JP5773369B2 - Method of recoating an object having a sealer part - Google Patents

Description

  The present invention relates to a method for recoating an object having a sealer portion.

  A coating film with various functions such as rust prevention and weather resistance is sequentially formed on the surface of an object such as an automobile body to protect the object and at the same time provide a beautiful appearance and an excellent design. ing. As a method for forming a multilayer coating film, an undercoating film such as an electrodeposition coating film is formed on an object having excellent conductivity, and an intermediate coating film, a base coating film and a clear coating film are formed thereon. A method of sequentially forming a top coat film made of a film is common.

  Incidentally, an object to be coated such as an automobile body has an extremely complicated structure. For example, in places such as doors, bonnet hoods, roofs, and the like that constitute an automobile body, there are joint portions or joint portions in which two plate-shaped steel plates are overlapped with each other. These joints or joints have a gap at the boundary. Such a gap is difficult to cover only by coating with a normal coating composition such as an intermediate coating composition, top coating base coating composition, and top coating clear coating composition. Furthermore, there is a problem that foreign matters such as water and dust are likely to enter the gaps at the boundary portions present at the joints or joints, and these foreign matters cause rust. Therefore, in general, such a joint portion or a joint portion is provided with a sealer portion by painting and filling a sealing agent. The coating and filling of the sealing agent is generally performed on a steel plate on which an electrodeposition coating film is formed. And an intermediate coating film and a top coating film are formed with respect to the to-be-coated object provided with the sealer part.

  The intermediate coating film and the top coating film in automobile body painting or the like have a great influence on the coating film and the appearance and design of the product. For this reason, if coating film defects such as blistering due to adhesion of foreign matter or generation of dents or repellency due to coating defects are found in the coating and baking and curing processes of intermediate coating film and top coating film, this coating film The application for providing the intermediate coating film and the top coating film is performed again on the portion where the defect exists or on the entire object to be coated. Such repainting is called recoating. In this recoating, a recoating coating comprising a multi-layer coating including an intermediate coating and a top coating already provided on the article to be coated, and an intermediate coating and a top coating provided by re-coating. Interlayer adhesion with the film is a problem. This is because when the interlayer adhesion is low, peeling occurs between the already provided multilayer coating film and the repaint coating film. And when using a water-based coating composition as an intermediate coating composition and a top-coat base coating composition, it turned out that the interlayer adhesiveness in a recoat is inferior especially in the to-be-coated article which has a sealer part.

  Japanese Patent Publication No. 7-39560 (Patent Document 1) describes a dehydration condensate of a polyvalent carboxylic acid containing an aromatic polycarboxylic acid and a polyhydric alcohol other than a cyclic aliphatic polyhydric alcohol, A polyester resin having a number average molecular weight of 2,000 to 10,000 and having an average of 2.1 to 2.8 hydroxyl groups in one molecule and a resin capable of reacting with the hydroxyl groups in a mass ratio of 90:10 to 60: A top coating composition for automobiles, characterized in that it is contained in a proportion of 40, is described (claim 1). In Patent Document 1, both the recoat adhesion and the scratch resistance are achieved by designing the amount of hydroxyl groups and the branched structure of the polyester resin contained in the top coat composition. On the other hand, the present invention is a method for recoating an object having a sealer part, and a component obtained by removing the pigment from the plasticizer and the first aqueous coating composition contained in the sealant used for forming the sealer part. The configuration is clearly different from the invention described in Patent Document 1 in that the physical properties are within a specific range.

  In JP-A-6-88056 (Patent Document 2), (A) a film-forming resin, (B) a cross-linking agent for heat-curing the resin (A), and (C) a length of 8 to 18 carbon atoms. It contains a phosphate ester, sulfonic acid or carboxylic acid having a chain alkyl group and having HLB 3 to 12, and the blended solid content of component (C) is relative to the total solid content of components (A) and (B) A coating composition having an improved interlayer adhesion is described, which is 0.1 to 5% by mass (claim 1). In Patent Document 2, it is described that the second base coat can be recoated without sanding the cured clear coating film by using the coating composition containing the component (C) for forming the second base coat. (Claim 4 etc.). On the other hand, the present invention is a method for recoating an object having a sealer part, and a component obtained by removing the pigment from the plasticizer and the first aqueous coating composition contained in the sealant used for forming the sealer part. The configuration is clearly different from the invention described in Patent Document 2 in that the physical properties are within a specific range.

  Japanese Patent Application Laid-Open No. 2005-146144 (Patent Document 3) discloses an automotive topcoat paint containing an antioxidant (Claim 1), and after coating and curing the topcoat paint, the topcoat paint. A method for repair coating of a top coat film (Claim 4) is described in which the coating is cured by repainting. In this patent document 3, the effect that the recoat adhesion of the top coat film is excellent even under overbaking conditions under a high NOx concentration is achieved by using an automotive top coat containing an antioxidant. ([0007] paragraph, etc.). On the other hand, the present invention is described in Patent Document 3 in that it is a method for recoating an article having a sealer part and that it is not characterized by including such an antioxidant in a top coating composition. The configuration is clearly different from the invention.

Japanese Examined Patent Publication No. 7-39560 JP-A-6-88056 JP 2005-146144 A

  An object of the present invention is to solve the above-described problems of the prior art. More specifically, the present invention has an object to improve interlayer adhesion between a cured coating film already provided on a coating object and a newly provided coating film in recoating the coating object having a sealer portion. And

The present invention
A first aqueous coating composition containing a pigment is applied to an object having a sealer portion to form an uncured first coating film, and then a second aqueous coating composition is applied to form an uncured second coating composition. A wet-on-wet coating process for forming a film and then applying a clear coating composition on the uncured second coating to form an uncured clear coating; and the resulting uncured first coating Baked and cured step of simultaneously baking and curing the second coating film and the clear coating film,
A method for recoating an object having a sealer part,
The object to be coated before recoating is a sealer portion, a cured first coating film formed on the sealer portion, a cured second coating film formed on the cured first coating, and this cured second coating. Already having a cured clear coating formed on the film,
This sealer part is a sealer part formed by a vinyl chloride plastisol sealant containing a vinyl chloride resin and a plasticizer,
The difference (ΔSP) between the SP value of the mixture of components obtained by removing the pigment from the first aqueous coating composition and the SP value of the plasticizer contained in the vinyl chloride plastisol sealing agent is 1.0 or less in absolute value. ,
The present invention provides a method for recoating an object having a sealer portion, whereby the above-mentioned problems are solved.

  By mixing 100 parts by weight of the mixture of the components obtained by removing the pigment from the first aqueous coating composition and 20 parts by weight of the plasticizer contained in the vinyl chloride plastisol sealing agent, and then heat-curing the resulting mixture It is preferable that the turbidity of the formed test cured coating film is 20 or less.

In addition, the first water-based paint composition is
A hydroxyl group-containing acrylic resin emulsion containing 27 to 65% by mass of a styrene monomer, having a water tolerance of 0.2 to 5 and a hexane tolerance of 5 to 25;
Hydroxyl group-containing polyester resin;
Melamine resin;
Carbodiimide;
An aqueous paint composition comprising an associative viscosity agent; and a pigment is preferred.

  The plasticizer contained in the vinyl chloride plastisol sealing agent is preferably one or more selected from the group consisting of phthalic acid esters, di- or tricarboxylic acid esters, phosphoric acid esters and epoxidized soybean oil. .

  The recoating method of the present invention is cured by recoating on a coating object having a multilayer coating film comprising a sealer portion, a cured first coating film, a cured second coating film and a cured clear coating film, which has already been provided. When providing a repainted film comprising the first coated film, the cured second coated film, and the cured clear coated film, there is no delamination between the multilayered film and the repainted film that have already been provided. It is characterized in that a coating film having excellent adhesion can be formed.

FIG. 1 is a schematic explanatory view of a coated product obtained by the recoating method of the present invention.

