JPH09187726A - High corrosion resistance electrodeposition coating film coating - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a highly corrosion-resistant coating material coated with an electrodeposition coating film having sufficient corrosion resistance even if the film thickness is thin. [Structure] A metal material with a film thickness of 5-12 μm and 0.4 μm
Coat an electrodeposition coating having Ra of m or less.

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal-made electrodeposition coating material having a sufficient corrosion resistance even though the film thickness is thinner than usual.

[0002] Electrodeposition paints are widely used as a corrosion-resistant primer coating for coating metal materials such as automobile bodies and parts because they have excellent corrosion resistance and throwing power and form a uniform coating film. By the way, in the conventional methods, a film thickness of 20 μm or more is usually required to secure sufficient corrosion resistance. If sufficient corrosion resistance can be secured even if this film thickness is reduced to about 1/2 of that of the conventional one, not only will the paint consumption be greatly saved, but also the amount of electricity and time will be saved, and resources and energy will be even more efficient. Can be used for

However, if the film thickness is reduced according to the conventional method, the corrosion resistance is remarkably lowered as the coating film becomes thinner. According to the present inventors, the cause of the decrease in corrosion resistance is closely related to the surface roughness of the coating film, that is, if the surface roughness is large, the distance from the substrate to the recessed point of the coating film ( It has been found that the minimum film thickness point) becomes smaller, and at that point, the corrosion accelerating substance passes through the coating film and reaches the interface with the substrate, which easily causes corrosion. Therefore, if the surface roughness is small, it is possible to secure a film thickness sufficient to prevent the passage of the corrosion accelerating substance even at the minimum film thickness point, so that it is possible to reduce the film thickness as a whole. The present invention is based on such knowledge.

DISCLOSURE OF THE INVENTION In the present invention, therefore, the metal material to be protected has a film thickness of 5 to 12 μm and a center line surface roughness Ra of 0.4 μ.
Provided is a highly corrosion-resistant coating formed by coating an electrodeposition coating film having a thickness of m or less, particularly a cationic electrodeposition coating film.

Detailed Discussion Ra measuring method using a stylus type surface roughness measuring device is JIS
B 0651. Ra here is based on this test method.

As described above, according to the conventional method, R
It is difficult to set a to 0.4 μm or less. So R
Special measures are required to set a to 0.4 μm or less. Ra can be generally improved by increasing the heat flow property during baking. However, modifying the coating composition to enhance heat flow should not adversely affect other performance. The following method was found to be effective for that purpose.

A. Adjustment of pigment concentration The paint contains various pigments for the purpose of coloring and anticorrosion. In order to reduce the occurrence of craters due to self-repelling and oil-repelling in electrodeposition coatings, a relatively large amount of extender pigment such as clay is added to rather suppress the flow property. Therefore, it is possible to improve the flowability by suppressing the pigment ratio in the coating film as low as possible within the range where a satisfactory cissing prevention effect is secured. There are a method of lowering the weight ratio (PWC) of the entire pigment in the coating film and a method of lowering the volume ratio (PVC) of the entire pigment in the coating film. PVC can be lowered by using a large amount of pigment having a large specific gravity while keeping PWC constant. Of course, both can be used together. In this case, the range in which the flowability can be improved without adversely affecting the other performances, particularly the cissing resistance, is generally 1 to 25% for PWC, preferably 5 to 15%, and for PVC is 0. 2-15%, preferably 1.
It is 5 to 7%.

B. Use of flow improver or surface smoothness improver In the epoxy cationic electrodeposition coating, a part of the epoxy ring is opened with a hydroxyl compound such as 2-ethylhexanol, nonylphenol or ethylene glycol mono-2-ethylhexyl ether. It is known to obtain cationic resins with improved heat flow properties. In addition, JP-A-5-287223 and JP-A-7-12 of the applicant.
6557 discloses cationic resins that improve the surface smoothness of acrylic and epoxy systems, respectively.
It is also an effective means to add a component capable of improving the flow property or the flatness of the surface to the paint. In particular, JP-A-7
Cationic resins derived from t-alkylphenol novolac epoxy resins disclosed in -126557 are particularly preferred as they can improve surface smoothness without adversely affecting other performances, especially topcoat adhesion.

