CN118662976A - Air filter medium, method for manufacturing same, filter pack, and air filter unit - Google Patents

Abstract

The present invention provides an air filter material and a method for manufacturing the same, a filter bag, and an air filter unit, which can suppress the increase in pressure loss of the air filter material caused by thermal fusion. The air filter material comprises a fluororesin porous membrane and a first support material for supporting the fluororesin porous membrane, wherein the fluororesin porous membrane is thermally fused to the first support material, the first support material comprises a core-sheath structure fiber including a first core portion and a first sheath portion having a lower melting point than the first core portion, and the first support material satisfies the following formula. Formula: Weight per unit area (g/m ² )/{average fiber cross-sectional area (cm ² )×material specific gravity (g/cm ³ )×thickness (cm)×1000000}≤380(m/cm ³ ).

Description

Air filter material and method for manufacturing the same, filter pack, and air filter unit

Technical Field

The invention relates to an air filter material, a filter bag, an air filter unit and a method for manufacturing the air filter material.

Background Art

In the past, for example, the porous membrane (hereinafter, sometimes referred to as PTFE porous membrane) consisting of polytetrafluoroethylene (hereinafter, sometimes referred to as PTFE) was used as an air filter. The PTFE porous membrane is thinner and sometimes it is difficult to maintain shape, therefore, it is used as filter material in the state of being stacked with an air permeability support material.

For example, in the air filter medium described in Patent Document 1 (Japanese Patent Application Laid-Open No. 2002-66226), a technique is proposed in which a filter medium is obtained by thermally fusing a relatively soft nonwoven fabric to a PTFE porous membrane.

Here, in the air filter material obtained by thermally fusing fluororesin porous membrane and supporting material, the change of fiber structure may be produced during thermal fusing. Therefore, compared with the pressure loss of the filter material in the state of only stacking before thermal fusing fluororesin porous membrane and supporting material, the pressure loss of the air filter material obtained by thermal fusing sometimes increases. Therefore, it is expected that the increase of the pressure loss of the air filter material caused by thermal fusing is suppressed to be smaller.

Prior art literature

Patent Literature

Patent Document 1: Japanese Patent Application Publication No. 2002-66226

Summary of the invention

The air filter material of the first aspect comprises a fluororesin porous membrane and a first supporting material. The first supporting material supports the fluororesin porous membrane. The fluororesin porous membrane is thermally fused to the first supporting material. The first supporting material has a core-sheath structure fiber including a first core portion and a first sheath portion having a lower melting point than the first core portion. The first supporting material satisfies the following formula. Formula: Unit area weight (g/m ² )/{average fiber cross-sectional area (cm ² )×material specific gravity (g/cm ³ )×thickness (cm)×1000000}≤380(m/cm ³ ).

In addition, assuming that the air filter material further includes a second support material and the fluororesin porous membrane is disposed between the first support material and the second support material, preferably both the first support material and the second support material have the above values of 380 (m/cm ³ ). In this case, the first support material and the second support material may have the same physical properties or different physical properties.

The fluororesin porous membrane may be composed of a single porous membrane or a plurality of porous membranes such as two porous membranes.

This air filter medium can suppress an increase in pressure loss compared to a filter medium in which the first support material and the fluororesin porous membrane are simply overlapped but not thermally fused to each other.

The air filter material of the second viewpoint is based on the air filter material of the first viewpoint, and further comprises a second support material for supporting the fluororesin porous membrane. The fluororesin porous membrane is located between the first support material and the second support material. The fluororesin porous membrane is thermally fused to the second support material. The second support material has a core-sheath structure fiber including a second core portion and a second sheath portion having a lower melting point than the second core portion. The second support material satisfies the following formula. Formula: Unit area weight (g/m ² )/{average fiber cross-sectional area (cm ² )×material specific gravity (g/cm ³ )×thickness (cm)×1000000}≤380(m/cm ³ ).

This air filter medium can suppress an increase in pressure loss compared to a filter medium in which the second support material and the fluororesin porous membrane are simply overlapped but not thermally fused to each other.

An air filter medium according to a third aspect is the air filter medium according to the first aspect or the second aspect, wherein the air filter medium has a dielectric breakdown voltage of 0.8 kV or more.

The air filter medium can protect the fluororesin porous membrane from static electricity and minimize damage to the fluororesin porous membrane.

An air filter medium according to a fourth aspect is the air filter medium according to any one of the first to third aspects, wherein a thickness of the air filter medium is 350 μm or more and 1000 μm or less.

This air filter medium can physically protect the fluororesin porous membrane and can be easily deformed into a pleated shape or the like.

The air filter material of the fifth viewpoint is based on the air filter material described in any of the first viewpoints to the fourth viewpoint, and the PF value is more than 20. The PF value is determined by the formula of PF value={-log((100-collection efficiency (%))/100)}/(pressure loss (Pa)/1000). In the calculation of the PF value, the pressure loss when air is passed through the air filter material at a flow rate of 5.3cm/second and the collection efficiency of the air filter material grasped by NaCl particles with a particle size of 0.1μm are used.

When using a relatively high-performance fluororesin porous membrane, the increase in pressure loss caused by the heat welding of the first support material is likely to increase. In this case, the air filter material can also suppress the increase in pressure loss caused by the heat welding of the first support material to a small extent.

An air filter medium according to a sixth aspect is the air filter medium according to any one of the first to fifth aspects, wherein a weight per unit area of the first support material is 25 g/m ² or more and 60 g/m ² or less.

This air filter medium can easily provide a first supporting material that can easily suppress an increase in pressure loss due to thermal fusion bonding with a porous fluororesin membrane.

An air filter medium according to a seventh aspect is the air filter medium according to any one of the first to sixth aspects, wherein an average fiber diameter of the first support material is 23 μm or more.

This air filter medium can easily provide a first supporting material that can easily suppress an increase in pressure loss due to thermal fusion bonding with a porous fluororesin membrane.

A filter pack according to an eighth aspect is the air filter medium according to any one of the first to seventh aspects, which is folded to form convex folds and concave folds.

This filter pack can suppress the pressure loss to a low level.

