JP2017220650A - Piezoelectric sensor having β-type polyvinylidene fluoride film and method for manufacturing the same - Google Patents

Abstract

A piezoelectric sensor provided with a highly flexible β-polyvinylidene fluoride film supported by electrodes without using a base material that causes adhesion problems, and a method for manufacturing the same. A PVDF sensor 1 includes a β-type polyvinylidene fluoride film, and a first electrode 20a and a second electrode 20b spaced apart from each other in the β-type polyvinylidene fluoride film. [Selection drawing] Fig. 1

Description

  The present invention relates to a piezoelectric sensor including a β-type polyvinylidene fluoride film and a method for manufacturing the same.

  Conventionally, polyvinylidene fluoride is known as a polymer piezoelectric material. This polyvinylidene fluoride has already been used as a piezoelectric material in various sensors such as hydrogen sensors, pressure sensors, ultrasonic sensors, acceleration sensors, and vibration sensors. From now on, information processing devices such as software, actuators, etc. Application to output devices is expected. Polyvinylidene fluoride has three types of crystal structures, α-type, β-type, and γ-type. Among them, only β-type has piezoelectricity. Such a polyvinylidene fluoride film having a β-type crystal structure (hereinafter referred to as “β-type polyvinylidene fluoride film”) is usually used to transfer the crystal structure from a non-polar α-type to a polar β-type. If the polyvinylidene fluoride having an α-type crystal structure is not subjected to polarization treatment, it cannot be produced. However, in order to perform the polarization treatment, a large facility such as an extruder or a polarization device is required, and there is a problem that the manufacturing cost is increased. Therefore, a production method of a β-type polyvinylidene fluoride film that can be produced with a simple equipment and a simple method has been developed (see, for example, Patent Document 1).

  By the way, the β-type polyvinylidene fluoride film has flexibility, and is expected to be applied to the medical field by utilizing this characteristic. For example, a method has been proposed in which an operation for cerebral infarction, aneurysm, angina, etc. is performed by mounting a minimally invasive sensor using a polyvinylidene fluoride-based material on an intravascular catheter, a guide wire, or the like. Examples of such minimally invasive surgical sensors include a blood flow sensor for measuring blood flow (see Non-Patent Document 1), a tactile sensor for grasping the state of a living body or an affected area with a sense like a human finger, and the like. Has been researched and developed.

  However, the β-type polyvinylidene fluoride film is known to have a problem of peeling because of its poor adhesion to the substrate. In order to improve this, a coating solution for forming a β-type polyvinylidene fluoride film with various improvements has been proposed. For example, in Patent Document 2, a silane coupling agent is added to a coating solution for forming a piezoelectric resin film, and in Patent Document 3, a liquid coating composition containing a vinylidene fluoride compound having a specific organosiloxane moiety. In Patent Document 4, a liquid containing a non-ferroelectric polymer composed of one kind selected from polyvinyl chloride, polyimides, polyetheramides, nylons, and polycyanoacrylates, or a mixture thereof. Each coating composition is prepared to improve adhesion. However, there is room for further improvement in the adhesion of the β-type polyvinylidene fluoride film to the substrate.

JP 2014-43514 A JP 2013-188667 A JP 2009-137842 A JP-A 63-145353

IEEE TRANSACTIONS ON BIO MEDICAL ENGINEERING, VOL. 62, NO. 1, JANUARY 2015, p. 188-p. 195

  In view of such circumstances, the present invention provides a piezoelectric sensor having a β-type polyvinylidene fluoride film excellent in flexibility and supported by an electrode without using a base material that causes adhesion problems, and a method for manufacturing the same. The purpose is to provide.

  According to a first aspect of the present invention for solving the above-described problems, a β-type polyvinylidene fluoride film, and a first electrode and a second electrode that are spaced apart from each other in the β-type polyvinylidene fluoride film are provided. The piezoelectric sensor includes a β-type polyvinylidene fluoride film.

  According to a second aspect of the present invention, the β-type polyvinylidene fluoride film according to the first aspect is characterized in that the first electrode and the second electrode are formed in a thread shape or a cloth shape. A piezoelectric sensor comprising:

  Further, a third aspect of the present invention includes polyvinylidene fluoride, a water-soluble polar solvent that dissolves the polyvinylidene fluoride and fixes it in β-type, and an organic solvent having a boiling point lower than that of the water-soluble polar solvent. A step of mixing to form a coating solution, and forming the coating film so that the first electrode and the second electrode are disposed in a coating film made of β-type polyvinylidene fluoride formed from the obtained coating solution And a step of drying the formed coating film, and a step of washing the dried coating film with water. A method for producing a piezoelectric sensor comprising a β-type polyvinylidene fluoride film is provided.

  In addition, a fourth aspect of the present invention includes a polyvinylidene fluoride, a water-soluble polar solvent that dissolves the polyvinylidene fluoride and fixes the β-type, and an organic solvent having a boiling point lower than that of the water-soluble polar solvent. A step of mixing to form a coating solution, a step of disposing the first electrode and the second electrode on the base material apart from each other, and a coating made of β-type polyvinylidene fluoride formed from the obtained coating solution Forming the coating film so that the first electrode and the second electrode are disposed in the film, drying the formed coating film, washing the dried coating film with water, A method for producing a piezoelectric sensor comprising a β-type polyvinylidene fluoride film, comprising the step of peeling the coating film.

