TWI642539B - Coated steel plate, method of manufacturing the same and cookware member - Google Patents

Abstract

The coated steel sheet (10) is formed by sequentially overlapping the steel sheet (11) and the top coating film (14). The topcoat film (14) includes polyimide (141) and hardened fluorenone (144). The area ratio of the hardened fluorenone (144) in the surface of the top coat film (14) is 5% or more. The coated steel sheet (10) is excellent in both heat resistance and antifouling properties, and is suitably used as a material for a member for a conditioning device.

Description

Coating steel plate, manufacturing method thereof, and member for conditioning device

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

In recent years, microwave ovens have been developed for supplying water vapor in a heating chamber. The heating chamber is generally composed of a coated steel sheet having heat resistance and food contamination resistance (hereinafter also referred to as "antifouling resistance"). The coated steel sheet is, for example, a metal plate, an undercoat film mainly composed of polyether fluorene, and a top coat coated with a tetrafluoroethylene/perfluoroalkyl vinyl ether copolymer (PFA) and having a PFA unevenly distributed on the surface. The coating film is formed by overlapping in order (for example, refer to Patent Document 1).

[Prior Art Literature]

[Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2005-262465

The coated steel sheet is excellent in both heat resistance and antifouling properties. However, in recent years, microwave ovens that can be conditioned at a higher temperature have been developed and supplied to the market. Therefore, the coated steel sheet used in such a conditioning apparatus is required to further improve heat resistance.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a coated steel sheet which further has both heat resistance and antifouling properties.

Further, it is a further object of the invention to provide a member for a conditioning tool comprising the coated steel sheet.

The present inventors have found that by combining polyimine with a specific anthrone, the fluorenone is appropriately dispersed and exposed on the surface of the polyimide film, and the coating is applied to the top surface of the coated steel sheet. The coating film is excellent not only in antifouling properties but also in excellent heat resistance. Further, research is further carried out to complete the present invention.

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

[1] A coated steel sheet having a coating film on a steel sheet, wherein the coating film comprises a top coating film comprising a polyimide and a hardening ketone, the surface coating film The hardened fluorenone in the surface has an occupied area ratio of 5% or more.

[2] The coated steel sheet according to [1], wherein the content of the hardened fluorenone in the top coating film is from 1 part by mass to 10 parts by mass per 100 parts by mass of the polyimine.

[3] The coated steel sheet according to [1], wherein the hardened fluorenone in the surface of the top coating film has an occupied area ratio of 5% to 70%.

[4] The coated steel sheet according to any one of [1] to [3] wherein the surface of the top coating film is the island structure of the polyimine and the hardened fluorenone.

[5] The coated steel sheet according to [4], wherein the island of the hardened fluorenone is substantially circular, and the area of each of the hardened fluorenketone islands is 300 μm ² or less.

[6] The coated steel sheet according to any one of [1] to [5] wherein the surface of the top coating film is measured by infrared spectrum analysis using an attenuated total reflectance (ATR) method. the ^1014cm-1 peak intensity ratio relative to the peak intensity of 1375cm ^-1 is a, the use of IR spectroscopy to determine the potassium bromide (KBr) of the topcoat coating method, the peak of 1014cm ^-1 When the ratio of the intensity to the peak intensity of 1375 cm ^-1 is defined as B, the ratio of the A to the B is 1.1 to 100.

[7] The coated steel sheet according to any one of [1] to [6] wherein the polyethylenimine has a Tg of from 270 °C to 400 °C.

Further, the present invention relates to a method of producing the following coated steel sheet.

[8] A method for producing a coated steel sheet, comprising: coating a surface coating coating on a coated original sheet comprising a steel sheet to form a top coating layer, heating the top coating layer, and performing the coating on the coated original sheet. Burning, thereby forming a step of coating a surface coating film comprising a precursor of polyimine, a sclerosing fluorenone, and a solvent, wherein the sclerosing fluorenone in the top coating is relative to The content of 100 parts by mass of the precursor of the polyimide is 1.0 part by mass or more, and the curable fluorenone is heated on the surface of the top coating layer so that the temperature of the steel sheet reaches 180° C. or higher. At least a portion of the floated surface is coated with a coating layer to form the topcoat film.

[9] The method for producing a coated steel sheet according to [8], wherein the surface coating is applied to the coated original sheet until the heating is started for 5 seconds to 60 seconds.

[10] The method for producing a coated steel sheet according to [8] or [9], wherein the The time from the heat until the temperature is reached is 30 seconds to 240 seconds.

[11] The method for producing a coated steel sheet according to any one of [8] to [10] wherein the steel sheet reaches a temperature of 200 ° C or higher.

[12] The method for producing a coated steel sheet according to any one of [8], wherein the top coating material is applied so that the film thickness of the top coating film is 2 μm to 20 μm.

[13] The method for producing a coated steel sheet according to any one of [8] to [12] wherein the content of the sclerosing fluorenone in the top coating is relative to the precursor of the polyimide 100 parts by mass, from 1 part by mass to 10 parts by mass.

[14] The method for producing a coated steel sheet according to any one of [8] to [13] wherein the steel sheet has a chemically synthesized treatment film on a surface of the steel sheet.

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

The coated steel sheet of the present invention can exhibit higher heat resistance and equivalent or equivalent antifouling properties as compared with the conventional fluororesin-coated steel sheet. Therefore, the coated steel sheet of the present invention is suitably used for a member for a conditioning apparatus used at a higher temperature.

10‧‧‧painted steel plate

11‧‧‧ steel plate

12‧‧‧Chemical synthetic treatment film

13‧‧‧Undercoat film

14, 51‧ ‧ face coating film

31‧‧‧Top coating layer

131‧‧‧Resin

132‧‧‧ Additives

141, 513‧‧‧ Polyimine

142‧‧‧Aluminum particles

143‧‧‧Inorganic additives

144, 512‧‧‧ hardened ketone

311‧‧‧Solvent

312‧‧‧Sclerosing ketone

514‧‧‧Contaminants

Fig. 1 is a view schematically showing a configuration of a coated steel sheet according to an embodiment of the present invention.

2A is a view schematically showing the behavior of components in the top coat layer, and FIG. 2B is a schematic representation of the surface dispersion hardening ketone on the top coat layer. FIG. 2C is a view schematically showing a state in which the surface of the top coat layer is hardened with fluorene.

3A is an electron micrograph showing a surface of a top coat film in a coated steel sheet 3 of the embodiment, which is taken by a scanning electron microscope, and FIG. 3B is a view showing a surface of a top coat film of a set of curable fluorenone. An electron micrograph of a reflected electron image taken with a scanning electron microscope.

Fig. 4 is a view schematically showing a sea-island structure in a top coat film and liquid contaminants attached to the coat film.

The coated steel sheet of the present invention has a coating film on the steel sheet. The coating film may contain, for example, the following surface coating film as the coating film on the outermost surface. The coating film may further include, for example, an undercoat film formed on the surface of the steel sheet or an intermediate coating film formed on the surface of the undercoat film. For example, as shown in FIG. 1, the coated steel sheet 10 of the present invention has a steel sheet 11, a chemical composition treatment film 12, a primer coating film 13, and a top coating film 14 which are stacked in this order. The undercoat film 13 is mainly composed of a resin 131, and may include an additive 132 such as various pigments as described below. The top coat film 14 is mainly composed of polyimine 141 as described below, and may contain additives such as aluminum particles 142 or inorganic additives 143. Further, the top coat film 14 contains the hardened fluorenone 144 which is present at least on the surface of the top coat film 14.

[steel plate]

The steel sheet can be appropriately selected from known steel sheets depending on the use of the coated steel sheet, desired properties, and the like. Examples of steel sheets include galvanized steel sheets (electrically plated Zn, hot-dip Zn), and alloyed galvanized steel sheets (alloyed alloyed molten alloy after Zn-plating) Zn-plated, galvanized alloy steel plate (melt-plated Zn-Mg, hot-dip Zn-Al-Mg, hot-dip Zn-Al), hot-dip Al-plated steel, hot-dipped Al-Si steel, stainless steel, and hot-dipped Al stainless steel board. From the viewpoint of improving the corrosion resistance in a high-temperature environment, it is preferably a hot-dip Al-plated steel sheet or a hot-dip Al-Si steel sheet or a stainless steel sheet, and it is preferable from the viewpoint of further improving corrosion resistance and microwave reflection efficiency. It is a hot-plated Al stainless steel plate.

