JP4873974B2 - Pre-coated metal plate and manufacturing method thereof - Google Patents

Description

  The present invention relates to a precoated metal plate having excellent image clarity, and has excellent image clarity especially for home appliances, building materials, civil engineering, machinery, automobiles, furniture, containers, and the like. It relates to a pre-coated metal plate.

  Pre-coated metal sheets with pre-colored coatings will be used instead of post-painted products that have been painted after processing conventional metal sheets on the outer panels in the home appliances, building materials, and automotive fields. It has become to. On the other hand, in these applications, there is an increasing demand for coating appearance with excellent sharpness from the viewpoint of design and design.

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

  On the other hand, the pre-coated metal plate is cut and processed after painting, so that the metal portion is exposed at the cut end face. The pre-coated metal plate is easily corroded from the cut end surface where the metal is exposed. In order to suppress this corrosion, the metal plate is subjected to a hexavalent chromium treatment called a chromate treatment as a chemical conversion treatment. As a general rule, a primer paint containing a chromium-based anticorrosive pigment is applied. Furthermore, in recent years, since hexavalent chromium is an environmentally hazardous substance, a technology for chemical conversion treatment other than chromium and a chromate-free pre-coated metal plate using a primer containing a rust preventive pigment other than chromium are being developed ( For example, see Non-Patent Document 1.) As rust preventive pigments contained in the primer of the pre-coated metal plate not containing Cr, Si-based rust preventive pigments and phosphoric acid-based rust preventive pigments are known (for example, see Patent Documents 4 to 6).

JP-A-7-150326 JP-A-1-304934 JP-A-10-66931 Japanese Patent Laid-Open No. 9-12931 JP 2001-212506 A Japanese Patent Laid-Open No. 11-222575 Ueda et al. “Chromate-free pre-coated steel sheet with excellent corrosion resistance”, Nippon Steel Technical Report, 377, P25 (2002)

  However, as described in Patent Document 1, the method of obtaining sharpness by controlling the surface roughness of the base material of the pre-coated metal plate is a metal plate that is the base material regardless of the coating film used. If the surface roughness of the steel can be controlled, a relatively high definition can be obtained. On the other hand, by rolling the metal with a rolling roll with adjusted surface roughness or polishing it with a polishing machine, The surface roughness of a certain metal plate must be controlled. For this reason, there is a drawback that it takes a lot of labor and cost to produce a pre-coated metal plate excellent in sharpness by this method. On the other hand, as described in Patent Document 2, the method of obtaining a pre-coated metal plate with excellent image clarity by applying a paint using a resin having a low molecular weight controls the surface roughness of the metal plate as a base material. However, it is difficult to provide other coating film performance, such as workability, because a specific resin must be used for the paint. is there.

  In contrast to these methods, as a method for obtaining a pre-coated metal plate which is relatively easy and excellent in sharpness, a transparent clear coating film is applied on a colored coating layer as described in Patent Document 3. The method is preferred. However, since pre-coated metal plates are generally applied in a continuous coating facility called a coil coating line or sheet coating line, the coating applied on the metal plate is dried and baked in a short time of about 20 to 180 seconds. Cured. When the coating film is cured in such a short time, the coating film cures and shrinks, and after drying and baking, many wrinkles are formed in the coating film, and the sharpness is liable to be deteriorated. In particular, clear clear paints that do not contain colored pigments are more susceptible to this curing shrinkage than paints that contain colored pigments, and pre-coated metal sheets that have been subjected to clear coating with excellent clarity in the pre-coated metal sheet production line. There was a problem that it was difficult to obtain.

  In addition, due to environmental problems in recent years, the demand for pre-coated metal plates that do not contain hexavalent Cr in the pre-coated metal plate is rapidly increasing. Due to the characteristics of these anticorrosive pigments, it has been difficult to obtain high sharpness for coating films containing anticorrosive pigments. Non-chromium rust preventive pigments such as Si-based and P-based ones are often porous on the surface of the pigment. It has been.

  Therefore, the present invention has been made in view of the above-described state of the art, and a pre-coated metal plate excellent in sharpness that can be easily and inexpensively manufactured using a pre-coated metal plate continuous coating facility. An object of the present invention is to provide a non-chromium pre-coated metal plate excellent in sharpness and a production method thereof.

  In order to solve the above-mentioned problems, the present inventors have intensively studied a technique for improving the clarity of a pre-coated metal sheet coating film, in particular, the clarity of a pre-coated metal sheet not containing Cr. . As a result, the curing shrinkage of the coating film that occurs when the coating film is cured is related to the resin content ratio in the coating film. I found it. Therefore, the transparent clear coating is coated on the coating with the colored coating, and transparent fine particles are added to the transparent clear coating to reduce the resin content in the clear coating. As a result, it was found that the clear coating hardening shrinkage was suppressed at the time of baking hardening, and a precoated metal plate with excellent sharpness could be obtained. This is because the curing shrinkage of the coating film is caused by a condensation reaction when the resin undergoes a cross-linking reaction. Therefore, by adding inorganic fine particles or other resin fine particles that do not cause a condensation reaction during curing, This is a technology that reduces the resin shrinkage due to the curing reaction in the coating film and suppresses the shrinkage rate during curing of the entire coating film. In addition, the fine particles contained in the transparent clear coating film have a smaller difference between the refractive index of the fine particle and the refractive index of the main resin of the clear coating film. It was found that it became transparent and the sharpness of the pre-coated metal plate was improved.

