Pressure detection device and pressure detection method

Abstract

The present invention provides a pressure detection device and a pressure detection method that can reliably measure static load. [Solution] The pressure detection device comprises a piezoelectric film sensor 1 having a structure in which a first electrode layer, a piezoelectric film, and a second electrode layer are sequentially stacked in that order; an analog-to-digital converter 50 connected to the piezoelectric film sensor 1; and a digital signal processing unit 60 that performs digital signal processing including DC offset compensation on the signal obtained from the analog-to-digital converter 50. The digital signal processing unit 60 is characterized in that it calculates the pressure applied to the piezoelectric film sensor 1 from the baseline signal obtained from the piezoelectric film sensor 1.

Description

[Technical Field]

[0001] The present invention relates to a pressure detection device and a pressure detection method that can be suitably used in sensors such as load cells, pressure gauges, mass meters, mat sensors, biosensors, and robot hands.

[0002] Piezoelectric films are known to exhibit excellent piezoelectric effects and are widely used in vibration power generation, sensor devices, and other applications. Piezoelectric film sensors, which use piezoelectric films, detect pressure by generating an electric charge corresponding to the force applied. In the prior art described in Patent Document 1 below, since the signal obtained from the piezoelectric film sensor is a differential quantity, the input signal supplied from the piezoelectric film is amplified using a charge amplifier or the like. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2008-82947 [Overview of the project] [Problems that the invention aims to solve]

[0004] As described in Patent Document 1 above, when a configuration is adopted in which the charge signal is integrated and output using a charge amplifier or the like to quantify the pressure, a slight drift occurs over time, making it unsuitable for measuring static load. In other words, piezoelectric film sensors were suitable for measuring dynamic loads with changing pressure, but not suitable for measuring static loads.

[0005] The inventors of this invention were able to realize that static load measurement is also possible using a piezoelectric film sensor, as the noise obtained when a static load is applied to the piezoelectric film sensor differs depending on the load. Therefore, the object of the present invention is to provide a pressure detection device and a pressure detection method that can reliably measure static load. [Means for solving the problem]

[0006] The pressure detection device or pressure detection method of the present invention has the following embodiments [1] to [7].

[0007] [1] A pressure detection device comprising a piezoelectric film sensor having a structure in which a first electrode layer, a piezoelectric film, and a second electrode layer are sequentially stacked in this order; an analog-to-digital converter connected to the piezoelectric film sensor; and a digital signal processing unit that performs digital signal processing including DC offset compensation on the signal obtained from the analog-to-digital converter, wherein the digital signal processing unit calculates the pressure applied to the piezoelectric film sensor from a baseline signal obtained from the piezoelectric film sensor.

[0008] [2] The pressure detection device according to [1], wherein the calculation calculates pressure from the amplitude intensity of the baseline signal obtained from the piezoelectric film sensor.

[0009] [3] The pressure detection device according to [1] or [2], wherein the piezoelectric film sensor has a non-adhesive region in the pressure detection region for detecting pressure, in which the piezoelectric film and the first electrode layer and / or the second electrode layer are not adhered.

[0010] [4] The pressure detection device according to any one of [1] to [3], wherein the piezoelectric film is an electret film or a triboelectric film.

[0011] [5] A pressure detection device according to any one of [1] to [4], wherein the pressure is a static load.

[0012] [6]A pressure detection method using a pressure sensor device comprising a piezoelectric film sensor having a structure in which a first electrode layer, a piezoelectric film, and a second electrode layer are sequentially laminated in this order, an analog-to-digital converter connected to the piezoelectric film sensor, and a digital signal processing unit that performs digital signal processing including DC offset compensation on the signal obtained from the analog-to-digital converter. The digital signal processing unit calculates the pressure applied to the piezoelectric film sensor from the baseline signal obtained from the piezoelectric film sensor.

[0013] [7]The pressure detection method according to [6], wherein the pressure is a static load.

Effect of the Invention

[0014] According to the present invention, it is possible to provide a pressure detection device and a pressure detection method capable of stably measuring a static load.

Brief Description of the Drawings

[0015] [Figure 1] It is a configuration diagram showing an example of a pressure detection device according to an embodiment of the present invention. [Figure 2] It is a diagram showing an example of a signal waveform when a conventional pressure detection device equipped with a piezoelectric film sensor receives a dynamic pressure. As the dynamic pressure, a weight was placed on the piezoelectric film sensor to apply a load, and the weight was removed from the piezoelectric film sensor to remove the load. [Figure 3] It is a diagram showing an example of a signal waveform in a state where there is no pressure on the piezoelectric film sensor. [Figure 4] It is a diagram showing an example of a signal waveform in a state where the piezoelectric film sensor receives a static pressure of 1 kg. [Figure 5] It is a diagram schematically showing the laminated structure of the piezoelectric film sensor in Example 1. [Figure 6] It is a diagram schematically showing the laminated structure of the piezoelectric film sensor in Example 2. [Figure 7] It is a partially enlarged view showing an example when unevenness is provided on the surface of the electrode layer. [Figure 8] This figure schematically shows the laminated configuration of the piezoelectric film sensor in Example 3. [Figure 9] This figure shows an example of a configuration for performing signal measurement method-1 using a pressure detection device in an embodiment. [Figure 10] This figure shows an example of a configuration for performing signal measurement method-2 using a pressure detection device in the embodiment. [Figure 11] This figure shows the baseline signals for no load, 1 kg load, and 3 kg load in Example 1. [Figure 12] This graph plots the Vpp values ​​for no load, 1kg load, 2kg load, and 3kg load in each of the signal measurement methods-1 for Examples 1 to 3. [Figure 13] This graph plots the Vpp values ​​in Example 1, specifically when the load was increased by 100g increments up to 1000g using signal measurement method-1, and then decreased by 100g increments. The error bars in the graph indicate the standard deviation. [Figure 14] This graph plots the Vrms values ​​in Example 1, specifically when the load was increased by 100g increments up to 1000g using signal measurement method-2, and then decreased by 100g increments. The error bars in the graph indicate the standard deviation. Detailed description of the invention

[0016] An embodiment of the pressure detection device of the present invention will be described below. However, the present invention is not limited thereto.

[0017] A pressure detection device according to one embodiment of the present invention (hereinafter also referred to as "this pressure detection device") comprises a piezoelectric film sensor 1, an analog-to-digital converter 50, and a digital signal processing unit 60, as shown in Figure 1. As shown in Figure 1, this pressure detection device converts the pressure signal detected by the piezoelectric film sensor 1 into a digital signal using the analog-to-digital converter 50, processes the received digital signal with the digital signal processing unit 60, and displays it on a screen or the like as a waveform, numerical value of signal strength, pressure value, etc.

[0018] The present invention is characterized by its ability to detect static load pressure using a piezoelectric film. Piezoelectric films are fundamentally materials that can sense pressure changes, rather than pressure itself. When pressure changes, an electromotive force is generated on both sides of the film. Therefore, by detecting the resulting electrical signal (waveform as shown in Figure 2) with detection equipment, it has been possible to sense the presence of a pressure change and utilize it in sensors. In other words, piezoelectric films have been used to detect the pressure of dynamic loads. The inventor focused on the noise in the baseline signal when there is no pressure change in the piezoelectric film, and noticed that the noise level of the baseline signal is higher with a weight (1 kg load) (see Figure 4) than without a weight (0 kg load) (see Figure 3). This led to the idea that it might be possible to detect the static load pressure using a piezoelectric film.

[0019] <Piezoelectric film sensor> The piezoelectric film sensor 1 has a structure in which a first electrode layer 20, a piezoelectric film 30, and a second electrode layer 20' are sequentially stacked in this order, as shown in Figure 5, for example. In addition, the piezoelectric film sensor 1 may also have a protective film 10 (10') or an electromagnetic shielding film 40 (40') laminated on it.

[0020] [Piezoelectric film] The piezoelectric film 30 is not particularly limited as long as it has piezoelectric properties, but an electret film or a triboelectric film can be used, and an electret film is preferred from the viewpoint of further enhancing the piezoelectric properties. However, triboelectric films have excellent water resistance, and sensors using a triboelectric film as the piezoelectric film tend to have good water resistance, so a triboelectric film is preferred depending on the application. The following explains electret films and triboelectric films.

[0021] (Electret film) Electret films are films that carry an electric charge due to the polarization of the film itself. They are broadly classified into two types: permanent dipole films, which are polarized by the dipole orientation of the polymer itself, and porous membrane films, which are made by applying an electrostatic treatment to a porous polymer film to trap charges inside air bubbles and form polarization in each pore. The former has dipoles polarized at the molecular level, i.e., on the order of Å to nm, while the dipole size of the latter depends on the size of the pores, and therefore generally has dipoles on the nm to μm scale, which are larger than those of permanent dipole electret films. For this reason, porous membrane electret films tend to have high piezoelectricity and excellent sensitivity.

[0022] The electret film used in this pressure detection device is preferably a porous film, and more preferably a porous film that has been charged, from the viewpoint of further enhancing its piezoelectric properties. In other words, it is preferable to use a film equivalent to the porous membrane type electret film described above.

[0023] When an electret film is a porous film, the method of creating porosity is not particularly limited, but examples include chemical or physical foaming and stretching. Among these, stretching is preferred because it yields a dense porous structure and allows for easy control of the pore shape.

[0024] The electret film is preferably a porous film, and its porosity is preferably greater than 0% and less than or equal to 50%. Porosity is a numerical value that indicates the proportion of the empty space in the electret film, and the larger the porosity, the larger the piezoelectric constant. From this viewpoint, the porosity is greater than 0%, preferably 5% or more, and more preferably 10% or more. On the other hand, it is preferable that the porosity of the electret film be 50% or less. When the porosity is 50% or less, a piezoelectric film with excellent pressure resistance can be obtained. From the above viewpoint, it is more preferable that the porosity be 40% or less, even more preferable that it be 35% or less, particularly preferable that it be 30% or less, and most preferable that it be 25% or less.

