WO2010114135A1 - Precoated metal sheet and process for producing same - Google Patents

Abstract

A precoated metal sheet having at least a topcoat layer that is a coating film formed as the uppermost layer and an intercoat layer that is a coating film underlying and adjoining the topcoat layer. The topcoat layer is a clear coating film comprising a silicone-grafted acrylic resin but containing no pigment. The intercoat layer comprises a melamine-cured or isocyanate-cured polyester resin and contains a coloring pigment. The coating film surface has an average coefficient of friction of 0.08 or lower, a hardness at 23ºC of 75-200 N/mm² in terms of universal hardness measured under a load of 5 mN, and a specular gloss of 50% or more when measured at an incidence angle of 20º and a receiving angle of 20º. The precoated metal sheet has appearance properties including gloss and clearly reflecting properties and has excellent mar resistance.

Description

Pre-coated metal plate and manufacturing method thereof

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 for home appliances, building materials, civil engineering, machinery, automobiles, furniture, containers, etc. The present invention relates to a pre-coated metal sheet having excellent scratch resistance and a method for producing the same.

For example, pre-coated metal that is processed in a state of coating a pre-colored coating film instead of post-coating products that have been painted after processing a conventional metal plate on the outer plate in the home appliance field, building material field, automobile field, etc. Boards are starting to be used. On the other hand, in these applications, there is an increasing demand for painting with a high gloss appearance from the viewpoint of design and design.

As a technique for increasing the gloss 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, as described in Patent Document 2, the molecular weight is low. A technique for coating a coating film using a resin, for example, a technique for coating a clear coating film on a colored coating layer as disclosed in Patent Document 3, is disclosed.

When industrially producing a pre-coated metal plate, it is generally manufactured by 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 with a rust prevention function is applied onto a metal plate with a coating device called a roll coater or curtain coater, baked in a hot air oven, etc., and then again colored with a coating device. Two times of coating and baking (typically called a two-coat two-bake method) are generally performed. Therefore, if you try to paint a clear paint film with excellent clarity on the colored layer, the number of paintings will be more than 3 times. Or, it was necessary to take measures such as coating the coil coating line twice. However, as 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 coating is applied repeatedly in an undried state.

On the other hand, since the precoated metal plate is used after being molded, it is required to have scratch resistance during molding. It is also important to prevent wrinkles that occur during transportation and manual assembly. 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. A coating material obtained by blending 1 to 2 parts by mass of an amine block of dodecylbenzenesulfonic acid with 100 parts by mass of the blended polyester-melamine resin has high coating film hardness, excellent scratch resistance, and excellent workability. A coating composition for a painted metal sheet is disclosed. Patent Documents 14 and 15 disclose a technique for increasing the hardness and improving the scratch resistance by adding glass fibers or glass beads to the coating film. Patent Documents 16 and 17 disclose techniques for improving the lubricity and improving the scratch resistance by adding resin beads or wax 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 JP-A-63-5938 JP-A-4-11671 JP 2004-98624 A JP 2004-34591 A

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 the surface of the metal plate, which is a base material, by rolling the metal with a rolling roll with adjusted surface roughness or polishing it with a polishing machine, etc. Roughness must be controlled. For this reason, it is difficult to industrially mass-produce a pre-coated metal plate having a high gloss by this method because it takes a lot of labor and cost.

On the other hand, the method of obtaining a pre-coated metal plate with high gloss by applying a paint using a resin having a low molecular weight is relatively simple compared to the method of controlling the surface roughness of the metal plate as the base material. Although it is possible to manufacture, it is difficult to impart other coating film performances such as workability because a specific resin must be used for the paint.

As a method of obtaining a precoated metal plate having a high gloss relatively easily without using a resin having a performance restriction, there is a method of applying a transparent clear coating on the colored coating layer of Patent Document 13. . The manufacturing problem when this method is applied to an existing 2-coating 2-bake coil coating line can be solved by applying wet-on-wet coating as described above. Patent Document 13), although excellent gloss can be obtained, sufficient scratch resistance cannot be obtained.

In addition, the technique of adding glass beads to the clear coating film on the colored coating film disclosed in Patent Documents 14 and 15 is effective in improving the coating film hardness, but satisfies the scratch resistance. Has not reached. In addition, the addition of wax to the clear coating film on the colored coating film disclosed in Patent Documents 16 and 17 improves the lubricity, but still does not provide sufficient scratch resistance. Further, the addition of glass beads and wax to these films is not suitable for applications that require a glossy appearance because it reduces the gloss of the coating film.

As described above, conventional techniques for precoated metal sheets with excellent design properties such as gloss and sharpness can be seen, but for precoated metal sheets with excellent scratch resistance in addition to design properties such as gloss and sharpness. The current situation is not disclosed.

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.

