JP2016138239A - Polymeric piezoelectric material and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polymeric piezoelectric material capable of maintaining piezoelectricity and excellent in heat resistance and transparency.SOLUTION: There is provided a polymeric piezoelectric material containing an optical active polymer (A) with weight average molecular weight of 500,000 to 1,000,000 and having stereocomplex crystallization rate (S) represented by following formula (X) measured by a differential scanning calorimeter (DSC) of 6% to 85%, homo crystallinity obtained by the DSC method of 5% to 80% and piezoelectric constant dmeasured by a stress-electrical charge method at 25°C, of 1pC/N. S={▵Hmsc/(▵Hmsc+▵Hmh)}×100 (X), where ▵Hmh represents melting enthalpy of a low melting point melting peak where a crystal melting peak temperature is less than 190°C by a DSC measurement and ▵Hmsc represents melting enthalpy of a high melting point melting peak where the crystal melting peak temperature is 190°C or more by a DSC measurement.SELECTED DRAWING: None

Description

  The present invention relates to a polymeric piezoelectric material and a method for producing the same.

Conventionally, PZT (PBZrO ₃ —PbTiO ₃ based solid solution), which is a ceramic material, has been widely used as the piezoelectric material. However, since PZT contains lead, currently, as a piezoelectric material, a polymer piezoelectric material (polymer piezoelectric film) having a low environmental load and high flexibility has come to be used.
As the polymer piezoelectric material, nylon 11, polyvinyl fluoride, polyvinyl chloride, polyurea, polyvinylidene fluoride (β type) (PVDF), vinylidene fluoride-trifluoroethylene copolymer (P (VDF-TrFE)) Pauling type polymers represented by (75/25) and the like are known.

In recent years, in addition to the above-described polymeric piezoelectric materials, polymeric piezoelectric materials using optically active helical chiral polymers (for example, polylactic acid-based polymers typified by polylactic acid) are known (for example, patents). Reference 1 and 2).
By the way, about polyester resins, such as polylactic acid, in order to improve heat resistance, various examination is made | formed.
For example, poly L-lactic acid consisting of only L-lactic acid units (hereinafter sometimes abbreviated as PLLA) and poly-D-lactic acid consisting only of D-lactic acid units (hereinafter sometimes abbreviated as PDLA) in solution or in a molten state. It has been reported that a stereocomplex is formed by mixing in the above. It is known that this stereocomplex polylactic acid has a high melting point and high crystallinity as compared with PLLA and PDLA, and is excellent in hydrolysis resistance and solvent resistance. A technique is known in which a stereo complex is formed using polylactic acid or the like to improve the heat and moisture resistance (Patent Document 3 and Non-Patent Document 1).
Moreover, the transparency of stereocomplex polylactic acid may deteriorate. In order to improve the transparency of the stereocomplex polylactic acid film, a technique using a nucleating agent or the like is known (for example, Patent Document 4).

JP-A-5-152638 JP 2005-213376 A JP 63-24014 A JP 2008-248162 A

Macromolecules, 24,5651 (1991)

Polymer piezoelectric materials using optically active polymers such as polylactic acid are required to maintain piezoelectricity and to be excellent in heat resistance and transparency.
However, as in Patent Document 3, when stereocomplex polylactic acid is used for the polymer piezoelectric material, the heat resistance is improved, but the transparency and piezoelectricity tend to be lowered.
Furthermore, when the method of improving transparency using a nucleating agent is employed for stereocomplex polylactic acid as in Patent Document 4, the nucleating agent may act as a thermal decomposition catalyst. As a result, the thermal decomposition reaction proceeds to cause a decrease in molecular weight during melt kneading, and the thermal stability (heat resistance) tends to decrease.

  Therefore, the present invention is to provide a polymeric piezoelectric material that can maintain piezoelectricity and is excellent in heat resistance and transparency, and a method for producing the same.

Specific means for achieving the above object are as follows.
<1> A stereocomplex crystallization ratio represented by the following formula (X), which includes an optically active polymer (A) having a weight average molecular weight of 50,000 to 1,000,000 and is measured by a differential scanning calorimeter (DSC) (S) is 6% to 85%, a homo crystallinity obtained by the DSC method is 5% to 80%, 25 stresses in ° C. - piezoelectric constant _{d 14} is 1 pC / N or more as measured by a charge method High molecular piezoelectric material.
S = {ΔHmsc / (ΔHmsc + ΔHmh)} × 100 (X)
(In the formula, ΔHmh represents the melting enthalpy of the low melting point melting peak having a crystal melting peak temperature of less than 190 ° C. by DSC measurement, and ΔHmsc is the high melting point melting peak having a crystal melting peak temperature of 190 ° C. or more by DSC measurement. Represents the melting enthalpy of
<2> The polymeric piezoelectric material according to <1>, wherein the stereocomplex crystallization ratio (S) is 6% to 28% and the homocrystallization degree is 20% to 80%.
<3> The polymeric piezoelectric material according to <1> or <2>, wherein the optically active polymer (A) includes, as a structural unit, 65 mol% or more of an L-form component or 65 mol% or more of a D-form component.
<4> The optically active polymer (A) includes an optically active polymer (B) having 90 mol% or more of L-form component, an optically active polymer (C) having 90 mol% or more of D-form component, and L <1> a polymer comprising at least one selected from the group consisting of an optically active polymer (D) which is a stereoblock copolymer having a body component and a D-form component each of more than 10 mol% and less than 90 mol% The polymeric piezoelectric material according to any one of to <3>.
<5> The weight average molecular weight of the optically active polymer (B), the weight average molecular weight of the optically active polymer (C), and the weight average molecular weight of the optically active polymer (D) are 50,000 to 1,000,000, respectively. <4> The polymeric piezoelectric material according to <4>.
<6> The polymeric piezoelectric material according to any one of <1> to <5>, wherein an internal haze with respect to visible light is 4.0% or less.
<7> The polymeric piezoelectric material according to any one of <1> to <6>, wherein an internal haze with respect to visible light is 2.0% or less.
<8> The product of the normalized molecular orientation MORc and the homocrystallinity is 25 to 700 when the reference thickness measured with a microwave transmission type molecular orientation meter is 50 μm, <1> to <7 The polymeric piezoelectric material according to any one of the above.
<9> Any one of <1> to <8>, wherein the optically active polymer (A) is a polylactic acid polymer having a main chain containing a repeating unit represented by the following structural formula (1). The polymeric piezoelectric material described in 1.

<10> The polymeric piezoelectric material according to any one of <1> to <9>, wherein the content of the optically active polymer (A) is 80% by mass or more.
<11> The polymeric piezoelectric material according to any one of <1> to <10>, wherein an internal haze with respect to visible light is 1.0% or less.
<12> A stabilizer having a weight average molecular weight of 200 to 60000 having at least one functional group selected from the group consisting of a carbodiimide group, an epoxy group, and an isocyanate group, and 100 masses of the optically active polymer (A). The polymeric piezoelectric material according to any one of <1> to <11>, wherein the stabilizer is contained in an amount of 0.01 to 10 parts by mass with respect to parts.
<13> The polymeric piezoelectric material according to <12>, wherein the stabilizer has at least one functional group selected from the group consisting of a carbodiimide group, an epoxy group, and an isocyanate group in one molecule.

<14> A method for producing the polymeric piezoelectric material according to any one of <1> to <13>, wherein a first step of obtaining a pre-crystallized film containing the optically active polymer (A) And a second step of stretching the pre-crystallized film mainly in a uniaxial direction.
<15> The method for producing a polymeric piezoelectric material according to <14>, wherein annealing is performed after the second step.
<16> A method for producing the polymeric piezoelectric material according to any one of <1> to <13>, wherein the film containing the optically active polymer (A) is mainly stretched in a uniaxial direction; And a step of annealing after the film is stretched.

  ADVANTAGE OF THE INVENTION According to this invention, the piezoelectricity which can maintain piezoelectricity, and was excellent in heat resistance and transparency, and its manufacturing method can be provided.

In this specification, a numerical range expressed using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.
Further, in the present specification, “film” is a concept including not only what is generally called “film” but also what is generally called “sheet”.

<Polymer piezoelectric material>
The polymeric piezoelectric material of the present invention includes an optically active polymer (A) having a weight average molecular weight of 50,000 to 1,000,000, and is represented by the following formula (X) measured by a differential scanning calorimeter (DSC). The stereocomplex crystallization rate (S) is 6% to 85%, the homocrystallization degree obtained by the DSC method is 5% to 80%, and the piezoelectric constant d measured by the stress-charge method at 25 ° C. ₁₄ is 1 pC / N or more.
S = {ΔHmsc / (ΔHmsc + ΔHmh)} × 100 (X)
(In the formula, ΔHmh represents the melting enthalpy of the low melting point melting peak having a crystal melting peak temperature of less than 190 ° C. by DSC measurement, and ΔHmsc is the high melting point melting peak having a crystal melting peak temperature of 190 ° C. or more by DSC measurement. Represents the melting enthalpy of

In general, for example, when a stereocomplex crystal of poly L-lactic acid and poly D-lactic acid is formed, the sign of the generated charge due to strain and the direction of strain due to voltage are reversed for poly L-lactic acid and poly D-lactic acid. Thereby, in the polymeric piezoelectric material which has the stereocomplex crystal which mixed poly L-lactic acid and poly D-lactic acid, the fall of piezoelectricity (piezoelectric constant) is seen. When equal amounts (50/50) of poly L-lactic acid and poly D-lactic acid are used, the piezoelectricity of the polymeric piezoelectric material becomes almost zero.
Furthermore, when poly L-lactic acid and poly D-lactic acid are used in equal amounts (50/50), the stereocomplex crystallization rate (S) described later tends to be a numerical value of 50% or more.
On the other hand, in the polymer piezoelectric material of the present invention, by adjusting the stereocomplex crystallization ratio (S) to be 6% to 85%, it is possible to maintain the piezoelectricity and to have excellent heat resistance and transparency. Realized.

  Furthermore, since the polymer piezoelectric material of the present invention has a homocrystallization degree of 5% or more obtained by the DSC method, the piezoelectricity of the polymer piezoelectric material is maintained. Moreover, it can suppress that the transparency of a polymeric piezoelectric material falls because the homocrystallization degree obtained by DSC method is 80% or less.

Further, a polymeric piezoelectric material of the present invention has piezoelectric properties are maintained as described above, specifically, the stress at 25 ° C. - piezoelectric constant d ₁₄ measured by the charge method is 1 pC / N or more.

-Stereo complex crystallization rate (S)-
The stereocomplex crystallization ratio (S) of the polymeric piezoelectric material of the present invention is 6% to 85%. When the stereocomplex crystallization ratio (S) is 6% or more, deformation due to heat is suppressed and heat resistance is excellent. When the stereocomplex crystallization ratio (S) is 85% or less, the piezoelectricity can be maintained and the transparency is excellent.

The stereocomplex crystallization rate (S) of the polymeric piezoelectric material is a value measured by a differential scanning calorimeter (DSC) and is calculated by the following formula (X).
S = {ΔHmsc / (ΔHmsc + ΔHmh)} × 100 (X)
(In the formula, ΔHmh represents the melting enthalpy of the low melting point melting peak having a crystal melting peak temperature of less than 190 ° C. by DSC measurement, and ΔHmsc is the high melting point melting peak having a crystal melting peak temperature of 190 ° C. or more by DSC measurement. Represents the melting enthalpy of
The polymeric piezoelectric material of the present invention includes, for example, a homophase crystal composed of an optically active polymer (B) described later, a homophase crystal composed of an optically active polymer (C), an optically active polymer (B), and And a stereocomplex phase crystal formed by mixing the optically active polymer (C). At this time, in DSC measurement, a low melting point crystal melting peak with a peak temperature of less than 190 ° C. corresponding to a melting peak of a homophase crystal and a high melting point crystal melting with a peak temperature of 190 ° C. or more corresponding to a melting peak of a stereocomplex phase crystal are usually used. A peak is observed.

