JP4757564B2 - Pre-coated metal plate, method for producing the same, and painted metal molded product - Google Patents

Description

  The present invention relates to a precoated metal plate having high gloss and excellent press formability, and in particular, press formability in home appliances, building materials, civil engineering, machinery, automobiles, furniture, containers, etc. The present invention relates to an excellent prepainted metal sheet for deep drawing, a method for producing the same, and a painted metal molded product.

  For home appliances, building materials, and automobiles, pre-coated metal sheets coated with a colored coating film have been used in place of conventional post-painted products that have been painted after processing. In particular, in recent years, the processing shapes of precoated metal sheets have also diversified, and the case of processing precoated metal sheets by deep drawing is increasing. When a pre-coated metal sheet is formed by a press machine, in addition to the problem of coating film cracking and coating film peeling at the processed part, a defect called coating galling caused by a press mold during pressing is a problem. The galling of the coating film is a phenomenon in which the press mold and the coating film surface are rubbed during pressing, and the coating film is peeled off or scraped off by this shearing force.

  In order to solve the problem of coating film defects when drawing such a pre-coated metal sheet, various techniques have been disclosed. For example, Patent Document 1 discloses a technique for suppressing the occurrence of cracking and peeling of the coating film during deep drawing by reducing the rubber-like equilibrium elastic modulus of the coating film applied to the precoated metal plate. . Further, Patent Document 2 discloses that a pre-coated metal plate is subjected to a chemical conversion treatment containing a silane coupling agent, tannic acid, fine silica, and resin, and is coated with a primer coating containing a phosphoric pigment. A technique for suppressing galling of the coating film during processing is disclosed.

JP 2001-323389 A Japanese Patent Laid-Open No. 2003-166079

  On the other hand, when the pre-coated metal sheet is formed by deep drawing, there is also a problem that the gloss is lowered at the forming portion. Therefore, in order to deep-draw the precoated metal sheet, it is common to use a low-gloss precoated metal sheet, in which the gloss reduction at the forming portion is not noticeable. However, as deep drawing using pre-coated metal plates has become widespread, there has been an increasing demand for pre-coated metal plates that do not easily lose gloss even in deep-drawn forming.

  Accordingly, the present invention has been made in view of such problems, and a high-gloss deep-drawing pre-coated metal plate that does not easily lose its gloss even when deep-drawing is performed, a manufacturing method thereof, and a coated metal. The object is to provide a molded product.

  As a result of intensive studies to develop a pre-coated metal plate that does not easily deteriorate in the processed part even when deep drawing is performed, the decrease in gloss in the processed part is caused by distortion in the coating film in the processed part. It was clarified that this was caused by the local elongation of the coating film that occurred in large numbers when When local elongation occurs in the coating film, the locally elongated portion is thinner than the non-stretched portion, so that fine irregularities are formed. And since light is irregularly reflected by this uneven part, when it sees macroscopically, gloss will fall and it will appear.

  Focusing on this point, the present inventors conducted research on a coating film that hardly undergoes local elongation when subjected to processing deformation, and as a result, the glass transition temperature (hereinafter referred to as Tg) of the coating film is low. It was found that local elongation hardly occurs when the temperature is 30 ° C. or lower. However, on the other hand, the pre-coated metal sheet having such a low Tg of the coating film has a soft coating film, and thus a new problem that the coating film is likely to be squeezed at the time of deep drawing. Therefore, the present inventors control the coating film hardness and the elongation at break of the coating film by adjusting the cross-linking density of the coating film, so that the coating film at the time of deep drawing is formed even for a coating film having a Tg of 30 ° C. It has been found that the galling is unlikely to occur.

The present invention has been completed based on such findings, and the gist of the present invention is as follows.
(1) In the precoat metal plate which has one or two or more coating layers on one or both sides of the metal plate: Among the coating layers, the outermost coating layer has (A) a glass transition temperature of 5 to 30. (B) the hardness at 23 ° C. is 2.5 N / mm ² or more in terms of universal hardness under a load of 5 mN, (C) the elongation at break at 23 ° C. is 100% or more, and (D) A precoated metal sheet, wherein the outermost coating film has a specular glossiness of 60% or more when measured under conditions of an incident angle and a light receiving angle of 60 °, respectively.
(2) The pre-coated metal sheet according to (1), wherein the coating film layer includes two or more layers, and a phosphorus-based compound is contained in a lowermost coating film among the coating film layers.
(3) The coating layer has two or more layers, and Ra (arithmetic mean roughness) of at least one interface among the interfaces between the coating layers is 0.3 to 0.8 μm. The precoated metal sheet according to (1) or (2).
(4) The method for producing a precoated metal sheet according to (2) or (3), wherein the coating layer is three or more layers, and the coating layer on the lowest layer among the coating layers. A method for producing a precoated metal sheet, wherein at least two layers are applied by multi-layer simultaneous application or wet-on-wet method.
(5) A pre-coated metal sheet according to any one of (1) to (3), which is formed by deep drawing to a forming height of 25 mm or more.
(6) A coated metal molded product formed by deep drawing to a molding height of 25 mm or more: having at least one coating layer or two or more coating layers on the outer surface, and being the outermost layer among the coating layers The coating film of (A) has a glass transition temperature of 5 to 30 ° C., (B) a hardness at 23 ° C. of 2.5 N / mm ² or more in terms of universal hardness under a load of 5 mN, and (D ) A coated metal molded product characterized in that it has a glossy portion that is 60% or more when the specular gloss of the outermost layer coating film is measured under conditions of an incident angle and a light receiving angle of 60 °.
(7) The coating layer has two or more layers, and the glossy portion has an Ra (arithmetic mean roughness) of 0.3 to 0.8 μm at least one of the interfaces between the coating layers. The painted metal molded article according to (6), characterized in that
(8) The painted metal molded product according to (6) or (7), wherein the glossy portion is a bottom surface of deep drawing.

