JP3593621B2 - Multilayer coating forming cationic electrodeposition coating composition - Google Patents

Description

【００５５】
上記組成に従って、適当な反応容器を用い、室温で２−エチルヘキサノールハーフブロック化ＴＤＩをジメチルエタノールアミンに加えた。混合物は発熱し、これを８０℃で１時間攪拌した。次いて、乳酸を仕込み、さらにブチルセロソルブを反応混合物を６５℃で約半時間攪拌し、四級化剤を得た。
【００５６】

【００５７】
上記組成に従って、ＥＰＯＮ８２９およびビスフェノールＡを適当な反応容器に仕込み、窒素雰囲気下１５０〜１６０℃へ加熱した。初期発熱反応が起こった。反応混合物を１５０〜１６０℃で約１時間反応させ、次いで、１２０℃へ冷却後、２−エチルヘキサノールハーフブロック化ＴＤＩを加えた。反応混合物を１１０〜１２０℃に約１時間保ち、次いで、ブチルセロソルブを加えた。次いで、８５〜９５℃に冷却して均一化し、さらに１）の四級化剤を加えた。酸価が１になるまで混合物を８５〜９５℃に保持し、顔料分散用ワニスを得た。樹脂固形分５０％
【００５８】
３）顔料分散ペースト
以下の成分混合物をサンドグラインドミルで分散し、粒度１０μ以下になるまで粉砕して顔料分散ペーストを得た。
【００５９】

【００６０】
実施例１〜６および比較例１〜３
製造例３〜９のアクリルエマルションＡ〜Ｇと、製造例１０のエポキシエマルションとを、表１に示す割合で混合し、脱イオン水を加え、固形分約２０％のカチオン電着塗料を得た。各塗料をリン酸亜鉛処理した冷延鋼板に乾燥膜厚約２０μｍになるように２００ボルトで３分間電着し、水洗後１８０℃で２０分間焼付けし、硬化塗膜の性能を評価し、表２に示す結果を得た。
【００６１】
【表１】

【００６２】
【表２】

【００６３】
１）硬化剤を含む各エマルション中の樹脂固形分重量比
２）硬化剤を除いた各エマルション中の樹脂固形分重量比
３）カチオン性アクリル樹脂１分子あたりのハーフブロックイソシアネート基の付加数
４）塗板をサンシャインウエザオメーターへ取付け、４００時間照射後６０°グロスを測定し、初期６０°グロスの保持率を求めた。
５）塗板でナイフで素地に達するクロスカットを入れ、ＪＩＳ Ｋ５４００に準じて塩水噴霧試験（５％食塩水，５５℃）を２４０時間行い、粘着テープによってカット部両側から剥離した剥離部の最大幅。
６）膜厚約２０μｍの硬化電着塗膜上にアルキッド系上塗り塗料（日本ペイント株式会社製オルガセレクトシルバー）を乾燥膜厚２５〜３０μｍにスプレー塗装し、１４０℃×２０分焼付けして得られる塗膜に１ｍｍ×１ｍｍのゴバン目１００個を作り、その表面に粘着テープを粘着し、急激に剥離した後の塗面に残ったゴバン目の数を記録した。
７）メチルイソブチルケトンをしみ込ませたガーゼで塗膜を１０往復こすり、乾燥後外観を評価した。
○：変化なし ×：白ボケ著しい
８）膜厚約２０μｍの硬化電着塗膜上にメタリックベース塗料（日本ペイント株式会社製０６シルバー）およびクリヤ塗料を塗装し、焼付けた後、携帯式写像解明度測定器（スガ試験機械株式会社製ＨＡ−ＮＳＩＣ）により写像鮮明度を測定した。鉄と鋼Ｖｏｌ．７７，Ｎｏ．７，１０７５−１０８６（１９９１）参照。[0001]
Background of the invention
The present invention relates to a cationic electrodeposition coating composition, particularly to a cationic electrodeposition coating composition having excellent corrosion resistance and weather resistance.
[0002]
Amine-modified epoxy resins, amine-modified acrylic resins, and the like are known as base resins used in cationic electrodeposition coatings, of which amine-modified epoxy resins have excellent corrosion resistance, and amine-modified acrylic resins have excellent weather resistance. Therefore, these performances are properly used depending on the application required. Since there is no known base resin which is excellent in both performances alone, there has been no choice but to blend epoxy-based and acrylic-based cationic resins in the field where both corrosion resistance and weather resistance are required. However, it goes without saying that the corrosion resistance and the weather resistance of the homogeneous blend system are inferior to the case where the epoxy cationic resin and the acrylic cationic resin are used alone.
