WO2014069477A1 - 圧電積層体 - Google Patents
圧電積層体 Download PDFInfo
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- WO2014069477A1 WO2014069477A1 PCT/JP2013/079309 JP2013079309W WO2014069477A1 WO 2014069477 A1 WO2014069477 A1 WO 2014069477A1 JP 2013079309 W JP2013079309 W JP 2013079309W WO 2014069477 A1 WO2014069477 A1 WO 2014069477A1
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- resin sheet
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- porous resin
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Images
Classifications
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- H10N30/80—Constructional details
- H10N30/85—Piezoelectric or electrostrictive active materials
- H10N30/857—Macromolecular compositions
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- D06N3/00—Artificial leather, oilcloth or other material obtained by covering fibrous webs with macromolecular material, e.g. resins, rubber or derivatives thereof
- D06N3/0002—Artificial leather, oilcloth or other material obtained by covering fibrous webs with macromolecular material, e.g. resins, rubber or derivatives thereof characterised by the substrate
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- D—TEXTILES; PAPER
- D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
- D06N—WALL, FLOOR, OR LIKE COVERING MATERIALS, e.g. LINOLEUM, OILCLOTH, ARTIFICIAL LEATHER, ROOFING FELT, CONSISTING OF A FIBROUS WEB COATED WITH A LAYER OF MACROMOLECULAR MATERIAL; FLEXIBLE SHEET MATERIAL NOT OTHERWISE PROVIDED FOR
- D06N3/00—Artificial leather, oilcloth or other material obtained by covering fibrous webs with macromolecular material, e.g. resins, rubber or derivatives thereof
- D06N3/0002—Artificial leather, oilcloth or other material obtained by covering fibrous webs with macromolecular material, e.g. resins, rubber or derivatives thereof characterised by the substrate
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- D—TEXTILES; PAPER
- D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
- D06N—WALL, FLOOR, OR LIKE COVERING MATERIALS, e.g. LINOLEUM, OILCLOTH, ARTIFICIAL LEATHER, ROOFING FELT, CONSISTING OF A FIBROUS WEB COATED WITH A LAYER OF MACROMOLECULAR MATERIAL; FLEXIBLE SHEET MATERIAL NOT OTHERWISE PROVIDED FOR
- D06N3/00—Artificial leather, oilcloth or other material obtained by covering fibrous webs with macromolecular material, e.g. resins, rubber or derivatives thereof
- D06N3/0056—Artificial leather, oilcloth or other material obtained by covering fibrous webs with macromolecular material, e.g. resins, rubber or derivatives thereof characterised by the compounding ingredients of the macro-molecular coating
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- D—TEXTILES; PAPER
- D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
- D06N—WALL, FLOOR, OR LIKE COVERING MATERIALS, e.g. LINOLEUM, OILCLOTH, ARTIFICIAL LEATHER, ROOFING FELT, CONSISTING OF A FIBROUS WEB COATED WITH A LAYER OF MACROMOLECULAR MATERIAL; FLEXIBLE SHEET MATERIAL NOT OTHERWISE PROVIDED FOR
- D06N3/00—Artificial leather, oilcloth or other material obtained by covering fibrous webs with macromolecular material, e.g. resins, rubber or derivatives thereof
- D06N3/04—Artificial leather, oilcloth or other material obtained by covering fibrous webs with macromolecular material, e.g. resins, rubber or derivatives thereof with macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
- D06N3/047—Artificial leather, oilcloth or other material obtained by covering fibrous webs with macromolecular material, e.g. resins, rubber or derivatives thereof with macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds with fluoropolymers
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- H01—ELECTRIC ELEMENTS
- H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
- H01G7/00—Capacitors in which the capacitance is varied by non-mechanical means; Processes of their manufacture
- H01G7/02—Electrets, i.e. having a permanently-polarised dielectric
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
- H01G7/00—Capacitors in which the capacitance is varied by non-mechanical means; Processes of their manufacture
- H01G7/02—Electrets, i.e. having a permanently-polarised dielectric
- H01G7/028—Electrets, i.e. having a permanently-polarised dielectric having a heterogeneous dielectric
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N30/00—Piezoelectric or electrostrictive devices
- H10N30/01—Manufacture or treatment
- H10N30/09—Forming piezoelectric or electrostrictive materials
- H10N30/092—Forming composite materials
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N30/00—Piezoelectric or electrostrictive devices
- H10N30/01—Manufacture or treatment
- H10N30/09—Forming piezoelectric or electrostrictive materials
- H10N30/098—Forming organic materials
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N30/00—Piezoelectric or electrostrictive devices
- H10N30/80—Constructional details
- H10N30/85—Piezoelectric or electrostrictive active materials
- H10N30/852—Composite materials, e.g. having 1-3 or 2-2 type connectivity
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N30/00—Piezoelectric or electrostrictive devices
- H10N30/80—Constructional details
- H10N30/88—Mounts; Supports; Enclosures; Casings
- H10N30/883—Additional insulation means preventing electrical, physical or chemical damage, e.g. protective coatings
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- D—TEXTILES; PAPER
- D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
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- D06N2201/00—Chemical constitution of the fibres, threads or yarns
- D06N2201/02—Synthetic macromolecular fibres
- D06N2201/029—Fluoropolymer fibres
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- D06N2203/00—Macromolecular materials of the coating layers
- D06N2203/04—Macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
- D06N2203/044—Fluoropolymers
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- D—TEXTILES; PAPER
- D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
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- D06N2205/00—Condition, form or state of the materials
- D06N2205/20—Cured materials, e.g. vulcanised, cross-linked
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- D06N2209/00—Properties of the materials
- D06N2209/04—Properties of the materials having electrical or magnetic properties
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- D—TEXTILES; PAPER
- D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
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- D06N2213/00—Others characteristics
- D06N2213/02—All layers being of the same kind of material, e.g. all layers being of polyolefins, all layers being of polyesters
Definitions
- the present invention relates to a piezoelectric laminate having a surface coating layer having a volume resistivity of a specific value or more on at least one surface of a porous resin sheet, and a piezoelectric sheet that can be used for the piezoelectric laminate.
- Piezoelectric materials using porous organic materials are being studied.
- EMFIT Finland
- EMFIT Finland
- This sheet has a structure in which independent pores are uniformly distributed throughout the sheet.
- the value of piezoelectricity gradually decreases with time. This is considered to be caused by the gradual electrical neutralization or decay of the polarized charge held in the adjacent porous structure.
- Patent Document 1 discloses a polymer porous electret in which a conductive layer is formed on the front and back surfaces of an organic polymer porous body, and an insulator is disposed on at least one of the front and back conductive layers.
- Patent Document 2 discloses an electret film comprising a core layer having pores and a surface layer having insulating properties on at least one surface thereof.
- Patent Document 3 discloses a laminated sheet in which an insulating plate is provided on at least one surface of a porous resin sheet.
- Patent Document 4 discloses a laminate in which a cover layer having a specific capacitance index is laminated on one side or both sides of a porous resin sheet.
- Patent Document 5 discloses a laminated film in which a non-porous fluororesin thin film is bonded to one or both sides of a porous fluororesin film.
- Patent Documents 1 to 5 do not discuss the difference in elastic modulus between the porous resin sheet and the layer laminated thereon.
- the conventional piezoelectric material has room for improvement in terms of charge retention over a long period of time and high piezoelectricity retention.
- An object of the present invention is to provide a piezoelectric laminate and a piezoelectric sheet that retain a polarized charge in a porous structure for a long time and retain a high piezoelectric rate.
- the present invention relates to the following [1] to [19], for example.
- a porous resin sheet Of the outer surface of the porous resin sheet, having at least a surface coating layer laminated on any one of the front and back surfaces of the porous resin sheet, A piezoelectric laminate in which the volume resistivity of the surface coating layer is 1 ⁇ 10 13 ⁇ ⁇ cm or more, and the elastic modulus of the porous resin sheet is different from that of the surface coating layer.
- the porous resin sheet is a sheet in which at least charge-induced hollow particles are dispersed in a matrix resin;
- the charge-induced hollow particles are particles in which a conductive substance is attached to at least a part of the surface of the hollow particles,
- the conductive substance is a substance having a higher conductivity than any of the hollow particles and the matrix resin.
- a piezoelectric sheet comprising a nonwoven fabric or a woven fabric formed from fibers made of an organic polymer.
- a piezoelectric sheet comprising a nonwoven fabric or woven fabric formed from fibers made of an inorganic material and having a porosity of 60% or more.
- a piezoelectric laminate in which the volume resistivity of the surface coating layer is 1 ⁇ 10 13 ⁇ ⁇ cm or more, and the elastic modulus of the piezoelectric sheet is different from that of the surface coating layer.
- the present invention it is possible to provide a piezoelectric laminate and a piezoelectric sheet that retain a polarized charge in a porous structure for a long time and retain a high piezoelectric rate.
- a surface coating layer having a volume resistivity within a specific range is laminated on at least one side of the back surface of the porous resin sheet, the charge retained on the porous resin sheet Is disconnected from the external environment, the charge attenuation is suppressed, and effectively functions to maintain the piezoelectric constant.
- the elastic modulus of the porous resin sheet constituting the piezoelectric laminate and the surface coating layer are different, it is possible to induce non-linear deformation with respect to compressive strain at the time of charge extraction.
- a piezoelectric laminate having a high piezoelectric rate can be provided.
- the piezoelectric sheet of the present invention including a nonwoven fabric or a woven fabric formed from fibers made of an organic polymer has a high porosity, excellent charge retention, and particularly high charge retention. Moreover, the piezoelectric sheet of the present invention including a nonwoven fabric or a woven fabric formed from fibers made of an inorganic material and having a porosity of 60% or more has high flexibility and high piezoelectricity.
- FIG. 1 shows the present invention schematically showing how charge-induced hollow particles 5 (hollow particles 3 having a conductive material 4 attached to the surface) and hollow particles 3 are dispersed in a matrix resin 2.
- FIG. 1 shows an example of the cross section of the porous resin sheet 1 used.
- 2A shows an SEM image of the cross section of the porous resin sheet obtained in Reference Example 1
- FIG. 2B shows an SEM image of the cross section of the porous resin sheet obtained in Reference Example 3.
- FIGS. 2A and 2B differ from each other in the manner of dispersion of the particles (charge-induced hollow particles 5 and / or hollow particles 3).
- FIG. 3A shows a uniform dispersion model diagram
- FIG. 3B shows a sea-island structure model diagram.
- FIG. 4 shows a flowchart of an example of a method for producing a porous resin sheet used in the present invention.
- FIG. 5 is a graph plotting the piezoelectric constant d 33 (pC / N) of the porous resin sheets obtained in Comparative Example 3 and Reference Examples 1 and 2 over time.
- FIG. 6 shows a graph in which the piezoelectric constant d 33 (pC / N) of the porous resin sheet obtained in Reference Example 3 is plotted over time.
- FIG. 5 is a graph plotting the piezoelectric constant d 33 (pC / N) of the porous resin sheets obtained in Comparative Example 3 and Reference Examples 1 and 2 over time.
- FIG. 6 shows a graph in which the piezoelectric constant d 33 (pC / N) of the porous resin sheet obtained in Reference Example 3 is plotted over time.
- FIG. 7 is a schematic cross-sectional view showing an example of the piezoelectric laminate of the present invention.
- FIG. 8 is a schematic cross-sectional view showing an example of the piezoelectric laminate of the present invention.
- FIG. 9 is a schematic cross-sectional view showing an example of the piezoelectric laminate of the present invention.
- FIG. 10 is a schematic cross-sectional view showing an example of the piezoelectric laminate of the present invention.
- FIG. 11 is a schematic cross-sectional view showing an example of the piezoelectric laminate of the present invention.
- FIG. 12 shows the evaluation results of the charge responsiveness of the piezoelectric laminates obtained in Examples 6 and 9.
- the piezoelectric laminate of the present invention has a porous resin sheet and a surface coating layer laminated on at least one of the front and back surfaces of the porous resin sheet among the outer surfaces of the porous resin sheet.
- a piezoelectric sheet including a nonwoven fabric or a woven fabric formed from a fiber made of an inorganic material and having a porosity of 60% or more, and at least the front and back surfaces of the piezoelectric sheet among the outer surfaces of the piezoelectric sheet And a surface coating layer laminated on any one surface.
- the volume resistivity of the surface coating layer is 1 ⁇ 10 13 ⁇ ⁇ cm or more, and the elastic modulus of the porous resin sheet or piezoelectric sheet is different from that of the surface coating layer.
- the porous resin sheet used in the present invention is preferably a sheet made of an organic material capable of holding an electric charge.
- the porous resin sheet made of such an organic material include a porous resin sheet made of a mixture of a matrix resin and at least charge-induced hollow particles, a sheet-like foam made of an organic polymer, and an organic polymer. Nonwoven fabrics or woven fabrics, stretched porous membranes made of organic polymers, and the like.
- hole is also mentioned.
- the thickness of the porous resin sheet is usually 10 ⁇ m to 1 mm, preferably 50 ⁇ m to 500 ⁇ m.
- organic polymer used as the raw material of the foam examples include polyurethane resin, polystyrene resin, vinyl acetate resin, polyethylene terephthalate resin, phenol resin, silicone resin, polyvinyl chloride resin, urea resin, acrylic resin, polyimide resin, fluorine Examples thereof include resins and ethylene propylene resins.
- Examples of the organic polymer used as a raw material for the nonwoven fabric or the woven fabric include polymers having a volume resistivity of 1.0 ⁇ 10 15 ⁇ ⁇ cm or more.
- polyamide resins (6-nylon, 6,6-nylon, etc.)
- Aromatic polyamide resins such as aramid
- polyolefin resins such as polyethylene and polypropylene
- polyester resins such as polyethylene terephthalate
- polyacrylonitrile phenolic resins, fluorine resins (polytetrafluoroethylene, polyfluorinated) Vinylidene, etc.), imide resins (polyimide, polyamideimide, bismaleimide, etc.).
- the organic polymer that has a high continuous usable temperature and does not have a dipole due to the molecule and crystal structure, or does not have a glass transition point in the operating temperature range of the piezoelectric laminate.
- the continuously usable temperature can be measured by a continuous use temperature test described in UL746B (UL standard), and is preferably 100 ° C. or higher, and more preferably 200 ° C. or higher.
- an organic polymer exhibiting water repellency is preferable.
- a polyolefin-based resin, an imide-based resin, and a fluorine-based resin are preferable, and in particular, polytetrafluoroethylene (PTFE) is more preferable.
- Examples of the organic polymer that is a raw material for the stretched porous membrane include polyethylene, polypropylene, polyvinylidene fluoride, and polytetrafluoroethylene.
- the porous resin sheet used in the present invention is preferably a sheet made of a mixture of a matrix resin and at least charge-induced hollow particles from the viewpoint that a high piezoelectric constant can be maintained over a long period of time.
- a porous resin sheet containing a nonwoven fabric made of an organic polymer and a piezoelectric sheet containing a nonwoven fabric formed from fibers made of an organic polymer. More preferred.
- porous resin sheet comprising a mixture of matrix resin and at least charge-induced hollow particles
- the porous resin sheet comprising a mixture of matrix resin and at least charge-inducing hollow particles is, for example, a porous resin sheet comprising a mixture in which at least charge-inducing hollow particles are dispersed in the matrix resin.
- the hollow conductive particles are particles in which a conductive substance is attached to at least a part of the surface of the hollow particles, and the conductive substance is preferably a substance having higher conductivity than the hollow particles and the matrix resin. .
- the initial value of the dielectric constant d 33 of such a porous resin sheet is preferably 110 pC / N or more, more preferably about 115 to 160 pC / N.
- the piezoelectric constant d 33 after 5 days is preferably 60 pC / N or more, more preferably 70 pC / N or more, and the piezoelectric constant d 33 after 25 days is preferably 50 pC / N or more.
- FIG. 1 is an example of such a porous resin sheet.
- a porous resin sheet (hereinafter also simply referred to as “resin sheet”) 1 in FIG. 1 is a hollow particle to which conductive material 4 is not attached (hereinafter also simply referred to as “conductive material-free particle”). 3 and charge-induced hollow particles 5 are dispersed in the matrix resin 2.
- the resin sheet 1 may not include the conductive material-free particles 3 in the resin sheet 1 (not shown).
