JP5155927B2 - Waterproof sound-permeable membrane, waterproof sound-permeable member and electrical product using the same - Google Patents

Description

  The present invention relates to a waterproof sound-permeable membrane used for an electric product (for example, a mobile phone) having a voice function. The present invention also relates to a waterproof sound-permeable member and an electrical product including the waterproof sound-permeable membrane.

  In recent years, development and popularization of portable information communication devices such as mobile phones has been rapidly progressing. Along with this, the frequency of use of equipment not only in the usual indoor and outdoor environments, but also in harsh conditions such as the coast and forest areas has increased. Ensuring is an important issue.

  One of the standards regarding the waterproofness of electrical products is “the degree of protection by the outline of the electrical machine (IP code)” defined in JIS C0920. In consideration of the above-mentioned use situation, waterproofness corresponding to “water protection class 7 (IPX7)” defined in the standard is desired. Even if an electrical product satisfying IPX7 is accidentally dropped into the water, it can be prevented from entering the product within a predetermined depth and time.

  In order to realize waterproofness equivalent to IPX7 in an electric product having a voice function such as a cellular phone, it is important how to waterproof a sound generating part and a sound receiving part such as a speaker, a microphone, and a buzzer. The housing of the electric product including the sound generation unit and / or the sound receiving unit is provided with openings for transmitting sound between these portions and the outside of the housing. This is because it is necessary to achieve both good sound transmission.

  A waterproof sound-permeable membrane is known as a member that prevents intrusion of water from the openings for the sound generation part and the sound receiving part into the inside of the housing while ensuring good sound permeability. The waterproof sound-permeable membrane is a thin film made of a material that hardly inhibits sound transmission. By closing the opening of the housing with a waterproof sound-permeable membrane, it is possible to achieve both sound permeability and waterproofness in the opening. A stretched porous membrane having a dispersed structure of innumerable pores generated by stretching is suitable for the waterproof sound-permeable membrane. In Japanese Patent Laid-Open No. 3-41182 (Patent Document 1), as a waterproof sound-permeable membrane having a stretched porous membrane, a waterproof membrane having a polytetrafluoroethylene (PTFE) porous membrane or an ultrahigh molecular weight polyethylene (UHMWPE) porous membrane is disclosed. Sound membranes are shown, and it is described that these waterproof sound-permeable membranes have both high waterproof properties and sound-permeable properties.

Japanese Patent Laid-Open No. 3-41182

  By closing the opening of the housing with a waterproof sound-permeable membrane having a stretched porous membrane, the waterproof and sound-permeable properties in the opening are ensured, but the sound-permeability test of the opening performed after the placement of the waterproof sound-permeable membrane In this case, “sound distortion” is often confirmed. Sound distortion is a kind of alteration of speech, and it is heard by human ears as “buzzing sound (vibrating sound that makes shoji paper shake)” or “flapping” or “cuttering” of sound. Conventionally, sound distortion has not been particularly taken into account, but with the improvement in performance of devices such as mobile phones and the provision of new information services (for example, the sound quality of incoming melody delivered to devices is It is important to improve satisfaction and the appeal of products). For this reason, a waterproof sound-permeable membrane that can achieve high waterproofness when it is placed in a part where sound is transmitted, such as an opening in an electrical product housing having a sound function, and suppresses the occurrence of sound distortion as much as possible. Is required.

  Note that the distortion of sound can be quantitatively expressed by a total harmonic distortion (THD). THD is a parameter that is widely used for characteristic evaluation of audio equipment, and is indicated by the ratio of the harmonic components in the output and the level of noise relative to the signal input to the equipment (generally a sine wave is used). The harmonic component is a component indicating a frequency that is an integral multiple of the frequency of the input signal. Placed when the THD of the sound measured when the waterproof sound-permeable membrane is arranged is significantly larger than the sound measured when the waterproof sound-permeable membrane is not arranged (this is a blank) It can be determined that sound distortion has occurred due to the waterproof sound-permeable membrane. Further, it can be determined that the greater the measured THD value, the greater the amount of sound distortion.

