JPS629625B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a novel composition for cationic electrodeposition coatings, and more particularly, to corrosion resistance of low-temperature curable coatings,
This invention relates to a novel composition for cationic electrodeposition coatings that exhibits excellent performance in terms of water resistance, hardness, etc. As electrodeposition coating methods, anodic deposition coating methods and cathodic deposition coating methods are conventionally known. Of these, the former method has been the mainstream in the past, but this method has several fundamental problems and cannot be said to be a method that fully satisfies the recent stringent demands for corrosion resistance. In other words, in the case of anodic deposition electrodeposition coating, since the metal to be coated is the anode, it is ionized during the electrodeposition coating and the metal base and chemical conversion coating are eluted, and some of the metal ions remaining in the deposited coating are removed by the coating. It tends to color the film and impair the corrosion resistance and alkali resistance of the paint film. On the other hand, in the case of cathodic deposition electrodeposition coating, there is no elution of metals or chemical conversion coatings, so there is no discoloration, and a coating film with excellent corrosion resistance and alkali resistance can be obtained. It is attracting a lot of interest. Various studies have been conducted on the resins used in this cathodic electrodeposition coating. Modified acrylic resins produced by radical copolymerization of unsaturated compounds with oxidation (Japanese Patent Publication No. 48-37147, etc.), iminoamine-containing resins produced by the reaction of acid anhydride groups with diamines (Japanese Patent Publication No. 119727-1987), etc. have been proposed. There is. However, coating films using these cathodically deposited resins generally have high curing temperatures, poor throwing power due to low conductivity of bath paints, poor stability of diluted paints, and significantly high raw material costs. There are drawbacks. In addition, in the case of anodic deposition type electrodeposition paints, melamine resins and phenolic resins are often used in combination to improve the performance of the coating film, but in the case of cathodic deposition type paints, the melamine resins and phenolic resins present in the resin are often used. Even if you add melamine resin, phenol resin, etc., which have basic amino groups and have the property of accelerating curing on the acidic side, the curing reaction may not be carried out sufficiently, so it is difficult to have sufficient curing properties. required. Recently, a method has been developed in which a basic amino compound is added to epoxidized polybutadiene and then made water-soluble with an acid (Japanese Patent Laid-Open No. 53-16048
However, this method requires many reaction steps because it is necessary to quaternize the amino group after the reaction between the epoxidized polybutadiene and the basic amino group, and moreover, it requires a crosslinking reaction due to oxidative hardening of carbon-carbon double bonds. However, the basic amino group inhibits the crosslinking reaction, and as a result, it is difficult to achieve a higher level of coating performance. The inventors of the present invention have conducted intensive studies to improve these shortcomings of the conventional technology, and have found that by ionizing epoxidized polybutadiene with sulfonium using a specific method, it can be made water-soluble in one step, and that the amino groups Unlike conventional ammonium salts such as water-soluble melamine and water-soluble phenol, it is possible to obtain a coating film with sufficient hardness by baking at a relatively low temperature because the crosslinking reaction accompanied by auto-oxidation of carbon-carbon double bonds is not suppressed, unlike in the case of conventional ammonium salts such as water-soluble melamine and water-soluble phenol. The present inventors have discovered that it is possible to use crosslinking agents whose use is limited in aqueous solutions, and that as a result, electrodeposited coatings with high performance can be obtained, and have completed the present invention. The object of the present invention is to provide a cationic electrolyte film that can be baked at low temperatures and has excellent mechanical strength such as hardness and impact resistance, as well as chemical properties such as corrosion resistance and water resistance. An object of the present invention is to provide a wearable composition. These objects of the present invention are to partially epoxidize liquid polybutadiene and treat it with a thioether and an acid to obtain a water-soluble or water-dispersible resin for use as a vehicle component in a cationic electrodeposition composition. It is achieved by doing so. The liquid polybutadiene used in the present invention may be any polybutadiene as long as it has a number average molecular weight of 500 to 5000, preferably 700 to 4000, and an iodine value of 100 to 500, preferably 150 to 480. Cis-1,4 polybutadiene, 1,2-polybutadiene, cis-1,4 bond and trans-1,4
