JPH09235494A - Cationic electrodeposition coating material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a cationic electrodeposition coating material excellent in weatherability by dispersing a cationic modified epoxy resin and a cross- linker comprising a blocked bicycloalkane polyisocyanate in an aq. medium contg. a neutralizing agent. SOLUTION: This cationic electrodeposition coating material contg. 2.0wt.% or lower org. solvent is obtd. by dispersing 95-45wt.% cationic modified epoxy resin and 5-55wt.% cross-linker in an aq. medium contg. a neutralizing agent (e.g. hydrochloric acid). The modified epoxy resin is prepd. by adding nonylphenol and then an active hydrogen compd. (e.g. diethanolamine) to a bisphenol A epoxy resin, etc., in an org. solvent and thermally reacting those reactants. The cross-linker is prepd. by dissolving dibutyltin dilaurate in a bicycloalkane polyisocyanate [e.g. 2,5- or 2,6-bis(isocyanatomethyl)-bicyclo(2,2,1) heptane] and adding a blocking agent (e.g. methyl ethyl ketoxime) to the polyisocyanate to react them.

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION The present invention relates to a cationic electrodeposition coating composition, and more particularly to a cationic electrodeposition coating composition of the type which forms a cured coating film by crosslinking a cationic modified epoxy resin with a blocked polyisocyanate crosslinking agent.

A cationically modified epoxy resin obtained by ring-opening the epoxy ring of an epoxy resin with a reactive hydrogen compound capable of introducing a cationic group such as an amine and a blocked polyisocyanate as a resin component of a coating film are used as a cationic electrode. The coating material is well known and widely used as a primer for automobile bodies and the like. When a blocked aromatic polyisocyanate is used as a crosslinking agent, the overcoat film turns yellow, so that a non-yellowing polyisocyanate compound is used for applications where it is necessary to avoid it. However, hexamethylene diisocyanate (HMD
I) and other aliphatic polycyanates have insufficient corrosion resistance, and include isophorone diisocyanate (IPDI), hydrogenated tolylene diisocyanate (hydrogenated TDI), hydrogenated diphenylmethane diisocyanate (hydrogenated MDI), hydrogenated xylylene diisocyanate (water). In systems using monocyclic alicyclic polyisocyanates such as XDI), the amount of organic solvent contained in the diluted paint must be relatively large in order to maintain the optimum electrodeposition property, which is a point of environmental pollution. Is not preferable.

According to the present invention, by using a blocked bicycloalkane-based polyisocyanate compound as a cross-linking agent, even if the organic solvent content is relatively small, the electrodeposition property is kept optimum, low temperature curing is possible, and smoothness is obtained. A cationic electrodeposition coating having excellent properties, corrosion resistance, and weather resistance can be obtained.

DISCLOSURE OF THE INVENTION The present invention relates to a cationic electrodeposition coating composition containing a dispersion prepared by dispersing a cationically modified epoxy resin and a crosslinking agent in an aqueous medium containing a neutralizing agent. According to the present invention, a blocked bicycloalkane-based polyisocyanate compound is used as the crosslinking agent.

Bicycloalkane-based polyisocyanate compounds are typically 2,5- or 2,6-bis (isocyanatomethyl) -bicyclo [2.2.1] heptane, their dimers and trimers. Or adducts with aliphatic polyhydric alcohols, which are preferably blocked with oximes or lactams.

Typically, the solids weight ratio of cationically modified epoxy resin to crosslinker in the coating is 95/5 to 45/50, preferably 85/15 to 70/30.
The organic solvent content of the diluted coating (state added to the electrodeposition bath) may be 2.0% by weight or less.

The present invention also relates to a coating method using the above electrodeposition coating material.

Detailed Discussion 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 of the present invention is disclosed in JP-A-54-
Known resins described in, for example, No. 4978 and No. 56-34186 may be used.

Typically, the entire epoxy ring of the bisphenol type epoxy resin is opened with an active hydrogen compound capable of introducing a cationic group, or a part of the epoxy ring is opened with another active hydrogen compound. And 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 oxazolidone ring in the chain, as disclosed in the Applicant's JP-A-5-306327. These epoxy resins have an amine equivalent of 0.3 to 4.0 meq / g after ring opening, more preferably 5 to 50% of them.
It is desirable to open the ring with an active hydrogen compound so that occupies a primary amino group.

As active hydrogen compounds capable of introducing a cationic group, 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; monoalcohols such as hexyl alcohol, 2-ethylhexanol, stearyl alcohol, monobutyl- or monohexyl ether of ethylene glycol or propylene glycol; aliphatic monocarboxylic acids such as stearic acid and octylic acid Acids; aliphatic hydroxycarboxylic acids such as glycolic acid, dimethylolpropionic acid, hydroxypivalic acid, lactic acid and citric acid; and mercaptoalkanols such as mercaptoethanol.

