JP2009148748A - Filter and filter unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a filter of a low pressure drop and high filtration accuracy capable of removing fine dust, bacteria, viruses and the like floating in air or in water. <P>SOLUTION: The filter is characterized by comprising a filter layer of a thickness of 50 μm or greater comprised of a fiber made from a thermoplastic rein and of a nanofiber of a fiber diameter of 1 to 500 nm by 0.5 to 70 mass%, having collection efficiency of 90% or greater with respect to particles of a mean diameter of 0.3 μm at an air flow rate of 3.2 m/min, and having an initial pressure drop of not greater than 980 Pa at an air flow rate of 3.2 m/min. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  It relates to filters and filter units.

  In recent years, demand for filtration systems such as desalination of seawater and reuse of wastewater has increased in response to an increase in global water consumption. In a high performance filtration system, a filter using a membrane is used as a filtering material such as a microfiltration (MF) membrane or a reverse osmosis (RO) membrane. However, filters using these membranes have very high collection performance, but high pressure loss, short lifespan, and the need to increase the number of filters to maintain stable operation. Therefore, the device is a large device.

  Therefore, a filter with high performance and low pressure loss is required. As a low-pressure loss filter, a filter using a woven or knitted fabric of a fiber, a nonwoven fabric, or the like is known, but the filtration performance is low and it cannot be used in the field of microfiltration. In order to improve the filtration accuracy of the filter, it is necessary to reduce the fiber diameter of the filtration layer and keep the pore diameter (pore size) small. However, in melt blown nonwoven fabrics currently used for many filters, patent literature 1 and so on, even if the resin viscosity is devised to make it ultrafine, the fiber diameter is about 1 μm at the lower limit, and it is possible to obtain a filter that can collect nano-sized foreign substances such as viruses. There wasn't.

  On the other hand, Patent Document 2 discloses a filter in which a fiber having an average fiber diameter of 217 nm by an electrospinning method is used as a filtration layer. Part of the particles flowed downstream, and the virus in water having a size of 10 to 100 nm could not be removed.

  Also, in air filters, the demand for air environment clarification is increasing in each field, and HEPA filters (High Efficiency Particulate Air Filter) and ULPA filters (Ultra Low Penetration Air Filter), which are ultra-high performance filters, The use has been expanded from the manufacturing factory of electronic components such as semiconductors used in the past to food factories and pharmaceutical factories.

  In recent years, as a high collection efficiency, an electrospinning method is a spinning solution in which a polymer is dissolved in a solvent. An electric field is applied between the spinning nozzle and the fiber collection drum, and the fibers discharged from the nozzle are made of ultrafine fibers. A filter is disclosed which is made into a component fiber (Patent Document 3). However, although the collection performance is improved, the pressure loss is also increased, and the performance of the filter is not sufficiently improved.

As described above, there has been a demand for a filter with high filtration accuracy that can remove fine viruses and particles in a fiber filter having high collection performance and low pressure loss.
JP 2002-151560 A Japanese Unexamined Patent Publication No. 2007-2222813 JP 2006-326579 A

  An object of the present invention is to provide a filter having high filtration accuracy and low pressure loss that can remove fine dust, bacteria, viruses, and the like floating in the air and water.

  That is, the present invention includes a filter layer having a thickness of 50 μm or more, comprising a fiber made of a thermoplastic resin, 0.5 to 70% by mass of nanofibers having a fiber diameter of 1 to 500 nm, and an air flow rate of 3. The filter has a collection efficiency of 90% or more for particles having an average particle diameter of 0.3 μm at 2 m / min and an initial pressure loss of 980 Pa or less at an air flow rate of 3.2 m / min.

  Moreover, this invention is a filter unit characterized by having the filter of this invention.

  The filter of the present invention is a microfiltration filter having a low pressure loss and made of a fiber that can remove fine dust, bacteria, viruses and the like floating in the air and water.

  In the filter of the present invention, the filtration layer includes fibers made of a thermoplastic resin. By including fibers made of a thermoplastic resin, heat sealing is possible, and the manufacturing process can be simplified and the adhesive strength can be improved. In addition, since the form retainability is enhanced by heat setting, it is possible to set a high operating pressure when using the filter, and to increase the processing amount per unit time. In addition, the volume can be reduced because it can be incinerated at the time of disposal.

