JP2009173861A - Aqueous primer for recoat and method for forming coating film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To develop an aqueous primer enabling recoat, particularly recoat in the same coating system of aqueous primer-aqueous based coating-two pack type acryl/polyisocyanate-curing top clear by finding such aqueous primer formulation as to enable recoat in same coating system in 3-wet coating system (3-coat 1-bake (3C1B) method) and taking measures to defect in the primer formulation. <P>SOLUTION: This aqueous primer for recoat is used for a coating film-forming method which comprises carrying out coating film formation comprising a step (a first coat) of applying an aqueous primer coating onto a member to be coated, a step (a second coat) of applying an aqueous base coating to a member in which the aqueous primer is kept in a wet state, a step (a third coat) of applying a clear coating to a member in wet state in which base coat has been carried out and a step (baking step) of baking and curing the coated three layers (first, second and third coat layers) at once and further carrying out recoat on the three layers, and the aqueous primer comprises (A) 20-35 pts.wt. chlorinated polyolefin emulsion, (B) 15-35 pts.wt. sulfonic acid group-containing polyurethane dispersion, (C) 20-35 pts.wt. epoxy group-containing acryl emulsion, (D) 5-15 pts.wt. curing agent and (E) 5-35 pts.wt. pigment-dispersing resin, based on 100 pts.wt. total solid content of (A), (B), (C), (D) and (E), and (F) a thickener and (G) a small amount of hydrophobic high-boiling point solvent. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  In the present invention, a 3Wet coating system (three coats and one bake) is applied to apply a water-based primer, apply a base paint and a clear paint by a wet-on-wet method, and bake and cure three layers at the same time. (3C1B) method), an aqueous primer for recoating used for further coating (recoating) on the three layers for the purpose of masking dust, unpainted, scratches, etc. generated on the first three layers; It is related with the coating-film formation method which can obtain the outstanding finishing external appearance using this aqueous primer for recoating.

  A primer that can be recoated is, for example, a surface layer of a clear layer, some scratches, and a design after a three-layer film composed of a water-based primer / water-based base coating / top clear is applied to a material made of polypropylene resin and dried. At the point of time when a malfunction occurs, even if the same coating as described above is performed on this three-layer film, it is an aqueous primer that does not cause any problems in adhesion and other film performance.

  As a method for coating a member such as a panel made of metal or resin constituting an automobile body, it is widely known that first, undercoating is performed by electrodeposition coating, then intermediate coating is performed, followed by overcoating for finishing. In the overcoating process, it is common to first perform base coating with a colored paint, and then perform clear coating with a clear paint.

  As a coating process for obtaining the above-mentioned multi-layer coating film, an undercoat is applied to the material by electrodeposition coating, and then heat-cured, and then an intermediate-coating is applied to the material, followed by heat-curing. The base coating and the clear coating were then performed, and the base coating and the clear coating were heated and cured together (3 coat 2 bake (3C2B) method).

  According to the coating process of the multilayer coating film of the 3 coat 2 bake (3C2B) method, it is possible to form a coating film that can sufficiently satisfy the design properties. In addition, running costs may increase.

  Conventionally, in automobiles where aesthetic appearance is regarded as important, since it is required to form a coating film with excellent coating performance such as smoothness, sharpness, and weather resistance, a solvent-based paint diluted with an organic solvent. However, it was generally used as an intermediate coating or base coating.

  In such a coating method, in recent years, from the viewpoint of reducing the environmental load, as a coating for intermediate coating and overcoating, a conventionally used organic solvent-based coating is shifted to a water-based coating (water-based coating). That is going on. In view of this, a painting method that shortens the painting time in a painting process using a water-based paint has been proposed.

  Therefore, in such intermediate coating and overcoating with a water-based paint, a 3-wet coating system is applied in which a water-based paint is used for the intermediate coating, then a colored water-based paint is applied in a wet state, and a clear coating is applied in a wet state, followed by baking. Or the coating method called a 3 coat 1 bake (3C1B) system is examined from a viewpoint which can aim at the improvement of production efficiency.

  In this 3-wet coating system (3-coat 1-bake (3C1B)) system, for example, in each coating process, the coating is applied in a wet state (wet-on-wet), so that the intermediate layer and the base layer Or between the intermediate coating process and the base coating process in order to prevent mixed layers between the base layer and the clear layer, and to prevent bumping of residual moisture in the baking process, and the base coating. It has been proposed to perform preheating (preheating) between the process and the clear coating process.

  By the way, plastic materials used for automobile bumpers and moldings generally have poor paint wettability and poor paintability. In particular, when the plastic material is a propylene resin or the like, since these resins are chemically inert, it is difficult to directly apply the top coat, including the adhesion to the material. Before applying, various solvent-based primers and aqueous primers have been applied. Aqueous primers such as low-temperature drying have been developed because water-based primers are particularly poor in adhesion to materials compared to solvent-type primers, and plastic materials are difficult to dry at high temperatures.

  For example, in Patent Document 1 below, an acid anhydride-modified chlorinated polyolefin aqueous resin, polyurethane dispersion is blended with a blocked isocyanate that enables low-temperature curing at 120 ° C., and the adhesiveness between the material and the topcoat is aligned. And an aqueous primer composed of blocked isocyanate.

  On the other hand, Patent Document 2 proposes an aqueous primer that uses an organic strong base to lower the temperature by blending polyurethane dispersion and aqueous epoxy resin into acid anhydride-modified chlorinated polyolefin due to the adhesion of plastic material and topcoat. Has been.

  However, in the past, the top clear generally used in the recoating is mostly a two-component acrylic polyol / polyisocyanate, and the aqueous primer proposed in Patent Documents 1 and 2 does not provide recoat adhesion. First, a recoat coating system for so-called repair was performed using a solvent-type primer. In other words, material-water-based primer-water-based base paint-2 liquid acrylic / polyisocyanate cured top clear-solvent primer-the above water-based base coat paint-the above top clear coat has been performed. Therefore, there has been a strong demand for an aqueous primer that can be recoated with the first primer.

JP 2004-307684 A JP 2004-002801 A

  The present invention applies a water-based primer coating when applying plastic exterior parts for automobiles, such as plastic bumpers, etc., and applies a base coating and a clear coating in a wet-on-wet system, and simultaneously baked and cured three layers. In the 3Wet coating system (3 coat 1 bake (3C1B) method), an aqueous primer formulation that enables recoating in the same coating system is found, and recoatable water that prevents unshelling that occurs at that time It is to develop a primer. In particular, an object is to develop an aqueous primer that enables recoating of an aqueous primer-aqueous base paint-2 liquid acrylic / polyisocyanate cured top clear in the same coating system.

  The present inventors have found that the above problems can be solved by using an aqueous primer for recoating having a specific composition, and have reached the present invention. In particular, in a compounding design centered on acid anhydride aqueous chlorinated polyolefin, a primer capable of adhering to a clear coating film was found by using a polyurethane dispersion having a specific range of 100% modulus. In particular, it has been found that a polyurethane dispersion having a sulfone group exerts a great effect.

  Overcoming the problem of water-based primer, the high shear area that came out at that time, that is, the reverse phenomenon of pinhole (foam bite) of the water-based primer at the time of painting, should be reduced viscosity in this high shear area And found that it can be solved by using a urethane-based associative thickener and a small amount of a hydrophobic high boiling point solvent instead of an alkali thickener. On the other hand, when the urethane associative thickener is used, cracks are generated on the surface of the edge of automobile parts and in the pooled area around the perforations, that is, where the film thickness is increased. It was found that it can be solved by using a sticky agent.

