JP2003200013A - Air filter medium, air filter pack and air filter unit using the same, and method of manufacturing air filter medium - Google Patents

Abstract

(57) [Problem] To provide an air filter medium in which the degree of increase in pressure loss and decrease in collection efficiency are suppressed. The filter medium includes a porous membrane and a first nonwoven fabric. The porous membrane is made of PTFE. First
The nonwoven is laminated on at least one side of the porous membrane. Then, the first nonwoven fabric includes a core 43 and a plurality of leaves 45.
And a core / leaf composite fiber consisting of The core 43 is
It is the first thermoplastic resin. The plurality of leaves 45 are made of a second thermoplastic resin having a melting point difference of 20 ° C. or more from the first thermoplastic resin, have a smaller diameter than the core 43, and extend in the circumferential direction on the outer peripheral side of the core 43. They are arranged at intervals.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an air filter medium, an air filter pack and an air filter unit using the same, and a method for manufacturing an air filter medium.

[0002]

2. Description of the Related Art Polytetrafluoroethylene (hereinafter referred to as PTF) is used as a high-performance air filter medium used for cleaning air in a clean room, liquid crystal or semiconductor manufacturing equipment.
There is a filter medium using a porous membrane made of E). This PTF
The E porous membrane is usually heat-sealed and laminated with an air-permeable support material arranged so as to sandwich the PTFE porous membrane from both sides in order to improve the membrane strength and improve the handleability. As such a breathable support material, a nonwoven fabric of core-sheath composite fibers having a polyester core and a polyethylene sheath is generally used. Non-woven fabric with a core / sheath structure is generally used as a breathable support material because only the sheath part melts and the core part does not melt during heat fusion lamination, so that shrinkage does not occur and heat fusion does not occur with wrinkles. This is because it can be laminated.

[0003]

By the way, trapping efficiency and pressure loss are characteristics which show the performance of the air filter medium. The PTFE porous membrane has a higher collection efficiency because the fibers are finer than conventional glass filter media, and
Pressure loss is kept low. However, when the PTFE porous membrane is heat-fused and laminated with a nonwoven fabric, the fiber structure is changed by receiving the pressure contact force from the nonwoven fabric. As a result, problems occur such as a defect in the air filter medium, an increase in pressure loss of the air filter medium, and a decrease in collection efficiency. The applicant's study found that the rigidity of the polyester used in the core of the nonwoven fabric greatly contributes to the pressure contact force exerted by the core / sheath structure nonwoven fabric on the PTFE porous membrane during heat fusion lamination. did. That is, since the conventional non-woven fabric uses a rigid polyester for the core, the PTF is not used during the heat fusion lamination.
It became clear that the E porous film was easily damaged.

Further, since the sheath portion of the non-woven fiber is fused to the PTFE porous membrane during heat fusion lamination, the PT of the portion is fused.
The FE porous membrane becomes clogged, which causes an increase in pressure loss. Furthermore, since the PTFE porous membrane as a filter medium has a small fiber diameter and fine mesh, the dust retention property was smaller than that of the conventional glass filter medium. An object of the present invention is to prevent wrinkles from being generated during heat fusion lamination, and to suppress the degree of increase in pressure loss and decrease in collection efficiency, an air filter medium, an air filter pack and an air filter unit, and An object of the present invention is to provide a method for manufacturing an air filter medium that suppresses an increase in pressure loss and a decrease in collection efficiency.

[0005]

An air filter medium according to a first aspect comprises a porous membrane and a first nonwoven fabric. The porous membrane is made of PTFE. The first nonwoven fabric has a melting point difference of 2 between the core portion made of the first thermoplastic resin and the first thermoplastic resin.
A core / leaf composite fiber composed of a second thermoplastic resin having a temperature of 0 ° C. or higher and having a diameter smaller than that of the core portion and comprising a plurality of leaf portions circumferentially arranged on the outer peripheral side of the core portion. It is configured. The core part and the leaf part may have a lower melting point as long as the difference between the melting point of one and the melting point of the other is 20 ° C. or more, and like the nonwoven fabric of the core / sheath structure, the melting point of the sheath part (leaf part). Does not have to be lower than the melting point of the core. In addition,
In the present invention, when the resin used for the core and the leaves does not have a melting point, the softening point is used instead.

The core / leaf composite fiber is composed of a core portion made of two kinds of thermoplastic resins and a plurality of leaf portions, and the fiber cross section is in a state in which a plurality of leaf portions surround the periphery of the core portion, The fibers of each leaf are much thinner and less rigid than the sheath of conventional core / sheath composite fibers. For this reason, PTFE
The pressure contact force that the PTFE porous membrane receives from the non-woven fabric when the non-woven fabric having the core / leaf structure is heat-sealed and laminated on the porous film is smaller than that when the non-woven fabric having the core / sheath structure is heat-sealed and laminated. Mechanical damage to the porous film is reduced. As a result, it is possible to obtain an air filter medium in which the degree of increase in pressure loss and the decrease in collection efficiency are suppressed.

In the conventional core / sheath structure non-woven fabric, particles in the outside air pass through the non-woven fabric and are directly captured by the PTFE porous membrane. In this air filter medium, the core / sheath structure non-woven fabric sheath is used. Since a plurality of leaf fibers having a smaller diameter than the portion fibers are arranged around the core portion, the non-woven fabric can serve as a prefilter. Therefore, with this air filter medium, it is possible to reduce the load on the PTFE porous membrane and improve the amount of dust retention of the entire air filter medium.

