A bending-resistant flexible flat cable and its preparation method and repair method

Abstract

The present invention discloses a bending-resistant flexible flat cable and a preparation method and a repair method thereof, which relate to the technical field of flexible flat cable preparation, wherein a hot melt adhesive is coated on a substrate cloth so that at least part of the hot melt adhesive penetrates into the pores of the substrate cloth to obtain an insulating film, and then the insulating film and the conductor are rolled to obtain the substrate cloth, wherein the substrate cloth is a polyester fiber plain weave cloth. The bending-resistant flexible flat cable prepared by the present invention selects an ultra-thin polyester fiber cloth as a substrate, and utilizes a complex interlocking structure formed at the interface between the substrate and the hot melt adhesive to reduce the slippage of the adhesive layer during the FFC molding process, and effectively solves the problems of adhesive layer shrinkage and shedding.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible flat cable preparation, and in particular to a bending-resistant flexible flat cable and a preparation method and a repair 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 membrane materials, such as excellent bending resistance.

[0003] FFC branch wiring is usually formed by bending. In the long-term harsh environment, there is a risk of delamination between the glue and the film, and between the glue and the copper wire at the bending position, which may cause leakage and burn the line, causing the system to start the protection program and stop working, short circuit, or even fire and explosion. The commonly used film of FFC is generally prepared by coating hot melt adhesive with PET film as the substrate, which often requires the use of a tackifier layer. However, due to material shrinkage, decreased viscosity, and stress caused by bending, it is easy to cause the substrate and the hot melt adhesive to debond, which brings safety hazards and limits its application in automotive power batteries. If the substrate is not used, on the one hand, the texture of the pure hot melt adhesive is relatively soft and the stiffness is not enough, which is easy to cause the glue to slip, uneven thickness, and film deformation during the hot pressing process. Secondly, if the substrate is not used, the mechanical properties of the material are also difficult to meet the use requirements. 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 bending-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 bending-resistant flexible flat cable comprises coating a hot melt adhesive on a base cloth so that at least part of the hot melt adhesive penetrates into the pores of the base cloth to obtain an insulating film, and then rolling the insulating film and a conductor to obtain the cable.

[0007] Preferably, the base cloth has a thickness of 20-50 μm, a fiber diameter of 10-25 μm, a base cloth pore size of 0.2-2 μm, and is a polyester fiber plain weave cloth.

[0008] Preferably, the coating method is carried out by blade coating, lamination or casting.

[0009] Preferably, the hot melt adhesive is subjected to heat processing before coating, the heat processing temperature is 150-300° C., and the viscosity of the hot melt adhesive at the heat processing temperature is 500-5000 cps.

[0010] Preferably, the hot melt adhesive is at least one of ethylene-vinyl acetate copolymer, polypropylene, polyester, polyurethane, and polyamide.

[0011] Preferably, the hot melt adhesive penetrates into the pores of the substrate cloth to a depth of 10-20 μm.

[0012] Preferably, the thickness of the outer rubber layer of the base cloth is 50-100 μm, and the thickness of the conductor wire is 90-110 μm.

[0013] Preferably, the rolling includes pre-rolling and main rolling, wherein the temperature of the pre-rolling is 120-160°C, the temperature of the main rolling is 140-200°C, and the rolling pressure is 0.1-0.3 MPa.

[0014] Preferably, before the hot melt adhesive is coated on the substrate cloth, the substrate cloth is subjected to a corona treatment.

[0015] The invention also discloses a bending-resistant flexible flat cable, which is prepared by adopting the above preparation method.

[0016] The present invention also discloses a method for repairing a bend-resistant flexible flat cable, which comprises dissolving hot melt adhesive in a solvent to obtain a hot melt adhesive solution with a viscosity of 50 to 500 cps, coating the hot melt adhesive solution on the surface of a substrate in a debonded area, and then placing the hot melt adhesive in a vacuum environment to allow the hot melt adhesive to penetrate into the debonded area and solidify.

[0017] The beneficial effects of the present invention are:

[0018] (1) The present invention provides a method for preparing a bending-resistant flexible flat cable, which selects ultra-thin polyester fiber cloth as a substrate and utilizes a complex interlocking structure formed at the interface between the substrate and the hot melt adhesive to reduce the slippage of the adhesive layer during the FFC molding process, thereby effectively solving the problems of adhesive layer shrinkage and shedding.