The stereocomplex crystallization ratio (S) of the polymeric piezoelectric material of the present invention is not particularly limited as long as it is 6% to 85%, but preferred ranges are as follows. First, the lower limit of the stereocomplex crystallization ratio (S) is 6%, but from the viewpoint of further improving heat resistance and maintaining high piezoelectricity, it is preferably 7%, and 8%. Is more preferably 10%, and particularly preferably 12%. The upper limit of the stereocomplex crystallization ratio (S) is 85%, but it is preferably 27% and more preferably 25% from the viewpoint of further improving transparency and maintaining piezoelectricity. It is preferably 21%, more preferably 17%.
What is necessary is just to measure a stereocomplex crystallization rate (S) and the homo crystallinity mentioned later using a well-known differential scanning calorimeter, for example, DSC-1 by Perkin-Elmer.

  In the present invention, for example, the mass ratio (B / C) of the optically active polymer, which will be described later, the content of the optically active polymer (D), and the crystallization and stretching conditions for producing the polymeric piezoelectric material are adjusted. Thus, the stereocomplex crystallization ratio (S) of the polymer piezoelectric material can be adjusted to a range of 6% to 85%.

  In the present invention, the upper limit of the stereocomplex crystallization ratio (S) of the polymer piezoelectric material may be 60% or 28% instead of 85%.

-Homocrystallinity-
The polymer piezoelectric material of the present invention has a homocrystallization degree of 5% to 80% obtained by the DSC method. Thereby, about a polymeric piezoelectric material, piezoelectricity is maintained highly and the fall of transparency is suppressed.
The homocrystallization degree of the polymeric piezoelectric material is a value measured by a differential scanning calorimeter (DSC), and is calculated by the following formula.
Homo crystallinity (%) = {ΔHmh (J / g) / Q (J / g)} × 100
(In the formula, ΔHmh represents the melting enthalpy of the low melting point melting peak having a crystal melting peak temperature of less than 190 ° C. by DSC measurement, and Q represents the heat of fusion when the homocrystal has a crystallinity of 100%.)

For example, when the optically active polymer (A) is polylactic acid, the homocrystal of polylactic acid is said to have a heat of fusion of 93 J / g if the crystallinity is 100%. ) It is calculated by the following formula.
Homo crystallinity (%) = {ΔHmh (J / g) / 93 (J / g)} × 100
(In the formula, ΔHmh represents the melting enthalpy of the low melting point melting peak whose crystal melting peak temperature is less than 190 ° C. by DSC measurement.)
The homocrystallization degree means the homocrystallization degree of poly L-lactic acid, the homo crystallization degree of poly D-lactic acid, the homo crystallization degree of the L-form component of the polylactic acid stereoblock copolymer, and the polylactic acid stereo. It is the sum total of the homocrystallization degree of the D-form component of a block copolymer.

  The homocrystallinity of the polymeric piezoelectric material of the present invention is 5% to 80%, preferably 25% to 60%, more preferably 30% to 50%, and still more preferably 30% to 40%. If the degree of homocrystallization is within the above range, the piezoelectricity and transparency of the polymeric piezoelectric material are well balanced, and when the polymeric piezoelectric material is stretched, whitening and breakage are unlikely to occur and it is easy to manufacture.

  In the present invention, for example, by adjusting the mass ratio (B / C) of the optically active polymer, the content of the optically active polymer (D), and the crystallization and stretching conditions when producing the polymeric piezoelectric material. The homocrystallinity of the polymeric piezoelectric material can be adjusted to a range of 5% to 80%.

  In the present invention, the lower limit of the homocrystallinity of the polymeric piezoelectric material may be 15% or 20% instead of 5%.

  In the present invention, the stereocomplex crystallization ratio (S) may be 6% to 28%, and the homocrystallinity may be 20% to 80%.

- piezoelectric constant _{d 14} -
Polymeric piezoelectric material of the present invention, the stress at 25 ° C. - piezoelectric constant d ₁₄ measured by the charge method is a 1 pC / N or more, the piezoelectric property is maintained.
The higher the piezoelectric constant d ₁₄ is, the larger the displacement of the polymer piezoelectric material with respect to the voltage applied to the polymer piezoelectric material, and conversely, the voltage generated with respect to the force applied to the polymer piezoelectric material increases. It is useful as a material.
Hereinafter, the stress - describing an example of a method for measuring a piezoelectric constant d ₁₄ due to charge method.

  First, the polymeric piezoelectric material is cut to 150 mm in a direction of 45 ° with respect to the stretching direction (MD direction) and 50 mm in a direction perpendicular to the direction of 45 ° to produce a rectangular test piece. Next, set the test piece obtained on the test stand of Showa Vacuum SIP-600, and deposit Al on one surface of the test piece so that the deposition thickness of aluminum (hereinafter referred to as Al) is about 50 nm. To do. Next, vapor deposition is similarly performed on the other side of the test piece, and Al is coated on both sides of the test piece to form an Al conductive layer.

  A test piece of 150 mm × 50 mm with an Al conductive layer formed on both sides is 120 mm in a direction of 45 ° with respect to the stretching direction (MD direction) of the polymer piezoelectric material, and 10 mm in a direction perpendicular to the direction of 45 °. Cut and cut out a rectangular film of 120 mm × 10 mm. This is a piezoelectric constant measurement sample.

The obtained sample is set in a tensile tester (manufactured by AND, TENSILON RTG-1250) with a distance between chucks of 70 mm so as not to be loosened. The force is periodically applied so that the applied force reciprocates between 4N and 9N at a crosshead speed of 5 mm / min. At this time, in order to measure the amount of charge generated in the sample according to the applied force, a capacitor having a capacitance Qm (F) is connected in parallel to the sample, and the voltage V between the terminals of the capacitor Cm (95 nF) is converted into a buffer amplifier. Measure through. The above measurement is performed under a temperature condition of 25 ° C. The generated charge amount Q (C) is calculated as the product of the capacitor capacitance Cm and the terminal voltage Vm. Piezoelectric constant d ₁₄ is calculated by the following equation.
d ₁₄ = (2 × t) / L × Cm · ΔVm / ΔF
t: Sample thickness (m)
L: Distance between chucks (m)
Cm: Capacitor capacity in parallel (F)
ΔVm / ΔF: Ratio of change in voltage between capacitor terminals to change in force

In the polymer piezoelectric material of the present invention, the stress at 25 ° C. - The piezoelectric constant _{d 14} measured by a charge method, and a 1 pC / N or more, preferably more than 2pC / N, more preferably at least 3pC / N, 4pC / N The above is more preferable. The upper limit of the piezoelectric constant d ₁₄ is not particularly limited, from the viewpoint of the balance, such as transparency, preferably less 50pc / N is a polymeric piezoelectric material using an optically active polymer, more preferably at most 30 pC / N.
From the viewpoint of the balance with similarly transparency is preferably a piezoelectric constant d ₁₄ measured by a resonance method is not more than 15pC / N.

  In the present specification, the “MD direction” is the direction in which the polymer piezoelectric material (polymer piezoelectric film) flows, and the “TD direction” is orthogonal to the MD direction, and the polymer direction. The direction is parallel to the main surface of the piezoelectric material (Transverse Direction).

-Transparency (internal haze)-
The transparency of the polymeric piezoelectric material can be evaluated, for example, by visual observation or haze measurement.
In the polymer piezoelectric material of the present invention, the internal haze with respect to visible light (hereinafter also simply referred to as “internal haze”) is preferably 40% or less, more preferably 20% or less, and more preferably 10% or less. Is more preferably 4.0% or less, particularly preferably 2.0% or less, and most preferably 1.0% or less.
The lower the internal haze of the polymeric piezoelectric material of the present embodiment, the better. However, from the viewpoint of balance with the piezoelectric constant and the like, it is preferably 0.01% to 15%, and preferably 0.01% to 10%. %, More preferably 0.1% to 5%, particularly preferably 0.1% to 4%, and most preferably 0.1% to 1.0%. preferable.

In this specification, “internal haze” refers to haze excluding haze due to the shape of the outer surface of the polymeric piezoelectric material.
Further, the “internal haze” herein is a value when measured at 25 ° C. in accordance with JIS-K7105 for a polymer piezoelectric material.

More specifically, the internal haze (hereinafter also referred to as “internal haze H1”) refers to a value measured as follows.
Specifically, first, a haze in the optical path length direction (hereinafter also referred to as “haze H2”) was measured for a cell having an optical path length of 10 mm filled with silicon oil. Next, a polymer piezoelectric material (polymer piezoelectric film) is immersed in the silicon oil of the cell so that the optical path length direction of the cell is parallel to the normal direction of the polymer piezoelectric material, and the polymer piezoelectric material is immersed in the cell. The haze in the optical path length direction (hereinafter also referred to as “haze H3”) of the formed cell is measured. Both haze H2 and haze H3 are measured at 25 ° C. in accordance with JIS-K7105.
Based on the measured haze H2 and haze H3, the internal haze H1 is obtained according to the following formula.
Internal haze (H1) = Haze (H3) -Haze (H2)

The haze H2 and the haze H3 can be measured using, for example, a haze measuring machine [manufactured by Tokyo Denshoku Co., Ltd., TC-HIII DPK].
Moreover, as the silicone oil, for example, “Shin-Etsu Silicone (trademark), model number KF-96-100CS” manufactured by Shin-Etsu Chemical Co., Ltd. can be used.

-Standardized molecular orientation MORc-
The polymer piezoelectric material of the present invention preferably has a normalized molecular orientation MORc of 2.0 to 15.0. Furthermore, in the present invention, from the viewpoint of improving the balance between the piezoelectricity and transparency of the polymeric piezoelectric material and enhancing the dimensional stability, the normalized molecular orientation MORc described later and the homocrystallinity of the polymeric piezoelectric material Is preferably 25 to 700.
The normalized molecular orientation MORc is a value determined based on “molecular orientation degree MOR” which is an index indicating the degree of orientation of the optically active polymer (A) described later.
Here, the molecular orientation degree MOR (Molecular Orientation Ratio) is measured by the following microwave measurement method. That is, a polymer piezoelectric material (sample) is placed in a microwave resonant waveguide of a known microwave molecular orientation measuring device (also referred to as a microwave transmission type molecular orientation meter) in the direction of microwave travel. The material is arranged so that the surface of the material (the surface of the film-like polymer piezoelectric material surface having the largest area) is vertical. Then, in a state where the sample is continuously irradiated with the microwave whose vibration direction is biased in one direction, the sample is rotated by 0 to 360 ° in a plane perpendicular to the traveling direction of the microwave, and the microwave transmitted through the sample is transmitted. The degree of molecular orientation MOR is determined by measuring the strength.

The normalized molecular orientation MORc is an MOR value when the reference thickness tc is 50 μm, and can be obtained by the following equation.
MORc = (tc / t) × (MOR-1) +1
(Tc: reference thickness to be corrected, t: sample thickness)
The normalized molecular orientation MORc can be measured with a known molecular orientation meter such as a microwave molecular orientation meter MOA-2012A or MOA-6000 manufactured by Oji Scientific Instruments Co., Ltd., at a resonance frequency in the vicinity of 4 GHz or 12 GHz.

