Polytetrafluoroethylene expanded porous membrane and ventilation filter material and filter member using the same

Abstract

In a polytetrafluoroethylene oriented porous film provided by the present invention, the through-thickness air permeability, expressed as Frazier air permeability, is 4 cm3 / (sec·cm2) or greater, and the total cohesive strength, as expressed by the product of the cohesive peel strength in an in-plane first direction and the cohesive peel strength in a second direction orthogonal in-plane to the first direction, is 1.9 (N / 20 mm)2 or greater. The oriented porous film is highly air permeable, and yet, when incorporated into a filter member, for example, resists damage during handling or placement of said member in a housing or the like.

Description

[Technical field]

[0001] The present invention relates to a polytetrafluoroethylene (hereinafter, referred to as "PTFE") expanded porous membrane, and a ventilation filter medium and a filter member using the same. [Background technology]

[0002] A filter member having a breathable filter material may be attached to the housing of various electrical products such as vehicle electrical components and mobile information terminals so as to cover the opening provided in the housing. The breathable filter material has air permeability in the thickness direction, while preventing the passage of foreign matter such as dust and water. By attaching the filter member, it is possible to ensure ventilation through the opening while preventing the passage of foreign matter through the opening. It is considered to use a PTFE expanded porous membrane as the breathable filter material.

[0003] Patent Document 1 discloses a highly breathable expanded porous PTFE membrane. Patent Document 2 discloses a highly breathable expanded porous PTFE membrane having high ball burst strength. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2009-297702 A [Patent Document 2] Special Publication No. 11-515036 Summary of the Invention [Problem to be solved by the invention]

[0005] For example, a highly breathable PTFE porous membrane can improve the breathability of a filter member, which allows the member to be made smaller. However, according to the study by the present inventors, when a filter member is provided with a highly breathable PTFE porous membrane, damage such as cracks is likely to occur in the PTFE porous membrane when the member is handled or placed in a housing or the like.

[0006] An object of the present invention is to provide an expanded porous PTFE membrane which, while being highly breathable, is unlikely to be damaged when, for example, it is incorporated into a filter member, when the member is handled or placed in a housing or the like. [Means for solving the problem]

[0007] The present invention relates to The air permeability in the thickness direction is expressed by the Fragile air permeability, and is 4 cm 3 / (second cm 2 ) or more, The total cohesive strength, which is the product of the peel cohesive strength in a first direction in the plane and the peel cohesive strength in a second direction perpendicular to the first direction in the plane, is 1.9 (N / 20 mm) 2 That's all. PTFE stretched porous membrane, to provide.

[0008] From another aspect, the present invention comprises: A ventilation filter material that has air permeability in the thickness direction and prevents the penetration of foreign matter in that direction, A ventilation filter material comprising the PTFE expanded porous membrane of the present invention, to provide.

[0009] From another aspect, the present invention provides a method for manufacturing a semiconductor device comprising: The filter has air permeability in the thickness direction and is equipped with an air permeable filter material that prevents the penetration of foreign matter in that direction. The filter member, wherein the ventilation filter material is the ventilation filter material of the present invention. to provide. Effect of the Invention

[0010] According to the present invention, a PTFE expanded porous membrane is achieved which has high breathability and, when incorporated into, for example, a filter member, is less likely to be damaged when the member is handled or placed in a housing or the like. [Brief description of the drawings]

[0011] [Figure 1]FIG. 1 is a cross-sectional view illustrating a schematic example of a PTFE expanded porous membrane of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view showing a schematic diagram of an example of the ventilation filter medium of the present invention. [Diagram 3] FIG. 2 is a cross-sectional view showing a schematic diagram of another example of the ventilation filter medium of the present invention. [Figure 4] FIG. 1 is a cross-sectional view illustrating an example of a filter member of the present invention. [Diagram 5] FIG. 3 is a cross-sectional view illustrating a schematic diagram of another example of the filter member of the present invention. [Figure 6] FIG. 4 is a cross-sectional view that illustrates a schematic diagram of still another example of the filter member of the present invention. [Figure 7] FIG. 2 is a cross-sectional view that illustrates a schematic diagram of another example of the filter member of the present invention. [Figure 8] FIG. 2 is a cross-sectional view illustrating an example of an embodiment of the present invention in which a filter member is supplied. [Figure 9A] 1 is an image of the surface of the PTFE expanded porous membrane of Example 4 observed with a scanning electron microscope (SEM). [Figure 9B] 1 is an image obtained by observing a cross section in the thickness direction (cut in the MD direction) of the PTFE expanded porous membrane of Example 4 by SEM. [Figure 10A] 1 is an image of the surface of the expanded porous PTFE membrane of Comparative Example 2 observed by SEM. [Figure 10B] 1 is an image obtained by observing a cross section in the thickness direction (cut in the MD direction) of the expanded porous PTFE membrane of Comparative Example 2 by SEM. [Figure 11A] 1 is an image of the surface of the expanded porous PTFE membrane of Comparative Example 8 observed by SEM. [Figure 11B] 1 is an image obtained by observing a cross section in the thickness direction (cut in the MD direction) of the expanded porous PTFE membrane of Comparative Example 8 by SEM. [Figure 12] 1 is a graph showing the relationship between the air permeability in the thickness direction and the total cohesive strength in the PTFE expanded porous membranes of Examples and Comparative Examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] An example of the expanded PTFE porous membrane of the present invention is shown in Fig. 1. The air permeability in the thickness direction of the expanded PTFE porous membrane 1 in Fig. 1 is expressed by Frazier air permeability and is 4 cm 3 / (second cm 2 ) or more. The air permeability is 4.5 cm 3 / (second cm 2 ) or more, 5.0cm 3 / (second cm 2 ) or more, 6.0cm 3 / (second cm 2 ) or more, 7.0cm 3 / (second cm 2 ) or more, even 8.0 cm 3 / (second cm 2 The upper limit of the air permeability may be, for example, 20.0 cm 3 / (second cm 2 ) or less. The Frazier air permeability is determined in accordance with the air permeability measurement method A (Fragile type method) defined in the Japanese Industrial Standards (hereinafter referred to as "JIS") L1096. Even if the size of the PTFE expanded porous membrane 1 is less than the size of the test piece in the Frazier type method (about 200 mm x 200 mm), the Frazier air permeability can be evaluated by using a measuring tool that limits the area of ​​the measurement area. One example of the measuring tool is a resin plate in which a through hole having a cross-sectional area corresponding to the area of ​​the desired measurement area is formed in the center. For example, a measuring tool in which a through hole having a circular cross section with a diameter of 1 mm or less is formed in the center can be used.

