JP2005213376A - Polymeric piezoelectric material comprising polylactic acid based resin and inorganic compound - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem wherein large piezoelectric effect cannot be obtained when simply drawing it although polylactic acid is known as a polymer exhibiting piezoelectric property, there is a problem in processability to a film in a method for enhancing the piezoelectric property by a forging method and there is no method capable of practically manufacturing a polylactic acid film having high piezoelectric property. <P>SOLUTION: The film exhibiting the high piezoelectric property can be obtained only by drawing it by combining an inorganic compound such as calcium phosphate, titanium oxide, silica and montmorillonite with polylactic acid. The film becomes a film provided with processability and transparency by further triturating the inorganic compound to a nano level and becomes a material utilizable for various kinds of usage. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  In the present invention, a polymer piezoelectric material used for a speaker, a microphone, a sensor, an actuator, etc. is subjected to a stretching treatment by compounding an inorganic compound with a polylactic acid resin having a characteristic that a polling treatment is unnecessary and there is no relaxation effect. The present invention relates to a polymer piezoelectric material having high piezoelectricity characterized by the following.

The piezoelectric phenomenon refers to a phenomenon in which polarization appears when stress is applied to a substance (positive piezoelectric effect), or a phenomenon in which distortion occurs when an electric field is applied (inverse piezoelectric effect). As piezoelectric materials, it is known that inorganic substances such as barium titanate (BaTiO ₃ ), PZT (PbZrO ₃ —PbTiO ₃ -based solid solution), and ZnO have a high piezoelectricity, and have been widely used for sensors and actuators. It was. If piezoelectricity can be imparted to the polymer, a film or a structure having a complicated shape can be easily produced, so that the application range is expected to be widened. Polymers are generally inhomogeneous systems of microcrystals and amorphous parts. If this state is irregular and macroscopically isotropic, there is no piezoelectricity, and some anisotropy is necessary to obtain piezoelectricity. Processing to give is required. Ferroelectric polymers such as polyvinylidene fluoride (PVDF) and vinylidene fluoride-trifluoroethylene (VDF / TrFE) copolymers, polar polymers such as vinylidene cyanide-vinyl acetate copolymer, nylon-11, Alternatively, in a composite such as PZT-vinylidene fluoride copolymer, PZT-polyoxymethylene, piezoelectricity is developed by applying a DC electric field called poling treatment to the film and aligning the dipoles in one direction. Among this type of piezoelectric polymer, it is known that a VDF / TrFE (75/25) copolymer gives a high piezoelectricity of about 40 pC / N. Meanwhile, polypeptides such as poly (glutaric acid γ-benzyl) and poly (glutaric acid γ-methyl), cellulose derivatives such as cellulose acetate and cyanoethyl cellulose, polylactic acid, polypropylene oxide, poly (β-hydroxybutyric acid) and the like These optically active polymers are known to exhibit piezoelectricity by mechanical stretching. Among optically active polymers, the piezoelectricity of a polymer crystal having a helical chirality such as polylactic acid is attributed to a C═O bond dipole existing in the direction of the helical axis. In the case of polylactic acid, since the volume fraction of the side chain occupied by the main chain is small, it can be said to be an ideal polymer having a large dipole per volume and an increase in the piezoelectricity of the system.

    In addition, in piezoelectric polymers that require poling treatment, foreign charges such as water and ions in the air adhere, and the dipole orientation aligned by poling treatment is relaxed, and the piezoelectricity decreases significantly over time. There is a problem in practical use. On the other hand, in the case of polylactic acid that exhibits piezoelectricity only by the stretching process, the poling process is unnecessary, so the piezoelectricity does not decrease over several years.

    A polymer piezoelectric material obtained by stretching a molded product of polylactic acid exhibits a high piezoelectricity of about 10 pC / N at room temperature (Patent Document 1). This value is the highest value among polymers that exhibit piezoelectricity only by stretching, but it is low compared to ferroelectric polymers that require poling treatment, but is practical with excellent stability over time. Expected to be a piezoelectric material.

  Polylactic acid exhibits piezoelectricity by stretching, but is smaller than a ferroelectric polymer such as PVF-TrFE. Many calculations have been made on the piezoelectricity derived from helical chirality such as polylactic acid (Non-patent Document 1), and it has been estimated to be several tens to several hundreds pC / N. It is presumed that the potential ability of is not fully exploited.

In order to make polylactic acid crystals highly oriented, there is a report example that produces high piezoelectricity of about 18 pC / N by a special orientation method called forging method, but this method does not produce a homogeneous film over a wide area. It was extremely difficult, and the range in which polylactic acid-based piezoelectric materials could be used was limited.
JP-A-5-152638 Yoshiro Tanabe, Future Materials, Vol. 3, No. 7 (2003), pp. 16-25

  An object of the present invention is to provide a polylactic acid film that exhibits high piezoelectricity only by a simple process that does not require a polling process.

  The present inventors have found that a film in which an inorganic compound is combined with polylactic acid can be a material that improves piezoelectricity only by stretching. In addition, the inventors have found that by making the inorganic fine particles into nanometer size, the processability and transparency of the composite film are good and the material can be used for various purposes.

