A piezoelectric thin film rapid stretching process

Abstract

The application discloses a kind of piezoelectric film fast stretching process, including the steps of precursor processing, granulation preparation, extrusion molding, fast stretching, high pressure polarization and winding into warehouse.The application can effectively improve the stretching speed and reduce energy consumption by replacing the traditional solid roller with a semi-solid stretching roller to reduce the self-weight.Secondly, the stretching unit with inclined vertical structure and the silicone or rubber anti-slip layer coated on the surface of the semi-solid stretching roller can not only compensate for the film slipping and high system tension problems that occur during high-speed stretching of horizontal and vertical structures respectively, but also further reduce the slipping effect by increasing the friction, effectively avoiding potential film wrinkles, uneven stretching hazards and equipment energy consumption defects.In addition, the high stretching rate can effectively prevent the recovery of the oriented PVDF molecular chain, thereby achieving efficient and fast preparation of piezoelectric film in the actual production process.

Description

Technical Field

[0001] This invention relates to the field of thin film preparation technology, and more specifically to a rapid stretching process for piezoelectric thin films. Background Technology

[0002] Polyvinylidene fluoride (PVDF) piezoelectric films are polymeric materials with excellent piezoelectric properties, finding wide application in sensors, actuators, energy harvesters, and especially in implantable medical devices and wearable electronics. Structurally, PVDF is a semi-crystalline polymer with multiple crystalline phases, including α, β, γ, δ, and ε phases. Among these, the β phase exhibits the strongest piezoelectric properties.

[0003] The formation of the piezoelectric β phase is due to the stress applied to the film during stretching. The stress applied along the stretching direction forces spherical crystals to transform into microfibrillary crystals. Typically, as stretching proceeds, the molecular chains gradually orient, a process accompanied by a phase transition that affects the crystallinity of the sample, and consequently, its piezoelectric properties. Generally, the stretching process is influenced by stretching temperature, stretching ratio, and stretching rate.

[0004] Generally, the higher the stretching ratio, the higher the β phase content and the better the piezoelectric properties. However, excessive stretching may cause the film to rupture. Excessive stretching temperature will cause the material to melt prematurely, while excessively low temperature is not conducive to the transformation of crystal structure. In terms of stretching rate, excessively low stretching speed will affect the actual production efficiency, while excessively high stretching speed will easily cause film slippage and insufficient tension in actual operation, resulting in poor film forming quality.

[0005] Current polyvinylidene fluoride (PVDF) film stretching technologies are mainly based on slow stretching at low temperatures (stretching temperature 60–90℃, stretching rate ≤50 mm / min), which is not conducive to the efficient and rapid preparation of piezoelectric films in actual production processes. Therefore, controlling rapid and effective stretching process parameters is crucial for preparing high-performance, high-quality PVDF piezoelectric films. Summary of the Invention

[0006] The technical problem solved by this invention is to provide a rapid stretching process for piezoelectric films.

[0007] The technical solution adopted by this invention to solve its technical problem is:

[0008] A rapid stretching process for piezoelectric thin films includes the following steps:

[0009] S1: Precursor treatment, polyvinylidene fluoride granules are added to a grinding and reaction equipment for grinding, crushing and sieving to prepare powder;

[0010] S2: Granulation preparation, the powder and processing aid are added to a vacuum mixer for vacuum stirring and mixing, and the mixed material is fed into a twin-screw extruder using a loss-in-weight feeding system. The material is extruded through a die to form a continuous strip. After the strip cools and solidifies, it is cut into small granules using a pelletizer to prepare resin granules.

[0011] S3: Extrusion molding. After drying the resin particles prepared in step S2, they are added to the extruder as needed. Under the action of the screw, the resin particles are fully mixed, melted and plasticized, and then extruded through the die onto the casting machine to solidify and form a preform.

[0012] S4: Rapid stretching. The pre-made film is pulled onto a film longitudinal stretching machine for rapid stretching. Before stretching, the stretching roller is preheated. The stretching roller is a semi-solid roller with a 0.1mm to 5mm silicone or rubber anti-slip thin layer on its surface. After stretching, the film is kept at a constant temperature for 5 to 30 minutes for annealing and then quenched to room temperature to prepare a semi-finished film.

[0013] S5: High voltage polarization, the semi-finished film is placed in a DC electric field for constant voltage polarization, and after cooling, the finished polyvinylidene fluoride piezoelectric film is obtained;

[0014] S6: Wind up and put into storage. The finished polyvinylidene fluoride piezoelectric film is wound up and put into storage.

