Polymer piezoelectric material injection molded body, piezoelectric element, and manufacturing device and method for manufacturing polymer piezoelectric material injection molded body

Abstract

The present invention relates to an injection molded body of a polymer piezoelectric material, a piezoelectric element, a manufacturing apparatus and a manufacturing method for an injection molded body of a polymer piezoelectric material, and provides an injection molded body of a polymer piezoelectric material and a piezoelectric element that exhibit a piezoelectric phenomenon having a stress application direction in a direction rotating around the b-axis and are easily applicable to practical devices, etc., and a manufacturing apparatus and a manufacturing method for an injection molded body of a polymer piezoelectric material that can manufacture the injection molded body of a polymer piezoelectric material. An injection molded body of a polymer piezoelectric material, characterized in that it has piezoelectricity and contains a helical chiral polymer crystal, the helical chiral polymer crystal is composed of a polymer chain, has a unit lattice with the a-axis, b-axis and c-axis as crystal axes, and the lengths of the crystal axes are b-axis < a-axis < c-axis, the c-axis is parallel to the long-chain direction of the polymer chain, and the helical chiral polymer crystal is a b-axis uniaxially oriented crystal.

Description

Technical Field

[0001] The present invention relates to a polymer piezoelectric material injection molded body, a piezoelectric element, a manufacturing device for the polymer piezoelectric material injection molded body, and a manufacturing method for the polymer piezoelectric material injection molded body. Background Art

[0002] Polymer piezoelectric materials using helical chiral polymers are known. These materials can be shaped using three-dimensional modeling devices, effectively utilizing their polymeric properties. Specifically, using a three-dimensional modeling device, it is possible to create structures with desired three-dimensional structures and piezoelectric properties.

[0003] For example, Patent Document 1 discloses heating a piezoelectric polymer to a temperature above its crystallization temperature but below its melting point; using a 3D printer to shape the molding material, whose viscosity decreases due to heating, to obtain a box-shaped structure; and using the resulting structure to fabricate a pressure-sensitive sensor. Furthermore, Patent Document 1 discloses heating the piezoelectric polymer to a temperature above its crystallization temperature but below its melting point to achieve orientation of the piezoelectric polymer, with the polylactic acid molecules oriented along the direction of movement of the nozzle of the 3D molding device. This uniaxial orientation of the piezoelectric polymer results in the structure exhibiting piezoelectricity.

[0004] Furthermore, polylactic acid is disclosed as a polymer piezoelectric material in Patent Document 1. Polylactic acid is a polymer having chirality and a helical main chain, that is, a helical chiral polymer.

[0005] In a polylactic acid polymer crystal, the helical axis of the molecule is the c-axis. By stretching a modeling material made of polylactic acid while laminating it using the nozzle of a three-dimensional modeling apparatus, a structure can be obtained in which the c-axis is uniaxially oriented in the direction of stretching. In such a structure, when shear stress is applied parallel to the stretching direction (the c-axis), an electric charge corresponding to the magnitude of the stress is generated in a direction intersecting the surface to which the shear stress is applied.

[0006] Patent Document 1: International Publication No. 2015 / 129291

[0007] However, shear stress is difficult to directly utilize in practical applications. Specifically, shear stress is a stress that acts in opposite directions along two mutually offset lines of action, each parallel to the c-axis. Shear stress is a stress with such properties and is therefore difficult to apply to practical devices. Summary of the Invention

[0008] The polymer piezoelectric material injection molded article according to an application example of the present invention is characterized in that it has piezoelectricity.

[0009] Comprising: a helical chiral polymer crystal, composed of polymer chains, having a unit lattice with a-axis, b-axis, and c-axis as crystal axes,

[0010] The lengths of the crystal axes are such that b-axis < a-axis < c-axis,

[0011] The c-axis is parallel to the long-chain direction of the polymer chain,

[0012] The helical chiral polymer crystal is a b-axis uniaxially oriented crystal.

[0013] The piezoelectric element according to an application example of the present invention is characterized by comprising:

[0014] An injection molded body of a polymer piezoelectric material according to an application example of the present invention; and

[0015] Two electrode layers sandwiching the injection molded body of the polymer piezoelectric material.

[0016] The manufacturing apparatus of an injection molded body of a polymer piezoelectric material according to an application example of the present invention is characterized by comprising:

[0017] A melting part that heats a raw material containing a helical chiral polymer to obtain a melt;

[0018] An injection part that injects the melt; and

[0019] A support surface that承接 the injected melt to obtain a piezoelectric injection molded body,

[0020] The temperature of the support surface is: above the phase transition temperature at which the helical chiral polymer undergoes a phase transition from a metastable phase to a stable phase and lower than the melting point of the helical chiral polymer.

[0021] The manufacturing method of an injection molded body of a polymer piezoelectric material according to an application example of the present invention is characterized by having:

[0022] A step of heating a raw material containing a helical chiral polymer to obtain a melt;

[0023] A step of injecting the melt from an injection part; and

[0024] A step of承接 the injected melt by a support surface to obtain a piezoelectric injection molded body,

[0025] The temperature of the support surface is: above the phase transition temperature at which the helical chiral polymer undergoes a phase transition from a metastable phase to a stable phase and lower than the melting point of the helical chiral polymer. Brief Description of the Drawings

[0026] Figure 1It is a perspective view showing a piezoelectric element according to an embodiment.

[0027] Figure 2A This is a schematic diagram showing the molecular structure of polylactic acid crystals.

[0028] Figure 2B This is a schematic diagram showing the molecular structure of polylactic acid crystals.

[0029] Figure 3 yes Figure 1 Schematic diagram of the piezoelectric layer included in the piezoelectric element shown.

[0030] Figure 4 It is a cross-sectional view showing an apparatus for producing a polymer piezoelectric material injection-molded body according to an embodiment.

[0031] Figure 5 Yes Figure 4 A three-dimensional view of a planar spiral member included in a manufacturing device.

[0032] Figure 6 It means in Figure 5 Schematic diagram of a planar spiral filled with material.

[0033] Figure 7 Yes Figure 4 A schematic diagram of a barrel included in a manufacturing apparatus.

