KR20160138978A - Coated Steel Sheet, Method for Producing Same and Member for Cooking Utensils - Google Patents

Abstract

The coated steel sheet 10 is composed of the steel sheet 11 and the overcoat film 14 superimposed in this order. The overcoat film 14 includes a polyimide 141 and a cured silicone 144. The occupied area ratio of the cured silicone 144 on the surface of the overcoat film 14 is 5% or more. The coated steel sheet 10 is excellent in both heat resistance and antifouling performance, and can be suitably used as a material for a cooking device member.

Description

Coated Steel Sheet, Method for Producing Same and Member for Cooking Utensils,

The present invention relates to a coated steel sheet excellent in heat resistance and antifouling performance, a method for producing the same, and a member for a cooking appliance including the coated steel sheet.

Recently, a microwave oven for supplying water vapor to a heating chamber has been developed. The heating chamber is generally composed of a coated steel sheet having heat resistance and food resistance (hereinafter also referred to as " contamination preventing performance "). The coated steel sheet can be obtained, for example, by coating a plated film mainly composed of a metal plate, polyethersulfone, and a coating film containing a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) (For example, refer to Patent Document 1).

Patent Document 1: Japanese Patent Application Laid-Open No. 2005-262465

The coated steel sheet is excellent in both heat resistance and antifouling performance. However, recently, a microwave oven capable of cooking at a higher temperature has been developed and supplied to the market. For this reason, the coated steel sheet used for such a cooking apparatus is required to have a further improved heat resistance.

The present invention has been made in view of the above points, and it is an object of the present invention to provide a coated steel sheet having both heat resistance and antifouling performance of a further layer. It is a further object of the present invention to provide a member for a cooking apparatus including the coated steel sheet.

The present inventors have found that by combining specific silicon with polyimide, silicon is appropriately dispersed and exposed on the surface of the coating film of polyimide and that this coating film is used for the coating film of the coated steel sheet, . ≪ / RTI > Further, the present invention was completed by further study.

That is, the present invention relates to the following coated steel sheet.

[1] A coated steel sheet having a coated film on a steel sheet, wherein the coated film comprises a coating film to be overlaid, wherein the coated film comprises polyimide and cured silicone, and the occupied area ratio of the cured silicon on the surface of the coated film is 5% Or more, painted steel plate.

[2] The coated steel sheet according to [1], wherein the content of the cured silicone in the overcoat film is 1 to 10 parts by mass relative to 100 parts by mass of the polyimide.

[3] The coated steel sheet according to [1] or [2], wherein occupancy area ratio of the cured silicone on the surface of the overcoat film is 5 to 70%.

[4] The coated steel sheet according to any one of the items [1] to [3], wherein the surface of the overcoat film has a sea-island structure with the polyimide and the cured silicone.

[5] The coated steel sheet according to [4], wherein the shape of the island of the cured silicone is substantially circular, and the area of each island of the cured silicone is 300 m ² or less.

[6] The method according to any one of the preceding claims of [1] to [5], the peak intensity of 1014cm ^-1 to the surface of the topcoat film to a peak intensity of 1375cm ^-1 as measured by infrared spectroscopic analysis by ATR method Let A be the ratio,

When measuring the topcoat film by infrared spectroscopy by KBr method, when defined as a ratio of a peak intensity of 1014cm ^-1 to a peak intensity of 1375cm ^-1 B,

Wherein the ratio of A to B is 1.1 to 100.

[7] The coated steel sheet according to any one of [1] to [6], wherein the Tg of the polyimide is 270 to 400 ° C.

The present invention also relates to a method for producing a coated steel sheet as described below.

[8] A method of manufacturing a coating film, comprising the steps of: applying a coating material to a coated original plate including a steel sheet to form an overcoat layer; and heating the overcoat layer to heat the coated original plate to form an overcoat film, Wherein the coating material contains a polyimide precursor, a curable silicone and a solvent, wherein the content of the curable silicone with respect to 100 parts by mass of the polyimide precursor in the overcoating paint is 1.0 part by mass or more, and at least a part of the curable silicone And the overcoat layer is lifted so that an arrival temperature of the steel sheet is 180 占 폚 or higher to form the overcoat film.

[9] The method for producing a coated steel sheet according to [8], wherein the coating time is from 5 to 60 seconds after the coating material is applied to the coated original plate and the heating is started.

[10] The method of producing a coated steel sheet according to [8] or [9], wherein the time from the start of heating to the arrival of the temperature reaches 30 to 240 seconds.

[11] A method for producing a coated steel sheet according to any one of the items [8] to [10], wherein the steel sheet has an arrival temperature of 200 ° C or higher.

[12] A method for producing a coated steel sheet according to any one of the items [8] to [11], wherein the overcoating paint is applied so that the film thickness of the overcoat film is 2 to 20 占 퐉.

[13] A production method of a coated steel sheet according to any one of the items [8] to [12], wherein the content of the curable silicone in the over coating is 1 to 10 parts by mass relative to 100 parts by mass of the polyimide precursor.

[14] A method for producing a coated steel sheet according to any one of the items [8] to [13], wherein the steel sheet has a chemical conversion coating on its surface

Further, the present invention relates to a member for a cooking apparatus including the above coated steel sheet.

The coated steel sheet according to the present invention can exhibit higher heat resistance and equivalent or higher contamination preventing performance than the conventional coated steel sheet in which the fluororesin is exposed. Therefore, the coated steel sheet according to the present invention can be suitably used for a member for a cooking apparatus used at a higher temperature.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a view schematically showing the structure of a coated steel sheet according to an embodiment of the present invention; FIG.
Fig. 2 (A) is a diagram schematically showing the behavior of components in the overcoat layer, Fig. 2 (B) is a diagram schematically showing a state in which cured silicone is dispersed on the surface of the overcoat layer, Is a diagram schematically showing a state in which cured silicon is collected on the surface of the overcoat layer.
3 (A) is an electron micrograph showing a reflected electron image obtained by photographing the surface of a coated film to be coated in the coated steel sheet 3 of the embodiment by a scanning electron microscope, (B) An electron micrograph showing a reflected electron image taken by a microscope.
4 is a diagram schematically showing the sea water structure in a coating film to be applied and the liquid contaminants attached to the coating film.

A coated steel sheet according to the present invention has a coated film on a steel sheet. The coating film may be a top coating film, for example, as long as it includes a coating film to be described later. The coating film may further include, for example, a coating film formed on the surface of the steel sheet or a coating film formed on the surface of the coating film. For example, as shown in Fig. 1, the coated steel sheet 10 according to the present invention has a structure in which the steel sheet 11, the chemical conversion coating film 12, the undercoat film 13, and the overcoat film 14 are stacked in this order Respectively. The undercoating film 13 is mainly composed of a resin 131 and may include additives 132 such as various pigments as described later. The overcoat film 14 is mainly composed of polyimide 141 and may include additives such as aluminum particles 142 and inorganic additive 143 as described later. Also, the overcoat film 14 comprises at least the cured silicon 144 present on its surface.

[Steel plate]

The steel sheet can be appropriately selected from known steel sheets in accordance with the intended use and the desired characteristics of the coated steel sheet. Examples of the steel sheet include galvanized steel sheets (electric Zn plating, molten Zn plating), galvanized galvanized steel sheets (galvannealed Zn-plated alloyed with Zn after galvanization), zinc alloy plated steel sheets (galvanized Zn- Al-Mg plating, molten Zn-Al plating), molten Al-plated steel sheet, molten Al-Si plated steel sheet, stainless steel sheet, and molten Al-plated stainless steel sheet. From the viewpoint of improving the corrosion resistance in a high-temperature environment, a molten Al-coated steel sheet, a fused Al-Si coated steel sheet, or a stainless steel sheet is preferable. From the standpoint of further enhancing the corrosion resistance and reflection efficiency of microwaves, .

