Iron coating film as well as preparation method and application thereof

Abstract

The invention belongs to the field of metal coating films, and particularly discloses an iron coating film and a preparation method and application thereof. According to the iron coating film disclosed by the invention, the epoxy group-terminated polyurethane, the heat-conducting filler modified by the silane coupling agent containing the epoxy group and the water-soluble dispersing agent are matched with one another, so that the heat conductivity, the adhesive property and the film-forming property of the iron coating film can be obviously improved, and the iron coating film is more suitable for being applied to preparation of household appliances.

Description

Technical Field

[0001] This invention belongs to the field of metal coating, specifically relating to an iron-coated film, its preparation method, and its application. Background Technology

[0002] The process of hot-melt bonding biaxially oriented plastic sheets, such as polyester film (BOPET), to a heated metal plate is called coated steel. It is widely used in food cans, chemical cans, miscellaneous cans, steel-coated composites for household appliances, and steel-coated composites for new building decoration. The film used in the production of coated steel is called steel-clad film, and commonly used plastic-based polymers include polyethylene terephthalate (PET, or polyester), polypropylene (PP), and polyethylene (PE). When steel-clad film is used in household appliances, electronic components generate heat, and if this heat cannot be effectively dissipated, it can damage the components.

[0003] Patent document CN202410088228.4 discloses a multilayer thermally conductive PET film and its preparation method. This thermally conductive PET film consists of multiple alternating layers of thermally conductive layers and a substrate layer. The thermally conductive layers are composed of PET matrix resin, thermally conductive fillers, and compatibilizers. The weight percentage of the PET matrix is ​​20-50%, the weight percentage of the thermally conductive fillers is 40-75%, and the weight percentage of the compatibilizer is 5-10%. The substrate layer is also made of PET matrix resin. The thermally conductive layer material and the substrate layer material are co-extruded using a micro-nano layering extrusion device to form an alternating multilayer structure, which is then biaxially stretched or cast into a film. This multilayer thermally conductive PET film exhibits differentiated thermal conductivity in the parallel and perpendicular directions, possesses excellent mechanical properties and stability, and can be applied in semiconductor devices such as light-emitting diodes, solar cells, and field-effect transistors. However, during its preparation, PET is directly melt-composite with thermally conductive filler. Since thermally conductive filler is an inorganic filler, although its addition will improve the heat resistance of PET material, it is not conducive to the cladding process. Moreover, its high content will lead to the sacrifice of some mechanical properties of the film and the film is prone to breakage when the film is biaxially stretched.

[0004] Patent document CN202410897097.4 discloses a graphene-based thermally conductive film and its preparation method. This method uses crystallization-assisted methods to achieve the longitudinal alignment of graphene sheets, which significantly improves the film's thermal conductivity. The oriented graphene sheets facilitate smoother electron transport within the film, thereby reducing thermal resistance and improving overall thermal conductivity. This invention uses graphene dissolved in a PVA / PVP aqueous solution coated onto a PET film. However, because graphene is a black thermally conductive material, it can only be used to make black products, making it unsuitable for the appliance lamination film field. Furthermore, the solution does not consider the cladding process. If other fillers are used to replace the black thermally conductive filler, it is necessary to change the solvent to dissolve the corresponding filler. However, during the coating process, using an unsuitable solvent can also affect the thermal conductivity and adhesion during cladding, resulting in poor adhesion and failure to meet usage requirements. Summary of the Invention

[0005] In view of the problems of poor thermal conductivity, heat dissipation and adhesion performance of the existing iron-clad films, the present invention will provide an iron-clad film, its preparation method and application.

[0006] To achieve the above objectives, the following technical solutions are specifically included: In a first aspect, the present invention provides an iron-clad film, comprising a PET base film and an adhesive layer disposed on at least one surface of the PET base film; the adhesive layer comprises the following components: epoxy-terminated polyurethane, a thermally conductive filler modified with an epoxy-containing silane coupling agent, and a water-soluble dispersant; The mass ratio of the epoxy-terminated polyurethane to the thermally conductive filler modified with an epoxy-containing silane coupling agent is (10-15):1. Based on the total mass of the adhesive layer, the mass percentage of the water-soluble dispersant is 0.1%-0.5%.

