Air filter media, manufacturing methods of air filter media, filter media for face masks, and filter media for pleated face masks.

Abstract

This invention provides an air filter material that minimizes pressure loss, is high-performance, and is less prone to clogging; a method for manufacturing the air filter material; a filter material for face masks; and a pleated filter material for face masks. The air filter media (30) of the present invention comprises a fluoropolymer porous membrane (31) and an air-permeable support material (32) laminated on the fluoropolymer porous membrane (31). For the fluoropolymer porous membrane (31), the pressure loss when air passes through at a flow rate of 5.3 cm / s is 80 Pa or less. Based on the pressure loss and the capture efficiency obtained by using NaCl particles with a particle size of 0.1 μm, the PF value determined by the following formula is 20 or more, and the thickness is 10 μm or more. When air containing polyalphaolefin particles with a median particle size of 0.25 μm is continuously passed through at a flow rate of 5.3 cm / s, the dust retention of the above-mentioned polyalphaolefin particles is 15.0 g / m when the pressure loss increases to the level of 250 Pa. 2 above.

Description

Technical Field

[0001] This invention relates to an air filter material, a method for manufacturing the air filter material, a filter material for face masks, and a pleated filter material for face masks. Background Technology

[0002] For a long time, porous membranes containing polytetrafluoroethylene (hereinafter, sometimes referred to as PTFE) have been used as air filters. Compared with glass fiber filter media, PTFE porous membranes are particularly suitable for HEPA (High Efficiency Particulate Air Filter) or ULPA (Ultra Low Permeation Air Filter) filters because of their higher dust capture efficiency when compared under the same pressure loss.

[0003] As such a filter, for example, an air filter material having a high-performance PTFE porous membrane is proposed, as described in Patent Document 1 (International Publication No. 2013 / 157647). Summary of the Invention

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

[0005] However, as an air filter material with a fluoropolymer porous membrane, it is required to minimize pressure loss while maintaining high performance and being resistant to clogging.

[0006] Technical solutions adopted to solve technical problems

[0007] The first viewpoint describes an air filter media comprising a fluoropolymer porous membrane and a support material deposited on the fluoropolymer porous membrane. The fluoropolymer porous membrane has a pressure loss of 80 Pa or less when air flows through it at a velocity of 5.3 cm / s. The PF (power factor) value of the fluoropolymer porous membrane is 20 or higher. The PF value is determined using the pressure loss and the capture efficiency obtained by using NaCl particles with a particle size of 0.1 μm, by the following formula: PF value = {-log((100 - capture efficiency (%)) / 100)} / (pressure loss (Pa) / 1000). The thickness of the fluoropolymer porous membrane is 10 μm or higher. The dust retention capacity of the fluoropolymer porous membrane is 15.0 g / m³. 2 The above refers to the amount of polyalphaolefin particles that are continuously passed through a fluoropolymer porous membrane at a flow rate of 5.3 cm / s, containing a median particle size of 0.25 μm, and the pressure loss at the fluoropolymer porous membrane increases to the level of 250 Pa.

[0008] Furthermore, the pressure loss, PF value, and dust retention capacity of the fluoropolymer porous membrane can all be set to values ​​under the uncharged state of the fluoropolymer porous membrane. Moreover, the uncharged state of the air filter media refers to the air filter media that has become uncharged after undergoing de-energization treatment according to "JIS B 9908-4 Part 4: Test Method for De-energization Treatment of Air Filter Units for Ventilation". Furthermore, compared to electret filters, fluoropolymer porous membranes can suppress the decrease in capture efficiency and maintain capture efficiency even when changing from a charged state to an uncharged state.

[0009] This air filter media exhibits low pressure loss due to the fluoropolymer porous membrane, which has a pressure loss of less than 80 Pa. Furthermore, the fluoropolymer porous membrane boasts high performance due to its PF value of 20 or higher. Moreover, the fluoropolymer porous membrane of this air filter media has a dust retention capacity of 15.0 g / m³. 2 The above conditions prevent blockages from forming.

[0010] The air filter media of the second viewpoint is the same as the air filter media of the first viewpoint, wherein the thickness of the fluoropolymer porous membrane is less than 50 μm.

[0011] The air filter media can be kept to a relatively small thickness.

[0012] The air filter media of the third viewpoint is the same as that of the first or second viewpoint, wherein the pressure loss variation coefficient of the air filter media is less than 6.0.

[0013] Furthermore, the coefficient of variation of pressure loss refers to the value obtained by dividing the standard deviation of the pressure loss distribution by the average value.

[0014] Regarding fluoropolymer porous membranes that aim to minimize pressure loss, pressure loss can easily vary across different parts of the membrane. However, for this air filter media, good homogeneity can be achieved by minimizing the coefficient of variation in pressure loss.

[0015] The air filter material of the fourth viewpoint is an air filter material as described in any of the first to third viewpoints, wherein the fluoropolymer porous membrane comprises fibrous polytetrafluoroethylene, a non-fibrous non-thermolyzable component, and a non-fibrous thermolyzable component with a melting point not exceeding 320°C.

[0016] Regarding the air filter media, for fluoropolymer porous membranes, relatively coarse fibers can be used to increase the number of pores and the thickness, thereby improving dust retention.

[0017] The air filter media of the fifth viewpoint is an air filter media as described in any of the first to fourth viewpoints, wherein the fluoropolymer porous membrane comprises modified polytetrafluoroethylene.

[0018] The air filter media is easy to ensure a large thickness, which can improve dust retention.

[0019] The sixth viewpoint is a method for manufacturing air filter media according to any one of the first to fifth viewpoints. This method comprises the following steps: preparing a fluoropolymer sheet using a fluoropolymer raw material; extending the fluoropolymer sheet along a first direction at an extension speed of 30% / second or less in the extension direction; and, after the step of extending along the first direction, extending it along a second direction orthogonal to the first direction. Here, the total elongation ratio obtained by extending in the first direction and extending in the second direction is 250 times or more and 800 times or less.

[0020] Furthermore, when the extension in the first direction is divided into two or more segments, it is sufficient to perform one of the extensions at a speed of 30% or less in the extension direction.

[0021] According to the manufacturing method of this air filter media, air filter media with low pressure loss, high performance and low clogging can be easily obtained.

[0022] The filter material for face masks of the seventh point has any one of the air filter materials of the first to fifth points, or is an air filter material manufactured by the manufacturing method of the sixth point.

[0023] The filter material used in this mask suppresses stuffiness during use, and it is high-performance and not prone to clogging.

[0024] The pleated mask filter material of the eighth aspect is a pleated mask filter material comprising a shape including mountain pleats and valley pleats, made from any of the air filter materials of the first to fifth aspects, or from an air filter material manufactured by the manufacturing method of the sixth aspect. When this pleated mask filter material continuously passes through air containing polyalphaolefin particles with a median particle size of 0.25 μm at a flow rate of 85 L / min, and is loaded with 200 mg of polyalphaolefin particles, the pressure loss when passing through air at a flow rate of 40 L / min in this state is less than 120 Pa.

[0025] The filter material used in this pleated mask can be used while maintaining a stuffy and comfortable feel, even after being subjected to a load. Attached Figure Description

[0026] Figure 1 This is a schematic cross-sectional view showing the layered structure of one of the air filter media.

[0027] Figure 2 This is a schematic cross-sectional view showing the layer composition of the air filter media (second one).

[0028] Figure 3 This is a schematic cross-sectional view showing the layer composition of the air filter media (third type).

[0029] Figure 4 This is a three-dimensional view of the appearance of the filter material used in pleated face masks.

[0030] Figure 5 This is a front view of the pleated filter material for a face mask, mounted on a base.

[0031] Figure 6 This is a side sectional view of the pleated filter material for a face mask, mounted on a base. Detailed Implementation

[0032] The following examples illustrate air filter media (hereinafter referred to as filter media), the manufacturing method of air filter media, filter media for face masks, and filter media for pleated face masks.

[0033] (1) Air filter media

[0034] The air filter media comprises a fluoropolymer porous membrane and a support material. The support material is deposited on the fluoropolymer porous membrane along the membrane thickness direction.

[0035] The pressure loss of air filter media can be below 80 Pa, preferably below 75 Pa. Furthermore, there is no particular limitation on the pressure loss of air filter media; it can be above 20 Pa. The pressure loss of air filter media can be measured when air flows through at a velocity of 5.3 cm / s.

[0036] Furthermore, the physical properties of the air filter media and the fluoropolymer porous membrane described in this embodiment represent values ​​in their uncharged, non-charged states. Furthermore, the uncharged state refers to a state where the filter media and fluoropolymer porous membrane are no longer charged after undergoing de-charging treatment according to "JIS B 9908-4 Part 4: Test Method for De-charging Treatment of Air Filter Units for Ventilation". While known filter media may exhibit improved capture efficiency when used in a charged state, such media cannot maintain their charged state effectively when used in a humid environment or due to moisture in human exhaled breath. In contrast, the air filter media and fluoropolymer porous membrane of this embodiment can suppress the decrease in capture efficiency even when in a non-charged state, thereby maintaining capture efficiency effectively.

[0037] As an air filter media, the PF value, determined by the following formula: PF value = {-log((100-capture efficiency (%)) / 100)} / (pressure loss (Pa) / 1000), is preferably 20 or higher, taking into account the pressure loss when air passes through at a flow rate of 5.3 cm / s and the capture efficiency obtained by using NaCl particles with a particle size of 0.1 μm.

[0038] The thickness of the air filter media is preferably 200 μm to 500 μm. The thickness of the air filter media refers to the value of the thickness when a load of 0.3 N is applied to the object being measured in a specific measuring device.