[0019] (2) The present invention produces a bending-resistant flexible flat cable. This structure can more conveniently exert the soft characteristics of the hot melt adhesive during the bending process. At the same time, the network structure can better release the stress of the FFC during the bending process, thereby achieving more beneficial bending resistance.

[0020] (3) A method for repairing a bending-resistant flexible flat cable prepared by the present invention can be used to repair the cable by filling the surface pores if the base material and the adhesive layer are damaged during long-term use. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the FFC structure. DETAILED DESCRIPTION

[0022] like Figure 1 As shown, the present invention provides an embodiment: a method for preparing a bending-resistant flexible flat cable, wherein hot melt adhesive is coated on a substrate cloth, so that the hot melt adhesive penetrates into the pores of the substrate cloth to obtain an insulating film, and then the insulating film and the conductor are rolled to obtain the cable. The present invention utilizes the complex interlocking structure formed at the interface between the substrate cloth and the hot melt adhesive to reduce the slippage of the adhesive layer during the FFC (flexible flat cable) molding process, and solves the problems of adhesive layer shrinkage and shedding in the prior art; that is, the hot melt adhesive is combined with the fiber, part of the fiber is embedded in the hot melt adhesive, and the hot melt adhesive itself forms an interlocking structure as a continuous phase; there is a significant difference from the direct interface bonding between the traditional hot melt adhesive and the PET film substrate.

[0023] In some embodiments, the thickness of the substrate cloth is 20-50 μm, specifically 20 μm, 25 μm, 30 μm, 40 μm or 50 μm; the fiber diameter is 10-25 μm, specifically 10 μm, 15 μm, 20 μm or 25 μm; the substrate pores are 0.2-2 μm, specifically 0.2 μm, 0.5 μm, 1 μm, 1.5 μm, 1.8 μm or 2 μm; the substrate cloth is a fiber cloth composed of fibers, if the pores of the fiber cloth are too large, the hot melt adhesive It will penetrate the entire fiber layer. On the one hand, if the bonding layer is too thick, it is not conducive to bending, and it is necessary to increase the amount of glue. On the other hand, it is not conducive to subsequent repair. If the pores of the fiber cloth are too small, the hot melt adhesive will have a small penetration depth or incomplete penetration, which will affect the bending resistance of the FFC. If the fiber diameter is large, the specific surface area of ​​the fiber cloth will increase, the bonding surface will decrease, and the interlocking structure will decrease, which is not conducive to the bending performance. If the fiber diameter is small, the cost of spinning will increase, and it will also easily make it more difficult to control the pore size of the fiber substrate cloth. Therefore, the pores of the substrate cloth are 0.2-2μm, and the fiber diameter in the substrate cloth is 10-25μm, which can better achieve the bending resistance effect required by this application.

[0024] The base fabric is a polyester fiber plain weave fabric. Compared with traditional polyester fiber membrane materials, the fibers of the fiber fabric of the present invention form a more dispersed and uniform combination with the hot melt adhesive. The fibers are relatively independent and do not interfere with each other. On the one hand, it is beneficial to the release of stress during the bending process, and on the other hand, it can effectively prevent the spread of local failure structures; therefore, it ultimately exhibits excellent bending resistance.

[0025] In some embodiments, the coating method is knife coating, laminating or casting.

[0026] In some embodiments, the hot melt adhesive is heat-processed before coating, the heat processing temperature is 150-300°C, specifically 150°C, 180°C, 200°C, 220°C, 250°C or 300°C, and the hot melt adhesive viscosity is 500-5000cps, specifically 500cps, 1000cps, 1500cps, 2000cps, 2500cps, 3000cps, 3500cps, 4000cps, 4500cps or 5000cps. The hot melt adhesive viscosity mentioned in this application is the viscosity under the heat processing temperature condition, that is, the corresponding viscosity under the condition of the heat processing temperature of 150-300°C.

[0027] In some embodiments, the hot melt adhesive is at least one of ethylene-vinyl acetate copolymer, polypropylene, polyester, polyurethane, and polyamide. It can be understood that the hot melt adhesive can be ethylene-vinyl acetate, polypropylene, polyester, polyurethane or polyamide alone; it can also be a combination of at least two of ethylene-vinyl acetate, polypropylene, polyester, polyurethane, and polyamide.

