JP2009051117A - Precoated metal sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a precoated metal plate which has an improved flex resistance and corrosion resistance while retaining an excellent antifouling property of a specific precoated layer. <P>SOLUTION: The precoated metal plate is composed of a metal plate having a ten-point average roughness Rz of 1.2-4.0 μm, a chemical conversion coat formed at least one surface of the metal plate and a resin coat formed on the chemical conversion coat. The resin coat is composed of an undercoat formed on the chemical conversion coat and a topcoat formed on the undercoat. The undercoat contains a polyester-based resin, a melamine-based resin and an epoxy-based resin and has a tensile strength of 20-50 MPa. The topcoat contains an acrylic resin, a colloidal silica having an average particle size of ≤0.1 μm in an amount of 1-10 wt.% of the dried topcoat and a silicone compound having an alkoxyl group in an amount of 0.1-5.0 wt.% of the dried topcoat. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an antifouling pre-coated metal plate used for outer plates, ceiling panels, signboards and the like of transportation equipment.

  In recent years, precoated metal plates have been adopted for outer plates, ceiling panels, signboards, and the like of transportation equipment. The reason is that the productivity is high and the cost is low as compared with the post-coating and pressure-sensitive adhesive films that have been mainstream in the past.

  A wide variety of functions can be imparted to the pre-coated metal plate in accordance with a request from the user. One of them is maintenance of aesthetics, resistance to dirt, and easy cleaning performance, that is, anti-stain properties are required for precoated metal sheets. In general, examples of the dirt substance include dust, earth and sand, dust, particulate matter in exhaust gas, and the like.

  Especially in the outdoors, since such a soiled substance is difficult to be washed away by rainwater, there is a problem that what is left behind in a streak form becomes black streaks after drying and the aesthetics are impaired. In the case of a ceiling, there is a problem that a lot of time and labor are required to remove the dirt if the dirt substance adheres after construction.

In order to solve these problems, Patent Document 1 discloses a silica-containing acrylic resin precoated metal-coated plate. Since the resin film used is hard, it is difficult for the dirt substance to enter, and since the resin film surface is hydrophilic, the dirt substance can be easily washed.
Japanese Patent Laid-Open No. 2004-082516

  When imparting aesthetics to the silica-containing acrylic resin precoated metal coated plate, various pigments or dyes are added. The addition amount is adjusted as appropriate, but the type and addition amount are likely to increase in order to meet the demands of users who demand a high-class feeling. In such a case, since the resin film becomes brittle, the resin film cracks at the bent portion, and the appearance of the resin film sometimes becomes a problem.

  Patent Document 2 discloses a coated metal plate that has excellent contamination resistance and can prevent the occurrence of cracks in the resin film. In this coated metal plate, a material containing a bisphenol A type epoxy resin having an alkylamine chain and an adduct type blocked isocyanate compound in the undercoat is used. Thereby, the resin film which consists of urethane bridge | crosslinking structures is formed, and it has a softness | flexibility and can obtain a tough resin film. In addition, as the top coating material, one containing an organic resin and a tetraalkoxysilane compound and having a glass transition temperature of 20 to 80 ° C. of the cured resin film is used. Thereby, it is excellent in stain resistance and can prevent the crack of a resin film effectively.

However, since the baking time is as long as 20 minutes, in order to apply it as it is to the precoat, the length of the drying furnace must be made extremely long or the production rate must be extremely low. As a result, there remains a problem that the manufacturing cost increases.
JP 2004-243546 A

Patent Document 3 discloses a contamination-resistant precoated aluminum plate having good bending workability. An undercoat layer is formed by baking a paint containing a polyester resin having a number average molecular weight in the range of 20000 to 30000 and a polydispersity in the range of 2 to 10 as a base resin. By setting the thickness of the undercoat layer in the range of 3 to 13 μm, the cohesive force of the cured resin film is increased. As a result, even if a fragile topcoat layer is cracked by bending, the undercoat layer does not follow the deformation of the topcoat layer, and the undercoat layer does not stretch and crack, so that the appearance of the bent portion can be improved.
JP 2006-247906 A

  By the way, in recent years, high performance corrosion resistance is required for precoated metal sheets. For example, in the case of an outer plate of a transportation device, iron powder or the like pierces the resin film, and corrosion tends to occur starting from that portion. In response to such a requirement, a method of increasing the thickness of the resin film can be considered. However, in the stain-resistant precoated aluminum plate disclosed in Patent Document 3, the polyester resin paint having a number average molecular weight of 20000 to 30000 used for the undercoat layer has a high viscosity, and there is a problem that the coating appearance is inferior when thickly applied. . For this reason, a method of repeatedly coating thin coating layers in multiple layers is conceivable, but the problem that the resin film deteriorates and the interlaminar adhesion deteriorates due to baking and drying each time it is overcoated.

