JP2009274379A - Pre-coated metal plate and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pre-coated metal plate having designability such as luster, sharpness or the like and excellent scratch resistance. <P>SOLUTION: In the pre-coated metal plate having at least two coating film layers, the top coating film layer is a pigment-free clear coating film and includes isocyanate curing type acrylic resin and having a glass transition temperature of 60-80°C, while the intermediate coating film layer of which includes colored pigment and melamine curing type or isocyanate curing type polyester resin and having a glass transition temperature of 30-50°C under the condition that the relationship between the film thickness T (μm) of the top coating film layer and the film thickness t (μm) of the intermediate coating film layer satisfie the inequality of 0.5≤T/t≤2. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a pre-coated metal plate and a method for producing the same, and in particular, for various uses such as home appliances, building materials, civil engineering, machinery, automobiles, furniture, containers, and the like, gloss, sharpness, etc. The present invention relates to a pre-coated metal sheet having excellent design properties and excellent scratch resistance, and a method for producing the same.

  For example, a pre-coated metal sheet coated with a pre-colored coating film is used instead of a post-painted product that has been painted after processing a conventional metal sheet on the outer sheet of the home appliance field, building material field, automobile field, etc. It has become like this. On the other hand, in these applications, there is an increasing demand for coating appearance with high gloss and sharpness from the viewpoint of design and design.

  As a technique for improving the gloss and sharpness of a coating film, for example, as described in Patent Document 1, a technique for reducing the surface roughness of a metal plate as a base material, for example, described in Patent Document 2 For example, a technique for coating a coating film using a resin having a low molecular weight, for example, a technique for coating a clear coating film on a colored coating layer as disclosed in Patent Document 3, is disclosed.

  When a precoat metal plate is produced industrially, it is generally manufactured in a continuous coating line called a coil coating line as described in Non-Patent Document 1, for example. In a normal coil coating line, a primer coating having a rust prevention function is applied onto a metal plate in a coating device called a roll coater or curtain coater, baked in a hot air oven or the like, and then colored again in the coating device. Two-time coating and two-time baking (generally referred to as a two-coat two-bake method) in which a paint is applied and baked are common. Therefore, even if you try to paint a clear paint film with excellent clarity on the colored layer, invest a large amount of equipment and add more coating equipment and ovens, or pass the coil coating line twice. It was necessary to take measures such as painting and painting. However, as a means for solving this problem, as described in Patent Documents 4 to 12, there is known a wet-on-wet coating method in which a paint is repeatedly applied in an undried state.

  On the other hand, pre-coated metal sheets are used after being molded after coating, so it is common to coat a flexible coating film with excellent workability, but on the other hand, such a coating film has poor scratch resistance. There was a drawback that it was easily damaged during transportation and processing. For example, in Patent Document 13, a polyester resin having a glass transition point of 5 to 40 ° C. and a number average molecular weight of 15,000 to 30,000 and a hexamethoxymethylolated melamine resin are adjusted to a mass ratio of 75/25 to 55/45. For coated metal plates with excellent red magic stainability and excellent workability due to the paint comprising 1 to 2 parts by weight of the amine block of dodecylbenzenesulfonic acid to 100 parts by weight of the blended polyester-melamine resin. A coating composition is disclosed. Patent Documents 14 and 15 disclose techniques for increasing the hardness and improving the scratch resistance by adding glass fibers or glass beads to the coating film.

JP-A-7-150326 JP-A-1-304934 JP-A-10-66931 JP-A-11-19581 Japanese Patent Laid-Open No. 11-19582 JP-A-11-19583 Japanese Patent Laid-Open No. 11-19484 Japanese Patent Laid-Open No. 11-19585 Japanese Patent Laid-Open No. 11-19586 Japanese Patent Laid-Open No. 11-57608 JP-A-11-76932 JP-A-11-76933 JP-A-2-269168 Japanese Patent Publication No. 63-5938 Japanese Examined Patent Publication No. 4-11671 Ueda et al., Coloring Materials, 72 (8), 525-531 (1999)

  However, the method of obtaining high gloss and high definition by controlling the surface roughness of the base material of the pre-coated metal sheet to be low, the surface roughness of the base metal sheet is whatever the coating film is used. Can control relatively high gloss and high clarity, while rolling the metal with a rolling roll with adjusted surface roughness or polishing with a polishing machine, etc. The surface roughness of a certain metal plate must be controlled. Therefore, there is a drawback that it takes a lot of labor and cost to produce a precoated metal plate having high gloss and sharpness by this method. On the other hand, the method of obtaining a pre-coated metal plate with high gloss and sharpness by applying a paint using a resin having a low molecular weight is compared to the method of obtaining by controlling the surface roughness of the metal plate as a base material. Although it can be produced relatively easily, it is difficult to impart other coating film performance, such as processability, because a specific resin must be used for the paint.