The air filter unit of the ninth aspect comprises: the air filter material described in any one of the first to seventh aspects, or a pleated filter material as the air filter material described in any one of the first to seventh aspects, the pleated filter material being folded in a manner to produce a convex fold portion and a concave fold portion; and a frame. The frame holds the air filter material or the pleated filter material.

This air filter unit can suppress pressure loss to be low.

The manufacturing method of the air filter material of the tenth aspect comprises the following steps: preparing a fluororesin porous membrane; preparing a first support material; and thermally fusing the fluororesin porous membrane to the first support material. The prepared first support material has a core-sheath structure fiber including a first core portion and a first sheath portion having a lower melting point than the first core portion. The prepared first support material satisfies the following formula. Formula: Unit area weight (g/m ² )/{average fiber cross-sectional area (cm ² )×material specific gravity (g/cm ³ )×thickness (cm)×1000000}≤380(m/cm ³ ).

According to the manufacture method of this air filter filter material, as the first support material thermally fused with fluororesin porous membrane, the support material of the above-mentioned unique physical property is used. Therefore, compared with the filter material in the state of being only overlapped with fluororesin porous membrane and not thermally fused mutually by the first support material, it is possible to obtain the air filter filter material that can suppress the increase of pressure loss to be smaller.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view showing a layer structure of an air filter medium (part 1).

FIG. 2 is a schematic cross-sectional view showing the layer structure of an air filter medium (part 2).

FIG3 is a schematic cross-sectional view showing the layer structure of an air filter medium (part 3).

FIG. 4 is a schematic diagram showing the structure of an apparatus for performing stretching in the longitudinal direction when viewed from the side.

FIG. 5 is a schematic diagram showing the structure of an apparatus for performing stretching in the width direction when viewed from the side.

FIG. 6 is a schematic perspective view of a device for performing stretching in the width direction.

FIG. 7 is a perspective view schematically showing the appearance of a filter pack.

FIG. 8 is a perspective view schematically showing the appearance of an air filter unit.

Description of symbols

1 Air filter unit

20 filter bags (pleated filter media)

25 Frame

30 Air filter media

31 Fluororesin porous membrane

32 first supporting material

33 Second supporting material

DETAILED DESCRIPTION

Hereinafter, an air filter medium (hereinafter, also simply referred to as a filter medium), a filter pack, an air filter unit, and a method for manufacturing the air filter medium will be described with examples.

(1) Air filter media

The air filter medium comprises a fluororesin porous membrane and a support material, wherein the support material is thermally fused to the fluororesin porous membrane in a state of being laminated on the fluororesin porous membrane in a membrane thickness direction.

The layer structure of air filter material is not particularly limited, for example, as shown in Figure 1 air filter material 30, can be fluororesin porous membrane 31 and the first supporting material 32 stacked in the air flow direction and constituted structure.The first supporting material 32 can be arranged on the leeward side of fluororesin porous membrane 31 as shown in Figure 1, and can also be arranged on the upwind side of fluororesin porous membrane 31 as shown in Figure 2.In addition, can also be as shown in Figure 3, the air filter material possesses the first supporting material 32 stacked on fluororesin porous membrane 31 in the air flow direction and the second supporting material 33 stacked on the side opposite to the first supporting material 32 sides of fluororesin porous membrane 31, and fluororesin porous membrane 31 is supported from the leeward side and upwind side these two sides.

The pressure loss of the air filter material can be, for example, below 250 Pa, preferably below 200 Pa. In addition, the pressure loss of the air filter material is not particularly limited, and can be more than 50 Pa. The pressure loss of the air filter material can be measured as the pressure loss when air is passed through at a flow rate of 5.3 cm/ seconds.

The air filter medium may have a particle collection efficiency of 99.00% or more, preferably 99.99% or more, when air containing NaCl particles having a particle size of 0.1 μm passes therethrough at a flow rate of 5.3 cm/sec.

As air filter material, the pressure loss and collection efficiency of NaCl particles with a particle size of 0.1 μm are used, which are determined by the following formula: PF value = {-log ((100-collection efficiency (%))/100)}/(pressure loss (Pa)/1000). The PF value determined is, for example, preferably more than 20, and more preferably more than 21. The PF value of the air filter material is mainly determined by the performance of the fluororesin porous membrane, but in the case of using a relatively high-performance fluororesin porous membrane with a high PF value in the air filter material, the increase in the pressure loss caused by the heat fusion of the first support material and/or the second support material to the fluororesin porous membrane is easy to become larger. In this case, by using the first support material and/or the second support material specified above, the increase in the pressure loss caused by the heat fusion can also be suppressed to be smaller.

The thickness of the air filter material is preferably, for example, more than 350 μm, more preferably more than 380 μm. Thus, it is easy to fully ensure the thickness of the first support material and/or the second support material for protecting the fluororesin porous membrane, and the fluororesin porous membrane can be physically protected. In the case of using in a state with a folded portion, from the viewpoint of suppressing the thickness of the folded portion from becoming too large, the thickness of the air filter material is preferably, for example, less than 1000 μm, more preferably less than 750 μm. By making the thickness of the air filter material not too large, deformation when deforming into a pleated shape, etc. becomes easy. In addition, the thickness of the air filter material is the value of the thickness when a load of 0.3N is applied to the measured object in a specific measuring device. For example, a film thickness meter (1D-110MH type, Mitutoyo (Mitutoyo) company system) can be used, 5 pieces of measured objects are overlapped to measure the overall film thickness, and the numerical value obtained by dividing the value by 5 is grasped as 1 film thickness.

The dielectric breakdown voltage of the air filter medium is preferably 0.8 kV or more, more preferably 0.85 kV or more. By sufficiently ensuring the dielectric breakdown voltage, the fluororesin porous membrane is prevented from being damaged by static electricity, and the state of leakage is prevented from occurring.

(2) Fluororesin porous membrane

The fluororesin porous membrane is mainly composed of fluororesin, and more preferably has a porous membrane structure, which has fibrils (fibers) and nodes (nodes) connected to the fibrils. Here, "mainly" means that the fluororesin contains the most when containing multiple components. The fluororesin porous membrane can, for example, contain more than 50% by weight of fluororesin relative to the weight of the fluororesin porous membrane, preferably contain more than 80% by weight of fluororesin, more preferably contain more than 95% by weight of fluororesin, or it can be composed only of fluororesin.

