JP2012007113A - Water-base coating material and multilayer coating film forming method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology for preventing the occurrence of so-called clusters, which is a coating film defect of water-base coating material used for coating film forming for an automobile.SOLUTION: This water-base coating material contains, in 100 mass% of resin solid content, (a) 10-60 mass% of solid content of acrylic resin emulsion, (b) 5-40 mass% of solid content of water-soluble acrylic resin, (c) 20-40 mass% of solid content of melamine resin, and (d) 0.1-5 mass% of nonion-modified olefine resin that is obtained by making 8-22C polyethylene glycol monochrome alkyl ether (iii) of HLB 10-20 react with a copolymer of 10-16C α-olefin compound (i) and carboxylic acid anhydride (ii) having unsaturated double bond, and has a solid content acid value of 20-60 mgKOH/g and a weight-average molecular weight of 10,000-100,000.

Description

  The present invention relates to an aqueous base paint used for forming a coating film on an automobile body or the like and a method for forming a multilayer coating film using the same.

  In recent years, considering the influence on the environment, in order to reduce the amount of the organic solvent contained in the paint, water-based paints have been studied. In automotive coatings, it is common to form a base coating and then form a clear coating thereon, but it has been practiced to make the base coating water-based in this system.

  As an aqueous base paint adapted to such a system, for example, JP-A-63-193968 (Patent Document 1) discloses a water-dispersible film-forming acrylic polymer that is an acrylic emulsion, a hydrophobic melamine resin, and a pigment. An aqueous coating composition is disclosed. Japanese Patent Application Laid-Open No. 63-265974 (Patent Document 2) discloses an aqueous coating material containing an emulsion resin having a core portion of a monomer having an alkyl group having 4 to 12 carbon atoms and a shell portion containing acrylamide or methacrylic acid. Each is disclosed.

  The present inventors have already proposed improvement of coating film appearance and workability in a coating method using an aqueous base paint in Japanese Patent Application Laid-Open No. 2001-240791 (Patent Document 3). In this technique, in a water-based base coat paint, the use of a specific monomer for the synthesis of an acrylic emulsion resin improves the familiarity with water, improves the appearance of the coating film, and adjusts the acid value to improve the paint workability. The technique of Patent Document 3 exhibits excellent performance and can be sufficiently used for automobile painting.

  By the way, at the time of application of the water-based base paint, a coating film defect called so-called “butsu” occurs. This is due to the fact that the pigment or resin contained in the paint is partially solidified in the paint or in the coating route to form a lump, which is then applied through a spray gun. Although it has been recognized for some time, no specific measures have been taken.

JP-A-63-193968 JP-A 63-265974 JP 2001-240791 A

  The present invention provides a technique for preventing the occurrence of so-called blistering, which is a coating film defect of an aqueous base paint used for forming a coating film for automobiles.

That is, in the present invention, the resin solid content is 100% by mass,
(A) Acrylic resin emulsion is 10-60 mass% in solid content,
(B) 5-40 mass% of water-soluble acrylic resin in solid content,
(C) Melamine resin is 20 to 40% by mass in solid content, and (d) Co-weight of α-olefin compound (i) having 10 to 16 carbon atoms and carboxylic anhydride (ii) having an unsaturated double bond Nonion having a solid content acid value of 20 to 60 mg KOH / g and a weight average molecular weight of 10,000 to 100,000, obtained by reacting a polyethylene glycol monoalkyl ether (iii) having 8 to 22 carbon atoms and HLB of 10 to 20 with the coalescence 0.1 to 5% by mass of modified olefin resin
A water-based paint containing is provided.

In the present invention, a water-based base coating is formed on an intermediate coating formed on a steel plate for automobiles to form a base coating, and then an organic solvent type clear coating is applied to form a clear coating. And a method of forming a multilayer coating film in which the base coating film and the clear coating film are heated and cured,
The water-based paint is in a resin solid content of 100% by mass,
(A) Acrylic resin emulsion is 10-60 mass% in solid content,
(B) 5-40 mass% of water-soluble acrylic resin in solid content,
(C) Melamine resin is 20 to 40% by mass in solid content, and (d) Co-weight of α-olefin compound (i) having 10 to 16 carbon atoms and carboxylic anhydride (ii) having an unsaturated double bond Nonion having a solid content acid value of 20 to 60 mg KOH / g and a weight average molecular weight of 10,000 to 100,000, obtained by reacting a polyethylene glycol monoalkyl ether (iii) having 8 to 22 carbon atoms and HLB of 10 to 20 with the coalescence 0.1 to 5% by mass of modified olefin resin
It also provides a method for forming a multilayer coating film characterized by containing.

  The acrylic resin emulsion (a) is preferably obtained by emulsion polymerization of a monomer mixture containing 0.2 to 20% by mass of a crosslinkable monomer.

  The crosslinkable monomer may preferably be allyl methacrylate, ethylene glycol dimethacrylate or divinylbenzene.

  The aqueous base paint of the present invention preferably further contains a glitter pigment.

  The aqueous base paint of the present invention preferably further contains a polyester resin.

  According to the study by the present inventors, so-called irregularities, which are defects in water-based base paints used in the formation of automobile topcoats, have already occurred during transport of paints to spray guns used during spray painting. discovered. The present inventors have attached a hydrophobic material in a water-based base paint with a pigment to a hose used when transporting the water-based base paint to a spray gun, in particular, a polypropylene hose, and the attached matter is peeled off. We move through the paint and paint it with the paint from the spray gun. Moreover, although it is necessary to stir the aqueous base paint, it is considered that a film sticks to the surface of the paint when stirring, and this film moves in the paint and causes a flaw.

  In any case, it is caused by aggregation, solidification or film formation of the hydrophobic material in the paint. In the present invention, when a specific nonionic modified olefin resin is blended in the aqueous base paint, aggregation or solidification of the hydrophobic material or film Phenomenon such as crystallization is effectively prevented, and irregularities that are coating film defects of the aqueous base paint can be prevented. In the present specification, evaluation for preventing fluff is expressed as stability (particularly adhesion stability). This is because the stability of the paint is lowered due to aggregation or solidification of the hydrophobic material that generates blisters, and components such as pigments adhere to the solidified product and appear as coating film defects (that is, blisters). It expresses.

The aqueous base paint of the present invention has a resin solid content of 100% by mass,
(A) Acrylic resin emulsion is 10-60 mass% in solid content,
(B) Water-soluble acrylic resin is 5 to 40% by mass in solid content, and (c) Melamine resin is 20 to 40% by mass in solid content,
(D) Polyethylene glycol monoester having 8 to 22 carbon atoms and HLB 10 to 18 is used as a copolymer of an α-olefin compound (i) having 10 to 16 carbon atoms and a carboxylic acid anhydride (ii) having an unsaturated double bond. 0.1-5% by mass of a nonionic modified olefin resin having a solid content acid value of 20-60 mg KOH / g and a weight average molecular weight of 10,000-100,000 obtained by reacting with alkyl ether (iii)
It is characterized by containing.

