Polytetrafluoroethylene stretched porous membrane and aeration filter material and filter member using the same

Abstract

In the provided polytetrafluoroethylene stretched porous membrane, the air permeability in the thickness direction is 4 cm³ / (sec·cm²) or more, as indicated by Frazier air permeability, and the total cohesive force, which is the product of the peeling cohesive force in the first direction within the plane and the peeling cohesive force in the second direction orthogonal to the first direction within the plane, is 1.9 (N / 20mm)² or more. The stretched porous membrane is highly permeable, and when embedded in, for example, a filter member, it is difficult for damage to occur during handling of the member or placement in a housing, etc.

Description

Technology Field

[0001] The present invention relates to a polytetrafluoroethylene (hereinafter referred to as “PTFE”) stretched porous membrane, and to an air-permeable filter material and filter member using the same. Background Technology

[0002] In the housing of various electrical products, such as automotive electronic components and portable information terminals, a filter member equipped with a ventilation filter material may be installed to cover an opening provided in the housing. The ventilation filter material has air permeability in the thickness direction while preventing the passage of foreign substances such as dust or water. By installing the filter member, ventilation through the opening can be ensured while preventing the passage of foreign substances through the opening. It is considered to use a PTFE stretched porous membrane as the ventilation filter material.

[0003] Patent Document 1 discloses a highly permeable PTFE stretched porous membrane. Patent Document 2 discloses a highly permeable PTFE stretched porous membrane having high ball rupture strength. Prior art literature

[0004] Japanese Patent Publication No. 2009-297702 and Japanese Patent Publication No. Hei 11-515036 The problem to be solved

[0005] According to the highly permeable PTFE stretched porous membrane, for example, the permeability of a filter member can be improved, thereby enabling the miniaturization of the member. However, according to the inventors' investigation, when a filter member is equipped with a highly permeable PTFE stretched porous membrane, damage such as cracking is prone to occur in the PTFE stretched porous membrane during handling or placement in a housing, etc.

[0006] The present invention aims to provide a PTFE stretched porous membrane that is highly permeable and, for example, when embedded in a filter member, is resistant to damage during handling of the member or placement in a housing, etc. means of solving the problem

[0007] The present invention is,

[0008] The air permeability in the thickness direction is 4cm, as indicated by the Frazier air permeability. 3 / ( seconds·cm 2 ) That is all,

[0009] The total cohesive force, represented by the product of the peeling cohesive force in the first direction within the plane and the peeling cohesive force in the second direction orthogonal to the first direction within the plane, is 1.9 (N / 20mm). 2 Lee Sang-in,

[0010] PTFE stretched porous membrane

[0011] It provides.

[0012] From another perspective, the present invention is,

[0013] It is a breathable filter material that has breathability in the thickness direction and prevents the passage of foreign matter in that direction, and

[0014] A breathable filter material having a PTFE stretched porous membrane according to the present invention

[0015] It provides.

[0016] From another perspective, the present invention,

[0017] It is equipped with a breathable filter material that has breathability in the thickness direction and prevents the passage of foreign matter in that direction, and

[0018] The above-mentioned aeration filter material is a filter member which is the aeration filter material of the present invention.

[0019] It provides. Effects of the invention

[0020] According to the present invention, a PTFE stretched porous membrane is achieved that is highly permeable and, for example, when embedded in a filter member, is unlikely to be damaged during handling of the member or placement in a housing, etc. Brief explanation of the drawing

[0021] FIG. 1 is a cross-sectional view schematically illustrating an example of a PTFE stretched porous membrane of the present invention. FIG. 2 is a cross-sectional view schematically illustrating an example of the air-permeable filter material of the present invention. FIG. 3 is a cross-sectional view schematically illustrating another example of the aeration filter material of the present invention. FIG. 4 is a cross-sectional view schematically illustrating an example of a filter member of the present invention. FIG. 5 is a cross-sectional view schematically illustrating another example of a filter member of the present invention. FIG. 6 is a cross-sectional view schematically illustrating another example of a filter member of the present invention. FIG. 7 is a cross-sectional view schematically illustrating an example of a filter member of the present invention different from the above. FIG. 8 is a cross-sectional view schematically illustrating an example of an embodiment of supplying a filter member of the present invention. Figure 9a is an image of the surface of the PTFE stretched porous membrane of Example 4 observed by a scanning electron microscope (SEM). Figure 9b is an image of the cross-section in the thickness direction (cut in the MD direction) of the PTFE stretched porous membrane of Example 4 observed by SEM. Figure 10a is an image of the surface of the PTFE stretched porous membrane of Comparative Example 2 observed by SEM. Figure 10b is an image of the cross-section in the thickness direction (cut in the MD direction) of the PTFE stretched porous membrane of Comparative Example 2 observed by SEM. Figure 11a is an image of the surface of the PTFE stretched porous membrane of Comparative Example 8 observed by SEM. Figure 11b is an image of the cross-section in the thickness direction (cut in the MD direction) of the PTFE stretched porous membrane of Comparative Example 8 observed by SEM. Figure 12 is a graph showing the relationship between air permeability in the thickness direction and total cohesion in PTFE stretched porous membranes of the examples and comparative examples. Specific details for implementing the invention

[0022] An example of the PTFE stretched porous membrane of the present invention is illustrated in FIG. 1. The air permeability in the thickness direction of the PTFE stretched porous membrane (1) of FIG. 1 is 4 cm, as indicated by the Frazier air permeability. 3 / ( seconds·cm 2 That is all. The airway in question is 4.5cm 3 / ( seconds·cm 2 ) or more, 5.0cm 3 / ( seconds·cm 2 ) or more, 6.0cm 3 / ( seconds·cm 2 ) or more, 7.0cm 3 / ( seconds·cm 2 ) Above, furthermore 8.0cm 3 / ( seconds·cm 2 It may be greater than ). The upper limit of the relevant airflow is, for example, 20.0 cm 3 / ( seconds·cm 2 ) is less than. Frazier air permeability is determined in accordance with the air permeability measurement method A (Frasier mold method) specified in Japanese Industrial Standard (hereinafter referred to as "JIS") L1096. In addition, even if the size of the PTFE stretched porous membrane (1) is smaller than the size of the test specimen (approx. 200 mm × 200 mm) in the Frazier mold method, the Frazier air permeability can be evaluated by using a measurement jig that limits the area of ​​the measurement area. An example of a measurement jig is a resin plate with a through hole formed in the center having a cross-sectional area corresponding to the desired measurement area. For example, a measurement jig with a through hole formed in the center having a circular cross-section with a diameter of 1 mm or less can be used.