Examples include polybutadiene containing a mixture of bonds and vinyl bonds. The terminal end of the polybutadiene may be non-functional or may have a hydroxyl group or a carboxyl group. However, if the molecular weight is less than 500, the drying properties and mechanical properties of the resulting coating film will be significantly reduced, and if the molecular weight is greater than 5000, gelation will easily occur in the epoxidation reaction and water solubility will also decrease. Tend. Furthermore, if the iodine value is too low, air curing properties will be poor, and if it is too high, the weather resistance and mechanical properties of the coating film will be impaired. Also 1.4-
Corrosion resistance tends to decrease as the number of bonds decreases, and from this point of view it is preferable that the number of 1,4-bonds is 30% or more, more preferably 40% or more. The epoxidation reaction of liquid polybutadiene may be carried out according to a conventional method, and can be easily carried out, for example, by using hydrogen peroxide or a peracid. At that time, the degree of epoxidation of the double bonds of polybutadiene must be such that the oxirane oxygen content is 1.5 to 13% by weight, preferably 3 to 12% by weight, and if the oxirane oxygen content is too low, it is water-solubilized or water-dispersed. If the amount is insufficient, it is not desirable as a paint, and if it is too much, the curing reactivity of the paint decreases, making it impossible to exhibit sufficient performance. In the present invention, such epoxidized polybutadiene is treated with a thioether and an acid to obtain a water-soluble or water-dispersible resin, and the thioethers used at this time include dimethyl thioether,
Dialkyl thioethers such as diethyl thioether, dipropyl thioether, dibutyl thioether, dihexyl thioether, dihydroxyalkyl thioethers such as thiodiethanol, thiodipropanol, thiodibutanol, phenyl thioethers such as diphenyl thioether, methyl phenyl thioether, and even tetra Examples include alicyclic thioethers such as methylene sulfide, among which those having 2 to 18 carbon atoms are preferred. The amount of these thioethers used is 0.2 to 1.2 mol, preferably 0.3 to 1 mol, per 1 mol of oxirane oxygen in the epoxidized polybutadiene. On the other hand, as the acid component, organic or inorganic acids such as formic acid, acetic acid, propionic acid, butyric acid, lactic acid, hydroxyacetic acid, hydrochloric acid, and phosphoric acid are used, and the amount used is 0.2 to 1.2 per mole of thioether. mol, preferably 0.4 to 1 mol. Water solubilization or water dispersion of epoxidized polybutadiene with thioether and acid is carried out in one step by adding water while stirring the system in the presence or absence of water. Although mixing may be carried out at room temperature, the temperature of It is advisable to thoroughly stir the mixture while heating to ~90°C, preferably 50~80°C. Further, in this case, a water-soluble solvent such as alcohol or ether can be used for the purpose of lowering the viscosity of the reaction mixture and obtaining a stable aqueous solution or aqueous dispersion. The pH of the aqueous composition thus obtained is suitably 2-9, preferably 4-7. By using only water-soluble or water-dispersible materials as resin components for electrodeposition paints, it is possible to cure them at lower temperatures than before, and a coating film with sufficient performance can be obtained. However, in order to further lower the baking temperature and increase the hardness of the coating film, melamine, which was previously thought to be ineffective with cationic electrodepositing resins that introduced basic amino groups, was used.
Water-soluble amino resins or water-soluble phenolic resins such as formaldehyde condensates of urea or benzoguanamine can be mixed. In the present invention, a composition for electrodeposition coating is usually prepared in a concentration of 3 to 30% by weight.