[0028] In some embodiments, the depth of the hot melt adhesive penetrating into the pores of the substrate cloth is controlled to be 10-20 μm, specifically 10 μm, 12 μm, 15 μm, 18 μm or 20 μm. If the depth is too small, the bonding surface between the hot melt adhesive and the substrate cloth is small, and the interlocking structure will not be strong enough, affecting the bonding force; if the depth is too large, that is, the bonding layer is thick, a greater stress will be formed during the bending process, which will have an adverse effect on the bending resistance. Therefore, the depth of the hot melt adhesive penetrating into the pores of the substrate cloth is controlled to be 10-20 μm to better achieve the bending resistance effect desired by the present application.

[0029] In some embodiments, the thickness of the outer adhesive layer of the substrate cloth is 50-100 μm, specifically 50 μm, 60 μm, 70 μm, 80 μm, 90 μm or 100 μm; the thickness of the conductor wire is 90-110 μm, specifically 90 μm, 95 μm, 100 μm, 105 μm or 110 μm; if the thickness of the adhesive layer is too small, the wire may not be fully wrapped, resulting in unqualified FFC performance; if the thickness is too large, it will increase the cost and weight. The conductor wire thickness is a conventional choice, and the selection of the adhesive layer thickness is based on the conductor wire thickness.

[0030] In some embodiments, the rolling includes pre-rolling and main rolling, wherein the temperature of the pre-rolling is 120-160°C, specifically 120°C, 130°C, 140°C, 150°C or 160°C, the temperature of the main rolling is 140-200°C, specifically 140°C, 150°C, 160°C, 170°C, 180°C, 190°C or 200°C, and the rolling pressure is 0.1-0.3Mpa, specifically 0.1Mpa, 0.2Mpa or 0.3Mpa.

[0031] In some embodiments, before the hot melt adhesive is applied to the substrate cloth, the substrate cloth is subjected to corona treatment. The specific process is: the PET substrate cloth is placed in a corona discharge device for corona oxidation treatment. Under the bombardment of high-energy ions, the free energy and roughness of the PET fiber surface can be increased. The surface energy of the substrate cloth fiber is increased, the roughness of the microstructure is increased, and the adhesion between the substrate cloth and the hot melt adhesive is increased, which can effectively strengthen the interface bonding.

[0032] The present invention also discloses a bending-resistant flexible flat cable, which is prepared by the above-mentioned preparation method; the bending-resistant flexible flat cable prepared by the present invention has a structure that can more conveniently exert the soft characteristics of the hot melt adhesive during the bending process, and at the same time, the network structure can better release the stress of the FFC during the bending process, thereby achieving more beneficial bending-resistant performance.

[0033] The present invention also discloses a method for repairing a bend-resistant flexible flat cable. If debonding occurs between the substrate and the adhesive layer, a hot melt adhesive solution with the same substrate as the adhesive layer can be prepared. The solution viscosity is 50 to 500 cps. A suitable volume of the solution is coated on the surface of the debonded substrate and then placed in a vacuum box with a vacuum degree of -0.2 to -0.1 MPa. The hot melt adhesive solution penetrates into the damaged interlocking structure. A small amount of solvent can dissolve part of the interlocking structure, thereby easily combining with the hot melt adhesive to achieve the purpose of repair.

[0034] 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.

[0035] Example 1

[0036] (1) Using EVA (ethylene-vinyl acetate copolymer) hot melt adhesive as the raw material, the base fabric (made of polyester fiber with a diameter of 20 μm) is 35 μm thick and the pore size of the base fabric is 0.5 μm;

[0037] (2) firstly placing the substrate fabric in a corona discharge device for corona treatment, wherein the corona value reaches 38 dynes, and then coating the substrate fabric with hot melt adhesive on one side by means of knife coating, wherein the knife coating temperature is 150° C. and the melt viscosity of the hot melt adhesive is about 1000 cps;

[0038] (3) by controlling the temperature, viscosity and substrate fabric, the single-sided penetration depth of the hot melt adhesive in the substrate fabric is 18 μm;

[0039] (4) By adjusting the melt flow rate and coating speed of the hot melt adhesive, the thickness of the outer adhesive layer of the substrate cloth is 70 μm to obtain an insulating film;

[0040] (5) FFC is rolled by two layers of insulation film and a 100 μm thick conductor copper wire in the middle. During rolling, the outer rubber layers of the two insulation films are close to the conductor wire. The temperature of the pre-rolling roller is 100°C, the temperature of the main rolling roller is 125°C, and the rolling pressure is 0.2 MPa.

[0041] The EVA-based bending-resistant FFC can be obtained by the above method.

