Polyolefin-based piezoelectric polymer composite material

Abstract

A piezoelectric composite material is disclosed that includes (a) an olefin copolymer and (b) a plurality of piezoelectric filler particles. The plurality of piezoelectric filler particles can be dispersed in the olefin copolymer. Also disclosed are films that include such piezoelectric composite materials and methods for preparing such films.

Description

Detailed Description of the Invention

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS none.

[0002] FIELD OF THE INVENTION The present invention is directed to the field of piezoelectric polymer composites, and in some embodiments, to flexible films comprising such piezoelectric polymer composites.

[0003] 〔background〕 Traditional wearable devices use eccentric rotating masses (ERMs) and linear resonant actuators (LRAs) to generate vibrations to receive user input or provide feedback. However, the inclusion of ERMs and LRAs in such devices adds bulk to these devices and impacts the mechanical flexibility of the device. Wearables and other devices could benefit from mechanical flexibility and low-voltage operation.

[0004] Piezoelectric devices have been explored as an alternative to overcome the drawbacks associated with ERM and LRA. Some of the piezoelectric materials explored include ceramics, single crystal piezoelectric materials, and polymeric piezoelectric materials. Ceramics have relatively high piezoelectric properties compared to polymers. StrainCeramics can have high acoustic impedance and poor electromechanical resonance, which makes them particularly suitable for actuators. However, ceramics suffer from high acoustic impedance and poor electromechanical resonance, resulting in poor acoustic matching and high background noise. Furthermore, ceramics can exhibit high stiffness and brittleness, making them difficult to fabricate on curved surfaces and limiting the design flexibility of transducers. Single-crystal piezoelectric materials such as quartz, tourmaline, or potassium sodium tartrate crystals have been attempted, but, like ceramics, no single piezoelectric material can achieve all the desired functionality for an application; performance is limited by the trade-off between high piezoelectric activity and low mechanical flexibility. Piezoelectric polymer materials such as polyvinylidene fluoride (PVDF) and polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) copolymer offer several advantages, including mechanical flexibility, light weight, and easy low-temperature processing. These polymer materials are well suited for device design and integration. Despite these advantages, these polymer materials are typically superior to ceramics, such as lead zirconate titanate (PZT), which is a leading-piezoelectric material. 33 range of 270-400 pC / N) compared to piezoelectric Strain The constant is low (d 33 However, they have drawbacks, such as a low sensitivity (~13–28 pC / N). They also require higher drive voltages, raising additional safety and cost concerns. Furthermore, PVDF requires secondary processing to form piezo-active beta-PVDF, which increases both operational and capital investments and limits its potential. In particular, the overall cost of production involving PVDF polymers hinders widespread commercial applications, leaving a need for cost-effective piezoelectric polymer solutions. Furthermore, the use, disposal, and recycling of halogenated polymers such as PVDF are subject to environmental regulations.

[0005] Piezoelectric polymer composites are a new class of materials that contain polymers and piezoelectric fillers, and are able to achieve the high piezoelectric properties of ceramics. StrainThey effectively combine the advantages of both types of materials: the high piezoelectric voltage constant (with appropriate piezoelectric fillers) and the high mechanical flexibility of polymers. Such materials can be tailored according to the properties, design or functional requirements of the intended application.

[0006] The drawbacks described herein are merely representative and are included to highlight problems the inventors have identified with existing piezoelectric materials. Embodiments of the piezoelectric materials described below, as well as others known in the art, may address some or all of the drawbacks.

[0007] [Summary] Disclosed herein are piezoelectric composites that provide cost-effective materials and films with one or more advantages of ease of processing, excellent piezoelectric properties, flexibility, and other mechanical properties. The high-performance piezoelectric materials are suitable for healthcare and biomedical applications, as well as sensors, actuators, and energy harvesters in wearable electronics.

[0008] The piezoelectric composite material can include an olefin copolymer. As used herein, the term "olefin copolymer" refers to a copolymer containing a first monomer of ethylene or propylene polymerized with 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, or 1-eicosene. A preferred embodiment may be composed of ethylene and octene. The olefin copolymer may include an olefin block copolymer, an olefin random copolymer, or some mixture of the two.

[0009] The piezoelectric composite material includes a plurality of piezoelectric filler particles dispersed in an olefin copolymer. The olefin copolymer may be present in an amount ranging from 20 to 80 volume percent, based on the total volume of the piezoelectric composite. The plurality of piezoelectric filler particles may be present in an amount ranging from 20 to 80 volume percent, based on the total volume of the piezoelectric composite. The olefin copolymer may include 10 to 40 weight percent octene in the copolymer, and the olefin copolymer is as follows:

[0010] [ka]