That is, the present invention
(1) a polymeric piezoelectric material comprising a polylactic acid resin and an inorganic compound;
(2) The polymeric piezoelectric material according to claim 1, wherein the inorganic compound is at least one compound selected from Group 2 element compounds of the periodic table, metal oxides, and layered inorganic compounds.
(3) The polymer piezoelectric material according to (2), wherein the group 2 element compound of the periodic table is a calcium compound,
(4) The polymeric piezoelectric material according to (2), wherein the metal oxide is silicon oxide or titanium oxide,
(5) The polymeric piezoelectric material according to (2), wherein the layered inorganic compound is a clay mineral,
(6) The polymer piezoelectric material according to (5), wherein the layered inorganic compound is treated with an organic cation,
(7) The polymeric piezoelectric material according to any one of (1) to (6) obtained by stretching.

    ADVANTAGE OF THE INVENTION According to this invention, after making an inorganic compound complex with a polylactic acid-type resin, the polylactic acid film which shows high piezoelectricity can be provided by performing an extending | stretching process. At this time, if the inorganic compound is miniaturized to a nano-level size, not only transparency but also piezoelectricity and workability can be further improved. Therefore, the inorganic compound is desirably particles having an average particle size of 500 nm or less.

    Moreover, when using a layered inorganic compound, it is desirable to carry out an organic cation treatment. The transparency of the polymeric piezoelectric material obtained by this treatment is improved.

    The polymeric piezoelectric material comprising the polylactic acid resin and the inorganic compound of the present invention can be used in the fields of various acoustic devices and members such as speakers and microphones, various sensors, displays, medical devices, and actuators.

  The present invention is a polymer piezoelectric material which is a composite material composed of a polylactic acid-based resin and an inorganic compound and which has been subjected to a stretching treatment in order to impart high piezoelectricity.

Polylactic acid resin The polylactic acid resin used in the present invention is polylactic acid, a copolymer of a polyfunctional compound copolymerizable with lactic acid, and a mixture thereof. Polylactic acid is L-polylactic acid, homopolymer, block copolymer, or graft copolymer of D-polylactic acid. The copolymerizable polyfunctional compounds are 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-hydroxymethylcaproic acid, Hydroxycarboxylic acids such as mandelic acid, glycolides, cyclic esters such as β-methyl-δ-valerolactone, γ-valerolactone, ε-caprolactone, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, Azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, te Polyvalent carboxylic acids such as phthalic acid, and anhydrides thereof, ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butane Diol, 2,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,9-nonanediol, 3-methyl-1,5-pentanediol, neopentyl glycol, tetramethylene glycol, 1 Polyhydric alcohols such as 1,4-hexanedimethanol, polysaccharides such as cellulose, aminocarboxylic acids such as α-amino acids, and the like. Copolymers of polyfunctional compounds copolymerizable with lactic acid are block copolymers or graft copolymers having a polylactic acid sequence capable of forming helical crystals.

Production method of polylactic acid resin The production method of the polylactic acid resin used in the present invention is not particularly limited. For example, lactic acid described in JP-A-59-096123 and JP-A-7-033861 Or by ring-opening polymerization using lactide which is a cyclic dimer of lactic acid described in US Pat. Nos. 2,668,182 and 4,057,357, etc. Can be manufactured.

Molecular Weight of Polylactic Acid Resin The weight average molecular weight (Mw) of the polylactic acid resin used in the present invention is not particularly limited as long as it can be stretched. As will be described later, some of the inorganic compounds produced by utilizing the sol-gel reaction are those in which inorganic molecules are introduced into the polylactic acid resin by covalent bonds by an ester-amide exchange reaction. In some cases, the molecular weight of the polylactic acid resin is decreased, but in reality, the molecular weight may not be decreased due to the bonding of inorganic molecules or the crosslinking of inorganic molecules. Therefore, the molecular weight of the polylactic acid resin used in the present invention is defined by the molecular weight before complexing with the inorganic compound, and is generally 10,000 to 10,000,000, preferably 30,000 to 3,000,000, more preferably 50,000 to 100. It is in the range of 10,000.

Inorganic Compound The inorganic compound used in the present invention is a compound selected from Group 2 element compounds of the periodic table, metal oxides, and layered inorganic compounds, and may be a mixture thereof.

    The periodic table group 2 element compound of the present invention is a compound containing one or more elements selected from periodic table group 2 elements having similar chemical properties such as beryllium, magnesium, calcium, strontium, barium, and radium. Among them, magnesium, calcium, strontium, and barium are preferable.

    The periodic table group 2 element compound of the present invention includes hydroxide, fluoride, chloride, bromide, iodide, borate, metaborate, carbonate, nitrate, nitrite, phosphoric acid (orthophosphoric acid) salt, Pyrophosphoric acid (diphosphoric acid) salt, metaphosphate, phosphonic acid (phosphorous acid) salt, diphosphonic acid (diphosphorous acid) salt, phosphinic acid (hypophosphorous acid) salt, sulfate, disulfate, thio Sulfate, sulfite, chromate, dichromate, perchlorate, isocyanate, thrombate, orthosilicate, metasilicate, formate, acetate, propionate, butyrate, Shu Examples of the acid salts include malate, malonate, succinate, glutarate, adipate, maleate, fumarate, lactate, malate, tartrate, benzoate, and phthalate.

    Examples of the periodic table group 2 element compound of the present invention are magnesium acetate, magnesium carbonate, magnesium chloride, magnesium silicofluoride, magnesium hydroxide, magnesium oxide, magnesium nitrate, magnesium sulfate, calcium acetate, calcium dihydrogen phosphate, calcium lactate , Calcium citrate, calcium hydroxide, calcium carbonate, calcium chloride, calcium nitrate, calcium sulfate, calcium thiosulfate, strontium hydroxide, strontium carbonate, strontium nitrate, strontium chloride, barium acetate, barium chloride, barium nitrate, barium sulfate, One or more compounds selected from barium hydroxide, barium fluoride and the like can be mentioned.

