JP5155071B2 - Laminated structure and filter medium comprising the same - Google Patents

Description

  The present invention relates to a laminated structure of two or more layers including a superfine fiber layer in which a thermocompression bonding portion is partially formed, and a filter medium comprising the same.

  In order to prevent environmental pollution caused by harmful substances and reduce contact with the human body, various factories use filters to collect harmful substances. Further, for the purpose of extending the life of the filter, the filter medium is used as a filter unit that is bent into a pleat shape and integrated with a frame in order to increase the filtration area. In addition, from the viewpoint of environmental protection, the regulation value of harmful substances contained in exhaust gas has become strict, and there is a demand for filter media having characteristics such as high collection efficiency, low pressure loss, and collection of fine particles. Yes.

  For high collection efficiency and the collection of fine particles, it is necessary to reduce the diameter of the fibers that make up the filter medium and to reduce the pore diameter. Therefore, filter medium made of ultrafine fibers is often used. ing. On the other hand, the rigidity of the filter media is also required for shape retention after pleating, but ultra-fine fibers often do not have the rigidity required for pleating and shape retention. A multi-layer filter medium integrated with the reinforcing layer of the ultrafine fiber layer is used.

  In addition, since the ultrafine fibers produced by the electrospinning method are used by being laminated on another substrate, fluffing and peeling from the substrate are also problematic, and the processability of the ultrafine fiber layer is low. . In order to solve such a problem, a method has been proposed in which the ultrafine fiber layer is fixed with a resin at a fine interval to prevent breakage of the ultrafine fiber layer (Patent Document 1). However, even in this method, there is a problem that fluff is generated in the ultrafine fiber layer or peeling between the layer and the substrate occurs due to strong friction caused by pleating.

On the other hand, as the filter medium, one in which a super extra fine fiber layer and a reinforcing layer are integrated can be used. Since the reinforcing layer also plays a role of extending the life of the filter, the reinforcing layer is thick. In addition, a filter having high bulkiness and rigidity capable of various processing is used as a filter. However, when the reinforcing layer is made thick, bulky, and rigid, there is a problem that it becomes difficult to pleat the filter medium.
JP 2007-224466 A

  An object of the present invention is to provide a laminated structure having good collection efficiency, low pressure loss, excellent pleatability, no fluffing at the pleat portion, and less delamination between layers, and a filter medium composed thereof. It is in.

As a result of studies by the present inventors, it has been found that the above problems can be achieved by the following configuration. That is, according to the present invention, a laminated structure composed of two or more layers, at least a superfine fiber layer having a diameter of 10 nm to 500 nm, and a non-woven fabric or a thermoplastic resin partly or entirely made of thermoplastic fibers is attached. plurality consists of a nonwoven fabric layer made of nonwoven, and the least also one surface of the laminated structure, a linear, wavy, or thermocompression bonded portions of the zigzag are formed, the heat crimping portion There is provided a laminated structure characterized by being arranged in parallel. Moreover, the filter medium which consists of the said laminated structure is provided.

  The laminated structure of the present invention is composed of a superfine fiber layer and a nonwoven fabric layer partly or entirely made of thermoplastic fibers or attached with a thermoplastic resin, and a linear, wavy or zigzag heat is applied to the part to be pleated. Since it has a crimping portion, the processing can be easily performed, and fluff does not occur in the pleated portion during the processing or subsequent use. Further, in the above laminated structure, the superfine fiber layer and the nonwoven fabric layer are joined and integrated by thermocompression bonding, the separation between the layers hardly occurs, the collection efficiency is good due to the presence of the superfine fiber layer, and the pleat portion Since there is no thermocompression bonding part, pressure loss is extremely small.

  The laminated structure of the present invention is a laminated structure composed of two or more layers, and includes at least a superfine fiber layer comprising a fiber structure of ultrafine fibers having a diameter of 10 nm to 500 nm, and a part or all of the thermoplastic fibers. It is a laminated structure which consists of the nonwoven fabric layer which consists of a nonwoven fabric which consists of a nonwoven fabric or a nonwoven fabric which the thermoplastic resin adhered.