The polymer piezoelectric material of the present invention preferably has a normalized molecular orientation MORc of 2.0 to 15.0, more preferably 2.5 to 10.0, and 3.5 to 8.0. More preferably, it is more preferably 4.0 to 7.0.
If the normalized molecular orientation MORc is 2.0 or more, there are many optically active polymer molecular chains (for example, polylactic acid molecular chains) arranged in the stretching direction, and as a result, the rate of formation of oriented crystals is increased. High piezoelectricity can be expressed.
If the normalized molecular orientation MORc is 15.0 or less, a decrease in transparency due to too many molecular chains of the optically active polymer that undergoes molecular orientation is suppressed, and as a result, the high transparency of the polymeric piezoelectric material is maintained. Is done.

  Further, the normalized molecular orientation MORc is controlled by crystallization conditions (for example, heating temperature and heating time) and stretching conditions (for example, stretching ratio, stretching temperature, and stretching speed) at the time of producing the polymeric piezoelectric material. sell.

-Product of normalized molecular orientation MORc and homocrystallinity-
In the present invention, the product of the normalized molecular orientation MORc and the homocrystallinity of the polymeric piezoelectric material is preferably 25-700. By adjusting to this range, the balance between the piezoelectricity and transparency of the polymeric piezoelectric material is good, and the dimensional stability is also high.
The product of the normalized molecular orientation MORc and the crystallinity of the polymer piezoelectric material is preferably 75 to 600, more preferably 100 to 500, still more preferably 150 to 300, and particularly preferably 160 to 210.

  For example, by adjusting the mass ratio (B / C) of the optically active polymer, the content of the optically active polymer (D), and the crystallization and stretching conditions when producing the polymeric piezoelectric material, the above product can be obtained. Can be adjusted within the above range.

-Tear strength-
The tear strength of the polymeric piezoelectric material of the present invention is measured according to the test method “right angle tear method” described in “Tear Strength of Plastic Films and Sheets” of JIS K 7128-3. It is evaluated based on the size.
Here, the crosshead speed of the tensile tester is 200 mm per minute, and the tear strength is calculated from the following equation.
T = F / d
(In the above formula, T represents the tear strength (N / mm), F represents the maximum tear load, and d represents the thickness (mm) of the test piece.)

  The thickness of the polymeric piezoelectric material (polymer piezoelectric film) of the present invention is not particularly limited, but is preferably 10 μm to 400 μm, more preferably 20 μm to 200 μm, still more preferably 20 μm to 100 μm, and more preferably 20 μm to 80 μm. Particularly preferred.

[Optically active polymer (A)]
The polymeric piezoelectric material of the present invention contains an optically active polymer (A) having a weight average molecular weight of 50,000 to 1,000,000. This optically active polymer (A) has a stereocomplex crystallization ratio (S) of 6% to 85%, a homocrystallinity of 5% to 80%, and 25 stresses in ° C. - piezoelectric constant d ₁₄ measured by the charge method is not particularly limited as long as 1 pC / N or more.

  For example, the optically active polymer (A) is preferably a polymer containing 65 mol% or more of the L-form component or 65 mol% or more of the D-form component as a structural unit. That is, the optically active polymer (A) is composed of 65% or more of L-form components that are monomer components and 35% or less of D-form components, or 65% or more of D-form components that are monomer components and It is preferably composed of 35% or less of L-form component. At this time, as long as the optically active polymer (A) satisfies that it is a polymer containing 65 mol% or more of the L-form component or 65 mol% or more of the D-form component, the L-form component and D A monomer other than the body component (for example, a copolymerizable polyfunctional compound described later) may be included. A stereocomplex crystal is obtained by crystallizing the optically active polymer (A).

  Furthermore, the optically active polymer (A) is more preferably a polymer containing 75 mol% or more of the L-form component or 75 mol% or more of the D-form component as a structural unit.

The optically active polymer (A) includes an optically active polymer (B) having 90 mol% or more of L-form component, an optically active polymer (C) having 90 mol% or more of D-form component, and an L-form component and D It is preferably a polymer composed of at least one selected from the group consisting of optically active polymers (D) which are stereoblock copolymers each having a body component of more than 10 mol% and less than 90 mol%.
Furthermore, the optically active polymer (A) may be a polymer composed of at least one of the optically active polymer (B) and the optically active polymer (C) and the optically active polymer (D).

The optically active polymer (B) is a polymer having 90 mol% or more of L-form component and optical activity, and preferably has a weight average molecular weight of 50,000 to 1,000,000.
The optically active polymer (B) is not particularly limited as long as it is a polymer having 90 mol% or more of L-form component, but preferably 95 mol% or more of L-form component, more preferably 98 mol% or more of L-form component. More preferably, it is a polymer containing 99 mol% or more of the L isomer component, more preferably 100 mol% of the L isomer component (consisting only of the L isomer component).

The optically active polymer (C) is a polymer having a D-form component of 90 mol% or more and having optical activity, and preferably has a weight average molecular weight of 50,000 to 1,000,000.
The optically active polymer (C) is not particularly limited as long as it has a D-form component of 90 mol% or more, but preferably has a D-form component of 95 mol% or more, and more preferably has a D-form component of 98 mol% or more. More preferably, it is a polymer containing 99 mol% or more of the D isomer component, more preferably 100 mol% of the D isomer component (consisting only of the D isomer component).

The optically active polymer (D) is a polymer that is a stereoblock copolymer having an L-form component and a D-form component each of more than 10 mol% and less than 90 mol%. The stereo block copolymer is a copolymer including a block composed of an L-form component and a block composed of a D-form component (stereo block portion), and may contain a portion other than the stereo block portion. In addition, the block which consists of a L body component and the block which consists of a D body component should just exist in an optically active polymer (D) at least one each.
In the optically active polymer (D), the block composed of the L component and the block composed of the D component (stereo block portion) are 70 mol% or more, preferably 80 mol% or more, more preferably 90 mol, in the structural unit. Accounted for over 50%. The optically active polymer (D) has a random copolymer portion of an L-form component and a D-form component (including a copolymerizable polyfunctional compound described later, if necessary) as a portion other than the stereoblock portion. You may do it.
Since the stereo block copolymer can easily form a stereo complex crystal, the heat resistance can be improved by including the stereo block copolymer in the polymer piezoelectric material.

  The optically active polymer (D) may be a stereoblock copolymer having an L-form component and a D-form component of 30 mol% to 70 mol%, respectively, and the ratio (molar ratio) of the L-form component and the D-form component. ) May be the same stereo block copolymer, or may be a stereo block copolymer (not including a portion other than the stereo block portion) having 50 mol% of each of the L-form component and the D-form component. When the ratio of the L-form component and the D-form component in the optically active polymer (D) is equal, the weight-average molecular weight of the block comprising the L-form component and the weight-average molecular weight of the block comprising the D-form component are substantially the same. Alternatively, the number of blocks composed of L-body components and the number of blocks composed of D-body components may be the same.

  As described above, the optically active polymer (A) is a polymer comprising at least one of the optically active polymer (B) and the optically active polymer (C) and the optically active polymer (D). There may be. At this time, by changing the ratio of the optically active polymer (D) in the optically active polymer (A), the homocrystallization degree and the stereocomplex crystallization rate can be adjusted. For example, in the optically active polymer (A), by increasing the amount of the optically active polymer (D) in which the ratios of the L-form component and the D-form component are the same, the degree of homocrystallization can be reduced, or the stereocomplex crystal. The conversion rate can be increased.

  When the optically active polymer (A) is a polymer composed of at least one of the optically active polymer (B) and the optically active polymer (C) and the optically active polymer (D), The ratio of the L-form component or the D-form component is preferably 65 mol% or more, and more preferably 70 mol% or more.

  The optically active polymer (A) is a polymer composed of the optically active polymer (B) and the optically active polymer (D), or a polymer composed of the optically active polymer (C) and the optically active polymer (D). It may be. Furthermore, the mass ratio (B / D) of the optically active polymer (B) to the optically active polymer (D) is preferably 35/65 or more, and more preferably 35/65 to 90/10. The mass ratio (C / D) of the optically active polymer (C) to the optically active polymer (D) is preferably 35/65 or more, and more preferably 35/65 to 90/10. . In particular, when the proportions of the L-form component and the D-form component in the optically active polymer (D) are equal (preferably, the proportion of the L-form component and the D-form component in the optically active polymer (D) is 50 mol%, respectively. Case) it is preferable to satisfy the numerical ranges of the mass ratio (B / D) and the mass ratio (C / D) described above.

The optically active polymer (A) is a polymer obtained by mixing the optically active polymer (B) and the optically active polymer (C). The mass ratio (B / C) of the molecule (B) is more preferably 10/90 to 35/65 or 90/10 to 65/35. By adjusting the mass ratio (B / C) to 10/90 to 35/65 or 90/10 to 65/35, the stereocomplex crystallization rate (S) is 6% to 85% (or 6% to 28%). Furthermore, the piezoelectricity of the polymer piezoelectric material can be maintained, and the heat resistance and transparency can be improved.
The polymer piezoelectric material of the present invention is excellent in heat resistance because its mass ratio (B / C) is not less than 10/90 or not more than 90/10, so that deformation due to heat is suppressed.
In addition, the polymer piezoelectric material of the present invention has a mass ratio (B / C) of 35/65 or less or 65/35 or more, so that the piezoelectricity can be maintained and the transparency is excellent.

  From the viewpoint of further increasing the piezoelectricity, the mass ratio (B / C) of the optically active polymer is preferably 10/90 to 20/80 or 90/10 to 80/20.

When the optically active polymer (A) is a polymer obtained by mixing the optically active polymer (B) and the optically active polymer (C), as the optically active polymer (A),
(1) A mixture of optically active polymers that are homopolymers of monomers having different steric configurations (L-form and D-form) (for example, optically active polymer (B), and L-lactic acid component is 100 mol%) A poly-L-lactic acid and an optically active polymer (C), and a blend of poly-D-lactic acid having a D-lactic acid component of 100 mol%),
(2) An optically active polymer (B) comprising 90 mol% or more of an L-form component, 10 mol% or less of a D-form component and at least one of the copolymerizable polyfunctional compounds described below (for example, stereo block co-polymer). A polymer, preferably a polylactic acid stereoblock copolymer), 90 mol% or more of a D isomer component, 10 mol% or less of an L isomer component, and at least one of a copolymerizable polyfunctional compound described later. A mixture of the active polymer (C) (for example, a stereoblock copolymer, preferably a polylactic acid stereoblock copolymer),
Etc.
The optically active polymer (A) may be a mixture of the aforementioned mixtures (the aforementioned (1) and (2)), the optically active polymer (D), other polymers, and the like. Furthermore, you may mix.

Examples of the optically active polymer (B), the optically active polymer (C), and the optically active polymer (D) include polypeptides, cellulose, cellulose derivatives, polylactic acid polymers, polypropylene oxide, and poly (β-hydroxy). And polymers such as butyric acid). Examples of the polypeptide include poly (glutarate γ-benzyl), poly (glutarate γ-methyl), and the like. Examples of the cellulose derivative include cellulose acetate and cyanoethyl cellulose.
Each of the optically active polymer (B), the optically active polymer (C), and the optically active polymer (D) may be the aforementioned one polymer, or the aforementioned two or more polymers. It may be a mixture of

  The optically active polymer (B) and the optically active polymer (C) each preferably have an optical purity of 95.00% ee or more from the viewpoint of improving the piezoelectricity of the polymeric piezoelectric material, and 97.00%. It is more preferably ee or more, more preferably 99.00% ee or more, and particularly preferably 99.99% ee or more. Desirably, it is 100.00% ee. By setting the optical purity of the optically active polymer (B) and the optically active polymer (C) within the above range, the crystallinity of the polymer crystal that exhibits piezoelectricity is increased, and as a result, the piezoelectricity is increased. it is conceivable that.

