阅读说明：本技术 具有高d33值的柔性低成本无铅压电复合材料 (Having a high D33Flexible low-cost lead-free piezoelectric composite material ) 是由 朱卜兰·哈利克 西布兰德·范德兹瓦赫 皮姆·格伦 杰西·阿方索·卡拉韦奥·福乐易斯卡斯 索马 于 2020-03-25 设计创作，主要内容包括：描述了无铅压电复合材料及其制备方法和用途。该无铅压电复合材料具有高柔性和高压电性能。(Lead-free piezoelectric composites and methods of making and using the same are described. The lead-free piezoelectric composite material has high flexibility and high piezoelectric performance.)

1. A lead-free piezoelectric composite comprising:

a polymer matrix having a dielectric constant greater than 30 at 20 ℃; and

greater than 10 volume percent of a lead-free piezoelectric material dispersed in a polymer matrix based on the total volume of the composite,

wherein the lead-free piezoelectric composite material has an elastic modulus of less than 1GPa and a piezoelectric coefficient d₃₃Greater than 20 pC/N.

2. The lead-free piezoelectric composite of claim 1, wherein the polymer matrix comprises a poly (vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) (PVDF-TrFE-CFE) terpolymer.

3. The lead-free piezoelectric composite material according to claim 2, wherein the polymer matrix is PVDF-TrFE-CFE.

4. The lead-free piezoelectric composite material according to any one of claims 1 to 2, wherein the content of the lead-free piezoelectric material is 30 to 70 vol%, preferably 40 to about 60 vol%, based on the total volume of the composite material.

5. The lead-free piezoelectric composite material according to any one of claims 1 to 2, wherein the piezoelectric material comprises barium titanate (BaTiO)₃) Potassium sodium niobate (KNaNb) O₃(KNN), potassium lithium sodium niobate (KLi) (NaNb) O₃(KLNN), hydroxyapatite, apatite, lithium sulfate monohydrate, sodium bismuth titanate, quartz, organic materials, preferably tartaric acid or poly (vinylidene fluoride) fibers, or combinations thereof.

6. The lead-free piezoelectric composite material according to any one of claims 1 to 2, wherein the polymer matrix is PVDF-TrFE-CFE and the piezoelectric material is BaTiO₃。

7. The lead-free piezoelectric composite material according to any one of claims 1 to 2, wherein the polymer matrix is PVDF-TrFE-CFE and the piezoelectric material is KLNN.

8. The lead-free piezoelectric composite material according to any one of claims 1 to 2, wherein the polymer matrix is PVDF-TrFE-CFE and the piezoelectric material is KNN.

9. The lead-free piezoelectric composite material according to any one of claims 1 to 2, wherein the composite material retains its d at a temperature of greater than 90 ℃₃₃The value is obtained.

10. The lead-free piezoelectric composite of any one of claims 1 to 2, wherein the composite is oriented at a lower polarization voltage under the influence of an electric field than the same polymer matrix without the lead-free piezoelectric filler.

11. The lead-free piezoelectric composite material according to any one of claims 1 to 2, wherein the composite material is a flexible sheet or film.

12. The lead-free piezoelectric polymer composite of claim 11, wherein the film or sheet has a thickness of 50 to 200 microns.

13. The lead-free piezoelectric composite according to any one of claims 1 to 2, further contained in an article.

14. The lead-free piezoelectric composite material of claim 13, wherein the article is a touch panel, a human-machine interface, an integrated keyboard, or a component of a wearable device.

15. A piezoelectric device comprising a lead-free piezoelectric polymer composite according to any one of claims 1 or 2, wherein the device is preferably a piezoelectric sensor, a piezoelectric transducer or a piezoelectric actuator, wherein the device is preferably mechanically flexible.

16. A method of forming the lead-free piezoelectric composite of any one of claims 1-2, the method comprising:

(a) adding lead-free piezoelectric particles to a solution comprising a dissolved polymeric material having a dielectric constant greater than 10 and a solvent to form a dispersion or suspension, wherein the lead-free piezoelectric particles are dispersed or suspended in the solution;

(b) forming a polymer matrix having lead-free piezoelectric particles dispersed therein; and

(c) and performing electric polarization treatment on the polymer matrix in which the lead-free piezoelectric particles are dispersed to form the lead-free piezoelectric composite material.

17. The method of claim 16, wherein forming a polymer matrix comprises:

(i) casting the dispersion on a substrate;

(ii) drying the polymer matrix at 25 ℃ to 80 ℃ to form a dried polymer matrix; and

(iii) the dried polymer matrix is annealed at a temperature of 80 ℃ to 150 ℃ for 1 hour to 50 hours, preferably at a temperature of 110 ℃ for 5 hours to 25 hours.

18. The method of claim 16, wherein inducing electrical polarization comprises applying a polarization field using corona discharge.

19. The method of claim 16, wherein the polymeric material is poly (vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) and the lead-free piezoelectric material is KLNN, KNN, BaTiO₃Or a combination thereof, the solvent is tetrahydrofuran, methyl ethyl ketone, dimethyl sulfoxide, ethyl acetate, amyl acetate, dimethylformamide, dimethylacetamide, or any combination thereof.