[Chemical Synthesis Treatment Film]

The steel sheet may have a chemically synthesized treatment film from the viewpoint of improving the corrosion resistance of the coated steel sheet and the coating film adhesion. The chemical synthesis treatment film is a thin layer formed by treatment with a coated substrate. Examples of chemical synthesis treatments include chromate treatment, chromium-free treatment, and phosphate treatment. The amount of adhesion of the chemical conversion treatment film is appropriately determined within a range effective for improving corrosion resistance and coating film adhesion. For example, the adhesion amount of the chromate film is an amount in which the total amount of adhesion in terms of Cr is 5 mg/m ² to 100 mg/m ² . Further, the amount of adhesion of the chrome-free film, for example, the Ti-Mo composite film, is from 10 mg/m ² to 500 mg/m ² in terms of total Ti and Mo conversion, and the adhesion amount of the fluoric acid-based film is fluorine-containing adhesion amount or total amount. The metal element conversion amount is an amount of 3 mg/m ² to 100 mg/m ² . Further, the amount of deposition of the phosphate film is an amount in which the phosphorus conversion amount is 0.1 g/m ² to 5 g/m ² .

The chemical synthesis treatment film can be formed by a known method. For example, the chemical synthesis treatment liquid may be applied to the surface of the steel sheet by a method such as a roll coating method, a spin coating method, a bar coating method, or a spray method, and may be dried without being washed with water. The drying temperature and the drying time are not particularly limited as long as the water can be evaporated. From the viewpoint of productivity, the drying temperature is preferably 60 ° C in the reach of the steel plate. The drying time is preferably from 2 seconds to 10 seconds at 150 °C.

[primer coating]

The coated steel sheet may further have a primer coating film on the surface of the steel sheet or the surface of the chemical synthesis treatment film from the viewpoint of improving the corrosion resistance of the coated steel sheet and the coating film adhesion. Usually, the undercoat film contains a resin as a matrix and an anti-rust pigment. The resin for the undercoat film may be the same as or different from the resin of the substrate of another coating film such as a top coat film. Examples of the type of the resin for the undercoat film include inorganic resins such as a polyester resin, an epoxy resin, an acrylic resin, a phenoxy resin, and a phthalate resin. Examples of the kind of the rust preventive pigment include magnesium phosphate, zirconium phosphate, zinc phosphate, aluminum tripolyphosphate, zinc phosphomolybdate, barium metaborate, and cerium oxide compound.

The undercoat film may further contain other components. For example, the undercoat film may also contain a crosslinking agent that crosslinks the organic resin. Examples of the kind of the crosslinking agent include a melamine resin and an isocyanate resin. Further, the undercoat film may further contain a coloring pigment, a metallic pigment or an extender pigment. Examples of the coloring pigment include titanium oxide, carbon black, chromium oxide, iron oxide, iron oxide, titanium yellow, cobalt blue, cobalt green, nigrosine, and phthalocyanine blue. Examples of metallic pigments include aluminum flakes (non-floating type), bronze flakes, copper flakes, stainless steel flakes, and nickel flakes. Examples of the extender pigments include barium sulfate, cerium oxide, and calcium carbonate.

Further, the undercoat film may also contain a pigment dispersant. Examples of the pigment dispersant include a solution of a polyaminoguanamine of an unsaturated carboxylic acid (a solvent such as an alkylbenzene/ethylene glycol monobutyl ether = 5/1), an amine salt of a polyether ester acid, and a low molecular weight polymerization. Ester compound.

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

[surface coating film]

The top coat film constitutes the surface of the coated steel sheet. Topcoat films include polyimine and hardened fluorenone.

[polyimine]

The polyimine may be one type or two or more types. From the viewpoint of improving the heat resistance and the strength of the top coat film, it is preferred that the polyimine contains an aromatic group in the main chain. The glass transition temperature (Tg) of the polyimine is usually preferably from 270 ° C to 400 ° C, more preferably from 300 ° C to 380 ° C, and still more preferably from 320 ° C in terms of heat resistance and adhesion. 360 ° C. The Tg of the polyimine can be measured using a dynamic viscoelasticity measuring device.

The polyimine is obtained by hardening a reaction product (precursor of polyimine) obtained by mixing a diamine and a tetracarboxylic dianhydride in a solvent. The glass transition point (Tg) of the polyimine may be designed depending on the combination or content ratio of the diamine and the tetracarboxylic dianhydride used. For example, a polyamine which modulates a Tg of from 270 ° C to 400 ° C. Examples of preferred diamines include amines such as 4,4'-oxydiaminobenzene (4,4'-diaminodiphenyl ether). a diamine in the para position or an amine such as 1,3-bis-(3-aminophenoxy)benzene or 4,4'-bis-(3-aminophenoxy)biphenyl A bit of a diamine. Wherein the diamine preferably comprises 4,4'-oxydiaminobenzene (4,4'-diaminodiphenyl ether) or 4,4'-bis-(3-aminophenoxyl) ) Biphenyl. Examples of preferred tetracarboxylic dianhydrides for preparing the Tg polyimine include pyromellitic anhydride (1,2,4,5-benzenetetracarboxylic dianhydride), 3,3', 4,4 '-benzophenone tetracarboxylic dianhydride and 3,3',4,4'-biphenyltetracarboxylic dianhydride. Among them, it is preferred that the tetracarboxylic dianhydride contains 3,3',4,4'-benzophenonetetracarboxylic dianhydride.

[hardened ketone]

The hardened fluorenone is an anthrone which is hardened by heating or the like when the top coating film is baked. The hardened fluorenone is obtained by thermal hardening or the like of the following sclerosing fluorenone.

If the content of the hardened fluorenone in the top coat film is too small, the hardened fluorenone located on the surface of the top coat film may be cut in advance due to repeated use of the coated steel sheet. Therefore, it is sometimes difficult to maintain antifouling properties for a long period of time. If the content of the hardened fluorenone in the top coat film is too large, the hardened fluorenone may contain uncured fluorenone. Therefore, the surface of the top coat film may be sticky, and the workability of the coated steel sheet may be degraded due to the stickiness. Further, if the content of the hardened fluorenone in the top coat film is too large, the adhesion of the hardened fluorenone in the top coat film is different due to the difference in linear expansion coefficient between the polyimide and the hardened fluorenone at a high temperature. It becomes insufficient, and sometimes the hardened ketone is peeled off from the top coating film. Therefore, the antifouling property of the coated steel sheet may become insufficient. From such a viewpoint, the content of the hardened fluorenone in the top coat film is preferably from 1 part by mass to 10 parts by mass, more preferably from 2 parts by mass to 6 parts by mass, per 100 parts by mass of the polybenzonitrile.

The top coat film may further contain other components within the range in which the effects of the present invention are obtained. Examples of the other components include aluminum particles, the coloring pigment, a pigment dispersing agent, and an inorganic additive.

The aluminum particles are blended in the top coat to impart design (metal feel) to the top coat. The purity of aluminum in the aluminum particles is not particularly limited. For example, the aluminum particles may be composed only of aluminum or an aluminum-based alloy. Examples of the shape of the aluminum particles include scaly (flaky), granular, plate-like, and massive. From the viewpoint of imparting a metallic feeling to the top coating film, the shape of the aluminum particles is preferably scaly. The content of aluminum particles in the topcoat film The amount is, for example, 0.1 parts by mass to 50 parts by mass based on 100 parts by mass of the polyimine.

Inorganic additives can also be formulated in topcoats to enhance the hardness and abrasion resistance of the topcoat. Examples of the inorganic additive include glass flakes, graphite flakes, synthetic mica flakes, cerium oxide flakes and the like, and scaly inorganic additive materials; and potassium titanate fibers, ash stone fibers, strontium carbide fibers, alumina fibers, alumina citrate Inorganic fiber such as salt fiber, cerium oxide fiber, rock wool, slag wool, glass fiber, carbon fiber.

