JPH05239385A - Cation electrodeposition paint - Google Patents

Abstract

PURPOSE:To provide a cationic electrodeposition paint which has high bath stability, prevents coating film defects by shocks, and can form a coating film of high corrosion resistance. CONSTITUTION:The objective cationic electrodeposition paint contains 0.5 to 50 pts.wt., based on 100 pts.wt. of the total resin solid components, of a polyurethane resin of 1,500 to 20,000 number-average molecular weight, prepared by introducing blocked isocyanate groups into the molecule through the urethane linkages formed by reaction of the hydroxyl group of a hydroxyl group- containing modified polybutadiene, resulting from addition reaction of 95 to 5 pts.wt. of an alkylene oxide to 5 to 95 pts.wt. of a hydroxyl-containing polybutadiene bearing two or more hydroxyl groups in the each molecule, with polyisocyanate groups.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cationic electrodeposition coating composition which has good bath stability for a long period of time, can prevent coating film defects due to impact, and can form a coating film with good corrosion resistance.

[0002]

2. Description of the Related Art Conventionally, cationic electrodeposition paints are capable of forming a coating film having good throwing power and excellent corrosion resistance, and therefore, members having many bag-like structures, such as automobiles and electric appliances, etc. It has been widely used for painting. Further, in recent years, in the field of automobile coating, rust-preventive steel sheets such as hot-dip galvanized steel sheets are often used for the purpose of improving the anticorrosion property of automobile bodies. There is a problem that the impact on the coating film due to the bounce of pebbles during running causes a significant defect in the coating film, and the coating film on the cold-rolled steel sheet also causes defects due to impact, although to a different degree. Improvement of impact resistance from the surface of the coating film has been demanded.

In order to improve the impact resistance, there is a method of softening the coating film by increasing the amount of the plastic modifier in the coating film. However, increasing the amount of the plastic modifier generally leads to anticorrosion. There is a problem of deterioration. In addition, it has been studied to mix a polybutadiene resin into a coating material, and it is known that it is effective in improving impact resistance. However, this material is used as a base resin for a cationic electrodeposition coating material such as an epoxy resin. Since the compatibility was poor, the stability of the electrodeposition bath became poor, and there were problems that the polybutadiene resin settled at the bottom of the electrodeposition bath, the piping was clogged, and the finished appearance of the coating film deteriorated. Furthermore, since neither the plasticity modifier nor the polybutadiene resin has a reactive group, the cationic electrodeposition coating composition containing these has a problem that the curability is poor.

Therefore, the present inventors have found that the bath stability is good,
As a result of diligent research to obtain a cationic electrodeposition coating capable of preventing coating defects due to impact and capable of forming a coating having good anticorrosion properties, a polyurethane having a blocked isocyanate group introduced into a modified polybutadiene resin molecule to which an alkylene oxide has been added The inventors have found that the above objects can be achieved by using a resin, and have reached the present invention.

[0005]

Means for Solving the Problems That is, the present invention provides a cationic electrodeposition coating composition in which 5 to 95 parts by weight of a hydroxyl group-containing polybutadiene having two or more hydroxyl groups in the molecule are subjected to an addition reaction with 95 to 5 parts by weight of an alkylene oxide. Polyurethane resin having a number average molecular weight of 1,500 to 20,000, which is obtained by introducing a blocked isocyanate group into a molecule through a urethane bond formed by a reaction between a hydroxyl group of the hydroxyl group-containing modified polybutadiene and an isocyanate group, The present invention provides a cationic electrodeposition coating composition containing 0.5 to 50 parts by weight in 100 parts by weight of solid content.

The polyurethane resin in the composition of the present invention is a polyurethane resin in which a blocked isocyanate group is introduced into the molecule through a urethane bond formed by a reaction between a hydroxyl group of a hydroxyl group-containing modified polybutadiene and an isocyanate group. The hydroxyl group-containing modified polybutadiene is
It can be easily obtained by subjecting a hydroxyl group-containing polybutadiene having two or more hydroxyl groups in the molecule and an alkylene oxide to an addition reaction by ring-opening and etherification of the alkylene oxide by a known method.

