A multi-layer fluorine film for heat sealing welding and preparation method thereof

Abstract

The present invention provides a multilayer fluorine film for heat sealing welding, the multilayer fluorine film comprises three fluorine film layers, including a first heat sealing welding layer, a structural support layer and a second heat sealing welding layer in sequence; the total thickness of the multilayer fluorine film is 10 to 250 μm; wherein the thickness of the structural support layer accounts for 60 to 98% of the total thickness, the thickness of the first heat sealing welding layer accounts for 1 to 20% of the total thickness, and the thickness of the second heat sealing welding layer accounts for 1 to 20% of the total thickness; the structural support layer is one or both of FEP fluorine film and PFA fluorine film, and the first and second heat sealing welding layers are ETFE fluorine films. The present invention changes the structure of the heat sealing welding material and optimizes the raw material composition of the structural support layer. The prepared multilayer fluorine film can reduce the initial sealing temperature of the heat sealing welding material while taking into account the temperature resistance and enhance the heat sealing strength of the heat sealing welding material, can solve the bonding problem of polytetrafluoroethylene products and other materials, and expand the application field of polytetrafluoroethylene products.

Description

Technical Field

[0001] The invention belongs to the technical field of thin films and relates to a multi-layer fluorine film for heat sealing welding and a preparation method thereof. Technical Background

[0002] With the progress of world industrial technology, especially the rapid development of aerospace, electronic semiconductor, chemical industry, environmental engineering, fluid machinery and other industries, these industrial fields are increasingly inseparable from anti-corrosion materials. Nowadays, various advanced anti-corrosion materials are constantly being introduced, among which polytetrafluoroethylene (PTFE) is known as the "King of Plastics". It is increasingly valued by people for its excellent chemical stability, high temperature resistance and corrosion resistance, non-stickiness, excellent lubrication performance and other characteristics. However, PTFE is a highly inert and difficult-to-bond material, and it is difficult to bond directly with ordinary adhesives.

[0003] There are many methods of plastic welding, such as hot plate welding, ultrasonic welding, laser welding, etc., all of which use the characteristics of thermoplastics melting under heat to melt the surfaces of two plastic parts at the same time, and make the two parts become one under the action of external force. The most important thing in thermal welding is the selection of welding film materials. Since polytetrafluoroethylene itself has low adhesion and is not easy to be wetted, it is necessary to select polytetrafluoroethylene welding materials with good solubility and melt fluidity and can be effectively wetted. At present, FEP or PFA materials are commonly used as polytetrafluoroethylene welding materials.

[0004] However, when FEP or PFA materials are used as polytetrafluoroethylene welding materials, the bonding seams are uneven after bonding and cannot meet the sealing and strength requirements of environmental protection and fluid engineering. The uneven and loose bonding seam structure can easily cause leakage of the bonding layer and insufficient strength, leading to separation of the welding structure. It also has disadvantages such as high initial sealing temperature, poor heat sealing strength, high process requirements, and complex construction process, which limit the application of polytetrafluoroethylene. Summary of the invention

[0005] Aiming at the shortcomings of the prior art polytetrafluoroethylene welding materials, such as uneven bonding seams, high initial sealing temperature, poor heat sealing strength, etc., the present invention provides a multilayer fluorine film for heat sealing welding and a preparation method thereof, which can be used for polytetrafluoroethylene welding materials.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A multi-layer fluorine film for heat sealing welding, characterized in that the multi-layer fluorine film includes three fluorine film layers, including a first heat sealing welding layer, a structural support layer and a second heat sealing welding layer in sequence; the total thickness of the multi-layer fluorine film is 10-250 μm; wherein the thickness of the structural support layer accounts for 60-98% of the total thickness, the thickness of the first heat sealing welding layer accounts for 1-20% of the total thickness, and the thickness of the second heat sealing welding layer accounts for 1-20% of the total thickness. The structural support layer is one or both of FEP fluorine film and PFA fluorine film; the first and second heat sealing welding layers are ETFE fluorine films.

