JPH09156036A - Manufacture of steel plate coated with fluorine-containing resin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a steel plate coated with resin film having excellent heat resisting adhesive property and heat resisting non-adhesive property, which is suitable for food cooking apparatus and heating cooking apparatus. SOLUTION: A surface of a steel plate is coated with a primer which contains a mixed resin of a fluoroplastic and a heat resisting resin, and baked. Thereafter, the steel plate is preheated, a tetrafluoride ethylene perfluoroalkyl vinyl ether copolymer film is attached with pressure and layered, electron radiations are applied at radiation dose of 5-50kGy from the film face, and the steel plate is heated again to 320 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a fluororesin film-coated steel sheet suitable for kitchen products such as food cooking equipment and heat cooking equipment.

[0002]

2. Description of the Related Art Fluororesin has excellent heat resistance, non-adhesiveness, stain resistance, etc.
It is widely used in baking utensils for cakes, food cookers such as frying pans, heating cookers such as microwave oven inner plates, jar inner pots, and gas table tops. In conventional food cooking appliances, cooking appliances, etc., a fluororesin or a mixed resin of a fluororesin and a heat-resistant resin is applied to the surface of a steel sheet and baked at a high temperature to form a fluororesin film. But,
Since it is formed by baking the fluorine-based paint, it is difficult to eliminate pinholes during the coating and baking processes. Therefore, non-adhesiveness and stain resistance cannot be maintained for a long period of time, and various defects may occur through the pinhole.

Pinholes are prevented by coating the surface of the steel sheet with a non-porous fluororesin film. For example, JP-A-52-124081 and JP-A-53-9
In Japanese Patent No. 8372, a non-porous film of a fluorine-containing polymer is laminated on the surface of a steel plate heated to a temperature equal to or higher than the melting point of the fluorine-containing polymer, and the non-porous film is attached to the steel plate by pressing with a rubber roll. In Japanese Unexamined Patent Publication No. 5-162243, a thermoplastic fluororesin film is heat-sealed on the surface of a steel sheet through an undercoating layer made of a mixed resin of a fluororesin and a heat-resistant resin. Further, in JP-A-6-344505 and JP-A-7-125136, the adhesion of the fluororesin film is improved by adjusting the temperature conditions of heating and reheating.

[0004]

However, under the conventional manufacturing conditions, it is difficult to obtain a fluororesin film-coated steel sheet satisfying both heat-resistant non-adhesiveness and heat-resistant adhesiveness. Particularly in applications such as food cooking appliances and food heating appliances, it is required to have excellent food sticking resistance, but conventional fluororesin film-coated steel sheets cannot provide sufficient food sticking resistance. The present invention has been devised to solve such a problem, by irradiating the fluorine-containing resin film attached to the steel sheet with an electron beam from the film surface side, the fluorine-containing resin with improved scorching resistance The purpose is to produce a resin film-coated steel sheet.

[0005]

In order to achieve the object of the method for producing a fluorine-containing resin film-coated steel sheet according to the present invention, a primer made of a mixed resin of a fluororesin and a heat-resistant resin is applied to a steel sheet surface and baked. After that, the steel plate is preheated, a tetrafluoroethylene perfluoroalkyl vinyl ether copolymer film is pressure-bonded and laminated, and an electron beam with a dose of 5 to 50 kGy is irradiated from the resin film surface side, and then the steel plate is heated to a temperature of 320 ° C or more. It is characterized by being reheated.
Examples of the steel sheet used include a 55% Al-Zn alloy plated steel sheet, an Al plated steel sheet, and a stainless steel sheet that have been subjected to a phosphate treatment, a coating type chromate treatment, or the like as needed. Prior to pressure bonding and lamination of a tetrafluoroethylene perfluoroalkyl vinyl ether copolymer film, a primer made of a mixed resin of a fluororesin and a heat resistant resin is applied to a steel plate and baked.