    As inorganic components of animal bone shells, calcium carbonate contained in shells and the like, and calcium phosphate contained in bones, teeth, fish phosphorus, and the like are main components of organic / inorganic complexes found in the living body. Among the poorly water-soluble fine particles, calcium compounds such as calcium phosphate and calcium carbonate are particularly preferably used because of their high affinity with organic substances.

    The calcium phosphate used in the present invention includes a portion derived from phosphoric acid and a total of 50% by weight of calcium atoms. Examples include hydroxyapatite, fluorapatite, chlorapatite, carbonate-containing apatite, magnesium-containing apatite, iron-containing apatite and other apatite compounds, tricalcium phosphate and the like.

The basic composition of the apatite compound contained in the calcium phosphate of the present invention is represented by M _x (RO ₄ ) _y X _z . When M site is calcium ion (Ca ²⁺ ), RO ₄ site is phosphate ion (PO ₄ ³⁻ ), and X site is hydroxide ion (OH ⁻ ), x = 10, y = 6, z = 2 It is a compound generally called hydroxyapatite. Each site of M, RO ₄ , and X can be replaced with various ions and can also be vacancies. The amount of substitution and the amount of vacancies vary depending on the type of ion, etc., but if the total of the portion derived from phosphoric acid and the calcium atom is contained in an amount of 50% by weight or more, the vacancies are substituted even if other ions are substituted. It doesn't matter.

If the total of the portion derived from phosphoric acid and the calcium atom is less than 50% by weight, the properties as calcium phosphate may be lost, which is not preferable. The M site is basically Ca ²⁺ , but examples of ion species that can be substituted include H ⁺ , Na ⁺ , K ⁺ , H ₃ O ⁺ , Sr ²⁺ , Ba ²⁺ , Cd ²⁺ , Pb ²⁺ , Zn ²⁺ , Mg ²⁺ , Fe ²⁺ , Mn ²⁺ , Ni ²⁺ , Cu ²⁺ , Hg ²⁺ , Ra ²⁺ , Al ³⁺ , Fe ³⁺ , Y ³⁺ , Ce ³⁺ , Nd ³⁺ , La ³⁺ , Dy ³⁺ , Eu ³⁺ , Zr ^4+, etc. It is done. The RO ₄ site is basically PO ₄ ³⁻ , but as examples of ion species that can be substituted, SO ₄ ²⁻ , CO ₃ ²⁻ , HPO ₄ ²⁻ , PO ₃ F ²⁻ , AsO ₄ ³⁻ , Examples thereof include VO ₄ ³⁻ , CrO ₄ ³⁻ , BO ₃ ³⁻ , SiO ₄ ⁴⁻ , GeO ₄ ⁴⁻ , BO ₄ ⁵⁻ , AlO ₄ ⁵⁻ , H ₄ O ₄ ⁴⁻ . Examples of ionic species and molecules that enter the X site include OH ⁻ , F ⁻ , Cl ⁻ , Br ⁻ , I ⁻ , O ²⁻ , CO ₃ ²⁻ , H ₂ O, and the like.

The metal oxide used in the present invention is produced by a solid phase method, a gas phase method, or a liquid phase method. SiO ₂ , TiO ₂ , Al ₂ O ₃ , ZrO ₂ , CeO ₂ , Ho ₂ O ₃ , Bi One or more compounds selected from ₂ O ₃ , Y ₂ O ₃ , SnO ₂ , ZnO, CuO, CoO, BaTiO ₃ , LiNbO ₃ , KTaO ₃ , InO—SnO, LiAlO ₂ , and mixtures thereof.

  In the solid phase method and the gas phase method, the metal oxide is produced as a powder, and is compounded by a method of kneading in a molten state with a polylactic acid resin or by distilling the solvent after mixing and dispersing in a solution. . In order to enable a stretching process and obtain a highly transparent film, it is necessary to uniformly combine both. Usually, the primary particles are often in an aggregated state. Alternatively, it is necessary to uniformly disperse the primary particles by mixing under high shear.

As a method for uniformly dispersing metal oxide fine particles in a polylactic acid-based resin, dispersibility is improved by a method of modifying the surface of fine particles with acidic groups and basic groups as described in JP-A-2003-138153. Can do. For example, hydrolysis of titanium alkoxide and surface modification of titanium dioxide fine particles produced by the synthesis method described in Japanese. Journal of Applied Physics, Vol. 37, pages 4603-4608 (1998) with acidic groups. By performing, the dispersibility in the organic solvent is improved. An acidic group is a group that releases H ⁺ in water and exhibits acidity, and examples thereof include a carboxyl group, a hydroxyl group, and a sulfone group, and a carboxyl group is preferable, and an organic compound having a carboxy group is saturated or not. Saturated carboxylic acid. Examples include acetic acid, propionic acid, acrylic acid, methacrylic acid, hexyl acid, octanoic acid, dodecanoic acid, stearic acid, oleic acid, benzoic acid and the like. Titanium dioxide ultrafine particles whose surface is modified with acidic groups are dispersed in alcohol such as ethanol or 1-butanol and heated under reflux or ultrasonic chemical treatment, and then a low polarity solvent such as toluene is added. Thus, the polarity of the solvent can be changed. A desired polymer can be dissolved in this, and a titanium dioxide fine particle polymer composition can be formed. Since titanium dioxide ultrafine particles modified with such acidic groups leave many active sites, the combination with the polymer to be selected may cause problems of yellow or red coloring, and the surface is modified with basic groups. This can be prevented by performing. A basic group is a group that receives H ⁺ in water and exhibits basicity, such as methylamine, propylamine, hexylamine, alkanolamines such as dodecylamine, ethanolamine, saturated or unsaturated aliphatic amines such as allylamine, etc. Amino compounds are used. When it is desired to dissolve and disperse the fine particles in a solvent having low polarity, an amine having a large number of methylene groups is selected. Further, titanium dioxide ultrafine particles whose surface is modified with both acidic groups and basic groups are dispersed in a desired solvent. The solvent used in the present invention varies depending on the polylactic acid resin to be used, but aromatic hydrocarbons such as toluene and xylene, halogenated hydrocarbons such as chloroform and trichloroethane, ketones such as acetone and methyl ethyl ketone, and N.I. N-dimethylformamide, N.I. Solvents such as N-dimethylacetamide and dimethylsulfoxide can be used.