C. Use of low-viscosity main resin It is natural that low-viscosity resin has good flowability, but since viscosity increases in proportion to the molecular weight, lowering the molecular weight of the main resin generally lowers the mechanical strength of the coating film. It is practically not applicable to the cationic resin of. Japanese Patent Application Laid-Open No. 5-306327 of the present applicant discloses a cationic resin for electrodeposition coating, which is derived from an epoxy resin having a resin skeleton containing an oxolidone ring. This resin has a lower viscosity than conventional epoxy-based cationic resins when compared at the same molecular weight level, so using this resin as the main resin can improve flowability without adversely affecting other properties of the coating film. it can.

D. Use of slow-reactive or low-viscosity curing agent In a cationic electrodeposition coating, a blocked polyisocyanate is mainly used as a curing agent, but a polyisocyanate which is originally in a slow reaction rate in a free form, for example, crude MDI.
It is also effective to select those blocked with (diphenylmethane diisocyanate) or those blocked with a blocking agent having a slow dissociation reaction rate, such as furfuryl alcohol or ethylene glycol monobutyl ether.

It is also an effective method to select a blocked product of a polyisocyanate compound of a type having a low viscosity when mixed with a main resin, for example, a blocked product of hexamethylene diisocyanate monomer. However, whichever method is used, the amount of the curing agent should be such that the active hydrogen of the main resin and the functional group of the curing agent ( The ratio of blocked NCO groups) is 1: 0.3
The ratio should be within the range of ˜1: 2, preferably 1: 0.8 to 1: 1.5.

The methods A to D described above are effective independently, but some of them can be used in combination. Further, the method of controlling Ra to 0.4 μm or less is not limited to these methods, and it goes without saying that the present invention can employ other methods effective for that purpose.

As is apparent from the above description, the subject matter of the present invention is not the electrodeposition coating itself or its composition. Therefore, it does not matter what kind of electrodeposition coating is used, but since it is mainly an epoxy-based cationic electrodeposition coating which is excellent in anticorrosive properties, it is mainly used for automobiles today. However, the present invention can be applied to anion electrodeposition coatings and cationic electrodeposition coatings other than epoxy type, for example, acrylic type and polybutadiene type electrodeposition coatings, and corresponding effects can be obtained.

Cationic Epoxy Resin A cationically modified epoxy resin, which is the main component of the film-forming resin component of the cationic electrodeposition coating composition, is disclosed in JP-A-54-4.
Known resins described in, for example, 978 and 56-34186 are mentioned.

Typically, all of the epoxy rings of the bisphenol type epoxy resin are opened with an active hydrogen compound capable of introducing a cationic group, or some epoxy rings are opened with another active hydrogen compound. , The remaining epoxy ring is opened 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, Epicoat 828
(Yukaka Shell Epoxy Co., Ltd., epoxy equivalent 180-1
90), Epicoat 1001 (the same, epoxy equivalent 450
~ 500), Epicoat 1010 (the same, epoxy equivalent 3
000 to 4000), and the latter commercially available products include Epicoat 807 and (the same, epoxy equivalent 170). It is also possible to start with an epoxy resin containing an oxadridone ring in the chain, as disclosed in the Applicant's JP-A-5-306327. As described above, this resin has a low viscosity and is effective in improving the flowability. These epoxy resins have 0.3 to 4.0 meq / after ring opening.
It is desirable to perform ring opening with an active hydrogen compound so that the amine equivalent of g is obtained.

