JP2019198833A - Filter medium for immersion type filter cartridge and immersion type filter cartridge - Google Patents

Abstract

To provide a filter medium for an immersion type filter cartridge and an immersion type filter cartridge which not only are excellent in filtration efficiency but also is low pressure loss and large throughput rate, and are further excellent in chemical resistance.SOLUTION: A filter medium for an immersion type filter cartridge includes a filter layer, where the filter layer includes nanofiber having a fiber diameter of 1000 nm or less, strength holding rate, after the filter medium is immersed for 7 days in 0.6 wt% sodium hypochlorite solution, is 80% or more.SELECTED DRAWING: None

Description

  The present invention relates to a filter medium for an immersion filter cartridge, not only excellent in filtration efficiency but also having a low pressure loss, a large throughput, and excellent chemical resistance, a method for producing the same, and an immersion filter cartridge.

  In the membrane separation activated sludge method (MBR), organic wastewater such as sewage and industrial wastewater is treated with activated sludge in a biological treatment tank, and the activated sludge mixed solution is solid-liquid separated with an immersion type membrane separator immersed in the biological treatment tank. It is a method. Compared with the conventional precipitation method, the process flow is simple, space-saving, and sludge removal can be reliably performed with a filter medium, and it is becoming widespread.

  Usually, a porous membrane made of organic fibers has been used as a filter medium used in such a membrane separation activated sludge method.

  However, the conventional filter medium has a problem that the pressure loss is large and the processing amount is small because the pore diameter is small. Examples of membranes with low pressure loss and high throughput include spunbond nonwoven fabrics and meltblown nonwoven fabrics, but due to non-uniform fiber diameters, there are problems with collection efficiency due to the presence of large pores. It was. In order to solve this, the hole diameter is sometimes reduced by calendering or the like, but even if the average hole diameter is reduced, not only does the hole diameter not be uniform, but also the pressure loss is increased due to the increase in density. There was a problem of increasing.

Further, in the membrane separation activated sludge method, the filter medium can be backwashed with alkali or acid once every one to several months to remove substances adhering to the surface, and sludge can be filtered over a long period of time. . Therefore, the filter medium must have chemical resistance against alkalis and acids.
As a method for improving chemical resistance, a method in which the surface of a porous polymer membrane is coated and fixed with insolubilized hydroxypropylcellulose (Patent Document 1), a porous base material with a hydrophilic polymer solution and a crosslinking agent solution Has disclosed a method of reacting a precursor compound in a high electron density region having π electrons after being immersed in (Patent Document 2). The effect was inadequate, such as a significant decrease in the amount.

Japanese Patent No. 5424145 JP2012-206115A

  The present invention has been made in view of the above background, and its purpose is not only excellent in filtration efficiency but also low pressure loss, large throughput, and further excellent in chemical resistance and a filter medium for immersion type filtration cartridge and immersion type It is to provide a filtration cartridge.

  As a result of intensive studies to achieve the above-mentioned problems, the inventors of the present invention are able to obtain a desired filter medium for an immersion filter cartridge by skillfully devising the filter layer in the filter medium for an immersion filter cartridge including the filter layer. As a result, the present invention has been completed.

  Thus, according to the present invention, “a filter medium for a submerged filtration cartridge including a filter layer, the filter layer includes nanofibers having a fiber diameter of 1000 nm or less, and the filter medium includes 0.6 wt% sodium hypochlorite. There is provided a filter medium for an immersion filter cartridge, wherein the strength retention after being immersed in an aqueous solution for 7 days is 80% or more.

In that case, it is preferable that the average pore diameter of the said filtration layer is 1.0 micrometer or less. Moreover, it is preferable that the Gurley air permeability of the said filtration layer is 10 second / 100cc or less. The nanofiber is preferably made of polypropylene fiber. Moreover, it is preferable that a binder fiber is further contained in the said filtration layer. Moreover, it is preferable that the said filtration layer consists of wet nonwoven fabrics.
Moreover, according to this invention, the immersion type filtration cartridge which uses the said filter medium for immersion type filtration cartridges is provided.

