JP4309017B2 - Coating method - Google Patents

Description

【００６０】
製造例８
カチオン電着塗料１〜１６の調製
製造例１で得たカチオン性基体樹脂、製造例２〜５で得た第２のブロックポリイソシアネート化合物（イ）〜（ニ）および表２に示す金属触媒を表２の組成および配合量に従って混合し、１時間撹拌して氷酢酸で中和したのち、脱イオン水を用いて希釈し、不揮発分約４０質量％の樹脂組成物を得た。次に、製造例６または７で得た顔料ペースト（Ａ）または（Ｂ）２７５質量部および脱イオン水を表２に示す量を常温で撹拌しながら徐々に加えてカチオン電着塗料１〜１６を調製した。
【００６１】
【表２】

【００６２】
実施例１〜１４及び比較例１〜７
厚さ０．８ｍｍの冷延鋼板を燐酸亜鉛処理剤（「サーフダインＳＤ２０００」、日本ペイント社製）を使用して化成処理した後、鋼板表面の一部にコロナ帯電型塗装ガン（「ＰＧ−１」、ＧＥＭＡ社製）を用いて、ポリエステル樹脂・ブロックポリイソシアネート系粉体塗料Ａ（「パウダックスＰ−１００」、日本ペイント社製）またはアクリルポリエステル樹脂・ブロックポリイソシアネート系粉体塗料Ｂ（「パウダックスＰ−３００」、日本ペイント社製）を、硬化膜厚５０μｍとなるよう塗装し、粉体塗膜を形成した。ここで適用した静電粉体塗装条件は、塗装ガン先端と被塗物距離：２０ｃｍ、塗装電圧：−８０ＫＶ、吐出量：１００ｇ／分、吐出圧：０．１ＭＰａであった。このようにして得られたスプレーダスト部分を有する粉体塗料による塗膜が形成された被塗物を、８０℃で１０分間プレヒートを行った。次にこの被塗基材を電着塗料浴に浸漬することによって、粉体塗膜が形成されていない領域に対し、表５に示すカチオン電着塗料を用いて、浴温３０℃、電着単独部位の乾燥膜厚が２５μｍとなるように３分間電着塗装し、電着塗膜を形成した。次いで、イオン交換水による洗浄工程を経て、表５に示す温度で２０分間焼付乾燥した。次いでアクリル・メラミン樹脂系上塗りベース塗料（「スーパーラックＭシルバーメタリック」、日本ペイント社製）を乾燥膜厚が１５μｍとなるように塗装し、セッティング後にアクリル・メラミン樹脂系上塗りクリヤー塗料（「スーパーラックＯクリヤー」、日本ペイント社製）を乾燥膜厚が３５μｍとなるように塗装し、セッティング後に１４０℃で３０分間焼付乾燥することにより塗装物を得た。この塗装物について、粉体塗膜と電着塗膜とが、ほぼ同膜厚で重なっている粉体塗膜と電着塗膜との塗り際部付近の耐食性および密着性を評価し、その結果を表５に示した。
【００６３】
評価方法
（１）耐食性
粉体塗膜と電着塗膜との塗り際部付近に、素地に達する線状のカットを入れた被塗物を５５℃の５％食塩水に２４０時間浸漬後の、カット部における両側剥離幅を測定した。以下の基準により評価した。
【００６４】
【表３】
○…両側剥離幅が５ｍｍ以内
×…両側剥離幅が５ｍｍ超
【００６５】
（２）密着性
４０℃のイオン交換水に２４０時間浸漬後に、碁盤目テープ法（１ｍｍ碁盤目）によりセロファン粘着テープに付着した塗膜の状態を、以下の基準により目視で評価した。
【００６６】
【表４】
○…テープに付着した塗膜なし
△…テープに付着した塗膜が碁盤目に１〜４９％付着
×…テープに付着した塗膜が碁盤目に５０％以上付着
【００６７】
【表５】

【００６８】
表５の結果から明らかのように、本実施例１〜１４の方法で得た塗装物は、耐食性および密着性が良好であった。一方、比較例１、３、４および７は、耐食性が、また比較例２、５および６は、密着性が満足できないものであった。
【００６９】
【発明の効果】
本発明は、粉体塗料による塗膜を形成した後に、電着塗膜を形成するリバース塗装において、ブロックポリイソシアネート硬化系の粉体塗料により粉体塗膜を形成し、特定の金属触媒を含み、特定温度範囲の硬化開始温度を有するカチオン電着塗料を用いて、電着塗膜を形成することにより、トータル膜厚の確保が困難な塗り際部において、粉体塗膜中に残存するイソシアネート基が電着塗膜中の金属触媒によって反応が適度に進行するよう制御されるため、導電性プライマーを塗装することなく、耐食性および密着性を改善した塗膜形成方法および塗装物を提供可能にした。
【００７０】
なお、本発明によれば、耐食性および密着性が良好な塗膜を得ることが可能なため、本発明で得られる塗装物は、自動車、二輪車等の乗物外板、家電業界等の塗膜耐食性および密着性が要求される用途において好ましく使用される。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a coating film forming method, and in particular, to a coating film forming method by a reverse coating method in which an electrodeposition coating film is formed with an electrodeposition coating after forming a coating film with a powder coating.