The film thickness of the top coat film is not particularly limited, and if the top coat film is too thin, heat resistance and antifouling properties in the coated steel sheet are insufficient, and if it is too thick, heat resistance and antifouling properties are sufficiently obtained. However, it may be inferior from the viewpoints of other reasons such as an increase in manufacturing cost or a decrease in workability of a coated steel sheet. From such a viewpoint, the film thickness of the top coat film is preferably from 2 μm to 20 μm, more preferably from 3 μm to 15 μm, still more preferably from 5 μm to 10 μm.

The area ratio of the hardened fluorenone in the surface of the top coat film is 5% or more. If the occupied area ratio is less than 5%, the following anti-fouling effect like the lotus effect may be insufficient. If the occupied area ratio is too large, as described above, the hardened fluorenone may be peeled off from the top coat film due to the difference in linear expansion coefficient between the polyfluorene and the hardened fluorenone at a high temperature, and the coated steel sheet may be prevented. The dirtiness becomes slightly insufficient. From this point of view, the occupied area ratio is preferably from 5% to 70%.

Further, the surface of the top coat film preferably contains a sea-island structure formed of polyimide and hardened fluorenone. Further, "sea" means a continuous phase in the surface of the topcoat film, and "island" means a dispersed phase in the surface of the topcoat film. The polyimine may be the "sea" of the island structure or the "island", and the hardened ketone may be the "island" of the island structure. It can also be "sea". In the sea-island structure, it is preferable that the polyamidimide is "sea" and the hardened ketone is "island" from the viewpoint of preventing stickiness due to excessive hardening of the fluorenone or reducing the workability of the coated steel sheet. Island structure.

Further, the island is substantially circular, and in view of the above, it is more preferable that the area of each island is 300 μm ² or less. Regarding the shape of the island, the term "substantially circular" means that the ratio of the long diameter to the short diameter is 0.9 to 1.1. Regarding the ratio of the substantially circular islands, the shape of the islands may be represented by the "substantially circular shape", and for example, 80% or more of the entire islands may correspond to the substantially circular shape.

The arrangement of the hardened fluorenone in the surface of the top coat film is as shown in Fig. 3A, and can be confirmed by using a reflected electron image of a scanning electron microscope (SEM). The occupied area ratio, the shape of the island, and the area of the island are obtained from image processing of the reflected electron image.

Further, the top coat film preferably has a ratio (A/B) of the A to the B of 1.1 to 100. Here, the term "A" refers to the surface of the topcoat film during spectral analysis by ATR method to (Attenuated total reflection, ATR) of the infrared peak intensity of 10 14 cm ^-1 with respect to peak intensity of 1375cm ^-1 ratio. Moreover, so-called "B" means utilizing infrared spectral analysis method KBr topcoat coating film, the peak intensity ratio of a peak intensity of 1375cm ^-1 to 1014cm ^-1 phase. In any of the above A and B, the peak intensity at 1014 cm ^-1 is derived from a ruthenium atom (Si-O-Si), and indicates the amount of hardened fluorenone present in the top coat film. Further, the peak intensity at 1375 cm ^-1 is derived from a nitrogen atom (CN), and indicates the amount of polyimine present in the top coat film.

The peak intensity is an infrared spectroscopy method that detects peak intensity, for example Measured by FT-IR. Moreover, the ATR method is a method of performing infrared spectrum analysis on a surface as is known. As is known from the KBr method, a KBr tablet in which a slice of a top coat film is uniformly dispersed, or a sample in which the slice is sandwiched by a KBr plate is used as a sample for infrared spectrum analysis. The section of the top coat film in the KBr method may be a slice of the peeling surface coating film, or a slice of the top coat film cut from the surface thereof to a depth of 80% or more of the thickness of the top coat film. Alternatively, in the case of producing a top coat film, a sample of a separately prepared top coat film may be used.

The ratio A/B less than 1.1 means that the inside of the top coat film is uniformly dispersed and hardened. Therefore, when the ratio A/B is less than 1.1, the amount of hardened ketone which appears on the surface of the top coat film may be insufficient. Therefore, the antifouling property of the coated steel sheet may not be sufficiently obtained. Further, the amount of the hardened ketone existing in the surface of the top coat film increases, and the adhesion of the top coat film may decrease, and the top coat film may be peeled off. On the other hand, when the ratio A/B exceeds 100, the amount of the hardened ketone in the vicinity of the surface of the top coat film may increase, and depending on the linear expansion coefficient of the polyimide and the hardened ketone at a high temperature, The peeling and the antifouling property are lowered.

From the viewpoint of exhibiting both the partial peeling and the antifouling property of the coating film in the top coating film, the A is preferably 0.1 to 1.0. If the A is less than 0.1, the antifouling property may be insufficient. If the A exceeds 1.0, partial peeling of the top coat film may occur. The B is not particularly limited. Usually, the hardened ketone is generally 0.01 to 0.09 in the top coat film and unevenly distributed on the surface of the top coat film.

[Manufacturing method of coated steel sheet]

The coated steel sheet can be manufactured by a method comprising the steps of: applying a top coat on a coated original plate comprising a steel sheet to form a top coat layer; and heating the top coat layer to coat the original sheet The second step of forming the top coat film is carried out by baking. The manufacturing method may further include other steps within the scope of obtaining the effects of the present invention.

[First step]

The original plate to be coated may be the steel sheet itself, a steel sheet having the chemically synthesized treatment film, or a steel sheet having the undercoat coating film. The undercoat film can be produced by applying a primer coating to the surface of a steel sheet or a chemically synthesized film and baking it.

The primer coating is prepared, for example, by mixing a material such as a resin of the undercoat film or a precursor thereof or an additive, and a solvent.

The solvent may be one type or two or more types. Examples of the solvent include N-methyl-2-pyrrolidone (NMP) or N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N,N-dimethyl Aprotic polar solvent such as imidazolidinone (DMI) or methyl isobutyl ketone (MIBK); ethers such as diethylene glycol dimethyl ether (DMDG) or diethylene glycol diethyl ether (DEDG); a halogenated aliphatic hydrocarbon such as methane or carbon tetrachloride; a hydrocarbon such as xylene; and an alcohol.

The primer coating 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, or a spray method. The baking temperature of the undercoat film is preferably, for example, a temperature at which the steel sheet reaches a temperature of from 150 ° C to 400 ° C, and the baking time is preferably from 30 seconds to 180 seconds.

The top coating contains a precursor of polyimine, a sclerosing fluorenone, and a solvent. The top coat may further contain other components such as the aluminum particles. The precursor of the polyimide is a polymer which constitutes a top coat film by heating or the like in the second step, for example, a polymer which becomes the polyimine by thermal ring closure, or a polymer which is dissolved in a top coat.醯imine and so on. That is, examples of the precursor of polyimine include polylysine and soluble polyimine.

The sclerosing fluorenone is composed of, for example, an anthrone composed of a structural unit of a decane and a functional group. The functional group is bonded to each other by heat, an active energy ray, a catalyst equal to an anthrone or a functional group. Examples of the functional group include a group having a carbon double bond such as a vinyl group or a (meth) acryl group, a hydroxyalkyl group such as a monohydroxydecyl group, an alkoxyalkyl group such as a methoxyalkyl group, a hydroxyl group or a methyl group. Phenolic group, epoxy group, amine group, isocyanate group.

When the molecular weight of the sclerosing fluorenone is too small, the curing property of the fluorenone tends to decrease, and if it is too large, the viscosity increases, and the surface of the top coat film may not be sufficiently exhibited. From this point of view, the number of structural units of the oxime in the sulfonic acid ketone is preferably from 2 to 5,000, more preferably from 10 to 2,000. The number of structural units can be determined by gel permeation chromatography (GPC).

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

Examples of the sclerosing fluorenone include various modified anthrones, and examples of the modified fluorenone include an amino group-modified fluorenone, a methanol-modified fluorenone, a methacryl-modified fluorenone, and B. Alkene-modified anthrone, stanol-modified anthrone, phenol-modified anthrone, epoxy-modified anthrone, isocyanate-modified anthrone, polyether-modified anthrone. In terms of long-term resistance to food contamination, polyether modified anthrone is particularly preferred.