[0011] The piezoelectric composite may further include a second polymer, and the second polymer may be polyethylene, polypropylene, ethylene copolymer, propylene copolymer, polyethylene terephthalate (PET), polycarbonate (PC), polybutylene terephthalate (PBT), poly( 1,4 -Cyclohexylidenecyclohexane- 1,4 -dicarboxylate) (PCCD), glycol-modified polycyclohexyl terephthalate (PCTG), poly(phenylene oxide) (PPO), polypropylene (PP), polyethylene (PE), polyvinyl chloride (PVC), polystyrene (PS), polymethyl methacrylate (PMMA), polyethyleneimine or polyetherimide (PEI) and their derivatives, thermoplastic elastomers (TPE), terephthalic acid (TPA) elastomers, poly(cyclohexanedimethylene terephthalate) (PCT), polyethylene naphthalate (PEN), polyamide (PA), polysulfone sulfonate (PSS), polyether ether ketone (PEEK), acrylonitrile butyldiene styrene (ABS), polyether ketone (PEKK), polyphenylene sulfide (PPS), copolymers thereof, or blends thereof.

[0012] In a piezoelectric composite material, the plurality of piezoelectric filler particles may include at least one of lead zirconate titanate (PZT), hydroxyapatite, apatite, lithium sulfate monohydrate, bismuth sodium titanate, quartz, tartaric acid fiber, poly(vinylidene fluoride) fiber, and barium. Formula (K,Na) (1-t) Li t Potassium sodium lithium niobate doped niobate (KNLN) having NbO3, wherein the variable "t" ranges from greater than 0.01 to less than 1 (0.01 < t < 1.00) (0.01 < t < 1.00), potassium sodium niobate (K,NaNb)O3 (KNN), or a combination thereof. When the piezoelectric filler particles are KNLN, the particles are 40 vol.% to 60 vol.% of the composite material.

[0013] The piezoelectric composite according to the present invention can be manufactured in different forms according to the requirements of the intended application. These include pellets, flakes, powders, fibers, films, etc. The flexible film can include any of the piezoelectric composite materials listed above. The film may have a piezoelectric Strain constant (d33 (pC / N)) in the range of about 6 to about 100, more preferably about 20 to about 50. The film may have a g33 of ~100~300 mV * m / N. The film may have an elongation at break (%) in the range of about 20 to 800. The film may have a thickness in the range of about 50 microns to about 500 microns.

[0014] The method for producing the above-described film may include the following steps: dissolving an olefin copolymer in an organic solvent to form an olefin copolymer solution, the olefin copolymer being formed by polymerizing a first monomer of ethylene or propylene with any of 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradene, 1-hexadene, 1-octadene, and 1-eicosene; adding a plurality of piezoelectric filler particles to the olefin copolymer solution to form a film precursor; forming a cast film precursor from the film precursor; and poling the cast film precursor. The cast film precursor may be annealed prior to poling. The cast film precursor may be poled at an electric field ranging from about 5 kV / mm to about 100 kV / mm for a time ranging from about 1 minute to about 120 minutes at a temperature ranging from about 60°C to about 120°C. The olefin copolymer is preferably an ethylene-octene copolymer.

[0015] Also disclosed within the context of the present invention are embodiments 1 to 19. Embodiment 1 is a plurality of piezoelectric filler particles dispersed in an olefin copolymer selected from the group consisting of 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-butene, 4-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, and 1-eicosene. Embodiment 2 is the piezoelectric composite of embodiment 1, wherein the olefin copolymer is present in an amount ranging from 20 to 80 volume %, based on the total volume of the piezoelectric composite. Embodiment 3 is the piezoelectric composite of any one of embodiments 1 to 2, wherein the plurality of piezoelectric filler particles are present in an amount ranging from 20 to 80 volume %, based on the total volume of the piezoelectric composite. Embodiment 4 is the piezoelectric composite of any one of aspects 1 to 3, wherein the olefin copolymer is an ethylene-octene copolymer represented by the general formula:

[0016] [ka]

[0017] Aspect 5 is a piezoelectric composite of any one of Aspects 1 to 4, wherein the ethylene-octene copolymer contains 10 to 40% by weight of octene. Aspect 6 is polyethylene, polypropylene, ethylene copolymer, propylene copolymer, polyethylene terephthalate (PET), polycarbonate (PC), polybutylene terephthalate (PBT), poly( 1,4 -cyclohexylidene cyclohexane- 1,4 -dicarboxylate)(PCCD), glycol-modified polycyclohexyl terephthalate (PCTG), poly(phenylene oxide) (PPO), polypropylene (PP), polyethylene (PE), polyvinyl chloride (PVC), polystyrene (PS), polymethyl methacrylate (PMMA), polyethyleneimine or polyetherimide (PEI) and its derivatives, thermoplastic elastomer (TPE), terephthalic acid (TPA) elastomer, poly(cyclohexane dimethylene terephthalate) (PCT), polyethylene naphthalate (PEN), polyamide (PA), polysulfone sulfonate (PSS), polyether ether ketone (PEEK), acrylonitrile butadiene styrene (ABS), polyether ketone ketone (PEKK), polyphenylene sulfide (PPS), their copolymers, or their blends. Aspect 7 is a piezoelectric composite of any one of Aspects 1 to 6, wherein a plurality of piezoelectric filler particles contain at least one of lead zirconate titanate (PZT), hydroxyapatite, apatite, lithium sulfate monohydrate, sodium bismuth titanate, quartz, tartaric acid. Fibers, poly(vinylidene fluoride) fibers, barium titanate, formula (K,Na) 1-t Li t Potassium sodium lithium niobate (KNLN) having NbO3, wherein the variable "t" is in the range of greater than 0.01 to less than 1 (0.01 < t). <1.00), potassium sodium niobate (K,NaNb)O3 (KNN), or a combination thereof. Aspect 8 is a piezoelectric composite of any one of Aspects 1 to 7, wherein a plurality of piezoelectric filler particles contain about 40 vol% to about 60 vol% of KNLN with respect to the total volume of the piezoelectric composite.

