Polymeric piezoelectric material injection molded body, piezoelectric element, manufacturing apparatus for polymeric piezoelectric material injection molded body, and manufacturing method for polymeric piezoelectric material injection molded body

Abstract

To provide a polymer piezoelectric material injection molded article and a piezoelectric element that exhibit piezoelectric phenomenon in which stress is applied in the direction of rotation around a b-axis and are easily applied to practical devices, etc., and a manufacturing device and a manufacturing method for a polymer piezoelectric material injection molded article that can manufacture the polymer piezoelectric material injection molded article.SOLUTION: A polymer piezoelectric material injection molded article having piezoelectricity is constituted by polymer chains, has a helical chiral polymer crystal having a unit cell with crystal axes along an a-axis, a b-axis and a c-axis, and the length of the crystal axis satisfies 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 has the b-axis uniaxially oriented.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a polymeric piezoelectric material injection-molded article, a piezoelectric element, a manufacturing apparatus for a polymeric piezoelectric material injection-molded article, and a manufacturing method for a polymeric piezoelectric material injection-molded article. [Background technology]

[0002] Polymeric piezoelectric materials using helical chiral polymers are known. Taking advantage of the characteristics of polymers, polymeric piezoelectric materials can be modeled using a three-dimensional modeling device. In other words, by using a three-dimensional modeling device, it is possible to model a structure having a desired three-dimensional structure and piezoelectricity.

[0003] For example, Patent Document 1 discloses that a piezoelectric polymer is heated to a temperature equal to or higher than its crystallization temperature and lower than its melting point, the modeling material whose viscosity has been reduced by heating is modeled using a 3D printer to obtain a box-shaped structure, and a pressure-sensitive sensor is produced using the resulting structure. It also discloses that heating to a temperature equal to or higher than its crystallization temperature and lower than its melting point enables the piezoelectric polymer to be oriented, and the molecules of polylactic acid are oriented along the direction of movement of the nozzle of the three-dimensional modeling device. By uniaxially orienting the piezoelectric polymer in this way, the structure exhibits piezoelectricity.

[0004] Furthermore, Patent Document 1 discloses polylactic acid as a polymeric piezoelectric material. Polylactic acid is a polymer that has chirality and whose main chain forms a helix, that is, a helical chiral polymer.

[0005] In a polymer crystal of polylactic acid, the helical axis of the molecule is the c-axis. When a modeling material made of polylactic acid is stretched and layered with the nozzle of a three-dimensional modeling device, a structure can be obtained in which the c-axis is uniaxially oriented in the direction of the stretching. When a shear stress is applied to such a structure parallel to the pulling direction (c-axis direction), an electric charge according to the magnitude of the stress is generated in a direction intersecting the plane to which the shear stress is applied. [Prior art documents]

Patent Document

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, shear stress is difficult to be directly utilized in practice. Specifically, shear stress acts in opposite directions along two action lines that are parallel to the c-axis but shifted from each other. Since shear stress has such properties, it is difficult to apply it to practical devices and the like.

Means for Solving the Problems

[0008] The injection-molded article of a polymer piezoelectric material according to an application example of the present invention contains polylactic acid crystals, which are helical chiral polymer crystals composed of polymer chains and having a unit cell with a-axis, b-axis, and c-axis as crystal axes, 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, the b-axis is uniaxially oriented, it is an injection-molded article having piezoelectricity, when subjected to θ-2θ measurement by X-ray diffraction, the θ-2θ profile has a peak corresponding to the (010) plane of polylactic acid crystal and when a rocking curve profile is obtained 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°.

[0009] The piezoelectric element according to an application example of the present invention is an injection-molded article of a polymer piezoelectric material according to an application example of the present invention, and two electrode layers sandwiching the injection-molded article of the polymer piezoelectric material The present invention is characterized by comprising:

[0010] An apparatus for manufacturing a polymeric piezoelectric material injection molded article according to an application example of the present invention includes: Heating raw materials containing helical chiral polymers and compress a melting section for obtaining a molten material by melting the melted material; An injection part that injects the molten material; a support surface for receiving the injected molten material to obtain an injection molded article having piezoelectric properties; Equipped with the temperature of the injection section is 20° C. or more higher than the melting point of the helical chiral polymer; The temperature of the support surface is equal to or higher than the phase transition temperature at which the helical chiral polymer transitions from a metastable phase to a stable phase and is lower than the melting point of the helical chiral polymer. the law of nature, The fusion portion is A flat screw for compressing the raw material; a barrel that forms a space portion that compresses the raw material together with the flat screw as the flat screw rotates; having The temperature of the barrel is within ±30°C of the temperature of the injection part. do.