  Furthermore, it is easy to apply a transparent clear coating on a pre-coated metal plate and one or more coating layers between the clear coating and the metal plate by simultaneous multi-layer coating or wet-on-wet method. It was found that a clear coating film can be applied on a colored coating film, and that a colored pre-coated metal plate coated with a clear coating film can be easily obtained by the conventional method of repeating coating and baking for each layer. In such multi-layer simultaneous coating or wet-on-wet coating methods, the wet film thickness of the coating film (thickness before drying) increases, and particularly the shrinkage of the coating film due to curing occurs. It was found that when coated with an added clear clear coating, curing shrinkage was greatly suppressed and a pre-coated metal plate with high image clarity was obtained.

The present invention has been completed based on such findings, and the gist of the present invention is as follows.
(1) A pre-coated metal plate having at least two coating layers on one or both sides of a metal plate, a transparent clear coating layer containing transparent fine particles as the outermost coating layer, and the clear coating At least one colored coating layer disposed between the film layer and the metal plate, and the refractive index ε _{P of the} fine particles contained in the clear coating layer is the main layer of the clear coating layer. The color of the colored coating layer when | ε _P −ε _B | ≦ 0.15 with respect to the refractive index ε _{B of the} resin and not covering the clear coating layer, and the colored coating layer color difference between the color of the colored coating layer in a state that the surface of covering the clear coating film layer of state, and are 1.5 or less in a color difference ΔE of Hunter color measurement meter, contained in the clear coating The amount of the fine particles added is 100 masses of the binder resin solid content of the clear coating film. And wherein 20 to 150 parts by mass der Rukoto respect, precoated metal sheet.
(2) The precoated metal sheet according to (1), wherein the lowermost coating film of the precoated metal sheet does not contain Cr and contains either one or both of Si and P.
( 3 ) The average particle size of the fine particles contained in the clear coating film is 0.1 to tμm when the film thickness of the clear coating film is t (μm), (1 ) Pre-coated metal plate.
( 4 ) Ra (arithmetic mean roughness) of the interface between the clear coating layer and the colored coating layer in direct contact with the clear coating layer is 0.3 to 0.8 μm. The precoated metal sheet according to (1), characterized in that
( 5 ) A method for producing a pre-coated metal plate having at least two or more coating layers on one or both surfaces of the metal plate, the transparent clear coating film comprising transparent fine particles as the outermost layer of the pre-coated metal plate A layer, and one or more colored coating layers disposed between the clear coating layer and the metal plate are applied by multilayer simultaneous coating or a wet-on-wet method, and in the clear coating layer Production of a pre-coated metal sheet, characterized in that the refractive index ε _{P of the} fine particles contained is | ε _P −ε _B | ≦ 0.15 with respect to the refractive index ε _B of the main resin of the clear coating film Method.
(6) Average particle size of the fine particles contained in the clear coating film is, the thickness of the clear coating film when the t ([mu] m), characterized in that it is a 0.1～Timyuemu, (5 The manufacturing method of the precoat metal plate as described in ) .

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the precoat metal plate excellent in sharpness by an easy manufacturing method. For this reason, it has become easier to apply pre-coated metal sheets to parts that require design properties that could only be handled by post-coating. The use of pre-coated metal sheets not only solves the problem of volatile organic solvents (VOC), which has been a problem in post-coating, but also reduces costs and eliminates the need for a small factory by eliminating coating equipment. Etc. are also achieved. Therefore, it can be said that the present invention is an industrially highly valuable invention.

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

  The pre-coated metal plate of the present invention has at least two coating layers on one or both sides of the metal plate, and specifically, a transparent clear coating containing transparent fine particles as the outermost coating layer. A film and at least one colored coating layer (colored coating layer) disposed between the clear coating layer and the metal plate, the clear coating layer on the colored coating layer By covering the film, the clarity of the coating surface is improved. However, with clear coatings alone, if they are baked and cured in a short time in a pre-coated metal sheet production facility, fine wrinkles due to curing shrinkage occur on the surface, and the clarity of the coating surface decreases. Therefore, in order to suppress the generation of fine wrinkles, it is necessary to add transparent fine particles to the clear coating film.

