JP6069078B2 - Waterproof sound-permeable membrane, manufacturing method thereof, and waterproof sound-permeable member - Google Patents

Description

  The present invention relates to a waterproof sound-permeable membrane, a manufacturing method thereof, and a waterproof sound-permeable member.

  In an electronic device such as a mobile phone or a digital video camera, an acoustic device is housed in a casing. These housings have openings for allowing the passage of sound. In order to prevent water from entering the housing, a waterproof sound-permeable membrane that prevents passage of water while allowing passage of sound is attached to the opening. In Patent Document 1, a polytetrafluoroethylene (PTFE) porous membrane is cited as a waterproof sound-permeable membrane.

JP 2009-047331 A

  When an electronic device having a PTFE porous membrane attached to a casing is repeatedly used in water, the PTFE porous membrane may be irreversibly deformed by water pressure, and the waterproofness of the PTFE porous membrane may be affected. According to the study of the present inventor, such deformation is also observed when a PTFE porous membrane having a high water pressure resistance measured by applying a water pressure only once is used. In order to suppress deformation of the PTFE porous membrane, the strength of the PTFE porous membrane may be increased. However, it is not easy to improve the waterproofness of the PTFE porous membrane when the water pressure is repeatedly applied while maintaining the sound permeability of the PTFE porous membrane. For example, if the surface density of the PTFE porous membrane is simply increased to improve the strength, the sound permeability of the membrane is lowered.

  In view of such circumstances, an object of the present invention is to improve a waterproof sound-permeable membrane.

The present invention
It has a sound transmission area consisting of a single layer polytetrafluoroethylene porous membrane,
The surface density of the porous membrane is 10 to 40 g / m ² ;
The air permeability in the thickness direction of the porous membrane is 9 to 30 seconds / 100 mL,
Provided is a waterproof sound-permeable membrane having a degree of firing of the porous membrane of 85 to 100.
However, the air permeability is a value given by the B method (Gurley method) of the air permeability measurement method defined in JIS L1096, and the degree of calcination is the heat of fusion of the unsintered polytetrafluoroethylene by ΔH ₁ When the heat of fusion of the polytetrafluoroethylene fired body is ΔH ₂ and the heat of fusion of the polytetrafluoroethylene porous membrane is ΔH ₃ , {(ΔH ₁ −ΔH ₃ ) / (ΔH ₁ −ΔH ₂ )} It is a value given by x100.

The present invention also provides:
A casing having an opening;
Provided is a waterproof sound-permeable member provided with the above-mentioned waterproof sound-permeable film, which is attached to the casing so as to close the opening.

The present invention also provides:
A method for producing a waterproof sound-permeable membrane having a sound-permeable region comprising a single-layer polytetrafluoroethylene porous membrane,
Step (a) in which a polytetrafluoroethylene green body is stretched in a first direction at a temperature of 327 ° C. or higher and then stretched in a second direction orthogonal to the first direction to obtain a polytetrafluoroethylene porous membrane When,
And (b) arranging an adhesive layer on the surface of the porous membrane so as to surround the sound transmission region,
In the step (a),
The temperature is set so that the degree of firing of the porous film is 85 to 100,
The draw ratio in the first direction and the draw ratio in the second direction so that the surface density of the porous film is 10 to 40 g / m ² and the air permeability in the thickness direction is 9 to 30 seconds / 100 ml. Determine
A method for producing a waterproof sound-permeable membrane is provided.
However, the degree of firing was defined as ΔH _{1 for} the heat of fusion of the non-fired polytetrafluoroethylene, ΔH _{2 for} the heat of fusion of the fired polytetrafluoroethylene, and ΔH ₃ for the heat of fusion of the polytetrafluoroethylene porous membrane. Sometimes, {(ΔH ₁ −ΔH ₃ ) / (ΔH ₁ −ΔH ₂ )} × 100, and the air permeability is the B method (Gurley of the air permeability measurement method defined in JIS L1096). This is the value given by

  The waterproof sound-permeable membrane of the present invention combines sound permeability that allows sound to pass well and water resistance that is difficult to deform even when repeated water pressure is applied. The waterproof sound-permeable membrane of the present invention can be suitably used for an electronic device in which an acoustic device is accommodated, which is assumed to be used in water.