The present inventors have intensively studied in order to obtain high gloss, sharpness, and sufficient scratch resistance from the knowledge so far. It has been found that it is not sufficient to increase only the property, and it is necessary to achieve both high coating film hardness and high lubricity. For this purpose, the top coating is a clear layer containing a silicone-grafted acrylic resin. It has been found that the coating film layer contains a melamine-curing or isocyanate-curing polyester resin, so that it is possible to achieve an improvement in the hardness of the coating film and a reduction in the coefficient of friction while ensuring high gloss. The present inventors have found that a precoated metal sheet having excellent design properties such as sharpness and scratch resistance and excellent workability 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 a coating layer on one side or both sides of a 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 contains a silicone graft acrylic resin and is a clear coating containing no pigment, the intermediate coating layer contains a melamine curable or isocyanate curable polyester resin, and , A coating film containing a coloring pigment,
Furthermore, the average friction coefficient of the coating layer surface of the coating layer is 0.08 or less, and the hardness of the coating layer surface at 23 ° C. is 75 to 200 N / mm ² in terms of universal hardness under a load of 5 mN, The precoated metal sheet is characterized in that the specular gloss on the surface of the coating layer is 50% or more when measured under conditions of an incident angle and a light receiving angle of 20 °, respectively.
[2] A pre-coated metal plate having a coating layer 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 contains a silicone-grafted acrylic resin and a clear coating containing a pigment; the intermediate coating layer contains a melamine-curable or isocyanate-curable polyester resin; and , A coating film containing a coloring pigment,
Furthermore, the average friction coefficient of the coating layer surface of the coating layer is 0.08 or less, and the hardness of the coating layer surface at 23 ° C. is 75 to 200 N / mm ² in terms of universal hardness under a load of 5 mN, The precoated metal sheet is characterized in that the specular gloss on the surface of the coating layer is 50% or more when measured under conditions of an incident angle and a light receiving angle of 20 °, respectively.
[3] The precoated metal sheet according to [2], wherein the top coating layer is a clear coating containing a bright pigment.
[4] The precoated metal sheet according to [1] or [2], wherein the top coating layer is a melamine curable type.
[5] The precoated metal sheet according to [1] or [2], wherein the top coating layer is an isocyanate curable type.
[6] The precoated metal sheet according to [5], wherein the isocyanate-curable top coating layer has an NCO / OH ratio of 0.05 to 0.5.
[7] The Ra (centerline average roughness) at the interface between the top coating layer and the intermediate coating layer is 0.3 to 0.8, [1] to [6] Pre-coated metal plate.
[8] The precoated metal sheet according to any one of [1] to [7], wherein the content of the silicone graft acrylic resin in the top coating film is 2 to 18% by mass in terms of silicone resin .
[9] The glass transition temperature of the top coating film is 30 to 67 ° C., the ratio of the silicone resin in the silicone graft acrylic resin contained in the top coating film is 3 to 20% by mass, The precoated metal sheet according to any one of [1] to [8], wherein the coating film has a glass transition temperature of 25 to 50 ° C.
[10] The precoat according to any one of [1] to [8], wherein the hardness of the coating layer surface at 23 ° C. is 150 to 200 N / mm ² as a universal hardness under a load of 5 mN. Metal plate.
[11] The precoated metal sheet according to [10] or [11], wherein the top coating layer is an isocyanate curable type.
[12] The precoated metal sheet according to [11], wherein the curing agent in the top coating layer is isophorone diisocyanate (IPDI).
[13] The precoated metal sheet according to [11] or [12], wherein the ratio of the curing agent in the top coating layer is 0.1 to 0.5.
[14] A pre-coated metal plate having a coating layer on one side or both sides of the metal plate,
The coating layer is at least a top coating layer that is a coating formed on the outermost surface, an intermediate layer that is in contact with the top coating layer, and an intermediate coating that is a lower layer coating that is in contact with the intermediate coating layer And having a layer
The top coating layer contains a silicone graft acrylic resin and is a clear coating containing no pigment, the intermediate coating layer contains a melamine curable or isocyanate curable polyester resin, and , A coating film containing a coloring pigment,
Furthermore, the average friction coefficient of the coating layer surface of the coating layer is 0.08 or less, and the hardness of the coating layer surface at 23 ° C. is 75 to 200 N / mm ² in terms of universal hardness under a load of 5 mN, The precoated metal sheet is characterized in that the specular gloss on the surface of the coating layer is 50% or more when measured under conditions of an incident angle and a light receiving angle of 20 °, respectively.
[15] The precoated metal sheet according to [14], wherein the intermediate layer contains a pigment.
[16] The precoated metal sheet according to [15], wherein the intermediate layer contains a luster pigment.
[17] The precoated metal according to any one of [14] to [16], wherein Ra (centerline average roughness) at the interface between the top coating layer and the intermediate layer is 0.3 to 0.8. Board.
[18] A method for producing a precoated metal sheet according to any one of [1] to [17],
A method for producing a pre-coated metal sheet, characterized in that the intermediate coating layer and the top coating layer are baked after being applied by multi-layer simultaneous application or wet-on-wet method, respectively.

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 manufacturing method thereof, and a coated metal molded product.

It is a schematic cross section for demonstrating the measuring method of centerline roughness Ra.

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

The pre-coated metal sheet of the present invention has two or more coating layers, and the top coating is a clear coating, so that the surface is smooth, and the incident angle and the light receiving angle are each measured at 20 °. High gloss with a specular gloss of 50% or more is obtained. Here, the clear coating film refers to a coating film having a low pigment concentration in the coating film, a low hiding power of the base, and a transparent feeling.

By adding a predetermined amount of silicone graft acrylic resin to the top coating film, the average friction coefficient is 0.08 or less, and the hardness at 23 ° C. is 75 to 200 N / mm ² or more in terms of universal hardness under a load of 5 mN. High lubricity and high hardness can be obtained, and both scratch resistance and high gloss can be achieved.

In order to ensure the scratch resistance of the pre-coated metal plate of the present invention, the average friction coefficient needs to be 0.08 or less. Here, the average friction coefficient is a load of 100 g of stainless steel balls (10 mmφ), 150 mm / min. The force F applied when moving on the precoated metal plate 110 mm in parallel under the above conditions was measured, and the average of the measured values of the force F at a plurality of locations in the remaining 100 mm range excluding the first 10 mm was calculated.

