JP3368399B2 - Cathodic electrodeposition coating composition containing copper and cerium - Google Patents

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cathodic electrodeposition coating composition, and more particularly to a composition having improved corrosion resistance to an untreated cold rolled steel sheet.

2. Description of the Related Art Electrodeposition coatings have excellent corrosion resistance and throwing power, and can form a uniform coating film.
Widely used mainly for parts primers. Conventional cationic electrodeposition paints can exhibit sufficient corrosion resistance for materials that have been completely treated with zinc phosphate, but corrosion resistance for materials with insufficient surface treatment. In order to secure it, it is necessary to use a lead compound such as basic lead silicate as a rust preventive pigment. However, the use of lead has come to be restricted due to its toxicity problem. Therefore, phosphoric acid-based pigments, molybdic acid-based pigments, boric acid-based pigments and the like have been investigated as non-toxic rust-preventive pigments replacing lead, but their rust-preventive properties are low. In addition, JP-A-2-279
773 discloses the use of iron oxide.
The '87 publication describes the use of bismuth hydroxide / tin, cerium hydroxide / tin, nickel hydroxide / tin. Further, JP-A-5-247385 describes the use of bismuth / tin, and JP-A-4-325527 describes the use of copper, nickel, zinc, cobalt, chromium, aluminum, manganese, zirconium, tin and iron. There is. None of these proposals has obtained the anticorrosion performance comparable to that of lead compounds.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The present invention is excellent in corrosion resistance equivalent to or higher than that without using a toxic anticorrosive pigment, particularly corrosion resistance to untreated cold-rolled steel sheet (salt spray, salt water). It is an object of the present invention to provide a cathodic electrodeposition coating composition capable of forming a coating film having dipping and dry / wet cycle corrosion).

Means for Solving the Problems The present invention provides a cathodic electrodeposition coating composition prepared by dispersing a hydrophilic film-forming resin having a cationic group and a cross-linking agent in an aqueous medium containing a neutralizing agent. A copper compound and a cerium compound are contained in a total amount of 0.01 to 2.0% by weight as a metal based on the solid content of the paint, and the copper / cerium weight ratio as a metal is 1/20 to 20/1. A cathodic electrocoat composition is provided.

The copper compound and the cerium compound used in the present invention are water-soluble salts of copper (II) and cerium (III), for example, organic monocarboxylic acid salts such as formates, acetates, propionates and lactates. Inorganic acid salts such as nitrates, phosphates and sulfates, and halides such as chlorides and bromides may be used. It is also possible to use oxides, hydroxides, salts which produce copper, ions and cerium ions in the paint bath.

Preferred copper compounds are monocarboxylic acid salts and compositional formulas [Cu (OH) ₂ ] _x [CuSiO ₃ ] _y [CuS
O ₄ ] _z [H ₂ O] _n and the weight fractions x, y, z and n are each 18
-80%, 0-12%, 20-60% and 100-
It is a double salt that is (x + y + z).

The preferred cerium compound is cerium (II
I) nitrates, cerium (III) monocarboxylates, cerium (IV) oxides and their hydrates.

The total amount of copper and cerium added as a metal is generally 0.01 to 2% by weight of the coating solid content,
It is preferably 0.1 to 0.8% by weight. If it is too small, a satisfactory corrosion resistance effect cannot be obtained, and if it is too large, smoothness and electrodeposition property (Coulomb efficiency, etc.) decrease. A cerium compound alone cannot provide a satisfactory corrosion resistance effect.

The introduction of the above-mentioned copper compound and cerium compound into the composition for electrodeposition coating composition is not particularly limited, and it can be carried out in the same manner as a usual pigment dispersion method.
A copper compound and a cerium compound may be previously dispersed in a dispersing resin to prepare a dispersion paste, and the dispersion paste may be blended. Alternatively, in the case of a water-soluble copper compound or a water-soluble cerium compound, the compound can be blended as it is after the resin emulsion for paint is prepared. As the pigment dispersion resin, general resins for cationic electrodeposition coatings (epoxy sulfonium salt type resin, epoxy quaternary ammonium salt type resin, epoxy type tertiary amine type resin, acrylic quaternary ammonium salt) are used. Mold resin) is used.