In the invention, the basis weight of the ultrafine fiber fiber structure constituting the ultrafine fiber layer is preferably 0.01 to ²⁰ g / m ² from the viewpoint of collection efficiency and pressure loss, and preferably 0.1 to 3 g. This is more preferably / m ² .

  The ultrafine fibers are preferably formed by electrospinning, sea-island spinning, or meltblowing, but fibers formed by electrospinning are preferred from the viewpoint that the fiber diameter can be easily achieved.

The polymer constituting the ultrafine fiber is not particularly limited as long as it can be formed into a fiber by a known method, and a polymer that can be spun by an electrospinning method is particularly preferable. Specific examples include, for example, polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polyacrylic acid, polyacrylonitrile-methacrylate copolymer, polyvinylidene chloride, polyvinyl chloride (PVC), and polyvinylidene chloride. Acrylate copolymer, polyethylene (PE), polypropylene (PP), aramid, polyparaphenylene terephthalamide, polyparaphenylene terephthalamide-3,4'-oxydiphenylene terephthalamide copolymer, polymetaphenylene iso Phthalamide, polyvinyl alcohol (PVA), polyvinyl acetate, cellulose, polyethylene sulfide, polyvinyl acetate, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polylactic acid (PLA), polyglycol Phosphoric acid (PGA), polyethersulfone, polyetherethersulfone, polyvinylidene fluoride (FVDF), polyurethane, poly (N-vinylpyrrolidone), polyvinylmethylketone, polyethyleneimide (PEI), polyoxymethylene (POM), poly Ring-opening polymers of ethylene oxide (PEO), nylon 6, nylon 66, etc., polyvinyl bromide, polychlorotrifluoroethylene, polychloroprene, norbornene monomers and hydrogenated products thereof, fibroin, natural rubber, chitin, chitosan Organic materials such as collagen, zein, and the like, and these may be copolymerized or mixed. Furthermore, silica, _{alumina, Y 2 O 3, ZrO 2} , may be an inorganic material that sol-gel method can be utilized, such as titania.

On the other hand, the basis weight of the nonwoven fabric constituting the nonwoven fabric layer is preferably 10 to 200 g / m ^{2 and} more preferably ²⁰ to 70 g / m ² from the viewpoint of filter performance and pleatability.

  The fiber constituting the nonwoven fabric is not particularly limited, and may be a synthetic fiber, a natural fiber or an inorganic fiber, as long as a part thereof includes a thermoplastic fiber or a thermoplastic resin. good. Examples of natural fibers include cellulose fibers and protein fibers, and examples of inorganic fibers include glass fibers, carbon fibers, and steel fibers. The polymer of the synthetic fiber is not particularly limited, and examples thereof include polyethylene, polypropylene, polyethylene terephthalate, polyacrylonitrile, nylons such as nylon 6 and nylon 66, and aromatic polyamides.

  In the present invention, in order to form a thermocompression bonding portion in the laminated structure, the nonwoven fabric must be a nonwoven fabric partly or entirely made of thermoplastic fibers, or a thermoplastic resin needs to be attached.

  The polymer constituting the thermoplastic fiber and the polymer constituting the thermoplastic resin are not particularly limited, and examples thereof include polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), and polyvinylidene chloride. , Polystyrene (PS), polytetrafluoroethylene (PTFE), acrylonitrile butadiene styrene resin, acrylic resin (PMMA), and the like.

  Although the diameter of the fiber which forms the said nonwoven fabric is not specifically limited, From the viewpoint of the rigidity of a laminated structure, 500 nm or more and 100 micrometers or less are preferable, and 1 micrometer or more and 100 micrometers or less are more preferable.

  When the nonwoven fabric is composed of thermoplastic fibers and other fibers, the weight ratio of the thermoplastic fibers to the total weight of the nonwoven fabric is preferably 5 to 100% by weight, and more preferably 40 to 100% by weight.

  Moreover, when the thermoplastic resin has adhered to the fiber which comprises the said nonwoven fabric, 5-50 weight% is preferable and the weight ratio with respect to the nonwoven fabric total weight of a thermoplastic resin is more preferable 10-50 weight%.

