JP2006089623A - Cationic electrodeposition coating composition using ene-thiol curing system and method for forming electrodeposition film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cationic electrodeposition coating containing remarkably decreased amount of a blocked isocyanate curing agent compared with conventional cationic electrodeposition coating. <P>SOLUTION: The cationic electrodeposition coating composition contains (A) an epoxy resin having an unsaturated group and a cationic group and (B) an epoxy resin having a thiol group and a cationic group. The cationic electrodeposition coating composition may further contain (C) a photopolymerization initiator, (D) a blocked isocyanate curing agent, (E) a compound having an unsaturated group and (F) a compound having thiol group. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a cationic electrodeposition coating composition in which a curing reaction proceeds by light and / or heat and an electrodeposition coating film forming method.

  In the cationic electrodeposition paint, blocked isocyanate is usually used as a curing agent. About this blocked isocyanate, it is thought that a block agent will detach | desorb and a hardening reaction will advance by heating. However, this desorbed blocking agent has problems such as adhering to the drying oven as dust or soot, or volatilizing in the air and polluting the air, reducing the amount of blocking agent. Expected.

  In order to solve this problem, a cationic electrodeposition coating that can be cured by light has been proposed (for example, see Patent Document 1). However, in an automobile body to which a cationic electrodeposition coating is applied, there is a portion that is not sufficiently irradiated with light such as a bag portion, so that it is technically difficult to cure only with light. For this reason, it is necessary to use hardening by heating together.

However, since the curing reaction in the photocurable cationic electrodeposition coating utilizes the addition of unsaturated groups, its thermosetting property is not sufficient. Therefore, in order to ensure thermosetting, it is necessary to use a large amount of blocked isocyanate, and it is substantially difficult to reduce the amount.
Japanese Patent Laid-Open No. 2004-190015

  An object of the present invention is to obtain a cationic electrodeposition coating material in which the content of a blocked isocyanate curing agent is significantly reduced as compared with a conventional cationic electrodeposition coating material.

The cationic electrodeposition coating composition of the present invention contains an unsaturated group and cationic group-containing epoxy resin (A) and a thiol group and cationic group-containing epoxy resin (B). Here, it may further contain a photopolymerization initiator (C) and / or a blocked isocyanate curing agent (D), and further contains an unsaturated group-containing compound (E) and / or a thiol group-containing compound (F). May be included.
The electrodeposition coating film forming method of the present invention is characterized in that the above cationic electrodeposition coating composition is electrodeposited onto a substrate and then irradiated with energy rays and / or heated.
The coating film of the present invention is obtained by the previous electrodeposition coating film forming method.

  According to the cationic electrodeposition coating composition of the present invention, the content of the blocked isocyanate curing agent can be greatly reduced. This is because the cationic electrodeposition coating composition of the present invention utilizes the ene-thiol reaction. That is, the addition reaction of the thiol group to the unsaturated bond proceeds even by heating alone. In addition, the reaction under irradiation of energy rays such as light has the advantage that it is not so sensitive to oxygen inhibition as it does not necessarily require a photopolymerization initiator, compared to conventional addition polymerization of unsaturated bonds. Yes. Therefore, even in a bag portion where light is not sufficiently irradiated, curability can be ensured without using a large amount of blocked isocyanate.

  In addition, when energy beam irradiation and heating are used in combination in the electrodeposition coating film forming method of the present invention, the surface of the uncured coating film is first flowed by heating with respect to the uncured coating film obtained by electrodeposition. Then, by irradiating the energy beam to fix the surface, an electrodeposition coating film with high surface smoothness can be obtained, and when another coating film is formed thereon, a multilayer coating with a high appearance is obtained. A membrane is obtained. In addition, immobilization of the coating film surface by the energy beam irradiation can be used for wet-on-wet coating, and multi-layer coating can also be performed by using wet-on-wet coating for the formation of the upper coating film. The number of baking for curing in the film can be reduced.

  The cationic electrodeposition coating composition of the present invention utilizes an ene-thiol reaction. In the ene-thiol reaction, a thiol group undergoes an addition reaction with respect to an unsaturated bond, and the reaction proceeds not only by light but also by heat.

  In the cationic electrodeposition coating composition of the present invention, the basic constituent components include an unsaturated group and cationic group-containing epoxy resin (A), and a thiol group and cationic group-containing epoxy resin (B).

Unsaturated and cationic group-containing epoxy resin (A)
The unsaturated group and cationic group-containing epoxy resin (A) contained in the cationic electrodeposition coating composition of the present invention is obtained by introducing an unsaturated group and a cationic group into an epoxy resin as a raw material.

  The epoxy resin used as the raw material is not particularly limited, and is a polyphenol polyglycidyl ether type that is a reaction product of a polycyclic phenol compound such as bisphenol A, bisphenol F, bisphenol S, phenol novolak, cresol novolak, and epichlorohydrin. The thing generally used for the electrodeposition coating materials, such as an epoxy resin, can be mentioned. Moreover, what extended these chain | strands by the bifunctional polyester polyol, polyether polyol, bisphenols, dibasic carboxylic acid, etc. can be used for these illustrated epoxy resins. When using an epoxy resin as the resin having an epoxy group, the epoxy equivalent is preferably 180 to 2500.

  The introduction of the unsaturated group into the epoxy resin can be performed by a method using an epoxy group of the epoxy resin or a method using a hydroxyl group generated by ring opening of the epoxy group. In the above method using an epoxy group, a compound having an unsaturated group is directly reacted with an epoxy resin. For this reason, the compound which has the said unsaturated group needs to have a functional group which can react with an epoxy group.

  Specific examples of the compound having an unsaturated group include allyl alcohol, 2-hydroxyethyl vinyl ether, 4-hydroxybutyl vinyl ether, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate. , Hydroxybutyl methacrylate, alcohols such as methacrylic alcohol, acrylic acid, methacrylic acid, ethacrylic acid, crotonic acid, maleic acid, phthalic acid, itaconic acid; maleic acid ethyl ester, fumaric acid ethyl ester, itaconic acid ethyl ester, succinic acid Half esters such as mono (meth) acryloyloxyethyl ester and phthalic acid mono (meth) acryloyloxyethyl ester Mention may be made of a carboxylic acid.

