JP2014090916A - Acoustic sensor, and acoustic monitoring device equipped with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an acoustic sensor whose frequency region for sound collection can be efficiently adjusted, and whose sound collection sensitivity is high.SOLUTION: An acoustic sensor 20 includes: a cylindrical spacer 21; a diaphragm 23 fitted to a spacer to close one side opening of the spacer; a back plate 26 for closing the another side opening of the spacer; a vibrating electrode film 27 provided on the back plate side surface of the diaphragm 23; a back electrode film 28 provided on the diaphragm side surface of the back plate 26; and an electret film 29. The diaphragm 23 is provided with a groove 24 formed on the inner side than an inner surface of the cylindrical spacer 21 to divide the diaphram 23 into an inside area 23i and an outside area 23o. The electret film 29 is formed on the back electrode film side surface of the vibrating electrode film 27 and on the inner side than the groove 24.

Description

  The present invention relates to an acoustic sensor including an electret film and an acoustic monitor device including the acoustic sensor.

  For example, a microphone is known as an acoustic sensor including an electret film (Patent Documents 1 and 2).

  The microphone described in Patent Document 1 includes a vibration film formed of a conductive material, a back electrode plate facing the vibration film, and a spacer for maintaining a distance between the back electrode plate and the vibration film. Yes. An electret film is formed on the back electrode plate on the surface facing the vibration film.

  In addition, the microphone described in Patent Document 2 is for maintaining a gap between a diaphragm formed of a conductive material, a case formed with a back surface facing the diaphragm, and the back surface of the case and the diaphragm. A spacer and an electret film formed on the back surface of the case are provided. This microphone is used to detect a sound having a relatively low frequency of 100 Hz or less, such as a Korotov sound that is generated when a person's artery is tightened.

  In addition, as a technique related to the present invention, a technique related to an electronic stethoscope using a microphone is known (Patent Documents 3 and 4). The electronic stethoscope includes a microphone, a housing as a stethoscope head case that houses the microphone, and an earphone that converts an electric signal from the microphone into sound.

JP 2011-82723 A JP 2011-10913 A JP-T 8-506495 JP 2011-19799 A

  As an acoustic sensor that can be used in an acoustic monitor device typified by an electronic stethoscope, an acoustic sensor that efficiently adjusts a frequency band for collecting sound and has high sound collection sensitivity is desired. However, the microphones described in Patent Documents 1 to 4 have a problem that the sound collection sensitivity is low.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an acoustic sensor that efficiently adjusts a frequency band for collecting sound and has high sound collection sensitivity, and an acoustic monitor device including the same.

The present invention is an acoustic sensor having the following configurations [1] to [9], and an acoustic monitor device having the following configurations [10] to [12].
[1] A cylindrical spacer having both ends open, a diaphragm attached to the spacer so as to block one opening of the spacer, and the other of the spacers facing the diaphragm A back plate that closes the opening, a vibrating electrode film that is formed of a conductive material and provided on the back plate side of the diaphragm, and is formed of a conductive material and provided on the diaphragm side of the back plate. A back electrode film and an electret film,
A groove for dividing the diaphragm into an inner region and an outer region is formed inside the inner surface of the spacer, and the electret film is one of the vibrating electrode film and the back electrode film. An acoustic sensor, which is formed on the other electrode film side of the electrode film and inside the groove.
[2] The acoustic sensor according to [1], wherein the groove is formed on the back plate side of the diaphragm.
[3] The acoustic sensor according to [1] or [2], wherein a weight is provided in a region opposite to the back plate of the diaphragm and inside the groove.
[4] An elastic member having elasticity and disposed between the end face on the one opening side of the spacer and the diaphragm, and the diaphragm is attached to the spacer via the elastic member. The acoustic sensor according to any one of [1] to [3].
[5] The acoustic sensor according to any one of [1] to [4], wherein the electret film is formed on the back plate side of the vibrating electrode film.
[6] The acoustic sensor according to any one of [1] to [5], wherein the electret film is obtained by injecting electric charge into a resin film using a fluoropolymer.
[7] The electret film is obtained by injecting electric charge into a resin film using a fluoropolymer (a) having an aliphatic ring in the main chain or a derivative (a ′) of the fluoropolymer (a). The acoustic sensor according to any one of [1] to [5].
[8] The acoustic sensor according to [7], wherein the fluoropolymer (a) has a reactive functional group.
[9] The resin film comprises the derivative (a ′), and the derivative (a ′) is a mixture or reaction product of the fluoropolymer (a) and a silane coupling agent having an amino group. The acoustic sensor according to [7] or [8], including an object.

[10] Sound information output that outputs, as sound information, a change in potential difference between the acoustic sensor of any one of [1] to [9] and vibration electrode film and back electrode film due to vibration of the diaphragm. And an acoustic monitor device.
[11] A cylindrical stethoscope head case having an opening formed on at least one end thereof, and a diaphragm for closing the opening of the stethoscope head case,
The acoustic sensor is disposed in the stethoscope head case, and a region inside the groove of the diaphragm of the acoustic sensor is attached to the diaphragm, and the change in the potential difference is detected as the sound information output device. The acoustic monitor device according to [10], including a pair of left and right earphones that output as
[12] A cylindrical stethoscope head case having an opening formed on at least one end thereof, a diaphragm for closing the opening of the stethoscope head case, and a stethoscope head case [3] An acoustic sensor and a pair of left and right earphones that output an electric signal as a sound, which is a change in potential difference between the vibrating electrode film and the back electrode film due to vibration of the diaphragm,
An acoustic monitor device, wherein the weight provided on the diaphragm of the acoustic sensor is attached to the diaphragm.

  ADVANTAGE OF THE INVENTION According to this invention, the frequency band which collects sound can be adjusted efficiently, and sound collection sensitivity can be improved.

It is sectional drawing of the acoustic sensor in one Embodiment which concerns on this invention. It is the II arrow directional view in FIG. It is a circuit diagram of an acoustic monitor device in one embodiment concerning the present invention. It is a circuit diagram of the modification of the acoustic monitor apparatus in one Embodiment which concerns on this invention. It is a principal part notched side view of the acoustic monitor apparatus (electronic stethoscope) in one Embodiment which concerns on this invention.

  An acoustic sensor according to the present invention has a cylindrical shape and is open at both ends, a diaphragm attached to the spacer so as to close one opening of the spacer, and the diaphragm. A back plate that closes the other opening of the spacer, a vibration electrode film that is formed of a conductive material and is provided on the back plate side of the vibration plate, and is formed of a conductive material, and the vibration plate of the back plate A back electrode film provided on the side, and an electret film, and the diaphragm is formed with a groove dividing the diaphragm into an inner region and an outer region inside the inner surface of the spacer, The electret film is formed on the other electrode film side of one of the vibrating electrode film and the back electrode film and inside the groove.

  In the acoustic sensor, of the vibrating electrode film provided on the diaphragm and the back electrode film provided on the back plate, the electrode film on which the electret film is not formed is caused by the surface charge of the electret film. A charge having a polarity opposite to the surface charge is electrostatically induced. When the diaphragm vibrates relative to the back plate, the distance between the electret film and the electrode film on which the electret film is not formed changes. For this reason, the amount of charge electrostatically induced in the electrode film on which the electret film is not formed changes with this distance change. As a result, the potential difference between the electrode film on which the electret film is formed and the electrode film on which the electret film is not formed changes with vibration. In the acoustic sensor, the change in the potential difference becomes sound information of the sound that vibrates the diaphragm.

  When the outer peripheral edge of the diaphragm is firmly fixed to the spacer, the vibration amplitude of the diaphragm is basically reduced, and the sound collection sensitivity tends to be lowered. However, in the present invention, a groove that divides the diaphragm into an outer region and an inner region is formed in the diaphragm, so even if the outer peripheral edge in the outer region of the diaphragm is firmly fixed to the spacer, The inner region of the diaphragm is likely to vibrate starting from the groove. For this reason, in the present invention, even if the outer peripheral edge of the diaphragm is firmly fixed to the spacer, the amplitude of the inner region in the vibration of the diaphragm is increased, and the sound collection sensitivity of the acoustic sensor can be increased.

  In addition, the sound collection sensitivity of the acoustic sensor increases as the surface charge density of the electret film increases. As will be described in detail later, the electret film retains a high surface charge density by using a resin film using a fluoropolymer as a charge retention medium constituting the electret film. By using a resin film using a fluoropolymer as the charge retention medium, the sound collection sensitivity of the acoustic sensor, particularly the sound collection sensitivity in a low frequency region can be increased.

