JP2007070682A - Steel sheet coated with fluororesin, and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steel sheet coated with a fluororesin which has adequate adhesiveness to the steel sheet having a surface treatment layer containing no chromium and is superior in corrosion resistance, lubricity, heat resistance and baked-stain resistance (unstickiness), and to provide a method for manufacturing the coated steel sheet by baking the steel sheet at a low temperature in an ultrashort period of time. <P>SOLUTION: The steel sheet coated with a fluororesin comprises: a steel sheet; the surface treatment layer containing no chromium formed on the surface; a primer layer containing 1 to 20 pts.mass of a silane coupling agent with respect to 100 pts.mass of a resin mainly containing a polyethersulfone resin; and the top layer mainly containing a polytetrafluoroethylene resin and the polyethersulfone resin. The manufacturing method comprises the steps of: forming the primer layer by baking it at the maximal arrival temperature for the steel sheet of 410°C or lower for 120 seconds or shorter; and forming the top layer at the maximal arrival temperature for the steel sheet of 410°C or lower for 120 seconds or shorter. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention is a fluororesin-coated steel sheet that does not have a chromate surface treatment layer and that can be applied to various products utilizing the lubricity, heat resistance, and non-adhesiveness that are the characteristics of fluororesin, and manufacturing the steel sheet by low-temperature and short-time firing. On how to do.

  Conventional fluororesin-coated steel sheets used as a base material zinc alloy-plated steel sheets such as stainless steel sheets, aluminum-plated steel sheets, and 55% aluminum / galvanized steel sheets. These base materials are relatively expensive, and in recent years, there is a strong demand for fluororesin-coated steel sheets with excellent heat resistance, and furthermore, the inherent lubricity of fluororesins based on galvanized steel sheets, which are relatively low in price. There is a growing demand for products that take advantage of.

By the way, the conventional fluororesin-coated steel sheet needs to be fired at a maximum steel sheet temperature exceeding 410 ° C., and is fired at a maximum steel sheet temperature of 380 to 410 ° C. in order to adhere the fluororesin film of the top layer. It took a long time of about 30 to 3 minutes. However, in the case of a galvanized steel sheet, when the maximum attained steel sheet temperature is heated to 350 ° C. or higher, a Zn—Fe alloy layer is formed at the interface between the steel sheet and the galvanized layer. When the alloy layer is thick, the workability of the galvanized layer is remarkably deteriorated, and there is a problem that the galvanized layer is peeled off from the steel sheet during bending. Furthermore, when heating to a firing temperature exceeding 410 ° C. at the highest steel sheet temperature, the melting point of zinc is reached, the zinc melts, plating unevenness occurs, the alloy layer is formed thick, and the plating adhesion is significantly deteriorated Because of this, it could not be put into practical use.
In addition, the top layer and the primer layer below the layer contain a large amount of additives (pigments) such as rust preventive pigments, colored pigments and extender pigments exceeding 40% by mass from the viewpoint of heat resistance and corrosion resistance. It was. Therefore, the content of the resin is relatively reduced, and the workability and adhesion of the top layer and the primer layer tend to decrease. As a result, the coating film is cracked, and the coating film and the steel plate Water and oxygen easily penetrated into the interface, leading to a decrease in corrosion resistance.

  Therefore, a method of reducing the firing temperature of the fluororesin coating (a method of improving heat resistance), for example, a method of applying a fluororesin mixed with a heat resistant resin to a metal and firing it under reduced pressure (Patent Document 1) Etc. have been proposed. Also, a method of improving the adhesion of the fluororesin coating to the steel sheet, for example, a method of applying a fluororesin primer on a metal surface and heating it to a temperature higher than the decomposition temperature of the resin and then melt-coating the fluororesin (Patent Document 2) ) Etc. have been proposed. Furthermore, a method (Patent Documents 3 to 8) in which a heat-resistant resin primer is applied to a plated steel sheet, the heat resistance is improved, and a fluororesin mixed with the heat-resistant resin is applied thereon (Patent Documents 3 to 8) is also proposed. .

  However, in spite of the various proposals as described above, it has not been possible to obtain a fluororesin-coated steel sheet that makes full use of the heat resistance and lubricity of the fluororesin coating and is excellent in corrosion resistance and seizure contamination. there were.

