Highly transparent pvdf piezoelectric film and preparation process thereof

Abstract

The application discloses a kind of high transparent PVDF piezoelectric film and preparation process thereof, specifically related to PVDF piezoelectric film manufacturing technical field, the raw materials are reselected and proportioned in the application, so that the transparency of PVDF piezoelectric film can be improved, the problem of yellowing of PVDF piezoelectric film can be reduced to a certain extent, and in the process of multiple longitudinal stretching, when the film is fully stretched and formed, the surface structure distribution is more uniform, and the compactness is higher, and the temperature and ratio of stretching are controlled, so that the fracture condition is not prone to occur, the stretching qualified rate is guaranteed, and after the PVDF piezoelectric film is bidirectionally stretched, the light transmittance abnormal point on the PVDF piezoelectric film is obtained, and the stretching area is determined according to the abnormal point distribution, secondary small-range stretching treatment is carried out, so that the area with lower light transmittance is stretched again, the thickness consistency and light transmittance uniformity of PVDF piezoelectric film are improved, and the output of defective products is reduced.

Description

Technical Field

[0001] This invention relates to the field of PVDF piezoelectric film manufacturing technology, and more specifically, to a highly transparent PVDF piezoelectric film and its preparation process. Background Technology

[0002] Polyvinylidene fluoride (PVDF) is a chain-like semi-crystalline polymer formed from (CH2-CF2) monomers. After mechanical stretching and high electric field polarization, it can generate strong piezoelectricity. PVDF piezoelectric films have high mechanical strength, low acoustic impedance, and are easy to process into large-area components and array components, meeting the development needs of industrial applications such as miniaturization, surface mounting, and multifunctional integration. At the same time, it also has the advantages of being lightweight, flexible, easy to process, inexpensive, and having good electrical resistance, providing a promising prospect for replacing ceramic piezoelectric materials in certain specific fields.

[0003] Currently, in the processing of PVDF piezoelectric films, the stretching process is a crucial step. Existing technologies typically inspect the thickness and thickness consistency of the PVDF piezoelectric film after production, rejecting substandard products as defective. However, this approach fails to reduce the likelihood of defective products being produced. Furthermore, the lack of precise control over the stretching temperature and ratio during production can easily lead to low density or breakage, resulting in a low yield rate. The produced PVDF piezoelectric films also exhibit low transparency and poor uniformity, leading to uneven light transmittance. Therefore, researching a new high-transparency PVDF piezoelectric film and its stretching process to address these issues is of great significance. Summary of the Invention

[0004] In order to overcome the above-mentioned defects of the prior art, the present invention provides a high-transparency PVDF piezoelectric film and its preparation process. The technical problem to be solved by the present invention is that it is difficult to reduce the yield of defective products in the prior art. At the same time, in the production process, the stretching temperature and ratio are not accurately controlled, which easily leads to low density or breakage, resulting in a low pass rate. Moreover, the PVDF piezoelectric film produced has low transparency and poor uniformity, resulting in insufficient light transmittance.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a highly transparent PVDF piezoelectric film, wherein the PVDF piezoelectric film comprises a solute, a solvent, an antioxidant, a color change inhibitor, a toughening agent, an ultraviolet absorber, and PVDF powder.

[0006] A stretching process for a highly transparent PVDF piezoelectric film, the stretching process comprising the following steps:

[0007] S1. Raw material preparation:

[0008] Solvent A is obtained by uniformly mixing the solute and solvent. Solvent B is obtained by uniformly mixing the antioxidant, color change inhibitor, toughening agent and ultraviolet absorber. Solvent B and solvent A are uniformly mixed, PVDF powder is added, and after uniform mixing, granulation is performed to obtain the raw material.

[0009] S2, Melt extrusion:

[0010] The extruder is preheated in the preheating section and then the temperature is controlled in the control section. The raw materials prepared in the above steps are poured into the extrusion equipment, so that the raw materials are extruded into PVDF piezoelectric film casting film through the die head via the barrel, filter and metering pump.