[0003]
Therefore, at the time of baking after electrodeposition coating, a layer rich in an epoxy-based cationic resin having excellent corrosion resistance is formed on the metal substrate side, and a layer rich in an acrylic-based cationic resin having excellent weather resistance is formed on the surface side. Blend compositions that separate into layers have been proposed. Such an epoxy / acrylic blend-based cationic electrodeposition coating composition is disclosed in, for example, the following prior art documents.
[0004]
JP-A-62-174277
JP-A-63-51470
JP-A-2-33069
JP-A-2-160876
[0005]
The acrylic cationic resin blended with the epoxy cationic resin in these prior arts is non-self-crosslinkable or nonionic. When these blends are separated into two layers, they are cross-linked and cured by the blocked polyisocyanate, which relatively migrates to the epoxy resin-rich layer, so if the acrylic resin is not self-crosslinkable, it will crosslink the acrylic resin-rich layer. The density tends to be unsatisfactory. Therefore, when a solvent-type paint is overcoated on the electrodeposition coating film, the solvent contained in the topcoat paint will damage the electrodeposition coating film, and a coating finish having an excellent appearance cannot be obtained.
[0006]
In a system in which a nonionic acrylic resin is blended, an amount sufficient to obtain satisfactory weather resistance cannot be blended because the acrylic resin itself has no electric charge.
[0007]
Generally, these epoxy / acrylic blend-based cationic electrodeposition paints are mainly used for two-coat finishing in which an overcoat layer is applied directly on an undercoat layer of an electrodeposition paint layer, and therefore, adhesion to the overcoat layer is important. . However, the ability of the blend to separate into two layers rich in each component and the adhesion to the overcoat layer of the surface layer rich in the separated acrylic component are difficult to achieve at the same time. None of the prior art epoxy / acrylic blend systems solve this problem.
[0008]
Disclosure of the present invention
It is therefore an object of the present invention to eliminate or mitigate the disadvantages of the prior art epoxy / acrylic blend-based cationic electrodeposition coating compositions.
[0009]
Therefore, the present invention
(A) an amine-modified epoxy cationic resin,
(B) a self-crosslinkable acrylic cationic resin and
(C) Blocked polyisocyanate curing agent
Is provided in an aqueous medium containing a neutralizing agent to provide a cationic electrodeposition coating composition. According to the present invention, the self-crosslinkable acrylic cationic resin can be obtained by introducing a blocked isocyanate group into the cationic acrylic resin by an addition reaction with a half-blocked diisocyanate compound.
[0010]
According to the present invention, the cationic acrylic resin as the starting resin of the component (b) has a solubility at least 0.5, preferably 0.5 to 2.0 lower than that of the epoxy cationic resin of the component (a). It has a parameter (SP) value. Thereby, the performance of separating the blend system of the component (a) and the component (b) into two layers rich in each component is enhanced.
[0011]
Further according to the invention, the resin of component (b) has a hydroxyl number of 100 to 200. This makes it possible to achieve both the performance of separating the coating film into two layers rich in the component (a) and the component (b), and the adhesion to the topcoat paint of the surface layer rich in the separated component (b). In addition, the relatively high hydroxyl number of the resin provides a crosslinking point with the blocked polyisocyanate curing agent and, in combination with imparting self-crosslinking properties, helps to increase the crosslinking density of the surface layer rich in component (b).
[0012]
The composition of the present invention comprises the epoxy cationic resin of the component (a) and the self-crosslinkable acrylic cationic resin of the component (b) in a weight ratio of solid content of 80 to 30 to the latter 20 to 70. Contains. This means that the component (b) itself has a charge required for electrodeposition and is self-crosslinking, so that the component (b) can be blended at a ratio satisfying the weather resistance. In such a case, a sufficient degree of curing can be obtained in which the appearance is not deteriorated by the overcoating.
[0013]
Description of the preferred embodiment
(A) component
Amine-modified epoxy cationic resins are well known in the field of cationic electrodeposition coatings. Generally, these are produced by opening the epoxy ring of a resin having a plurality of epoxy groups in the molecule by reaction with a primary amine, secondary amine or tertiary amine salt. A typical example of the starting resin is a polyphenol polyglycidyl ether type epoxy resin which is a reaction product of a polycyclic phenol compound such as bisphenol A, bisphenol F, bisphenol S, phenol novolak, and cresol novolak with epichlorohydrin.