[0023] The total cohesive force of the PTFE stretched porous membrane (1) is 1.9 (N / 20mm) 2That is all. The total cohesive force is represented by the product of the peel cohesive force in the first direction within the plane of the PTFE stretched porous membrane (1) and the peel cohesive force in the second direction orthogonal to the first direction within the plane. The first direction is, for example, the MD direction. The second direction is, for example, the TD direction. The total cohesive force is 2.0 (N / 20 mm) 2 Above, 2.5 (N / 20mm) 2 Above, 2.8 (N / 20mm) 2 Above, further 3.0(N / 20mm) 2 It may be greater than or equal to. The upper limit of total cohesion is, for example, 25.0 (N / 20mm) 2 Less than or equal to, 20.0 (N / 20mm) 2 Below, 15.0 (N / 20mm) 2 Below, 10.0 (N / 20mm) 2 Below, furthermore 8.0(N / 20mm) 2 It is acceptable to do the following.

[0024] A stretched PTFE porous membrane is typically formed by stretching an unstretched PTFE sheet, which is the original sheet, in two mutually orthogonal directions within the sheet plane, for example, the MD direction and the TD direction. The stretching conditions for each direction are typically different, and for this reason, the mechanical properties of the membrane are typically different between the two mutually orthogonal directions. According to the inventors' investigation, for example, when embedded in a filter member, if the membrane has high peel cohesive force in one direction but low peel cohesive force in a different direction, the membrane tends to break during handling of the member or placement in a housing. The total cohesive force is the product of the peel cohesive force in the first direction within the plane and the peel cohesive force in the second direction orthogonal to the first direction within the plane. According to the inventors' investigation, the total cohesive force is 1.9 (N / 20mm) 2 The above PTFE stretched porous membrane (1) can be judged to have high peeling cohesion on average in the in-plane direction of the membrane.

[0025] The peeling cohesive force in the first direction in the PTFE stretched porous membrane (1) may be, for example, 1.70 (N / 20mm) or more, 1.80 (N / 20mm) or more, 1.90 (N / 20mm) or more, and furthermore 2.00 (N / 20mm) or more.

[0026] The peeling cohesive force in the second direction in the PTFE stretched porous membrane (1) may be, for example, 1.15 (N / 20mm) or more, 1.20 (N / 20mm) or more, 1.40 (N / 20mm) or more, 1.50 (N / 20mm) or more, 1.60 (N / 20mm) or more, and furthermore, 1.70 (N / 20mm) or more.

[0027] The average cohesive force of the PTFE stretched porous membrane (1), represented by the average (arithmetic mean) of the peel cohesive force in the first direction and the peel cohesive force in the second direction, may be, for example, 1.40 (N / 20mm) or more, 1.50 (N / 20mm) or more, 1.60 (N / 20mm) or more, 1.70 (N / 20mm) or more, and furthermore, 1.80 (N / 20mm) or more. In this other aspect, the present invention has a thickness direction air permeability, indicated by Frazier air permeability, of 4cm 3 / ( seconds·cm 2 A polytetrafluoroethylene stretched porous membrane is disclosed, wherein the average cohesive force, represented by the average (arithmetic mean) of the peeling cohesive force in the first direction and the peeling cohesive force in the second direction, is 1.40 (N / 20mm) or higher.

[0028] In the PTFE stretched porous membrane (1), air permeability in the thickness direction and overall cohesiveness can coexist at a high level. The PTFE stretched porous membrane (1) has air permeability in the thickness direction P T , total cohesion C T Expressed as, Equation C T ≥-0.33×P T It may satisfy +3.67, and Equation C T ≥-0.57×P T It is okay to satisfy +6.14.

[0029] In this specification, PTFE includes modified PTFE. In other words, the PTFE stretched porous membrane (1) includes a stretched porous membrane of modified PTFE. Modified PTFE is a copolymer of tetrafluoroethylene (hereinafter referred to as “TFE”) and a modified comonomer. The content of TFE units in the copolymer is, for example, 95 mass% or more, preferably 97 mass% or more, and more preferably 99 mass% or more. The modified comonomer is, for example, at least one selected from ethylene, perfluoroalkyl vinyl ether, hexafluoropropylene, and perfluoromethyl vinyl ether. However, modified PTFE may be excluded from PTFE. In other words, PTFE may be unmodified PTFE (a homopolymer of TFE).

[0030] The standard specific gravity (SSG) of PTFE may be 2.18 or less. The SSG is specified in JIS K6935-1.

[0031] The weight per unit area of ​​the PTFE stretched porous membrane (1) is, for example, 1.0 g / m² 2 That is all, 7.0g / m² 2 Above, 8.0g / m² 2 Above, 10.0g / m² 2 Above, 12.0g / m² 2 Above, furthermore 13.0 g / m 2 It may be greater than or equal to. The upper limit of weight per unit area is, for example, 87.2 g / m² 2 The following applies. The weight per unit area can be calculated by dividing the weight of the PTFE stretched porous membrane (1) by the area of ​​the main surface.

[0032] The thickness of the PTFE stretched porous film (1) may be, for example, 10 μm or more, 30 μm or more, 35 μm or more, 40 μm or more, and furthermore 45 μm or more. The upper limit of the thickness may be, for example, 200 μm or less, and may be 100 μm or less.

