JP5392471B2 - Electrostrictive polymer material, method for producing the same, and electronic component - Google Patents

Description

  The present invention relates to an electrostrictive polymer material, a method for producing the same, and an electronic component, and more specifically, an electrostrictive polymer material suitable for use in an artificial muscle, a method for producing the same, and the electrostrictive polymer material. The present invention relates to an electronic component such as an electrostrictive actuator.

  In recent years, artificial muscles have attracted attention for application to robots, care devices, rehabilitation devices, and the like, and have been actively studied. However, this type of artificial muscle material obtains a desired amount of strain by applying a low electric field. A highly rigid material that can be used and that does not easily elastically deform when strain occurs is desired.

  Under such circumstances, the electrostrictive material is distorted in proportion to the square of the electric field strength, so that it is considered possible to obtain a large amount of strain by applying a low electric field. Among them, electrostrictive polymer materials are expected to be applied to artificial muscles because they can be reduced in size and weight.

  Non-Patent Document 1 discloses that a polymerization ratio of vinylidene fluoride (hereinafter referred to as “VDF”) and chlorotrifluoroethylene (hereinafter referred to as “CTFE”) is 88/12. An electrostrictive polymer material made of a polymer, that is, poly (VDF-CTFE) (hereinafter referred to as “P (VDF-CTFE)”) is described.

  In Non-Patent Document 1, the amount of strain increases linearly in proportion to the approximate square of the applied electric field, the amount of strain due to electrostriction when an electric field of 250 MV / m is applied is 5.5%, and 820 MPa. An electrostrictive polymer material having a Young's modulus is described. Here, the amount of strain is expressed as a percentage of the total length of the raw material before strain. For example, when the electric field is applied to the entire length of 1 mm and the strain is 1 μm, the strain amount is 0.1% (= 1). / 1000 × 100).

Qiming Zhang, Zhongyang Chang, “Electropolymers for Mechtronics and Artificial Muscles”, Handbook of Organics and Photonics, volume 0, American Scientific Publishers, 2006, p.35-38

  However, although Non-Patent Document 1 can obtain a polymer material having a strain amount of 5.5% when a high electric field of 250 MV / m is applied, the Young's modulus (longitudinal elastic modulus) is as low as about 820 MPa. That is, even if the strain is generated and greatly displaced, the Young's modulus is low, and the elastic deformation easily occurs with a relatively small stress load. For this reason, a large force cannot be exhibited when strain occurs, and it is still insufficient as an electrostrictive polymer material for artificial muscle.

  The present invention has been made in view of such circumstances. A desired amount of strain can be obtained by applying a low electric field, the residual polarization is small, and a large force is stably obtained when strain occurs. It is an object of the present invention to provide an electrostrictive polymer material excellent in dielectric strength, a method for producing the same, and an electronic component such as an electrostrictive actuator.

  In the case of an electrostrictive material, it is necessary to polarize it in order to be distorted. Therefore, it is desirable that the coercive electric field is low. Further, it is desirable that the residual strain in the state where the applied electric field is “0” is as small as possible. Therefore, it is desirable that the residual polarization is small even if the applied electric field is extended.

  On the other hand, PVDF is known as a piezoelectric material having ferroelectricity, and transitions from a paraelectric phase (β phase) to a ferroelectric phase (α phase) by stretching the PVDF into a sheet shape.

  However, PVDF alone tends to increase the remanent polarization when stretched, and the electrostriction constant is low, so when attempting to obtain a desired large amount of strain, the element must be obtained before obtaining such amount of strain. There is a risk of being destroyed.

Therefore, when the present inventor conducted earnest research, a copolymer was prepared by containing 3 to 6% of CTFE in the polymerization ratio in VDF, and this copolymer was 1.5 to 2.5 times larger . It has been found that by stretching at a stretching ratio, it is possible to suppress an increase in remanent polarization compared to before stretching, and to obtain a desired large strain amount without destroying the element. In addition, it can be distorted with a low electric field, has a large Young's modulus, and can generate a large force that is highly rigid and not easily elastically deformed, even when the strain occurs and is greatly displaced. In addition, the knowledge that an electrostrictive polymer material excellent in the above can be obtained was also obtained.

