Porous electret film and laminated piezoelectric sheet

Abstract

To provide a porous electret film which has high piezoelectricity and excellent temporal stability of piezoelectricity, and a laminated piezoelectric sheet in which the porous electret film and an electrode are laminated.SOLUTION: A porous electret film contains a polyolefinic resin (A) and a styrenic thermoplastic elastomer (B), wherein an average aspect ratio of a hole is 4.0 or more and 20 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a porous electret film and a laminate using the porous electret film. This relates to a layered piezoelectric sheet. [Background technology]

[0002] Electrets are materials that are thermally or electrically conductive, such as polymeric materials or inorganic materials that do not easily conduct electricity. The treatment causes a portion of the material to be semi-permanently polarized. For example, a porous electret using a porous resin film is known to exhibit an excellent piezoelectric effect. It is known to be widely used in actuators, oscillators, sonar, vibration power generation, sensors, etc. In order to obtain an electret film with excellent piezoelectricity, charge injection is required. When this happens, it becomes necessary to polarize the film at a higher voltage and inject more charge. do.

[0003] As an example of a porous electret, Patent Document 1 discloses a porous electret using β crystals of a polypropylene resin. Compressible polyolefin films using microporous membranes have been proposed. Polypropylene resin is a polymer with low polarity, and its chemical structure has an electric charge in the molecular skeleton. It is difficult to localize it, so a high piezoelectric constant cannot be obtained by itself. A high piezoelectric constant is achieved by introducing air with a different dielectric constant and trapping electric charges. . [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-55114 Summary of the Invention [Problem to be solved by the invention]

[0005] With the recent development of flexible electronics, porous electret films have become pressure-sensitive. Research is underway into bendable devices using microporous membranes. Because the ret film can be manufactured in large areas at low cost, it is suitable for flexible devices. It is attracting attention as a potential application. However, conventional electret films using microporous membranes have a piezoelectric effect after charging. There was an issue with the efficacy decreasing over time. Therefore, the present invention provides a porous electrolytic capacitor having high piezoelectricity and excellent stability of the piezoelectricity over time. a porous electret film, a piezoelectric sheet having the porous electret film and an electrode layer, and The present invention aims to provide a sensor device using an electrically conductive sheet. [Means for solving the problem]

[0006] As a result of extensive research to solve the above problems, the present inventors have found that polyolefin resin (A) and a styrene-based thermoplastic elastomer (B), a porous electret film having an average aspect ratio of pores of 4.0 or more and 20 or less; By doing so, it has been found that high piezoelectricity and stability over time of the piezoelectricity can be obtained, and the present invention has been It has come to completion.

[0007] That is, the present invention is summarized as follows. [1] Contains polyolefin resin (A) and styrene-based thermoplastic elastomer (B) A porous electret film with an average aspect ratio of pores of 4.0 or more and 20 or less. A porous electret film. [2] The polyolefin resin (A) at a temperature of 230°C and a load of 2.16 kg [1] The porous element according to [1], wherein the melt flow rate (MFR(A)) is 8 g / 10 min or more. Cultret film. [3] The styrene content of the styrene-based thermoplastic elastomer (B) is 10% by mass or more. The porous electret film according to [1] or [2], wherein the content is 50% by mass or less. [4] The melt strength of the thermoplastic elastomer (B) at a temperature of 200°C and a load of 10 kg Any of [1] to [3] whose flow rate (MFR(B)) is 2.0 g / 10 min or less The porous electret film according to any one of the preceding claims. [5] The polyolefin resin (A) at a temperature of 230°C and a load of 2.16 kg The melt flow rate (MFR(A)) and the temperature of the styrene-based thermoplastic elastomer (B) The difference between the melt flow rate (MFR(B)) at 200°C and a load of 10 kg (MFR [1] to [4], wherein (A)-MFR(B)) is 6 g / 10 min or more. Perforated electret film. [6] The polyolefin resin (A) is a polypropylene resin. [1] to [5] The porous electret film according to any one of the preceding items. [7] The porous electret according to any one of [1] to [6], which contains a β-crystal nucleating agent (C). film. [8] At least one of the porous electret films according to any one of [1] to [7]. A piezoelectric sheet with an electrode layer on one side. [9] A sensor device using the piezoelectric sheet described in [8]. [Effects of the Invention]

[0008] According to the present invention, a porous electret having high piezoelectricity and excellent stability of piezoelectricity over time is provided. and a laminated piezoelectric sheet in which the porous electret film and an electrode are laminated. It can be provided. DETAILED DESCRIPTION OF THE INVENTION

[0009] The following describes in detail the embodiments of the present invention. These are merely examples (typical examples), and the present invention is not limited to these contents as long as it does not exceed the gist of the invention. do not have.

[0010] In the present invention, when it is written as "x to y" (x and y are arbitrary numbers), unless otherwise specified, Unless otherwise specified, "greater than x and less than y" is used in conjunction with "preferably greater than x" or "preferably It also includes the meaning of "smaller than y." Also, when "x or more" (x is any number) is written, it means "preferred" unless otherwise specified. "is greater than x" is included, and "is less than y" (where y is any number) is included. Unless otherwise specified, the meaning of "preferably smaller than y" is also included. Furthermore, "x and / or y (x and y are optional configurations)" means at least one of x and y. It means three things: x only, y only, and x and y.

[0011] [Porous electret film] The electret film is a permanent dipole type polarized by the dipole orientation of the polymer itself. The porous polymer film is charged to trap the charge inside the bubbles, They can be broadly divided into porous membrane types, which form polarization in the pores, and porous membrane types. The former has a dipole polarized at the molecular level, i.e., on the order of Å to nm. However, since the size of the latter dipole depends on the size of the vacancy, it is generally considered to be a permanent dipole type electron. It has a dipole of nm to μm size, which is larger than that of the Toretto film. The electret film has high piezoelectricity.

[0012] In the present invention, a porous film is used as the electret in order to further enhance the piezoelectric properties. In addition, the electret film is made of a porous film that has been electrically charged. That is, it corresponds to the porous membrane type electret film. The method for making the porous electret film porous is not particularly limited, but for example, chemical or These include physical foaming and stretching to create pores. Porosity is preferably achieved by stretching, as the shape is easily controlled.

[0013] <Aspect ratio> The aspect of the pores in the porous electret film of the present invention (also referred to as "the film") The aspect ratio of the pores is 4.0 or more and 20 or less. The pores become more easily deformed by pressure applied in the film thickness direction, resulting in piezoelectricity. It is possible to obtain a porous electret film with high piezoelectric constant stability over time. From the above viewpoints, the average aspect ratio of the pores is preferably 4.1 or more or 15 or less. Preferably, it is 4.2 or more or 10 or less, and more preferably, it is 4.3 or more or 8.0 It is more preferable that the value is 4.4 or more or 7.0 or less. .

[0014] <Average pore diameter> The average pore size of the pores is preferably 0.01 μm or more and 5.0 μm or less. When the diameter is within the above range, it is easy to obtain a film that is excellent in sensitivity to pressure. Therefore, it is more preferable that the thickness is 0.05 μm or more or 4.0 μm or less, and 0.10 μm or less It is more preferably 0.5 μm or more or 3.0 μm or less, or more preferably 0.5 μm or more or 2.0 μm or less. In the present invention, the length of the major axis of the elliptical hole is preferably less than 1 / 2 mm. , is defined as the pore diameter. The aspect ratio and average pore size of the pores can be determined by the method described in the Examples. .