  Further, the conventional galvanized steel sheet has a chromate layer provided on the galvanized layer from the viewpoint of corrosion resistance, and the chromate layer is extremely excellent in terms of heat resistance and adhesion. However, chromium-based surface treatment agents have recently been designated as environmentally hazardous substances and cannot be used, so the development of alternative technologies has been an urgent task. Therefore, various non-chromium surface treatment agents and surface treatment methods for forming a chromium-free non-chromium surface treatment layer as an alternative to the chromate layer have been proposed, but many of the surface treatment layers obtained by these have corrosion resistance, There was a problem that the adhesion did not reach the chromate layer.

Japanese Patent Laid-Open No. 56-4430 JP 56-77142 A JP-A 61-137534 JP 61-138567 A JP-A-61-193842 Japanese Patent Laid-Open No. 4-94768 Japanese Patent Laid-Open No. 5-8347 JP-A-6-91805

  The object of the present invention is to solve such problems of the prior art. That is, firing of the top layer containing polytetrafluoroethylene resin (fluororesin) without using an environmentally hazardous substance such as a chromium-based surface treatment agent for forming the surface treatment layer, the maximum steel plate temperature of 410 ° C. or less At a temperature of 120 seconds or less, avoiding problems due to the high temperature and long time heating of the resin, and in the case of a galvanized steel sheet, interfacial peeling from the steel sheet of the galvanized layer An object of the present invention is to provide a fluororesin-coated steel sheet having no cracks at a low price and to provide a manufacturing method thereof.

  The present invention has a non-chromium surface treatment layer on a steel sheet surface, a primer layer mainly composed of a polyethersulfone resin on the layer, and a polytetrafluoroethylene resin and a polyethersulfone on the layer. A ratio of 1 to 20 parts by mass of a silane coupling agent with respect to 100 parts by mass of a resin whose main component is a polyethersulfone resin, the fluororesin-coated steel sheet having a top layer mainly composed of a resin It is a fluororesin-coated steel sheet characterized by containing.

  In the fluororesin-coated steel sheet of the present invention, the silane coupling agent of the primer layer is preferably an aminosilane coupling agent or an epoxy silane coupling agent.

  In the fluororesin-coated steel sheet of the present invention, the primer layer has a polyethersulfone resin of 60 to 100 parts by mass, a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin of 0 to 40 parts by mass, and a polytetrafluoroethylene resin of 0 to 100 parts. It is preferable that the silane coupling agent is contained at a ratio of 1 to 20 parts by mass with respect to 100 parts by mass of the resin having a composition of 10 parts by mass.

  In the fluororesin-coated steel sheet of the present invention, the primer layer has a polyethersulfone resin of 60 to 100 parts by mass, a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin of 0 to 40 parts by mass, and a polytetrafluoroethylene resin of 0 to 100 parts. The pigment content is preferably 40 parts by mass or less with respect to 100 parts by mass as a total of 100 parts by mass of the resin having a composition of 10 parts by mass and 1 to 20 parts by mass of the silane coupling agent.

  In the fluororesin-coated steel sheet of the present invention, the top layer has a polytetrafluoroethylene resin of 30 to 60 parts by mass, a polyethersulfone resin of 10 to 70 parts by mass, and a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin of 0 to It preferably contains a resin having a composition of 40 parts by mass.

  In the fluororesin-coated steel sheet of the present invention, the top layer has a polytetrafluoroethylene resin of 30 to 60 parts by mass, a polyethersulfone resin of 10 to 70 parts by mass, and a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin of 0 to It is preferable that the pigment is contained at a ratio of 40 parts by mass or less with respect to 100 parts by mass in total of the resin having a composition of 40 parts by mass.

  In the fluororesin-coated steel sheet of the present invention, the surface treatment layer is preferably made of a zirconia surface treatment agent, a silane coupling agent, or a titanium coupling agent.

  In the fluororesin-coated steel sheet of the present invention, the steel sheet is preferably a hot-dip galvanized steel sheet, a hot-dip 5% aluminum / zinc alloy-plated steel sheet, or an electrogalvanized steel sheet.

  The present invention also has a non-chromium surface treating agent layer on the steel sheet surface, a primer layer mainly composed of a polyethersulfone resin on the layer, a polytetrafluoroethylene resin on the layer, and A method for producing a fluororesin-coated steel sheet having a top layer mainly composed of a polyethersulfone resin, wherein the primer layer contains 1 silane coupling agent per 100 parts by mass of the resin mainly composed of the polyethersulfone resin. After applying the primer so as to contain at a ratio of ˜20 parts by mass and firing at a maximum steel sheet temperature of 410 ° C. or less for 120 seconds or less, the main component is polytetrafluoroethylene resin and polyethersulfone resin. Fluororesin coating characterized by applying a top coat and firing at a maximum steel sheet temperature of 410 ° C. or lower for 120 seconds or shorter A method of manufacturing the plate is,.

