KR102595641B1 - Composition for fritting of piezoelectric element, method for manufacturing same, and printer for piezoelectric element using same - Google Patents

Abstract

The present invention relates to a composition for printing a piezoelectric element for forming a piezoelectric element by constructing a DLP-based real-time polling process system, a manufacturing method thereof, and a printer for a piezoelectric element using the same. Adding and stirring PVDF-HFP, which is formed by copolymerizing PVDF (polyvinylidene fluoride) and HFP (hexa fluoropropylene) according to the present invention, to a solvent, adding a photocurable polymer to the stirred solution, and adding a photocurable polymer to the stirred solution. It includes the step of preparing a composition for printing a piezoelectric element by degassing the solution.

Description

Composition for printing a piezoelectric element, a manufacturing method thereof, and a printer for a piezoelectric element using the same {Composition for fritting of piezoelectric element, method for manufacturing same, and printer for piezoelectric element using same}

The present invention relates to a composition for printing piezoelectric elements, and more specifically, to a composition for printing piezoelectric elements for forming a piezoelectric element by constructing a DLP-based real-time polling process system, a manufacturing method thereof, and a printer for piezoelectric elements using the same. It's about.

PVDF (Polyvinylidene fluoride) is used as a key material in piezoelectric device technology due to its high flexibility and piezoelectric ability. In general, the process of converting the natural α phase to the β phase as a way to increase the piezoelectricity of PVDF involves stretching the polymer axially and then applying a high electric field to align the dipole structure. However, this polling operation is avoided as it is a costly, dangerous, and cumbersome process because it applies high voltage for at least several hours.

Recently, EPAM (Electric Poling-Assisted Additive Manufacturing) technology, which can create 3D structures by performing 3D printing and poling simultaneously, was developed and applied to the production of piezoelectric elements using FDM-type 3D printing.

However, due to the nature of the FDM structure, disadvantages of the material extrusion method such as narrow nozzle range, high melting temperature, and slow deposition rate were pointed out. On the other hand, because the DLP process investigates large-area beam projects, it can be an alternative to create large-area 3D structures at faster process speeds and without the need for high-temperature conditions.

However, DLP systems require a post-polling process step, and so far no efforts have been made to reduce this.

Therefore, the purpose of the present invention is to provide a composition for printing piezoelectric elements for forming a piezoelectric element by constructing a DLP-based real-time polling process system, a method for manufacturing the same, and a printer for piezoelectric elements using the same.

The method for producing a composition for printing a piezoelectric element according to the present invention includes adding PVDF-HFP, which is formed by copolymerizing PVDF (polyvinylidene fluoride) and HFP (hexa fluoropropylene), to a solvent and first stirring, and adding photocuring to the stirred solution. It includes adding a polymer and secondary stirring, and degassing the solution to which the photo-curable polymer has been added to prepare a composition for printing a piezoelectric element.

In the method of manufacturing a composition for printing a piezoelectric element according to the present invention, the first stirring step is characterized in that PVDF-HFP is added to a solvent and stirred at 15 to 35° C. for 1 to 5 hours.

In the method for producing a composition for printing a piezoelectric element according to the present invention, the composition for printing a piezoelectric element includes 20 to 60 wt% of the PVDF-HFP.

The composition for printing a piezoelectric element according to the present invention is characterized by comprising PVDF-HFP, which is formed by copolymerizing PVDF (polyvinylidene fluoride) and HFP (hexa fluoropropylene), and a photocurable polymer.

The printer for piezoelectric elements according to the present invention includes a printing material containing a printing composition containing PVDF-HFP and a photocurable polymer formed by copolymerizing PVDF (polyvinylidene fluoride) and HFP (hexa fluoropropylene), and a tray provided with electrodes. , a plate provided on the upper part of the tray, which moves up and down with respect to the tray, and on which a piezoelectric element is formed on the lower surface by the printing material, and which is provided on the lower part of the tray, and irradiates UV in the direction of the tray to It is characterized by comprising an irradiation unit that forms a piezoelectric element on a plate, and a polarization alignment unit that is connected to the electrode and the plate and applies power to perform polarization alignment on the printing material.