[0015] <Porosity> The porosity of the present film is preferably 10% or more and 80% or less. This is a value that indicates the ratio of the void portion of the electret film. The higher the void ratio, the greater the piezoelectric From the above viewpoint, the porosity is 20% or more, preferably 30% or more. , and more preferably 40% or more. On the other hand, the porosity of the porous electret film is preferably 80% or less. If the ratio is 80% or less, the piezoelectric film can have excellent pressure resistance. From this viewpoint, the porosity is more preferably 75% or less, and even more preferably 70% or less. It is more preferable that the ratio is 60% or less, and particularly preferable that the ratio is 60% or less. The porosity of the present film can be calculated from the density of the resin composition by the method described in the examples. can.

[0016] <Air permeability> There is no particular limitation on the air permeability of the present film, but it is preferably 30,000 sec / dL or less, more preferably 10,000 sec / dL or less. Preferably, it is 10,000 sec / dL or less, more preferably, it is 1,000 sec / dL or less, and particularly preferably, it is 1,000 sec / dL or less. The viscosity is preferably 800 sec / dL or less, and most preferably 100 sec / dL or less. By having the air permeability be equal to or less than the above upper limit, it tends to be easier to suppress the change in piezoelectricity over time. On the other hand, although there is no particular lower limit, it is preferable that the lower limit is 1 sec / dL or more. It is more preferable that it is 3 seconds / dL or more, and even more preferable that it is 5 seconds / dL or more.

[0017] "Air permeability" indicates the difficulty of air passing through in the thickness direction of the film, specifically 1 It is expressed as the number of seconds required for 00 mL of air to pass through the film. The smaller the value, the easier it is to pass through, and the larger the value, the harder it is to pass through. That is, the smaller the value, the higher the interconnectivity of the film in the thickness direction. The larger the value, the lower the interconnectivity in the thickness direction of the film. This is the degree of connection of pores in the thickness direction of the film. The porous electret film has a unique mechanism that traps electric charges inside the bubbles. It is preferable that the porous material contains many standing cells (closed pores), and that the porous material contains many interconnected pores (open pores). ) was thought to be preferable. However, for reasons not clear, By having an appropriate number of through holes so that the above range is achieved, it is surprisingly possible to obtain stable piezoelectricity. This has revealed a tendency for Air permeability (seconds / 100 mL) can be measured in accordance with JIS P8117:2009. Specifically, it can be measured by the method described in the Examples.

[0018] <piezoelectric constant d 33 > The piezoelectric constant d of this film 33 The absolute value of the piezoelectric constant is preferably 40 pC / N or more. constant d 33 The absolute value of 40 pC / N or more is sufficient for use as a sensor. From the above viewpoint, the piezoelectric constant d 33 The absolute value of is 50pC / N Preferably, 60 pC / N or more is more preferable, and 70 pC / N or more is even more preferable. . In particular, 90 pC / N or more is preferable, 100 pC / N or more is more preferable, and 130 pC / N or more is more preferable. 150 pC / N or more is more preferable, and 200 pC / N or more is even more preferable. The above is particularly preferred. On the other hand, the piezoelectric constant d 33 The absolute value of the piezoelectric constant d3 is preferably 10,000 pC / N or less. The absolute value of 3 is 10,000 pC / N or less, making it suitable for use as a sensor or actuator. From this viewpoint, the piezoelectric constant d 33 The absolute value of is preferably 8000 pC / N or less, and more preferably 5000 pC / N or less. preferable. The piezoelectric constant is measured by the method described in the examples.

[0019] This film has a piezoelectric constant d 33 The initial value of d 33 (Initial) Piezoelectric constant d after storage for one month at a temperature of 24°C and a relative humidity of 50% 33 d 33 (1 month later) The retention rate of the piezoelectric constant after one month (d 33 retention rate) is 6 It is preferable that it is 5% or more. 33 With a retention rate of 65% or more, it is stable over time. From this viewpoint, the retention rate is preferably or 70% or more, more preferably 75% or more, even more preferably 80% or more, and particularly preferably Preferably, it is 90% or more, and most preferably 100%.

[0020] To keep the absolute value of the piezoelectric constant within a specified range, it is necessary to optimize the conditions for charging the film. and methods for adjusting the size, shape and porosity of pores in porous films. do. More specifically, the porous electret film retains electric charges at the interface between the pores and the resin. Therefore, the larger the pore surface area, the more charge can be held. The smaller the noise and the greater the number of holes, the larger the pore surface area and the greater the piezoelectricity. . In addition, the holes in the porous electret film are compressed and deformed by pressure, changing the value of the dipole. Therefore, the pore size is small and the size The more uniform the size and shape, the smaller the variation in piezoelectricity.

[0021] <Thickness> The thickness of the film is preferably 10 μm or more, more preferably 15 μm or more, and is preferably 20 μm or more. On the other hand, the upper limit of the thickness of the present film is 200 μm or less. It is preferable that the thickness is 150 μm or less, more preferably 100 μm or less. , 80 μm or less is even more preferable, and 50 μm or less is particularly preferable. By having the thickness in the above range, a porous electret film having excellent handling properties and piezoelectricity can be obtained. You can get the film. Furthermore, if the thickness is 50 μm or less, it will become a thin and physically flexible film. It is thought that the amount of deformation of the pores increases when a certain pressure is applied. As a result, polarization changes tend to occur more easily, making porous electret films particularly highly piezoelectric. This is preferable in that

[0022] <Resin composition> The resin composition constituting the present film (also referred to as "the present composition") will be described below. The composition comprises a polyolefin resin (A) and a styrene-based thermoplastic elastomer (B). Among them, the resin composition containing polyolefin resin (A) as the main component is It is preferable that the resin composition is a resin composition having the above properties. The "main component" in this composition refers to the resin component contained in this composition. More specifically, when the total amount of the resin composition is 100 mass%, 1 The upper limit is 00% by mass, preferably 50% by mass or more, more preferably 55% by mass or more, More preferably, it refers to a resin that accounts for 60% by mass or more. " is a mixture of polyolefin resin (A) and styrene thermoplastic elastomer (B). In addition, polyolefin resin (A) and styrene resin (B) described later may be added as needed. Resin components other than the elastomer (B) can be mentioned.

[0023] 1. Polyolefin resin (A) Examples of the polyolefin resin (A) include homopolypropylene (propylene alone) and polymers), or propylene and ethylene, 1-butene, 1-pentene, 1-hexene, 1- Randomly mixed with α-olefins such as heptene, 1-octene, 1-nonene, or 1-decene Examples of the polyolefin resin include a polyolefin copolymer and a polyolefin block copolymer. The polyolefin resin (A) may be used alone or in combination of two or more. Among these, homopolypropylene is preferred from the viewpoint of mechanical strength. .

[0024] When the polyolefin resin (A) is a polypropylene resin, its isotactic The pentad fraction is not particularly limited, but is preferably 80 mol % or more and 99 mol % or less. More preferably, it is 3 mol % or more and 98 mol % or less, and even more preferably, it is 85 mol % or more and 97 mol % or less. The isotactic pentad fraction indicates stereoregularity, and the isotactic pentad fraction If the adsorption ratio is too low, sufficient porosity may not be achieved by stretching. The upper limit of the isotactic pentad fraction is the upper limit that can be obtained industrially at present. However, in the future, if a resin with even higher regularity is developed at the industrial level, This does not necessarily mean that The isotactic pentad fraction consists of any five consecutive propylene units. The five methyl groups in the side chains are all positioned in the same direction relative to the main chain formed by the carbon-carbon bonds. The signal assignment in the methyl group region is A.Za Based on Melli et al., Macromol., 8, 687 (1975) .

[0025] The Mw / Mn of the polyolefin resin (A) is not particularly limited, but is preferably 1.5 or more and 10.0 or less. Preferably, the ratio is 2.0 or more and 8.0 or less, more preferably 2.0 or more and 6.0 or less. Mw / Mn is a parameter that indicates the molecular weight distribution, and the smaller the Mw / Mn, the lower the distribution. By setting the Mw / Mn ratio to the above lower limit or higher, sufficient extrusion is possible. On the other hand, when Mw / Mn is set to the above upper limit or less, By doing so, sufficient mechanical strength can be ensured. In the present invention, Mw / Mn is determined by GPC (gel permeation chromatography). ) method.

