Air filter media

Abstract

The present invention provides an air filter material that can achieve good collection efficiency while keeping pressure loss to a minimum. [Solution] An air filter filter material (30a, 30b, 30c, 30d) having a porous membrane (31, 31a, 31b) having fibers, wherein the fiber density / geometric mean fiber diameter ratio in the porous membrane (31, 31a, 31b) is 1.9 or more and 4.2 or less.

Description

[Technical Field]

[0001] This disclosure relates to air filter media. [Background technology]

[0002] Conventionally, air filter media made of glass fibers have been widely used to capture dust and other particles in the air, but these have a high pressure loss.

[0003] In response to this, it has been proposed that, for example, by devising the manufacturing conditions, a polytetrafluoroethylene porous membrane with high collection efficiency and low pressure loss can be obtained, such as the air filter material described in Patent Document 1 (Japanese Patent Publication No. 10-030031). [Disclosure of the Invention] [Problems that the invention aims to solve]

[0004] However, further improvements are desired in air filter media to achieve good collection efficiency while keeping pressure loss low. [Means for solving the problem]

[0005] The air filter material relating to the first aspect is an air filter material having a porous membrane with fibers, wherein the ratio of fiber density / geometric mean fiber diameter to the geometric mean fiber diameter of the fibers in the porous membrane is 1.9 or more and 4.2 or less.

[0006] This air filter material allows for a low number of fibers used to capture a single target organism, thereby maintaining good collection efficiency while minimizing pressure loss.

[0007] The air filter material relating to the second aspect is the air filter material relating to the first aspect, wherein the geometric mean fiber diameter of the fibers in the porous membrane is 98 nm or larger.

[0008] This air filter media increases the structural strength of the filter media by increasing the fiber diameter of the porous membrane, while also suppressing clogging of the filter media because the distance between fibers can be easily widened.

[0009] The air filter material relating to the third aspect is an air filter material relating to either the first or second aspect, wherein the geometric mean fiber diameter of the fibers in the porous membrane is 199 nm or less.

[0010] This air filter material makes it possible to improve collection efficiency.

[0011] The air filter media relating to the fourth aspect is an air filter media relating to either the first or third aspect, and the fiber density in the porous membrane is 0.45 fibers / μm or less.

[0012] This air filter media is effective at reducing pressure loss.

[0013] The air filter media relating to the fifth perspective is an air filter media relating to any of the first, second, or fourth perspectives, and the fiber density in the porous membrane is 0.26 fibers / μm or more.

[0014] This air filter media makes it easy to improve collection efficiency.

[0015] The air filter material relating to the sixth perspective is an air filter material relating to any of the first, second, or fifth perspectives, and the porous membrane is a fluororesin porous membrane.

[0016] This air filter material can be made to have improved chemical resistance.

[0017] The air filter material relating to the seventh aspect is the air filter material relating to the sixth aspect, and the porous fluororesin membrane contains homo-PTFE and modified PTFE.

[0018] This air filter media is designed to minimize pressure loss while maintaining good collection efficiency.

[0019] The air filter filter medium according to the 8th aspect is the air filter filter medium according to either the 6th aspect or the 7th aspect, and for the fluororesin porous membrane, the pressure loss when air passes through at a flow rate of 5.3 cm / second, and the particle collection efficiency when air containing polyalphaolefin particles with a particle diameter of 0.1 μm passes through at a flow rate of 5.3 cm / second are used, and the PF value determined by the following formula: PF value = {-log((100 - collection efficiency (%)) / 100)} / (pressure loss (Pa) / 1000) is 35 or more.

[0020] This air filter filter medium can easily suppress the pressure loss while achieving good collection efficiency for collection targets with small particle diameters.

[0021] The air filter filter medium according to the 9th aspect is the air filter filter medium according to any one of the 6th to 8th aspects, and the geometric mean fiber diameter of the fibers in the fluororesin porous membrane is 117 nm or less.

[0022] This air filter filter medium can achieve good collection efficiency.

[0023] The air filter filter medium according to the 10th aspect is the air filter filter medium according to any one of the 6th to 9th aspects, and the filling rate in the fluororesin porous membrane is 1.4% or more and 4.0% or less.

[0024] This air filter filter medium can easily increase the PF value.

[0025] The air filter filter medium according to the 11th aspect is the air filter filter medium according to any one of the 6th to 10th aspects, and the basis weight of the fluororesin porous membrane is 1.1 g / m 2 or more.

[0026] This air filter filter medium can easily increase the collection efficiency.

[0027] The air filter filter medium according to the 12th aspect is the air filter filter medium according to any one of the 6th to 11th aspects, and the thickness of the fluororesin porous membrane is 19 μm or more.

[0028] This air filter media makes it easy to improve collection efficiency.

[0029] The air filter material relating to the 13th aspect is an air filter material relating to any of the 1st to 5th aspects, and the porous membrane is a polyolefin porous membrane.

[0030] Because this air filter material uses polyolefin, which has weaker bonds than carbon-fluorine bonds, it can reduce the environmental impact.

[0031] The air filter material relating to the 14th aspect is the same as the air filter material relating to the 13th aspect, and the polyolefin porous membrane has a PF value of 32 or more, which is determined by the following formula: PF value = {-log((100-collection efficiency (%)) / 100)} / (pressure loss (Pa) / 1000), using the pressure loss when air is passed through at a flow rate of 5.3 cm / second and the particle collection efficiency when air containing polyalphaolefin particles with a particle size of 0.1 μm is passed through at a flow rate of 5.3 cm / second.

[0032] This air filter media is designed to effectively capture small particles while minimizing pressure loss.

[0033] The air filter material relating to the 15th aspect is an air filter material relating to either the 13th or 14th aspect, wherein the geometric mean fiber diameter of the fibers in the polyolefin porous membrane is 120 nm or less.

[0034] This air filter material makes it possible to improve collection efficiency.

[0035] The air filter material relating to the 16th aspect is an air filter material relating to any of the 13th to 15th aspects, wherein the packing density of the polyolefin porous membrane is 4.0% or more and 8.0% or less.

[0036] This air filter media makes it easy to increase the PF value.

[0037] The air filter media relating to the 17th aspect is an air filter media relating to any of the 13th to the 16th aspect, and the basis weight of the polyolefin porous membrane is 0.8 g / m². 2 That's all.

[0038] This air filter media makes it easy to improve collection efficiency.

[0039] The air filter material relating to the 18th viewpoint is an air filter material relating to either the 13th viewpoint or the 17th viewpoint, and the thickness of the polyolefin porous membrane is 11 μm or more.

[0040] This air filter media makes it easy to improve collection efficiency. [Brief explanation of the drawing]

[0041] [Figure 1] This is a schematic cross-sectional view showing the layer structure of the air filter media 30a. [Figure 2] This is a schematic cross-sectional view showing the layer structure of the air filter media 30b. [Figure 3] This is a schematic cross-sectional view showing the layer structure of the air filter media 30c. [Figure 4] This is a schematic cross-sectional view showing the layer structure of the air filter media 30d. [Figure 5] This is a perspective view of the filter pack. [Figure 6] This is a perspective view of the air filter unit. [Figure 7] This graph shows the PF value for a particle size of 0.1 relative to the fiber density / geometric mean fiber diameter of a porous membrane. [Modes for carrying out the invention]

[0042] The following will explain an example of one embodiment of an air filter media.

[0043] (1) Air filter media The air filter media comprises a porous membrane containing fibers.

[0044] The air filter media may consist of a porous membrane laminated with, for example, a permeable support material as described below.

[0045] For example, as shown in Figure 1, the air filter media 30a may be constructed by stacking a permeable support material 21 and a porous membrane 31 in order in the direction of airflow. Here, the porous membrane 31 may be positioned either upstream or downstream of the permeable support material 21 in the airflow.

[0046] For example, as shown in Figure 2, the air filter media 30b may be configured such that the upstream permeable support material 21a, the porous membrane 31, and the downstream permeable support material 21b are stacked in order in the direction of airflow.

[0047] Furthermore, as shown in Figure 3, the air filter media 30c may be configured such that the upstream permeable support material 21a, the first porous membrane 31a, the second porous membrane 31b, and the downstream permeable support material 21b are stacked in order in the direction of airflow.

[0048] Furthermore, as shown in Figure 4, the air filter media 30d may be configured such that the upstream permeable support material 21a, the first porous membrane 31a, the intermediate permeable support material 21c, the second porous membrane 31b, and the downstream permeable support material 21b are stacked in order in the direction of airflow.

[0049] Furthermore, a pre-collection layer, which is a membrane with lower pressure loss and lower collection efficiency, may be provided upstream of the porous membrane 31 or the first porous membrane 31a.

[0050] The method of overlapping these films and materials is not particularly limited. They may be bonded by partial melting due to heating or by utilizing the anchoring effect of melting hot-melt resin, or they may be bonded using reactive adhesives, or they may simply be placed on top of each other.