[0013] The total cohesive strength of the PTFE expanded porous membrane 1 is 1.9 (N / 20 mm) 2 That is all. The total cohesive strength is expressed by the product of the peel cohesive strength in a first direction in the plane of the PTFE expanded porous membrane 1 and the peel cohesive strength in a second direction perpendicular to the first direction in the plane. The first direction is, for example, the MD direction. The second direction is, for example, the TD direction. The total cohesive strength is 2.0 (N / 20 mm). 2 More than 2.5 (N / 20mm) 2 Above, 2.8(N / 20mm) 2 Above 3.0 (N / 20mm) 2The upper limit of the total cohesive strength may be, for example, 25.0 (N / 20 mm). 2 Less than or equal to 20.0 (N / 20mm) 2 Below, 15.0(N / 20mm) 2 Below, 10.0(N / 20mm) 2 Below, 8.0 (N / 20mm) 2 It may be the following.

[0014] A PTFE expanded porous membrane is usually formed by stretching an unstretched PTFE sheet, which is an original sheet, in two mutually perpendicular directions in the sheet plane, for example, in the MD direction and the TD direction. The stretching conditions for each direction are usually different, and therefore the mechanical properties of the membrane usually differ between the two mutually perpendicular directions. According to the study by the present inventors, for example, when incorporated into a filter member, even if the membrane has a high peel cohesive strength in one direction, if the peel cohesive strength in a different direction is low, the membrane tends to be damaged when the member is handled or placed in a housing. The total cohesive strength is the product of the peel cohesive strength in a first direction in the plane and the peel cohesive strength in a second direction perpendicular to the first direction in the plane. According to the study by the present inventors, when the total cohesive strength is 1.9 (N / 20 mm) 2 The expanded PTFE porous membrane 1 having the above properties can be judged to have a high peel cohesive strength on average in the in-plane direction of the membrane.

[0015] The peel cohesive strength in the first direction of the PTFE expanded porous membrane 1 may be, for example, 1.70 (N / 20 mm) or more, 1.80 (N / 20 mm) or more, 1.90 (N / 20 mm) or more, or even 2.00 (N / 20 mm) or more.

[0016] The peel cohesive strength in the second direction of the PTFE expanded porous membrane 1 may be, for example, 1.15 (N / 20 mm) or more, 1.20 (N / 20 mm) or more, 1.40 (N / 20 mm) or more, 1.50 (N / 20 mm) or more, 1.60 (N / 20 mm) or more, or even 1.70 (N / 20 mm) or more.

[0017] The average cohesive strength of the PTFE expanded porous membrane 1, which is represented by the average (arithmetic mean) of the peel cohesive strength in the first direction and the peel cohesive strength in the second direction, is, for example, 1.40 (N / 20 mm) or more, and may be 1.50 (N / 20 mm) or more, 1.60 (N / 20 mm) or more, 1.70 (N / 20 mm) or more, or even 1.80 (N / 20 mm) or more. 3 / (second cm 2 ) or more, and the average cohesive strength, expressed as the average (arithmetic mean) of the peel cohesive strength in the first direction and the peel cohesive strength in the second direction, is 1.40 (N / 20 mm) or more.

[0018] The PTFE expanded porous membrane 1 can achieve both high levels of air permeability in the thickness direction and high levels of total cohesive strength. T , the total cohesive strength is C T and express the formula C T ≧-0.33×P T +3.67 or formula C T ≧-0.57×P T +6.14 may be met.

[0019] In this specification, PTFE includes modified PTFE. In other words, the PTFE expanded porous membrane 1 includes a expanded porous membrane of modified PTFE. The 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% by mass or more, preferably 97% by mass or more, and more preferably 99% by 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 (TFE homopolymer).

[0020] The standard specific gravity (SSG) of the PTFE may be 2.18 or less. The SSG is defined in JIS K6935-1.

[0021] The basis weight of the PTFE expanded porous membrane 1 is, for example, 1.0 g / m 2 More than 7.0 g / m 2 More than 8.0g / m 2 More than 10.0g / m 2 More than 12.0g / m 2 Above 13.0g / m 2 The upper limit of the basis weight is, for example, 87.2 g / m 2 The basis weight can be calculated by dividing the weight of the expanded porous PTFE membrane 1 by the area of ​​the main surface.

[0022] The thickness of the PTFE expanded porous membrane 1 is, for example, 10 μm or more, and may be 30 μm or more, 35 μm or more, 40 μm or more, or even 45 μm or more. The upper limit of the thickness is, for example, 200 μm or less, and may be 100 μm or less.