[0011] A method for producing a polymeric piezoelectric material injection molded article according to an application example of the present invention includes the steps of: Heating raw materials containing helical chiral polymers and compress obtaining a melt; injecting the molten material from an injection portion; receiving the injected molten material on a support surface to obtain an injection molded article having piezoelectric properties; having the temperature of the injection section is 20° C. or more higher than the melting point of the helical chiral polymer; the temperature of the support surface is equal to or higher than a phase transition temperature at which the helical chiral polymer undergoes a phase transition from a metastable phase to a stable phase and is lower than a melting point of the helical chiral polymer; The step of obtaining the molten material is a step of heating and compressing the raw material using a flat screw that compresses the raw material and a barrel that forms a space portion that compresses the raw material together with the flat screw as the flat screw rotates, The temperature of the barrel is within ±30°C of the temperature of the injection part. do. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a perspective view showing a piezoelectric element according to an embodiment. [Figure 2A] FIG. 1 is a schematic diagram showing the molecular structure of polylactic acid crystals. [Figure 2B] FIG. 1 is a schematic diagram showing the molecular structure of polylactic acid crystals. [Diagram 3] 2 is a schematic diagram of a piezoelectric layer included in the piezoelectric element shown in FIG. 1. [Figure 4] FIG. 2 is a cross-sectional view showing a manufacturing apparatus for a polymeric piezoelectric material injection molded article according to an embodiment. [Diagram 5] FIG. 5 is a perspective view showing a flat screw provided in the manufacturing apparatus of FIG. 4. [Figure 6] FIG. 6 is a schematic diagram showing the flat screw of FIG. 5 being filled with material. [Figure 7] FIG. 5 is a schematic view showing a barrel equipped in the manufacturing apparatus of FIG. [Figure 8] 1 is a flowchart for explaining a method for manufacturing a polymeric piezoelectric material injection molded article according to an embodiment. [Figure 9] 1 is a graph showing a part of a melting endothermic curve obtained by DSC measurement performed on raw material polylactic acid pellets. [Figure 10] 4 shows θ-2θ profiles obtained by θ-2θ measurement using an X-ray diffractometer for the piezoelectric test pieces obtained in the examples and comparative examples. [Figure 11] This shows the rocking curve profile for each piezoelectric test piece when the 2θ position is fixed at 16.7°. [Figure 12]This shows the rocking curve profile for each piezoelectric test piece when the 2θ position was fixed at 14.7°. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, the polymeric piezoelectric material injection molded article, the piezoelectric element, the manufacturing apparatus for the polymeric piezoelectric material injection molded article, and the manufacturing method for the polymeric piezoelectric material injection molded article of the present invention will be described in detail with reference to the accompanying drawings.

[0014] 1. Polymeric piezoelectric material injection molding and piezoelectric element First, a polymeric piezoelectric material injection molded article and a piezoelectric element according to the embodiment will be described. FIG. 1 is a perspective view showing a piezoelectric element according to an embodiment.

[0015] 1 includes a laminate 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 which are opposite surfaces. 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.

[0016] The piezoelectric element 100 may include other components in addition to these components. For example, an adhesive layer or the like may be interposed between the piezoelectric layer 200 and the first electrode layer 300 and the second electrode layer 400. In addition, a protective film or the like may be provided to cover the laminate 500.

[0017] The planar shape of the laminate 500 shown in FIG. 1 is circular. That is, the piezoelectric layer 200, the first electrode layer 300, and the second electrode layer 400 are each circular in plan view. The circular shape includes, for example, a perfect circle, an ellipse, an oval, and the like, but is preferably a perfect circle. 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 10% or less of the length of the major axis. The major axis is the longest axis that can be taken in plan view, and the minor axis is an axis that passes through the midpoint of the major axis in plan view and is perpendicular to the major axis. Note that these planar shapes are not limited to circular and may be other shapes. In this specification, a planar view refers to a view along the thickness direction of the piezoelectric layer 200.

[0018] 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.

[0019] The other end of the first wiring 800 and the other end of the second wiring 900 are each connected to, for example, a power supply device (not shown). This allows a voltage to be applied between the first electrode layer 300 and the second electrode layer 400, causing the piezoelectric layer 200 to exhibit an inverse piezoelectric effect. In this case, the piezoelectric element 100 is used by being incorporated into a device such as an actuator, a vibration generating element, or an ultrasonic motor.

[0020] The other end of the first wiring 800 and the other end of the second wiring 900 may be connected to, for example, a charge detection device (not shown). This allows the charge generated by the piezoelectric effect in the piezoelectric layer 200 to be taken out from the first electrode layer 300 and the second electrode layer 400, and the charge amount to be detected by the charge detection device. Based on the detected charge amount, the force applied to the piezoelectric layer 200 can be obtained, or the power required for switching or power generation can be generated. In this case, the piezoelectric element 100 is incorporated into devices such as various force sensors such as tactile sensors and force sensors, various switches, and power generation elements. The piezoelectric element 100 may also be connected to a voltage detection device. This allows the voltage generated by the piezoelectric effect to be detected by the voltage detection device.

[0021] Examples of materials constituting the first electrode layer 300 and the second electrode layer 400 include metal materials such as simple metal elements such as gold, silver, platinum, copper, nickel, aluminum, indium, tin, zinc, and palladium, or alloys and intermetallic compounds containing these metal elements, as well as resin materials such as conductive polymers.

[0022] 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.

[0023] The average thickness of the piezoelectric layer 200 is not particularly limited, but is preferably 10 μm or more, more preferably 30 μm to 50 mm, and even more preferably 50 μm to 5 mm, so that the piezoelectric layer 200 has sufficient piezoelectric performance.

[0024] The piezoelectric layer 200 is an injection-molded body containing a helical chiral polymer crystal and having piezoelectricity. This piezoelectric layer 200 is a polymer piezoelectric material injection-molded body according to the embodiment. A helical chiral polymer refers to a polymer having a helical molecular structure and molecular optical activity. And a helical chiral polymer crystal refers to a crystal of such a helical chiral polymer.