[0002]
[Prior art]
For coating on automobile bodies, after forming a coating film with a powder coating, in reverse coating, where an electrodeposition coating film is formed with an electrodeposition coating, in the vicinity of the coating area between the powder coating film and the electrodeposition coating film It was difficult to ensure the total film thickness, and the corrosion resistance was insufficient. As a technique for solving this problem, in Japanese Patent Application Laid-Open No. 9-206663, a conductive primer is applied in advance to a portion that is in the vicinity of the application portion of an object to be coated before forming a coating film with a powder coating material. However, Japanese Patent Laid-Open No. 9-206664 discloses that after forming a coating film with a powder coating material, a conductive primer is applied to a portion near the coating portion before the electrodeposition coating film is formed. A method is described.
[0003]
[Problems to be solved by the invention]
The coating method using the above-mentioned conductive primer is one of the measures for improving the vicinity of the above-mentioned coating area where it is difficult to ensure the total film thickness, but it requires a separate process for coating the conductive primer. . In addition, it is difficult to say that corrosion resistance and adhesion are sufficient even in the vicinity of the above-mentioned coating portion even if these methods are used.
[0004]
The problem to be solved by the present invention is that, in the above reverse coating system, it is difficult to ensure the total film thickness, and in the vicinity of the coating edge, without using a conductive primer, the corrosion resistance and adhesion in the vicinity of the coating edge. It is providing the coating-film formation method in which property is performed favorably.
[0005]
[Means for Solving the Problems]
As a result of intensive studies in view of the above-described problems, the present inventors have completed the present invention. That is, this invention provides the method of forming a coating film on the surface of the electroconductive target object including the process of following (1)-(5).
[0006]
(1) A step of applying a thermosetting powder coating containing a first block polyisocyanate compound and a thermosetting resin to the surface of a conductive object to form a powder coating film,
(2) a step of heating the powder coating film under a condition in which the thermosetting powder coating melts but does not cause a thermal crosslinking reaction;
(3) A second block polyisocyanate compound, a cationic base resin, and a metal catalyst that accelerates the curing of the thermosetting powder coating, and the amount of metal in the metal catalyst is 100% by mass of the solid content of the coating The cationic electrodeposition coating composition is 0.1 to 0.5 parts by mass with respect to parts, the curing start temperature is 100 to 150 ° C., and the pH of the electrodeposition coating liquid during coating is 5.7 to 6.7. A process of forming an electrodeposition coating on an unpainted portion of the surface of the conductive object by performing electrodeposition coating using
(4) a step of washing the coating film formed on the surface of the conductive article, and
(5) A step of curing the coating film by heating to a temperature of 160 to 200 ° C.
[0007]
The metal in the metal catalyst used in the step (3) is preferably one or more selected from the group consisting of tin, lead, bismuth, copper and zinc.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail.
[0009]
Coating method
As the conductive coating applied to the coating film forming method of the present invention, various metal plates such as cold-rolled steel plates, various plated steel plates, stainless steel plates, aluminum plates or processed products, the surface of these metals by degreasing or chemical conversion treatment, etc. Examples thereof include various treated metal plates or processed products, and plastic plates or processed products subjected to conductive treatment by applying a conductive primer or the like. The coating film formation method of this invention forms a coating film through these processes to the following (1)-(5) sequentially.
[0010]
(1) Powder coating process
Step (1) in the present invention is a step of forming a powder coating film by applying a thermosetting powder coating to the surface of a conductive article.
[0011]
The thermosetting powder coating used in step (1) of the present invention is an epoxy resin, an acrylic resin, a polyester resin, a polyester / epoxy resin blended with an epoxy resin and a polyester resin, or an acrylic / epoxy blended with an epoxy resin and an acrylic resin. A thermosetting powder coating containing a thermosetting resin such as a resin and a first block polyisocyanate compound as a curing agent.
[0012]
Examples of the epoxy resin include glycidyl ester resins, glycidyl ether resins such as condensates of bisphenol A and epichlorohydrin, alicyclic epoxy resins, linear aliphatic epoxy resins, bromine-containing epoxy resins, phenol novolac epoxy resins, Examples thereof include compounds containing two or more oxirane groups in the molecule such as cresol novolac epoxy resin.
[0013]
Examples of the acrylic resin include styrene, (meth) acrylic acid, methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, and iso-butyl (meth) acrylate. Examples thereof include those obtained by polymerizing monomers such as tert-butyl (meth) acrylate, glycidyl (meth) acrylate, and 2-methylglycidyl methacrylate by an ordinary method.
[0014]
Moreover, as a polyester resin, the condensate obtained by heat-condensing a polybasic acid and a polyhydric alcohol is mentioned. Examples of the polybasic acid include maleic acid, terephthalic acid, isophthalic acid, phthalic acid, succinic acid, glutamic acid, adipic acid, sebacic acid, and the like. Examples of the polyhydric alcohol include ethylene glycol, diethylene glycol, and propanediol. , Pentanediol, hexanediol, neopentyl glycol, trimethylolpropane, pentaerythritol and the like.