  That is, first, the present invention includes a step of applying a water-based primer paint on a member to be coated (first coat), and a step of applying a water-based base paint to a member whose water-based primer is wet (second coat). ) Step, a step of applying a clear paint to the base-coated wet member (third coating), and a step of baking and curing the three coated layers (first to third coating layers) at a time (baking) It is an invention of an aqueous primer for recoating used in a coating film forming method for further coating (recoating) on the three layers after forming the coating film, wherein the aqueous primer for recoating is (A) a chlorinated polyolefin emulsion, (B) Polyurethane dispersion, (C) epoxy group-containing acrylic emulsion, (D) curing agent, (E) pigment dispersion resin, (F) thickener, and (G) a small amount of hydrophobic high boiling point. In a total solid content of 100 parts (A) + (B) + (C) + (D) + (E), including solvent, (A) = 20-35 parts, (B) = 15-35 parts, (C) = 20-35 parts, (D) = 5-15 parts, (E) = 5-35 parts.

The (B) sulfonic acid group-containing polyurethane dispersion used in the present invention preferably has a 100% modulus at 20 ° C. of less than 0.3 to 10 (N / mm ² ).

  In the aqueous primer for recoating of the present invention, the total solid content of (A) + (B) + (C) + (D) + (E) in the total solid content of the paint is preferably 40 to 70% by mass. .

  The (D) curing agent used in the present invention is preferably a melamine resin and / or a blocked isocyanate.

  The (F) thickener used in the present invention is a urethane-associative thickener and preferably has a weight average molecular weight of 5,000 to 10,000.

  As the hydrophobic high boiling point solvent used in the present invention, one or more selected from 2-ethylhexanol, diethylene glycol monomethyl ether, and ethylene glycol mono-2-ethylhexyl ether are preferably exemplified, and these are 1 to 10 in all paints. It is preferable to blend by mass%.

  In the present invention, the member to be coated is preferably a plastic member.

  Secondly, in the present invention, a water-based primer is applied (first coat) on a member to be coated, and a water-based primer is applied to a member in which the water-based primer is wet (second coat). A clear paint is applied to the wet member (third coat), and the three layers (first to third coat layers) applied are baked and cured (baked) at one time to form a coating film. Further, a water-based primer is applied (first recoat), a water-based base paint is applied to the intermediately coated wet member (second recoat), and a clear paint is applied to the base-coated wet member (third Recoating) and coating the three layers (first to third recoating layers) at one time by baking and curing (baking) to form a coating film forming coating (recoating). (A) chlorinated polyolefin emulsion, (B) polyurethane dispersion, (C) epoxy group-containing acrylic emulsion, (D) curing agent, (E) pigment dispersion resin, (F) thickener, and (G) In a total of 100 parts of (A) + (B) + (C) + (D) + (E) containing a small amount of hydrophobic high boiling point solvent, (A) = 20 to 35 parts, (B) = 15-35 parts, (C) = 20-35 parts, (D) = 5-15 parts, (E) = 5-35 parts.

  In the coating film forming method of the present invention, it is preferable that the third coating clear coating used is a two-component curable acrylic / polyisocyanate coating.

  In the coating film forming method of the present invention, it is preferable that the first coat water-based primer paint and the recoat water-based primer paint are the same.

  The coating film forming method of the present invention is characterized in that the member to be coated is a plastic member.

  By using the aqueous primer for recoating of the specific composition of the present invention, the adhesion on the clear coating film is improved, and the pinhole (foaming edge) of the aqueous primer and the accumulated thick film around the edge and the hole It has become possible to suppress the occurrence of surface layer cracks in the part.

  The (A) acid anhydride-modified chlorinated polyolefin emulsion used in the aqueous primer of the present invention will be described. The acid anhydride-modified chlorinated polyolefin is not particularly limited as long as it is a derivative synthesized from a chlorinated polyolefin resin and an acid anhydride. The acid anhydride-modified chlorinated polyolefin resin may be only one type or two or more types.

  In the present invention, the acid anhydride-modified chlorinated polyolefin emulsion resin means an acid anhydride-modified chlorinated polyolefin emulsion resin itself in an emulsion state, and does not include other emulsion resins. To do.

  The chlorine content of the chlorinated polyolefin resin used when obtaining the acid anhydride-modified chlorinated polyolefin emulsion resin is 10 to 30% by mass, more preferably 15 to 22% by mass in the acid anhydride-modified chlorinated polyolefin resin. % Is good. When the chlorine content in the acid anhydride-modified chlorinated polyolefin resin is less than 10% by mass, emulsification of the acid anhydride-modified chlorinated polypropylene resin is difficult to emulsify, whereas when it exceeds 30% by mass, There is a possibility that the adhesion to the polyolefin material, particularly the adhesion to the polypropylene material, may be insufficient.

  Although there is no restriction | limiting in particular as an acid anhydride used when obtaining the said acid anhydride modified chlorinated polyolefin resin, For example, maleic anhydride, citraconic anhydride, itaconic anhydride etc. are mentioned preferably.

  The content of the acid anhydride in the acid anhydride-modified chlorinated polyolefin resin is preferably 1 to 10% by mass, and more preferably 1.2 to 5% by mass. If the amount of acid anhydride in the acid anhydride-modified chlorinated polyolefin resin is less than 1% by mass, the acid anhydride-modified chlorinated polyolefin resin may be difficult to emulsify and the stability of the aqueous coating may be deteriorated. If it exceeds 10% by mass, the hydrophilicity of the primer coating becomes too large, and the water resistance may decrease, which is not preferable.

  The weight average molecular weight of the acid anhydride-modified chlorinated polyolefin resin is preferably in the range of 20,000 to 200,000, and more preferably in the range of 50,000 to 120,000. When the weight average molecular weight is less than 20,000, the strength as a primer coating film is lowered, and the adhesion with the material tends to be reduced or the cohesive failure in the primer coating film tends to occur. On the other hand, if it exceeds 200,000, it becomes difficult to emulsify and the stability of the paint may be deteriorated, and the wettability with the polyolefin material is lowered, and as a result, the adhesion with the material tends to be lowered. is there.

  The acid anhydride-modified chlorinated polyolefin emulsion used in the aqueous primer of the present invention is 20 to 35% by mass in the solid content of all resins (including polyurethane dispersion, epoxy acrylic resin, pigment fraction resin, and curing agent) in the paint. Preferably there is. When the acid anhydride-modified chlorinated polyolefin emulsion resin solid content is less than 20% by mass in the total resin solid content in the aqueous primer coating, the adhesion to the polyolefin material tends to be poor, whereas 35% by mass. If it exceeds 50%, the appearance may be poor, and the adhesion to the underlying clear film will be poor during recoating.

  As a method for emulsifying the acid anhydride-modified chlorinated polyolefin resin, a generally used emulsification method such as a mechanical emulsification method, a method using an emulsifier or a basic substance, or a combination thereof may be used. I can do it. The usage of the emulsifier and the amount of the emulsifier may be appropriately set depending on the acid anhydride-modified polyolefin resin, the basic substance, the amount of water, and the like. When a basic substance is used, it may be set as appropriate depending on the amount of the acid anhydride-modified chlorinated polyolefin resin, water, etc. In particular, the acid functional group of the acid anhydride-modified chlorinated polyolefin resin or emulsifier is sufficiently medium. It is preferable to set in consideration of the amount to be summed and that the pH of the resulting emulsion is 7 to 11, more preferably 7.5 to 10.5. If the pH of the resulting acid anhydride-modified chlorinated polyolefin emulsion is less than 7, the stability of the emulsion becomes poor. On the other hand, if it exceeds 11, free basic substances remain and the water resistance becomes poor. It is not preferable.

  Although there is no restriction | limiting in particular about the particle size of the said acid anhydride modified chlorinated polyolefin emulsion, It is preferable that it is 0.01-10 micrometers. If it is less than 0.01 μm, a large amount of an emulsifier is required, and the water resistance of the coating film may be lowered. On the other hand, if it exceeds 10 μm, the stability of the emulsion may be deteriorated.