- the charge-induced hollow particles are those in which a conductive substance is attached to the surface of the hollow particles (which may be all or only part of the surface).
- the conductivity of the charge-induced hollow particles and the conductive material is preferably higher than the conductivity of the matrix resin and the conductive material-free particles.
- the resin sheet 1 in which the conductive substance-free particles 3 and the charge-inducing hollow particles 5 are used together and mixed is preferable because it is considered that the conductive path composed of the charge-inducing hollow particles 5 can be blocked.
- the charge retention rate of the resin sheet 1 is improved, and it is considered that high piezoelectric characteristics can be maintained over a long period of time.
- a porous resin sheet made of a mixture of a matrix resin and at least charge-induced hollow particles was actually produced, and the cross section thereof was imaged with a scanning electron microscope [SEM].
- the SEM images are shown in (A) and (B) of FIG.
- the scanning electron microscope used for imaging is “S-3400” manufactured by Hitachi High-Technologies Corporation, and the magnification is 100 times.
- the SEM image of FIG. 2 (A) seems to have these particles uniformly dispersed in the resin sheet, and the SEM image of FIG. 2 (B) gathers the particles in a lump (island) shape. Each island appears to be evenly distributed.
- FIGS. 3A and 3B a uniform dispersion model and a sea-island structure model are shown in FIGS. 3A and 3B, respectively.
- FIG. 3A as in FIG. 1, the charge-induced hollow particles 5 and the conductive material-free particles 3 are uniformly dispersed, whereas in FIG.
- the particle-containing particles 3 and / or the charge-induced hollow particles 5 contain island structures a and b having a high agglomeration ratio and a large hollow ratio, and the island structure parts a and b are uniformly dispersed.
- an embodiment shown by a dotted line surrounded by a and b in FIG. can be mentioned.
- the island a is a mode in which the particles 3 surround the particles 5 existing in the center of the island
- the island b is a mode in which the particles 5 are not in the center but exist in the outermost layer of the island.
- the island a is preferable. It is thought that the island shown in FIG. 3B can be regarded as a pseudo large hollow particle.
- the resin sheet by charge-induced hollow particles 5 It is difficult to form a conductive path leading to the surface, and in particular, the resin sheet 1 containing the island a has a conductive path that does not include a conductive substance around the charge-induced hollow particles 5, and thus has a conductive path. Is difficult to form. For this reason, the charge retention rate of the resin sheet 1 is improved, and the sea-island structure model in FIG. 3B has a slower decay of piezoelectric characteristics over time than the uniform dispersion model in FIG. It is assumed that high piezoelectric characteristics can be maintained.
- FIG. 3B The details of FIG. 3B are as follows.
- Other examples of the sea-island structure include a sea structure with a small hollow ratio (that is, a structure portion with a low content of the particles 3 and / or particles 5), and an island structure with a large hollow ratio (that is, the particles 3 and / or the particles 5). And a structure composed of a structural part having a high content ratio.
- a high piezoelectricity is expressed in an island structure with a large hollow ratio, and a sea structure with a small hollow ratio prevents physical approach between polarized charges and suppresses a decrease in piezoelectricity.
- the resin sheet 1 having such a sea-island structure that is, the particles 3 and / or the particles 5 are non-uniformly dispersed inside the sheet, both high piezoelectricity and long-term piezoelectric characteristics can be maintained. It is speculated that it is possible.
- charge-induced hollow particles 5 In the charge-inducing hollow particles 5 used for the resin sheet 1, the conductive substance 4 is attached to at least a part or the entire surface of the hollow particles. Such charge-inducing hollow particles 5 can be obtained, for example, by attaching or vapor-depositing the conductive material 4 on at least a part of the surface of the hollow particles, and at least a part of the surface as a hollow particle.
- particles having a carbon atom-attached substance hereinafter also referred to as “surface-treated particles”
- they can be obtained by heat treatment under conditions that carbonize the substance having the carbon atom. Specifically, it can be obtained in the following “pre-carbonization method” step (1a), “post-carbonization method” step (2 ′) and “deposition method” step (1c).
- the conductive material-free particles 3 are particles whose inside is sealed, that is, particles having a space independent from the outside, and are preferably particles whose structure is not easily destroyed when melt-kneaded with the matrix resin 2. Examples of such hollow particles include glass particles, ceramic particles, and organic polymer particles, and hollow particles made of an insulating material are preferable.
- the inside of the particles 3 may be either vacuum or normal pressure depending on the use of the obtained sheet, and in the case of normal pressure, it is often filled with air or the like.
- the particles 3 may be hollow particles with no conductive substance adhering to the surface thereof, or may be the glass-made particles as they are (untreated particles), a substance having a carbon atom on the surface, or the like. May be attached.
- hollow glass particles examples include soda lime glass, soda lime borosilicate glass, borosilicate glass, borosilicate soda glass, sodium silicate glass, aluminosilicate glass, and the like.
- the glass content of the glass hollow particles is preferably 10 to 30% by volume. If the glass content is 10% by volume or more, since the hollow particles have sufficient mechanical strength, it is difficult to be destroyed in the resin sheet manufacturing process, and the hollow structure can be maintained. A high porosity can be secured.
- Ceramic hollow particles examples include hollow particles made of alumina.
- both hollow particles made of an already-expanded organic polymer and hollow particles made of a thermally-expandable organic polymer can be used.
- the already-expanded organic polymer for example, Cross-linked styrene-acrylic polymers, acrylonitrile-based polymers, and the like can be mentioned, and examples of the thermally expandable organic polymer include acrylonitrile-based polymers.
- the size of the conductive material-free particles 3 is not particularly limited, but the use of particles having a 50% particle diameter (cumulative median diameter) of 1 to 100 ⁇ m provides high piezoelectric properties and high charge. It is preferable at the point that the resin sheet which ensures the retention rate and the mechanical strength of the sheet itself is obtained.
- the particle diameter of the hollow particles is measured based on a dynamic light scattering method.
- the conductive material-free particles 3 have an independent pore structure, they can maintain a constant elasticity over a long period of time even when a continuous external stress is applied to the resin sheet, and most of the piezoelectric properties of the resin sheet can be maintained. Do not decrease.
- the conductive substance 4 is attached to part or all of the surface of the hollow particles, and has a function of holding electric charge in the resin sheet.
- the conductive substance 4 is preferably a substance having a higher conductivity than the conductive substance-free particles 3 and the matrix resin 2, and more preferably has a conductivity of 1.0 ⁇ 10 ⁇ 10 S / cm or more. It is a substance.
- the conductivity is measured using a double ring electrode method based on the conductivity of a single conductive substance.
- the resin sheet 1 When the following polarization treatment is performed during the production of the resin sheet 1 due to the presence of the conductive material 4 on the surface of the hollow particles, a charge may be injected into the resin sheet 1 at a lower voltage.
- the piezoelectric characteristics of the resin sheet 1 can be maintained over a long period of time.
- the resin sheet 1 can exhibit a high piezoelectric initial value and a long-term property retention characteristic by including the conductive material-free particles 3 and the charge-induced hollow particles 5. it can.
- the conductive substance attached to or deposited on the hollow particles is preferably one or more selected from the group consisting of carbon, graphite, platinum, gold, and ITO (indium tin oxide).
- the conductive substance 4 is obtained by heat-treating the substance having carbon atoms attached to the surface of the surface-treated particles in the matrix resin 2 in an oxygen-blocking atmosphere (as a result, the substance is probably carbonized. It may be a material obtained. For example, it can be obtained by carbonizing a material having carbon atoms by heat treatment (at a temperature equal to or higher than its thermal decomposition temperature, usually at a temperature equal to or higher than the melting point of the matrix resin and lower than its decomposition temperature).
- the substance having a carbon atom to be subjected to such heat treatment is preferably a substance containing a hydrocarbon group, for example, a surfactant, a silane coupling agent, an aluminate series containing a hydrocarbon group.
- a surfactant for example, a surfactant, a silane coupling agent, an aluminate series containing a hydrocarbon group.
- a coupling agent and a titanate coupling agent may be mentioned.
- the substance having a hydrocarbon group a substance having a thermal decomposition start temperature under normal pressure of usually 100 to 300 ° C., preferably 150 to 250 ° C., is the operability when obtaining the charge-induced hollow particles 5. It is desirable in terms of Further, the thermal decomposition start temperature (carbonization temperature) of the substance containing a hydrocarbon group is more specifically a temperature that is usually 50 ° C. or more lower than the thermal decomposition temperature of the matrix resin 2, preferably a temperature that is 100 ° C. or more lower. It is desirable from the viewpoint of ease of heat treatment temperature control.
- the surfactant will be described in detail.
- the surfactant include nonionic, zwitterionic, and cationic surfactants having a hydrocarbon group.
- the matrix resin under oxygen blocking conditions
- It is heated to a temperature higher than the decomposition temperature of the surfactant and thermally decomposed to become a conductive material (probably decomposed into carbon, water, amorphous surfactant thermal decomposition products, etc.), and no environmental load is generated.
- Inexpensive materials are desirable, and surfactants such as those described in the Internet homepage “http://www.ecosci.jp/sa/sa.html” and the like can be mentioned.
- Nonionic surfactants include fatty acid diethanolamide ⁇ R—CON (CH 2 CH 2 OH) 2 , R: an alkyl group of C1-20, preferably an alkyl group of about C5-15 ⁇ , specifically, For example, C 11 H 23 —CON (CH 2 CH 2 OH) 2, etc., polyoxyethylene alkyl ether (AE) [higher alcohol type, R—O (CH 2 CH 2 O) n H, R: about C1-20 Alkyl group, n: 1 to 30, preferably an integer of about 5 to 15], specifically, for example, C 12 H 25 —O (CH 2 CH 2 O) 8 H, and the like, polyoxyethylene alkylphenyl ether (APE) ⁇ (R— (C 6 H 4 ) O (CH 2 CH 2 O) n H, R: C1-20 alkyl group, preferably about C5-15 alkyl group, n: 1-30, preferably Is an integer of about 5 to 15) ⁇ Thereof include, for example, C 9 H 19
- zwitterionic surfactants include alkylcarboxybetaines [betaines] ⁇ RN + (CH 3 ) 2 .CH 2 COO ⁇ , R: C1-20, preferably about C5-15 alkyl groups ⁇ , specifically Specifically, for example, C 12 H 25 —N + (CH 3 ) 2 .CH 2 COO ⁇ and the like can be mentioned.
- nonionic surfactants are preferable from the viewpoint of suppressing charge decay of the porous resin sheet, and among these, polyoxyethylene alkyl ether is particularly preferable.
- a fluorine-based surfactant having a perfluoroalkyl group as a substance having a carbon atom and having excellent wettability, permeability and the like can be mentioned.
- perfluoroalkyl carboxylic acid (CF 3 (CF 2 ) n COOH, n: repeating unit) PFOA
- fluorine telomer alcohol F (CF 2 ) n CH 2 CH 2 OH, n: repeating unit
- nonionic surfactant for example, a nonionic surfactant of “Nonion ID-206” manufactured by NOF Corporation (thermal decomposition starting temperature under normal pressure: 150 ° C.) can be preferably used.
- fluorine-based surfactant include fluorine-containing surfactant (Surflon) “S-241” (thermal decomposition start temperature under normal pressure: 220 ° C.) manufactured by AGC Seimi Chemical Co., Ltd.
- Nonionic fluorosurfactant or anionic fluorosurfactant such as a commercial product of Neos Co., Ltd.
- “Factent 251” thermal decomposition start temperature under normal pressure: 220 ° C.
- the adhesion amount of the surfactant is about 0.1 to 5 wt% with respect to 100 wt% of the weight of the hollow particles.
- the matrix resin 2 is not particularly limited, and examples thereof include resins having a thermal decomposition starting temperature of 150 to 450 ° C., for example, a copolymer [PFA] of tetrafluoroethylene and perfluoroalkyl vinyl ether (for example, apparent density: 1.
- a copolymer [PFA] of tetrafluoroethylene and perfluoroalkyl vinyl ether for example, apparent density: 1.
- thermoplastic resin from the viewpoint of easy work of uniformly dispersing the conductive material-free particles 3 and / or the charge-induced hollow particles 5.
- the matrix resin 2 is preferably a material that is different in charging tendency from the hollow particles that are easily charged positively from the viewpoint of charging characteristics, and that is more distant from the charge train, such as a fluorine-containing resin or an imide resin. Preferably there is.
- the “material farther away in the charged column” used in this specification is the fiber society edition, “Fiber manual (raw material edition)”, Maruzen (1968), and fluorine-containing resins in which the charged column is positioned on the negative side of the glass hollow particles based on the charged column table disclosed in Hidetoshi Tsuchida, Taku Shinohara, Polymer, 16, 347 (1967) The material etc. are mentioned.
- the matrix resin 2 is preferably a resin having a high melting temperature and a high thermal decomposition starting temperature from the viewpoint of heat resistance, for example, a fluorine-containing resin or an imide resin.
- the carbon atom-containing substance is heat-treated to obtain a desired conductivity. Pyrolysis higher than the minimum temperature required to become (possibly carbonized), ie the pyrolysis onset temperature of a substance having carbon atoms (referred to as the temperature when reduced by 5% in the measurement of thermal raw materials in air) A matrix resin 2 having a starting temperature is preferred.
- a resin having a thermal decomposition start temperature in the range of 150 to 450 ° C. is preferable, and a resin having a thermal decomposition start temperature in the range of 300 to 450 ° C. is more preferable.
- PFA pyrolysis start temperature
- Fluorine-containing resin such as FEP (thermal decomposition start temperature: about 400 ° C.), ETFE (thermal decomposition start temperature: about 360 ° C.), PCTFE (thermal decomposition start temperature: about 340 ° C.), polyimide, etc.
- an imide resin such as (thermal decomposition start temperature: about 400 ° C.) or bismaleimide (thermal decomposition start temperature: about 400 ° C.).
- the obtained resin sheet 1 is more preferable because it is excellent in heat resistance and weather resistance, and particularly excellent in the temporal stability of piezoelectric characteristics at a high temperature of 80 ° C. or higher.
- Method for producing porous resin sheet 1 is not particularly limited, for example, any of “pre-carbonization method”, “post-carbonization method” and “evaporation method” as shown in FIG. 4 can be adopted.
- the following “two-stage dispersion method” is applied in the pre-carbonization method and the vapor deposition method step (2) and the post-carbonization method step (2 ′). The method of doing is mentioned.
- the pre-carbonization method is Step (1a): Heat-treating the surface-treated particles and thermally decomposing the adhering substance of the particles, thereby causing a part or all of the particles to become electrically conductive (possibly carbonized), and at least a part of the surface of the hollow particles.
- Step (2) a step of melt-kneading the charge-inducing hollow particles obtained in step (1a), the matrix resin and, if necessary, particles not containing a conductive material, and then forming into a sheet
- 3) It includes a step of injecting electric charge into the sheet by subjecting the sheet obtained in the step (2) to polarization treatment.
- charge-induced hollow particles are formed in the step (1a).
- the substance having a carbon atom is a surfactant containing a hydrocarbon group
- the surface-treated particles are prepared by diluting a surfactant containing a hydrocarbon group with an appropriate solvent (for example, methyl alcohol), It can be obtained by a method of immersing hollow particles in the obtained surfactant solution.
- the amount of the surfactant used is preferably less than 5%, more preferably about 0.1 to 1.0%, based on the weight of the hollow particles, although it depends on the type of the surfactant. .
- the amount of the surfactant exceeds 5% with respect to the weight of the hollow particles, there is a possibility that the electric charge easily escapes from the porous resin sheet. On the other hand, if it is less than 0.1%, it may be difficult to form a conductive substance on the surface of the hollow particles.
- Examples of the heat treatment in the above step (1a) include, for example, a treatment at 250 to 400 ° C. for 10 to 120 minutes by blocking oxygen. Such heat treatment yields charge-induced hollow particles, probably because at least a portion (preferably all) of the carbon-containing functional group portion of the substance having carbon atoms is probably carbonized. In addition, it is considered that a conductive substance is formed on at least a part (preferably all) of the surface of the hollow particles.
- the charge-induced hollow particles obtained in the step (1a) are kneaded with the matrix resin and, if necessary, the conductive material-free particles, and then molded to obtain a porous resin sheet.
- This porous resin sheet can be produced by a conventionally known method.