  As a method for obtaining a pre-coated metal plate having relatively high gloss and sharpness relatively easily, a method of coating a transparent clear coating on the colored coating layer is suitable. Furthermore, using a general coil coating line, in order to apply a plurality of design coatings such as a colored coating layer and a clear coating layer on top of applying a rust preventive coating, add a coating device and an oven. An unnecessary wet-on-wet coating is preferred. However, even if a flexible clear coating film for normal pre-coated metal sheet is formed by wet-on-wet coating, the scratch resistance is not improved. Therefore, in order to obtain a pre-coated metal plate having high gloss, sharpness, scratch resistance, and workability, a polyester-melamine-based paint using the technique of Patent Document 13 is wet-on-wet coated and applied. Although the performance was confirmed, it was excellent in gloss and sharpness, but sufficient scratch resistance could not be obtained. This is considered to be because the clear coating film did not contain a pigment, so that a sufficient coating film hardness could not be obtained. In addition, in order to improve the scratch resistance, the addition of glass beads to the clear coating on the colored coating was examined using the techniques of Patent Documents 14 and 15, but the scratch resistance was improved. , Glossiness and sharpness have deteriorated.

  As described above, the disclosed prior art as a pre-coated metal plate excellent in either design properties such as gloss and sharpness, and scratch resistance can be seen, but design properties such as gloss and sharpness, and scratch resistance. At present, there are almost no pre-coated metal plates excellent in both properties.

  Therefore, the present invention has been made in view of such problems, and an object of the present invention is to provide a precoated metal sheet having high gloss and sharpness and excellent scratch resistance, and a method for producing the same.

  By applying a clear coating with high gloss, sharpness, and coating film hardness on the colored layer, the present inventors have obtained a pre-coated metal plate that is excellent in both design properties such as gloss, sharpness, and scratch resistance. As a result of intensive studies, it was found that by applying a clear coating using an acrylic resin having a glass transition temperature of 60 ° C. or higher on the colored layer, the design properties such as gloss and sharpness, and scratch resistance were improved. It has been found that a precoated metal plate excellent in both can be obtained. However, on the other hand, since the acrylic resin having a high glass transition temperature of the coating film has a hard coating film, there is a new problem that the processability tends to deteriorate. Accordingly, the present inventors have used an isocyanate compound as a cross-linking agent for a clear coating film using this acrylic resin, and further, a melamine curable type or isocyanate curable type polyester resin in which a glass transition temperature is defined as a base resin for a colored layer. In addition, by prescribing the relationship between the thickness of the colored layer and the thickness of the top clear layer, the precoat is excellent in both design properties such as gloss and sharpness, and scratch resistance, and also in processability. It has been found that a metal plate can be obtained.

The present invention has been completed based on such knowledge, and the gist of the present invention is as follows.
(1) A pre-coated metal plate having at least two coating layers on one or both sides of a metal plate, wherein the coating layer is a top coating layer that is a coating formed on the outermost surface; An intermediate coating layer that is a lower layer coating in contact with the top coating layer, and the top coating layer is a clear coating that does not contain a pigment, and contains an isocyanate curable acrylic resin, The glass transition temperature of the top coating layer is 60 to 80 ° C., the intermediate coating layer contains a color pigment, and contains a melamine-curable or isocyanate-curable polyester resin, and the intermediate coating The glass transition temperature of the coating film is 30 to 50 ° C., and the relationship between the film thickness T (μm) of the top coating film layer and the film thickness t (μm) of the intermediate coating film layer is 0.5 ≦ T / Pre-coated metal sheet, wherein t ≦ 2
(2) A concentration gradient layer of the acrylic resin and the polyester resin having a thickness of 0.1 to 1.5 μm is formed at the interface between the acrylic resin of the top coating layer and the polyester resin of the intermediate coating layer. The precoated metal sheet according to (1), characterized by comprising:
(3) The concentration of the color pigment in the intermediate coating layer is 20% by mass or less based on the total mass of the intermediate coating layer (1) or (2) The precoat metal plate as described in 2.
(4) The precoated metal sheet according to any one of (1) to (3), wherein the color pigment of the intermediate coating film layer is black or metallic.
(5) The precoat metal according to any one of (1) to (4), wherein the top coating layer has a —Si—O—Si— bond in a resin skeleton forming the coating. Board.
(6) It is a manufacturing method of the precoat metal plate in any one of (1)-(5), Comprising: The said intermediate coating film layer and the said top coating film layer are apply | coated by a multilayer simultaneous application or a wet on wet system. The manufacturing method of the precoat metal plate characterized by the above-mentioned.

  According to the present invention, it is possible to provide a pre-coated metal plate that has high gloss and sharpness, and has excellent scratch resistance and workability, a method for producing the same, and a coated metal molded product.

  Hereinafter, preferred embodiments of the present invention will be described in detail.

  The precoat metal plate of the present invention is a precoat metal plate having at least two multilayer coating layers on one side or both sides of the metal plate, wherein the coating layer is a coating formed on the outermost surface. It has at least an intermediate coating film layer that is a lower coating film in contact with the top coating layer, and the intermediate coating film layer contains a color pigment, and is a melamine curable type or an isocyanate curable type. A polyester resin is contained, and the glass transition temperature of the coating film is 30 to 50 ° C., and the top coating layer is a clear coating film containing no pigment, and contains an isocyanate-curable acrylic resin, and The glass transition temperature of the top coating film is 60 to 80 ° C., and the relationship between the film thickness t (μm) of the intermediate coating film layer and the film thickness T (μm) of the top coating layer is 0.5 ≦ T / t ≦ 2 ing.