Aqueous base paint The aqueous base paint used in the method for forming a multilayer coating film of the present invention has (a) an acrylic resin emulsion in a solid content of 10 to 60% by mass, and (b) a water-soluble acrylic resin in a solid content of 5 to 40. % By mass, (c) 20-40% by mass of the melamine resin in solid content, and (d) a specific nonionic modified olefin resin, and if necessary, a pigment. Each component will be described.

Ingredient (a)
The acrylic resin emulsion of component (a) is obtained by emulsion polymerization of a mixture of α, β-ethylenically unsaturated monomers. The monomer mixture can have an acid value and a hydroxyl value by including an α, β-ethylenically unsaturated monomer having an acid group or a hydroxyl group therein. The acid value and the hydroxyl value contribute to water solubility and crosslinkability.

  Examples of the α, β-ethylenically unsaturated monomer having an acid group include acrylic acid, methacrylic acid, acrylic acid dimer, crotonic acid, 2-acryloyloxyethylphthalic acid, 2-acryloyloxyethyl succinic acid, ω- Carboxy-polycaprolactone mono (meth) acrylate, isocrotonic acid, α-hydro-ω-((1-oxo-2-propenyl) oxy) poly (oxy (1-oxo-1,6-hexanediyl)), maleic acid , Fumaric acid, itaconic acid, 3-vinylsalicylic acid, 3-vinylacetylsalicylic acid, 2-acryloyloxyethyl acid phosphate, 2-acrylamido-2-methylpropanesulfonic acid, and the like. Among these, acrylic acid, methacrylic acid, and acrylic acid dimer are preferable.

  On the other hand, as the α, β-ethylenically unsaturated monomer having a hydroxyl group, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, allyl alcohol, methacryl alcohol, (meth) Mention may be made of adducts of hydroxyethyl acrylate and ε-caprolactone. Among these, preferred are hydroxyethyl (meth) acrylate, hydroxybutyl (meth) acrylate, and an adduct of hydroxyethyl (meth) acrylate and ε-caprolactone.

  Furthermore, the monomer mixture may further contain other α, β-ethylenically unsaturated monomers. Examples of the other α, β-ethylenically unsaturated monomers include (meth) acrylate esters (for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, (meth) acrylic). N-butyl acid, isobutyl (meth) acrylate, t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl methacrylate, phenyl acrylate, isobornyl (meth) acrylate, cyclohexyl methacrylate, ( (Meth) acrylic acid t-butylcyclohexyl, (meth) acrylic acid dicyclopentadienyl, (meth) acrylic acid dihydrodicyclopentadienyl, etc.), polymerizable amide compounds (for example, (meth) acrylamide, N-methylol ( (Meth) acrylamide, N-butoxymethyl (meth) acrylic N, N-dimethyl (meth) acrylamide, N, N-dibutyl (meth) acrylamide, N, N-dioctyl (meth) acrylamide, N-monobutyl (meth) acrylamide, N-monooctyl (meth) acrylamide 2, 4-dihydroxy-4′-vinylbenzophenone, N- (2-hydroxyethyl) acrylamide, N- (2-hydroxyethyl) methacrylamide, etc.), polymerizable aromatic compounds (for example, styrene, α-methylstyrene, vinyl ketone, t-butylstyrene, parachlorostyrene, vinylnaphthalene, etc.), polymerizable nitriles (eg, acrylonitrile, methacrylonitrile, etc.), α-olefins (eg, ethylene, propylene, etc.), vinyl esters (eg, vinyl acetate, propionic acid) Vinyl), dienes ( Examples thereof include butadiene and isoprene), polymerizable aromatic compounds, polymerizable nitriles, α-olefins, vinyl esters, and dienes. These can be selected depending on the purpose, but (meth) acrylamide is preferably used when hydrophilicity is easily imparted.

  The monomer mixture forming the acrylic resin emulsion of component (a) contains 0.2 to 20% by mass, preferably 0.5 to 20% by mass of a crosslinkable monomer based on the total amount of monomers, as necessary. When the crosslinkable monomer is less than 0.2% by mass, the solid content during coating tends to decrease and sagging tends to occur. Further, the orientation of the glitter pigment is disturbed and the flip-flop property (FF property) is lowered. When the crosslinkable monomer exceeds 20% by mass, the resin tends to gel and the synthesis of the emulsion tends to be difficult.

  The crosslinkable monomer is a compound having two or more radically polymerizable ethylenically unsaturated groups in the molecule. For example, divinylbenzene, ethylene glycol di (meth) acrylate, hexanediol di (meth) acrylate, polyethylene glycol Di (meth) acrylate, allyl (meth) acrylate, 1,4-butanediol di (meth) acrylate, 1,6-hexane di (meth) acrylate, neopentyl glycol di (meth) acrylate, pentaerythritol di (meth) acrylate And diaryl compounds such as triallyl cyanurate, pentaerythritol tri (meth) acrylate, trimethylolpropane tri (meth) acrylate, and dipentaerythritol hexa (meth) acrylate. The crosslinkable monomer may be a combination of the above monomers. Preferred crosslinkable monomers are allyl (meth) acrylate, ethylene glycol di (meth) acrylate and divinylbenzene. This is because these crosslinkable monomers are relatively easy to handle. In this specification, “(meth) acryl” means both acrylic and methacrylic.

  The acrylic resin emulsion (a) preferably has an acid value or a hydroxyl value as required. The acid value or hydroxyl value of the acrylic resin is substantially the same as the acid value or hydroxyl value of the monomer mixture in which it is synthesized. The monomer mixture used in the present invention has an acid value of preferably 3 to 50 mgKOH / g, more preferably 7 to 40 mgKOH / g. If the acid value is less than 3 mgKOH / g, the workability cannot be improved, and if it exceeds 50 mgKOH / g, the water resistance of the coating film decreases. On the other hand, when the aqueous base coating material needs to have curability, the monomer mixture needs to have a hydroxyl value of 10 to 150 mgKOH / g, preferably 20 to 100 mgKOH / g. When the hydroxyl value is less than 10 mgKOH / g, sufficient curability cannot be obtained, and when it exceeds 150 mgKOH / g, the water resistance of the coating film is lowered. Moreover, it is preferable from the point of the mechanical physical property of the coating film obtained that the glass transition temperature of the polymer obtained by copolymerizing the said monomer mixture is between -20-80 degreeC.

  The acrylic resin emulsion contained in the aqueous base paint of the present invention is obtained by emulsion polymerization of the monomer mixture. The emulsion polymerization carried out here can be carried out using a generally well-known method. Specifically, it can be carried out by dissolving the emulsifier in water or an aqueous medium containing an organic solvent such as alcohol as required, and dropping the monomer mixture and the polymerization initiator under heating and stirring. . A monomer mixture emulsified in advance using an emulsifier and water may be similarly dropped.