[0014]
The starting resin can be chain-extended using a bifunctional polyester polyol, polyether polyol, bisphenols, dibasic carboxylic acid or the like before the ring opening reaction of the epoxy ring with the amine. Alternatively, an oxazolidone ring-containing epoxy resin may be produced directly by a diisocyanate compound or by reaction with a bisurethane obtained by blocking the diisocyanate compound with a lower alcohol such as methanol or ethanol, and then reacted with an amine. See JP-A-5-306327 of the present applicant. Before the reaction with the amine, the starting resin may be used to adjust the molecular weight or the amine equivalent, to improve the heat flow property, etc., for some epoxy rings to be 2-ethylhexanol, nonylphenol or ethylene glycol mono-2. A monohydroxy compound such as -ethylhexyl ether or propylene glycol mono-2-ethylhexyl ether can also be used.
[0015]
The starting material containing the resin modified with a chain extension and / or a monohydroxy compound then opens the epoxy ring by reaction with an amine to introduce an amino group. Examples of amines that can be used include primary amines such as butylamine, octylamine, diethylamine, dibutylamine, methylbutylamine, monoethanolamine, diethanolamine, N-methylethanolamine, triethylamine, N, N-dimethylethanolamine. , Secondary or tertiary amine salts. Secondary amines containing ketimine-blocked primary amino groups, such as aminoethylethanolamine methyl isobutyl ketimine, are often used. These amines must be reacted in at least an equivalent amount to the epoxy ring so as to open all remaining epoxy rings.
[0016]
(B) component
The cationic acrylic resin can be produced by a ring-opening addition reaction between an amine and an acrylic copolymer containing a plurality of oxirane rings and a plurality of hydroxy groups in a molecule. Such acrylic polymers include (i) glycidyl (meth) acrylate and (ii) a hydroxyl group-containing acrylic monomer such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, Placcel FA and FM. It can be obtained by copolymerizing an addition reaction product of 2-hydroxyethyl (meth) acrylate and caprolactone, known as a series, with (iii) other acrylic and / or non-acrylic monomers. Examples of other acrylic and non-acrylic monomers include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate. A) acrylate, t-butyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, styrene, vinyltoluene, α-methylstyrene, (meth) acrylonitrile, (meth) acrylamide , Vinyl acetate and the like.
[0017]
This oxy ring-containing acrylic resin is obtained by completely converting the oxirane ring of the epoxy resin to a primary amine, just as in the case of producing the component (a) by opening the oxirane ring of the epoxy resin with an amine and introducing a cationic group. The ring is opened by a reaction with a secondary amine or a tertiary amine salt to obtain a cationic acrylic resin.
[0018]
As another method, a cationic acrylic resin can be directly produced by copolymerizing an acrylic monomer having an amino group with another monomer. In this case, N, N-dimethylaminoethyl (meth) acrylate, N, N-di-t-butylaminoethyl (meth) is used instead of glycidyl (meth) acrylate previously used for producing the oxirane ring-containing acrylic resin. A cationic acrylic resin is directly obtained by using an amino group-containing acrylic monomer such as acrylate and copolymerizing it with a hydroxyl group-containing acrylic monomer and other acrylic and / or non-acrylic monomers.
[0019]
The cationic acrylic resin is obtained by copolymerizing the monomers by a conventional method so that the number average molecular weight of the polymer is in the range of 1,000 to 20,000, preferably 2,000 to 10,000. .
[0020]
The cationic acrylic resin must have an SP value that is at least 0.5, preferably 0.5 to 2.0 lower than the SP value of component (a). The SP value of the copolymer can be determined by calculation based on the SP value of the homopolymer of the constituent monomers and the weight fraction of each constituent monomer in the monomer mixture. Therefore, if the SP value of the component (a) used is known by actual measurement, it is possible to design a cationic acrylic resin having a desired SP value. The SP value is an index indicating the polarity of the resin, and can be measured, for example, using a turbidity method by titration with water and hexane. Since this resin needs to be designed to have a relatively low SP value, monomers having a low homopolymer SP value as copolymerized monomers, for example, t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, An alkyl (meth) acrylate having an alkyl group of 4 or more such as lauryl (meth) acrylate or stearyl (meth) acrylate may be used, and the SP value of the resin may be designed in a desired range. In order for the composition of the present invention to separate into two layers, the SP value of this resin must be at least 0.5 lower than the SP value of component (a). However, if the difference between the SP values is too large, the adhesion of the overcoat also decreases, so that the difference is preferably not more than 2.0.
