JP4600386B2 - Multi-layer coating film, multi-layer coating method, and automobile painted with multi-layer coating - Google Patents

Description

  The present invention relates to a multilayer coating film having a double clear layer, a coating method for a multilayer coating film having a double clear layer, and an automobile coated with a multilayer coating film having a double clear layer.

  A coating composition using a polyisocyanate composition is widely used as a coating material for buildings, automobiles, information appliances and the like because of its excellent appearance, weather resistance, and durability. Above all, in applications where high quality appearance and excellent weather resistance and durability are required, such as automotive top coat applications, a two-component polyurethane paint that can form a dense cross-linked coating and has a good finished appearance. Is highly appreciated.

  For automotive top coat applications, in addition to high-quality appearance, excellent weather resistance and durability, it also has a high glass transition temperature (hereinafter referred to as Tg), good scratch resistance, and higher hardness. A composition is desired. Conventionally, when preparing such a coating composition, an acrylic polyol or polyester polyol having a relatively high molecular weight is used as the main polyol composition, and hexamethylene diisocyanate is used as the curing agent polyisocyanate composition. (Hereinafter referred to as HDI) polyisocyanate compositions obtained by isocyanurating diisocyanates such as HDI, and polyisocyanate compositions having a higher number of functional groups by using isocyanurates using diisocyanates such as HDI and polyhydric alcohols as raw materials It was.

  For example, the following Patent Document 1 discloses a multilayer coating film composed of one or more colored coating films and one or more transparent coating films, the uppermost transparent coating film having (A) a weight average molecular weight. 1000 or less, a hydroxyl group-containing compound having a hydroxyl value of 200 to 800 and (B) a polyisocyanate compound, and the ratio of both components is 0.5 / 1 to 2.0 / 1 in terms of a molar ratio of NCO / OH. A method for forming a multilayer coating film formed from a certain high solid content coating composition is disclosed.

  As described above, the automobile body is first coated with an electrodeposition paint and baked to form an intermediate coating film on which an overcoat consisting of a base coating film and a clear coating film is applied. .

  The clear coating is formed in order to protect the underlying base coating and the like and enhance the appearance of the substrate to be coated, but is generally performed wet-on-wet. Moreover, in order to obtain a higher appearance, it is known to form two or more clear coating films. These methods are called double clear coatings. When the under clear layer (first clear coating) is baked and cured to form a top clear layer (second clear coating), adhesion and coating appearance In some cases, the under-clear layer (first clear coating film) formed in order to ensure the thickness is polished.

  In the following Patent Document 2, when the first clear coating film in the double clear coating film is baked and cured, the second clear coating film is formed without polishing the formed first clear coating film. There are disclosed a thermosetting clear paint capable of obtaining a high-appearance coating film, a method for forming a multilayer coating film using the thermosetting clear paint, and a coated product coated by this method. Specifically, in order to form a first clear coating of a multilayer coating sequentially having a base coating, a first clear coating, and a second clear coating on a substrate to be coated, The use of a thermosetting clear paint containing an acrylic resin, a polyester oligomer, an iminomethylol-type methylated melamine resin and an iminomethylol-type butylated melamine resin is disclosed.

JP 2002-138247 A JP 2003-277678 A

  As described above, a urethane clear coating system is known, and a double clear coating system is known for non-urethane systems. However, a double clear coating system using a two-component urethane cross-linking system is not known. In addition, the conventional double clear coating requires the use of two types of paints, that is, the under clear paint and the top clear paint, and also requires the use of these two kinds of paint methods. Specifically, in order to apply two types of clear paint, intermediate layer coating ⇒ bake ⇒ base layer coating ⇒ preheat ⇒ under clear layer coating ⇒ top clear layer after the first step consisting of bake The so-called twice rotation of the second step consisting of painting and baking is required.

  Therefore, an object of the present invention is to find conditions for practically performing a double clear coating system to which a two-component urethane crosslinking system that has not been conventionally practiced is applied. This makes it possible to perform a so-called one-time rotation consisting of intermediate coating layer → bake → base layer coating → preheat → under clear layer coating → preheat → top clear layer coating → bake.