  The present invention has been made on the basis of such knowledge, and the electrostrictive polymer material according to the present invention is a sheet-like co-polymer with a polymerization ratio of VDF and CTFE of 97/3 to 94/6. The copolymer is characterized in that the copolymer is stretched in a predetermined direction so that the stretch ratio is 1.5 to 2.5 times.

  The electrostrictive polymer material of the present invention is characterized by having a Young's modulus of 1 GPa or more.

  Furthermore, in the method for producing an electrostrictive polymer material according to the present invention, a copolymer prepared by setting a polymerization ratio of VDF and CTFE to 97/3 to 94/6 is prepared, and the copolymer is placed in a solvent. A solution is prepared by dissolving, and then the solution is molded into a sheet to produce a molded body, and the molded body is stretched 1.5 to 2.5 times in a predetermined direction. .

  The electronic component according to the present invention is characterized in that the electrostrictive polymer material is used.

  According to the electrostrictive polymer material of the present invention, the electrostrictive polymer material is composed of a sheet-like copolymer having a polymerization ratio of VDF and CTFE of 97/3 to 94/6, and a draw ratio of 1.5 to 2.5 times. The copolymer is stretched in a predetermined direction so that a desired amount of strain can be obtained by applying a low electric field, an increase in remanent polarization can be suppressed, and a Young's modulus is large and strain is reduced. Even if it occurs, it is possible to obtain an electrostrictive polymer material that can exert a large force and has an excellent dielectric strength.

  In addition, since the Young's modulus is 1 GPa or more, it is possible to obtain a highly rigid electrostrictive polymer material that is not easily elastically deformed against a stress load even when a large strain occurs.

  According to the method for producing an electrostrictive polymer material of the present invention, a copolymer prepared with a polymerization ratio of VDF and CTFE of 97/3 to 94/6 is prepared, and the copolymer is dissolved in a solvent. Then, the solution is molded into a sheet to produce a molded body, and the molded body is stretched 1.5 to 2.5 times in a predetermined direction. An electrostrictive polymer material with more excellent ferroelectricity can be obtained by making it a dielectric and further stretching.

  According to the electronic component of the present invention, since the electrostrictive polymer material is used, the electrostrictive polymer material has a desired amount of distortion when applied with a low electric field, and can exert a great force even when distorted. It is possible to obtain an electronic component such as an electrostrictive actuator suitable for an application such as an artificial muscle having a good dielectric strength.

It is sectional drawing which shows typically one Embodiment of the electrostrictive actuator as an electronic component manufactured using the electrostrictive polymer material which concerns on this invention. 1 is a plan view of an electrostrictive polymer material in Example 1. FIG. It is the characteristic view which showed DE hysteresis curve after 2 time extending | stretching of P (VDF-CTFE) in sample number 1 with DE hysteresis curve before extending | stretching. It is the characteristic view which showed DE hysteresis curve after 2 time extending | stretching of PVDF in sample number 2 with DE hysteresis curve before extending | stretching. 6 is a front view of a displacement measurement sample produced in Example 2. FIG. It is a side view of the sample for displacement measurement of FIG.

  Next, an embodiment of the present invention will be described in detail.

  FIG. 1 is a cross-sectional view schematically showing one embodiment of an electrostrictive actuator as an electronic component manufactured using an electrostrictive polymer material according to the present invention.

  In the electrostrictive actuator 1, electrodes 3a and 3b made of Pt, Ni, Au, or the like are formed on the upper and lower surfaces of the first element body 2a, and the electrode 3b is formed on the lower surface of the first element body 2a. The 2nd element main body 2b is stuck in the form which pinches | interposes.

  In addition, the electrostrictive actuator 1 is configured such that the base end is supported by the support member 4 and the tip is displaced in the arrow X direction by the electrostrictive effect by applying a voltage to the electrodes 3a and 3b. .

  The first and second element bodies 2a and 2b are formed of the electrostrictive polymer material of the present invention.

  That is, the electrostrictive polymer material is a sheet-like material prepared so that the polymerization ratio of VDF represented by the chemical formula (A) and CTFE represented by the chemical formula (B) is 97/3 to 94/6. It is formed of a copolymer.

