JP6581876B2 - Ventilation membrane and microphone - Google Patents

Description

  The present invention relates to a gas permeable membrane and a microphone.

  Housings such as smartphones and mobile phones have openings for placing acoustic conversion components such as microphones and speakers. In order to prevent water and dust from entering the inside of the housing, an air permeable membrane that does not transmit water is often disposed in such an opening. As the gas permeable membrane, for example, a polytetrafluoroethylene (PTFE) porous film is used.

  The manufacturing process of the microphone includes, for example, a process of attaching a PTFE porous film as a gas permeable membrane to a micro electro mechanical systems (MEMS) microphone. In this step, a solder reflow furnace is passed in order to attach a gas permeable membrane to the MEMS microphone.

  The microphone needs to have a certain degree of air permeability for its use. However, since the PTFE porous film is produced by uniaxial stretching or biaxial stretching, it shrinks in a high temperature environment such as a reflow furnace. Shrinked PTFE porous films may not have sufficient breathability for use in microphones.

  In order to suppress the shrinkage of the PTFE porous film, Patent Document 1 describes that the porous fluororesin film is held in a shape-fixed state, lower than the melting point of the fluororesin, and the difference from the melting point is within 30 ° C. A method for producing a porous PTFE membrane including an annealing step of holding at a temperature for 1 to 20 hours is described.

  Patent Document 2 describes that a metal net is coated with a layer of polyetheretherketone (PEEK), and a porous polytetrafluoroethylene layer is laminated on the coated metal net. Has been.

International Publication No. 2015/002002 Japanese National Patent Publication No. 10-513119

  The porous PTFE membrane described in Patent Document 1 has a single-layer structure composed of only a PTFE membrane. Therefore, there is a problem of shrinkage in a high temperature environment. Moreover, since the laminate described in Patent Document 2 uses a metal net, it is not excellent in workability such as cutting and punching. Also, a metal mesh coated with a layer of PEEK is very hard. Therefore, this metal net is not excellent in flexibility, and is easily cracked even if it is slightly bent. Furthermore, there is a problem that the chemical resistance of PEEK is inferior to that of PTFE.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a gas permeable membrane having high heat resistance and water resistance and sufficient air permeability, and a microphone including the gas permeable membrane.

According to the first aspect of the present invention, it includes a polytetrafluoroethylene porous film and a fluororesin-containing air-permeable material layer laminated on the polytetrafluoroethylene porous film, for 10 minutes at a temperature of 300 ° C. by heat treatment, Ri both thermal shrinkage der less than 3% of the perpendicular TD direction to the MD direction and the MD direction, the reduction rate of Frazier air permeation amount by the heat treatment is less than 10% der Ru breathable film Provided.

  According to the second aspect of the present invention, there is provided a microphone including the gas permeable membrane according to the first aspect.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the air permeable membrane which has high heat resistance and water resistance, and has sufficient air permeability, and the microphone provided with this air permeable membrane.

Sectional drawing which shows schematically an example of the air permeable membrane which concerns on 1st Embodiment. The enlarged plan view which shows roughly the fluororesin containing ventilation material layer whose woven structure is mesh shape. Sectional drawing which shows roughly an example in case a fluororesin layer is a 2 layer structure. The graph which shows the dimensional change rate of the air permeable film which concerns on an Example and a comparative example. The graph which shows the air flow rate change rate of the air permeable film which concerns on an Example and a comparative example.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described.
The gas permeable membrane according to the present embodiment includes a polytetrafluoroethylene porous film and a fluororesin-containing gas permeable material layer laminated on the polytetrafluoroethylene porous film, and extends for 10 minutes at a temperature of 300 ° C. The heat shrinkage rate in both one direction and the direction perpendicular to the one direction by heat treatment is less than 3%. A method for measuring the thermal shrinkage will be described later.

  The PTFE porous film has a porous structure composed of an amorphous node portion and a fibril portion drawn from the node portion. Such a porous structure can be fine compared to the structure of other breathable materials such as nonwoven fabrics. Therefore, the gas permeable membrane including the PTFE porous film can have high water resistance.