The above-mentioned effect is that the core / leaf non-woven fabric is made of PTF.
E This is an air filter medium that is heat-fused and laminated on at least one side of a porous membrane, and is effective if a non-woven fabric having a core / leaf structure is disposed on the upstream side as a filter. Nonwoven fabric with leaf structure-PTF
E porous membrane, core / leaf structure non-woven fabric-PTFE porous membrane-core /
A combination of a non-woven fabric having a leaf structure, a non-woven fabric having a core / leaf structure, a porous PTFE membrane, and a non-woven fabric having a core / sheath structure may be used. When a plurality of PTFE porous membranes are used, a non-woven fabric having a core / leaf structure may be arranged on the most upstream side as a filter, and the air filter medium has a core / leaf non-woven fabric-PTFE porous membrane. -PTFE porous membrane, core / leaf structure non-woven fabric-PTFE porous membrane-PTFE porous membrane-Core / leaf structure non-woven fabric or core / sheath structure non-woven fabric, core / leaf structure non-woven fabric-PTFE porous membrane-core / leaf structure non-woven fabric Nonwoven fabric or core / sheath structure non-woven fabric-PTFE porous membrane, core / leaf structure non-woven fabric-P
A combination of TFE porous membrane-nonwoven fabric having a core / leaf structure or nonwoven fabric having a core / sheath structure-PTFE porous membrane-nonwoven fabric having a core / leaf structure or nonwoven fabric having a core / sheath structure may be used.

According to a second aspect of the present invention, in the air filter medium according to the first aspect, the first thermoplastic resin has a lower melting point than the second thermoplastic resin. In this air filter medium, the resin of the core portion is melted during the heat fusion lamination with the non-woven PTFE porous membrane and passes through the gaps of the leaf portions, and P
Fusing with the TFE porous membrane can be achieved. In this case, in the core / sheath structure non-woven fabric, the melted thick fibers in the sheath part are brought into contact with and fused to the PTFE porous membrane, whereas in the core / leaf structure non-woven fabric, they exude from the gaps between the leaf parts. The core resin is PTF
E The phenomenon of fusion occurs when it comes into contact with the porous film.

Therefore, in this air filter medium,
Compared to the case of using the core / sheath structure non-woven fabric, the pressure contact force to the PTFE porous membrane during heat fusion lamination becomes smaller,
Damage to the FE porous film is mitigated and PTF
E The clogging portion of the porous film is reduced. An air filter medium according to a third aspect is the air filter medium according to the first aspect, wherein the second thermoplastic resin has a lower melting point than the first thermoplastic resin.

In this air filter medium, the non-woven PT
During the heat fusion lamination with the FE porous membrane, the fine leaf fibers are melted, and fusion with the PTFE porous membrane can be achieved. In this case, in the non-woven fabric having the core / sheath structure, the melted thick fibers in the sheath part are brought into contact with the PTFE porous membrane to be fused, whereas
In a non-woven fabric having a leaf structure, the fibers of the leaves are much thinner than the core-sheath fibers.

Therefore, in this air filter medium,
Compared to the case of using the core / sheath structure non-woven fabric, the pressure contact force to the PTFE porous membrane during heat fusion lamination becomes smaller,
Damage to the FE porous film is mitigated and PTF
E The clogging portion of the porous film is reduced. An air filter medium according to a fourth aspect includes a porous membrane and a first nonwoven fabric. The porous film is made of PTFE. The first nonwoven fabric is heat-sealed and laminated on at least one side of the porous membrane. Each of the fibers of the non-woven fabric is made of two kinds of thermoplastic resin having a melting point difference of 20 ° C. or more, has at least one dent in the fiber cross section, and has an A value of 0.9 or less in the following formula. A long-fiber non-woven fabric composed of certain irregular-shaped composite long fibers,
It is characterized in that the long-fiber nonwoven fabric has a partial heat-bonded portion, and the low melting point polymer is melted or softened in the partial heat-bonded portion to bond the constituent fibers to each other and integrate them as a whole. [Equation 1] A = r / R r: radius of inscribed circle in fiber cross section R: radius of circumscribed circle in fiber cross section In this air filter medium, the first nonwoven fabric is made of two kinds of thermoplastic resins and has a fiber cross section. As a result of having one or more depressions and having a certain degree of irregularity, it has a core / leaf structure. Therefore, the pressure contact force that the PTFE porous membrane receives from the nonwoven fabric when the nonwoven fabric having the core / leaf structure is heat-sealed and laminated on the PTFE porous film is smaller than that when the nonwoven fabric having the core / sheath structure is heat-sealed and laminated. This allows PTFE
Mechanical damage to the porous film is reduced. As a result, it is possible to obtain an air filter medium in which the degree of increase in pressure loss and the decrease in collection efficiency are suppressed.

Further, in this air filter medium, since the non-woven fabric has one or more depressions in the fiber cross section and has a specific degree of irregularity to increase the surface area, particles are likely to come into contact with each other, It has a filter-like function. Therefore, with this air filter medium, the amount of dust retention as the entire filter medium is improved. An air filter medium according to a fifth aspect is the air filter medium according to any one of the first to fourth aspects, in which the first nonwoven fabric is heat-sealed and laminated on both surfaces of the porous membrane.