  The present inventor has found that the above problem can be solved by changing the ratio of the main component and the curing agent of the two-component urethane cross-linking system between the under clear layer and the top clear layer, and has reached the present invention.

  That is, first, the present invention is an invention of a multilayer coating film comprising at least an intermediate coating layer, a base layer, and a clear layer applied on an object to be coated, wherein the clear layer has two layers. The ratio (OH / NCO) of the hydroxyl group amount of the hydroxyl group-containing compound (component A) and the isocyanate group amount of the polyisocyanate (component B) in the underclear layer in contact with the base layer, comprising the above two-component polyurethane coating film, It is characterized by being larger than the ratio (OH / NCO) of the hydroxyl group amount of the hydroxyl group-containing compound (component A) to the isocyanate group amount of the polyisocyanate (component B) in the top clear layer in contact with the underclear layer.

  The multi-layer coating film of the present invention has a high quality because it is a double clear coating system having two or more clear layers, and since both the under clear layer and the top clear layer are two-component polyurethane coating films. Excellent appearance, excellent weather resistance, durability, good scratch resistance, and high hardness. Further, by making the amount of hydroxyl group of the hydroxyl group-containing compound (component A) in the underclear layer richer than that of the polyisocyanate (component B), the hydroxyl group remaining after the formation of the underclear layer is rich in the polyisocyanate in the next top clear layer. It is possible to react strongly with the isocyanate group of (B component).

  As a specific ratio (OH / NCO) of the hydroxyl group amount of the hydroxyl group-containing compound (component A) and the isocyanate group amount of the polyisocyanate (component B), the hydroxyl group amount of the hydroxyl group-containing compound (component A) in the underclear layer Polyisocyanate (component B) isocyanate group amount ratio (OH / NCO) = 1 / 0.8 to 1 / 0.5, the hydroxyl group content of the hydroxyl group-containing compound (component A) in the top clear layer and polyisocyanate The ratio of the isocyanate group amount (OH / NCO) of (Component B) is preferably 1/1 to 1 / 1.5.

  The multilayer coating film of the present invention is not particularly limited as the object to be coated, and is used for various applications that require high-quality coating film appearance and excellent durability. For example, it is preferably applied to at least one selected from metal, plastic, ceramic, and wood.

  2ndly, this invention is invention of the coating method of said multilayer coating film, The process of apply | coating an intermediate coating layer, the process of apply | coating a base layer, and a clear layer are apply | coated on to-be-coated object. A method of coating a multi-layer coating film comprising at least a step, wherein the step of applying the clear layer comprises a step of applying two or more two-component polyurethane-based coating films, wherein the under-clear layer is in contact with the base layer The ratio (OH / NCO) of the amount of hydroxyl group of the hydroxyl group-containing compound (component A) to the amount of isocyanate group of the polyisocyanate (component B) is the amount of hydroxyl group of the hydroxyl group-containing compound (component A) in the top clear layer in contact with the underclear layer. The under-clear layer and the top-clear layer are applied with a ratio larger than the ratio (OH / NCO) of the isocyanate groups of polyisocyanate (component B).

  In the coating method of the present invention, since both the under clear layer and the top clear layer use a two-component polyurethane-based coating film, the amount of the hydroxyl group of the hydroxyl group-containing compound (component A) as the main agent and the polyisocyanate (B A double clear coating system can be established only by controlling the supply ratio (OH / NCO) of the isocyanate group amount of the component.

  As the supply ratio (OH / NCO) of the amount of hydroxyl group of the hydroxyl group-containing compound (component A) as the main agent and the amount of isocyanate group of the polyisocyanate (component B) as the curing agent, the underclear layer is a hydroxyl group-containing compound (component A). ) And the ratio of hydroxyl group of polyisocyanate (component B) (OH / NCO) = 1 / 0.8 to 1 / 0.5, and the hydroxyl group-containing compound in the top clear layer (component A) As described above, the coating is preferably performed at a ratio (OH / NCO) = 1/1 to 1 / 1.5 of the amount of the hydroxyl group and the amount of the isocyanate group of the polyisocyanate (component B).