[0011] S3. Stretching treatment:

[0012] S301. The heating roller is preheated, and the obtained PVDF piezoelectric film is transversely pre-stretched through the heating roller. Then, under the combined action of the hot air circulation system, the film is preheated by air heating. After cooling, buffering, stretching and shaping, the transverse stretching operation is completed to obtain the semi-finished PVDF piezoelectric film.

[0013] S302, and place the obtained semi-finished PVDF piezoelectric film on the surface of the stretching equipment for multiple longitudinal stretching treatment. After the PVDF piezoelectric film is fully heated to 60-80℃, the stretching equipment uses a longitudinal step-by-step stretching method to stretch the PVDF piezoelectric film longitudinally, stretching it 3-5 times to fully stretch and shape it. Heat and cure for 10-20 minutes, and then cool it in the cooling section for heat setting treatment.

[0014] S303. The PVDF piezoelectric film is transferred to the secondary stretching device. At the same time, abnormal points of light transmittance on the PVDF piezoelectric film are obtained, and the stretching area is determined according to the distribution of abnormal points. The force of the secondary stretching device at different stretching positions is controlled to perform stretching in both the transverse and longitudinal directions. The stretching temperature is kept constant, and the consistency of light transmittance of the PVDF piezoelectric film at different positions is adjusted to perform the secondary stretching process of the film.

[0015] S4. Subsequent processing:

[0016] It is then sent to subsequent processing steps for polarization and testing.

[0017] As a further aspect of the present invention: the solvent is N,N-dimethylacetamide or anhydrous ethanol, in parts by mass of 8-12.

[0018] The solute is AgNO3, with a mass fraction of 8-12.

[0019] The antioxidant is a mixture of thioester antioxidants and phosphite antioxidants in a ratio of 3:2, with a mass fraction of 0.1-0.5.

[0020] As a further aspect of the present invention: the toughening agent is one or more equal mixtures of liquid polysulfide rubber, liquid acrylate rubber, liquid polybutadiene rubber and nitrile rubber, with a mass fraction of 12-15.

[0021] The ultraviolet absorber is one or more of the following: salicylates, benzophenones, benzotriazoles, substituted acrylonitriles, and triazines, in equal proportions, with a mass fraction of 0.1-0.5.

[0022] The color-changing inhibitor is one or more of benzotriazole, methylbenzotriazole and methylbenzotriazole potassium, in a mass fraction of 1-1.5.

[0023] As a further aspect of the present invention: the extrusion temperature of the extruder is 160-220℃, and the speed is 7-12 rpm.

[0024] As a further aspect of the present invention: the temperature threshold for stretching is 80-100℃, the preheating temperature of the heating roller is 30-50℃, and the stretching ratio is 1.1-1.5.

[0025] As a further aspect of the present invention: the stretching rate during the multiple unidirectional stretching treatment is 45 mm / min, and the stretching ratio is 3-5.

[0026] As a further aspect of the present invention: the heat setting temperature is 100-120℃.

[0027] The temperature of the horizontal cooling section is 35-90℃, and the air pressure frequency of the cooling section is 80-90%.

[0028] As a further aspect of the present invention, the specific steps for performing the secondary stretching are as follows:

[0029] S3031. Place the PVDF piezoelectric film in the secondary stretching device and perform winding treatment. At the same time, ensure that the secondary stretching device is sealed and set the temperature to 80-90℃.

[0030] S3032. A surface light source is set above the PVDF piezoelectric film, and a light guide plate is set to make the light evenly distributed on the surface of the PVDF piezoelectric film. At the same time, an image acquisition device is set at a corresponding position below the PVDF piezoelectric film to collect the light transmitted through the PVDF piezoelectric film.

[0031] S3033. The image acquired by the image acquisition device is cropped to remove external interference and grayscale processing is performed to obtain the grayscale value of each pixel. A grayscale threshold is set. When the grayscale value of a pixel is greater than the set grayscale threshold, the pixel is marked as an abnormal point.

[0032] S3034. Then determine the distribution area of ​​the abnormal points, and slowly stretch the abnormal point locations individually. At the same time, monitor the pixel values ​​of the abnormal points during the stretching process until the pixel values ​​of most abnormal points are within the set grayscale threshold. Stop stretching, complete the secondary stretching of the current area and perform shaping processing.

