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WO2009081943A1 - Double-layer coating film formation method - Google Patents

Double-layer coating film formation method Download PDF

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Publication number
WO2009081943A1
WO2009081943A1 PCT/JP2008/073459 JP2008073459W WO2009081943A1 WO 2009081943 A1 WO2009081943 A1 WO 2009081943A1 JP 2008073459 W JP2008073459 W JP 2008073459W WO 2009081943 A1 WO2009081943 A1 WO 2009081943A1
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WO
WIPO (PCT)
Prior art keywords
coating film
value
uncured
clear
meth
Prior art date
Application number
PCT/JP2008/073459
Other languages
French (fr)
Japanese (ja)
Inventor
Hideaki Tsujioka
Junji Shimada
Hisaki Tanabe
Junya Ogawa
Original Assignee
Nippon Paint Co., Ltd.
Toyota Jidosha Kabushiki Kaisha
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Nippon Paint Co., Ltd., Toyota Jidosha Kabushiki Kaisha filed Critical Nippon Paint Co., Ltd.
Priority to DE112008003485T priority Critical patent/DE112008003485T5/en
Priority to GB1010643.3A priority patent/GB2468255B8/en
Priority to JP2009547113A priority patent/JP5342457B2/en
Publication of WO2009081943A1 publication Critical patent/WO2009081943A1/en

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    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D133/00—Coating compositions based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Coating compositions based on derivatives of such polymers
    • C09D133/04—Homopolymers or copolymers of esters
    • C09D133/06—Homopolymers or copolymers of esters of esters containing only carbon, hydrogen and oxygen, the oxygen atom being present only as part of the carboxyl radical
    • C09D133/062—Copolymers with monomers not covered by C09D133/06
    • C09D133/066—Copolymers with monomers not covered by C09D133/06 containing -OH groups
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D1/00—Processes for applying liquids or other fluent materials
    • B05D1/36—Successively applying liquids or other fluent materials, e.g. without intermediate treatment
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
    • B05D7/24—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials for applying particular liquids or other fluent materials
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
    • B05D7/50—Multilayers
    • B05D7/52—Two layers
    • B05D7/53—Base coat plus clear coat type
    • B05D7/532—Base coat plus clear coat type the two layers being cured or baked together, i.e. wet on wet
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
    • B05D7/50—Multilayers
    • B05D7/52—Two layers
    • B05D7/53—Base coat plus clear coat type
    • B05D7/534—Base coat plus clear coat type the first layer being let to dry at least partially before applying the second layer
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G18/00—Polymeric products of isocyanates or isothiocyanates
    • C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
    • C08G18/28—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the compounds used containing active hydrogen
    • C08G18/40—High-molecular-weight compounds
    • C08G18/62—Polymers of compounds having carbon-to-carbon double bonds
    • C08G18/6216—Polymers of alpha-beta ethylenically unsaturated carboxylic acids or of derivatives thereof
    • C08G18/625—Polymers of alpha-beta ethylenically unsaturated carboxylic acids; hydrolyzed polymers of esters of these acids
    • C08G18/6254—Polymers of alpha-beta ethylenically unsaturated carboxylic acids and of esters of these acids containing hydroxy groups
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G18/00—Polymeric products of isocyanates or isothiocyanates
    • C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
    • C08G18/70—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the isocyanates or isothiocyanates used
    • C08G18/72—Polyisocyanates or polyisothiocyanates
    • C08G18/77—Polyisocyanates or polyisothiocyanates having heteroatoms in addition to the isocyanate or isothiocyanate nitrogen and oxygen or sulfur
    • C08G18/78—Nitrogen
    • C08G18/79—Nitrogen characterised by the polyisocyanates used, these having groups formed by oligomerisation of isocyanates or isothiocyanates
    • C08G18/791—Nitrogen characterised by the polyisocyanates used, these having groups formed by oligomerisation of isocyanates or isothiocyanates containing isocyanurate groups
    • C08G18/792—Nitrogen characterised by the polyisocyanates used, these having groups formed by oligomerisation of isocyanates or isothiocyanates containing isocyanurate groups formed by oligomerisation of aliphatic and/or cycloaliphatic isocyanates or isothiocyanates
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D133/00—Coating compositions based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Coating compositions based on derivatives of such polymers
    • C09D133/04—Homopolymers or copolymers of esters
    • C09D133/06—Homopolymers or copolymers of esters of esters containing only carbon, hydrogen and oxygen, the oxygen atom being present only as part of the carboxyl radical
    • C09D133/08—Homopolymers or copolymers of acrylic acid esters
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D175/00—Coating compositions based on polyureas or polyurethanes; Coating compositions based on derivatives of such polymers
    • C09D175/04—Polyurethanes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D1/00—Processes for applying liquids or other fluent materials
    • B05D1/02—Processes for applying liquids or other fluent materials performed by spraying
    • B05D1/04—Processes for applying liquids or other fluent materials performed by spraying involving the use of an electrostatic field
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D2202/00—Metallic substrate
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D2503/00—Polyurethanes

Definitions

  • the present invention relates to a method for forming a multilayer coating film.
  • top coat film containing a base paint film and a clear paint film.
  • clear coating film constitutes the outermost layer in the coating film of an automobile body or the like, various physical properties such as design properties, acid resistance, and scratch resistance are required.
  • acrylic / melamine resin thermosetting paint has been used as a clear paint for automobile painting.
  • the coating film obtained by using such a melamine resin as a curing agent is inferior in acid resistance, it is likely to be deteriorated by acid rain, and there is a risk of causing a problem in appearance.
  • Examples of such clear paints other than the acrylic / melamine resin thermosetting type include urethane-based paints (for example, see Patent Document 1). JP-A-2005-787
  • a urethane-based paint can obtain a coating film excellent in acid resistance and scratch resistance
  • a clear coating film is formed on the uncured base coating film using a urethane-based paint, and the base coating film and the clear coating film are formed.
  • a top coat film is formed by so-called two-coat one-bake in which the film is heated and cured at a temperature of 120 ° C. or more at the same time, the acrylic resin (acrylic polyol) in the clear coating composition penetrates into the uncured base coat film. May affect the appearance of the coating film.
  • the base paint composition is a metallic paint having a glitter pigment
  • the penetration of the components in the clear paint composition disturbs the arrangement of the glitter pigment in the uncured base coating, resulting in highlights.
  • a phenomenon called color reversion of the base coating film in which the shade (bright surface) becomes bright while the (front surface) becomes dark may occur, and the coating film appearance may deteriorate. Therefore, urethane-based paints are difficult to obtain coating films having excellent design properties as clear paints for automotive coatings, especially clear paints for automotive coatings for markets where high design properties are required. There was a problem.
  • an object of the present invention is to provide a multilayer coating film forming method capable of forming a multilayer coating film having excellent acid resistance and scratch resistance.
  • the present invention includes a step (1) of applying a base paint to a base material to form an uncured base coating film, A step (2) of forming an uncured clear coating film by applying a clear coating on the uncured base coating film obtained in the step (1); and A multilayer coating film forming method comprising the step (3) of heating and curing the uncured base coating film and the uncured clear coating film obtained in the steps (1) and (2) to form a multilayer coating film.
  • the L value of the uncured base coating film is 70 to 105 at 25 degrees reflection and 20 to 50 at 75 degrees reflection;
  • the ⁇ L value obtained by subtracting the L value of the uncured base coating film from the L value of the multilayer coating film by 25 ° reflection is ⁇ 0.3 to 0.15,
  • the ⁇ L value obtained by subtracting the L value of the uncured base coating film from the L value of the multilayer coating film by 75-degree reflection is ⁇ 0.2 to 0.4.
  • the clear paint contains 10 to 15% by mass of a long-chain (meth) acrylic acid ester monomer whose ester part is a linear hydrocarbon group having 9 to 15 carbon atoms, based on the total amount of monomer solids, and also contains a carboxyl group
  • An acrylic resin obtained from a monomer mixture containing a (meth) acrylic monomer and a hydroxyl group-containing (meth) acrylic monomer, having a number average molecular weight of 4000 to 6000 and a solid content acid value of 1 to 5 mgKOH / g, a polyisocyanate compound,
  • a method for forming a multilayer coating film which is a clear coating composition containing crosslinked resin particles.
  • the clear coating composition preferably contains 0.1 to 10% by mass of crosslinked resin particles based on the total solid content of the coating composition.
  • the multilayer coating film forming method may include a step (P) of forming an intermediate coating film by applying an intermediate coating before the step (1).
  • the present invention it is possible to form a multi-layer coating film having high brightness, a high design appearance with suppressed color reversion, and excellent acid resistance and scratch resistance.
  • FIG. 1 is a diagram schematically showing a method for measuring the L value.
  • an uncured base coating film having high brightness such as a metallic base coating film
  • An uncured base coating film having excellent design properties because the color return of the base coating film is likely to be manifested in a 2-coat 1-bake coating method. Is difficult to form.
  • an uncured base coating film is formed so that the L value satisfies the above (a), and the clear coating composition is applied to the uncured base coating film.
  • the acrylic resin contained in the clear coating composition is relatively long. Since it has a straight chain hydrocarbon group having 9 to 15 carbon atoms as a side chain, when the clear coating is applied in the formation process of the top coat film by 2 coats and 1 bake, the acrylic resin is sterilized due to the steric hindrance of the straight chain hydrocarbon group. This is considered to be because the resin can be prevented from penetrating into the uncured base coating film. Furthermore, it can be considered that making the acrylic resin have a high acid value is effective in preventing the penetration of the acrylic resin into the uncured base coating film.
  • the paint colors can be classified into three types according to the L value of the highlight of the cured base single film.
  • a deep color having an L value of less than 40, a medium color of 40 to 80, and a light color of 80 or more.
  • the intermediate color to the light color with a large L value of the highlight can be obtained by laminating a clear coating film so that the flip-flop property is high and the design property is high.
  • a membrane can be obtained.
  • the L value fluctuates even with a slight disturbance in the orientation of the glitter pigment due to the mixed layer of the base coating and the clear coating, so that the L value of the highlight and the L value in the shade are likely to increase.
  • the flip-flop property is also likely to deteriorate.
  • the multilayer coating film forming method of the present invention includes a step (1) of applying a base coating to a base material to form an uncured base coating film.
  • a base coating a brightener base paint containing a base resin component, a bright pigment, a colored pigment, an extender pigment, a solvent and the like can be used.
  • This base coating composition is of an aqueous or organic solvent type including an aqueous dispersion or an organic solvent dispersion.
  • the aqueous solvent and organic solvent are not particularly limited, and conventionally known solvents can be used.
  • the base resin component contained in these base paints is composed of a base resin and, if necessary, a base curing agent. Using the base resin component, the glitter pigment and, if necessary, the color pigment are dispersed in the glitter base coating.
  • the base resin examples include acrylic resin, polyester resin, polyurethane resin, alkyd resin, epoxy resin, and polyether resin. Of these resins, acrylic resins, polyester resins, and polyurethane resins are preferably used. These resins may be used alone or in combination of two or more.
  • the base resin generally has a curable type and a lacquer type, but a curable type is preferably used.
  • a curable type is used, a base curing agent such as a melamine resin, a (block) isocyanate compound, an oxazoline compound and a carbodiimide compound is used in combination with the base resin.
  • This base curing agent can be included in the base resin component to allow the curing reaction to proceed later under heating or at room temperature.
  • a curable type base resin and a non-curable type resin can be used in combination.
  • the preferred mass ratio of the base resin and the base curing agent in the solid content of the paint is 90/10 to 50/50, more preferably 85/15 to 60/40. If the amount of the base curing agent is so small that the mass ratio between the base resin and the base curing agent deviates from 90/10, sufficient crosslinking in the coating film may not be obtained. On the other hand, when the amount of the base curing agent is so large that this ratio is deviated from 50/50, the storage stability of the coating material is lowered and the curing rate is increased, which may deteriorate the appearance of the coating film.
  • an etherified melamine resin can be used in addition to those described above.
  • the etherified melamine resin is obtained by etherifying melamine with an alcohol such as methanol or butanol.
  • a non-colored or colored scale-like metallic luster material such as aluminum, copper, zinc, iron, nickel, tin, aluminum oxide or an alloy, or a mixture thereof, or interference mica powder
  • bright pigments such as non-colored colored bright materials such as colored mica powder, white mica powder, graphite and glass flakes.
  • extender pigments such as barita powder, precipitated barium sulfate, barium carbonate, gypsum, clay, silica, talc, magnesium carbonate, and alumina white, and colored pigments.
  • coloring pigments examples include azo lake pigments, phthalocyanine pigments, indigo pigments, perylene pigments, quinophthalone pigments, dioxazine pigments, quinacridone pigments, isoindolinone pigments, diketopyrrolopyrrole pigments, and benzimidazolones.
  • Organic pigments such as system pigments and metal complex pigments, and inorganic pigments such as yellow lead, yellow iron oxide, bengara, titanium dioxide, and carbon black. The amount of the pigment can be arbitrarily set according to the desired performance and hue. These pigments may be used alone or in combination of two or more.
  • the base paint is a wax such as a polyamide wax which is a lubricating dispersion of an aliphatic amide or a polyethylene wax which is a colloidal dispersion mainly composed of oxidized polyethylene, a curing catalyst, an ultraviolet absorber, and an antioxidant.
  • a wax such as a polyamide wax which is a lubricating dispersion of an aliphatic amide or a polyethylene wax which is a colloidal dispersion mainly composed of oxidized polyethylene, a curing catalyst, an ultraviolet absorber, and an antioxidant.
  • Leveling agents, surface conditioners such as silicone and organic polymers, anti-sagging agents, thickeners, antifoaming agents, lubricants, crosslinkable polymer particles (microgel), and the like can be appropriately added.
