Flexible circuit composite film and preparation method and application thereof

Abstract

The invention provides a flexible circuit composite film and a preparation method and application thereof, and belongs to the technical field of flexible circuit substrates. The flexible circuit composite film provided by the invention comprises a flexible fabric layer, a bonding layer and a laser-induced graphene composite film which are sequentially arranged from top to bottom, and the laser-induced graphene composite film comprises a graphene circuit layer and a polyimide fiber film; and the graphene circuit layer is in contact with the bonding layer. According to the invention, the graphene circuit layer is packaged between the flexible fabric and the polyimide film through the sandwich structure, so that the performance degradation of the graphene circuit caused by external mechanical friction, oxidation or a humid environment is effectively avoided, and the durability and reliability of the circuit are remarkably improved; according to the structure, the composite film can be used as a high-reliability flexible circuit board and can also be used as a safe and stable flexible electric heating element.

Description

Technical Field

[0001] This invention belongs to the field of flexible circuit substrate technology, specifically relating to a flexible circuit composite film, its preparation method, and its application. Background Technology

[0002] With the rapid development of wearable devices, flexible displays, and soft robots, the demand for flexible circuit boards is increasing daily. An ideal flexible circuit board should possess excellent flexibility, bendability, heat resistance, and stable electrical properties. Traditional printed circuit boards are rigid and brittle, making it difficult to meet these requirements. Simultaneously, there is a significant demand for flexible, safe, and efficient electric heating elements in fields such as smart wearables, automotive seat heating, and medical therapy.

[0003] Polyimide (PI) is widely used as a substrate for flexible circuits due to its excellent high-temperature resistance, mechanical strength, and chemical stability. Laser-induced graphene (LIG) technology is a technique that directly generates porous graphene on the polymer surface through laser etching, allowing for customized patterning and offering advantages such as rapid processing, no need for masks, and no need for chemical reagents. However, commercially available PI films have limited flexibility and permeability, and are prone to fatigue cracking under repeated dynamic bending. Furthermore, LIG ​​circuits generated directly on a single PI film surface in existing technologies are exposed and susceptible to mechanical scratches, oxidation, or humid environments, leading to performance degradation or even failure. In addition, while LIG's excellent electrothermal conversion properties allow for electric heating, exposed heating circuits pose safety risks and have a short lifespan.

[0004] Therefore, there is an urgent need to develop a flexible composite film that can effectively protect circuits and has excellent overall flexibility, so as to expand its dual application in the fields of flexible circuits and electric heating. Summary of the Invention

[0005] The purpose of this invention is to provide a flexible circuit composite film, its preparation method and application. This invention encapsulates a graphene circuit layer between a flexible fabric and a PI film through a "sandwich" structure, which effectively protects the circuit and significantly improves the durability and reliability of the circuit. This structure allows the composite film to be used as both a highly reliable flexible circuit board and a flexible electric heating element.

[0006] To achieve the objectives of this invention, the following technical solutions are provided: A flexible circuit composite film includes a flexible fabric layer, an adhesive layer, and a laser-induced graphene composite film arranged sequentially from top to bottom. The laser-induced graphene composite film includes a graphene circuit layer and a polyimide fiber film. The graphene circuit layer and the adhesive layer are in contact.

[0007] Preferably, the flexible fabric includes one or more of polyimide fiber fabric, aramid fabric, pre-oxidized filament fiber fabric, cellulose fiber fabric or glass fiber fabric.

[0008] Preferably, the adhesive layer comprises one or more of polyurethane, polyamide, polyethylene, polypropylene, and polyester.

[0009] Preferably, the method for preparing the polyimide fiber membrane includes the following steps: Preparation of polyamic acid spinning solution; The polyamic acid spinning solution was electrospun to obtain a polyamic acid fiber membrane. The polyamic acid fiber membrane is subjected to imidization treatment to obtain the polyimide fiber membrane.

[0010] Preferably, the polyamic acid spinning solution comprises polyamic acid and a polar solvent; the polar solvent comprises one or more of N-methylpyrrolidone, N,N-dimethylformamide and N,N-dimethylacetamide; The mass fraction of the polyamic acid spinning solution is 8-20%.

