Preparation method of piezoelectric fiber layer and piezoelectric fiber composite material

Abstract

The invention belongs to the technical field of piezoelectric functional materials, and discloses a preparation method of a piezoelectric fiber layer and a piezoelectric fiber composite material. Injecting glue into the piezoelectric ceramic with the glue injection groove by adopting a polymer matrix filling device; the polymer matrix filling device injects glue from one end of the piezoelectric ceramic with the glue injection groove, and controls the glue injection pressure and the glue injection flow rate until the glue flows out of the polymer matrix from the other end of the piezoelectric ceramic; after the flowing-out volume of the polymer matrix is 2-3 times of the total volume of the glue injection groove, glue injection is completed; carrying out vacuum curing to obtain a composite block of piezoelectric ceramics and a polymer matrix, and slicing according to a set thickness to obtain a piezoelectric fiber layer; the piezoelectric fiber layer is attached between two packaging films engraved with the interdigital electrodes, the whole packaging films are placed between cover plates coated with lubricating oil, and the piezoelectric fiber composite material is obtained after vacuum pressurization curing.

Description

Technical Field

[0001] The present invention relates to the technical field of piezoelectric functional materials, and in particular to a method for preparing a piezoelectric fiber layer and a piezoelectric fiber composite material. Background Art

[0002] Piezoelectric fiber composites are composite materials that combine piezoelectric fibers with matrix materials to form composite materials with excellent flexibility and electromechanical coupling properties. They show wide application potential in many fields such as vibration control, energy harvesting, and health testing. Especially in the vibration suppression of electromechanical coupling systems, they can effectively sense and respond to external vibration signals, and achieve real-time vibration suppression through their inverse piezoelectric effect. Piezoelectric fiber composites can generate electrical signals when subjected to mechanical vibrations, and feed these signals back to the control system, thereby realizing the detection and feedback regulation of the vibration source. In addition, piezoelectric fiber composites can also convert electrical signals into force or displacement through reverse action and apply them to the structure to eliminate or reduce the amplitude of vibration. Therefore, it is particularly important to achieve low-cost and high-quality preparation of piezoelectric fiber composites. Piezoelectric fiber composites are mainly composed of a piezoelectric fiber layer, a bonding layer, and an encapsulation film layer engraved with interdigital electrodes. Among them, the piezoelectric fiber layer is composed of piezoelectric ceramic fibers and a polymer matrix. It is the key to the piezoelectric fiber composite material's ability to produce piezoelectric effect, and is also called the active layer of the piezoelectric fiber composite material; the packaging film layer engraved with interdigitated electrodes is composed of metal electrodes and packaging films drawn according to a specific pattern. The metal electrodes are used to introduce an electric field into the piezoelectric fiber layer, and the packaging film plays a role in protection and fixation; the bonding layer is a polymer matrix, and epoxy resin-based materials are often used, which is mainly used for bonding between the piezoelectric fiber layer and the packaging film layer engraved with interdigitated electrodes.

[0003] There are currently three relatively mature preparation processes for the preparation of piezoelectric fiber layers, namely direct cutting composite method, cutting filling method and cutting lamination method. The literature "Zhang Xuewu, Zeng Tao, Zhao Cheng, et al. Research and Application of Macro Fiber Composite Materials and Their Actuators [J]. Mechanical Engineering Materials, 2020, 44(06): 77-81." introduces the preparation process of piezoelectric fiber composite materials. The preparation process methods of the three piezoelectric fiber layers are as follows.

[0004] The direct cutting composite method is to stick a piezoelectric ceramic sheet of a specific thickness on a carrier film, and then use a precision dicing machine to cut the piezoelectric ceramic sheet into an array of piezoelectric ceramic fibers arranged periodically at equal intervals, and then composite the polymer matrix with the piezoelectric ceramic fiber array formed by cutting to obtain a piezoelectric fiber layer. When the direct cutting composite method is used to prepare the piezoelectric fiber layer, the spacing between the piezoelectric fibers can be more accurately controlled by a precision dicing machine, thereby obtaining a high-quality piezoelectric ceramic fiber array, and because of the small thickness, the polymer matrix and the piezoelectric ceramic can be fully in contact during the polymer matrix composite, avoiding the formation of defects such as bubbles or cavities in the polymer matrix. However, the precision dicing machine used in this method is expensive, and this method can only be processed on a single piece, with low efficiency, and is not suitable for batch preparation.

[0005] The cutting and filling method is to use a wire cutter or other cutting equipment to cut out equally spaced glue injection grooves according to the required width of the piezoelectric ceramic fiber in the prepared piezoelectric ceramic block (the piezoelectric ceramic block is not completely cut through during cutting, but a portion is reserved at the bottom for fixing the ceramic array), and then the polymer matrix is ​​poured into the cut glue injection groove. After the polymer matrix is ​​solidified, the composite block of the piezoelectric ceramic and the polymer matrix is ​​cut into thin slices according to the required thickness to obtain the prepared piezoelectric fiber layer. The use of the cutting and filling method to prepare the piezoelectric fiber layer can improve the preparation efficiency and is suitable for mass production. However, when filling the polymer matrix, this method is prone to defects such as bubbles or cavities in the groove due to the small width and deepness of the glue injection groove.