[0051] Furthermore, the air filter media preferably has a particle collection efficiency of 95.0% or higher, more preferably 99.5% or higher, and even more preferably 99.95% or higher, when air containing polyalphaolefin (PAO) particles with a particle size of 0.1 μm is passed through it at a flow rate of 5.3 cm / second.

[0052] The air filter media preferably has a pressure loss of less than 250 Pa when air is passed through it at a flow velocity of 5.3 cm / second, more preferably less than 200 Pa, and may be between 30 Pa and 190 Pa.

[0053] (2) Porous membrane The air filter media comprises a porous membrane containing fibers.

[0054] The porous membrane has a fiber density / geometric mean fiber diameter ratio of 1.9 to 4.2. This reduces the amount of fiber that does not contribute well to the collection of the target material, thereby minimizing the decrease in collection efficiency while reducing pressure loss and increasing the PF value. Although there is a general tendency for the PF value to increase as the geometric mean fiber diameter decreases, using the above parameter obtained by dividing the fiber density by the geometric mean fiber diameter suppresses the influence of the geometric mean fiber diameter of the fibers in the porous membrane on the PF value. The fiber density / geometric mean fiber diameter ratio is more preferably 2.4 to 3.9, and even more preferably 2.5 to 3.8.

[0055] The geometric mean fiber diameter of the fibers in the porous membrane is preferably 98 nm or larger, and more preferably 110 nm or larger. This makes it possible to increase the structural strength of the porous membrane, and because the inter-fiber distance in the porous membrane tends to widen, clogging of the air filter media is suppressed.

[0056] In porous membranes, the geometric mean fiber diameter is preferably 199 nm or less. This makes it easier to increase the PF value of the porous membrane.

[0057] The geometric mean fiber diameter may also be calculated by randomly selecting 50 fibers from a scanning electron microscope image and using that as the geometric mean fiber diameter.

[0058] From the viewpoint of easily improving collection efficiency, the fiber density in the porous membrane is preferably 0.26 fibers / μm or more, and more preferably 0.35 fibers / μm or more. Furthermore, from the viewpoint of reducing pressure loss, the fiber density in the porous membrane is preferably 0.45 fibers / μm or less. The fiber density can be adjusted by, for example, heating the obtained porous membrane at a predetermined temperature to eliminate some of the fibers. Alternatively, the fiber density can also be adjusted by mixing components that are less likely to produce fibers with components that are more likely to produce fibers in the raw materials used to obtain the porous membrane, thereby adjusting the degree of fiber appearance.

[0059] From the viewpoint of easily improving collection efficiency, the packing density of the porous membrane is preferably 1.4% or more, and more preferably 2.0% or more. Furthermore, from the viewpoint of reducing pressure loss, the packing density of the porous membrane is preferably 8.0% or less.

[0060] For porous membranes, the basis weight is 0.80 g / m², from the perspective of maximizing collection efficiency. 2 The above is preferable. Furthermore, the basis weight of the porous membrane should be 4.0 g / m² from the viewpoint of reducing pressure loss. 2 Preferably, it is 2.0 g / m 2 The following is more preferable:

[0061] The thickness of the porous membrane is preferably 11 μm or more from the viewpoint of easily improving collection efficiency. Furthermore, the thickness of the porous membrane is preferably 150 μm or less, more preferably 100 μm or less, and even more preferably 50 μm or less from the viewpoint of reducing pressure loss.

[0062] Preferably, the porous membrane has a PF value of 32 or higher, which is determined by the following formula: PF value = {-log((100-collection efficiency (%)) / 100)} / (pressure loss (Pa) / 1000), using the pressure loss when air is passed through at a flow rate of 5.3 cm / second and the particle collection efficiency when air containing polyalphaolefin particles with a particle size of 0.1 μm is passed through at a flow rate of 5.3 cm / second. This porous membrane makes it easy to keep the pressure loss low while maintaining good collection efficiency for targets with small particle sizes.

[0063] The pressure loss in the porous membrane is preferably 200 Pa or less, more preferably 170 Pa or less, and even more preferably 150 Pa or less.

[0064] For porous membranes, the particle collection efficiency when air containing polyalphaolefin particles with a particle size of 0.1 μm is passed through at a flow rate of 5.3 cm / second is preferably 99% or higher, more preferably 99.9% or higher, and even more preferably 99.95% or higher. The relationship between collection efficiency and transmittance is as follows: Collection efficiency (%) = 100 (%) - Transmittance (%).

[0065] Furthermore, from the viewpoint of suppressing clogging of the porous membrane by ensuring a large number of voids inside the porous membrane, it is preferable that the thickness of the porous membrane is 12 μm or more and the pressure loss is 200 Pa or less.

[0066] The fibers of the porous membrane described above are not particularly limited, but fluororesin porous membranes, polyolefin porous membranes, and the like are preferred.

[0067] (3) Fluoropolymer porous membrane The porous fluororesin membrane preferably mainly contains a fluororesin such as PTFE (polytetrafluoroethylene). Here, "mainly" means that if multiple components are present, the fluororesin is the most abundant component. This improves the chemical resistance of the filter material. The mass percentage of fluororesin fibers in the porous fluororesin membrane may be, for example, 50% by mass or more, preferably 90% by mass or more, and more preferably 99% by mass or more. The porous fluororesin membrane may consist only of fluororesin fibers.

[0068] The geometric mean fiber diameter of the fibers in the porous fluororesin film is preferably 199 nm or less, more preferably 119 nm or less, and even more preferably 117 nm or less. This makes it easier to increase the PF value of the porous fluororesin film.

[0069] From the viewpoint of easily improving collection efficiency, the packing density of the porous fluororesin membrane is preferably 1.4% or more, and more preferably 2.0% or more. From the viewpoint of reducing pressure loss, the packing density of the porous fluororesin membrane is preferably 4.0% or less.

[0070] The basis weight of the porous fluororesin film is 1.1 g / m², chosen from the viewpoint of easily improving collection efficiency. 2 Preferably, it should be 1.3 g / m 2 It is more preferable that the above conditions are met.

[0071] From the viewpoint of easily improving collection efficiency, the thickness of the porous fluororesin film is preferably 19 μm or more.

[0072] The porous fluororesin membrane preferably has a PF value of 35 or higher, and more preferably 40 or higher, determined by the following formula: PF value = {-log((100-collection efficiency (%)) / 100)} / (pressure loss (Pa) / 1000), using the pressure loss when air is passed through at a flow rate of 5.3 cm / second and the particle collection efficiency when air containing polyalphaolefin particles with a particle size of 0.1 μm is passed through at a flow rate of 5.3 cm / second. This porous fluororesin membrane makes it easy to keep the pressure loss low while maintaining good collection efficiency for targets with small particle sizes.

[0073] Furthermore, from the viewpoint of suppressing clogging of the porous fluororesin membrane by ensuring a large number of voids inside the porous fluororesin membrane, it is preferable that the thickness of the porous fluororesin membrane is 19 μm or more and the pressure loss is 170 Pa or less.

[0074] The porous fluororesin membrane preferably has a porous membrane structure that includes the aforementioned fibers, and has fibrils (fibers) (not shown) and nodes (knots) connected to the fibrils.

[0075] In addition, components that differ from the fluororesin in a porous fluororesin film include, for example, inorganic fillers, which are non-fusible, non-fiberizable components (component B) described later.

[0076] The fluororesin used in the porous fluororesin membrane may consist of one component or two or more components. An example of a fluororesin consisting of two or more components is a mixture of three components: fibrous PTFE (hereinafter also referred to as component A), a non-fibrous, non-thermally processable component (hereinafter also referred to as component B), and a non-fibrous, heat-melt processable component with a melting point of less than 320°C (hereinafter also referred to as component C). Preferably, the porous fluororesin membrane consists of a combination of these three components. Compared to a porous PTFE (high molecular weight PTFE) membrane, a porous fluororesin membrane composed of these three components has a larger void structure and a thicker film thickness, allowing it to capture fine particles in the gas over a wider area in the thickness direction of the filter material, thereby improving dust retention. By composing the porous fluororesin membrane from these three components, it becomes possible to particularly increase the dust retention capacity of liquid particles compared to solid particles.

[0077] The following provides a more detailed explanation of the three ingredients mentioned above.

