JP2011202048A - Method for coating cationic electrocoating composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for coating a cationic electrocoating composition capable of forming an excellent coated film with a limited rust-preventing property and rust-preventing property on an untreated steel sheet without containing a harmful material such as a lead compound and a chromium compound.SOLUTION: The coating method uses the cationic electrocoating composition containing (A) a cationic amine-modified epoxy resin (a base resin) obtained by cationizing an amine-modified epoxy resin obtained by reacting an epoxy resin with an amine, (B) a blocked polyisocyanate (a curing agent resin), (C) zinc oxide and (D) zirconium hydroxide. The coating method is useful for the electrocoating of a body of an automobile, a part thereof, an electric apparatus or the like.

Description

  The present invention relates to a coating method of a cationic electrodeposition coating composition that can exhibit excellent rust prevention properties, particularly for untreated steel sheets, without containing harmful substances such as lead compounds and chromium compounds.

  Electrodeposition coating has better throwing power and less environmental pollution compared to air spray coating and electrostatic spray coating for automobile body and its parts, and parts with a bag structure such as electric appliances. Therefore, it has been widely put to practical use as a primer coating. And the antirust pigment is added for the purpose of improving the antirust quality further.

  As typical anti-rust pigments, there are lead compounds and chromium compounds. However, in view of recent trends in environmental regulations and legal regulations, paints containing such harmful substances are not preferable. Therefore, in recent years, non-toxic or low-toxic rust preventive pigments have been developed, and cationic electrodeposition coating compositions using these have been put into practical use.

  Patent Documents 1 to 6 can be cited as cationic electrodeposition coating compositions using non-toxic or low-toxic rust preventive pigments. Specifically, for anti-corrosive pigments, Patent Documents 1 and 2 describe bismuth compounds, Patent Document 3 describes tungsten oxide, Patent Document 4 describes condensed aluminum phosphate compounds, and Patent Document 5 describes The phosphate compound is described. However, these technologies are limited to conventional cationic electrodeposition coating compositions that use rust preventive pigments that contain harmful substances such as lead compounds and chromium compounds in terms of rust resistance on untreated steel sheets. There is a problem that sufficient rust preventive power cannot be obtained as compared with the method of painting objects.

  Further, in Patent Document 6, a zirconium compound is described as a rust preventive pigment in addition to a bismuth compound, but the zirconium compound is not superior in rust preventive property than the bismuth compound, and has a limit rust preventive property. The anticorrosive property on the non-treated steel sheet is about the same as the above-mentioned Patent Documents 1 to 5. Therefore, the electrodeposition paint which does not contain harmful substances such as lead compounds and chromium compounds still has insufficient rust prevention performance.

JP 2000-230151 A JP-A-11-106687 JP-A-6-220371 JP 2001-329221 A Japanese Patent Laid-Open No. 9-241546 JP 2000-290542 A

  The present invention was devised in view of the current state of the prior art, and its purpose is to contain no harmful substances such as lead compounds and chromium compounds, and to limit rust prevention and rust prevention on untreated steel sheets. Provides a coating method for a cationic electrodeposition coating composition that exhibits superior characteristics compared to the existing coating method for a cationic electrodeposition coating composition using a non-toxic or low-toxic antirust pigment. There is.

  As a result of diligent studies to achieve the above object, the present invention dramatically improves rust prevention by using zinc oxide and zirconium hydroxide together as a rust preventive agent. By blending with amine-modified epoxy resin (base resin) and blocked polyisocyanate (curing agent), it has superior rust prevention and superior rust prevention on untreated steel sheet compared to existing electrodeposition coating compositions. The inventors have found that this can be achieved, and have completed the present invention.

  That is, the present invention includes (A) a cationic amine-modified epoxy resin (base resin) obtained by cationizing an amine-modified epoxy resin obtained by reacting an amine with an epoxy resin, and (B) a blocked polyisocyanate (curing agent resin). ), (C) a zinc oxide, and (D) a cationic electrodeposition coating composition containing zirconium hydroxide.

  According to the present invention, without containing harmful substances such as lead compounds and chromium compounds, the limit rust resistance (especially salt water spray test and warm salt water immersion test) and rust resistance on untreated steel sheet (especially Achieved the same or better characteristics in conventional cationic electrodeposition coating compositions using anti-corrosive pigments containing toxic substances such as lead compounds and chromium compounds in salt spray resistance tests and warm salt water immersion tests) Is done. Therefore, the coating method of the cationic electrodeposition coating composition of the present invention is extremely useful for electrodeposition coating of automobile bodies, parts thereof, electric appliances and the like.