  On the other hand, in the method using a hydroxyl group generated by ring opening of the epoxy group, an unsaturated group-containing compound having an isocyanate group at the terminal is first produced, and this is converted into a hydroxyl group generated by ring opening of the epoxy group. It is preferable to add. Such an unsaturated group-containing compound having an isocyanate group at the terminal can be obtained by reacting a polyisocyanate compound with the alcohol having the unsaturated group.

  Examples of the polyisocyanate compound include alkylene diisocyanates such as trimethylene diisocyanate, trimethylhexamethylene diisocyanate, tetramethylene diisocyanate and hexamethylene diisocyanate; cycloalkylene diisocyanates such as bis (isocyanatemethyl) cyclohexane, cyclopentane diisocyanate, cyclohexane diisocyanate and isophorone diisocyanate. Aromatic diisocyanates such as tolylene diisocyanate, phenylene diisocyanate, diphenylmethane diisocyanate, diphenyl ether diisocyanate; araliphatic diisocyanates such as xylylene diisocyanate, diisocyanate diethylbenzene; triphenylmethane triisocyanate, Polymerized polyisocyanates such as triisocyanates such as reisocyanate benzene and triisocyanate toluene, tetraisocyanates such as diphenyldimethylmethane tetraisocyanate, dimers or trimers of tolylene diisocyanate; ethylene glycol, propylene glycol in the above polyisocyanate compounds And terminal isocyanate-containing compounds obtained by reacting low molecular active hydrogen-containing organic compounds such as diethylene glycol, trimethylolpropane, hydrogenated bisphenol A, hexanetriol, glycerin, pentaerythritol, castor oil, and triethanolamine.

  On the other hand, the introduction of the cationic group is performed by reacting the compound capable of introducing the cationic group with the epoxy group of the epoxy resin. Examples of the compound capable of introducing the cationic group include primary amine, secondary amine, tertiary amine acid salt, a mixture of sulfide and acid, and the like. Specific examples include butylamine, octylamine, diethylamine, dibutylamine, methylbutylamine, monoethanolamine, diethanolamine, N-methylethanolamine, triethylamine hydrochloride, N, N-dimethylethanolamine acetate, diethyl disulfide / acetic acid mixture, etc. In addition, secondary amines in which primary amines such as ketimine of aminoethylethanolamine and diketimine of diethylenetriamine are blocked may be mentioned. A plurality of these may be used in combination.

  The introduction of the unsaturated group and the introduction of the cationic group into the epoxy resin may be carried out first as necessary, but the hydroxyl group produced by opening the epoxy group for the introduction of the unsaturated group When using a cationic group, it is preferable to introduce a cationic group first to open the ring of the epoxy group. The introduction of unsaturated groups and cationic groups into the epoxy resin is not special and can be performed by a generally well-known method.

  It is preferable that the equivalent of the said unsaturated group in the unsaturated group and cationic group containing epoxy resin (A) obtained in this way is 100-10000. On the other hand, the equivalent of the cationic group generated by the introduction of the cationic group is preferably 250 to 4000.

Thiol group and cationic group-containing epoxy resin (B)
The thiol group and cationic group-containing epoxy resin (B) contained in the cationic electrodeposition coating composition of the present invention is obtained by introducing an thiol group and a cationic group into an epoxy resin as a raw material.

  About this thiol group and cationic group containing epoxy resin (B), the description of the above (A) component is applicable by replacing the unsaturated group in (A) component with a thiol group. Here, examples of the thiol compound having a functional group capable of reacting with an epoxy resin include alcohols such as 2-mercaptoethanol, 1-thioglycerol, glycerol monothioglycolate, 4-mercaptophenol, and thioglycolic acid. Carboxylic acids such as 3-mercaptopropionic acid, 2-mercaptopropionic acid, thiomalic acid, mercaptoisobutyric acid, meso-2,3-dimercaptoisobutyric acid, thiosalicylic acid, 2-aminoethanethiol, 2-aminobenzenethiol, Examples include amines such as 4-aminobenzenethiol and cysteine.

  It is preferable that the equivalent of the said thiol group in the thiol group and cationic group containing epoxy resin (B) obtained in this way is 100-10000. On the other hand, the equivalent of the cationic group generated by cation modification is preferably 250 to 4000.

Photopolymerization initiator (C)
The cationic electrodeposition coating composition of the present invention may contain a photopolymerization initiator (C) in order to promote the reaction between the unsaturated group and the thiol group by light irradiation. Examples of the photopolymerization initiator (C) include benzoins such as benzoin, benzoin isopropyl ether and benzoin isobutyl ether; benzophenones such as benzophenone and 4,4′-bis (dimethylamino) benzophenone (Michler's ketone); xanthone, Xanthones such as thioxanthone; 2-phenyl-2-hydroxy-acetophenone, α, α-dichloro-4-phenoxy-acetophenone, 1-hydroxycyclohexyl-phenyl ketone, 2,2-diethoxyacetophenone, 2-hydroxy-2- Acetophenones such as methyl-1-phenyl-propan-1-one, 2-hydroxy-2-methyl-propiophenone, 2,2-dimethoxy-2-phenylacetophenone (benzyldimethyl ketal); In addition, ethyl 4-dimethylaminobenzoate, 4,4′-diazidostilbenzene-2,2′-disulfonic acid, 1-phenyl-1,2-propanedione-2- (o-ethoxycarbonyl) oxime, etc. Can be mentioned.

  As commercially available products, for example, Cyracure UVI-6970, Cyracure UVI-6974, Cyracure UVI-6990, Cyracure UVI-6950 (manufactured by Union Carbide), Irgacure 651, Darocur 1173, Darocur 4265, Irgacure 369, Irgacure 184, Irgacure 819, Darocur TPO, Irgacure 261 (manufactured by Ciba Specialty Chemicals), SP-150, SP-170 (manufactured by Asahi Denka Kogyo Co., Ltd.), DACAT-II (manufactured by Daicel Chemical Industries), CI- 2734, CI-2758, CI-2855 (manufactured by Nippon Soda Co., Ltd.), PI-2074 (manufactured by Rhone-Poulenc), FFC509 (manufactured by 3M), BBI102 (manufactured by Midori Chemical Co., Ltd.) and the like.