[Chemical conversion film]

The steel sheet may have a chemical conversion coating film from the viewpoint of improving corrosion resistance and coating film adhesion of the coated steel sheet. The chemical conversion coating is a thin layer formed by a coating process. Examples of the chemical treatment include a chromate treatment, a chrome-free treatment, and a phosphate treatment. The deposition amount of the chemical conversion coating can be appropriately determined within a range effective for improving the corrosion resistance and the coating film adhesion. For example, the amount of deposition of the chromate film is such that the total amount of Cr converted coating becomes 5 to 100 mg / m ² . Further, in terms of Cr-free coatings, for example, Ti-Mo coating weight of the composite coating film is the amount of the total Ti and Mo in terms of coating weight being 10 ~ 500mg / m ^2, the fluorine acid coating weight of the total coating is fluorine terms of coating weight or the total metallic elements The amount of adhesion is 3 to 100 mg / m ² . In addition, the amount of deposition of the phosphate coating is such that the conversion amount in terms of phosphorus is 0.1 to 5 g / m ² .

The chemical conversion coating can be formed by a known method. For example, the chemical conversion treatment liquid may be applied to the surface of a steel sheet by a roll coating method, a spin coating method, a bar coating method, a spraying method or the like, and dried without washing with water. The drying temperature and the drying time are not particularly limited as long as moisture can be evaporated. From the viewpoint of productivity, the drying temperature is preferably 60 to 150 DEG C at the arrival temperature of the steel sheet, and the drying time is preferably 2 to 10 seconds.

[Undercoat]

The coated steel sheet may further have an undercoating film on the surface of the steel sheet or the surface of the chemical conversion coating film from the viewpoint of improving the corrosion resistance and coating film adhesion of the coated steel sheet. Normally, the undercoat film contains a resin as a base and a rust preventive pigment. The resin of the undercoating film may be the same as or different from the resin as the base of another coating film such as an overcoat film. Examples of the kinds of the resin of the undercoating film include inorganic resins such as polyester resin, epoxy resin, acrylic resin, phenoxy resin, and silicate resin. Examples of the types of the rustproof pigments include magnesium phosphate, zirconium phosphate, zinc phosphate, aluminum tripolyphosphate, zinc phosphomolybdate, barium borate and silica-based compounds.

The undercoating film may further contain other components. For example, the undercoating film may contain a crosslinking agent for crosslinking the organic resin. Examples of the kind of the cross-linking agent include a melamine resin and an isocyanate resin. The undercoating film may further contain a coloring pigment, a metallic pigment or an extender pigment. Examples of colored pigments include titanium oxide, carbon black, chromium oxide, iron oxide, red iron oxide, titanium yellow, cobalt blue, cobalt green, aniline black and phthalocyanine blue. Examples of metallic pigments include aluminum flakes (non-leafing type), bronze flakes, copper flakes, stainless steel flakes and nickel flakes. Examples of extender pigments include barium sulfate, silica and calcium carbonate.

The undercoat film may contain a pigment dispersant. Examples of the pigment dispersant include a solution of a polyaminoamide of an unsaturated carboxylic acid (solvent is, for example, alkylbenzene / ethylene glycol monobutyl ether = 5/1), an amine salt of a polyetherester acid, and a low molecular polyester Based compounds.

The film thickness of the underlying coating is, for example, 0.5 to 30 μm.

[Coating film]

The coated film constitutes the surface of the coated steel sheet. Coating films include polyimide and cured silicone.

[Polyimide]

The number of the polyimides may be one or two or more. It is preferable that the polyimide includes an aromatic group in the main chain from the viewpoint of enhancing the heat resistance and the strength of the overcoat film. The glass transition temperature (Tg) of the polyimide is generally from 270 to 400 캜, more preferably from 300 to 380 캜, still more preferably from 320 to 360 캜, from the viewpoints of heat resistance and adhesion. The Tg of the polyimide can be measured by a dynamic viscoelastic (dynamic viscoelastic) measuring apparatus.

The polyimide is obtained by curing a reaction product (polyimide precursor) by mixing a diamine and a tetracarboxylic acid dianhydride in a solvent. The glass transition point (Tg) of the polyimide can be designed according to the combination or content ratio of the diamine and tetracarboxylic dianhydride to be used. Examples of suitable diamines for preparing a polyimide having a Tg of 270 to 400 占 폚 include para diamine such as 4,4'-oxydiaminobenzene (4,4'-diaminodiphenyl ether) Diamines or diamines whose amino group is in the meta position, such as 1,3-bis- (3-aminophenoxy) benzene and 4,4'-bis- (3-aminophenoxy) biphenyl . Among them, it is preferable that the diamine includes 4,4'-oxydiaminobenzene (4,4'-diaminodiphenyl ether) or 4,4'-bis- (3-aminophenoxy) biphenyl . Examples of the tetracarboxylic dianhydride that is preferable for preparing the polyimide of Tg include pyromellitic anhydride (1,2,4,5-benzene tetracarboxylic dianhydride), 3,3 ', 4,4'-benzo Phenone tetracarboxylic dianhydride, and 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride. Among them, it is preferable that the tetracarboxylic dianhydride includes 3,3 ', 4,4'-benzophenonetetracarboxylic dianhydride.

[Cured silicone]

The cured silicone is silicon cured by heat or the like during the heat treatment of the overcoat film. The cured silicone is obtained by thermal curing or the like of the curable silicone which will be described later.

If the content of the cured silicone in the coating film to be overlaid is too small, the cured silicone located on the surface of the coating film to be overlaid may be peeled off early due to repeated use of the coated steel sheet. For this reason, it may become difficult to maintain the pollution prevention performance over a long period of time. If the content of the cured silicone in the overcoat film is too large, the uncured silicone may be contained in the cured silicone. For this reason, stickiness occurs on the surface of the overcoat film, and the workability of the coated steel sheet may be lowered due to this sticking. If the content of the cured silicone in the overcoat film is too large, the adhesion of the cured silicone in the overcoat film becomes insufficient due to the difference in the coefficient of linear expansion between the polyimide and the cured silicone at high temperatures, have. For this reason, there are cases where the contamination preventing performance of the coated steel sheet becomes insufficient. From this point of view, the content of the cured silicone in the overcoat film is preferably 1 to 10 parts by mass, more preferably 2 to 6 parts by mass with respect to 100 parts by mass of the polyimide.

The overcoat film may further contain other components within the range in which the effect of the present invention can be obtained. Examples of other components include aluminum particles, the above-mentioned coloring pigments, pigment dispersants, and inorganic additives.

The aluminum particles are compounded in the overlay paint in order to impart design (metallic feeling) to the overcoat coat. The purity of aluminum in the aluminum particles is not particularly limited. For example, the aluminum particles may be composed solely of aluminum or may be composed of an aluminum-based alloy. Examples of the shape of the aluminum particles include scaly (flaky), granular, platy, and agglomerated forms. From the viewpoint of imparting metallic feeling to the coated film, it is preferable that the aluminum particles have a scaly shape. The content of aluminum particles in the coated film is, for example, 0.1 to 50 parts by mass based on 100 parts by mass of the polyimide.

The inorganic additive may be incorporated in the overcoat paint to improve the hardness and abrasion resistance of the overcoat film. Examples of the inorganic additive include scaly inorganic additives such as glass flakes, graphite flakes, synthetic mica flakes and silica flakes, and inorganic fillers such as potassium titanate fiber, wollastonite fiber, silicon carbide fiber, alumina fiber, alumina silicate fiber, , Rock wool, slag wool, glass fiber, and carbon fiber.

Though the thickness of the coating film to be applied is not particularly limited, if the coating film is too thin, the heat resistance and the antifouling performance of the coated steel sheet may be insufficient. If the coating film is too thick, heat resistance and antifouling performance can be sufficiently obtained. And the workability of the coated steel sheet may be deteriorated. From this viewpoint, the film thickness of the overcoat film is preferably 2 to 20 占 퐉, more preferably 3 to 15 占 퐉, and still more preferably 5 to 10 占 퐉.