  As a result of intensive studies, the present inventors have found that the occurrence of sound distortion due to the arrangement of the waterproof sound-permeable membrane is characteristic of the stretched porous membrane that constitutes the membrane. The present inventors have found that anisotropy has a great influence and that the generation of sound distortion is suppressed by the relaxation of the anisotropy, thereby completing the present invention.

  The waterproof sound-permeable membrane of the present invention has two or more stretched porous membranes laminated and integrated, and the direction of primary stretching of at least two membranes selected from the two or more stretched porous membranes is the membrane. As viewed from the direction perpendicular to the main surface of the two, they are orthogonal or oblique to each other.

  The waterproof sound-permeable member of the present invention includes the waterproof sound-permeable film of the present invention and a support joined to the waterproof sound-permeable film.

  An electrical product according to the present invention is an electrical product having a voice function, wherein at least one selected from a sound generation unit for outputting sound and a sound reception unit for inputting sound, and the sound generation unit and / or reception unit. A waterproof sound-permeable membrane capable of transmitting sound between the sound portion and the outside and suppressing water intrusion into the sound generation portion and / or the sound-receiving portion, wherein the waterproof sound-permeable membrane is the waterproof sound-permeable membrane of the present invention. The sound membrane.

  The stretched porous membrane is formed by uniaxially stretching or biaxially stretching (typically biaxially stretching) a sheet made of a resin constituting the porous membrane. At this time, in uniaxial stretching, stretching in only one direction is performed, and in biaxial stretching, the state of the film shape change during stretching differs between the first-stage stretching and the second-stage stretching. Therefore, the obtained stretched porous membrane has a large anisotropy in the mechanical characteristics in the in-plane direction. For example, the stretching direction of the first stage in the stretched porous membrane formed by biaxial stretching or the stretching direction of the stretched porous membrane formed by uniaxial stretching (in this specification, these directions are referred to as “primary stretching directions”. The tensile strength in the in-plane direction orthogonal to this (in the film formed by biaxial stretching, the second stretching direction: secondary stretching direction) is about 3 to 20 times the tensile strength. In addition, the stress-strain (elongation) characteristics (SS characteristics) measured when performing a tensile test in each direction are also very different from each other. In the test in the primary stretching direction, the maximum strength is reached with a slight elongation. In contrast, in the test in the in-plane direction perpendicular to the film, the film is greatly elongated by low stress (see FIG. 1). In the first-stage stretching in the uniaxial stretching and the biaxial stretching, the fiber formation of the resin and the change in which the fibrous resin is stretched in the stretching direction occur. In the second-stage stretching in the biaxial stretching, Changes occur that mainly increase the spacing between adjacent fibers.

  In the waterproof sound-permeable membrane of the present invention, two or more stretched porous membranes are laminated and integrated, and the primary stretching direction of at least two membranes selected from the two or more stretched porous membranes is the main surface of the membrane. By introducing structures orthogonal or oblique to each other when viewed from the direction perpendicular to the direction, the anisotropy of the mechanical properties in the in-plane direction of the film is relaxed. This relaxation of anisotropy provides a high waterproof property derived from the stretched porous membrane when the waterproof sound-permeable membrane is disposed at a portion where sound is transmitted, such as the opening of the housing, and the sound. The occurrence of distortion is suppressed.