[0015] Furthermore, in step S1, the particle size of the powder is 10μm to 500μm.

[0016] Furthermore, in step S2, the melt index of the resin particles is 3-22 g / 10 min, 230°C, 5 kg.

[0017] Furthermore, in step S3, the drying temperature is 80-120℃, and the drying time is 9-15h; the screw and die working temperature of the extruder is 170-220℃, and the screw speed is 25-50rpm; the casting roller temperature of the casting machine is set to 40-110℃.

[0018] Furthermore, in step S3, a desiccant is added during the drying process for dehumidification.

[0019] Furthermore, in step S4, the stretching rate of the stretching machine is 0.5 to 2 m / min, the stretching temperature is 130 to 150°C, and the stretching ratio is 4 to 6 times.

[0020] Furthermore, in step S4, the stretching unit is selected as an inclined vertical structure.

[0021] Furthermore, in step S5, the polarization voltage is 50–100 kV / mm, the polarization time is 10–60 min, the polarization temperature is room temperature (25°C), and the relative humidity is 40%.

[0022] The beneficial effects of this invention are:

[0023] 1. This invention effectively increases stretching speed and reduces energy consumption by using semi-solid stretching rollers instead of traditional solid rollers to reduce weight. Secondly, the use of a slanted vertical stretching unit and the coating of the semi-solid stretching rollers with a silicone or rubber anti-slip layer not only compensates for the film slippage and excessive system tension issues that occur with horizontal and vertical structures under high-speed stretching, respectively, but also further reduces slippage by increasing friction, effectively avoiding potential defects such as film wrinkles, uneven stretching, and excessive equipment energy consumption.

[0024] 2. This invention improves the stretching rate through a rapid stretching process. A higher stretching rate can effectively prevent the recovery of the oriented PVDF molecular chains, thus well preserving the β phase in the PVDF film, thereby enabling efficient and rapid preparation of piezoelectric films in actual production processes. Attached Figure Description

[0025] Figure 1 This is a process flow diagram of the present invention;

[0026] Figure 2 This is a process flow diagram of granulation preparation in this invention;

[0027] Figure 3 This is a process flow diagram of extrusion molding in this invention;

[0028] Figure 4 This is a process flow diagram of rapid stretching in this invention;

[0029] Figure 5 This is a schematic cross-sectional view of the stretching roller in the rapid stretching process of this invention;

[0030] The diagram is marked as follows:

[0031] 1. Semi-solid roller; 2. Anti-slip thin layer. Detailed Implementation

[0032] To make the above-mentioned contents, objectives, and beneficial effects of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0033] It should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0034] like Figure 1-4 As shown, the present invention provides a rapid stretching process for piezoelectric thin films, comprising the following steps:

[0035] S1: Precursor Treatment. Polyvinylidene fluoride (PVDF) granules are added to a grinding and reaction apparatus for grinding and pulverizing. This apparatus includes, but is not limited to, ball mills, roller presses, air jet mills, and high-shear mixers. Through repeated intense mixing, pulverization, and even shearing and activation processes within the grinding and reaction apparatus, powder with a smaller particle size is produced.

[0036] Furthermore, the powder is sieved to obtain a powder precursor with a particle size of 10–500 μm. Preferably, the particle size is 50–500 μm.

[0037] S2: Granulation Preparation. The powder precursor, plasticizer, stabilizer, antioxidant, and other processing aids are added to a vacuum mixer and mixed thoroughly. Then, a loss-in-weight feeding system is used to feed the mixture into a twin-screw extruder, which then extrudes it through a die to form a continuous strip. After the strip cools and solidifies, a pelletizer is used to cut the cooled strip into small granules. Melt flow index is tested for later use.

[0038] Furthermore, the melt index (MR) of the granulated material is 3–22 (g / 10min, 230°C, 5kg). Preferably, the melt index of the granulated material is 15–20 (g / 10min, 230°C, 5kg).

[0039] S3: Extrusion Molding. The granules prepared in step S2 are dried and then added to an extruder as needed. Under the action of the screw, the granules are thoroughly mixed, melted, and plasticized, and then extruded through a die. To ensure the stability of the processing and the consistency of product quality, the plasticized raw material liquid is pushed into the casting die by a melt metering pump, and a hot air box is placed at the die to reduce heat loss before melt molding. The raw material liquid is then extruded through the die onto a casting machine to solidify and form a pre-made film.