[0025] Examples of the helical chiral polymer include polypeptides, cellulose derivatives, polylactic acid, polypropylene oxide, poly-β-hydroxybutyric acid, and the like. The helical chiral polymer crystal used in this embodiment is composed of polymer chains and has a unit cell with the a-axis, b-axis, and c-axis as crystal axes. In this embodiment, the a-axis, b-axis, and c-axis are such that the crystal axis lengths are b-axis < a-axis < c-axis. Note that in a polymer crystal, it is common for the crystal axis parallel to the long-chain direction of the polymer chain to be long. Therefore, in this embodiment, the long-chain direction of the polymer chain is defined as the c-axis.

[0026] Hereinafter, polylactic acid will be described as an example of the helical chiral polymer. As optically active polylactic acids, L-type polylactic acid (PLLA) and D-type polylactic acid (PDLA) are known. Hereinafter, L-type polylactic acid, particularly the stable α-phase L-type polylactic acid among the crystal phases of L-type polylactic acid, will be described as an example. In the following description, the α-phase L-type polylactic acid is simply referred to as "polylactic acid".

[0027] FIG. 2A and FIG. 2B are schematic diagrams showing the molecular structures of polylactic acid crystals, respectively. As shown in FIGS. 2A and 2B, the molecular structure of the polylactic acid crystal has a helical structure. The crystal system of the polylactic acid crystal is orthorhombic (rhombic), and the length of the a-axis of the unit cell 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. Note that FIG. 2A shows a plane including the a-axis and c-axis of the polylactic acid crystal, and FIG. 2B shows a plane including the a-axis and b-axis of the polylactic acid crystal.

[0028] 3 is a schematic diagram of a piezoelectric layer 200 included in the piezoelectric element shown in FIG. 1. The piezoelectric layer 200 may contain polylactic acid crystals, but preferably contains polylactic acid crystals as a 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 even more preferably 70% by mass or more. In addition to polylactic acid crystals, the piezoelectric layer 200 may contain, for example, amorphous polylactic acid. In addition to the above-mentioned α-phase L-type polylactic acid, the piezoelectric layer 200 may contain L-type polylactic acid of metastable phases such as α' phase and β phase, or D-type polylactic acid.

[0029] The piezoelectric layer 200 according to this embodiment includes crystals in which the polylactic acid is b-axis oriented. The b-axis orientation refers to a state in which the b-axis of the polylactic acid is uniaxially oriented. The direction in which the b-axis is oriented is not particularly limited, but in this embodiment, the b-axis is oriented in the thickness direction of the piezoelectric layer 200, that is, in a direction perpendicular to 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.

[0030] The above-mentioned orientation state is shown in Fig. 3. In Fig. 3, the molecular structure of polylactic acid is represented by a helix SP. The axis of progression of the helix SP is parallel to the c-axis. As shown in Fig. 3, in the piezoelectric layer 200, the c-axes of polylactic acid are oriented in various directions within the plane, while the b-axis is uniaxially oriented in the thickness direction.

[0031] 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 electric dipole of C=O is induced in the helical structure, and polarization appears 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 two-fold symmetry. Therefore, in an optically active helical chiral polymer, when the tilt angle with respect to the shear stress is θ, a 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, about 64% of the effective force acts when it is oriented in the shear stress direction. Therefore, similar to the case of in-plane orientation, polarization appears in the thickness direction of the piezoelectric layer 200.

[0032] In addition, in the case of c-axis in-plane orientation, the polarization that occurs usually changes depending on the direction of the c-axis and the angle of the applied shear stress, but in this embodiment, the polarization occurs regardless of the angle of the shear stress. Therefore, when a rotational stress is applied as shown by the arrow in FIG. 3, polarization appears in the thickness direction of the piezoelectric layer 200.

[0033] By extracting the charges generated by this polarization from the first electrode layer 300 and the second electrode layer 400, the piezoelectric element 100 functions as a sensor that detects the shear stress and rotational stress applied to the piezoelectric layer 200. In addition, by applying a voltage between the first electrode layer 300 and the second electrode layer 400, it is possible to generate a shear stress and a rotational stress in the piezoelectric layer 200.

[0034] By realizing such 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 a piezoelectric element 100 with excellent piezoelectric characteristics.

[0035] The b-axis of polylactic acid is uniaxially oriented, which can be identified by obtaining and analyzing an X-ray diffraction profile of the piezoelectric layer 200. Specifically, first, a θ-2θ measurement is performed on the piezoelectric layer 200 using an X-ray diffractometer to obtain a θ-2θ profile.

[0036] When the b-axis of polylactic acid is uniaxially oriented, the θ-2θ profile obtained by θ-2θ measurement in an X-ray diffractometer has a peak corresponding to the (010) plane of polylactic acid. This peak is observed at 2θ = 14.7° ± 1.5°. Note that this peak position is the peak position by θ-2θ measurement using characteristic X-rays of CuKα1 with a wavelength of 1.5404 Å.

[0037] Subsequently, a pole figure when the 2θ position is fixed to the peak corresponding to the (010) plane of polylactic acid is obtained, for example, a pole figure when fixed to 2θ = 14.7°. In this pole figure, contour lines showing a decrease in diffraction intensity can be obtained in a substantially concentric shape from the center where ψ = 0°.

[0038] Furthermore, based on this pole figure, a rocking curve profile which is a profile when ψ is changed is obtained. When the b-axis of polylactic acid is uniaxially oriented, in the rocking curve profile obtained for the peak corresponding to the (010) plane of polylactic acid, there is a peak at ψ = 0°.