[0018] A ninth embodiment is a film comprising the piezoelectric composite of any one of the first to eighth embodiments. A tenth embodiment is a film comprising the film having a piezoelectricity ranging from about 6 to about 100. Strain constant (d 33 (pC / N)) in the range of about 20 to about 50. Strain Embodiment 12 is the film of any one of Embodiments 9-11, wherein the piezoelectric voltage constant (g33 (mV.m / N)) is about 100 to 300. Embodiment 13 is the film of any one of Embodiments 9-12, wherein the film has a thickness ranging from about 50 microns to about 500 microns. Embodiment 14 is the film of any one of Embodiments 9-13, wherein the film has an elongation at break ranging from about 20% to about 800%. Embodiment 15 is the film of any one of Embodiments 9-14, wherein the film is present in an article of manufacture.

[0019] Example 16 is a method for preparing the film of any one of claims 9 to 15, the method comprising: dissolving an olefin copolymer in an organic solvent to form an olefin copolymer solution including a first monomer of ethylene or propylene, polymerized with 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, or 1-eicosene; adding a plurality of piezoelectric filler particles to the olefin copolymer solution to form a film precursor; forming a cast film precursor from the film precursor; and poling the cast film precursor. Example 17 is the method of Example 16, wherein the cast film precursor is annealed prior to poling. Example 18 is the method of any one of Examples 16-17, wherein the olefin copolymer is an ethylene-octene copolymer. Aspect 19 is the method of any one of aspects 16 to 18, wherein the cast film precursor is poled in an electric field ranging from about 5 kV / mm to about 100 kV / mm for a time period ranging from about 1 minute to about 120 minutes. It is heated at a temperature ranging from about 60°C to about 120°C for several minutes. The terms "about" or "approximately" are defined as close as understood by one of ordinary skill in the art. In one non-limiting embodiment, the term is defined as within 10%, preferably within 5%, more preferably within 1%, and most preferably within 0.5%.

[0020] The terms "wt.%," "vol.%," and "mol.%" refer to the weight, volume, or mole percentage of a component, respectively, based on the total weight, volume, or moles of the material containing the component. In a non-limiting example, 10 moles of a component in 100 moles of a material refers to 10 mole % of the component. The term "M" refers to the molar concentration of a component, based on moles per liter of volume. The term "mM" means one thousandth of an "M." Numerical ranges used throughout this disclosure are intended to include all values ​​and ranges therebetween unless otherwise specified. For example, a boiling point range of 50°C to 100°C includes all temperatures and ranges between 50°C and 100°C, inclusive.

[0021] When used in conjunction with the terms "comprising," "comprise," "having," or "having" in the claims or specification, the use of the words "a" or "an" can mean "one," but is also consistent with the meaning of "one or more," "at least one." "Comprising" (and any inclusive form such as "comprising" and "comprising"), "having" (and any inclusive form such as "having" and "having"), "including" (and any inclusive form such as "comprising" and "comprising"), or "having" (and any inclusive form such as "having" and "having") is inclusive or open-ended and does not exclude additional, unrecited elements or method steps. The processes of the present invention may "comprise," "essentially comprise," or "consist of" certain ingredients, components, compositions, etc. disclosed throughout the disclosure.

[0022] Other objects, features, and advantages of the present invention will become apparent from the following figures, detailed description, and examples. It should be understood, however, that the figures, detailed description, and examples, while indicating specific embodiments of the present invention, are given by way of illustration only and are not meant to be limiting. Furthermore, it is contemplated that changes and modifications within the spirit and scope of the present invention will become apparent to those skilled in the art from this detailed description. In further embodiments, features of specific embodiments can be combined with features of other embodiments. For example, features of one embodiment can be combined with features of any of the other embodiments. In further embodiments, additional features can be added to the specific embodiments described herein.

[0023] BRIEF DESCRIPTION OF THE DRAWINGS For a more complete understanding, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

[0024] FIG. 1 shows a diagram of a polymer-ceramic piezoelectric composite according to an embodiment of the present disclosure.

[0025] FIG. 2 is a graph of dielectric constant as a function of frequency for a piezoelectric polymer composite according to an embodiment of the present disclosure.