[0078] (3-1) Component A: PTFE that can be converted into fiber PTFE that can be fiberized is, for example, high molecular weight PTFE obtained from emulsion polymerization or suspension polymerization of tetrafluoroethylene (TFE). Here, high molecular weight means a molecular weight that is easily fiberized during stretching when creating a porous fluororesin film, yields long fibrils, has a standard specific gravity (SSG) of 2.130 to 2.230, and does not substantially melt and flow due to its high melt viscosity. From the viewpoint of easy fiberization and obtaining long fibrils, the SSG of fiberized PTFE is preferably 2.130 to 2.190, and more preferably 2.140 to 2.170. If the SSG is too high, the stretchability of the mixture of components A to C may deteriorate, and if the SSG is too low, the rollability may deteriorate, the homogeneity of the porous fluororesin film may deteriorate, and the pressure drop of the porous fluororesin film may increase. Furthermore, from the viewpoint of easy fiberization and obtaining long fibrils, PTFE obtained by emulsion polymerization is preferred. Standard specific gravity (SSG) is measured in accordance with ASTM D 4895.

[0079] Whether or not a material is fibrous, that is, whether or not it can be formed into fibers, can be determined by whether or not paste extrusion, a typical method for molding high molecular weight PTFE powder made from TFE polymers, is possible. Paste extrusion is usually possible because high molecular weight PTFE has fibrous properties. If an unfired molded body obtained by paste extrusion has no substantial strength or elongation, for example, if the elongation is 0% and it breaks when pulled, it can be considered that it is not fibrous.

[0080] The above-mentioned high molecular weight PTFE may be modified polytetrafluoroethylene (hereinafter referred to as modified PTFE), homopolytetrafluoroethylene (hereinafter referred to as homoPTFE), or a mixture of modified PTFE and homoPTFE. Homo-PTFE is not particularly limited, and any homo-PTFE disclosed in Japanese Patent Publication No. 53-60979, Japanese Patent Publication No. 57-135, Japanese Patent Publication No. 61-16907, Japanese Patent Publication No. 62-104816, Japanese Patent Publication No. 62-190206, Japanese Patent 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., can be suitably used. Among these, homo-PTFE disclosed in Japanese Patent Publication No. 57-135, Japanese Patent 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. 2010 / 113950, etc., which have high stretchability, is preferred.

[0081] Modified PTFE consists of TFE and monomers other than TFE (hereinafter referred to as modified monomers). Modified PTFE can be uniformly modified by the modified monomer, modified in the early stages of the polymerization reaction, or modified in the final stages of the polymerization reaction, but is not limited to these. Modified PTFE can preferably be those disclosed in, for example, Japanese Patent Publication No. 60-42446, Japanese Patent Publication No. 61-16907, Japanese Patent Publication No. 62-104816, Japanese Patent Publication No. 62-190206, Japanese Patent Publication No. 64-1711, Japanese Patent Publication No. 2-261810, Japanese Patent Publication No. 11-240917, Japanese Patent Publication No. 11-240918, International Publication Brochure No. 2003 / 033555, International Publication Brochure No. 2005 / 061567, International Publication Brochure No. 2007 / 005361, International Publication Brochure No. 2011 / 055824, International Publication Brochure No. 2013 / 027850, etc. Among these, modified PTFE disclosed in Japanese Patent Publication No. 61-16907, Japanese Patent Publication No. 62-104816, Japanese Patent Publication No. 64-1711, Japanese Patent Publication No. 11-240917, International Publication No. 2003 / 033555, International Publication No. 2005 / 061567, International Publication No. 2007 / 005361, International Publication No. 2011 / 055824, etc., which have high stretchability, is preferred.

[0082] Modified PTFE contains TFE units based on TFE and modified monomer units based on modified monomers. Modified monomer units are a part of the molecular structure of modified PTFE that originates from the modified monomer. Modified PTFE preferably contains 0.001 to 0.500% by weight of modified monomer units, and more preferably 0.01 to 0.30% by weight of total monomer units. Total monomer units are the parts of the molecular structure of modified PTFE that originate from all monomers.

[0083] The modified monomer is not particularly limited as long as it can copolymerize with TFE, and examples include perfluoroolefins such as hexafluoropropylene (HFP); chlorofluoroolefins such as chlorotrifluoroethylene (CTFE); hydrogen-containing fluoroolefins such as trifluoroethylene and vinylidene fluoride (VDF); perfluorovinyl ether; perfluoroalkylethylene (PFAE); ethylene, etc. One or more modified monomers may be used.

[0084] Perfluorovinyl ethers are not particularly limited and include, for example, perfluorounsaturated compounds represented by the following general formula (1). CF2 = CF - ORf ... (1) In the formula, Rf represents a perfluoroorganic group.

[0085] In this specification, a perfluoroorganic group is an organic group in which all hydrogen atoms bonded to a carbon atom are replaced with fluorine atoms. The above perfluoroorganic group may have an ether oxygen.

[0086] Examples of perfluorovinyl ethers include perfluoro(alkyl vinyl ether) (PAVE) in which Rf in the above general formula (1) is a perfluoroalkyl group having 1 to 10 carbon atoms. The number of carbon atoms in the perfluoroalkyl group is preferably 1 to 5. Examples of perfluoroalkyl groups in PAVE include perfluoromethyl group, perfluoroethyl group, perfluoropropyl group, perfluorobutyl group, perfluoropentyl group, and perfluorohexyl group. Perfluoropropyl vinyl ether (PPVE) and perfluoromethyl vinyl ether (PMVE) are preferred PAVEs.

[0087] The perfluoroalkylethylene (PFAE) mentioned above is not particularly limited and includes, for example, perfluorobutylethylene (PFBE), perfluorohexylethylene (PFHE), and the like.

[0088] In modified PTFE, the modified monomer is preferably at least one selected from the group consisting of HFP, CTFE, VDF, PAVE, PFAE, and ethylene.

[0089] Homo-PTFE is preferably included in more than 50% by weight of the PTFE that can be fiberized, particularly from the viewpoint of being easily fiberized and yielding fibrils with long fiber lengths.

[0090] Furthermore, the PTFE that can be formed into fibers may be a combination of several of the above-mentioned components.

[0091] From the viewpoint of maintaining the fibrous structure of the porous fluororesin membrane, it is preferable that the amount of PTFE that can be formed into fibers exceeds 50% by weight of the porous fluororesin membrane.

[0092] (3-2) Component B: Non-thermal melt-processable component that does not form fibers The non-fiber-forming, non-thermal-meltable components are mainly distributed as non-fiber particles in the knots, and they work to suppress the fiber formation of PTFE that can be fiberized.

[0093] Examples of non-thermal melt-processable components that do not form fibers include thermoplastic components such as low molecular weight PTFE, thermosetting resins, inorganic fillers, and mixtures thereof.

[0094] Thermoplastic components are preferably those with a melting point of 320°C or higher and a high melt viscosity. For example, low molecular weight PTFE has a high melt viscosity, so it can remain in the knots even when processed at temperatures above its melting point. In this specification, low molecular weight PTFE refers to a number average molecular weight of 600,000 or less, a melting point of 320°C to 335°C, and a melt viscosity at 380°C of 100 Pa·s to 7.0 × 10⁻⁶. 5 It is Pa·s PTFE (see Japanese Patent Publication No. 10-147617).

[0095] Methods for producing low molecular weight PTFE include a method of thermal decomposition by contact reaction at high temperature between high molecular weight PTFE powder (molding powder) obtained from suspension polymerization of TFE or high molecular weight PTFE powder (fine powder) obtained from emulsion polymerization of TFE and a specific fluoride (see Japanese Patent Publication No. 61-162503), a method of irradiating the above high molecular weight PTFE powder or molded body with ionizing radiation (see Japanese Patent 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.). Low molecular weight PTFE may be homo-PTFE, similar to PTFE that can be formed into fibers, or it may be modified PTFE containing the aforementioned modified monomer.

[0096] Low molecular weight PTFE does not fibrousize. The presence or absence of fibrous properties can be determined by the method described above. Unfired molded bodies obtained by paste extrusion of low molecular weight PTFE have virtually no strength or elongation; for example, they have 0% elongation and will break when pulled.

[0097] The low molecular weight PTFE is not particularly limited, but it is preferably such that its melt viscosity at 380°C is 1000 Pa·s or higher, more preferably 5000 Pa·s or higher, and even more preferably 10000 Pa·s or higher. When the melt viscosity is high in this way, even if the heat-melt processable component that does not fiberize as component C melts during the production of the porous fluororesin film, the non-heat-melt processable component that does not fiberize can remain in the knots, thereby suppressing fiberization.

[0098] Examples of thermosetting resins include epoxy, silicone, polyester, polyurethane, polyimide, phenol, and mixtures thereof. From the viewpoint of ease of co-coagulation (described later), thermosetting resins dispersed in water in an uncured state are preferably used. All of these thermosetting resins are available commercially.

[0099] Examples of inorganic fillers include talc, mica, calcium silicate, glass fibers, calcium carbonate, magnesium carbonate, carbon fibers, barium sulfate, calcium sulfate, and mixtures thereof. Among these, talc is preferred due to its affinity and specific gravity with high molecular weight PTFE that can be formed into fibers. From the viewpoint of forming a stable dispersion during the production of porous fluororesin films, inorganic fillers with a particle size of 3 μm to 20 μm are preferred. The particle size is the average particle size and is measured by laser diffraction / scattering. All of these inorganic fillers can be obtained commercially.

