A high temperature resistant flexible flat cable and preparation method thereof

Abstract

The invention discloses a high temperature resistant flexible flat cable and a preparation method thereof, which relates to the technical field of flat cable production, wherein a modified high melting point crystalline polymer is sequentially cast and stretched to obtain a stretched film, and then the stretched film is cross-linked by ultraviolet radiation to obtain a substrate-free film, and finally the film is composited and rolled with a conductor to obtain the FFC. The FFC is prepared by rolling the substrate-free film with the conductor, and the FFC has excellent temperature resistance, mechanical properties and shrinkage resistance, avoids the risk of degumming of the FFC during long-term use, and simplifies the raw materials and preparation process.

Description

Technical Field

[0001] The present invention relates to the technical field of flat cable production, and in particular to a high temperature resistant flexible flat cable and a preparation method thereof. Background Art

[0002] Flexible flat cable (FFC) has the advantages of being soft, easy to bend, thin, small, simple to connect, easy to disassemble, and easy to solve electromagnetic shielding (EMI). The number and spacing of wires can be arbitrarily selected, making it easy to connect, reduce the size of electronic products, reduce costs, and improve efficiency. With the development of intelligent automobiles, the number of automotive electronic devices has increased, and the use of data transmission lines has increased accordingly. Lightweight wiring harnesses are becoming more and more important for reducing the energy consumption of single vehicles. The development of FFC has promoted the development of lightweight automotive wiring harnesses, but at the same time it has also put forward higher requirements on the performance of film materials, such as higher heat resistance, long-term environment and reliability of use.

[0003] The films used in traditional FFCs are mostly based on PET, with hot melt adhesive coated on the substrate, and then the upper and lower layers of the film are rolled together with the conductor wiring. The FFC prepared by this technical solution will have the following problems when used in the automotive field. For example, the hot melt adhesives commonly used on the film, such as EVA and polyurethane, have poor heat resistance and are at risk of degumming in a high temperature environment for a long time. Secondly, the preparation of the film usually needs to consider the compatibility of the hot melt adhesive with the substrate, and sometimes it is necessary to add a tackifier layer to prevent the substrate from degumming, which brings great trouble to the preparation process and will also cause more reliability problems during use, bringing safety hazards. Summary of the invention

[0004] The object of the present invention is to solve at least one of the technical problems existing in the prior art and to provide a high temperature resistant flexible flat cable and a preparation method thereof.

[0005] The technical solution of the present invention is as follows:

[0006] A method for preparing a high-temperature resistant flexible flat cable comprises the following steps: using a modified high-melting-point crystalline polymer, sequentially casting and stretching to obtain a stretched film, then cross-linking the stretched film by ultraviolet radiation to obtain a substrate-free film, and finally rolling the conductor to obtain the stretched film.

[0007] Preferably, the method comprises the following steps:

[0008] S1: Select a high melting point crystalline polymer with a melting point of 120-200°C;

[0009] S2: melt-blending the photoinitiator, the photosensitizer and the high melting point crystalline polymer and granulating them to obtain a blend;

[0010] S3: forming a film of the blend by extrusion casting at a film forming temperature of 150-250° C. to obtain a cast film;

[0011] S4: biaxially stretching the cast film to obtain a stretched film;

[0012] S5: partially cross-linking the stretched film by ultraviolet irradiation, and then shaping and cutting by cooling rollers to obtain a film without substrate;

[0013] S6: The substrate-free film and the conductor are subjected to pre-rolling and main rolling to obtain a product.

[0014] As a preferred embodiment of the present invention, in step S4, the biaxial stretching is specifically: the longitudinal stretching ratio is 2 to 4, the transverse stretching ratio is 3 to 6; and the stretching temperature is 100 to 180°C.

[0015] As a preferred embodiment of the present invention, in step S5, the ultraviolet irradiation is specifically: the stretched film is continuously passed through an ultraviolet irradiation oven, the length of the ultraviolet irradiation oven is 0.5-2m, the light source power is 500-1500w, and the wavelength is 365nm.