[0023] The average pore size of the PTFE expanded porous membrane 1 is, for example, 1.0 μm or more, and may be 2.0 μm or more, 3.0 μm or more, or even 3.5 μm or more. The upper limit of the average pore size is, for example, 20 μm or less. The average pore size can be evaluated in accordance with ASTM F316. The average pore size may be evaluated using a commercially available evaluation device (for example, Perm-Porometer, manufactured by Porous Material) that complies with the above regulations.

[0024] The porosity of the PTFE expanded porous membrane 1 is, for example, 80% or more, and may be 85% or more, 88% or more, or even 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 (area of ​​the main surface) of the membrane and the true density of PTFE into the following formula. The true density of PTFE is 2.18 g / cm 3 It is. Porosity (%) = {1 - (mass [g] / (thickness [cm] x area [cm 2 ]×True density [g / cm 3 ]))}×100

[0025] The bulk density of the PTFE expanded porous membrane 1 is, for example, 0.30 g / cm 3 Less than or equal to 0.28 g / cm 3 Below, 0.26g / cm 3 Below 0.25g / cm 3 Below, 0.23g / cm 3 Below that, 0.22g / cm 3 The lower limit of the bulk density may be, for example, 0.08 g / cm 3 That is all. The appropriate range of bulk density contributes to achieving a porous PTFE membrane that is highly breathable and difficult to break. The bulk density can be determined from the basis weight and thickness of the porous PTFE membrane 1.

[0026] The water pressure resistance (limit water pressure resistance) of the PTFE expanded porous membrane 1 is, for example, 30 kPa or more, and may be 35 kPa or more, 40 kPa or more, 44 kPa or more, or even 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 using a measuring tool in accordance with the water resistance test A method (low water pressure method) or B method (high water pressure method) specified in JIS L1092.

[0027] An example of the measurement tool is a stainless steel disk with a diameter of 47 mm and a through hole (with a circular cross section) with a diameter of 1 mm in the center. This disk has a thickness that does not deform due to the water pressure applied when measuring the water resistance. Measurement of the water resistance using this measurement tool can be carried out as follows.

[0028] The PTFE expanded porous membrane 1 to be evaluated is fixed to one side of the measuring jig so as to cover the opening of the through hole of the measuring jig. The fixing is performed so that water does not leak from the fixed part of the membrane during the measurement of the water pressure resistance. To fix the membrane, a double-sided adhesive tape with a water passage hole having a shape that matches the shape of the opening can be used. The double-sided adhesive tape may be placed between the measuring jig and the membrane so that the circumference of the water passage hole and the circumference of the opening match. Next, the measuring jig with the membrane fixed is set in the test device so that the surface opposite to the fixing surface of the membrane becomes the water pressure application surface 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 place on the membrane surface of the PTFE expanded porous membrane 1. The measured water pressure resistance can be the water pressure resistance of the PTFE expanded porous membrane 1. The test equipment used may have the same configuration as the water resistance test equipment exemplified in JIS L1092 and a test piece mounting structure in which the above-mentioned measuring tool can be set.

[0029] The expanded porous PTFE membrane 1 may be a single-layer membrane.

[0030] The PTFE expanded porous membrane 1 may be subjected to a liquid-repellent treatment such as a water-repellent treatment or an oil-repellent treatment. The liquid-repellent treatment can be performed by coating with a liquid-repellent substance such as a fluorine-based compound. A known method can be used for the coating.

[0031] The PTFE expanded porous membrane 1 may be colored. The coloring can be performed, for example, by dyeing the PTFE expanded porous membrane 1 or by making the PTFE expanded porous membrane 1 contain a colorant. The coloring can be performed so that light having a wavelength in the range of 380 to 500 nm is absorbed. In this case, the PTFE expanded porous membrane 1 can be colored blue, gray, brown, pink, green, yellow, or the like.

[0032] The PTFE expanded porous membrane 1 can be used, for example, as a breathable filter material that has breathability in the thickness direction and prevents the penetration of foreign matter in the thickness direction. Examples of foreign matter include particles such as dust and liquid water such as water droplets. However, the use of the PTFE expanded porous membrane 1 is not limited to the above examples.

[0033] The expanded PTFE porous membrane 1 can be produced, for example, by the following method A. The expanded PTFE porous membrane 1 may be a membrane obtained by method A. However, the method for producing the expanded PTFE porous membrane 1 is not limited to method A.

[0034] [Method A] Stretching an unsintered PTFE sheet in a predetermined direction at a stretching temperature below the melting point of PTFE (Stretching A); The sheet that has been subjected to the stretching step A is baked at a temperature equal to or higher than the melting point of PTFE (baking step B); The sheet subjected to the baking B is further stretched in a direction different from the above-mentioned predetermined direction at a stretching temperature lower than the melting point of PTFE (stretching C).

[0035] (Stretching A) In the stretching A, the unsintered PTFE sheet is stretched in a predetermined direction at a stretching temperature lower than the melting point of PTFE (343°C, which is the melting point of the crystal). The stretching A can be performed, for example, in a heating furnace controlled to a temperature (stretching temperature) at which the stretching A is performed. The stretching A can be performed, for example, by roll stretching. However, the method of performing the stretching A is not limited to the above example.

[0036] The stretching temperature of the stretching A is, for example, 200 to 340°C, and may be 280 to 330°C.

