A method for preparing PVDF-based piezoelectric products based on anti-chain relaxation micro-injection molding process

Abstract

This invention provides a method for preparing PVDF-based piezoelectric products using a micro-injection molding process based on anti-chain relaxation. The method involves melt-blending 94–98.5 parts by weight of PVDF, 1–5 parts by weight of ionic liquid, and 0.5–1 parts by weight of one-dimensional / two-dimensional carbon-based conductive filler to obtain a polyvinylidene fluoride composite material. This material is then injected into a mold for the desired piezoelectric product using a micro-injection molding machine, resulting in the PVDF-based piezoelectric product. This method utilizes the strong shear field involved in the micro-injection molding process to promote the orientation of PVDF molecular chains. Combined with the introduction of ionic liquid to induce the formation of polar crystals in the PVDF piezoelectric material and suppress the local thermal relaxation behavior of the PVDF molecular chains, this significantly reduces PVDF chain relaxation, facilitating the formation of a highly oriented β-polar phase and substantially improving the piezoelectric performance of PVDF-based piezoelectric devices.

Description

Technical Field

[0001] This invention belongs to the field of process technology for preparing micro injection molded piezoelectric devices, and relates to a method for preparing PVDF-based piezoelectric products based on anti-chain relaxation micro injection molding process, which is mainly applied in the fields of sensors and self-powered equipment. Background Technology

[0002] With the rapid development of Internet of Things (IoT) technology, society has an increasing demand for smart devices, wearable devices, and miniature sensors. To achieve miniaturization, convenience, and high efficiency in these devices, miniature piezoelectric devices, as a technology that can efficiently convert mechanical energy into electrical energy, are gradually becoming an important direction in the fields of energy harvesting 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), and are therefore widely used in energy harvesting, sensors, and micro-actuators. However, currently commercially available PVDF-based piezoelectric materials still have certain limitations in piezoelectric performance, especially in self-powered devices, where existing PVDF materials struggle to meet the requirements for efficient energy harvesting and high-sensitivity detection.

[0004] Furthermore, while traditional processing methods can fabricate PVDF piezoelectric films, they still face numerous challenges in the production of high-efficiency piezoelectric devices, particularly in maintaining the orientation of molecular chains and improving piezoelectric performance, which requires further breakthroughs. The piezoelectric properties of PVDF originate from its electroactive phase, a result of dipole orientation within the crystalline region. Specifically, the fabrication of commercially available piezoelectric PVDF devices currently involves two key steps. The first step involves expanding the molecular chains at 110°C using mechanical stretching techniques to induce a transformation from a nonpolar to a polar crystal. This processing temperature is significantly lower than the melting point of PVDF (170°C), aiming to significantly reduce the system's energy and suppress chain relaxation. The other key step is placing the material in an ultra-high electric field, causing the dipoles to rotate around their axes, thereby achieving a non-zero macroscopic dipole moment.

[0005] Despite the excellent thermoplastic processing properties of PVDF, traditional melt processing methods struggle to prepare piezoelectric PVDF materials with high content of oriented β-polar crystals. This challenge stems from the complex interaction between molecular chain orientation and chain relaxation in PVDF materials. When processing temperatures exceed the melting point of PVDF and a strong shear field is lacking, the molecular chains tend to relax, reverting to a thermodynamically stable random coiled configuration. However, this problem is clearly detrimental when fabricating high-performance PVDF-based piezoelectric devices. Even with polar crystal-inducing modifiers, the all-trans molecular chains of PVDF become disordered, leading to the cancellation of dipoles formed by polar crystals. Therefore, applying an external field during thermoplastic processing to counteract chain relaxation is crucial for maintaining non-zero dipole moments. To overcome these issues, micro-injection molding technology, based on its extremely strong shear field and precise microstructure molding capabilities, has emerged as an effective approach to address these challenges in recent years.

[0006] Currently, although some studies have improved the performance of PVDF piezoelectric devices through micro-injection molding technology, how to further optimize the manufacturing process, enhance the piezoelectric properties of the material, and achieve efficient and low-cost mass production remains an urgent problem to be solved. Therefore, a PVDF-based micro-injection molding process technology that can balance high piezoelectric performance and facilitate industrialization would greatly benefit the industrialization of related technologies and have a promising market prospect. Summary of the Invention

[0007] To address the problems in the background art, this invention provides a method for preparing PVDF-based piezoelectric products based on anti-chain relaxation micro-injection molding. This 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 suppress the local thermal relaxation behavior of PVDF molecular chains, thereby greatly reducing the PVDF chain relaxation phenomenon. This is beneficial for the formation of highly oriented β polar phases and significantly improves the piezoelectric performance of PVDF-based piezoelectric devices.