  The (B) polyurethane dispersion used for the aqueous primer of the present invention will be described. Polyurethane dispersion is dibutyltin dilaurate, a polyfunctional isocyanate compound, a polyol having two or more hydroxyl groups in a molecule, and a hydrophilizing agent having both a hydroxyl group and a carboxylic acid group such as dimethylolpropanediol or dimethylolbutanediol. In the presence of a catalyst such as, the urethane prepolymer obtained by reacting in an isocyanate group excess state, neutralizes the carboxylic acid with an organic base such as amines or an inorganic base such as sodium hydroxide or potassium hydroxide, After adding ion-exchanged water to make it water-based, and further synthesize urethane preversion that has been increased in molecular weight by a chain extender, or urethane prepolymer that does not have carboxylic acid, carboxylic acid, sulfonic acid, ethylene glycol, etc. Chains using diols or diamines with hydrophilic groups Urethane dispersion obtained by neutralizing with the above basic substance to make it aqueous, and then further increasing the molecular weight using a chain extender, if necessary; Version etc. can be mentioned. More preferably, it is a urethane dispersion made water-based using a sulfonic acid group.

  Examples of the polyfunctional isocyanate compound include 1,6-hexane diisocyanate, lysine diisocyanate, isophorone diisocyanate, cyclohexane-1,4-diisocyanate, xylylene diisocyanate, 2,4-tolylene diisocyanate, and 2,6-tolylene diisocyanate. Examples thereof include diisocyanate compounds and polyfunctional isocyanate compounds such as adducts, burettes, and isocyanurates.

  Examples of the polyol include polyester polyol, polyether polyol, and polycarbonate polyol.

  Examples of the chain extender include low molecular weight diol compounds such as ethylene glycol, propylene glycol, 1,4-butanediol, neopentyl glycol, furashidimethanol, diethylene glycol, triethylene glycol, and tetraethylene glycol, and ethylene oxide, Polyether diol compounds obtained by addition polymerization of propylene oxide, tetrahydrofuran, etc .; the above low molecular weight diol compounds and dicarboxylic acids such as (anhydrous) succinic acid, adipic acid, (anhydrous) phthalic acid, etc. Polyester diols having: polyhydric alcohols such as trimethylolethane and trimethylolbropan; aminoalcohols such as monoethanolamine, diethanolamine and triethanolamine; ethylene Amine, propylene diamine, butylene diamine, hexamethylene diamine, phenylene diamine, toluene diamine, xylene diamine, diamine compounds such as isophoronediamine; water, ammonia, hydrazine, may be mentioned dibasic acid hydrazide and the like.

  At the time of recoating, the water-based primer is applied onto the clear coating film of the two-component curable acrylic resin / polyisocyanate curing agent, and after setting, preheating is performed, followed by the aqueous base coating, followed by preheating, and the clear coating is applied. Is done. There is currently a process of baking and drying at 120 ° C. after setting. At this time, the clear coating of the base coating is a two-part curable acrylic urethane coating, and for adhesion, an aqueous urethane dispersion resin having a urethane bond on the aqueous primer coated thereon. Must exist. Adhesion between the upper and lower sides is improved due to similarities between the similar materials (because the solubility parameters are the same) and the fact that the cohesive energy between the upper and lower sides is similar and the hydrogen bonding force due to having a urethane skeleton is large. Can be considered. On the other hand, when the solid content of the urethane resin was increased to a certain level or more in the aqueous primer, it was found that the interlayer adhesion decreased slightly. This is presumably because the cohesive force due to urethane in the recoat primer film became too large, and the contact points between urethanes at the interface with the base clear decreased. We have recoated aqueous primer that can ensure the interlayer adhesion by setting the content of urethane dispersion in the aqueous primer and its 100% modulus range to some extent even when the entire recoated film is finally cured. Could be developed.

100% modulus of the urethane dispersions resin in the present invention is preferably ^{0.3N / mm 2 ~10N / mm 2} . With urethane dispersion resins having a 100% modulus exceeding 10 N / mm ² , the cohesive force of the recoat ply film becomes too large due to baking and curing, and the number of contact points of the urethane resin with the base decreases, and the cohesive strength of the base clear A decrease in adhesion due to differences and a decrease in adhesion due to a decrease in contact points are assumed. If the 100% modulus of the aqueous urethane dispersion resin is less than 0.3 N / mm ² , the cohesive force of the primer coating film becomes too low, and there is a risk of cohesive failure / peeling in the adhesion evaluation. The polyurethane dispersion preferably has a sulfonic acid group. By having a sulfonic acid group, it is possible to obtain a stronger recoatable aqueous primer by increasing the hydrogen bonding force with the base clear.

  The solid content of the aqueous urethane dispersion resin in the total solid content of (A) to (E) in the aqueous primer is preferably 15 to 35% by mass. If it is less than 15% by mass, cohesive failure or peeling may occur in the adhesion test evaluation after the water resistance test. On the other hand, if it exceeds 35% by mass, the cohesive force becomes too larger than that of the underlying clear film, and there is a risk of peeling between the underlying clear layers, which is not desirable.

  The (C) epoxy group-containing acrylic emulsion used in the present invention will be described. In water-based paints, a large number of hydrophilic groups are necessarily required in order to stabilize the resin in an aqueous medium. For example, carboxyl group, hydroxyl group, amino group and the like. When many such hydrophilic groups are contained, various problems occur in the water resistance test. For example, a large amount of water is absorbed, and whitening, blistering, correlative peeling from the lower film and the upper film due to water swelling are likely to occur. In the present invention, as a result of investigating how to reduce the amount in the primer coating film, particularly focusing on the carboxyl group of the pigment-dispersing aqueous resin, by incorporating a resin having an epoxy group, It has been found that the reaction of epoxy groups is carried out during baking and drying. Moreover, the coating film cohesive force was also improved by this crosslinking reaction.

  As for epoxy resin, bisphenol type and novolac type are exposed outdoors, and in the case of white or mica coatings, the ultraviolet rays of sunlight may reach the primer, resulting in yellowing deterioration of the primer coating and overcoating. There is a concern of affecting the discoloration of the coating film, which is undesirable. It was confirmed that the epoxy group-containing acrylic resin in which a glycidyl group was introduced into the acrylic resin did not cause the above discoloration.

  The acrylic resin can be obtained by copolymerizing a radical polymerizable monomer having a glycidyl group and another radical polymerizable monomer. For example, addition of glycidyl methacrylate or glycidyl acrylate to (meth) acrylic acid, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, hydroxyethyl acrylate and ε-caprolactone Functional group-containing monomers such as products, and further as (meth) acrylic acid alkyl ester, methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, N-butyl (meth) acrylate, T-butyl (meth) acrylate, isobutyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, (meth ) Copolymerization with lauryl acrylate It can be provided for the purpose by an aqueous emulsion.

  The aqueous emulsion can be obtained by solvent polymerization and then emulsification in water using forced stirring or an emulsifier, or emulsion polymerization in water using an emulsifier.

  The amount of the glycidyl group-containing monomer in the epoxy acrylic emulsion solid content is preferably 30 to 60% by mass.

  In the epoxy emulsion obtained from emulsion polymerization, it is necessary to pay attention to the amount of emulsifier. This is because it may remain in the coating film to reduce water resistance and the like.

  In the present invention, the epoxy acrylic emulsion is preferably 20 to 35% by mass in the total solid content from (A) to (E). If it is less than 20% by mass, there is a risk of cohesive failure / peeling of the primer film in the adhesion evaluation after the water resistance test. If it exceeds 35% by mass, the degree of cross-linking becomes too large, cross-linking distortion occurs, and there is a concern that delamination may occur with the underlying clear film in the initial adhesion.