A typical example of a stress-strain (elongation) curve (SS curve) measured during a tensile test in the primary stretching direction in the stretched porous membrane is orthogonal to the primary stretching direction in the stretched porous membrane. It is a schematic diagram which shows a typical example of the SS curve measured at the time of the tensile test to an in-plane direction. It is sectional drawing which shows typically an example of the waterproof sound-permeable membrane of this invention. It is the top view which looked at the waterproof sound-permeable membrane shown in FIG. 2 from the direction perpendicular | vertical to the main surface (it looked in the direction of arrow A of FIG. 2). It is the figure which observed an example of the PTFE porous membrane with the scanning electron microscope (SEM). It is a perspective view which shows an example of the waterproof sound-permeable member of this invention. It is a top view which shows another example of the waterproof sound-permeable member of this invention. It is a front view which shows an example of the mobile telephone which is an example of the electric product of this invention. It is a rear view which shows an example of the mobile telephone which is an example of the electric product of this invention.

  The present invention will be described below with reference to the drawings.

  The waterproof sound-permeable membrane 1 shown in FIG. 2 has a structure in which two stretched porous membranes 11 and 12 are laminated and integrated. As shown in FIG. 3, the stretched porous membranes 11 and 12 constituting the waterproof sound-permeable membrane 1 have their primary stretching directions (directions of arrows B and C, respectively) perpendicular to the main surfaces of the membranes 11 and 12. When viewed from various directions (when viewed in the direction of arrow A shown in FIG. 2), they are orthogonal to each other. The waterproof sound-permeable membrane 1 exhibits high waterproof properties derived from the stretched porous membrane. In addition, the waterproof sound-permeable membrane 1 has a waterproof sound-permeable membrane having only one stretched porous membrane, or two or more stretched porous membranes. In comparison, the occurrence of sound distortion due to the arrangement in a portion where sound is transmitted, such as an opening in a housing of an electric product having a sound function, is suppressed.

  In the waterproof sound-permeable membrane 1, the anisotropy of the mechanical characteristics in the in-plane direction of the membrane is relaxed compared to the conventional waterproof sound-permeable membrane, so that the occurrence of sound distortion is suppressed. One of the mechanisms by which the generation of sound distortion is suppressed by relaxation of anisotropy is considered to be suppression of “wrinkles”.

  If there are wrinkles in the waterproof sound-permeable membrane in the state where the sound is transmitted, depending on the shape and density of the wrinkles, a resonance phenomenon occurs in the waterproof sound-permeable membrane during sound transmission, and harmonics are generated. It is considered that sound distortion occurs due to the occurrence. When the present inventors have analyzed a waterproof sound-permeable membrane where sound distortion is observed, many wrinkles are generated in parallel to the primary stretching direction of the stretched porous membrane constituting the membrane. It became clear. Further analysis showed that the anisotropy of the mechanical properties in the in-plane direction of the stretched porous membrane was a factor causing wrinkles in a specific direction. For example, even when the stress applied to the stretched porous membrane is uniform in all in-plane directions of the waterproof sound-permeable membrane (for example, when it is cut into a predetermined shape) in FIG. As shown, since the amount of strain generated with respect to the applied stress differs in each direction, wrinkles are generated in a specific direction. In the waterproof sound-permeable membrane of the present invention, since the anisotropy of the mechanical characteristics in the in-plane direction is relaxed and becomes more isotropic, the generation of such wrinkles is suppressed, and the distortion of sound is reduced. The occurrence is thought to be suppressed.

  The structure of the waterproof sound-permeable membrane of the present invention includes (1) two or more stretched porous membranes laminated and integrated, and (2) at least two membranes selected from these two or more stretched porous membranes. The primary stretching direction is not particularly limited as long as it has a structure that is orthogonal or oblique to each other when viewed from the direction perpendicular to the main surface of the film.

  The number of stretched porous membranes of the waterproof sound-permeable membrane of the present invention may be an arbitrary number of 2 or more, but is preferably an even number because the above-described relaxation of anisotropy becomes more reliable. Moreover, since the freedom degree of arrangement | positioning of each film | membrane when laminating | stacking and integrating | stretching a stretched porous membrane becomes high, so that there are many stretched porous membranes, relaxation of anisotropy can be ensured more reliably. However, as the number of stretched porous membranes increases, the surface density of the waterproof sound-permeable membrane tends to increase, and the excessive surface density affects the sound permeability of the waterproof sound-permeable membrane, such as an increase in sound pressure loss. Therefore, it is necessary to select the number of stretched porous membranes according to the acoustic characteristics to be obtained.