  • these additives By blending these additives at a ratio of 15 parts by mass or less with respect to 100 parts by mass (based on solid content) of the base resin component, the performance of the paint or coating film can be improved.
  • the upper limit of the pigment concentration (PWC) with respect to the solid content of the base paint is preferably 65% by mass. Moreover, it is preferable that the minimum is 5 mass%. Further, the solid content concentration of the base coating is preferably in the range of a lower limit of 15% by mass and an upper limit of 60% by mass.
  • the method of applying the base paint include multi-stage coating, preferably two-stage coating using an air electrostatic spray or a rotary atomizing electrostatic coater. By performing this coating method, the designability can be improved. Or the coating method which combined the air electrostatic spray and the rotary atomization type electrostatic coating machine as an application method of a base coating material is mentioned.
  • the dry film thickness of the topcoat base coating film is preferably 5 to 50 ⁇ m per coat, and more preferably 10 to 30 ⁇ m.
  • the obtained uncured base coating film may be preheated.
  • pre-heating By applying pre-heating after applying the base coating material to form an uncured base coating film, a multilayer coating film having a better finished appearance can be finally obtained.
  • uncured refers to a state where the film is not completely cured, and includes a state of a coating film that has been preheated after coating.
  • “Preheating” can be performed by standing or heating at room temperature to 100 ° C., which is lower than the temperature used in the heat curing (baking) treatment, for 1 to 10 minutes.
  • the uncured base coating film obtained by performing the step (1) has an L value of 70 to 105 at 25 degrees reflection and 20 to 50 at 75 degrees reflection.
  • an uncured clear coating film is formed on the uncured base coating film by a clear coating described later, and is cured by heating.
  • the L value (brightness) is an index used to represent the color of the object to be measured by the Lab color system (hunter color system), and the value of the object to be measured increases as the value increases.
  • the L value in the 25-degree reflection is from the light source at an angle of 25 degrees when the light-receiving part at a position perpendicular to the coating film to be measured is 0 degrees. It means L value of light received by irradiating light.
  • the L value in 75-degree reflection means the L value of light received by irradiating light from the light source at an angle of 75 degrees from the light receiving unit.
  • the L value can be determined, for example, by measuring using a variable angle color difference meter (for example, “CM-512m3” manufactured by Minolta).
  • the clear coating composition includes a long-chain (meth) acrylic acid ester monomer whose ester part is a linear hydrocarbon group having 9 to 15 carbon atoms, a carboxyl group-containing (meth) acrylic monomer, and a hydroxyl group-containing (meth) acrylic. It is obtained from a monomer mixture containing monomers and contains an acrylic resin having a number average molecular weight of 4000 to 6000 and a solid content acid value of 1 to 5 mgKOH / g, a polyisocyanate compound, and crosslinked resin particles.
  • the acrylic resin comprises a long-chain (meth) acrylic acid ester monomer whose ester part is a linear hydrocarbon group having 9 to 15 carbon atoms, a carboxyl group-containing (meth) acrylic monomer, and a hydroxyl group-containing (meth) acrylic monomer. It is obtained from the monomer mixture containing.
  • the long chain (meth) acrylic acid ester monomer is, for example, the following general formula (A)
  • R represents hydrogen or a methyl group
  • n represents a natural number of 8 to 14
  • the long-chain (meth) acrylate monomer is not particularly limited as long as the ester portion is a straight chain hydrocarbon group having 9 to 15 carbon atoms.
  • lauryl (meth) acrylate, (meth) ) Tridecyl acrylate, decyl (meth) acrylate, and nonyl (meth) acrylate may use only 1 type and may use 2 or more types together.
  • the content of the long-chain (meth) acrylate monomer in the monomer mixture is 10 to 15% by mass with respect to the total amount of monomer solids. If it is less than 10% by mass, it is difficult to sufficiently suppress the influence of the clear coating film on the base coating film side. On the other hand, when it exceeds 15 mass%, there exists a possibility that the adhesiveness in the case of repainting may fall.
  • the carboxyl group-containing (meth) acrylic monomer is not particularly limited, and examples thereof include acrylic acid, methacrylic acid, acrylic acid dimer, crotonic acid, isocrotonic acid, and maleic acid. These may use only 1 type and may use 2 or more types together. Of these, acrylic acid and methacrylic acid are preferable.
  • a carboxyl group-containing (meth) acrylic monomer By using a carboxyl group-containing (meth) acrylic monomer, a coating film having excellent design properties can be formed. Such an effect is presumed to be because the apparent molecular weight of the acrylic resin can be increased by the association of carboxyl groups, and thus the penetration of the acrylic resin into the base coating film can be prevented.
  • the hydroxyl group-containing (meth) acrylic monomer is not particularly limited.
  • hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, allyl alcohol, methacryl alcohol examples include adducts of hydroxyethyl (meth) acrylate and ⁇ -caprolactone. These may use only 1 type and may use 2 or more types together.
  • the above-mentioned acrylic resin can be obtained from the monomer mixture containing the long-chain (meth) acrylic acid ester monomer, the carboxyl group-containing (meth) acrylic monomer and the hydroxyl group-containing (meth) acrylic monomer.
  • the monomer mixture may contain other unsaturated monomers.
  • Examples of the other unsaturated monomer include, for example, (meth) acrylic acid ester, methyl (meth) acrylate, ethyl (meth) acrylate, i-propyl (meth) acrylate, and n-butyl (meth) acrylate.
  • (Meth) acrylic acid alkyl esters having 1 to 8 carbon atoms in the ester moiety such as i-butyl (meth) acrylate, t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate;
  • (Meth) acrylic acid cyclic hydrocarbon esters such as phenyl acrylate, cyclohexyl (meth) acrylate; (meth) acrylate isobornyl; (poly) ethylene glycol mono (meth) acrylate, polyethylene glycol mono ( (Meth) acrylic acid polyalkylene glycol esters such as (meth) acrylate; and
  • alkoxyalkyl (meth) acrylate having 1 to 3 carbon atoms (meth) acrylamide; vinyl compounds such as styrene, ⁇ -methylstyrene, vinyl acetate, vinyl propionate, vinyl benzoate, vinyltoluene, acrylonitrile; And
  • the polymerization method for obtaining the acrylic resin is not particularly limited, and known methods such as solution polymerization, dispersion polymerization, and emulsion polymerization can be used.
  • the acrylic resin has a number average molecular weight (Mn) of 4000 to 6000.
  • Mn number average molecular weight
  • a number average molecular weight (Mn) is a number average molecular weight of polystyrene conversion measured by GPC (gel permeation chromatography).
  • the acrylic resin preferably has a solid content acid value of 1 to 5 mgKOH / g.
  • the solid content acid value By making the solid content acid value within the above range, the apparent molecular weight can be increased by the association of carboxyl groups, so that the penetration of the acrylic resin into the base coating film can be prevented, and the excellent design properties It is because a coating film can be formed.
  • the solid content acid value is less than 1 mg KOH / g, the number of points of association decreases and it becomes difficult to increase the apparent molecular weight, which may make it difficult to form a coating film having excellent design properties. .
  • the solid content acid value exceeds 5 mgKOH / g, the viscosity becomes too high and it may be difficult to obtain a coating composition having a high solid content.
  • the above acrylic resin preferably has a solid content hydroxyl value of 50 to 140 mgKOH / g.
  • solid content hydroxyl value is less than 50 mgKOH / g.
  • the solid content hydroxyl value exceeds 140 mgKOH / g, the water resistance of the coating film may decrease.
  • the solid content hydroxyl value is more preferably 80 to 140 mgKOH / g.
  • the said solid content acid value and hydroxyl value can be adjusted with the compounding ratio of a raw material monomer.
  • the above acrylic resin preferably has a glass transition temperature (Tg value) of ⁇ 30 to 50 ° C. If the Tg value is less than ⁇ 30 ° C., the coating film hardness may decrease, and the coating film thickness may vary due to variations in the coating liquid temperature. On the other hand, when it exceeds 50 ° C., the viscosity becomes too high and it may be difficult to form a coating composition having a high solid content.
  • the acrylic resin preferably has a Tg value of ⁇ 10 to 30 ° C.
  • the Tg value of the acrylic resin can be calculated, for example, by calculating from the known Tg value and the composition ratio of the constituent monomer or homopolymer.
  • the clear coating composition contains a polyisocyanate compound.
  • the polyisocyanate compound is not particularly limited as long as it is a compound having two or more isocyanate groups.
  • Aliphatic isocyanates such as 1,3-cyclopentane diisocyanate, 1,4-cyclohexane diisocyanate, 1,2-cyclohexane diisocyanate, and the like, xylylene diisocyanate (XDI), 2,4-tolylene diisocyanate (TDI) ), Aromatic isocyanates such as 2,6-tolylene diisocyanate, isophorone diisocyanate (IPDI), norbornane diisocyanate Alicyclic isocyanates such Tomechiru, these isocyanurate body, can be given burette body, multimers of the adduct and the like and mixtures. Among these, a nurate body is preferable from the viewpoint of weather resistance.
  • the functional group amount ratio between the NCO group of the polyisocyanate compound and the carboxyl group and / or hydroxyl group of the acrylic resin is preferably 1 / 1.5 to 1.5 / 1.
  • the functional group amount ratio is more preferably 1.4 / 1 to 1 / 1.4.
  • the crosslinked resin particles have a rheology control effect, exhibit a high effect on sagging at the time of coating and heat curing, and at the same time contribute to stabilization of the L value of the coating film.
  • Such crosslinked resin particles are not particularly limited and can be appropriately selected from those obvious to those skilled in the art.
  • the content of the crosslinked resin particles is preferably 0.01 to 10% by mass, more preferably 0.1 to 10% by mass, based on the resin solid content of the clear coating composition. More preferably, it is ⁇ 5% by mass. When the content is less than 0.01% by mass, the rheology control effect may not be obtained. When the content exceeds 10% by mass, the smoothness of the resulting coating film may be adversely affected.
  • an ultraviolet absorber In the clear coating composition, an ultraviolet absorber, a hindered amine light stabilizer, an antioxidant, a surface conditioner, and the like may be blended.
  • the clear coating composition is preferably a two-component curable coating composition comprising the acrylic resin-containing composition and the polyisocyanate compound.
  • the method for applying the clear coating composition include micro-microbell and a coating method using a rotary atomizing electrostatic coater called microbell.
  • the clear coating composition can be applied by the above method after mixing them before use.
  • the coating film thickness of the clear coating composition is preferably in the range of a lower limit of 20 ⁇ m and an upper limit of 60 ⁇ m in terms of dry film thickness.
  • the base uncured coating film and the clear uncured coating film formed by the above method are simultaneously heated and cured to form a multilayer coating film.
  • the heating temperature is preferably performed within a range of a lower limit of 100 ° C. and an upper limit of 180 ° C. More preferably, the lower limit is 120 ° C and the upper limit is 160 ° C.
  • the heat-curing time varies depending on the curing temperature or the like, but when it is carried out at the above-mentioned heat-curing temperature, it is appropriate that it is 10-30 minutes.
  • the multi-layer coating film thus obtained has a ⁇ L value which is a value obtained by subtracting the L value of the uncured base coating film from the L value of the multi-layer coating film by 25-degree reflection, and is ⁇ 0.3.
  • the ⁇ L value obtained by subtracting the L value of the uncured base coating film from the L value of the multilayer coating film by 75-degree reflection is ⁇ 0.2 to 0.4. is there.
  • a multilayer coating film having a ⁇ L value within the above range has an appearance with a high design property that suppresses the occurrence of color reversion.
  • the film thickness of the multilayer coating film is preferably in the range of a lower limit of 30 ⁇ m and an upper limit of 80 ⁇ m.
  • the multilayer coating film obtained by the above method is excellent in coating film properties such as scratch resistance, acid resistance and solvent resistance, and has high design properties.
  • the base material it can be used for, for example, metal molded products, plastic molded products, foams, etc., but as base materials for forming a multilayer coating film for automobiles, iron, aluminum, zinc-based substrates and these Examples thereof include metal molded products such as alloys, plastic molded products, and the like. It is preferable to apply to metal molded products that can be subjected to cationic electrodeposition coating.
  • the base material is preferably subjected to a chemical conversion treatment on the surface.
  • an electrodeposition coating film may be formed on the substrate.
  • the electrodeposition paint the cation type and the anion type can be used. From the viewpoint of anticorrosion, a cation type electrodeposition paint is preferable.
  • the intermediate coating material that can be used in the step (P) a conventionally used intermediate coating material can be used.
  • the intermediate coating may be a water-based paint or a solvent-type paint.
  • examples of the components of these paints include intermediate coating resin components, colored pigments, extender pigments, and aqueous and / or organic solvents.
  • the intermediate coating resin component is composed of an intermediate coating resin and, if necessary, an intermediate coating curing agent.
  • an intermediate coating curing agent As the intermediate coating resin component, intermediate coating curing agent, coloring pigment, extender pigment, various additives and solvent contained in the intermediate coating, any of those described for the above-mentioned base coating can be used.
  • the pigment concentration (PWC) with respect to the solid content of the intermediate coating is preferably in the range of a lower limit of 30% by mass and an upper limit of 65% by mass.
  • the upper limit is more preferably 50% by mass.
  • the solid content concentration of the intermediate coating is preferably in the range of 35% by mass to 65% by mass.
  • Examples of methods for applying the intermediate coating include those using a spray method, a roll coater method, and the like. Specifically, it uses air electrostatic sprays called “react guns” or rotary atomizing electrostatic coatings called “micro-micro ( ⁇ ) bell”, “micro ( ⁇ ) bell”, “metabell”, etc. It is preferable to paint using a machine. Among these, it is particularly preferable to perform the coating using a rotary atomizing electrostatic coating machine.
  • a preferable dry film thickness of the intermediate coating film is 5 to 80 ⁇ m, and more preferably 10 to 50 ⁇ m.