[0039] By confirming such a peak, it can be confirmed that the b-axis of polylactic acid is well uniaxially oriented.

[0040] As described above, the piezoelectric layer 200 which is a polymer piezoelectric material injection molded body according to this embodiment contains helical chiral polymer crystals and is an injection molded body having piezoelectricity. As described above, helical chiral polymer crystals are crystals of a polymer having a molecular structure of a helical structure and having molecular optical activity. And in this embodiment, helical chiral polymer crystals have a unit cell having a-axis, b-axis and c-axis as crystal axes and are crystals composed of polymer chains. Further, helical chiral polymer crystals satisfy the relationship that the length of the crystal axis is 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.

[0041] According to this configuration, at least, a piezoelectric layer 200 is obtained that exhibits a piezoelectric phenomenon in which the stress application direction is in the direction of rotation around the b-axis. Furthermore, when a voltage is applied to such a piezoelectric layer 200, an inverse piezoelectric phenomenon in which the stress generation direction is in the direction of rotation around the b-axis is exhibited. Therefore, such a piezoelectric layer 200 exhibits not only the piezoelectricity associated with shear stress exhibited by conventional piezoelectric layers, but also the piezoelectricity of rotation, which contributes to the realization of a piezoelectric element 100 that is easy to use. Specifically, the piezoelectric layer 200 can be applied to devices such as a sensor that detects rotational stress and an actuator that utilizes rotational stress. Therefore, the piezoelectric layer 200 can realize a highly practical piezoelectric element 100.

[0042] Moreover, the helical chiral polymer crystals contained in the piezoelectric layer 200 are polylactic acid crystals, as described above. Polylactic acid has relatively high mechanical strength and excellent moldability, and is therefore particularly useful as a material for injection-molded bodies. In other words, by including polylactic acid crystals, the mechanical strength and moldability of the piezoelectric layer 200 can be improved.

[0043] Moreover, the piezoelectric element 100 according to this embodiment includes a piezoelectric layer 200 that is an injection-molded polymeric piezoelectric material, and a first electrode layer 300 and a second electrode layer 400 that sandwich the piezoelectric layer 200 therebetween.

[0044] This configuration makes it possible to realize a piezoelectric element 100 that exhibits a piezoelectric phenomenon associated with rotational stress and an inverse piezoelectric phenomenon in which the direction of stress generation is the rotational direction. Such a piezoelectric element 100 is suitable for use in devices such as actuators, vibration generating elements, ultrasonic motors, tactile sensors, force sensors, power generating elements, and various switches.

[0045] 2. Manufacturing equipment for polymer piezoelectric material injection molding Next, a manufacturing apparatus for an injection-molded polymeric piezoelectric material according to an embodiment will be described.

[0046] Fig. 4 is a cross-sectional view showing a manufacturing apparatus for a polymeric piezoelectric material injection-molded article according to an embodiment. Fig. 5 is a perspective view showing a flat screw included in the manufacturing apparatus of Fig. 4. Fig. 6 is a schematic diagram showing a state in which the flat screw of Fig. 5 is filled with material. Fig. 7 is a schematic diagram showing a barrel included in the manufacturing apparatus of Fig. 4.

[0047] In addition, in Fig. 4 to Fig. 7, the X-axis, Y-axis, and Z-axis are set as three mutually orthogonal axes. Each axis is represented by an arrow, with the tip end side being "plus" and the base end side being "minus." In the following explanation, for example, "X-axis direction" includes both the plus and minus directions of the X-axis. Furthermore, the X-axis and Y-axis directions are directions in a horizontal plane, and the Z-axis direction is the vertical direction.

[0048] 4 is a manufacturing apparatus for manufacturing a polymeric piezoelectric material injection-molded body 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.

[0049] The injection unit 21 heats the pellets 19, which are raw material, to obtain a molten material 19a, and then injects the obtained molten material 19a. The stage unit 22 receives the injected molten material 19a, obtains a deposit 19b, and obtains a three-dimensional object 19c formed by stacking the deposits 19b. The control unit 18 controls various operations of the injection unit 21 and the stage unit 22.

[0050] The injection unit 21 shown in FIG. 4 includes a hopper 2, a supply pipe 3, a flat screw 4, a barrel 5, a motor 6, and a nozzle 10 (injection part).

[0051] The hopper 2 is a container that contains pellets 19. The supply pipe 3 is a pipe that connects the hopper 2 and the flat screw 4.

[0052] The injection unit 21 also has a screw case 40. The flat screw 4 is housed in a space formed between the screw case 40 and the barrel 5. The pellets 19 housed in the hopper 2 are supplied to this space through the supply pipe 3.

[0053] The flat screw 4 is connected to the rotating shaft of a motor 6 and rotates by the power of the motor 6. The flat screw 4 also has a spiral notch 4b extending from the circumferential surface 4a to the central portion 4c, as shown in Figures 5 and 6. The pellets 19 supplied into the screw case 40 are compressed while moving through the space 20 formed by the notch 4b and the barrel 5 as the flat screw 4 rotates.

[0054] The barrel 5 incorporates a heater 7. The pellets 19 compressed in the space portion 20 are melted (plasticized) by the heat of the heater 7 to become a molten material 19a. Therefore, the flat screw 4 and the barrel 5 constitute a melting section 45 that heats and melts the pellets 19.