The occupied area ratio of the cured silicone on the surface of the coated film to be coated is 5% or more. If the occupied area ratio is less than 5%, the contamination prevention effect of the Lotus effect described later may become insufficient. If the occupied area ratio is too large, the cured silicone may peel off from the coated film due to the difference in the coefficient of linear expansion between the polyimide and the cured silicone at high temperatures, as described above, and the contamination preventing performance of the coated steel sheet may become insufficient. From this viewpoint, the occupied area ratio is preferably 5 to 70%.

It is preferable that the surface of the coating film to be overlaid includes a sea-island structure of polyimide and cured silicone. On the other hand, "sea" means a continuous phase on the surface of the coating film to be applied, and "island" means a dispersed phase (dispersed phase) on the surface of the coating film to be coated. The polyimide may be "sea" or "island" of the sea-island structure, and the cured silicone may be "figure" or "sea" of the sea-island structure. Among the above sea-island structures, the sea-island structure in which the polyimide is the "sea" and the cured silicone is the "sea" is preferable from the viewpoint of preventing occurrence of stickiness caused by too much content of the cured silicone, Do.

The island is almost circular, and the area of each island is 300 μm ² Or less, from the viewpoint of the above. Regarding the shape of the island, "substantially circular" means that the ratio of the major axis to the minor axis is 0.9 to 1.1. As for the ratio of the substantially circular islands, the shape of the islands may be represented by the above-mentioned " almost circular ". For example, 80% or more of the islands are substantially circular It is good.

The arrangement of the cured silicon on the surface of the coating film to be overlaid can be confirmed by a reflection electron image using a scanning electron microscope (SEM) shown in Fig. 3 (A). The occupied area ratio, the shape of the islands and the area of the islands can be obtained by image processing of this reflected electron image.

It is preferable that the coating film to be coated has a ratio (A / B) of the following A to B below from 1.1 to 100. Here, "A" is defined as the ratio of the peak intensity of 1014cm ^-1 to a peak intensity of 1375cm ^-1, as measured for the surface of the topcoat film by infrared spectroscopic analysis by ATR method. In addition, the ratio of, the peak intensity of 1014cm ^-1 to a peak intensity of 1375cm ^-1, as measured by "B" refers to the topcoat film-infrared spectroscopy by KBr method. In both of A and B, the peak intensity at 1014 cm ^-1 is derived from silicon atoms (Si-O-Si) and indicates the amount of cured silicon present in the coating film to be overlaid. The peak intensity at 1375 cm ^-1 is derived from the nitrogen atom (CN) and indicates the amount of polyimide present in the coating film to be overlaid.

The above peak intensity is measured by infrared spectroscopy, for example, FT-IR, in which the intensity of the peak is detected. The ATR method is a method of performing infrared spectroscopy on the surface as is well known. The KBr method is a method for purifying KBr in which slices of a coating film to be coated are uniformly dispersed or a sample in which the slice is sandwiched between plates of KBr as a sample to perform infrared spectroscopic analysis. In the KBr method, the slice of the overcoat film may be peeled off or the overcoat film may be cut to a depth of 80% or more of the thickness of the coating film to be applied from the surface thereof. Alternatively, when an overcoat film is to be produced, it is possible to use a separately prepared overcoat film sample.

When the ratio A / B is less than 1.1, it means that the cured silicone is uniformly dispersed in the coating film to be coated. Therefore, when the ratio A / B is less than 1.1, the amount of the cured silicone appearing on the surface of the coating film to be overlaid may become insufficient. For this reason, there is a case that the contamination preventing performance of the coated steel sheet can not be sufficiently obtained. In addition, the amount of the cured silicone present in the coating film to be overlaid increases, so that the adhesion of the overcoat film is lowered, and the overcoat film may peel off. On the other hand, if the ratio A / B is more than 100, the amount of the cured silicone increases in the vicinity of the surface of the overcoat film, and the above-mentioned peeling and the dirt- There may be a drop.

The above-mentioned A is preferably 0.1 to 1.0 from the viewpoint of exhibiting both the partial peeling prevention of the coating film and the antifouling performance in the above-mentioned overcoating film. If A is less than 0.1, the antifouling performance may be insufficient. If A is more than 1.0, the above-mentioned overcoating film may partially peel off. The above-mentioned B is usually 0.01 to 0.09, though not particularly limited, since the cured silicone is usually localized on the surface of the coating film to be coated.

[Manufacturing method of painted steel sheet]

Wherein the coated steel sheet comprises a first step of applying an overcoating paint to a coated original plate including a steel sheet to form an overcoat paint layer, and a second step of forming an overcoat layer by heating the overcoat layer, And the like. This manufacturing method may further include other steps as long as the effect of the present invention can be obtained.

[First Step]

The coated base plate may be a steel plate itself, a steel plate having the above-mentioned chemical conversion coating, or a steel plate having the above-mentioned base coat. The undercoating film can be produced by applying the undercoat paint to the surface of the steel sheet or the chemical conversion coating film and heat-treating the same.

The undercoating material is prepared, for example, by mixing a solvent and a material such as the resin of the above-mentioned undercoating film, the precursor thereof, or an additive.

The solvent may be one kind or two kinds or more. Examples of the solvent include N-methyl-2-pyrrolidone (NMP), N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMAc), N, N-dimethylimidazolidinone DMI), and methyl isobutyl ketone (MIBK); Ethers such as diethylene glycol dimethyl ether (DMDG) and diethylene glycol diethyl ether (DEDG); Halogenated aliphatic hydrocarbons such as methylene chloride and carbon tetrachloride; Hydrocarbons such as xylene; And alcohols.

The undercoat can be applied by a known method such as a roll coating method, a flow coating method, a curtain flow method, a bar coating method, and a spraying method. The heat treatment temperature of the undercoating film is preferably, for example, a temperature at which the steel sheet reaches a temperature of 150 to 400 ° C, and the heat treatment time is preferably 30 to 180 seconds.

The overlay paint contains a polyimide precursor, a curable silicone, and a solvent. The overcoating paint may further contain other components such as the above-mentioned aluminum particles. The polyimide precursor is a polymer constituting the coating film to be applied by heating or the like in the second step. For example, the polyimide precursor may be a polymer that becomes the polyimide by thermal cyclization or polyimide dissolved in the over coating to be. Namely, examples of the polyimide precursor include a polyamic acid and a soluble polyimide.

The curable silicone is composed of, for example, silicon and functional groups composed of structural units of siloxane. These functional groups are bonded to silicon or functional groups by heat, active energy rays, catalysts, or the like. Examples of the functional group include a group having a carbon-carbon double bond such as a vinyl group or a (meth) acryloyl group, a hydroxysilyl group such as a monohydroxy silyl group, an alkoxysilyl group such as a methoxysilyl group, a hydroxyl group, , A phenol group, an epoxy group, an amino group, and an isocyanate group.

If the molecular weight of the curable silicone is too small, the curability of the silicone tends to deteriorate. If the molecular weight is too large, the viscosity tends to rise and the silicone may not sufficiently appear on the surface of the applied coating film. From this viewpoint, the number of the structural units of the siloxane in the curable silicone is preferably 2 to 5000, more preferably 10 to 2000. The number of the structural units can be measured by a gel permeation chromatograph (GPC).

The equivalent (g / mol) of the functional group in the curable silicone is preferably 2 to 60,000, more preferably 10 to 30,000, from the viewpoint of reactivity. The equivalent amount of the functional group can be measured by, for example, nuclear magnetic resonance spectroscopy (NMR).

Examples of the curable silicone include various modified silicones. Examples of the modified silicone include amino group-modified silicone, carbinol-modified silicone, methacryl-modified silicone, vinyl-modified silicone, silanol-modified silicone, phenol- , Isocyanate-modified silicone, and polyether-modified silicone. Polyether-modified silicone is particularly preferable from the viewpoint of resistance to food stains over a long period of time.

The solvent may be one or more. The solvent is used from the viewpoints of improving the compatibility between the polyimide precursor and the curable silicone and adjusting the viscosity of the overcoat paint. As the solvent for the overcoat paint, the same solvent as the solvent for the undercoat can be used. The amount of the solvent for the over coating may be one or more, and may be the same as or different from the solvent for the undercoat. The overcoating paint can be applied to the surface of the steel sheet, the chemical conversion coating film or the undercoating film by the same method as the coating method of the undercoating paint.