The number average molecular weight of the hydroxyl group-containing polybutadiene used is preferably such that the resulting modified polybutadiene has a number average molecular weight in the range of 1,400 to 19,000, and usually, preferably a number average molecular weight of about 1,000 to.
It is in the range of about 15,000 and may be linear or branched. The number of hydroxyl groups in one molecule of hydroxyl group-containing polybutadiene is not particularly limited as long as it is 2 or more, but 2 to 5 are usually used. Examples of commercially available products of hydroxyl group-containing polybutadiene include R-15HT and R-45HT manufactured by Idemitsu Petrochemical Co., Ltd.

The alkylene oxide used in the above reaction is not particularly limited, but usually has 2 carbon atoms.
4 to 4, that is, ethylene oxide, propylene oxide or butylene oxide is used. Among them, propylene oxide is particularly preferable from the viewpoint of water resistance of the resulting coating film and stability of electrodeposition bath.

In the above reaction, the ratio of the hydroxyl group-containing polybutadiene and the alkylene oxide is 100, the sum of the two.
Of the parts by weight, the former 5 to 95 parts by weight, the latter 5 to 95 parts by weight,
The former is 40 to 70 parts by weight and the latter is 60 to 30 parts by weight. When the amount of the hydroxyl group-containing polybutadiene exceeds 95 parts by weight, the compatibility with other resins such as the epoxy resin in the cationic electrodeposition coating composition of the present invention is deteriorated, which is not preferable, while the amount of the hydroxyl group-containing polybutadiene is less than 5 parts by weight. Then, the impact resistance of the obtained coating film becomes insufficient.

The hydroxyl group-containing modified polybutadiene obtained by the above reaction has a number average molecular weight of 1,400 to 19,0.
It is preferably 00 and has two or more hydroxyl groups in one molecule. Examples of commercial products of this hydroxyl group-containing modified polybutadiene include ES- manufactured by Asahi Glass Co., Ltd.
B6010, ES-B6030, etc. are mentioned.

The above-mentioned polyurethane resin is (1) a polyisocyanate compound (hereinafter, referred to as
It is abbreviated as "partially blocked polyisocyanate". ) Is used, or (2) by using an unblocked polyisocyanate compound in an amount exceeding the equivalent amount with respect to the hydroxyl groups in the hydroxyl group-containing modified polybutadiene, and then reacting the unreacted isocyanate groups. Obtainable.

Examples of the unblocked polyisocyanate compound include aliphatic diisocyanates such as hexamethylene diisocyanate or trimethylhexamethylene diisocyanate; cycloaliphatic diisocyanates such as hydrogenated xylylene diisocyanate or isophorone diisocyanate; tolylene diisocyanate or Organic diisocyanates such as aromatic diisocyanates such as 4,4'-diphenylmethane diisocyanate itself, or adducts of these organic diisocyanates with polyhydric alcohols, low molecular weight polyester resins or water, or the organic diisocyanates described above. Cyclic polymers of the same group, further isocyanate biuret, triphenylmethane-4,4 ', 4 " -Triisocyanate, 1,3,5
-Triisocyanatobenzene, 2,4,6-triisocyanatotoluene, 4,4'-dimethyldiphenylmethane-2,2 ', 5,5'-tetraisocyanate and the like 3
Examples thereof include organic polyisocyanates having at least one isocyanate group.

In order to block a part of the isocyanate groups of the polyisocyanate compound, or after the urethane-forming reaction of the hydroxyl group-containing modified polybutadiene and the polyisocyanate compound in the equivalent amount or more, the remaining unreacted isocyanate groups are blocked. Examples of the blocking agent used include phenols such as phenol and t-butylphenol; lactams such as ε-caprolactam; alcohols such as ethylene glycol monoethyl ether and benzyl alcohol; oximes such as methylethylketoxime and cyclohexanone oxime; Active methylene type such as dimethyl malonate and ethyl acetoacetate, other mercaptan type, acid amide type, imide type, amine type, imidazole type, urea type, carbamic acid ester type, imine type, sub-type Blocking agent such as an acid salt can be used.