  Suitable polymerization initiators include azo oily compounds (for example, azobisisobutyronitrile, 2,2′-azobis (2-methylbutyronitrile) and 2,2′-azobis (2,4 -Dimethylvaleronitrile) and the like, and aqueous compounds (for example, anionic 4,4'-azobis (4-cyanovaleric acid), 2,2-azobis (N- (2-carboxyethyl) -2-methylpropion) Amidine and cationic 2,2′-azobis (2-methylpropionamidine)); and redox oily peroxides (eg, benzoyl peroxide, parachlorobenzoyl peroxide, lauroyl peroxide and t-butyl perbenzoate) Etc.), and aqueous peroxides such as potassium persulfate and ammonium persulfate It is below.

  As the emulsifier, those commonly used by those skilled in the art can be used. However, reactive emulsifiers such as Antox MS-60 (manufactured by Nippon Emulsifier Co., Ltd.), Eleminol JS-2 (manufactured by Sanyo Chemical Industries Ltd.) Adekaria soap NE-20 (Asahi Denka Co., Ltd.) and Aqualon HS-10 (Daiichi Kogyo Seiyaku Co., Ltd.) are particularly preferred.

  In order to adjust the molecular weight, a mercaptan such as lauryl mercaptan and a chain transfer agent such as α-methylstyrene dimer may be used as necessary.

  The reaction temperature is determined by the initiator, and for example, it is preferably 60 to 90 ° C. for an azo initiator and 30 to 70 ° C. for a redox system. In general, the reaction time is 1 to 8 hours. The amount of the initiator relative to the total amount of the monomer mixture is generally 0.1 to 5% by mass, preferably 0.2 to 2% by mass.

  The emulsion polymerization can be performed in multiple stages, for example, in two stages. That is, first, a part (monomer mixture 1) of the α, β-ethylenically unsaturated monomer mixture is subjected to emulsion polymerization, and the remainder of the α, β-ethylenically unsaturated monomer mixture (monomer mixture 2) is added thereto. In addition, emulsion polymerization is performed.

  The monomer mixture 1 preferably contains an α, β-ethylenically unsaturated monomer having an amide group from the viewpoint of preventing the compatibility with the clear coating film. At this time, it is more preferable that the monomer mixture 2 does not contain an α, β-ethylenically unsaturated monomer having an amide group. Since the mixture of monomer mixtures 1 and 2 is the monomer mixture, the requirement for the α, β-ethylenically unsaturated monomer mixture described above is the combination of monomer mixtures 1 and 2. Will meet.

  The particle diameter of the acrylic resin emulsion is preferably in the range of 0.01 to 1.0 μm. When the particle diameter is less than 0.01 μm, the effect of improving workability is small, and when it exceeds 1.0 μm, the appearance of the resulting coating film may be deteriorated. The particle size can be adjusted, for example, by adjusting the monomer composition and emulsion polymerization conditions.

  The said acrylic resin emulsion can be used by pH 5-10 by neutralizing with a base as needed. This is because the stability in this pH region is high. This neutralization is preferably carried out by adding a tertiary amine such as dimethylethanolamine or triethylamine to the system before or after emulsion polymerization.

  The acrylic resin emulsion of component (a) is blended in the aqueous base paint in an amount of 10 to 60% by mass, preferably 15 to 50% by mass. If it is less than 10% by mass, high solid differentiation and good FF properties cannot be obtained. When it exceeds 60 mass%, the viscosity increase at the time of application will be too fast, and color unevenness of the resulting coating will occur.

Ingredient (b)
The aqueous base paint of the present invention contains a water-soluble acrylic resin (b). The water-soluble acrylic resin is contained in the aqueous base paint in an amount of 5 to 40% by mass, preferably 10 to 30% by mass. When it is less than 5% by mass, the viscosity increase during coating is too fast, and color unevenness of the resulting coating film occurs. When it exceeds 40 mass%, favorable FF property will not come out.

  The water-soluble acrylic resin has a number average molecular weight of 3,000 to 50,000, preferably 6,000 to 30,000. If it is less than 3000, workability and curability are not sufficient, and if it exceeds 50000, the non-volatile content at the time of coating becomes too low, and workability is rather deteriorated. In the present specification, the number average molecular weight and the weight average molecular weight can be measured and determined by gel permeation chromatography (GPC) using a polystyrene standard sample standard.

  The water-soluble acrylic resin preferably has an acid value of 10 to 100 mg KOH / g, more preferably 20 to 80 mg KOH / g. When the upper limit is exceeded, the water resistance of the coating film is lowered, and when the lower limit is exceeded, the water dispersibility of the resin is reduced. Decreases. Further, it preferably has a hydroxyl value of 20 to 180 mgKOH / g, more preferably 30 to 160 mgKOH / g. When the upper limit is exceeded, the water resistance of the coating film decreases, and when the lower limit is exceeded, the curability of the coating film decreases.

  This water-soluble acrylic resin has an α, β-ethylenically unsaturated monomer having an acid group described in the previous monomer mixture as an essential component, and performs solution polymerization together with other α, β-ethylenically unsaturated monomers. Can be obtained.

  The water-soluble acrylic resin is usually neutralized with a basic compound, for example, an organic amine such as monomethylamine, dimethylamine, trimethylamine, triethylamine, diisopropylamine, monoethanolamine, diethanolamine, and dimethylethanolamine, and added to water. Although it dissolves and uses, this neutralization may be performed with respect to water-soluble acrylic resin itself, or may be performed at the time of manufacture of the water-based base coating material mentioned later.

Ingredient (c)
The aqueous base paint of the present invention contains melamine resin (c) as a curing agent. The melamine resin may be water-soluble or water-insoluble. Among the melamine resins, it is preferable in terms of stability to use a water tolerance of 3.0 or more. The water tolerance used here is for evaluating the degree of hydrophilicity, and the higher the value, the higher the hydrophilicity. The water tolerance value was measured by mixing 0.5 g of a sample in 10 ml of acetone and dispersing in a 100 ml beaker at 25 ° C., and gradually adding ion-exchanged water using a burette until the mixture became cloudy. The amount (ml) of ion exchange water required is measured, and this amount (ml) of ion exchange water is used as a water tolerance value.

  The content of the melamine resin is preferably 20 to 40% by mass with respect to the resin solid content in the aqueous base coat composition. If it is less than 20% by mass, the curability is lowered, and if it exceeds 40% by mass, the stability of the paint may be lowered.

Ingredient (d)
In the present invention, a carboxylic acid anhydride having an α-olefin compound (i) having 10 to 16 carbon atoms and an unsaturated double bond in an aqueous base coating material in order to ensure the emulsion stabilization ability for the hydrophobic material in the system. A solid content acid value of 20 to 60 mg KOH / g, a weight average molecular weight of 10, obtained by reacting a copolymer with (ii) with a polyethylene glycol monoalkyl ether (iii) having 8 to 22 carbon atoms and 10 to 20 HLB. 000-100,000 nonionic modified olefin resin is added in an amount of 0.1-5 wt%, preferably 0.5-3 wt%. When the addition amount is less than 0.1% by mass, the stability of the coating material (particularly, adhesion stability) is lowered and fluffing occurs. If it exceeds 5% by mass, the thixotropic index value (TI value) of the paint is lowered and the coating quality is deteriorated.