The fluororesin which is a component of the primer is selected from polytetrafluoroethylene resin, tetrafluoroethylene perfluoroalkyl vinyl ether copolymer resin and tetrafluoroethylene-6 fluoropropylene copolymer resin. At least one resin is used. As the heat resistant resin, at least one resin selected from a polyimide resin, a polyamideimide resin, a polyether sulfone resin, and a polyphenyl sulfone resin is used. Coloring pigments, rust preventive pigments, extender pigments and the like are added to the primer as needed. The primer layer has a dry coating thickness of 2
It is applied to the surface of the steel sheet so as to have a thickness of about 20 μm. The primer is a fluororesin-dispersed / heat-resistant resin-soluble paint containing a fluororesin that is not soluble in a solvent, and is therefore a thixotropic paint and has relatively poor roll coatability. Therefore, it is preferable to apply the primer to the steel sheet by roll coating by the top feed type full reverse method.

The pressure-bonding / lamination of the tetrafluoroethylene perfluoroalkyl vinyl ether copolymer film onto the primer-coated steel sheet can be carried out immediately after the primer is coated and baked. Alternatively, the primer may be applied and dried at about 200 ° C., and then once cooled to room temperature when the heat resistant resin does not melt. The temperature of the steel sheet when the tetrafluoroethylene perfluoroalkyl vinyl ether copolymer film is pressure-bonded may be equal to or higher than the melting point of the tetrafluoroethylene perfluoroalkyl vinyl ether copolymer film. Immediately after stacking, reheating is performed, or cooling is performed once to room temperature and then reheating. For reheating, a general catenary hot stove, a floater hot stove, an electromagnetic induction heating stove, etc. are used. Further, the resin film-coated steel sheet may be roll-pressed before cooling after reheating.
The cooling may be either rapid cooling such as water cooling or slow cooling. In the reheating, the reheating time can be divided.

Polytetrafluoroethylene resin, which has the most characteristics of fluororesin, has the highest heat resistance, chemical resistance and high frequency characteristics among thermoplastic resins, and has a unique low friction coefficient and non-adhesiveness. I have it. However, it cannot be melt-molded because it does not flow even when the temperature exceeds the melting point. A polytetrafluoroethylene-6-fluoropropylene copolymer resin that retains the properties of the polytetrafluoroethylene resin as much as possible and is melt-moldable has a low melting point of about 50 ° C., and therefore has poor heat resistance. On the other hand, the tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin is melt-moldable, has a high melting point of 302 to 310 ° C., and has a continuous use temperature of 26.
It is as high as 0 ° C. Moreover, the properties such as chemical resistance, low friction and non-adhesiveness are comparable to those of polytetrafluoroethylene resin, and the print design of the film is excellent. Therefore,
It is the most suitable fluororesin for film-coated steel sheets that require heat resistance, non-adhesiveness and design printability.

As the tetrafluoroethylene perfluoroalkyl vinyl ether copolymer film, a film having no pinhole is used, and the film is not particularly limited, but 2
A film having a thickness of 0 to 100 μm is preferable. Also, if necessary, a heat-resistant color pigment is added for coloring, or a pattern is printed on the pressure-bonding surface of the primer with a printing ink consisting of a heat-resistant ink and a heat-resistant printing ink binder. Is used. Heat resistant printing ink binders include tetrafluoroethylene perfluoroalkyl vinyl ether copolymer resin, polytetrafluoroethylene resin, and the like. Further, in order to improve the adhesion to the primer, the surface of the tetrafluoroethylene perfluoroalkyl vinyl ether copolymer film on the primer side may be subjected to corona discharge treatment. By irradiating the electron beam from the resin film surface side prior to reheating, the reheating temperature can be lowered, and the decrease in heat resistance and non-adhesiveness can be suppressed. As the irradiation electron beam, an electron beam of less than 300 kcV, which is generally called a low energy type, is sufficient, but other electron beams or γ-rays can also be used. The irradiation electron beam dose is 5
Adjusted to a range of ˜50 kGy.

[0010]

The fluororesin film-coated steel sheet used for food cookers, heat cookers and the like is required to have excellent food scorching resistance. The resistance to food scorching is
It is judged by heat-resistant non-stick property and heat-resistant adhesive property. Heat-resistant non-adhesiveness is, for example, soy sauce: sugar: egg = 1: 1: 1 mixture and milk are dripped on the surface of the fluororesin film in an amount of about 0.5 ml, and this is put in a heating furnace at 260 ° C for 1 hour, After cooling, it is evaluated whether the mixed solution of soy sauce: sugar: egg = 1: 1: 1 and milk can be easily removed without sticking to the fluororesin film. In addition, sufficient heat-resistant adhesiveness is required so that no blistering occurs between the fluororesin film and a primer made of a mixed resin of a fluororesin and a heat-resistant resin during this food scorching resistance test. Furthermore, regarding the anti-sticking property, even if a mixed solution of soy sauce: sugar: egg = 1: 1: 1 and milk is dropped, and heating and cooling are repeated for about 20 cycles at 260 ° C. for 1 hour, heat-resistant non-adhesiveness and It is desired that the heat resistant adhesive property is maintained.