[0033] The average pore diameter of the PTFE stretched porous membrane (1) may be, for example, 1.0 μm or more, 2.0 μm or more, 3.0 μm or more, and furthermore, 3.5 μm or more. The upper limit of the average pore diameter is, for example, 20 μm or less. The average pore diameter can be evaluated in accordance with ASTM F316. For evaluating the average pore diameter, a commercially available evaluation device (e.g., a Perm-Porometer made of Porous Material) in accordance with the above standard may be used.

[0034] The porosity of the PTFE stretched porous membrane (1) may be, for example, 80% or more, 85% or more, 88% or more, and furthermore, 90% or more. The upper limit of the porosity is, for example, 99% or less. The porosity can be calculated by substituting the mass, thickness, area (surface area), and true density of PTFE of the membrane into the following formula. In addition, the true density of PTFE is 2.18 g / cm³ 3 am.

[0035] Porosity (%) = {1 - (mass [g] / (thickness [cm] × area [cm²]} 2 ]×True density[g / cm² 3 ]))}×100

[0036] The bulk density of the PTFE stretched porous membrane (1) is, for example, 0.30 g / cm³ 3 Below, 0.28 g / cm³ 3 Below, 0.26 g / cm³ 3 Below, 0.25g / cm³ 3 Below, 0.23g / cm³ 3 Below, furthermore 0.22 g / cm³ 3 It may be less than or equal to this. The lower limit of bulk density is, for example, 0.08 g / cm³. 3 That is all. An appropriate range of bulk density contributes to the achievement of a PTFE stretched porous membrane that is highly permeable and resistant to breakage. The bulk density can be obtained from the weight and thickness per unit area of ​​the PTFE stretched porous membrane (1).

[0037] The water pressure resistance (limit water pressure resistance) of the PTFE stretched porous membrane (1) may be, for example, 30 kPa or more, 35 kPa or more, 40 kPa or more, 44 kPa or more, and furthermore 50 kPa or more. The upper limit of the water pressure resistance is, for example, 500 kPa or less. The water pressure resistance can be measured as follows by using a measuring jig in accordance with the water resistance test method A (low pressure method) or method B (high pressure method) specified in JIS L1092.

[0038] An example of a measuring jig is a stainless steel disc with a diameter of 47 mm, having a through hole (with a circular cross-section) with a diameter of 1 mm in the center. This disc has a thickness that is not deformed by the water pressure applied when measuring water pressure. The measurement of water pressure using this measuring jig can be performed as follows.

[0039] A PTFE stretched porous membrane (1) to be evaluated is fixed to one side of the measuring jig to cover the opening of the through hole of the measuring jig. The fixing is done so that water does not leak from the fixed part of the membrane during the measurement of water pressure resistance. For fixing the membrane, a double-sided adhesive tape with a water passage hole punched in the center having a shape matching the shape of the opening may be used. The double-sided adhesive tape should be placed between the measuring jig and the membrane so that the circumference of the water passage hole matches the circumference of the opening. Next, the measuring jig with the membrane fixed is set in a test device such that the side opposite to the fixed surface of the membrane becomes the surface for applying water pressure during measurement, and the water pressure resistance is measured according to the water resistance test method A (low water pressure method) or method B (high water pressure method) of JIS L1092. However, the water pressure resistance is measured based on the water pressure when water comes out from one spot on the membrane surface of the PTFE stretched porous membrane (1). The measured water pressure can be the water pressure of the PTFE stretched porous membrane (1). For the test device, a device having a configuration similar to the water resistance test device exemplified in JIS L1092 and a test specimen mounting structure capable of setting the measurement jig can be used.

[0040] The PTFE stretched porous membrane (1) may be a single layer membrane.

[0041] The PTFE stretched porous membrane (1) may be subjected to liquid-repellent treatment, such as water-repellent treatment and oil-repellent treatment. Liquid-repellent treatment can be performed by coating with a liquid-repellent material such as a fluorine-based compound. Known methods may be employed for the coating.

[0042] The PTFE stretched porous membrane (1) may be subjected to a coloring treatment. The coloring treatment may be performed, for example, by dyeing the PTFE stretched porous membrane (1) or by including a coloring agent in the PTFE stretched porous membrane (1). The coloring treatment may be performed such that light having a wavelength in the range of 380 to 500 nm is absorbed. In this case, the PTFE stretched porous membrane (1) may be colored blue, gray, brown, pink, green, yellow, etc.

[0043] The PTFE stretched porous membrane (1) can be used as a breathable filter material that, for example, has breathability in the thickness direction and prevents the passage of foreign matter in that direction. Examples of foreign matter include particles such as dust and liquids such as water droplets. However, the use of the PTFE stretched porous membrane (1) is not limited to the above examples.

[0044] The PTFE stretched porous membrane (1) can be manufactured, for example, by the following method A. The PTFE stretched porous membrane (1) may be a membrane obtained by method A. However, the method of manufacturing the PTFE stretched porous membrane (1) is not limited to method A.

[0045] [Method A]

[0046] A microscopic PTFE sheet is stretched in a predetermined direction at a stretching temperature below the melting point of PTFE (stretch A);

[0047] The sheet that has undergone stretching A is fired at a temperature above the melting point of PTFE (firing B);

[0048] The sheet that has undergone firing B is further stretched in a direction different from the above-mentioned predetermined direction at a stretching temperature below the melting point of PTFE (stretching C).

[0049] (Yeonshin A)

[0050] In stretching A, a micro-PTFE sheet is stretched in a predetermined direction at a stretching temperature below the melting point of PTFE (the melting point of the crystal, 343°C). Stretching A may be performed, for example, in a heating furnace controlled to the temperature (stretching temperature) at which stretching A is performed. Stretching A may be performed, for example, by roll stretching. However, the method of performing stretching A is not limited to the above examples.