[0025] Porosity can be calculated, for example, by measuring the actual mass W1 of the sample, calculating the mass W0 when the porosity is 0% based on the density of the resin composition constituting the electret film, and then using these values ​​based on the following formula (1). Porosity (%)={(W0-W1) / W0}×100 (1)

[0026] The average pore diameter in the film thickness direction of the above-mentioned pores is preferably 1 μm or less. When the average pore diameter is 1 μm or less, it is easier to obtain a film with excellent sensitivity to pressure. From this viewpoint, the average pore diameter in the film thickness direction of the pores is preferably 0.5 μm or less, and more preferably 0.1 μm or less. Furthermore, the standard deviation in the pore size distribution of the above-mentioned pores is preferably 0.05 μm or less, more preferably 0.04 μm or less, and even more preferably 0.03 μm or less. On the other hand, the coefficient of variation of the pore size is preferably 2.0 or less, more preferably 1.0 or less, and even more preferably 0.8 or less. By having such a pore size distribution, an electret film can be obtained in which the pore size is uniform and the positional stability of the signal intensity is excellent.

[0027] The average aspect ratio of the pores in the electret film is preferably 4.0 or less. When the average aspect ratio of the pores is 4.0 or less, the variation in the pores tends to decrease, and as a result, it becomes easier to achieve a coefficient of variation of 0.5 or less for the absolute value of the piezoelectric constant. From this viewpoint, the average aspect ratio of the pores is more preferably 3.8 or less, even more preferably 3.6 or less, and particularly preferably 3.4 or less. On the other hand, there are no specific restrictions on the lower limit; it just needs to be 1.0 or higher. Furthermore, the coefficient of variation in the aspect ratio distribution is preferably 3.0 or less, more preferably 2.5 or less, and even more preferably 2.0 or less. Having such a value for the coefficient of variation in the aspect ratio distribution makes it possible to obtain an electret film with high piezoelectricity and excellent positional stability of signal intensity.

[0028] The average pore diameter in the thickness direction of the film and the average aspect ratio of the pores can be determined, for example, by observing the average pore diameter and aspect ratio in the thickness direction of the pores from a cross-sectional SEM image of an electret film and calculating the average value.

[0029] The thickness of the electret film is preferably 10 μm or more, more preferably 15 μm or more, and even more preferably 20 μm or more. On the other hand, the upper limit of the thickness of the electret film according to the present invention is preferably 200 μm or less, more preferably 150 μm or less, even more preferably 100 μm or less, and even more preferably 80 μm or less. If the thickness is below the upper limit mentioned above, it becomes a thin film and a physically flexible film, which means that the deformation of the pores when a certain pressure is applied will be large. As a result, polarization changes are more likely to occur, which is preferable because it allows for the acquisition of an electret film with particularly high piezoelectricity. On the other hand, if the thickness is above the lower limit mentioned above, an electret film with excellent handling properties can be obtained.

[0030] The resin composition constituting the electret film is not particularly limited, but examples include polyolefin resins, fluororesins, vinyl chloride resins, polystyrene resins, butadiene resins, polyester resins, and acrylic resins. Of these, polyolefin resins are preferably used from the viewpoint of having a low environmental impact and being easy to electrostatically treat.

[0031] When using polyolefin resins as the main component, it is preferable to use polypropylene resins as the main component. The main component refers to a polyolefin resin content in the electret film that is 50% by mass or more, preferably 70% by mass or more and 99.9999% by mass or less, more preferably 80% by mass or more and 99.999% by mass or less, and even more preferably 90% by mass or more and 99.99% by mass or less.

[0032] Examples of polypropylene resins include homopolypropylene (propylene homopolymer), or random copolymers or block copolymers of propylene with α-olefins such as ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, or 1-decene. Among these, homopolypropylene is more preferably used from the viewpoint of mechanical strength.

[0033] Furthermore, the polypropylene resin preferably has an isotactic pentad fraction exhibiting stereoregularity of 80% to 99%, more preferably 83% to 98%, and even more preferably 85% to 97%. If the isotactic pentad fraction is 80% or higher, the mechanical strength is good. On the other hand, the upper limit of the isotactic pentad fraction is currently defined as the upper limit achievable industrially, but this may not apply if resins with even higher orderliness are developed at an industrial level in the future. The isotactic pentad fraction refers to the stereostructure or ratio in which the five methyl groups of the side chain are all located in the same direction relative to the carbon-carbon bonded main chain composed of any five consecutive propylene units. The assignment of signals in the methyl group region is based on A. Zambelli et al. (Macromol. 8, It conforms to 687 (1975).

[0034] Furthermore, the polypropylene resin preferably has a molecular weight distribution parameter, Mw / Mn, of 1.5 to 10.0. More preferably, it is 2.0 to 8.0, and even more preferably 2.0 to 6.0. A smaller Mw / Mn ratio indicates a narrower molecular weight distribution. However, by setting the Mw / Mn ratio to 1.5 or higher, sufficient extrusion moldability can be obtained, making industrial mass production possible. On the other hand, by setting the Mw / Mn ratio to 10.0 or lower, sufficient mechanical strength can be ensured. Mw / Mn is measured as a polystyrene equivalent value by GPC (Gel Per Emission Chromatography).

[0035] Furthermore, while the melt flow rate (MFR) of the polypropylene resin is not particularly limited, it is generally preferable that the MFR is between 0.5 g / 10 min and 15 g / 10 min, and more preferably between 1.0 g / 10 min and 10 g / 10 min. By setting the MFR to 0.5g / 10min or higher, sufficient melt viscosity can be achieved during molding, ensuring high productivity. On the other hand, by setting the MFR to 15g / 10min or lower, sufficient strength can be ensured. The MFR is measured in accordance with JIS K7210-1 (2014) under conditions of 230°C temperature and 2.16 kg load.

[0036] Furthermore, the method for producing polypropylene resins is not particularly limited, and examples include known polymerization methods using known polymerization catalysts, such as multi-site catalysts represented by Ziegler-Natta type catalysts and single-site catalysts represented by metallocene catalysts.

[0037] More specifically, commercially available polypropylene resins include products such as "Novatec PP," "WINTEC," and "WAYMAX" (manufactured by Nippon Polypropylene Co., Ltd.), "Versify," "Notio," and "Toughmer XR" (manufactured by Mitsui Chemicals, Inc.), "Zelus" and "Thermoran" (manufactured by Mitsubishi Chemical Corporation), "Sumitomo Noblen" and "Toughselenium" (manufactured by Sumitomo Chemical Co., Ltd.), "Prime Polypropylene" and "Prime TPO" (manufactured by Prime Polymer Co., Ltd.), "Adflex," "Adsyl," and "HMS-PP (PF814)" (manufactured by Sun Allomer Co., Ltd.), and "Inspire" (manufactured by Dow Chemical Corporation).

[0038] It is more preferable that the polypropylene resin has a β-crystal formation ability of 70% or more. Non-porous film-like materials made from a resin composition mainly composed of a polypropylene resin containing a large amount of β-crystals exhibit excellent piezoelectricity even after electrostatic treatment, but even better piezoelectricity can be obtained by stretching them to form a porous structure. Forming a porous structure using β-crystals is advantageous for preparing a porous structure because the porous structure is dense, as porosity occurs during the process of β-crystals in the polypropylene resin transitioning to α-crystals during the stretching process, and it does not depend on particle size or dispersion diameter compared to conventionally known methods of porosity formation by adding inorganic fillers or incompatible organic substances. Porous films using β-crystals have a dense porous structure, and the surface area of ​​the pores is large, making it easier to trap more charge during charging treatment. Since porous electret films exhibit piezoelectricity due to charges trapped at the interface between pores and the matrix, a dense porous structure in the film tends to result in good piezoelectric properties. Furthermore, a dense porous structure results in very short distances between pores, making it easier for trapped charges to be fixed by mutual Coulomb forces. This makes it difficult for trapped charges to discharge, and thus prevents a decrease in the properties of the electret film.

[0039] The ability of electret film to form β crystals can be considered an indicator that the polypropylene resin formed β crystals in the non-porous film before stretching. If the polypropylene resin in the non-porous film before stretching forms β crystals, then stretching will create many fine and uniform pores, resulting in excellent mechanical properties and superior dielectric strength due to the formation of fine and uniform pores.

[0040] The presence or absence of β-crystal formation ability in an electret film is determined by performing differential thermal analysis of the electret film using a differential scanning calorimeter and checking whether or not a crystal melting peak temperature originating from the β-crystal of the polypropylene resin is detected. Specifically, when a laminated porous film is heated from 40°C to 200°C at a heating rate of 10°C / min using a differential scanning calorimeter, held for 1 minute, then cooled from 200°C to 40°C at a cooling rate of 10°C / min, held for 1 minute, and then reheated from 40°C to 200°C at a heating rate of 10°C / min, if the crystal melting peak temperature (Tmβ) originating from the β crystal of the polypropylene resin is detected during the reheating, it is determined that the film has the ability to form β crystals.