  However, since the PTFE porous film is manufactured by a method including a drawing step, it contains residual stress. This residual stress works to return to the state before stretching when the PTFE porous film is used in a high temperature environment. That is, a single PTFE porous film shrinks in a high temperature environment.

  The gas permeable membrane according to this embodiment is obtained by laminating a fluororesin-containing gas permeable material layer on this PTFE porous film. This fluororesin-containing ventilation material layer can suppress thermal shrinkage of the PTFE porous film. Therefore, this gas permeable membrane has a heat shrinkage rate of less than 3% in both one direction and a direction perpendicular to the one direction by heat treatment for 10 minutes at a temperature of 300 ° C.

  The heat shrinkage rate is preferably close to 0%, and the lower limit may be 0%. The thermal shrinkage is preferably in the range of 0.5% to 2.0%. It is preferable that the heat shrinkage rate is within this range because the decrease rate of the Frazier type air flow rate of the gas permeable membrane before and after the heat treatment is less than 10%, and variation in the air flow rate due to heating can be suppressed.

  The fluororesin-containing breathable material layer can have a breathability that does not impair the breathability of the PTFE porous film. Therefore, the gas permeable membrane in which the fluororesin-containing gas permeable material is laminated on the PTFE porous film can have sufficient gas permeability.

  Thus, according to the gas permeable membrane of this embodiment, heat resistance and water resistance can be increased, and sufficient gas permeability can be obtained.

  Hereinafter, the present embodiment will be described with reference to the drawings. In addition, the same referential mark is attached | subjected to the component which exhibits the same or similar function through all the drawings, and the overlapping description is abbreviate | omitted.

FIG. 1 is a cross-sectional view schematically showing an example of a gas permeable membrane according to the present embodiment.
As shown in FIG. 1, the gas permeable membrane 1 includes a PTFE porous film 2 and a fluororesin-containing gas permeable material layer 5. The fluororesin-containing ventilation material layer 5 includes, for example, a breathable support material 3 and a fluororesin layer 4. The fluororesin layer 4 is impregnated in the breathable support material 3.

  The PTFE porous film 2 is substantially made of PTFE. The PTFE porous film 2 may be baked. When the thickness of the PTFE porous film 2 is excessively small, the water resistance may not be sufficient, the handling during processing is poor, and the gas permeable membrane may be easily heat-shrinked in a high temperature environment. When the thickness of the PTFE porous film 2 is excessively large, the air permeability may not be sufficient. Further, in this case, since the shrinkage force of the fluororesin layer 4 is stronger than the rigidity of the breathable support material 3, the breathable film may be warped by heat treatment.

  The fluororesin-containing ventilation material layer 5 is laminated only on one side of the PTFE porous film 2. The fluororesin-containing ventilation material layer 5 may be laminated on both surfaces of the PTFE porous film 2. When laminated on only one side, the area where the fluororesin layer 4 blocks the pores of the PTFE porous film 2 can be reduced, so that sufficient air permeability is easily secured. When laminated on both sides, the gas permeable membrane 1 is unlikely to warp even in a high temperature environment.

The fluororesin-containing breathable material layer 5 includes a breathable support material 3. The breathable support material 3 includes, for example, one or more fibers selected from the group consisting of glass cloth, aramid cloth, and metal fiber cloth. The breathable support material 3 may be made of one or more kinds of fibers selected from the group consisting of glass cloth and aramid cloth. When the air-permeable support material 3 is made of glass cloth, it is excellent in dimensional stability, cutability at the time of processing, and flexibility, stamping workability is stable, and chemical resistance is also excellent. The woven structure of the fluororesin-containing air-permeable material layer 5 may be mesh-like or non-mesh-like. Here, the mesh shape means a case where an opening ratio ε (%) representing an open area per unit area is within a range of 10% to 70%. The aperture ratio ε (%) can be calculated by the equation ε = A ² / (A + d) ² × 100. In the formula, d indicates the wire diameter of the flattened woven fabric, and A indicates the mesh opening. The aperture ratio will be described below with reference to the drawings.