[0016] As a preferred embodiment of the present invention, the photoinitiator includes at least one of benzoins, benzyls, alkylbenzene coppers and acylphosphorus oxides, and the added amount thereof is 0.2-1% by mass relative to the high melting point crystalline polymer.

[0017] As a preferred embodiment of the present invention, the photosensitizer is at least one of trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, and 1,3,5-triallyl isocyanurate, and the added amount thereof is 1 to 5% by mass relative to the high melting point crystalline polymer;

[0018] As a preferred embodiment of the present invention, the temperature of the ultraviolet irradiation oven is controlled at 100-200° C., and the UV curing of the stretched film is carried out at this temperature.

[0019] As a preferred embodiment of the present invention, in step S6, the pre-rolling temperature is 120-160°C, the main rolling temperature is 140-200°C, and the pressure is 0.1-0.3 MPa.

[0020] As a preferred embodiment of the present invention, in step S6, the diameter of the conductor is 90-110 μm, and the thickness of the substrate-free film is 50-100 μm.

[0021] The invention also discloses a high temperature resistant flexible flat cable, which is prepared by any of the above preparation methods.

[0022] The beneficial effects of the present invention are:

[0023] (1) The method for preparing a high temperature resistant flexible flat cable of the present invention adopts the method of rolling a non-substrate film with a conductor to prepare an FFC, thereby avoiding the risk of degumming of the FFC during long-term use and simplifying the raw materials and the preparation process.

[0024] (2) The present invention provides a method for preparing a high temperature resistant flexible flat cable, which uses a high melting point crystalline polymer and can effectively improve the shrinkage and mechanical properties of the material after biaxial stretching through casting.

[0025] (3) The present invention provides a method for preparing a high temperature resistant flexible flat cable, which utilizes ultraviolet radiation to partially cross-link the biaxially stretched product, thereby further improving the temperature resistance, mechanical properties and shrinkage of the film, and ensuring good stiffness during the hot pressing process, thereby avoiding rubber slippage and film deformation; and enabling the film to meet the requirements of molding processing and use performance without being attached to the substrate.

[0026] (4) The high temperature resistant flexible flat cable of the present invention has excellent temperature resistance, mechanical properties and shrinkage resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a process flow chart of the present invention;

[0028] Figure 2 It is a schematic diagram of the FFC structure. DETAILED DESCRIPTION

[0029] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. If no specific techniques or conditions are specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used that do not specify the manufacturer are all conventional products that can be obtained commercially.

[0030] At present, the film generally uses solvent-free hot melt adhesive or solvent-cured adhesive (such as epoxy, polyurethane) as the adhesive layer and the substrate. If the substrate is discarded, the pure hot melt adhesive is soft in texture and not stiff enough, which can easily cause the adhesive to slip, uneven thickness and film deformation during the hot pressing process. Secondly, the mechanical properties of the material are also difficult to meet the use requirements. Therefore, the use of a substrate can conveniently and effectively solve these problems; and the solvent-cured adhesive has good fluidity and very low viscosity, and requires a substrate to support the molding. Therefore, the use of a substrate in the prior art can provide good convenience and practicality. However, with the development of industry technology, the performance requirements for the film are more stringent, and it is necessary to consider the temperature resistance of the substrate itself, the adhesion of the substrate to the adhesive at high temperature, etc. Based on the understanding of the prior art, it is generally difficult for technicians in this field to think of using a film without a substrate to prepare FFC.

[0031] However, the present application develops a method for preparing a high temperature resistant flexible flat cable, referring to Figure 1 , using modified high melting point crystalline polymer, sequentially cast and stretched to obtain a stretched film, then cross-linked the stretched film by ultraviolet radiation to obtain a substrate-free film, and finally rolled with a conductor to obtain FFC. The microstructure of FFC is referenced Figure 2 .

