A flexible conductive shielding film and its preparation method

Abstract

The present invention discloses a flexible conductive shielding film and a preparation method thereof. The flexible conductive shielding film is formed by a heat-softening conductive layer or a heat-softening conductive layer connected to a conductive shielding layer at least on one side, and the heat-softening conductive layer and the conductive shielding layer are overlapped and connected. The flexible conductive shielding film disclosed by the present invention is a composite film whose folding part can be heated and softened. After being softened, it is attached to the folding part of the electronic product, and there will be no tensile stress on the wire. After returning to room temperature, it remains in the softened state. At the same time, other non-heat-softening parts of the composite film can have high conductive shielding performance. The flexible conductive shielding film can be widely applied to new consumer electronic products, especially mobile phones, to solve the problems of flexible screens of mobile phones in this regard. Moreover, the preparation process of the flexible shielding film is simple, easy to prepare, and only requires heat pressing, which is suitable for large-scale industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic shielding, and particularly relates to a flexible conductive shielding film and a preparation method thereof. Background Art

[0002] Electronic components usually generate electrical energy, magnetic energy, and electromagnetic energy. The electrical energy, magnetic energy, and electromagnetic energy respectively generated by multiple electronic components will interfere with the performance of other electronic components in an electronic device. In order to protect the electronic components and reduce interference, it is necessary to perform shielding treatment on the electronic components. However, the existing conductive cloth is generally directly covered on the electronic components to be shielded or covered through a conductive adhesive. Especially for a single-chip microcomputer, there are many pins with very small exposed gaps. Wrapping the conductive cloth on it is very likely to cause short circuits in the pins of the electronic components.

[0003] In recent years, with the new flexible requirements put forward by people for electronic products, flexible electronic products have developed rapidly. People hope that electronic products can be bent, curled, or rolled up for convenient carrying and use. The flexibility of electronic products poses flexible requirements on conductive shielding materials. Traditional brittle conductive shielding films will crack after folding, resulting in poor conductive performance. At the same time, the existing flexible conductive materials will also apply stress to the lead wires of flexible circuit boards after folding. The "hair-thin" lead wires cannot withstand this stress, which will cause the lead wires to break. Therefore, the conductive shielding of the entire area of flexible circuit boards is an unsolved problem. Summary of the Invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a flexible conductive shielding film and a preparation method thereof.

[0005] The purpose of the present invention is achieved through the following technical solutions: A flexible conductive shielding film, the flexible conductive shielding film is formed by a heat-softening conductive layer or at least one side of the heat-softening conductive layer is connected to a conductive shielding layer, and the heat-softening conductive layer and the conductive shielding layer are overlapped and connected.

[0006] Further, the heat-softening conductive layer is a thermoplastic matrix or a conductive shielding material formed by a hot melt adhesive and conductive particles.

[0007] Further, the conductive shielding layer is a high-temperature softening conductive layer, which is a conductive layer formed by a thermoplastic matrix or a hot melt adhesive and conductive particles, and the softening temperature of the high-temperature softening conductive layer is greater than the softening temperature of the heat-softening conductive layer. This thermoplastic matrix or hot melt adhesive needs to be subjected to a higher temperature to undergo a structural change, which has an obvious difference from the softening temperature of the heat-softening conductive layer.

[0008] Further, the thermoplastic matrix is thermoplastic acrylic, thermoplastic polyurethane, polyester, polyurethane elastomer, polypropylene, polyethylene, polyvinyl chloride, polystyrene, acrylonitrile-butadiene-styrene, polymethyl methacrylate, polyoxymethylene, polyamide, polycarbonate or polyphenylene ether. The thermoplastic matrix softens after heating and is easy to stretch, and maintains its structure unchanged after returning to room temperature.

[0009] Further, the hot melt adhesive is polyolefin hot melt adhesive, polyester hot melt adhesive, polyamide hot melt adhesive, polyurethane hot melt adhesive, styrene and its block copolymer hot melt adhesive or new type hot melt adhesive.