In the present embodiment, the optical purity of the optically active polymer (optically active polymer (B) and optically active polymer (C)) is a value calculated by the following formula.
Optical purity (% ee) = 100 × | L body weight−D body weight | / (L body weight + D body weight)
That is, “the amount difference (absolute value) between the amount of L-form [mass%] of optically active polymer and the amount of D-form [mass%] of optically active polymer” is “the amount of L-form of optically active polymer”. The value obtained by multiplying (multiplying) the value obtained by dividing (dividing) the amount [mass%] by the total amount of the amount [mass%] of the optically active polymer D-form [mass%] and multiplying it by 100. And

  In addition, the value obtained by the method using a high performance liquid chromatography (HPLC) is used for the quantity [mass%] of the L body of an optically active polymer, and the quantity [mass%] of the D body of an optically active polymer. Details of the specific measurement are as follows.

-Measurement of L and D amounts of optically active polymer-
A sample containing 1.0 g of optically active polymer is weighed in a 50 mL Erlenmeyer flask, and 2.5 mL of IPA (isopropyl alcohol) and 5 mL of 5.0 mol / L sodium hydroxide solution are added. Next, the Erlenmeyer flask containing the sample solution is placed in a water bath at a temperature of 40 ° C. and stirred for about 5 hours until the optically active polymer is completely hydrolyzed.

The sample solution is cooled to room temperature, neutralized by adding 20 mL of a 1.0 mol / L hydrochloric acid solution, and the Erlenmeyer flask is sealed and mixed well. Dispense 1.0 mL of the sample solution into a 25 mL volumetric flask and prepare HPLC sample solution 1 with 25 mL of mobile phase. 5 μL of the HPLC sample solution 1 is injected into the HPLC apparatus, the D / L body peak area of the optically active polymer is determined under the following HPLC conditions, and the amounts of L body and D body are calculated.
-HPLC measurement conditions-
・ Column Optical resolution column, SUMICHIRAL OA5000 manufactured by Sumika Chemical Analysis Co., Ltd.
・ Measuring device: JASCO Corporation liquid chromatography column temperature: 25 ℃
Mobile phase 1.0 mM-copper (II) sulfate buffer / IPA = 98/2 (V / V)
Copper (II) sulfate / IPA / water = 156.4 mg / 20 mL / 980 mL
・ Mobile phase flow rate 1.0ml / min ・ Detector UV detector (UV254nm)

  The optically active polymer (B) and the optically active polymer (C) (optically active polymer (A)) are represented by the following structural formula (1) from the viewpoint of increasing optical purity and improving piezoelectricity. A polylactic acid polymer having a main chain containing a unit is preferred. The optically active polymer (D) is also preferably a polylactic acid polymer having a main chain containing a repeating unit represented by the following structural formula (1) from the viewpoint of improving piezoelectricity.

  The polylactic acid polymer having the repeating unit represented by the structural formula (1) as the main chain is preferably polylactic acid, and the optically active polymer (B) is most preferably a homopolymer of L-lactic acid (PLLA). Preferably, the optically active polymer (C) is most preferably a homopolymer (PDLA) of D-lactic acid.

  The polylactic acid polymer refers to “polylactic acid”, “copolymer of L-lactic acid or D-lactic acid and a copolymerizable polyfunctional compound”, or a mixture of both. The above-mentioned “polylactic acid” is a polymer in which lactic acid is polymerized by an ester bond and is connected for a long time, a lactide method via lactide, and a direct polymerization method in which lactic acid is heated in a solvent under reduced pressure and polymerized while removing water. It is known that it can be manufactured by, for example. Examples of the “polylactic acid” include a homopolymer of L-lactic acid, a homopolymer of D-lactic acid, a block copolymer including at least one polymer of L-lactic acid and D-lactic acid, and L-lactic acid and D-lactic acid. Examples thereof include a graft copolymer containing at least one polymer of lactic acid. At this time, as the optically active polymer (B), a homopolymer of L-lactic acid (PLLA), a block copolymer containing 90 mol% or more of L-lactic acid component and 10 mol% or less of D-lactic acid component, or Examples of the optically active polymer (C) include D-lactic acid homopolymer (PDLA), a D-lactic acid component of 90 mol% or more, and an L-lactic acid component of 10 mol% or less. A block copolymer or a graft copolymer is mentioned. Examples of the optically active polymer (D) include a stereo block copolymer containing an L-lactic acid component and a D-lactic acid component each of more than 10 mol% and less than 90 mol%.

  Examples of the “copolymerizable polyfunctional compound” include glycolic acid, dimethyl glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 2-hydroxypropanoic acid, 3-hydroxypropanoic acid, 2-hydroxyvaleric acid, 3 -Hydroxyvaleric acid, 4-hydroxyvaleric acid, 5-hydroxyvaleric acid, 2-hydroxycaproic acid, 3-hydroxycaproic acid, 4-hydroxycaproic acid, 5-hydroxycaproic acid, 6-hydroxycaproic acid, 6-hydroxy Hydroxycarboxylic acids such as methyl caproic acid and mandelic acid, glycolides, cyclic esters such as β-methyl-δ-valerolactone, γ-valerolactone and ε-caprolactone, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid , Pimelic acid, azelaic acid, sebacic acid, undecanedioic acid, Polycarboxylic acids such as candioic acid and terephthalic acid, and anhydrides thereof, ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1 , 4-butanediol, 2,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,9-nonanediol, 3-methyl-1,5-pentanediol, neopentyl glycol, tetra Examples thereof include polyhydric alcohols such as methylene glycol and 1,4-hexanedimethanol, polysaccharides such as cellulose, and aminocarboxylic acids such as α-amino acids.

  Examples of the “copolymerizable polyfunctional compound” include the compounds described in paragraph 0028 of International Publication No. 2013/054918 pamphlet.

  Examples of the “copolymer of L-lactic acid or D-lactic acid and a copolymerizable polyfunctional compound” include a block copolymer or a graft copolymer having a polylactic acid sequence capable of forming a helical crystal. Can be mentioned.

  Moreover, it is preferable that the density | concentration of the structure originating in the copolymer component in an optically active polymer is 20 mol% or less. For example, when the optically active polymer is a polylactic acid polymer, a structure derived from lactic acid (L-lactic acid, D-lactic acid) in the polylactic acid polymer and a compound copolymerizable with lactic acid (copolymer component) The copolymer component is preferably 20 mol% or less with respect to the total number of moles of the structure derived from

The optically active polymer (for example, polylactic acid polymer) is obtained by, for example, directly dehydrating and condensing lactic acid described in JP-A-59-096123 and JP-A-7-033861. US Pat. Nos. 2,668,182 and 4,057,357 and the like can be produced by a ring-opening polymerization method using lactide, which is a cyclic dimer of lactic acid.
Furthermore, the optically active polymer (eg, polylactic acid-based polymer) obtained by each of the above production methods is produced by, for example, the lactide method in order to achieve an optical purity of 95.00% ee or higher. In this case, it is preferable to polymerize lactide whose optical purity is improved to 95.00% ee or higher by crystallization operation.

The optically active polymer (A) is preferably a polymer obtained by mixing poly L-lactic acid and poly D-lactic acid. At this time, by crystallizing the optically active polymer (A), a eutectic (stereocomplex crystal) in which poly L-lactic acid and poly D-lactic acid have a racemic crystal structure is obtained.
The melting point (melting peak by DSC measurement) of poly L-lactic acid homocrystal or poly D-lactic acid homocrystal is generally 160 to 180 ° C., whereas the melting point of the stereocomplex crystal (melting by DSC measurement). The peak is generally 190-240 ° C.

-Weight average molecular weight of optically active polymer-
The optically active polymer (B), optically active polymer (C) and optically active polymer (D) (hereinafter also referred to as “optically active polymer”) used in the present invention have a weight average molecular weight (Mw), It is preferably 50,000 to 1,000,000. When the lower limit of the weight average molecular weight of the optically active polymer is 50,000 or more, the mechanical strength when the polymer piezoelectric material is formed into a molded body is improved. The lower limit of the weight average molecular weight of the optically active polymer is preferably 100,000 or more, and more preferably 150,000 or more. On the other hand, when the upper limit of the weight average molecular weight of the optically active polymer is 1,000,000 or less, the moldability when a polymer piezoelectric material is obtained by molding (for example, extrusion molding) is improved.
The upper limit of the weight average molecular weight is preferably 800,000 or less, and more preferably 300,000 or less.

  The weight average molecular weight of the optically active polymer (A) is preferably 50,000 to 1,000,000, and preferably 100,000 to 300,000 from the viewpoint of improving the moldability of the polymeric piezoelectric material.

  The molecular weight distribution (Mw / Mn) of the optically active polymer (A) is preferably 1.1 to 5, and more preferably 1.2 to 4, from the viewpoint of strength. Furthermore, it is preferable that it is 1.4-3. In addition, the weight average molecular weight Mw and molecular weight distribution (Mw / Mn) of the optically active polymer (optically active polymers (A) to (C)) are determined by the following GPC measurement method using gel permeation chromatography (GPC). , Measured.

-GPC measuring device-
Waters GPC-100
-Column-
Made by Showa Denko KK, Shodex LF-804
-Sample preparation-
The optically active polymer is dissolved in a solvent (for example, chloroform) at 40 ° C. to prepare a sample solution having a concentration of 1 mg / ml.
-Measurement conditions-
0.1 ml of the sample solution is introduced into the column at a solvent [chloroform], a temperature of 40 ° C., and a flow rate of 1 ml / min.

  The sample concentration in the sample solution separated by the column is measured with a differential refractometer. A universal calibration curve is prepared using a polystyrene standard sample, and the weight average molecular weight (Mw) and molecular weight distribution (Mw / Mn) of the optically active polymer are calculated.

Commercially available polylactic acid may be used as the polylactic acid polymer. Commercially available polylactic acid, for example, PURAC Co. PURASORB (PD, PL), manufactured by Mitsui Chemicals, Inc. of LACEA (H-100, H- 400), NatureWorks LLC Corp. ^Ingeo TM Biopolymer, and the like.

  When a polylactic acid polymer is used as the optically active polymer, the optically active polymer is produced by the lactide method or the direct polymerization method in order to increase the weight average molecular weight (Mw) of the polylactic acid polymer to 50,000 or more. It is preferable to do.

In the polymeric piezoelectric material of the present invention, the content of the optically active polymer (A) is not particularly limited, but is preferably 80% by mass or more based on the total mass of the polymeric piezoelectric material.
When the content is 80% by mass or more, the piezoelectric constant tends to be larger.

[Stabilizer]
The polymeric piezoelectric material of the present invention contains a compound having a weight average molecular weight of 200 to 60000 having at least one functional group selected from the group consisting of a carbodiimide group, an epoxy group, and an isocyanate group as a stabilizer. Also good. Thereby, the heat-and-moisture resistance of the polymeric piezoelectric material is further improved.
Furthermore, the polymeric piezoelectric material of the present invention preferably has at least one functional group selected from the group consisting of a carbodiimide group, an epoxy group, and an isocyanate group in one molecule as a stabilizer.
As the stabilizer, “Stabilizer (B)” described in paragraphs 0039 to 0055 of International Publication No. 2013/054918 can be used.