The solvent may be one type or two or more types. A solvent is used from the viewpoint of improving the compatibility of the precursor of the polyimide and the curable fluorenone, or adjusting the viscosity of the top coat. As the solvent for the top coat, the same solvent as the solvent of the undercoat can be used. The solvent for the top coat may be one or more, which may be the same as or different from the solvent of the primer. Further, the top coat can be applied to the surface of the steel sheet, the chemically synthesized film or the undercoat film by the same method as the method of applying the primer.

The content of the curable fluorenone in the top coating material is 1.0 part by mass or more based on 100 parts by mass of the precursor of the polyimine. When the content is less than 1.0 part by mass, the area ratio of the hardened fluorenone in the surface of the top coat film may be less than 5%. The content of the sclerosing fluorenone in the top coat is as described above, and the antifouling property due to repeated use is prevented from decreasing, or the antifouling property due to partial peeling of the top coat film is lowered. The precursor of the quinone imine is preferably 100 parts by mass, preferably 1 part by mass to 10 parts by mass, more preferably 2 parts by mass to 6 parts by mass.

The top coat is preferably applied to the steel sheet, the chemically synthesized film or the undercoat film so that the film thickness of the top coat film is 2 μm to 20 μm. The thickness of the top coat film can be adjusted according to the thickness of the top coat layer (the amount of the coat applied). The thickness of the top coat layer can be adjusted according to the viscosity of the top coat, the coating method of the paint, the number of times the paint is applied, and the like.

[Second step]

In the second step, a surface coating layer in which at least a part of the curable anthrone is floated on the surface of the top coating layer is heated to a temperature of 180 ° C or higher to form a top coating film. Here, the "top coating layer that floats at least a part of the sclerosing fluorenone on the surface of the top coating layer" means a layer in which a part of the curable fluorenone appears on the surface of the top coating layer, and Also included is a layer of a portion of the sclerosing fluorenone that reaches the surface of the topcoat layer and which is not yet visible on the surface (which may be referred to as the layer that is substantially apparent on the surface).

When the sclerosing fluorenone has thermosetting property, the precursor of the polyimine can be imidized by the heating and the curing of the sclerosing fluorenone can be performed. In the case where the sclerosing fluorenone does not have the thermosetting property, the production method may further include a further step of curing the sclerosing fluorenone. For example, when the curable fluorenone has photocurability, in addition to the heating step, further irradiation of light onto the polyimide film formed in the heating step can cure the curable fluorenone. Further, in the case where the sclerosing fluorenone has a property of being hardened by heat and light, the manufacturing method may further include, after the heating step, irradiating light which hardens the sclerosing fluorenone to the surface of the top coating film. A step of. In this case, it is preferable from the viewpoint of sufficiently curing the curable fluorenone on the surface of the top coat film. Examples of the irradiated light include ultraviolet rays.

When the temperature is less than 180 ° C, even if the curable fluorenone has thermosetting property, the curing of the curable fluorenone is insufficient, and the surface coating film has a sticky feeling and is not due to the curable fluorenone. Hardening sometimes reduces the workability of the coated steel sheet. Further, in some cases, the difference in the linear expansion coefficient between the polyimide and the curable fluorenone at a high temperature causes peeling and deterioration of the antifouling property. If the temperature reaches 200 ° C or higher, then it is rapid It is more preferable from the viewpoint of polyimidization of the precursor of polyimine.

Heating the top coat layer to the said temperature, or further comprising a suitable step for hardening the sulphur fluorenone, whereby the sclerosing fluorenone is suitably present on the surface of the top coat film. The polyimidization of the precursor of the polyimine in the layer and the thermal hardening of the curable anthrone are performed to form the top coat film. The amount of sclerosing fluorenone in the layer can be adjusted depending on the heating rate after the formation of the top coat layer, the standby time until heating, or the temperature reached. In other words, the curable fluorenone may be floated while heating the topcoat layer, or the sclerosing fluorenone may be sufficiently floated after the topcoat layer is applied, and then heated rapidly to maintain its state. From the viewpoint of stably achieving a desired distribution of the curable fluorenone in the top coat film, the latter is preferable.

In the former case, from the viewpoint of controlling the distribution of the curable fluorenone in the surface of the top coat film, the top coat is applied to the coated original sheet until the temperature of the steel sheet reaches the temperature reached (heating) The time) is preferably from 30 seconds to 240 seconds. When the heating time is less than 30 seconds, the amount of the curable fluorenone which appears on the surface of the top coat film may be insufficient. When the heating time exceeds 240 seconds, the amount of the sclerosing fluorenone which appears on the surface of the top coat film may be excessive. From this point of view, the heating time is more preferably from 30 seconds to 240 seconds.

In the latter case, the time (standby time) from the application of the top coat to the application of the original plate to the start of heating is preferably from 5 seconds to 60 seconds. When the standby time is less than 5 seconds, the curable fluorenone may not be sufficiently exhibited on the surface of the top coat layer, and the amount of the curable fluorenone in the inside of the layer may be increased. In this case, as mentioned above, sometimes The adhesion of the coating film is lowered, and the surface coating film is peeled off. When the standby time exceeds 60 seconds, substantially all of the curable fluorenone appears on the surface of the top coat layer, and peeling occurs due to the difference in linear expansion coefficient between the polyimide and the hardened ketone at a high temperature. And the antifouling property is reduced. The standby time can be adjusted, for example, according to the conveying speed of the steel sheet between the coating device of the top coat material and the heating device of the steel sheet.

Further, the heating time in the latter case, that is, the time from the standby time until the temperature of the steel sheet reaches the reaching temperature, is preferably 30 seconds to 180 seconds from the viewpoint of the heating time of the former. More preferably 30 seconds to 150 seconds.

Fig. 2A is a view schematically showing the behavior of components in the top coat layer. In the layer 31 of the top coat, as shown in Fig. 2A, the solvent 311 indicated by the white triangle (?) in Fig. 2A evaporates, and the hardenable fluorenone 312 represented by the white circle (?) in Fig. 2A is based on the substrate. The resin (precursor of polyimine) has a surface free energy difference that moves toward the surface of the layer. At this time, it is considered that the liquid particles of the curable fluorenone move toward the surface of the layer while being stacked on each other.

Fig. 2B is a view schematically showing a state in which the surface of the top coat layer is dispersed and the curable fluorenone is present. As shown in FIG. 2B, while the collection of the liquid particles of the curable fluorenone which appears on the surface of the top coat layer is not sufficiently developed, the layer is heated and cured to have a surface of the top coat layer. A top coat film of a fine island structure in which fine islands (the island is a sclerosing fluorenone) are dispersed (see FIG. 3A).

2C is a view schematically showing a state in which the surface-hardening fluorenone is collected in the top coat layer, and FIG. 3B is a view showing a surface of the top coat film of the curable fluorene ketone by a scanning electron microscope. Electron microscope image of electronic image sheet. As shown in Fig. 2C, if the liquid particles of the curable fluorenone which appear on the surface of the top coat layer are sufficiently aggregated, as shown in the photograph of Fig. 3B, the surface of the top coat layer having a relatively large island is present. The surface of the island structure is coated with a film. The thickness of the islands in any of the island structures is thinner by several 10 nm.

The heat resistance of the top coat film is mainly caused by polyimide, and the antifouling property in the surface of the top coat film is mainly caused by hardening ketone. Therefore, in the top coat film formed of the top coat layer as shown in FIG. 2B or FIG. 2C, since the island of hardened ketone is present, it exhibits high antifouling property.

Fig. 4 is a view schematically showing a sea-island structure in a top coat film and liquid contaminants attached to the coat film. The top coat film 51 has a fine island structure including a continuous phase of polyimine 513 and a dispersed phase of hardened fluorenone 512.

As shown in FIG. 4, a liquid contaminant 514 is attached to the surface of the top coat film 51. The size of the island of hardened fluorenone 512 in the island structure is sufficiently smaller than the droplets of the contaminant 514. Further, the density of the island of the hardened fluorenone 512 in the surface of the top coat film 51 is sufficiently high. Therefore, the droplets of the contaminant 514 are attached to the surface of the top coat film 51 across a plurality of islands.