[0032] The present invention adopts a modified high-melting-point crystalline polymer to obtain a substrate-free film after biaxial stretching by casting, which can effectively improve the shrinkage and mechanical properties of the material. The biaxial stretching product is partially cross-linked by ultraviolet radiation to further improve the temperature resistance, mechanical properties and shrinkage resistance of the film. Finally, the substrate-free film and the conductor are rolled to obtain FFC, thereby avoiding the risk of degumming of FFC during long-term use.

[0033] In some embodiments, the method specifically includes the following steps:

[0034] S1: Select a high melting point crystalline polymer with a melting point of 120-200°C;

[0035] S2: melt-blending the photoinitiator, the photosensitizer and the high melting point crystalline polymer and extruding and granulating them to obtain a blend;

[0036] S3: forming a film of the blend by extrusion casting at a film forming temperature of 150-250° C. to obtain a cast film;

[0037] S4: biaxially stretching the cast film to obtain a stretched film;

[0038] S5: partially cross-linking the stretched film by ultraviolet irradiation, and then shaping and cutting by cooling rollers to obtain a film without substrate;

[0039] S6: The substrate-free film and the conductor are subjected to pre-rolling and main rolling to obtain a product.

[0040] In some embodiments, the biaxial stretching is specifically as follows: the longitudinal stretching ratio is 2 to 4, and the longitudinal stretching ratio can be specifically 2, 3 or 4; the transverse stretching ratio is 3 to 6, and the transverse stretching ratio can be specifically 3, 4, 5 or 6; the stretching temperature is 100 to 180°C, and the stretching temperature can be specifically 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C or 180°C.

[0041] In some embodiments, in step S5, the ultraviolet irradiation is specifically: the stretched film is continuously passed through an ultraviolet irradiation oven, the length of the ultraviolet irradiation oven is 0.5 to 2 m, the light source power is 500 to 1500 w, and the wavelength is 365 nm.

[0042] In some embodiments, the photoinitiator includes at least one of benzoin, benzil, alkylbenzene copper, and acylphosphorus oxide, and the added amount is 0.2-1% by mass to the high melting point crystalline polymer. If the added amount is too small, the purpose of the photoinitiator to improve the double bond crosslinking of the polymer cannot be achieved, and the crosslinking is not sufficient; if the added amount is too large, it will lead to a waste of raw materials.

[0043] In some embodiments, the photosensitizer is at least one of trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, and 1,3,5-triallyl isocyanurate, and the added amount thereof is 1-5% by mass relative to the high melting point crystalline polymer.

[0044] In some embodiments, the temperature of the UV irradiation oven is controlled at 100-200°C, specifically 100°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C or 200°C, and the UV (ultraviolet) curing of the stretched film is carried out at this temperature.

[0045] In some embodiments, in step S6, the pre-rolling temperature is 120-160°C, specifically 120°C, 130°C, 140°C, 150°C or 160°C; the main rolling temperature is 140-200°C, specifically 140°C, 150°C, 160°C, 170°C, 180°C or 200°C; the pressure is 0.1-0.3Mpa, specifically 0.1Mpa, 0.2Mpa or 0.3Mpa.

[0046] In some embodiments, in step S6, the diameter of the conductor is 90-110 μm, specifically 90 μm, 100 μm or 110 μm; the thickness of the substrate-free film is 50-100 μm, specifically 50 μm, 60 μm, 70 μm, 80 μm, 90 μm or 100 μm.

[0047] The present invention also discloses a high temperature resistant flexible flat cable, which is prepared by any of the preparation methods described above and has excellent temperature resistance, mechanical properties and shrinkage.

[0048] The technical solution of the present invention is further described below with reference to specific embodiments.