  According to a fifth aspect of the present invention, the substrate includes any one of polyethylene terephthalate, polyethylene naphthalate, polyether sulfone, polyamide, polyimide, polyvinylidene chloride, and polycarbonate. The method of manufacturing a piezoelectric sensor including the β-type polyvinylidene fluoride film according to the fourth aspect.

  According to a sixth aspect of the present invention, in any one of the third to fifth aspects, the first electrode and the second electrode are formed in a thread shape or a cloth shape. There is a method for manufacturing a piezoelectric sensor including such a β-type polyvinylidene fluoride film.

  ADVANTAGE OF THE INVENTION According to this invention, the piezoelectric sensor which comprises the beta-type polyvinylidene fluoride film | membrane excellent in the softness | flexibility supported by an electrode, without using the base material which the adhesion problem produces can be provided, and its manufacturing method. .

It is a perspective view which shows typically the structure of the piezoelectric sensor which comprises the beta type polyvinylidene fluoride film concerning this embodiment. BRIEF DESCRIPTION OF THE DRAWINGS It is a figure for demonstrating the manufacturing method of the piezoelectric sensor which comprises the beta type polyvinylidene fluoride film concerning this embodiment, (a) is the front view which shows the state which has arrange | positioned the electrode on the base material, and its AA FIG. 2B is a cross-sectional view taken along line ′, and FIG. 4B is a front view showing a state where electrodes are disposed in a β-type polyvinylidene fluoride film and a cross-sectional view taken along line BB ′, and FIG. It is the front view which shows the state which peeled the polyvinylidene fluoride film | membrane, and its CC 'line sectional drawing. (A) is a graph which shows the measurement result of the tapping test of the PVDF sensor of Example 1, (b) shows the measurement result of the tapping test of the laminated sensor produced by superposing two PVDF sensors of Example 2. It is a graph. It is a perspective view which shows typically the structure of the piezoelectric sensor which comprises (beta) -type polyvinylidene fluoride film | membrane and eight electrodes. It is a perspective view which shows typically the structure of the piezoelectric sensor which comprises (beta) -type polyvinylidene fluoride film | membrane and a textile-like electrode. It is a figure which shows typically the structure of the piezoelectric sensor which comprises (beta) -type polyvinylidene fluoride film | membrane and a matrix-like electrode, (a) is a perspective view, (b) is a front view.

Hereinafter, the present invention will be described in detail based on embodiments.
(Piezoelectric sensor with β-type polyvinylidene fluoride film)
FIG. 1 is a perspective view schematically showing the structure of a piezoelectric sensor including a β-type polyvinylidene fluoride film according to an embodiment of the present invention. As shown in the figure, a piezoelectric sensor having a β-type polyvinylidene fluoride film (hereinafter referred to as “PVDF sensor 1”) is separated from a β-type polyvinylidene fluoride film (hereinafter referred to as “PVDF film 10”). The first electrode 20a and the second electrode 20b are disposed. The PVDF sensor 1 has a structure in which the PVDF film 10 is supported by the flexible first electrode 20a and the second electrode 20b without using a base material that causes adhesion problems. The sensor as a whole is excellent in flexibility without hindering the characteristic flexibility.

  The PVDF film 10 is mainly composed of β-type polyvinylidene fluoride and has a high purity. If the PVDF film 10 functions as β-type polyvinylidene fluoride, a mixture of α-type polyvinylidene fluoride and γ-type polyvinylidene fluoride may be used. Is included. Here, high purity means that the film contains almost no components other than polyvinylidene fluoride (hereinafter also referred to as “PVDF”).

β-type polyvinylidene fluoride consists of a repeating chain of (—CF ₂ —CH ₂ —) _{n and} a conformation structure in which the molecular chain is all-trans. For this reason, β-type polyvinylidene fluoride has a direction of spontaneous polarization aligned from a fluorine atom to a hydrogen atom, that is, in a direction perpendicular to the molecular chain, and is a material having excellent piezoelectric characteristics.

  The PVDF film 10 is a film made of granular crystal grains having an average particle diameter of 8 μm to 9 μm and having a volume porosity of 48% to 53%.

The volume porosity was calculated by the following formula (1).
Volume porosity (%) = ((true PVDF mass−apparent PVDF mass) / true PVDF mass) × 100 (1)

However, the true PVDF mass is (theoretical density 1.78 g / cm ³ ) × (volume of the produced PVDF film 10), and the apparent PVDF mass is an actually measured value by a weighing meter.

  Such a PVDF film 10 is a porous film having a large volume porosity and having a plurality of voids between crystal grains. Due to the presence of these voids, the PVDF film 10 has excellent strain characteristics. On the other hand, the β-type polyvinylidene fluoride film produced by a conventional stretching method has a flat surface and no granular crystal grains are observed.

  Therefore, the PVDF film 10 made of granular crystal grains according to the present embodiment is distinguished from the conventional β-type polyvinylidene fluoride film. For example, as a piezoelectric film, the PVDF film 10 has high sensitivity and is used in a piezoelectric sensor. A sensor having stable detection characteristics can be realized.