[0006] The cutting and laminating method first cuts the piezoelectric ceramic block into several piezoelectric ceramic sheets of the same specifications according to the required size, then takes a piezoelectric ceramic sheet and evenly applies a thin layer of polymer matrix on its upper surface, and then fits it to the lower surface of another piezoelectric ceramic sheet. After the polymer matrix is ​​solidified, this step is repeated until the required number of piezoelectric ceramic sheets is obtained. Finally, the composite block of piezoelectric ceramic and polymer matrix is ​​cut into sheets according to the required thickness to obtain the prepared piezoelectric fiber layer. The cutting and laminating method can improve the utilization rate of materials and reduce the preparation cost when preparing piezoelectric fiber layers. However, this method is difficult to control the thickness of the polymer matrix between each layer of piezoelectric ceramic sheets, which easily causes uneven thickness of the polymer matrix between each layer of piezoelectric ceramic sheets, and each layer of polymer matrix requires a lot of time to solidify, and the preparation efficiency is low.

[0007] The three relatively mature piezoelectric fiber layer preparation methods mentioned above have their own advantages and disadvantages. Among them, the cutting and filling method is the most widely used due to its low preparation cost and simple operation. However, the traditional cutting and filling method mostly uses the natural flow of the polymer matrix when filling the polymer matrix, which has low filling efficiency and is prone to defects such as bubbles or holes. If the formation of defects such as bubbles or holes can be effectively controlled while improving the filling efficiency of the polymer matrix, its advantages can be further expanded.

[0008] After the piezoelectric fiber layer is prepared, it is encapsulated using an encapsulation film engraved with interdigital electrodes and a polymer matrix, and a piezoelectric fiber composite material is obtained after vacuum pressurization curing. The piezoelectric fiber composite material is welded with positive and negative electrodes and then polarized in an oil bath to obtain a piezoelectric fiber composite material that can produce positive and negative piezoelectric effects. The literature "Xu D, Hu Y, Chen H, et al. Fabrication and property of flexible macro fiber composites for vibration-based energy harvesting [J]. Ceramics International, 2023, 49 (9): 14291-14301." and the patent "201910010496.3" introduce a hot pressing packaging method for piezoelectric fiber composites.

[0009] In summary, the traditional cutting and filling method for preparing piezoelectric fiber layers, when pouring the polymer matrix, due to the small width and deep groove of the injection groove and the poor fluidity of the polymer matrix, it is easy to form defects such as bubbles or holes in the groove, which seriously affects the intensity of the polarization electric field that can be applied when the piezoelectric fiber composite material is polarized after the subsequent packaging is completed, resulting in low preparation yield and poor performance.

[0010] When the piezoelectric fiber layer is encapsulated using a packaging film engraved with interdigitated electrodes and a polymer matrix, stress is generated inside the prepared piezoelectric fiber composite material when the polymer matrix is ​​solidified, causing the prepared piezoelectric fiber composite material to bend. This phenomenon has a significant impact on the quality of the piezoelectric fiber composite material. Summary of the invention

[0011] The present invention provides a method for preparing a piezoelectric fiber layer and a piezoelectric fiber composite material. The method can effectively reduce the formation of defects such as bubbles or holes in the piezoelectric fiber layer while improving the filling efficiency of the polymer matrix, and can ensure that the prepared piezoelectric fiber composite material is flat and has no bends.

[0012] The technical scheme adopted by the present invention is as follows: a method for preparing a piezoelectric fiber layer and a piezoelectric fiber composite material, using a polymer matrix filling device to inject glue into a piezoelectric ceramic with a glue injection groove; the polymer matrix filling device injects glue from one end of the piezoelectric ceramic with the glue injection groove, controls the glue injection pressure and the glue injection flow rate until the polymer matrix flows out from the other end of the piezoelectric ceramic; after the volume of the polymer matrix flowing out is 2 to 3 times the total volume of the glue injection groove, the glue injection is completed; after vacuum curing, a composite block of piezoelectric ceramic and polymer matrix is ​​obtained, and sliced ​​according to a set thickness to obtain a piezoelectric fiber layer; the piezoelectric fiber layer is bonded between two packaging films engraved with interdigital electrodes, and the whole is placed between cover plates coated with lubricating oil, and the piezoelectric fiber composite material is obtained after vacuum pressurization curing.

[0013] The injection pressure is controlled between 0.025MPa and 0.075MPa.

[0014] The injection flow rate is controlled between 1 ml / min and 7.5 ml / min.