  Here, the reason why the polymerization ratio of VDF and CTFE was set to 97/3 to 94/6 is as follows.

  PVDF, which is a polymer of VDF, transitions from a paraelectric phase (α phase) to a ferroelectric phase (β phase) by being stretched into a sheet shape, and becomes a ferroelectric material.

  However, with PVDF alone, when the stretching process is performed, the coercive electric field Ec can be reduced substantially the same as PVDF before stretching, but the remanent polarization Pr increases, and therefore the residual strain increases. Moreover, PVDF alone has a low electrostriction constant, and when an electric field is applied, the element may be destroyed before a desired amount of strain is obtained.

  However, when the present inventor has intensively studied, by mixing VDF with CTFE having high viscoelasticity to produce a copolymer, the residual polarization Pr is kept at the same level as before stretching while keeping the coercive electric field Ec low. It was found that it can be suppressed.

  Therefore, the electrostrictive polymer material is composed of a copolymer obtained by mixing CTFE with VDF, that is, P (VDF-CTFE).

  However, in order to suppress the increase in remanent polarization Pr due to stretching and to secure a desired electrostriction constant, the content of CTFE is required to be at least 3% in terms of polymerization ratio.

  On the other hand, when CTFE is included in a polymerization ratio of 6% or more, the viscoelasticity is excessively increased, the Young's modulus is decreased to less than 1 GPa, and the withstand voltage is significantly decreased.

  Therefore, in this embodiment, a sheet-like copolymer prepared so that the polymerization ratio of VDF and CTFE is 97/3 to 94/6 is used.

  Moreover, the said copolymer is extended | stretched in the predetermined direction so that the draw ratio Z shown by Numerical formula (1) may be 1.5 to 2.5 times.

Z = x / x ₀ (1)
Here, x ₀ is the sheet length before stretching, x is a sheet length after the stretching.

  That is, as described above, by stretching a sheet-like copolymer having a polymerization ratio of VDF and CTFE of 97/3 to 94/6, a ferroelectric material having a small remanent polarization and a large Young's modulus can be obtained. it can.

  However, when the draw ratio Z is less than 1.5, sufficient ferroelectricity cannot be obtained, and when an electric field is applied, the element is destroyed before obtaining a desired strain amount. There is a fear. On the other hand, when the draw ratio Z exceeds 2.5 times, a thinned portion is generated in the sheet, and it may be difficult to ensure insulation in a high electric field.

  Therefore, in this embodiment, the stretching process is performed so that the stretching ratio Z is 1.5 to 2.5 times.

  Thus, in this embodiment, the electrostrictive polymer material is a sheet-like copolymer in which the polymerization ratio of VDF and CTFE is 97/3 to 94/6, and the draw ratio is 1.5 to Since the copolymer is stretched in a predetermined direction so as to be 2.5 times, the coercive electric field is low, the increase in remanent polarization is suppressed as compared to before stretching, and the Young's modulus is large and the dielectric strength is excellent. Thus, an electrostrictive polymer material having desired electrostrictive characteristics with a large amplitude can be obtained.

  And this electrostrictive polymer material can be manufactured as follows.

  First, a copolymer P (VDF-CTFE) having a polymerization ratio of VDF and CTFE of 97/3 to 94/6 is prepared. Next, the solution is dissolved in a solvent by using a stirrer such as an air motor so that the copolymer becomes 10 to 20% by weight to prepare a solution.

  Here, the solvent is not particularly limited, but N, N-dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP) and the like can be preferably used.

  Next, this solution is molded using a doctor blade method or the like, and a sheet-like molded body having a predetermined thickness (for example, 10 to 20 μm) is produced and dried.

  Thereafter, both ends of the molded body are held with a predetermined jig and stretched to have a length of 1.5 to 2.5 times. Thus, an electrostrictive polymer material having a sheet thickness of about 1 / 1.5 to 1 / 2.5 before stretching can be produced.

  As described above, the electrostrictive polymer material is obtained by dissolving a copolymer P (VDF-CTFE) having a predetermined polymerization ratio in a solvent, and then forming a sheet formed into a sheet 1.5 to 2.5 times longer. Thus, it is possible to obtain a ferroelectric material at a stage before stretching, and by further stretching, an electrostrictive polymer material with improved ferroelectricity can be obtained.