[0041] The presence or absence of the aforementioned β-crystal formation ability can also be determined from the diffraction profile obtained by X-ray diffraction measurement of an electret film subjected to a specific heat treatment. Specifically, an electret film in which β-crystals have been formed and grown by heat treatment at a temperature of 170-190°C, which is above the crystal melting peak temperature of the polypropylene resin, and then slow cooling is performed, and if diffraction peaks originating from the (300) plane of the β-crystals of the polypropylene resin are detected in the range of 2θ = 16.0° to 16.5°, it is determined that the film has the ability to form β-crystals. For further details on the β-crystal structure and X-ray diffraction measurements of polypropylene resins, please refer to Macromol. Chem. 187, 643-652 (1986), Prog. Polym. Sci. Vol. 16, 361-404 (1991), Macromol. Symp. 89, 499-511 (1995), Macromol. Chem. 75, 134 (1964), and the references cited in these publications.

[0042] Methods for obtaining the β-crystal formation ability of the polypropylene resin mentioned above include methods that do not add substances that promote the formation of α-crystals in the polypropylene resin, methods that add a polypropylene resin that has been treated to generate peroxide radicals as described in Japanese Patent Publication No. 3739481, and methods that add a β-crystal nucleating agent. However, in the present invention, it is particularly preferable to obtain β-crystal activity by adding a β-crystal nucleating agent. By adding a β-crystal nucleating agent, the formation of β-crystals in the polypropylene resin can be promoted more homogeneously and efficiently, and an electret film having β-crystal formation ability can be obtained.

[0043] The degree of β-crystal formation ability can be quantified by measuring the β-crystal formation ability. The β-crystal formation ability of the electret film is preferably 60% or more, more preferably 70% or more, even more preferably 80% or more, and particularly preferably 90% or more. A β-crystal formation ability of 60% or more allows the material to exhibit suitable piezoelectric properties when used as a laminated piezoelectric sheet. There is no particular upper limit, but it is preferable that it be 100% or less. The β-crystal formation ability can be calculated, for example, by the following method.

[0044] The DSC measurement of the electret film is performed using the method described below. First, the temperature is increased from 40°C to 200°C at a rate of 10°C / min under a nitrogen atmosphere, held for 1 minute, and then cooled to 40°C at a rate of 10°C / min. After holding for 1 minute, the temperature is increased again at a rate of 10°C / min. The melting peaks observed are determined as follows: melting peaks in the temperature range of 145-157°C are considered β-crystal melting peaks, and melting peaks observed above 158°C are considered α-crystal melting peaks. The heat of fusion for each is determined from the area of ​​the region enclosed by the baseline drawn based on the flat area on the high-temperature side and the peaks. The heat of fusion for the α-crystal is denoted as ΔHα, and the heat of fusion for the β-crystal is denoted as ΔHβ. The calculation is performed using the following equation (2). β crystal formation ability (%)=[ΔHβ / (ΔHα+ΔHβ)]×100 (2)

[0045] To obtain excellent piezoelectric properties, electret films preferably contain a β-nucleating agent. The inclusion of a β-nucleating agent imparts the ability to generate β crystals.

[0046] Examples of β-nucleating agents include amide compounds; tetraoxaspiro compounds; quinacridones; nanoscale iron oxides; alkali or alkaline earth metal salts of carboxylic acids, such as potassium 1,2-hydroxystearate, magnesium benzoate or magnesium succinate, or magnesium phthalate; aromatic sulfonic acid compounds, such as sodium benzenesulfonate or sodium naphthalenesulfonate; di or triesters of di or tribasic carboxylic acids; phthalocyanine pigments, such as phthalocyanine blue; two-component compounds consisting of component A, which is an organic dibasic acid, and component B, which is an oxide, hydroxide, or salt of a Group 2 metal in the periodic table; and compositions consisting of cyclic phosphorus compounds and magnesium compounds. If necessary, two or more β-nucleating agents from these may be mixed and used.

[0047] Among these β-nucleating agents, amide compounds are preferred in terms of the piezoelectric properties of the resulting piezoelectric film. Examples of amide compounds include N,N'-dicyclohexyl-2,6-naphthalenedicarboxyamide, N,N'-dicyclohexyl terephthalamide, and N,N'-diphenylhexanediamide, with N,N'-dicyclohexyl-2,6-naphthalenedicarboxyamide being particularly preferred. Because amide compounds have a highly polar amide group, they can localize the charge in the crystal structure, and are thought to have high piezoelectric properties.

[0048] Highly polar compounds, such as amide compounds, have a problem of poor dispersibility and tendency to aggregate due to electrostatic interactions with low-polarity polypropylene resins. However, common β-nucleating agents have the property of dissolving in polypropylene resins within a certain temperature range. This property allows the β-nucleating agent to be uniformly dispersed in the polypropylene resin, making it easier for crystals derived from the β-nucleating agent to precipitate uniformly. Therefore, it is believed that highly polar amide compound crystals can be uniformly dispersed in a low-polarity polypropylene resin, resulting in high piezoelectricity.

[0049] Specific examples of commercially available β-nucleating agents include "NJester NU-100" manufactured by Shin Nippon Rika Co., Ltd., and specific examples of propylene resins with added β-nucleating agents include "Bepol B-022SP" polypropylene from Aristech, "Beta(β)-PP BE60-7032" polypropylene from Borealis, and "BNX BETAPP-LN" polypropylene from Mayzo.

[0050] The content of the β-nucleating agent in the electret film can be appropriately adjusted depending on the type of β-nucleating agent or the composition of the polypropylene resin, but it is preferably 0.0001 parts by mass or more and 5.0 parts by mass or less per 100 parts by mass of the polypropylene resin, more preferably 0.001 parts by mass or more and 3.0 parts by mass or less, and even more preferably 0.01 parts by mass or more and 1.0 part by mass or less. If the β-crystal nucleating agent content is 0.0001 parts by mass or more, sufficient β-crystals can be generated and grown in the polypropylene resin during manufacturing, ensuring sufficient β-crystal generation ability and resulting in good piezoelectric properties for the electret film. Furthermore, sufficient β-crystal generation ability can be ensured even when stretched to form a porous film, and an electret film with the desired piezoelectric properties can be obtained by electrostatic treatment. On the other hand, adding 5.0 parts by mass or less is economically advantageous and preferable because it does not cause bleeding of the β-nucleating agent onto the film surface.

[0051] The above resin composition may contain components other than the β-nucleating agent, as long as they do not impair the properties of the electret film. For example, it may contain resins other than polyolefin resins, such as polystyrene resins, polyvinyl chloride resins, polyvinylidene chloride resins, chlorinated polyethylene resins, polyester resins, polycarbonate resins, polyamide resins, polyacetal resins, acrylic resins, ethylene vinyl acetate copolymers, polymethylpentene resins, polyvinyl alcohol resins, cyclic olefin resins, polylactic acid resins, polybutylene succinate resins, polyacrylonitrile resins, and polyethylene oxide resins. Examples include polystyrene resins, cellulose resins, polyimide resins, polyurethane resins, polyphenylene sulfide resins, polyphenylene ether resins, polyvinyl acetal resins, polybutadiene resins, polybutene resins, polyamide-imide resins, polyamide-bismaleimide resins, polyarylate resins, polyetherimide resins, polyetheretherketone resins, polyetherketone resins, polyethersulfone resins, polyketone resins, polysulfone resins, aramid resins, and fluorine resins.

[0052] Electret films may contain additives to an extent that does not impair their properties. Examples of such additives include recycled resins generated from trimming losses such as edges, inorganic particles such as silica, talc, kaolin, and calcium carbonate, pigments such as titanium dioxide and carbon black, flame retardants, weather stabilizers, heat stabilizers, antistatic agents, melt viscosity modifiers, crosslinking agents, lubricants, nucleating agents, plasticizers, anti-aging agents, antioxidants, light stabilizers, UV absorbers, neutralizing agents, anti-fogging agents, anti-blocking agents, slip agents, and colorants, which are added for the purpose of improving and adjusting moldability, productivity, and various physical properties of electret films.

[0053] (Method of manufacturing electret film) An example of a method for manufacturing electret film is described below.

[0054] Electret films can be manufactured, for example, through a film formation process, a stretching process, and an electrostatic treatment process. The following describes the film formation process, stretching process, and electrostatic treatment process in order.

[0055] In the film-forming process, a non-porous film-like material consisting of the materials constituting the electret film is formed. The film-forming process is not particularly limited as long as the materials constituting the electret film are formed by known methods, but for example, the resin composition (material resin) constituting the electret film may be heated and melted to form a film, and specifically, the film may be formed by the T-die method, the inflation method, etc., with the T-die method being preferred. Furthermore, in practical terms, it is preferable to melt-extrude the resin material from a T-die and cast it using a cast roll (chill roll, cast drum, etc.).

[0056] The materials constituting the electret film may be kneaded in a kneading device before being formed into a film. The kneading device used for kneading is not particularly limited. For example, known extruders such as single-screw extruders, twin-screw extruders, and multi-screw extruders can be used. Furthermore, depending on the equipment structure and requirements, a vacuum pump may be connected to the vent port of the extruder to remove moisture and low molecular weight substances.

[0057] As described above, when using a cast roll, it is preferable to extrude the film-like molten resin (resin composition) extruded from the T-die onto the cast roll and form it into a film-like material by taking it up while keeping it in close contact with the rotating cast roll. To ensure that the film-like material adheres to the cast roll, a touch roll, air knife, or electro-adhesion device may be attached to the cast roll. Furthermore, when forming the molten resin (resin composition) into a film while cooling it, the temperature of the cast roll is preferably 100°C or higher. More preferably 110°C or higher, and even more preferably 120°C or higher. In this invention, the porosity can also be increased by opening holes in the crystalline and amorphous portions of the polypropylene resin during the stretching process. Therefore, it is preferable to set the temperature of the cast roll to 100°C or higher to obtain a non-porous film with a high degree of crystallinity. Furthermore, the upper limit of the cast roll temperature is preferably 140°C or lower, more preferably 135°C or lower, and even more preferably 130°C or lower. By setting the cast roll temperature to 140°C or lower, peeling from the cast roll during film formation is facilitated.