[0039] The specific layer composition of the air filter media described above is not particularly limited; for example, such as... Figure 1 As shown in the air filter media 30, it may have a fluoropolymer porous membrane 31 and a permeable support material 32 deposited downstream of the fluoropolymer porous membrane 31 in the airflow direction. Also, for example, such as... Figure 2 As shown in the air filter media 30, it may also have a fluoropolymer porous membrane 31 and a breathable support material 32 deposited on the upstream side of the fluoropolymer porous membrane 31 in the airflow direction. Furthermore, for example, such as... Figure 3 As shown in the air filter media 30, it may also have a fluoropolymer porous membrane 31 and a breathable support material 32 laminated on both the upstream and downstream sides of the fluoropolymer porous membrane 31 in the airflow direction.

[0040] Furthermore, there are no particular limitations on the method of overlapping these films or layers. They can be bonded by utilizing the anchoring effect caused by partial melting due to heating or the melting of hot melt resin, or by using reactive adhesives, or simply by overlapping.

[0041] The following examples illustrate the relationships between the various layers.

[0042] (2) Fluoropolymer porous membrane

[0043] The pressure loss of the fluoropolymer porous membrane when air flows through it at a velocity of 5.3 cm / s is 80 Pa or less, preferably 75 Pa or less, and more preferably 72 Pa or less. Furthermore, the pressure loss of the fluoropolymer porous membrane is not particularly limited and can be 20 Pa or more. Moreover, from the viewpoint of suppressing the decrease in capture efficiency and easily obtaining a fluoropolymer porous membrane with good overall homogeneity, the pressure loss of the fluoropolymer porous membrane is preferably 40 Pa or more.

[0044] The PF value of the fluoropolymer porous membrane is 20 or higher, preferably 22 or higher. The PF value is determined by the pressure loss when air flows through at a velocity of 5.3 cm / s and the capture efficiency obtained by using NaCl particles with a particle size of 0.1 μm, using the following formula: PF value = {-log((100 - capture efficiency (%)) / 100)} / (pressure loss (Pa) / 1000).

[0045] The thickness of the fluoropolymer porous membrane is 10 μm or more. This facilitates the acquisition of porous membranes with improved dust retention capacity for polyalphaolefin particles. Furthermore, regarding the thickness of the fluoropolymer porous membrane, from the viewpoint of preventing excessive thickness at the folded-in areas when used in a configuration with folded-in sections, a thickness of 50 μm or less is preferred. The thickness of the fluoropolymer porous membrane refers to the value of the thickness when a load of 0.3 N is applied to the object being measured in a specific measuring apparatus.

[0046] The dust retention capacity of the polyalphaolefin particles in the fluoropolymer porous membrane is 15.0 g / m³. 2 The above refers to the weight per unit area of ​​polyalphaolefin particles retained within the fluoropolymer porous membrane when air containing polyalphaolefin particles with a median particle size of 0.25 μm is continuously passed through the membrane at a flow rate of 5.3 cm / s, and the pressure loss of the membrane increases to approximately 250 Pa. This retention capacity is 15.0 g / m³. 2 Therefore, even if oil-containing gas passes through when using air filter media, the increase in pressure loss of the air filter media can be suppressed, and it can be used continuously without clogging.

[0047] Furthermore, the coefficient of variation for pressure loss is preferably 6.0 or less. This coefficient of variation for pressure loss (CV value) is the value obtained by dividing the standard deviation of the pressure loss distribution throughout the fluoropolymer porous membrane by the average value of the pressure loss. Generally, for fluoropolymer porous membranes that aim to minimize pressure loss, the pressure loss at each part of the membrane tends to vary. However, in the air filter material of this embodiment, the coefficient of variation for pressure loss is 6.0 or less, and even with a porous membrane exhibiting low pressure loss, good homogeneity can be achieved through uniform stretching. In particular, filter materials for face masks have a relatively small total area (e.g., 500 cm²). 2 Below or 350cm 2 Therefore, it is particularly ideal to suppress the formation of areas where local quality deterioration occurs. Thus, air filter media that can suppress the coefficient of variation in pressure loss are especially suitable for use as filter media in face masks.

[0048] Furthermore, fluoropolymer porous membranes can achieve a roughly uniform filling rate in the thickness direction, or they can vary the filling rate in the thickness direction. For fluoropolymer porous membranes with varying filling rates in the thickness direction, it is preferable that the filling rate of the upper portion is lower than that of the lower portion (gradient density porous membrane).

[0049] Fluororubber porous membranes are composed of fluororesin, preferably mainly composed of fluororesin, and more preferably have a porous membrane structure having fibrils (not shown) and nodes (nodules) connected to the fibrils. Here, "mainly" means that in the case of containing multiple components, the fluororesin content is the highest. For example, a fluororesin porous membrane may contain more than 50% by weight of fluororesin relative to its weight, preferably more than 80% by weight, more preferably more than 95% by weight, or may be composed solely of fluororesin.

[0050] As a component that differs from fluororesin in the fluoropolymer porous membrane, an example of an inorganic filler that is a non-melt-processable component (component B) that does not fibrousize can be cited.

[0051] The fluoropolymer used in fluoropolymer porous membranes may contain one component or two or more components. For example, a fluoropolymer may contain fibrous PTFE (hereinafter referred to as component A). Alternatively, a fluoropolymer may be a mixture of three components: component A, a non-fibrous, non-thermal-melt-processable component (hereinafter referred to as component B), and a non-fibrous, thermally-melt-processable component with a melting point below 320°C (hereinafter referred to as component C).

[0052] (2-1) Component A: Fiber-compatible PTFE

[0053] Fiberable PTFE, for example, possesses extensibility and non-melt processability. Furthermore, "non-melt processability" refers to its high melt viscosity, which prevents it from flowing easily in the molten state, thus making melt processing difficult. For fiberable PTFE, a melt viscosity of 1×10⁻⁶ at 380°C is preferably preferred. 8 Pa·S or above.

[0054] Fiberizable PTFE can be, for example, high molecular weight PTFE obtained through 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, resulting in long fibers, and a standard specific gravity (SSG) of 2.130–2.230, meaning it has a high melt viscosity but does not substantially melt and flow. From the viewpoint of obtaining easily fiberizable and long fibers, the SSG of fiberizable PTFE is preferably 2.130–2.190, and more preferably 2.140–2.170. If the SSG is too high, the extensibility may deteriorate; if the SSG is too low, the calenderability may deteriorate, leading to poor homogeneity of the porous membrane and potentially increased pressure loss. The aforementioned standard specific gravity (SSG) is determined according to ASTM D 4895.

[0055] Furthermore, from the viewpoint of obtaining fibrils that are easy to fibrous and have a long fiber length, PTFE obtained through emulsion polymerization is preferred. Generally, emulsion polymerization can be carried out in an aqueous medium containing TFE, or monomers other than TFE, dispersants, and polymerization initiators. Moreover, emulsion polymerization is preferably carried out under stirring conditions set so that the generated PTFE microparticles do not agglomerate, with steady stirring. Regarding emulsion polymerization, the polymerization temperature is typically 20–100°C, preferably 50–85°C, and the polymerization pressure is typically 0.5–3.0 MPa. As the polymerization initiator in emulsion polymerization, free radical polymerization initiators, redox polymerization initiators, etc., are preferred. From the perspective of suppressing the formation of low molecular weight PTFE and thus obtaining PTFE with a low SSG, the less the amount of polymerization initiator, the better. However, if too little is used, the polymerization rate tends to become too low; if too much is used, PTFE with a high SSG tends to be formed.

[0056] PTFE can also be a fine powder obtained through emulsion polymerization. The fine powder can be obtained by recovering PTFE microparticles from an aqueous dispersion of PTFE obtained through the aforementioned emulsion polymerization, allowing them to condense, and then drying them. The fine powder containing the aforementioned PTFE has good extrusion processability; for example, it can be extruded as a slurry at an extrusion pressure of 20 MPa or less. Furthermore, the extrusion pressure is measured under the conditions of a reduction ratio of 100, an extrusion speed of 51 cm / min, and 25°C, during slurry extrusion through a damping orifice (diameter 2.5 cm, land length 1.1 cm, and inlet angle 30°). Generally, slurry extrusion molding involves mixing the aforementioned fine powder with an extrusion aid (lubricant), pre-forming, and then extruding. The extrusion aid is not particularly limited and previously known agents can be used, but petroleum-based hydrocarbons with a boiling point of 150°C or higher, such as naphtha, are preferred. The amount of extrusion aid used varies depending on the type of extrusion aid, and is generally 5 to 50 parts by weight (P) per 100 parts by weight of PTFE powder. More preferably, it is 10 to 40 parts by weight, and even more preferably 25 to 35 parts by weight. Preforming and extrusion can be carried out using previously known methods, with appropriate conditions selected.

[0057] Furthermore, the presence or absence of fibrous properties, i.e., whether it can be fibrous, can be determined by whether slurry extrusion, a representative method for molding high molecular weight PTFE powder made from TFE polymers, is possible. Generally, slurry extrusion is possible because high molecular weight PTFE possesses fibrous properties. In cases where the unbaked molded body obtained by slurry extrusion substantially lacks strength and elongation—for example, an elongation of 0% that breaks upon stretching—it can be considered to lack fibrous properties.

[0058] 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. Furthermore, from the viewpoint of maintaining the formability of polytetrafluoroethylene well, the content ratio of modified PTFE in the high molecular weight PTFE is preferably 10% by weight or more and 98% by weight or less, more preferably 50% by weight or more and 95% by weight or less. There are no particular limitations on the homopolymer PTFE, and Japanese Patent Application Publication Nos. 53-60979, 57-135, 61-16907, 62-104816, 62-190206, 63-137906, and 2000-1 are suitable examples. Homopolymer PTFE disclosed in Japanese Patent Publication No. 43727, Japanese Patent Application Publication No. 2002-201217, International Publication No. 2007 / 046345, International Publication No. 2007 / 119829, International Publication No. 2009 / 001894, International Publication No. 2010 / 113950, and International Publication No. 2013 / 027850. Among them, the preferred materials are the homopolymer PTFE disclosed in 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, which have high elongation properties.

