances (eg, solidified solids of paint components) accumulated in the electrodeposition tank. 1 includes a wire mesh filter chamber 2, a CP filter chamber 3, and a pipe 4 connecting the electrodeposition tank 1, the wire mesh filter chamber 2, and the CP filter chamber 3, as shown in FIG. It becomes. The CP filter is a filter provided with a Knoe filter in order to remove finer foreign substances or coarse particles, and the Knoe filter installed therein is a filter for removing a micron-order foreign substance. Here, the metal constituting the electrodeposition paint circulation circuit is a metal constituting the above-mentioned circulation circuit, and specifically includes iron and the like.

The electrodeposition paint which can be used in the present invention is a lead-free cationic electrodeposition paint. In the present invention, “lead-free” means that it contains substantially no lead, and that it does not contain lead in an amount that adversely affects the environment. Specifically, the concentration of the lead compound in the electrodeposition bath is 50 ppm, preferably 20 ppm.
It means that lead is not contained in an amount exceeding pm.

[0008] The cationic electrodeposition coating composition of the present invention contains various additives such as a binder, a pigment, a solvent and a corrosion resistance imparting agent in an aqueous medium. The binder contains a cationic resin having a functional group and a curing agent for curing the resin.

In the present invention, a cationic epoxy resin is used as a cationic resin, in which an active hydrogen compound such as an amine is reacted with an epoxy ring of the epoxy resin, and the epoxy group is opened to introduce a cationic group. A blocked polyisocyanate in which isocyanate groups of the polyisocyanate are blocked is used.

Cationic Epoxy Resin The cationic epoxy resin used in the present invention includes an epoxy resin modified with an amine. This cationic epoxy resin is disclosed in JP-A-54-4978 and JP-A-56-3974.
A known resin described in, for example, Japanese Patent No. 4186 may be used.

[0011] The cationic epoxy resin is typically
All of the epoxy ring of the bisphenol type epoxy resin is opened with an active hydrogen compound capable of introducing a cationic group,
Alternatively, it is produced by opening a part of the epoxy ring with another active hydrogen compound 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. The former commercial product is Epikote 828
(Yuika Shell Epoxy Co., epoxy equivalent 180 ~ 19
0), epicoat 1001 (same as above, epoxy equivalent 450-
500), Epicoat 1010 (same epoxy equivalent 30)
00-4000), and the latter commercially available products include Epicoat 807 (same as above, epoxy equivalent: 170).

JP-A-5-306327, No. 0004
An oxazolidone ring-containing epoxy resin as described in the formula in the paragraph, 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 blocked polyisocyanate and a polyepoxide blocked with a lower alcohol such as methanol are heated and maintained in the presence of a basic catalyst to reduce the by-produced lower alcohol. It is obtained by distilling off from the system.

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

It is known that the reaction of a bifunctional epoxy resin with a diisocyanate blocked with a monoalcohol (ie bisurethane) results in an epoxy resin containing an oxazolidone ring. Specific examples and production methods of this oxazolidone ring-containing epoxy resin are described, for example, in JP-A-2000-128959, 0012 to 0.
It is described in paragraph 047.

[0017] These epoxy resins may be modified with suitable resins such as polyester polyols, polyether polyols, and monofunctional alkylphenols. Further, the epoxy resin can be chain-extended by utilizing a reaction between an epoxy group and a diol or dicarboxylic acid.

[0018] These epoxy resins are used after 0.3 to 0.3 ring opening.
It is desirable to open the ring with an active hydrogen compound such that the amine equivalent is 4.0 meq / g, more preferably 5 to 50% of which is occupied by a primary amino group.

Examples of the active hydrogen compound capable of introducing a cationic group include primary amine, secondary amine, and tertiary amine acid salts.
There are sulfide 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. In addition to salts and mixtures of diethyl disulfide and acetic acid, there are secondary amines in which primary amines such as aminoethylethanolamine ketimine and diethylenetriamine diketimine are blocked. The amines may be used in combination of two or more.

Curing agent The polyisocyanate used in the curing agent of the present invention is:
A compound having two or more isocyanate groups in the molecule. As the polyisocyanate, for example, aliphatic,
Any of alicyclic, aromatic and aromatic-aliphatic systems may be used.

