Method for preparing PVDF (Polyvinylidene Fluoride)-based piezoelectric product based on reverse chain relaxation micro injection molding process

Abstract

The invention provides a method for preparing a PVDF (Polyvinylidene Fluoride)-based piezoelectric product based on a reverse chain relaxation micro injection molding process, which comprises the following steps of: melting and blending 94-98.5 parts by weight of PVDF, 1-5 parts by weight of ionic liquid and 0.5-1 part by weight of one-dimensional / two-dimensional carbon series conductive filler to prepare a polyvinylidene fluoride-based composite material, then injecting the polyvinylidene fluoride-based composite material into a mold of the required piezoelectric product in a micro injection molding machine, and finally obtaining the PVDF-based piezoelectric product based on the reverse chain relaxation micro injection molding process. And performing micro injection molding to obtain the PVDF-based piezoelectric product. According to the method, orientation of PVDF molecular chains is promoted by utilizing a strong shear force field involved in a micro injection molding process, and an ionic liquid is introduced to induce formation of PVDF piezoelectric polar crystals and inhibit local thermal relaxation behaviors of the PVDF molecular chains, so that the purpose of greatly reducing the PVDF chain relaxation phenomenon is achieved, formation of a highly-oriented beta polar phase is facilitated, and the performance of the PVDF piezoelectric film is improved. And the piezoelectric property of the PVDF-based piezoelectric device is remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparing micro injection molding piezoelectric devices, and relates to a method for preparing PVDF-based piezoelectric products based on an anti-chain relaxation micro injection molding process, which is mainly used in the fields of sensors and self-powered equipment. Background Art

[0002] With the rapid development of Internet of Things (IoT) technology, society has an increasing demand for smart devices, wearable devices and micro sensors. In order to achieve the miniaturization, convenience and high performance of these devices, micro piezoelectric devices, as a technology that can efficiently convert mechanical energy into electrical energy, have gradually become an important direction in the field of energy collection and sensing.

[0003] Piezoelectric materials, especially polyvinylidene fluoride (PVDF), are widely used in various piezoelectric devices due to their excellent piezoelectric properties, good processability, flexibility and cost-effectiveness. PVDF piezoelectric devices can generate electrical signals through external mechanical strain (such as pressure and vibration), so they are widely used in energy harvesting, sensors and micro-actuators. However, the current commercial PVDF-based piezoelectric materials still have certain limitations in piezoelectric performance, especially in self-powered devices. Existing PVDF materials are difficult to meet the requirements of efficient energy harvesting and high-sensitivity detection.

[0004] In addition, although traditional processing methods can prepare PVDF piezoelectric films, they still face many challenges in the production of high-performance piezoelectric devices, especially in how to maintain the orientation of molecular chains and improve piezoelectric performance. Further breakthroughs are needed. The piezoelectric properties of PVDF originate from its electroactive phase, which is the result of dipole orientation in the crystal region. Specifically, the current manufacture of commercial piezoelectric PVDF devices includes two key steps. The first step is to expand the molecular chain and induce the transformation of non-polar crystals to polar crystals using mechanical stretching technology at 110°C. The processing temperature at this stage is significantly lower than the melting point of PVDF (170°C), and its purpose is to significantly reduce the energy of the system to inhibit chain relaxation. Another key step is to place the material in an ultra-high electric field to cause the dipoles to rotate around the axis, thereby achieving a non-zero macroscopic dipole moment.

[0005] Although PVDF has excellent thermoplastic processing properties, it is difficult to prepare piezoelectric PVDF materials with a high content of oriented β-polar crystals by conventional melt processing methods. This challenge stems from the complex interaction between molecular chain orientation and chain relaxation in PVDF materials. When the processing temperature exceeds the melting point of PVDF and there is a lack of a strong shear field, the molecular chains tend to relax and return to a thermodynamically stable random curled configuration. However, the above problems are obviously unfavorable when preparing high-performance PVDF-based piezoelectric devices. Even in the presence of polar crystal-inducing modifiers, the all-trans molecular chains of PVDF become disordered, resulting in the mutual cancellation of dipoles formed by polar crystals. Therefore, applying an external field to offset chain relaxation during thermoplastic processing is crucial to maintain a non-zero dipole moment. In order to overcome these problems, in recent years, micro-injection molding processing technology has become an effective way to address these challenges based on its extremely strong shear force field and precise microstructure molding capabilities.