  The sound collection frequency band of the acoustic sensor is a frequency band centered on the natural frequency of the vibration system including the diaphragm and the vibrating electrode film. For this reason, the sound collection frequency band of the acoustic sensor can be changed by changing the natural frequency of the vibration system. In the vibration system, the natural frequency becomes smaller as the distance between the two opposite positions with respect to the inner region of the diaphragm becomes larger at a predetermined position in the groove where the vibration starts. In other words, in the vibration system, the natural frequency increases as the distance between the two opposing portions decreases. Therefore, in the present invention, the sound collection frequency band can be efficiently adjusted by changing the interval between two opposing grooves.

  By connecting a sound information output device that outputs a change in potential difference between the vibrating electrode film and the back electrode film as sound information to the acoustic sensor, an acoustic monitor device is connected to the acoustic sensor and the sound information output device. Can be configured. The sound information output from the sound information output device includes not only the sound itself that vibrates the diaphragm itself but also information indicating the acoustic characteristics of the sound graphically, information indicating numerically, and the like.

  An example of an acoustic monitor device is an electronic stethoscope. In this case, the acoustic sensor is incorporated in a stethoscope head, and an electrical signal from the acoustic sensor is output to a pair of earphones as a sound information output device. When the acoustic sensor is used as a sound collection sensor for a stethoscope, the acoustic sensor can collect heart abdominal sounds, excess heart sounds, heart noise, blood vessel sounds, Korotov sounds, lung sounds, and abdominal visceral sounds. preferable. All of these sounds have a relatively low frequency. Therefore, it is preferable to use a fluorine-containing polymer capable of enhancing sound collection sensitivity in a low frequency region as the resin film (A) which is a kind of material forming the electret film of the acoustic sensor. Furthermore, while suppressing an increase in the size of the stethoscope head and the acoustic sensor incorporated in the stethoscope head, the natural frequency in the vibration system of the acoustic sensor is reduced to lower the sound collection frequency range of the acoustic sensor. In addition, it is preferable to provide a weight on the diaphragm.

  In the present invention, the acoustic monitor device is not limited to an electronic stethoscope. For example, instead of the earphone, a speaker that allows many people to hear the generated sound at the same time, a display that displays acoustic characteristics as sound information, and a printer that prints acoustic characteristics may be connected to the acoustic sensor. . The acoustic monitor device may be a device for monitoring not only the sound generated from the human body but also other sounds, for example, fluid sound in piping, internal sounds of containers, buildings, and the like.

  Hereinafter, an embodiment of an acoustic sensor according to the present invention and an acoustic monitor device including the acoustic sensor will be described with reference to the drawings.

[Configuration of acoustic monitor device]
FIG. 5 shows an acoustic monitor device of the present embodiment.
The acoustic monitor device of the present embodiment is an electronic stethoscope, and includes a stethoscope head 1 that comes into contact with a target human body and the like, and a pair of left and right earphones 2 as sound information output devices that are worn on the ears of a doctor or the like. I have.

  The stethoscope head 1 includes a cylindrical stethoscope head case 10 having a circular opening 11 formed at one end thereof, a diaphragm 12 that closes the opening 11 of the stethoscope head case 10, and the stethoscope head case 10. The disposed acoustic sensor 20 and an electrical circuit 15 that amplifies an electrical signal from the acoustic sensor 20 are provided. The diaphragm 12 has a disk shape so as to close the circular opening 11 of the stethoscope head case 10. The thickness of the diaphragm 12 is, for example, 200 μm. Examples of the material for forming the diaphragm 12 include inorganic materials such as glass, and organic materials such as polyethylene terephthalate, polyimide, polycarbonate, and acrylic resin. The acoustic sensor 20 is bonded to the surface 12 b of the diaphragm 12 facing the inside of the stethoscope head case 10. The electric circuit 15 is fixed to a substrate constituting the acoustic sensor 20. The electric circuit 15 and each earphone 2 are connected by an earphone cord 3.

[Configuration of acoustic sensor]
FIG. 1 shows a cross-sectional view of the acoustic sensor 20.
The acoustic sensor 20 has a cylindrical shape, a spacer 21 having both ends opened (21 a, 21 b), a disk-shaped diaphragm 23 that closes one opening 21 a of the spacer 21, and the diaphragm 23. The disk-like back plate 26 that covers the other opening 21 b of the spacer 21, the vibrating electrode film 27 formed on the back plate-side surface 23 b of the diaphragm 23, and the diaphragm-side surface 26 a of the back plate 26. The back electrode film 28 is formed on the diaphragm 27, the electret film 29 is formed on the diaphragm-side surface 27b of the vibration electrode film 27, and the surface 23a of the diaphragm 23 opposite to the back plate 26 is fixed to the surface 23a. A weight 31 and an elastic member 32 disposed between the end face 21c on the one opening 21a side of the spacer 21 and the diaphragm 23.

  The spacer 21 is for maintaining a gap between the outer peripheral edge of the diaphragm 23 and the outer peripheral edge of the back plate 26. The material of the spacer 21 is not particularly limited, and may be a conductive material such as metal or an insulating material. However, the material of the spacer 21 is preferably an insulating material from the viewpoint of weight reduction of the acoustic sensor 20 and durability (resistance of discharge) of the electret film 29. As the insulating material, an organic material is preferable.

The diaphragm 23 and the back plate 26 are made of an insulating material. The resistance value of the insulating material is preferably 10 ¹⁰ Ωcm or more, and particularly preferably 10 ¹² Ωcm or more, in terms of volume specific resistance value. Specific examples of the insulating material include inorganic materials such as glass, and organic materials such as polyethylene terephthalate, polyimide, polycarbonate, and acrylic resin.

  The disk-shaped diaphragm 23, the back plate 26, and the cylindrical spacer 21 all have an outer diameter D1 of 20 mm in this embodiment. Further, the thickness D2 of the diaphragm 23 is 0.4 mm, and the thickness D3 of the back plate 26 is 0.4 mm. A thickness D4 obtained by adding the thickness of the spacer 21 and the thickness of the elastic member 32 is 0.1 mm.

  A groove 24 is formed in the surface 23b on the back plate side of the disc-shaped diaphragm 23. The groove 24 is recessed on the side opposite to the back plate side. The groove 24 is formed by, for example, etching or machining. The groove width and groove depth D5 of the groove 24 are preferably 1/20 to 1/8 of the thickness D2 of the diaphragm 23 when the diaphragm 23 is made of glass. A thickness of 1/13 to 1/10 of the thickness D2 is particularly preferable. Specifically, in the present embodiment, since the thickness D4 of the diaphragm 23 is 0.4 mm, the groove width and the groove depth D3 of the groove 24 are 0.02 (20 μm) to 0.05 (50 μm). ) Is preferable, and 0.03 (30 μm) to 0.04 (40 μm) is particularly preferable.

  FIG. 2 is a view taken in the direction of arrow II in FIG. The groove 24 extends in the circumferential direction Dc with reference to the center C of the disc-shaped diaphragm 23. For this reason, the diaphragm 23 is divided into an inner region 23 i and an outer region 23 o by the groove 24. However, the groove 24 is not formed at 360 ° with respect to the center C of the disc-shaped diaphragm 23, and a part of the circumferential direction Dc with respect to the center C (hereinafter, referred to as a flat portion 25). ) Is not formed. As will be described later, the groove 24 forms the signal line 18 from the vibrating electrode film 27 formed in the inner surface 23 i of the diaphragm 23 in the surface 23 b on the back plate side of the diaphragm 23. This is for extending to the outside of the groove 24, that is, the outside region 23 o through the flat portion 25 that is not formed. The diameter D6 (see FIG. 1) of the inner peripheral edge of the groove 24 extending in the circumferential direction Dc is, for example, 10 mm in this embodiment.

  The vibration electrode film 27 is formed in the inner surface 23 i of the vibration plate 23 in the surface 23 b on the rear plate side of the vibration plate 23. Further, the back electrode film 28 is formed in a region including the region facing the inner region 23 i of the diaphragm 23 in the surface 26 a on the diaphragm side of the back plate 26.

Each of the vibrating electrode film 27 and the back electrode film 28 (hereinafter, the vibrating electrode film 27 and the back electrode film 28 may be simply referred to as an electrode film) may be composed of a single layer. These layers may be formed, and a structure having a distribution in composition may be formed.
The thickness of the electrode film (in the case of a plurality of layers, the total thickness) is preferably 10 to 1,000 nm, and particularly preferably 100 to 500 nm. When the thickness is within the above range, the conductivity and productivity are excellent. The thickness can be measured by, for example, a stylus type surface shape measuring instrument (such as DEKTAK8 manufactured by ULVAC).

The material for forming the electrode film is not particularly limited as long as it has conductivity. The resistance value of the material is preferably 0.1 Ωcm or less, particularly preferably 0.01 Ωcm or less in terms of volume resistivity.
Specific examples of the conductive material include gold, silver, copper, nickel, chromium, aluminum, titanium, tungsten, molybdenum, tin, cobalt, palladium, platinum, and alloys containing at least one of these as a main component. Can be mentioned. Moreover, organic conductive films composed of metal oxide conductive films such as ITO (Indium Tin Oxide) and IZO (Indium Zinc Oxide), polyaniline, polypyrrole, polythiophene conductive polymer (PEDOT / PSS), carbon nanotubes and the like can also be exemplified.