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

[0009] A method for preparing PVDF-based piezoelectric products based on anti-chain relaxation micro-injection molding process mainly includes the following steps:

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

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

[0012] 1-5 parts ionic liquid

[0013] 0.5 to 1 part of one-dimensional / two-dimensional carbon-based conductive filler.

[0014] The total amount of the polyvinylidene fluoride, ionic liquid and one-dimensional / two-dimensional carbon-based conductive filler is 100 parts.

[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) Polyvinylidene fluoride composite material is prepared by melt blending of the raw materials prepared in step (1);

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

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

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

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

[0021] In this paper, the polyvinylidene fluoride composite material is prepared by melt blending of the raw materials described in step (2). Conventional melt blending technology known in the art can be selected, which aims to form a uniformly dispersed mixture of the components in the PVDF matrix. For example, melt blending can be performed using a mixer or screw extruder. Since the composite material finally prepared in step (2) needs to be added to the micro injection molding machine in the next step, it is further preferred to use a composite powder / granule form that is easy to feed into the micro injection molding machine. Those skilled in the art should know that after melt blending, conventional processes such as crushing / granulation should be used to obtain powder / granules. It should be noted that the specific form of powder / granules mainly depends on the form of raw materials that can be processed by the micro injection molding machine. Those skilled in the art can choose a suitable composite raw material form according to the instructions for use of the micro injection molding machine.

[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 polyvinylidene fluoride composite material. Specifically, the prepared raw materials of each component are melt-blended in a mixer or a twin-screw extruder to prepare polyvinylidene fluoride composite material.

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

[0024] In one technical solution, to facilitate feeding into a micro injection molding machine, the polyvinylidene fluoride composite material in step (2) is pulverized to obtain polyvinylidene fluoride composite powder with an average particle size of 0.1-0.2 mm. The pulverization method is a conventional process in the field, such as using a mechanical crusher, an air jet mill, or a cryogenic mill.

[0025] In this paper, the PVDF-based piezoelectric products prepared by micro-injection molding in step (3) can be prepared by different molds to obtain different piezoelectric products, such as circular piezoelectric sheets used to prepare micro piezoelectric generators.

[0026] The main inventive point of this invention lies in the first-time use of anti-chain relaxation micro-injection molding to prepare PVDF-based piezoelectric products. The strong shear field involved in the micro-injection molding process promotes the directional alignment of PVDF molecular chains. Combined with the introduction of ionic liquids to induce the formation of polar crystals in PVDF piezoelectric products while suppressing local thermal relaxation of PVDF molecular chains, this significantly reduces PVDF chain relaxation, facilitating 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 PVDF piezoelectric products prepared by micro-injection molding is limited (approximately 40-50%). However, the introduced ionic liquid can induce the formation of polar crystals in PVDF piezoelectric products and suppress local thermal relaxation of PVDF molecular chains. Furthermore, the strong shear field generated by the micro-injection molding process promotes the orientation of PVDF molecular chains, which is beneficial for forming more efficient polar crystals and chain crystal structures. All these factors contribute to the piezoelectric properties of piezoelectric products prepared using the method of this invention being significantly higher than those of piezoelectric products of the same size prepared by conventional melt molding processes.

[0027] It should be noted that although ionic liquids exhibit impressive synergistic enhancement effects in micro-injection molding processes, the introduction of ionic liquids into conventional melt molding processes (such as hot pressing) has shown that PVDF tends to crystallize into isotropic polar spherulites, contributing nothing to piezoelectric properties. Furthermore, the ionic liquids introduced in this invention primarily rely on one-dimensional / two-dimensional carbon-based conductive fillers uniformly dispersed in the PVDF matrix resin as templates. Without these fillers, a template oriented according to the shear field cannot be formed, severely limiting the orientation of dipoles, reducing the macroscopic dipole moment, and consequently hindering piezoelectric output.

[0028] It is important to note that while the synergistic introduction of one-dimensional / two-dimensional carbon-based conductive fillers and ionic liquids helps improve piezoelectric properties, the amount added may affect the mechanical properties of the final product. According to the principle of the piezoelectric effect, the influence of fillers on the mechanical properties of the product may also affect the optimal value of the piezoelectric output. Therefore, the impact of fillers on the mechanical properties of the product should be minimized. Based on this, the raw material ratios of the components proposed in this invention are within the range optimized through comparative experiments.