  FIG. 2 is an enlarged plan view schematically showing a fluororesin-containing ventilation material layer having a mesh structure. In FIG. 2, d shows the wire diameter of the flat woven fabric, and A shows the mesh opening. When the wire diameter d is d = 0.6 mm and the aperture A is A = 0.9 mm, the aperture ratio ε (%) = 36.

  The opening ratio ε of the fluororesin-containing ventilation material layer 5 is, for example, in the range of 1% to 70%. When the opening ratio ε is within this range, even if the fluororesin-containing air-permeable material layer 5 is laminated on the PTFE porous film 2, the air permeability of the PTFE porous film 2 is not hindered.

  The fluororesin layer 4 carried on the air-permeable support material 3 may have a single layer structure or a multi-layer structure in which two or more layers are laminated. The fluororesin layer 4 may block some of the holes of the air-permeable support material 3, but it is desirable that all of the holes are not blocked. By supporting the fluororesin layer 4 on the breathable support material 3, the fluororesin-containing vent material layer 5 and the PTFE porous film 2 can be integrated. That is, the fluororesin layer 4 plays a role of integrating the fluororesin-containing ventilation material layer 5 and the PTFE porous film 2. Since the compatibility between the PTFE porous film 2 and the fluororesin layer 4 is good, the fluororesin-containing air-permeable material layer 5 and the PTFE porous film 2 are unlikely to peel at the interface between them.

  Furthermore, as for the fluororesin containing ventilation material layer 5 and the PTFE porous film 2, the fluororesin is exposed on the outermost surface. Therefore, the gas permeable membrane 1 in which these are integrated is excellent in chemical resistance.

  The fluororesin layer 4 includes, for example, at least one selected from the group consisting of PTFE, perfluoroalkoxyalkane (PFA), and perfluoroethylenepropene copolymer (FEP). The fluororesin layer 4 may be made of at least one selected from the group consisting of PTFE, PFA and FEP.

  FIG. 3 is a cross-sectional view schematically showing a case where the fluororesin layer 4 has a two-layer structure. In FIG. 3, the fluororesin layer 4 includes a first fluororesin layer 41 and a second fluororesin layer 42. The first fluororesin layer 41 is formed on both surfaces of the breathable support material 3. The second fluororesin layer 42 is formed on both first fluororesin layers.

  The first fluororesin layer 41 contains PTFE. The first fluororesin layer 41 may further contain a fluororesin other than PTFE. The second fluororesin layer 42 contains a meltable fluororesin such as PFA. The second fluororesin layer 42 may further contain PTFE.

  Here, as an example, a case where the first fluororesin layer 41 is PTFE and the second fluororesin layer 42 is PFA will be described. In this case, the fluororesin-containing ventilation material layer 5 and the PTFE porous film 2 can be easily integrated. This is because PFA is supported on the outermost surface of the fluororesin layer 4. Further, in this case, it is preferable because the raw material cost is low compared to the case where the fluororesin layer 4 is made of only a meltable fluororesin.

  The layer thickness of the 1st fluororesin layer 41 exists in the range of 50 micrometers-500 micrometers, for example. The layer thickness of the second fluororesin layer 42 is, for example, in the range of 0.5 μm to 3 μm, and preferably in the range of 1 μm to 2 μm.

  When the thickness of the first fluororesin layer 41 and the thickness of the second fluororesin layer 42 are within the above ranges, the amount of fluororesin supported as the second fluororesin layer 42 is relatively Few. Therefore, even if the above integration is performed, the fluororesin included in the second fluororesin layer 42 does not easily block the holes in the PTFE porous film 2.

  The Gurley-type air permeability of the single PTFE porous film 2 is, for example, 30 seconds or less, preferably 5 seconds or less, and more preferably 2 seconds or less. When the PTFE porous film 2 is used as a gas permeable membrane included in a microphone, the Gurley air permeability is preferably 2 seconds or less. As long as sufficient water resistance is maintained, the PTFE porous film 2 preferably has a low Gurley air permeability value. A method for measuring the Gurley air permeability will be described later.