- the matrix resin is a thermoplastic resin
- the charge-induced hollow particles and the matrix are formed by a molding machine such as a single-screw or twin-screw extruder.
- the resin is molded into a sheet using, for example, a pressure molding machine or a T die.
- the melting temperature is preferably 10 to 50 ° C. higher than the melting point of the matrix resin.
- the melting time is preferably 1 to 30 minutes.
- the heating temperature at the time of molding is preferably 10 to 50 ° C. higher than the melt kneading temperature, and is preferably a temperature lower than the thermal decomposition start temperature of the matrix resin.
- the heating time is preferably 10 to 120 minutes.
- the elasticity of the matrix resin is changed by adding elasticity control aids (eg, silicone resin fine particles, styrene resin fine particles, acrylic resin fine particles, etc.) at the kneading stage before the sheet is manufactured.
- elasticity control aids eg, silicone resin fine particles, styrene resin fine particles, acrylic resin fine particles, etc.
- Sensitivity to stress can be optimized.
- step (3) by applying a polarization treatment to the sheet obtained in the step (2), charges can be injected into the sheet. More specifically, charges are injected by subjecting the sheet surface formed in step (2) to a polarization treatment such as corona discharge. It is considered that the injected charges are concentrated on the shell portion (conductive material portion) of the charge-inducing hollow particles and induce polarization in the hollow structure. A part of the induced charge is considered to be held at the interface between the charge-induced hollow particles and the matrix resin.
- the sheet obtained in the step (3) can take out electric charges through the front and back surfaces of the sheet by applying a compressive load in the sheet thickness direction. That is, charge transfer occurs with respect to the external load (electric circuit), and an electromotive force is obtained.
- a step of obtaining a sheet containing charge-induced hollow particles in which conductivity is generated in the substance having the conductive particles and at least a part of the surface of the hollow particles is attached; and step (3): obtained in step (2 ′) A step of injecting electric charge into the sheet by subjecting the sheet to polarization treatment.
- Examples of the step (1b) include the same method as the method for obtaining the surface-treated particles in the step (1a) described above.
- the melt kneading temperature in the step (2 ′) is preferably 10 to 100 ° C. higher than the melting point of the matrix resin, and more preferably 10 to 50 ° C. higher.
- the melting time is preferably 1 to 30 minutes.
- the heating temperature at the time of molding is preferably a temperature 10 to 50 ° C. higher than the melt kneading temperature, and a temperature lower than the thermal decomposition start temperature of the matrix resin.
- the heating time is preferably 10 to 120 minutes.
- the conductivity of the substance having carbon atoms is caused, specifically, it is lower than the thermal decomposition start temperature of the matrix resin, at a temperature of 100 to 350 ° C. for about 10 minutes to 6 hours, under reduced pressure to increased pressure ( (Example: 0.1 Pa to 10 MPa) is preferable from the viewpoint of the performance of the obtained sheet (eg, the initial value of the piezoelectricity is high and the decrease in the piezoelectricity with time is small).
- reduced pressure to increased pressure (Example: 0.1 Pa to 10 MPa) is preferable from the viewpoint of the performance of the obtained sheet (eg, the initial value of the piezoelectricity is high and the decrease in the piezoelectricity with time is small).
- the matrix resin for example, FEP (melting point: 260 ° C., thermal decomposition start temperature: 400 ° C.) will be described as an example of the matrix resin.
- the surface-treated particles and the FEP are melt-kneaded (typically about 300 to 310 ° C. for about 30 minutes) by a molding machine such as a single-screw or twin-screw extruder.
- the matrix resin is thermally decomposed at a temperature higher than the melt kneading temperature (eg, about 10 to 50 ° C.).
- pressurization is performed under air cooling conditions (eg, normal temperature) or under heating to a desired shape at a pressure of 40 to 150 kgf / cm 2 .
- the carbon-containing functional group portion of the substance having carbon atoms covering the surface of the hollow particles is preferably at least a part thereof (preferably Are all thermally decomposed and carbonized in a non-supplying atmosphere of oxygen, and as a result, charge-induced hollow particles having a conductive substance attached to the surface of the hollow particles can be obtained.
- Process (3) is as described above.
- Step (1c) A step of obtaining charge-induced hollow particles in which a conductive substance is attached to at least a part of the surface of the hollow particles by depositing a conductive material on at least a part of the surface of the hollow particles;
- Step (2) The step of kneading the charge-inducing hollow particles obtained in Step (1c), the matrix resin and, if necessary, the conductive material-free particles, and then molding into a sheet;
- Step (3) It includes a step of injecting electric charge into the sheet by subjecting the sheet obtained in the step (2) to polarization treatment.
- the charge-induced hollow particles can be formed by depositing a conductive substance on at least a part (preferably all) of the surface of the hollow particles.
- the conductive material that can be vapor-deposited include carbon, graphite, platinum, gold, and ITO, and may be used alone or in combination of two or more.
- a conventionally well-known method can be employ
- Steps (2) and (3) are the same as those described above.
- a conductive material may be attached to the surface of the hollow particles by plating.
- FIG. 3 (B) an island structure portion as indicated by symbols a and b (aggregates having a high content of particles 3 and / or particles 5, preferably aggregates having a high content of particles 3 and particles 5).
- the resin sheet 1 in which is uniformly dispersed can be manufactured as follows.
- step (2) of the pre-carbonization method and the vapor deposition method and the step (2 ′) of the post-carbonization method instead of “charge-inducing hollow particles 5” or “surface-treated particles”, “charge-inducing hollow Aggregates obtained by kneading particles 5 or surface-treated particles, conductive material-free particles 3 and a resin having a higher viscosity than matrix resin 2 (hereinafter also referred to as “aggregate resin”) ”
- the resin sheet 1 having a sea-island structure can be produced in the same manner as any of the pre-carbonization method, the post-carbonization method, and the vapor deposition method except that is used.
- the agglomerated structure is less likely to collapse, and a resin sheet having the desired island structure remains. Obtainable.
- the hollow ratio of the island structure (that is, the aggregate in which the content of particles 3 and / or particles 5 is higher than that of the sea structure) contained in the resin sheet 1 is 30 to 80% by volume.
- the hollow ratio of the sea structure that is, the structure having a low content of particles 3 and / or particles 5
- the distance between the island structures can be maintained and the charges polarized in the island structure can be maintained over a long period.
- the hollowness of the resin sheet 1 having a sea-island structure is preferably 10 to 70% by volume, more preferably 15 to 60% by volume. It is desirable in terms of maintaining the mechanical strength.
- the hollow ratio of the resin sheet having the sea structure, the island structure, and the sea-island structure is calculated by the following formula based on the amount of the material used for the sheet preparation.
- Hollow ratio (%) ((volume A ⁇ volume B) / volume A) ⁇ 100 Volume A: Volume calculated from material weight and material specific gravity (true specific gravity) Volume B: Volume calculated from material weight and specific gravity excluding hollow structure
- the obtained resin sheet 1 having a sea-island structure When the hollow ratio of the resin sheet 1 having a sea-island structure is less than 10% by volume, the obtained resin sheet cannot store a sufficient charge, and the obtained resin sheet 1 may not ensure a sufficient piezoelectric rate as a piezoelectric material. is there. Further, when the hollowness exceeds 70% by volume, the distance between the island structures is substantially close, so that the effect of forming the sea-island structure is reduced, that is, the purpose of enhancing the retention of piezoelectric characteristics cannot be achieved. There is a case.
- the size of the island structure is preferably about 0.1 to 1.0 times the thickness of the sheet molding.
- the resin for aggregates is preferably a resin having a viscosity higher than that of the matrix resin 2 at the time of kneading and molding, and examples thereof include the resins exemplified as the matrix resin 2.
- a resin having an elastic modulus different from that of the matrix resin it is preferable to use a resin having an elastic modulus different from that of the matrix resin as the aggregate resin.
- a resin sheet manufactured using a resin having a modulus of elasticity different from that of the matrix resin as an agglomerate resin undergoes non-linear deformation with respect to compressive strain during charge extraction. Deformation takes place and can therefore show a high piezoelectricity.
- the difference in elastic modulus between the aggregate resin and the matrix resin is preferably 10 MPa or more from the viewpoint that the initial value of the piezoelectricity is high and the retention rate can be increased.
- the elastic modulus of these resins can be measured based on the following method based on JIS K7210.
- the resin used as a raw material was formed into a 3 cm ⁇ 3 cm ⁇ 2 mm sheet by a known method, and the obtained sheet was tested with a universal compression tester (manufactured by Minebea Co., Ltd .; “Technograph TG-50kN”) at a test speed of 5 mm / Measure in minutes, create a compressive stress-strain curve from the measured value, and calculate based on this.
- a fluorine-containing resin or an imide-based resin as the aggregate resin and the matrix resin from the viewpoint of the heat resistance and weather resistance of the resin sheet.
- agglomerates those obtained by further forming a layer composed of agglomerates on the surface of the agglomerates prepared as described above can be used. It is called "dispersion method".
- the three-stage dispersion method is preferable because it is easy to form the island structure a in FIG.
- the piezoelectric sheet of the present invention may include a non-woven fabric or a woven fabric formed from fibers made of an organic polymer, and may be only the non-woven fabric or the woven fabric, or a conventionally known layer or the like on the surface of the non-woven fabric or the woven fabric.
- a laminated body may be used.
- Nonwoven fabrics or woven fabrics can be produced by producing fibers by a known method, collecting the obtained fibers into a nonwoven fabric, or weaving them into a woven fabric and molding them.
- a fiber made of an organic polymer can be produced by an electrospinning method, a melt spinning method, a melt electrospinning method, a spunbond method (melt blow method), or a wet method.
- the nonwoven fabric formed from the fiber obtained by the electrospinning method has a small fiber diameter, a high hollow ratio, and a high specific surface area, a piezoelectric laminate including a piezoelectric sheet obtained from such a nonwoven fabric Is preferable because it exhibits high piezoelectric characteristics.
- the fiber made of the organic polymer has an average fiber diameter of preferably 0.05 to 50 ⁇ m, more preferably 0.1 to 20 ⁇ m, and further preferably 0.5 ⁇ m to 5 ⁇ m.
- the piezoelectric sheet including the fiber can form a sufficient space for holding electric charges by increasing the fiber surface area, and the fiber distribution is uniform even when the thin film is formed. It is preferable from the viewpoint that the property can be increased.
- the average fiber diameter of the fiber is decreased by decreasing the humidity, decreasing the nozzle diameter, increasing the applied voltage, or increasing the voltage density during electrospinning. There is a tendency.
- the average fiber diameter is randomly selected by observing a scanning electron microscope (SEM) region for the fiber (group) to be measured, and observing this region by SEM (magnification: 10,000 times). This is a value calculated based on the measurement results obtained by selecting 20 fibers and measuring the fiber diameter (major axis) of each of these fibers.
- SEM scanning electron microscope
- the fiber diameter variation coefficient of the fiber is preferably 0.7 or less, more preferably 0.01 to 0.5.
- the fiber may be produced by an electrospinning method using a spinning solution containing an organic polymer and, if necessary, a solvent.
- the organic polymer is contained, for example, in an amount of 5 to 100% by weight, preferably 5 to 80% by weight, and more preferably 10 to 70% by weight in the spinning solution, depending on the type of the organic polymer.
- the solvent is not particularly limited as long as it can dissolve or disperse the organic polymer.
- water dimethylacetamide, dimethylformamide, tetrahydrofuran, methylpyrrolidone, xylene, acetone, chloroform, ethylbenzene, cyclohexane, benzene
- examples include sulfolane, methanol, ethanol, phenol, pyridine, propylene carbonate, acetonitrile, trichloroethane, hexafluoroisopropanol, and diethyl ether.
- These solvents may be used individually by 1 type, and may be used as a mixed solvent which combined 2 or more types.
- the solvent is contained in the spinning solution in an amount of, for example, 0 to 90% by weight, preferably 10 to 90% by weight, more preferably 25 to 80% by weight.
- the spinning solution may further contain additives such as a surfactant, a dispersant, a charge adjusting agent, functional particles, an adhesive, a viscosity adjusting agent, and a fiber forming agent.
- additives such as a surfactant, a dispersant, a charge adjusting agent, functional particles, an adhesive, a viscosity adjusting agent, and a fiber forming agent.
- the surfactant examples include a fluorine-based surfactant (a surfactant having a fluorine atom.
- a fluorine-based surfactant a surfactant having a fluorine atom.
- an ammonium salt of an acid having a perfluoroalkyl group a hydrocarbon-based surfactant (the main chain is an alkyl group).
- Surfactants silicone surfactants (surfactants having silicon atoms), and the like.
- fluorosurfactant If it is a commercial item as said fluorosurfactant, it is a footgent (registered trademark) 100 (anionic fluorosurfactant), a footgent (registered trademark) 310 (cationic fluorosurfactant). (Made by Neos Co., Ltd.), Megafac F114 (anionic fluorosurfactant, manufactured by DIC Corporation), Surflon S-231 (amphoteric fluorosurfactant, manufactured by Asahi Glass Co., Ltd.), etc. Is mentioned.
- the amount of the surfactant used is, for example, 0.01 to 5% by weight, preferably 0.1 to 3% by weight in the spinning solution.
- the fiber forming agent is preferably a polymer having high solubility in a solvent, such as polyethylene oxide, polyethylene glycol, dextran, alginic acid, chitosan, starch, polyvinylpyrrolidone, polyacrylic acid, polymethacrylic acid, polyacrylamide, cellulose. And polyvinyl alcohol.
- a solvent such as polyethylene oxide, polyethylene glycol, dextran, alginic acid, chitosan, starch, polyvinylpyrrolidone, polyacrylic acid, polymethacrylic acid, polyacrylamide, cellulose.
- a solvent such as polyethylene oxide, polyethylene glycol, dextran, alginic acid, chitosan, starch, polyvinylpyrrolidone, polyacrylic acid, polymethacrylic acid, polyacrylamide, cellulose.
- polyvinyl alcohol such as polyvinyl alcohol.
- the amount of the fiber forming agent used is, for example, 0.1 to 15% by weight, preferably 1 to 10% by weight in the spinning solution, although it depends on the viscosity and solubility of the solvent.
- the spinning solution can be produced by mixing the above-mentioned organic polymer, solvent and, if necessary, additives by a conventionally known method.
- spinning solution (1) Spinning containing 30 to 70% by weight, preferably 35 to 60% by weight of polytetrafluoroethylene (PTFE), and 0.1 to 10% by weight, preferably 1 to 7% by weight, of a fiber forming agent liquid
- the applied voltage during this electrospinning is preferably 1 to 100 kV, more preferably 5 to 50 kV, and still more preferably 10 to 40 kV.
- the tip diameter (outer diameter) of the spinning nozzle is preferably 0.1 to 2.0 mm, more preferably 0.2 to 1.6 mm.
- the applied voltage is preferably 10 to 50 kV, more preferably 10 to 40 kV, and the tip diameter (outer diameter) of the spinning nozzle is used. ) Is preferably 0.3 to 1.6 mm.
- a method for producing the fiber a method for producing a fiber made of PTFE by an electrospinning method will be specifically described.
- a method for producing the PTFE fiber a conventionally known production method can be adopted, and examples thereof include the following method described in JP-T-2012-515850.
- Providing a spinning solution comprising PTFE, a fiber forming agent and a solvent and having a viscosity of at least 50,000 cP Spinning the spinning solution from a nozzle and forming a fiber by electrostatic traction; Collecting the fibers on a collector to produce a precursor;
- An electrospinning method such as a method including forming a PTFE fiber by firing the precursor and removing the solvent and the fiber forming agent can be employed.
- the step of producing the fiber and the step of collecting the fiber into a sheet and forming the non-woven fabric may be performed separately or simultaneously ( That is, a nonwoven fabric may be formed by collecting fibers while collecting fibers).
- a step of producing a fiber using an electrospinning method, and a step of accumulating the obtained fibers in a sheet shape to form a nonwoven fabric may be performed simultaneously, or a step of producing a fiber. After performing, you may perform the process of accumulating the fiber obtained by the wet method in a sheet form, and shape
- an aqueous dispersion containing the fiber may be deposited on a mesh, for example, and formed into a sheet shape.
- the fiber length of the fiber is preferably 0.5 to 100 mm, preferably 1 to 50 mm.