[0037] The stretching ratio of the stretching A is, for example, 1.5 to 10.0 times, and may be 2.0 to 8.0 times. When both the air permeability in the thickness direction and the total cohesive strength are to be achieved at a higher level, the stretching ratio is preferably 4.0 to 5.0 times. When both the air permeability in the thickness direction and the total cohesive strength are to be achieved at a high level while improving the water pressure resistance, the stretching ratio is preferably 3.0 to 4.0 times.

[0038] The direction of stretching A (predetermined direction) is, for example, the MD direction of the PTFE sheet. When the PTFE sheet is in a strip shape, the direction of stretching A may be the longitudinal direction of the PTFE sheet.

[0039] It is preferable that the stretching A is performed in a state where the degree of stretching per unit time is suppressed. It is considered that the suppressed stretching A contributes to the formation of the PTFE expanded porous membrane 1 having high breathability and total cohesive strength. The PTFE expanded porous membrane 1 has a node / fibril structure having a plurality of nodes and fibrils connecting the plurality of nodes. The nodes are the aggregated parts of PTFE. According to the study by the present inventors, the suppressed stretching A and the subsequent baking B tend to form nodes that are elongated not only in the in-plane direction but also in the film thickness direction. The nodes that are elongated in the film thickness direction can suppress the cohesive failure of the PTFE expanded porous membrane 1 regardless of the direction in which the force is applied, and have a low degree of inhibition of the breathability in the film thickness direction. Therefore, it is presumed that the node / fibril structure having the nodes contributes to the high breathability and total cohesive strength of the PTFE expanded porous membrane 1. The suppressed stretching can be performed, for example, by reducing the stretching ratio per unit time. The stretching ratio per time is expressed by the strain rate, and may be, for example, 0.5 to 5.0 / min, 0.5 to 3.0 / min, or even 0.5 to 2.0 / min. The strain rate can be determined by dividing the stretching speed (m / min) by the stretching distance (m). The strain rate is usually constant in stretching A.

[0040] (Firing B) In the baking B, the sheet that has been subjected to the stretching A is baked at a temperature equal to or higher than the melting point of PTFE. The baking B can be carried out, for example, in a heating furnace controlled to a temperature at which the baking B is carried out (baking temperature).

[0041] 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.

[0042] It is preferable to perform the baking B in a state where the sheet is not stretched. It is presumed that performing the baking in this state between the stretching A and the stretching C contributes to the formation of a PTFE expanded porous film having high air permeability and total cohesive strength. According to the study by the present inventors, the nodes formed by the stretching A are heat-fixed by the baking B, and the structure of the nodes is maintained even by the stretching C which expands the voids between the fibrils. However, slight stretching or shrinkage to correct the slackness or stretching of the sheet which may occur due to temperature changes is permitted. The stretching ratio permitted in the baking B is, for example, 0.80 to 2.00 times, and preferably 0.90 to 1.10 times. A stretching ratio of less than 1 means shrinkage. The PTFE expanded porous film 1 obtained through the baking B is a fired film. From this aspect, the PTFE expanded porous film 1 may be a fired film.

[0043] (Stretching C) In the stretching C, the sheet that has been subjected to the baking B is further stretched in a direction different from the above-mentioned predetermined direction at a stretching temperature lower than the melting point of PTFE. The stretching C can be performed, for example, in a heating furnace controlled to a temperature (stretching temperature) at which the stretching C is performed. The stretching C can be performed, for example, by tenter stretching. However, the method for performing the stretching C is not limited to the above example.

[0044] The stretching temperature in the stretching C is, for example, 40 to 340°C, and may be 100 to 330°C.

[0045] The stretching ratio in the stretching C is, for example, 2 to 15 times, and may be 4 to 10 times.

[0046] The direction of stretching C is typically a direction approximately perpendicular to the direction of stretching A in the sheet plane. The direction of stretching C is, for example, the TD direction of the PTFE sheet. When the PTFE sheet is in a strip shape, the direction of stretching C may be the width direction of the PTFE sheet.

[0047] In the method A, stretching other than the stretching A and the stretching C may be performed as necessary. However, it is preferable that the first stretching performed on the PTFE sheet is the stretching A. In the method A, only the stretching A and the stretching C may be performed as the stretching of the PTFE sheet. The stretching A, the baking B, and the stretching C may be performed consecutively.

[0048] The expanded porous PTFE membrane 1 obtained by method A is typically a biaxially expanded membrane. From this aspect, the expanded porous PTFE membrane 1 may be a biaxially expanded membrane.

[0049] The unsintered PTFE sheet to be subjected to method A can be formed, for example, by forming a mixture of PTFE fine powder and a liquid lubricant into a sheet by extrusion and / or rolling. The liquid lubricant is preferably removed from the PTFE sheet before stretching A by a method such as heating or extraction. In addition, after removing the liquid lubricant, it is preferable not to apply a compressive force in the thickness direction of the unsintered PTFE sheet. In other words, it is preferable to stretch a PTFE sheet (non-densified sheet) that has not been densified by applying the compressive force.

[0050] For the PTFE fine powder, commercially available products such as Polyflon F-104 (manufactured by Daikin Industries), Fluon CD-123E, Fluon CD-145E (manufactured by AGC), and Teflon 6J (manufactured by Mitsui-Chemours Fluoro Products) can be used.

[0051] Examples of the liquid lubricant include liquid paraffin, naphtha, white oil, hydrocarbon oil 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 can wet the surface of the PTFE fine powder and can be removed after forming the mixture into a sheet.

[0052] The mixing ratio of the PTFE fine powder and the liquid lubricant is usually about 5 to 50 parts by weight of the liquid lubricant to 100 parts by weight of the PTFE fine powder.