[0006] At present, although some studies have improved the performance of PVDF piezoelectric devices through micro-injection molding technology, how to further optimize the manufacturing process, improve the piezoelectric properties of the material, and achieve efficient and low-cost mass production are still urgent problems to be solved. Therefore, if there is a PVDF-based micro-injection molding process technology solution that can take into account both high piezoelectric performance and facilitate industrial implementation and transformation, it will greatly facilitate the industrial implementation of related technologies and have a better market prospect. Summary of the invention

[0007] In order to solve the problems in the background technology, the present invention provides a method for preparing PVDF-based piezoelectric products based on the reverse chain relaxation micro-injection molding process. The method utilizes the strong shear force field involved in the micro-injection molding process to promote the orientation of PVDF molecular chains, combined with the introduction of ionic liquids to induce the formation of PVDF piezoelectric polar crystals and inhibit the local thermal relaxation behavior of PVDF molecular chains, thereby achieving the purpose of greatly reducing the PVDF chain relaxation phenomenon, which is conducive to the formation of a highly oriented β-polar phase and significantly improves the piezoelectric properties of PVDF-based piezoelectric devices.

[0008] To achieve the above-mentioned purpose, the present invention is implemented by adopting a technical solution consisting of the following technical measures.

[0009] A method for preparing a PVDF-based piezoelectric product based on a reverse chain relaxation micro-injection molding process, which mainly comprises the following steps:

[0010] (1) Prepare the following raw materials by weight:

[0011] Polyvinylidene fluoride (PVDF) 94-98.5 parts,

[0012] 1 to 5 parts of ionic liquid,

[0013] One-dimensional / two-dimensional carbon conductive filler 0.5-1 part,

[0014] The polyvinylidene fluoride, ionic liquid and one-dimensional / two-dimensional carbon conductive filler are 100 parts in total;

[0015] The ionic liquid is selected from any one of 1-ethyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-benzyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium tetrafluoroborate, and 1-alkyl-3-methylimidazolium tetrafluoroborate;

[0016] (2) preparing a polyvinylidene fluoride composite material by melt blending the raw materials of each component prepared in step (1);

[0017] (3) injecting the polyvinylidene fluoride composite material obtained in step (2) into a mold of a desired piezoelectric product in a micro injection molding machine, and preparing a PVDF-based piezoelectric product by micro injection molding;

[0018] The process conditions of micro injection molding are as follows: injection speed 50-600 mm / s, mold temperature 30-90° C., melt temperature 180-210° C., holding pressure and cooling time 5-15 s.

[0019] In this article, the Chinese name of the PVDF in step (1) is polyvinylidene fluoride. Those skilled in the art can select a suitable PVDF model according to specific needs, preferably a PVDF model currently commonly used in piezoelectric devices.

[0020] In this article, the one-dimensional / two-dimensional carbon-based conductive filler in step (1) is a one-dimensional / two-dimensional carbon-based material commonly used as a conductive filler in the prior art, such as any one or more of carbon nanotubes, carbon nanofibers, graphene and carbon nanosheets.

[0021] In this article, the raw materials of each component described in step (2) are melt blended to prepare a polyvinylidene fluoride-based composite material. A conventional melt blending process technology known in the art can be selected, which is intended to form a uniformly dispersed mixture of each component in the PVDF matrix, such as using an internal mixer or a screw extruder for melt blending. Because the composite material finally prepared in step (2) needs to be added to a micro injection molding machine in the next step, it is further preferred to be a composite powder / granule form that is convenient for feeding to the micro injection molding machine. Those skilled in the art should know that after melt blending, conventional process means such as crushing / granulation should be used to obtain powder / granule; it should be noted that the specific form of the powder / granule is mainly selected depending on the processable raw material form of the micro injection molding machine. Those skilled in the art can select a suitable composite raw material form according to the instructions for use of the micro injection molding machine used.

[0022] In one of the technical solutions, in order to further enhance the interaction between the ionic liquid and the one-dimensional / two-dimensional carbon-based conductive filler, the raw materials of each component in step (2) are melt-blended to prepare a polyvinylidene fluoride based composite material, specifically, the prepared raw materials of each component are melt-blended in an internal mixer or a twin-screw extruder to prepare a polyvinylidene fluoride based composite material;

[0023] The process parameters for melt blending in an internal mixer or a twin-screw extruder are as follows: temperature of 180-210° C., rotation speed of 50-80 rpm, and cooling after melt blending for 5-10 minutes.

[0024] In one technical solution, in order to facilitate feeding into the micro injection molding machine, the polyvinylidene fluoride based composite material in step (2) is crushed to obtain polyvinylidene fluoride based composite powder with an average particle size of 0.1 to 0.2 mm. The crushing method is a conventional process in the art, such as a mechanical crusher, a jet mill, a low temperature mill, etc.