    There is also a method of compounding a metal oxide in a polymer compound solution by a method of synthesizing a metal oxide by a liquid phase method typified by a sol-gel method. As the liquid phase method, a method of producing a metal oxide by a so-called sol-gel reaction in which metal organic and inorganic substances are hydrolyzed and condensed is suitable. In this method, when a sol-gel reaction is carried out in the presence of a polylactic acid resin using a metal compound that is miscible with the polylactic acid resin solution as a starting material, the separation between the polylactic acid resin and the metal oxide is suppressed. A uniformly mixed and dispersed film can be obtained. The metal compounds used are tetramethoxysilane (TMOS), tetraethoxysilane (TEOS), tetrapropoxysilane, tetraisopropoxysilane, methyltrimethoxysilane, methyltriethoxysilane, methyltripropoxysilane, methyltributoxysilane, ethyl Trimethoxysilane, ethyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, isopropyltrimethoxysilane, isopropyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane , Trifluoromethyltrimethoxysilane, trifluoromethyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, Enyltrimethoxysilane, phenyltriethoxysilane, 2- (3,4 epoxycyclohexyl) ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropyl Methyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, p-styryltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-acryloxypropyltriethoxysilane, 3-chloropropyltriethoxysilane, 3-mercapto Alkoxysilanes such as propylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-isocyanatopropyltriethoxysilane, tetramethoxytitanium, tetraethoxytitanium, titanium isopropoxide, aluminum butoxide, zirconium tetra-n-butoxide Metal alkoxides such as zirconium tetraisopropoxide, vanadyl ethoxide, barium isopropoxide, calcium ethoxide, chlorides such as silicon tetrachloride, zirconium tetrachloride, titanium tetrachloride, aluminum chloride, zirconium oxychloride, oxychloride Oxychlorides such as aluminum, nitrates such as yttrium nitrate and nickel nitrate, metal acetylates such as indium acetylacetonate and zinc acetylacetonate Examples thereof include metal carboxylates such as cetonate, lead acetate, yttrium stearate, and barium oxalate.

    When an alkoxysilane having an amino group is used in carrying out this reaction, the amino group reacts with the ester group of the polylactic acid resin, whereby a metal oxide can be introduced into the polylactic acid resin by a covalent bond. Since this reaction involves the cleavage of the main chain of the polylactic acid resin, the molecular weight is lowered, but the mechanical strength of the film is maintained by the formation of the metal oxide by the sol-gel reaction. An alkoxysilane having an amino group has two reactive groups, an amino group and an alkoxy group, in the molecule. Therefore, when the reaction is performed in the presence of a polylactic acid resin, the sol is reacted after the reaction between the amino group and the ester group. -There are a method of performing a gel reaction, a method of proceeding both at the same time, and an intermediate method thereof, and either can be selected depending on the target complex structure. When the reaction with the amino group is prioritized, the structure becomes more uniform, and when the sol-gel reaction is prioritized, the structure tends to be separated.

  The alkoxysilane having an amino group is 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, N-2 (aminoethyl) 3 -Aminopropylmethyldimethoxysilane, N-2 (aminoethyl) 3-aminopropyltrimethoxysilane, 2-aminoethylaminomethyltrimethoxysilane, 3-aminopropyldimethylethoxysilane, 2- (2-aminoethylthioethyl) Triethoxysilane, p-aminophenyltrimethoxysilane, N-phenyl-3-aminopropylmethyldimethoxysilane, N-phenyl-3-aminopropylmethyldiethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane Can be mentioned N- phenyl-3-aminopropyltriethoxysilane, etc., but is not limited thereto, can also be used in combination of two or more selected from these.

  The sol-gel reaction is performed according to a known method. When performing a sol-gel reaction in the presence of a polymer, add a small amount of water in a solvent that can dissolve both the polymer compound and the electrolyte salt, and add an acid catalyst or a base catalyst as necessary. The reaction is carried out with stirring in a temperature range from room temperature to the boiling point of the solvent, with dehydration as necessary.