[0051] The stretching temperature of stretching A is, for example, 200 to 340°C, and may be 280 to 330°C.

[0052] The elongation ratio of elongation A is, for example, 1.5 to 10.0 times, and may be 2.0 to 8.0 times. When air permeability in the thickness direction and overall cohesiveness are combined at a higher level, the elongation ratio is preferably 4.0 to 5.0 times. When water pressure resistance is improved while air permeability in the thickness direction and overall cohesiveness are combined at a high level, the elongation ratio is preferably 3.0 to 4.0 times.

[0053] The direction of stretching A (a predetermined direction) is, for example, the MD direction of the PTFE sheet. If the PTFE sheet is strip-shaped, the direction of stretching A may be the length direction of the PTFE sheet.

[0054] It is preferable to perform stretching A while suppressing the degree of stretching per hour. It is believed that suppressed stretching A contributes to the formation of a PTFE stretched porous membrane (1) having high air permeability and overall cohesiveness. The PTFE stretched porous membrane (1) has a node / fibril structure having a plurality of nodes and fibrils connecting the plurality of nodes. Additionally, the nodes are the cohesive parts of PTFE. According to the inventors' investigation, there is a tendency for nodes to be formed that are extended not only in the in-plane direction but also in the membrane thickness direction by suppressed stretching A and subsequent firing B. Nodes that are extended in the membrane thickness direction can suppress the breakdown of cohesiveness of the PTFE stretched porous membrane (1) regardless of the direction in which force is applied, and the degree of impediment to air permeability in the membrane thickness direction is low. For this reason, it is presumed that the node / fibril structure having said nodes contributes to the high air permeability and overall cohesiveness of the PTFE stretched porous membrane (1). Suppressed elongation can be achieved, for example, by reducing the elongation ratio per hour. The elongation ratio per hour is indicated by the strain rate, for example, 0.5 to 5.0 / min, 0.5 to 3.0 / min, and further 0.5 to 2.0 / min. The strain rate can be calculated by dividing the elongation speed (m / min) by the elongation distance (m). The strain rate is typically kept constant during elongation A.

[0055] (Fire B)

[0056] In firing B, the sheet that has undergone stretching A is fired at a temperature above the melting point of PTFE. Firing B can be carried out, for example, in a furnace controlled to a temperature (firing temperature) at which firing B is carried out.

[0057] The firing temperature is, for example, 350 to 400°C, and may be 355 to 395°C. The firing time is, for example, 10 to 40 seconds, and may be 12 to 38 seconds.

[0058] It is preferable to perform firing B in a state where the sheet is not stretched. It is presumed that performing firing in this state between stretching A and stretching C contributes to the formation of a PTFE stretched porous material having high air permeability and overall cohesiveness. According to the inventors' investigation, the nodes formed by stretching A are heat-set by firing B, and thereby the structure of the nodes is maintained even by stretching C, which expands the gaps between the fibrils. However, slight stretching or shrinkage is permitted to correct loosening or elongation of the sheet that may occur due to changes in temperature. The stretching ratio permitted in firing B is, for example, 0.80 to 2.00 times, and 0.90 to 1.10 times is preferred. A stretching ratio of less than 1 indicates shrinkage. Furthermore, the PTFE stretched porous membrane (1) obtained through firing B is a fired membrane. In this respect, the PTFE stretched porous membrane (1) may be a fired membrane.

[0059] (Yeonsin C)

[0060] In stretching C, the sheet that has undergone firing B is further stretched in a direction different from the above-mentioned predetermined direction at a stretching temperature below the melting point of PTFE. Stretching C can be performed, for example, in a heating furnace controlled to the temperature (stretching temperature) at which stretching C is performed. Stretching C can be performed, for example, by tenter stretching. However, the method of performing stretching C is not limited to the above examples.

[0061] The stretching temperature of stretching C is, for example, 40 to 340°C, and may be 100 to 330°C.

[0062] The elongation ratio of elongation C is, for example, 2 to 15 times, and may be 4 to 10 times.

[0063] The direction of stretching C is typically approximately perpendicular to the direction of stretching A within the sheet plane. The direction of stretching C is, for example, the TD direction of the PTFE sheet. If the PTFE sheet is strip-shaped, the direction of stretching C may be the width direction of the PTFE sheet.

[0064] In Method A, other stretching methods other than Stretch A and Stretch C may be performed as needed. However, it is preferable that the initial stretching performed on the PTFE sheet is Stretch A. In Method A, only Stretch A and Stretch C may be performed as stretching of the PTFE sheet. Stretch A, Sintering B, and Stretch C may be performed continuously.

[0065] The PTFE stretched porous membrane (1) obtained by method A is typically a biaxially stretched membrane. In this respect, the PTFE stretched porous membrane (1) may be a biaxially stretched membrane.

[0066] The microscopic PTFE sheet provided in Method A can be formed, for example, by forming a mixture of PTFE fine powder and a liquid lubricant into a sheet shape by extrusion and / or rolling. It is preferable to remove the liquid lubricant from the PTFE sheet before stretching A by means such as heating or extraction. Furthermore, it is preferable not to apply a compressive force in the thickness direction of the microscopic PTFE sheet after removing the liquid lubricant; in other words, it is preferable to stretch a PTFE sheet (non-densified sheet) that has not undergone densification by the application of the compressive force.

[0067] For PTFE fine powder, commercially available products such as Polyfron F-104 (Daikin Kogyo), Fluon CD-123E, Fluon CD-145E (AGC), and Teflon 6J (Mitsui Kemmers Fluoro Products) can be used.

[0068] Examples of liquid lubricants include liquid paraffin, naphtha, white oil, hydrocarbon oils such as toluene and xylene, various alcohols, ketones, and esters. However, the liquid lubricant is not limited to the above examples as long as it is possible to wet the surface of the PTFE fine powder and remove the mixture after forming it into a sheet.

