Method for manufacturing a painted metal member

Abstract

To provide a coated metal member that includes a resin layer containing a fluororesin and has undergone molding, the molded part being less prone to cracking, the coated metal member featuring high designability.SOLUTION: The present invention provides a method for producing a coated metal member that includes a metal member and a resin layer disposed on the metal member and containing a fluororesin, the metal member and the resin layer having undergone molding. The method includes the step of heating the coated metal member to remove cracks occurring in the molded part of the resin layer.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a painted metal member having excellent appearance properties.

Background Art

[0002] In recent years, metal members that have been subjected to various forming processes such as embossing and bending are used in various applications. The forming process is often performed after forming a resin layer on a flat metal member.

[0003] However, when performing a forming process in a state where a resin layer is formed on a metal member, the resin layer in the formed portion is likely to be stretched and discolored. For example, in the case of a resin layer having a low brightness color, the formed portion was likely to appear white. In Patent Document 1, it has been proposed to enhance the design properties of a painted metal member by utilizing this phenomenon. Specifically, a technique is disclosed in which an embossed portion is discolored white to make it appear as if a deeper embossing process has been performed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] As in Patent Document 1, discoloration (e.g., whitening) of the molded portion may be preferable in some cases. However, depending on the use of the painted metal member, it is often preferable that the molded portion does not discolor. However, it is difficult to suppress discoloration of the molded portion, and discoloration was particularly likely to occur when the resin layer contained a fluororesin. Fluororesins have high crystallinity, and when stretched, they crystallize along the stretching direction. The crystallized portion has extremely low stretchability compared to other portions. Also, when pigments or the like are blended, they break at these points and the stretchability decreases. Therefore, when performing molding on a state where a resin layer containing a fluororesin is formed on a metal member, the crystallized portion does not stretch sufficiently, or many minute cracks occur in the molded portion starting from the pigment. FIG. 1A is a photograph (a photograph observed with a scanning electron microscope) of a cross section in the thickness direction of the molded portion when a resin layer 20 containing a fluororesin is formed on a metal member 10 (steel plate 11 and plating layer 12) and this is Erichsen processed. FIG. 1B is an enlarged view of the portion surrounded by the broken line in FIG. 1A. As shown in FIGS. 1A and 1B, when processing a painted metal member having a resin layer 20 containing a fluororesin, streak unevenness occurs in the resin layer 20 along the processing direction. When such cracks occur in the molded portion, light is diffusely reflected in the region, so that the molded portion becomes white and conspicuous.

[0006] An object of the present invention is to provide a method for manufacturing a highly designed painted metal member having a resin layer containing a fluororesin and being molded, and having few cracks in the molded portion.

Means for Solving the Problems

[0007] The present invention provides a method for manufacturing the following painted metal member. A method for manufacturing a painted metal member having a metal member and a resin layer containing a fluororesin disposed on the metal member, the metal member and the resin layer being molded, the method comprising a step of heating the painted metal member to remove cracks generated in the molded portion of the resin layer.

Effects of the Invention

[0008] According to the method for manufacturing a painted metal member of the present invention, cracks generated in the formed portion by forming processes or the like can be removed. Therefore, according to the manufacturing method of the present invention, it is possible to manufacture a painted metal member with high design quality applicable to various uses.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0010] In the method for manufacturing a painted metal member of the present invention, a step of heating the painted metal member to remove cracks generated in the formed portion of the resin layer is performed.

[0011] As described above, in the resin layer containing a fluororesin, cracks were likely to occur in the formed part. In contrast, as a result of intensive studies by the present inventors, it was revealed that when the painted metal member with such cracks was heated, the resin layer softened and the width and depth of the cracks decreased, making the discoloration of the formed part less noticeable. This is presumably because the resin layer around the cracks entered the voids and the unevenness was alleviated. Furthermore, it is also considered that the crystalline part of the fluororesin in the formed part melts, reducing the difference from the surrounding amorphous part, which also contributes to a reduction in the refractive index change in that part. According to such a method for manufacturing a painted substrate of the present invention, a painted metal member with less discoloration in the formed part and high design quality can be obtained. Hereinafter, the method for manufacturing a painted metal member of the present invention will be described in detail.