  About the said photoinitiator (C), in order to raise the function further, a photosensitization promoter can be used together. Examples of photosensitizers that can be used in combination include triethylamine, triethanolamine, methyldiethanolamine, methyl 4-dimethylaminobenzoate, ethyl 4-dimethylaminobenzoate, isoamyl 4-dimethylaminobenzoate, benzoic acid (2 -Dimethylamino) ethyl, Michler's ketone, tertiary amines such as 4,4'-diethylaminobenzophenone, alkylphosphine such as triphenylphosphine, and thioethers such as β-thiodiglycol.

Block isocyanate curing agent (D)
The cationic electrodeposition coating composition of the present invention can contain a blocked isocyanate curing agent (D) as necessary.
As said block isocyanate hardening | curing agent (D), what is generally used for the cationic electrodeposition coating material can be used. This blocked isocyanate curing agent (D) is obtained by adding an active hydrogen compound to the previous polyisocyanate compound. Examples of the active hydrogen compound include lower and higher alcohols such as methanol, ethanol, butanol and 2-ethylhexanol; cellosolves such as ethyl cellosolve, butyl cellosolve and hexyl cellosolve; furfuryl alcohol and alkyl group-substituted furfuryl alcohol. Aliphatic or heterocyclic alcohols such as; phenols such as phenol, m-cresol, p-nitrophenol, p-chlorophenol, and nonylphenol; oximes such as methyl ethyl ketone oxime, methyl isobutyl ketone oxime, acetone oxime, and cyclohexane oxime Active methylene compounds such as acetylacetone, ethyl acetoacetate, and ethyl malonate; other examples include caprolactam.
When the blocked isocyanate curing agent (D) is included, two or more kinds can be used in combination.

Unsaturated group-containing compound (E) and thiol group-containing compound (F)
The cationic electrodeposition coating composition of the present invention may contain an unsaturated group-containing compound (E) and / or a thiol group-containing compound (F). The functional groups possessed by these compounds are functional groups used in the ene-thiol reaction, and these two types of functional groups are also included in the two types of epoxy resins mentioned above.

  Examples of the unsaturated group-containing compound (E) include compounds having at least one radical polymerizable unsaturated group in the molecule. From the viewpoint of curability, those having two or more unsaturated groups are preferred.

  Examples of the unsaturated group-containing compound (E) having two unsaturated groups include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, and propylene glycol di (meth) acrylate. , Dipropylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate Bisphenol A ethylene oxide modified di (meth) acrylate, bisphenol A propylene oxide modified di (meth) acrylate, 2-hydroxy-1-acryloxy-3-methacryloxypropane, trisyl Rhodecane dimethanol di (meth) acrylate, di (meth) acryloyloxyethyl acid phosphate, Kayarad HX-220,620, R-604, MANDA (above Nippon Kayaku), Photomer 3016 (manufactured by Cognis Co., Ltd., epoxy oligomer) Etc.

  Furthermore, as the unsaturated group-containing compound (E) having two or more unsaturated groups, for example, trimethylolpropane tri (meth) acrylate, trimethylolpropane ethylene oxide modified tri (meth) acrylate, trimethylolpropane propylene oxide modified tri (Meth) acrylate, glycerin tri (meth) acrylate, glycerin ethylene oxide modified tri (meth) acrylate, glycerin propylene oxide modified tri (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, isocyanuric acid Examples thereof include ethylene oxide-modified triacrylate and dipentaerythritol hexa (meth) acrylate. In addition, as said unsaturated group containing compound (E) which has only one said unsaturated group, the acrylic monomers used for manufacturing an acrylic polymer can be mentioned. These compounds (E) are usually used for the photocuring reaction, and can be used in combination of two or more.

  On the other hand, as the thiol group-containing compound (F), ethylene glycol bisthioglycolate, butanediol bisthioglycolate, hexanediol bisthioglycolate, trimethylolpropane tristhioglycolate, pentaerythritol tetrakisthioglycolate, polyethylene Glycol bisthioglycolate, ethylene glycol bisthiopropionate, butanediol bisthiopropionate, hexanediol bisthiopropionate, trimethylolpropane tristhiopropionate, pentaerythritol tetrakisthiopropionate, polyethylene glycol bis Thiopropionate, 3,6-dioxa-1,8-octanedithiol, 1,6 hexanedithiol, 4,4′-thiobisbenzenedithiol, p-xylenedithiol, m-xylenedithiol, 2,2 ′-(ethylenedithio) diethanethiol, 1,5-dimercapto-3-thiapentane, 2-di-n-butylamino-4,6-trimercapto-S -Triazine, 2-phenylamino-4,6-trimercapto-S-triazine, 2,4,6-trimercapto-S-triazine and the like. Moreover, it can manufacture using the compound which has reactive functional groups other than thiol groups and thiol groups like mercaptoethanol. For example, by reacting a urethane prepolymer obtained by reacting one end of diisocyanate with the hydroxyl group of mercaptoethanol with a polyol, one having a plurality of thiol groups can be obtained.

Cationic electrodeposition coating composition The cationic electrodeposition coating composition of the present invention comprises an unsaturated group and cationic group-containing epoxy resin (A) and a thiol group and cationic group-containing epoxy resin (B).

  Here, the ratio of the unsaturated group and cationic group-containing epoxy resin (A) to the thiol group and cationic group-containing epoxy resin (B) is such that the ratio of the unsaturated group and the thiol group is 0. It is preferably 5/1 to 1 / 0.5. Outside these ranges, curability may be insufficient.

  On the other hand, when the photopolymerization initiator (C) is included, the amount is the sum of the unsaturated group and cationic group-containing epoxy resin (A) component and the thiol group and cationic group-containing epoxy resin (B) component. It is preferable that it is 0.1 to 10% with respect to the mass. Further preferred lower and upper limits are 0.5% and 5%, respectively. When a photosensitizer is used in combination with the photopolymerization initiator (C), the mass can be 0.5 to 5% based on the total mass of the component (A) and the component (B). .

  In addition, when the cationic electrodeposition coating composition of the present invention contains a blocked isocyanate curing agent (D), the content thereof includes the unsaturated group and cationic group-containing epoxy resin (A) component, the thiol group, and the cationic property. Group-containing epoxy resin (preferably 50% or less with respect to the total mass of component B).