  In the present invention, the laminated structure is composed of the above ultrafine fiber layer and the nonwoven fabric layer, and at least one surface of the laminated structure is formed with a linear, wavy, or zigzag thermocompression bonding portion. It is important that a plurality of the thermocompression bonding portions are arranged in parallel. Since the pleating process is performed in the thermocompression bonding part, the pleating process can be easily performed, and the pleated part (bending part) that is easily worn during the process or the subsequent use is thermally fused. There is no fluff of ultra-fine fibers, and delamination hardly occurs. Further, in the above fiber structure, the superfine fiber layer is laminated, so that the collection efficiency is good and the pressure loss can be reduced, but the thermocompression bonding part is formed only in the pleat part, and gas or Since the liquid is not mainly in the part through which it passes, the above performance can be exhibited without regret.

When the shape of the above-mentioned thermocompression bonding part is a wave shape or a zigzag shape, the width of the thermocompression bonding part is 1 with respect to the width between two tangent lines in contact with the wavy or zigzag thermocompression bonding part. / 2 or more and less than 1, more preferably 1/2 to 3/4. In addition, the thickness of the thermocompression bonding portion of the laminated structure is a portion of a portion that is not thermocompression-bonded (hereinafter sometimes referred to as a non-thermocompression bonding portion) from the viewpoint of pleating workability and embrittlement of the laminated structure by thermocompression bonding. 5-70% is preferable with respect to thickness. Moreover, in the surface which has the thermocompression bonding part of a laminated structure, the area ratio of the thermocompression bonding part with respect to the whole surface is 0.1 to 50% from a viewpoint of the adhesiveness of each layer of a filter medium, and a pressure loss.

  The nonwoven fabric can be produced by a spunbond method, a melt blow method, a flash spinning method, a tow opening method, a paper making method, a carding method, an airlaid method, a filament orthogonal method, or the like. These nonwoven fabrics may be used as they are, but antistatic processing, water repellent processing, hydrophilic processing, and the like may be applied depending on the purpose.

  Furthermore, a fiber structure of ultrafine fibers is formed on the nonwoven fabric layer. In the present invention, a method for forming ultrafine fibers can be preferably exemplified by an electrospinning method.

  The electrospinning method is a method of forming a super fine fiber by applying a high voltage to the polymer solution capable of forming the super fine fiber and spraying it on the fiber structure. Further, the fiber diameter of the obtained ultrafine fiber depends on the applied voltage, the solution concentration, the spray scattering distance, and the like, and can be set to an arbitrary fiber diameter by adjusting these conditions.

  The solvent for dissolving the polymer described above varies depending on the material and is not particularly limited. For example, water, acetone, chloroform, methanol, ethanol, propanol, toluene, tetrahydrofuran, benzene, cyclohexane, benzyl alcohol, 1 , 4-dioxane, methylene chloride, carbon tetrachloride, pyridine, trichloroethane, acetic acid, formic acid, hexafluoroisopropanol, N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, Acetonitrile can be mentioned.

  More specifically, as a solvent in the case of wholly aromatic polyamide, N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, etc. are used, and in the case of polyacrylonitrile. As the solvent, N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide and the like can be used.

  As conditions for electrospinning, the concentration is 1 to 16%, the voltage is 5.0 to 70 kV, the spinning distance is 5.0 to 50 cm, and the voltage per unit distance is 0.5 to 7.0 kv / cm. Is preferred.

  Specifically, a polymer solution in which a wholly aromatic polyamide polymer and a solvent are dissolved at a weight ratio of 5:95 to 16:84 is prepared, and the fiber diameter described above is obtained by carrying out under a voltage of 5 to 70 kV. Aramid ultrafine fibers can be produced.

  Examples of the spinning solution supply include a method of extruding from a nozzle and a base, and a method of supplying the spinning solution by attaching it to a disk or drum immersed in the spinning solution so that it becomes a required amount and continuously rotating it. When supplying from a nozzle or a nozzle | cap | die, since the internal diameter of a discharge part has no correlation with the fiber diameter of a super extra fine fiber, there is no limitation.

  After forming the ultrafine fiber layer on the nonwoven fabric layer, these layers are partially thermocompression bonded. The method for forming the thermocompression bonding part is not particularly limited, but thermal compression with an embossing roll is preferable. The embossing roll temperature is preferably in the temperature range of ± 50 ° C. of the melting point of the thermoplastic fiber or resin contained in the nonwoven fabric layer, and more preferably in the temperature range of melting point −20 ° C. to melting point + 20 ° C.