  An object of this invention is to provide the precoat metal plate which improved the bending resistance and corrosion resistance, maintaining the outstanding antifouling property of a specific topcoat layer.

  The present invention according to claim 1 is a metal plate having a ten-point average roughness Rz of 1.2 to 4.0 μm, a conversion coating formed on at least one surface of the metal plate, and formed on the conversion coating. A pre-coated metal plate comprising a resin film, wherein the resin film comprises an undercoat layer formed on the chemical conversion film and an overcoat layer formed on the undercoat layer, and the undercoat layer comprises a polyester resin and a melamine resin. And an epoxy resin, and has a tensile strength of 20 to 50 MPa, and the overcoat layer is an acrylic resin and 1 to 10 of the dried overcoat layer having an average particle size of 0.1 μm or less. A pre-coated metal plate comprising wt% colloidal silica and 0.1 to 5.0 wt% of a silicone compound having an alkoxyl group in the dried overcoat layer.

  According to the present invention, in the present invention, the undercoat layer has a thickness (a) of 29 to 50 μm, the overcoat layer has a thickness (b) of 3 to 13 μm, and a / b is 3 to 10 did.

In the present invention, by setting the ten-point average roughness Rz on the surface of the metal plate within a specific range, the adhesion between the metal plate and the undercoat layer can be improved by the anchor effect. Moreover, in the undercoat layer, by making the tensile strength within an appropriate range while using a predetermined type of resin, the adhesion between the undercoat layer and the chemical conversion film, and the adhesion between the undercoat layer and the overcoat layer can be improved. The bending resistance and corrosion resistance of the resin film are also improved.
Furthermore, antifouling property and bending resistance can be improved by containing a predetermined kind of resin, silica and silicone compound in the topcoat layer, and making the content of silica and silicone compound within a predetermined range.
In addition, by setting the thickness a of the undercoat layer and the thickness b of the topcoat layer in a specific range and a / b in a specific range, the resin film is excellent without significantly reducing the bending resistance. Good interlayer adhesion and corrosion resistance can be achieved while maintaining antifouling properties.

A. Metal plate The metal plate used in the present invention is not particularly limited, but has sufficient strength to form an outer plate, a ceiling panel, a signboard, etc. of transportation equipment, and has sufficient formability. Are preferably used. For example, although an aluminum plate, a hot dip galvanized steel plate, a hot dip galvanized steel plate, etc. are mentioned, it is preferable to use the aluminum plate which is excellent in recyclability and excellent in corrosion resistance. As the aluminum plate, pure aluminum, 3000 series or 5000 series aluminum alloy or the like is preferably used.

The ten-point average roughness Rz of the metal plate surface used in the present invention is in the range of 1.2 to 4.0 μm. If it is less than 1.2 micrometers, the anchor effect with respect to a chemical conversion film is small, and the adhesiveness after a bending process is inferior. On the other hand, when it exceeds 4.0 μm, the metal plate surface is easily cracked, so that the appearance of the bent portion is inferior. The specific method for adjusting the surface roughness of the metal plate is not particularly limited,
(A) The rolling roll surface is polished by appropriate conditions or processed by means such as shot blasting, electric discharge machining, laser machining, etc., and the surface shape of the rolling roll is adjusted appropriately, and the irregularities on the rolling roll surface during rolling A method of transferring the shape to a metal plate,
(B) a method of adjusting the shape and distribution of oil pits and the like formed on the surface of the metal plate during rolling by adjusting the rolling speed and the viscosity of the lubricating oil for rolling;
Etc. In practice, the method (a) or (b) may be appropriately selected so that the surface state is reliably and stably satisfied.