  In the method for producing a fluororesin-coated steel plate of the present invention, the primer is fired at a maximum steel plate temperature of 250 to 410 ° C. for 120 to 20 seconds, and the top coat is fired at a maximum steel plate temperature of 350 to 410 ° C. for 120 to 20 °. It is preferable to carry out for 2 seconds.

  In the fluororesin-coated steel sheet of the present invention, the primer layer has excellent adhesion to both the non-chromium surface treatment layer and the top layer. Since firing can be completed in a short time, compared to conventional chromate-based surface-treated fluororesin-coated steel sheets, the original properties of fluororesin, such as heat resistance, lubricity, and corrosion resistance, can be fully utilized. In addition, since the content of the pigment in the primer layer and the top layer can be reduced, it is excellent in terms of processability, productivity, environmental pollution, and price.

  The present invention reduces the pigment content of the primer layer by adding a silane coupling agent to a primer layer mainly composed of a polyethersulfone resin (hereinafter also simply referred to as PES), thereby providing a non-chromium surface treatment layer. The adhesion between the polytetrafluoroethylene resin (hereinafter also simply referred to as PTFE) and the top layer mainly composed of PES is improved, and the firing temperature and time of the top layer are simultaneously reduced. It is a particularly successful invention.

  The present invention provides a non-chromium surface treating agent layer on a steel sheet surface, a primer layer containing 1 to 20 parts by mass of a silane coupling agent with respect to 100 parts by mass of a resin mainly composed of PES, and PTFE and This is a fluororesin-coated steel sheet having a top layer mainly composed of PES in this order.

  Moreover, this invention has a non-chromium type surface treating agent layer on the steel plate surface, and on this layer, 1 to 20 parts by mass of a silane coupling agent is added to 100 parts by mass of a resin mainly composed of PES. A method for producing a fluororesin-coated steel sheet having a primer layer contained in a proportion, and a top layer mainly composed of PTFE and PES on the layer, wherein the primer is applied at a maximum steel sheet temperature of 410 ° C. or less. The fluororesin-coated steel sheet is formed by firing for 120 seconds or less to form a primer layer, and then applying a top coating, and firing at a maximum steel sheet temperature of 410 ° C. or less for 120 seconds or less to form a top layer. It is a manufacturing method.

(steel sheet)
The steel sheets used in the present invention are cold rolled steel sheets, hot rolled steel sheets, electrogalvanized steel sheets, electrogalvanized nickel plated steel sheets, nickel plated steel sheets, hot dip galvanized steel sheets, molten 5% aluminum / zinc alloy plated steel sheets, molten 55 % Aluminum / zinc alloy plated steel sheet, stainless steel sheet, chrome plated steel sheet, etc. Preferable are various galvanized steel sheets. Particularly preferred are electrogalvanized steel sheets, hot-dip galvanized steel sheets, and hot-dip 5% aluminum / zinc alloy-plated steel sheets. The weight per unit area (one side) of the galvanized steel sheet is preferably 10 to ²⁰⁰ g / m ² . The basis weight may be different between the front side and the back side of the steel plate.

(Base adjustment)
The steel plate used in the present invention preferably removes as much dirt and contaminants as possible on the steel plate surface before applying the surface treatment agent. The substrate preparation method and conditions for the removal are not limited, but general blasting treatment, general degreasing treatment with alkali, surfactant, organic solvent, pickling treatment, brush with brush such as brush roll, etc. Examples are brush processing to be dropped.

(Surface treatment layer)
The steel plate used in the present invention is surface-treated with a non-chromium surface treatment agent before forming the primer layer. Examples of the non-chrome surface treatment agent include a zirconia surface treatment agent, a silane coupling agent, a titanium coupling agent, a silica surface treatment agent, and an organic resin surface treatment agent. Particularly preferred are zirconia surface treatment agents, silane coupling agents, and titanium coupling agents.
A commercially available product can be used as the zirconia-based surface treatment agent.
Examples of the silane coupling agent include epoxy silanes, vinyl silanes, mercapto silanes, amino silanes, and the like, but the same silane coupling agents used for the primer layer described later can be used. Preference is given to epoxysilanes and aminosilanes.
Titanium coupling agents include isopropyl triisostearoyl titanate, isopropyl tri-n-dodecylbenzenesulfonyl titanate, isopropyl tris (dioctyl pyrophosphate) titanate, tetraisopropyl bis (ditridecyl phosphite) titanate, tetraoctylbici (ditridecyl) Phosphite) titanate, tetra (2,2-diallyloxymethyl-1-butyl) bisi (ditridecyl phosphite) titanate, bis (dioctyl pyrophosphate) oxyacetate titanate, bis (dioctyl pyrophosphate) ethylene titanate, orthopropyltri (N-aminoethyl) titanate and the like are exemplified.