The reaction between the blocking agent and the isocyanate group in the polyisocyanate compound or the polyisocyanate compound-modified polybutadiene having a residual isocyanate group is carried out by heating both at 50 to 100 ° C. for about 2 to 5 hours. You can A tin compound may be used as a catalyst if necessary.

In the method (1), when a part of the isocyanate groups of the polyisocyanate compound is blocked to obtain a partially blocked polyisocyanate, one isocyanate group in the polyisocyanate compound remains unblocked. It is preferable to carry out the reaction at a mixing ratio of.

In the above method (1), the reaction between the hydroxyl group-containing modified polybutadiene and the partially blocked polyisocyanate can be carried out by a known reaction method between a hydroxyl group and an isocyanate group. The reaction is carried out until the isocyanate groups are substantially eliminated at a blending ratio such that the blocked isocyanate groups are introduced. This reaction can usually be carried out by reacting at 20 to 100 ° C. for about 1 to 10 hours in the presence of a reaction catalyst such as a tin catalyst. By this reaction, a blocked isocyanate group is introduced into the molecule via the urethane bond.

In the method (2), the urethane-forming reaction between the hydroxyl group-containing modified polybutadiene and the polyisocyanate compound can be carried out by a known reaction method between a hydroxyl group and an isocyanate group. In this reaction, a polyisocyanate compound exceeding the equivalent amount is used with respect to the hydroxyl groups in the hydroxyl group-containing modified polybutadiene, and a predetermined amount of isocyanate groups is introduced into one molecule of the product. This reaction can usually be carried out by reacting in the presence of a reaction catalyst such as a tin-based catalyst at 20 to 100 ° C. for about 1 to 10 hours. The unreacted isocyanate group in the obtained product is blocked by the blocking agent to obtain a polyurethane resin having a blocked isocyanate group in the molecule.

The polyurethane resin obtained by the above methods (1) and (2) has a number average molecular weight of 1,500 to 2
The number of blocked isocyanate groups in the polyurethane resin is not particularly limited, but the average number in the polyurethane resin molecule is not particularly limited. At 1.5 ~
Suitably it has 5 and more preferably 2 to 3 blocked isocyanate groups. If the number average molecular weight of the polyurethane resin is less than 1,500, the impact resistance of the resulting coating film is not sufficiently improved, while the number average molecular weight of 2 is
If it exceeds 50,000, the bath stability of the obtained electrodeposition coating composition will be deteriorated.

Regarding the blocked isocyanate group in the polyurethane resin, the blocking agent is dissociated by baking, and the regenerated isocyanate group reacts with the functional group such as the base resin,
Contributes to crosslinking and curing. By selecting a blocked isocyanate group that dissociates the blocking agent at a low temperature, low temperature curability can be imparted to the electrodeposition coating composition. In addition, by increasing the number of blocked isocyanate groups in the molecule, the degree of crosslinking of the obtained electrodeposition coating film can be increased.

In the paint of the present invention, other resins used together with the above polyurethane resin are known resins for cationic electrodeposition paints (hereinafter abbreviated as "cationic electrodeposition resins"), for example, amine-added epoxy. Resins typified by resins, for example (i) polyepoxide compounds and adducts of primary mono- and polyamines, secondary mono- and polyamines, and primary and secondary mixed polyamines (for example, US Pat. No. 3,984,299 (See specification); (ii) Addition product of polyepoxide compound with ketiminated secondary mono- and polyamine having primary amino group (see, for example, US Pat. No. 4,017,438); (iii) A reaction product obtained by etherification of a polyepoxide compound and a ketiminized hydroxy compound having a primary amino group (eg, In JP-A-59-43013
(See Japanese Patent Publication) and the like.