  Examples of the α-olefin having 10 to 16 carbon atoms in the copolymer of the α-olefin compound having 10 to 16 carbon atoms and the carboxylic anhydride having an unsaturated double bond include 1-decene, 1-dodecene, 1- Examples include tetradecene, 1-hexadecene and mixtures thereof.

  Examples of the carboxylic acid anhydride (ii) having an unsaturated double bond that is copolymerized with the α-olefin compound (i) include maleic acid, maleated polybutene, or a mixture thereof. Maleic acid is preferable.

  The copolymerization method of the α-olefin compound (i) and the carboxylic acid anhydride (ii) having an unsaturated double bond may be performed without a solvent or in combination with a solvent. The carboxylic acid anhydride (ii) having an unsaturated double bond may be charged together with the α-olefin compound (i) or may be gradually added to the polymerization system. These polymerization methods are not particularly limited. Polymerization initiators used here include azobis compounds such as azobisisobutyronitrile and azobis 2,4-dimethylvaleronitrile, cumene hydroperoxide, t-butyl hydroperoxide, benzoyl peroxide, diisopropyl peroxycarbonate, diisopropyl Examples thereof include peroxides such as t-butyl peroxide, lauroyl peroxide, t-butyl peroxybenzoate, potassium persulfate, and ammonium persulfate. Although not particularly limited to these, it is preferable to use an organic peroxide or an organic azo compound.

  The copolymer is reacted with a specific polyethylene glycol monoalkyl ether (iii) to form a predetermined nonionic modified olefin resin (d). The polyethylene glycol monoalkyl ether has 8 to 22 carbon atoms, preferably 10 to 20 carbon atoms, and 10 to 20 HLB, preferably 12 to 18 carbon atoms. HLB is an index representing hydrophilicity represented by (molecular weight of hydrophilic portion) ÷ (total molecular weight) × 20. When the carbon number is out of the above range, adhesion stability is reduced. Further, even if the HLB is outside the predetermined range, the adhesion stability is deteriorated.

  In the reaction, a copolymer of an α-olefin compound (i) and a carboxylic acid anhydride (ii) having an unsaturated double bond and a specific polyethylene glycol monoalkyl ether (iii) are charged into a reaction kettle, about 70 ° C. To 180 ° C. for several hours, the desired product can be obtained. You may add a solvent as needed. The final solid content acid value is preferably 20 to 60 mg KOH / g, preferably 25 to 50, and the weight average molecular weight is 10,000 to 100,000, preferably 20000 to 80,000. When the acid value is out of the above range, the adhesion stability is deteriorated. When the weight average molecular weight is less than 10,000, various performances of the coating film are deteriorated, and when it exceeds 100,000, adhesion stability is deteriorated.

  In the case of further aqueousization, the resulting reaction product can be easily aqueousized by neutralizing with an alkaline component such as a hydroxide or an organic amine. Specific examples include sodium hydroxide, potassium hydroxide, lithium hydroxide, aqueous ammonia, triethylamine, and triethanolamine, but are not necessarily limited thereto.

Other Components The aqueous base paint of the present invention contains a pigment. Examples of pigments include glitter pigments and colored pigments. The shape of the glitter pigment is not particularly limited, and may be colored. For example, the pigment having an average particle diameter (D ₅₀ ) of 2 to ₅₀ μm and a thickness of 0.1 to 5 μm Is preferred. Those having an average particle diameter in the range of 10 to 35 μm are excellent in glitter and are more preferably used. Specific examples include non-colored or colored metallic brightening agents such as aluminum, copper, zinc, iron, nickel, tin, and aluminum oxide, and alloys, and mixtures thereof. In addition, interference mica pigments, white mica pigments, graphite pigments, and the like are included in this.

  On the other hand, as the colored pigment, for example, organic azo chelate pigment, insoluble azo pigment, condensed azo pigment, phthalocyanine pigment, indigo pigment, perinone pigment, perylene pigment, dioxane pigment, quinacridone pigment, isoindo Examples thereof include linone pigments and metal complex pigments. Examples of inorganic pigments include chrome lead, yellow iron oxide, bengara, carbon black, and titanium dioxide.

  The total pigment concentration (PWC) in the aqueous base paint of the present invention is preferably 0.1 to 50% by mass. More preferably, it is 0.5-40 mass%, Most preferably, it is 1.0-30 mass%. When the upper limit is exceeded, the appearance of the coating film deteriorates. When a bright pigment is included, the pigment concentration (PWC) is generally preferably 18.0% by mass or less. When the upper limit is exceeded, the appearance of the coating film deteriorates. More preferably, it is 0.01-15.0 mass%, Most preferably, it is 0.01-13.0 mass%.

  Furthermore, other viscosity control agents can be added to the water-based base paint of the present invention in order to prevent familiarity with the top coat film and to ensure coating workability. As the viscosity control agent, those generally showing thixotropy can be used, for example, polyamide-based ones such as crosslinked or non-crosslinked resin particles, swelling dispersions of fatty acid amides, amide fatty acids, and long-chain polyaminoamide phosphates. Viscosity develops depending on the shape of polyethylene, such as colloidal swelling dispersion of polyethylene oxide, organic bentonite such as organic acid smectite clay, montmorillonite, inorganic pigments such as aluminum silicate and barium sulfate, etc. A flat pigment etc. can be mentioned.

  In the aqueous metallic base paint used in the present invention, in addition to the above-mentioned components, additives usually added to the paint, such as surface conditioners, thickeners, antioxidants, UV inhibitors, antifoaming agents, etc. You may mix | blend. These compounding amounts are within the range known to those skilled in the art.

  In addition to the melamine resin curing agent of component (c), the aqueous base paint may contain other curing agents. As such a hardening | curing agent, what is generally used for the coating material can be used. Examples of such compounds include blocked isocyanates, epoxy compounds, aziridine compounds, carbodiimide compounds, oxazoline compounds, and metal ions. A blocked isocyanate resin is generally used from the viewpoint of various performances and costs of the obtained coating film.

  The blocked isocyanate resin can be obtained by adding a blocking agent having active hydrogen to a polyisocyanate such as trimethylene diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, isophorone diisocyanate, etc. Dissociate to generate an isocyanate group.