As the transparent fine particles used in the present invention, inorganic fine particles or fine particles of another resin that does not cause a condensation reaction during curing can be used. Examples of such fine particles include inorganic fine particles such as alumina fine particles, barium sulfate fine particles, calcium carbonate fine particles, and glass fine particles, acrylic resin fine particles, polystyrene resin fine particles, epoxy resin fine particles, and polyester resin fine particles. Organic transparent fine particles can be used. As these fine particles, commercially available fine particles or reagents may be used. Moreover, you may grind | pulverize and use a solid substance. The addition amount of the transparent fine particles, Ru 20-150 parts by der the binder resin 100 parts by weight of the solid content of the coating film. If the amount is less than 20 parts by mass, the resin content ratio in the coating film is high, so there is a possibility that the effect of suppressing the curing shrinkage of the coating film may not be exhibited. , There is a risk that the adhesion of the coating film is reduced. Also, the particle size is not particularly specified and can be appropriately selected as necessary. However, according to the knowledge of the inventors, when the film thickness of the clear coating film is t (μm), the average particle size is 0. 1 μm to t (μm) is preferable. If the average particle size of the fine particles is less than 0.1 μm, the addition of the fine particles to the clear paint may cause the paint to thicken significantly, making it difficult to paint. When added, irregularities are formed on the surface of the clear coating film, which may reduce the sharpness.

The pre-coated metal sheet of the present invention comprises the color of the colored coating layer in a state where the transparent clear coating layer is not coated, and the colored coating layer in the state where the transparent clear coating layer is coated on the colored coating layer. The color difference from the color is 1.5 or less as the color difference ΔE of the Hunter colorimeter. The color difference between the color of the colored coating layer not coated with the transparent clear coating layer and the color when the transparent clear coating layer is coated on the colored coating layer is the color difference ΔE of the Hunter colorimeter. If it exceeds 5, the transparency of the clear coating film is lowered, so that the sharpness is lowered. ΔE is more preferably 1.0 or less. In order to make the color difference ΔE 1.5 or less, it is necessary to make the difference in refractive index between the main resin in the clear coating film and the fine particles contained in the clear coating film smaller. The refractive index ε _{P of the} fine particles contained in the clear coating film needs to be | ε _P −ε _B | ≦ 0.15 with respect to the refractive index ε _B of the main resin of the clear coating film. If | ε _P −ε _B |> 0.15, the transparency of the clear coating film is lowered, and the sharpness may be lowered. The refractive index of the resin or fine particles may be measured with a commercially available refractive index measuring device, or the refractive index of each substance described in the literature may be used. If | ε _P −ε _B | ≦ 0.10, the color of the colored coating layer not covering the transparent clear coating layer and the state where the transparent clear coating layer is coated on the colored coating layer The color difference from the color tends to be 1.0 or less as the color difference ΔE of the Hunter colorimeter, which is more preferable.

  As the resin used for the clear coating film of the present invention, generally known coating resins, for example, polyester resin type, epoxy resin type, urethane resin type, acrylic resin type, melamine resin type, fluorine type coating film can be used. . A commercially available clear paint may be used. The glass transition temperature (Tg) of these resins is more preferably 10 to 100 ° C. If the Tg is less than 10 ° C, the surface hardness of the coating film may be reduced, and if it exceeds 100 ° C, the processability may be inferior.

  If necessary, generally known curing agents such as melamine resin and isocyanate may be added. In addition, generally known additives such as wax, antifoaming agent, leveling agent and the like may be added.

  As the colored coating film between the transparent clear coating film layer and the metal plate of the present invention, generally known colored coating films can be used. A commercially available paint can be used as the paint for forming the colored coating film. It is even better to use commercially available precoat paints. When a colored paint is produced by blending resin and pigment, generally known paint resins such as polyester resin, epoxy resin, urethane resin, acrylic resin, melamine resin, and fluorine resin are used. The thing using a coating film can be used. As the coloring pigment, generally known coloring pigments, for example, inorganic pigments such as carbon black, titanium oxide and zinc white, organic pigments of various colors, metallic pigments such as aluminum and nickel, pearl pigments and the like can be used. These pigments may be commercially available or reagents. You may use what grind | pulverized the solid substance. Moreover, generally known curing agents such as melamine resins and isocyanates may be added as curing agents for coatings.

  If the lowermost coating film of the pre-coated metal plate does not contain Cr and contains one or both of Si and P, it is more preferable because corrosion resistance is improved without containing environmentally hazardous substances. P is contained in zinc phosphate, aluminum phosphate, and the like, and Si is an element contained in silica and the like, all of which have a function of improving corrosion resistance. As the compound containing P and Si, generally known compounds, for example, compounds containing Si or P such as silica, Ca ion exchange silica, zinc phosphate, aluminum tripolyphosphate, and the like can be used. These compounds may be those commercially available as reagents or those commercially available as industrial products such as pigments. These compounds may be added in combination. In particular, Ca ion-exchanged silica or aluminum dihydrogen tripolyphosphate is more preferable because of its excellent corrosion resistance. As the Ca ion exchange silica, “SHIELDEX (registered trademark)” manufactured by GRACE, and “K-WHITE” manufactured by Teika Co., etc., can be used as the aluminum tripolyphosphate. The addition amount of Si compound or P compound can be changed as necessary, but the addition amount of Si compound or P compound, and when these are used in combination or in combination, the total addition amount is 100 mass of resin solid content. It is more preferable that it is 10-120 mass parts with respect to a part. If it is less than 10 parts by mass, the corrosion resistance is inferior, and if it exceeds 120 parts by mass, the coating film becomes brittle and the workability may be inferior. In the lowermost layer coating film, other pigments and compounds may be added as necessary. In general, these P-based and Si-based anti-corrosion pigments have a coating film that tends to have poor sharpness. However, the pre-coated metal of the present invention does not deteriorate sharpness and has high sharpness and high corrosion resistance. Since it can be given, it is more suitable. As described above, according to the present invention, it is possible to improve the sharpness, which has been a problem with the precoating metal plate that does not include the hexavalent Cr, which is an environmentally hazardous substance, until now. It became.