Specific examples of the polyisocyanate include aromatic diisocyanates such as tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), p-phenylene diisocyanate, and naphthalene diisocyanate; hexamethylene diisocyanate (HDI); Aliphatic diisocyanates having 3 to 12 carbon atoms, such as 1,4-trimethylhexane diisocyanate and lysine diisocyanate; 1,4-cyclohexane diisocyanate (CDI), isophorone diisocyanate (IPDI), 4,4′-dicyclohexylmethane diisocyanate (water MDI), methylcyclohexane diisocyanate, isopropylidene dicyclohexyl-4,4'-diisocyanate, and 1,3
-Diisocyanatomethylcyclohexane (hydrogenated XD
I), C5-C18 such as hydrogenated TDI, 2,5- or 2,6-bis (isocyanatomethyl) -bicyclo [2.2.1] heptane (also referred to as norbornane diisocyanate), and the like. Aliphatic diisocyanates having an aromatic ring such as xylylene diisocyanate (XDI) and tetramethyl xylylene diisocyanate (TMXDI); modified products of these diisocyanates (urethane compounds, carbodiimides, uretdione, uretimines, Viewlets and / or
Or isocyanurate modified product); These can be used alone or in combination of two or more.

The polyisocyanate is ethylene glycol, propylene glycol, trimethylolpropane,
Polyhydric alcohols such as hexanetriol and NCO / O
An adduct or prepolymer obtained by reacting at an H ratio of 2 or more may also be used as a curing agent.

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

As the blocking agent, low-temperature curing (160 ° C.)
Below), lactam blocking agents such as ε-caprolactam, δ-valerolactam, γ-butyrolactam and β-propiolactam, and formaldoxime, acetoaldoxime, acetoxime, methylethylketoxime, diacetylmonooxime It is preferable to use an oxime blocking agent such as cyclohexane oxime.

The binder containing the cationic epoxy resin and the curing agent generally contains 2% of the total solid content of the electrodeposition coating composition.
It is contained in the electrodeposition coating composition in an amount occupying 5 to 85% by weight, preferably 40 to 70% by weight.

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 color pigments such as titanium white, carbon black and red iron,
Extenders such as kaolin, talc, aluminum silicate, calcium carbonate, mica, clay and silica, zinc phosphate, iron phosphate, aluminum phosphate, calcium phosphate, zinc phosphite, zinc cyanide, zinc oxide, tripolyphosphoric acid Rust preventing pigments such as aluminum, zinc molybdate, aluminum molybdate, calcium molybdate, aluminum phosphomolybdate, and zinc aluminum phosphomolybdate.

The pigment is generally contained in the electrodeposition coating composition in an amount of 1 to 35% by weight, preferably 15 to 30% by weight of the total solids of the electrodeposition coating composition.

When a pigment-dispersed paste pigment is used as a component of an electrodeposition coating material, the pigment is generally dispersed in an aqueous medium at a high concentration in advance to form a paste.
This is because, since the pigment is in a powder form, it is difficult to disperse the pigment in a low concentration uniform state used in the electrodeposition coating composition in one step. Generally, such a paste is 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-dispersing resin, a cationic or nonionic low-molecular-weight surfactant or a cationic polymer such as a modified epoxy resin having a quaternary ammonium group and / or a tertiary sulfonium group is generally used. As the aqueous medium, ion exchange water, water containing a small amount of alcohols, or the like 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 paint composition The cationic electrodeposition paint composition used in the present invention is a pigment dispersion containing a cationic epoxy resin, a blocked polyisocyanate curing agent, a neutralizing agent and a molybdate-based pigment capable of eluting molybdate ions. It is prepared by dispersing a paste in an aqueous medium containing a neutralizing agent.

Specifically, a predetermined amount of the above-mentioned cationic epoxy resin and the blocked polyisocyanate curing agent are blended and uniformly mixed.
The emulsion is dispersed in an aqueous medium containing a neutralizing agent to obtain an emulsion of a mixture of a cationic epoxy resin and a blocked polyisocyanate curing agent (hereinafter referred to as a main emulsion).

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

However, the method for producing an emulsion of a cationic epoxy resin and a blocked polyisocyanate curing agent is as follows.
The method is not limited to the method described above. For example, the above three components may be separately emulsified, or all three components may be mixed and then emulsified.

The amount of the above-mentioned blocked polyisocyanate curing agent is sufficient to give a good cured coating film by reacting with an active hydrogen-containing functional group such as an amino group or a hydroxyl group in the above-mentioned cationic epoxy resin during curing by heating. The amount is generally 90/10 to 50/50, preferably 80/20 in terms of the solid content weight ratio of the cationic epoxy resin to the blocked polyisocyanate curing agent.
~ 65/35.

The above-mentioned pigment dispersion paste is blended so that the above-mentioned pigment accounts for 1 to 35% with respect to the total resin solid content in the cationic electrodeposition paint.

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 above-mentioned blocked polyisocyanate curing agent.

The cationic electrodeposition coating composition used in the present invention comprises a water-miscible organic solvent, a surfactant, an antioxidant,
Conventional paint additives such as UV absorbers can be included.