[0034] Figure 8 This is a flowchart for explaining a method for producing a polymer piezoelectric material injection-molded body according to an embodiment.

[0035] Figure 9 This is a diagram showing a portion of a melting endothermic curve obtained by DSC measurement of polylactic acid pellets as a raw material.

[0036] Figure 10 This is a θ-2θ profile obtained by measuring the θ-2θ of the piezoelectric test pieces obtained in Examples and Comparative Examples using an X-ray diffractometer.

[0037] Figure 11 This is the rocking curve profile when the 2θ position of each piezoelectric test piece is fixed at 16.7°.

[0038] Figure 12 This is the rocking curve profile when the 2θ position of each piezoelectric test piece is fixed at 14.7°.

[0039] Explanation of symbols

[0040] 1: Three-dimensional object manufacturing device; 2: Hopper; 3: Supply pipe; 4: Planar screw; 4a: Circumferential surface; 4b: Incision; 4c: Central portion; 5: Cylinder; 5a: Connecting hole; 5b: Slot; 6: Motor; 7: Heater; 9: Heater; 10: Nozzle; 10a: Nozzle hole; 11: Plate; 11a: Upper surface; 12: First stage; 13: Second stage; 14: Base; 15: First drive unit; 16: Second drive unit; 17: Third drive unit; 18: Control unit; 19: Particles; 19a: Melt ; 19b: deposit; 19c: three-dimensional object; 20: space part; 21: injection molding unit; 22: stage unit; 40: spiral shell; 45: melting part; 100: piezoelectric element; 200: piezoelectric layer; 201: first surface; 202: second surface; 300: first electrode layer; 400: second electrode layer; 500: laminated body; 800: first wiring; 900: second wiring; D1: injection molding direction; S102: melting process; S104: injection molding process; S106: molding process; SP: spiral. DETAILED DESCRIPTION

[0041] Hereinafter, the polymer piezoelectric material injection-molded article, the piezoelectric element, the apparatus for producing the polymer piezoelectric material injection-molded article, and the method for producing the polymer piezoelectric material injection-molded article of the present invention will be described in detail with reference to the accompanying drawings.

[0042] 1. Polymer piezoelectric material injection molding and piezoelectric elements

[0043] First, a piezoelectric polymer injection-molded product and a piezoelectric element according to an embodiment will be described.

[0044] Figure 1 It is a perspective view showing a piezoelectric element according to an embodiment.

[0045] Figure 1 The illustrated piezoelectric element 100 includes a stacked body 500 having a piezoelectric layer 200, a first electrode layer 300, and a second electrode layer 400. The piezoelectric layer 200 has a first surface 201 and a second surface 202 that are mutually front-to-back. The first electrode layer 300 is provided on the first surface 201 of the piezoelectric layer 200. The second electrode layer 400 is provided on the second surface 202 of the piezoelectric layer 200.

[0046] It should be noted that the piezoelectric element 100 may also include components other than these components. For example, an adhesive layer may be inserted between the piezoelectric layer 200 and the first and second electrode layers 300 and 400. In addition, a protective film may be provided to cover the laminate 500.

[0047] Figure 1The top view shape of the stacked body 500 shown is circular. That is, the top view shape of each of the piezoelectric layer 200, the first electrode layer 300, and the second electrode layer 400 is circular. Examples of a circle include a perfect circle, an ellipse, an oblong circle, etc., but a perfect circle is preferred. A perfect circle refers to a shape that is circular and the difference between the length of the major axis and the length of the minor axis is less than 10% of the length of the major axis. The major axis refers to the longest axis that can be taken when viewed from above, and the minor axis refers to the axis that passes through the midpoint of the major axis and is orthogonal to the major axis when viewed from above. It should be noted that these top view shapes are not limited to circles, and may be other shapes. In this specification, top view refers to observation along the thickness direction of the piezoelectric layer 200.

[0048] A first wiring 800 and a second wiring 900 are connected to the piezoelectric element 100 . One end of the first wiring 800 is connected to the center of the circular first electrode layer 300 . One end of the second wiring 900 is connected to the center of the circular second electrode layer 400 .

[0049] The other ends of the first wiring 800 and the second wiring 900 are each connected to, for example, a power supply device (not shown). Thus, applying a voltage between the first electrode layer 300 and the second electrode layer 400 can cause the piezoelectric layer 200 to exhibit an inverse piezoelectric effect. In this case, the piezoelectric element 100 is incorporated into devices such as actuators, vibration-generating elements, and ultrasonic motors.

[0050] In addition, the other end of the first wiring 800 and the other end of the second wiring 900 can also be connected to a charge detection device not shown in the figure, for example. In this way, the charge generated by the piezoelectric effect in the piezoelectric layer 200 can be taken out from the first electrode layer 300 and the second electrode layer 400, so that the charge detection device can detect the amount of charge. Based on the detected amount of charge, the force applied to the piezoelectric layer 200 can be calculated, or the power required for switching action or power generation can be generated. In this case, the piezoelectric element 100 is assembled into various force sensors such as tactile sensors and force sensors, various switches, power generation elements and other devices for use. In addition, the piezoelectric element 100 can also be connected to a voltage detection device. Thus, the voltage generated by the piezoelectric effect can be detected by the voltage detection device.

[0051] As constituent materials of the first electrode layer 300 and the second electrode layer 400, in addition to metal materials such as single substances of metal elements such as gold, silver, platinum, copper, nickel, aluminum, indium, tin, zinc, and palladium, or alloys and intermetallic compounds containing these metal elements, resin materials such as conductive polymers can also be listed.

[0052] The average thickness of the first electrode layer 300 and the second electrode layer 400 is not particularly limited, but is preferably 0.05 μm or more and 500 μm or less, and more preferably 0.50 μm or more and 300 μm or less.

[0053] The average thickness of the piezoelectric layer 200 is not particularly limited, preferably 10 μm or more, more preferably 30 μm or more and 50 mm or less, and still more preferably 50 μm or more and 5 mm or less. Thus, the piezoelectric layer 200 has sufficient piezoelectric properties.