  Further, when the cationic electrodeposition coating composition of the present invention contains an unsaturated group-containing compound (E) and / or a thiol group-containing compound (F), the unsaturated group and thiol group as the entire cationic electrodeposition coating composition Is preferably 0.5 / 1 to 1 / 0.5. Outside these ranges, curability may be insufficient. The total mass of the component (D), the component (E), and the component (F) is preferably 50% or less based on the total mass of the component (A) and the component (B). More preferably, it is 35% or less.

  In addition to the above components, the cationic electrodeposition coating composition of the present invention is a general cationic electrodeposition such as a curing catalyst, a color pigment, an extender pigment, an antirust pigment, an antirust agent, an organic solvent, a pigment dispersant, and a surface conditioner. Additives used in paints can be included.

  The cationic electrodeposition coating composition of the present invention is prepared by adding an acid in an aqueous medium to the unsaturated group and cationic group-containing epoxy resin (A) and the thiol group and cationic group-containing epoxy resin (B). It is performed based on emulsification. The component (A) and the component (B) are preferably emulsified separately and then mixed. As the acid used in the emulsification, organic acids such as formic acid, acetic acid and lactic acid are preferable. The usage-amount of the said acid can be 15-30 mg equivalent with respect to 100 g of resin solid content of the cationic group which an epoxy resin has.

Moreover, in the said manufacture, components other than said (A) component and (B) component can be included in an emulsion by mixing with said (A) component and (B) component at the time of emulsification. Alternatively, it can be added later.
The solid content of the cationic electrodeposition coating composition of the present invention thus obtained is preferably 15 to 25% by mass.

Electrodeposition coating film forming method The electrodeposition coating film formation method of the present invention is characterized in that after the cationic electrodeposition coating composition is electrodeposited onto a substrate, it is irradiated with energy rays and / or heated. To do. Although the said base material will not be specifically limited if it can energize, A motor vehicle body and components are preferable. As conditions for performing the electrodeposition coating, for example, a solid content concentration of 15 to 25%, a pH of 5.5 to 9, a bath temperature of 15 to 35 ° C., and a voltage of 100 to 400 V can be used. The above conditions are preferably set so that the film thickness of the electrodeposition coating film obtained here is 10 to 30 μm in terms of dry film thickness.

  The cationic electrodeposition coating composition used in the electrodeposition coating film forming method of the present invention utilizes an ene-thiol reaction, and the reaction proceeds not only by ultraviolet rays, electron beams and visible light, but also by heat. For this reason, in the electrodeposition coating film forming method of the present invention, a cured film can be obtained by irradiation with energy rays and / or heating.

  In the electrodeposition coating film forming method of the present invention, only energy beam irradiation, only heating, and combined use of energy beam irradiation and heating are possible, but from the viewpoint of curability, only heating or energy beam irradiation and The combined use with heating is preferable, and the combined use of energy beam irradiation and heating is particularly preferable from the viewpoints of ensuring the coating film smoothness and wet-on-wet suitability described below.

  As the energy beam, ultraviolet rays, X-rays, electron beams, near infrared rays, visible light, or the like can be used. The active energy ray defined in the present invention does not include heat-related energy such as infrared rays, high frequency waves, and microwaves. However, near infrared rays are energy related to heat, but there are initiators having an initiating ability in this wavelength region, so they are included in the energy rays.

  In the case of irradiating the ultraviolet rays, various light sources can be used, such as a mercury arc lamp, a xenon arc lamp, a fluorescent lamp, a carbon arc lamp, and a tungsten-halogen copying lamp. On the other hand, the sources of electron beams include Cockcroft type, Cockcroft Walton type, Fan de Graaf type, Resonant transformer type, Transformer type, Insulated core transformer type, Dynamitron type, Linear filament type and High frequency type These electron beam generators can be used.

The irradiation conditions of the energy rays vary depending on the amounts and molecular weights of unsaturated groups and thiol groups, but when the active energy rays are ultraviolet rays, generally in the wavelength range of 200 to 400 nm, 1 to 10000 mJ / Cm ² can do. If the irradiation is insufficient, the intended smoothness may not be obtained. Moreover, there is no particular problem if the irradiation is excessive, but excessive irradiation may lead to energy waste. On the other hand, when using an electron beam, it is preferable to perform using the electron beam irradiation apparatus whose energy is 50-500 kEV.

  On the other hand, the heating conditions in the method for forming an electrodeposition coating film of the present invention vary depending on the amounts and molecular weights of unsaturated groups and thiol groups, as in the previous energy beam irradiation conditions. Can be set in minutes.

  When using the energy beam irradiation and heating in combination, the uncured coating film obtained by electrodeposition is first heated slightly to flow the surface of the uncured coating film, and then the energy beam is applied. It is preferable that the surface is fixed by irradiation, and finally heated again to be cured. Thereby, an electrodeposition coating film with high surface smoothness can be obtained.

  The heating for causing the surface of the uncured coating to flow is not performed in order to advance the curing reaction of the coating, but is milder than general baking conditions. However, even if a part of the curing reaction of the coating proceeds by the heating, there is no particular problem as long as it flows.

  The heating conditions for the surface flow can be selected, for example, from a temperature range in which the lower limit temperature is equal to or higher than the glass transition temperature of the resin component and the upper limit is equal to or lower than the curing temperature. The heating time here can be set to a time at which curing does not proceed by heating at the selected temperature. Moreover, since the conditions for heating for a short time at a temperature higher than the curing temperature are also conceivable, it is preferable to finally determine the heating conditions by performing heating under various conditions. The glass transition temperature can be obtained by measuring with an analytical instrument such as Tg-DTA or TMA, or can be inferred from the measured value of the coating film obtained by curing. By this heating, the solvent present in the uncured coating film is volatilized and the coating film surface flows.