[0012] In the method for manufacturing a painted metal member of the present invention, a painted metal member in which the laminated part of the metal member and the resin layer has been formed is prepared. Note that the forming process in this specification may be any process for forming the laminated part of the metal and the resin layer into a desired shape, and examples thereof include bending, drawing, roll forming, embossing, and the like.

[0013] The type and manufacturing method of the painted metal member for removing cracks are not particularly limited. For example, it may be one in which a paint is applied on a metal member to form a resin layer and then formed. On the other hand, it may be one in which a metal member is formed and then a resin layer is formed on the metal member. Furthermore, a commercially available painted metal member or the like may also be used. However, when a paint containing a fluororesin is applied on a metal member to form a resin layer and then the metal member and the resin layer are formed, the above-mentioned cracks are more likely to occur in the formed part. Therefore, from the viewpoint of sufficiently obtaining the effects of the present invention, the painted metal member is preferably one in which a resin layer is formed on a metal member and then formed.

[0014] Further, the painted metal member may be one immediately after the formation of the resin layer or the molding process, or may be one after a long period has elapsed since the formation of the resin layer or the molding process. In any case, according to the method for manufacturing the painted metal member of the present invention, cracks generated in the molded portion of the resin layer can be removed.

[0015] The shape of the painted metal member is not particularly limited, and may be, for example, a plate-shaped member or a strip-shaped member, or may be a member having a three-dimensional structure. Here, the thickness of the metal member in the painted metal member is not particularly limited and is appropriately selected according to the use of the painted metal member and the molding process. Further, the thickness of the metal member may be constant or may be partially different. However, if the metal member is excessively thick, it is difficult to mold it into a desired shape. Therefore, the thickness of the metal member is usually preferably 3.0 mm or less, and more preferably 0.2 mm or more and 1.2 mm or less.

[0016] Also, the material of the metal member is not particularly limited, and includes plated steel sheets such as hot-dip Zn-plated steel sheet, hot-dip Zn-55% Al alloy-plated steel sheet, hot-dip Zn-Al-Mg alloy-plated steel sheet, hot-dip Al-plated steel sheet, electro-galvanized steel sheet, electro-copper-plated steel sheet; steel sheets such as ordinary steel sheet and stainless steel sheet; aluminum plate; copper plate, etc. Among these, in the case of a hot-dip Zn-Al-Mg alloy-plated steel sheet having a plating layer containing Zn, Al, and Mg, since the plating layer is relatively hard, the plating layer may crack due to the molding process. And, in the painted metal member in which the resin layer is disposed on such a metal member, cracks may also occur in the resin layer on the plating layer. On the other hand, in the method for manufacturing the painted metal member of the present invention, even when the plating layer cracks and cracks occur in the resin layer, the cracks can be removed by heating described later.

[0017] Further, between the metal member and the resin layer of the painted metal member, a chemical conversion coating film, an undercoat film, etc. may be disposed within a range that does not inhibit the effects of the present invention. The type of the chemical conversion coating film is not particularly limited. Examples of the chemical conversion treatment include chromate treatment, chromium-free treatment, phosphate treatment, etc. The adhesion amount of the chemical conversion coating film is not particularly limited as long as it is within a range effective for improving the corrosion resistance.

[0018] The undercoat coating film is a layer formed directly on the metal member or on the conversion coating film, and may be a layer that improves the adhesion of the resin layer or the corrosion resistance of the metal member.