[0025] In this article, the PVDF-based piezoelectric product prepared by micro injection molding in step (3) can be prepared by different molds to obtain different piezoelectric products, such as a circular piezoelectric sheet for preparing a micro piezoelectric generator.

[0026] The main inventive point of the present invention is that the reverse chain relaxation micro-injection molding process is used for the first time to prepare PVDF-based piezoelectric products, and the strong shear force field involved in the micro-injection molding process is used to promote the directional arrangement of PVDF molecular chains. The ionic liquid is introduced to induce the formation of PVDF piezoelectric polar crystals while suppressing the local thermal relaxation behavior of PVDF molecular chains, thereby achieving the purpose of greatly reducing the relaxation phenomenon of PVDF chains, which is conducive to the formation of highly oriented β-polar phases and significantly improving the piezoelectric properties of PVDF-based piezoelectric products. If only carbon-based conductive fillers are added to the PVDF matrix, the polar crystal content of the PVDF piezoelectric products prepared by the micro-injection molding process is limited (about 40-50%); and the ionic liquid introduced in addition can induce the formation of PVDF piezoelectric polar crystals and suppress the local thermal relaxation behavior of PVDF molecular chains. In addition, the strong shear force field generated by the micro-injection molding process promotes the orientation of PVDF molecular chains, which is conducive to the formation of more efficient polar crystals and string crystal structures. The above factors all make the piezoelectric products prepared by the method of the present invention have significantly higher piezoelectric properties than the piezoelectric products prepared by the conventional melt molding process of the same size.

[0027] It should be noted that although ionic liquids have an impressive synergistic enhancement effect in micro injection molding processes, if ionic liquids are introduced into conventional melt molding processes (such as hot pressing molding), experimental results show that PVDF is easy to crystallize into isotropic polar spherulites, which does not contribute to piezoelectric performance. In addition, the ionic liquid introduced in the present invention mainly relies on a one-dimensional / two-dimensional carbon-based conductive filler uniformly dispersed in the PVDF matrix resin as a template. If a one-dimensional / two-dimensional carbon-based conductive filler is not added, a template oriented with a shear force field cannot be formed, which will greatly limit the orientation arrangement of the dipoles, reduce the macroscopic dipole moment, and thus be detrimental to the piezoelectric output.

[0028] It is important to note that the introduction of one-dimensional / two-dimensional carbon conductive fillers and ionic liquids together can help improve piezoelectric performance, but the amount of addition may affect the mechanical properties of the final product. According to the principle of piezoelectric effect, the effect of fillers on the mechanical properties of the product may also affect the optimal value of the piezoelectric output of the product. Therefore, the filler should be minimized in terms of its effect on the mechanical properties of the product. Based on this, the raw material ratio of each component proposed in the present invention is within the range optimized by comparative experiments.

[0029] The present invention has the following beneficial effects:

[0030] 1. Based on experimental results, the present invention determines the modified formula and micro injection molding process parameters including temperature, shear rate and injection speed to suppress the chain relaxation behavior at high temperature and ensure the high content and stability of the piezoelectric β-polar phase, thereby obtaining a piezoelectric power generation device with optimized performance.

[0031] 2. The technical solution of the present invention is completely suitable for ionic liquid modified PVDF-based composite materials, and has higher piezoelectric performance than piezoelectric products prepared by existing melt processing technology, providing practical process technology conditions for subsequent industrial production. The micro injection molding process also has simpler process steps and easier large-scale industrial production capabilities.

[0032] 3. The PVDF-based piezoelectric product prepared by the micro-injection molding process of the present invention effectively improves the directional arrangement of PVDF molecular chains in the flow direction through the synergistic effect of filler modification and the strong shear force field of micro-injection molding. Compared with PVDF products prepared by conventional melt processing methods, it has anisotropic polar crystal characteristics, and the skewers structure formed by it cannot be achieved by conventional preparation methods.

[0033] 4. The PVDF-based disc-type piezoelectric product prepared by the present invention based on micro injection molding technology has the advantages of simple production process, easy operation, low manufacturing cost, and large-scale continuous production. The whole process does not require post-processing of the product or additional process conditions, and is suitable for industrial transformation. The micro injection-molded disc-type piezoelectric product involved in the present invention can be used in the preparation of piezoelectric generator devices, and has application potential in the fields of piezoelectric sensing and energy capture. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The following are actual comparison photos of the sample of Example 1 of the present invention (left) and the sample of Comparative Example 5 (right).

[0035] Figure 2 This is a surface electron microscope photograph of the etched PVDF-based disc-type piezoelectric product prepared in Example 1 of the present invention. It is obvious that a shish-kebab structure is formed along the flow direction after etching, and carbon nanotubes are observed to be distributed therein.