  • the uncured intermediate coating film thus formed can be baked and cured at 120 to 160 ° C. for a predetermined time to obtain a cured intermediate coating film.
  • the base paint and the clear paint can be applied on the cured intermediate coating film thus obtained.
  • the above base coating and clear coating are applied wet-on-wet on the obtained uncured intermediate coating, and the uncured base coating and clear coating are applied on the uncured intermediate coating.
  • parts means “parts by mass” unless otherwise specified.
  • alkyl methacrylate acrylate ester SL (manufactured by Mitsubishi Rayon Co., Ltd.) having a mixing ratio (mass basis) of lauryl methacrylate / tridecyl methacrylate of 4/6 was used.
  • Alkyl methacrylate Acryester SL (Mitsubishi Rayon Co., Ltd.) in which lauryl methacrylate / tridecyl methacrylate has a mixing ratio of 4/6 (mass basis)
  • a monomer suspension was prepared by vigorously stirring 10 parts of this zwitterionic group-containing polyester resin, 140 parts of deionized water, 1 part of dimethylethanolamine, 50 parts of styrene and 50 parts of ethylene glycol dimethacrylate in a stainless steel beaker.
  • an aqueous initiator solution was prepared by mixing 0.5 part of azobiscyanoyoshinoic acid, 40 parts of deionized water, and 0.32 part of dimethylethanolamine.
  • a glass container equipped with a thermometer, stirring blades, nitrogen inlet tube, cooling condenser and dropping funnel is charged with 5 parts of the above zwitterion group-containing polyester resin, 280 parts of deionized water and 0.5 part of dimethylethanolamine, and 80 ° C. The temperature was raised to. To this, 251 parts of the monomer suspension and 40.82 parts of the aqueous initiator solution were simultaneously added dropwise over 60 minutes, and the reaction was further continued for 60 minutes, and then the reaction was terminated. An emulsion containing crosslinked resin particles having a particle diameter of 55 nm measured by a dynamic light scattering method was obtained. Butyl acetate was added to this emulsion, water was removed by azeotropic distillation under reduced pressure, and the medium was replaced with butyl acetate to obtain a crosslinked resin particle solution having a resin solid content of 20%.
  • Each of the acrylic resins A to C is 68.68 parts in terms of resin solids, Sumidur N3300 (isocyanurate type isocyanate compound) manufactured by Sumika Bayer Urethane Co., Ltd., 31.32 parts, and Tinuvin 928 (UV manufactured by Ciba Specialty Chemicals) Agent) 2 parts, Tinuvin 292 (Company light stabilizer) 1 part, Cross-linked resin particles 4 parts, Modaflow (Monsanto surface conditioner) 0.1 part, blended with a disperser to clear the paint Compositions A to C were obtained.
  • the clear coating composition A that did not contain the crosslinked resin particles was designated as clear coating composition D.
  • the multilayer coating film by the said base coating material and clear coating composition was apply
  • the silver metallic base paint was applied to the test plate so that the dry film thickness was 15 ⁇ m, and baked and dried at 140 ° C. for 30 minutes to produce a base single-layer coating test plate.
  • the present invention is suitable as a method for forming a multi-layer coating film for automobile painting with a high brightness such as a metallic color, particularly as a method for forming a multi-layer coating film for automobile coating for a market that requires high designability. Can be used.

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Abstract

Disclosed is a double-layer coating film formation method that includes a step (1) wherein a base coating is applied to a substrate to form an uncured base coating film, a step (2) wherein a clear coating is applied on the uncured base coating film obtained in the aforementioned step (1) to form an uncured clear coating film, and a step (3) wherein the uncured base coating film and uncured clear coating film obtained in the aforementioned step (1) and step (2) are heat cured to form a double-layer coating film. This double-layer coating film formation method is characterized by (a) the L value of the aforementioned uncured base coating film being 70 to 105 in 25° reflection and 20 to 50 in 75° reflection, (b) the value of ΔL, found by subtracting the L value for the aforementioned uncured base coating film from the L value of the aforementioned double-layer coating film at 25° reflection, being -0.3 to 0.15, and (c) the value of ΔL, found by subtracting the L value of the aforementioned uncured base coating film from the L value of the aforementioned double-layer coating film at 75° reflection, being -0.2 to 0.4. Also, the aforementioned clear coating is a clear coating compound that contains: an acrylic resin, which is obtained from a monomer mixture containing 10 to 15% by mass long-chain (meth)acrylic acid ester monomer, in which the ester portion is a straight-chain hydrocarbon group of 9 to 15 carbon atoms, relative to the total quantity of monomer solids, a carboxy group-containing (meth)acrylic monomer, and a hydroxy group-containing (meth)acrylic monomer, the number-average molecular weight of which being 4000 to 6000 and the solids acid number of which being 1 to 5 mg KOH/g; a polyisocyanate compound; and cross-linked resin particles. The double-layer coating film formation method makes possible the formation of a double-layer coating film of superior design, acid resistance, and scratch resistance.

Description

複層塗膜形成方法Multi-layer coating formation method
　本発明は、複層塗膜形成方法に関する。 The present invention relates to a method for forming a multilayer coating film.
　自動車の車体等の塗装においては、ベース塗膜及びクリヤー塗膜を含有する上塗り塗膜を形成することが広く行われている。特にクリヤー塗膜は、自動車車体等の塗膜における最外層を構成するものであることから、意匠性、耐酸性、耐擦り傷性等の諸物性が求められている。 In the coating of automobile bodies and the like, it is widely practiced to form a top coat film containing a base paint film and a clear paint film. In particular, since the clear coating film constitutes the outermost layer in the coating film of an automobile body or the like, various physical properties such as design properties, acid resistance, and scratch resistance are required.
　従来、自動車塗装用のクリヤー塗料として、アクリル／メラミン樹脂熱硬化型塗料が使用されていた。しかし、このようなメラミン樹脂を硬化剤として用いることにより得られる塗膜は、耐酸性に劣るため、酸性雨により劣化され易く、外観上の不具合を生じるおそれがあった。 Conventionally, acrylic / melamine resin thermosetting paint has been used as a clear paint for automobile painting. However, since the coating film obtained by using such a melamine resin as a curing agent is inferior in acid resistance, it is likely to be deteriorated by acid rain, and there is a risk of causing a problem in appearance.
　このようなアクリル／メラミン樹脂熱硬化型以外のクリヤー塗料としては、例えば、ウレタン系塗料（例えば、特許文献１参照）等が存在する。
特開２００５－７８７号公報 Examples of such clear paints other than the acrylic / melamine resin thermosetting type include urethane-based paints (for example, see Patent Document 1).
JP-A-2005-787
　しかしながら、ウレタン系塗料は、耐酸性及び耐擦り傷性に優れた塗膜を得ることができるものの、未硬化ベース塗膜上に、ウレタン系塗料によりクリヤー塗膜を形成し、ベース塗膜及びクリヤー塗膜を同時に１２０℃以上の温度で加熱硬化させる所謂２コート１ベークによる上塗り塗膜の形成を行った場合、クリヤー塗料組成物中のアクリル樹脂（アクリルポリオール）が未硬化ベース塗膜中へ浸透して塗膜外観に影響を与える場合があった。 However, although a urethane-based paint can obtain a coating film excellent in acid resistance and scratch resistance, a clear coating film is formed on the uncured base coating film using a urethane-based paint, and the base coating film and the clear coating film are formed. When a top coat film is formed by so-called two-coat one-bake in which the film is heated and cured at a temperature of 120 ° C. or more at the same time, the acrylic resin (acrylic polyol) in the clear coating composition penetrates into the uncured base coat film. May affect the appearance of the coating film.
　特に、ベース塗料組成物が光輝性顔料を有するメタリック塗料である場合、クリヤー塗料組成物中の成分の浸透によって、未硬化ベース塗膜中の光輝性顔料の配列が乱され、その結果、ハイライト（正面）が暗くなる一方でシェード（すかし面）が明るくなるベース塗膜の色戻りと呼ばれる現象が発生し、塗膜外観が悪化する場合があった。
　そのため、ウレタン系塗料は、自動車塗装用のクリヤー塗料、特に、高い意匠性が要求される市場向けの自動車塗装用のクリヤー塗料としては、優れた意匠性を有する塗膜を得ることが困難であるという問題があった。 In particular, when the base paint composition is a metallic paint having a glitter pigment, the penetration of the components in the clear paint composition disturbs the arrangement of the glitter pigment in the uncured base coating, resulting in highlights. A phenomenon called color reversion of the base coating film in which the shade (bright surface) becomes bright while the (front surface) becomes dark may occur, and the coating film appearance may deteriorate.
Therefore, urethane-based paints are difficult to obtain coating films having excellent design properties as clear paints for automotive coatings, especially clear paints for automotive coatings for markets where high design properties are required. There was a problem.
　本発明は上記の現状に鑑み、メタリックベース塗膜等の明度の高いベース塗膜を含む複層塗膜を形成する場合に、色戻りの発現を抑えベース塗膜の本来有する高い意匠性を有するとともに、耐酸性及び耐擦り傷性にも優れた複層塗膜を形成することができる複層塗膜形成方法を提供することを目的とするものである。 In view of the above-mentioned present situation, the present invention suppresses the occurrence of color reversion when forming a multilayer coating film including a base coating film with high brightness such as a metallic base coating film, and has a high design characteristic that the base coating film originally has. In addition, an object of the present invention is to provide a multilayer coating film forming method capable of forming a multilayer coating film having excellent acid resistance and scratch resistance.
　本発明は、基材に対して、ベース塗料を塗布して未硬化ベース塗膜を形成する工程（１）、
　上記工程（１）で得られた未硬化ベース塗膜上に、クリヤー塗料を塗布して未硬化クリヤー塗膜を形成する工程（２）、及び、
　上記工程（１）及び工程（２）で得られた未硬化ベース塗膜及び未硬化クリヤー塗膜を加熱硬化して複層塗膜を形成する工程（３）を含む複層塗膜形成方法であって、
　（ａ）上記未硬化ベース塗膜のＬ値が、２５度反射において７０～１０５であり、かつ、７５度反射において２０～５０であり、
　（ｂ）２５度反射による上記複層塗膜のＬ値から上記未硬化ベース塗膜のＬ値を差し引いて求められる値であるΔＬ値が、－０．３～０．１５であり、
　（ｃ）７５度反射による上記複層塗膜のＬ値から上記未硬化ベース塗膜のＬ値を差し引いて求められる値であるΔＬ値が、－０．２～０．４であり、
かつ、
　上記クリヤー塗料が、エステル部が炭素数９～１５の直鎖炭化水素基である長鎖（メタ）アクリル酸エステルモノマーをモノマー固形分全量に対して１０～１５質量％含み、かつ、カルボキシル基含有（メタ）アクリルモノマー及び水酸基含有（メタ）アクリルモノマーを含むモノマー混合物から得られ、数平均分子量が４０００～６０００、固形分酸価が１～５ｍｇＫＯＨ／ｇであるアクリル樹脂と、ポリイソシアネート化合物と、架橋樹脂粒子とを含むクリヤー塗料組成物であることを特徴とする複層塗膜形成方法である。 The present invention includes a step (1) of applying a base paint to a base material to form an uncured base coating film,
A step (2) of forming an uncured clear coating film by applying a clear coating on the uncured base coating film obtained in the step (1); and
A multilayer coating film forming method comprising the step (3) of heating and curing the uncured base coating film and the uncured clear coating film obtained in the steps (1) and (2) to form a multilayer coating film. There,
(A) the L value of the uncured base coating film is 70 to 105 at 25 degrees reflection and 20 to 50 at 75 degrees reflection;
(B) The ΔL value obtained by subtracting the L value of the uncured base coating film from the L value of the multilayer coating film by 25 ° reflection is −0.3 to 0.15,
(C) The ΔL value obtained by subtracting the L value of the uncured base coating film from the L value of the multilayer coating film by 75-degree reflection is −0.2 to 0.4.
And,
The clear paint contains 10 to 15% by mass of a long-chain (meth) acrylic acid ester monomer whose ester part is a linear hydrocarbon group having 9 to 15 carbon atoms, based on the total amount of monomer solids, and also contains a carboxyl group An acrylic resin obtained from a monomer mixture containing a (meth) acrylic monomer and a hydroxyl group-containing (meth) acrylic monomer, having a number average molecular weight of 4000 to 6000 and a solid content acid value of 1 to 5 mgKOH / g, a polyisocyanate compound, A method for forming a multilayer coating film, which is a clear coating composition containing crosslinked resin particles.
　上記クリヤー塗料組成物は、架橋樹脂粒子を、塗料組成物の全固形分に対して０．１～１０質量％含むことが好ましい。
　上記複層塗膜形成方法は、上記工程（１）以前に、中塗り塗料を塗布して中塗り塗膜を形成する工程（Ｐ）を含むものであってもよい。 The clear coating composition preferably contains 0.1 to 10% by mass of crosslinked resin particles based on the total solid content of the coating composition.
The multilayer coating film forming method may include a step (P) of forming an intermediate coating film by applying an intermediate coating before the step (1).
　本発明によれば、明度が高く、色戻りの発現を抑えた意匠性の高い外観を有するとともに、耐酸性及び耐擦り傷性にも優れた複層塗膜を形成することができる。 According to the present invention, it is possible to form a multi-layer coating film having high brightness, a high design appearance with suppressed color reversion, and excellent acid resistance and scratch resistance.
図１は、Ｌ値の測定方法を模式的に示す図である。FIG. 1 is a diagram schematically showing a method for measuring the L value.
　以下に本発明を詳細に説明する。 The present invention will be described in detail below.