Compared with the polyimine 513 as the sea, the surface tension of the hardened fluorenone 512 as an island is small, and therefore the droplets of the contaminant 514 are exposed to the contact surface with the islands in the island structure. The role of the contact angle becomes larger. Therefore, it is considered that the surface of the top coat film 51 exhibits excellent liquid repellency, and it is easy to remove the droplets of the contaminant 514, and it is difficult to scorch the contaminant when heated.

Thus, regarding the antifouling effect of the top coat film 51, the attached liquid droplets From the viewpoint of the contact property, it is considered to have the same effect as the lotus effect (a phenomenon in which a large gap does not enter the liquid on a surface having fine irregularities and a large contact angle with the appearance of the liquid).

As is clear from the above description, the surface of the top coat film having the polyimide resin as the matrix resin is stably distributed and the fluorenone is hardened, whereby any liquid component having excellent heat resistance and hydrophilicity and lipophilicity can be formed. A top coat film having excellent antifouling properties. In particular, from the viewpoint of improving the durability and uniformity of the antifouling property, it is more effective to construct a fine island structure having a hardened ketone as an island on the surface of the top coat film.

As described above, the coated steel sheet of the present invention is excellent in both heat resistance and antifouling properties. Therefore, in particular, for the antifouling property, the fine sea-island structure is employed, whereby it is found that the antifouling property is more excellent for liquid stains. Therefore, as in the heating chamber of the microwave oven such as a steam-heatable microwave oven, if it is used at a temperature close to 350 ° C, it is preferably used as a member for constituting a portion where droplets are attached or a precoat thereof. Steel plate.

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

[Examples]

[Modulation of Polyimine Precursor A~E]

120.3 g of DMAc (N,N-dimethylacetamide) as a solvent and 1,3-bis-(3-aminophenoxy)benzene as a diamine were placed in a 300 mL separable flask (manufactured by Mitsui Chemicals, Inc.) 23.0 g (78.7 mmol) was dissolved. 17.1 g (78.3 mmol) of pyromellitic anhydride (1,2,4,5-benzenetetracarboxylic dianhydride) (manufactured by Daicel Co., Ltd.) as a tetracarboxylic dianhydride was added thereto. Varnish A containing a polybendimimine precursor (polyproline) A.

The same method as in the varnish A was used except that DMAc 138.3 g and 78.7 mmol of 4,4'-bis-(3-aminophenoxy)biphenyl (manufactured by Mitsui Chemicals, Inc.) were used. Varnish B of polyimine precursor B.

In addition to DMAc 103.1g, the diamine uses 4,4'-oxydiaminobenzene (4,4'-diaminodiphenyl ether) (manufactured by Seika Co., Ltd.) and 1,3-bis-(3- Aminophenoxy)benzene, a total of 78.7 mmol based on a molar ratio of 9:1, and tetracarboxylic acid dianhydride using pyromellitic anhydride (1,2,4,5-benzenetetracarboxylic dianhydride) and 3, 3',4,4'-benzophenonetetracarboxylic dianhydride (manufactured by Daicel Co., Ltd.) was obtained by the same method as varnish A except that the total molar ratio of 9:1 was 78.3 mmol. Varnish C containing polyimine precursor C.

In addition to using DMAc 101.0 g, the diamine used 78.7 mmol of 4,4'-oxydiaminobenzene (4,4'-diaminodiphenyl ether), and the tetracarboxylic dianhydride used pyromellitic anhydride (1) , 2,4,5-benzenetetracarboxylic dianhydride) and 3,3',4,4'-benzophenonetetracarboxylic dianhydride (manufactured by Daicel Co., Ltd.) to Moire ratio 9 A varnish D containing a polyimine precursor D was obtained by the same method as varnish A except that the total of 78.3 mmol was calculated.

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

The obtained diamine (DA) and tetracarboxylic dianhydride (TD) as raw materials of the polyimide precursors (PIpre) A to E and the glass transition temperature Tg of the precursor are shown in Table 1. The content of the polyimine precursors A to E in the varnishes A to E was 25.0% by mass.

[Modulation of top coat]

The sclerosing fluorenone F~H shown in Table 2 above was prepared. The sclerosing fluorenone F~H is a thermosetting fluorenone which is hardened by heat. The specific gravity (SG), viscosity (Vis), functional group equivalent (EW _FG ), compound name and product name of the sclerosing fluorenone F to H are shown in Table 2. In Table 2, "BYK-377" is manufactured by BYK-Chemie, and BYK is a registered trademark of BYK-Chemie. "X22-4039" is manufactured by Shin-Etsu Chemical Co., Ltd. "FZ-2191" is manufactured by Toray Dow Corning Co., Ltd.

The varnish A, the solvent, the pigment dispersant, and the coloring pigment were added to a plastic container, and an appropriate amount of glass beads was added, and the plastic container was shaken by a paint shaker for 8 hours. Then, the glass beads were removed, and the curable anthrone F was added to the obtained mixed liquid, and the mixture was stirred at 1000 rpm using a propeller stirrer to prepare a coating material for a top coating film (top coating) a. The content of the nonvolatile matter (solid content) in the top coating material a was 22.13% by mass. In addition, "carbon black MA100" is manufactured by Mitsubishi Chemical Corporation. "DISPERBYK-130" is manufactured by BYK-Chemie, Inc., and "DISPERBYK" is a registered trademark of BYK-Chemie. Further, the content of the nonvolatile matter is a total of the nonvolatile components (28.56 parts by mass) of the polyimide intermediate, the thermosetting fluorenone, the coloring pigment, and the pigment dispersant with respect to the total amount of the materials ( The ratio of 129.05 parts by mass).

The top coat b-m was prepared in the same manner as the top coat a except that the raw materials shown in Table 3 were used in the amounts shown in Table 3. The composition of the top coatings a to m is shown in Table 3. In Table 3, "Cw" indicates the content of the varnish, "PI-pre" indicates the polyimide precursor, "Cnv1" indicates the content of the non-volatile component in the varnish, and "S-pre" indicates the sclerosing ketone. Cs represents the content of the curable fluorenone, "Csol" represents the content of the solvent, "Cpig" represents the content of the coloring pigment, "Cda" represents the content of the pigment dispersant, and "Ctotal" represents the total content of the components, "Cnv2 The content of the non-volatile component in the top coat is indicated, and "R _S/P " represents the mass fraction of the curable fluorenone relative to 100 parts by mass of the polyimide precursor. The content other than Cnv1 is the content in the top coat film.

[Production of coated steel sheets 1 to 30]

A SUS430 plate (plate thickness: 0.4 mm) of No. 4 polished finish was prepared. Further, alkali degreasing and chemical synthesis treatment were carried out as a coating pretreatment. The alkali degreasing was carried out by spraying a surface cleaning brush 155 (concentration: 2% by mass) manufactured by Nippon Paint Co., Ltd. on the surface of the stainless steel plate, washing with hot water at 60 ° C for 10 seconds, and then performing water washing. The chemical synthesis treatment was carried out by applying NRC300 manufactured by Nippon Paint Co., Ltd. to the surface of the stainless steel plate in a manner of a Cr adhesion amount of 50 mg/m ² , and then drying at a temperature at which the temperature of the stainless steel plate reached 80 ° C. The chromate treatment of the coating liquid.

Then, on the surface of the stainless steel plate after the pretreatment, that is, the chemically synthesized film on the stainless steel plate, the top coat a is applied by a bar coater so that the dry film thickness becomes 5 μm, and the layer of the top coat a is applied. Formed on a stainless steel plate.

Then, the layer of the top coating layer a was heated at a temperature at which the temperature of the stainless steel plate reached 350 ° C, and the layer was baked on a stainless steel plate to obtain a coated steel sheet 1 having a top coat film formed of the layer. When the coated steel sheet 1 was produced, the application time of the surface coating material a was 15 seconds until the start of heating, and the heating time until the temperature reached was 130 seconds.