[0054] The piezoelectric layer 200 contains a helical chiral polymer crystal and is an injection molded body having piezoelectricity. The piezoelectric layer 200 is a polymer piezoelectric material injection molded body according to the embodiment. The helical chiral polymer refers to a polymer having a helical structure and molecular optical activity. In addition, the helical chiral polymer crystal refers to a crystal of such a helical chiral polymer.

[0055] Examples of the helical chiral polymer include polypeptides, cellulose derivatives, polylactic acid, polypropylene oxide, poly-β-hydroxybutyric acid, etc. The helical chiral polymer crystal used in the present embodiment is composed of polymer chains and has a unit lattice with a-axis, b-axis, and c-axis as crystal axes. In the present embodiment, the lengths of the crystal axes of the a-axis, b-axis, and c-axis are b-axis < a-axis < c-axis. It should be noted that in polymer crystals, the crystal axis parallel to the long-chain direction of the polymer chain usually becomes longer. Therefore, in the present embodiment, the long-chain direction of the polymer chain is taken as the c-axis.

[0056] Hereinafter, polylactic acid will be taken as an example of the helical chiral polymer for explanation. As optically active polylactic acid, L-polylactic acid (PLLA) and D-polylactic acid (PDLA) are known. Hereinafter, L-polylactic acid, particularly α-phase L-polylactic acid stable in the crystalline phase of L-polylactic acid, will be taken as an example for explanation. It should be noted that in the following description, α-phase L-polylactic acid will be simply referred to as "polylactic acid".

[0057] Figure 2A and Figure 2B are schematic diagrams showing the molecular structure of polylactic acid crystals.

[0058] As Figure 2A and Figure 2B shown, the molecular structure of the polylactic acid crystal has a helical structure. The crystal system of the polylactic acid crystal is a orthorhombic crystal, and the length of the a-axis of the unit lattice is about 1.06 nm, the length of the b-axis is about 0.61 nm, and the length of the c-axis is about 2.88 nm. It should be noted that Figure 2A illustrates the plane containing the a-axis and c-axis in the polylactic acid crystal, Figure 2B illustrates the plane containing the a-axis and b-axis in the polylactic acid crystal.

[0059] Figure 3 is Figure 1The schematic diagram of the piezoelectric layer 200 of the piezoelectric element shown in FIG. The piezoelectric layer 200 only needs to contain polylactic acid crystals, but preferably uses polylactic acid crystals as the main material. The content of polylactic acid crystals in the piezoelectric layer 200 is preferably 30% by mass or more, more preferably 50% by mass or more, and further preferably 70% by mass or more. It should be noted that, in addition to polylactic acid crystals, the piezoelectric layer 200 may also contain, for example, amorphous polylactic acid. In addition, in addition to the above-mentioned α-phase L-type polylactic acid, the piezoelectric layer 200 may also contain L-type polylactic acid such as α' phase and β phase as quasi-stable phases, and may also contain D-type polylactic acid.

[0060] The piezoelectric layer 200 of this embodiment comprises polylactic acid crystals with b-axis orientation. B-axis orientation refers to the state in which the b-axis of the polylactic acid is uniaxially oriented. The direction of the b-axis orientation is not particularly limited; in this embodiment, it is perpendicular to the thickness direction of the piezoelectric layer 200, i.e., the plane in which the piezoelectric layer 200 extends. Meanwhile, in this embodiment, the c-axis of the polylactic acid is oriented within the plane of the piezoelectric layer 200.

[0061] exist Figure 3 The above-mentioned orientation state is schematically shown in FIG. Figure 3 In the figure, the molecular structure of polylactic acid is represented by a helix SP. The running axis of the helix SP is parallel to the c-axis. Figure 3 As shown, in the piezoelectric layer 200 , the c-axis of the polylactic acid is oriented in various directions in the plane, while the b-axis is uniaxially oriented in the thickness direction.

[0062] In a helical chiral polymer such as polylactic acid, when a shear stress parallel to the c-axis is applied, a rotational motion of the C=O electric dipole is induced within the helical structure, and polarization occurs in a direction intersecting the shear plane containing the two applied shear stress vectors. In this case, the helical structure of the helical chiral polymer necessarily has quadratic symmetry. Therefore, in an optically active helical chiral polymer, when the tilt angle relative to the shear stress is set to θ, the force corresponding to the product of the shear stress and the absolute value of cosθ effectively acts. Therefore, when the direction of the helix SP of the piezoelectric layer 200 is random, approximately 64% of the time when it is oriented in the direction of the shear stress, it effectively acts. Therefore, as in the case of in-plane orientation, polarization occurs in the thickness direction of the piezoelectric layer 200.

[0063] In the case of c-axis in-plane orientation, the generated polarization usually changes depending on the direction of the c-axis and the angle of the applied shear stress, but in this embodiment, the polarization is generated independently of the angle of the shear stress. Figure 3 When a rotational stress is applied as indicated by the middle arrow, polarization occurs in the thickness direction of the piezoelectric layer 200 .

[0064] By extracting the charge generated by this polarization from the first electrode layer 300 and the second electrode layer 400, the piezoelectric element 100 functions as a sensor for detecting shear stress and rotational stress applied to the piezoelectric layer 200. Furthermore, by applying a voltage between the first electrode layer 300 and the second electrode layer 400, shear stress and rotational stress can be generated in the piezoelectric layer 200.

[0065] By exhibiting such a uniaxial orientation of the b-axis in the piezoelectric layer 200 , the piezoelectric constant can be increased compared to a case where the b-axis is not oriented, thereby realizing the piezoelectric element 100 having excellent piezoelectric characteristics.

[0066] The b-axis uniaxial orientation of the polylactic acid can be determined by obtaining and analyzing the X-ray diffraction profile of the piezoelectric layer 200. Specifically, first, the piezoelectric layer 200 is measured using an X-ray diffraction device to obtain a θ-2θ profile.

[0067] In the case of uniaxial orientation of the b-axis of polylactic acid, the θ-2θ profile obtained by the θ-2θ measurement in the X-ray diffraction device has a peak corresponding to the (010) plane of polylactic acid. This peak can be observed at 2θ = 14.7° ± 1.5°. It should be noted that the peak position is obtained by using the wavelength The peak position is obtained by θ-2θ measurement of characteristic X-rays of CuKα1.