The content of the curable silicone with respect to 100 parts by mass of the polyimide precursor in the overlay paint is 1.0 part by mass or more. If the content is less than 1.0 part by mass, the occupied area ratio of the cured silicone may be less than 5% on the surface of the overcoat film. As described above, the content of the curable silicone in the overcoat paint is preferably from 100 parts by mass to 100 parts by mass in terms of preventing the deterioration of the antifouling performance by repeated use and the deterioration of the antifouling performance due to the partial peeling of the overcoat film Is preferably 1 to 10 parts by mass, more preferably 2 to 6 parts by mass.

The overcoating paint is preferably applied to the steel sheet, the chemical conversion coating film or the undercoat film so that the thickness of the overcoat film is 2 to 20 占 퐉. The thickness of the applied coating film can be adjusted by the thickness of the overcoat layer (coating amount of the coating material). The thickness of the overcoat layer can be adjusted by the viscosity of the overcoat paint, the application method of the paint, the number of coatings of the paint, and the like.

[Second Step]

In the second step, the overcoating layer on which at least a part of the curable silicone is floated on the surface thereof is heated so that the reaching temperature of the steel sheet is 180 占 폚 or higher, thereby forming a coating film to be overlaid. Here, the " overcoat layer in which at least a part of the curable silicone is floated on its surface " refers to the layer in which a part of the curable silicone appears on the surface thereof, and a part of the curable silicone is about to reach the surface But also the corresponding layer (substantially corresponding to the layer which is said to appear on the surface) which has not yet appeared on the surface.

When the curable silicone has a thermosetting property, it is possible to cure the curable silicone together with the imidization of the polyimide precursor by the above-mentioned heating. When the curable silicone does not have the above-mentioned thermosetting property, the manufacturing method may include another step of curing the curable silicone. For example, when the curable silicone has photo-curability, it is possible to cure the curable silicone by further irradiating light to the polyimide film formed by the heating process in addition to the above-mentioned heating process. When the curable silicone is cured by both heat and light, the manufacturing method may further include a step of irradiating the surface of the coating film to be cured with light for curing the curable silicone after the heating step . In this case, it is preferable from the viewpoint of sufficiently curing the curable silicone on the surface of the applied coating film. Examples of light to be irradiated include ultraviolet rays.

If the ultimate temperature is less than 180 캜, even if the curable silicone has a thermosetting property, the curing of the curable silicone is insufficient and sticky to the overcoat film occurs, and the processability of the coated steel sheet May be lowered. In addition, peeling and deterioration of the antifouling performance may be caused by a difference in coefficient of linear expansion between the polyimide and the curable silicone under high temperature. When the temperature reaches 200 占 폚 or higher, it is more preferable from the viewpoint of rapid polyimide formation of the polyimide precursor.

The cured silicone is appropriately displayed on the surface of the coating film to be overlaid by further heating the overcoat layer to the temperature of arrival, Polyimidization of the precursor and thermal curing of the curable silicone are performed to form the above-mentioned over coating film. The amount by which the curable silicone floats in the layer can be adjusted by the heating rate after forming the overcoating layer, the waiting time until the heating, or the arrival temperature. That is, the curable silicone may be floated while heating the overcoat layer, or may be quickly heated so as to maintain the state after the curable silicone is sufficiently floated in the overcoat layer. The latter is preferable from the viewpoint of stably realizing the desired distribution of the curable silicone in the coating film to be overlaid.

In the case of the former, it is preferable to set the time (heating time) from the application of the overcoat paint to the coated original plate until the temperature of the steel sheet reaches the above-mentioned reached temperature in the range of 30 to 240 seconds to control the distribution of the curable silicone . If the heating time is less than 30 seconds, the amount of the curable silicone appearing on the surface of the coating film to be overlaid may become insufficient. If the heating time exceeds 240 seconds, the amount of the curable silicone appearing on the surface of the applied coating film may be excessively large. From this viewpoint, the heating time is more preferably 30 to 240 seconds.

In the latter case, it is preferable that the time (waiting time) from the application of the overcoating paint to the original plate to the start of heating is 5 to 60 seconds. If the waiting time is less than 5 seconds, the curable silicone does not sufficiently appear on the surface of the overcoat layer, and the amount of the curable silicone present in the layer may increase. In this case, as described above, the adhesion of the overcoat film may deteriorate and the overcoat film may peel off. When the waiting time exceeds 60 seconds, substantially all of the curable silicone appears on the surface of the coating layer to be overlaid, and peeling and deterioration of the antifouling performance are caused due to the difference in coefficient of linear expansion between the polyimide and the cured silicone under high temperature have. The waiting time can be adjusted, for example, by using the conveying speed of the steel sheet between the coating device of the over coating material and the heating device of the steel sheet.

It is preferable that the heating time in the latter case, that is, the time from the waiting time to the temperature of the steel sheet until reaching the reached temperature is 30 to 180 seconds from the viewpoint of the electron heating time, Is more preferable.

Fig. 2 (A) is a diagram schematically showing the behavior of components in the overcoat layer. In the overcoat layer 31, the solvent 311 represented by triangle (?) Is evaporated as shown in FIG. 2A, and the curable silicone (represented by a circle in FIG. 2A) 312) migrate toward the surface of the layer due to the difference in surface free energy with the base resin (polyimide precursor). At this time, it is considered that droplet particles of the curable silicone aggregate and move toward the surface of the layer.

2B is a diagram schematically showing a state in which curable silicone is dispersed on the surface of the overcoat layer. As shown in FIG. 2 (B), by heating and curing the layer before the set of the droplet particles of the curable silicone appearing on the surface of the overcoat layer sufficiently progress, A coating film having a fine sea-island structure in which a curable silicone is dispersed is formed on the surface (see Fig. 3 (A)).

Fig. 2 (C) is a view schematically showing the state in which the curable silicone is collected on the surface of the overcoat layer, Fig. 3 (B) Is an electron micrograph showing a reflected electron image. As shown in the photograph of FIG. 3 (B), when the droplet particles of the curable silicone appearing on the surface of the overcoat paint layer are sufficiently aggregated as shown in FIG. 2 (C) A coating film having a structure on its surface is produced. The islands in any sea structure have thinner thicknesses of several tens of nm.

The heat resistance of the coated film is mainly due to polyimide, and the antifouling performance on the surface of the coated film is mainly due to the cured silicone. Therefore, in the overcoat film formed of the overcoat layer shown in Fig. 2B or Fig. 2C, the presence of the island of cured silicone results in a high antifouling performance.

4 is a diagram schematically showing the sea water structure in a coating film to be applied and the liquid contaminants attached to the coating film. The overcoat film 51 has a fine sea-island structure composed of a continuous phase of the polyimide 513 and a dispersed phase of the cured silicon 512.

On the surface of the overcoat film 51, liquid contaminants 514 adhere to the surface, as shown in Fig. The size of the island of the cured silicone 512 in the sea-island structure is sufficiently smaller than the droplet of the contaminant 514. In addition, the density of the islands of the cured silicon 512 on the surface of the overcoat film 51 is sufficiently high. Therefore, the droplet as the contaminant 514 adheres to the surface of the coated film 51 over the plurality of islands.

The surface tension of the hardened silicon 512 which is an island is smaller than the polyimide 513 which is the sea, the liquid droplet 514, which is the contaminant 514, The larger the contact angle is. Therefore, it is considered that the surface of the overcoating film 51 exhibits excellent lyophobicity, facilitating the removal of the droplets as the contaminants 514, and making it difficult for the contaminants to be caught on heating.

As described above, from the viewpoint of the contact property to the adhering liquid, the effect of preventing the coating of the overcoat film 51 is enhanced by the lotus effect (a large number of gaps that are irregular and rough on the rough surface, The phenomenon that the contact angle becomes large).