The surface density of the waterproof sound-permeable membrane of the present invention is preferably 1 to ²⁰ g / m ² (in total of a plurality of layers). A waterproof sound-permeable membrane having an area density in this range has sufficient physical strength, low sound pressure loss, and excellent sound permeability. The surface density is more preferably ² to 10 g / m ² .

  In the waterproof sound-permeable membrane of the present invention, the primary stretching directions of at least two stretched porous membranes are orthogonal or oblique to each other when viewed from a direction perpendicular to the main surface of the membrane. The primary stretching direction of the at least two stretched porous membranes is preferably orthogonal to each other when viewed from the direction perpendicular to the main surface of the membrane. In this case, the stretched porous membrane of the waterproof sound-permeable membrane has Even when the number is small (typically, the number of stretched porous membranes is 2), the above-described relaxation of anisotropy becomes more reliable. In addition, orthogonal means that the crossing angle in each direction is approximately 90 ° (preferably including a range of plus or minus 3 ° centering on 90 °). On the other hand, the crossing angle in each direction during oblique crossing is typically 10 ° or more and less than 90 °, preferably 30 ° or more and less than 90 °, and more preferably 45 ° or more and less than 90 °.

  In the waterproof sound-permeable membrane 1 shown in FIG. 2, the two stretched porous membranes 11 and 12 whose primary stretching directions are orthogonal to each other are adjacent to each other. However, as long as the effect of the present invention is obtained, other than the stretched porous membrane An arbitrary layer may be disposed between the two stretched porous membranes. In other words, as long as the effect of the present invention is obtained, the two or more stretched porous membranes may be laminated and integrated with any layer other than the stretched porous membrane disposed therebetween. Similarly, the two or more stretched porous membranes may be laminated and integrated with any layer other than the stretched porous membrane as long as the effects of the present invention are obtained.

  The waterproof property of the waterproof sound-permeable membrane of the present invention is preferably 9.8 kPa or more in terms of the water pressure value measured using a water resistance tester (high water pressure method) described in JIS L1092. The water pressure resistance of 9.8 kPa means that it can withstand the water pressure at a water depth of 1 m. In this case, a waterproof property corresponding to IPX7 defined in JIS C0920 is obtained. In order to more reliably obtain the waterproof property corresponding to IPX7, it is preferable that the waterproof sound-permeable membrane has a water pressure resistance of 100 kPa or more with the above value.

  Such a high water pressure resistance can be obtained, for example, by setting the average pore diameter of at least one stretched porous membrane of the waterproof sound-permeable membrane to 1 μm or less. Since higher waterproofness is obtained, the average pore diameter of at least one stretched porous membrane is preferably 0.7 μm or less, and more preferably 0.5 μm or less. At this time, even if the average pore diameter of the other stretched porous membrane included in the waterproof sound-permeable membrane exceeds 1 μm, the waterproof property of the waterproof sound-permeable membrane is not affected. For example, the average pore size of at least one stretched porous membrane is 1 μm or less, but even when the average pore size of two or more stretched porous membranes exceeds 5 μm, the same high waterproofness can be obtained.

  In addition, as a measuring method of the average pore diameter for the stretched porous membrane, a measuring method described in ASTM F316-86 is generally widespread, and an automated measuring device is commercially available (for example, US Porous Material Inc. More available Perm-Porometer). In this method, a stretched porous membrane immersed in a liquid having a known surface tension is fixed to a holder, and pressure is applied from one side to expel the liquid from the membrane, and the average pore diameter is obtained from the pressure. This method is not only simple and high in reproducibility, but also excellent in that the measuring apparatus can be completely automated.