The base resin has a number average molecular weight of 100 to 10 derived from a bisphenol type epoxy resin.
000, preferably 1000 to 3000 are available. The base equivalent of the base resin may be in the usual range, specifically 40 to 150 (milliequivalent / 100g), and preferably 60 to 100 (milliequivalent / 100g). In particular, a dealcoholization reaction between an epoxy resin and a bisurethane compound reacted with a diisocyanate compound or a heterourethane compound reacted with another active hydrogen compound as disclosed in JP-A-5-306327 of the present applicant The oxazolidone ring-modified epoxy resin obtained by the above is preferably used.

[0011] As the crosslinking agent, blocked polyisocyanate compound is used.

The blocked isocyanate crosslinking agent can be obtained by an addition reaction between a polyfunctional isocyanate compound and an isocyanate blocking agent. Aliphatic, cycloaliphatic or aromatic polyisocyanates are used as polyfunctional isocyanate compounds. For example, tolylene diisocyanate, xylylene diisocyanate,
4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate and its isocyanurate body are mentioned. On the other hand, in the isocyanate blocking agent, the blocked isocyanate compound formed by addition is stable at room temperature and can dissociate the block when heated to 100 to 200 ° C. to regenerate a free isocyanate group. desirable. For example, lactam compounds (ε-caprolactam, γ-butyrolactam, etc.), phenol compounds (phenol, cresol, xylenol, etc.), alcohol compounds (methanol, ethanol,
Furfuryl alcohol, butyrocellosolve, etc.) and oxime-based compounds (methyl ethyl ketone oxime, cyclohexanone oxime, etc.).

As the curing catalyst, tin compounds (dibutyltin oxide, dibutyltin dilaurate, etc.) can be used.

The amount of the blocked isocyanate crosslinking agent added is preferably determined by the ratio with the base resin. Usually, the ratio of the base resin to the cross-linking agent is 90 / as solid content.
It is set to 10-50 / 50. When the ratio of the cross-linking agent is small, sufficient curability cannot be obtained, and conversely, when the ratio is too large, the heating loss may increase.

Neutralization and water solubilization of the cathodic electrocoating composition of the present invention are carried out by using the base resin and the curing agent as water-soluble materials such as formic acid, acetic acid, propionic acid, lactic acid, citric acid, malic acid, tartaric acid and acrylic acid. It is carried out by dispersing in an aqueous medium containing an organic acid or an inorganic acid such as hydrochloric acid or phosphoric acid as a neutralizing agent.

The cathodic electrodeposition coating composition of the present invention may further contain conventional coating additives, if desired, such as coloring pigments such as titanium white, carbon black and red iron oxide, talc, calcium carbonate, clay and silica. The extender pigment may be dispersed with a pigment dispersion resin and added as a pigment dispersion paste. If necessary, other rust preventive pigments, such as chromium-based pigments (strontium chromate, zinc chromate), lead-based pigments (basic lead silicate, basic lead chromate, lead tin, cyanamide lead, etc.), phosphoric acid-based pigments Pigments (aluminum phosphate, zinc phosphate, calcium phosphate, etc.), molybdic acid-based pigments (aluminum phosphomolybdate, zinc phosphomolybdate, etc.), boric acid pigments (barium metaborate, etc.), surface conditioners, organic solvents, etc. Paint additives can be included.

The cathode electrodeposition coating composition of the present invention can be applied to a desired substrate surface by cationic electrodeposition coating. Cationic electrodeposition coating is carried out according to a method known per se, and generally has a solid content of 5 to 40% by weight, preferably 1
Usually, an electrodeposition bath comprising the cathodic electrodeposition coating composition of the present invention, which is diluted with deionized water so as to be 5 to 25% by weight and further adjusted to have a pH within the range of 5.5 to 8.5, is used. , Bath temperature 20
It can be performed under conditions of a load voltage of 100 to 450 V, adjusted to a temperature of 35 to 35 ° C.

The film thickness of the electrodeposition coating that can be formed using the cathodic electrodeposition coating composition of the present invention is not particularly limited, but generally 5 to 60 μm, preferably based on the cured coating film. Is suitably in the range of 10 to 40 μm. The baking temperature of the coating film is generally 100 to 200.
It is suitable to bake at a temperature of 150 ° C., preferably 150 to 180 ° C. for a time of 10 to 30 minutes.