[0049] Example 1

[0050] (1) Using polypropylene hot melt adhesive as raw material, the melting point is 145° C., melt blending a photoinitiator, a photosensitizer and the polypropylene hot melt adhesive in a single screw and extruding granulation to obtain a blend, and then casting the blend at a casting temperature of 210° C. and passing through a stainless steel cold roller to obtain a cast film; wherein the photoinitiator is benzophenone, and the mass ratio of the addition amount to the polypropylene hot melt adhesive is 0.3wt%, and the photosensitizer is trimethylolpropane triacrylate (TMPTA), and the mass ratio of the addition amount to the polypropylene hot melt adhesive is 2wt%;

[0051] (2) stretching the cast film at a longitudinal stretch ratio of 3.5, a transverse stretch ratio of 3.5, and a stretching temperature of 120° C. to obtain a stretched film;

[0052] (3) The stretched film is continuously subjected to ultraviolet irradiation cross-linking in an ultraviolet irradiation oven, the irradiation cross-linking temperature is 135° C., the length of the ultraviolet irradiation oven is 1 m, the power of the ultraviolet light source is 1000 W, and the wavelength is 365 nm;

[0053] (4) The hot melt adhesive film after UV radiation cross-linking is shaped by a cold roller to obtain a substrate-free film;

[0054] (5) FFC is formed by rolling two layers of substrate-free film and an intermediate conductor (the thickness of the substrate-free film is controlled to be 80 μm, and the conductor diameter is 100 μm), where the temperature of the pre-pressing roller is 150°C, the temperature of the main pressing roller is 165°C, and the pressure is 0.2 MPa.

[0055] (6) The polypropylene-based high temperature resistant FFC can be obtained by the above method.

[0056] Example 2

[0057] (1) Using polyester hot melt adhesive as raw material, the melting point is 132° C., melt blending a photoinitiator, a photosensitizer and the polyester hot melt adhesive in a single screw and extruding granulation to obtain a blend, and then subjecting the blend to casting at a casting temperature of 180° C. and casting on a stainless steel cold roll to obtain a cast film;

[0058] (2) stretching the cast film at a longitudinal stretch ratio of 3, a transverse stretch ratio of 3, and a stretching temperature of 110° C. to obtain a stretched film;

[0059] (3) The stretched film is continuously subjected to ultraviolet irradiation crosslinking in an ultraviolet irradiation oven, wherein the photoinitiator is benzophenone, the mass ratio of the addition amount to the polyester hot melt adhesive is 0.5wt%, the photosensitizer is trimethylolpropane triacrylate (TMPTA), the mass ratio of the addition amount to the polyester hot melt adhesive is 2.5wt%, the irradiation crosslinking temperature is 125°C, the length of the ultraviolet irradiation oven is 1m, the ultraviolet light source power is 1000w, and the wavelength is 365nm;

[0060] (4) The hot melt adhesive film after UV radiation cross-linking is shaped by a cold roller to obtain a substrate-free film;

[0061] (5) FFC is formed by rolling two layers of substrate-free film and an intermediate conductor (the thickness of the substrate-free film is controlled to be 80 μm, and the conductor diameter is 100 μm), where the temperature of the pre-pressing roller is 135°C, the temperature of the main pressing roller is 150°C, and the pressure is 0.2 MPa.

[0062] (6) The polyester-based high temperature resistant FFC can be obtained by the above method.

[0063] Example 3

[0064] (1) Using polyamide hot melt adhesive as raw material, the melting point is 180° C., melt-blending a photoinitiator, a photosensitizer and the polyamide hot melt adhesive in a single screw and extruding granulation to obtain a blend, and then subjecting the blend to casting at a casting temperature of 210° C. and casting by a stainless steel cold roll to obtain a cast film;

[0065] (2) stretching the cast film at a longitudinal stretch ratio of 2, a transverse stretch ratio of 2, and a stretching temperature of 160° C. to obtain a stretched film;