Next, an energy ray is irradiated to the coating film in which the surface has flowed. Thereby, the coating-film surface can be fixed in the flowed state, ie, a state with high smoothness. The irradiation conditions vary depending on the amount of unsaturated bonds of the coating material used and the molecular weight of the binder component, but when the energy rays are ultraviolet rays, generally in the wavelength range of 200 to 400 nm, 1 to 10000 mJ / Cm ² can do. If the irradiation is insufficient, the intended smoothness may not be obtained. Moreover, there is no particular problem if the irradiation is excessive, but excessive irradiation may lead to energy waste. In addition, since irradiation of the said energy ray needs to be performed in the state by which the state which the coating-film surface flowed was maintained, the one where the interval of previous heating and this irradiation has few is preferable.
The second heating is performed to cure the coating film. The conditions are in accordance with the heating conditions listed above, and are generally performed at a so-called curing temperature.

  Moreover, the electrodeposition coating film forming method using both energy beam irradiation and heating according to the present invention can be applied to wet-on-wet coating. In other words, the uncured electrodeposition coating film obtained by electrodeposition is irradiated with energy rays to cure the surface of the electrodeposition coating film, thus forming a state in which another coating can be applied. is there. At this time, as described above, the smoothness of the coating film can be improved by heating and performing the flow. And after forming an uncured coating film using another coating material on the electrodeposition coating film whose surface has been fixed in this way, a multi-layer cured coating film is obtained by baking these simultaneously. Furthermore, a multilayer cured coating film can be obtained by forming another uncured coating film on the uncured coating film and baking these simultaneously.

When performing such wet-on-wet coating, it is common to form an uncured intermediate coating film by applying an intermediate coating to the electrodeposition coating with the surface fixed. .
Intermediate coatings in automobile coatings should conceal the unevenness of the electrodeposition coating as the base, ensure surface smoothness, and provide coating properties such as impact resistance, chipping resistance, and weather resistance. Is usually formed for the purpose.

  Examples of the intermediate coating material include two types, an intermediate coating material curable by irradiation with energy rays and heating, and a thermosetting intermediate coating material.

  The above thermosetting intermediate coating is well known. That is, the thermosetting intermediate coating generally contains a binder component and a pigment. The binder component usually comprises a resin having a curable functional group and a curing agent. Examples of the resin having a curable functional group include a polyester resin, an acrylic resin, an alkyd resin, an epoxy resin, and a urethane resin that are generally used as a coating resin. Moreover, it does not specifically limit as a curable functional group which these resins have, A carboxyl group, a hydroxyl group, an epoxy group, an isocyanate group etc. can be mentioned. Further, as the curing agent, a curing agent well known by those skilled in the art can be appropriately selected according to the type of the curable functional group.

  In general, from the viewpoint of pigment dispersibility and coating workability, the resin having a curable functional group is a polyester resin and / or an acrylic resin having a hydroxyl group, and the curing agent is a polyisocyanate and / or a melamine resin. It is preferable that Furthermore, since the intermediate coating film requires impact resistance and chipping resistance, the resin having a curable functional group is particularly preferably a polyester resin. In addition, from the viewpoint of storage stability, the above polyisocyanate has a blocking agent well known by those skilled in the art, such as alcohols such as butyl cellosolve and 2-ethylhexanol, and oximes such as methyl ethyl ketoxime. It is preferably blocked.

  In addition, from the viewpoint of impact resistance and chipping resistance, a component having a softer property than the generally used coating resin such as polyether polyol resin and rubber component may be contained as a binder component. . Furthermore, it is preferable to contain a viscosity control agent and a non-aqueous dispersion resin for the purpose of preventing mixed layers in wet-on-wet coating.

  As the pigment contained in the thermosetting intermediate coating material, a color pigment and an extender pigment are generally used. Examples of the color pigment include inorganic color pigments such as titanium dioxide, carbon black, graphite, chrome lead, yellow iron oxide, and bengara; azo chelate pigments, insoluble azo pigments, condensed azo pigments, phthalocyanine pigments, indigo Examples thereof include organic coloring pigments such as pigments, perinone pigments, perylene pigments, dioxane pigments, quinacridone pigments, isoindolinone pigments, and metal complex pigments. Examples of the extender pigment include calcium carbonate, barium sulfate, kaolin, aluminum silicate (clay), and talc. In addition to the color pigment and extender pigment, a bright pigment can be included as necessary.

  In addition to the above components, the thermosetting intermediate coating is well known by those skilled in the art, such as a pigment dispersant, a surface conditioner, a viscosity controller, an ultraviolet absorber, and an antioxidant, as necessary. Various additives can be included. Such a thermosetting intermediate coating is generally preferably a solution type, and can take the form of an organic solvent type, an aqueous type (water-soluble, water-dispersible, emulsion), or a non-aqueous dispersion type.

  On the other hand, an intermediate coating that can be cured by irradiation with energy rays and heating can be obtained by introducing a functional group that reacts by irradiation with energy rays into the binder component of the thermosetting intermediate coating. As described above, the functional group that reacts upon irradiation with the energy beam is preferably an unsaturated bond. In addition to simply blending a resin having a plurality of unsaturated bonds with the original binder component, the introduction of the unsaturated bond is not limited to the binder component contained in the thermosetting intermediate coating material. It can also be performed by reacting a compound having an unsaturated bond and a reactive functional group other than the unsaturated bond, such as acrylic acid or glycidyl (meth) acrylate. In particular, since the binder component of a thermosetting intermediate coating usually has a carboxyl group in many cases, it is effective to use (meth) acrylate in the latter method.

  When the intermediate coating material curable by irradiation with energy rays and heating contains an unsaturated bond, the amount is preferably 0.1 to 10 mmol per 1 g of resin solid content. If the amount is less than 0.1 mmol, the reaction due to the irradiation of the energy beam does not proceed, and there is a possibility that the coating with wet-on-wet may be difficult. is there.

  When an unsaturated bond is introduced into the binder component, it is preferable to use an ene / thiol curing system as in the cationic electrodeposition coating composition of the present invention. That is, it is preferable to add polythiol which is a component having a plurality of thiol groups. The polythiol can be produced using a compound having a thiol group and a reactive functional group other than a thiol group, such as mercaptoethanol. For example, a polythiol can be obtained by reacting a urethane prepolymer obtained by reacting one end of diisocyanate with the hydroxyl group of the mercaptoethanol with a polyol.

  When the intermediate coating material contains polythiol, it is preferable to use an amount corresponding to the functional group equivalent of the unsaturated bond. When the unsaturated bond is consumed by its own addition polymerization, the amount of the polythiol can be adjusted accordingly. Such addition polymerization by the unsaturated bond itself can proceed by appropriately containing a photopolymerization initiator and / or a thermal polymerization initiator as described in the electrodeposition coating.