  ADVANTAGE OF THE INVENTION According to this invention, it is a filter medium for immersion type filter cartridges, and it is not only excellent in filtration efficiency, but also has a low pressure loss and a large throughput, and further has excellent chemical resistance. Is obtained.

  Hereinafter, embodiments of the present invention will be described in detail. First, the filter medium for an immersion filtration cartridge of the present invention includes a filtration layer, and the filtration layer includes nanofibers having a fiber diameter of 1000 nm or less.

  Here, the nanofiber referred to in the present invention has a fiber diameter of 1000 nm or less (preferably 200 to 800 nm, more preferably 400 to 750 nm). The fiber diameter is the single fiber diameter of the nanofiber. If the fiber diameter is larger than 1000 nm, the filtration efficiency may decrease. On the other hand, when the fiber diameter is smaller than 200 nm, the dispersibility of the nanofibers is lowered and the filtration efficiency may be lowered.

  The fiber diameter can be measured by taking a cross-sectional photograph of a single fiber at a magnification of 30000 with a transmission electron microscope TEM. At that time, in a TEM having a length measurement function, measurement can be performed using the length measurement function. In a TEM without a length measuring function, a photograph taken may be enlarged and copied and measured with a ruler in consideration of the scale.

  At that time, when the cross-sectional shape of the single fiber is an atypical cross-section other than the round cross-section, the diameter of the circumscribed circle of the cross-section of the single fiber is used.

  The nanofiber preferably has a fiber length of 0.4 to 1.5 mm. If the fiber length is less than 0.4 mm, the processability may be reduced. On the other hand, if the fiber length is longer than 1.5 mm, it becomes an aggregated fiber lump due to poor dispersibility, and there is a concern that the filtration efficiency and strength are lowered. Further, the ratio L / D of the fiber length L to the fiber diameter D is preferably in the range of 200 to 4000 (more preferably 800 to 2500).

  The fiber type of the nanofiber is not particularly limited, and examples thereof include polyester fiber, polyphenylene sulfide fiber, polypropylene fiber, polyethylene fiber, and aliphatic polyamide fiber. Of these, polypropylene fibers are preferred from the viewpoint of excellent chemical resistance to an aqueous sodium hypochlorite solution.

  Although the manufacturing method of the said nanofiber is not specifically limited, The method disclosed by the international publication 2005/095686 pamphlet and the international publication 2008/130019 pamphlet is preferable. That is, it consists of an island component composed of a fiber-forming thermoplastic polymer and a polymer that is more easily dissolved in an alkaline aqueous solution than the fiber-forming thermoplastic polymer (hereinafter also referred to as “easily soluble polymer”). It is preferable that the composite fiber having the sea component is subjected to alkali weight reduction processing and the sea component is dissolved and removed.

  Here, when the dissolution rate ratio of the aqueous alkali-soluble polymer that forms the sea component to the fiber-forming thermoplastic polymer that forms the island component is 200 or more (preferably 300 to 3000), the island separation property is good. It is preferable.

  Preferable examples of the easily soluble polymer forming the sea component include polyesters, aliphatic polyamides, and polyolefins such as polyethylene and polystyrene, which are particularly good in fiber formation. More specifically, polylactic acid, an ultrahigh molecular weight polyalkylene oxide condensation polymer, and a copolymerized polyester of polyalkylene glycol compound and 5-sodium sulfoisophthalic acid are preferable because they are easily dissolved in an alkaline aqueous solution. Here, the alkaline aqueous solution refers to potassium hydroxide, sodium hydroxide aqueous solution and the like. Other than this, combinations of sea components and solutions for dissolving the sea components include formic acid for aliphatic polyamides such as nylon 6 and nylon 66, trichlorethylene for polystyrene, and polyethylene (especially high-pressure low-density polyethylene and straight chain). Examples thereof include hydrocarbon solvents such as hot toluene and xylene for the low-density polyethylene and hot water for polyvinyl alcohol and ethylene-modified vinyl alcohol polymers.