[0066] (3) The stretched film is continuously subjected to ultraviolet irradiation crosslinking in an ultraviolet irradiation oven, wherein the photoinitiator is benzophenone, the mass ratio of the addition amount to the polyamide hot melt adhesive is 0.8wt%, the photosensitizer is trimethylolpropane triacrylate (TMPTA), the mass ratio of the addition amount to the polyamide hot melt adhesive is 3wt%, the irradiation crosslinking temperature is 125°C, the length of the ultraviolet irradiation oven is 1m, the ultraviolet light source power is 1000w, and the wavelength is 365nm;

[0067] (4) The hot melt adhesive film after UV radiation cross-linking is shaped by a cold roller to obtain a substrate-free film;

[0068] (5) FFC is formed by rolling two layers of substrate-free film and an intermediate conductor (the thickness of the substrate-free film is controlled to be 80 μm, and the conductor diameter is 100 μm), where the temperature of the pre-pressing roller is 175°C, the temperature of the main pressing roller is 190°C, and the pressure is 0.2 MPa.

[0069] (6) The polyamide-based high temperature resistant FFC can be obtained by the above method.

[0070] Comparative Example 1 (cross-linking without UV radiation)

[0071] (1) Using polypropylene hot melt adhesive as raw material, the melting point is 145°C, melt blending and extrusion granulation in a single screw to obtain a blend, and then casting the blend at a casting temperature of 210°C and passing through a stainless steel cold roll to obtain a cast film;

[0072] (2) stretching the cast film at a longitudinal stretch ratio of 3.5, a transverse stretch ratio of 3.5, and a stretching temperature of 120° C. to obtain a stretched film;

[0073] (3) The stretched film is shaped by a cold roller;

[0074] (4) FFC is formed by rolling two layers of substrate-free insulation film and an intermediate conductor (the thickness of the substrate-free film is controlled to be 80 μm, and the conductor diameter is 100 μm), where the temperature of the pre-pressing roller is 150°C, the temperature of the main pressing roller is 165°C, and the pressure is 0.2 MPa.

[0075] (5) Polypropylene-based FFC can be obtained through the above method.

[0076] Comparative Example 2 (no biaxial stretching)

[0077] (1) Using polypropylene hot melt adhesive as raw material, the melting point is 145°C, a photoinitiator, a photosensitizer and the polypropylene hot melt adhesive are melt-blended in a single screw and extruded into granules to obtain a blend, which is then cast at a temperature of 210°C and coated on a PET substrate;

[0078] (2) The adhesive film attached to the PET substrate is then continuously cross-linked by ultraviolet radiation in an ultraviolet radiation oven, wherein the photoinitiator is benzophenone, the addition amount is 0.3wt% of the mass ratio of the polypropylene hot melt adhesive, the photosensitizer is TMPTA, the addition amount is 2wt% of the mass ratio of the polypropylene hot melt adhesive, the radiation cross-linking temperature is 135°C, the length of the ultraviolet radiation oven is 1m, the ultraviolet light source power is 1000w, and the wavelength is 365nm;

[0079] (3) The hot melt adhesive film after UV radiation cross-linking is shaped by a cold roller;

[0080] (4) FFC is formed by rolling two layers of substrate-free insulation film and an intermediate conductor (the thickness of the substrate-free film is controlled to be 80 μm, and the conductor diameter is 100 μm), where the temperature of the pre-pressing roller is 150°C, the temperature of the main pressing roller is 165°C, and the pressure is 0.2 MPa.

[0081] (5) High temperature resistant FFC can be obtained by the above method.

[0082] Comparative Example 3

[0083] (1) Using polypropylene hot melt adhesive as raw material, the melting point is 145°C, a photoinitiator, a photosensitizer and the polypropylene hot melt adhesive are melt-blended in a single screw and extruded into granules to obtain a blend, which is then cast at a temperature of 210°C and coated on a PET substrate;

[0084] (2) The adhesive film attached to the PET substrate is then continuously cross-linked by ultraviolet radiation in an ultraviolet radiation oven, wherein the photoinitiator is benzophenone, the addition amount is 0.6wt% of the mass ratio of the polypropylene hot melt adhesive, the photosensitizer is TMPTA, the addition amount is 4wt% of the mass ratio of the polypropylene hot melt adhesive, the radiation cross-linking temperature is 135°C, the length of the ultraviolet radiation oven is 1m, the ultraviolet light source power is 1000w, and the wavelength is 365nm;