  In the coating method of the present invention, the ratio of the hydroxyl group amount of these hydroxyl group-containing compounds (component A) and the isocyanate group amount of polyisocyanate (component B) (OH / NCO) is changed between the under clear layer and the top clear layer. It is possible to apply continuously.

  Moreover, in the coating method of the present invention, since both the under clear layer and the top clear layer are two-component polyurethane-based coatings, the intermediate coating layer coating → bake⇒base layer coating⇒preheating⇒under clear layer coating⇒ Pre-clear ⇒ Top clear layer coating ⇒ Double clear coating is possible by so-called one turn consisting of bake. Here, as the optimum conditions for preheating after applying the underclear layer, the point A (90 ° C., 18 minutes) in coordinates with the preheating temperature (° C.) as the x axis and the preheating time (minutes) as the y axis, It is a range surrounded by point B (90 ° C., 10 minutes), point C (120 ° C., 3 minutes), and point D (120 ° C., 18 minutes).

In the coating method of the present invention, as described above, one or more selected from metals, plastics, ceramics, and wood are preferably mentioned as the object to be coated.
Thirdly, the present invention is an automobile coated with the multilayer coating film.

  The multi-layer coating film of the present invention has a high quality because it is a double clear coating system having two or more clear layers, and since both the under clear layer and the top clear layer are two-component polyurethane coating films. Excellent appearance, excellent weather resistance, durability, good scratch resistance, and high hardness.

  Moreover, in the coating method of the present invention, since both the under clear layer and the top clear layer are two-component polyurethane-based coatings, the intermediate coating layer coating → bake⇒base layer coating⇒preheating⇒under clear layer coating⇒ Pre-clear ⇒ Top clear layer coating ⇒ Double clear coating is possible by so-called one turn consisting of bake.

  FIG. 1 shows a two-stage coating process called a two-turn process having a conventional process 1 and process 2. As shown in Fig. 1, in order to apply two types of clear paint, intermediate layer coating ⇒ bake ⇒ base layer coating ⇒ preheat ⇒ under clear layer coating ⇒ after the first step consisting of bake, the top Clear layer coating ⇒ So-called twice rotation of the second step consisting of baking is required.

  FIG. 2 shows a one-step coating process called one-time turning in which double clear coating is performed in a one-step process. As shown in Fig. 2, the double clear coating system using the two-component urethane cross-linking system is applied to the intermediate coating layer ⇒ bake ⇒ base layer coating ⇒ preheating ⇒ underclear layer coating ⇒ preheating ⇒ top clear layer coating ⇒ bae So-called one-time turning made of

  In the present invention, by using a double clear coating system to which a two-component urethane cross-linking system is applied, intermediate coating layer painting → bake⇒base layer coating⇒preheating⇒under clear layer coating⇒preheating⇒top clear layer coating⇒bay The so-called one-time turning made of cucumber has become possible. In the present invention, since the urethane-based paint in which the component ratio is changed is used for the under clear layer coating and the top clear layer coating, it is not limited to the conventional two-time rotation (two-stage method), but the one time as described above. It is also possible to adopt a spinning process (one-stage method).

  FIG. 3 shows the preheating temperature found after the under-clear layer coating and before the top coat layer coating in the one-step coating process called one-time turning in which the double clear coating is performed in a one-step process. And the optimal conditions of time. As shown in FIG. 3, in the coordinates where the preheating temperature (° C.) is the x axis and the preheating time (min) is the y axis, point A (90 ° C., 18 minutes), point B (90 ° C., 10 minutes), The range surrounded by point C (120 ° C., 3 minutes) and point D (120 ° C., 18 minutes) is the optimum preheating condition.

  In one turn, a two-component urethane-based paint with high curing reactivity is used, the base layer and below are concealed by preheating after painting the under clear layer, and sufficient finish can be ensured by top clear layer painting.

Hereinafter, each layer constituting the present invention and each component used in the present invention will be described.
As the intermediate coating layer and the base layer in the present invention, known ones can be widely used for automobile coating or the like.

  In the present invention, the two-component polyurethane-based coating film used for the underclear layer and the top clear layer is formed from a hydroxyl group-containing compound (A component) as a main agent and a polyisocyanate (B component) as a curing agent.