  Examples of the thermoplastic resin include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyester such as polylactic acid (PLA), nylon 6 (N6), nylon 6, 6 (N66), nylon 12 (N12), and the like. Polyamides such as polyamide, polyethylene (PE) and polypropylene (PP), and polyarylenes such as polyphenylene sulfide (PPS) are included.

  The melting point of the thermoplastic resin is preferably 160 ° C. or higher. By doing so, it can also be used to treat high boiling liquids such as oil. Here, the melting point refers to a temperature at which crystals melt in a crystalline resin, and in an amorphous resin that does not exhibit a clear melting point, the Vicat softening point, heat distortion temperature, and the like correspond to the melting point. For example, PLA is 170 ° C, PET is 255 ° C, N6 is 220 ° C, and PPS is 280 ° C.

  Moreover, it is preferable that the thermoplastic resin which forms the filter layer of a filter has chemical resistance. By doing so, it can also be used for treatment of waste liquid containing chemicals. For example, N6 and N66 have resistance to alkali, and PE, PP, and PPS have resistance to both acid and alkali.

  The thermoplastic resin may contain additives such as particles, a flame retardant, and an antistatic agent as necessary, and other components may be copolymerized.

  As a quantity of the fiber which consists of a thermoplastic resin in a filtration layer, 60 mass% or more is preferable from the point of heat-sealing property or pleat form retention.

  On the other hand, it is preferable that the filtration layer does not contain any of metal fibers, glass fibers, rock fibers, ore fibers, and mineral fibers from the viewpoint of developing heat sealability and pleat form retention. Further, it is preferable from the point of disposal because the volume can be greatly reduced by incineration at the time of disposal after use.

  In the filter of the present invention, it is important that the filtration layer comprises nanofibers having a fiber diameter of 1 to 500 nm. Such a nanofiber is as fine as 1/1000 to 1/10 that of an ultrafine fiber in a filter manufactured by a conventional melt-blowing method, and enables removal of fine substances that could not be achieved by a conventional fiber filter. . In addition, the operating pressure can be much lower than that of a conventional microfiltration filter using a porous membrane.

  By making the fiber diameter of the nanofibers 500 nm or less, it is possible to obtain the effect of removing fine substances and low pressure loss. Moreover, by setting it as 1 nm or more, it can be set as the filter which maintained fiber strength and was excellent in handling property.

  As content of the nanofiber in a filtration layer, it is important to set it as 0.5-70 mass%. By setting the content to 0.5% by mass or more, the effect of removing the fine substance can be obtained. Moreover, it can prevent that a pressure loss becomes high by setting it as 70 mass% or less.

  As a method for producing nanofibers, for example, two or more kinds of polymers having different solubility in a solvent are mixed and melted to form a polymer alloy melt, which is spun into fiber and the easily soluble polymer is removed with a solvent. By doing so, the hardly soluble island component in a polymer alloy can be obtained as a nanofiber.

  In addition, when nanofibers are used as raw materials for nonwoven fabrics and papermaking, they are staple fibers that are cut in the range of 1 to 100 mm and cut fibers that are cut in the range of 0.1 to 10 mm. Either a method of removing the easily soluble polymer component with a solvent and then cutting to an arbitrary cut length, or a method of removing the easily soluble polymer component after cutting the polymer alloy fiber can be employed. .

In a nanofiber having a small fiber diameter, fusion between fibers is likely to occur due to frictional heat or pressing between the cutting blade and the fiber when the fiber is cut. If there is fusion, it becomes difficult to disperse the fibers one by one. Therefore, if the fusion occurs significantly, the fibers are biased and the performance cannot be fully expressed.
In addition, once nanofibers aggregate, the nanofibers strongly aggregate between the fibers, and the fibers are difficult to redisperse. Therefore, when nanofiber is used as a papermaking raw material, the polymer alloy fiber is cut and then the easily soluble polymer is removed in the solvent, so that the solvent of the easily soluble polymer becomes a dispersion medium, and the nanofibers aggregate. Can be suppressed. In addition, when making paper, the solvent is replaced with water. By interposing water between the nanofibers, it is possible to obtain highly dispersed nanofibers for papermaking without aggregation of the fibers. It becomes. Therefore, a method of removing the easily soluble polymer after cutting the polymer alloy fiber is preferable.