It is sectional drawing which shows typically an example of the waterproof sound-permeable membrane of this invention. It is a perspective view which shows typically an example of the waterproof sound-permeable membrane of this invention. It is an expanded sectional view showing typically an example of the waterproof sound-permeable member of the present invention. It is an expanded sectional view showing typically an example of electronic equipment to which the waterproof sound-permeable membrane of the present invention was applied. It is a schematic diagram for demonstrating the evaluation method of a waterproof sound-permeable membrane used in the Example.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a cross-sectional view of the waterproof sound-permeable membrane 10 of this embodiment, and FIG. 2 is a perspective view of the waterproof sound-permeable membrane 10. The waterproof sound-permeable membrane 10 has a sound-permeable region 13c that allows passage of sound and a peripheral region 13p that surrounds the sound-permeable region 13c. The sound conduction region 13 c is configured by a single-layer polytetrafluoroethylene (PTFE) porous film 11. The peripheral region 13p includes a PTFE porous membrane 11 and an adhesive layer 12. The adhesive layer may be composed only of an adhesive, but may be a double-sided tape.

The surface density of the PTFE porous membrane 11 is 10 to 40 g / m ² . The air permeability in the thickness direction of the porous PTFE membrane 11 is 9 to 30 seconds / 100 mL as a value given by the air permeability measurement method B (Gurley method) defined in JIS L1096. The degree of firing of the PTFE porous membrane 11 is 85-100. Since the ranges of the surface density, the air permeability, and the firing degree are set as described above, the waterproof sound-permeable membrane 10 suppresses the deformation of the sound-transmitting region 13c and the sound when passing through the sound-transmitting region 13c. Loss is suppressed. The surface density of the PTFE porous membrane 11 is preferably 15 to 35 g / m ² . The air permeability of the PTFE porous membrane 11 is preferably 12 to 28 seconds / 100 mL. The degree of firing of the PTFE porous membrane 11 is preferably 88-100. The degree of firing can be controlled by the processing temperature of the PTFE porous membrane 11, for example, the stretching temperature. The degree of firing is also affected by the microporous structure of the film when exposed to high temperatures. For this reason, the degree of firing also depends on the draw ratio.

  From the viewpoint of ensuring sound transmission, it is desirable that the surface density is small and the air permeability is large. However, for compatibility with waterproofness, the surface density and the air permeability are preferably within the above ranges.

  The degree of firing may be in the range of 85-95. From the viewpoint of improving waterproofness, the higher the degree of firing, the better. On the other hand, in order to achieve a high degree of firing, setting the stretching temperature high should be avoided from the viewpoint of reducing manufacturing costs. According to the study of the present inventor (examples described later), practical waterproofness can be realized if the degree of firing is 85 or more. Therefore, considering the mass production of the waterproof sound-permeable membrane, the firing degree is appropriately about 85 to 95.

The degree of firing is {(ΔH ₁ −ΔH ₃ ) / when the heat of fusion of the PTFE green body is ΔH ₁ , the heat of fusion of the PTFE fired body is ΔH ₂ , and the heat of fusion of the PTFE porous membrane 11 is ΔH _3. (ΔH ₁ −ΔH ₂ )} × 100. Specifically, the degree of calcination can be measured by using a differential scanning calorimeter (DSC) and determining the area of the endothermic peak in accordance with the procedure described in the item [Baking degree] in the examples described later. The endothermic peak by DSC of the PTFE fired body (completely fired body, firing degree 100) has a top at 320 to 330 ° C., and the endothermic peak by DSC of the PTFE unfired body (completely fired body, firing degree 0) is: It has a top at 330-350 ° C. The endothermic peak of the PTFE incompletely fired body having a firing degree of less than 100 has a broader shape than these endothermic peaks, and has two peaks at 320 to 330 ° C and 330 to 350 ° C, for example, 320 to 330 It has one peak that exists at 0C and one shoulder that exists at 330-350C. When the PTFE porous membrane is heated to about 400 ° C. in order to measure the heat of fusion ΔH ₃ , the PTFE porous membrane becomes a completely fired body. The heat of fusion ΔH ₂ can be calculated by measuring the heat of fusion again for this completely fired body. However, it can also be calculated by measuring the heat of fusion of the fired body obtained by firing the PTFE green body.