[0033] S3035. Control the winding equipment to perform winding processing, so that the part of the PVDF piezoelectric film that has been detected is wound up, while the part of the PVDF piezoelectric film that has not been detected is located between the surface light source and the image acquisition equipment. Repeat the above steps until the detection and stretching processing of all PVDF piezoelectric films is completed.

[0034] As a further aspect of the present invention: the width of the surface light source illumination is greater than or equal to the width of the PVDF piezoelectric film winding, and the acquisition area of ​​the image acquisition device is greater than the illumination area of ​​the surface light source.

[0035] A highly transparent PVDF piezoelectric film is prepared by any of the above-described preparation processes. The highly transparent PVDF piezoelectric film contains PVDF powder with a particle size of 20-40 nm, which is obtained after being treated with carbon tetrafluoride plasma for 3-5 min.

[0036] The beneficial effects of this invention are as follows:

[0037] 1. This invention improves the transparency of PVDF piezoelectric films by reselecting and reproducing raw materials. During the multiple longitudinal stretching process, the microstructure of the PVDF piezoelectric film changes from spherulites to lamellars, and finally from lamellars to a fibrous structure. When the film is fully stretched, its surface microstructure distribution is relatively uniform and its density is high. At the same time, the stretching temperature and stretching ratio are controlled to prevent breakage and ensure the stretching pass rate. Furthermore, after the PVDF piezoelectric film is biaxially stretched, abnormal light transmittance points on the PVDF piezoelectric film are obtained, and the stretching area is determined based on the distribution of abnormal points. A second small-scale stretching process is then performed to stretch the areas with low light transmittance, thereby improving the thickness consistency and light transmittance uniformity of the PVDF piezoelectric film and reducing the output of defective products.

[0038] 2. By adding antioxidants, ultraviolet absorbers and color change inhibitors during the preparation of raw materials, this invention can reduce the problem of yellowing and discoloration of PVDF piezoelectric films after long-term use to a certain extent, thus making the service life of PVDF piezoelectric films longer than that of PVDF piezoelectric films prepared by previous processes.

[0039] 3. After plasma treatment, the PVDF powder of the present invention reaches a suitable particle size range, which not only improves light transmittance and flexibility, but also facilitates subsequent processing, further enhancing its compatibility with other raw materials. This makes it easier to prepare reliable and durable piezoelectric films and gives it broad application prospects in fields such as flexible electronics and optical devices. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the preparation process of the present invention;

[0041] Figure 2 This is a schematic diagram of the stretching process of the present invention;

[0042] Figure 3 This is a schematic diagram of the secondary stretching process of the present invention;

[0043] Figure 4 This is a schematic diagram of the mixing process for preparing the raw materials of this invention;

[0044] Figure 5 This is a schematic diagram of the longitudinal stretching process of the present invention. Detailed Implementation

[0045] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0046] Example 1:

[0047] like Figure 1-5 As shown, a highly transparent PVDF piezoelectric film is provided. The PVDF piezoelectric film comprises a solute, a solvent, an antioxidant, a color change inhibitor, a toughening agent, an ultraviolet absorber, and PVDF powder.

[0048] A stretching process for a high-transparency PVDF piezoelectric film, comprising the following steps:

[0049] S1. Raw material preparation:

[0050] Solvent A is obtained by uniformly mixing the solute and solvent. Solvent B is obtained by uniformly mixing the antioxidant, color change inhibitor, toughening agent and ultraviolet absorber. Solvent B and solvent A are uniformly mixed, PVDF powder is added, and after uniform mixing, granulation is performed to obtain the raw material.

[0051] S2, Melt extrusion:

[0052] The extruder is preheated in the preheating section and then the temperature is controlled in the control section. The raw materials prepared in the above steps are poured into the extrusion equipment, so that the raw materials are extruded into PVDF piezoelectric film casting film through the die head via the barrel, filter and metering pump.