[0058] In the resulting non-porous film-like material, the thickness of the effective portion excluding both ends is preferably 20 μm or more and 800 μm or less, more preferably 30 μm or more, even more preferably 40 μm or more, even more preferably 50 μm or more, and even more preferably 700 μm or less, even more preferably 600 μm or less, and even more preferably 500 μm or less. If the thickness of the non-porous membrane is 20 μm or more, breakage during stretching can be prevented, and if the thickness of the non-porous membrane is 800 μm or less, stretching of the non-porous membrane can be made easier. Regarding the layer structure of the non-porous film electret material, it may not be limited to the single-layer structure described above, but may also be a combination of other layers.

[0059] The resulting non-porous film can be subjected to electrostatic treatment as is, or it can be subjected to stretching treatment. By stretching the non-porous film, it can be easily converted into a porous film. In the stretching process, uniaxial stretching or biaxial stretching is preferable for non-porous film-like materials, but uniaxial stretching is preferred. Uniaxial stretching tends to shorten the time required for the stretching process and improve productivity. Uniaxial stretching may be longitudinal uniaxial stretching or transverse uniaxial stretching. Biaxial stretching may be simultaneous biaxial stretching or sequential biaxial stretching. Of these, sequential biaxial stretching makes it relatively easy to control the porous structure and balance other physical properties such as mechanical strength and shrinkage rate. Furthermore, stretching of a membrane-like material in the direction of flow (MD) is called "longitudinal stretching," while stretching in a direction perpendicular to the direction of flow (TD) is called "transverse stretching."

[0060] The stretching temperature needs to be selected appropriately depending on the composition of the resin composition used, the crystal melting peak temperature, the degree of crystallinity, etc., but the longitudinal stretching temperature is preferably 60°C to 140°C, and more preferably 80°C to 120°C. Setting the longitudinal stretching temperature to 140°C or lower is preferable because it allows stretching without breakage below the melting point of the main component, the polypropylene resin. On the other hand, setting the longitudinal stretching temperature to 60°C or higher is preferable because it suppresses breakage during stretching.

[0061] The transverse stretching temperature is preferably 90°C to 160°C, and more preferably 100°C to 150°C. By having the transverse stretching temperature within the specified range, pores can be sufficiently formed, the porosity can be increased, and sufficient piezoelectricity can be achieved. Furthermore, in the case of sequential biaxial stretching, for example, voids created during longitudinal stretching can be enlarged, increasing the porosity of the porous layer and allowing it to have sufficient piezoelectric properties. The temperatures described above are for uniaxial stretching or sequential biaxial stretching. However, for simultaneous biaxial stretching, the stretching temperature should be adjusted within the range of preferably 90°C to 160°C, and more preferably 100°C to 150°C, from the above viewpoint.

[0062] The stretching ratio can be arbitrarily selected according to the desired porosity, but the stretching ratio per uniaxial stretch is preferably 1.1 times or more and 20 times or less, more preferably 1.5 times or more and 18 times or less, even more preferably 4 times or more and 16 times or less, and even more preferably 4 times or more and 10 times or less. By setting the stretching ratio per uniaxial stretch to 1.1 times or more, whitening progresses, and sufficient porosity is created by stretching. On the other hand, by setting the stretching ratio to 20 times or less, the porosity is suppressed, and a porous film with excellent pressure resistance can be obtained. Furthermore, in the case of sequential biaxial stretching, stretching each axis at the stretching ratio specified above prevents deformation of voids created during the previous stretching step during the subsequent stretching step.

[0063] An electret film according to the present invention can be obtained by performing an electrostatic treatment on a non-porous film obtained in a film-forming process, or on a porous film obtained through a stretching process. The electrostatic treatment may be continuous or batch. The electrodes used for the electrostatic treatment may be a method in which the film is passed between electrodes such as wire electrodes, roll electrodes, or plate electrodes on the front and back of the film and an electric field is applied between the electrodes, or electrodes may be formed directly on the front and back of the film by coating or vapor deposition and then an electric field is applied. Of these methods, the method using wire electrodes or plate electrodes is preferred from the viewpoint of uniformity of the electric field in film charging, and among these, the method using wire electrodes is particularly preferred from the viewpoint of excellent voltage application efficiency. The applied electric field is preferably 0.1 MV / m to 10 MV / m, more preferably 0.2 MV / m to 8 MV / m, and even more preferably 0.3 MV / m to 6 MV / m. A field of 0.1 MV / m or higher allows for excellent piezoelectric properties. A field of 10 MV / m or lower has the effect of reducing dielectric breakdown during charging.

[0064] Furthermore, the electret film according to the present invention can be subjected to surface treatments such as corona treatment, plasma treatment, printing, coating, and vapor deposition, as well as perforation, as necessary, without impairing the present invention, and several electret films according to the present invention can be stacked depending on the application.

[0065] (Friction-charging film) The triboelectric film becomes charged through a charging mechanism based on frictional power generation, and exhibits piezoelectric properties by acting as a dielectric. The charging mechanism based on frictional power generation has a structure in which two (a pair) charged parts made of the triboelectric film face each other with a gap in between. When the triboelectric film comes into contact, separates, rubs, etc., positively charged and negatively charged parts are created, efficiently generating a charging voltage.

[0066] The material of the triboelectric film is not particularly limited as long as it is a material capable of being electrically charged. Examples include polymers (resins), nonmetallic substances, and metallic substances. Examples of polymers include silicone resins (polydimethylsiloxane (PDMS), etc.), fluororesins (polytetrafluoroethylene (PTFE), etc.), polyimide, polyvinyl chloride, polystyrene, polyolefins (polyethylene, polypropylene, etc.), polyester resins (polyethylene terephthalate (PET), etc.), polycarbonate resins, acrylic resins (polymethyl methacrylate (PMMA), etc.), polyamide resins (nylon, etc.), and cellulose. Examples of nonmetallic substances include oxides of silica and alumina. Examples of metallic substances include aluminum, iron, nickel, silver, gold, platinum, copper, chromium, titanium, molybdenum, indium metal, and alloys of these metals. From the viewpoint of easily generating a charging mechanism by triboelectricity, silicone resins (polydimethylsiloxane (PDMS), etc.), fluororesins (polytetrafluoroethylene (PTFE), etc.), and polyvinyl chloride are preferred. Polyvinyl chloride (vinyl chloride resin) is more preferable from the viewpoint of good durability due to its good electrostatic properties and toughness as a triboelectric film.

[0067] The vinyl chloride resin has a Vicat softening temperature of preferably 75°C or higher, more preferably 78°C or higher, and even more preferably 90°C or higher. There is no particular upper limit, but typically resins with a temperature of 140°C or lower are used, and preferably 130°C or lower. This range is preferable because it tends to result in a high chlorination rate due to the chlorine contained in the resin, which induces a high negative triboelectric series characteristic and makes it easy to provide a high triboelectric voltage. Furthermore, if the Vicat softening temperature is significantly lower than 75°C, while moldability is excellent, the chlorination rate tends to be low, leading to a decrease in negative triboelectric series characteristics and a decrease in triboelectric charging characteristics. On the other hand, if the Vicat softening temperature is significantly higher than 140°C, moldability decreases significantly, making thin film molding difficult. Specifically, the chlorinated polyvinyl chloride resin described in International Publication No. 2013 / 081133 and on page 74 of the non-patent document "Vinyl Chloride Factbook" (edited by the Japan Vinyl Chloride Industry and Environment Association, published February 2005) is preferred because it easily achieves a high Vicat softening temperature of 80°C or higher. Furthermore, while other resins can be added to achieve a higher Vicat softening temperature, the addition of resins tends to decrease the chlorination rate and thus the triboelectric properties. The Vicat softening temperature is measured in accordance with JIS K7206. Unless there are specific problems, the B50 method is used.

[0068] The silicone resin is not particularly limited as long as it is a polymer compound having a main skeleton formed by siloxane bonds. Its molecular weight is usually 2000 or more, may be 4000 or more, and is usually 500,000 or less, may be 200,000 or less. The shape of the silicone resin is not particularly limited, but in the case of a film, the Shore A hardness may be 20° or more, preferably 40° or more. The upper limit is preferably 90° or less. Particularly preferably 40° to 70°. The tensile strength may be 5 MPa or more, and may be 15 MPa or less. The silicone resin is generally preferably what is called silicone rubber, specifically methyl silicone rubber, vinyl-methyl silicone rubber, phenyl-methyl silicone rubber, etc.

[0069] The relative permittivity (εr) of the triboelectric film as a dielectric is preferably 2 or higher, more preferably 3 or higher, even more preferably 5 or higher, and particularly preferably 8 or higher. There is no upper limit to the relative permittivity, but a higher value is preferable. The relative permittivity can be calculated from the following equation (3) by forming electrodes on both sides of the layer of the material to be measured (sample) to create a parallel plate capacitor and measuring the capacitance C of the capacitor. C = ε0·εr·A / d (3) Here, εr is the relative permittivity, ε0 ​​is the permittivity of vacuum, A is the area of ​​the capacitor, and d is the thickness of the layer of the material being measured. The capacitance C of the capacitor can be measured using an LCR meter, impedance analyzer, etc.