  The main component, hydroxyl group-containing compound (component A: polyol), is an oligomeric polyol that is generally used in the polyurethane technology field. By mixing and reacting with the polyisocyanate that is a curing agent, the underclear layer and top clear are obtained. It is the main component that forms the layer.

  Examples of such a hydroxyl group-containing compound (component A: polyol) include polyether polyol, polyester polyol, and acrylic polyol. Examples of polyether polyols include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, glycerin, trimethylolpropane, pentaerythritol, glucose, sorbitol, sucrose and one or more polyhydric alcohols such as propylene oxide and ethylene. There are polyols obtained by adding one or more of oxide, butylene oxide, styrene oxide and the like, and polyoxytetramethylene polyols obtained by adding tetrahydrofuran to the polyhydric alcohol by ring-opening polymerization. .

  Polyester polyols include ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, cyclohexanedimethanol, glycerin, trimethylolpropane, pentaerythritol, or other low molecular weight polyhydric alcohols and glutar. Condensation polymers with one or more of acid, adipic acid, pimelic acid, speric acid, sebacic acid, terephthalic acid, isophthalic acid, dimer acid, hydrogenated dimer acid or other low molecular dicarboxylic acid or oligomeric acid, Examples include polyols such as ring-opening polymers of ring-opening esters such as propiolactone, caprolactone, and valerolactone.

  Moreover, in acrylic copolymers, β-hydroxyethyl acrylate, β-hydroxypropyl acrylate, 2-hydroxypropyl acrylate, β-hydroxybutyl acrylate, 4-hydroxybutyl acrylate, β-hydroxypentyl acrylate, etc. Hydroxyalkyl esters of acrylic acid or similar hydroxyalkyl esters of methacrylic acid, acrylic acid monoesters of polyhydric alcohols such as glycerin and trimethylolpropane, or methacrylic acid monoesters similar to these, N-methylolacrylamide or N- An acrylic polyol having two or more hydroxyl groups in one molecule using a monoethylenically unsaturated monomer having a hydroxyl group such as methylol methacrylamide as a copolymerization monomer can be used.

  Other examples include phenol resin polyols, epoxy polyols, polybutadiene polyols, polyisoprene polyols, polyester-polyether polyols, polymer polyols obtained by adding or dispersing monomers such as acrylic and styrene, urea-dispersed polyols, and carbonate polyols. It can be used as a polyol of the invention. These polyols can be used not only in a general solvent type but also in a non-aqueous dispersion (NAD) type. In particular, acrylic polyol is desirable from the viewpoint of durability.

  The molecular weight of the hydroxyl group-containing compound (component A: polyol) used in the present invention is 2000 to 50000 in terms of weight average molecular weight, preferably 8000 to 30000. When the molecular weight is smaller than 2000, the curability and durability of the coating film are not sufficient, and when it is larger than 50000, the finishing property of the coating film is not sufficient.

  Furthermore, the hydroxyl value of these hydroxyl group-containing compounds (component A: polyol) is 20 to 200 KOHmg / g, preferably 30 to 170 KOHmg / g. When the hydroxyl value is less than 20 KOHmg / g, the durability and contamination of the coating film are poor, and when it exceeds 170 KOHmg / g, the durability and flexibility of the coating film are not sufficient.

  Moreover, the glass transition point of these hydroxyl-containing compounds (A component: polyol) is -20 degreeC-150 degreeC, Preferably it is -10 degreeC-100 degreeC. When it becomes lower than −20 ° C., the durability of the formed coating film tends to deteriorate. Conversely, when the temperature is higher than 150 ° C., flexibility and durability are inferior.

  Examples of the polyisocyanate (component B) that is a curing agent include toluene diisocyanate (TDI), 4,4-diphenylmethane diisocyanate (pure-MDI), polymeric MDI, xylylene diisocyanate (XDI), hexamethylene diisocyanate (HMDI), and isophorone diisocyanate. (IPDI), hydrogenated XDI, hydrogenated MDI, and other isocyanate monomers such as allohanate, biuret, dimerization (uretidione), trimerization (isocyanurate), adduct formation, carbodiimide reaction, reaction with polyester polyol and caprolactam, etc. Derivatives and mixtures thereof can be used. These polyisocyanates (component B) are preferably used as a solution in a solvent not containing active hydrogen. Furthermore, these polyisocyanates (component B) can also be used in the form of blocked isocyanates using blocking agents such as alcohols, phenols, ε-caprolactam, oximes, and active methylene compounds. These polyisocyanates (component B) are also preferably used as a solution in a solvent containing no active hydrogen.