[0036] Figure 3 The transmission electron microscope comparison photos of the PVDF-based disc-type piezoelectric products prepared in Example 1 (left) of the present invention and Comparative Example 3 (right) show that the carbon nanotubes are oriented under the strong shear force field, and in comparison, the samples without ionic liquid contain obvious agglomerated carbon nanotubes.

[0037] Figure 4 The infrared test comparison spectra of the samples prepared in Example 1 and Comparative Examples 1 to 5 of the present invention are shown in FIG. -1 The characteristic absorption peak of β crystal is 763cm -1 This is the characteristic absorption peak of α crystal.

[0038] Figure 5 The two-dimensional small-angle X-ray scattering comparison diagrams of the PVDF-based disc-type piezoelectric products prepared in Example 1 (left) of the present invention and Comparative Example 5 (right). Among them, the two-dimensional small-angle X-ray scattering diagram of the sample in Example 1 shows a vertically symmetrical water droplet-shaped scattering pattern in the meridian direction and a left-right symmetrical scattering stripe in the equatorial direction. This pattern is a typical skewer small-angle scattering pattern; compared with the sample in Comparative Example 5, the two-dimensional small-angle X-ray scattering diagram shows weak circular scattering without obvious orientation.

[0039] Figure 6 The open circuit voltage-time comparison diagram of the samples prepared in Example 1 of the present invention and Comparative Examples 1 to 5. It can be seen that the addition of carbon nanotubes and ionic liquids can significantly increase the open circuit voltage; compared with the piezoelectric parts prepared by the traditional hot pressing process, the sample in Example 1 has a significantly improved open circuit voltage.

[0040] Figure 7The short-circuit current-time comparison diagram of the samples prepared in Example 1 of the present invention and Comparative Examples 1 to 5. It can be seen that the addition of carbon nanotubes and ionic liquids can significantly increase the short-circuit current; compared with the piezoelectric parts prepared by the traditional hot pressing process, the sample in Example 1 has a significantly improved short-circuit current. DETAILED DESCRIPTION

[0041] In order to further understand the present invention, the preferred embodiments of the present invention are described below in conjunction with examples, but it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the invention. Those skilled in the art can refer to the content of this article and appropriately improve the process parameters to achieve it. It is particularly important to point out that all similar substitutions and modifications are obvious to those skilled in the art, and they are all considered to be included in the present invention. The methods and applications of the present invention have been described through preferred embodiments, and relevant personnel can obviously change or appropriately change and combine the methods and applications described herein without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention. Although it is believed that those of ordinary skill in the art fully understand the following terms, the following definitions are still stated to help illustrate the subject matter disclosed by the present invention.

[0042] A method for preparing a PVDF-based piezoelectric product based on a reverse chain relaxation micro-injection molding process, which mainly comprises the following steps:

[0043] (1) Prepare the following raw materials by weight:

[0044] Polyvinylidene fluoride (PVDF) 94-98.5 parts,

[0045] 1 to 5 parts of ionic liquid,

[0046] One-dimensional / two-dimensional carbon conductive filler 0.5-1 part,

[0047] The polyvinylidene fluoride, ionic liquid and one-dimensional / two-dimensional carbon conductive filler are 100 parts in total;

[0048] The ionic liquid is selected from any one of 1-ethyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-benzyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium tetrafluoroborate, and 1-alkyl-3-methylimidazolium tetrafluoroborate;

[0049] (2) preparing a polyvinylidene fluoride composite material by melt blending the raw materials of each component prepared in step (1);

[0050] (3) injecting the polyvinylidene fluoride composite material obtained in step (2) into a mold of a desired piezoelectric product in a micro injection molding machine, and preparing a PVDF-based piezoelectric product by micro injection molding;

[0051] The process conditions of micro injection molding are as follows: injection speed 50-600 mm / s, mold temperature 30-90° C., melt temperature 180-210° C., holding pressure and cooling time 5-15 s.

[0052] In this article, the Chinese name of the PVDF in step (1) is polyvinylidene fluoride. Those skilled in the art can select a suitable PVDF model according to specific needs, preferably a PVDF model currently commonly used in piezoelectric devices.

[0053] In this article, the one-dimensional / two-dimensional carbon-based conductive filler in step (1) is a one-dimensional / two-dimensional carbon-based material conventionally used as a conductive filler in the prior art. In one embodiment, for example, any one or more of carbon nanotubes, carbon nanofibers, graphene and carbon nanosheets are selected.