[0055] As shown in FIG. 7, the barrel 5 has a communication hole 5a extending in the Z-axis direction and a plurality of grooves 5b formed on the surface facing the flat screw 4. The communication hole 5a is provided at a position corresponding to the central portion 4c of the flat screw 4. A nozzle 10 is provided on the negative Z-axis side of the communication hole 5a. The nozzle 10 has a nozzle hole 10a. The communication hole 5a is connected to the nozzle hole 10a. Therefore, the molten material 19a that has been moved to the central portion 4c of the flat screw 4 while being pressurized is injected from the nozzle hole 10a by using the pressure as a driving force, successively passing through the grooves 5b and the communication hole 5a.

[0056] Further, 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.

[0057] The stage unit 22 shown in FIG. 4 includes a plate 11, a first stage 12, a second stage 13, a base section 14, a first driving section 15, a second driving section 16, and a third driving section 17.

[0058] The plate 11 has an upper surface 11a facing the positive side of the Z axis. This upper surface 11a is a support surface that receives and deposits the molten material 19a injected from the nozzle hole 10a. As a result, a deposit 19b is obtained on the upper surface 11a. Then, the deposits 19b are piled up to form a three-dimensional object 19c having a desired shape. The plate 11 is placed on a first stage 12.

[0059] The first stage 12 can move the plate 11 in the X-axis direction by the power of the first drive unit 15. The first stage 12 is placed on the second stage 13.

[0060] The second stage 13 moves the first stage 12 in the Y-axis direction by the power of the second drive unit 16. This allows the second stage 13 to move the plate 11 in the Y-axis direction.

[0061] The base unit 14 moves the second stage 13 in the Z-axis direction by the power of the third drive unit 17. This allows the base unit 14 to move the plate 11 in the Z-axis direction.

[0062] 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 manner, it is possible to move the relative position of the nozzle hole 10a with respect to the plate 11 without changing the position of the nozzle 10. Therefore, by moving the position of the plate 11 three-dimensionally while ejecting the molten material 19a from the nozzle hole 10a, it is possible to deposit the molten material 19a three-dimensionally. As a result, it is possible to form a three-dimensional object 19c of any shape.

[0063] 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 be moved three-dimensionally. Also, of the three axes, the X-axis, the Y-axis, and the Z-axis, the stage unit 22 may move the plate 11 along one or two axes, and move the nozzle 10 along the remaining axis.

[0064] Furthermore, the three-dimensional object manufacturing device 1 is a so-called 3D printer, but the manufacturing device for the polymer piezoelectric material injection molded body is not limited to a 3D printer and may be, for example, an injection molding machine. The injection molding machine is equipped with a mold having a cavity of any shape. The molten material 19a injected from the nozzle 10 is filled into the cavity. The filled material is then released from the mold to obtain an injection molded body. In this case, the support surface that receives the molten material is not the above-mentioned upper surface 11a but the inner surface of the cavity. Therefore, in this specification, "molding" includes molding using a mold and modeling using a 3D printer.

[0065] 4 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 while coordinating them with each other.

[0066] The control unit 18 can be realized by, for example, a computer having a processor such as a CPU (Central Processing Unit), a memory such as a RAM (Random Access Memory) or a ROM (Read Only Memory), and an interface such as a USB (Universal Serial Bus). Programs and data are stored in the memory. The processor reads out and executes programs from the memory to control the operations of the injection unit 21 and the stage unit 22.

[0067] As described above, the three-dimensional model manufacturing apparatus 1, which is a manufacturing apparatus for a polymeric piezoelectric material injection molded body according to this embodiment, includes the flat screw 4 and barrel 5 as the melting section 45, the nozzle 10 as the injection section, and the upper surface 11a as the support surface. The flat screw 4 and barrel 5 heat the pellets 19, which are raw materials 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 model 19c, which is an injection molded body having piezoelectricity. The temperature of the upper surface 11a, that is, the temperature of the plate 11, is set to a temperature equal to or 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 undergoes a phase transition from a metastable phase to a stable phase.

[0068] According to such a three-dimensional object manufacturing apparatus 1, the molten material 19a is ejected at high pressure and deposited on the upper surface 11a.

[0069] FIG. 4 shows a schematic diagram of a three-dimensional object 19c manufactured by the three-dimensional object manufacturing apparatus 1. Since the melt 19a is injected under high pressure, a force is applied to the deposit 19b formed by depositing the melt 19a on the upper surface 11a in the injection direction D1. For this reason, when the deposit 19b contains, for example, polylactic acid as a helical chiral polymer, the axis of progression of the helix SP of the molecular structure of polylactic acid, i.e., the longest c-axis in the unit lattice of polylactic acid, is oriented along the upper surface 11a. In addition, the shortest b-axis in the unit lattice of polylactic acid is uniaxially oriented in a direction intersecting with the upper surface 11a. The deposit 19b is cooled to obtain a three-dimensional object 19c. In this manner, a piezoelectric layer 200 can be obtained.

[0070] As described above, such a piezoelectric layer 200 exhibits a piezoelectric phenomenon associated with rotational stress, and is therefore easy to use when applied to, for example, sensors, actuators, and the like.

[0071] In addition, by optimizing the temperature of the plate 11, the deposit 19b can be cooled in a temperature range where no phase transition to a metastable phase occurs, that is, in 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 good piezoelectric properties is obtained.

[0072] Furthermore, by depositing a plurality of deposits 19b as necessary, a three-dimensional object 19c thicker than one layer of deposit 19b can be obtained. This makes it easy to increase the thickness of the piezoelectric layer 200. The three-dimensional object 19c may be formed of one layer of deposit 19b.