Example Synthesis Example 1 (Synthesis of oxazolidone ring-containing base 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) 92 g, methyl isobutyl ketone 95 g and dibutyltin dilaurate 0.5 g were added, and 21 g of methanol was further added dropwise while stirring this. The reaction started from room temperature and was heated to 60 ° C. according to the invention. Then 3
After continuing the reaction for 0 minutes, ethylene glycol mono-
57 g of 2-ethylhexyl ether was added dropwise from the dropping funnel, and bisphenol A-propylene oxide 5 was added.
42 g of molar adduct was added. The reaction is mainly 60 ° C to 65 ° C.
The measurement was carried out in the range of ° C and continued until the isocyanate group disappeared while measuring the IR spectrum. Next, 365 g of an epoxy resin having an epoxy equivalent of 188, which was synthesized from bisphenol A and epichlorohydrin i, was added, and the temperature was raised to 125 ° C. Then, 1.0 g of benzyldimethylamine was added and reacted at 130 ° C. until the epoxy equivalent became 410. Subsequently, when 87 g of bisphenol A was added to the reaction vessel and reacted at 120 ° C., the epoxy equivalent was 119.
It became 0. Then cool down and diethanolamine 11
g, N-methylethanolamine 24 g, and aminoethylethanolamine ketimine compound (79% by weight methyl isobutyl ketone solution) 25 g were added and reacted at 110 ° C. for 2 hours. Then, it was diluted with methyl isobutyl ketone to a nonvolatile content of 80% to obtain an oxazolidone ring-containing base resin.

Synthesis Example 2 (Compound of Blocked Isocyanate
Adult) stirrer, condenser, nitrogen inlet tube, and A flask with a thermometer and a dropping funnel. Hexamethylene diisocyanate trimer (Coronate H
X: manufactured by Nippon Polyurethane Co., Ltd.) and ε-caprolactam 11.3 g. Then, the contents in the flask were heated to 80 ° C. and uniformly dissolved. To this, 32 g of methyl isobutyl ketone, 0.05 g of dibutyltin dilaurate and 0.05 g of 1,8-diazabicyclo (5,4,0) -7-undecene were added.
While stirring this while bubbling nitrogen through it, 78.3 g of methyl ethyl ketoxime was added dropwise from the dropping funnel over 1 hour while paying attention to heat generation. The reaction was carried out until the isocyanate group disappeared in the IR spectrum to obtain a blocked isocyanate crosslinking agent.

Synthesis Example 3 (Production of Pigment Dispersion Resin) A flask equipped with a stirrer, a cooler, a nitrogen injection tube, a thermometer and a dropping funnel was prepared. To this flask, 222.0 g of isophorone diisocyanate was added, diluted with 39.1 g of methyl isobutyl ketone, and then 0.2 g of dibutyltin dilaurate was added. After raising the temperature to 50 ° C., 2-
131.5 g of ethylhexanol was added dropwise from a dropping funnel over 2 hours while stirring while bubbling nitrogen. The reaction temperature during this period was maintained at 50 ° C. by cooling appropriately. As a result, 2-ethylhexanol half-blocked isophorone diisocyanate was obtained. (Solid content 90%)

Another flask equipped with a stirrer, a condenser, a nitrogen injection tube, a thermometer and a dropping funnel was prepared. To this flask, 376.0 g of Epon 828 (Epoxy resin manufactured by Shell Chemical Co., Ltd.) and 114.0 g of bisphenol A were added, heated to 130 ° C. under a nitrogen atmosphere, 0.75 g of dimethylbenzylamine was added, and an exothermic reaction at 170 ° C. for 1 hour. By the reaction, a bisphenol A type epoxy resin having an epoxy equivalent of 490 was obtained. Then 14
After cooling to 0 ° C., 198.4 g of the above-mentioned 2-ethylhexanol half-blocked isophorone diisocyanate was added and allowed to react at 140 ° C. for 1 hour, after which 161.8 g of ethylene glycol monobutyl ether was added and the reaction mixture was cooled to 100 ° C. did. Thiodiethanol 3
66.0 g, dimethylolpropionic acid 134.0 g,
And 144.0 g of deionized water were added, and the temperature was 70 ° C to 75 ° C.
To give an acid number of 0.241, and then
It was diluted with ethylene glycol monobutyl ether 353.3 to obtain a pigment dispersion resin having a sulfonium conversion rate of 82%.
(Solid content 50%)

Synthesis Example 4 (Preparation of Pigment Dispersion Paste) Carbon black, kaolin, and titanium dioxide were dispersed in the pigment dispersion resin obtained in Synthesis Example 3 in the following formulation, and the mixture was pulverized and prepared by a sand mill to prepare a pigment dispersion paste. Obtained.