[0053] The thickness of the unsintered PTFE sheet can be adjusted depending on the desired thickness of the expanded porous PTFE membrane 1, and is, for example, about 0.05 to 0.5 mm.

[0054] In method A, any step can be carried out after stretching C, if necessary. An example of such a step is heat setting, which holds the sheet at a temperature equal to or higher than the melting point of PTFE. Heat setting maintains the structure of the stretched sheet. Heat setting can be carried out in the same manner as sintering B. Heat setting may be carried out continuously following stretching C.

[0055] [Ventilated filter material] An example of the ventilation filter medium of the present invention is shown in FIG. 2. The ventilation filter medium 2 (2A) of FIG. 2 includes a PTFE expanded porous membrane 1. Another example of the ventilation filter medium of the present invention is shown in FIG. 3. The ventilation filter medium 2 (2B) of FIG. 3 further includes a breathable support material 3. The breathable support material 3 is laminated to the PTFE expanded porous membrane. The breathable support material 3 can improve the strength and handling of the ventilation filter medium 2.

[0056] The breathable support material 3 usually has higher breathability in the thickness direction than the PTFE expanded porous membrane 1. Examples of the breathable support material 3 are woven fabric, nonwoven fabric, net, and mesh. Examples of materials constituting the breathable support material 3 are polyester such as polyethylene terephthalate (PET), polyolefin such as polyethylene (PE) and polypropylene (PP), and aramid resin. The shape of the breathable support material 3 may be the same as or different from the shape of the PTFE expanded porous membrane 1 when viewed perpendicularly to the main surface of the ventilation filter material 2. The breathable support material 3 may have a shape corresponding to the peripheral portion of the PTFE expanded porous membrane 1 when viewed perpendicularly to the main surface of the ventilation filter material 2. When the shape of the PTFE expanded porous membrane 1 is circular, the shape is a ring. The configuration and shape of the breathable support material 3 are not limited to the above example.

[0057] The ventilation filter material 2B has one breathable support material 3 arranged on one side of the PTFE stretched porous membrane 1. The ventilation filter material 2 may have two or more breathable support materials 3. In the ventilation filter material 2, the breathable support material 3 may be arranged on both sides of the PTFE stretched porous membrane 1. The PTFE stretched porous membrane 1 and the breathable support material 3 may be joined by welding such as heat welding and ultrasonic welding, adhesive or pressure sensitive adhesive.

[0058] The ventilation filter medium 2 may include any layers and / or members other than those described above.

[0059] The thickness of the ventilation filter medium 2 is, for example, 10 to 300 μm, and may be 50 to 200 μm.

[0060] The weight of the ventilation filter medium 2 is, for example, 1.0 to 200.0 g / m 2 and 10.0 to 100.0 g / m 2 may be also possible.

[0061] The breathable filter medium 2 can have the same properties as the expanded porous PTFE membrane 1, for example, air permeability in the thickness direction and / or water pressure resistance.

[0062] The ventilation filter medium 2 may be subjected to a liquid repellent treatment and / or a coloring treatment.

[0063] The shape of the aeration filter material 2 is, for example, a polygon including a square and a rectangle, a circle, an ellipse, or a strip, as viewed perpendicularly to the main surface of the aeration filter material 2. 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 roll. In addition, if necessary, it may be wound in a state in which it is laminated with a release sheet (separator).

[0064] The area of ​​the aeration filter material 2, which is a leaf having a polygonal, circular, elliptical or other shape, is 675 mm 2 May be less than 175mm 2 The lower limit of the area may be, for example, 0.20 mm 2That is all. The ventilation filter medium 2 having this area is suitable for use in a miniaturized filter member. However, the area of ​​the ventilation filter medium 2 may be larger depending on the application.

[0065] The ventilation filter medium 2 can be used, for example, as a filter member. However, the use of the ventilation filter medium 2 is not limited to the above example.

[0066] [Filter material] An example of the filter member of the present invention is shown in Fig. 4. The filter member 4 (4A) in Fig. 4 has air permeability in the thickness direction and includes the above-described air permeable filter material 2 as an air permeable filter material that prevents the penetration of foreign matter in that direction. The filter member 4A is, for example, a member that is placed on a surface of an object having an opening, and ensures ventilation through the opening while preventing the penetration of foreign matter through the opening. In this case, the filter member 4A is usually placed so that the air permeable filter material 2 covers the opening of the object.

[0067] The filter member 4A includes an adhesive layer 5 disposed on one side of the ventilation filter medium 2. The ventilation filter medium 2 and the adhesive layer 5 are directly bonded to each other. The filter member 4A can be disposed on the above-mentioned surface of the object via the adhesive layer 5.

[0068] When the filter member 4 is handled and placed on an object, a strong force may be applied to the filter member 4 in a specific direction. However, the ventilation filter medium 2 includes the PTFE expanded porous membrane 1 having a high total cohesive strength. Therefore, for example, the filter member 4 can be manufactured without limiting the mounting direction of the ventilation filter medium 2 (or the PTFE expanded porous membrane 1) to the filter member 4.

[0069] Examples of the adhesive constituting the adhesive layer 5 include acrylic adhesives, silicone adhesives, urethane adhesives, epoxy adhesives, and rubber adhesives. When it is necessary to consider using the filter member 4 under high temperatures, 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 a phenolic resin, an epoxy resin, a urea resin, a polyurethane resin, a melamine resin, or a polyester resin.

[0070] The outer circumference of the ventilation filter material 2 and the outer circumference of the adhesive layer 5 are aligned when viewed perpendicularly to the main surface of the ventilation filter material 2. The shape of the adhesive layer 5 corresponds to the peripheral portion of the ventilation filter material 2 when viewed perpendicularly to the main surface of the ventilation filter material 2. The region of the ventilation filter material 2 to which the adhesive layer 5 is not bonded can be the ventilation region of the filter member 4A. However, the shape of the adhesive layer 5 is not limited to the above example.

[0071] The area of ​​the ventilation area is, for example, 40 mm 2 The filter member 4 having an area of ​​the ventilation region within this range is suitable for placement in an object having a small opening, for example. The lower limit of the area of ​​the ventilation region is, for example, 0.008 mm 2 However, the area of ​​the ventilation region may be larger depending on the type of object on which the filter member 4 is placed.

[0072] Modified examples of the filter member 4 are shown below. The filter member 4 (4B) in Fig. 5 further includes a base layer 6 disposed on one side of the ventilation filter medium 2, and has the same configuration as the filter member 4A, except that the ventilation filter medium 2 and the adhesive layer 5 are joined via the base layer 6. The base layer 6 can improve the strength and ease of handling of the filter member 4, and can suppress damage to the ventilation filter medium 2 during handling or placement on an object.

[0073] Examples of materials constituting the base layer 6 include polyolefins such as PE and PP, polyesters such as PET, silicone resins, polycarbonates, polyimides, polyamideimides, polyphenylene sulfide, polyether ether ketones (PEEK), polyvinyl chloride, fluororesins, and metals such as aluminum and stainless steel. Examples of fluororesins include PTFE, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers (PFA), tetrafluoroethylene-hexafluoropropylene copolymers (FEP), and tetrafluoroethylene-ethylene copolymers (ETFE). However, the materials constituting the base layer 6 are not limited to the above examples.

[0074] The outer circumference of the ventilation filter material 2 and the outer circumference of the base material layer 6 are the same when viewed perpendicularly to the main surface of the ventilation filter material 2. The shape of the base material layer 6 is a shape corresponding to the peripheral part of the ventilation filter material 2 when viewed perpendicularly to the main surface of the ventilation filter material 2. The region of the ventilation filter material 2 to which the base material layer 6 is not bonded can be the ventilation region of the filter member 4B. However, the shape of the base material layer 6 is not limited to the above example.

[0075] The ventilation filter material 2 and the base layer 6 may be joined by an adhesive or a bonding agent, or may be joined by welding such as heat welding and ultrasonic welding. The ventilation filter material 2 and the base layer 6 may be joined by an adhesive layer. The adhesive layer may have the same structure as the adhesive layer 5. The base layer 6 and the adhesive layer 5 may be the base and adhesive layer of a single-sided adhesive tape or a double-sided adhesive tape, respectively.

[0076] The filter member 4 (4C) in Fig. 6 has the same structure as the filter member 4B, except that it further includes a base layer 6 (6B) arranged on the other side of the ventilation filter medium 2. The ventilation filter medium 2 is sandwiched between a pair of base layers 6 (6A, 6B). This sandwiching structure can further improve the strength and ease of handling of the filter member 4.

[0077] The filter member 4 (4D) in FIG. 7 further includes a tab film 7, and has the same configuration as the filter member 4C, except that the base layer 6 (6B) and the tab film 7 are joined via an adhesive layer 5 (5B). The tab film 7 has a tab that protrudes outward from the outer periphery 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 usually removed when the filter member 4D is used. The tab film 7 can be made of the same material as the material that constitutes the base layer 6. The tab film 7 is usually removed by gripping the tab and lifting it up. At this time, a strong force is applied to the ventilation filter material 2 in the lifting direction.

[0078] The filter member 4 can be supplied by, for example, a member supply sheet. FIG. 8 shows an example of a member supply assembly in which the filter member 4 is supplied by the sheet. The member supply assembly 10 in FIG. 8 includes a member supply sheet 9 and a filter member 4 (4D) arranged on the sheet 9. The filter member 4 is arranged on the sheet 9 via an adhesive layer 5 (5A). The member supply assembly 10 can efficiently supply the filter member 4, for example, in a step of placing the filter member 4 on the surface of an object. A plurality of filter members 4 may be arranged on the sheet 9.

[0079] The filter member 4 may be placed on the sheet 9 via an adhesive layer provided on the surface of the sheet 9 on which the filter member 4 is placed. The adhesive layer on the surface on which the filter member 4 is placed is preferably weakly adhesive.

[0080] Since the expanded porous PTFE membrane 1 is not easily damaged, depending on the configuration of the filter member 4, for example, it may be possible to lift and peel the filter member 4 off from the sheet 9 without damaging the membrane 1.

[0081] Examples of materials constituting the sheet 9 include paper, metal, resin, and composite materials thereof. Examples of metal include stainless steel and aluminum. Examples of resin include polyester such as PET, and polyolefin 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 a sheet or strip shape. When the sheet 9 is in a strip shape, the member supply assembly 10 may be wound to form a roll.

[0082] Examples of the object on which the filter member 4 is disposed are the housing of an electronic device and the housing of an electrical component for a vehicle. The filter member 4 can be disposed on the outer surface and / or inner surface of the housing. In this case, the opening may be an air vent and / or a sound vent provided in the housing. Examples of electronic devices are wearable devices such as smart watches 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 electrical components for a vehicle are lamps and ECUs. However, the object is not limited to the above examples.

[0083] The foreign matter that is prevented from passing through by the arrangement of the filter member 4 is, for example, particles such as dust, and liquid water such as water droplets. EXAMPLES

[0084] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0085] The evaluation method for the expanded porous PTFE membrane is shown below.

[0086] Thickness Ten measurement points were randomly determined, and the average thickness measured at each measurement point using a dial gauge (flat gauge with a diameter of 10 mm, measuring force of 15 N or less) was taken as the thickness of the expanded porous PTFE membrane.

[0087] [Metaku] The basis weight was determined by the method described above.

[0088] [Water resistance (limit water resistance)] The water pressure resistance was determined by the above-mentioned method in accordance with the provisions of the water resistance test method B (high water pressure method) specified in JIS L1092.

[0089] [Porosity] The porosity was determined by the method described above.

[0090] [Air permeability through thickness] The air permeability in the thickness direction (Fragile air permeability) was determined by the above-mentioned method in accordance with the provisions of the air permeability measurement method A specified in JIS L1096.

[0091] [Total cohesion] The total cohesive strength was determined by the following method. First, the PTFE stretched porous membrane to be measured was cut into a rectangle (length 150 mm x width 20 mm). Next, two double-sided adhesive tapes (manufactured by Nitto Denko, No. 5610) having the same shape as the PTFE stretched porous membrane were prepared. Next, each double-sided adhesive tape was attached to one side and the other side of the PTFE stretched porous membrane with the outer periphery aligned. Next, two rectangular PET films (manufactured by Toray, Lumirror S10#25, thickness 25 μm) having a length of 200 mm x width of 20 mm were prepared, and each PET film was attached to one side and the other side of the PTFE stretched porous membrane with the double-sided adhesive tape. The PET films were attached so that both ends in the width direction of each PET film were aligned with both ends in the width direction of the PTFE stretched porous membrane, and one end in the longitudinal direction of each PET film was aligned with one end in the longitudinal direction of the PTFE stretched porous membrane. This ensured that the other end of the PET film in the longitudinal direction had a length (50 mm) that allowed the chuck of the tensile tester to stably grip the PET film. Next, a pressure roller with a load of 19.6 N was moved back and forth once so that a pressure force was applied in the thickness direction of the laminate of PET film / double-sided adhesive tape / PTFE expanded porous membrane / double-sided adhesive tape / PET film. Thereafter, the laminate was left at room temperature for 12 hours and then at 60°C for 1 hour before starting the tensile test to obtain a test specimen. Note that test specimen S was cut from the same PTFE expanded porous membrane with the long side aligned in the MD direction of the membrane. MD and a test piece S cut out with its long side aligned with the TD direction of the film. TD We prepared the following.

[0092] Next, a tensile tester (Tensilon Universal Tester RTF, manufactured by A&D) was prepared. The test piece was held horizontally, and the free end of one PET film was bent upward and attached to the upper chuck of the tensile tester, and the free end of the other PET film was bent downward and attached to the lower chuck of the tensile tester. Next, a tensile test (T-shaped peel test) was performed under the conditions of a measurement temperature of 23 ± 5 ° C, a measurement humidity of 50 ± 5% RH, and a tensile speed of 300 mm / min, in which the free end of one PET film was pulled upward and the free end of the other PET film was pulled downward, causing cohesive failure in the PTFE stretched porous membrane. After the displacement of the PET film due to cohesive failure began, the stress between the chucks measured during the initial 25 mm displacement was ignored, and the average value of the measured stress values ​​recorded continuously during the subsequent 50 mm displacement was taken as the peel cohesive strength (unit: N / 20 mm) of the PTFE stretched porous membrane. Test piece S MD The peel cohesive strength in the MD direction was obtained from the specimen S. TD From the peel cohesion strength in the TD direction, the peel cohesion strength in the TD direction was calculated. Next, the total cohesion strength was calculated as the product of both the peel cohesion strengths.

[0093] Example 1 100 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 were uniformly mixed to form a PTFE paste. The PTFE paste was then subjected to a pressure of 2.5 MPa (25 kg / cm) using an FT die. 2 The mixture was extruded under a pressure of 1000 MPa (0.25 kgf / cm2) and then rolled with a pair of metal rolls to obtain a strip-shaped PTFE sheet (unstretched, thickness 0.2 mm) with a uniform thickness. The obtained PTFE sheet was then heated to remove the liquid lubricant.

[0094] Next, the PTFE sheet was continuously fed and uniaxially stretched in the longitudinal direction in a heating furnace maintained at 300°C (Stretching A). The stretching ratio was 3.0 times. Stretching A was performed by roll stretching, and the strain rate was 1.66 / min.

[0095] Next, the sheet after the stretching A was baked (baking B) by passing through a heating furnace maintained at 375° C. without being stretched. The time for passing through the heating furnace was 17 seconds.

[0096] Next, the sheet after the baking B was uniaxially stretched in the width direction in a heating furnace maintained at 330°C (stretching C). The stretching ratio was 10 times. Stretching C was performed by tenter stretching. The area stretching ratio in Example 1 was 30 times. Next, the sheet after the stretching C was heat-set by passing through a heating furnace maintained at 380°C without stretching, to obtain a PTFE stretched porous membrane.

[0097] (Examples 2 to 7) The expanded PTFE porous membranes of Examples 2 to 7 were obtained in the same manner as in Example 1, except that the conditions for stretching A, baking B, stretching C, and heat setting were set as shown in the following Table 1. The conditions for Example 1 are also shown in Table 1.

[0098] Comparative Example 1 The unstretched PTFE sheet prepared in Example 1 was continuously fed and uniaxially stretched in the longitudinal direction in a heating furnace maintained at 300°C (Stretching A). The stretching ratio was 3.5 times. Stretching A was performed by roll stretching, and the strain rate was 2.24 / min.

[0099] Next, the sheet after the stretching A was baked (baking B) by passing through a heating furnace maintained at 375° C. without being stretched. The time for passing through the heating furnace was 17 seconds.

[0100] Next, the sheet after the baking B was uniaxially stretched in the width direction in a heating furnace maintained at 375°C (stretching D). The stretching ratio was 10 times. Stretching D was performed by tenter stretching. The areal stretching ratio of Comparative Example 1 was 35 times. Next, the sheet after stretching D was heat-set by passing through a heating furnace maintained at 375°C without stretching to obtain a PTFE stretched porous membrane. The conditions of Comparative Example 1 are summarized in Table 1 below.

[0101] [Table 1]

[0102] Comparative Example 2 An unstretched PTFE sheet (with a thickness of 0.13 mm by changing the rolling conditions) prepared in the same manner as in Example 1 was continuously fed and uniaxially stretched in the longitudinal direction in a heating furnace maintained at 375°C (Stretching E). The stretching ratio was 4.5 times. Stretching E was performed by roll stretching, and the strain rate was 2.43 / min.

[0103] Next, without firing, the sheet after Stretching E was uniaxially stretched in the width direction in a heating furnace maintained at 330°C (Stretching F). The stretching ratio was 10 times. Stretching F was performed by tenter stretching. The areal stretching ratio of Comparative Example 2 was 45 times. Next, the sheet after Stretching F was heat-set by passing through a heating furnace maintained at 380°C without stretching to obtain a stretched porous PTFE membrane. The conditions of Comparative Example 2 are summarized in Table 2 below.

[0104] (Comparative Examples 3 to 5) The unstretched PTFE sheet prepared in Example 1 was used, and the conditions for stretching E, stretching F and heat fixing were set as shown in Table 2 below. The PTFE stretched porous membranes of Comparative Examples 3 to 5 were obtained in the same manner as in Comparative Example 2, except that the conditions for stretching E, stretching F and heat fixing were set as shown in Table 2 below.

[0105] (Comparative Examples 6 to 8) The PTFE fine powder used was SSG2.19, and the thickness of the unstretched PTFE sheet, and the conditions for stretching E, stretching F, and heat fixing were set as shown in Table 2 below. The PTFE stretched porous membranes of Comparative Examples 6 to 8 were obtained in the same manner as in Comparative Example 2.

[0106] [Table 2]

[0107] The evaluation results of each PTFE porous membrane are shown in Table 3 below.

[0108] [Table 3]

[0109] The SEM images of the surfaces of the PTFE porous membranes of Example 4, Comparative Example 2, and Comparative Example 8 are shown in Figs. 9A, 10A, and 11A, respectively. The SEM images of the cross sections (cut in MD direction) of the PTFE porous membranes of Example 4, Comparative Example 2, and Comparative Example 8 in the thickness direction are shown in Figs. 9B, 10B, and 11B, respectively. In addition, the SEM images of the cross sections show the evaluation substrate used for SEM observation together with the PTFE porous membrane. As shown in Figs. 9A to 11B, in the PTFE porous membrane of Example 4, unlike the membranes of Comparative Examples 2 and 8, nodes were formed that extended long not only in the in-plane direction but also in the membrane thickness direction. In addition, similar nodes were formed in the other Examples. In addition, the average pore size of the PTFE porous membranes of each Example is 3.5 μm or more.

[0110] The relationship between the air permeability in the thickness direction and the total cohesive strength in the PTFE expanded porous membranes of the Examples and Comparative Examples is shown in Figure 12. As shown in Figure 12, the PTFE expanded porous membranes of the Examples had higher air permeability and total cohesive strength than those of the Comparative Examples. In addition, the PTFE expanded porous membranes of the Examples had a higher air permeability in the thickness direction than the PTFE expanded porous membranes of the Comparative Examples. T , the total cohesive strength is C T and express the formula C T ≧-0.33×P T The PTFE expanded porous membranes of Examples 3, 4, 5 and 7 satisfied the formula C T ≧-0.57×P T It met the +6.14 standard. [Industrial Applicability]

[0111] The expanded porous PTFE membrane of the present invention can be used, for example, as a ventilation filter medium.

Claims

1. The air permeability in the thickness direction is expressed by the Frazier air permeability of 4 cm 3 / (second / cm 2 ) and The total cohesive strength, which is the product of the peel cohesive strength in a first direction in the plane and the peel cohesive strength in a second direction perpendicular to the first direction in the plane, is 1.9 (N / 20 mm). 2 That's all. Expanded porous polytetrafluoroethylene membrane.

2. Weight per unit area is 7.0g / m 2 The expanded porous polytetrafluoroethylene membrane according to claim 1 .

3. 3. The expanded porous polytetrafluoroethylene membrane according to claim 1, having a thickness of 30 μm or more.

4. A ventilation filter material that has air permeability in the thickness direction and prevents the penetration of foreign matter in that direction, A ventilation filter medium comprising the polytetrafluoroethylene expanded porous membrane according to any one of claims 1 to 3.

5. The breathable filter medium according to claim 4, further comprising an air-permeable support material laminated to the polytetrafluoroethylene porous membrane.

6. The filter has air permeability in the thickness direction and is equipped with an air permeable filter material that prevents the penetration of foreign matter in that direction. The filter member, wherein the ventilation filter material is the ventilation filter material according to claim 4 or 5.

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