In the printer for piezoelectric elements according to the present invention, the electrode is characterized in that it contains ITO (Indium Tin Oxide) and PET (polyethylene terephthalate).

In the printer for piezoelectric elements according to the present invention, the printing composition is cured by the irradiation unit after polarization alignment occurs by the polarization alignment unit to form the piezoelectric element.

The composition for printing piezoelectric elements according to the present invention can produce piezoelectric elements with high sensitivity, mechanical flexibility, durability, and a large area.

In addition, the composition for printing piezoelectric elements according to the present invention produces piezoelectric elements with a high piezoelectric coefficient, and can significantly shorten the manufacturing time by more than 10 times compared to existing EPAM (Electric Poling-Assisted Additive Manufacturing) technology.

1 is a flowchart showing a method of manufacturing a composition for printing a piezoelectric element according to an embodiment of the present invention.
Figure 2 is a diagram showing the configuration of a printer for piezoelectric elements according to an embodiment of the present invention.
Figure 3 is a schematic diagram briefly showing the printing process of a printer for a piezoelectric element and a printer for a piezoelectric element without a polarization alignment unit according to an embodiment of the present invention.
Figure 4 is a graph for explaining the characteristics of a composition for printing a piezoelectric element according to an embodiment of the present invention.
Figure 5 is a graph showing rheological performance according to mixing ratio of printing materials.
Figure 6 is a graph showing the output voltage sensitivity of printed piezoelectric elements with different mass fractions.
Figure 7 is a graph showing the results of a polarity conversion test of a piezoelectric element manufactured according to an embodiment of the present invention.
Figure 8 is a graph to explain the applicability of the piezoelectric element manufactured according to an embodiment of the present invention.

It should be noted that in the following description, only the parts necessary to understand the embodiments of the present invention will be described, and descriptions of other parts will be omitted to the extent that they do not distract from the gist of the present invention.

The terms or words used in the specification and claims described below should not be construed as limited to their usual or dictionary meanings, and the inventor should use the concept of terminology appropriately to explain his/her invention in the best way. It must be interpreted as meaning and concept consistent with the technical idea of the present invention based on the principle that it can be defined clearly. Therefore, the embodiments described in this specification and the configurations shown in the drawings are only preferred embodiments of the present invention, and do not represent the entire technical idea of the present invention, and therefore, various equivalents can be substituted for them at the time of filing the present application. It should be understood that there may be variations.

Hereinafter, embodiments of the present invention will be described in more detail with reference to the attached drawings.

1 is a flowchart showing a method of manufacturing a composition for printing a piezoelectric element according to an embodiment of the present invention.

Referring to Figure 1, first, in step S10, PVDF-HFP, which is formed by copolymerizing PVDF (polyvinylidene fluoride) and HFP (hexa fluoropropylene), is added to the solvent and stirred. At this time, PVDF-HFP can be added to the solvent and stirred at 15 to 35°C for 1 to 5 hours.

Here, DMF (dimethyl formamide) may be used as the solvent, but the solvent is not limited thereto, and solvents such as NMP (N-methyl pyrrolidone), acetone, and dimethylacetamide may also be used.

Next, in step S20, the photocurable polymer is added to the solution produced in step S10 and then dispersed. Here, the photocurable polymer can be polycarbonate curable resin (PCR), and the polycarbonate curable resin can be added to a solution containing PVDF-HFP and then stirred for 14 to 34 hours to uniformly disperse.

Then, in step S30, the solution in which the photo-curable polymer is dispersed is degassed to prepare a composition for printing a piezoelectric element. Here, the degassing can be done on its own by maintaining it at room temperature for 1 to 5 hours. The composition for printing the manufactured piezoelectric element may contain 20 to 60 wt% of PVDF-HFP.

Since the composition for printing piezoelectric elements prepared here includes PVDF-HFP, which is formed by copolymerizing HFP and PVDF, which are ferroelectric polymers with relatively high electric displacement polarization, the piezoelectric material has flexibility and chemical resistance when compared to the PVDF polymer alone. Devices can be manufactured.

In addition, the manufactured composition for printing piezoelectric elements can be optimized rheologically and functionally by adding PVDF-HFP to the photocurable polymer solution to maximize the piezoelectric coefficient.