[0040] Furthermore, the granules are dried at a temperature of 80–120°C for 9–15 hours, and a desiccant is added for dehumidification. The desiccant can be any one of anhydrous calcium chloride, silica gel, phosphorus pentoxide, molecular sieve, or activated carbon.

[0041] Furthermore, the screw and die of the extruder operate at a temperature of 170–220°C, the screw speed is 25–50 rpm, and the casting roll temperature is set to 40–110°C, using electric heating.

[0042] Preferably, the cooling roller is cooled by condensate.

[0043] S4: Rapid stretching. The pre-made film is drawn onto a film longitudinal stretching machine for stretching. Before stretching, the rollers are preheated to the stretching temperature and held for 10 minutes. Then, continuous uniaxial stretching is performed according to the preset parameters. The stretched sample is kept at a constant temperature for 5-30 minutes for annealing and quenched to room temperature to eliminate internal stress and obtain a semi-finished film.

[0044] Furthermore, such as Figure 5 As shown, the stretching roller 1 is a semi-solid roller instead of a traditional solid roller, which can improve the stretching speed and reduce energy consumption.

[0045] Furthermore, such as Figure 5 As shown, the surface of the stretching roller is covered with a 0.1-5mm silicone or rubber anti-slip layer 2, which can reduce the problem of film slippage.

[0046] Furthermore, the stretching unit adopts an inclined vertical structure instead of the traditional horizontal and vertical structures, while achieving continuous stretching.

[0047] Furthermore, the stretching rate is controlled at 0.5–2 m / min, the stretching temperature is controlled at 130–150℃, and the stretching ratio is controlled at 4–6 times.

[0048] S5: High-voltage polarization. The semi-finished film is placed in a DC electric field for constant-voltage polarization. After cooling, the finished polyvinylidene fluoride piezoelectric film is obtained and a discharge test is performed. 33 .

[0049] Furthermore, based on the thickness of the polarized film, the polarization voltage is set to 50–100 kV / mm, the polarization time to 10–60 min, the polarization temperature to room temperature (25°C), and the relative humidity to 40%.

[0050] S6: Rewind the film and put the finished film into storage.

[0051] Example 1:

[0052] S1: Precursor treatment. PVDF granules are mixed with an appropriate amount of ethanol and added to a ball mill. Through multiple mixing, crushing, and sieving processes in the reactor, powder with an average particle size of 100 μm is produced.

[0053] S2: Granulation Preparation. The screened powder is mixed evenly with processing aids such as plasticizers, stabilizers, and antioxidants in a vacuum mixer. The mixed material is then fed into a twin-screw extruder using a loss-in-weight feeding system, and subsequently extruded through a die to form continuous material strips. The cooled material strips are then cut into fine granules using a pelletizer. The granule melt index is selected as 15 (g / 10min, 230℃, 5kg), and it is ready for use.

[0054] S3: Extrusion Molding. Before extrusion, the prepared PVDF granules are dried in an 80℃ oven for 15 hours, and anhydrous CaCl2 is added as a desiccant for dehumidification. Then, the granules are poured into the extrusion hopper in batches as needed, controlling the screw and die temperature of the extruder at 190–200℃ and the screw speed at 25 rpm. The casting roll is preheated from room temperature to 80℃ for 10 minutes. Then, a single screw pushes the molten raw material into the casting flat die through a melt metering pump and then onto the casting machine for cooling and shaping, followed by winding to obtain a pre-cast film with a thickness of 200 μm.

[0055] S4: Rapid stretching. The pre-made film is drawn onto an inclined vertical film stretching machine, and a layer of anti-slip silicone with a thickness of about 1 mm is wrapped around the semi-solid stretching rollers. Before stretching, the rollers are preheated to 130℃ and held for 10 minutes. Then, the film is stretched 4 times at 130℃ at a constant speed of 0.5 m / s. The stretched sample is then annealed at a constant temperature for 30 minutes and quenched to room temperature to eliminate internal stress, thus obtaining a semi-finished film.

[0056] S5: High-voltage polarization. The semi-finished film is placed in a DC electric field for constant temperature, humidity, and voltage polarization. The polarization voltage is set to 80kV / mm. After cooling, the finished PVDF piezoelectric film is obtained, and a discharge test is performed. 33 ;

[0057] S6: Rewinding and warehousing of finished film.

[0058] Example 2:

[0059] S1: Precursor treatment. PVDF granules are added to a high-shear mixer and subjected to multiple mixing, crushing, and sieving processes in the reactor to produce powder with an average particle size of 150 μm.