[0015]
The first blocked isocyanate compound blended as a curing agent in the thermosetting powder coating material includes a compound that dissociates and generates an isocyanate group, such as uretdione. This first blocked polyisocyanate compound is a polyisocyanate compound blocked with a blocking agent. Preferred examples of the polyisocyanate compound include triglycidyl isocyanate, xylylene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, and uretdiones thereof. Examples of preferable blocking agents include lactams such as ε-caprolactam.
[0016]
In addition, as a curing agent, an aliphatic polyvalent carboxylic acid such as sebacic acid, an aminoplast resin, an aliphatic acid anhydride, an amine compound, dicyandiamide, a phenol resin, an epoxy resin, etc., an amount that does not interfere with the effect of the polyisocyanate compound It is also possible to use together.
[0017]
The thermosetting resin / curing agent solid content mass ratio of the thermosetting powder coating is preferably 55/45 to 90/10, more preferably 60/40 to 85/15. If it is out of the range of 55/45 to 90/10, there is a risk of causing a problem in curability.
[0018]
In addition, the above powder coating is composed of pigments such as colored pigments, rust preventive pigments or extender pigments; surface preparation agents; antifoaming agents such as benzoin and benzoin derivatives; anti-waxing agents; curing catalysts; plasticizers; Various additives such as an agent, a pigment dispersant, a flame retardant, and a fluidity imparting agent can be included.
[0019]
The particle size of the powder coating is preferably 10 to 50 μm in terms of average particle size, and if it is less than 10 μm, the production cost may be increased to pulverize the particle size, and if it exceeds 50 μm, the appearance of the coating film may be deteriorated. is there.
[0020]
Examples of the powder paint include “Powax P-100” (polyester resin), “Powax P-200” (polyester resin), “Powax P-300” (acrylic polyester resin), “Powax”. P-500 "(polyester resin system)," Powdax P-700 "(polyester resin system, both manufactured by Nippon Paint Co., Ltd.) and the like are preferable.
[0021]
The above-mentioned powder coating material is applied to a conductive object to be surface-treated if necessary by an electrostatic powder coating method. As the electrostatic powder coating method, a corona charging method or a friction charging method can be used.
[0022]
In the above electrostatic powder coating method, after grounding the object to be coated, the powder coating gun is sprayed onto the conductive object using a powder coating gun such as a corona charging type coating gun or a friction charging type coating gun. Is done. The preferable conditions for coating are as follows: coating voltage: −50 to −100 KV, discharge amount: 50 to 400 g / min, discharge pressure: 0.05 to 0.2 MPa, coated from the tip of the coating gun with a corona charging type coating gun The distance to the object is 10 to 50 cm. By coating within these ranges, the particles in the powder coating are electrostatically attached to the conductive object to form an uncured particle layer. The cured film thickness of the powder coating in this step is preferably 15 to 100 μm.
[0023]
(2) Hot melt preheating process
Step (2) in the present invention is a step of applying hot melt preheating. The heat melting preheating is a step of heating the powder coating film under the condition that the powder coating is melted by heat but does not cause a thermal crosslinking reaction. For example, a powder coating film made of a powder coating is heated completely for 1 to 15 minutes under heating conditions that do not completely cure and melt, and does not cause a crosslinking reaction as a coating film. The temperature at this time varies depending on the type of powder coating used, but is specifically a temperature of 70 to 150 ° C, preferably 70 to 120 ° C. By this hot melt preheating step, it is possible to prevent the uncured coating film from the powder coating material from being peeled off from the coating material when the coating material is immersed in the electrodeposition coating material bath in the step (3).
[0024]
(3) Cationic electrodeposition coating process
In this step (3), subsequent to the above step (2), the conductive coating having a coating film on the surface is immersed in a bath containing a cationic electrodeposition coating, and the conductive coating is performed by an electrodeposition coating method. An electrodeposition coating film is formed on the unpainted portion. The cationic electrodeposition coating contains a second block polyisocyanate compound, a cationic base resin that reacts with the second block polyisocyanate compound, and a metal catalyst that accelerates the curing of the thermosetting powder coating, and the metal in the metal catalyst. The amount is 0.1 to 0.5 parts by mass with respect to 100 parts by mass of the solid content of the coating, the curing start temperature is 100 to 150 ° C., and the pH of the electrodeposition coating liquid during coating is 5.7 to 6. 7.
[0025]
In this specification, the unpainted portion of the conductive object is a region where the coating film by the powder coating is not coated or a hole is generated in the coating film by the powder coating such as the powder coating dust part. The area where Coating film formation with powder coating can be formed sufficiently uniformly on a planar object to be coated, but is uniform when the object to be coated has a non-planar portion such as an uneven shape, a curved shape, or a bag shape. However, it is difficult to form the coating film, and an area where the coating film made of the powder coating is not sufficiently formed or not formed at all occurs. Therefore, in this process (3), an electrodeposition coating film is formed in the area | region of the unpainted part of the electroconductive to-be-coated object formed in the said process (1) and (2).