Examples of the compound (carbodiimide compound) containing a carbodiimide group in one molecule that can be used as a stabilizer include monocarbodiimide compounds, polycarbodiimide compounds, and cyclic carbodiimide compounds.
As the monocarbodiimide compound, dicyclohexylcarbodiimide, bis-2,6-diisopropylphenylcarbodiimide, and the like are preferable.
Moreover, as a polycarbodiimide compound, what was manufactured by the various method can be used. Conventional methods for producing polycarbodiimides (for example, U.S. Pat. No. 2,941,956, JP-B-47-33279, J.0rg.Chem.28, 2069-2075 (1963), Chemical Review 1981, Vol. 81 No. 1). 4, p619-621) can be used. Specifically, a carbodiimide compound described in Japanese Patent No. 4084953 can also be used.
Examples of the polycarbodiimide compound include poly (4,4′-dicyclohexylmethanecarbodiimide), poly (N, N′-di-2,6-diisopropylphenylcarbodiimide), poly (1,3,5-triisopropylphenylene-2, 4-carbodiimide and the like.
The cyclic carbodiimide compound can be synthesized based on the method described in JP2011-256337A.
As the carbodiimide compound, commercially available products may be used. For example, B2756 (trade name) manufactured by Tokyo Chemical Industry Co., Ltd., Carbodilite LA-1, manufactured by Nisshinbo Chemical Co., Ltd., Stabaxol P, Stabaxol P400, Stabaxol I (any Product name).

  As a compound (isocyanate compound) containing an isocyanate group in one molecule that can be used as a stabilizer, 3- (triethoxysilyl) propyl isocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4′-diphenylmethane diisocyanate, 2,4′-diphenylmethane diisocyanate, 2,2′-diphenylmethane diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, isophorone diisocyanate, and the like. It is done.

  As a compound (epoxy compound) containing an epoxy group in one molecule that can be used as a stabilizer, phenyl glycidyl ether, diethylene glycol diglycidyl ether, bisphenol A-diglycidyl ether, hydrogenated bisphenol A-diglycidyl ether, phenol novolak Type epoxy resin, cresol novolac type epoxy resin, epoxidized polybutadiene and the like.

Although the weight average molecular weight of the stabilizer is 200 to 60000 as described above, 200 to 30000 is more preferable, and 300 to 18000 is more preferable.
When the weight average molecular weight of the stabilizer is within the above range, the stabilizer is more easily moved, and the effect of improving the heat and moisture resistance is more effectively exhibited.
The weight average molecular weight of the stabilizer is particularly preferably 200 to 900. In addition, the weight average molecular weight 200-900 substantially corresponds with the number average molecular weight 200-900. Further, when the weight average molecular weight is 200 to 900, the molecular weight distribution may be 1.0. In this case, “weight average molecular weight 200 to 900” can be simply referred to as “molecular weight 200 to 900”. .

When the polymeric piezoelectric material contains a stabilizer, the polymeric piezoelectric material may contain only one kind of stabilizer or two or more kinds.
When the polymer piezoelectric material includes an optically active polymer and a stabilizer, the content of the stabilizer (the total content when there are two or more kinds; the same shall apply hereinafter) is 100 parts by mass of the optically active polymer. On the other hand, it is preferably 0.01 to 10 parts by mass, more preferably 0.01 to 5 parts by mass, still more preferably 0.1 to 3 parts by mass, It is particularly preferable that the amount is from 5 parts by mass to 2 parts by mass.
When the content is 0.01 parts by mass or more, the heat and humidity resistance is further improved.
Moreover, the transparency fall is suppressed more as the said content is 10 mass parts or less.

A preferred embodiment of the stabilizer is a stabilizer (S1) having one or more functional groups selected from the group consisting of a carbodiimide group, an epoxy group, and an isocyanate group, and having a number average molecular weight of 200 to 900. And a stabilizer (S2) having one or more functional groups selected from the group consisting of a carbodiimide group, an epoxy group, and an isocyanate group in one molecule, and having a weight average molecular weight of 1000 to 60000 The mode of using these together is mentioned. The weight average molecular weight of the stabilizer (S1) having a number average molecular weight of 200 to 900 is approximately 200 to 900, and the number average molecular weight and the weight average molecular weight of the stabilizer (S1) are almost the same value. .
When the stabilizer (S1) and the stabilizer (S2) are used in combination as the stabilizer, it is preferable that a large amount of the stabilizer (S1) is contained from the viewpoint of improving transparency.
Specifically, the stabilizer (S2) is preferably in the range of 10 parts by mass to 150 parts by mass with respect to 100 parts by mass of the stabilizer (S1), from the viewpoint of achieving both transparency and wet heat resistance. The range of 30 to 100 parts by mass is more preferable, and the range of 50 to 100 parts by mass is particularly preferable.

  Hereinafter, specific examples (stabilizers SS-1 to SS-3) of the stabilizer will be shown.

Hereinafter, about the stabilizer SS-1 to SS-3, a compound name, a commercial item, etc. are shown.
-Stabilizer SS-1 The compound name is bis-2,6-diisopropylphenylcarbodiimide. The weight average molecular weight (in this example, simply equal to “molecular weight”) is 363. Commercially available products include “Stabaxol I” manufactured by Rhein Chemie and “B2756” manufactured by Tokyo Chemical Industry.
-Stabilizer SS-2 The compound name is poly (4,4'-dicyclohexylmethanecarbodiimide). As a commercially available product, “Carbodilite LA-1” manufactured by Nisshinbo Chemical Co., Ltd. may be mentioned as having a weight average molecular weight of about 2000.
-Stabilizer SS-3 The compound name is poly (1,3,5-triisopropylphenylene-2,4-carbodiimide). As a commercially available product, “Stabaxol P” manufactured by Rhein Chemie Co., Ltd. can be mentioned as having a weight average molecular weight of about 3000. Further, “Stabaxol P400” manufactured by Rhein Chemie is listed as having a weight average molecular weight of 20,000.

(Antioxidant)
Moreover, the polymeric piezoelectric material of the present invention may contain an antioxidant. The antioxidant is at least one compound selected from the group consisting of hindered phenol compounds, hindered amine compounds, phosphite compounds, and thioether compounds.
Moreover, it is preferable to use a hindered phenol compound or a hindered amine compound as the antioxidant. Thereby, the polymeric piezoelectric material which is excellent also in heat-and-moisture resistance and transparency can be provided.

(Other ingredients)
The polymer piezoelectric material according to the present embodiment is a known resin typified by polyvinylidene fluoride, polyethylene resin or polystyrene resin, an inorganic filler such as silica, hydroxyapatite, and montmorillonite, as long as the effects of the present invention are not impaired. It may contain other components such as a known crystal nucleating agent such as phthalocyanine.
When the polymeric piezoelectric material includes a component other than the optically active polymer, the content of the component other than the optically active polymer is preferably 20% by mass or less based on the total mass of the polymeric piezoelectric material. % Or less is more preferable.
In addition, it is preferable that a polymeric piezoelectric material does not contain components other than the optically active polymer which has optical activity from a transparency viewpoint.

  The polymeric piezoelectric material of the present embodiment has the above-described optically active polymer (optically active polymer (B), optically active polymer (C) and optically active polymer (D) as long as the effects of the present invention are not impaired. An optically active polymer other than)) may be included.

<Method for producing polymer piezoelectric material>
As a method for producing the polymeric piezoelectric material of the present invention, a stereocomplex crystal containing an optically active polymer (A) having a weight average molecular weight of 50,000 to 1,000,000 and measured by a differential scanning calorimeter (DSC) The degree of conversion (S) can be adjusted to 6% to 85% (or 6% to 28%), and the homocrystallization degree obtained by the DSC method can be adjusted to 5% to 80% (or 20% to 80%). stress at 25 ° C. - not particularly limited as long as it is a method that the piezoelectric constant d ₁₄ measured by the charge process can be adjusted to more than 1 pC / N.
As this method, for example, crystallization and stretching (any of which may be the first) are performed on an amorphous film containing the optically active polymer described above, and the crystallization and stretching It is possible to use a method of adjusting each of these conditions.
Here, “crystallization” is a concept including preliminary crystallization described later and annealing treatment described later.

  The amorphous film refers to a film obtained by heating a mixture containing the optically active polymer (A) to a temperature equal to or higher than the melting point Tm of the optically active polymer (A) and then rapidly cooling it. . An example of the rapid cooling temperature is 50 ° C.

  The method for producing a stereocomplex crystal by crystallizing the optically active polymer (A) is not particularly limited. For example, i) a method of casting a solution by dissolving the optically active polymer (A) in a solvent. Ii) a method of crystallizing by slowly cooling from a molten state to near room temperature by heat, iii) a method of cooling from a molten state by heat to a predetermined temperature and crystallizing at that temperature, and iv) from a molten state by heat to room temperature A method of cooling to the vicinity, then raising the temperature to a predetermined temperature and crystallizing at that temperature, and v) a method of generating an oriented crystal by stretching the optically active polymer (A) in an amorphous state or a pre-crystallized state. Etc.

In the method for producing a polymeric piezoelectric material of the present invention, an optically active polymer (optically active polymer (B), optically active polymer (C), A mixture of an optically active polymer (D) or the like, or a mixture of an optically active polymer and at least one of a stabilizer, an antioxidant and other components may be used.
The above mixture is preferably a mixture obtained by melt-kneading.
For example, the optically active polymer to be mixed (with a stabilizer, antioxidant, and other components as necessary) is used with a melt kneader (Toyo Seiki Seisakusho, Lab Plast Mixer), and the mixer rotation speed An optically active polymer blend can be obtained by melt-kneading for 5 to 20 minutes under the conditions of 30 to 70 rpm and 180 to 270 ° C.

  Hereinafter, although the embodiment of the manufacturing method of the polymeric piezoelectric material of the present invention will be described, the method of manufacturing the polymeric piezoelectric material of the present invention is not limited to the following embodiment.

  The polymer piezoelectric material manufacturing method of the present embodiment includes, for example, a first step of obtaining a precrystallized film containing the optically active polymer (A), and stretching the precrystallized film mainly in a uniaxial direction ( A second step) which may be performed in the direction different from the stretching direction simultaneously or sequentially while stretching mainly in a uniaxial direction.

In general, increasing the force applied to the film during stretching promotes the orientation of the optically active polymer and increases the piezoelectric constant, while crystallization progresses and the crystal size increases, so that the internal haze increases. There is a tendency. If force is simply applied to the film, crystals that are not oriented like spherulites are formed. A crystal having a low orientation such as a spherulite increases the internal haze, but hardly contributes to an increase in piezoelectric constant.
Therefore, in order to form a film having a high piezoelectric constant and a low internal haze, it is preferable to efficiently form oriented crystals that contribute to the piezoelectric constant with a minute size that does not increase the internal haze.

From the above point, for example, after preparing the pre-crystallized film in which the inside of the film is pre-crystallized to form fine crystals (microcrystals) before stretching, the pre-crystallized film is stretched, thereby The stretching force can be efficiently applied to the polymer portion having low crystallinity between the microcrystals in the crystallized film. Thereby, the optically active polymer can be efficiently oriented in the main stretching direction.
Specifically, by stretching the pre-crystallized film, finely oriented crystals are generated in the polymer portion having low crystallinity between the microcrystals and at the same time generated by pre-crystallization. The spherulites are broken, and the lamellar crystals constituting the spherulites are oriented in the stretching direction in a daisy chain connected to the tie molecular chain.
Therefore, by stretching the pre-crystallized film, a film having a low internal haze can be obtained without greatly reducing the piezoelectric constant. Furthermore, a polymer piezoelectric material having excellent dimensional stability can be obtained by adjusting the manufacturing conditions.

