WO2013141305A1 - 複層塗膜形成方法 - Google Patents
複層塗膜形成方法 Download PDFInfo
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- WO2013141305A1 WO2013141305A1 PCT/JP2013/058097 JP2013058097W WO2013141305A1 WO 2013141305 A1 WO2013141305 A1 WO 2013141305A1 JP 2013058097 W JP2013058097 W JP 2013058097W WO 2013141305 A1 WO2013141305 A1 WO 2013141305A1
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- coating film
- water
- uncured
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- film
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- 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
- B05D1/38—Successively applying liquids or other fluent materials, e.g. without intermediate treatment with intermediate treatment
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- 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
- B05D3/00—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials
- B05D3/02—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials by baking
- B05D3/0254—After-treatment
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- 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
- B05D7/56—Three layers or more
- B05D7/57—Three layers or more the last layer being a clear coat
- B05D7/574—Three layers or more the last layer being a clear coat at least some layers being let to dry at least partially before applying the next layer
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- 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
- C08G18/08—Processes
- C08G18/0804—Manufacture of polymers containing ionic or ionogenic groups
- C08G18/0819—Manufacture of polymers containing ionic or ionogenic groups containing anionic or anionogenic groups
- C08G18/0823—Manufacture of polymers containing ionic or ionogenic groups containing anionic or anionogenic groups containing carboxylate salt groups or groups forming them
-
- 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
- C08G18/08—Processes
- C08G18/10—Prepolymer processes involving reaction of isocyanates or isothiocyanates with compounds having active hydrogen in a first reaction step
- C08G18/12—Prepolymer processes involving reaction of isocyanates or isothiocyanates with compounds having active hydrogen in a first reaction step using two or more compounds having active hydrogen in the first polymerisation step
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- 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
- C08G18/30—Low-molecular-weight compounds
- C08G18/34—Carboxylic acids; Esters thereof with monohydroxyl compounds
- C08G18/348—Hydroxycarboxylic acids
-
- 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
- C08G18/42—Polycondensates having carboxylic or carbonic ester groups in the main chain
- C08G18/44—Polycarbonates
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- 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
- C08G18/65—Low-molecular-weight compounds having active hydrogen with high-molecular-weight compounds having active hydrogen
- C08G18/66—Compounds of groups C08G18/42, C08G18/48, or C08G18/52
- C08G18/6633—Compounds of group C08G18/42
- C08G18/6659—Compounds of group C08G18/42 with compounds of group C08G18/34
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- 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
- C08G18/74—Polyisocyanates or polyisothiocyanates cyclic
- C08G18/75—Polyisocyanates or polyisothiocyanates cyclic cycloaliphatic
- C08G18/751—Polyisocyanates or polyisothiocyanates cyclic cycloaliphatic containing only one cycloaliphatic ring
- C08G18/752—Polyisocyanates or polyisothiocyanates cyclic cycloaliphatic containing only one cycloaliphatic ring containing at least one isocyanate or isothiocyanate group linked to the cycloaliphatic ring by means of an aliphatic group
- C08G18/753—Polyisocyanates or polyisothiocyanates cyclic cycloaliphatic containing only one cycloaliphatic ring containing at least one isocyanate or isothiocyanate group linked to the cycloaliphatic ring by means of an aliphatic group containing one isocyanate or isothiocyanate group linked to the cycloaliphatic ring by means of an aliphatic group having a primary carbon atom next to the isocyanate or isothiocyanate group
- C08G18/755—Polyisocyanates or polyisothiocyanates cyclic cycloaliphatic containing only one cycloaliphatic ring containing at least one isocyanate or isothiocyanate group linked to the cycloaliphatic ring by means of an aliphatic group containing one isocyanate or isothiocyanate group linked to the cycloaliphatic ring by means of an aliphatic group having a primary carbon atom next to the isocyanate or isothiocyanate group and at least one isocyanate or isothiocyanate group linked to a secondary carbon atom of the cycloaliphatic ring, e.g. isophorone diisocyanate
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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
- C09D175/00—Coating compositions based on polyureas or polyurethanes; Coating compositions based on derivatives of such polymers
- C09D175/04—Polyurethanes
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- 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
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- 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
- B05D2420/00—Indexing scheme corresponding to the position of each layer within a multilayer coating relative to the substrate
- B05D2420/02—Indexing scheme corresponding to the position of each layer within a multilayer coating relative to the substrate second layer from the substrate side
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- 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
- B05D2420/00—Indexing scheme corresponding to the position of each layer within a multilayer coating relative to the substrate
- B05D2420/03—Indexing scheme corresponding to the position of each layer within a multilayer coating relative to the substrate third layer from the substrate side
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- 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
- B05D2420/00—Indexing scheme corresponding to the position of each layer within a multilayer coating relative to the substrate
- B05D2420/04—Indexing scheme corresponding to the position of each layer within a multilayer coating relative to the substrate fourth layer from the substrate side
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- 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
- B05D2501/00—Varnish or unspecified clear coat
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- 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
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- 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
- B05D7/14—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 to metal, e.g. car bodies
Definitions
- the present invention relates to a method for forming a multilayer coating film in an automobile. More specifically, the present invention relates to a method for forming a multilayer coating film by three-wet coating that exhibits excellent chipping resistance while maintaining the smoothness of the multilayer coating film.
- an uncured base coat film formed on an automobile body sequentially provided with an electrodeposition coating film and an intermediate coating film (hereinafter referred to as “first base coating film” in this specification).
- first base coating film an electrodeposition coating film and an intermediate coating film
- second base coating film a two-coat / one-bake multilayer coating film obtained by a two-coat / one-bake coating method in which an uncured clear coating film is heated and cured at once
- electrodeposition Three obtained by a three-wet coating method in which an uncured first base coating film, an uncured second base coating film and an uncured clear coating film formed on an automobile body provided with a coating film are heated and cured at a time.
- the three base multilayer coating has a two-coat / one-bake multilayer thickness to ensure the smoothness of the coating. It is necessary to thin than the first base coating film layer. As a result, the chipping resistance of the multilayer coating film is reduced, and when the stepping stone collides with the coating film while traveling, the multilayer coating film is destroyed, and the scratch extends to the steel plate or the electrodeposition coating with the steel plate. There was a problem of peeling off at the interface with the film or at the interface between the electrodeposition coating film and the first base coating film.
- Patent Document 1 discloses an aqueous intermediate coating composition containing an acrylic emulsion resin formed from a specific unsaturated monomer, a hydroxyl group-containing resin, a curing agent, and a color pigment having a specific solid content.
- Patent Document 2 a multi-layer coating is applied by sequentially applying an anti-chipping coating, an intermediate coating, a base coating, and a clear coating on the electrodeposition coating formed on the steel plate.
- a coating film forming method for forming a film is disclosed.
- An object of the present invention is to provide a method for forming a multilayer coating film that exhibits excellent chipping resistance while maintaining the smoothness of the multilayer coating film in a three-wet coating method.
- the present invention [1] A step (1) of forming an uncured first base coating film by coating a first water-based base coating material on an automobile body provided with an electrodeposition coating film so that the dry coating film has a dry coating thickness of 10 to 40 ⁇ m. ; On the uncured first base coating film obtained in the above step (1), the second aqueous base paint is applied so that the dried coating film has a thickness of 5 to 30 ⁇ m to form an uncured second base coating film.
- Step (2) After the uncured first base coating film and the uncured second base coating film obtained in steps (1) and (2) are heat-dried, the clear coating is adjusted so that the dried coating film has a thickness of 10 to 70 ⁇ m.
- a step (3) of forming an uncured clear coating by coating then, the uncured first base coating and the uncured second base coating obtained in steps (1), (2) and (3) Forming a multilayer coating film comprising the step (4) of simultaneously heating and curing the film and the uncured clear coating film to form a multilayer coating film comprising the first base coating film, the second base coating film and the clear coating film;
- the method 20 of the multilayer coating film in which the dry film thickness of the first base coating film is 25 ⁇ m, the drying film thickness of the second base coating film is 10 ⁇ m, and the dry film thickness of the clear coating film is 30 ⁇ m.
- the elongation at 40 ° C. is 40 to 60%, the tensile strength is 400 to 600 kgf / m 2 , and the ratio of the viscosity term to the elastic term at ⁇ 20 ° C. (tan ⁇ ) is 0.04 to 0.06.
- a method for forming a multilayer coating film is 40 to 60%, the tensile strength is 400 to 600 kgf / m 2 , and the ratio of the viscosity term to the elastic term at ⁇ 20 ° C. (tan ⁇ ) is 0.04 to 0.06.
- a polyisocyanate component (a1) a polyisocyanate component
- a polyol a2
- a3 a polyol
- a4 a carboxyl group neutralizing component
- water a5
- the water-dispersed polyurethane composition comprises a polycarbonate diol (a2-1) and a carboxyl group-containing diol (a2-2) in a molar ratio of 1: 0.8 to 1: 2 [3] or [ 4] is provided.