That is, the composition for printing piezoelectric elements according to an embodiment of the present invention can produce a piezoelectric element with high sensitivity, mechanical flexibility, durability, and a large area.

In addition, the composition for printing piezoelectric elements according to an embodiment of the present invention produces a piezoelectric element with a high piezoelectric coefficient, and can significantly shorten the manufacturing time by more than 10 times compared to existing EPAM (Electric Poling-Assisted Additive Manufacturing) technology.

Hereinafter, a printer for piezoelectric elements according to an embodiment of the present invention will be described in detail.

Figure 2 is a diagram showing the configuration of a printer for piezoelectric elements according to an embodiment of the present invention.

Referring to FIG. 2, the printer 100 for a piezoelectric element according to an embodiment of the present invention may be a 3D printer based on DLP (Digital Light Processing).

This printer 100 for piezoelectric elements may be configured to include a tray 10, a plate 20, an irradiation unit 30, and a polarization alignment unit 40.

The tray 10 may be provided with a printing material containing a printing composition containing PVDF-HFP, which is formed by copolymerizing PVDF (polyvinylidene fluoride) and HFP (hexa fluoropropylene), and a photocurable polymer, and electrodes.

The tray 10 may have an open top, and a space is formed inside to accommodate electrodes and printing materials. At this time, the internal space of the tray 10 may be formed larger than the area of the plate 20 so that the plate 20, which will be described later, can be inserted and come into contact with the printing material.

In addition, the tray 10 is made of a transparent material so that light emitted from the irradiation unit 30 provided at the bottom can pass through and be irradiated to the printing material.

Here, the electrode may be in the form of a film containing indium tin oxide (ITO) and polyethylene terephthalate (PET). These electrodes may be attached to the lower surface of the tray 10.

The printing material may be the composition for printing the piezoelectric element described above, and may be provided inside a tray to which electrodes are attached.

The plate 20 may be provided on the top of the tray 10 and may be configured to move up and down in the direction of the tray 10. That is, the plate 20 moves downward in the direction of the tray 10 and comes into contact with the printing material. At the moment of contact, the irradiation unit 30 operates and irradiates light, and a part of the piezoelectric element of a preset shape is formed on the lower surface. can be formed. In this way, while the plate 20 repeatedly moves up and down, a piezoelectric element, which is a result of 3D printing, may be formed in the lower area. This plate 20 may be formed of metal.

The irradiation unit 30 may be provided at the bottom of the tray 10 and is arranged in an array to irradiate light to the tray 10. This irradiation unit 30 may be a plurality of DLP projectors.

The irradiation unit 30 forms a cross-sectional image by irradiating light corresponding to each assigned unit image. In other words, since the irradiation unit 30 irradiates light corresponding to the cross-sectional image of the molded product to be printed, photocuring of a large area is possible, so a large-sized molded product with high resolution can be manufactured at once without dividing it. An example in which the irradiation unit 30 is installed at the bottom of the tray 10 and radiates light to the upper tray 10 is disclosed.

Meanwhile, the irradiation unit 30 may consider manufacturing a single DLP projector of the same size as a plurality of DLP projectors to form a cross-sectional image. Assuming that one DLP projector and multiple DLP projectors have the same resolution, the resolution of a cross-sectional image formed by multiple DLP projectors is higher. That is, there is a problem that the resolution of a cross-sectional image formed by one DLP projector is lower than that of a cross-sectional image formed by a plurality of DLP projectors. Therefore, in this embodiment, the irradiation unit 30 is described as having a plurality of DLP projectors. This irradiation unit 30 can output ultraviolet rays (UV), but is not limited to this and can also output visible light depending on the material of the printing material.

The polarization alignment unit 40 is electrically connected to each of the electrodes provided in the tray 10 and the plate 20, and applies power to perform polarization alignment on the printing material. This polarization alignment unit 40 can perform polarization alignment by applying DC power before curing the printing material by the irradiation unit 30.

Hereinafter, the characteristics of the printer for piezoelectric elements according to an embodiment of the present invention will be described in detail.