[0007] In the iron-clad film of this invention, the epoxy-terminated polyurethane, the thermally conductive filler modified with an epoxy-containing silane coupling agent, and the water-soluble dispersant work together to significantly improve the thermal conductivity, adhesion, and film-forming properties of the iron-clad film. Specifically, the thermally conductive filler modified with the epoxy-containing silane coupling agent is hydrolyzed and coated with the modified thermally conductive filler, forming a silicon oxide coating layer on its surface. This improves the compatibility and dispersibility between the thermally conductive filler and the epoxy-terminated polyurethane. Furthermore, the presence of the water-soluble dispersant further enhances the dispersion effect of the thermally conductive filler in the system, improving the thermal conductivity, adhesion, and film-forming properties of the iron-clad film. In addition, the epoxy-terminated polyurethane volatilizes moisture and undergoes a film-forming reaction (increasing the molecular weight of the polyurethane) during the adhesion of the iron-clad film to the metal substrate (the transverse stretching process), improving its film-forming properties and preventing film breakage during film formation. Overall, the iron-clad film possesses excellent thermal conductivity, adhesion, and film-forming properties.

[0008] Preferably, the mass ratio of the epoxy-terminated polyurethane to the thermally conductive filler modified with an epoxy-containing silane coupling agent is (12-13.5):1.

[0009] Preferably, the thickness of the PET base film is 10-25 μm.

[0010] Preferably, the thickness of the adhesive layer is 1-15 μm.

[0011] Preferably, the PET base film is a copolyester with a melting point of 220-230°C and an intrinsic viscosity of 0.6-0.8 dl / g, which is tested according to Method A in GB / T 14190.

[0012] Preferably, the preparation method of the epoxy-terminated polyurethane includes the following steps: S1. Polyethylene glycol (PEG) and 2,2-dimethylolpropionic acid (DMPA) are dehydrated under vacuum to obtain pretreated polyethylene glycol and 2,2-dimethylolpropionic acid (DMPA). S2. The pretreated polyethylene glycol and 2,2-dimethylolpropionic acid (DMPA) are subjected to a first-stage reaction, isophorone diisocyanate (IPDI) is added to carry out a second-stage reaction, and ethylene glycol is added to carry out a third-stage reaction to obtain a polyurethane prepolymer. S3. Mix the epoxy group-containing silane coupling agent, triethylamine and water to obtain a premix; S4. The premix and the polyurethane prepolymer are mixed and subjected to a fourth-stage reaction to obtain epoxy-terminated polyurethane.

[0013] More preferably, in step S1, the polyethylene glycol includes at least one of PEG400, PEG500, PEG600, PEG800 or PEG1000.

[0014] More preferably, in step S1, the temperature of the dehydration treatment is 90-110℃, and the time of the dehydration treatment is 4-5h.

[0015] More preferably, in step S1, the mass ratio of polyethylene glycol (PEG) to 2,2-dimethylolpropionic acid (DMPA) is 100:(5-15).

[0016] More preferably, based on 100 parts by weight of the polyethylene glycol (PEG) in step S1, the isophorone diisocyanate (IPDI) in step S2 is 50-70 parts by weight.

[0017] More preferably, based on 100 parts by weight of the polyethylene glycol (PEG) in step S1, the ethylene glycol in step S2 is 1-10 parts by weight.

[0018] More preferably, in step S2, the temperatures of the first stage reaction, the second stage reaction, and the third stage reaction are each independently selected from 75-90°C, and the times of the first stage reaction, the second stage reaction, and the third stage reaction are each independently selected from 0.5-5h.

[0019] More preferably, in step S2, isophorone diisocyanate (IPDI) is added by dripping for 30-45 minutes.

[0020] More preferably, in step S2, ethylene glycol is added by dropping, and the dropping time is 3-5 minutes.

[0021] More preferably, in step S3, the mass ratio of the epoxy group-containing silane coupling agent, triethylamine, and water is 10:(1-8):(200-500).

[0022] More preferably, in step S3, the epoxy-containing silane coupling agent includes γ-glycidyl etheroxypropyltrimethoxysilane (KH560). This invention uses KH560, an epoxy-containing silane, to modify polyurethane, resulting in polyurethane with epoxy groups at the ends. This improves the compatibility and dispersibility of the KH560-modified thermally conductive filler in polyurethane resin, and also enhances the adhesion between the polyurethane resin and PET material.

[0023] More preferably, in step S3, the reaction time of the fourth stage is 0.5-2 hours, and the reaction temperature of the fourth stage is room temperature.