The fragile air flow rate of the single PTFE porous film 2 is, for example, 0.1 cm ³ / (cm ² · sec) or more, preferably 0.3 cm ³ / (cm ² · sec) or more, more preferably It is 1.4 cm ³ / (cm ² · sec) or more, more preferably 3 cm ³ / (cm ² · sec) or more. As long as sufficient water resistance is maintained, it is preferable that the PTFE porous film 2 has a large amount of fragile aeration. A method for measuring the Frazier airflow will be described later.

The fragile air flow rate of the single fluororesin-containing air-permeable material layer 5 is, for example, 0.1 cm ³ / (cm ² · sec) or more, preferably 0.8 cm ³ / (cm ² · sec) or more, and more It is preferably 1.4 cm ³ / (cm ² · sec) or more, more preferably 12 cm ³ / (cm ² · sec) or more.

  The breathability of the single fluororesin-containing breathable material layer 5 is very high. Therefore, the Gurley-type air permeability of the single fluororesin-containing ventilation material layer 5 is less than 1 second, the measurement error is large, and the reliability of the measurement value is low.

  The Gurley air permeability of the gas permeable membrane 1 is, for example, 30 seconds or less, and preferably 2 seconds or less. The Gurley air permeability of the gas permeable membrane 1 is preferably not changed even when the gas permeable membrane 1 is subjected to heat treatment at a temperature of 300 ° C. for 10 minutes. The Gurley air permeability of the gas permeable membrane 1 after being subjected to this heat treatment is, for example, 30 seconds or less, and preferably 2 seconds or less. When the Gurley-type air permeability of the gas permeable membrane 1 after the heat treatment is 2 seconds or less, the gas permeable membrane 1 has a sufficiently high air permeability and can be suitably used for a microphone.

The fragile air flow rate of the gas permeable membrane 1 is, for example, 0.1 cm ³ / (cm ² · sec) or more, and preferably 1.4 cm ³ / (cm ² · sec) or more. It is preferable that the fragile air flow rate of the gas permeable membrane 1 does not change even if the gas permeable membrane 1 is subjected to a heat treatment at a temperature of 300 ° C. for 10 minutes. The reduction rate of the Frazier type air flow rate of the gas permeable membrane 1 when this heat treatment is performed is, for example, less than 10%, preferably less than 8%.

<Measurement method of thermal shrinkage>
The test piece is cut into 100 mm × 100 mm, and heat-treated at 300 ° C. for 10 minutes using an electric furnace (STPH-200, manufactured by Espec Corp.). Then, the longitudinal (machine direction: MD direction) and lateral (vertical direction: TD direction) lengths of the test pieces are measured with a steel ruler.

  When the PTFE porous film included in the gas permeable membrane as a test piece is manufactured by uniaxial stretching, typically, the length of the test piece in the MD direction is shrunk by heat treatment, and the test piece The length in the TD direction expands by heat treatment. On the other hand, when the PTFE porous film provided in the gas permeable membrane as a test piece is produced by biaxial stretching, typically, the length in the MD direction of the test piece is shrunk by heat treatment, The length of the test piece in the TD direction is also shrunk by heat treatment.

  For any length, when the length after the heat treatment is smaller than that before measurement, that is, when contracted in a certain direction, the length of the most contracted portion is measured. For any length, when the length after the heat treatment is larger than before measurement, that is, when the length is expanded in a certain direction, the length of the most expanded portion is measured.

  When shrinkage or expansion in any direction cannot be confirmed by visual observation, first, measure the dimensions of both ends of a side substantially parallel to the direction perpendicular to the MD (TD) direction and three points near the midpoint of this side. Among these three dimensions, the dimension of the most deformed part from 100 mm before the heat treatment is defined as the dimension in the MD (TD) direction. In addition, a measured value shall be the value which rounded off to the first decimal place. For example, 99.5 mm is read as 100 mm, and 100.4 mm is read as 100 mm.

  For each of the MD direction and the TD direction, the heat shrinkage rate is calculated by multiplying the length measured after the heat treatment with respect to the length before the heat treatment (100 mm) by 100.

<Measurement method of Gurley type air permeability>
The Gurley type air permeability is measured according to JIS P 8117 using, for example, an automatic Gurley type densometer manufactured by Yasuda Seiki Seisakusho Co., Ltd. as an apparatus.