  The PTFE porous membrane 11 of the present embodiment is an in-plane direction perpendicular to the thickness direction of the membrane 11, and has a tensile strength measured in accordance with JIS K7113 of 13N or more, for example, 14N or more and 23N or less. A first direction that is maximum in the in-plane direction, a thickness direction and a direction perpendicular to the first direction, and a tensile strength measured in accordance with JIS K7113 is 5N or more, for example, 5.2N or more and 15N or less. Direction. A PTFE porous membrane made porous by biaxial stretching usually has a porous structure composed of nodes and fibrils, and has the maximum tensile strength in the direction in which the fibrils develop and extend. The PTFE porous membrane 11 of the present embodiment is suitable not only for the maximum strength in the in-plane direction but also for the strength in the direction orthogonal to the direction in which the maximum strength is obtained. Yes. In the PTFE porous membrane obtained by the manufacturing method described later, the first direction corresponds to the stretching direction (longitudinal direction) in the first stretching step, and the second direction corresponds to the stretching direction (width direction) in the second stretching step. appear.

  The waterproof sound-permeable membrane 10 of the present embodiment includes a double-sided tape as the adhesive layer 12 for bonding the waterproof sound-permeable membrane 10 to a counterpart material (housing or the like). The double-sided tape is affixed to the surface 11 f of the peripheral edge portion 11 p of the PTFE porous membrane 11. An adhesive layer such as a double-sided tape is disposed on the surface of the PTFE porous membrane 11 so as to surround the sound passing region 13c. In addition, the adhesion layer 12 may be formed in the back surface 11b, and may be formed in both the surface 11f and the back surface 11b.

  The front surface 11f and / or the back surface 11b of the PTFE porous membrane 11 may be subjected to water repellent treatment or oil repellent treatment. The water repellent treatment or the oil repellent treatment can be carried out, for example, by impregnating the surface 11f and / or the back surface 11b with a material having a surface tension lower than that of PTFE.

  The PTFE porous membrane 11 may contain colorants such as pigments and dyes. Examples of the dye include azo dyes and oil-soluble dyes. An example of a preferred colorant is carbon black.

  FIG. 3 shows a waterproof sound-permeable member 20 in which the waterproof sound-permeable membrane 10 is disposed. The waterproof sound-permeable member 20 includes a housing part 21 having an opening 22 and a waterproof sound-permeable membrane 10 attached to the housing part 21 so as to close the opening 22. The waterproof sound-permeable membrane 10 is fixed to the housing portion 21 by the adhesive force of the adhesive layer 12. The adhesive layer 12 may be omitted, and the PTFE porous membrane 11 may be directly fixed to the housing portion 21 by heat lamination or the like. In this case, the waterproof sound-permeable membrane 10 is composed of the single-layer PTFE porous membrane 11 also in the peripheral region 13p.

  As an example of an electronic device to which a waterproof sound-permeable membrane including the PTFE porous membrane 11 is applied, a mobile phone 30 is shown in FIG. The waterproof sound-permeable membrane 110 in the mobile phone 30 is the same as the waterproof sound-permeable membrane 10 except that a double-sided tape is attached to the back surface 11b of the PTFE porous film 11 as the adhesive layer 12. .