[0068] Next, a pole diagram is obtained when the 2θ position is fixed at the peak corresponding to the (010) plane of polylactic acid, for example, when 2θ = 14.7°. In this pole diagram, contour lines with decreasing diffraction intensity can be obtained in a roughly concentric circle pattern from the center at ψ = 0°.

[0069] Furthermore, based on this extreme point diagram, a rocking curve profile is obtained when ψ is varied. When the b-axis of polylactic acid is uniaxially oriented, the rocking curve profile obtained for the peak corresponding to the (010) plane of polylactic acid has a peak at ψ = 0°.

[0070] By confirming such a peak, it can be confirmed that the b-axis of the polylactic acid is well uniaxially oriented.

[0071] As described above, the piezoelectric layer 200 of the injection molded body of the polymer piezoelectric material according to this embodiment contains a helical chiral polymer crystal, and is an injection molded body having piezoelectricity. As described above, the helical chiral polymer crystal has a helical molecular structure and is a crystal of a polymer having molecular optical activity. In addition, in this embodiment, the helical chiral polymer crystal is a crystal having a unit lattice with the a-axis, b-axis, and c-axis as crystal axes and composed of polymer chains. In addition, the helical chiral polymer crystal is a crystal in which the lengths of the crystal axes satisfy the relationship of b-axis < a-axis < c-axis, the c-axis is parallel to the long-chain direction of the polymer chain, and the b-axis is uniaxially oriented.

[0072] According to such a configuration, a piezoelectric layer 200 that exhibits a piezoelectric phenomenon having a stress application direction at least in the direction of rotation around the b-axis can be obtained. In addition, when a voltage is applied to such a piezoelectric layer 200, an inverse piezoelectric phenomenon having a stress generation direction in the direction of rotation around the b-axis is exhibited. Therefore, the piezoelectric layer 200 not only exhibits piezoelectricity accompanied by the shear stress exhibited by the conventional piezoelectric layer, but also exhibits rotational piezoelectricity, which helps to realize a piezoelectric element 100 that is convenient to use. Specifically, the piezoelectric layer 200 can be applied to devices such as sensors for detecting rotational stress and actuators using rotational stress. Therefore, according to the piezoelectric layer 200, a piezoelectric element 100 with high practicality can be realized.

[0073] In addition, as described above, the helical chiral polymer crystal contained in the piezoelectric layer 200 is a polylactic acid crystal. Polylactic acid has high mechanical strength and excellent moldability, and is therefore particularly useful as a material for injection molded bodies. That is, by containing polylactic acid crystals, the mechanical strength and moldability of the piezoelectric layer 200 can be improved.

[0074] In addition, the piezoelectric element 100 according to this embodiment includes a piezoelectric layer 200 that is an injection molded body of a polymer piezoelectric material, a first electrode layer 300 that sandwiches the piezoelectric layer 200, and a second electrode layer 400.

[0075] According to such a configuration, a piezoelectric element 100 that exhibits a piezoelectric phenomenon accompanied by rotational stress and an inverse piezoelectric phenomenon having a stress generation direction in the rotational direction can be realized. Such a piezoelectric element 100 is preferably used for devices such as actuators, vibration generating elements, ultrasonic motors, tactile sensors, force sensors, power generation elements, and various switches. <00 .00188>

[0076] 2. Manufacturing apparatus for injection molded body of polymer piezoelectric material

[0077] Next, a manufacturing apparatus for an injection molded body of a polymer piezoelectric material according to the embodiment will be described.

[0078] Figure 4It is a cross-sectional view showing an apparatus for producing a polymer piezoelectric material injection-molded body according to an embodiment. Figure 5 Yes Figure 4 A three-dimensional view of a planar spiral member included in a manufacturing device. Figure 6 It means in Figure 5 Schematic diagram of a planar spiral filled with material. Figure 7 Yes Figure 4 A schematic diagram of a barrel included in a manufacturing apparatus.

[0079] It should be noted that in Figures 4 to 7 In the , the X-axis, Y-axis, and Z-axis are defined as three mutually orthogonal axes. Each axis is represented by an arrow, with the distal end being "positive" and the proximal end being "negative." In the following description, for example, "X-axis direction" includes both the positive and negative directions of the X-axis. Furthermore, the X-axis and Y-axis directions are directions within the horizontal plane, while the Z-axis direction is the vertical direction.

[0080] Figure 4 The three-dimensional object manufacturing apparatus 1 shown is an apparatus for manufacturing polymer piezoelectric material injection molded products according to the embodiment, and is a so-called 3D printer. The three-dimensional object manufacturing apparatus 1 includes an injection unit 21 , a stage unit 22 , and a control unit 18 .

[0081] Injection unit 21 heats pellets 19, serving as raw material, to produce a melt 19a, which is then injected. Stage unit 22 receives injected melt 19a, producing a deposit 19b and a three-dimensional object 19c formed by stacking these deposits 19b. Control unit 18 controls various operations of injection unit 21 and stage unit 22.

[0082] Figure 4 The injection unit 21 shown includes a hopper 2, a supply pipe 3, a flat screw 4, a barrel 5, a motor 6, and a nozzle 10 (injection section).

[0083] The hopper 2 is a container for storing pellets 19. The supply pipe 3 is a pipe connecting the hopper 2 and the flat screw 4.

[0084] In addition, the injection unit 21 has a screw housing 40. The flat screw 4 is housed in a space formed between the screw housing 40 and the barrel 5. The pellets 19 housed in the hopper 2 are supplied to the space via the supply pipe 3.

[0085] The plane spiral member 4 is connected to the rotating shaft of the motor 6 and rotates by the power of the motor 6. Figure 5 as well as Figure 6As shown, the plane screw 4 has a spiral cutout 4b extending from the circumferential surface 4a to the central portion 4c. The particles 19 supplied to the screw housing 40 move and are compressed in the space 20 formed by the cutout 4b and the barrel 5 as the plane screw 4 rotates.