[0059] Modified PTFE includes TFE and monomers other than TFE (hereinafter referred to as modified monomers). Examples of modified PTFE include those obtained by homogeneous modification using modified monomers, those modified at the initial stage of polymerization, and those modified at the end of polymerization, but these are not particularly limited to these methods. Preferably, modified PTFE is a TFE copolymer obtained by polymerizing a trace amount of monomers other than TFE together with TFE, within a range that does not significantly impair the properties of the TFE homopolymer. Modified PTFE may be suitably disclosed, for example, in 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, and International Publication No. 2013 / 027850. Among them, the modified PTFE with high elongation properties disclosed in 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 are preferred.

[0060] Modified PTFE comprises TFE-based TFE units and modified monomer units based on modified monomers. The modified monomer units are part of the molecular structure of the modified PTFE and are derived from the modified monomers. Preferably, the modified PTFE contains modified monomer units at a weight percentage of 0.001 to 0.500% of the total monomer units, more preferably 0.01 to 0.30% by weight. All monomer units are derived from all monomers in the molecular structure of the modified PTFE.

[0061] There are no particular limitations on the modifying monomer, as long as it can copolymerize with TFE. Examples include: perfluoroolefins such as hexafluoropropylene (HFP); chlorofluoroolefins such as trifluorochloroethylene (CTFE); hydrogen-containing fluoroolefins such as trifluoroethylene and vinylidene fluoride (VDF); perfluoroethylene ethers; perfluoroalkyl ethylene (PFAE); and ethylene. One or more modifying monomers can be used.

[0062] There are no particular limitations on perfluoroethylene ethers, for example, perfluorounsaturated compounds represented by the following general formula (1) can be cited.

[0063] CF2=CF-ORf···(1)

[0064] In the formula, Rf represents a perfluorinated organic group.

[0065] In this specification, a perfluorinated organic group is an organic group in which all hydrogen atoms bonded to carbon atoms are replaced by fluorine atoms. The aforementioned perfluorinated organic groups may possess ether oxygen.

[0066] Examples of perfluoroethylene ethers (PAVEs) are perfluoro(alkyl vinyl ethers) in which Rf is a perfluoroalkyl group having 1 to 10 carbon atoms. The perfluoroalkyl group preferably has 1 to 5 carbon atoms. Examples of perfluoroalkyl groups in PAVEs include perfluoromethyl, perfluoroethyl, perfluoropropyl, perfluorobutyl, perfluoropentyl, and perfluorohexyl. Perfluoropropyl vinyl ether (PPVE) and perfluoromethyl vinyl ether (PMVE) are preferred PAVEs.

[0067] The above-mentioned perfluoroalkyl ethylene (PFAE) is not particularly limited; for example, perfluorobutylethylene (PFBE) and perfluorohexylethylene (PFHE) can be cited.

[0068] The modifying monomer used in modified PTFE is preferably selected from at least one of the group consisting of HFP, CTFE, VDF, PAVE, PFAE and ethylene.

[0069] In particular, from the viewpoint that fibrils that are easy to fiberize and have a long fiber length can be obtained, when using components B and C below to form a fluoropolymer porous membrane, it is preferable to use homopolymer PTFE containing more than 50% by weight of fibrillable PTFE.

[0070] When a fluoropolymer porous membrane contains not only the aforementioned fiber-forming PTFE (component A), but also a non-fiberable, non-thermally meltable component (component B), and a non-fiberable, thermoly meltable component with a melting point below 320°C (component C), components B and C can be selected as follows. Compared to previous fiberable PTFE (high molecular weight PTFE) porous membranes, the fluoropolymer porous membrane containing these three components has more pores and a thicker membrane structure, thereby capturing microparticles in the gas over a wider area along the thickness direction of the filter material, thus improving dust retention. By including these three components in the fluoropolymer porous membrane, the dust retention capacity for liquid particles can be increased, especially compared to solid particles.

[0071] (2-2) Component B: Non-thermal-melting processable component that will not become fibrous.

[0072] Non-thermal-melting processable components that do not fibrose mainly exist as non-fibrous particles in the nodular region, playing a role in inhibiting the fibrosis of fibrous PTFE.

[0073] Examples of non-thermoplastic, non-fibrous processable components include: thermoplastic components such as low molecular weight PTFE, thermosetting resins, inorganic fillers, and mixtures thereof.

[0074] Thermoplastic components have a melting point above 320°C, and higher melt viscosity is preferred. For example, low molecular weight PTFE, due to its high melt viscosity, can remain at the nodular portion even when processed at temperatures above its melting point. In this specification, low molecular weight PTFE refers to PTFE with a number average molecular weight of 600,000 or less, a melting point of 320°C to 335°C, 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).

[0075] Examples of methods for manufacturing low molecular weight PTFE include: a method of thermally decomposing high molecular weight PTFE powder (molded powder) obtained by suspension polymerization of TFE or high molecular weight PTFE powder (FP: fine powder) obtained by emulsion polymerization of TFE with a specific fluoride through contact reaction at high temperature (see Japanese Patent Application Publication No. 61-162503); a method of irradiating the above-mentioned 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.). Like fibrous PTFE, low molecular weight PTFE can be homopolymer PTFE or modified PTFE containing the aforementioned modified monomers.

[0076] Low molecular weight PTFE is not fibrous. The presence or absence of fibrous properties can be determined using the methods described above. Unbaked molded articles obtained by extruding low molecular weight PTFE through slurry essentially lack strength and elongation; for example, the elongation is 0%, and they will break under tension.

[0077] There are no particular limitations on the low molecular weight PTFE, but the melt viscosity at 380°C is preferably 1000 Pa·s or higher, more preferably 5000 Pa·s or higher, and even more preferably 10000 Pa·s or higher. In this way, if the melt viscosity is high, even if the non-fibrous and heat-meltable components of the C component melt during the manufacture of porous membranes, the non-fibrous, non-heat-meltable components can remain at the nodule sites, thereby inhibiting fibrosis.

[0078] Examples of thermosetting resins include epoxy, silicone, polyester, polyurethane, polyimide, phenol, and mixtures thereof. From the perspective of the workability of co-condensation, it is ideal to use resins dispersed in water in their uncured state. These thermosetting resins are all available commercially available.

[0079] Examples of inorganic fillers include talc, mica, calcium silicate, glass fiber, calcium carbonate, magnesium carbonate, carbon fiber, barium sulfate, calcium sulfate, and mixtures thereof. Among these, talc is preferred due to its affinity for fiber-forming high molecular weight PTFE and its specific gravity. Regarding inorganic fillers, from the viewpoint of forming a stable dispersion during the manufacture of porous membranes, fillers with a particle size of 3 μm to 20 μm are preferred. The particle size is the average particle size, which can be determined by laser diffraction-scattering. These inorganic fillers are all commercially available.

[0080] Furthermore, the non-fibrous, non-melting processable component can be a combination of several of the above-mentioned components.

[0081] The non-fibrous, non-thermal-melt-processable component preferably comprises 1% to 50% by weight of the porous membrane. By keeping the content of the non-fibrous, non-thermal-melt-processable component at 50% by weight or less, the fibrous structure of the porous membrane is easily maintained. The non-fibrous, non-thermal-melt-processable component preferably comprises 20% to 40% by weight, more preferably 30% by weight. By comprising 20% ​​to 40% by weight, the fibrosis of fibrous PTFE can be more effectively suppressed.

[0082] (2-3) Component C: Components with a melting point below 320℃ that will not become fibrous and are suitable for heat-melting processing.

[0083] The non-fibrous, heat-meltable component with a melting point not exceeding 320°C (hereinafter also referred to as a non-fibrous and heat-meltable component) has fluidity when melted, and can be melted and fixed to the nodule during the manufacturing of the porous membrane (during stretching). Thus, even if the overall strength of the porous membrane is increased and it is compressed in subsequent steps, the deterioration of the filter performance can be suppressed.

[0084] The component that does not fibrousize and is heat-meltable preferably exhibits a melt viscosity of less than 10,000 Pa·s at 380°C. Furthermore, the melting point of the component that does not fibrousize and is heat-meltable is defined as the peak of the melt heat profile obtained by heating it to above the melting point and completely melting it once using a differential scanning calorimeter (DSC) at a heating rate of 10°C / min, cooling it to below the melting point at a heating rate of 10°C / min, and then heating it again at a heating rate of 10°C / min.

[0085] Examples of non-fibrous and heat-meltable components include: heat-meltable fluoropolymers, polystyrene, polyethylene terephthalate (PET), polyester, polyamides, and other resins, or mixtures thereof, which can adequately exhibit meltability and flowability at the stretching temperature during the manufacture of porous membranes. Among these, heat-meltable fluoropolymers are preferred due to their excellent heat resistance and chemical resistance at the stretching temperature during the manufacture of porous membranes. Examples of heat-meltable fluoropolymers include fluoropolymers comprising copolymer units derived from at least one fluorinated vinyl unsaturated monomer, preferably two or more monomers, as shown in the following general formula (2); wherein...

[0086] RCF=CR2···(2)

[0087] (In the formula, R is independently selected from H, F, Cl, 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 this case, all R can be the same, any two R can be the same and equal to the other 1 R, or all R can be different from each other).

[0088] The use of compounds represented by general formula (2) is not limited, but can be exemplified by: perfluoroolefins such as vinyl fluoride, VDF, trifluoroethylene, TFE, HFP, CTFE, dichlorodifluoroethylene, chlorofluoroolefins such as CTFE, PFBE, PFHE, perfluoroalkyl ethylene, perfluoro-1,3-dioxane and mixtures thereof.