Heat-resistant adhesion is improved by setting a high reheating temperature. For example, the adhesiveness of the fluororesin film to the primer is practically insufficient before reheating, but it can be improved to a level according to the application by reheating. Further, the high reheating temperature is effective in developing sufficient heat resistant adhesiveness and shortening the reheating time. However, the heat-resisting non-adhesiveness significantly decreases as the reheating temperature rises. The present inventors
Various investigations and studies have been conducted on the phenomenon that the heat resistance and non-stickiness decrease with the increase of the reheating temperature. In the case of a tetrafluoroethylene perfluoroalkyl vinyl ether copolymer film, which is a heat-resistant resin, oxygen existing near the film surface during reheating is heated even at a temperature at which heat resistance in the bulk is not a problem. Found to oxidize. The surface oxidation makes the surface of the film easy to adapt to the above-mentioned mixed liquid or milk, resulting in a decrease in heat resistance and non-adhesiveness. The surface oxidation of the film can be explained by the decrease of the water-resistant contact angle of the film surface with the increase of the reheating temperature, and the decrease of the F atom concentration and the increase of the O atom concentration in the extreme surface layer as a result of the photoelectron spectroscopy analysis of the film surface. That is, the heat-resistant adhesiveness is a characteristic of the interface between the resin film and the primer, while the heat-resistant non-adhesiveness is a characteristic of the outer surface layer of the resin film.

Therefore, according to the present invention,
In order to secure sufficient heat resistant adhesiveness and heat resistant non-stickiness,
The electron beam was set to be irradiated at a dose of 5 to 50 kGy. By the electron beam irradiation, the molecular chain of the tetrafluoroethylene perfluoroalkyl vinyl ether copolymer forming the film and the fluororesin, which is a component of the primer, is broken, and the molecular weight is reduced. As a result, the melt viscosity is reduced, and melt diffusion with the fluororesin existing on the primer surface is likely to occur during reheating. Therefore, even when reheated at a low temperature, excellent heat-resistant adhesiveness is exhibited. However, in order to obtain sufficient heat resistant adhesion, a steel plate temperature of 320 ° C. or higher is required. On the other hand, as the reheating temperature rises, the surface oxidation of the tetrafluoroethylene perfluoroalkyl vinyl ether copolymer film becomes remarkable, and the heat resistance and non-adhesiveness of the film are significantly reduced.

In this respect, the molecular chain divided by the electron beam irradiation is easy to move. Therefore, the oxidized portion of the molecular chain located in the film surface layer portion is likely to be a thermodynamically stable low energy surface, that is, it is easy to sneak into the inside of the film, instead, the non-oxidized portion momentarily under reheating. It migrates to the surface and begins to form. As a result, oxidation during reheating is suppressed, and excellent heat resistance and non-adhesiveness can be obtained. Further, since the reheating temperature can be lowered, it is not necessary to reheat at a high temperature, and sufficient characteristics can be exhibited at a reheating temperature of less than 400 ° C. In order to effectively obtain such an effect by electron beam irradiation, it is necessary to adjust the dose within the range of 5 to 50 kGy. When the dose is less than 5 kGy, the molecular chain is less fragmented, so that the heat-resistant adhesiveness is low, and the oxidized portion of the film surface layer portion is less likely to penetrate.
On the contrary, when the dose exceeds 50 kGy, the molecular chains are excessively divided, and cracks occur on the film surface during reheating,
In a food scorching resistance test, a mixed solution or the like is likely to physically enter.