If the average coefficient of friction exceeds 0.08, the frictional force when foreign matter comes into contact with the surface of the pre-coated metal sheet and rubs against the mold during molding is increased, and the surface of the film is destroyed, resulting in poor scratch resistance. By setting the average friction coefficient to 0.08 or less, the frictional force when the precoated metal plate surface is rubbed with a mold or foreign matter is reduced, and the scratch resistance is improved. In order to obtain stable scratch resistance, the average friction coefficient is more preferably 0.05 or less.

Further, in order to ensure the scratch resistance of the precoated metal sheet of the present invention, it is necessary that the surface has a universal hardness of 75 to 200 N / mm ² . Here, universal hardness refers to the coating hardness measurement method described in DIN 50359-1 in Germany, and is a square pyramid made of diamond with a face angle of 136 ° (Vickers hardness described in JIS-Z-2244). The same as the indenter used in the test) is pressed against the material surface, and the hardness is calculated from the indentation depth under the applied load conditions. The universal hardness in the present invention is measured under the conditions of a temperature of 23 ° C. and an indentation load of 5 mN and using a micro hardness meter described in this DIN standard. When the universal hardness is less than 75 N / mm ² , even if the average friction coefficient is 0.08 or less, the coating film hardness is low, so that the scratch resistance is poor. If the universal hardness exceeds 200 N / mm ² , the coating film becomes too hard and it is difficult to ensure processability, which is not suitable. The universal hardness is preferably 75 to 200 N / mm ² .
When wear resistance is also required, the universal hardness is preferably controlled to 150 to 200 N / mm ² .

Further, the specular gloss of the precoated metal sheet coating surface of the present invention can be measured according to JIS Z 8741, and it is necessary to be 50% or more when the incident angle and the light receiving angle are each measured at 20 °. If it is less than 50%, the appearance quality is poor.

As described above, the top coating layer of the precoated metal sheet of the present invention is characterized by containing a silicone graft acrylic resin. The silicone graft acrylic resin is obtained by graft polymerization of a silicone resin on an acrylic resin main chain. Excellent lubricity can be effectively obtained by the excellent strength and transparency of the acrylic resin of the main chain and the property that the silicone resin hanging from the main chain is easily coordinated to the surface of the coating film. Further, since the silicone resin has relatively high strength in addition to high lubricity, it is possible to form a coating film excellent in gloss, hardness and lubricity by containing a silicone graft acrylic resin in the top coating layer.
By making the top coating layer of the precoated metal sheet of the present invention a clear coating containing a pigment, the design can be further improved.
By making the top coating layer of the pre-coated metal plate of the present invention a clear coating film containing a bright pigment, in addition to improving the design properties, the wrinkle resistance becomes less noticeable, and the anti-glare property can also be improved. .

The content of the silicone graft acrylic resin in the top coating film is preferably 2 to 20% by mass in terms of silicone resin. When the content of the silicone graft acrylic resin in the coating film is less than 2% by mass, the lubricity is not sufficient and it is difficult to ensure scratch resistance. If it exceeds 20% by mass, the storage stability of the paint may be lowered, and stable production becomes difficult. In addition, "silicone resin conversion" here means expressing content of a silicone graft acrylic resin using content of the total amount of the silicone monomer contained in a top coating film.

Resins other than silicone-grafted acrylic contained in the top coating can be used without problems as long as they are compatible with silicone-grafted acrylic resin, but have excellent compatibility with silicone-grafted acrylic resin, and excellent strength. Acrylic resin having transparency is most suitable.

The crosslinking agent for the top coating film is preferably a melamine resin or an isocyanate compound. The melamine resin has higher hardness than the isocyanate compound, and it is easy to obtain a predetermined coating film hardness. However, if the melamine resin is concentrated on the surface of the coating film by using an amine block of dodecylbenzenesulfonic acid, etc., the silicone resin becomes difficult to coordinate on the surface of the coating film, which may reduce the lubricity.
The blending amount when the melamine resin is used as a crosslinking agent is preferably 5 to 30 parts by mass with respect to 100 parts by mass of the silicone graft acrylic resin from the viewpoint of ensuring the hardness and lubricity of the top coating film. .
On the other hand, if the melamine resin is used as a crosslinking agent and left at high temperature, the reaction with the silicone-grafted acrylic resin tends to proceed and the storage stability of the paint may be inferior. Is more preferable than melamine resin.
In general, when an isocyanate compound is used, the molar ratio of NCO / OH is 0.9 / 1.0 or more. This is because it is considered that when the NCO / OH molar ratio is lower than 0.9 / 1.0, crosslinking is insufficient and the coating becomes too soft.
However, as a result of detailed investigation of the relationship between the NCO / OH molar ratio and performance, the present inventors have found that the NCO / OH molar ratio is usually optimal when a silicone-grafted acrylic resin is used as the main resin. It has been found that the hardness and workability can be balanced at a higher order when the NCO / OH molar ratio is 0.05 / 1.0 to 0.5 / 1.0, which is lower than the previously stated value. This is because the silicone graft acrylic resin is harder than the isocyanate compound, so the NCO / OH molar ratio is low, that is, the amount of the isocyanate compound is small, so that a hard coating film is obtained and the crosslink density is low, so that high workability is achieved. It is estimated that However, when the molar ratio of NCO / OH is lower than 0.05 / 1.0, the crosslinking density is too low, and the coating film hardness may not be obtained.
When isophorone diisocyanate is used as the isocyanate compound, it is easy to obtain a high coating film hardness. This is because isophorone diisocyanate has a hard skeleton.
When an isocyanate compound is used as a coating film curing agent, it is usually necessary to set the NCO / OH molar ratio to 0.9 / 1.0 or more. This is because when the molar ratio of NCO / OH is less than 0.9 / 1.0, the amount of isocyanate groups contributing to the crosslinking reaction becomes too small, and the effect of improving the film hardness by the crosslinking reaction is insufficient and the coating film becomes too soft. it is conceivable that.
However, in the case of the present invention using a silicone graft acrylic resin as the main resin, if the NCO / OH molar ratio is 0.9 / 1.0 or more, the NCO / OH molar ratio is less than 0.9 / 1.0. It was found that the coating film hardness was lower than that of the product. As a result of detailed investigation of the relationship between the molar ratio of NCO / OH and performance in the case of using a silicone-grafted acrylic resin as a main resin, the present inventors have considered that the molar ratio of NCO / OH is usually optimum. It was found that the hardness and workability can be balanced in a high order by setting the value to 0.05 / 1.0 to 0.5 / 1.0, which is lower than the value.
This is because the hardness of the silicone graft acrylic resin is higher and harder than that of the isocyanate compound, so that a lower NCO / OH molar ratio, that is, a smaller amount of isocyanate compound gives a harder coating film, and crosslinking It is presumed that because the density is low, the ductility is excellent and high workability is obtained. However, if the molar ratio of NCO / OH is lower than 0.05 / 1.0, the crosslinking density is too low, and the film strength itself may be lowered without sufficient film formation, which is not preferable.
When isophorone diisocyanate is used as the isocyanate compound, it is easy to obtain a high coating film hardness. This is because isophorone diisocyanate has a hard skeleton.