[0089] Furthermore, the fluoropolymer may also comprise a copolymer derived from the copolymerization of at least one monomer represented by general formula (2) above with at least one copolymerizable comonomer represented by general formula (1) above and / or general formula (3) below; wherein

[0090] R2C=CR2···(3)

[0091] (In the formula, R is independently selected from H, Cl, alkyl with 1 to 8 carbon atoms, aryl with 6 to 8 carbon atoms, and cyclic alkyl with 3 to 10 carbon atoms; in this case, all R can be the same, any two or more R can be the same and these two or more R can be different from other R, or all R can be different from each other; when there are multiple of the above-mentioned other R, they can be different from each other).

[0092] Examples of compounds represented by general formula (1) include perfluoro(alkyl vinyl ether) (PAVE). Preferred PAVEs are perfluoropropyl vinyl ether (PPVE) and perfluoromethyl vinyl ether (PMVE).

[0093] Examples of compounds represented by general formula (3) include ethylene, propylene, etc.

[0094] More specific examples of fluoropolymers include: polyvinylidene 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 of the above general formula (2) with at least one monomer of the above general formula (1) and / or at least one monomer of the above general formula (3).

[0095] Examples of such 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 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, etc., or mixtures thereof.

[0096] Furthermore, the non-fibrous and heat-meltable components can be a combination of several of the above-mentioned components.

[0097] The content of the non-fibrous and heat-meltable component in the porous membrane is preferably 0.1% by weight or more and not more than 20% by weight. By not exceeding 20% ​​by weight, even the non-fibrous and heat-meltable component is dispersed throughout the porous membrane except for the nodular portions, thus suppressing the increase in pressure loss of the porous membrane. Furthermore, by not exceeding 20% ​​by weight, it becomes easier to achieve high-ratio stretching of 40 times or more. By ensuring the content of the non-fibrous and heat-meltable component in the porous membrane is 0.1% by weight or more, even when subjected to compressive forces in subsequent steps, the degradation of the filter performance of the porous membrane is easily and sufficiently suppressed. The content of the non-fibrous and heat-meltable component in the porous membrane is preferably 15% by weight or less, more preferably 10% by weight or less. Furthermore, from the viewpoint of ensuring the strength of the porous membrane, the content of the non-fibrous and heat-meltable component in the porous membrane is preferably 0.5% by weight or more. More preferably, it is around 5% by weight.

[0098] In order to achieve good stretching with an area ratio of 40 to 800 times, the content of the component that does not become fibrous and can be heat-melted is preferably less than 10% by weight.

[0099] (2-4) Method for manufacturing fluoropolymer porous membranes

[0100] Secondly, an example is given to illustrate the manufacturing method of filter media for air filters.

[0101] When manufacturing fluoropolymer porous membranes, fluoropolymers can be used, preferably component A above or the three components described above.

[0102] The form of the three components A to C described above is not particularly limited, and may be, for example, the following compositions, mixed powders, and molding materials. The compositions, mixed powders, and molding materials all contain components A, B, and C as described above, and contain, for example, 0.1% by weight or more but less than 20% by weight of component C.

[0103] The raw materials for porous membranes can be in the form of mixed powders as described below, or non-powder mixtures, or molding materials or compositions as described below. Examples of mixed powders include: fine powders obtained by co-condensation as used in the examples below; powders obtained by mixing two of the three raw materials by co-condensation and then mixing the third component using a mixer; and powders obtained by mixing the three raw materials using a mixer. Examples of non-powder mixtures include: porous bodies (e.g., porous membranes) and aqueous dispersions containing the three components.

[0104] Molding materials refer to those modified for processing in order to shape the composition, such as those made by adding processing aids (liquid lubricants, etc.), adjusting particle size, or pre-forming. Molding materials may contain known additives in addition to the three components mentioned above. Examples of known additives include: carbon nanotubes, carbon black and other carbon materials, pigments, photocatalysts, activated carbon, antibacterial agents, adsorbents, deodorizers, etc.

[0105] 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 conventional mixer; obtaining a co-condensed powder by co-condensing three aqueous dispersions containing components A, B, and C respectively; and mixing a mixed powder obtained by pre-co-condensing an aqueous dispersion containing any two of components A, B, and C with the powder of the remaining component using a conventional mixer. Among these methods, the composition obtained by co-condensing three aqueous dispersions containing components A, B, and C respectively is preferred due to the ease with which the three different components can be uniformly dispersed.

[0106] The size of the mixed powder obtained by co-condensation is not particularly limited, for example, the average particle size is 100 μm to 1000 μm, preferably 300 μm to 800 μm. In this case, the average particle size can be determined according to JIS K6891. The apparent density of the mixed powder obtained by co-condensation is not particularly limited, for example, it is 0.40 g / ml to 0.60 g / ml, preferably 0.45 g / ml to 0.55 g / ml. The apparent density can be determined according to JIS K6892.

[0107] As an example of the above-mentioned co-condensation method, the following can be cited:

[0108] (i) A method of condensation after mixing an aqueous dispersion of component A, an aqueous dispersion of component B, and an aqueous dispersion of component C;

[0109] (ii) A method of adding powders of the other two components to an aqueous dispersion of any one of components A, B, and C, followed by condensation.

[0110] (iii) A method of adding powder of any one of components A, B, and C to a mixed aqueous dispersion prepared by mixing aqueous dispersions of the remaining two components, followed by coagulation; and

[0111] (iv) A method of pre-mixing aqueous dispersions of any two components A, B, and C and then condensing them to obtain a mixed powder of the two components, adding the mixed powder to an aqueous dispersion of the remaining component, and then condensing the mixture.

[0112] As for the co-condensation method described above, the method described in (i) is preferred in terms of the ease with which the three components can be uniformly dispersed.

[0113] Regarding the co-condensation performed using the methods described in (i) to (iv) above, it is preferable to perform co-condensation by adding any one of the following: 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; or organic solvents such as acetone and methanol.

[0114] The form of component A before mixing is not particularly limited; it can be an aqueous dispersion of the aforementioned fibrous PTFE or a powder. Examples of powders (especially the aforementioned FP: fine powder) include: "Teflon 6-J" (hereinafter, Teflon is a registered trademark), "Teflon 6C-J", "Teflon 62-J", etc., manufactured by Mitsui Dupont Fluorochemicals; "Polyflon F106", "Polyflon F104", "Polyflon F201", "Polyflon F302", etc., manufactured by Daikin Industries; "Fluon CD123", "Fluon CD1", "Fluon CD141", "Fluon CD145", etc., manufactured by Asahi Glass; and "Teflon 60", "Teflon 60 X", "Teflon 601A", "Teflon 601 X", "Teflon 613A", "Teflon 613A", etc., manufactured by DuPont. Types include "X", "Teflon605XTX", and "Teflon669 X". Fine powders can also be obtained by condensing and drying an aqueous dispersion of fibrous PTFE (the polymerized aqueous dispersion) obtained by emulsification polymerization of TFE.

[0115] The aqueous dispersion of fibrous PTFE can be either the polymerized aqueous dispersion described above or a commercially available aqueous dispersion. Examples of preferred manufacturing methods for polymerized fibrous PTFE aqueous dispersions include those disclosed in the aforementioned publications, which disclose homopolymer PTFE. Examples of commercially available fibrous PTFE aqueous dispersions 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. Commercially available aqueous dispersions of fibrous PTFE typically contain 2-10 parts by weight of nonionic surfactants to maintain stability. This can lead to residual nonionic surfactants in the mixed powder obtained through co-condensation, potentially causing problems such as discoloration of the porous structure. Therefore, a fully polymerized aqueous dispersion of fibrous PTFE is preferable.

[0116] The form of component B before mixing is not particularly limited. When component B is low molecular weight PTFE, the form before mixing is not particularly limited; 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; "Rublon L-5" and "Rublon L-5F" manufactured by Daikin Industries; "Fluon L169J", "Fluon L170J", and "Fluon L172J" manufactured by Asahi Glass; and "KTL-F" and "KTL-500F" manufactured by Kitamura Corporation.

[0117] As an aqueous dispersion of low molecular weight PTFE, it can be an aqueous dispersion obtained by emulsification polymerization of the above-mentioned TFE, or it can be a commercially available aqueous dispersion. Alternatively, it can be prepared by dispersing micro-powder in water using surfactants or the like. Examples of preferred methods for producing a polymerizable fibrous PTFE aqueous dispersion include those disclosed in 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 PTFE aqueous dispersions include "Rublon LDW-410" manufactured by Daikin Industries, Ltd. To maintain stability, commercially available aqueous dispersions of low molecular weight PTFE often contain 2 to 10 parts by weight of nonionic surfactants relative to 100 parts by weight of PTFE. However, these nonionic surfactants can easily remain in the mixed powder obtained through co-condensation, potentially causing problems such as discoloration of the porous structure. Therefore, a fully polymerized aqueous dispersion is preferable for low molecular weight PTFE.

[0118] Furthermore, when using inorganic fillers as component B, the form before mixing is not particularly limited, but an aqueous dispersion is preferred. Examples of inorganic fillers include "TALC P2" manufactured by NIPPON TALC Co., Ltd., and "LMR-100" manufactured by FUJITALC INDUSTRIAL Co., Ltd. These can be used after appropriate surface treatment with silane coupling agents and dispersion of the powder in water. Among these, for the sake of dispersibility in water, it is preferable to use a secondary pulverized product obtained by jet milling (such as "TALC P2").

[0119] As component C, examples include various resins such as acrylic acid, polyurethane, and PET, in addition to fluoropolymers such as FEP and PFA. The form before mixing is not particularly limited, but an aqueous dispersion is preferred. Regarding aqueous dispersions, in the case of resins obtained through emulsion polymerization, in addition to using the polymerization process as is to complete the dispersion, resin powder can also be dispersed in water using surfactants or the like. Regarding component C, an aqueous dispersion is prepared by dispersing a specific amount in water, containing 0.1% by weight or more and not exceeding 20% ​​by weight in a porous membrane.

[0120] There are no particular limitations on the co-condensation method, but it is preferable to apply mechanical stirring after mixing the three aqueous dispersions.