[0100] Furthermore, the non-fusible, non-fiber-forming components may be a combination of several of the above-mentioned components.

[0101] The non-fiber-forming, non-heat-melt-processable component is preferably contained in the porous fluororesin film at an amount of 1% to 50% by weight. A content of 50% or less of the non-fiber-forming, non-heat-melt-processable component makes it easier to maintain the fibrous structure of the porous fluororesin film. The non-fiber-forming, non-heat-melt-processable component is preferably contained at an amount of 20% to 40% by weight, and more preferably at 30% by weight. A content of 20% to 40% by weight more effectively suppresses the fiber formation of PTFE that may undergo fiber formation.

[0102] (3-3) Component C: A heat-meltable component with a melting point of less than 320°C that does not form fibers. Non-fiber-forming, heat-melt-processable components with a melting point of less than 320°C (hereinafter also referred to as non-fiber-forming, heat-melt-processable components) have fluidity when melted, allowing them to melt during the manufacturing (stretching) of the porous fluororesin film and solidify at the knots, thereby increasing the overall strength of the porous fluororesin film and suppressing deterioration of filter performance even if it is compressed in subsequent processes.

[0103] The non-fibrous, heat-melt-processable component preferably exhibits a melt viscosity of less than 10,000 Pa·s at 380°C. The melting point of the non-fibrous, heat-melt-processable component is defined as the peak of the heat of fusion curve obtained by heating the material to above its melting point at a rate of 10°C / min using a differential scanning calorimeter (DSC), completely melting it once, cooling it to below its melting point at 10°C / min, and then heating it again at 10°C / min.

[0104] Examples of heat-meltable components that do not form fibers include heat-meltable fluoropolymers, polystyrene, polyethylene terephthalate (PET), polyester, polyamide, and other resins, or mixtures thereof, that can sufficiently exhibit meltability and fluidity at the stretching temperature during the production of porous fluororesin films. Among these, heat-meltable fluoropolymers are preferred due to their excellent heat resistance at the stretching temperature during the production of porous fluororesin films and their excellent chemical resistance. Heat-meltable fluoropolymers are given by the following general formula (2) RCF = CR2 ···(2) Examples of fluoropolymers include those comprising copolymer units derived from at least one fluorinated ethylenically unsaturated monomer represented by the formula (wherein R is independently selected from H, F, Cl, an alkyl group with 1 to 8 carbon atoms, an aryl group with 6 to 8 carbon atoms, a cyclic alkyl group with 3 to 10 carbon atoms, and a perfluoroalkyl group with 1 to 8 carbon atoms. In this case, all R may be the same, any two R may be the same and the remaining R may be different from the others, or all R may be different from each other.) preferably two or more monomers.

[0105] Useful examples of compounds represented by general formula (2) include, but are not limited to, perfluoroolefins such as fluoroethylene, VDF, trifluoroethylene, TFE, and HFP; chlorofluoroolefins such as CTFE and dichlorodifluoroethylene; (perfluoroalkyl)ethylenes such as PFBE and PFHE; perfluoro-1,3-dioxole and mixtures thereof.

[0106] Furthermore, the fluoropolymer comprises at least one monomer represented by the above general formula (2), The above general formula (1) and / or the following general formula (3) R2C = CR2···(3) This may also include copolymers derived from copolymerization with at least one copolymerizable comonomer represented by (wherein R is independently selected from H, Cl, an alkyl group with 1 to 8 carbon atoms, an aryl group with 6 to 8 carbon atoms, and a cyclic alkyl group with 3 to 10 carbon atoms. In this case, all R may be the same, or two or more R may be the same and these two or more R may be different from the remaining R, or all R may be different from each other. If there are multiple other R, they may be different from each other.)

[0107] A useful example of a compound represented by general formula (1) is perfluoro(alkyl vinyl ether) (PAVE). Preferred PAVEs include perfluoropropyl vinyl ether (PPVE) and perfluoromethyl vinyl ether (PMVE).

[0108] Useful examples of compounds represented by general formula (3) include ethylene and propylene.

[0109] More specific examples of fluoropolymers include polyfluoroethylene derived from the polymerization of fluoroethylene, 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 of the above general formula (2) and at least one monomer represented by the above general formula (1) and / or at least one monomer represented by the above general formula (3).

[0110] Examples of such polymers include polymers having copolymer units derived from VDF and hexafluoropropylene (HFP), and polymers derived from TFE and at least one copolymerizable comonomer other than TFE (at least 3% by weight). Examples of the latter type of fluoropolymers include TFE / PAVE copolymer (PFA), TFE / PAVE / CTFE copolymer, TFE / HFP copolymer (FEP), TFE / ethylene copolymer (ETFE), TFE / HFP / ethylene copolymer (EFEP), TFE / VDF copolymer, TFE / VDF / HFP copolymer, TFE / VDF / CTFE copolymer, etc., or mixtures thereof.

[0111] Furthermore, the heat-meltable components that do not form fibers may be a combination of several of the above-mentioned components.

[0112] The content of the non-fibrous, heat-melt-processable component in the porous fluororesin membrane is preferably 0.1% by weight or more and less than 20% by weight. A content of less than 20% by weight prevents the non-fibrous, heat-melt-processable component from dispersing to areas other than the knots within the porous fluororesin membrane, thus suppressing increased pressure loss. Furthermore, a content of less than 20% by weight facilitates stretching at high expansion ratios of 40 times or more, as described later. A content of 0.1% by weight or more of the non-fibrous, heat-melt-processable component in the porous fluororesin membrane helps to sufficiently suppress deterioration of the filter performance of the porous fluororesin membrane even if compressive force is applied in subsequent processes. The content of the non-fibrous, heat-melt-processable component in the porous fluororesin membrane is preferably 15% by weight or less, and more preferably 10% by weight or less. Furthermore, from the viewpoint of ensuring the strength of the porous fluororesin membrane, the content of the non-fibrous, heat-melt-processable component in the porous fluororesin membrane is preferably 0.5% by weight or more. In particular, a concentration of approximately 5% by weight is preferred.

[0113] The content of heat-melt-processable components that do not form fibers is preferably 10% by weight or less in order to ensure good stretching at an elongation area ratio of 40 to 800 times.

[0114] In the porous fluororesin membrane composed of the three components described above, the fibrils mainly consist of component A, and the nodal regions consist of components A to C. These nodal regions are formed relatively large within the porous fluororesin membrane, thereby forming a thick porous fluororesin membrane. Furthermore, because these nodal regions contain a heat-meltable component that does not become fibrous, they are relatively rigid and act like pillars supporting the porous fluororesin membrane in the thickness direction. Therefore, even if the membrane is subjected to compressive forces in the thickness direction during subsequent processes such as lamination of breathable support materials or pleating described later, it is possible to suppress a decrease in the filter performance of the porous fluororesin membrane.

[0115] (4) Polyolefin porous membrane The polyolefin porous membrane preferably mainly contains polyolefin. This allows for the use of a polyolefin porous membrane, which has weaker bonds than carbon-fluorine bonds, as the porous membrane in the air filter media, thereby reducing the environmental burden.

[0116] Polyolefin porous membranes are not limited to those in which all components are composed of 100 wt% polyolefins (i.e., those composed solely of polyolefins). The mass percentage of polyolefins in a polyolefin porous membrane is, for example, 60 wt% or more, preferably 80 wt% or more, more preferably 90 wt% or more, and even more preferably 95 wt% or more.

[0117] Polyolefin is more preferable than polyester resins such as PET (polyethylene terephthalate) from the viewpoints of being easily able to reduce the average fiber diameter and being easily able to improve chemical resistance. Here, the chemical resistance may be, for example, that the performance is maintained well even in an environment where hydrofluoric acid (HF) exists. In addition, the antistatic treatment may be, for example, a treatment in accordance with the description of JIS B 9908-4:2019. Further, polyolefin is more preferable than SBS-based resins (Styrene-Butadiene-Styrene) and ES-based resins (Ethylene-Styrene) from the viewpoint of being easily able to reduce the average fiber diameter.

[0118] The polyolefin porous membrane may contain polyolefin fibers, and may be polypropylene fibers, polybutene fibers, polyethylene fibers, ethylene-propylene copolymer fibers, and mixed fibers thereof among others. Among them, as the polyolefin fibers, polyethylene fibers are preferable from the viewpoint of being easily able to obtain finer ones as the average fiber diameter.

[0119] The polyolefin porous membrane is preferably a stretched porous membrane of a polyolefin film. By stretching the polyolefin film in a direction intersecting the thickness, it is easy to generate relatively thin fibers from the crystals.