[First step (pre-crystallization step)]
The first step in the present embodiment is a step of obtaining a pre-crystallized film by heating an amorphous film containing the optically active polymer (A). The amorphous film containing the optically active polymer (A) may contain a stabilizer, an antioxidant, and at least one of other components (for example, a stabilizer).

  Specifically, as the treatment through the first step and the second step in the present embodiment, 1) a film in an amorphous state is heat-treated to obtain a pre-crystallized film (the first step). The pre-crystallized film thus obtained may be set in a drawing apparatus and then drawn (second step) (off-line processing), or 2) an amorphous film is set in a drawing apparatus. The pre-crystallized film is heated by a stretching device (above, the first step), and the obtained pre-crystallized film is continuously stretched by the stretching device (the second step). It is good (inline processing).

In the first step, the heating temperature T for pre-crystallizing the amorphous film containing the optically active polymer (A) is not particularly limited, but the piezoelectricity and transparency of the polymer piezoelectric material to be produced, etc. In terms of increasing, it is preferable that the temperature is set so that the glass transition temperature Tg of the optically active polymer (A) and the following formula are satisfied, and the homocrystallization degree is 1% to 20%.
Tg−40 ° C. ≦ T ≦ Tg + 40 ° C.
(Tg represents the glass transition temperature of the optically active polymer (A).)

  The glass transition temperature Tg [° C.] of the optically active polymer (A) and the melting point Tm [° C.] of the optically active polymer (A) described above are determined using the differential scanning calorimeter (DSC). For the optically active polymer (A), the glass transition temperature (Tg) obtained as the inflection point of the curve and the endothermic reaction from the melting endothermic curve when the temperature is increased at a temperature rising rate of 10 ° C./min. It is temperature (Tm) confirmed as a peak value of.

  In the first step, the heat treatment time for pre-crystallization satisfies the desired degree of homocrystallinity, and preferably the normalized molecular orientation MORc of the polymer piezoelectric material after stretching (after the second step) and The product of the polymer piezoelectric material after stretching with the homocrystallization degree is preferably 25 to 700, more preferably 75 to 600, still more preferably 100 to 500, particularly preferably 150 to 300, and most preferably 160 to 210. It may be adjusted so that As the heat treatment time becomes longer, the degree of homocrystallization after stretching increases, and the normalized molecular orientation MORc after stretching also increases. When the heat treatment time is shortened, the homocrystallinity after stretching is also lowered, and the normalized molecular orientation MORc after stretching is also lowered.

  If the degree of homocrystallization of the pre-crystallized film before stretching increases, the film becomes harder and a greater stretching stress is applied to the film, so that the portion with relatively low crystallinity in the film also becomes more oriented, and after stretching It is considered that the normalized molecular orientation MORc is also increased. Conversely, when the pre-crystallized film before stretching has a low degree of homocrystallinity, the film becomes soft and stretching stress is less likely to be applied to the film, so the portion with relatively low crystallinity in the film is also weakly oriented. Thus, the normalized molecular orientation MORc after stretching is also considered to be low.

  The heat treatment time varies depending on the kind or amount of the heat treatment temperature, the thickness of the film, the molecular weight of the resin constituting the film, the additive, and the like. In addition, the substantial heat treatment time for crystallizing the film is preheating at a temperature at which the amorphous film is crystallized in the preheating that may be performed before the stretching step (second step) described below. This corresponds to the sum of the preheating time and the heat treatment time in the precrystallization step before preheating.

  The heat treatment time for the amorphous film is preferably 5 seconds to 60 minutes, and more preferably 1 minute to 30 minutes from the viewpoint of stabilizing the production conditions. For example, when pre-crystallizing an amorphous film containing a polylactic acid resin as the optically active polymer (A), it is heated at 20 ° C. to 170 ° C. for 5 seconds to 60 minutes (preferably 1 minute to 30 minutes). It is preferable to do.

In this embodiment, in order to efficiently impart piezoelectricity and transparency to the stretched film, it is preferable to adjust the homocrystallization degree of the pre-crystallized film before stretching.
In other words, the reason why the piezoelectricity and the like are improved by stretching is that the spherulite is presumed to be in a spherulitic state. Orientation improves the piezoelectricity (piezoelectric constant d ₁₄ ), while stretching stress is applied to a portion having a relatively low crystallinity via the spherulite, and the orientation of this relatively low portion is promoted, and the piezoelectricity (piezoelectricity) This is because the constant d ₁₄ ) is considered to be improved.

  The homocrystallinity of the stretched film is set to be 5% to 80% (or 20% to 80%), preferably 25% to 60%, more preferably 30% to 50%, More preferably, it is set to be 30% to 40%. Therefore, the homocrystallization degree immediately before stretching of the pre-crystallized film is set to be 1% to 20%, preferably 2% to 10%. What is necessary is just to perform the homocrystallization degree of a pre-crystallized film similarly to the measurement of the homocrystallization degree of the polymeric piezoelectric material after extending | stretching.

  The thickness of the pre-crystallized film is mainly determined by the thickness of the polymeric piezoelectric material to be obtained by stretching in the second step and the stretching ratio, but is preferably 50 μm to 1000 μm, more preferably about 200 μm to 800 μm. It is.

[Second step (stretching step)]
The stretching method in the second step (stretching step) is not particularly limited. However, the stretching method for forming oriented crystals (also referred to as main stretching), or stretching for forming oriented crystals, A method in which stretching performed in a direction crossing the stretching direction is combined. A polymer piezoelectric material having a large principal surface area can also be obtained by stretching the polymer piezoelectric material.

As for the area of the main surface in the present embodiment, the area of the main surface of the polymeric piezoelectric material is preferably 5 mm ² or more, and more preferably 10 mm ² or more.

By stretching the polymer piezoelectric material mainly in one direction, the molecular chain of polylactic acid polymer contained in the polymer piezoelectric material can be oriented in one direction and aligned with high density, which is higher It is estimated that piezoelectricity can be obtained.
Here, it has been known that a polylactic acid stereocomplex biaxially stretched film having no piezoelectricity has high transparency. It was clarified that when a stereocomplex crystal was formed in the polymer piezoelectric material, haze was lowered. Although the cause of this is not clear, it is considered that a stereo complex having a high crystallization speed preferentially crystallizes when oriented in one direction, and voids are generated around it.
Therefore, higher piezoelectricity and transparency can be obtained by stretching the polymer piezoelectric material mainly in one direction, and higher heat resistance can be obtained by forming a stereocomplex crystal in the polymer piezoelectric material. It is done.

In the stretching step, the stretching ratio of the main stretching is preferably 2 to 8 times, more preferably 3 to
The pre-crystallized film may be stretched so as to be 5 times, more preferably 3 to 4 times.

In the stretching process, when stretching (main stretching) for enhancing piezoelectricity, the pre-crystallized film is stretched simultaneously or sequentially in a direction intersecting with the main stretching direction (also called secondary stretching). You may say).
Here, “sequential stretching” refers to a stretching method in which stretching is performed in a uniaxial direction and then stretching in a direction intersecting with the stretching direction.
When secondary stretching is performed in the stretching step, the stretching ratio of the secondary stretching is preferably 1 to 3 times, more preferably 1.1 to 2.5 times, and 1.2 to 2.0. Double is more preferred.

  In the stretching step, the polymer piezoelectric material is stretched mainly in one direction, so that the stereocomplex crystallization ratio (S) of the polymer piezoelectric material of the present invention is 6% to 85% (or 6% to 28%). Or it can adjust to the above-mentioned preferable range.

  The stretching speed is not particularly limited, but usually, the main stretching speed and the secondary stretching speed are adjusted according to the stretching ratio. The stretching speed may be set to a speed usually used, and is not particularly limited, but is often adjusted to a speed at which the film does not break during stretching.

  The stretching temperature of the polymeric piezoelectric material is preferably in the temperature range of about 10 ° C. to 20 ° C. higher than the glass transition temperature of the polymeric piezoelectric material when the polymeric piezoelectric material is stretched only by tensile force.

When the pre-crystallized film is stretched, preheating may be performed to facilitate stretching of the film immediately before stretching.
This preheating is generally performed in order to soften the film before stretching and make it easy to stretch. Therefore, the preheating is performed under the condition that the film before stretching is not crystallized and hardened. It is normal.
However, as described above, in the present embodiment, since pre-crystallization is performed before stretching, the pre-heating may be performed together with pre-crystallization. Specifically, preheating and precrystallization can be performed by performing preheating at a temperature higher or longer than the normal temperature in accordance with the heating temperature and heat treatment time in the precrystallization step described above.

[Annealing process]
From the viewpoint of improving the piezoelectric constant, it is preferable that the polymer piezoelectric material after the stretching treatment is subjected to a certain heat treatment (hereinafter also referred to as “annealing treatment”). The temperature of the annealing treatment is preferably about 80 ° C to 160 ° C, and more preferably 100 ° C to 155 ° C.
The temperature application method for the annealing treatment is not particularly limited, and examples thereof include a method of directly heating using a hot air heater or an infrared heater, a method of immersing the polymer piezoelectric material in a liquid such as heated silicon oil, and the like. At this time, when the polymer piezoelectric material is deformed by linear expansion, it is difficult to obtain a practically flat material. Therefore, a certain tensile stress (for example, 0.01 MPa to 100 MPa) is applied to the polymer piezoelectric material, It is preferable to apply temperature while preventing the piezoelectric polymer material from sagging.

  The temperature application time for the annealing treatment is preferably 1 second to 60 minutes, more preferably 1 second to 300 seconds, and even more preferably heating in the range of 1 second to 60 seconds. By annealing for 60 minutes or less, it is possible to suppress a decrease in the degree of orientation caused by the growth of spherulites from the molecular chains of the amorphous portion at a temperature higher than the glass transition temperature of the polymeric piezoelectric material. As a result, a decrease in piezoelectricity can be suppressed.

The polymeric piezoelectric material annealed as described above is preferably cooled rapidly after the annealing treatment.
In the annealing process, “rapidly cool” means that the annealed polymer piezoelectric material is immersed in, for example, ice water immediately after the annealing process and cooled to at least the glass transition temperature Tg or less. It means that no other treatment is included in the dipping time.

The rapid cooling method includes a method of immersing the annealed polymer piezoelectric material in a coolant such as ethanol, methanol, or liquid nitrogen containing water, ice water, ethanol, or dry ice, or by spraying a liquid spray with a low vapor pressure to evaporate. The method of cooling by latent heat is mentioned.
To continuously cool the polymer piezoelectric material, it is possible to rapidly cool the polymer piezoelectric material by bringing it into contact with a metal roll controlled to a temperature not higher than the glass transition temperature Tg of the polymer piezoelectric material. It is. Further, the number of times of cooling may be only once, or may be two or more. Furthermore, annealing and cooling can be alternately repeated. In addition, when the annealing is performed on the polymer piezoelectric material that has been subjected to the above-described stretching treatment, the polymer piezoelectric material after the annealing may shrink as compared to before the annealing.

<Applications of polymeric piezoelectric materials>
The polymer piezoelectric material of the present invention is a speaker, headphones, touch panel, remote controller, microphone, underwater microphone, ultrasonic transducer, ultrasonic applied measuring instrument, piezoelectric vibrator, mechanical filter, piezoelectric transformer, delay device, sensor, acceleration. Sensor, Shock sensor, Vibration sensor, Pressure sensor, Tactile sensor, Electric field sensor, Sound pressure sensor, Display, Fan, Pump, Variable focus mirror, Sound insulation material, Sound insulation material, Keyboard, Sound device, Information processing machine, Measuring device, The polymer piezoelectric material of the present invention can be used particularly in the field of various sensors because it can be used in various fields such as medical equipment and can maintain high sensor sensitivity when used in a device. preferable.
The polymeric piezoelectric material of the present invention can also be used as a touch panel combined with a display device. As the display device, for example, a liquid crystal panel, an organic EL panel, or the like can be used.
Moreover, the polymeric piezoelectric material of this invention can also be used in combination with the touch panel (position detection member) of another system as a pressure sensor. Examples of the detection method of the position detection member include an anti-film method, a capacitance method, a surface acoustic wave method, an infrared method, and an optical method.