[0024] Preferably, the preparation method of the thermally conductive filler modified with the epoxy group-containing silane coupling agent includes the following steps: S1. Mix the epoxy group-containing silane coupling agent with water to obtain a mixture; adjust the pH of the mixture to 4-6 and heat it to 60-70℃ for hydrolysis to obtain the first mixture; S2. React the thermally conductive filler and the first mixture to obtain a second mixture; S3. The second mixture is dried to obtain a thermally conductive filler modified with an epoxy group silane coupling agent.

[0025] More preferably, in step S1, the epoxy-containing silane coupling agent includes γ-glycidoxypropyltrimethoxysilane (KH560).

[0026] More preferably, in step S1, the mass ratio of the epoxy-containing silane coupling agent to water is 1-2:8-9.

[0027] More preferably, in step S1, the hydrolysis time is 30-60 minutes, the hydrolysis is carried out under stirring, and the stirring speed is 300-500 rpm.

[0028] More preferably, in step S2, the mass ratio of the thermally conductive filler to the first mixture is (3-4):(6-7).

[0029] More preferably, in step S2, the reaction time is 30-60 minutes.

[0030] More preferably, in step S3, the drying temperature is 100-110℃.

[0031] Preferably, the thermally conductive filler modified with an epoxy-containing silane coupling agent includes at least one of boron nitride and metal oxide.

[0032] More preferably, the average particle size of the thermally conductive filler is 2-5 μm.

[0033] Preferably, the adhesive layer further includes 0.1-5% by weight of pigment.

[0034] More preferably, the pigment includes at least one of inorganic pigments or organic pigments, and more specifically, it may include at least one of titanium dioxide, phthalocyanine blue, and golden red.

[0035] Preferably, the water-soluble dispersant comprises polyethylene glycol lauryl ether. Using polyethylene glycol lauryl ether as a dispersant further improves the dispersion effect of the modified thermally conductive filler in epoxy-terminated polyurethane.

[0036] Secondly, the present invention provides a method for preparing the aforementioned iron-coated film, comprising the following steps: S1. Add water-soluble dispersant to epoxy-terminated polyurethane and mix evenly. Then add thermally conductive filler modified with epoxy-containing silane coupling agent and optional pigment in sequence and mix evenly to obtain premix of adhesive layer. S2. The PET chips are sequentially subjected to crystallization treatment, drying treatment, extrusion casting and longitudinal stretching to obtain longitudinally stretched PET sheets; S3. The premixed adhesive layer is coated on at least one surface of the longitudinally stretched PET sheet, and then transversely stretched and shaped in sequence to obtain an iron-clad film.

[0037] In this invention, a coating process is used to bond the premixed adhesive layer to a PET base film. After the thermally conductive adhesive layer is coated onto the PET film, under high-temperature conditions, some epoxy groups in the epoxy-terminated polyurethane undergo ring-opening, thereby bonding with the partially melted resin on the PET film surface. This improves the adhesion between the polyurethane and the PET film. While maintaining good film-forming properties, the prepared iron-clad film exhibits excellent thermal conductivity and adhesion. Furthermore, during the iron-clad film coating process, some of the unopened epoxy groups in the adhesive layer undergo ring-opening again upon heating, bonding with the metal surface and further enhancing the adhesion between the polyurethane and the metal substrate. This preparation method is environmentally friendly, simple to operate, and easily scalable for industrial production.

[0038] Preferably, in step S1, the mixing is carried out under stirring, the stirring speed is 300-500 rpm, and the stirring time is 5-10 min.

[0039] Preferably, in step S2, the temperature of the crystallization treatment is 150-160℃, and the time of the crystallization treatment is 30-60 min.

[0040] Preferably, in step S2, the drying temperature is 140-150℃ and the drying time is 4-6 hours.

[0041] Preferably, in step S2, the temperature of the extruded sheet is 250-270°C, and the extruded sheet is cooled to room temperature after extrusion.

[0042] Preferably, in step S2, the longitudinal stretching ratio is 3-4 times, and the longitudinal stretching is preheated at a temperature of 70-75°C. The longitudinal stretching temperature is 80-85°C, and the longitudinal stretching is cooled to room temperature.

[0043] Preferably, in step S3, the stretching ratio of the transverse stretching is 3-4 times, and the transverse stretching is preheated beforehand. The temperature of the preheating treatment is 90-100℃, and the temperature of the transverse stretching is 100-110℃.