In an air filter medium in which a nonwoven fabric is heat-sealed and laminated on both sides of the PTFE porous membrane, the pressure contact force which the PTFE porous membrane receives from the nonwoven fabric during the heat-sealing lamination is P
This is larger than when a nonwoven fabric is heat-sealed and laminated on one side of the TFE porous membrane. However, in this air filter medium, since a nonwoven fabric having a core / leaf structure is used, damage to the PTFE porous membrane from the nonwoven fabric is caused by:
It is reduced as compared to the case where a core / sheath structure nonwoven fabric is used. Therefore, here, even in the case of the air filter medium in which both sides of the PTFE porous membrane are supported by the nonwoven fabric, it is possible to suppress the extent to which the pressure loss increases and the collection efficiency decreases.

An air filter medium according to a sixth aspect of the present invention is the air filter medium according to any one of the first to fourth aspects, wherein the first non-woven fabric is heat-fused and laminated on one surface of the porous membrane to form the second non-woven fabric. Further prepared. The second non-woven fabric is
While being heat-fused and laminated on the other surface of the porous film,
The core / sheath composite fiber is composed of a core portion and a sheath portion having a melting point lower than that of the core portion.

As described above, in the air filter medium of the present invention, as long as the first nonwoven fabric is arranged on the upstream side, the kind of the nonwoven fabric arranged on the downstream side is not particularly limited. Here, in particular, the case where the first non-woven fabric is arranged on the upstream side of the PTFE porous membrane and the second non-woven fabric is arranged on the downstream side,
In this case, the generation of wrinkles at the time of heat fusion lamination is suppressed, and the increase in pressure loss and the decrease in collection efficiency are suppressed.

An air filter medium according to a seventh aspect is the air filter medium according to any one of the first to sixth aspects,
From the pressure loss when air is allowed to permeate at a flow rate of 5.3 cm / sec and the collection efficiency measured using silica particles having a particle size of 0.10 μm or more and 0.12 μm or less, the following formula [Formula 2] PF ₁ = [-Log (transmittance (%) / 100) / pressure loss (Pa)] × 100 (where, transmittance (%) = 100−collection efficiency (%)) PF ₁ value calculated according to Is 22, preferably 25,
More preferably, it exceeds 32.

For an air filter medium having a high PF ₁ value, P
Since the fibers of the TFE porous membrane are finer and have a finer fiber structure with a smaller packing rate, the damage to the high PF ₁ value air filter medium from the nonwoven fabric during heat fusion lamination is low PF ₁ value air. Larger than filter media. Therefore, the degree of increase in the pressure loss of the air filter medium and the decrease in the collection efficiency due to the heat-sealing lamination of the non-woven fabric are also large.

Therefore, in this air filter medium, particularly, the air filter medium having a high PF ₁ value has a core / leaf structure as a non-woven fabric, so that the PTFE porous membrane is damaged during heat fusion lamination. I am trying to reduce it. An air filter medium according to claim 8 is the air filter medium according to any one of claims 1 to 7, which has a collection efficiency of particles having a particle size of 0.3 μm or more when the velocity of the filter medium permeating air is 1.4 cm / sec. 99.97
% And a pressure loss of 15 Pa or more and 250 Pa or less when the filter medium permeation wind velocity is 1.4 cm / sec.

An air filter unit having such performance is generally used in HEPA (High Efficiency Particulul).
ate Air) It has a standard as a filter and is suitable for use in a space where high cleanliness is required, but since it has a fine fiber structure, damage during heat fusion lamination tends to be large. . Therefore, here, by using a non-woven fabric having a core / leaf structure, it is possible to prevent the fiber structure from being damaged at the time of heat-sealing lamination and to ensure the function as a HEPA filter.

In the air filter medium according to claim 9 or the air filter medium according to any one of claims 1 to 7, the particle size is 0.1 when the air velocity passing through the filter medium is 1.4 cm / sec.
It is used for an air filter unit having a collection efficiency of particles of 1 μm or more of 99.9999% or more and a pressure loss of 30 Pa or more and 250 Pa or less when the flow velocity of the filter medium is 1.4 cm / sec.

An air filter unit having such characteristics is generally used in ULPA (Ultralow Penetration Ai).
r) It has a standard as a filter and is suitable for use in a space that requires a higher degree of cleanliness than the HEPA filter, but because it has a finer fiber structure than the HEPA filter, heat fusion The damage during lamination will be even greater.

Therefore, here, by using a non-woven fabric having a core / leaf structure, it is possible to prevent the fiber structure from being damaged at the time of heat fusion lamination, and to ensure the function as a ULPA filter. An air filter pack according to a tenth aspect is formed by forming the air filter medium according to any one of the first to ninth aspects into a predetermined shape.

The air filter medium is generally processed into a predetermined shape in order to be further processed as an air filter unit or the like, but in such processing,
It may be damaged by the pressure contact force from a member or the like attached to the processing device. However, in this air filter pack, since the non-woven fabric having the core / leaf structure is adopted as the non-woven fabric, damage to the air filter medium is reduced even during such processing.

The air filter pack according to claim 11 is
In the air filter pack according to claim 10, the predetermined shape is a pleated shape. The air filter medium is pleated (folded) to be processed into an air filter unit. At this time, for example, when the air filter medium is folded by a reciprocating type by two folding blades, the air filter medium and the folding blades rub against each other. May occur, and a shear force may act between the PTFE porous membrane and the nonwoven fabric. However, in this air filter pack, since the non-woven fabric having the core / leaf structure, which is less rigid than the fibers of the non-woven fabric having the core / sheath structure, is used as the non-woven fabric, damage to the PTFE porous membrane during pleating is reduced.

An air filter unit according to a twelfth aspect comprises the air filter pack according to the tenth or eleventh aspect, and an outer frame body for accommodating the air filter pack. In this air filter unit, a non-woven fabric having a core / leaf structure is used as the air filter medium, so that when the air filter unit is processed, PT is used.
Damage to the FE porous film is reduced, and defects as an air filter unit are suppressed.