[0054] In this article, the raw materials of each component described in step (2) are melt blended to prepare a polyvinylidene fluoride-based composite material. A conventional melt blending process technology known in the art can be selected, which is intended to form a uniformly dispersed mixture of each component in the PVDF matrix, such as using an internal mixer or a screw extruder for melt blending. Because the composite material finally prepared in step (2) needs to be added to a micro injection molding machine in the next step, it is further preferred to be a composite powder / granule form that is convenient for feeding to the micro injection molding machine. Those skilled in the art should know that after melt blending, conventional process means such as crushing / granulation should be used to obtain powder / granule; it should be noted that the specific form of the powder / granule is mainly selected depending on the processable raw material form of the micro injection molding machine. Those skilled in the art can select a suitable composite raw material form according to the instructions for use of the micro injection molding machine used.

[0055] In one embodiment, in order to further enhance the interaction between the ionic liquid and the one-dimensional / two-dimensional carbon-based conductive filler, the raw materials of each component in step (2) are melt-blended to prepare a polyvinylidene fluoride based composite material, specifically, the prepared raw materials of each component are melt-blended in an internal mixer or a twin-screw extruder to prepare a polyvinylidene fluoride based composite material;

[0056] The process parameters for melt blending in an internal mixer or a twin-screw extruder are as follows: temperature of 180-210° C., rotation speed of 50-80 rpm, and cooling after melt blending for 5-10 minutes.

[0057] In one embodiment, in order to facilitate feeding into the micro injection molding machine, the polyvinylidene fluoride based composite material in step (2) is crushed to obtain polyvinylidene fluoride based composite powder with an average particle size of 0.1 to 0.2 mm. The crushing method is conventional in the art, such as a mechanical crusher, a jet mill, a low temperature mill, etc.

[0058] In this article, the PVDF-based piezoelectric product prepared by micro injection molding in step (3) can be prepared by different molds to obtain different piezoelectric products, such as a circular piezoelectric sheet for preparing a micro piezoelectric generator.

[0059] In one embodiment, the ionic liquid in step (1) is 1 to 5 parts, for example, 1 part, 1.5 parts, 2 parts, 2.5 parts, 3 parts, 3.5 parts, 4 parts, 4.5 parts, 5 parts or any range or point value therebetween; the one-dimensional / two-dimensional carbon-based conductive filler is 0.5 to 1 part, for example, 0.5 parts, 0.6 parts, 0.7 parts, 0.8 parts, 0.9 parts, 1 part or any range or point value therebetween.

[0060] In one embodiment, the injection speed in step (3) is 50 to 600 mm / s, for example, 50 mm / s, 60 mm / s, 70 mm / s, 80 mm / s, 90 mm / s, 100 mm / s, 110 mm / s, 120 mm / s, 130 mm / s, 140 mm / s, 150 mm / s, 160 mm / s, 170 mm / s, 180 mm / s, 190 mm / s, 200 mm / s, 210 mm / s, 220 mm / s, 230 mm / s. m / s, 240mm / s, 250mm / s, 260mm / s, 270mm / s, 280mm / s, 290mm / s, 300mm / s, 310mm / s, 320mm / s, 330mm / s, 340mm / s, 350mm / s, 360mm / s, 370mm / s, 380mm / s, 390mm / s, 400mm / s, 410mm / s, 420mm / s, 430mm / s, 440mm / s, 450mm / s, 460mm / s, 470mm / s, 480mm / s, 490mm / s, 500mm / s, 510mm / s, 520mm / s, 530mm / s, 540mm / s, 550mm / s, 560mm / s, 570mm / s, 580mm / s, 590mm / s, 600mm / s or any range or point value therebetween; the mold temperature is 30-90°C, for example 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 76°C, 77°C, 78°C, 79°C, 80°C, 81°C, 82°C, 83°C, 84°C, 85°C, 86°C, 87°C, 88°C, 89°C, 90°C, 91°C, 92°C, 93°C, 94°C, 95°C, 96°C, 97°C, 98°C, 99°C, 100°C, 101°C, 102°C, 103°C, 104°C 0℃, 75℃, 80℃, 85℃, 90℃ or any range or point value therebetween; the melt temperature is 180-210℃, for example, 180℃, 185℃, 190℃, 195℃, 200℃, 205℃, 210℃ or any range or point value therebetween; the holding and cooling time is 5-15s, for example, 5s, 6s, 7s, 8s, 9s, 10s, 11s, 12s, 13s, 14s, 15s or any point value therebetween, and the holding time and cooling time may be the same or different.