  The porosity of the stretched porous membrane is not particularly limited, but is preferably 60 to 95%, more preferably 75 to 95%.

  The stretched porous membrane is, for example, a polytetrafluoroethylene (PTFE) porous membrane. In the waterproof sound-permeable membrane of the present invention, it is preferable that at least one stretched porous membrane is a PTFE porous membrane.

  The PTFE porous membrane is a stretched porous membrane formed by uniaxially stretching or biaxially stretching a PTFE sheet, and has a structure in which pores formed by stretching are dispersed innumerably (see FIG. 4). As shown in FIG. 4, each pore is surrounded by fine fibers called fibrils. Further, depending on the pores, an aggregate of PTFE called a node is in contact therewith. Although it depends on the stretching conditions, most of the fibrils in the PTFE porous membrane are stretched in the primary stretching direction.

  The stretched porous membrane may be, for example, an ultra high molecular weight polyethylene (UHMWPE) porous membrane. The UHMWPE porous membrane is a stretched porous membrane formed by uniaxially stretching or biaxially stretching a UHMWPE sheet, and has a pore structure similar to that of the PTFE porous membrane.

  The film constituting the waterproof sound-permeable film of the present invention may be subjected to water repellent treatment with a water repellent such as a fluorine-containing polymer. In this case, the waterproof property of the waterproof sound-permeable membrane is further increased.

  The waterproof sound-permeable membrane of the present invention includes, for example, two or more stretched porous membranes, and the primary stretching direction of at least two membranes selected from the two or more stretched porous membranes is perpendicular to the main surface of the membrane. They can be laminated and integrated so as to be orthogonal or oblique to each other when viewed from the direction.

  The stretched porous membrane to be laminated and integrated can be produced by a known method. Stretching during production of the stretched porous membrane may be uniaxial stretching or biaxial stretching.

  The method of laminating the stretched porous membrane is not particularly limited as long as the primary stretch direction of at least two stretched porous membranes can be laminated so as to be orthogonal or oblique to each other when viewed from the direction perpendicular to the main surface of the membrane. . Two or more stretched porous membranes laminated can be integrated by pressure bonding, or pressure bonding and baking. For press bonding and firing, for example, a press die or a hot roll can be used.

  When forming the waterproof sound-permeable membrane of the present invention, steps other than the lamination and integration step of the stretched porous membrane described above may be performed at any time as necessary.

  An example of the waterproof sound-permeable member of the present invention is shown in FIG. The waterproof sound-permeable member 2 shown in FIG. 5 has a ring-shaped waterproof sound-permeable membrane 1 according to the present invention in which the shape seen from a direction perpendicular to the main surface of the membrane is a circle, and a peripheral portion of the membrane 1. And a support 21 made of a sheet. The form in which the support 21 is joined to the waterproof sound-permeable membrane 1 reinforces the waterproof sound-permeable membrane 1 and facilitates its handling. Moreover, since the support body 21 becomes an allowance to the part in which the waterproof sound-permeable member 2 is arrange | positioned, such as opening in a housing | casing, the attachment operation | work of the waterproof sound-permeable membrane 1 becomes easy. Furthermore, since the support body 21 is joined only to the peripheral edge portion of the waterproof sound-permeable membrane 1, it is possible to ensure better acoustic characteristics than the form in which the support body is joined to the entire waterproof sound-permeable membrane 1.

  The shape of the support 21 is not particularly limited. For example, as shown in FIG. 6, a support body 21 made of a frame-like sheet joined to the peripheral edge of a waterproof sound-permeable membrane 1 having a rectangular shape when viewed from a direction perpendicular to the main surface of the membrane. Also good. In the waterproof sound-permeable membrane 1 of the present invention, since the anisotropy of the mechanical characteristics in the in-plane direction is relaxed, the waterproof sound-permeable membrane 1 and the support body 21 having such a shape are used. Even when the member 2 is formed, the occurrence of sound distortion is suppressed by suppressing the occurrence of wrinkles in the waterproof sound-permeable membrane 1.