[0120] Examples of the polyolefin film include those having a melting point of 105°C to 115°C and a density of 0.92 g / cm 3 the following LDPE (low density polyethylene), those having a melting point of 125°C to 135°C and a density of 0.94 g / cm 3 or more of HDPE (high density polyethylene), those having a melting point of 120°C to 125°C and a density of 0.92 g / cm 3 or less of LLDPE (linear low density polyethylene), those having a melting point of 130°C to 138°C and a density of 0.94 g / cm 3Examples include UHMWPE (ultra-high molecular weight polyethylene) as described above. Furthermore, from the viewpoint of improving moldability and strength, it is preferable that the polyolefin film be a mixture of UHMWPE (ultra-high molecular weight polyethylene) with one or more of LDPE (low-density polyethylene), HDPE (high-density polyethylene), and LLDPE (linear low-density polyethylene).

[0121] The porosity of the polyolefin film is preferably, for example, 55% to 70%.

[0122] The thickness of the polyolefin film is preferably, for example, 10.0 μm or more and 150 μm or less, and more preferably 30.0 μm or more and 120.0 μm or less.

[0123] The average pore size of the polyolefin film is preferably, for example, 10 μm or more and 80 μm or less.

[0124] The weight-average molecular weight Mw of a polyolefin film is, for example, 3.0 × 10⁻⁶. 5 The above 300.0 × 10 5 The following is preferable. The weight-average molecular weight Mw may be a value obtained by, for example, GPC (gel permeation chromatography).

[0125] Polyolefin films may be obtained by, for example, a dry film-forming method or a wet film-forming method. In the wet film-forming method, a polyolefin film is obtained by stretching a mixture of polyolefin and a volatile or non-volatile solvent, whereas in the dry film-forming method, a polyolefin film is obtained by stretching polyolefin in the absence of a volatile or non-volatile solvent. Here, from the viewpoint of easily increasing the porosity and making the structure uniform, it is preferable that the polyolefin film is obtained by a wet film-forming method. As an example of a dry film-forming method, a method may be used in which pelletized polyethylene and a volatile agent such as an aromatic hydrocarbon such as decalin are melt-kneaded, extruded, cooled and crystallized, and then heated to dry and remove the solvent. As an example of a wet film-forming method, a method may be used in which pelletized polyethylene and a non-volatile solvent such as liquid paraffin are melt-kneaded, extruded and cooled and crystallized, the non-volatile solvent is removed by a known washing method, dried, and further stretched as necessary.

[0126] The geometric mean fiber diameter of the fibers in the polyolefin porous membrane is preferably 199 nm or less, more preferably 120 nm or less, and even more preferably 119 nm or less. This makes it easier to increase the PF value of the polyolefin porous membrane.

[0127] From the viewpoint of easily improving collection efficiency, the packing density of the polyolefin porous membrane is preferably 4.0% or more, and more preferably 4.5% or more. From the viewpoint of reducing pressure loss, the packing density of the polyolefin porous membrane is preferably 8.0% or less, and more preferably 7.5% or less.

[0128] For porous polyolefin membranes, the basis weight is 0.80 g / m², from the viewpoint of easily improving collection efficiency. 2 Preferably, it is 0.85 g / m 2 It is more preferable that the above conditions are met.

[0129] The thickness of the polyolefin porous membrane is preferably 11.0 μm or more, and more preferably 12.0 μm or more, from the viewpoint of easily improving collection efficiency.

[0130] The polyolefin porous membrane preferably has a PF value of 32 or higher, and more preferably 33 or higher, determined by the following formula: PF value = {-log((100-collection efficiency (%)) / 100)} / (pressure loss (Pa) / 1000), using the pressure loss when air is passed through at a flow rate of 5.3 cm / second and the particle collection efficiency when air containing polyalphaolefin particles with a particle size of 0.1 μm is passed through at a flow rate of 5.3 cm / second. This polyolefin porous membrane makes it easy to keep the pressure loss low while maintaining good collection efficiency for targets with small particle sizes.

[0131] Furthermore, from the viewpoint of suppressing clogging of the polyolefin porous membrane by ensuring a large number of voids inside the polyolefin porous membrane, it is preferable that the thickness of the polyolefin porous membrane is 12 μm or more and the pressure loss is 200 Pa or less.

[0132] (5) Breathable support material Even if the porous membrane is thin or otherwise difficult to support on its own, the breathable support material can support the porous membrane, making it possible to make the porous membrane stand upright.

[0133] The material and structure of the breathable support material are not particularly limited, but examples include nonwoven fabrics, woven fabrics, metal meshes, and resin nets. Among these, nonwoven fabrics with heat-sealing properties are preferred in terms of strength, collection ability, flexibility, and workability. Preferred nonwoven fabrics include nonwoven fabrics in which some or all of the constituent fibers have a core / sheath structure, two-layer nonwoven fabrics consisting of two layers: a layer of fibers made of a low-melting-point material and a layer of fibers made of a high-melting-point material, and nonwoven fabrics on which a heat-sealing resin is coated on the surface. Examples of such nonwoven fabrics include spunbond nonwoven fabrics. Furthermore, for nonwoven fabrics with a core / sheath structure, it is preferable that the core component has a higher melting point than the sheath component. For example, combinations of core / sheath materials include PET / PE and high-melting-point polyester / low-melting-point polyester. Examples of low-melting-point / high-melting-point material combinations for two-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 a heat-sealable resin on their surface include PET nonwoven fabric coated with EVA (ethylene vinyl acetate copolymer resin) and PET nonwoven fabric coated with an olefin resin.

[0134] The material of the nonwoven fabric is not particularly limited, and polyolefins (PE, PP, etc.), polyamides, polyesters (PET, etc.), aromatic polyamides, or composites thereof can be used.

[0135] The breathable support material can be joined to the porous membrane by heating, by melting a portion of the breathable support material, by melting a hot-melt resin, by utilizing the anchoring effect, or by using adhesive such as a reactive adhesive.

[0136] Compared to the porous membrane described above, the breathable support material has extremely low pressure loss, collection efficiency, and dust retention capacity. The pressure loss and collection efficiency may be 5% or less of those of the porous membrane, and may even be considered substantially zero.

[0137] The pressure loss of the permeable support material is preferably 10 Pa or less, and more preferably 5 Pa or less. The collection efficiency of NaCl particles with a diameter of 0.1 μm in the permeable support material may be considered to be substantially 0 or nearly 0.

[0138] Furthermore, the thickness of the breathable support material is preferably 0.3 mm or less, and more preferably 0.25 mm or less.

[0139] Furthermore, the basis weight of the breathable support material is, for example, 20 g / m². 2 More than 50g / m 2 The following is preferable:

[0140] (6) Examples of Uses Air filter media are used in applications such as the following: Fields such as ULPA filters (Ultra low Penetration Air Filters) (for semiconductor manufacturing), HEPA filters (for hospitals and semiconductor manufacturing), cylindrical cartridge 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® filters (for industrial use), catalytic filters (for exhaust gas treatment), adsorbent filters (for HDD integration), adsorbent vent filters (for HDD integration), vent filters (for HDD integration, etc.), vacuum cleaner filters (for vacuum cleaners), general-purpose multi-layer felt materials, gas turbine cartridge filters (for compatible products for gas turbines), cooling filters (for electronic equipment housings), etc. Freeze-drying materials such as containers for freeze-drying; ventilation materials for automobiles, including electronic circuits and lamps; container applications such as container caps; protective ventilation applications for electronic equipment; and ventilation / internal pressure regulation applications such as medical ventilation; Liquid filtration fields such as semiconductor liquid filtration filters (for semiconductor manufacturing), hydrophilic filters (for semiconductor manufacturing), chemical filters (for chemical treatment), filters for pure water production lines (for pure water production), and backwash type liquid filtration filters (for industrial wastewater treatment).

[0141] Air filter media are particularly preferably used in food processing plants, pharmaceutical factories, clean rooms, or air purifiers.

[0142] Furthermore, air filter media are most effective when used in environments where mold growth is a particular concern. For example, air filter media are preferably used in environments with a relative humidity of 60% or higher, more preferably in environments with a temperature of 20 degrees Celsius or higher and a relative humidity of 60% or higher, and even more preferably in environments with a temperature of 25 degrees Celsius or higher and a relative humidity of 70% or higher.

[0143] (7) Filter pack Next, we will explain the filter pack with reference to Figure 5.

[0144] Figure 5 is an external perspective view of the filter pack 20.

[0145] The filter pack 20 is equipped with the air filter media described above (for example, air filter media 30a to 30d, etc.). The air filter media of the filter pack 20 is a processed filter media that has been processed into a zigzag shape (pleated) by alternating mountain folds and valley folds. The pleating can be done, for example, by a rotary folding machine. The folding width of the filter media is not particularly limited, but is for example between 25 mm and 280 mm. Because the filter pack 20 is pleated, the folding area of ​​the filter media when used in an air filter unit can be increased, thereby making it possible to obtain an air filter unit with high collection efficiency.