[0008] Preferably, the thickness of the structural support layer accounts for 70-90% of the total thickness, the thickness of the first heat-sealing welding layer accounts for 5-15% of the total thickness, and the thickness of the second heat-sealing welding layer accounts for 5-15% of the total thickness. Preferably, the initial sealing temperature of the multi-layer fluorine film is 275-350°C, the heat-sealing strength is 24-45N / 15mm, and the maximum long-term use temperature is greater than 215°C.

[0009] Preferably, the total thickness of the heat-welded multi-layer fluorine film is 50 to 200 μm.

[0010] Preferably, the fluororesin used has a melt index of 5 to 20 g / 10 min, a tensile strength of 20 to 50 MPa, and a tensile elongation of 200 to 400%.

[0011] Preferably, when the support layer material is FEP, the initial sealing temperature of the multilayer fluorine film is 275±2°C, the heat sealing strength is 24-25N / 15mm, and the maximum long-term use temperature is 220±2°C. When the support layer material is PFA, the initial sealing temperature of the multilayer fluorine film is 340-350°C, the heat sealing strength is 35-45N / 15mm, and the maximum long-term use temperature is 215-225°C. Further preferably, the resin used in the structural support layer also includes 5-10wt% of functional additives. Functional additives can improve the tensile strength, thermal conductivity and melt strength of the multilayer welded fluorine film during welding. Preferably, the content of the functional additive is 5-8%.

[0012] More preferably, the functional additive is one or a mixture of nano boron nitride, nano calcium sulfate whisker, nano talc powder, nano silicon dioxide. More preferably, the functional additive is one or a mixture of nano boron nitride, nano talc powder, nano silicon dioxide.

[0013] Preferably, the ETFE is ethylene-tetrafluoroethylene-perfluoromethyl vinyl ether terpolymer. Further preferably, the ETFE used in the first and second heat-seal welding layers has a melt index of 5-20 g / 10 min, a tensile strength of 20-50 MPa, and a tensile elongation of 200%-400%.

[0014] The present invention also provides a method for preparing the above-mentioned multi-layer fluorine film for heat sealing welding, which is prepared by multi-layer co-extrusion casting or film blowing, comprising the following steps:

[0015] (1) melt-blending one or both of FEP or PFA with a functional additive, extruding and granulating, and drying to obtain a supporting layer fluororesin raw material;

[0016] (2) Extruding the raw materials of the first welding sealing layer, the supporting layer, and the second welding sealing layer into a melt through an extruder, and then compounding them in a casting die or a blown film die to obtain a three-layer fluorine film primary product;

[0017] (3) The prepared three-layer fluorine film initial product is cooled and shaped to obtain a multi-layer fluorine film finished product for heat sealing and welding.

[0018] Preferably, the extrusion temperature in step (1) is 220-350° C., the screw speed is 15-80 r / min, and the drying conditions are: 100-140° C., 6-10 h.

[0019] Preferably, in step (2), an extrusion cast film unit comprising three extruders A, B, and C is used, wherein extruders A and C are used to extrude two outer heat-sealed welding layers, and extruder B is used to extrude the structural support layer. By controlling the rotation speed of the three extruders and thereby adjusting the melt flow rate of each extruder, the thickness of the first welding sealing layer, the second welding sealing layer, and the structural support layer can be adjusted.

[0020] Further preferably, the process parameters of the extruder in step (2) are as follows:

[0021] A, C extruder: screw aspect ratio is 20-30; barrel has four heating zones, zone 1 is 220-340℃, zone 2 is 230-350℃, zone 3 is 230-360℃, zone 4 is 230-370℃;

[0022] B extruder: The screw aspect ratio is 25-30, and the barrel has four heating zones, zone 1 is 210-340°C, zone 2 is 220-340°C, zone 3 is 220-350°C, and zone 4 is 220-350°C;

[0023] Further preferably, in step (2), the die is preferably a casting die; and the temperature of the casting die is 250 to 370°C.