[0070] For the outermost layer of a triboelectric film, the portion that generates friction through contact is preferably made of the following materials. Specifically, the outermost layer material can be a polymer, a nonmetallic substance, or a metallic substance. Examples of polymers include those mentioned above and melamine resin. Examples of nonmetallic substances include oxides of silica and alumina. Examples of metallic substances include aluminum, iron, nickel, silver, gold, platinum, copper, chromium, titanium, molybdenum, indium metal, and alloys of these metals. As long as the two (pair) charged parts made of the triboelectric film generate a positively charged part and a negatively charged part, the combination of triboelectric films is not particularly limited. However, from the viewpoint of easily accumulating positive and negative charges, a combination of triboelectric films made of different materials is preferred. A combination of a triboelectric film made of polymer (resin) and a triboelectric film made of a metallic substance is more preferred because it tends to have good chargeability. Furthermore, if the electrode layer described later has chargeability, it can also function as one of the charged parts in a structure where the two (pair) charged parts face each other with a gap in between. From the viewpoint of ensuring the flexibility of the laminated piezoelectric sheet by keeping the film thickness small and obtaining good chargeability, it is preferable to combine a triboelectric film made of polymer (resin) with an electrode layer that has chargeability.

[0071] [Electrode layer] The piezoelectric film sensor 1 has a first electrode layer 20 and a second electrode layer 20'. The first electrode layer 20 and the second electrode layer 20' are provided so as to sandwich the piezoelectric film 30, with one being used as the positive electrode and the other as the negative electrode. Each electrode layer 20, 20' only needs to be conductive and can be formed using, for example, metal foils such as aluminum foil, copper foil, silver foil, gold foil, nickel foil, tin foil, and alloy foil, carbon sheets, or resin films having a conductive layer. A resin film having a conductive layer can be formed by bonding a metal foil, which serves as the conductive layer, to a resin film using an adhesive or other bonding agent. Alternatively, the resin film can be formed by dissolving it with heat or a solvent and bonding it to the metal foil, or by applying a metal film to the surface of the resin film using known methods such as vapor deposition. The resin film is not particularly limited, but polyethylene terephthalate film can be used. For each electrode layer 20, 20', a resin film having a conductive layer formed by laminating an aluminum foil as a conductive layer onto a polyethylene terephthalate film as a resin film is preferred. Figures 5-6 illustrate an example in which an aluminum foil 21 is laminated with a polyethylene terephthalate film 22 as the electrode layer 20 (20').

[0072] The thickness of each electrode layer 20,20′ is not particularly limited, but is preferably 2 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more. It is also preferably 300 μm or less, more preferably 250 μm or less, and even more preferably 210 μm or less. By ensuring that the thickness of each electrode layer 20, 20' is greater than or equal to the above range, conductive stability can be achieved as an electrode. On the other hand, by ensuring that the thickness of each electrode layer 20, 20' is less than or equal to the above range, the flexibility of the piezoelectric film 1 can be ensured.

[0073] The electrode surfaces of each electrode layer 20, 20' may be smooth or uneven.

[0074] [Electromagnetic shielding film] The piezoelectric film sensor 1 may have at least one electromagnetic shielding film 40 (40'). The electromagnetic shielding film 40 shields electromagnetic waves and suppresses the application of external noise to the electrodes. The electromagnetic shielding film 40 can be made of a known material having electromagnetic shielding properties and is not particularly limited, but for example, metal foil or commercially available metal tape is preferable from the viewpoint of being readily available, inexpensive, and thin. Examples of materials for metal foil and metal tape include aluminum, nickel, copper, silver, tin, and alloys of these metals and / or other metals. The materials exemplified above may be used as a single layer electromagnetic shielding layer, or they may be used in a laminated form with other layers. For example, to improve the handling of the electrodes, a resin film may be provided on at least one side of the layer made of the electromagnetic shielding material, either directly or via an adhesive layer. Polyethylene terephthalate film can be used as the resin film. The electromagnetic shielding film 40 may be made of the same material as the electrode layer 20, or of a different material. From the viewpoint of mass production, it is preferable that it be made of the same material as the electrode, and a configuration in which polyethylene terephthalate film is laminated with aluminum foil is preferred. As an example of the electromagnetic shielding film 40 (40'), Figures 5 and 6 show a configuration in which aluminum foil 41 is laminated with polyethylene terephthalate film 42.

[0075] The thickness of the electromagnetic shielding film 40 is not particularly limited, but is preferably 2 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more. It is also preferably 300 μm or less, more preferably 250 μm or less, and even more preferably 210 μm or less. If the thickness of the electromagnetic shielding film 40 is greater than or equal to the above range, conductivity can be obtained as an electromagnetic shielding film, and electromagnetic shielding properties can be achieved. On the other hand, if the thickness of the electromagnetic shielding film 40 is less than or equal to the above range, the flexibility of the piezoelectric film 1 can be ensured.

[0076] The surface of the electromagnetic shielding film 40 may be smooth or it may have an uneven surface.

[0077] [Protective film] The piezoelectric film sensor 1 may have at least one protective film 10(10′). The protective film 10 is preferably provided so as to cover the piezoelectric film 30, the electrode layers 20, 20' and the electromagnetic shielding film 40, in order to improve the water resistance of the piezoelectric film sensor 1. Furthermore, it is more preferable that the protective film 10 be provided in at least two layers on the piezoelectric film sensor 1 in order to protect both the front and back surfaces of the piezoelectric film sensor 1. The protective film 10 may be bonded and integrated with the electromagnetic shielding film 40 or the electrode layers 20, 20' via an adhesive layer or a tack layer.

[0078] The film that can be used as the protective film 10 is not particularly limited, but resin films such as polyester resin films, polyolefin resin films, acrylic resin films, polystyrene resin films, polycarbonate resin films, and fluoropolymer resin films can be suitably used, and films in which hot melt resin is laminated onto these films can also be used from the viewpoint of heat welding properties. These films can be easily obtained as commercially available laminate films.

[0079] The thickness of the protective film 10 is preferably 1 μm or more and 300 μm or less, more preferably 5 μm or more and 200 μm or less, even more preferably 10 μm or more and 150 μm or less, and even more preferably 20 μm or more and 120 μm or less. If the thickness of the protective film 10 is greater than or equal to the above range, sufficient water resistance can be provided to the piezoelectric film sensor 1. If the thickness of the protective film 10 is less than or equal to the above range, the pressure applied to the piezoelectric film sensor 1 can be easily transmitted to the piezoelectric film 30, and the flexibility of the piezoelectric film sensor 1 can be ensured.

[0080] [Other layers] In order to improve handling, electrical characteristics, and sensor performance when manufacturing the piezoelectric film sensor 1, functional layers such as electrode tabs, spacers, adhesive layers, fixing layers, buffer layers, conductive layers, insulating layers, dielectric layers, and vibration transmission layers may be added in addition to the above-described configuration. The piezoelectric film sensor 1 preferably has electrode tabs to electrically connect each electrode layer 20, 20' and the electromagnetic shielding film 40 to other electronic components. The electrode tabs may be in any configuration as long as they are provided to connect each electrode layer 20, 20' and the electromagnetic shielding film 40, for example, they may be formed on the protective film 10 or on the piezoelectric film 30. Furthermore, they may be formed on each electrode layer 20, 20', on the electromagnetic shielding film 40, or sandwiched between them. Furthermore, if the electromagnetic shielding film 40 is provided in multiple layers, the electrode tabs may be provided according to the number of layers of the electromagnetic shielding film 40. Furthermore, the piezoelectric film sensor 1 may have a fixing layer to suppress displacement of the piezoelectric film 30, each electrode layer 20, 20' and / or the electromagnetic shielding film 40 when the piezoelectric film sensor 1 is bent. The fixing method is not particularly limited, but it may be fixed by attaching it with single-sided adhesive tape or the like so that all or part of the end face of the piezoelectric film sensor 1 is covered from the outside.

[0081] <Manufacturing method for piezoelectric film sensors> The piezoelectric film sensor 1 can be obtained by laminating the piezoelectric film 30 manufactured by the above method, each electrode layer 20, 20', an electromagnetic shielding film 40, and a protective film 10. The lamination order is not critical; the first electrode layer 20, the piezoelectric film 30, and the second electrode layer 20' must be laminated in this order. Examples include a laminated structure with the electromagnetic shielding film 40, the first electrode layer 20, the piezoelectric film 30, and the second electrode layer 20', and a laminated structure with the electromagnetic shielding film 40, the first electrode layer 20, the piezoelectric film 30, the second electrode layer 20', and the electromagnetic shielding film 40'. In these laminated structures, functional layers can be appropriately provided between layers and / or outside the layers. Furthermore, if the piezoelectric film sensor 1 has a protective film 10, it is preferable to have the protective film 10 outside the electromagnetic shielding film 40, or outside each electrode layer 20, 20' in a configuration where the electromagnetic shielding film 40 is not present. Specifically, for example, as shown in Figure 5, a laminated configuration can be used in which a protective film 10, an electromagnetic shielding film 40, a first electrode layer 20, a piezoelectric film 30, a second electrode layer 20', and a protective film 10' are arranged in this order. In this case, a protective film 10 with an electromagnetic shielding film 40 laminated on it is prepared, the two electrode layers 20 and 20' are superimposed so that they face each other with the piezoelectric film 30 in between, the electromagnetic shielding film 40 and one electrode layer 20 are in contact, and the other electrode layer 20' and the protective film 10' are bonded together using an adhesive. In addition, for example, as shown in Figure 6, a laminated configuration can be used in which the protective film 10, electromagnetic shielding film 40, first electrode layer 20, piezoelectric film 30, second electrode layer 20', electromagnetic shielding film 40, and protective film 10' are arranged in this order.