[0053] S3. Stretching treatment:

[0054] S301. The heating roller is preheated, and the obtained PVDF piezoelectric film is transversely pre-stretched through the heating roller. Then, under the combined action of the hot air circulation system, the film is preheated by air heating. After cooling, buffering, stretching and shaping, the transverse stretching operation is completed to obtain the semi-finished PVDF piezoelectric film.

[0055] S302, and place the obtained semi-finished PVDF piezoelectric film on the surface of the stretching equipment for multiple longitudinal stretching treatment. After the PVDF piezoelectric film is fully heated to 60°C, the stretching equipment uses a longitudinal step-by-step stretching method to stretch the PVDF piezoelectric film longitudinally, stretching it 3 times to fully stretch and shape it. Heat it up and cure it for 10-20 minutes, and then cool it in the cooling section for heat setting treatment. Through the heat setting treatment, the film can be further crystallized and oriented, reducing internal stress and improving dimensional stability.

[0056] S303. The PVDF piezoelectric film is transferred to the secondary stretching device. At the same time, abnormal points of light transmittance on the PVDF piezoelectric film are obtained, and the stretching area is determined according to the distribution of abnormal points. The force of the secondary stretching device at different stretching positions is controlled to perform stretching in both the transverse and longitudinal directions. The stretching temperature is kept constant, and the consistency of light transmittance of the PVDF piezoelectric film at different positions is adjusted to perform the secondary stretching process of the film.

[0057] S4. Subsequent processing:

[0058] It is then sent to subsequent processing steps for polarization and testing.

[0059] Anhydrous ethanol was used as the solvent, with a mass fraction of 8 parts.

[0060] The solute is AgNO3, and the mass fraction is 8.

[0061] The antioxidant is a mixture of thioester antioxidants and phosphite antioxidants in a ratio of 3:2, with a mass fraction of 0.1.

[0062] The toughening agent is liquid polysulfide rubber, with a mass fraction of 12.

[0063] The ultraviolet absorber is a salicylic acid ester, with a mass fraction of 0.1.

[0064] The color-changing inhibitor used was benzotriazole, with a mass fraction of 1.

[0065] The extrusion temperature of the extruder is 160℃, and the extrusion speed is controlled at 7-12 rpm.

[0066] The temperature threshold for stretching is 80-100℃, the preheating temperature of the heating roller is 30℃, and the stretching ratio is 1.1.

[0067] The stretching rate during multiple uniaxial stretching is 45 mm / min, and the stretching ratio is 3.

[0068] The heat setting temperature is 100℃.

[0069] The temperature of the horizontal cooling section is 35℃, and the air pressure frequency of the cooling section is 80%.

[0070] The specific steps for performing secondary stretching are as follows:

[0071] S3031. Place the PVDF piezoelectric film in the secondary stretching device and perform winding treatment. At the same time, ensure that the secondary stretching device is sealed and set the temperature to 80℃.

[0072] S3032. A surface light source is set above the PVDF piezoelectric film, and a light guide plate is set to make the light evenly distributed on the surface of the PVDF piezoelectric film. At the same time, an image acquisition device is set at a corresponding position below the PVDF piezoelectric film to collect the light transmitted through the PVDF piezoelectric film.

[0073] S3033. The image acquired by the image acquisition device is cropped to remove external interference and grayscale processing is performed to obtain the grayscale value of each pixel. A grayscale threshold is set. When the grayscale value of a pixel is greater than the set grayscale threshold, the pixel is marked as an abnormal point.

[0074] S3034. Then determine the distribution area of ​​the abnormal points, and slowly stretch the abnormal point locations individually. At the same time, monitor the pixel values ​​of the abnormal points during the stretching process until the pixel values ​​of most abnormal points are within the set grayscale threshold. Stop stretching, complete the secondary stretching of the current area and perform shaping processing.

[0075] S3035. Control the winding equipment to perform winding processing, so that the part of the PVDF piezoelectric film that has been detected is wound up, while the part of the PVDF piezoelectric film that has not been detected is located between the surface light source and the image acquisition equipment. Repeat the above steps until the detection and stretching processing of all PVDF piezoelectric films is completed.