20. The method of claim 16, wherein the ratio of polymeric material to solvent is from 1:5 to 1: 10.

Background

A. Field of the invention

The present invention generally relates to lead-free piezoelectric composites having high flexibility and high piezoelectric properties.

B. Background of the invention

For human-computer interaction or wearable devices, new materials are needed that are both mechanically flexible and can operate at lower voltages. A smart watch is an example of such a device. Conventional smartwatches may utilize an Eccentric Rotating Mass (ERM) to generate vibrations. These watches can be connected to a smartphone via bluetooth and each caller can be assigned a unique vibration rhythm, which enables the caller to be identified without looking at the phone screen or the watch display. The problem with wearable devices, including ERM, is significant. To overcome the weight problem, linear drivers (LA) have been incorporated into wearable devices. The linear actuator uses a voice coil that is pressed by a mass attached to a spring. When an alternating field is applied to the coil, the spring vibrates at the resonant frequency, thereby vibrating the mass. The linear actuator is lighter than the ERM. However, they also have significant problems due to their structure and the masses attached thereto. In addition, the wearable device can be thick due to the poor flexibility and bulk of the LA.

To overcome the problems of ERM and LA, studies have been made on piezoelectric materials. The piezoelectric material may be ceramic, single crystal in nature, or polymeric. Ceramics, in contrast to polymersHas relatively high dielectric constant and good electromechanical coupling coefficient. Ceramics are subject to high acoustic impedance, which results in poor acoustic matching of the ceramic to media such as water and human tissue, through which signals are typically transmitted or received. In addition, ceramics can exhibit high stiffness and brittleness and cannot be made into curved surfaces, thus limiting the design flexibility of a given sensor. Furthermore, the electromechanical resonance of the piezoelectric ceramic generates high noise, which is an unnecessary disturbance in sensor engineering. Lead is commonly used in piezoelectric ceramics to achieve acceptable piezoelectric constants. Lead is commonly used in piezoelectric ceramics to achieve acceptable piezoelectric constants. However, lead is a heavy metal and is toxic. Lead-free piezoelectric ceramics have a low piezoelectric constant, and thus it is difficult to achieve acceptable piezoelectric performance. E.g. d of PZT₃₃About 270pC/N to 400pC/N, a d much higher than about 190pC/N for barium titanate₃₃. The single crystal piezoelectric material may include quartz tourmaline and sodium potassium tartrate crystals. Other single crystals may include lead meta-niobate (PbNb)₂O₆) Or relaxation oscillator systems, e.g. Pb (Sc)_1/2Nb_1/2)O₃-PbTiO₃、Pb(In_1/2Nb_1/2)O₃-PbTiO₃、Pb(Yb_1/2Nb_1/2)O₃-PbTiO₃And (1-2X) BiScO₃-×PbTiO₃. Like ceramics, any piezoelectric material (ceramic, crystalline, or polymer) does not provide all of the characteristics required for an application, and thus its performance is limited by the balance between high voltage electrical activity and low density and mechanical flexibility.

Piezoelectric polymer materials such as PVDF and PVDF-TrFE copolymers have a number of advantages including mechanical flexibility, light weight, low temperature and ease of processing. Despite these advantages, it is compatible with ceramics (d of PZT)₃₃In the range of 270pC/N to 400pC/N), the problem with these materials is the low piezoelectric response (d)₃₃About 13pC/N to 28pC/N) and requires higher driving voltages, which raises additional safety and cost issues.

Some attempts have been made to solve the above problems. For example, Fris et al, U.S. patent application publication No. 2015/0134061 describesA spinal implant and a method of making a spinal implant includes dispersing a piezoelectric ceramic in a polymer matrix. Unfortunately, d of the resulting composite₃₃The value of (pC/N) is low, less than 3. In another example, JP2016-219804 to Tetsuhiro et al describes a method of preparing a lead-free piezoelectric polymeric material, including the use of an affinity modifier, such as a surfactant, to aid in dispersing the particles in the polymer matrix. Affinity modifiers can be difficult and/or costly to remove from the desired polymer matrix.

While various different methods of producing piezoelectric material composites have been attempted, there remains a need to produce lead-free piezoelectric composites having balanced desired piezoelectric properties and mechanical flexibility.

Disclosure of Invention

One discovery provides a solution to at least some of the problems associated with flexible devices (e.g., wearable devices). A prerequisite for this solution is the discovery of lead-free piezoelectric composites whose structure is such that they comprise a polymer matrix having a dielectric constant greater than 30 at 20 ℃. The matrix may support greater than 10 volume percent of the lead-free piezoelectric material, based on the total volume of the composite. Such lead-free materials may be dispersed in a polymer matrix. This results in a composite material having a modulus of elasticity of less than 1GPa and a piezoelectric coefficient d₃₃Greater than 20 pC/N. The lead-free piezoelectric composite material used in the present invention has the advantage of flexibility and higher barrier force compared to polymer-based actuators such as PVDF-based actuators. The composite piezoelectric material of the invention can also be used for replacing a linear driver to make a wearable device thinner, thereby reducing the production cost of the wearable device. Other advantages of the present invention may include the incorporation of lead-free piezoelectric composites into a band of a wearable device that has a "wrist-band" like feel that may completely or partially cover a body part (e.g., wrist, arm, leg, finger, hand, head, neck, foot, etc.).