  In the filter of the present invention, it is preferable that the filtration layer further comprises fibers having a fiber diameter of 1 to 70 μm. By including fibers with a fiber diameter of 1 μm or more in addition to nanofibers, the size of the micropores can be kept moderate and pressure loss can be suppressed. On the other hand, by making it 70 μm or less, it is uniformly dispersed with the nanofibers to prevent excessive deviation from the fiber diameter of the nanofibers, keep the fibers intertwined, and maintain the size of the pore diameter and the strength of the filtration layer. can do.

  In the filter of the present invention, it is preferable that the filter layer includes fibers fibrillated. The fibrillated fiber forms the body of the filtration layer and contributes to improving the strength, while improving the entanglement with the nanofiber and preventing the fiber from dropping off.

  In the filter of the present invention, it is also preferred that the filtration layer comprises binder fibers. The binder fiber bonds the fibers constituting the filtration layer by melt softening of the adhesive component, and contributes to the improvement of strength. Moreover, by using a fibrous binder, the intersections of the fibers can be efficiently bonded, and the fine pores in the filtration layer can be prevented from being blocked.

  Examples of the form of the filtration layer include a spunbond nonwoven fabric, a melt blown nonwoven fabric, a needle punched nonwoven fabric, a spunlace nonwoven fabric, a thermal bond nonwoven fabric, a resin bond nonwoven fabric, and a wet nonwoven fabric. Of these, wet nonwoven fabrics are preferred because the nanofibers are uniformly dispersed.

  As a method for producing a dispersion used in the production of a wet nonwoven fabric, it is preferable to separately prepare a dispersion of nanofibers and a dispersion of other fibers, and then mix both dispersions. By doing so, nanofibers having a very small fiber diameter compared to other fibers and having an aspect ratio of 100 times or more can be coexisted with other fibers and uniformly dispersed.

  The thickness of the filtration layer containing nanofibers is important to be 50 μm or more. By doing so, the nanofibers are three-dimensionally arranged in the filtration layer while maintaining voids in the filtration layer, and pressure loss can be reduced. Furthermore, by collecting the object to be collected while drawing it into the filtration layer, it is possible to collect it while suppressing a rapid increase in pressure loss. When the thickness is less than 50 μm, the nanofiber layer is easily arranged in the planar direction, the nanofibers are densely arranged, and the pressure loss tends to be high. On the other hand, the upper limit value of the thickness of the filtration layer is preferably 2 mm or less. By doing so, it is easy to pleat, and a sufficient filtration area can be secured even when pleating is performed and the filter unit is incorporated.

  In the filter of the present invention, the average flow pore size of the filtration layer is preferably 50 nm to 20 μm, more preferably 100 nm to 10 μm, and further preferably 500 nm to 5 μm. The fine through-holes existing in the filtration layer are represented by an average flow pore size, and the effect of improving the collection efficiency can be obtained by setting it to 20 μm or less. Moreover, pressure loss can be suppressed by setting it as 50 nm or more. Moreover, if the maximum pore diameter (bubble point diameter) of the filtration layer exceeds 20 μm, there is a high possibility that the trapping object cannot be trapped and flows out downstream of the filter, and the trapping performance decreases. More preferably, it is 10 μm or less. Most preferably, it is preferably in the vicinity of a value indicating the maximum frequency of the pore size distribution, that is, the pressure loss in filtration is reduced without disturbing the flow of the filtration fluid by the pore size in the filtration layer being substantially uniform. It becomes possible to keep.

  The filtration layer in the filter of the present invention preferably has a bending resilience (Gurley method) of 2.0 mN or more as defined in JIS L 1096: 1999. By doing so, it can prevent that the filtration layer itself deform | transforms with a fluid pressure, and a pressure loss arises.

  Alternatively, the filter of the present invention preferably has a support layer comprising fibers having a fiber diameter of 1 to 70 μm on both sides or one side of the filtration layer. Also by doing so, it is possible to prevent the filtration layer itself from being deformed by the fluid pressure and causing pressure loss. Since the filtration layer in the filter of the present invention contains nanofibers having a fiber diameter of 1 to 500 nm, it may be soft depending on the composition design of the constituent fibers, and in this case, the support layer is provided. It is valid. In addition, by providing a support layer on the upstream side, it also functions as a prefilter, contributing to protection of the filtration layer and longer life.

  The filter of the present invention has a trapping efficiency of 90% or more for particles having an average particle diameter of 0.3 μm at an air flow rate of 3.2 m / min, and an initial pressure loss of 980 Pa or less at an air flow rate of 3.2 m / min. is there. That is, the filter has a high filtration accuracy capable of removing fine dust, bacteria, viruses and the like floating in the air and water, and can suppress the pressure loss to a low level.