[0044] Preferably, in step S3, the shaping temperature is 200-220°C, and the shaping is further cooled to room temperature.

[0045] Thirdly, the present invention provides a household appliance, including a metal substrate and a metal-clad film disposed on the surface of the metal substrate, wherein the adhesive layer of the metal-clad film is located on the side closer to the metal substrate. The metal-clad film of the present invention has good coating adhesion, film-forming performance, and thermal conductivity, and it uses a non-black thermally conductive filler, making it more suitable for application in the manufacture of household appliances.

[0046] Compared with the prior art, the present invention has the following beneficial effects: In the iron-clad film of the present invention, the epoxy-terminated polyurethane, the thermally conductive filler modified with epoxy-containing silane coupling agent and the water-soluble dispersant work together to significantly improve the thermal conductivity, adhesion and film-forming properties of the iron-clad film, making it more suitable for use in the manufacture of household appliances. Detailed Implementation

[0047] To better illustrate the purpose, technical solution, and advantages of this invention, specific embodiments will be used to further explain the invention below. Unless otherwise specified, the test methods used in the embodiments and / or comparative examples are conventional methods; the materials and reagents used, unless otherwise specified, are commercially available.

[0048] Raw material information: PET chips: LM503, melting point 230℃, intrinsic viscosity 0.66dl / g, Yizheng Petrochemical, China; Polyethylene glycol lauryl ether: DiYi Chemical; Common waterborne polyurethane: DIC, HYDRAN APX-101H.

[0049] Example 1 A method for preparing an iron-coated film includes the following steps: (1) Preparation of epoxy-terminated polyurethane: S1. 100 parts by weight of PEG500 and 10 parts by weight of 2,2-dimethylolpropionic acid (DMPA) were dehydrated at a vacuum of 0.01 MPa and a temperature of 100 °C for 4.5 h. S2. Place the treated PEG500 and DMPA into a reaction vessel, and under nitrogen protection, heat to 85°C while stirring, and maintain the temperature for 30 minutes to carry out the reaction. S3. Add 65 parts by weight of isophorone diisocyanate (IPDI) dropwise into the above reaction vessel, with the addition time controlled at 40 min. After the addition is completed, continue the reaction at a constant temperature for 3.5 h. S4. Add 5 parts by weight of ethylene glycol to the above reaction vessel, with the addition time controlled at 4 min. After the addition is completed, continue to react at a constant temperature for 2.5 h, and then lower the temperature to 35 °C to obtain polyurethane prepolymer. S5. Mix 10 parts by weight of silane coupling agent KH560, 5 parts by weight of triethylamine and 300 parts by weight of deionized water evenly to obtain a premix. S6. Add the premixed material dropwise into the polyurethane prepolymer in the reactor while stirring. The time should be controlled at 1 hour. After the addition is complete, react for 1 hour to obtain epoxy-terminated polyurethane.

[0050] (2) Preparation of KH560 modified thermally conductive filler: S1. KH560 and deionized water were mixed at a weight ratio of 1:9 to obtain a solution. The pH of the solution was then adjusted to 5 with hydrochloric acid. The solution was then heated to 65°C while stirring at a stirring speed of 400 rpm for 40 min to obtain the first mixture by hydrolysis. S2. Mix the thermally conductive filler and the first mixture at a mass ratio of 3:7, then heat to 65°C while stirring at a stirring speed of 400 rpm for 40 minutes to obtain the second mixture. S3. Place the second mixture in a 105℃ oven to dry the moisture, and obtain KH560 modified thermally conductive filler.

[0051] (3) Preparation of the adhesive layer: S1. Add the water-soluble dispersant to the epoxy-terminated polyurethane and stir until homogeneous. The stirring speed is 400 rpm and the stirring time is 50 min. S2. Then, while stirring, add KH560 modified thermally conductive filler at a stirring speed of 400 rpm for 8 minutes. S4. Finally, while stirring, add the metallic pigment at a stirring speed of 600 rpm for 4 minutes to obtain the premix of the adhesive layer.

[0052] (4) Preparation of iron-coated film: S1: Place the PET chips into a crystallization dryer and crystallize them at 160℃ for 50 minutes to obtain crystallized PET chips; S2: Place the crystalline PET slices into a PET drying device and dry them at 140℃ for 5 hours to control the PET moisture content to less than 100PPM for later use. S3: The dried PET chips are fed into a single screw to extrude cast sheets at an extrusion temperature of 260°C and then cooled to 35°C.