[0076] The width of the surface light source illumination is greater than or equal to the width of the PVDF piezoelectric film winding, and the acquisition area of ​​the image acquisition device is greater than the illumination area of ​​the surface light source.

[0077] Example 2:

[0078] like Figure 1-5As shown, a highly transparent PVDF piezoelectric film is provided. The PVDF piezoelectric film comprises a solute, a solvent, an antioxidant, a color change inhibitor, a toughening agent, an ultraviolet absorber, and PVDF powder.

[0079] A stretching process for a high-transparency PVDF piezoelectric film, comprising the following steps:

[0080] S1. Raw material preparation:

[0081] Solvent A is obtained by uniformly mixing the solute and solvent. Solvent B is obtained by uniformly mixing the antioxidant, color change inhibitor, toughening agent and ultraviolet absorber. Solvent B and solvent A are uniformly mixed, PVDF powder is added, and after uniform mixing, granulation is performed to obtain the raw material.

[0082] S2, Melt extrusion:

[0083] The extruder is preheated in the preheating section and then the temperature is controlled in the control section. The raw materials prepared in the above steps are poured into the extrusion equipment, so that the raw materials are extruded into PVDF piezoelectric film casting film through the die head via the barrel, filter and metering pump.

[0084] S3. Stretching treatment:

[0085] S301. The heating roller is preheated, and the obtained PVDF piezoelectric film is transversely pre-stretched through the heating roller. Then, under the combined action of the hot air circulation system, the film is preheated by air heating. After cooling, buffering, stretching and shaping, the transverse stretching operation is completed to obtain the semi-finished PVDF piezoelectric film.

[0086] S302, and place the obtained semi-finished PVDF piezoelectric film on the surface of the stretching equipment for multiple longitudinal stretching treatment. After the PVDF piezoelectric film is fully heated to 70°C, the stretching equipment uses a longitudinal step-by-step stretching method to stretch the PVDF piezoelectric film longitudinally, stretching it 4 times to fully stretch and shape it. Heat it up and cure it for 10-20 minutes, and then cool it in the cooling section for heat setting treatment. Through the heat setting treatment, the film can be further crystallized and oriented, reducing internal stress and improving dimensional stability.

[0087] S303. The PVDF piezoelectric film is transferred to the secondary stretching device. At the same time, abnormal points of light transmittance on the PVDF piezoelectric film are obtained, and the stretching area is determined according to the distribution of abnormal points. The force of the secondary stretching device at different stretching positions is controlled to perform stretching in both the transverse and longitudinal directions. The stretching temperature is kept constant, and the consistency of light transmittance of the PVDF piezoelectric film at different positions is adjusted to perform the secondary stretching process of the film.

[0088] S4. Subsequent processing:

[0089] It is then sent to subsequent processing steps for polarization and testing.

[0090] The solvent used is N,N-dimethylacetamide, with a mass fraction of 10.

[0091] The solute is AgNO3, and the mass fraction is 10.

[0092] The antioxidant is a mixture of thioester antioxidants and phosphite antioxidants in a ratio of 3:2, with a mass fraction of 0.3.

[0093] The toughening agent is a mixture of liquid acrylate rubber and liquid polybutadiene rubber in equal proportions, with a mass fraction of 13.

[0094] The ultraviolet absorber is a mixture of equal parts of acrylonitrile and triazine, with a mass fraction of 0.3.

[0095] The color-changing inhibitor is a mixture of methylbenzotriazole and methylbenzotriazole potassium in equal proportions, with a mass ratio of 1.3.

[0096] The extrusion temperature of the extruder is 200℃, and the extrusion speed is controlled at 7-12 rpm.

[0097] The temperature threshold for stretching is 80-100℃, the preheating temperature of the heating roller is 45℃, and the stretching ratio is 1.5.

[0098] The stretching rate during multiple uniaxial stretching is 45 mm / min, and the stretching ratio is 5.

[0099] The heat setting temperature is 100℃.

[0100] The temperature of the horizontal cooling section is 90℃, and the air pressure frequency of the cooling section is 90%.