[0011] Preferably, the electrospinning process parameters include: voltage of 8~20 kV, receiving distance of 10~25 cm, spinning solution supply rate of 0.2~2 mL / h, and ambient humidity of 10~60%.

[0012] Preferably, the imidization treatment includes a first stage and a second stage performed sequentially; The temperature of the first stage is 200~250 ℃, and the holding time is 0.5~1h; the temperature of the second stage is 350~400 ℃, and the holding time is 1~2h.

[0013] The present invention also provides a method for preparing the flexible circuit composite film described in the above technical solution, comprising the following steps: A graphene circuit layer was constructed on the surface of a polyimide fiber membrane using laser-induced graphene technology to obtain a laser-induced graphene composite film. An adhesive layer is used to bond one side of the laser-induced graphene composite film containing the graphene circuit layer to a flexible fabric layer to obtain the flexible circuit composite film.

[0014] Preferably, the process parameters for laser-induced graphene include: laser power of 5~20 W, scanning speed of 10~500 mm / s, and scanning line spacing of 0.01~0.1 mm; The bonding is a hot-press composite, wherein the hot-press composite temperature is 100~200 ℃, the pressure is 1.0~3.0 MPa, and the heat and pressure holding time is 60~120 s.

[0015] The present invention also provides the application of the flexible circuit composite film described in the above technical solution or the flexible circuit composite film prepared by the preparation method described in the above technical solution in wearable devices, flexible displays, soft robots or electric heating.

[0016] This invention provides a flexible circuit composite film, comprising a flexible fabric layer, an adhesive layer, and a laser-induced graphene composite film arranged sequentially from top to bottom. The laser-induced graphene composite film includes a graphene circuit layer and a polyimide fiber film; the graphene circuit layer and the adhesive layer are in contact. This invention encapsulates the laser-induced graphene circuit layer between the flexible fabric and the PI film using a "sandwich" structure, effectively avoiding performance degradation caused by external mechanical friction, oxidation, or humid environments, significantly improving the durability and reliability of the circuit. This structure allows the flexible circuit composite film to be used both as a highly reliable flexible circuit board and as a safe and stable flexible electric heating element.

[0017] Furthermore, the PI film prepared by electrospinning and the flexible fabric used for encapsulation both possess ultra-flexibility. Their porous fiber structure provides anchoring points for the penetration of the adhesive layer, forming a strong mechanical interlock. The interlayer peel strength is high, and the overall flexible circuit composite film can withstand repeated bending and rolling without delamination. Moreover, the graphene circuit layer of this invention has high electrothermal conversion efficiency. By optimizing the circuit design (such as rectangular, serpentine, and grid shapes) through laser-induced graphene technology, rapid and uniform heating can be achieved. The sandwich structure ensures uniform heat diffusion outwards while avoiding localized overheating and circuit oxidation, thus improving heating life and safety.

[0018] This invention also provides a method for preparing flexible circuit composite films. The entire preparation process does not require complex etching processes or large amounts of chemical reagents. Laser-induced graphene technology enables direct, rapid, environmentally friendly, and patterned circuits, which can be prepared by simple hot-pressing composite. The process is simple and suitable for large-scale production.

[0019] The flexible circuit composite film provided by this invention combines excellent flexibility, stable conductivity, reliable electroheating function, and reliable structural integrity. By precisely optimizing laser parameters and circuit design, conductive patterns with different impedances and current carrying capacities can be customized and fabricated, making it highly suitable for flexible circuit fields such as flexible circuit boards, flexible sensors, and wearable electronic devices that require high reliability. At the same time, its stable electrothermal conversion performance is also perfectly suited for flexible electroheating fields such as smart thermal clothing, car seat heating, and medical physiotherapy. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the flexible circuit composite film of the present invention, wherein 1-flexible fabric layer, 2-adhesive layer, 3-graphene circuit layer, and 4-polyimide film; Figure 2 This is an infrared thermal image of the flexible circuit composite film obtained in Example 2 after heating. Figure 3 This is an infrared thermal image of the flexible circuit composite film obtained in Example 3 after heating; Figure 4 This is an infrared thermal image of the flexible circuit composite film obtained in Example 4 after heating. Figure 5 The image shows an infrared thermal image of the flexible circuit composite film obtained in Example 1 after 450 bends. Figure 6 The image shows a comparison of infrared thermal images of the flexible circuit composite film obtained in Example 1 before and after 450 bends. Detailed Implementation