  First, as described above, the pre-coated metal plate top coating layer of the present invention is characterized by using an isocyanate curable acrylic resin having a glass transition temperature of 60 to 80 ° C.

  Here, acrylic resins generally have higher transparency and higher hardness than other resins, and when applied to the top coat of painted metal sheets, design properties such as sharpness and gloss, and scratch resistance. Such excellent characteristics can be obtained. However, acrylic resins have the disadvantages of low ductility and poor processability. In particular, when a melamine resin is used as a curing agent, this decrease in ductility becomes significant. This is because the melamine resin has a high self-condensability, so that the melamine resin itself has a hard skeleton, and since it has many functional groups, the crosslink density with the acrylic resin is increased, and so on. This is because the film has a low film thickness.

  The present inventors have found that by limiting the curing agent to an isocyanate compound, the workability can be maintained without deteriorating the scratch resistance, the design properties such as the sharpness and gloss, and the scratch resistance. This is because the number of functional groups of the isocyanate compound is about 2, 3 and less than that of the melamine resin, and the crosslink density with the acrylic resin is not so high, and the skeleton of the isocyanate compound is flexible, resulting in excellent ductility. A film having good processability can be obtained. Furthermore, by setting the glass transition temperature of this isocyanate-curable acrylic resin to 60 to 80 ° C., design properties such as sharpness and gloss, scratch resistance, and workability can be obtained simultaneously. When the glass transition temperature of the isocyanate curable acrylic resin is less than 60 ° C., the crosslinking density is low and sufficient hardness cannot be obtained, so that the scratch resistance is deteriorated. The processability deteriorates due to the decrease.

  Next, the intermediate coating film layer, which is a lower coating film in contact with the top coating layer of the precoated metal plate of the present invention, contains a color pigment, has a glass transition temperature of 30 to 50 ° C., and further has a melamine curing as a base resin. It is characterized by using a polyester resin of a mold type or an isocyanate curable type.

  As mentioned above, the use of an isocyanate-curing acrylic resin with a glass transition temperature of 60 to 80 ° C as the top coating layer keeps the design properties such as sharpness and luster, and scratch resistance while maintaining a certain degree of processing. In order to obtain the required design performance such as sharpness and gloss, scratch resistance, and workability, not satisfying the target performance of the present inventors. Uses an isocyanate-curable acrylic resin having a glass transition temperature of 60 to 80 ° C. as the top coating layer, and further uses a melamine-curable or isocyanate-curable polyester resin as the base resin for the intermediate coating layer. The glass transition temperature of the intermediate coating film layer is controlled to 30 to 50 ° C., and the relationship between the film thickness t (μm) of the intermediate coating film layer and the film thickness T (μm) of the top coating layer is 0. It has been found that it is necessary to satisfy 5 ≦ T / t ≦ 2.

  The reason why the main resin of the intermediate coating layer is limited to the polyester resin is to ensure workability by using a polyester resin having excellent ductility and adhesion as the intermediate coating layer. Furthermore, the reason for limiting the glass transition temperature of the intermediate coating layer is to achieve both scratch resistance and workability. When the surface of a pre-coated metal plate having a top coating layer with high coating hardness is rubbed, the deformability of the intermediate coating layer is too low if the glass transition temperature of the intermediate coating layer is less than 30 ° C. Is excessive, and the top coating layer can no longer follow the deformation of the intermediate coating layer, which is likely to cause scratches. On the other hand, when the glass transition temperature exceeds 50 ° C., the glass transition temperature is too high, and the ductility of the intermediate coating layer itself is lowered, so that workability is deteriorated.

  In addition, the glass transition temperature of the coating film in the precoat metal plate of this invention is a glass transition temperature as a bulk of the coating film after adding these in the case of the coating film containing a pigment and a hardening | curing agent. The glass transition temperature of the coating film may be measured using a differential scanning calorimeter (generally called DSC) after peeling the coating film applied to the precoated metal plate, or coated as a precoated metal plate. Measurement may be performed using a thermomechanical analyzer (generally called TMA). Moreover, you may measure by a generally well-known method. It is known that the glass transition temperature of the coating film has some errors depending on the measuring equipment and measurement conditions. Therefore, in the present invention, when measured by any one of a plurality of generally known glass transition temperature measurement methods, that is, a method using DSC or a method using TMA, the glass transition temperature of the coating film is measured. Is included within the scope of the present invention. Since the glass transition temperature of the coating film is mainly governed by the glass transition temperature of the base resin, the glass transition temperature of the coating film can be adjusted by controlling the glass transition temperature of the base resin.

  As described above, the relationship between the thickness t (μm) of the intermediate coating layer of the present invention and the thickness T (μm) of the top coating layer is 0.5 ≦ T / t ≦ 2. It is a feature.

  If T / t is less than 0.5, the leveling by the top coating is insufficient, so that the design properties such as gloss and sharpness are inferior, and the effect of scratch resistance by the top coating is insufficient. Therefore, it is unsuitable. When T / t exceeds 2, the film thickness of the hard topcoat becomes excessive, the balance between hardness and ductility with the intermediate coating layer is lost, and workability deteriorates.