  The Ra (arithmetic mean roughness) of the interface between the transparent clear coating layer of the precoated metal plate of the present invention and the colored coating layer between the clear coating layer and the metal plate is 0.3-0. When the thickness is 8 μm, the adhesion of the coating film is increased, which is more preferable. If the Ra at the interface between the two coating films is less than 0.3 μm, the adhesion at the coating film interface may be reduced. In general, when the coatings are laminated, the adhesion of the coatings is maintained by physical bonds such as chemical bonds, hydrogen bonds, van der Waals forces, etc., but Ra between coating layers is 0.3 or more. By doing so, in addition to these adhesion forces, adhesion force due to the anchor effect is imparted. However, if the Ra of the interface between the two coating films exceeds 0.8 μm, the appearance when the top paint is applied may be affected and the gloss may be lowered. In order to give Ra to the interface between the coating layers, it can be achieved by performing multi-layer simultaneous application or wet-on-wet coating. Multi-layer simultaneous coating is a method in which a plurality of coating liquids are simultaneously laminated on a substrate, such as a slot die coater or a slide hopper type curtain coater, and then dried and baked simultaneously in multiple layers. In addition, wet-on-wet coating is a method in which a coating solution is applied on a substrate, and then another coating solution is further applied on the substrate before the coating solution dries. In this method, the multilayer coating liquid is simultaneously dried and baked. In this way, by coating the undried coating liquid and applying it simultaneously, the coating liquid of each layer is slightly mixed in the vicinity of the interface of the laminated coating film, thereby generating irregularities (that is, Ra) at the interface. be able to. In general, when two or more coating films are applied by the aforementioned wet-on-wet or multi-layer simultaneous coating, Ra of these coating film interfaces becomes 0.3 to 0.8 μm.

  In the present invention, the Ra of this interface can be measured by the following method (that is, a method basically in accordance with JIS B.0601.4.2: 2001).

  That is, after taking a vertical cross section of the interface whose surface roughness Ra is to be measured with a micrograph, the unevenness (roughness curve) of the interface is traced, and JIS. B. 0601.4.2: 2001 The arithmetic average roughness Ra of the interface can be obtained according to a predetermined formula.

  As a wet-on-wet coating method, after coating a coating layer by a generally known coating method such as roll coater, dip, curtain flow coater, roller curtain coater, etc., before drying and baking this coating layer Furthermore, it is coated by a method that can be applied in a non-contact manner with a generally known substrate such as curtain flow coating, roller curtain coating, slide hopper type curtain coater, slot die coater, etc. At the same time, it can be painted by dry baking. Moreover, as a multilayer simultaneous application method, a method of applying by coating different paints from two or more parallel slits, such as a slide hopper curtain coater, can be used. .

  The pre-coated metal sheet of the present invention is a generally known coating method such as roll coater coating, dip coating, curtain flow coater, roller curtain coater, slide hopper type curtain flow coater, etc., and a method of coating and baking each layer one by one You may paint by repeating the process twice or more, but the current two-coat two-bake coating line is better if you use the wet-on-wet or multi-layer simultaneous coating method to coat and bake two or more layers at once. In addition to being capable of multi-layer coating, Ra at the coating film interface is 0.3 to 0.8 μm, which improves the adhesion, which is more preferable.

  Moreover, generally known drying baking methods, such as a hot air oven, a direct-fired oven, a far-infrared oven, and an induction heating oven, can be used as a drying baking method in coating.

  As 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, and the like can be given. The surface of these materials may be plated. Examples of plating types include zinc plating, aluminum plating, copper plating, and nickel plating. 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.