[0069] The mixing ratio of PTFE fine powder and liquid lubricant is typically about 5 to 50 parts by weight of liquid lubricant per 100 parts by weight of PTFE fine powder.

[0070] The thickness of the microscopic PTFE sheet can be adjusted according to the desired thickness of the PTFE stretched porous membrane (1), for example, about 0.05 to 0.5 mm.

[0071] In Method A, any process may be performed after stretching C as needed. An example of a process is heat setting, which involves holding the sheet at a temperature above the melting point of PTFE. By heat setting, the structure of the stretched sheet is maintained. Heat setting may be performed in the same manner as firing B. Heat setting may be performed continuously following stretching C.

[0072] [Aeration filter media]

[0073] An example of the air-permeable filter material of the present invention is illustrated in FIG. 2. The air-permeable filter material (2(2A)) of FIG. 2 comprises a PTFE stretched porous membrane (1). Another example of the air-permeable filter material of the present invention is illustrated in FIG. 3. The air-permeable filter material (2(2B)) of FIG. 3 further comprises a breathable support material (3). The breathable support material (3) is laminated onto the PTFE stretched porous membrane. The breathable support material (3) can improve the strength and handling properties of the air-permeable filter material (2).

[0074] The breathable support material (3) typically has high breathability in the thickness direction compared to the PTFE stretched porous membrane (1). Examples of the breathable support material (3) are woven fabrics, nonwoven fabrics, nets, and meshes. Examples of materials constituting the breathable support material (3) include polyesters such as polyethylene terephthalate (PET), polyolefins such as polyethylene (PE) and polypropylene (PP), and aramid resins. The shape of the breathable support material (3) may be the same as or different from the shape of the PTFE stretched porous membrane (1) when viewed perpendicularly to the main surface of the breathable filter material (2). The breathable support material (3) may have a shape corresponding to the periphery of the PTFE stretched porous membrane (1) when viewed perpendicularly to the main surface of the breathable filter material (2). If the shape of the PTFE stretched porous membrane (1) is circular, the shape is a ring shape. The composition and shape of the breathable support material (3) are not limited to the above examples.

[0075] The air-permeable filter material (2B) is provided with one air-permeable support material (3) disposed on one side of the PTFE stretched porous membrane (1). The air-permeable filter material (2) may be provided with two or more air-permeable support materials (3). In the air-permeable filter material (2), air-permeable support materials (3) may be disposed on both sides of the PTFE stretched porous membrane (1). The PTFE stretched porous membrane (1) and the air-permeable support material (3) may be joined by welding, such as thermal welding and ultrasonic welding, or by an adhesive or adhesive.

[0076] The ventilation filter material (2) may have any layer and / or member other than that described above.

[0077] The thickness of the air filter material (2) is, for example, 10 to 300 μm, and may be 50 to 200 μm.

[0078] The weight per unit area of ​​the aeration filter material (2) is, for example, 1.0 to 200.0 g / m² 2 and 10.0 to 100.0 g / m² 2 It is okay to continue.

[0079] The air-permeable filter material (2) may have the same characteristics as the PTFE stretched porous membrane (1), for example, air permeability in the thickness direction and / or water pressure resistance.

[0080] The aeration filter material (2) may be treated with liquid removal and / or coloring.

[0081] The shape of the aeration filter material (2) is, when viewed perpendicularly to the main surface of the aeration filter material (2), a polygon including, for example, a square and a rectangle, a circle, an ellipse, or a strip. The corners of the polygon may be rounded. However, the shape of the aeration filter material (2) is not limited to the above examples. The strip-shaped aeration filter material (2) may be wound to form a wound body. Additionally, if necessary, it may be wound in a laminated state with a release sheet (separator).

[0082] The area of ​​the single-leaf air-permeable filter material (2) having the shape of a polygon, circle, ellipse, etc., is 675 mm 2 It may be less than 175mm 2 It may be less than or equal to. The lower limit of the area is, for example, 0.20mm 2 That is all. The air-permeable filter material (2) having the said area is suitable for use in a miniaturized filter member. However, the area of ​​the air-permeable filter material (2) may be larger depending on the application.

[0083] The aeration filter material (2) can be used, for example, in a filter member. However, the use of the aeration filter material (2) is not limited to the above examples.

[0084] [Filter Absence]

[0085] An example of a filter member of the present invention is illustrated in FIG. 4. The filter member (4(4A)) of FIG. 4 is a ventilation filter material that has air permeability in the thickness direction and prevents the passage of foreign matter in that direction, and is equipped with the ventilation filter material (2) described above. The filter member (4A) is a member that is disposed on the surface of an object having a surface having an opening, for example, to prevent the passage of foreign matter through the opening while ensuring air permeability through the opening. In this case, the filter member (4A) is typically disposed such that the ventilation filter material (2) covers the opening of the object.

[0086] The filter member (4A) has an adhesive layer (5) disposed on one side of the air-permeable filter material (2). The air-permeable filter material (2) and the adhesive layer (5) are directly bonded. The filter member (4A) can be disposed on the surface of the object through the adhesive layer (5).

[0087] When handling the filter member (4) and placing it on an object, a strong force may be applied to the member (4) in a specific direction. However, the air-permeable filter material (2) is provided with a PTFE stretched porous membrane (1) having high overall cohesive strength. Therefore, for example, the filter member (4) can be manufactured without limiting the direction of insertion of the air-permeable filter material (2) (or PTFE stretched porous membrane (1)) into the filter member (4).

[0088] Examples of adhesives constituting the adhesive layer (5) include acrylic adhesives, silicone adhesives, urethane adhesives, epoxy adhesives, and rubber adhesives. If it is necessary to consider the use of the filter member (4) under high temperature, it is preferable to select an acrylic adhesive or a silicone adhesive, particularly a silicone adhesive, which has excellent heat resistance. The adhesive layer (5) may be a double-sided adhesive tape without a substrate. The adhesive may be a curable adhesive such as phenolic resin, epoxy resin, urea resin, polyurethane resin, melamine resin, and polyester resin.