[0073] In this way, the three-dimensional structure 19c may be formed of a laminate in which a plurality of unit layers, each of which is a deposit 19b, are laminated. Even in this case, the b-axis of the helical chiral polymer is uniaxially oriented in the thickness direction of the deposit 19b. This allows a piezoelectric layer 200 with high piezoelectricity and uniaxially oriented b-axis to be obtained regardless of the thickness.

[0074] The temperature of the nozzle 10 (injection part) is preferably equal to or higher than the melting point of the helical chiral polymer. This allows the helical chiral polymer contained in the melt 19a to be maintained in a good molten state until just before injection. As a result, a piezoelectric layer 200 having a high degree of uniaxial orientation of the b-axis can be obtained. Such a piezoelectric layer 200 has good piezoelectric properties.

[0075] The temperature of the nozzle 10 may be any temperature equal to or higher than the melting point of the helical chiral polymer, but is preferably set to be 10°C or more higher than the melting point, more preferably 20°C or more higher than the melting point and lower than the thermal decomposition temperature of the helical chiral polymer, and even more preferably 30°C or more higher than the melting point and 10°C or more lower than the thermal decomposition temperature.

[0076] For example, the melting point of α-phase L-type polylactic acid is about 182° C., and the thermal decomposition temperature is about 250° C. Therefore, the temperature of the nozzle 10 for injecting the melt 19a containing polylactic acid is preferably set to 192° C. or higher, more preferably set to 202° C. or higher and lower than 250° C., and even more preferably set to 212° C. or higher and 240° C. or lower.

[0077] The temperature of the barrel 5 is not particularly limited, but is preferably within a range of ±30° C., and more preferably within a range of ±15° C., of the temperature of the nozzle 10. This improves the kneading property by the flat screw 4, and ultimately makes it possible to produce a piezoelectric layer 200 having a particularly high degree of uniaxial orientation of the b-axis.

[0078] Furthermore, when the helical chiral polymer is polylactic acid, it is particularly preferable to set the temperature of the upper surface 11a (support surface) according to the phase transition temperature from the metastable phase to the stable phase. Specifically, the α' phase is known as the metastable phase of polylactic acid, and the α phase is known as the stable phase. Therefore, it is preferable to set the temperature of the upper surface 11a to a temperature equal to or higher than the phase transition temperature at which the α' phase transitions to the α phase, and lower than the melting point of polylactic acid. This prevents the molten material 19a from being rapidly cooled, and prevents the formation of the metastable phase. As a result, it is possible to manufacture a piezoelectric layer 200 that has high piezoelectricity and is mainly made of a stable phase that is chemically stable.

[0079] The temperature of the upper surface 11a, i.e., the temperature of the plate 11, may be any temperature that is equal to or higher than the phase transition temperature and lower than the melting point of polylactic acid, but is preferably set to a temperature 10°C or higher than the phase transition temperature and 10°C or lower than the melting point of polylactic acid, and more preferably set to a temperature 20°C or higher than the phase transition temperature and 30°C or lower than the melting point of polylactic acid. Specifically, the phase transition temperature of polylactic acid from the α' phase to the α phase is approximately 96°C. Therefore, the temperature of the plate 11 is preferably set to a temperature of 106°C or higher and 172°C or lower, and more preferably set to a temperature of 116°C or higher and 152°C or lower.

[0080] As described above, the melting section 45 has the flat screw 4. The flat screw 4 compresses the pellets 19, which are the raw material. This achieves a higher degree of uniaxial orientation of the b-axis of the helical chiral polymer. Furthermore, the flat screw 4 can efficiently knead and compress even a small number of pellets 19 in a short time compared to other screws. This shortens the time it takes for the pellets 19 to melt, making it less likely that deterioration of the molten material 19a will occur due to heating, oxidation, or the like.

[0081] Although the flat screw 4 has many advantages for the reasons mentioned above, the flat screw 4 may be substituted with any screw that exhibits a similar function.

[0082] The inner diameter of the 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. By setting the inner diameter of the nozzle hole 10a within the above range, it is possible to apply sufficient pressure to the melt 19a and maintain a good kneaded state. As a result, it is possible to achieve a higher degree of uniaxial orientation of the b-axis of the helical chiral polymer in the piezoelectric layer 200.

[0083] 3. Manufacturing method of polymeric piezoelectric material injection molding Next, a method for producing an injection-molded polymeric piezoelectric material according to the embodiment will be described.

[0084] 8 is a flowchart for explaining a method for manufacturing a polymeric piezoelectric material injection molded article according to the embodiment. In the following, a manufacturing method using the three-dimensional object manufacturing apparatus 1 shown in FIGS. 4 to 7 will be described.

[0085] 8 includes a melting step S102 for obtaining a molten material 19a, an injection step S104 for injecting the molten material 19a, and a modeling step S106 for obtaining a three-dimensional model 19c that is an injection-molded body. Each step will be described below in order.

[0086] 3.1.Melting process In the melting step S102, pellets 19 containing a helical chiral polymer are supplied to a space formed between the screw case 40 and the barrel 5. The pellets 19 are melted while moving through a space portion 20 formed by the flat screw 4 and the barrel 5, which is a melting portion 45, to become a melt 19a. The melt 19a is compressed as the flat screw 4 rotates.

[0087] 3.2. Injection process 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 is injected by the pressure.