Example

1. Printing materials

The printing material was prepared by mixing PVDF-HFP and the polycarbonate curable resin used. That is, 1g PVDF-FHP was added to 5ml DMF solution, and the mixture was stirred at 25°C for 3 hours to obtain a transparent and homogeneous solution. Next, 1g PCR was added and stirred for 24 hours to disperse. Then, the mixed solution was degassed at room temperature for 3 hours to prepare a printing composition containing 50 wt% of PVDF-HFP.

2. Printing

First, a transparent ITO coating film was attached to the inner surface of the tray and used as an electrode. Additionally, the printing material with a size of 30 x 30 x 0.5 mm was loaded between the ITO film and the metal plate. Then, direct current (DC) power was applied to the plate and tray for 5 minutes and UV cured at 405 nm. The printing resolution used was a total thickness of 100㎛ along the plate movement direction for all samples. After printing, the sample was washed with ethanol.

3. Fabrication of piezoelectric elements

To manufacture the piezoelectric element, commercial silver paste was printed on the top of a 3D printed film (area: 2 cm x 2 cm) using a screen printing process. Next, an ITO-PET film was attached to the bottom surface of the film. Next, nickel tape was attached to both sides of the device as the top and bottom electrode lines, and then PP tape was used to encapsulate the piezoelectric element.

Meanwhile, Figure 3 is a schematic diagram briefly showing the printing process of a printer for a piezoelectric element and a printer for a piezoelectric element without a polarization alignment unit according to an embodiment of the present invention.

Referring to Figure 3, (a) is a schematic diagram showing the printing process of a printer for piezoelectric elements without a polarization alignment unit, and (b) is a schematic diagram showing the printing process of a printer for piezoelectric elements according to an embodiment of the present invention. .

As shown in (a), it can be seen that the directions of PVDF-HFP dipoles in the mixed ink are randomly distributed and do not represent the overall polarization.

On the other hand, as shown in (b), when a high DC electric field was applied to the ink mixture in the tray in the embodiment of the present invention, the PVDF-HFP dipoles were aligned in the uniform direction of the electric field.

Additionally, when the mixed ink was exposed to UV light, the photoinitiator absorbed light energy and dissociated into active free radicals to initiate free radical-catalyzed polymerization of PCR. After free radicals are generated, polymerization of PCR begins, increasing the chain length and eventually forming an extensive cross-linking network. During the photopolymerization process, PVDF dipoles aligned along the direction of the electric field are trapped within the three-dimensional cross-linked structure of PCR.

Accordingly, embodiments of the present invention with an in-suit polling process can provide a new perspective for developing stages of a product. In other words, compared to existing methods, the dipole direction as well as cost and time can be greatly reduced at the same time.

Figure 4 is a graph for explaining the characteristics of a composition for printing a piezoelectric element according to an embodiment of the present invention.

Meanwhile, to obtain the best ink and maximum piezoelectricity, it is necessary to determine the effect of PVDF-HFP concentration on the performance and printability of printed samples.

Therefore, 20 to 60 wt% PVDF-HFP was prepared and the piezoelectricity of the printed sample was simplified using a quasi-static d33 meter as shown in (a).

The results show that the d33 of the 3D printed samples increased as the loading PVDF-HFP content increased from 1 pC/N for 20 wt% PVDF-HFP to 42 pC/N for 60 wt% PVDF-HFP.

The increase in piezoelectric coefficient can be attributed to the increase in the content of piezoelectric material.

Additionally, it is worth noting that no film formation is observed when the PVDF-HFP weight percent exceeds 60%. This is because the content of photopolymerization resin is too low and the crosslinking density is low to form a film.

In addition, it was confirmed that the higher the PCR concentration, the more solidified and the lower the function. Therefore, the 3D printed sample can maintain its shape and optimal piezoelectric performance when the PCR weight ratio is 50 wt%.

In order to improve the piezoelectric properties of piezoelectric elements, it is essential to carry out polarization treatment under a high DC electric field. (b) shows the d33 change of 3D printed PVDF-HFP samples using in situ poling at different poling electric fields (0.3-1 kV).

d33 was low under low poling electric field conditions and increased dramatically as the poling electric field increased. Above the maximum polarized electric field, the mixed ink may be electrically destroyed by insulation breakdown and discharge due to the high electric field, resulting in loss of communication between the 3D printer and computer.