As is clear from the above description, by stably distributing the cured silicone on the surface of the overcoat film made of polyimide as the base resin, it is possible to provide a coating film having excellent heat resistance and excellent antifouling performance for any hydrophilic and lipophilic liquid components. It is possible to form a coating film. In particular, it is more effective from the standpoint of enhancing the durability and uniformity of the antifouling performance on the surface of the coating film to be coated with a fine sea-island structure containing cured silicone as an island.

As described above, the coated steel sheet according to the present invention is excellent in both heat resistance and contamination prevention performance. Therefore, particularly with respect to the antifouling performance, the above-mentioned fine water-surface structure is employed, thereby exhibiting excellent antifouling performance against liquid contaminants. Therefore, it is preferable to use a member for cooking, such as a microwave oven capable of steam heating, at a temperature close to 350 ° C such as a heating chamber of a microwave oven and a member for constituting a portion where adherence of droplets occurs, And can be suitably used.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to these Examples.

<Examples>

[Preparation of polyimide precursors A to E]

120.3 g of DMAc (N, N-dimethylacetamide) as a solvent and 23.0 g (78.7 mmol) of diamine 1,3-bis- (3-aminophenoxy) benzene (manufactured by Mitsui Chemical Co., Ltd.) were added to a 300 mL separable flask ). Thereto was added 17.1 g (78.3 mmol) of anhydrous pyromellitic acid (1,2,4,5-benzenetetracarboxylic dianhydride) (Daicel Co., Ltd.), tetracarboxylic dianhydride, to obtain a polyimide precursor Acid) A was obtained.

Except that 138.3 g of DMAc and 78.7 mmol of 4,4'-bis- (3-aminophenoxy) biphenyl (manufactured by Mitsui Chemicals, Inc.) were added to diamine in the same manner as in the case of the varnish A. The polyimide precursor B Was obtained.

DMAc, and 4,4'-oxydiaminobenzene (4,4'-diaminodiphenyl ether) (manufactured by Seika Corporation) and 1,3-bis- (3-aminophenoxy) benzene as diamine , And a molar ratio of 9: 1 were used as a tetracarboxylic acid dianhydride. The tetracarboxylic dianhydride was obtained by reacting pyromellitic anhydride (1,2,4,5-benzenetetracarboxylic dianhydride) with 3,3 ', 4,4' -Benzophenone tetracarboxylic acid dianhydride (Daicel Co., Ltd.) was used in a molar ratio of 9: 1, the total amount of 78.3 mmol was used. Varnish C containing the polyimide precursor C was obtained in the same manner as in the case of the varnish A.

DMAc and 78.7 mmol of 4,4'-oxydiaminobenzene (4,4'-diaminodiphenyl ether) were used as the diamine. As the tetracarboxylic dianhydride, anhydrous pyromellitic acid (1, 2,4,5-benzenetetracarboxylic acid dianhydride) and 3,3 ', 4,4'-benzophenonetetracarboxylic dianhydride (Daicel Co., Ltd.) in a molar ratio of 9: 1 were used in a total amount of 78.3 mmol , Varnish D containing the polyimide precursor D was obtained in the same manner as in Varnish A.

Varnish E containing polyimide precursor E was obtained in the same manner as in Varnish A, except that 98.7 g of DMAc and 78.7 mmol of 4,4'-oxydiaminobenzene were used as the diamine.

Table 1 below shows the diamine (DA), tetracarboxylic dianhydride (TD), and the glass transition temperature Tg of the precursors, which are the raw materials of the polyimide precursors (PIpre) A to E obtained. The content of the polyimide precursors A to E in the varnishes A to E was 25.0 mass%.

[Preparation of Coating Paints]

Curable silicones F to H shown in Table 2 below were prepared. All of the curable silicones F to H are thermosetting silicones which are cured by heat. Table 2 shows the specific gravity (SG), viscosity (Vis), equivalent weight (EWFG), compound name and product name of the curable silicone F to H. &Quot; BYK-377 &quot; in Table 2 is manufactured by Big Chemie, and &quot; BYK &quot; "X22-4039" is manufactured by Shin-Etsu Chemical Co., Ltd. &Quot; FZ-2191 &quot; is manufactured by TORAY DOW CORNING CO., LTD.

The following varnish A, a solvent, a pigment dispersant, and a coloring pigment were put into a poly container, an appropriate amount of glass beads were added, and the poly container was shaken with a paint shaker for 8 hours. Thereafter, the glass beads were removed, the curable silicone F was added to the obtained mixed solution, and the mixture was stirred at 1000 rpm using a propeller stirrer to prepare a paint (overcoat) a for the overcoat film. The content of the nonvolatile component (solid content) in the coating composition a is 22.13% by mass. On the other hand, &quot; carbon black MA100 &quot; is manufactured by Mitsubishi Chemical Corporation. "DISPERBYK-130" is manufactured by Big Chemie, and "DISPER BYK" is a registered trademark of the company. The content of the nonvolatile component is a ratio of the total amount (28.56 parts by mass) of the nonvolatile component in the polyimide precursor, the thermosetting silicone, the coloring pigment and the pigment dispersant to the total amount of the following materials (129.05 parts by mass).

Varnish A: 100 parts by mass

Curable silicone F: 1.25 parts by mass

Solvent (N, N-dimethylacetamide): 25 parts by mass

Coloring pigment (carbon black MA100): 1.8 parts by mass

Pigment dispersant (DISPERBYK-130): 1 part by mass

Coating materials b to m were prepared in the same manner as in the case of the overcoating material a except that the materials shown in the following Table 3 were used in the amounts shown in Table 3. [ The compositions of the overcoating paints a to m are shown in Table 3. In Table 3, "Cw" is the content of the varnish, "PI-pre" is the polyimide precursor, "Cnv1" is the content of the nonvolatile component in the varnish, "S- Quot; represents the content of the curable silicone, &quot; Csol &quot; represents the content of the solvent, &quot; Cpig &quot; represents the content of the colored pigment, &quot; Cda &quot; represents the content of the pigment dispersant, Represents the content of the non-volatile component in the overcoat paint, and "R _{S / P} " represents the mass part of the curable silicone relative to 100 parts by mass of the polyimide precursor. The content other than Cnv1 is the content in the coating film to be coated.

[Production of painted steel sheets 1 to 30]

A plate (plate thickness: 0.4 mm) of SUS430 whose surface finish was No. 4 polishing finish was prepared. Alkali degreasing and chemical treatment were performed as a pretreatment for coating. Alkali degreasing is a treatment in which Surf Cleaner 155 (concentration: 2% by mass) manufactured by Nippon Paint Co., Ltd. is sprayed on the surface of the above stainless steel plate, and then washed with hot water at 60 캜 for 10 seconds and then washed with water. The chemical conversion treatment was carried out in the same manner as in Example 1 except that the NRC300 manufactured by Nippon Paint Co., Ltd. was coated on the surface of the stainless steel sheet so as to have a Cr adhered amount of 50 mg / m &lt; ^{2 &} Processing.

Then, the overcoating paint a was coated on the surface of the stainless steel plate after the paint pretreatment, that is, on the chemical conversion coating on the stainless steel plate so that the dry film thickness was 5 μm with a bar coater to form a layer of the overcoat paint a on the stainless steel plate did.

Then, the layer of the coating material a was heated at a temperature at which the temperature reached 350 DEG C of the stainless steel sheet, and the layer was heat-treated on the stainless steel sheet to obtain the coated steel sheet 1 having the overcoat film formed from the layer. In the production of the coated steel sheet 1, the waiting time from the application of the overcoat a to the start of heating was 15 seconds, and the heating time from the start of heating to the reached temperature was 130 seconds.