Examples of active hydrogen compounds capable of introducing a cationic group include acid salts of primary amine, secondary amine and tertiary amine,
Or there is a sulphide / acid mixture. Examples include butylamine, octylamine, diethylamine,
Dibutylamine, methylbutylamine, monoethanolamine, diethanolamine, N-methylethanolamine, triethylamine hydrochloride, N, N-dimethylethanolamine acetate, diethyldisulfide / acetic acid mixture, as well as aminoethylethanolamine ketimine and diethylenetriamine There are secondary amines obtained by blocking primary amines such as diketimine. The amines may be used in combination of two or more.

Other active hydrogen compounds that can be used to open the epoxy ring include phenol, cresol,
Monophenols such as nonylphenol and nitrophenol; hexyl alcohol, 2-ethylhexanol, stearyl alcohol, monobutyl alcohol such as monobutyl- or monohexyl ether of ethylene glycol or propylene glycol; aliphatic monocarboxylic acids such as stearic acid and acetic acid Glycolic acid,
Aliphatic hydroxycarboxylic acids such as dimethylolpropionic acid, hydroxypivalic acid, lactic acid, citric acid; and mercaptoalkanols such as mercaptoethanol.

Curing agent As the curing agent, a melamine resin and a blocked polyisocyanate compound can be used, but a blocked polyisocyanate compound is preferable.

The blocked polyisocyanate compound is an addition reaction product of a theoretical amount of the polyisocyanate compound and an isocyanate blocking agent, and is a curing agent for the main resin. As this polyisocyanate compound,
For example, tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate (MD
I), phenylene diisocyanate, bis (isocyanate methyl) cyclohexane, tetramethylene diisocyanate, hexamethylene diisocyanate, methylene diisocyanate, isophorone diisocyanate, aromatic compounds such as dimers or trimers of these diisocyanate compounds, alicyclic compounds, and aliphatic compounds. Examples thereof include a terminal isocyanate-containing prepolymer obtained by reacting a polyisocyanate compound and an excess amount of these isocyanate compounds with a low-molecular active hydrogen-containing compound such as ethylene glycol, propylene glycol, trimethylolpropane, hexanetriol, and castor oil. Further, the isocyanate blocking agent is one which blocks by adding to the isocyanate group of the polyisocyanate compound. It is important that the blocked polyisocyanate compound formed by addition is stable at room temperature and can dissociate the blocking agent to regenerate a free isocyanate group when heated above the dissociation temperature.

Specifically, phenol-based blocking agents such as phenol, cresol, xylenol, chlorophenol and ethylphenol; ε-caprolactam,
lactam blocking agents such as δ-palerolactam, γ-butyrolactam and β-propiolactam; active methylene blocking agents such as ethyl acetoacetate and acetylacetone; methanol, ethanol, propanol,
Butanol, amyl alcohol, furfuryl alcohol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, propylene glycol monomethyl ether, benzyl alcohol, methyl glycolate, butyl glycolate, diacetone alcohol, lactic acid Alcohol blocking agents such as methyl and ethyl lactate; oxime blocking agents such as formaldoxime, acetoaldoxime, acetoxime, methylethylketoxime, diacetylmonooxime, cyclohexaneoxime; butylmercaptan, hexylmercaptan, t-butylmercaptan, thiophenol. , Methylthiophenol, ethylthiophenol, etc. Mercaptan blocking agent; imide blocking agents such as succinic acid imide and maleic acid imide; acid amide, acid amide blocking agents such as benzamide xylidine, aniline, butylamine, amine blocking agents, such as dibutylamine; imidazole,
Examples thereof include imidazole blocking agents such as 2-ethylimidazole; imine blocking agents such as ethyleneimine and propyleneimine. Of these, oxime-based blocking agents such as methyl ethyl ketoxime are particularly suitable.

The method of controlling Ra to 0.4 or less by selecting the blocked polyisocyanate curing agent has been described above.