The glass transition temperature of the top layer is preferably 30 to 67 ° C. When the glass transition temperature is lower than 30 ° C., the coating film hardness is lowered and the scratch resistance may be inferior. When the glass transition temperature is higher than 67 ° C., the coating film hardness is excessively increased and becomes brittle, and the workability may be lowered.

The ratio of the silicone resin in the silicone graft acrylic resin is preferably 3 to 20% by mass. When the ratio of the silicone resin in the silicone graft acrylic resin is lower than 3% by mass, the coordination of the silicone resin to the surface of the top coating layer becomes insufficient, the lubricity becomes low, and the scratch resistance may be inferior. When the ratio of the silicone resin in the silicone graft acrylic resin is higher than 20% by mass, the storage stability of the paint may be lowered.

The film thickness of the top coating layer is preferably 1 to 10 μm. If the film thickness of the top coating layer is less than 1 μm, the intermediate coating layer cannot be completely covered, and gloss and lubricity may be lowered. If the film thickness of the top coating layer exceeds 10 μm, the workability may be reduced. Moreover, it is not preferable also in terms of cost.

The intermediate coating layer contains a melamine curable or isocyanate curable polyester resin and also contains a color pigment. Further, the glass transition temperature of the intermediate coating layer is preferably 25 to 50 ° C. 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 film layer is to make the hardness and workability compatible. If the glass transition temperature of the intermediate coating film layer is less than 25 ° C., the hardness may be insufficient. If it exceeds ° C., the workability may be insufficient, so the glass transition temperature of the intermediate coating layer is set to 25 to 50 ° C.

In addition, the intermediate coating film can be used in combination with a resin other than the polyester resin of the main resin, but in order to ensure the ductility and adhesion that are the characteristics of the polyester resin described above, the polyester to be included in the intermediate coating The concentration of the resin is preferably 70% by mass or more. The type of resin other than the polyester resin that can be used for the intermediate coating film is not particularly limited, and a resin that does not adversely affect the performance and paintability of the coating film can be appropriately selected and used as necessary.

The thickness of the intermediate coating layer is preferably 5 to 20 μm. Since the precoat metal plate of the present invention has a configuration in which the top coating layer is harder than the intermediate coating layer, as the thickness of the intermediate coating layer increases, the hardness of the entire coating layer of the intermediate coating layer increases. When the film thickness of the intermediate coating layer exceeds 20 μm, the universal hardness may be 75 N / mm ² or less. Therefore, the thickness is preferably 20 μm or less. Further, if the film thickness of the intermediate coating film layer is less than 5 μm, the concealment ratio by the pigment may be lowered and it may be difficult to produce a color, so the film thickness of the intermediate coating film is preferably 5 μm or more. Further, from the viewpoint of securing the ductility of the film, the film thickness of the intermediate coating film is preferably 5 μm or more.

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.
The Ra (centerline average roughness) at the interface between the top coating layer and the intermediate coating layer of the present invention is more preferably 0.3 to 0.8 μm. If Ra at the interface of the coating film is less than 0.3 μm, the adhesion at the coating film interface may be lowered. In general, when the coating films are laminated, the adhesion of the coating films is maintained by physical bonds such as chemical bonds, hydrogen bonds and van der Waals forces between the coating films. By setting it as the above, in addition to these adhesion forces, the adhesion force by an anchor effect is provided. However, if the Ra of the interface of each coating film exceeds 0.8 μm, the appearance may be affected and the gloss may be lowered.
Here, in the present invention, the interface Ra can be measured by the following method (basically, a method according to JIS-B-0601-1982).
After photographing a vertical cross section of the interface whose surface roughness Ra is to be measured with a micrograph, the unevenness of the interface is traced, and in accordance with a predetermined formula (see Examples described later) defined in JIS-B-0601-1982. The center line average roughness of this interface can be obtained.