[0019] The undercoat coating film is formed, for example, by applying an undercoat paint containing a resin to the surface of the metal member or the conversion coating film and drying (or curing) it. The type of resin contained in the undercoat paint is not particularly limited. Examples of the resin include polyester, epoxy resin, acrylic resin, etc. Epoxy resin is particularly preferable because it has high polarity and good adhesion to the metal member. Also, the thickness of the undercoat coating film is appropriately selected according to the use and type of the final painted metal member, and is, for example, about 5 μm.

[0020] On the other hand, the resin layer is a layer disposed on the above-mentioned metal member, and may be a layer containing at least a fluorine-based resin. The resin layer may be disposed so as to cover only a partial area of the metal member, or may be disposed so as to cover the entire surface of the entire area of the metal member. Further, it may be disposed directly on the metal member, or may be disposed via another layer (for example, a conversion coating film or an undercoat layer, etc.). The resin layer is usually disposed on the outermost surface of the painted metal member.

[0021] The thickness of the resin layer is appropriately selected according to the use of the painted metal member, the processing method, etc., but is usually preferably 50 μm or less. When the thickness of the resin layer is 50 μm or less, it is difficult for waki (bubbly bulges or holes) to occur during the film formation of the resin layer. Also, when the thickness of the resin layer is 50 μm or less, the adhesion to the above-mentioned metal member tends to be good, and peeling, etc. hardly occurs during the forming process. On the other hand, the thickness of the resin layer is preferably, for example, 10 μm or more. When the thickness of the resin layer is 10 μm or more, when the heating described later is performed, the resin layer of the processed portion is likely to soften or melt, and it is easy to remove cracks. The thickness of the resin layer is more preferably 10 μm or more and 50 μm or less, and even more preferably 15 μm or more and 30 μm or less.

[0022] The resin layer may contain only a fluororesin, or may further contain other resins. The amount of the fluororesin in the resin layer is appropriately selected according to the type of the fluororesin, desired properties, etc., but is preferably 40% by mass or more and 85% by mass or less, more preferably 50% by mass or more and 80% by mass or less, based on the total amount of the resins in the resin layer. When the amount of the fluororesin in the resin layer is 50% by mass or more based on the total amount of the resins, the durability, chemical resistance, heat resistance, abrasion resistance, weather resistance, corrosion resistance, stain resistance, etc. of the resin layer tend to be further improved. The resin layer may contain only one type of fluororesin, or may contain two or more types.

[0023] The type of the fluororesin is not particularly limited, and examples thereof include polyvinylidene fluoride resins. The amount of the polyvinylidene fluoride resin in the resin layer is not particularly limited, but when the resin layer contains a fluororesin and an acrylic resin described later, the amount of the polyvinylidene fluoride resin based on the total amount of the fluororesin and the acrylic resin is preferably 40% by mass or more, more preferably 40% by mass or more and 85% by mass or less, and even more preferably 50% by mass or more and 80% by mass or less. When the amount of the polyvinylidene fluoride resin is within this range, the durability, chemical resistance, heat resistance, abrasion resistance, weather resistance, corrosion resistance, stain resistance, etc. of the resin layer tend to be further improved.

[0024] Specific examples of the above polyvinylidene fluoride resins include polyvinylidene fluoride (PVDF) which is a homopolymer of 1,1-difluoroethylene, copolymers of 1,1-difluoroethylene and hexafluoropropylene, etc. Among these, copolymers of 1,1-difluoroethylene and hexafluoropropylene, etc. are preferred because of their high processability.

[0025] The type of resin other than the fluororesin contained in the resin layer is not particularly limited, but an acrylic resin is preferred. When the resin layer contains an acrylic resin, excessive crystallization of the fluororesin can be suppressed, making it easier to suppress the occurrence of cracks in the molding process section. Also, when the resin layer contains a pigment or the like, it is also possible to enhance the dispersibility of these by the acrylic resin. Further, when the resin layer contains an acrylic resin, the adhesion between the metal member and the resin layer tends to be good.