  The ten-point average roughness Rz is measured by using, for example, a confocal microscope HD100 manufactured by Lasertec Corporation. A three-dimensional image of the surface of the metal plate is measured with an objective lens 50 times, and a ten-point average roughness Rz is measured in an arbitrarily selected 322 μm square area. At this time, the filter size of the median filter is set to 5 * 5. The arithmetic average value of Rz is calculated by measuring 5 times. Note that Rz may be obtained by other measurement methods.

B. The chemical conversion film provided between the chemical conversion metal sheet and the undercoat layer is not particularly limited as long as it improves the adhesion between the two. For example, when an aluminum plate is used as the metal plate, a chemical conversion film formed with a phosphate chromate treatment solution that is inexpensive and easy to manage the bath solution, or a coating-type zirconium treatment that does not require any water washing without any change in the treatment solution components The chemical conversion film formed by (1) can be used. Such a chemical conversion treatment is performed by spraying a predetermined chemical conversion treatment solution on the aluminum plate or immersing the aluminum plate in the treatment solution at a predetermined temperature for a predetermined time. In addition to the chromate treatment, a chemical conversion film formed with a phosphating solution can also be used for the hot dip galvanized steel plate and the hot dip galvanized steel plate.

  Before the chemical conversion treatment, in order to remove the dirt on the surface of the metal plate or to adjust the surface properties, the metal plate is treated with acid such as sulfuric acid, nitric acid, phosphoric acid, or caustic soda, sodium phosphate, It is desirable to perform alkali treatment such as sodium silicate. Such a surface treatment is also performed by spraying a predetermined surface treatment liquid on the metal plate or immersing the metal plate in the treatment liquid at a predetermined temperature for a predetermined time.

C. A resin film is formed on the resin film chemical conversion film. The resin film is composed of an undercoat layer formed on the chemical conversion film and an overcoat layer formed thereon.

C-1. Undercoat layer The undercoat layer is formed by blending a polyester resin with a melamine resin and an epoxy resin as essential components in a specific ratio, and applying a paint in which these are dissolved or dispersed in an appropriate solvent.

C-1-1. Polyester Resin In the present invention, a polyester resin is used as the base resin for the undercoat layer. As the polyester resin, alkyd resin, modified alkyd resin, oil-free polyester resin, unsaturated polyester resin and the like are used. The alkyd resin has a skeleton of a condensate of a polybasic acid such as phthalic anhydride and a polyhydric alcohol such as glycerin, which is modified with fats and oils such as cutting oil. It is possible to improve the wetting of the chemical conversion film by imparting flexibility to the resin by oil modification and reducing the surface tension of the resin. Depending on the type and amount of fats and oils used, it is classified into ultra-short oil, short oil, medium oil, long oil, and ultra-long oil. As the modified alkyd resin, there can be used a phenol-modified alkyd resin obtained by adding a phenol resin and reacting at a later stage of synthesis of the alkyd resin, a silicone-modified alkyd resin modified with a hydroxysilane, an alkoxysilane intermediate or the like. The oil-free polyester resin means a polyester resin that is not oil-modified, and can be obtained by condensing a polybasic acid such as phthalic acid, isophthalic acid or terephthalic acid and a polyhydric alcohol such as propylene glycol or neopentyl glycol. . The unsaturated polyester resin is a polyester resin having an unsaturated group in the main chain, and can be obtained by condensing a polybasic acid such as maleic anhydride or fumaric acid and a polyhydric alcohol such as propylene glycol.

  The number average molecular weight of the polyester resin is preferably in the range of 1000 to 20000. More preferably, it is the range of 1000-9000. When the number average molecular weight is less than 1000, the entanglement between the molecules decreases, and the resin is easily broken during bending. When the number average molecular weight increases, the viscosity of the paint increases, so that the paintability tends to be inferior. If the number average molecular weight of the polyester-based resin exceeds 20000, multilayer coating is required to improve the corrosion resistance of the precoated metal sheet, but this results in poor interlayer adhesion between the multilayers. The number average molecular weight is measured by GPC (gel exclusion chromatography).

C-1-2. Melamine resin In the present invention, a melamine resin is used as a curing agent for a polyester resin. As the melamine resin, a fully alkylated melamine resin or a partially alkylated melamine resin having an imino group or a methylol group in the molecule can be used. As the type of the alkyl group, a methyl group or a butyl group is mainly used, and it is preferable to use a butyl group having a low viscosity when formed into a paint and excellent in wettability and leveling properties. When a melamine resin is used as a curing agent for a polyester resin, basically, the curing reaction tends to compete with the self-condensation reaction of the melamine resin, and it is preferable to appropriately select the structure of the melamine resin.