[0010] The hot melt adhesive is a plastic adhesive, whose physical state changes with temperature within a certain temperature range, while its chemical properties remain unchanged, and it is non-toxic and odorless; polyolefin hot melt adhesives such as polyethylene hot melt adhesive and polypropylene hot melt adhesive, ethylene and its copolymer hot melt adhesives such as ethylene-vinyl acetate copolymer (EVA) hot melt adhesive, and comonomers also include propylene, vinyl acetate, acrylic acid (ester), maleic anhydride, vinyl chloride, etc., polyester hot melt adhesives, polyamide hot melt adhesives, polyurethane hot melt adhesives, styrene and its block copolymer hot melt adhesives include SBS and SIS.

[0011] Further, the conductive shielding layer is a thermosetting conductive layer, which is a conductive shielding material formed by a two-component resin and conductive particles. The two-component resin (including resin and curing agent) forms a firm three-dimensional network structure to bond the conductive particles together, and its structure is not damaged or softened after heating.

[0012] The thermosetting matrix includes epoxy resin, acrylic acid, polyurethane, unsaturated polyester, phenolic resin, silicone resin, silicone rubber, etc.

[0013] Further, the conductive particles include gold powder, silver powder, silver-coated copper powder, nickel powder, copper powder, carbon black, graphene, carbon nanotubes or conductive fibers.

[0014] Further, the conductive shielding layer is conductive cloth, metal foil, or metal-coated conductive film.

[0015] A preparation method of a flexible conductive shielding film is to separately prepare a heat-softening conductive material and a conductive shielding material, overlap at least one side of the heat-softening material with the conductive shielding material, and form a flexible conductive shielding film after heat pressing.

[0016] Further, the heating temperature is 60 - 200 °C.

[0017] When the flexible conductive shielding film of the present invention is in use, the flexible conductive shielding film is placed in an oven at a temperature of 60 to 200 °C to heat and soften the conductive layer, but the conductive shielding layer is not softened. Immediately, the flexible conductive shielding film is attached to the flexible circuit board. The heated and softened conductive layer area is attached to the folding part, and the conductive shielding layer is attached to the non-folding part. After cooling, the existing structure is maintained.

[0018] The present invention has the following advantages: The present invention discloses a flexible conductive shielding film, which is a composite film whose folding part can be heated and softened. After being softened, it is attached to the folding part of the electronic product, and there will be no tensile stress on the wire. After returning to room temperature, it remains in the softened state. At the same time, the other non-heated and softened parts of the composite film can have high conductive shielding performance. The flexible conductive shielding film can be widely used in new consumer electronic products, especially mobile phones, to solve the problems of flexible screens of mobile phones in this regard. Moreover, the preparation process of the flexible shielding film is simple, easy to prepare, and only requires heating and pressing, which is suitable for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic structural diagram of the flexible conductive shielding film of Experimental Example 1.

[0020] Figure 2 It is a schematic structural diagram of the flexible conductive shielding film of Experimental Example 2.

[0021] Figure 3 It is a schematic structural diagram of the flexible conductive shielding films of Experimental Examples 3 and 4. DETAILED DESCRIPTION OF THE INVENTION

[0022] The following further describes the present invention in conjunction with embodiments. The protection scope of the present invention is not limited to the following:

[0023] Embodiment 1

[0024] A flexible conductive shielding film, which is formed by connecting a heat-softening conductive layer and a conductive shielding layer, and the heat-softening conductive layer and the conductive shielding layer are overlapped and connected.

[0025] The heat-softening conductive layer is a conductive shielding material formed by hot melt adhesive and conductive particles graphene, and the hot melt adhesive is polyethylene hot melt adhesive.

[0026] The conductive shielding layer is a high-temperature softening conductive layer, which is a conductive layer formed by a thermoplastic matrix acrylonitrile-butadiene-styrene and conductive fibers.

[0027] A preparation method of a flexible conductive shielding film, which respectively prepares a heat-softening conductive material and a conductive shielding material, overlaps one side of the heat-softening material with a quarter of the area of the conductive shielding material, and forms a flexible conductive shielding film after heat pressing. The heating temperature is 120-160°C.

[0028] Example 2:

[0029] A flexible conductive shielding film, which is a heat-softening conductive layer.

[0030] The heat-softening conductive layer is a conductive shielding material formed by a thermoplastic matrix and conductive particles.

[0031] The thermoplastic matrix is thermoplastic acrylic acid, and the conductive particles are gold powder.