The polyepoxide compound used for producing the above polyamine resin is a compound having two or more epoxy groups in one molecule, and is generally at least 200, preferably 400 to 4,000, and more preferably 800 to.
Those having a number average molecular weight within the range of 2,000 are suitable, and those obtained by reacting a polyphenol compound with epichlorohydrin are particularly preferable.

Examples of polyphenol compounds which can be used for forming the polyepoxide compound include bis (4
-Hydroxyphenyl) -2,2-propane, 4,4 '
-Dihydroxybenzophenone, bis (4-hydroxyphenyl) -1,1-ethane, bis- (4-hydroxyphenyl) -1,1-isobutane, bis (4-hydroxy-tert-butyl-phenyl) -2,2- Propane, bis (2-hydroxynaphthyl) methane, 1,5-
Dihydroxynaphthalene, bis (2,4-dihydroxyphenyl) methane, tetra (4-hydroxyphenyl)
-1,1,2,2-ethane, 4,4'-dihydroxyphenyl sulfone, phenol novolac, cresol novolac and the like can be mentioned.

The polyepoxide compound may be one partially reacted with a polyol, a polyether polyol, a polyester polyol, a polyamidoamine, a polycarboxylic acid, a polyisocyanate compound, etc., and further, ε-caprolactone, an acrylic monomer, etc. May be graft-polymerized.

When good weather resistance is required for the electrodeposition coating film formed using the coating composition of the present invention, an amino group-containing acrylic resin having excellent weather resistance or a cationic type electrodeposition resin is used. It is convenient to use the nonionic acrylic resin alone or in combination with the amine-added epoxy resin.

Further, the electrodeposition coating composition of the present invention comprises a cross-linking agent such as a blocked polyisocyanate blocked with an alcohol, a phenol, a tertiary hydroxylamine or an oxime or a melamine resin, and a pigment dispersion, if necessary. A resin for use may be contained.

In the electrodeposition coating composition of the present invention, the blending amount of the polyurethane resin is 0. 0 based on 100 parts by weight of the total solid content of the resin, which is the total of the polyurethane resin, the cationic electrodeposition resin, the crosslinking agent and the pigment dispersing resin. 5 to 50 parts by weight, preferably 1 to 20 parts by weight. If the blending amount is less than 0.5 part by weight, the effect of improving impact resistance is not sufficient, while 5
If it is more than 0 parts by weight, the bath stability of the electrodeposition bath becomes poor,
It is not preferable because sediment is generated at the bottom of the electrodeposition bath.

The cationic electrodeposition coating composition of the present invention can be prepared by mixing the above-mentioned polyurethane resin and, if necessary, a crosslinking agent before or after the neutralization of the cationic electrodeposition resin and then neutralizing it. After hydration, it is dispersed in water, that is, emulsified, or by emulsifying a cationic electrodeposition resin with a polyurethane resin and, if necessary, a crosslinking agent. The neutralization can be performed with a water-soluble organic acid such as formic acid, acetic acid, lactic acid.

The cationic electrodeposition coating composition of the present invention may further contain conventional coating additives such as coloring pigments such as titanium white, carbon black, red iron oxide, and yellow lead, if necessary;
Extender pigments such as talc, calcium carbonate, mica, clay, silica; anti-corrosion pigments such as chromium pigments such as strontium chromate and zinc chromate; lead pigments such as basic lead silicate and lead chromate; ,
An aqueous solvent and a curing catalyst may be included. The pigment is usually blended as a pigment paste dispersed in a pigment dispersion resin.

The cationic electrodeposition coating composition of the present invention can be applied to the desired substrate surface by cationic electrodeposition coating. Cationic electrodeposition coating follows methods known per se and generally has a solid content of about 5 to 40% by weight, preferably 1%.
Dilute with deionized water etc. to be 5 to 25% by weight,
Further, an electrodeposition bath comprising the cationic electrodeposition coating composition of the present invention whose pH is adjusted within the range of 5.5 to 8.0 usually has a bath temperature of 15 to 3
The object to be coated can be used as a cathode under the conditions of a load voltage of 100 to 400 V adjusted to 5 ° C.