[0053] S4: The cast PET sheet is stretched longitudinally by a stretching ratio of 4 times. The preheating temperature before stretching is 70℃, the stretching temperature is 80℃, and the temperature is cooled to 35℃. S5: Apply a layer of premixed adhesive to one surface of the longitudinally stretched PET sheet. The thickness of the coating layer is adjusted according to the product thickness. S6: The coated PET sheet is stretched laterally by a stretching ratio of 4 times. The preheating temperature before stretching is 95℃, the stretching temperature is 110℃, and the stretching temperature is 210℃. After stretching, it is shaped at a setting temperature of 210℃ and then cooled to 30℃ to obtain the iron-coated film.

[0054] For details on the types and quantities of raw materials, as well as the thickness of each layer of the final product, please refer to Table 1.

[0055] Examples 2-5 The only difference between Examples 2-5 and Example 1 is that the mass ratio of epoxy-terminated polyurethane to KH560 modified thermally conductive filler is different, as detailed in Table 1. The rest are the same.

[0056] Examples 6-7 The only difference between Examples 6 and 7 and Example 1 is the thickness of the PET base film and the adhesive layer, as detailed in Table 1. The rest are the same.

[0057] Example 8 The only difference between Example 8 and Example 1 is that the type of thermally conductive filler is different, as detailed in Table 1; the rest are the same.

[0058] Comparative Example 1 The only difference between this comparative example and Example 1 is that step (1) of preparing epoxy-terminated polyurethane was not performed, and an equal mass of ordinary waterborne polyurethane was used to replace epoxy-terminated polyurethane. The rest are the same.

[0059] Comparative Example 2 The only difference between this comparative example and Example 1 is that in step (2), KH560 is replaced with an equal mass of γ-aminopropyltriethoxysilane (KH550), and the rest are the same.

[0060] Comparative Example 3 The only difference between this comparative example and Example 1 is that the preparation process of (2) KH560 modified thermally conductive filler was not carried out, and boron nitride of equal mass was used to replace KH560 modified boron nitride. The rest are the same.

[0061] Comparative Example 4 The only difference between this comparative example and Example 1 is that no water-soluble dispersant was added during the preparation of the adhesive layer in step (3), otherwise the same.

[0062] Table 1 The appearance, smoothness, and spots of the prepared iron-clad film were observed to evaluate its film-forming properties. The results are shown in Table 2. The iron-clad films obtained in the above examples and comparative examples were tested for adhesion and thermal conductivity. Adhesion was tested according to GB4156 standard "Metal Cupping Test Method," where the adhesive layer adheres to the metal substrate on one side, and the shorter the peel length of the cupping adhesion, the better the adhesion. Thermal conductivity was tested according to GB / T 10294-2008 standard; the higher the thermal conductivity coefficient, the better the thermal conductivity. The test results are shown in Table 2.

[0063] Table 2 As can be seen from the above embodiments, the iron-clad film of the present invention has a small cup-shaped adhesion peel length (less than 0.5 mm) in the adhesion performance test, and has excellent adhesion performance to metals; moreover, its thermal conductivity is greater than 7.5 W / mK, with outstanding thermal conductivity, and its film-forming performance is also good, with a smooth film surface and no obvious appearance defects.

[0064] As shown in Example 1 and Comparative Examples 1-2, epoxy-terminated polyurethane, KH560-modified thermally conductive filler, and water-soluble dispersant can synergistically improve the adhesion, thermal conductivity, and film-forming properties of the iron-clad film, thus achieving excellent adhesion, thermal conductivity, and film-forming properties. Furthermore, Comparative Example 3 shows that a silane coupling agent containing epoxy groups is needed to modify the thermally conductive filler to improve the adhesion, thermal conductivity, and film-forming properties of the iron-clad film. Meanwhile, Comparative Example 4 shows that the water-soluble dispersant enhances the adhesion, thermal conductivity, and film-forming properties of the iron-clad film.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. An iron-clad film, characterized in that, The invention includes a PET base film and an adhesive layer disposed on at least one surface of the PET base film; the adhesive layer comprises the following components: epoxy-terminated polyurethane, thermally conductive filler modified with an epoxy-containing silane coupling agent, and a water-soluble dispersant; The mass ratio of the epoxy-terminated polyurethane to the thermally conductive filler modified with an epoxy-containing silane coupling agent is (10-15):

1. Based on the total mass of the adhesive layer, the mass percentage of the water-soluble dispersant is 0.1%-0.5%.

2. The iron-coated film as described in claim 1, characterized in that, The mass ratio of the epoxy-terminated polyurethane to the thermally conductive filler modified with an epoxy-containing silane coupling agent is (12-13.5):

1.