[0086] The barrel 5 has a built-in heater 7. The pellets 19 compressed in the space 20 are melted (plasticized) by the heat of the heater 7 to form a melt 19a. Therefore, the flat screw 4 and the barrel 5 form a melting portion 45 that heats and melts the pellets 19.

[0087] Barrel 5 Figure 7 As shown, it has a connecting hole 5a extending in the Z-axis direction and a plurality of grooves 5b formed on the surface facing the planar spiral 4. The connecting hole 5a is provided at a position corresponding to the central portion 4c of the planar spiral 4. In addition, a nozzle 10 is provided on the negative side of the Z-axis of the connecting hole 5a. The nozzle 10 has a nozzle hole 10a. The connecting hole 5a is connected to the nozzle hole 10a. Therefore, the molten material 19a that is moved to the central portion 4c of the planar spiral 4 while being pressurized uses its pressure as a driving force and is injected from the nozzle hole 10a in sequence through the grooves 5b and the connecting hole 5a.

[0088] Furthermore, the nozzle 10 has a built-in heater 9. The temperature of the melt 19a passing through the nozzle hole 10a is controlled by the heater 9 to a desired temperature.

[0089] Figure 4 The stage unit 22 shown includes a plate 11 , a first stage 12 , a second stage 13 , a base 14 , a first drive unit 15 , a second drive unit 16 , and a third drive unit 17 .

[0090] The plate 11 has an upper surface 11a facing the positive Z-axis. This upper surface 11a serves as a support surface for receiving and depositing the melt 19a injected from the nozzle hole 10a. This creates a deposit 19b on the upper surface 11a. The deposit 19b then stacks to form a three-dimensional object 19c of the desired shape. The plate 11 is placed on the first stage 12.

[0091] The first stage 12 can move the plate 11 in the X-axis direction by the power of the first driving unit 15 . The first stage 12 is placed on the second stage 13 .

[0092] The second stage 13 moves the first stage 12 in the Y-axis direction by the power of the second driving unit 16. Thus, the second stage 13 can move the plate 11 in the Y-axis direction.

[0093] The base portion 14 moves the second stage 13 in the Z-axis direction by the power of the third driving portion 17. Thus, the base portion 14 can move the plate 11 in the Z-axis direction.

[0094] Therefore, the stage unit 22 functions as a so-called XYZ stage that moves the plate 11 to any position in three-dimensional space. By moving the plate 11 in this way, the relative position of the nozzle hole 10a with respect to the plate 11 can be moved without changing the position of the nozzle 10. Thus, while the molten material 19a is being injected from the nozzle hole 10a, the position of the plate 11 is moved three-dimensionally, allowing the molten material 19a to accumulate three-dimensionally. As a result, a three-dimensional object 19c of any desired shape can be formed.

[0095] It should be noted that in this embodiment, the plate 11 having the upper surface 11a is moved three-dimensionally, but the nozzle 10, in other words, the injection unit 21 may also be moved three-dimensionally. Furthermore, the plate 11 may be moved along one or two of the three axes, the X-axis, the Y-axis, and the Z-axis, by the stage unit 22, while the nozzle 10 may be moved along the remaining axes.

[0096] In addition, the three-dimensional object manufacturing device 1 is a so-called 3D printer, but the manufacturing device of the polymer piezoelectric material injection molded body is not limited to a 3D printer, and can also be an injection molding machine, for example. The injection molding machine has a molding mold with a mold cavity of any shape. In addition, the molten material 19a injected from the nozzle 10 is filled into the mold cavity. Then, the injection molded body can be obtained by demolding the filler from the molding mold. In this case, the supporting surface that receives the molten material is not the above-mentioned upper surface 11a, but the inner surface of the mold cavity. Therefore, in this specification, "molding" includes molding using a molding mold and modeling using a 3D printer.

[0097] Figure 4 The control unit 18 shown is electrically connected to the injection unit 21 and the stage unit 22. The control unit 18 controls the operation of the injection unit 21 and the operation of the stage unit 22 in coordination with each other.

[0098] The control unit 18 can be implemented, for example, by a computer having a processor such as a CPU (Central Processing Unit), memory such as RAM (Random Access Memory) and ROM (Read Only Memory), and an interface such as a USB (Universal Serial Bus). The memory stores programs and data. The processor reads and executes programs from the memory to control the operations of the injection unit 21 and stage unit 22.

[0099] As described above, the three-dimensional object manufacturing device 1, which is a manufacturing device for the polymer piezoelectric material injection-molded body involved in this embodiment, includes a flat screw 4 and a barrel 5 as a melting section 45, a nozzle 10 as an injection section, and an upper surface 11a as a support surface. The flat screw 4 and the barrel 5 heat the pellets 19 as a raw material containing a helical chiral polymer to obtain a melt 19a. The nozzle 10 injects the melt 19a. The upper surface 11a receives the injected melt 19a to obtain a three-dimensional object 19c as an injection-molded body having piezoelectricity. The temperature of the upper surface 11a, that is, the temperature of the plate 11, is a temperature that is higher than the phase transition temperature of the helical chiral polymer and lower than the melting point. The phase transition temperature refers to the temperature at which the helical chiral polymer transitions from a quasi-stable phase to a stable phase.

[0100] With such a three-dimensional object manufacturing apparatus 1 , the melt 19 a is injected at a relatively high pressure and deposited on the upper surface 11 a .

[0101] Figure 4 A three-dimensional object 19c manufactured by the three-dimensional object manufacturing device 1 is schematically shown. Since the melt 19a is injected at a relatively high pressure, a force pressing in the injection direction D1 is applied to the deposit 19b formed by the melt 19a deposited on the upper surface 11a. Therefore, when the deposit 19b contains, for example, polylactic acid as a helical chiral polymer, the axis of travel of the helix SP possessed by the molecular structure of the polylactic acid, that is, the longest c-axis in the unit lattice of the polylactic acid, is oriented along the upper surface 11a. In addition, the shortest b-axis in the unit lattice of the polylactic acid is uniaxially oriented in a direction intersecting the upper surface 11a. By cooling this deposit 19b, the three-dimensional object 19c can be obtained. In this way, the piezoelectric layer 200 can be obtained.