- the amount of the fiber used is preferably 0.1 to 10% by weight, more preferably 0.1 to 5% by weight, based on the total amount of the aqueous dispersion. If the fiber is used within this range, water can be efficiently utilized in the accumulation (papermaking) process, and the dispersion state of the fiber is improved, so that a uniform wet nonwoven fabric can be obtained.
- the aqueous dispersion is added with a dispersant or an oil agent composed of a cationic, anionic, or nonionic surfactant, or an antifoaming agent that suppresses the generation of bubbles. May be.
- the woven fabric formed from the fiber can be manufactured by a method including a step of manufacturing the fiber and a step of weaving the fiber into a sheet to form a woven fabric.
- a method of weaving the fiber into a sheet a conventionally known weaving method can be used, and examples thereof include a water jet room, an air jet room, and a rapier room.
- the basis weight of the nonwoven fabric and the woven fabric is preferably 100 g / m 2 or less, more preferably 0.1 to 20 g / m 2 .
- the thickness of the nonwoven fabric and woven fabric is usually 10 ⁇ m to 1 mm, preferably 50 ⁇ m to 500 ⁇ m.
- the basis weight and thickness tend to increase by increasing the spinning time or increasing the number of spinning nozzles.
- the porosity of the nonwoven fabric and woven fabric is preferably 60% or more, more preferably 80 to 99%.
- the porosity of the nonwoven fabric and the woven fabric is within the above range, the charge retention amount of the piezoelectric sheet is increased, which is preferable.
- the porosity when the organic polymer is PTFE is calculated by the following method. (True density of PTFE ⁇ apparent density) ⁇ 100 / true density of PTFE
- the non-woven fabric and woven fabric are obtained by accumulating or weaving the fibers in a sheet shape.
- Such non-woven fabric and woven fabric are composed of a single layer, or composed of two or more layers having different materials and fiber diameters. Any of these may be used.
- the piezoelectric sheet of the present invention is excellent in charge retention and has a high charge retention amount, it can be used for various applications as a piezoelectric (electret) element.
- it can be preferably used as an actuator, a sensing material, and a power generation material because it can generate a charge response to mechanical energy due to vibration or microstress and convert it into electrical energy.
- Piezoelectric sheet including nonwoven fabric or woven fabric formed from fibers made of inorganic material The porosity of the piezoelectric sheet including a nonwoven fabric or a woven fabric formed from a fiber made of an inorganic material is 60% or more, preferably 80 to 99%. When the porosity is within the above range, the piezoelectric sheet is preferable because it exhibits high flexibility and a high charge retention amount.
- Examples of the inorganic material include glass and ceramics.
- the piezoelectric sheet can be manufactured by manufacturing fibers made of an inorganic material by a known method, collecting the obtained fibers into a nonwoven fabric, or weaving them into a woven fabric and molding them.
- a fiber made of an inorganic material can be produced by an electrospinning method, a melt spinning method, a melt electrospinning method, a spunbond method (melt blow method), or a wet method.
- the nonwoven fabric formed from the fiber obtained by the electrospinning method has a small fiber diameter, a high hollow ratio, and a high specific surface area, a piezoelectric laminate including a piezoelectric sheet obtained from such a nonwoven fabric Is preferable because it exhibits high flexibility and piezoelectric properties.
- the fibers made of the inorganic material preferably have an average fiber diameter of 0.05 to 50 ⁇ m, more preferably 0.1 to 20 ⁇ m, and still more preferably 0.5 ⁇ m to 5 ⁇ m.
- the average fiber diameter is within the above range, the piezoelectric sheet including the fiber can form a sufficient space for holding electric charges by increasing the fiber surface area, and the fiber distribution is uniform even when the thin film is formed. It is preferable from the viewpoint that the property can be increased.
- the fiber diameter variation coefficient of the fiber is preferably 0.7 or less, more preferably 0.01 to 0.5.
- the fiber diameter variation coefficient is within the above range, the fiber diameter of the fiber becomes uniform, and the charge retention of the obtained piezoelectric sheet can be improved. It is preferable in terms of having porosity.
- the basis weight of the nonwoven fabric and the woven fabric is preferably 100 g / m 2 or less, more preferably 0.1 to 20 g / m 2 .
- the thickness of the nonwoven fabric and woven fabric is usually 10 ⁇ m to 1 mm, preferably 50 ⁇ m to 500 ⁇ m.
- the piezoelectric sheet of the present invention is excellent in charge retention and has a high charge retention amount, it can be used for various applications as a piezoelectric (electret) element.
- a surface coating layer is laminated on at least one of the front and back surfaces of the porous resin sheet or piezoelectric sheet among the outer surfaces of the porous resin sheet or piezoelectric sheet. Become. This surface coating layer covers the front and back surfaces of the porous resin sheet or the piezoelectric sheet from the standpoint of obtaining a piezoelectric laminate that retains electric charge for a long time and retains a high piezoelectric rate. It is preferable that the front and back surfaces and the end surfaces are covered.
- the “front and back surfaces of the porous resin sheet or piezoelectric sheet” refers to two surfaces having the largest area among the outer surfaces (six surfaces) of the sheet.
- the “end surface of the piezoelectric sheet” means four surfaces excluding the front and back surfaces of the outer surface (six surfaces) of the sheet.
- the volume resistivity of the surface coating layer is 1 ⁇ 10 13 ⁇ ⁇ cm or more, preferably 1 ⁇ 10 14 ⁇ ⁇ cm or more. If it exists in this range, it is preferable at the point of the long-term charge retention improvement in a porous resin sheet or a piezoelectric sheet.
- the volume resistivity is measured based on the double ring electrode method using a single surface coating layer (film) to be measured.
- the elastic modulus of the surface coating layer may be different from that of the porous resin sheet or piezoelectric sheet, and may be higher or lower than the elastic modulus of the porous resin sheet or piezoelectric sheet. .
- the difference in elastic modulus between the surface coating layer and the porous resin sheet or piezoelectric sheet is preferably 10 MPa or more, more preferably 50 MPa or more. If it exists in this range, it is preferable at the point which nonlinear deformation
- the surface coating layer preferably has a relative dielectric constant of 2 to 100. If the relative permittivity is within this range, when charge is applied by corona discharge, the charge is concentrated inside the surface coating layer having a high dielectric constant, and the surface coating layer and the porous resin Electric charges tend to be held at the interface with the sheet or piezoelectric sheet. Furthermore, since the held electric charges move to the hollow structure in the porous resin sheet or piezoelectric sheet, the electric charge holding amount as the entire piezoelectric laminate is increased, and the initial value of piezoelectricity is improved.
- the thickness of the surface coating layer is usually 1 ⁇ m or more, and preferably 30% or less of the thickness of the porous resin sheet or piezoelectric sheet.
- the thickness is less than 1 ⁇ m, for example, when the surface coating layer is formed using a film for the surface coating layer, the handleability of the film is poor, and the insulation due to film defects (pinholes) decreases. Such a problem may occur, which is not preferable.
- the thickness of the surface coating layer exceeds 30% of the porous resin sheet or piezoelectric sheet, it is necessary to set a high corona discharge voltage when injecting charges into the porous resin sheet or piezoelectric sheet. Therefore, it tends to be difficult to put it to practical use industrially.
- the surface coating layer is formed on the front and back surfaces of the porous resin sheet or piezoelectric sheet, if the thickness of each surface coating layer is different from each other, the resulting piezoelectric laminate is compressed by the laminate. This is preferable because non-linear deformation easily occurs with respect to strain and tends to exhibit a high piezoelectric characteristic.
- thermosetting resin examples include, for example, polyimide, epoxy resin, thermosetting fluororubber (eg, vinylidene fluoride rubber), polyurethane, phenol resin, imide resin (eg, polyimide, polyamideimide, bismaleimide, etc.), silicone resin Etc.
- thermoplastic resin examples include acrylic resin, methacrylic resin, polypropylene, polyamide, vinyl chloride resin, silicone resin, fluororesin (eg, polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), ethylene-tetra Fluoroethylene copolymer (ETFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), etc.), nylon, polystyrene , High density polyethylene, silicone rubber, low density polyethylene, polyphenylene sulfide, polyethylene oxide, polysulfone, vinylidene chloride, and the like.
- fluororesin eg, polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), ethylene-tetra Fluoro
- the surface coating layer can be formed by a conventionally known method. For example, when a thermosetting resin is used, the surface coating layer is heated on at least one side of the back surface of the porous resin sheet or piezoelectric sheet, that is, on one side or both sides. It can be formed by applying and drying a solution obtained by dissolving a curable resin and a curing agent (crosslinking agent) in a solvent. Moreover, it can also form by apply
- a conventionally known curing agent can be used as the curing agent.
- a conventionally known curing agent can be used.
- 2,5-dimethyl-2,5-di (t-butylperoxy) hexane (trade name: Perhexa 25B (NOF Corporation) Product)
- triallyl isocyanurate (trade name: TAIC (manufactured by NOF Corporation)) and the like.
- the amount of the curing agent used is usually 1 to 20% by weight, preferably 1 to 10% by weight, based on 100 parts by weight of the resin.
- solvent used here examples include tetrahydrofuran (THF), toluene, benzene, acetone, ethylbenzene, and the like.
- THF tetrahydrofuran
- the amount of the solvent used is usually 100 to 5000 parts by weight, preferably 200 to 3000 parts by weight with respect to 100 parts by weight of the resin.
- the surface coating layer is formed (laminated) by previously forming a surface coating layer (film for) and laminating it by thermocompression bonding with a porous resin sheet or piezoelectric sheet. It may be used.
- thermoplastic resin a thermosetting resin, or a photocurable resin
- a molding method for example, a molding machine such as a single-screw or twin-screw extruder.
- the method include mixing a resin, and if necessary, a curing agent and a solvent, and then molding the sheet into a sheet or the like with a pressure molding machine, a T-die, or the like.
- the molding temperature is usually about the same as the melting temperature of the resin
- thermosetting resin it is usually about the same as the curing temperature of the resin.
- the piezoelectric laminate of the present invention may have an intermediate layer between the porous resin sheet or the piezoelectric sheet and the surface coating layer. Moreover, when the piezoelectric laminated body of this invention has two or more porous resin sheets or piezoelectric sheets, you may have an intermediate
- the intermediate layer is preferably a layer made of an organic material.
- organic materials include copolymers of tetrafluoroethylene and perfluoroalkyl vinyl ether [PFA], copolymers of tetrafluoroethylene and hexafluoropropylene [FEP], and polychlorotrifluoroethylene [PCTFE].
- Copolymer of tetrafluoroethylene and ethylene [ETFE], polyvinylidene fluoride [PVdF], polyvinyl fluoride [PVF], copolymer of tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride [THV], poly Fluorine-containing resins such as tetrafluoroethylene, polyvinylidene fluoride, copolymers of ethylene and chlorotrifluoroethylene [ECTFE]; polyolefin-based resins such as polypropylene and polyethylene; polystyrene, polymer Vinyl polymers such as polymethacrylate, poly (meth) acrylic acid ester, polyvinyl chloride, polyvinylidene chloride; polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polylactic acid, polyhydroxyalkanoate, polybutylene succinate, polyethylene Polyester polymers such as succinate and polyethylene succinate
- Imide resins such as engineering plastics such as polycarbonate and cycloolefins, or unsaturated polyesters, vinyl ester resins, diallyl phthalates Resin, epoxy resin, polyurethane, silicon resin, polyimide, alkyd resin, furan resin, dichloropentadiene resin, acrylic resin, thermosetting resin such as allyl carbonate resin, and the like, and foam of the organic polymer, A stretched porous membrane, a nonwoven fabric, a woven fabric, a gel-like / rubber-like body, or the like can also be used.
- Thermoplastic resins such as engineering plastics such as polycarbonate and cycloolefins, or unsaturated polyesters, vinyl ester resins, diallyl phthalates Resin, epoxy resin, polyurethane, silicon resin, polyimide, alkyd resin, furan resin, dichloropentadiene resin, acrylic resin, thermosetting resin such as allyl carbonate resin, and the like, and foam of the organic polymer
- polyamides such as aramid, polyamideimide, bismaleimide, polytetrafluoroethylene, polyvinylidene fluoride, PFA, FEP, ETFE, PCTFE, and ECTFE are more preferable from the viewpoints of heat resistance and weather resistance.
- the elastic modulus of the intermediate layer is preferably a layer different from the elastic modulus of the porous resin sheet, the piezoelectric sheet and / or the surface coating layer, and the porous resin sheet, the piezoelectric sheet and / or the surface A layer higher or lower than the elastic modulus of the coating layer may be used.
- the obtained piezoelectric laminate is likely to cause non-linear deformation with respect to the compressive strain of the laminate, and is high. This is preferable because it shows the piezoelectricity.
- the difference in elastic modulus between the intermediate layer and the surface coating layer and / or the porous resin sheet or piezoelectric sheet is usually 10 MPa or more, preferably 50 MPa or more. If it exists in this range, it is preferable at the point which nonlinear deformation
- a surface coating layer is laminated on one side of the front and back surfaces of the porous resin sheet (FIG. 7), and a surface coating layer is laminated on both sides of the front and back surfaces of the porous resin sheet.
- a surface coating layer is formed on both the front and back surfaces and the end surface of the porous resin sheet (FIG. 9), and an intermediate layer is laminated on one surface of the porous resin sheet.
- a surface coating layer is formed on both surfaces and end surfaces (FIG. 10). Two layers of porous resin sheets are laminated via an intermediate layer, and surface coating layers are formed on both the front and back surfaces and end surfaces of this laminate. (FIG. 11).
- the piezoelectric laminate of the present invention can form a new interface capable of holding electric charge between the porous resin sheet or the piezoelectric sheet and the surface coating layer, so that the piezoelectric rate is improved and the interface is held at such an interface.
- the amount of charge that can be held synergistically by moving the generated charges to the hollow structure of the porous resin sheet or piezoelectric sheet increases, thereby contributing to an improvement in piezoelectricity.
- the surface covering layer functions to prevent the electric charge held in the porous resin sheet or the piezoelectric sheet from being attenuated by being electrically connected to the external environment. It works effectively on the retention of
- the piezoelectric laminate of the present invention by providing a difference in elastic modulus between the porous resin sheet or the piezoelectric sheet and the surface coating layer, nonlinear deformation is likely to occur with respect to compressive strain at the time of charge extraction, A high piezoelectricity of about 100 to 300 (unit: d 33 (pC / N)) can be exhibited.
- the piezoelectric laminate of the present invention Since the piezoelectric laminate of the present invention generates a charge response even at a minute stress, and further, the surface charge responsiveness to the stress can be adjusted by controlling the structure of the porous resin sheet or the piezoelectric sheet. Sensing materials such as actuators, vibrators, pressure sensors, vibration force sensors, and pressure sensors that can be used in automobiles, outdoors, and factories, and power generation materials that use electromotive force generated by pressure and vibration as power sources Can do. In addition, a method of storing the electromotive force in a power storage mechanism and using it is also included.
- the piezoelectric laminate of the present invention has heat resistance, moisture resistance, and weather resistance, it can also be used outdoors under high temperature and high humidity environments that could not be used with conventional piezoelectric materials such as PVDF. Is possible.
- Example 1 A laminate in which a surface coating layer is provided on one side of the front and back sides of a porous resin sheet (single side coating type piezoelectric laminate) ⁇ Preparation of porous resin sheet> Fluororesin (Daikin Industries FEP, NP101) (thermal decomposition start temperature: 400 ° C .; conductivity: 1.0 ⁇ 10 ⁇ 16 S / cm; MFR: 24 g / 10 min (ASTM D2116); melting point: 255 ° C.
- Fluororesin (Daikin Industries FEP, NP101) (thermal decomposition start temperature: 400 ° C .; conductivity: 1.0 ⁇ 10 ⁇ 16 S / cm; MFR: 24 g / 10 min (ASTM D2116); melting point: 255 ° C.
- the specific gravity and true specific gravity of FEP is 2.1 g / cm 3
- the true specific gravity of hollow glass beads is 0.6 g / cm 3 (see Sumitomo 3M Co., Ltd., product catalog “Glass Bubbles-High Performance Additive”). )
- the specific gravity excluding the hollow structure of the hollow particles was calculated as 2.5 g / cm 3 .