The pre-coated metal plate of the present invention coats a transparent clear coating on the colored coating layer. Therefore, when manufacturing with the existing two-coat two-bake specification equipment, an additional coating device and oven, or coil It is necessary to pass the coating line twice. However, by applying the top coating film and the intermediate coating film by simultaneous multilayer coating or wet-on-wetting, the pre-coated metal sheet of the present invention can be manufactured with existing two-coat two-bake specification equipment. Further, the above-mentioned Ra of the interface can be achieved by multilayer simultaneous application or wet-on-wet, and a good processed part appearance can be obtained by applying the multilayer simultaneous application or wet-on-wet as described later. Therefore, it is preferable also from these points.

The multilayer simultaneous application in the present invention 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 in multiple layers simultaneously.

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.

By these methods, by laminating the coating liquids in an undried state and applying them simultaneously, the coating liquid of each layer is slightly mixed at the interface, so that a concentration gradient layer can be formed at the interface. The concentration gradient layer in the present invention has a structure in which the top coating film side is hard and gradually becomes softer toward the intermediate coating film layer side. Therefore, even if a crack occurs in the hard top coating layer by bending or the like, the progress of the crack is suppressed by the concentration gradient layer at the interface and does not reach the intermediate coating layer. Since the top coating layer is clear, if the cracks remain only in the top coating layer, the effect on the appearance is minimal and does not cause a problem. In addition, by laminating the dried coating liquid and applying it simultaneously, the coating liquid of each layer is slightly mixed at the interface, so that excellent adhesion between the intermediate coating film layer and the top coating film layer is obtained. can get.

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.

For the color pigment added to the intermediate coating film layer of the precoated metal plate of the present invention, generally known inorganic pigments, organic pigments and metallic pigments can be used. Specific examples include carbon black, titanium oxide, zinc white, naphthol red, disazo yellow, disazopyrazolone orange, aluminum pigment, nickel pigment, and the like. In general, when the color is black or dark, it is easy to notice wrinkles and it is difficult to secure the light fastness, but the present invention has no problem even if it is black or dark. It is effective and exhibits good scratch resistance.

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 dip galvanized steel plates, aluminum plated steel plates, aluminum-zinc alloyed steel plates, etc. Applicable.

When 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. The treatment “Surfcoat (registered trademark) NRC1000” or the like can be used.

The pre-coated metal plate of the present invention can be coated with a primer coating film having a rust preventive paint function as required. 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 film to be applied to the pre-coated metal plate of the present invention is generally applied by a known coating method such as a roll coater, roller curtain coater, ringer roll coater, spray coating, etc. 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.

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

A glass reactor equipped with a mechanical stirrer, thermometer, condenser, and dry nitrogen gas inlet is charged with 100 parts by mass of isopropyl alcohol in a flask, heated to 80 ° C. in a dry nitrogen atmosphere, and mixed as shown in Table 1. The liquid was dropped in a dropping funnel over 2 hours, and then kept at the same temperature for 4 hours, after which the reaction was terminated. In this way, a graft copolymer solution was obtained. The graft copolymer solutions obtained from the mixed solutions 1 to 12 are referred to as graft copolymer solutions 1 to 12.
A commercially available silicone graft acrylic resin was also used. “Reseda (registered trademark) GS-1015” (glass transition temperature 54 ° C.) manufactured by Toa Gosei Co., Ltd. was used.

In addition, “Udable (registered trademark) S-2710” (glass transition temperature 40 ° C.) and “Acryset (registered trademark) AST-5892” (glass transition temperature 70 ° C.), which are acrylic resins manufactured by Nippon Shokubai Co., Ltd., are also used. (Top 16-16 in Table 2).

Furthermore, “Byron (registered trademark) GK810” (glass transition temperature 46 ° C.), which is an amorphous polyester resin manufactured by Toyobo Co., Ltd., was used as a comparative level in which no silicone draft acrylic resin was used.

As a crosslinking 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., a fully alkyl methylated melamine resin manufactured by Mitsui Cytec. (Hereinafter referred to as methylated melamine) “Cymel (registered trademark) 303”, an isocyanate compound manufactured by Sumika Bayer Urethane Co., Ltd. “Desmodur BL3175 (trade name)” (hereinafter referred to as HDI), “Death” “Module BL4265SN (trade name)” (hereinafter referred to as IPDI), “Desmodule BL1265MPA / X (trade name)” (hereinafter referred to as TDI), “Duranate E402-B80T” (hereinafter referred to as HDI ▲ 2) manufactured by Asahi Kasei Chemicals ▼) was used.
As bright pigments, aluminum flake “Aluminum paste CR-9800RM (trade name)” (average particle size 8 μm) manufactured by Asahi Kasei Metals Co., Ltd., aluminum flake “Lupaste 7220NS (trade name)” manufactured by Toyo Aluminum Co., Ltd. (average particle size 25 μm) Was used.

A commercially available microcrystalline wax was used as the wax used in the comparative material.
In addition, the dilution solvent used what was mixed with cyclohexanone: solvesso 150 = 1: 1 by mass ratio.

Next, the intermediate coating used in the experiment will be described in detail.

As a 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 crosslinking 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. was used. Commercially available aluminum flakes were used, commercially available carbon black was used for black pigments, commercially available titanium oxide was used for white pigments, and commercially available bengara was used for red pigments. : Solvesso 150 = 1: 1 was used.

Details of the produced top paint and intermediate coating are shown in Table 2, Table 2-2, and Table 3, respectively. In addition, the glass transition temperature of the coating film is a thermomechanical analyzer “SSC5200 series T manufactured by Seiko Electronics Co., Ltd.
With “MA / SS120C”, the probe at the time of measurement was measured using a needle probe.