  A microphone 33 is accommodated in the housing 38 of the mobile phone 30. The housing 38 is provided with a sound collection port 39 for guiding sound from the outside to the microphone 33. In the package 35 of the microphone 33, a sound collecting unit 34 for converting sound into an electric signal is accommodated. The package 35 is a rectangular parallelepiped with a hollow inside, and a sound collection port 36 for guiding the sound introduced from the sound collection port 39 of the housing 38 to the sound collection unit 34 of the microphone 33 is provided on one surface of the package 35. It has been. The respective sound collection ports 36 and 39 are joined via the waterproof sound-permeable membrane 110 while being closed by the waterproof sound-permeable membrane 110. The microphone 33 is electrically connected to the circuit board 31 of the mobile phone 30 through a terminal (not shown) provided on the bottom surface of the package 35, and an electric signal converted from sound by the sound collecting unit 34 is The signal is output to the circuit board 31 via the terminal. In the mobile phone 30, foreign matter such as dust and water enters the sound collection unit 34 of the microphone 33 from the sound collection ports 36 and 39 by the waterproof sound-permeable membrane 110 arranged so as to block the sound collection ports 36 and 39. While preventing the sound, the sound can be passed to the sound collection unit 34, and the performance of the microphone 33 can be ensured while reducing the occurrence of noise and the failure in the microphone 33.

  Next, an example of a manufacturing method suitable for manufacturing a waterproof sound-permeable membrane having a sound-permeable region made of a single layer PTFE porous membrane as described above will be described.

  This production method includes, as a method for producing a PTFE porous membrane, a molding step for obtaining a polytetrafluoroethylene green body, a first stretching step and a second stretching step for stretching the polytetrafluoroethylene green body while heating. Is provided.

  In the molding process, a mixture obtained by adding a liquid lubricant to PTFE fine powder is extruded or rolled by at least one of an extrusion method and a rolling method, and is formed into a sheet extending in a predetermined direction, so that polytetrafluoroethylene is not fired Get the body.

  The PTFE fine powder used in the molding step is not particularly limited, and various commercially available products can be used. However, from the viewpoint of obtaining a porous PTFE membrane having high water resistance, it is preferable to use high molecular weight PTFE fine powder in the molding step. Examples of preferable PTFE fine powder include Polyflon F-101HE (manufactured by Daikin Industries), Fullon CD-123 (manufactured by Asahi Glass Co., Ltd.), Teflon 6J (manufactured by Mitsui / Dupont Fluorochemical Co., Ltd.)

  The liquid lubricant used in the molding step is not particularly limited as long as it can wet the PTFE fine powder and can be removed by a method such as evaporation or extraction. Examples of such liquid lubricants include hydrocarbons such as liquid paraffin, naphtha, toluene, xylene, and the like, and alcohols, ketones, esters, and fluorinated solvents. Also, a mixture of two or more of these examples may be used. The addition amount of the lubricant varies depending on the molding method of the sheet-like molded body, but is usually about 5 to 50 parts by weight with respect to 100 parts by weight of the PTFE fine powder.

  In a specific example, PTFE fine powder wet with a liquid lubricant is compressed by a cylinder and extruded from a ram extruder to form a sheet. This sheet is rolled to an appropriate thickness (usually 0.05 to 0.50 mm) between a pair of rolls. Thereafter, the liquid lubricant is driven off by a heating method or an extraction method. In this way, an unbaked polytetrafluoroethylene is obtained.

  In the first stretching step, the polytetrafluoroethylene green body obtained in the molding step is stretched at the first stretching temperature at the first stretching ratio in the longitudinal direction perpendicular to the thickness direction of the polytetrafluoroethylene green body. To obtain an intermediate.

  The first stretching temperature is 327 ° C. (melting point of polytetrafluoroethylene) or more, for example, 327 to 400 ° C. Setting the first stretching temperature as high as this is advantageous in obtaining a PTFE porous membrane having a firing degree of 85 to 100 and small deformation due to external force. The first stretching temperature is preferably 350 to 390 ° C.

  The first draw ratio is, for example, 2 to 10 times. Setting the upper limit of the first draw ratio as described above means that the water resistance of the waterproof sound-permeable membrane decreases due to excessive pores in the PTFE porous membrane (water leakage from the pores of the PTFE porous membrane). This is advantageous in that it can be suppressed. Further, when the first draw ratio is excessively low, the PTFE porous membrane may be reduced by a low first draw ratio or by limiting the second draw ratio that can be employed in the second drawing step described later to a small value. Although the surface density may be excessive, such a problem is unlikely to occur when the lower limit of the first draw ratio is set as described above. The first draw ratio is preferably 2.2 to 7 times. In another preferable example, the first draw ratio is 2 to 5 times.