[0026] The amount of the acrylic resin in the resin layer is appropriately selected according to the use of the painted metal member, the type of the acrylic resin, etc., but is preferably 15% by mass or more and 60% by mass or less, more preferably 20% by mass or more and 50% by mass or less, based on the total amount of the resin in the resin layer. Also, the mass ratio of the fluororesin to the acrylic resin in the resin layer is preferably 40:60 to 85:15, more preferably 50:50 to 80:20. When the amount of the acrylic resin is within this range, it becomes easier to prevent the occurrence of cracks in the resin layer without impairing the properties derived from the fluororesin such as weather resistance, corrosion resistance, and stain resistance. The resin layer may contain only one kind of acrylic resin or two or more kinds.

[0027] It is preferable that the glass transition temperature of the above acrylic resin is low, for example, 70°C or lower is preferable, 50°C or lower is more preferable, and 30°C or lower is even more preferable. When the glass transition temperature of the acrylic resin in the resin layer is 70°C or lower, the moldability of the resin layer tends to be good. The glass transition temperature of the above acrylic resin may be a value calculated according to the FOX's equation from the monomer composition, or may be a value measured by differential thermal analysis (DTA).

[0028] Also, the weight average molecular weight of the acrylic resin is preferably 50,000 or more and 200,000 or less, more preferably 70,000 or more and 150,000 or less. When the weight average molecular weight of the acrylic resin is within this range, the moldability of the resin layer tends to be good.

[0029] Examples of acrylic resins include homopolymers and copolymers of acrylic monomers such as methyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, and butyl methacrylate, and copolymers of these acrylic monomers with other monomers.

[0030] Among these, the acrylic resin is particularly preferably a copolymer of methyl methacrylate, ethyl acrylate, and an ester compound of (meth)acrylic acid and an alcohol having 1 to 6 carbon atoms. The copolymer is likely to have appropriate hardness due to methyl methacrylate and ethyl acrylate. Further, the copolymer has an appropriate affinity with the fluororesin.

[0031] In addition to the fluororesin and the acrylic resin, the resin layer may further contain a coloring pigment, an extender pigment, etc. When the resin layer contains a coloring pigment, an extender pigment, etc., cracks may occur starting from the coloring pigment or the extender pigment during molding. In contrast, in the method for manufacturing a coated metal member of the present invention, even if such cracks occur, the cracks can be removed by heating described later.

[0032] The type of the coloring pigment is not particularly limited, and it may be a known organic coloring pigment, a known inorganic coloring pigment, or a composite oxide fired pigment containing a metal component. Further, the coloring pigment may be a known metallic pigment, a known pearl pigment, etc. The color of the coloring pigment is not particularly limited, but for example, when the resin layer contains a coloring pigment with low lightness, whitening of the molded portion is likely to be conspicuous. Therefore, the present invention is very effective when the resin layer contains a pigment with low lightness coloring.

[0033] The number average particle diameter of the coloring pigment is appropriately selected according to the type of the coloring pigment, etc. Usually, it is 3 μm or less, and preferably 0.01 μm or more and 1.5 μm. The amount of the coloring pigment in the resin layer is preferably, for example, 10% by mass or more and 40% by mass or less.

[0034] On the one hand, known extender pigments can be used as the extender pigment, and examples thereof include particles such as barium sulfate, titanium oxide, silica, and calcium carbonate. The number average particle diameter of the extender pigment is preferably 0.01 μm or more and 1 μm or less. Further, the amount of the extender pigment particles in the resin layer is preferably 0.1% by volume or more and 10% by volume or less.

[0035] The melting point of the resin layer is preferably 120°C or more and 185°C or less, and more preferably 135°C or more and 170°C or less. When the melting point of the resin layer is 185°C or less, the fluororesin is likely to soften when the painted metal member is heated, and cracks are likely to be removed. On the other hand, when the melting point of the resin layer is 120°C or more, the heat resistance of the resin layer is likely to be good. The melting point of the resin layer is specified by a differential scanning calorimeter (DSC).