  The present invention is not limited to the above embodiment. The molecular weight of the electrostrictive polymer material is not particularly limited, and for example, a copolymer P (VDF-CTFE) having a molecular weight of 200,000 to 600,000 can be preferably used. In the above embodiment, the electrostrictive actuator is exemplified as the electronic component. However, it is needless to say that other chip type electrostrictive components can be similarly applied.

[Sample preparation]
A copolymer made of P (VDF-CTFE) having a polymerization ratio of VDF and CTFE of 96/4 was prepared.

  And P (VDF-CTFE) was dissolved in DMF for several hours using an air motor so that P (VDF-CTFE) might become 10 to 20 weight%, and the solution was obtained.

  Next, using a doctor blade method, a molded body having a thickness of 10 to 20 μm was produced and dried at a temperature of 70 ° C.

  Next, the obtained molded body is cut into a predetermined size, and then both ends are held, and heated at 110 ° C., and stretched in the horizontal and lateral directions so as to be twice as long as the molded body dimension. An electrostrictive polymer material of No. 1 was obtained.

  The thickness of the electrostrictive polymer material was about ½ of the thickness of the molded body, that is, 5 to 10 μm.

  Next, as shown in FIG. 2, the electrostrictive polymer material 11 of sample number 1 is cut so that the length L1 is 30 mm and the width W is 20 mm, and the sputter is performed so that the distance t from the end surface is 2 mm. Pt electrodes 12 were formed on the upper and lower surfaces of the electrostrictive polymer material 11 by the method.

  As a comparative example, an electrostrictive polymer material of sample number 2 was prepared in the same manner and procedure as sample number 1 except that PVDF alone was used instead of P (VDF-CTFE).

(Sample evaluation)
For sample numbers 1 and 2, FCE-1 type manufactured by Toyo Technica Co., Ltd. was used, and DE hysteresis curves before stretching and after 2-fold stretching were measured.

  FIG. 3 shows the DE hysteresis curve of sample number 1. In the figure, the solid line is the sample after stretching twice, and the broken line is the sample before stretching. In addition, Pr1 and Pr1 ′ are remanent polarization of the sample after 2 times stretching and the sample before stretching, respectively, and Ec1 and Ec1 ′ are coercive electric fields of the sample after 2 times stretching and the sample before stretching, respectively.

  FIG. 4 shows the DE hysteresis curve of Sample No. 2. In the figure, the solid line is the sample after double stretching, and the broken line is the sample before stretching. In addition, Pr2 and Pr2 ′ are remanent polarization of the sample after 2 times stretching and the sample before stretching, respectively, and Ec2 and Ec2 ′ are coercive electric fields of the sample after 2 times stretching and the sample before stretching, respectively.

  As is clear from FIG. 4, the coercive electric field Ec2 of the sample after 2 times stretching is about 85 MV / m, which is smaller than the coercive electric field Ec2 ′ (≈120 MV / m) of the sample before stretching. The residual polarization Pr2 of the sample after double stretching is increased as compared with the residual polarization P2 ′ of the sample before stretching, and it is considered that the residual strain becomes larger than that before stretching.

  On the other hand, as is clear from FIG. 3, sample No. 1 has a coercive electric field of about 85 MV / m, which is smaller than the sample before extension, as in sample No. 2 (Ec1). <Ec1 ′) and the remanent polarization is suppressed to the same extent as compared with the sample before stretching (Pr1≈Pr1 ′).

  That is, the sample No. 1 sample has a coercive electric field substantially equal to that of the sample No. 2 sample, and the residual polarization is suppressed from increasing by performing the stretching process. Therefore, it was found that an electrostrictive polymer material which can be distorted by a low electric field and has a small residual strain as compared with the sample of sample number 2 can be obtained.

  In addition, with respect to Sample No. 1, a Fourier transform infrared spectrophotometer (FT-IR) is used for a sample before stretching and a sample after stretching twice, and a ferroelectric phase (β phase) and a paraelectric phase (α phase) ) And the ratio β / α were 2.0, the sample before stretching was 2.0, whereas the sample after 2 times stretching was 12.6. By performing the stretching treatment, the ferroelectricity was greatly increased. It turns out that it improves.