  The cationic electrodeposition coating composition used in the present invention comprises (A) a cationic amine-modified epoxy resin (base resin) obtained by cationizing an amine-modified epoxy resin obtained by reacting an epoxy resin with an amine, (B) It contains a blocked polyisocyanate (curing agent resin), (C) zinc oxide, and (D) zirconium hydroxide.

  (A) Base resin is a cationic amine-modified epoxy resin obtained by cationizing an amine-modified epoxy resin obtained by reacting an epoxy resin with an amine. The epoxy resin before amine modification is preferably an epoxy resin having two epoxy groups in one molecule on average, and its epoxy equivalent is preferably 400 to 3000, particularly 500 to 1500. The main component constituting the epoxy resin is glycidyl ether of dihydric phenol. Examples of the dihydric phenol include resorcin, hydroquinone, 2,2-bis- (4-hydroxyphenyl) -propane, 4,4′-dihydroxybenzophenone, 1,1-bis- (4-hydroxyphenyl) -methane, 1, 1-bis- (4-hydroxyphenyl) -ethane, 4,4′-dihydroxybiphenyl and the like can be mentioned, but 2,2-bis- (4-hydroxyphenyl) -propane, so-called bisphenol A is particularly preferable. is there.

  (A) Glycidyl ethers, such as a polyol, a polyalkyl polyol, a polyalkylphenol, can also be added to a base resin as a flexible modifier as needed. As the introduction method, these flexible glycidyl ethers are reacted with an excess of a dihydric phenol to obtain an initial condensate, and then the chain length is extended to a target molecular weight by the reaction with a divalent phenol glycidyl ether. The method is exemplified as one having good reaction efficiency, but is not limited thereto. As the dihydric phenol used in the above dihydric phenol or glycidyl ether of dihydric phenol, resorcin, hydroquinone, 2,2-bis- (4-hydroxyphenyl) -propane, 4,4′-dihydroxybenzophenone, Examples include 1,1-bis- (4-hydroxyphenyl) -methane, 1,1-bis- (4-hydroxyphenyl) -ethane, 4,4′-dihydroxybiphenyl, and the like is particularly preferably 2. , 2-bis- (4-hydroxyphenyl) -propane, so-called bisphenol A.

  Moreover, flexibility can be imparted to the hydroxyl group present in the epoxy skeleton, for example, by adding an isocyanate half-blocked with a polyol, and the molecular weight can be adjusted.

  Reactions of diglycidyl ethers such as polyols, polyalkyl polyols, and polyalkylphenols with dihydric phenol diglycidyl ethers and dihydric phenols can be carried out in a solvent-free melt, but a system with a small amount of solvent added. It is also possible to do this. The solvent is not particularly limited as long as it does not react with the epoxy group. The reaction temperature is suitably 70 to 180 ° C.

  As amines to be reacted with the epoxy resin, methylamine, ethylamine, n-propylamine, isopropylamine, monoethanolamine, diethylamine, diethanolamine, N-methylethanolamine, N-ethylethanolamine, ethylenediamine, diethylenetriamine, hydroxyethylaminoethylamine , Ethylaminoethylamine, methylaminopropylamine, dimethylaminopropylamine and the like, or a mixture thereof. In the reaction between the epoxy resin and the amine, the primary amino group may be blocked by reacting with a ketone in advance, and then the remaining active hydrogen may be reacted with the epoxy group.

  The amination in which the epoxy resin and the amine are reacted can be carried out in a solvent or in a melt without a solvent, and the reaction temperature is suitably 40 to 150 ° C.

  The amine-modified epoxy resin can be cationized by neutralizing the amino group with a protonic acid. Preferred examples of the protonic acid include formic acid, lactic acid, acetic acid, propionic acid, citric acid, malic acid, sulfamic acid, and the like, or a mixture thereof. The neutralization degree of the acid is preferably 15 to 85%.