As a component different from the fluororesin contained in the porous fluororesin membrane, there can be mentioned, for example, an inorganic filler which is a non-melt-processable component that does not form fibers.

The fluororesin used for the fluororesin porous membrane can be composed of one component or more than two components. In addition, as the fluororesin, for example, a fluororesin comprising PTFE that can be fibrosified can be cited. In addition, as the fluororesin, a mixture of PTFE that can be fibrosified, a non-thermal melt processable component that can not be fibrosified, and a melting point lower than 320° C. can be cited of three components that can be heat-melt processed.

PTFE that can be fibrillated is a high molecular weight PTFE obtained by emulsion polymerization or suspension polymerization of tetrafluoroethylene (TFE). The high molecular weight mentioned here refers to the molecular weight of the size of easy fibrillation during stretching when the porous membrane is made, the fiber with long fiber length can be obtained, the standard specific gravity (SSG) is 2.130-2.230, the melt viscosity is high, and therefore it is substantially non-melting flow. Whether it can be fibrillated can be judged by whether the representative method of high molecular weight PTFE powder molding made of TFE polymer can be carried out, i.e., paste extrusion. In the case where the unfired molded body obtained by paste extrusion does not have substantial strength or elongation, for example, in the case where the elongation is 0%, it will break if stretched, it can be regarded as not having fibrillation. High molecular weight PTFE can be modified polytetrafluoroethylene, homopolytetrafluoroethylene, or a mixture of modified PTFE and homopolyPTFE.

As non-heat-melt processable components that do not form fibers, there can be listed thermoplastic components such as low molecular weight PTFE, thermosetting resins, inorganic fillers, and mixtures thereof. Low molecular weight PTFE is PTFE having 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 ⁵ Pa·s at 380°C.

The heat-melt processable component that does not undergo fiberization and has a melting point of less than 320° C. preferably exhibits a melt viscosity of less than 10,000 Pa·s at 380° C. The melting point of the heat-melt processable component that does not undergo fiberization is the peak of a melting heat curve obtained when the component is heated to a temperature above the melting point at a heating rate of 10° C./min using a differential scanning calorimeter (DSC) and is temporarily completely melted, cooled to a temperature below the melting point at 10° C./min, and then heated again at 10° C./min.

These fiberizable PTFE, non-heat-melt-processable components that do not fiberize, and non-heat-melt-processable components that do fiberize with a melting point of less than 320° C. can be components described in detail in International Publication No. 2020/067182, etc.

In addition, the method for manufacturing a porous fluororesin membrane uses fine powder obtained by coagulation and co-coagulation of TFE emulsion polymerization, and after dehydration and drying, a liquid lubricant (extrusion aid) is mixed and paste extrusion is performed to obtain a sheet-like extrudate. The liquid lubricant is removed from the unfired film obtained by rolling the sheet-like extrudate using a calendering roller, etc., and the film is stretched to obtain a porous fluororesin membrane.

The pressure loss of the porous fluororesin membrane thus obtained when air is passed through at a flow rate of 5.3 cm/sec is 250 Pa or less, preferably 200 Pa or less. The pressure loss of the porous fluororesin membrane is not particularly limited and may be 50 Pa or more, or 80 Pa or more.

When air containing NaCl particles having a particle size of 0.1 μm is passed through the porous fluororesin membrane at a flow rate of 5.3 cm/sec, the particle collection efficiency can be 99.00% or more, preferably 99.99% or more.

In addition, the PF value of the fluororesin porous membrane is 20 or more, more preferably 21 or more. The PF value is a value determined by the following formula: PF value = {-log ((100-collection efficiency (%))/100)}/(pressure loss (Pa)/1000) using the pressure loss and collection efficiency grasped by NaCl particles with a particle size of 0.1 μm.

In addition, the thickness of the fluororesin porous membrane can be, for example, 1.0 μm or more, preferably 3.0 μm or more. By increasing the thickness of the fluororesin porous membrane, the dust accumulation can be increased. In addition, the thickness of the fluororesin porous membrane is, for example, 100 μm or less, preferably 50.0 μm or less. The thickness of the fluororesin porous membrane can be measured, for example, using a film thickness meter (1D-110MH type, made by Mitutoyo Co., Ltd.), 5 pieces of measurement objects are overlapped to measure the overall film thickness, and the value obtained by dividing the value by 5 is used as the thickness of 1 piece of film to grasp.

The average fiber diameter of the fluororesin porous membrane may be, for example, 0.01 μm or more, preferably 0.05 μm or more, and more preferably 0.08 μm or more. The average fiber diameter of the fluororesin porous membrane may be, for example, 0.5 μm or less, preferably 0.25 μm or less, and more preferably 0.2 μm or less. The average fiber diameter may be calculated as the number average fiber diameter by randomly selecting 50 fibers from an image of a scanning electron microscope photograph.

(3) Supporting material

The fluororesin porous membrane is supported by being stacked with a supporting material. Therefore, even if the film thickness of the fluororesin porous membrane is thin and difficult to stand on its own, the fluororesin porous membrane can be erected by the supporting material. In addition, it is possible to ensure the strength as an air filter filter material, and even when folded into a specific shape, it is easy to keep the shape. As a supporting material, it can be only a first supporting material stacked on one side of the air flow direction relative to the fluororesin porous membrane, and it is also possible to further have a second supporting material stacked on one side of the air flow direction opposite to the first supporting material side relative to the fluororesin porous membrane. The material of the supporting material is not particularly limited, and for example, nonwoven fabrics, woven fabrics, etc. can be cited. Here, as nonwoven fabrics, for example, spunbonded nonwoven fabrics are preferred.

(3-1) First Supporting Material

The air filter material is provided with a first support material disposed on either the upstream side or the downstream side of the airflow passing direction relative to the fluororesin porous membrane. The first support material has a first core-sheath structure fiber including a first core portion and a first sheath portion having a melting point lower than the first core portion. When the first support material is thermally fused to the fluororesin porous membrane, at least a portion of the first sheath portion having a melting point lower than the first core portion is melted, thereby thermally fusion bonding the fluororesin porous membrane to the first support material.