  The filter unit of the present invention has the filter of the present invention. In the filter unit of the present invention, the filter of the present invention is preferably pleated in a zigzag shape. By doing so, the filtration area can be maintained even in a compact form.

[Measuring method]
(1) Cross-sectional observation of polymer alloy fiber An ultra-thin section was cut out in the cross-sectional direction of the polymer alloy fiber, and observed with a transmission electron microscope (TEM) (H-7100FA type manufactured by Hitachi, Ltd.) at a magnification of 40000 times. In addition, metal dyeing was performed as needed.

(2) Cross-sectional observation of the filtration layer A cross-section of the filtration layer was cut out, a platinum-palladium alloy was vapor-deposited on the cross-section, and observed with a scanning electron microscope (SEM) (S-4000 type manufactured by Hitachi, Ltd.).

(3) Diameter of the fiber constituting the filtration layer The diameter of the ultrafine fiber was calculated from the cross-sectional photograph of the filtration layer by SEM, and a simple average value thereof was obtained.

  The filtration layer was observed in five fields of view at two different magnifications. That is, five fields of view having a magnification of 1000 times and a field size of 600 μm square were taken at different locations, and the diameters of 50 fibers having a diameter of 1 nm to 500 nm randomly extracted in the field of view were observed in increments of 10 nm. In addition, five fields of view having a magnification of 200 times and a field size of 3 mm square were taken at different locations, and the diameters of 50 fibers randomly extracted in the field of view with a diameter exceeding 500 nm were observed in 1 μm increments.

  And for a total of 10 fields of view of two magnifications × 5, taking into consideration the field size and the thickness of the layer, the distribution of the fiber diameter per unit cross-sectional area of the filtration layer is taken, and the ultrafine fibers defined in the present invention Average diameter was calculated.

(4) Mass ratio of fibers constituting the filtration layer For the fiber diameter distribution data obtained in (3) above, the representative value of the diameter of the section of the fiber diameter and the fiber material occupied in the section (nylon 6 etc. ), The weight per unit length of the fiber was calculated, and the frequency according to the number was weighted with the frequency according to the mass. The mass ratio of the nanofibers defined in the present invention was calculated from the fiber diameter distribution data weighted by the frequency.

(5) Average flow pore size and maximum pore size Measured by the method defined in ASTM F316-86.
As a measuring device, a “palm porometer” manufactured by PMI was used, a “Galvic” manufactured by PMI was used as a measuring reagent, a cylinder pressure was set to 150 kPa, and measurement was performed under the conditions of WET UP-DRY UP. .

(6) Pressure loss of filter media Using an apparatus according to JIS B 9908: 2001 format 3, the upstream and downstream pressures of the filter were measured at a passing wind speed of 3.2 m / min. The difference in pressure on the downstream side was defined as pressure loss.

(7) Collection efficiency of filter medium Using a device according to JIS B 9908: 2001 format 3, polystyrene standard particles having a particle size of 0.305 μm and a standard deviation of particle size of 0.0084 as dust (“Uniform Latex” by Ceradyne) Particles ”), measured with a particle counter (KC-22A, manufactured by Rion Co., Ltd.) in a measurement particle size range of 0.3 to 0.5 μm at a filter passing air velocity of 3.2 m / min, and collected by the following formula Efficiency was calculated.
Collection efficiency (%) = (1-C ₂ / C ₁ ) × 100
Here, C ₁ : the number of dusts on the upstream side of the filter C ₂ : the number of dusts on the downstream side of the filter.

(8) Performance evaluation of filter unit for air filtration (Examples 4, 5 and Comparative Example 6)
JIS B 9927: 1999 is applied mutatis mutandis, and polystyrene standard particles (“Uniform Latex Particles” manufactured by Ceradyne) with a particle size of 0.305 μm and a particle size standard deviation of 0.0084 are used as dust, and the flow rate through the filter is 10 m ³ / min. The particle size was measured using a particle counter (KC-22A manufactured by Rion Co., Ltd.) in a measurement particle size range of 0.3 to 0.5 μm, and the collection efficiency was calculated by the same formula as (7) above.
Further, the differential pressure before and after the filter at the time of this measurement was measured, and the difference between the upstream pressure and the downstream pressure was taken as the pressure loss.

(9) Performance evaluation of filter unit for liquid filtration (Example 6, Comparative Example 7)
One filter was installed in a cartridge filter housing (1TS manufactured by Advantech Co., Ltd.) so as not to bypass the filtration liquid due to leakage, and pure water was passed at a filtration flow rate of 20 L / min as a pre-measurement washing.

  Polystyrene monodisperse latex beads (particle size: 1.0 ± 0.4 μm) were added as dust to pure water to a concentration of 1 ppm to obtain a filtration solution.

  The liquid for filtration was allowed to flow at a filtration flow rate of 20 L / min. After 1 hour, the liquid before and after the filter was sampled, and the particle size range from 0.5 to 0.5 was measured using a liquid particle counter (KL-11B, manufactured by Rion). Measurement was performed at 1.0 μm, and the collection efficiency was calculated by the same formula as (7) above.

  Further, the differential pressure before and after the filter at the time of this measurement was measured, and the difference between the upstream pressure and the downstream pressure was taken as the pressure loss.

[Examples 1 and 2 and Comparative Example 1]
(Nanofiber)
(Polymer alloy chip)
40% by mass of nylon 6 having a melting point of 220 ° C. and 60% by mass of poly L lactic acid (optical purity of 99.5% or more) having a melting point of 170 ° C. are melt-kneaded at 220 ° C. using a biaxial extrusion kneader. Thus, a polymer alloy chip was obtained.

(Tow of polymer alloy fiber)
The polymer alloy chip was put into a melt spinning apparatus for staples equipped with a single-screw extruder, melted at 235 ° C., and led to a spin block. Then, the polymer alloy melt was filtered through a metal nonwoven fabric having a limit filtration diameter of 15 μm, and discharged from a die having a spinning temperature of 235 ° C., a discharge hole having a pore diameter of 0.3 mm, and a die surface temperature of 215 ° C.

  The discharged linear molten polymer was cooled and solidified with cooling air, oil was applied, and the polymer was taken up at a spinning speed of 1350 m / min.

  After combining the obtained undrawn yarn, a polymer alloy fiber having a single fiber fineness of 3.0 dtex and a total fineness of 500,000 dtex was drawn and heat-treated at a drawing temperature of 90 ° C., a draw ratio of 3.04 times, and a heat setting temperature of 130 ° C. Got tow. The obtained polymer alloy fiber had a strength of 3.4 cN / dtex and an elongation of 45%. Moreover, it was confirmed by observation of a cross section of the obtained polymer alloy fiber that a sea-island structure in which poly-L lactic acid is a sea component and nylon 6 is an island component in which ultrafine dispersion is formed is formed.

(Sea removal, cutting, beating)
The polymer alloy fiber tow was immersed in a 5% aqueous sodium hydroxide solution at 95 ° C. for 1 hour while being hydrolyzed to remove 99% or more of the poly-L lactic acid component in the polymer alloy fiber (desealing). . Next, the mixture was neutralized with acetic acid, washed with water and dried to obtain nanofiber bundles.

This fiber bundle was cut to a length of 1 mm to obtain a cut nanofiber fiber bundle.
The fiber bundle of the cut nanofibers was charged into a test Niagara Beata (manufactured by Kumagaya Riki Kogyo Co., Ltd.) per 10 liters of water, preliminarily beaten for 5 minutes, drained and collected. Subsequently, the recovered material was charged into an automatic PFI mill (manufactured by Kumagaya Rikyu Kogyo Co., Ltd.) and beaten for 6 minutes at a rotation speed of 1500 rpm and a clearance of 0.2 mm. Then, the recovered material that contained water and became clay-like was dried in a hot air dryer at 80 ° C. for 24 hours to obtain nanofibers.
The fiber diameter of the obtained nanofiber was 110 to 180 nm, and the number average was 150 nm.

(Other fibers)
PET fiber having a cut length of 5 mm and a fineness of 0.1 dtex (fiber diameter of 3.2 μm) as the main fiber, and wood pulp having a Canadian standard freeness of 450 ml as defined in JIS P 8121: 1995 as the fibrillated fiber, As a binder fiber, Kuraray “Sophit” N-720 (fineness: 2.2 dtex (fiber diameter: 14.3 μm), fiber length: 5 mm) was used.