  As the supply ratio (OH / NCO) of the amount of hydroxyl group of the hydroxyl group-containing compound (component A) as the main agent and the amount of isocyanate group of the polyisocyanate (component B) as the curing agent, the underclear layer is a hydroxyl group-containing compound (component A). ) And the ratio of hydroxyl group of polyisocyanate (component B) (OH / NCO) = 1 / 0.8 to 1 / 0.5, and the hydroxyl group-containing compound in the top clear layer (component A) As described above, the coating is preferably performed at a ratio (OH / NCO) = 1/1 to 1 / 1.5 of the amount of the hydroxyl group and the amount of the isocyanate group of the polyisocyanate (component B). At this time, even if the ratio of OH / NCO is small or large, the durability and curability of the coating film are inferior, so that the durability of the coating film as a whole laminated coating film is inferior.

  In the present invention, the two-component urethane paint that forms the under clear layer and the top clear layer may be mixed with a color pigment to form a colored (enamel) coating film. Examples of such color pigments include titanium oxide, zinc oxide, carbon black, ferric oxide (bengal), lead chromate (molybdate orange), yellow lead, yellow iron oxide, ocher, ultramarine, and cobalt green. Organic pigments such as pigments, azo, naphthol, pyrazolone, anthraquinone, perylene, quinacridone, and quinophthalone can be used. It is also possible to use extender pigments such as heavy calcium carbonate, clay, kaolin, talc, precipitated barium sulfate, barium carbonate, white carbon, diatomaceous earth.

  In addition, it is possible to add various additives that can be normally added to the paint to such an extent that the effects of the present invention are not affected. Examples of such additives include plasticizers, antiseptics, antifungal agents, algae inhibitors, antifoaming agents, leveling agents, pigment dispersants, anti-settling agents, anti-sagging agents, matting agents, and UV absorbers. can give.

  Examples of the present invention and comparative examples are shown below. A multilayer coating film was formed in the following steps, and its performance was evaluated.

[Comparative Example 1]
(1) A zinc phosphate treated 150 × 300 × 0.8 mm dull steel plate was used as a material to be coated.
(2) Power Knicks 310 (trade name, an isocyanate curable epoxy resin electrodeposition paint manufactured by Nippon Paint Co., Ltd.) was electrodeposited so that the dry film thickness was 20 μm, and baked at 160 ° C. for 30 minutes.
(3) Olga P-30 (trade name, Nippon Paint Co., Ltd., melamine curable polyester resin-based intermediate coating) is spray-coated to a dry film thickness of 35 μm, baked at 140 ° C. for 30 minutes, and then cooled. Thus, an intermediate coated substrate was obtained.
(4) AQUALEX AR-2000 (trade name, melamine curable acrylic resin-based aqueous topcoat base paint manufactured by Nippon Paint Co., Ltd.) was spray-coated to a dry film thickness of 15 μm, and then preheated at 80 ° C.
(5) The coated plate is allowed to cool to room temperature, and as a clear, Super Lac O-171 (trade name, acrylic melamine curable clear paint manufactured by Nippon Paint Co., Ltd.) is applied to a dry film thickness of 35 μm, at 140 ° C. Heat cured for 30 minutes.
(6) Again, the coated plate is allowed to cool to room temperature, and as a clear, Mac Flow O-1820 (trade name, acid epoxy cured clear paint manufactured by Nippon Paint Co., Ltd.) is applied to a dry film thickness of 35 μm, 140 ° C. For 30 minutes to form a multilayer coating on the substrate.
(7) After preparing the coated plate, an adhesion test and a finished appearance evaluation were performed.