  According to the present invention, it is possible to provide a high-gloss pre-coated metal plate that is not easily lowered in gloss at the processed part even when deep drawing is performed and is excellent in press formability, a manufacturing method thereof, and a coated metal molded product. Therefore, according to the present invention, it has become possible to manufacture a molded part having a complicated shape, which could only be dealt with by post-coating so far, using a pre-coated metal plate.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the present specification and drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

The precoated metal plate of the present invention has at least one coating layer on one or both surfaces of the metal plate. Here, the outermost coating layer among the coating layers is (A) Tg of 5 to 30 ° C., (B) Hardness under 23 ° C. and 5 mN load is 2.5 N / mm ² or more in terms of universal hardness. And (C) physical properties of elongation at break at 23 ° C. of 100% or more, and (D) the specular gloss of the outermost coating layer is 60% or more under the conditions of an incident angle and a reflection angle of 60 °. It is characterized by being.

  As the coating layer used for the pre-coated metal plate of the present invention, generally known coatings such as polyester resin-based, epoxy resin-based, urethane resin-based, acrylic resin-based and melamine resin-based coatings can be used. These coating films may be used as clear paints containing no pigments, or may contain pigments. Further, generally adding a known curing agent such as melamine resin, isocyanate, etc. is preferable because the coating film hardness is increased.

  In the case of a coating film containing a pigment or a curing agent, the Tg of the coating film on the outermost surface in the precoated metal sheet of the present invention is the Tg as the bulk of the coating film after adding these. The Tg of the coating film may be measured using a differential scanning calorimeter (generally referred to as DSC) after peeling off the coating film applied to the pre-coated metal plate, or in a state where it is applied as a pre-coated metal plate The measurement may be performed using a thermomechanical analyzer (generally called TMA). Moreover, you may measure by a generally well-known method. In addition, it is known that the Tg of the coating film has some errors depending on the measuring equipment and measurement conditions. Therefore, in the present invention, the coating film Tg is 5 to 30 ° C. when measured by any one of a plurality of generally known Tg measuring methods, that is, a method using DSC or a method using TMA. If it is in the range, it is included in the present invention. Since the Tg of the coating film is mainly governed by the Tg of the binder resin, the coating film Tg can be adjusted by controlling the Tg of the binder resin. Since it may be considered that the Tg of the binder resin substantially correlates with the Tg of the coating film, the binder resin used preferably has a Tg of 5 to 30 ° C. Alternatively, a plurality of resins having different Tg may be mixed and the Tg of the entire mixed resin may be set to 5 to 30 ° C.

If the coating film Tg is less than 5 ° C, the hardness of the entire coating film is too low, and it is difficult to secure a universal hardness of 2.5 N / mm ² or more under a load of 23 ° C and 5 mN. is there. On the other hand, if the coating film Tg is higher than 30 ° C., when the precoated metal sheet is formed, the gloss of the coating film is reduced in the processed portion, which is not suitable. The coating film Tg is more preferably 10 to 28 ° C.

  The coating film hardness of the precoated metal sheet of the present invention can be adjusted mainly by the type and amount of crosslinking agent contained in the coating film. 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.

As the type of curing agent, melamine resin or isocyanate is effective, and the universal hardness increases as the amount of these added increases. Universal hardness tends to be higher for melamine curing agents than for isocyanate curing agents. The addition amount of the melamine resin is more preferably 5 to 120 parts by mass with respect to 100 parts by mass of the main resin solid content. If the addition amount of the melamine resin relative to 100 parts by mass of the main resin solid content is less than 5 parts by mass, the universal hardness at 23 ° C. may be less than ^2.5 N / mm ^2, and the addition amount of the melamine resin is 120 parts by mass. If it is too high, the elongation at break may be less than 100%. If the universal hardness at 23 ° C. is less than ^2.5 N / mm ² , it is not suitable because galling of the coating film is likely to occur when press molding is performed under severe conditions.

  Moreover, since the universal hardness may change depending on the type and amount of pigment added, the universal hardness of the coating film may be adjusted by controlling these.

  As the pigment, generally known rust preventive pigments, colored pigments, metallic pigments, pearl pigments, extender pigments and the like can be used. Examples of rust preventive pigments include chromium anticorrosive pigments such as strontium chromate, potassium chromate, barium chromate and calcium chromate, and chromate-free anticorrosive pigments such as zinc phosphate, aluminum tripolyphosphate, silica and calcium ion exchange silica. Rust pigments can be used. As the color pigment, generally known pigments such as carbon black, titanium oxide, zinc white, naphthol red, disazo yellow, disazopyrazolone orange and the like can be used. It may be an inorganic pigment or an organic pigment. The metallic pigment is a generally known metallic pigment such as an aluminum pigment or a nickel pigment, and a particulate pigment or a flake pigment may be used. As the extender pigment, generally known extender pigments such as calcium carbonate, barium sulfate, and talc can be used. As these pigments, reagents may be used or commercially available ones may be used. A plurality of these various pigments may be used in combination.