  The (D) curing agent used in the present invention will be described. In the present invention, recoat adhesion in a water resistance test is also important, and for this purpose, a curing agent for performing a crosslinking reaction is necessary. That is, a crosslinked coating film is required to prevent the coating film from being deteriorated by the water resistance test, and is particularly effective in preventing adhesion due to the coating film cohesive failure after the water resistance test by recoating.

  Although it does not specifically limit as a hardening | curing agent used for the aqueous primer for recoating of this invention, If the stability as an aqueous coating material is considered, an aqueous | water-based melamine resin, an aqueous | water-based blocked isocyanate, etc. are preferable. Melamine resin is more preferable from the viewpoint of cost. Although it does not specifically limit as a melamine resin, What is necessary is just a methoxy type melamine or a methoxy butoxy mixed type melamine. Butoxy type melamine can be used by making it water-based by a method using an emulsifier, an acrylic resin, an alkyd resin or the like as an emulsifier. A methoxy-type or butoxy-type melamine resin is more preferable because it can be stabilized in water without using an emulsifier. For example, Cymel series Cymel 300, 301, 303, 350, 370, 771, 325, 327, 703, 712, 715, 701, 267, 285, 232, 235, 236, 238, Nippon Cytec Industries, Ltd. 211, 254, 204, 212, 202, 207 and the like.

  Hereinafter, the blocked isocyanate compound used as a curing agent in the present invention will be described. The blocked isocyanate compound starting component is a di- or poly-isocyanate compound and mixtures thereof. However, these components react with a blocking agent to obtain a blocked isocyanate compound.

  Preferred di- or poly-isocyanate compounds are aliphatic, alicyclic, araliphatic and heterocyclic polyisocyanates. Polyisocyanates containing carbodiimide groups, polyisocyanates containing allophanate groups, polyisocyanates containing isocyanurate groups, polyisocyanates containing urethane and / or urea groups, polyisocyanates containing acylated urea groups, polyisocyanates containing burette groups, Polyisocyanates produced by heteropolymerization reactions, polyisocyanates containing ester groups, preferably diisocyanates containing uretdione groups and diisocyanates containing urea groups are also suitable.

  Specific examples of the di- or polyisocyanate compound include the following. p-xylylene diisocyanate, 1,5-diisocyanatomethylnaphthalene, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, 1-methylbenzene 2,5-diisocyanate, 1,3 dimethylbenzene 4,6-diisocyanate 1,4-dimethylbenzene 2,5-diisocyanate, 1-nitrobenzene 2,5-diisocyanate, 1-methoxybenzene 2,4-diisocyanate, 1-methoxybenzene 2,5-diisocyanate, 1,3-dimethoxybenzene 4,6 -Diisocyanate, azobenzene 4,4'-diisocyanate, diphenyl ether 4,4'-diisocyanate, diphenylmethane 4,4'-diisocyanate, diphenyldimethylmethane 4,4'-diisocyanate, naphthalene 1 5-diisocyanate, 3,3′-dimethylbiphenyl 4,4′-diisocyanate, diphenyl disulfide 4,4′-diisocyanate, diphenylsulfone 4,4′-diisocyanate, 1-methylbenzene 2,4,6-triisocyanate, 1 , 3,5-trimethylbenzene 2,4,6-triisocyanate, triphenylmethane 4,4 ′, 4 ″ -triisocyanate, 4,4′-diisocyanato- (1,2) -diphenylethane, dimer 1 -Methyl-2,4-phenylene diisocyanate, dimer 1-isopropyl-2,4-phenylene diisocyanate, dimer 2,4 'diisocyanatodiphenyl sulfide, 3,3'-diisocyanato-4,4'-dimethyl -N, N'-diphenylurea, 3,3'-diisocyanato-2,2 -Dimethyl-N, N'-diphenylurea, 3,3'-diisocyanato-2,4'-dimethyl-N, N'-diphenylurea, N, N'-bis [4 (4-isocyanatophenylmethyl) phenyl ] Urea, N, N′-bis [4 (2-isocyanatophenylmethyl) phenyl] urea.

  Examples of the blocking agent used to obtain the blocked isocyanate compound include oxime compounds (acetooxime, methyl ethyl ketoxime, methyl isobutyl ketoxime, etc.), lactams (ε-caprolactam, etc.), active methylene compounds (diethyl malonate, acetylacetone, Ethyl acetoacetate), phenols (phenol, m-cresol, etc.), alcohols (methanol, ethanol, n-butanol, etc.), hydroxyl group-containing ethers (methyl cellosolve, butyl cellosolve, etc.), hydroxyl group-containing esters (methyl lactate) , Amyl lactate, etc.), mercaptans (eg, butyl mercaptan, hexyl mercaptan), acid amides (eg, acetanilide, acrylic amide, dimer acid amide), imidazoles (imidazole, - etc. ethylimidazole), imides (succinimide, phthalic acid imide), amines (such as dicyclohexylamine), and mixtures of two or more thereof.

  It is preferable to use a hardening | curing agent in 5-15 mass% in said (A)-(E) total solid content. If it is less than 5% by mass, the degree of crosslinking of the coating film becomes low, and there is a possibility that the adhesion failure after the water resistance test will cause cohesive failure and peeling of the primer film, resulting in poor adhesion. If it exceeds 15% by mass, the primer coating film has a high degree of cross-linking and the hardness coming from the melamine skeleton, so that the internal distortion increases, and there is a risk of poor film-to-film adhesion with the underlying clear.

  The (E) pigment-dispersed resin used in the present invention will be described. The aqueous primer for recoating of the present invention preferably contains a pigment. For this purpose, a pigment paste is required, and it is preferable to use a pigment dispersion resin. Dispersion of the pigment in the acid anhydride-modified chlorinated polyolefin emulsion or urethane dispersion resin as a coating film forming component is not preferable because the coating stability is insufficient.

  As a pigment dispersion resin, it is necessary to suppress aggregation and sedimentation by adsorbing to various pigments. The pigment dispersion resin is not particularly limited as long as it has the pigment dispersion function and has no adverse effects on recoatability, workability, and paint stability as a coating film forming component. For example, an acrylic resin and an alkyd resin are preferable. Moreover, it is preferable that it is water-soluble, and the resin of a particle state in water like an emulsion or a dispersion is not preferable. The water-soluble acrylic resin preferably has an acid value of 40 to 80. When the acid value is less than 40, the adsorption to the pigment is insufficient, and the coating stability may be deteriorated. On the contrary, if the acid value exceeds 80, the hydrophilicity in the coating film is increased, and the water resistance may be lowered. As a weight average molecular weight, 15,000-50,000 (polystyrene conversion by GPC) is preferable. If it is less than 15,000, the adsorptivity to the pigment is slightly lowered and there is a risk of pigment aggregation, and if it exceeds 50,000, the viscosity as a water-soluble resin becomes very high. This is not preferable because handling becomes difficult.

  The pigment-dispersed resin is preferably 5 to 16% by mass in the total solid content of (A) + (B) + (C) + (D) + (E). If it is less than 5%, the pigment cannot be dispersed well, and the stability of the pigment may be lowered. On the other hand, if it exceeds 15% by mass, it is not preferable because it may cause aggregation / breakage due to adhesion after the water resistance test.