  (B) The curing agent resin is a blocked polyisocyanate obtained by reacting a polyisocyanate and a blocking agent. The polyisocyanate is an aromatic or aliphatic (including alicyclic) polyisocyanate, such as 2,4- or 2,6-tolylene diisocyanate and a mixture thereof, p-phenylene diisocyanate, diphenylmethane-4,4 ′. -Diisocyanate, polymethylene polyphenyl diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, 1,3 or 1,4-bis- (isocyanate methyl) -cyclohexane, dicyclohexylmethane-4,4'-diisocyanate, bis- ( Isocyanatomethyl) -norbornane, 3 or 4-isocyanatomethyl-1-methylcyclohexyl isocyanate, m- or p-xylylene diisocyanate, m- or - tetramethylxylylene diisocyanate, more may be mentioned biuret modified product or an isocyanurate modified product of the isocyanate.

  Furthermore, what connected a part of isocyanate group of the said isocyanate with the polyol can be mentioned. For example, ethylene glycol, propylene glycol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, triethylene glycol, low molecular diols such as 1,4-cyclohexanediol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polylactone Examples thereof include oligomeric diols such as diols, polyisocyanates linked with polyols such as trimethylolethane, trimethylolpropane, and pentaerythritol, and mixtures thereof.

  Examples of the blocking agent include aliphatic alcohol compounds such as methanol, ethanol, n-butanol and 2-ethylhexanol, cellosolve compounds such as ethylene glycol monobutyl ether and ethylene glycol monohexyl ether, diethylene glycol monoethyl ether and diethylene glycol monobutyl ether. Carbitol compounds, oxime compounds such as acetone oxime, methyl ethyl ketone oxime and cyclohexanone oxime, lactam compounds such as ε-caprolactam, phenol compounds such as phenol, cresol and xylenol, active methylene such as ethyl acetoacetate and diethyl malonate Mention may be made of group-containing compounds.

  The reaction between the polyisocyanate and the blocking agent can be carried out in a solvent or in a melt. Solvents used for the reaction include solvents that do not react with polyisocyanates, such as ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, cyclohexane, and isophorone, and aromatics such as benzene, toluene, xylene, chlorobenzene, and nitrobenzene. Examples thereof include hydrocarbons, cyclic ethers such as tetrahydrofuran, and halogenated hydrocarbons such as chloroform. Although there is no limitation in particular about reaction temperature, Preferably it is 30-150 degreeC.

  (C) A commercial item can be used for zinc oxide, for example, 1 type of zinc oxide prescribed | regulated by JISK-1410, 2 types of zinc oxide, and 3 types of zinc oxide can be mentioned.

  Examples of (D) zirconium hydroxide include R zirconium hydroxide and NN zirconium hydroxide manufactured by Daiichi Elemental Chemical Co., Ltd. Zirconium hydroxide is insoluble in water and does not dissolve or ionize in the paint. (D) Zirconium hydroxide is different from zirconyl nitrate, zirconyl acetate, zirconyl sulfate and the like which are ionized when mixed with water.

  Since the cationic electrodeposition coating composition used in the present invention uses zinc oxide and zirconium hydroxide in combination, it has a limit of rust prevention (particularly, salt spray resistance test and warm salt water immersion test) and on an untreated steel sheet. In rust prevention (especially salt water spray test and warm salt water immersion test), characteristics equal to or better than conventional cationic electrodeposition coating compositions using rust preventive pigments containing harmful substances such as lead compounds and chromium compounds Is achieved. When zinc oxide or zirconium hydroxide is used alone, the effects of the present invention are not achieved.

  The contents of zinc oxide and zirconium hydroxide used in the cationic electrodeposition coating composition used in the present invention are not particularly limited, but preferably each is 100 parts by weight of the total resin solid content in the coating composition. It is 0.1-15 weight part, More preferably, each is 0.1-10 weight part. In addition, the content ratio of (A) cationic amine-modified epoxy resin (base resin) and (B) blocked polyisocyanate (curing agent resin) in the coating composition is 90 to 40/10 to 10 in terms of solid content weight ratio. 60, preferably 85-40 / 15-60, more preferably 80-55 / 20-45.

  In addition to the components (A), (B), (C) and (D) described above, the cationic electrodeposition coating composition used in the present invention may further contain an ordinary coating additive such as titanium as required. Color pigments such as white, carbon black, and bengara, extenders such as kaolin, talc, aluminum silicate, calcium carbonate, mica, clay, silica, zinc phosphate, iron phosphate, aluminum phosphate, calcium phosphate, aluminum tripolyphosphate, molybdenum Additives such as rust preventive pigments such as zinc oxide, aluminum molybdate, calcium molybdate, and bismuth compounds, antifoaming agents, repellency inhibitors, aqueous solvents, curing catalysts, and the like can be contained. In addition, other resins such as acrylic resin, polyester resin, urethane resin, and butadiene resin can be contained.