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

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

[0031] 2. The technical solution of this invention is perfectly suited for ionic liquid-modified PVDF-based composite materials, exhibiting higher piezoelectric properties than piezoelectric products prepared using existing melt processing techniques, and providing practical process technology guidance for subsequent industrial production. The micro-injection molding process also features simplified process steps and easier large-scale industrial production capabilities.

[0032] 3. The PVDF substrate piezoelectric products prepared by the present invention utilize micro-injection molding technology. Through the synergistic effect of filler modification and strong shear force field of micro-injection, the directional arrangement of PVDF molecular chains in the flow direction is effectively improved. Compared with PVDF products prepared by conventional melt processing methods, it has anisotropic polar crystal characteristics, and the resulting string crystal structure cannot be achieved by conventional preparation methods.

[0033] 4. The PVDF-based disc piezoelectric products prepared by this invention using micro-injection molding technology have advantages such as simple production process, ease of operation, low manufacturing cost, and the ability to be produced continuously on a large scale. The entire process requires no post-processing of the parts or additional process conditions, making it suitable for industrial transformation. The micro-injection molded disc piezoelectric products involved in this invention can be applied to the preparation of piezoelectric generator devices and have application potential in piezoelectric sensing, energy harvesting, and other fields. Attached Figure Description

[0034] Figure 1 This is a photograph comparing the sample (left) of Example 1 of the present invention with the sample (right) of Comparative Example 5.

[0035] Figure 2 This is an electron microscope (EM) image of the surface of the PVDF-based disc piezoelectric product prepared in Example 1 of this invention after etching. A crystalline structure formed along the flow direction after etching is clearly visible, and carbon nanotubes can be observed distributed within it.

[0036] Figure 3 These are transmission electron microscopy (TEM) images comparing the PVDF-based disc piezoelectric products prepared in Example 1 (left) and Comparative Example 3 (right) of this invention. It is clearly visible that the carbon nanotubes are oriented under strong shear force, while the sample without ionic liquid shows obvious agglomeration of carbon nanotubes.

[0037] Figure 4 The images show comparative infrared spectra of the samples prepared in Example 1 and Comparative Examples 1-5 of this invention. In the figures, 840 cm⁻¹... -1 The characteristic absorption peak of β crystal is at 763 cm⁻¹. -1 The peak at this location is a characteristic absorption peak of α crystals.

[0038] Figure 5 The images show a comparison of two-dimensional small-angle X-ray scattering (SAXS) of PVDF-based disc piezoelectric products prepared in Example 1 (left) and Comparative Example 5 (right). In Example 1, the SAXS pattern shows symmetrical teardrop-shaped scattering patterns along the meridian and symmetrical scattering stripes along the equator, typical of cascading small-angle scattering patterns. In contrast, the SAXS pattern of Comparative Example 5 exhibits weak, ring-shaped scattering with no clear orientation.

[0039] Figure 6 This is a comparison of open-circuit voltage-time for the samples prepared in Example 1 and Comparative Examples 1-5 of this invention. It can be seen that the addition of carbon nanotubes and ionic liquids can significantly improve the open-circuit voltage; compared with piezoelectric components prepared by traditional hot-pressing processes, the sample in Example 1 exhibits a significantly improved open-circuit voltage.

[0040] Figure 7This is a comparison graph of short-circuit current-time for samples prepared in Example 1 and Comparative Examples 1-5 of this invention. It can be seen that the addition of carbon nanotubes and ionic liquids can significantly increase the short-circuit current; compared with piezoelectric components prepared by traditional hot pressing processes, the sample in Example 1 exhibits a significantly improved short-circuit current. Detailed Implementation

[0041] To further understand the present invention, preferred embodiments are described below with reference to examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims. Those skilled in the art can refer to the content of this document to appropriately improve the process parameters. In particular, it should be noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included within the scope of the present invention. The methods and applications of the present invention have been described through preferred embodiments, and those skilled in the art can obviously make modifications or appropriate changes and combinations to the methods and applications described herein without departing from the content, spirit and scope of the present invention to realize and apply the technology of the present invention. Although it is believed that those skilled in the art will fully understand the following terms, the following definitions are set forth to help illustrate the subject matter disclosed in the present invention.

[0042] A method for preparing PVDF-based piezoelectric products based on anti-chain relaxation micro-injection molding process mainly includes the following steps:

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

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

[0045] 1-5 parts ionic liquid

[0046] 0.5 to 1 part of one-dimensional / two-dimensional carbon-based conductive filler.