  In addition, when the film thickness t of the intermediate coating film layer is 3 μm or less, the concealment rate by the pigment in the intermediate coating film becomes insufficient, and the toning may be insufficient. Moreover, when the total film thickness of the film thickness t of the intermediate coating film layer and the film thickness T of the top coating film layer exceeds 50 μm, it is not preferable from the viewpoint of cost.

  The pre-coated metal plate of the present invention preferably has a concentration gradient layer of acrylic resin and polyester resin having a thickness of 0.1 to 1.5 μm at the interface between the top coating layer and the intermediate coating layer. This concentration gradient layer is a layer having a gradient structure in which the acrylic resin and the polyester resin are diffused at the interface between the top coating layer and the intermediate coating layer. Then, it can be formed by recoating the top coating before drying. Since the acrylic resin of the top coating layer has high hardness and the polyester resin of the intermediate coating layer is flexible, the concentration gradient layer in the present invention is hard on the top coating side and gradually toward the intermediate coating layer side. The structure becomes softer. Therefore, even if cracks occur in the hard top coating layer by bending or the like, the progress of the cracks is suppressed by the concentration gradient layer, and does not reach the intermediate coating layer. Since the top coating layer is clear, the appearance is hardly impaired if cracks remain only in the top coating layer. If the thickness of the concentration gradient layer at the interface is less than 0.1 μm, it may be difficult to stop the progress of cracks, and it is difficult to confirm the presence / absence of the concentration gradient layer. On the other hand, if the thickness of the concentration gradient layer at the interface exceeds 1.5 μm, the appearance may be impaired.

  In the precoated metal sheet of the present invention, it is preferable that the top coating and the intermediate coating are applied by simultaneous multi-layer coating or wet on wet. Multi-layer simultaneous application is a method in which a plurality of coating liquids such as a slot die coater or a slide hopper type curtain coater are simultaneously applied to a substrate and then dried and baked simultaneously in multiple layers. In addition, wet-on-wet coating means that after coating the coating liquid on the substrate once, another coating liquid is further coated on it in the wet state before the coating liquid dries. The multi-layer coating liquid is simultaneously dried and baked. For example, the lower layer coating film is applied with a roll coater or a curtain flow coater, and the upper layer coating film is applied with a coating method such as a curtain flow coater before baking this. Later, a multilayer coating film of a lower layer coating film and an upper layer coating film is baked simultaneously. In this way, by laminating the coating liquids in an undried state and applying them simultaneously, the coating liquids of the respective layers are slightly mixed at the interface, whereby a concentration gradient layer can be formed at the interface. Generally, a concentration gradient layer having a thickness of 0.1 to 1.5 μm can be obtained by coating by the above-mentioned simultaneous multilayer coating or wet-on-wet.

  The multi-layer simultaneous coating of the present invention, or a method of simultaneously baking a wet-on-wet coating film, is a commonly known coating baking furnace, for example, a hot air drying furnace, an induction heating furnace, an infrared heating furnace, or a combination thereof. A furnace or the like can be used.

  In the present invention, the thickness of the concentration gradient layer of the acrylic resin and the polyester resin at the interface between the top coating layer and the intermediate coating layer can be measured, for example, by the following method.

  Using a nano indenter (such as Tribo Indenter manufactured by Hysitron), a vertical cross section in the vicinity of the interface between the top coating layer and the intermediate coating layer is used to push the indenter in the direction perpendicular to the interface and measure the change in hardness. A layer showing the hardness between the top coating layer and the intermediate coating layer can be determined as a concentration gradient layer. It is desirable to collect data with an indenter spacing of about 0.1 μm.

  Generally known inorganic pigments, organic pigments, and metallic pigments can be used as the color pigment added to the intermediate coating layer of the precoated metal sheet of the present invention. Examples thereof include carbon black, titanium oxide, zinc white, naphthol red, disazo yellow, disazopyrazolone orange, aluminum pigment, nickel pigment and the like.

  The amount of the color pigment added to the intermediate coating layer of the precoated metal sheet of the present invention is preferably 20% by mass or less based on the total mass of the intermediate coating layer. In general, the color pigment is harder than the base resin of the coating film, so increasing the amount of the color pigment added increases the film hardness and improves the scratch resistance, but if the addition amount exceeds 20% by mass, the film ductility decreases. This is because processability is deteriorated and film formability is lowered. As described above, the smaller the amount of the color pigment added, the lower the film hardness, and it becomes difficult to impart scratch resistance, so the effect of the present invention is that the amount of the color pigment added to the intermediate coating layer is It becomes more remarkable at 20 mass% or less. On the other hand, from the viewpoint of design properties and the like, the amount of the color pigment added to the intermediate coating film layer is preferably 2% by mass or more.

  Black and metallic colors are more suitable as color pigments to be added to the intermediate coating layer because the appearance can be ensured even if the concentration of the color pigment to be added is relatively low.