[0101] The specific steps for performing secondary stretching are as follows:

[0102] S3031. Place the PVDF piezoelectric film in the secondary stretching device and perform winding treatment, while ensuring that the secondary stretching device is sealed and setting the temperature to 90℃.

[0103] S3032. A surface light source is set above the PVDF piezoelectric film, and a light guide plate is set to make the light evenly distributed on the surface of the PVDF piezoelectric film. At the same time, an image acquisition device is set at a corresponding position below the PVDF piezoelectric film to collect the light transmitted through the PVDF piezoelectric film.

[0104] S3033. The image acquired by the image acquisition device is cropped to remove external interference and grayscale processing is performed to obtain the grayscale value of each pixel. A grayscale threshold is set. When the grayscale value of a pixel is greater than the set grayscale threshold, the pixel is marked as an abnormal point.

[0105] S3034. Then determine the distribution area of ​​the abnormal points, and slowly stretch the abnormal point locations individually. At the same time, monitor the pixel values ​​of the abnormal points during the stretching process until the pixel values ​​of most abnormal points are within the set grayscale threshold. Stop stretching, complete the secondary stretching of the current area and perform shaping processing.

[0106] S3035. Control the winding equipment to perform winding processing, so that the part of the PVDF piezoelectric film that has been detected is wound up, while the part of the PVDF piezoelectric film that has not been detected is located between the surface light source and the image acquisition equipment. Repeat the above steps until the detection and stretching processing of all PVDF piezoelectric films is completed.

[0107] The width of the surface light source illumination is greater than or equal to the width of the PVDF piezoelectric film winding, and the acquisition area of ​​the image acquisition device is greater than the illumination area of ​​the surface light source.

[0108] Example 3

[0109] The difference from Example 2 is as follows: S1, Raw material preparation: Solvent A is obtained by uniformly mixing the solute and solvent. Solvent B is obtained by uniformly mixing the antioxidant, discoloration inhibitor, toughening agent and ultraviolet absorber. Solvent B and solvent A are uniformly mixed and then PVDF powder is added. After uniform mixing again, the mixture is granulated to obtain the raw material.

[0110] The PVDF powder is first subjected to carbon tetrafluoride plasma treatment for 4 minutes before use to reduce its particle size to 30 nm.

[0111] Comparative Example 1

[0112] The difference from Example 2 is that the specific steps of the secondary stretching are not disclosed:

[0113] S3031. Place the PVDF piezoelectric film in the secondary stretching device and perform winding treatment, while ensuring that the secondary stretching device is sealed and setting the temperature to 90℃.

[0114] S3032. A surface light source is set above the PVDF piezoelectric film, and a light guide plate is set to make the light evenly distributed on the surface of the PVDF piezoelectric film. At the same time, an image acquisition device is set at a corresponding position below the PVDF piezoelectric film to collect the light transmitted through the PVDF piezoelectric film.

[0115] S3033. The image acquired by the image acquisition device is cropped to remove external interference and grayscale processing is performed to obtain the grayscale value of each pixel. A grayscale threshold is set. When the grayscale value of a pixel is greater than the set grayscale threshold, the pixel is marked as an abnormal point.

[0116] S3034. Then determine the distribution area of ​​the abnormal points, and slowly stretch the abnormal point locations individually. At the same time, monitor the pixel values ​​of the abnormal points during the stretching process until the pixel values ​​of most abnormal points are within the set grayscale threshold. Stop stretching, complete the secondary stretching of the current area and perform shaping processing.

[0117] S3035. Control the winding equipment to perform winding processing, so that the part of the PVDF piezoelectric film that has been detected is wound up, while the part of the PVDF piezoelectric film that has not been detected is located between the surface light source and the image acquisition equipment. Repeat the above steps until the detection and stretching processing of all PVDF piezoelectric films is completed.

[0118] The width of the surface light source illumination is greater than or equal to the width of the PVDF piezoelectric film winding, and the acquisition area of ​​the image acquisition device is greater than the illumination area of ​​the surface light source.