[0146] The filter pack 20 may further include spacers (not shown) for maintaining the pleat spacing when used in an air filter unit, in addition to the air filter media. The material of the spacers is not particularly limited, but hot melt resin can be preferably used.

[0147] (8) Air filter unit Next, the air filter unit 1 will be described with reference to Figure 6.

[0148] Figure 6 is an external perspective view of the air filter unit 1.

[0149] The air filter unit 1 comprises the air filter material or filter pack described above, and a frame 25 that holds the air filter material or filter pack. In other words, the air filter unit may be manufactured so that the air filter material, which is not folded in a mountain or valley pattern, is held in the frame, or so that the filter pack 20 is held in the frame 25. The air filter unit 1 shown in Figure 6 is manufactured using the filter pack 20 and the frame 25.

[0150] The frame 25 is made, for example, by combining sheet metal or by molding resin, and the space between the filter pack 20 and the frame 25 is preferably sealed with a sealant. The sealant is for preventing leakage between the filter pack 20 and the frame 25, and for example, a resin such as epoxy, acrylic, or urethane is used.

[0151] The air filter unit 1, comprising a filter pack 20 and a frame 25, may be a mini-pleated type air filter unit in which one flat, extending filter pack 20 is housed inside the frame 25, or it may be a V-bank type air filter unit or a single-header type air filter unit in which multiple flat, extending filter packs are arranged and held in the frame. [Examples]

[0152] The contents of this disclosure will be specifically explained below with reference to examples and comparative examples.

[0153] (Example 1) For Example 1, an air filter media with the configuration shown in Figure 2 was prepared.

[0154] Specifically, the upstream breathable support material 21a and the downstream breathable support material 21b are both spunbond nonwoven fabrics made of fibers with a core / sheath structure using PET as the core and PE as the sheath (average fiber diameter 20 μm, basis weight 40 g / m²). 2 A material with a thickness of 0.2 mm was used. Furthermore, the porous membrane 31 sandwiched between the upstream permeable support material 21a and the downstream permeable support material 21b was obtained by the following process.

[0155] As the FP raw material for the porous membrane used in the air filter media of Example 1, a mixed powder was used, which consisted of a fine powder of perfluoroalkyl vinyl ether-modified polytetrafluoroethylene (manufactured by Daikin Industries, Ltd., product name: F302), a copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether, and a fine powder of polytetrafluoroethylene with an average molecular weight of 6.5 million (manufactured by Daikin Industries, Ltd., product name: F106), mixed in a weight ratio of 75:25, and 24 parts by weight of an extrusion aid (liquid lubricant) per 100 parts by weight of the mixed powder.

[0156] Next, the mixture was extruded using a paste extruder fitted with a sheet die to obtain a sheet-shaped molded body. This sheet-shaped molded body was formed into a film using a calender roll heated to 60°C to obtain a PTFE film. This film was passed through a hot air drying oven at 190°C to evaporate and remove the hydrocarbon oil. Next, the unfired PTFE film was stretched from a size of 70 mm × 70 mm to 203 mm × 500 mm under a predetermined temperature environment (250°C), and then further stretched from a size of 70 mm × 70 mm to 500 mm × 500 mm to obtain a porous film with a total stretching ratio of 1057 times.

[0157] (Example 2) The porous membrane of Example 1 was further heated for 30 seconds in an ambient temperature of 340°C to obtain the porous membrane of Example 2. Otherwise, the air filter material of Example 2 was obtained in the same manner as in Example 1.

[0158] (Example 3) The porous membrane of Example 1 was further heated for 60 seconds in an ambient temperature of 340°C to obtain the porous membrane of Example 3, and the air filter material of Example 3 was obtained in the same manner as in Example 1.

[0159] (Example 4) The porous membrane of Example 1 was further heated for 120 seconds in an ambient temperature of 340°C to obtain the porous membrane of Example 4. Otherwise, the air filter material of Example 4 was obtained in the same manner as in Example 1.

[0160] (Example 5) Except for changing the stretching conditions of the porous membrane in Example 1 from 70 mm × 70 mm to 203 mm × 500 mm under a predetermined temperature environment (250°C), and then further stretching from 70 mm × 70 mm to 500 mm × 500 mm, thereby obtaining the porous membrane of Example 5 with a total stretching ratio of 364 times, the air filter material of Example 5 was obtained in the same manner as in Example 1.

[0161] (Example 6) The porous membrane of Example 5 was further heated for 30 seconds in an ambient temperature of 340°C to obtain the porous membrane of Example 6. Otherwise, the procedure was the same as in Example 5 to obtain the air filter material of Example 6.

[0162] (Example 7) An air filter material for Example 7 was obtained in the same manner as in Example 1, except that the porous membrane of Example 1 was replaced with the porous membrane of Example 7 as described below. The porous membrane of Example 7 was a polyolefin porous membrane prepared by stretching a polyethylene film under predetermined stretching conditions. Specifically, the polyethylene film used was obtained by a wet film formation method and had a thickness of 92 μm, an average pore size of 35 nm, and a weight-average molecular weight of 500,000. The polyethylene film was prepared by biaxial stretching using a batch-type biaxial stretcher at a stretching temperature of 120°C, with a stretching speed of 5 mm / s in the MD direction (Machine Direction) and 3 mm / s in the TD direction (Transverse Direction), resulting in a magnification of 8 times in both the MD and TD directions and an area magnification of 64 times.

[0163] (Example 8) An air filter material for Example 7 was obtained in the same manner as in Example 1, except that the porous membrane of Example 1 was replaced with the porous membrane of Example 7 as described below. The porous membrane of Example 8 was a polyolefin porous membrane prepared by stretching a polyethylene film under predetermined stretching conditions. Specifically, the polyethylene film used was obtained by a wet film formation method and had a thickness of 92 μm, an average pore size of 35 nm, and a weight-average molecular weight of 500,000. The polyethylene film was prepared by biaxial stretching using a batch-type biaxial stretcher at a stretching temperature of 120°C, with a stretching speed of 3 mm / s in the MD direction (Machine Direction) and a stretching speed of 3 mm / s in the TD direction (Transverse Direction), resulting in a magnification of 8 in the MD direction, a magnification of 8 in the TD direction, and an area magnification of 64.

[0164] (Comparative Example 1) Comparative Example 1 was obtained in the same manner as in Example 1, except that a processed tape was obtained by embossing an unfired PTFE film obtained in the same manner as in Example 1 with an average height of 250 μm, a diameter of 2 mm, and a spacing of 4 mm. This tape was then stretched from a size of 70 mm × 70 mm to 203 mm × 500 mm at a predetermined temperature (250°C), and then further stretched from a size of 70 mm × 70 mm to 500 mm × 500 mm to obtain a porous film with a total stretching ratio of 1057 times.

[0165] (Comparative Example 2) Comparative Example 2 was obtained in the same manner as in Example 1, except that an embossed tape with an average height of 250 μm, a diameter of 2 mm, and a spacing of 4 mm was applied to an unfired PTFE film obtained in the same manner as in Example 1, and then stretched from a size of 70 mm × 70 mm to 203 mm × 500 mm at a predetermined temperature environment (230°C), and then further stretched from a size of 70 mm × 70 mm to 500 mm × 500 mm to obtain a porous film with a total stretching ratio of 1057 times.

[0166] (Comparative Example 3) For the porous membrane used in the air filter media of Comparative Example 3, the FP raw material was a mixture of fine powder of perfluoroalkyl vinyl ether-modified polytetrafluoroethylene (manufactured by Daikin Industries, Ltd., product name: F302), which is a copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether, and fine powder of polytetrafluoroethylene with an average molecular weight of 6.5 million (manufactured by Daikin Industries, Ltd., product name: F106), mixed in a weight ratio of 75:25, and 29 parts by weight of an extrusion aid (liquid lubricant) per 100 parts by weight of the mixed powder.

[0167] Next, the mixture was extruded using a paste extruder fitted with a sheet die to obtain a sheet-shaped molded body. This sheet-shaped molded body was formed into a film using a calender roll heated to 60°C to obtain a PTFE film. This PTFE film was passed through a hot air drying oven at 190°C to evaporate and remove the hydrocarbon oil, obtaining a strip-shaped unfired PTFE film (raw tape) with a thickness of 300 μm and an average width of 170 mm. Next, the unfired PTFE film was stretched from a size of 70 mm × 70 mm to 500 mm × 500 mm under a predetermined temperature environment (250°C) to obtain the porous membrane of Comparative Example 3. Except for obtaining the porous membrane of Comparative Example 3 in this way, the air filter material of Comparative Example 3 was obtained in the same manner as in Example 1.