  The intermediate coating is preferably applied to the previous electrodeposition coating film by spraying. An air electrostatic spray or a rotary atomizing electrostatic coater can be used for this coating. Although the dry film thickness of the said intermediate coating film changes with uses, it is preferable that it is 5-50 micrometers. If the upper limit is exceeded, sharpness may be reduced, or defects such as sagging or bake-curing may occur during painting, and if the lower limit is exceeded, the appearance may deteriorate.

  After the intermediate coating is applied, these may be baked at the same time as the previously formed electrodeposition coating film, but it is also possible to perform wet-on-wet coating. Further, when wet-on-wet coating is performed, the process after intermediate coating varies depending on the type of intermediate coating. That is, when the intermediate coating is an intermediate coating that can be cured by irradiation with energy rays and heating, the step of irradiating the energy rays is performed. On the other hand, when the intermediate coating material is a thermosetting intermediate coating material, a process called preheating is performed.

  For the irradiation of the energy beam to the uncured intermediate coating film, the contents described in the energy beam irradiation step for the electrodeposition coating film can be applied as they are. On the other hand, the preheating step is a step of blowing or heating, for example, at room temperature to 100 ° C. for 1 to 10 minutes after applying the paint.

  Next, after the energy ray irradiation process or the preheating process for the uncured intermediate coating film, a base coating is applied to form an uncured base coating film. The base coating film belongs to the top coating film and is usually used in combination with a clear coating film for the purpose of imparting design properties. Examples of the base paint include two kinds of base paints that can be cured by irradiation with energy rays and heating, and thermosetting base paints.

  The thermosetting base paint is well known so far and contains a binder component and a pigment. As the binder component, those mentioned above for the thermosetting intermediate coating can be used, but considering the physical properties of the top coat film, the resin having a curable functional group is an acrylic resin having a hydroxyl group. It is preferable. Moreover, as a hardening | curing agent, it is preferable that they are the polyisocyanate and / or melamine resin which may be blocked.

  Further, as the pigment contained in the thermosetting base paint, a bright pigment is usually used in addition to the above-mentioned colored pigment and extender pigment. Examples of the glitter pigment include aluminum powder, mica powder, glass powder, bronze powder, aluminum powder, and titanium powder.

  The thermosetting base coating material may contain various additives mentioned in the thermosetting intermediate coating material, if necessary, in addition to the above components, but has a function of preventing mixing in wet-on-wet coating. Preferably. The thermosetting base paint can take various forms as mentioned in the above-mentioned thermosetting intermediate coating, but it is preferably an aqueous form from the viewpoint of environmental protection.

  On the other hand, the base paint curable by irradiation with energy rays and heating has a functional group, preferably an unsaturated bond, that reacts with the binder component of the thermosetting base paint by irradiation with energy rays, as in the case of the intermediate coating. It can be obtained by introducing. When the base paint curable by irradiation with energy rays and heating contains an unsaturated bond, the amount is preferably 0.1 to 10 mmol per 1 g of resin solid content.

  The base paint thus obtained can be applied in the same manner as the intermediate paint. Here, in order to improve the design, multi-stage coating by air electrostatic spraying, preferably coating by two stages, or coating combining air electrostatic spraying and the above-mentioned rotary atomizing electrostatic coating machine. It is preferable to carry out by a method. Although the dry film thickness of the said base coating film changes with uses, it is preferable that it is 5-35 micrometers. If the upper limit is exceeded, the sharpness may be lowered or the coating workability may be lowered. If the lower limit is not reached, the target design property may not be exhibited.

  The uncured base coating film thus formed can be baked together with the two lower coating films previously formed, but it is also possible to perform wet-on-wet coating. Further, when performing wet-on-wet coating, an energy ray irradiation process or a preheating process is performed depending on the type of base paint used for the coating. These conditions can be set in accordance with the previous intermediate coating. A clear paint is applied to the uncured base coating film thus obtained, and an uncured clear coating film is formed. The clear coating film is used in combination with the base coating film, and is formed for the purpose of smoothing the unevenness of the base coating film and for providing design properties in addition to the purpose of protecting the base coating film. Sometimes.

  When the clear coating film formed here is located in the uppermost layer of the multilayer coating film, the clear coating material for forming the clear coating film is not special, and a general coating well known to those skilled in the art. Things can be used.

  Examples of the binder component contained in such a general clear paint include acrylic resins having a curable functional group, polyester resins, epoxy resins, urethane resins, and the like, depending on the curable functional group. Used in combination with a hardener. As the curing agent, amino resins and polyisocyanates which may be blocked are well known. Here, from the viewpoint of transparency, an acrylic resin and / or a combination of a polyester resin and an amino resin, and from the viewpoint of acid etching resistance, an acrylic resin using a carboxylic acid / epoxy curing system and / or It is preferable to use a polyester resin.

  The clear paint generally does not contain a pigment, but the clear paint used here may contain the above-mentioned pigment components to the extent that transparency is not impaired in order to impart design properties. Further, like the above two types of paints, various additives can be included, but it is preferable that those for preventing mixed layers in wet-on-wet coating are included. As a paint form of the clear paint, a powder type may be used in addition to the solution type. In view of the appearance of the resulting coating film, a solvent type is preferable. In addition, it is preferable to select the said clear coating material considering the combination with the uncured base coating film formed previously.

  Application of the clear coating to the uncured base coating can be performed in the same manner as the previous base coating. Although the dry film thickness of a clear coating film changes with uses, it is preferable that it is 10-70 micrometers. If the upper limit is exceeded, the sharpness of the coating film and the coating workability may be reduced, and if it is less than the lower limit, the appearance may be reduced.

  Baking is performed as the last step for a plurality of uncured coating films formed through the above steps. The baking conditions can be set, for example, at 110 to 200 ° C. for 10 to 60 minutes in accordance with the curing conditions of the paint used.

  As mentioned above, the formation of the multilayer coating film composed of the electrodeposition coating film, the intermediate coating film, the base coating film, and the clear coating film has been described. However, this method is limited to the formation of the multilayer coating film composed of these four layers. It can be applied to the formation of various automotive multilayer coatings.