[Example 1]
(1) A zinc phosphate treated 150 × 300 × 0.8 mm dull steel plate was used as a material to be coated.
(2) Power Knicks 310 (trade name, an isocyanate curable epoxy resin electrodeposition paint manufactured by Nippon Paint Co., Ltd.) was electrodeposited so that the dry film thickness was 20 μm, and baked at 160 ° C. for 30 minutes.
(3) Olga P-30 (trade name, Nippon Paint Co., Ltd., melamine curable polyester resin-based intermediate coating) is spray-coated to a dry film thickness of 35 μm, baked at 140 ° C. for 30 minutes, and then cooled. Thus, an intermediate coated substrate was obtained.
(4) AQUALEX AR-2000 (trade name, melamine curable acrylic resin-based aqueous topcoat base paint manufactured by Nippon Paint Co., Ltd.) was spray-coated to a dry film thickness of 15 μm, and then preheated at 80 ° C.
(5) The coated plate is allowed to cool to room temperature, and a clear polyurexel O-1100 (trade name, urethane curable clear paint manufactured by Nippon Paint Co., Ltd.) with a base agent / curing agent ratio of 1 / 0.7 as a clear film is dried. It was coated to 35 μm and cured by heating at 140 ° C. for 30 minutes.
(6) The coated plate is allowed to cool again to room temperature, and Polyurexel O-1100 (trade name, urethane curable clear paint manufactured by Nippon Paint Co., Ltd.) with the main agent / curing agent ratio = 1 / 1.2 is dried as clear. The coating was applied to a film thickness of 35 μm and cured by heating at 140 ° C. for 30 minutes to form a multilayer coating film on the substrate.
(7) After preparing the coated plate, an adhesion test and a finished appearance evaluation were performed.

[Comparative Example 2]
(1) A zinc phosphate treated 150 × 300 × 0.8 mm dull steel plate was used as a material to be coated.
(2) Power Knicks 310 (trade name, an isocyanate curable epoxy resin electrodeposition paint manufactured by Nippon Paint Co., Ltd.) was electrodeposited so that the dry film thickness was 20 μm, and baked at 160 ° C. for 30 minutes.
(3) Olga P-30 (trade name, Nippon Paint Co., Ltd., melamine curable polyester resin-based intermediate coating) is spray-coated to a dry film thickness of 35 μm, baked at 140 ° C. for 30 minutes, and then cooled. Thus, an intermediate coated substrate was obtained.
(4) AQUALEX AR-2000 (trade name, melamine curable acrylic resin-based aqueous topcoat paint manufactured by Nippon Paint Co., Ltd.) was spray-coated to a dry film thickness of 15 μm, and then preheated at 80 ° C.
(5) The coated plate is allowed to cool to room temperature, and as a clear, Mac Flow O-1820 (trade name, acid epoxy cured clear paint manufactured by Nippon Paint Co., Ltd.) is applied to a dry film thickness of 35 μm, and 30 ° C. at 30 ° C. Heat cured for minutes.
(6) Again, the coated plate was allowed to cool to room temperature, and as a clear, Mac Flow O-1820 (trade name, acid epoxy curing clear paint made by Nippon Paint Co., Ltd.) with the main agent / curing agent ratio = 1 / 1.2 The coating was applied to a dry film thickness of 35 μm and cured by heating at 140 ° C. for 30 minutes to form a multilayer coating film on the substrate.
(7) After preparing the coated plate, an adhesion test and a finished appearance evaluation were performed.