(Constituent fiber dispersion)
The nanofibers were mixed and stirred in water so as to be 0.5% by mass to disperse the fibers, thereby obtaining a nanofiber dispersion. The other fibers were mixed and stirred in water to disperse the fibers, thereby obtaining a dispersion of other fibers. The nanofiber dispersion and another fiber dispersion were mixed to obtain a dispersion of constituent fibers.
The fraction of each constituent fiber in the constituent fiber dispersion was as shown in Table 1.

(Paper)
The dispersion of the constituent fibers was made into paper at a speed of 20 m / min using an inclined wire type paper machine and dried at 120 ° C. using a Yankee drum dryer to obtain a filter medium.

[Example 3]
(Nanofiber)
Before dipping in a 5% aqueous sodium hydroxide solution at 95 ° C., the polymer alloy fiber tow was cut into 1 mm length, and hydrolyzed, neutralized and washed with water in the same manner as in Example 1. Thereafter, beating was conducted in the same manner as in Example 1 to adjust the moisture content to 60% to obtain nanofibers.

(Other fibers)
The same one as used in Example 1 was used.

(Constituent fiber dispersion)
The same one as used in Example 1 was used.

(Paper)
A filter medium was obtained in the same manner as in Example 1 using the above-described dispersion of constituent fibers.

[Comparative Example 2]
(Nanofiber)
The same one as used in Example 1 was used.

(Other fibers)
Other fibers were not used.

(Constituent fiber dispersion)
The nanofibers were mixed and stirred in water so as to be 0.5% by mass to disperse the fibers, thereby obtaining a dispersion of constituent fibers.

(Paper)
A filter medium was obtained in the same manner as in Example 1 except that the dispersion liquid of the constituent fibers was used.

[Comparative Example 3]
(Nanofiber)
The same one as used in Example 1 was used.

(Other fibers)
The same one as used in Example 1 was used.

(Constituent fiber dispersion)
The above-mentioned nanofibers and the above-mentioned other fibers are combined without separately preparing a dispersion of nanofibers and a dispersion of other fibers, and mixed and stirred so as to be 0.5% by mass in water to disperse the fibers. To obtain a dispersion of the constituent fibers.

(Paper)
A filter medium was obtained in the same manner as in Example 1 except that the dispersion liquid of the constituent fibers was used.

[Comparative Example 4]
(Nanofiber)
The same one as used in Example 1 was used.

(Other fibers)
A PET fiber having a cut length of 5 mm and a fineness of 0.04 dtex (fiber diameter of 2.0 μm) was used as the main fiber, and a wood pulp having a Canadian standard freeness of 450 ml as defined in JIS P8121: 1995 was used as the fibrillated fiber. . No binder fiber was used.

(Constituent fiber dispersion)
The above-mentioned nanofibers and the above-mentioned other fibers are combined without separately preparing a dispersion of nanofibers and a dispersion of other fibers, and mixed and stirred so as to be 0.5% by mass in water to disperse the fibers. To obtain a dispersion of the constituent fibers.

(Paper)
A filter medium was obtained in the same manner as in Example 1 except that the dispersion liquid of the constituent fibers was used.

[Comparative Example 5]
(Nanofiber)
The same one as used in Example 1 was used.

(Other fibers)
The same one as used in Example 1 was used.

(Constituent fiber dispersion)
The same one as used in Example 1 was used.

(Paper)
Paper making was performed in the same manner as in Example 1 using the above dispersion of constituent fibers to obtain a wet nonwoven fabric.

(Pressure treatment)
The wet nonwoven fabric was subjected to pressure heat treatment by passing between a pair of metal rolls having a roll interval of 30 μm and a temperature of 120 ° C. at a speed of 2 m / min, to obtain a filter medium.

[Example 4]
(Filtration layer)
The same filter medium as obtained in Example 1 was used as the filter layer.

(Support layer)
A polyester spunbonded nonwoven fabric (“Acstar” G2200-1S manufactured by Toray Industries, Inc.) was used as the support layer.

(Laminated filter media)
The support layer was disposed on one side of the filtration layer, and was adhered with ethylene vinyl acetate copolymer (EVA) hot melt powder so as not to impair air permeability, thereby obtaining a laminated filter medium having a two-layer structure.

(Filter unit for air filtration)
The laminated filter medium was pleated with a height of 65 mm and a pitch of 4 mm. This was cut into 586 mm x 586 mm, the periphery was surrounded by a 12 mm thick plywood, and the ends were bonded so as not to leak air to obtain a filter unit for air filtration.