  Among polyester polymers, polyethylene terephthalate copolymer having an intrinsic viscosity of 0.4 to 0.6 obtained by copolymerizing 6 to 12 mol% of 5-sodium sulfoisophthalic acid and 3 to 10% by weight of polyethylene glycol having a molecular weight of 4000 to 12000. Polymerized polyester is preferred. Here, 5-sodium sulfoisophthalic acid contributes to improving hydrophilicity and melt viscosity, and polyethylene glycol (PEG) improves hydrophilicity. In addition, PEG has a hydrophilicity increasing action that is considered to be due to its higher-order structure as the molecular weight increases. However, since the reactivity becomes poor and a blend system is produced, problems arise in terms of heat resistance and spinning stability. There is a fear. Moreover, when the copolymerization amount is 10% by weight or more, the melt viscosity may be lowered.

  On the other hand, the poorly soluble polymer that forms the island component is a polymer that finally forms nanofibers, and suitable examples include polyamides, polyesters, polyolefins, polyphenylene sulfide (PPS), and the like. Specifically, in applications requiring mechanical strength and heat resistance, polyesters include polyethylene terephthalate (hereinafter sometimes referred to as “PET”), polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, These are the main repeating units, aromatic dicarboxylic acids such as isophthalic acid and 5-sulfoisophthalic acid metal salts, aliphatic dicarboxylic acids such as adipic acid and sebacic acid, hydroxycarboxylic acid condensates such as ε-caprolactone, diethylene glycol and the like Copolymers with glycol components such as trimethylene glycol, tetramethylene glycol and hexamethylene glycol are preferred. Of the polyamides, aliphatic polyamides such as nylon 6 and nylon 66 are preferable. On the other hand, polyolefins are difficult to be attacked by acids and alkalis, etc., and have a characteristic that they can be used as binder components after being taken out as ultrafine fibers due to their relatively low melting point. High density polyethylene, medium density polyethylene, high pressure method Preferred examples include low density polyethylene, linear low density polyethylene, isotactic polypropylene, ethylene propylene copolymer, ethylene copolymer of vinyl monomers such as maleic anhydride, and the like. The island component is not limited to a round cross section, but may be an irregular cross section such as a triangular cross section or a flat cross section.

  About the polymer that forms the sea component and the polymer that forms the island component, organic fillers, antioxidants, and heat-stable as necessary, as long as they do not affect the properties of the fine fiber after extraction. Various additives such as additives, light stabilizers, flame retardants, lubricants, antistatic agents, rust preventives, crosslinking agents, foaming agents, fluorescent agents, surface smoothing agents, surface gloss improvers, mold release improvers such as fluororesins, etc. Even if it contains an agent, it is acceptable.

  For the polymer that forms the sea component and the polymer that forms the island component, organic fillers, antioxidants, and heat-stable as necessary, as long as they do not affect the properties of the yarn and the properties of the nanofiber after extraction. Various additives such as additives, light stabilizers, flame retardants, lubricants, antistatic agents, rust preventives, crosslinking agents, foaming agents, fluorescent agents, surface smoothing agents, surface gloss improvers, mold release improvers such as fluororesins, etc. Even if it contains an agent, it is acceptable.

  In the sea-island type composite fiber, it is preferable that the melt viscosity of the sea component at the time of melt spinning is larger than the melt viscosity of the island component polymer. In such a relationship, even if the composite weight ratio of the sea components is less than 40%, it is easy to prevent the islands from being joined.

  A preferred melt viscosity ratio (sea / island) is in the range of 1.1 to 2.0, especially 1.3 to 1.5. If this ratio is less than 1.1 times, the island components are likely to be joined during melt spinning, whereas if it exceeds 2.0 times, the viscosity difference is too large and the spinning tone tends to be lowered.