[0021]
In the cationic acrylic resin thus obtained, a blocked isocyanate group is introduced by an addition reaction with a half-blocked diisocyanate compound. Half-block diisocyanate is obtained by blocking one isocyanate group of a diisocyanate compound with a known blocking agent. Examples of the diisocyanate compound include aromatic diisocyanates such as tolylene diisocyanate (TDI), 4,4′-diphenylmethane diisocyanate (MDI) and xylylene diisocyanate (XDI), hexamethylene diisocyanate (HMDI), isophorone diisocyanate (IPDI), 4,4 Aliphatic and cycloaliphatic diisocyanates such as' -methylenebis (cyclohexyl isocyanate), trimethylhexamethylene diisocyanate may be used.
[0022]
Blocking agents which can be used are well known in the art and include aliphatic alcohols such as n-butanol, 2-ethylhexanol, ethylene glycol monobutyl ether, cyclohexanol; phenols such as phenol, nitrophenol, cresol and nonylphenol; Oximes such as dimethyl ketoxime, methyl ethyl ketoxime and methyl isobutyl ketoxime; and lactams such as caprolactam. The half-block diisocyanate is added at least one molecule per one molecule of the cationic acrylic resin.
[0023]
In the case of producing the component (b) starting from the oxirane ring-containing acrylic resin described above, the introduction of the cationic group and the introduction of the blocked isocyanate group are performed in reverse order, that is, the blocked isocyanate group is introduced first, and then the cationic group is introduced. It is also possible to introduce a functional group.
[0024]
Component (b) must have a hydroxyl number in the range of 100-200. This can be designed beforehand by calculation from the weight fraction of hydroxyl group-containing monomers in the monomer mixture. If the hydroxyl value does not reach this range, the overcoat adhesion is unsatisfactory, and if it exceeds this range, the water resistance becomes unsatisfactory.
[0025]
In the cationic electrodeposition coating composition containing the epoxy / acrylic cationic resin blend according to the prior art cited above, the cationic acrylic resin to which a cationic group is introduced and half-blocked isocyanate is added is not blended. The component (b) of the present invention is self-crosslinking, so that the acrylic resin surface layer can be satisfactorily cured after being separated into two layers, and has a sufficient weather resistance because it itself has a charge necessary for electrodeposition. It is possible to blend at a high ratio to obtain the property.
[0026]
(C) component
Block polycyanate compounds are widely used as external crosslinking agents in the coatings field. These blocked not only the diisocyanate compounds described above with respect to the half-blocked isocyanate compounds, but also trifunctional or higher polyisocyanate compounds such as trimethylolpropane adducts and trimers with the known blocking agents described above. Things. However, unlike half-blocked diisocyanates, all isocyanate groups must be blocked.
[0027]
Paint composition
The coating composition of the present invention preferably contains the component (a) and the component (b) in a weight ratio of solid content of 80:20 to 30:70. In this range, a good balance between corrosion resistance and weather resistance is achieved. The coating may be performed by separately dispersing or emulsifying the components (a) and (b) together with the component (c) in an aqueous medium containing a neutralizing agent, and then blending the components. The component (b) and the component (c) may be simultaneously dispersed or emulsified in an aqueous medium containing a neutralizing agent.
[0028]
The neutralizing agent is an inorganic or organic acid such as hydrochloric acid, nitric acid, phosphoric acid, formic acid, acetic acid, lactic acid, sulfamic acid and acetylglycine. The aqueous medium is water or a mixture of water and an organic solvent. Examples of solvents that can be used include hydrocarbons (eg, xylene or toluene), alcohols (eg, methyl alcohol, n-butyl alcohol, isopropyl alcohol, 2-ethylhexyl alcohol, ethylene glycol, propylene glycol), ethers ( For example, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, propylene glycol monoethyl ether, 3-methyl-3-methoxybutanol, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether), ketones (for example, methyl Isobutyl ketone, cyclohexanone, isophorone, acetylacetone), esters (eg, ethylene glycol monoethyl) Chromatography ether acetate, ethylene glycol monobutyl ether acetate) or mixtures thereof.