C-1-3. Epoxy resin In the present invention, an epoxy resin is used to improve the adhesion of the undercoat layer. It was found that the adhesiveness with the topcoat layer was inferior only by adding a polyester resin and a melamine resin to the undercoat layer. The inventors of the present invention have conducted intensive studies and found that the adhesiveness of the undercoat layer to the overcoat layer and the chemical conversion film is improved by appropriately blending the epoxy resin as described later. Epoxy resins include glycidyl ether types such as bisphenol A and bisphenol B, glycidyl ester types such as glycidyl hexahydrophthalate, glycidyl amine types such as tetraglycidyldiaminodiphenylmethane, and 3,4-epoxycyclohexaylmethyl. Cyclic oxirane types such as 3,4-epoxycyclohexanecarboxylate are used.

C-1-4. In the present invention, when the total weight of the polyester resin and the melamine resin is 100 parts, the mixing ratio of the polyester resin and the melamine resin is the polyester resin. : As a melamine resin, it is blended at a ratio of 65 parts: 35 parts to 90 parts: 10 parts. In this relation, if the polyester resin is less than 65 parts (the melamine resin exceeds 35 parts), the self-condensate of the melamine resin increases, and the resin film easily breaks during bending, resulting in bending resistance. Is inferior. On the other hand, when the polyester-based resin exceeds 90 parts (the melamine-based resin is less than 10 parts), the number of cross-linking points decreases, and the resin film easily breaks during bending, resulting in poor bending resistance.

  If the epoxy resin is not blended at all as described above, a hard melamine resin self-condensate is present on the surface of the undercoat layer, so that the adhesion between the undercoat layer and the topcoat layer is poor. Therefore, in the present invention, the epoxy resin is blended at a ratio of 4 to 18 parts with respect to 100 parts of the total weight of the polyester resin and the melamine resin. Thereby, since adhesiveness with a chemical conversion film and a topcoat layer improves in undercoat, the corrosion resistance of a resin film improves. Furthermore, deformation of the topcoat layer during bending can be alleviated, and cracks can be reduced. When the blending ratio of the epoxy resin is less than 4 parts with respect to 100 parts of the total weight of the polyester resin and the melamine resin, the functional group of the undercoat layer that contributes to adhesion with the chemical conversion film or the overcoat layer is insufficient. The adhesion of the resin film is inferior. On the other hand, if it exceeds 18 parts, the entanglement of the resin film becomes excessive, the resin film becomes difficult to stretch, and the bending resistance is inferior.

C-1-5. Additives Undercoat paints used in the present invention include leveling agents, anti-waxing agents, stabilizers, anti-settling agents, etc. used in ordinary paints to ensure paintability and general performance as precoat materials. You may add suitably. Furthermore, pigments and dyes may be added as appropriate in order to color the resin film.

C-1-6. Formation of the undercoat layer Polyester resin, melamine resin, and epoxy resin are essential components, and a paint in which these are dissolved or dispersed in an appropriate solvent is applied onto the chemical conversion film by a roll coater, and then predetermined in an oven at a predetermined temperature. Process for hours and bake dry. As the solvent, cyclohexane, isophorone, isobutyl alcohol, xylene, ethylbenzene, methyl ethyl ketone, diacetone alcohol, ethylene glycol monobutyl ether, or the like is used. In addition, it may replace with a roll coater and may apply | coat a coating material with an air spray, a bar coater, etc. The baking conditions are usually PMT (maximum plate temperature) 160 to 300 ° C. and 10 to 120 seconds.

C-1-7. Undercoat layer thickness a
The thickness a of the undercoat layer is preferably in the range of 8 to 50 μm. If it is less than 8 micrometers, corrosion resistance will be inferior. On the other hand, if the thickness exceeds 50 μm, the bending of the undercoating layer tends to break following the cracking of the hard overcoating layer, resulting in poor bending resistance. When high performance corrosion resistance is required for the precoated metal plate, the thickness of the undercoat layer is preferably 29 to 50 μm. The corrosion resistance tends to improve as the thickness increases, but the bending resistance tends to be inferior. If it is less than 29 μm, high-performance corrosion resistance cannot be obtained, and if it exceeds 50 μm, the bending resistance is inferior.