[0024]

Examples 1 to 8 and Comparative Examples 1 to 6 350 g (solid content) of the base resin obtained in Synthesis Example 1 and 150 g (solid content) of the cross-linking agent obtained in Synthesis Example 2 were mixed to prepare ethylene glycol mono. 2-Ethylhexyl ether was added so as to be 3% (15 g) based on the solid content. Next, glacial acetic acid was added to neutralize the rate of neutralization to 40.5% and neutralized.
Ion-exchanged water was added and the mixture was slowly diluted, and then methyl isobutyl ketone was removed under reduced pressure so that the solid content was 36.0%.

Emulsion 20 thus obtained
To 00 g, various pigment pastes 46 obtained in Synthesis Example 4
0.0 g, ion-exchanged water 2252.0 g, and 1.0 wt% of dibutyltin oxide with respect to the resin solid content were added and mixed to prepare an electrodeposition coating composition having a solid content of 20.0 wt%.

The copper and cerium compounds were added directly to the paint in the case of acetate and nitrate, otherwise replacing some of the titanium dioxide in the pigment paste.
It was adjusted to the addition amount (% by weight) as the metal shown in 2.

In this electrodeposition paint bath, the surface (not yet) was used as a cathode.
The treated cold-rolled steel sheet was dipped, electrodeposited to a dry film thickness of 20 μm, cured at 160 ° C. for 10 minutes, and the coating film was evaluated. Table 1 shows the results of Examples, and Table 2 shows the results of Comparative Examples.

[0029]

[Table 1]

[0030]

[Table 2]

Footnote 1 of Tables 1 and 2 ) Copper double salt: [Cu (OH) ₂ ] _x [CuSiO ₃ ] _y [CuSO ₄ ] _z [H ₂ O] _n Weight fraction x / y / z = 50 / 3.2 / 35 2) coating smoothness: the appearance of the coating film was visually evaluated. ○: Good △: Slightly bad ×: Poor XX; Not electrodepositable 3) Salt spray test: A cross cut reaching the substrate with a knife was put on the coated plate, and a salt spray test (5% saline solution, 35 ° C ×)
480 h). 4) Salt water immersion test: A cut that reaches the substrate with a knife was put in a coated plate, and a salt water immersion test (5% saline solution, 55 ° C x 120)
h) was performed. Peeling = maximum peeling width (mm) from cut part ○; less than 3 mm △; 3 to 6 mm ×; 6 mm or more Blister = number of blisters on coated surface / 15 cm × 7 cm ○; very few △; few ×; many

Continuation of front page (56) Reference JP-A-56-99222 (JP, A) JP-A-4-325572 (JP, A) JP-A-5-140487 (JP, A) JP-A-5-306327 (JP , A) JP-A-6-9908 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C09D 1/00-10/00 C09D 101/00-201/10 WPI / L ( QUESTEL)

Claims (4)

(57) [Claims] 1. A cathodic electrocoating composition comprising a hydrophilic film-forming resin having a cationic group and a cross-linking agent dispersed in an aqueous medium containing a neutralizing agent. A cathode electrodeposition coating composition comprising a compound and a cerium compound as a metal in a total amount of 0.01 to 2.0% by weight, and having a metal / copper cerium weight ratio of 1/20 to 20/1. 2. A copper compound is an organic monocarboxylic acid salt or a composition formula [Cu (OH) ₂ ] _x [CuSiO ₃ ] _y [CuS
O ₄ ] _z [H ₂ O] _n (where x, y, z, and n are weight fractions, and each is 1
8-80%, 0-12%, 20-60% and 100-
(X + y + z). 2. The cathodic electrocoating composition according to claim 1, which is a compound of 1). 3. A hydrophilic film-forming resin having a cation group is a resin obtained by ring-opening an epoxy ring containing a plurality of oxazolidone rings in a resin skeleton with an active hydrogen compound capable of introducing a cation group. Item 1 or 2 is a cathodic electrocoating composition. 4. The cathodic electrocoating composition according to claim 1, wherein the crosslinking agent is a blocked polyisocyanate.