　本発明の複層塗膜形成方法は、（１）上記（ａ）を満たす未硬化ベース塗膜を形成した後、（２）上記未硬化ベース塗膜上に上記クリヤー塗料を塗布して未硬化クリヤー塗膜を形成し、（３）上記未硬化ベース塗膜及び上記未硬化クリヤー塗膜を加熱硬化し、上記（ｂ）、（ｃ）を満たす複層塗膜を形成するものである。
　メタリックベース塗膜等、明度の高い未硬化ベース塗膜は、一般的に２コート１ベークの塗装方法においてベース塗膜の色戻りが発現し易いものであるため、優れた意匠性を有する塗膜の形成が困難である。
　しかしながら、本発明の複層塗膜形成方法によれば、Ｌ値が上記（ａ）を満たすように未硬化ベース塗膜を形成し、上記未硬化ベース塗膜に上記クリヤー塗料を塗布して未硬化クリヤー塗膜を形成し、加熱硬化することにより、明度が高く、色戻りの発現を抑えた意匠性の高い外観を有する複層塗膜を形成することができる。 In the multilayer coating film forming method of the present invention, (1) after forming an uncured base coating film satisfying the above (a), (2) applying the clear coating material on the uncured base coating film and uncuring A clear coating film is formed, and (3) the uncured base coating film and the uncured clear coating film are cured by heating to form a multilayer coating film that satisfies the above (b) and (c).
An uncured base coating film having high brightness, such as a metallic base coating film, is generally a film having excellent design properties because the color return of the base coating film is likely to be manifested in a 2-coat 1-bake coating method. Is difficult to form.
However, according to the method for forming a multilayer coating film of the present invention, an uncured base coating film is formed so that the L value satisfies the above (a), and the clear coating composition is applied to the uncured base coating film. By forming a cured clear coating film and curing by heating, it is possible to form a multilayer coating film having high appearance and a high design appearance with suppressed color reversion.
　本発明の複層塗膜形成方法によって、色戻りの発現を抑えベース塗膜の本来有する高い意匠性を維持することができる理由は、上記クリヤー塗料組成物に含まれるアクリル樹脂が、比較的長い炭素数９～１５の直鎖炭化水素基を側鎖として有するため、２コート１ベークによる上塗り塗膜の形成工程において、クリヤー塗料を塗布した際、上記直鎖炭化水素基の立体障害によって、アクリル樹脂が未硬化のベース塗膜に浸透することを防止することができるからであると考えられる。更に、アクリル樹脂を酸価の高いものとすることも、アクリル樹脂の未硬化のベース塗膜への浸透を防止することに効果を有すると考えられる。 The reason why it is possible to suppress the occurrence of color reversion and maintain the high designability inherent in the base coating film by the method for forming a multilayer coating film of the present invention is that the acrylic resin contained in the clear coating composition is relatively long. Since it has a straight chain hydrocarbon group having 9 to 15 carbon atoms as a side chain, when the clear coating is applied in the formation process of the top coat film by 2 coats and 1 bake, the acrylic resin is sterilized due to the steric hindrance of the straight chain hydrocarbon group. This is considered to be because the resin can be prevented from penetrating into the uncured base coating film. Furthermore, it can be considered that making the acrylic resin have a high acid value is effective in preventing the penetration of the acrylic resin into the uncured base coating film.
　塗色は、硬化したベース単膜のハイライトのＬ値によって、３種類に分類することができる。まず、Ｌ値が４０未満である濃彩色、次に４０以上８０未満の中彩色、８０以上の淡彩色である。ここで、光輝性顔料を含んだベース単膜において、ハイライトのＬ値が大きい中彩色から淡彩色は、クリヤー塗膜を積層することで、フリップフロップ性が高く、意匠性の高い複層塗膜を得ることができる。
　しかしながら、ベース塗膜とクリヤー塗膜との混層による僅かな光輝性顔料の配向の乱れでも、Ｌ値が変動するため、ハイライトのＬ値の低下及びシェードでのＬ値の増大が起こりやすく、フリップフロップ性も低下し易い。また、硬化したベース塗膜のハイライトのＬ値が小さい濃彩色では、元々のハイライトでのＬ値が小さいので、ベース塗膜とクリヤー塗膜との混層によって光輝性顔料の配向の乱れが僅かである場合には、Ｌ値の変化として現れ難い。
　従って、特に、中彩色から淡彩色ではベース層との混層を制御することができるクリヤー塗料組成物が必要である。 The paint colors can be classified into three types according to the L value of the highlight of the cured base single film. First, a deep color having an L value of less than 40, a medium color of 40 to 80, and a light color of 80 or more. Here, in the base single film containing the glitter pigment, the intermediate color to the light color with a large L value of the highlight can be obtained by laminating a clear coating film so that the flip-flop property is high and the design property is high. A membrane can be obtained.
However, the L value fluctuates even with a slight disturbance in the orientation of the glitter pigment due to the mixed layer of the base coating and the clear coating, so that the L value of the highlight and the L value in the shade are likely to increase. The flip-flop property is also likely to deteriorate. Further, in the dark color where the L value of the highlight of the cured base coating film is small, the L value in the original highlight is small, so the orientation of the glitter pigment is disturbed by the mixed layer of the base coating film and the clear coating film. If it is slight, it is difficult to appear as a change in the L value.
Therefore, there is a need for a clear coating composition that can control the mixed layer with the base layer, particularly for medium to light colors.
　本発明の複層塗膜形成方法は、基材に対して、ベース塗料を塗布して未硬化ベース塗膜を形成する工程（１）を有する。
　上記ベース塗料としては、ベース樹脂成分、光輝性顔料、着色顔料、体質顔料、溶媒等を含有する光輝剤系ベース塗料を用いることができる。このベース塗料組成物は、水分散系又は有機溶媒分散系を含む、水系又は有機溶媒系のものである。水性溶媒、有機溶媒としては、特に限定されるものではなく、従来公知のものを用いることができる。 The multilayer coating film forming method of the present invention includes a step (1) of applying a base coating to a base material to form an uncured base coating film.
As the base paint, a brightener base paint containing a base resin component, a bright pigment, a colored pigment, an extender pigment, a solvent and the like can be used. This base coating composition is of an aqueous or organic solvent type including an aqueous dispersion or an organic solvent dispersion. The aqueous solvent and organic solvent are not particularly limited, and conventionally known solvents can be used.
　これらのベース塗料に含まれるベース樹脂成分は、ベース樹脂と必要に応じてベース硬化剤とから構成される。ベース樹脂成分を使用して、光輝剤系ベース塗料では光輝性顔料と必要に応じて着色顔料が分散される。 The base resin component contained in these base paints is composed of a base resin and, if necessary, a base curing agent. Using the base resin component, the glitter pigment and, if necessary, the color pigment are dispersed in the glitter base coating.
　上記ベース樹脂として、例えば、アクリル樹脂、ポリエステル樹脂、ポリウレタン樹脂、アルキド樹脂、エポキシ樹脂、ポリエーテル樹脂などが挙げられる。これらの樹脂のうち、アクリル樹脂、ポリエステル樹脂、ポリウレタン樹脂が好ましく使用される。これらの樹脂は、１種を単独で用いてもよく、あるいは２種以上を組み合わせて用いてもよい。 Examples of the base resin include acrylic resin, polyester resin, polyurethane resin, alkyd resin, epoxy resin, and polyether resin. Of these resins, acrylic resins, polyester resins, and polyurethane resins are preferably used. These resins may be used alone or in combination of two or more.
　ベース樹脂には一般に、硬化可能なタイプとラッカータイプとがあるが、硬化可能なタイプのものが好ましく使用される。硬化可能なタイプを使用する場合は、ベース樹脂と併せて、メラミン樹脂、（ブロック）イソシアネート化合物、オキサゾリン化合物及びカルボジイミド化合物などのベース硬化剤を使用する。このベース硬化剤を、ベース樹脂成分中に含めて、後に加熱下又は常温下において硬化反応を進行させることができる。また、硬化可能なタイプのベース樹脂と、硬化可能ではないタイプのものとを併用することもできる。 The base resin generally has a curable type and a lacquer type, but a curable type is preferably used. When a curable type is used, a base curing agent such as a melamine resin, a (block) isocyanate compound, an oxazoline compound and a carbodiimide compound is used in combination with the base resin. This base curing agent can be included in the base resin component to allow the curing reaction to proceed later under heating or at room temperature. Further, a curable type base resin and a non-curable type resin can be used in combination.
　ベース硬化剤が含まれる場合、塗料固形分中におけるベース樹脂とベース硬化剤との好ましい質量割合は、９０／１０～５０／５０、より好ましくは８５／１５～６０／４０である。ベース樹脂とベース硬化剤との質量割合が９０／１０から外れる程、ベース硬化剤の量が少ない場合は、塗膜中の十分な架橋が得られないことがある。一方、この割合が５０／５０から外れる程、ベース硬化剤の量が多い場合は、塗料の貯蔵安定性が低下するとともに硬化速度が大きくなり、塗膜外観が悪くなる恐れがある。 When the base curing agent is included, the preferred mass ratio of the base resin and the base curing agent in the solid content of the paint is 90/10 to 50/50, more preferably 85/15 to 60/40. If the amount of the base curing agent is so small that the mass ratio between the base resin and the base curing agent deviates from 90/10, sufficient crosslinking in the coating film may not be obtained. On the other hand, when the amount of the base curing agent is so large that this ratio is deviated from 50/50, the storage stability of the coating material is lowered and the curing rate is increased, which may deteriorate the appearance of the coating film.
　ベース硬化剤として、上述したものの他にエーテル化メラミン樹脂を使用することができる。エーテル化メラミン樹脂は、メラミンをメタノールやブタノール等のアルコールでエーテル化することにより得られる。 As the base curing agent, an etherified melamine resin can be used in addition to those described above. The etherified melamine resin is obtained by etherifying melamine with an alcohol such as methanol or butanol.
　ベース塗料に含まれる顔料として、アルミニウム、銅、亜鉛、鉄、ニッケル、スズ、酸化アルミニウム等の金属または合金等の無着色若しくは着色された鱗片状の金属製光輝材及びその混合物、又は干渉マイカ粉、着色マイカ粉、ホワイトマイカ粉、グラファイト、ガラスフレーク等の無着色有色の光輝材等の光輝性顔料が挙げられる。
　また、上記光輝性顔料以外には、例えば、バリタ粉、沈殿性硫酸バリウム、炭酸バリウム、石膏、クレー、シリカ、タルク、炭酸マグネシウム、アルミナホワイトなどの体質顔料、及び着色顔料などが挙げられる。着色顔料として、例えば、アゾレーキ系顔料、フタロシアニン系顔料、インジゴ系顔料、ペリレン系顔料、キノフタロン系顔料、ジオキサジン系顔料、キナクリドン系顔料、イソインドリノン系顔料、ジケトピロロピロール系顔料、ベンズイミダゾロン系顔料、金属錯体顔料等の有機顔料、あるいは黄鉛、黄色酸化鉄、ベンガラ、二酸化チタン、カーボンブラック等の無機顔料が挙げられる。顔料の量は、所望の性能及び色相を発現するのに合わせて任意に設定できる。これら顔料は、１種のみ単独で用いてもよく、また２種以上を併用して用いてもよい。 As a pigment contained in the base paint, a non-colored or colored scale-like metallic luster material such as aluminum, copper, zinc, iron, nickel, tin, aluminum oxide or an alloy, or a mixture thereof, or interference mica powder And bright pigments such as non-colored colored bright materials such as colored mica powder, white mica powder, graphite and glass flakes.
In addition to the glitter pigment, for example, extender pigments such as barita powder, precipitated barium sulfate, barium carbonate, gypsum, clay, silica, talc, magnesium carbonate, and alumina white, and colored pigments. Examples of coloring pigments include azo lake pigments, phthalocyanine pigments, indigo pigments, perylene pigments, quinophthalone pigments, dioxazine pigments, quinacridone pigments, isoindolinone pigments, diketopyrrolopyrrole pigments, and benzimidazolones. Organic pigments such as system pigments and metal complex pigments, and inorganic pigments such as yellow lead, yellow iron oxide, bengara, titanium dioxide, and carbon black. The amount of the pigment can be arbitrarily set according to the desired performance and hue. These pigments may be used alone or in combination of two or more.
　ベース塗料は、上記成分の他に、脂肪族アミドの潤滑分散体であるポリアミドワックスや酸化ポリエチレンを主体としたコロイド状分散体であるポリエチレンワックスなどのワックス、硬化触媒、紫外線吸収剤、酸化防止剤、レベリング剤、シリコーンや有機高分子等の表面調整剤、タレ止め剤、増粘剤、消泡剤、滑剤、架橋性重合体粒子（ミクロゲル）等を適宜添加することができる。これらの添加剤を、ベース樹脂成分１００質量部（固形分基準）に対して１５質量部以下の割合で配合することにより、塗料や塗膜の性能を改善することができる。 In addition to the above components, the base paint is a wax such as a polyamide wax which is a lubricating dispersion of an aliphatic amide or a polyethylene wax which is a colloidal dispersion mainly composed of oxidized polyethylene, a curing catalyst, an ultraviolet absorber, and an antioxidant. , Leveling agents, surface conditioners such as silicone and organic polymers, anti-sagging agents, thickeners, antifoaming agents, lubricants, crosslinkable polymer particles (microgel), and the like can be appropriately added. By blending these additives at a ratio of 15 parts by mass or less with respect to 100 parts by mass (based on solid content) of the base resin component, the performance of the paint or coating film can be improved.
　ベース塗料の塗料固形分に対する顔料の濃度（ＰＷＣ）は、上限６５質量％であるのが好ましい。また、その下限は５質量％であることが好ましい。また、ベース塗料の固形分濃度は、下限１５質量％上限６０質量％の範囲が好ましい。 The upper limit of the pigment concentration (PWC) with respect to the solid content of the base paint is preferably 65% by mass. Moreover, it is preferable that the minimum is 5 mass%. Further, the solid content concentration of the base coating is preferably in the range of a lower limit of 15% by mass and an upper limit of 60% by mass.