  The method for preparing the cationic electrodeposition coating composition used in the present invention is not particularly limited. For example, (A) a base resin and (B) a curing agent resin are charged into a reaction vessel, and stirred and mixed thoroughly. Then, an acid is added to cationize the amino group of the amine-modified epoxy resin, and water is added to prepare an emulsion. On the other hand, an acid and water are added to the base resin to prepare a water-soluble vehicle. Add (C) zinc oxide and (D) zirconium hydroxide to this, and add color pigments and additives as needed, and then disperse to the required particle size with a disperser such as a sand mill to produce a pigment paste The emulsion thus obtained and the pigment paste can be mixed.

  The cationic electrodeposition coating composition obtained as described above can be usually applied to the surface of a desired base by known cationic electrodeposition coating in a state dispersed in water. Specifically, the solid content concentration of the paint is preferably about 5 to 40% by weight, more preferably 15 to 25% by weight, the pH is adjusted to 5 to 8, the bath temperature is 15 to 35 ° C., and the load voltage is 100. Under the condition of ~ 450V, the object to be coated can be applied as a cathode. After the coated object is washed with water, a cured coating film can be obtained by baking at 100 to 200 ° C. for 10 to 30 minutes in a baking oven. Although the film thickness of the coating film obtained from the coating method of the cationic electrodeposition coating composition of the present invention is not particularly limited, 5 to 60 μm, preferably 10 to 40 μm is appropriate for the cured coating film.

  The excellent effects of the coating method of the cationic electrodeposition coating composition of the present invention are shown by the following examples, but the present invention is not limited to these examples.

(Manufacture of base resin A1)
Base resin A1 was manufactured by the method shown below using the raw materials shown in Table 1. Raw materials (1), (2), and (3) were charged into a 3 liter four-necked flask equipped with a stirrer, a thermometer, and a cooling tube, and the temperature was raised to 150 ° C. by stirring and heating. After holding at 150 ° C. for 6 hours, the raw material (4) was gradually added and cooled to 80 ° C. Next, the raw material (5) was charged and the temperature was raised to 100 ° C. After holding at 100 ° C. for 2 hours, it was cooled to 80 ° C. and taken out. The obtained base resin A1 had a solid content of 70%.

(Manufacture of base resin A2)
Base resin A2 was manufactured by the method shown below using the raw materials shown in Table 2. Raw materials (1), (2), (3), and (4) were charged into a 5-liter four-necked flask equipped with a stirrer, thermometer, and cooling tube, and the temperature was raised to 150 ° C. by stirring and heating. . After holding at 150 ° C. for 6 hours, the raw material (5) was gradually added and cooled to 80 ° C. Next, the raw material (6) was charged and the temperature was raised to 100 ° C. After holding at 100 ° C. for 2 hours, it was cooled to 80 ° C. and taken out. The obtained base resin A2 had a solid content of 70%.

(Production of curing agent resin B)
Curing agent resin B was manufactured by the method shown below using the raw materials shown in Table 3. Raw materials (1) and (2) were charged into a 5 liter four-necked flask equipped with a stirrer, a thermometer, and a cooling tube, and the temperature was raised to 100 ° C. by stirring and heating. Thereafter, while keeping the temperature in the flask at 100 ° C., a solution of the raw material (4) previously dissolved in the raw material (3) was charged over 1 hour and reacted at 100 ° C. for 2 hours. Next, the raw material (5) was added dropwise over 1 hour while maintaining the same temperature. After the addition, the material (5) was further maintained at 100 ° C. for 2 hours, and then cooled to 80 ° C. and taken out. The obtained curing agent resin B had a solid content of 75%.

[Preparation of Emulsion E1]
857 parts by weight of base resin A1, 400 parts by weight of curing agent resin B, and 50 parts by weight of propylene glycol monophenyl ether were charged into a reaction vessel equipped with a stirrer, a thermometer, a cooler, and a decompression device. After thorough mixing, 35.6 parts by weight of 50% lactic acid was added to the reaction vessel, stirred at 40 to 70 ° C. for 30 minutes, and then 701 parts by weight of deionized water was added. Subsequently, emulsification was performed at the same time while removing a predetermined amount of solvent at about 70 ° C. under a pressure of 300 to 600 mmHg (gauge pressure). Thereafter, 1296 parts by weight of deionized water was added to obtain an emulsion E1 having a solid content of 30%.