  Moreover, it does not restrict | limit especially as a pigment, A normal colored pigment, a metallic pigment, and an extender are mentioned. Examples of the color pigment include titanium dioxide, zinc oxide, basic lead sulfate, calcium leadate, zinc phosphate, aluminum phosphate, zinc molybdate, calcium molybdate, bitumen, ultramarine blue, cobalt blue, copper phthalocyanine blue, indium Dunslon Blue, Yellow Lead, Synthetic Yellow Iron Oxide, Transparent Brown (Yellow), Bismuth Vanadate, Titanium Yellow, Zinc Yellow (Zinc Yellow), Strontium Chromate, Lead Cyanamide, Monoazo Yellow, Disazo, Isoindolinone Yellow, Metal Complex Salt Azo yellow, quinophthalone yellow, benzimidazolone yellow, red bean, transparent red bean (red), red lead, monoazo red, unsubstituted quinacridone red, azo lake (Mn salt), quinacridone magenta, anthanthrone orange, dianthraquinonyl red, Rylene Maroon, Perylene Red, Diketopyrrolopyrrole Chrome Vermilion, Basic Lead Chromate, Chromium Oxide, Chlorinated Phthalocyanine Green, Brominated Phthalocyanine Green, Pyrazolone Orange, Benzimidazolone Orange, Dioxazine Violet, Perylene Violet, etc. It is done. Examples of metallic pigments include aluminum powder, flaky aluminum oxide, pearl mica, and flaky mica. These pigments can be used alone or in combination of two or more.

  The blending ratio of the pigment is usually 120 parts by weight or less, preferably 20 to 100 parts by weight with respect to 100 parts by weight of the resin component.

  The (F) thickener used in the present invention will be described. Water-soluble thickeners are used in various applications such as latex and water-based paints. Examples include various polyacrylamide polymers, polyethylene oxide, polyvinyl pyrrolidone, polyvinyl alcohol, polyacrylic acid and other synthetic polymers, casein, alginic acid, methyl cellulose and carboxymethyl cellulose, methyl hydroxyethyl cellulose, methyl hydroxypropyl cellulose, hydroxyethyl cellulose, and Examples thereof include cellulose ethers such as hydrophobically substituted derivatives, natural polysaccharides such as gum arabic, tragacanth gum and guar gum. In recent years, a group of compounds, collectively called associative thickeners, have been developed. Structurally, it is a nonionic molecule having a higher alkyl group as a hydrophobic group at both ends of polyethylene glycol. A characteristic of this associative thickener is that it has a large effect as a thickener despite a low molecular weight compound having a molecular weight of about several thousand to 100,000. Functionally, there is a decrease in solution viscosity with increasing shear force. This property exists both in the aqueous solution of the compound itself and in the case of a composition such as latex or aqueous paint, and is a major feature of the associative thickener.

  About the method of synthesize | combining the associative type thickener used for this invention, it can synthesize | combine using a well-known urethanation reaction. For example, it can be synthesized by reacting a polyether monool having an alkyl chain having 12 to 23 carbon atoms with a diisocyanate for 2 to 10 hours. It can also be synthesized by reacting polyether diol with diisocyanate and then reacting with the alcohol having the alkyl chain. As a specific reaction, a synthesis method in which polyether monool, polyether diol, and diisocyanate are collectively charged may be used. Or after reacting polyether diol and diisocyanate, the method of making it react with polyether monool may be used.

  The reaction temperature is desirably about 60 to 100 ° C. Moreover, as needed, as a catalyst used for a urethanation reaction, a dibutyltin dilaurate, a cobalt naphthenate, a tin octylate etc. are mentioned as an amine compound and a metal containing compound, for example. Further, in the associative thickener synthesis, a solvent can be used as necessary. However, it is necessary to prevent side reactions from occurring, aromatic solvents such as toluene and xylene, n-hexane as an aliphatic solvent, cyclohexane as an alicyclic solvent, ethyl acetate and butyl acetate as an ester solvent. As the ketone system, methyl ethyl ketone, methyl isobutyl ketone, or the like can be used.

  The molecular weight design of the associative thickener can be adjusted by the molecular weight of the polyether monool containing an alkyl chain, the molecular weight of diisocyanate, and the equivalent blending of these.

  The associative thickener that can be used in the present invention has a weight molecular weight of 5000 to 10,000, and exhibits a sufficient thickening function without causing micro cracks on the surface of the paint film in the paint reservoir at the edge of the paint member. Can do. When the weight average molecular weight exceeds 10,000, the surface layer microcrack of the coating film occurs at the edge portion of the coating member as described above, which is undesirable because it adversely affects the appearance of the topcoat.

  Paint is likely to accumulate on the painted coating member edge portion, and it tends to be thicker than a general surface as a coating film. When the coating is dried, as the water evaporates, the thickener becomes thicker in the surface layer, the thickener having a strong cohesive force having a urethane skeleton and a high molecular weight is considered to cause cracks in the surface layer.

  On the other hand, when the weight average molecular weight is less than 5,000, the above-mentioned cracks do not occur, but the thickening effect of the water-based paint is small, and it is necessary to add a considerable amount for the desired thickening. There is a possibility that the performance of the coating film such as property may be lowered, which is not desirable.

  The painting method of the present invention can be used as it is without any change in the conventional painting apparatus and painting conditions of an automobile parts painting line. Subsequent baking is also possible under the same conditions as before. That is, the water-based primer coating composition used in the present invention is applied to a predetermined film thickness (5 to 18 μm) with a normal coating apparatus, and thereafter, base coating, clear coating, baking (120 to 130 ° C., 20 to 20 ° C.). 60 minutes), an excellent cured coating film that is heated and does not impair the appearance quality such as yellowing, dripping, cracking, swelling and shrinkage can be obtained.

  In the recoat primer of the present invention, a light interference pigment, an extender pigment, a dispersant, an anti-settling agent, an organic solvent, a reaction accelerator (for example, an organic tin compound), an antifoaming agent, and a thickener, if necessary. In addition, known additives such as a rust inhibitor, an ultraviolet absorber, and a surface conditioner can be appropriately blended.

  The recoat primer of the present invention is prepared by blending each of the above components together with water by a known method and water-solubilizing or dispersing the resin component, for example, the solid content concentration is preferably 20 to 60% by weight, preferably Is prepared to be 35 to 60% by weight.

  The coating film thickness of the recoat primer of the present invention is, for example, 5 to 18 μm, preferably 5 to 15 μm as the film thickness after baking.

  The water-based base paint used in the present invention is not particularly limited, and a base water-based paint comprising the same components as the recoat primer of the present invention and containing a water-soluble or water-dispersible resin component, a curing agent and a pigment is used. It is done. For example, a resin component such as an acrylic resin, a polyester resin, an alkyd resin, a urethane resin, or an epoxy resin having a carboxyl group or a hydroxyl group, a crosslinking agent such as a block polyisocyanate, a melamine resin, or a urea resin, a pigment, and other It can be prepared by dissolving or dispersing the additive in water.

  For example, if a metallic pigment such as aluminum powder, flaky aluminum oxide, pearl mica, or flaky mica is used as the pigment, a metallic or pearly coating film can be formed. The pigment content in the base water-based paint is such that the coating film formed by the base coating has transparency and the color of the intermediate coating layer can be visually recognized through the coating film. .

  The aqueous base paint is prepared such that the solid content concentration is, for example, 20 to 50% by weight, preferably 25 to 45% by weight.

The method for applying the aqueous base paint is not particularly limited, and for example, an air spray method, an airless spray method, an electrostatic coating method, or the like is used. More specifically, for example, a bell coating method is used, and the coating conditions include, for example, a bell rotation speed of 25,000 to 35000 min ⁻¹ , a shaving air pressure of 1.0 to 2.0 kg / cm ² , and a gun distance of 20 to 30 cm. The discharge amount is 150 to 350 mL.

  The coating thickness of the aqueous base paint is, for example, 10 to 100 μm, preferably 10 to 25 μm, as the thickness after baking.