[0089] The outer circumference of the air-permeable filter material (2) and the outer circumference of the adhesive layer (5) coincide when viewed perpendicularly to the main surface of the air-permeable filter material (2). Additionally, the shape of the adhesive layer (5) corresponds to the periphery of the air-permeable filter material (2) when viewed perpendicularly to the main surface of the air-permeable filter material (2). The area of ​​the air-permeable filter material (2) where the adhesive layer (5) is not bonded can be designated as the air-permeable area of ​​the filter member (4A). However, the shape of the adhesive layer (5) is not limited to the above example.

[0090] The area of ​​the ventilation zone is, for example, 40mm 2 The following applies. A filter member (4) having an air circulation area within the specified range is suitable for placement, for example, in an object having a small-diameter opening. The lower limit of the air circulation area is, for example, 0.008 mm. 2 That is all. However, the area of ​​the ventilation zone may be larger depending on the type of object on which the filter member (4) is placed.

[0091] A modified example of the filter member (4) is shown below. The filter member (4(4B)) of FIG. 5 has the same configuration as the filter member (4A), except that it further comprises a substrate layer (6) disposed on one side of the air-permeable filter material (2), and the air-permeable filter material (2) and the adhesive layer (5) are bonded together through the substrate layer (6). The substrate layer (6) can improve the strength and handling of the filter member (4) and can suppress damage to the air-permeable filter material (2) during handling or placement on an object.

[0092] Examples of materials constituting the substrate layer (6) include polyolefins such as PE and PP, polyesters such as PET, silicone resin, polycarbonate, polyimide, polyamideimide, polyphenylene sulfide, polyetheretherketone (PEEK), polyvinyl chloride, fluoropolymer, and metals such as aluminum and stainless steel. Examples of fluoropolymers include PTFE, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and tetrafluoroethylene-ethylene copolymer (ETFE). However, the materials constituting the substrate layer (6) are not limited to the above examples.

[0093] The outer circumference of the air-permeable filter material (2) and the outer circumference of the substrate layer (6) coincide when viewed perpendicularly to the main surface of the air-permeable filter material (2). Additionally, the shape of the substrate layer (6) corresponds to the periphery of the air-permeable filter material (2) when viewed perpendicularly to the main surface of the air-permeable filter material (2). The area of ​​the air-permeable filter material (2) where the substrate layer (6) is not bonded can be designated as the air-permeable area of ​​the filter member (4B). However, the shape of the substrate layer (6) is not limited to the above example.

[0094] The air-permeable filter material (2) and the substrate layer (6) may be joined by an adhesive or adhesive, or by welding such as thermal welding or ultrasonic welding. The air-permeable filter material (2) and the substrate layer (6) may be joined by an adhesive layer. The adhesive layer may have the same composition as the adhesive layer (5). The substrate layer (6) and the adhesive layer (5) may each be the substrate and adhesive layer of a single-sided adhesive tape or a double-sided adhesive tape.

[0095] The filter member (4(4C)) of FIG. 6 has the same configuration as the filter member (4B), except that it further comprises a substrate layer (6(6B)) disposed on the other side of the air-permeable filter material (2). The air-permeable filter material (2) is supported by being fitted between a pair of substrate layers (6(6A, 6B)). This fitted support structure can further improve the strength and handling of the filter member (4).

[0096] The filter member (4(4D)) of FIG. 7 has the same configuration as the filter member (4C), except that it further comprises a tab film (7) and the base layer (6(6B)) and the tab film (7) are bonded together via an adhesive layer (5(5B)). The tab film (7) has a tab that protrudes outwardly from the outer edge of the base layer (6B) when viewed perpendicularly to the main surface of the base layer (6B). The filter member (4D) can be handled or placed on the surface of an object by gripping the tab. The tab film (7) is typically removed when the filter member (4D) is used. The tab film (7) may be composed of the same material as the material constituting the base layer (6). Additionally, the tab film (7) is typically removed by gripping the tab and lifting it up. At this time, a strong force is applied to the air-permeable filter material (2) in the lifting direction.

[0097] The filter member (4) can be supplied, for example, by a sheet for supplying members. An example of a member supply assembly, which is a supply mode of the filter member (4) by said sheet, is illustrated in FIG. 8. The member supply assembly (10) of FIG. 8 comprises a sheet (9) for supplying members and a filter member (4 (4D)) disposed on the sheet (9). The filter member (4) is disposed on the sheet (9) via an adhesive layer (5 (5A)). According to the member supply assembly (10), the filter member (4) can be efficiently supplied for, for example, a process of placing it on the surface of an object. A plurality of filter members (4) may be disposed on the sheet (9).

[0098] The filter member (4) may be disposed on the sheet (9) via an adhesive layer provided on the placement surface of the filter member (4) in the sheet (9). It is preferable that the adhesive layer on the placement surface be weakly adhesive.

[0099] Since the PTFE stretched porous membrane (1) is unlikely to be damaged, depending on the configuration of the filter member (4), for example, it is possible to lift and peel off the filter member (4) from the sheet (9) without damaging the membrane (1).

[0100] Examples of materials constituting the sheet (9) include paper, metal, resin, and composite materials thereof. Metals include, for example, stainless steel and aluminum. Resins include, for example, polyester such as PET, and polyolefins such as PE and PP. However, the materials constituting the sheet (9) are not limited to the above examples. The sheet (9) may be in the form of a single sheet or a strip. If the sheet (9) is in the form of a strip, the material supply assembly (10) may be wound to form a wound body.