[Preparation of Emulsion E2]
857 parts by weight of base resin A2, 400 parts by weight of curing agent resin B, and 50 parts by weight of propylene glycol monophenyl ether were charged into a reaction vessel equipped with a stirrer, a thermometer, a cooler, and a decompression device. After thorough mixing, 35.6 parts by weight of 50% lactic acid was added to the reaction vessel, stirred at 40 to 70 ° C. for 30 minutes, and then 701 parts by weight of deionized water was added. Subsequently, emulsification was performed at the same time while removing a predetermined amount of solvent at about 70 ° C. under a pressure of 300 to 600 mmHg (gauge pressure). Thereafter, 1296 parts by weight of deionized water was added to obtain an emulsion E2 having a solid content of 30%.

[Preparation of pigment paste]
Each raw material was charged into a container with the formulation shown in Table 4 and Table 5, and after sufficiently stirring with a dissolver, it was dispersed with a horizontal sand mill until the particle gauge particle size became 10 μm or less to obtain pigment pastes P1 to P10.

Examples 1-8, Comparative Examples 1-5
In the composition shown in Tables 6 and 7, to 948 parts by weight of the emulsion, 431 parts by weight of pigment paste, 1621 parts by weight of deionized water, and if necessary, parts by weight of zinc oxide and zirconium hydroxide described in Tables 6 and 7 are added. Thus, the cationic electrodeposition paints of Examples 1 to 8 and Comparative Examples 1 to 5 were obtained.

[Test plate preparation method]
Using the above-mentioned cationic electrodeposition paint, the carbon electrode as the anode, the degreased cold rolled steel sheet (manufactured by Partec Co., Ltd., 0.8 × 70 × 150 mm, no chemical conversion treatment) as the cathode, and the electrodeposition paint temperature Electrodeposition coating was performed at 30 ° C., a coating voltage of 200 to 300 V, and a film thickness after baking of 15 μm, and baking was performed at 170 ° C. for 20 minutes to obtain each test plate.

The following (1) to (4) were evaluated for the electrodeposited test plate.
(1) Coated surface smoothness Ra (center line average roughness) of the coated surface of the test plate was measured with a surface roughness meter (manufactured by Mitutoyo Corporation) and evaluated. When Ra is 0.15 μm or less, ◎, when 0.15 to 0.20 μm, ◯, when 0.20 to 0.25 μm, Δ, and when 0.25 μm or more, ×.
(2) Solvent resistance The coating film on the test plate was wiped with a solvent of ethanol / acetone (weight ratio 1/1).
(3) Salt spray resistance
It carried out according to JIS-Z-2731. A scratch reaching the substrate was put on the electrodeposited surface with a cutter knife, and the rust width after 480 hours was evaluated. The smaller the rust width, the better the performance.
(4) Salt water immersion test
After dipping the test plate in 50%, 5% saline for 480 hours, washing with water and air-drying, applying cellophane adhesive tape to the entire test surface so as not to contain air bubbles, and then peeling off the tape The ratio (%) of the coating film peeled area to the entire surface was measured. The smaller the peeled area, the better the performance.

[Evaluation results]
Tables 8 and 9 show the coating film performance evaluation results of Examples 1 to 8 and Comparative Examples 1 to 5.

  As can be seen from the results in Tables 8 and 9, in Examples 1 to 8 in which zinc oxide and zirconium hydroxide are used in combination, the rust prevention performance is superior to Comparative Examples 1 to 5 in the salt spray resistance test and the warm salt water immersion test. It is the result.

  The method of applying the cationic electrodeposition coating composition of the present invention is a conventional cationic electrodeposition containing a rust preventive pigment such as a lead compound or a chromium compound in the limit rust prevention and rust prevention on an untreated steel sheet. Since characteristics equal to or better than those of the coating method using the coating composition are achieved, it is useful for electrodeposition coating of automobile bodies, parts thereof, electric appliances and the like.

Claims (1)

  (A) Cationic amine-modified epoxy resin (base resin) obtained by cationizing an amine-modified epoxy resin obtained by reacting an amine with an epoxy resin, (B) Blocked polyisocyanate (curing agent resin), (C) Oxidation A coating method comprising using a cationic electrodeposition coating composition containing zinc and (D) zirconium hydroxide.