[0088] 3.3. Molding process In the modeling step S106, the injected molten material 19a is received by the upper surface 11a of the plate 11. As a result, a deposit 19b is obtained on the upper surface 11a, and by stacking these, a three-dimensional model 19c is obtained.

[0089] As described above, the manufacturing method shown in FIG. 8 includes a melting step S102 for obtaining a melt 19a, an injection step S104 for injecting the melt 19a, and a modeling step S106 for obtaining a three-dimensional model 19c that is 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 step S104, the melt 19a is injected from a nozzle 10 (injection section). In the modeling step S106, the injected melt 19a is received by an upper surface 11a (support surface) of a plate 11 to obtain a three-dimensional model 19c having piezoelectricity. The temperature of the upper surface 11a, that is, the temperature of the plate 11, is set to a temperature equal to or higher than the phase transition temperature and lower than the melting point of the helical chiral polymer. The phase transition temperature is the temperature at which the helical chiral polymer undergoes a phase transition from a metastable phase to a stable phase.

[0090] With this configuration, when the shortest crystal axis of the helical chiral polymer is the b-axis, it is possible to obtain a deposit 19b in which the b-axis is uniaxially oriented in the thickness direction of the deposit 19b. By cooling the deposit 19b, a three-dimensional object 19c is obtained. In this manner, a piezoelectric layer 200 can be obtained.

[0091] As described above, such a piezoelectric layer 200 exhibits a piezoelectric phenomenon associated with rotational stress in addition to shear stress, and is therefore easy to use when applied to, for example, sensors, actuators, etc.

[0092] In addition, by optimizing the temperature of the plate 11, the deposit 19b can be cooled in a temperature range where no phase transition to a metastable phase occurs, that is, in 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 good piezoelectric properties is obtained.

[0093] The polymeric piezoelectric material injection molded body, the piezoelectric element, the manufacturing apparatus for the polymeric piezoelectric material injection molded body, and the manufacturing method for the polymeric piezoelectric material injection molded body of the present invention have been described above based on the illustrated embodiments, but the polymeric piezoelectric material injection molded body, the manufacturing apparatus for the polymeric piezoelectric material injection molded body, and the piezoelectric element of the present invention are not limited to the above embodiments, and for example, each part of the above embodiments may be replaced with an arbitrary configuration having the same function, or an arbitrary configuration may be added to the above embodiments. Furthermore, the manufacturing method for the polymeric piezoelectric material injection molded body of the present invention is not limited to the above embodiments, and for example, an arbitrary purpose step may be added to the above embodiments. EXAMPLES

[0094] Next, specific examples of the present invention will be described. 4. Manufacturing of Piezoelectric Test Pieces (Example) First, as an example of a helical chiral polymer, we prepared pellets of poly(L-lactic acid) (PLLA) manufactured by BMG Co., Ltd. The melting point of this poly(lactic acid) was 182°C, the thermal decomposition temperature was 250°C, and the phase transition temperature from the α' phase to the α phase was 96°C.

[0095] Next, pellets of polylactic acid were placed in the 3D modeling device shown in Figure 1, and the molten material was ejected while being folded back in a certain direction to obtain a piezoelectric test piece consisting of a two-layered deposit. The obtained piezoelectric test piece was a disk with a diameter of 30 mm.

[0096] The inner diameter of the nozzle was 0.3 mm, the nozzle temperature was 225°C, the barrel temperature was 215°C, and the plate temperature was 120°C.

[0097] Comparative Example 1 Except for changing the plate temperature to 50°C, a piezoelectric test piece was obtained in the same manner as in the example.

[0098] Comparative Example 2 Except for changing the plate temperature to 80°C, a piezoelectric test piece was obtained in the same manner as in the example.

[0099] Comparative Example 3 Except for changing the plate temperature to 100°C, a piezoelectric test piece was obtained in the same manner as in the example.

[0100] 5. Evaluation of raw materials and piezoelectric test specimens 5.1. Differential Scanning Calorimetry (DSC) of Raw Materials First, the raw material polylactic acid pellets were subjected to DSC measurement. A differential scanning calorimeter "Q1000" manufactured by TA Instruments was used for the measurement. In the DSC measurement, the melting endothermic curve was obtained while changing the temperature in three processes, the first heating process, the temperature drop process, and the second heating process. Specifically, in the first heating process, the temperature was raised from -20°C to 270°C at a heating rate of 5°C / min. In the temperature drop process, the temperature was lowered from 270°C to -20°C at a temperature drop rate of 5°C / min. In the second heating process, the temperature was raised from -20°C to 270°C in a heating process of 5°C / min.

[0101] A part of the obtained melting endothermic curve is shown in Figure 9. Figure 9 is a graph showing a part of the melting endothermic curve obtained by DSC measurement performed on the raw material polylactic acid pellets. As shown in Figure 9, in the first heating process, the melting point was observed at 181.75°C. In the second heating process, the phase transition temperature from the metastable α' phase to the stable α phase was observed at 95.91°C.

[0102] 5.2. X-ray diffraction of piezoelectric test specimen Next, the piezoelectric test pieces obtained in the examples and comparative examples were subjected to θ-2θ measurement by a focusing method using an X-ray diffractometer. In addition, the X-ray detector was fixed at a predetermined 2θ position, and rocking curve profile measurements were performed by changing the incident angle. The X-ray diffractometer used was an XRD measurement device "X'Pert" manufactured by Panalytical. In addition, characteristic X-rays of CuKα1 with a wavelength of 1.5404 Å were used for X-ray diffraction.