[0061] The main inventive point of the present invention is that the reverse chain relaxation micro-injection molding process is used for the first time to prepare PVDF-based piezoelectric products, and the strong shear force field involved in the micro-injection molding process is used to promote the directional arrangement of PVDF molecular chains. The ionic liquid is introduced to induce the formation of PVDF piezoelectric polar crystals while suppressing the local thermal relaxation behavior of PVDF molecular chains, thereby achieving the purpose of greatly reducing the relaxation phenomenon of PVDF chains, which is conducive to the formation of highly oriented β-polar phases and significantly improving the piezoelectric properties of PVDF-based piezoelectric products. If only carbon-based conductive fillers are added to the PVDF matrix, the polar crystal content of the PVDF piezoelectric products prepared by the micro-injection molding process is limited (about 40-50%); and the ionic liquid introduced in addition can induce the formation of PVDF piezoelectric polar crystals and suppress the local thermal relaxation behavior of PVDF molecular chains. In addition, the strong shear force field generated by the micro-injection molding process promotes the orientation of PVDF molecular chains, which is conducive to the formation of more efficient polar crystals and string crystal structures. The above factors all make the piezoelectric products prepared by the method of the present invention have significantly higher piezoelectric properties than the piezoelectric products prepared by the conventional melt molding process of the same size.

[0062] It should be noted that although ionic liquids have an impressive synergistic enhancement effect in micro injection molding processes, if ionic liquids are introduced into conventional melt molding processes (such as hot pressing molding), experimental results show that PVDF is easy to crystallize into isotropic polar spherulites, which does not contribute to piezoelectric performance. In addition, the ionic liquid introduced in the present invention mainly relies on a one-dimensional / two-dimensional carbon-based conductive filler uniformly dispersed in the PVDF matrix resin as a template. If a one-dimensional / two-dimensional carbon-based conductive filler is not added, a template oriented with a shear force field cannot be formed, which will greatly limit the orientation arrangement of the dipoles, reduce the macroscopic dipole moment, and thus be detrimental to the piezoelectric output.

[0063] It is important to note that the introduction of one-dimensional / two-dimensional carbon conductive fillers and ionic liquids together can help improve piezoelectric performance, but the amount of addition may affect the mechanical properties of the final product. According to the principle of piezoelectric effect, the effect of fillers on the mechanical properties of the product may also affect the optimal value of the piezoelectric output of the product. Therefore, the filler should be minimized in terms of its effect on the mechanical properties of the product. Based on this, the raw material ratio of each component proposed in the present invention is within the range optimized by comparative experiments.

[0064] The present invention will be further explained in detail with reference to the following examples. However, it should be understood by those skilled in the art that these examples are provided for illustrative purposes only and are not intended to limit the present invention.

[0065] Example

[0066] The embodiments of the present application will be described in detail below in conjunction with the examples, but it will be appreciated by those skilled in the art that the following examples are only used to illustrate the present application and should not be considered as limiting the scope of the present application. The specific conditions not specified in the examples are carried out according to the conditions recommended by normal conditions or manufacturers. The reagents used or the instruments not specified by the manufacturer are all conventional products that can be obtained commercially. The application should not be construed as being limited to the specific examples described.

[0067] 1. Raw materials

[0068] Polyvinylidene fluoride (PVDF) FR906, purchased from Shanghai San Ai Fu New Material Technology Co., Ltd., China;

[0069] Multi-walled carbon nanotubes (CNTs) NC7000, purchased from Nanocyl Company, Belgium;

[0070] Ionic liquid (IL, 1-ethyl-3-methylimidazolium acetate) was purchased from Aladdin Biotechnology Co., Ltd. (Shanghai).

[0071] 2. Preparation method

[0072] (1) Prepare the following raw materials by weight:

[0073] Polyvinylidene fluoride (PVDF) 97.5 parts,

[0074] Ionic liquid (IL) 2 parts,

[0075] Multi-walled carbon nanotubes (CNTs) 0.5 parts;

[0076] (2) melt-blending the raw materials of each component prepared in step (1) in an internal mixer to prepare a polyvinylidene fluoride based composite material, and then crushing it in a crusher to obtain a polyvinylidene fluoride based composite powder;

[0077] The process parameters for melt blending in the internal mixer are as follows: temperature of 190°C, rotation speed of 80 rpm, and cooling after melt blending for 10 minutes;

[0078] (3) injecting the polyvinylidene fluoride composite powder obtained in step (2) into a mold of a disc-type piezoelectric product in a micro injection molding machine, and preparing a PVDF-based disc-type piezoelectric product by micro injection molding;

[0079] The process conditions of micro injection molding are as follows: injection speed 200 mm / s, mold temperature 90° C., melt temperature 190° C., holding pressure and cooling time 10 s.

[0080] The prepared PVDF-based disc-type piezoelectric product has a disc structure with a diameter of 12 mm and a thickness of 0.5 mm.