  Generally, the universal hardness tends to be higher for white pigments such as titanium oxide and extender pigments than for carbon black and organic pigments. In addition, the higher the addition amount, the higher the universal altitude tends to be. However, when the addition amount is too high, the coating film becomes brittle and the elongation at break becomes less than 100%. Less than 60 mass parts is more suitable with respect to mass parts. When it exceeds 60 parts by mass, the elongation at break of the coating film at 23 ° C. may be less than 100%. In addition, the universal hardness of the coating film can be adjusted by controlling the molecular weight of the coating film resin. When the molecular weight of the coating resin is reduced, the molecular weight between the crosslinking points after the coating is cured is reduced, and the crosslinking density is substantially increased, so that the universal hardness is increased. However, if the molecular weight of the coating film is too small, the elongation at break of the coating film at 23 ° C. may be reduced to less than 100%, and therefore the molecular weight is more preferably 10,000 or more. Further, those having a molecular weight of more than 50000 are difficult to dissolve in a solvent, and there is a concern that it may be difficult to form a paint.

In addition, if the elongation at break of the coating film of the precoated metal sheet of the present invention is less than 100% at 23 ° C., it is not suitable because cracks are likely to occur from the bent portion during press working. The elongation referred to in the present invention is [elongation] = {[elongation (ΔL)] / [initial length (L ₀ )]} × 100 (%). The rate of elongation is defined below to avoid confusion, as some references have different definitions. The method for measuring the elongation at break of each coating film is as follows: a coating film obtained by peeling each layer of the coating film coated on the precoated metal plate from the metal plate, or a substrate having a peelability such as a fluororesin sheet in advance. After coating and baking under the same conditions as the precoated metal plate, a coating film prepared by peeling the coating film from the substrate can be used. The elongation at break can be measured by pulling the coated film thus prepared until it breaks in a 23 ° C. atmosphere using a tensile tester.

As another method, a metal plate that has already been coated is tightly bent 180 ° in an atmosphere of 23 ° C. with the coating layer side facing outward, and the presence or absence of cracks in the coating film at the curvature portion is observed with a microscope. If no cracks are observed, it can be determined that the elongation at break of the coating film is 100% or more (hereinafter, this method is referred to as a bending method). As shown in FIG. 1, when a material bent tightly by 180 ° is viewed from the cross-sectional direction, a portion called a neutral surface where no distortion occurs at the central portion in the thickness direction of the bent portion of the material. Will occur. It is known that tensile strain occurs outside the bend from the neutral plane and compressive strain occurs inside. Here, assuming that the outermost surface of the bent portion of the metal plate is a semicircle having the metal plate thickness t as the curvature radius, the outermost surface when the metal plate is tightly bent by the following equation 1 is used. It can be seen that the elongation (ε _s ) of the outer surface can be calculated and is 100%. As is clear from FIG. 1 and Equation 1, in the case of the technique for obtaining the elongation percentage of the coating film by the bending method, the thickness of the metal plate as the base material is theoretically any thickness. Even if a metal plate is used, the value obtained is the same and there is no problem.

・・・（式１）

... (Formula 1)

  In order to guide this concept, it is possible to refer to general material dynamics literature such as Terufumi Machida; “Easy-to-understand material strength studies”, publisher: Ohm Publishing Co., Ltd., 1999, etc.

  Therefore, when the pre-coated metal sheet is bent 180 ° so that the coating film side is on the outside, it can be assumed that the elongation rate of the coating film has reached 100%, and cracks are recognized in the coating film at this time. If not, the elongation at break of the coating can be considered to be 100% or more. Microscopic observation of the occurrence of cracks in the coating film of the coated metal plate 180 ° closely bent may be observed from the surface of the coating film or from the cross section. In the present invention, as a method of measuring the elongation at break of the coating film, either a method obtained by a tensile test of a coating film or a method of observing the occurrence of cracks by closely bending a coated metal plate by 180 ° May be adopted. When the elongation at break of any one of the coating films to be coated on the precoated metal sheet of the present invention is less than 100%, cracks and peeling of the coating film occur in the processed part when processed into a strict shape. There is a risk of poor appearance and poor corrosion resistance at the machined part.

  The specular glossiness of the coating film of the precoated metal sheet of the present invention needs to be 60% or more when measured in an unprocessed state with an incident angle and a light receiving angle of 60 °. When the specular gloss at 60 ° is less than 60%, it is not necessary to apply the present invention because the gloss reduction of the coating film at the molded portion is not noticeable. When the specular gloss is 80% or more, the effect of the present invention is more exhibited, which is more preferable. The mirror gloss of the coating film is JIS. K. 5600.4.7: 1999, which means the specular gloss. The gloss of the coating film is generally 80% or more unless adjusted using a matting agent or the like. When adjusting the gloss to a low level, it can be adjusted using a matting agent such as silica. In addition, it can be adjusted using other generally known gloss adjusting agents.

The coating film of the precoated metal sheet of the present invention may be a single layer or two or more layers. When there are two or more coating films, the physical properties of the outermost coating film are (A) a glass transition temperature of 5 to 30 ° C., (B) a universal hardness of 2.5 N / mm ² or more, ( C) It is necessary that the elongation at break is a physical property of 100% or more, and (D) the specular gloss of the coating film is 60% or more when measured at an incident angle and a light receiving angle of 60 °. . The physical properties of the lower layer coating may be outside this range, but if one or more of these physical property ranges are satisfied, the moldability is better and the coating film gloss at the molded part is further reduced. This is more suitable because it becomes difficult to do so.