　ベース塗料の塗布方法として、具体的には、エアー静電スプレーまたは回転霧化式静電塗装機による多ステージ塗装、好ましくは２ステージ塗装を挙げることができる。この塗布方法を行なうことによって、意匠性を高めることができる。又は、ベース塗料の塗布方法として、エアー静電スプレーと回転霧化式の静電塗装機とを組合せた塗装方法が挙げられる。上塗りベース塗膜の乾燥膜厚は、１コートにつき５～５０μｍが好ましく、１０～３０μｍがより好ましい。 Specific examples of the method of applying the base paint include multi-stage coating, preferably two-stage coating using an air electrostatic spray or a rotary atomizing electrostatic coater. By performing this coating method, the designability can be improved. Or the coating method which combined the air electrostatic spray and the rotary atomization type electrostatic coating machine as an application method of a base coating material is mentioned. The dry film thickness of the topcoat base coating film is preferably 5 to 50 μm per coat, and more preferably 10 to 30 μm.
　得られた未硬化のベース塗膜はプレヒートを行ってもよい。ベース塗料を塗布した後にプレヒートを行って未硬化のベース塗膜を形成することによって、最終的に、より良好な仕上り外観を有する複層塗膜を得ることができる。なお本発明において「未硬化」とは、完全に硬化していない状態をいい、塗布後、プレヒートが行なわれた塗膜の状態も含むものである。「プレヒート」は、加熱硬化（焼付け）処理で用いられる温度より低い温度である室温～１００℃で、１～１０分間放置又は加熱することにより、行なうことができる。 The obtained uncured base coating film may be preheated. By applying pre-heating after applying the base coating material to form an uncured base coating film, a multilayer coating film having a better finished appearance can be finally obtained. In the present invention, “uncured” refers to a state where the film is not completely cured, and includes a state of a coating film that has been preheated after coating. “Preheating” can be performed by standing or heating at room temperature to 100 ° C., which is lower than the temperature used in the heat curing (baking) treatment, for 1 to 10 minutes.
　上記工程（１）を行うことにより得られる未硬化のベース塗膜は、Ｌ値が２５度反射において７０～１０５であり、かつ、７５度反射において２０～５０である。
　本発明においては、Ｌ値が当該範囲内である未硬化ベース塗膜を形成した後に、上記未硬化ベース塗膜上に、後述するクリヤー塗料により未硬化クリヤー塗膜を形成し、加熱硬化することにより、明度が高く、色戻りの発現を抑えベース塗膜の本来有する高い意匠性を維持する複層塗膜を形成することができる。
　なお、本発明において、Ｌ値（明度）は、Ｌａｂ表色系（ハンター表色系）による、被測定物の色を表すのに用いられる指標であり、その数値が増加するに従って被測定物の白色度が増すことを意味し、その数値が低下するに従って被測定物の黒色度が増すことを意味する。本発明において、２５度反射におけるＬ値は、図１に示すように、測定対象である塗膜に対して垂直位置にある受光部を０度とした場合に、２５度となる角度で光源から光を照射して受光される光のＬ値を意味する。また、同様に、７５度反射におけるＬ値は、受光部から７５度の角度で光源から光を照射して受光される光のＬ値を意味する。Ｌ値は、例えば、変角色差計（例えば、「ＣＭ－５１２ｍ３」ミノルタ社製）等を用いて測定することで決定することができる。 The uncured base coating film obtained by performing the step (1) has an L value of 70 to 105 at 25 degrees reflection and 20 to 50 at 75 degrees reflection.
In the present invention, after forming an uncured base coating film having an L value within the range, an uncured clear coating film is formed on the uncured base coating film by a clear coating described later, and is cured by heating. Thus, it is possible to form a multilayer coating film that has high brightness, suppresses color reversion, and maintains the high design properties inherent in the base coating film.
In the present invention, the L value (brightness) is an index used to represent the color of the object to be measured by the Lab color system (hunter color system), and the value of the object to be measured increases as the value increases. It means that the whiteness increases, and the blackness of the object to be measured increases as the numerical value decreases. In the present invention, as shown in FIG. 1, the L value in the 25-degree reflection is from the light source at an angle of 25 degrees when the light-receiving part at a position perpendicular to the coating film to be measured is 0 degrees. It means L value of light received by irradiating light. Similarly, the L value in 75-degree reflection means the L value of light received by irradiating light from the light source at an angle of 75 degrees from the light receiving unit. The L value can be determined, for example, by measuring using a variable angle color difference meter (for example, “CM-512m3” manufactured by Minolta).
　上記工程（１）で未硬化ベース塗膜を形成した後、上記未硬化ベース塗膜上に、クリヤー塗料を塗布して未硬化クリヤー塗膜を形成する。
　上記クリヤー塗料組成物は、エステル部が炭素数９～１５の直鎖炭化水素基である長鎖（メタ）アクリル酸エステルモノマー、カルボキシル基含有（メタ）アクリルモノマー、及び、水酸基含有（メタ）アクリルモノマーを含んだモノマー混合物から得られ、数平均分子量が４０００～６０００、固形分酸価が１～５ｍｇＫＯＨ／ｇであるアクリル樹脂と、ポリイソシアネート化合物と、架橋樹脂粒子とを含むものである。 After forming an uncured base coating film in the step (1), a clear coating is applied on the uncured base coating film to form an uncured clear coating film.
The clear coating composition includes a long-chain (meth) acrylic acid ester monomer whose ester part is a linear hydrocarbon group having 9 to 15 carbon atoms, a carboxyl group-containing (meth) acrylic monomer, and a hydroxyl group-containing (meth) acrylic. It is obtained from a monomer mixture containing monomers and contains an acrylic resin having a number average molecular weight of 4000 to 6000 and a solid content acid value of 1 to 5 mgKOH / g, a polyisocyanate compound, and crosslinked resin particles.
　上記アクリル樹脂は、エステル部が炭素数９～１５の直鎖炭化水素基である長鎖（メタ）アクリル酸エステルモノマー、カルボキシル基含有（メタ）アクリルモノマー、及び、水酸基含有（メタ）アクリルモノマーを含むモノマー混合物から得られるものである。 The acrylic resin comprises a long-chain (meth) acrylic acid ester monomer whose ester part is a linear hydrocarbon group having 9 to 15 carbon atoms, a carboxyl group-containing (meth) acrylic monomer, and a hydroxyl group-containing (meth) acrylic monomer. It is obtained from the monomer mixture containing.
　上記長鎖（メタ）アクリル酸エステルモノマーは、例えば、下記一般式（Ａ） The long chain (meth) acrylic acid ester monomer is, for example, the following general formula (A)
Figure JPOXMLDOC01-appb-C000001
Figure JPOXMLDOC01-appb-C000001
　（式中、Ｒは水素又はメチル基、ｎは８～１４の自然数を表す）で表されるものである。 (Wherein R represents hydrogen or a methyl group, and n represents a natural number of 8 to 14).
　上記長鎖（メタ）アクリル酸エステルモノマーとしては、エステル部が炭素数９～１５の直鎖炭化水素基であれば、特に限定されるものではなく、例えば、（メタ）アクリル酸ラウリル、（メタ）アクリル酸トリデシル、（メタ）アクリル酸デシル、（メタ）アクリル酸ノニルを挙げることができる。これらは、１種のみを用いてもよく、２種以上を併用してもよい。 The long-chain (meth) acrylate monomer is not particularly limited as long as the ester portion is a straight chain hydrocarbon group having 9 to 15 carbon atoms. For example, lauryl (meth) acrylate, (meth) ) Tridecyl acrylate, decyl (meth) acrylate, and nonyl (meth) acrylate. These may use only 1 type and may use 2 or more types together.
　上記モノマー混合物中の長鎖（メタ）アクリル酸エステルモノマーの含有量は、モノマー固形分全量に対して１０～１５質量％である。
　１０質量％未満であると、クリヤー塗膜のベース塗膜側への影響を充分に抑制することが困難である。一方、１５質量％を超えると、再塗装の際の密着性が低下するおそれがある。 The content of the long-chain (meth) acrylate monomer in the monomer mixture is 10 to 15% by mass with respect to the total amount of monomer solids.
If it is less than 10% by mass, it is difficult to sufficiently suppress the influence of the clear coating film on the base coating film side. On the other hand, when it exceeds 15 mass%, there exists a possibility that the adhesiveness in the case of repainting may fall.
　上記カルボキシル基含有（メタ）アクリルモノマーとしては、特に限定されるものではなく、例えば、アクリル酸、メタクリル酸、アクリル酸二量体、クロトン酸、イソクロトン酸、マレイン酸を挙げることができる。これらは、１種のみを用いてもよく、２種以上を併用してもよい。なかでも、アクリル酸、メタクリル酸が好ましい。
　カルボキシル基含有（メタ）アクリルモノマーを用いることにより、優れた意匠性の塗膜を形成することができる。このような効果は、カルボキシル基の会合によって上記アクリル樹脂の見かけの分子量を高めることができるため、上記アクリル樹脂のベース塗膜への浸透を防止することができるからであると推測される。 The carboxyl group-containing (meth) acrylic monomer is not particularly limited, and examples thereof include acrylic acid, methacrylic acid, acrylic acid dimer, crotonic acid, isocrotonic acid, and maleic acid. These may use only 1 type and may use 2 or more types together. Of these, acrylic acid and methacrylic acid are preferable.
By using a carboxyl group-containing (meth) acrylic monomer, a coating film having excellent design properties can be formed. Such an effect is presumed to be because the apparent molecular weight of the acrylic resin can be increased by the association of carboxyl groups, and thus the penetration of the acrylic resin into the base coating film can be prevented.
　上記水酸基含有（メタ）アクリルモノマーは、特に限定されるものではなく、例えば、（メタ）アクリル酸ヒドロキシエチル、（メタ）アクリル酸ヒドロキシプロピル、（メタ）アクリル酸ヒドロキシブチル、アリルアルコール、メタクリルアルコール、（メタ）アクリル酸ヒドロキシエチルとε－カプロラクトンとの付加物等を挙げることができる。これらは、１種のみを用いてもよく、２種以上を併用してもよい。 The hydroxyl group-containing (meth) acrylic monomer is not particularly limited. For example, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, allyl alcohol, methacryl alcohol, Examples include adducts of hydroxyethyl (meth) acrylate and ε-caprolactone. These may use only 1 type and may use 2 or more types together.
　上述した長鎖（メタ）アクリル酸エステルモノマー、カルボキシル基含有（メタ）アクリルモノマー及び水酸基含有（メタ）アクリルモノマーを含んだモノマー混合物から、上記アクリル樹脂を得ることができる。また、上記モノマー混合物は、その他の不飽和モノマーを含有してもよい。 The above-mentioned acrylic resin can be obtained from the monomer mixture containing the long-chain (meth) acrylic acid ester monomer, the carboxyl group-containing (meth) acrylic monomer and the hydroxyl group-containing (meth) acrylic monomer. The monomer mixture may contain other unsaturated monomers.
　上記その他の不飽和モノマーとしては、例えば、（メタ）アクリル酸エステルとして、（メタ）アクリル酸メチル、（メタ）アクリル酸エチル、（メタ）アクリル酸ｉ－プロピル、（メタ）アクリル酸ｎ－ブチル、（メタ）アクリル酸ｉ－ブチル、（メタ）アクリル酸ｔ－ブチル、（メタ）アクリル酸２－エチルヘキシル等のエステル部の炭素数が１～８の（メタ）アクリル酸アルキルエステル；（メタ）アクリル酸フェニル、（メタ）アクリル酸シクロヘキシル等の（メタ）アクリル酸環状炭化水素エステル；（メタ）アクリル酸イソボロニル；（ポリ）エチレングリコールモノ（メタ）アクリレート、重合度２～１０のポリエチレングリコールモノ（メタ）アクリレート等の（メタ）アクリル酸ポリアルキレングリコールエステル；及び、炭素数１～３のアルコキシアルキル（メタ）アクリレート等のほか、（メタ）アクリルアミド；スチレン、α－メチルスチレン、酢酸ビニル、プロピオン酸ビニル、安息香酸ビニル、ビニルトルエン、アクリロニトリル等のビニル化合物；並びに、クロトン酸エステル類；マレイン酸ジエステル類、イタコン酸ジエステル類等の不飽和二塩基酸のジエステルを挙げることができる。上記その他の不飽和モノマーは、それぞれ単独で使用してもよく、２種以上を併用してもよい。 Examples of the other unsaturated monomer include, for example, (meth) acrylic acid ester, methyl (meth) acrylate, ethyl (meth) acrylate, i-propyl (meth) acrylate, and n-butyl (meth) acrylate. (Meth) acrylic acid alkyl esters having 1 to 8 carbon atoms in the ester moiety such as i-butyl (meth) acrylate, t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate; (Meth) acrylic acid cyclic hydrocarbon esters such as phenyl acrylate, cyclohexyl (meth) acrylate; (meth) acrylate isobornyl; (poly) ethylene glycol mono (meth) acrylate, polyethylene glycol mono ( (Meth) acrylic acid polyalkylene glycol esters such as (meth) acrylate; and In addition to alkoxyalkyl (meth) acrylate having 1 to 3 carbon atoms, (meth) acrylamide; vinyl compounds such as styrene, α-methylstyrene, vinyl acetate, vinyl propionate, vinyl benzoate, vinyltoluene, acrylonitrile; And diesters of unsaturated dibasic acids such as maleic acid diesters and itaconic acid diesters. The other unsaturated monomers may be used alone or in combination of two or more.