- Thermosetting resin (Fluorine rubber, Daiel G912, manufactured by Daikin Industries, Ltd.) (fluorine concentration: 70.5% by weight, specific gravity (23 ° C.): 1.91 (JIS K6268), Mooney viscosity (ML1 + 10 ⁇ 100 ° C.): About 77 (JIS K6300-1)), 0.5 g of triallyl isocyanurate (trade name: TAIC, manufactured by NOF Corporation) as a curing agent, and 2,5-dimethyl-2,5-di (t -Butylperoxy) hexane (trade name: Perhexa 25B, manufactured by NOF Corporation) 0.1 g and a solvent (THF, manufactured by Wako Pure Chemical Industries, Ltd.) dissolved in 200 g of the porous resin sheet
- One side surface one side of the front and back surfaces
- the volume resistivity of this surface coating layer was 1.0 ⁇ 10 13 ⁇ ⁇ cm.
- the volume resistivity of the surface coating layer was measured based on the double ring electrode method using the surface coating layer alone. Hereinafter, the volume resistivity of the surface coating layer was measured by the same method.
- the piezoelectric laminate was subjected to polarization treatment by corona discharge for 3 minutes at a room temperature of 12.5 mm, a voltage between electrodes of 3 kV, and room temperature using a corona discharge device manufactured by Kasuga Electric Co., Ltd.
- a rectangular electrode made of aluminum foil (“FOIL” manufactured by Mitsubishi Aluminum Co., Ltd., 11 ⁇ m) was provided on both surfaces to produce a sample for evaluation.
- Example 1 Porous resin sheet used in Example 1 Using only the porous resin sheet produced in Example 1, the piezoelectricity was measured in the same manner as in Example 1. The results are also shown in Table 1.
- Example 2 A laminate in which a surface coating layer is provided on both the front and back surfaces of a porous resin sheet (a double-sided coated piezoelectric laminate) ⁇ Preparation of porous resin sheet> 18.6 g of hollow glass beads (iM30K manufactured by Sumitomo 3M) were mixed with 100 g of fluororesin (FEP, NP-101 manufactured by Daikin Industries, Ltd.). The hollow ratio of the mixture was 30%. The hollow ratio was measured by the same method as in Example 1. The obtained mixture was molded in the same manner as in Example 1 to obtain a 3 cm ⁇ 3 cm ⁇ 0.2 mm sheet (porous resin sheet).
- a fluororesin sheet (PFA film “AF0025” manufactured by Daikin Industries, Ltd., 25 ⁇ m, volume resistivity 1.0 ⁇ 10 18 ⁇ ⁇ cm) is stacked on both surfaces (both front and back surfaces) of the porous resin sheet, A laminated body (piezoelectric laminated body) was formed by pressure-bonding by holding at a pressure of 2 MPa for 180 seconds with a hot press at ° C. The elastic modulus was measured in the same manner as in Example 1, and the piezoelectric modulus was measured in the same manner as in Example 1 using the obtained laminate.
- the charged sample for evaluation is allowed to stand in an atmosphere of room temperature (20 ° C.) and humidity of 20%, and the piezoelectric constant after 1 day and 5 days is measured in the same manner as in Example 1. It was measured. The results are also shown in Table 1.
- Example 2 Porous resin sheet used in Example 2 Using only the porous resin sheet produced in Example 2, the piezoelectricity was measured in the same manner as in Example 2. The results are also shown in Table 1.
- Example 3 A laminate in which a surface coating layer is provided on both the front and back surfaces of a porous resin sheet made of PTFE nonwoven fabric (double-side coated PTFE nonwoven fabric piezoelectric laminate) ⁇ Preparation of porous resin sheet> Porous made of PTFE nonwoven fabric (porosity 80%, elastic modulus 6 MPa) having a thickness of 60 ⁇ m, accumulated by polytetrafluoroethylene (PTFE) fibers in a sheet form by an electrospinning method described in JP-T-2012-515850 Quality resin sheet was manufactured.
- PTFE nonwoven fabric porosity 80%, elastic modulus 6 MPa
- the porosity was measured based on the following method. Apparent value calculated using the weight of a test piece cut out of a 4 cm square (4 cm length, 4 cm width) of a porous resin sheet and the thickness measured with a micrometer (LITEMEMATIC VL-50, manufactured by Mitutoyo Corporation) The porosity was calculated by the following formula using the density of (True density of PTFE ⁇ apparent density) ⁇ 100 / true density of PTFE
- the obtained PTFE nonwoven fabric was used, and as a fluororesin sheet for the surface coating layer, a PFA film (“AF0012”, 12.5 ⁇ m, volume resistivity 1.0 ⁇ 10 18 ⁇ , manufactured by Daikin Industries, Ltd.)
- a piezoelectric laminate was formed by the same method as in Example 2 except that cm) was used.
- the elastic modulus was measured in the same manner as in Example 1, and the piezoelectric modulus was measured in the same manner as in Example 1 using the obtained laminate.
- Example 4 A laminate in which a surface coating layer is provided on both the front and back surfaces and the end surface of a porous resin sheet made of PTFE nonwoven fabric (double-sided and end-face-coated PTFE nonwoven fabric piezoelectric laminate) ⁇ Preparation of porous resin sheet>
- PTFE nonwoven fabric porosity 80%, thickness 0.06 mm, elastic modulus 6 MPa, average fiber diameter 1.3 ⁇ m, fiber diameter standard deviation 0.4, fiber diameter variation coefficient 0.3
- this was coated on four end faces of the porous resin sheet on which the surface coating layer was formed, and was thermally cured at 150 ° C. for 15 minutes to form an end face coating layer, thereby obtaining a piezoelectric laminate.
- the volume resistivity of the end face coating layer was 1.0 ⁇ 10 13 ⁇ ⁇ cm.
- the elastic modulus was measured in the same manner as in Example 1, and the piezoelectric modulus was measured in the same manner as in Example 1 using the obtained laminate. After measuring the initial piezoelectric constant, the charged sample for evaluation is allowed to stand in an atmosphere of room temperature (20 ° C.) and humidity of 20%, and the piezoelectric constant after 1 day and 5 days is measured in the same manner as in Example 1. It was measured. The results are also shown in Table 2.
- the hollowness of the sample sheet was 30% by volume.
- the surfactant that has adhered to the surface of the hollow particles by the sheet preparation step is assumed to be partly or wholly carbonized, and has a conductivity of 1.0 ⁇ 10 ⁇ 10 S / cm. It was.
- the conductivity of the conductive material on the surface of the hollow particles is measured by forming a surfactant coating layer on a glass substrate and heating the coating layer under reduced pressure (oxygen-blocking environment) at 300 ° C. for a predetermined time.
- the produced carbonized layer was measured based on a double ring electrode method using a resistivity meter (digital super insulation / microammeter DSM-8104 (manufactured by Hioki Electric Co., Ltd.)).
- the obtained sample sheet was subjected to a polarization treatment by corona discharge for 3 minutes at a room temperature of 12.5 mm, a voltage between electrodes of 3 kV and a room temperature using a corona discharge device manufactured by Kasuga Electric Co., Ltd. Manufactured.
- a constant AC acceleration ⁇ (frequency: 90 to 300 Hz, size: 2 to 10 m / s 2 ) is applied in the thickness direction of the sample for evaluation under the condition of a room temperature (20 ° C.) and a humidity of 20%.
- the response charge at that time was measured, and the initial piezoelectric constant d 33 (pC / N) was determined (this time is 0 day).
- the charged sample for evaluation was allowed to stand in an atmosphere of 20% humidity at room temperature (20 ° C.), and after 2, 3, 5, 10, 11, 20, and 27 days, the piezoelectric material was subjected to the same method.
- the rate d 33 was determined.
- Reference Example 2 In Reference Example 1, a porous resin sheet was produced in the same manner as in Reference Example 1 except that the nonionic surfactant used with respect to the weight of the hollow particles was changed to 0.5% by weight. Then, the piezoelectric performance was evaluated in the same manner as in Reference Example 1, and the results are shown in Table 3 and FIG.
- d 33 of the porous resin sheet produced in the reference example is maintained at 60 pC / N or more even after the lapse of 5 days, and the conductive material adheres to the surface. It can be seen that the piezoelectric property retention is high as compared with the porous resin sheet of Comparative Example 3 using no hollow particles.
- Example 5 Evaluation of heat resistance of piezoelectric laminate
- the piezoelectric laminate manufactured in Example 2 and evaluated five days later was heat-treated by being left in an electric furnace maintained at 80 ° C. for 100 hours. Thereafter, the sample was taken out of the electric furnace, cooled to room temperature, and then evaluated for piezoelectric characteristics in the same manner as in Example 1 (corresponding to measurement after 9 days from the date of manufacture).
- d 33 of the porous resin sheet after the heat treatment was 61 pC / N, and the characteristics equivalent to those before the heat treatment were maintained. From this, it became clear that the porous resin sheet for piezoelectric elements of the present invention has heat resistance that does not deactivate the piezoelectric characteristics even in a high temperature environment such as 80 ° C.
- NEOFLON FEP manufactured by Daikin Industries, Ltd., model number: NP101, specific gravity: 2.1 g / cm 3 , conductivity: 1.0 ⁇ 10 ⁇ 15 S / cm; MFR: 24 g / 10 min (ASTM D2116 ), Viscosity at 300 ° C .: 1.0 ⁇ 10 4 poise, melting point 255 ° C. (according to ASTM D2116), apparent density 1.21 g / ml (according to JIS K6891)) 29.0 g using a lab plast mill After kneading at 300 ° C. for 5 minutes, and further charging 23.0 g of the island structure pellets as an island structure, the island-island structure pellets were prepared by kneading at 300 ° C. for 10 minutes.
- the ratio of the sea-island structure was calculated from the weight and density of each material and the amount of hollow particle glass.
- a mold was formed to have a size of 3 cm ⁇ 3 cm ⁇ 0.2 mm to obtain a sample sheet.
- the sea-island structure pellets were placed in a mold, heated at 350 ° C./1 h, and then compressed at 3 MPa under air cooling to form a sample sheet.
- the surfactant attached to the surface of the hollow particles was a conductive substance having a conductivity of 1.0 ⁇ 10 ⁇ 10 S / cm.
- the conductivity is measured by forming a surfactant coating layer on a glass substrate and heating the coating layer at 300 ° C. for a predetermined time under reduced pressure (oxygen-blocking environment). The measurement was performed based on the double ring electrode method using a meter (digital super insulation / microammeter DSM-8104 (manufactured by Hioki Electric Co., Ltd.)).
- Example 6 A laminate in which a surface coating layer is provided on both the front and back surfaces and an end surface of a porous resin sheet made of a PTFE nonwoven fabric (double-sided and end-surface-coated wet PTFE nonwoven fabric piezoelectric laminate)
- a PTFE nonwoven fabric having a thickness of 125 ⁇ m was produced by the wet papermaking method described in JP-A-3-97993 (PTFE nonwoven fabric 1, elastic modulus 10 MPa).
- a piezoelectric laminate was manufactured in the same manner as in Example 4 except that the obtained PTFE nonwoven fabric 1 was used as a porous resin sheet, and the piezoelectric constant was measured. The results are shown in Table 5.
- the 5-day retention of the piezoelectric properties of the piezoelectric laminates obtained in Examples 6 to 10 is a value calculated by the formula “piezoelectricity on the 5th day ⁇ 100 / initial value”.
- Example 7 A laminate in which a surface coating layer is provided on both surfaces and end surfaces of a porous resin sheet made of a PTFE nonwoven fabric (both surfaces and end surface coating type wet PTFE nonwoven fabric piezoelectric laminate)
- a PTFE nonwoven fabric having a thickness of 300 ⁇ m was produced by the wet papermaking method described in JP-A-3-97993 (PTFE nonwoven fabric 1 ′, elastic modulus 12 MPa).
- a piezoelectric laminate was produced in the same manner as in Example 4 except that the obtained PTFE nonwoven fabric 1 ′ was used as a porous resin sheet, and the piezoelectric constant was measured. The results are shown in Table 5.
- Example 8 A laminate in which a surface coating layer is provided on both the front and back surfaces and an end surface of a porous resin sheet made of a PTFE nonwoven fabric (both surface and end surface coating type electrospun PTFE nonwoven fabric piezoelectric laminate) PTFE fibers were accumulated in a sheet form by the electrospinning method described in JP-T-2012-515850 to produce a PTFE nonwoven fabric (elastic modulus 6 MPa) having a thickness of 50 ⁇ m (PTFE nonwoven fabric 2).
- a piezoelectric laminate was manufactured in the same manner as in Example 4 except that the obtained PTFE nonwoven fabric 2 was used as a porous resin sheet, and the piezoelectric constant was measured. The results are shown in Table 5.
- Example 9 A laminate in which a surface coating layer is provided on both the front and back surfaces and an end surface of a porous resin sheet made of PTFE nonwoven fabric (both surface and end surface coating type electrospun PTFE nonwoven fabric piezoelectric laminate) PTFE fibers were accumulated in a sheet form by electrospinning described in JP-T-2012-515850 to produce a PTFE nonwoven fabric (elastic modulus of 6 MPa) having a thickness of 100 ⁇ m (PTFE nonwoven fabric 2 ′).
- a piezoelectric laminate was manufactured in the same manner as in Example 4 except that the obtained PTFE nonwoven fabric 2 ′ was used as a porous resin sheet, and the piezoelectric constant was measured. The results are shown in Table 5.
- Example 10 A laminate in which surface coating layers are provided on both the front and back surfaces and the end surface of a porous resin sheet made of an expanded PTFE membrane (double-sided and end-surface coated type expanded PTFE porous membrane piezoelectric laminate).
- a piezoelectric laminate was manufactured in the same manner as in Example 4 except that an expanded PTFE membrane (porosity 78%, average pore diameter 0.30 ⁇ m, thickness 50 ⁇ m, elastic modulus 4 MPa) was used as the porous resin sheet. The piezoelectric characteristics were evaluated. The results are shown in Table 5.
- Example 9 ⁇ Evaluation of charge response to stress> About the piezoelectric laminated body manufactured in Example 6 and Example 9, the charge responsiveness with respect to stress was evaluated with the following method.
- the piezoelectric laminates manufactured in Example 6 and Example 9 were cut into 3 cm squares, and using a corona discharge device manufactured by Kasuga Electric Co., Ltd., a distance of 12.5 mm between electrodes, a voltage between electrodes of 3 kV, and 3 at room temperature. Polarization by corona discharge was performed for a minute. Thereafter, stress (N / cm) when compressively deformed by stress (1 mm / min head speed) using a load cell in the thickness direction of the laminate under a room temperature (20 ° C.) atmosphere and a humidity of 20%. 2 ) The response charge (pC / cm 2 ) on the surface of the laminate with respect to 2 ) was measured by a charge amplifier. The result is shown in FIG.
- the piezoelectric laminate of the present invention generates a charge response even at a minute stress, and the charge responsiveness to the stress differs by controlling the structure of the piezoelectric sheet.
- the rise of the charge amount change with respect to stress is steep, and can be preferably used as a highly sensitive sensing material.
- the piezoelectric laminate produced in Example 6 can be preferably used as a high-sensitivity sensing material under a minute stress because the amount of change at a stress of 0.1 N / cm 2 or less is large.
- the piezoelectric laminate of the present invention retains high piezoelectric characteristics even under high temperature and high humidity environment conditions.
- Example 11 A laminate in which a surface coating layer is provided on both the front and back surfaces and the end surface of a porous resin sheet made of a nonwoven fabric made of glass (double-sided and edge-coated glass nonwoven fabric piezoelectric laminate) Example 4 except that a non-woven fabric made of glass (manufactured by Toyo Filter Paper Co., Ltd., glass fiber filter paper GA-55, thickness 0.25 mm, porosity 90%, elastic modulus 110 MPa) was used as the porous resin sheet. Piezoelectric laminates were manufactured in the same manner and evaluated for piezoelectric characteristics. The results are shown in Table 7.
- the porosity of the porous resin sheet used in Example 11 was calculated by the following formula by cutting out a test piece, calculating the sample density from the measurement result of the size and weight of the test piece.
- the density of the solid substance in the glass was 2.4 g / cm 3 .