[0081] In order to facilitate the testing of piezoelectric performance, the prepared PVDF-based disc-type piezoelectric product was assembled into a piezoelectric generator, which was mainly composed of a packaging film, a lower conductive layer, an upper conductive layer and a PVDF-based disc-type piezoelectric product. The lower conductive layer, the PVDF-based disc-type piezoelectric product and the upper conductive layer were stacked in sequence and wrapped by a packaging film.

[0082] The packaging film is made of polyimide (PI), the upper conductive layer and the lower conductive layer are made of copper foil, and the size of the upper conductive layer and the lower conductive layer is similar to the disc body structure of the PVDF-based disc-type piezoelectric product to meet the upper and lower coverage of the piezoelectric product.

[0083] 3. Test methods

[0084] The microstructure was observed on a field emission scanning electron microscope (SEM) InspectF (FEI, Finland) with an accelerating voltage of 15 kV. A transmission microscopic image of the sample was obtained using a JEOL JEM-100CX transmission electron microscope (TEM) (JEOL, Japan) at an accelerating voltage of 20 kV. A two-dimensional small-angle X-ray scattering (2D-SAXS) test was performed on a two-dimensional small-angle X-ray scattering instrument Xeuss 2.0 (Xenocs, France), with the distance between the sample and the detector being 2495.3 mm. A Nicolet iS50 Fourier transform infrared spectrometer (FT-IR) (Thermo Scientific, USA) was used to analyze the crystal composition of the sample in attenuated total reflection mode and calculate the β-crystalline phase content. A Linmot linear motor (NTI AG, Switzerland) was used to apply a periodic impact force to the sample, with the acceleration set to 5 m / s. 2 ,The output voltage signal was collected by a Keithley 6514 system electrometer (Keithley, USA).

[0085] Example 1

[0086] In Example 1, a PVDF-based disc-type piezoelectric product was prepared as a sample according to the steps of “2. Preparation method” above.

[0087] The test showed that the prepared PVDF-based disc-type piezoelectric product had a polar crystal content of 72% and a 2 Under acceleration impact, its open circuit voltage and short circuit current are 8.2V and 140nA respectively.

[0088] Comparative Example 1

[0089] Comparative Example 1 refers to the above-mentioned "2. Preparation method" step, but no ionic liquid (IL) and multi-walled carbon nanotubes (CNTs) are added in step (1), that is, 100 parts of polyvinylidene fluoride (PVDF) are used as raw materials, and finally a PVDF-based disc-type piezoelectric product is prepared as a comparative sample.

[0090] The test showed that the prepared PVDF-based disc-type piezoelectric product had a polar crystal content of 31% at 5 m / s. 2 Under acceleration impact, its open circuit voltage and short circuit current are 0.7V and 18nA respectively.

[0091] Comparative Example 2

[0092] Comparative Example 2 refers to the above-mentioned "2. Preparation method" step, but multi-walled carbon nanotubes (CNTs) are not added in step (1), that is, 98 parts of polyvinylidene fluoride (PVDF) and 2 parts of ionic liquid (IL) are used as raw materials, and finally a PVDF-based disc-type piezoelectric product is prepared as a comparative sample.

[0093] The test showed that the prepared PVDF-based disc-type piezoelectric product had a polar crystal content of 78% and a 2 Under acceleration impact, its open circuit voltage and short circuit current are 4V and 80nA respectively.

[0094] Comparative Example 3

[0095] Comparative Example 3 refers to the above-mentioned "2. Preparation method" step, but no ionic liquid (IL) is added in step (1), that is, 99.5 parts of polyvinylidene fluoride (PVDF) and 0.5 parts of multi-walled carbon nanotubes (CNTs) are used as raw materials, and finally a PVDF-based disc-type piezoelectric product is prepared as a comparative sample.

[0096] The test showed that the prepared PVDF-based disc-type piezoelectric product had a polar crystal content of 34% at 5 m / s. 2 Under acceleration impact, its open circuit voltage and short circuit current are 1.2V and 70nA respectively.

[0097] Comparative Example 4

[0098] Comparative Example 4 is prepared based on a traditional hot pressing process, comprising the following steps:

[0099] (1) Prepare the following raw materials by weight:

[0100] Polyvinylidene fluoride (PVDF) 99.5 parts,

[0101] Multi-walled carbon nanotubes (CNTs) 0.5 parts;

[0102] (2) melt-blending the raw materials of each component prepared in step (1) in an internal mixer to prepare a polyvinylidene fluoride based composite material, and then crushing it in a crusher to obtain a polyvinylidene fluoride based composite powder;

[0103] The process parameters for melt blending in the internal mixer are as follows: temperature of 190°C, rotation speed of 80 rpm, and cooling after melt blending for 10 minutes;

[0104] (3) placing the polyvinylidene fluoride composite powder obtained in step (2) in a hot pressing mold, and preparing a PVDF-based disc-type piezoelectric product as a comparison sample by hot pressing;

[0105] The process conditions of hot pressing molding are as follows: pressure of 10 MPa, melt temperature of 190°C, holding pressure and cooling time of 10 seconds.