  The surface of the metal plate used in the present invention is more preferably subjected to a known chemical conversion treatment because adhesion between the metal plate and the coating layer is improved. For the chemical conversion treatment, a zinc phosphate chemical conversion treatment or the like can be used. As the non-chromate 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 Application Laid-Open No. 53-9238 is known. (Technology in which an aqueous solution containing thiourea and tannic acid is used as a chemical conversion treatment), Japanese Patent Application Laid-Open No. 9-241576 (Technology related to chemical conversion treatment in which a specific resin and a silane coupling agent are blended), Japanese Patent Application Laid-Open No. 2001-89868 (tannin) Alternatively, tannic acid, a silane coupling agent, a technology relating to a chemical conversion treatment agent for a precoat metal containing fine particle silica, JP-A-2001-316845 (silane coupling agent, water-dispersible silica, zirconium compound or titanium compound, water-soluble acrylic) Technology relating to surface treatment agent containing resin), JP 20 No. 2-60959 (Technology relating to chemical conversion treatment comprising tetravalent titanium compound, phosphate, tannin or tannic acid), Japanese Patent Application Laid-Open No. 2002-38280 (inorganic organic composite film containing titanium compound and fluoride is used as a base treatment) Technology relating to non-chromium coated steel sheet used), JP 2002-266081 A (Technology relating to chemical conversion treatment including titanium hydrofluoric acid, zirconium hydrofluoric acid, silica, tannic acid, water-dispersible organic resin), JP You may use the well-known technique described in 2003-253464 gazette (technique regarding a chemical conversion treatment steel plate containing specific water-soluble resin, a titanium compound, a zirconium compound, and a silane coupling agent). For these chemical conversion treatments, commercially available products can also be used.

Example 1
Details of the experiment of Example 1 will be described below.
First, the details of the top coat used in the experiment of Example 1 will be described.
“Byron (registered trademark) GK140” (Tg: 20 ° C., number average molecular weight: 13,000, hereinafter referred to as polyester), which is an amorphous polyester resin manufactured by Toyobo Co., Ltd., and fluorine resin manufactured by Asahi Glass Co., Ltd. LUMIFLON (registered trademark) LF552 ”(Tg: 20 ° C., number average molecular weight 12000, hereinafter referred to as fluorine), epoxy resin“ EPICLON (registered trademark) 7050 ”(hereinafter referred to as epoxy) manufactured by Dainippon Ink and Chemicals, Japan An acrylic resin “Alloset (registered trademark) 5535” (hereinafter referred to as “acrylic”) manufactured by Catalyst Co. was used as a binder resin. Since “Byron (registered trademark) GK140” and “EPICLON (registered trademark) 7050” and “Alloset (registered trademark) 5535” are in the form of pellets or flakes, they are organic solvents (cyclohexanone: solvesso 150 = 1: 1 by mass). Used in a mixed state). In addition, “LUMIFLON (registered trademark) LF552” is a type in which the resin is already dissolved in an organic solvent, so that it is used as it is.

  Next, “Cymel (registered trademark) 303” which is a fully alkyl methylated melamine resin (hereinafter referred to as melamine resin) manufactured by Mitsui Cytec Co., Ltd. is used as a crosslinking agent. Mixed. The amount of mixing was such that [polyester: melamine = 70: 30] by the mass ratio of each resin solid content. Furthermore, an amine block type acidic catalyst “Catalyst 602” manufactured by Mitsui Cytec Co., Ltd. was added as a reaction catalyst in an amount of 1.0 mass% based on the total resin solid content. The clear paint used for the experiment was prepared by the above procedure.

  Next, “AO-502” (average particle size 0.7 μm) manufactured by Shin-Etsu Quartz Co., Ltd. and barium sulfate fine particles (reagents were pulverized in a mortar and sieved to an average particle size of 5 μm) as alumina fine particles were prepared. ), Cross-linked polymethacrylic sanmethyl resin fine particles “MBX-5” (average particle size 5 μm, hereinafter referred to as “acrylic”) manufactured by Sekisui Plastics Co., Ltd. as acrylic fine particles with respect to 100 mass parts of the total resin solid content. By adding 50 parts by mass, a top coating was prepared.

  For the coating resin used in this experiment, the refractive index of the resin was measured in advance using an Abbe refractometer “NAR-1T”. For the fine particles used in this experiment, the measurement method described in “Section 10 Refractive Index” of “Pigment Handbook” edited by Japan Pigment Technical Association (Seibundo Shinkosha, published on June 1, 1959) is used. Accordingly, the refractive index was measured by using a Larsen oil immersion method in which fine particles were immersed in a liquid whose refractive index was generally known, and observed with an optical microscope. And the difference of the refractive index of resin of each coating material and the refractive index of the fine particle added to this was calculated | required.

Next, the details of the intermediate coating and undercoating used in the experiment will be described.
For the intermediate coating, “Byron (registered trademark) 63CS” (Tg: 7 ° C., number average molecular weight: 20000), an amorphous polyester resin manufactured by Toyobo Co., Ltd., and a complete cross-linking agent manufactured by Mitsui Cytec Co., Ltd. “Cymel (registered trademark) 303”, which is an alkyl-type methylated melamine resin (hereinafter referred to as melamine resin), is mixed so that the mass ratio of the resin solids is [polyester: melamine = 70: 30] To this was added 1.0% by mass of an acidic catalyst (“Catalyst 602” manufactured by Mitsui Cytec Co., Ltd.) to produce a clear coating. Furthermore, 100 parts by mass of titanium oxide “Typaque CR-95” manufactured by Ishihara Sangyo Co., Ltd. was added to 100 parts by mass of the total resin solid content in the prepared clear paint to produce a white intermediate coating.