  The aqueous base paint may include a volatile material, for example, a bright pigment. Examples of glitter pigments include aluminum flake pigment, metal oxide-coated silica flake pigment, graphite pigment, interference mica pigment, colored mica pigment, metal titanium flake pigment, stainless steel flake pigment, metal-plated glass flake pigment, metal oxide coating Examples thereof include glass flake pigments and hologram pigments.

  Furthermore, when each coating film is preheated by the coating method of the present invention, it is preferable to perform hot air drying at 60 to 100 ° C. for 1 to 5 minutes in order to cause crosslinking in the coating film.

  The clear paint used for clear coating is not particularly limited as long as it is a two-component curable paint. For example, it can be prepared from a resin component such as an acrylic polyol resin or a polyester polyol resin, a curing agent composed of a polyisocyanate compound, other additives, and an organic solvent. Among these, an acrylic polyol resin and a polyisocyanate compound are preferably used from the viewpoint of weather resistance by using a curing agent.

  In addition, the clear paint can contain a base color pigment or a metallic pigment as long as it does not impair the transparency, and can further contain extender pigments, ultraviolet absorbers and the like as appropriate.

  The clear coating is prepared such that the solid content concentration is, for example, 30 to 70% by weight, preferably 40 to 60% by weight.

  The method of applying the clear paint is not particularly limited, and for example, an air spray method, an airless spray method, an electrostatic coating method, or the like is used. Preferably, a bell coating method is used.

[Examples and Comparative Examples]
Hereafter, the manufacture example of each component is shown.
(Synthesis example of acid anhydride-modified chlorinated emulsion)
A reactor equipped with a stirring blade, a thermometer, a temperature control thermistor device, a dripping device, and a cooling pipe was added to a maleic anhydride-modified chlorinated polyolefin resin ("Supercron 892LS"; manufactured by Nippon Paper Industries Co., Ltd .: chlorine content 22 %, Weight average molecular weight 70,000 to 80,000) 288 parts, surfactant ("Emulgen 920" manufactured by Kao Corporation) 62 parts, aromatic hydrocarbon solvent "Solvesso 100" manufactured by Exxon) 74 parts, carbitol acetate After charging 32 parts, the temperature was raised to 110 ° C. and heated at this temperature for 1 hour to dissolve the resin and the like, and then cooled to 100 ° C. or lower. Next, 710 parts of ion-exchanged water in which 6 parts of dimethylethanolamine was dissolved was added dropwise over 1 hour with stirring to carry out phase inversion emulsification. Then, it cooled to room temperature and filtered with the 400 mesh metal-mesh, and the maleic anhydride modified chlorinated polyolefin emulsion was obtained. The non-volatile content of this emulsion was 30% by mass.

(Synthesis example 1: Synthesis example of sulfonic acid group-containing polyurethane dispersion)
1100 parts adipic acid and 3 methyl-1,5-pentanediol while passing nitrogen gas through a pressure-resistant reaction vessel equipped with a stirring blade, thermometer, temperature control, dripping device, reflux device with sample collection port and cooling tube, and nitrogen introduction tube 900 parts and 0.5 parts of tetrabutyl titanate were charged, the reaction temperature of the liquid in the container was set at 170 ° C., an ester reaction was performed by dehydration, and the reaction was continued until the acid value became 0.3 mgKOH / g or less. Subsequently, the reaction was carried out under reduced pressure conditions of 180 ° C. and 5 kPa or less for 2 hours to obtain a polyester having a hydroxyl value of 112 mgKOH / g and an acid value of 0.2 mgKOH / g. Then, in another reaction vessel equipped with the same apparatus as the above reaction vessel, 500 parts of this polyester polyol, 134 parts of dimethyl 5-sulfosodimethylisophthalate and 2 parts of tetrabutyl titanate were charged in the same manner as above. Then, the esterification reaction was carried out at a reaction temperature of 180 ° C. while passing nitrogen gas, and finally a sulfonic acid group-containing polyester having a molecular weight of 2117, a hydroxyl value of 53 mgKOH / g and an acid value of 0.3 mgKOH / g was obtained. .

(Synthesis Example 2: Synthesis example of sulfonic acid group-containing urethane dispersion having a low 100% modulus)
280 parts of the above sulfonic acid group-containing polyester (Synthesis Example 1), 200 parts of polybutylene adipate, 35 parts of 1,4-butanediol, 118 parts of hexamethylene diisocyanate and 400 parts of methyl ethyl ketone, stirring blade, thermometer, temperature control A urethane prepolymer having an NCO content of 1% is charged into a reaction vessel equipped with a dripping device, a sample collection port and a cooling tube while passing nitrogen gas, and the urethanation reaction is carried out while maintaining the liquid temperature at 75 ° C. with stirring. Obtained. Subsequently, the temperature in the reaction vessel was lowered to 40 ° C., and 955 parts of ion-exchanged water was uniformly added dropwise with sufficient stirring to perform phase inversion emulsification. Next, the internal temperature was lowered to room temperature, and an adipic acid hydrazide aqueous solution in which 13 parts of adipic acid hydrazide and 110 parts of ion-exchanged water were mixed was added to carry out amine elongation. Next, the solvent temperature was raised to 60 ° C. in a slightly reduced pressure state, and when the solvent was removed, ion-exchanged water was added so that the solid content of the polyurethane dispersion was 35%, and the sulfonic acid group-containing polyurethane Dispersion (B1) was obtained. The acid value was 11 mgKOH / g. The 100% modulus of this dry film thickness of 100 μm was 2.

(Synthesis Example 3; Synthesis Example of Urethane Dispersion Containing Sulfonic Acid Group with Large 100% Modulus)
A urethane dispersion (B2) was obtained in exactly the same formulation and steps except that only hexamethylene diisocyanate was replaced with 156 parts of isophorone diisocyanate in the same reaction step as performed in (Synthesis Example 2). Also in this case, the solid content was adjusted to 35% by adding ion-exchanged water at the final time point, and the acid value was 11 mgKOH / g. The 100% modulus of this dry film thickness of 100 μm was 16.

(Manufacture of epoxy group-containing acrylic resin)
In a reaction vessel equipped with a stirring blade, a thermometer, a dripping device, a temperature control device, a nitrogen gas introduction tube and a cooling tube, 37 parts of ion-exchanged water was charged and the temperature was raised to 80 ° C. Each operation was performed while stirring the internal solution from the temperature rise to the completion of the reaction. On the other hand, in an emulsifier (TK Robotics RM type; manufactured by Primics Co., Ltd.), 21 parts of ion-exchanged water, 1 part of a surfactant Newcol 710 and 1 part of Newcol 740 (both are a surfactant and a Japanese emulsifier) (Made by Co., Ltd.) and homogeneously dissolved with stirring.

  While stirring continuously, a polymerizable monomer mixed solution composed of 6 parts of n-butyl acrylate, 8 parts of ethylhexyl methacrylate and 14 parts of glycidyl methacrylate was gradually dropped into the emulsifier to prepare a pre-emulsion liquid.

  On the other hand, a polymerization catalyst solution comprising 7 parts of ion-exchanged water and 1.1 parts of ammonium persulfate (emulsion polymerization catalyst) was prepared, and the pre-emulsion liquid and the polymerization catalyst liquid were added to the reaction vessel from separate dropping funnels. The solution was added dropwise over 3 hours. The temperature inside the reaction vessel was maintained at 80 ° C., and emulsion polymerization was carried out with stirring. The pre-emulsion liquid was directly dropped from the reaction vessel while maintaining the emulsified state with an emulsifier. After 3 hours, only a polymerization catalyst solution consisting of 4 parts of ion exchange water and an ammonium persulfate polymerization catalyst was added dropwise over 1 hour while maintaining the internal temperature at 80 ° C. Thereafter, the mixture was aged at 80 ° C. for 1 hour and cooled to obtain an epoxy group-containing acrylic emulsion. The non-volatile content of this product was 30%. The amount of the epoxy group-containing monomer in the resin solid content 100 is 50% by mass.