The formation method of an electrode film is not specifically limited, A well-known method can be utilized as a formation method of an electroconductive thin film, such as a physical vapor deposition method and an electroless plating method.
Examples of physical vapor deposition include sputtering, vacuum vapor deposition, and ion plating.
The electroless plating method is selected on the surface of the substrate on which the catalyst has adhered by immersing the substrate with the catalyst on the surface in an electroless plating solution containing a metal salt, reducing agent, etc., and the reducing power of electrons generated from the reducing agent. In this method, a metal is deposited to form an electroless plating film.
As metal salts contained in the electroless plating solution, nickel salts (nickel sulfate, nickel chloride, nickel hypophosphite, etc.), cupric salts (copper sulfate, copper chloride, pyrophosphoric acid, etc.), cobalt salts ( Cobalt sulfate, cobalt chloride, etc.), noble metal salts (chloroplatinic acid, chloroauric acid, dinitrodiammine platinum, silver nitrate, etc.).
Examples of the reducing agent contained in the electroless plating solution include sodium hypophosphite, formaldehyde, sodium tetrahydroborate, dialkylamine borane, hydrazine and the like.
When forming a conductive thin film by an electroless plating method, it is preferable to attach a catalyst to the surface of the substrate in advance before forming the conductive thin film. Examples of the catalyst include metal fine particles, metal-supported fine particles, colloids, and organometallic complexes.

  The electret film 29 is a film-like charge holding medium in which a homo charge (independent charge) is held therein by injecting positive or negative charge. The electret film 29 is formed on the surface of the vibrating electrode film 27, that is, on the surface 27 b of the vibrating electrode film 27 on the back electrode film side. The charge carrier, the film formation method, and the charge injection method will be described in detail later.

The elastic member 32 has a ring shape, and is disposed between the end surface 21c on the one opening 21a side of the spacer 21 and the outer peripheral edge of the diaphragm 23 as described above. The elastic member 32 is bonded to the end face 21 c on the one opening 21 a side of the spacer 21 and the outer peripheral edge of the diaphragm 23. That is, the diaphragm 23 is attached to the spacer 21 via the elastic member 32.
As a material for forming the elastic member 32, a known material having flexibility can be used. The elastic member 32 is preferably a double-sided tape in which an adhesive is applied to both sides of a base material made of a forming material in that it has a function of adhering the diaphragm 23 to the spacer 21. The substrate is preferably a film or a nonwoven fabric. For example, 9347 (product number) manufactured by 3M may be used. The thickness of the elastic member 32 is, for example, 150 μm.

  The weight 31 is bonded to the center portion of the disc-shaped diaphragm 23 in the surface 23a of the diaphragm 23 opposite to the back plate 26. The material for forming the weight 31 is preferably relatively high in specific gravity among metals that are relatively inexpensive and easy to handle, for example, copper. The weight 31 is further bonded to a surface 12b of the diaphragm 12 facing the inside of the stethoscope head case 10 as shown in FIG. The acoustic sensor 20 is attached to the diaphragm 12 by the weight 31 being bonded to the diaphragm 12.

  The weight 31 is for adjusting the natural frequency of the vibration system including the diaphragm 23, the vibrating electrode film 27, and the electret film 29 that vibrates with the vibration of the diaphragm 12. For this reason, the weight of the weight 31 is appropriately set depending on the value of the natural frequency of the vibration system.

[Configuration of electrical circuit]
FIG. 3 shows a circuit diagram of the electric circuit 15. The electric circuit 15 includes an amplifier 16 and a battery 17 for driving the amplifier 16.
The vibrating electrode film 27 and the back electrode film 28 are both electrically connected to the earphone 2 and the signal line 18. The amplifier 16 is provided in the signal line 18. Among the signal lines 18, the signal line 18 closer to the earphone 2 than the electric circuit 15 constitutes a part of the earphone cord 3 described above.
As shown in FIG. 5, the electric circuit 15 is fixed to the surface of the acoustic sensor 20 opposite to the weight 31, that is, the surface opposite to the diaphragm side of the back plate 26.

[Operations of acoustic monitor device and acoustic sensor]
For example, when the stethoscope head 1 of an electronic stethoscope that is an acoustic monitor device is brought into contact with a target part of a human body, the diaphragm 12 of the stethoscope head 1 vibrates due to vibration of the target part or sound generated from the vicinity of the target part ( FIG. 4). Since the acoustic sensor 20 is attached to the diaphragm 12, the entire acoustic sensor 20 vibrates with the vibration of the diaphragm 12. However, among the components of the acoustic sensor 20, the amplitude of the diaphragm 23 is larger than the amplitude of the back plate 26. This is because the only member interposed between the diaphragm 12 and the diaphragm 23 is the weight 31 with respect to the diaphragm 23, while the weight 31, the diaphragm 23, the elastic member 32, the spacer 21 and the back plate 26 are This is because there are many. Therefore, the diaphragm 23 vibrates relative to the back plate 26. The amplitude direction V of the vibration is a direction in which the diaphragm 23 and the back plate 26 are arranged.

  When the diaphragm 23 is not vibrating relative to the back plate 26, the back electrode film 28 formed on the surface of the back plate 26 has a surface of the electret film 29 attached to the diaphragm 23. A certain charge having a polarity opposite to that of the surface charge is electrostatically induced by the charge. In a state where the vibration plate 23 vibrates relative to the back plate 26, the distance between the electret film 29 and the back electrode film 28 changes. For this reason, the amount of charge electrostatically induced in the back electrode film 28 changes with this distance change. As a result, the potential difference between the vibrating electrode film 27 on which the electret film 29 is formed and the back electrode film 28 changes with vibration. The change in the potential difference is sent as an electrical signal to the earphone 2 through the signal line 18, and is reproduced as sound by the earphone 2 and output.

[Operations and effects of acoustic monitoring device and acoustic sensor]
The sound collection sensitivity of the acoustic sensor 20 increases as the amplitude of the vibration of the diaphragm 23 accompanying the vibration of the diaphragm 12 increases. When the outer peripheral edge of the diaphragm 23 is firmly fixed to the spacer 21, the amplitude of the vibration of the diaphragm 23 accompanying the diaphragm 12 is basically reduced. However, in this embodiment, since the diaphragm 23 is formed in the diaphragm 23 to divide the diaphragm 23 into the outer region 23o and the inner region 23i, the outer peripheral edge portion in the outer region 23o of the diaphragm 23 is a spacer. Even if firmly fixed to 21, the inner region 23 i of the diaphragm 23 tends to vibrate starting from the groove 24. For this reason, in this embodiment, even if the outer peripheral edge part of the diaphragm 23 is firmly fixed to the spacer 21, the amplitude of the inner region 23i in the vibration of the diaphragm 23 accompanying the vibration increases in the diaphragm 12, and the acoustic sensor The sound collection sensitivity of 20 can be increased.

  In addition, the sound collection sensitivity of the acoustic sensor 20 increases as the surface charge density of the electret film 29 increases. As will be described in detail later, a resin using a fluorine-containing polymer, particularly a fluorine-containing polymer (a), or a derivative (a ′) of the fluorine-containing polymer (a) as a charge retention medium constituting the electret film 29 By using the film, the charge holding performance of the charge holding medium is enhanced, and the electret film 29 formed by injecting charges into the charge holding medium has a high surface charge density. By using a resin film using a fluorine-containing polymer, particularly a fluorine-containing polymer (a), or a derivative (a ′) of the fluorine-containing polymer (a) as a charge holding medium, the sound collection sensitivity of the acoustic sensor 20 is obtained. Can be increased.

The sound collection frequency band of the acoustic sensor 20 is a frequency band centering on the natural frequency of the vibration system including the diaphragm 23, the vibration electrode film 27, and the electret film 29. For this reason, the sound collection frequency band of the acoustic sensor 20 can be changed by changing the natural frequency of the vibration system.
When considering the vibration of the vibration system, a doubly supported beam can be used as a model of the vibration system. The dual-support beam has a lower natural frequency as the distance between the beam support points increases. In addition, the natural frequency decreases as the beam density increases. For this reason, in the vibration system in the acoustic sensor 20 of the present embodiment, the natural frequency decreases as the diameter D6 (see FIG. 1) of the inner peripheral edge of the groove 24 corresponding to the distance between the fulcrums of the beam increases. Further, in the vibration system, the natural frequency decreases as the weight 31 that affects the density of the vibration system increases.
Therefore, in the present embodiment, the sound collection frequency band can be efficiently adjusted by changing the diameter D6 of the inner peripheral edge of the groove 24 or changing the weight of the weight 31.