Other advantages of the lead-free piezoelectric composite material of the present invention include high flexibility (elastic modulus less than 1GPa) and higher piezoelectric performance (d of PVDF) than PVDF₃₃15pC/N to 30pC/N, and a piezoelectric composite materialOf the material d₃₃From 40pC/N to 52 pC/N). The composite of the present invention may have a low polarization voltage compared to PVDF (e.g., PVDF typically has a polarization voltage of about 80KV/mm to 180KV/mm, while the composite of the present invention has a polarization voltage of 8KV/mm to 12 KV/mm). The composite material of the present invention retains mechanical flexibility even at high lead-free piezoelectric filler loading (e.g., at or above 10% loading). Furthermore, the low processing temperature of the composite material of the invention allows the integration of different materials (e.g. polymers) that usually decompose easily upon heating. Lower processing temperatures may also reduce the production cost of the piezoelectric composite of the present invention compared to PVDF and PVDF-based materials.

In one aspect of the invention, a lead-free piezoelectric composite is described. The lead-free piezoelectric composite comprises a polymer matrix having a dielectric constant greater than 30 at 20 ℃, and comprises greater than 10 volume percent of the lead-free piezoelectric material dispersed throughout the polymer matrix, based on the total volume of the composite. The lead-free piezoelectric composite material has an elastic modulus of less than 1GPa and a piezoelectric coefficient d₃₃Greater than 20 pC/N. The polymer matrix comprises a poly (vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) (PVDF-TrFE-CFE) terpolymer. In a preferred embodiment, the polymer matrix is PVDF-TrFE-CFE. The lead-free piezoelectric material may be used in an amount of greater than 10 volume percent or 30 volume percent to 70 volume percent, preferably 40 volume percent to about 60 volume percent, based on the total volume of the composite. The lead-free piezoelectric material may include barium titanate (BaTiO)₃) Potassium sodium niobate (KNaNb) O₃(KNN), potassium lithium sodium niobate (KLi) (NaNb) O₃(KLNN), hydroxyapatite, apatite, lithium sulfate monohydrate, sodium bismuth titanate, quartz, organic materials (preferably tartaric acid or poly (vinylidene fluoride) fibers), or combinations thereof. In a particular embodiment, the polymer matrix is PVDF-TrFE-CFE and the piezoelectric material is BaTiO₃KLNN or KNN. The lead-free piezoelectric composite material of the present invention can maintain its d when subjected to a temperature of more than 90 c, preferably more than 90 c or 90 c to 130 c₃₃The value is obtained. Compared with the same polymer matrix without the lead-free piezoelectric filler, the lead-free piezoelectric composite material can be fixed under lower polarization voltage under the action of an electric fieldAnd (3) direction. In certain embodiments, the lead-free piezoelectric composite of the present invention may be a flexible sheet or film. The thickness of such a sheet or film can be up to 50 to 200 microns.

The lead-free composite of the present invention may be included in an article. The article of manufacture may comprise a touch panel, a human-machine interface, an integrated keyboard, or a component of a wearable device.

In another aspect of the invention, a piezoelectric device can include the lead-free piezoelectric polymer composite of the invention. The device may be a piezoelectric sensor, a piezoelectric transducer or a piezoelectric actuator. In a preferred embodiment, the device is mechanically flexible.

In another aspect of the invention, a method of forming the lead-free piezoelectric composite of the invention is described. The method comprises (a) adding lead-free piezoelectric ceramic particles to a solution comprising a dissolved polymeric material having a dielectric constant greater than 10 and a solvent to form a dispersion or suspension in which the lead-free piezoelectric particles are dispersed or suspended in the solution, (b) forming a polymer matrix in which the lead-free piezoelectric particles are dispersed or suspended, and (c) subjecting the polymer matrix in which the lead-free piezoelectric particles are dispersed to an electrical polarization treatment to form the lead-free piezoelectric composite of the present invention. The ratio of polymeric material to solvent may be from 1:5 to 1: 10. Forming the polymer matrix may comprise (i) casting the dispersion on a substrate, (ii) drying at 25 ℃ to 80 ℃ to form a polymer matrix, and (iii) annealing the dried polymer matrix at a temperature of 80 ℃ to 150 ℃ for 1 to 50 hours, preferably at a temperature of 110 ℃ for 5 to 25 hours. Inducing electrical polarization may include applying a polarization field using corona discharge. In a particular aspect, the polymer material may be PVDF-TrFE-CFE and the lead-free piezoelectric material may be KLNN, KNN, BaTiO₃Or a combination thereof, and the solvent may be tetrahydrofuran, methyl ethyl ketone, dimethyl sulfoxide, ethyl acetate, amyl acetate, dimethylformamide, dimethylacetamide, or any combination thereof.

Other embodiments of the invention are discussed in the present application. Any embodiment discussed in relation to one aspect of the invention is also applicable to other aspects of the invention and vice versa. Each embodiment described herein is understood to be an embodiment applicable to other aspects of the invention. It is contemplated that any embodiment discussed herein may be implemented with respect to the methods or compositions of the present invention, and vice versa. In addition, the methods of the present invention can also be practiced using the compositions and kits of the present invention.