[0024] Preferably, in step (3), the cooling and shaping conditions are: cooling and shaping by traction rollers, the temperature of the traction and shaping rollers is 10 to 200° C., the traction speed is 0.5 to 55 m / s, and the winding speed is 0.5 to 55 m / s.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] Compared with the prior art, the present invention provides a high-performance multi-layer fluorine film for heat-sealing welding by changing the structure of the heat-sealing welding material and further optimizing the raw material composition of the structural support layer. The multi-layer fluorine film prepared by the present invention can reduce the initial sealing temperature of the heat-sealing welding material and enhance the heat-sealing strength of the heat-sealing welding material while taking into account the temperature resistance of the fluorine film. The heat-sealing welding construction process is simple, which can solve the bonding problem of polytetrafluoroethylene products and other materials and expand the application field of polytetrafluoroethylene products.

[0027] The multi-layer fluorine film for heat sealing and welding provided by the present invention has a three-layer structure as a whole, adopts co-extrusion melting, FEP and / or PFA and ETFE are compounded by melt distributor FEEDBLOCK in front of the die head, and then enter the mold, so that a uniform film with a three-layer structure can be obtained, without the need for additional adhesive layers and lamination steps. The molding process is simple, there is no solvent residue, and no pollution is caused during the manufacturing and use process. In addition, the multi-layer fluorine film for heat sealing and welding of the present invention can also adjust the thickness of the structural support layer according to actual needs to prepare heat sealing and welding fluorine films with different application requirements.

[0028] For example, when the thickness of the support layer is 81-98% of the film thickness, it can be used for welding of polytetrafluoroethylene lining structures, and is suitable for fields with high requirements on welding seal strength and compactness of the structure; when the thickness of the support layer is 70-80% of the film thickness, it can be used for welding and bonding of polytetrafluoroethylene pipes or components, and is suitable for the field of rigid welding and bonding of structural parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the structure of heat-sealed and welded multi-layer fluorine film. DETAILED DESCRIPTION

[0030] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be pointed out that the embodiments described below are intended to facilitate the understanding of the present invention and do not have any limiting effect on the present invention.

[0031] The resins used in the embodiments of the present invention, such as tetrafluoroethylene-hexafluoropropylene binary copolymer and ethylene-tetrafluoroethylene-perfluoromethyl vinyl ether ternary copolymer, are all commercially available products.

[0032] Embodiment 1:

[0033] A multi-layer fluorine film for heat sealing and welding, with a total thickness of 50 μm, is composed of a first heat sealing and welding layer, a structural support layer and a second heat sealing and welding layer. The thickness of the structural support layer is 40 μm, the thickness of the first heat sealing and welding layer is 5 μm, and the thickness of the second heat sealing and welding layer is 5 μm.

[0034] The structural support layer is composed of the following raw materials in parts by weight: 99 wt% tetrafluoroethylene-hexafluoropropylene binary copolymer and 1 wt% nano boron nitride, wherein the weight percentage of tetrafluoroethylene in the tetrafluoroethylene-hexafluoropropylene binary copolymer is 50%, and the melt index is 10.2 g / 10 min.

[0035] The resin raw materials used for the first heat-seal welding layer and the second heat-seal welding layer are ethylene-tetrafluoroethylene-perfluoromethyl vinyl ether terpolymer. The weight percentage of tetrafluoroethylene in the ethylene-tetrafluoroethylene-perfluoromethyl vinyl ether terpolymer is 45%, the weight percentage of ethylene is 45%, the weight percentage of perfluoromethyl vinyl ether is 10%, and the melt index of the ethylene-tetrafluoroethylene-perfluoromethyl vinyl ether terpolymer is 15.2 g / 10 min.