An air filter unit according to a thirteenth aspect is the air filter unit according to the twelfth aspect, wherein the first non-woven fabric is arranged on the upstream side during use. In this air filter unit, since the first non-woven fabric having the core / leaf structure is arranged on the upstream side, the function of the first non-woven fabric as a pre-filter can be sufficiently exerted, and the dust retention of the entire air filter medium is maintained. The amount can be improved. In addition,
When in use means mainly when the air filter unit is installed at a predetermined installation location, and upstream means the outside air side during use, that is, the side where the outside air is sucked.

A method for manufacturing an air filter medium according to a fourteenth aspect comprises a first step and a second step. In the first step, a porous film made of PTFE is produced. In the second step, the core portion made of the first thermoplastic resin and the second thermoplastic resin having a melting point difference of 20 ° C. or more with the first thermoplastic resin have a smaller diameter than the core portion, and the outer peripheral side of the core portion. The first non-woven fabric composed of core / leaf composite fibers composed of a plurality of leaf portions arranged at regular intervals in the circumferential direction is heat-sealed and laminated on at least one side of the porous membrane.

According to this manufacturing method, since the non-woven fabric having the core / leaf structure is heat-sealed and laminated on the PTFE porous membrane, the non-woven fabric having the core / sheath structure is heat-sealed and laminated at the time of pressure welding. The damage received is reduced. Therefore, here, it is possible to obtain the air filter medium in which the degree of increase in pressure loss and the decrease in collection efficiency are suppressed.

A method for manufacturing an air filter medium according to a fifteenth aspect comprises a first step and a second step. In the first step, a porous film made of PTFE is produced. In the second step, a heteromorphic composite made of two kinds of thermoplastic resins having a melting point difference of 20 ° C. or more, having at least one or more depressions in the fiber cross section, and having an A value of 0.9 or less in the following formula. A long-fiber non-woven fabric composed of long fibers, the long-fiber non-woven fabric has a partial heat-bonded portion, and the low-melting point polymer is melted or softened in the partial heat-bonded portion to bond the constituent fibers to each other and integrate them as a whole. The first nonwoven fabric, which is characterized in that it is heat-sealed and laminated on at least one surface of the porous membrane. [Formula 1] A = r / R r: radius of inscribed circle in fiber cross section R: radius of circumscribed circle in fiber cross section In this manufacturing method as well, in the same manner as in the manufacturing method of claim 14, PT
Since a non-woven fabric having a core / leaf structure is heat-sealed and laminated on the FE porous film, damages caused by pressure welding are reduced as compared with a case where a non-woven fabric having a core / sheath structure is heat-sealed and laminated. Therefore, also here, it is possible to obtain the air filter medium in which the degree of increase in pressure loss and the degree of decrease in collection efficiency are suppressed.

[0031]

BEST MODE FOR CARRYING OUT THE INVENTION [Air Filter Unit] An air filter unit according to an embodiment of the present invention includes an air filter medium and a frame for accommodating the air filter medium. The air filter medium consists of a PTFE porous membrane and PT
A sheet material obtained by heat-sealing and laminating two permeable support materials arranged so as to sandwich the FE porous film from both sides.

The porous PTFE film has a thickness of 0.05.
Is about 60 μm, and the fiber diameter is 0.05 to 0.2 μm.
(Preferably 0.05 to 0.14 μm, more preferably 0.05 to 0.1 μm) and a PF ₁ value of more than 22 (preferably 25, more preferably 32) is used. Non-woven fabric has a basis weight of 15 to 500 g / m
² (preferably 20 to 150 g / m ^2, more preferably 20
˜70 g / m ² ) is used. Further, as shown in FIG. 1, this non-woven fabric is composed of a core portion 43 made of two kinds of thermoplastic resins and a core / leaf composite fiber 41 made of a plurality of leaf portions 45, and the plurality of leaf portions 45 are made of a core portion. They are arranged on the outer peripheral side of 43 at intervals in the circumferential direction. That is,
The core / leaf composite fiber has a fiber cross section in which a plurality of leaves 45 surround the periphery of the core 43. Further, each leaf portion 45 has a smaller diameter than the core portion 43.

Examples of the thermoplastic resin forming the core portion 43 and the leaf portion 45 include polyester polymers, polyamide polymers, polyolefin polymers (polyethylene, polypropylene) and the like. The two kinds of thermoplastic resins forming the core / leaf composite fiber are appropriately selected so that the difference in melting point between the core portion 43 and the leaf portion 45 (difference in softening point for those having no melting point) is 20 ° C. or more. When the difference in melting point is less than 20 ° C., the thermoplastic resin having a higher melting point is melted or softened and adhered to the heat roll 19 (described later) during the heat fusion lamination, resulting in deterioration in operability. It is not preferable because the air filter medium may be crushed or shrink and wrinkles may be contained in the filter medium.

From another perspective, this core / leaf composite fiber 41 has at least one recess 47 in the fiber cross section as shown in FIG. is there. [Equation 1] A = r / R (r: radius of inscribed circle in fiber cross section, R: radius of circumscribed circle in fiber cross section) The core / leaf composite fiber has a specific degree of irregularity and is at least one. Since it has three or more depressions, the surface area of the fiber is large, the area in contact with the dust is high, and the dust collecting property is improved. Moreover, since the collected dust can be stored in the recess, the dust collecting performance as the prefilter is further improved.