C-1-8. Tensile strength of the undercoat layer The tensile strength of the undercoat layer is 20 to 50 MPa. If it is less than 20 MPa, the entanglement and crosslinking points of the resin contained in the undercoat layer are too small, and the resin film is easily broken during bending, resulting in poor bending resistance. On the other hand, when it exceeds 50 MPa, there are too many entanglements and cross-linking points of the resin, and the bending resistance is inferior without being able to follow the irregularities on the surface of the metal plate.

  The tensile strength of the undercoat layer is measured by performing a tensile test using a free film. The free film is formed by forming an undercoat layer on a Teflon (registered trademark) sheet and then peeling it off from the Teflon (registered trademark) sheet. The test piece is a strip of 20 mm width and 120 mm length. The undercoat layer thickness is 14 μm. In the tensile test, the distance between chucks is 50 mm at 25 ° C., and the tensile strength is measured at a tensile speed of 20 mm / min. The tensile strength of the undercoat layer can be appropriately adjusted depending on the type and blending ratio of the resin.

C-2. Overcoat layer An overcoat layer is formed on the undercoat layer. The topcoat layer is formed by baking and painting a paint in which an acrylic resin, colloidal silica, and a silicone compound containing an alkoxyl group are contained as essential components, and these are dissolved or dispersed in an appropriate solvent.

C-2-1. Acrylic Resin In the present invention, an acrylic resin is used as the base resin for the overcoat layer. Acrylic resins are generally used in many paints because they have good overall coating performance and are relatively inexpensive. Especially, the gloss of the coating surface can be made relatively high, and they are relatively hard. A smooth coating film can be formed.

  Acrylic resins are copolymers of acrylic acid, methacrylic acid, etc. and their esters, but such acrylic resins contain a small amount of epoxy resins, melamine resins, fluorine resins, urethane resins, etc. It may be blended.

C-2-2. Immediately after applying a coating material was added colloidal silica colloidal silica, the colloidal silica has been uniformly dispersed in the coating film, the colloidal silica concentration in the coating surface increases during baking and drying. When exposed in this state, it reacts with moisture and rainwater in the air, and a highly hydrophilic silanol group is generated on the surface, so that the water contact angle in the overcoat layer that is the resin film surface can be lowered. As a result, rainwater or the like that has fallen on the surface of the resin film flows smoothly and does not accumulate easily, and the attached dirt can be easily removed. In addition, the addition of colloidal silica makes the overcoat layer hard and makes it difficult for earth and sand, dust, dust, particulate matter in exhaust gas, etc. to be buried in the resin film.

  The average particle size of colloidal silica is 0.1 μm or less. By setting the particle size of colloidal silk to 0.1 μm or less, the spacing between silanol groups present on the surface of the overcoat layer can be narrowed to increase the density of existence. As a result, water wetting on the resin film surface can be improved. When the average particle diameter of colloidal silica exceeds 0.1 μm, the cracking of the resin film tends to occur in the bending process as a starting point of the crack of the resin film.

  The content of colloidal silica is in the range of 1 to 10% by weight based on the total weight of the dried topcoat layer. If it is less than 1% by weight, the hydrophilic effect cannot be sufficiently obtained, and attached rainwater or the like tends to accumulate, making it difficult to remove dirt. If it exceeds 10% by weight, the overcoat layer becomes hard, the starting point of the resin film cracking increases, and cracking is likely to occur during bending.

C-2-3. In order to improve the hydrophilicity immediately after the coating of the silicone compound overcoat layer containing an alkoxyl group, it is preferable to add a silicone compound containing an alkoxyl group. The content of the silicone compound containing an alkoxyl group is in the range of 0.1 to 5.0% by weight with respect to the total weight of the dried topcoat layer. If it is less than 0.1% by weight, the effect of improving hydrophilicity cannot be sufficiently obtained and the antifouling property is poor. If it exceeds 5.0% by weight, the effect of improving the hydrophilicity is saturated and uneconomical.

  As the silicone compound containing an alkoxyl group, those having an average degree of polymerization of 3 to 50 are preferably used. If the average degree of polymerization is less than 3, it is difficult to be hydrolyzed, so that the effect of improving hydrophilicity cannot be obtained. If the average degree of polymerization exceeds 50, gelation tends to occur and a problem arises in paintability.