[0082] When laminating the piezoelectric film 30 and the electrode layer 20, and / or when laminating the electrode layer 20 and the electromagnetic shielding film 40, it is preferable from the viewpoint of ensuring the mechanical strength of the piezoelectric film sensor to have an adhesive layer in the pressure detection region of the piezoelectric film sensor 1 that adheres the piezoelectric film 30 and the electrode layer 20, and / or adheres the electrode layer 20 and the electromagnetic shielding film 40.

[0083] When laminating the piezoelectric film 30 and the electrode layer 20, and / or when laminating the electrode layer 20 and the electromagnetic shielding film 40, it is preferable from the viewpoint of improving the signal strength of the piezoelectric film sensor that the pressure detection region of the piezoelectric film sensor 1 has non-adherent regions where the piezoelectric film 30 and the electrode layer 20 are not adhered, or where the electrode layer 20 and the electromagnetic shielding film 40 are not adhered. By not completely adhering the piezoelectric film 30 and the electrode layer 20, or the electrode layer 20 and the electromagnetic shielding film 40, the piezoelectric properties are further improved. This is thought to be because, in the non-adhesive region, when a pressure signal is applied, the piezoelectric film 30 and the electrode layers 20, 20' themselves vibrate, amplifying the pressure signal and resulting in a strong response signal. This effect tends to be more effective when detecting biological signals with low-frequency components, such as respiration. Furthermore, the presence of a non-adhesive region reduces the transfer of charge from the piezoelectric film 30 to the adhesive layer, thus maintaining the good chargeability of the piezoelectric film 30 and suppressing the deterioration of its piezoelectric properties.

[0084] For the reasons stated above, it is preferable that the piezoelectric film sensor 1 has a non-adhesive area ratio of 40% or more in the pressure sensing region. Excellent piezoelectric properties can be obtained by having a non-adhesive area ratio of 40% or more in the pressure sensing region. From this viewpoint, a non-adhesive area ratio of 42% or more is preferable, 45% or more is more preferable, and 50% or more is even preferable. On the other hand, there is no particular limit to the upper limit of the area ratio of the non-adhered area, and it may be 100%, but from the viewpoint of preventing misalignment of the piezoelectric film, electromagnetic shielding layer, and electrodes during the lamination process of the laminated piezoelectric sheet, it is preferable that it be 98% or less, more preferably 95% or less, and even more preferably 90% or less.

[0085] The portion other than the non-adhesive region mentioned above, the so-called adhesive region, can be described as a partial adhesive layer. The adhesive layer may or may not be conductive. From the viewpoint of effectively utilizing the electrostatic shielding effect of the electromagnetic shielding film 40, it is preferable that it is not conductive. Furthermore, from the viewpoint of stabilizing the conductivity with the tabs when electrode tabs are provided, it is preferable that it be conductive. Examples of adhesive layers include adhesive layers, thermoplastic adhesive layers, thermosetting adhesive layers, photocurable adhesive layers, and moisture-curable resin layers. From the viewpoint of facilitating the lamination process of the laminated piezoelectric sheet, an adhesive layer is preferred. The adhesive layer may be a pressure-sensitive adhesive layer or not, but it is preferable to use a pressure-sensitive adhesive layer. By using an adhesive layer, each electrode layer 20, 20' and the protective film 10 can be bonded to each electrode layer 20, 20' and the protective film 10 simply by laminating them with the adhesive layer in between and applying pressure. If the adhesive layer is an adhesive layer, it is preferable that it be composed of an adhesive. There are no particular restrictions on the adhesive, but examples include acrylic adhesives, urethane adhesives, synthetic rubber adhesives, natural rubber adhesives, and silicone adhesives, and among these, acrylic adhesives are preferred. The adhesive contains a main polymer such as an acrylic resin, urethane resin, synthetic rubber, natural rubber, or silicone resin, and the main polymer may contain at least one additive selected from crosslinking agents, tackifiers, plasticizers, softeners, metal deactivators, antioxidants, pigments, dyes, and the like. The adhesive area can be any part of the piezoelectric film 30, electrode layer 20, or electromagnetic shielding film 40 as long as a non-adherent area is secured. However, from the viewpoint of suppressing misalignment of each layer, it is preferable to adhere the peripheral portions of the piezoelectric film 30, electrode layer 20, and / or electromagnetic shielding film 40, which are the long sides and / or short sides.

[0086] When the piezoelectric film sensor 1 is laminated, it is preferable to have an air gap between the piezoelectric film 30 and each electrode layer 20, 20', and / or between each electrode layer 20, 20' and the electromagnetic shielding film 40. It is believed that having an air gap makes it easier for deformation due to pressure to be transmitted by the piezoelectric film 30, resulting in improved response sensitivity. The void is preferably 0.5 μm or more and 500 μm or less in height when the piezoelectric film sensor 1 is viewed in cross-section. The lower limit is more preferably 1 μm or more, even more preferably 5 μm or more, even more preferably 10 μm or more, and particularly preferably 20 μm or more. The upper limit is even more preferably 400 μm or less, and particularly preferably 300 μm or less. Because the height of the air gap is within the above range, sufficient space is secured for the piezoelectric film 30 and each electrode layer 20, 20' itself to vibrate when a pressure signal is applied, making them more susceptible to vibration, which tends to amplify the pressure signal and produce a strong response signal. Furthermore, when the vibration of the pressure signal is transmitted through the air layer between the piezoelectric film 30 and each electrode layer 20, 20' provided by the air gap of the above height range, the vibration is reflected at the interface between the piezoelectric film and the air layer, and at the interface between the electrode layer and the air layer, which is expected to amplify the pressure signal and strengthen the response signal.

[0087] Furthermore, from the same viewpoint as above, the pitch spacing of the gaps when the piezoelectric film sensor 1 is viewed in cross-section is preferably 0.5 mm or more and 50 mm or less. As a lower limit, it is more preferably 1 mm or more, and even more preferably 2 mm or more. As an upper limit, it is even more preferably 30 mm or less, and particularly preferably 10 mm or less. Furthermore, from the same viewpoint as above, the width of the air gap when the piezoelectric film sensor 1 is viewed in cross-section is preferably 0.5 mm or more and 50 mm or less. As a lower limit, 1 mm or more is more preferable, and 2 mm or more is even more preferable. As an upper limit, 20 mm or less is more preferable, 10 mm or less is even more preferable, and 1 mm or less is particularly preferable. When the width of the air gap is greater than or equal to the lower limit, a sufficient spatial region is secured in which the piezoelectric film 30 and / or each electrode layer 20, 20' can vibrate, and furthermore, the interface regions between the piezoelectric film 30 and the air layer, and between each electrode layer 20, 20' and the air layer are also secured, which tends to result in a strong response signal. Also, when it is less than or equal to the upper limit, the air gap is secured even when bending or deflection occurs in the laminated piezoelectric sheet. The combination of the void pitch and width is arbitrary, but it is preferable that the following equation (4) is satisfied when the void pitch is d and the void width is w. d≦2w (4) By satisfying equation (4), sufficient spatial region is secured for the piezoelectric film 30 and each electrode layer 20, 20' itself to vibrate when a pressure signal is applied, making them more susceptible to vibration, which tends to amplify the pressure signal and yield a strong response signal.

[0088] Methods for setting the height and pitch spacing of the voids within the above range include: (1) applying a textured surface to the side of the piezoelectric film 30 and / or each electrode layer 20, 20' facing the piezoelectric film-electrode layer to form a void of a predetermined size; (2) adjusting the thickness and pitch of the adhesive layer in the adhesive region other than the non-adhesive region (A) between each electrode layer 20, 20' and the electromagnetic shielding film 40; and (3) interposing a spacer between each electrode layer 20, 20' and the piezoelectric film 30. Among these, methods (1) or (2) are preferred from the viewpoint of superior mass productivity. Method (1) is more preferred from the viewpoint of simplifying the lamination process of the laminated piezoelectric sheet. In method (1), if a void exists between the piezoelectric film 30 and each electrode layer 20, 20', the textured surface applied to the piezoelectric film 30 and / or each electrode layer 20, 20' may be applied to only one side or both sides. Applying a textured surface to the side of the electrode layer facing the piezoelectric film-electrode layer is preferred from the viewpoint of obtaining the optimal void. Furthermore, two or more of these methods may be used in combination.

[0089] When the piezoelectric film 30 and / or the surface of each electrode layer 20, 20' facing the piezoelectric film-electrode layer is given a textured surface, the shape of the textured pattern is arbitrary, but examples include dot-shaped, grid-shaped, and stripe-shaped patterns. Figure 7 shows an example of a dot-shaped textured pattern. When the gaps created by the textured pattern are considered as gaps, the height of the protrusions or depth of the recesses in each textured unit is defined as the height of the gap. Here, the height of the protrusions or the depth of the recesses in a unit of unevenness refers to the vertical length relative to the highest and lowest points of the unit of unevenness when viewing a longitudinal cross-section of an electrode layer having an uneven pattern, cut in the thickness direction along the arrangement of the unevenness pattern. Note that since the height of the protrusions is also the depth of the recesses, there is usually no need to strictly distinguish between the height of the protrusions and the depth of the recesses.

[0090] Furthermore, when a gap formed by an uneven pattern is considered a gap, the spacing between adjacent protrusions or recesses in the above-mentioned uneven pattern is defined as the gap pitch. The spacing between adjacent protrusions or recesses refers to the average value of the spacing between adjacent protrusions or recesses when the above-mentioned uneven pattern is viewed from above. The spacing between adjacent protrusions or recesses does not necessarily have to be constant.

[0091] The thickness of the piezoelectric film sensor 1 is preferably 50 μm or more and 3000 μm or less. For the lower limit, 70 μm is more preferable, and 100 μm is even more preferable. On the other hand, for the upper limit, 2000 μm is more preferable, and 1500 μm is even more preferable. If the thickness is 50 μm or more, a laminated piezoelectric sheet with excellent handling and piezoelectric properties can be obtained. Furthermore, if the thickness is 3000 μm or less, it can be bent into a curved shape, making subsequent processing and transportation easy.