- Porosity (1 ⁇ (sample density / solid density in glass)) ⁇ 100 (%)
- Porous resin sheet (the structure is the same before and after the polarization treatment in step (3)) 2 ... Matrix resin 3 ... Hollow particles 4 ... Conductive material 5 ... Charge-induced hollow particles 6 ... Piezoelectric laminate 7 ... Porous resin sheet 8 ... Surface coating layer 9 ... Middle layer
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Abstract
Description
特許文献2には、空孔を有するコア層と、その少なくとも片面に絶縁性を有する表面層からなるエレクトレット化フィルムが開示されている。
特許文献4には、多孔質樹脂シートの片面または両面に特定のキャパシタンス指標を有するカバー層が積層された積層体が開示されている。
[1]
多孔質樹脂シートと、
前記多孔質樹脂シートの外表面のうちで、少なくとも前記多孔質樹脂シートの表裏面の何れか1方面に積層された表面被覆層と
を有し、
前記表面被覆層の体積抵抗率が1×1013Ω・cm以上であり、前記多孔質樹脂シートと表面被覆層との弾性率が異なる、圧電積層体。
前記多孔質樹脂シートと前記表面被覆層との弾性率の差が10MPa以上である、上記[1]に記載の圧電積層体。
前記表面被覆層の比誘電率が2~100である上記[1]または[2]に記載の圧電積層体。
前記表面被覆層が、前記多孔質樹脂シートの表裏面および端面を被覆している、上記[1]~[3]のいずれかに記載の圧電積層体。
前記多孔質樹脂シートが、少なくとも電荷誘起性中空粒子がマトリックス樹脂に分散しているシートであり、
該電荷誘起性中空粒子は、中空粒子の表面の少なくとも一部に導電性物質が付着している粒子であり、
該導電性物質は、中空粒子およびマトリックス樹脂のうちの何れよりも導電率が高い物質である、
上記[1]~[4]のいずれかに記載の圧電積層体。
前記多孔質樹脂シートが、有機ポリマーからなるファイバーから成形される不織布または織布を含む圧電性シートである、上記[1]~[4]のいずれかに記載の圧電積層体。
[7]
前記ファイバーの平均繊維径が0.05~50μmであり、繊維径変動係数が0.7以下である、上記[6]に記載の圧電積層体。
[8]
前記圧電性シートの空孔率が60%以上である、上記[6]または[7]に記載の圧電積層体。
前記有機ポリマーが、分子および結晶構造に起因する双極子を持たない有機ポリマーである、上記[6]~[8]のいずれかに記載の圧電積層体。
[10]
前記有機ポリマーがポリテトラフルオロエチレンである、上記[6]~[9]のいずれかに記載の圧電積層体。
有機ポリマーからなるファイバーから成形される不織布または織布を含む圧電性シート。
[12]
前記ファイバーの平均繊維径が0.05~50μmであり、繊維径変動係数が0.7以下である上記[11]に記載の圧電性シート。
[13]
空孔率が60%以上である上記[11]または[12]に記載の圧電性シート。
前記有機ポリマーが、分子および結晶構造に起因する双極子を持たない有機ポリマーである、上記[11]~[13]のいずれかに記載の圧電性シート。
[15]
前記有機ポリマーがポリテトラフルオロエチレンである、上記[11]~[14]のいずれかに記載の圧電性シート。
無機材料からなるファイバーから成形される不織布または織布を含み、空孔率が60%以上である圧電性シート。
前記ファイバーの平均繊維径が0.05~50μmであり、繊維径変動係数が0.7以下である上記[16]に記載の圧電性シート。
上記[16]または[17]に記載の圧電性シートと、
前記圧電性シートの外表面のうちで、少なくとも前記圧電性シートの表裏面の何れか1方面に積層された表面被覆層と
を有し、
前記表面被覆層の体積抵抗率が1×1013Ω・cm以上であり、前記圧電性シートと表面被覆層との弾性率が異なる、圧電積層体。
[19]
前記表面被覆層が、前記圧電性シートの表裏面および端面に形成されている、上記[18]に記載の圧電積層体。
また、無機材料からなるファイバーから成形される不織布または織布を含み、空孔率が60%以上である本発明の圧電性シートは、高い柔軟性および高い圧電率を有する。
本発明の圧電積層体は、多孔質樹脂シートと、該多孔質樹脂シートの外表面のうちで、少なくとも前記多孔質樹脂シートの表裏面の何れか1方面に積層された表面被覆層と
を有する、または、
無機材料からなるファイバーから成形される不織布または織布を含み、空孔率が60%以上である圧電性シートと、該圧電性シートの外表面のうちで、少なくとも前記圧電性シートの表裏面の何れか1方面に積層された表面被覆層とを有する。
前記表面被覆層の体積抵抗率は1×1013Ω・cm以上であり、前記多孔質樹脂シートまたは圧電性シートと表面被覆層との弾性率が異なる。
本発明で用いられる多孔質樹脂シートとしては、電荷を保持し得る有機系材料からなるシートであることが好ましい。このような有機系材料からなる多孔質樹脂シートとしては、例えば、マトリックス樹脂と少なくとも電荷誘起性中空粒子との混合物からなる多孔質樹脂シート、有機重合体からなるシート状の発泡体、有機ポリマーからなる不織布または織布、有機重合体からなる延伸多孔質膜などが挙げられる。また、有機重合体中に分散させた相分離化剤を、超臨界二酸化炭素などの抽出剤を用いて除去し、空孔を形成する方法によって形成されるシートも挙げられる。
マトリックス樹脂と少なくとも電荷誘起性中空粒子との混合物からなる多孔質樹脂シートとしては、例えば、少なくとも電荷誘起性中空粒子がマトリックス樹脂に分散している混合物からなる多孔質樹脂シートであり、該電荷誘起性中空粒子は、中空粒子の表面の少なくとも一部に導電性物質が付着している粒子であり、該導電性物質は、該中空粒子およびマトリックス樹脂よりも導電率が高い物質であることが好ましい。
図1における、多孔質樹脂シート(以下、単に「樹脂シート」ともいう。)1は、導電性物質4が付着していない中空粒子(以下、単に「導電性物質不含粒子」ともいう。)3、および電荷誘起性中空粒子5がマトリックス樹脂2中に分散している。なお、前記樹脂シート1は、導電性物質不含粒子3が樹脂シート1中に存在しなくてもよい(図示せず)。
いずれの樹脂シートにも、電荷誘起性中空粒子5と導電性物質不含粒子3とが特定の割合で含有されていると考えられるが、両者の粒子を画像上区別することはできない。図2(A)のSEM画像は、それらの粒子が該樹脂シート中に均一に分散しているように見え、図2(B)のSEM画像は、それらの粒子が塊(島)状に集まり、各島が均一に分散しているように見える。
図3(B)に示す島は、擬似的に大きな中空粒子としてとらえることができると考えられる。
海島構造の他の一例としては、中空率が小さい海構造(すなわち、粒子3および/または粒子5の含有率が低い構造部)、中空率が大きい島構造(すなわち、粒子3および/または粒子5の含有率が高い構造部)から構成されるものが挙げられる。中空率が大きい島構造で高い圧電率を発現させ、中空率が小さい海構造が分極された電荷同士の物理的な接近を妨げ、圧電率の低下を抑制する。このような海島構造を有する樹脂シート1を用いることにより、すなわち粒子3および/または粒子5がシート内部にて不均一に分散して存在することにより、高い圧電率および長期圧電特性維持を両立させることができると推察される。
樹脂シート1に用いる電荷誘起性中空粒子5は、中空粒子の表面の少なくとも一部または全面に、導電性物質4が付着している。
このような電荷誘起性中空粒子5は、例えば、中空粒子の表面の少なくとも一部に導電性物質4を付着または蒸着させることで得ることができ、また、中空粒子として、その表面の少なくとも一部に炭素原子を有する物質が付着した粒子(以下「表面処理粒子」ともいう。)を用いる場合には、該炭素原子を有する物質を炭化するような条件で加熱処理することで得ることもできる。具体的には、下記「前炭化法」の工程(1a)、「後炭化法」の工程(2')および「蒸着法」の工程(1c)で得ることができる。
導電性物質不含粒子3は、その内部が密閉状態、すなわち外部から独立した空間を有する粒子であり、マトリックス樹脂2と溶融混練する際にその構造が破壊され難い粒子であることが好ましい。このような中空粒子としては、例えば、ガラス製の粒子、セラミックス製の粒子、有機系高分子製の粒子等が挙げられ、絶縁性の材料からなる中空粒子が好ましい。前記粒子3の内部は、得られるシートの用途に応じて真空、常圧のいずれでもよく、常圧の場合は空気等で満たされることが多い。
なお、前記粒子3は、導電性物質がその表面に付着していない中空粒子であればよく、前記ガラス製等の粒子そのまま(未処理の粒子)でもよく、その表面に炭素原子を有する物質等が付着していてもよい。
前記導電性物質4は、中空粒子の表面の一部または全部に付着しており、樹脂シートにおいて電荷を保持する作用を有するものである。この導電性物質4は、導電性物質不含粒子3およびマトリックス樹脂2よりも導電率が高い物質であることが好ましく、より好ましくは、導電率が1.0×10-10S/cm以上の物質である。導電率は、導電性物質単体の導電率に基づいて、二重リング電極法を用いて測定される。
前記マトリックス樹脂2は特に限定されないが、熱分解開始温度が150~450℃である樹脂が挙げられ、例えばテトラフルオロエチレンとパーフルオロアルキルビニールエーテルの共重合体〔PFA〕(例えば見掛け密度:1.0~1.2g/ml(ASTM D2116準拠))、テトラフルオロエチレンとヘキサフルオロプロピレンの共重合体〔FEP〕(例えば見掛け密度:1.0~1.2g/ml)、ポリクロロトリフルオロエチレン〔PCTFE〕(例えば見掛け密度:0.9~1.2g/ml)、テトラフルオロエチレンとエチレンの共重合体〔ETFE〕(例えば見掛け密度:1.0~1.2g/ml)、ポリビニリデンフルオライド〔PVdF〕、ポリビニルフルオライド〔PVF〕、テトラフルオロエチレンとヘキサフルオロプロピレンとビニリデンフルオライドとの共重合体〔THV〕等の含フッ素系樹脂;ポリプロピレン、ポリエチレン等のポリオレフィン系樹脂;ポリスチレン、ポリメチルメタクリレート、ポリ(メタ)アクリル酸エステル、ポリ塩化ビニル、ポリ塩化ビニリデン等のビニル系重合体;ポリエチレンテレフタレート、ポリブチレンテレフタレート、ポリエチレンナフタレート、ポリ乳酸、ポリヒドロキシアルカノエート、ポリブチレンサクシネート、ポリエチレンサクシネート、ポリエチレンサクシネートアジペート等のポリエステル系重合体;6-ナイロン、6,6-ナイロン、11-ナイロン、12-ナイロン等のポリアミド系樹脂;ポリイミド、ポリアミドイミド、ポリエーテルイミド、ビスマレイミド等のイミド系樹脂;ポリカーボネートやシクロオレフィン類等のエンジニアリングプラスチック類などの熱可塑性樹脂、または、不飽和ポリエステル、ビニルエステル樹脂、ジアリルフタレート樹脂、エポキシ樹脂、ポリウレタン、ケイ素系樹脂、アルキド樹脂、フラン樹脂、ジクロペンタジエン樹脂、アクリル樹脂、アリルカーボネート樹脂等の熱硬化性樹脂などが挙げられる。
このような含フッ素系樹脂やイミド系樹脂を用いる場合、得られる樹脂シート1が耐熱性および耐候性に優れ、特に80℃以上の高温における圧電特性の経時安定性に優れるためより好ましい。
本発明で用いる樹脂シート1の製造方法は、特に制限されないが、例えば、図4に示すような、「前炭化法」、「後炭化法」および「蒸着法」のいずれかを採用できる。
また、樹脂シート1中に前記の海島構造を形成させる一例としては、前炭化法および蒸着法の工程(2)ならびに後炭化法の工程(2')において、下記「二段階分散法」を適用する方法が挙げられる。
前炭化法は、
工程(1a):表面処理粒子を熱処理し、該粒子の付着物質を熱分解することによって、その一部または全部に導電性を生じさせ(おそらく炭化され)、中空粒子の表面の少なくとも一部に導電性物質が付着した電荷誘起性中空粒子を得る工程;
工程(2):工程(1a)で得られた、電荷誘起性中空粒子と、マトリックス樹脂と必要により導電性物質不含粒子とを、溶融混練した後、シート状に成形する工程;ならびに
工程(3):工程(2)で得られたシートに分極処理を施すことによって、該シートに電荷を注入する工程
を含む。
なお、前記表面処理粒子は、炭素原子を有する物質が、炭化水素基を含む界面活性剤である場合、例えば、炭化水素基を含む界面活性剤を適当な溶媒(例えばメチルアルコール)で希釈し、得られる界面活性剤溶液に中空粒子を浸漬させる方法などで得ることができる。この場合、界面活性剤の使用量は、その界面活性剤の種類にもよるが、中空粒子の重量に対して、5%未満が好ましく、より好ましくは0.1~1.0%程度である。中空粒子重量に対して界面活性剤の量が5%を超えると、多孔質樹脂シートから電荷が逃げやすくなるおそれがある。また、0.1%未満であると、中空粒子表面に導電性物質が形成され難い場合がある。
成形時の加熱温度は、前記溶融混練温度より10~50℃高い温度であることが好ましく、かつ、マトリックス樹脂の熱分解開始温度未満の温度が好ましい。また、加熱時間は、10~120分間が好ましい。
注入された電荷は、電荷誘起性中空粒子の殻部分(導電性物質部分)に集中し、中空構造に分極を誘起させると考えられる。誘起された電荷の一部は、電荷誘起性中空粒子とマトリックス樹脂との界面に保持されると考えられる。
後炭化法は、
工程(1b):室温~100℃程度、10分~2時間程度、常圧下(必要であれば減圧または加圧下)の条件下で、中空粒子の表面の一部または全部を、炭素原子を有する物質で被覆し表面処理粒子を得る工程;
工程(2'):工程(1b)で得られた、表面処理粒子と、マトリックス樹脂と、必要により導電性物質不含粒子とを溶融混練した後、必要によりマトリックス樹脂の融点以上、分解温度未満の温度であって、前記溶融混練温度と同等またはより高い温度(例:10~60℃高い温度)でシート状に成形するとともに(炭素原子を有する物質を熱分解することで)、炭素原子を有する物質に導電性を生じさせ、中空粒子の表面の少なくとも一部に導電性物質が付着した電荷誘起性中空粒子を含むシートを得る工程;ならびに
工程(3):工程(2')で得られたシートに分極処理を施すことによって、該シートに電荷を注入する工程
を含む。
成形時の加熱温度は、前記溶融混練温度より10~50℃高い温度であり、かつ、マトリックス樹脂の熱分解開始温度未満の温度が好ましい。また、加熱時間は、10~120分間が好ましい。
蒸着法は、
工程(1c):中空粒子の表面の少なくとも一部に導電材料を蒸着させることによって、中空粒子の表面の少なくとも一部に導電性物質が付着した電荷誘起性中空粒子を得る工程;
工程(2):工程(1c)で得られた電荷誘起性中空粒子と、マトリックス樹脂と必要により導電性物質不含粒子とを混練した後、シート状に成形する工程;および
工程(3):工程(2)で得られたシートに分極処理を施すことによって、該シートに電荷を注入する工程
を含む。
蒸着可能な導電材料としては、例えば、カーボン、グラファイト、白金、金およびITOなどが挙げられ、一種単独で用いても二種以上併用してもよい。蒸着方法は従来公知の方法を採用することができる。
図3(B)中、符号aおよびbに示すような島構造部(粒子3および/または粒子5の含有率が高い凝集物、好ましくは、粒子3および粒子5の含有率が高い凝集物)が均一に分散している樹脂シート1は、以下のようにして製造することができる。
海島構造を有する樹脂シート1の中空率は、好ましくは10~70体積%、より好ましくは15~60体積%であることが、得られる樹脂シートの圧電率の初期値とその保持性、長期間の機械強度保持の点で望ましい。