<Measurement method of Frazier type air flow rate>
The fragile air flow rate is measured according to JIS L 1096 using, for example, an FP type fragile permeameter manufactured by Toyo Seiki Co., Ltd. as an apparatus.

Next, a method for manufacturing a gas permeable membrane according to this embodiment will be described.
First, a PTFE porous film 2 is produced as described below.

  PTFE fine powder is prepared, and 20 to 30 parts by mass of hydrocarbon oil is mixed with 100 parts by mass of the powder. After this mixture is stirred to be uniform, the paste is extruded and preformed. The obtained preform is rolled using, for example, a metal rolling roll. In this way, an unsintered tape that is a precursor of the PTFE porous film 2 is obtained. Although the shape of an unbaked tape is not specifically limited, For example, it is a rectangle or a substantially square.

  This green tape is stretched at a temperature of less than the melting point in the previously rolled direction, that is, in the longitudinal direction at a magnification of 2 to 6 times. The temperature at this time is 280 degreeC, for example. By stretching at a temperature below the melting point, fibrils are drawn between the nodes of PTFE. As a result, a cavity is formed in the PTFE tape, and the PTFE tape can be made porous.

  Next, baking is performed at a temperature equal to or higher than the melting point. The temperature equal to or higher than the melting point is, for example, 360 ° C. The unsintered PTFE tape that has been made porous by stretching as described above has poor dimensional stability and may shrink gradually even at room temperature. This shrinkage can be prevented by heat-setting the unsintered PTFE tape by firing at a temperature equal to or higher than the melting point.

  Subsequently, the fired PTFE film is stretched again at a temperature lower than the melting point. The redrawing temperature is, for example, 250 ° C. This stretching is performed, for example, at a magnification of 2 to 6 times in the longitudinal direction. By performing this re-stretching, a highly porous PTFE porous film 2 can be obtained. The Gurley-type air permeability of the PTFE porous film 2 after this restretching is, for example, 2 seconds or less.

  Here, although the method to manufacture the PTFE porous film 2 by uniaxial stretching was demonstrated, you may manufacture the PTFE porous film 2 by biaxial stretching.

  The fluororesin-containing ventilation material layer 5 can be manufactured as follows. First, the breathable support material 3 is immersed in an aqueous dispersion of PTFE fine particles, taken out from the dispersion, and then the solvent is dried and then fired. This operation is repeated several times to produce the fluororesin layer 4. When the fluororesin layer 4 has a multi-layer structure, for example, after producing the first fluororesin layer 41 made of PTFE by the above operation, the breathable support material 3 provided with the first fluororesin layer 41 is Further, it is immersed in an aqueous dispersion of PFA fine particles. Thereafter, the solvent is dried and then baked to produce the second fluororesin layer 42 made of PFA.

  When the fluororesin layer 4 is produced, a fluororesin film can be used in place of the aqueous dispersion containing the fluororesin particles.

  The fluororesin-containing ventilation material layer 5 may be a commercially available product.

  The PTFE porous film 2 produced above and the fluororesin-containing ventilation material layer 5 are bonded together using, for example, a roll laminator. This bonding is performed under the conditions that the roll temperature is in the range of 360 ° C. to 420 ° C., the linear pressure is in the range of 20 N / cm to 60 N / cm, and the roll speed is in the range of 1 m / min to 4 m / min. . By bonding the PTFE porous film 2 and the fluororesin-containing air-permeable material layer 5 under such conditions, the heat treatment for 10 minutes at a temperature of 300 ° C. results in one direction and a direction perpendicular to the one direction. A gas permeable membrane having a thermal shrinkage ratio of less than 3% can be produced.

  As described above, the roll temperature is, for example, 360 ° C to 420 ° C, preferably 380 ° C to 400 ° C. If the roll temperature is lower than 360 ° C., poor fusion may occur, and if it exceeds 420 ° C., PTFE is decomposed, which is not preferable.

  As described above, the linear pressure is, for example, 20 N / cm to 60 N / cm, and preferably 30 N / cm to 40 N / cm. If the linear pressure is lower than 20 N / cm, there is a possibility of causing poor fusion, and if it exceeds 60 N / cm, the pores of the PTFE porous film may be largely crushed and the air flow rate may be reduced.