The recoating method of the present invention comprises:
A first aqueous coating composition is applied to the article to form an uncured first coating film, then a second aqueous coating composition is applied to form an uncured second coating film, and then uncoated. Applying a clear coating composition on a cured second coating, wet-on-wet coating process, and baking the resulting uncured first, second and clear coatings simultaneously Curing process,
Is a method for recoating an object having a sealer portion.
The object to be coated before being recoated by the method of the present invention is a sealer portion, a cured first coating film formed on the sealer portion, and a cured second coating film formed on the cured first coating film. And a cured clear coating formed on the cured second coating. And this sealer part is a sealer part formed with the vinyl chloride plastisol sealing agent containing a vinyl chloride resin and a plasticizer. In the present invention, the difference (ΔSP) between the SP value of the mixture of the components excluding the pigment from the first aqueous coating composition and the SP value of the plasticizer contained in the vinyl chloride plastisol sealing agent is an absolute value. It is 1.0 or less.

The object to be coated before being recoated by the method of the present invention comprises a sealer portion, a cured first coating film formed on the sealer portion, and a cured first coating film formed on the cured first coating film. This is an article to be coated that already has two coating films, a cured clear coating film formed on the cured second coating film. The cured first coating film, cured second coating film, and cured clear coating film to be coated before being recoated by the method of the present invention are the first aqueous coating composition and the second aqueous coating composition described in detail below. And a coating film formed using a clear coating composition. The cured first coating film, the cured second coating film, and the cured clear coating film, which are to be coated before recoating, are coating films formed by the wet-on-wet coating process described in detail below. Alternatively, it may be a coating film formed by a coating process including a heat curing process as required after coating each coating composition.

  Examples of the substrate used as the article to be coated include metal substrates such as iron, copper, aluminum, tin, zinc, and alloys containing these metals. These substrates are preferably subjected to a chemical conversion treatment (for example, a zirconium chemical conversion treatment, a zinc phosphate chemical conversion treatment, etc.), and then an electrodeposition coating film is formed by electrodeposition coating. As an electrodeposition coating composition used for electrodeposition coating, a known cationic electrodeposition coating composition or anion electrodeposition coating composition can be used. As the electrodeposition coating conditions and the bake curing conditions, for example, conditions usually used in electrodeposition coating of automobile bodies can be used.

Sealer Part In the present invention, the article to be coated has a sealer part. This sealer portion is formed by coating a vinyl chloride plastisol sealing agent containing a vinyl chloride resin and a plasticizer on an object to be coated.

  Examples of the vinyl chloride resin contained in the vinyl chloride plastisol sealing agent include vinyl chloride homopolymers and copolymers of vinyl chloride and other monomers such as vinyl acetate. These vinyl chloride homopolymers and copolymers may be used in combination.

  Examples of the plasticizer contained in the vinyl chloride plastisol sealing agent include phthalic acid esters such as dioctyl phthalate, di-2-ethylhexyl phthalate, diisononyl phthalate, and octyl butyl phthalate, sebacic acid esters, and azelaic acid esters. And phosphoric acid esters such as di- or tricarboxylic acid esters, triphenyl phosphate and tricresyl phosphate, and epoxy plasticizers such as epoxidized soybean oil. As the plasticizer, a high-boiling organic solvent can also be used.

  In the present invention, the difference (ΔSP) between the SP value of the mixture of components obtained by removing the pigment from the first aqueous coating composition and the SP value of the plasticizer contained in the vinyl chloride plastisol sealing agent is 1 in absolute value. The condition is that the value is 0.0 or less. Here, considering the range of the SP value of the mixture of components obtained by removing the pigment from the first aqueous coating composition, the SP value of the plasticizer is preferably in the range of, for example, 10.1 to 11.8. More preferably, it is 6 to 11.8.

  The SP value is an abbreviation for solubility parameter (solubility parameter) and is a measure of solubility. The SP value indicates that the larger the value, the higher the polarity, and the smaller the value, the lower the polarity. SP values are SUH, CLARKE, J. P. S. A-1, 5, 1671-1681 (1967).

  More specifically, it can be measured by the following method. At a measurement temperature of 20 ° C., 0.5 g of a component for measuring SP value is weighed into a 100 ml beaker, 10 ml of a good solvent (acetone) is added using a whole pipette, and dissolved with a magnetic stirrer to prepare a diluted solution. Next, a 50 ml burette is used for this diluted solution, a low SP poor solvent (n-hexane) is gradually dripped, and the point at which the diluted solution has become cloudy is defined as a dripping amount of the low SP poor solvent. Separately, the high SP poor solvent (ion-exchanged water) is gradually dropped into the diluted solution, and the point at which the diluted solution becomes turbid is taken as the dripping amount of the high SP poor solvent. The SP value of each component can be calculated from the amount of dripping up to the turbid point of each poor solvent.

  Vinyl chloride plastisol sealants include alkaline earth metal carbonates and sulfates as required, mica, silica, talc, diatomaceous earth, kaolin and other fillers, epoxy, acrylic, polyamide, isocyanate, etc. A general adhesion-imparting agent, a stabilizer such as a metal salt such as zinc, lead, barium, tin, or calcium, a thixotropic agent such as surface-treated calcium carbonate, or ultrafine silica powder can be used.

  After applying such a vinyl chloride plastisol sealing agent, a sealer part is formed on the object to be coated by curing under a heat curing condition generally used.

First aqueous coating composition In the recoating method of the present invention, the cured first coating film to be coated before recoating and the first coating film newly formed by the recoating method of the present invention are as follows. It is preferably formed by the first aqueous coating composition described. By doing so, it is possible to prevent a decrease in interlayer adhesion between the cured clear coating film and the first coating film as described later.

  The first aqueous coating composition used in the formation of the first coating film is a hydroxyl group-containing acrylic resin emulsion, a hydroxyl group-containing polyester resin, a melamine resin, a carbodiimide, an associative viscosity agent, and a dispersion or solution in an aqueous medium. Contains pigments. The first aqueous coating composition may further contain additives as necessary.

Hydroxyl group-containing acrylic resin emulsion The hydroxyl group-containing acrylic resin emulsion contains a styrene-based monomer as an essential monomer, and further includes (meth) acrylic acid alkyl ester (a), carboxyl group-containing unsaturated monomer (b), and hydroxyl group-containing unsaturated monomer ( The monomer mixture containing c) can be obtained by emulsion polymerization. In addition, you may use the compound illustrated below as a component of a monomer mixture, combining 1 type (s) or 2 or more types as appropriate.

  By blending a styrene monomer with the acrylic resin emulsion, a hydrophobic effect is exhibited, and dripping at the time of application of the first aqueous coating composition can be significantly prevented.

  Examples of the styrenic monomer include styrene, α-methylstyrene, α-methylstyrene dimer, vinyltoluene, and the like. Among these, styrene is particularly preferable from the viewpoint of hydrophobicity, cost, availability, and the like.

  The content of the styrenic monomer is 27 to 65% by mass, preferably 30 to 55% by mass, more preferably 32 to 50% by mass, based on the total amount of monomers used for the synthesis of the acrylic resin emulsion. When the content of the styrenic monomer is less than 27% by mass, a hydrophobic effect cannot be obtained, and sagging may occur when the obtained first aqueous coating composition is applied. Moreover, when content of a styrene-type monomer exceeds 65 mass%, there exists a possibility that various performances of the 1st coating film formed from the 1st aqueous coating material composition obtained may fall.

  Further, by blending the styrene monomer with the above content in the acrylic resin emulsion, the water tolerance of the acrylic resin emulsion is 0.2 to 5, preferably 0.3 to 4, and the hexane tolerance is 5 to 25, preferably It can be adjusted to 6-23. In this specification, water tolerance is for evaluating the degree of hydrophilicity, and the higher the value, the higher the hydrophilicity, and hexane tolerance is for evaluating the degree of hydrophobicity. The higher the value, the higher the hydrophobicity.

  If the water tolerance is out of the above range, the compatibility with other components may be reduced. Further, when the water tolerance is less than 0.2, the storage stability of the first aqueous coating composition in an aqueous medium may be lowered, and when it exceeds 5, the water resistance of the obtained coating film is lowered. There is also.

  If the hexane tolerance is outside the above range, the compatibility with other components may be reduced. Further, if the hexane tolerance is less than 5, the coating film may become turbid and the appearance of the coating film may be lowered. If it exceeds 25, the storage stability of the first aqueous coating composition in an aqueous medium is increased. It may decrease.