[0026]
The electrodeposition paint used in this step contains the second block polyisocyanate compound and the cationic base resin, but further contains a metal catalyst that accelerates the curing reaction of the powder paint used in step (1). 0.1-0.5 mass part is included with respect to 100 mass parts. If less than 0.1 parts by weight, the electrodeposition coating is insufficiently cured, resulting in insufficient corrosion resistance in the vicinity of the coating part, and if exceeding 0.5 parts by weight, the powder coating is too hard to be cured, Adhesiveness with the repeated coating film on the powder coating film in the vicinity of the above-mentioned coating portion decreases. By applying the electrodeposition coating film containing the metal catalyst to the hot melt preheated powder coating film, an appropriate reaction occurs between the polyisocyanate compound and the metal catalyst in the uncured powder coating film. Adhesion and corrosion resistance in the vicinity of the coated portion can be improved.
[0027]
The metal catalyst is preferably one in which the metal in the metal catalyst is one or more selected from tin, lead, bismuth, copper, zinc, cobalt, and nickel. More preferred are one or more selected from tin, lead, bismuth, copper and zinc. These metal catalysts are usually in the form of organic compound salts, organic acid salts, basic metal salts, and inorganic acid salts. The said metal catalyst can mix and use 2 or more types containing the same kind or different kind of metal as needed. Examples of organic compound salts include dibutyltin oxide, dioctyltin oxide, bisacetylacetonate zinc, and bisacetylacetonate copper. Examples of organic acid salts include dibutyltin dilaurate, dibutyltin diacetate, lead acetate, 2 -Lead ethylhexanoate, bismuth naphthenate, bismuth lactate, bismuth dimethylolpropionate, bismuth octylate, copper 2-ethylhexanoate, zinc octylate, zinc acetate, etc. Basic metal salts include, for example, basic Lead silicate, basic bismuth carbonate, bismuth hydroxide, basic copper carbonate, copper hydroxide, zinc hydroxide, basic zinc silicate, basic zinc carbonate, etc., as inorganic acid salts, for example, tin chloride, Examples include tin sulfate, lead nitrate, bismuth nitrate, copper sulfate, zinc carbonate, and zinc sulfate.
[0028]
Among these, particularly preferred are organic tin compounds such as dibutyltin oxide, dioctyltin oxide, dibutyltin dilaurate, bismuth compounds such as bismuth octylate, bismuth dimethylolpropionate, bismuth lactate and bismuth nitrate, zinc acetate, octyl Zinc compounds such as zinc acid and zinc sulfate.
[0029]
Examples of the cationic base resin include a base resin which is used for obtaining a higher anticorrosion property and is commonly used as a cationic electrodeposition coating. For example, an amino-epoxy resin, a resin obtained by aminating an oxazolidone ring-containing epoxy resin, and the like can be given. Usually, these are used by opening the epoxy ring of the epoxy resin with an amine such as a primary amine, secondary amine, or tertiary amine and cationizing it.
[0030]
Examples of the epoxy resin that is a starting material of the cationic base resin include polyphenol polyglycidyl which is a reaction product of a polycyclic phenol compound such as bisphenol A, bisphenol F, bisphenol S, phenol novolak, cresol novolak, and epichlorohydrin. Examples include ether type epoxy resins.
[0031]
The above cationic base resin is preferably a resin having an amino value of 30 to 130, more preferably 40 to 80, and a number average molecular weight of 1000 to 20000. When the amino value is less than 30, it is difficult to be water-soluble, and when it exceeds 130, the electrical conductivity becomes high and the gas pinhole property is lowered, or there is a problem in the electrodeposition coating workability such as the coulomb efficiency and the re-dissolvability. May occur.
[0032]
Among the examples of the cationic base resin, it is preferable to use a modified epoxy resin containing an oxazolidone ring in the molecule. This modified epoxy resin can be obtained by dealcoholizing a bisurethane compound reacted with a diisocyanate compound or a heterourethane compound reacted with another active hydrogen compound and the epoxy resin. If a modified epoxy resin containing an oxazolidone ring is used as a base resin, an electrodeposition coating film excellent in heat resistance can be obtained.
[0033]
Examples of water-soluble organic acids used for neutralization include formic acid, acetic acid, propionic acid, lactic acid, citric acid, malic acid, tartaric acid, and acrylic acid, and inorganic acids include hydrochloric acid, phosphoric acid, nitric acid, sulfamic acid, and the like. it can. Preferred water-soluble organic or inorganic acids are acetic acid, lactic acid, propionic acid, formic acid, and nitric acid.
[0034]
The second block polyisocyanate compound contained in the cationic electrodeposition paint used in the coating film forming method of the present invention is an isocyanate group contained in a polyisocyanate compound such as an aromatic polyisocyanate or an alicyclic polyisocyanate. Can be obtained by completely or partially blocking with a blocking agent.