A self-crosslinking amine-modified epoxy resin obtained by adding a half-blocked polyisocyanate compound to the secondary hydroxyl group in the chain of the polyepoxy resin and then opening the terminal epoxy ring with an amine or the like is the main resin and crosslinked. You may use it as all or one part of an agent. The self-crosslinking amine-modified epoxy resin is obtained by blocking not all of the isocyanate groups of the polyisocyanate compound with the above-mentioned blocking agent and carrying out an addition reaction between the remaining free isocyanate groups and the secondary hydroxyl groups of the epoxy resin. In the same manner as the main resin, it can be produced by opening the epoxy ring with an active hydrogen compound capable of introducing a cationic group such as amine.

Electrodeposition Coating Composition The electrodeposition coating composition is prepared by dispersing the main resin, the curing agent and, if used, the surface smoothness controlling resin in an aqueous medium containing a neutralizing agent. The surface smoothness control resin is dispersed in an aqueous medium containing a main resin and a cross-linking agent in one place and a neutralizing agent, or is dispersed separately from the main resin by an appropriate cationic resin and then dispersed in a dispersion liquid of the main resin. It can be added and compounded. Neutralizers include hydrochloric acid, nitric acid, phosphoric acid,
It is an inorganic or organic acid such as formic acid, acetic acid, lactic acid.

The amount of crosslinking agent must be sufficient to react with functional groups such as hydroxyl groups in the resin during curing to give a good cured coating, generally 5 to 50% by weight of resin solids.
Is used. The amount of neutralizing agent is sufficient to neutralize at least 20%, preferably 30-60%, of the amino groups of the resin.

The surface smoothness control resin is used in an amount of 0.05 to 30% by weight, preferably 0.5 to 20% by weight, based on the total solid content of the main resin and the curing agent. If this amount is less than 0.05% by weight, the effect of improving the surface smoothness is not obtained, and if it exceeds 30% by weight, the surface smoothness is rather deteriorated.

The electrodeposition coating composition may contain a tin compound such as dibutyltin dilaurate and dibutyltin oxide in a system containing a blocked polyisocyanate, and a usual urethane cleavage catalyst. The amount is usually 0.1 to 5% by weight of the blocked polyisocyanate compound.

The electrodeposition coating composition includes coloring pigments such as titanium dioxide, carbon black and red iron oxide, rust preventive pigments such as basic lead silicate and aluminum phosphomolybdate, extender pigments such as kaolin, clay and talc, and water-miscible pigments. It may contain conventional additives for coatings such as a water-soluble organic solvent, a surfactant, an antioxidant and an ultraviolet absorber. The specific method of controlling the surface smoothness by PWC and PVC has been described above.

Production Example 1 Synthesis of main resin flask equipped with stirrer, condenser, nitrogen injection tube, thermometer and dropping funnel Epoxy equivalent synthesized from bisphenol A and epichlorohydrin 475 parts by weight of epoxy resin 285 parts by weight and epoxy equivalent: 950 Weigh out 380 parts by weight of the epoxy resin of 77 parts by weight of P-nonylphenol and 82 parts by weight of methyl isobutyl ketone.
After raising the temperature and dissolving uniformly, 3.0 g of benzyldimethylamine was added and reacted at a reaction temperature of 150 ° C. until the epoxy equivalent became 1140. Then cool down,
19 parts by weight of diethanolamine, 27 parts by weight of N-methylethanolamine and ketimine compound of aminoethylethanolamine (79% methyl isobutyl ketone solution)
31 parts by weight was added and the reaction was continued at 110 ° C. for 2 hours.
Then, the main resin I was obtained by diluting with methyl isobutyl ketone until the nonvolatile content became 80%.

