JP3501007B2 - Precoated steel sheet and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a precoated steel sheet having excellent heat resistance and non-adhesiveness, which is suitable for use in, for example, a microwave oven door plate, a compartment, or the like where food sticking is a problem. The present invention relates to a manufacturing method.

[0002]

2. Description of the Related Art Pre-coated steel sheets used for microwave oven door plates and refrigerators are required to have excellent heat resistance because they are used in a temperature range of over 200 ° C. It is also necessary to have excellent tackiness.

A normal precoated steel sheet using an epoxy resin or the like for the undercoat layer and an acrylic resin, a polyester resin or the like for the overcoat layer has a heat resistance temperature of the coating film of about 120 to 130 ° C. and is used for such an application. Can not. Conventionally, for such applications, a paint containing a tetrafluoroethylene resin (PTFE) as a main component, or a paint containing the above resin as a main component and a heat resistant resin such as a polyether sulfone resin (PES) A pre-coated steel sheet produced by painting and baking on a painting line is used (Japanese Patent Laid-Open Publication No. Sho 6).
1-1111378, JP-A-9-52070, etc.).

[0004]

The melting point of tetrafluoroethylene resin (PTFE) is as high as 327 ° C. Therefore, in order to obtain the required coating film performance, apply 380 to 380 steel plates on the coating line.
It is necessary to heat the coating film by heating it to a high temperature of about 390 ° C., which not only increases the cost but also reduces the productivity of the coating line due to the restriction of the heating capacity of the oven.

In view of the above circumstances, it is an object of the present invention to provide a precoated steel sheet which can be baked at a low temperature and is excellent in heat resistance and non-adhesiveness, and a method for producing the same.

[0006]

The means of the present invention for solving the above problems are as follows.

(1) Polyether sulfone resin, tetrafluoroethylene resin, and copolymer resin of tetrafluoroethylene and perfluoroalkyl vinyl ether on the surface of a chromium-plated steel sheet or a stainless steel sheet subjected to an inorganic chemical conversion treatment. And a tetrafluoroethylene copolymer resin of tetrafluoroethylene and hexafluoropropylene as a main component, the tetrafluoroethylene resin and the tetrafluoroethylene copolymerization with respect to 100 parts by weight of the polyether sulfone resin. A pre-coated steel sheet having a coating layer having a film thickness of 3 to 20 μm, which is formed by applying and baking a coating material having a resin compounding ratio of 20 to 40 parts by weight and 50 to 80 parts by weight, respectively (first invention).

(2) Polyether sulfone resin, tetrafluoroethylene resin and copolymer resin of tetrafluoroethylene and perfluoroalkyl vinyl ether on the surface of a chrome-plated steel sheet or a stainless steel sheet subjected to an inorganic chemical conversion treatment. And a tetrafluoroethylene copolymer resin of tetrafluoroethylene and hexafluoropropylene as a main component, the tetrafluoroethylene resin and the tetrafluoroethylene copolymerization with respect to 100 parts by weight of the polyether sulfone resin. A coating material having a resin compounding ratio of 20 to 40 parts by weight and 50 to 80 parts by weight is applied, and the baking time X (seconds) and the baking temperature Y (° C) satisfy the expressions (5) and (6). Baking under the conditions
A method for producing a precoated steel sheet, which comprises forming a coating film layer having a thickness of 20 μm (second invention). Y ≧ (4000 / X) +280 (5) Y ≦ (7000 / X) +280 (6) where Y ≦ 380 and X ≦ 100