It is appropriate to mix ordinary pigments such as carbon black, anti-corrosion pigments, and body pigments in an amount of 400 parts by weight or less per 100 parts by weight of resin, and add anti-aging agents, fillers, etc. as desired. You can also. The cationic electrodeposition coating composition of the present invention thus prepared can be baked at a relatively low temperature;
Shows excellent performance in coating film hardness, flexibility, corrosion resistance, and water resistance. The present invention will be explained in more detail with reference to Examples below. Note that all parts and percentages in Examples and Reference Examples are based on weight. Reference Example Sample A Liquid polybutadiene (number average molecular weight 1100, 30 Viscosity at °C: 800 centipoise, cis-1/4 type bond content by infrared absorption spectrum: 53%, trans-1/4 type bond content: 9%,
and 300 parts of toluene
The solution was dissolved in 300 parts, and 9 parts of sodium acetate was added thereto. Add 500 parts of peracetic acid (41%) to this mixture.
After adding slowly over a period of time, an additional 30
The reaction was carried out at ℃ for 4 hours. Thereafter, the reaction product was washed with water, an aqueous solution of caustic soda, and water in this order, and finally the solvent was removed under reduced pressure to obtain epoxidized polybutadiene with an oxirane oxygen content of 10.1%. For 100 parts of this epoxidized polybutadiene, 75 parts of 2,2'-thiodiethanol, 50 parts of lactic acid, and 30 parts of water.
of water and stirred at 65℃ for 30 minutes to obtain a transparent homogeneous liquid. Add distilled water to the liquid to obtain a solid concentration of 40%.
A water-soluble varnish with a pH of 5.9 was obtained. Sample B During the water solubilization process during the production of sample A, 2.
Water solubilization was carried out in the same manner except that 56 parts of diethylthioether was used instead of 75 parts of 2'-thiodiethanol to obtain a water-soluble varnish with a solid content concentration of 40% and a pH of 5.7. Sample C Instead of the polybutadiene used in the production of sample A, commercially available liquid cis-1,4 polybutadiene (trade name Polyoil 110, manufactured by Hyulus, number average molecular weight 1600, cis-1,4 = 74%, trans-
1.4 = 25%, vinyl = 1%)
All reactions were carried out in the same manner as in Sample A, and epoxidized polybutadiene containing 8.9% oxirane oxygen was obtained. 66.1 parts of 2,2'-thiodiethanol and lactic acid per 100 parts of this epoxidized polybutadiene.
A water-soluble varnish with a solid content concentration of 40% and a pH of 6.0 was obtained in the same manner as Sample A except that 45 parts and 30 parts of water were used. Sample D Instead of the epoxidized polybutadiene in Sample A,
Commercially available epoxidized 1,2-polybutadiene (manufactured by Nippon Soda Co., Ltd., number average molecular weight 1000, 90% vinyl 1.
2-polybutadiene epoxidized oxirane with oxygen content of 7.7%),
61.6 parts of thiodiethanol, 38 parts of lactic acid, 30 parts of water
A water-soluble varnish with a solid content concentration of 40% and a pH of 5.8 was obtained in the same manner as in Sample A except that the sample A was used. Sample E Nickel naphthenate-diethylaluminum chloride-1.3 in benzene solvent with water as catalyst
- Liquid polypentadiene obtained by polymerizing pentadiene (number average molecular weight 3200, iodine value 347, cis (1.4 + 1.2) = 75.9%, trans (1.4 +
1・2)=24.1%) was used instead of polybutadiene in sample A to epoxidize the oxirane oxygen content.
A 9.0% epoxidized product was obtained, and then 100 parts of this epoxidized product was mixed with 66.5 parts of 2,2'-thiodiethanol,
It was water-solubilized in the same manner as Sample A using 45 parts of lactic acid and 30 parts of water to obtain a water-soluble varnish with a solid content concentration of 40% and a pH of 5.5. Sample F For sample A, 100 parts of commercially available epoxidized soybean oil (manufactured by Asahi Denka Kogyo Co., Ltd., oxirane oxygen content 5%) were mixed with 40 parts of 2,2'-thiodiethanol, 27 parts of lactic acid, and 30 parts of water. Disperse in water in the same manner as
An aqueous dispersion of 38.5% and pH 5.1 was obtained. Example 1 Water-soluble or water-dispersible varnish prepared in Reference Example
100 parts of titanium oxide, 25 parts of titanium oxide, and 0.3 parts of carbon black were mixed and stirred for 1 hour using a pigment disperser to obtain a paste-like dispersion. 126 parts of this dispersion and 150 parts of the water-soluble or water-dispersible varnish obtained in Reference Example were mixed, and distilled water was added to prepare a coating liquid having a solid content of 10% and a pH of 5 to 7. This was used as an electrodeposition solution, and electricity was applied for 2 minutes at a voltage of 100 to 250V with a bath temperature of 25℃ and a distance between electrodes of 7cm using a dull steel plate treated with iron phosphate as a cathode. Take out the test piece, wash it with water, air dry it, and then heat it at the specified temperature for 30 minutes.