[0026] In this composition, the polyolefin resin (A) was The melt flow rate (MFR(A)) in the When the melt flow rate (MFR(A)) has such a value, the polyolefin When dispersing the styrene elastomer (B) described later in the styrene resin (A), Since the dispersion diameter of the elastomer (B) becomes larger, it becomes easier to adjust the pore diameter to the above-mentioned lower limit or more. As a result, the piezoelectricity of the film can be improved. From this viewpoint, the melt flow rate (MFR(A)) is preferably 9 g / 10 min or more. It is preferable that the viscosity is 10 g / 10 min or more, more preferable that the viscosity is 11 g / 10 min or more. On the other hand, the upper limit is preferably 20 g / 10 min or less, more preferably 18 g / 10 min or less, It is more preferable that the MFR is 16 g / 10 min or less. This allows the system to have sufficient strength. When two or more polyolefin resins (A) are used in combination, at least one It is sufficient that the polyolefin resin (A) has the above MFR value. The MFR of the polyolefin resin (A) in the present invention is determined in accordance with JIS K7210-1 (2014) and measured at a temperature of 230°C and a load of 2.16 kg. .

[0027] Examples of the polyolefin resin (A) include products under the trade names "Novatec PP" and "WIN TEC (Japan Polypropylene Corporation); Notio and Toughmer XR (Mitsui Chemicals Co., Ltd.); "Zelas", "Thermorun" (manufactured by Mitsubishi Chemical Corporation); "Sumitomo Noble "," "Tafthren" (Sumitomo Chemical Co., Ltd.); "Prime PP" and "Prime TPO" ( Prime Polymer Co., Ltd.); "Adflex", "Adsyl", "HMS-PP ( PF814) (by SunAllomer Co., Ltd.); "Versify", "Inspire" (by Commercially available products such as those manufactured by U Chemical Co., Ltd. can be used.

[0028] The content of the polyolefin resin (A) in the composition is 50% by mass or more and 95% by mass or less. The content is preferably 55% by mass or more and 90% by mass or less, more preferably 60% by mass or more and 85% by mass or less. When the content of the polyolefin resin (A) is within the above range, it is more preferable that the content is 0.05 wt % or less. , a polyolefin resin (A) is used as the matrix, and a styrene-based thermoplastic elastomer (B ) can form a sea-island structure with domains, and when stretched, a porous structure is easily formed. become.

[0029] 2. Styrene-based thermoplastic elastomer (B) Styrene-based thermoplastic elastomer (B) is a thermoplastic elastomer based on styrene. It is a type of elastomer resin that consists of a soft component (e.g., butadiene component) and a hard component (e.g., styrene It is a copolymer consisting of a continuum of carbon and olefins, specifically, the double bonds of the carbon of the copolymer Some have been hydrogenated to make them single bonds.

[0030] The copolymer may be a random copolymer, a block copolymer, a graft copolymer, or the like. In addition, block copolymers include those with linear block structures and those with radial branch structures. Any of the structures may be used in the present invention.

[0031] The film contains the styrene-based thermoplastic resin (A) in a matrix of the polyolefin-based resin (A). The plastic elastomer (B) forms a sea-island structure that forms domains, allowing efficient It is possible to obtain a film with a fine and highly uniform porous structure, and the shape and diameter of the pores can be controlled. It becomes easier to control.

[0032] Examples of the styrene-based thermoplastic elastomer (B) include styrene-olefin-styrene. Examples include styrene copolymers (B1) and styrene-olefin copolymers (B2). Examples of the styrene-olefin-styrene copolymer (B1) include styrene-butadiene copolymers. Diene-styrene copolymer (SBS), styrene-butadiene-butylene-styrene copolymer Polymer (SBBS), styrene-ethylene-butadiene-styrene copolymer (SEBS), Styrene-isoprene-styrene copolymer (SIS), styrene-ethylene-propylene -styrene copolymer (SEPS), styrene-ethylene-ethylene-propylene-styrene Examples include ethylene glycol copolymers (SEEPS). Examples of the styrene-olefin copolymer (B2) include styrene-butadiene copolymers. Polymer (SBR), hydrogenated styrene-butadiene copolymer (SEB), styrene-isopropyl copolymer (SIR), styrene-ethylene-propylene copolymer (SEP), etc. can be done. The styrene-based thermoplastic elastomer (B) exemplified above may be used alone. Alternatively, two or more types may be used in combination.

[0033] Among the above, if the compatibility with the polyolefin resin (A) is low, a porous structure is likely to be formed. Therefore, from the viewpoint of forming a porous structure, it is preferable to use a structure in which both ends are styrene polymers. On the other hand, it is preferable that the resin having the above structure is used as the main component. In order to disperse the thermoplastic elastomer (B), it is necessary to make it compatible with the polyolefin resin (A). Highly resistant ethylene component (hydrogenated butadiene component), ethylene-propylene component (hydrogenated isopropyl It is preferable that the main component of the porous structure is a resin containing a butylene component. From the viewpoint of the structure formability, the styrene-olefin-styrene copolymer (B1) as the main component is From the viewpoint of dispersibility of the styrene-based thermoplastic elastomer (B), it is preferable to use SEP It is preferable that the main component is SEPS, SEBS or SEEPS, and from both of the above viewpoints, Therefore, it is more preferable to use SEPS or SEEPS as the main component, and among them, it is preferable to use SEEPS as the main component. It is particularly preferred to use it as a component. The "main component" of the styrene-based thermoplastic elastomer (B) is the component contained in the composition. This refers to the resin with the highest content of styrene-based thermoplastic elastomer (B) used in Specifically, when the total amount of the styrene-based thermoplastic elastomer (B) is taken as 100% by mass, The upper limit is 100% by mass, and preferably 50% by mass or more, more preferably 55% by mass or more. More preferably, it refers to a resin that accounts for 60% by mass or more.

[0034] Furthermore, from the viewpoint of achieving a higher level of both piezoelectricity and mechanical properties, The styrene-based thermoplastic elastomer (B) contained in the composition is styrene-olefin- It is preferred to contain a styrene copolymer (B1) and a styrene-olefin copolymer (B2). By combining two or more types of styrene-based thermoplastic elastomer (B), The uniformity of the porous structure obtained by the process can be improved.

[0035] In the porous film of the present invention, within the domains of the styrene-based thermoplastic elastomer (B), The cleavage that occurs during stretching is the starting point for the formation of pores. The larger the domain, the larger the pores. Among the elastomers (B), styrene-olefin-styrene copolymers (B1) are the most In addition, the styrene-olefin copolymer is preferably applied to the surface of the domain. The uneven distribution of the copolymer (B2) improves the dispersion of domains and the uniformity of the porous structure. can be increased.

[0036] The styrene content of the styrene-based thermoplastic elastomer (B) is 10% by mass or more and 50% by mass or less. % or less, and more preferably 10% by mass or more and 45% by mass or less. If the content is equal to or greater than the lower limit, domains can be effectively formed in the polyolefin resin (A). If the styrene content is equal to or less than the upper limit, the formation of excessively large domains can be suppressed. The styrene-based thermoplastic elastomer (B) contained in the composition can be When two or more types are used, the styrene content is the total of the styrene-based thermoplastic elastomer (B). This refers to the total amount of

[0037] The resin that is the main component of the styrene-based thermoplastic elastomer (B) contained in the composition The weight average molecular weight (Mw) of the copolymer is not particularly limited, but is preferably 100,000 or more, and more preferably 150,000 or more and more preferably 100,000 or more. 100,000 or less is more preferable, 150,000 to 800,000 is more preferable, and 150,000 to 600,000 is more preferable. More preferably, 150,000 to 500,000 is more preferable, and 150,000 to 400,000 is more preferable. More preferably, 150,000 to 350,000 is even more preferable, and 150,000 to 300,000 is particularly preferable. preferable. In addition, the main component of the styrene-based thermoplastic elastomer (B) contained in the composition is The Mw / Mn of the resin is not particularly limited, but is preferably 1.00 or more and 1.50 or less, and more preferably 1. It is more preferably 00 or more and 1.40 or less, and even more preferably 1.05 or more and 1.20 or less.