The first electrode 20a and the second electrode 20b is arranged in the PVDF film 10 spaced apart by a distance _{d 1} from one another. In the present embodiment, the distance d ₁ is 200 μm, but is not particularly limited as long as the PVDF sensor 1 functions as a sensor. For example, the distance d ₁ is set in a range of 50 μm to 500 μm according to the application of the sensor. can do. When the distance d ₁ between the first electrode 20a and the second electrode 20b is set to be less than 50 μm, the details will be described later, but due to thermal contraction of the PVDF film 10 during drying, the first electrode 20a and the second electrode 20b Contact with each other causes poor contact. On the other hand, when the distance d ₁ is set to a value exceeding 500 μm, the electric capacity (capacitance) decreases and the electric signal attenuates. In either case, it becomes a factor that degrades the function of the PVDF sensor 1, which is not preferable.

  As described above, the first electrode 20a and the second electrode 20b support the PVDF film 10 without hindering flexibility, which is a feature of the PVDF film 10, and function as electrodes. The first electrode 20a and the second electrode 20b are not particularly limited as long as they have both conductivity and flexibility, and examples thereof include those formed in a thread shape or a cloth shape. These can be selected and applied according to the application of the sensor.

Examples of the thread-like electrode (thread-like body) include a material having excellent flexibility such as a metal plating wire obtained by performing metal plating on synthetic fiber such as polyester, rayon, nylon, polypropylene, polyurethane, and a thin metal wire. Can do. The metal plating wire may be either a monofilament or a twisted yarn, but a twisted yarn is preferable in consideration of strength. The metal material used in the plating process is not particularly limited. For example, silver (Ag), gold (Au), titanium (Ti), palladium (Pd), platinum (Pt), copper (Cu), or alloys thereof These general electrode materials can be applied and can be appropriately selected according to the application. Further, the thickness d ₂ of the filament (first electrode 20a and second electrode 20b) is not particularly limited and those which may be appropriately selected depending on the application, it can be used in 1 denier to 100 denier . One denier is the mass of a 9000 m yarn expressed in grams. In the case of using the a bundle a plurality of metal wires as filament, the diameter (corresponding to the thickness d ₂ of the filament mentioned above) is not particularly limited and those which may be appropriately selected depending on the application Considering the flexibility of the PVDF sensor 1, even when a plurality of metal wires are bundled, the diameter may be set to 500 μmΦ or less, and is preferably about 10 μmΦ to 100 μmΦ.

  Examples of the cloth-like electrode (cloth-like body) include a woven fabric woven by twisted yarn, a knitted fabric knitted by twisted yarn, or a yarn woven roughly in a mesh shape (mesh-like body). Among them, a woven fabric or a mesh-like body is preferable. In addition, the number of twisted yarns used for the above-mentioned woven fabric, knitted fabric and mesh-like body is not limited, and can be appropriately selected according to the application.

  Moreover, the 1st electrode 20a and the 2nd electrode 20b can be used properly according to a use, The same electrode form may be applied to these, and a different electrode form may be applied, respectively. For example, a filament may be applied to each of the first electrode 20a and the second electrode 20b, or a cloth may be applied to one electrode and a filament may be applied to the other electrode. Good. In the latter case, the cloth-like body functions as one electrode (common electrode). Alternatively, a plurality of filaments may be applied to the first electrode 20a and the second electrode 20b, respectively, to form an electrode having a matrix structure. That is, the first electrode 20a and the second electrode 20b are arranged with a plurality of first electrodes 20a (first electrode group) spaced apart from each other and with a plurality of spaced apart ones. This is a wire mesh electrode having a plurality of second electrodes 20b (second electrode group) provided to intersect the first electrode 20a. With such a configuration, the wire mesh electrode allows the first electrode group and the second electrode group to function as a common electrode, or is separately sensed between each first electrode 20a and each second electrode 20b. Is possible.

In the present embodiment, the first electrode 20a and second electrode 20b, and applying the same yarn material having a thickness d _2. That is, a 50 μmφ Ag-plated yarn obtained by performing silver plating on a polyester yarn material was used. In addition to using these two electrodes, the number of electrodes may be increased as necessary. An example using other electrodes than the present embodiment will be described later.

  Since the PVDF sensor 1 according to the present embodiment includes the PVDF film 10 having excellent strain characteristics, for example, compared with a pressure sensor including a β-type polyvinylidene fluoride film formed by a conventional stretching method, for example, an output voltage Indicates a stable potential change, and the detection sensitivity is known to be several times better (see Patent Document 1). Thereby, it is possible to realize a highly reliable pressure sensor having high sensitivity and stable detection characteristics. Further, the PVDF sensor 1 has a structure that is supported by the flexible first electrode 20a and the second electrode 20b without using a base material that causes adhesion problems. Therefore, a pressure sensor excellent in flexibility can be realized.

  In addition to the pressure sensor, the PVDF film 10 having such excellent strain characteristics includes various piezoelectric sensors such as a piezoelectric hydrogen sensor, an ultrasonic sensor, an acceleration sensor, a vibration sensor, and an impact sensor, as well as a blood flow sensor. It can be widely used for biosensors such as sensors for minimally invasive surgery such as tactile sensors.