  In this specification, water tolerance is a value that can be measured as follows. The measurement temperature is 20 ° C., 0.5 g of the resin to be measured is weighed into a 100 ml beaker, 10 ml of acetone is added using a whole pipette, and the resin is dissolved in acetone with a magnetic stirrer. Next, deionized water is added dropwise to the acetone solution prepared above using a 50 ml burette, and the amount of water dropped (ml) at the point where turbidity occurs is taken as water tolerance. In addition, hexane tolerance is the dripping amount (ml) of hexane measured by replacing the water in the water tolerance with n-hexane.

  The hydroxyl group-containing acrylic resin emulsion is preferably a hydroxyl group-containing acrylic resin emulsion containing 27 to 65% by mass of a styrene monomer, having a water tolerance of 0.2 to 5 and a hexane tolerance of 5 to 25. By using such a hydroxyl group-containing acrylic resin, dripping at the time of application of the first aqueous coating composition obtained can be significantly prevented, and the appearance of the coating film is improved.

  The (meth) acrylic acid alkyl ester (a) is used for constituting the main skeleton of the acrylic resin emulsion. Specific examples of the (meth) acrylic acid alkyl ester (a) include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, and (meth) acrylic. Isobutyl acid, t-butyl (meth) acrylate, hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, ( Examples thereof include dodecyl (meth) acrylate and stearyl (meth) acrylate.

  The carboxyl group-containing unsaturated monomer (b) is used for improving the storage stability of the resulting acrylic resin emulsion and for promoting the curing reaction with a curing agent such as a melamine resin at the time of coating film formation.

  Examples of the carboxyl group-containing unsaturated monomer include acrylic acid, methacrylic acid, itaconic acid, maleic anhydride, and fumaric acid.

  The hydroxyl group-containing unsaturated monomer (c) imparts hydrophilicity based on a hydroxyl group to an acrylic resin emulsion, and increases workability and storage stability when used as a coating material, and also includes a melamine resin and an isocyanate curing agent. It is used for imparting the curing reactivity.

  Examples of the hydroxyl group-containing unsaturated monomer (c) include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, and ε-caprolactone-modified acrylic monomer. It is done.

  The monomer mixture may contain at least one monomer selected from the group consisting of (meth) acrylonitrile and (meth) acrylamide as other components.

  Further, the monomer mixture may contain a crosslinkable monomer such as a carbonyl group-containing unsaturated monomer, a hydrolyzable polymerizable silyl group-containing monomer, and various polyfunctional vinyl monomers.

  Emulsion polymerization can be carried out by heating the monomer mixture in an aqueous medium with stirring in the presence of a radical polymerization initiator and an emulsifier. The reaction temperature is, for example, about 30 to 100 ° C., and the reaction time is preferably about 1 to 10 hours. The reaction temperature is adjusted by batch addition or temporary dropping of the monomer mixture or monomer pre-emulsified liquid in a reaction vessel charged with water and emulsifier It is good to do.

  It does not specifically limit as said radical polymerization initiator, The well-known initiator normally used by emulsion polymerization of an acrylic resin can be used.

  The emulsifier is not particularly limited, and is a micelle having a hydrocarbon group having 6 or more carbon atoms and a hydrophilic part such as a carboxylate, a sulfonate, or a sulfate partial ester in the same molecule. An anionic or nonionic emulsifier selected from compounds is used.

  In addition, as emulsion polymerization, any one of the usual single-stage continuous monomer uniform dropping method, core-shell polymerization method that is a multi-stage monomer feed method, and power feed polymerization method that continuously changes the monomer composition to be fed during polymerization, etc. A polymerization method can be used.

  In this way, the hydroxyl group-containing acrylic resin emulsion used in the present invention is prepared. Although the weight average molecular weight of the obtained acrylic resin is not particularly limited, it is generally about 50,000 to 1,000,000, for example, about 100,000 to 800,000.

  The hydroxyl value of the hydroxyl group-containing acrylic resin emulsion is in the range of 5 to 80 mgKOH / g, preferably 10 to 70 mgKOH / g. By setting the hydroxyl value of the resin within this range, the resin has moderate hydrophilicity, and when used as a coating composition containing a resin emulsion, the workability and storage stability increase, and the melamine resin and isocyanate-based curing. The curing reactivity with the agent is also sufficient. When the hydroxyl value is less than 5 mgKOH / g, the curing reaction with the curing agent is insufficient, the mechanical strength of the coating film is insufficient, chipping resistance is poor, and water resistance and solvent resistance are also poor. On the other hand, when the hydroxyl value exceeds 80 mgKOH / g, the water resistance of the obtained coating film is lowered, the compatibility with the curing agent is poor, the coating film is distorted, and the curing reaction occurs non-uniformly, As a result, various performances of the coating film, particularly chipping resistance, solvent resistance and water resistance are inferior. The compounding quantity of a hydroxyl-containing unsaturated monomer (c) is selected so that the hydroxyl value of resin may become the said range.

  The solid content acid value of the hydroxyl group-containing acrylic resin emulsion is 3 to 50 mgKOH / g, preferably 5 to 30 mgKOH / g. By setting the solid content acid value of the resin within this range, the storage stability of the resin emulsion and the first aqueous coating composition using the resin emulsion is improved, and a curing agent such as a melamine resin at the time of coating film formation The curing reaction of this occurs sufficiently, and various performances, chipping resistance and water resistance of the coating film are improved. When the acid value of the resin is less than 3 mgKOH / g, the storage stability is inferior, and the curing reaction with a curing agent such as a melamine resin is not sufficiently performed, so that various performances, chipping resistance, and water resistance of the coating film are inferior. On the other hand, when the acid value of the resin exceeds 50 mgKOH / g, the polymerizability of the resin is lowered, the storage stability is deteriorated, or the water resistance of the obtained coating film is inferior. The compounding quantity of the said carboxyl group-containing unsaturated monomer (b) is adjusted so that the acid value of resin may become the said range.

  The glass transition temperature (Tg) of the hydroxyl group-containing acrylic resin emulsion is −10 ° C. to 40 ° C., preferably −7 ° C. to 35 ° C., more preferably −5 ° C. to 30 ° C. By setting the Tg of the resin in this range, when the first aqueous coating composition containing the acrylic resin emulsion is used in the wet-on-wet system, the affinity and adhesion with the undercoat and topcoat are improved, and the wet Familiarity at the interface with the upper coating of the state is good and no inversion occurs. Moreover, the moderate softness | flexibility of the coating film finally obtained is acquired, and chipping resistance is improved. As a result, a multilayer coating film having a very high appearance can be formed. When the Tg of the resin is less than −10 ° C., the mechanical strength of the coating film is insufficient and the chipping resistance is weak. On the other hand, if the Tg of the resin exceeds 40 ° C., the coating film becomes hard and brittle, so that the impact resistance is lacking and the chipping resistance is weakened. The type and amount of each monomer component are selected so that the Tg of the resin falls within the above range.

  A basic compound is added to the obtained hydroxyl group-containing acrylic resin emulsion in order to neutralize part or all of the carboxyl groups and maintain the storage stability of the acrylic resin emulsion. Examples of these basic compounds include ammonia, various amines, and alkali metals.

Hydroxyl group-containing polyester resin As the hydroxyl group-containing polyester resin, a polyester resin obtained by condensing a polyhydric alcohol component and a polybasic acid component, or in addition to a polyhydric alcohol component and a polybasic acid component, castor oil, dehydrated castor oil, In addition to the acid component and the alcohol component, an oil component which is one kind or a mixture of two or more kinds of paulownia oil, safflower oil, soybean oil, linseed oil, tall oil, coconut oil, and the like, An alkyd resin obtained by reacting the three may be used. Moreover, the polyester resin which grafted acrylic resin and vinyl resin can also be used.

  The number average molecular weight (Mn) of the hydroxyl group-containing polyester resin is 800 to 10,000, preferably 1,000 to 8,000. When the Mn is less than 800, the storage stability when the polyester resin is dispersed in water decreases, and when it exceeds 10,000, the viscosity of the resin increases. Sex is reduced.