  At this time, the polymeric piezoelectric material of the present invention is preferably used as a piezoelectric element having at least two surfaces and electrodes provided on the surfaces. The electrodes only need to be provided on at least two surfaces of the polymeric piezoelectric material. Although it does not restrict | limit especially as said electrode, For example, ITO, ZnO, IZO (trademark), IGZO, a conductive polymer, silver nanowire, a metal mesh etc. are used.

  Further, the polymer piezoelectric material of the present invention and an electrode can be repeatedly stacked and used as a laminated piezoelectric element. As an example, a unit in which an electrode and a polymer piezoelectric material are repeatedly stacked, and the main surface of the polymer piezoelectric material that is not covered with an electrode is covered with an electrode. Specifically, the unit having two repetitions is a laminated piezoelectric element in which electrodes, polymer piezoelectric material, electrodes, polymer piezoelectric material, and electrodes are stacked in this order. Of the polymer piezoelectric materials used in the laminated piezoelectric element, one layer of the polymer piezoelectric material may be the polymer piezoelectric material of the present invention, and the other layers may not be the polymer piezoelectric material of the present invention.

  For example, when the optically active polymer (A) is a polymer obtained by mixing the optically active polymer (B) and the optically active polymer (C), the mass ratio (B / C) of the optically active polymer is 10 The polymer piezoelectric material of the present invention (first polymer piezoelectric material) of / 90 to 35/65 has a mass ratio (B / C) of 10/90 to 35/65 through the electrode. When laminated with a molecular piezoelectric material (second polymer piezoelectric material), the uniaxial stretching direction (main stretching direction) of the first polymer piezoelectric material is changed to the uniaxial stretching direction (main stretching) of the second polymer piezoelectric material. The direction of displacement of the first and second polymer piezoelectric materials can be made uniform, and the piezoelectricity of the entire laminated piezoelectric element is increased.

  On the other hand, when the mass ratio (B / C) of the optically active polymer is 10/90 to 35/65, the polymer piezoelectric material of the present invention (first polymer piezoelectric material) has a mass ratio (B / C) via an electrode. When laminated with the polymeric piezoelectric material (third polymeric piezoelectric material) of the present invention in which C) is 90/10 to 65/35, the uniaxial stretching direction (main stretching direction) of the first polymeric piezoelectric material Are arranged so as to be substantially parallel to the uniaxial stretching direction (main stretching direction) of the third polymeric piezoelectric material, the displacement directions of the first polymeric piezoelectric material and the third polymeric piezoelectric material can be aligned. This is preferable because the piezoelectricity of the entire laminated piezoelectric element is enhanced.

  In particular, when an electrode is provided on the main surface of the polymeric piezoelectric material, it is preferable to provide a transparent electrode. Here, the transparency of the electrode specifically means that the internal haze is 40% or less and the total light transmittance is 60% or more.

  The piezoelectric element using the polymeric piezoelectric material of the present invention can be applied to the above-described various piezoelectric devices such as speakers and touch panels. In particular, a piezoelectric element provided with a transparent electrode is suitable for application to a speaker, a touch panel, an actuator, and the like.

Hereinafter, the embodiment of the present invention will be described more specifically by way of examples. However, the present embodiment is not limited to the following examples unless it exceeds the gist of the present invention.
In this example, PLLA is an optically active polymer having an L-lactic acid component (L-form component) of 90 mol% or more, and PDLA is an optical activity having a D-lactic acid component (D-form component) of 90 mol% or more. It is a polymer.

[Example 1]
PLLA (product name: Ingeo ^™ biopolymer, brand: 4032D, Mw = 200,000, Mw / Mn = 1.87, L-lactic acid component 98.5%) 90 parts by mass and Purec PDLA (Purac Technical High) IV Garade, Mw = 150,000, Mw / Mn = 1.94, D-lactic acid component 99.5%) with respect to 10 parts by mass, stabilizer [Stabaxol I (70 parts by mass) manufactured by Rhein Chemie, and Nisshinbo Chemical Co., Ltd. Mixture of Carbodilite LA-1 (30 parts by mass) manufactured by the company] 1.0 part by mass was added and dry blended to prepare a raw material.
The prepared raw material was put into an extrusion molding machine hopper, extruded from a T die while being heated to 240 ° C., and contacted with a cast roll at 50 ° C. for 0.3 minutes to form a pre-crystallized film having a thickness of 150 μm ( Pre-crystallization step). The homocrystallization degree of the pre-crystallized film was measured and found to be 6%.
The obtained pre-crystallized film was stretched at a stretching speed of 10 m / min by roll-to-roll while heating to 70 ° C., and uniaxially stretched in the MD direction up to 3.5 times (stretching step). The thickness of the obtained film was 49.2 μm.
Thereafter, the uniaxially stretched film is annealed by roll-to-roll on a roll heated to 145 ° C. for 15 seconds, and then rapidly cooled to produce a crystalline polymer piezoelectric material (polymer piezoelectric material). (Annealing process).

[Examples 2 and 3]
Polymeric piezoelectric materials of Examples 2 and 3 were produced in the same manner as in Example 1 except that PLLA manufactured by NatureWorks LLC and PDLA manufactured by Purac were mixed at a mass ratio shown in Table 1.

Example 4
A polymer piezoelectric material of Example 4 was produced in the same manner as in Example 1 except that PDLA manufactured by Purac was changed to PDLA produced in Production Example 1 below.

<Production Example 1>
First, D-lactide manufactured by Purac was hydrolyzed, and a raw material containing 99.5 mol% or more of lactic acid (raw material containing 90% by mass of lactic acid) was prepared. 500 parts by mass of this raw material and 1.18 parts by mass of a reagent tin (II) chloride dihydrate (manufactured by Wako Pure Chemical Industries, Ltd.) were charged into a round bottom flask equipped with a Dean-Stark trap. After replacing the inside of the round bottom flask with nitrogen, the temperature was raised to 130 ° C. with an oil bath heated to 150 ° C. under normal pressure and nitrogen atmosphere. The inside of the flask was gradually depressurized and held at 50 mmHg for 2 hours. Next, after releasing the pressure in the flask to normal pressure, 40 parts by mass of xylene was added to the flask. The Dean Stark trap was then replaced with a Dean Stark trap filled with xylene. Next, the oil bath temperature was raised to 180 ° C., the pressure in the flask was reduced to 500 mmHg, and the reaction solution temperature was maintained at 150 ° C. for 20 hours, and transparent PDLA was obtained. When GPC measurement was performed on the obtained PDLA, the weight average molecular weight (Mw) was 30000. The obtained PDLA is an optically active polymer having a D-lactic acid component (D-form component) of 99.5 mol% or more.

[Comparative Examples 1-4]
Next, polymeric piezoelectric materials of Comparative Examples 1 to 4 were prepared in the same manner as in Example 1 except that PLLA manufactured by NatureWorks LLC and PDLA manufactured by Purac were mixed at a mass ratio shown in Table 1.

<Production Example 2>
500 g (5.0 mol) of 90 mass% L-lactic acid (L-form 99.5 mol% lactic acid) manufactured by Purac and 1.18 g of reagent tin (II) chloride dihydrate (manufactured by Wako Pure Chemical Industries, Ltd.) (0.005 mol) was charged into a 1000 ml round bottom flask equipped with a Dean-Stark trap. After replacing the inside of the round bottom flask with nitrogen, the temperature was raised to 130 ° C. with an oil bath heated to 150 ° C. under normal pressure and nitrogen atmosphere. The inside of the round bottom flask was gradually depressurized and maintained at 50 mmHg for 2 hours. Next, after releasing the inside of the round bottom flask to normal pressure, 40 g of xylene was added into the round bottom flask. The Dean Stark trap was then replaced with a Dean Stark trap filled with xylene. Next, the oil bath temperature was raised to 180 ° C., the inside of the round bottom flask was decompressed to 500 mmHg, and the reaction solution temperature was maintained at 150 ° C. for 20 hours to obtain a transparent PLLA. When GPC measurement was performed on the obtained PLLA, the weight average molecular weight (Mw) was 20000.
Furthermore, 6.55 g (0.065 mol) of succinic anhydride was added to the round bottom flask and stirred at an oil bath temperature of 150 ° C. for 2 hours to convert the terminal hydroxyl group of the PLLA into a carboxyl group. Thereafter, the inside of the round bottom flask was released to normal pressure, 300 g of xylene was added for dilution, and the resulting solution was extracted, and the xylene was air-dried under a nitrogen stream. The solid after air drying was washed twice with 1.0 L of 2-propanol containing 1% by mass of 35% by mass hydrochloric acid, filtered, and then the filtered solid was further washed several times with methanol to 50 ° C. And dried under reduced pressure to obtain 340 g of white PLLA [PLLA (1)]. When GPC measurement was performed on the PLLA (1), the weight average molecular weight (Mw) was 20000.

<Production Example 3>
The same as Production Example 1-1 except that 90% by mass L-lactic acid was changed to 90% by mass D-lactic acid (hydrolyzed D-lactide manufactured by Purac, lactic acid having a D-form of 99.9 mol% or more). PDLA [PDLA (1)] was obtained. When GPC measurement was performed on the PDLA (1), the weight average molecular weight (Mw) was 20000.

<Production Example 4>
A 1000 ml round bottom flask was charged with 75 g PLLA (1) synthesized in Production Example 2, 75 g PDLA (1) synthesized in Production Example 3 and 120 mg (0.2 mmol) magnesium stearate. After replacing the inside of the round bottom flask with nitrogen, 150 g of tetralin was inserted, and the temperature was raised to 210 ° C. under normal pressure and nitrogen atmosphere. Next, 4.86 g of hexamethylene diisocyanate (28.9 mmol, 1.05 equivalent of isocyanate group based on the number of terminal functional groups of PLLA (1) and PDLA (1)) was added to the round bottom flask, and 1 at 200 ° C. Reacted for hours. After adding 750 mg of PEP-36 (manufactured by ADEKA) and 750 mg of Irganox 1010 (manufactured by Ciba Specialty Chemicals), 1000 g of tetralin was added, the solution was cooled, the precipitate was filtered and dried to obtain a white powder resin (polylactic acid type) 150 g of polymer) was obtained. The weight average molecular weight of the obtained resin was measured and found to be 200,000. The obtained resin is stereoblock polylactic acid (sb-PLA) in which 5 units of PLLA and PDLA having an Mw of 20000 are connected. The stereoblock polylactic acid obtained in this production example is polylactic acid (L-form component / D-form component = 50/50) containing 50 mol% of the L-form component and 50 mol% of the D-form component.

Example 5
A polymer piezoelectric material of Example 5 was produced in the same manner as in Example 1, except that Purac's PDLA was changed to sb-PLA produced in Production Example 4.
When calculating the L-form ratio and D-form ratio in Table 2, the L-form component was 100% for the mixed PLLA, and the L-form component was 50 mol% and the D-form component was 50 mol% for sb-PLA. (The same applies to Examples 6 to 8 and Comparative Example 5).

Example 6
A polymer piezoelectric material of Example 6 was produced in the same manner as in Example 2 except that PDAC manufactured by Purac was changed to sb-PLA produced in Production Example 4 above.