[0121] After co-condensation, the mixture is dehydrated, dried, and mixed with a liquid lubricant (extrusion aid) before extrusion. The liquid lubricant is not particularly limited to any substance that can wet the surface of the PTFE powder and can be removed after the mixture obtained through co-condensation is formed into a film. Examples include: liquid paraffin, naphtha, white oil, hydrocarbon oils such as toluene and xylene, alcohols, ketones, and esters.

[0122] The mixture obtained by co-condensation is formed into a film by mixing with a liquid lubricant and then extruding and calendering using previously known methods. Here, the amount of liquid lubricant mixed with the fluororesin (e.g., the mixture obtained by co-condensation) is preferably 10 to 40 parts by weight, and more preferably 25 to 35 parts by weight, relative to 100 parts by weight of the fluororesin. By increasing the amount of liquid lubricant, it is easier to ensure a larger thickness while keeping the filling rate low, thereby reducing pressure loss. Furthermore, by reducing the amount of liquid lubricant, it is easier to improve the capture efficiency of the obtained fluororesin porous membrane and also easier to reduce the coefficient of variation of pressure loss.

[0123] Extrusion can be performed through slurry extrusion, plunger extrusion, etc., but slurry extrusion is preferred. The sheet extruded by slurry extrusion is calendered using a calendering roller or similar method under heating conditions, for example, at a temperature of 40°C to 80°C. The thickness of the resulting calendered film can be set based on the thickness of the target porous film, typically between 100 μm and 1000 μm, possibly between 100 μm and 400 μm, and preferably between 150 μm and 350 μm.

[0124] Subsequently, the liquid lubricant is removed from the uncalcined film, which is the calcined product. The removal of the liquid lubricant can be carried out by heating, extraction, or a combination thereof. Regarding the heating temperature when using the heating method, there is no particular limitation when using the three components A to C, as long as it is below 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.

[0125] Here, regarding the calendered material after the liquid lubricant has been removed, from the viewpoint of sufficiently ensuring the thickness of the obtained fluoropolymer porous film and reducing pressure loss, it is preferable to perform a heat treatment at a temperature atmosphere of 250°C to 325°C for more than 1 minute before stretching. The temperature of this heat treatment can be, for example, below 320°C, preferably below the melting point of the fluoropolymer used to make the fluoropolymer porous film. When the calendered material is heated at a heating rate of 10°C / min using a differential scanning calorimeter, and multiple endothermic curves (primary melting point, secondary melting point) appear on the crystallization melting curve, it can also be below the maximum peak temperature (primary melting point). Furthermore, from the viewpoint of sufficiently ensuring thickness and sufficiently reducing pressure loss, the heat treatment temperature can be, for example, 260°C or higher, or 280°C or higher, or the temperature at which liquid lubricant is removed from the unbaked film of the rolled material by heating, or the stretching temperature (the temperature at which the first stretching is performed in the case of biaxial stretching) or higher. Moreover, the duration of the heat treatment is not particularly limited, but depending on the desired effect of the heat treatment, it can be set to, for example, 1 minute or more but less than 2 hours, or 30 minutes or more but less than 1 hour.

[0126] Furthermore, while there are no particular limitations on obtaining fluoropolymer porous membranes with different filling rates in the thickness direction, it is preferable to perform the heat treatment in such a way that the temperature of the side with the reduced filling rate is higher than the temperature of the side with the increased filling rate, and preferably that the heat treatment temperature of the upper part is higher than that of the lower part. Furthermore, the lower part can also be cooled to a temperature below room temperature. Moreover, regarding the heat treatment temperature, from the viewpoint of generating a sufficient density difference, the temperature difference between the upper and lower parts can be 100°C or more, preferably 200°C or more, and more preferably 300°C or more. Also, it is preferable to perform the heat treatment in such a way that the heating time of the side with the reduced filling rate is extended and the heating time of the side with the increased filling rate is shortened. In this way, by stretching the obtained calendered material, the filling rate of the upper side can be reduced and the filling rate of the lower side can be increased.

[0127] In this way, calendered materials that have had liquid lubricant removed or calendered materials that have undergone further heat treatment are extended. Furthermore, in cases containing non-fibrous hot-melt processable components and non-fibrous non-hot-melt processable components, the extension is performed at a temperature above the melting point of the non-fibrous hot-melt processable components and below the decomposition temperature of the non-fibrous non-hot-melt processable components.

[0128] Furthermore, when using a non-fibrous hot-melt processable component in the manufacture of fluoropolymer porous membranes, the non-fibrous hot-melt processable component melts during the stretching process and is subsequently fixed to the nodule portion, 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 that transport the calendered material, or a combination of these settings.

[0129] The extension includes extension in a first direction and extension in a second direction, preferably orthogonal to the first direction. Here, extension in the second direction can be performed after extension in the first direction. Alternatively, extension in the first direction and extension in the second direction can be performed simultaneously. Furthermore, extension in the first direction at a first extension speed can be followed by extension in the first direction at a second extension speed, and then extension in the second direction. In this embodiment, the first direction is the length direction of the rolled material (longitudinal: MD direction (Machine Direction), and the second direction is the width direction of the rolled material (transverse: TD direction). Furthermore, the extension can also be performed simultaneously while multiple rolled materials are stacked.

[0130] The area ratio during the stretching of the calendered material can be between 250 and 800 times, preferably between 300 and 600 times, and more preferably between 400 and 580 times. By sufficiently increasing the stretch ratio, the fluoropolymer porous membrane can have more fibers, which facilitates improved capture efficiency and increases the uniformity of stretching, thus minimizing the variation coefficient of pressure loss. This is preferable in this respect. Furthermore, by sufficiently decreasing the stretch ratio, the thickness of the fluoropolymer porous membrane can be prevented from becoming too small, and the dust retention capacity can be prevented from decreasing. This is preferable in this respect.

[0131] During stretching, from the viewpoint of easily increasing the thickness of the obtained fluoropolymer porous membrane to improve dust retention, reduce pressure loss, and minimize the coefficient of variation of pressure loss, it is preferable to stretch at a stretching speed of 30% / second or less in the stretching direction, and more preferably to stretch at a stretching speed of 20% / 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, but from the viewpoint of ensuring sufficient thickness and reducing pressure loss, it is preferable to achieve a stretching speed of 30% / second or less in the first longitudinal stretching. When longitudinal stretching is performed in two stages with different stretching speeds, it is preferable to stretch at a stretching speed of 30% / second or less in either stretching direction in either stage. Furthermore, when using a table test device or the like to stretch simultaneously in the longitudinal and transverse directions from a top view, it is preferable to achieve a stretching speed of 30% / second or less in either the longitudinal or transverse stretching direction. Furthermore, the extension speed is not limited to longitudinal and lateral directions; for example, the extension speed in the extension direction can be set to 1% / second or higher.

[0132] Furthermore, the stretching rate is the value obtained by dividing the stretching ratio (%) by the time (seconds) required for the stretching, where the stretching ratio (%) is the ratio of the length after stretching to the length before stretching (length after stretching / length before stretching). Moreover, slowing down the stretching rate in this manner is preferable from the perspective of further reducing the pressure loss of the obtained porous membrane.

[0133] Furthermore, from the viewpoint of increasing the thickness of the obtained fluoropolymer porous membrane to further reduce pressure loss, it is preferable to perform the above-mentioned heat treatment on the calender before stretching, and then stretch it at a low speed as described above.

[0134] 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 270°C. Furthermore, the temperature when extending in the second direction is preferably 200°C to 300°C, more preferably 250°C to 290°C.

[0135] Furthermore, regarding the stretching of the aforementioned calendered material (also known as uncalcined fluoropolymer), it is known that the stretching temperature, stretch 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 uncalcined fluoropolymer reveals unique characteristics different from other resins. Generally, the tensile tension of resin materials increases with elongation. The range of the elastic region and the point of fracture vary depending on the material and evaluation conditions. On the other hand, the tensile tension generally tends to increase with elongation. In contrast, the tensile tension of uncalcined fluoropolymer shows a peak at a certain elongation and then gradually decreases. This indicates that there is a region in the uncalcined fluoropolymer where the unstretched portion is stronger than the stretched portion.

[0136] If we apply this to the behavior during stretching, in the case of a typical resin, during stretching, the weakest part within the stretching surface begins to stretch. However, because the stretched part becomes stronger than the unstretched part, the second weakest unstretched part gradually stretches, thereby expanding the stretching area and achieving overall stretching. On the other hand, in the case of uncalcined fluororesin, if the stretching part reaches the aforementioned "region where the unstretched part is stronger than the stretched part," the already stretched part will stretch further. As a result, the unstretched part remains as a node (nodule, unstretched part). If the stretching speed slows down, this phenomenon becomes more pronounced, resulting in larger nodes (nodules, unstretched parts). By utilizing this phenomenon during stretching, the physical properties of the stretched body can be adjusted according to various applications.

[0137] For the fluoropolymer porous membrane of this embodiment, it is preferable to obtain a lower density extended body. In the case of biaxial stretching, applying a low stretching speed, especially in the first stretching, is more effective. Here, larger nodes (nodular portions, unstretched portions) remain. Compared with the previous case where only PTFE was used as the raw material, the above-mentioned phenomenon caused by the low stretching speed becomes more significant when using a non-fibrillated, non-thermal-melting processable component. Even when a thicker molded body is desired, the stretching speed can be increased compared with the case where only PTFE was used as the raw material.

[0138] For porous membranes obtained in this manner, heat curing is preferred to achieve mechanical strength and dimensional stability. The temperature for heat curing can be above or below the melting point of PTFE, preferably between 250°C and 400°C.