- the multilayer coating film forming method of the present invention when the first base coating film, the second base coating film, and the clear coating film each have a film thickness within a predetermined range, the elongation of the multilayer coating film at 20 ° C.
- Ratio, viscosity, and ratio of viscosity term to elastic term at ⁇ 20 ° C. are in a specific range, thus ensuring smoothness and preventing pitching without reducing curability It is possible to provide a multi-layer coating film capable of achieving good performance.
- the present invention relates to a three-wet coating method in which a first base coating film, a second base coating film, and a clear coating film are simultaneously formed on an automobile body provided with an electrodeposition coating film.
- the dry film thickness of the base coating film is 25 ⁇ m
- the dry film thickness of the second base coating film is 10 ⁇ m
- the dry film thickness of the clear coating film is 30 ⁇ m
- the elongation at 20 ° C. is Provided is a method for forming a multilayer coating film having 40 to 60%, tensile strength of 400 to 600 kgf / m 2 , and ratio of viscosity term to elastic term at -20 ° C. (tan ⁇ ) of 0.04 to 0.06. To do.
- a first aqueous base paint is applied on an automobile body provided with an electrodeposition coating film, and a second aqueous base paint is applied without curing the first aqueous base paint.
- the obtained uncured first base coating film and second base coating film are heated and dried, and then the clear coating is applied wet-on-wet, and then the first base coating film, the second base coating film, and the clear coating are applied.
- the film is simultaneously heated and cured to form a multilayer coating film composed of the first base coating film, the second base coating film, and the clear coating film.
- wet-on-wet refers to a coating method in which a plurality of coating films are applied without being cured.
- an automobile body provided with an electrodeposition coating film is used as an object to be coated.
- the electrodeposition coating is formed by applying an electrodeposition coating to an automobile body and heating and curing.
- the automobile body include iron, copper, aluminum, tin, zinc, alloys containing these metals, and plating or vapor deposition products using these metals.
- the electrodeposition paint is not particularly limited, and a known cationic electrodeposition paint or anion electrodeposition paint can be used. However, it is preferable to use a cationic electrodeposition paint having excellent corrosion resistance. Electrodeposition coating and heat curing may be performed by the methods and conditions usually used for electrodeposition coating of automobile bodies.
- an uncured first base coating film is formed by coating the first water-based base coating material on the electrodeposition coating film.
- the first water-based base paint is, for example, an air electrostatic spray commonly called “react gun”, commonly called “micro-microbell ( ⁇ bell)”, “microbell ( ⁇ bell)”, “metallic bell (metabell)”, etc. It can be applied by spraying using a rotary atomizing electrostatic coating machine.
- the first water-based base coating is adjusted so that the thickness of the dry coating of the first base coating obtained is 10 to 40 ⁇ m, preferably 15 to 30 ⁇ m.
- the film thickness is less than 10 ⁇ m, the appearance and chipping resistance of the resulting coating film are reduced, and when it exceeds 40 ⁇ m, problems such as sagging during coating and pinholes during heat curing occur.
- a second water-based base coating is applied onto the uncured first base coating to form an uncured second base coating, and then the uncured first base coating and the uncured second base.
- the coating film is dried by heating.
- the coating amount of the second water-based base paint is adjusted so that the resulting second base coating film has a dry film thickness of 5 to 30 ⁇ m, preferably 5 to 25 ⁇ m. If the film thickness is less than 5 ⁇ m, the background is not sufficiently concealed or color unevenness occurs. If the film thickness exceeds 30 ⁇ m, defects such as sagging during coating and pinholes during heat curing occur.
- the obtained uncured first base coating film and uncured second base coating film are heated and dried before the clear coating is applied. Drying conditions are, for example, 40 to 100 ° C. for 30 seconds to 10 minutes.
- a clear coating is applied on the uncured first base coating film and the uncured second base coating film that have been dried by heating to form an uncured clear coating film.
- the coating amount of the clear coating is adjusted so that the resulting clear coating has a dry coating thickness of 10 to 70 ⁇ m, preferably 15 to 60 ⁇ m. If the film thickness is less than 10 ⁇ m, unevenness at the time of coating, and the appearance such as glossiness of the obtained multilayer coating film will decrease, and if it exceeds 70 ⁇ m, the smoothness of the coating film obtained will decrease, A malfunction may occur.
- the uncured first base coating film, the uncured second base coating film, and the uncured clear coating film are cured by heating at the same time.
- the heat curing is performed by heating to a temperature of 110 to 180 ° C., preferably 120 to 160 ° C., for example.
- the hardened multilayer coating film of high crosslinking degree can be obtained. If the heating temperature is less than 110 ° C, curing tends to be insufficient, and if it exceeds 180 ° C, the resulting multilayer coating film may be hard and brittle.
- the heating time can be appropriately set according to the above temperature, and for example, when the temperature is 120 to 160 ° C., it is 10 to 60 minutes.
- the dry film thickness of the first base coating film is 25 ⁇ m
- the dry film thickness of the second base coating film is 10 ⁇ m
- the clear film When the dry film thickness of the single coating film is 30 ⁇ m, the elongation at 20 ° C. is 40 to 60%, preferably 40 to 57%. If the elongation of the multi-layer coating film is less than 40% under these conditions, the peeling of the coating film with increased chipping resistance will increase or the rust will increase, and if it exceeds 60%, the water resistance and solvent resistance will increase. Inferior. The tensile strength at 20 ° C.
- the ratio of the viscosity term to the elastic term at -20 ° C. (tan ⁇ ) is 0.04 to 0.06.
- the ratio (tan ⁇ ) under this condition is less than 0.04, peeling of the coating film with respect to chipping resistance increases, and when it exceeds 0.06, the generation of rust increases.
- the elongation and tensile strength can be measured by a stress strain characteristic measuring method. Specifically, it was applied to a polypropylene test plate by air spray so that the first base coating film was 25 ⁇ m, the second base coating film was 10 ⁇ m, and the clear coating film was 30 ⁇ m as a single dry film. A multilayer coating film obtained by heating and curing at 140 ° C. for 30 minutes is peeled off from the test plate and cut into a size of 10 ⁇ 70 mm to obtain a test piece.
- the stress-strain characteristics are measured using an autograph AGS-G type and an analog meter (manufactured by Shimadzu Corporation) at a measurement length of 50 mm, a temperature of 20 ° C., and a pulling speed of 10 mm / min.
- the tensile strength is obtained from the slope of the graph immediately after the tensile test.
- the elongation is the elongation of the test piece read from the graph [the axial length of the test piece before the test is 50 (mm), and the axial length L (mm) until the test piece breaks.
- the elongation percentage (%) (L ⁇ 50) ⁇ 100/50].
- the ratio of the viscosity term to the elastic term was determined by air spraying on a polypropylene test plate, the dry thickness of the single film being 25 ⁇ m for the first base film, 10 ⁇ m for the second base film, Is coated to a thickness of 30 ⁇ m, and heat-cured at 140 ° C. for 30 minutes.
- tan ⁇ of ⁇ 20 ° C. is obtained from the phase difference generated between the stress generated during the temperature rise and the vibration strain.
- the measurement frequency is 11 Hz, and the temperature increase rate is 2 ° C./min.
- the first water-based base paint used in the method of the present invention includes a water-dispersible polyurethane composition (A), a water-dispersible acrylic resin (B), and a curing agent (C).
- the water-dispersed polyurethane composition (A) has a polyisocyanate component (a1) that may contain diisocyanate as an essential component and other polyisocyanate as an optional component, and a weight average molecular weight of 1,500 to 5,000.
- the polycarbonate diol (a2-1) and the carboxyl group-containing diol (a2-2) are essential components, and other polyol components (a2) which may contain other polyols as optional components, monoamine compounds as essential components, and diamines It is obtained from an amine component (a3) which may contain a compound as an optional component, a carboxyl group neutralizing component (a4), and water (a5).
- weight average molecular weight and the number average molecular weight in the present specification are values measured with a polystyrene standard by a GPC (gel permeation chromatography) method.
- the diisocyanate that is an essential component of the polyisocyanate component (a1) used in the present invention is not particularly limited, and known diisocyanates can be used alone or in combination of two or more.
- the diisocyanate is preferably an alicyclic diisocyanate, and more preferably isophorone diisocyanate and dicyclohexylmethane-4,4′-diisocyanate, because the resulting polyurethane molecule and the coating film obtained therefrom are excellent in hydrolysis resistance.
- the above-mentioned diisocyanate may be used in the form of a modified product such as carbodiimide modification, isocyanurate modification, biuret modification, or may be used in the form of a blocked isocyanate blocked with various blocking agents.