  Next, the number of islands is preferably 100 or more (more preferably 500 to 2000). The sea-island composite weight ratio (sea: island) is preferably in the range of 20:80 to 80:20. Within such a range, the thickness of the sea component between the islands can be reduced, the sea component can be easily dissolved and removed, and the conversion of the island component into nanofibers is facilitated. Here, when the proportion of the sea component exceeds 80%, the thickness of the sea component becomes too thick. On the other hand, when the proportion is less than 20%, the amount of the sea component becomes too small, and there is a possibility that joining between islands is likely to occur. There is.

  As a die used for melt spinning, an arbitrary one such as a hollow pin group for forming an island component or a group having a fine hole group (pinless) can be used. For example, even in a spinneret in which an island component extruded from a hollow pin or a fine hole and a sea component flow designed to fill the gap between them are merged and compressed to form a sea island cross section. Good. The discharged sea-island type composite fiber is solidified by cooling air and taken up by a rotating roller or an ejector set at a predetermined take-up speed to obtain an undrawn yarn (birefringence index Δn is preferably 0.05 or less). . The take-up speed is not particularly limited, but is preferably 200 to 5000 m / min. If it is 200 m / min or less, the productivity may decrease. Further, if it is 5000 m / min or more, the spinning stability may be lowered.

  The obtained undrawn yarn may be subjected to the cutting step or the subsequent extraction step (alkaline weight loss processing) as it is, if necessary, after being made into a drawn yarn via a drawing step or a heat treatment step, and then the cutting step or You may use for a subsequent extraction process (alkali weight reduction process). At that time, the stretching step may be a separate stretching method in which spinning and stretching are performed in separate steps, or a straight stretching method in which stretching is performed immediately after spinning in one process. The order of the cutting process and the extraction process may be reversed.

  Such cutting is preferably performed by using a guillotine cutter, a rotary cutter, or the like with undrawn yarn or drawn yarn as it is or with a tow bundled in units of tens to millions.

When the above-mentioned sea-island type composite fiber is subjected to alkali weight reduction processing to form a nanofiber, the ratio of fiber to alkaline solution (bath ratio) is preferably 0.1 to 5%, more preferably 0.4 to 3%. It is preferable that If it is less than 0.1%, the contact between the fiber and the alkali liquid is large, but the processability such as drainage may be difficult. On the other hand, if the amount exceeds 5%, the amount of fibers is too large, and there is a risk of entanglement between fibers during alkali weight reduction processing. The bath ratio is defined by the following formula.
Bath ratio (%) = (Fiber mass (gr) / Alkaline aqueous solution mass (gr)) × 100

  Moreover, it is preferable that the processing time of an alkali weight reduction process is 5 to 60 minutes, Furthermore, it is preferable that it is 10 to 30 minutes. If it is less than 5 minutes, the alkali weight loss may be insufficient. On the other hand, if it exceeds 60 minutes, the island components may be reduced.

  In the alkali weight reduction processing, the alkali concentration is preferably 2% to 10%. If it is less than 2%, the alkali is insufficient, and the weight loss rate may be extremely slow. On the other hand, if it exceeds 10%, the weight loss of alkali proceeds too much and there is a risk that the weight may be reduced to the island portion.

  As a method for reducing the alkali, the sea-island type composite fiber is poured into an alkali solution, subjected to an alkali weight-reducing treatment under a predetermined condition and time, once subjected to a dehydration step, and then again poured into water, such as acetic acid and oxalic acid. Neutralization and dilution using organic acid and final dehydration method, or after alkali reduction treatment for a predetermined time, neutralization treatment is first performed, water is further injected to dilute, and then dehydration is performed. And the like. In the former, since it is processed in a batch type, it can be manufactured (processed) in a small amount, but the neutralization process takes time, so the productivity is slightly worse. The latter can be produced semi-continuously, but has a problem that a lot of aqueous acid solution and a lot of water are required for dilution during the neutralization treatment. The treatment equipment is not limited in any way, but from the viewpoint of preventing fiber dropping during dehydration, the opening ratio (area ratio of the opening portion per unit area) as disclosed in Japanese Patent No. 3678511 is 10 to 10. It is preferable to use a 50% mesh-like material (for example, non-alkaline hydrolyzable bag). If the open area ratio is less than 10%, moisture loss is extremely poor, and if it exceeds 50%, fibers may fall off.