[0085] (3) The hot melt adhesive film after UV radiation cross-linking is shaped by a cold roller;

[0086] (4) FFC is formed by rolling two layers of substrate-free insulation film and an intermediate conductor (the thickness of the substrate-free film is controlled to be 80 μm, and the conductor diameter is 100 μm), where the temperature of the pre-pressing roller is 150°C, the temperature of the main pressing roller is 165°C, and the pressure is 0.2 MPa.

[0087] (5) High temperature resistant FFC can be obtained by the above method.

[0088] The above embodiments and comparative examples were subjected to performance tests, and the test results are shown in Table 1.

[0089] Peeling force (peeling of glue and conductor wire) test method: Cut FFC into 20mm*100mm specimens; open the copper wire and the film and fix them on the clamp of the tensile testing machine, with the lower clamp clamping the film and the upper clamp clamping the copper wire; adjust the speed of the tensile testing machine to 50mm / min, keep the sample angle at -180°, peel upward 10mm, record the tension-displacement relationship curve during the test, observe the curve changes during the test, and record the peeling force.

[0090] High temperature resistance performance test method: Test the peeling size in the range of 100℃~200℃. The peeling force test method is as shown above. The temperature resistance is determined by judging failure when the peeling force is less than ≥61g / mm.

[0091] Determination of gel content: The gel content of the cross-linked film is tested. The gel content is usually tested by centrifugation, and the steps are as follows: Take the prepared substrate-free film, add an appropriate amount of solvent (the mass volume ratio of the substrate-free film to the solvent is 1%, and the solvent is a xylene solution), and stir it thoroughly to make it evenly dispersed, place the mixed solution in a centrifuge, and centrifuge to obtain the upper liquid and precipitate, dry the precipitate in a thermostat at 120°C for 3 hours, and divide the weight of the precipitate by the total weight of the substrate-free film to obtain the gel content.

[0092] Table 1 Performance test results of embodiments and comparative examples

[0093]

[0094] In automotive FFC, its temperature resistance is generally required to be above 125°C. It can be seen from the data in Table 1 that after cross-linking (Examples 1-3, Comparative Examples 2 and 3), its temperature resistance meets the requirements, while the uncross-linked non-substrate film (Comparative Example 1) has poor temperature resistance and is easy to deform. The gel content represents the mass ratio of the three-dimensional network polymer formed after cross-linking. Table 1 shows that the gel content is more suitable at 25% to 30%. When it is greater than 40% (Comparative Example 3), it will affect the movement of the group, thereby affecting its bonding performance. The bonding performance of the glue and the conductor must meet the index of peeling force ≥ 61g / mm after heat treatment (125°C, 1000h). It can be seen from the data that after heat treatment at 125°C, the peeling force of the uncross-linked or highly cross-linked film decreases greatly and cannot meet the technical indicators.

[0095] As can be seen from the table above, the performance of the embodiment is better than that of the comparative example. The reason is that the embodiment uses ultraviolet radiation to partially crosslink the biaxially stretched product, further improves the temperature resistance, mechanical properties and shrinkage of the film, and ensures good stiffness during the hot pressing process to avoid rubber slippage and film deformation; the film can meet the requirements of molding and use performance without being attached to the substrate; and the difference between Examples 1, 2 and 3 comes from the influence of the material's own characteristics. Among them, the polyamide in Example 3 has a higher melting point, so its temperature resistance is the best. This difference can meet the occasions with higher requirements for temperature resistance. Among them, Comparative Example 1 is not crosslinked, the sample has poor heat resistance, and the appearance has shrunk and deformed; and it can be seen from Comparative Examples 1 and Comparative Examples 3 that when the heat resistance is not enough or the gel content is too high, after long-term high-temperature treatment, the bonding performance of the glue and the conductor is significantly deteriorated. The embodiment overcomes the disadvantages of the above comparative examples. At the same time, excessive crosslinking affects the movement of the molecular chain and causes poor bonding effect, and excessively low crosslinking does not significantly improve the temperature resistance. Therefore, it is necessary to regulate the crosslinking effect, that is, to provide a suitable crosslinking range to obtain a good gain effect. In contrast, in Example 2, the sample was not obtained by biaxial stretching, and the peeling force after heat treatment was very low. The reason for this is that the unstretched crystallinity is relatively high, and the small number of amorphous regions results in fewer bondable groups. In addition, the high crystallinity leads to a large degree of shrinkage, which easily leads to a low degree of interface bonding.