[0047] The total amount of the polyvinylidene fluoride, ionic liquid and one-dimensional / two-dimensional carbon-based conductive filler is 100 parts.

[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) Polyvinylidene fluoride composite material is prepared by melt blending of the raw materials prepared in step (1);

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

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

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

[0053] In this document, the one-dimensional / two-dimensional carbon-based conductive filler mentioned in step (1) is a one-dimensional / two-dimensional carbon-based material commonly 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 paper, the polyvinylidene fluoride composite material is prepared by melt blending of the raw materials described in step (2). Conventional melt blending technology known in the art can be selected, which aims to form a uniformly dispersed mixture of the components in the PVDF matrix. For example, melt blending can be performed using a mixer or screw extruder. Since the composite material finally prepared in step (2) needs to be added to the micro injection molding machine in the next step, it is further preferred to use a composite powder / granule form that is easy to feed into the micro injection molding machine. Those skilled in the art should know that after melt blending, conventional processes such as crushing / granulation should be used to obtain powder / granules. It should be noted that the specific form of powder / granules mainly depends on the form of raw materials that can be processed by the micro injection molding machine. Those skilled in the art can choose a suitable composite raw material form according to the instructions for use of the micro injection molding machine.

[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 polyvinylidene fluoride composite material. Specifically, the prepared raw materials of each component are melt-blended in a mixer or a twin-screw extruder to prepare polyvinylidene fluoride composite material.

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

[0057] In one embodiment, to facilitate feeding into the micro injection molding machine, the polyvinylidene fluoride composite material in step (2) is pulverized to obtain polyvinylidene fluoride composite powder with an average particle size of 0.1–0.2 mm. The pulverization method is a conventional process in the art, such as using a mechanical crusher, an air jet mill, or a cryogenic mill.

[0058] In this paper, the PVDF-based piezoelectric products prepared by micro-injection molding in step (3) can be prepared by different molds to obtain different piezoelectric products, such as circular piezoelectric sheets used to prepare micro piezoelectric generators.

[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 between them; 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 between them.

[0060] In one embodiment, the injection speed in step (3) is 50–600 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 between them; mold temperature is 30~90℃, for example 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 7 0℃, 75℃, 80℃, 85℃, 90℃ or any range or point value between them; melt temperature is 180~210℃, for example 180℃, 185℃, 190℃, 195℃, 200℃, 205℃, 210℃ or any range or point value between them; pressure holding and cooling time is 5~15s, for example 5s, 6s, 7s, 8s, 9s, 10s, 11s, 12s, 13s, 14s, 15s or any point value between them, and the pressure holding time and cooling time can be the same or different.

[0061] The main inventive point of this invention lies in the first-time use of anti-chain relaxation micro-injection molding to prepare PVDF-based piezoelectric products. The strong shear field involved in the micro-injection molding process promotes the directional alignment of PVDF molecular chains. Combined with the introduction of ionic liquids to induce the formation of polar crystals in PVDF piezoelectric products while suppressing local thermal relaxation of PVDF molecular chains, this significantly reduces PVDF chain relaxation, facilitating 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 PVDF piezoelectric products prepared by micro-injection molding is limited (approximately 40-50%). However, the introduced ionic liquid can induce the formation of polar crystals in PVDF piezoelectric products and suppress local thermal relaxation of PVDF molecular chains. Furthermore, the strong shear field generated by the micro-injection molding process promotes the orientation of PVDF molecular chains, which is beneficial for forming more efficient polar crystals and chain crystal structures. All these factors contribute to the piezoelectric properties of piezoelectric products prepared using the method of this invention being significantly higher than those of piezoelectric products of the same size prepared by conventional melt molding processes.

[0062] It should be noted that although ionic liquids exhibit impressive synergistic enhancement effects in micro-injection molding processes, the introduction of ionic liquids into conventional melt molding processes (such as hot pressing) has shown that PVDF tends to crystallize into isotropic polar spherulites, contributing nothing to piezoelectric properties. Furthermore, the ionic liquids introduced in this invention primarily rely on one-dimensional / two-dimensional carbon-based conductive fillers uniformly dispersed in the PVDF matrix resin as templates. Without these fillers, a template oriented according to the shear field cannot be formed, severely limiting the orientation of dipoles, reducing the macroscopic dipole moment, and consequently hindering piezoelectric output.