  As described above, the roll speed is, for example, 1 m / min to 4 m / min. If the roll speed is lower than 1 m / min, the production efficiency is poor, and if it is higher than 4 m / min, there is a possibility that poor fusion occurs.

  As described above, the gas permeable membrane according to the present embodiment can be manufactured. The gas permeable membrane includes a PTFE porous film and a fluororesin-containing gas permeable material layer laminated on the PTFE porous film, and is perpendicular to the one direction by heat treatment for 10 minutes at a temperature of 300 ° C. The thermal contraction rate in both directions is less than 3%. Therefore, it has high heat resistance and water resistance and has sufficient air permeability.

(Second Embodiment)
According to this embodiment, a microphone is provided. The microphone can be manufactured by a known method except that the microphone includes the gas permeable membrane according to the first embodiment. In addition, since the microphone includes the gas permeable membrane according to the first embodiment, the microphone has high heat resistance and water resistance, and has sufficient air permeability.

  Furthermore, even if the manufacturing process of the microphone includes a process performed in a high temperature environment such as a solder reflow process, the gas permeable membrane is unlikely to thermally contract. Therefore, the microphone after the solder reflow process has sufficient air permeability (frequency characteristics).

  Examples will be described below. In the examples, various measurements were performed by the method described in the first embodiment.

Example 1
<Preparation of PTFE porous film>
To 100 parts by mass of PTFE fine powder (CD-1) manufactured by Asahi Glass Co., Ltd., 26 parts by mass of hydrocarbon oil (ExxonMobil Corp., Isopar M) were uniformly mixed. This mixture was paste-extruded and preformed into a rod shape. This preform was passed between a pair of metal rolling rolls to obtain a rectangular green tape having a thickness of 0.2 mm and a width of 180 mm. Next, this green tape is stretched 2.7 times in the direction of the previous rolling, that is, the longitudinal direction (machine direction: MD) at a temperature lower than the melting point (280 ° C.) using a roll stretching machine, and further roll-stretched. And calcining at a temperature equal to or higher than the melting point (360 ° C.). Furthermore, it was stretched 5 times in the longitudinal direction at a temperature of 250 ° C. using a roll stretching machine to obtain a fired PTFE film having a thickness of 0.1 mm.

When the fragile air flow rate of this baked PTFE film was measured, it was 18 cm ³ / (cm ² · sec).

<Composite of PTFE porous film and fluororesin-containing ventilation material>
A porous fabric FGB207-6 manufactured by Chukoh Chemical Industry Co., Ltd. was prepared as a fluororesin-containing ventilation material. The breathable support material of this breathable material was a plain woven glass cloth, and the fluororesin contained in this breathable material was PTFE. Further, this ventilation material was non-mesh, the wire diameter d was about 0.36 mm, the mesh opening A was about 0.07 mm, and the opening ratio ε (%) was about 2.7%. .
When the fragile air permeability and the Gurley air permeability of this fluororesin-containing ventilation material were measured, the fragile air permeability was 20 cm ³ / (cm ² · sec), and the Gurley air permeability was less than 0.1 seconds. Met.

Using a roll laminator, a fluororesin-containing air-permeable material was laminated on the PTFE porous film at a roll temperature of 400 ° C., a linear pressure of 40 N / cm, and a roll speed of 2 m / min to produce an air-permeable membrane. The Frazier-type air flow rate of this gas permeable membrane was measured and found to be 1.4 cm ³ / (cm ² · sec).

(Comparative Example 1)
Example 1 except that a non-woven fabric (manufactured by Unitika Ltd., Elves (weight per unit: 15 g / m ² )) was used instead of the fluororesin-containing ventilation material, and the roll temperature was 140 ° C. and the roll speed was 3 m / min. A gas permeable membrane was prepared in the same manner as described above. The Frazier-type air flow rate of this gas permeable membrane was measured and found to be 0.9 cm ³ / (cm ² · sec).