[0036] The processing and preparation steps of the multi-layer fluorine film for heat sealing welding are as follows:

[0037] (1) The raw materials of the structural support layer are mixed in a high-speed mixer according to the proportion, and melt-blended by a twin-screw extruder. The twin-screw extruder is heated in four zones, with heating zone 1 at 295° C., heating zone 2 at 315° C., heating zone 3 at 325° C., and heating zone 4 at 350° C. The screw speed is 20 r / min, and after traction granulation, the mixture is dried at 120° C. for 8 h, and sealed for use;

[0038] (2) An extrusion cast film unit containing three extruders is used, wherein extruders A and C are used to extrude two outer heat-sealed welding layers, and extruder B is used to extrude a structural support layer. The melt extruded by the three-layer extruders is compounded in a casting die to obtain a three-layer fluorine film primary product; the casting die temperature is 280°C for the A and C end molds, and 360°C for the B end mold.

[0039] The process parameters of the extruder are as follows:

[0040] A, C extruder: screw aspect ratio is 28; barrel has four heating zones, zone 1 is 250℃, zone 2 is 265℃, zone 3 is 275℃, zone 4 is 280℃;

[0041] B extruder: The screw aspect ratio is 28, and the barrel has four heating zones, zone 1 is 290°C, zone 2 is 325°C, zone 3 is 340°C, and zone 4 is 350°C;

[0042] (3) The prepared three-layer fluorine film primary product is cooled and shaped by a traction roller: the temperature of the traction and shaping roller is 100° C., the traction speed is 20 m / s, and the winding speed is 20 m / s;

[0043] (4) The three-layer fluorine film after shaping is subjected to static elimination and tension winding; the thickness is detected and adjusted by an online thickness gauge, and the film is trimmed and wound to obtain a multi-layer fluorine film product for heat sealing and welding.

[0044] The initial sealing temperature, heat sealing strength and long-term use temperature of the prepared fluorine film are shown in Table 1.

[0045] Embodiment 2:

[0046] A multi-layer fluorine film for heat sealing and welding, with a total thickness of 100 μm, is composed of a first heat sealing and welding layer, a structural support layer and a second heat sealing and welding layer. The thickness of the structural support layer is 70 μm, the thickness of the first heat sealing and welding layer is 15 μm, and the thickness of the second heat sealing and welding layer is 15 μm.

[0047] The structural support layer is composed of the following raw materials in parts by weight: 95 wt% of tetrafluoroethylene-hexafluoropropylene binary copolymer and 5 wt% of nano silicon dioxide, wherein the weight percentage of tetrafluoroethylene in the tetrafluoroethylene-hexafluoropropylene binary copolymer is 50%.

[0048] The resin used in the first heat-seal welding layer and the second heat-seal welding layer is ethylene-tetrafluoroethylene-perfluoromethyl vinyl ether terpolymer. The weight percentage of tetrafluoroethylene in the ethylene-tetrafluoroethylene-perfluoromethyl vinyl ether terpolymer is 45%, the weight percentage of ethylene is 45%, the weight percentage of perfluoromethyl vinyl ether is 10%, and the melt index of the ethylene-tetrafluoroethylene-perfluoromethyl vinyl ether terpolymer is 17.7 g / 10 min.

[0049] The processing and preparation steps of the multi-layer fluorine film for heat sealing welding are as follows:

[0050] The processing method is the same as that of Example 1, except that the filler added to the structural layer is nano-silicon dioxide and the mass fraction of the filler is different.

[0051] The initial sealing temperature, heat sealing strength and long-term use temperature of the prepared fluorine film are shown in Table 1.

[0052] Embodiment 3:

[0053] A multi-layer fluorine film for heat sealing and welding, with a total thickness of 150 μm, is composed of a first heat sealing and welding layer, a structural support layer and a second heat sealing and welding layer. The thickness of the structural support layer is 120 μm, the thickness of the first heat sealing and welding layer is 15 μm, and the thickness of the second heat sealing and welding layer is 15 μm.

[0054] The structural support layer is composed of the following raw materials in parts by weight: 95 wt % of fusible polytetrafluoroethylene PFA (melting index is 5 g / 10 min) and 5 wt % of nano talc powder.