[0035]
The electrodeposition paint used in this step has a curing start temperature in the range of 100 to 150 ° C. When the curing start temperature is less than 100 ° C., the appearance of the coating film is poor due to a decrease in the flowability of the electrodeposition coating film, and the storage stability of the electrodeposition paint is also decreased. When the curing start temperature exceeds 150 ° C., the corrosion resistance in the vicinity of the coated portion is insufficient. A more preferable curing start temperature is 100 to 140 ° C.
[0036]
In order to set the curing start temperature to 100 to 150 ° C., a second blocked polyisocyanate compound in which a polyisocyanate compound and a blocking agent are combined so that the dissociation temperature of the blocking agent falls within this range is used.
[0037]
As the polyisocyanate compound, trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, 1,2-propylene diisocyanate, 1,2-butylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, Aliphatic compounds such as ethylidene diisocyanate and butylidene diisocyanate, aliphatic cyclic compounds such as 1,3-cyclopentane diisocyanate, 1,4-cyclohexane diisocyanate, 1,2-cyclohexane diisocyanate and isophorone diisocyanate, and aliphatics such as norbornane diisocyanate Bicyclic compound, m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4 Aromatic compounds such as diphenyl diisocyanate, 1,5-naphthalene diisocyanate, 1,4-naphthalene diisocyanate, 4,4′-diphenylmethane diisocyanate, 2,4- or 2,6-toluene diisocyanate or mixtures thereof, 4,4 '-Toluidine diisocyanate, aliphatic-aromatic compounds such as 1,4-xylene diisocyanate, dianisidine diisocyanate, 4,4'-diphenyl ether diisocyanate, nucleus-substituted aromatic compounds such as chlorodiphenyl diisocyanate, triphenylmethane-4,4 ', 4' '-triisocyanate, 1,3,5-triisocyanatebenzene, 2,4,6-triisocyanatotoluene and other triisocyanates, 4,4'-diphenyl-dimethylmethane- ', 2', 5,5'-tetra isocyanate such as tetra-isocyanate, toluene diisocyanate dimer, and the like polymerized polyisocyanates such as toluene diisocyanate trimer. Moreover, what polyfunctionalized said polyisocyanate with polyhydric alcohol like a trimethylol propane can be used.
[0038]
As the blocking agent dissociating at a temperature of 100 to 150 ° C., in the case of aromatic polyisocyanate, halogenated alcohols such as 1-chloro-2-propanol and ethylene chlorohydrin, n-propanol and furfuryl alcohol , Aliphatic or heterocyclic alcohols such as alkyl group-substituted furfuryl alcohol, phenols such as phenol, m-cresol, p-nitrophenol, p-chlorophenol, nonylphenol, methyl ethyl ketone oxime, methyl isobutyl ketone oxime, acetone oxime , Oximes such as cyclohexane oxime, active methylene compounds such as acetylacetone, ethyl acetoacetate, ethyl malonate, and others, caprolactam, and the like. Particularly preferred are oximes, The alcohol compound is furfuryl alcohol and alkyl group-substituted furfuryl alcohol. In the case of aliphatic polyisocyanates, phenols and oximes are preferred among the above.
[0039]
In addition, as long as hardening start temperature does not become outside the said range, another blocking agent can be mixed and used. In this case, the other blocking agent is preferably used in an amount such that the equivalent is 50% or less with respect to the blocking agent that dissociates at a temperature of 100 to 150 ° C. As such other blocking agents, those having a dissociation temperature of less than 160 ° C. are preferable. For example, aliphatic alcohols such as methanol, ethanol and isopanol, aromatic alcohols such as benzyl alcohol, ethylene glycol monomethyl ether, ethylene glycol mono Examples include glycol ethers such as ethyl ether, ethylene glycol monobutyl ether, and diethylene glycol monomethyl ether.
[0040]
When mixing and using such a blocking agent, you may use what made two types of blocking agents react simultaneously with polyisocyanate, or you may mix and use the block polyisocyanate blocked with each blocking agent. Good.
[0041]
The solid content mass ratio of the cationic base resin / second block polyisocyanate compound in the cationic electrodeposition coating is preferably 50/50 to 90/10, and more preferably 60/40 to 80/20. If it is out of the range of 50/50 to 90/10, there is a possibility of causing a problem in curability.
[0042]
The cationic electrodeposition paint contains water as a solvent, but as an organic solvent, ethyl cellosolve, propyl cellosolve, butyl cellosolve, 2-ethylhexyl cellosolve, n-hexyl cellosolve, propylene glycol monomethyl ether, propylene glycol monophenyl ether, methanol, Water-miscible organic solvents such as ethanol, isopropyl alcohol, n-butanol, isobutanol, ethylene glycol dimethyl ether, diacetone alcohol, acetone, methyl ethyl ketone, methoxy butanol, dioxane, ethylene glycol monoethyl ether acetate, xylene, toluene, methyl isobutyl Water immiscibility of ketone, hexane, carbon tetrachloride, 2-ethylhexanol, isophorone, cyclohexane, benzene, etc. It can include an organic solvent. The amount of the organic solvent is preferably 0.1 to 10 parts by mass per 100 parts by mass of the total solid content of the cationic base resin and the curing agent. Preferred organic solvents are propylene glycol monomethyl ether, propyl cellosolve, butyl cellosolve, 2-ethylhexyl cellosolve, n-hexyl cellosolve, propylene glycol monophenyl ether, isophorone.