[0022] This invention provides a flexible circuit composite film, comprising a flexible fabric layer, an adhesive layer, and a laser-induced graphene composite film arranged sequentially from top to bottom. The laser-induced graphene composite film includes a graphene circuit layer and a polyimide fiber film; the graphene circuit layer and the adhesive layer are in contact.

[0023] In this invention, unless otherwise specified, all raw materials used in the preparation are commercially available products well known to those skilled in the art.

[0024] In this invention, the flexible fabric includes one or more of polyimide fiber fabric, aramid fabric, pre-oxidized filament fiber fabric, cellulose fiber fabric, and glass fiber fabric, and in specific embodiments, it can be polyimide fiber fabric; the thickness of the flexible fabric layer can be 0.1~3 mm, and in specific embodiments, it can be 0.5, 1.2, 1.8, or 2.5 mm. This invention encapsulates the laser-induced graphene circuit layer between the flexible fabric and the PI film using a "sandwich" structure, effectively avoiding performance degradation caused by external mechanical friction, oxidation, or humid environments, significantly improving the durability and reliability of the circuit. This structure allows the flexible circuit composite film to be used both as a highly reliable flexible circuit board and as a safe and stable flexible electric heating element.

[0025] In this invention, the adhesive layer comprises one or more of polyurethane (TPU), polyamide (PA), polyethylene (PE), polypropylene (PP), and polyester (PES), and in a specific embodiment, it may be polyurethane; the thickness of the adhesive layer is 0.025~0.4 mm, and in a specific embodiment, it may be 0.03 or 0.035 mm.

[0026] In this invention, the method for preparing the polyimide film includes the following steps: Preparation of polyamic acid spinning solution; The polyamic acid spinning solution was electrospun to obtain a polyamic acid fiber membrane. The polyamic acid fiber membrane is subjected to imidization treatment to obtain the polyimide membrane.

[0027] In this invention, the polyamic acid (PAA) is obtained by polycondensation of 4,4'-diaminodiphenyl ether (ODA) and pyromellitic dianhydride (PMDA); the polycondensation process is not particularly limited in this invention, and methods and parameters well known to those skilled in the art can be used.

[0028] In this invention, the polyamic acid spinning solution comprises polyamic acid and a polar solvent; the polar solvent comprises one or more of N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMAC), and in a specific embodiment, it can be N,N-dimethylacetamide; the mass fraction of the polyamic acid spinning solution is 8~20%, and in a specific embodiment, it can be 10, 12, 15, or 17%. This invention does not specifically limit the preparation method of the polyamic acid spinning solution; in a specific embodiment, it can be obtained by dispersing ODA in N,N-dimethylacetamide at 0°C, mixing it with PMDA, and then maintaining the reaction in an ice bath for 5 hours.

[0029] In this invention, the electrospinning process parameters include: a voltage of 8~20 kV, which can be 10, 13 or 15 kV in specific embodiments; a receiving distance of 10~25 cm, which can be 15 or 20 cm in specific embodiments; a spinning solution supply rate of 0.2~2 mL / h, which can be 0.8, 1.0 or 1.5 mL / h in specific embodiments; an ambient humidity of 0~60%, which can be 10, 25, 40 or 55% in specific embodiments; and an electrospinning substrate that can be aluminum foil.

[0030] In this invention, the imidization treatment includes a first stage and a second stage performed sequentially; the temperature of the first stage is 200~250 ℃, and in a specific embodiment it can be 220 or 230 ℃, with a holding time of 0.5~1 h; the temperature of the second stage is 350~400 ℃, and in a specific embodiment it can be 360 ​​or 380 ℃, with a holding time of 1~2 h; in this invention, the heating rate to the first and second imidization treatments is 5~10 ℃ / min; the imidization treatment is carried out in a muffle furnace; the imidization treatment is followed by cooling; the cooling can be natural cooling.