  For example, when the multilayer coating film to be finally obtained does not include an intermediate coating film, a top coating film is formed on the electrodeposition coating film. For example, when the top coat film is composed only of a coating film obtained using a so-called solid type paint containing a color pigment, the solid type coating film is formed on the electrodeposition coating film obtained in the previous step. A coating film is applied, and the above-mentioned electrodeposition coating film and an uncured coating film obtained from the solid type coating are simultaneously heat-cured to obtain a multilayer coating film.

  In the electrodeposition coating film forming method of the present invention, a known wet-on-wet coating system is used as it is, except that a cationic electrodeposition coating composition using an ene-thiol reaction is used for forming the electrodeposition coating film. be able to. That is, using a cationic electrodeposition coating composition utilizing the ene-thiol reaction, an electrodeposition coating film, an intermediate coating film, and a wet-on-wet coating method are formed, and a base coating film and a clear coating film are formed thereon. After applying a known two-coat one-bake system to form, or forming an electrodeposition coating using a cationic electrodeposition coating composition utilizing an ene-thiol reaction, an intermediate coating, a base coating, and a clear coating A known three-coat one-bake system for forming a film can be applied. In addition to this, a known method of forming the base coating film and the clear coating film described above in two or more layers can be incorporated in a part of the forming method of the present invention in the same manner. It is also possible to perform four coats and one bake as all paints for forming an electrodeposition coating film, an intermediate coating film, and a base coating film that can be cured by irradiation with energy rays and heating. Furthermore, the clear paint for forming the clear coating film may also be a paint that can be cured by irradiation with energy rays and heating.

Coating the coating membrane of the present invention are those obtained by previous forming an electrocoating film method. As described in the above description of the electrodeposition coating film forming method, the film thickness of the coating film obtained as the automobile multilayer coating film is, for example, 30 to 300 μm.

  In the following production examples and examples, “part” and “%” are based on mass.

Production Example 1 Production of unsaturated group and cationic group-containing epoxy resin (A) In a reaction vessel equipped with a stirrer, a cooling tube, a nitrogen introduction tube, a dropping funnel, and a temperature controller, 222 parts of isophorone diisocyanate, 151 parts of methyl isobutyl ketone, 0.2 part of dibutyltin dilaurate and 0.07 part of 2,6-di-t-butyl-p-cresol were charged and heated to 40 ° C. 130 parts of 2-hydroxyethyl acrylate was dripped here over 30 minutes, and the unsaturated group containing prepolymer was obtained by stirring for 4 hours.

  Next, 950 parts of Epototo YD-014 (manufactured by Tohto Kasei Co., Ltd., bisphenol A type epoxy resin having an epoxy equivalent of 950) in a reaction vessel equipped with a stirrer, a cooling tube, a nitrogen introducing tube, a dropping funnel and a temperature controller, methyl isobutyl 370 parts of ketone, 43.3 parts of 2-ethylhexanoic acid, 1.35 parts of tetrabutylammonium bromide and 0.27 parts of 2,6-di-t-butyl-p-cresol until the epoxy equivalent is 1350 Stir at 140 ° C. Next, the system was cooled to 100 ° C., 52.6 parts of methylethanolamine was added, and the mixture was stirred for 1 hour, and then the above unsaturated group-containing prepolymer was added dropwise over 30 minutes. After completion of the dropping, the mixture was stirred for 2 hours to obtain an unsaturated group-equivalent epoxy resin (A) having an unsaturated group equivalent of 1400 and a solid content of 72.9%.

Production Example 2 Production of thiol group and cationic group-containing epoxy resin (B) In a reaction vessel equipped with a stirrer, a cooling tube, a nitrogen introduction tube, a dropping funnel, and a temperature controller, 222 parts of isophorone diisocyanate and methyl 128 parts of isobutyl ketone was charged and heated to 100 ° C. in a nitrogen atmosphere. 7mer part of 2-mercaptoethanol was dripped here over 30 minutes, and the thiol group containing prepolymer was obtained by stirring for 2 hours.

  Next, 950 parts of Epototo YD-014 (manufactured by Tohto Kasei Co., Ltd., bisphenol A type epoxy resin having an epoxy equivalent of 950) in a reaction vessel equipped with a stirrer, a cooling tube, a nitrogen introducing tube, a dropping funnel and a temperature controller, methyl isobutyl 392 parts of ketone, 43.3 parts of 2-ethylhexanoic acid and 1.29 parts of tetrabutylammonium bromide were charged and stirred at 140 ° C. under a nitrogen atmosphere until the epoxy equivalent reached 1290. Subsequently, the system was cooled to 100 ° C., and the previous thiol group-containing prepolymer was dropped over 30 minutes. After completion of the dropwise addition, the mixture was stirred for 2 hours, 52.6 parts of methylethanolamine was added, and the mixture was stirred for 1 hour, whereby a thiol group equivalent 1400, thiol group and cationic group-containing epoxy resin (B) was obtained.

Production Example 3 Production of Blocked Isocyanate Curing Agent (D) In a reaction vessel equipped with a stirrer, a cooling tube, a nitrogen introduction tube, a dropping funnel, and a temperature controller, Sumidur N3300 (manufactured by Sumika Bayer Urethane Co., Ltd., hexamethylene diisocyanate) Trimer) 199.1 parts and 31.6 parts of methyl isobutyl ketone were charged, and heated and held at 40 ° C. in a nitrogen atmosphere. Next, 0.2 part of dibutyltin dilaurate was added, and further 87.0 parts of methyl ethyl ketone oxime was dropped from the dropping funnel over 2 hours. After completion of the dropping, the reaction was continued at 70 ° C. until the absorption of the isocyanate group disappeared by the infrared absorption spectrum. I let you. After completion of the reaction, 38.1 parts of methyl isobutyl ketone and 1.6 parts of n-butanol were added and cooled to obtain a blocked isocyanate curing agent (D) having a solid content of 80.0%.