The organic resin surface treatment agent may be at least one resin having at least one functional group selected from a hydroxyl group, an isocyanate group, a carboxyl group, a glycidyl group, and an amino group. Examples of the resin include epoxy resin, alkyd resin, acrylic resin, urethane resin, polyvinyl butyral resin, phenol resin, and melamine resin. The epoxy resin is not limited to bisphenol type epoxy resins such as bisphenol A type epoxy resin and bisphenol F type epoxy resin. For example, an epoxy resin whose end is modified with an amine such as n-propylamine, diethylamine, ethanolamine or diethanolamine is used as the organic resin surface treatment agent. Preferable is polyvinyl butyral resin from the viewpoint of corrosion resistance and the like.
Phosphate treating agents and chromate treating agents known as chemical conversion treating agents are not preferred because they may cause water pollution and environmental pollution.

The non-chromium surface treatment layer of the present invention is formed on the steel sheet surface by applying a non-chromium surface treatment agent by a conventional method such as dipping or roll coater.
The adhesion amount (one side) of the non-chrome surface treatment agent is 5 to 2000 mg / m ² , preferably 30 to 1000 mg / m ² . When the adhesion amount is less than 5 mg / m ² , the adhesion between the steel plate surface and the primer layer is insufficient. On the other hand, if the adhesion amount is more than 2000 mg / m ² , the workability deteriorates and the cost increases.

(Primer layer)
The primer layer of the present invention is a proportion of 1 to 20 parts by mass, preferably 5 to 15 parts by mass, more preferably 5 to 10 parts by mass of the silane coupling agent with respect to 100 parts by mass of the resin mainly composed of PES. It is a coating layer to contain. When the ratio of the silane coupling agent is less than 1 part by mass, the adhesion between the steel plate and the primer layer is insufficiently improved. Conversely, when the ratio exceeds 20 parts by mass, the primer layer becomes brittle and bent. During processing, the primer layer may break and the top layer may peel off.

  The resin mainly composed of PES is a resin containing 60 to 100 parts by mass of PES in 100 parts by mass of the resin component. By setting it as this composition, resin which has this PES as a main component can improve the adhesiveness of a primer layer and a top layer more. Moreover, it is good also as resin which has this PES as a main component and contains the tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin (henceforth only PFA) in the ratio of 40 mass parts or less. By using this composition, the resin containing PES as a main component can further improve the adhesion between the primer layer and the top layer, and the effect of adding PFA is remarkable in low-temperature firing at 350 to 380 ° C. Expressed in On the contrary, when the ratio of the PFA is more than 40 parts by mass, the adhesion between the steel plate and the primer layer becomes insufficient. Furthermore, when PTFE is contained in an amount of 10 parts by mass or less with respect to 60 to 100 parts by mass of PES and 0 to 40 parts by mass of PFA, there is an improvement in adhesion between the primer layer and the top layer, which is more preferable.

PES is a resin (Tg: 225 ° C.) in which paraphenylene groups are alternately bonded by sulfone groups and ether groups, and includes those in which a small amount of a third component is co-condensed. PES is a flame-retardant amorphous engineering resin excellent in heat resistance and processability, and is commercially available, for example, as “Sumika Excel PES” (manufactured by Sumitomo Chemical Co., Ltd.).
PFA is a fluororesin that can be melt-molded with a perfluoroalkylvinylpolyether content of about 2.8 to 4.0% by mass, and is usually solid, “Neofuron PFA” (manufactured by Daikin Industries) "Teflon PFA" (manufactured by Mitsui DuPont Fluorochemical Co., Ltd.), "Aflon PFA" (manufactured by Asahi Glass Co., Ltd.), and the like.
PTFE is a non-adhesive and self-lubricating engineering resin that has excellent heat resistance, chemical resistance, electrical properties, and abrasion resistance, but is difficult to melt mold. It is commercially available as a powder, such as “Polyflon TFE” (manufactured by Daikin Industries), “Teflon TFE” (manufactured by Mitsui / DuPont Fluorochemical Co., Ltd.), “Aflon TFE” (manufactured by Asahi Glass Co., Ltd.), and the like.