[0029]
The amount of the blocked polyisocyanate curing agent must be sufficient to react with the functional groups of the hydroxyl groups in the resin during curing to give a good cured coating, and generally the components (a) and (b) 10-100 parts by weight per 100 parts by weight of total solids are used. The amount of neutralizing agent is sufficient to neutralize at least 20%, preferably 30-60%, of the amino groups in the resin.
[0030]
The coating can include a urethane cleavage catalyst such as dibutyltin dilaurate, tin acetate. The amount is usually 0.1 to 5% by weight of the blocked polyisocyanate curing agent.
[0031]
The paints further include coloring pigments such as titanium dioxide, carbon black and red iron oxide, rust preventive pigments such as basic lead silicate and aluminum phosphomolybdate, extender pigments such as kaolin, clay and talc, as well as surfactants and antioxidants. And conventional paint additives such as agents, UV absorbers and the like.
[0032]
The electrodeposition is performed by adjusting the non-volatile content of the coating material to about 15 to 25%, using the material to be coated as a cathode, a bath temperature of 15 to 35 ° C., and a load voltage of 100 to 400 V under a dry film thickness of 10 to 50 μm, preferably 20 to 50 μm. It can be carried out by electrodeposition to ４０40 μm and baking at 100 to 200 ° C., preferably 140 to 180 ° C. for 10 to 30 minutes. Thereafter, a two-coat finish excellent in adhesion and appearance can be obtained by overcoating on the electrodeposition coating film and baking by an ordinary method. Although this method is a two-coat two-bake coating method, a two-coat one-bake coating method in which a top coat is applied on the electrodeposition coating film before baking by wet-on-wet and both are baked simultaneously is also possible.
[0033]
As the topcoat paint, a normal topcoat paint can be used, for example, an acrylic resin, an alkyd resin or a combination of a polyester resin and a melamine resin, an aminoplast-curable paint, an acid-epoxy-curable paint, a one-part urethane paint and a silanol-curable paint A paint or the like is used. The form of the paint may be any of a solvent type, an aqueous type and a powder type. Before applying the top coat, a paint for imparting chipping resistance or the like may be applied in advance, if necessary.
[0034]
Hereinafter, the present invention will be illustrated by Production Examples, Examples and Comparative Examples. In these, parts and percentages are by weight unless otherwise specified.
[0035]
Production Example 1
In a five-necked flask equipped with a reflux condenser, a stirrer, and a dropping funnel, 187.2 parts of methyl isobutyl ketone and 168 parts of hexamethylene diisocyanate were charged and heated to 50 ° C. under a nitrogen atmosphere. To this, 0.5 part of dibutyltin dilaurate was added, and 113.1 parts of methyl ethyl ketoxime was added dropwise from the dropping funnel over about 30 minutes. After the completion of the addition, the mixture was reacted at the same temperature for about 1 hour, cooled, and cooled to a half block of NCO equivalent 402. A diisocyanate solution was obtained. 60% solids
[0036]
Production Example 2
In a five-necked flask equipped with a reflux condenser, a stirrer, a dropping funnel and a nitrogen inlet tube, 199.1 parts of hexamethine diisocyanate trimer (Coronate EH) and 31.6 parts of methyl isobutyl ketone were charged, and charged under a nitrogen atmosphere. Heated and maintained at ℃. To this, 0.2 part of dibutyltin dilaurate was added, and 87.0 parts of methyl ethyl ketoxime was added dropwise from the dropping funnel over 2 hours. After completion of the dropwise addition, the mixture was reacted at 70 ° C. until the peak of the isocyanate group disappeared in the IR spectrum. After the completion of the reaction, 38.1 parts of methyl isobutyl ketone and 1.6 parts of butanol were added, and the mixture was cooled to obtain a blocked polyisocyanate curing agent having a solid content of 80%.