[Example 2]
(1) A zinc phosphate treated 150 × 300 × 0.8 mm dull steel plate was used as a material to be coated.
(2) Power Knicks 310 (trade name, an isocyanate curable epoxy resin electrodeposition paint manufactured by Nippon Paint Co., Ltd.) was electrodeposited so that the dry film thickness was 20 μm, and baked at 160 ° C. for 30 minutes.
(3) Olga P-30 (trade name, Nippon Paint Co., Ltd., melamine curable polyester resin-based intermediate coating) is spray-coated to a dry film thickness of 35 μm, baked at 140 ° C. for 30 minutes, and then cooled. Thus, an intermediate coated substrate was obtained.
(4) AQUALEX AR-2000 (trade name, melamine curable acrylic resin-based aqueous topcoat base paint manufactured by Nippon Paint Co., Ltd.) was spray-coated to a dry film thickness of 15 μm, and then preheated at 80 ° C.
(5) The coated plate is allowed to cool to room temperature, and a clear polyurexel O-1100 (trade name, urethane curable clear paint manufactured by Nippon Paint Co., Ltd.) with a base agent / curing agent ratio = 1 / 0.7 as a clear film is dried. It was coated to 35 μm and preheated at 100 ° C. for 10 minutes.
(6) The coated plate is allowed to cool again to room temperature, and Polyurexel O-1100 (trade name, urethane curable clear paint manufactured by Nippon Paint Co., Ltd.) with the main agent / curing agent ratio = 1 / 1.2 is dried as clear. The coating was applied to a film thickness of 35 μm and cured by heating at 140 ° C. for 30 minutes to form a multilayer coating film on the substrate.
(7) After preparing the coated plate, an adhesion test and a finished appearance evaluation were performed.

[Comparative Example 3]
(1) A zinc phosphate treated 150 × 300 × 0.8 mm dull steel plate was used as a material to be coated.
(2) Power Knicks 310 (trade name, an isocyanate curable epoxy resin electrodeposition paint manufactured by Nippon Paint Co., Ltd.) was electrodeposited so that the dry film thickness was 20 μm, and baked at 160 ° C. for 30 minutes.
(3) Olga P-30 (trade name, Nippon Paint Co., Ltd., melamine curable polyester resin-based intermediate coating) is spray-coated to a dry film thickness of 35 μm, baked at 140 ° C. for 30 minutes, and then cooled. Thus, an intermediate coated substrate was obtained.
(4) AQUALEX AR-2000 (trade name, melamine curable acrylic resin-based aqueous topcoat base paint manufactured by Nippon Paint Co., Ltd.) was spray-coated to a dry film thickness of 15 μm, and then preheated at 80 ° C.
(5) The coated plate is allowed to cool to room temperature, and as a clear, Super Lac O-171 (trade name, acrylic melamine curable clear paint manufactured by Nippon Paint Co., Ltd.) is applied to a dry film thickness of 35 μm, at 100 ° C. Preheated for 10 minutes.
(6) Again, the coated plate is allowed to cool to room temperature, and as a clear, Mac Flow O-1820 (trade name, acid epoxy cured clear paint manufactured by Nippon Paint Co., Ltd.) is applied to a dry film thickness of 35 μm, 140 ° C. For 30 minutes to form a multilayer coating on the substrate.
(7) After preparing the coated plate, an adhesion test and a finished appearance evaluation were performed.

[Adhesion test method]
A cross-cut adhesion test was performed according to the following procedure.
(1) A small cutter knife is vertically applied to the coating surface of the test piece, 11 equidistant parallel lines reaching the substrate are drawn, and 11 equidistant parallel lines intersecting the parallel lines are drawn to obtain 4 pieces. Draw 100 squares surrounded by straight lines.
(2) At a temperature of 20 ± 2 ° C. and a humidity of 65 ± 5%, the adhesive tape (width: 24 mm) is uniformly crimped with a fingertip so as not to contain bubbles on the coated surface of the test piece that has been cut off. Hold one end of the adhesive tape and pull it abruptly to remove the tape from the specimen.
(3) It is determined that there is no peeling = O and there is peeling = X.

[Finishability evaluation]
Finished performance was implemented. Visually evaluate the finished appearance, and in order from the worst, × → Δ → ○ → ◎.
Table 1 below shows the reaction systems of Examples 1 and 2 and Comparative Examples 1 to 3 and the performance evaluation results.

  In Comparative Example 2, the reason why the adhesiveness is “x” is that when the current material is used for underclear, the amount of hydroxyl groups in the underclear decreases, and thus the adhesiveness is not exhibited. Moreover, in Comparative Example 3, the reason why the finished appearance is x is that the performance is not exhibited unless baking is performed at 140 ° C. after under-clear coating, and the adhesion and finished appearance are x.