[0039]

The present invention will be described in more detail and specifically with reference to the following examples.

[Preparation of Cationic Electrodeposition Coating Liquid] Production Example 1 Production of Amine-Modified Epoxy Resin A flask equipped with a stirrer, a cooler, a nitrogen injection tube, a thermometer and a dropping funnel was prepared. 2 in this flask
4- / 2,6-tolylene diisocyanate (weight ratio = 8
/ 2) 54.0 g, methyl isobutyl ketone (hereinafter MI)
136 g) and 0.5 g of dibutyltin dilaurate were added thereto, and methanol was added thereto with stirring.
0.9 g was further added dropwise. The reaction was started at room temperature and heated to 60 ° C. due to exotherm. Thereafter, after continuing the reaction for 30 minutes, 54 g of ethylene glycol mono-2-ethylhexyl ether was dropped from the dropping funnel over 1 hour. The reaction was performed mainly in the range of 60 to 65 ° C., and was continued until the isocyanate group disappeared while measuring the IR spectrum.

Next, 285.0 g of an epoxy resin having an epoxy equivalent of 950 synthesized from bisphenol F and epichlorohydrin was added, and the temperature was raised to 125 ° C. afterwards,
0.62 g of benzyldimethylamine was added and reacted until the epoxy equivalent became 1120. During that time, methanol produced as a by-product was distilled off using a decanter. Then cool down,
29.1 g of diethanolamine, 21.5 g of N-methylethanolamine and 32.9 g of ketiminated aminoethylethanolamine (79% by weight MIBK solution)
And reacted at 110 ° C. for 2 hours. After that, MIB
The mixture was diluted with K to a nonvolatile content of 80% to obtain an amine-modified epoxy resin.

Production Example 2 Blocked Polyisocyanate Hard
Preparation of Agent In a flask equipped with a stirrer, condenser, nitrogen inlet tube, thermometer and dropping funnel, 206 g of 2,5- and 2,6-bis (isocyanatomethyl) -bidiclo [2,2,1] heptane 206 g (Nonvolatile content 50%), 95.2 g of MIBK and 0.02 g of dibutyltin dilaurate were weighed, and 7
The temperature was raised to 0 ° C. After dissolving uniformly, 174 g of methyl ethyl ketoxime was added dropwise over 2 hours. After completion of the dropwise addition, the reaction was continued until the isocyanate group disappeared by IR analysis while maintaining the reaction temperature at 70 ° C. to obtain a blocked polyisocyanate curing agent.

Production Example 3 The amine-modified epoxy resin obtained in Production Example 1 and Production Example 2
7 with the blocked polyisocyanate curing agent obtained in
The mixture was mixed at 0:30. Then 90% in advance
The mixture obtained above was added to ion-exchanged water to which acetic acid was added to obtain an emulsion. The neutralization rate at that time is 4
2.5%. Thereafter, MIBK was removed so that the solid content became 36.0%, and a main emulsion was prepared.

Production Example 4 Production of Pigment Dispersion Paste <Preparation of Pigment Dispersion Resin> Stirrer, cooling pipe, nitrogen injection pipe,
A flask equipped with a thermometer and a dropping funnel was prepared. In this flask, add isophorone diisocyanate 22
After adding 2.0 parts and diluting with 39.1 parts of methyl isobutyl ketone, 0.2 parts of dibutyltin laurate was added.
After the temperature was raised to 50 ° C., 131.5 parts of 2-ethylhexanol was dropped from the dropping funnel over 2 hours while stirring while bubbling nitrogen. By appropriately cooling, the reaction temperature was maintained at 50 ° C during this time. As a result, 2-ethylhexanol half-blocked isophorone diisocyanate was obtained. (Solid content 90%)

In a reaction vessel equipped with a stirrer, a cooling pipe and a nitrogen injection pipe, 351.6 parts of Epon 828 (epoxy resin manufactured by Shell Chemical Co., epoxy equivalent 190) and bisphenol A
99.2 parts were charged, heated to 130 ° C. under a nitrogen atmosphere, and 1.41 parts of benzyldimethylamine was added.
By reacting at 0 ° C. for about 1 hour, an epoxy equivalent of 4
Thus, 50 bisphenol A type epoxy resins were obtained.