　上記アクリル樹脂を得るための重合方法は、特に限定されるものではなく、溶液重合、分散重合、乳化重合等の公知の方法を使用することができる。 The polymerization method for obtaining the acrylic resin is not particularly limited, and known methods such as solution polymerization, dispersion polymerization, and emulsion polymerization can be used.
　上記アクリル樹脂は、数平均分子量（Ｍｎ）が４０００～６０００である。数平均分子量（Ｍｎ）が４０００未満であると、塗料の硬化性が充分ではなく、６０００を超えると、粘度が高くなり、高固形分の塗料組成物になりにくい場合がある。
　なお、本明細書において、数平均分子量（Ｍｎ）は、ＧＰＣ（ゲルパーミエーションクロマトグラフィー）で測定したポリスチレン換算の数平均分子量である。 The acrylic resin has a number average molecular weight (Mn) of 4000 to 6000. When the number average molecular weight (Mn) is less than 4,000, the curability of the coating is not sufficient, and when it exceeds 6000, the viscosity becomes high and it may be difficult to form a coating composition having a high solid content.
In addition, in this specification, a number average molecular weight (Mn) is a number average molecular weight of polystyrene conversion measured by GPC (gel permeation chromatography).
　上記アクリル樹脂は、固形分酸価が１～５ｍｇＫＯＨ／ｇであることが好ましい。
固形分酸価を上記範囲内とすることにより、カルボキシル基の会合によって見かけの分子量を高めることができるため、上記アクリル樹脂のベース塗膜への浸透を防止することができ、優れた意匠性の塗膜を形成することができるからである。
固形分酸価が１ｍｇＫＯＨ／ｇ未満であると、会合する点が少なくなり、見かけの分子量を上昇させることが困難になるため、優れた意匠性を有する塗膜の形成が困難になるおそれがある。固形分酸価が５ｍｇＫＯＨ／ｇを超えると、粘度が高くなりすぎ、高固形分の塗料組成物になりにくい場合がある。 The acrylic resin preferably has a solid content acid value of 1 to 5 mgKOH / g.
By making the solid content acid value within the above range, the apparent molecular weight can be increased by the association of carboxyl groups, so that the penetration of the acrylic resin into the base coating film can be prevented, and the excellent design properties It is because a coating film can be formed.
If the solid content acid value is less than 1 mg KOH / g, the number of points of association decreases and it becomes difficult to increase the apparent molecular weight, which may make it difficult to form a coating film having excellent design properties. . When the solid content acid value exceeds 5 mgKOH / g, the viscosity becomes too high and it may be difficult to obtain a coating composition having a high solid content.
　上記アクリル樹脂は、固形分水酸基価が５０～１４０ｍｇＫＯＨ／ｇであることが好ましい。固形分水酸基価が５０ｍｇＫＯＨ／ｇ未満であると、硬化性が低下するおそれがある。固形分水酸基価が１４０ｍｇＫＯＨ／ｇを超えると、塗膜の耐水性が低下するおそれがある。固形分水酸基価は８０～１４０ｍｇＫＯＨ／ｇであることがより好ましい。なお、上記固形分酸価及び水酸基価は、原料モノマーの配合比によって調整することができる。 The above acrylic resin preferably has a solid content hydroxyl value of 50 to 140 mgKOH / g. There exists a possibility that sclerosis | hardenability may fall that solid content hydroxyl value is less than 50 mgKOH / g. When the solid content hydroxyl value exceeds 140 mgKOH / g, the water resistance of the coating film may decrease. The solid content hydroxyl value is more preferably 80 to 140 mgKOH / g. In addition, the said solid content acid value and hydroxyl value can be adjusted with the compounding ratio of a raw material monomer.
　上記アクリル樹脂は、ガラス転移点温度（Ｔｇ値）が－３０～５０℃であることが好ましい。Ｔｇ値が－３０℃未満であると、塗膜硬度が低下するおそれがあり、また、塗料液温度の変動によって形成される塗膜の膜厚にばらつきが生じるおそれがある。一方、５０℃を超えると、粘度が高くなりすぎ、高固形分の塗料組成物になりにくい場合がある。上記アクリル樹脂のＴｇ値は、－１０～３０℃であることがより好ましい。 The above acrylic resin preferably has a glass transition temperature (Tg value) of −30 to 50 ° C. If the Tg value is less than −30 ° C., the coating film hardness may decrease, and the coating film thickness may vary due to variations in the coating liquid temperature. On the other hand, when it exceeds 50 ° C., the viscosity becomes too high and it may be difficult to form a coating composition having a high solid content. The acrylic resin preferably has a Tg value of −10 to 30 ° C.
　上記アクリル樹脂のＴｇ値は、例えば、構成するモノマー又はホモポリマーの既知のＴｇ値と組成比とから計算することによって算出することができる。 The Tg value of the acrylic resin can be calculated, for example, by calculating from the known Tg value and the composition ratio of the constituent monomer or homopolymer.
　上記クリヤー塗料組成物は、ポリイソシアネート化合物を含むものである。
　上記ポリイソシアネート化合物としては、２以上のイソシアネート基を有する化合物であれば、特に限定されず、例えば、トリメチレンジイソシアネート、テトラメチレンジイソシアネート、ペンタメチレンジイソシアネート、ヘキサメチレンジイソシアネート（ＨＭＤＩ）、トリメチルヘキサメチレンジイソシアネート等の脂肪族イソシアネート、１，３－シクロペンタンジイソシアネート、１，４－シクロヘキサンジイソシアネート、１，２－シクロヘキサンジイソシアネート等の脂肪族環式イソシアネート、キシリレンジイソシアネート（ＸＤＩ）、２，４－トリレンジイソシアネート（ＴＤＩ）、２，６－トリレンジイソシアネート等の芳香族イソシアネート、イソホロンジイソシアネート（ＩＰＤＩ）、ノルボルナンジイソシアネートメチル等の脂環族イソシアネート、これらのヌレート体、ビューレット体、アダクト体等の多量体及び混合物等を挙げることができる。なかでも、耐候性の点から、ヌレート体が好ましい。 The clear coating composition contains a polyisocyanate compound.
The polyisocyanate compound is not particularly limited as long as it is a compound having two or more isocyanate groups. For example, trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate (HMDI), trimethylhexamethylene diisocyanate and the like. Aliphatic isocyanates such as 1,3-cyclopentane diisocyanate, 1,4-cyclohexane diisocyanate, 1,2-cyclohexane diisocyanate, and the like, xylylene diisocyanate (XDI), 2,4-tolylene diisocyanate (TDI) ), Aromatic isocyanates such as 2,6-tolylene diisocyanate, isophorone diisocyanate (IPDI), norbornane diisocyanate Alicyclic isocyanates such Tomechiru, these isocyanurate body, can be given burette body, multimers of the adduct and the like and mixtures. Among these, a nurate body is preferable from the viewpoint of weather resistance.
　上記ポリイソシアネート化合物が有するＮＣＯ基と、上記アクリル樹脂が有するカルボキシル基及び／又は水酸基との官能基量比は、１／１．５～１．５／１であることが好ましい。上記官能基量比が１／１．５未満であると、硬化性が不十分となり、１．５／１を超えると、硬化膜が固くなりすぎ脆くなる。上記官能基量比は、１．４／１～１／１．４であることがより好ましい。 The functional group amount ratio between the NCO group of the polyisocyanate compound and the carboxyl group and / or hydroxyl group of the acrylic resin is preferably 1 / 1.5 to 1.5 / 1. When the functional group amount ratio is less than 1 / 1.5, curability becomes insufficient, and when it exceeds 1.5 / 1, the cured film becomes too hard and brittle. The functional group amount ratio is more preferably 1.4 / 1 to 1 / 1.4.
　上記架橋樹脂粒子は、レオロジーコントロール効果を有し、塗装時や加熱硬化時のタレ止めに高い効果を発揮すると同時に、塗膜のＬ値の安定化に寄与する。このような架橋樹脂粒子としては特に限定されず、当業者によって自明のものから適宜選択することができる。
　上記架橋樹脂粒子の含有量は、クリヤー塗料組成物の樹脂固形分に対して０．０１～１０質量％であることが好ましく、０．１～１０質量％であることがより好ましく、０．５～５質量％であることがさらに好ましい。上記含有量が０．０１質量％を下回る場合は、レオロジーコントロール効果が得られないおそれがあり、また、１０質量％を超える場合は、得られる塗膜の平滑性に悪影響を及ぼすおそれがある。 The crosslinked resin particles have a rheology control effect, exhibit a high effect on sagging at the time of coating and heat curing, and at the same time contribute to stabilization of the L value of the coating film. Such crosslinked resin particles are not particularly limited and can be appropriately selected from those obvious to those skilled in the art.
The content of the crosslinked resin particles is preferably 0.01 to 10% by mass, more preferably 0.1 to 10% by mass, based on the resin solid content of the clear coating composition. More preferably, it is ˜5% by mass. When the content is less than 0.01% by mass, the rheology control effect may not be obtained. When the content exceeds 10% by mass, the smoothness of the resulting coating film may be adversely affected.
　上記クリヤー塗料組成物中には、紫外線吸収剤、ヒンダードアミン光安定剤、酸化防止剤、表面調整剤等を配合しても良い。 In the clear coating composition, an ultraviolet absorber, a hindered amine light stabilizer, an antioxidant, a surface conditioner, and the like may be blended.
　上記クリヤー塗料組成物は、上記アクリル樹脂を含有する組成物と、上記ポリイソシアネート化合物との２液硬化型の塗料組成物であることが好ましい。 The clear coating composition is preferably a two-component curable coating composition comprising the acrylic resin-containing composition and the polyisocyanate compound.
　上記クリヤー塗料組成物を塗装する方法としては、具体的には、マイクロマイクロベル、マイクロベルと呼ばれる回転霧化式の静電塗装機による塗装方法を挙げることができる。上記クリヤー塗料組成物が２液硬化型である場合には、両者を使用前に混合した後に、上記方法により上記クリヤー塗料組成物を塗装することができる。上記クリヤー塗料組成物の塗装膜厚は、乾燥膜厚で下限２０μｍ、上限６０μｍの範囲内であることが好ましい。 Specific examples of the method for applying the clear coating composition include micro-microbell and a coating method using a rotary atomizing electrostatic coater called microbell. In the case where the clear coating composition is a two-component curable type, the clear coating composition can be applied by the above method after mixing them before use. The coating film thickness of the clear coating composition is preferably in the range of a lower limit of 20 μm and an upper limit of 60 μm in terms of dry film thickness.
　上記の方法によって形成されたベース未硬化塗膜及びクリヤー未硬化塗膜は、同時に加熱されて硬化し、複層塗膜を形成する。上記加熱温度は、下限１００℃、上限１８０℃の範囲内で行うことが好ましい。また、下限１２０℃、上限１６０℃であることがより好ましい。加熱硬化時間は硬化温度等によって変化するが、上記加熱硬化温度で行う場合は、１０～３０分であることが適当である。 The base uncured coating film and the clear uncured coating film formed by the above method are simultaneously heated and cured to form a multilayer coating film. The heating temperature is preferably performed within a range of a lower limit of 100 ° C. and an upper limit of 180 ° C. More preferably, the lower limit is 120 ° C and the upper limit is 160 ° C. The heat-curing time varies depending on the curing temperature or the like, but when it is carried out at the above-mentioned heat-curing temperature, it is appropriate that it is 10-30 minutes.
　このようにして得られる複層塗膜は、２５度反射による該複層塗膜のＬ値から上記未硬化ベース塗膜のＬ値を差し引いて求められる値であるΔＬ値が、－０．３～０．１５であり、７５度反射による該複層塗膜のＬ値から上記未硬化ベース塗膜のＬ値を差し引いて求められる値であるΔＬ値が、－０．２～０．４である。ΔＬ値が上記範囲内である複層塗膜は、色戻りの発現を抑えた意匠性の高い外観を有するものである。 The multi-layer coating film thus obtained has a ΔL value which is a value obtained by subtracting the L value of the uncured base coating film from the L value of the multi-layer coating film by 25-degree reflection, and is −0.3. The ΔL value obtained by subtracting the L value of the uncured base coating film from the L value of the multilayer coating film by 75-degree reflection is −0.2 to 0.4. is there. A multilayer coating film having a ΔL value within the above range has an appearance with a high design property that suppresses the occurrence of color reversion.
　上記複層塗膜の膜厚は、下限３０μｍ、上限８０μｍの範囲内であることが好ましい。上記方法によって得られた複層塗膜は、耐擦り傷性及び耐酸性及び耐溶剤性等の塗膜物性に優れており、意匠性の高いものである。 The film thickness of the multilayer coating film is preferably in the range of a lower limit of 30 μm and an upper limit of 80 μm. The multilayer coating film obtained by the above method is excellent in coating film properties such as scratch resistance, acid resistance and solvent resistance, and has high design properties.
　上記基材としては、例えば金属成型品、プラスチック成型品、発泡体等に用いることができるが、自動車用の複層塗膜を形成させる基材としては、鉄、アルミニウム、亜鉛系基材及びこれらの合金等の金属成型品やプラスチック成型品等を挙げることができる。カチオン電着塗装可能な金属成型品に対して適用することが好ましい。上記基材は、表面が化成処理されていることが好ましい。更に、基材は、電着塗膜が形成されていてもよい。上記電着塗料としては、上記カチオン型及びアニオン型を使用することができるが、防食性の観点から、カチオン型電着塗料であることが好ましい。 As the above-mentioned base material, it can be used for, for example, metal molded products, plastic molded products, foams, etc., but as base materials for forming a multilayer coating film for automobiles, iron, aluminum, zinc-based substrates and these Examples thereof include metal molded products such as alloys, plastic molded products, and the like. It is preferable to apply to metal molded products that can be subjected to cationic electrodeposition coating. The base material is preferably subjected to a chemical conversion treatment on the surface. Furthermore, an electrodeposition coating film may be formed on the substrate. As the electrodeposition paint, the cation type and the anion type can be used. From the viewpoint of anticorrosion, a cation type electrodeposition paint is preferable.