  In addition, for the undercoat paint, a clear paint that does not contain the pigment of the FL641EU primer made by Nippon Fine Coatings, a commercially available undercoat paint, is prepared. Produced. The anticorrosive pigment used in this experiment is “K-WHITE # 105” (hereinafter referred to as “P-type anticorrosive pigment”), a tripolyaluminum dihydrogen phosphate manufactured by Teika, and calcium ion exchange silica manufactured by GRACE. “SHIELDEX (registered trademark) C303” (hereinafter referred to as Si-based rust preventive pigment) was used. Sample: 50 parts by weight of P-type anti-corrosion pigment added to 100 parts by weight of paint resin solids, 50 parts by weight of Si-type anti-rust pigment added to 100 parts by weight of paint resin solids , 30 parts by mass of Si-based rust preventive pigment and 20 parts by mass of P-type rust preventive pigment were prepared for 100 parts by mass of the coating resin solid content. We also prepared one that does not contain any anti-rust pigments.

  The prepared top coat is shown in Table 1, and details of the intermediate coat and undercoat are shown in Table 2.

Hereinafter, the details of the precoated metal plate used in the experiment of Example 1 will be described.
Hot-dip galvanized steel sheet "Silver Zinc" (hereinafter referred to as GI) manufactured by Nippon Steel Corporation, zinc-nickel alloy-plated steel sheet "Zinclite" (hereinafter referred to as ZL) manufactured by Nippon Steel Corporation An electrogalvanized steel sheet “JINCOAT” (hereinafter referred to as EG) manufactured by Nippon Steel Corp. was prepared as an original plate. A plate thickness of 0.6 mm was used. The amount of ZL plating used in this experiment was 20 g / m ^{2 on} one side, and the amount of nickel in the plating layer was 12%. The GI plating adhesion amount was 60 mg / m ² on one side, and the EG plating adhesion amount was 20 g / m ² on one side.

Next, the prepared original plate is spray degreased with 50% aqueous solution of 2% by weight of 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 liquid “CT-E300N” was applied with a roll coater and dried in a hot air oven. The drying condition in the hot air oven was 60 ° C. at the ultimate temperature of the steel plate. The coating amount of the chromate-free treatment was applied so that the total solid content was 200 g / m ² .

  Next, the prepared primer coating is applied to one side of the chemical-treated metal plate, and the gray color of “FL100HQ”, a back coating made by Nippon Fine Coatings, is applied to the other side using a roll coater. Then, it was dried and hardened under the condition that the ultimate plate temperature of the metal plate was 210 ° C. in an induction heating furnace in which hot air was blown. After drying and baking, water was sprayed on the painted metal plate and cooled. Next, two layers of the intermediate coating and top coating are applied simultaneously on the undercoat film using 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 coatings were simultaneously dried and cured. Then, after dry baking, water was sprayed onto the coated metal plate and water-cooled to produce a three-layer pre-coated metal plate (hereinafter, this coating method is referred to as “3C2B” coating). In addition, if necessary, only the intermediate coating was applied by the same method (no top coating was applied), and a two-layer pre-coated metal plate that was dried and cured was also prepared (hereinafter, this coating method is referred to as “2C2B”). Called).

  If necessary, apply only one layer of intermediate coating on the undercoat using a roll coater, and after baking as described above, apply one layer of top coating again on the intermediate coating using a roll coater. A three-layer pre-coated metal plate that was painted and baked was also prepared (the coating method in this procedure is referred to as “3C3B coating”).

  Regarding the coating film thickness of the prepared precoated steel sheet, the surface undercoat film was 5 μm in terms of dry film thickness, the intermediate coat film was 15 μm, and the topcoat film was 10 μm. The film thickness of the back coating was 5 μm in terms of dry film thickness. These film thicknesses can be adjusted by adjusting the rotational peripheral speed of the roll and the pressing pressure between the rolls and the paint viscosity in the case of a roll coater, and the paint application pressure and paint viscosity in the case of a slide hopper type curtain coater. Controlled. Each film thickness was measured with an electromagnetic film thickness meter “LE-200J” manufactured by KET.

  In addition, when preparing each pre-coated metal plate, samples with only the undercoat and the intermediate coat were prepared without applying the top coat, and the color and topcoat were applied without the top coat. The color tone in the state was measured with a hunter color meter, and the color difference ΔE of the hunter color meter of these colors was obtained. In the case where ΔE is 1.0 or less, ◯, in the case where ΔE is more than 1.0 and 1.5 or less, Δ, and in the case where ΔE is more than 1.5, ×.