  Examples of the layered inorganic compound used in the present invention include clay minerals, layered phosphates, and hydrotalcites. The clay mineral may be a natural mineral or a synthetic mineral by hydrothermal synthesis, a melting method, a solid phase method, or the like, and may be crystalline or amorphous. Examples of clay minerals used in the present invention include smectites such as montmorillonite, beidellite, saponite and hectorite, kaolinites such as kaolinite and halosite, dioctahedral vermiculite, trioctahedral vermiculite and the like. Layered silicates such as vermiculite, teniolite, tetrasilicic mica, mascobite, illite, sericite, phlogopite, biotite, kanemite, macatite, magadiite, kenyaite, talc, chlorite (chlorite) Can be mentioned.

    These layered inorganic compounds are preferable because the dispersibility in the polylactic acid-based resin is improved by performing an organic cation treatment in advance, and the composite resin has good transparency. Organic cations are octylamine, dodecylamine, octadecylamine, trioctylamine, dimethyldodecylamine, didodecylmonomethylamine, tetraethylammonium salt, octadecyltrimethylammonium salt, dimethyldioctadecylammonium salt, dihydroxyethylmethyloctadecylammonium salt, methyldodecylbis Organic ammonium salts such as (polyethylene glycol) ammonium salt, methyldiethyl (polypropylene glycol) ammonium salt, organic such as tetraethylphosphonium, tetrabutylphosphonium, hexadecyltributylphosphonium, tetrakis (hydroxymethyl) phosphonium, 2-hydroxyethyltriphenylphosphonium Phosphonium salt, n-butylpyridinium salt, dodecy Pyridinium salt, organic pyridinium salt, such as hexadecyl pyridinium salts, organic sulfonium salts and the like.

Polylactic acid resin-inorganic compound composite structure These inorganic compounds have a structure in which an inorganic compound is phase separated in a polylactic acid resin matrix, a structure in which a polylactic acid resin is phase separated in an inorganic matrix, and polylactic acid and an inorganic compound. It is possible to adopt any of so-called IPN (interpenetrating polymer network) structures in which are mixed at the molecular level. The phase separation structure may be a continuous shape such as layered, lamellar or cylindrical, or a discontinuous structure such as a sea-island structure. In general, when a continuous structure is taken, the inorganic compound can be produced by a sol-gel reaction. On the other hand, the discontinuous structure is generally a structure in which the other component is dispersed in the form of particles in the matrix, and the size of the particles is generally in the range of 1 nm to 10 μm. Often made by mixing and dispersing compounds. The size of the particles is preferably as fine as possible within this range for applications where the transparency of the composite is required, 500 nm or less, more preferably 250 nm or less, and even more preferably 100 nm. It is as follows. Finer particles not only improve transparency, but also tend to improve piezoelectricity itself, and may improve workability such as stretching, bending, cutting, adhesion, coating, and vapor deposition. Usually, a compounding method is adopted so as to make it finer. In the case of a metal oxide, the structure or dispersion state can be controlled by applying the surface modification method of the fine particles or the sol-gel method as described above, and the size of the fine particles can be controlled. It is also possible to do.

    The layered inorganic compound has a structure in which particles are dispersed, but if an untreated one is used, transparency may be poor. By performing the organic cation treatment, the interlayer distance of the layered inorganic compound is sufficiently widened, and delamination and a polylactic acid resin are inserted between the layers, thereby improving dispersibility and obtaining a film with good transparency. In the case of a layered compound, a method of performing an organic cation treatment is often preferable because not only transparency is improved by improving dispersibility but also piezoelectricity itself and processability are improved.

Stretching of Composite Film Stretching of the polylactic acid-based resin-inorganic compound composite film may be any of uniaxial stretching, biaxial stretching, and multiaxial stretching. The stretching conditions vary depending on the inorganic compound used, and are usually higher than the glass transition temperature of the polylactic acid resin and generally in the temperature range of 60 ° C to 200 ° C, preferably 80 to 180 ° C. It is also possible to perform so-called cold drawing. When extending | stretching at high temperature, it is performed in inert gas atmosphere as needed. The stretching method is not particularly limited as long as it is a known method, and is usually stretched 2 to 10 times, preferably about 2 to 6 times by a tenter method.

(Embodiment)
Hereinafter, the present invention will be described in more detail with reference to examples. These examples illustrate one embodiment of the invention and are not intended to limit the invention. The physical properties of the resin composition and the like were measured and evaluated according to the following methods.
(1) Transparency (haze value)
About the sheet | seat or film obtained by the predetermined | prescribed method, after leaving to stand in 23 degreeC and the conditions of 50% of relative humidity for 3 days, haze was measured using the haze meter (made by Nippon Denshoku Industries Co., Ltd.). In addition, it turns out that it is excellent in transparency, so that a haze value is small.
(2) Piezoelectricity About a uniaxially stretched film with a thickness of 0.24 to 0.72 μm obtained by a predetermined method, using a “Rheograph Roid S-1 type” manufactured by Toyo Seiki Seisakusho, in a frequency range of 0.8 to 140 Hz. The complex piezoelectric constant d14 = d14'-id14 "of the test piece was measured at room temperature. The higher the complex piezoelectric constant, the better the piezoelectricity. The measurement was performed after measuring the haze.
(3) Particle size The particle size is determined by laser diffraction particle size distribution measurement, scanning electron microscope (SEM) observation, TEM (transmission electron microscope) observation, etc., according to the size and state, and the average value thereof. (Median diameter) is shown.