Here, if the pressure loss of the filter material of the state of only making the fluororesin porous membrane and the first supporting material stacked without mutual thermal fusion is compared with the pressure loss of the air filter filter material obtained by thermal fusion of the first supporting material and the fluororesin porous membrane, it can be known that the pressure loss of the air filter filter material obtained by thermal fusion of the fluororesin porous membrane and the first supporting material is larger due to the change of the fiber structure caused by thermal fusion. Moreover, the inventors, etc. have conducted in-depth research in order to suppress the increase of the pressure loss during the thermal fusion, and the result is newly found: the fewer the contact points of the fluororesin porous membrane and the first supporting material, the more the increase of the pressure loss caused by thermal fusion can be suppressed. The inventors, etc. have found through further research that as the first supporting material used for thermal fusion of the fluororesin porous membrane in the air filter filter material, it is preferred to use the first supporting material with a short average total fiber length per unit volume. As the average total fiber length per unit volume, the unit area weight (g/m ² ), average fiber cross-sectional area (cm ² ), material specific gravity (g/cm ³ ) and thickness (cm) of the first supporting material can be used, represented by the following formula 1.

Formula 1: Weight per unit area (g/m ² )/{average fiber cross-sectional area (cm ² )×material specific gravity (g/cm ³ )×thickness (cm)×1000000}

Furthermore, the inventors have found that the average total fiber length per unit volume of the first support material preferably satisfies the following formula 2 from the viewpoint of suppressing an increase in pressure loss of the obtained air filter medium.

Formula 2: Weight per unit area (g/m ² )/{average fiber cross-sectional area (cm ² )×material specific gravity (g/cm ³ )×thickness (cm)×1000000}≤380 (m/cm ³ )

The value of the first support material calculated by the above-mentioned formula 2 is preferably 350 (m/cm ³ ) or less, and more preferably 300 (m/cm ³ ) or less.

This can reduce the number of contact points between the first support material and the porous fluororesin membrane, and even when the first sheath portion of the first support material is melted and thermally welded to the porous fluororesin membrane, an increase in pressure loss of the resulting air filter medium can be suppressed.

In addition, the melting point of the first core portion is preferably 30°C or higher than the melting point of the first sheath portion, more preferably 50°C or higher. Thus, the first support material can be suppressed from melting as a whole during heat fusion. The components of the first core portion can include polyesters such as polyethylene terephthalate (PET), or their composite materials. The components of the first sheath portion can include polyolefins such as polyethylene (PE) or polypropylene (PP), polyamides (PA), or their composite materials. In addition, the combination of the components of the first core portion and the first sheath portion is not particularly limited. For example, the first core portion can be polyesters such as polyethylene terephthalate, and the first sheath portion can be polyolefins such as polyethylene. It can also be that the first core portion is a high-melting-point polyester and the first sheath portion is a low-melting-point polyester having a melting point lower than that of the high-melting-point polyester.

It is preferred that the pressure loss of the first supporting material when air is passed therethrough at a flow rate of 5.3 cm/sec is, for example, 10 Pa or less.

When the first support allows air containing NaCl particles having a particle size of 0.1 μm to pass through at a flow rate of 5.3 cm/sec, the particle collection efficiency may be 10% or less, preferably 5% or less.

The thickness of the first support material is preferably 500 μm or less, and more preferably 300 μm or less. In addition, when the fluororesin porous membrane is folded and deformed into a non-flat shape such as a pleated shape for use, the thickness of the air-permeable support material is preferably 140 μm or more from the viewpoint of easily maintaining the shape. In addition, from the viewpoint of ensuring the insulation breakdown voltage and easily protecting the fluororesin porous membrane from the influence of external static electricity, the thickness of the first support material is preferably 195 μm or more, and more preferably 200 μm or more.

From the viewpoint of reducing the number of sites in contact with the fluororesin porous membrane, the average fiber diameter of the first support material is preferably 23 μm or more, more preferably 25 μm or more. In addition, the average fiber diameter of the first support material can be, for example, 50 μm or less, or 40 μm or less. The average fiber diameter can be evaluated as an object by using fibers within a specified range of an image observed using a microscope, for example, the number average fiber diameter of 200 fibers can be set.

The weight per unit area of the first support material is not particularly limited, and may be, for example, 25 g/m ² or more and 60 g/m ² or less.

The material specific gravity of the first support member is not particularly limited, and may be, for example, 0.8 or more and 1.4 or less.

(3-2) Second Supporting Material

The air filter material preferably further comprises a second support material, which is arranged on either the upstream side or the downstream side in the airflow passing direction relative to the fluororesin porous membrane, and is arranged on the side opposite to the side provided with the first support material relative to the fluororesin porous membrane. The second support material preferably comprises a second core-sheath structure fiber, wherein the second core-sheath structure fiber comprises a second core portion and a second sheath portion having a lower melting point than the second core portion.

Furthermore, as long as the value calculated by the above formula of the first support material is 380 (m/cm ³ ) or less, the value calculated by the above formula for the second support material is not particularly limited, but the second support material also preferably satisfies the following formula 3.

Formula 3: Weight per unit area (g/m ² )/{average fiber cross-sectional area (cm ² )×material specific gravity (g/cm ³ )×thickness (cm)×1000000}≤380 (m/cm ³ )

The value of the second support material calculated by the above-mentioned formula 3 is preferably 350 (m/cm ³ ) or less, and more preferably 300 (m/cm ³ ) or less.

Thus, the contact point of the second supporting material and the fluororesin porous membrane can be reduced, even when the second sheath portion of the second supporting material is melted and thermally welded with the fluororesin porous membrane, the increase of the pressure losses of the air filter material obtained can be suppressed. In addition, by supporting the fluororesin porous membrane from both sides with supporting material, the operability of the air filter material improves.

In addition, the second supporting material is the same as the first supporting material, and the melting point of the second core is preferably 30°C or more higher than the melting point of the second sheath, more preferably 50°C or more higher. Thus, the overall melting of the second supporting material can be suppressed during heat welding. The components of the second core can be, for example, polyesters such as polyethylene terephthalate, or their composite materials. The components of the second sheath can be, for example, polyolefins such as polyethylene or polypropylene, polyamides, or their composite materials. In addition, the combination of the components of the second core and the second sheath is not particularly limited. For example, the second core can be polyesters such as polyethylene terephthalate, and the second sheath can be polyolefins such as polyethylene, or the second core can be a high-melting-point polyester and the second sheath can be a low-melting-point polyester having a melting point lower than that of the high-melting-point polyester.