To further confirm the superiority of the embodiment of the present invention, 3D printed PVDF-HFP samples without in situ poling were prepared and then electrical poling was performed at 1 kV for different times at room temperature.

After applying 10 hours of electrical polling treatment, the 3D printed PVDF-HFP sample without in situ polling can obtain d33 values similar to the in situ polling counterpart, as shown in (c). This phenomenon is caused by a three-dimensional cross-linking network that hinders the movement of the PVDF-HFP dipoles.

Figure 5 is a graph showing rheological performance according to mixing ratio of printing materials. That is, Figure 5 shows the rheological performance of a series of photocurable inks with different mixing ratios of PVDF-HFP to PCR (weight ratios of 10:0, 7:3, 6:4, 5:5, 4:6, and 0:10, respectively). It shows.

Meanwhile, the range of ratio for piezoelectric ability has been narrowed, but in actual DLP printing, ink fluidity according to viscosity, which affects film formation, must be investigated.

(a) shows the change in viscosity of photocurable ink as a function of shear rate.

As the shear rate increased, the viscosity of the mixture decreased, resulting in the shear thinning behavior commonly found in printing systems.

Newtonian behavior was observed in the PVDF-HFP solution, but PCR, which has strong non-newtonian properties, induced a shear thinning effect. Therefore, the zero-shear viscosity values were listed in the order of PCR addition: 45700 cP (4:6), 37720 cP (5:5), 30800 cP (6:4), and 20466 cP (7:3).

Additionally, the photocurable ink had to undergo pre-shearing to observe thixotropy as shown in (b). A significant hysteresis effect on the viscosity of the photocurable ink was observed during increasing and decreasing shear rate, suggesting that the ink would level well in a short period of time, within a few seconds.

Additionally, the yield stress calculated by Bingham equation 31 as shown in (c) supports the fact that all inks have a sufficiently low yield value to flow within the printing system and that PCR plays a major role in increasing viscosity. Therefore, the rheological properties of the mixed ink ensure proper ink filling and leveling of empty spaces during printing.

Figure 6 is a graph showing the electrical output voltage sensitivity of printed piezoelectric elements with different mass fractions.

As the impact force increased to 50 N, a strong dependence of the piezoelectric output voltage on the applied strain was observed.

The output voltage increased almost linearly as the external impact force increased. In general, as the external impact force increases, stronger deformation results in higher output voltage and higher piezoelectric potential energy.

The results show that the voltage increases with increasing external force even when the mass fraction of the sensor is different.

The voltage sensitivity of the printed piezoelectric sensor (S = △V / △P, where △V is the relative variation of the output voltage signal and △P is the relative variation of the applied pressure) can be obtained as a graph with a linear slope.

According to the fitted linear equations, the printed piezoelectric sensor exhibits high impact force sensitivity (235 mV/N) over a wide pressure range (1-50 N).

It is noted that the ultra-large linear response area of 3D printed sensors can provide a stable testing process and avoid complex calibration processes.

Additionally, (c) shows the output voltage of the 3D printed sensor at different impact frequencies under a constant pressure of 50N.

The results show that the output voltage of the printed sensor increases proportionally as the impact frequency increases. The increase in output voltage of the 3D printing sensor according to frequency can be explained by the decrease in impedance according to strain rate.

Figure 7 is a graph showing the polarity switching test results.

Meanwhile, the widely accepted polarity reversal test was used to verify that the output signal was actually generated by the 3D printed piezoelectric sensor.

As shown in (a), switching of the polarity of the output signal was obtained when the electrode connections were reversed.

When the electrodes of the 3D printed sensor were connected forward to the measurement circuit, the 3D printed sensor produced a positive electrical signal in the pressure release movement and then measured a negative output in the reverse connection.

Clearly, the electrical output signal switching that occurs by changing the electrode connections fully demonstrates that the energy harvesting signal is generated by the piezoelectricity of the 3D printed sensor.