[0015] The polymer matrix filling device includes: an air compressor, an air intake pipe 4, a gas throttle valve 5, a glue storage tank 3, a glue injection pipe 7 and a glue injection nozzle 9; the air compressor is connected to one end of the glue storage tank 3 through the air intake pipe 4; the gas throttle valve 5 is arranged on the air intake pipe 4 to throttle and adjust the pressure; the polymer matrix is ​​stored in the glue storage tank 3; the other end of the glue storage tank 3 is connected to the glue injection nozzle 9 through the glue injection pipe 7; the glue injection nozzle 9 is inserted into one end face of the piezoelectric ceramic with a glue injection groove for glue injection.

[0016] The glue injection nozzle 9 is open at both ends. One end is a circular glue injection port connected to the glue injection tube 7, and its inner diameter is larger than the outer diameter of the glue injection tube 7. The other end is a square glue outlet connected to the piezoelectric ceramic, and its size is larger than the width and thickness of the piezoelectric ceramic. The interior of the glue injection nozzle 9 is a cavity with a gradient change.

[0017] The polymer matrix is ​​mixed evenly and squeezed into the glue storage tank 3, which is placed in a vacuum drying oven and evacuated to 0.04Mpa-0.06Mpa to remove bubbles for 10-15 minutes. The polymer matrix is ​​DP460 epoxy resin or other epoxy resin-based materials. The glue storage tank 3 after the bubbles are removed is used for glue injection.

[0018] During the vacuum curing, the piezoelectric ceramic after the injection is placed on the polymer matrix curing device, and placed in a vacuum oven and evacuated to 0.04Mpa-0.06Mpa. The polymer matrix curing temperature is 20°C-80°C, and the curing time is 3 hours-24 hours.

[0019] The vacuum pressure curing is pressurized to 6Mpa-12MPa, evacuated to 0.04Mpa-0.06Mpa, the curing temperature is 20°C-80°C, and the curing time is 3 hours-24 hours.

[0020] The piezoelectric fiber composite material is welded with positive and negative electrodes and then polarized in an oil bath to obtain a piezoelectric fiber composite material that produces positive and negative piezoelectric effects.

[0021] The polarization medium of the oil bath polarization is silicone oil, the polarization electric field is between 1.00 kV / mm and 2.77 kV / mm, the polarization time is between 10 min and 30 min, and the polarization temperature is between 20° C. and 80° C.

[0022] Furthermore, the cover plate may be a PU plate.

[0023] The beneficial effects of the present invention are as follows: when the present invention is used to prepare piezoelectric fiber layers and piezoelectric fiber composite materials, the operation is simple, the equipment cost is low, the degree of automation is high, the preparation efficiency is high, the prepared piezoelectric fiber layer has few defects such as bubbles or holes, the prepared piezoelectric fiber composite material is flat and has no bending, and the piezoelectric fiber layer is tightly fitted to the packaging film engraved with interdigitated electrodes. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the polymer matrix filling device designed in the present invention;

[0025] Figure 2 It is a schematic diagram of the polymer matrix curing device designed in the present invention;

[0026] Figure 3 is a flow chart for preparing the piezoelectric fiber layer in the present invention;

[0027] Figure 4 It is a structural schematic diagram of the glue injection nozzle designed in the present invention;

[0028] Figure 5 A partial enlarged view of the piezoelectric fiber layer prepared by the present invention;

[0029] Figure 6 It is a partial enlarged view of the piezoelectric fiber layer prepared in Comparative Example 1;

[0030] Figure 7 This is a partial enlarged view of the piezoelectric fiber layer prepared in Comparative Example 2 where the injection flow rate is too high.

[0031] Explanation of the reference numbers: 1-glue injection base; 2-piezoelectric ceramic; 3-glue storage tank; 4-intake pipe; 5-gas throttle valve; 6-glue storage tank bracket; 7-glue injection hose; 8-horizontal base; 9-glue injection nozzle; 10-rubber band; 11-UV film. DETAILED DESCRIPTION

[0032] The present invention provides a method for preparing a piezoelectric fiber layer and a piezoelectric fiber composite material. The method can effectively reduce the formation of defects such as bubbles or holes in the piezoelectric fiber layer while improving the filling efficiency of the polymer matrix, and can ensure that the prepared piezoelectric fiber composite material is flat and has no bends.

[0033] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] A method for preparing a piezoelectric fiber layer and a piezoelectric fiber composite material, comprising:

[0035] Use a wire cutting machine to cut out equally spaced glue injection grooves from the piezoelectric ceramic 2 (the bottom of the piezoelectric ceramic is not completely cut through), and after cutting, place the piezoelectric ceramic in an ultrasonic cleaning machine to clean the piezoelectric ceramic debris, thereby obtaining a piezoelectric ceramic with glue injection grooves;

[0036] Paste the UV film 11 on the upper surface of the piezoelectric ceramic with the glue injection groove to seal the upper surface. Note that the upper surface should not be completely sealed. The length of the UV film 11 is slightly smaller than the length of the piezoelectric ceramic with the glue injection groove, in order to facilitate the discharge of bubbles during the later vacuuming.