- the diisocyanate content (% by mass) in the polyisocyanate component (a1) is preferably 50% or more, and more preferably 70% or more. If the diisocyanate content is less than 50%, the compatibility with the other components of the first aqueous base paint may be deteriorated.
- the weight average molecular weight of the polycarbonate diol (a2-1), which is an essential component of the polyol component (a2) used in the present invention, is preferably 1,500 to 5,000.
- the weight average molecular weight is less than 1,500, sufficient adhesion of the coating film to the substrate cannot be obtained, and when it exceeds 5,000, the dispersion stability of the water-dispersible polyurethane composition (A) is reduced or coated. The impact resistance of the film is reduced.
- the diol used as a raw material for the polycarbonate diol is not particularly limited, and examples thereof include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,4-butanediol, neopentyl glycol, 3-methyl-2,4-pentanediol, 2,4-pentanediol, 1,5-pentanediol Low molecular diols such as 3-methyl-1,5-pentanediol, 2-methyl-2,4-pentanediol, 2,4-diethyl-1,5-pentanediol and 1,6-hexanediol. 1,6-Hexanediol is preferable because it is inexpensive and easily available.
- the carboxyl group-containing diol (a2-2) which is another essential component of the polyol component (a2), is used to introduce a hydrophilic group into the polyurethane molecule. Since the hydrophilic group to be introduced is preferably in a form in which a carboxyl group is neutralized, examples of the carboxyl group-containing diol (a2-2) include dimethylolpropionic acid, dimethylolbutanoic acid, dimethylolbutyric acid, and dimethylol. Examples include valeric acid. These carboxyl group-containing diols can be used alone or in combination of two or more.
- polyol compounds that can be arbitrarily blended as the polyol component (a2) are not particularly limited, and known polyols can be used alone or in combination of two or more.
- the polyol compound include low molecular polyols, polyether polyols, polybutadiene polyols, silicone polyols, polyols having an ester bond, and the like.
- the composition ratio of the polycarbonate diol (a2-1) having a weight average molecular weight of 1,500 to 5,000 is preferably 50 to 97% by mass, more preferably 75 to 95% by mass. . If the composition ratio of the polycarbonate diol (a2-1) is less than 50% by mass, a coating film having sufficient strength may not be obtained. If it exceeds 97% by mass, the resulting polyurethane composition is dispersed in water. May deteriorate.
- the composition ratio of the carboxyl group-containing diol (a2-2) is preferably 3 to 30% by mass, and more preferably 5 to 25% by mass.
- the molar ratio of the polycarbonate diol (a2-1) and the carboxyl group-containing diol (a2-2) contained in the polyol (a2) is preferably 1: 0.8 to 1: 2, more preferably 1: 1. It is used at a blending ratio of ⁇ 1: 1.75, more preferably 1: 1.2 ⁇ 1: 1.5. If the amount of the carboxyl group-containing diol (a2-2) is less than 1: 0.8, the water dispersibility may be lowered and the storage stability of the paint may be lowered. On the other hand, when the amount of the carboxyl group-containing diol (a2-2) is larger than 1: 2, the chipping resistance of the resulting multilayer coating film may be lowered, which is not preferable.
- the monoamine compound that is an essential component of the amine component (a3) used in the present invention is not particularly limited, and known compounds can be used alone or in combination of two or more.
- the monoamine compounds include alkylamines such as ethylamine, propylamine, 2-propylamine, butylamine, 2-butylamine, tert-butylamine and isobutylamine; aromatic amines such as aniline, methylaniline, phenylnaphthylamine and naphthylamine; cyclohexaneamine Alicyclic amines such as methylcyclohexaneamine; ether amines such as 2-methoxyethylamine, 3-methoxypropylamine, 2- (2-methoxyethoxy) ethylamine; ethanolamine, propanolamine, butylethanolamine, 1-amino- 2-methyl-2-propanol, 2-amino-2-methylpropanol, diethanolamine, diisoprop
- the diamine compound that can be optionally blended as the amine component (a3) used in the present invention is not particularly limited, and known diamine compounds can be used alone or in combination of two or more.
- the neutralizing agent used in the carboxyl group-neutralizing component (a4) used in the present invention is a basic compound that reacts with the carboxyl group of the carboxyl group-containing diol to form a hydrophilic salt.
- the basic compound is not particularly limited, and examples thereof include trialkylamines such as trimethylamine, triethylamine, and tributylamine, N, N-dimethylethanolamine, N, N-dimethylpropanolamine, and N, N-dipropylethanolamine.
- N, N-dialkylalkanolamines such as 1-dimethylamino-2-methyl-2-propanol
- tertiary alkanolamines such as N-alkyl-N, N-dialkanolamines and triethanolamine
- examples include amine compounds, ammonia, trimethylammonium hydroxide, sodium hydroxide, potassium hydroxide, and lithium hydroxide.
- a tertiary amine compound is preferable because the obtained water-dispersible polyurethane composition (A) has good dispersion stability.
- an internal branching agent and an internal cross-linking agent that give a branching or cross-linking structure to the polyurethane molecule may be used. Good.
- these internal branching agent and internal cross-linking agent include melamine and methylol melamine.
- the method for producing the water-dispersed polyurethane composition (A) is not particularly limited, and a known method can be applied.
- the production method is preferably a method in which a prepolymer or a polymer is synthesized in a solvent that is inert to the reaction and has a high affinity with water, and then this is fed to water and dispersed.
- the carboxyl group neutralizing component (a4) may be added in advance to the water to be fed, or may be added after the feeding.
- the method (a) is preferable because the composition and reaction can be easily controlled and good dispersibility can be obtained.
- Examples of the solvent that is inert to the reaction and has a high affinity for water used in the above preferred production method include acetone, methyl ethyl ketone, dioxane, tetrahydrofuran, N-methyl-2-pyrrolidone, and the like. Can do. These solvents are usually used in an amount of 3 to 100% by mass with respect to the total amount of the raw materials used for producing the prepolymer.
- the blending ratio is not limited unless otherwise specified.
- the compounding ratio can be replaced with a molar ratio of the isocyanate group in the polyisocyanate component (a1) and the isocyanate reactive group in the polyol component (a2) and the amine component (a3) at the stage of reaction.
- the molar ratio of the isocyanate reactive groups in the polyol component (a2) and the amine component (a3) to the isocyanate groups in the polyisocyanate component (a1) is preferably 0.5 to 2.0.
- the molar ratio of the isocyanate reactive group in the polyol component (a2) to the isocyanate group in the polyisocyanate component (a1) is preferably from 0.3 to 1.0, more preferably from 0.5 to 0.9.
- the molar ratio of the isocyanate reactive group in the amine component (a3) to the isocyanate group in the polyisocyanate component (a1) is preferably 0.1 to 1.0, more preferably 0.2 to 0.5. If there are insufficient unreacted isocyanate groups in the dispersed polyurethane molecules, the coating adhesion and strength of the coating may decrease when used as a paint, and if present in excess, unreacted isocyanate groups will disperse the paint. It may adversely affect the stability and physical properties of the resulting coating.
- the neutralization rate by the carboxyl group neutralizing component (a4) can be set within a range that gives sufficient dispersion stability to the obtained water-dispersed polyurethane composition (A). 0.5 to 2.0 times equivalent is preferable with respect to the number of moles of carboxyl groups in the polyol component (a2), and 0.7 to 1.5 times equivalent is more preferable.
- Examples of the form of the water-dispersible polyurethane composition (A) include emulsions, suspensions, colloidal dispersions, and aqueous solutions.
- an emulsifier such as a surfactant is used alone or in combination of two or more. Can be used.
- the particle diameter in the case of emulsions, suspensions, and colloidal dispersions in which particles are dispersed in water is not particularly limited, but in order to maintain a good dispersion state, the median diameter D50 is preferably 100 to 3000 nm. 100 to 2000 nm is more preferable. The median diameter D50 can be measured by, for example, a laser light scattering method.
- emulsifier a known anionic surfactant or nonionic surfactant is preferable because good dispersion or emulsification can be obtained.
- the amount of the emulsifier used is preferably 0.01 to 0.3, more preferably 0.05 to 0.2, in terms of mass ratio with respect to the polyurethane composition 1. If the mass ratio is less than 0.01, sufficient dispersibility may not be obtained, and if it exceeds 0.3, physical properties such as water resistance, strength, and elongation of the coating obtained from the first water-based base coating material are deteriorated. There is a fear.
- the solid content is preferably 10 to 70% by mass, more preferably 20 to 60% by mass, from the viewpoint of dispersibility and coating workability.
- the number average molecular weight of the polyurethane composition dispersed in the water-dispersed polyurethane composition (A) is preferably from 5,000 to 200,000, more preferably from 10,000 to 50,000. If it is less than 5,000, the chipping resistance may be reduced, and if it exceeds 200,000, the cleanability of the paint piping of the coating line may be reduced. Further, the hydroxyl value is not particularly limited, and any value can be selected and is usually 0 to 100 mgKOH / g.