It is preferred that the pressure loss of the second supporting material when air is passed therethrough at a flow rate of 5.3 cm/sec is, for example, 10 Pa or less.

When the second support allows air containing NaCl particles having a particle size of 0.1 μm to pass through at a flow rate of 5.3 cm/sec, the particle collection efficiency may be 10% or less, preferably 5% or less.

The thickness of the second support material is preferably 500 μm or less, and more preferably 300 μm or less. In addition, when the fluororesin porous membrane is folded and deformed into a non-flat shape such as a pleated shape for use, the thickness of the air-permeable support material is preferably 140 μm or more from the viewpoint of easily maintaining the shape. In addition, from the viewpoint of ensuring the insulation breakdown voltage and easily protecting the fluororesin porous membrane from the influence of external static electricity, the thickness of the second support material is preferably 195 μm or more, and more preferably 200 μm or more.

From the viewpoint of reducing the number of sites in contact with the fluororesin porous membrane, the average fiber diameter of the second support material is preferably 23 μm or more, more preferably 25 μm or more. In addition, the average fiber diameter of the second support material can be, for example, 50 μm or less, or 40 μm or less. The average fiber diameter can be evaluated as an object by using fibers within a specified range of an image observed using a microscope, for example, the number average fiber diameter of 200 fibers can be set.

The weight per unit area of the second support material is not particularly limited, and may be, for example, 25 g/m ² or more and 60 g/m ² or less.

The material specific gravity of the second support member is not particularly limited, and may be, for example, 0.8 or more and 1.4 or less.

(4) Bonding of fluororesin porous membrane and support material, etc.

Hereinafter, the step of stretching the porous fluororesin membrane and the subsequent steps of bonding with a support material will be described.

The fluororesin sheet wound in a roll shape or the like can be stretched using, for example, the apparatus shown in FIG. 4 or the apparatus shown in FIG. 5 or FIG. 6 .

In the apparatus shown in Fig. 4, the fluororesin sheet wound in a roll is provided as a roll 41, and the longitudinally stretched sheet stretched in the longitudinal direction (longitudinal direction) is wound around a winding roll 42. In addition, 43 to 45 denote rolls, 46 and 47 denote heating rolls, and 48 to 52 denote rolls.

Next, the lengthwise stretching sheet is stretched in the width direction using the device shown in Figures 5 and 6. Specifically, the wound lengthwise stretching sheet is set on a roller 61, and is fed out in sequence while being stretched in the width direction using a tenter 65. In the tenter 65, the two ends of the stretching sheet in the width direction are in a state of being clamped by opposite continuous clamps not shown in the figure, respectively, and the opposite continuous clamps are separated from each other while the stretching sheet is fed out, thereby stretching in the width direction. The continuous clamp is configured to be transported from the upstream side to the downstream side along a line that can be adjusted to a specific shape. In addition, the tenter 65 can preheat the stretching sheet in the preheating area 62 on the upstream side, stretch the stretching sheet in the width direction in the middle stretching area 63 while being heated to a specified temperature, and heat fix the stretched sheet in the heat fixing area 64 on the downstream side. The fluororesin porous membrane 31 that has been thermally fixed is overlapped with the first supporting material 32 and the second supporting material 33 that is set up as needed, and is thermally laminated using a combination of a heated hot plate and an opposing plate of a hot pressing device or a pair of heated rollers 66, thereby becoming an air filter material 30 and being wound on a roller 67.

The first sheath portion of the first support material 32 and the second sheath portion of the second support material 33 are partially melted when heated by a combination of a heated hot plate and an opposing plate of a hot pressing device or a pair of heating rollers 66, and attached to the fluororesin porous membrane 31. In this way, the first support material 32 and the second support material 33 are thermally fused to the fluororesin porous membrane 31, thereby obtaining the air filter material 30.

(5) Filtering Packets

Next, the filter pack according to the present embodiment will be described with reference to FIG. 7 .

FIG. 7 is a perspective view of the appearance of the filter pack 20 according to the present embodiment.

The filter pack 20 is provided with the air filter material (for example, the air filter material 30) of the above description. The air filter material of the filter pack 20 is a processed filter material that is processed (pleated) into a serrated shape in which a convex folding portion and a concave folding portion are alternately repeated. The pleated processing can be performed, for example, by a rotary folding machine. The folding width of the filter material is not particularly limited, for example, more than 25 mm and less than 280 mm. The filter pack 20 can increase the folding area of the filter material used in the case of the air filter unit by being subjected to the pleated processing, thereby, an air filter unit with high collection efficiency can be obtained.

In addition to having filter material, filter bag 20 can also be equipped with a spacer (not shown) for maintaining the pleat interval when used for the air filter unit. The material of the spacer is not particularly limited, and hot-melt resin can be preferably used. In addition, it can also be that the air filter filter material 30 has a plurality of embossed protrusions, which are utilized to maintain the pleat interval.

(6) Air filter unit

Next, the air filter unit 1 will be described with reference to FIG. 8 .

FIG. 8 is an external perspective view of the air filter unit 1 according to the present embodiment.

Air filter unit 1 possesses the air filter material or filter bag of the above description, and the framework 25 that air filter material or filter bag are held. Air filter unit can be made in the mode that filter material that does not carry out convex folding and concave folding is held in framework, and can also be made in the mode that filter bag 20 is held in framework 25. Air filter unit 1 shown in Fig. 8 is made using filter bag 20 and framework 25.

The frame 25 is made of, for example, a combination of plates or resin molding, and the filter pack 20 and the frame 25 are preferably sealed with a sealant. The sealant is used to prevent leakage between the filter pack 20 and the frame 25, and for example, a sealant made of epoxy, acrylic, polyurethane or other resin is used.

The air filter unit 1 having a filter pack 20 and a frame 25 can be a micro-pleated air filter unit in which a filter pack 20 extending in a flat plate shape is housed inside the frame 25 and is held therein, or it can be a V-bank type air filter unit or a single header type air filter unit in which a plurality of filter packs extending in a flat plate shape are arranged and held in the frame.