[0037] The glue injection nozzle 9 is designed according to the size of the piezoelectric ceramic to be injected with glue. Both ends of the glue injection nozzle 9 are open. One end is a circular glue injection port whose inner diameter is slightly larger than the outer diameter of the glue injection tube 7 used. The other end is a square glue outlet whose size is slightly larger than the width and thickness of the piezoelectric ceramic 2. The inside of the glue injection nozzle 9 is a cavity with a gradient change. The glue injection nozzle 9 can be made by 3D printing equipment or machine tool turning. The material of the glue injection nozzle 9 is plastic or metal, and the glue injection tube 7 is a plastic round tube.

[0038] After the polymer matrix is ​​mixed evenly, it is squeezed into the glue storage tank 3, and the glue storage tank 3 containing the polymer matrix is ​​placed in a vacuum drying oven and evacuated to 0.04Mpa~0.06Mpa to remove bubbles for 10~15 minutes. The polymer matrix is ​​DP460 epoxy resin or other epoxy resin-based materials; the injection pressure is controlled between 0.025MPa~0.075MPa according to the injection amount, DP460 curing time and bubble amount; the injection flow rate is 1ml / min~7.5ml / min. When the injection pressure is less than 0.025MPa or the injection flow rate is less than 1ml / min, the injection flow rate will be too slow to meet the preparation efficiency requirements. At the same time, the fluidity and adhesion will deteriorate due to the curing of the glue, resulting in the glue and piezoelectric ceramics not being tightly adhered. When the injection pressure is greater than 0.075MPa, the glue will flow too fast, resulting in bubbles, glue overflow, glue leakage and other problems. When the injection flow rate is greater than 7.5ml / min, the glue flows too fast and cannot fully infiltrate the piezoelectric ceramics, resulting in incomplete filling and glue breaking.

[0039] After removing the bubbles, use the glue injection tube 7 to connect the glue storage tank 3 with the glue injection port of the glue injection nozzle 9, insert the rear end face of the piezoelectric ceramic with the glue injection groove pasted with the UV film 11 into the glue outlet of the glue injection nozzle 9, and use glue to seal the connection. After the sealing is completed, insert the glue injection nozzle 9 into the card slot of the glue injection base 1, so that the piezoelectric ceramic is tilted upward at a certain angle to facilitate the control of the flow rate during the subsequent glue injection;

[0040] The other end of the glue storage tank 3 is connected to the gas throttle valve 5 through the air intake pipe 4, and the gas throttle valve 5 is connected to the air compressor through the air intake pipe 4. The air compressor is started and the gas throttle valve 5 is slowly adjusted so that the polymer matrix is ​​gradually filled into the glue injection groove of the piezoelectric ceramic with the glue injection groove attached with the UV film 11;

[0041] After the polymer matrix flows out from the front end face of the piezoelectric ceramic with the injection groove attached with the UV film, the injection is continued. After the polymer matrix flows out for a period of time, until the volume of the polymer matrix flowing out is 2 to 3 times the total volume of the injection groove, the gas throttle valve and the air compressor are closed in turn. After the polymer matrix is ​​filled, the front end face is sealed with the UV film 11 and the injection tube 7 is pulled out from the injection port of the injection nozzle 9.

[0042] The piezoelectric ceramic with a glue injection groove and a UV film 11 pasted thereon after being filled with a polymer matrix is ​​placed together with a glue injection nozzle 9 in a horizontal base 8, one end of the glue injection nozzle with a glue injection port is placed in the slot of the horizontal base 8, and is fixed with a rubber band 10 to form a polymer matrix curing device;

[0043] After the fixation is completed, the polymer matrix curing device is placed in a vacuum drying oven to perform vacuum curing of the polymer matrix;

[0044] During vacuum curing, the vacuum drying oven is evacuated to 0.04Mpa-0.06Mpa, the curing temperature of the polymer matrix is ​​20°C-80°C, and the curing time is continuously adjustable between 3 hours and 24 hours according to the curing temperature. After the vacuum curing is completed, the rubber band 10 is removed and the horizontal base 8 is removed;

[0045] Use a wire cutter to cut off the glue injection nozzle 9 along the edge of the glue outlet;

[0046] After irradiating all previously pasted UV films 11 with an ultraviolet lamp, all pasted UV films are removed;

[0047] Use a blade to scrape off excess polymer matrix to obtain a composite block of piezoelectric ceramic and polymer matrix;

[0048] The composite block of piezoelectric ceramics and polymer matrix is ​​fixed on a wire cutting machine and cut into thin slices according to a required thickness to obtain a prepared piezoelectric fiber layer.