3. The iron-coated film as described in claim 1, characterized in that, Includes at least one of the following: The thickness of the PET base film is 10-25 μm; The thickness of the adhesive layer is 1-15 μm.

4. The iron-clad film as described in claim 1, characterized in that, The PET base film is a copolyester with a melting point of 220-230℃ and an intrinsic viscosity of 0.6-0.8 dl / g.

5. The iron-clad film as described in claim 1, characterized in that, The preparation method of the epoxy-terminated polyurethane includes the following steps: S1. Polyethylene glycol and 2,2-dimethylolpropionic acid are dehydrated under vacuum to obtain pretreated polyethylene glycol and 2,2-dimethylolpropionic acid. S2. The pretreated polyethylene glycol and 2,2-dimethylolpropionic acid are subjected to a first-stage reaction, isophorone diisocyanate (IPDI) is added for a second-stage reaction, and ethylene glycol is added for a third-stage reaction to obtain a polyurethane prepolymer. S3. Mix the epoxy group-containing silane coupling agent, triethylamine and water to obtain a premix; S4. The premix and the polyurethane prepolymer are mixed and subjected to a fourth-stage reaction to obtain epoxy-terminated polyurethane.

6. The iron-clad film as described in claim 1, characterized in that, The preparation method of the thermally conductive filler modified with the epoxy group-containing silane coupling agent includes the following steps: S1. Mix the epoxy group-containing silane coupling agent with water to obtain a mixture; adjust the pH of the mixture to 4-6 and heat it to 60-70℃ for hydrolysis to obtain the first mixture; S2. React the thermally conductive filler and the first mixture to obtain a second mixture; S3. The second mixture is dried to obtain a thermally conductive filler modified with an epoxy group silane coupling agent.

7. The iron-clad film as described in claim 1, characterized in that, Includes at least one of the following ACs: A. The thermally conductive filler modified with an epoxy-containing silane coupling agent includes at least one of boron nitride and metal oxide; B. The adhesive layer further includes 0.1-5% pigment by weight; C. The water-soluble dispersant includes polyethylene glycol lauryl ether.

8. A method for preparing the iron-coated film according to claims 1-7, characterized in that, Includes the following steps: S1. Add water-soluble dispersant to epoxy-terminated polyurethane and mix evenly. Then add thermally conductive filler modified with epoxy-containing silane coupling agent and optional pigment in sequence and mix evenly to obtain premix of adhesive layer. S2. The PET chips are sequentially subjected to crystallization treatment, drying treatment, extrusion casting and longitudinal stretching to obtain longitudinally stretched PET sheets; S3. The premixed adhesive layer is coated on at least one surface of the longitudinally stretched PET sheet, and then transversely stretched and shaped in sequence to obtain an iron-clad film.

9. The method for preparing the iron-coated film as described in claim 8, characterized in that, Includes at least one of the following: In step S1, the mixing is carried out under stirring, the stirring speed is 300-500 rpm, and the stirring time is 5-10 min; In step S2, the temperature of the crystallization treatment is 150-160℃, and the time of the crystallization treatment is 30-60 min; In step S2, the drying temperature is 140-150℃, and the drying time is 4-6 hours. In step S2, the temperature of the extruded sheet is 250-270°C, and the extruded sheet is cooled to room temperature after extrusion. In step S2, the longitudinal stretching ratio is 3-4 times, and the longitudinal stretching is preheated at a temperature of 70-75°C. The longitudinal stretching temperature is 80-85°C, and the longitudinal stretching is cooled to room temperature. In step S3, the stretching ratio of the transverse stretching is 3-4 times, and the transverse stretching is preheated before the stretching. The temperature of the preheating is 90-100℃, and the stretching temperature is 100-110℃. In step S3, the shaping temperature is 200-220℃, and the shaping is followed by cooling to room temperature.

10. A household appliance, characterized in that, The invention includes a metal substrate and an iron-clad film as described in any one of claims 1-7 disposed on the surface of the metal substrate, wherein the adhesive layer in the iron-clad film is located on the side closer to the metal substrate.

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