The details of the evaluation method for the prepared precoated metal sheet are described below.
1. Measurement of sharpness of pre-coated metal plate Gd value was measured with a portable sharpness gloss meter “PGD” (manufactured by Tokyo Kodenshi) for the sharpness of the coating film on the surface of the prepared pre-coated metal plate.
2. Corrosion resistance test Cut scratches were made on the surface of the pre-coated metal sheet that had been coated with the top coating, and a salt spray test was performed by the method described in JIS K 5540.9.1. Salt water was sprayed on the surface of the test piece with the cross cut. The test time was 240 hours for a sample using GI with a high plating adhesion amount on the original plate, and 120 hours for a sample using EG and ZL with a low plating adhesion amount on the original plate. Then, the maximum swollen width of the coating film from the cut portion on the surface side is measured. If the cut portion swollen width is 3 mm or less on one side, ○, if the cut portion swollen width is more than 3 mm and less than 5 mm on one side, Δ, cut portion swollen width Was evaluated as x when it was more than 5 mm on one side.
3. Ra measurement of coating film interface Cut the pre-coated metal plate vertically so that the cross-section of the coating film can be observed, embed the cut pre-coated metal plate in the resin, then polish the cross section, and 3500 times scanning electron microscope A cross-sectional photograph of the coating film was taken. Next, a transparent resin sheet (using a commercially available OHP sheet) was placed on the photograph to precisely trace the unevenness at the coating film interface. Then, as shown in FIG. 2, the area of the vertical line portion was measured by an image processing apparatus, and Ra was calculated from the following formula as an average value.

5. Coating film adhesion evaluation When the coating film surface of the precoated metal sheet processed with 180 ° adhesion bending (generally referred to as 0T bending) is attached with an adhesive tape with tape, the coating film is peeled off vigorously. The remaining state was observed visually. The evaluation of coating film peeling was evaluated as ◯ when there was no peeling of the coating film, Δ when the film was slightly peeled, and x when the coating film had a clear large peeling.

Details of the evaluation results are described below.
Table 3 shows the evaluation results of the pre-coated metal plate produced. The precoated metal plate of the embodiment of the present invention comprises a transparent clear coating film containing transparent fine particles in the outermost coating layer (top coating layer) and a colored coating layer (inside the clear coating layer). Color difference between the color of a colored coating layer having a coating layer and a transparent clear coating layer not coated with a transparent clear coating layer on the colored coating layer However, by setting the color difference ΔE of the hunter color meter to 1.5 or less, a precoated metal plate having excellent sharpness could be obtained (Examples PCM-2 , 3 , 7 , 10 , 11 , 13 to 15). , 17-19, 21-23). Since these do not contain Cr, they are more suitable in terms of environment. Further, among these samples, those in which neither Si nor P is contained in the lowermost layer coating film are inferior in corrosion resistance. Therefore, it is more preferable to include one or both of these. In addition, when Comparative Example PCM-24 and Comparative Example PCM-25 are compared, those containing P-type anticorrosive pigment or Si-type anticorrosive pigment in the undercoat (Comparative Example PCM-24) do not contain this. Since the sharpness is inferior to (Comparative Example PCM-25), it can be seen that the present invention is effective in improving the sharpness of PCM including these.

Further, the refractive index ε _{P of the} fine particles contained in the transparent clear coating film of the example of the present invention is | ε _P −ε _B | ≦ 0.15 with respect to the refractive index ε _B of the main resin of the clear coating film. If present (Examples PCM-2, 3, 6, 7, 10, 11, 13-15, 17-19, 21-23), the color of the colored coating layer not covering the transparent clear coating layer The color difference from the color in the state where the transparent clear coating is coated on the colored coating layer is likely to be 1.5 or less as the color difference ΔE of the Hunter colorimeter, which is more preferable.

  Further, Ra (arithmetic mean roughness) of the interface between the transparent clear coating layer of the precoated metal sheet of the embodiment of the present invention and the colored coating layer on the lower side of the clear coating layer is 0.3 to Those having a thickness of 0.8 μm (Example PCM-3) are more preferable because Ra is more excellent in coating film adhesion than those having an Ra outside this range (Example PCM-19). Further, when the comparative example PCM-4 and the comparative example PCM-20 are compared, the 3C2B coating tends to be less sharp than the 3C3B coating. Therefore, the pre-coated metal sheet of the present invention can be applied to multiple simultaneous coatings such as 3C2B coating. It turns out that it is more effective to manufacture by wet-on-wet coating.

(Example 2)
Details of the experiment of Example 2 will be described below.
First, the details of the paint used in the experiment of Example 2 will be described.
“Byron (registered trademark) GK140” (polyester), which is an amorphous polyester resin manufactured by Toyobo Co., Ltd., is dissolved in an organic solvent (using a mixture of cyclohexanone: solvesso 150 = 1: 1 by mass), To this, “Cymel (registered trademark) 303”, which is a fully alkyl methylated melamine resin (hereinafter referred to as “melamine resin”) manufactured by Mitsui Cytec Co., Ltd., was mixed with the above-described polyester resin. The amount of mixing was such that [polyester: melamine = 70: 30] by the mass ratio of each resin solid content. Further, as a reaction catalyst, an amine block type acidic catalyst “Catalyst 602” manufactured by Mitsui Cytec Co., Ltd. was added in an amount of 1.0% by mass with respect to the total resin solids, thereby preparing a clear paint used in the experiment.