[0168] (Comparative Example 4) For the porous membrane used in the air filter media of Comparative Example 4, the FP raw material was a mixture of fine powder of perfluoroalkyl vinyl ether-modified polytetrafluoroethylene (manufactured by Daikin Industries, Ltd., product name: F302), which is a copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether, and fine powder of polytetrafluoroethylene with an average molecular weight of 6.5 million (manufactured by Daikin Industries, Ltd., product name: F106), mixed in a weight ratio of 75:25, and 28 parts by weight of an extrusion aid (liquid lubricant) per 100 parts by weight of the mixed powder.

[0169] Next, the mixture was extruded using a paste extruder fitted with a sheet die to obtain a sheet-shaped molded body. This sheet-shaped molded body was formed into a film using a calender roll heated to 60°C to obtain a PTFE film. This PTFE film was passed through a hot air drying oven at 190°C to evaporate and remove the hydrocarbon oil, obtaining a strip-shaped unfired PTFE film (raw tape) with a thickness of 300 μm and an average width of 160 mm. Next, the unfired PTFE film was stretched from a size of 70 mm × 70 mm to 500 mm × 500 mm under a predetermined temperature environment (250°C) to obtain the porous membrane of Comparative Example 4. Except for obtaining the porous membrane of Comparative Example 4 in this way, the air filter material of Comparative Example 4 was obtained in the same manner as in Example 1.

[0170] (Comparative Example 5) The air filter material for Comparative Example 5 was obtained in the same manner as in Example 1, except that the FP raw material for the porous membrane was changed from the FP raw material for the porous membrane of Example 1 to the following.

[0171] Specifically, the FP raw material for the porous membrane used in the air filter media of Comparative Example 5 was a mixed powder consisting of three components: PTFE that can be formed into fibers (component A), a non-fiberizable, non-thermally processable component (component B), and a non-fiberizable, heat-melt processable component with a melting point of less than 320°C (component C)).

[0172] First, 66.5% by weight (polymer equivalent) of a PTFE aqueous dispersion (component A) with an SSG of 2.160, prepared in accordance with 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) with a melt viscosity of 20,000 Pa·s measured using a flow tester method at 380°C, prepared in accordance with the method described in International Publication No. 2009 / 020187, and 5% by weight (polymer equivalent) of an FEP aqueous dispersion (component C) with a melting point of 215°C, prepared in accordance with the method described in Japanese Patent Publication No. 2010-235667 were mixed. Co-coagulation was then performed by adding 500 ml of a 1% aluminum nitrate aqueous solution as a coagulant and stirring. After draining the water from the resulting powder using a sieve, it was further dried in a hot air drying oven at 135°C for 18 hours to obtain a mixed powder of the three components.

[0173] Next, 33 parts by weight of hydrocarbon oil (IP Solvent 2028, manufactured by Idemitsu Kosan Co., Ltd.) was added to 100 parts by weight of the mixture as an extruder liquid lubricant at 20°C (33 parts by weight per 100 parts by weight of the mixed powder) and mixed. Then, the resulting mixture was extruded using a paste extruder to obtain a round bar-shaped molded body. This round bar-shaped molded body was formed into a film using a calender roll heated to 70°C to obtain a PTFE film. This PTFE film was passed through a hot air drying oven at 190°C to evaporate and remove the hydrocarbon oil, obtaining a strip-shaped unfired PTFE film (raw tape) with an average thickness of 300 μm and an average width of 150 mm. Next, the unfired PTFE film was stretched from a size of 70 mm × 70 mm to 500 mm × 500 mm in a predetermined temperature environment (250°C) to obtain the porous film of Comparative Example 5. Except for obtaining the porous film of Comparative Example 5 in this way, the air filter material of Comparative Example 5 was obtained in the same manner as in Example 1.

[0174] (Comparative Example 6) The air filter material for Comparative Example 6 was obtained in the same manner as in Example 1, except that the FP raw material for the porous membrane was changed from the FP raw material for the porous membrane of Example 1 to the following, in order to obtain the porous membrane of Comparative Example 6.

[0175] Specifically, the FP raw material for the porous membrane used in the air filter media of Comparative Example 6 was a mixed powder consisting of three components: PTFE that can be formed into fibers (component A), a non-fiberizable, non-thermally processable component (component B), and a non-fiberizable, heat-melt processable component with a melting point of less than 320°C (component C)).

[0176] First, 66.5% by weight (polymer equivalent) of a PTFE aqueous dispersion (component A) with an SSG of 2.160, prepared in accordance with 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) with a melt viscosity of 20,000 Pa·s measured using a flow tester method at 380°C, prepared in accordance with the method described in International Publication No. 2009 / 020187, and 5% by weight (polymer equivalent) of an FEP aqueous dispersion (component C) with a melting point of 215°C, prepared in accordance with the method described in Japanese Patent Publication No. 2010-235667 were mixed. Co-coagulation was then performed by adding 500 ml of a 1% aluminum nitrate aqueous solution as a coagulant and stirring. After draining the water from the resulting powder using a sieve, it was further dried in a hot air drying oven at 135°C for 18 hours to obtain a mixed powder of the three components.

[0177] Next, 33 parts by weight of hydrocarbon oil (IP Solvent 2028, manufactured by Idemitsu Kosan Co., Ltd.) was added to 100 parts by weight of the mixture as an extruder liquid lubricant at 20°C (33 parts by weight per 100 parts by weight of the mixed powder) and mixed. Then, the obtained mixture was extruded using a paste extruder to obtain a round bar-shaped molded body. This round bar-shaped molded body was formed into a film using a calender roll heated to 70°C to obtain a PTFE film. This film was passed through a hot air drying oven at 190°C to evaporate and remove the hydrocarbon oil, obtaining a strip-shaped unfired PTFE film (raw tape) with an average thickness of 300 μm and an average width of 150 mm. Next, the unfired PTFE film was stretched from a size of 70 mm × 70 mm to 500 mm × 500 mm in a predetermined temperature environment (250°C) to obtain the porous film of Comparative Example 6. Except for obtaining the porous film of Comparative Example 6 in this way, the air filter material of Comparative Example 6 was obtained in the same manner as in Example 1.

[0178] (Comparative Example 7) The air filter material for Comparative Example 7 was obtained in the same manner as in Example 1, except that the FP raw material for the porous membrane was changed from the FP raw material for the porous membrane of Example 1 to the following, and that the porous membrane of Comparative Example 7 was heated for 60 seconds in an environment with an ambient temperature of 340°C at the end.

[0179] Specifically, as the FP raw material for the porous membrane used in the air filter media of Comparative Example 7, a mixture of 100 parts by weight of homo-PTFE (Fine Powder of Polytetrafluoroethylene with an average molecular weight of 6.5 million, manufactured by Daikin Industries, Ltd., product name: F106) and a predetermined amount (29 parts by weight) of an extrusion aid (liquid lubricant) was used.

[0180] Next, the mixture was extruded using a paste extruder fitted with a sheet die to obtain a sheet-shaped molded body. This sheet-shaped molded body was formed into a film using a calender roll heated to 70°C to obtain a PTFE film. This film was passed through a hot air drying oven at 200°C to evaporate and remove the extrusion aid, obtaining a strip-shaped unfired PTFE film (raw tape) with a predetermined average thickness (300 μm) and an average width of 100 mm. Next, the unfired PTFE film was stretched from a size of 70 mm × 70 mm to 250 mm × 240 mm in a predetermined temperature environment (250°C), and then further stretched from a size of 70 mm × 70 mm to 500 mm × 500 mm to obtain the porous membrane of Comparative Example 7 with a total stretching ratio of 625 times. Except for obtaining the porous membrane of Comparative Example 7 in this way, the air filter material of Comparative Example 7 was obtained in the same manner as in Example 1.

[0181] (Comparative Example 8) The air filter material for Comparative Example 8 was obtained in the same manner as in Example 1, except that the FP raw material for the porous membrane was changed from the FP raw material for the porous membrane of Example 1 to the following.

[0182] For the porous membrane used in the air filter media of Comparative Example 8, the FP raw material was a mixture of 100 parts by weight of polytetrafluoroethylene fine powder (manufactured by Daikin Industries, Ltd., product name: F106) homo-PTFE with an average molecular weight of 6.5 million, and a predetermined amount (32 parts by weight) of an extrusion aid (liquid lubricant).