(Production Example 1)
A round bottom separable flask equipped with a stirrer, a thermometer and a pH meter was charged with 55.3 g of calcium hydroxide (manufactured by Iriko Sangyo) and 1744.7 g of distilled water, and stirred vigorously to obtain a suspension. After adjusting the temperature of the suspension to 40 ° C, an aqueous solution in which 211.4 g of 75% phosphoric acid (Mitsui Chemicals) was diluted to 20.0% and 988.6 g of distilled water were mixed and dissolved was continuously added using a microtube pump. For 2 hours. After the addition, the reaction was further carried out at 40 ° C. for 2 hours to obtain a calcium phosphate fine particle dispersion solution. This reaction was performed twice under the same conditions. Each of these reaction liquids was left to stand overnight and 50 vol% was precipitated. The supernatant liquid was discarded, both liquids were mixed, and the supernatant liquid separated by leaving for 2 days was removed to prepare a calcium phosphate dispersion slurry. The solid content concentration of this slurry was 5.92%. In addition, calcium phosphate (A) powder used for complexing with polylactic acid is a medium fluidized dryer (MSD-100A: using zirconia medium φ2 mm) manufactured by Nara Machinery Co., Ltd. Prepared by drying. When calcium phosphate (A) powder was dispersed in distilled water and the particle size was measured by a laser diffraction particle size distribution analyzer SALD-2000J manufactured by Shimadzu Corporation, it was 6.5 μm. Moreover, when Pt vapor deposition was given to the powder surface and the scanning electron microscope (SEM) observation made from Hitachi, Ltd. was performed, a mode that the particle | grains became the aggregate | assembly of the primary particle of 25-40 nm was observed.
(Production Example 2)
In a round bottom separable flask equipped with a stirrer and thermometer, 427.188 g of distilled water was added to 12.124 g of citric acid monohydrate (special grade, manufactured by Junsei Chemical Co., Ltd.) and dissolved uniformly. g was added. 29.50 g of calcium hydroxide (Irigo Sangyo) was added with stirring to form a suspension. The suspension was stirred at a stirring speed of 300 rpm at room temperature, and a microtube pump was used to mix 112.77 g of phosphoric acid aqueous solution in which 75% phosphoric acid (Mitsui Chemicals) was diluted to 20.8% and 207.23 g of distilled water. After continuous addition over 30 minutes, the mixture was further stirred for 1 hour to obtain a sodium citrate / calcium phosphate complex (1.25: 98.75) dispersion. The suspension, which was 18.4 ° C. before the addition, rose to 25.7 ° C. after the reaction. The pH of the obtained dispersion solution was 12.22. This reaction was performed 5 times under the same conditions. When these reaction solutions were mixed and allowed to stand overnight, 50 vol% settled. The supernatant was discarded, and the separated supernatant was removed by leaving it for another week to prepare a calcium phosphate dispersion slurry. The solid content concentration of this slurry was 7.2%. The citrate-treated calcium phosphate (B) powder used in the complexing with polylactic acid is a medium fluid dryer manufactured by Nara Machinery Co., Ltd. Prepared by drying under. When calcium phosphate (A) powder was dispersed in distilled water and the particle size was measured by a laser diffraction particle size distribution analyzer SALD-2000J manufactured by Shimadzu Corporation, it was 6.8 μm.

10 parts by weight of fully dried polylactic acid (registered trademark Lacia, H-100, manufactured by Mitsui Chemicals) was dissolved in 10 parts by weight of chloroform and mixed with 0.53 parts by weight of calcium phosphate (A) powder produced in Production Example 1. After that, it was transferred to a glass petri dish to prepare a cast film. Since this film had a poor dispersion state of the HAp powder, the film was finely crushed, melted at 120 ° C., compressed at 10 MPa for 10 minutes, and then compressed and cooled again at 10 MPa with a compression molding machine set at 85 ° C. A 15 mm thick sheet was formed. This polylactic acid-HAp composite film was uniaxially stretched 2.0 times at 80 ° C. to obtain a film having a thickness of 26 μm. The piezoelectricity of the obtained film was evaluated. The results are shown in Table 1. Here, the absolute value d of the complex piezoelectric constant is shown.

    10 parts by weight of sufficiently dried polylactic acid (Mitsui Chemicals, registered trademark Lacia, H-100) was dissolved in 10 parts by weight of chloroform, and the citric acid-treated calcium phosphate (B) powder 0.20 produced in Production Example 2 was obtained. After mixing the weight part, the glass petri dish was moved and the cast film was produced. Since this film was poorly dispersed in the HAp powder, the film was finely crushed, melted at 120 ° C., compressed at 10 MPa for 10 minutes, and then compressed and cooled again at 10 MPa with a compression molding machine set at 85 ° C. A 15 mm thick sheet was formed. This polylactic acid-HAp composite film was uniaxially stretched 2.5 times at 80 ° C. to obtain a film having a thickness of 31 μm. The piezoelectricity of the obtained film was evaluated. The results are shown in Table 1.

    The same operation as in Example 2 was performed except that the film was uniaxially stretched 3.0 times at 80 ° C. to obtain a polylactic acid-calcium phosphate (B) composite film having a thickness of 50 μm. The piezoelectricity of the obtained film was evaluated. The results are shown in Table 1.