  The silane coupling agent effectively works to improve the adhesion between the primer layer and the steel sheet whose base material is adjusted, and the adhesion between the primer layer and the top layer. The silane coupling agent is vinyl silane coupling agent, epoxy silane coupling agent, styryl silane coupling agent, methacryloxy silane coupling agent, acryloxy silane coupling agent, amino silane coupling agent, ureido silane coupling agent, chloropropyl. Silane coupling agent, mercaptosilane coupling agent, sulfide silane coupling agent, isocyanate silane coupling agent, etc., epoxy silane coupling agent, aminosilane coupling agent, mercaptosilane coupling agent, sulfide silane coupling An agent is preferred, and an epoxy silane coupling agent and an amino silane coupling agent are particularly preferred. Specifically, γ-glycidyloxypropyltrimethoxysilane, γ- (2-aminoethyl) aminopropyltrimethoxysilane, and the like are preferable.

The primer layer of the present invention can further contain additives (pigments) such as rust preventive pigments, colored pigments and extender pigments, as long as the composition of the resin and the silane coupling agent is not destroyed.
Examples of the rust preventive pigment include zinc phosphate, aluminum phosphate, molybdate, silicate, and aluminum biphosphate.
Examples of the color pigment include titanium oxide, carbon black, graphite, copper / iron / manganese composite oxide, cobalt black, dial, titanium yellow, aluminum pigment, and color mica.
The extender pigments are barium sulfate, talc, mica, calcium carbonate, potassium titanate, aluminum borate, silica powder and the like.
Other additives are antifoaming agents, dispersants, leveling agents and the like.
It is not necessary to add the pigment in an amount of 40 parts by mass or more with respect to 100 parts by mass of the dry residue of the primer layer as in the prior art, and it is 40 parts by mass or less, preferably 5 to 0 parts by mass. When it exceeds 40 parts by mass, the bending workability is lowered, and the top layer is likely to be peeled off at the bending processed part.

The primer layer of the present invention is formed, for example, by applying a dispersion containing a silane coupling agent to the surface of a steel sheet and firing it by a conventional method. Firing is performed using a firing furnace at a maximum steel sheet temperature of 410 ° C. or less and 120 seconds or less, preferably 250 to 410 ° C. and 120 to 20 seconds, more preferably 250 to 380 ° C. and 30 to 60 seconds. In the present invention, when the maximum steel sheet temperature exceeds 410 ° C., the risk of zinc melting increases when a galvanized steel sheet is used, so the maximum steel sheet temperature is set to 410 ° C. or lower. On the other hand, in order to ensure the adhesion of the primer, the maximum reached steel plate temperature is preferably 250 ° C. or higher. Further, if the firing time exceeds 120 seconds, the effect is only saturated, and the cost is increased. And it is preferable to set it as 20 seconds or more in order to ensure the adhesiveness of a primer.
In the case of firing at a high temperature side within the temperature range, the firing time can be performed on the short time side within the time range. Moreover, when baking on the long time side within this time range, baking temperature can be implemented on the low temperature side within this temperature range. The firing temperature or firing time that is more than necessary does not have a particular advantage, but increases the firing cost.
The adhesion amount (one side) of the primer layer is 5 to 30 g / m ² , preferably 10 to 20 g / m ² . If the adhesion amount is less than 5 g / m ² , the adhesion to the steel sheet expected for the primer layer is insufficient, and conversely if it exceeds 30 g / m ² , the workability deteriorates and the cost increases. .

  The primer is prepared by, for example, dispersing PFA and PTFE in a solution in which a resin such as PES is dissolved in a solvent containing N-methylpyrrolidone as a main component, and then dissolving a silane coupling agent and stirring. To prepare. Co-solvents include aromatic solvents such as toluene and xylene, ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, and diisobutyl ketone, petroleum solvents such as “Solvesso 100” and “Solvesso 150”, ethylene glycol monomethyl ether, ethylene An ether solvent such as glycol monobutyl ether is used. The auxiliary solvent can be added up to about 40% by mass relative to the main solvent N-methylpyrrolidone.