[0038] When a film made of the present composition is stretched at least uniaxially to form a porous film, the resin before stretching is The resin composition contains a polyolefin resin (A) and a styrene-based thermoplastic elastomer (B). The morphology of the polymer is an important factor in the formation of the porous structure. It exists as a domain in a matrix mainly composed of olefin-based resin (A). It is important that the styrene-based thermoplastic elastomer (B) is present in a spherical shape.

[0039] Generally, a resin composition having a matrix / domain sea-island structure is melt-extruded and cooled to solidify. In this case, the resin composition is extruded and flows from a shaping device such as a die or a nozzle. It is cooled and solidified using cooling and solidification equipment such as a cast roll (cooling roll), air cooling, or water cooling. At this time, the resin composition melts and stretches in the gap between the shaping equipment and the cooling and solidifying equipment. Therefore, the weight average molecular weight of the domain, styrene-based thermoplastic elastomer (B), is small. In this case, a resin composition in which the domains are elongated in the flow direction (extrusion direction) is obtained. If the in is stretched in the flow direction (extrusion direction), the area of ​​the domain particles in the flow direction becomes large. Therefore, the domains are less likely to split apart due to stress in the flow direction (extrusion direction). However, the porous structure may not be sufficiently formed.

[0040] On the other hand, the weight average molecular weight of the domain, styrene-based thermoplastic elastomer (B), is large. If the domain is not stretched, the domain is less susceptible to the influence of melt stretching, and the domain in the resin composition before stretching is If the domains are spherical, they will be more resistant to stress in the flow direction (extrusion direction). It is thought that the cleavage within the domains is more likely to occur, resulting in the formation of a porous structure. .

[0041] For this reason, the main component of the styrene-based thermoplastic elastomer (B) It is preferable that the weight average molecular weight (Mw) of the resin is within the above range. The number average molecular weight Mn and weight average molecular weight M of the resin that is the main component of the plastic elastomer (B) When the ratio (molecular weight distribution) Mw / Mn of w) is within the above range, the dispersion diameter of the formed domains is This is more preferable because it is easier to make the mixture uniform.

[0042] The styrene-based thermoplastic elastomer (B) contained in this composition was subjected to a test at a temperature of 200°C and a load of 1 The melt flow rate (MFR(B)) measured at 0 kg is 2.0 g / 10 min or less. It is preferable. The styrene-based thermoplastic elastomer (B) dispersed in the composition is a polyolefin The shape of the polymer changes depending on the difference in viscosity with the base resin (A). If the thermoplastic elastomer is a ethylene-based elastomer, the viscosity difference with the polyolefin-based resin (A) will be large. The spherically dispersed domains tend to have a large aspect ratio. The resulting porous structure is more uniform than the domains obtained by the subsequent stretching process. It is possible to obtain a porous film that is thin yet has excellent stability of physical properties. From this viewpoint, the melt flow rate (MFR(B)) is preferably 1.0 g / 10 min or less. Preferably, 0.5 g / 10 min or less is more preferred, and 0.1 g / 10 min or less is even more preferred. stomach. The lower limit is not particularly limited, but is usually 0 g / 10 min, ie, a state where the material does not flow. When two or more types of styrene-based thermoplastic elastomers (B) are used, at least one type It is sufficient that the styrene-based thermoplastic elastomer (B) has the above MFR value. Among them, if the main component is a styrene-based thermoplastic elastomer whose MFR is within the above range, During the stretching process, stress tends to concentrate inside the domain, making it difficult for openings to occur. This is preferable in that it is thin and can be easily made porous. The MFR of the styrene-based thermoplastic elastomer (B) in the present invention is determined in accordance with JIS K Measured in accordance with 7210-1 (2014) at a temperature of 200°C and a load of 10 kg. value.

[0043] The content of the styrene-based thermoplastic elastomer in the composition is 5% by mass or more and 50% by mass or less. % or less, more preferably 10% by mass or more and 45% by mass or less, and more preferably 15% by mass or more and 40% by mass or less. It is more preferable that the content of the styrene-based thermoplastic elastomer (B) is in the above range. When the temperature is within this range, the polyolefin resin (A) is used as the matrix and the styrene-based thermoplastic elastomer is used as the polymer. A sea-island structure with the ester (B) as the domain can be formed, and a porous structure is formed when stretched. It becomes easier to achieve.

[0044] The polyolefin resin (A) in this composition was subjected to a temperature of 230°C and a load of 2.16 kg. and the melt flow rate (MFR(A)) of the styrene-based thermoplastic elastomer (B) at a temperature of 200°C and a load of 10 kg (MFR(B)) The difference (MFR(A)-MFR(B)) is preferably 6 g / 10 min or more. The difference is 6g / 10min or more, which means that the porous element has excellent piezoelectricity and stability over time. A cullet film can be obtained. From the above viewpoint, the melt flow rate (MFR(A)) of the polyolefin resin (A) ) and the melt flow rate (MFR(B)) of the styrene-based thermoplastic elastomer (B) ) and the difference (MFR(A)-MFR(B)) is preferably 7 g / 10 min or more, It is more preferably 8 g / 10 min or more, and even more preferably 10 g / 10 min or more. In addition, the difference (MFR(A)-MFR(B)) is 2. It is preferably 0 g / 10 min or less, and more preferably 15 g / 10 min or less. . In addition, the present composition may contain two or more polyolefin resins (A) and / or two or more styrene resins. If it contains a propylene-based thermoplastic elastomer (B), the polyolefin with the highest MFR (A) value is used. A styrene-based resin (A) and a styrene-based thermoplastic elastomer (B) with the lowest MFR (B) value. The difference is

[0045] By using this composition as the resin composition constituting the electret film, The reason why the electrical conductivity and stability over time are good is not clear, but the following points are thought to be the cause. The combination of the polyolefin resin (A) and the styrene thermoplastic elastomer (B) of the present invention This is thought to be because the use of lamination allows the formation of large pores that are easily deformed by pressure. can be.

[0046] 3. Nucleating Agent (C) The composition comprises a polyolefin resin (A) and a styrene-based thermoplastic elastomer (B). When the polyolefin resin (A) is stretched to form pores, the rigidity of the polyolefin resin (A) can be increased. The composition may contain a crystal nucleating agent (C), which is believed to be effective in forming voids. As the nucleating agent (C), an α-crystal nucleating agent or a β-crystal nucleating agent is preferred. From the viewpoint of excellent heat resistance, an α-crystal nucleating agent is preferred. On the other hand, from the viewpoint of thermal fusion bonding, a β-crystal nucleating agent is preferred. Examples of the α-crystal nucleating agent include dibenzylidene sorbitol (manufactured by New Japan Chemical Co., Ltd., product number "ADK STAB NA-11", "ADK STAB NA-27", "ADK STAB NA-902", "ADK STAB NA-21", "ADK STAB NA-7 1" (all five types listed on the left are manufactured by ADEKA Corporation), a mixture of magnesium stearate and silica Masterbatch containing the compound (manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd., product name "High Cycle Master") ), 2-hydroxy-2-oxo-4,6,10,12-tetra-tert-butyl-1 ,3,2-Dibenzo[d,g]perhydrodioxaphosphalocin sodium salt Masterbatch (manufactured by ADEKA Corporation, product name "ADEKA STAB M-701") is used. can.

