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EP-4036995-B1 - INJECTION-MOLDED ARTICLE OF POLYMER PIEZOELECTRIC MATERIAL, APPARATUS AND METHOD FOR MANUFACTURING THE SAME, AND PIEZOELECTRIC ELEMENT

EP4036995B1EP 4036995 B1EP4036995 B1EP 4036995B1EP-4036995-B1

Inventors

  • Yonemura, Takayuki
  • TSUNOYA, AKIHIKO
  • MURAYAMA, KOICHI

Dates

Publication Date
20260513
Application Date
20220128

Claims (9)

  1. An injection-molded article (200) of polymer piezoelectric material, comprising: a helical chiral polymer constituted by a polymer chain and having a unit cell with an a-axis, a b-axis, and a c-axis as crystal axes; wherein b-axis < a-axis < c-axis in terms of lengths of the crystal axes, the c-axis is parallel to a long chain direction of the polymer chain, the helical chiral polymer is a crystal, the injection-molded article has piezoelectricity, the injection-molded article is constituted by a laminate in which a plurality of unit layers is laminated, and characterized in that the b-axis of the crystal is uniaxially oriented in a thickness direction of the unit layers.
  2. The injection-molded article (200) of polymer piezoelectric material according to claim 1, wherein the helical chiral polymer is a polylactic acid.
  3. The injection-molded article (200) of polymer piezoelectric material according to claim 2, wherein a θ-2θ profile in X-ray diffraction measurements has a peak corresponding to a (010) plane of the polylactic acid, and when a rocking curve profile is acquired for the peak corresponding to the (010) plane, the rocking curve profile has a peak at ψ = 0°.
  4. A piezoelectric element (500) comprising: the injection-molded article (200) of polymer piezoelectric material according to any one of claims 1 to 3; and two electrode layers (300, 400) configured to sandwich the injection-molded article of polymer piezoelectric material.
  5. An apparatus (1) for manufacturing an injection-molded article (200) of polymer piezoelectric material according to any one of claims 1 to 3, the apparatus comprising: a raw material containing a helical chiral polymer; a melting unit (45) configured to heat the raw material to obtain a molten material; an injection portion (21) configured to inject the molten material; and a support surface (11a) configured to receive the molten material injected to obtain an injection-molded article having piezoelectricity; characterized in that the apparatus is configured to heat the support surface to a temperature greater than or equal to a phase transition temperature of the helical chiral polymer at which a phase transition from a metastable phase to a stable phase takes place, and less than a melting point of the helical chiral polymer.
  6. The apparatus (1) for manufacturing the injection-molded article (200) of polymer piezoelectric material according to claim 5, wherein the apparatus is configured to heat the injection portion (21) to a temperature greater than or equal to the melting point of the helical chiral polymer.
  7. The apparatus (1) for manufacturing the injection-molded article (200) of polymer piezoelectric material according to claims 5 or 6, wherein the melting unit (45) includes a flat screw (4) configured to compress the raw material.
  8. The apparatus (1) for manufacturing the injection-molded article (200) of polymer piezoelectric material according to any one of claims 5 to 7, wherein the helical chiral polymer is a polylactic acid, and the apparatus is configured to heat the support surface (11a) to a temperature greater than or equal to a phase transition temperature of the polylactic acid at which a phase transition from an α'-phase, to an α-phase, takes place, and less than a melting point of the polylactic acid.
  9. A method for manufacturing an injection-molded article (200) of polymer piezoelectric material according to any one of claims 1 to 3, the method comprising: heating a raw material containing a helical chiral polymer to obtain a molten material; injecting the molten material from an injection portion (21); and receiving the injected molten material at a support surface (11a) to obtain an injection-molded article having piezoelectricity; characterized in that a temperature of the support surface is greater than or equal to a phase transition temperature of the helical chiral polymer at which a phase transition from a metastable phase to a stable phase takes place, and less than a melting point of the helical chiral polymer.