[0036] The method for forming the resin layer is not particularly limited, and it can be a layer formed by a known method. For example, a layer can be formed by applying a paint containing the fluororesin, an acrylic resin, and, if necessary, a coloring pigment, an extender pigment, etc. onto a metal member and solidifying it.

[0037] The application of the paint can be carried out by a known method such as roll coating, curtain flow coating, spray coating, dip coating, etc. The application amount of the paint is appropriately adjusted according to the desired thickness of each layer described above.

[0038] Further, the solidification of the paint can be carried out by a known method of baking the paint on the metal member by heating. For example, a method of heating the metal member coated with the paint to about 200 to 260°C can be mentioned. After the paint is solidified, the painted metal member is cooled, but the cooling rate is not particularly limited, and it may be rapidly cooled, for example. Examples of the cooling method include air cooling, water cooling, natural cooling, contact with a cooling member, etc., and these may be combined.

[0039] Incidentally, the above paint may further contain a solvent. The type of the solvent is not particularly limited, and for example, hydrocarbon solvents such as toluene and xylene; ester solvents such as ethyl acetate and butyl acetate; ether solvents such as cellosolve; and any of ketone solvents such as methyl isobutyl ketone, methyl ethyl ketone, isophorone, and cyclohexanone can be used.

[0040] In addition, the above paint may further contain other additives in addition to the solvent. Examples of the additives include a curing agent, a curing catalyst, and the like.

[0041] The curing agent is not particularly limited as long as it can crosslink a fluororesin or an acrylic resin during curing (baking) of the paint. Examples thereof include melamine compounds and isocyanate compounds. Examples of the melamine compounds include imino group type, methylol imino group type, methylol group type, or fully alkyl group type melamine compounds. The isocyanate compound may be any of aromatic type, aliphatic type, and alicyclic type, and examples thereof include m-xylene diisocyanate, hexamethylene diisocyanate, naphthalene diisocyanate, isophorone diisocyanate, and blocked compounds thereof.

[0042] The curing catalyst may be a component that promotes the curing of a fluororesin or an acrylic resin or the above crosslinking, and known compounds can be used.

[0043] After preparing the above coated metal member, the coated metal member is heated to remove cracks generated in the molded portion of the resin layer. In this specification, the molded portion refers to a portion deformed by molding and an area surrounding the same. As described above, when molding is performed, discoloration is likely to occur in the resin layer in these portions. Further, the crack as used in this specification refers to a void having a length of 2 μm or more confirmed when observing a cross section in the thickness direction of the resin layer. Incidentally, the upper limit of the crack length, that is, the upper limit of the crack length that can be removed by the method of the present invention is usually about 20 μm. When observing the cross section in the thickness direction of the coated metal member, the coated metal member may be embedded with an arbitrary embedding resin, cut, and the cross section may be observed.

[0044] The heating time and heating temperature of the painted metal member are not particularly limited as long as the temperature and time do not make the cracks conspicuous. However, from the viewpoint of sufficiently removing the cracks, it is preferable to perform heating until the temperature of the resin layer becomes higher than the softening temperature of the fluororesin in the resin layer.

[0045] However, depending on the heating method, it may be difficult to accurately measure the temperature of the surface of the resin layer. For example, when heating is performed by frame treatment or the like, when the resin layer is irradiated with a flame, it is difficult to accurately measure the temperature of the resin layer. Therefore, when heating is performed at least from the resin layer side, that is, when heating is performed only from the resin layer side or when heating is performed from both sides, the temperature is measured from the metal member side, and the maximum temperature y [° C] of the metal member and the time x [seconds] until the metal member reaches the maximum temperature y [° C] from 20 ° C satisfy the following formula. It is preferable to set the heating time and heating temperature. y ≧ 80x 0.15 (0 <x ≦ 45, y ≦ 300)

[0046] Here, when heating is performed from the resin layer side, the temperature of the metal member and the surface temperature of the resin layer do not necessarily match. When the maximum temperature y [° C] of the metal member and the time x [seconds] until the metal member reaches the maximum temperature satisfy the above formula, even if the temperature of the metal member is low, the surface temperature of the resin layer is higher than the melting point of the resin layer (usually about 130 to 170 ° C), and the cracks are removed as described above. The maximum temperature y [° C] and time x [seconds] of the metal member are derived by measuring the surface temperature from the metal member side from the start to the end of heating.