When the acoustic sensor 20 is applied to an electronic stethoscope, it is preferable that abdominal visceral sounds and the like can be collected in addition to heart sounds, excessive heart sounds, heart noises, blood vessel sounds, Korotov sounds, lung sounds, and the like. Since all of these sounds have a relatively low frequency, the sound collection frequency band of the acoustic sensor 20 is preferably a low frequency band of about 1 to 100 Hz.
In the acoustic sensor 20 of the present embodiment, by increasing the diameter D6 of the inner peripheral edge of the groove 24, the natural frequency of the vibration system is reduced and the sound collection frequency band is reduced. However, increasing the diameter D6 of the inner peripheral edge of the groove 24 is to increase the diameter of the spacer 21 which is the diameter of the acoustic sensor 20, so that the stethoscope head 1 incorporating the acoustic sensor 20 is increased in size. Connected. Therefore, in the present embodiment, the weight 31 is attached to the diaphragm 23 to increase the weight of the vibration system of the acoustic sensor 20, so that the acoustic sensor 20 and the stethoscope head 1 incorporating the same are not enlarged. The sound collection frequency band of the acoustic sensor 20 is set to about 0.1 to 100 Hz.

  By the way, the vibration system in the acoustic sensor 20 can be configured with only the vibrating electrode film 27 without the diaphragm 23. However, when the weight 31 is provided in order to make the sound collection frequency band of the acoustic sensor 20 about 0.1 to 100 Hz without increasing the size of the acoustic sensor 20, the vibration electrode film 27 vibrates even if the weight 31 is attached. Therefore, the vibration system cannot be constituted by the vibration electrode film 27 alone. Therefore, in the present embodiment, the diaphragm 23 is provided in order to ensure the strength that can withstand vibration even when the weight 31 is attached, and the weight 31 is attached to the diaphragm 23.

  Since the diaphragm 23 needs to have a strength that can withstand vibration even when the weight 31 is attached, if the outer peripheral edge of the diaphragm 23 is firmly fixed to the spacer 21, as described above, the vibration of the diaphragm 12 is prevented. The amplitude in the vibration of the diaphragm 23 accompanying it becomes small, and the sound collection sensitivity of the acoustic sensor 20 falls. However, in this embodiment, as will be repeated, a groove 24 is formed in the diaphragm 23 inside the outer peripheral edge fixed to the spacer 21, and the inner region of the diaphragm 23 starts from the groove 24. Since 23i is easy to vibrate and the amplitude of the central portion of the diaphragm 23 is increased, the acoustic sensor 20 can be highly sensitive.

  That is, in the present embodiment, the sound collection frequency band of the acoustic sensor 20 is set to a low frequency band of about 0.1 to 100 Hz without increasing the size of the acoustic sensor 20 and the stethoscope head 1 incorporating the acoustic sensor 20. In order to realize sensitivity, not only the vibration electrode film 27 but also the vibration plate 23 is provided in the vibration system of the acoustic sensor 20, a weight 31 is attached to the vibration plate 23, and a groove 24 is formed in the vibration plate 23. Yes.

Further, in this embodiment, since the diaphragm 23 is attached to the spacer 21 via the elastic member 32, the collection of high-frequency frictional sound generated when the stethoscope head 1 is slid on the surface of the human body is suppressed. be able to.
The diaphragm 23 vibrates with the vibration of the diaphragm 12 of the stethoscope head 1. The vibration of the diaphragm 23 is transmitted through the elastic member 32 and the spacer 21 to the back plate 26 on which the back electrode film 28 is formed. However, most of the high frequency vibration is absorbed by the elastic member 32 in the process in which the vibration of the diaphragm 23 is transmitted to the back plate 26. For this reason, even if the diaphragm 12 vibrates at high frequency, the back plate 26 on which the back electrode film 28 is formed does not vibrate relative to the diaphragm 23. Therefore, in the present embodiment, it is possible to suppress the collection of high-frequency frictional sound that occurs when the stethoscope head 1 is slid on the surface of the human body.

[Electret film]
An insulating material conventionally used for electrets can be used for the charge retention medium constituting the electret film. The insulating material may be an organic insulating material or an inorganic insulating material.
Examples of organic insulating materials include polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and tetrafluoroethylene-ethylene copolymer. Fluoropolymers (fluorine resins) such as (ETFE); hydrocarbon polymers such as polypropylene, polystyrene, and cycloolefin copolymers; polycarbonates; materials derived from these polymers.
Examples of the material derived from the polymer include a mixture of the polymer and other components other than the polymer, a reaction product of the polymer and other components other than the polymer, and the like.
Examples of the inorganic insulating material include a silicon oxide film and a silicon nitride film formed by thermal oxidation or plasma CVD.
The charge retention medium is preferably a resin film using a fluoropolymer because it has high insulating properties and low water absorption. In addition, since it has excellent surface potential and charge retention stability (both room temperature stability and heating stability), a polymer having an aliphatic ring structure in the main chain or a material derived from the polymer is used. The resin film used is preferred. A resin film (hereinafter sometimes referred to as resin film (A)) using a fluoropolymer (a) having an aliphatic ring in the main chain or a derivative (a ′) of the fluoropolymer (a). Particularly preferred.
The resin film (A) has high charge retention performance by using the fluoropolymer (a) or derivative (a ′), and the electret formed by injecting charge into the resin film (A) has a high surface charge. Has a density.

(Resin film (A))
The resin film (A) is formed using a fluoropolymer (a) having an aliphatic ring in the main chain or a derivative (a ′) of the fluoropolymer (a), that is, mainly containing them. To do.
The derivative (a ′), which will be described in detail later, is a mixture of the fluoropolymer (a) and other components other than the fluoropolymer (a), the fluoropolymer (a) and the fluoropolymer. The reaction product with other components other than (a), etc. are mentioned. When the resin film (A) contains the reaction product, the fluoropolymer (a) used for forming the reaction product or a part of other components is unreacted in the resin film (A). It may remain as it is.

<Fluoropolymer (a)>
The fluorinated polymer (a) is a fluorinated polymer having an aliphatic ring in the main chain.
In the fluorine-containing polymer (a), the fluorine atom may be bonded to the carbon atom constituting the main chain or may be bonded to the side chain. The fluorine atom is preferably bonded to the carbon atom constituting the main chain because it is suitable for electretization with a low water absorption and low dielectric constant, high dielectric breakdown voltage, and high volume resistivity.

“Having an aliphatic ring in the main chain” means that at least one of the carbon atoms constituting the ring skeleton of the aliphatic ring is a carbon atom constituting the main chain of the fluoropolymer (a). means.
For example, when the fluoropolymer (a) is obtained by polymerization of a monomer having a polymerizable double bond, carbon derived from the polymerizable double bond of the monomer used for the polymerization At least one of the atoms becomes a carbon atom constituting the main chain. For example, when the fluorine-containing polymer (a) is a fluorine-containing polymer obtained by polymerizing a cyclic monomer as described later, two polymerizable double bonds constituting the cyclic monomer are included. The carbon atom becomes the carbon atom constituting the main chain. Further, in the case of a fluorinated polymer obtained by cyclopolymerizing a monomer having two polymerizable double bonds, among the four carbon atoms constituting the two polymerizable double bonds At least two are carbon atoms constituting the main chain.

“Aliphatic ring” refers to a ring having no aromaticity. The aliphatic ring may be saturated or unsaturated. The aliphatic ring may have a carbocyclic structure in which the ring skeleton is composed only of carbon atoms, and has a heterocyclic structure that includes atoms other than carbon atoms (heteroatoms) in the ring skeleton. Also good. Examples of the hetero atom include an oxygen atom and a nitrogen atom.
The number of atoms constituting the ring skeleton of the aliphatic ring is preferably 4 to 7, and particularly preferably 5 to 6. That is, the aliphatic ring is preferably a 4- to 7-membered ring, particularly preferably a 5- to 6-membered ring.
The aliphatic ring may or may not have a substituent. The phrase “which may have a substituent” means that a substituent (an atom or group other than a hydrogen atom) may be bonded to an atom constituting the ring skeleton of the aliphatic ring.

The aliphatic ring may be a non-fluorinated aliphatic ring or a fluorinated aliphatic ring.
The non-fluorinated aliphatic ring is an aliphatic ring that does not contain a fluorine atom in the structure. Specifically, as the non-fluorinated aliphatic ring, a saturated or unsaturated aliphatic hydrocarbon ring, and a part of carbon atoms in the aliphatic hydrocarbon ring is substituted with a hetero atom such as an oxygen atom or a nitrogen atom. An aliphatic heterocyclic ring etc. are mentioned.
The fluorine-containing aliphatic ring is an aliphatic ring containing a fluorine atom in the structure. Examples of the fluorinated aliphatic ring include an aliphatic ring in which a substituent containing a fluorine atom (hereinafter referred to as a fluorinated group) is bonded to a carbon atom constituting the ring skeleton of the aliphatic ring. Examples of the fluorine-containing group include a fluorine atom, a perfluoroalkyl group, a perfluoroalkoxy group, and ═CF ₂ .
The fluorine-containing aliphatic ring or non-fluorine-containing aliphatic ring may have a substituent other than the fluorine-containing group.
As the aliphatic ring, a fluorine-containing aliphatic ring is preferable from the viewpoint of excellent charge retention performance.