C-2-4. In order for the pigment or dye topcoat layer to exhibit a desired color, it is preferable to include one or more pigments or dyes in the topcoat layer. As the pigment, for example, titanium oxide and carbon black are preferable, and as the dye, for example, phthalocyanine blue is preferable. Their content is appropriately adjusted according to the required color.

C-2-5. Formation of the topcoat layer An acrylic resin, colloidal silica, and a silicone compound containing an alkoxy group are essential components, and a paint in which these are dissolved or dispersed is applied onto the undercoat layer by a roll coater, and is heated in an oven at a predetermined temperature. Process for a predetermined time and bake and dry. As the solvent, xylene, ethyl acetate, butyl acetate, isophorone, cyclohexanone, or the like is used. In addition, it may replace with a roll coater and may apply | coat a coating material with an air spray, a bar coater, etc. As baking conditions, it is 10 to 120 seconds at PMT (maximum reach | attainment board temperature) 160-300 degreeC.

C-2-6. Top coat thickness b
The thickness b of the overcoat layer is preferably in the range of 3 to 13 μm. If it is less than 3 μm, the overcoat layer deteriorates and the antifouling property is inferior in an actual environment. On the other hand, even if it exceeds 13 μm, the performance is saturated and uneconomical.

C-3. Ratio of undercoat layer thickness a / overcoat layer thickness b The ratio (a / b) of the thickness a of the undercoat layer to the thickness b of the overcoat layer is such that the thickness a of the undercoat layer is 29 to 50 μm and the overcoat layer The thickness b of the layer is preferably 3 to 13 μm and is preferably in the range of 3 to 10. If this ratio is less than 3, the undercoat layer cannot be made thick, so that high-performance corrosion resistance cannot be obtained. When this ratio exceeds 10, the undercoat layer becomes too thick with respect to the overcoat layer, so that the resin film is easily broken and the bending resistance is inferior.

  Hereinafter, the present invention will be described in detail with reference to examples. In addition, this invention is not limited to a following example, unless the range of a claim is exceeded.

Examples 1-12 and Comparative Examples 1-9
As a metal plate, an aluminum plate of A5052P-H34 (Examples 1 to 10, 13 to 14, Comparative Examples 1 to 12), a hot dip galvanized steel plate (Example 11), and a hot dip zinc-aluminum alloy steel plate (Example 12) Was used. All the metal plates had a thickness of 0.6 mm. These metal plates were degreased by a spray method with a commercially available alkaline degreasing agent, and then washed with water. Furthermore, a chemical conversion treatment was performed, followed by washing with water and drying. In the chemical conversion treatment, phosphoric acid chromate treatment (Examples 1 to 6, 9, 10, 13, 14, Comparative Examples 1 to 12), chromate treatment (Examples 11 and 12), and coating-type zirconium treatment were performed (Examples). 7, 8). The chemical conversion film was measured with a fluorescent X-ray analyzer.

  Next, an undercoat layer was formed on the chemical conversion film. Polyester resin (oil-free polyester resin, number average molecular weight 4000), melamine resin (butylated melamine resin) and epoxy resin (bisphenol A type epoxy resin) dispersed in cyclohexanone solvent (all paints The resin amount was 50% by weight) as a coating for the undercoat layer. The undercoat layer coating was applied onto the chemical conversion film with a bar coater and baked at a PMT (maximum ultimate plate temperature) of 210 ° C. and a baking time of 50 seconds to form an undercoat layer.

  Further, an overcoat layer was formed on the undercoat layer. A paint in which an acrylic resin, colloidal silica, and an alkoxyl group-containing silicone compound (average polymerization degree 10) are dispersed in butyl acetate as a solvent (the acrylic resin content in the paint is 50% by weight) was prepared as a paint for the topcoat layer. This overcoat layer coating was applied onto the undercoat layer with a bar coater and baked at PMT 241 ° C. and a baking time of 50 seconds to form an overcoat layer to prepare a precoated metal plate.

  In addition, about 10-point average roughness Rz of the metal plate surface, it measured using Lasertec Co., Ltd. confocal microscope HD100. A three-dimensional image of the surface of the metal plate was measured with an objective lens of 50 times, and five area portions of 322 μm square were arbitrarily selected. Ten points of roughness were measured at each 322 μm square portion, and the arithmetic average was taken as the ten point average roughness Rz of that portion. Furthermore, the arithmetic average value was calculated also about five ten-point average roughness Rz, and it was set as the ten-point average roughness Rz of the metal plate sample.