[0047] Here, the maximum temperature y [° C] of the metal member is more preferably 300 ° C or lower, and even more preferably 200 ° C or lower, from the viewpoint of not deteriorating the resin layer. Further, the time x [seconds] until the metal member reaches the maximum temperature from 20 ° C may be 45 seconds or less, more preferably 35 seconds or less, and even more preferably 20 seconds or less.

[0048] The heating method of the painted metal member is not particularly limited, and for example, heating by an oven or heating by flame treatment may be used. Also, the entire painted metal member may be heated, or only the area where cracks have occurred and its vicinity may be heated. When only the area where cracks have occurred and its vicinity are heated, the temperature of the metal member in the area to be heated is measured.

[0049] Here, when heating in an oven, a known oven for heating the painted metal member can be used, and it is appropriately selected according to the shape of the painted metal member, etc. For example, batch-type or continuous ovens generally called drying ovens can be used. For example, a batch-type drying oven (also referred to as a "safe oven") may be used, and specific examples thereof include a low-temperature thermostat (model Mini Catalina MRLV-11) manufactured by Isuzu Manufacturing Co., Ltd., an automatic discharge type dryer (model ATO-101) manufactured by Togami Thermal Science Co., Ltd., and a simple explosion-proof dryer (model TNAT-1000) manufactured by Togami Thermal Science Co., Ltd.

[0050] When heating in an oven, not only heating from the heat source but also heating by warm air or hot air may be carried out in combination to adjust the temperature rise rate of the painted metal member, etc.

[0051] On the other hand, when heating the painted metal member by flame treatment, it is preferable to place the painted metal member on a conveyor such as a belt conveyor and move it in a certain direction while radiating a flame with a burner for flame treatment. At this time, the radiation of the flame is preferably performed on the resin layer.

[0052] Here, the flame treatment amount is preferably 100 to 600 kJ / m 2 is preferable. The "flame treatment amount" in this specification is the amount of heat per unit area of the metal member calculated based on the supply amount of combustion gas such as LP gas. The flame treatment amount can be adjusted by the distance between the burner head of the burner for flame treatment and the surface of the resin layer, the conveyance speed of the resin layer, etc. When the flame treatment amount is 100 kJ / m 2 or more, the surface of the resin layer is likely to be uniformly treated. On the other hand, when the flame treatment amount is 600 kJ / m2 The resin layer is less likely to turn yellow under the following conditions.

[0053] (Use of the coated metal member) The use of the coated metal member manufactured by the above method is not particularly limited, and it can be used for a wide variety of members and applications that use metal members. As described above, according to the manufacturing method of the present invention, a coated metal member with few cracks and high design quality can be obtained in the formed portion. Therefore, the coated metal member can be used for various applications that require design quality.

[0054] Examples of uses include interior decorative building materials such as roofs, walls, partitions, doors, ceiling materials, floor materials, elevator doors, and elevator interior panels for housing; various housing facilities such as range hoods and bathroom interior members; furniture such as desks, chairs, lockers, and shelves; home appliances such as refrigerator exteriors, microwave oven exteriors, computer casings, and air conditioner casings; and vehicle members such as automobile interiors and railway vehicle interiors. However, the uses of the coated metal member are not limited to these.

Examples

[0055] Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited by these examples.