中空率(%)=((体積A-体積B)/体積A)×100
体積A:材料重量および材料比重(真比重)より算出される体積
体積B:材料重量および、中空構造を除いた比重より算出される体積
凝集体用樹脂として、マトリックス樹脂と弾性率が異なる樹脂を用いて製造された樹脂シートは、電荷の取り出しの際の圧縮歪に対して非線形の変形を起こすため、微小な応力によって樹脂シート全体の変形が起こり、よって高い圧電率を示すことができる。
これら樹脂の弾性率は、JIS K7210に準拠し、以下の方法に基づいて測定できる。
原料となる樹脂を公知の方法により3cm×3cm×2mmのシート状に成形し、得られたシートを万能圧縮試験機(ミネベア(株)製;「テクノグラフTG-50kN」)で試験速度5mm/分で測定し、測定値から圧縮応力-ひずみ曲線を作成し、これに基づいて算出する。
本発明の圧電性シートは、有機ポリマーからなるファイバーから成形される不織布または織布を含めばよく、該不織布または織布のみでもよいし、該不織布または織布の表面に従来公知の層等が積層した積層体であってもよい。
不織布または織布は、公知の方法によりファイバーを製造し、得られたファイバーを不織布状に集積または織布状に製織し、成形することで製造することができる。
前記繊維径変動係数は、以下の式より算出する。
繊維径変動係数=標準偏差/平均繊維径
電界紡糸法を用いて有機ポリマーからなるファイバーを製造するには、例えば有機ポリマーおよび必要に応じ溶媒を含む紡糸液を用いて電界紡糸法によりファイバーを製造すればよい。
前記有機ポリマーは、その種類などにも依存するが、紡糸液中に、例えば5~100重量%、好ましくは5~80重量%、より好ましくは10~70重量%含まれる。
紡糸液(1):ポリテトラフルオロエチレン(PTFE)を30~70重量%、好ましくは35~60重量%含み、繊維形成剤を0.1~10重量%、好ましくは1~7重量%含む紡糸液
PTFE、繊維形成剤および溶媒を含み、少なくとも50,000cPの粘度を有する紡糸液を提供するステップと;
紡糸液をノズルより紡糸し静電的牽引力によりファイバー化するステップと;
前記ファイバーをコレクターの上に集め、前駆体を生成するステップと;
前記前駆体を焼成して前記溶媒および前記繊維形成剤を除去することによってPTFEファイバーを形成するステップとを含む方法
などの電界紡糸法を採用することができる。
以下に、前記ファイバーを用いて不織布を成形する工程について説明する。
前記ファイバーを用いて不織布を成形するには、前記ファイバーを製造する工程、および前記ファイバーをシート状に集積して不織布を成形する工程を、別途独立に行ってもよく、同時に行ってもよい(すなわち、ファイバーを製造しつつシート状に集積して、不織布を形成してもよい)。具体的には、例えば、電界紡糸法を用いてファイバーを製造する工程、および得られたファイバーをシート状に集積して不織布を成形する工程を同時に行ってもよいし、ファイバーを製造する工程を行った後に、湿式法により得られたファイバーをシート状に集積して不織布を成形する工程を行ってもよい。
湿式法により不織布を成形する方法としては、たとえば前記ファイバーを含有する水分散液を、例えばメッシュ上に堆積させてシート状に成形すればよい。
前記ファイバーから成形される織布は、前記ファイバーを製造する工程、および前記ファイバーをシート状に製織して織布を成形する工程を含む方法で製造できる。
ファイバーをシート状に製織する方法としては、従来公知の製織方法を用いることができ、例えば、ウォータージェットルーム、エアージェットルーム、レピアルームなどの方法が挙げられる。
前記不織布および織布の厚さは、通常10μm~1mm、好ましくは50μm~500μmである。
例えば、前記有機ポリマーがPTFEである場合の空孔率は、以下の方法により算出する。
(PTFEの真密度-見掛けの密度)×100/PTFEの真密度
無機材料からなるファイバーから成形される不織布または織布を含む圧電性シートの空孔率は、60%以上、好ましくは80~99%である。空孔率が前記範囲内である場合には、圧電性シートは、高い柔軟性を示し、電荷保持量が高くなるため好ましい。
前記不織布および織布の厚さは、通常10μm~1mm、好ましくは50μm~500μmである。
本発明の圧電積層体は、前記多孔質樹脂シートまたは圧電性シートの外表面のうちで、少なくとも前記多孔質樹脂シートまたは圧電性シートの表裏面の何れか1方面に表面被覆層が積層されてなる。この表面被覆層は、長時間に亘って電荷を保持し、高い圧電率を保持する圧電積層体が得られるなどの点から、前記多孔質樹脂シートまたは圧電性シートの表裏面を被覆していることが好ましく、表裏面および端面を被覆していることが好ましい。
なお、本発明において、「多孔質樹脂シートまたは圧電性シートの表裏面」とは、該シートの外表面(6面)のうち、最も面積の大きい2面のことをいい、「多孔質樹脂シートまたは圧電性シートの端面」とは、該シートの外表面(6面)のうち、表裏面を除く4面のことをいう。
前記表面被覆層の体積抵抗率は、1×1013Ω・cm以上であり、好ましくは1×1014Ω・cm以上である。この範囲にあれば、多孔質樹脂シートまたは圧電性シート内の長期電荷保持性向上の点で好ましい。
体積抵抗率は、測定したい表面被覆層単体(フィルム)を用いて二重リング電極法に基づいて測定される。
前記表面被覆層の弾性率は、前記多孔質樹脂シートまたは圧電性シートの弾性率と異なるものであればよく、前記多孔質樹脂シートまたは圧電性シートの弾性率より高いものでも、低いものでもよい。また、この場合の前記表面被覆層と前記多孔質樹脂シートまたは圧電性シートとの弾性率の差は、好ましくは10MPa以上、より好ましくは50MPa以上である。この範囲にあれば、圧電積層体の圧縮時に非線形変形が起こりやすい点で好ましい。
前記表面被覆層の比誘電率は、好ましくは2~100である。
比誘電率がこの範囲内にあれば、コロナ放電による電荷印加を行う場合には、その際に、誘電率が高い表面被覆層の内部に電荷が集中し、また、表面被覆層と多孔質樹脂シートまたは圧電性シートとの界面にも電荷が保持されやすい傾向にある。さらに、保持された電荷は前記多孔質樹脂シートまたは圧電性シート中の中空構造に移動するために、圧電積層体全体としての電荷保持量が増大して、圧電率の初期値が向上する。
前記表面被覆層の厚さは、通常1μm以上であり、好ましくは多孔質樹脂シートまたは圧電性シートの厚さの30%以下である。厚さが、1μm未満では、例えば、表面被覆層用のフィルムを用いて、表面被覆層を形成する場合、該フィルムの取扱性が悪く、かつ、フィルム欠陥(ピンホール)による絶縁性が低下する等の問題が生じる可能性があり好ましくない。また、前記表面被覆層の厚さが多孔質樹脂シートまたは圧電性シートの30%を超える場合は、多孔質樹脂シートまたは圧電性シート中に電荷を注入する際のコロナ放電電圧を高く設定する必要があるため工業的に実用化が困難になる傾向にある。
前記表面被覆層の材料は、前記物性を兼ね備える層を得ることができれば特に限定されないが、熱硬化性樹脂または熱可塑性樹脂が挙げられる。熱硬化性樹脂の例示としては、例えばポリイミド、エポキシ樹脂、熱硬化性フッ素ゴム(たとえばフッ化ビニリデン系ゴム)、ポリウレタン、フェノール樹脂、イミド樹脂(たとえばポリイミド、ポリアミドイミド、ビスマレイミドなど)、シリコーン樹脂等が挙げられる。熱可塑性樹脂の例示としては、例えばアクリル樹脂、メタクリル樹脂、ポリプロピレン、ポリアミド、塩化ビニル樹脂、シリコーン樹脂、フッ素樹脂(たとえばポリテトラフルオロエチレン(PTFE)、ポリクロロトリフルオロエチレン(PCTFE)、エチレン-テトラフルオロエチレン共重合体(ETFE)、ポリフッ化ビニリデン(PVDF)、テトラフルオロエチレン・パーフルオロアルキルビニルエーテル共重合体(PFA)、テトラフルオロエチレン・ヘキサフルオロプロピレン共重合体(FEP)など)、ナイロン、ポリスチレン、高密度ポリエチレン、シリコーンゴム、低密度ポリエチレン、ポリフェニレンスルフィド、ポリエチレンオキサイド、ポリスルホン、塩化ビニリデンなどが挙げられる。
前記表面被覆層は、従来公知の方法により形成可能であり、例えば熱硬化性樹脂を用いる場合は、前記多孔質樹脂シートまたは圧電性シートの裏表面の少なくとも1方面、すなわち片面または両面に、熱硬化性樹脂と硬化剤(架橋剤)とを溶剤に溶かした液を塗布・乾燥させることにより形成することができる。また、光硬化性樹脂を塗布し、光硬化させることにより形成することもできる。
硬化剤の使用量は、前記樹脂100重量部に対して、通常1~20重量%、好ましくは1~10重量%である。
溶剤の使用量は、前記樹脂100重量部に対して、通常100~5000重量部、好ましくは200~3000重量部である。
本発明の圧電積層体は、多孔質樹脂シートまたは圧電性シートと表面被覆層との間に中間層を有していてもよい。
また、本発明の圧電積層体が、2枚以上の多孔質樹脂シートまたは圧電性シートを有する場合、これらシート間に中間層を有していてもよい。
このような有機系材料としては、例えばテトラフルオロエチレンとパーフルオロアルキルビニールエーテルの共重合体〔PFA〕、テトラフルオロエチレンとヘキサフルオロプロピレンの共重合体〔FEP〕、ポリクロロトリフルオロエチレン〔PCTFE〕、テトラフルオロエチレンとエチレンの共重合体〔ETFE〕、ポリビニリデンフルオライド〔PVdF〕、ポリビニルフルオライド〔PVF〕、テトラフルオロエチレンとヘキサフルオロプロピレンとビニリデンフルオライドとの共重合体〔THV〕、ポリテトラフルオロエチレン、ポリフッ化ビニリデン、エチレンとクロロトリフルオロエチレンとの共重合体〔ECTFE〕等の含フッ素系樹脂;ポリプロピレン、ポリエチレン等のポリオレフィン系樹脂;ポリスチレン、ポリメチルメタクリレート、ポリ(メタ)アクリル酸エステル、ポリ塩化ビニル、ポリ塩化ビニリデン等のビニル系重合体;ポリエチレンテレフタレート、ポリブチレンテレフタレート、ポリエチレンナフタレート、ポリ乳酸、ポリヒドロキシアルカノエート、ポリブチレンサクシネート、ポリエチレンサクシネート、ポリエチレンサクシネートアジペート等のポリエステル系重合体;6-ナイロン、6,6-ナイロン、11-ナイロン、12-ナイロン、アラミド等のポリアミド類;ポリイミド、ポリアミドイミド、ポリエーテルイミド、ビスマレイミド等のイミド系樹脂;ポリカーボネートやシクロオレフィン類等のエンジニアリングプラスチック類などの熱可塑性樹脂、または、不飽和ポリエステル、ビニルエステル樹脂、ジアリルフタレート樹脂、エポキシ樹脂、ポリウレタン、ケイ素系樹脂、ポリイミド、アルキド樹脂、フラン樹脂、ジクロペンタジエン樹脂、アクリル樹脂、アリルカーボネート樹脂等の熱硬化性樹脂などを用いることができ、さらに前記有機ポリマーの発泡体、延伸多孔質膜、不織布、織布またはゲル状・ゴム状体などを用いることもできる。
前記中間層の弾性率は、前記多孔質樹脂シートや圧電性シートおよび/または前記表面被覆層の弾性率と異なる層であることが好ましく、前記多孔質樹脂シートや圧電性シートおよび/または前記表面被覆層の弾性率より高い層でも、低い層を用いてもよい。多孔質樹脂シートまたは圧電性シートと表面被覆層とは異なる弾性率を有する中間層を用いることが、得られる圧電積層体が、該積層体の圧縮歪に対して非線形の変形を起こしやすく、高い圧電率を示すため好ましい。
この場合の前記中間層と前記表面被覆層および/または前記多孔質樹脂シートや圧電性シートとの弾性率の差は、通常10MPa以上、好ましくは50MPa以上である。この範囲にあれば、本発明の圧電積層体の圧縮時に非線形の変形が起こりやすい点で好ましい。
本発明の圧電積層体としては、多孔質樹脂シートの表裏面の片面に表面被覆層が積層されたもの(図7)、多孔質樹脂シートの表裏面の両面に表面被覆層が積層されたもの(図8)、多孔質樹脂シートの表裏面の両面および端面に表面被覆層が形成されたもの(図9)、多孔質樹脂シートの片面に中間層が積層され、この積層体の表裏面の両面および端面に表面被覆層が形成されたもの(図10)、2層の多孔質樹脂シートが中間層を介して積層され、この積層体の表裏面の両面および端面に表面被覆層が形成されたもの(図11)などが挙げられる。
<多孔質樹脂シートの作製>
フッ素樹脂(ダイキン工業製FEP、NP101)(熱分解開始温度:400℃;導電率:1.0×10-16S/cm;MFR:24g/10分(ASTM D2116);融点:255℃(ASTM D2116);見掛け密度1.21g/ml(JIS K6891))100gに中空粒子として中空ガラスビーズ(ポッターズバロティーニ社製、60P18、導電率:1.0×10-14S/cm)4.3gを混合した。混合物の中空率は10%であった。
中空率(体積%)=((体積A-体積B)/体積A)×100
体積A:材料重量および材料比重(真比重)より算出される体積
体積B:材料重量および、中空粒子の中空構造を除いた比重より算出される体積
得られた混合物を下記の条件で成形し、3cm×3cm×0.3mmのシートを得た。
前記混合物を3cm×3cmの圧縮成形用金型に投入し、無加圧で350℃/1hの条件で加熱した。加熱後、空冷下60kgf/cm2の面圧で加圧しながら150℃まで冷却して多孔質樹脂シートを得た。
熱硬化性樹脂(ダイキン工業(株)製フッ素ゴム、ダイエルG912)(フッ素濃度:70.5重量%、比重(23℃):1.91(JIS K6268)、ムーニー粘度(ML1+10・100℃):約77(JIS K6300-1))10gと、硬化剤としてトリアリルイソシアヌレート(商品名:TAIC、日油(株)製)0.5gと、2,5-ジメチル-2,5-ジ(t-ブチルパーオキシ)ヘキサン(商品名:パーヘキサ25B、日油(株)製)0.1gとを溶剤(和光純薬工業(株)製、THF)200gに溶かした液を、前記多孔質樹脂シートの片側表面(表裏面の1方面)にアプリケーターを用いて塗布して乾燥させ、160℃で15分加熱することにより加硫させて、多孔質樹脂シートの片面に、該シートより弾性率の小さい表面被覆層を形成し、圧電積層体を得た。
前記表面被覆層の体積抵抗率は、表面被覆層単体を用いて二重リング電極法に基づいて測定した。以下、表面被覆層の体積抵抗率は、同様の方法で測定した。
得られた多孔質樹脂シートおよび表面被覆層の弾性率を、インデンテーションテスター(エリオニクス社製、ENT-2100)を用いて測定した。
前記圧電積層体を、春日電機(株)製のコロナ放電装置を用いて、電極間距離12.5mm、電極間電圧3kV、室温下で3分間コロナ放電による分極処理を行い、その後、積層体の両面に、アルミ箔からなる矩形電極(三菱アルミ(株)製の「FOIL」、11μm)を設けて、評価用サンプルを作製した。
室温(20℃)雰囲気下、湿度20%の条件で、評価用サンプルの厚さ方向に一定の交流加速度α(周波数:90~300Hz、大きさ:2~10m/s2)を与え、その時の応答電荷を測定し、初期の圧電率d33(pC/N)を測定した(この時点を0日とする。)。この結果を表1に示す。
実施例1で作製した多孔質樹脂シートのみを用いて、実施例1と同様の方法で圧電率を測定した。その結果を表1に併せて示す。
<多孔質樹脂シートの作製>
フッ素樹脂(ダイキン工業(株)製FEP、NP-101)100gに中空ガラスビーズ(住友スリーエム(株)製iM30K)18.6gを混合した。混合物の中空率は30%であった。前記中空率は、実施例1と同様の方法により測定した。得られた混合物を実施例1と同様の方法で成形し、3cm×3cm×0.2mmのシート(多孔質樹脂シート)を得た。