(Synthesis example of pigment dispersion resin for aqueous primer)
Into a reaction vessel equipped with a stirring blade, a thermometer, a dripping device, a temperature control device, a nitrogen gas introduction tube and a cooling tube, 55 parts of propylene glycol monomethyl ether ether was introduced and the temperature was raised to 120 ° C. with stirring while introducing nitrogen gas. Warm up. Next, 12 parts of 2-hydroxyethyl methacrylate, 9 parts of methacrylic acid, 35 parts of isobutyl methacrylate, 44 parts of n-butyl acrylate, and 1 part of t-butyl peroxy-2-ethylhexanate are mixed with propylene glycol. The solution dissolved in 8 parts was added dropwise over 3 hours with internal stirring.

  Then, after completion of the dropwise addition, after aging reaction at 120 ° C. for 1 hour, a solution in which 0.1 part of t-butylperoxy-2-ethylhexanate was dissolved in 4 parts of propylene glycol monomethyl ether was further added for 1 hour. Over the reaction vessel. In either case, the internal stirring state and the 120 ° C. liquid temperature were maintained. Thereafter, the mixture was aged at 120 ° C. for 2 hours with stirring, then the internal liquid temperature was cooled to 70 ° C., 9.5 parts of dimethylaminoethanol was added dropwise, and the mixture was stirred for 30 minutes. Further, while maintaining the internal liquid temperature at 70 ° C. and stirring, 167 parts of ion-exchanged water was slowly dropped and cooled to obtain a water-soluble acrylic resin solution. The non-volatile content was adjusted to 30% using ion-exchanged water.

  The pH of the obtained water-soluble acrylic resin solution was 8.2, and the weight average molecular weight of the acrylic resin was 42000 (GPC in terms of polystyrene).

[Production example of pigment dispersion paste]
A stainless steel cylindrical stirring vessel equipped with a stirrer was charged with 33.3 parts of the pigment dispersion resin for aqueous primer in the above production example, and 21 parts of ion-exchanged water was added with stirring. Subsequently, 2.0 parts of pigment dispersion ratio SURFYNOL GA (nonvolatile content = 78%; manufactured by Air Products) was added with stirring. With sufficient stirring, 0.4 part of antifoaming split Nopco 8034-L (non-volatile content: 100%; manufactured by San Nopco) was added. While continuing to stir, the matte silica nip seal SS-50B (manufactured by Tosoh Silica) 11.3 parts, conductive carbon carbon ECP600JD (manufactured by Lion Corporation) 9.0 parts, titanium R-960 ( 48.2 parts (manufactured by Du Pont)) were charged in order, and finally 3.9 parts of ion-exchanged water and then 12.2 parts of Cymel 701 (manufactured by Cytec Industries, Inc .; nonvolatile content = 82%) were added. With sufficient stirring, the mixture was stirred for 15 minutes until the whole became uniform to prepare a pigment mill base. The mill base was subjected to pigment dispersion by a sand grinder mill to prepare a pigment dispersion paste for an aqueous primer. This had a non-volatile content of 64% and a pigment concentration (PWC) of 75.8%.

  The blending ratio of the pigment dispersion paste is as shown in Table 1 below.

(Associative thickener production example)
(Synthesis Example 1)
6645 parts by mass of an adduct (number average molecular weight 3320) of cetyl alcohol and 70 mol of ethylene oxide was dehydrated at 100 ° C. for 3 hours under reduced pressure, and the water content of the adduct was reduced to 0.005%. It was as follows.

  Next, the mixture was cooled to 70 ° C. under atmospheric pressure, 168 parts of hexamethylene diisocyanate and 0.7 parts by mass of dibutyltin dilaurate were added, the temperature was raised to 80 ° C. in a nitrogen atmosphere, and the reaction was carried out at this temperature for 5 hours. The obtained urethane compound was viscous liquid, and the weight average molecular weight in GPC measurement in terms of polystyrene was 8,000.

  The mixture of 15% by mass of this urethane compound, 24% by mass of propylpropylene glycol and 61% by mass of ion-exchanged water was stirred with a disper to produce an associative thickener.

(Synthesis Example 2)
9285 parts by mass of an adduct (number average molecular weight 4640) of cetyl alcohol and 100 mol of ethylene oxide was dehydrated under reduced pressure using the same method and conditions as in the production example of associative thickener (Synthesis Example 1), and the water content was reduced to 0. 0.005% or less, then cooled to 70 ° C. under atmospheric pressure, added 168 parts by mass of hexamethylene diisocyanate and 0.9 parts by mass of dibutyltin dilaurate, heated to 80 ° C. in a nitrogen atmosphere, and allowed to react for 5 hours. It was. The obtained urethane compound was viscous liquid, and the weight average molecular weight in terms of polystyrene was 12,000.

  The mixture of 15% by mass of this urethane compound, 24% by mass of propylpropylene glycol and 61% by mass of ion-exchanged water was stirred with a disper to produce an associative thickener.

(Synthesis Example 3)
3125 parts by mass of an adduct of cetyl alcohol and 30 mol of ethylene oxide (number average molecular weight 1560) was dehydrated under reduced pressure using the same method and conditions as in the production example of associative thickener (Synthesis Example 1), and the water content was reduced to 0. 0.005% or less, then cooled to 70 ° C. under atmospheric pressure, added 168 parts by mass of hexamethylene diisocyanate and 0.3 parts by mass of dibutyltin dilaurate, heated to 80 ° C. in a nitrogen atmosphere and allowed to react for 5 hours. It was.

  The obtained urethane compound was viscous liquid, and the weight average molecular weight in terms of polystyrene was 4000.

  The mixture of 15% by mass of this urethane compound, 24% by mass of propylpropylene glycol and 61% by mass of ion-exchanged water was stirred with a disper to produce an associative thickener.

[Example 1]
A stainless steel container equipped with a stirrer was charged with 100 parts of the epoxy group-containing acrylic resin, and the following were sequentially charged with stirring to prepare an aqueous primer.
Acid anhydride-modified chlorinated polyolefin emulsion resin (A) 100 parts urethane dispersion production example (Synthesis example 1, 100% modulus 2) 57 parts Cymel 701 12.2 parts Pigment dispersion paste production example 10 parts urethane associative thickener (Synthesis example 1, Mw = 8000) 0.14 parts 2 ethylhexanol 6 parts Surface conditioner Surfynol 440 (made by Air Products) 3.5 parts ion-exchanged water 136.54 parts The non-volatile content of this paint is 32 masses %Met.

[Examples 2 to 5]
In the same procedure, the primers of Examples 1 to 5 were prepared with the formulation shown in Table 2.
[Comparative Examples 1-5]
In the same procedure, primers of Comparative Examples 1 to 5 were prepared with the formulation shown in Table 3.
[Comparative Examples 6-9]
In the same procedure, primers of Comparative Examples 6 to 9 were prepared with the formulations shown in Table 3. However, in Comparative Example 6, an alkali swelling type thickener (Primal ASE-60) was used, in Comparative Example 7, a urethane dispersion (Synthesis Example 2: 100% modulus 16) was used, and in Comparative Example 8, a urethane-associated type thickening was used. An agent (Synthesis Example 2: Mw = 12000) was used, and in Comparative Example 9, a urethane-associative thickener (Synthesis Example 3: Mw = 4000) was used.

[Performance evaluation]
Each test piece was prepared by the recoat coating film preparation method, and the initial adhesion (recoating primary adhesion), the water-resistant secondary adhesion, the cracking property, and the crack property evaluation were performed, and the results are shown in Tables 2, 3 and 4.