(Method for manufacturing piezoelectric sensor having β-type polyvinylidene fluoride film)
FIG. 2 is a view for explaining a method of manufacturing a piezoelectric sensor having a β-type polyvinylidene fluoride film. FIG. 2A is a front view showing a state in which electrodes are arranged on a substrate, and its AA ′. (B) is a front view showing a state in which electrodes are arranged in a β-type polyvinylidene fluoride film and a BB ′ line cross-sectional view thereof, and (c) is a β-type polyvinyl fluoride from a substrate. It is the front view which shows the state which peeled the vinylidene fluoride film | membrane, and its CC 'sectional view taken on the line. In each cross-sectional view, a pair of pedestals 40a and 40b described later are omitted.

  As shown in the figure, the PVDF sensor 1 manufacturing method does not require large-scale equipment, and manufactures the PVDF sensor 1 having excellent piezoelectric characteristics, high purity, and excellent flexibility by a simple method using a solution coating method. It is.

  The manufacturing method of the PVDF sensor 1 having such excellent characteristics is obtained by mixing a water-soluble polar solvent that dissolves polyvinylidene fluoride and fixing it in a β-type, and an organic solvent having a boiling point lower than that of the water-soluble polar solvent. A step of forming a coating solution, a step of disposing the first electrode 20a and the second electrode 20b on the base material 30 apart from each other, and a coating made of β-type polyvinylidene fluoride formed from the obtained coating solution A step of forming a coating film so that the first electrode 20a and the second electrode 20b are disposed in the film, a step of drying the formed coating film, and washing the dried coating film with water and applying from the substrate 30 And a step of peeling the film.

  Such a PVDF sensor 1 is manufactured by dissolving polyvinylidene fluoride in a water-soluble polar solvent that dissolves polyvinylidene fluoride and fixing it in β-type, and an organic solvent having a boiling point lower than that of the water-soluble polar solvent. After forming a film on the substrate 30 so that the first electrode 20a and the second electrode 20b are disposed therein, the organic solvent is removed to form a porous film, which is washed with water The PVDF sensor 1 provided with the high-purity PVDF film 10 is manufactured by removing the polar solvent and peeling from the base material 30.

Hereinafter, each step will be described.
The coating liquid formation process consists of mixing polyvinylidene fluoride, a water-soluble polar solvent that dissolves polyvinylidene fluoride and fixing it in β-type, and an organic solvent having a boiling point lower than that of the water-soluble polar solvent. It is a process to do. Specifically, a polyvinylidene fluoride powder is dissolved in a predetermined water-soluble polar solvent and a predetermined organic solvent to prepare a coating solution containing polyvinylidene fluoride.

  Here, the polyvinylidene fluoride used in the present embodiment is not only a polymer of vinylidene fluoride alone but also a vinylidene fluoride monomer, as long as it is a β-type polyvinylidene fluoride film and exhibits piezoelectric characteristics. Copolymers with other monomers containing fluorine may also be used. In the present embodiment, these are collectively referred to simply as polyvinylidene fluoride. Since such polyvinylidene fluoride is used after being dissolved in a solvent, it is preferably used in a powder form, but may be in the form of flakes or lumps.

  In addition, the predetermined water-soluble polar solvent used in the present embodiment has a function of dissolving polyvinylidene fluoride and immobilizing the polyvinylidene fluoride in β-type. For example, hexamethylphosphoric triamide (HMPA) And phosphoric acid amide compounds such as dimethylacetamide, dimethylformamide, and dimethyl sulfoxide. The phosphoric acid amide compound includes not only a triamide such as a hexaalkylphosphoric acid triamide but also a monoamide, a diamide, or a mixture thereof. Among these, hexamethyl phosphate triamide is particularly preferable, and hexamethyl phosphate triamide is used in this embodiment.

  Here, the water-soluble polar solvent has the function of immobilizing polyvinylidene fluoride in β-type when the polyvinylidene fluoride is transferred to the β-type crystal structure and immobilized in a state of being compatible with polyvinylidene fluoride. Say. In addition, immobilization to β-type includes not only those that are completely immobilized to β-type, but also those that are fixed so that β-type is superior to α-type. What is necessary is just to fix so that vinylidene may become what has desired piezoelectricity.

  Moreover, the water solubility of a water-soluble polar solvent means the water solubility of the grade which can remove a solvent from a coating film by the water washing peeling process mentioned later.

  The organic solvent having a boiling point lower than that of the water-soluble polar solvent means a solvent having a saturated vapor pressure at a drying temperature described later, which is higher than that of the water-soluble polar solvent and has a high evaporation rate. For this reason, in the drying step of the coating film described later, by heating to about the boiling temperature of the organic solvent, only the organic solvent can be evaporated while the water-soluble polar solvent remains in the coating film. It can be a porous membrane. Such an organic solvent is compatible with polyvinylidene fluoride and a water-soluble polar solvent, and may be appropriately selected according to the type of the water-soluble polar solvent to be used.

  Examples of the organic solvent having a boiling point lower than that of the water-soluble polar solvent include acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, dimethylformamide, diethylformamide, dimethylacetamide, diethylacetamide, dimethylbutyramide, N-methylpyrrolidone, and the like. A mixed solvent can be mentioned. Among these, it is preferable to use at least one selected from the group consisting of acetone and dimethylformamide. In this embodiment, acetone is used in view of easiness of evaporation.