[0047] Other examples of α-crystal nucleating agents include inorganic nucleating agents such as silica, talc, and calcium carbonate. Organic (metallic carboxylate) types include calcium stearate and benzoic acid. Sodium, Aluminum Benzoate, Aluminum Dibenzoate, Potassium Benzoate ate, lithium benzoate, sodium β-naphthalate sodium cyclohexyl carboxylate carboxylate, metal pimelate, metal rosinate, etc. There are also sorbitol and its derivatives, phosphate ester metal salts, and polymers. Types include poly-3-methylbutene-1, polyvinylcycloalkane, and polyvinyl Trialkylsilane, EPR, Kevlar (registered trademark) fiber, 2,2'-methylenebisphosphate Examples include sodium tris(4,6-di-tert-butylphenyl). The content of the α-crystal nucleating agent in the composition is 100 parts by mass of the resin component in the composition. The amount is preferably 0.001 parts by mass or more and 10 parts by mass or less, and more preferably 0.005 parts by mass or more and 5 parts by mass or less. More preferably, 0.01 parts by mass or more and 2 parts by mass or less is more preferable, and 0.05 parts by mass or less is even more preferable. The content of the α-crystal nucleating agent is more preferably 0.001 parts by mass or more and 1.5 parts by mass or less. On the other hand, when the content of the α-crystal nucleating agent is 10 parts by mass, the formation of α-crystals can be sufficiently achieved. If it is less than this, bleeding, plate-out, and powdering of the α-crystal nucleating agent will not occur during the film-making process or secondary processing. This is preferable in that there is no risk of falling off or the like and the cost is low.

[0048] Examples of the β-crystal nucleating agent include amide compounds, tetraoxaspiro compounds, and quinacridones. ; nanoscale iron oxide; 1,2-hydroxystearate potassium, Magnesium benzoate, magnesium succinate, magnesium phthalate, etc. Alkali or alkaline earth metal salts of carboxylic acids; sodium benzenesulfonate or aromatic sulfonic acid compounds such as sodium naphthalene sulfonate; Di- or triesters of tribasic carboxylic acids; phthalocyanine blue, etc. Phthalocyanine pigments; Component A is an organic dibasic acid and Component B is an acid of a metal from Group IIA of the periodic table. A binary compound consisting of a cyclic phosphorus compound and a component B which is a phosphate, hydroxide or salt; Examples of the composition include a composition comprising a magnesium compound. In addition, specific types of nucleating agents are described in JP-A-2003-306585 and JP-A-2003-306585. This is described in Japanese Patent Publication No. 06-289566 and Japanese Patent Application Laid-Open No. 09-194650.

[0049] Among these β-crystal nucleating agents, amide compounds are preferred in terms of the piezoelectricity of the resulting piezoelectric film. As an amide compound, N,N'-dicyclohexyl-2,6-naphthalenedicarboxylic acid boxamide, N,N'-dicyclohexylterephthalamide, N,N'-diphenylhetero Xanthamide, among others, N,N'-dicyclohexyl-2,6-naphthalene Dicarboxyamide is preferred. Amide compounds have a highly polar amide group, so they are easy to crystallize. It is believed that electric charges can be localized within the structure, resulting in high piezoelectricity.

[0050] Highly polar compounds such as amide compounds are electrostatically incompatible with polypropylene resins, which have low polarity. However, the problem is that the dispersibility is poor and the particles tend to aggregate due to the interaction between the particles. A typical β-crystal nucleating agent has the property of dissolving in polypropylene resins within a certain temperature range. This property allows the β-crystal nucleating agent to be uniformly dispersed in the polypropylene resin, This makes it easier for the original crystals to precipitate uniformly. In this way, the crystals of the highly polar amide compound are uniformly distributed in the polypropylene resin with low polarity. It is believed that uniform dispersion of the particles can contribute to improving the piezoelectricity.

[0051] A specific example of a commercially available β-crystal nucleating agent is the β-crystal nucleating agent "N-Jester" manufactured by New Japan Chemical Co., Ltd. NU-100" and specific examples of propylene resins containing β-crystal nucleating agents include Arist Bepol B-022SP polypropylene manufactured by Tech, and Borealis polypropylene Propylene "Beta(β)-PP BE60-7032", polypropylene manufactured by Mayzo Examples include Ren's "BNX BETAPP-LN".

[0052] The content of the β-crystal nucleating agent in the present film varies depending on the type of β-crystal nucleating agent or the composition of the polypropylene resin. It can be adjusted appropriately by using the following methods, but the recommended amount is 0. 0001 parts by mass or more and 5.0 parts by mass or less, preferably 0.001 parts by mass or more and 3.0 parts by mass or less More preferably, the amount is 0.01 part by mass or more and 1.0 part by mass or less. If the content of the β-crystal nucleating agent is 0.0001 parts by mass or more, polypropylene is sufficiently used during production. It is possible to generate and grow β crystals of pyrene-based resins, and sufficient β crystal generation capacity can be secured, resulting in porous electrets. The piezoelectricity of the film is improved. In addition, sufficient β crystals are formed even when the film is stretched to form a porous film. This porous electret film can ensure the desired piezoelectricity by charging. is obtained. On the other hand, if the amount is 5.0 parts by mass or less, it is economically advantageous and does not adhere to the film surface. This is preferable because there is no bleeding of the β crystal nucleating agent.

[0053] As a commercially available product of the β crystal nucleating agent, for example, the β crystal nucleating agent "NJester N" manufactured by New Japan Chemical Co., Ltd. U-100" and specific examples of polypropylene containing β-crystal nucleating agents include Aristec Polypropylene "BepolB-022SP" manufactured by H Co., Ltd., Polypropylene manufactured by Borealis Co., Ltd. Pyrene "Beta(β)-PPBE60-7032", Mayzo Polypropylene " Examples include "BNXBETAPP-LN".

[0054] The ratio of the β-crystal nucleating agent to the polyolefin resin (A) varies depending on the type of the β-crystal nucleating agent or the polyolefin resin (A). It is preferable to appropriately adjust the composition of the polyolefin resin (A). Therefore, the content of the β-crystal nucleating agent is 0.000 with respect to 100 parts by mass of the polyolefin resin (A). It is preferably 1 to 5.0 parts by mass, and more preferably 0.001 parts by mass or more or 3.0 parts by mass. It is more preferable that the amount is 0.01 parts by mass or more, or 1.0 parts by mass or more. If the amount is 0.0001 parts by mass or more, the amount is sufficient for the purpose of production. It is possible to generate and grow β crystals of polyolefin resin (A), ensuring sufficient β crystal activity. When the piezoelectric element is used as a sensor device, the desired piezoelectric performance can be obtained. If the temperature is lower than this, it is economically advantageous and prevents bleeding of the β-crystal nucleating agent onto the surface of the porous film. It's preferable because it's simple. In addition, if a resin layer containing polyolefin is used in addition to the resin layer made of polyolefin resin (A), When layers that contain β-crystal nucleating agents are laminated, even if the amount of β-crystal nucleating agent added to each layer is the same, The porous structure of each layer can be adjusted appropriately by changing the amount of the β-crystal nucleating agent added. Cut.