[0014]

EXAMPLE A SUS430 stainless steel plate having a plate thickness of 0.45 mm was degreased, subjected to a coating type chromate treatment, and a mixed resin composed of polytetrafluoroethylene resin / polyether sulfone resin was coated at a dry film thickness of 7 μm, and 400 Baked at ° C. Then, a transparent tetrafluoroethylene perfluoroalkyl vinyl ether copolymer film having a thickness of 40 μm was adjusted so as to be pressure bonded at a steel plate temperature of 380 ° C., laminated, and cooled with water. Then, after irradiating with an electron beam under the conditions shown in Table 1, it was reheated to the steel plate temperature shown in Table 1 and immediately cooled with water. Table 1 also shows the heat-resistant adhesiveness, heat-resistant non-adhesiveness, water-resistant contact angle of the resin film surface after polishing, and O / F atomic ratio based on photoelectron spectroscopic analysis of the obtained resin film-coated steel sheet.

The heat-resistant adhesiveness and heat-resistant non-adhesiveness shown in Table 1 are values obtained by the above-mentioned food burning test, and soy sauce: sugar: egg = 1: 1: 1 mixture and milk are resin films. Heat-resistant non-stickiness is evaluated as "excellent" when it can be removed without scorching on the surface, "poor" when it cannot be removed due to scorching, and heat-resistant adhesiveness when blistering does not occur between the primer and the resin film. Was "excellent", and the case where blisters occurred was evaluated as "poor". Then, the same test was repeated for the test pieces having “excellent” in both heat-resistant non-adhesiveness and heat-resistant adhesiveness until the respective characteristics were not “excellent”. In Table 1, the number of times of repetition indicates the heat resistant adhesive property and the heat resistant non-adhesive property. In addition, in applications such as food cooking utensils and heat cooking utensils, it is preferable that the number of repetitions in which "excellence" is maintained is 20 or more. Table 1
As can be seen from the above, in Test Nos. 1 to 6, which were reheated after the electron beam irradiation, sufficient heat resistance and non-adhesiveness were exhibited even after repeating the food scorching resistance test 20 times or more. It is speculated that this is because the heat resistant adhesiveness was increased by reheating at low temperature by electron beam irradiation.

On the other hand, test numbers 7 and 8 without electron beam irradiation
Then, although it showed the same heat resistance and non-adhesiveness as those of the examples of the present invention, the heat resistance adhesion was inferior. Similarly for test number 9,
Both the heat resistant adhesiveness and the heat resistant non-tackiness were inferior. In Test No. 10 in which the reheating temperature was set low, the heat-resistant non-adhesiveness was good, but the heat-resistant adhesiveness was poor. In the test number 11 in which the electron dose was set high, both the heat-resistant adhesive property and the heat-resistant non-adhesive property were good, but the molecular weight of the tetrafluoroethylene perfluoroalkyl vinyl ether copolymer became too small by the electron beam irradiation, and the film cracked. There has occurred. As is clear from this comparison, by setting the electron dose to 5 to 50 kGy and reheating at 320 ° C. or higher, a fluorine-containing resin film-coated steel sheet excellent in both heat resistant adhesiveness and heat resistant non-adhesiveness can be obtained. Is confirmed.

[0017]

[0018]

As described above, in the present invention, after the tetrafluoroethylene perfluoroalkyl vinyl ether copolymer film is attached to the surface of the steel sheet via the primer and the electron beam is irradiated from the film surface side. , Reheating. The reheating temperature can be lowered by electron beam irradiation, oxidation of the surface layer of the film is suppressed, and eventually deterioration of heat resistance and non-adhesiveness is prevented. As a result, it is possible to obtain a resin film-coated steel sheet that is excellent in both heat-resistant adhesiveness and heat-resistant non-adhesiveness and is suitable as a food cooking appliance, a heating cooking appliance, and the like.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location B32B 31/20 7148-4F B32B 31/20 (72) Inventor Kenji Koshiishi 7 Takatani Shinmachi, Ichikawa City, Chiba Prefecture No. 1 Nisshin Steel Co., Ltd. Technical Research Center

Claims (1)

[Claims] 1. A primer made of a mixed resin of a fluororesin and a heat-resistant resin is applied to the surface of a steel sheet and baked, and then the steel sheet is preheated and a tetrafluoroethylene perfluoroalkyl vinyl ether copolymer film is pressure-bonded and laminated. , Irradiating an electron beam with a dose of 5 to 50 kGy from the resin film surface side,
Then, a method for producing a fluorine-containing resin film-coated steel sheet in which the steel sheet is reheated to a plate temperature of 320 ° C. or higher.