Also, a clear paint of FL641EU primer, which is a polyester primer for PCM manufactured by Japan Fine Coatings Co., Ltd., was prepared, and K-WHITE # 105 was used with a 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, details of the pre-coated metal plate used in the experiment of the example 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 primer coating is applied on one side of the chemical-treated metal plate, and the other side is coated with the gray color of “FL100HQ”, which is the back side coating, on a roll coater, and hot air is blown into the induction heating. It was dried and cured in a furnace 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 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)”). ).

Further, only one layer of the intermediate coating was applied on the primer coating film with a roll coater and baked as described above, and then one layer of the top coating was applied again on the intermediate coating film with a roll coater and baked. A three-layer pre-coated metal plate was also prepared (the coating method in this procedure is referred to as “coating method (iii)”).
In addition, an intermediate coating, an intermediate coating, and a top coating are simultaneously laminated on the primer coating by a slide hopper type curtain coater, and the ultimate temperature of the metal plate is 230 in an induction heating furnace in which hot air is blown. The laminated coating film was simultaneously dried and cured under the condition of ° C. Then, after drying and baking, water was sprayed onto the coated metal plate and water-cooled to prepare a four-layer pre-coated metal plate (hereinafter, this coating method is referred to as “coating method (iv)”). ).
Also, only one layer of intermediate coating is applied on the primer coating with a roll coater, baked, and one layer of intermediate coating is applied again on the intermediate coating with a roll coater, baked, and again on the intermediate coating. A four-layer pre-coated metal plate was also prepared by applying a single layer of top coating on a roll coater and baking it (the coating method in this procedure is referred to as “coating method (v)”).

Hereinafter, the details of the evaluation method of the pre-coated metal plate prepared in the experiment will be described.

1. Universal hardness It measured using the micro hardness meter "Fischerscope (trademark) H100" by a Fischer Instruments company. The ambient temperature during the measurement was 23 ° C., and the universal hardness (HU (N / mm ² )) was measured under the condition that the pressing load was 5 mN for 60 seconds with a Vickers indenter with a face angle of 136 ° square pyramid.

2. Lubricant HEIDON-14 was used and a stainless steel ball (10 mmφ) was loaded at 100 g, 150 mm / min. Under this condition, the force F applied when the precoated metal plate was moved in parallel by 110 mm was measured, and the average friction coefficient was calculated. In addition, the measurement location was made into five places within the remaining 100mm range except the first 10mm.

3. Specular Gloss Measurement of Pre-Coated Metal Plate Specular Gloss was measured using a “digital variable angle gloss meter” manufactured by Suga Test Instruments Co., Ltd. under conditions of an incident angle and a light receiving angle of 20 °. The 20 ° gloss of the primary reference plate (No. 99B076) manufactured by Suga Test Instruments Co., Ltd. was adjusted to 88%, and the 20 ° gloss of the secondary reference plate (No. 99W076) was adjusted to 15%.

4). Scratch resistance test Using HEIDON-14, a 10 yen coin was brought into contact with the pre-coated metal plate at 45 °, and a load was applied in the vertical direction.
The presence or absence of scratches when the pre-coated metal plate was reciprocated once at 50 mm / min in the horizontal direction was visually determined and evaluated with the maximum load at which no scratches were observed.
○: 50 g or more Δ: 20 g or more and less than 50 g ×: less than 20 g
Pencil hardness According to the method of JIS-K 5400 8.4.1 (1993), the scratch resistance of the coating film was examined by scratching the coating film when the pencil core hardness was changed. The highest hardness at which no scratch was observed was defined as the pencil hardness of the coating film, and was evaluated as follows.
○: H or more, Δ: 3B or more and less than H, ×: 4B

5). 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 coating film peeling is observed with a total length of less than half with respect to the total length of the film is evaluated as △, and the case where coating film peeling is recognized with a total length of more than half with respect to the total length of the bent portion is evaluated as x. did.

6). Color value The L value was measured according to JIS Z 8722 with a spectrocolorimeter (manufactured by Suga Test Instruments, model MSC-45-2B).

7). Storage stability of paint 200 g of paint was placed in a paint can (1 liter, outer diameter φ112 mm, height 130 mm), covered, and stored at 40 ° C., and the presence or absence of gelation of the paint was examined. Those that were not gelled in 6 months were marked with ◯, those that gelled in 3-6 months were marked with Δ, and those that gelled in 0-3 months were marked with x. In addition, the state in which the paint can was not leaked to the outside even after the paint can was inverted and left for 1 hour was defined as gelation.
8). Anti-thickening resistance of paint 200 g of paint was placed in a paint can (1 liter, outer diameter φ112 mm, height 130 mm), covered, and stored at 50 ° C. for 1 hour, and the anti-thickening resistance of the paint was investigated.
The viscosity was adjusted to 20 ° C., filled into an Iwata cup, and the number of seconds until the whole amount flowed out was measured using a stopwatch. The value obtained by dividing the number of seconds of the paint after storage (measured by the Iwata cup) by the viscosity of the paint before storage is less than 1.5, the value of 1.5 or more and less than 3 is △, 3 or more Was marked with x.
9. Measurement of boundary surface Ra Ra of the boundary surface between the intermediate coating layer and the top coating layer is obtained by cutting the coating film of each example in a direction perpendicular to the coating direction, embedding in a resin, and polishing the coating film. The cross section perpendicular to the surface of the film was smoothed and evaluated by a photograph taken with a scanning microscope of 3500 times. After covering the top of the photo with a transparent sheet used for OHP and tracing the unevenness of the boundary surface precisely, as shown in the figure, measure the area of the vertical line part with an image processing device as the average value Ra was calculated from the equation. In addition, l (el) was 3 mm.

The details of the evaluation results are described below.