[0102] As described above, since such a piezoelectric layer 200 exhibits a piezoelectric phenomenon accompanied by rotational stress, it is easy to use when applied to, for example, a sensor, an actuator, or the like.

[0103] Furthermore, by optimizing the temperature of the plate 11, the cooling of the deposit 19b can be performed within a temperature range where a phase transition to a quasi-stable phase does not occur, that is, within a temperature range where the deposit 19b is maintained in a stable phase. This allows the degree of uniaxial orientation of the b-axis to be sufficiently increased. Consequently, a piezoelectric layer 200 with excellent piezoelectric properties can be obtained.

[0104] Furthermore, by stacking multiple deposits 19b as needed, a three-dimensional object 19c thicker than a single layer of deposits 19b can be obtained. This facilitates thickening of the piezoelectric layer 200. Note that the three-dimensional object 19c may also be composed of a single layer of deposits 19b.

[0105] In this way, the three-dimensional object 19c can also be composed of a stack of multiple deposits 19b as unit layers. In this case, the b-axis of the helical chiral polymer is also uniaxially oriented along the thickness direction of the deposit 19b. As a result, a piezoelectric layer 200 with high piezoelectricity and uniaxial b-axis orientation can be obtained even at any thickness.

[0106] The temperature of the nozzle 10 (injection molding unit) is preferably above the melting point of the helical chiral polymer. This maintains the helical chiral polymer contained in the melt 19a in a well-melted state until just before injection molding. As a result, a piezoelectric layer 200 with a high degree of uniaxial orientation along the b-axis can be obtained. Such a piezoelectric layer 200 exhibits excellent piezoelectric properties.

[0107] The temperature of the nozzle 10 only needs to be above the melting point of the helical chiral polymer, and is preferably set to be 10°C higher than the melting point, more preferably 20°C higher than the melting point and lower than the thermal decomposition temperature of the helical chiral polymer, and further preferably 30°C higher than the melting point and 10°C lower than the thermal decomposition temperature.

[0108] For example, the melting point of α-phase L-type polylactic acid is approximately 182° C., and its thermal decomposition temperature is approximately 250° C. Therefore, the temperature of the nozzle 10 for injecting the melt 19 a containing polylactic acid is preferably set to 192° C. or higher, more preferably 202° C. or higher and lower than 250° C., and even more preferably 212° C. or higher and 240° C. or lower.

[0109] The temperature of the barrel 5 is not particularly limited, but is preferably within the range of ±30°C, more preferably ±15°C relative to the temperature of the nozzle 10. This improves the kneading properties of the planar screw 4, and ultimately enables the production of a piezoelectric layer 200 having a particularly high degree of uniaxial orientation of the b-axis.

[0110] In addition, in the case where the helical chiral polymer is polylactic acid, it is particularly preferred to set the temperature of the upper surface 11a (support surface) according to the phase transition temperature from the quasi-stable phase to the stable phase. Specifically, the quasi-stable phase of polylactic acid is known to be the α' phase, and the stable phase is known to be the α phase. Therefore, the temperature of the upper surface 11a is preferably set to be above the phase transition temperature from the α' phase to the α phase and below the melting point of polylactic acid. Thereby, the rapid cooling of the melt 19a can be suppressed, and the generation of the quasi-stable phase can be suppressed. As a result, a piezoelectric layer 200 with high piezoelectricity and a chemically stable stable phase as the main material can be manufactured.

[0111] The temperature of the upper surface 11a, that is, the temperature of the plate 11, only needs to be above the phase transition temperature of the polylactic acid and below its melting point. It is preferably set to at least 10°C above the phase transition temperature and at least 10°C below the melting point of the polylactic acid, and more preferably at least 20°C above the phase transition temperature and at least 30°C below the melting point of the polylactic acid. Specifically, the phase transition temperature from the α' phase to the α phase of polylactic acid is approximately 96°C. Therefore, the temperature of the plate 11 is preferably set to at least 106°C and below 172°C, and more preferably at least 116°C and below 152°C.

[0112] In addition, the melting section 45 has the planar spiral 4 as described above. The planar spiral 4 compresses the particles 19 as the raw material. Thus, the uniaxial orientation of the b-axis of the spiral chiral polymer is achieved with a higher degree of orientation. In addition, the planar spiral 4 can efficiently mix and compress even fewer particles 19 in a short time compared to other spirals. Therefore, the time for the particles 19 to melt can be shortened, and the deterioration of the melt 19a caused by heating or oxidation etc. can be less likely to occur.

[0113] It should be noted that the planar spiral 4 has many advantages for the reasons described above, but a spiral that exhibits the same function may be used instead of the planar spiral 4 .

[0114] The inner diameter of nozzle hole 10a is not particularly limited, but is preferably 0.1 mm to 3.0 mm, more preferably 0.2 mm to 0.5 mm. Setting the inner diameter of nozzle hole 10a within this range allows sufficient pressure to be applied to melt 19a, maintaining a well-kneaded state. As a result, uniaxial orientation of the helical chiral polymer in piezoelectric layer 200 along its b-axis can be achieved with a higher degree of orientation.

[0115] 3. Method for manufacturing polymer piezoelectric material injection molded body

[0116] Next, a method for producing a polymer piezoelectric material injection-molded article according to an embodiment will be described.

[0117] Figure 8 This is a flowchart for explaining a method for manufacturing a polymer piezoelectric material injection molded body according to an embodiment of the present invention. Figures 4 to 7 A manufacturing method of the three-dimensional object manufacturing apparatus 1 shown will be described.

[0118] Figure 8 The manufacturing method shown includes a melting step S102 for obtaining a melt 19a, an injection step S104 for injecting the melt 19a, and a molding step S106 for obtaining a three-dimensional molded object 19c as an injection-molded body.

[0119] 3.1. Melting process

[0120] In the melting step S102, particles 19 containing a helical chiral polymer are supplied to the space formed between the screw housing 40 and the barrel 5. Particles 19 move and melt in the space 20 formed by the planar screw 4 and the barrel 5, which serves as the melting zone 45, to form a melt 19a. The melt 19a is compressed as the planar screw 4 rotates.