[0042] Example 2

[0043] (1) Using PP (polypropylene) hot melt adhesive as the raw material, the base fabric (made of polyester fiber with a diameter of 15 μm) is 25 μm thick and the pore size of the base fabric is 1.5 μm;

[0044] (2) firstly placing the substrate fabric in a corona discharge device for corona treatment, with the corona value reaching 38 dynes, and then coating the hot melt adhesive on one side of the substrate fabric by blade coating, with the blade coating temperature being 230° C. and the melt viscosity being about 1500 cps;

[0045] (3) by controlling the temperature, viscosity and substrate, the single-sided penetration depth of the melt into the substrate cloth is 12 μm;

[0046] (4) By adjusting the melt flow rate and coating speed, the thickness of the outer adhesive layer of the substrate is 80 μm to obtain an insulating film;

[0047] (5) FFC is formed by rolling two layers of insulation film and a 100 μm thick conductor copper wire in the middle. During rolling, the outer rubber layer of the two insulation films is close to the conductor wire. The temperature of the pre-pressing roller is 150°C, the temperature of the main pressing roller is 180°C, and the pre-pressing pressure is 0.2 MPa.

[0048] (6) The PP-based bending-resistant FFC can be obtained by the above method.

[0049] Example 3

[0050] (1) PES (polyester) hot melt adhesive is used as the raw material, the selected base fabric (made of polyester fiber with a diameter of 15 μm) has a thickness of 25 μm and a pore size of 1.5 μm;

[0051] (2) firstly placing the substrate fabric in a corona discharge device for corona treatment, with the corona value reaching 38 dynes, and then coating the hot melt adhesive on one side of the substrate fabric by blade coating, with the blade coating temperature being 190° C. and the melt viscosity being about 1200 cps;

[0052] (3) by controlling the temperature, viscosity and substrate, the single-sided penetration depth of the melt in the substrate cloth is 15 μm;

[0053] (4) By adjusting the melt flow rate and coating speed, the thickness of the outer adhesive layer of the substrate is 80 μm to obtain an insulating film;

[0054] (5) FFC is formed by rolling two layers of insulation film and a 100 μm thick conductor copper wire in the middle. During rolling, the outer rubber layer of the two insulation films is close to the conductor wire. The temperature of the pre-pressing roller is 150°C, the temperature of the main pressing roller is 180°C, and the pre-pressing pressure is 0.2 MPa.

[0055] (6) The PES-based bending-resistant FFC can be obtained by the above method.

[0056] Example 4 (repair test)

[0057] (1) A PP-based bending-resistant FFC was prepared according to Example 2, and the FFC was placed on a bending-resistant testing machine for testing until local debonding;

[0058] (2) dissolving PP in xylene to obtain a 100 cps polypropylene solution, applying a sufficient amount of the polypropylene solution to the surface of the substrate in the degumming area, and then placing it in a vacuum environment of -0.1 MPa to allow the solution to completely penetrate the degumming area;

[0059] (3) When the solvent evaporates and dries, the repair process is completed, and a repaired PP-based bending-resistant FFC is obtained.

[0060] Comparative Example 1 (no substrate cloth)

[0061] (1) Using PP (polypropylene) hot melt adhesive as raw material, the film is cast by a casting machine at a casting temperature of 210°C;

[0062] (2) adjusting the casting rate to achieve a glue layer thickness of 80 μm;

[0063] (3) FFC is formed by rolling two layers of substrate-free insulating films and a 100 μm thick conductor copper busbar in the middle, wherein the temperature of the pre-pressing roller is 150°C, the temperature of the main pressing roller is 180°C, and the pre-pressing pressure is 0.2 MPa;

[0064] (4) The substrate-free FFC can be obtained by the above method.

[0065] Comparative Example 2

[0066] This comparative example is a change made on the basis of Example 2. The base cloth (made of polyester fiber with a diameter of 30 μm) with a thickness of 50 μm is selected. The rest is the same as Example 2.

[0067] Comparative Example 3

[0068] This comparative example is a change made on the basis of Example 2. Specifically, the pores of the substrate cloth are 0.1 μm, and the rest are the same as Example 2.

[0069] Comparative Example 4

[0070] This comparative example is a change made on the basis of Example 2, specifically, the pores of the base cloth are 4 μm, and the rest are the same as Example 2.