[0037]
Production Example 3
56.3 parts of methyl isobutyl ketone is charged into a five-necked flask equipped with a reflux condenser, a stirrer, a dropping funnel and a nitrogen inlet tube, and heated and maintained at 115 ° C. under a nitrogen atmosphere. To this, 16.0 parts of glycidyl methacrylate, 4.2 parts of 2-hydroxyethyl methacrylate, 14.8 parts of 2-hydroxypropyl methacrylate, 58.1 parts of n-butyl methacrylate, 6.9 parts of t-butyl methacrylate, and t A mixture of 4.0 parts of -butyl peroctoate was dropped from the dropping funnel over 3 hours. After completion of the dropwise addition, the mixture was maintained at 115 ° C. for about 1 hour, 0.5 parts of t-butyl peroctoate was added dropwise, and the mixture was maintained at 115 ° C. for about 30 minutes to obtain a resin solution having a solid content of 65%. Number average molecular weight (Mn) 6000
[0038]
After cooling, 8.5 parts of N-methylethanolamine was added thereto and reacted at 120 ° C. for 2 hours under a nitrogen atmosphere to obtain an amine-added acrylic resin solution having a solid content of about 67%.
[0039]
Next, the solution was cooled to 70 ° C., 0.1 part of dibutyltin dilaurate was added, and 10.3 parts of the half-block diisocyanate solution of Production Example 1 was added dropwise as a solid from a dropping funnel over about 30 minutes. The reaction was continued until the peak of the isocyanate group disappeared.
[0040]
This solution was kept at 60 ° C., and 21.7 parts (solid content) of the block polycyanate curing agent of Production Example 2 was added and mixed, and then kept at 50 ° C. for 30 minutes under a nitrogen atmosphere, and 2.6 parts of acetic acid was added. In addition, the mixture was neutralized and slowly diluted with deionized water to obtain an acrylic emulsion A having a solid content of 30%. Hydroxyl value 157 mgKOH / g solid content, SP value of cationic acrylic resin 10.3
[0041]
Production Example 4
In the same manner as in Production Example 3, 10.0 parts of glycidyl methacrylate, 18.0 parts of 2-hydroxypropyl methacrylate, 56.8 parts of lauryl methacrylate, and 15.2 parts of styrene were polymerized to give a number average molecular weight of 6000 and a solid content of 65%. Was obtained.
[0042]
This resin was reacted with 5.3 parts of N-methylethanolamine in the same manner as in Production Example 3, further added with 15.1 parts of a half-block diisocyanate solid content of Production Example 1, and mixed with the curing agent of Production Example 2. After neutralizing with acetic acid and diluting with deionized water, an acrylic emulsion B having a solid content of 30% was obtained. Hydroxyl value 107 mgKOH / g solid content, SP value of cationic acrylic resin 9.2
[0043]
Production Example 5
An acrylic emulsion C having a solid content of 30% was obtained in the same manner as in Production Example 3 except that the addition amount of the half-block diisocyanate in Production Example 1 was changed to 30.2 parts as a solid content. Hydroxyl number 121mgKOH / g solid content
[0044]
Production Example 6
50 parts of methyl isobutyl ketone is charged into a five-necked flask equipped with a reflux condenser, a stirrer and a nitrogen inlet tube, and heated and maintained at 115 ° C. under a nitrogen atmosphere. 20.0 parts of 2-hydroxyethyl methacrylate, 21.3 parts of 2-hydroxypropyl methacrylate, 19.1 parts of 2-ethylhexyl methacrylate, 15.0 parts of N, N-dimethylaminoethyl methacrylate, 24.9 parts of lauryl methacrylate , And a mixture of 4.0 parts of t-butyl peroctoate were added dropwise from the dropping funnel over 3 hours, and after completion of the addition, the mixture was maintained at 115 ° C. for about 1 hour, and 0.5 part of t-butyl peroctoate was added dropwise. Then, the temperature was maintained at 115 ° C. for about 30 minutes to obtain a resin solution having a solid content of 65%. Number average molecular weight 6000, SP value 10.9
[0045]
This resin was reacted with 10.3 parts of the solid content of the half-block diisocyanate of Production Example 1 in the same manner as in Production Example 3, mixed with the curing agent of Production Example 2, neutralized with acetic acid, diluted with deionized water, and solidified. A 30% acrylic emulsion D was obtained. Hydroxyl value 140mgKOH / g solid content
[0046]
Production Example 7 (emulsion for comparative example)
In the same manner as in Production Example 3, 10.0 parts of glycidyl methacrylate, 7.0 parts of 2-hydroxyethyl methacrylate, 36.5 parts of methyl methacrylate, and 46.5 parts of n-butyl acrylate were polymerized, and the number average molecular weight was 6,000, A 65% resin solution was obtained.