[0043]
The cationic electrodeposition coating material may contain crosslinkable resin particles, a pigment, and various additives, if necessary, in addition to the above components. By including the crosslinkable resin particles, it is possible to promote the film thickness retention effect of the edge portion of the substrate to be coated. Such crosslinkable resin particles may be any resin such as acrylic resin, epoxy resin, phenol resin, melamine resin, etc., but are crosslinkable particles using acrylic resin for ease of production. Is particularly preferred. In addition, it is preferable that the average particle diameter is 0.02-30 micrometers.
[0044]
Further, as the above pigments, coloring pigments such as titanium oxide, bengara, carbon black, extender pigments such as aluminum silicate, precipitated barium sulfate, and phosphomolybdic acid and aluminum, iron, titanium, zirconium, manganese, cobalt, nickel, copper, Phosphormolybdate, tripolyphosphoric acid, metaphosphoric acid, pyrophosphoric acid, etc., which are salts with divalent or trivalent metal salts such as zinc and silicon, and condensed phosphates, which are salts of the above divalent or trivalent metal salts Specifically, rust preventive pigments such as aluminum dihydrogen triphosphate, aluminum metaphosphate, and ferric pyrophosphate can be added.
[0045]
The cationic electrodeposition coating composition used in the coating film forming method of the present invention can be obtained by dispersing the above components in an aqueous medium containing the water-soluble organic acid or inorganic acid mentioned above as a neutralizing agent. The pH of the electrodeposition coating liquid during electrodeposition coating is 5.7 to 6.7. If the pH is less than 5.7, the coulomb efficiency of the electrodeposition coating is lowered and the throwing power is lowered. On the other hand, if the pH exceeds 6.7, the metal catalyst in the electrodeposition paint bath is unstable and easily precipitates, and the effective catalyst function is lowered. A more preferred pH is 5.8 to 6.5. The pH can be adjusted by using the same acid as that used for neutralization of the resin, or by adjusting the amine value of the resin and the acid value of the neutralizing acid.
[0046]
10-40 micrometers is preferable and, as for the dry film thickness of the electrodeposition coating film obtained at this process, 15-30 micrometers is more preferable.
[0047]
The conditions for electrodeposition coating in this step are set to, for example, coating voltage: 100 to 450 V, coating time: 1 to 5 minutes, electrodeposition liquid temperature: 20 to 35 ° C., electrodeposition liquid solid content: 5 to 40%. can do.
[0048]
(4) Water washing process
The step (4) of the present invention is a step of washing the article to be coated pulled up from the electrodeposition bath with washing water after the step (3). The above water washing is usually carried out over several orders, but except for the final water washing, filtrate, industrial water or tap water is used, and deionized water is used for the final water washing. This washing with water can be carried out by spraying or dipping, but is preferred because washing with spraying is efficient. The preferred spray pressure is 0.3-3 kg / cm.²It is.
[0049]
(5) Curing process
In the step (5) of the present invention, the coating film obtained in the above steps (1) to (4) is simultaneously heat-cured at a baking temperature of 160 to 200 ° C. When the baking temperature is less than 160 ° C., the corrosion resistance near the above-mentioned coating portion decreases, and when it exceeds 200 ° C., the curing of the powder coating film is promoted too much. Adhesiveness with the coating film to be stacked is lowered. Preferably, it is 170-190 degreeC. A preferred heating time is 10 to 90 minutes.
[0050]
Painted
By the coating film forming method of the present invention, a coated product having a coating film obtained from a powder coating and a coating film obtained from a cationic electrodeposition coating on a conductive object to be coated is obtained. Depending on the purpose of application, a desired intermediate coating film or top coating film can be further formed on the coated product.
[0051]
【Example】
EXAMPLES Next, although an Example and a comparative example are given and this invention is demonstrated more concretely, this invention is not limited only to these Examples. In addition, unless otherwise indicated, a compounding quantity represents a mass part.
[0052]
Production Example 1
Production of cationic substrate resin
While maintaining 1000 parts by weight of diglycidyl ether of bisphenol A (epoxy equivalent 910) at 70 ° C. with stirring, it is dissolved in 463 parts by weight of ethylene glycol monoethyl ether, and further 80.3 parts by weight of diethylamine is added. Reaction was performed for a time to obtain a cationic base resin.