[0055] 4. Other ingredients In the resin composition according to the present invention, polyisocyanate may be used within a range that does not impair the effects of the present invention. The composition may contain a resin component other than the olefin resin (A) and the styrene elastomer (B). stomach. Examples of resins other than polyolefin resins include polystyrene resins and polyvinyl chloride resins. vinyl resin, polyvinylidene chloride resin, chlorinated polyethylene resin, polyester resin Polycarbonate resin, polyamide resin, polyacetal resin, acrylic resin Fat, ethylene vinyl acetate copolymer, polymethylpentene resin, polyvinyl alcohol resin Resins, cyclic olefin resins, polylactic acid resins, polybutylene succinate resins, poly Acrylonitrile resin, polyethylene oxide resin, cellulose resin, polyimide Polyurethane resin, polyphenylene sulfide resin, polyphenylene ether resin ester resins, polyvinyl acetal resins, polybutadiene resins, polybutene resins, Polyamide-imide resin, polyamide-bismaleimide resin, polyarylate resin, poly Polyetherimide resin, polyetheretherketone resin, polyetherketone resin Grease, polyethersulfone resin, polyketone resin, polysulfone resin, aramid resins, fluorine-based resins, etc.

[0056] The film may contain additives to the extent that they do not impair its properties. The additives are effective in improving moldability, productivity, and various physical properties of the porous electret film. It is added to improve and adjust the product, and is recycled from trimming waste such as ears. Resin, inorganic particles such as silica, talc, kaolin, calcium carbonate, titanium oxide, carbon Pigments such as black, flame retardants, weather stabilizers, heat stabilizers, antistatic agents, melt viscosity improvers , crosslinking agents, lubricants, nucleating agents, plasticizers, antioxidants, antioxidants, light stabilizers, UV absorbers, Examples of additives include additives such as a lubricating agent, an anti-fogging agent, an anti-blocking agent, a slip agent, and a colorant.

[0057] [Method of manufacturing porous electret film] The method for producing the present film will be described below. This is an example of a method for manufacturing a porous electret filter, and the manufacturing method described below is It is not limited to rooms.

[0058] The present film is preferably produced through a film-forming step, a stretching step, and a charging step. The film-forming step, the stretching step, and the charging step will be described below in order.

[0059] (Film forming process) In the film-forming process, a non-porous film made of a material constituting a porous electret film is formed. In the film-forming process, the material constituting the porous electret film is prepared by a known method. There is no particular limitation as long as the film is formed from the resin constituting the porous electret film. The composition (material resin) is heated and melted to form a film, specifically, by the T-die method. The film can be formed by an inflation method or the like, and among these, the T-die method is preferably used. stomach. In practical use, the material resin is melt-extruded from a T-die and cast rolled (chill roll, It is preferable to carry out cast molding using a casting drum or the like.

[0060] The materials that make up the porous electret film are kneaded in a kneading device and then formed into a film. The kneading device used for kneading is not particularly limited. For example, a single screw extruder, a twin screw extruder, Known extruders such as a single-screw extruder and a multi-screw extruder can be used. In addition, depending on the equipment structure and necessity, a pressure reducer may be connected to the vent port of the extruder to reduce moisture. and low molecular weight substances may be removed.

[0061] When using a cast roll as described above, the film-like molten The resin (resin composition) is extruded onto a casting roll and adhered to the rotating casting roll. The film is then tightly attached to the casting roll. In order to achieve this, a touch roll, air knife, electric contact device, etc. are attached to the cast roll. Good too. In addition, when molding the molten resin (resin composition) into a film while cooling it, the temperature must be 60°C or higher for 15 minutes. Preferably 0°C or lower, more preferably 70°C or higher and 140°C or lower, and more preferably 80°C or higher and 130°C or lower is more preferable, and 90°C or higher and 120°C or lower is even more preferable. When the temperature of the casting roll is equal to or higher than the lower limit, the polyolefin resin (A) Crystallization proceeds sufficiently, and a porous structure is formed. If the stretching temperature is below the upper limit, the sheet before stretching may fuse with the roll, causing problems such as film breakage. This makes it less likely to occur.

[0062] In the obtained non-porous membrane, the thickness of the effective part excluding both ends is 20 μm or more and 800 μm or less. It is preferable that the thickness is 30 μm or less, more preferably 40 μm or more, and most preferably 30 μm or more. It is more preferable that the thickness is 50 μm or more, and it is even more preferable that the thickness is 700 μm or less. Among these, 600 μm or less is more preferable, and 500 μm or less is even more preferable. I wish. If the thickness of the non-porous membrane is 20 μm or more, breakage can be prevented during stretching, and the non-porous membrane If the thickness of the nonporous membrane material is 800 μm or less, the nonporous membrane material can be easily stretched. Regarding the layer structure of the non-porous film of this film, not only the single layer structure as described above but also other It may also be a combination of layers.

[0063] (Stretching process) The obtained non-porous membrane may be subjected to charging treatment as it is, but it may also be subjected to stretching treatment. It is preferable to carry out a stretching process on the non-porous membrane material. It can be made into a porous film. Note that stretching in the machine direction (MD) of a film is called "longitudinal stretching," and stretching perpendicular to the machine direction is called "longitudinal stretching." Stretching in the direction (TD) is called "transverse stretching."

[0064] The stretching temperature is appropriately adjusted depending on the composition of the resin composition used, the crystal melting peak temperature, the crystallinity, etc. The longitudinal stretching temperature is preferably 0 to 50°C, more preferably 5 to 40°C. If the longitudinal stretching temperature is equal to or lower than the upper limit, stress is concentrated inside the domain during stretching. On the other hand, if the longitudinal stretching temperature is equal to or higher than the lower limit, This is preferable because breakage during stretching can be suppressed.

[0065] The transverse stretching temperature is preferably 100 to 155°C, more preferably 110 to 150°C. By setting the transverse stretching temperature within the specified range, pores are sufficiently formed. In this case, the porosity can be increased and sufficient piezoelectricity can be obtained.

[0066] The stretching ratio may be selected arbitrarily according to the desired porosity. The elongation ratio is preferably 1.1 times or more and 20 times or less, and more preferably 1.5 times or more and 18 times or less. More preferably, it is 4 times or more and 16 times or less, and even more preferably, it is 4 times or more and 10 times or less. It is less than double. By setting the stretching ratio per uniaxial stretching to 1.1 times or more, whitening progresses and the multi-layer structure due to stretching is reduced. In addition, by setting the stretching ratio to 20 times or less, the porosity is suppressed and the film becomes more durable. A porous film with excellent pressure resistance can be obtained. In the case of sequential biaxial stretching, the film is stretched at the stretch ratio specified above for each axis. Therefore, the voids generated during the previous stretching will not be deformed during the subsequent stretching.

[0067] (Charging process) The non-porous film obtained in the film-making process or the porous film obtained through the stretching process is subjected to an electrification treatment. The film can be obtained by carrying out the above steps. The charging process can be continuous or by using a battery. The electrodes used for charging are needle electrodes on the front and back of the film, and wire electrodes. A film is placed between electrodes, such as roll electrodes or plate electrodes, and an electric field is applied between the electrodes. Alternatively, electrodes may be formed directly on the front and back of the film by coating or vapor deposition, and then an electric field may be applied. Among these methods, the method using a wire electrode or a plate electrode is This is preferable from the viewpoint of uniformity of the electric field when charging the film. On the other hand, it is also preferable from the viewpoint of excellent voltage application efficiency. Among these, a method using a needle electrode or a wire electrode is preferred. The applied electric field is preferably 0.1 MV / m or more and 10 MV / m or less, more preferably is 0.2MV / m or more and 8MV / m or less, more preferably 0.3MV / m or more and 6MV / m or less When the piezoelectric constant is 0.1MV / m or more, excellent piezoelectricity can be obtained. A value of MV / m or less has the effect of reducing dielectric breakdown during charging processing.

[0068] Furthermore, the present film may be subjected to corona treatment or plasma treatment as needed within the scope of the present invention. Surface treatments such as acrylic, printing, coating, vapor deposition, and even perforation can be applied. It is also possible to stack several sheets of this film depending on the application.