(Comparative Example 2)
A PTFE porous film was produced in the same manner as in Example 1. However, a fluororesin-containing ventilation material was not laminated on this PTFE porous film.

(Measurement of heat shrinkage rate and air flow rate change rate)
The gas permeable membranes according to Example 1, Comparative Example 1 and Comparative Example 2 were each cut to 100 mm × 100 mm, and the air flow rate was measured by the Frazier method. Subsequently, it heat-processed over 10 minutes at 100 degreeC using the electric furnace. Thereafter, the heat shrinkage rate and the air flow rate were measured.

  Then, each gas permeable membrane was heat-treated at 200 ° C. for 10 minutes, and the heat shrinkage rate and the air flow rate were measured in the same manner as described above. Then, each gas permeable membrane was heat-treated at 300 ° C. for 10 minutes, and the heat shrinkage rate and the air flow rate were measured in the same manner as described above. The results of thermal shrinkage rate for each example are shown in Table 1 and FIG. In Table 1, the column of “Measurement Value” indicates the length in the MD direction or the TD direction for the test piece after the heat treatment. In the column of “thermal contraction rate”, a numerical value indicated by a negative sign (−) indicates that the gas permeable membrane has expanded in the measurement direction.

  In addition, Table 2 and FIG. 4 show the results of the change rate of the Frazier airflow rate for each example. In Table 2, the column “Measured Value” indicates the measured value of the Frazier type air flow rate, and the numerical value in parentheses indicates the value of the second decimal place.

  From Table 1 and FIG. 3, it can be seen that the gas permeable membrane according to Example 1 is not contracted by heat treatment at 300 ° C. in both the MD direction and the TD direction. On the other hand, the air-permeable membrane according to Comparative Example 1 using a nonwoven fabric instead of the fluororesin-containing air-permeable material layer is thermally shrunk even after heat treatment at 100 ° C., and the heat shrinkage rate after heat treatment at 300 ° C. cannot be measured. Met. Moreover, it turns out that the comparative example 2 of a PTFE porous film single-piece | unit has produced the heat shrink significantly after each heat processing of 100 degreeC, 200 degreeC, and 300 degreeC.

  Referring to Table 2 and FIG. 4, it can be seen that the gas permeable membrane according to Example 1 hardly changed due to the heat treatment, and thus the gas flow rate was not substantially changed. On the other hand, it can be seen that the shape of the gas permeable membranes according to Comparative Example 1 and Comparative Example 2 significantly changed due to the heat treatment, and the air flow rate also changed significantly.

  The reason why the air flow rate of the gas permeable membrane according to Example 1 is increased by the heat treatment will be described. The fluororesin-containing ventilation material layer provided in the gas permeable membrane of Example 1 is opened in, for example, a mesh shape with the above-described aperture ratio.

  When this PTFE porous film and the fluororesin-containing ventilation material layer are integrated, the PTFE porous film is not in contact with the opened portion of the fluororesin-containing ventilation material layer, and the portion of the fiber that is not open In contact with and integrated. Hereinafter, a portion where the PTFE porous film and the fluororesin-containing ventilation material layer are in contact is referred to as a contact portion, and a portion where the PTFE porous film is not in contact is referred to as a non-contact portion.

  When this gas permeable membrane is subjected to heat treatment, the PTFE porous film in the non-contact portion is not supported by the fluororesin-containing gas permeable material layer, and thus contracts in the stretched direction. At this time, the PTFE porous film in the contact portion also shrinks in the in-plane direction toward the opened portion of the fluororesin-containing ventilation material layer.

  As the PTFE porous film is deformed in this manner, the air flow rate of the gas permeable membrane is increased by the heat treatment.

  Next, regarding the gas permeable membrane according to Example 1, the change in the gas flow rate due to the heat treatment was measured as described below.