(Recoating film creation method)
Spray coating (dry film thickness 8μm) with a wiper 71 (manufactured by Anest Iwata) on a polypropylene material (70 mm × 150 mm × 3 mm) wiped with isopropyl alcohol in an environment of 25 ° C./70% RH at 80 ° C. Preheated for 3 minutes.

  Next, an aqueous base paint (AR-2000, manufactured by Nippon Paint Co., Ltd., acrylic melamine type) was spray-coated (dry film thickness 15 μm) with Weider 71 (manufactured by Anest Iwata), and preheated at 80 ° C. for 5 minutes.

  Next, a clear paint (R-2500-1, clear base (made by Nippon Bee Chemical Co., Acrylic) / H-2500-1 curing agent made by Nihon Bee Chemical Co., polyisocyanate) is used as Weider 71 (made by Anest Iwata) Spray coating (dry film thickness 30 μm), setting at 25 ° C./70% RH for 10 minutes, and then drying at 120 ° C. for 35 minutes to obtain a test piece.

  The obtained test piece was allowed to stand for 3 days in an environment of 30 ° C./70% RH, and then the above primer, aqueous base, and clear paint were recoated under the same coating conditions to prepare a recoat evaluation coated plate.

  The obtained test piece was subjected to a cross-cut peel test by the following method after 72 hours at 20 ° C. under 70% RH.

(Re-coating initial value cross-cut peel test)
In accordance with JIS K5600-5-6, a peel test with a grid pattern was performed. 100 square grids of 2 mm square were prepared, a peel test was performed with an adhesive tape, and even one test piece was evaluated as adhesiveness x.

(Waterproof secondary adhesion evaluation method on the recoat side)
The test piece created by the above method is immersed in a water resistant bath at 40 ° C. for 240 H. After pulling up after completion of the immersion, a cross cellophane tape (registered trademark) peel test was performed within 1 hour in accordance with JIS K5600-5-6. 100 grids of 2 mm square were prepared, and a cellophane tape peeling test was performed to count the number of grids that were not peeled off.

  The evaluation skewers are as follows. 0/100 (no peeling) was set as ◯, and 1/100 to 100/100 (with peeling) was set as x.

(Waki evaluation)
The aqueous primer paint prepared in Examples 1 to 5 and Comparative Examples 1 to 9 was applied to an IPA wiped polypropylene material (70 mm × 150 mm × 3 mm) to a dry film thickness of 10 μm in an environment of 25 ° C./70% RH. After setting for 15 seconds, preheating was performed at 80 ° C. for 3 minutes in a drying furnace.

  After preheating, it is taken out from the drying furnace and allowed to stand for 10 minutes in an environment of 25 ° C./70% RH. Then, a clear paint is spray-coated (dry film thickness 20 μm), and in an environment of 25 ° C./70% RH. After setting for 10 minutes, the test piece was dried by drying at 120 ° C. for 35 minutes.

  The obtained coated plate was evaluated and evaluated by visual inspection. The evaluation criteria are as follows. The case where there was no armpit was marked with ◯, and the case where there was one or more armpits was marked with ×.

(Crack evaluation)
After wiping and degreasing a polypropylene material (70 mm × 75 mm × 3 mm) whose center portion was cut into a circle of 50 mmφ with isopropyl alcohol, under a 70% RH (relative humidity) environment at 25 ° C., Painted with Weider 71 (manufactured by Anest Iwata Co., Ltd.) (dry film thickness 15 μm), left in the above environment for 30 seconds, and then placed in a drying furnace with a furnace temperature of 60 ° C. and a furnace wind speed of 4 m / second for 3 minutes. Dried. After cooling, the crack evaluation of the pool part around the circle of the coated plate was performed visually. If there was even one crack, it was rated as x, and no crack was marked as ◯.

  From the results of Tables 2, 3 and 4, it can be seen that the primer for recoating of the present invention satisfies various performances in combination with the 3Wet coating system.

  According to the present invention, it is possible to perform recoating in the same coating system in a 3 Wet coating system (3 coat 1 bake (3C1B) method). In particular, it is possible to recoat water-based primer-water-based base paint-2 liquid acrylic / polyisocyanate cured top clear in the same coating system. The coating method of the present invention is preferably applied particularly to members constituting automobile parts.

Claims (11)

  A process of applying a water-based primer paint on a member to be coated (first coat), a process of applying a water-based base paint to a member in which the water-based primer is wet (second coat), and a wet state in which the base is coated After the formation of a coating film comprising the step of applying a clear paint on the member (third coating) and the step of baking and curing the three layers (first to third coating layers) at a time (baking), the three layers An aqueous primer for recoating used in a method for forming a coating film to be further coated (recoated), wherein (A) a chlorinated polyolefin emulsion, (B) a sulfonic acid group-containing polyurethane dispersion, (C) an epoxy group-containing acrylic emulsion, (D) a curing agent, (E) a pigment-dispersed resin, (F) a thickener, and (G) a small amount of a hydrophobic high-boiling solvent, and (A) + (B) + (C) + ( ) + (E) in a total solid content of 100 parts, (A) = 20-35 parts, (B) = 15-35 parts, (C) = 20-35 parts, (D) = 5-15 parts, (E) = 5 to 35 parts of an aqueous primer for recoating. ^2. The aqueous primer for recoating according to claim 1, wherein the (B) sulfonic acid group-containing polyurethane dispersion has a 100% modulus at 20 ° C. of less than 0.3 to 10 (N / mm ² ). .   3. The recoat according to claim 1, wherein the total solid content of (A) + (B) + (C) + (D) + (E) in all paints is 40 to 70% by mass. Water based primer.   The aqueous primer for recoating according to any one of claims 1 to 3, wherein the (D) curing agent is a melamine resin and / or a blocked isocyanate.   The aqueous primer for recoating according to any one of claims 1 to 4, wherein the (F) thickener is a urethane-associative thickener and has a weight average molecular weight of 5000 to 10,000.   The hydrophobic high boiling point solvent is one or more selected from 2-ethylhexanol, diethylene glycol monomethyl ether, and ethylene glycol mono-2-ethylhexyl ether, and is blended in an amount of 1 to 10% by mass in the total paint. The aqueous primer for recoating according to any one of claims 1 to 5.   The aqueous primer for recoating according to any one of claims 1 to 6, wherein the member to be coated is a plastic member.   A water-based primer is applied on the member to be coated (first coat), a water-based primer is applied to a member in which the water-based primer is wet (second coat), and a clear paint is applied to the base-coated wet member. After coating (third coating), the coated three layers (first to third coating layers) were baked and cured (baked) at once to form a coating film, and then an aqueous primer was further coated on the three layers (first coating). 1), a water-based base paint is applied to the wet-coated member (second recoat), and a clear paint is applied to the wet-coated member (third recoat). It is a coating film forming method in which a layer (first to third recoat layers) is baked and cured (baked) at a time to form a coating film (recoating), wherein (A) a chlorinated polyolefin emulsion, (B) sulfo An acid group-containing polyurethane dispersion, (C) an epoxy group-containing acrylic emulsion, (D) a curing agent, (E) a pigment dispersion resin, (F) a thickener, and (G) a small amount of a hydrophobic high-boiling solvent, In a total solid content of 100 parts of (A) + (B) + (C) + (D) + (E), (A) = 20-35 parts, (B) = 15-35 parts, (C) = A coating film forming method using an aqueous primer for recoating of 20 to 35 parts, (D) = 5 to 15 parts, and (E) = 5 to 35 parts.   9. The method for forming a coating film according to claim 8, wherein the third coating clear coating is a two-component curable acrylic polyisocyanate coating.   10. The method for forming a coating film according to claim 8, wherein the first primer aqueous primer paint and the recoat aqueous primer paint are the same.   The method for forming a coating film according to claim 8, wherein the member to be coated is a plastic member.