The following includes definitions of various terms and phrases used in the specification.

The term "about" or "approximately" is defined as close to as understood by one of ordinary skill in the art. In one non-limiting embodiment, these terms are defined as being within 10%, preferably within 5%, more preferably within 1%, and most preferably within 0.5%.

The terms "weight%", "volume%" or "mole%" refer to the weight percent, volume percent or mole percent of a component, respectively, based on the total weight, volume or moles of the component. In a non-limiting example, 10 grams of a component in 100 grams of material is 10 weight percent of the component.

The term "substantially" and variations thereof are defined to include ranges within 10%, within 5%, within 1%, or within 0.5%.

The terms "inhibit" or "reduce" or "prevent" or "avoid" as used in the claims and/or the specification includes any measurable reduction or complete inhibition that achieves the desired result.

The term "effective" as used in the specification and/or claims refers to being sufficient to achieve a desired, expected, or predicted result.

The use of quantitative terms may mean "one" when used in conjunction with any of the terms "comprising," including, "" containing, "or" having "in the claims or specification, but also consistent with the meaning of" one or more, "" at least one, "and" one or more than one.

The words "comprising," "having," "including," or "containing" are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

The piezoelectric composite of the present invention may "comprise" or "consist essentially of" or "consist of" certain ingredients, components, compositions, etc. disclosed throughout this specification. In one non-limiting aspect, with respect to the transitional phrase "consisting essentially of," the basic and novel characteristics of the piezoelectric composite of the present invention are high flexibility and high piezoelectric characteristics as compared to PVDF.

Other objects, features and advantages of the present invention will become apparent from the following drawings, detailed description and examples. It should be understood, however, that the detailed description, drawings, detailed description, and examples of the present invention are given by way of illustration only and not by way of limitation. In addition, it is contemplated that alterations and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. In other embodiments, features from specific embodiments may be combined with features of other embodiments. For example, features from one embodiment may be combined with features from any of the other embodiments. In other embodiments, additional features may be added to the specific embodiments described herein.

Drawings

The advantages of the present invention will become apparent to those skilled in the art from the following detailed description, with reference to the accompanying drawings.

FIG. 1 shows the piezoelectric coefficient d of comparative piezoelectric composites₃₃(pC/N) as the volume fraction of PZT increases, and the piezoelectric coefficient d of the lead-free piezoelectric composite material of the present invention₃₃(pC/N) as a function of increasing KLNN volume fraction.

Fig. 2 shows the change in dielectric constant of the comparative piezoelectric composite with increasing volume fraction of PZT, and the change in dielectric constant of the piezoelectric composite of the present invention with increasing volume fraction of KLNN.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings. The drawings may not be to scale.

Detailed Description

Hair brushClear flexible lead-free piezoelectric composites with high dielectric constant values can provide solutions to at least some of the problems with PVDF-based and ceramic-based piezoelectric composites. This solution is premised on the use of a polymer matrix (such as PVDF-TrFE-CFE) having a dielectric constant greater than 30 at 20 ℃, with at least 10 volume percent of the lead-free piezoelectric material dispersed throughout the polymer matrix, based on the total volume of the composite. The lead-free piezoelectric composite material can have a piezoelectric coefficient d greater than 20pC/N₃₃And flexible (e.g., elastic modulus less than 1 GPa). By combining polymer-based materials with ceramic-based materials, the composite materials of the present invention can produce lead-free piezoelectric materials with desirable piezoelectric and mechanical properties, which are advantageous for flexible sensor-based applications and/or wearable devices and articles.

These and other non-limiting aspects of the invention are discussed in further detail in the following sections.

A. Material

1. Piezoelectric material

The piezoelectric material may be any lead-free ceramic or single crystal material. Non-limiting examples of piezoelectric materials include perovskite-group inorganic compounds. Non-limiting examples of the piezoelectric ceramic having a perovskite structure include barium titanate (BaTiO)₃) Potassium sodium niobate (KNaNb) O₃(KNN), potassium lithium sodium niobate (KLi) (NaNb) O₃(KLNN), hydroxyapatite, apatite, lithium sulfate monohydrate, sodium bismuth titanate, quartz, organic materials (preferably tartaric acid or poly (vinylidene fluoride) fibers), or combinations thereof. The lead-free piezoelectric particles may have a particle size of 200nm to 3000nm, or at least greater than, equal to, or between: 200nm, 225nm, 250nm, 275nm, 300nm, 325nm, 350nm, 375nm, 400nm, 425nm, 450nm, 475nm, 500nm, 525nm, 550nm, 575nm, 600nm, 625nm, 650nm, 675nm, 700nm, 725nm, 750nm, 775nm, 800nm, 825nm, 850nm, 875nm, 900nm, 925nm, 950nm, 975nm, 1000nm, 1500nm, 2000nm, 2500nm, and 3000 nm. For example, BaTiO₃The particle size of (a) may be from 200nm to 500nm, or from 250nm to 400nm, or from 300nm to 350 nm. In another example, the KNLN particle size may be 1000nmTo 3000nm (1 micron to 3 microns), or 1500nm to 2500 nm. Table 1 lists the properties of some lead-free piezoelectric materials.