Preferred fluorine-containing polymers (a) include the following fluorine-containing cyclic polymers (I) and fluorine-containing cyclic polymers (II).
Fluorinated cyclic polymer (I): a polymer having units based on a cyclic fluorinated monomer.
Fluorine-containing cyclic polymer (II): a polymer having units formed by cyclopolymerization of a diene fluorine-containing monomer.
“Cyclic polymer” means a polymer having a cyclic structure.
“Unit” means a repeating unit constituting a polymer.
Hereinafter, the compound represented by the formula (1) is also referred to as “compound (1)”. The same applies to units, compounds and the like represented by other formulas. For example, the unit represented by formula (3-1) is also referred to as “unit (3-1)”.

The fluorinated cyclic polymer (I) has units based on a cyclic fluorinated monomer.
“Cyclic fluorine-containing monomer” means a monomer having a polymerizable double bond between carbon atoms constituting a fluorine-containing aliphatic ring, or a carbon atom constituting a fluorine-containing aliphatic ring and a fluorine-containing fat. It is a monomer having a polymerizable double bond with a carbon atom outside the group ring.
As the cyclic fluorine-containing monomer, the following compound (1) or compound (2) is preferable.

［式中、Ｘ^１、Ｘ^２、Ｘ^３、Ｘ^４、Ｙ^１およびＹ^２は、それぞれ独立に、フッ素原子、エーテル性酸素原子（−Ｏ−）を含んでいてもよいペルフルオロアルキル基、またはエーテル性酸素原子を含んでいてもよいペルフルオロアルコキシ基である。Ｘ^３およびＸ^４は相互に結合して環を形成してもよい。］

[Wherein, X ¹ , X ² , X ³ , X ⁴ , Y ¹ and Y ² each independently represent a fluorine atom, a perfluoroalkyl group optionally containing an etheric oxygen atom (—O—), or A perfluoroalkoxy group which may contain an etheric oxygen atom. X ³ and X ⁴ may be bonded to each other to form a ring. ]

The perfluoroalkyl group in X ¹ , X ² , X ³ , X ⁴ , Y ¹ and Y ² preferably has 1 to 7 carbon atoms, and particularly preferably 1 to 4 carbon atoms. The perfluoroalkyl group is preferably linear or branched, and particularly preferably linear. Specific examples include a trifluoromethyl group, a pentafluoroethyl group, a heptafluoropropyl group, and the like, and a trifluoromethyl group is particularly preferable.
The perfluoroalkoxy group in X ¹ , X ² , X ³ , X ⁴ , Y ¹ and Y ² is particularly preferably a trifluoromethoxy group.

In formula (1), X ¹ is preferably a fluorine atom.
X ² is preferably a fluorine atom, a trifluoromethyl group, or a perfluoroalkoxy group having 1 to 4 carbon atoms, and particularly preferably a fluorine atom or a trifluoromethoxy group.
X ³ and X ⁴ are each independently preferably a fluorine atom or a perfluoroalkyl group having 1 to 4 carbon atoms, and particularly preferably a fluorine atom or a trifluoromethyl group.
X ³ and X ⁴ may be bonded to each other to form a ring. The number of atoms constituting the ring skeleton of the ring is preferably 4-7, and particularly preferably 5-6.
Preferable specific examples of compound (1) include compounds (1-1) to (1-5).

In Formula (2), Y ¹ and Y ² are each independently preferably a fluorine atom, a C 1-4 perfluoroalkyl group or a C 1-4 perfluoroalkoxy group, and a fluorine atom or a trifluoromethyl group is preferred. Particularly preferred.
Preferable specific examples of compound (2) include compounds (2-1) to (2-2).

The fluorinated cyclic polymer (I) may be composed only of units formed by the cyclic fluorinated monomer, or may be a copolymer having the units and other units. Good.
However, the proportion of units based on the cyclic fluorinated monomer in the fluorinated cyclic polymer (I) is 20 mol% or more based on the total of all repeating units constituting the fluorinated cyclic polymer (I). Is preferable, 40 mol% or more is more preferable, and 100 mol% may be sufficient.
The other monomer is not particularly limited as long as it is copolymerizable with the cyclic fluorine-containing monomer. Specific examples include diene fluorine-containing monomers, monomers having a reactive functional group in the side chain, tetrafluoroethylene, chlorotrifluoroethylene, perfluoro (methyl vinyl ether), and the like. Examples of the diene-based fluorine-containing monomer include the same as those mentioned in the description of the fluorine-containing cyclic polymer (II) described later. Examples of the monomer having a reactive functional group in the side chain include monomers having a polymerizable double bond and a reactive functional group. The polymerizable double _{bond, CF 2 = CF-, CF 2} = CH-, CH 2 = CF-, CFH = CF-, CFH = CH-, CF 2 = C-, include CF = CF-, etc. . Examples of the reactive functional group include the same functional groups as those described in the explanation of the fluorine-containing cyclic polymer (II) described later.
A polymer obtained by copolymerization of a cyclic fluorinated monomer and a diene fluorinated monomer is considered as a fluorinated cyclic polymer (I).

The fluorinated cyclic polymer (II) has units formed by cyclopolymerization of a diene fluorinated monomer.
The “diene fluorine-containing monomer” is a monomer having two polymerizable double bonds and fluorine atoms. Although it does not specifically limit as this polymerizable double bond, A vinyl group, an allyl group, an acryloyl group, and a methacryloyl group are preferable.
As the diene fluorine-containing monomer, the following compound (3) is preferable.
_{CF 2 = CF-Q-CF} = CF 2 ··· (3).
In formula (3), Q may contain an etheric oxygen atom, and a part of fluorine atoms may be substituted with a halogen atom other than fluorine atoms, preferably 1 to 5 carbon atoms, preferably 1 to 3 carbon atoms. These are perfluoroalkylene groups which may have a branch. Examples of halogen atoms other than fluorine include chlorine atom and bromine atom.
Q is preferably a perfluoroalkylene group containing an etheric oxygen atom. In that case, the etheric oxygen atom in the perfluoroalkylene group may be present at one end of the group, may be present at both ends of the group, and is present between the carbon atoms of the group. It may be. From the viewpoint of cyclopolymerizability, it is preferably present at one end of the group.

Specific examples of the compound (3) include the following compounds.
CF ₂ = CFOCF ₂ CF = CF ₂ ,
CF ₂ = CFOCF (CF ₃ ) CF═CF ₂ ,
CF ₂ = CFOCF ₂ CF ₂ CF = CF ₂ ,
CF ₂ = CFOCF ₂ CF (CF ₃ ) CF═CF ₂ ,
CF ₂ = CFOCF (CF ₃ ) CF ₂ CF = CF ₂ ,
CF ₂ = CFOCFClCF ₂ CF = CF ₂ ,
_{CF 2 = CFOCCl 2 CF 2 CF} = CF 2,
CF ₂ = CFOCF ₂ OCF = CF ₂ ,
_{CF 2 = CFOC (CF 3)} 2 OCF = CF 2,
CF ₂ = CFOCF ₂ CF (OCF ₃ ) CF═CF ₂ ,
CF ₂ = CFCF ₂ CF = CF ₂ ,
CF ₂ = CFCF ₂ CF ₂ CF = CF ₂ ,
_{CF 2 = CFCF 2 OCF 2 CF} = CF 2.

  Examples of the unit formed by the cyclopolymerization of the compound (3) include the following units (3-1) to (3-4).

The fluorinated polymer (a) preferably has a reactive functional group.
The “reactive functional group” is bonded by reacting with other components blended between the molecules of the fluoropolymer (a) or together with the fluoropolymer (a) when heating or the like is performed. Means a reactive group capable of forming.
For example, as the other component, a silane coupling agent described later or a compound having a molecular weight of 50 to 2,000 having two or more polar functional groups (excluding the silane coupling agent) (hereinafter referred to as a polyvalent polar compound). ) And reacting them to form a reaction product, the reaction in which the fluoropolymer (a) can react with the functional group of the silane coupling agent or the polar functional group of the polyvalent polar compound It preferably has a functional functional group.
As the reactive functional group possessed by the fluoropolymer (a), in view of ease of introduction into the polymer, strength of interaction with the silane coupling agent or the polyvalent polar compound, etc., a carboxy group , An acid halide group, an alkoxycarbonyl group, a carbonyloxy group, a carbonate group, a sulfo group, a phosphono group, a hydroxy group, a thiol group, a silanol group, and an alkoxysilyl group, preferably at least one selected from the group consisting of a carboxy group or an alkoxy group A carbonyl group is particularly preferred.
The reactive functional group may be bonded to the terminal of the main chain of the fluoropolymer (a) or may be bonded to the side chain. From the viewpoint of easy production, it is preferably bonded to the end of the main chain. That is, the most preferable embodiment as the fluoropolymer (a) is to have a carboxy group or an alkoxycarbonyl group at the end of the main chain.