In the cantilever method, the bending resistance of the nonwoven fabric of two or more layers including the ultrafine fiber layer in which the thermocompression bonding part is partially formed in the present invention is preferably 7 cm or more from the viewpoint of pleating workability and pleated shape maintenance.
Although the processing method of a pleat is not specifically limited, A reciprocating pleating machine, a rotary pleating machine, etc. can be used.

  The use of the laminated structure of the present invention is not limited in any way, but since it includes a layer made of ultrafine fibers, it has characteristics such as low pressure loss and high collection efficiency, and therefore is preferably used as a filter. Moreover, since the fiber structure of two or more layers has a thermocompression bonding part on one side or both sides thereof, it can be easily processed into a pleated shape, and is more preferably used as a pleated filter material.

  Hereinafter, the present invention will be described in more detail based on examples. However, the present invention is not limited by the following examples. In addition, each characteristic value in an Example was measured with the following method.

(1) Fiber diameter About 100 fibers arbitrarily sampled from the ultra-fine fiber layer, it was measured with a scanning electron microscope JSM6330F (manufactured by JEOL), and the average value of the fiber diameters was obtained. The measurement was performed at a magnification of 30,000 times.

(2) Bending softness Determined according to the cantilever method described in JIS L1096.

(3) The ratio of the thickness of the thermocompression bonding part to the thickness of the non-thermocompression bonding part The thickness of the thermocompression bonding part and the non-thermocompression bonding part was obtained by observing the cross section of the laminated structure at a magnification of 100 times with JSM6330F (manufactured by JEOL). Measurement was performed on 10 arbitrarily sampled portions, and an average value was obtained. From the measured average value, the ratio of the thickness of the thermocompression bonding part to the non-thermocompression bonding part was calculated.

(4) Evaluation of filter performance Using filters obtained by reworking the filters of Examples and Comparative Examples into flat plates, 0.3 μm NaCl particle-containing air for testing was used as a test filter so that the surface speed was 5.3 cm / s. The pressure difference before and after the filter was measured with a micro differential pressure gauge, and the NaCl particle concentrations C _IN and C _OUT on the upstream side and downstream side of the filter were measured with a particle counter, respectively, and the collection efficiency was determined by the following equation. .
Collection efficiency (%) = (1−C _IN / C _OUT ) × 100

(5) Evaluation of pleat processability Evaluation of pleat processability is: ○ for pleat tips that are uniform and acute, pleat tips that are somewhat uniform and acute, and pleat tips that are uneven and partially obtuse X.

(6) Evaluation of delamination In the evaluation of delamination of the thermocompression bonding part after pleating, the case where the thermocompression bonding part was not peeled was evaluated as ◯, and the case where the thermocompression bonding part was peeled off was evaluated as x.

(7) Evaluation of fluffing Evaluation of fluffing of the pleated part was made by judging that no fluffing was evaluated as “◯”, some fluffing that was not conspicuous was “Δ”, and that fluffing was conspicuous as “x”.

[Example 1]
For the nonwoven fabric layer, a spunbond nonwoven fabric made of polypropylene having an average fiber diameter of 25 μm and a basis weight of 50 g / m ² was used.
The target polymer was produced by the interfacial polymerization method. That is, 14.2 g of isophthalic acid chloride was dissolved in 100 ml of tetrahydrofuran dehydrated with sodium metal, and while stirring, a solution in which 7.41 g of metaphenylenediamine was dissolved in 100 ml of tetrahydrohyran was gradually added as a trickle and became cloudy. An emulsion was prepared. Stirring was continued for about 5 minutes, and then an aqueous solution in which 14.8 g of sodium carbonate and 28.0 g of sodium chloride were dissolved in 300 ml of water was quickly added, and the mixture was vigorously stirred for about 5 minutes. The obtained white polymer was allowed to stand and precipitate, and the transparent aqueous solution phase was removed and filtered to obtain an aromatic polyamide polymer (polymetaphenylene isophthalamide).