Crosslinking Agent The blocked polyisocyanate crosslinking agent used in the present invention is a bicycloalkane-based polyisocyanate compound whose isocyanate group is blocked with a known blocking agent. When this cross-linking agent is used, there is no overcoat yellowing similar to aliphatic and other alicyclic polyisocyanates, it also has better corrosion resistance than aliphatic polyisocyanates, and less than other alicyclic polyisocyanates. The optimum electrodeposition property can be obtained with the organic solvent content, and a coating having excellent coating film smoothness can be obtained.

A typical example of the bicycloalkane-based polyisocyanate compound is 2,5- or 2,6-bis (isocyanatomethyl) -bicyclo [2.2.1] heptane (also referred to as norbornane diisocyanate).
Their mixtures, dimers (biurets), trimers (isocyanurates), and ethylene glycol,
NCO / with aliphatic polyhydric alcohols such as propylene glycol, trimethylolpropane, and hexanetriol
An adduct or prepolymer obtained by reacting at an OH ratio of 2 or more can be used. Further, the isocyanate blocking agent is one which blocks by adding to the isocyanate group of the polyisocyanate compound. The blocked polyisocyanate compound formed by the addition must be stable at room temperature and capable of dissociating 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, 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, methyl lactate and ethyl lactate. Oxime blocking agents such as formaldoxime, acetoaldoxime, acetoxime, methylethylketoxime, diacetylmonooxime, cyclohexanone oxime; butyl mercaptan, hexyl mercaptan, t-butyl mercaptan, thiophenol, methylthiophenol, Mercaptan-based broth such as ethylthiophenol Click agent; imide blocking agents such as succinic acid imide and maleic acid imide; acid amide, acid amide blocking agents such as benzamide, imidazole type blocking agents such as 2-ethyl imidazole; and the like. Of these, when low temperature curing (100 ° C. or more and 160 ° C. or less) is desired, it is preferable to use lactam-based and oxime-based blocking agents.

Electrodeposition Paint The electrodeposition paint of the present invention is prepared by dispersing the above-mentioned cationically modified epoxy resin and a crosslinking agent in an aqueous medium containing a neutralizing agent. 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 is that which achieves a neutralization of at least 20%, preferably 30-60%.

The amount of crosslinking agent must be sufficient to react with the active hydrogen-containing functional groups such as primary and secondary amino groups and hydroxyl groups in the resin during curing to give a good cured coating, Generally 95/5 to 45/50, preferably 85/1, expressed as a solids weight ratio of resin to crosslinker.
It is in the range of 5 to 70/30.

The electrodeposition paint is dibutyltin dilaurate,
It may include tin compounds such as dibutyltin oxide, and conventional urethane cleavage catalysts. The amount is usually 0.1 to 5% by weight of the blocked polyisocyanate compound.

Electrodeposition paints include coloring pigments such as titanium dioxide, carbon black and red iron oxide, basic lead silicate, rust preventive pigments such as 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. Here, the amount of the organic solvent may be such that its content in the diluted coating material is 2.0% by weight or less. This is an advantage over monocyclic alicyclic isocyanate-based cross-linking agents such as hydrogenated MDI and IPDI in which the amount of solvent must be more than 2.0% by weight in order to keep the electrodeposition property optimal, and the corrosion resistance and low solvent HMDI in terms of compatibility with quantity
The profit is superior to.

The following Preparations and Examples are given by way of illustration only and not limitation. In these, "parts" and "%" are based on weight unless otherwise specified.

Production Example 1 Synthesis of Main A Fat A A flask equipped with a stirrer, a cooler, a nitrogen injection tube, a thermometer and a dropping funnel was equipped with 285.0 parts of an epoxy resin of 475 and an epoxy equivalent of epoxy resin 475 synthesized from bisphenol A and epichlorohydrin. 950 epoxy resin 3
80 parts, p-nonylphenol 77.0 parts and methyl isobutyl ketone 82.4 parts were respectively weighed, heated and uniformly dissolved, and then benzyldimethylamine 3.0.
Part, and reacted at a reaction temperature of 150 ° C. to obtain an epoxy equivalent of 1
The reaction was allowed to reach 140. Then, the mixture was cooled, and 19.2 parts of diethanolamine, 27.0 parts of N-methylethanolamine and a ketimine compound of aminoethylethanolamine (79% methyl isobutyl ketone solution) were added.
6 parts were added and the reaction was continued at 110 ° C. for 2 hours. Then, the main resin A was obtained by diluting with methyl isobutyl ketone until the nonvolatile content became 80%.