- the water-dispersed acrylic resin (B) used in the first aqueous base paint of the present invention comprises (meth) acrylic acid alkyl ester (i), carboxyl group-containing ethylenically unsaturated monomer (ii), and hydroxyl group-containing
- a monomer mixture containing the ethylenically unsaturated monomer (iii) can be obtained by emulsion polymerization by a conventional method.
- the compound illustrated below as a component of a monomer mixture can be used individually or in combination of 2 or more types as appropriate.
- “meth (acrylic)” represents both acrylic and methacrylic.
- (meth) acrylic acid alkyl ester (i) is used to constitute the main skeleton of the acrylic resin emulsion.
- Examples of the (meth) acrylic acid alkyl ester (i) include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, and (meth) acrylic acid. Isobutyl, t-butyl (meth) acrylate, hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, (meth ) Dodecyl acrylate and stearyl (meth) acrylate.
- the carboxyl group-containing ethylenically unsaturated monomer (ii) improves the storage stability, mechanical stability, stability against freezing and the like of the resulting acrylic resin emulsion, and is used with a curing agent such as an amino resin during coating film formation. Used to accelerate the curing reaction.
- carboxyl group-containing ethylenically unsaturated monomer examples include acrylic acid, methacrylic acid, crotonic acid, isocrotonic acid, ethacrylic acid, propylacrylic acid, isopropylacrylic acid, itaconic acid, maleic anhydride and fumaric acid.
- the hydroxyl group-containing ethylenically unsaturated monomer (iii) imparts hydrophilicity based on hydroxyl group to the acrylic resin emulsion, and increases the storage stability, mechanical stability and stability against freezing when this is used as a paint, Used to impart curing reactivity with amino resins and polyisocyanates.
- hydroxyl group-containing ethylenically unsaturated monomer (iii) examples include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, N-methylolacrylamide, allyl alcohol, and the like. and ⁇ -caprolactone-modified acrylic monomer.
- the monomer mixture may contain at least one monomer selected from the group consisting of a styrene monomer, (meth) acrylonitrile, and (meth) acrylamide as an optional component.
- a styrene monomer examples include ⁇ -methylstyrene in addition to styrene.
- the monomer mixture may contain a crosslinkable monomer such as a carbonyl group-containing ethylenically unsaturated monomer, a hydrolyzable polymerizable silyl group-containing monomer, and various polyfunctional vinyl monomers. In that case, the water-dispersed acrylic resin emulsion obtained is self-crosslinkable.
- Emulsion polymerization can be carried out by heating the monomer mixture in an aqueous liquid with stirring in the presence of a radical polymerization initiator and an emulsifier.
- the reaction temperature is, for example, about 30 to 100 ° C., and the reaction time is preferably about 1 to 10 hours.
- the monomer mixture or the monomer pre-emulsified liquid is added all at once or dropped dropwise to a reaction vessel charged with water and an emulsifier. It is recommended to adjust
- radical polymerization initiator known initiators usually used in emulsion polymerization of acrylic resins can be used.
- the emulsifier is not particularly limited, and examples thereof include an anionic surfactant and a nonionic surfactant described in the water-dispersible polyurethane composition (A). These are used individually or in combination of 2 or more types.
- Emulsion polymerization can be performed by any one of the usual one-step continuous monomer uniform dropping method, core-shell polymerization method which is a multi-stage monomer feed method, and power feed polymerization method which continuously changes the monomer composition fed during the polymerization. Can be legal.
- the glass transition temperature (Tg) of the mixture of the monomer components is preferably in the range of ⁇ 50 ° C. to 20 ° C.
- Tg glass transition temperature
- the acid value of the mixture of the monomer components is preferably 2 to 60 mgKOH / g.
- the acid value is preferably 2 to 60 mgKOH / g.
- the hydroxyl value of the mixture of the monomer components is preferably 10 to 120 mgKOH / g.
- the resin has moderate hydrophilicity, and when used as a coating composition containing a resin emulsion, storage stability, mechanical stability and stability against freezing are increased, and melamine is added. Curing reactivity with resin and isocyanate curing agent is also sufficient. More preferably, it is 20 to 100 mgKOH / g.
- a basic compound is added to the water-dispersed acrylic resin.
- Resin (B) is manufactured.
- these basic compounds ammonia, various amines, alkali metals and the like are usually used, and they are also used appropriately in the present invention.
- the 1st water-based base coating material by adding a hardening
- curing agent (C) As the curing agent (C), a curing reaction occurs with one or both of the water-dispersed polyurethane composition (A) and the water-dispersed acrylic resin (B), and the curing agent (C) can be blended in the first aqueous base paint.
- amino resins and / or blocked isocyanate resins are particularly preferably used.
- the amino resin is not particularly limited, and for example, a methylated melamine resin, a butylated melamine resin, or a methylbutyl mixed melamine resin can be used.
- a methylated melamine resin such as “Cymel 303” and “Cymel 254” manufactured by Mitsui Chemicals
- Uban series such as “Uban 226” and “Uban 20N60”
- Sumi manufactured by Sumitomo Chemical Co., Ltd.
- Marl series a methylated melamine resin, a butylated melamine resin, or a methylbutyl mixed melamine resin.
- the blocked isocyanate resin is obtained by adding a blocking agent having active hydrogen to polyisocyanate, and the blocking agent is dissociated by heating to generate an isocyanate group.
- the water-dispersed polyurethane composition (A) And those that react with the functional groups in the water-dispersible acrylic resin (B) and cure.
- the blocked isocyanate resin is not particularly limited.
- typical polyisocyanates include fats such as trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, and trimethylhexamethylene diisocyanate.
- Aliphatic isocyanates such as 1,3-cyclopentane diisocyanate, 1,4-cyclohexane diisocyanate, 1,2-cyclohexane diisocyanate; xylylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate Aromatic isocyanates such as isocyanates; Cycloaliphatic isocyanates such as isophorone diisocyanate and norbornane diisocyanate methyl It can be used multimers and mixtures such as these isocyanurate body.
- the blocking agent examples include halogenated hydrocarbons, methanol, ethanol, n-propanol, isopropanol, furfuryl alcohol, alkyl group-substituted furfuryl alcohol, benzyl alcohol, and other aliphatic, aromatic or heterocyclic alcohols; methyl ethyl ketone Examples include oximes such as oxime, methyl isobutyl ketone oxime, acetone oxime, and cyclohexane oxime; caprolactam and the like. Of these, oximes and alcohols are preferred.
- a catalyst for dissociating the blocking agent can be further used.
- the chipping resistance of the multilayer coating film from the viewpoint of buffering action of external force and energy propagation, the elongation rate and tensile strength of the multilayer coating film and the value of tan ⁇ indicating the balance are extremely important. Those having a high elongation and a low tensile strength tend to increase the damage caused by chipping, and those having a low elongation and a high tensile strength tend to deepen the damage caused by chipping. Further, the chipping resistance is determined by the value of tan ⁇ indicating the balance between the elongation and the tensile strength.
- the solid content of the water-dispersed polyurethane composition (A) in the resin solid content of the first aqueous base paint is the ratio of the viscosity term to the elongation rate, tensile strength, and elastic term of the finally obtained multilayer coating film. Influence. As the solid content increases, the elongation increases and the tensile strength tends to decrease.
- the solid content is preferably 20 to 40% by mass, more preferably 25 to 35% by mass. When the solid content is less than 20% by mass, the effect of improving the chipping resistance of the obtained multilayer coating film is reduced, and when it exceeds 40% by mass, the solvent resistance of the obtained multilayer coating film is lowered. In some cases, the effects of the present invention may not be exhibited.
- the solid content of the water-dispersible acrylic resin (B) is preferably 5 to 10% by mass in the solid content of the coating resin.
- the solid content of the water-dispersible acrylic resin (B) is less than 5% by mass, the chipping resistance of the obtained multilayer coating film tends to be lowered, and when it exceeds 10% by mass, the multilayer obtained There exists a tendency for the water resistance of a coating film to fall, and all may not show the effect of the present invention.
- the solid content of the curing agent (C) in the resin solid content of the first water-based base paint is preferably 5 to 50% by mass, more preferably 5 to 30% by mass in the solid content of the paint resin.
- the content is less than 5% by mass, the water resistance of the resulting multilayer coating tends to decrease.
- it exceeds 50 mass% there exists a tendency for the chipping property of the multilayer coating film obtained to fall.
- the first water-based base paint of the present invention further includes other resin components, organic or inorganic materials.
- Various additives such as various color pigments and extender pigments and thickeners can be included.
- the other resin components are not particularly limited, and examples thereof include water-soluble acrylic resins and water-soluble polyester resins other than those already described. These resin components are preferably blended in a proportion of 50% by mass or less based on the solid content of all the resins contained in the first aqueous base paint.