[0060] S2: Granulation Preparation. The screened powder is mixed evenly with processing aids such as plasticizers, stabilizers, and antioxidants in a vacuum mixer. The mixed material is then fed into a twin-screw extruder using a loss-in-weight feeding system, and subsequently extruded through a die to form continuous material strips. The cooled material strips are then cut into fine granules using a pelletizer. The granule melt index is selected as 18 (g / 10min, 230℃, 5kg), and it is ready for use.

[0061] S3: Extrusion Molding. Before extrusion, the prepared PVDF granules are dried in a 90℃ oven for 12 hours, and anhydrous P2O5 desiccant is added for dehumidification. Then, they are poured into the extrusion hopper in batches as needed, controlling the screw and die temperature of the extruder at 180-190℃ and the screw speed at 35 rpm. The casting roll is preheated from room temperature to 90℃ for 10 minutes. Then, a single screw pushes the molten raw material into the casting flat die through a melt metering pump and then onto the casting machine for cooling and shaping, followed by winding to obtain a pre-cast film with a thickness of 205 μm.

[0062] S4: Rapid stretching. The pre-made film is drawn onto an inclined vertical film stretching machine, and a layer of anti-slip silicone with a thickness of about 1 mm is wrapped around the semi-solid stretching rollers. Before stretching, the rollers are preheated to 140℃ and held for 10 minutes. Then, the film is stretched 5 times at 140℃ at a constant speed of 1 m / s. The stretched sample is then annealed at a constant temperature for 20 minutes and quenched to room temperature to eliminate internal stress, thus obtaining a semi-finished film.

[0063] S5: High-voltage polarization. The semi-finished film is placed in a DC electric field for constant temperature, humidity, and voltage polarization. The polarization voltage is set to 70kV / mm. After cooling, the finished PVDF piezoelectric film is obtained, and a discharge test is performed. 33 ;

[0064] S6: Rewinding and warehousing of finished film.

[0065] Example 3:

[0066] S1: Precursor treatment. PVDF granules are added to a high-shear mixer and subjected to multiple mixing, crushing, and sieving processes in the reactor to produce powder with an average particle size of 200 μm.

[0067] S2: Granulation Preparation. The screened powder is mixed evenly with processing aids such as plasticizers, stabilizers, and antioxidants in a vacuum mixer. The mixed material is then fed into a twin-screw extruder using a loss-in-weight feeding system, and subsequently extruded through a die to form continuous material strips. The cooled material strips are then cut into fine granules using a pelletizer. The granule melt index is selected as 20 (g / 10min, 230℃, 5kg), and it is ready for use.

[0068] S3: Extrusion Molding. Before extrusion, the prepared PVDF granules are dried in a 100℃ oven for 9 hours and dehumidified with molecular sieves. Then, they are poured into the extrusion hopper in batches as needed, controlling the screw and die temperature of the extruder at 175–185℃ and the screw speed at 45 rpm. The casting roll is preheated from room temperature to 110℃ for 10 minutes. Then, a single screw pushes the molten raw material into the casting flat die through a melt metering pump and then onto the casting machine for cooling and shaping, followed by winding to obtain a pre-cast film with a thickness of 195 μm.

[0069] S4: Rapid stretching. The pre-made film is drawn onto an inclined vertical film stretching machine, and a layer of anti-slip silicone with a thickness of about 1 mm is wrapped around the semi-solid stretching rollers. Before stretching, the rollers are preheated to 150℃ and held for 10 minutes. Then, the film is stretched 6 times at 150℃ at a constant speed of 2 m / s. The stretched sample is then annealed at a constant temperature for 10 minutes and quenched to room temperature to eliminate internal stress, thus obtaining a semi-finished film.

[0070] S5: High-voltage polarization. The semi-finished film is placed in a DC electric field for constant temperature, humidity, and voltage polarization. The polarization voltage is set to 60kV / mm. After cooling, the finished PVDF piezoelectric film is obtained, and a discharge test is performed. 33 ;

[0071] S6: Rewinding and warehousing of finished film.

[0072] Example 4:

[0073] S1: Precursor treatment. PVDF granules are added to a high-shear mixer and subjected to multiple mixing, crushing, and sieving processes in the reactor to produce powder with an average particle size of 200 μm.

[0074] S2: Granulation Preparation. The screened powder is mixed evenly with processing aids such as plasticizers, stabilizers, and antioxidants in a vacuum mixer. The mixed material is then fed into a twin-screw extruder using a loss-in-weight feeding system, and subsequently extruded through a die to form continuous material strips. The cooled material strips are then cut into fine granules using a pelletizer. The granule melt index is selected as 20 (g / 10min, 230℃, 5kg), and it is ready for use.