In addition to changing the type of top coat, standby time, heating time, and coating surface after coating, until the time of baking is changed as shown in Tables 4 and 5 above, The coated steel sheets 2 to 29 were produced in the same manner as in the case of the coated steel sheet 1. Further, for each of the coated steel sheets 1 to 29, the dry film thickness, the occupied area ratio, the distribution of the hardened ketone, the shape of the hardened ketone, the maximum area of the island, and the peak intensity ratio of FT-IR were determined. The type of top coat in the coated steel sheets 1 to 29, the dry film thickness (Tf) of the top coat film, the standby time (Tw), the heating time (Temp-h), the temperature reached (Temp-a), and the top coat The area ratio (Rarea), the distribution state, the distribution shape, the maximum area of the island (Smax), and the peak intensity ratio (A/B) of the hardened fluorenone in the coating film are shown in Tables 4 and 5.

The dry film thickness is obtained by a weight method, which is obtained by subtracting the weight of the steel sheet by mechanical removal of the coating film by a bead spraying method or the like, and determining the weight of the coating film by dividing the steel sheet area by the weight of the steel sheet after coating. And film density.

Further, using a scanning electron microscope, the surface of the top coat film was observed by reflecting the electron image at 100 times to 3000 times (the magnification of the distribution pattern was clearly known), and a photograph image of the electronic image of any five parts was taken. The photo image is subjected to digital processing, and the area ratio of the portion of the photo-enriched fluorenone in each photographic image is calculated, and the average value of the area ratios of the photographic images of the five portions is taken as the occupied area ratio.

Further, the photographic image was observed, and the case where the dispersed phase of the hardened fluorenone or the polyimine was found in the continuous phase of the polyimine or the hardened fluorenone was determined as the "island" of the sea-island structure. Further, the case where the sea-island structure was not found was judged as "continuous". Further, the shape of the island and the area of the island are obtained. In addition, any five parts of the 5 mm ² region in which the presence or absence of the sea-island structure was judged to be sufficiently plausible by the scanning electron microscope was observed, and the case where the sea-island structure was not found was judged to be "continuous".

Regarding the shape of the island, the flatness ratio (ratio of the long side to the short side) of the island shape in the photographic image was calculated. In addition, when the number of islands having an aspect ratio of 0.9 to 1.1 is 95% or more of the total number of islands in the photographic image, it is determined to be "substantially circular", and 80% or more and less than 95% are considered. It is judged as "a part of a substantially circular shape", and it is judged as "unshaped" when it is less than 80%.

As an example, an electron micrograph of a reflected electron image taken by a scanning electron microscope showing the surface of the top coat film in the coated steel sheet 3 of the example is shown in FIG. 3A. In the coated steel sheet 3, a top coat film having a fine sea-island structure in which fine islands (islands are hardened ketones) are formed on the surface of the coated steel sheet 3.

Moreover, the area of the largest island among the five photo images is set as the largest area of the island. When a part of the shape of the island is substantially circular or indefinite, the measurement of the maximum area may be difficult due to the complexity of the shape, and the maximum area of the island in this case is obtained as a rough value, Table 4 and Table 5 Indicated in brackets.

Moreover, the use of FT-IR ATR method, incident angle: 45 °, measurement range: topcoat coating film surface condition 1000cm ^-1 ~ 3000cm ^-1 was measured, the measurement results obtained, to obtain a peak intensity of 1014cm ^-1 (a1) The ratio (a1/a2) of the peak intensity (a2) to 1375 cm ^-1 is "A" in the peak intensity ratio. In addition, a test piece was taken from a coated steel sheet peeling surface, or a test piece was taken by a mini plate (manufactured by ST JAPAN Co., Ltd.) to a depth of 4 μm, and a sample prepared by the KBr method was measured by FT-IR. As a result, the ratio (b1/b2) of the peak intensity (b1) of 1014 cm ^{-1 to} the peak intensity (b2) of 1375 cm ^-1 was determined, and it was set as "B" in the peak intensity. Then, the ratio of the A to the B is obtained as the peak intensity ratio.

In the coated steel sheet 12, since the top coating material 1 does not contain the thermosetting anthrone, the distribution (island) of the hardened fluorenone in the surface of the coating film was not found. Therefore, none of A and B of the peak intensity ratio A/B was obtained. Further, in the coated steel sheet 13, since the top coating material m does not contain the polyimide precursor, the hardened ketone constitutes the entire surface of the coating film, and the island of the hardened ketone in the surface of the coating film is not found. Therefore, none of A and B of the peak intensity ratio A/B was obtained. Further, regarding the coated steel sheet 28, the hardened ketone is sea, and the polyimide is distributed in the form of an amorphous island. In addition, the "distribution state" of either of the coated steel sheets 19 and the coated steel sheets 29 is "continuous". Therefore, the "maximum area of the island (Smax)" is not obtained for any of the coated steel sheets.

Further, the coated steel sheet 30 was produced in the same manner as the coated steel sheet 3 except that the chemical synthesis treatment was not performed. The surface coating film of the coated steel sheet 30 was observed and measured in the same manner as the coated steel sheet 1. As a result, the occupied area ratio of the hardened fluorenone was 35%, the distribution state was "island", and the distribution shape was "substantially rounded". The maximum area of the island is 100 μm ² and the peak intensity ratio A/B is 30.

[Evaluation]

The coated steel sheets 1 to 30 were evaluated for the items.

[film adhesion]

(1) Processing adhesion (Ad-1)

Each of the coated steel sheets 1 to 30 was cut to a width of about 2 times the width of 70 mm, and the surface of the coated coating film was bent 2T on the front side, and the processed portion (bent portion) was peeled off by a transparent tape to obtain the time. The residual ratio of the top coat film was evaluated by the above criteria. Further, the residual ratio of the top coat film was 50 mm in which 10 mm of both ends of the bent portion was removed, and the size of the remaining portion of the coating film was measured with a ruler, and the ratio of the area of the remaining portion to the area of the 50 mm wide region was calculated.

(Evaluation criteria for coating film adhesion)

A: The residual rate is 100%

B: The residual rate is 95% or more and less than 100%.

C: The residual rate is 90% or more and less than 95%

D: The residual rate is 80% or more and less than 90%

E: The residual rate is 70% or more and less than 80%.

F: Residual rate is 50% or more and less than 70%

G: Residual rate is less than 50%

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

Each of the coated steel sheets 1 to 30 was immersed in boiling water for 2 hours, and the residual film coating rate at the time of peeling the checkerboard tape on which the top coat film was applied was determined, and evaluated based on the evaluation criteria.

[heat resistance]

Each of the coated steel sheets 1 to 30 was stored at 250 ° C, 300 ° C, and 350 ° C for 24 hours, and then the residual film coating rate at the time of peeling the checkerboard tape on which the top coat film was applied was determined, and the evaluation was performed. Benchmarks are evaluated.

[Food resistance]

(1) Initial food contamination resistance (AP-1)

The food was placed on each of the surface coating films of the coated steel sheets 1 to 30 in an untested state, and the coated steel sheets were heated at 250 ° C for 1 hour, and then the wiping state was observed by wiping the food contaminants from the coated steel sheets with a paper towel. The food uses four kinds of salad oil, butter, soy sauce and sauce, and the state of wiping is observed for each food type. Then, the evaluation was performed using the evaluation criteria.

(Evaluation criteria for food contamination resistance)

A: Each food can be easily removed by wiping with a paper towel.

B: Each food can be removed by wiping with a paper towel (no residue after)

C: One type of food can be removed by wiping with a paper towel, but there are residues (the other three can be removed)

D: One type of food can not be removed with a paper towel (the other three can be removed)

E: Two kinds of foods can not be removed with a paper towel (the other two can be removed)

F: 3 kinds of foods can not be removed with a paper towel (the other one can be removed)

G: All kinds of foods are wiped and cannot be removed.

(2) Food contamination resistance after heat resistance test (AP-2)

The test of the condition (1) was carried out except that the food was placed on the coated steel sheet after heating at 350 ° C for 24 hours, and the wiping state of each food was observed, and the evaluation was performed based on the evaluation criteria.

(3) Food contamination resistance in continuous use (continuous test, AP-3)

The test of the condition (1) was repeated 10 times using the same coated steel sheet, and the wiping state of each of the foods of the tenth time was observed, and the evaluation was performed based on the above criteria.