[0121] 3.2. Injection molding process

[0122] In the injection step S104, the melt 19a is injected from the nozzle 10. The melt 19a is compressed by the flat screw 4 and injected by the pressure.

[0123] 3.3. Modeling process

[0124] In the molding step S106, the injected melt 19a is received by the upper surface 11a of the plate 11. This forms a deposit 19b on the upper surface 11a, and by stacking these deposits, a three-dimensional molded object 19c is obtained.

[0125] As mentioned above, Figure 8 The manufacturing method shown includes a melting step S102 for obtaining a melt 19a, an injection molding step S104 for injecting the melt 19a, and a molding step S106 for obtaining a three-dimensional molded object 19c as an injection-molded body. In the melting step S102, pellets 19 (raw material) containing a helical chiral polymer are heated to obtain the melt 19a. In the injection molding step S104, the melt 19a is injected from the nozzle 10 (injection molding part). In the molding step S106, the injected melt 19a is received by the upper surface 11a (support surface) of the plate 11 to obtain a three-dimensional molded object 19c having piezoelectric properties. The temperature of the upper surface 11a, that is, the temperature of the plate 11, is a temperature that is higher than the phase transition temperature of the helical chiral polymer and lower than the melting point. The phase transition temperature is the temperature at which the helical chiral polymer transitions from a quasi-stable phase to a stable phase.

[0126] With this configuration, when the shortest crystal axis of the helical chiral polymer is the b-axis, a deposit 19b can be obtained in which the b-axis is uniaxially oriented along the thickness direction of the deposit 19b. By cooling this deposit 19b, a three-dimensional object 19c can be obtained. In this way, a piezoelectric layer 200 can be obtained.

[0127] As described above, such a piezoelectric layer 200 exhibits a piezoelectric phenomenon accompanied by rotational stress in addition to shear stress, and therefore is easy to use when applied to, for example, a sensor, an actuator, or the like.

[0128] Furthermore, by optimizing the temperature of the plate 11, the cooling of the deposit 19b can be performed within a temperature range where a phase transition to a quasi-stable phase does not occur, that is, within a temperature range where the deposit 19b is maintained in a stable phase. This allows the degree of uniaxial orientation of the b-axis to be sufficiently increased. As a result, a piezoelectric layer 200 with excellent piezoelectric properties can be obtained.

[0129] While the polymer piezoelectric material injection molded body, piezoelectric element, apparatus for manufacturing a polymer piezoelectric material injection molded body, and method for manufacturing a polymer piezoelectric material injection molded body of the present invention have been described above based on the illustrated embodiments, the polymer piezoelectric material injection molded body, apparatus for manufacturing a polymer piezoelectric material injection molded body, and piezoelectric element of the present invention are not limited to the aforementioned embodiments. For example, the various parts of the aforementioned embodiments may be replaced with any structure having the same function, and any structure may be added to the aforementioned embodiments. Furthermore, the method for manufacturing a polymer piezoelectric material injection molded body of the present invention is not limited to the aforementioned embodiments. For example, any process for any purpose may be added to the aforementioned embodiments.

[0130] Example

[0131] Next, specific examples of the present invention will be described.

[0132] 4. Fabrication of Piezoelectric Test Specimens

[0133] Example

[0134] First, as an example of a helical chiral polymer, pellets of L-type polylactic acid (PLLA) manufactured by BMG Co., Ltd. were prepared. This polylactic acid has a melting point of 182°C, a thermal decomposition temperature of 250°C, and a phase transition temperature from α' phase to α phase of 96°C.

[0135] Then, to Figure 1 The three-dimensional object manufacturing device shown in the figure feeds polylactic acid pellets and injects the melt while swirls it in a certain direction, producing a piezoelectric test piece consisting of a two-layered deposit. The resulting piezoelectric test piece is a circular plate with a diameter of 30 mm.

[0136] It should be noted that the inner diameter of the nozzle was 0.3 mm, the temperature of the nozzle was 225°C, the temperature of the barrel was 215°C, and the temperature of the plate was 120°C.

[0137] Comparative Example 1

[0138] A piezoelectric test piece was obtained in the same manner as in Example except that the temperature of the plate was changed to 50°C.

[0139] Comparative Example 2

[0140] A piezoelectric test piece was obtained in the same manner as in Example except that the temperature of the plate was changed to 80°C.

[0141] Comparative Example 3

[0142] A piezoelectric test piece was obtained in the same manner as in Example except that the temperature of the plate was changed to 100°C.

[0143] 5. Evaluation of raw materials and piezoelectric test pieces

[0144] 5.1. Differential Scanning Calorimetry (DSC) of Raw Materials

[0145] First, DSC measurements were performed on the polylactic acid pellets used as the raw material. The measurements were performed using a differential scanning calorimeter "Q1000" manufactured by TA Instruments. The DSC measurements involved varying the temperature over three steps: a first heating step, a cooling step, and a second heating step, while simultaneously acquiring melting endothermic curves. Specifically, in the first heating step, the temperature was increased from -20°C to 270°C at a heating rate of 5°C / minute. In the cooling step, the temperature was decreased from 270°C to -20°C at a cooling rate of 5°C / minute. In the second heating step, the temperature was increased from -20°C to 270°C at a heating rate of 5°C / minute.

[0146] A portion of the obtained melting endothermic curve is shown in Figure 9 . Figure 9 This is a diagram showing a portion of a melting endothermic curve obtained by DSC measurement of polylactic acid pellets as a raw material. Figure 9 As shown, in the first temperature-raising process, the melting point was observed at 181.75° C. In the second temperature-raising process, the phase transition temperature from the α′ phase, which is a quasi-stable phase, to the α phase, which is a stable phase, was observed at 95.91° C.