  If necessary, the water-based base coating material of the present invention may further contain a polyester resin. The polyester resin is obtained by condensation polymerization of an acid component and an alcohol component. The acid component is not particularly limited, and examples thereof include polyvalent carboxylic acid compounds such as adipic acid, sebacic acid, isophthalic acid, and phthalic anhydride, and anhydrides thereof. Furthermore, as an acid component, a compound having a carboxylic acid group and a hydroxyl group in one molecule such as dimethylolpropionic acid can be used. Moreover, it does not specifically limit as said alcohol component, Polyhydric alcohol compounds, such as ethylene glycol, a trimethylol propane, neopentyl glycol, can be mentioned. The polyester resin preferably has a resin solid content acid value of 20 to 80 mgKOH / g and a number average molecular weight of 1000 to 15000. The polyester resin is added to suppress color unevenness of the obtained coating film. The compounding quantity in the coating material of a polyester resin is 5-30 mass%, Preferably it is 10-20 mass%. If it is less than 5% by mass, the effect of suppressing color unevenness is small, and if it is more than 30% by mass, the FF property may be lowered.

  The method for producing the paint used in the present invention is not particularly limited, including those described later, and all methods well known to those skilled in the art such as kneading and dispersing a compound such as a pigment using a kneader or a roll. Can be used.

  The water-based base paint of the present invention mainly comprises an organic solvent-type clear coating after a water-based base paint is formed by coating a water-based base paint on a top coat paint for automobiles, particularly an intermediate coat film formed on a steel plate for automobiles. It is used in a so-called two-coat one-bake multilayer coating method in which a coating is applied to form a clear coating, and the base coating and the clear coating are heated and cured. Therefore, a method for forming a multilayer coating film in which a clear paint is applied after the aqueous base paint is applied will be described.

Organic solvent type clear paint The organic solvent type clear paint is not particularly limited, and a clear paint containing a film-forming resin and a curing agent can be used. Furthermore, a color pigment can also be contained as long as it does not interfere with the design of the base.

  Preferred examples of the organic solvent-type clear coating include a combination of an acrylic resin and / or a polyester resin with an amino resin and / or an isocyanate resin, or a carboxylic acid / epoxy curing system from the viewpoint of transparency or acid etching resistance. An acrylic resin and / or a polyester resin system having

  Furthermore, it is preferable that a viscosity control agent is added to the organic solvent-type clear coating material in order to ensure coating workability. As the viscosity control agent, those generally showing thixotropy can be used. As such a thing, what was described in the above-mentioned aqueous | water-based basecoat composition can be used, for example. Moreover, a curing catalyst, a surface conditioner, etc. can be included if necessary.

The coating film forming method of the present invention can be advantageously used for various substrates such as metals, plastics, foams, etc., particularly metal surfaces, and castings. Can be used particularly preferably.

  Examples of the metal products include iron, copper, aluminum, tin, zinc and the like and alloys containing these metals. Specific examples include automobile bodies and parts such as passenger cars, trucks, motorcycles, and buses. These metals are particularly preferably those subjected to chemical conversion treatment with phosphate, chromate or the like in advance.

  An electrodeposition coating film may be formed on the chemical conversion treated steel sheet. As this electrodeposition coating, a cation type and an anion type can be used, but the cationic type electrodeposition coating composition is excellent in corrosion resistance. This is preferable because it gives a multilayer coating film.

  Examples of the plastic product include polypropylene resin, polycarbonate resin, urethane resin, polyester resin, polystyrene resin, ABS resin, vinyl chloride resin, polyamide resin and the like. Specific examples include automobile parts such as spoilers, bumpers, mirror covers, grills, and door knobs. These plastic products are preferably those washed with steam or neutral detergent with trichloroethane, and may further be provided with a primer coating for enabling electrostatic coating.

  If necessary, an intermediate coating film may be formed on the substrate. An intermediate coating is used to form the intermediate coating film. The intermediate coating contains a film-forming resin, a curing agent, various organic and inorganic color pigments, extender pigments, and the like.

  The film-forming resin contained in the intermediate coating is not particularly limited, and film-forming resins such as acrylic resin, polyester resin, alkyd resin, epoxy resin, and urethane resin can be used. It is used in combination with the curing agent mentioned in the previous aqueous base coat composition. An amino resin and / or an isocyanate resin is generally used in view of various performances and costs of the obtained coating film.

  As the color pigment contained in the intermediate coating composition, those described in the description of the aqueous base coat composition can be used in the same manner. As a standard, it is preferable to use a so-called color intermediate coating that combines carbon black and titanium dioxide as main pigments with a gray intermediate coating or a set gray that combines the hue of the top coating and various colored pigments. . Furthermore, flat pigments such as aluminum powder and mica powder may be added. In these intermediate coating materials, in addition to the above components, additives usually added to the coating material, for example, surface conditioners, antioxidants, antifoaming agents and the like may be blended.

Multilayer coating film forming method In the multilayer coating film forming method of the present invention, a base coating film and an organic solvent-type clear coating composition using an aqueous base coating material are coated on an object on which an electrodeposition coating film and an intermediate coating film are formed if necessary. The clear coating film can be formed sequentially.

  In the present invention, when an aqueous base paint is applied to an automobile body, in order to enhance the appearance, it is applied in multiple stages by air electrostatic spray painting, preferably in two stages, or air electrostatic spray painting. , A method of forming a coating film by a coating method combined with a rotary atomizing electrostatic coating machine called “μμ (micro micro) bell”, “μ (micro) bell” or “metabell” Can be used.

  In the present invention, the film thickness of the coating film when applied with a water-based base paint varies depending on the desired application, but in many cases, 10 to 30 μm is useful. If the upper limit is exceeded, sharpness may deteriorate, or defects such as unevenness or flow may occur during coating. If the lower limit is exceeded, the substrate cannot be concealed and film breakage occurs.

  In the multilayer coating film forming method of the present invention, a clear coating is further applied on the uncured base coating to form a clear coating (wet-on-wet coating), omitting the baking and drying oven. It is preferable from the viewpoint of economy and environment. In order to obtain a good finished coating film, it is desirable to heat the uncured base coating film at 40 to 100 ° C. for 2 to 10 minutes before applying the clear coating.

  In the coating film forming method of the present invention, the clear coating film that is applied after forming the base coating film is formed to smooth and protect the unevenness, flickering, and the like caused by the base coating film. Specifically, as a coating method, it is preferable to form the coating film by a rotary atomizing electrostatic coating machine such as the μμ bell or μbell described above.

  The dry film thickness of the clear coating film formed from the clear coating is generally preferably about 10 to 80 μm, more preferably about 20 to 60 μm. If the upper limit is exceeded, workability problems such as peeling or sagging may occur during painting, and if the lower limit is not reached, the underlying irregularities cannot be concealed.

  The clear coating film obtained as described above is preferably formed by so-called two-coat one-bake, which is baked together with an uncured base coating film as described above. By setting the baking temperature to 80 to 180 ° C, preferably 120 to 160 ° C, a cured coating film having a high degree of crosslinking can be obtained. If the upper limit is exceeded, the coating film becomes hard and brittle, and if it is less than the lower limit, curing is not sufficient. The curing time varies depending on the curing temperature, but 10 to 30 minutes at 120 to 160 ° C. is appropriate.