[0106] The prepared PVDF-based disc-type piezoelectric product has a disc structure with a diameter of 12 mm and a thickness of 0.5 mm.

[0107] The test showed that the prepared PVDF-based disc-type piezoelectric product had a polar crystal content of 30% at 5 m / s. 2 Under acceleration impact, its open circuit voltage and short circuit current are 1.2V and 20nA respectively.

[0108] Comparative Example 5

[0109] Comparative Example 5 is prepared based on a traditional hot pressing process, comprising the following steps:

[0110] (1) Prepare the following raw materials by weight:

[0111] Polyvinylidene fluoride (PVDF) 97.5 parts,

[0112] Ionic liquid (IL) 2 parts,

[0113] Multi-walled carbon nanotubes (CNTs) 0.5 parts;

[0114] (2) melt-blending the raw materials of each component prepared in step (1) in an internal mixer to prepare a polyvinylidene fluoride based composite material, and then crushing it in a crusher to obtain a polyvinylidene fluoride based composite powder;

[0115] The process parameters for melt blending in the internal mixer are as follows: temperature of 190°C, rotation speed of 80 rpm, and cooling after melt blending for 10 minutes;

[0116] (3) placing the polyvinylidene fluoride composite powder obtained in step (2) in a hot pressing mold, and preparing a PVDF-based disc-type piezoelectric product as a comparison sample by hot pressing;

[0117] The process conditions of hot pressing molding are as follows: pressure of 10 MPa, melt temperature of 190°C, holding pressure and cooling time of 10 seconds.

[0118] The prepared PVDF-based disc-type piezoelectric product has a disc structure with a diameter of 12 mm and a thickness of 0.5 mm.

[0119] The test showed that the prepared PVDF-based disc-type piezoelectric product had a polar crystal content of 73% and a 2 Under acceleration impact, its open circuit voltage and short circuit current are 2.5V and 75nA respectively.

[0120] The rest of the test results are as follows Figures 1 to 7 shown.

[0121] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for preparing PVDF-based piezoelectric products based on reverse chain relaxation micro-injection molding process, characterized in that The main steps include: (1) Prepare the following raw materials by weight: 94-98.5 parts of polyvinylidene fluoride, 1 to 5 parts of ionic liquid, One-dimensional / two-dimensional carbon conductive filler 0.5-1 part, The polyvinylidene fluoride, ionic liquid and one-dimensional / two-dimensional carbon conductive filler are 100 parts in total; The ionic liquid is selected from any one of 1-ethyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-benzyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium tetrafluoroborate, and 1-alkyl-3-methylimidazolium tetrafluoroborate; (2) preparing a polyvinylidene fluoride composite material by melt blending the raw materials of each component prepared in step (1); (3) injecting the polyvinylidene fluoride composite material obtained in step (2) into a mold of a desired piezoelectric product in a micro injection molding machine, and preparing a PVDF-based piezoelectric product by micro injection molding; The process conditions of micro injection molding are as follows: injection speed 50-600 mm / s, mold temperature 30-90° C., melt temperature 180-210° C., holding pressure and cooling time 5-15 s.

2. The method according to claim 1, characterized in that: The one-dimensional / two-dimensional carbon conductive filler in step (1) includes any one or more of carbon nanotubes, carbon nanofibers, graphene and carbon nanosheets.

3. The method according to claim 1, characterized in that: The various raw materials described in step (2) are melt-blended to prepare a polyvinylidene fluoride based composite material, specifically, the prepared raw materials are melt-blended in an internal mixer or a twin-screw extruder to prepare a polyvinylidene fluoride based composite material; The process parameters for melt blending in an internal mixer or a twin-screw extruder are as follows: temperature of 180-210° C., rotation speed of 50-80 rpm, and cooling after melt blending for 5-10 minutes.

4. The PVDF-based piezoelectric product prepared by the method for preparing PVDF-based piezoelectric products based on reverse chain relaxation micro-injection molding process as described in claim 1.

5. The PVDF-based piezoelectric product as claimed in claim 4 is applied in the field of sensors and self-powered equipment.

6. The PVDF-based piezoelectric product as claimed in claim 4 is applied to a piezoelectric generator.

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