Tables 4 to 7 show the precoated metal sheets prepared in the present invention and the evaluation results. 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 average friction coefficient and universal hardness As an influence of average friction coefficient and universal hardness, Example No. 1-No. No. 19 and Comparative Example No. 20-No. 28.

The pre-coated metal plates of the present invention (Examples 1 to 19) had excellent scratch resistance, gloss and workability.

Those having an average friction coefficient exceeding 0.08 (Comparative Examples-22, 25) are inadequate because of their poor scratch resistance. Those having a universal hardness of less than 75 N / mm ² (Comparative Examples-20, 26) are inadequate because of their poor scratch resistance. Those having a universal hardness exceeding 200 N / mm ² (Comparative Examples-21, 27) are inadequate because of poor workability.

(2) Influence of top coating type and intermediate coating type The top coating layer is a clear coating that does not contain a pigment, and the silicone graft acrylic resin content in the top coating is 2 ~ in terms of silicone resin. 18% by mass, the intermediate coating film layer contains a color pigment, a melamine-curable or isocyanate-curable polyester resin, and the intermediate coating film has a glass transition temperature of 25 to 50 ° C., Contains a silicone graft acrylic resin having a glass transition temperature of 30 to 67 ° C. in the top coating film, a ratio of the silicone resin in the silicone graft acrylic resin of 3 to 20% by mass, and the intermediate coating film layer contains a color pigment Further, those containing a melamine curable or isocyanate curable polyester resin and having a glass transition temperature of 25 to 50 ° C. (Examples 1 to 19) are excellent. It had excellent scratch resistance, gloss, and processability. The content of the silicone graft acrylic resin in the top coating exceeds 18% by mass in terms of silicone resin (Examples-20 and 21), and the ratio of the silicone resin in the silicone graft acrylic resin exceeds 20% by mass. The one (Example-21) tended to have relatively low storage stability of the paint.

When the glass transition temperature of the top coating layer is less than 30 ° C. (Comparative Example-22) and the glass transition temperature of the intermediate coating film is less than 25 ° C. (Comparative Example-26), the universal hardness tends to decrease. Yes, the scratch resistance is poor, the content of the silicone graft acrylic resin in the top coating is less than 2% by mass in terms of silicone resin (Comparative Example-24, 25), the ratio of the silicone resin in the silicone graft acrylic resin Of less than 3% by mass (Comparative Example -24) had a tendency for the coefficient of dynamic friction to decrease and the scratch resistance was poor.

Those having a glass transition temperature of the top coating layer exceeding 67 ° C. (Comparative Example-23) and those having a glass transition temperature of the intermediate coating film exceeding 50 ° C. (Comparative Example-27) tend to have too high universal hardness. The processability was inferior.

In the case where a large amount of wax is added to the top coating layer to obtain a universal hardness of 75 N / mm ² or more and an average friction coefficient of 0.08 or less (Comparative Example-28), the specular gloss is less than 50% and the gloss is inferior. Therefore, it is unsuitable.

(3) Influence of film thickness When the film thickness of the top coating layer was 0.5 μm (Example-29), the lubricity was slightly lowered and the scratch resistance was slightly inferior. When the film thickness of the top coating layer was 12 μm (Example-35), the workability tended to slightly decrease. The film thickness of the top coating layer is more preferably 1 to 10 μm.

When the film thickness of the intermediate coating film layer was 3 μm (Example-36), the L value was slightly increased and black color was less likely to be produced. When the film thickness of the intermediate coating layer was 22 μm (Example-43), the hardness slightly decreased and the scratch resistance tended to decrease. The film thickness of the intermediate coating layer is more preferably 5 to 20 μm.

(4) Influence of coloring type of intermediate coating layer Even if it is other than the invention of the present application, light-colored systems such as white and silver satisfy scratch resistance, but in dark-colored systems such as black and red, prevent scratches. (Comparative Examples 48 to 51) are not possible. On the other hand, it can be seen that the present invention has good scratch resistance not only in the light color system but also in the dark color system, and has excellent scratch resistance performance (Examples 44 to 47).

In addition, performance (gloss, workability) other than scratch resistance shows good performance regardless of the color of the intermediate coating film layer in both the comparative example and the present invention.

(5) Effect of coating method The intermediate layer and the top layer coated and baked one by one (Example-54) are more workable than those prepared by simultaneous multilayer coating and wet-on-wet coating. In addition, the adhesiveness tended to decrease. From this result, it can be seen that those prepared by simultaneous multi-layer coating and wet-on-wet coating have improved workability and adhesion, and are more suitable.
(6) Effect of bright pigment The effect of bright pigment is shown in Table A. When the top coating layer contains a luster pigment (Examples -57 to 60), the pencil hardness tended to be improved by making the scratches less noticeable.
(7) Influence of crosslinking agent type The influence of crosslinking agent type is shown in Table B. Those using an isocyanate compound as a cross-linking agent (Examples -63 to 77) tended to have better resistance to thickening of the top paint. It can be seen that when the molar ratio of NCO / OH is 0.05 to 0.3 / 1.0 (Examples -68 to 70), higher scratch resistance is obtained, which is more preferable.
(8) Regarding wear resistance, Table C shows wear resistance. When the hardness of the coating layer surface at 23 ° C. was 150 to 200 N / mm ² in terms of universal hardness under a 5 mN load (Examples 80 to 88), there was a tendency that high wear resistance could be imparted.
Isophorone diisocyanate (IPDI) was used as the isocyanate compound, and the NCO / OH molar ratio of 0.1 to 0.5 / 1.0 (Examples-82, 85, 86) tended to have excellent wear resistance.
(9) Influence of the interface Ra between the intermediate coating layer and the top layer Table D shows the influence of the interface Ra between the intermediate coating layer and the top layer. Interfacial Ra between the intermediate coating layer and the top layer is 0.3 to 0.8 (Examples-89, 91, 93, 95, 97, 99, 101, 103, 105, 107), workability and adhesion It can be seen that this is improved and more suitable.
(10) Influence of intermediate coating layer The influence of the intermediate coating layer is shown in Table E. Those having a bright pigment in the intermediate coating layer (Examples -109 to 128) tended to improve the pencil hardness due to the scratch being less noticeable.
(11) Influence of interface Ra between intermediate coating layer and top layer Table D shows the influence of interface Ra between the intermediate coating layer and the top layer. When the interface Ra between the intermediate coating layer and the top layer is 0.3 to 0.8 (Examples 109 to 118), it can be seen that the workability and the adhesion are improved, which is more preferable.