[0026] [Figure 3 a ) Figure 3 a is according to an embodiment of the present disclosure PVDF and Piezoelectric Polymer Composite Body Temperature Function as Piezoelectric strain constant This is a graph of FIG. 3b includes images of the physical appearance of a PVDF and piezoelectric polymer composite according to an embodiment of the present disclosure (before and after heating). FIG. 4 is a graph of a tensile stress-strain plot of a piezoelectric polymer composite according to an embodiment of the present disclosure.

[0027] [Detailed explanation] 1 shows a diagram of a polymer ceramic piezoelectric composite according to an embodiment of the present disclosure. The composite 100 includes a polymer matrix 102 and a piezoelectric ceramic filler 104 dispersed in the polymer matrix 102. The piezoelectric ceramic filler 104 may be in the form of particles or may be dispersed throughout the polymer matrix 102. The polymer matrix 102 may include an olefin copolymer, as described in more detail in the embodiments described below.

[0028] Olefin copolymer-based piezoelectric composites offer a unique solution to some of the challenges and limitations described above. The composites contain piezoelectric filler particles dispersed in an olefin copolymer. The olefin copolymer can be present in an amount ranging from 20 vol.% to 80 vol.%, alternatively from 30 vol.% to 70 vol.%, alternatively from 45 vol.% to 65 vol.%, alternatively from 40 vol.% to 60 vol.%, or approximately 40 vol.% based on the total volume of the piezoelectric composite. The piezoelectric filler particles can be present in an amount ranging from 20 vol.% to 80 vol.%, alternatively from 30 vol.% to 70 vol.%, alternatively from 40 vol.% to 60 vol.%, or approximately 60 vol.% based on the total volume of the piezoelectric composite.

[0029] The term "olefin copolymer" as used in this disclosure refers to a copolymer comprising a first monomer of ethylene or propylene polymerized with 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, or 1-eicosene. A preferred embodiment may be composed of ethylene and octene. The olefin copolymer may comprise an olefin block copolymer, an olefin random copolymer, or a mixture of the two.

[0030] In some embodiments, the second polymer included in the polymer matrix is polyethylene, polypropylene, ethylene copolymer, propylene copolymer, polyethylene terephthalate (PET), polycarbonate (PC), polybutylene terephthalate (PBT), poly( 1,4 -cyclohexylidene cyclohexane ) - 1,4 -dicarboxylate)(PCCD), glycol-modified polycyclohexyl terephthalate (PCTG), poly(phenylene oxide)(PPO), polypropylene (PP), polyethylene (PE), polyvinyl chloride (PVC), polystyrene (PS), polymethyl methacrylate (PMMA), polyethyleneimine or polyetherimide (PEI) and its derivatives, thermoplastic elastomer (TPE), terephthalic acid (TPA) elastomer, poly(cyclohexane dimethylene terephthalate)(PCT), polyethylene naphthalate (PEN), polyamide (PA), polysulfone sulfonate (PSS), polyether ether ketone (PEEK), acrylonitrile butadiene styrene (ABS), polyether ketone ketone (PEKK), polyphenylene sulfide (PPS), their copolymers, or blends thereof. In some preferred embodiments of the present invention, the second polymer is polycarbonate (PC).

[0031] The plurality of piezoelectric filler particles can include particles of lead zirconate titanate (PZT), hydroxyapatite, apatite, lithium sulfate monohydrate, bismuth sodium titanate, quartz, tartaric acid fiber, poly(vinylidene fluoride) fiber, barium titanate, lithium-doped potassium sodium niobate. These particles have the formula (K,Na) 1-t Li t NbO3 (KNLN), where the variable "t" is in the range greater than 0.01 and less than 1.00 (0.01 < t < 1.00), potassium sodium niobate (K,NaNb)O3 (KNN), or combinations thereof. In some exemplary embodiments, each of the plurality of piezoelectric filler particles has the formula (K,Na) 1-t Lit Potassium sodium lithium niobate (KNLN) having NbO3, wherein the variable "t" ranges from greater than 0.01 to less than 1.00 (0.01 < t < 1.00). In some exemplary embodiments, each of the plurality of piezoelectric filler particles has a formula K where the variable "t" is equal to 0.03 0.485 Na 0.485 Li 0.03 represented by NbO3.

[0032] The plurality of piezoelectric filler particles have a particle size distribution D in the range from about 3 to about 50, or alternatively from about 4 to about 20, or alternatively from about 10 to about 15 50 (μm), and / or D from about 10 to about 500, from about 20 to about 100 90 (μm). As used throughout this disclosure, the expression "particle size distribution" refers to the number of particles falling into each of the various size ranges given as a percentage of the total number of all sizes in the sample of interest. The parameter "D 90 " represents the point of the size distribution in which up to 90% of the total volume of the material in the sample is included. For example, when the parameter "D 90 " is 844 microns, it means that 90% of the sample is of a size of 844 microns or less. Similarly, the parameter "D 50 " means the point of the size distribution in which up to 50% of the material is included, and the parameter "D 10 " means the point of the size distribution in which up to 10% is included. % of the substance is included. The particle size distribution can be measured by any of the known techniques commonly used in the industry for such measurements, such as laser diffraction techniques or dynamic light scattering techniques. The piezoelectric filler particles can have a size and form suitable for piezoelectric applications.