[0075] S3: Extrusion Molding. Before extrusion, the prepared PVDF granules are dried in a 100℃ oven for 9 hours, and activated carbon is added for dehumidification. Then, they are poured into the extrusion hopper in batches as needed, and the temperature of the extruder screw and die is controlled at 175~185℃, and the screw speed is 45rpm. The temperature of the casting roll is preheated from room temperature to 110℃ for 10 minutes. Then, the single screw pushes the molten raw material liquid into the casting flat die through the melt metering pump and then conveys it to the casting machine for cooling and shaping, and then winding to obtain a pre-formed film with a thickness of 195μm;

[0076] S4: Rapid stretching. The pre-made film is drawn onto an inclined vertical film stretching machine, and a layer of anti-slip silicone with a thickness of about 1 mm is wrapped around the semi-solid stretching rollers. Before stretching, the rollers are preheated to 150℃ and held for 10 minutes. Then, the film is stretched 6 times at 150℃ at a constant speed of 50 mm / s. The stretched sample is then annealed at a constant temperature for 10 minutes and quenched to room temperature to eliminate internal stress, thus obtaining a semi-finished film.

[0077] S5: High-voltage polarization. The semi-finished film is placed in a DC electric field for constant temperature, humidity, and voltage polarization. The polarization voltage is set to 60kV / mm. After cooling, the finished PVDF piezoelectric film is obtained, and a discharge test is performed. 33 ;

[0078] S6: Rewinding and warehousing of finished film.

[0079] The tensile parameters, thickness, and measured piezoelectric constants of the piezoelectric films prepared in Examples 1-4 are shown in Table 1.

[0080] Table 1

[0081]

[0082] As can be seen from the table above, by using the rapid stretching process of the piezoelectric thin film of the present invention to increase the stretching rate of the film, not only can the molecular chains be oriented rapidly to the maximum extent, resulting in a significant improvement in piezoelectric properties, but it can also greatly improve the actual film production efficiency.

[0083] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A rapid stretching process for piezoelectric thin films, characterized in that: Includes the following steps: S1: Precursor treatment, polyvinylidene fluoride granules are added to a grinding and reaction equipment for grinding, crushing and sieving to prepare powder; S2: Granulation preparation: The powder and processing aids are added to a vacuum mixer for vacuum stirring and mixing until uniform. The mixed material is then fed into a twin-screw extruder using a loss-in-weight feeding system and extruded through a die to form a continuous material strip. After the material strip cools and solidifies, it is cut into small particles using a pelletizer to prepare resin particles. The melt index of the resin particles is 3g / 10min~22g / 10min, 230℃, 5kg. S3: Extrusion molding. After drying the resin particles obtained in step S2, they are added to an extruder as needed. Under the action of the screw, the resin particles are fully mixed, melted, and plasticized, and then extruded through a die onto a casting machine for curing to obtain a pre-formed film. The drying temperature is 80℃~120℃, and the drying time is 9h~15h. The screw and die working temperature of the extruder is 170℃~220℃, and the screw speed is 25rpm~50rpm. The casting roller temperature of the casting machine is set to 40℃~110℃. S4: Rapid stretching. The pre-formed film is drawn onto a film longitudinal stretching machine for rapid stretching. Before stretching, the stretching rollers are preheated. The stretching rollers are semi-solid rollers with a 0.1mm~5mm thick silicone or rubber anti-slip layer on their surface. After stretching, the film is annealed at a constant temperature for 5~30 minutes and then quenched to room temperature to obtain a semi-finished film. The stretching speed of the stretching machine is 0.5m / min~2m / min, the stretching temperature is 130℃~150℃, and the stretching ratio is 4~6 times. S5: High-voltage polarization: The semi-finished film is placed in a DC electric field for constant voltage polarization. After cooling, the finished polyvinylidene fluoride piezoelectric film is obtained. The polarization voltage is 50kV / mm~100kV / mm, the polarization time is 10min~60min, the polarization temperature is room temperature (25℃), and the relative humidity is 40%. S6: Wind up and put into storage. The finished polyvinylidene fluoride piezoelectric film is wound up and put into storage.

2. The rapid stretching process for piezoelectric thin films according to claim 1, characterized in that: In step S1, the particle size of the powder is 10μm to 500μm.

3. The rapid stretching process for piezoelectric thin films according to claim 1, characterized in that: In step S3, a desiccant is added during the drying process to remove moisture.

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