The coated steel sheets 2 to 4 were prepared in the same manner as the coated steel sheet 1 except that the type of the applied paint, the waiting time, the heating time, and the time until the heat treatment after application of the overcoat paint were changed as shown in Tables 4 and 5 below. 29, respectively. Then, for each of the coated steel plates 1 to 29, the dried film thickness, the occupied area ratio, the distribution and shape of the cured silicon, the maximum area of the island (island), and the peak intensity ratio of FT-IR were obtained. (Tf), the waiting time (Tw), the heating time (Temp-h), the arrival temperature (Temp-a) of the overcoat film, the cured silicone Table 4 and Table 5 show the occupied area ratio (Rarea), distribution state, distribution shape, maximum area (Smax) of the island and peak intensity ratio (A / B).

The dry film thickness is determined by subtracting the weight of the steel sheet after mechanically removing the coated film from the weight of the steel sheet after coating by means of a beads shot method or the like to determine the weight of the coated film and dividing by the steel sheet area and coating film density Respectively.

Further, the surface of the coated film is observed with a scanning electron microscope at a magnification of 100 to 3,000 times (a magnification at which the distribution form can clearly be seen) using a scanning electron microscope, photographed at five arbitrary positions and photographed , The obtained photographic images were digitally processed, the area ratio of the hardened silicon portions was calculated in each photographic image, and the average value of the area ratios of the photographic images at the five locations was taken as the occupied area ratio.

It was also determined that the photographic image was observed and that the dispersed phase of the cured silicone or polyimide was recognized in the continuous phase of the polyimide or the cured silicone as the "island" of the sea-island structure. In addition, the case in which the sea-island structure was not recognized was judged as &quot; continuous &quot;. Then, the shape of the island and the area of the island are obtained. On the other hand, when any arbitrary five points in the 5 mm ² region considered to be capable of reasonably judging the presence or absence of a sea-island structure with a scanning electron microscope could be observed, it was judged &quot; continuous &quot;

With respect to the shape of the island, the flatness ratio (the ratio of the long side to the short side) of the shape of the island in the photographic image was calculated. When the number of islands having a flatness ratio of 0.9 to 1.1 is 95% or more of the total number of islands in the photographic image, it is judged to be &quot; substantially circular &quot;, and when 80% or more and less than 95% Partly almost circular &quot;, and judging the case of less than 80% to be &quot; amorphous &quot;.

As an example, FIG. 3 (A) shows an electron micrograph showing a reflection electron image obtained by photographing the surface of the coated film to be coated in the coated steel sheet 3 of the embodiment by a scanning electron microscope. It can be seen from the coated steel sheet 3 that a coating film having a fine sea-island structure in which fine islands (island-cured silicon) is dispersed is formed on the surface thereof.

In addition, the area of the maximum degree (island) among the five photographic images was determined as the maximum area of the island. In the case where the shape of the islands is a substantially circular or irregular shape, it is difficult to measure the maximum area because of the complicated shape. In this case, the maximum area of the islands in this case is obtained as a rough value, And in Table 5 in parentheses.

The surface of the coated film to be coated was measured by the FT-IRATR method under conditions of an incident angle of 45 ^° and a measurement range of 1000 to 3000 cm ^{-1. From} the obtained measurement results, the peak intensity (a2) at 1375 cm ^-1 was found to be 1014 cm The ratio (a1 / a2) of the peak intensity (a1) of the peak intensity ( ^{-1) to} the peak intensity (a1) was determined to be &quot; A &quot; The samples were peeled off from the painted steel sheet or were cut to a depth of 4 mu m with a Mini-Plane (manufactured by S-T Japan Co., Ltd.) as it measured by IR, to obtain a non-(b1 / b2) of the peak intensity (b1) of 1014cm ^-1 to the peak intensity (b2) of 1375cm ^-1 from the results obtained, and a "B" at the peak strength, and, The ratio of A to B was obtained as the peak intensity ratio.

In the painted steel plate 12, since the overcoat l did not contain the thermosetting silicone, the distribution (island) of the hardened silicone was not observed on the surface of the coating film. Therefore, neither A nor B of peak intensity ratio A / B could be obtained. In the painted steel plate 13, since the overcoating paint m does not contain the polyimide precursor, the cured silicone constitutes the entire surface of the coated film, and the islands of the cured silicone can not be seen on the surface of the coated film. Therefore, neither A nor B of peak intensity ratio A / B could be obtained. Further, in the coated steel plate 28, the cured silicone became sea (sea), and the polyimide was distributed as irregularly shaped islands. In the painted steel plate 19 and the painted steel plate 29, since the "distribution state" was "continuous", neither the maximum area (Smax) of the island nor the steel plate was found.

The coated steel sheet 30 was produced in the same manner as the coated steel sheet 3 except that the above-described chemical treatment was not performed. The coated layer of the coated steel sheet 30 was observed and measured in the same manner as in the coated steel sheet 1, and the occupied area ratio of the cured silicon was 35%, the distribution state was "island" and the distribution shape was "almost circular" , The maximum area of the island was 100 μm ² , and the peak intensity ratio A / B was 30.

[evaluation]

Painted steel sheets 1 to 30 were evaluated for the following items.

[Coating film adhesion]

(1) Processing Adhesion (Ad-1)

Each of the coated steel sheets 1 to 30 was cut into a length of about 70 mm in width and about twice the width of the coated steel sheets 1 to 30 and then bent 2T with the coating film applied to the outside to peel off the tape with a cellophane tape. And the residual ratio was evaluated based on the following criteria. The remaining percentage of the coating film to be coated was determined by measuring the dimension of the portion where the coating film remained, out of 50 mm excluding both ends of the bent portion, and calculating the ratio of the area of the remaining portion to the area of the 50 mm width region.

(Evaluation Criteria of Coating Film Adhesion)

A: The residual ratio is 100%

B: Remaining ratio of 95% or more and less than 100%

C: Residual ratio is 90% or more and less than 95%

D: Residual ratio is 80% or more and less than 90%

E: the residual ratio is 70% or more and less than 80%

F: 50% or more and less than 70%

G: residual ratio less than 50%

(2) Water resistance Secondary adhesion (Ad-2)

After each of the painted steel sheets 1 to 30 was immersed in a boiling water for 2 hours, the remaining percentage of the coated film when the peeled coating tape was peeled off was evaluated and evaluated based on the above evaluation criteria.

[Heat resistance]

After each of coated steel sheets 1 to 30 was stored at respective temperatures of 250 ° C, 300 ° C and 350 ° C for 24 hours, the remaining percentage of the coated film when peel-off tape peeling of the coated film was carried out was determined. I appreciated.

[Contamination of food]

(1) Initial food contamination (AP-1)

The food was placed on each coated film of the coated steel plates 1 to 30 in the untested state, and the coated steel sheet was heated at 250 DEG C for 1 hour, and then wiped off from the coated steel sheet when the food contaminants were wiped off with a tissue was observed . In the food, four kinds of salad oil, butter, soy sauce and sauce were used and the state wiped was observed for each food type. Then, evaluation was made based on the following evaluation criteria.

(Evaluation criteria for food contamination)

A: Easy to remove when each food is wiped with tissue

B: Each food can be removed if rubbed with a tissue (no residue)

C: One type of food can be removed by rubbing with a tissue, but there are residues (the other three species can be removed)

D: One type of food can not be removed even if rubbed with a tissue (the other three types can be removed)

E: Two kinds of food can not be removed even if rubbed with tissue (two other types can be removed)

F: Three kinds of food can not be removed even if rubbed with tissue (one other type can be removed)

G: All types of food can not be rubbed off

(2) Contamination of food after heat resistance test (AP-2)

The test was carried out under the conditions of the above (1), except that the coated steel sheet after heating at 350 占 폚 for 24 hours was put on the food, and the wiped condition of each food was observed and evaluated by the above evaluation criteria.

(3) Food contamination during continuous use (continuous test, AP-3)

The test under the above conditions (1) was repeated 10 times on the same coated steel sheet, and the state of each of the tenth foods wiped off was observed and evaluated based on the above criteria.

The results are shown in Table 6.

[Preparation and evaluation of clear coated steel sheet]

The following materials were stirred at 1000 rpm using a propeller stirrer to prepare a coating material (clear paint) for coating the coating. That is, the clear paint is prepared in the same manner as the overcoating paint c, except that the color pigment and the pigment dispersant are not blended. The content of the nonvolatile component of the clear paint is 16.83 mass%, and the amount of the curable silicone (S) relative to 100 mass parts of the polyimide precursor (P) is 5.0 mass parts.