Metal plate material and Rz, conversion coating type and coating amount (Cr amount in phosphoric acid chromate treatment and chromate treatment, Zr amount in coating type zirconium treatment), blending amount of each component of undercoat layer (polyester resin) And the total weight of the melamine resin and 100 parts of the polyester resin and the melamine resin, and for the epoxy resin, the number of parts of the polyester resin and the melamine resin relative to the total weight of 100 parts) and the layer thickness , The content of each component of the topcoat layer (% by weight relative to the total weight of the dried topcoat layer), the average particle size and layer thickness of colloidal silica, the ratio of the thickness a of the undercoat layer to the thickness b of the topcoat layer (a / B) is shown in Table 1.
In Comparative Example 9, the undercoat layer does not contain an epoxy resin, in Comparative Example 7, the overcoat layer does not contain colloidal silica, and in Comparative Example 8, the overcoat layer contains an alkoxyl group-containing silicone compound. Is not contained.

  Next, the tensile strength of the undercoat layer was measured. An undercoat layer coating composition shown in Table 1 was applied onto a Teflon (registered trademark) sheet, and an undercoat layer was formed under the same conditions as in the Examples and Comparative Examples. The coating amount was adjusted so that the thickness of each undercoat layer was 14 μm. Subsequently, the undercoat layer was peeled from the Teflon (registered trademark) sheet, and a strip-like undercoat layer having a width of 20 mm, a length of 120 mm, and a thickness of 14 μm was used as a test piece. In the tensile test, the distance between chucks was set to 50 mm at 25 ° C., and the tensile strength was measured at a tensile speed of 20 mm / min. The results are shown in Table 2.

  The following performance evaluation was performed using the precoat metal plate produced in Examples 1-14 and Comparative Examples 1-12. In the evaluation, ○, ○ △, and Δ were acceptable (usable), and Δx and x were unacceptable (unusable).

(1) Antifouling property (a) Carbon contamination resistance An aqueous solution in which 5% by weight of carbon black was suspended was spray-coated on the surface of the resin film, and then dried in a thermostatic bath at 60 ° C for 1 hour. Next, the ΔL value after the carbon black adhering to the resin film surface in running water was wiped with gauze and dried was measured. The ΔL value is defined as the L value after the test minus the L value before the test.
○: ΔL ≧ −7
×: ΔL <−7

(B) Red Magic Ink Removal Resin Resin after drawing a line with a commercially available Sakuraname (registered trademark) red magic ink on a 3 cm × 5 cm portion and leaving it for 24 hours, and then rubbing 20 times with a Kimwipe soaked in ethanol The red magic remaining on the surface of the film was visually evaluated.
○: Completely removable.
X: There is a trace.

(2) Adhesion After the precoated metal plate was immersed in boiling water for 2 hours, 100 1 mm square grids were drawn, a tape peeling test was performed, and the peeling state of the resin film was visually observed.
◯: No peeling from the metal plate or chemical conversion film of the resin film, and no separation between layers in the resin film.
X: There is peeling of at least one of peeling from the metal plate or chemical film of the resin film and peeling between each layer in the resin film.

(3) Bending resistance (a) Appearance of bent portion The bending state of the bent portion of the resin film was visually observed at 5T with a bending radius set to 5 times the thickness of the metal plate and visually observed.
○: Resin film cracking is hardly observed.
○ Δ: Resin film cracking is observed but slight.
Δ: Resin film cracking is clearly recognized, but about 1/4 of the bent portion.
Δ ×: Resin film cracking is clearly recognized, but about half of the bent portion.
X: Resin film cracking is observed on the entire surface.

(B) Bending part adhesion The tape peeling test was performed and the peeling state of the resin film was observed.
○: No peeling.
○ △: There is peeling in an area of less than 10%.
Δ: There is peeling in an area of 10 or more and less than 50%.
Δ ×: peeling in an area of 50% or more.
X: The entire surface is peeled off.

(4) Corrosion resistance A CASS test was performed for 48 hours or 120 hours according to JIS Z 2371, and the state of corrosion was visually observed.
○: Corrosion area ratio is less than 0.1%.
○ △: Corrosion area ratio is 0.1% or more and less than 1%.
Δ: Corrosion area ratio is 1% or more and less than 2%.
Δ: Corrosion area ratio is 2% or more and less than 5%.
X: Corrosion area ratio is 5% or more.