(3) On the surface of a chromium-plated steel sheet or a stainless steel sheet or a zinc-based plated steel sheet that has been subjected to an inorganic chemical conversion treatment, a polyether sulfone resin, and
It contains tetrafluoroethylene copolymer resin, which is a copolymer resin of tetrafluoroethylene and perfluoroalkyl vinyl ether and a copolymer resin of tetrafluoroethylene and hexafluoropropylene, as the main component, and is based on 100 parts by weight of polyether sulfone resin. An undercoat layer having a film thickness of 3 to 10 μm, which is formed by applying and baking a paint having a mixing ratio of the tetrafluoroethylene copolymer resin of 40 to 100 parts by weight, a polyether sulfone resin, a tetrafluoroethylene resin, Also, it contains a tetrafluoroethylene copolymer resin of perfluoroalkyl vinyl ether and a tetrafluoroethylene copolymer resin composed of a copolymer resin of tetrafluoroethylene and hexafluoropropylene as main components, and 100 wt. Tetrafluoride for parts The mixing ratio of the resin and tetrafluoroethylene copolymer resin, each 20 to 40 parts by weight, 50-8
Film thickness 3 formed by coating and baking 0 parts by weight of paint
A precoated steel sheet (third invention), characterized in that an overcoat layer of ˜20 μm is laminated in order.

(4) Polyethersulfone resin, and copolymerization of tetrafluoroethylene and perfluoroalkyl vinyl ether on the surface of a chrome-plated steel sheet, or a stainless steel sheet or a zinc-plated steel sheet that has been subjected to an inorganic surface treatment. Resin and tetrafluoroethylene-copolymer resin of tetrafluoroethylene and hexafluoropropylene as a main component, containing as a main component, the blending ratio of tetrafluoroethylene copolymer resin to 100 parts by weight of polyether sulfone resin. 40 to 100 parts by weight of the coating material is applied and baked at a temperature in the range of 180 to 250 ° C. to form an undercoat layer having a film thickness of 3 to 10 μm. Fon resin, tetrafluoroethylene resin, and tetrafluoroethylene and perfluoroalkyl vinyl It contains a tetrafluoroethylene copolymer resin composed of a copolymer resin with ether and a tetrafluoroethylene / hexafluoropropylene copolymer resin as a main component, and the tetrafluoroethylene resin with respect to 100 parts by weight of a polyether sulfone resin and The compounding ratio of the tetrafluoroethylene copolymer resin is 20 to 40 parts by weight and 50, respectively.
~ 80 parts by weight of paint applied, baking time X (seconds)
And a baking temperature Y (° C) satisfy the equations (7) and (8) to form an overcoat layer having a film thickness of 3 to 20 µm. 4 invention). Y ≧ (4000 / X) +280 (7) Y ≦ (7000 / X) +280 (8) where Y ≦ 380 and X ≦ 100

In the present invention, a low-melting point tetrafluoroethylene and a perfluoroalkyl vinyl ether are added to the coating layer in addition to a polyether sulfone resin (hereinafter referred to as PES) and a tetrafluoroethylene resin (hereinafter referred to as PTFE) in a specific mixing ratio. By using a coating material containing a tetrafluoroethylene copolymer resin composed of a copolymer resin of tetrafluoroethylene and hexafluoropropylene (hereinafter referred to as FEP), In comparison, even if the baking temperature is lowered, excellent non-adhesiveness and heat resistance can be obtained.

Further, a specific blending ratio of a polyether sulfone resin (hereinafter, PES), a copolymer resin of tetrafluoroethylene and perfluoroalkyl vinyl ether (hereinafter, PFA), and tetrafluoroethylene and hexafluoropropylene are used. Copolymer resin (hereinafter FE
An undercoat layer and an overcoat layer are formed by forming a subbing layer using a coating material containing a tetrafluoroethylene copolymerization resin consisting of P) as a main component, and further forming the coating layer as an overcoat layer. Combined with the addition of the above-mentioned tetrafluoroethylene copolymer resin to both of them, the precoat steel sheet which can improve the adhesion between the undercoat layer and the overcoat layer and is excellent in workability and secondary adhesion can be obtained. .

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The precoated steel sheet and the method for producing the same according to the present invention will be described below.

In the first and second inventions, a chromium-plated steel plate (so-called tin-free steel) or a stainless steel plate is used as the base steel plate. In the third invention and the fourth invention, as the base steel sheet, a zinc-based plated steel sheet is further used in addition to the above steel sheet. As the zinc-based plated steel sheet, a zinc-based plated steel sheet in which a plated layer of pure zinc or a zinc-aluminum alloy is formed on the iron surface by hot dipping or electroplating can be used.