[0147] 5.2. X-ray diffraction of piezoelectric test pieces

[0148] Next, the piezoelectric test pieces obtained in the examples and comparative examples were subjected to θ-2θ measurement using the focusing method of an X-ray diffractometer. In addition, the X-ray detector was fixed at a predetermined 2θ position, and the rocking curve profile was measured by changing the incident angle. The X-ray diffractometer used was an XRD measuring device "X'Pert" manufactured by Panalytical. In addition, in the X-ray diffraction, a wavelength of Characteristic X-rays of CuKα1.

[0149] Figure 10 This is a θ-2θ profile obtained by θ-2θ measurement of the piezoelectric test pieces obtained in Examples and Comparative Examples.

[0150] like Figure 10 As shown, no peak was observed in the θ-2θ profile obtained from the piezoelectric test piece obtained in Comparative Example 1. Therefore, it was found that in the piezoelectric test piece obtained in Comparative Example 1, the polylactic acid was not crystallized.

[0151] In the θ-2θ profiles obtained from the piezoelectric test pieces obtained in Comparative Examples 2 and 3, a peak was observed near 2θ = 16.5°. On the other hand, in the θ-2θ profile obtained from the piezoelectric test piece obtained in Example, a peak was also observed near 2θ = 16.7°. These peaks are believed to correspond to the (110) plane / (200) plane.

[0152] Therefore, for the piezoelectric test pieces obtained in the examples and comparative examples, rocking curve profiles were obtained when the 2θ position was fixed at 16.7°.

[0153] Figure 11 This is the rocking curve profile when the 2θ position of each piezoelectric test piece is fixed at 16.7°.

[0154] exist Figure 11 In the rocking curve profile obtained from the piezoelectric test piece obtained in Example, a peak due to uniaxial orientation of a certain crystal plane was observed near ψ = ±30°.

[0155] On the other hand, in the θ-2θ profile obtained from the piezoelectric test piece obtained in the example, Figure 10 As shown in FIG. 2 , a peak is also observed near 2θ = 14.7°, which is considered to correspond to the (010) plane.

[0156] Therefore, for the piezoelectric test pieces obtained in the examples and comparative examples, rocking curve profiles were obtained when the 2θ position was fixed at 14.7°.

[0157] Figure 12 This is the rocking curve profile when the 2θ position of each piezoelectric test piece is fixed at 14.7°.

[0158] exist Figure 12 In the rocking curve profile obtained from the piezoelectric test piece obtained in Example, a peak was observed at ψ = 0° only. Therefore, it is known that the piezoelectric test piece obtained in Example contains crystals with (010) orientation, so-called uniaxial orientation of the b-axis.

[0159] It should be noted that in Figure 12 In the rocking curve profile shown, the full width at half maximum (FWHM) of the peak originating from the uniaxial orientation of the b-axis is approximately 31°. This full width at half maximum is preferably 50° or less, and more preferably 40° or less. This indicates that a sufficient degree of orientation has been achieved.

Claims

1. A polymer piezoelectric material injection molded body, characterized in that: It has piezoelectricity, comprising: polylactic acid crystals that are helical chiral polymer crystals, composed of polymer chains, having a unit cell with a-axis, b-axis, and c-axis as crystal axes, the lengths of the crystal axes are such that b-axis < a-axis < c-axis, the c-axis is parallel to the long-chain direction of the polymer chains, the b-axis is uniaxially oriented, when performing θ-2θ measurement by X-ray diffraction, the θ-2θ profile has a peak corresponding to the (010) plane of polylactic acid, when obtaining a rocking curve profile for the peak corresponding to the (010) plane, the rocking curve profile has a peak with a half-value width of 50° or less at ψ = 0°.

2. The injection molded body of the polymeric piezoelectric material according to claim 1, wherein, it is composed of a laminate formed by laminating multiple unit layers, the b-axis is uniaxially oriented in the thickness direction of the unit layer.

3. A piezoelectric element, characterized in that: It includes: the injection molded body of the polymeric piezoelectric material according to claim 1 or 2; and two electrode layers that sandwich the injection molded body of the polymeric piezoelectric material.

4. A manufacturing device for a polymer piezoelectric material injection molded body according to claim 1, characterized in that: It includes: a melting part that heats and compresses a raw material containing a helical chiral polymer to obtain a melt; an injection part that injects the melt; and a supporting surface that receives the injected melt to obtain an injection molded body with piezoelectricity, the temperature of the injection part is 20°C or more higher than the melting point of the helical chiral polymer, the temperature of the supporting surface is: above the phase transition temperature of the helical chiral polymer and lower than the melting point of the helical chiral polymer, and the phase transition temperature of the helical chiral polymer is: the temperature at which the helical chiral polymer undergoes a phase transition from a metastable phase to a stable phase, the melting part has: a planar spiral member that compresses the raw material; and a barrel that, as the planar spiral member rotates, forms a space part together with the planar spiral member to compress the raw material, the temperature of the barrel is within the range of the temperature of the injection part ±30°C.

5. The manufacturing device of the injection molded body of the polymeric piezoelectric material according to claim 4, wherein, the temperature of the supporting surface is: above the phase transition temperature of the polylactic acid and lower than the melting point of the polylactic acid, and the phase transition temperature of the polylactic acid is: the temperature at which the polylactic acid undergoes a phase transition from the α'-phase as the metastable phase to the α-phase as the stable phase.

6. A method for manufacturing a polymer piezoelectric material injection molded body according to claim 1, characterized in that: It has: a melting process that heats and compresses a raw material containing a helical chiral polymer to obtain a melt; an injection process that injects the melt from the injection part; and a shaping process that a supporting surface receives the injected melt to obtain an injection molded body with piezoelectricity, the temperature of the injection part is 20°C or more higher than the melting point of the helical chiral polymer, the temperature of the supporting surface is: above the phase transition temperature of the helical chiral polymer and lower than the melting point of the helical chiral polymer, and the phase transition temperature of the helical chiral polymer is: the temperature at which the helical chiral polymer undergoes a phase transition from a metastable phase to a stable phase, The melting process is a process of heating and compressing the raw material using a planar screw and a barrel. The planar screw compresses the raw material, and the barrel forms a space portion for compressing the raw material together with the planar screw as the planar screw rotates. The temperature of the barrel is within the range of ±30° C. of the temperature of the injection molding part.

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