TABLE 1

2. Polymer and method of making same

The piezoelectric composite of the present invention may include a polymer matrix having a dielectric constant greater than 30 at 20 ℃. The polymer matrix may comprise a thermosetting polymer, copolymer and/or monomer, a thermoplastic polymer, copolymer and/or monomer or a thermosetting/thermoplastic polymer or copolymer blend.

Non-limiting examples of thermoset polymer matrices include those including epoxy resins, unsaturated polyester resins, polyurethanes, bakelite, duroplasts, urea formaldehyde, diallyl phthalate, ethylene oxide, polyimides, cyanate esters of polycyanurates, dicyclopentadiene, phenolic resins, benzophenonesAn oxazine, a copolymer thereof, or a blend thereof. In a particularly preferred embodiment, the thermosetting polymer matrix is an epoxy resin. The epoxy resin may include diglycidyl ether bisphenol a and polyoxypropylene diamine. In another case, the polymer matrix may be a thermoplastic polymer matrix. Non-limiting examples of thermoplastic polymer matrices include those comprising polyethylene terephthalate (PET), Polycarbonate (PC) polymers, polybutylene terephthalate (PBT), poly (1, 4-cyclohexylene cyclohexane-1, 4-dicarboxylate) (PCCD), alcoholized polycyclohexylene terephthalate (PCTG), polyphenylene oxide (PPO), polypropylene (PP), Polyethylene (PE), polyvinyl chloride (PVC), Polystyrene (PS), polymethyl methacrylate (PMMA), polyethyleneimine or Polyetherimide (PEI) and derivatives thereof, thermoplastic elastomers (TPE), terephthalic acid (TPA) elastomers, polycyclohexanedimethanol terephthalate (PCT), polyethylene naphthalate (PEN), Polyamides (PA), polysulfone sulfonates (PSS), sulfonates of polysulfone, polyethers.Ether Ketone (PEEK), Acrylonitrile Butadiene Styrene (ABS), polyether ketone (PEKK), polyphenylene sulfide (PPS), and copolymers or blends thereof.

Non-limiting examples of thermoplastic polymers that may be used in the context of the present invention include poly (vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) (PVDF-TrFE-CFE) terpolymers, odd numbered nylons, cyano polymers, polyethylene terephthalate (PET), Polycarbonate (PC) polymers, polybutylene terephthalate (PBT), poly (1, 4-cyclohexylene cyclohexane-1, 4-dicarboxylate) (PCCD), alcoholized polycyclohexylene terephthalate (PCTG), poly (phenylene oxide) (PPO), polypropylene (PP), Polyethylene (PE), polyvinyl chloride (PVC), Polystyrene (PS), polymethyl methacrylate (PMMA), polyethyleneimine or polyether imide (PEI) and derivatives thereof, thermoplastic elastomers (TPE), terephthalic acid (TPA) elastomers, Poly (cyclohexanedimethanol cyclohexane terephthalate) (PCT), polyethylene naphthalate (PEN), Polyamide (PA), polysulfone sulfonate (PSS), sulfonate esters of polysulfone, Polyetheretherketone (PEEK), Polyetherketoneketone (PEKK), Acrylonitrile Butadiene Styrene (ABS), polyphenylene sulfide (PPS), copolymers thereof or blends thereof. In a preferred case, PVDF-TRFE-CFE having a dielectric constant of about 50 is used.

The polymer may comprise additives to form a polymer matrix containing the additives. Non-limiting examples of additives include coupling agents, antioxidants, heat stabilizers, flow modifiers, colorants, and the like, or any combination thereof.

B. Preparation method of piezoelectric composite material

The piezoelectric composite material of the present invention may be prepared by a solution casting method or a molding method. A polymer solution as described in the materials section can be obtained. The solution may comprise a solvent and a polymer as described in the materials section, preferably PVDF-TRFE-CFE. Non-limiting examples of solvents include Tetrahydrofuran (THF), Methyl Ethyl Ketone (MEK), dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP), or combinations thereof. The ratio of polymer to solvent can be 1:5 to 1:10, 1:6 to 1:9, or about 1: 8. In some embodiments, the solution comprises at least 10%, 20%, 30%, 40%, or 50% by weight of any one, equal to any one, or any in between, or about 12.5% by weight of PVDF-TRFE-CFE. In some embodiments, the lead-free polymer composites of the present invention do not use a compatibility improving agent.

The piezoelectric material may be dispersed or suspended in a polymer solution. The piezoelectric material may be a plurality (e.g., 2 or more than 2, suitably 5 or more than 5, 10 or more than 10, 50 or more than 50, 100 or more than 100, 500 or more than 500, 1000 or more than 100, etc.) of lead-free piezoelectric particles. The lead-free piezoelectric particles may be dispersed into the solution by any suitable method, including mixing, stirring, folding, or otherwise incorporating the lead-free piezoelectric particles into a matrix, such that the particles are uniformly dispersed or suspended in the matrix. In some embodiments, the solution is added to the piezoelectric material.