  Incidentally, an attempt was made to measure a DE hysteresis curve by preparing a copolymer having a polymerization ratio of VDF and CTFE of 80/20. However, as is clear from Example 2 described later, when the polymerization ratio is 80/20, resistance The voltage became extremely low and the DE hysteresis curve could not be measured.

  For the copolymers of Sample Nos. 1 and 2, in addition to the sample before stretching and the sample after 2-fold stretching shown in [Example 1], the stretching ratio was 1.5 in the same manner and procedure as in [Example 1]. Double and 2.5-fold samples were prepared and designated as sample numbers 11 and 12, respectively.

  Further, a copolymer having a polymerization ratio of VDF and CTFE of 80/20 was prepared in the same manner and procedure as in [Example 1], and the sample before stretching and the stretching ratio were 1.5 times, 2 times, 2 times, A sample of 5 times was prepared and designated as sample number 13.

  With respect to each of samples Nos. 11 to 13, a withstand voltage was measured by applying a DC voltage at a boosting rate of 300 V / s.

  Moreover, the Young's modulus was measured about the sample before extending | stretching among the sample numbers 11-13, and the sample after 2 time extending | stretching using the viscoelasticity meter (RSAIII by Rheometric Science).

  Furthermore, among the sample numbers 11 to 13, Pt electrodes 12a and 12b were formed on the upper and lower surfaces of the sample before stretching and the sample after double stretching.

  On the other hand, for the pre-stretched sample and the double-stretched sample in which the Pt electrode was not formed, a sheet was prepared by cutting the length L2 to 25 mm and the width W to 20 mm.

  And as shown in FIG.5 and FIG.6, these sheet | seats 13 are stuck to the surface in which the Pt electrode 12a was formed through the epoxy resin 14, and each of the sample numbers 11-13 which use the sheet | seat 13 as an inactive layer An electrostrictive actuator was fabricated.

  Next, one end in the longitudinal direction of these samples is held by a support member (not shown), and a voltage is applied to the Pt electrodes 12a and 12b to distort each sample in the direction of arrow B. The laser beam was irradiated in the direction of arrow A using LK-GD500 manufactured by the company. Then, the applied electric field was measured when the strain amount was 0.20% and 0.50%.

  Table 1 shows the measurement results of each sample.

  Sample No. 12 is formed of PVDF alone and has a sufficiently high withstand voltage. However, since the electrostriction constant is small, the sample was destroyed before the strain amount reached 0.20% or 0.50%.

  Sample No. 13 had an excessive CTFE content, so the withstand voltage was extremely low, and the sample was destroyed before the strain amount reached 0.20% or 0.50%. Moreover, the Young's modulus is small, and it has been found that the material is not suitable for an electrostrictive material for artificial muscle.

  On the other hand, Sample No. 11 has a Young's modulus of 3.255 GPa, which is dramatically improved as compared with that before stretching (1.685 GPa) by performing the stretching treatment, and 97.3 MV / m and 111.9 MV / m. It was found that by applying an electric field, electrostrictive actuators having strain amounts of 0.20% and 0.50% can be obtained, respectively, and it can be driven with an applied electric field having a sufficient margin with respect to the breakdown electric field.

  It is useful for artificial muscles such as robots, care devices, and rehabilitation devices.

2a First element body (electrostrictive polymer material)
2b Second element body (electrostrictive polymer material)

Claims (4)

A sheet-like copolymer having a polymerization ratio of vinylidene fluoride and chlorotrifluoroethylene of 97/3 to 94/6,
An electrostrictive polymer material, wherein the copolymer is stretched in a predetermined direction so that a stretching ratio is 1.5 to 2.5 times.   The electrostrictive polymer material according to claim 1, wherein Young's modulus is 1 GPa or more.   A copolymer having a polymerization ratio of vinylidene fluoride and chlorotrifluoroethylene of 97/3 to 94/6 was prepared, and the copolymer was dissolved in a solvent to prepare a solution. A method for producing an electrostrictive polymer material, comprising forming a molded body by molding a solution into a sheet and stretching the molded body in a predetermined direction by 1.5 to 2.5 times.   An electronic component, wherein the electrostrictive polymer material according to claim 1 or 2 is used.

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