Titanium tetrachloride (Wako reagent special grade) 15ml (0.138mol) was measured in a 200ml three-necked flask in a nitrogen atmosphere, the reaction system was kept at 0 ° C, then 15ml of ion-exchanged water was added drop by drop, and yellow oily titanium oxychloride A (TiOCl ₂ ) solution (9.2 mol / l) was obtained. A mixture of 600 ml of ethanol and 400 ml of ion-exchanged water was placed in a 1 l three-necked flask, placed in an oil bath and stirred in a nitrogen atmosphere. After the temperature reached 60 ° C. and stabilized, a 1 mol / l TiOCl ₂ solution obtained by diluting 4 ml of the previously prepared TiOCl ₂ solution with 36.8 ml of ion-exchanged water was added dropwise. After 6 hours, the resulting precipitate of ultrafine titanium dioxide particles was centrifuged and washed with 50 ml of ethyl acetate. The centrifugation and washing operations were performed three times in total, and then ethyl acetate was removed to obtain titanium dioxide ultrafine particles. Titanium dioxide ultrafine particles were dispersed in 50 ml of acetic acid and stirred at room temperature for 60 hours. The precipitate was centrifuged and washed three times with ethyl acetate. A part was taken out, dried at 120 ° C. under reduced pressure for 6 hours, and the infrared spectrum was measured by the KBr tablet method. As a result, the peak of the carboxylate group (—COO ⁻ ) indicating acetic acid modification on the surface of titanium dioxide was measured. Acetic acid-modified titanium dioxide ultrafine particles (1 g in a dry state) obtained in the above manner were added in a wet state to 100 ml of 1-butanol, and sonication was carried out for 1 hour. To this, 100 ml of toluene was added to obtain a transparent solution in which titanium dioxide ultrafine particles were uniformly dispersed. After adding 50 ml of n-hexylamine to this solution and stirring for 1 hour, the produced precipitate was collected by centrifugation, and the operations of washing with methanol and centrifugation were repeated twice. A part was taken out, dried, and then subjected to infrared spectrum measurement with a KBr tablet, and it was confirmed that the surface of the titanium dioxide ultrafine particles was modified with both acetic acid and amine. When the acetic acid / n-hexylamine-modified titanium dioxide ultrafine particles were added to 40 ml of chloroform, a uniformly dispersed transparent solution was obtained. Separately prepared a solution prepared by dissolving 9 g of sufficiently dried polylactic acid (registered trademark Lacia, H-100, manufactured by Mitsui Chemicals) in 80 ml of chloroform, mixed with a solution of titanium dioxide ultrafine particles, and stirred at room temperature for 30 minutes. . This solution was further poured into 500 ml of heptane for reprecipitation, and the precipitate was collected by filtration. After drying the precipitate at 60 ° C. for 10 hours, the powder was pressed at 100 kg / cm ² and 180 ° C. for 2 minutes to obtain a colorless and transparent film having a thickness of 100 μm. From the transmission electron microscope observation of the obtained film, it was confirmed that the titanium dioxide ultrafine particles having a particle diameter of 3 to 5 nm were uniformly dispersed in the polymer without any aggregation. Moreover, it was confirmed by measuring the thermogravimetric change that the blending amount of the titanium dioxide ultrafine particles in the film was 10% by weight.

    10 parts by weight of sufficiently dried polylactic acid (Mitsui Chemicals, registered trademark Lacia, H-100) is dissolved in 90 parts by weight of THF, 0.28 parts by weight of tetramethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.), 3-aminopropyltrimethoxy 0.03 part by weight of silane (manufactured by Shin-Etsu Chemical Co., Ltd.) and 0.11 part by weight of 0.1N hydrochloric acid aqueous solution were added and mixed uniformly, and the reaction was carried out at 60 ° C. for 5 hours. The white solid produced by pouring the transparent reaction solution into a large amount of methanol at this temperature was filtered off, washed thoroughly with methanol, and then vacuum dried. The amount of silica contained in the polylactic acid-silica composite was about 0.5% when examined by the residue when heated in air to 800 ° C. with TGA. This composite was dissolved in chloroform and cast into a glass petri dish to form a film. Further, the cast film was roll-stretched twice at 70 ° C. by a roll stretching machine manufactured by Imoto Co., and then uniaxially stretched 1.5 times at 70 ° C. to obtain a film having a thickness of 23 μm. The piezoelectricity of the obtained film was evaluated. The results are shown in Table 1.

    10 parts by weight of sufficiently dried polylactic acid (Mitsui Chemicals, registered trademark Lacia, H-100) is dissolved in 90 parts by weight of THF, and 0.64 parts by weight of tetramethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.), N-2 (aminoethyl) ) 0.07 part by weight of 3-aminopropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.) and 0.28 part by weight of a 0.1N hydrochloric acid aqueous solution were added and mixed uniformly, followed by reaction at 60 ° C. for 5 hours. The white solid produced by pouring the transparent reaction solution into a large amount of methanol at this temperature was filtered off, washed thoroughly with methanol, and then vacuum dried. The polylactic acid-silica composite had a weight average molecular weight of 168,800, and the amount of silica contained in the polylactic acid-silica composite was about 1.3% when examined by the residue when heated in air to 800 ° C. with TGA. . This composite was dissolved in chloroform and cast into a glass petri dish to form a film. Further, the cast film was roll-stretched twice at 70 ° C. by a roll stretching machine manufactured by Imoto Co., and then uniaxially stretched 1.5 times at 70 ° C. to obtain a film having a thickness of 23 μm. The piezoelectricity of the obtained film was evaluated. The results are shown in Table 1.

    The cast film obtained in the same manner as in Example 6 was uniaxially stretched three times at 60 ° C. with a stretching machine manufactured by Imoto Co., Ltd. to obtain a film having a thickness of 59 μm. The piezoelectricity of the obtained film was evaluated. The results are shown in Table 1.