The results are shown in Table 6.

[Production and evaluation of transparent coated steel sheets]

Using a propeller mixer, the raw material was stirred at 1000 rpm, and the surface was coated. Film coating (clear coating). That is, the clear coating material was prepared in the same manner as the top coating material c except that the coloring pigment and the pigment dispersing agent were not prepared. The content of the non-volatile component of the clear coating material was 16.83 mass%, and the amount of the curable anthrone (S) relative to 100 parts by mass of the polyimine precursor (P) was 5.0 parts by mass.

A coated steel sheet 31 was produced in the same manner as the coated steel sheet 1 except that the clear coating material was used. When the surface of the coated steel sheet 31 was coated with a clear coating film and observed and measured in the same manner as the coated steel sheet 1, the area ratio of the hardened fluorenone was 35%, the distribution state was "island", and the distribution shape was "substantially The circular shape has a maximum area of 100 μm ² and a peak intensity ratio A/B of 30.

Moreover, the coated steel sheets 31 were evaluated for the coating film adhesion, heat resistance, and food contamination resistance, respectively, and as a result, the same results as those of the coated steel sheets 3 in Table 6 were obtained.

[Production of coated steel sheets 32 and 33]

A molten Al-9% Si-plated steel sheet (thickness: 0.4 mm, single-side plating adhesion amount: 40 g/m ² ) was prepared as a steel sheet. The alkali degreasing was carried out, and as a coating pretreatment, Ti-based chromium-free treatment was carried out as a chemical synthesis treatment. The chemical synthesis treatment liquid used titanium hydrofluoride (H ₂ TiF ₆ : 0.1 mol/L), and the chemical synthesis treatment liquid was applied onto the surface of the plated steel sheet so that the adhesion amount of Ti became 10 mg/m ² . And let it dry.

On the other hand, 30 parts by mass of aluminum dihydrogen phosphate, magnesium triphosphate, is added as a rust preventive pigment to 100 parts by mass of the polyimide precursor B, and the primer coating film is prepared. material. The primer coating film coating was applied to the chemical conversion treatment film of the plated steel sheet so that the dried film thickness was 5 μm, and the steel plate was heated at a temperature of 280° C. to produce a polyimide. The undercoat film is formed.

The surface of the undercoat film produced at room temperature was coated with the top coat c under the same conditions as those of the coated steel sheet 3, and heated to prepare a top coat film. In this manner, the coated steel sheet 32 is produced. Further, the coated steel sheet 33 was produced in the same manner as the coated steel sheet 32 except that the undercoat film was not formed.

[Evaluation]

The coated steel sheets 32 and 33 were evaluated for the coating film adhesion, heat resistance, and food contamination resistance, respectively. Further, the coated steel sheets 32 and 33 were evaluated for the corrosion resistance.

[Corrosion resistance]

The flat portions (portions other than the end cut surfaces) of the coated steel sheets 32 and 33 were cross-cut, and 5% salt water was sprayed on the coating film of the coated steel sheet while maintaining the temperature at 35 ° C to carry out the salt spray test. (According to SST, JIS Z2371) 240 hours. After the test, the maximum expansion width of the cross-cut portion was observed, and evaluation was performed on the evaluation criteria. The results are shown in Table 7.

(Evaluation criteria for corrosion resistance)

A: The maximum expansion range is less than 1mm

B: The maximum expansion range is 1mm or more and less than 2mm.

C: The maximum expansion range is 2mm or more and less than 3mm

D: The maximum expansion range is 3mm or more and less than 4mm.

E: The maximum expansion range is 4mm or more

The coated steel sheets 1 to 5, 7 to 11, and 14 to 33 are all excellent in coating film adhesion, heat resistance, and food contamination resistance, and have at least no practical problem as a member for a conditioning tool. The coated steel sheets 32 and 33 indicate that there is no practical problem in terms of corrosion resistance as at least a member for the conditioning tool.

On the other hand, the coated steel sheet 6 is not practically useful in terms of food contamination resistance. The reason for this is considered to be that the area ratio of the hardened fluorenone in the surface of the top coat film is insufficient. Further, the coated steel sheet 12 is also insufficiently practical in terms of resistance to food contamination. The reason is considered to be that the base material of the top coat film is only polyimine (since the top coat film does not contain hardened fluorenone). Further, the coated steel sheet 13 is not practically practical in terms of coating film adhesion, heat resistance, and food contamination resistance. The reason is considered to be that the base material of the top coat film is only hardened fluorenone (the top coat film does not contain polyimide).

According to the above, it is understood that the steel sheet and the coating film are stacked in this order, and the coating film includes a top coating film comprising a polyimide and a hardened ketone and constituting a surface of the coated steel sheet. A coated steel sheet having a hardened fluorenone having an area ratio of 5% or more in the surface of the surface of the surface coating film is used as a coated steel sheet for a member for a conditioning device, and is excellent in both heat resistance and antifouling properties.

Moreover, for example, the coated steel sheets 3 and 7 are all resistant to food compared with the coated steel sheet 6. The product is more excellent in terms of pollution. Further, for example, the coated steel sheets 3 and 8 are more excellent in food contamination resistance after the heat resistance test than the coated steel sheets 9. From the above, it is understood that the content of the hardened fluorenone in the top coat film is more preferably from 1 part by mass to 10 parts by mass per 100 parts by mass of the polyimide.

Further, for example, the coated steel sheets 3, 7, and 14 are more excellent in food contamination resistance than the coated steel sheets 6. Further, for example, the coated steel sheets 3, 8, and 17 are more excellent in food contamination resistance after the heat resistance test than the coated steel sheet 9. From the above, it is understood that the occupation ratio of the hardened fluorenone in the surface of the top coat film is 5% to 70% from the viewpoint of the durability of the antifouling property.

Further, for example, the coated steel sheet 3 is superior to the coated steel sheet 29 in terms of food contamination resistance after the heat resistance test and the continuous test. From the above, it is understood that the surface of the top coat film is more effective as a sea-island structure of a polyimide and a hardened fluorenone from the viewpoint of durability of the antifouling property. Further, for example, the coated steel sheet 27 is more excellent in food contamination resistance after the heat resistance test than the coated steel sheet 28. From the above, it is understood that the surface of the top coat film is more effective as a sea-island structure formed by the sea of the hardened fluorene and the island of the hardened fluorenone from the viewpoint of the durability of the antifouling property.

Further, among the coated steel sheets 15 to 18, the coated steel sheets 15 to 17 are more excellent in food contamination resistance after the heat resistance test than the coated steel sheets 18. Further, in the case of coating the steel sheets 20, 21, and 22, the coated steel sheets 20 to 22 are superior in coating film adhesion, food contamination resistance after heat resistance test, and food contamination resistance in continuous test. . From the viewpoint of the durability of the antifouling property or the coating film adhesion, the area of each of the hardened ketone islands on the surface of the top coat film is 300 μm ² or less, or the top coat is applied. The shape of the hardened ketone island in the surface of the film is substantially circular and more effective.

Further, among the coated steel sheets 15 to 18, the coated steel sheets 15 and 16 are more excellent in food contamination resistance after the heat resistance test than the coated steel sheets 17 and 18. Further, among the coated steel sheets 24 to 27, the coated steel sheets 25 and 26 are superior to the coated steel sheet 24 in terms of food contamination resistance, and are in comparison with the coated steel sheet 27 after the heat resistance test and in the continuous test. It is more excellent in food contamination resistance. From the above can be seen, the viewpoint of durability of the antifouling property, the coating film using the topcoat to the surface of the ATR infrared spectrum measurement method, the peak intensity of 1014cm ^-1 with respect to peak intensity of 1375cm ^-1 When the ratio is defined as A, when the top coat film is measured by infrared spectrum analysis by the KBr method, the ratio of the peak intensity of 1014 cm ^{-1 to} the peak intensity of 1375 cm ^-1 is defined as B, and the ratio A of A to B is B is more effective from 1.1 to 100.