[Examples 7 and 8]
In Example 5, the polymeric piezoelectric materials of Examples 7 and 8 were produced in the same manner except that PLLA made by NatureWorks LLC and sb-PLA produced in Production Example 4 were mixed at a mass ratio shown in Table 2. did.

[Comparative Example 5]
The polymer piezoelectric material of Comparative Example 5 was prepared in the same manner as in Example 5 except that only sb-PLA produced in Production Example 4 was used as a polylactic acid polymer without mixing PLLA manufactured by NatureWorks LLC. The material was made.

<Measurement and evaluation of physical properties>
For the polymeric piezoelectric materials of Examples 1 to 8 and Comparative Examples 1 to 5 obtained as described above, the piezoelectric constant, internal haze, homocrystallinity, stereocomplex crystallization rate, MORc, and tear strength, respectively. (Examples 1 and 4), azimuth axis standard deviation and MD shrinkage after heat treatment were measured and calculated, and thermal deformation was evaluated. In addition, the weight average molecular weight (Mw) of PLLA, PDLA, and sb-PLA used in Examples 1-8 and Comparative Examples 1-5 was measured by the above-mentioned GPC measuring method.
The evaluation results are shown in Tables 1 and 2.
Specifically, the measurement was performed as follows.

- piezoelectric constant _{d 14} (stress - charge method) -
The piezoelectric constant (specifically, the piezoelectric constant d ₁₄ (stress-charge method)) of the polymer piezoelectric material was measured according to the above-described “example of method for measuring the piezoelectric constant d ₁₄ by the stress-charge method”.

-Internal haze-
The “internal haze” in the present application refers to the internal haze of the polymeric piezoelectric material of the present invention, and is measured by the following method.
Specifically, the internal haze (hereinafter also referred to as internal haze (H1)) of each polymer piezoelectric material of Examples and Comparative Examples was measured by measuring light transmittance in the thickness direction. More specifically, haze (H2) is measured in advance by sandwiching only silicon oil (Shin-Etsu Silicone (trademark) manufactured by Shin-Etsu Chemical Co., Ltd., model number: KF96-100CS) between two glass plates. The film-like polymer piezoelectric material whose surface was uniformly coated with 2 was sandwiched between two glass plates, the haze (H3) was measured, and the difference between these examples was taken as in the following formula. The internal haze (H1) of each polymeric piezoelectric material was obtained.
Internal haze (H1) = Haze (H3) -Haze (H2)

The haze (H2) and haze (H3) in the above formula were measured by measuring the light transmittance in the thickness direction using the following apparatus under the following measurement conditions.
Measuring device: manufactured by Tokyo Denshoku Co., Ltd., HAZE METER TC-HIIIDPK
Sample size: 30mm width x 30mm length
Measurement conditions: Conforms to JIS-K7105 Measurement temperature: Room temperature (25 ° C.)

-Homocrystallinity and stereocomplex crystallinity-
Each of the polymeric piezoelectric materials of Examples and Comparative Examples is accurately weighed in an amount of 10 mg, and a differential scanning calorimeter (DSC-1 manufactured by Perkin Elmer Co.) is used, and the heating rate is 10 ° C./min. The temperature was raised to 250 ° C., and the crystal melting temperature (Tmh), (Tmsc), the heat of crystal melting (ΔHmh), and (ΔHmsc) were measured.
The homocrystallinity (Xc) and stereocomplex crystallization rate (S) are based on the following formula based on the low-temperature phase crystal heat of fusion (ΔHmh) below 190 ° C. and the high-temperature phase crystal heat of fusion (ΔHmsc) above 190 ° C. Respectively.
Homo crystallinity (%) = ΔHmh / 93 × 100
Stereo complex crystallization rate (%) = ΔHmsc / (ΔHmh + ΔHmsc) × 100

-Standardized molecular orientation MORc-
About each polymeric piezoelectric material of an Example and a comparative example, normalized molecular orientation MORc was measured by Oji Scientific Instruments Co., Ltd. microwave system molecular orientation meter MOA-6000. The reference thickness tc was set to 50 μm.
Moreover, the product of the normalized molecular orientation MORc and the stereocomplex crystallization rate (S) was calculated.

-Tear strength-
About each polymeric piezoelectric material of an Example and a comparative example, based on the test method "right-angled tear method" described in "Plastic film and sheet tear strength" of JIS K 7128-3, tear strength in MD direction Was measured.
In the measurement of tear strength, the crosshead speed of the tensile tester was 200 mm per minute.
The tear strength (T) was calculated from the following equation.
T = F / d
In the above formula, T represents the tear strength (N / mm), F represents the maximum tear load, and d represents the thickness (mm) of the test piece.

-Thermal deformation-
A sample having a length in the MD direction of 50 mm and a length in the TD direction of 50 mm was cut out from each polymeric piezoelectric material of the example and the comparative example. The cut sample was placed on a Teflon (registered trademark) sheet, placed in an oven at 150 ° C., and heat-treated for 30 minutes. The sample after heat treatment was slowly cooled, and this sample was visually observed, and deformation due to heat treatment was evaluated according to the following criteria.
A: No change in sample shape before and after heat treatment B: Part of sample deformed after heat treatment compared to before heat treatment and slight swell occurred C: Whole sample deformed greatly after heat treatment compared to before heat treatment, Swelling occurred

-Azimuth axis standard deviation after heat treatment-
About each polymeric piezoelectric material of an Example and a comparative example, the azimuth-axis standard deviation after heat processing was computed on the following test conditions and methods.
First, a sample having a length in the MD direction of 50 mm and a length in the TD direction of 50 mm was cut out from each polymer piezoelectric material of the example and the comparative example. The cut sample was placed on a Teflon (registered trademark) sheet, placed in an oven at 150 ° C., and heat-treated for 30 minutes. Using the birefringence evaluation system WPA-100 manufactured by Photonic Lattice, the phase difference information (phase difference value and azimuth axis) was obtained in a 50 mm × 50 mm range with a resolution of 0.14 mm. With respect to the obtained information, 357 azimuth axis values were extracted from the MD position 25 mm TD position 0 mm to the MD position 25 mm TD position 50 mm, and the azimuth axis standard deviation (the azimuth axis standard deviation after heat treatment) was calculated. The greater the azimuth standard deviation after heat treatment, the greater the disorder of sample orientation due to heat treatment.

-MD contraction-
About each polymeric piezoelectric material of the Example and the comparative example, MD shrinkage was computed on condition of the following.
First, a sample having a length in the MD direction of 50 mm and a length in the TD direction of 50 mm was cut out from each polymer piezoelectric material of the example and the comparative example. The cut sample was marked with two marks in the MD direction at intervals of 5 mm (interval a), then placed on a Teflon (registered trademark) sheet, placed in an oven at 150 ° C., and subjected to heat treatment for 30 minutes (none load). The sample after the heat treatment was gradually cooled, and the distance between the two marks on the sample (interval b) was measured. From the interval a and the interval b, the MD shrinkage (MD thermal shrinkage rate) at 150 ° C. of each sample was calculated by the following formula.
MD heat shrinkage rate (%) = ((interval a−interval b) / interval a) × 100

About each polymeric piezoelectric material of Examples 1-4, piezoelectricity was able to be maintained and it was excellent in heat resistance and transparency.
More specifically, each polymer piezoelectric material of Examples 1 to 4 was superior in piezoelectricity and transparency as compared to each polymer piezoelectric material of Comparative Examples 3 and 4. Moreover, each polymeric piezoelectric material of Examples 1-4 was excellent in heat resistance compared with each polymeric piezoelectric material of Comparative Examples 1 and 2.

About each polymeric piezoelectric material of Examples 5-8, coexistence with maintenance of piezoelectricity and the outstanding heat resistance and transparency was possible.
On the other hand, the polymer piezoelectric material of Comparative Example 5 could not ensure the piezoelectricity.

Claims (16)

Including an optically active polymer (A) having a weight average molecular weight of 50,000 to 1,000,000,
The stereocomplex crystallization ratio (S) represented by the following formula (X), measured with a differential scanning calorimeter (DSC), is 6% to 85%,
The homocrystallinity obtained by DSC method is 5% to 80%,
Stress at 25 ° C. - polymeric piezoelectric material the piezoelectric constant _{d 14} is 1 pC / N or more as measured by a charge method.
S = {ΔHmsc / (ΔHmsc + ΔHmh)} × 100 (X)
(In the formula, ΔHmh represents the melting enthalpy of the low melting point melting peak having a crystal melting peak temperature of less than 190 ° C. by DSC measurement, and ΔHmsc is the high melting point melting peak having a crystal melting peak temperature of 190 ° C. or more by DSC measurement. Represents the melting enthalpy of   2. The polymeric piezoelectric material according to claim 1, wherein the stereocomplex crystallization ratio (S) is 6% to 28%, and the homocrystallization degree is 20% to 80%.   3. The polymeric piezoelectric material according to claim 1, wherein the optically active polymer (A) contains 65 mol% or more of an L-form component or 65 mol% or more of a D-form component as a structural unit.   The optically active polymer (A) includes an optically active polymer (B) having an L-form component of 90 mol% or more, an optically active polymer (C) having a D-form component of 90 mol% or more, and an L-form component and A polymer comprising at least one selected from the group consisting of optically active polymers (D) which are stereoblock copolymers each having a D-form component of more than 10 mol% and less than 90 mol%. 4. The polymeric piezoelectric material according to any one of 3 above.   The weight average molecular weight of the optically active polymer (B), the weight average molecular weight of the optically active polymer (C), and the weight average molecular weight of the optically active polymer (D) are 50,000 to 1,000,000, respectively. 4. The polymeric piezoelectric material according to 4.   The polymeric piezoelectric material according to any one of claims 1 to 5, wherein an internal haze with respect to visible light is 4.0% or less.   The polymeric piezoelectric material according to any one of claims 1 to 6, wherein an internal haze with respect to visible light is 2.0% or less.   The product of the normalized molecular orientation MORc and the homocrystallinity when the reference thickness measured with a microwave transmission type molecular orientation meter is 50 μm is 25 to 700. 2. The polymeric piezoelectric material according to claim 1. The optically active polymer (A) is a polylactic acid polymer having a main chain including a repeating unit represented by the following structural formula (1). High molecular piezoelectric material.

  The polymeric piezoelectric material according to any one of claims 1 to 9, wherein the content of the optically active polymer (A) is 80% by mass or more.   The polymeric piezoelectric material according to any one of claims 1 to 10, wherein an internal haze with respect to visible light is 1.0% or less.   A stabilizer having a weight average molecular weight of 200 to 60,000 having at least one functional group selected from the group consisting of a carbodiimide group, an epoxy group, and an isocyanate group, and 100 parts by mass of the optically active polymer (A) The polymeric piezoelectric material according to claim 1, wherein the stabilizer is contained in an amount of 0.01 to 10 parts by mass.   The polymeric piezoelectric material according to claim 12, wherein the stabilizer has at least one functional group selected from the group consisting of a carbodiimide group, an epoxy group, and an isocyanate group in one molecule. A method for producing the polymeric piezoelectric material according to any one of claims 1 to 13,
A first step of obtaining a pre-crystallized film containing the optically active polymer (A);
A second step of stretching the pre-crystallized film mainly in a uniaxial direction;
A method for producing a polymeric piezoelectric material, comprising:   The method for producing a polymeric piezoelectric material according to claim 14, wherein an annealing treatment is performed after the second step. A method for producing the polymeric piezoelectric material according to any one of claims 1 to 13,
Stretching the film containing the optically active polymer (A) mainly in a uniaxial direction;
A step of annealing after stretching the film;
A method for producing a polymeric piezoelectric material comprising: