Air filter medium, filter pack, air filter unit, and method of manufacturing these

Abstract

The objective is to provide an air filter media, filter bag, air filter unit, and a method for manufacturing the same, which have a thickness and low fill rate. The air filter media includes a fluoropolymer porous membrane having a portion with a fill rate of 3.5% or less, and the thickness of the portion with a fill rate of 3.5% or less is 45 μm or more.

Description

Technical Field

[0001] This disclosure relates to an air conditioning filter media, filter pack, air filter unit, and a method of manufacturing the same. Background Technology

[0002] Currently, to achieve sufficiently clean spaces, porous membranes made of polytetrafluoroethylene (PTFE) are used as dust collection filters (hereinafter referred to as PTFE porous membranes). Compared to glass fiber filter media, PTFE porous membranes have higher dust collection efficiency under the same pressure loss. Therefore, HEPA filters (High Efficiency Particulate Air Filters) and ULPA filters (Ultra-Low Permeability Air Filters) are particularly preferred.

[0003] As such a filter, for example, the air filter material described in Patent Document 1 (Japanese Patent Application Publication No. 2001-170461) proposes to increase the dust storage capacity by setting the thickness of the PTFE porous membrane to about 10 μm and the filling rate to about 5%. Summary of the Invention

[0004] The technical problem that the invention aims to solve

[0005] However, as a fluoropolymer porous membrane, no fluoropolymer porous membrane with thickness and low filling rate has been proposed to date.

[0006] In view of the above, the purpose of this disclosure is to provide an air filter media, filter bag, air filter unit, and a method for manufacturing the same, which have a thickness and low fill rate.

[0007] Technical solutions used to solve technical problems

[0008] The first viewpoint's air filter media includes a fluoropolymer porous membrane. The fluoropolymer porous membrane has a portion with a fill rate of less than 3.5%. The thickness of the portion of the fluoropolymer porous membrane with a fill rate of less than 3.5% is greater than 45 μm.

[0009] For this fluoropolymer porous membrane, as long as the portion with a filling rate of less than 3.5% includes 45μm or more, the fluoropolymer porous membrane can be composed of a single porous membrane with a filling rate that does not change substantially in the airflow direction, or it can be composed of a single porous membrane with a filling rate that changes in the airflow direction, or it can be composed of multiple porous membranes with a filling rate that does not change substantially or changes in the airflow direction stacked together.

[0010] The air filter media can have thickness and low fill rate.

[0011] Based on the air filter media described in the first viewpoint, the air filter media of the second viewpoint has a portion with a fill rate of 2.5% or less. The thickness of the portion of the fluoropolymer porous membrane with a fill rate of 2.5% or less is 50 μm or more.

[0012] For this fluoropolymer porous membrane, it is sufficient to include a portion with a filling rate of less than 2.5% that is more than 50 μm. The fluoropolymer porous membrane can be composed of a single porous membrane with a filling rate that does not change substantially in the airflow direction, or it can be composed of a single porous membrane with a filling rate that changes in the airflow direction, or it can be composed of multiple porous membranes with a filling rate that does not change substantially or changes in the airflow direction stacked together.

[0013] This allows the air filter media to have sufficient thickness and a lower fill rate.

[0014] Based on the air filter media described in the first or second viewpoint, in the air filter media of the third viewpoint, the pressure loss and collection efficiency, which are obtained by utilizing polyalphaolefin particles with a particle diameter of 0.3 μm, are used to determine the PF value by the following formula: PF value = {-log((100-collection efficiency (%)) / 100)} / (pressure loss (Pa) / 1000), wherein the PF value is 17 or higher.

[0015] The air filter media includes a fluoropolymer porous membrane with a thickness and low fill rate, which ensures a high PF value.

[0016] Based on the air filter media described in any of the first to third viewpoints, in the air filter media of the fourth viewpoint, regarding the air filter media, when air comprising polyalphaolefin particles with a median diameter of 0.25 μm is continuously ventilated at a flow rate of 5.3 cm / s, resulting in a pressure loss increase of 250 Pa, the dust storage capacity of the polyalphaolefin particles is 30.0 g / m³. 2 above.

[0017] Furthermore, the preferred dust storage capacity is 50.0 g / m³. 2 above.

[0018] The air filter media includes a fluoropolymer porous membrane with a thickness and low fill rate, which ensures a high dust storage capacity.

[0019] Based on the air filter media described in any of the first to fourth viewpoints, in the air filter media of the fifth viewpoint, the pressure loss when air passes through at a flow rate of 5.3 cm / s is less than 200 Pa.

[0020] The air filter media includes a fluoropolymer porous membrane with a thickness and low fill rate, which can suppress pressure loss to a low level.

[0021] Based on the air filter media described in any one of the first to fifth viewpoints, in the air filter media of the sixth viewpoint, the average pore size of the first fluororesin porous membrane is 2.5 μm or more.

[0022] The air filter media includes a fluoropolymer porous membrane with a thickness and low fill rate, which can increase dust storage capacity.

[0023] Based on the air filter media described in any one of the first to sixth viewpoints, in the air filter media of the seventh viewpoint, the fluoropolymer porous membrane includes a first fluoropolymer porous membrane and a second fluoropolymer porous membrane. The first fluoropolymer porous membrane has a fill rate of 3.5% or less and a thickness of 45 μm or more. The second fluoropolymer porous membrane is disposed downstream of the first fluoropolymer porous membrane in the airflow. The fill rate of the second fluoropolymer porous membrane is greater than or equal to the fill rate of the first fluoropolymer porous membrane.

[0024] In addition, the filling rate of the second fluororesin porous membrane is preferably higher than that of the first fluororesin porous membrane.

[0025] In addition, the filling rates of the first fluoropolymer porous membrane and the second fluoropolymer porous membrane can also remain essentially unchanged in the direction of airflow.

[0026] In this air filter media, a first fluoropolymer porous membrane with a thickness and low filling rate is disposed upstream of a second fluoropolymer porous membrane, which can suppress pore clogging of the second fluoropolymer porous membrane and increase dust storage capacity.

[0027] Based on the air filter media described in any one of the first to seventh viewpoints, in the air filter media of the eighth viewpoint, the fluoropolymer porous membrane has at least one inclined density porous membrane, wherein the density of the airflow downstream of the inclined density porous membrane is greater than the density of the airflow upstream of the membrane.

[0028] The density of this tilted density porous membrane can vary gradually from the upstream side of the airflow to the downstream side, or it can vary in segments.

[0029] Furthermore, the porous membrane mentioned here does not include porous membranes obtained by bonding multiple porous membranes together.

[0030] Furthermore, there are no particular limitations on the tilt density porous membrane. For example, it can also be obtained by stretching it under conditions where the temperatures on one side and the other side are different or after heat treatment at different temperatures.

[0031] In this air filter material, the fluoropolymer porous membrane has a thickness and a low fill rate. By capturing larger dust particles on the upstream side of the airflow and smaller dust particles on the downstream side of the airflow, it can suppress pore clogging and ensure a large amount of dust storage.

[0032] Based on the air filter media described in any one of the first to sixth viewpoints, in the air filter media of the ninth viewpoint, the fluoropolymer porous membrane is a porous membrane with a filling rate of less than 3.5% and a thickness of more than 45 μm.

[0033] Furthermore, the porous membrane mentioned here does not include porous membranes obtained by bonding multiple porous membranes together.

[0034] Furthermore, the fluoropolymer porous membrane mentioned above uses polyalphaolefin particles with a particle diameter of 0.3 μm to determine the pressure loss and collection efficiency, and the PF value is determined by the following formula: PF value = {-log((100-collection efficiency (%)) / 100)} / (pressure loss (Pa) / 1000), wherein the PF value is preferably 17 or higher.

[0035] Furthermore, regarding the aforementioned fluoropolymer porous membrane, ideally, when air containing polyalphaolefin (PAO) particles with a median diameter of 0.25 μm is continuously ventilated at a flow rate of 5.3 cm / s, the dust storage capacity of these PAO particles when the pressure loss increases by 250 Pa is 30.0 g / m³. 2 Ideally, the dust storage capacity should be 50.0 g / m³. 2 above.

[0036] Furthermore, preferably, the pressure loss when air flows through the aforementioned fluoropolymer porous membrane at a flow rate of 5.3 cm / s is less than 200 Pa.

[0037] In this air filter media, the fluoropolymer porous membrane can have a thickness and a low filling rate.

[0038] Furthermore, for example, when the aforementioned fluoropolymer porous membrane is configured together with a separate, independent air filter media with a higher fill rate and used on the upstream side of the airflow, the load applied to the downstream air filter media can be reduced.

[0039] Based on the air filter media described in any of the first to ninth viewpoints, the air filter media of the tenth viewpoint further includes a pre-trapping membrane. The pre-trapping membrane is disposed upstream of the fluoropolymer porous membrane. The pressure loss when air flows through the pre-trapping membrane at a flow rate of 5.3 cm / s is 15 Pa to 55 Pa. When air comprising polyalphaolefin particles with a particle diameter of 0.3 μm flows through the pre-trapping membrane at a flow rate of 5.3 cm / s, the pre-trapping membrane has a trapping efficiency of 25% to less than 80% for the polyalphaolefin particles. Regarding the pre-trapping membrane, using the pressure loss and trapping efficiency obtained from the polyalphaolefin particles with a particle diameter of 0.3 μm, the PF value is determined by the following formula: PF value = {-log((100 - trapping efficiency (%)) / 100)} / (pressure loss (Pa) / 1000), where the PF value is 7 to 15.

[0040] There are no particular limitations on the pre-collection membrane described above; for example, its thickness can be 0.4 mm or less. Furthermore, when the air filter media has a first fluoropolymer porous membrane and a second fluoropolymer porous membrane, it is preferable that the ratio of the pre-collection membrane's PF value to the PF value when the first and second fluoropolymer porous membranes are laminated, i.e., "PF value of the pre-collection membrane / PF value when the first and second fluoropolymer porous membranes are laminated", is 0.20 to 0.45 or less.

[0041] The air filter media also uses a pre-capture membrane, which ensures sufficient dust storage.

[0042] Furthermore, from the viewpoint of making the air filter media thinner while ensuring sufficient dust storage capacity, the air filter media described in the first to ninth viewpoints preferably do not have such a pre-collection membrane. Moreover, when the air filter is folded into an air filter unit for use, from the viewpoint of increasing the total area of ​​the folded portion and increasing the spacing of the raised creases to suppress the increase in pressure loss, it is also preferable not to have such a pre-collection membrane.

[0043] Based on the air filter media described in any one of the first to tenth viewpoints, in the air filter media of the eleventh viewpoint, the portion of the fluoropolymer porous membrane containing at least 3.5% or less of the filler content comprises modified polytetrafluoroethylene.

[0044] In addition, the portion of the fluoropolymer porous membrane with a filling rate of at least 3.5% may also include both modified polytetrafluoroethylene and homopolymer polytetrafluoroethylene.

[0045] In this air filter media, the portion of the fluoropolymer porous membrane with a filling rate of at least 3.5% includes modified polytetrafluoroethylene, thus making it easy to suppress the filling rate to a low level.

[0046] Based on the air filter media described in any of the first to eleventh viewpoints, the air filter media of the twelfth viewpoint includes a fluoropolymer porous membrane, which is mainly composed of polytetrafluoroethylene that can be fibrous, a non-fibrous non-thermal-meltable component, and a component with a melting point of less than 320°C that can be thermally melted but does not fibrous.

[0047] Existing porous PTFE membranes, which are mainly composed of fibrous PTFE (high molecular weight PTFE), contain a large number of fine fibrils with small diameters. Each fiber has a large surface area and a high capture efficiency. However, these porous PTFE membranes are relatively thin and have a lot of overlap between the fibers. Therefore, they cannot store a large number of particles, and the high capture efficiency of each fiber cannot be effectively utilized.

[0048] In contrast, since the air filter material is mainly composed of three components: polytetrafluoroethylene that can be fibrous, a non-fibrous, non-thermally meltable component, and a component with a melting point of less than 320°C that can be fibrous but can be thermally melted, it can increase the dust storage capacity compared to existing PTFE porous membranes due to the larger fibers that increase the number of pores and the thickness.

[0049] Based on the air filter described in any of the first to twelfth viewpoints, in the air filter media of the thirteenth viewpoint, the air filter media further includes a breathable support layer, which is disposed on the upstream side and / or downstream side of the airflow relative to the fluoropolymer porous membrane.

[0050] The breathable support layer can also be disposed on both the upstream and downstream sides of the airflow relative to the fluoropolymer porous membrane.

[0051] There are no particular limitations on the breathable support layer, but preferably, the pressure loss of the breathable support layer is smaller than that of the fluoropolymer porous membrane (e.g., less than half, less than 1 / 10, etc.).

[0052] The air filter media includes a breathable support layer, which increases its strength.

[0053] The air filter bag of the fourteenth viewpoint includes the air filter material described in any of the first to thirteenth viewpoints, wherein the air filter material is processed into a serrated shape formed by alternating outward and inward folds. Furthermore, the term "filter bag" is not particularly limited; for example, it may not be a flat sheet, but rather a serrated shape folded by alternating outward and inward folds, and its shape can be adjusted to accommodate it in any frame.

[0054] The air filter unit of the fifteenth view includes the air filter media described in any of the first to thirteenth views or the filter pack described in the fourteenth view, and a frame for holding the air filter media or filter pack.

[0055] The sixteenth viewpoint's method for manufacturing air filter media includes a step of preparing an unburned membrane containing polytetrafluoroethylene (PTFE) and a step of obtaining a porous membrane. In the step of obtaining the porous membrane, the unburned membrane is extended along a first direction and then along a second direction orthogonal to the first direction. Here, before extending the unburned membrane along the first direction, the unburned membrane is heated for at least one minute at a temperature of 250°C to 325°C.

[0056] According to this manufacturing method, it is possible to obtain air filter media including a fluoropolymer porous membrane with thickness and low filling rate.

[0057] The method for manufacturing air filter media according to the seventeenth point includes a step of preparing an unburned membrane containing polytetrafluoroethylene and a step of obtaining a porous membrane. In the step of obtaining a porous membrane, the stretched unburned membrane is stretched in such a way that a portion is formed by stretching at a stretching speed of 30% / second or less in the stretching direction.

[0058] Furthermore, in the case of biaxial extension, an extension speed of 30% / second or less is sufficient in either the longitudinal or transverse direction. Additionally, when extending in a plane using a test bench or similar device, sequentially or simultaneously in the longitudinal and transverse directions, it is sufficient to produce a portion formed by extension that satisfies the aforementioned extension speed in either the longitudinal or transverse direction.

[0059] The extension speed is the value obtained by dividing the extension ratio (%) by the time (in seconds) taken for the extension (vertical extension in the case of vertical extension, horizontal extension in the case of horizontal extension, and at least one of the vertical and horizontal extensions).

[0060] In addition, elongation (%) refers to the ratio of the elongated length of the unfired film to the length before elongation (length after elongation / length before elongation). In the case of longitudinal elongation, it is the ratio of the length before and after longitudinal elongation; in the case of transverse elongation, it is the ratio of the length before and after transverse elongation; and in the case of simultaneous longitudinal and transverse elongation, it is the ratio of at least one of the lengths.

[0061] According to this manufacturing method, it is possible to obtain air filter media including a fluoropolymer porous membrane with thickness and low filling rate.

[0062] The method for manufacturing a filter bag according to the eighteenth point includes the following steps: alternating between outward and inward folds to process the air filter material obtained by the method for manufacturing air filter material according to the sixteenth or seventeenth point into a serrated shape.

[0063] The method for manufacturing an air filter unit according to the nineteenth point includes the following steps: holding an air filter material obtained by the method for manufacturing air filter media according to the sixteenth or seventeenth point, or a filter pack obtained by the method for manufacturing filter pack according to the eighteenth point, in a frame. Attached Figure Description

[0064] Figure 1 This is a schematic cross-sectional view showing the layer structure of one of the air filter media.

[0065] Figure 2 This is a schematic cross-sectional view showing the layer structure of the air filter media (second one).

[0066] Figure 3 This is a schematic cross-sectional view showing the layer structure of the air filter media (third type).

[0067] Figure 4 This is a schematic cross-sectional view showing the layer structure of the air filter media (fourth one).

[0068] Figure 5 This is a schematic cross-sectional view showing the layer structure of the air filter media (fifth one).

[0069] Figure 6 This is a 3D view of the filter bag.

[0070] Figure 7 This is a 3D view of the air filter unit.

[0071] Figure 8 This is a perspective view of an air filter unit that uses spacers. Detailed Implementation

[0072] The following describes, by way of example, air filter media (hereinafter referred to as filter media), filter packs, air filter units, and their manufacturing methods.

[0073] (1) Air filter media

[0074] There is no particular limitation on the pressure loss of the air filter media. For example, it is preferably less than 200 Pa, but can be more than 20 Pa and less than 185 Pa, and is more preferably more than 40 Pa and less than 150 Pa.

[0075] As an air filter media, the pressure loss and collection efficiency are determined by using polyalphaolefin particles with a particle diameter of 0.3 μm, and the PF value is determined by the following formula: PF value = {-log((100-collection efficiency (%)) / 100)} / (pressure loss (Pa) / 1000), wherein the PF value is preferably 17 or higher.

[0076] As an air filter media, when air comprising polyalphaolefin particles with a median diameter of 0.25 μm is continuously ventilated at a flow rate of 5.3 cm / s, causing a pressure drop of 250 Pa, the dust storage capacity of the polyalphaolefin particles can be 30.0 g / m³. 2 The above values ​​are preferably 40.0 or higher, and more preferably 50.0 or higher. Therefore, for air filter media that can adequately ensure the dust storage capacity for liquid particles, the reduction in liquid particle capture efficiency can be suppressed.

[0077] The thickness of the air filter media is not particularly limited; for example, it can be between 300 μm and 1000 μm, preferably between 400 μm and 800 μm. The thickness of the air filter media is the value of the thickness when a load of 0.3 N is applied to the object being measured in a specific measuring device.

[0078] The specific layer structure of the air filter media described above is not particularly limited; for example, the layer structure shown below can be exemplified.

[0079] Can Figure 1 As shown in the air filter media 30, it is configured such that a fluoropolymer porous membrane 31 and a breathable support membrane 33 are stacked in the airflow direction. The breathable support membrane 33 can be disposed on the leeward side of the fluoropolymer porous membrane 31, or on the upwind side, or on both the upwind and leeward sides.

[0080] It is also possible to Figure 2As shown in the air filter media 30, it is configured such that a fluoropolymer porous membrane 31 and a breathable support membrane 33 are stacked in the airflow direction. The fluoropolymer porous membrane 31 is configured to have a first fluoropolymer porous membrane 31a and a second fluoropolymer porous membrane 31b, with the second fluoropolymer porous membrane 31b disposed downstream of the first fluoropolymer porous membrane 31a. In this case, the breathable support membrane 33 can be disposed on the leeward side relative to the first fluoropolymer porous membrane 31a and the second fluoropolymer porous membrane 31b, or on the upwind side, or on both the upwind and leeward sides. Furthermore, the breathable support membrane 33 can also be disposed between the first fluoropolymer porous membrane 31a and the second fluoropolymer porous membrane 31b.

[0081] It is also possible to Figure 3 As shown in the air filter media 30, it is configured such that a fluoropolymer porous membrane 31 and a breathable support membrane 33 are stacked in the airflow direction, wherein the fluoropolymer porous membrane 31 is configured to have multiple (e.g., two) identical fluoropolymer porous membranes 31c. In this case, the breathable support membrane 33 can be disposed on the leeward side, the upwind side, or both sides of the multiple identical fluoropolymer porous membranes 31c. Furthermore, the breathable support membrane 33 can also be disposed between the multiple identical fluoropolymer porous membranes 31c.

[0082] Other than that Figure 4 As shown in the air filter media 30, a pre-collecting membrane 34, a fluoropolymer porous membrane 31, and a breathable support membrane 33 are stacked in the airflow direction, wherein the fluoropolymer porous membrane 31 is disposed downstream of the pre-collecting membrane 34. In this case, the breathable support membrane 33 may be disposed on the leeward side relative to the pre-collecting membrane 34 and the fluoropolymer porous membrane 31, or on the upwind side, or on both the upwind and leeward sides. Furthermore, the breathable support membrane 33 may also be disposed between the pre-collecting membrane 34 and the fluoropolymer porous membrane 31.

[0083] Other than that Figure 5 As shown in the air filter media 30, it is configured such that a fluoropolymer porous membrane 31, an upstream ventilable support membrane 33a, and a downstream ventilable support membrane 33b are stacked in the airflow direction, wherein the upstream ventilable support membrane 33a is disposed on the upstream side relative to the fluoropolymer porous membrane 31, and the downstream ventilable support membrane 33b is disposed on the downstream side relative to the fluoropolymer porous membrane 31.

[0084] In addition, these fluoropolymer porous membranes 31 are not limited to being homogeneous in the airflow direction, but may also have a density difference in the airflow direction.

[0085] Furthermore, there are no particular limitations on the overlapping method of the aforementioned films and layers. They can be bonded using the anchoring effect generated by local melting caused by heating or the melting of hot-melt resin, or they can be bonded using reactive adhesives, or they can simply be stacked. In addition, since it is a bonding process, the thickness of each film and layer does not change substantially.

[0086] The following examples illustrate the relationships between the various layers.

[0087] (2) Fluoropolymer porous membrane

[0088] The fluoropolymer porous membrane is mainly composed of fluoropolymer, preferably having a porous membrane structure, wherein the porous membrane structure has fibrils (not shown) and nodes (nodules) connected to the fibrils.

[0089] Here, "mainly" means that, in the case of multiple types of components, the most abundant component is fluororesin. For example, the fluororesin porous membrane may contain 50% or more fluororesin by weight relative to the weight of the fluororesin porous membrane, preferably 80% or more fluororesin, more preferably 95% or more fluororesin, and may also be composed solely of fluororesin. When the fluororesin porous membrane is composed of multiple identical fluororesin porous membranes, and when the fluororesin porous membrane is a first fluororesin porous membrane or a second fluororesin porous membrane, the aforementioned proportion of fluororesin is also the same.

[0090] As a component different from fluoropolymers, inorganic fillers, such as those described later as non-melt-processable components (component B) that do not fibrousize, can be listed as examples.

[0091] The fluororesin used in fluororesin porous membranes can be composed of one component or two or more components. Furthermore, examples of fluororesins composed of two or more components include a mixture of three components: fibrous PTFE (hereinafter referred to as component A), a non-fibrous, non-thermally meltable component (hereinafter referred to as component B), and a component with a melting point less than 320°C that is non-fibrous but capable of being thermally meltable (hereinafter referred to as component C). Fluororesin porous membranes are preferably composed of a combination of these three components. Compared to conventional fibrous PTFE (high molecular weight PTFE) porous membranes, fluororesin porous membranes composed of the above three components have a membrane structure with more pores and a thicker membrane thickness. Therefore, these fluororesin porous membranes can capture gaseous particles over a wider area in the thickness direction of the filter media, thereby increasing dust storage capacity. By composing fluororesin porous membranes with the above three components, the dust storage capacity for liquid particles can be significantly increased compared to the dust storage capacity for solid particles.

[0092] The following is a more detailed explanation of the three components mentioned above.

[0093] (2-1) Component A: PTFE capable of fiberization

[0094] Fiberizable PTFE includes, for example, high molecular weight PTFE obtained by emulsion polymerization or suspension polymerization of tetrafluoroethylene (TFE). Here, "high molecular weight" refers to a molecular weight that allows for easy fiberization during the fabrication of porous membranes, yielding long fibrils; a standard specific gravity (SSG) of 2.130–2.230; and substantial melt flow due to high melt viscosity. Ideally, the SSG of fiberizable PTFE should be 2.130–2.190, and more ideally, 2.140–2.170. If the SSG is too high, the extensibility of the mixture of components A–C may deteriorate; if the SSG is too low, rollability may deteriorate, the homogeneity of the porous membrane may worsen, and the pressure loss of the porous membrane may increase. Furthermore, from the viewpoint of easy fiberization and obtaining long fibrils, PTFE obtained through emulsion polymerization is ideal. Standard specific gravity (SSG) is determined based on ASTM D 4895.

[0095] Whether a material possesses fibrous properties, i.e., its ability to be fibrous, can be determined by whether it can be extruded as a paste. The aforementioned paste extrusion is a representative method for molding high-molecular-weight PTFE powder made from TFE polymers. Generally, paste extrusion is possible because high-molecular-weight PTFE possesses fibrous properties. If the unfired molded body obtained through paste extrusion lacks substantial strength and elongation—for example, if the elongation is 0% and it breaks easily when pulled—it can be considered as lacking fibrous properties.

[0096] The aforementioned high molecular weight PTFE can be modified polytetrafluoroethylene (hereinafter referred to as modified PTFE), homopolymer polytetrafluoroethylene (hereinafter referred to as homopolymer PTFE), or a mixture of modified PTFE and homopolymer PTFE. There are no particular limitations on the homopolymer PTFE, but the homopolymer PTFE disclosed in the following documents is preferred: Japanese Patent Application Publication No. 53-60979, Japanese Patent Application Publication No. 57-135, Japanese Patent Application Publication No. 61-16907, Japanese Patent Application Publication No. 62-104816, Japanese Patent Application Publication No. 62-190206, and Japanese Patent Application Publication No. 63-137906. Japanese Patent Publication No. 2000-143727, Japanese Patent Publication No. 2002-201217, International Publication No. 2007 / 046345, International Publication No. 2007 / 119829, International Publication No. 2009 / 001894, International Publication No. 2010 / 113950, International Publication No. 2013 / 027850, etc. Ideally, homopolymer PTFE with high elongation properties should be used, as disclosed in the following documents: Japanese Patent Application Publication No. 57-135, Japanese Patent Application Publication No. 63-137906, Japanese Patent Application Publication No. 2000-143727, Japanese Patent Application Publication No. 2002-201217, International Publication No. 2007 / 046345, International Publication No. 2007 / 119829, and International Publication No. 2010 / 113950.

[0097] Modified PTFE is composed of TFE and monomers other than TFE (hereinafter referred to as modified monomers). Examples of modified PTFE include those obtained by uniform modification of modified monomers, those obtained by modification at the initial stage of polymerization, and those obtained by modification at the end of polymerization, but there are no particular limitations on the type of modified PTFE. For example, modified PTFE disclosed in the following documents can be preferred: Japanese Patent Application Publication No. 60-42446, Japanese Patent Application Publication No. 61-16907, Japanese Patent Application Publication No. 62-104816, Japanese Patent Application Publication No. 62-190206, Japanese Patent Application Publication No. 64-1711, Japanese Patent Application Publication No. 2-261810, Japanese Patent Application Publication No. 11-240917, Japanese Patent Application Publication No. 11-240918, International Publication No. 2003 / 033555, International Publication No. 2005 / 061567, International Publication No. 2007 / 005361, International Publication No. 2011 / 055824, International Publication No. 2013 / 027850, etc. Ideally, modified PTFE with high elongation properties, as disclosed in the following documents, should be used: Japanese Patent Application Publication No. 61-16907, Japanese Patent Application Publication No. 62-104816, Japanese Patent Application Publication No. 64-1711, Japanese Patent Application Publication No. 11-240917, International Publication No. 2003 / 033555, International Publication No. 2005 / 061567, International Publication No. 2007 / 005361, and International Publication No. 2011 / 055824.

[0098] Modified PTFE includes TFE units based on TFE and modified monomer units based on modified monomers. Modified monomer units are part of the molecular structure of modified PTFE and are derived from the modified monomers. For modified PTFE, the content of modified monomer units is preferably 0.001 to 0.500% by weight of the total monomer units, and more ideally, 0.01 to 0.30% by weight. The total monomer units refer to the portion of the modified PTFE molecular structure derived from all monomers.

[0099] There are no particular limitations on the type of monomer used for copolymerization, as long as it can copolymerize with TFE. Examples include perfluoroolefins such as hexafluoropropylene (HFP), chlorofluoroolefins such as trifluorochloroethylene (CTFE), hydrofluoroolefins such as trifluoroethylene and vinylidene fluoride (VDF), perfluorovinyl ethers, perfluoroalkyl ethylene (PFAE), and ethylene. The monomer used can be one type or multiple types.

[0100] There are no particular limitations on perfluorovinyl ethers; for example, perfluorounsaturated compounds represented by the following general formula (1) can be listed.

[0101] CF2 = CF - ORf…(1)

[0102] In the formula, Rf represents a perfluorinated organic group.

[0103] In this specification, a perfluorinated organic group is an organic group formed by replacing all hydrogen atoms bonded to carbon atoms with fluorine atoms. The aforementioned perfluorinated organic groups may also have ether oxygen.

[0104] Examples of perfluorovinyl ethers include perfluoro(alkylvinyl ether) (PAVE), where Rf in the general formula (1) is a perfluoroalkyl group having 1 to 10 carbon atoms. Ideally, the perfluoroalkyl group has 1 to 5 carbon atoms. Examples of perfluoroalkyl groups in PAVE include perfluoromethyl, perfluoroethyl, perfluoropropyl, perfluorobutyl, perfluoropentyl, and perfluorohexyl. Ideal PAVEs are perfluoropropyl vinyl ether (PPVE) and perfluoromethyl vinyl ether (PMVE).

[0105] The term perfluoroalkyl ethylene (PFAE) is not specifically limited; for example, perfluorobutyl ethylene (PFBE) and perfluorohexyl ethylene (PFHE) can be listed.

[0106] Ideally, the modifying monomer used in modified PTFE should be at least one selected from the group consisting of HFP, CTFE, VDF, PAVE, PFAE and ethylene.

[0107] From the perspective of easy fiberization and obtaining long fiber lengths, it is ideal to have a homopolymer PTFE content exceeding 50% by weight of the PTFE that can be fiberized.

[0108] In addition, fibrous PTFE can also be composed of a combination of the above-mentioned components.

[0109] From the perspective of maintaining the fibrous structure of porous membranes, it is ideal to have a fibrous PTFE content exceeding 50% of the porous membrane's weight.

[0110] (2-2) Component B: Non-thermal-melting processable component that will not become fibrous.

[0111] Non-fibrous, non-thermal-melting processable components, as non-fibrous particles, are mainly concentrated in the nodular portion, thereby inhibiting the fibrosis of fibrous PTFE.

[0112] Examples of non-thermolyzable processable components that do not fibrousize include thermoplastic components such as low molecular weight PTFE, thermosetting resins, inorganic fillers, and mixtures of these components.

[0113] Ideally, the thermoplastic component should have a melting point of 320°C or higher and a high melt viscosity. For example, because low molecular weight PTFE has a high melt viscosity, it can be processed at temperatures above its melting point and remain at the nodule. In this specification, low molecular weight PTFE is defined as having an index-average molecular weight of 600,000 or less, a melting point of 320°C or higher but 335°C or lower, and a melt viscosity of 100 Pa·s to 7.0 × 10⁻⁶ Pa·s at 380°C. 5 Pa·s of PTFE (refer to Japanese Patent Application Publication No. 10-147617).

[0114] Methods for manufacturing low molecular weight PTFE include: a method of thermally decomposing high molecular weight PTFE powder (molding powder) obtained by suspension polymerization of TFE or high molecular weight PTFE powder (PF: fine powder) obtained by emulsification polymerization of TFE by contacting and reacting with a specific fluoride at high temperature (see Japanese Patent Application Publication No. 61-162503); a method of irradiating the aforementioned high molecular weight PTFE powder or molded body with ionizing radiation (see Japanese Patent Application Publication No. 48-78252); and a method of directly polymerizing TFE together with a chain transfer agent (see International Publication No. 2004 / 050727, International Publication No. 2009 / 020187, International Publication No. 2010 / 114033, etc.). Similar to fibrous PTFE, low molecular weight PTFE can be homopolymer PTFE or modified PTFE including the aforementioned modified monomers.

[0115] Low molecular weight PTFE does not exhibit fibrous properties. The presence of fibrous properties can be determined using the methods described above. For low molecular weight PTFE, unfired molded bodies obtained through paste extrusion do not possess substantial strength and elongation; for example, they may have an elongation of 0% and break easily when pulled.

[0116] There are no particular limitations on low molecular weight PTFE, but ideally, its melt viscosity at 380°C should be 1000 Pa·s or higher. More ideally, it should be 5000 Pa·s or higher, and even more ideally, it should be 10000 Pa·s or higher. In this way, if the melt viscosity is high, during the manufacture of porous membranes, even if the non-fibrous but heat-meltable components (C components) melt, the non-fibrous, non-heat-meltable components can remain at the nodule sites, thereby inhibiting fibrosis.

[0117] Examples of thermosetting resins include epoxy resins, silicone resins, polyester resins, polyurethane resins, polyimide resins, phenolic resins, and mixtures thereof. From the viewpoint of workability of the copolymerization process described later, it is preferable to use a resin that is water-dispersed in its uncured state as the thermosetting resin. All of the above-mentioned thermosetting resins are commercially available.

[0118] Examples of inorganic fillers include talc, mica, calcium silicate, glass fiber, calcium carbonate, magnesium carbonate, carbon fiber, barium sulfate, calcium sulfate, and mixtures of the above. Among these, talc is preferred from the perspective of its affinity for high molecular weight PTFE (which can be fibrous) and its specific gravity. From the viewpoint of forming a stable dispersion during the manufacture of porous membranes, inorganic fillers with a particle diameter of 3 μm to 20 μm are preferred. Particle diameter refers to the average particle diameter and is measured by laser diffraction scattering. All of these inorganic fillers are commercially available.

[0119] In addition, non-melting processable components that do not fibrose can also be composed of a combination of the above-mentioned components.

[0120] Ideally, the content of the non-fibrous, non-thermolyzable processable component should be between 1% and 50% by weight of the porous membrane. Maintaining the fibrous structure of the porous membrane is easier by keeping the content of the non-fibrous, non-thermolyzable processable component below 50% by weight. Ideally, the content of the non-fibrous, non-thermolyzable processable component should be between 20% and 40% by weight, and even more ideally, 30% by weight. Maintaining the content at 20% to 40% by weight allows for more effective suppression of the fibrous formation of fibrous PTFE.

[0121] (2-3) Component C: Components with a melting point below 320℃ that do not become fibrous but can be hot-melted.

[0122] Components with a melting point of less than 320°C that do not fibrousize but can be heat-melted (hereinafter also referred to as components that do not fibrousize but can be heat-melted) have fluidity when melted. Therefore, these components can melt and solidify at the nodule when manufacturing porous membranes (during stretching), thereby improving the overall strength of the porous membrane and suppressing the deterioration of filtration performance even when compressed in subsequent processes.

[0123] Ideally, the component that does not fibrousize but can be heat-melted should have a melt viscosity of less than 10,000 Pa·s at 380°C. Furthermore, the melting point of the component that does not fibrousize but can be heat-melted is the peak value of the heat of fusion curve obtained by differential scanning calorimetry (DSC) under the following conditions: the component is heated to above its melting point at a heating rate of 10°C / min and completely melted in one step; then, the component is cooled to below its melting point at a heating rate of 10°C / min, and then heated again at a heating rate of 10°C / min.

[0124] As components that do not fibrousize but can be heat-melted in chemical processes, examples include heat-melting fluoropolymers, polystyrene, polyethylene terephthalate (PET), polyesters, polyamides, and other resins or mixtures of the above resins, which can fully utilize their meltability and flowability at the stretching temperature during the manufacture of porous membranes. Among these, heat-melting fluoropolymers are ideal from the viewpoint of excellent heat resistance and reagent resistance at the stretching temperature during the manufacture of porous membranes. Examples of heat-melting fluoropolymers include those derived from the following general formula (2).

[0125] RCF=CR2…(2)

[0126] (In the formula, R is independently selected from hydrogen, fluorine, chlorine, alkyl with 1 to 8 carbon atoms, aryl with 6 to 8 carbon atoms, cyclic alkyl with 3 to 10 carbon atoms, and perfluoroalkyl with 1 to 8 carbon atoms. In the above cases, all R can be the same; furthermore, any two R can be the same and the remaining R can be different from the two R mentioned above, and all R can also be different from each other.) represents a fluoropolymer derived from at least one fluorinated vinyl unsaturated monomer, preferably a copolymer unit derived from two or more monomers.

[0127] There are no limitations on the examples of compounds represented by general formula (2), and examples include perfluoroolefins such as vinyl fluoride, VDF, trifluoroethylene, TFE, HFP, CTFE, dichlorodifluoroethylene, (perfluoroalkyl) ethylene such as PFBE, PFHE, perfluoro-1,3-dioxane and mixtures thereof.

[0128] Furthermore, fluoropolymers can also include copolymers, which are formed by reacting at least one monomer represented by the above general formula (2) with...

[0129] From the above general formula (1) and / or the following general formula (3)

[0130] R2C=CR2…(3)

[0131] (In the formula, R is independently selected from hydrogen, chlorine, alkyl with 1 to 8 carbon atoms, aryl with 6 to 8 carbon atoms, and cyclic alkyl with 3 to 10 carbon atoms. In the above cases, all Rs may be the same; in addition, any two or more Rs may be the same and the remaining Rs may be different from the two or more Rs mentioned above; or all Rs may be different from each other. If there are multiple Rs mentioned above, they may also be different from each other.) is derived by copolymerization of at least one copolymeric comonomer represented by R.

[0132] Examples of compounds represented by general formula (1) include perfluoro(alkyl vinyl ether) (PAVE). Among the above-mentioned PAVEs, perfluoropropyl vinyl ether (PPVE) and perfluoromethyl vinyl ether (PMVE) are more desirable.

[0133] Examples of compounds represented by general formula (3) include ethylene, propylene, etc.

[0134] More specific examples of fluoropolymers include polyvinyl fluoride derived from the polymerization of vinyl fluoride, polyvinylidene fluoride (PVDF) derived from the polymerization of vinylidene fluoride (VDF), polychlorotrifluoroethylene (PCTFE) derived from the polymerization of chlorotrifluoroethylene (CTFE), fluoropolymers derived from the copolymerization of two or more different monomers represented by the above general formula (2), and fluoropolymers derived from the copolymerization of at least one monomer represented by the above general formula (2) with at least one monomer represented by the above general formula (1) and / or at least one monomer represented by the above general formula (3).

[0135] Examples of the aforementioned polymers include polymers having copolymer units derived from VDF and hexafluoropropylene (HFP), and polymers derived from TFE and at least one comonomer other than TFE (at least 3% by weight). Examples of the latter type of fluoropolymers include TFE / PAVE copolymers (PFA), TFE / PAVE / CTFE copolymers, TFE / HFP copolymers (FEP), TFE / ethylene copolymers (ETFE), TFE / HFP / ethylene copolymers (EFEP), TFE / VDF copolymers, TFE / VDF / HFP copolymers, TFE / VDF / CTFE copolymers, and mixtures of the above copolymers.

[0136] In addition, components that do not fibrousize but can be heat-melted can also be composed of multiple of the above components.

[0137] Ideally, the content of the component that does not fibrousize but can be heat-melted in the porous membrane is 0.1% by weight or more and less than 20% by weight. By ensuring that the content of the aforementioned component that does not fibrousize but can be heat-melted in the porous membrane is less than 20% by weight, even if the component is dispersed in the portion of the porous membrane other than the nodules, the pressure loss of the porous membrane can be suppressed. Furthermore, by ensuring that the content of the aforementioned component is less than 20% by weight, it is easy to extend the membrane at a high ratio of 40 times or more, as described later. By ensuring that the content of the component that does not fibrousize but can be heat-melted in the porous membrane is 0.1% by weight or more, even when compression or other forces are applied in subsequent processes, the deterioration of the filtration performance of the porous membrane can be effectively suppressed. Ideally, the content of the component that does not fibrousize but can be heat-melted in the porous membrane is 15% by weight or less, and more ideally, 10% by weight or less. Furthermore, from the viewpoint of ensuring the strength of the porous membrane, it is ideal that the content of the component that does not fibrousize but can be heat-melted in the porous membrane is 0.5% by weight or more. Among these, it is particularly ideal that the above content is around 5% by weight.

[0138] In order to achieve good elongation at an elongation area ratio of 40 to 800 times, it is ideal to have a content of less than 10% by weight of components that do not become fibrous but can be heat-melted.

[0139] In the porous membrane composed of the three components described above, the fibrils are mainly composed of component A, and the nodular portions are composed of components A to C. These nodular portions are formed relatively large within the porous membrane, resulting in a thicker porous membrane. Furthermore, these nodular portions include components that do not fibrousize but can be heat-fused, making them relatively robust and capable of acting as pillars supporting the porous membrane along its thickness direction. Therefore, even under compressive forces in the thickness direction during subsequent processes such as the lamination of the breathable support membrane and the pleating process described later, the reduction in the filtration performance of the porous membrane can be suppressed.

[0140] (2-4) Other properties of fluoropolymer porous membranes

[0141] When the air filter media comprises only one piece of fluoropolymer porous membrane, the thickness of the portion of the fluoropolymer porous membrane with a filling rate of 3.5% or less can be 45 μm or more, 50 μm or more, 100 μm or more, or 150 μm or more. Furthermore, the thickness of the portion with a filling rate of 2.5% or less can be 50 μm or more, 100 μm or more, or 150 μm or more. Similarly, the thickness of the portion with a filling rate of 2.0% or less can be 50 μm or more, 100 μm or more, or 150 μm or more. The filling rate of the aforementioned single fluoropolymer porous membrane is not particularly limited, but is preferably 0.5% or more, or it can be 1.0% or more.

[0142] Furthermore, the aforementioned single fluoropolymer porous membrane may include modified polytetrafluoroethylene (PTFE), preferably including modified PTFE and homopolymer PTFE. Examples of modified PTFE include copolymers of tetrafluoroethylene and perfluoroalkyl vinyl ethers, copolymers of tetrafluoroethylene and hexafluoropropylene, copolymers of tetrafluoroethylene and perfluoropropyl vinyl ethers, copolymers of tetrafluoroethylene and trifluorochloroethylene, and mixtures thereof. From the viewpoint of maintaining good formability of the PTFE, it is preferable that the content of modified PTFE in the fluoropolymer porous membrane is 10% by weight or more and 98% by weight or less, more preferably 50% by weight or more and 95% by weight or less.

[0143] The filling rate of the aforementioned single fluoropolymer porous membrane can be approximately uniform in the thickness direction or can vary in the thickness direction. For a fluoropolymer porous membrane with varying filling rate in the thickness direction, it is preferable that the filling rate on the upwind side is lower than that on the downwind side (in the case of inclined density porous membranes). Regarding the difference between the upwind and downwind filling rates, for a single fluoropolymer porous membrane, for example, the ratio of dust storage amount of PAO particles on the upwind side to dust storage amount of PAO particles on the downwind side can be 1.2 to 5.0 or less, preferably 1.5 to 3.0 or less, and the dust storage amount of PAO particles on the upwind side is preferably 35.0 g / m³. 2 Above 70.0g / m 2 The preferred dust storage capacity of PAO particles on the leeward side is 10.0 g / m³. 2 Above and below 35.0 g / m 2 .

[0144] The thickness of the aforementioned single fluoropolymer porous membrane is not particularly limited; it can be 45μm or more, 50μm or more, 100μm or more, or even 150μm or more. Membranes thinner than 45μm are more prone to cracking.

[0145] As the aforementioned fluoropolymer porous membrane, the pressure loss and collection efficiency, which are obtained by utilizing polyalphaolefin particles with a particle diameter of 0.3 μm, are used to determine the PF value by the following formula: PF value = {-log((100-collection efficiency (%)) / 100)} / (pressure loss (Pa) / 1000), wherein the PF value is preferably 17 or more, more preferably 20 or more, and even more preferably 25 or more.

[0146] Furthermore, regarding the aforementioned single fluoropolymer porous membrane, it is preferable that the dust storage capacity of the polyalphaolefin particles, corresponding to a pressure drop of 250 Pa, when air comprising polyalphaolefin particles with a median diameter of 0.25 μm is continuously ventilated through the fluoropolymer porous membrane at a flow rate of 5.3 cm / s, is 30.0 g / m³. 2 The above, more preferably 50.0 g / m 2 The above is further preferred to be 90.0 g / m 2 above.

[0147] Regarding the aforementioned single fluoropolymer porous membrane, the pressure loss when air flows through the fluoropolymer porous membrane at a flow rate of 5.3 cm / s is preferably 200 Pa or less, more preferably 185 Pa or less.

[0148] Regarding the aforementioned single fluoropolymer porous membrane, its average pore size is preferably 2.5 μm or more, and more preferably 4.0 μm or more.

[0149] When the air filter media comprises multiple fluoropolymer porous membranes, such as a first fluoropolymer porous membrane and a second fluoropolymer porous membrane, the thickness of the portion of the first fluoropolymer porous membrane used on the upwind side, where the filling rate is 3.5% or less, can be 45 μm or more; the thickness of the portion with a filling rate of 3.5% or less can be 50 μm or more; the thickness of the portion with a filling rate of 3.5% or less can be 100 μm or more; and the thickness of the portion with a filling rate of 3.5% or less can be 150 μm or more. Furthermore, in this first fluoropolymer porous membrane, the thickness of the portion with a filling rate of 2.5% or less can be 50 μm or more; the thickness of the portion with a filling rate of 2.5% or less can be 100 μm or more; and the thickness of the portion with a filling rate of 2.5% or less can be 150 μm or more. Furthermore, in this first fluororesin porous membrane, the thickness of the portion with a filling rate of 2.0% or less can be 50 μm or more, the thickness of the portion with a filling rate of 2.0% or less can be 100 μm or more, and the thickness of the portion with a filling rate of 2.0% or less can be 150 μm or more. The filling rate of this first fluororesin porous membrane is not particularly limited; for example, it is preferably 0.5% or more, but it can also be 1.0% or more.

[0150] Furthermore, the first fluoropolymer porous membrane may include modified polytetrafluoroethylene (PTFE), preferably including modified PTFE and homopolymer PTFE. Examples of modified PTFE include copolymers of tetrafluoroethylene and perfluoroalkyl vinyl ethers, copolymers of tetrafluoroethylene and hexafluoropropylene, copolymers of tetrafluoroethylene and perfluoropropyl vinyl ethers, copolymers of tetrafluoroethylene and trifluorochloroethylene, and mixtures thereof. From the viewpoint of maintaining good formability of the PTFE, it is preferable that the content of modified PTFE in the fluoropolymer porous membrane is 10% by weight or more and 98% by weight or less, more preferably 50% by weight or more and 95% by weight or less.

[0151] The thickness of the aforementioned first fluororesin porous membrane is not particularly limited; it can be 45 μm or more, 50 μm or more, 100 μm or more, or 150 μm or more. If the thickness of the first fluororesin porous membrane is thinner than 45 μm, the dust collection load acting on the second fluororesin porous membrane, which is located further downstream, will increase excessively, making the second fluororesin porous membrane prone to pore blockage at an early stage.

[0152] As the first fluoropolymer porous membrane, the pressure loss and collection efficiency obtained by using polyalphaolefin particles with a particle diameter of 0.3 μm are used, and the PF value is determined by the following formula: PF value = {-log((100-collection efficiency (%)) / 100)} / (pressure loss (Pa) / 1000), wherein the PF value is preferably 17 or more, more preferably 20 or more, and even more preferably 25 or more.

[0153] Regarding the first fluoropolymer porous membrane, preferably, the dust storage capacity of the polyalphaolefin particles, corresponding to a pressure drop of 250 Pa, when air comprising polyalphaolefin particles with a median diameter of 0.25 μm is continuously ventilated through the fluoropolymer porous membrane at a flow rate of 5.3 cm / s, is 30.0 g / m³. 2 The above, more preferably 50.0 g / m 2 The above is further preferred to be 90.0 g / m 2 above.

[0154] Regarding the first fluoropolymer porous membrane, the pressure loss when air flows through the fluoropolymer porous membrane at a flow rate of 5.3 cm / s is preferably 200 Pa or less, more preferably 185 Pa or less.

[0155] Regarding the first fluororesin porous membrane, its average pore size is preferably 3.5 μm or more, and more preferably 4.0 μm or more.

[0156] Furthermore, the second fluororesin porous membrane disposed on the downstream side of the airflow relative to the first fluororesin porous membrane may also be the same porous membrane as the first fluororesin porous membrane. However, from the viewpoint of improving the overall dust storage capacity of the air filter material, it is preferable to use a fluororesin porous membrane with a filling rate greater than that of the first fluororesin porous membrane.

[0157] Furthermore, the thickness of the second fluororesin porous membrane is preferably thinner than that of the first fluororesin porous membrane, and can be 5 μm or more, preferably 40 μm or more. The thickness of the second fluororesin porous membrane can be, for example, 100 μm or less.

[0158] (2-5) Method for manufacturing fluoropolymer porous membranes

[0159] Next, the manufacturing method of air filter media will be explained by way of example.

[0160] In the fabrication of fluoropolymer porous membranes, fluoropolymers can be used, and preferably the three components described above.

[0161] The forms of the three components A to C described above are not particularly limited; for example, they may be the compositions, mixed powders, and molding materials described later. First, the compositions, mixed powders, and molding materials that serve as raw materials for porous membranes will be described.

[0162] The composition, mixed powder, and molding material all include components A, B, and C as described above, with component C comprising, for example, 0.1% by weight or more and less than 20% by weight of the total. Components A, B, and C are the same as the aforementioned fibrous PTFE, non-fibrous non-thermal-melt-processable components, and non-fibrous but thermomelt-processable components for porous membranes.

[0163] The forming material is, for example, a porous membrane forming material used to form a porous membrane, which is used as a filter material for capturing particles in a gas.

[0164] The raw materials for porous membranes can be in the form of mixed powders as described later, or non-powder mixtures. Furthermore, they can be forming materials or components as described later. Examples of mixed powders include, for example, micronized powders obtained by co-precipitation used in the embodiments described later, powders obtained by mixing two of the three raw materials through co-precipitation and then mixing them with another material using a mixer, and powders obtained by mixing the three raw materials using a mixer. Examples of non-powder mixtures include, for example, shaped bodies such as porous bodies (e.g., porous membranes), and aqueous dispersions comprising the three components.

[0165] In order to shape the composition, the forming material can be a material that has been modified for processing, such as a material with added processing aids (liquid lubricants, etc.), a material with adjusted particle size, or a material that has been pre-shaped. For example, in addition to the three components mentioned above, the forming material can also include known additives. Examples of known additives include carbon materials such as carbon nanotubes and carbon black, pigments, photocatalysts, activated carbon, antibacterial agents, adsorbents, and deodorizing agents.

[0166] The composition can be manufactured by various methods. For example, when the composition is a mixed powder, it can be manufactured by methods such as: mixing powders of component A, component B, and component C using a general mixer; obtaining a co-precipitated powder by co-precipitating three aqueous dispersions comprising components A, B, and C respectively; or mixing a mixed powder obtained by pre-co-precipitating an aqueous dispersion comprising any two of components A, B, and C with the powder of the remaining component using a general mixer. According to such methods, a preferred extended material can be obtained in any manufacturing method. Ideally, the composition should be obtained by co-precipitating three aqueous dispersions comprising components A, B, and C respectively, as the three different components are easily and uniformly dispersed.

[0167] There are no particular limitations on the size of the mixed powder obtained by co-precipitation; for example, the average particle size is 100 μm to 1000 μm, and ideally it is 300 μm to 800 μm. In the above cases, the average particle size is determined according to JIS K6891. There are no particular limitations on the apparent density of the mixed powder obtained by co-precipitation; for example, it is 0.40 g / ml to 0.60 g / ml, and ideally it is 0.45 g / ml to 0.55 g / ml. The apparent density is determined according to JIS K6892.

[0168] As a method for the aforementioned co-precipitation, the following methods can be cited as examples:

[0169] (i) A method of mixing an aqueous dispersion of component A, an aqueous dispersion of component B, and an aqueous dispersion of component C and then subjecting them to coagulation.

[0170] (ii) A method of adding powders of the remaining two components to an aqueous dispersion of any one of components A, B, and C, followed by coagulation;

[0171] (iii) A method of adding the powder of any one of the components A, B, and C to a mixed aqueous dispersion prepared by mixing the aqueous dispersions of the remaining two components and then allowing it to precipitate.

[0172] (Ⅳ) A method of adding a mixed powder of two components obtained by pre-mixing and precipitating any two aqueous dispersions of components A, B, and C to an aqueous dispersion of the remaining component and then precipitating the mixture.

[0173] Of the co-precipitation methods described above, method (i) is the most ideal in terms of the ease with which the three components can be evenly dispersed.

[0174] In the co-precipitation based on the methods described in (i) to (iv) above, it is ideal to add, for example, any of the following components and carry out co-precipitation: acids such as nitric acid, hydrochloric acid, and sulfuric acid; metal salts such as magnesium chloride, calcium chloride, sodium chloride, aluminum sulfate, magnesium sulfate, barium sulfate, sodium bicarbonate, and sodium carbonate; and organic solvents such as acetone and methanol.

[0175] The form of component A before mixing is not particularly limited; it can be an aqueous dispersion of the fibrous PTFE or a powder. Examples of powders (especially the aforementioned FP: micro powder) include: "Teflon 6-J" (hereinafter Teflon is a registered trademark), "Teflon 6C-J", and "Teflon 62-J" manufactured by Mitsui DuPont Fluorochemicals Co., Ltd.; and "Polyflon F106" (hereinafter Polyflon is a registered trademark) manufactured by Daikin Industries, Ltd. Polyflon F104, Polyflon F201, Polyflon F302, etc.; Fluon CD123 (hereinafter Fluon is a registered trademark), Fluon CD1, Fluon CD141, Fluon CD145, etc. manufactured by Asahi Glass Co., Ltd.; Teflon 60, Teflon 60 X, Teflon 601A, Teflon 601 X, Teflon 613A, Teflon 613A X, Teflon 605XT X, Teflon 669 X, etc. manufactured by DuPont. A fine powder can be obtained by precipitating and drying an aqueous dispersion of fibrous PTFE (the polymerized aqueous dispersion) obtained through the emulsification polymerization of TFE.

[0176] The aqueous dispersion of fibrous PTFE can be either the polymerized aqueous dispersion described above or a commercially available aqueous dispersion. As a preferred method for manufacturing the polymerized aqueous dispersion of fibrous PTFE, the methods disclosed in the aforementioned publications, which list homopolymer PTFE as a disclosed product, can be cited. Commercially available aqueous dispersions of fibrous PTFE include: "Polyflon D-110", "Polyflon D-210", "Polyflon D-210C", and "Polyflon D-310" manufactured by Daikin Industries, Ltd.; "Teflon 31-JR" and "Teflon 34-JR" manufactured by Mitsui-DuPont Fluorochemicals, Ltd.; and "Fluon AD911L", "Fluon AD912L", and "AD938L" manufactured by Asahi Glass Co., Ltd. For commercially available aqueous dispersions of fibrous PTFE, 2 to 10 parts by weight of nonionic surfactants are typically added per 100 parts by weight of PTFE to maintain stability. Therefore, the mixed powder obtained through copolymerization may contain residual nonionic surfactants, potentially causing problems such as discoloration of the porous structure. Thus, a fully polymerized aqueous dispersion is ideal for fibrous PTFE.

[0177] There are no particular limitations on the form of component B before mixing. When component B is low molecular weight PTFE, there are no particular limitations on the form of component B before mixing. It can be an aqueous dispersion or a powder (generally referred to as PTFE micro powder or micro powder). Examples of low molecular weight PTFE powders include: "MP1300-J" manufactured by Mitsui-DuPont Fluorochemicals Co., Ltd.; "Lubron L-5" (hereinafter Lubron is a registered trademark) and "Lubron L-5F" manufactured by Daikin Industries, Ltd.; "Fluon L169J", "Fluon L170J", and "Fluon L172J" manufactured by Asahi Glass Co., Ltd.; and "KTL-F" and "KTL-500F" manufactured by Kitamura Co., Ltd.

[0178] As an aqueous dispersion of low molecular weight PTFE, it can be a polymerized aqueous dispersion obtained by emulsification polymerization of the aforementioned TFE, or a commercially available aqueous dispersion. Alternatively, an aqueous dispersion prepared by dispersing microparticles in water using surfactants or the like can also be used. Preferred methods for producing a polymerized, fibrous aqueous dispersion of PTFE include those disclosed in the following documents: Japanese Patent Application Publication No. 7-165828, Japanese Patent Application Publication No. 10-147617, Japanese Patent Application Publication No. 2006-063140, Japanese Patent Application Publication No. 2009-1745, and International Publication No. 2009 / 020187. Examples of commercially available, fibrous aqueous dispersions of PTFE include "LubronLDW-410" manufactured by Daikin Industries, Ltd. For commercially available aqueous dispersions of low molecular weight PTFE, to maintain stability, 2 to 10 parts by weight of nonionic surfactants are added per 100 parts by weight of PTFE in the aqueous dispersion. Therefore, the mixed powder obtained through copolymerization may have residual nonionic surfactants, potentially causing problems such as coloration of the porous structure. Thus, a fully polymerized aqueous dispersion is ideal for low molecular weight PTFE.

[0179] Furthermore, when using inorganic fillers as component B, there are no particular limitations on the form of component B before mixing; an aqueous dispersion is preferable. Examples of inorganic fillers include "Talc P2" manufactured by Nippon Talc Co., Ltd., and "LMR-100" manufactured by Fuji Talc Industries, Ltd. The talc is used by dispersing the powder in water through surface treatment with a silane coupling agent or similar method. From the perspective of water dispersibility, a secondary pulverized product based on an air jet mill (such as "Talc P2") is preferable.

[0180] As component C, in addition to fluoropolymers such as FEP and PFA, other resins such as acrylic acid, polyurethane, and PET can also be listed. The form of component C before mixing is not particularly limited, but an aqueous dispersion is preferred. When the aqueous dispersion is a resin obtained through emulsification polymerization, in addition to using the polymerized dispersion directly, an aqueous dispersion formed by dispersing resin powder in water using a surfactant or the like can also be used. A specified amount of component C is dispersed in water to prepare the aqueous dispersion, ensuring that the content of component C in the porous membrane is 0.1% by weight or more and less than 20% by weight.

[0181] There are no particular limitations on the co-precipitation method. Ideally, mechanical stirring should be applied after mixing the three aqueous dispersions.

[0182] After copolymerization and precipitation, the mixture is dehydrated, dried, mixed with a liquid lubricant (extrusion aid), and extruded. The liquid lubricant is not particularly limited to any substance capable of wetting the surface of the PTFE powder and being removable after the mixture obtained through copolymerization and precipitation has been formed into a thin film. Examples include flowing paraffin wax, naphtha, white oil, hydrocarbon oils such as toluene and xylene, alcohols, ketones, and esters.

[0183] After mixing the mixture obtained by copolymerization with a liquid lubricant, it is extruded and rolled into a film using existing known methods. Extrusion can be carried out by paste extrusion, plunger extrusion, etc., with paste extrusion being the most ideal method. The sheet extruded by paste extrusion is rolled under heated conditions, for example, at a temperature of 40°C to 80°C, using calendering rolls or the like. The thickness of the resulting film-like rolled product is set according to the thickness of the target porous film, typically between 100 μm and 1000 μm, or between 100 μm and 400 μm.

[0184] Next, the liquid lubricant is removed from the unburned film, which is the rolled product. The liquid lubricant is removed by heating, extraction, or a combination of the above methods. When using the three components A to C, there is no particular limitation on the heating temperature when using the heating method, as long as it is lower than the melting point of the heat-melting processable component that will not fibrousize; for example, it can be 100°C to 250°C or 180°C to 200°C.

[0185] From the viewpoint of reducing the filling rate of the obtained fluoropolymer porous membrane and minimizing its pressure loss, it is preferable to perform a heat treatment at a temperature of 250°C to 325°C for at least one minute before stretching the rolled material after removing the liquid lubricant. This heat treatment temperature can be, for example, below 320°C, preferably lower than the melting point of the fluoropolymer used to make the fluoropolymer porous membrane. If multiple endothermic curves (primary melting point, secondary melting point) appear on the crystal melting curve when the rolled material is heated at a heating rate of 10°C / min using a differential scanning calorimeter, the heat treatment temperature can also be lower than the maximum peak temperature (primary melting point). Furthermore, from the viewpoint of sufficiently minimizing the filling rate and pressure loss, the heat treatment temperature can be, for example, above 260°C, above 280°C, above the temperature at which the liquid lubricant is removed from the rolled material (i.e., the unfired film) by heating, or above the stretching temperature (the temperature at which the first stretching is performed in the case of biaxial stretching). In addition, there is no particular limitation on the duration of heat treatment. It can be more than one minute and less than two hours, or more than thirty minutes and less than one hour, depending on the desired heat treatment effect.

[0186] Furthermore, while there are no particular limitations on obtaining a fluoropolymer porous membrane with a different filling rate in the thickness direction, it is preferable to perform the heat treatment in such a way that the temperature on the side with a lower filling rate is higher than the temperature on the side with a higher filling rate. More preferably, the temperature of the upper-side portion during heat treatment is higher than that of the lower-side portion. Additionally, the lower-side portion can be cooled to a temperature lower than room temperature. Regarding the heat treatment temperature, from the viewpoint of generating a sufficient density difference, the temperature difference between the upper-side and lower-side portions can be 100°C or more, preferably 200°C or more, and more preferably 300°C or more. Furthermore, during the heat treatment, it is preferable to increase the heating time on the side with a lower filling rate and shorten the heating time on the side with a higher filling rate. Thus, by extending the resulting rolled product, the filling rate on the upper side can be reduced and the filling rate on the lower side can be increased.

[0187] In the manner described above, the rolled product after the liquid lubricant has been removed, or the rolled product after further heat treatment, is extended. Furthermore, in the case of a product containing both a non-fibrous hot-melt processable component and a non-fibrous non-hot-melt processable component, the extension is performed at a temperature above the melting point of the non-fibrous hot-melt processable component and below the decomposition temperature of the non-fibrous non-hot-melt processable component.

[0188] Furthermore, when a non-fibrous hot-melt processable component is used in the fabrication of a fluoropolymer porous membrane, the non-fibrous hot-melt processable component melts during the stretching process and then solidifies at the nodule, thereby strengthening the thickness direction of the porous membrane. The stretching temperature can be set by the temperature of the stretching furnace or the temperature of the heating rollers used to transport the rolled material, or a combination of the above settings.

[0189] The extension includes extension toward a first direction, and preferably, also includes extension toward a second direction orthogonal to the first direction. Here, extension toward the first direction can be performed before extension toward the second direction, or both extension toward the first and second directions can be performed simultaneously. When using a porous membrane as filter material for an air filter after embossing, it is ideal to also extend toward the second direction. In this embodiment, the first direction is the length direction (longitudinal: MD direction) of the rolled material, and the second direction is the width direction (transverse: TD direction) of the rolled material. Furthermore, the extension can also be performed simultaneously while multiple rolled materials are overlapped.

[0190] The aforementioned rolled material is stretched at an elongation area ratio of 40 to 800 times.

[0191] From the viewpoint of reducing the filling rate of the resulting fluoropolymer porous membrane and minimizing pressure loss during stretching, it is preferable to stretch in a manner that produces a portion stretched at a stretching speed of 30% / second or less in the stretching direction; more preferably, it is preferable to stretch in a manner that produces a portion stretched at a stretching speed of 20% / second or less in the stretching direction; and even more preferably, it is preferable to stretch in a manner that produces a portion stretched at a stretching speed of 10% / second or less in the stretching direction. In the case of biaxial stretching, it is sufficient to achieve a stretching speed of 30% / second or less in either the longitudinal or transverse direction; however, it is preferable to achieve a stretching speed of 30% / second or less when performing longitudinal stretching first. Furthermore, when the fluoropolymer porous membrane is stretched simultaneously in both the longitudinal and transverse directions in a plane using a test bench or similar apparatus, it is preferable to achieve a stretching speed of 30% / second or less in either the longitudinal or transverse stretching direction. In addition, the stretching speed is not limited in the longitudinal and transverse directions; for example, it can be 1% / second or more.

[0192] Furthermore, the stretching rate is the value obtained by dividing the stretching ratio (%) by the time (seconds) taken for the stretching, and the stretching ratio (%) is the ratio of the length after stretching to the length before stretching (length after stretching / length before stretching). In addition, it is ideal to further reduce the pressure loss of the obtained porous membrane by slowing down the stretching rate as described above and by using the above three components of raw materials.

[0193] Furthermore, from the viewpoint of further reducing the filling rate of the obtained fluoropolymer porous membrane and further reducing the pressure loss, it is preferable to subject the rolled material to the above-mentioned heat treatment before stretching and to stretch it at a low speed as described above.

[0194] In the case of biaxial extension, the temperature when extending in the first direction is preferably 200°C to 300°C, more preferably 230°C to 250°C, and the temperature when extending in the second direction is preferably 200°C to 300°C, more preferably 230°C to 250°C.

[0195] Regarding the stretching of the aforementioned rolled material (also known as unburned fluoropolymer), it is known that the stretching temperature, stretching ratio, and stretching speed affect the physical properties of the stretched material. The SS curve (a graph showing the relationship between tensile tension and elongation) of unburned fluoropolymer shows unique characteristics different from other resins. Generally, the tensile tension of resin materials increases with elongation. It is quite common that the range of the elastic region and the point of fracture vary depending on the material and evaluation conditions; on the other hand, tensile tension tends to increase with elongation. In contrast, the tensile tension of unburned fluoropolymer shows a peak at a certain elongation and then gradually decreases. This indicates that unburned fluoropolymer has a region where the unstretched portion is stronger than the stretched portion.

[0196] If we replace the above description with the behavior during stretching, in the case of a typical resin, during stretching, the weakest part within the stretching surface begins to elongate, and the stretched part becomes stronger than the unstretched part. Therefore, subsequently, the weaker unstretched part begins to stretch, expanding the stretching area and thus achieving overall stretching. On the other hand, in the case of an unburned fluororesin, if the elongated part enters the aforementioned "region where the unstretched part is stronger than the stretched part," the already stretched part extends further, resulting in the unstretched part remaining as a knot (nodule, unstretched part). If the stretching speed slows down, the above phenomenon becomes more pronounced, leaving even larger knots (nodules, unstretched parts). By utilizing the above phenomenon during stretching, the physical properties of the stretched body can be adjusted according to various applications.

[0197] In this embodiment, it is preferable to obtain an extended body with a lower density. In the case of biaxial extension, it is effective to apply a low extension speed specifically to the first extension. Here, compared with the case where there are large residual knots (nodules, unextended portions) and only conventional PTFE is used as the raw material, the above-mentioned phenomenon caused by the low extension speed becomes more obvious when using a non-thermal-melting processable component that does not fibrousize. Even when it is desired to obtain a molded body with a low filling rate, the extension speed can be increased compared with the case where only PTFE is used as the raw material.

[0198] To obtain mechanical strength and dimensional stability, it is ideal to heat-fix the porous membrane obtained as described above. The temperature for heat fixing can be above or below the melting point of PTFE, ideally between 250°C and 400°C.

[0199] Furthermore, when obtaining a second fluororesin porous membrane with physical properties different from those of the first fluororesin porous membrane, for example, compared to the production of the first fluororesin porous membrane, by changing the method of reducing the amount of liquid lubricant relative to 100 parts by weight of fluororesin during the production of the second fluororesin porous membrane, the average pore size of the obtained porous membrane can be reduced. This results in a second fluororesin porous membrane with a greater pressure loss and a higher collection efficiency than the first fluororesin porous membrane. In the above case, it is ideal that the difference in the amount of liquid lubricant (liquid lubricant dosage difference or auxiliary dosage difference) relative to 100 parts by weight of fluororesin is 1 part by weight or less and 4 parts by weight. By making the auxiliary dosage difference 1 part by weight or more, an appropriate difference in average pore size can be generated between the two porous membranes. By making the auxiliary dosage difference 4 parts by weight or less, the deterioration of the uniformity of the extension can be suppressed. The uniformity of stretching refers to the following concept: in porous membranes produced through stretching, deviations in characteristics such as trapping efficiency and pressure loss are reduced, and these characteristics become uniform throughout the entire porous membrane. For example, the difference in liquid lubricant dosage is 2 parts by weight.

[0200] The amount of liquid lubricant used in the production of the fluororesin porous membrane is preferably 30 parts by weight or more and 37 parts by weight or less, relative to 100 parts by weight of fluororesin. By using the above-mentioned amount of liquid lubricant of 30 parts by weight or more, pressure loss can be reduced, and the overall pressure loss of the filter material can be less than 200 Pa. In addition, by using the above-mentioned amount of liquid lubricant of 37 parts by weight or less, the formability of the unburned membrane (green tape) can be ensured, and the following situation can be suppressed: the pore size of the first fluororesin porous membrane becomes too large, causing particles to flow through the first fluororesin porous membrane without being captured and flow downstream, thereby causing the burden on the second fluororesin porous membrane on the downstream side to become too great.

[0201] In particular, it is ideal that the amount of liquid lubricant used in manufacturing the first fluororesin porous membrane is, for example, 34 to 36 parts by weight relative to 100 parts by weight of fluororesin. For example, if 31 to 34 parts by weight of liquid lubricant are used to manufacture the second fluororesin porous membrane while satisfying a difference of 1 to 4 parts by weight, and in contrast, 34 to 36 parts by weight of liquid lubricant are used to manufacture the first fluororesin porous membrane, the dust storage capacity of the filter material can be significantly increased.

[0202] In addition, the difference in average pore size between the first fluororesin porous membrane and the second fluororesin porous membrane can also be achieved by making the proportions of the three components mentioned above different between the two porous membranes.

[0203] (3) Breathable support membrane

[0204] A breathable support membrane is positioned upstream or downstream of the fluoropolymer porous membrane, or both, to support it. Therefore, even if the fluoropolymer porous membrane is difficult to stand upright on its own due to its thinness, it can be supported by the breathable support membrane. Furthermore, its strength as an air filter media is guaranteed, and it is easy to handle.

[0205] The material and structure of the breathable support membrane are not particularly limited; examples include nonwoven fabrics, woven fabrics, metal meshes, and resin meshes. From the viewpoints of strength, trapping properties, softness, and workability, heat-sealable nonwoven fabrics are preferred. Ideally, the nonwoven fabric is a double-layer nonwoven fabric consisting of a core / sheath structure partially or entirely of the fibers, a nonwoven fabric composed of a fiber layer made of a low-melting-point material and a fiber layer made of a high-melting-point material, and a nonwoven fabric coated with a heat-sealable resin. Spunbond nonwoven fabrics are an example of such nonwoven fabrics. Furthermore, in nonwoven fabrics with a core / sheath structure, it is ideal that the melting point of the core component is higher than that of the sheath component. For example, combinations of core / sheath materials include PET / PE and high-melting-point polyester / low-melting-point polyester. Combinations of low-melting-point and high-melting-point materials in double-layer nonwoven fabrics include PE / PET, PP / PET, PBT / PET, and low-melting-point PET / high-melting-point PET. Examples of nonwoven fabrics coated with heat-sealing resins include PET nonwoven fabrics coated with EVA (ethylene vinyl acetate copolymer resin) and PET nonwoven fabrics coated with olefin resins.

[0206] There are no particular restrictions on the material of nonwoven fabrics. They can be made of polyolefins (PE, PP, etc.), polyamides, polyesters (PET, etc.), aromatic polyamides, or composites of the above materials.

[0207] By heating and melting a portion of the breathable support membrane or by melting a hot-melt resin, and by using an anchoring effect or by using a reactive adhesive, the breathable support membrane can be bonded to a fluoropolymer porous membrane.

[0208] Compared to the aforementioned fluoropolymer porous membranes, the pressure loss, collection efficiency, and dust storage capacity of the breathable support membrane can all be very low, even practically zero. For example, the pressure loss of the breathable support membrane is preferably 10 Pa or less, more preferably 5 Pa or less, and even more preferably 1 Pa or less. Furthermore, the collection efficiency of the breathable support membrane for polyalphaolefin particles with a diameter of 0.3 μm can be practically zero or nearly zero. The thickness of the breathable support membrane is preferably 0.3 mm or less, more preferably 0.25 mm or less. Preferably, the unit area mass of the breathable support membrane is, for example, 20 g / m³. 2 Above 50g / m 2 the following.

[0209] (4) Pre-collection membrane

[0210] The pre-collection membrane is positioned upstream of the fluorinated resin porous membrane and is capable of capturing a portion of the dust in the airflow.

[0211] From the perspective of minimizing the overall pressure loss of the air filter media, the pressure loss of the pre-capture membrane when air passes through at a flow rate of 5.3 cm / s is preferably 5 Pa or more and less than 55 Pa, more preferably 15 Pa or more and less than 45 Pa.

[0212] Furthermore, the pre-capture membrane preferably has a capture efficiency of 15% or more and less than 85% for polyalphaolefin particles with a diameter of 0.3 μm, more preferably 30% and less than 75%.

[0213] Furthermore, the thickness of the pre-collecting membrane is not particularly limited and can be 100.0 μm or more, preferably 200.0 μm or more. From the viewpoint of facilitating the folding operation when folding the air filter media into pleats, the upper limit of the pre-collecting membrane thickness is preferably 800.0 μm, more preferably 600.0 μm. Additionally, the thickness of the pre-collecting membrane is preferably greater than the thickness of the fluoropolymer porous membrane used in conjunction with it.

[0214] There is no particular limitation on the unit area mass of the pre-collection membrane; for example, it can be set to 10 g / m³. 2 Above 70g / m 2 The preferred value is 25g / m³. 2 Above 50g / m 2 the following.

[0215] Furthermore, the first fluoropolymer porous membrane disposed upstream of the second fluoropolymer porous membrane also has a pre-collection function relative to the second fluoropolymer porous membrane. However, the first fluoropolymer porous membrane can achieve the same level of performance as the pre-collection membrane with a thinner thickness. In this regard, from the viewpoint of keeping the thickness thinner, a pre-collection membrane may not be necessary in an air filter media configured with both a first fluoropolymer porous membrane and a second fluoropolymer porous membrane.

[0216] There are no particular limitations on the pre-capture membrane described above. It can be made of glass fiber filter media, or it can be a nonwoven fabric or fiber layer structure made of fibrous material manufactured by one of the following methods: melt-blowing, electrospinning, island-type process, or a combination of the above methods. Examples of the combination methods include melt spinning or electret blowing. The island-type process refers to a method in which, for example, when fibers are formed by discharging from multiple outlets, different raw materials are arranged according to the discharge path, so that some raw materials form the sea portion and other different raw materials form the island portion, thereby giving the fiber cross-section an island structure. Here, it is possible to spin the polymers of two or more components of the island and melt the sea portion in subsequent processing, leaving the island portion as fiber. Furthermore, the bulk density and extensibility can be adjusted by the combination of raw materials in the discharge path. In the melt-blowing process, molten polymer is discharged from a nozzle using an extruder, and heated air is blown out along the nozzle to form a yarn. Here, by adjusting the amount of polymer discharged per unit time from the nozzle and the blowing speed of the heated air, finer diameter yarns can be obtained. Furthermore, the physical properties of the yarns can vary depending on the melt viscosity of the polymer used. Examples of materials that can be used to manufacture the pre-capture membrane include polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyamide (PA), polyacrylonitrile (PAN), polyvinylidene fluoride (PVdF), polyvinyl alcohol (PVA), polyurethane (PU), and mixtures of the above materials.

[0217] Since the pre-collecting membrane is used in conjunction with the fluoropolymer porous membrane, in order to suppress the opening of pores in the fluoropolymer porous membrane by sparks generated by static electricity, it is preferable that the pre-collecting membrane is made of glass fiber filter material, which is not easily charged. Furthermore, glass fiber filter material including the aforementioned physical properties can be manufactured, and such glass fiber filter material is also commercially available.

[0218] (5) Examples of applications

[0219] Air filter media is used for applications such as the following:

[0220] ULPA filters (ultra-low permeability air filters) (for semiconductor manufacturing), HEPA filters (for hospitals and semiconductor manufacturing), cylindrical filters (for industrial use), bag filters (for industrial use), heat-resistant bag filters (for exhaust gas treatment), heat-resistant pleated filters (for exhaust gas treatment), SINBRAN (registered trademark) filters (for industrial use), catalyst filters (for exhaust gas treatment), filters with adsorbents (for HDD assembly), air-purifying filters with adsorbents (for HDD assembly), air-purifying filters (for HDD assembly, etc.), vacuum cleaner filters (for vacuum cleaners), general-purpose multi-layer felt components, cartridge filters for gas turbines (for gas turbine compatible products), cooling filters (for electronic equipment enclosures), etc.

[0221] Freeze-drying materials for containers, etc.; ventilation materials for automobiles for circuits and lamps; container applications for container lids, etc.; protective ventilation applications for electronic devices, etc.; and ventilation applications for medical purposes, etc., in the field of ventilation / internal pressure regulation.

[0222] Applications include semiconductor liquid filters (for semiconductor manufacturing), hydrophilic filters (for semiconductor manufacturing), filters for chemical products (for pharmaceutical liquid treatment), filters for pure water production lines (for pure water production), and backwashing liquid filters (for industrial wastewater treatment).

[0223] Furthermore, air filter media can also be used in cleanrooms, such as medical cleanrooms or cleanrooms in pharmaceutical factories, to suppress the decrease in capture efficiency even when the target of capture is droplet particles.

[0224] (6) Filter pack

[0225] Next, refer to Figure 6 The filter package of this embodiment will be described.

[0226] Figure 6 This is a perspective view of the filter pack 20 in this embodiment.

[0227] The filter pack 20 includes the air filter media described above (e.g., air filter media 30, etc.). The air filter media of the filter pack 20 is a finished filter media that has been processed into a serrated shape with alternating outward and inward folds (pleating). For example, the pleating process can be performed using a rotary pleating machine. The pleating width of the filter media is not particularly limited, and can be, for example, between 25 mm and 280 mm. Because the filter pack 20 is pleated, the folded area of ​​the filter media can be increased when the filter pack 40 is used in an air filter unit, thereby obtaining an air filter unit with higher capture efficiency.

[0228] In addition, in the filter bag after pleating, the interval between the top of adjacent outward folds or the interval between the bottom of adjacent inward folds is, for example, 5 to 10 mm. Preferably, the width of the filter bag per 100 mm (the length in the direction orthogonal to each outward fold or each inward fold) is 10 to 20 pleats (the number of outward or inward folds).

[0229] In addition to the filter media, the filter pack 20 may also include septa (not shown) for maintaining the pleat spacing when the filter pack 40 is used in an air filter unit. The material of the septa is not particularly limited, but hot-melt resin or corrugated aluminum spacers are preferred. Furthermore, the air filter media 30 may also have multiple embossed protrusions, which maintain the pleat spacing.

[0230] (7) Air filter unit

[0231] Next, refer to Figure 7 The air filter unit 1 will be described.

[0232] Figure 7 This is a perspective view of the air filter unit 1 of this embodiment.

[0233] The air filter unit 1 includes the air filter media or filter bag described above and a frame 25 for holding the air filter media or filter bag. In other words, the air filter unit can be made such that the filter media is held in the frame without any outward or inward folds, or the filter bag 20 is held in the frame 25. Figure 7 The air filter unit 1 shown is made of filter bag 20 and frame 25.

[0234] The frame 25 is made, for example, by combining sheets or molding resin. Ideally, the filter bag 20 and the frame 25 are sealed with a sealant. The sealant is used to prevent leakage between the filter bag 20 and the frame 25, and can be made of materials such as epoxy, acrylic, polyurethane, etc.

[0235] The air filter unit 1, which includes the filter bag 20 and the frame 25, can be a mini pleated type air filter unit in which a single filter bag 20 extending in a flat shape is held inside the frame 25, or it can be a V-bank type air filter unit or a single manifold type air filter unit in which multiple filter bags extending in a flat shape are held side by side in the frame.

[0236] Furthermore, the air filter unit 1, which includes the filter bag 20 and the frame 25, can be as follows: Figure 8As shown, the separator-type air filter unit 1 is formed by alternately folding back the air filter medium 30 to form a corrugated shape, and spacers 50, such as those with corrugated processing, are arranged in the valleys of the air filter medium 30 formed by the alternate folding. According to the above air filter unit 1, even during use, the pleat spacing of the air filter medium 30 alternately folded back to form a corrugated shape can be stably maintained by the spacers 50.

[0237] <Examples>

[0238] Hereinafter, examples and comparative examples are shown, and the content of the present disclosure will be specifically described.

[0239] (Examples 1 to 4)

[0240] As the air filter media for Examples 1 to 4, air filter media having the Figure 5 structure shown were prepared. Specifically, the air filter medium has a fluororesin porous membrane, an upstream breathable support membrane provided on the upstream side of the fluororesin porous membrane, and a downstream breathable support membrane provided on the downstream side of the fluororesin porous membrane. As the upstream breathable support membrane and the downstream breathable support membrane, spunbond nonwoven fabrics (average fiber diameter: 24 μm, basis weight: 40 g / m 2 , thickness: 0.2 mm) composed of fibers having a core / shell structure with PET as the core and PE as the sheath were used (additionally, the capture efficiency can be regarded as substantially zero or approximately zero). In addition, in Examples 1 to 4, no heat treatment was performed before stretching. In Examples 1 to 4, the same FP raw material was used, the draw ratio was also set to be the same, and the stretching speed in the MD direction was changed to produce each air filter medium.

[0241] In addition, as the FP raw material for Examples 1 to 4, a mixed powder composed of three components (fibrous PTFE (Component A), non-fibrous non-thermoplastic processing component (Component B), and non-fibrous but thermoplastic processing component (Component C) with a melting point less than 320 °C) and an extrusion aid (liquid lubricant) with a weight of 32.0% of the weight of the mixed powder were mixed.

[0242] More specifically, co-precipitation was carried out as follows: 66.5% by weight (polymer equivalent) of an aqueous PTFE dispersion (component A) with an SSG of 2.160 prepared according to the method described in Comparative Example 3 of International Publication No. 2005 / 061567, 28.5% by weight (polymer equivalent) of a low molecular weight PTFE aqueous dispersion (component B) prepared according to the method described in International Publication No. 2009 / 020187 and having a melt viscosity of 20000 Pa·s determined by flow method at 380°C, and 5% by weight (polymer equivalent) of an FEP aqueous dispersion with a melting point of 215°C prepared according to the method described in Japanese Patent Application Publication No. 2010-235667, were mixed, and 500 ml of a 1% aluminum nitrate aqueous solution was added as a coagulant, and the mixture was stirred. Next, after removing the moisture from the generated powder using a sieve, the powder is dried in a hot air drying oven at a temperature of 135°C for 18 hours to obtain a mixed powder of the three components.

[0243] Then, 32.0 parts by weight of hydrocarbon oil (IPSolvent 2028 manufactured by Idemitsu Kosan Co., Ltd.) was added to every 100 parts by weight of the mixture at a temperature of 20°C as an extrusion liquid lubricant, and the mixture was mixed. Next, the resulting mixture was extruded using a paste extrusion apparatus equipped with a sheet mold to obtain a sheet-shaped molded body. The sheet-shaped molded body was then formed into a film using calendering rolls heated to 70°C to obtain a PTFE film. The film was then passed through a hot air drying oven at 250°C to evaporate and remove the hydrocarbon oil, thereby obtaining a strip-shaped unburned PTFE film with an average thickness of 300 μm and an average width of 175 mm. Then, for each embodiment, the unburned PTFE film was stretched along its long side at a specified stretch ratio and stretching speed. The stretching temperature was 250°C. Next, for each embodiment, the stretched, unburnt film was stretched along its width direction at a predetermined stretching ratio and speed using a clamping radiating machine, and then heat-fixed. The stretching temperature at this time was 250°C. Thus, a porous membrane was obtained.

[0244] (Examples 5-9)

[0245] Regarding the air filter media of Examples 5-9, such as Figure 5As shown, an air filter media is also configured having a fluoropolymer porous membrane, an upstream-side air-permeable support membrane disposed upstream of the fluoropolymer porous membrane, and a downstream-side air-permeable support membrane disposed downstream of the fluoropolymer porous membrane. Both the upstream-side and downstream-side air-permeable support membranes use the same air-permeable support membranes used in Examples 1-4 above. Furthermore, in Examples 5-9, the unburned films obtained by removing the extruded liquid lubricant were all heat-treated (at 320°C for 1.0 hour) before stretching. In Examples 5-7, the same FP raw material was used, the stretching ratio was set to the same, and the stretching speed in the MD direction was changed to produce each air filter media. In Examples 7-9, the same FP raw material was used, the stretching ratio and the stretching speed in the MD and TD directions were set to the same, and only the stretching ratio in the MD direction was changed to produce each air filter media.

[0246] In addition, in Examples 5 to 9, the conditions not specifically specified are the same as those in Example 1 above.

[0247] (Examples 10 and 11)

[0248] Regarding the air filter media in Examples 10 and 11, such as Figure 5As shown, an air filter media is also configured with a fluoropolymer porous membrane, an upstream-side ventilable support membrane disposed upstream of the fluoropolymer porous membrane, and a downstream-side ventilable support membrane disposed downstream of the fluoropolymer porous membrane. Both the upstream-side and downstream-side ventilable support membranes use the same ventilable support membranes used in Examples 1-4 described above. Furthermore, in Examples 10 and 11, no heat treatment was performed before stretching. In Examples 10 and 11, the stretching ratio, MD, and TD directions were the same, but the FP raw material used was different, thus producing each air filter media. Specifically, the FP raw material of Example 10 was prepared by mixing a mixed powder with an extrusion aid (liquid lubricant) at a weight of 28% of the mixed powder. The mixed powder was prepared by copolymerizing and mixing fine powder of perfluoroalkyl vinyl ether modified polytetrafluoroethylene (manufactured by Daikin Industries, Ltd., product name: F302) and fine powder of polytetrafluoroethylene with an average molecular weight of 6.5 million (manufactured by Daikin Industries, Ltd., product name: F106) at a weight ratio of 75:25. Furthermore, as the FP raw material of Example Eleven, an FP raw material was used, which was a mixture of a mixed powder and an extrusion aid (liquid lubricant) weighing 28% of the weight of the mixed powder. The mixed powder was prepared by copolymerizing and mixing fine powder of perfluoroalkyl vinyl ether modified polytetrafluoroethylene (manufactured by Daikin Industries, Ltd., product name: F302) and fine powder of polytetrafluoroethylene with an average molecular weight of 6.5 million (manufactured by Daikin Industries, Ltd., product name: F106) at a weight ratio of 90:10.

[0249] In addition, in Examples 10 and 11, the conditions not specifically specified are the same as those in Example 1 above.

[0250] (Comparative Example 1, Example 12)

[0251] In the air filter media of Comparative Example 1 and Example 12, relative to Figure 2 The air filter media shown further includes an upstream-side ventilable support membrane at its upstream side. Specifically, the air filter media is configured to have an upstream-side ventilable support membrane, a first fluoropolymer porous membrane disposed downstream of the upstream-side ventilable support membrane, a second fluoropolymer porous membrane disposed downstream of the first fluoropolymer porous membrane, and a downstream-side ventilable support membrane disposed downstream of the second fluoropolymer porous membrane. Furthermore, the upstream-side and downstream-side ventilable support membranes use the same ventilable support membranes as those used in Examples 1-4 described above. Additionally, in Comparative Example 1 and Example 12, no heat treatment was performed before stretching. In Comparative Example 1 and Example 12, the stretching ratio was set to be the same.

[0252] In Comparative Example 1, two unburned films were overlapped, and the stretching temperature in the MD direction was set to 300°C, the stretching speed was set to 40.2% / second, and a continuous-clamping radiating machine was used. The stretching temperature in the TD direction was set to 290°C, the stretching speed was set to 114.5% / second, and the heat-fixing temperature was set to 390°C. One of the two unburned films served as the unburned film of the first fluoropolymer porous membrane, which was prepared by mixing a mixed powder consisting of the above three components with an extrusion aid (liquid lubricant) at a weight of 31.5% of the weight of the mixed powder as the FP raw material. The other unburned film served as the unburned film of the second fluoropolymer porous membrane, which was prepared by mixing a mixed powder consisting of the above three components with an extrusion aid (liquid lubricant) at a weight of 33.0% of the weight of the mixed powder as the FP raw material.

[0253] In Example Twelve, two unburned films were overlapped, and the stretching temperature in the MD direction was set to 300°C, the stretching speed was set to 40.2% / second, and a continuous-clamping radiating machine was used. The stretching temperature in the TD direction was set to 290°C, the stretching speed was set to 114.5% / second, and the heat-fixing temperature was set to 390°C. One of the two unburned films served as the unburned film of the first fluororesin porous membrane, which was a mixture of the above three components. The powder and an extrusion aid (liquid lubricant) weighing 32.5% of the weight of the mixed powder are used as FP raw materials and mixed together. The other unburned film of the two unburned films is used as the unburned film of the second fluoropolymer porous membrane. It is made by mixing fine powder of perfluoroalkyl vinyl ether modified polytetrafluoroethylene (manufactured by Daikin Industries, Ltd., product name: F302) and an extrusion aid (liquid lubricant) weighing 27.0% of the weight of the powder as FP raw materials.

[0254] (Examples XIII-XV, Comparative Example 2)

[0255] Regarding the air filter media of Examples 13-15 and Comparative Example 2, such as Figure 5 As shown, an air filter media is also configured with a fluoropolymer porous membrane, an upstream-side air-permeable support membrane disposed upstream of the fluoropolymer porous membrane, and a downstream-side air-permeable support membrane disposed downstream of the fluoropolymer porous membrane. Both the upstream-side and downstream-side air-permeable support membranes use the same air-permeable support membranes used in Examples 1-4 described above. Furthermore, in Examples 13-15 and Comparative Example 2, no heat treatment was performed before stretching. In Examples 13-14 and Comparative Example 2, the stretching ratio was set to be the same. In Examples 13-15 and Comparative Example 2, different FP raw materials were used to manufacture each air filter media.

[0256] In Example 13, as the FP raw material, a substance was used which was a mixture of fine powder of perfluoroalkyl vinyl ether modified polytetrafluoroethylene (manufactured by Daikin Industries, Ltd., product name: F302) and an extrusion aid (liquid lubricant) weighing 27.0% of the powder. The stretching speed in the MD direction was set to 57.1% / second, and the stretching speed in the TD direction was set to 57.1% / second.

[0257] In Comparative Example 2, as the FP raw material, a substance was used which was a mixture of fine polytetrafluoroethylene powder with an average molecular weight of 6.5 million (manufactured by Daikin Industries, Ltd., product name: F106) and an extrusion aid (liquid lubricant) weighing 32.5% of the weight of the fine powder. The elongation speed in the MD direction was set to 57.1% / second, and the elongation speed in the TD direction was set to 57.1% / second.

[0258] In Example 14, as the FP raw material, a substance was used that was a mixture of a powder consisting of the above three components and an extrusion aid (liquid lubricant) weighing 32.5% of the weight of the powder. The elongation speed in the MD direction was set to 57.1% / second, and the elongation speed in the TD direction was set to 57.1% / second.

[0259] In Example 15, as the FP raw material, a substance was used which was a mixture of fine powder of perfluoroalkyl vinyl ether modified polytetrafluoroethylene (manufactured by Daikin Industries, Ltd., product name: F302) and an extrusion aid (liquid lubricant) weighing 25% of the powder. The stretching speed in the MD direction was set to 142.9% / second, and the stretching speed in the TD direction was set to 142.9% / second.

[0260] Furthermore, in Examples 13 to 15, the conditions not specifically specified are the same as those in Example 1 above.

[0261] (Examples 16-18)

[0262] In the air filter media of Example Sixteen, in Figure 3An upstream ventilable support membrane is provided on the upstream side of the air filter media shown. Specifically, the air filter media is configured to have an upstream ventilable support membrane, a first fluoropolymer porous membrane disposed downstream of the upstream ventilable support membrane, a second fluoropolymer porous membrane disposed downstream of the first fluoropolymer porous membrane, and a downstream ventilable support membrane disposed downstream of the second fluoropolymer porous membrane. The second fluoropolymer porous membrane has the same physical properties as the first fluoropolymer porous membrane, and the upstream and downstream ventilable support membranes use the same ventilable support membranes used in Examples 1-4 described above. In the air filter media of Example 17, relative to... Figure 2 The air filter media shown further includes an upstream-side ventilable support membrane on its upstream side. Specifically, the air filter media is configured to have an upstream-side ventilable support membrane, a first fluoropolymer porous membrane disposed downstream of the upstream-side ventilable support membrane, a second fluoropolymer porous membrane disposed downstream of the first fluoropolymer porous membrane, and a downstream-side ventilable support membrane disposed downstream of the second fluoropolymer porous membrane. The second fluoropolymer porous membrane has the same physical properties as the first fluoropolymer porous membrane, and the physical properties of the second fluoropolymer porous membrane are different from those of the first fluoropolymer porous membrane. Furthermore, the upstream-side and downstream-side ventilable support membranes use the same ventilable support membranes used in Examples 1-4 described above. Regarding the air filter media of Example 18, as... Figure 5 As shown, an air filter media is also configured with a fluoropolymer porous membrane, an upstream-side ventilable support membrane disposed upstream of the fluoropolymer porous membrane, and a downstream-side ventilable support membrane disposed downstream of the fluoropolymer porous membrane. The upstream-side and downstream-side ventilable support membranes use the same ventilable support membranes as those used in Examples 1 to 4 described above. Furthermore, in Examples 16 to 18, no heat treatment was performed before stretching. In Examples 16 to 18, the stretching ratio was set to be the same. In Examples 16 to 18, different FP raw materials were used to manufacture each air filter media.

[0263] In Example 16, regarding the first fluoropolymer porous membrane, as the FP raw material, two unburned films were overlapped, formed by mixing fine powder of perfluoroalkyl vinyl ether modified polytetrafluoroethylene (manufactured by Daikin Industries, Ltd., product name: F302) and 25% by weight of the powder extrusion aid (liquid lubricant). The stretching temperature in the MD direction was set to 250°C, and the stretching speed was set to 142.9% / second. The stretching temperature in the TD direction was also set to 250°C, and the stretching speed was set to 142.9% / second. The second fluoropolymer porous membrane used was the same fluoropolymer porous membrane as the first fluoropolymer porous membrane.

[0264] In Example 17, two unburned films were overlapped, and the stretching temperature in the MD direction was set to 250°C and the stretching speed was set to 142.9% / second. The stretching temperature in the TD direction was also set to 250°C and the stretching speed was set to 142.9% / second. One of the two unburned films served as the unburned film of the first fluoropolymer porous membrane. It was prepared by mixing fine powder of perfluoroalkyl vinyl ether modified polytetrafluoroethylene (manufactured by Daikin Industries, Ltd., product name: F302) and 25.0% by weight of extrusion aid (liquid lubricant) as FP raw material. The other unburned film served as the unburned film of the second fluoropolymer porous membrane. It was prepared by mixing a mixed powder consisting of the above three components and 30.0% by weight of extrusion aid (liquid lubricant) as FP raw material.

[0265] In Example 18, as the FP raw material, a substance was used which was a mixture of fine powder of perfluoroalkyl vinyl ether modified polytetrafluoroethylene (manufactured by Daikin Industries, Ltd., product name: F302) and an extrusion aid (liquid lubricant) weighing 25.0% of the powder. The stretching speed in the MD direction was set to 142.9% / second, and the stretching speed in the TD direction was set to 142.9% / second.

[0266] In addition, in Examples 16 to 18, the conditions not specifically specified are the same as those in Example 1 above.

[0267] (Example 19)

[0268] Regarding the air filter media of Example 19, such as Figure 4 As shown, the air filter media is configured to have a pre-collecting membrane, a fluoropolymer porous membrane disposed downstream of the pre-collecting membrane, and a breathable support membrane disposed further downstream of the fluoropolymer porous membrane. The breathable support membrane is the same breathable support membrane used in Examples 1 to 4 above.

[0269] In Example 19, the fluoropolymer porous membrane used as the FP raw material was a mixture of a mixed powder consisting of the above three components and an extrusion aid (liquid lubricant) at a weight of 32% of the mixed powder. The unburned film obtained after removing the extruded liquid lubricant was heat-treated (at 320°C for 1.0 hour) before stretching. Furthermore, during the stretching process after heat treatment, the stretching speed in the MD direction was set to 42.9% / second, and the stretching speed in the TD direction was set to 142.9% / second. The pre-trapping membrane used had a dust storage capacity of 28.8 g / m³ when the pressure loss increased by 250 Pa due to polyalphaolefin particles with a median diameter of 0.25 μm.2 The meltblown nonwoven fabric made of PP (with a unit area mass of 33.00 g / m²) 2 The thickness is 270.0 μm, the fill rate is 13.00%, and the average fiber diameter is 2.1 μm.

[0270] In addition, in Example 19, the conditions not specifically specified are the same as those in Example 1 above.

[0271] (Example 20)

[0272] Regarding the air filter media of Example 20, such as Figure 5 As shown, an air filter media is also configured with a fluoropolymer porous membrane, an upstream-side ventilable support membrane disposed upstream of the fluoropolymer porous membrane, and a downstream-side ventilable support membrane disposed downstream of the fluoropolymer porous membrane. Both the upstream-side and downstream-side ventilable support membranes use the same ventilable support membranes used in Examples 1-4 above. Furthermore, the fluoropolymer porous membrane in Example 20 uses a tilted-density porous membrane with a lower filler ratio on the upwind side and a higher filler ratio on the downwind side. As the FP raw material, this tilted-density porous membrane uses a mixture of a mixed powder consisting of the above three components and an extrusion aid (liquid lubricant) at 32% of the weight of the mixed powder. In addition, for the 600 μm thick rolled material (i.e., the unfired film) after the extrusion aids were evaporated and removed, a two-minute unilateral heat treatment was performed, followed by stretching (similar to Example 1, the stretching temperature was 250°C on both the upwind and downwind sides). The unilateral heat treatment involved placing a heating plate on the upwind side and heating it to 320°C, then cooling the downwind side to 3°C using a coolant. The side where the heating plate was placed on the upwind side and heated to 320°C was designated as the upstream side, and the dust accumulation on this upstream side was measured. The side where the downwind side was cooled to 3°C using a coolant was designated as the downstream side, and the dust accumulation on this downstream side was also measured.

[0273] In addition, in Example 20, the conditions not specifically specified are the same as those in Example 1 above.

[0274] (Example 21)

[0275] Regarding the air filter media of Example 21, such as Figure 5 As shown, an air filter media is also configured with a fluoropolymer porous membrane, an upstream-side ventilable support membrane disposed upstream of the fluoropolymer porous membrane, and a downstream-side ventilable support membrane disposed downstream of the fluoropolymer porous membrane. Both the upstream-side and downstream-side ventilable support membranes use the same ventilable support membranes used in Examples 1 to 4 described above. In Example 21, no heat treatment was performed before the extension was carried out.

[0276] In Example 21, the same FP raw material as in Example 10 was used as the FP raw material. Furthermore, a mixture was used, consisting of a copolymerized powder obtained by mixing and blending the same powder as in Example 10, and an extrusion aid (liquid lubricant) at 23% of the weight of the mixed powder. In Example 21, the mixture obtained in the above manner was extruded using a paste extrusion apparatus equipped with a sheet mold to obtain a sheet-shaped molded body. The sheet-shaped molded body was then formed into a film using calendering rolls heated to 70°C to obtain a PTFE film. The film was then passed through a hot air drying oven at 250°C to evaporate and remove hydrocarbon oils, thereby obtaining a strip-shaped unburned PTFE film with an average thickness of 600 μm and an average width of 170 mm. Then, the unfired PTFE film was longitudinally stretched using a heated three-roller stretching device at a stretching temperature of 250°C in the long side MD direction and a stretching speed of 28.7% / second. Next, the unfired PTFE film was stretched using a continuous stretching device capable of continuous clamping at a stretching temperature of 300°C in the width direction and a stretching speed of 88% / second. Finally, it was heat-fixed at 390°C. Through the above method, the air filter media of Example 21 was obtained.

[0277] In addition, the physical properties measured in the examples and comparative examples are described below.

[0278] (Mass per unit area of ​​fluoropolymer porous membrane)

[0279] The mass per unit area is defined as the mass (g) of a 4.0cm × 12.0cm rectangular sample measured on a precision balance, divided by the area (0.0048m²). 2 The value obtained.

[0280] (Thickness of the fluoropolymer porous membrane)

[0281] Using a film thickness gauge (1D-110MH type, manufactured by Mitutoyo Co., Ltd.), five test objects were overlapped and the overall film thickness was measured. The measured value was then divided by 5 to obtain the film thickness of one piece.

[0282] (Filling rate of fluoropolymer porous membrane)

[0283] The filling rate of the porous membrane is calculated using the following formula.

[0284] Filling rate (%) = (mass per unit area of ​​filter media) / (thickness of filter media) / (specific gravity of raw material) × 100

[0285] (Pore size of fluoropolymer porous membrane)

[0286] The mean flow pore size, as determined according to ASTM F316-86, is set as the pore size (mean flow path diameter) of the porous membrane. Actual measurements were performed using a Coulter barometer [manufactured by Coulter Electronics (UK)].

[0287] (Pressure loss)

[0288] The test sample of the air filter media was placed on a filter holder with a diameter of 100 mm. The inlet side was pressurized by a compressor, and the air flow rate was adjusted to 5.3 cm / s using a flow meter. Then, the pressure loss was measured using a pressure gauge.

[0289] (Dust storage capacity for polyalphaolefin particles: PHC)

[0290] The evaluation was conducted through a pressure loss rise test when polyalphaolefin (PAO) particles (liquid particles) flowed through the filter. Specifically, a differential pressure gauge (U-tube manometer) was used to continuously ventilate air containing PAO particles at a flow rate of 5.3 cm / s through an effective filter area of ​​50 cm². 2 The pressure loss of the sample filter material was measured over a period of time. When the pressure loss increased to 250 Pa, the dust storage capacity (g / m²) per unit area of ​​the filter material, representing the weight of PAO particles retained in the filter material, was calculated. 2 Furthermore, PAO particles (with a median diameter of 0.25 μm) produced by a Raskin nozzle were used, and the concentration of PAO particles was set to approximately 1 million to 6 million particles / cm³. 3 .

[0291] Regarding HEPA filter media, there is no defined dust storage capacity. However, it is recommended that in a typical HEPA unit, the initial pressure drop of the filter be set to approximately 250 Pa or less, and the filter replacement interval is generally defined as the point at which the pressure drop exceeds twice the initial pressure drop. Furthermore, the initial pressure drop of standard HEPA glass filter media is approximately 250–300 Pa. Therefore, the endpoint of the aforementioned test used to evaluate the dust storage capacity of air filter media is set at the point when the pressure drop rises to 250 Pa.

[0292] (PF value for polyalphaolefin particles with a particle diameter of 0.3 μm)

[0293] Using polyalphaolefin particles with a particle diameter of 0.3 μm, the PF value was calculated based on the pressure loss of the filter media and the collection efficiency (collection efficiency of polyalphaolefin particles with a particle diameter of 0.3 μm) according to the following formula.

[0294] PF value = {-log((100-Collection efficiency (%)) / 100)} / (Pressure loss (Pa) / 1000)

[0295] (Collection efficiency for polyalphaolefin (PAO) particles (liquid particles) with a particle diameter of 0.3 μm)

[0296] The collection efficiency was evaluated by passing polyalphaolefin (PAO) particles (liquid particles) through the filter and by a pressure loss rise test. The efficiency was assessed when air containing PAO particles was continuously ventilated at a flow rate of 5.3 cm / s through an effective filtration area of ​​50 cm². 2 When selecting the sample filter material, the collection efficiency was calculated based on the upstream concentration C1 and the downstream concentration C2 using the mathematical formula (1-C2) / C1×100. Furthermore, PAO particles (with a median diameter of 0.3 μm) generated by a Raskin nozzle were used, and the concentration of PAO particles was set to approximately 1 million to 6 million particles / cm³. 3 .

[0297] The physical properties of each layer and the whole of the fluoropolymer porous membrane, the first fluoropolymer porous membrane, the second fluoropolymer porous membrane, and the air filter media including these membranes (in the state of being set before the filter bag and air filter unit) of each embodiment and comparative example are shown in the table below. Here, “mass per unit area,” “thickness,” “fill rate,” and “pore size” in each table refer to physical properties related only to the “fluoropolymer porous membrane,” “first fluoropolymer porous membrane,” and “second fluoropolymer porous membrane,” while “pressure loss,” “PHC,” “PF value,” and “capture efficiency” refer to physical properties related to the air filter media further integrated with the ventilable support membrane.

[0298] (Table 1)

[0299]

[0300] (Table 2)

[0301]

[0302] (Table 3)

[0303]

[0304] (Table 4)

[0305]

[0306] (Table 5)

[0307]

[0308] (Table 6)

[0309]

[0310] (Table 7)

[0311]

[0312] (Table 8)

[0313]

[0314] (Table 9)

[0315]

[0316] [Air filter unit]

[0317] The air filter media of Example 21 described above was used and manufactured in the following manner. Figure 8 The air filter unit shown.

[0318] The air filter media of Example 21 is folded using a rotary folding machine, with outward and inward folds made every 260mm to create a serrated filter media. Then, corrugated aluminum spacers are inserted into the folds of the filter media from both the upwind and downwind sides to obtain a filter bag with a longitudinal dimension of 590mm × a transverse dimension of 590mm. The number of folds is 80. The resulting filter bag is then fixed to an aluminum frame with external dimensions of 610mm × 610mm (longitudinal × transverse), internal dimensions of 580mm × 580mm (longitudinal × transverse), and a depth of 290mm. The filter bag is then bonded and sealed to the frame using polyurethane adhesive to obtain... Figure 8 The shown is an interval-type air filter unit.

[0319] The pressure loss and collection efficiency of the air filter unit obtained in the above manner were measured in the following manner.

[0320] (Pressure loss of the air filter unit)

[0321] Place the air filter unit in a rectangular duct and adjust the airflow to achieve an air volume of 56m³. 3 / min, and pressure is measured using pressure gauges on the upstream and downstream sides of the air filter unit to obtain the pressure difference between the upstream and downstream sides as the pressure loss of the air filter unit.

[0322] (Air filter unit's capture efficiency)

[0323] Similar to the measurement of pressure loss in the air filter unit, the air filter unit was placed in a rectangular duct, and the airflow was adjusted to achieve an air volume of 56 m³ / h. 3 / min, PAO particles with a diameter of 0.3μm were introduced into the upstream side of the air filter unit. The concentration of PAO particles on the upstream and downstream sides of the air filter unit was measured using a light scattering particle counter. The collection efficiency of the air filter unit was calculated using the same mathematical formula as that used to calculate the collection efficiency of the filter media.

[0324] According to the above measurements, the pressure loss of the air filter unit made using the air filter media of Example 21 is 177 Pa, and the collection efficiency is 99.9995%.

[0325] The embodiments of this disclosure have been described above, but it should be understood that various changes in form and detail can be made without departing from the spirit and scope of this disclosure as set forth in the claims.

[0326] Symbol Explanation

[0327] 1. Air filter unit;

[0328] 20 filter packs;

[0329] 25. Frame;

[0330] 30. Air filter media;

[0331] 31. Fluoropolymer porous membrane;

[0332] 31a First fluoropolymer porous membrane (fluoropolymer porous membrane);

[0333] 31b Second fluoropolymer porous membrane (fluoropolymer porous membrane);

[0334] 33. Ventilation support membrane;

[0335] 34. Pre-collection membrane.

[0336] Existing technical documents

[0337] Patent documents

[0338] Patent document 1: Japanese Patent Application Publication No. 2001-170461.

Claims

1. An air filter media, characterized in that, The air filter media includes a fluoropolymer porous membrane, wherein the fluoropolymer porous membrane has a portion with a fill rate of less than 3.5%. The thickness of the portion with a fill rate of less than 3.5% is 45 μm or more. The air filter media is obtained by the following method of manufacturing air filter media, which includes the following steps: Prepare an unburnt film containing polytetrafluoroethylene; as well as The unfired thin film is extended along a first direction and then along a second direction orthogonal to the first direction to obtain a porous membrane. Before extending the unburned film along the first direction, the unburned film is heated for more than one minute at a temperature of 250°C to 325°C. Alternatively, the air filter media may be obtained by a method for manufacturing air filter media comprising the following steps: Prepare an unburnt film containing polytetrafluoroethylene; To extend the unfired film; as well as The unburned thin film is stretched in such a way that a portion is formed by stretching at a stretching speed of 30% / second or less in the stretching direction, thereby obtaining a porous film.

2. The air filter media as described in claim 1, characterized in that, The fluoropolymer porous membrane has a portion with a filler content of less than 2.5%. The thickness of the portion with a fill rate of less than 2.5% is 50 μm or more.

3. The air filter media as described in claim 1 or 2, characterized in that, Regarding air filter media, the pressure loss and collection efficiency determined by using polyalphaolefin particles with a particle diameter of 0.3 μm are PF values ​​of 17 or higher, which are determined by the following formula: PF value = {-log((100-collection efficiency (%)) / 100)} / (pressure loss (Pa) / 1000).

4. The air filter media as described in claim 1 or 2, characterized in that, Regarding the air filter media, when air comprising polyalphaolefin particles with a median diameter of 0.25 μm is continuously ventilated at a flow rate of 5.3 cm / s, resulting in a pressure loss increase of 250 Pa, the dust storage capacity of the polyalphaolefin particles is 30.0 g / m³. 2 above.

5. The air filter media as described in claim 1 or 2, characterized in that, Regarding the air filter media, the pressure loss when air flows through at a velocity of 5.3 cm / s is less than 200 Pa.

6. The air filter media as described in claim 1 or 2, characterized in that, The average pore size of the fluoropolymer porous membrane is greater than 2.5 μm.

7. The air filter media as described in claim 1 or 2, characterized in that, The fluoropolymer porous membrane comprises: A first fluoropolymer porous membrane, wherein the filling rate of the first fluoropolymer porous membrane is 3.5% or less, and the thickness of the first fluoropolymer porous membrane is 45 μm or more; and A second fluoropolymer porous membrane is disposed downstream of the first fluoropolymer porous membrane in the gas flow, and the filling rate of the second fluoropolymer porous membrane is greater than that of the first fluoropolymer porous membrane.

8. The air filter media as described in claim 1 or 2, characterized in that, The fluoropolymer porous membrane has at least one inclined density porous membrane, wherein the density of the gas flow downstream of the inclined density porous membrane is greater than the density of the gas flow upstream of the inclined density porous membrane.

9. The air filter media as described in claim 1 or 2, characterized in that, The fluoropolymer porous membrane is a membrane with a filling rate of less than 3.5% and a thickness of more than 45 μm.

10. The air filter media as described in claim 1 or 2, characterized in that, The air filter media further includes a pre-collection membrane, which is disposed upstream of the airflow relative to the fluoropolymer porous membrane. In the pre-collection membrane, The pressure loss when air flows through the pre-collection membrane at a velocity of 5.3 cm / s is between 15 Pa and 55 Pa. When air comprising polyalphaolefin particles with a diameter of 0.3 μm is passed through the pre-collecting membrane at a flow rate of 5.3 cm / s, the pre-collecting membrane has a collection efficiency of more than 25% and less than 80% for the polyalphaolefin particles. Using the pressure loss and capture efficiency obtained from polyalphaolefin particles with a particle diameter of 0.3 μm, the PF value is determined by the following formula: PF value = {-log((100-capture efficiency (%)) / 100)} / (pressure loss (Pa) / 1000).

11. The air filter media as described in claim 1 or 2, characterized in that, At least 3.5% of the fluoropolymer porous membrane contains modified polytetrafluoroethylene.

12. The air filter media as described in claim 1 or 2, characterized in that, The portion of the fluoropolymer porous membrane with a filling rate of at least 3.5% comprises fibrous polytetrafluoroethylene, a non-fibrous non-thermal-melt-processable component, and a non-fibrous but thermally-melt-processable component with a melting point of less than 320°C.

13. The air filter media as described in claim 1 or 2, characterized in that, The air filter media further includes a breathable support layer, which is disposed upstream and / or downstream of the airflow relative to the fluoropolymer porous membrane.

14. A filter bag, characterized in that, The filter pack includes the air filter media as described in claim 1 or 2. The air filter media is processed into a serrated shape formed by alternating outward and inward folds.

15. An air filter unit, characterized in that, include: The air filter media according to claim 1 or 2; as well as A frame for holding the air filter media.

16. A method for manufacturing a filter bag, characterized in that, Includes the following processes: The air filter material of claim 1 or 2 is processed into a sawtooth shape by alternating and repeating outward and inward folds.

17. A method for manufacturing an air filter unit, characterized in that, Includes the following processes: The air filter media as described in claim 1 or 2, or the filter pack obtained by the manufacturing method of the filter pack as described in claim 16, is held in the frame.

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