Production Example 2 Synthesis of Main Resin 54 parts by weight of 2.4 / 2.6-tolylene diisocyanate (80/20 wt ratio) was added to a flask equipped with a stirrer, a cooler, a nitrogen injection tube, a thermometer and a dropping funnel. 136 parts by weight of methyl isobutyl ketone and 0.5 parts by weight of dibutyltin dilaurate were weighed out, and 11 parts by weight of methanol was added dropwise from the dropping funnel over 30 minutes while stirring. The temperature started from room temperature and was raised to 60 ° C. Then, after continuing the reaction for 30 minutes, ethylene glycol mono 2
54 parts by weight of ethylhexyl ether was added dropwise from the dropping funnel over 1 hour. The reaction was carried out mainly while maintaining the temperature in the range of 60 ° C to 65 ° C. The reaction continued until the isocyanate groups disappeared by infrared spectroscopy. Thereafter, 285 parts by weight of an epoxy resin having an epoxy equivalent of 475 and 380 parts by weight of an epoxy resin having an epoxy equivalent of 950, which were synthesized from bisphenol F and epichlorohydrin, were added to a reaction vessel, uniformly mixed, and heated to 120 ° C. 0.62 parts by weight of amine was added, and by-product methanol was distilled off using a decanter and reacted until the epoxy equivalent became 1120. After cooling, 29 parts by weight of diethanolamine, 22 parts by weight of N-methylethanolamine, and 33 parts by weight of a ketimine compound of aminoethylethanolamine (79% methyl isobutyl ketone solution) were added. The reaction is performed at 110 ° C and 2
Allowed to react for hours. Non-volatile content of 8 with methyl isobutyl ketone
The main resin II was obtained by diluting to 0%.

Production Example 3 Synthesis of Hardener I Trimer of hexamethylene diisocyanate (Coronate HX: made by Nippon Polyurethane) in a flask equipped with a stirrer, a cooler, a nitrogen injection tube, a thermometer and a dropping funnel 1
99 g, 32 g of methyl isobutyl ketone and 0.1 g of dibutyltin dilaurate were weighed out and stirred, and while bubbling nitrogen, methyl ethyl ketoxime 87.0 g
Was dropped from the dropping funnel over 1 hour. Temperature is 50 ℃
The temperature was raised to 70 ° C. for the first time. The reaction was continued until the absorption of NCO group disappeared by infrared spectroscopy.

Production Example 4 Synthesis of Hardener II Crude MDI (Coronate 1) was added to a flask equipped with a stirrer, condenser, nitrogen injection tube, thermometer and dropping funnel.
104: made by Nippon Polyurethane) 199 g, methyl isobutyl ketone 32 g and dibutyltin dilaurate 0.
While weighing 1 g, stirring and bubbling nitrogen, 8 g of furfuryl alcohol was added dropwise from a dropping funnel over 1 hour. The temperature started from 50 ° C. and increased to 70 ° C. The reaction was continued until the absorption of NCO group disappeared by infrared spectroscopy.

Production Example 5 Synthesis of surface smoothness control resin P-alkyl substituted phenol novolac type epoxy resin (manufactured by Tohto Kasei Co., Ltd .: epoxy equivalent) : 311, alkyl = t-butyl group, number average molecular weight: 1160) 311 parts by weight, and 96 parts by weight of methyl isobutyl ketone were weighed and heated to 80 ° C. to uniformly dissolve them. After cooling to 40 ° C., 74 parts by weight of N-methylethanolamine was added to the reaction vessel while paying attention to heat generation. Then, the reaction was continued at 80 ° C., and the reaction was continued until the epoxy group disappeared (epoxy equivalent measurement, reaction trace by infrared spectrometer). Further, 114 parts by weight of ε-caprolactone was weighed out, and while continuing to raise the temperature to 120 ° C., 1.141 parts by weight of dibutyltin oxide was added to the reaction vessel and reacted at a reaction temperature of 140 ° C. This was continued until the absorption based on caprolactone (690 cm ^-1 ) disappeared. Then, the mixture was cooled and 29 parts by weight of methyl isobutyl ketone was added to obtain a surface smoothness control resin. Nonvolatile matter: 80.
1%.

Production Example 6 Preparation of Pigment Dispersion Pastes I and II Pigment Dispersion Paste I was prepared by mixing the components in the following composition and pulverizing with a sand grind mill until the particle size became 10 μm or less.
And II were prepared.