- the water-soluble acrylic resin can be obtained by solution polymerization of a mixture of polymerizable unsaturated monomers.
- the polymerizable unsaturated monomer include (meth) acrylic acid alkyl ester (i), carboxyl group-containing ethylenically unsaturated monomer (ii), and hydroxyl group-containing ethylene described in the water-dispersed acrylic resin (B).
- the unsaturated monomer (iii) can be used.
- Water-soluble acrylic resins are neutralized with organic compounds such as basic compounds such as monomethylamine, dimethylamine, trimethylamine, triethylamine, diisopropylamine, monoethanolamine, diethanolamine and dimethylethanolamine and dissolved in water. Can be used.
- organic compounds such as basic compounds such as monomethylamine, dimethylamine, trimethylamine, triethylamine, diisopropylamine, monoethanolamine, diethanolamine and dimethylethanolamine and dissolved in water. Can be used.
- Such a water-soluble acrylic resin preferably has a resin solid content acid value of 35 to 100 mg / KOH, and more preferably 40 to 80 mg / KOH.
- the number average molecular weight of the water-soluble acrylic resin is preferably 3,000 to 15,000. If the number average molecular weight is greater than 15,000, the viscosity of the paint may be too high, and if it is less than 3,000, the water resistance of the coating film may be reduced.
- water-soluble polyester resin examples include ethylene glycol, diethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, and 2,2-diethyl.
- Aromatic polycarboxylic acids and acid anhydrides such as acid, isophthalic acid, terephthalic acid, trimellitic anhydride, tetrabromophthalic anhydride, tetrachlorophthalic anhydride, pyromellitic anhydride; he
- the water-soluble polyester resin can be used after being dissolved in water by neutralizing with the basic compound described in the above water-soluble acrylic resin.
- the number average molecular weight of the water-soluble polyester resin is preferably 800 to 10,000, more preferably 1,000 to 8,000. If the number average molecular weight is less than 800, the stability of the polyester resin when water-solubilized decreases, and if it exceeds 10,000, the viscosity of the resin increases. Sex is reduced.
- the solid acid value of the water-soluble polyester resin is preferably 15 to 100 mgKOH / g, and more preferably 20 to 80 mgKOH / g.
- the solid content acid value is less than 15 mgKOH / g, the stability of the polyester resin in an aqueous system is lowered, and when it exceeds 100 mgKOH / g, the water resistance of the resulting coating film is lowered.
- the colored pigment examples include organic azo lake pigments, insoluble azo pigments, condensed azo pigments, phthalocyanine pigments, indigo pigments, perinone pigments, perylene pigments, dioxazine pigments, quinacridone pigments, and isoindoids.
- inorganic pigments calcium carbonate, barium sulfate, clay, talc and the like are used as inorganic pigments such as linone pigments and metal complex pigments, inorganic chrome yellow, yellow iron oxide, red iron oxide, carbon black, titanium dioxide and the like.
- inorganic pigments such as linone pigments and metal complex pigments, inorganic chrome yellow, yellow iron oxide, red iron oxide, carbon black, titanium dioxide and the like.
- flat pigments such as aluminum powder and graphite powder may be added.
- the pigment preferably has a pigment weight content (PWC) of 10 to 60% by mass with respect to the total mass of the solid content of the resin and the total mass of the pigment contained in the first aqueous base paint. If it is less than 10% by mass, the base concealing property may be lowered. When it exceeds 60 mass%, the viscosity at the time of hardening will be increased, and the smoothness of the obtained multilayer coating film may be lowered.
- PWC pigment weight content
- the method for producing the first water-based base paint of the present invention is not particularly limited, and all methods known to those skilled in the art can be used. Further, the form of the first aqueous base paint of the present invention is not particularly limited as long as it is aqueous, and examples thereof include water-soluble, water-dispersed, and aqueous emulsion forms.
- the second aqueous base paint used in the method of the present invention is not particularly limited, and examples thereof include a film-forming resin, a curing agent, a bright pigment, a pigment such as a colored pigment and an extender pigment, various additives, and the like. Can be included.
- a film-forming resin for example, a polyester resin, an acrylic resin, a urethane resin, a carbonate resin, and an epoxy resin can be used. From the viewpoint of pigment dispersibility and workability, a combination of an acrylic resin and / or a polyester resin and a melamine resin is preferable.
- the curing agent, pigment, and various additives those used in the first aqueous base paint described above can be used.
- the preparation of the second water-based base paint can also be performed by the same method as the preparation of the first water-based base paint.
- the pigment concentration (PWC) contained in the second aqueous base paint is preferably 0.1 to 50% by mass, more preferably 0.5 to 40% by mass, and further preferably 1 to 30% by mass. is there. If the pigment concentration is less than 0.1% by mass, the effect of the pigment cannot be obtained, and if it exceeds 50% by mass, the appearance of the resulting coating film may be deteriorated.
- the paint form of the second water-based base paint is not particularly limited, and may be any of water solubility, water dispersibility, and emulsion.
- the clear paint used in the method of the present invention is not particularly limited, and examples thereof include those containing a film-forming resin, a curing agent and other additives. Although it does not specifically limit as a film-forming resin, For example, an acrylic resin, a polyester resin, an epoxy resin, a urethane resin etc. are mentioned. These can be used in combination with a curing agent such as an amino resin and / or an isocyanate resin. From the viewpoint of transparency or acid etching resistance, it is preferable to use a combination of an acrylic resin and / or a polyester resin and an amino resin, or an acrylic resin and / or a polyester resin having a carboxylic acid / epoxy curing system.
- the coating form of the clear paint may be any of an organic solvent type, an aqueous type (water-soluble, water-dispersible, emulsion), a non-water-dispersed type, and a powder type. Can be used.
- part means “part by mass” unless otherwise specified.
- Production Example 1 Production of Water-dispersed Polyurethane Composition A 0.26 mol part of polycarbonate diol having a weight average molecular weight of 2,000 obtained from 1,6-hexanediol, 1.0 mol part of isophorone diisocyanate, and 0.02 part of dimethylolpropionic acid. N-methyl-2-pyrrolidone of 36 mol parts and 39% by mass of these total masses was charged into a reaction flask and reacted at 125 ° C. for 2 hours under a nitrogen stream to obtain a prepolymer.
- Production Example 2 Production of Water-dispersed Polyurethane Composition B 0.13 mol part of polycarbonate diol having a weight average molecular weight of 2,000 obtained from 1,6-hexanediol, 1.0 mol part of isophorone diisocyanate, dimethylolpropionic acid, 0. 36 mol parts, 40% by mass of these total masses of N-methyl-2-pyrrolidone were charged into a reaction flask and reacted at 125 ° C. for 2 hours under a nitrogen stream to obtain a prepolymer.
- the prepolymer 500 g obtained above was dissolved in 15 minutes in 600 g of water in which 0.25 g of the silicone-based antifoaming agent SE-21, 31.0 g of triethylamine, 0.315 g of ethylenediamine and 5.35 g of monoethanolamine were dissolved. It was dripped. Furthermore, it stirred at 40 degreeC for 30 minutes until absorption derived from an isocyanate group disappeared by IR measurement, and obtained a water-dispersed polyurethane composition B having a solid content of 32.0%. The number average molecular weight of the polyurethane composition dispersed therein was measured in the same manner as in Production Example 1 and found to be 22,000.
- Production Example 3 Production of Water-dispersed Polyurethane Composition C 0.26 mol part of polycarbonate diol having a weight average molecular weight of 1,000 obtained from 1,6-hexanediol, 1.0 mol part of isophorone diisocyanate, 0. 1 part of dimethylolpropionic acid. 36 mol parts, 40% by mass of these total masses of N-methyl-2-pyrrolidone were charged into a reaction flask and reacted at 125 ° C. for 2 hours under a nitrogen stream to obtain a prepolymer.
- the prepolymer 500 g obtained above was dissolved in 15 minutes in 600 g of water in which 0.25 g of the silicone-based antifoaming agent SE-21, 22.0 g of triethylamine, 0.315 g of ethylenediamine, and 5.35 g of monoethanolamine were dissolved. It was dripped. Furthermore, it stirred for 30 minutes at 40 degreeC until absorption derived from an isocyanate group disappeared by IR measurement, to obtain a water-dispersed polyurethane composition C having a solid content of 31.7%. When the number average molecular weight of the polyurethane composition dispersed therein was measured in the same manner as in Production Example 1, it was 17,000.
- Production Example 4 Production of Water-dispersed Polyurethane Composition D 0.26 mol part of polycarbonate diol having a weight average molecular weight of 1,000 obtained from 1,6-hexanediol, and 1.0 mol part of dicyclohexylmethane-4,4′-diisocyanate , 0.36 mol part of dimethylolpropionic acid and 40% by mass of N-methyl-2-pyrrolidone of the total mass were charged into a reaction flask and reacted at 125 ° C. for 2 hours under a nitrogen stream to obtain a prepolymer. It was.