  The material of the support 21 is not particularly limited, but a thermoplastic resin or metal is suitable. The thermoplastic resin is, for example, polyolefin such as polyethylene (PE) or polypropylene (PP), polyester such as polyethylene terephthalate (PET) or polycarbonate (PC), polyimide, or a composite material thereof. The metal is a metal having excellent corrosion resistance, such as stainless steel or aluminum.

  The thickness of the support 21 is, for example, 5 to 500 μm, and preferably 25 to 200 μm. When attention is paid to the function as an attachment margin, the ring width (frame width: difference between the outer shape and the inner diameter) is suitably about 0.5 to 2 mm. The support 21 may be a foam made of the above resin.

  The joining method of the waterproof sound-permeable membrane 1 and the support 21 is not particularly limited, and for example, methods such as heat welding, ultrasonic welding, adhesion using an adhesive, and adhesion using a double-sided tape can be applied. In particular, adhesion with a double-sided tape is preferable because adhesion between the waterproof sound-permeable membrane 1 and the support 21 is easy.

  7A and 7B show an example of an electrical product of the present invention including the waterproof sound-permeable membrane 1. The electric product shown in FIGS. 7A and 7B is a mobile phone 5. The casing 9 of the mobile phone 5 is provided with openings for sound generation units and sound reception units such as a speaker 6, a microphone 7, and a buzzer 8. The waterproof sound-permeable membrane 1 is attached to the housing 9 from the inside so as to close these openings. Thereby, the penetration | invasion of the water and dust to the inside of the housing | casing 9 is blocked | prevented and a sound generation part and a sound receiving part are protected. Moreover, generation | occurrence | production of the distortion of the sound by arrangement | positioning of the waterproof sound-permeable membrane 1 is suppressed.

  The waterproof sound-permeable membrane 1 is attached to the housing 9 by, for example, sticking using a double-sided tape, heat welding, high frequency welding, ultrasonic welding so that water does not enter from the joint with the housing 9. It is performed by such methods. The waterproof sound-permeable membrane 1 may be attached to the housing 9 via the support 21, that is, as the waterproof sound-permeable member 2.

  The waterproof sound-permeable membrane 1 can be applied not only to the mobile phone 5 but also to an electric product including at least one selected from a sound generation unit for outputting sound and a sound receiving unit for inputting sound. Specifically, the present invention can be applied to various electric products having voice functions such as notebook computers, electronic notebooks, digital cameras, and portable audio.

  Hereinafter, the present invention will be described more specifically with reference to examples. The present invention is not limited to the following examples.

  First, a method for evaluating the characteristics of the PTFE porous membrane used for the production of the waterproof sound-permeable membrane and the acoustic characteristics of the produced waterproof sound-permeable membrane will be described.

[Average pore size]
The average pore diameter of the PTFE porous membrane was determined according to ASTM F316-86 using a Perm-Porometer manufactured by Porous Material Inc. For the measurement, a fluorine-based solvent (manufactured by 3M, FC-40, surface tension 16 mN / m) was used.

[Air flow rate]
The air flow rate of the PTFE porous membrane depends on the Gurley number (the time required for 100 mL of air to permeate the porous membrane when a predetermined pressure is applied) according to JIS P8117 (Gurley test method). Asked.

[Area density]
The surface density of the PTFE porous membrane was determined by measuring the mass of the punched portion after punching the porous membrane with a φ47 mm punch and converting it to a mass per 1 m ² .

[Water pressure resistance]
The water pressure resistance of the PTFE porous membrane was determined using a water resistance tester (high water pressure method) described in JIS L1092. However, since the film was remarkably deformed in the area defined in JIS L1092, a stainless steel mesh (opening diameter 2 mm) was placed on the opposite side of the pressure surface of the film, and measurement was performed in a state where deformation was suppressed.