[0069] [Laminated piezoelectric sheet] The laminated piezoelectric sheet in which the porous electret film and the electrodes are laminated is also included in the present invention. Furthermore, a laminated piezoelectric sheet on which a protective film is laminated is also within the scope of the present invention. do.

[0070] <Electrode> The laminated piezoelectric sheet of the present invention has at least one electrode. It is preferable that at least two layers are provided so as to sandwich the PET film. The electrode layer may be made of any conductive material, such as aluminum foil, copper foil, silver foil, gold foil, or nickel. Kel foil, tin foil, carbon sheet, etc. are preferably used.

[0071] The thickness of the electrode is preferably 2 μm or more and 100 μm or less, and more preferably 3 μm or more and 50 μm or less. Preferably, it is 5 μm or more and 30 μm or less. By making the thickness of the electrode 2 μm or more, the electrode can exhibit stable conductivity. By keeping the electrode thickness below 100 μm, the flexibility of the laminated piezoelectric sheet can be increased. This can be done.

[0072] <Protective film> The laminated piezoelectric sheet of the present invention preferably has at least one protective film. The protective film is preferably a porous film. The protective film prevents deterioration of the porous electret film due to moisture. Cut. The protective film is made of porous electret film to enhance the water resistance of the laminated piezoelectric sheet. It is preferable that the insulating film is provided so as to cover the film and the electrodes. The protective film protects both the front and back surfaces of the porous electret film and the electrodes. Therefore, it is more preferable that at least two layers are provided in the present laminated piezoelectric sheet.

[0073] Furthermore, since the protective film of the present invention is a porous film, the laminated piezoelectric sheet The applied pressure is easily dispersed, so the force is propagated over a wide area of ​​the porous electret film. The method for making the protective film porous is not particularly limited, but examples thereof include For example, chemical or physical foaming and stretching can be used to make the material porous. Porosity is preferably achieved by stretching, since this allows for a good structure and the shape of the pores can be easily controlled.

[0074] Protective films include polyester resin films and polyolefin resin films. , acrylic resin film, polystyrene resin film, polycarbonate resin film Resin films such as fluorine-based resin films can be suitably used. From this viewpoint, films in which hot melt resin is laminated onto these films can also be used. These films are also readily available as commercially available laminate films. Among these, it is preferable that the protective film is made of the same material as the porous electret film. Therefore, the porous electret film is preferably made of a polyolefin resin. When using a polyolefin resin film, it is recommended to use a polyolefin resin film as the protective film. In addition, as a material for the porous electret film, for example, a polypropylene-based resin is preferable. When using a polypropylene resin film, it is recommended to use a polypropylene resin film as the protective film. preferable. If the same material is used for the protective film and the porous electret film, the dimensional change due to temperature Since the amount of deformation is the same, even if the laminated piezoelectric sheet is subjected to temperature changes such as heat processing, there will be no wrinkles or warping. It is less likely to cause cracks.

[0075] Specifically, the protective film preferably contains a polyolefin resin as a main component. It is more preferable that the protective film contains a polypropylene-based resin as the main component. When fin-based resin or polypropylene-based resin is the main component, the details of the content are as follows: This is similar to what was described for the cullet film. Among these, the protective film is made of a resin composition whose main component is polypropylene resin containing a large amount of β crystals. It is preferable that the β-crystal nucleating agent is a material having the ability to form β-crystals. It is more preferable that the protective film contains the β crystal. This is advantageous for preparing a porous structure. Regarding the physical properties and characteristics of the main component resin of the protective film, Therefore, the polypropylene resin used in the protective film may be the same as that used in the film. The details are as explained in the porous electret film.

[0076] The protective film may contain additives such as heat stabilizers and acid stabilizers to the extent that the properties of the film are not impaired. antioxidants, ultraviolet absorbers, light stabilizers, nucleating agents, colorants, antistatic agents, hydrolysis inhibitors, Various additives such as lubricants, flame retardants, conductive agents, elastomers, etc. may be appropriately contained.

[0077] The porosity of the protective film of the present invention is preferably more than 0% and not more than 50%, and more preferably 5% or more and 40% or less. more preferably, 10% or more and 30% or less, even more preferably, 15% or more. It's nice. By making the porosity of the protective film greater than 0%, the pressure applied to the laminated piezoelectric sheet is As the force is easily dispersed, it is easy for the force to propagate over a wide area of ​​the porous electret film, and the piezoelectric properties Furthermore, by setting the porosity of the protective film to 50% or less, the laminated piezoelectric sheet The impact resistance of the product is improved.

[0078] The thickness of the protective film of the present invention is preferably 1 μm or more and 100 μm or less, and more preferably 5 μm or more and 50 μm or less. It is more preferable that the thickness is 10 μm or more and 40 μm or less, and further more preferable that the thickness is 20 μm or more and 30 μm or less. It is even more preferable that the thickness is 0 μm or less. The thickness of the protective film is 1 μm or more, which ensures sufficient water resistance of the laminated piezoelectric sheet. In addition, by making the thickness of the protective film 100 μm or less, The pressure applied to the piezoelectric sheet is easily transmitted to the porous electret film, and The flexibility of this laminated piezoelectric sheet can be ensured.

[0079] <Method of manufacturing laminated piezoelectric sheet> The laminated piezoelectric sheet of the present invention is a porous electret film produced by the above method. The protective film and the electrode are laminated in the order of lamination from the outside. The order is preferably film, electrode, and porous electret film. For example, a protective film, an electrode, a porous electret film, an electrode, and a protective film are In the case of a laminated structure in which the electrodes are provided in this order, the two electrodes and the protective film are attached using an adhesive. After lamination, the two electrodes face each other with the porous electret film in between. The protective film may be overlapped as shown in FIG. 1 and the end of the protective film may be heat-sealed to seal the film.

[0080] In addition, the laminated piezoelectric sheet is a laminate of a porous electret film, electrodes, and a protective film. After the layering, the edges of the protective film may be fused to form a bag. However, the sealing method is not limited to the above, and may be a heat seal method or the like. When the bag-shaped electrode is used, it is preferable to provide two layers of electrode and protective film. For example, For example, put the protective film, electrode, porous electret film, electrode, and protective film in this order. and then heating and heat-sealing the ends of the protective films to form a bag shape. When using two protective films, the edges of the two protective films should be aligned before lamination. The portions may be partially fused together in advance. The ends of the protective film may be bonded together by a method other than heat sealing.

[0081] <Applications of porous electret film> This film can be used in, for example, actuators, oscillators, sonar, vibration power generation, sensors, etc. The porous electret film is not particularly limited, but may be, for example, By implementing wire wiring and forming an insulating film to create a piezoelectric element, It converts pressure into voltage and can detect pressure acting on a piezoelectric film or generate electricity. This can be done. Among these, it is preferable to use it as a sensor device.

[0082] [Sensor Device] The laminated piezoelectric sheet of the present invention can be used as a sensor device by providing lead wires and circuit mounting. It is possible. This laminated piezoelectric sheet has excellent water resistance and piezoelectric properties, so sensors equipped with this laminated piezoelectric sheet are The devices include vibration power generation, water level gauge, acoustic detector, mat sensor, robot hand Do etc. are preferred. [Example]

[0083] Examples and comparative examples are given below to explain the film and laminated piezoelectric sheet in more detail. However, the present invention is not limited to these.