[0139] The fluoropolymer porous membrane can be a single layer or a multilayer formed by laminating a first fluoropolymer porous membrane and a second fluoropolymer porous membrane. The amount of liquid lubricant used during manufacturing is preferably 25 to 35 parts by weight relative to 100 parts by weight of the fluoropolymer. Using 25 parts by weight or more reduces pressure loss, making it easier to adjust the overall pressure loss of the filter media to below 80 Pa. Furthermore, using 35 parts by weight or less ensures the formability of the unbaked membrane (unprocessed strip), preventing the pore size of the first fluoropolymer porous membrane from becoming too large, allowing microparticles to pass through uncaptured and flow downstream, thus preventing excessive burden on the downstream second fluoropolymer porous membrane.

[0140] In particular, the amount of liquid lubricant used in manufacturing the first fluoropolymer porous membrane is preferably 30 to 35 parts by weight relative to 100 parts by weight of fluoropolymer. For example, within a range of 1 to 4 parts by weight difference in liquid lubricant dosage, 26 to 31 parts by weight are used to manufacture the second fluoropolymer porous membrane, while 30 to 35 parts by weight are used to manufacture the first fluoropolymer porous membrane, thereby significantly improving the dust retention capacity of the filter material.

[0141] Furthermore, the difference in average pore size between the first fluororesin porous membrane and the second fluororesin porous membrane can also be achieved by varying the proportions of the three components between the two porous membranes.

[0142] (3) Breathable support material

[0143] A breathable support material is disposed on the upstream or downstream side of the fluoropolymer porous membrane, or both the upstream and downstream sides, to support the fluoropolymer porous membrane. Therefore, even if the fluoropolymer porous membrane is difficult to stand upright due to its thinness, it can be supported by the breathable support material to make it stand upright. Furthermore, the strength of the membrane as an air filter material can be ensured, and it is easy to maintain its shape even when folded into a specific shape.

[0144] The material and structure of the breathable support material are not particularly limited, and examples include: non-woven fabric, woven fabric, metal mesh, resin mesh, etc. Among these, non-woven fabric with heat-melting properties is preferred in terms of strength, trapping ability, softness, and workability. The non-woven fabric is preferably: a non-woven fabric having a core / sheath structure as part or all of the fibers; a double-layer non-woven fabric comprising 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 a non-woven fabric with a surface coated with a heat-melting resin. Spunbond non-woven fabric is an example of such a non-woven fabric. Furthermore, the core / sheath structure of the non-woven fabric is preferably one where 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, high-melting-point polyester / low-melting-point polyester. Combinations of low-melting-point and high-melting-point materials in double-layer non-woven fabrics include: PE / PET, PP / PET, PBT / PET, low-melting-point PET / high-melting-point PET. Examples of nonwoven fabrics coated with hot-melt resins include PET nonwoven fabrics coated with EVA (ethylene-vinyl acetate copolymer resin) and PET nonwoven fabrics coated with olefin resin.

[0145] There are no particular restrictions on the material of non-woven fabrics; polyolefins (PE, PP, etc.), polyamides, polyesters (PET, etc.), aromatic polyamides, or composite materials thereof can be used.

[0146] The breathable support material can be bonded to the fluoropolymer porous membrane by heating to melt a portion of the breathable support material, by melting the hot melt resin, and by using the anchoring effect or by using reactive adhesives.

[0147] The breathable support material can also be one with extremely low pressure loss, capture efficiency, and dust retention compared to the aforementioned fluoropolymer porous membrane, essentially negligible. The pressure loss of the breathable support material is preferably below 10 Pa, more preferably below 5 Pa, and even more preferably below 1 Pa. Furthermore, the capture efficiency of the breathable support material can also be substantially negligible or approximately negligible.

[0148] The thickness of the breathable support material is preferably 500 μm or less, and more preferably 300 μm or less. Furthermore, when using a fluoropolymer porous membrane folded into a pleated shape, the thickness of the breathable support material is preferably 200 μm or more from the viewpoint of easily maintaining the pleat shape.

[0149] (4) Applications of air filter media

[0150] The air filter material of this embodiment has low pressure loss, so from the viewpoint of suppressing stuffiness during use, it is preferably used for face masks.

[0151] As a mask, it is preferable to use one that can prevent dust, fumes, bacteria, viruses and other substances from entering the body through the mouth and nose.

[0152] As a type of mask, it can be a general-purpose mask, a dust mask, or a medical mask. Furthermore, as a shape, it can be any of the following: flat, pleated, or three-dimensional. Pleated masks can be worn with the pleats unfolded. Three-dimensional masks can also be beak-shaped, tapering towards the front.

[0153] (5) Filter material for pleated face masks

[0154] Regarding the pleated mask filter material of this embodiment, examples include using the above-mentioned air filter material, which is processed by alternating and repeatedly making mountain pleats and valley pleats (pleating processing) with the filter material surfaces facing each other to form a serrated shape, thereby forming pleated portions, and the overall shape is approximately cuboid, with the mountain pleats forming the upper surface and the valley pleats forming the lower surface; or a concentric circle pleated shape in which multiple mountain pleats are arranged in a concentric circle on the upper surface and multiple valley pleats are arranged in a concentric circle on the lower surface.

[0155] For the pleated mask filter material of this embodiment, Figure 4 The image shows a three-dimensional view of the exterior. Figure 5 The image shows a front view of a pleated filter material for a face mask, mounted on a base. Figure 6 The image shows a side sectional view of a pleated mask filter material mounted on a base.

[0156] like Figure 4-6 As shown, the pleated mask filter material can be a pleated mask filter material 20 that is installed in the opening 2a of a base 2 made of resin or the like that which does not have a filtering function. More preferably, the pleated mask filter material 20 is installed in a base 2 that has a filter material exchange installation opening 2a. Furthermore, a cord 3 for installation to the ears can be provided from the base 2.

[0157] The distance between adjacent pleats and valleys in pleated mask filter material, i.e., the fold height, is preferably set to 10mm or more and 40mm or less. By setting the fold height to 10mm or more, the bending process when forming the pleats and valleys of the air filter material becomes easier. Furthermore, by setting the fold height to 40mm or less, the increase in pressure loss caused by the pleated shape of the pleated mask filter material can be suppressed.

[0158] The distance between adjacent pleats or between adjacent valley pleats in pleated mask filter material, i.e., the pleat spacing, is preferably 2.0 mm to 4.5 mm. A pleat spacing of 2.0 mm or more can suppress the increase in pressure loss caused by the pleated shape. Furthermore, a pleat spacing of 4.5 mm or less ensures that the total area of ​​the air filter material usable with the pleated mask filter material is sufficiently large.

[0159] Furthermore, regarding the spacing between the opposing filter material surfaces in a pleated mask, for example, it can be ensured using spacers such as hot-melt resin as spacer members, or by using protrusions formed by embossing the filter material surfaces. Also, the filter material for a pleated mask can be simply folded in without spacers or embossing. In this case, airflow can still pass between the pleats on the upper side.

[0160] Furthermore, the area of ​​the upper surface of the pleated filter material for the mask, which is installed in the opening formed in the base, can be set to, for example, 22 cm². 2 Above 61cm 2 Furthermore, when the upper surface of the wind is set to a rectangle, for example, the length of the diagonal can be set to 4.5cm or more and 11cm or less.

[0161] Based on the viewpoint that even after capturing an object to a certain extent, it is easy to maintain a low pressure loss and a good capture efficiency, the total area of ​​the filter material for pleated masks is preferably set at 200cm². 2 The above is preferably set to 300cm. 2 That's all. Furthermore, from the viewpoint that the area and fold height of the upper surface of the filter material for pleated masks are of a size that facilitates use and achieves effective pleat spacing, the total area of ​​the filter material for pleated masks is preferably set to 1300 cm². 2 the following.

[0162] Regarding the filter material for pleated face masks, when air containing 200 mg of polyalphaolefin particles with a median particle size of 0.25 μm is continuously passed through at a flow rate of 85 L / min, and the material is loaded with these particles, the pressure loss when passing through air at a flow rate of 40 L / min under these conditions is preferably below 120 Pa, more preferably below 100 Pa, and even more preferably below 80 Pa. This allows the mask to be designed so that even under continuous use, users do not easily experience a feeling of stuffiness.

[0163] [Example]

[0164] The following examples and comparative examples illustrate the contents of the present invention in detail.

[0165] (Examples 1-6, Comparative Examples 1-6)

[0166] The FP raw material for the fluoropolymer porous membrane used in the air filter material of Example 1 is a mixed powder composed of three components: fiber-forming PTFE (component A), a non-fiberable non-thermal-melt-processable component (component B), and a non-fiberable thermally-melt-processable component with a melting point not exceeding 320°C (component C)).

[0167] More specifically, firstly, 66.5% by weight (polymer conversion) 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 conversion) of a low molecular weight aqueous PTFE dispersion (component B) with a melt viscosity of 20000 Pa·s measured by a flow tester at 380°C prepared according to the method described in International Publication No. 2009 / 020187, and 5% by weight (polymer conversion) of an aqueous FEP dispersion (component C) 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. The mixture was stirred to perform co-coagulation. Then, after sieving the water off the generated powder using a sieve, it is dried in a hot air drying oven at 135°C for 18 hours to obtain a mixed powder of the above three components.

[0168] Subsequently, 29.0 parts by weight (29.0 parts by weight relative to 100 parts by weight of the mixed powder) of hydrocarbon oil (IP Solvent 2028 manufactured by IDEMITSU Co., Ltd.) was added to the mixture at 20°C as an extrusion liquid lubricant and mixed. Next, the obtained mixture was extruded using a slurry extrusion apparatus to obtain a cylindrical profile. This cylindrical profile was then formed into a film using a calendering roller 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, resulting in a strip-shaped unbaked PTFE film (unprocessed strip) with an average thickness of 300 μm and an average width of 150 mm. Next, the unbaked PTFE film was stretched along its length (MD direction) at a specific stretch ratio (10x) and a specific stretching speed (13.8% / second) under specific temperature conditions (250°C). Next, using a tenter frame capable of holding the stretched unbaked film, the film is stretched along the width direction (TD direction) at a specific stretch ratio (45 times) and a specific stretching speed (330% / second) under a specific temperature environment (288°C), and then heat-fixed at a temperature of 390°C. This yields a fluoropolymer porous membrane.