  Si derived from the alkoxysilane or a hydrolysis condensate of alkoxysilane can be contained in the top coating film of the present invention. When the precoated metal plate is used outdoors, there is a concern about the deterioration of gloss and sharpness due to the adhesion of dirt, in particular, rain dripping contamination or dirt adhesion due to rain streak contamination. However, by adding Si derived from alkoxysilane or a hydrolysis-condensation product of alkoxysilane in the top coating film of the present invention, hydrophilicity is imparted to the coating film surface without impairing surface gloss and workability. By adding hydrophilicity, it is easy to wash off deposits attached to the surface of the coating film due to rain, etc. when used outdoors, and it is difficult to attach raindrops etc. Since a fall is suppressed, it is more suitable. Although the addition amount of the alkoxysilane of the present invention and the hydrolysis condensate of alkoxysilane is not particularly limited, it is preferably 5 to 40 parts by mass with respect to 100 parts by mass of the base resin solid content in the top coating film. . The alkoxysilane added to the top coating film of the present invention is generally known, for example, tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane. Ethyltriethoxysilane, dimethoxydiethoxysilane, dimethoxydipropoxysilane and the like can be used. Moreover, the hydrolysis condensate of these alkoxysilanes may be sufficient.

  The precoat metal plate of the present invention can be coated with a primer coating film having a rust preventive paint function, if necessary. When the primer coating is applied, the corrosion resistance of the metal plate is improved, which is more preferable. As the primer coating film to be applied to the pre-coated metal plate of the present invention, generally known primer coating films for pre-coated metal plates, for example, polyester-based primers, epoxy-based primers, urethane-based primers and the like can be used. The curing agent for the primer coating film may be either melamine type or isocyanate type. As the rust preventive pigment to be added to the primer coating, generally known pigments such as chromate, phosphoric acid and silica can be used, but those other than chromate are more suitable because they are more environmentally friendly. is there. The primer coating to be applied to the pre-coated metal plate of the present invention is generally applied by a known coating method, for example, a roll coater, a roller curtain coater, a ringer roll coater, a spray coating, etc., and then a generally known coating baking furnace For example, it can be baked in a hot air drying furnace, an induction heating furnace, an infrared heating furnace, or a furnace using these in combination.

  For the metal plate used in the present invention, generally known metal materials can be used. The metal material may be an alloy material. For example, a steel plate, a stainless steel plate, an aluminum plate, an aluminum alloy plate, a titanium plate, a copper plate, etc. are mentioned. The surface of these materials may be plated. Examples of the type of plating include zinc plating, aluminum plating, copper plating, nickel plating and the like. These alloy platings may be used. In the case of steel plates, generally known steel plates and plated steel plates such as hot dip galvanized steel plates, electrogalvanized steel plates, zinc-nickel alloy plated steel plates, hot galvannealed steel plates, aluminum plated steel plates, aluminum-zinc alloyed steel plates, etc. Applicable.

If the surface of the metal plate used in the present invention is generally subjected to a known chemical conversion treatment, the adhesion between the metal plate and the coating layer is improved, which is more preferable. As the chemical conversion treatment, zinc phosphate chemical conversion treatment, coating chromate treatment, electrolytic chromic acid treatment, reaction chromate treatment, chromate-free chemical conversion treatment, or the like can be used. As the chromate-free chemical conversion treatment, those treated with an aqueous solution containing a silane coupling agent, a zirconium compound, a titanium compound, tannin or tannic acid, a resin, silica and the like are known, and Japanese Patent Laid-Open No. 53-9238 is known. JP-A-9-241576, JP-A-2001-89868, JP-A-2001-316845, JP-A-2002-60959, JP-A-2002-38280, JP-A-2002-266081, You may use the well-known technique described in Kaikai 2003-253464 etc. These chemical conversion treatments are commercially available, for example, chromate treatment “ZM-1300AN” manufactured by Nihon Parkerizing Co., Ltd., chromate-free chemical conversion treatment “CT-E300N” manufactured by Nihon Parkerizing Co., Ltd., and trivalent chromium-based chemical conversion manufactured by Nippon Paint Co., Ltd. Treatment "Surf Coat (registered trademark) NRC1000 "etc. can be used.

  Next, the present invention will be described in more detail using examples, but the present invention is not limited to the following examples.

Details of the experiment will be described below.
First, the intermediate coating material used in the experiment will be described in detail.

  As the base resin, “Byron (registered trademark) GK140” (glass transition temperature 20 ° C.), “Byron (registered trademark) GK360” (glass transition temperature 36 ° C.), “Byron (manufactured by Toyobo Co., Ltd.)” (Registered trademark) GK110 "(glass transition temperature 50 ° C) and" Byron (registered trademark) 660 "(glass transition temperature 55 ° C) were used. If necessary, they were mixed to adjust the glass transition temperature of the resin. As a cross-linking agent, “Super Becamine (registered trademark) J830” which is a butylated melamine resin (hereinafter referred to as butylated melamine) manufactured by Dainippon Ink and Chemicals, Inc., “Desmodule BL3175 (manufactured by Sumika Bayer Urethane Co., Ltd.) Product name) "(hereinafter referred to as HDI). As the coloring pigment, a commercially available aluminum flake was used for the metallic pigment, a commercially available carbon black was used for the black pigment, and a commercially available titanium oxide was used for the white pigment. The solvent used was a mixture of cyclohexanone: solvesso 150 = 1: 1 by mass ratio.