[0049] A thin layer of polymer matrix is ​​evenly applied on the packaging film engraved with interdigital electrodes, and then the piezoelectric fiber layer is pasted on the packaging film engraved with interdigital electrodes (note that the fiber length direction of the piezoelectric fiber layer is as perpendicular as possible to the length direction of the interdigital electrodes). After pasting, it is placed between two PU boards and vacuum pressurized and pre-cured using a small press and a vacuum drying oven;

[0050] During pre-curing, the small press is pressurized to 6Mpa~12MPa, and the vacuum drying oven is evacuated to 0.04Mpa~0.06Mpa during pre-curing. Pre-curing is carried out for 30 minutes at 20℃;

[0051] The material of the interdigital electrodes is copper, and the encapsulation film is polyimide film;

[0052] Use a puncher to punch holes in another packaging film engraved with interdigital electrodes for subsequent welding of positive and negative electrode wires, then evenly apply a thin layer of polymer matrix, and align and bond it with the previous packaging film engraved with interdigital electrodes that has been pre-cured. During the bonding process, the piezoelectric fiber layer is wrapped between the two, and the interdigital electrodes on the two packaging films should be aligned as much as possible. After the bonding is completed, it is placed between two PU plates coated with an appropriate amount of lubricating oil and vacuum pressurized and cured using a small press and a vacuum drying oven to obtain a piezoelectric fiber composite material;

[0053] During vacuum pressurization curing, the small press is pressurized to 6Mpa~12MPa. A proper amount of lubricating oil should be applied between the PU plates during pressurization. The vacuum drying oven is evacuated to 0.04Mpa~0.06Mpa. The curing time can be continuously adjusted between 3 hours and 24 hours according to the curing temperature (20℃~80℃);

[0054] Positive and negative electrode wires are respectively welded at the punched holes of the piezoelectric fiber composite material, and then the piezoelectric fiber composite material is subjected to oil bath polarization.

[0055] The polarization medium is silicone oil, the polarization electric field is 1.00 kV / mm to 2.77 kV / mm, the polarization time is 10 min to 30 min, and the polarization temperature is 20° C. to 80° C.

[0056] Example

[0057] like Figures 1 to 6 As shown, the method for preparing the piezoelectric fiber layer and the piezoelectric fiber composite material provided by the present invention comprises the following steps:

[0058] Step 1: Fix a piezoelectric ceramic block with a length, width and thickness of 85mm×28mm×5mm on a wire cutting machine, wherein the length direction of the piezoelectric ceramic block is parallel to the cutting sand line with a diameter of 0.2mm of the wire cutting machine, and the width direction of the piezoelectric ceramic block is perpendicular to the cutting sand line with a diameter of 0.2mm of the wire cutting machine. Feed the knife along the thickness direction of the piezoelectric ceramic block, cut a 4mm deep glue injection groove, and then withdraw the cutting sand line to the initial cutting point. Then move the cutting sand line 0.6mm along the width direction of the piezoelectric ceramic block, and then repeat step 1 until 46 glue injection grooves are cut. After the glue injection grooves are cut, put the piezoelectric ceramic block with the glue injection grooves into an ultrasonic cleaning machine to clean the piezoelectric ceramic debris;

[0059] Step 2: Cut out a UV film with a length of 82 mm and a width of 35 mm, respectively, for sealing the upper surface of the piezoelectric ceramic with the glue injection groove. The UV film reserves a 3 mm opening at one end of the front end surface of the piezoelectric ceramic with the glue injection groove for the discharge of bubbles in the polymer matrix during subsequent vacuuming. Cut out a UV film with a length of 35 mm and a width of 10 mm, respectively, for sealing the front end surface of the piezoelectric ceramic with the glue injection groove after the glue injection is completed;

[0060] Step 3: squeeze the mixed DP460 epoxy resin into the glue storage tank, and put the glue storage tank with DP460 epoxy resin into a vacuum drying oven to evacuate to 0.04Mpa~0.06Mpa to remove bubbles for 10~15 minutes;

[0061] Step 4: After removing the bubbles, insert the glue injection tube into the glue injection port of the glue injection nozzle, insert the rear end face of the piezoelectric ceramic with the glue injection groove pasted with the UV film into the glue outlet of the glue injection nozzle, and use 502 glue to seal the connection of the glue outlet of the glue injection nozzle. Figure 4 As shown, the air compressor is then started and the gas throttle valve is adjusted so that the DP460 epoxy resin is gradually filled into the glue injection groove of the piezoelectric ceramic with the glue injection groove attached with the UV film through the glue injection nozzle. After the DP460 epoxy resin flows out from the front end surface of the piezoelectric ceramic with the glue injection groove attached with the UV film, the glue injection is continued. After the DP460 epoxy resin flows out from the front end surface for a period of time, the gas throttle valve and the air compressor are closed in sequence. After the DP460 epoxy resin is filled, the gas throttle valve and the air compressor are closed in sequence. After that, the UV film with a length and width of 35 mm and 10 mm cut previously is used to seal the front end surface and the glue injection tube is pulled out from the glue injection port of the glue injection nozzle.