[0119] According to GB2410-80 Test Method for Transmittance and Haze of Transparent Plastics, the transmittance of the PVDF piezoelectric films obtained in Examples 1-3 and Comparative Example 1 were measured respectively. The transmittance of Example 1 reached 90.5%, the transmittance of Example 2 reached 91%, the transmittance of Example 3 reached 92.4%, and the transmittance of Comparative Example 1 was 86.2%. Subsequent testing revealed that the thickness of the PVDF piezoelectric films in Examples 1-3 was relatively consistent, while the thickness distribution of the PVDF piezoelectric film in Comparative Example 1 was uneven.

[0120] In summary, this invention improves the transparency of PVDF piezoelectric films by reselecting and reproducing raw materials. During the multiple longitudinal stretching process, the microstructure of the PVDF piezoelectric film changes from spherulites to lamellars, and finally from lamellars to a fibrous structure. When the film is fully stretched, its surface microstructure distribution is relatively uniform and its density is high. Furthermore, by controlling the stretching temperature and stretching ratio, breakage is less likely, ensuring a high stretching yield. After biaxial stretching of the PVDF piezoelectric film, abnormal light transmittance points are identified, and the stretching area is determined based on the distribution of these abnormal points. A second, smaller-scale stretching process is then performed to further stretch areas with low light transmittance, thereby improving the transparency of the PVDF piezoelectric film. The invention improves thickness consistency and light transmission uniformity, reducing the production of defective products. Furthermore, by adding antioxidants, UV absorbers, and discoloration inhibitors during the raw material preparation process, the invention can also reduce the yellowing and discoloration of PVDF piezoelectric films after prolonged use, resulting in a longer service life compared to PVDF piezoelectric films prepared by previous processes. In addition, the PVDF powder of this invention, after plasma treatment, achieves a suitable particle size, which not only improves light transmission and flexibility but also facilitates subsequent processing, further enhancing its compatibility with other raw materials. This makes it easier to prepare reliable and durable piezoelectric films, giving them broad application prospects in fields such as flexible electronics and optical devices.

[0121] Finally, it should be noted that although the present invention has been described in detail above with general descriptions and specific embodiments, the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A process for preparing a highly transparent PVDF piezoelectric thin film, characterized in that: Includes the following steps: S1. Raw material preparation: Solvent A is obtained by mixing the solute and solvent. Solvent B is obtained by mixing the antioxidant, color change inhibitor, toughening agent and ultraviolet absorber. Solvent B and solvent A are mixed evenly, and then PVDF powder is added. After mixing evenly, the mixture is granulated to obtain the raw material. S2, Melt extrusion: The preheating section of the extrusion equipment is preheated, and the temperature is controlled by the control section. The raw material S1 is poured into the extrusion equipment, and after passing through the barrel, filter and metering pump, it is extruded from the die head to form a PVDF piezoelectric film casting film. S3. Stretching treatment: S301. Preheat the heating roller, and then pre-stretch the PVDF piezoelectric film casting film of S2 laterally through the heating roller. Then, under the combined action of the hot air circulation system, air heating is completed to obtain a preheated film. The preheated film is then subjected to lateral stretching through cooling, buffering, stretching and shaping to obtain a semi-finished PVDF piezoelectric film. S302. Place the semi-finished PVDF piezoelectric film on the surface of the stretching equipment for multiple longitudinal stretching treatment. When the PVDF piezoelectric film is heated to 60-80℃, the PVDF piezoelectric film is stretched longitudinally in a step-by-step manner with a stretching ratio of 3-5. Then, heat it to cure for 6-8 hours and then cool it in the cooling section for heat setting. S303. The PVDF piezoelectric film is transferred to the secondary stretching device. At the same time, abnormal points of light transmittance on the PVDF piezoelectric film are obtained, and the stretching area is determined according to the distribution of abnormal points. The force of the secondary stretching device at different stretching positions is controlled to perform stretching in both the transverse and longitudinal directions. The stretching temperature is kept constant, and the consistency of light transmittance of the PVDF piezoelectric film at different positions is adjusted to perform the secondary stretching process of the film. S4. Subsequent processing: The PVDF piezoelectric film after secondary stretching is sent to subsequent processing for polarization and testing to obtain a highly transparent PVDF piezoelectric film.