The core / leaf composite fiber in the present embodiment is a multi-leaf type composite cross section in which both the core portion and the leaf portion are exposed on the fiber surface. The low melting point resin may be arranged on either the core or the leaf. The composite ratio of the core part and the leaf part is more preferably core / leaf = 40/60 to 80/20. The A value indicates the degree of irregularity of the cross-sectional shape of the fiber, and the closer the A value is to 1, the shallower the recess is. On the other hand, the smaller the A value, the greater the recess depth of the recess. Will be things. When the A value exceeds 0.9, the degree of irregularity of the fiber decreases,
The depression of the depression is shallow, dust cannot be stored, and the effect of having the depression disappears. On the other hand, although the lower limit of the A value is not particularly limited, it is preferably about 0.3. When the A value is less than 0.3, the effect of collecting fine dust in the hollow portion of the fiber is improved, but the spinnability in producing the fiber tends to be unstable.

The nonwoven fabric as the air-permeable support material for an air filter medium of the present invention has a partial heat-pressure contact portion, and the low melting point polymer is melted or softened at the partial heat-pressure contact portion to integrate the constituent fibers with each other. There is. As a method of performing partial thermal pressure welding, a method of performing partial thermal pressure welding through an embossing device or the like, a method of partially performing thermal fusion bonding through an ultrasonic welding machine, and the like can be effectively used.

By this heat pressure contact, the low melting point polymer existing at the portion contacting the convex portion of the embossing roll is melted or softened to be resinified, and the constituent fibers are adhered to each other to be integrated. Therefore, the obtained long-fiber nonwoven fabric is
The mechanical properties and dimensional stability are improved, and the pleats have good rigidity and proper workability. This non-woven fabric is
The fibers of each leaf portion 45 are much thinner and less rigid than the sheath portion of the conventional core / sheath composite fiber. Therefore, P
Even when it is heat-sealed and laminated on the TFE porous membrane, PT
The pressure contact force that the FE porous membrane receives from the non-woven fabric is smaller than that in the case where the non-woven fabric having the core / sheath structure is heat-sealed and laminated,
The mechanical damage to the PTFE porous membrane will be reduced.

The air filter medium thus constructed has a pressure loss of 50 to 980 pa and a particle diameter of 0.10 to 10 when the air is permeated at a flow rate of 5.3 cm / sec.
Collection efficiency of 0.12 μm silica particles is 99.0% or more (preferably 99.9% or more, more preferably 99.9%).
9% or more). Also, the air filter media is
The air filter pack is alternately folded back to have a corrugated shape every 15 to 150 mm. Air filter
The space between adjacent folded-back portions is maintained at about 2 to 15 mm by a spacer or a corrugated separator.

The frame body is formed by assembling four aluminum frame members, and the air filter pack is housed in the inner space. The frame and the air filter medium are sealed with an adhesive or the like to maintain airtightness to form an air filter unit. The air filter unit configured as described above preferably has a collection efficiency of 99.97% or more for particles having a particle size of 0.3 μm or more when the filter medium permeation wind velocity is 1.4 cm / sec. When the wind speed is 1.4 cm / sec, the collection efficiency of particles having a particle size of 0.1 μm or more is 9
It is more preferably at least 9.9999%.

[Method for Manufacturing Air Filter Medium] This method for manufacturing an air filter medium comprises a porous film producing step and a heat fusion laminating step. In the porous film manufacturing process,
A PTFE porous membrane is produced as described in detail in the examples below.

In the heat-sealing laminating step, the nonwoven fabric composed of the core / leaf composite fibers 41 is heat-sealed and laminated on at least one side of the PTFE porous membrane. In the heat-sealing laminating step, the nonwoven fabric is heat-sealed and laminated on the heat roll 19 (see FIG. 4) arranged on one side of the porous film while being arranged between the PTFE porous film and the heat roll 19. To be done.

[0042]

Examples [Production of PTFE porous membrane] First, PTFE fine powder having a number average molecular weight of 6.2 million (“Polyflon Fine Powder F-104” manufactured by Daikin Industries, Ltd.
U ") 100 parts by weight, 32 parts by weight of a hydrocarbon oil (" ISOPER "manufactured by Esso Oil Co., Ltd.) as an extrusion aid was added and mixed.

Next, this mixture was formed into a round bar shape by paste extrusion. Then, this round bar shaped body is formed into a film by a calender roll heated to 70 ° C.,
A PTFE film was obtained. This film is passed through a hot air drying oven at 250 ° C. to remove the extrusion aid by evaporation to give an average thickness of 20.
An unfired film having a thickness of 0 μm and an average width of 150 mm was obtained. Next, this unsintered PTFE film was stretched in the longitudinal direction at a stretch ratio of 7.5 using the apparatus shown in FIG. The unbaked film was set on roll 1, and the stretched film was wound on winding roll 2. The stretching temperature is 250
Performed at ° C. In FIG. 3, 3 to 9 are rolls and 1
0 is a heat roll, 11 is a cooling roll, and 12 is a roll.