(Top layer)
The top layer in the resin-coated steel sheet of the present invention is mainly composed of PTFE and PES. By using these as the main ingredients, seizure contamination (non-adhesiveness) and adhesion between the primer and the steel sheet are good. Can be. Here, having PTFE and PES as main components means that both are included and the total amount of both is 60 parts by mass or more. The top layer is preferably a resin composition having 30 to 60 parts by mass of PTFE and 10 to 70 parts by mass of PES. When the ratio of PTFE is less than 30 parts by mass or the ratio of PES is more than 70 parts by mass, the lubricity and seizure contamination are liable to decrease. On the contrary, when the ratio of PTFE is more than 60 parts by mass or the ratio of PES is less than 10 parts by mass, the adhesion between the primer and the steel sheet tends to be deteriorated.
When the PFA is further contained in an amount of 40 parts by mass or less with respect to the composition, the adhesion between the primer and the top layer is improved even when the firing temperature of the top layer is low, and the fluororesin is exposed on the top surface layer. Lubricity and seizure contamination are improved.
Each resin is the same type of resin used for the primer layer described above. Of course, the top layer and the primer layer do not need to be made of the same brand resin, that is, it is not necessary to use exactly the same resin. Different ones can be used.

  The top layer may further contain a pigment in a proportion of 40 parts by mass or less, preferably 5 to 30 parts by mass, more preferably 10 to 30 parts by mass with respect to 100 parts by mass of the resin. As the pigment, the same kind as that contained in the primer layer can be used. The main purpose of adding the pigment to the top layer is coloring, which is often different from the type of primer pigment.

  The top layer in the resin-coated steel sheet of the present invention is formed by applying a top coating containing a resin such as PTFE on the primer layer by a conventional method and baking it. Firing is performed in an extremely short time of 120 seconds or less at an atmospheric temperature of 500 ° C. or less using a firing furnace. By changing the ambient temperature and firing time depending on the line speed, the thickness of the steel plate, etc., the maximum reached steel plate temperature is 410 ° C. or lower and 120 seconds or shorter, preferably 350 to 410 ° C. for 120 to 20 seconds, more preferably 380 to 410 ° C. Performed in 100-30 seconds. When firing at a higher temperature within the maximum steel sheet temperature range, the firing time can be performed on the short time side within the time range. Moreover, when baking on the long time side within this time range, baking temperature can be implemented on the low temperature side within this temperature range.

When the highest steel plate temperature exceeds 410 ° C., the risk of zinc melting increases when a galvanized steel plate is used. Therefore, the highest steel plate temperature is set to 410 ° C. or lower. When the maximum steel sheet temperature is less than 350 ° C., seizure contamination is reduced, so that the temperature is preferably 350 ° C. or higher.
Further, if the firing time is less than 20 seconds, the seizure contamination property is similarly reduced. Therefore, it is preferably 20 seconds or longer, and if it exceeds 120 seconds, the effect is saturated and the cost is increased. Therefore, it shall be 120 seconds or less.
Adhesion amount of the top layer (one side) is preferably 1 to 30 g / ^{m 2,} more preferably at 8 to 20 g / ^{m 2.} If the adhesion amount is less than 1 g / m ² , the heat resistance and seizure contamination expected for the top layer tend to be insufficient, and conversely if it exceeds 30 g / m ² , the coating film becomes thicker during firing. The solvent inside the film bumps and a coating film defect called aside occurs, and the workability, corrosion resistance, seizure contamination, and the like tend to deteriorate. The top layer may form the same coating film on the front and back surfaces, but may form another coating film on the back surface.

The top coat is obtained by dissolving PES in the solvent used for preparing the primer and dispersing PTFE in the PES solution. If necessary, additives (pigments) such as coloring pigments, extender pigments, rust preventive pigments, etc., are added and stirred within the range where the composition ratio of the resin is not lost.
The fluororesin-coated steel sheet on which the top coat is applied and the top layer is formed is cooled to obtain a product. If necessary, after firing, when the steel sheet temperature is rapidly cooled from a temperature of 300 ° C. or higher to a rate of 5 ° C./second or more, the effect as the top layer is further improved.

Next, the present invention will be described in more detail with reference to comparative examples.
(Examples 1-14, Comparative Examples 1-8)
Table 1 shows the resins and silane coupling agents [γ-glycidyloxypropyltrimethoxysilane (A), γ- (2-aminoethyl) aminopropyltrimethoxy used for the preparation of the primers (P1 to P12, PH1 to PH2). Silane (B)] and the mass composition of the pigment are shown, and Table 2 shows the mass composition of the resin and the pigment used for the preparation of the top coat (T1 to T10, TH1 to TH2). However, a pigment composition is content in the layer after baking of a primer layer and a top layer.
Table 3 shows the conditions in which a non-chromium surface treatment agent layer was provided on the surface of the hot dip galvanized steel sheet, a primer and a top coat were applied, and baked to form a primer layer and a top layer. Table 4 shows the evaluation results of the performance tests (bending test, cross cut Eriksen test, pencil hardness test, dynamic friction test, seizure contamination test) of the obtained fluororesin-coated steel sheet.