[0056] 1. Preparation of the coated metal member (1) Formation of the resin layer As the metal members, SGEL (registered trademark) manufactured by Nippon Steel & Sumitomo Metal Corporation (thickness 0.27 mm, double-sided plating adhesion amount 120 g / m 2 , hereinafter also referred to as "SGL") and galvanized steel sheet (registered trademark) manufactured by Nippon Steel & Sumitomo Metal Corporation (thickness 0.27 mm, double-sided plating adhesion amount 120 g / m 2 , hereinafter also referred to as "GL") were used. After degreasing these metal members with alkali, a coating-type chromate treatment was carried out. A modified epoxy resin-based primer (manufactured by Nippon Paint Industrial Coatings Co., Ltd., Uniflon 600) was applied to these metal members with a roll coater so that the dry film thickness became 5 μm, and baked to a maximum plate temperature of 215 °C to form an undercoat layer.

[0057] On the one hand, as the fluororesin, polyvinylidene fluoride (manufactured by Arkema, Kynar500, hereinafter also referred to as "fluororesin A") was prepared. Further, as the fluororesin, a copolymer resin of 1,1-difluoroethylene (VDF) and hexafluoropropylene (HFP) (manufactured by Arkema, KynarFlexLBG, hereinafter also referred to as "fluororesin B") was prepared.

[0058] Furthermore, as the acrylic resin, a polymer containing methyl methacrylate (MMA) and ethyl acrylate (EA) in a weight ratio of 70 / 30 was synthesized and prepared by a conventional method. As the pigment particles, composite oxide pigments (manufactured by Dainichi Seika Kogyo Co., Ltd., DiPyroxide Black #9596, average particle diameter: 0.7 μm, hereinafter also referred to as "pigment A") were prepared. Also, as the pigment particles, composite oxide pigments (manufactured by Dainichi Seika Kogyo Co., Ltd., DiPyroxide Blue #9453, average particle diameter: 0.7 μm, hereinafter also referred to as "pigment B") were prepared.

[0059] As shown in Table 1 and Table 2, the above fluororesin (fluororesin A or fluororesin B) and acrylic resin were blended at a ratio of 50% by mass to 80% by mass: 50% by mass to 20% by mass. Further, a pigment (pigment A or pigment B) in an amount of 25% by mass based on the total mass of the solid content was blended and mixed to prepare a topcoat paint. Then, it was baked for 60 seconds so that the maximum reached plate temperature was 250°C, and a resin layer was formed on the metal member (SGL or GL) and the undercoat layer.

[0060] (2) Molding process Thereafter, with respect to the metal member formed with the resin layer, using an Erichsen tester in accordance with JIS K5600-5-2, extrusion processing was performed at a processing temperature of 23°C and a drawing height of 6 mm. The formed processing part of the obtained painted metal member was visually observed. As a result, annular cracks (whitening) as shown in Fig. 2A occurred in the Erichsen processing part (formed processing part). In addition, in this region, when observing the cross-section in the thickness direction, a large number of cracks with a length of 2 μm or more occurred. An enlarged photograph taken with a scanning electron microscope of the whitened part is shown in Fig. 2B, and a photograph taken of the cross-section in the thickness direction is shown in Fig. 2C.

[0061] 2. Removal of cracks by heating The above-mentioned painted metal member was subjected to frame treatment or heat treatment in an oven as follows. The maximum temperature y [°C] of the metal member and the time x [seconds] until the metal member reached the maximum temperature are shown in Table 1 and Table 2. The temperature x [°C] of the metal member was measured from the metal member side with a non-contact temperature sensor.

[0062] In addition, Fig. 3A shows a photograph of the painted metal member shown in Fig. 2A after frame treatment, Fig. 3B shows a photograph taken with a scanning electron microscope of the formed processing part (the same position as Fig. 2B) after frame treatment, and Fig. 3C shows a photograph taken of the cross-section in the thickness direction.