  The hydroxyl value of the hydroxyl group-containing polyester resin is 35 to 170 mgKOH / g, preferably 50 to 150 mgKOH / g. When the hydroxyl value is less than 35 mgKOH / g, the curability of the resulting coating film decreases, and when it exceeds 170 mgKOH / g, the chipping resistance of the coating film decreases.

  The hydroxyl group-containing polyester resin preferably has an acid value of 15 to 100 mgKOH / g. Preferably it is 20-80 mgKOH / g. When the acid value is less than 15 mgKOH / g, the water dispersion stability of the polyester resin is lowered, and when it exceeds 100 mgKOH / g, the water resistance when formed into a coating film is lowered.

  Moreover, it is preferable that Tg of the said hydroxyl-containing polyester resin is -40-50 degreeC. When the said glass transition temperature is less than -40 degreeC, there exists a possibility that the hardness of the coating film obtained may fall, and when it exceeds 50 degreeC, there exists a possibility that base concealment property may fall. More preferably, it is -40-10 degreeC. Tg can be measured by a differential scanning calorimeter (DSC) or the like.

  Examples of the polyhydric alcohol component include, for example, ethylene glycol, diethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2, Diols such as 2-diethyl-1,3-propanediol and neopentyl glycol, and trivalent or higher polyol components such as trimethylolpropane, trimethylolethane, glycerin and pentaerythritol, and 2,2-dimethylolpropion Examples thereof include hydroxycarboxylic acid components such as acid, 2,2-dimethylolbutanoic acid, 2,2-dimethylolpentanoic acid, 2,2-dimethylolhexanoic acid, and 2,2-dimethyloloctanoic acid.

  Examples of the polybasic acid component include aromatic polycarboxylic acids such as phthalic anhydride, isophthalic acid, terephthalic acid, trimellitic anhydride, tetrabromophthalic anhydride, tetrachlorophthalic anhydride, pyromellitic anhydride, and the like. And acid anhydrides; alicyclic polycarboxylic acids and anhydrides such as hexahydrophthalic anhydride, tetrahydrophthalic anhydride, 1,4- and 1,3-cyclohexanedicarboxylic acid; maleic anhydride, fumaric acid, succinic anhydride And polybasic acid components such as aliphatic polycarboxylic acids such as adipic acid, sebacic acid and azelaic acid and anhydrides, and anhydrides thereof. A monobasic acid such as benzoic acid or t-butylbenzoic acid may be used in combination as necessary.

  When preparing a polyester resin, as reaction components, mono-epoxide compounds such as monohydric alcohol, Cardura E (trade name: manufactured by Ciel Chemical), and lactones such as ε-caprolactone may be used in combination.

  The hydroxyl group-containing polyester resin can be easily made aqueous by adjusting its acid value and neutralizing the carboxyl group with a basic compound in the same manner as the hydroxyl group-containing acrylic resin emulsion.

The melamine resin is not particularly limited as long as it can cause a curing reaction with an acrylic resin or a hydroxyl group-containing polyester resin contained as an emulsion and can be blended in the first aqueous coating composition. An imino melamine resin is preferable, and examples thereof include Cymel 211 (Imino melamine resin, trade name) manufactured by Mitsui Cytec Co., Ltd. and Cymel 327 (Imino melamine resin, trade name manufactured by Mitsui Cytech Co., Ltd.).

  Also, alkyl etherified melamine resins that are alkyl etherized are preferred, and melamine resins substituted with methoxy groups and / or butoxy groups are more preferred. As such melamine resins, those having a methoxy group alone, Cymel 325, Cymel 327, Cymel 370, Mycoat 723; those having both a methoxy group and a butoxy group, Cymel 202, Cymel 204, Cymel 232, Cymel 235, Cymel 236, Cymel 238, Cymel 254, Cymel 266, Cymel 267 (all trade names, manufactured by Mitsui Cytec); My Coat 506 (trade name, Mitsui Cytech, Inc.) having a butoxy group alone Product), Uban 20N60, Uban 20SE (both trade names, manufactured by Mitsui Chemicals) and the like. These may be used alone or in combination of two or more.

As carbodiimide carbodiimide compounds, those prepared by various methods can be used, but basically those obtained by synthesizing isocyanate-terminated carbodiimides by condensation reaction involving decarbonization of organic diisocyanates. Can do. More specifically, in the production of a carbodiimide compound, a carbodiimide compound containing at least two isocyanate groups in one molecule and a polyol having a hydroxyl group at the molecular end, the molar amount of the isocyanate group of the carbodiimide compound is the polyol. Hydrophilized modified carbodiimide compound obtained by reacting at a ratio exceeding the molar amount of the hydroxyl group of the above, and reacting the reaction product obtained in the above step with a hydrophilizing agent having active hydrogen and a hydrophilic moiety Can be mentioned as preferred.

  The carbodiimide compound containing at least two isocyanate groups in one molecule is not particularly limited, but is preferably a carbodiimide compound having isocyanate groups at both ends from the viewpoint of reactivity. A method for producing a carbodiimide compound having isocyanate groups at both ends is well known by those skilled in the art. For example, a condensation reaction involving decarbonization of an organic diisocyanate can be used.

Associative Viscosity Agent The associative viscosity agent used in the first aqueous coating composition of the present invention is not particularly limited. For example, commercially available products (hereinafter referred to as trade names) include Adecanol UH-420 and Adecanol. Examples thereof include UH-462, Adecanol UH-472, Adecanol UH-540, Adecanol UH-814N (manufactured by ADEKA), Primal RH-1020 (manufactured by Rohm & Haas), and Kuraray Poval (manufactured by Kuraray). These may be used alone or in combination of two or more.

  The content of the viscosity agent of the present invention is preferably 0.05 to 2.0 mass%, more preferably 0.5 to 1.8 mass%, based on the resin solid content in the first aqueous coating composition. . Within this range, the viscosity of the first aqueous coating composition is further improved.

  By blending the associative viscosity agent, the viscosity of the first aqueous coating composition can be increased, and the occurrence of dripping can be suppressed when the first aqueous coating composition is applied. Moreover, the mixed layer between a 1st coating film and a 2nd coating film can be suppressed more. As a result, compared to the case where no viscosity agent is contained, the coating workability during coating is improved, and the finished appearance of the resulting coating film can be made excellent.

  The content of the associative viscosity agent is preferably 0.01 parts by mass lower limit and 20 parts by mass upper limit with respect to 100 parts by mass of resin solid content of the first aqueous coating composition, and 0.1 parts by mass lower limit. The upper limit is more preferably 10 parts by mass. If it is less than 0.01 parts by mass, the thickening effect cannot be obtained, and sagging may occur during coating. If it exceeds 20 parts by mass, the appearance and various performances of the resulting coating film may be reduced. is there.

  In the first aqueous coating composition, the blending ratio of the hydroxyl group-containing acrylic resin emulsion and the associative viscosity agent is 100 / 0.1 to 100/50, preferably 100/1 to 100/10 (solid content mass ratio). Hydroxyl group-containing acrylic resin emulsion / associative viscosity agent). When the blending ratio is within the above range, effects such as excellent storage stability of the first aqueous coating composition, improved workability during coating, and excellent finished appearance of the coating film can be obtained.

Other resin 1st water-based coating composition may contain an additional resin component, another additive component, etc. further as needed besides the said component. Although it does not specifically limit as an additional resin component, For example, a polyester resin, a water-soluble acrylic resin, a polyether resin, an epoxy resin etc. can be mentioned.

Pigment The first aqueous coating composition contains a pigment in addition to the above components. This pigment is generally added to the coating composition in a state prepared beforehand in the state of a pigment dispersion paste.

Pigment dispersion paste A pigment dispersion paste is obtained by previously dispersing a pigment and a pigment dispersant in a small amount of an aqueous medium. The pigment dispersant is a resin having a structure including a pigment affinity part and a hydrophilic part. Examples of the pigment affinity portion and the hydrophilic portion include nonionic, cationic and anionic functional groups. The pigment dispersant may have two or more of the above functional groups in one molecule.