[0031] In this invention, the thickness of the PI film is 0.1~2 mm, and in specific embodiments it can be 0.3, 0.5, 1.0 or 1.7 mm.

[0032] The present invention also provides a method for preparing the flexible circuit composite film described in the above technical solution, comprising the following steps: A graphene circuit layer was constructed on the surface of a polyimide fiber membrane using laser-induced graphene technology to obtain a laser-induced graphene composite film. An adhesive layer is used to bond one side of the laser-induced graphene composite film containing the graphene circuit layer to a flexible fabric layer to obtain the flexible circuit composite film.

[0033] In this invention, the graphene circuit layer can be rectangular, and most preferably square.

[0034] In this invention, the process parameters for laser-induced graphene include: laser power of 5~20 W, which can be 10 or 18 W in specific embodiments; scanning speed of 10~500 mm / s, which can be 50, 130, 240, 300 or 410 mm / s in specific embodiments; and scanning line spacing of 0.01~0.1 mm, which can be 0.05 or 0.08 mm in specific embodiments. Specifically, a CO2 laser is used for scanning and preparation of the laser-induced graphene in this invention. The graphene circuit layer of this invention is partially generated from polyimide under laser-induced high temperature. Laser induction has the advantages of good effect and stability, and the shape of the graphene circuit layer can be customized to achieve uniform heating. Simultaneously, this invention uses electrospun polyimide film to achieve the integration of flexible fabric and induction substrate, overcoming the disadvantage of edge wrinkles after laser induction of traditional commercial polyimide films.

[0035] In this invention, the bonding is hot-pressing composite; the temperature of the hot-pressing composite is 100~200℃, and in a specific embodiment it can be 120, 150 or 190℃; the pressure is 1.0~3.0 MPa, and in a specific embodiment it can be 1.5 or 2.0 MPa; the heat preservation and pressure preservation time is 60~120 s, and in a specific embodiment it can be 90 s.

[0036] The present invention also provides the application of the flexible circuit composite film described in the above technical solution or the flexible circuit composite film prepared by the preparation method described in the above technical solution in wearable devices, flexible displays, soft robots or electric heating.

[0037] To further illustrate the present invention, the flexible circuit composite film, its preparation method, and its application provided by the present invention will be described in detail below with reference to the accompanying drawings and embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0038] Example 1 1) Preparation of PAA spinning solution: 2.15g ODA was dispersed in 27.5mL DMAC under strong stirring (200rpm) at 0℃; 2.35g PMDA was gradually added to the resulting dispersion system, and the reaction was maintained in an ice bath for 5h to obtain PAA spinning solution.

[0039] 2) Preparation of PAA electrospun film: The above PAA spinning solution was injected into the electrospinning device, the voltage was set to 13 kV, the receiving distance was 15 cm, the spinning solution flow rate was 1.0 mL / h, and the ambient humidity was controlled at 40%. The fibers were collected on the roller receiver covered with aluminum foil to obtain a PAA electrospun film with a thickness of about 0.3 mm.

[0040] 3) Imidinated PI film: The obtained PAA electrospun film was peeled off from the aluminum foil and placed in a muffle furnace for imidization treatment in air atmosphere. The temperature was increased from room temperature to 250°C at 5°C / min and held for 1 hour, then increased to 380°C at 5°C / min and held for 1.5 hours. After natural cooling to room temperature, a flexible PI electrospun film with a pore size of approximately 1.6 μm was obtained.

[0041] 4) Laser-induced graphene: Take a piece of the above PI film and scan its surface with a CO2 laser. The laser power is 3.6W, the scanning speed is 280mm / s, and the scanning line spacing is 0.05mm to prepare a rectangular graphene conductive circuit with a width of 1cm and a length of 5cm.

[0042] 5) Hot-pressing lamination: Take another PI film as the flexible fabric layer, and place a 0.1 mm thick TPU film between the lower laser-induced graphene PI film and the upper PI film to form a "sandwich" preform. Place it in a flatbed hot press and hot press it at 150℃ and 1.0 MPa for 90 seconds. After natural cooling, a flexible circuit composite film is obtained.