Varnish C: 100 parts by mass

Curable silicone F: 1.25 parts by mass

N, N-dimethylacetamide: 25 parts by mass

A painted steel plate 31 was produced in the same manner as the painted steel plate 1 except that the clear paint was used. The overlapped clear coating film of the painted steel plate 31 was observed and measured in the same manner as in the coated steel plate 1, and the occupied area ratio of the cured silicone was 35%. The distribution state was "island" , The maximum area of the island was 100 μm ² , and the peak intensity ratio A / B was 30.

The coated steel sheet 31 was evaluated for each of the above-described film adhesion, heat resistance and resistance to food stains, and the same results as those of the coated steel sheet 3 in Table 6 were obtained.

[Production of painted steel plates 32 and 33]

A molten Al-9% Si-plated steel sheet (plate thickness: 0.4 mm, one side plating adhesion amount: 40 g / m ² ) was prepared as a steel plate. The above alkali degreasing was performed as a pretreatment for coating, and a Ti-based chromium-free treatment was performed as a chemical treatment. The chemical conversion treatment liquid was applied to the surface of the plated steel sheet using titanium hydrofluoric acid (H ₂ TiF ₆ : 0.1 mol / L) so that the adhesion amount of Ti became 10 mg / m ² and dried.

On the other hand, 30 parts by mass of aluminum dihydrogen phosphate-magnesium tripolyphosphate as a rust-preventive pigment was added to 100 parts by mass of polyimide precursor B to prepare an undercoating paint. The undercoat paint was applied to the chemically treated coating of the plated steel sheet so as to have a dry film thickness of 5 mu m and heated to a temperature at which the plated steel sheet reached 280 DEG C to prepare a primer coat composed of polyimide.

Coating paint c was coated on the surface of the undercoating film that had become room temperature under the same conditions as those of the coated steel plate 3 and heated to produce a coating film to be overlaid. Thus, a coated steel plate 32 was produced. A coated steel plate 33 was produced in the same manner as in the case of the coated steel plate 32 except that the undercoating film was not formed.

[evaluation]

The coated steel plates 32 and 33 were evaluated for each of the above-described film adhesion, heat resistance and resistance to food contamination. The coated steel plates 32 and 33 were evaluated for the following corrosion resistance.

[Corrosion resistance]

(SST, according to JIS Z2371) in which 5% brine was sprayed onto the coating film of the coated steel sheet in an environment where the cross-cut was applied to the flat portions (portions other than the end cut surface) of the coated steel plates 32 and 33 ) For 240 hours. After the test, the maximum swelling width of the crosscut portion was observed and evaluated according to the following evaluation criteria. The results are shown in Table 7.

(Evaluation Criteria for Corrosion Resistance)

A: Maximum swelling width less than 1 mm

B: Maximum swelling width of 1 mm or more and less than 2 mm

C: Maximum swelling width is 2 mm or more and less than 3 mm

D: Maximum swelling width is 3 mm or more and less than 4 mm

E: Maximum swelling width of 4 mm or more

Coated steel plates 1 to 5, 7 to 11, and 14 to 33 exhibit practically no problem in terms of coating film adhesion, heat resistance, and stain resistance to food, at least as members for cooking utensils. Moreover, the coated steel plates 32 and 33 exhibit performance that is practically problematic in terms of corrosion resistance, at least for a cooking device.

On the other hand, the coated steel sheet 6 was practically insufficient in stain resistance to food. This is presumably because the occupied area ratio of the cured silicon on the surface of the overcoat film was insufficient at 4%. In addition, the painted steel plate 12 was practically insufficient in terms of food stain resistance. This is considered to be because the substrate of the coating film to be coated is only polyimide (since the coating film to be coated does not contain cured silicone). In addition, the coated steel sheet 13 was practically inadequate in terms of coating film adhesion, heat resistance, and food stain resistance. This is considered to be because the substrate of the coating film to be coated is only the cured silicon (the coating film does not contain polyimide).

From the above, it can be seen from the above that the coating film composed of the steel sheet and the coating film overlap in this order, and the coating film includes the coating film to be overlaid, the coating film comprising polyimide and cured silicone, and constituting the surface of the coated steel sheet, A coated steel sheet having a occupied area ratio of cured silicone of 5% or more is a coated steel sheet for a cooking apparatus member, and both of heat resistance and antifouling performance are excellent.

Further, for example, the painted steel plates 3 and 7 are superior to the painted steel plate 6 in stain resistance to food. Further, for example, the painted steel sheets 3 and 8 are superior to the painted steel sheet 9 in stain resistance to food after the heat resistance test. From the above, it can be seen that the content of the cured silicone in the coated film is 1 to 10 parts by mass based on 100 parts by mass of the polyimide, more effective from the viewpoint of durability of the antifouling performance.

In addition, for example, the painted steel plates 3, 7 and 14 are superior to the painted steel plate 6 in terms of food fouling resistance. In addition, for example, the painted steel plates 3, 8, and 17 are superior to the painted steel plate 9 in stain resistance to food after the heat resistance test. From the above, it can be seen that the area occupied by the cured silicon on the surface of the overcoat film is 5 to 70%, which is more effective from the viewpoint of durability of the antifouling performance.

Further, for example, the painted steel plate 3 is superior to the painted steel plate 29 in resistance to food stains after the heat resistance test and the continuous test. From the above, it can be seen that the surface of the coating film to be overlaid with the sea-island structure of polyimide and cured silicone is more effective from the viewpoint of durability of the antifouling performance. Further, for example, the coated steel plate 27 is superior to the coated steel plate 28 in staining resistance to food after the heat resistance test. From the above, it can be seen that the surface of the overcoat film is more effective in terms of durability of the antifouling performance than that of the islands structure of the sea of polyimide and the island of cured silicone.

In the coated steel sheets 15 to 18, the coated steel sheets 15 to 17 are superior to the coated steel sheet 18 in stain resistance to food after the heat resistance test. Further, in the painted steel sheets 20 to 22, the coated steel sheets 20, 21 and 22 are superior in paint film adhesion, food fouling resistance after the heat resistance test, and food fouling resistance in the continuous test. From the above, it can be seen that the area of each island of cured silicon on the surface of the overcoat film is 300 μm ² Or the shape of the island of the cured silicone on the surface of the overcoat film is almost circular is more effective in terms of durability of the antifouling performance or coating film adhesion.

In the coated steel sheets 15 to 18, the coated steel sheets 15 and 16 are superior to the coated steel sheets 17 and 18 in staining resistance to food after the heat resistance test. In the coated steel plates 24 to 27, the coated steel plates 25 and 26 are superior to the coated steel plate 24 in stain resistance to food, and compared to the coated steel plate 27, in terms of the resistance to food stains after the heat resistance test and the continuous test outstanding. From the above, by the coating film that coats, and the ratio A of the peak intensity of 1014cm ^-1 to a peak intensity of 1375cm ^-1 when measured by the infrared spectroscopic analysis of the surface of the topcoat film in the ATR method infrared spectroscopy on KBr method that of as measured in analysis, when it is defined as a ratio of a peak intensity of 1014cm ^-1 to a peak intensity of 1375cm ^-1 B, a ratio a / B of a to B of 1.1 to 100 and the antifouling performance It is more effective in terms of durability.

In the coated steel sheets 1 to 5, the coated steel sheets 2 to 5 are superior to the coated steel sheets 1 in heat resistance at 250 DEG C, and the coated steel sheets 2 and 5 are superior to the coated steel sheets 1 in heat resistance at 300 DEG C, And 4 are superior to each other, and when the heat resistance at 350 占 폚 is higher than that of the coated steel sheet 1, the coated steel sheets 2 and 5 are excellent, the coated steel sheet 4 is more excellent and the coated steel sheet 3 is further excellent. In addition, the initial stain resistance of the foodstuff was superior to that of the coated steel sheet 1, and the stained steel sheets 2 to 5 were superior to the coated steel sheet 1 in the case of food stains after the heat resistance test or continuous test. Painted Steel Sheets 3 ~ 5 are superior. From the above, it can be seen that the polyimide having a Tg of 270 to 400 DEG C is more effective from the viewpoint of heat resistance and durability of the antifouling performance.