  The multilayer coating film of the present invention exhibits a high quality appearance, excellent weather resistance, durability, good scratch resistance, and higher hardness, and thus is suitable as a coating film for automobiles and the like. In addition, in the coating method of the present invention, it is possible to establish a double clear coating system by controlling the supply ratio of the main agent and the curing agent with only one kind of paint, and in addition, the intermediate coating layer coating ⇒ bake ⇒ base Layer coating ⇒ Preheating ⇒ Under clear layer coating ⇒ Preheating ⇒ Top clear layer coating ⇒ Bake the double clear coating by so-called one-time rotation, contributing to simplification and cost reduction of coating.

The painting process of the two-stage method called two times turning is shown. The painting process of the one-step method called one turn is shown. The optimum conditions of preheat temperature and time after under clear layer coating and before top coat layer coating are shown.

Claims (9)

  A multi-layer coating film comprising at least an intermediate coating layer, a base layer, and a clear layer applied on an object to be coated, the clear layer comprising two or more two-component polyurethane-based coating films, The ratio (OH / NCO) of the hydroxyl group content of the hydroxyl group-containing compound (component A) to the isocyanate group content of the polyisocyanate (component B) in the under clear layer in contact with the base layer is the hydroxyl group content in the top clear layer in contact with the under clear layer. The multilayer coating film characterized by being larger than the ratio (OH / NCO) of the amount of hydroxyl groups of the compound (component A) and the amount of isocyanate groups of the polyisocyanate (component B).   The ratio (OH / NCO) of the amount of hydroxyl group of the hydroxyl group-containing compound (component A) to the amount of isocyanate group of polyisocyanate (component B) in the underclear layer is 1 / 0.8 to 1 / 0.5, and the top The ratio (OH / NCO) of the hydroxyl group amount of the hydroxyl group-containing compound (component A) and the isocyanate group amount of the polyisocyanate (component B) in the clear layer is from 1/1 to 1 / 1.5. 2. The multilayer coating film according to 1.   The multilayer coating film according to claim 1 or 2, wherein the object to be coated is at least one selected from metal, plastic, ceramic, and wood.   A method for coating a multilayer coating film comprising at least a step of applying an intermediate coating layer, a step of applying a base layer, and a step of applying a clear layer on an object to be coated, wherein the clear layer is applied The process consists of a process of applying a two-component or more two-component polyurethane coating film, and the amount of hydroxyl group of the hydroxyl group-containing compound (component A) and the amount of isocyanate group of the polyisocyanate (component B) in the underclear layer in contact with the base layer The ratio (OH / NCO) is made larger than the ratio (OH / NCO) of the hydroxyl group content of the hydroxyl group-containing compound (component A) and the isocyanate group amount of polyisocyanate (component B) in the top clear layer in contact with the underclear layer. A method for coating a multilayer coating film, comprising applying the under clear layer and the top clear layer.   The underclear layer was applied at a ratio (OH / NCO) of the hydroxyl group amount of the hydroxyl group-containing compound (component A) and the isocyanate group amount of the polyisocyanate (component B) at 1 / 0.8 to 1 / 0.5, The ratio (OH / NCO) of the hydroxyl group amount of the hydroxyl group-containing compound (component A) and the isocyanate group amount of the polyisocyanate (component B) in the top clear layer is 1/1 to 1 / 1.5. The coating method of the multilayer coating film of Claim 4.   The under clear layer and the top clear layer are continuously applied by changing the ratio of hydroxyl groups of these hydroxyl group-containing compounds (component A) and isocyanate groups of polyisocyanate (component B) (OH / NCO). The coating method of the multilayer coating film of Claim 4 or 5 characterized by the above-mentioned.   Pre-coating after application of the underclear layer is performed at coordinates A (90 ° C., 18 minutes), B (90 ° C., 10 minutes), C point (120 degreeC, 3 minutes), and the range enclosed by D point (120 degreeC, 18 minutes), The coating method of the multilayer coating film of Claim 4 or 5 characterized by the above-mentioned.   The method of coating a multilayer coating film according to any one of claims 4 to 7, wherein the object to be coated is at least one selected from metal, plastic, ceramic, and wood. An automobile body coated with the multilayer coating film according to any one of claims 1 to 3.

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