  Furthermore, after alkali weight reduction processing, in order to improve the dispersibility of the fiber, a dispersant (for example, model YM-81 manufactured by Takamatsu Oils & Fats Co., Ltd.) is added to the fiber surface in an amount of 0.1 to 5. It is preferable to deposit 0% by weight.

  In the filter medium for an immersion filter cartridge of the present invention, the filtration layer is preferably made of a wet nonwoven fabric. Wet nonwoven fabrics have less variation in properties related to filter performance such as basis weight, fiber diameter, and air permeability, and superior filtration efficiency compared to nonwoven fabrics made by the spunbond method, melt blow method, electrospinning method, etc. preferable.

  The filtration layer preferably contains not only nanofibers but also binder fibers. At this time, the weight ratio of the nanofibers is in the range of 50 to 90% by weight with respect to the weight of the filtration layer, and the weight ratio of the binder weight is in the range of 10 to 50% by weight with respect to the weight of the filtration layer. Preferably there is.

  The binder fiber is a heat-bondable fiber. By including binder fibers in the filtration layer, effects such as strength of the nonwoven fabric, network structure, and bulk improvement due to shrinkage can be obtained. As the binder fiber, undrawn yarn or composite fiber having a single fiber fineness of 1.0 dtex or less (more preferably 0.0001 to 0.3 dtex) is preferable. The fiber length of the binder fiber is preferably 3 to 10 mm.

  Among the binder fibers, the unstretched yarn is preferably an unstretched polyester fiber spun at a spinning speed of 600 to 1500 m / min. Examples of the polyester include polyethylene terephthalate, polytrimethylene terephthalate, and polybutylene terephthalate. Preferably, polyethylene terephthalate and a copolymer polyester containing the same as a main component are preferable for reasons such as productivity and dispersibility in water.

  Among the binder fibers, as the composite fiber, a polymer component that exhibits a fusion bonding effect depending on the dryer temperature at the time of papermaking, for example, an amorphous copolyester, is disposed in the sheath, and the melting point of these polymers is 20 ° C. A core-sheath type composite fiber in which another polymer higher than the above is disposed in the core is preferred. Moreover, forms, such as an eccentric core-sheath-type composite fiber and a side-by-side type composite fiber, can also be used.

  Here, it is preferable from the viewpoint of cost that the above-mentioned non-crystalline copolymer polyester uses terephthalic acid, isophthalic acid, ethylene glycol and diethylene glycol as main components.

  Furthermore, it is a non-binder fiber that helps disperse the nanofibers and contributes to the improvement of the porosity, and even if fibers with a finer finer than nanofibers are included in the layer made of wet nonwoven fabric (layer containing nanofibers) Good. As the fiber having a fineness greater than that of the nanofiber, the above-described polyester fiber having a uniform fiber diameter and good dispersibility is preferable. Also, various paper fiber materials can be used depending on the amount and purpose, such as wood pulp, natural pulp, synthetic pulp mainly composed of aramid and polyethylene, nylon, acrylic, vinylon, rayon, etc. A synthetic fiber or semi-synthetic fiber containing may be mixed and added.

  The wet nonwoven fabric can be obtained by making a paper using the above-mentioned fibers using a normal long paper machine, a short paper machine, a round paper machine, etc., and then thermally bonding the binder fiber.

In the thus obtained filtration layer, it is important that the strength is maintained at 80% or more after being immersed in a 0.6 wt% sodium hypochlorite aqueous solution at 40 ° C. for 7 days. However, the strength retention is calculated by the following formula.
Strength retention (%) = tensile strength after immersion in aqueous sodium hypochlorite solution (N / 15 mm) / tensile strength before immersion in aqueous sodium hypochlorite solution (N / 15 mm) × 100
In addition, the tensile strength of the filtration layer is measured based on JIS P8113 (tensile strength and test method of paper and paperboard).