Next, the obtained longitudinally stretched film is
A device shown in the left half of Fig. 4 that can be sandwiched between continuous clips.
Stretching in the width direction with a tenter at a draw ratio of 30 times
Then, heat fixation was performed. The stretching temperature at this time is 290 ° C.
The fixed temperature was 360 ° C. and the stretching speed was 330% / sec.
It was. The physical properties of the PTFE porous membrane at this time are as follows.
there were. Pressure loss: 150Pa Collection efficiency: 99.999981% PF₁Value: 44.0 In FIG. 4, 14 is an unwinding roll and 15 is a pre-roll.
Heat zone, 16 is stretching zone, 17 is heat setting zone, 1
9 is a heat-fusing laminating roll, 21 is a take-up roll
Shown respectively. <Example 1> A non-woven fabric was formed on both surfaces of the above PTFE porous membrane.
Polyethylene / polyester core / leaf structure
Woven fabric ("Arsima A0404WT" manufactured by Unitika Ltd.)
"O" unit weight 40g / m²  Core: Polyethylene Leaf: Po
Reester) and the device shown in the right half of FIG.
By heat-sealing, an air filter medium was obtained. This
The heat fusion conditions at that time were as follows. Heating temperature: 160 ℃ Line speed: 15m / min Unwinding tension: 50g / cm <Example 2> As a nonwoven fabric, one surface of the PTFE porous membrane
The non-woven fabric of the core / leaf structure of Example 1 was used for
Has a polyethylene / polyester core / sheath structure
Non-woven fabric with core / sheath structure (“Elves T” manufactured by Unitika Ltd.)
"0403 WDO" with a unit weight of 40 g / m²) Of FIG.
In the device shown in the right half, the core / sheath structure is attached to the heat roll 19 side.
Except for arranging the non-woven fabric, in the same manner as in Example 1,
A filter material was obtained. <Example 3> As a non-woven fabric, a porous PTFE film was formed on both sides of the porous film.
Core / leaf with core / sheath structure of polyethylene / polyester
Structural non-woven fabric ("Super Alcy" manufactured by Unitika Ltd.)
Ma A0405WJK "weight 40g / m²  Core: Polyae
Example except that the stellate leaf part: polyethylene) was used.
An air filter medium was obtained in the same manner as in 1. <Example 4> One side of a PTFE porous membrane as a nonwoven fabric
The core / leaf structure non-woven fabric of Example 3 was used for the
Core / sheath having a core / sheath structure of polyethylene / polyester
Nonwoven fabric with structure (“Elves T040” manufactured by Unitika Ltd.)
3WDO "weight 40g / m ²), The right half of FIG.
The non-woven fabric with a core / sheath structure is placed on the hot roll side with the device shown in
Air filter medium as in Example 1 except that the filter was placed
Got <Comparative Example 1> As a non-woven fabric, polyethylene / polyester
Non-woven fabric with a core / sheath structure (Unitika
Co., Ltd. "Elves T0403WDO" with a unit weight of 40g
/ M ²) Was used in the same manner as in Example 1 except that
A filter material was obtained.

Table 1 shows a comparison of the physical properties of the air filter media of Examples 1 to 4 and Comparative Example 1.

[0046]

[Table 1] As shown in Table 1, in the case of using a nonwoven fabric having a core / leaf structure as the nonwoven fabric (Examples 1 to 4), compared to the case of using a nonwoven fabric having a core / sheath structure of polyethylene / polyester (Comparative Example 1) It can be seen that the increase in pressure loss of the air filter medium is small and the decrease in collection efficiency is small. It can also be seen that the dust retention characteristics are also improved. <Examples 5 to 8> The air filter media produced in Examples 1 to 4 were pleated to a height of 5.5 cm with a reciprocating folder, and after the pleats, a temperature of 90 ° C was applied to bend them. After this, open the pleated air filter media once, apply a spacer made of polyamide hot melt resin, start up again in a pleated form with a reciprocating starter,
An air filter pack was obtained by cutting into a size of 58 cm × 58 cm. The pleat interval at this time is 3.125 m.
It was m / 1 pleats.

Next, the outer dimensions are 61 cm × 61 cm and the inner dimensions are 58.
Prepare an anodized aluminum frame with a size of cm x 58 cm and a thickness of 6.5 cm, put a pleated air filter pack inside this frame, and seal the air filter pack periphery and aluminum frame with urethane adhesive A filter unit was produced. <Comparative Example 2> An air filter unit was produced in the same manner as in Example 5 except that the air filter medium produced in Comparative Example 1 was used.

Table 2 shows a comparison of the physical properties of the air filter units of Examples 5 to 8 and Comparative Example 2.

[0049]

[Table 2] As shown in Table 2, in the case where the air filter unit was manufactured from the filter medium using the nonwoven fabric of the core / leaf structure as the nonwoven fabric (Examples 5 to 8), the filter medium using the nonwoven fabric of the core / sheath structure of polyethylene / polyester. From this, it can be seen that a high-performance air filter unit with less reduction in collection efficiency can be manufactured as compared with the case of manufacturing an air filter unit (Comparative Example 2).