前記多孔質樹脂シートの両面(表裏面の両面)に、フッ素樹脂シート(ダイキン工業(株)製PFAフィルム「AF0025」、25μm、体積抵抗率1.0×1018Ω・cm)を重ね、300℃の熱プレスで2MPaの圧力で180秒間保持することにより圧着させて積層体(圧電積層体)を形成した。実施例1と同様に、弾性率を測定し、また、得られた積層体を用いて、実施例1と同様の方法で圧電率を測定した。初期の圧電率を測定後、帯電している評価用サンプルを室温(20℃)、湿度20%の雰囲気に静置し、1日および5日経過後の圧電率を実施例1と同様の方法で測定した。その結果を表1に併せて示す。
実施例2で作製した多孔質樹脂シートのみを用いて、実施例2と同様の方法で圧電率を測定した。その結果を表1に併せて示す。
<多孔質樹脂シートの作製>
特表2012-515850号公報に記載の電界紡糸法により、ポリテトラフルオロエチレン(PTFE)ファイバーをシート状に集積し、厚さ60μmのPTFE不織布(空孔率80%、弾性率6MPa)からなる多孔質樹脂シートを製造した。
空孔率は、以下の方法に基づいて測定した。
多孔質樹脂シートを4cm角(縦4cm、横4cm)に切り出した試験片の重量と、マイクロメーター(LITEMATIC VL-50、(株)ミツトヨ製)により測定された厚さを用いて算出された見掛けの密度を用いて、空孔率を下記式により算出した。
(PTFEの真密度-見掛けの密度)×100/PTFEの真密度
平均繊維径の測定は、多孔質樹脂シートについて、無作為にSEM観察の領域を選び、この領域をSEM観察(装置:S-3400((株)日立ハイテクノロジーズ製)、倍率10000倍)して無作為に20本の繊維を選び、これらの繊維の測定結果に基づいて、平均繊維径(算術)、繊維径標準偏差および繊維径変動係数を算出した。平均繊維径は1.3μm、繊維径標準偏差は0.4、繊維径変動係数は0.3であった。
繊維径変動係数は、以下の式より算出した。
繊維径変動係数=繊維径標準偏差/平均繊維径
多孔質樹脂シートとして、得られたPTFE不織布を用い、表面被覆層のフッ素樹脂シートとして、ダイキン工業(株)製PFAフィルム(「AF0012」、12.5μm、体積抵抗率1.0×1018Ω・cm)を用いた以外は、実施例2と同様の方法で圧電積層体を形成した。実施例1と同様に、弾性率を測定し、また、得られた積層体を用いて、実施例1と同様の方法で圧電率を測定した。初期の圧電率を測定後、帯電している評価用サンプルを室温(20℃)、湿度20%の雰囲気に静置し、1日および5日経過の圧電率を実施例1と同様の方法で測定した。その結果を表2に併せて示す。
<多孔質樹脂シートの作製>
実施例3と同様の操作により、PTFE不織布(空孔率80%、厚さ0.06mm、弾性率6MPa、平均繊維径1.3μm、繊維径標準偏差0.4、繊維径変動係数0.3)からなる多孔質樹脂シートを製造した。
実施例3と同様の操作により、得られた多孔質樹脂シートの表裏面の両面に表面被覆層を形成した。続いて、ふっ素ゴム(ダイキン工業(株)製、ダイエルG912)100重量部をトルエン1000重量部に溶解させたものに、2,5-ジメチル-2,5-ジ(t-ブチルパーオキシ)ヘキサン(商品名:パーヘキサ25B(日油(株)製))を2重量部、および、トリアリルイソシアヌレート(商品名:TAIC(日油(株)製))を5重量部加えたものを端面被覆材料として、これを前記表面被覆層を形成した多孔質樹脂シートの4つの端面にコーティングし、150℃15分の条件で熱硬化させて端面被覆層を形成することで、圧電積層体を得た。なお、この端面被覆層の体積抵抗率は、1.0×1013Ω・cmであった。
(多孔質樹脂シートの製造)
中空粒子として、住友スリーエム(株)製の3MTM グラスバブルズ「iM30K」(組成がソーダ石灰ほうケイ酸ガラスであり、50%粒子径が16μmであり、ガラス量(計算値)が24(体積比%)であり、導電率が1.0×10-13S/cmである。)を用い、中空粒子の重量に対して、1重量%のノニオン系界面活性剤(日油(株)製のノニオンID-206;ポリオキシエチレンイソデシルエーテル、熱分解開始温度:150℃)で、中空粒子の表面を被覆した。具体的には、所定量の界面活性剤をメチルアルコールで50倍に希釈した液中に、中空粒子を浸漬させて被覆した。中空粒子表面へのノニオン系界面活性剤による被覆はSEMを用いて確認した。
前記シート作製工程により、中空粒子表面に付着していた界面活性剤は、その一部または全部が炭化されたと想定され、導電率が1.0×10-10S/cmである導電性物質となっていた。
得られた多孔質樹脂シート(3cm×3cm×0.5mm厚)の両面に、アルミ箔からなる矩形電極(三菱アルミ(株)製の「FOIL」;厚さ11μm)を設けて評価用サンプルを作製した。
その後、帯電している評価用サンプルを室温(20℃)で湿度20%の雰囲気下に静置し、2、3、5、10、11、20および27日経過後に、それぞれ同様の方法で圧電率d33を求めた。
その結果を表3および図5に示す。なお、得られたデータはすべてn=3の平均値である。
参考例1において、中空粒子の重量に対して使用するノニオン系界面活性剤を0.5重量%に変更した以外は参考例1と同様にして多孔質樹脂シートを製造した。そして、参考例1と同様にしてその圧電性能を評価し、その結果を表3および図5に示す。
参考例1において、中空粒子の重量に対して使用するノニオン系界面活性剤を0%に変更した(すなわち中空粒子を界面活性剤で被覆しなかった)以外は参考例1と同様にして多孔質樹脂シートを製造した。そして、参考例1と同様にしてその圧電性能を評価し、その結果を表3および図5に示す。
(圧電積層体の耐熱特性評価)
実施例2で製造し、5日後の評価を行った圧電積層体を、80℃に維持した電気炉内に100時間静置することにより、熱処理を行った。その後、サンプルを電気炉より取り出し、室温まで空冷後、実施例1と同様に圧電特性の評価を行った(製造日より9日経過後の測定に相当する)。その結果、熱処理後の多孔質樹脂シートのd33は61pC/Nであり、熱処理前と同等の特性を維持していた。このことから、本発明の圧電素子用多孔質樹脂シートは、80℃などでの高温環境下においても、圧電特性を失活しない耐熱性を有していることが明らかとなった。
<島構造用ペレットの作製>
中空粒子として、中空ガラスビーズ(ポッターズバロティーニ社製、60P18、導電率が1.0×10-14S/cm)(組成がほうケイ酸ガラスであり、粒子径が16μmであり、真比重が0.6g/cm3であり、中空粒子を中実体と仮定した比重が2.5g/cm3であり、ガラス量(計算値)が24(体積比%)である。)を用い、中空粒子の重量(100重量%)に対して、1重量%のノニオン系界面活性剤(日油(株)製のノニオンID-206;熱分解開始温度:150℃)で、中空粒子の表面を被覆した。具体的には、所定量の界面活性剤をメチルアルコールで50重量倍に希釈した液中に常温、常圧下で、中空粒子を浸漬させて被覆した。なお、このノニオン系界面活性剤(ノニオンID-206)には溶剤は含まれていない。
海構造として、ネオフロンFEP(ダイキン工業(株)製、型番:NP101、比重:2.1g/cm3、導電率が1.0×10-15S/cm;MFR:24g/10分(ASTM D2116準拠)、300℃での粘度:1.0×104poise、融点255℃(ASTM D2116準拠)、見掛密度1.21g/ml(JIS K6891準拠))29.0gをラボプラストミルを用いて300℃で5分間混練し、さらに島構造として前記島構造用ペレット23.0gを投入した後、300℃で10分間混練することで海島構造用ペレットを作成した。
前記海島構造の割合は、各材料重量および密度、中空粒子ガラス量より算出した。
海島構造用ペレットを原料として用いて、寸法3cm×3cm×0.2mmになるように金型成形し、サンプルシートを得た。
具体的には、海島構造用ペレットを金型に入れ、350℃/1hで加熱後、空冷下3MPaで圧縮してサンプルシートを成形した。
また、中空粒子表面に付着していた界面活性剤は、導電率が1.0×10-10S/cmである導電性物質となっていた。
前記サンプルシートを、春日電機(株)製のコロナ放電装置を用いて、電極間距離12.5mm、電極間電圧3kV、室温下で3分間コロナ放電による分極処理を行い、多孔質樹脂シートを製造した。その後、シートの両面に、アルミ箔からなる矩形電極(三菱アルミ(株)製の「FOIL」、11μm)を設けて、評価用サンプルシートを作製した。
室温(20℃)雰囲気下、湿度20%の条件で、評価用サンプルシートの厚さ方向に一定の交流加速度α(周波数:90~300Hz、大きさ:2~10m/s2)を与え、その時の応答電荷を測定し、初期の圧電率d33(pC/N)を求めた。(この時点を0日とする。)
その後、帯電している評価用シートを室温(20℃)、湿度20%の雰囲気に静置し1、5および22日経過後に、それぞれ同様の方法で圧電率d33を求めた。
その結果を表4に示す。
特開平3-97993号公報に記載の湿式抄紙法により、厚さ125μmのPTFE不織布を製造した(PTFE不織布1、弾性率10MPa)。得られたPTFE不織布1を多孔質樹脂シートとして用いた以外は実施例4と同様の操作により圧電積層体を製造し、圧電率を測定した。その結果を表5に示す。
なお、実施例6~10で得られた圧電積層体の圧電特性の5日目保持率は、式「5日目の圧電率×100/初期値」で算出した値である。
特開平3-97993号公報に記載の湿式抄紙法により、厚さ300μmのPTFE不織布を製造した(PTFE不織布1'、弾性率12MPa)。得られたPTFE不織布1'を多孔質樹脂シートとして用いた以外は実施例4と同様の操作により圧電積層体を製造し、圧電率を測定した。その結果を表5に示す。
特表2012-515850号公報に記載の電界紡糸法により、PTFEファイバーをシート状に集積し、厚さ50μmのPTFE不織布(弾性率6MPa)を製造した(PTFE不織布2)。得られたPTFE不織布2を多孔質樹脂シートとして用いた以外は実施例4と同様の操作により圧電積層体を製造し、圧電率を測定した。その結果を表5に示す。
特表2012-515850号公報に記載の電界紡糸法により、PTFEファイバーをシート状に集積し、厚さ100μmのPTFE不織布(弾性率6MPa)を製造した(PTFE不織布2')。得られたPTFE不織布2'を多孔質樹脂シートとして用いた以外は実施例4と同様の操作により圧電積層体を製造し、圧電率を測定した。その結果を表5に示す。
多孔質樹脂シートとして、延伸PTFE膜(空孔率78%、平均細孔径0.30μm、厚さ50μm、弾性率4MPa)を用いた以外は実施例4と同様の操作により圧電積層体を製造し、圧電特性を評価した。その結果を表5に示す。
実施例6および実施例9で製造された圧電積層体について、下記手法により応力に対する電荷応答性の評価を行った。
実施例6および実施例9で製造された圧電積層体を3cm角に切り出し、春日電機(株)製のコロナ放電装置を用いて、電極間距離12.5mm、電極間電圧3kV、室温下で3分間コロナ放電による分極処理を行った。その後、室温(20℃)雰囲気下、湿度20%の条件で、積層体の厚さ方向にロードセルを用いて応力(1mm/分のヘッドスピード)により圧縮変形させた際の、応力(N/cm2)に対する積層体表面の応答電荷(pC/cm2)をチャージアンプにより測定した。その結果を図12に示す。
実施例8で製造された圧電積層体について、下記手法により高温高湿耐久性試験を行った。
実施例8にて製造された圧電積層体を、室温乾燥条件(25℃、相対湿度25%)または高温高湿条件(85℃、相対湿度85%)で200時間保管した後の圧電率を、実施例1と同様の方法で測定した。その結果をそれぞれ表6に示す。
多孔質樹脂シートとして、ガラスからなる不織布(東洋濾紙(株)製、硝子繊維ろ紙GA-55、厚さ0.25mm、空孔率90%、弾性率110MPa)を用いた以外は実施例4と同様の操作により圧電積層体を製造し、圧電特性を評価した。その結果を表7に示す。
空孔率=(1-(サンプル密度/ガラス中実体密度))×100(%)
2・・・マトリックス樹脂
3・・・中空粒子
4・・・導電性物質
5・・・電荷誘起性中空粒子
6・・・圧電積層体
7・・・多孔質樹脂シート
8・・・表面被覆層
9・・・中間層
Claims (19)
- 多孔質樹脂シートと、
前記多孔質樹脂シートの外表面のうちで、少なくとも前記多孔質樹脂シートの表裏面の何れか1方面に積層された表面被覆層と
を有し、
前記表面被覆層の体積抵抗率が1×1013Ω・cm以上であり、前記多孔質樹脂シートと表面被覆層との弾性率が異なる、圧電積層体。 - 前記多孔質樹脂シートと前記表面被覆層との弾性率の差が10MPa以上である、請求項1に記載の圧電積層体。
- 前記表面被覆層の比誘電率が2~100である、請求項1または2に記載の圧電積層体。
- 前記表面被覆層が、前記多孔質樹脂シートの表裏面および端面を被覆している、請求項1~3のいずれか1項に記載の圧電積層体。
- 前記多孔質樹脂シートが、少なくとも電荷誘起性中空粒子がマトリックス樹脂に分散しているシートであり、
該電荷誘起性中空粒子は、中空粒子の表面の少なくとも一部に導電性物質が付着している粒子であり、
該導電性物質は、中空粒子およびマトリックス樹脂のうちの何れよりも導電率が高い物質である、
請求項1~4のいずれか1項に記載の圧電積層体。 - 前記多孔質樹脂シートが、有機ポリマーからなるファイバーから成形される不織布または織布を含む圧電性シートである、請求項1~4のいずれか1項に記載の圧電積層体。
- 前記ファイバーの平均繊維径が0.05~50μmであり、繊維径変動係数が0.7以下である、請求項6に記載の圧電積層体。
- 前記圧電性シートの空孔率が60%以上である、請求項6または7に記載の圧電積層体。
- 前記有機ポリマーが、分子および結晶構造に起因する双極子を持たない有機ポリマーである、請求項6~8のいずれか1項に記載の圧電積層体。
- 前記有機ポリマーがポリテトラフルオロエチレンである、請求項6~9のいずれか1項に記載の圧電積層体。
- 有機ポリマーからなるファイバーから成形される不織布または織布を含む圧電性シート。
- 前記ファイバーの平均繊維径が0.05~50μmであり、繊維径変動係数が0.7以下である請求項11に記載の圧電性シート。
- 空孔率が60%以上である、請求項11または12に記載の圧電性シート。
- 前記有機ポリマーが、分子および結晶構造に起因する双極子を持たない有機ポリマーである、請求項11~13のいずれか1項に記載の圧電性シート。
- 前記有機ポリマーがポリテトラフルオロエチレンである、請求項11~14のいずれか1項に記載の圧電性シート。
- 無機材料からなるファイバーから成形される不織布または織布を含み、空孔率が60%以上である圧電性シート。
- 前記ファイバーの平均繊維径が0.05~50μmであり、繊維径変動係数が0.7以下である請求項16に記載の圧電性シート。
- 請求項16または17に記載の圧電性シートと、
前記圧電性シートの外表面のうちで、少なくとも前記圧電性シートの表裏面の何れか1方面に積層された表面被覆層と
を有し、
前記表面被覆層の体積抵抗率が1×1013Ω・cm以上であり、前記圧電性シートと表面被覆層との弾性率が異なる、圧電積層体。 - 前記表面被覆層が、前記圧電性シートの表裏面および端面に形成されている、請求項18に記載の圧電積層体。
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TW201425033A (zh) | 2014-07-01 |
CN104756213A (zh) | 2015-07-01 |
JP2015035576A (ja) | 2015-02-19 |
JP5615988B1 (ja) | 2014-10-29 |
JPWO2014069477A1 (ja) | 2016-09-08 |
TWI614131B (zh) | 2018-02-11 |
US10998488B2 (en) | 2021-05-04 |
US20150295163A1 (en) | 2015-10-15 |
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