  Next, the top paint used in the experiment will be described in detail.

  As a base resin, “Udable (registered trademark) S-2818” (glass transition temperature 55 ° C.) “Udable (registered trademark) S-5166” (glass transition temperature 60 ° C.) “acrylic” manufactured by Nippon Shokubai Co., Ltd. (Registered trademark) AST-5893 ”(glass transition temperature 65 ° C.),“ Acryset (registered trademark) AST-5892 ”(glass transition temperature 70 ° C.),“ Udouble® S-2816 ”(glass transition temperature 75 ° C), "Acryset (registered trademark) AST-5278" (glass transition temperature 80 ° C), "Acryset (registered trademark) AST-5247" (glass transition temperature 100 ° C), an amorphous polyester resin manufactured by Toyobo "Byron (registered trademark) 200" (glass transition temperature 67 ° C), "Byron (registered trademark) GK360" (glass transition temperature 3 ℃) was used. If necessary, they were mixed to adjust the glass transition temperature of the resin. As a cross-linking agent, “Desmodule BL3175 (trade name)” (hereinafter referred to as “HDI”) manufactured by Sumika Bayer Urethane Co., Ltd., “Desmophen 2170 (trade name)” (hereinafter referred to as “MDI”), and completely manufactured by Mitsui Cytec “Cymel (registered trademark) 303” which is an alkyl type methylated melamine resin (hereinafter referred to as methylated melamine) was used. In addition, the dilution solvent used what was mixed with cyclohexanone: solvesso 150 = 1: 1 by mass ratio.

  Details of the prepared intermediate coating and top coating are shown in Tables 1 and 2, respectively. The glass transition temperature of the coating film was measured with a thermomechanical analyzer “SSC5200 series TMA / SS120C” manufactured by Seiko Denshi Co., Ltd., and a probe at the time of measurement was used.

  In addition, a clear paint of FL641EU primer, which is a polyester primer for PCM manufactured by Nippon Fine Coatings Co., Ltd., was prepared, and “K-WHITE # 105” was prepared with tripolyaluminum dihydrogen phosphate manufactured by Teika, which is a chromate-free rust preventive pigment. Was added to 30 parts by mass with respect to 100 parts by mass of the solid content of the clear coating material to prepare a chromate-free primer.

  Hereinafter, the details of the precoated metal plate used in the experiments of the examples will be described.

A hot-dip galvanized steel sheet “Silver Zinc (registered trademark)” (hereinafter referred to as GI) manufactured by Nippon Steel Corp. was prepared as an original plate. A plate thickness of 0.6 mm was used. The plating adhesion amount was 60 mg / m ² on one side.

Next, the prepared original plate is spray-degreased with a 2% by weight, 50 ° C. aqueous solution of an alkaline degreasing solution “FC-4336” manufactured by Nihon Parkerizing Co., Ltd., washed with water, dried, and then chromate-free formed by Nihon Parkerizing Co., Ltd. The treatment “CT-E300N” was applied with a roll coater and dried in a hot air oven. The drying conditions in the hot air oven were 60 ° C. at the ultimate plate temperature of the steel plate. The coating amount of the chromate-free treatment was applied so that the total solid content was 200 g / m ² .

  Next, the prepared primer coating is applied to one side of the metal sheet that has been subjected to chemical conversion treatment, and the gray color of “FL100HQ”, which is a back coating made by Nippon Fine Coatings, is applied to the other side using a roll coater. The coating was applied so that the dry film thickness was 5 μm, and was dried and cured in an induction heating furnace in which hot air was blown under the condition that the ultimate temperature of the metal plate was 210 ° C. And after dry baking, water was wiped with a spray to the painted metal plate, and water-cooled.

  Next, on the primer coating, intermediate coating and top coating are simultaneously laminated in a slide hopper type curtain coater, and the ultimate temperature of the metal plate is 230 ° C in an induction heating furnace blown with hot air. Under these conditions, the laminated coating films were simultaneously dried and cured. Then, after drying and baking, water was sprayed onto the coated metal plate and water-cooled to prepare a three-layer pre-coated metal plate (hereinafter, this coating method is referred to as “painting method (i)”) ).

  If necessary, apply only one layer of intermediate coating on the primer coating with a roller curtain coater, and then apply the top coating with a roller curtain coater on the primer coating before drying it. Were simultaneously dried and cured. Then, after drying and baking, water was sprayed onto the coated metal plate and water-cooled to prepare a three-layer pre-coated metal plate (hereinafter, this coating method is referred to as “coating method (ii)”). ).

  If necessary, apply only one layer of intermediate coating on the primer coating with a roll coater, and after baking as described above, apply one layer of top coating on the intermediate coating again with a roll coater. A three-layer pre-coated metal plate that was painted and baked was also prepared (the coating method in this procedure is referred to as “coating method (iii)”).