[0092] Furthermore, the piezoelectric film sensor 1 may be formed into a bag shape by laminating the piezoelectric film 30, each electrode layer 20, 20', the electromagnetic shielding film 40, and the protective film 10, and then fusing the edges of the protective film 10. The method of fusing the edges is not particularly limited and may be heat sealing or the like. When forming a bag shape, it is preferable to provide two layers of protective film 10. For example, it is preferable to laminate the protective film 10, electromagnetic shielding film 40, first electrode layer 20, piezoelectric film 30, second electrode layer 20', and protective film 10' in this order, and then heat-seal the ends of the protective film 10 together to form a bag shape. If two protective films 10 are used, the edges of the two protective films 10 and 10' may be partially fused together beforehand before lamination. Furthermore, the edges of the protective films 10 and 10' may be bonded together by means other than heat fusion.

[0093] <Analog-to-Digital Converter 50> The analog-to-digital converter 50 is a device that converts an analog signal obtained from the piezoelectric film sensor 1 into a digital signal, and is connected to the first electrode layer 20 and the second electrode layer 20' of the piezoelectric film sensor 1 by an electric wire. The analog-to-digital converter 50 can be a commercially available one, for example, an analog-to-digital converter manufactured by Digilent (product name "Analog Discovery Pro") can be used. The piezoelectric film sensor 1 and the analog-to-digital converter 50 are connected via AC coupling or DC coupling. With AC coupling, the DC component of the electrical signal is removed, so the AC component is sent to the analog-to-digital converter 50. From the viewpoint of improving the measurement resolution by removing the DC component of the electrical signal, AC coupling is preferred.

[0094] <Digital signal processing unit 60> The digital signal processing unit 60 performs digital signal processing, calculates the signal obtained from the analog-to-digital converter 50, and calculates the pressure applied to the piezoelectric film sensor 1 based on the baseline signal obtained from the piezoelectric film sensor 1. The digital signal processing unit 60 includes DC offset compensation, which corrects the DC component and compensates for deviations from the zero reference point of the signal. As a result, the baseline signal can be obtained. The baseline signal is the output signal due to the static load when the object to be measured or the parts necessary for measurement are placed on the piezoelectric film sensor 1. The necessary parts are not particularly limited, but examples include a sample holder, load distribution plate, and screws. Furthermore, when determining the baseline signal, processing to remove the dynamic load component included in the measured signal may be performed using frequency analysis, time-domain extraction, etc. The digital signal processing unit 60 can use a commercially available personal computer (PC) and analyze the data using data analysis software to calculate the pressure applied to the piezoelectric film sensor 1 and display it as a waveform on the screen. For example, Matlab from Mathworks can be used as data analysis software.

[0095] This pressure detection device obtains an analog signal from a piezoelectric film sensor 1, AC-couples it to obtain a baseline signal, converts this baseline signal to a digital signal using an analog-to-digital converter 50, and analyzes the digital signal using a digital signal processing unit 60 to measure the static load pressure from the amplitude intensity of the baseline signal. For example, as shown in Figure 3 or Figure 4, the noise amplitude differs when there is no load (0 kg) and when there is a load (1 kg). Therefore, by analyzing the noise amplitude data, the weight of the piezoelectric film sensor 1 can be measured.

[0096] In addition to the analog-to-digital converter 50 and the digital signal processing unit 60, this pressure detection device may also be equipped with an amplifier, filters such as a low-pass filter, high-pass filter, band-pass filter, and band-stop filter, and a digital-to-analog converter. In particular, when the detection signal is weak, it is preferable to include an amplifier from the viewpoint of improving the accuracy of signal processing. Furthermore, it is preferable to include filters from the viewpoint of blocking signals other than the baseline signal, and it is preferable to include a low-pass filter, band-pass filter, and band-stop filter. The above filters can include Butterworth filters, Chebyshev filters, Elliptic filters, and Bessel filters. Butterworth filters and Chebyshev filters are more preferable because they tend to produce better processed signals.

[0097] More specifically, the following two signal measurement methods can be cited. However, the signal measurement methods are not limited to these. First, the pressure detection device measures the baseline signal from the piezoelectric film sensor 1 for 1 second with the weight stationary. Next, the baseline signal is AC coupled and digitized using the analog-to-digital converter 50. Subsequently, the peak-to-peak amplitude of the voltage is read from the digitized baseline signal, and the average value for 1 second is obtained. Furthermore, the same measurement is repeated 10 times, and the average value of the 1 second averages from the 10 measurements is averaged to obtain the Vrms , pp , , , ,

[0099] , Calculate the value, V pp The weight of the weight can be measured by calculating from the value.

[0098] The second is the same as above. First, with this pressure detection device, measure the baseline signal from the piezoelectric film sensor 1 for 1 second with the weight stationary. Next, AC-couple and digitize the baseline signal with an analog-to-digital converter 50. Subsequently, read the peak-to-peak amplitude of the voltage from the digitized baseline signal to obtain the average value for 1 second. Further, repeat the same measurement 10 times and average the average values for 1 second for the 10 times to calculate the V pp Calculate the value and calculate the standard deviation. And V rms Read the value of the peak value V of the voltage in the baseline signal i and obtain the V for 1 second from the following formula (5) rms as the value. TIFF2026111119000002.tif31170(V ave is the average value of the baseline signal voltage (V pp value), n is the number of measurement peaks) The above V rms The weight of the weight can be measured by calculating from the value.

[0099] The digital processing unit of this pressure detection device may perform digital processing analysis other than that used to calculate the voltage value from the baseline signal. Specifically, it includes signal amplification processing, filter processing such as low-pass filter, high-pass filter, band-pass filter, band-stop filter, noise removal processing, frequency analysis processing such as Fourier transform, wavelet transform, Hilbert transform, and signal separation processing such as independent component analysis, principal component analysis, etc. In particular, when the detection signal is weak, it is preferable to amplify the signal to improve the accuracy of signal processing. Furthermore, it is preferable to perform filtering to block signals other than the baseline signal, and it is even more preferable to perform low-pass filtering, band-pass filtering, or band-stop filtering. Examples of filters that can be used for the above filtering include Butterworth filters, Chebyshev filters, Elliptic filters, and Bessel filters. Butterworth filters and Chebyshev filters are preferred because they tend to produce better processed signals.

[0100] As shown in the embodiments described later, this pressure detection device has a linear relationship between the weight of the weight placed on the piezoelectric film sensor 1 and the voltage, so it is considered that static load can be measured by the piezoelectric film sensor 1. In this way, this pressure detection device makes it possible to measure the pressure of a static load using the piezoelectric film 30, and can be applied to sensors such as load cells, pressure gauges, mass meters, mat sensors, biosensors, and robot hands. [Examples]

[0101] The pressure detection device of the present invention will be described in more detail below with reference to examples. However, the present invention is not limited in any way to the following examples.

[0102] Electret films, which will serve as piezoelectric films in each embodiment, were fabricated using the following materials.

[0103] (Polypropylene resin) • A-1; Homopolypropylene (Novatec PP FY6HA, MFR: 2.4g / 10 min [230℃, 2.16kg load], Mw / Mn=3.2, manufactured by Nippon Polypropylene Co., Ltd.)

[0104] (β-crystal nucleating agent) • B-1: N,N'-Dicyclohexyl-2,6-Naphthalenedicarboxamide (manufactured by Shin-Nippon Rika Co., Ltd., NU-100)

[0105] (Antioxidant) • C-1; A 1:1 mixture of tris(2,4-di-t-butylphenyl) phosphite and tetrakis[3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionic acid]pentaerythritol (IRGANOX-B225, manufactured by BASF).

[0106] (Electret film) A mixture for electret film, which forms a piezoelectric film, was obtained by mixing 100 parts by mass of polypropylene resin (A-1), 0.2 parts by mass of β-nucleating agent (B-1), and 0.1 parts by mass of antioxidant (C-1), and melt-extruding it at 280°C using a twin-screw extruder. The electret film mixture was fed into an extruder connected to a T-die with a lip opening of 1 mm and molded, and guided to a cast roll to obtain a non-porous film with a thickness of 320 μm. Subsequently, it was stretched five times laterally at a stretching temperature of 120°C using a film tenter (manufactured by Kyoto Machinery Co., Ltd.) to obtain a porous film with a thickness of 60 μm. The resulting porous film had a porosity of 18% and a β-crystal formation ability of 70%. The average pore diameter in the film thickness direction was 0.04 μm, the standard deviation of the pore diameter was 0.02 μm, and the coefficient of variation was 0.6. Furthermore, the average aspect ratio of the voids (length in the stretching direction / length in the film thickness direction) was 2.7. The standard deviation of the aspect ratio was 2.8, and the coefficient of variation was 1.0. The obtained film was placed on a grounding plate, and a voltage of 15kV was applied using wire electrodes with a distance of 20mm between the electrodes to perform a charging treatment, thereby obtaining an electret film that would become a piezoelectric film.

[0107] (Example 1) The layer configuration of the piezoelectric film sensor used in Example 1 will be explained with reference to Figure 5. For the electromagnetic shielding layer, an electromagnetic shielding film 40 was prepared by laminating aluminum foil 41 (10 μm thick) and polyethylene terephthalate film 42 (75 μm thick). Next, an electrode film was prepared for the electrode layer 20 by laminating aluminum foil 21 (10 μm thick) with a convex surface and polyethylene terephthalate film 22 (75 μm thick). As shown in Figure 7, the electrode film had a height of 50 μm for the convex portion, a pitch interval (convex spacing) of 6 mm, and a diameter of 2 mm for the convex portion. Next, a cold laminate film (50 μm thick) was prepared as the protective film 10 (10'), comprising a base layer made of polyethylene terephthalate resin cut to a 110 mm square and an adhesive layer made of acrylic adhesive.