Surface contaminants on the hot-dip galvanized steel sheet [plate thickness 0.5 mm, hot-dip galvanized coating amount (one side) 125 g / m ² ] were removed by washing with acetone. A zirconium-based non-chromium surface treatment agent (manufactured by Nihon Parkerizing Co., Ltd .; CT-E224) was applied to the surface of the hot-dip galvanized steel sheet (20 × 30 cm) after washing using a bar coater and dried. The coating amount (one side) after drying was 750 mg / m ² as zirconia.

Next, a primer having the composition shown in Table 1 was applied to the hot-dip galvanized steel sheet after the surface treatment with a bar coater under the conditions shown in Table 3, and baked in a furnace to form a primer layer. The adhesion amount (one side) of the primer layer was 15 g / m ² . Next, the top coat of the composition shown in Table 2 was applied with a bar coater under the conditions shown in Table 3, and baked in a furnace to form a top layer. The adhesion amount (one side) of the top layer was 15 g / m ² . Thereafter, it was immediately cooled with water.

The primer was prepared by mixing a resin, a silane coupling agent, and a pigment with a ball mill so as to have the composition shown in Table 1. The components and composition of the pigment contained in the primer are carbon black: titanium oxide (TiO): silica (SiO ₂ ) = 1: 1: 1, and used for preparing the primer as a kneaded material obtained by kneading in advance. did.
The top coating was prepared by mixing a resin and a pigment with a ball mill so as to have the composition shown in Table 2. The components and composition of the pigment contained in the top coat were carbon black: aluminum paste: silica (SiO ₂ ) = 1: 1: 2, and used as a kneaded product obtained by kneading in advance for the preparation of the top coat. .

  A test piece (50 x 50 mm) is cut out from the obtained fluororesin-coated hot-dip galvanized steel sheet, and the top layer adhesion (bending test, cross-cut elixir), pencil hardness, lubricity (dynamic friction coefficient), and seizure contamination Each was measured by the following method.

(Bending test)
It measured according to the rule of the bending test of JIS G3312 (paint hot-dip galvanized steel sheet and steel strip). That is, it was bent by a manual vise along the center line of three test pieces. In order to change the degree of bending, 0 to 2 plates having the same thickness as that of the test piece were sandwiched and distinguished, 0T bending, 1T bending, and 2T bending. The evaluation was performed by attaching a cellophane tape (length: 50 mm) to the bent portion and then peeling it off, and visually observing the total line area of the peeled portion of the coating layer above the surface treatment agent layer. The evaluation criteria are as follows.
5 points: No peeling 4 points: Less than 10% 3 points: 10% or more and less than 25% 2 points: 25% or more and less than 50% 1 point: More than 50%

(Cross-cut Eriksen test)
The measurement was performed according to the rules of the cross-cut test of JIS G3312 (painted hot-dip galvanized steel sheet and steel strip). That is, one test piece (50 × 50 mm) was cut out separately, and 100 1 mm square grids reaching the hot dip galvanized layer with a cutter knife were produced in the center of the test piece. The center of the grid was extruded 6 mm with an Eriksen test machine, cellophane tape was applied to the extruded conical portion, and then peeled off. Evaluation was made based on the number of grids where the upper layer coating did not peel off from the surface treatment agent layer.

(Pencil hardness test)
Measured according to JIS K5600 5-4 (coating general test method) scratch hardness (pencil method). That is, a test piece (50 × 50 mm) was separately cut out and scratched with a pencil, and the surface layer surface defect was determined by visual observation.

(Dynamic friction test)
A test piece (50 × 150 mm) was cut out and a surface property measuring instrument (“HEIDON” -14D type, manufactured by Shinto Kagaku Co., Ltd.) was used, using a 10 mmφ stainless steel ball as the measurement indenter, a load of 200 g, and a moving speed of 100 mm. The dynamic friction coefficient at a distance of 50 mm was measured at / min, and the median value of the dynamic friction coefficient waveform within the measurement distance was adopted.