- the prepolymer 500 g obtained above was dissolved in 15 minutes in 600 g of water in which 0.25 g of the silicone-based antifoaming agent SE-21, 22.00 g of triethylamine, 0.315 g of ethylenediamine, and 5.35 g of monoethanolamine were dissolved. It was dripped. Furthermore, it stirred for 30 minutes at 40 degreeC until absorption derived from isocyanate group disappeared by IR measurement, and the water-dispersed polyurethane composition D having a solid content of 31.7% was obtained. The number average molecular weight of the polyurethane composition dispersed therein was measured in the same manner as in Production Example 1 and found to be 15,000.
- Production Example 5 Production of water-dispersed acrylic resin A reaction vessel for producing an acrylic resin emulsion equipped with a stirrer, a thermometer, a dropping funnel, a reflux condenser, a nitrogen introduction tube, and the like, was charged with 445 parts of water and Newcol 293 ( 5 parts of an anionic emulsifier manufactured by Nippon Emulsifier Co., Ltd. was charged, and the temperature was raised to 75 ° C. with stirring.
- Newcol 293 5 parts of an anionic emulsifier manufactured by Nippon Emulsifier Co., Ltd. was charged, and the temperature was raised to 75 ° C. with stirring.
- Monomer mixture comprising 45 parts of methyl methacrylate, 299 parts of butyl acrylate, 50 parts of styrene, 92 parts of 2-hydroxyethyl acrylate, 14 parts of methacrylic acid and 20 parts of ethylene glycol dimethacrylate (resin acid value: 18 mgKOH / g, Hydroxyl value: 85 mg KOH / g, Tg: ⁇ 22 ° C.), a mixture of 240 parts of water and 30 parts of Neucor 293 was emulsified using a homogenizer, and the monomer pre-emulsion was stirred in the reaction vessel for 3 hours. While dripping.
- an aqueous solution in which 1 part of ammonium persulfate as a polymerization initiator was dissolved in 50 parts of water was uniformly dropped into the reaction vessel until the end of the dropping of the monomer pre-emulsified solution.
- the reaction was further continued at 80 ° C. for 1 hour, and then cooled.
- an aqueous solution in which 2 parts of dimethylaminoethanol was dissolved in 20 parts of water was added to obtain a water-dispersed acrylic resin having a nonvolatile content of 40.6% by mass.
- the pH of the obtained water-dispersed acrylic resin was adjusted to 7.2 using a 30% aqueous dimethylaminoethanol solution.
- Production Example 6 Production Example of Water-Soluble Acrylic Resin A reaction vessel was charged with 76 parts of ethylene glycol monomethyl ether, 45 parts of styrene, 63 parts of methyl methacrylate, 48 parts of 2-hydroxyethyl methacrylate, 117 parts of n-butyl acrylate, 27 parts of methacrylic acid. 60 parts of the monomer mixture consisting of 3 parts of azobisisobutyronitrile was added and the temperature was raised to 120 ° C. with stirring.
- Production Example 7 Production Example of Water-Soluble Polyester Resin 20.51 parts of ethylene glycol, 12.91 parts of trimethylolpropane, and 51.70 parts of phthalic anhydride were added, and after esterification at 160 to 220 ° C. for 5 hours, Further, 14.88 parts of trimellitic anhydride was added and reacted at 180 ° C. for 1 hour to obtain a polyester resin having an acid value of 50 mgKOH / g, a hydroxyl value of 60 mgKOH / g and a number average molecular weight of 2,000. This was neutralized with dimethylethanolamine to obtain a water-soluble polyester resin having a neutralization rate of 80% and a nonvolatile content of 35% by mass.
- Example 1 Production example of first water-based base paint 28.3 parts of water-dispersible polyurethane composition (A) (solid content: 8.9 parts), 4.9 parts of water-dispersible acrylic resin (solid content: 2.0 parts), water-soluble Acrylic resin 10.6 parts (solid content 5.3 parts) and water-soluble polyester resin 15.1 parts (solid content 5.3 parts), Cymel 327 (trade name, melamine resin manufactured by Nippon Cytec Industries, Ltd.) as a curing agent After mixing 8.4 parts (solid content 7.6 parts), Adecanol UH814 (trade name, urethane association type thickener manufactured by ADEKA) was mixed and stirred, and the water-dispersed polyurethane composition (A) was coated with a coating resin.
- A solid content: 8.9 parts
- 4.9 parts of water-dispersible acrylic resin solid content: 2.0 parts
- water-soluble Acrylic resin 10.6 parts solid content 5.3 parts
- water-soluble polyester resin 15.1 parts solid content 5.3 parts
- Cymel 327 trade name, melamine
- a first aqueous base paint containing 30 parts as a solid content with respect to 100 parts as a solid content was obtained.
- a pigment 27 parts of rutile titanium oxide, 48 parts of barium sulfate and 9 parts of carbon black were blended with respect to 100 parts of the total solid content of the coating resin.
- These pigments were preliminarily mixed with a water-soluble acrylic resin, deionized water and an antifoaming agent, and then dispersed in a glass bead medium with a paint conditioner.
- Example of production of second water-based base paint AQUALEX AR-2100NH-730 (trade name, water-based solid base paint manufactured by Nippon Paint Co., Ltd.) and water-dispersible polyurethane composition (A) Mixing and stirring were performed so that the solid content was 30 parts with respect to 100 parts to obtain a second aqueous base paint.
- a zinc phosphate-treated dull steel plate is electrodeposited with Powernics 150 (trade name, cationic electrodeposition coating made by Nippon Paint Co., Ltd.) so that the dry coating thickness becomes 20 ⁇ m, and at 160 ° C.
- a steel plate substrate was prepared by cooling after heat curing for 30 minutes.
- the first aqueous base paint is applied to the obtained substrate with a rotary atomizing electrostatic coating apparatus so that the dry film thickness is 25 ⁇ m, and then the second aqueous base paint is applied to the rotary atomizing electrostatic coating. It was coated with an apparatus so that the dry film thickness was 10 ⁇ m, and preheated at 80 ° C. for 3 minutes. In addition, the interval for 6 minutes was put between application
- a test piece on which a multilayer coating film was formed was formed.
- a multilayer coating film was formed in the same manner except that a polypropylene test plate was used instead of the steel plate substrate, and air spray was used instead of the rotary atomizing electrostatic coating apparatus. Thereafter, a test piece for stress strain characteristics obtained by cutting the multilayer coating film from a polypropylene test plate into a size of 10 ⁇ 70 mm and a test piece for viscoelasticity taken out after cutting into a size of 5 ⁇ 20 mm. Produced.
- the test piece on which the multi-layer coating film obtained as described above was formed was immersed in warm water at 40 ° C. for 10 days and then taken out, and the scratching phenomenon on the coating film surface caused by the swelling of the coating film on the test piece was visually evaluated. did.
- the test piece in which the Chijimi phenomenon did not occur was evaluated as ⁇ , the generated test piece was evaluated as ⁇ , and the results are shown in Table 1.
- Examples 2 to 5 and Comparative Examples 1 to 9 As shown in Table 1, Examples of the first water-based base paint and the second water-based base paint each containing a predetermined amount of the water-dispersible polyurethane composition (A) as a solid content with respect to 100 parts of the paint resin solid content. 1 and obtained in the same manner. Furthermore, in the same manner as in Example 1, after obtaining a test piece on which a multilayer coating film was formed, various evaluation tests were performed. The results are shown in Table 1. In addition, as a clear paint of Examples 2 to 5 and Comparative Example 7, Macflow O-1900 (trade name, manufactured by Nippon Paint Co., Ltd., acid epoxy curable clear paint) was used instead of O-100.
- Macflow O-1900 trade name, manufactured by Nippon Paint Co., Ltd., acid epoxy curable clear paint
- the elongation ratio of the multilayer coating film at 20 ° C. is 40 to 60%
- the tensile strength is 400 to 600 kgf / m 2
- the ratio of the viscosity term to the elastic term at ⁇ 20 ° C. (tan ⁇ ) Satisfying the requirement of a value in the range of 0.04 to 0.06
- the multilayer coating films of Examples 1 to 5 exhibited excellent physical properties that cleared all target values and items.
- any one or more of chipping resistance, water resistance or solvent resistance is used. Undesirable evaluation results were shown in the item.
- the multi-layer coating film forming method of the present invention can be used for forming a multi-layer coating film having both appearance and chipping resistance on an automobile body.