The dispersion or suspension may be subjected to conditions to form the piezoelectric composite of the present invention. In this specification, the terms dispersion and suspension are used interchangeably. In one example, the dispersion comprises PVDF-TRFE-CFE and barium titanate. In another example, the dispersion comprises PVDF-TRFE-CFE and KLNN. In some embodiments, the dispersion may be shaped or cast. Shaping or casting may include changing the dispersion to a desired form by mechanical or physical processes. Shaping or casting may also include placing the dispersion into a container or receptacle as desired so that it retains its shape or form. It should be noted that the shaped shape need not be the final shape, as additional processing (e.g., machining, shaping, etc.) may be performed on the final cured composite material. The shaping or casting of the dispersion in the process described herein is primarily to impart some initial structure to the dispersion prior to further processing. Rigid or particular shapes can be obtained, but are not required.

Casting includes casting the dispersion onto a casting surface. Non-limiting examples of casting include air casting (e.g., a series of air flow conduits where the dispersion is evaporated by controlling the solvent over a specified time, such as 24 to 48 hours), solvent casting, or dip casting (e.g., spreading the dispersion onto a conveyor belt and through a bath or liquid where the liquid in the bath is exchanged for the solvent). The dispersion can be spread on the casting surface by means of a blade, a roll-coating bar or any flat extrusion die.

During casting and molding, the solvent may be removed, leaving the dispersion on the substrate or in the mold. Heating may be applied to aid in the removal of the solvent. For example, the molding material may be heated at least one, equal to any, or between any two temperatures of 25 ℃, 30 ℃, 35 ℃, 40 ℃, 45 ℃, 50 ℃, 55 ℃, 60 ℃, 65 ℃, 70 ℃, 75 ℃, and 80 ℃. The resulting shaped polymer composite can be annealed at least one of, equal to, or between any two temperatures for a desired time (e.g., 5 hours, 10 hours, 15 hours, 20 hours, 25 hours, 30 hours, 35 hours, 40 hours, 45 hours, 50 hours, or any range therebetween) at 80 ℃, 85 ℃, 90 ℃, 95 ℃, 100 ℃, 105 ℃, 110 ℃, 115 ℃, 120 ℃, 125 ℃, 130 ℃, 135 ℃, 140 ℃, 145 ℃, and 150 ℃. The shaped material may be a film, sheet, or the like.

After annealing, the shaped polymer composite may be subjected to conditions that induce electrical polarization in the lead-free piezoelectric material (e.g., plurality of particles) in the polymer composite. During electrical polarization, the piezoelectric particles may be connected to each other in a linear or semi-linear fashion (e.g., chains of particles). The piezoelectric particle column is suitably formed by stacking or arranging more than one chain. In one non-limiting example, the shaped polymer composite may be polarized. For example, the polymer composite may be polarized with a selected electric field at room temperature, or at a selected electric field at a selected temperature (e.g., after cooling of the composite), with at least one of the selected electric field and the selected temperature being selected according to a desired dipole orientation, a desired polarization strength, or characteristics of the article.

The temperature at which the poling is carried out may be in accordance with the desired dipole orientation and/or the desired poling strength, or in accordance with the desired stress state of the finished driver. For example, the polarization of the polymer composite can be operated at a selected cooling temperature range, by a selected heating temperature, or by a selected heating temperature and cooling temperature range. In some cases, polarization may occur at a "range" (e.g., a selected range) of temperatures, rather than at a particular constant temperature. In some embodiments, the polarization temperature should be at least, equal to, or at a temperature between: 80 deg.C, 85 deg.C, 90 deg.C, 95 deg.C, 100 deg.C, 105 deg.C, 110 deg.C, 115 deg.C and 120 deg.C. The voltage level parameter to which the polarization is applied may be selected in a variety of ways. For example, the applied voltage level parameter may be selected to be constant or to vary over a period of time (e.g., ramped). In some embodiments, electrode polarization is performed by corona discharge with a voltage of 6kV/m to 15kV/m or 10kV/m to 13kV/m or any range or value therebetween, with an electrode gap of 0.5cm to 1.5cm or about 1cm for a desired time (e.g., about 1 hour).

C. Piezoelectric composite material

The piezoelectric composite may include a polymer and a lead-free piezoelectric material. The piezoelectric composite may comprise a polymer matrix-forming polymer in a content of at least one of, equal to, or between: 10, 20, 30, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, and 99 wt%. The amount of lead-free piezoelectric additive present in the polymer matrix may be at least, equal to, or between any two of: 10 volume%, 15 volume%, 20 volume%, 25 volume%, 30 volume%, 35 volume%, 40 volume%, 45 volume%, 50 volume%, 55 volume%, 60 volume%, 65 volume% and 70 volume%. In some embodiments, the piezoelectric composite comprises PVDF-TRFE-CFE and 20 to 60 volume percent or 40 to 60 volume percent barium titanate particles. In some embodiments, the piezoelectric composite comprises PVDF-TRFE-CFE and 20 to 60 volume percent or 40 to 60 volume percent KLNN particles. In some embodiments, a piezoelectric composite comprises, consists of, or consists essentially of PVDF-TRFE-CFE and 20 to 60 volume percent barium titanate particles having an average particle size of 200 to 500 nm. In some embodiments, the piezoelectric composite comprises, consists of, or consists essentially of PVDF-TRFE-CFE and 20 to 60 volume percent KLNN particles.