(7) Examples of use

The air filter medium, the filter pack, and the air filter unit of the present embodiment are used, for example, in the following applications.

ULPA filters (Ultra low Penetration Air Filters) (for semiconductor manufacturing), HEPA filters (for hospitals and semiconductor manufacturing), cartridge filters (for industrial use), bag filters (for industrial use), heat-resistant bag filters (for exhaust gas treatment), heat-resistant pleated filters (for exhaust gas treatment), SINBRAN (registered trademark) filters (for industrial use), catalyst filters (for exhaust gas treatment), filters with adsorbents (for HDD assembly), ventilation filters with adsorbents (for HDD assembly), ventilation filters (for HDD assembly, etc.), filters for vacuum cleaners (for vacuum cleaners), general-purpose multilayer felt materials, cartridge filters for gas turbines (for interchangeable parts for gas turbines), cooling filters (for electronic equipment housings), and other fields.

Freeze-drying materials such as freeze-drying containers, automotive ventilation materials for electronic circuits and lamps, container applications such as container caps, protective ventilation applications for electronic equipment, ventilation applications for medical use, and other ventilation/internal pressure adjustment fields.

Flat, pleated, three-dimensional masks (to prevent dust, fumes, bacteria, viruses, etc. from entering the body through the mouth and nose).

[Example]

Hereinafter, examples and comparative examples are shown to specifically describe the contents of the present disclosure.

(Example 1)

For every 1 kg of PTFE fine powder with an average molecular weight of 6.5 million ("Polyflon Fine Powder F106" manufactured by Daikin Industries, Ltd.), 300 g of hydrocarbon oil ("IPSolvent 2028" manufactured by Idemitsu Kosan Co., Ltd.) as an extrusion liquid lubricant is added at 20°C and mixed. Next, the obtained mixture is extruded using a paste extrusion device to obtain a round rod-shaped molded body. The round rod-shaped molded body is formed into a sheet using a calender roll heated to 70°C to obtain a fluororesin sheet. The fluororesin sheet is passed through a hot air drying furnace at 250°C to evaporate and remove the hydrocarbon oil, thereby obtaining a strip-shaped unfired fluororesin sheet with an average thickness of 200 μm and an average width of 150 mm.

Next, the unsintered fluororesin sheet was stretched in the longitudinal direction at a stretching ratio of 5. The stretching temperature in the longitudinal direction was 250° C. Here, the stretching ratio speed (%/s) in the longitudinal direction was 150 (%/s).

Next, the stretched unsintered fluororesin sheet was stretched in the width direction at a stretching ratio of 36 times using a tenter capable of continuous clamping. The stretching temperature in the width direction stretching was 290°C.

Here, with respect to the fluororesin porous membrane obtained by stretching the fluororesin sheet, a first support material is stacked on the upwind side in the passing direction of the air flow, and a second support material is stacked on the leeward side, and the first support material and the second support material are thermally fused to the fluororesin porous membrane using a hot pressing device, thereby obtaining the air filter material of Example 1. In addition, a hot plate heated to 160° C. is clamped with an opposing plate, and a load of 0.4 MPa is applied for 8 seconds, thereby performing thermal lamination using a hot pressing device.

The first supporting material on the upwind side used in Example 1 was a spunbonded nonwoven fabric (average fiber diameter 26 μm, unit weight 40 g/m ² , thickness 210 μm) composed of fibers having a core/sheath structure with PET as a core and PE as a sheath. The second supporting material on the leeward side used in Example 1 was a spunbonded nonwoven fabric (average fiber diameter 26 μm, unit weight 40 g/m ² , thickness 210 μm) composed of fibers having a core/sheath structure with PET as a core and PE as a sheath.

(Example 2)

290 g of hydrocarbon oil (IPSolvent 2028, manufactured by Idemitsu Kosan Co., Ltd.) as an extrusion liquid lubricant was added to each 1 kg of PTFE fine powder ("Polyflon Fine Powder F106" manufactured by Daikin Industries, Ltd.) with an average molecular weight of 6.5 million and mixed at 20°C. Next, the obtained mixture was extruded using a paste extrusion device to obtain a round rod-shaped molded body. The round rod-shaped molded body was formed into a sheet using a calendering roll heated to 70°C to obtain a fluororesin sheet. The fluororesin sheet was passed through a hot air drying furnace at 250°C to evaporate and remove the hydrocarbon oil, thereby obtaining a strip-shaped unfired fluororesin sheet with an average thickness of 200 μm and an average width of 150 mm.

Next, the unsintered fluororesin sheet was stretched in the longitudinal direction at a stretching ratio of 5. The stretching temperature in the longitudinal direction was 250° C. Here, the stretching ratio speed (%/s) in the longitudinal direction was 150 (%/s).

Next, the stretched unsintered fluororesin sheet was stretched in the width direction at a stretching ratio of 36 times using a tenter capable of continuous clamping. The stretching temperature in the width direction stretching was 290°C.

Here, with respect to the fluororesin porous membrane obtained by stretching the fluororesin sheet, a first support material is stacked on the upwind side in the passing direction of the air flow, and a second support material is stacked on the leeward side, and the first support material and the second support material are thermally fused to the fluororesin porous membrane using a hot pressing device, thereby obtaining the air filter material of Example 2. In addition, a hot plate heated to 160° C. is clamped with an opposing plate, and a load of 0.4 MPa is applied for 8 seconds, thereby performing thermal lamination using a hot pressing device.

The first support material on the upwind side used in Example 2 was a spunbonded nonwoven fabric (average fiber diameter 37 μm, unit weight 40 g/m ² , thickness 210 μm) composed of fibers having a core/sheath structure with PET as a core and PE as a sheath. The second support material on the leeward side used in Example 2 was a spunbonded nonwoven fabric (average fiber diameter 37 μm, unit weight 40 g/m ² , thickness 210 μm) composed of fibers having a core/sheath structure with PET as a core and PE as a sheath.