[0033] An example method for preparing a piezoelectric ceramic filler includes (a) adding a mixture of metal precursor compounds to an organic solvent to form a suspension; (b) subsequently homogenizing the suspension, followed by filtering and drying in an oven at a temperature of at least 100°C to remove the solvent and form a metal salt mixture composition; and (c) loading the thus-formed metal salt mixture composition into an alumina crucible and subjecting the metal salt mixture composition to a first firing step and then a second firing step to form piezoelectric filler particles. The fired filler particles can be ground using a mortar and pestle. The first firing step can include heating the metal salt mixture composition at a heating rate of about 5°C / min, followed by increasing the temperature to at least 1000°C. The temperature can be maintained for at least 3 hours, after which the metal salt mixture composition can be cooled to a temperature of at least 30°C at a cooling rate of about 5°C / min. The second firing step is similar to the first firing step, except that the powder sample can be heated to a temperature of at least 950°C at a heating rate of 1°C / min. The temperature can then be maintained for at least 10 hours. Metal precursor compounds that can be used to prepare the piezoelectric filler particles can be metal carbonates, such as sodium carbonate or potassium carbonate, or metal oxides, such as niobium oxide.

[0034] In some embodiments, a film can include a piezoelectric composite according to any of the described embodiments. A method for preparing such a film including a piezoelectric composite can include the following steps: (a) dissolving an olefin copolymer in an organic solvent to form an olefin copolymer solution; (b) adding a plurality of piezoelectric filler particles to the olefin copolymer solution to form a film precursor; (c) casting the film precursor onto a substrate and subsequently drying to form a cast film precursor; and (d) poling the cast film precursor to form a piezoelectric composite film. Films including piezoelectric composites can be prepared without secondary processing, unlike examples in which PVDF-based films are subjected to uniaxial stretching and / or surface treatment to induce piezoelectric properties. In some embodiments, the process can be solventless and includes mixing the olefin copolymer and piezoelectric filler particles, followed by compression molding. The resulting mixture can be subjected to annealing and poling.

[0035] In some embodiments, the substrate is a glass plate. Non-limiting examples of organic solvents used to prepare the film include 1,2-dichlorobenzene, 1,2,4-trichlorobenzene, cyclohexane, toluene, xylene, or combinations thereof. The ratio of olefin copolymer to organic solvent can range from 1:5 to 1:15, from 1:6 to 1:9, or about 1:8. With respect to the olefin copolymer solution, in some embodiments, the solution contains at least one of, or equal to, or any of the following: 10 wt%, 20 wt%, 30 wt%, 40 wt%, or 50 wt%, or about 12.5 wt%.

[0036] In some embodiments, casting the film precursor can include placing the film precursor on a substrate. Non-limiting examples of casting include air casting (e.g., passing the film precursor under a series of airflow ducts that control the evaporation of the organic solvent over a specific set period, such as 24-48 hours), solvent casting, or emulsion casting (e.g., spreading the film precursor on a moving belt and passing it through a bath or liquid that exchanges the liquid in the bath with the organic solvent). Spreading the film precursor onto the substrate can be accomplished using a doctor blade, rolling spreader bar, or other suitable device.

[0037] In some embodiments, the cast film is dried at any temperature between 25°C and 80°C, alternatively at any temperature between 45°C and 70°C, to remove the organic solvent and form a cast film precursor. The cast film precursor may be annealed prior to poling. Annealing of the film can be carried out at any temperature between 80°C and 150°C for a time ranging from 1 hour to 50 hours. Preferably, the film is annealed at a temperature of 110°C for 5 hours to 25 hours.

[0038] The term "poling" as used throughout this disclosure refers to the process of inducing electric polarization in a material to specifically orient piezoelectric filler particles. During electric polarization, piezoelectric filler particles may be connected to one another in a linear or semi-linear configuration (e.g., chains of particles). Columns of piezoelectric particles are suitably formed by stacking or aligning two or more chains. For example, a cast film precursor may be poled in a selected electric field at room temperature (e.g., after cooling of the composite), or in a selected electric field at a selected temperature. The selected temperature may be selected, for example, according to the transition temperature (Tg / Tm) of the polymer matrix and the Curie temperature of the piezoelectric filler. In some cases, poling may occur over a "range" (e.g., a selected range) of temperatures rather than at a specific, constant temperature. The applied voltage level parameters for poling can be selected in a variety of ways. For example, the applied voltage level parameters may be selected to vary (e.g., ramp) over a period of time. In some embodiments, poling is performed using corona discharge in a corona polarizer with an electrode gap of 0.5 cm to 1.5 cm, or preferably about 1 cm, for a desired time. In accordance with the present invention, such a poling technique is referred to as "corona poling."