  The pigment dispersant is not particularly limited, and a pigment dispersant that can efficiently disperse the pigment with a small amount of the pigment dispersant is preferable. For example, commercially available products (hereinafter, trade names) can also be used. Specifically, Disperbyk 190, Disperbyk 181, Disperbyk 182 (polymer co-polymers), which are anionic and nonionic dispersants manufactured by Big Chemie, Inc., can be used. Polymer), Disperbyk 184 (polymer copolymer), EFKAPOLYMER 4550, an anionic / nonionic dispersant manufactured by EFKA, Solsperse 27000, a nonionic dispersant manufactured by Abyssia, Solsperse 41000, an anionic dispersant, And Solsperse 53095.

  The pigment dispersion paste is obtained by mixing and dispersing a pigment dispersant and a pigment according to a known method.

  Although it will not specifically limit if it is a pigment used for a normal water-based paint, A colored pigment is preferable from the point which improves a weather resistance and ensures concealment property. In particular, titanium dioxide is more preferable because it is excellent in color concealment and is inexpensive.

  Examples of pigments other than titanium dioxide include azo chelate pigments, insoluble azo pigments, condensed azo pigments, phthalocyanine pigments, indigo pigments, perinone pigments, perylene pigments, dioxane pigments, quinacridone pigments, and isoindolinone. Organic pigments such as pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, and metal complex pigments; inorganic pigments such as yellow lead, yellow iron oxide, Bengala, and carbon black. These pigments may be used in combination with extender pigments such as calcium carbonate, barium sulfate, clay, and talc.

  As the pigment, a standard gray paint having carbon black and titanium dioxide as main pigments can also be used. In addition, it is also possible to use a paint in which the top coat paint is combined with lightness or hue or a combination of various color pigments.

  The pigment preferably has a pigment weight content (PWC) of 10 to 60% by mass with respect to the solid content of all the resins contained in the first aqueous coating composition and the total mass of the pigment. If it is less than 10% by mass, the concealability may be lowered. When it exceeds 60 mass%, viscosity increase at the time of hardening will be caused, flow property may fall and a coating-film external appearance may fall.

  Examples of other additives include additives that are usually added in addition to the above components, such as thickeners, fillers, ultraviolet absorbers, antioxidants, antifoaming agents, and surface conditioners. These compounding amounts are within the range known to those skilled in the art.

The first aqueous coating composition is desirably based on the total resin solid content to be blended,
1-30% by mass of a hydroxyl group-containing acrylic resin emulsion, preferably 2-25% by mass, more preferably 4-20% by mass;
5-70% by mass of a hydroxyl group-containing polyester resin, preferably 20-65% by mass, more preferably 40-60% by mass;
Melamine resin 10-40% by weight, preferably 20-37% by weight, more preferably 25-35% by weight;
A carbodiimide compound of 3 to 25% by mass, preferably 5 to 15% by mass, more preferably 7 to 12% by mass; and an associative viscosity agent 0.05 to 2% by mass, preferably 0.1 to 1.5% by mass, More preferably, it contains 0.2 to 1.2% by mass. When each content is in the above range, sagging can be significantly prevented when the first aqueous coating composition is applied, and the appearance of the obtained coating film is improved.

  The first aqueous coating composition is prepared by mixing the above-mentioned hydroxyl group-containing acrylic resin emulsion, hydroxyl group-containing polyester resin, melamine resin, carbodiimide, associative viscosity agent, and the like.

  The ratio of the hydroxyl group-containing acrylic resin emulsion to the hydroxyl group-containing polyester resin is a solid content mass ratio of 1/1 to 1/20 (hydroxyl group-containing acrylic resin emulsion / hydroxyl group-containing polyester resin). When this ratio exceeds 1/1, the viscosity of the coating film increases, the smoothness of the first coating film decreases, and the appearance decreases. If it is less than 1/20, the water absorption rate and elution rate increase, and the appearance tends to deteriorate.

  Appropriate amounts of the additional resin component, pigment dispersion paste and other additives may be mixed.

  The form of the first aqueous coating composition is not particularly limited as long as it is aqueous. For example, it may be in the form of water-soluble, water-dispersed, aqueous emulsion or the like.

  In the recoating method of the present invention, the difference (ΔSP) between the SP value of the mixture of the components excluding the pigment from the first aqueous coating composition and the SP value of the plasticizer contained in the vinyl chloride plastisol sealing agent is an absolute value. And 1.0 or less. The absolute value is preferably 0.7 or less. Here, the “mixture of components obtained by removing the pigment from the first aqueous coating composition” means a composition prepared without using the pigment dispersion paste in the preparation of the first aqueous coating composition. This “mixture of components excluding pigment from the first aqueous coating composition” corresponds to a mixture of a resin component, a curing agent and a solvent, such as a hydroxyl group-containing acrylic resin emulsion, a hydroxyl group-containing polyester resin, a melamine resin, a carbodiimide. And mixtures of solvents. The SP value of this mixture is measured by the method described above.

  According to the study by the present inventors, in the recoating method for the object to be coated having the sealer part, the main factor for reducing the interlayer adhesion of the repainted coating film provided by the recoating is the vinyl chloride plastisol used for the formation of the sealer part. It was found to be a plasticizer included in the sealant. The vinyl chloride plastisol sealing agent generally contains a large amount of plasticizer such as about 100 to 180 parts by mass with respect to 100 parts by mass of the vinyl chloride resin. Since the plasticizer contained in the sealing agent has a high boiling point, it remains in the formed sealer part. And the plasticizer contained in this sealer part permeate | transmits the multilayer coating film already provided, and the surface of a multilayer coating film (Clear coating film (14) in FIG. 1 and 1st coating film (15)) Gradually shift (bleed) to the interface. Thus, the multilayer coating film (21) already provided by bleeding the plasticizer contained in the sealer portion at the interface between the clear coating film (14) and the first coating film (15), Interlayer adhesion decreases with the repainted coating film (22) provided by recoating, resulting in problems such as interfacial peeling.

  Here, the difference (ΔSP) between the SP value of the mixture of the components obtained by removing the pigment from the first aqueous coating composition forming the first coating film and the SP value of the plasticizer contained in the vinyl chloride plastisol sealing agent is When the absolute value is 1.0 or less, bleeding of the plasticizer can be effectively suppressed. When the above ΔSP is 1.0 or less in absolute value, the compatibility between the mixture of components such as the resin component contained in the first aqueous coating composition and the plasticizer contained in the vinyl chloride plastisol sealing agent is high. It becomes good. As a result, in the first coating film (12) in the multilayer coating film (21) that has already been provided, the plasticizer that has migrated from the sealer portion (11) is well dispersed, and as a result, the multilayer coating film that has already been provided. The amount of the plasticizer that bleeds between the interface between the layer coating film (21) and the repainted coating film (22) provided by recoating is reduced. Furthermore, since the compatibility of the component such as the resin component contained in the first aqueous coating composition and the plasticizer contained in the vinyl chloride plastisol sealing agent is good, the multilayer coating film (already provided) 21) and the plasticizer bleed between the interfaces between the repainted coating film (22) provided by recoating and dispersed in the first coating film (15) constituting the repainted coating film (22); Become. Thereby, the quantity of the plasticizer which exists between the interfaces of the multilayer coating film (21) already provided and the repainting coating film (22) provided by recoating will be reduced. Thus, by reducing the amount of plasticizer present between the interfaces of the multilayer coating (21) and the repainting coating (22), it is possible to prevent a decrease in interlayer adhesion between these coatings. This makes it possible to prevent problems such as interface peeling.