It is desirable that the pre-coated steel sheet used for the microwave oven door plate, the inside of the refrigerator, etc. has excellent corrosion resistance. Practically, a corrosion resistance level as high as that of a chrome-plated steel plate is sufficient, but when higher corrosion resistance is required, it is preferable to use a stainless steel plate or a zinc-based plated steel plate having excellent corrosion resistance. In actual use, the base steel sheet may be appropriately selected in consideration of the application and corrosion resistance.

Considering the corrosion resistance and workability, the coating amount of zinc-based plated steel sheet is 15 to 90 g / m ² per side.
It is desirable to be within the range. This is because if the coating weight is less than 15 g / m ² per side, the corrosion resistance is insufficient, and if it exceeds 90 g / m ² per side, cracking due to the plating layer tends to occur during molding.

When a stainless steel plate or a zinc-based plated steel plate is used as the base steel plate, in order to improve the adhesion between the base steel plate and the coating layer to obtain excellent workability, corrosion resistance and secondary adhesion, It is necessary to form an inorganic chemical conversion treatment layer on the surface of the steel sheet. Inorganic chemical conversion treatment layer is for zinc-based plated steel sheet, phosphate treatment such as zinc phosphate treatment or electrolytic chromate treatment, inorganic chemical conversion treatment such as chromate treatment such as coating type chromate, for stainless steel sheet, coating type chromate It is formed by an inorganic chemical conversion treatment such as a treatment. In the case of tin-free steel, since the hydrated chromium oxide film is formed on the metallic chromium layer, it is not necessary to further perform an inorganic chemical conversion treatment.

In the precoated steel sheet of the present invention, the baking temperature of the coating layer is higher than that of a normal precoated steel sheet. When the chemical conversion treatment layer is formed by the phosphate treatment, the adhesion during processing may be slightly deteriorated. Therefore, when superior adhesion is required, the chemical conversion treatment layer is preferably formed by the chromate treatment. .

When the chemical conversion treatment layer is formed by chromate treatment, silica, phosphoric acid or the like may be added to the chromate treatment liquid in order to improve corrosion resistance and adhesion. The amount of chromate film is 10 in terms of metallic chromium per one side of steel plate.
It is preferably in the range of 150 mg / m ² .

In the first invention and the second invention, a paint containing PES, PTFE, and a tetrafluoroethylene copolymer resin composed of PFA and FEP as a main component is applied onto the original plate and baked, Form a coating layer.

PES, PTFE and PFA + in the paint
The compounding ratio of FEP is P based on 100 parts by weight of PES.
The compounding ratio of TFE is 20 to 40 parts by weight, PFA + FEP
The compounding ratio is 50 to 80 parts by weight.

When the compounding ratio of PTFE exceeds 40 parts by weight with respect to 100 parts by weight of PES, the effect of improving the tackiness and heat resistance is saturated, and on the contrary, the flowability of the paint is deteriorated and the appearance is poor. If it is less than 20 parts by weight, the non-adhesiveness and heat resistance will be poor, and the friction coefficient will be high and the lubricity will be poor.

The blending ratio of PFA + FEP is PES100.
When it exceeds 80 parts by weight, the effect of improving non-adhesiveness is saturated, and on the contrary, the flowability of the paint is deteriorated, resulting in poor appearance, and when it is less than 50 parts by weight, non-adhesiveness is increased. Inferior, high friction coefficient and poor lubricity.

In the above invention, excellent heat resistance and non-adhesiveness can be obtained even if the coating material is baked at a low temperature for the following reason.

PFA is excellent in heat resistance and FEP is inferior in heat resistance but has a low melting point. When these two kinds of resins are used together and baked at a low temperature, FEP melts and PFA becomes a semi-molten film. The coating film obtained above is excellent in heat resistance and non-adhesiveness even though it is baked at a low temperature. In order to obtain the above effect, the compounding ratio of FEP and PFA is FEP / PFA =
It is more preferably 30/70 to 70/30.

If desired, color pigments and aluminum powder may be added to the paint.