  In this embodiment, the above-mentioned polyvinylidene fluoride, a water-soluble polar solvent that dissolves polyvinylidene fluoride and fixes it to β-type, and an organic solvent having a boiling point lower than that of the water-soluble polar solvent are mixed to form a coating solution. However, the volume ratio of the water-soluble polar solvent and the organic solvent having a boiling point lower than that of the water-soluble polar solvent is particularly limited as long as it can form a coating film that can maintain a porous shape after drying as described above. What is necessary is just to contain 10 volume%-80 volume% of organic solvents. This is because when the organic solvent is less than 10% by volume, a porous film is not formed when the organic solvent is removed, and when it is more than 80% by volume, the shape of the film cannot be maintained. Preferably, the volume ratio of the water-soluble polar solvent to the organic solvent is in the range of 1: 3 to 3: 1.

  The content of polyvinylidene fluoride is preferably in the range of 3.5% by mass or more, and more preferably 5% by mass to 6.5% by mass with respect to the total mass of the water-soluble polar solvent. % Range.

  More preferably, when hexamethylphosphoric triamide is used as the water-soluble polar solvent, the volume ratio of hexamethylphosphoric triamide to acetone is 1: 1 and the content of polyvinylidene fluoride is hexamethylphosphoric triamide. The total mass is 6.5% by mass.

  Next, an arrangement process of the first electrode 20a and the second electrode 20b will be described. The disposing step of the first electrode 20a and the second electrode 20b is a step of disposing the first electrode 20a and the second electrode 20b on the base material 30 so as to be separated from each other. As shown in FIG. 2A, first, a pair of pedestals 40a and 40b are prepared and arranged on the base material 30 so that the distance between them is 1 cm to 10 cm. Next, the first electrode 20a and the second electrode 20b are placed and stretched on the pedestals 40a and 40b with an interval of 100 μm to 500 μm. At this time, the tension of the first electrode 20a and the second electrode 20b is 5 to 100 g.

In the present embodiment, the above-described Ag plating yarn is used as the first electrode 20a and the second electrode 20b, the separation distance (distance d ₁ ) between the first electrode 20a and the second electrode 20b is 500 μm, The tension was 10 g weight.

  Next, the coating film forming process will be described. This forming step is obtained in the coating liquid forming step so as to include the first electrode 20a and the second electrode 20b disposed on the base material 30 in the disposing step of the first electrode 20a and the second electrode 20b. In this step, a coating film is formed using the coating solution thus obtained. As shown in FIG. 2B, in the present embodiment, the obtained coating solution is embedded in the coating solution in the first electrode 20a and the second electrode 20b disposed on the substrate 30. An amount was added dropwise. Thereby, the 1st electrode 20a and the 2nd electrode 20b can be arrange | positioned in the coating film obtained through the drying process and the water washing peeling process mentioned later.

  The method for forming the coating film is not particularly limited as long as the first electrode 20a and the second electrode 20b can be arranged in the coating film to form a film. For example, as in Example 1 described later, the substrate A method of forming a film without using 30 or a method of forming a film by immersing the first electrode 20a and the second electrode 20b in a coating solution may be used. It can select suitably according to the number and form of the 1st electrode 20a and the 2nd electrode 20b to apply.

  The base material 30 is not particularly limited as long as it can be easily peeled off by water washing without being in close contact with the coating film containing the first electrode 20a and the second electrode 20b in the water washing peeling process described later. . Examples of such a substrate 30 include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethersulfone (PES), polyamide (PA), polyimide (PI), polyvinylidene chloride (PVDC), Examples include polycarbonate (PC). In the present embodiment, polyethylene terephthalate is used as the base material 30.

  In the present embodiment, the formed coating film is dried in the drying step. This step is a step of drying the coating film including the first electrode 20a and the second electrode 20b formed on the substrate 30 to form a porous film.

  Specifically, only the organic solvent having a boiling point lower than that of the water-soluble polar solvent is removed from the coating film made of the coating liquid containing polyvinylidene fluoride dropped on the base material 30 to form a porous dry film. It is a process to do.

  In this embodiment, since acetone is used as the organic solvent and polyethylene terephthalate is applied as the substrate 30, for example, the coating film is set to about 70 ° C. which is several tens of degrees higher than the boiling point of acetone (about 56 ° C.). By heating, only acetone is evaporated from the coating film to form the above-mentioned dry film. In the case of a method of forming a film without using the substrate 30 as in Example 1 described later, the heating may be performed at a drying temperature of about 90 ° C.

  In order to remove only the organic solvent from the coating film, the obtained dry film is composed of a predetermined water-soluble polar solvent and polyvinylidene fluoride, and becomes a porous film having a plurality of voids, that is, a porous film. Further, in the above-mentioned dry film, due to the presence of a predetermined water-soluble polar solvent, the direction of spontaneous polarization of the polyvinylidene fluoride film is aligned in a certain direction, and the crystal structure of this film is maintained in the β type. Also from the result of the absorption spectrum by infrared spectroscopy, it has been confirmed that the crystal structure of the polyvinylidene fluoride film contained in the dry film is β-type (see, for example, Patent Document 1).

  Examples of the heating device used in the drying process include an RTA (Rapid Thermal Annealing) device that heats by irradiation with an infrared lamp and a hot plate. In this embodiment, a hot plate is used.