[0063] (Frame treatment) The above-mentioned painted metal member was placed on a conveyor and frame treatment was performed on the resin layer. An F-3000 manufactured by Flynn Burner (USA) was used as the frame treatment burner. In addition, as the combustible gas, a mixed gas (LP gas: clean dry air (volume ratio) = 1:25) obtained by mixing LP gas (combustion gas) and clean dry air with a gas mixer was used. Also, the flow rate of each gas was 1 cm at the flame outlet of the burner. 2The LP gas (combustion gas) was adjusted to 1.67 L / min and the clean dry air was adjusted to 41.7 L / min. The length of the flame outlet of the burner head in the conveying direction of the painted metal member was set to 4 mm. On the other hand, the length of the flame outlet of the burner head in the direction perpendicular to the conveying direction was set to 450 mm. Furthermore, the distance between the flame outlet of the burner head and the surface of the resin layer was adjusted, and the maximum temperature y [°C] reached by the metal member and the time x [seconds] required for the metal member to reach the temperature y [°C] from 20 °C were adjusted.

[0064] (Heating by oven) The above-mentioned painted metal member was placed on a conveyor and heated for a predetermined time in an oven (automatic discharge type dryer (model ATO-101) manufactured by Togami Thermal Science Co., Ltd.) set to a desired temperature. The maximum temperature y [°C] reached by the metal member and the time x [seconds] required for the metal member to reach the temperature y [°C] were adjusted according to the set temperature of the oven and the hot air blowing speed in the oven.

[0065] 3. Evaluation The painted metal member with cracks after the above heating was visually observed, and whether the cracks (whitened parts) were removed was confirmed according to the following criteria. 〇: The reduction in the whitened area was 70% or more. ×: The reduction in the whitened area was less than 70%.

[0066]

Table 1

[0067]

Table 2

[0068] As shown in Table 1 and Table 2 above, the maximum temperature y (°C) of the metal member and the time x (seconds) required for the metal member to reach the maximum temperature satisfy y ≧ 80 × x. 0.15When heat-treated by frame treatment or in an oven to meet the requirements, the cracks (whitening) generated in the molding section could be eliminated. Also, in the painted metal member after frame treatment as shown in FIGS. 3A and 3B, the voids (cracks) generated in the molding section had been eliminated.

Industrial Applicability

[0069] According to the method for manufacturing a painted metal member of the present invention, a painted metal member with few cracks in the molding section of the resin layer and high design quality can be obtained. The painted metal member is applicable to various fields.

Explanation of Reference Numerals

[0070] 10 Metal member 11 Steel plate 12 Plating layer 20 Resin layer

Claims

1. A method for manufacturing a coated metal member having a metal member and a resin layer disposed on the metal member and containing an acrylic resin and a fluororesin, wherein a step of forming the resin layer on the metal member; a step of shaping the metal member on which the resin layer is formed; a step of heating a shaped portion of the coated metal member on which the resin layer is formed, in this order, and the fluororesin contains a polyvinylidene resin, in the resin layer, the mass ratio of the fluororesin and the acrylic resin is 40:60 to 85:15, and in the step of heating the shaped portion, the maximum temperature y [°C] of the metal member and the time x [seconds] for the metal member to reach the maximum temperature y from 20°C satisfy the following formula: y ≧ 80x^0.15 (1 ≦ x ≦ 45, y ≦ 200) A method for manufacturing a coated metal member.

2. The step of heating the shaped portion is a step of performing a frame treatment on the resin layer side. The method for manufacturing a coated metal member according to Claim 1. The method for manufacturing a coated metal member according to Claim 1.

3. The step of shaping the metal member and the resin layer is a step of performing one or more processes selected from the group consisting of bending, drawing, roll forming, and embossing. The method for manufacturing a coated metal member according to Claim 1. The method for manufacturing a coated metal member according to Claim 1.

4. The metal member is a plated steel sheet having a plating layer, and the plating layer contains Al, Zn, and Mg. The method for manufacturing a coated metal member according to any one of Claims 1 to 3. ​

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