[0032] A preparation method of a flexible conductive shielding film, which prepares a heat-softening conductive material, adds gold powder after heating the thermoplastic matrix, coats it into a film, and forms a flexible conductive shielding film.

[0033] Example 3:

[0034] A flexible conductive shielding film, which is formed by connecting a heat-softening conductive layer and a conductive shielding layer, and the heat-softening conductive layer and the conductive shielding layer are overlapped and connected.

[0035] The heat-softening conductive layer is a conductive shielding material formed by vinyl acetate-based hot melt adhesive and silver-coated copper powder as conductive particles;

[0036] The conductive shielding layer is a high-temperature softening conductive layer, which is a conductive layer formed by SBS-based hot melt adhesive and carbon black as conductive particles, and the softening temperature of the high-temperature softening conductive layer is higher than that of the heat-softening conductive layer.

[0037] The conductive shielding layer is conductive cloth, metal foil, or metal-coated conductive film.

[0038] A preparation method of a flexible conductive shielding film, which respectively prepares a heat-softening conductive material and a conductive shielding material, coats them into films, overlaps one side of the heat-softening material with a half of the area of the conductive shielding material, and forms a flexible conductive shielding film after heat pressing. The heating temperature is 80-140°C.

[0039] Example 4

[0040] A flexible conductive shielding film, which is formed by connecting the left and right sides of a heat-softening conductive layer with a conductive shielding layer, and the heat-softening conductive layer and the conductive shielding layer are overlapped and connected.

[0041] The heat-softening conductive layer is a conductive shielding material formed by polyester-based hot melt adhesive and carbon nanotubes as conductive particles.

[0042] The conductive shielding layer includes a high-temperature softening conductive layer, which is a conductive layer formed by hot-melt adhesive styrene and conductive particles graphene. The hot-melt adhesive needs to be subjected to a higher temperature to undergo a structural change, which is significantly different from the softening temperature of the heating-softening conductive layer.

[0043] A method for preparing a flexible conductive shielding film, which respectively prepares a heating-softening conductive material and a conductive shielding material, coats them into thin films respectively to form three thin films, overlaps the left and right sides of the heating-softening material with one-third of the thin film areas of the two conductive shielding material thin films respectively, and forms a flexible conductive shielding film after heating and pressing. The heating temperature is 80-170 °C.

[0044] Example 5:

[0045] A flexible conductive shielding film, wherein the flexible conductive shielding film is formed by connecting the left and right sides of a heating-softening conductive layer with a conductive shielding layer, and the heating-softening conductive layer and the conductive shielding layer are overlapped and connected.

[0046] The heating-softening conductive layer is a conductive shielding material formed by a thermoplastic matrix polymethyl methacrylate and conductive particles gold powder.

[0047] The conductive shielding layer is a thermosetting conductive layer, which is a conductive shielding material formed by a two-component resin and conductive particles nickel powder. The two-component resin (including resin and curing agent) forms a firm three-dimensional network structure to bond the conductive particles together, and the structure is not damaged or softened after heating.

[0048] A method for preparing a flexible conductive shielding film, which respectively prepares a heating-softening conductive material and a conductive shielding material, coats them into thin films respectively to form three thin films, overlaps the left and right sides of the heating-softening material with one-fourth of the thin film areas of the two conductive shielding material thin films respectively, and forms a flexible conductive shielding film after heating and pressing. The heating temperature is 100-160 °C.

[0049] Example 6:

[0050] A flexible conductive shielding film, wherein the flexible conductive shielding film is formed by connecting the left and right sides of a heating-softening conductive layer with a conductive shielding layer, and the heating-softening conductive layer and the conductive shielding layer are overlapped and connected.

[0051] The heating-softening conductive layer is a conductive shielding material formed by a thermoplastic matrix polyurethane and conductive particles silver powder.

[0052] The conductive shielding layer is a metal-coated conductive film.

[0053] A preparation method of a flexible conductive shielding film, preparing a heat-softening conductive material, coating it into a film, overlapping the left and right sides of the heat-softening material with a quarter of the area of the metal-coated conductive film respectively, and forming a flexible conductive shielding film after heat pressing. The heating temperature is 60 - 120 °C.