  Moreover, you may add an antifoamer, a slip agent, a pigment dispersant, a leveling agent, wax, etc. in the coating material used for the precoat metal plate of this invention as needed. In addition, if the coating film contains wax, the slipperiness of the coating film surface is improved, so that it is easier to process during pressing, which is more preferable.

  When the coating film of the precoated metal sheet of the present invention has two or more layers, it is more preferable to include a phosphorus compound in the lowermost film because the corrosion resistance and the adhesion between the metal sheet and the coating film are improved. Although the detailed mechanism has not been clarified, a coating film containing a phosphorus compound has a function to relieve the stress when a shear stress acts on the coating film. Hard to be destroyed by stress. Therefore, even if a precoated metal plate containing this in the lowermost layer coating is pressed, damage to the coating is unlikely to occur, which is more preferable. As the phosphorus compound, generally known compounds such as zinc phosphate and aluminum phosphate can be used. These compounds may be those commercially available as reagents or those commercially available as industrial products such as pigments. Examples of commercially available industrial products include “K-WHITE”, a tripolyaluminum dihydrogen phosphate manufactured by Teika, and “EXPERT (registered trademark) series”, a zinc phosphate-based pigment manufactured by Toho Pigment. Etc. can be used. These compounds may be added in combination. Further, in addition to the phosphorus compound, other rust preventive pigments may be used in combination. In particular, Ca ion exchange silica is more suitable because it is excellent in corrosion resistance. As the Ca ion exchange silica, “SHIELDEX (registered trademark)” manufactured by GRACE may be used.

  The addition amount of the phosphorus compound in the undercoat coating is more preferably 5 to 150 parts by mass with respect to 100 parts by mass of the resin solid content. If it is less than 5 parts by mass, the corrosion resistance is inferior, and if it exceeds 150 parts by mass, the coating film becomes brittle and the workability may be inferior. You may add another pigment and a compound in a lower layer coating film as needed.

  When the pre-coated metal sheet of the present invention has two or more coating layers, it is more preferable that Ra (arithmetic mean roughness) of at least one interface between the coating layers is 0.3 to 0.8 μm. is there. If the Ra at the interface of each coating film is less than 0.3 μm, the adhesion at the coating film interface may be reduced. 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 when the top paint is applied is affected, and the gloss may be lowered. In particular, the adjustment of Ra is effective when two or more top coats are applied over the lowermost coating layer. Here, the top coat paint refers to all the paints coated on the lowermost coat layer (the coat layer in contact with the metal plate). In general, the lowermost layer paint is added with a resin such as a primer paint with good adhesion in order to ensure adhesion between the metal plate and the top coat applied on the metal plate. A certain degree of adhesion can be ensured without adjusting Ra at the interface between the film layer and the top coat layer to be coated thereon. In contrast, in general, a resin for improving adhesion is often not added to the top coating, so when two layers of the top coating are applied, Ra of the interface between the two layers is set. When the thickness is 0.3 to 0.8 μm, adhesion is secured, which is more preferable. Further, when there are three or more top coat layers, the interface that controls Ra of the interface between the coating layers within the above range may be at least one of the interfaces. Further, any two or more interfaces or all the interfaces may be used.

  Ra can be imparted to the interface between the coating layers by simultaneous multilayer coating or wet-on-wet coating. Multi-layer simultaneous coating is applied to the substrate in a state where multiple layers of coating liquid are laminated at the same time using a slot die coater or slide hopper type curtain coater, etc., and then the multi-layer coating is simultaneously dried and baked. It is a method to make it. In addition, wet-on-wet coating means that after a coating solution is once coated on a substrate, another coating solution is further coated on the substrate before the coating solution is dried. In this method, the multilayer coating liquid is simultaneously dried and baked. In this way, by laminating the coating liquids in an undried state and applying them simultaneously, the coating liquids of each layer are slightly mixed in the vicinity of the interface of the laminated coating film, thereby generating irregularities (that is, Ra) at the interface. Can do. In general, when two or more coating films are coated by the above-described 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 (see the following example).

  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. In addition, as a multi-layer simultaneous coating method, a method of coating 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 the plating include zinc plating, aluminum plating, copper plating, nickel plating, and the like, and may be alloy plating of these. 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. 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, treatment 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 is known. Japanese Laid-Open Patent Publication Nos. 9-241576, 2001-89868, 2001-316845, 2002-60959, 2002-38280, 2002-266081, 2003 You may use the well-known technique described in -253464 gazette etc. These chemical conversion treatments are commercially available, for example, chromate treatment agent “ZM-1300AN” manufactured by Nippon Parkerizing Co., Ltd., chromate-free chemical conversion treatment agent “CT-E300N” manufactured by Nippon Parkerizing Co., Ltd., trivalent chromium manufactured by Nippon Paint Co., Ltd. The chemical conversion treatment agent “Surfcoat ™ NRC1000” or the like can be used.

A painted metal molded product that is deep-drawn to a molding height of 25 mm or more using the pre-coated metal plate of the present invention is more preferable because gloss degradation at the processed part is hardly observed. In particular, the bottom surface of the coated metal molded product formed using the precoated metal sheet of the present invention has almost no gloss reduction, and the specular glossiness is 60% or more when measured under the conditions of an incident angle and a light receiving angle of 60 °. Therefore, it is more preferable. In addition, the coating layer of the coated metal molded product formed using the precoated metal sheet of the present invention has an initial physical property of the precoated metal sheet after processing, and has a glass transition temperature of 5 to 30 ° C and 23 ° C. Is suitable because it satisfies the universal hardness under a load of 5 mN of 2.5 N / mm ² or more and the coating performance is ensured. Also, the pre-coated metal plate before forming has two or more coating films, and has a portion where Ra (arithmetic mean roughness) of at least one interface between each coating film layer is 0.3 to 0.8 μm Painted metal moldings that have been molded are more suitable because Ra (arithmetic mean roughness) of at least one interface between the coating layers of the molding is 0.3 to 0.8 μm, and the coating film adhesion is excellent. It is.