  In the second stretching step, the intermediate is stretched at the second stretching temperature at the second stretching temperature in the width direction perpendicular to the thickness direction and the longitudinal direction.

The second stretching temperature is, for example, 40 to 400 ° C. The second draw ratio is, for example, 3 to 20 times. Setting the second stretching temperature and the second stretching ratio in this range is advantageous from the viewpoint of obtaining both a porous film having high water resistance and preventing breakage of the intermediate during stretching. . The second stretching temperature is preferably 100 to 300 ° C. The second draw ratio is preferably 4 to 10 times. In the present embodiment, the first stretching ratio and the second stretching ratio are determined so that the surface density of the PTFE porous membrane is 10 to 40 g / m ² and the air permeability in the thickness direction is 9 to 30 seconds / 100 mL.

  In the above example, the PTFE porous membrane is manufactured by the molding step, the first stretching step, and the second stretching step. However, when a PTFE porous membrane subjected to water-repellent treatment or oil-repellent treatment should be obtained. The water repellent treatment or the oil repellent treatment may be performed after the second stretching step. The material for water repellent treatment or oil repellent treatment (treatment agent) can be obtained, for example, by blending a water repellent or an oil repellent with a solvent. Specific examples of such a water repellent or oil repellent include perfluoroalkyl acrylate and perfluoroalkyl methacrylate.

  Further, when a colored PTFE porous membrane is to be obtained, a solution obtained by dissolving a dye or a pigment in a solvent may be applied to the PTFE porous membrane using a kiss coater or the like and dried. Moreover, a black PTFE porous membrane can also be obtained by including carbon in the mixture in the molding step.

  In the case where an adhesive layer is provided, the adhesive layer may be disposed on the surface of the PTFE porous membrane so as to surround the sound transmission region.

Example 1
20 parts by weight of a liquid lubricant (n-dodecane, manufactured by Japan Energy) was uniformly mixed with 100 parts by weight of PTFE fine powder (F101HE, manufactured by Daikin Industries). The resulting mixture was compressed with a cylinder and then ram extruded to obtain a sheet. The obtained sheet was passed through a metal rolling roll in a state containing a liquid lubricant, compressed to a thickness of 0.2 mm, and dried by heating at 150 ° C. to remove the liquid lubricant. This obtained the unbaking sheet-like molded object. This sheet-like molded body was stretched at a magnification of 2.5 times in the longitudinal direction at 370 ° C., and then stretched at a magnification of 6 times in the width direction at 150 ° C. In this way, a PTFE porous membrane E1 was obtained.

(Example 2)
A PTFE porous membrane E2 was obtained by the same procedure as in Example 1 except that when the sheet-shaped molded body was stretched in the longitudinal direction, it was stretched 3 times in the longitudinal direction.

(Example 3)
A PTFE porous membrane E3 was obtained by the same procedure as in Example 1 except that when the sheet-shaped molded body was stretched in the longitudinal direction, it was stretched 5 times in the longitudinal direction.

(Comparative Example 1)
A PTFE porous membrane was obtained in the same manner as in Example 1 except that the film was stretched 8 times in the longitudinal direction at 250 ° C. and 45 times in the width direction at 150 ° C. Two PTFE porous membranes were prepared, and the two PTFE porous membranes were laminated so that their longitudinal directions coincided. The resulting laminate was heated in a 400 ° C. oven for 3 minutes. Thus, a PTFE porous membrane C1 laminated was obtained.

(Comparative Example 2)
When obtaining each of the two porous PTFE membranes, a laminated PTFE porous membrane C2 was obtained by the same procedure as in Comparative Example 1 except that the two porous PTFE membranes were stretched 10 times in the width direction.