[0053]
Production Example 2
Production of second block polyisocyanate compound (a)
To 174 parts by mass of toluene diisocyanate (80/20 mixture of 2,4-toluene diisocyanate / 2,6-toluene diisocyanate) charged in the reaction vessel, 87 parts by mass of methyl ethyl ketone oxime was maintained at a reaction temperature of 50 ° C. or lower by external cooling. While dropping gradually, half-block polyisocyanate was obtained. Subsequently, 45 parts by mass of trimethylolpropane and 0.05 parts by mass of dibutyltin dilaurate were added and reacted at 120 ° C. for 90 minutes. The obtained reaction product was diluted with 131 parts by mass of ethylene glycol monoethyl ether to obtain a blocked polyisocyanate compound (I).
[0054]
Production Example 3
Production of second block polyisocyanate compound (b)
To 174 parts by mass of toluene diisocyanate (2,4-toluene diisocyanate / 2,6-toluene diisocyanate 80/20 mixture) charged in the reaction vessel, 30.5 parts by mass of methyl ethyl ketone oxime was cooled to 50 ° C. at the reaction temperature by external cooling. While maintaining the following conditions, the solution is gradually dropped to allow complete reaction, followed by complete reaction of 34.3 parts by mass of furfuryl alcohol in the same manner, and further by reaction of 35.4 parts by mass of ethylene glycol monobutyl ether. Half block polyisocyanate was obtained. Subsequently, 45 parts by mass of trimethylolpropane and 0.05 parts by mass of dibutyltin dilaurate were added and reacted at 120 ° C. for 90 minutes. The obtained reaction product was diluted with 137 parts by mass of ethylene glycol monoethyl ether to obtain a second block polyisocyanate compound (B).
[0055]
Production Example 4
Production of second block polyisocyanate compound (c)
174 parts by mass of toluene diisocyanate (80/20 mixture of 2,4-toluene diisocyanate / 2,6-toluene diisocyanate) charged in the reaction vessel, 30.5 parts by mass of methyl ethyl ketone oxime, and reaction temperature of 50 ° C. or less by external cooling The mixture was gradually dropped while maintaining the temperature to allow complete reaction, and then 76.7 parts by mass of ethylene glycol monobutyl ether was reacted in the same manner to obtain a half-block polyisocyanate. Subsequently, 45 parts by mass of trimethylolpropane and 0.05 parts by mass of dibutyltin dilaurate were added and reacted at 120 ° C. for 90 minutes. The obtained reaction product was diluted with 140 parts by mass of ethylene glycol monoethyl ether to obtain a blocked polyisocyanate compound (C).
[0056]
Production Example 5
Production of second block polyisocyanate compound (d)
To 174 parts by mass of toluene diisocyanate (80/20 mixture of 2,4-toluene diisocyanate / 2,6-toluene diisocyanate) charged in the reaction vessel, 130 parts by mass of 2-ethylhexyl alcohol was used, and the reaction temperature was 50 ° C. or less by external cooling. While maintaining the temperature, the solution was gradually dropped to obtain a half-block polyisocyanate. Subsequently, 45 parts by mass of trimethylolpropane and 0.05 parts by mass of dibutyltin dilaurate were added and reacted at 120 ° C. for 90 minutes. The obtained reaction product was diluted with 150 parts by mass of ethylene glycol monoethyl ether to obtain a blocked polyisocyanate compound (d).
[0057]
Production Example 6
Production of pigment paste (A)
Based on the formulation shown in Table 1, after adding glacial acetic acid and deionized water to the cationic base resin and dissolving, the pigment was added and stirred with a disper for about 1 hour. Glass beads were added to this mixture and dispersed with a sand mill to 20 μm or less, and the glass beads were separated by filtration. The obtained pigment paste (A) had a nonvolatile content of 50% by mass.
[0058]
Production Example 7
Manufacture of pigment paste (B)
The pigment paste (B) obtained by the same method as the pigment paste (A) based on the formulation shown in Table 1 had a nonvolatile content of 50% by mass.
[0059]
[Table 1]

[0060]
Production Example 8
Preparation of cationic electrodeposition paints 1-16
The cationic base resin obtained in Production Example 1, the second block polyisocyanate compounds (a) to (d) obtained in Production Examples 2 to 5 and the metal catalyst shown in Table 2 were mixed according to the composition and blending amount in Table 2. After stirring for 1 hour and neutralizing with glacial acetic acid, the mixture was diluted with deionized water to obtain a resin composition having a nonvolatile content of about 40% by mass. Next, 275 parts by mass of the pigment paste (A) or (B) obtained in Production Example 6 or 7 and the amounts shown in Table 2 were gradually added at room temperature with stirring to add cationic electrodeposition paints 1-16. Was prepared.