  The results are shown in Table 3.

  In Examples 1 to 14, a precoated metal plate in which a chemical conversion film is formed on at least one surface of a metal plate having a ten-point average roughness Rz in the range of 1.2 μm to 4.0 μm, and a resin film is formed thereon. The resin film comprises an undercoat layer and an overcoat layer. The undercoat layer is made of a polyester resin, a melamine resin, and an epoxy resin, and has a tensile strength in the range of 20 to 50 MPa. The overcoat layer contains 1% to 10% of the dry weight of colloidal silica having an average particle size of 0.1 μm or less and 0.1% to 5.0% of the silicone compound having an alkoxyl group in the dry weight in the acrylic resin. . In such Examples 1-14, antifouling property, adhesiveness, bending resistance and corrosion resistance were good.

  In particular, in Examples 5 to 8, the film thickness a of the undercoat layer is in the range of 29 μm to 50 μm, the film thickness b of the overcoat layer is in the range of 3 to 13 μm, and a / b is in the range of 3 to 10 Therefore, the corrosion resistance was improved as compared with the other invention examples.

In Comparative Example 1, since the ten-point average roughness Rz of the metal plate was less than 1.2 μm, the bending resistance was inferior.
In Comparative Example 2, since the ten-point average roughness Rz of the metal plate exceeded 4.0 μm, the bending resistance was inferior.
In Comparative Examples 3 and 4, since the tensile strength of the undercoat layer was less than 20 MPa, the bending resistance was inferior.
In Comparative Example 5, since the tensile strength of the undercoat layer exceeded 50 MPa, the bending resistance was inferior.
In Comparative Example 6, since the average particle size of the colloidal silica of the overcoat layer exceeded 0.1 μm, the bending resistance was inferior.
In Comparative Example 7, the antifouling property was inferior because colloidal silica was not contained in the overcoat layer.
In Comparative Example 8, the antifouling property was inferior because no silicone compound having an alkoxyl group was contained in the overcoat layer.
In Comparative Example 9, since no epoxy resin was blended in the undercoat layer, the adhesion was inferior, and the bending resistance and the corrosion resistance were inferior.
In Comparative Example 10, the antifouling property was inferior because the amount of colloidal silica added to the overcoat layer was less than 1% by weight.
In Comparative Example 11, the bending resistance was inferior because the amount of colloidal silica added to the overcoat layer exceeded 10% by weight.
In Comparative Example 12, the antifouling property was inferior because the amount of the silicone compound having an alkoxyl group in the overcoat layer was less than 0.1% by weight.

  In the present invention, the adhesion of the undercoat layer can be improved by the anchor effect on the surface of the metal plate using the surface metal plate having a ten-point average roughness Rz in a specific range. Further, the adhesion between the undercoat layer, the chemical conversion film and the overcoat layer can be improved by using an undercoat layer having a predetermined type of resin and a tensile strength within a predetermined range. As a result, the bending resistance and corrosion resistance of the resin film are also improved. Furthermore, antifouling property and bending resistance can be improved by using a predetermined type of resin, silica and silicone compound, and an overcoat layer having a predetermined range of silica and silicone compound content.

Claims (2)

A pre-coated metal comprising a metal plate having a ten-point average roughness Rz of 1.2 to 4.0 μm, a chemical conversion film formed on at least one surface of the metal plate, and a resin film formed on the chemical conversion film In the board,
The resin film comprises an undercoat layer formed on the chemical conversion film and an overcoat layer formed on the undercoat layer, the undercoat layer contains a polyester resin, a melamine resin, and an epoxy resin, and 20 The topcoat layer has an tensile strength of ˜50 MPa, the topcoat layer has an acrylic resin, 1 to 10% by weight of colloidal silica of the dry topcoat layer having an average particle size of 0.1 μm or less, and a dry topcoat layer And 0.1 to 5.0% by weight of a silicone compound having an alkoxyl group.   2. The undercoat layer according to claim 1, wherein the undercoat layer has a thickness (a) of 29-50 μm, the overcoat layer has a thickness (b) of 3-13 μm, and a / b is 3-10. Pre-coated metal plate.