[0062] Step 5: Place the piezoelectric ceramic with the glue injection groove and the UV film after filling with DP460 epoxy resin together with the glue injection nozzle in the horizontal base 8, wherein one end of the glue injection nozzle with the glue injection port is placed in the slot of the horizontal base 8, and use a rubber band 10 to fix the piezoelectric ceramic with the glue injection groove and the UV film after filling with DP460 epoxy resin, the glue injection nozzle and the horizontal base 8 to form a polymer matrix curing device, such as Figure 2 As shown;

[0063] Step 6: Place the fixed polymer matrix curing device into a vacuum drying oven, close the door and evacuate to 0.04Mpa to 0.06Mpa. The curing time can be continuously adjusted between 3 hours and 24 hours according to the curing temperature (20°C to 80°C);

[0064] Step 7: After curing is completed, the polymer matrix curing device is taken out from the vacuum drying oven, and the rubber band 10 is removed, the horizontal base 8 is removed, and then the glue injection nozzle is cut off along the edge of the glue outlet of the glue injection nozzle using a wire cutting machine;

[0065] Step 8: Use an ultraviolet lamp to irradiate the UV film on the upper surface and the front end of the piezoelectric ceramic for 5 minutes, then remove the UV film and use a blade to gently scrape off the excess DP460 epoxy resin on the surface;

[0066] Step 9: Use 502 glue to glue the lower surface of the composite block of piezoelectric ceramics and DP460 epoxy resin to the rotating platform of the wire cutting machine, and cut the composite block of piezoelectric ceramics and DP460 epoxy resin into several thin slices with a thickness of 0.2 mm. Repeat this process several times to obtain several prepared piezoelectric fiber layers;

[0067] Step 10: Evenly apply a thin layer of DP460 epoxy resin on the polyimide film engraved with interdigital electrodes, and then paste the piezoelectric fiber layer on the polyimide film engraved with interdigital electrodes (note that the fiber length direction of the piezoelectric fiber layer should be as perpendicular as possible to the length direction of the interdigital electrodes). After pasting, place it between two PU boards and use a small press (pressurized to 6Mpa~12MPa) and a vacuum drying oven (vacuumed to 0.04Mpa~0.06Mpa) to pre-cure for 30 minutes under vacuum pressure at 20°C;

[0068] Step 11: Use a puncher to punch holes in another polyimide film engraved with interdigital electrodes for subsequent welding of positive and negative wires, then evenly apply a thin layer of DP460 epoxy resin, and align and bond it with the pre-cured previous polyimide film engraved with interdigital electrodes. During the bonding process, the piezoelectric fiber layer is wrapped between the two, and the interdigital electrodes on the two polyimide films should be aligned as much as possible. After bonding, place it between two PU boards coated with an appropriate amount of lubricating oil and use a small press (pressurized to 6Mpa~12MPa) and a vacuum drying oven (evacuated to 0.04Mpa~0.06Mpa) for vacuum pressure curing. The curing time is continuously adjustable between 3 hours and 24 hours according to the curing temperature (20℃~80℃), and a piezoelectric fiber composite material is obtained;

[0069] Step 12: Weld the positive and negative wires at the punched holes of the piezoelectric fiber composite material respectively, and perform oil bath polarization on it, wherein: the polarization medium is silicone oil, the polarization electric field is 1.00kV / mm~2.77kV / mm, the polarization time is 10min~30min, and the polarization temperature is 20℃~80℃.

[0070] The piezoelectric fiber layer prepared by this method was observed by optical microscope. Figure 5 As shown. The DP460 epoxy resin is completely filled into the injection groove, and no cavities or a large number of bubbles are generated. It is observed that the piezoelectric fiber composite material prepared by this method is flat, without bending or bubbles, and the piezoelectric fiber layer and the polyimide film engraved with interdigital electrodes are tightly attached.

[0071] Furthermore, the polymer matrix filling device includes: using an air compressor as an air source, and after throttling and regulating the pressure through a gas throttle valve, using compressed gas to push the polymer matrix in the glue storage tank through a special glue injection nozzle to inject into the glue injection groove of the piezoelectric ceramic; using a horizontal base 8 and a rubber band 10 to fix the piezoelectric ceramic with the glue injection groove after filling the polymer matrix, to form a polymer matrix curing device; placing the polymer matrix curing device in a vacuum drying oven to perform vacuum curing of the polymer matrix; after curing, using a wire cutter to cut off the glue injection nozzle along the edge of the glue injection nozzle to obtain a composite block of piezoelectric ceramics and polymer matrix; using a wire cutter to slice the composite block of piezoelectric ceramics and polymer matrix to obtain a piezoelectric fiber layer. When filling the polymer matrix, the filling rate of the polymer matrix is ​​controlled by adjusting the knob of the gas throttle valve, and the filling is stopped after the polymer matrix flows out from the front end of the piezoelectric ceramic for a period of time, so as to reduce the probability of holes and bubbles appearing in the prepared piezoelectric fiber layer.

[0072] Furthermore, the piezoelectric ceramic is a PZT-based piezoelectric ceramic.

[0073] Furthermore, the width of the glue injection groove is continuously adjustable between 0.18 mm and 0.99 mm, and the groove spacing is continuously adjustable between 0.20 mm and 1.00 mm.