    A cast film was obtained in the same manner as in Example 7 except that polylactic acid (manufactured by Boehringer, L207) was used. Further, the cast film was uniaxially stretched 3 times at 60 ° C. with a stretching machine manufactured by Imoto Co., Ltd., to obtain a film having a thickness of 76 μm. The piezoelectricity of the obtained film was evaluated. The results are shown in Table 1.

    A cast film was obtained in the same manner as in Example 7 except that polylactic acid (Lacty 5000, manufactured by Shimadzu Corporation) was used. Further, the cast film was uniaxially stretched three times at 60 ° C. by a stretching machine manufactured by Imoto Co., Ltd. to obtain a film having a thickness of 61 μm. The piezoelectricity of the obtained film was evaluated. The results are shown in Table 1.

    100 parts by weight of fully dried polylactic acid (registered trademark Lacia, H-100, manufactured by Mitsui Chemicals) and 5 parts by weight of montmorillonite (trade name Bengel A, manufactured by Toyoshun Yoko Co., Ltd.) not subjected to organic treatment The resin composition (A) was obtained by melting and mixing under the condition of a cylinder temperature of 200 ° C. using a HAAKE double screw extruder. Next, the resin composition (A1) was dried well, and a predetermined amount was sandwiched between two brass plates, an aluminum plate and a release film, melted at 200 ° C., compressed at 10 MPa for 3 minutes, and then set to 20 ° C. The sheet was compressed and cooled again at 10 MPa with a compression molding machine to form a sheet having a thickness of 0.2 mm. The transparency (total haze value) of the obtained sheet was 37.6%. Further, the formed sheet was uniaxially stretched 3 times at 60 ° C. by a stretching machine manufactured by Imoto Co., Ltd. to obtain a film having a thickness of 57 μm. The piezoelectricity of the obtained film was evaluated. The results are shown in Table 1.

    Montmorillonite (trade name: Sven E, manufactured by Toyosune Yoko Co., Ltd.) treated with organic cation using 100 parts by weight of fully dried polylactic acid (Mitsui Chemicals, registered Lacia, H-100) and quaternary ammonium cation ) 5 parts by weight was melted and mixed in a twin-screw extruder manufactured by HAAKE under the condition of a cylinder temperature of 200 ° C. to obtain a resin composition (B). Next, this was mixed and molded in the same manner as in Example 10. The transparency (total haze value) of the obtained sheet was 18.6%. The piezoelectricity of the film obtained by stretching in the same manner as in Example 10 was evaluated. The results are shown in Table 1.

    Montmorillonite (trade name: Sven NX, manufactured by HOJUN) 5 which has been subjected to organic cation treatment using 100 parts by weight of polylactic acid (Mitsui Chemicals, registered Lacia, H-100) and quaternary ammonium cation 5 Weight parts were mixed in the same manner as in Example 10 to obtain a resin composition (C). Next, this was mixed and molded in the same manner as in Example 10. The transparency (total haze value) of the obtained sheet was 24.7%. The piezoelectricity of the film obtained by stretching in the same manner as in Example 10 was evaluated. The results are shown in Table 1.

(Comparative Example 1)
Molding and evaluation were performed under the same conditions as in Example 1 using only 100 parts by weight of the same polylactic acid used in Example 1. However, the stretching conditions were selected as favorable conditions when there was no inorganic material. The results are shown in Table 1.

(Comparative Example 2)
Molding and evaluation were performed under the same conditions as in Example 1 using only 100 parts by weight of the same polylactic acid used in Example 1. However, the stretching conditions were selected as favorable conditions when there was no inorganic material. The results are shown in Table 1.

    In Examples 11 and 12, when montmorillonite was treated with an organic cation, the dispersion state was improved and the haze was lowered. this is. Since the haze value is small, it can be used for applications such as a sound insulation material, a sound insulation material, and a speaker in applications where display applications, visibility and designability are required.

  The polymeric piezoelectric material of the present invention can improve piezoelectricity by compounding an inorganic compound with polylactic acid that does not require a poling treatment and has no relaxation phenomenon, and further reduces the size of the inorganic compound to a nanometer size. By making it small, as a piezoelectric film with excellent workability and transparency, headphones, speakers, microphones, underwater microphones, acceleration sensors, impact sensors, vibration sensors, pressure sensors, tactile sensors, electric field sensors, sound pressure sensors, It can be used in displays, fans, pumps, variable focus mirrors, ultrasonic transducers, piezoelectric transformers, sound insulation materials, sound insulation materials, actuators, keyboards, etc., in acoustic equipment, information processing equipment, measuring equipment, medical equipment and other fields. .

Claims (7)

  A polymeric piezoelectric material comprising a polylactic acid resin and an inorganic compound.     2. The polymeric piezoelectric material according to claim 1, wherein the inorganic compound is at least one compound selected from Group 2 element compounds of the periodic table, metal oxides, and layered inorganic compounds.   The polymeric piezoelectric material according to claim 2, wherein the group 2 element compound of the periodic table is a calcium compound.   The polymeric piezoelectric material according to claim 2, wherein the metal oxide is either silicon oxide or titanium oxide.   The polymeric piezoelectric material according to claim 2, wherein the layered inorganic compound is a clay mineral.     6. The polymeric piezoelectric material according to claim 5, wherein the layered inorganic compound is treated with an organic cation.   The polymeric piezoelectric material according to any one of claims 1 to 6, wherein the polymeric piezoelectric material is stretched.