[0047]
To this resin was added 5.3 parts of N-methylethanolamine, reacted with 10.3 parts of a half-block diisocyanate solid content as in Production Example 3, mixed with the curing agent of Production Example 2, and neutralized with acetic acid. After dilution with water, an acrylic emulsion E having a solid content of 30% was obtained. Hydroxyl value 82mgKOH / g solid content, SP value of cationic acrylic resin 10.4
[0048]
Production Example 8 (emulsion for comparative example)
In the same manner as in Production Example 3, 10.0 parts of glycidyl methacrylate, 12.0 parts of 2-hydroxyethyl acrylate, 9.9 parts of methyl acrylate, 47.2 parts of methyl methacrylate, and 20.9 parts of ethyl acrylate were polymerized, A resin solution having a number average molecular weight of 6000 and a solid content of 65% was obtained.
[0049]
To this solution was added 9.1 parts of dibutylamine, mixed with the curing agent of Production Example 2 in the same manner as in Production Example 3 without adding half-block diisocyanate, neutralized with acetic acid, diluted with water, and solidified. An acrylic emulsion F of 30% was obtained. Hydroxyl value 86 mg / KOH / g solid content, SP value of cationic acrylic resin 11.2
[0050]
Production Example 9 (emulsion for comparative example)
An acrylic emulsion G having a solid content of 30% was produced in the same manner as in Production Example 3 except that the half-block diisocyanate was not added. Hydroxyl number 179mgKOH / g solid content
[0051]
Production Example 10
In a five-necked flask equipped with a reflux condenser, a stirrer, a dropping funnel and a nitrogen inlet tube, 840 parts of hexamethylene diisocyanate, 609 parts of methyl isobutyl ketone, and 0.9 parts of dibutyltin dilaurate were charged, and the temperature was raised to 50 ° C. To this, 223.5 parts of trimethylolpropane was gradually dropped while keeping the internal temperature not exceeding 60 ° C. Next, 435 parts of methyl ethyl ketoxime was added dropwise while keeping the internal temperature not exceeding 70 ° C. After completion of the dropwise addition, the mixture was kept at 70 ° C. for 1 hour until the peak of the isocyanate group disappeared from the IR spectrum, butanol (32 parts) was added, and the mixture was cooled to prepare a blocked isocyanate curing agent. 70% solids
[0052]
Separately, in a similar reaction vessel, 950 parts of a bisphenol-type epoxy resin having an epoxy equivalent of 950 (Epitoto YD-014 manufactured by Toto Kasei Co., Ltd.) and 237.5 parts of methyl isobutyl ketone (MIBK) are charged and heated to 100 ° C. And completely dissolved. To this, 73.4 parts of a 73% MIBK solution of diethylenetriamine MIBK diketimine and 60.1 parts of N-methylethanolamine were added and reacted at 115 ° C. for 1 hour to prepare a cationic epoxy resin solution. 80.5% resin solids, SP value 11.4
[0053]
832.3 parts of this cationic epoxy resin solution, 471.4 parts of the above-obtained blocked polyisocyanate curing agent solution, and 65.0 parts of n-hexyl cellosolve were mixed, neutralized with 18.5 parts of glacial acetic acid, and then removed. The mixture was slowly diluted with 1737.8 parts of ionic water and the organic solvent was removed under reduced pressure to obtain an epoxy emulsion having a solid content of 36.0%.
[0054]
Production Example 11 (Pigment dispersion paste)

[0055]
According to the above composition, 2-ethylhexanol half-blocked TDI was added to dimethylethanolamine at room temperature using an appropriate reaction vessel. The mixture exothermed and was stirred at 80 ° C. for 1 hour. Next, lactic acid was charged, and butyl cellosolve was further stirred at 65 ° C. for about half an hour to obtain a quaternizing agent.
[0056]

[0057]
According to the above composition, EPON829 and bisphenol A were charged into a suitable reaction vessel and heated to 150 to 160 ° C under a nitrogen atmosphere. An initial exothermic reaction occurred. The reaction mixture was reacted at 150 to 160 ° C. for about 1 hour, and then cooled to 120 ° C., and then 2-ethylhexanol half-blocked TDI was added. The reaction mixture was kept at 110-120 ° C. for about 1 hour, then butyl cellosolve was added. Then, the mixture was cooled to 85 to 95 ° C. to homogenize, and the quaternizing agent of 1) was further added. The mixture was kept at 85 to 95 ° C. until the acid value became 1, and a varnish for dispersing a pigment was obtained. Resin solid content 50%
[0058]
3) Pigment dispersion paste
The following mixture of components was dispersed in a sand grind mill and pulverized until the particle size became 10 μm or less to obtain a pigment dispersion paste.