[0101] Examples of objects on which the filter member (4) is placed include housings of electronic devices and housings of automotive electronic components. The filter member (4) may be placed on the outer surface and / or inner surface of the housing. In this case, the opening may be a ventilation opening and / or a sound opening provided in the housing. Examples of electronic devices include wearable devices such as smartwatches and wristbands; various cameras including action cameras and security cameras; information and communication devices such as mobile phones, smartphones, and tablets; virtual reality (VR) devices; augmented reality (AR) devices; and sensor devices. Examples of automotive electronic components include lamps and ECUs. However, the objects are not limited to the above examples.

[0102] The foreign matter that is prevented from passing by the arrangement of the filter member (4) is, for example, particles such as dust, liquid water such as water droplets.

[0103] Examples

[0104] The present invention will be explained in more detail below by way of examples. The present invention is not limited to the following examples.

[0105] This describes a method for evaluating PTFE stretched porous membranes.

[0106] [thickness]

[0107] Ten measurement points were randomly selected, and the average value of the thickness obtained at each measurement point by a dial gauge (a flat measuring ruler with a diameter of 10 mm, a measuring force of 15 N or less) was taken as the thickness of the PTFE stretched porous film.

[0108] [Weight per unit area]

[0109] The weight per unit area was calculated by the method described above.

[0110] [Water Pressure (Limit Water Pressure)]

[0111] The water pressure resistance was determined by the method described above in accordance with the provisions of the water resistance test method B (high pressure method) specified in JIS L1092.

[0112] [Porosity]

[0113] The porosity was calculated by the method described above.

[0114] [Breathability in the thickness direction]

[0115] The air permeability in the thickness direction (Frasier air permeability) was obtained by the above-described method in accordance with the specifications of the air permeability measurement method A set forth in JIS L1096.

[0116] [Total Cohesion]

[0117] The total cohesive force was determined by the following method. First, the PTFE stretched porous membrane to be measured was cut into a rectangle (length 150 mm × width 20 mm). Next, two double-sided adhesive tapes (Nitto Denko, No. 5610) having the same shape as the PTFE stretched porous membrane were prepared. Next, each double-sided adhesive tape was bonded to one side and the other side of the PTFE stretched porous membrane by aligning their outer peripheries. Next, two rectangular PET films (Toray, Lumirror S10#25, thickness 25 μm) with length 200 mm × width 20 mm were prepared, and each PET film was bonded to one side and the other side of the PTFE stretched porous membrane by the above double-sided adhesive tapes. The bonding of the PET films was performed such that both ends in the width direction of each PET film coincided with both ends in the width direction of the PTFE stretched porous membrane, and one end in the length direction of each PET film coincided with one end in the length direction of the PTFE stretched porous membrane. As a result, a length (50 mm) was secured at the other end in the length direction of the PET film, allowing the chuck of the tensile testing machine to stably grip the PET film. Next, a compression roller with a load of 19.6 N was reciprocated once to apply a compressive force in the thickness direction of the laminate of PET film / double-sided adhesive tape / PTFE stretched porous membrane / double-sided adhesive tape / PET film. Subsequently, the specimen was left at room temperature for 12 hours and then at 60°C for 1 hour until the tensile test was started to obtain the specimen. In addition, regarding the same PTFE stretched porous membrane, a specimen S was cut by aligning the longer side in the MD direction of the membrane. MD Wow, test specimen S cut with the longer side aligned in the TD direction of the membrane. TD prepared.

[0118] Next, a tensile testing machine (A&D, Tensilon Universal Testing Machine RTF) was prepared. The test specimens were held horizontally, and one free end of the PET film was bent upward and installed on the upper chuck of the tensile testing machine, while the other free end of the PET film was bent downward and installed on the lower chuck of the tensile testing machine. Next, under conditions of a measurement temperature of 23±5℃, a measurement humidity of 50±5% RH, and a tensile speed of 300 mm / min, a tensile test (T-peel test) was performed by stretching one free end of the PET film upward and the other free end of the PET film downward to induce cohesive fracture in the stretched porous PTFE film. After the displacement of the PET film due to cohesive fracture began, the intercalation stress measured at an initial displacement of 25 mm was ignored, and the average value of the continuously recorded stress measurements at a subsequent displacement of 50 mm was defined as the peel cohesive force (unit: N / 20 mm) of the stretched PTFE porous membrane. Specimen S MD From this, the peel cohesion in the MD direction was calculated. Test specimen S TD From this, the peeling cohesive force in the TD direction was calculated. Next, the total cohesive force was calculated as the product of the peeling cohesive forces on both sides.

[0119] (Example 1)

[0120] A PTFE paste was formed by uniformly mixing 100 parts by weight of PTFE fine powder (unmodified, standard specific gravity (SSG) 2.16) and 19.7 parts by weight of an aliphatic hydrocarbon as a liquid lubricant. Next, the formed PTFE paste was subjected to 2.5 MPa (25 kg / cm²) using an FT die. 2 It was extruded into a sheet under pressure and further rolled by a pair of metal rolls to obtain a strip-shaped PTFE sheet (unoriented, thickness 0.2 mm) with adjusted thickness. Next, the obtained PTFE sheet was heated to remove the liquid lubricant.

[0121] Next, while continuously feeding the PTFE sheet, it was uniaxially stretched in the longitudinal direction in a heating furnace maintained at 300°C (stretch A). The stretching ratio was set to 3.0 times. Stretch A was performed by roll stretching, and the deformation rate was set to 1.66 / min.

[0122] Next, the sheet after stretching A was fired by passing it through a heating furnace maintained at 375°C without stretching (firing B). The time of passage through the heating furnace was set to 17 seconds.

[0123] Next, the sheet after firing B was uniaxially stretched in the width direction in a furnace maintained at 330°C (stretch C). The stretching ratio was set to 10 times. Stretch C was performed by tenter stretching. The area stretching ratio of Example 1 was 30 times. Next, the sheet after stretching C was heat-set by passing it through a furnace maintained at 380°C without stretching, thereby obtaining a stretched PTFE porous membrane.