Additionally, there is a need to evaluate the stability and durability of 3D printed sensors by considering actual applications in real life. The mechanical durability of the printed sensor was verified through a dynamic load test performed for 10,000 cycles with a pressure of 50 N at 4 Hz, as shown in (b). The output voltage showed no fluctuation during repetitive load tests.

Figure 8 is a graph to explain the applicability of the piezoelectric element manufactured according to an embodiment of the present invention.

Referring to (a), to further investigate the applicability of the 3D printed piezoelectric sensor, a glass bottle (20 g) was dropped vertically on the piezoelectric sensor. As the drop height increases from 2 cm to 12 cm, the 3D printed piezoelectric sensor produces output voltages ranging from 1.7 V to 7.8 V. This indicates that the 3D printed piezoelectric sensor can not only be used to distinguish between different pressures, but can also act as an impact energy harvester by converting mechanical energy into electrical energy.

To demonstrate the potential of 3D printed piezoelectric sensors for detecting human movement, we systematically investigated their electrical output performance under various force conditions.

Referring to (b) and (c), the piezoelectric output voltage was generated by the 3D printed piezoelectric sensor under tapping and compressing conditions, respectively.

These results show that output voltage values of ~2.5 V and ~6.1 V were generated by the piezoelectric element under finger tapping and hand compression conditions, respectively.

Therefore, it indicates that 3D printed sensor devices can be used for potential real-time/practical applications to collect biomechanical energy or detect human movements.

Referring to (d), another application using the puzzle-like structure of printed piezoelectric film is shown for use in a large area.

Because it is difficult to produce large-area products due to the limitations of the DLP system, large-area structures can be easily produced by connecting each 3D printed piece. As shown in the photo, four printed puzzles were used as one large-area touch sensor, and its performance was proven to be excellent.

Meanwhile, the embodiments disclosed in the specification and drawings are merely provided as specific examples to aid understanding, and are not intended to limit the scope of the present invention. It is obvious to those skilled in the art that in addition to the embodiments disclosed herein, other modifications based on the technical idea of the present invention can be implemented.

10: tray 20: plate
30: irradiation unit 40: polarization alignment unit
100: printer

Claims (7)

Adding PVDF-HFP, which is formed by copolymerizing PVDF (polyvinylidene fluoride) and HFP (hexa fluoropropylene), to a solvent and first stirring;
Adding a photo-curable polymer to the stirred solution and performing secondary stirring;
Preparing a composition for printing a piezoelectric element by degassing the solution to which the photo-curable polymer has been added;
Including,
The photo-curable polymer is a polycarbonate curing resin.
Method for producing a composition for printing piezoelectric elements. According to paragraph 1,
The first stirring step is,
A method of producing a composition for printing a piezoelectric element, comprising adding PVDF-HFP to a solvent and stirring at 15 to 35°C for 1 to 5 hours. According to paragraph 2,
The composition for printing the piezoelectric element is,
A method for producing a composition for printing a piezoelectric element, comprising 20 to 60 wt% of the PVDF-HFP. It includes PVDF-HFP and a photocurable polymer formed by copolymerizing PVDF (polyvinylidene fluoride) and HFP (hexa fluoropropylene),
A composition for printing a piezoelectric element, wherein the photo-curable polymer is a polycarbonate curing resin. A printing material containing a printing composition containing PVDF-HFP, which is formed by copolymerizing PVDF (polyvinylidene fluoride) and HFP (hexa fluoropropylene), and a photocurable polymer, and a tray provided with electrodes;
A plate provided on the upper part of the tray, moves up and down with respect to the tray, and has a piezoelectric element formed on its lower surface by the printing material;
an irradiation unit provided at the bottom of the tray to irradiate UV light in the direction of the tray to form a piezoelectric element on the plate;
a polarization alignment unit connected to the electrode and the plate and applying power to perform polarization alignment on the printing material;
Including,
A printer for a piezoelectric element, wherein the photo-curable polymer is a polycarbonate curing resin. According to clause 5,
The electrode is,
A printer for piezoelectric elements comprising ITO (Indium Tin Oxide) and PET (polyethylene terephthalate). According to clause 5,
The printing composition is,
A printer for a piezoelectric element, characterized in that polarization alignment occurs by the polarization alignment unit and then curing by the irradiation unit to form the piezoelectric element.

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