[0103] FIG. 10 shows θ-2θ profiles obtained by θ-2θ measurement for the piezoelectric test pieces obtained in the example and each comparative example.

[0104] 10, 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 the polylactic acid was not crystallized in the piezoelectric test piece obtained in Comparative Example 1.

[0105] 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 profiles obtained from the piezoelectric test pieces obtained in the examples, a peak was observed near 2θ=16.7°. These peaks are considered to correspond to the (110) plane / (200) plane.

[0106] 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°.

[0107] FIG. 11 shows the rocking curve profile for each piezoelectric test piece when the 2θ position was fixed at 16.7°.

[0108] In FIG. 11, a peak due to the uniaxial orientation of some crystal plane was observed near ψ=±30° only in the rocking curve profile acquired from the piezoelectric test piece obtained in the example.

[0109] On the other hand, in the θ-2θ profile obtained from the piezoelectric test piece obtained in the example, a peak was observed near 2θ=14.7° as shown in Fig. 10. This peak is considered to correspond to the (010) plane.

[0110] 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°.

[0111] FIG. 12 shows the rocking curve profile for each piezoelectric test piece when the 2θ position was fixed at 14.7°.

[0112] In Fig. 12, a peak was observed at ψ = 0° only in the rocking curve profile obtained from the piezoelectric test piece obtained in the example. Therefore, it was found that the piezoelectric test piece obtained in the example contains crystals with (010) orientation, that is, uniaxial orientation of the b axis.

[0113] In the rocking curve profile shown in Fig. 12, the full width at half maximum (FWHM) of the peak resulting from the uniaxial orientation of the b-axis is about 31°. This full width at half maximum is preferably 50° or less, and more preferably 40° or less. This allows it to be considered that a sufficient degree of orientation has been obtained. [Explanation of symbols]

[0114] 1...3D object manufacturing device, 2...hopper, 3...supply pipe, 4...flat screw, 4a...circumferential surface, 4b...notch, 4c...center, 5...barrel, 5a...communication hole, 5b...groove, 6...motor, 7...heater, 9...heater, 10...nozzle, 10a...nozzle hole, 11...plate, 11a...upper surface, 12...first stage, 13...second stage, 14...base portion, 15...first drive portion, 16...second drive portion, 17...third drive portion, 18...control portion, 19...pellets, Reference Signs List 19a...melt, 19b...deposit, 19c...three-dimensional object, 20...space, 21...injection unit, 22...stage unit, 40...screw case, 45...melt portion, 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 direction, S102...melting process, S104...injection process, S106...modeling process, SP...spiral

Claims

1. The polylactic acid crystal is a helical chiral polymer crystal composed of polymer chains and having a unit cell with a-axis, b-axis and c-axis as crystal axes, 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; The b-axis is uniaxially oriented, An injection molded article having piezoelectric properties, When subjected to θ-2θ measurement by X-ray diffraction, the θ-2θ profile has a peak corresponding to the (010) plane of the polylactic acid crystal, A polymeric piezoelectric material injection-molded product, characterized in that when a rocking curve profile is obtained for a peak corresponding to the (010) plane, the rocking curve profile has a peak at ψ = 0° with a half-width of 50° or less.

2. It is composed of a laminated body formed by stacking a plurality of unit layers, The polymeric piezoelectric material injection molded article according to claim 1 , wherein the b-axis is uniaxially oriented in the thickness direction of the unit layer.

3. The polymeric piezoelectric material injection molded article according to claim 1 or 2, Two electrode layers sandwiching the polymeric piezoelectric material injection molded body; A piezoelectric element comprising:

4. a melting section for heating and compressing a raw material containing a helical chiral polymer to obtain a melt; An injection part that injects the molten material; a support surface for receiving the injected molten material to obtain an injection molded article having piezoelectric properties; Equipped with 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 support surface is equal to or higher than a phase transition temperature at which the helical chiral polymer undergoes a phase transition from a metastable phase to a stable phase and is lower than a melting point of the helical chiral polymer; The fusion portion is A flat screw for compressing the raw material; a barrel that forms a space portion that compresses the raw material together with the flat screw as the flat screw rotates; having 13. An apparatus for manufacturing a polymeric piezoelectric material injection molded article, wherein the temperature of the barrel is within a range of ±30° C. of the temperature of the injection section.

5. the helical chiral polymer is polylactic acid; 5. The apparatus for manufacturing a polymer piezoelectric material injection molded article according to claim 4, wherein the temperature of the support surface is equal to or higher than the phase transition temperature at which the polylactic acid undergoes a phase transition from the metastable α' phase to the stable α phase, and is lower than the melting point of the polylactic acid.

6. A step of heating and compressing a raw material containing a helical chiral polymer to obtain a melt; injecting the molten material from an injection portion; receiving the injected molten material on a support surface to obtain an injection molded article having piezoelectric properties; having 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 support surface is equal to or higher than a phase transition temperature at which the helical chiral polymer undergoes a phase transition from a metastable phase to a stable phase and is lower than a melting point of the helical chiral polymer; The step of obtaining the molten material is a step of heating and compressing the raw material using a flat screw that compresses the raw material and a barrel that forms a space portion that compresses the raw material together with the flat screw as the flat screw rotates, A method for producing a polymeric piezoelectric material injection molded article, characterized in that the temperature of the barrel is within a range of ±30°C of the temperature of the injection section.

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