[Tensile strength]
The tensile strength in the in-plane direction of the PTFE porous membrane was evaluated as follows.

  After punching out the PTFE porous membrane to be evaluated into the shape of 2 dumbbells described in JIS K7113, the obtained test piece was subjected to a tensile tester (manufactured by A & D, Tensilon Universal Tester MODEL: RTC- 1310A-PL) by performing a tensile test. The tensile strength was measured with respect to the direction of primary stretching and the direction of secondary stretching in the PTFE porous membrane, respectively (the PTFE porous membrane used in the examples is a membrane formed by sequential biaxial stretching, Regarding the tensile strength in the in-plane direction, the maximum value is shown in the primary stretching direction and the minimum value is shown in the secondary stretching direction). The distance between chucks during the tensile test was 95 mm, the tensile speed was 200 mm / min, and the measurement temperature was 25 ° C.

The tensile strength is a value obtained by dividing the maximum load load (N) when the waterproof sound-permeable membrane is broken by the tensile test by the cross-sectional area (mm ² ) of the waterproof sound-permeable membrane before the tensile test. In addition, the width | variety of the test piece was 6 mm, and the thickness of the test piece was measured for each test piece with the dial gauge.

[Acoustic characteristics]
The acoustic characteristics of the produced waterproof sound-permeable membrane were evaluated as follows.

  First, a simulated housing (made of polystyrene, outer shape 67 × 37 × 12 mm) assuming a mobile phone housing was prepared. This simulated housing has no opening except that one speaker mounting hole (φ = 13 mm) and one speaker cable conduction hole are provided. Next, a double-sided tape (Nitto Denko, No. 5620A, thickness 0.2 mm) is punched into a ring shape with an outer diameter of 16 mm and an inner diameter of 13 mm, and a speaker ( Affixed with SCG-16A from Star Seimitsu. The speaker cable was led out of the simulated housing through the conduction hole. After the speaker cable was led out, the conduction hole was closed with a putty.

  Next, the waterproof sound-permeable membrane produced in each Example and Comparative Example was punched into a circle having a diameter of 16 mm using a Thomson mold, and the waterproof sound-permeable membrane punched out was simulated using the ring-shaped double-sided tape. Affixed to the outside of the speaker mounting hole. When attaching the waterproof sound-permeable membrane to the simulated housing, the waterproof sound-permeable membrane covers the entire speaker mounting hole, and between the double-sided tape and the simulated housing, and between the waterproof sound-permeable membrane and the double-sided tape. The gap was not made.

  Next, connect the speaker cable and microphone (B & K, Type 2669) to the acoustic evaluation device (B & K, Multi-analyzer System 3560-B-030), and place the microphone 50 mm away from the speaker mounting hole in the simulated housing. Arranged. Next, SSR analysis (test signal 20 Hz to 20 kHz, sweep) was selected and executed as the evaluation method, and the acoustic characteristics (THD, sound pressure loss) of the waterproof sound-permeable membrane were evaluated. In addition, the sound pressure of the blank separately measured without attaching a waterproof sound-permeable membrane was 84 dB (average of frequencies 1 kHz, 1.6 kHz, 2 kHz, and 3.2 kHz).

  The total harmonic distortion THD is automatically obtained from the test signal input to the speaker from the acoustic evaluation apparatus and the signal received by the microphone, and it is determined that the smaller the value, the less the sound distortion occurs. it can. The sound pressure loss is a value obtained by subtracting the sound pressure measured with the waterproof sound-permeable membrane attached from the sound pressure of the blank. As the sound pressure loss is smaller, it can be determined that the volume output from the speaker is maintained.

Example 1
NTF1026 made by Nitto Denko was prepared as a PTFE porous membrane. NTF1026 is a PTFE porous membrane formed by biaxial stretching. The average pore diameter, surface density, air flow rate, water pressure resistance, tensile strength evaluation results and thickness are as shown in Table 1 below.