[0039] In some embodiments, the cast film precursor is poled at an electric field ranging from about 5 kV / mm to about 100 kV / mm, or alternatively from about 10 kV / mm to about 80 kV / mm, or alternatively from about 20 kV / mm to about 60 kV / mm, for a time ranging from about 1 minute to about 120 minutes, or alternatively from about 20 minutes to about 100 minutes, or alternatively from about 50 minutes to about 80 minutes, and at a temperature ranging from about 60°C to about 120°C, or alternatively from about 70°C to about 100°C, where the temperature for poling can be determined according to the transition temperature (Tg / Tm) of the polymer matrix and the Curie temperature of the piezoelectric filler.

[0040] Films comprising the piezoelectric composites of the described embodiments exhibit high values ​​of piezoelectricity while retaining adequate mechanical flexibility. Strain constant (d33 In some embodiments, the films demonstrate excellent piezoelectric properties by demonstrating a piezoelectric constant (pC / N) in the range of about 2 to about 100, alternatively in the range of about 15 to about 80, alternatively in the range of about 40 to about 60. Strain constant (d 33 The expression "pC / N" stands for picocoulomb per Newton and refers to the mechanical strain produced by a piezoelectric film per unit of applied electric field, or the charge produced by the film per unit of applied mechanical stress. Strain The constant can be measured by a suitable piezometer such as the d33 meter. 33 The higher the value of , the higher the amount of charge generated per unit of mechanical stress applied to the film, indicating better piezoelectric properties and higher sensitivity, making it suitable for piezoelectric sensors and devices.

[0041] Another property of the film is the piezoelectric voltage constant (g 33 The piezoelectric voltage constant (g) is in the range of 50 to 400, alternatively 80 to 300, alternatively 120 to 250. The piezoelectric voltage constant refers to the electric field generated by a piezoelectric material per unit of applied mechanical stress, or the mechanical strain experienced by a piezoelectric material per unit of applied electrical displacement. As will be appreciated by those skilled in the art, films comprising the piezoelectric composites of the present invention have a high piezoelectric voltage constant (g), which means high sensitivity for piezoelectric applications such as those used in piezoelectric sensors. 33 (mV-m / N)) is the piezoelectric voltage constant (g 33 (mV-m / N)) is calculated by the formula (d 33 / ε) (d 33 is piezoelectric Strain (The "ε" is the dielectric constant.) This film has a piezoelectric constant ranging from about 2 to about 100. Strain constant (d 33 (pC / N)), and the piezoelectric voltage constant (g 33 (mV-m / N)).

[0042] In some embodiments, the film has a thickness ranging from 50 microns to 500 microns, alternatively from 60 microns to 400 microns, alternatively from 100 microns to 250 microns. Films comprising piezoelectric composites have a tensile strength ranging from 2 MPa to 7.5 MPa as measured according to ASTM D882 appropriate for the particular product application.

[0043] In some embodiments, the film has an elongation at break in the range of about 20% to 800%.

[0044] In some embodiments, a film containing the piezoelectric composite of the present invention is present in a product. In some embodiments of the present invention, the product is a component of a touch panel, a human-machine interface, an integrated keyboard, or a wearable device. A polymer composite according to aspects of the disclosed invention may be deposited as a thin film on a substrate and formed into a piezoelectric device. In some embodiments, the polymer composite is a mechanically flexible thin film formed on a flexible substrate as part of the fabrication of a flexible electronic device. A percent elongation at break value can be used to indicate the mechanical flexibility of a material. In some embodiments, the percent elongation at break of the piezoelectric composite film is greater than 25%. Such an electronic device can include a piezoelectric sensor configured to generate an analog signal proportional to the amount of deflection applied to the piezoelectric sensor by a user. The piezoelectric sensor can be integrated into a mobile device to receive user input for controlling the mobile device. In one example of a wearable medical device, mechanical vibrations of a body organ, such as a heartbeat, can be converted into an electrical signal and transmitted to a smartphone or other computing device via Bluetooth, Wi-Fi, or other signals. In another example of the use of piezoelectric materials, the material can be used as a transducer to convert and output a signal, such as by configuring the piezoelectric material as a speaker or buzzer to convert the signal into an audible sound. In yet another use case for piezoelectric materials, the material is transparent and can be incorporated into electronic displays to create touchscreen devices that can display information to a user and receive user feedback on the displayed information through taps on the screen.

[0045] Thus, embodiments describing piezoelectric composites and films including such piezoelectric composites can have one or more advantages of ease of processing, excellent piezoelectric properties while retaining adequate flexibility, and / or mechanical properties. As shown in the examples below, piezoelectric composites and films including such piezoelectric composites can exhibit piezoelectric properties. Strain The piezoelectric characteristic has a balance between the constant and the piezoelectric voltage constant.

[0046] Specific examples demonstrating some embodiments of the present invention are provided below. The examples are for illustrative purposes only and are not intended to limit the present invention. The embodiments and aspects disclosed herein are not mutually exclusive, and such aspects and embodiments can be combined in any manner. Those skilled in the art will readily recognize parameters that can be changed or modified to produce essentially the same results.