The relative dielectric constant of the fluoropolymer (a) is preferably 1.8 to 8, more preferably 1.8 to 5, further preferably 1.8 to 3, particularly preferably 1.8 to 2.7. .8 to 2.3 is most preferable. When the relative dielectric constant is not less than the lower limit of the above range, the amount of charge that can be stored as an electret is high, and when it is not more than the upper limit, the electrical insulation and the charge retention stability as an electret are excellent. The relative dielectric constant is measured at a frequency of 1 MHz in accordance with ASTM D150.
In addition, since the resin film (A) is a part responsible for charge retention as an electret, it is preferable that the fluoropolymer (a) has a high volume resistivity and a high dielectric breakdown strength.
The volume resistivity of the fluoropolymer (a) is preferably from 10 ¹⁰ to 10 ²⁰ Ωcm, particularly preferably from 10 ¹⁶ to 10 ¹⁹ Ωcm. The volume resistivity is measured according to ASTM D257.
The dielectric breakdown strength of the fluoropolymer (a) is preferably from 10 to 25 kV / mm, particularly preferably from 15 to 22 kV / mm. The dielectric breakdown strength is measured according to ASTM D149.
The refractive index of the fluorinated polymer (a) is preferably 1.2 to 2 from the viewpoint of reducing the difference in refractive index from the substrate, suppressing light interference due to birefringence and the like, and ensuring transparency. 2 to 1.5 is particularly preferable.

The weight average molecular weight (Mw) of the fluoropolymer (a) is preferably 50,000 or more, more preferably 150,000 or more, further preferably 200,000 or more, and particularly preferably 250,000 or more. When Mw is 50,000 or more, film formation is easy. In particular, when it is 200,000 or more, the heat resistance of the film is improved, and the thermal stability of the retained charge is improved when an electret is formed. On the other hand, if the weight average molecular weight (Mw) is too large, it is difficult to dissolve in a solvent, and there is a possibility that problems such as limitation of the film forming process may occur. Therefore, the weight average molecular weight (Mw) of the fluoropolymer (a) is preferably 1 million or less, more preferably 850,000 or less, further preferably 650,000 or less, and particularly preferably 550,000 or less.
In this specification, the weight average molecular weight (Mw) of the fluorine-containing polymer (a) is determined by the Chemical Society of Japan, 2001, NO. 12, p. It is a value calculated using the relational expression ([η] = 1.7 × 10 ⁻⁴ × Mw ^0.60 ) between Mw and intrinsic viscosity [η] (30 ° C.) described in 661.
Intrinsic viscosity [η] (30 ° C.) (unit: dl / g) is a value measured by an Ubbelohde viscometer at 30 ° C. using perfluoro (2-butyltetrahydrofuran) as a solvent.

As the fluoropolymer (a), one synthesized by polymerizing the above-described monomers may be used, or a commercially available product may be used.
CYTOP (registered trademark, manufactured by Asahi Glass Co., Ltd.) is a commercially available fluoropolymer having a fluorine-containing aliphatic ring containing an etheric oxygen atom in the main chain and having a carboxy group or an alkoxycarbonyl group at the end of the main chain. Is mentioned.

<Derivative (a ′)>
As the derivative (a ′), as described above, a mixture of the fluoropolymer (a) and other components other than the fluoropolymer (a), a fluoropolymer (a) and a fluoropolymer ( Reaction products with other components other than a) and the like can be mentioned.
Unlike the reaction product, the mixture means a state in which the fluoropolymer (a) and other components other than the fluoropolymer (a) are mixed without reacting.
As the reaction product, for example, when the coating liquid in which the fluoropolymer (a) and the other components are dissolved in a solvent is heated (e.g., when the solvent is evaporated to form a film), each component is What is produced | generated by reacting is mentioned. In addition, when the fluoropolymer (a) and other components other than the fluoropolymer (a) are reacted, the fluoropolymer (a) and the fluoropolymer (a The other components other than) will be a mixture.
As other components to be mixed or reacted with the fluoropolymer (a), a silane coupling agent or a polyvalent polar compound is preferable, and a silane coupling agent is particularly preferable. As a result, the charge retention performance (thermal stability of the retained charge, stability over time, etc.) of the formed resin film (A) is improved. The effect of improving the charge retention performance is particularly remarkable when the fluoropolymer (a) has a carboxy group or an alkoxycarbonyl group at the end of the main chain.
The effect of improving the charge retention performance is that the fluoropolymer (a) and the silane coupling agent or polypolar compound cause nanophase separation, and a nanocluster structure derived from the silane coupling agent or polypolar compound is formed. The nanocluster structure is presumed to function as a site for storing charges in the electret.
In the derivative (a ′), the silane coupling agent or the polyvalent polar compound may be present in a state where molecules are reacted with each other.

It does not specifically limit as a silane coupling agent, It can utilize over a wide range including a conventionally well-known or well-known thing.
As the silane coupling agent, a silane coupling agent having an amino group is preferable.
Considering availability, etc., particularly preferred silane coupling agents are γ-aminopropylmethyldiethoxysilane, γ-aminopropylmethyldimethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N- (β-aminoethyl) -γ-aminopropyltrimethoxysilane, N- (β-aminoethyl) -γ-aminopropylmethyldimethoxysilane, and N- (β-aminoethyl) -γ-aminopropyltriethoxy One or more selected from silane.

A silane coupling agent may be used individually by 1 type, and may use 2 or more types together.
0.1-20 mass% is preferable with respect to the total amount of a fluoropolymer (a) and a silane coupling agent, and, as for the compounding quantity of a silane coupling agent, 0.3-10 mass% is more preferable, 0.5-5 mass% is especially preferable. When the amount is within the above range, a uniform solution can be easily obtained when dissolved in a solvent together with the fluoropolymer (a) to form a coating solution.

The polyvalent polar compound is preferably a compound having two or more polar functional groups and a molecular weight of 50 to 2,000 (excluding the silane coupling agent), and a compound having a molecular weight of 100 to 2,000 (however, the silane The coupling agent is excluded.) Is particularly preferable. When the molecular weight of the polyvalent polar compound is not less than the lower limit of the above range, the molecular weight is high, so that it is difficult to volatilize and it is easy to remain in the film after film formation. Moreover, compatibility with a fluoropolymer (a) becomes favorable as it is below the upper limit of the said range.
The “polar functional group” is a functional group having one or both of the following properties (1a) and (1b).
(1a) Two or more types of atoms having different electronegativity are included, and the functional group has polarity due to polarization.
(1b) Polarization is caused by the difference in electronegativity with carbon bonded to the functional group.

Specific examples of the polar functional group having only the above characteristic (1a) include a hydroxyphenyl group.
Specific examples of the polar functional group having only the characteristic (1b) include a primary amino group (—NH ₂ ), a secondary amino group (—NH—), a hydroxyl group, and a thiol group.
Specific examples of the polar functional group having both the above characteristics (1a) and (1b) include sulfo group, phosphono group, carboxyl group, alkoxycarbonyl group, acid halide group, formyl group, isocyanate group, cyano group, carbonyl group. And an oxy group (—C (O) —O—) carbonate group (—O—C (O) —O—).

  Examples of the polyvalent polar compound include pentane-1,5-diamine, hexane-1,6-diamine, cyclohexane-1,2-diamine, cyclohexane-1,3-diamine, cyclohexane-1,4-diamine, and 1,2. -Diaminobenzene, 1,3-diaminobenzene, 1,4-diaminobenzene, triaminomethylamine, tris (2-aminoethyl) amine, tris (3-aminopropyl) amine, cyclohexane-1,3,5-triamine , Cyclohexane-1,2,4-triamine, 1,3,5-triaminobenzene, 1,2,4-triaminobenzene, 2,4,6-triaminotoluene, 1,3,5-tris (2 -Aminoethyl) benzene, 1,2,4-tris (2-aminoethyl) benzene, 2,4,6-tris (2-aminoethyl) to At least one selected from the group consisting of ene, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and polyethyleneimine is preferable, and tris (2-aminoethyl) amine, tris (3-aminopropyl) amine, cyclohexane-1,3 -At least one selected from the group consisting of diamine, hexane-1,6-diamine, diethylenetriamine and polyethyleneimine is particularly preferred.