  In addition, if necessary, on the primer coating, intermediate coating and top coating are simultaneously layered on a slide hopper type curtain coater and left in a wet state for 1 hour, followed by induction with hot air. The laminated coating film was simultaneously dried and cured in a heating furnace under the condition that the ultimate plate temperature of the metal plate was 230 ° C. Then, after drying and baking, water was sprayed onto the coated metal plate and water-cooled to prepare a three-layer pre-coated metal plate (hereinafter, this coating method is referred to as “painting method (iv)”). ).

  To confirm the concentration gradient layer, the vertical cross section in the vicinity of the interface was measured using a Tribo Indenter manufactured by Hystron Corp., and the hardness was measured at intervals of 0.1 μm by pressing the indenter sequentially in the direction perpendicular to the interface. A layer showing hardness between the layers is a concentration gradient layer, the thickness is 0.1 μm or more and 1.5 μm or less is ◯, and the concentration gradient layer is less than 0.1 μm and cannot be confirmed x (−), The thing over 5 micrometers was made into x (+).

  The film thicknesses of the intermediate coating layer and the top coating layer were determined from secondary electron images of the coating cross section. However, when having a concentration gradient layer between the intermediate coating layer and the top coating layer, the center of the thickness of the concentration gradient layer was the interface between the intermediate coating layer and the top coating layer.

Hereinafter, the details of the evaluation method of the pre-coated metal plate produced in the experiment will be described.
1. Scratch resistance of pre-coated metal plate Scratch resistance was measured by pencil hardness. According to the method of 8.4.1 (1993) of JIS-K 5400, the scratch resistance of the coating film is examined by scratching the coating film when the hardness of the pencil core is changed. The highest hardness at which no film was observed was defined as the pencil hardness of the coating film.
2. Measurement of sharpness of pre-coated metal plate The Gd value was measured with a portable sharpness gloss meter “PGD” (manufactured by Tokyo Kodenshi) for the sharpness of the coating film on the surface of the prepared pre-coated metal plate.
3. Specular Gloss Measurement of Pre-Coated Metal Plate Coating Specular Glossiness was measured under the conditions of an incident angle and a light receiving angle of 20 ° C. using a “digital variable angle gloss meter” manufactured by Suga Test Instruments Co., Ltd.
4). Coating Film Workability Test The prepared precoated metal plate was bent 180 ° (adhesion bending), and the coating film in the processed part was visually observed to check for cracks in the coating film. When the 180 ° bending was performed, the pre-coated metal plate was bent so that the surface of the pre-coated metal plate was outside the bending, and the contact bending was performed (generally known as 0T bending). Then, the processed part is visually observed, ○ when there is no coating film cracking or peeling, △ when there are slight cracks or peeling on the coating film, cracks reaching the primer coating or metal plate on the coating The case where there was or peeling was evaluated as x. In addition, a processed part adhesion test is also performed in which the tape is attached to the processed part and peeled off. When the adhesiveness after the tape is peeled is visually observed, no clear peeling is observed in the coating film. The case where film peeling was observed was evaluated as Δ, and the case where coating film peeling was observed in a total length of more than half the total length of the bent portion was evaluated as x.
5. Raindrop pollution The prepared samples were subjected to an exposure test for 3 months at an outdoor exposure test site near the coast of Futtsu City, Chiba Prefecture. For the samples after the test, the presence or absence of raindrops was evaluated visually, ○ when there was no raindrops, △ when raindrops were observed slightly, and × when raindrops were clearly observed. evaluated.

  Details of the evaluation results will be described below.

  In Tables 3-8, the precoat metal plate created by this invention and its evaluation result are shown. In addition, although the effect of this invention is demonstrated using the test material which gave the primer coating film, also when not giving a primer coating film, the performance similar to what gave the primer coating film is acquired.

(1) Influence of glass transition temperature, cross-linking agent type, and base resin type of top coating layer As an effect of glass transition temperature, cross-linking agent type, and base resin type of top coating layer, Examples No. 1-No. No. 10 and a comparative example. 11-No. 17 shows.

  The precoated metal plates (Examples 1 to 10) of the present invention had excellent scratch resistance, design properties such as sharpness and gloss, and workability.

  Those having a glass transition temperature of the top coating of 60 ° C. (Examples 1 and 6) have pencil hardness, and those having a glass transition temperature of the top coating of 80 ° C. (Examples 5 and 10) are workability. However, the glass transition temperature of the top coating is more preferably 65 to 75 ° C. because it tends to slightly decrease.

  A glass film having a glass transition temperature of less than 60 ° C. (Comparative Examples 11 and 12) is not suitable because it has poor scratch resistance. Acrylic resin having a glass transition temperature exceeding 80 ° C. (Comparative Examples 13 and 14) is unsuitable because of poor workability. A material using melamine resin (methylated melamine) as a curing agent for the top coating layer (Comparative Example-15) is unsuitable because of poor processability. Those using a polyester resin as the base resin for the top coating layer (Comparative Examples 16, 17) are inadequate because of their poor scratch resistance.

(2) Influence of the glass transition temperature of the intermediate coating film layer As an influence of the glass transition temperature of the intermediate coating film layer, Example No. 18-No. No. 29 and a comparative example No. 30-No. 33.