[0043] Example 2 Steps 1) to 3) are the same as in Example 1, preparing PI electrospun films; 4) Laser-induced graphene: Take a piece of the above-mentioned PI film and scan its surface using a CO2 laser. The laser power is 6W, the scanning speed is 280mm / s, and the scanning line spacing is 0.05mm to prepare a rectangular graphene conductive circuit with a width of 8cm and a length of 12cm. 5) Hot-pressed composite: Use a specification of 200g / m². 2 Aramid 1414 nonwoven fabric (Kaidun New Materials) was used as the flexible fabric layer. A 0.1 mm thick TPU film was placed between the lower laser-induced graphene PI film and the upper aramid nonwoven fabric to form a "sandwich" preform. This preform was then placed in a flatbed hot press and hot-pressed at 150°C and 1.0 MPa for 90 seconds. After natural cooling, a flexible circuit composite film was obtained.

[0044] Example 3 Steps 1) to 3) are the same as in Example 1, preparing PI electrospun films; 4) Laser-induced graphene: Take a piece of the above-mentioned PI film and scan its surface using a CO2 laser. The laser power is 4.5W, the scanning speed is 280mm / s, and the scanning line spacing is 0.05mm to prepare a rectangular graphene conductive circuit with a width of 6cm and a length of 6cm. 5) Hot-press lamination: Take a piece of modified flame-retardant PP (polypropylene) nonwoven fabric (1.6 meters wide, 110g basis weight, brand Nongguanjia) as the flexible fabric layer, and place a 0.1 mm thick TPU film between the lower laser-induced graphene PI film and the upper PP nonwoven fabric to form a "sandwich" preform. Place it in a flatbed hot press and hot press at 150℃ and 1.0 MPa pressure for 90 seconds. After natural cooling, a flexible circuit composite film is obtained.

[0045] Example 4 Steps 1) to 3) are the same as in Example 1, preparing PI electrospun films; 4) Laser-induced graphene: Take a piece of the above PI film and scan its surface with a CO2 laser. The laser power is 3.6W, the scanning speed is 280mm / s, and the scanning line spacing is 0.05mm to prepare a rectangular graphene conductive circuit with a width of 1cm and a length of 5cm.

[0046] 5) Hot-press lamination: A modified flame-retardant PP (polypropylene) nonwoven fabric is used as the flexible fabric layer. A 0.1 mm thick TPU film is placed between the lower laser-induced graphene PI film and the upper PP nonwoven fabric to form a "sandwich" preform. This preform is then placed in a flatbed hot press and hot-pressed at 150℃ and 1.0 MPa for 90 seconds. After natural cooling, a flexible circuit composite film is obtained.

[0047] Comparative Example 1 TURBOSUN silicone rubber 12W nickel-cadmium alloy resistance wire, model 10037963069675.

[0048] Test case Electric heating performance test: A 12V DC voltage was applied to both ends of the flexible circuit composite film obtained in Examples 1 to 4 through conductive cloth tape. When the voltage was applied, the surface temperature of the flexible circuit composite film rose and reached equilibrium. An infrared thermal imager was used to observe whether the temperature distribution of the heating area was uniform and whether there were obvious overheating spots. The stable temperature was recorded.

[0049] Figures 2-4 These are infrared thermal images of the flexible circuit composite films obtained in Examples 2-4 after heating; Figures 2-4 The results show that when a direct voltage of 12V is applied, the stable temperature of the flexible circuit composite film obtained in Example 1 is 55℃, the stable temperature of the flexible circuit composite film obtained in Example 2 is 140℃, and the stable temperature of the flexible circuit composite film obtained in Example 3 is 97℃. This indicates that the graphene pattern is a crucial factor determining the heating temperature of the electric heating film and whether the final temperature of the prepared electric heating film is stable. Under the premise of a fixed heating area and a fixed applied voltage, the closer the pattern is to a square (i.e., the closer the aspect ratio is to 1:1, the closer it is to sheet resistance), the lower its total resistance. Tests showed that the total resistance of the flexible circuit composite film with a width of 8cm and a length of 12cm obtained in Example 2 was 30Ω, the total resistance of the flexible circuit composite film with a width of 6cm and a length of 6cm obtained in Example 3 was 14Ω, and the total resistance of the flexible circuit composite film with a width of 1cm and a length of 5cm obtained in Example 4 was 80Ω. A lower total resistance means greater total power consumption, and therefore, a stronger overall heating effect (higher steady-state temperature).