Abstract
Description
例えば、特許文献1には、特定の不飽和モノマーから生成したアクリル系エマルション樹脂、水酸基含有樹脂、硬化剤および特定の固形分含量の着色顔料を含む水性中塗り塗料組成物が開示されている。
また、特許文献2には、鋼板上に形成された電着塗膜上に、塗膜物性値を限定した耐チッピング塗料、中塗り塗料、ベースコート塗料およびクリヤーコート塗料を順次塗り重ねて複層塗膜を形成する塗膜形成方法が開示されている。
しかしながら、特許文献1の組成物では、耐チッピング性に有効なウレタン結合のような凝集力が強い結合基が樹脂骨格内に存在しないために、中塗り塗膜での耐チッピング性が不充分であった。また、スリーウェット塗装方法では最低溶融粘度が低いために、加熱硬化時の中塗り塗料とベース塗料との混層制御が不充分であり、ツーコート・ワンベーク塗装方法よりも外観が低下するという問題があった。
また、特許文献2の塗膜形成方法では、中塗り塗膜に扁平顔料が含まれ、石などが衝突した際の衝撃緩和を塗膜水平方向に分散させるため、鋼板と電着塗膜との界面や電着塗膜と中塗り塗膜との界面の剥離は抑制できるが、中塗り塗膜での塗膜水平方向の剥離する面積が増大し、車体の外観を損なうという問題があった。
すなわち、本発明は、
[1] 電着塗膜を備えた自動車車体上に、第1水性ベース塗料を乾燥塗膜が10~40μmとなるように塗装して未硬化の第1ベース塗膜を形成する工程(1);
上記工程(1)で得られた未硬化の第1ベース塗膜上に第2水性ベース塗料を乾燥塗膜が5~30μmとなるように塗装して未硬化の第2ベース塗膜を形成する工程(2);
工程(1)および(2)で得られた未硬化の第1ベース塗膜および未硬化の第2ベース塗膜を加熱乾燥させた後に、クリヤー塗料を乾燥塗膜が10~70μmとなるように塗装して未硬化のクリヤー塗膜を形成する工程(3);ついで
工程(1)、(2)および(3)で得られた未硬化の第1ベース塗膜、未硬化の第2ベース塗膜および未硬化のクリヤー塗膜を同時に加熱硬化させて第1ベース塗膜、第2ベース塗膜およびクリヤー塗膜からなる複層塗膜を形成する工程(4)を含む、複層塗膜形成方法において、
第1ベース塗膜単膜の乾燥膜厚が25μm、第2ベース塗膜単膜の乾燥膜厚が10μm、および、クリヤー塗膜単膜の乾燥膜厚が30μmである複層塗膜の、20℃における伸び率が40~60%であり、抗張力が400~600kgf/m2であり、-20℃における弾性項に対する粘性項の比(tanδ)が0.04~0.06であることを特徴とする複層塗膜形成方法;
[4] ポリカーボネートジオール(a2-1)が重量平均分子量1,500~5,000を有する[3]に記載の複層塗膜形成方法;
を提供する。
このうち、水分散型ポリウレタン組成物(A)は、ジイソシアネートを必須成分とし、他のポリイソシアネートを任意成分として含んでいてもよいポリイソシアネート成分(a1)、重量平均分子量1,500~5,000のポリカーボネートジオール(a2-1)とカルボキシル基含有ジオール(a2-2)とを必須成分とし、他のポリオールを任意成分として含んでいてもよいポリオール成分(a2)、モノアミン化合物を必須成分とし、ジアミン化合物を任意成分として含んでいてもよいアミン成分(a3)、カルボキシル基中和成分(a4)、および水(a5)から得られる。
また、水酸基価についても、特に限定されるものではなく、任意の値を選択することができ、通常0~100mgKOH/gである。
また、モノマー混合物は、カルボニル基含有エチレン性不飽和モノマー、加水分解重合性シリル基含有モノマー、種々の多官能ビニルモノマーなどの架橋性モノマーを含んでいてもよい。その場合、得られる水分散型アクリル樹脂エマルションは自己架橋性となる。
硬化剤(C)としては、水分散型ポリウレタン組成物(A)および水分散型アクリル樹脂(B)のどちらか一方、または両方と硬化反応を生じ、第1水性ベース塗料に配合できるものであれば特に限定されるものではないが、例えば、アミノ樹脂および/またはブロックイソシアネート樹脂が特に好ましく用いられる。
1,6-ヘキサンジオールから得られる重量平均分子量2,000のポリカーボネートジオール0.26モル部、イソホロンジイソシアネート1.0モル部、ジメチロールプロピオン酸0.36モル部、これらの全質量の39質量%のN-メチル-2-ピロリドンを反応フラスコに仕込み、窒素気流下で、125℃で2時間反応させプレポリマーを得た。シリコーン系消泡剤SE-21(商品名、ワッカーシリコン社製)0.25g、トリエチルアミン22.0g、エチレンジアミン0.315g、モノエタノールアミン5.35gを溶解した600gの水に、上記で得られたプレポリマー500gを15分で滴下した。IR測定でイソシアネート基由来の吸収が消失するまで40℃で撹拌して、固形分31.5%の水分散型ポリウレタン組成物Aを得た。これに分散しているポリウレタン組成物の数平均分子量をGPC法によるポリスチレン標準で測定したところ、30,000であった。
1,6-ヘキサンジオールから得られる重量平均分子量2,000のポリカーボネートジオール0.13モル部、イソホロンジイソシアネート1.0モル部、ジメチロールプロピオン酸0.36モル部、これらの全質量の40質量%のN-メチル-2-ピロリドンを反応フラスコに仕込み、窒素気流下で、125℃で2時間反応させ、プレポリマーを得た。上記シリコーン系消泡剤SE-21を0.25g、トリエチルアミン31.0g、エチレンジアミン0.315g、モノエタノールアミン5.35gを溶解した600gの水に、上記で得られたプレポリマー500gを15分で滴下した。さらにIR測定でイソシアネート基由来の吸収が消失するまで40℃で30分撹拌して、固形分32.0%の水分散型ポリウレタン組成物Bを得た。これに分散しているポリウレタン組成物の数平均分子量を上記製造例1と同様に測定したところ、22,000であった。
1,6-ヘキサンジオールから得られる重量平均分子量1,000のポリカーボネートジオール0.26モル部、イソホロンジイソシアネート1.0モル部、ジメチロールプロピオン酸0.36モル部、これらの全質量の40質量%のN-メチル-2-ピロリドンを反応フラスコに仕込み、窒素気流下で、125℃で2時間反応させ、プレポリマーを得た。上記シリコーン系消泡剤SE-21を0.25g、トリエチルアミン22.0g、エチレンジアミン0.315g、モノエタノールアミン5.35gを溶解した600gの水に、上記で得られたプレポリマー500gを15分で滴下した。さらにIR測定でイソシアネート基由来の吸収が消失するまで、40℃で30分撹拌して、固形分31.7%の水分散型ポリウレタン組成物Cを得た。これに分散しているポリウレタン組成物の数平均分子量を上記製造例1と同様に測定したところ、17,000であった。
1,6-ヘキサンジオールから得られる重量平均分子量1,000のポリカーボネートジオール0.26モル部、ジシクロヘキシルメタン-4,4’-ジイソシアネート1.0モル部、ジメチロールプロピオン酸0.36モル部、これらの全質量の40質量%のN-メチル-2-ピロリドンを反応フラスコに仕込み、窒素気流下で、125℃で2時間反応させ、プレポリマーを得た。上記シリコーン系消泡剤SE-21を0.25g、トリエチルアミン22.00g、エチレンジアミン0.315g、モノエタノールアミン5.35gを溶解した600gの水に、上記で得られたプレポリマー500gを15分で滴下した。さらにIR測定でイソシアネート基由来の吸収が消失するまで、40℃で30分撹拌して、固形分31.7%の水分散型ポリウレタン組成物Dを得た。これに分散しているポリウレタン組成物の数平均分子量を上記製造例1と同様に測定したところ、15,000であった。
攪拌機、温度計、滴下ロート、還流冷却器および窒素導入管などを備えた通常のアクリル系樹脂エマルション製造用の反応容器に、水445部およびニューコール293(日本乳化剤社製アニオン系乳化剤)5部を仕込み、攪拌しながら75℃に昇温した。メタクリル酸メチル45部、アクリル酸ブチル299部、スチレン50部、アクリル酸2-ヒドロキシエチル92部、メタクリル酸14部およびエチレングリコールジメタクリレート20部からなるモノマー混合物(樹脂の酸価:18mgKOH/g、水酸基価:85mgKOH/g、Tg:-22℃)、水240部およびニューコール293 30部の混合物を、ホモジナイザーを用いて乳化し、そのモノマープレ乳化液を上記反応容器中に3時間にわたって攪拌しながら滴下した。モノマープレ乳化液の滴下と併行して、重合開始剤として過硫酸アンモニウム1部を水50部に溶解した水溶液を、上記反応容器中に上記モノマープレ乳化液の滴下終了時まで均等に滴下した。モノマープレ乳化液の滴下終了後、さらに80℃で1時間反応を継続し、その後、冷却した。冷却後、ジメチルアミノエタノール2部を水20部に溶解した水溶液を投入し、不揮発分40.6質量%の水分散型アクリル樹脂を得た。