In this example, the pressure loss, the collection efficiency, the transmittance and the PF _{1 of the} PTFE porous membrane and the air filter medium were
The values and dust retention characteristics, the pressure loss of the air filter unit, the collection efficiency, the transmittance and the PF ₂ value were measured as follows. [Pressure loss of PTFE porous membrane and air filter media (P
a)] A measurement sample of the PTFE porous membrane and the air filter medium was set in a filter holder having a diameter of 100 mm, the inlet side was pressurized by a compressor, and the flow rate of air was adjusted to 5.3 cm / sec by a velocity meter. Then, the pressure loss at this time was measured with a manometer. [Collection efficiency (%) of PTFE porous membrane and air filter media] Set the measurement sample of PTFE porous membrane and air filter media in a filter holder with a diameter of 100 mm, pressurize the inlet side with a compressor, and permeate air with a flow meter. The flow rate was adjusted to 5.3 cm / sec. In this state, the particle concentration of 0.10 to 0.12 μm is 10 ⁸ from the upstream side.
Particle counter (PMS LAS-X-CRT)
PARTICLE MEASURING SYSTEM
M INC. The number of permeation particles having a particle diameter of 0.10 to 0.12 μm was determined by (PMS) (the same applies hereinafter), and the ratio of the number of particles upstream and downstream was determined. That is, when the upstream particle concentration was Ci and the downstream particle concentration was Co, the collection efficiency of the measurement sample calculated by the following formula was obtained. [Equation 3] Collection efficiency (%) = (1-Co / Ci) × 100 For an air filter medium having a very high collection efficiency, the sampling time is increased by increasing the suction time. The measurement was performed. For example, if the suction time is increased 10 times, the number of count particles on the downstream side is increased 10 times, and the measurement sensitivity is increased 10 times. [Permeability (%) of PTFE porous membrane and air filter media]
The transmittance of the PTFE porous membrane and the air filter medium was determined by the following formula. [Equation 4] Permeability (%) = 100−Collection efficiency (%) [PF value of PTFE porous membrane and air filter medium] PTF
E The PF ₁ value of the porous film and air filter media is PTFE
It was determined by substituting the pressure loss and the transmittance of the porous membrane and the air filter medium into the following equation. [Equation 5] PF ₁ value = [-log (transmittance (%) / 100) / (pressure loss (Pa) /9.8)] × 100 [dust retention characteristic of air filter medium] Measurement sample of air filter medium Was set in a filter holder having a diameter of 100 mm, the inlet side was pressurized by a compressor, and the flow rate of air permeation was adjusted to 10.6 cm / sec by a velocity meter. In this state, the particle concentration of 0.5 μm from the upstream side is 1 × 10 ⁸ particles /
ft ³ of polystyrene latex was flown, and the pressure loss at this time was measured with a manometer. And the time which becomes twice the initial pressure loss was measured. The air filter medium was measured so that the non-woven fabric having a core / leaf structure was placed on the upstream side. [Pressure Loss (Pa) of Air Filter Unit] Using the device shown in FIG. 5, after the air filter unit is attached, the air velocity passing through the air filter medium is adjusted to 1.4 cm / sec. The pressure loss before and after the unit was measured with a manometer. In FIG. 5, 31 is a blower, 32 and 32 'are HEPA filters, 33 is a test particle introduction pipe, 34 and 34' are straightening plates, 35 is an upstream side test particle collection pipe, and 36 is a static pressure measurement hole. , 37 is a test air filter unit, 38 is a downstream side particle sampling pipe for testing, 3
Reference numeral 9 denotes a laminar flow meter. [Capture efficiency (%) of air filter unit] Using the device shown in Fig. 5, after installing the air filter unit, adjust the wind speed passing through the air filter media to be 1.4 cm / sec. The particle size is 0.10 to 0.12 on the upstream side.
Flowing silica particles with a concentration of 1 × 10 ⁹ / ft ^{3 in} μm and measuring the number of particles with a particle size of 0.1 to 0.12 μm on the downstream side with a particle counter, the ratio of the number of particles on the upstream side and the downstream side I asked. That is, when the upstream particle concentration was Ci and the downstream particle concentration was Co, the collection efficiency of the measurement air filter unit calculated by the following formula was obtained. [Equation 3] Collection efficiency (%) = (1-Co / Ci) × 100 [Transmittance of air filter unit (%)] The transmittance of the air filter unit was determined by the following formula. [Equation 4] Permeability (%) = 100−Collection efficiency (%) [PF value of air filter unit] For the PF ₂ value of the air filter unit, substitute the pressure loss and the transmittance of the air filter unit into the following formula. Was obtained by doing. [Equation 5] PF ₂ value = [− log (transmittance (%) / 100) / (pressure loss (Pa) /9.8)] × 100 In the various measuring methods of the present invention, silica particles are used. However, particles of organic substances, inorganic substances, and ceramics such as polystyrene latex and sodium chloride may be used.

[0051]

EFFECT OF THE INVENTION The nonwoven fabric used in the present invention is composed of core / leaf composite fibers, which are thinner and less rigid than the conventional core / sheath composite fibers in the sheath portion. In this case, the pressure contact force that the PTFE porous membrane receives from the nonwoven fabric is smaller than that when the core / sheath structure nonwoven fabric is heat-sealed and laminated, and the mechanical damage to the PTFE porous membrane is reduced.

Therefore, according to the present invention, it is possible to obtain an air filter medium in which the degree of increase in pressure loss and the decrease in collection efficiency are suppressed.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a cross section of a core / leaf composite fiber used as a nonwoven fabric of an air filter medium according to an embodiment of the present invention.

FIG. 2 is a view schematically showing a cross section of the core / leaf composite fiber from another viewpoint.

FIG. 3 is a schematic view showing an apparatus used for stretching a PTFE film in a longitudinal direction.

FIG. 4 Stretching of PTFE film in the width direction (left half)
And a device (right half) for heat-fusing and laminating a nonwoven fabric on a PTFE film.

FIG. 5 is a schematic view showing a pressure loss measuring device of an air filter unit according to an embodiment of the present invention.