[0050] Test Example 2 The flexible circuit composite film obtained in Example 1 was subjected to 450 bends, and the heating effect before and after bending was tested according to the method described in Test Example 1.

[0051] Figure 5 This is an infrared thermal image of the flexible circuit composite film obtained in Example 1 after 450 bends. Figure 6 The image shows a comparison of infrared thermal images of the flexible circuit composite film obtained in Example 1 before and after 450 bends. Figure 6 The left side is before the bend, and the right side is after the bend; from Figure 5 and Figure 6 The results showed that the heating temperature decreased slightly, but the uniformity was still acceptable. The temperature in the middle part decreased slightly, proving that the composite film can be cut and integrated into clothing or protective gear as a flexible, safe and efficient heating element.

[0052] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A flexible circuit composite film, characterized in that, The device comprises, from top to bottom, a flexible fabric layer, an adhesive layer, and a laser-induced graphene composite film, wherein the laser-induced graphene composite film includes a graphene circuit layer and a polyimide fiber film; the graphene circuit layer and the adhesive layer are in contact.

2. The flexible circuit composite film according to claim 1, characterized in that, The flexible fabric includes one or more of the following: polyimide fiber fabric, aramid fabric, pre-oxidized filament fiber fabric, cellulose fiber fabric, or glass fiber fabric.

3. The flexible circuit composite film according to claim 1, characterized in that, The adhesive layer comprises one or more of polyurethane, polyamide, polyethylene, polypropylene, and polyester.

4. The flexible circuit composite film according to claim 1, characterized in that, The method for preparing the polyimide fiber membrane includes the following steps: Preparation of polyamic acid spinning solution; The polyamic acid spinning solution was electrospun to obtain a polyamic acid fiber membrane. The polyamic acid fiber membrane is subjected to imidization treatment to obtain the polyimide fiber membrane.

5. The flexible circuit composite film according to claim 4, characterized in that, The polyamic acid spinning solution comprises polyamic acid and a polar solvent; the polar solvent comprises one or more of N-methylpyrrolidone, N,N-dimethylformamide and N,N-dimethylacetamide; The mass fraction of the polyamic acid spinning solution is 8-20%.

6. The flexible circuit composite film according to claim 4 or 5, characterized in that, The electrospinning process parameters include: voltage of 8~20 kV, receiving distance of 10~25 cm, spinning solution supply rate of 0.2~2 mL / h, and ambient humidity of 10~60%.

7. The flexible circuit composite film according to claim 4, characterized in that, The imidization treatment includes a first stage and a second stage performed sequentially. The temperature of the first stage is 200~250 ℃, and the holding time is 0.5~1h; the temperature of the second stage is 350~400℃, and the holding time is 1~2h.

8. The method for preparing the flexible circuit composite film according to any one of claims 1 to 7, characterized in that, Includes the following steps: A graphene circuit layer was constructed on the surface of a polyimide fiber membrane using laser-induced graphene technology to obtain a laser-induced graphene composite film. An adhesive layer is used to bond one side of the laser-induced graphene composite film containing the graphene circuit layer to a flexible fabric layer to obtain the flexible circuit composite film.

9. The preparation method according to claim 8, characterized in that, The process parameters for laser-induced graphene include: laser power of 5~20 W, scanning speed of 10~500 mm / s, and scanning line spacing of 0.01~0.1 mm. The bonding is a hot-press composite, wherein the hot-press composite temperature is 100~200 ℃, the pressure is 1.0~3.0 MPa, and the heat and pressure holding time is 60~120 s.

10. The application of the flexible circuit composite film according to any one of claims 1 to 7 or the flexible circuit composite film prepared by the preparation method according to claim 8 or 9 in wearable devices, flexible displays, soft robots or electric heating.

Images