[0124] (Examples 2 to 7)

[0125] PTFE stretched porous membranes of Examples 2 to 7 were obtained in the same manner as Example 1, except that the conditions for stretching A, firing B, stretching C, and heat setting were set as shown in Table 1 below. In addition, the conditions of Example 1 are also shown in Table 1.

[0126] (Comparative Example 1)

[0127] While continuously feeding the unoriented PTFE sheet prepared in Example 1, it was uniaxially stretched in the longitudinal direction in a heating furnace maintained at 300°C (Stretch A). The stretching ratio was set to 3.5 times. Stretch A was performed by roll stretching, and the deformation speed was set to 2.24 / min.

[0128] Next, the sheet after stretching A was fired by passing it through a heating furnace maintained at 375°C without stretching (firing B). The time of passage through the heating furnace was set to 17 seconds.

[0129] Next, the sheet after firing B was uniaxially stretched in the width direction (stretch D) in a furnace maintained at 375°C. The stretching ratio was set to 10 times. Stretch D was performed by tenter stretching. The area stretching ratio of Comparative Example 1 was 35 times. Next, the sheet after stretching D was heat-set by passing it through a furnace maintained at 375°C without stretching to obtain a stretched PTFE porous membrane. The conditions of Comparative Example 1 are summarized in Table 1 below.

[0130]

[0131] (Comparative Example 2)

[0132] An unoriented PTFE sheet prepared in the same manner as in Example 1 (however, by changing the rolling conditions, it has a thickness of 0.13 mm) was continuously fed and uniaxially stretched in the longitudinal direction in a heating furnace maintained at 375°C (stretching E). The stretching ratio was set to 4.5 times. Stretching E was performed by roll stretching, and the deformation rate was set to 2.43 / min.

[0133] Next, without performing sintering, the sheet after stretching E was uniaxially stretched in the width direction in a furnace maintained at 330°C (stretching F). The stretching ratio was set to 10 times. Stretching F was performed by tenter stretching. The area stretching ratio of Comparative Example 2 was 45 times. Next, the sheet after stretching F was heat-set by passing it through a furnace maintained at 380°C without stretching, thereby obtaining a stretched PTFE porous membrane. The conditions of Comparative Example 2 are summarized in Table 2 below.

[0134] (Comparative Examples 3 to 5)

[0135] PTFE stretched porous membranes of Comparative Examples 3 to 5 were obtained in the same manner as Comparative Example 2, except that the unoriented PTFE sheet prepared in Example 1 was used and the conditions for stretching E, stretching F, and heat setting were set to the conditions shown in Table 2 below.

[0136] (Comparative Examples 6 to 8)

[0137] PTFE stretched porous membranes of Comparative Examples 6 to 8 were obtained in the same manner as Comparative Example 2, except that SSG 2.19 was used as the PTFE fine powder, and the thickness of the unoriented PTFE sheet and the conditions of stretching E, stretching F, and heat setting were set to the conditions shown in Table 2 below.

[0138]

[0139] The evaluation results of each PTFE stretched porous membrane are shown in Table 3 below.

[0140]

[0141] SEM images of the surface of the PTFE stretched porous membranes of Example 4, Comparative Example 2, and Comparative Example 8 are shown in FIGS. 9a, 10a, and 11a, respectively. SEM images of the cross-section (cut in the MD direction) in the thickness direction of the PTFE stretched porous membranes of Example 4, Comparative Example 2, and Comparative Example 8 are shown in FIGS. 9b, 10b, and 11b, respectively. In addition, the evaluation substrate used for SEM observation is shown together with the PTFE stretched porous membrane in the cross-sectional SEM images. As shown in FIGS. 9a to 11b, in the PTFE stretched porous membrane of Example 4, unlike the membranes of Comparative Examples 2 and 8, nodes were formed that extended not only in the in-plane direction but also in the membrane thickness direction. In addition, similar nodes were formed in the other examples as well. In addition, the average pore diameter of the PTFE stretched porous membranes of each example is 3.5 μm or more.

[0142] Figure 12 illustrates the relationship between air permeability in the thickness direction and total cohesive force in the PTFE stretched porous membranes of the example and comparative example. As shown in Figure 12, the PTFE stretched porous membrane of the example had higher air permeability and total cohesive force compared to that of the comparative example. In addition, the PTFE stretched porous membrane of the example had an air permeability in the thickness direction P T , total cohesion C T Expressed as, Equation C T ≥-0.33×P T It satisfied +3.67. The PTFE stretched porous membranes of Examples 3, 4, 5, and 7 were Formula C T ≥-0.57×P T It was satisfying +6.14. Industrial applicability

[0143] The PTFE stretched porous membrane of the present invention can be used, for example, as an aeration filter material.

Claims

Claim 1 The air permeability in the thickness direction is 4cm, as indicated by the Frazier air permeability. 3 / ( seconds·cm 2 ) and the total cohesive force, represented by the product of the peeling cohesive force in the first direction within the plane and the peeling cohesive force in the second direction orthogonal to the first direction within the plane, is 1.9 (N / 20mm) 2 Polytetrafluoroethylene stretched porous membrane. Claim 2 In paragraph 1, the weight per unit area is 7.0 g / m² 2 Polytetrafluoroethylene stretched porous membrane. Claim 3 A polytetrafluoroethylene stretched porous membrane having a thickness of 30 μm or more, according to claim 1 or 2. Claim 4 A breathable filter material having breathability in the thickness direction and preventing the passage of foreign matter in that direction, and comprising a polytetrafluoroethylene stretched porous membrane as described in claim 1 or 2. Claim 5 A breathable filter material according to claim 4, further comprising a breathable support material laminated to the polytetrafluoroethylene stretched porous membrane. Claim 6 A filter member having a breathable filter material that has breathability in the thickness direction and prevents the passage of foreign matter in that direction, wherein the breathable filter material is the breathable filter material described in claim 4.

Images