[0055] The resin raw materials used for the first heat-seal welding layer and the second heat-seal welding layer are ethylene-tetrafluoroethylene-perfluoromethyl vinyl ether terpolymer. The weight percentage of tetrafluoroethylene in the ethylene-tetrafluoroethylene-perfluoromethyl vinyl ether terpolymer is 45%, the weight percentage of ethylene is 45%, the weight percentage of perfluoromethyl vinyl ether is 10%, and the melt index of the ethylene-tetrafluoroethylene-perfluoromethyl vinyl ether terpolymer is 16g / 10min.

[0056] The processing method is as follows:

[0057] (1) The raw materials and additives of the structural support layer are mixed in a high-speed mixer according to a ratio, and melt-blended through a twin-screw extruder. The twin-screw extruder is heated in four zones, with heating zone 1 at 295°C, heating zone 2 at 315°C, heating zone 3 at 325°C, and heating zone 4 at 380°C. The screw speed is 20 r / min. After traction granulation, the mixture is dried at 120°C for 8 hours and sealed for use. The additive used is nano-talcum powder with a mass fraction of 5wt%.

[0058] (2) An extrusion cast film unit containing three extruders is used, wherein extruders A and C are used to extrude two outer heat-sealed welding layers, and extruder B is used to extrude a structural support layer. The melt extruded by the three-layer extruder is compounded in a casting die to obtain a three-layer fluorine film primary product; the casting die temperature is 280°C for the A and C end molds, and 380°C for the B end mold.

[0059] The process parameters of the extruder are as follows:

[0060] A, C extruder: screw aspect ratio is 28; barrel has four heating zones, zone 1 is 250℃, zone 2 is 265℃, zone 3 is 275℃, zone 4 is 280℃;

[0061] B extruder: The screw aspect ratio is 28, and the barrel has four heating zones, zone 1 is 300°C, zone 2 is 315°C, zone 3 is 345°C, and zone 4 is 380°C;

[0062] (3) The prepared three-layer fluorine film initial product is cooled and shaped by a traction roller: the temperature of the traction and shaping roller is 120° C., the traction speed is 20 m / s, and the winding speed is 30 m / s;

[0063] (4) The three-layer fluorine film after shaping is subjected to static elimination and tension winding; the thickness is detected and adjusted by an online thickness gauge, and the film is trimmed and wound to obtain a multi-layer fluorine film product for heat sealing and welding.

[0064] The initial sealing temperature, heat sealing strength and long-term use temperature of the prepared fluorine film are shown in Table 1.

[0065] Embodiment 4:

[0066] A heat-sealed welded multi-layer fluorine film has a total thickness of 200 μm, and the heat-sealed welded multi-layer fluorine film consists of a first heat-sealed welded layer, a structural support layer and a second heat-sealed welded layer. The thickness of the structural support layer is 180 μm, the thickness of the first heat-sealed welded layer is 10 μm, and the thickness of the second heat-sealed welded layer is 10 μm.

[0067] The structural support layer is composed of the following raw materials in parts by weight: 92 wt % of fusible polytetrafluoroethylene PFA (melting index is 14 g / 10 min) and 8 wt % of nano talc powder.

[0068] The resin used in the first heat-seal welding layer and the second heat-seal welding layer is ethylene-tetrafluoroethylene-perfluoromethyl vinyl ether terpolymer. The weight percentage of tetrafluoroethylene in the ethylene-tetrafluoroethylene-perfluoromethyl vinyl ether terpolymer is 45%, the weight percentage of ethylene is 45%, the weight percentage of perfluoromethyl vinyl ether is 10%, and the melt index of the ethylene-tetrafluoroethylene-perfluoromethyl vinyl ether terpolymer is 6g / 10min.

[0069] The processing method of the multi-layer fluorine film for heat sealing welding is the same as that of Example 3, except that the content of the auxiliary agent used is different.

[0070] Embodiment 5:

[0071] A multi-layer fluorine film for heat sealing and welding, with a total thickness of 100 μm, a thickness of the structural support layer of 66 μm, a thickness of the first heat sealing and welding layer of 17 μm, and a thickness of the second heat sealing and welding layer of 17 μm. Other aspects are the same as those of Example 2.