  In many cases, the film thickness of the multilayer coating film formed in the present invention is 30 to 300 μm, preferably 50 to 250 μm. When the upper limit is exceeded, film physical properties such as a cooling cycle decrease, and when the lower limit is exceeded, the strength of the film itself decreases.

  EXAMPLES Hereinafter, although a specific Example is given and this invention is demonstrated in detail, this invention is not limited by a following example. Hereinafter, “part” means “part by mass”.

Production Example 1 Production of acrylic resin emulsion 1 126.5 parts of deionized water was added to a reaction vessel, and the mixture was heated to 80 ° C. while being mixed and stirred in a nitrogen stream. Next, 27.61 parts of methyl acrylate, 53.04 parts of ethyl acrylate, 4.00 parts of styrene, 9.28 parts of 2-hydroxyethyl methacrylate, 3.07 parts of methacrylic acid and 3.00 parts of allyl methacrylate Monomer mixture 100 parts, Aqualon HS-10 (polyoxyethylene alkyl propenyl phenyl ether sulfate ester, Daiichi Kogyo Seiyaku Co., Ltd.) 0.7 parts, Adeka Soap NE-20 (α- [1-[(allyloxy) methyl]) 2- (nonylphenoxy) ethyl] -ω-hydroxyoxyethylene (manufactured by Asahi Denka Co., Ltd.), 0.5 part, and a monomer emulsion comprising 80 parts of deionized water, 0.3 part of ammonium persulfate, and deionized water An initiator solution consisting of 10 parts was dropped into the reaction vessel in parallel over 2 hours. After completion of the dropping, aging was performed at the same temperature for 2 hours. Next, after cooling to 40 ° C. and filtration through a 400 mesh filter, 70 parts of deionized water and 0.32 part of dimethylaminoethanol were added to adjust the pH to 6.5, the average particle size was 150 nm, the non-volatile content was 25%, the solid content was A single-layer acrylic resin emulsion 1 having an acid value of 20 mgKOH / g and a hydroxyl value of 40 mgKOH / g was obtained.

Production Example 2 Production of Acrylic Resin Emulsion 2 In Production Example 1, the amount of methyl acrylate was changed to 30.61 parts, and the same procedure as in Production Example 1 was conducted except that allyl methacrylate was not blended. A single-layer acrylic resin emulsion 2 having a diameter of 150 nm, a nonvolatile content of 25%, a solid content acid value of 20 mgKOH / g, and a hydroxyl value of 40 mgKOH / g was obtained.

Production Example 3 Production of water-soluble acrylic resin 23.89 parts of tripropylene glycol methyl ether and 16.11 parts of propylene glycol methyl ether were added to a reaction vessel, and the mixture was heated to 105 ° C. with mixing and stirring in a nitrogen stream. Next, a monomer mixture containing 13.1 parts of methyl methacrylate, 68.4 parts of ethyl acrylate, 11.6 parts of 2-hydroxyethyl methacrylate and 6.9 parts of methacrylic acid was prepared. An initiator solution consisting of 10.0 parts of propylene glycol methyl ether and 1 part of tertiary butyl peroxy 2-ethylhexanoate was dropped into the reaction vessel in parallel over 3 hours. After completion of the dropping, aging was performed at the same temperature for 0.5 hours.

  Further, an initiator solution consisting of 5.0 parts of tripropylene glycol methyl ether and 0.3 part of tertiary butyl peroxy 2-ethylhexanoate was dropped into the reaction vessel over 0.5 hours. After completion of the dropping, aging was performed at the same temperature for 2 hours.

  After removing 16.1 parts of the solvent at 110 ° C. under reduced pressure (70 torr) using a solvent removal apparatus, 204 parts of deionized water and 7.1 parts of dimethylaminoethanol were added to obtain a water-soluble acrylic resin solution. The obtained water-soluble acrylic resin solution had a nonvolatile content of 30%, a solid content acid value of 40 mg KOH / g, a hydroxyl value of 50 mg KOH / g, and a viscosity of 140 poise (E-type viscometer 1 rpm / 25 ° C.).

Production Example 4 Production of polyester resin In a reaction vessel equipped with a stirrer, condenser and thermometer, 372 parts of dimethyl terephthalic acid, 380 parts of dimethyl isophthalic acid, 576 parts of 2-methyl-1,3-propanediol, 1,5-pentanediol 222 parts and 0.41 part of tetrabutyl titanate were charged, and a transesterification reaction was carried out over 4 hours while heating from 160 ° C to 230 ° C. Next, the pressure inside the system was gradually reduced, the pressure was reduced to 5 mmHg over 20 minutes, and the pressure was further reduced to a vacuum of 0.3 mmHg or less, and a polycondensation reaction was performed at 260 ° C. for 40 minutes. The mixture was cooled to 220 ° C. in a nitrogen atmosphere, 23 parts of trimellitic anhydride was added, and a reaction was performed at 220 ° C. for 30 minutes to obtain a polyester resin. As a result of NMR compositional analysis, the obtained polyester resin had a carboxylic acid component in a molar ratio of terephthalic acid / isophthalic acid / trimellitic acid: 48/49/3, and a polyol component in a molar ratio of 2-methyl-1 , 3-propanediol / 1,5-pentanediol: 65/35. That is, when the total amount of each of the polycarboxylic acid component and the polyol component is 100 mol%, the aromatic dicarboxylic acid is 97 mol%, the isophthalic acid is 49 mol%, the total amount of the predetermined diol is 65 mol%, ethylene glycol Was 0 mol%.

About the obtained resin, the characteristic value was measured as follows.
(1) Number average molecular weight: It was 12000 when measured by gel permeation chromatography (GPC) using polystyrene standard sample standards.
(2) Acid value: 0.2 g of a sample was precisely weighed and dissolved in 20 ml of chloroform, and then titrated with 0.01 N potassium hydroxide (ethanol solution) to find 16.1 mg KOH / g.

  To 100 parts of this polyester resin, 40 parts of butyl cellosolve and 2.7 parts of triethylamine were added, followed by stirring at 80 ° C. for 1 hour for dissolution. Next, 193 parts of ion-exchanged water was gently added to obtain a polyester aqueous dispersion 1 containing a polyester resin having a nonvolatile content of 30%. In order to measure the average particle size, only ion-exchanged water is put into a dedicated cell, and only 1 drop of this dispersion is mixed, and the resin solid content concentration is adjusted to 0.1% by mass to measure the dynamic light scattering particle size. It was 35 nm when measured at 20 degreeC with apparatus LB-500 (made by Horiba, Ltd.).