When the film thickness of the coating film layer is less than 3 μm, the friction coefficient becomes high, and the non-adhesiveness, workability and corrosion resistance are deteriorated, and when the film thickness exceeds 20 μm, the appearance after coating becomes poor, and Workability and secondary adhesion deteriorate. Therefore, the film thickness of the coating layer needs to be in the range of 3 to 20 μm.

When the coating film coated with the above coating material is baked under the conditions that the baking time X (seconds) and the baking temperature Y (° C.) satisfy the expressions (9) and (10), non-adhesiveness, Pre-coated steel sheets with excellent workability and lubricity can be manufactured inexpensively without impairing the productivity of the coating line. Y ≧ (4000 / X) +280 (9) Y ≦ (7000 / X) +280 (10) where Y ≦ 380 and X ≦ 100

If the baking conditions of the coating film do not satisfy the expression (9) and the baking is performed at a low temperature for a short time, the PFA is insufficiently melted and the workability and lubricity are deteriorated. In addition, when the baking conditions do not satisfy the formula (10) and are baked at a high temperature for a long time, there is no effect of improving the workability and lubricity, and conversely, the energy cost is increased and the productivity of the coating line is decreased. Therefore, the object of the present invention of obtaining a precoated steel sheet which is excellent in non-stickiness by low temperature baking is also violated.

Further, in the present invention, an undercoat layer is formed on the surface of the chromium-plated steel sheet or the stainless steel sheet or the zinc-based plated steel sheet which has been subjected to the inorganic chemical conversion treatment described above, and the above-mentioned coating layer is formed thereon. The film layer may be baked under the above baking conditions to form an overcoat layer. By doing so, the corrosion resistance and adhesion of the precoated steel sheet can be further improved (third invention, fourth invention).

In this case, the undercoat layer is PES and PF.
A paint (undercoat paint) containing A and FEP as a main component of a tetrafluoroethylene copolymer resin is applied and baked to form.

The blending ratio of the tetrafluoroethylene copolymer resin (hereinafter, PFA + FEP) to PES in the undercoat paint is within the range of 40 to 100 with respect to 100 parts by weight of PES.

The blending ratio of PFA + FEP is PES10.
If the amount is more than 100 parts by weight, the adhesion to the base becomes slightly inferior to 0 parts by weight, and if it is less than 40 parts by weight, the adhesion to the topcoat is poor, and thus both the workability and the secondary adhesion are deteriorated. .

A rust preventive pigment may be added to the undercoat layer in order to impart corrosion resistance. As the rust preventive pigment to be blended, hardly soluble chromates, lead salts, etc. can be widely used, and there is no particular limitation on the type. It is preferably less than 30 parts by weight with respect to parts.

If the thickness of the undercoat layer is less than 3 μm, the corrosion resistance is lowered, and if it exceeds 10 μm, not only the effect of improving the corrosion resistance is saturated, but also the workability is lowered and the coating cost is increased. It is limited to the range of 3 to 10 μm.

The baking temperature of the undercoat layer is 180 to 250 ° C.
It is necessary to be within the range. Baking temperature is 180
If it is less than ℃, the workability and coating adhesion will be insufficient,
On the other hand, when the baking temperature exceeds 250 ° C., not only the workability and coating film adhesion but also the coating film appearance is deteriorated.

In forming each of the above coating layers,
The coating material can be applied by a known coating method such as a roll coater or curtain flow. The coating applied as described above can be baked by a known baking method such as a hot air drying method, an induction heating method and an infrared heating method.

In the precoated steel sheet according to the above, the coating layer can be baked at a low temperature in the coating line, and the productivity of the coating line can be improved, so that the manufacturing cost of the precoated steel sheet can be reduced.

[0039]

EXAMPLES Next, the precoated steel sheet of the present invention will be further described by way of Examples in comparison with Comparative Examples.

Tin-free steel, galvanized steel sheet (plating amount 20 g /
m ² ), hot-dip galvanized steel sheet (plating amount 30 g / m ² ) and stainless steel sheet. For galvanized steel sheet and hot-dip galvanized steel sheet, a further coating amount of 40 mg / m ²
To form an inorganic chemical conversion treatment coating by applying the coating type chromate treatment or the zinc phosphate treatment with a coating amount of 1.2 g / m ² .
Also, for stainless steel sheets, the coating amount is 40 mg /
m ² coating type chromate treatment was applied to form an inorganic chemical conversion treatment film.