[0072] Comparative Example 1:

[0073] A fluorine film for heat sealing welding, with a thickness of 50 μm, is made solely of an ethylene-tetrafluoroethylene-perfluoromethyl vinyl ether terpolymer, wherein the ethylene-tetrafluoroethylene-perfluoromethyl vinyl ether terpolymer is the same as that of Example 1.

[0074] The processing method is the same as in Example 1, except that only B extrusion is used, and the die is replaced with a single-layer structure. The extruder temperature is set the same as the A or C extruder temperature in Example 1.

[0075] The initial sealing temperature, heat sealing strength and long-term use temperature of the prepared fluorine film are shown in Table 1.

[0076] Comparative Example 2:

[0077] A fluorine film for heat sealing welding, with a thickness of 50 μm, is made of a tetrafluoroethylene-hexafluoropropylene binary copolymer, wherein the tetrafluoroethylene-hexafluoropropylene binary copolymer is the same as that of Example 1.

[0078] The processing method is the same as in Example 1, except that only the B extruder is used, and the temperature of the extruder B is set to the same temperature as the B extruder in Example 1.

[0079] The initial sealing temperature, heat sealing strength and long-term use temperature of the prepared fluorine film are shown in Table 1.

[0080] Comparative Example 3:

[0081] A fluorine film for heat sealing welding, with a thickness of 50 μm, is made of fusible polytetrafluoroethylene, and the fusible polytetrafluoroethylene is the same as that in Example 3.

[0082] The processing method is the same as that in Example 3, except that only the B extruder is used, and the temperature setting of the extruder B is the same as that of the B extruder in Example 3.

[0083] Comparative Example 4:

[0084] A multi-layer fluorine film for heat sealing welding, which is the same as Example 2 except that no auxiliary agent is added.

[0085] The initial sealing temperature, heat sealing strength and long-term use temperature of the prepared fluorine film are shown in Table 1.

[0086] Heat seal strength refers to the standard "QB / T 2358-1998 Test Method for Heat Seal Strength of Plastic Film Packaging Bags". Use a sampling knife to take heat-sealed samples with a width of (15±0.1) mm and an unfolded length of (100±1) mm. Take 10 samples from each heat-sealed film. Age the sample at room temperature for 48 hours, set the clamp distance of the universal tensile testing machine to 50 mm, clamp the two ends of the sample on the two clamps of the universal tensile testing machine, and make the axis of the sample coincide with the center line of the upper and lower clamps in the longitudinal direction. Set the test speed to 300 mm / min, read the maximum load force F when the sample breaks, repeat 5 times, and take the average value as the heat seal strength.

[0087] Table 1

[0088]

[0089] As can be seen from Table 1, compared with single-layer FEP or PAF films, composite-layer welding films have higher heat-sealing strength than single-layer ETFE films because the outer ETFE welding layer can effectively reduce the initial sealing temperature during heat sealing and maintain good heat-sealing strength. This is because the interaction of the multi-layer fluorine film not only improves the mechanical strength of the welding part after heat sealing molding, but also improves the melt flow performance during heat sealing, which facilitates the rapid filling of welding materials. Under the same multi-layer fluorine film conditions, adding a certain amount of additives can change the heat-sealing strength, initial sealing temperature and maximum long-term use temperature of the multi-layer fluorine film. However, if the filler is added too much, the material will begin to show anisotropy due to its poor dispersion, which is not conducive to improving the mechanical properties of the material. The appropriate filler filling amount can make it evenly dispersed in the matrix and form a certain network connectivity.