Next, after the reaction solution was cooled to 140 ° C., 218.3 parts (solid content: 196.5 parts) of 2-ethylhexanol half-blocked isophorone diisocyanate prepared above was added, and kept at 140 ° C. for 1 hour. . Here, dipropylene glycol monobutyl ether 17
The reaction solution was cooled to 100 ° C., and SHP-100 (1- (2-hydroxyethylthio) -2-propanol, manufactured by Sanyo Chemical Co., Ltd.) 408.0 was added.
, 134.0 parts of dimethylolpropionic acid and 144.0 parts of deionized water were added and reacted at 70 to 75 ° C until the acid value became 3.0 or less. By this reaction, a tertiary onium group-containing epoxy resin having a tertiary sulfonium conversion of 70.6% was obtained. This was diluted with 324.8 parts of dipropylene glycol monobutyl ether and 1204.8 parts of ion-exchanged water to obtain an epoxy-based tertiary onium salt-type pigment dispersion resin. (Resin solid content 30%)

<Preparation of Pigment-Dispersed Paste> 400 g of the pigment-dispersed resin obtained above (resin solid content: 120 g), and a prescribed amount of a zinc molybdate-based rust preventive pigment “SHE” for each Example
R-WHITE 101 ed plus "(trade name, manufactured by Sherwin Williams Co., Ltd.), 8 g of carbon black, and 72 g of kaolin were charged into a sand glide mill, and dispersed until the particle size became 10 μm or less, to obtain a pigment dispersion paste.

Example 1 In the above <Preparation of Pigment Dispersion Paste>, a zinc molybdate-based rust preventive pigment “SHER-WHITE 101 ed” was used.
plus ”(Sherwin Williams Co., Ltd.)
A pigment dispersion paste was prepared with the addition amount of (trade name) being 3% by weight based on the total pigment. The pigment dispersion paste 460 is added to 2000 parts of the main emulsion obtained above.
Parts and 1% of dibutyltin oxide based on the solid content, and ion-exchanged water was added to obtain a cationic electrodeposition coating material 1 having a solid content of 20.0%.

Examples 2, 3 Zinc molybdate based rust preventive pigment "SHER-WHITE"
Example 1 except that the pigment dispersion paste was prepared such that the amount of “101 ed plus” (trade name, manufactured by Sherwin Williams Co., Ltd.) was 6% by weight and 10% by weight, respectively, based on all the pigments. In the same manner as in the above, cationic electrodeposition paints 2 and 3 were prepared.

Comparative Example 1 Zinc molybdate rust preventive pigment "SHER-WHITE"
A cationic electrodeposition paint 0 was prepared in the same manner as in Example 1 except that a pigment dispersion paste was prepared without adding "101 ed plus" (trade name, manufactured by Sherwin Williams KK).

[Corrosion test of steel material by each electrodeposition paint] Piping member of SGP10A subjected to welding treatment (weight: 35 g)
Was placed in 3000 ml of each of the cationic electrodeposition coatings 0, 1, 2, and 3 prepared in the examples and comparative examples, and kept at 40 ° C. to test the corrosiveness of the steel material. Corrosion was assessed by weight loss of steel up to 4 weeks. The evaluation results are shown in FIG. Data is the average of two steels. This result shows that adding only 3% by weight of a zinc molybdate anticorrosive pigment capable of dissolving molybdate ions into the pigment gives a remarkable rust-preventive effect, and the addition amount is 6% by weight.
It shows that increasing the content to 10% by weight enhances the rust prevention effect.

[0052]

According to the electrodeposition coating using a lead-free cationic electrodeposition coating, a relatively inexpensive molybdate ion-eluting pigment is blended as a part of the pigment, which adversely affects the formed coating film. The corrosion of the paint circulation circuit can be effectively prevented without giving.

[Brief description of the drawings]

FIG. 1 is a schematic circuit diagram of an electrodeposition paint circulation circuit.

FIG. 2 is a graph showing the results of a corrosion test of the electrodeposition paints of Examples and Comparative Examples.

[Explanation of symbols]

 1: electrodeposition tank, 2: wire mesh filter room, 3: CP filter room, 4: piping.

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Miaki Okumura 19-17 Ikedanakamachi, Neyagawa-shi, Osaka F-term in Japan Paint Co., Ltd. (reference) 4J038 DB391 DG302 HA246 KA05 KA08 KA08 NA03 PA04

Claims (4)

[Claims] 1. A method for preventing corrosion of metals constituting a circuit of an electrodeposition paint circulation circuit, wherein molybdate ions are added to a lead-free cationic electrodeposition paint bath so as to have a concentration of 5 to 500 ppm. 2. The method according to claim 1, wherein the molybdate ions are supplied by blending a molybdate pigment capable of eluting the molybdate ions into the electrodeposition paint. 3. The method for preventing corrosion according to claim 1, wherein the metal constituting the electrodeposition paint circulation circuit is iron. 4. A lead-free cationic electrodeposition coating composition comprising a molybdic acid-based pigment in an amount of 0.01 to 1.0% by weight in the electrodeposition coating composition and having excellent anticorrosion properties in an electrodeposition coating circuit.