Production Example 2 Synthesis of Main Resin B Using the same apparatus as in Production Example 1, bisphenol A type epoxy resin, epoxy equivalent 188) 752.0 parts, methanol 77.0 parts, methyl isobutyl ketone 200.3 parts and Dibutyltin dilaurate (0.3 parts) was charged, and the mixture was stirred at room temperature to form a uniform solution, and a 2,4- / 2,6-tolylene diisocyanate 80/20 (weight ratio) mixture 174.
When 2 parts was added dropwise over 50 minutes, the temperature in the system reached 70 ° C. due to heat generation. IR spectrum showed absorption 1730 cm ^-1 based on the carbonyl group of disappearance and urethane absorption of 2280 cm ^-1 based on the isocyanate.
After adding 2.7 parts of N, N-dimethylbenzylamine,
The temperature in the system was raised to 120 ° C., and by-product methanol was distilled off using a decanter until the epoxy equivalent reached 463. The IR spectrum shows the disappearance of absorption at 1730 cm ^-1 based on the carbonyl group of urethane and 1750c based on the carbonyl group of the oxazolidone ring.
The appearance of absorption of m ^-1 was shown. p-nonylphenol 22
While adding 0.0 parts and 83.3 parts of methyl isobutyl ketone and maintaining the temperature of 125 ° C., the epoxy equivalent was 114.
The reaction was run until 6 was reached. Cool the system to a temperature of 110 ° C., and use aminoethylethanolamine ketimine (79% by weight methyl isobutyl ketone solution) 4
After adding 7.2 parts, diethanolamine 42.0 parts, N-methyl ethanolamine 30.0 parts, and methyl isobutyl ketone 17.3 parts, it heated up and made it react at 120 degreeC for 2 hours. Thus, a main resin B having a nonvolatile content of 80% was obtained.

Production Example 3 Synthesis of Crosslinking Agent I A flask equipped with a stirrer, a condenser, a nitrogen introducing tube, a thermometer and a dropping funnel was charged with 2,5- and 2,6-bis (isocyanatomethyl) -bicyclo [2]. 2.2.1] Heptane (Mitsui Toatsu Co., Ltd., NCO equivalent = 103) 723
Parts, 333 parts of methyl isobutyl ketone, and 0.01 of dibutyltin silarate were weighed and heated to 70 ° C. After uniform dissolution, methyl ethyl ketoxime 61
0 parts were added dropwise over 2 hours. Reaction temperature 70 after dropping
The reaction was carried out until the NCO group disappeared by IR analysis while maintaining the temperature at 0 ° C to obtain a crosslinking agent I.

Production Example 4 Synthesis of Crosslinking Agent II Using the same equipment as in Production Example 3, 2,5- and 2,6-
Bis (isocyanatomethyl) -bicyclo [2.2.
1] Heptane isocyanurate type trimer (manufactured by Mitsui Toatsu Co., Ltd.) 500 parts (nonvolatile content 50%) and dibutyltin dilaurate 0.01 parts were weighed and heated to 70 ° C. After uniformly dissolving, 100 parts of methyl ethyl ketoxime was added to 2 parts.
It was dropped over time. After completion of dropping, the reaction was carried out by IR analysis until the NCO group disappeared while the reaction temperature was kept at 70 ° C. to obtain a crosslinking agent III.

Production Example 5 Synthesis of Crosslinking Agent III (for Comparative Example) Using the same apparatus as in Production Example 3, an isocyanurate type trimer of hexamethylene diisocyanate (Coronate H) is used.
X, Nippon Polyurethane Co., Ltd.) 199 parts, methyl isobutyl ketone 32 parts, and dibutyltin dilaurate 0.2.
Parts were weighed and heated to 50 ° C. Methyl ethyl ketoxime 87 while cooling from the outside and maintaining the temperature at 50 ° C
Parts were added dropwise over 2 hours. After completion of the dropping, the temperature was raised to 70 ° C., and the reaction was carried out while maintaining this temperature until the NCO group disappeared by IR analysis to obtain a crosslinking agent III.

Production Example 6 Synthesis of Crosslinking Agent IV (for Comparative Example) Using the same apparatus as in Production Example 3, 134 parts of trimethylolpropane, 300 parts of toluene, and 1669 parts of isophorone diisocyanate were charged and reacted for 8 hours with stirring. Let Next, the mixture was cooled to 50 ° C., and 147 parts of methyl ethyl ketoxime was added dropwise over 1 hour while maintaining the same temperature. After completion of the dropping, the reaction was carried out by IR analysis until the NCO group disappeared while maintaining the temperature at 50 ° C. to obtain a cross-linking agent IV.