Production Example 5 Synthesis of phosphoric acid group-containing acrylic resin 40 parts of ethoxypropanol was charged into a 1 liter reaction vessel equipped with a stirrer, a temperature controller, and a cooling tube, and 4 parts of styrene, 35.96 parts of n-butyl acrylate, Ethylhexyl methacrylate 18.45 parts, 2-hydroxyethyl methacrylate 13.92 parts, methacrylic acid 7.67 parts, ethoxypropanol 20 parts, Phosmer PP (Acid phosphooxyhexa (oxypropylene) monomethacrylate) 20 manufactured by Unichemical Co., Ltd. 40 parts of the dissolved solution and 121.7 parts of a monomer solution consisting of 1.7 parts of azobisisobutyronitrile were added dropwise at 120 ° C. for 3 hours, and stirring was further continued for 1 hour. The obtained resin was an acrylic acid varnish having an acid value of 105 mgKOH / g, of which an acid value of 55 mgKOH / g based on a phosphoric acid group, a hydroxyl value of 60 mgKOH / g and a number average molecular weight of 6000, and a nonvolatile content of 63%.

Production Example 6 Synthesis of Nonion-Modified Olefin Resin 1 Linearene 16 (α-olefin mixture commercially available from Idemitsu Kosan Co., Ltd .; content of carbon 16: 99.4%) 390 g of tert-butyl peroxide 1.4 g and toluene 10 g After charging the flask and replacing with nitrogen gas, while heating and stirring at 150 ° C., 110 g of maleic anhydride is 3.7 g every 2 minutes, and 1.4 g of di-t-butyl peroxide is 0.7 g every 20 minutes. Added in increments. After completion of the addition, the reaction was kept at 160 ° C. for 2 hours. Thereafter, 944 g of Emulgen 420 (polyethylene glycol monoalkyl ether commercially available from Kao Corporation; alkyl carbon number 18) with HLB = 16.6 was added, and the reaction was further continued for 2 hours. Thereafter, the mixture was cooled to 100 ° C. or lower and diluted with 3-methyl-3-methoxybutanol to a solid content concentration of 50%. The obtained nonionic modified olefin resin 1 had an acid value of 44 mgKOH / g and a weight average molecular weight of 48,000. Table 1 shows the formulation and the acid value and weight average molecular weight of the obtained nonionic modified olefin resin 1.

Production Example 7 Synthesis of Nonionic Modified Olefin Resins 2 to 5 Nonionic modified olefin resins 2 to 5 were synthesized in the same manner as in Production Example 6 except that the formulation shown in Table 1 below was used. The acid values and weight average molecular weights of the obtained nonionic modified olefin resins 2 to 5 are also shown in Table 1.

Example 1
160 parts of the acrylic resin emulsion 1 obtained in Production Example 1 of the manufacturer of the aqueous metallic base paint , 10 parts of 10% by weight dimethylaminoethanol, 33 parts of the water-soluble acrylic resin of Production Example 3 (resin solid content 30%), 33 parts of polyester resin of Production Example 4 (resin solid content 30%), 38 parts of Cymel 204 (mixed alkylated melamine resin, solid content 80%, water tolerance 3.6 ml, manufactured by Mitsui Cytec Co., Ltd.) as a melamine resin, Prime Pol PX-1000 (Sanyo Kasei Kogyo Co., Ltd., bifunctional polyether polyol) 10 parts, Nonionic modified olefin resin 1 obtained in Production Example 6 2 parts, Luster pigment Alpaste MH8801 (Asahi Kasei Aluminum pigment) 21 parts (Solid content 65%, PWC 12%), phosphoric acid group-containing acrylic resin 5 parts, lauryl acid 0.3 parts of sulfate is added, and further 30 parts of 2-ethylhexanol and 3.3 parts of Adecanol UH-814N (ADEKA thickener, solid content 30%) are uniformly dispersed to obtain an aqueous metallic base paint. It was.

The obtained paint, the stability (antifouling stability to polypropylene cups) was evaluated by the following method. The results of adhesion stability are shown in Table 2. Further, the thixotropic index (TI value) was measured by the following method, and the results are also shown in Table 2. Table 2 also describes the blending amounts of the acrylic resin emulsion and the nonionic modified olefin resin.

The antifouling stable aqueous metallic base coating 300g Evaluation method resulting in charged in a polypropylene cup, and stirred for 1 week with a magnetic stirrer. The entered paint to polypropylene cup was transferred while filtering with 200 mesh network to another container. The polypropylene cup was washed with water, it was observed state of adhesion of the aluminum pigment wall visually. Moreover, the presence or absence of a filtration residue was also confirmed. The results were evaluated according to the following criteria.

Rank 5: the wall of a polypropylene cup without aluminum pigment coated, also no filtration residue.
Rank 4: a wall surface of a polypropylene cup no aluminum pigment coated, filter residue is observed slightly.
Rank 3: adhesion of the aluminum pigment in the wall of the polypropylene cup was observed slightly, filter residue is also slightly observed.
Rank 2: adhesion of the aluminum pigment to the wall of a polypropylene cup Many are observed, filter residue is also slightly observed.
Rank 1: adhesion of the aluminum pigment to the wall of a polypropylene cup Many are observed, filter residue is also often observed.

Thixotropic index value (TI value)
The obtained water-based metallic base paint is made to have a viscosity of 3500-4500 mPa · s at a rotational speed of 6 rpm at 25 ° C. with a digital display type rotary viscometer Visco Basic Plus (B-type viscometer manufactured by Viscotec). After adjusting the viscosity with pure water, the viscosity at 25 ° C. at a rotation speed of 60 rpm is measured, and (viscosity at a rotation speed of 6 rpm) / (viscosity at a rotation speed of 60 rpm) is calculated and thixotropic. An index value (TI value) was used. A TI value of 5 or higher was evaluated as excellent.

Example 2
In Example 1 above, an aqueous metallic base paint was formed in the same manner as in Example 1 except that 2 parts of nonionic modified olefin resin 2 was used instead of nonionic modified olefin resin 1. About the obtained water-based metallic base coating material, the adhesion stability evaluation and the TI value were determined in the same manner as in Example 1. The results are shown in Table 2.

Example 3
In Example 1 above, an aqueous metallic base paint was formed in the same manner as in Example 1 except that 2 parts of nonionic modified olefin resin 3 was used instead of nonionic modified olefin resin 1. About the obtained water-based metallic base coating material, the adhesion stability evaluation and the TI value were determined in the same manner as in Example 1. The results are shown in Table 2.

Example 4
In Example 1 above, an aqueous metallic base paint was formed in the same manner as in Example 1 except that 0.5 part of nonionic modified olefin resin 2 was used instead of nonionic modified olefin resin 1. About the obtained water-based metallic base coating material, the adhesion stability evaluation and the TI value were determined in the same manner as in Example 1. The results are shown in Table 2.

Example 5
In the above Example 1, using 2 parts of a nonionic modified olefin resin 2 in place of the nonionic modified olefin resin 1, except that 160 mass parts of acrylic resin emulsion 2 obtained an acrylic resin emulsion 1 in Production Example 2 Example 1 to form a water-based metallic base paint. About the obtained water-based metallic base coating material, the adhesion stability evaluation and the TI value were determined in the same manner as in Example 1. The results are shown in Table 2.

Comparative Example 1
In Example 1 described above, an aqueous metallic base paint was formed in the same manner as in Example 1 except that the nonionic modified olefin resin 1 was not added. About the obtained water-based metallic base coating material, the adhesion stability evaluation and the TI value were determined in the same manner as in Example 1. The results are shown in Table 2.