(Example 3)

In Example 3, an air filter material was produced in the same manner as in Example 1, except that a spunbonded nonwoven fabric (average fiber diameter 37 μm, unit weight 30 g/m ^{2 , thickness 350 μm) composed of fibers having a core/sheath structure with PET as a core and PP as a sheath was used as a first support material for the air filter material, and a spunbonded nonwoven fabric (average fiber diameter 37 μm, unit weight 30 g/m 2} , thickness 350 μm) composed of fibers having a core/sheath structure with PET as a core and ^PP as a sheath was used as a second support material for the air filter material. The air filter material was subjected to heat lamination using a hot plate heated to 195° C. and a load of 0.4 MPa was applied for 8 seconds.

(Example 4)

In Example 4, an air filter material was produced in the same manner as in Example 1, except that a spunbonded nonwoven fabric (average fiber diameter 37 μm, unit weight 50 g/m ² , thickness 400 μm) composed of fibers having a core/sheath structure with PET as a core and PP as a sheath was used as a first support material for the air filter material, and a spunbonded nonwoven fabric (average fiber diameter 37 μm, unit weight 50 g/m ² , thickness 400 μm) composed of fibers having a core/sheath structure with PET as a core and PP as a sheath was used as a second support material for the air filter material. The air filter material was subjected to heat lamination using a hot plate heated to 195° C. and applying a load of 0.4 MPa for 8 seconds.

(Example 5)

In Example 5, air filter materials were prepared in the same manner as in Example 1, except that a spunbonded nonwoven fabric (average fiber diameter 37 μm, unit weight 30 g/m ² , thickness 190 μm) composed of fibers having a core/sheath structure with PET as a core and PE as a sheath was used as the first supporting material for the air filter material, and a spunbonded nonwoven fabric (average fiber diameter 37 μm, unit weight 30 g/m ² , thickness 190 μm) composed of fibers having a core/sheath structure with PET as a core and PE as a sheath was used as the second supporting material for the air filter material.

(Comparative Example 1)

In Comparative Example 1, an air filter medium was obtained in the same manner as in Example 2 except that the first support material and the second support material used for the air filter medium were changed as described below.

The first supporting material on the upwind side used in Comparative Example 1 was a spunbonded nonwoven fabric (average fiber diameter 20 μm, unit weight 40 g/m ² , thickness 280 μm) composed of fibers having a core/sheath structure with PET as a core and PE as a sheath. The second supporting material on the leeward side used in Comparative Example 1 was a spunbonded nonwoven fabric (average fiber diameter 20 μm, unit weight 40 g/m ² , thickness 200 μm) composed of fibers having a core/sheath structure with PET as a core and PE as a sheath.

In addition, various physical properties measured in Examples 1 to 5 and Comparative Example 1 are as follows.

(Pressure loss of laminated products)

A sample in which only the first support and the second support were laminated on the fluororesin porous membrane but not thermally fused was placed on a filter holder with a diameter of 100 mm, the inlet side was pressurized with a compressor, and the air flow rate was adjusted to 5.3 cm/sec with a flow meter. The pressure loss at this time was then measured with a manometer.

(Pressure loss of air filter media)

The air filter medium sample was placed on a filter holder with a diameter of 100 mm, the inlet side was pressurized by a compressor, and the air flow rate was adjusted to 5.3 cm/sec by a flow meter. The pressure loss at this time was then measured by a manometer.

(Increase in pressure loss due to thermal welding)

The amount of increase in pressure loss due to thermal fusion was calculated by subtracting the value obtained by measuring the pressure loss in the laminated product from the value obtained by measuring the pressure loss in the air filter medium.

(Thickness of fluororesin porous membrane)

Using a film thickness meter (1D-110MH, manufactured by Mitutoyo Corporation), five sheets of the measurement object were stacked, the total film thickness was measured, and the value obtained by dividing the value by 5 was defined as the film thickness of one sheet.

(Thickness of first supporting member, thickness of second supporting member)

An ABS digital indicator (ID-C112CX manufactured by Mitutoyo Corporation) was fixed to an instrument stand, and the thickness value when a load of 0.3 N was applied to the measurement object was read.

(Thickness of air filter media)

An ABS digital indicator (ID-C112CX manufactured by Mitutoyo Corporation) was fixed to an instrument stand, and the thickness value when a load of 0.3 N was applied to the measurement object was read.

(Weight per unit area of the first supporting material, weight per unit area of the second supporting material)

The weight per unit area is a value obtained by dividing the mass (g) measured by a precision balance on a sample cut into a 4.0 cm×12.0 cm rectangular shape by the area (0.0048 m ² ).

(Average fiber diameter of the first support material, average fiber diameter of the second support material)

Use a scanning electron microscope (SEM) to photograph the surface of the sample at 1000-5000 times, draw two orthogonal lines on the photographed image, and measure the thickness of the image of the fiber intersecting these lines as the fiber diameter. The number of fibers measured is more than 200. For the fiber diameter obtained in this way, a log-normal plot is drawn with the horizontal axis as the fiber diameter and the vertical axis as the cumulative frequency, and the value with a cumulative frequency of 50% is taken as the average fiber diameter. Regarding the geometric standard deviation representing the distribution of fiber diameter, based on the results of the above log-normal plot, the fiber diameter with a cumulative frequency of 50% and the fiber diameter with a cumulative frequency of 84% are read and calculated using the following formula.

Geometric standard deviation [-] = cumulative frequency 84% fiber diameter / cumulative frequency 50% fiber diameter

(Total fiber length per unit volume of the first support material, total fiber length per unit volume of the second support material)

The value calculated by weight per unit area (g/m ² )/{average fiber cross-sectional area (cm ² )×material specific gravity (g/cm ³ )×thickness (cm)×1,000,000} was defined as the total fiber length per unit volume.

(Average fiber cross-sectional area of the first support material, average fiber cross-sectional area of the second support material)

The average fiber diameter obtained in the above-mentioned measurement (average fiber diameter of the first support member, average fiber diameter of the second support member) is used as a value calculated by assuming a cross-sectional shape as a circle.

(Total fiber length of supporting material)

The total fiber length per unit volume of the first support material + the total fiber length per unit volume of the second support material was calculated as the total total fiber length of the support material.