[0084] <Measurement method> (1) Melt flow rate (MFR) Polyolefin resin (A) conforms to JIS K7210-1 (2014) The MFR(A) was measured under the conditions of a temperature of 230°C and a load of 2.16 kg. In addition, styrene-based thermoplastic elastomer (B) is In accordance with the 2014 standard, MFR(B) was measured at a temperature of 200°C and a load of 10 kg. The difference between the obtained MFR(A) and MFR(B) values ​​(MFR(A) - MFR(B) ) was calculated. In addition, if the material did not flow in the above MFR measurement, the MFR value was set to 0. did.

[0085] (2) Thickness Cut the film into 10cm squares and measure it with a dial gauge with a graduation of 1 / 1000mm. The sample was divided into nine equal parts, and the film thickness was measured at nine points, and the average value was taken as the thickness.

[0086] (3) Air resistance (air permeability) at 25°C Air resistance measured in an air atmosphere at 25°C in accordance with JIS P8117:2009 The measuring device used was a digital Oken-type dedicated air permeability measuring machine (manufactured by Asahi Seiko Co., Ltd.).

[0087] (4) Porosity This film was cut into a 10 cm square, and the density ρ1 (apparent density) was measured. % density ρ0 (true density) is calculated, and the porosity is calculated from these values ​​using the following formula: did. Porosity (%)=(1-ρ1 / ρ0)×100

[0088] (5) Average pore size and aspect ratio The porous films prepared in the examples and comparative examples were cut in the TD direction and the cut surfaces were analyzed by scanning electron microscope. The images were taken using a microscope (SEM) at a magnification of 1000x. Analysis was performed using image analysis software (Image-J). The SEM image was cut out to a range of 1280 x 360 pixels (512 pixels = 50 μm). Image brightness and contrast are adjusted and binarized so that the resin part is white and the void part is black. After this, median processing (Median value 1.0) is applied to the resulting image to remove noise. The film was removed and a binary image of the cross section was obtained. An ellipse approximation analysis was performed on the black areas (holes) of the obtained binary image, and the long axis and The length of the minor axis is measured, and the average ratio of the length of the major axis to the length of the minor axis (major axis / minor axis) is calculated. It is defined as the aspect ratio of the hole. The average value of the major axis length of the pores obtained by the above analysis is shown in Table 1 as the average pore diameter. Ta.

[0089] (6) Piezoelectric constant d 33 The piezoelectric film was cut into a piece 50 mm wide x 50 mm long to serve as a measurement sample. Using a Techno piezometer, the specimen on the measurement sample was divided into nine equal parts. The piezoelectric constant in the thickness direction (d 33 ) was measured by the quasi-static method and the average value was calculated. The terminal of the piezometer is cylindrical with a diameter of 8 mm, and the clamp load is 0.4 N and the static load is 1.0 Measurements were carried out with a dynamic load of 1.3N. The piezoelectric constant (d 33 (Initial)) and at a temperature of 24°C and a relative humidity of 50% Piezoelectric constant (d 33 (After 1 month)) was measured, and from these values, the following formula was used Based on 33 The retention rate was calculated. 33 A retention rate of 65% or more is considered to be stable over time. was judged to be good. d 33 Retention rate (%)=(d 33 (1 month later) / d 33 (Initial)) x 100

[0090] <Material> (Polyolefin resin (A)) Homopolypropylene (weight average molecular weight (Mw): 254,300, molecular weight distribution (Mw / Mn):5.03, MFR(230℃, 2.16kg):10g / 10min)

[0091] (Styrene-based thermoplastic elastomer (B)) Styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS )(Weight average molecular weight (Mw): 196,000, molecular weight distribution (Mw / Mn): 1.07, MFR (230℃, 2.16kg): No flow, MFR (200℃, 10kg): No flow Styrene content: 32% by mass

[0092] (Nucleating Agent (C)) β-crystal nucleating agent (3,6-bis[4-(N-cyclohexylcarbamoyl)phenyl]-2, 4,8,10-tetraoxaspiro[5.5]undecane

[0093] <Preparation of porous film> (Examples 1-6, Comparative Examples 1 and 2) 60% by mass of polyolefin resin (A) and styrene-based thermoplastic elastomer (B) 40% by mass, and the nucleating agent (C) is added in an amount of 0.0 parts by mass per 100 parts by mass of the resin component. The materials mixed at a ratio of 5 parts by mass were fed into a φ40 mm twin-screw extruder and melted at a set temperature of 205°C. After melt-kneading, the mixture is formed into a sheet using a T-die, and then the sheet is placed on a cast roll set at 95°C. The sheet was cooled and solidified to obtain a pre-stretched sheet having a thickness of 220 μm. Thereafter, the obtained unstretched sheet was placed between a roll (X) set at 20°C and a roll (X) set at 20°C. Between the rolls (Y), the film was stretched at the ratio shown in the table. The film was then subjected to high-temperature heat treatment on the roll (P) to obtain a MD-stretched porous film. The MD stretched porous film was placed in a film tenter made by Kyoto Kikai Co., Ltd. at a preheat temperature of 145°C. After preheating at 145°C, the film was stretched in the transverse direction at the ratio shown in the table at a stretching temperature of 145°C, and then stretched at 155°C. A heat treatment was carried out to obtain a biaxially stretched porous film. The obtained porous film was placed on an earth plate, and wire electrodes were used, with the distance between the electrodes being 30 mm. The porous electrolytic capacitor was charged by applying a voltage of 10 kV at an electrode moving speed of 40 mm / sec. A trot film was obtained. The evaluation results of the obtained porous electret film are summarized in Table 1.

[0094] [Table 1]

[0095] Examples 1 to 6 contain a polyolefin resin and a styrene-based thermoplastic elastomer, It is a porous electret film with a predetermined aspect ratio and has high piezoelectric properties. In addition, the stability over time was also excellent. On the other hand, in Comparative Examples 1 and 2, the aspect ratio was not within the predetermined range, and the stability of the piezoelectric properties over time was poor. It was inferior. [Industrial Applicability]

[0096] This film has excellent piezoelectricity and stability over time. The laminated piezoelectric sheet manufactured using film is a piezoelectric film with excellent stability of signal strength. Such sensor devices and other products are useful, and the technology of the present invention is This is a technology with great industrial value.

Claims

1. A porous elastomer comprising a polyolefin resin (A) and a styrene-based thermoplastic elastomer (B). A rectret film having an average aspect ratio of pores of 4.0 or more and 20 or less. Perforated electret film.

2. The melt flow rate of the polyolefin resin (A) was measured at a temperature of 230° C. and a load of 2.16 kg.

2. The porous electret according to claim 1, wherein the roll rate (MFR(A)) is 8 g / 10 min or more. Red film.

3. The styrene content of the styrene-based thermoplastic elastomer (B) is 10% by mass or more and 50% by mass or less.

2. The porous electret film according to claim 1, wherein the porous electret film has a molecular weight of 0.1 or less.

4. The melt flow rate of the thermoplastic elastomer (B) at a temperature of 200°C and a load of 10 kg 2. The porous electret according to claim 1, wherein the melt flow rate (MFR(B)) is 2.0 g / 10 min or less. Red film.

5. The melt flow rate of the polyolefin resin (A) was measured at a temperature of 230° C. and a load of 2.16 kg. The styrene-based thermoplastic elastomer (B) is mixed with the low-molecular weight elastomer (MFR(A)) at a temperature of 20 The difference between the melt flow rate (MFR(A)) at 0°C and a load of 10 kg (MFR(B)) The porous electret filter according to claim 1, wherein the MFR (B) is 6 g / 10 min or more. Room.

6. The porous membrane according to claim 1, wherein the polyolefin resin (A) is a polypropylene resin. Electret film.

7. The porous electret film according to claim 1, comprising a β-crystal nucleating agent (C).

8. At least one surface of the porous electret film according to any one of claims 1 to 7 A laminated piezoelectric sheet provided with an electrode layer.

9. A sensor device using the laminated piezoelectric sheet according to claim 8.

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