Comparative Example 2
In Example 1 above, an aqueous metallic base paint was formed in the same manner as in Example 1 except that 2 parts of nonionic modified olefin resin 4 was used instead of nonionic modified olefin resin 1. About the obtained water-based metallic base coating material, the adhesion stability evaluation and the TI value were determined in the same manner as in Example 1. The results are shown in Table 2.

Comparative Example 3
In Example 1 above, an aqueous metallic base paint was formed in the same manner as in Example 1 except that 2 parts of nonionic modified olefin resin 5 was used instead of nonionic modified olefin resin 1. About the obtained water-based metallic base coating material, the adhesion stability evaluation and the TI value were determined in the same manner as in Example 1. The results are shown in Table 2.

Comparative Example 4
In the said Example 1, it processed similarly to Example 1 except using 6 parts of nonionic modified olefin resin 1, and formed the water-based metallic base coating material. About the obtained water-based metallic base coating material, the adhesion stability evaluation and the TI value were determined in the same manner as in Example 1. The results are shown in Table 2.

注）アクリル樹脂エマルションおよびノニオン変性オレフィン樹脂は固形分質量で表示している。

Note) Acrylic resin emulsion and nonionic modified olefin resin are shown in solid mass.

As is clear from the above examples, when a predetermined amount of the nonionic modified olefin resin of the present invention is added, the adhesion stability is high and the TI value is also high. On the other hand, Comparative Example 1 is an example in which the nonionic modified olefin resin is not added, but the adhesion stability is very poor. Comparative Example 2 is an example using a nonionic modified olefin resin having a solid acid value of 17 which is outside the scope of the present invention, but the adhesion stability is very poor. Comparative Example 3 is an example using a nonionic modified olefin resin having a solid acid value of 62, which is outside the scope of the present invention, but the anti-adhesion stability has increased, but the TI value is smaller than 5. It has become to. Comparative Example 4 is an example in which the addition amount of the nonionic modified olefin resin is 6 parts by mass , which is higher than the predetermined blending amount of the present invention, and although the adhesion stability is excellent, the TI value is not an acceptable value.

<Multi-layer coating film formation method (2 coats / 1 bake)>
Cathodic electrodeposition paint "Power Top U-50" (manufactured by Nippon Paint Co., Ltd.) is electrodeposited onto a dull steel sheet with a thickness of 0.8mm, length 30cm, width 40cm treated with zinc phosphate so that the dry film thickness is 20 µm. Painted and baked at 160 ° C. for 30 minutes, pre-diluted gray intermediate coating “Olga OP-30” (Nippon Paint Co., Ltd.) in 25 seconds (measured at 20 ° C. using a No. 4 Ford cup) Polyester / melamine-based paint) was applied in two stages by air spraying to a dry film thickness of 35 μm, and baked at 140 ° C. for 30 minutes.

  After cooling, the aqueous metallic base paint of the previous production example was diluted to 6000 mPa · s (measured at 20 ° C. under the condition of 6 rpm using a B-type viscometer) using deionized water. Two-stage coating was performed with a “cartridge bell” so that the dry film thickness was 15 μm under conditions of room temperature of 23 ° C. and humidity of 68%. An interval setting of 1 minute 30 seconds was performed between the two coatings. After the second application, setting was performed with an interval of 1 minute and 30 seconds. Thereafter, preheating was performed at 80 ° C. for 5 minutes.

  After preheating, the coated plate was allowed to cool to room temperature, applied as a clear coating material, Macflow-O-1810 (solvent type clear coating material manufactured by Nippon Paint Co., Ltd.), coated in one stage to a dry film thickness of 35 μm, and set for 7 minutes. Next, the coated plate was baked at 140 ° C. for 30 minutes with a dryer to obtain a multilayer coating film. In any case, the coating film appearance was good.

  The multilayer coating film forming method of the present invention can be used when forming a high-appearance coating film such as an automobile body.

Claims (10)

In 100% by mass of resin solid content,
(A) Acrylic resin emulsion is 10-60 mass% in solid content,
(B) 5-40 mass% of water-soluble acrylic resin in solid content,
(C) Melamine resin is 20 to 40% by mass in solid content, and (d) Co-weight of α-olefin compound (i) having 10 to 16 carbon atoms and carboxylic acid anhydride (ii) having an unsaturated double bond Nonionic compound having a solid content acid value of 20 to 60 mg KOH / g and a weight average molecular weight of 10,000 to 100,000, obtained by reacting a polyethylene glycol monoalkyl ether (iii) having 8 to 22 carbon atoms and HLB of 10 to 20 with the coalescence 0.1 to 5% by mass of modified olefin resin
Contains water-based paint. The aqueous base paint according to claim 1, wherein the acrylic resin emulsion (a) is obtained by emulsion polymerization of a monomer mixture containing 0.2 to 20% by mass of a crosslinkable monomer.
  The water-based paint according to claim 2, wherein the crosslinkable monomer is allyl methacrylate, ethylene glycol dimethacrylate or divinylbenzene.   The method for forming a multilayer coating film according to claim 1, wherein the aqueous base paint further contains a luster pigment.   The method for forming a multilayer coating film according to claim 1, wherein the aqueous base paint further contains a polyester resin. The base coating film is formed by coating a water-based base paint on the intermediate coating film formed on the steel sheet for automobiles to form a base coating film, and then applying an organic solvent type clear coating composition to form the clear coating film. And a clear coating film is heated and cured to form a multilayer coating film,
The water-based paint is in a resin solid content of 100% by mass,
(A) Acrylic resin emulsion is 10-60 mass% in solid content,
(B) 5-40 mass% of water-soluble acrylic resin in solid content,
(C) Melamine resin is 20 to 40% by mass in solid content, and (d) Co-weight of α-olefin compound (i) having 10 to 16 carbon atoms and carboxylic acid anhydride (ii) having an unsaturated double bond Nonionic compound having a solid content acid value of 20 to 60 mg KOH / g and a weight average molecular weight of 10,000 to 100,000, obtained by reacting a polyethylene glycol monoalkyl ether (iii) having 8 to 22 carbon atoms and HLB of 10 to 20 with the coalescence 0.1 to 5% by mass of modified olefin resin
A method for forming a multilayer coating film, comprising:   The method for forming a multilayer coating film according to claim 6, wherein the acrylic resin emulsion (a) is obtained by emulsion polymerization of a monomer mixture containing 0.2 to 20% by mass of a crosslinkable monomer.   The method for forming a multilayer coating film according to claim 7, wherein the crosslinkable monomer is allyl methacrylate, ethylene glycol dimethacrylate, or divinylbenzene.   The method for forming a multilayer coating film according to claim 6, wherein the aqueous base paint further contains a luster pigment.   The method for forming a multilayer coating film according to claim 6, wherein the aqueous base paint further contains a polyester resin.