Production Example 7 Pigment Dispersion Paste Epoxy equivalent of bisphenol type epoxy resin was reacted with 2-ethylhexynol half-blocked isophorone diisocyanate to give 1- (2-hydroxyethylthio) -2-propanol and dimethylolpropionic acid. Resin varnish for dispersion of pigments, which has been converted to tertiary sulfonium with
25.0 parts (sulfonium conversion rate 70.6%, resin solid content 60%), ion-exchanged water 400.0 parts, carbon black 6.0 parts, kaolin 124.0 parts, titanium dioxide 35
0.0 part and 20.0 parts of basic lead silicate were put into a sand glide mill and dispersed until the particle size became 10 μm or less to obtain a pigment dispersion paste.

Examples and Comparative Examples A base resin and a cross-linking agent were uniformly mixed in a solid content ratio shown in Table 1, and then ethylene glycol mono-2-ethylhexyl ether was added to 3% of the solid content. Was added to. Glacial acetic acid was added to this to neutralize it so that the neutralization rate was 43.0%, and ion-exchanged water was further added to slowly dilute. Then, methyl isobutyl ketone was removed under reduced pressure so that the solid content became 36.0% to prepare a main emulsion.

Next, 200.0 parts of the main emulsion, 460.0 parts of the pigment paste of Production Example 7, and 22 of ion-exchanged water.
52.0 parts of 1% dibutyltin oxide was mixed with the solid content to prepare a cationic electrodeposition coating composition with a solid content of 20.0%.

The obtained coating composition was electrodeposited on a zinc phosphate treated cold-rolled steel sheet so that the dry film thickness was 20 μm, and then 1
After baking at 50 ° C. for 10 minutes, the cured coating film was evaluated. The results are shown in Table 1.

[0031]

[Table 1]

Evaluation method Ra (center line average surface roughness): Measured with a surface roughness meter E-30A manufactured by Tokyo Seimitsu Co., Ltd. ◯: <0.25 μm Δ: 0.25 to 0.35 μm ×:> 0.35 μm Saltwater immersion corrosion resistance: The cut portion was peeled off with tape after being immersed in 5% saline solution at 55 ° C. for 240 hours, and the both sides of the cut portion were peeled off. The peel width was evaluated. ○: <3 mm △: 4-6 mm ×:> 6 mm Outdoor exposure Weather resistance: Outdoor exposure (Okinawa) The blister state of the cut part after 6 months was evaluated. ◯: No action Δ: Detectable blister ×: blister over the whole coating film Tg: dynamic Tg measured by dynamic viscoelasticity. ○:> 110 ° C △: <110 ° C

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ryoichi Murakami 19-17 Ikedanaka-cho, Neyagawa-shi, Osaka Japan Paint Co., Ltd.

Claims (10)

[Claims] 1. A cationic electrodeposition coating composition comprising a dispersion prepared by dispersing a cationically modified epoxy resin and a crosslinking agent in an aqueous medium containing a neutralizing agent, wherein the crosslinking agent is a blocked bicycloalkane-based poly. A cationic electrodeposition coating composition, which is an isocyanate compound. 2. The bicycloalkane-based polyisocyanate compound is 2,5- or 2,6-bis (isocyanatomethyl) -bicyclo [2.2.1] heptane, a dimer, trimer, or The cationic electrodeposition coating composition according to claim 1, which is an adduct with an aliphatic polyhydric alcohol. 3. The cationic electrodeposition coating composition according to claim 2, wherein the blocking agent of the crosslinking agent is a blocking agent which dissociates at 100 to 160 ° C. 4. The cationic electrodeposition coating composition according to claim 2, wherein the blocking agent for the crosslinking agent is an oxime or a lactam. 5. The cationic modified epoxy resin is a modified epoxy resin obtained by ring-opening an epoxy ring of a polyglycidyl ether type epoxy resin by reaction with an active hydrogen compound capable of introducing a cationic group. Cationic electrodeposition paint of any one of 4. 6. The cationic electrodeposition coating composition according to claim 5, wherein the polyglycidyl ether type epoxy resin is a bisphenol epoxy resin. 7. The cationic electrodeposition coating composition according to claim 5, wherein the polyglycidyl ether type epoxy resin is a polyglycidyl ether type epoxy resin containing an oxazolidone ring in the molecule. 8. The weight ratio of the solid content of the cationically modified epoxy resin to the cross-linking agent in the paint is 95/5 to 45/50.
The cationic electrodeposition coating composition according to any one of claims 1 to 7. 9. The cationic electrodeposition coating composition according to claim 1, wherein the amount of the organic solvent in the coating composition is 2.0% by weight or less. 10. A coating method, which comprises subjecting the coating material according to any one of claims 1 to 9 to electrodeposition coating with an object to be coated as a cathode, and baking and curing the coating film.