In certain embodiments, the piezoelectric composite may have any shape or form. In certain embodiments, the piezoelectric composite is a film or a sheet. In certain embodiments, the film or sheet has a thickness dimension of from 50 microns to 200 microns, or at least, equal to, or between any two of: 50 microns, 60 microns, 70 microns, 80 microns, 90 microns, 100 microns, 110 microns, 120 microns, 130 microns, 140 microns, 150 microns, 160 microns, 170 microns, 180 microns, 190 microns, and 200 microns.

The characteristics of the piezoelectric composite material include electrical characteristics and mechanical characteristics. Non-limiting examples of electrical properties may include piezoelectric constant, dielectric constant, and the like. D of the piezoelectric composite₃₃Greater than any of, equal to, or between any of: 20pC/N, 25pC/N, 30pC/N, 35pC/N, 40pC/N, 45pC/N, 50pC/N, 55pC/N, 56pC/N, 57pC/N, 58pC/N, 59pC/N, and 60 pC/N. The dielectric constant of the piezoelectric composite material may be 30 to 210, or at least one of, equal to, or between: 30. 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, 180, 185, 190, 195, 200, 205, and 210. The lead-free piezoelectric composite material has a storage modulus of 100 to 325MPa, or at least, equal to, or between any two of: 100MPa, 125MPa, 150MPa, 175MPa, 200MPa, 225MPa, 250MPa, 275MPa, 300MPa, 325 MPa. The storage modulus can be measured according to ISO 6721 at room temperature and 0.2% tension at 1 Hz. The lead-free piezoelectric composite may have an elongation at break of 100% to 500% under uniaxial loading at room temperature (e.g., 25 ℃ to 35 ℃). Elongation at break can be measured using a standard dynamic mechanical analyzer, such as a RDAIII analyzer (TA Instruments, u.s.a.). The lead-free piezoelectric composite material may have an elastic modulus of less than 1GPa, or 0.1GPa to 0.99GPaOr less than any of the following, equal to any of the following, or between any two of the following: 0.1GPa, 0.25GPa, 0.5GPa, 0.75GPa, 0.8GPa, 0.9GPa and 0.99 GPa. The modulus of elasticity can be measured with a universal tensile tester. Notably, the composite material maintained piezoelectric performance without depolarization when the test temperature reached 110 ℃.

D. Device and article

The piezoelectric composite of the present invention may be incorporated into a device. Preferably, the device is flexible. In certain particular instances, the piezoelectric composites of the present invention may be used to fabricate articles having curved surfaces, flexible surfaces, deformable surfaces, and the like. Non-limiting examples of such articles include piezoelectric sensors, piezoelectric transducers, piezoelectric actuators. These components may be used in touch sensitive devices, electronic devices (e.g., smartphones, tablets, computers, etc.), virtual reality devices, augmented reality devices, fixtures with flexibility, such as adjustably mounted wireless headsets and/or earplugs, curved communication helmets, pharmaceutical lots, flexible identity cards, flexible sporting goods, packaging materials, medical devices, and/or the presence of flexible materials simplifies final product design, engineering, and/or mass production applications.

Examples

The present invention will be described in more detail by way of specific examples. The following examples are given for illustrative purposes only and are not intended to limit the invention in any way. Those skilled in the art will readily recognize various key parameters, and may change or modify these parameters to produce substantially the same results.

Example 1

(preparation of piezoelectric Material of the invention)

PVDF-TrFE-CFE(RT^TMCFE Standard ingredient powder) from Arkema group (France)And (4) obtaining the product. BaTiO 2₃(BT) was obtained from Inframat corporation (USA). KLNN is according to WO 2016 to Bella et al157092, respectively. PVDF-TrFE-CFE was dissolved in Tetrahydrofuran (THF) by magnetic stirring at a polymer to solvent ratio of 1:8 in an oil bath at 50rpm for 1 hour at 25 ℃. After the polymer was completely dissolved, different volume fractions of BT or KLNN were added to the solution and stirred at 300rpm for 30 minutes to completely homogenize the BT or KLNN powder in the PVDF-TrFE-CFE solution. After homogenization, the mixture was cast on a glass plate, or a glass plate wrapped with aluminum foil. The cast film is dried at room temperature and then annealed at 110 ℃ for 2 to 5 hours under atmospheric conditions. The sample was polarized at 110 ℃ for 0.5 hour at a voltage of 10 KV/mm. Table 2 lists the properties of PZT and lead-free piezoelectric materials. Table 3 lists the compositions of the lead-free piezoelectric composites of the present invention.

TABLE 2

TABLE 3

Unsupported piezoelectric composite membrane

Aluminum foil support film

Piezoelectric composite membrane prepared by corona polarization technology

FIG. 1 shows d₃₃Change with increasing PZT volume fraction (comparative sample) and KLNN volume fraction. FIG. 2 shows the change in dielectric constant with increasing volume fraction of PZT (comparative sample) and volume fraction of KLNN. Although d of KLNN sample₃₃Lower, but results are acceptable for lead-free materials because of the higher d₃₃A lower dielectric constant and a higher curie temperature. The PZT and lead-free piezoelectric ceramics, barium titanate and KLNN described in this invention are all perovskites. The properties of the piezoelectric ceramics are summarized in table 2.