A polyvalent polar compound may be used individually by 1 type, and may use 2 or more types together. For example, a compound having two polar functional groups and a compound having three or more polar functional groups may be mixed and used.
The blending amount of the polyvalent polar compound is preferably from 0.01 to 30% by weight, particularly preferably from 0.05 to 10% by weight, based on the blending amount of the fluoropolymer (a). The effect by mix | blending a polyvalent polar compound is fully acquired as this compounding quantity is more than the lower limit of the said range. When the blending amount is not more than the upper limit of the above range, the miscibility with the fluoropolymer (a) is good and the distribution in the coating liquid becomes uniform.

(Method for forming resin film (A))
It does not specifically limit as a formation method of a resin film (A), A well-known method can be utilized. For example, a coating solution obtained by dissolving the fluorinated polymer (a) in a solvent, or a coating obtained by dissolving the fluorinated polymer (a) and other components other than the fluorinated polymer (a) in a solvent. A resin film (A) is formed using the liquid. As said other component, as above-mentioned, a silane coupling agent or a polyvalent polar compound is preferable, and a silane coupling agent is especially preferable.

As the solvent, a solvent that dissolves at least the fluoropolymer (a) is used, and when it contains other components, the solvent that dissolves the fluoropolymer (a) dissolves the other components. If present, the solvent alone can be a uniform solution. Moreover, you may use together the other solvent which melt | dissolves this other component.
Specific examples of the solvent include a protic solvent, an aprotic solvent, and the like, and a solvent that dissolves a component to be blended in the coating liquid may be appropriately selected.
The “protic solvent” is a solvent having a proton donating property. An “aprotic solvent” is a solvent that does not have proton donating properties.

Examples of the protic solvent include the following protic non-fluorinated solvents and protic fluorinated solvents.
Methanol, ethanol, 1-propanol, isopropyl alcohol, 1-butanol, 2-butanol, t-butanol, pentanol, hexanol, 1-octanol, 2-octanol, ethylene glycol, ethylene glycol monomethyl ether, propylene glycol monomethyl ether, propylene Protic non-fluorinated solvents such as glycol monobutyl ether, propylene glycol, and methyl lactate.
Protic fluorine-containing solvents such as 2- (perfluorooctyl) ethanol and other fluorine-containing alcohols, fluorine-containing carboxylic acids, amides of fluorine-containing carboxylic acids, and fluorine-containing sulfonic acids.

Examples of the aprotic solvent include the following aprotic non-fluorinated solvents and aprotic fluorinated solvents.
Hexane, cyclohexane, heptane, octane, decane, dodecane, decalin, acetone, cyclohexanone, 2-butanone, dimethoxyethane, monomethyl ether, ethyl acetate, butyl acetate, diglyme, triglyme, propylene glycol monomethyl ether monoacetate (PGMEA), N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMA), N-methylpyrrolidone, tetrahydrofuran, anisole, dichloromethane, dichloroethane, chloroform, carbon tetrachloride, chlorobenzene, dichlorobenzene, benzene, toluene, xylene, ethylbenzene, Aprotic non-fluorine-containing solvents such as mesitylene, tetralin and methylnaphthalene.

  Polyfluoroaromatic compounds such as 1,4-bis (trifluoromethyl) benzene, polyfluorotrialkylamine compounds such as perfluorotributylamine, polyfluorocycloalkane compounds such as perfluorodecalin, and perfluoro (2-butyltetrahydrofuran) Aprotic fluorine-containing solvents such as polyfluorocyclic ether compounds, perfluoropolyethers, polyfluoroalkane compounds, hydrofluoroethers (HFE);

These solvents may be used alone or in combination of two or more. In addition to these, a wide range of compounds can be used.
Among these, the solvent used for dissolving the fluoropolymer (a) is preferably an aprotic fluorine-containing solvent because the solubility of the fluoropolymer (a) is large and a good solvent.
The solvent for dissolving the silane coupling agent or the polyvalent polar compound is preferably a protic fluorine-containing solvent.
The boiling point of the solvent is preferably 65 to 220 ° C., and particularly preferably 100 to 220 ° C., because a uniform film can be easily formed during coating.

The solvent used for preparing the coating liquid preferably has a low water content. The water content is preferably 100 mass ppm or less, and particularly preferably 20 mass ppm or less.
The concentration of the fluoropolymer (a) in the coating liquid is preferably from 0.1 to 30% by mass, particularly preferably from 0.5 to 20% by mass.
What is necessary is just to set the solid content concentration of a coating liquid suitably according to the film thickness to form. Usually, it is 0.1-30 mass%, and 0.5-20 mass% is preferable.
The solid content is calculated by heating the coating liquid whose mass was measured at 200 ° C. for 1 hour under normal pressure to distill off the solvent and measuring the mass of the remaining solid content.

The coating liquid may be obtained by preparing a composition containing each component in advance and dissolving it in a solvent, or by dissolving each component in a solvent and mixing each solution.
As a method for producing the composition in the case of preparing a composition containing each component in advance, the solid and the solid, or the solid and the liquid may be mixed by kneading, eutectic extrusion, etc. Each solution dissolved in may be mixed. Among these, it is particularly preferable to mix each solution.
When the fluorine-containing polymer (a) and the silane coupling agent are used in combination, the coating liquid is a polymer solution obtained by dissolving the fluorine-containing polymer (a) in an aprotic fluorine-containing solvent, and the silane coupling agent is protonated. It is preferable to obtain a silane coupling agent solution dissolved in a fluorinated solvent and to mix the polymer solution and the silane coupling agent solution.

The coating film can be formed, for example, by coating the surface of the substrate with a coating liquid and drying it by baking or the like.
As the coating method, a conventionally known method for forming a film from a solution can be used and is not particularly limited. For example, a spin coat method, a roll coat method, a cast method, a dipping method, a water cast method, a Langmuir-Blodget method, a die coat method, an ink jet method, a spray coat method and the like can be mentioned. Printing techniques such as letterpress printing, gravure printing, lithographic printing, screen printing, flexographic printing, and the like can also be used.
Drying may be performed by air drying at normal temperature, but is preferably performed by heating and baking. The baking temperature is preferably equal to or higher than the boiling point of the solvent, and particularly at a high temperature of 230 ° C. or higher, the reaction between the added silane coupling agent or polyvalent polar compound and the fluoropolymer (a) is sufficiently performed. It is particularly preferable in terms of completion.

  When the resin film (A) is formed using the fluoropolymer (a) or derivative (a ′) described above, the surface of the substrate on which the resin film (A) is formed has bonding properties with the substrate. In order to ensure, it is preferable to form with chromium, aluminum, copper, etc. If the surface of the substrate on which the resin film (A) is formed is formed of gold, platinum, or pure nickel, the resin film (A) is not bonded to the substrate. Therefore, when the resin film (A) is formed on the diaphragm 23, the surface of the diaphragm 23 is made of a conductive material excluding gold, platinum, and pure nickel among the materials described above as the electrode film forming material. Preferably it is formed. Therefore, if gold, platinum, or pure nickel is used as the main forming material of the diaphragm 23, it is preferable to form a film of chromium, aluminum, or the like on the surface of gold, platinum, or pure nickel.

(Charge injection)
By injecting charges into the resin film (A), the resin film (A) becomes the electret film 29.
The method for injecting charges into the resin film (A) is not particularly limited as long as it is a method for charging an insulator generally. For example, the corona discharge method described in GMSessler, Electrets Third Edition, pp20, Chapter 2.2 “Charging and Polarizing Methods” (Laplacian Press, 1998), electron beam collision method, ion beam collision method, radiation irradiation method, light irradiation method, A contact charging method, a liquid contact charging method, or the like is applicable. In the present invention, it is particularly preferable to use a corona discharge method or an electron beam collision method.
As a temperature condition for injecting the charge, it is maintained after the injection that the temperature is higher than the glass transition temperature (Tg) of the fluoropolymer (a) or the derivative (a ′) contained in the resin film (A). It is preferable from the viewpoint of charge stability, and it is particularly preferable to carry out under a temperature condition of about Tg + 10 ° C. to Tg + 20 ° C.
As an applied voltage at the time of injecting electric charges, it is preferable to apply a high voltage as long as it is not higher than the dielectric breakdown voltage of the resin film (A). In the present invention, the applied voltage to the resin film (A) is 6 to 30 kV, preferably 8 to 15 kV for a positive charge, and -6 to -30 kV, preferably -8 to -15 kV for a negative charge.
Since the fluoropolymer (a) or the derivative (a ′) can hold a negative charge more stably than a positive charge, the applied voltage is preferably a negative charge. In this case, the electret surface potential is negative.