[0035] Ingredient I II pigment dispersing resin ^* 125.0 g 125.0 g deionized water 400.0 g 400.0 g carbon black 8.5 g 3.5 g kaolin 172.0 22.0 g titanium oxide 245.0 g 400.0 g phosphorus Aluminum molybdate 75.0 g 75.0 g * Sulfonium salt type, Nippon Paint Co., Ltd., resin solid content 75%

Examples 1 to 6 Main resin / curing agent / surface smoothness control resin were mixed at a solid content ratio in a composition as shown in Table 1, and ethylene glycol monohexyl ether was added at 2 wt% based on the solid content. After adding and neutralizing with glacial acetic acid to a neutralization ratio of 42.5%, it was slowly diluted with ion-exchanged water. This is solid content 3
Methyl isobutyl ketone was removed under reduced pressure so that the concentration became 6.0%. The obtained main elm john, the pigment dispersion paste, and the ion-exchanged water were added in the number of parts by weight shown in Table 1 to prepare a cationic electrodeposition coating composition having a solid content of 20.0%. The prepared coating material was electrodeposited on a zinc phosphate-treated cold-rolled steel sheet to a dry film thickness of 8 μm, and baked at 160 ° C. for 10 minutes. After that, various coating film evaluations were performed. The obtained results are shown in Table 1.

Comparative Examples 1 to 3 Coating materials were prepared in the same manner as in Examples 1 to 6 with the compounding ingredients shown in Table 1, and electrodeposition baking was performed to evaluate the coating films. The obtained results are shown in Table 1.

[0038]

[Table 1]

As can be seen from Table 1, when Comparative Example 1 and Example 4 are compared, the main resins, PVC and PWC are the same, but Example 4 uses slow-acting slow curing agent II. Ra is 0.4 μm or less. Comparing Comparative Example 2 with Example 3, Ra is 0.4 μm or less in Example 3 because the blending amount of the pigment paste I is small and therefore PVC and PWC are small.
In Examples 1 and 2, the compounding amount of the pigment paste was smaller than in Comparative Example 3, and PVC and PWC were small, so that Ra was 0.4 μm or less.

Evaluation method 1) Corrosion resistance A cross-cut flaw was added to the electrodeposition coating film with a knife so as to reach the base material, and a salt spray test (3% saline solution, 35 ° C x 800) was performed.
hr), and the maximum peeling width from the cut portion was measured with an adhesive tape. ○: <3 mm △: 3 to 6 mm ×:> 6 mm 2) Gas pinholes Number of pinholes per 50 cm ² of cured coating film when electrodeposited at 260 V ○: No pinholes △: Less than 10 ×: 10 3) Covering power Techno Cosmos 1993, V issued by Nippon Paint Co., Ltd.
ol. The measurement was carried out using a 4-box throwing power measuring device described on pages 3,44-51. JP-A-7-286297
reference. Unit μm

Claims (7)

[Claims] 1. A highly corrosion-resistant coated product obtained by coating a metal material with an electrodeposition coating film having a film thickness of 5 to 12 μm and a center line average surface roughness Ra of 0.4 μm or less. 2. The coated article according to claim 1, wherein the electrodeposition coating film is a cationic electrodeposition coating film. 3. The pigment weight concentration PWC in the coating film is 1 to 25%.
The coating of claim 2 which is 4. The pigment volume concentration PVC in the coating film is 0.2 to 1.
The coating of claim 2 which is 5%. 5. The coating composition according to claim 2, wherein the cationic electrodeposition coating composition for forming a coating film contains a coating film flowability improving component. 6. The coating according to claim 2, wherein the curing agent of the cationic electrodeposition coating composition forming the coating film is a slow-acting curing agent. 7. A coating film having a film thickness of 5 to 12 μm and a center line average surface roughness Ra of 0.4 μm or less, which is formed by an electrodeposition coating method on an object to be protected. Anticorrosion method for metal coated objects.