  In the present invention, a nonwoven fabric sheet using nanofibers having a uniform fiber diameter can form a structure having a uniform pore diameter, and therefore has a fine pore diameter and a high diameter despite its small basis weight and thickness. Has filtration efficiency. Furthermore, by reducing the Gurley air permeability of the filtration layer, a filter medium having a small pressure loss when water is permeated and a large throughput per unit time can be obtained. This is presumably due to the fact that even if the pore diameter is very small, the pore diameter is uniform and many exist.

  Here, the average pore diameter of the filtration layer is preferably 1.0 μm or less (more preferably 0.1 to 1.0 μm). Moreover, it is preferable that the Gurley air permeability of the said filtration layer is 10 second / 100cc or less (more preferably 1-10 second / 100cc).

  In the filter medium for the immersion type filtration cartridge of the present invention, it is preferable that a support layer is also included in addition to the filtration layer.

Such a support layer is preferably a low-density nonwoven fabric. The density is preferably in the range of 0.1 to 0.7 g / cm ³ . When the density is less than 0.1 g / cm ³ , the handleability may be deteriorated. Conversely, if the density is greater than 0.7 g / cm ³ , a high water treatment amount may not be obtained.

  The support layer is not limited to a wet nonwoven fabric, and may be a nonwoven fabric produced by a spunbond method, a melt blow method, an electrospinning method, or the like.

  Examples of the fibers constituting the support layer include polyester fibers as described above, polyphenylene sulfide fibers, polypropylene fibers, polyethylene fibers, and aliphatic polyamide fibers.

  Since the filter medium for an immersion filter cartridge of the present invention has the above-described configuration, it not only has excellent filtration efficiency, but also has a low pressure loss, a large throughput, and excellent chemical resistance.

  The immersion type filtration cartridge of the present invention is formed by using the above-mentioned filter medium for an immersion type filtration cartridge, and not only has excellent filtration efficiency but also has a low pressure loss, a large amount of treatment, and excellent chemical resistance.

Next, although the Example and comparative example of this invention are explained in full detail, this invention is not limited by these. In addition, each measurement item in an Example was measured with the following method.
(1) Fiber diameter Using a transmission electron microscope TEM (with length measurement function), a fiber cross-sectional photograph was taken and measured at a magnification of 30000 times. However, the diameter of the circumscribed circle in the cross section of the single fiber was used as the fiber diameter (average value of n number 5).
(2) Fiber length Using a scanning electron microscope (SEM), the ultrafine short fiber (short fiber A) before being dissolved and removed from the sea component was laid on the base, and the fiber length L was measured 20 to 500 times (n The average value of Formula 5). At that time, the fiber length L was measured by utilizing the length measurement function of the SEM.
(3) Weight per unit area The basis weight was measured based on JIS P8124 (Measuring basis weight of paper).
(4) Thickness Thickness was measured based on JIS P8118 (Method for measuring thickness and density of paper and paperboard). The measurement load was 75 g / cm ² and measurement was performed with n = 5, and the average value was obtained.
(5) Melt viscosity The polymer after drying is set in an orifice set to the spinning temperature at spinning, melted and held for 5 minutes, extruded under several levels of load, and the shear rate and melt viscosity at that time are plotted. To do. Based on the data, a shear rate-melt viscosity curve was prepared, and the melt viscosity when the shear rate was 1000 sec ⁻¹ was read.
(6) Average pore diameter It measured with the palm porometer made from PMI.
(7) Gurley air permeability JIS P8117 (Paper and paperboard air permeability test method) was carried out.
(8) Chemical resistance The strength retention after the filter layer was immersed in a 0.6 wt% sodium hypochlorite aqueous solution at 40 ° C for 7 days was determined from the following formula.
Strength retention (%) = tensile strength after immersion in aqueous sodium hypochlorite solution (N / 15 mm) / tensile strength before immersion in aqueous sodium hypochlorite solution (N / 15 mm) × 100
In addition, the tensile strength of the filtration layer was measured based on JIS P8113 (tensile strength and test method of paper and paperboard).
Here, 80 to 100% of the strength retention was evaluated as ◯, 50 to 80% as Δ, and 0 to 50% as ×.