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

  Hereinafter, the details of the test material used in this example will be described.

  First, the details of the paint used in this example will be described.

  “Byron (registered trademark) 63CS” (Tg: 7 ° C., number average molecular weight: 20000) which is an amorphous polyester resin manufactured by Toyobo Co., Ltd. and “Byron (registered trademark)” which is an amorphous polyester resin manufactured by Toyobo Co., Ltd. ) GK890 "(Tg: 17 ° C, number average molecular weight: 11000)," Byron (registered trademark) GK140 "(Tg: 20 ° C, number average molecular weight: 13000)," Byron (registered trademark) GK780 "(Tg: 36 ° C) , Number average molecular weight: 11000), “Byron (registered trademark) GK880” (Tg: 84 ° C., number average molecular weight: 18000), “Byron (registered trademark) 220” (Tg: 53 ° C., number average molecular weight: 3000) Used as a binder resin. “Byron (registered trademark) 63CS” was used as it was because the polyester resin was already dissolved in an organic solvent (mixed in a mass ratio of cyclohexanone: solvesso 150 = 1: 1). Since the other resins are in the form of pellets, flakes or sheets, they were used by dissolving them in an organic solvent (using a mixture of cyclohexanone: solvesso 150 = 1: 1 by mass ratio).

  Next, “Cymel (registered trademark) 303” which is a fully alkyl methylated melamine resin (hereinafter referred to as melamine resin or HMMM) manufactured by Mitsui Cytec Co., Ltd. is used as a crosslinking agent. And mixed. Furthermore, “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 in this example was prepared by the above procedure.

  Next, a top coating was prepared by adding a necessary amount of titanium oxide “Taipeku CR95” (hereinafter referred to as Ti-based) manufactured by Ishihara Sangyo Co., Ltd. to the clear coating prepared. A clear coating without titanium oxide was also prepared as needed.

  For the lowermost layer paint (hereinafter referred to as “undercoat paint”), a clear paint of FL641EU primer made by Nippon Fine Coatings, which is a commercially available undercoat paint, is prepared, and a necessary amount of anti-corrosive pigment is added to this. By doing so, an undercoat paint was prepared. The anti-corrosion pigment used in this example is K-WHITE # 105 (hereinafter referred to as “AL phosphate”) manufactured by Teika Co., Ltd., and “SHIELDEX” which is calcium ion-exchanged silica manufactured by GRACE. (Registered trademark) C303 "(hereinafter referred to as Ca silica) was used. Moreover, what added the titanium oxide "Taipaque CR95" (henceforth titanium oxide) by Ishihara Sangyo Co., Ltd. as needed was also produced. In addition, silica “AEROSIL (registered trademark) 200” manufactured by Nippon Aerosil Co., Ltd. was added as appropriate as a matting material as necessary, and the gloss of the coating film was adjusted to 60% and 40% as 60 ° specular gloss. Produced.

  Details of the prepared undercoat are shown in Table 1, and details of the top coat are shown in Table 2. In Table 2, the titanium oxide-containing paint (top coat-1 to 12) is referred to as top coat coloring paint, and the clear paint without any pigment (top coat-13 to 15) is referred to as top coat clear.

  Hereinafter, the details of the precoated metal plate used in this example will be described.

Zinc-nickel alloy-plated steel sheet “Zinclite” (hereinafter referred to as ZL) manufactured by Nippon Steel Corporation, electrogalvanized steel sheet “JINCOAT” (hereinafter referred to as EG) manufactured by Nippon Steel Corporation, Shin A hot-dip galvanized steel sheet “Silver Zinc” (hereinafter referred to as GI) manufactured by Nippon Steel Co., Ltd. was prepared as an original sheet. A plate thickness of 0.6 mm was used. The plating adhesion amount of ZL used in this example was 20 g / m ^{2 on} one side, and the nickel amount in the plating layer was 12%. The EG plating adhesion amount was 20 g / m ² on one side, and the GI plating adhesion amount was 60 mg / 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 agent “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, paint the undercoat paint on one side of the chemical-treated metal plate and the other side with the gray color of “FL100HQ”, the back paint made by Nihon Fine Coatings, on the roll coater. In the induction heating furnace in which hot air was blown, the metal plate was dried and cured under the condition that the ultimate plate temperature was 210 ° C. After drying and baking, water was sprayed on the painted metal plate and cooled.

  Next, the top coat color paint is applied onto the undercoat film with a roller curtain coater, and the coated film is dried at the same time in an induction heating furnace blown with hot air under the condition that the ultimate plate temperature of the metal plate is 230 ° C. Cured. After drying and baking, water was sprayed onto the coated metal plate and water-cooled to prepare a two-layer pre-coated metal plate (hereinafter, the coating method in this procedure is referred to as “painting method (i)”. Called).

  In addition, if necessary, a 1-coat pre-coated metal sheet was also prepared by coating only one coat of the top-colored paint on the chemical-treated metal sheet with a roll coater (hereinafter referred to as “painting method” in this procedure). Method (ii) ").