[0090] The embodiments described above provide a detailed description of the technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements and equivalent substitutions made within the scope of the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A multilayer fluorine film for heat sealing welding, characterized in that: The multi-layer fluorine film includes three fluorine film layers, which include a first heat-sealing welding layer, a structural support layer and a second heat-sealing welding layer in sequence; the total thickness of the multi-layer fluorine film is 10-250 μm; wherein the thickness of the structural support layer accounts for 60-98% of the total thickness, the thickness of the first heat-sealing welding layer accounts for 1-20% of the total thickness, and the thickness of the second heat-sealing welding layer accounts for 1-20% of the total thickness; the structural support layer is one or both of FEP fluorine film and PFA fluorine film, and the first and second heat-sealing welding layers are ethylene-tetrafluoroethylene-perfluoromethyl vinyl ether terpolymer fluorine films; The structural support layer further contains 5-10wt% of a functional additive, wherein the functional additive is one or a mixture of nano boron nitride, nano calcium sulfate whisker, nano talc, and nano silicon dioxide; The initial sealing temperature of the multi-layer fluorine film is 275~350℃, the heat sealing strength is 24~45N / 15mm, the melting index of the fluorine resin used in the structural support layer and the heat sealing welding layer is 5~20g / 10min, the tensile strength is 20~50MPa, and the tensile elongation is 200~400%.

2. The multi-layer fluorine film for heat sealing welding according to claim 1, characterized in that: The thickness of the structural support layer accounts for 70-90% of the total thickness, the thickness of the first heat-sealed welding layer accounts for 5-15% of the total thickness, and the thickness of the second heat-sealed welding layer accounts for 5-15% of the total thickness.

3. The multi-layer fluorine film for heat sealing welding according to claim 1, characterized in that: The total thickness of the multi-layer fluorine film for heat sealing welding is 50-200 μm.

4. The multi-layer fluorine film for heat sealing welding according to claim 1, characterized in that: When the support layer material is FEP, the initial sealing temperature of the multi-layer fluorine film is 275±2°C, and the heat sealing strength is 24~25N / 15mm; When the support layer material is PFA, the initial sealing temperature of the multi-layer fluorine film is 340-350° C., and the heat sealing strength is 35-45 N / 15 mm.

5. The multi-layer fluorine film for heat sealing welding according to claim 1, characterized in that: The content of the functional additive is 5-8wt%.

6. The multi-layer fluorine film for heat sealing welding according to claim 1, characterized in that: The functional additive is one or a mixture of nano boron nitride, nano talcum powder and nano silicon dioxide.

7. The method for preparing the multi-layer fluorine film for heat sealing welding according to any one of claims 1 to 6, characterized in that: It is made by multi-layer co-extrusion casting or blowing film, including the following steps: (1) Melting and blending one or both of FEP or PFA with functional additives, extruding and granulating, and drying to obtain a supporting layer fluororesin raw material; (2) The raw materials of the first heat-sealing welding layer, the structural support layer, and the second heat-sealing welding layer are extruded into a melt through an extruder, and then compounded in a casting die or a blown film die to obtain a three-layer fluorine film primary product; (3) The prepared three-layer fluorine film initial product is cooled and shaped to obtain a multi-layer fluorine film finished product for heat sealing and welding.

8. The preparation method according to claim 7, characterized in that: The extrusion granulation temperature in step (1) is 220-350°C, the screw speed is 15-80 r / min, and the drying conditions are: 100-140°C, 6-10h.

9. The preparation method according to claim 7, characterized in that: In step (2), an extrusion cast film unit comprising three extruders A, B and C is used, wherein extruder A and extruder C are used to extrude two outer heat-sealing welding layers, and extruder B is used to extrude a structural support layer.

10. The preparation method according to claim 9, characterized in that: The process parameters of the extruder in step (2) are as follows: A, C extruder: screw aspect ratio is 20~30; barrel has four heating zones, zone 1 is 220~340℃, zone 2 is 230~350℃, zone 3 is 230~360℃, zone 4 is 230~370℃; B extruder: The screw aspect ratio is 25-30, and the barrel has four heating zones, zone 1 is 210~340℃, zone 2 is 220~340℃, zone 3 is 220~350℃, and zone 4 is 220~350℃.

11. The preparation method according to claim 10, characterized in that: In step (2), the die is a casting die; and the temperature of the casting die is 250-370°C.

12. The preparation method according to claim 10, characterized in that: In step (3), the cooling and shaping conditions are: cooling and shaping by using a traction roller, the traction roller temperature is 10~200°C, the traction speed is 0.5~55 m / s, and the winding speed is 0.5~55 m / s.

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