Further, in the coated steel sheets 1 to 5, the coated steel sheets 2 to 5 are superior to the coated steel sheets 1 in terms of heat resistance at 250 ° C, and the coated steel sheets 2 and 5 are superior to the coated sheets in heat resistance at 300 ° C. The coated steel sheet 1 is more excellent in the coated steel sheets 3 and 4, and the coated steel sheets 2 and 5 are superior to the coated steel sheet 1 in terms of heat resistance at 350 ° C, and the coated steel sheet 4 is more excellent, and the coated steel sheet 3 is further excellent. Moreover, in the initial resistance to food contamination, the coated steel plate 2~5 is superior to the coated steel plate 1, and the coated steel plate 2~5 is superior to the coated steel plate 1 in terms of food resistance after heat resistance test or continuous test. The coated steel plate 3~5 is better than the coated steel plate 2. From the above, it is understood that the polyethylenimine has a Tg of from 270 ° C to 400 ° C from the viewpoint of durability against heat resistance and antifouling properties.

Further, in the coated steel sheets 20 to 23, in terms of coating film adhesion, the coating is applied. The order of the steel sheets 20, 21, 22, and 23 is excellent, and in terms of heat resistance, any of the coated steel sheets is also generally good, and the coated steel sheets 21 to 23 are superior to the coated steel sheets in the heat resistance test and the food contamination resistance in the continuous test. The steel plate 20 is mounted, and the coated steel sheets 22 and 23 are superior to the coated steel sheet 21. According to the above, it is understood that the step of applying a top coat coating layer on a coated original plate comprising a steel sheet, forming a top coat layer, and heating the top coat layer, and baking the coated original sheet to form a top coat film, The top coat paint contains a precursor of polyimine, a curable fluorenone, and a solvent, and at least a part of the curable fluorenone is heated on the surface of the top coat layer so that the temperature of the steel sheet reaches 180° C. or higher. When the top surface is coated with a coating layer to form a top coating film, it is possible to provide a coated steel sheet which is excellent in both heat resistance and antifouling properties as a coated steel sheet for a member for a conditioning tool.

Further, among the coated steel sheets 24 to 27, the coated steel sheets 25 and 26 are superior to the coated steel sheet 24 in terms of food contamination resistance, and are in comparison with the coated steel sheet 27 after the heat resistance test and in the continuous test. It is more excellent in food contamination resistance. According to the above, it is understood that it is more effective to apply the top coat material to the original plate to be coated until the start of heating (standby time) is 5 seconds to 60 seconds from the viewpoint of providing a coated steel sheet having excellent antifouling properties. .

Further, in the coated steel sheets 24 and 25, the coated steel sheet 25 is superior to the coated steel sheet 24 in terms of food contamination resistance. Further, among the coated steel sheets 27 and 29, the coated steel sheet 27 is superior to the coated steel sheet 29 in terms of food contamination resistance after the heat resistance test. From the above, it is understood that from the viewpoint of providing a coated steel sheet having excellent antifouling properties, it is more effective to start the heating until the time until the temperature is reached (the burning time) is 30 seconds to 240 seconds.

Further, among the coated steel sheets 21 and 22, the coated steel sheet 22 is superior to the coated steel sheet 21 in terms of coating film adhesion, heat resistance test, and food contamination resistance in continuous test. From the above, it is understood that the steel sheet reaches a temperature of 200 ° C or higher from the viewpoint of providing a coated steel sheet excellent in durability of coating film adhesion and antifouling properties.

Further, among the coated steel sheets 14 and 15, the coated steel sheet 15 is superior to the coated steel sheet 14 in terms of food contamination resistance in the continuous test. Further, among the coated steel sheets 16 and 17, the coated steel sheet 16 is superior to the coated steel sheet 17 in terms of food contamination resistance after the heat resistance test. From the above, it is understood that it is more effective to apply the top coat coating so that the film thickness of the top coat film is 2 μm to 20 μm from the viewpoint of providing a coated steel sheet having excellent antifouling properties.

Further, for example, the coated steel sheets 3 and 7 are more excellent in food contamination resistance than the coated steel sheets 6. Further, for example, the coated steel sheets 3 and 8 are more excellent in food contamination resistance after the heat resistance test than the coated steel sheets 9. According to the above, it is understood that the content of the curable anthrone in the top coating is 1 mass based on 100 parts by mass of the precursor of the polyimide, from the viewpoint of the coated steel sheet having excellent antifouling properties. More than 10 parts by mass is more effective.

Further, for example, the coated steel sheet 3 is more excellent in coating film adhesion than the coated steel sheet 30. From the above, it is understood that it is more effective to provide a chemically synthesized film on the surface of the steel sheet from the viewpoint of providing a coated steel sheet excellent in coating film adhesion.

[Industrial availability]

The coated steel sheet of the present invention has 5% or more of the surface of the surface coated film. The area occupied has a hardened fluorenone on the surface of the topcoat film. Therefore, compared with the coated steel sheet which has a fluororesin in the surface of a top surface coating film, it has the same anti- Therefore, the coated steel sheet of the present invention is suitably used for the material of a machine which requires antifouling properties in a higher temperature environment. Therefore, according to the coated steel sheet of the present invention, further development of a heating conditioning apparatus which contributes to the use of more specific heating energy conditioning such as heating at a higher temperature or steam heating is expected.

Claims (12)

A coated steel sheet having a coating film on a steel sheet, wherein the coating film comprises a top coating film comprising a polyimide and a hardening ketone, the surface of the top coating film The content ratio of the hardened fluorenone is 5% or more, and the content of the hardened fluorenone in the top coat film is 1 part by mass to 10 parts by mass based on 100 parts by mass of the polyimine. The coated steel sheet according to claim 1, wherein the hardened fluorenone in the surface of the top coating film has an occupied area ratio of 5% to 70%. The coated steel sheet according to claim 1, wherein the surface of the top coating film has an island structure, and the sea-island structure has an island phase of the polyimine and an island of the hardened fluorenone. . The coated steel sheet according to claim 3, wherein the island of the hardened fluorenone is substantially circular, and the area of each of the hardened ketone islands is 300 μm ² or less. The patentable scope of the application of the coated steel plate to item 1, wherein when the use of infrared spectroscopy to measure the attenuated total reflection surface of the topcoat coating film, 10 14 cm ^-1 with respect to peak intensity of the peak 1375cm ^-1 The ratio of the intensity is set to A, and when the surface coating film is measured by infrared spectrum analysis using the potassium bromide method, when the ratio of the peak intensity of 1014 cm ^{-1 to} the peak intensity of 1375 cm ^-1 is defined as B, The ratio of A to the B is 1.1 to 100. The coated steel sheet according to claim 1, wherein the polythenimine has a Tg of from 270 ° C to 400 ° C. A method for producing a coated steel sheet, comprising: applying a top coating on a coated original plate comprising a steel sheet to form a top coating layer, and heating the top coating layer to perform the coating on the coated original sheet Burning, thereby forming a step of coating a surface coating film comprising a precursor of polyimine, a sclerosing fluorenone, and a solvent, wherein the sclerosing fluorenone in the top coating is relative to The content of the polyethyleneimine precursor is 100 parts by mass or more, and the heating time is 5 seconds to 70 seconds after the top coating material is applied to the coated original sheet. The hardening ketone is heated in the surface of the top coating layer in such a manner that the temperature of the steel sheet reaches 180° C. or higher and the time until the temperature is reached after the heating is started is 30 seconds to 240 seconds. At least a portion of the top surface of the coating layer is applied to form the topcoat film. The method for producing a coated steel sheet according to claim 7, wherein the steel sheet reaches a temperature of 200 ° C or higher. The method for producing a coated steel sheet according to claim 7, wherein the top coating material is applied so that the film thickness of the top coating film is 2 μm to 20 μm. The method for producing a coated steel sheet according to the seventh aspect of the invention, wherein The content of the curable anthrone in the top coat is 1 part by mass to 10 parts by mass based on 100 parts by mass of the precursor of the polyimide. The method for producing a coated steel sheet according to any one of claims 7 to 10, wherein the steel sheet has a chemically synthesized treatment film on the surface of the steel sheet. A member for a conditioning apparatus, comprising the coated steel sheet according to any one of claims 1 to 6.