  In addition, if necessary, one layer of the undercoat paint is baked, and then two types of topcoat paint (topcoat coloring paint and topcoat clear paint) are simultaneously applied in two layers on a slide hopper type curtain coater. By baking at the same time, a total of three layers were coated (baking was performed twice) to prepare a pre-coated metal plate (the coating method in this procedure is referred to as “coating method (iii)”).

  Furthermore, one layer of the undercoat paint was baked, and then the top coat color paint was applied with a roller curtain coater, and then the top coat clear paint was applied with a roller curtain coater and dried before it was dried. A total of three layers were coated by baking two layers of the top coat at the same time (baking was performed twice) to prepare a pre-coated metal plate (the coating method in this procedure is referred to as “coating method (iv)”).

  Also, coat only one layer of the top-colored paint on the undercoat film with a roll coater, bak it in the manner described above, and then apply another layer of clear paint on the coat film with a roll coater and bake again. Thus, a total of three layers were coated (baking was performed three times), and a pre-coated metal plate was also produced (the coating method in this procedure is referred to as “painting method (v)”).

  Regarding the thickness of each pre-coated steel sheet, the roll peripheral speed and paint viscosity for roll coaters and roller curtain coaters, and the paint application pressure and paint viscosity for slide hopper curtain coaters are used. It was controlled by adjusting. The undercoat film thickness was 5 μm, the topcoat film thickness was 15 μm, the topcoat clear film thickness was 10 μm, and the backcoat film thickness was 5 μm (all dry film thicknesses). Each film thickness was measured with an electromagnetic film thickness meter “LE-200J” manufactured by KET, and the vertical cut surface of each sample was observed with a microscope to reconfirm that the film thickness was as required. .

  Table 3 describes the details of the prepared precoated metal sheet.

  Hereinafter, the details of the evaluation method of the prepared precoated metal sheet will be described.

1. Measurement of glass transition temperature of coating film of pre-coated metal plate Tg of the coating film was measured with a thermomechanical analyzer “SSC5200 series TMA / SS120C” manufactured by Seiko Denshi. The probe used for the measurement was a needle probe.

2. Universal hardness measurement of coating film of pre-coated metal plate It was measured using a micro hardness meter “Fischer Scope (registered trademark) H100” manufactured by Fischer Instruments. The atmospheric temperature during the measurement was 23 ° C., and the universal hardness (HU (N / mm ² )) when the pressing load was 5 mN was measured with this measuring instrument.

3. Measurement of elongation at break of coating film The prepared precoated metal plate was subjected to 180 ° bending processing (adhesion bending processing) in a 23 ° C. atmosphere so that the surface to which the top coating film was applied became the outside. Next, the processed part was observed with a 10 × microscope, and the presence or absence of cracks in the coating film was investigated. Furthermore, the vicinity of the center of the processed part of the processed precoated metal plate is cut vertically so that the cross section can be observed, the cut precoated metal plate is embedded in the resin, and then the cross section is polished to obtain 10 times and 500 times. The cross section was observed with a microscope. And the presence or absence of the crack generation of each coating film layer was observed. In this way, each coating layer is observed, and when all the coating layers are not cracked by observing with a 500 × microscope, the elongation at break of the coating is 100% or more. If the coating film shows very slight cracks with a 10x microscope and clearly shows cracks with a 500x microscope, it is assumed that the estimated elongation is slightly less than 100%. When a clear crack was generated with a 10-fold microscope, the elongation at break of the coating film was clearly less than 100% and evaluated as x.

4). 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 60 °.

5. Ra measurement of coating film interface Cut the precoated metal plate vertically so that the cross section of the coating film can be observed, bury the cut precoated metal plate in the resin, polish the cross section, and apply it by scanning electron microscope of 3500 times A cross-sectional picture of the membrane was taken. Next, a transparent resin sheet (using a commercially available OHP sheet) was placed on the photograph, and the unevenness at the coating film interface was traced in good faith. Then, as shown in FIG. 2, the area of the vertical line (shaded area) is measured by an image processing apparatus, and Ra is calculated from the measured area as an average value in the X-axis direction of FIG. Calculated.

・・・（式２）

... (Formula 2)

6). Corrosion resistance test Cut scratches reaching the base metal 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 carried out according to the method described in JIS K5400.99.1. Salt water was sprayed on the surface of the test piece with the cross cut. The test time was 240 hours. Then, the film swollen width from the cut portion on the surface side is measured, ○ when the cut portion swollen width is 3 mm or less on one side, Δ when the cut portion swollen width is more than 3 mm and less than 5 mm on one side, and the cut portion swollen width is The case of more than 5 mm on one side was evaluated as x.

7). Measurement of specular gloss after processing pre-coated metal plate Set the pre-coated metal plate cut into strips with a width of 50 mm in a tensile tester so that the distance between the jigs is 100 mm, and the jig under the conditions of a pulling speed of 200 mm / min. Pulling was performed until the distance was 110 mm. Then, the sample after the pulling process was taken out, and the specular gloss at the center of the sample was measured using a “digital gonio-gloss meter” manufactured by Suga Test Instruments Co., Ltd. under the conditions of an incident angle and a light receiving angle of 60 °. . The gloss retention (= [mirror surface 60 ° gloss after processing] × 100 / [mirror surface 60 ° gloss before processing]) was calculated from the measurement result.
In this experiment, the reason why the specular gloss was measured when a sample with a distance between jigs of 100 mm was pulled to a distance between jigs of 110 mm was empirically determined to be 60 ° specular gloss when processed under these conditions. This is because the present inventors have found that when the rate is 85% or more, it is difficult to reduce the gloss at the deep-drawn formed part.