[0047] [Example] Methods for producing piezoelectric composites include: (a) dissolving an olefin copolymer in an organic solvent to form an olefin copolymer solution; (b) adding a plurality of piezoelectric filler particles to the olefin copolymer solution to form a film precursor; (c) casting the film precursor onto a substrate and subsequently drying to form a cast film precursor; and (d) poling the cast film precursor to form a piezoelectric film.

[0048] Specifically, the olefin copolymer resin was dissolved in toluene. Then, while stirring at 200–250 rpm using a magnetic stirrer, the desired amount of filler was slowly added. After stirring for 30–60 minutes, the mixture was cast onto a substrate using a doctor blade to form a thin film, which was then dried outdoors. The drying time was adjusted depending on the blade gap used to fabricate the composite. After drying, the film was peeled off from the glass plate and annealed under nitrogen. A very high-quality film was obtained. The composition of the piezoelectric polymer composite prepared according to the above procedure is shown in Table 1.

[0049] Dielectric properties For electrical measurements, circular gold electrodes with diameters of 20 and 10 mm were deposited on both sides of the composite film using a sputter coater. The film was sandwiched between the electrodes and mounted in a sample cell. The dielectric constant was measured at room temperature using an Alpha A High Frequency Dielectric / Impedance Analyzer (frequency range: 100 Hz to 1 MHz).

[0050] The dielectric constant was measured at various frequencies for the piezoelectric composite containing olefin copolymer and 45 vol.% KNLN, and the results are shown in Figure 2.

[0051] Piezoelectric response Piezoelectric composite films (3 cm x 3 cm) were corona-poled to demonstrate their piezoelectric response. Corona poling of the piezoelectric composites was performed under the conditions detailed below. The needle was held at a high electric field (typically 100 kV / nm), the poling temperature was ~70 °C, the electrode gap was 1 cm, and the poling time was 1 h. The sample was then cooled to room temperature under the same applied voltage. After holding the polarized film for at least 24 h, the piezoelectric strain constant (d33) of the polarized film was measured at ambient temperature using a Berlin court type d33 meter (PM300, Piezo Test, UK) at a frequency of 110 Hz, a clamping force of 10 N, and a vibration force of 0.25 N.

[0052] Piezoelectric Strain The constants were also measured as a function of temperature. The poled PVDF and piezo composite films were kept at a predefined temperature in an oven for 1 hour and then cooled to room temperature before measuring d33. Piezoelectric data were acquired at 20°C temperature intervals (60, 80, 100, 120, 140, 160, 180, and 200°C).

[0053] mechanical properties The tensile properties of the composite films were measured at room temperature using a Universal Tensile Machine according to ASTM D882 at a crosshead speed of 500 mm / min. 4 Shown below.

[0054] Three different olefin copolymers, ethylene-octene copolymers with different octene contents (12, 18, and 35 wt%), were selected as the polymer matrix for fabricating the piezoelectric polymer composites. The different olefin copolymers with distinctly different properties are shown in Table 2. It can be seen that the thermal transition temperatures (Tg and Tm) and modulus of the olefin copolymers decrease significantly with increasing octene content. The piezoelectric properties of the piezoelectric polymer composites (Examples 2, 6, and 7) were Strain The effect of the octene content of the olefin copolymer on the constant d33 is summarized in Table 1. Figure 2 shows the frequency dependence of the dielectric constant of Example 2. The dielectric constant of the composite film at 100 Hz was determined to be 18, and the piezoelectric voltage constant g33 was determined to be ∼276 mV.m / N. Figure 3a shows the piezoelectric constant of the poled PVDF and piezoelectric composite (Example 2). Strain The temperature dependence of the constants is compared. Figure 3b shows the effect of temperature on the physical appearance of both films. It is clear that the piezocomposite exhibits a higher piezoelectric constant than PVDF throughout the temperature range investigated. The piezocomposite film remains unchanged in appearance even when heated at 200 °C, whereas the PVDF film turns light brown when heat-treated under the same conditions. Practical applications of piezoelectric devices require materials that are stable within their operating temperature range. This result demonstrates the higher operating temperature range of polyolefin-based piezoelectric composites compared to piezoelectric PVDF. The stress-strain curves for Example 2 are shown in Figure 4. The composite film with a 45 vol% KNLN loading exhibited an elongation at break of 433% and a significant increase in modulus from 3 MPa of the parent polymer to 57 MPa.

[0055] A comparison of Examples 1, 2, and 3 (Table 1) demonstrates the effect of KNLN volume percent on the d33 of piezoelectric polymer composites. A sharp increase in d33 was observed when the KNLN loading was increased from 25 to 45 volume percent. Examples 2, 4, and 5 demonstrate piezoelectric composite compositions containing ethylene-octene copolymer (35 weight percent octene) and three different fillers: KNLN (Example 2), barium titanate (BT) (Example 4), and lead zirconate titanate (PZT) (Example 5). Our research demonstrates that the d33 value of piezoelectric composites can be tailored by appropriately selecting the appropriate amount of filler, filler particle size and size distribution, and an appropriate solvent for preparing the piezoelectric composite.