Electrospinning was performed according to the method described in JP-A-2006-336173 to produce ultrafine fibers. That is, the obtained aromatic polyamide polymer (polymetaphenylene isophthalamide) was dissolved in N, N-dimethylacetamide so as to be 10% by weight, and an electric field was applied so as to be 1 kV / cm. Then, an ultrafine fiber layer was formed on the spunbonded nonwoven fabric as the lower layer. The basis weight of this ultrafine fiber layer was 0.1 g / m ² .
The obtained ultrafine fibers were observed with a scanning electron microscope, the fiber diameter was measured, and the average value is shown in Table 1.

Next, this laminated body is made of a metal by using a heating roller (upper roller) and a smooth heat-resistant resin roller (lower roller) that are linearly engraved in a direction orthogonal to the rotation direction, and a thermocompression bonding portion of the emboss. The embossing with a width of 60 mm and the area ratio of the thermocompression bonding part in the laminate is 10%. The temperature of the upper roller is 160 ° C., the linear pressure between the upper and lower rollers is 0.5 t / 30 cm. The interval was set to 0.05 mm to obtain a two-layer fiber structure including a super extra fine fiber layer having a thermocompression bonding portion and a nonwoven fabric layer.
The bending resistance of the obtained two-layer fiber structure was measured and pleated at intervals of the thermocompression bonding portion with a reciprocating pleating machine.
The obtained two-layer fiber structure was excellent in pleatability, no delamination was observed, and no fluffing of ultrafine fibers was observed. The results are shown in Table 1.

[Example 2]
A two-layer laminated structure was produced in the same manner as in Example 1 except that the upper roller was changed to a heating roller having an embossed thermocompression bonding portion having a width of 80 mm and an area ratio of the thermocompression bonding portion of the laminate of 20%. The obtained two-layer fiber structure was excellent in pleatability, no delamination was observed, and no fluffing of ultrafine fibers was observed. These results are shown in Table 1.

[Example 3]
Other than changing the upper roller to a heating roller made of metal and wavyly engraved in the direction perpendicular to the rotation direction, the embossed thermocompression bonding part width is 80 mm, and the area ratio of the thermocompression bonding part in the laminate is 20% Produced a two-layer laminated structure in the same manner as in Example 1. The obtained two-layer fiber structure was excellent in pleatability, no delamination was observed, and no fluffing of ultrafine fibers was observed. These results are shown in Table 1.

[Examples 4 to 5]
A two-layered fiber structure was produced in the same manner as in Example 1 except that the electrospinning time was changed. The obtained two-layer fiber structure was excellent in pleatability, no delamination was observed, and no fluffing of ultrafine fibers was observed. These results are shown in Table 1.

[Example 6]
A fiber structure consisting of two layers was produced in the same manner as in Example 1 except that the basis weight of the nonwoven fabric layer was changed to 70 g / m ² . The obtained two-layer fiber structure was excellent in pleatability, no delamination was observed, and no fluffing of ultrafine fibers was observed. These results are shown in Table 1.

[Example 7]
A two-layer fiber structure was produced in the same manner as in Example 1 except that the aromatic polyamide polymer (polymetaphenylene isophthalamide) was dissolved in N, N-dimethylacetamide so as to be 16% by weight. The obtained two-layer fiber structure was excellent in pleatability, no delamination was observed, and no fluffing of ultrafine fibers was observed. These results are shown in Table 1.

[Example 8]
A two-layer laminated structure was produced in the same manner as in Example 1 except that the upper roller was changed to a heating roller having a thermocompression bonding area ratio of 40% in the laminated body. The obtained two-layer fiber structure was excellent in pleatability, no delamination was observed, and no fluffing of ultrafine fibers was observed. The pressure loss was slightly higher but at a practical level. These results are shown in Table 1.

[Example 9]
The upper roller is made of metal and has a wave-shaped engraving shown in FIG. 2 in a direction perpendicular to the rotation direction. The thermocompression bonding section has a width (a) of 60 mm and a tangential width (b) in contact with the thermocompression bonding section. A two-layer laminate structure was produced in the same manner as in Example 1 except that the heating roller was changed to 90 mm, a / b was 2/3, and the area ratio of the thermocompression bonding portion in the laminate was 40%. The obtained two-layer fiber structure was excellent in pleatability, no delamination was observed, and no fluffing of ultrafine fibers was observed. These results are shown in Table 1.