8). Draw bead test The draw bead test is known as a test method for evaluating the slidability during press molding and the scratching property of the material by the mold. When the pre-coated metal sheet is evaluated by this experimental method, mold galling of the paint film that occurs during press forming is reproduced, and a pre-coated metal sheet that is prone to galling of the paint film during press forming is also coated by this test method. Peeling due to film galling is observed. In this experiment, as shown in FIG. 3, the sample was sandwiched between the convex mold and the concave mold, and the sample was loaded with a load of 200 mm / mm with a pressing load of 0.6 t and 1.0 t. It was carried out by observing the appearance of the coating film when pulled out at a rate of min. The surface roughness of the mold was adjusted to Ra = 0.8 μm. Also, when carrying out this test, apply volatile lubricant “G-6215FS” manufactured by Nippon Kogyo Oil Co., Ltd. to the surface of the sample coating film, and the evaluation surface (the surface to which the back coating is not applied) is indented. The mold was pressed so as to be on the mold side. And the presence or absence of the crack generation | occurrence | production of the coating-film surface of the sample after drawing was investigated, and the following reference | standard evaluated. The case where the peeling of the coating film is not observed even under the condition of the pressing load of 0.6 t or the condition of 1.0 t, the peeling of the coating film is not recognized under the pressing load condition of 0.6 t, but the condition of 1.0 t The case where peeling of the coating film was observed was evaluated as Δ, and the case where peeling of the coating film was observed under the condition of a pressing load of 0.6 t or 1.0 t was evaluated as x.

9. Square tube forming test The prepared pre-coated metal sheet was deep-drawn into a rectangular tube shape so that the evaluation surface (the surface not provided with the back coating film) was outside the molded product. The mold used for the rectangular tube molding was as follows. That is, the punch size was 40 mm square, the punch corner R was 5 mm, the punch shoulder R was 5 mm, and the die shoulder R was 5 mm. The surface roughness of the mold was Ra with a mirror finish of 0.1 μm or less. The blank size of the material was a circle of φ100 mm, and the wrinkle holding pressure was 0.8 t. The molding height was implemented at three levels of 20 mm, 25 mm and 30 mm. In addition, after the forming process, the presence or absence of coating film peeling or cracking (hereinafter referred to as processability) of the processed part of the precoated metal sheet is observed visually and with a 10 × microscope, and observed with either the visual or microscopic method. Even when peeling or cracking was not observed, ○, peeling or cracking was observed with a microscope, but when these were not visually observed, Δ was observed, and peeling or cracking was also observed visually. The case was evaluated as x. Further, the glossiness of the molded product was visually observed, and it was evaluated as ◯ when no gloss reduction was observed in the processed part, and × when the gloss reduction was clearly observed.

(Gloss measurement of square tube molding)
The specular glossiness of the bottom of the square tube molded product having a molding height of 25 mm and 30 mm obtained in the above “9. Square tube molding test” was measured using the “Digital Variable Glossmeter” manufactured by Suga Test Instruments Co., Ltd. The measurement was performed under the condition of a light receiving angle of 60 °.

(Ra measurement at the coating film interface of the rectangular tube molding)
Cut out any part of the bottom of the square tube molding with the molding height of 25 mm and 30 mm obtained in “9. Square tube forming test” above, cut it vertically so that the cross section of the coating film can be observed, and cut the coating After embedding the metal plate in the resin, the cross section was polished, and a cross-sectional photograph of the coating film was taken with a scanning electron microscope of 3500 times. Next, a transparent resin sheet (using a commercially available OHP sheet) was placed on the photograph to accurately trace the unevenness at the coating film interface. Then, as shown in FIG. 2, the area of the vertical line portion was measured by the image processing apparatus, and Ra was calculated from the above equation 2 as the average value. If the metal plate observed at the cross section of the molded product is bent by molding, it is parallel to the surface of the metal plate or the outermost surface of the coating film coated on the metal plate. A straight line was drawn and used as the center line of the interface.

  Details of the evaluation results will be described below.

  Table 4 shows the evaluation results of the pre-coated metal plates produced. Although the pre-coated metal plates (Examples Nos. 1 to 17) according to the examples of the present invention have high gloss, the gloss reduction at the processed portion when deep drawing is small, In the draw bead test that reproduces coating galling during continuous pressing, coating galling is less likely to occur, and there is no peeling or cracking of the coating film in the processed part. In addition, undercoat paints that do not contain a phosphorus compound (Examples 11, 12, and 13) are very slight in the draw bead test and square tube molding, but tend to cause coating film cracking and film peeling. Therefore, it is more preferable that a phosphorus compound is contained in the undercoat coating film. Moreover, since the Ra of the interface between the coating films deviates from 0.3 to 0.8 (Example-17), the coating film tends to peel off in the draw bead test. 0.3 to 0.8 is more preferable. As described above, since the pre-coated metal plates having Ra of the interface between the coating films of 0.3 to 0.8 are prepared by simultaneous multilayer coating or wet-on-wet coating, Since the coating film adhesion is improved and the coating film is hardly peeled off by pressing or the like, it is more preferable. In addition, the molded product obtained by deep drawing using the pre-coated metal plate according to the example of the present invention has no cracks or peeling of the coating film, and gloss reduction of the processed part is not visually observed. , Has an excellent appearance.