(Comparative Example 3)
A PTFE porous membrane C3 was obtained by the same procedure as in Example 1 except that the film was stretched 1.8 times in the longitudinal direction.

  The PTFE porous membranes E1 to E3 and C1 to C3 were examined for surface density, air permeability, water pressure resistance, repeated water pressure resistance, sound loss, tensile strength, and firing degree as follows.

[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 .

[Air permeability]
The air permeability of the PTFE porous membrane is based on the B method (Gurley test method) defined in JIS L1096. When a predetermined pressure is applied, 100 mL of air passes through the porous membrane. Required time).

[Tensile strength]
The tensile strength of the PTFE porous membrane was determined by cutting the porous membrane into the shape of dumbbell No. 2 described in JIS K7113, and then using the tensile tester (A & D Co., Tensilon Universal Testing Machine). The tensile test was carried out under the following conditions using MODEL Ten RTC-1310A-PL). The tensile strength was measured with respect to each of the longitudinal direction and the width direction of the PTFE porous membrane.
Distance between chucks: 95mm
Tensile speed: 200 mm / min Measurement temperature: 25 ° C.

The tensile strength is a value obtained by dividing the maximum load load (N) when the PTFE porous membrane is ruptured by the tensile test by the cross-sectional area (mm ² ) of the PTFE porous 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. Moreover, the tensile strength shown in Table 1 is an average value of three measurements.

[Water pressure resistance]
The water pressure resistance was determined using a water resistance tester (Method B: 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 having an opening diameter of 2 mm or 10 mm was installed on the opposite side of the pressure surface of the film, and the water pressure resistance was measured in a state where deformation was suppressed.

[Repeated water pressure]
Repeated water pressure resistance was performed using a water resistance tester described in JIS L1092, similarly to the water pressure resistance test. Specifically, a test in which a water pressure of 150 kPa (corresponding to a water pressure of 15 m in depth) was applied to the PTFE porous membrane and held for 30 minutes was repeated 5 times. Thereafter, the presence or absence of water leakage was observed, and the quality was judged. The acceptance criteria are as follows.
A: No water leak B: Water leak

  In addition, it can be considered that the sample having no water leakage in this test has waterproofness corresponding to IPX8 defined in JIS C0920.

[Sound loss]
The sound loss in the samples was evaluated as follows.

  First, as shown in FIG. 5, a simulated housing 41 (made of acrylic, length 70 × width 50 × height 15 mm) imitating the housing of a mobile phone was prepared. The simulated housing 41 includes two parts 41a and 41b, and the parts 41a and 41b can be fitted together. A mounting hole 42 (φ = 13 mm) is provided in the portion 41a. By fitting the portions 41 a and 41 b to each other, a space in which no opening other than the attachment hole 42 and the conduction port 43 of the lead wire 44 is formed in the simulated housing 41 is formed.

  Separately, the PTFE porous membranes produced in each of the examples and comparative examples (in FIG. 5, the reference numeral 211 is attached to the PTFE porous membrane) was punched into a circle having a diameter of 16 mm using a Thomson mold. . Next, double-sided tape 212 punched into a ring shape having an outer diameter of 16 mm and an inner diameter of 13 mm was attached to the peripheral portions of both main surfaces of the punched PTFE porous membrane. After that, the PTFE porous membrane was attached to the speaker 45 (Star Precision Co., Ltd., SCC-16A, φ = 16 mm) serving as a sound source via one double-sided tape 212.

  Next, the speaker 45 to which the PTFE porous film is attached is attached to the attachment hole 42 in the portion 41 a of the simulated housing 41, the PTFE porous film faces the attachment hole 42, and the PTFE porous film closes the attachment hole 42. Thus, it fixed from the surface which becomes an inner side when it fits with the part 41b. The speaker 45 is fixed to the portion 41a by a double-sided tape 212 attached to the surface of the PTFE porous film opposite to the speaker 45, and at this time, the double-sided tape 212 does not cover the mounting hole 42. At the same time, care was taken that the mounting hole 42 was completely blocked by the PTFE porous membrane.