Here, an example in which the resin film (A) is directly formed on the surface of the vibrating electrode film 27 formed on the vibration plate 23 and the charge is injected has been shown, but the manufacturing method of the electret film 29 is described here. It is not limited. For example, after a resin film (A) is formed on an arbitrary substrate and peeled off from the substrate, this is disposed on the surface of the vibration electrode film 27 formed on the vibration plate 23, and the resin film (A) is formed on the resin film (A). The electret film 29 may be formed by injecting electric charges. Further, after forming a resin film (A) on an arbitrary substrate and injecting an electric charge into the electret film 29, the electret film 29 is peeled off from the substrate, and this is formed on the vibration plate 23. You may arrange | position on the surface of the electrode film 27. FIG.
When the resin film (A) is formed on a substrate different from the diaphragm 23 and the charge is injected on the substrate, the substrate may be grounded when the charge is injected into the obtained laminate. A substrate that can be connected to is used. Preferred materials include, for example, conductivity such as gold, silver, copper, nickel, chromium, aluminum, titanium, tungsten, molybdenum, tin, cobalt, palladium, platinum, and an alloy containing at least one of these as a main component. These metals are mentioned. In addition, even if the material is a substrate other than a conductive metal, for example, an inorganic material such as glass, or an insulating material such as an organic material such as polyethylene terephthalate, polyimide, polycarbonate, or acrylic resin (insulating substrate), Metal film by sputtering, vapor deposition, wet coating, etc. on the surface, or metal oxides such as ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide), zinc oxide, titanium dioxide, tin oxide; polyaniline, polypyrrole, PEDOT / PSS, an organic conductive material made of carbon nanotubes or the like may be used. A semiconductor material such as silicon can also be used as a substrate if the same surface treatment is performed or the semiconductor material itself has a low resistance value. The resistance value of the substrate material is preferably 0.1 Ωcm or less, particularly preferably 0.01 Ωcm or less, in terms of volume resistivity. With such a low-resistance substrate material, the electret film 29 can be formed by injecting a charge as it is into the laminate formed on the substrate.

[Modification of Embodiment]
The spacer 21 of the acoustic sensor 20 of the above embodiment has a cylindrical shape. However, the present invention is not limited to this, and may be a polygonal cylinder shape or the like. In this case, the diaphragm 23, the back plate, and 26 have shapes corresponding to the openings 21a and 21b of the polygonal cylindrical spacer 21.

  In the above embodiment, the diaphragm 23 is bonded to the spacer 21 via the elastic member 32, and the back plate 26 is bonded to the spacer 21. However, the diaphragm 23 and the back plate 26 may be firmly fixed to the spacer 21 by the frame material without using an adhesive.

  In the above embodiment, the electret film 29 is formed on the surface of the vibrating electrode film 27 on the back electrode film side. However, the electret film 29 may be formed on the surface of the back electrode film 28 on the vibration electrode film side.

In the above embodiment, the dimensions of each part of the acoustic sensor 20 described with reference to FIG. 1 are the dimensions of an acoustic sensor for an electronic stethoscope, and the sound collection frequency band is about 0.1 to 100 Hz. It is a suitable dimension. For this reason, when the acoustic sensor 20 is not used for an electronic stethoscope or when the sound collection frequency band is not set to about 0.1 to 100 Hz, dimensions different from the dimensions exemplified above may be adopted.
In particular, the diameter D6 of the inner peripheral edge of the groove 24, which is one of the adjustment parameters of the sound collection frequency band, may be appropriately changed so that the target sound collection frequency band is obtained.

  The acoustic monitor device of the above embodiment includes the electric circuit 15 in which the amplifier 16 is disposed in the signal line 18 that electrically connects the vibrating electrode film 27 and the back electrode film 28 and the earphone 2. However, when the acoustic sensor 20 with high sound collection sensitivity is used and the output of the reproduced sound does not need to be increased so much as in the present embodiment, as shown in FIG. The amplifier 16 may not be disposed in the signal line 18 that electrically connects the membrane 28 and the earphone 2. That is, the electric circuit 15 may not be provided.

  In the above embodiment, the diaphragm 23 is attached to the spacer 21 via the elastic member 32. However, when there is no need to suppress the collection of high-frequency sound, the diaphragm 23 may be directly attached to the spacer 21 without using the elastic member 32.

  In the above embodiment, the weight 31 is attached to the diaphragm 23 in order to reduce the sound collection frequency band without increasing the outer diameter of the diaphragm 23 and the spacer 21. However, when the outer diameters of the diaphragm 23 and the spacer 21 may be increased, or when it is not necessary to lower the sound collection frequency band, the weight 31 may not be attached to the diaphragm 23.

The acoustic monitor apparatus of the above embodiment is an electronic stethoscope. However, the present invention is not limited to this. For example, instead of the earphone 2 of the electronic stethoscope, a speaker that allows many people to hear the generated sound at the same time may be connected to the acoustic sensor 20. Instead of the earphone 2, a display that displays acoustic characteristics as sound information or a printer that prints acoustic characteristics on paper may be connected to the acoustic sensor 20. That is, the sound information output device may be other than the earphone 2, and may be a speaker, a display, a printer, or the like.
The acoustic monitor device may be a device for monitoring not only the sound generated from the human body but also other sounds, for example, fluid sound in piping, internal sounds of containers, buildings, and the like.
Therefore, the acoustic sensor 20 may be used not only for an electronic stethoscope but also for other acoustic monitor devices.

  DESCRIPTION OF SYMBOLS 1 ... Stethoscope head, 2 ... Earphone, 3 ... Earphone cord, 10 ... Stethoscope head case, 11 ... Opening, 12 ... Diaphragm, 15 ... Electric circuit, 16 ... Amplifier, 17 ... Battery, 18 ... Signal line, 20 ... Acoustic sensor, 21 ... spacer, 23 ... diaphragm, 23i ... inner region, 23o ... outer region, 24 ... groove, 25 ... flat part, 26 ... back plate, 27 ... vibrating electrode film, 28 ... back electrode film, 29 ... Electret film, 31 ... weight, 32 ... elastic member

Claims (12)

A spacer that is cylindrical and open at both ends;
A diaphragm attached to the spacer so as to block one opening of the spacer;
A back plate facing the diaphragm and closing the other opening of the spacer;
A vibrating electrode film formed of a conductive material and provided on the back plate side of the diaphragm;
A back electrode film formed of a conductive material and provided on the diaphragm side of the back plate;
An electret film;
With
In the diaphragm, a groove that divides the diaphragm into an inner region and an outer region is formed inside the inner surface of the spacer,
The electret film is formed on the other electrode film side of one of the vibrating electrode film and the back electrode film, and on the inner side of the groove,
An acoustic sensor.   The acoustic sensor according to claim 1, wherein the groove is formed on the back plate side of the diaphragm.   The acoustic sensor according to claim 1, wherein a weight is provided in a region on the opposite side of the rear plate of the diaphragm and inside the groove. An elastic member having elasticity, and being arranged between the one opening side end face of the spacer and the diaphragm;
The acoustic sensor according to any one of claims 1 to 3, wherein the diaphragm is attached to the spacer via the elastic member.   The acoustic sensor according to any one of claims 1 to 4, wherein the electret film is formed on the back plate side of the vibrating electrode film.   The acoustic sensor according to any one of claims 1 to 5, wherein the electret film is obtained by injecting electric charge into a resin film using a fluoropolymer.   The electret film is obtained by injecting electric charge into a resin film using a fluoropolymer (a) having an aliphatic ring in the main chain or a derivative (a ′) of the fluoropolymer (a). Item 6. The acoustic sensor according to any one of Items 1 to 5.   The acoustic sensor according to claim 7, wherein the fluoropolymer (a) has a reactive functional group.   The resin film uses the derivative (a ′), and the derivative (a ′) includes a mixture or a reaction product of the fluoropolymer (a) and a silane coupling agent having an amino group. The acoustic sensor according to claim 7 or 8. The acoustic sensor according to any one of claims 1 to 9,
A sound information output device for outputting a change in potential difference between the vibrating electrode film and the back electrode film due to vibration of the diaphragm as sound information;
An acoustic monitor device comprising: A cylindrical stethoscope head case having an opening formed on at least one end;
A diaphragm that closes the opening of the stethoscope head case;
With
The acoustic sensor is disposed in the stethoscope head case, and an area inside the groove of the diaphragm of the acoustic sensor is attached to the diaphragm,
The sound information output device has a pair of left and right earphones that output the change in potential difference as sound,
The acoustic monitor device according to claim 10. A cylindrical stethoscope head case having an opening formed on at least one end;
A diaphragm that closes the opening of the stethoscope head case;
The acoustic sensor according to claim 3 disposed in the stethoscope head case;
A pair of left and right earphones that output an electric signal as sound, which is a change in potential difference between the vibrating electrode film and the back electrode film due to vibration of the diaphragm;
With
The weight provided on the diaphragm of the acoustic sensor is attached to the diaphragm;
Acoustic monitor device.

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