In the context of the present invention, at least 20 embodiments are presently described. Embodiment 1 is a lead-free piezoelectric composite material. The composite material comprisesA polymer matrix having a dielectric constant greater than 30 at 20 ℃; and greater than 10 volume percent of a lead-free piezoelectric material dispersed throughout the polymer matrix based on the total volume of the composite. The lead-free piezoelectric composite material has an elastic modulus of less than 1GPa and a piezoelectric coefficient d₃₃Greater than 20 pC/N. Embodiment 2 is the lead-free piezoelectric composite of embodiment 1, wherein the polymer matrix comprises a poly (vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) (PVDF-TrFE-CFE) terpolymer. Embodiment 3 is the lead-free piezoelectric composite of any one of embodiments 1 or 2, wherein the polymer matrix is PVDF-TrFE-CFE. Embodiment 4 is the lead-free piezoelectric composite of any one of embodiments 1 to 3, wherein the lead-free piezoelectric material is present in an amount of 30 to 70 volume percent, preferably 40 to about 60 volume percent, based on the total volume of the composite. Embodiment 5 is the lead-free piezoelectric composite of any one of embodiments 1 to 4, wherein the piezoelectric material comprises barium titanate (BaTiO)₃) Potassium sodium niobate (KNaNb) O₃(KNN), potassium lithium sodium niobate (KLi) (NaNb) O₃(KLNN), hydroxyapatite, apatite, lithium sulfate monohydrate, sodium bismuth titanate, quartz, organic materials, preferably tartaric acid or poly (vinylidene fluoride) fibers, or combinations thereof. Embodiment 6 is the lead-free piezoelectric composite of any one of embodiments 1 to 5, wherein the polymer matrix is PVDF-TrFE-CFE and the piezoelectric material is BaTiO₃. Embodiment 7 is the lead-free piezoelectric composite of any one of embodiments 1 to 6, wherein the polymer matrix is PVDF-TrFE-CFE and the piezoelectric material is KLNN. Embodiment 8 is the lead-free piezoelectric composite of any one of embodiments 1 to 7, wherein the polymer matrix is PVDF-TrFE-CFE and the piezoelectric material is KNN. Embodiment 9 is the lead-free piezoelectric composite of any one of embodiments 1 to 8, wherein the composite retains its d at a temperature greater than 90 degrees c₃₃The value is obtained. Embodiment 10 is the lead-free piezoelectric composite of any one of embodiments 1 to 9, wherein the composite has a lower directional polarization voltage under an electric field than the same polymer matrix without the lead-free piezoelectric filler. Embodiment 11 is the lead-free piezoelectric composite of any one of embodiments 1 to 10, wherein the composite is flexibleA sheet or film of nature. Embodiment 12 is the lead-free piezoelectric polymer composite of embodiment 11, wherein the film or sheet has a thickness of 50 to 200 microns. Embodiment 13 is the lead-free piezoelectric composite of any one of embodiments 1 to 12, further comprised in an article. Embodiment 14 is the lead-free piezoelectric composite of embodiment 13, wherein the article is a touch panel, a human-machine interface, an integrated keyboard, or a component of a wearable device.

Embodiment 15 is a piezoelectric device comprising the lead-free piezoelectric composite of any one of embodiments 1 to 12, wherein the device is preferably a piezoelectric sensor, a piezoelectric transducer, or a piezoelectric actuator, the device preferably having mechanical flexibility. Embodiment 16 is a method of forming the lead-free piezoelectric composite of any of embodiments 1 to 12, the method comprising (a) adding lead-free piezoelectric particles to a solution comprising a dissolved polymeric material having a dielectric constant greater than 10 and a solvent to form a dispersion or suspension, wherein the lead-free piezoelectric particles are dispersed or suspended in the solution; (b) forming a polymer matrix having lead-free piezoelectric particles dispersed or suspended therein, and (c) subjecting the polymer matrix having lead-free piezoelectric particles dispersed therein to an electric polarization treatment to form the lead-free piezoelectric composite material of any one of embodiments 1 to 12. Embodiment 17 is the method of embodiment 16, wherein forming the polymer matrix comprises: (i) casting the dispersion on a substrate, (ii) drying the polymer matrix at 25 ℃ to 80 ℃ to form a polymer matrix, and (iii) annealing the dried polymer matrix at 80 ℃ to 150 ℃ for 1 hour to 50 hours, preferably at a temperature of 110 ℃ for 5 hours to 25 hours. Embodiment 18 is the method of any one of embodiments 16 to 17, wherein inducing electrical polarization comprises applying a polarizing field using corona discharge. Embodiment 19 is the method of any one of embodiments 16 to 18, wherein the polymeric material is poly (vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) and the lead-free piezoelectric material is KLNN, KNN, BaTiO₃Or a combination thereof, the solvent is tetrahydrofuran, methyl ethyl ketone, dimethyl sulfoxide, ethyl acetate, amyl acetate, dimethylformamide, dimethylacetamide, or any combination thereof. Embodiment 20 is the method of any one of embodiments 16 to 19A process wherein the ratio of polymeric material to solvent is from 1:5 to 1: 10.

Although the embodiments of the present application and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the embodiments as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure provided above, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.