  Next, the lead wire 44 of the speaker 45 is led to the outside of the simulated housing 41 through the conduction port 43, and the portions 41a and 41b are fitted together to measure the sound loss of the PTFE porous membrane. 41 was formed. The conduction port 43 was closed with putty after the lead wire 44 was led out.

  Next, the lead wire 44 and a microphone (a combination of Type 2669 and Type 4192 manufactured by Bruel & Kjar) and a sound transmission evaluation device (3560-B-030 manufactured by Bruel & Kjar) are connected to the speaker 45. A microphone was placed at a position 50 mm away from the center.

  The sound volume received by the microphone in such a state and the sound volume received by the microphone in the same state except that the porous PTFE membrane was omitted were measured, and the sound loss (dB) was evaluated from the difference between them. did. The frequency of the sound used for the measurement was 1000 Hz. The smaller the sound loss, the better the original sound is reproduced. If the loss is 5 dB or less, it can be said that sound transmission is high.

[Baking degree]
Measure the heat of fusion ΔH ₁ of an unfired sheet-shaped molded body before stretching, the heat of fusion ΔH ₂ of a fired body obtained by completely firing the sheet-shaped molded body, and the heat of fusion ΔH ₃ of a porous PTFE membrane. did. Heats of fusion ΔH ₁ , ΔH ₂ and ΔH ₃ were measured using a differential scanning calorimeter (DSC: DSC 200 F3 Mia, manufactured by Bruker AXS Co., Ltd.). The heat of fusion can be determined based on the area of the portion surrounded by the baseline of the heat of fusion curve and the endothermic curve.

In measuring the heat of fusion ΔH ₁ , first, a sample of 15 ± 5 mg was weighed from the sheet-like molded body. Next, the weighed sample was placed in an aluminum pan of DSC and heated from room temperature to 400 ° C. at a temperature rising rate of 10 ° C./min. The peak position of the endothermic peak of the sheet-like molded body that was an unsintered body of PTFE was at 330 to 350 ° C.

In the measurement of the heat of fusion ΔH ₂ , a fired body obtained by heating at the time of measuring the heat of fusion ΔH ₁ was used. First, the fired body obtained was cooled from 400 ° C. to 250 ° C. at a cooling rate of 10 ° C./min, and then reheated to 400 ° C. at a temperature rising rate of 10 ° C./min, and the heat of fusion ΔH ₂ was measured. did. The peak position of the endothermic peak of each sintered body of PTFE was in the range of 320 to 340 ° C.

In the measurement of heat of fusion ΔH ₃ , a sample of 15 ± 5 mg was weighed from the PTFE porous membrane obtained from each example and comparative example. Next, the weighed sample was placed in an aluminum pan of DSC and heated from room temperature to 400 ° C. at a heating rate of 10 ° C./min, and the heat of fusion ΔH ₃ was measured. The peak position of the endothermic peak of each PTFE porous membrane was in the range of 320 to 350 ° C.

The degree of firing S was calculated based on the following equation from the obtained heats of fusion ΔH ₁ , ΔH ₂ and ΔH ₃ .
S = {(ΔH ₁ −ΔH ₃ ) / (ΔH ₁ −ΔH ₂ )} × 100

  Table 1 shows the results of measuring the surface density, air permeability, water pressure resistance, water pressure resistance, repeated water pressure resistance, sound loss, tensile strength and degree of firing for the PTFE porous membranes E1 to E3 and C1 to C3.

In Examples 1 to 3, in which the surface density is in the range of 10 to 40 g / m ² , the air permeability is in the range of 9 to 30 seconds / 100 mL, and the firing degree is in the range of 85 to 100, the repeated water pressure resistance is A was determined. Therefore, even if PTFE porous membranes E1 to E3 of Examples 1 to 3 are placed in a casing (electronic device) to which a water pressure of about 15 m is applied and water pressure is repeatedly applied, it is difficult to cause water leakage due to deformation. It can be said. In Examples 1 to 3, the sound loss was 5 dB or less. Therefore, it can be said that the PTFE porous membranes E1 to E3 can be suitably used for a housing that requires sound permeability.