　また、本発明の複層塗膜形成方法においては、工程（１）以前に、上記基材に中塗り塗料を塗布して中塗り塗膜を得る工程（Ｐ）を含むことが好ましい。
　上記（Ｐ）の工程で使用可能な中塗り塗料としては、通常用いられている中塗り塗料を用いることができる。 Moreover, in the multilayer coating-film formation method of this invention, it is preferable to include the process (P) of apply | coating an intermediate coating material to the said base material and obtaining an intermediate coating film before a process (1).
As the intermediate coating material that can be used in the step (P), a conventionally used intermediate coating material can be used.
　上記中塗り塗料としては、水性塗料であってもよく、また溶剤型塗料であってもよい。これらの塗料の成分としては、中塗り樹脂成分、着色顔料、体質顔料、そして水性溶媒及び／又は有機溶媒が挙げられる。中塗り樹脂成分は、中塗り塗料樹脂及び、必要に応じて中塗り硬化剤から構成される。上記中塗り塗料に含まれる中塗り樹脂成分、中塗り硬化剤、着色顔料、体質顔料、各種添加剤及び溶媒としては、上述したベース塗料に関して記載したものをいずれも使用することができる。 The intermediate coating may be a water-based paint or a solvent-type paint. Examples of the components of these paints include intermediate coating resin components, colored pigments, extender pigments, and aqueous and / or organic solvents. The intermediate coating resin component is composed of an intermediate coating resin and, if necessary, an intermediate coating curing agent. As the intermediate coating resin component, intermediate coating curing agent, coloring pigment, extender pigment, various additives and solvent contained in the intermediate coating, any of those described for the above-mentioned base coating can be used.
　中塗り塗料の塗料固形分に対する顔料の濃度（ＰＷＣ）は、下限３０質量％上限６５質量％の範囲であるのが好ましい。上記上限は５０質量％であることがより好ましい。また、中塗り塗料の固形分濃度は、下限３５質量％上限６５質量％の範囲が好ましい。 The pigment concentration (PWC) with respect to the solid content of the intermediate coating is preferably in the range of a lower limit of 30% by mass and an upper limit of 65% by mass. The upper limit is more preferably 50% by mass. The solid content concentration of the intermediate coating is preferably in the range of 35% by mass to 65% by mass.
　中塗り塗料の塗布方法として、スプレー法、ロールコーター法などを用いたものが挙げられる。具体的には、「リアクトガン」といわれるエアー静電スプレーを用いたり、「マイクロ・マイクロ（μμ）ベル」、「マイクロ（μ）ベル」、「メタベル」などといわれる回転霧化式の静電塗装機を用いたりして塗装するのが好ましい。この中で、回転霧化式の静電塗装機を用いて塗装するのが、特に好ましい。中塗り塗膜の好ましい乾燥膜厚は５～８０μｍであり、１０～５０μｍがより好ましい。 中 Examples of methods for applying the intermediate coating include those using a spray method, a roll coater method, and the like. Specifically, it uses air electrostatic sprays called “react guns” or rotary atomizing electrostatic coatings called “micro-micro (μμ) bell”, “micro (μ) bell”, “metabell”, etc. It is preferable to paint using a machine. Among these, it is particularly preferable to perform the coating using a rotary atomizing electrostatic coating machine. A preferable dry film thickness of the intermediate coating film is 5 to 80 μm, and more preferably 10 to 50 μm.
　こうして形成された未硬化の中塗り塗膜を、１２０～１６０℃で所定時間焼付けて硬化させて、硬化した中塗り塗膜を得ることができる。こうして得られた硬化した中塗り塗膜の上に、上記ベース塗料及び上記クリヤー塗料を塗布することができる。 The uncured intermediate coating film thus formed can be baked and cured at 120 to 160 ° C. for a predetermined time to obtain a cured intermediate coating film. The base paint and the clear paint can be applied on the cured intermediate coating film thus obtained.
　また、得られた未硬化の中塗り塗膜上に上記ベース塗料及びクリヤー塗料を、ウェットオンウェットで塗布して、未硬化の中塗り塗膜上に、未硬化のベース塗膜及びクリヤー塗膜を順次形成することが好ましい。このようにウェットオンウェットでベース塗料及びクリヤー塗料を塗布する場合、中塗り塗料を塗布した後にプレヒートを行って未硬化の中塗り塗膜を形成することによって、最終的に、より良好な仕上り外観を有する複層塗膜を得ることができる。 In addition, the above base coating and clear coating are applied wet-on-wet on the obtained uncured intermediate coating, and the uncured base coating and clear coating are applied on the uncured intermediate coating. Are preferably formed sequentially. In this way, when applying base paint and clear paint in wet-on-wet, by applying pre-heating after applying the intermediate coating, an uncured intermediate coating film is formed, and finally a better finished appearance Can be obtained.
　以下に実施例を挙げて本発明を更に詳しく説明するが、本発明はこれら実施例のみに限定されるものではない。また実施例中、「部」は特に断りのない限り「質量部」を意味する。 Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. In the examples, “parts” means “parts by mass” unless otherwise specified.
　［合成例ａ］
　温度計、撹拌羽根、窒素導入管、冷却コンデンサー及び滴下ロートを備えた反応容器に、プロピレングリコールモノメチルエーテルアセテート４４８部を加え、窒素雰囲気下１２０℃に加温した。その容器に、滴下ロートを用いてプロピレングリコールモノメチルエーテルアセテート１００部、ｔｅｒｔ－ブチルパーオキシ２－エチルヘキサノエート１０５部、並びに、モノマー配合としてスチレン２００部、アクリル酸－ｎ－ブチル６７部、メタクリル酸アルキル１００部、メタクリル酸イソボロニル２７０部、アクリル酸－４－ヒドロキシブチル３６０部及びメタクリル酸３部からなるモノマー混合液を３時間かけて等速滴下した。その後１２０℃で０．５時間保持し、後滴下溶液として５０部のプロピレングリコールモノメチルエーテルアセテートに溶解したｔｅｒｔ－ブチルパーオキシ２－エチルヘキサノエート１０部を３０分で等速滴下した。更に、１２０℃で１時間加温を続けた。
　その結果、計算Ｔｇ５．３℃、固形分酸価２ｍｇＫＯＨ／ｇ、水酸基価１４０ｍｇＫＯＨ／ｇ、ＧＰＣを用いて得られた標準ポリスチレン換算で数平均分子量（Ｍｎ）４６００、重量平均分子量（Ｍｗ）１１３００、樹脂固形分は６２．５％のアクリル樹脂Ａを得た。なお、メタクリル酸アルキルとしては、メタクリル酸ラウリル／メタクリル酸トリデシルの混合比（質量基準）が４／６であるアクリエステルＳＬ（三菱レイヨン社製）を用いた。 [Synthesis Example a]
448 parts of propylene glycol monomethyl ether acetate was added to a reaction vessel equipped with a thermometer, a stirring blade, a nitrogen introducing tube, a cooling condenser and a dropping funnel, and heated to 120 ° C. in a nitrogen atmosphere. In the container, using a dropping funnel, 100 parts of propylene glycol monomethyl ether acetate, 105 parts of tert-butylperoxy 2-ethylhexanoate, 200 parts of styrene as a monomer, 67 parts of acrylic acid-n-butyl, methacrylic A monomer mixed solution composed of 100 parts of alkyl acid, 270 parts of isobornyl methacrylate, 360 parts of 4-hydroxybutyl acrylate and 3 parts of methacrylic acid was added dropwise at a constant rate over 3 hours. Thereafter, the mixture was kept at 120 ° C. for 0.5 hour, and 10 parts of tert-butylperoxy 2-ethylhexanoate dissolved in 50 parts of propylene glycol monomethyl ether acetate was added dropwise at a constant rate over 30 minutes. Furthermore, heating was continued at 120 ° C. for 1 hour.
As a result, calculated Tg 5.3 ° C., solid content acid value 2 mgKOH / g, hydroxyl value 140 mgKOH / g, number average molecular weight (Mn) 4600, weight average molecular weight (Mw) 11300 in terms of standard polystyrene obtained using GPC, An acrylic resin A having a resin solid content of 62.5% was obtained. In addition, as alkyl methacrylate, acrylate ester SL (manufactured by Mitsubishi Rayon Co., Ltd.) having a mixing ratio (mass basis) of lauryl methacrylate / tridecyl methacrylate of 4/6 was used.
　［合成例ｂ、ｃ］
　表１に示すモノマー混合液および後滴下溶液を用いること以外は合成例ａと同様にして、表１に示すアクリル樹脂Ｂ、Ｃを得た。各樹脂の計算Ｔｇ、固形分酸価、水酸基価、数平均分子量及び樹脂固形分を示した。 [Synthesis Examples b and c]
Acrylic resins B and C shown in Table 1 were obtained in the same manner as in Synthesis Example a except that the monomer mixture and the post-drop solution shown in Table 1 were used. The calculated Tg, solid content acid value, hydroxyl value, number average molecular weight and resin solid content of each resin are shown.
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
　＊）メタクリル酸アルキル：メタクリル酸ラウリル／メタクリル酸トリデシルが混合比４／６（質量基準）であるアクリエステルＳＬ（三菱レイヨン社製） *) Alkyl methacrylate: Acryester SL (Mitsubishi Rayon Co., Ltd.) in which lauryl methacrylate / tridecyl methacrylate has a mixing ratio of 4/6 (mass basis)
　［合成例ｅ］架橋樹脂粒子の合成
　温度計、撹拌羽根、窒素導入管、冷却コンデンサー及びデカンターを備えたガラス容器に、ビスヒドロキシエチルタウリン２１３部、ネオペンチルグリコール２０８部、無水フタル酸２９６部、アゼライン酸３７６部及びキシレン３０部を仕込み昇温した。反応により生成した水はキシレンと共沸させて除去した。還流開始より約３時間かけて反応液温を２１０℃とし、カルボン酸相当の固形分酸価が１３５ｍｇＫＯＨ／ｇになるまで攪拌と脱水を継続して反応させた。液温を１４０℃まで冷却した後、「カージュラＥ１０」（シェル社製のバーサチック酸グルシジルエステル）５００部を３０分で滴下し、その後２時間攪拌を継続して反応を終了した。固形分酸価５５ｍｇＫＯＨ／ｇ、水酸基価９１ｍｇＫＯＨ／g及び数平均分子量１２５０の両性イオン基含有ポリエステル樹脂を得た。
　この両性イオン基含有ポリエステル樹脂１０部、脱イオン水１４０部、ジメチルエタノールアミン１部、スチレン５０部及びエチレングリコールジメタクリレート５０部をステンレス製ビーカー中で激しく攪拌することによりモノマー懸濁液を調製した。また、アゾビスシアノ吉相酸０．５部、脱イオン水４０部及びジメチルエタノールアミン０．３２部を混合することにより開始剤水溶液を調製した。
　温度計、撹拌羽根、窒素導入管、冷却コンデンサー及び滴下ロートを備えたガラス容器に、上記両性イオン基含有ポリエステル樹脂５部、脱イオン水２８０部及びジメチルエタノールアミン０．５部を仕込み、８０℃に昇温した。ここに上記モノマー懸濁液２５１部と開始剤水溶液４０．８２部とを同時に６０分かけて滴下し、更に６０分反応を継続した後、反応を終了させた。動的光散乱法で測定した粒子径５５ｎｍを有する架橋樹脂粒子を含んだエマルジョンが得られた。このエマルジョンに酢酸ブチルを加え、減圧下で共沸蒸留により水を除去し、媒体を酢酸ブチルに置換して、樹脂固形分２０％の架橋樹脂粒子溶液を得た。 [Synthesis Example e] Synthesis of Crosslinked Resin Particles In a glass container equipped with a thermometer, stirring blade, nitrogen inlet tube, cooling condenser and decanter, 213 parts of bishydroxyethyl taurine, 208 parts of neopentyl glycol, 296 parts of phthalic anhydride, 376 parts of azelaic acid and 30 parts of xylene were charged and the temperature was raised. Water produced by the reaction was removed by azeotropy with xylene. The reaction liquid temperature was adjusted to 210 ° C. over about 3 hours from the start of refluxing, and stirring and dehydration were continued until the solid content acid value corresponding to carboxylic acid reached 135 mgKOH / g. After cooling the liquid temperature to 140 ° C., 500 parts of “Cardura E10” (Versic acid glycidyl ester manufactured by Shell) was dropped in 30 minutes, and then the stirring was continued for 2 hours to complete the reaction. An amphoteric ion group-containing polyester resin having a solid content acid value of 55 mgKOH / g, a hydroxyl value of 91 mgKOH / g and a number average molecular weight of 1250 was obtained.
A monomer suspension was prepared by vigorously stirring 10 parts of this zwitterionic group-containing polyester resin, 140 parts of deionized water, 1 part of dimethylethanolamine, 50 parts of styrene and 50 parts of ethylene glycol dimethacrylate in a stainless steel beaker. . In addition, an aqueous initiator solution was prepared by mixing 0.5 part of azobiscyanoyoshinoic acid, 40 parts of deionized water, and 0.32 part of dimethylethanolamine.
A glass container equipped with a thermometer, stirring blades, nitrogen inlet tube, cooling condenser and dropping funnel is charged with 5 parts of the above zwitterion group-containing polyester resin, 280 parts of deionized water and 0.5 part of dimethylethanolamine, and 80 ° C. The temperature was raised to. To this, 251 parts of the monomer suspension and 40.82 parts of the aqueous initiator solution were simultaneously added dropwise over 60 minutes, and the reaction was further continued for 60 minutes, and then the reaction was terminated. An emulsion containing crosslinked resin particles having a particle diameter of 55 nm measured by a dynamic light scattering method was obtained. Butyl acetate was added to this emulsion, water was removed by azeotropic distillation under reduced pressure, and the medium was replaced with butyl acetate to obtain a crosslinked resin particle solution having a resin solid content of 20%.