  Next, a top coating material was prepared by adding a necessary amount of barium sulfate fine particles (reagent crushed with a mortar and then making the average particle size 5 μm with a sieve) to the clear coating material thus prepared.

  The refractive index of the resin (polyester) and fine particles (barium sulfate) of the top coat film prepared in this experiment was measured in the experiment of Example 1, and the refractive index of polyester is 1.55 and the refractive index of barium sulfate is 1.5. 1.64, the refractive index difference between the two is known to be 0.09.

  In this experiment, “white intermediate coating” described in Table 2 of Example 1 was used as the intermediate coating material, and “P, Si-based undercoating” described in Table 2 of Example 1 was used as the undercoating film.

  Table 4 shows the details of the top coating material produced in the experiment of Example 2.

Hereinafter, the details of the precoated metal plate used in the experiment of Example 2 will be described.
In this experiment, a precoated metal plate was produced in the same manner as in the experiment of Example 1. The film thickness of each coating film was also the same as in Example 1. The evaluation method of the experiment of Example 2 was the same as that described in Example 1.

  The evaluation results of Example 2 are shown in Table 5.

The addition amount of fine particles contained in the transparent clear coating film (top coating film) of the precoated metal plate of the embodiment of the present invention is 20 to 150 parts by mass with respect to 100 parts by mass of the binder resin solid content of the coating film (Examples PCM-27 to 29) are more suitable because they are excellent in sharpness and excellent in coating film adhesion. The amount of fine particles contained in the transparent clear coating (top coating) is less than 20 with respect to 100 parts by mass of the binder resin solid content of the coating ( Reference Example PCM-26). Since the amount added was small, when the coating was dried and cured, the coating was apt to cure and shrink and the sharpness tended to be low. However, the clear coating film does not contain fine particles at all (Comparative Example PCM-25), and if even a small amount of fine particles are contained, the coating film hardly cures and shrinks at the time of dry curing, and the sharpness is high. On the other hand, the amount of fine particles contained in the transparent clear coating film (top coating film) exceeds 150 parts by mass with respect to 100 parts by mass of the binder resin solid content of the coating ( Reference Example PCM-30). The film adhesion tended to be low. This is thought to be because the coating became brittle because the amount of fine particles added in the clear coating was too large. Therefore, the amount of fine particles contained in the transparent clear coating film (top coating film) needs to be 150 parts by mass or less with respect to 100 parts by mass of the binder resin solid content of the coating film.

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

Claims (6)

In a pre-coated metal plate having at least two coating layers on one side or both sides of the metal plate,
A transparent clear coating layer containing transparent fine particles as an outermost coating layer, and at least one colored coating layer disposed between the clear coating layer and the metal plate The refractive index ε _{P of the} fine particles contained in the clear coating film is | ε _P −ε _B | ≦ 0.15 with respect to the refractive index ε _B of the main resin of the clear coating film,
Color difference between the color of the colored coating layer when the clear coating layer is not coated and the color of the colored coating layer when the clear coating layer is coated on the surface of the colored coating layer but state, and are 1.5 or less in the color difference ΔE of the Hunter color measurement meter,
The amount of the fine particles contained in the clear coating, characterized in 20 to 150 parts by mass der Rukoto the binder resin 100 parts by weight of the solid content of the clear coating film, precoated metal sheet.   2. The precoated metal sheet according to claim 1, wherein the lowermost coating film of the precoated metal sheet does not contain Cr and contains either one or both of Si and P.   The average particle diameter of the fine particles contained in the clear coating film is 0.1 to tμm, where t (μm) is the thickness of the clear coating film. Pre-coated metal plate.   Ra (arithmetic mean roughness) of an interface between the clear coating layer and the colored coating layer in direct contact with the clear coating layer is 0.3 to 0.8 μm The precoated metal sheet according to claim 1. A method for producing a pre-coated metal plate having at least two coating layers on one or both sides of a metal plate,
A transparent clear coating layer containing transparent fine particles as the outermost layer of the pre-coated metal plate, and one or more colored coating layers disposed between the clear coating layer and the metal plate The refractive index ε _{P of the} fine particles contained in the clear coating film is applied by simultaneous coating or wet-on-wet method, and the refractive index ε _B of the main resin of the clear coating film is | ε _P −ε _B | ≦ 0.15 der is,
The amount of the fine particles contained in the clear coating film, wherein the 20 to 150 parts by mass der Rukoto the binder resin 100 parts by weight of the solid content of the clear coating film, method of manufacturing the pre-coated metal sheet . The average particle size of the fine particles contained in the clear coating film is, the thickness of the clear coating film when the t ([mu] m), characterized in that it is a 0.1～Timyuemu, claim 5 Manufacturing method of the precoat metal plate.