  As shown in FIG. 2 (c), in this embodiment, in the washing and peeling step, the porous film (dried film) formed by drying is washed with water, and this film is peeled off from the substrate 30. The water washing and peeling step is a step of washing the dried film with water to remove the water-soluble polar solvent and peeling the film from the substrate 30. Washing with water may be performed by running water, immersion in water, or the like. In this embodiment, the substrate 30 on which a porous film obtained by drying is washed with pure water for about 1 minute, and a water-soluble polar solvent such as hexamethylphosphoric triamide in the film is removed. The PVDF film 10 was obtained by peeling from the substrate 30.

  Since the dried film is a porous film by evaporation of acetone, it is considered that a water-soluble polar solvent, for example, hexamethylphosphoric triamide is removed from the dried film by washing with water. In addition, it was confirmed that the direction of spontaneous polarization of polyvinylidene fluoride was maintained even after removal of water-soluble polar solvent such as hexamethylphosphoric triamide that fixed polyvinylidene fluoride to β-type by washing with water from the dried film (See Patent Document 1). Therefore, the PVDF film 10 can be obtained by rinsing with water to form a film having excellent piezoelectric properties, high purity and excellent flexibility, and peeling from the substrate 30. In general, since a coating film made of β-type polyvinylidene fluoride has low adhesion to the base material 30 such as polyethylene terephthalate and is easily peeled off, it can be easily peeled off from the base material 30 by washing with water. Further, when peeling from the substrate 30, the first electrode 20a and the second electrode 20b disposed in the film are not detached. The film thickness of the formed coating film is about 70 μm to 300 μm.

  In addition, a porous film having a larger volume porosity can be formed by desorption of a predetermined water-soluble polar solvent. Due to the porosity, this membrane has excellent strain characteristics.

  In the present embodiment, an organic solvent having a boiling point lower than that of the water-soluble polar solvent is mixed with the coating solution in order to form a film having high purity and excellent porosity. Then, in the drying step, the organic solvent is first evaporated while leaving the water-soluble polar solvent in the coating film, so that the remaining film becomes a porous dry film, and in the subsequent washing and peeling step, the drying is performed. A water-soluble polar solvent is further desorbed from the membrane to obtain a more porous membrane. The PVDF film 10 having high purity and excellent porosity can be formed by the two steps of the drying step and the water detachment step.

  Furthermore, according to the manufacturing method of the present embodiment, the porosity of the film, that is, the volume porosity, is controlled by changing the mixing ratio of the organic solvent having a boiling point lower than that of the water-soluble polar solvent mixed in the coating solution. It is possible. Specifically, by increasing the mixing ratio of such organic solvents, the organic solvent that evaporates in the drying step can be increased, the porosity of the PVDF membrane 10 can be increased, and the volume porosity can be increased.

  As described above, according to the method for manufacturing the PVDF sensor 1 according to the present embodiment, a large-scale facility is not required, and the coating liquid forming process, the first electrode 20a and the second electrode 20b arranging process, A simple method comprising only a coating film forming process and a drying process in which the first electrode 20a and the second electrode 20b are disposed, and a water washing and peeling process of the dried coating film, provides excellent piezoelectric properties, high purity, and excellent flexibility. The PVDF sensor 1 including the PVDF film 10 can be manufactured. In addition, the manufacturing of such a PVDF sensor 1 has a small number of manufacturing steps, and therefore has a small environmental load and can reduce manufacturing costs. By mounting such a film having excellent piezoelectric characteristics and high purity as a piezoelectric film on various sensors, a sensor having excellent detection characteristics can be realized. Furthermore, since the PVDF sensor 1 excellent in flexibility can be manufactured, it can be applied to a biosensor or the like that can be deformed according to the fixing target of the sensor.

Hereinafter, the present invention will be described in more detail based on examples.
Example 1
In Example 1, a PVDF sensor including a PVDF film having two electrodes disposed therein was manufactured by a manufacturing method different from that of the PVDF sensor 1 described above. First, β-type polyvinylidene fluoride (hereinafter referred to as “PVDF”) is added to a mixed solution (HMPA: acetone = 3: 4) composed of hexamethylphosphoric triamide (hereinafter referred to as “HMPA”) and acetone (purity> 99.5%). Α type PVDF powder (manufactured by Polysciences) is added so as to be 14 wt% with respect to the total mass of the mixed solution, and stirred at 40 ° C. for 60 minutes until the PVDF powder is dissolved, A coating solution containing uniform PVDF (14 wt% PVDF solution) was obtained.

  Next, as the first electrode and the second electrode, two Ag metal wires (50 μmΦ) were prepared, and in addition, a set of pedestals arranged with a predetermined interval was prepared (see FIG. 2). Next, two Ag metal wires were placed on the set of pedestals with an interval of 200 μm between them, and they were stretched with a tension of 10 g, and this state was maintained.

  Next, 100 μL of the obtained coating solution was applied to the two Ag metal wires with a brush to obtain a PVDF-containing film containing these Ag metal wires inside. And this PVDF containing film | membrane was dried on the 90 degreeC heater for 1 hour, and the dry film | membrane was obtained. The obtained dried film was washed with pure water for 2 minutes together with the two Ag metal wires contained therein to obtain a PVDF film having a thickness of 140 μm. Further, it was confirmed that the two Ag metal wires were not detached from the obtained PVDF film. As a result, a PVDF sensor including a PVDF film was obtained. Since the PVDF film was thermally contracted, the distance between the two Ag metal wires was 130 μm.