[Example 1]
Polypropylene is used as the island component, 4% by weight of polyethylene glycol having an average molecular weight of 4000 is used as the sea component, and modified polyethylene terephthalate copolymerized with 9 mol% of 5-sodium sulfoisophthalic acid. 836 sea-island type composite undrawn yarn was melt-spun at a spinning temperature of 210 ° C. and a spinning speed of 1500 m / min, and wound up once. The alkali weight loss rate ratio between the sea component and the island component was 1000 times. This was stretched 3 times and cut to 0.4 mm with a guillotine cutter to obtain a sea-island type composite fiber. This was reduced by 50% with a 4% NaOH aqueous solution at 50 ° C., and nanofibers made of polyethylene terephthalate (PET) fibers having a fiber diameter of 400 nm and a cut length of 0.4 mm were obtained as main fibers.

  On the other hand, a core-sheath composite fiber having a core of polypropylene and a sheath of polyethylene was spun by a conventional method to obtain a 0.3 dtex binder fiber.

  Next, the nanofiber (80 wt%) and the binder fiber (20 wt%) were mixed and stirred, and then wet papermaking was performed with an inclined short net paper machine and dried at a Yankee dryer at 130 ° C to obtain a wet nonwoven fabric serving as a filtration layer.

[Example 2]
In Example 1, it was the same as Example 1 except that the fiber diameter of the nanofiber constituting the filtration layer was changed to 700 nm.

[Comparative Example 1]
In Example 1, it was made the same as Example 1 except having changed the fiber diameter of the nanofiber which comprises a filtration layer into 1100 nm. The filtration layer obtained by this method had an average pore diameter of 1.0 μm or more, a low collection rate of 1 μm, and was not suitable as a filter medium for a submerged membrane cartridge.

[Example 3]
The filter medium obtained in Example 2 was calendered so that the average pore size was 1 μm or less. The filter medium obtained by such a method has a Gurley of 10 seconds / 100 cc or more, has a high initial pressure loss, and is not satisfactory as a filter medium for a submerged membrane cartridge.

[Comparative Example 2]
In Example 2, the nanofiber material constituting the filtration layer is nylon 6, the binder fiber is nylon nanofiber unstretched yarn (fiber diameter 1.2 μm), the nanofiber (60 wt%), and the binder fiber ( 40 wt%) was mixed and stirred, and then wet papermaking was performed with a slanted short net paper machine and dried at a Yankee dryer at 140 ° C. to obtain a wet nonwoven fabric serving as a filtration layer.

  ADVANTAGE OF THE INVENTION According to this invention, not only is it excellent in filtration efficiency, but also a low pressure loss and a large amount of processing are provided, and further, a filter medium for an immersion type filtration cartridge and an immersion type filtration cartridge excellent in chemical resistance are provided. It ’s big.

Claims (7)

  A filter medium for a submerged filtration cartridge including a filter layer, wherein the filter layer includes nanofibers having a fiber diameter of 1000 nm or less, and the filter medium is immersed in a 0.6 wt% sodium hypochlorite aqueous solution for 7 days. A filter medium for an immersion type filtration cartridge, wherein the retention rate is 80% or more.   The filter medium for an immersion filter cartridge according to claim 1, wherein the filter layer has an average pore size of 1.0 μm or less.   The filter medium for an immersion filter cartridge according to claim 1 or 2, wherein the filtration layer has a Gurley air permeability of 10 seconds / 100 cc or less.   The filter medium for an immersion type filtration cartridge according to any one of claims 1 to 3, wherein the nanofiber is made of polypropylene fiber.   The filter medium for an immersion filter cartridge according to any one of claims 1 to 4, wherein the filter layer further contains binder fibers.   The filter medium for an immersion type filtration cartridge according to any one of claims 1 to 5, wherein the filtration layer is made of a wet nonwoven fabric.   An immersion type filtration cartridge using the filter medium for an immersion type filtration cartridge according to claim 1.