反応容器にエチレングリコールモノメチルエーテル76部を仕込み、スチレン45部、メチルメタクリレート63部、2-ヒドロキシエチルメタクリレート48部、n-ブチルアクリレート117部、メタクリル酸27部およびアゾビスイソブチロニトリル3部からなるモノマー混合物のうち60部を加えて撹拌下、温度を120℃にした。120℃になると同時に上記モノマー混合液243部を3時間で等速滴下し、さらにその温度で1時間反応させて酸価が58mgKOH/g、水酸基価が70mgKOH/g、数平均分子量が10,000のアクリル樹脂を得た。これをジメチルエタノールアミンで中和して中和率80%、不揮発分50質量%の水溶性アクリル樹脂を得た。
エチレングリコール20.51部、トリメチロールプロパン12.91部、および無水フタル酸51.70部を加え、160~220℃で5時間エステル化反応させた後、さらに無水トリメリット酸14.88部を加えて180℃で1時間反応させて酸価が50mgKOH/g、水酸基価が60mgKOH/g、数平均分子量2,000のポリエステル樹脂を得た。これをジメチルエタノールアミンで中和して中和率80%、不揮発分35質量%の水溶性ポリエステル樹脂を得た。
第1水性ベース塗料の製造例
水分散型ポリウレタン組成物(A)28.3部(固形分8.9部)、水分散型アクリル樹脂4.9部(固形分2.0部)、水溶性アクリル樹脂10.6部(固形分5.3部)および水溶性ポリエステル樹脂15.1部(固形分5.3部)に、硬化剤としてサイメル327(商品名、日本サイテックインダストリーズ社製メラミン樹脂)8.4部(固形分7.6部)を混合した後、アデカノールUH814(商品名、ADEKA社製ウレタン会合型増粘剤)を混合攪拌し、水分散型ポリウレタン組成物(A)を塗料樹脂固形分100部に対して固形分として30部含まれる第1水性ベース塗料を得た。
但し顔料としては、塗料樹脂固形分合計100部に対してルチル型酸化チタン27部、硫酸バリウム48部およびカーボンブラック9部を配合した。
尚、これらの顔料は、予め水溶性アクリル樹脂と脱イオン水、消泡剤を加え、予備混合を行った後、ペイントコンディショナーにてガラスビーズ媒体中で分散処理した。
アクアレックスAR-2100NH-730(商品名、日本ペイント社製水性ソリッドベース塗料)と水分散型ポリウレタン組成物(A)をアクアレックスAR-2100NH-730の樹脂固形分100部に対して固形分が30部となるように混合攪拌し、第2水性ベース塗料を得た。
リン酸亜鉛処理したダル鋼板に、パワーニクス150(商品名、日本ペイント社製カチオン電着塗料)を、乾燥塗膜が20μmとなるように電着塗装し、160℃で30分間の加熱硬化後冷却して、鋼板基板を準備した。
また、鋼板基板に代えてポリプロピレン製試験板を使用し、かつ、回転霧化式静電塗装装置に代えてエアースプレーを用いたこと以外、同様にして複層塗膜を形成した。その後、複層塗膜をポリプロピレン製試験板から10×70mmの大きさに切断して取り出した応力歪特性用試験片と、5×20mmの大きさに切断して取り出した粘弾性用試験片を作製した。
応力歪特性
<伸び率・抗張力>
作製した応力歪特性用試験片を、オートグラフAGS-G型およびアナログメーター(島津製作所社製)を用いて、測定長さ50mm、温度20℃、引っ張り速度10mm/minで測定を行った。抗張力は、引っ張り試験直後のグラフの傾きより得た。また、伸び率は、グラフから読み取った試験片の伸び〔試験前の試験片の軸方向の長さを50(mm)、試験片が破断するまでの軸方向の長さL(mm)とする場合に、伸び率(%)=(L-50)×100/50〕より得た。
作製した粘弾性用試験片を、強制伸縮振動型粘弾性測定装置(オリエンテック社製、商品名「バイブロン」)を用いて、昇温時に発生する応力と振動ひずみの間に生じる位相差から-20℃のtanδを求めた。なお、測定周波数は11Hz、昇温速度は2℃/分とした。
グラベロテスター試験機(スガ試験機社製)を用いて、7号砕石50gを35cmの距離から2kgf/cm2の空気圧で、上記試験片の複層塗膜に90°の角度で衝突させた。水洗乾燥後、ニチバン社製工業用ガムテープを用いて剥離した
塗膜片を除去し、その後、塗膜のはがれの程度を目視により評価した。その後、塩水噴霧試験を行い、傷が鋼板にまで達している際に発生する錆の状態を目視にて評価した。塗膜のはがれおよび錆の状態は以下の評価基準にて評価した。結果を表1に示した。
1 ほとんどない
2 わずかにあるが外観上問題ないレベル
3 やや大きく、または、やや多く、かつ、外観上問題のあるレベル
4 大きい、または、多い
5 著しく大きい、または、著しく多い
上記のようにして得た複層塗膜を形成した試験片を、40℃の温水に10日間浸漬した後に取り出して、試験片の塗膜の膨潤によって生じる塗膜表面のチヂミ現象を目視で評価した。チヂミ現象が生じなかった試験片を○と評価し、生じた試験片を×と評価し、結果を表1に示した。
複層塗膜を形成した試験片に1滴のキシレン(0.1~0.3cc)を落とし、室温にて30分間放置した後に拭き取り、塗膜の部位の膨潤および膨潤によって生じる塗膜表面のチヂミ現象を目視で評価した。膨潤やチヂミ現象が生じなかった試験片を○と評価し、生じた試験片を×と評価し、結果を表1に示した。
表1に記載のとおり、水分散型ポリウレタン組成物(A)を、塗料樹脂固形分100部に対して固形分として各々所定量含まれる第1水性ベース塗料および第2水性ベース塗料を、実施例1と同様にして得た。
さらに、実施例1と同様にして、複層塗膜の形成された試験片を得た後、各種評価試験を実施した。結果を表1に示した。なお、実施例2~5および比較例7のクリヤー塗料としては、O-100に代えて、マックフローO-1900(商品名、日本ペイント社製、酸エポキシ硬化型クリヤー塗料)を用いた。
Claims (5)
- 電着塗膜を備えた自動車車体上に、第1水性ベース塗料を乾燥塗膜が10~40μmとなるように塗装して未硬化の第1ベース塗膜を形成する工程(1);
上記工程(1)で得られた未硬化の第1ベース塗膜上に第2水性ベース塗料を乾燥塗膜が5~30μmとなるように塗装して未硬化の第2ベース塗膜を形成する工程(2);
工程(1)および(2)で得られた未硬化の第1ベース塗膜および未硬化の第2ベース塗膜を加熱乾燥させた後に、クリヤー塗料を乾燥塗膜が10~70μmとなるように塗装して未硬化のクリヤー塗膜を形成する工程(3);ついで
工程(1)、(2)および(3)で得られた未硬化の第1ベース塗膜、未硬化の第2ベース塗膜および未硬化のクリヤー塗膜を同時に加熱硬化させて第1ベース塗膜、第2ベース塗膜およびクリヤー塗膜からなる複層塗膜を形成する工程(4)を含む、複層塗膜形成方法において、
第1ベース塗膜単膜の乾燥膜厚が25μm、第2ベース塗膜単膜の乾燥膜厚が10μm、および、クリヤー塗膜単膜の乾燥膜厚が30μmである複層塗膜の、20℃における伸び率が40~60%であり、抗張力が400~600kgf/m2であり、-20℃における弾性項に対する粘性項の比(tanδ)が0.04~0.06であることを特徴とする複層塗膜形成方法。 - 前記第1水性ベース塗料が、ポリイソシアネート成分(a1)、ポリオール(a2)、アミン成分(a3)、カルボキシル基中和成分(a4)および水(a5)から得られる水分散型ポリウレタン組成物(A)を含む請求項1に記載の複層塗膜形成方法。
- 前記ポリオール(a2)がポリカーボネートジオール(a2-1)およびカルボキシル基含有ジオール(a2-2)を含んでいる請求項2に記載の複層塗膜形成方法。
- ポリカーボネートジオール(a2-1)が重量平均分子量1,500~5,000を有する請求項3に記載の複層塗膜形成方法。
- 水分散型ポリウレタン組成物が、1:0.8~1:2のモル比であるポリカーボネートジオール(a2-1)とカルボキシル基含有ジオール(a2-2)とを含む請求項3または4に記載の複層塗膜形成方法。
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