On the other hand, when the Tg of the coating film exceeds 30 ° C. (Comparative Example-18, 20-24), the gloss retention after processing is low, and even when a rectangular tube is molded, the gloss is clearly reduced visually. , Unsuitable. However, since the initial gloss of the coating film is less than 60% even if the Tg of the coating film exceeds 30 ° C. (Comparative Example-19), since the original initial gloss is low, it is difficult to reduce the gloss even after processing. There is no need to apply the invention. A film having a glass transition temperature of 7 ° C. and a universal hardness of 2.6 N / mm ² under the conditions of 23 ° C. and a load of 5 mN (Example 1) is a draw bead test. The coating film tends to be peeled off compared with the above, and the coating film has a glass transition temperature of 7 ° C. and a universal hardness of less than 2.5 N / mm ² under the conditions of 23 ° C. and 5 mN load (Comparative Example— 25) and those having a universal hardness of less than 2.5 N / mm ² under the conditions of a glass transition temperature of less than 5 ° C. and a load of 23 ° C. and 5 mN (Comparative Example-26) Since peeling occurs, the coating film Tg is more preferably 5 ° C. or more, the universal hardness is 23 N ° C., and a load of 5 mN is more preferably 2.5 N / mm ² or more. In addition, those having a coating elongation at break of less than 100% (Comparative Examples-21 to 23) are unsuitable because the coating tends to be peeled off or cracked when formed into a square tube.

  Next, Table 5 shows the evaluation results of the molded product formed by using the precoated metal plate produced in this example. Each of the molded articles (Example Nos. Molded articles -1 to 17) molded using the precoated metal plate according to the example of the present invention has a 60 ° specular gloss and an appearance of 60% or more. , The appearance was excellent with no cracking or peeling of the coating film in the processed part. On the other hand, the molded product (Comparative Example No. molded product-18 to 26) formed using a pre-coated metal plate outside the range defined in the present invention has low gloss or cracks or peeling of the coating film at the processed part. The appearance was poor.

  According to the present invention, it is possible to provide a high-gloss pre-coated metal plate that is not easily lowered in gloss at the processed part even when deep drawing is performed and is excellent in press formability, a manufacturing method thereof, and a coated metal molded product. Therefore, according to the present invention, it has become possible to manufacture a molded part having a complicated shape, which could only be dealt with by post-coating so far, using a pre-coated metal plate.

  In addition, by using a molded product obtained by deep drawing the pre-coated metal sheet of the present invention, it is possible not only to solve the problem of volatile organic solvent (VOC), which has been a problem in post-coating, but also by the user. Cost reduction and factory space savings can be achieved by eliminating coating equipment. Therefore, it can be said that the present invention is an industrially highly valuable invention.

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

  The present invention relates to a precoated metal plate having high gloss and excellent press formability, and in particular, press formability in home appliances, building materials, civil engineering, machinery, automobiles, furniture, containers, etc. The present invention relates to an excellent prepainted metal sheet for deep drawing, a method for producing the same, and a painted metal molded product.

It is a figure shown about the bending method of the breaking elongation measuring method of the coating film of the precoat metal plate of this invention. It is a figure which shows the measuring method of Ra of the coating-film interface of the precoat metal plate of this invention. It is a figure which shows the draw bead test method which evaluates the coating film galling property of the precoat metal plate of this invention.

Claims (8)

In a pre-coated metal plate having one or two or more coating layers on one or both sides of the metal plate:
Of the coating layers, the outermost coating layer has (A) a glass transition temperature of 5 to 30 ° C. and (B) a hardness at 23 ° C. of 2.5 N / mm ^{2 in} terms of universal hardness under a load of 5 mN ^2. (C) The elongation at break at 23 ° C. is 100% or more, and (D) the specular gloss of the outermost coating film is measured under the conditions of an incident angle and a light receiving angle of 60 °, respectively. A pre-coated metal sheet characterized by being 60% or more. The coating layer is two or more layers,
The precoated metal sheet according to claim 1, wherein the lowermost coating film of the coating layer contains a phosphorus compound. The coating layer is two or more layers,
The precoated metal sheet according to claim 1 or 2, wherein Ra (arithmetic mean roughness) of at least one of the interfaces between the coating layers is 0.3 to 0.8 µm. It is a manufacturing method of the precoat metal plate of Claim 2 or 3, Comprising:
The coating layer is three or more layers,
A method for producing a pre-coated metal sheet, wherein at least two layers on the lowermost coating layer among the coating layers are applied by multi-layer simultaneous application or a wet-on-wet method.   A pre-coated metal sheet according to any one of claims 1 to 3, which is formed by deep drawing to a forming height of 25 mm or more. A painted metal molded product formed by deep drawing to a molding height of 25 mm or more:
Having at least one or two or more coating layers on the outer surface;
Of the coating layers, the outermost coating layer has (A) a glass transition temperature of 5 to 30 ° C. and (B) a hardness at 23 ° C. of 2.5 N / mm ^{2 in} terms of universal hardness under a load of 5 mN ^2. And (D) characterized in that it has a glossy part that is 60% or more when the specular gloss of the outermost layer coating film is measured under conditions of an incident angle and a light receiving angle of 60 °, Painted metal molding. The coating layer is two or more layers,
The painted metal molding according to claim 6, wherein the glossy portion has Ra (arithmetic mean roughness) of at least one interface among the interfaces between the coating layers between 0.3 and 0.8 µm. object. The painted metal molded product according to claim 6 or 7, wherein the glossy portion is a bottom surface of deep drawing.

Images