[0108] The above electret film, cut into 100mm squares, was laminated in the following order: protective film 10' / electrode film (negative electrode) 20' / electret film 30 / electrode film (positive electrode) 20 / electromagnetic shielding film 40 / protective film 10. Electrode films 20 and 20' were positioned so that the aluminum foil side faced inward (towards the electret film). Similarly, the polyethylene terephthalate film 42 side of the electromagnetic shielding film 40 was positioned so that it faced inward (towards the electret film). In this configuration, electrode film (positive electrode) 20 was connected to the positive electrode signal extraction line, and electrode film (negative electrode) 20' and electromagnetic shielding film 40 were connected to the negative electrode signal extraction line. To prevent short circuits between electrode films 20 and 20' and electromagnetic shielding film 40, and to ensure that the electret film 30, electrode films 20 and 20', and electromagnetic shielding film 40 did not protrude from protective films 10 and 10', the ends of protective films 10 and 10' were bonded together to create the piezoelectric film sensor 1.

[0109] The positive and negative signal extraction lines of the fabricated piezoelectric film sensor 1 were connected to a Digilent Analog-to-Digital Converter (Analog Discovery Pro), and the USB cable from the Analog-to-Digital Converter was further connected to a Mouse Computer (MousePro) which serves as the digital processing unit, thereby configuring the pressure detection device of Example 1.

[0110] (Example 2) The layer configuration of the piezoelectric film sensor used in Example 2 will be explained with reference to Figure 6. For the electromagnetic shielding layer, an electromagnetic shielding film 40 was prepared by laminating aluminum foil 41 (10 μm thick) and polyethylene terephthalate film 42 (75 μm thick). Next, an electrode film 20 was prepared by laminating aluminum foil 21 (10 μm thick) and polyethylene terephthalate film 22 (75 μm thick) to create an uneven surface with the aluminum foil surface being convex. As shown in Figure 7, the electrode film had a height of 50 μm for the convex portion, a pitch interval (convex spacing) of 6 mm, and a diameter of 2 mm for the convex portion. Next, a cold laminate film (50 μm thick) was prepared as the protective film 10 (10'), comprising a base layer made of polyethylene terephthalate resin cut to a 110 mm square and an adhesive layer made of acrylic adhesive.

[0111] The above electret film, cut into 100mm squares, was laminated in the following order: protective film 10' / electromagnetic shielding film 40' / electrode film (negative electrode) 20' / electret film 30 / electrode film (positive electrode) 20 / electromagnetic shielding film 40 / protective film 10. Electrode films 20 and 20' were positioned so that the aluminum foil side faced inward (towards the electret film). Similarly, electromagnetic shielding films 40 and 40' were positioned so that the polyethylene terephthalate film 42 side faced inward (towards the electret film). In this configuration, electrode film (positive electrode) 20 and electromagnetic shielding film 40' were connected to the positive electrode signal extraction line, and electrode film (negative electrode) 20' and electromagnetic shielding film 40 were connected to the negative electrode signal extraction line. A piezoelectric film sensor 1' was fabricated by bonding the edges of the protective films 10 and 10' together, ensuring that the electrode films 20 and 20' and the electromagnetic shielding films 40 and 40' do not short-circuit, and that the electret film 30, electrode films 20 and 20', and electromagnetic shielding films 40 and 40' do not protrude from the protective films 10 and 10'. The pressure detection device of Example 2 was constructed by using the fabricated piezoelectric film sensor 1' in the same manner as in Example 1.

[0112] (Example 3) The layer configuration of the piezoelectric film sensor used in Example 3 will be explained with reference to Figure 8. A piezoelectric film sensor 1'' was fabricated in the same manner as in Example 1, except that the electrode layer 20 (20′) used was an electrode film made by laminating a smooth aluminum foil 21 (10 μm thick) and a polyethylene terephthalate film 22 (75 μm thick). A pressure detection device was constructed by using the fabricated piezoelectric film sensor 1″ in the same manner as in Example 1.

[0113] (Signal measurement method) Using the pressure detection devices of Examples 1 to 3, baseline signals from each piezoelectric film sensor 1, 1', and 1'' were measured and data processed in the following manner.

[0114] (Signal measurement method - 1) A 10cm x 10cm (3mm thick) plastic plate P was placed on the piezoelectric film sensor 1 (1′,1″), and a load was applied by stacking 500g cube-shaped weights (approximately 5cm square) on the plastic plate, as shown in Figure 9. With the weights stationary, the baseline signal from the piezoelectric film sensor 1 was measured for 1 second using a pressure detection device. During measurement, the baseline signal was digitized using an analog-to-digital converter at a sampling rate of 400 Hz and in AC coupling mode. The peak-to-peak amplitude of the digitized baseline signal was read and averaged to obtain a 1-second average value. This measurement was then repeated 10 times, and the average of the 1-second average values ​​from these 10 measurements was calculated. pp The values ​​were calculated. MathWorks' MATLAB was used for the calculations on a digital processing computer.

[0115] (Signal measurement method - 2) A 10cm x 10cm (3mm thick) plastic plate P was placed on the piezoelectric film sensor 1 (1′,1″), and a load was applied by arranging 100g weights on the plastic plate as shown in Figure 10. With the weights stationary, the baseline signal from the piezoelectric film sensor 1 was measured for 1 second using a pressure detection device. During measurement, the baseline signal was digitized using an analog-to-digital converter at a sampling rate of 400 Hz and in AC coupling mode. The peak-to-peak amplitude of the digitized baseline signal was read and averaged to obtain the average value over 1 second. This measurement was then repeated 10 times to obtain the 10 1-second V values. pp V averaged from the values pp The values ​​and standard deviations were calculated. Also, V rms The value is the peak voltage V in the baseline signal. i Read the value and use the following formula (5) to determine the value of V for 1 second. rms It was set as the value. TIFF2026111119000003.tif31170(V ave This is the average value of the baseline signal voltage (V pp (Value), n is the number of measured peaks) The calculations were performed using Matlab, a digital processing computer developed by Mathworks.

[0116] (Signal measurement method - 1) Measurements were performed using signal measurement method-1 for Examples 1 to 3. Figure 11 shows the baseline signal for Example 1, plotted for no load, 1 kg load, and 3 kg load. It was observed that the voltage amplitude of the baseline signal increased with increasing load. V when the load is changed in Examples 1-3 pp The values ​​are shown in Figure 12. V for Examples 1-3 pp The coefficient of determination R when the correlation between each value and the load is determined by linear regression. 2 This is shown in Table 1.

[0117] [Table 1]

[0118] These results show that the voltage amplitude of the baseline signal V increases with increasing load. pp A tendency for the values ​​to increase linearly was observed.

[0119] For Example 1, measurements were performed using signal measurement method-2. The V was measured when the load was increased by 100g increments, and then decreased by 100g increments once it reached 1000g. pp The values ​​are shown in Figure 13, V rms The values ​​are shown in Figure 14. Also, V pp Value and V rms The coefficient of determination R when the correlation between each value and the load is determined by linear regression. 2 The standard deviations for each value at a load of 1000g are shown in Table 2 below.

[0120] [Table 2]

[0121] These results show that the voltage amplitude of the baseline signal V increases with increasing load. pp Value, Vrms A linear trend of increasing values ​​was observed for both. [Explanation of Symbols]

[0122] 1. Piezoelectric film sensor 10 (10') Protective film 20 1st electrode layer 20′ second electrode layer 21 Aluminum foil 22 Polyethylene terephthalate film 30 Piezoelectric film 40 (40') Electromagnetic Shielding Film 41 Aluminum foil 42 Polyethylene terephthalate film 50 Analog-to-Digital Converter 60 Digital signal processing unit

Claims

1. The piezoelectric film sensor has a structure in which a first electrode layer, a piezoelectric film, and a second electrode layer are sequentially stacked in this order; an analog-to-digital converter connected to the piezoelectric film sensor; and a digital signal processing unit that performs digital signal processing, including DC offset compensation, on the signal obtained from the analog-to-digital converter. The digital signal processing unit is a pressure detection device that calculates the pressure applied to the piezoelectric film sensor from the baseline signal obtained from the piezoelectric film sensor.

2. The pressure detection device according to claim 1, wherein the calculation involves calculating pressure from the amplitude intensity of the baseline signal obtained from the piezoelectric film sensor.

3. The pressure detection device according to claim 1, wherein the pressure detection region of the piezoelectric film sensor has a non-adhesive region in which the piezoelectric film and the first electrode layer and / or the second electrode layer are not adhered.

4. The pressure detection device according to claim 1, wherein the piezoelectric film is an electret film or a triboelectric film.

5. The pressure detection device according to any one of claims 1 to 4, wherein the pressure is a static load.

6. A pressure detection device is used that comprises a piezoelectric film sensor having a structure in which a first electrode layer, a piezoelectric film, and a second electrode layer are sequentially stacked in this order; an analog-to-digital converter connected to the piezoelectric film sensor; and a digital signal processing unit that performs digital signal processing, including DC offset compensation, on the signal obtained from the analog-to-digital converter. The digital signal processing unit calculates the pressure applied to the piezoelectric film sensor from a baseline signal obtained from the piezoelectric film sensor, and is a pressure detection method.

7. The pressure detection method according to claim 6, wherein the pressure is a static load.

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