As described above, the preferred embodiments of the present invention have been described with reference to the accompanying drawings, but it goes without saying that the present invention is not limited to such examples. 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 (18)

1. A pre-coated metal plate having a coating layer 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 contains a silicone graft acrylic resin and is a clear coating containing no pigment, the intermediate coating layer contains a melamine curable or isocyanate curable polyester resin, and , A coating film containing a coloring pigment,
   Furthermore, the average friction coefficient of the coating layer surface of the coating layer is 0.08 or less, and the hardness of the coating layer surface at 23 ° C. is 75 to 200 N / mm ² in terms of universal hardness under a load of 5 mN, The precoated metal sheet is characterized in that the specular gloss on the surface of the coating layer is 50% or more when measured under conditions of an incident angle and a light receiving angle of 20 °, respectively.
2. A pre-coated metal plate having a coating layer 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 contains a silicone-grafted acrylic resin and a clear coating containing a pigment; the intermediate coating layer contains a melamine-curable or isocyanate-curable polyester resin; and , A coating film containing a coloring pigment,
   Furthermore, the average friction coefficient of the coating layer surface of the coating layer is 0.08 or less, and the hardness of the coating layer surface at 23 ° C. is 75 to 200 N / mm ² in terms of universal hardness under a load of 5 mN, The precoated metal sheet is characterized in that the specular gloss on the surface of the coating layer is 50% or more when measured under conditions of an incident angle and a light receiving angle of 20 °, respectively.
3. The precoated metal sheet according to claim 2, wherein the top coating layer is a clear coating containing a bright pigment.
4. The pre-coated metal sheet according to claim 1 or 2, wherein the top coating layer is a melamine curable type.
5. The pre-coated metal sheet according to claim 1 or 2, wherein the top coating layer is an isocyanate curable type.
6. The precoated metal sheet according to claim 5, wherein the isocyanate-curable top coating layer has an NCO / OH ratio of 0.05 to 0.5.
7. The precoated metal sheet according to any one of claims 1 to 6, wherein Ra (center line average roughness) of an interface between the top coating layer and the intermediate coating layer is 0.3 to 0.8.
8. The precoated metal sheet according to any one of claims 1 to 7, wherein the content of the silicone graft acrylic resin in the top coating film is 2 to 18% by mass in terms of silicone resin.
9. The glass transition temperature of the top coating film is 30 to 67 ° C., the ratio of the silicone resin in the silicone graft acrylic resin contained in the top coating film is 3 to 20% by mass, and the intermediate coating film The precoated metal sheet according to any one of claims 1 to 8, wherein the glass transition temperature is 25 to 50 ° C.
10. The precoated metal sheet according to any one of claims 1 to 8, wherein the hardness of the coating layer surface at 23 ° C is 150 to 200 N / mm ² in terms of universal hardness under a load of 5 mN.
11. The precoated metal sheet according to claim 10 or 11, wherein the top coating layer is of an isocyanate curable type.
12. The precoated metal sheet according to claim 11, wherein the curing agent in the top coating layer is isophorone diisocyanate (IPDI).
13. The precoated metal sheet according to claim 11 or 12, wherein a ratio of the curing agent in the top coating layer is 0.1 to 0.5.
14. A pre-coated metal plate having a coating layer on one or both sides of the metal plate,
    The coating layer is at least a top coating layer that is a coating formed on the outermost surface, an intermediate layer that is in contact with the top coating layer, and an intermediate coating that is a lower layer coating that is in contact with the intermediate coating layer And having a layer
    The top coating layer contains a silicone graft acrylic resin and is a clear coating containing no pigment, the intermediate coating layer contains a melamine curable or isocyanate curable polyester resin, and , A coating film containing a coloring pigment,
    Furthermore, the average friction coefficient of the coating layer surface of the coating layer is 0.08 or less, and the hardness of the coating layer surface at 23 ° C. is 75 to 200 N / mm ² in terms of universal hardness under a load of 5 mN, The precoated metal sheet is characterized in that the specular gloss on the surface of the coating layer is 50% or more when measured under conditions of an incident angle and a light receiving angle of 20 °, respectively.
15. The precoated metal sheet according to claim 14, wherein the intermediate layer contains a pigment.
16. The precoated metal sheet according to claim 15, wherein the intermediate layer contains a bright pigment.
17. The precoated metal sheet according to any one of claims 14 to 16, wherein Ra (center line average roughness) of an interface between the top coating layer and the intermediate layer is 0.3 to 0.8.
18. A method for producing a precoated metal sheet according to any one of claims 1 to 17,
    A method for producing a pre-coated metal sheet, characterized in that the intermediate coating layer and the top coating layer are baked after being applied by multi-layer simultaneous application or wet-on-wet method, respectively.

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