[0096] The above-mentioned embodiments only express the preferred implementation modes of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that, for ordinary technicians in this field, various other corresponding changes and deformations can be made according to the technical solutions and concepts described above, and all these changes and deformations should fall within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a high temperature resistant flexible flat cable, characterized in that: A high melting point crystalline polymer is used, and cast and stretched in sequence to obtain a stretched film, and then the stretched film is cross-linked by ultraviolet radiation to obtain a substrate-free film, and finally rolled with a conductor to obtain; The following steps are involved: S1: selecting a high melting point crystalline polymer, the melting point of which is 120-200° C.; the high melting point crystalline polymer is one of polypropylene hot melt adhesive, polyester hot melt adhesive, and polyamide hot melt adhesive; S2: melt-blending the photoinitiator, the photosensitizer and the high melting point crystalline polymer and extruding and granulating them to obtain a blend; S3: forming a film of the blend by extrusion casting at a film forming temperature of 150-250° C. to obtain a cast film; S4: biaxially stretching the cast film to obtain a stretched film; S5: partially cross-linking the stretched film by ultraviolet irradiation, and then shaping and cutting by cooling rollers to obtain a film without substrate; S6: Pre-rolling and main-rolling the substrate-free film and the conductor to obtain a film; Biaxial stretching is specifically: longitudinal stretching ratio is 2~4, transverse stretching ratio is 3~6; stretching temperature is 100~180℃; The photoinitiator includes at least one of benzoin, benzil, alkylbenzene copper, and acylphosphorus oxide, and the added amount thereof accounts for 0.2-1% of the mass percentage of the high melting point crystalline polymer; The photosensitizer is at least one of trimethylolpropane triacrylate, trimethylolpropane trimethacrylate and 1,3,5-triallyl isocyanurate, and the amount of the photosensitizer added is 1-5% by mass of the high melting point crystalline polymer; The gel content of high temperature resistant flexible flat cables is between 25% and 30%. The gel content indicates the mass ratio of three-dimensional network polymers formed after cross-linking.

2. The method for preparing a high temperature resistant flexible flat cable according to claim 1, characterized in that: In step S5, the ultraviolet irradiation is specifically: the stretched film is continuously passed through an ultraviolet irradiation oven, the length of the ultraviolet irradiation oven is 0.5-2m, the light source power is 500-1500w, and the wavelength is 365nm.

3. The method for preparing a high temperature resistant flexible flat cable according to claim 1, characterized in that: The temperature of the ultraviolet irradiation oven is controlled at 100-200° C., and the UV curing of the stretched film is carried out at this temperature.

4. The method for preparing a high temperature resistant flexible flat cable according to claim 1, characterized in that: In step S6, the pre-roll pressing temperature is 120-160°C, the main rolling temperature is 140-200°C, and the pressure is 0.1-0.3 MPa.

5. The method for preparing a high temperature resistant flexible flat cable according to claim 1, characterized in that: In step S6, the diameter of the conductor is 90-110 μm, and the thickness of the substrate-free film is 50-100 μm.

6. A high temperature resistant flexible flat cable, characterized in that: The method is prepared by any one of claims 1 to 5.

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