  The gas permeable membrane according to Example 1 was heat-treated at 300 ° C. for 10 minutes using an electric furnace, and the Gurley air permeability and the Frazier air permeability were measured. Then, it heat-processed again for 10 minutes at 300 degreeC, and measured the Gurley type | formula air permeability and the fragile type air flow. This procedure was repeated until the total heat treatment time was 1 hour. The results are shown in Table 3 below. In Table 3, the numbers in parentheses in the column of “1.2 s” and the column of “2.5 s” indicate the value of the second decimal place, and the row of “rate of change after 60 minutes (%)” The change rate of the Gurley-type air permeability and the change rate of the Frazier-type air flow rate from the gas-permeable membrane with a treatment time of 0 minutes are shown. In addition, the column of “1.2 s” and the column of “2.5 s” are the Gurley air permeability at 0 min before measuring the Frazier air flow rate.

  As shown in Table 3, in the gas permeable membrane according to Example 1, even when the heat treatment was performed for 60 minutes, the decrease rate of the Frazier type air flow rate was less than 10%.

(Manufacture of microphones)
Furthermore, using the gas permeable membrane according to Example 1, a microphone including a solder reflow process was manufactured. In this solder reflow process, solder was printed on the wiring board, a gas permeable film was placed on the solder, and the board including the gas permeable film was heated at 260 ° C. for 1 minute. After heating, the mixture was allowed to cool at room temperature, and the same heat treatment was performed again. This heat treatment and cooling at room temperature were performed three times in total.

Since the air permeable membrane according to Example 1 has high heat resistance, the obtained microphone had almost no change in air permeability (frequency characteristics).
Hereinafter, the invention described in the scope of claims of the present application will be appended.
[1]
A polytetrafluoroethylene porous film;
A fluororesin-containing ventilation material layer laminated on the polytetrafluoroethylene porous film,
A gas permeable membrane having a heat shrinkage rate of less than 3% in one direction and a direction perpendicular to the one direction by heat treatment at a temperature of 300 ° C. for 10 minutes.
[2]
The gas permeable membrane according to [1], wherein a decrease rate of the Frazier type air flow rate by the heat treatment is less than 10%.
[3]
The ventilation film according to [1] or [2], wherein the fluororesin-containing ventilation material layer has an opening ratio ε (%) representing an opening area per unit area within a range of 1% to 70%. .
[4]
The fluororesin-containing breathable material layer includes a breathable support material containing one or more fibers selected from the group consisting of glass cloth and aramid cloth, and the fluororesin is supported on the breathable support material [ 1]-[3].
[5]
The ventilation film according to any one of [1] to [4], wherein the fluororesin of the ventilation material layer includes polytetrafluoroethylene and perfluoroalkoxyalkane.
[6]
The gas permeable membrane according to any one of [1] to [5], wherein the Gurley air permeability is 30 seconds or less.
[7]
[1] A microphone provided with the gas permeable membrane according to any one of [6].

  DESCRIPTION OF SYMBOLS 1 ... Breathable membrane, 2 ... PTFE porous film, 3 ... Breathable support material, 4 ... Fluorine resin layer, 5 ... Fluorine resin containing breathable material layer, 41 ... 1st fluororesin layer, 42 ... 2nd fluororesin Layer, d ... diameter, A ... opening.

Claims (6)

A polytetrafluoroethylene porous film;
A fluororesin-containing ventilation material layer laminated on the polytetrafluoroethylene porous film,
By heat treatment over 10 minutes at a temperature of 300 ° C., Ri both thermal shrinkage less than 3% der the perpendicular TD direction to the MD direction and the MD direction,
Reduction rate of Frazier air permeation amount by the heat treatment is less than 10% der Ru breathable film. 2. The gas permeable membrane according to claim 1, wherein the fluororesin-containing gas permeable material layer has an opening ratio ε (%) representing an open area per unit area within a range of 1% to 70%. The fluororesin-containing breathable material layer includes a breathable support material containing at least one fiber selected from the group consisting of glass cloth and aramid cloth, and the fluororesin is supported on the breathable support material. Item 3. The gas permeable membrane according to Item 1 or 2 . The gas permeable membrane according to any one of claims 1 to 3 , wherein the fluororesin of the gas permeable material layer includes polytetrafluoroethylene and perfluoroalkoxyalkane. The gas permeable membrane according to any one of claims 1 to 4 , having a Gurley air permeability of 30 seconds or less. A microphone comprising the gas permeable membrane according to any one of claims 1 to 5 .