[0063] It is important to note that while the synergistic introduction of one-dimensional / two-dimensional carbon-based conductive fillers and ionic liquids helps improve piezoelectric properties, the amount added may affect the mechanical properties of the final product. According to the principle of the piezoelectric effect, the influence of fillers on the mechanical properties of the product may also affect the optimal value of the piezoelectric output. Therefore, the impact of fillers on the mechanical properties of the product should be minimized. Based on this, the raw material ratios of the components proposed in this invention are within the range optimized through comparative experiments.

[0064] The present application will be further explained in detail below with reference to embodiments. However, those skilled in the art should understand that these embodiments are provided for illustrative purposes only and are not intended to limit the present application.

[0065] Example

[0066] The embodiments of this application will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be construed as limiting the scope of this application. Where specific conditions are not specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply. Where the manufacturers of reagents or instruments are not specified, they are all commercially available conventional products. This application should not be construed as being limited to the specific embodiments described.

[0067] 1. Raw materials

[0068] Polyvinylidene fluoride (PVDF) FR906 was purchased from Shanghai Sanaifu New Material Technology Co., Ltd., China.

[0069] Multi-walled carbon nanotubes (CNTs) NC7000 were purchased from Nanocyl in Belgium.

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

[0071] 2. Preparation method

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

[0073] 97.5 parts of polyvinylidene fluoride (PVDF)

[0074] 2 parts of ionic liquid (IL)

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

[0076] (2) The raw materials of each component prepared in step (1) are melt-blended in an internal mixer to prepare polyvinylidene fluoride composite material, and then crushed by a crusher to obtain polyvinylidene fluoride composite powder.

[0077] The process parameters for melt blending in the internal mixer are: temperature 190℃, rotation speed 80rpm, and cooling after melt blending for 10 minutes.

[0078] (3) The polyvinylidene fluoride composite powder obtained in step (2) is injected into the mold of the disc piezoelectric product in a micro injection molding machine, and the PVDF-based disc piezoelectric product is prepared by micro injection molding.

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

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

[0081] To facilitate testing of piezoelectric performance, the prepared PVDF-based disc piezoelectric products were assembled into a piezoelectric generator. This piezoelectric generator mainly consists of an encapsulation film, a lower conductive layer, an upper conductive layer, and the PVDF-based disc piezoelectric products. The lower conductive layer, the PVDF-based disc piezoelectric products, and the upper conductive layer are stacked in sequence and encapsulated by the encapsulation film.

[0082] The encapsulation film is made of polyimide (PI), and the upper and lower conductive layers are made of copper foil. The dimensions of the upper and lower conductive layers are approximately the disc structure of a PVDF-based disc piezoelectric product to satisfy the need for top and bottom coverage of the piezoelectric product.

[0083] 3. Testing Methods

[0084] The microstructure was observed using a field emission scanning electron microscope (SEM) InspectF (FEI, Finland) with an accelerating voltage of 15 kV. Transmission electron microscope (TEM) images of the samples were acquired using a JEOL JEM-100CX (JEOL, Japan) at an accelerating voltage of 20 kV. Two-dimensional small-angle X-ray scattering (2D-SAXS) was performed using a Xeuss 2.0 (Xenocs, France) spectrometer, with a sample-detector distance of 2495.3 mm. The crystal composition of the samples was analyzed and the β-phase content was calculated using a Nicolet iS50 Fourier transform infrared spectrometer (FT-IR) (Thermo Scientific, USA) in attenuated total reflection mode. A periodic cyclic impact force was applied to the samples using a Linmot linear motor (NTI AG, Switzerland) with an acceleration set to 5 m / s². 2 The output voltage signal is acquired by a Keithley 6514 system electrometer (Keithley Corporation, USA).

[0085] Example 1

[0086] Example 1 is a PVDF-based disc piezoelectric product prepared according to the steps in "2. Preparation Method" above.

[0087] Testing revealed that the prepared PVDF-based disc piezoelectric product had a polar crystal content of 72% and exhibited a polar crystal content of 5 m / s. 2 Under the impact of acceleration, 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 steps in "2. Preparation Method" above, but ionic liquid (IL) and multi-walled carbon nanotubes (CNTs) were not added in step (1). 100 parts of polyvinylidene fluoride (PVDF) were used as raw materials to finally prepare PVDF-based disc piezoelectric products as comparative samples.