(Example 2)
In Example 2, a PVDF sensor having three (first to third electrodes) electrodes of the PVDF sensor 1 described above was manufactured. First, in the same manner as in Example 1, an α-type PVDF powder, which is a raw material of PVDF, is mixed with a mixed solution (volume ratio 50:50) composed of HMPA and acetone at 10 wt% with respect to the total mass of the mixed solution. In addition, the mixture was stirred for 30 minutes in a kneader until the PVDF powder was dissolved to obtain a coating solution containing uniform PVDF (10 wt% PVDF solution).

  Next, a PET film as a base material and three Ag-plated yarns as a first electrode to a third electrode were prepared, and a set of pedestals arranged at regular intervals on the PET film was prepared (see FIG. 2). Next, three Ag-plated yarns were placed on a set of pedestals with an interval of 500 μm from each other, and these were stretched with a tension of 20 g and maintained in this state.

  Next, 200 μL of the obtained coating solution was dropped onto three Ag plating yarns to obtain a PVDF-containing film in which these plating yarns were contained inside. This PVDF-containing film is in contact with the PET film. And this PVDF containing film | membrane was dried on the 70 degreeC hotplate for 5 hours, and the dry film | membrane was obtained. The obtained dry film was washed with pure water for 2 minutes together with the three Ag plating yarns and PET film contained therein, and it was confirmed that the PVDF-containing film was peeled off. As a result, a PVDF film having a thickness of 200 μm was formed to obtain a PVDF sensor.

(Test Example 1)
A tapping test was performed on the laminate (laminated sensor) of the PVDF sensor of Example 1 and the PVDF sensor of Example 2. Specifically, each PVDF sensor was put in a vinyl bag, and whether or not an electric signal was received when it was lightly tapped with a finger was confirmed. Here, the laminated sensor is a laminated body of PVDF sensors obtained by preparing two PVDF sensors obtained in Example 2, and superposing and pressing them. In this laminated sensor, three Ag plated yarns arranged in the upper PVDF film are used as one common electrode, and three Ag plated yarns arranged in the lower PVDF film are used as the other common electrode. did.

  Moreover, the above-mentioned laminated sensor can also be used by individually connecting the upper and lower electrodes. In this case, it is possible to obtain position information by appropriately processing the strength of the pressure signal. For example, each electrode made of Ag plating yarns on the upper side and the lower side is assigned a number (electrode number) so that it can be distinguished from each other, and the lower electrode number and the strongest upper electrode from which the strongest signal can be obtained. By recording the number as position information and sequentially recording the passage of time, the moving direction of the measurement object can be specified. In such a method of use, the number of electrodes is adjusted in accordance with the area, and a processor is necessary because signal processing requires high-speed processing to some extent.

  FIG. 3A is a graph showing the measurement result of the tapping test of the PVDF sensor of Example 1, and FIG. 3B is the measurement result of the tapping test of the laminated sensor manufactured by superposing two PVDF sensors of Example 2. It is a graph which shows. As shown in the drawing, an electrical signal is obtained when the PVDF sensor of Example 1 and the above-described laminated sensor are both lightly tapped with a finger. However, the above-described laminated sensor has an electric capacity due to an increase in the area of the sensor. Due to the increased effect, electrical signals were observed larger.

  From the above, the PVDF sensor provided with the PVDF film is highly sensitive and stable even when the PVDF sensor is used alone or when a PVDF sensor laminate comprising a plurality of PVDF sensors is used. It can be used as a highly reliable pressure sensor that shows potential changes. In Test Example 1, two Ag metal wires and six Ag-plated yarns were used as the electrodes. Since both function as sensors, the above-described yarn-like electrodes (filamentous bodies) are laminated. It was confirmed that the structure can be applied regardless of the form. For example, in position sensing, one or two metal wires (threads) are bonded to a predetermined place on a structure of cloth electrodes (cloth bodies) and piezoelectric elements (PVDF films). A sensor that emits a signal indicating that pressure has been applied to the position can be realized. In addition, by stacking three or four piezoelectric elements including electrodes (thread-like bodies and / or cloth-like bodies), an element having a function suitable for various applications can be realized.

(Other embodiments)
Although one embodiment of the present invention has been described above, the basic configuration of the present invention is not limited to the above-described embodiment. For example, in the above-described embodiment, the β-type polyvinylidene fluoride film is applied to the pressure sensor as a piezoelectric film, but other than the pressure sensor, a piezoelectric hydrogen sensor, an ultrasonic sensor, an acceleration sensor, a vibration sensor, an impact sensor, and the like can be used. It can be widely applied to various sensors. It can also be used for information processing devices such as circuits and software, and output devices such as actuators and transducers. Furthermore, it can also be used for various biosensors such as minimally invasive surgical sensors such as blood flow sensors and tactile sensors.

  Further, in the present embodiment, a description has been given by taking, as an example, a thread-like electrode (filamentous body) using an Ag metal wire and an Ag plating thread as an electrode form. The form can be changed as appropriate. For example, you may use the electrode of the form which is mentioned later.