[0061]
[Table 2]

[0062]
Examples 1-14 and Comparative Examples 1-7
A cold-rolled steel sheet having a thickness of 0.8 mm was subjected to chemical conversion treatment using a zinc phosphate treatment agent (“Surfdyne SD2000”, manufactured by Nippon Paint Co., Ltd.), and then a corona charging type coating gun (“PG- 1 ", manufactured by GEMA), polyester resin / block polyisocyanate powder coating A (" Powdax P-100 ", manufactured by Nippon Paint) or acrylic polyester resin / block polyisocyanate powder coating B ( “Powdax P-300” (manufactured by Nippon Paint Co., Ltd.) was applied to a cured film thickness of 50 μm to form a powder coating. The electrostatic powder coating conditions applied here were the distance between the tip of the coating gun and the object to be coated: 20 cm, the coating voltage: -80 KV, the discharge amount: 100 g / min, and the discharge pressure: 0.1 MPa. The article to be coated on which the coating film made of the powder coating material having the spray dust portion thus obtained was preheated at 80 ° C. for 10 minutes. Next, by immersing the substrate to be coated in an electrodeposition paint bath, a cationic electrodeposition paint shown in Table 5 was used for the region where the powder coating film was not formed, and the electrode temperature was 30 ° C. Electrodeposition coating was carried out for 3 minutes so that the dry film thickness of the single part was 25 μm to form an electrodeposition coating film. Next, after being washed with ion-exchanged water, it was baked and dried at the temperature shown in Table 5 for 20 minutes. Next, an acrylic / melamine resin-based overcoat base paint ("Super Lac M Silver Metallic", manufactured by Nippon Paint Co., Ltd.) was applied so that the dry film thickness was 15 μm. “Clear” (manufactured by Nippon Paint Co., Ltd.) was applied so that the dry film thickness was 35 μm, and after setting, it was baked and dried at 140 ° C. for 30 minutes to obtain a coated product. About this coating, the powder coating film and the electrodeposition coating film were evaluated for corrosion resistance and adhesion in the vicinity of the coating portion between the powder coating film and the electrodeposition coating film, which were overlapped with almost the same film thickness. The results are shown in Table 5.
[0063]
Evaluation methods
(1) Corrosion resistance
Peeling on both sides of the cut part after immersing the object to be coated with a linear cut reaching the substrate in a 5% saline solution at 55 ° C. for 240 hours in the vicinity of the application part of the powder coating film and the electrodeposition coating film The width was measured. Evaluation was made according to the following criteria.
[0064]
[Table 3]
○: Both sides peeling width is within 5mm
×: Both sides peel width is over 5mm
[0065]
(2) Adhesion
After immersing in ion-exchanged water at 40 ° C. for 240 hours, the state of the coating film adhered to the cellophane adhesive tape by the cross-cut tape method (1 mm cross-cut) was visually evaluated according to the following criteria.
[0066]
[Table 4]
○: No paint film attached to the tape
Δ: 1-49% of coating film on tape
×: 50% or more of the coating film on the tape adheres to the grid
[0067]
[Table 5]

[0068]
As is clear from the results in Table 5, the coated products obtained by the methods of Examples 1 to 14 had good corrosion resistance and adhesion. On the other hand, Comparative Examples 1, 3, 4 and 7 were unsatisfactory in corrosion resistance, and Comparative Examples 2, 5 and 6 were unsatisfactory in adhesion.
[0069]
【The invention's effect】
In the reverse coating in which an electrodeposition coating film is formed after forming a coating film with a powder coating, the present invention forms a powder coating with a block polyisocyanate curing type powder coating, and includes a specific metal catalyst. Isocyanate remaining in the powder coating film at the coating end where it is difficult to ensure the total film thickness by forming an electrodeposition coating film using a cationic electrodeposition coating material having a curing start temperature in a specific temperature range Since the base is controlled by the metal catalyst in the electrodeposition coating so that the reaction proceeds appropriately, it is possible to provide a coating formation method and a coated product with improved corrosion resistance and adhesion without applying a conductive primer. did.
[0070]
In addition, according to the present invention, since it is possible to obtain a coating film having good corrosion resistance and adhesion, the coated material obtained in the present invention is a coating film corrosion resistance of automobiles, motorcycles, etc. And is preferably used in applications where adhesion is required.

Claims (2)

A method of forming a coating film on the surface of a conductive article including the following steps (1) to (5):
(1) A step of applying a thermosetting powder coating containing a first block polyisocyanate compound and a thermosetting resin to the surface of a conductive object to form a powder coating film,
(2) a step of heating the powder coating film under conditions where the thermosetting powder coating melts hot but does not cause a thermal crosslinking reaction;
(3) containing a second block polyisocyanate compound , a cationic base resin containing a modified epoxy resin containing an oxazolidone ring in the molecule, and a metal catalyst for promoting the curing of the thermosetting powder coating, The metal amount in the metal catalyst is 0.1 to 0.5 parts by mass with respect to 100 parts by mass of the solid content of the coating, the curing start temperature is 100 to 150 ° C., and the pH of the electrodeposition coating liquid at the time of coating is 5 Performing electrodeposition coating using a cationic electrodeposition paint that is .7 to 6.7, and forming an electrodeposition coating film on an unpainted portion of the surface of the conductive article;
(4) A step of washing the coating film formed on the surface of the conductive article, and (5) a step of curing the coating film by heating to a temperature of 160 to 200 ° C.   The coating film forming method according to claim 1, wherein the metal in the metal catalyst is one or more selected from the group consisting of tin, lead, bismuth, copper, and zinc.