  As shown in Table 1, the water pressure resistance of NTF1026 is 240 kPa, and a waterproof property corresponding to IPX7 defined in JIS C0920 can be obtained with this membrane alone.

  Next, two NTFs 1026 were cut out in a rectangular shape, and the two cut out NTFs 1026 were laminated so that the primary stretching direction of each film was perpendicular to the direction perpendicular to the main surface of each film. Next, the two laminated films are pressure-bonded with a press (applied pressure 100 kPa, pressure-bonding time 5 seconds), and then fired in a state of being fixed to a stainless steel frame (firing oven temperature 360 ° C., baking time 1 minute). ), A waterproof sound-permeable membrane.

(Example 2)
A waterproof sound-permeable membrane was obtained in the same manner as in Example 1 except that firing was not performed.

(Comparative Example 1)
One NTF1026 was used as it was as a waterproof sound-permeable membrane without being laminated and integrated with another stretched porous membrane.

(Comparative Example 2)
Two NTFs 1026 cut out in a rectangular shape as in Example 1 were laminated so that the primary stretching direction of each film was parallel when viewed from the direction perpendicular to the main surface of each film. Next, the two laminated films were pressed and fired in the same manner as in Example 1 to obtain a waterproof sound-permeable film.

  The evaluation results of the acoustic characteristics for the waterproof sound-permeable membranes produced in Examples 1 and 2 and Comparative Examples 1 and 2 are shown in Table 2 below. Both THD and sound pressure loss indicate values at input signals of 400 Hz and 800 Hz.

  As shown in Table 2, in Examples 1 and 2, although the sound pressure loss was slightly increased compared to Comparative Example 1 using only one PTFE porous membrane, THD was compared with Comparative Example and Comparative Example 2. Decreased significantly.

  The waterproof sound-permeable membrane of the present invention is suitable for use in electrical products such as beaches and forests, where the place of use is spreading widely from ordinary indoors and outdoors in recent years due to its high waterproofness. In addition, since the waterproof sound-permeable membrane of the present invention suppresses the occurrence of sound distortion when placed in a portion where sound is transmitted, the sound quality generated from the speaker or the sound quality input to the microphone is regarded as important. It is suitable for use in electrical products.

DESCRIPTION OF SYMBOLS 1 Waterproof sound-permeable membrane 11, 12 Stretched porous membrane 2 Waterproof sound-permeable member 21 Support body 5 Mobile phone 6 Speaker 7 Microphone 8 Buzzer 9 Case

Claims (6)

Having two or more stretched porous membranes laminated and integrated;
A waterproof sound-permeable membrane in which the direction of primary stretching of at least two membranes selected from the two or more stretched porous membranes is orthogonal or oblique to each other when viewed from a direction perpendicular to the main surface of the membrane.   The waterproof sound-permeable membrane according to claim 1, wherein primary stretching directions of at least two membranes selected from the two or more stretched porous membranes are orthogonal to each other when viewed from a direction perpendicular to the main surface of the membrane. .   The waterproof sound-permeable membrane according to claim 1, wherein the at least one stretched porous membrane is a polytetrafluoroethylene (PTFE) porous membrane. The waterproof sound-permeable membrane according to any one of claims 1 to 3,
A waterproof sound-permeable member comprising a support joined to the waterproof sound-permeable film.   The waterproof sound-permeable member according to claim 4, wherein the support is a ring-shaped or frame-shaped sheet disposed at a peripheral edge of the waterproof sound-permeable membrane. An electrical product with a voice function,
Sound can be transmitted between the sound generation unit and / or the sound receiving unit and the outside, and at least one selected from a sound generation unit for outputting sound and a sound receiving unit for inputting sound, and the sound generation unit and And / or a waterproof sound-permeable membrane that suppresses the entry of water into the sound receiving part,
An electrical product, wherein the waterproof sound-permeable membrane is the waterproof sound-permeable membrane according to any one of claims 1 to 3.