  FIG. 4 is a perspective view schematically showing the structure of a piezoelectric sensor having a β-type polyvinylidene fluoride film and eight electrodes. As in the PVDF sensor 2 shown in FIG. 4, the first electrodes 21 a to 21 d made of four Ag plated yarns are disposed inside the PVDF film 11 on the upper surface side of the PVDF film 11, and the PVDF film 11 Four second electrodes 22a to 22d made of four Ag plating yarns may be disposed on the lower surface side of the first electrode. With such a configuration, the first electrodes 21a to 21d can be used as one electrode (common electrode), and the second electrodes 22a to 22d can be used as the common electrode as well. Alternatively, among the first electrodes 21a to 21d, the first electrodes 21a and 21b and the first electrodes 21c and 21d are used as common electrodes, respectively. Similarly, among the second electrodes 22a to 22d, the second electrodes 22a and 22b and the second electrodes By using the electrodes 22c and 22d as common electrodes, sensing can be performed between the upper and lower common electrodes.

  FIG. 5 is a perspective view schematically showing the structure of a piezoelectric sensor including a β-type polyvinylidene fluoride film and a woven electrode. Like the PVDF sensor 3 shown in FIG. 5, a woven fabric in which twisted yarns made of a plurality of Ag plated yarns are woven on the upper surface side of the PVDF film 12 is arranged as the first electrode 23 a inside the PVDF film 12. A fabric woven with twisted yarns made of a plurality of Ag plating yarns may be disposed on the lower surface side of the PVDF film 12 as the second electrode 23b. With such a configuration, the range of applications of the sensor can be expanded. The first electrode 23a and the second electrode 23b may be knitted electrodes.

  FIGS. 6A and 6B are diagrams schematically showing a structure of a piezoelectric sensor including a β-type polyvinylidene fluoride film and a matrix electrode, where FIG. 6A is a perspective view and FIG. 6B is a front view. As in the PVDF sensor 4 shown in FIG. 6, twisted yarns each made of a plurality of Ag plated yarns may be applied to the two electrodes to form an electrode having a matrix structure. That is, the two electrodes are disposed in the PVDF film 13 with a first electrode group consisting of the first electrodes 24a to 24d spaced apart from each other and spaced apart from each other, and It is a wire mesh electrode which has the 2nd electrode group which consists of 2nd electrode 25a-25d provided crossing 1st electrode 24a-24d. With such a configuration, the wire mesh electrode can function as the common electrode for the first electrode group and the second electrode group described above, or between the first electrodes 24a to 24d and the second electrodes 25a to 25d. Can be individually sensed.

  Further, in the present embodiment, the components shown in the drawings, that is, the thickness, width, relative positional relationship, etc. of the base material, the film, the electrode, etc. are exaggerated in explaining the present invention. There is a case. Further, the term “upper” in the present specification does not limit that the positional relationship between the constituent elements is “directly above”. For example, the expression “first electrode on a substrate” includes the case where the first electrode is disposed above the substrate. In addition, the expressions “first electrode on substrate” and “PVDF film on substrate” refer to other components between the substrate and the first electrode or between the substrate and the PVDF film. Does not exclude inclusions.

  INDUSTRIAL APPLICABILITY The present invention can be used in medical fields such as various biosensors in addition to industrial fields such as various sensors, information processing devices, and output devices using the piezoelectric characteristics of β-type polyvinylidene fluoride films.

1, 2, 3, 4 PVDF sensor 10, 11, 12, 13 PVDF membrane 20a, 21a-21d, 23a, 24a-24d 1st electrode 20b, 22a-22d, 23b, 25a-25d 2nd electrode 30 Base material 40a 40b pedestal

Claims (6)

β-type polyvinylidene fluoride film,
A piezoelectric sensor comprising a β-type polyvinylidene fluoride film, wherein the β-type polyvinylidene fluoride film includes a first electrode and a second electrode that are spaced apart from each other.   2. The piezoelectric sensor having a β-type polyvinylidene fluoride film according to claim 1, wherein the first electrode and the second electrode are formed in a thread shape or a cloth shape. Mixing polyvinylidene fluoride, a water-soluble polar solvent that dissolves the polyvinylidene fluoride and fixing it to β-type, and an organic solvent having a boiling point lower than that of the water-soluble polar solvent to form a coating solution;
Forming the coating film such that the first electrode and the second electrode are disposed in the coating film made of β-type polyvinylidene fluoride formed from the obtained coating liquid;
A step of drying the formed coating film;
And a step of washing the dried coating film with water. A method for producing a piezoelectric sensor comprising a β-type polyvinylidene fluoride film. Mixing polyvinylidene fluoride, a water-soluble polar solvent that dissolves the polyvinylidene fluoride and fixing it to β-type, and an organic solvent having a boiling point lower than that of the water-soluble polar solvent to form a coating solution;
Disposing the first electrode and the second electrode on the substrate apart from each other;
Forming the coating film so that the first electrode and the second electrode are disposed in a coating film made of β-type polyvinylidene fluoride formed from the obtained coating liquid;
A step of drying the formed coating film;
And a step of washing the dried coating film with water and peeling the coating film from the substrate. A method for producing a piezoelectric sensor comprising a β-type polyvinylidene fluoride film.   The β-type polyvinylidene fluoride film according to claim 4, wherein the base material includes any one of polyethylene terephthalate, polyethylene naphthalate, polyether sulfone, polyamide, polyimide, polyvinylidene chloride, and polycarbonate. A method for manufacturing a piezoelectric sensor.   The β-type polyvinylidene fluoride film according to any one of claims 3 to 5, wherein the first electrode and the second electrode are formed in a thread shape or a cloth shape. A method for manufacturing a piezoelectric sensor.

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