　［クリヤー塗料組成物Ａ～Ｄの製造］
　各々アクリル樹脂Ａ～Ｃを樹脂固形分で６８．６８部、住化バイエルウレタン社製スミジュールＮ３３００（イソシアヌレート型イソシアネート化合物）を３１．３２部、チヌビン９２８（チバ・スペシャリティ・ケミカルズ社製紫外線吸収剤）２部、チヌビン２９２（同社製光安定剤）１部、架橋樹脂粒子４部、及び、モダフロー（モンサント社製表面調整剤）０．１部を配合し、ディスパーで攪拌することによってクリヤー塗料組成物Ａ～Ｃを得た。また、クリヤー塗料組成物Ａの架橋樹脂粒子を含まなかったものをクリヤー塗料組成物Ｄとした。
　上記各クリヤー塗料組成物をプロピレングリコールモノメチルエーテルアセテート／３－エトキシプロピオン酸エチル＝１／２（質量比）からなるシンナーによってＮｏ．４フォードカップで２５秒／２０℃となるように希釈した。 [Production of Clear Coating Compositions A to D]
Each of the acrylic resins A to C is 68.68 parts in terms of resin solids, Sumidur N3300 (isocyanurate type isocyanate compound) manufactured by Sumika Bayer Urethane Co., Ltd., 31.32 parts, and Tinuvin 928 (UV manufactured by Ciba Specialty Chemicals) Agent) 2 parts, Tinuvin 292 (Company light stabilizer) 1 part, Cross-linked resin particles 4 parts, Modaflow (Monsanto surface conditioner) 0.1 part, blended with a disperser to clear the paint Compositions A to C were obtained. The clear coating composition A that did not contain the crosslinked resin particles was designated as clear coating composition D.
Each of the above clear coating compositions was subjected to No. 1 using a thinner composed of propylene glycol monomethyl ether acetate / 3-ethyl ethyl ethoxypropionate = 1/2 (mass ratio). Dilute to 25 seconds / 20 ° C. with 4 Ford cups.
　［実施例１、２、比較例１、２］
　リン酸処理鋼板に日本ペイント社製カチオン電着塗料「パワートップＵ－５０」及びグレー中塗り塗料「オルガＰ－３０」（いずれも商品名）を、それぞれ乾燥膜厚が２５μｍ及び４０μｍになるように塗装して加熱硬化させた試験板に、日本ペイント社製水性塗料「アクアレックスＡＲ－２０００」（商品名）の１Ｆ７（シルバー系）、４Ｐ７（ベージュ系）、４Ｒ３（ベージュ系）、１Ｄ２（グレー系）の各塗色を塗布した。
　その上にウェットオンウェットでクリヤー塗料組成物Ａ～Ｄを各々塗布して１４０℃で３０分間焼付け乾燥を行い、塗装方式として２コート１ベークの塗装試験板を作製した。
　なお、上記ベース塗料及びクリヤー塗料組成物による複層塗膜は、乾燥膜厚がそれぞれ１５μｍ及び４０μｍとなるように塗装した。なお、別途、上記試験板に上記シルバーメタリックベース塗料を乾燥膜厚が１５μｍとなるように塗布して、１４０℃で３０分間焼付け乾燥を行い、ベース単層塗膜の塗装試験板を作製した。 [Examples 1 and 2, Comparative Examples 1 and 2]
Cathode electrodeposition paint “Power Top U-50” and gray intermediate paint “Orga P-30” (both trade names) manufactured by Nippon Paint Co., Ltd. on the phosphoric acid-treated steel sheet so that the dry film thicknesses are 25 μm and 40 μm, respectively. 1F7 (silver-based), 4P7 (beige-based), 4R3 (beige-based), 1D2 (water-based paint “AQUAREX AR-2000” (trade name) manufactured by Nippon Paint Co., Ltd. Each coating color (gray) was applied.
Then, the clear coating compositions A to D were respectively applied wet-on-wet and baked and dried at 140 ° C. for 30 minutes to prepare a 2-coat 1-bake coating test plate.
In addition, the multilayer coating film by the said base coating material and clear coating composition was apply | coated so that the dry film thickness might be 15 micrometers and 40 micrometers, respectively. Separately, the silver metallic base paint was applied to the test plate so that the dry film thickness was 15 μm, and baked and dried at 140 ° C. for 30 minutes to produce a base single-layer coating test plate.
　［評価方法］
　上述した方法により得られた塗装試験板を用いて、下記（１）、（２）の方法で評価した。評価結果を表２に示す。 [Evaluation methods]
Evaluation was performed by the following methods (1) and (2) using the coating test plate obtained by the method described above. The evaluation results are shown in Table 2.
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003















　（１）Ｌ値
　対応するメタリックベース単層塗膜を基準とし、２コート１ベークにより得られたメタリック塗膜との色差を測定した。
　測定は、図１に模式的に示すとおり、ミノルタ社製ＣＭ－５１２ｍ３で行い、受光角２５°（ハイライト）、７５°（シェード）におけるＬ値を測定し、次式により、ΔＬ値を算出した。
　ΔＬ値＝（複層塗膜のＬ値）－（未硬化ベース単層塗膜のＬ値） (1) L value The color difference with the metallic coating film obtained by 2 coat 1 baking was measured on the basis of the corresponding metallic base single layer coating film.
As schematically shown in FIG. 1, measurement is performed with CM-512m3 manufactured by Minolta, and L values are measured at light receiving angles of 25 ° (highlight) and 75 ° (shade), and ΔL value is calculated by the following equation. did.
ΔL value = (L value of multilayer coating film) − (L value of uncured base single layer coating film)
　（２）目視観察
　目視判定による塗膜外観として、得られた複層塗膜のハイライトとシェードとのフリップフロップ性を評価した。評価基準としては以下の通りとした。
○：ハイライトとシェードとでＬ値の差が大きく、フリップフロップ性が強い。
△：ハイライトとシェードとでＬ値の差は余り大きくなく、フリップフロップ性は弱い。
×：ベース塗膜とクリヤー塗膜とが混層しており、フリップフロップ性が非常に弱い。
××：ベース塗膜とクリヤー塗膜との混層が酷く、フリップフロップ性がない。 (2) Visual observation The flip-flop property of the highlight and shade of the obtained multilayer coating film was evaluated as the coating film appearance by visual judgment. The evaluation criteria are as follows.
○: The difference in L value between the highlight and the shade is large, and the flip-flop property is strong.
(Triangle | delta): The difference of L value is not so large by highlight and a shade, and flip-flop property is weak.
X: The base coating film and the clear coating film are mixed, and the flip-flop property is very weak.
XX: The mixed layer of the base coating film and the clear coating film is severe, and there is no flip-flop property.
　実施例１、２では、ベース塗膜が１Ｆ７、４Ｐ７、４Ｒ３、１Ｄ２のいずれのベース塗料によるものであっても、色戻りの発現を抑えた意匠性の高い外観を有する複層塗膜を得ることができた。
　これに対し、原料としてメタクリル酸アルキルを含まないアクリル樹脂を配合したクリヤー塗料組成物を用いた比較例１では、ベース塗膜の色戻りが生じており、意匠性の高い複層塗膜を得ることはできなかった。また、架橋樹脂粒子を配合しなかったクリヤー塗料組成物を用いた比較例２でも、ベース塗膜の色戻りが生じており、意匠性の高い複層塗膜を得ることはできなかった。特に、ベース塗膜のＬ値が高い淡彩色ほど、色戻りが顕著に生じることがわかった。 In Examples 1 and 2, even if the base coating film is made of any one of the base paints of 1F7, 4P7, 4R3, and 1D2, a multilayer coating film having a high design appearance that suppresses the appearance of color return is obtained. I was able to.
On the other hand, in Comparative Example 1 using a clear coating composition containing an acrylic resin that does not contain alkyl methacrylate as a raw material, color reversion of the base coating film occurs, and a multilayer coating film with high design properties is obtained. I couldn't. Further, in Comparative Example 2 using the clear coating composition in which the crosslinked resin particles were not blended, the base coating film was recolored, and it was not possible to obtain a multi-layer coating film with high design properties. In particular, it has been found that color reversion occurs more markedly as the base coating film has a higher L value.
　本発明は、メタリック色等の明度が高い色の自動車塗装用の複層塗膜形成方法、なかでも、高い意匠性が要求される市場向けの自動車塗装用の複層塗膜形成方法として好適に用いることができる。 INDUSTRIAL APPLICABILITY The present invention is suitable as a method for forming a multi-layer coating film for automobile painting with a high brightness such as a metallic color, particularly as a method for forming a multi-layer coating film for automobile coating for a market that requires high designability. Can be used.

Claims (3)

  1. 　基材に対して、ベース塗料を塗布して未硬化ベース塗膜を形成する工程（１）、
    　前記工程（１）で得られた未硬化ベース塗膜上に、クリヤー塗料を塗布して未硬化クリヤー塗膜を形成する工程（２）、及び、
    　前記工程（１）及び工程（２）で得られた未硬化ベース塗膜及び未硬化クリヤー塗膜を加熱硬化して複層塗膜を形成する工程（３）を含む複層塗膜形成方法であって、
    　（ａ）前記未硬化ベース塗膜のＬ値が、２５度反射において７０～１０５であり、かつ、７５度反射において２０～５０であり、
    　（ｂ）２５度反射による前記複層塗膜のＬ値から前記未硬化ベース塗膜のＬ値を差し引いて求められる値であるΔＬ値が、－０．３～０．１５であり、
    　（ｃ）７５度反射による前記複層塗膜のＬ値から前記未硬化ベース塗膜のＬ値を差し引いて求められる値であるΔＬ値が、－０．２～０．４であり、
    かつ、
    　前記クリヤー塗料が、エステル部が炭素数９～１５の直鎖炭化水素基である長鎖（メタ）アクリル酸エステルモノマーをモノマー固形分全量に対して１０～１５質量％含み、かつ、カルボキシル基含有（メタ）アクリルモノマー及び水酸基含有（メタ）アクリルモノマーを含むモノマー混合物から得られ、数平均分子量が４０００～６０００、固形分酸価が１～５ｍｇＫＯＨ／ｇであるアクリル樹脂と、ポリイソシアネート化合物と、架橋樹脂粒子とを含むクリヤー塗料組成物である
    ことを特徴とする複層塗膜形成方法。     A step (1) of applying a base coating to a substrate to form an uncured base coating;
    A step (2) of applying a clear coating on the uncured base coating obtained in the step (1) to form an uncured clear coating; and
    A multilayer coating film forming method comprising the step (3) of heating and curing the uncured base coating film and the uncured clear coating film obtained in the steps (1) and (2) to form a multilayer coating film. There,
    (A) the L value of the uncured base coating film is 70 to 105 at 25 degrees reflection and 20 to 50 at 75 degrees reflection;
    (B) The ΔL value obtained by subtracting the L value of the uncured base coating film from the L value of the multilayer coating film by 25 degree reflection is −0.3 to 0.15,
    (C) The ΔL value, which is a value obtained by subtracting the L value of the uncured base coating film from the L value of the multilayer coating film by 75 degree reflection, is −0.2 to 0.4,
    And,
    The clear coating contains 10 to 15% by mass of a long-chain (meth) acrylic acid ester monomer whose ester part is a linear hydrocarbon group having 9 to 15 carbon atoms, and contains a carboxyl group. An acrylic resin obtained from a monomer mixture containing a (meth) acrylic monomer and a hydroxyl group-containing (meth) acrylic monomer, having a number average molecular weight of 4000 to 6000 and a solid content acid value of 1 to 5 mgKOH / g, a polyisocyanate compound, A method for forming a multilayer coating film, which is a clear coating composition containing crosslinked resin particles.
  2. 　前記クリヤー塗料組成物は、架橋樹脂粒子を、塗料組成物の全固形分に対して０．１～１０質量％含む請求項１に記載の複層塗膜形成方法。 The method for forming a multilayer coating film according to claim 1, wherein the clear coating composition contains 0.1 to 10% by mass of crosslinked resin particles with respect to the total solid content of the coating composition.
  3. 　前記工程（１）以前に、中塗り塗料を塗布して中塗り塗膜を形成する工程（Ｐ）を含んでいる請求項１又は２に記載の複層塗膜形成方法。 The method for forming a multilayer coating film according to claim 1 or 2, comprising a step (P) of forming an intermediate coating film by applying an intermediate coating before the step (1).
PCT/JP2008/073459 2007-12-25 2008-12-24 Double-layer coating film formation method WO2009081943A1 (en)

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JP5850775B2 (en) * 2012-03-22 2016-02-03 本田技研工業株式会社 Multi-layer coating formation method

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JP2003301028A (en) * 2002-04-11 2003-10-21 Nippon Paint Co Ltd Curable resin composition, clear coating composition and method of forming multilayer coating film
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JP2006291111A (en) * 2005-04-13 2006-10-26 Basf Coatings Japan Ltd Coating composition, coating finishing method, and coated article
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JP2003301028A (en) * 2002-04-11 2003-10-21 Nippon Paint Co Ltd Curable resin composition, clear coating composition and method of forming multilayer coating film
JP2006169396A (en) * 2004-12-16 2006-06-29 Kansai Paint Co Ltd Amino resin aqueous dispersion composition and thermosetting aqueous coating material composition
JP2006291111A (en) * 2005-04-13 2006-10-26 Basf Coatings Japan Ltd Coating composition, coating finishing method, and coated article
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