Next, each of the steel sheets obtained above was coated with the following undercoat paint and topcoat paint, or only the topcoat paint with a roll coater, and then baked in a hot air drying oven under the conditions prescribed in the method of the present invention. Forming a layer, and the specimen of the precoated steel sheet of the present invention (hereinafter referred to as the specimen of the present invention) No. 1 to
23 was adjusted.

For comparison, a pre-coated steel plate specimen (hereinafter, referred to as
(Comparison specimen) No. 1-9 were adjusted.

Undercoat layer: PES / PFA + FEP (weight ratio shown in Tables 1 to 3) Topcoat layer: PES / PTFE / PFA + FEP (weight ratio shown in Tables 1 to 3) Aluminum powder 3 parts by weight (/ Resin 100 parts by weight) Tables 1 and 2 show the sample No. of the present invention. 1 to 23, base type (plating type and plating amount), type of chemical conversion treatment layer,
The PES / PFA + FEP weight ratio of the undercoat layer, the film thickness, and the PES / PTFE / PFA + FEP weight ratio of the overcoat layer of the overcoat layer, the baking temperature, the baking time, and the film thickness are shown.

[0044]

[Table 1]

[0045]

[Table 2]

Table 3 shows the comparative sample No. Substrate types 1 to 9 (plating layer type and plating amount), chemical conversion treatment layer type, PES / PFA + FEP weight ratio of undercoat layer, film thickness and PES / PTFE / PFA + FEP of topcoat layer of topcoat layer
The weight ratio, baking temperature, baking time, and film thickness are shown.

[0047]

[Table 3]

The appearance of the coating film, non-adhesiveness, friction coefficient, workability, secondary adhesion and corrosion resistance of each of the present invention specimen and the comparative specimen were evaluated by the performance tests described below. The results are also shown in Tables 1 to 3.

(1) Appearance of coating film The coating film after baking was visually observed, and the observation results were evaluated as follows. ◎: When there is no armpit or swelling ○: When there is almost no armpit or swelling △: When a little armpit or swelling occurs ×: When there is significant armpit or swelling

(2) Non-adhesive non-adhesive boiled coating film, a mixture of sugar, soy sauce and eggs in a weight ratio of 1: 1: 1 was added dropwise, heated to 250 ° C., left for 1 hour and naturally cooled. After that, scorching was removed with a nail, the removal condition was visually observed, and the observation result was evaluated by the following. ◎: When there is no stickiness or discoloration ○: When there is almost no stickiness or discoloration △: When a little stickiness or discoloration occurs ×: When stickiness or discoloration occurs remarkably

(3) Friction coefficient Using the friction coefficient measuring device "HEIDON 10", the static friction coefficient μ (=) from the inclination angle θ when the stainless steel board weighing 150 g placed on the inclined specimen starts to slide. ta
nθ) was obtained and evaluated by the following. ⊚: When μ is less than 0.12 ○: When μ is 0.12 to less than 0.18 Δ: When μ is less than 0.18 to 0.22 ×: When μ is 0.22 or more

(4) Workability After the test piece was tightly bent at 0t-180 °, cellophane tape was attached to the bent portion, which was then peeled off, and the peeled area of the coating film at the bent portion was evaluated by the following. ◎: No peeling ○: Peeling area is 1 to less than 5% △: Peeling area is 5 to less than 30% ×: Peeling area is 30% or more

(5) Secondary Adhesion After the coating film of the test piece was put into the coating film of the test piece with a cutter knife so as to form a grid-like notch having a size of 10 × 10, and the test piece was set to 9 mm by an Erichsen tester. Was extruded, then allowed to stand in boiling water for 3 hours, then allowed to stand for 24 hours, then a scotch tape was attached to the indented portion and peeled off. . ⊚: When the peeled area is less than 5% ○: When the peeled area is 5 to less than 10% Δ: When the peeled area is less than 10 to 30% ×: When the peeled area is 30% or more

(6) Corrosion resistance A cross-shaped notch reaching the metal base of the coating film is formed in the test piece, and the test piece having such a notch on the cloth is 240 based on JIS Z2371.
A salt spray test was performed for a period of time, and the ratio of the generated rusted area to the entire area was evaluated as the rusting rate according to the following. ◎: When the rusting rate is less than 10% ○: When the rusting rate is 10 to less than 25% △: When the rusting rate is 25 to less than 50% ×: When the rusting rate is 50% or more Table 1 ~ From Table 3, the following is clear.