The thickness of the electrodeposition coating which can be formed using the cationic electrodeposition coating composition of the present invention is not particularly limited,
Generally, the range of 10 to 60 μm, preferably 30 to 50 μm is suitable based on the cured coating film. The baking and curing temperature of the coating film is generally 100 to 200 ° C., preferably 150 to 180 ° C., and it is suitable to bake in the range of about 10 to 30 minutes.

[0031]

ACTION AND EFFECT OF THE INVENTION The cationic electrodeposition coating composition of the present invention comprises
As a part of the resin component, it has a polyurethane resin in which a blocked isocyanate group is introduced into the molecule, and since this blocked isocyanate group contributes to crosslinking, the corrosion resistance of the coating film is improved, and the polyurethane resin Since is modified by adding alkylene oxide to polybutadiene, it greatly contributes to the improvement of the impact resistance of the coating film and has good stability in water and shows good bath stability.

[0032]

EXAMPLES The present invention will be described in more detail below with reference to examples. In the following, "%" and "parts" are based on weight.

Production Example 1 of Polyurethane Resin Production Example 1 A flask equipped with a stirrer, a thermometer, and a reflux condenser,
Polypropylene glycol modified polybutadiene "ES-
B6010 "(manufactured by Asahi Glass Co., Ltd., polypropylene glycol content 20%, hydroxyl value 34.7 mg KOH / g, number average molecular weight about 3,500) was diluted by adding 58.7 parts of methyl ethyl ketone to 196.9 parts. After adding 0.035 parts of dibutyl tin dilaurate and 22.9 parts of "Takenate 500" (Takeda Birdish Urethane Co., Ltd., xylylene diisocyanate), 4 while paying attention to heat generation.
The temperature was raised to 0 ° C. The reaction was carried out at 40 ° C. for 1 hour to obtain an isocyanate adduct having 2.38% of isocyanato groups.
To this was added 10.6 parts of methyl ethyl ketoxime, and 8
By reacting at 0 ° C. for 3 hours until the isocyanate group disappears, a polyurethane resin liquid (1) having a solid content of 80% is obtained.
Got The obtained resin has a number average molecular weight of about 3,800,
Moreover, it had an average of two blocked isocyanate groups in one molecule.

Production Example 2 A polyurethane resin liquid (2) was obtained in the same manner as in Production Example 1 except that 20.5 parts of hexamethylene diisocyanate was used instead of 22.9 parts of "Takenate 500". .. The isocyanate adduct before reaction with methyl ethyl ketoxime contained 2.41% isocyanato groups.
I had. Further, the obtained polyurethane resin had a number average molecular weight of about 3,700 and had an average of 2 blocked isocyanate groups in one molecule.

Production Example 3 A polyurethane resin liquid (3) was obtained in the same manner as in Production Example 1 except that 27.0 parts of isophorone diisocyanate was used instead of 22.9 parts of "Takenate 500". The isocyanate adduct before reaction with methyl ethyl ketoxime had 2.34% isocyanato groups. The obtained polyurethane resin had a number average molecular weight of about 3,700 and had an average of two blocked isocyanate groups in one molecule.

Production of Cationic Electrodeposition Resin Production Example 4 1,900 parts of Epicoat 1004 ^{(* 1)} was dissolved in 1,012 parts of butyl cellosolve, 124 parts of diethylamine was added dropwise at 80 to 100 ° C., and then maintained at 120 ° C. for 2 hours. An epoxy resin-amine adduct having an amine value of 47 was obtained.

Next, 1,000 parts of a dimer acid type polyamide resin (trade name "Versamide 460", manufactured by Henkel Hakusui Co., Ltd.) having an amine value of 100 was dissolved in 429 parts of methyl isobutyl ketone and heated under reflux at 130 to 150 ° C. Then, the produced water was distilled off to change the terminal amino group of the amide resin to ketimine. This was kept at 150 ° C. for about 3 hours and cooled to 60 ° C. after the distillation of water was stopped. Then add this to the epoxy resin-amine adduct,
The mixture was heated to 100 ° C., kept for 1 hour and then cooled to room temperature to obtain an epoxy resin-amine-polyamide addition resin varnish (4) having a solid content of 68% and an amine value of 65.