[0074] Furthermore, the UV film has a backing adhesive, and the size is adjusted according to the size of the piezoelectric ceramic.

[0075] Furthermore, the glue injection nozzle is specially designed with openings at both ends. One end is a circular glue injection port with an inner diameter slightly larger than the outer diameter of the glue injection tube used, and the other end is a square glue outlet with a size slightly larger than the width and thickness of the piezoelectric ceramic used. The interior of the glue injection nozzle is a gradient-changing cavity. The glue injection nozzle can be made using 3D printing equipment or machine tool turning, and the material is plastic or metal.

[0076] Furthermore, the polymer matrix is ​​an epoxy resin-based material.

[0077] The method for preparing the piezoelectric fiber layer proposed in the present invention is characterized in that the horizontal base 8 is made of plastic and has a slot matching the glue injection nozzle. After filling the polymer matrix, the piezoelectric ceramic with a glue injection slot pasted with a UV film, the horizontal base 8, the glue injection nozzle and the rubber band 10 together constitute a polymer matrix curing device.

[0078] Furthermore, when the composite block of the piezoelectric ceramic and the polymer matrix is ​​sliced, the thickness of the piezoelectric fiber layer is continuously adjustable between 0.16 mm and 0.50 mm.

[0079] Furthermore, the material of the interdigitated electrode is metal such as copper, the finger width is continuously adjustable between 0.10 mm and 0.20 mm, the finger spacing is continuously adjustable between 0.50 mm and 0.80 mm, and the electrode thickness is continuously adjustable between 0.015 mm and 0.020 mm.

[0080] Furthermore, the packaging film is made of materials such as polyimide, polyamide 6, polyetheretherketone, etc., and its thickness is continuously adjustable between 0.02mm and 0.08mm.

[0081] In the preparation method proposed in the present invention, the piezoelectric fiber composite material is placed between PU plates coated with an appropriate amount of lubricating oil during vacuum pressure curing. The role of the lubricating oil is to provide a small activity space for the piezoelectric fiber composite material during curing to release the stress generated by the curing of the polymer matrix, so as to ensure that the prepared piezoelectric fiber composite material is flat and has no bends.

[0082] The glue injection method uses an air compressor and a gas throttle valve to provide compressed gas with adjustable pressure and flow to slowly push the polymer matrix in the glue storage tank through the glue injection nozzle and gradually fill it into the piezoelectric ceramic glue injection groove. This can effectively reduce the problem of defects such as bubbles or holes formed in the glue injection groove and can improve the filling efficiency of the polymer matrix, laying the foundation for the large-scale preparation of piezoelectric fiber layers.

[0083] The prepared piezoelectric fiber layer is vacuum-pressurized and packaged using a packaging film engraved with interdigital electrodes and a polymer matrix. The uncured piezoelectric fiber composite material is placed between two PU plates coated with an appropriate amount of lubricating oil and then pressurized and vacuum-cured. This method can make the prepared piezoelectric fiber composite material flat and without bending.

[0084] The method for preparing the piezoelectric fiber layer and the piezoelectric fiber composite material provided by the present invention is simple to operate, the required equipment cost is low, the degree of automation is high, the preparation efficiency is high, and defects such as bubbles or holes caused by various factors during the filling of the polymer matrix can be effectively controlled. The prepared piezoelectric fiber composite material is flat, without bending or bubbles, and the piezoelectric fiber layer is tightly attached to the packaging film engraved with interdigitated electrodes, which saves preparation costs and can effectively improve production efficiency and preparation yield.

[0085] Comparative Example 1:

[0086] When filling the polymer matrix, the glue is injected by hand-pushing the syringe. Since the speed and thrust of the syringe cannot be evenly controlled, the polymer matrix is ​​filled fast or slow, resulting in the polymer matrix being unable to fully infiltrate the piezoelectric ceramics, and a large number of bubbles and cavities are generated in the glue injection groove, such as Figure 6 shown.

[0087] Comparative Example 2:

[0088] When using the polymer matrix filling device for glue injection, the pressure of the compressed gas should be controlled between 0.025 and 0.075 MPa. When the pressure is less than 0.025 MPa, the polymer matrix cannot be filled normally. When the pressure is greater than 0.075 MPa, the polymer matrix is ​​likely to burst the UV pasted and overflow. The injection flow rate should be controlled at about 3 ml / min to ensure that the polymer matrix fully infiltrates the piezoelectric ceramics, and stop injecting glue after the polymer matrix flows out of the front end of the piezoelectric ceramics by 2 to 3 times the total volume of the injection groove, so as to fully reduce the amount of cavities or bubbles in the injection groove. According to the operation time of DP460, the injection flow rate should be greater than 1 ml / min, otherwise the glue will be difficult to inject and the adhesion will deteriorate due to the curing of the glue. When the injection flow rate is greater than 7.5 ml / min, the glue flows too fast and cannot fully infiltrate the piezoelectric ceramics, which will lead to incomplete filling and glue breaking. Figure 7 shown.