(Baking contamination test)
A test piece (45 mmφ) was punched out with a press. Contaminated liquid [prepared by stirring and mixing chicken egg: sugar: soy sauce = 1: 1: 1 (mass ratio)] at the center of the test piece, 0.5 ml was dropped from the top of about 2 mm, and attached at 260 ° C. for 1 hour. Heated. After standing to cool, the test piece was immersed in water, and seized contaminants were removed with a sponge scrubber. The removal area of the contaminant was visually observed and evaluated. The evaluation criteria are as follows.
◎: Less than 20% ○: 20% or more and less than 50% △: More than 50%

(Comprehensive evaluation)
A hot dip galvanized steel sheet that has a non-chromium surface treatment agent layer with insufficient adhesion and that has not been put to practical use since firing at a temperature exceeding the highest steel sheet temperature of 410 ° C. causes melting of the galvanizing. Even if it is a fluororesin-coated steel sheet used as a base material, adhesion is improved by using a primer containing a suitable amount of a silane coupling agent in PES, and even at a maximum steel sheet temperature of 410 ° C or less, Since the firing is completed in a short time, it is clear that the fluororesin-coated steel sheet was obtained without causing the zinc plating to melt.

  The fluororesin-coated steel sheet of the present invention is used as a household heating product such as a frying pan, an industrial material such as piping, or a building material.

Claims (10)

  A steel plate surface has a non-chromium surface treatment layer, a primer layer mainly composed of a polyethersulfone resin on the layer, and a polytetrafluoroethylene resin and a polyethersulfone resin on the layer. A fluororesin-coated steel sheet having a top layer, wherein the primer layer contains 1 to 20 parts by mass of a silane coupling agent with respect to 100 parts by mass of a resin mainly composed of a polyethersulfone resin. Fluorine resin coated steel sheet.   The fluororesin-coated steel sheet according to claim 1, wherein the silane coupling agent of the primer layer is an aminosilane coupling agent or an epoxysilane coupling agent.   The primer layer is composed of 60-100 parts by mass of a polyethersulfone resin, 0-40 parts by mass of a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin, and 0-10 parts by mass of a polytetrafluoroethylene resin. The fluororesin-coated steel sheet according to claim 1 or 2, comprising a silane coupling agent in a proportion of 1 to 20 parts by mass with respect to 100 parts by mass in total.   The primer layer is composed of 60-100 parts by mass of a polyethersulfone resin, 0-40 parts by mass of a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin, and 0-10 parts by mass of a polytetrafluoroethylene resin. The fluororesin-coated steel sheet according to any one of claims 1 to 3, wherein the pigment content is 40 parts by mass or less based on 100 parts by mass in total of 100 parts by mass in total and 1 to 20 parts by mass of the silane coupling agent. .   A resin having a composition in which the top layer is composed of 30 to 60 parts by mass of a polytetrafluoroethylene resin, 10 to 70 parts by mass of a polyethersulfone resin, and 0 to 40 parts by mass of a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin. The fluororesin-coated steel sheet according to any one of claims 1 to 4.   Resin having a composition in which the top layer is composed of 30 to 60 parts by mass of a polytetrafluoroethylene resin, 10 to 70 parts by mass of a polyethersulfone resin, and 0 to 40 parts by mass of a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin. The fluororesin-coated steel sheet according to any one of claims 1 to 5, comprising a pigment in a proportion of 40 parts by mass or less with respect to 100 parts by mass in total.   The fluororesin-coated steel sheet according to any one of claims 1 to 6, wherein the surface treatment layer is made of a zirconia surface treatment agent, a silane coupling agent, or a titanium coupling agent.   The fluororesin-coated steel sheet according to any one of claims 1 to 7, wherein the steel sheet is a hot-dip galvanized steel sheet, a molten 5% aluminum / zinc alloy-plated steel sheet, or an electrogalvanized steel sheet.   The steel plate has a non-chromium surface treatment agent layer on the surface, a primer layer mainly composed of a polyethersulfone resin on the layer, and a polytetrafluoroethylene resin and a polyethersulfone resin on the layer. A method for producing a fluororesin-coated steel sheet having a top layer as a component, wherein the primer layer is a proportion of 1 to 20 parts by mass of a silane coupling agent with respect to 100 parts by mass of a resin mainly composed of a polyethersulfone resin. After applying the primer so that it is contained in, and firing at a maximum steel plate temperature of 410 ° C. or less for a time of 120 seconds or less, apply a top coating composition mainly composed of polytetrafluoroethylene resin and polyethersulfone resin, A method for producing a fluororesin-coated steel sheet, characterized by firing at a maximum steel sheet temperature of 410 ° C. or less for a time of 120 seconds or less.   In the method for producing the fluororesin-coated steel plate, the primer is fired at a maximum steel plate temperature of 250 to 410 ° C. for 120 to 20 seconds, and the top coat is fired at a maximum steel plate temperature of 350 to 410 ° C. for 120 to 20 seconds. A method for producing a fluororesin-coated steel sheet according to claim 9.