The difference (ΔSP) between the SP value of the mixture of the components obtained by removing the pigment from the first aqueous coating composition and the SP value of the plasticizer contained in the vinyl chloride plastisol sealing agent is as follows. It can be adjusted by varying the SP value of the mixture of the excluded components. Specifically, it can be adjusted by the kind and blending amount of the hydroxyl group-containing acrylic resin emulsion, the hydroxyl group-containing polyester resin, the melamine resin, and the carbodiimide.
For example, in the case of a hydroxyl group-containing acrylic resin emulsion, the types and blends of styrene monomers, (meth) acrylic acid esters (a), carboxyl group-containing unsaturated monomers (b), and hydroxyl group-containing unsaturated monomers (c) used for obtaining It can be adjusted according to the amount. Specifically, the SP value tends to decrease when the amount of the styrene monomer is increased or when the ester portion of the (meth) acrylic ester is long, and the carboxyl group-containing unsaturated monomer When the blending amount of the hydroxyl group-containing unsaturated monomer is increased, the SP value tends to increase.
Similarly, it can adjust with the kind and compounding quantity of the polyhydric alcohol component and polybasic acid component which are used in order to obtain a hydroxyl-containing polyester resin.

In the present invention, 100 parts by mass of a mixture of components obtained by removing the pigment from the first aqueous coating composition and 20 parts by mass of a plasticizer contained in the vinyl chloride plastisol sealing agent are further mixed, and then the resulting mixture is mixed. An embodiment in which the turbidity of the test cured coating film formed by heat curing is 20 or less is preferable. The turbidity in the test cured coating film is an index indicating the compatibility between the mixture of components obtained by removing the pigment from the first aqueous coating composition and the plasticizer. The higher the turbidity, the lower the compatibility of these components, and the lower the turbidity, the higher the compatibility of these components.
The turbidity can be adjusted by blending and blending a mixture of components obtained by removing the pigment from the first aqueous coating composition. As a specific adjustment method, the method described in the adjustment of the SP value can be given.

  In the present invention, the turbidity of the test cured coating is measured by measuring the total light transmittance (Tt) and scattered light transmittance (Td), and then turbidity (Th) = scattered light transmittance (Td) / total light. It can be calculated by transmittance (Tt) × 100. The total light transmittance and the scattered light transmittance can be measured using an integrating sphere light transmittance measuring device. Examples of the integrating sphere light transmittance measuring device include NDH-2000 (Nippon Denshoku Industries Co., Ltd. haze meter).

Second aqueous coating composition As the second aqueous coating composition used in the method of the present invention, a coating composition that is usually used as an aqueous base coating composition for automobile body coating can be used. As the second aqueous coating composition, for example, it contains a film-forming resin, a curing agent, a bright pigment, a pigment such as a coloring pigment or an extender pigment, various additives, etc. in a state dispersed or dissolved in an aqueous medium. Things can be mentioned. As the film-forming resin, for example, a polyester resin, an acrylic resin, a urethane resin, a carbonate resin, and an epoxy resin can be used. From the viewpoint of pigment dispersibility and workability, a combination of an acrylic resin and / or a polyester resin and a melamine resin is preferable. Commonly used curing agents, pigments, and various additives can also be used.

  The second aqueous coating composition can be prepared by the same method as the first aqueous coating composition. Further, the form of the second aqueous coating composition is not particularly limited as long as it is aqueous. For example, it may be in the form of water-soluble, water-dispersed, aqueous emulsion or the like.

Clear coating composition The clear coating composition used in the method of the present invention may be any coating composition that is usually used as a clear coating composition in the field of painting such as automobile bodies. For example, what contains a film-forming resin, a hardening | curing agent, and another additive in the state disperse | distributed or melt | dissolved in the medium can be mentioned. Examples of the film-forming resin include acrylic resin, polyester resin, epoxy resin, and urethane resin. These may be used in combination with a curing agent such as an amino resin and / or an isocyanate resin. From the viewpoint of transparency or acid etching resistance, it is preferable to use a combination of an acrylic resin and / or a polyester resin and an amino resin, or an acrylic resin and / or a polyester resin having a carboxylic acid / epoxy curing system.

  The coating form of the clear coating composition may be any of organic solvent type, aqueous type (water-soluble, water-dispersible, emulsion), non-water-dispersed type, and powder type. Various additives such as a regulator, an ultraviolet absorber, an antioxidant, a viscosity modifier, and a stabilizer may be included.

Recoating method In the method of the present invention, the object to be coated before recoating is a sealer part, a cured first coating film formed on the sealer part, and a cured second coating film formed on the cured first coating film. This is a method for recoating (repainting) an object having a film, a cured clear coating film formed on the cured second coating film. A first aqueous coating composition is first applied to such an object to form an uncured first coating film. The first water-based paint composition is, for example, an air electrostatic spray commonly called “react gun”, commonly called “micro-microbell (μμbell)”, “microbell (μbell)”, “metallic bell (metabell)”. It can be applied by spraying using a rotary atomizing type electrostatic coating machine.
The cured first coating film and the cured second coating film are preferably obtained from the first aqueous coating composition and the second aqueous coating composition, respectively.

  The coating amount of the first aqueous coating composition is generally adjusted so that the film thickness of the dried coating film is 10 to 40 μm, preferably 15 to 30 μm. If the dry film thickness is less than 10 μm, the appearance and chipping resistance of the resulting coating film may be reduced, and if it exceeds 40 μm, problems such as sagging during coating and pinholes during baking hardening may occur.

  The first coating film is preferably pre-dried (preheated) by heating or blowing air before applying the second aqueous coating composition. By performing preliminary drying (preheating), there is an advantage that generation of cracks due to bumping of water remaining in the coating film in the process of baking the multilayer coating film can be effectively prevented. Furthermore, when the second aqueous coating composition is applied onto the uncured first coating film, it is likely to be mixed with the base and the appearance may be lowered.

  Next, the second aqueous coating composition and the clear coating composition are sequentially applied on the uncured first coating film by wet-on-wet to form an uncured second coating film and a clear coating film. Here, the wet-on-wet coating refers to coating with a degree of preliminary drying (preheating) without curing a plurality of coating films.

  The coating amount of the second aqueous coating composition is generally adjusted so that the film thickness of the dried coating film is 10 to 30 μm. If the dry film thickness is less than 10 μm, the masking of the base may be insufficient or color unevenness may occur. If it exceeds 30 μm, sagging may occur during coating, or pinholes may occur during heat curing. There is a risk.

  The coating amount of the clear coating composition is usually adjusted so that the dry film thickness of the coating film is 10 to 70 μm. When the dry film thickness is less than 10 μm, the appearance such as glossiness of the multilayer coating film is deteriorated, and when it exceeds 70 μm, the sharpness is deteriorated or defects such as unevenness and flow occur at the time of coating.

  Next, the uncured first coating film, the second coating film, and the clear coating film are simultaneously baked and cured. Baking is usually performed by heating to a temperature of 110 to 180 ° C, preferably 120 to 160 ° C. Thereby, a cured coating film having a high degree of crosslinking can be obtained. If the heating temperature is less than 110 ° C, curing tends to be insufficient, and if it exceeds 180 ° C, the resulting coating film may be hard and brittle. Although the time to heat can be suitably set according to the said temperature, for example, when temperature is 120-160 degreeC, it is 10 to 60 minutes.

  The following examples further illustrate the present invention, but the present invention is not limited thereto. In the examples, “parts” and “%” are based on mass unless otherwise specified.

Production Example 1 Preparation of Hydroxyl-Containing Acrylic Resin Emulsion In a reaction vessel for producing a typical acrylic resin emulsion equipped with a stirrer, a thermometer, a dropping funnel, a reflux condenser, a nitrogen introducing tube, etc., 445 parts of water and New Coal 293 5 parts (manufactured by Nippon Emulsifier Co., Ltd.) were charged and heated to 75 ° C. while stirring. 1.53 parts of methacrylic acid, 8.28 parts of 2-ethylhexyl acrylate, 45 parts of styrene, 21.73 parts of n-butyl acrylate, 24.6 parts of a monomer mixture containing 23.45 parts of ethyl acrylate, 240 parts of water and New Coal 30 parts of the monomer mixture 293 was emulsified using a homogenizer, and the monomer pre-emulsified solution was added dropwise to the reaction vessel over 3 hours with stirring. In parallel with the dropping of the monomer pre-emulsified solution, an aqueous solution in which 1 part of ammonium persulfate as a polymerization initiator was dissolved in 50 parts of water was uniformly dropped into the reaction vessel until the end of the dropping of the monomer pre-emulsified solution. After completion of the dropwise addition of the monomer pre-emulsion, the reaction was further continued at 80 ° C. for 1 hour, and then cooled. After cooling, an aqueous solution in which 2 parts of dimethylaminoethanol was dissolved in 20 parts of water was added to obtain a hydroxyl group-containing acrylic resin emulsion having a nonvolatile content of 40.6% by mass, a solid content acid value of 10 mgKOH / g, and a hydroxyl value of 40 mgKOH / g. . The pH of the acrylic resin emulsion was adjusted to 7.2 using a 30% aqueous dimethylaminoethanol solution.