[0059]

[0060]
Examples 1 to 6 and Comparative Examples 1 to 3
The acrylic emulsions A to G of Production Examples 3 to 9 and the epoxy emulsion of Production Example 10 were mixed at the ratio shown in Table 1, and deionized water was added to obtain a cationic electrodeposition paint having a solid content of about 20%. . Each paint was electrodeposited on a cold-rolled steel sheet treated with zinc phosphate at 200 volts for 3 minutes to a dry film thickness of about 20 μm, washed with water and baked at 180 ° C. for 20 minutes to evaluate the performance of the cured coating film. The results shown in FIG.
[0061]
[Table 1]

[0062]
[Table 2]

[0063]
1) Resin solids weight ratio in each emulsion containing curing agent
2) Resin solids weight ratio in each emulsion excluding curing agent
3) Number of added half-blocked isocyanate groups per molecule of cationic acrylic resin
4) The coated plate was attached to a sunshine weatherometer, and after irradiating for 400 hours, 60 ° gloss was measured to determine the initial 60 ° gloss retention.
5) Make a cross cut to reach the substrate with a knife using a coated plate, conduct a salt spray test (5% saline, 55 ° C) for 240 hours in accordance with JIS K5400, and use a pressure-sensitive adhesive tape to remove the maximum width of the peeled part peeled from both sides of the cut part. .
6) An alkyd top coat (Nippon Paint Co., Ltd. Olga Select Silver) is spray-coated on a cured electrodeposition coating film having a thickness of about 20 μm to a dry thickness of 25 to 30 μm, and baked at 140 ° C. for 20 minutes. One hundred squares of 1 mm × 1 mm squares were formed on the coating film, and an adhesive tape was adhered to the surface, and the number of squares remaining on the coated surface after abrupt peeling was recorded.
7) The coating film was rubbed 10 times with gauze impregnated with methyl isobutyl ketone, and dried to evaluate the appearance.
：: No change ×: Significant white blur
8) A metallic base paint (06 silver manufactured by Nippon Paint Co., Ltd.) and a clear paint are applied on the cured electrodeposition coating film having a film thickness of about 20 μm, and after baking, a portable mapping resolution measuring instrument (Suga Test Machine Co., Ltd.) HA-NSIC) was used to measure the image definition. Iron and Steel Vol. 77, no. 7, 1075-1086 (1991).

Claims (6)

(A) an amine-modified epoxy cationic resin,
(B) a self-crosslinkable acrylic resin having a hydroxyl value of 100 to 200 obtained by adding a half-block diisocyanate compound to a cationic acrylic resin having a solubility parameter at least 0.5 lower than that of the amine-modified epoxy-based cationic resin to introduce a blocked isocyanate group; The cationic cationic resin and the (c) blocked polyisocyanate curing agent are dispersed in an aqueous medium containing a neutralizing agent, and the solid content ratio of the components (a) and (b) is 80:20 to 30: 70. A cationic electrodeposition coating composition, which is 70. The component (b) may optionally comprise (i) introduction of an amino group into the oxirane ring-containing acrylic resin by ring opening of the oxirane ring with an amine, and (ii) introduction of a blocked isocyanate group by an addition reaction with a half-blocked isocyanate compound. The composition according to claim 1, which is a self-crosslinkable acrylic cationic resin obtained by performing the above steps in order. The component (b) is a self-crosslinkable acrylic cationic resin obtained by adding a blocked isocyanate group by reacting a half-blocked isocyanate compound to an acrylic resin containing an amino group-containing acrylic monomer and a hydroxyl group-containing acrylic monomer. The composition of claim 1. The composition according to any one of claims 1 to 3, comprising 10 to 100 parts by weight of the solid component (c) per 100 parts by weight of the total solid content of the component (a) and the component (b). Coating characterized by coating and baking the electrodeposition coating composition according to any one of claims 1 to 4 on an object to be coated, and then coating and baking a solvent type coating, powder coating or water-based coating thereon. Method. After applying the electrodeposition coating composition according to any one of claims 1 to 4 to an object to be coated, a solvent type coating, a powder coating or a water-based coating is applied thereon by wet-on-wet, and the whole is baked simultaneously. A coating method characterized by the following.