[Example 5]
(Filtration layer)
The same filter medium as obtained in Example 3 was used as the filter layer.

(Support layer)
The same one as used in Example 4 was used.

(Laminated filter media)
A laminated filter medium having a two-layer structure was obtained in the same manner as in Example 4 except that the above filtration layer was used.

(Filter unit for air filtration)
An air filtration filter unit was obtained in the same manner as in Example 4 except that the laminated filter medium was used.

[Comparative Example 6]
(Filtration layer)
The same filter medium as that obtained in Comparative Example 1 was used as the filtration layer.

(Support layer)
The same one as used in Example 4 was used.

(Laminated filter media)
A laminated filter medium having a two-layer structure was obtained in the same manner as in Example 4 except that the above filtration layer was used.

(Filter unit for air filtration)
An air filtration filter unit was obtained in the same manner as in Example 4 except that the laminated filter medium was used.

[Example 6]
(Filtration layer)
The same filter medium as obtained in Example 2 was used as the filter layer.

(Support layer)
A polypropylene spunbonded nonwoven fabric (PS-114 manufactured by Mitsui Chemicals) was used as a support layer.

(Laminated filter media)
The support layer was disposed on both sides of the filtration layer, and was adhered with EVA hot melt powder so as not to impair air permeability, thereby obtaining a three-layer laminated filter medium.

(Filter unit for liquid filtration)
The laminated filter medium was subjected to pleating processing with a peak height of 10 mm and a peak interval of 3 mm. This was wound into a roll shape, incorporated into a polypropylene hollow cylinder having an inner diameter of 25 mm, an outer diameter of 70 mm, and a length of 245 mm, and the ends were bonded so as not to leak liquid, thereby obtaining a liquid filtration filter unit.

[Comparative Example 7]
(Filtration layer)
The same filter medium as that obtained in Comparative Example 2 was used as the filtration layer.

(Support layer)
The same one as used in Example 6 was used.

(Laminated filter media)
A laminated filter medium having a three-layer structure was obtained in the same manner as in Example 6 except that the above filtration layer was used.

(Filter unit for liquid filtration)
A liquid filtration filter unit was obtained in the same manner as in Example 6 except that the laminated filter medium was used.

  Air conditioning filter units for factories and offices, air purifier filters, air conditioner filters, equipment filters built into various devices, ultra-high performance filters used in factories such as electronics, food, pharmaceuticals, and biotechnology It can be suitably used for various air filters such as HEPA filters, ULPA filters, nuclear power plants used in areas that handle radioactive substances such as nuclear power plants, and air filters and cabin filters for automobiles. In addition, as liquid filters, manufacturing of ultra-pure water used in the manufacturing of electronics industry, steam water for power generation turbines, pharmaceuticals, etc., recording media such as magnetic tape, optical films, etc. Filtration filters for coating solutions used in manufacturing processes, filtration filters for resist solutions and pigment solutions such as semiconductors and liquid crystal displays, precision filtration filters used in food and beverage manufacturing processes, and water filtration such as filtration of drainage and water and sewage It can also be suitably used for various liquid filters such as filters.

Claims (9)

  An average at an air flow rate of 3.2 m / min, comprising fibers made of a thermoplastic resin, having a filtration layer having a thickness of 50 μm or more and containing 0.5 to 70% by mass of nanofibers having a fiber diameter of 1 to 500 nm. A filter having a collection efficiency of 90% or more for particles having a particle size of 0.3 μm and an initial pressure loss of 980 Pa or less at an air flow rate of 3.2 m / min.   The filter according to claim 1, wherein the filtration layer comprises fibers having a fiber diameter of 1 to 70 μm.   The filter according to claim 1 or 2, wherein the filtration layer comprises fibrillated fibers.   The filter according to claim 1, wherein the filtration layer comprises binder fibers.   The filter according to claims 1 to 4, wherein the filtration layer does not contain any of metal fibers, glass fibers, rock fibers, ore fibers, and mineral fibers.   The filter according to claim 1, wherein the filtration layer is a wet nonwoven fabric.   The filter according to any one of claims 1 to 6, wherein the filtration layer has an average flow pore size of 50 nm to 20 µm.   The filter according to any one of claims 1 to 7, further comprising a support layer comprising fibers having a fiber diameter of 1 to 70 µm on both sides or one side of the filtration layer.   A filter unit comprising the filter according to claim 1.