Comparative sample No. 1 having no chemical conversion treatment layer formed thereon No. 1 was poor in workability and secondary adhesion.

PT for 100 parts by weight of PES in the coating layer
Specimen No. for comparison whose ratio of FE is below the range of the present invention.
2. PFA + FE for 100 parts by weight of PES in the coating layer
The comparative specimen No. in which the proportion of P is below the range of the present invention. Four
All have poor non-adhesiveness and high friction coefficient. The comparative sample No. in which the proportion of PTFE with respect to 100 parts by weight of PES in the coating layer exceeds the range of the present invention. 3. Comparative sample No. 3 in which the ratio of PFA + FEP to 100 parts by weight of PES of the coating layer exceeds the range of the present invention. No. 5 had a bad coating film appearance.

Further, the comparative sample No. having a coating layer thickness less than the range of the present invention. No. 6 has a high friction coefficient, is poor in non-adhesiveness, workability and corrosion resistance, and has a coating layer thickness exceeding the range of the present invention. No. 7 had poor coating film appearance, processability, and secondary adhesion.

Specimen No. 3 for comparison whose baking temperature under the baking conditions of the coating layer is below the range of the present invention defined by the above formula (9). No. 8 had a high friction coefficient, was poor in non-adhesiveness, and had poor workability. Comparative sample No. No. 1 whose baking temperature under the above baking conditions greatly exceeds the range of the present invention defined by the above formula (10). In No. 9, the coating film was deteriorated because the baking temperature was too high, so that the friction coefficient was high and the coating film appearance, non-adhesiveness, processability and secondary adhesion were poor.

On the other hand, No. 1 of the present invention example. 1-23
Had a low coefficient of friction and was excellent in all of the coating film appearance, non-adhesiveness, processability and secondary adhesion.

[0060]

As described above, the precoated steel sheet of the present invention is excellent in heat resistance, non-adhesiveness, and corrosion resistance. Suitable for use in different parts.

According to the present invention, the coating layer can be baked at a low temperature in the coating line, and the productivity of the coating line can be improved, so that the manufacturing cost of the precoated steel sheet can be reduced.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI // (C09D 181/06 C09D 127: 12 127: 12) (72) Inventor Akio Yamamoto 1-2-1, Marunouchi, Chiyoda-ku, Tokyo (56) Reference JP 61-34044 (JP, A) JP 4-329134 (JP, A) JP 2000-26786 (JP, A) JP 61-111378 ( JP, A) JP 61-111352 (JP, A) JP 63-193965 (JP, A) JP 6-264000 (JP, A) JP 8-3508 (JP, A) JP Flat 8-300560 (JP, A) JP 9-52070 (JP, A) JP 9-39156 (JP, A) JP 9-52069 (JP, A) Special Table 10-508066 (JP , A) Special table HEI-50-509036 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C09D 181/00-181/10 C09D 127/00-127/24

Claims (4)