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

[0091] Comparative Example 2

[0092] Comparative Example 2 is based on the steps in "2. Preparation Method" above, but multi-walled carbon nanotubes (CNTs) were not added in step (1). 98 parts of polyvinylidene fluoride (PVDF) and 2 parts of ionic liquid (IL) were used as raw materials to finally prepare PVDF-based disc piezoelectric products as comparative samples.

[0093] Testing revealed that the prepared PVDF-based disc piezoelectric product had a polar crystal content of 78% and exhibited a polar crystal content of 5 m / s. 2 Under the impact of acceleration, its open-circuit voltage and short-circuit current are 4V and 80nA, respectively.

[0094] Comparative Example 3

[0095] Comparative Example 3 refers to the steps in "2. Preparation Method" above, but ionic liquid (IL) was not added in step (1). 99.5 parts of polyvinylidene fluoride (PVDF) and 0.5 parts of multi-walled carbon nanotubes (CNTs) were used as raw materials to finally prepare PVDF-based disc piezoelectric products as comparative samples.

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

[0097] Comparative Example 4

[0098] Comparative Example 4 was prepared using a traditional hot pressing process, including the following steps:

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

[0100] 99.5 parts of polyvinylidene fluoride (PVDF)

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

[0102] (2) The raw materials of each component prepared in step (1) are melt-blended in an internal mixer to prepare polyvinylidene fluoride composite material, and then crushed by a crusher to obtain polyvinylidene fluoride composite powder.

[0103] The process parameters for melt blending in the internal mixer are: temperature 190℃, rotation speed 80rpm, and cooling after melt blending for 10 minutes.

[0104] (3) The polyvinylidene fluoride composite powder obtained in step (2) is placed in a hot press mold and a PVDF-based disc piezoelectric product is prepared by hot pressing as a comparative sample.

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

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

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

[0108] Comparative Example 5

[0109] Comparative Example 5 was prepared using a traditional hot-pressing process, including the following steps:

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

[0111] 97.5 parts of polyvinylidene fluoride (PVDF)

[0112] 2 parts of ionic liquid (IL)

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

[0114] (2) The raw materials of each component prepared in step (1) are melt-blended in an internal mixer to prepare polyvinylidene fluoride composite material, and then crushed by a crusher to obtain polyvinylidene fluoride composite powder.

[0115] The process parameters for melt blending in the internal mixer are: temperature 190℃, rotation speed 80rpm, and cooling after melt blending for 10 minutes.

[0116] (3) The polyvinylidene fluoride composite powder obtained in step (2) is placed in a hot press mold and a PVDF-based disc piezoelectric product is prepared by hot pressing as a comparative sample.

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

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

[0119] Testing revealed that the prepared PVDF-based disc piezoelectric product had a polar crystal content of 73% and a polar crystal content of 5 m / s. 2 Under the impact of acceleration, its open-circuit voltage and short-circuit current are 2.5V and 75nA, respectively.

[0120] Other test results are as follows Figures 1-7 As shown.

[0121] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing PVDF-based piezoelectric products based on anti-chain relaxation micro-injection molding process, characterized in that... Includes the following steps: (1) Prepare raw materials comprising the following components by weight: 97.5 parts of polyvinylidene fluoride, 2 parts of 1-ethyl-3-methylimidazolium acetate, 0.5 parts of multi-walled carbon nanotubes The total amount of polyvinylidene fluoride, 1-ethyl-3-methylimidazolium acetate and multi-walled carbon nanotubes is 100 parts; (2) Polyvinylidene fluoride composite material is prepared by melt blending of the raw materials prepared in step (1); (3) The polyvinylidene fluoride composite material obtained in step (2) is injected into the mold of the desired piezoelectric product in a micro injection molding machine, and the PVDF-based piezoelectric product is prepared by micro injection molding. The process conditions for micro-injection molding are as follows: injection speed 50~600mm / s, mold temperature 30~90℃, melt temperature 180~210℃, and holding pressure and cooling time 5~15s.

2. The method according to claim 1, characterized in that: In step (2), the raw materials of each component are melt-blended to prepare polyvinylidene fluoride composite material. Specifically, the prepared raw materials of each component are melt-blended in a mixer or a twin-screw extruder to prepare polyvinylidene fluoride composite material. The process parameters for melt blending in a mixer or twin-screw extruder are as follows: temperature 180~210℃, speed 50~80rpm, and cooling after melt blending for 5~10 minutes.

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

4. The PVDF-based piezoelectric products as described in claim 3 are applied in the fields of sensors and self-powered equipment.

5. The PVDF-based piezoelectric product as described in claim 3 is applied to a piezoelectric generator.

Images