[0054] Experimental Example 1

[0055] A flexible conductive shielding film, with only one layer, as Figure 1 shown, that is, adding silver powder to acrylic hot melt adhesive in a ratio of 2:1, adding 20% butyl acetate solvent and 0.1% silicone wetting and leveling agent to form a filled conductive composite material, scraping and coating it into a conductive film, with a thickness of 40 μm after drying, a surface resistance of 100 mΩ / □, baking it at a high temperature of 120 °C after curing, immediately laminating it on a flexible circuit board after softening, and still firmly adhering to the flexible circuit board after the conductive film returns to room temperature. At this time, the surface resistance of the conductive film is the same as that before the softening treatment.

[0056] Experimental Example 2

[0057] A flexible conductive shielding film, with two layers, as Figure 2 shown, the first layer: after melting TPU at a high temperature, adding silver-coated copper powder to the melted hot melt adhesive in a certain ratio of 1:1 to form a conductive material 1, coating it into a film with a thickness of 50 μm, and the surface resistance after curing is 355 mΩ / □. Build the right one-third width of it on the second-layer copper foil (conductive material 2), and hot press and connect these materials together with a flat vulcanizer at the softening temperature of the hot melt adhesive of 100 °C and a pressure of 10 Mpa. At this time, the materials of the flexible conductive shielding film (i.e., the composite conductive film) from left to right are conductive material 1, the joint of conductive materials 1 and 2, and conductive material 2. Measure the conductive performance of this composite material at room temperature and find that the thickness of the conductive film in area 1 is reduced to 20 μm, the surface resistance is 115 mΩ / □, and the conductive performance is increased by about 3 times, and the surface resistance of the copper foil thickness remains unchanged. Place the composite conductive film on a heating plate and bake it at a high temperature of 160 °C. The area of conductive material 1 softens (in a state where it can be drawn into filaments with a little force), and the area of conductive material 2 does not soften. Laminating the area of conductive material 1 on one side and the folding part of the flexible circuit board, and the other side is laminated with the joint of conductive materials 1 and 2 and the copper foil. The surface resistance of the conductive film in area 1 after softening lamination and returning to room temperature is still 115 mΩ / □ unchanged.

[0058] Experimental Example 3

[0059] A flexible conductive shielding film, with three layers, as Figure 3As shown in the figure, the first layer and the third layer: Graphite is added to thermoplastic polyurethane in a ratio of 4:1, and 25% butyl acetate solvent, 0.1% silicone wetting and leveling agent, and 1% silicone defoaming agent are added to form conductive materials 1 and 3. They are coated into a film with a certain thickness and baked at 80 °C. After returning to room temperature, the sheet resistance of conductive materials 1 and 3 is 2.5 Ω / □. The second layer: Graphite is added to thermoplastic polyurethane with a lower softening temperature in a certain ratio of 4:1, and 0.1% silicone wetting and leveling agent and 1% silicone defoaming agent are added to form conductive material 2. It is coated into a film with a certain thickness and baked at 40 °C. After returning to room temperature, the sheet resistance of conductive material 2 is 5.5 Ω / □. The conductive materials are arranged in the order of 1, 2, 3, and conductive material 2 is laid flat at one-fourth of conductive material 1, and conductive material 3 is laid flat at one-fourth of conductive material 2. The three conductive materials are compacted by a calender and adhered to each other to form a multi-layer composite conductive film. The composite conductive film is placed in an oven at 100 °C for baking. The area of conductive material 2, that is, the middle area, softens, but the 1 area and the 3 area do not soften. Immediately, the composite material is attached to the flexible circuit board. The area of conductive material 2 is attached to the folding part, the area of conductive material 1 is attached to one side, and the area of conductive material 3 is attached to the other side. After the composite conductive film cools, it maintains the existing structure.