[0071] Comparative Example 5

[0072] This comparative example is a change made on the basis of Example 2, specifically, the melt viscosity is 8000 cps, and the rest is the same as Example 2.

[0073] Comparative Example 6

[0074] This comparative example is a change made on the basis of Example 2, specifically, the melt viscosity is 200 cps, and the rest is the same as Example 2.

[0075] The advantages of the present technology are illustrated by the results of Examples 1-4 and Comparative Examples 1-6: the product is qualified if it is bent more than 10 times without debonding. The test results are shown in Table 1.

[0076] Testing method for bending resistance: Use a bending tester to perform a 180° bending test on the FFC body (bending radius 0.5mm). No cracking is allowed after bending 10 times.

[0077] The test method for the number of folding endurance after the double 85 test: the FFC body is placed at 85°C and 85RH for 1000 hours using a bending tester and then subjected to a 180° bending test (bending radius 0.5mm). No cracking is allowed after 10 bends.

[0078] Table 1 Performance test results of embodiments and comparative examples

[0079]

[0080]

[0081] As can be seen from the above table, Examples 1-3 can withstand bending times of more than 48 times, and the surface is flat and there is no degumming. This is mainly due to the selection of ultra-thin polyester fiber cloth as the substrate, and the use of the complex interlocking structure formed at the interface between the substrate and the hot melt adhesive, which reduces the slippage of the adhesive layer during the FFC molding process and effectively solves the problems of adhesive layer shrinkage and shedding. The reason for the deformation of Comparative Example 1 is that there is no fiber cloth substrate support, and the cooling crystallization shrinkage during the hot pressing cooling process is prone to deformation; while in Comparative Example 2, the increase in fiber diameter reduces the specific surface area and thus reduces the interlocking structure, the bending resistance is significantly reduced, and it fails after the double 85 test. Similarly, too small pores in the substrate will affect the penetration of the hot melt adhesive, which is not conducive to the formation of the interlocking structure, resulting in a significant reduction in the number of bending times. Although too large pores can increase the penetration depth, it causes excessive bending stress and easily causes degumming. After the double 85 test, it was degummed and failed after 6 bends. Secondly, the viscosity of the hot melt adhesive affects the penetration depth. If the penetration depth is too small, the bonding surface between the hot melt adhesive and the base cloth will be small, and the interlocking structure will not be strong enough, affecting the bonding strength. If the penetration depth is too large, that is, the bonding layer is thick, greater stress will be generated during the bending process, which will have an adverse effect on the bending resistance.

[0082] 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 bending-resistant flexible flat cable, characterized in that: The hot melt adhesive is coated on one side of the base cloth, so that part of the hot melt adhesive penetrates into the pores of the base cloth to obtain an insulating film, and then the insulating film and the conductor wire are rolled to obtain; The depth of penetration of the hot melt adhesive into the pores of the substrate cloth is 10-20 μm; The thickness of the outer rubber layer of the substrate cloth is 50-100 μm; The thickness of the base cloth is 20-50 μm, the fiber diameter is 10-25 μm, the base pore is 0.2-2 μm, and the base cloth is a polyester fiber plain weave cloth.

2. The method for preparing a bending-resistant flexible flat cable according to claim 1, characterized in that: The coating method is knife coating, laminating or casting.

3. The method for preparing a bending-resistant flexible flat cable according to claim 1, characterized in that: The hot melt adhesive is subjected to heat processing before coating, the heat processing temperature is 150-300° C., and the viscosity of the hot melt adhesive at the heat processing temperature is 500-5000 cps.

4. The method for preparing a bending-resistant flexible flat cable according to claim 1, characterized in that: The hot melt adhesive is at least one of ethylene-vinyl acetate copolymer, polypropylene, polyester, polyurethane, and polyamide.

5. The method for preparing a bending-resistant flexible flat cable according to claim 1, characterized in that: The conductor line has a thickness of 90-110 μm.

6. The method for preparing a bending-resistant flexible flat cable according to claim 1, characterized in that: The rolling process includes pre-rolling and main rolling, wherein the temperature of the pre-rolling is 120-160° C., the temperature of the main rolling is 140-200° C., and the rolling pressure is 0.1-0.3 MPa.

7. The method for preparing a bending-resistant flexible flat cable according to claim 1, characterized in that: Before the hot melt adhesive is applied to the substrate fabric, the substrate fabric is subjected to corona treatment.

8. A bending-resistant flexible flat cable, characterized in that: The method is prepared by any one of claims 1 to 7.

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