The resulting acrylic resin emulsion had a styrene content of 45% by mass, a water tolerance of 1, a hexane tolerance of 20, and a Tg of 13.1 ° C.
These physical property values were measured according to the following procedures.

Styrene content (mass%): The mass of styrene relative to the total solid mass of the acrylic resin emulsion prepared in Production Example 1 is expressed as a percentage (mass%).
Water tolerance (ml): 0.5 g of an acrylic resin sample of the acrylic resin emulsion prepared in Production Example 1 is weighed in a beaker, and acetone (10 ml) is added to prepare an acetone solution. Water is dropped into the acetone solution until the acetone solution becomes cloudy, and the water titration (ml) at the point where the solution becomes cloudy is taken as water tolerance.
Hexane tolerance (ml): 0.5 g of an acrylic resin sample of the acrylic resin emulsion prepared in Production Example 1 is weighed in a beaker, and acetone (10 ml) is added to prepare an acetone solution. Hexane is added dropwise until the acetone solution becomes cloudy, and the hexane titration (ml) at the point where the solution becomes cloudy is defined as hexane tolerance.

  The hydroxyl value, solid content acid value, and Tg of the emulsion resin of the hydroxyl group-containing acrylic resin emulsion can be obtained by actually measuring the emulsion resin, but can also be obtained by calculation from the blending amount of the monomer mixture.

Production Example 2: Preparation of hydroxyl group-containing polyester resin In a reactor, 25.6 parts of isophthalic acid, 22.8 parts of phthalic anhydride, 5.6 parts of adipic acid, 19.3 parts of trimethylolpropane, 26.7 parts of neopentyl glycol , 17.5 parts of ε-caprolactone and 0.1 part of dibutyltin oxide were added, and the temperature was raised to 170 ° C. with mixing and stirring. Thereafter, while the temperature was raised to 220 ° C. over 3 hours, water produced by the condensation reaction was removed until the acid value reached 8 mgKOH / g. Next, 7.9 parts of trimellitic anhydride was added and reacted at 150 ° C. for 1 hour to obtain a polyester resin having an acid value of 40 mgKOH / g. Further, after cooling to 100 ° C., 11.2 parts of butyl cellosolve was added and stirred until uniform, and after cooling to 60 ° C., 98.8 parts of ion-exchanged water and 5.9 parts of dimethylethanolamine were added, and the solid content was 50% by weight. Thus, a hydroxyl group-containing polyester resin having a solid content acid value of 40 mgKOH / g, a hydroxyl value of 110 mgKOH / g, a number average molecular weight of 2870, and a Tg of −3 ° C. was obtained.
Tg of the hydroxyl group-containing polyester resin was measured using a differential scanning calorimeter (DSC220C) manufactured by Seiko Instruments Inc. [Measurement conditions: sample amount 10 mg, rising rate 10 ° C./min, measurement temperature -20 to 100 ° C.] .

Production Example 3 Preparation of Carbodiimide Compound 3,930 parts of 4,4-dicyclohexylmethane diisocyanate were reacted with 79 parts of 3-methyl-1-phenyl-2-phospholene-1-oxide as a carbodiimidization catalyst at 180 ° C. for 16 hours. A carbodiimide compound having four carbodiimide groups per molecule and having isocyanate groups at both ends was obtained. To this, 1296 parts of polyethylene glycol monomethyl ether having an average of 9 repeating units of oxyethylene group and 2 parts of dibutyltin dilaurate are added, heated at 90 ° C. for 2 hours, and carbodiimide whose terminals are isocyanate groups and hydrophilic groups. A compound was obtained. Next, 3,000 parts of GP-3000 (manufactured by Sanyo Chemical Co., Ltd.) having a structure in which 16.7 mol of propylene oxide corresponding to the OR1 group was added to the three hydroxyl groups of glycerin on average were added at 90 ° C. The reaction was performed for 6 hours. It was confirmed that the isocyanate group disappeared from the reaction product by IR. To this, 18,800 parts of deionized water was added and stirred to obtain an aqueous dispersion of a carbodiimide compound having a resin solid content of 30% by mass.

Production Example 4: Preparation of Pigment Dispersion Paste Disperbyk 190 (Bion Chemie Anionic Nonionic Dispersant, Product Name) 4.5 parts BYK-011 (Bic Chemie Antifoam) 0.5 parts, ion-exchanged water 22 After 9 parts and 72.1 parts of rutile titanium dioxide were premixed, a glass bead medium was added in a paint conditioner and mixed and dispersed at room temperature until the particle size became 5 μm or less to obtain a pigment dispersion paste.

Production Example 5-1: Preparation of first aqueous coating composition (1) 24.6 parts of a hydroxyl group-containing acrylic resin emulsion prepared in Production Example 1, 99.9 parts of a hydroxyl group-containing polyester resin prepared in Production Example 2, and a curing agent After mixing 37.5 parts of Cymel 211 (Imino melamine resin, trade name) manufactured by Mitsui Cytec Co., Ltd., 33.3 parts of the carbodiimide compound prepared in Production Example 3, and 139 parts of the pigment dispersion paste prepared in Production Example 4 Adecanol UH-814N (urethane associative viscosity agent, active ingredient 30%, manufactured by ADEKA, trade name) 3.33 parts was mixed and stirred to obtain a first aqueous coating composition (1).

Production Example 6-1: Preparation of first water-based paint composition (2) Instead of 37.5 parts of Cymel 211, 18.75 parts of Cymel 211, Cymel 254 (imino-type melamine resin manufactured by Mitsui Cytec Co., Ltd., trade name) ) A first aqueous coating composition (2) was obtained in the same manner as in Production Example 5-1, except that 18.75 parts were blended.

Production Example 5-2 and Production Example 6-2: Preparation of a mixture of components obtained by removing the pigment from the first aqueous coating composition (1) and a mixture of components obtained by removing the pigment from the first aqueous coating composition (2) Except that the pigment dispersion paste prepared in Production Example 4 was not blended, the same as in Production Examples 5-1 and 6-1, a mixture of components excluding the pigment from the first aqueous coating composition (1) and 1 A mixture of components obtained by removing the pigment from the aqueous coating composition (2) was obtained.
When the SP value of the mixture thus obtained was measured by a dropping method using acetone as a good solvent and n-hexane as a poor solvent, the SP value of the component obtained by removing the pigment from the first aqueous coating composition (1) was measured. The SP value of the mixture was 11.9, and the SP value of the mixture of components obtained by removing the pigment from the first aqueous coating composition (2) was 11.6.

Example 1
A vinyl chloride plastisol sealing agent containing diisononyl phthalate (DINP) as a plasticizer was applied onto a steel plate having a cured electrodeposition coating film, and baked and cured at 140 ° C. for 14 minutes to form a sealer part. In addition, it was 10.6 when SP value of this plasticizer was measured like manufacture example 5-2.
The SP values of the plasticizers used in the following examples and comparative examples were all measured by the same method as described above.

On the obtained substrate, the first aqueous coating composition (2) prepared in Production Example 6-1 was applied by air spray coating so that the dry film thickness was 20 μm, and preheated at 80 ° C. for 5 minutes. It was. Subsequently, Aqualex AR-2000 silver metallic (Nippon Paint's water-based metallic base paint, trade name) was applied by air spray coating so that the dry film thickness was 10 μm, and preheated at 80 ° C. for 3 minutes. Thereafter, MacFlow O-1800-4 clear (an acid epoxy curable clear coating composition, trade name, manufactured by Nippon Paint Co., Ltd.) was applied by air spray coating so that the dry film thickness was 35 μm, and then 30 ° C. at 140 ° C. Heat-curing for a minute was performed to obtain a coated article having a sealer portion, a cured first coating film, a cured second coating film, and a cured clear coating film.
The same first water-based paint composition, second water-based paint composition and clear paint composition as those used for obtaining the above-mentioned coated material were prepared in the same manner as described above. Repainting was done by painting and baking and curing.