[0060] Experimental Example 4

[0061] A flexible conductive shielding film has three layers, as Figure 3 shown. The middle layer: Flaky silver-coated copper powder is added to TPU with a solid content of 20% in a ratio of 1:1. After adding 0.05% silicone wetting and leveling agent and 1% silicone defoaming agent, conductive material 2 is formed. It is coated into a 40-μm-thick film and baked at 60 °C. After returning to room temperature, the sheet resistance of conductive material 2 is 710 mΩ / □. Conductive materials 1 and 3 are conductive fabrics commonly used inside mobile phones. The conductive materials are arranged in the order of 1, 2, 3 on the release film. Conductive film 2 is the middle layer, and conductive material 2 is laid flat at one-fourth of conductive materials 1 and 3. A release film is also placed on top of this material and placed on a heating plate. It is heated at 160 °C. After putting on heat-resistant gloves, gently press the connection with your hand. It is easy for different materials to adhere to each other to form a multi-layer composite conductive film. After being placed at room temperature and cooled, the adhered structure remains unchanged, and the sheet resistance of the middle layer, that is, conductive material 2, is still 710 mΩ / □, and the thickness remains unchanged. When in use, the composite conductive film is placed in an oven at 160 °C for baking. The area of conductive material 2, that is, the middle layer, softens, but the 1 area and the 3 area do not soften. Immediately, the composite material is attached to the flexible circuit board. The area of conductive material 2 is attached to the folding part, the area of conductive material 1 is attached to one side, and the area of conductive material 3 is attached to the other side. After the composite conductive film cools, it maintains the existing structure.

[0062] A flexible conductive shielding film provided by the present invention can be designed into multiple layers according to product requirements, such as 5 layers, which are, from left to right, conductive shielding layer 1, heating and softening layer 1, conductive shielding layer 2, heating and softening layer 2, and conductive shielding layer 3. Specifically designed according to product requirements, the heating and softening conductive layer is located at the folding part of the product, and the conductive shielding layer is located at the non-folding part.

[0063] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and all are covered by the protection scope of the present invention.

Claims

1. A flexible conductive shielding film, characterized in that, The flexible conductive shielding film is formed by a heat-softening conductive layer or a heat-softening conductive layer connected to a conductive shielding layer at least on one side, and the heat-softening conductive layer and the conductive shielding layer are overlapped and connected; The heat-softening conductive layer is a conductive shielding material formed by a hot melt adhesive and conductive particles; The conductive shielding layer is a high-temperature softening conductive layer, which is a thermoplastic matrix or a conductive layer formed by a hot melt adhesive and conductive particles, and the softening temperature of the high-temperature softening conductive layer is higher than that of the heat-softening conductive layer; When the flexible conductive shielding film is used, the flexible conductive shielding film is placed in an oven at a temperature of 60-120 °C or 140 °C. The heat-softening conductive layer softens, but the conductive shielding layer does not soften. Immediately, the flexible conductive shielding film is attached to the flexible circuit board. The area of the heat-softening conductive layer is attached to the folding part, and the conductive shielding layer is attached to the non-folding part. After cooling, the existing structure is maintained; Among them, the hot melt adhesive is a polyolefin hot melt adhesive, a polyester hot melt adhesive, a polyamide hot melt adhesive, a polyurethane hot melt adhesive, a styrene and its block copolymer hot melt adhesive or a new type of hot melt adhesive; the conductive particles include gold powder, silver powder, silver-coated copper powder, nickel powder, copper powder, carbon black, graphene, carbon nanotubes or conductive fibers.

2. The flexible conductive shielding film according to claim 1, characterized in that The thermoplastic matrix is thermoplastic acrylic, thermoplastic polyurethane, polyester, polyurethane elastomer, polypropylene, polyethylene, polyvinyl chloride, polystyrene, acrylonitrile-butadiene-styrene, polymethyl methacrylate, polyoxymethylene, polyamide, polycarbonate or polyphenylene ether.

3. A flexible conductive shielding film according to claim 1, wherein The conductive shielding layer is a thermosetting conductive layer, which is a conductive shielding material formed by a two-component resin and conductive particles.

4. A flexible conductive shielding film according to claim 1, characterized in that, The conductive shielding layer is a conductive cloth, a metal foil, or a metal-coated conductive film.

5. The preparation method of a flexible conductive shielding film according to claim 1, characterized in that The heat-softening material and the conductive shielding material are prepared separately. At least one side of the heat-softening material is overlapped with the conductive shielding material, and after heating and pressing, a flexible conductive shielding film is formed. Among them, the heating temperature is 60-120 °C or 140 °C.

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