Production Example 4 Emulsification of unsaturated group and cationic group-containing epoxy resin (A) No. 1
The unsaturated group and cationic group-containing epoxy resin (A) obtained in Production Example 1 was mixed with 309 parts of trimethylolpropane trimethacrylate, and then Darocur 4265 (Ciba Specialty Chemicals) as a photopolymerization initiator (C). After adding 16.5 parts and 28.9 parts acetic acid, slowly add 3331 parts deionized water with vigorous stirring, and then add methyl isobutyl ketone and deionized water until the solid content is 33%. Removal of emulsion A-1 containing an unsaturated group was obtained.

Production Example 5 Emulsification of unsaturated resin and cationic group-containing epoxy resin (A) 2
The unsaturated group and cationic group-containing epoxy resin (A) obtained in Production Example 1 was mixed with 1846 parts of trimethylolpropane trimethacrylate and 340 parts of the blocked isocyanate curing agent (D) obtained in Production Example 3. Next, after adding 18.9 parts of monobutyltin tris (octanoic acid) salt and 18.9 parts of Darocur 4265 and 28.9 parts of acetic acid as a photopolymerization initiator (C), deionized water 3843 with strong stirring. Then, methyl isobutyl ketone and deionized water were removed until the solid content was 33% to obtain an emulsion A-2 containing an unsaturated group and a curing agent.

Production Example 6 Emulsification of Epoxy Resin (A) Containing Thiol Group and Cationic Group (1)
In 1867 parts of the thiol group and cationic group-containing epoxy resin (B) obtained in Production Example 2, 364 parts of trimethylolpropane tris (3-mercaptopropionate) were mixed, and then used as a photopolymerization initiator (C). After adding 17.1 parts Darocur 4265 and 30 parts acetic acid, slowly add 3439 parts deionized water with vigorous stirring, then remove methyl isobutyl ketone and deionized water until the solids content is 33% Thus, an emulsion B-1 containing a thiol group was obtained.

Production Example 7 Emulsification of Epoxy Resin (A) Containing Thiol Group and Cationic Group (2)
1867 parts of the thiol group and cationic group-containing epoxy resin (B) obtained in Production Example 2 and 416 parts of trimethylolpropane tris (3-mercaptopropionate) and the blocked isocyanate curing agent obtained in Production Example 3 (D ) 240 parts are mixed, and then 19.5 parts monobutyltin tris (octanoic acid) salt, 19.5 parts Darocur 4265 and 30 parts acetic acid are added as a photoinitiator (C), followed by strong stirring. 3961 parts of deionized water was gradually added, and then methyl isobutyl ketone and deionized water were removed until the solid content was 33% to obtain an emulsion B-2 containing a thiol group and a curing agent.

Example 1 The emulsion A-1 containing an unsaturated group in the cationic electrodeposition coating composition production example 4 not containing the blocked isocyanate curing agent (D) and the emulsion B-1 containing a thiol group in production example 6 A cationic electrodeposition coating composition having a solid content of 20% was obtained by mixing the unsaturated groups and thiol groups so as to be equivalent and diluting with ion-exchanged water.

Example 2 Cationic electrodeposition coating composition containing blocked isocyanate curing agent (D) Emulsion A-2 containing unsaturated groups in Production Example 5 and Emulsion B-1 containing thiol groups in Production Example 7 The cation electrodeposition coating composition having a solid content of 20% was obtained by mixing the saturated group and the thiol group so as to be equivalent and diluting with ion-exchanged water.

Comparative Examples 1 and 2
The emulsion A-2 containing an unsaturated group of Production Example 4 and the emulsion A-2 containing an unsaturated group of Production Example 5 were each diluted with ion-exchanged water as they were, thereby forming an electrodeposition coating composition having a solid content of 20%. Two kinds of things were obtained.

Example 3 Formation of Electrodeposition Coating Film Using four types of cationic electrodeposition coating compositions prepared in Examples 1 and 2 and Comparative Examples 1 and 2, a dry film thickness was applied to a zinc phosphate-treated cold rolled steel sheet. The electrodeposition was performed so that the thickness of the film became 20 μm. The uncured electrodeposition coating film obtained by washing with water was baked at 150 ° C. for 30 minutes or dried at 80 ° C. for 10 minutes, and then kept at that temperature, a 6 kW ultraviolet light source (manufactured by Fusion UV Systems, D-bulb) was irradiated with ultraviolet rays of 5000 mJ / Cm ² for about 2 seconds, and further heated at 150 ° C. for 10 minutes to obtain a cured coating film. The gel fraction of the obtained 6 types of cured coating films was measured. The results are shown in Table 1.

The gel fraction was measured by the following procedure.
(1) Measure the mass of the test plate (2) Measure the mass of the test plate after forming the cured coating film.
(3) The test plate is immersed in acetone and treated for 5 hours in a heated and refluxed state.
(4) The test plate after treatment is dried and the mass is measured.
(5) For the value obtained by subtracting the mass of (1) from the mass of (4),
Divide by the value obtained by subtracting the mass of (1) from the mass of (2),
The product obtained by multiplying this by 100 was taken as the gel fraction.

  As the results of Examples 1 and 2 show, it was confirmed that the cationic electrodeposition coating composition of the present invention was sufficiently cured both in the heating alone and in the combined use of light irradiation and heating. In particular, it has been found that the curability can be improved by partially using a blocked isocyanate curing agent. On the other hand, it can be seen from the results of Comparative Examples 1 and 2 that even when a blocked isocyanate curing agent is contained, sufficient curability cannot be obtained simply by combining only with an unsaturated bond or a thiol bond.

  The cationic electrodeposition coating composition and the electrodeposition coating film forming method of the present invention can be applied to the film formation of an automobile body.

Claims (6)

  A cationic electrodeposition coating composition comprising an unsaturated group and cationic group-containing epoxy resin (A) and a thiol group and cationic group-containing epoxy resin (B).   Furthermore, the cationic electrodeposition coating composition of Claim 1 containing a photoinitiator (C).   The cationic electrodeposition coating composition according to claim 1 or 2, further comprising a blocked isocyanate curing agent (D).   Furthermore, the cationic electrodeposition coating composition as described in any one of Claims 1-3 containing an unsaturated group containing compound (E) and / or a thiol group containing compound (F).   Electrodeposition coating formation, characterized in that the cationic electrodeposition coating composition according to any one of claims 1 to 4 is electrodeposited on a substrate and then irradiated with energy rays and / or heated. Method.   A coating film obtained by the electrodeposition coating film forming method according to claim 5.