[0089] Comparative Example 3:

[0090] When packaging the piezoelectric fiber layer, the piezoelectric fiber layer should be attached between two packaging films with interdigital electrodes, and placed as a whole between PU plates coated with lubricating oil before vacuum pressurization and curing. If an appropriate amount of lubricating oil is not applied, the stress generated during the curing of the polymer matrix will cause the prepared piezoelectric fiber composite material to bend.

Claims

1. A method for preparing a piezoelectric fiber layer and a piezoelectric fiber composite material, characterized in that: A polymer matrix filling device is used to inject glue into a piezoelectric ceramic with a glue injection groove; the polymer matrix filling device injects glue from one end of the piezoelectric ceramic with the glue injection groove, and controls the injection pressure and the injection flow rate until the polymer matrix flows out from the other end of the piezoelectric ceramic; after the volume of the polymer matrix flowing out is 2 to 3 times the total volume of the glue injection groove, the injection is completed; after vacuum curing, a composite block of the piezoelectric ceramic and the polymer matrix is ​​obtained, and sliced ​​according to a set thickness to obtain a piezoelectric fiber layer; the piezoelectric fiber layer is bonded between two packaging films engraved with interdigital electrodes, and the whole is placed between cover plates coated with lubricating oil, and a piezoelectric fiber composite material is obtained after vacuum pressurization curing.

2. The method for preparing the piezoelectric fiber layer and the piezoelectric fiber composite material according to claim 1, characterized in that: The injection pressure is controlled between 0.025MPa and 0.075MPa.

3. The method for preparing the piezoelectric fiber layer and the piezoelectric fiber composite material according to claim 1, characterized in that: The injection flow rate is controlled between 1 ml / min and 7.5 ml / min.

4. The method for preparing the piezoelectric fiber layer and the piezoelectric fiber composite material according to claim 1, characterized in that: The polymer matrix filling device comprises: an air compressor, an air intake pipe (4), a gas throttle valve (5), a glue storage tank (3), a glue injection pipe (7) and a glue injection nozzle (9); the air compressor is connected to one end of the glue storage tank (3) via the air intake pipe (4); the air intake pipe (4) is provided with a gas throttle valve (5) for throttling and regulating pressure; the polymer matrix is ​​stored in the glue storage tank (3); the other end of the glue storage tank (3) is connected to the glue injection nozzle via the glue injection pipe (7); the glue injection nozzle is inserted into one end face of a piezoelectric ceramic with a glue injection groove for glue injection.

5. The method for preparing the piezoelectric fiber layer and the piezoelectric fiber composite material according to claim 4, characterized in that: The glue injection nozzle is open at both ends, one end is a circular glue injection port connected to the glue injection tube (7), and its inner diameter is larger than the outer diameter of the glue injection tube (7), and the other end is a square glue outlet connected to the piezoelectric ceramic, and its size is larger than the width and thickness of the piezoelectric ceramic; the interior of the glue injection nozzle is a cavity with a gradient change.

6. The method for preparing the piezoelectric fiber layer and the piezoelectric fiber composite material according to claim 5, characterized in that: The polymer matrix is ​​mixed evenly and squeezed into a glue storage tank (3). The glue storage tank (3) is placed in a vacuum drying oven and evacuated to 0.04Mpa-0.06Mpa to remove bubbles for 10-15 minutes. The polymer matrix is ​​DP460 epoxy resin or other epoxy resin-based materials. The glue storage tank (3) after the bubbles are removed is used for glue injection.

7. The method for preparing a piezoelectric fiber layer and a piezoelectric fiber composite material according to claim 1, characterized in that: During the vacuum curing, the piezoelectric ceramic after the injection is placed on the polymer matrix curing device, and placed in a vacuum oven and evacuated to 0.04Mpa-0.06Mpa. The polymer matrix curing temperature is 20°C-80°C, and the curing time is 3 hours-24 hours.

8. The method for preparing a piezoelectric fiber layer and a piezoelectric fiber composite material according to claim 1, characterized in that: The vacuum pressure curing is pressurized to 6Mpa-12MPa, evacuated to 0.04Mpa-0.06Mpa, the curing temperature is 20°C-80°C, and the curing time is 3 hours-24 hours.

9. The method for preparing a piezoelectric fiber layer and a piezoelectric fiber composite material according to claim 1, characterized in that: The piezoelectric fiber composite material is welded with positive and negative electrodes and then polarized in an oil bath to obtain a piezoelectric fiber composite material that produces positive and negative piezoelectric effects.

10. The method for preparing the piezoelectric fiber layer and the piezoelectric fiber composite material according to claim 9, characterized in that: The polarization medium of the oil bath polarization is silicone oil, the polarization electric field is between 1.00 kV / mm and 2.77 kV / mm, the polarization time is between 10 min and 30 min, and the polarization temperature is between 20° C. and 80° C.

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