  The waterproof sound-permeable membrane of the present invention can be suitably used for an electronic device in which an acoustic device is accommodated, which is assumed to be used in water. Specifically, it can be suitably used for a mobile phone, a digital video camera, and the like.

DESCRIPTION OF SYMBOLS 10,110 Waterproof sound-permeable membrane 11, 211 PTFE porous membrane 11b Back surface 11f Front surface 11p Peripheral part 12,212 Adhesive layer (double-sided tape)
13c Sound-transmitting area 13p Peripheral area 20 Waterproof sound-transmitting member 21 Housing part 22 Opening 30 Mobile phone 31 Circuit board 33 Microphone 34 Sound collecting part 35 Package 36 Sound collecting port 38 Housing 39 Sound collecting port 41 Simulated housing 41a, 41b Part 42 Mounting hole 43 Conduction port 44 Lead wire 45 Speaker

Claims (6)

It has a sound transmission area consisting of a single layer polytetrafluoroethylene porous membrane,
The surface density of the porous membrane is 10 to 40 g / m ² ;
The air permeability in the thickness direction of the porous membrane is 9 to 30 seconds / 100 mL,
A waterproof sound-permeable membrane, wherein the porous membrane has a firing degree of 85 to 100.
However, the air permeability is a value given by the B method (Gurley method) of the air permeability measurement method defined in JIS L1096, and the degree of calcination is the heat of fusion of the unsintered polytetrafluoroethylene by ΔH ₁ When the heat of fusion of the polytetrafluoroethylene fired body is ΔH ₂ and the heat of fusion of the polytetrafluoroethylene porous membrane is ΔH ₃ , {(ΔH ₁ −ΔH ₃ ) / (ΔH ₁ −ΔH ₂ )} It is a value given by x100.   The waterproof sound-permeable membrane according to claim 1, wherein the degree of firing of the porous membrane is 85 to 95.   The polytetrafluoroethylene porous membrane has a first direction having a tensile strength measured in accordance with JIS K7113 of 13 N or more and a maximum in an in-plane direction perpendicular to the thickness direction of the porous membrane, The waterproof sound-permeable membrane according to claim 1 or 2, comprising a second direction perpendicular to the thickness direction and the first direction and having a tensile strength measured in accordance with JIS K7113 of 5 N or more.   The waterproof sound-permeable membrane according to any one of claims 1 to 3, further comprising an adhesive layer disposed on a surface of the porous membrane so as to surround the sound-permeable region. A casing having an opening;
A waterproof sound-permeable member comprising the waterproof sound-permeable membrane according to any one of claims 1 to 4, which is attached to the housing portion so as to close the opening. A method for producing a waterproof sound-permeable membrane having a sound-permeable region comprising a single-layer polytetrafluoroethylene porous membrane,
Step (a) in which a polytetrafluoroethylene green body is stretched in a first direction at a temperature of 327 ° C. or higher and then stretched in a second direction orthogonal to the first direction to obtain a polytetrafluoroethylene porous membrane When,
And (b) arranging an adhesive layer on the surface of the porous membrane so as to surround the sound transmission region,
In the step (a),
The temperature is set so that the degree of firing of the porous film is 85 to 100,
The draw ratio in the first direction and the draw ratio in the second direction so that the surface density of the porous film is 10 to 40 g / m ² and the air permeability in the thickness direction is 9 to 30 seconds / 100 ml. Determine
A method for producing a waterproof sound-permeable membrane.
However, the degree of firing was defined as ΔH _{1 for} the heat of fusion of the non-fired polytetrafluoroethylene, ΔH _{2 for} the heat of fusion of the fired polytetrafluoroethylene, and ΔH ₃ for the heat of fusion of the polytetrafluoroethylene porous membrane. Sometimes, {(ΔH ₁ −ΔH ₃ ) / (ΔH ₁ −ΔH ₂ )} × 100, and the air permeability is the B method (Gurley of the air permeability measurement method defined in JIS L1096). This is the value given by

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