In the case of the coated steel sheets 20 to 23, the coated steel sheets 20, 21, 22 and 23 exhibited excellent adhesion in terms of film adhesion. All the coated steel sheets were generally good in heat resistance, The coated steel plates 21 to 23 are superior to the steel plate 20 and the coated steel plates 22 and 23 are superior to the coated steel plate 21. As described above, the method includes the steps of applying an overcoating paint to a coated original plate including a steel sheet to form an overcoat paint layer, and a step of heating the overcoat paint layer to heat the coated original plate to form an overcoat film. It is preferable that the overcoating layer containing a polyimide precursor, a curable silicone and a solvent and having at least a part of the curable silicone floating on the surface thereof is heated so that the arrival temperature of the steel sheet is 180 ° C or higher to form an overcoat film It is possible to provide a coated steel sheet excellent in both heat resistance and antifouling performance as a coated steel sheet for a cooking apparatus member.

In the coated steel plates 24 to 27, the coated steel plates 25 and 26 are superior to the coated steel plate 24 in stain resistance to food, and compared to the coated steel plate 27, in terms of the resistance to food stains after the heat resistance test and the continuous test outstanding. From the above, it can be seen that the coated steel sheet is more effective in terms of providing a coated steel sheet having excellent durability with respect to contamination prevention performance, in which the time (waiting time) from the application of the overcoating paint to the coated original plate to the start of heating is 5 to 60 seconds have.

Further, in the painted steel plates 24 and 25, the painted steel plate 25 is superior to the painted steel plate 24 in stain resistance to food. In the painted steel plates 27 and 29, the painted steel plate 27 is superior to the painted steel plate 29 in resistance to food contamination after the heat resistance test. From the above, it can be seen that the time from the start of heating to the time of reaching the reaching temperature (heat treatment time) is 30 to 240 seconds, which is more effective from the viewpoint of providing a coated steel sheet having excellent durability against contamination.

In the painted steel plates 21 and 22, the painted steel plate 22 is superior to the painted steel plate 21 in terms of food fouling resistance after coating film adhesion, heat resistance test and continuous test. From the above, it can be seen that a steel sheet having an ultimate temperature of 200 ° C or higher is more effective from the viewpoint of providing a coated steel sheet excellent in coating film adhesion and durability against contamination.

In the painted steel sheets 14 and 15, the painted steel sheet 15 is superior to the painted steel sheet 14 in resistance to food contamination in the continuous test. In the painted steel sheets 16 and 17, the painted steel sheet 16 is superior to the painted steel sheet 17 in stain resistance to food after the heat resistance test. From the above, it can be seen that it is more effective from the viewpoint of providing a coated steel sheet excellent in durability of the antifouling performance to coat the overcoat paint so that the film thickness of the overcoat film becomes 2 to 20 mu m.

In addition, for example, the painted steel plates 3 and 7 are superior to the painted steel plate 6 in the food stain resistance. In addition, for example, the painted steel sheets 3 and 8 are superior to the painted steel sheet 9 in terms of stain resistance to food after the heat resistance test. From the above, it can be seen that the content of the curable silicone in the over coat paint is 1 to 10 parts by mass with respect to 100 parts by mass of the polyimide precursor, which is more effective from the viewpoint of providing a coated steel sheet excellent in durability against contamination.

In addition, for example, the coated steel sheet 3 is superior to the coated steel sheet 30 in coating film adhesion. From the above, it can be seen that having a chemical conversion coating on the surface of a steel sheet is more effective from the viewpoint of providing a coated steel sheet having excellent coating film adhesion.

The present application claims priority based on Japanese Patent Application No. 2014-072302 filed on March 31, 2014. The contents of the application specification and drawings are all incorporated herein by reference.

&Lt; Industrial applicability >

The coated steel sheet of the present invention contains cured silicone on the surface of the overcoat film at an occupied area ratio of 5% or more on the surface of the overcoat film. Therefore, the coated steel sheet has the same or higher antifouling performance as the coated steel sheet on the surface of the coating film to be coated with the fluororesin, and has higher heat resistance. Therefore, the coated steel sheet of the present invention can be suitably used for a material of an apparatus that requires the antifouling performance in a higher temperature environment. Therefore, it is expected that the coated steel sheet of the present invention contributes to the new development of the heating cooking utensil capable of cooking using more specific heating such as heating at a higher temperature or steam heating.

10 painted steel plate
11 steel plate
12 Chemical conversion coating
13 Base coat
14, 51 Coating film
31 Overcoat layer
131 resin
132 Additives
141, 513 polyimide
142 aluminum particles
143 Inorganic additives
144, 512 Cured silicone
311 Solvent
312 Curable silicone
514 Contaminants

Claims (15)

A coated steel sheet having a coated film on a steel sheet,
Wherein the coating film comprises a coating film to be overlaid,
Wherein the overcoat film comprises polyimide and cured silicone,
Wherein a occupied area ratio of the cured silicon on the surface of the overcoat film is 5% or more. The method according to claim 1,
Wherein the content of the cured silicone in the overcoat film is 1 to 10 parts by mass relative to 100 parts by mass of the polyimide. 3. The method according to claim 1 or 2,
Wherein the occupied area ratio of the cured silicone on the surface of the overcoat film is 5 to 70%. 4. The method according to any one of claims 1 to 3,
Wherein the surface of the overcoat film has the sea-island structure of the polyimide and the cured silicone. 5. The method of claim 4,
Wherein the shape of the island of the hardened silicon is substantially circular and the area of the island of each of the hardened silicon is 300 μm ² or less. 6. The method according to any one of claims 1 to 5,
When measuring the surface of the topcoat film by infrared spectroscopic analysis by ATR method, and that a ratio of a peak intensity of 1014cm ^-1 to a peak intensity of 1375cm ^-1 A,
When measuring the topcoat film by infrared spectroscopy by KBr method, when defined as a ratio of a peak intensity of 1014cm ^-1 to a peak intensity of 1375cm ^-1 B,
Wherein the ratio of A to B is 1.1 to 100. 7. The method according to any one of claims 1 to 6,
Wherein the polyimide has a Tg of 270 to 400 占 폚. A step of applying a paint to be applied to the coated original plate including a steel sheet to form an overcoat layer,
And a step of heating the overcoat layer to form a coating film to be overcoated by heat-treating the overcoat layer,
Wherein the over coating comprises a polyimide precursor, a curable silicone and a solvent,
The content of the curable silicone relative to 100 parts by mass of the polyimide precursor in the overlay paint is 1.0 part by mass or more,
Wherein the overcoating layer on which at least a part of the curable silicone is floated is heated so that the reaching temperature of the steel sheet is 180 占 폚 or higher to form the overcoat film. 9. The method of claim 8,
Wherein the time from the application of the overcoat paint to the coated original plate to the start of the heating is 5 to 60 seconds. 10. The method according to claim 8 or 9,
Wherein the time from the initiation of the heating to the arrival of the temperature reaches 30 to 240 seconds. 11. The method according to any one of claims 8 to 10,
Wherein an arrival temperature of the steel sheet is 200 DEG C or more. The method according to any one of claims 8 to 11,
Wherein the overcoating paint is applied so that the film thickness of the overcoat film is 2 to 20 占 퐉. 13. The method according to any one of claims 8 to 12,
Wherein the content of the curable silicone in the overlay paint is 1 to 10 parts by mass relative to 100 parts by mass of the polyimide precursor. 14. The method according to any one of claims 8 to 13,
Wherein the steel sheet has a chemical conversion coating on its surface. A cooking appliance member comprising the coated steel sheet according to any one of claims 1 to 7.

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