Bake for a minute. The performance of the obtained baked film was measured, and the results shown in Table 1 were obtained.

[Table] Comparative Example 1 100 parts of epoxidized polybutadiene with an oxirane oxygen content of 10.0% obtained in the manufacturing process of Sample A was mixed with 60 parts of diethanolamine and 10 parts of xylene and reacted at 150°C for 9 hours. After the xylene was distilled off under reduced pressure, lactic acid equivalent to 0.7 equivalents of the amino group was added, mixed well, and distilled water was added to give a solid concentration of 38% and pH 6.0. A water-soluble varnish was obtained. Using this varnish, electrodeposition was applied in the same manner as in Example 1 and baked at 190°C for 30 minutes.The resulting coating film had a thickness of 20 μm, a pencil hardness of H, and a salt spray resistance of 130. It was time. Example 2 In Sample A of Example 1, 25 parts of water-soluble melamine resin (Cymel 303, manufactured by American Cyanamid Co., Ltd.) was added to 75 parts of the solid content, and electrocoated in the same manner as in Example 1 to give 170 parts. When baked at ℃ for 30 minutes, a smooth coating film with a thickness of 22 μm was obtained. The properties of this coating film were a pencil hardness of 3H, a DuPont impact test (1/2 inch) of 500 g and 30 cm, a salt spray resistance of 450 hours, and a water resistance of 800 hours. Comparative Example 2 100 parts of a commercially available bisphenol type epoxy resin (manufactured by Ciel Chemical Co., Ltd., Epicoat 1001) was dissolved in 50 parts of ethylene glycol monobutyl ether, and 45 parts of 2,2'-thiodiethanol and lactic acid were dissolved in this.
32 parts and 30 parts of distilled water were added and stirred at 65°C for 30 minutes, resulting in a cloudy aqueous dispersion. This pH is 5.4
It was hot. 25 parts of water-soluble melamine resin (Cymel 303, manufactured by American Cyanamid Co., Ltd.) was added to 75 parts of the solid content of this material, and electrodeposition was applied in the same manner as in Example 2 (coating voltage: 150 V) at 170°C. 30
After baking for minutes, a coating film with a thickness of 21 μm and no gloss was obtained, the pencil hardness was H, the Dupont impact test (1/2 inch) passed 500 g, 25 cm, salt spray resistance was 320 hours, and water resistance was 550 hours. It was hot.

Claims (1)

[Scope of Claims] 1. Water-soluble or water-soluble polybutadiene obtained by treating epoxidized polybutadiene, which is obtained by epoxidizing liquid polybutadiene with a number average molecular weight of 500 to 5000 so that the oxirane oxygen content is 1.5 to 13% by weight, with a thioether and an acid. A composition for cationic electrodeposition coating, characterized by containing a dispersible resin. 2. The composition according to claim 1, wherein the amount of thioether used is 0.2 to 1.2 mol per 1 mol of oxirane oxygen. 3 The amount of acid used is 0.2 to 1 mole of thioether
A composition according to claim 2, wherein the composition is 1.2 moles. 4. The composition according to claim 1, wherein the polybutadiene contains 30% or more of 1.4 to 30% bonds. 5. The composition according to claim 1, wherein the thioether has 2 to 18 carbon atoms.