(Collection efficiency of laminated product for NaCl particles with a particle size of 0.1 μm)

According to the method described in Appendix 5 (regulations) of JIS B9928 for the generation method of NaCl aerosol (pressurized spray method), the NaCl particles generated by the atomizer were classified into a particle size of 0.1 μm using an electrostatic classifier (manufactured by TSI), and the particles were charged and neutralized using americium 241. The permeation flow rate was adjusted to 5.3 cm/sec, and a particle counter (manufactured by TSI, CNC) was used to determine the number of particles before and after the laminated product in which only the first supporting material and the second supporting material were laminated on the fluororesin porous membrane without heat fusion. The collection efficiency was calculated using the following formula.

Collection efficiency (%) = (CO/CI) × 100

CO = the number of NaCl particles with a particle size of 0.1 μm captured by the measurement sample

CI = the number of NaCl particles with a particle size of 0.1 μm supplied to the measurement sample

(Transmittance of NaCl particles with a particle size of 0.1 μm in the laminate)

The value obtained by {100(%) - collection efficiency of the laminated product for NaCl particles with a particle size of 0.1 μm (%)} was taken as the transmittance (%) of the laminated product for NaCl particles with a particle size of 0.1 μm.

(Collection efficiency of air filter media for NaCl particles with a particle size of 0.1 μm)

According to the method described in Appendix 5 (regulations) of JIS B9928 for the generation method of NaCl aerosol (pressurized spray method), the NaCl particles generated by the atomizer were classified into a particle size of 0.1 μm using an electrostatic classifier (manufactured by TSI), the particles were charged and neutralized using americium 241, and the permeation flow rate was adjusted to 5.3 cm/sec. A particle counter (manufactured by TSI, CNC) was used to determine the number of particles before and after the air filter material, and the collection efficiency was calculated using the following formula.

Collection efficiency (%) = (CO/CI) × 100

CO = the number of NaCl particles with a particle size of 0.1 μm captured by the measurement sample

CI = the number of NaCl particles with a particle size of 0.1 μm supplied to the measurement sample

(Permeability of NaCl particles with a particle size of 0.1 μm in the air filter medium)

The value obtained by {100(%) - collection efficiency of NaCl particles with a particle size of 0.1 μm by the air filter medium (%)} was defined as the permeability (%) of NaCl particles with a particle size of 0.1 μm by the air filter medium.

(Transmittance ratio)

The value obtained by {the permeability of NaCl particles with a particle size of 0.1 μm in the air filter medium/the permeability of NaCl particles with a particle size of 0.1 μm in the laminated product} was calculated as the permeability ratio.

(PF value of NaCl particles with a particle size of 0.1 μm in air filter media)

Using NaCl particles with a particle size of 0.1 μm, the PF value was calculated according to the following formula from the pressure loss and collection efficiency (collection efficiency of NaCl particles with a particle size of 0.1 μm) of the air filter medium.

PF value = {-log ((100-collection efficiency (%))/100)}/(pressure loss (Pa)/1000)

(Dielectric breakdown voltage of air filter media)

The dielectric breakdown voltage of the target air filter medium sample was measured by a short-time (rapid voltage increase) test in accordance with JIS C2110-1 solid electrical insulating materials - Test methods for dielectric breakdown strength.

The physical properties of the air filter media of Examples 1 to 5 and Comparative Example 1 are shown in the following table.

【Table 1】

As mentioned above, although embodiment of this disclosure is described, it should be understood that various changes in form and detail are possible without departing from the spirit and scope of this disclosure described in the claims.

Claims (10)

1. An air filter medium (30), comprising: A fluororesin porous membrane (31); and a first support material (32) supporting the fluororesin porous membrane, The porous fluororesin membrane is thermally fused to the first support material. The first support material has a core-sheath structure fiber including a first core portion and a first sheath portion having a lower melting point than the first core portion. The first supporting material satisfies the following formula: Formula: Weight per unit area (g/m ² )/{average fiber cross-sectional area (cm ² )×material specific gravity (g/cm ³ )×thickness (cm)×1000000}≤380 (m/cm ³ ). 2. The air filter material according to claim 1, wherein: The air filter medium further comprises a second support material (33) supporting the fluororesin porous membrane. The porous fluororesin membrane is located between the first support material and the second support material. The porous fluororesin membrane is thermally fused to the second support material. The second support material has a core-sheath structure fiber including a second core portion and a second sheath portion having a lower melting point than the second core portion. The second supporting material satisfies the following formula: Formula: Weight per unit area (g/m ² )/{average fiber cross-sectional area (cm ² )×material specific gravity (g/cm ³ )×thickness (cm)×1000000}≤380 (m/cm ³ ). 3. The air filter material according to claim 1 or 2, wherein: The dielectric breakdown voltage of the air filter material is above 0.8 kV. 4. The air filter material according to claim 1 or 2, wherein: The air filter medium has a thickness of 350 μm or more and 1000 μm or less. 5. The air filter material according to claim 1 or 2, wherein: The PF value determined by the pressure loss when air is passed through the air filter material at a flow rate of 5.3 cm/sec and the collection efficiency of NaCl particles with a particle size of 0.1 μm is 20 or above, as determined by the following formula: PF value = {-log((100-collection efficiency (%))/100)}/(pressure loss (Pa)/1000). 6. The air filter material according to claim 1 or 2, wherein: The first support material has a weight per unit area of 25 g/m ² or more and 60 g/m ² or less. 7. The air filter medium according to claim 1 or 2, wherein: The first support material has an average fiber diameter of 23 μm or more. 8. A filter pack (20), which is the air filter medium according to claim 1 or 2, and is folded in a shape so as to generate convex folds and concave folds. 9. An air filter unit (1), comprising: The air filter material according to claim 1 or 2, or a pleated filter material (20) as the air filter material according to claim 1 or 2, wherein the pleated filter material (20) is folded in a manner to produce convex folds and concave folds; and A frame (25) holds the air filter medium or the pleated filter medium. 10. A method for manufacturing an air filter medium (30), comprising the following steps: Preparing a fluororesin porous membrane (31); preparing a first support material (32); and thermally welding the porous fluororesin membrane to the first support material, The first support material (32) has a core-sheath structure fiber including a first core portion and a first sheath portion having a lower melting point than the first core portion, and satisfies the following formula: Formula: Weight per unit area (g/m ² )/{average fiber cross-sectional area (cm ² )×material specific gravity (g/cm ³ )×thickness (cm)×1000000}≤380 (m/cm ³ ).