  The pre-coated metal sheets (Examples 18 to 29) of the present invention had excellent scratch resistance, design properties such as sharpness and gloss, and workability.

  When the glass transition temperature of the intermediate coating film is 30 ° C. (Examples-18 and 24), the pencil hardness is high, and when the glass transition temperature of the intermediate coating film is 50 ° C. (Examples 22 and 28), it is workability. However, the glass transition temperature of the intermediate coating film is more preferably 35 to 45 ° C because it tends to slightly decrease. An intermediate coating film having a glass transition temperature of less than 30 ° C. (Comparative Example-30, 31) is unsuitable because of poor scratch resistance. Those having a glass transition temperature of the intermediate coating film exceeding 50 ° C. (Comparative Examples −32, 33) are unsuitable because of poor workability.

(3) Relationship between the thickness of the intermediate coating layer and the thickness of the top coating layer As the relationship between the thickness of the intermediate coating layer and the thickness of the top coating layer, Example No. 34-No. 75 and Comparative Example No. 76-No. 81. The precoated metal plates of the present invention (Examples -34 to 75) had excellent scratch resistance, design properties such as sharpness and gloss, and workability. Samples having T / t of 0.5 (Examples 34, 41, 48, 55, 62, 69) have pencil hardness, gloss and sharpness, and those having T / t of 2 (Example-40) , 47, 54, 61, 68, 75), the workability tends to be slightly lowered, so 0.75 ≦ T / t ≦ 1.75 is more preferable.

  Those having T / t of less than 0.5 (Comparative Examples -76 to 78) are unsuitable because they are poor in scratch resistance, gloss and sharpness. Those having a T / t exceeding 2 (Comparative Examples -79 to 81) are unsuitable because of poor workability.

(4) Influence of the gradient structure layer between the top coating layer and the intermediate coating layer The gradient structure layer between the top coating layer and the intermediate coating layer is 0.1 μm (Example 84) , 88) tended to decrease the workability. The one with the gradient structure layer between the top coating layer and the intermediate coating layer prepared by drying and curing after standing for 1 hour after the simultaneous multilayer coating exceeds 1.5 μm (Examples-85, 89) , Gloss and sharpness tended to decrease. In the case of simultaneous multi-layer coating and wet-on-wet coating, and immediately dried and cured, the concentration gradient layer at the interface between the top coating layer and the intermediate coating layer was in the range of 0.1 to 1.5 μm. It was. Usually, after simultaneous multi-layer coating and wet-on-wet coating, the material is immediately dried and cured, so that it can be seen that those produced by such a method have improved processability and are more suitable.

(5) Influence of coloring species of intermediate coating layer The amount of the coloring pigment added to the intermediate coating layer of the present invention exceeds 20% by mass (Examples-92, 93, 96, 97, 98, 101, 102, 105, 106, 107) tend to have low processability, and the present invention is more effective when the amount of the color pigment added to the intermediate coating layer is 20% by mass or less. Recognize. For black and metallic colors, the amount of color pigment added in the coating is usually 20% by mass or less, which proves particularly effective.

(6) Effect of tetramethoxysilane addition to top coating layer When Si derived from alkoxysilane or a hydrolysis condensate of alkoxysilane is contained in the top coating of the precoated metal sheet of the present invention (Example 109 to 109) 111, 113 to 115), and those not including this (Examples -108, 112), are more suitable because the raindrop resistance is improved.

As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to this example. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

Claims (6)

A pre-coated metal plate having at least two coating layers on one or both sides of the metal plate,
The coating layer has at least a top coating layer that is a coating formed on the outermost surface, and an intermediate coating layer that is a lower layer coating in contact with the top coating layer,
The top coating layer is a clear coating containing no pigment, contains an isocyanate curable acrylic resin, and the glass transition temperature of the top coating layer is 60 to 80 ° C.,
The intermediate coating film layer contains a color pigment, and contains a melamine-curable or isocyanate-curable polyester resin, and the glass transition temperature of the intermediate coating film is 30 to 50 ° C.
A precoated metal sheet, wherein the relationship between the film thickness T (μm) of the top coating layer and the film thickness t (μm) of the intermediate coating layer is 0.5 ≦ T / t ≦ 2. .   It has a concentration gradient layer of the acrylic resin and the polyester resin having a thickness of 0.1 to 1.5 μm at the interface between the acrylic resin of the top coating layer and the polyester resin of the intermediate coating layer. The precoated metal sheet according to claim 1, characterized in that it is characterized in that   The precoat metal according to claim 1 or 2, wherein the concentration of the color pigment in the intermediate coating layer is 20% by mass or less based on the total mass of the intermediate coating layer. Board.   The pre-coated metal sheet according to any one of claims 1 to 3, wherein the colored pigment of the intermediate coating layer is black or metallic.   The precoated metal sheet according to any one of claims 1 to 4, wherein the top coating layer has a -Si-O-Si- bond in a resin skeleton forming the coating. It is a manufacturing method of the precoat metal plate according to any one of claims 1 to 5,
The method for producing a precoated metal sheet, wherein the intermediate coating layer and the top coating layer are applied by multilayer simultaneous application or a wet-on-wet method.