[0183] Next, the mixture was extruded using a paste extruder equipped with a sheet die to obtain a sheet-shaped molded body. This sheet-shaped molded body was formed into a film using a calender roll heated to 80°C to obtain a PTFE film. This film was passed through a hot air drying oven at 190°C to evaporate and remove the extrusion aid, obtaining a strip-shaped unfired PTFE film (raw tape) with a predetermined average thickness (200 μm) and an average width of 135 mm. Next, the unfired PTFE film was longitudinally stretched using a heated three-roll stretching device at a predetermined temperature (22°C), a predetermined stretching ratio (12 times), and a predetermined stretching speed (50 m / min) in the longitudinal direction (MD direction). Next, it was transversely stretched using a tenter-type continuous stretching device capable of continuous clipping at a predetermined temperature (22°C), a predetermined stretching ratio (40 times), and a predetermined stretching speed (30 m / min) in the width direction (TD direction), and then heat-set at a temperature of 390°C. This obtained the porous film of Comparative Example 8. The air filter material for Comparative Example 8 was obtained in the same manner as in Example 1, except that the porous membrane for Comparative Example 8 was obtained in this way.

[0184] (Comparative Example 9) The air filter material for Comparative Example 9 was obtained in the same manner as in Example 1, except that a glass filter material (HB7633 from Hollingsworth & Vose) was used instead of the porous membrane of Example 1.

[0185] The following physical properties were measured for the above examples and comparative examples.

[0186] (Thickness of porous membrane) Using a film thickness gauge (ID-C112CX model, manufactured by Mitutoyo Corporation), five samples were stacked together, and the total film thickness was measured. This value was then divided by five to determine the film thickness of a single sample.

[0187] (Balance of porous membrane) The basis weight was determined by dividing the mass (g) of a sample cut into a rectangle of a predetermined area, measured using a precision balance, by the area.

[0188] (Geometric mean fiber diameter of porous membrane) The surface of the test sample was imaged at 4000x magnification using a scanning electron microscope (SEM). A predetermined center line was drawn on one of the captured images, and the thickness of the fiber images intersecting these lines was measured as the fiber diameter. At least 100 fibers were measured. The resulting fiber diameters were plotted on a log-normal scale with fiber diameter on the x-axis and cumulative frequency on the y-axis. The value at which the cumulative frequency reached 50% was defined as the geometric mean fiber diameter. The geometric standard deviation representing the fiber diameter distribution was calculated from the results of the log-normal plot described above, by reading the fiber diameters at 50% and 84% cumulative frequency, using the following formula. Geometric standard deviation [-] = Cumulative frequency 84% fiber diameter / Cumulative frequency 50% fiber diameter

[0189] (filling rate of porous membrane) The packing efficiency of the porous membrane was determined according to the following formula. Filling rate (%) = (Basis weight of porous membrane) / (Thickness of porous membrane) / (Specific gravity of raw material) × 100

[0190] Here, the basis is the mass (g) of a sample cut into a 4.0cm x 12.0cm rectangle, measured using a precision balance, multiplied by the area (0.0048m²). 2 The value was obtained by dividing by ).

[0191] (Fiber density of porous membranes) The surface of the test sample was imaged at 4000x magnification using a scanning electron microscope (SEM). The captured images were subjected to a predetermined binarization process to reduce the influence of fibers at different depth positions. Linear density was calculated by drawing a predetermined center line on the binarized image data, counting the number of fibers on the center line, and dividing the count by the length of the center line in the binarized image data.

[0192] (Fiber density of porous membrane / geometric mean fiber diameter) The fiber density of the porous membrane described above was calculated by dividing it by the geometric mean fiber diameter described above.

[0193] (Pressure loss in air filter media) A sample of air filter media was placed in a 90mm diameter filter holder, the inlet side was pressurized with a compressor, and the airflow rate was adjusted to 5.3 cm / second using a flow meter. The pressure loss at this time was then measured with a differential pressure gauge.

[0194] (Transmittance of polyalphaolefin particles in air filter media) The permeability of polyalphaolefin (PAO) particles (liquid particles) was evaluated. Specifically, air containing PAO particles was filtered over an effective filtration area of ​​50 cm². 2 The sample filter media was passed through at a flow rate of 5.3 cm / second, and the number of particles before and after the filter media was determined using a particle counter. The transmittance was then calculated using the following formula. Transmittance (%)=(CO / CI)×100 Collection efficiency (%) = 100 - Transmittance (%) CO = Number of polyalphaolefin particles downstream of the sample being measured. CI = Number of polyalphaolefin particles upstream of the sample being measured

[0195] The PAO particles used were those generated with a Ruskin nozzle (median particle diameters of 0.06 μm, 0.1 μm, 0.15 μm, 0.2 μm, and 0.3 μm), and the concentration of PAO particles was approximately 1 million to 6 million particles / cm³. 3 That's what I decided.

[0196] Furthermore, the transmittance for each particle size was plotted on a graph, and the Most Penetrating Particle Size (MPPS) was determined from the approximation curve, and the transmittance at that MPPS was calculated.

[0197] (PF value of polyalphaolefin particles in air filter media) Based on the pressure loss and collection efficiency (collection efficiency of polyalphaolefin particles) of the air filter media, the PF value was determined for each particle size of polyalphaolefin and for MPPS according to the following formula. PF value = {-log((100 - collection efficiency (%)) / 100)} / (pressure loss (Pa) / 1000)

[0198] The physical properties of the air filter media and their porous membranes for each example and comparative example are shown in Tables 1, 2, and 3 below. Figure 7 shows a graph of the PF value for a particle size of 0.1 relative to the fiber density / geometric mean fiber diameter of the porous membrane. [Table 1] [Table 2] [Table 3]

[0199] (Note) While embodiments of this disclosure have been described above, it should be understood that various modifications to the form and details are possible without departing from the spirit and scope of this disclosure as described in the claims. [Explanation of Symbols]

[0200] 1. Air filter unit 20 filter packs 25 Frame 30a, 30b, 30c, 30d Air filter media 21 Breathable support material 21a Upstream breathable support material 21b Downstream breathable support material 21c Intermediate breathable support material 31 Porous membrane 31a First porous membrane 31b Second porous membrane [Prior art documents] [Patent Documents]

[0201] [Patent Document 1] Japanese Patent Application Publication No. 10-030031

Claims

1. An air filter filter material (30a, 30b, 30c, 30d) comprising a porous membrane (31, 31a, 31b) having fibers, The ratio of fiber density to geometric mean fiber diameter in the porous membrane, which is the ratio of fiber density to geometric mean fiber diameter in the porous membrane, is 1.9 or more and 4.2 or less. Air filter media.

2. The geometric mean fiber diameter of the fibers in the porous membrane is 98 nm or greater. The air filter material according to claim 1.

3. The geometric mean fiber diameter of the fibers in the porous membrane is 199 nm or less. The air filter material according to claim 1 or 2.

4. The fiber density in the porous membrane is 0.45 fibers / μm or less. The air filter material according to claim 1 or 2.

5. The fiber density in the porous membrane is 0.26 fibers / μm or more. The air filter material according to claim 1 or 2.

6. The porous membrane is a fluororesin porous membrane. The air filter material according to claim 1 or 2.

7. The aforementioned porous fluororesin film contains homo-PTFE and modified PTFE. The air filter material according to claim 6.

8. The porous fluororesin membrane has a PF value of 35 or more, which is determined by the following formula: PF value = {-log((100 - collection efficiency (%)) / 100)} / (pressure loss (Pa) / 1000), using the pressure loss when air is passed through at a flow rate of 5.3 cm / second and the particle collection efficiency when air containing polyalphaolefin particles with a particle size of 0.1 μm is passed through at a flow rate of 5.3 cm / second. The air filter material according to claim 6.

9. The geometric mean fiber diameter of the fibers in the fluororesin porous membrane is 117 nm or less. The air filter material according to claim 6.

10. The filling density in the aforementioned porous fluororesin film is 1.4% or more and 4.0% or less. The air filter material according to claim 6.

11. The basis weight of the aforementioned porous fluororesin film is 1.1 g / m². ２ That's all. The air filter material according to claim 6.

12. The thickness of the aforementioned porous fluororesin film is 19 μm or more. The air filter material according to claim 6.

13. The porous membrane is a polyolefin porous membrane. The air filter material according to claim 1 or 2.

14. The aforementioned porous polyolefin membrane has a PF value of 32 or greater, which is determined by the following formula: PF value = {-log((100 - collection efficiency (%)) / 100)} / (pressure loss (Pa) / 1000), using the pressure loss when air is passed through at a flow rate of 5.3 cm / second and the particle collection efficiency when air containing polyalphaolefin particles with a particle size of 0.1 μm is passed through at a flow rate of 5.3 cm / second. The air filter material according to claim 13.

15. The geometric mean fiber diameter of the fibers in the polyolefin porous membrane is 120 nm or less. The air filter material according to claim 13.

16. The packing density in the aforementioned polyolefin porous membrane is 4.0% or more and 8.0% or less. The air filter material according to claim 13.

17. The basis weight of the aforementioned polyolefin porous film is 0.8 g / m². ２ That's all. The air filter material according to claim 13.

18. The thickness of the aforementioned polyolefin porous film is 11 μm or more. The air filter material according to claim 13.

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