2. The preparation process of the high-transparency PVDF piezoelectric thin film according to claim 1, characterized in that: The solvent is N,N-dimethylacetamide or anhydrous ethanol, in parts by mass of 8-12; the solute is AgNO3, in parts by mass of 8-12. The antioxidant is a mixture of thioester antioxidants and phosphite antioxidants in a ratio of 3:2, with a mass fraction of 0.1-0.

5.

3. The preparation process of the high-transparency PVDF piezoelectric thin film according to claim 1, characterized in that: The toughening agent is one or more equal-ratio mixtures of liquid polysulfide rubber, liquid acrylate rubber, liquid polybutadiene rubber and nitrile rubber, with a mass fraction of 12-15. The ultraviolet absorber is one or more of the following: salicylates, benzophenones, benzotriazoles, substituted acrylonitriles, and triazines, in equal proportions, with a mass fraction of 0.1-0.

5. The color-changing inhibitor is one or more of benzotriazole, methylbenzotriazole and methylbenzotriazole potassium, in a mass fraction of 1-1.

5.

4. The preparation process of the high-transparency PVDF piezoelectric thin film according to claim 1, characterized in that: The extrusion temperature of the extrusion equipment is 160-220℃, and the extrusion speed is controlled at 7-12 rpm.

5. The preparation process of the high-transparency PVDF piezoelectric thin film according to claim 1, characterized in that: The temperature threshold for stretching is 80-100℃, the preheating temperature of the heating roller is 30-50℃, and the stretching ratio is 1.1-1.

5.

6. The preparation process of the high-transparency PVDF piezoelectric thin film according to claim 1, characterized in that: The stretching rate during multiple uniaxial stretching is 45 mm / min.

7. The preparation process of the high-transparency PVDF piezoelectric thin film according to claim 1, characterized in that: The heat setting temperature is 100-120℃; The temperature of the horizontal cooling section is 35-90℃, and the air pressure frequency of the cooling section is 80-90%.

8. The preparation process of the high-transparency PVDF piezoelectric thin film according to claim 1, characterized in that: The specific steps for secondary stretching are as follows: S3031. Place the PVDF piezoelectric film in the secondary stretching device and perform winding treatment, while ensuring that the secondary stretching device is sealed and setting the temperature to 80-90℃. S3032. A surface light source is set above the PVDF piezoelectric film, and a light guide plate is set to make the light evenly distributed on the surface of the PVDF piezoelectric film. At the same time, an image acquisition device is set at a corresponding position below the PVDF piezoelectric film to collect the light transmitted through the PVDF piezoelectric film. S3033. The image acquired by the image acquisition device is cropped to remove external interference and grayscale processing is performed to obtain the grayscale value of each pixel. A grayscale threshold is set. When the grayscale value of a pixel is greater than the set grayscale threshold, the pixel is marked as an abnormal point. S3034. Then determine the distribution area of ​​the abnormal points, and slowly stretch the abnormal point locations individually. At the same time, monitor the pixel values ​​of the abnormal points during the stretching process until the pixel values ​​of most abnormal points are within the set grayscale threshold. Stop stretching, complete the secondary stretching of the current area and perform shaping processing. S3035. Control the winding equipment to perform winding processing, winding up the portion of the PVDF piezoelectric film that has been inspected, while the uninspected portion of the PVDF piezoelectric film is located between the surface light source and the image acquisition equipment. Repeat the above steps until the inspection and stretching processing of all PVDF piezoelectric films is completed.

9. The preparation process of the high-transparency PVDF piezoelectric thin film according to claim 8, characterized in that: The width of the surface light source illumination is greater than or equal to the width of the PVDF piezoelectric film winding, and the acquisition area of ​​the image acquisition device is greater than the illumination area of ​​the surface light source.

10. A highly transparent PVDF piezoelectric film, characterized in that: The highly transparent PVDF piezoelectric film is prepared by any one of the preparation processes according to claims 1-9, wherein the PVDF powder with a particle size of 20-40 nm is obtained by subjecting the PVDF powder with a particle size of 20-40 nm to carbon tetrafluoride plasma treatment for 3-5 min.

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