[0169] Furthermore, regarding the fluoropolymer porous membranes used in the air filter media of Examples 2-5 and Comparative Examples 3-5, each fluoropolymer porous membrane was obtained by using the same FP raw material as in Example 1, while changing the amount of extrusion aid (liquid lubricant), unprocessed tape thickness, MD temperature, MD ratio, MD stretching speed, TD temperature, TD ratio, and total ratio as shown in Table 1.

[0170] As the FP raw material for the fluoropolymer porous membrane used in the air filter media of Example 6 and Comparative Example 6, a mixture of powder and extrusion aid (liquid lubricant) was used. The powder was made by mixing fine powder of perfluoroalkyl vinyl ether modified polytetrafluoroethylene (manufactured by Daikin Industries, Ltd., product name: F302), a copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether, with fine powder of polytetrafluoroethylene with an average molecular weight of 6.5 million (manufactured by Daikin Industries, Ltd., trade name: F106) at a weight ratio of 75:25. The extrusion aid (liquid lubricant) was in a specific amount relative to 100 parts by weight of the powder (26 parts by weight in Example 6 and 23 parts by weight in Comparative Example 6).

[0171] Next, the mixture is extruded using a slurry extrusion device equipped with a sheet die to obtain a sheet-shaped molded body. This sheet-shaped molded body is then formed into a film shape using a calendering roller heated to 70°C to obtain a PTFE film. The film is then passed through a hot air drying oven at 250°C to evaporate and remove hydrocarbon oils, thereby obtaining a strip-shaped unbaked PTFE film (unprocessed strip) with a specific average thickness (220 μm in Example 6, 600 μm in Comparative Example 6) and an average width of 170 mm. Next, using a heated three-roll stretching device, the unbaked PTFE film is longitudinally stretched along its length (MD direction) at a specific stretch ratio (7.5 times in Example 6, 10 times in Comparative Example 6) and a specific stretching speed (19.7% / second in Example 6, 28.7% / second in Comparative Example 6) under a specific temperature environment (250°C). Next, using a continuously clamping tenter-type continuous stretching device, the membrane was laterally stretched along the width direction (TD direction) at a specific stretching ratio (45 times in Example 6 and 20 times in Comparative Example 6) and a specific stretching speed (330% / second) under a specific temperature environment (283°C in Example 6 and 300°C in Comparative Example 6), and then heat-fixed at a temperature of 390°C. This yielded a fluoropolymer porous membrane.

[0172] The FP raw material for the fluoropolymer porous membrane used in the air filter media of Comparative Examples 1-2 is a mixture of fine powder of polytetrafluoroethylene with an average molecular weight of 6.5 million (manufactured by Daikin Industries, Ltd., trade name: F106) and an extrusion aid (liquid lubricant) in a specific amount (30 parts by weight) relative to 100 parts by weight of homopolymer PTFE.

[0173] Next, the mixture was extruded using a slurry extrusion device equipped with a sheet die to obtain a sheet-shaped molded body. The sheet-shaped molded body was then shaped into a film shape using a calendering roller heated to 70°C to obtain a PTFE film. The film was then passed through a hot air drying oven at 200°C to evaporate and remove the extrusion aids, thereby obtaining a strip-shaped unbaked PTFE film (unprocessed strip) with a specific average thickness (200 μm) and an average width of 170 mm. Next, the unbaked PTFE film was longitudinally stretched along the length direction (MD direction) at a specific stretch ratio (10 times for Comparative Example 1 and 48 times for Comparative Example 2) and a specific stretching speed (29.5% / s for Comparative Example 1 and 553.9% / s for Comparative Example 2) under specific temperature conditions (300°C for Comparative Example 1 and 250°C for Comparative Example 2) in a specific temperature environment (300°C for Comparative Example 1 and 250°C for Comparative Example 2). Next, using a continuous stretching device of the tenter frame that can be continuously clamped, the membrane was stretched laterally along the width direction (TD direction) at a specific stretching ratio (30 times for Comparative Example 1 and 36 times for Comparative Example 2) and a specific stretching speed (330% / second) under a specific temperature environment (290°C), and then heat-fixed at a temperature of 390°C. This yielded a fluoropolymer porous membrane.

[0174] The fluoropolymer porous membranes used in the air filter media of Examples 1-6 and Comparative Examples 1-6, obtained as described above, were obtained by thermally fusing an air-permeable support material to both its upstream and downstream sides. Furthermore, the air-permeable support material uses a spunbond nonwoven fabric comprising fibers with a core / sheath structure (average fiber diameter 24 μm, area weight 40 g / m²) containing fibers with a core of PET and a sheath of PE. 2 (The thickness is 0.2mm) (Furthermore, the capture efficiency can be considered to be essentially 0 or approximately 0).

[0175] Furthermore, the physical properties measured in Examples 1-6 and Comparative Examples 1-6 are as follows.

[0176] (Pressure loss of air filter media)

[0177] The test sample of the air filter media was placed in a filter holder with a diameter of 100 mm. The compressor was used to pressurize the filter at the inlet side, and the air flow rate was adjusted to 5.3 cm / s using a flow meter. Then, the pressure loss was measured using a differential pressure gauge.

[0178] (The capture efficiency of air filter media for NaCl particles with a diameter of 0.1 μm)

[0179] According to the method described in Annex 5 of JIS B9928 (specified) for the generation of NaCl aerosol (pressurized spray method), the NaCl particles generated by the atomizer are classified into 0.1 μm particles using an electrostatic classifier (manufactured by TSI Corporation). After neutralizing the particles with Americium 241, the permeation flow rate is adjusted to 5.3 cm / s. The number of particles before and after the filter material used as the test sample is determined using a particle counter (CNC manufactured by TSI Corporation), and the capture efficiency is calculated using the following formula.

[0180] Transmittance (%) = (CO / CI) × 100

[0181] Capture efficiency (%) = 100 - Transmittance (%)

[0182] CO = The number of NaCl particles at 0.1 μm downstream of the sample.

[0183] CI = The number of NaCl particles at 0.1 μm on the upstream side of the sample.

[0184] (PF value of air filter media for NaCl particles with a diameter of 0.1 μm)

[0185] Using NaCl particles with a diameter of 0.1 μm, the PF value is calculated according to the following formula based on the pressure loss and capture efficiency (capture efficiency for NaCl particles with a diameter of 0.1 μm) of the air filter media.

[0186] PF value = {-log((100 - capture efficiency (%)) / 100)} / (pressure loss (Pa) / 1000)

[0187] (Thickness of fluororesin porous membrane)

[0188] Using a film thickness gauge (ID-C112CX type, manufactured by Mitutoyo), the overall film thickness was measured by overlapping 5 test pieces. The value obtained by dividing the overall thickness by 5 was taken as the film thickness of one piece.

[0189] (Dust retention capacity of polyalphaolefin particles in air filter media: PHC)

[0190] The evaluation was conducted through a pressure loss rise test during the permeation of polyalphaolefin (PAO) particles (liquid particles). Specifically, the pressure loss was measured over time using a differential pressure gauge at a flow rate of 5.3 cm / s into an effective filtration area of ​​50 cm². 2The pressure loss of the sample filter material when continuously passing through air containing PAO particles was calculated. When the pressure loss increased to 250 Pa, the weight of the PAO particles retained in the filter material per unit area, i.e., the dust retention capacity (g / m²), was determined. 2 Furthermore, the PAO particles used are PAO particles (with a median particle size of 0.25 μm) generated through a Laskin nozzle, and the concentration of PAO particles is set to approximately 1 million to 6 million / cm³. 3 .

[0191] (Coefficient of variation (CV value) of pressure loss of air filter media)

[0192] A roll of air filter media (650 mm in width) is pulled out to a length of approximately 5 m, including the front end. The media is then divided into 25 sections every 200 mm along its length and into 4 sections every 130 mm along its width (excluding the ends). Pressure loss is measured at each of the 100 grid-like sections using filter holders with a diameter of 100 mm. The pressure loss is measured continuously at multiple grid-like sections by moving the media along its length using a measuring device equipped with at least five filter holders along its width. The standard deviation is then calculated from the pressure loss distribution, and the standard deviation is divided by the average pressure loss of all measured sections to determine the coefficient of variation (CV) (%).

[0193] (Dust retention capacity of NaCl particles in air filter media)

[0194] The evaluation was conducted through a pressure loss rise test during the permeation of NaCl particles (solid particles). Specifically, a differential pressure gauge was used to measure the pressure loss rise over time when a flow rate of 5.3 cm / s was applied to an effective filtration area of ​​50 cm². 2 The pressure loss of the sample filter material when continuously passing through air containing NaCl particles was calculated. When the pressure loss increased to 250 Pa, the weight of the NaCl particles retained in the filter material per unit area, i.e., the dust retention capacity (g / m²), was determined. 2 Furthermore, the NaCl particles used are NaCl particles (with a median particle size of 0.1 μm) generated by an atomizer, and the NaCl particle concentration is set to approximately 5 to 7 million particles / cm³. 3 Furthermore, regarding the dust retention capacity of NaCl particles in the air filter media, only the air filter media of Example 1 was measured, and it was 2.5 g / m³. 2 .

[0195] The various physical properties of the air filter media of each of Examples 1-6 and Comparative Examples 1-6 are shown in the following table.

[0196] [Table 1]

[0197]

[0198] As shown in Table 1, in Examples 1 to 6, air filter media with low pressure loss, high capture efficiency, film thickness within a specific range, high PAO dust retention capacity, and good homogeneity were obtained.

[0199] In Comparative Examples 1 and 2, which used homopolymer PTFE as raw material, the generation of fine fibers was not suppressed, and a thicker film thickness could not be maintained, resulting in a significant decrease in PAO dust retention. Furthermore, in Comparative Example 1, the pressure loss increased. In Comparative Example 2, which was prepared to reduce pressure loss, the film thickness and PAO dust retention both decreased further.