[0056] [Table 1]

[0057] [Table 2]

[0058] Thus, disclosed herein are superior piezoelectric composite materials and films made from the composite materials. [Brief explanation of the drawings]

[0059] [Figure 1] FIG. 1 shows a diagram of a polymer-ceramic piezoelectric composite according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a graph of the dielectric constant as a function of frequency for a piezoelectric polymer composite according to an embodiment of the present disclosure. [Figure 3a] Figure 3a shows the effect of temperature on the piezoelectric strain constant of polarized PVDF and Example 2 (polarized). [Figure 3b] Figure 3b shows the effect of temperature on the physical appearance of the film before and after heating. [Figure 4] FIG. 4 is a tensile stress-strain plot of the piezoelectric polymer composite.

Claims

1. A piezoelectric composite, including: an olefin copolymer comprising a first monomer of ethylene or propylene polymerized with any of 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, and 1-eicosene; and a plurality of piezoelectric filler particles dispersed in the olefin copolymer; And, the plurality of piezoelectric filler particles comprise at least one of lead zirconate titanate (PZT), hydroxyapatite, apatite, lithium sulfate monohydrate, bismuth sodium titanate, quartz, tartaric acid fibers, poly(vinylidene fluoride) fibers, barium titanate, lithium doped potassium sodium niobate (KNLN) having the formula (K,Na) 1-t Li t NbO 3 (wherein the variable “t” is in the range of from greater than 0.01 to less than 1 (0.01<t<1.00)), potassium sodium niobate (K,NaNb)O 3 (KNN), or a combination thereof; Piezoelectric composites.

2. 10. The piezoelectric composite of claim 1, wherein the olefin copolymer is present in an amount ranging from 20 to 80 volume percent, based on the total volume of the piezoelectric composite.

3. 10. The piezoelectric composite of claim 1, wherein the plurality of piezoelectric filler particles are present in an amount ranging from 20 to 80 volume percent, based on the total volume of the piezoelectric composite.

4. 2. The piezoelectric composite of claim 1, wherein the olefin copolymer is an ethylene-octene copolymer.

5. 5. The piezoelectric composite of claim 4, wherein the ethylene-octene copolymer contains 10 to 40 weight percent octene.

6. At least one of the following: polyethylene; polypropylene; ethylene copolymer; propylene copolymer; polyethylene terephthalate (PET); polycarbonate (PC); polybutylene terephthalate (PBT); poly(1,4-cyclohexylidenecyclohexane-1,4-dicarboxylate) (PCCD); glycol-modified polycyclohexyl terephthalate (PCTG); poly(phenylene oxide) (PPO); polypropylene (PP); polyethylene (PE); polyvinyl chloride (PVC); polystyrene (PS); polymethyl methacrylate poly(methyl methacrylate) (PMMA); polyethyleneimine or polyetherimide (PEI) and their derivatives; thermoplastic elastomers (TPE); terephthalic acid (TPA) elastomers; poly(cyclohexanedimethylene terephthalate) (PCT); polyethylene naphthalate (PEN); polyamide (PA); polysulfone sulfonic acid (PSS); polyether ether ketone (PEEK); acrylonitrile butadiene styrene (ABS); polyether ketone ketone (PEKK); polyphenylene sulfide (PPS); copolymers thereof; or mixtures thereof.

10. The piezoelectric composite of claim 1, further comprising:

7. 10. The piezoelectric composite of claim 1, wherein the plurality of piezoelectric filler particles comprises 40% to 60% by volume of KNLN, based on the total volume of the piezoelectric composite.

8. A film comprising the piezoelectric composite of any one of claims 1 to 7.

9. The film has a piezoelectric strain constant (d ３３ 9. The film of claim 8 having a molecular weight of 1.25 (pC / N).

10. 9. The film of claim 8, wherein the film has a piezoelectric voltage constant (g33 (mV.m / N)) of 100 to 300.

11. The film of claim 8, wherein the film has a thickness in the range of 50 microns to 500 microns.

12. A method for preparing a film according to any one of claims 8 to 11, comprising the steps of: dissolving an olefin copolymer in an organic solvent to form an olefin copolymer solution, said olefin copolymer comprising a first monomer of ethylene or propylene polymerized with any of 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, and 1-eicosene; adding a plurality of piezoelectric filler particles to the olefin copolymer solution to form a film precursor; forming a cast film precursor from said film precursor; and Poling the cast film precursor.

13. The method of claim 12 , wherein the cast film precursor is annealed prior to poling.

14. 13. The method of claim 12, wherein the cast film precursor is poled in an electric field ranging from 5 kV / mm to 100 kV / mm for a time ranging from 1 minute to 120 minutes at a temperature ranging from 60°C to 120°C.

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