[Example 10]
The upper roller is made of metal and has a zigzag engraving shown in FIG. 3 in a direction perpendicular to the rotation direction. The width (a) of the thermocompression bonding part is 60 mm, and the width of the tangent line in contact with the thermocompression bonding part (b). Was a 90 mm, a / b was 2/3, and a two-layer laminated structure was produced in the same manner as in Example 1 except that the heating roller had a thermocompression bonding area ratio of 40%. The obtained two-layer fiber structure was excellent in pleatability, no delamination was observed, and no fluffing of ultrafine fibers was observed. These results are shown in Table 1.

[Comparative Example 1]
According to the same production method as in Example 1, the same operation as in Example 1 was performed except that embossing was not performed. The obtained two-layer fiber structure was inferior in pleatability, easily peeled between layers, and fluffing of ultrafine fibers was observed. The results are shown in Table 1.

[Comparative Example 2]
The upper roller, the heating of the area ratio 7.8% of the thermocompression bonded portions of the laminate, embossing thermocompression bonding number 62dot ^/ cm 2 (thermocompression bonding area per 1 dot 0.0013 cm ²⁾ and so as punctate (circular) A two-layer laminated structure was produced in the same manner as in Example 1 except that the roll was changed. Although the obtained two-layer fiber structure was not peeled between layers, it was inferior in pleatability, and fluffing of ultrafine fibers was observed. These results are shown in Table 1.

  According to the present invention, it becomes easy to pleat a fiber structure having a high collection efficiency, a low pressure loss, and a fine particle collection ability, and further, fluffing of ultrafine fibers in the pleat portion is suppressed. Since the pressure loss when processed into a filter unit is reduced and a filter unit with high collection efficiency can be obtained, it is useful for the textile industry.

It is the schematic of the surface of the laminated structure of this invention which has a linear thermocompression bonding part. It is the schematic of the surface of the laminated structure of this invention which has a wavy thermocompression bonding part. It is the schematic of the surface of the laminated structure of this invention which has a zigzag thermocompression bonding part. It is the schematic of the cross section of the laminated structure of this invention.

Explanation of symbols

A Thermocompression bonding part a Width of thermocompression bonding part b Width between two tangent lines in contact with thermocompression bonding part c Thermocompression bonding part thickness d Non-thermocompression bonding part thickness

Claims (9)

A laminated structure composed of two or more layers, at least an ultrafine fiber layer made of a fiber structure of ultrafine fibers having a diameter of 10 nm to 500 nm, and a nonwoven fabric or a thermoplastic resin partly or entirely made of thermoplastic fibers. consists of a nonwoven fabric layer made of deposited non-woven fabric, and, in least also one surface of the laminated structure, a linear, wavy, or thermocompression bonded portions of the zigzag are formed, the heat crimping portion A multilayer structure characterized by being arranged in parallel in a plurality. For two width between tangent to the thermocompression bonded portions of the wavy or zigzag-like, layered structure of claim 1, wherein the width of the thermocompression bonded portions is 1 / 2-3 / 4. The laminated structure according to claim 1 or 2 , wherein the thickness of the thermocompression bonding part is 5 to 70% of the thickness of the part not thermocompression bonded. The laminated structure according to any one of claims 1 to 3 , wherein an area ratio of the thermocompression bonding portion to the whole surface is 0.1 to 50% on the surface having the thermocompression bonding portion of the laminated structure. The laminated structure according to any one of claims 1 to 4 , wherein the bending resistance of the laminated structure by a cantilever method is 7 cm or more. The laminated structure according to any one of claims 1 to 5, wherein the thermocompression bonding part is formed by thermocompression bonding with a pair of embossing rolls or an embossing roll and a flat roll. The laminated structure according to any one of claims 1 to 6, wherein the laminated structure is bent into a pleat shape at a thermocompression bonding portion. Two tangents in contact with the wavy or zigzag thermocompression bonding part are parallel so that the surface having the crimping part sandwiches the wavy or zigzag crimping part and circumscribes the crimping part, respectively, and has a maximum distance. The laminated structure according to claim 2, wherein the two tangent lines are drawn to each other. The filter medium which consists of a laminated structure of any one of Claims 1-8 .

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