Examples 1 to 6 and Comparative Examples 1 and 2 The polyurethane resin liquids (1), (2), obtained as described above,
(3), epoxy resin-amine-polyamide addition resin varnish (4) and 2-ethylhexyl alcohol blocked product of xylylene diisocyanate (hereinafter referred to as "XDI
It is abbreviated as "diblock compound". ) Was mixed so as to give each solid content by weight shown in Table 2 below, and 1 part of lead acetate and 15 parts of 10% acetic acid were added to each of the obtained mixed liquids, and the mixture was stirred uniformly and then vigorously stirred. While adding 450 parts of deionized water over about 15 minutes, a clear emulsion for cationic electrodeposition having a solid content of about 35% was obtained. To 271 parts of this clear emulsion, 69.7 parts of a pigment paste having the formulation shown in the following Table 1 was added with stirring, and deionized water 294.2 was added.
It was diluted with 1 part to obtain a cationic electrodeposition coating composition. The resin content in Table 2 is shown by the solid content weight. (* 1) Epicoat 1004: Bisphenol A type epoxy resin manufactured by Yuka Shell Epoxy Co., which has an epoxy equivalent of about 950.

[0039]

[Table 1]

The cationic electrodeposition paints obtained in the above Examples and Comparative Examples were subjected to chemical conversion treatment with Palbond # 3030 (manufactured by Nippon Parkerizing Co., Ltd.) zinc phosphate treating agent, 0.8 × 1.
A 50 × 70 mm hot-dip galvanized steel sheet was dipped, and the electrodeposition coating was performed using it as a cathode. The coating condition is voltage 3
An electrodeposition coating film having a film thickness (based on the dry film thickness) of about 20 μm was formed at 00 V, washed with water, and then baked at 180 ° C. for 20 minutes with an electric hot air dryer to obtain a coated steel sheet.

Tests were carried out on the bath stability of each electrodeposition bath and the impact resistance and corrosion resistance of the obtained coated steel sheet. The test results are shown in Table 2 below. The test was conducted according to the following test method.

Bath stability: The obtained electrodeposition coating composition was stirred at 30 ° C. for 1 month and then filtered through a 400-mesh wire net, and the amount of the residue was evaluated according to the following criteria. ◯: Residual amount less than 10 mg / l Δ: Residual amount 10 mg / l or more and less than 100 mg / l ×: Residual amount 100 mg / l or more

Impact resistance: Using a DuPont type impact tester, a test was conducted under the conditions of a diameter of the hammer of 1/2 inch, a falling weight height of 50 cm and a measuring atmosphere of 20 ° C. evaluated. ◯: No abnormality Δ: Some small cracks are observed. X: A large crack is seen.

Anticorrosion property: JI
A salt spray test was conducted according to S Z2371 for 840 hours. The degree of rust and blistering on the steel sheet at that time was evaluated. ○: No abnormalities such as rust and blisters △: Slight spots and blisters occurred ×: Spots and blisters were noticeable

[0045]

[Table 2]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masa Enomoto 4-17-1, Higashi-Hachiman, Hiratsuka-shi, Kanagawa Kansai Paint Co., Ltd.

Claims (1)

[Claims] 1. A cationic electrodeposition coating composition, which comprises hydroxyl group-containing polybutadienes 5 to 9 having two or more hydroxyl groups in the molecule.
A number obtained by introducing a blocked isocyanate group into a molecule through a urethane bond formed by a reaction between a hydroxyl group of a hydroxyl group-containing modified polybutadiene obtained by an addition reaction of 5 parts by weight and 95 to 5 parts by weight of an alkylene oxide and an isocyanate group. A polyurethane resin having an average molecular weight of 1,500 to 20,000 is added in an amount of 0.5 to 50 in 100 parts by weight of the total resin solid content.
A cationic electrodeposition coating composition, characterized by containing parts by weight.