(57) [Claims] 1. A polyether sulfone resin, a tetrafluoroethylene resin and a copolymer resin of tetrafluoroethylene and a perfluoroalkyl vinyl ether are provided on the surface of a chromium-plated steel sheet or a stainless steel sheet subjected to an inorganic chemical conversion treatment. , A tetrafluoroethylene copolymer resin containing tetrafluoroethylene and hexafluoropropylene as a main component, and a tetrafluoroethylene resin and a tetrafluoroethylene copolymer resin based on 100 parts by weight of a polyether sulfone resin. A pre-coated steel sheet having a coating layer having a film thickness of 3 to 20 μm, which is formed by applying and baking a coating material having a mixing ratio of 20 to 40 parts by weight and 50 to 80 parts by weight, respectively. 2. A surface of a chromium-plated steel sheet or a stainless steel sheet subjected to an inorganic chemical conversion treatment, and a polyether sulfone resin, a tetrafluoroethylene resin and a copolymer resin of tetrafluoroethylene and a perfluoroalkyl vinyl ether. , A tetrafluoroethylene copolymer resin containing tetrafluoroethylene and hexafluoropropylene as a main component, and a tetrafluoroethylene resin and a tetrafluoroethylene copolymer resin based on 100 parts by weight of a polyether sulfone resin. The coating composition is applied in a proportion of 20 to 40 parts by weight and 50 to 80 parts by weight, respectively, and the baking time X (seconds) and the baking temperature Y (° C) satisfy the expressions (1) and (2). Baking under conditions, film thickness 3 ~
A method for producing a precoated steel sheet, which comprises forming a coating layer having a thickness of 20 μm. Y ≧ (4000 / X) +280 (1) Y ≦ (7000 / X) +280 (2) where Y ≦ 380 and X ≦ 100 3. A polyether sulfone resin and a copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether on the surface of a chromium-plated steel sheet or a stainless steel sheet or a zinc-based plated steel sheet subjected to an inorganic chemical conversion treatment. Resin and tetrafluoroethylene-copolymer resin of tetrafluoroethylene and hexafluoropropylene as a main component, containing as a main component, the blending ratio of tetrafluoroethylene copolymer resin to 100 parts by weight of polyether sulfone resin. 40 to 100 parts by weight of a paint is applied and baked to form an undercoat layer having a film thickness of 3 to 10 μm, a polyether sulfone resin, a tetrafluoroethylene resin, and tetrafluoroethylene and a perfluoroalkyl vinyl ether. Copolymer resin, tetrafluoroethylene and hexaf It contains a tetrafluoroethylene copolymer resin composed of a copolymer resin with oropropylene as a main component, and the mixing ratio of the tetrafluoroethylene resin and the tetrafluoroethylene copolymer resin to 100 parts by weight of the polyether sulfone resin is respectively 20-40 parts by weight, 50-80
Coating thickness of 3 parts by weight, formed by applying and baking paint
A precoated steel sheet, which is obtained by sequentially laminating an overcoat layer of 20 μm. 4. A polyether sulfone resin and a copolymer resin of tetrafluoroethylene and perfluoroalkyl vinyl ether on the surface of a chromium-plated steel sheet, or a stainless steel sheet or a zinc-plated steel sheet that has been subjected to an inorganic surface treatment. And tetrafluoroethylene-hexafluoropropylene copolymer resin, which is a copolymer resin of tetrafluoroethylene and hexafluoropropylene, as a main component, and the mixing ratio of the tetrafluoroethylene copolymer resin to 100 parts by weight of the polyether sulfone resin is 40. ~ 100 parts by weight of the coating material is applied and baked at a temperature in the range of 180 to 250 ° C.
An undercoat layer having a film thickness of 3 to 10 μm is formed, and then a polyether sulfone resin, a tetrafluoroethylene resin, and a copolymer resin of tetrafluoroethylene and perfluoroalkyl vinyl ether are formed on the undercoat layer, It contains tetrafluoroethylene copolymer resin, which is a copolymer resin of tetrafluoroethylene and hexafluoropropylene, as a main component, and is composed of tetrafluoroethylene resin and tetrafluoroethylene copolymer resin based on 100 parts by weight of polyether sulfone resin. Blending ratio is 20-40 parts by weight, 50-8, respectively
0 parts by weight of the coating material is applied, and baking is performed under the conditions that the baking time X (second) and the baking temperature Y (° C) satisfy the expressions (3) and (4), and the top coating having a film thickness of 3 to 20 μm is applied. A method for producing a precoated steel sheet, which comprises forming a layer. Y ≧ (4000 / X) +280 (3) Y ≦ (7000 / X) +280 (4) where Y ≦ 380 and X ≦ 100