  A test cured coating for turbidity measurement was prepared according to the following procedure. 20 parts by mass of the plasticizer contained in the vinyl chloride plastisol sealing agent used in Example 1 was obtained by Production Example 6-2, which was a mixture of components obtained by removing the pigment from the first aqueous coating composition (2). The ingredients were mixed in 100 parts by weight. The obtained mixture was applied on a glass plate using a 19 MIL film applicator (doctor blade), and then heat cured at 140 ° C. for 30 minutes to form a test cured coating film. It was 19 when the turbidity of the obtained test cured coating film was measured.

The turbidity of the test cured coating was measured according to the following.
The total light transmittance and scattered light transmittance of the obtained test cured coating film were measured using NDH-2000 (Nippon Denshoku Industries Co., Ltd. haze meter). Using this total light transmittance (Tt) and scattered light transmittance (Td), turbidity was calculated according to the following formula. The turbidity in the test cured coating film is one index indicating the compatibility between the component obtained by removing the pigment from the first aqueous coating composition and the plasticizer. The higher the turbidity, the lower the compatibility of these components, and the lower the turbidity, the higher the compatibility of these components.
Turbidity (Th) = scattered light transmittance (Td) / total light transmittance (Tt) × 100

Examples 2 to 5 and Comparative Examples 1 to 5
Based on Tables 1 and 2, the sealer part, the cured first coating film, the cured second coating film and the cured clear coating film were the same as in Example 1 except that the plasticizer and the first aqueous coating composition were used. An article to be coated was prepared. Subsequently, repainting was performed in the same manner as in Example 1 except that the first aqueous coating composition was used based on Tables 1 and 2.

  Further, based on Tables 1 and 2, the pigment was removed from the first aqueous coating composition in the same manner as in Example 1 except that a mixture of the plasticizer and the component obtained by removing the pigment from the first aqueous coating composition was used. The difference (ΔSP) between the SP value of the mixture of the components and the SP value of the plasticizer was calculated, and the turbidity of the test cured coating film was measured. The results are shown in Tables 1 and 2.

  The following evaluation was performed using the repainted coatings obtained in the above Examples and Comparative Examples.

While maintaining the cutting edge of a cutter knife (NT cutter (trade name) S-type, A-type or equivalent) on the painted surface obtained by repainting the inter-layer adhesion test , the angle of about 30 degrees with respect to the painted surface Incisions of grids at intervals of 2 mm reaching the substrate were made to make 100 grids. An adhesive tape (adhesive tape manufactured by Nichiban Co., Ltd.) was uniformly pressure-bonded so that no air bubbles remained on it. The adhesive tape was peeled off at a stretch while holding one end of the adhesive tape and maintaining an angle of 30 degrees with respect to the coating surface. At this time, [number of grids of grids not peeled] / [number of grids of grids = 100] was determined by visual judgment. The results are shown in Tables 1 and 2.

混合物のＳＰ値：第１水性塗料組成物から顔料を除いた成分の混合物のＳＰ値
可塑剤の種類：塩化ビニルプラスチゾルシーリング剤に含まれる可塑剤
ＳＰ値の差（絶対値表記）：第１水性塗料組成物から顔料を除いた成分の混合物のＳＰ値と、塩化ビニルプラスチゾルシーリング剤に含まれる可塑剤のＳＰ値との差（△ＳＰ）の絶対値
ＤＩＮＰ：フタル酸ジイソノニル
ＤＥＨＰ：フタル酸ジ−２−エチルヘキシル
ＤＯＰ：フタル酸ジオクチル
ＤＩＮＡ：アジピン酸ジイソノニル
ＤＯＡ：アジピン酸ジオクチル

SP value of the mixture: SP value of the mixture of components obtained by removing the pigment from the first aqueous coating composition Type of plasticizer: Difference in plasticizer SP value contained in the vinyl chloride plastisol sealing agent (absolute value notation): First aqueous Absolute value of difference (ΔSP) between SP value of mixture of components excluding pigment from coating composition and SP value of plasticizer contained in vinyl chloride plastisol sealing agent DINP: diisononyl phthalate DEHP: diphthalate 2-ethylhexyl DOP: dioctyl phthalate DINA: diisononyl adipate DOA: dioctyl adipate

In each of Examples 1 to 5, the difference (ΔSP) between the SP value of the mixture of components obtained by removing the pigment from the first aqueous coating composition and the SP value of the plasticizer contained in the vinyl chloride plastisol sealing agent Is an experimental example in which the absolute value is 1.0 or less. In any of these cases, it was confirmed that the interlaminar adhesion in the coated product obtained by repainting was high and the recoatability was excellent.
In each of Comparative Examples 1 to 5, the difference (ΔSP) between the SP value of the mixture of the components obtained by removing the pigment from the first aqueous coating composition and the SP value of the plasticizer contained in the vinyl chloride plastisol sealing agent was It is an experimental example exceeding 1.0 in absolute value. In these cases, it was confirmed that the interlayer adhesion between the coated product obtained by repainting and the first coating film was low.

  By the recoating method of the present invention, on the object to be coated having a multilayer coating film composed of a sealer portion, a cured first coating film, a cured second coating film and a cured clear coating film, which has already been provided, it is cured by recoating. When providing a repainted film comprising the first coated film, the cured second coated film, and the cured clear coated film, there is no delamination between the multilayered film and the repainted film that have already been provided. A coating film excellent in adhesion can be formed. The method of the present invention is highly useful as a recoating method in the coating field where the appearance of a coating film has a great influence on the appearance and design of a product, such as automobile painting.

1: Recoated coating 11: Sealer portion 12: First coating 13: Second coating 14: Clear coating 15: First coating 16: Second coating 17: Clear coating 21: Already provided Multi-layer coating film 22: Repaint coating film provided by recoating

Claims (4)

A first aqueous coating composition containing a pigment is applied to an object having a sealer portion to form an uncured first coating film, and then a second aqueous coating composition is applied to form an uncured second coating composition. A wet-on-wet coating process for forming a film and then applying a clear coating composition on the uncured second coating to form an uncured clear coating; and the resulting uncured first coating Baked and cured step of simultaneously baking and curing the second coating film and the clear coating film,
A method for recoating an object having a sealer part,
The object to be coated before recoating is a sealer portion, a cured first coating film formed on the sealer portion, a cured second coating film formed on the cured first coating, and the cured second coating. Already having a cured clear coating formed on the film,
The sealer part is a sealer part formed by a vinyl chloride plastisol sealant containing a vinyl chloride resin and a plasticizer,
The absolute value of the difference (ΔSP) between the SP value of the mixture of the components excluding the pigment from the first aqueous coating composition and the SP value of the plasticizer contained in the vinyl chloride plastisol sealing agent is 1.0 or less. ,
A method for recoating an object having a sealer portion. By mixing 100 parts by weight of a mixture of components excluding the pigment from the first aqueous coating composition and 20 parts by weight of a plasticizer contained in the vinyl chloride plastisol sealing agent, and then heat-curing the resulting mixture The turbidity of the formed test cured coating film is 20 or less,
The recoating method according to claim 1. The first aqueous coating composition is
A hydroxyl group-containing acrylic resin emulsion containing 27 to 65% by mass of a styrene monomer, having a water tolerance of 0.2 to 5 and a hexane tolerance of 5 to 25;
Hydroxyl group-containing polyester resin;
Melamine resin;
Carbodiimide;
The recoating method according to claim 1, which is an aqueous coating composition containing an associative viscosity agent; and a pigment.   The plasticizer contained in the vinyl chloride plastisol sealing agent is one or more selected from the group consisting of phthalic acid esters, di- or tricarboxylic acid esters, phosphoric acid esters, and epoxy plasticizers. 3. The recoating method according to any one of 3.

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