[0200] In Comparative Example 3, which used the same raw materials as Examples 1-5, and Comparative Example 6, which used the same raw materials as Example 6, the total elongation ratio was less than 250 times, and the homogeneity of the elongated film decreased significantly. In Comparative Example 4, which used the same raw materials as Examples 1-5, the total elongation ratio was greater than 800 times, and the elongation speed in the MD direction was faster, so the film thickness could not be maintained, and the PAO dust retention was low.

[0201] The stuffiness experienced when used as a mask varies depending on the shape and folded area of ​​the mask. However, based on the stuffiness experienced during processing and use, the pressure loss of the air filter material is set to below 80 Pa. Comparative Example 5 is an example where the pressure loss of the air filter material exceeds 80 Pa and does not meet the performance requirements of the air filter material.

[0202] (Examples 7, 8, and Comparative Example 7)

[0203] Examples 7 and 8 are pleated mask filter materials obtained by folding the air filter material of Example 1 into mountain and valley pleats. Comparative Example 7 is a pleated mask filter material obtained by folding the air filter material of Comparative Example 2 into mountain and valley pleats. The pleated filter materials of Examples 7, 8, and Comparative Example 7 are all folded in a manner that forms a generally rectangular parallelepiped shape. Examples 7, 8, and Comparative Example 7 are respectively manufactured to have the total area, fold height, number of pleats, and opening area as described in Table 2.

[0204] Here, total area refers to the area of ​​the air filter media used to fold into pleats.

[0205] The term "fold height" refers to the distance between adjacent mountain folds and valley folds.

[0206] The number of pleats refers to the number of pleats arranged on the upper side of the airflow in a roughly rectangular pleated mask filter material.

[0207] The opening area refers to the area of ​​the rectangular portion at the upper end of the airflow in a roughly cuboid pleated mask filter material.

[0208] Furthermore, the pleated mask filter materials of Examples 7, 8, and Comparative Example 7 are interchangeable pleated filter materials used in mask bases having specific filter material mounting portions. The capture efficiency and pressure loss were measured using the aforementioned approximately cuboid-shaped pleated mask filter material itself.

[0209] (Example 9)

[0210] Example 9 is a three-dimensional mask filter material made from the air filter material of Example 1, in a roughly beak-shaped form. The mask filter material of Example 9 has a contoured portion that contacts the face, and a shape typical of a dust mask formed by the contoured portion bulging forward from the center of the front view.

[0211] (Example for reference)

[0212] The reference example is a flat, plain gauze mask, rather than one that is pleated as in Examples 7 and 8.

[0213] (Pressure loss (before load))

[0214] Each test sample was mounted on the sample holder, and pressurized at the inlet side using a compressor. The air permeation flow rate was adjusted to 40 L / min using a flow meter. Then, the pressure loss was measured using a differential pressure gauge.

[0215] (Pressure loss when loaded with 200mg of PAO particles)

[0216] For each test sample loaded with 200 mg of air containing polyalphaolefin particles with a median particle size of 0.25 μm, continuously passed through at a flow rate of 85 L / min, the pressure loss at this point was measured using a differential pressure gauge. This pressure loss was then converted to the pressure loss at a filter material permeation velocity equivalent to 40 L / min, and the resulting value was taken as the pressure loss when ventilating at 40 L / min with a 200 mg load.

[0217] (Capture efficiency and transmittance ratio before and after loading 200mg of PAO particles)

[0218] The capture efficiency was evaluated by loading polyalphaolefin (PAO) particles (liquid particles) and performing a pressure loss rise test. When each test sample was loaded with air containing PAO particles at a flow rate of 85 L / min, the transmittance, capture efficiency, and transmittance ratio were calculated based on the upstream concentration C1 and the downstream concentration C2.

[0219] Transmittance (%) = (C2 / C1) × 100

[0220] Capture efficiency (%) = 100 - Transmittance (%)

[0221] Transmittance ratio = Transmittance (after load) / Transmittance (before load)

[0222] Furthermore, PAO particles (with a median particle size of 0.25 μm) generated through a Raskin nozzle were used, with a concentration of approximately 1 million to 6 million particles / cm³. The capture efficiency was measured before loading (as the initial state) and after loading (as the state after loading 200 mg of air containing polyalphaolefin particles with a median particle size of 0.25 μm at a flow rate of 85 L / min).

[0223] Furthermore, the transmittance of the state after loading 200 mg of air containing polyalphaolefin particles with a median particle size of 0.25 μm, which is continuously passed through at a flow rate of 85 L / min, is divided by the transmittance before loading, which is the initial state, and the result is used as the transmittance ratio (transmittance after loading / transmittance before loading).

[0224] (Pressure loss when loaded with 100 mg of NaCl particles)

[0225] For a sample loaded with 100 mg of NaCl particles containing a median particle size of 0.1 μm, continuously passed through air at a flow rate of 85 L / min, the pressure loss at this point was measured using a differential pressure gauge. This pressure loss was then converted to the pressure loss equivalent to 40 L / min based on the filter media permeation velocity. The resulting value was taken as the pressure loss when ventilating at 40 L / min with a load of 200 mg.

[0226] Furthermore, for the pleated mask filter material of Example 7, the pressure loss when loaded with 100 mg of NaCl particles with a median particle size of 0.1 μm was measured, and the result was 123 Pa.

[0227] (Capture efficiency before and after loading 100 mg of NaCl particles)

[0228] For the samples mounted on the sample holder, similar to the "Capture Efficiency of Air Filter Material for NaCl Particles with a Median Particle Size of 0.1 μm" in Table 1 above, measurements were taken before loading (as the initial state) and after loading (as the state after loading 100 mg of air containing NaCl particles with a median particle size of 0.1 μm at a flow rate of 85 L / min). Furthermore, for the pleated mask filter material of Example 7, the capture efficiency was measured before loading 100 mg of NaCl particles with a median particle size of 0.1 μm and after loading. The capture efficiency of the pleated mask filter material of Example 7 before loading was 99.065%. Also, the capture efficiency of the pleated mask filter material of Example 7 increased with the loading of NaCl particles, and the capture efficiency after loading was higher than the capture efficiency before loading.

[0229] The various physical properties of Examples 7-9, Comparative Example 7, and Reference Example are shown in the following table.

[0230] [Table 2]

[0231]

[0232] As can be seen from Table 2 above, in Examples 7 to 9 made using the air filter material of Example 1, the pressure loss before the load on the mask can be suppressed to be low, while maintaining a high capture efficiency, and the increase in pressure loss after loading PAO particles can be suppressed to be small.

[0233] On the other hand, in Comparative Example 7, which was made using the air filter media of Comparative Example 2, the pressure loss when loaded with 200 mg of PAO particles increased significantly compared with the pressure loss before loading.

[0234] The embodiments of the present invention have been described above, but it should be understood that various changes in manner or details may be made without departing from the spirit and scope of the present invention as described in the claims.

[0235] [Symbol Explanation]

[0236] 2: Base

[0237] 2a: Opening

[0238] 3: Rope

[0239] 20: Filter material for pleated face masks

[0240] 30: Air filter media

[0241] 31: Fluoropolymer porous membrane

[0242] 32: Breathable support material (support material)

[0243] [Previous Technical Documents]

[0244] [Patent Literature]

[0245] [Patent Document 1] International Publication No. 2013 / 157647.

Claims

1. An air filter media (30), comprising: Fluoropolymer porous membrane (31); and Support material (32) laminated on at least one side of the fluoropolymer porous membrane, Its features are, For the aforementioned fluoropolymer porous membrane, the pressure loss when air flows through at a velocity of 5.3 cm / s is less than 80 Pa. For the fluoropolymer porous membrane, based on the pressure loss and the capture efficiency obtained by using NaCl particles with a particle size of 0.1 μm, the PF value, determined by the following formula: PF value = {-log((100 - capture efficiency (%) / 100)} / (pressure loss (Pa) / 1000), is 20 or higher. For the aforementioned fluororesin porous membrane, the thickness is 10 μm or more and 50 μm or less. For the aforementioned fluoropolymer porous membrane, when air containing polyalphaolefin particles with a median particle size of 0.25 μm is continuously passed through at a flow rate of 5.3 cm / s, the dust retention capacity of the polyalphaolefin particles is 15.0 g / m³ when the pressure loss increases by 250 Pa. 2 above, The air filter media is manufactured by the following method, which includes the following steps: Fluoropolymer raw materials are used to produce fluoropolymer sheets; The fluoropolymer sheet is extended along the first direction at an extension speed of less than 30% / second in the extension direction. as well as Following the step of extending along the first direction, it extends along a second direction orthogonal to the first direction. The total extension ratio is between 250 and 800 times.

2. The air filter media as described in claim 1, characterized in that, The coefficient of variation for pressure loss is below 6.

0.

3. The air filter media as described in claim 1 or 2, characterized in that, The fluoropolymer porous membrane comprises fibrous polytetrafluoroethylene, a non-fibrous non-thermal-melt-processable component, and a non-fibrous thermally-melt-processable component with a melting point below 320°C.

4. The air filter media as described in claim 1 or 2, characterized in that, The fluoropolymer porous membrane contains modified polytetrafluoroethylene.

5. A filter material for face masks, characterized in that, An air filter media comprising any one of claims 1 to 4.

6. A pleated filter material (20) for a face mask, wherein the air filter material according to any one of claims 1 to 4 is formed in a shape including mountain pleats and valley pleats, characterized in that, When air containing polyalphaolefin particles with a median particle size of 0.25 μm is continuously passed through the pleated mask filter material in this state at a flow rate of 40 L / min at a flow rate of 85 L / min, and the filter material is loaded with 200 mg of polyalphaolefin particles, the pressure loss is less than 120 Pa.

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