Description

BACKGROUND 1. Technical Field The present disclosure relates to an injection-molded article of polymer piezoelectric material, a piezoelectric element, an apparatus for manufacturing an injection-molded article of polymer piezoelectric material, and a method for manufacturing an injection-molded article of polymer piezoelectric material. 2. Related Art Polymer piezoelectric materials that use helical chiral polymers are known. It is possible to shape polymer piezoelectric materials by a three-dimensional shaping apparatus while taking advantage of their features as polymer. In other words, by using a three-dimensional shaping apparatus, it is possible to shape a structure having a desired three-dimensional structure and having piezoelectricity. For example, WO 2015/129291 discloses: heating a piezoelectric polymer to a temperature greater than or equal to its crystallization temperature and less than its melting point; shaping a shaping material having a reduced viscosity due to heating using a 3D printer to obtain a box-shaped structure; and fabricating a pressure sensor using the obtained structure. It is also disclosed that heating to a temperature greater than or equal to the crystallization temperature and less than the melting point enables the piezoelectric polymer to be oriented, and that molecules of polylactic acid are oriented along the movement direction of the nozzle of the three-dimensional shaping apparatus. By uniaxially orienting the piezoelectric polymer in this way, the structure exhibits piezoelectricity. Moreover, WO 2015/129291 discloses polylactic acid as a polymer piezoelectric material. Polylactic acid is a polymer that has chirality and of which the principal chain is helical-shaped. As such, polylactic acid is a helical chiral polymer, In a polymer of polylactic acid, the screw axis of the molecule is c-axis. When a shaping material containing polylactic acid is laminated while being pulled by the nozzle of the three-dimensional shaping apparatus, a structure can be obtained in which the c-axes are uniaxially oriented in the pulling direction. In such a structure, when shear stress is applied in parallel with the pulling direction (c-axis direction), a charge corresponding to the magnitude of the stress is generated in a direction intersecting the surface to which the shear stress is applied. However, shear stress is difficult to utilize as is for practical use. Specifically, shear stress is stress that acts in directions opposite to each other along two lines of action, each of the two lines of action being parallel to the c-axis but shifted from each other. Being stress having such properties, shear stress is difficult to apply to practical devices and the like. EP 3258508 A1 discloses a polymeric piezoelectric film, including a helical chiral polymer having a weight average molecular weight of from 50,000 to 1,000,000 and optical activity. In the film a crystallinity given by a DSC method is from 20% to 80%, and a standardized molecular orientation is from 3.5 to 15.0 when a reference thickness measured by a microwave transmission-type molecular orientation meter is 50 µm. US 2020/078998 A1 is also relevant relating to a injection molding apparatus. SUMMARY An injection-molded article of polymer piezoelectric material according to the invention is defined in claim 1. A piezoelectric element according to the invention includes: the injection-molded article of polymer piezoelectric material as above, and two electrode layers configured to sandwich the injection-molded article of polymer piezoelectric material. An apparatus for manufacturing an injection-molded article of polymer piezoelectric material according to the invention is defined in claim 5. A method for manufacturing an injection-molded article of polymer piezoelectric material according to the invention is defined in claim 9. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view illustrating a piezoelectric element according to an embodiment.FIG. 2A is a schematic view illustrating a molecular structure of a polylactic acid.FIG. 2B is a schematic view illustrating a molecular structure of a polylactic acid.FIG. 3 is a schematic view of a piezoelectric layer included in the piezoelectric element illustrated in FIG. 1.FIG. 4 is a cross-sectional view illustrating an apparatus for manufacturing an injection-molded article of polymer piezoelectric material according to an embodiment.FIG. 5 is a perspective view illustrating a flat screw included in the apparatus for manufacturing of FIG. 4.FIG. 6 is a schematic view illustrating a state in which the flat screw of FIG. 5 is filled with a material.FIG. 7 is a schematic view illustrating a barrel included in the apparatus for manufacturing of FIG. 4.FIG. 8 is a flowchart for describing a method for manufacturing an injection-molded article of polymer piezoelectric material according to an embodiment.FIG. 9 is a graph showing a portion of a melting endotherm curve obt