[Explanation of symbols]

41 core / leaf composite fiber 43 core 45 leaf 47 recess

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B01D 46/54 B01D 46/54 69/10 69/10 71/36 71/36 D04H 3/14 D04H 3 / 14 A (72) Inventor Hideyuki Kiyotani 1-1, Nishiichitsuya, Settsu-shi, Osaka Daikin Industrial Co., Ltd. Yodogawa Seisakusho F-term (reference) 4D006 GA44 HA71 MA09 MB01 MC30X NA47 NA66 PA01 PB17 4D019 AA01 BA13 BB03 BB08 BB10 BD01 CA02 CB06 DA04 DA06 4D058 JA13 JB14 JB23 JB25 JB39 SA04 4L047 AA21 AA27 AB10 BA08 BA24 CA05 CA06 DA00

Claims (16)

[Claims] 1. A porous membrane made of polytetrafluoroethylene, and a first non-woven fabric heat-sealed and laminated on at least one side of the porous membrane, wherein the first non-woven fabric is made of a first thermoplastic resin. When,
It is made of a second thermoplastic resin having a melting point difference of 20 ° C. or more with the first thermoplastic resin, has a diameter smaller than that of the core portion, and is arranged at an outer circumferential side of the core portion with a circumferential interval. An air filter medium composed of a core / leaf composite fiber composed of a plurality of leaves. 2. The air filter medium according to claim 1, wherein the first thermoplastic resin has a lower melting point than the second thermoplastic resin. 3. The air filter medium according to claim 1, wherein the second thermoplastic resin has a melting point lower than that of the first thermoplastic resin. 4. A porous membrane made of polytetrafluoroethylene, and a first non-woven fabric that is heat-fused and laminated on at least one side of the porous membrane, wherein the first non-woven fabric has a melting point difference of 20 ° C. or more. A long-fiber non-woven fabric composed of different types of thermoplastic resin, having at least one or more dents in the fiber cross-section, and composed of deformed composite long fibers having an A value of 0.9 or less in the following formula. Has a partial heat-pressure contact portion, the low melting point polymer is melted or softened in the partial heat-pressure contact portion to bond the constituent fibers to each other, and are integrated as a whole,
Air filter media. [Equation 1] A = r / R r: radius of inscribed circle in fiber cross section R: radius of circumscribed circle in fiber cross section 5. The air filter medium according to claim 1, wherein the first nonwoven fabric is heat-sealed and laminated on both sides of the porous membrane. 6. The first non-woven fabric is heat-fused and laminated on one surface of the porous film, is heat-fused and laminated on the other surface of the porous film, and has a core portion and a melting point higher than that of the core portion. The air filter medium according to any one of claims 1 to 4, further comprising a second nonwoven fabric composed of a core / sheath composite fiber having a low sheath portion. 7. A pressure loss when air is permeated at a flow rate of 5.3 cm / sec and a particle size of 0.10 μm or more and 0.12 μm.
From the collection efficiency measured using silica particles of m or less, the following formula [Formula 2] PF ₁ = [-log (transmittance (%) / 100) / pressure loss (Pa)] × 100 (where The air filter medium according to any one of claims 1 to 6, which has a PF ₁ value calculated according to a ratio (%) = 100−collection efficiency (%). 8. The collection efficiency of silica particles having a particle size of 0.3 μm or more is 99.97% or more and the filtration medium permeation velocity is 1.4 cm when the filtration medium permeation velocity is 1.4 cm / sec.
/ Pa second, the pressure loss is 15 Pa or more and 250 Pa
The air filter medium according to any one of claims 1 to 7, which is used in the following air filter unit. 9. The collection efficiency of silica particles having a particle size of 0.1 μm or more is 99.9999% or more and the filtration medium permeation velocity is 1.4 when the permeation velocity of the filtration medium is 1.4 cm / sec.
Pressure loss in the case of cm / sec is 30 Pa or more 250
The air filter medium according to any one of claims 1 to 7, which is used in an air filter unit having Pa or less. 10. An air filter pack comprising the air filter medium according to any one of claims 1 to 9 formed in a predetermined shape. 11. The air filter pack according to claim 10, wherein the predetermined shape is a pleat shape. 12. An air filter unit comprising the air filter pack according to claim 10 or 11, and an outer frame body in which the air filter pack is housed. 13. The air filter unit according to claim 12, wherein the first non-woven fabric is arranged on the upstream side during use. 14. A first step of producing a porous film made of polytetrafluoroethylene; a second melting point difference of 20 ° C. or more between a core portion made of a first thermoplastic resin and the first thermoplastic resin. A first core / leaf composite fiber made of a thermoplastic resin and having a diameter smaller than that of the core portion, and a plurality of leaf portions circumferentially arranged on the outer peripheral side of the core portion. A second step of heat-fusing and laminating a nonwoven fabric on at least one side of the porous membrane. 15. A first step for producing a porous film made of polytetrafluoroethylene, and two kinds of thermoplastic resins having a melting point difference of 20 ° C. or more, and having at least one or more dents in a fiber cross section. However, in the following formula, a long-fiber non-woven fabric composed of irregularly-shaped composite long fibers having an A value of 0.9 or less. The long-fiber non-woven fabric has a partial heat-bonding portion, and the low-melting polymer melts in the partial heat-pressing portion. Alternatively, the first non-woven fabric is characterized in that the constituent fibers are adhered to each other by softening and integrated as a whole, and the first non-woven fabric is heat-fused and laminated on at least one surface of the porous membrane.
A method of manufacturing an air filter medium, comprising: [Equation 1] A = r / R r: radius of inscribed circle in fiber cross section R: radius of circumscribed circle in fiber cross section 16. In the second step, the first nonwoven fabric comprises
The heat-sealing roll disposed on one surface side of the porous film, and heat-sealed and laminated to the porous film in a state of being disposed between the porous film and the heat roll, 16. Manufacturing method of air filter media.