JP6884033B2 - Filter media for immersion type filtration cartridge and immersion type filtration cartridge - Google Patents

Description

The present invention relates to a filter medium for an immersion type filtration cartridge, which is not only excellent in filtration performance but also has a large processing amount due to a low pressure loss and maintains its performance for a long period of time. ..

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 mixture is solid-liquid separated by an immersion type membrane separation device immersed in the biological treatment tank. The method. Compared with the conventional settling method, the treatment flow is simple, the space is saved, and sludge can be reliably removed by the filter medium, and it is becoming widespread.
Conventionally, a porous membrane made of organic fibers has been often used as a filter medium used in such a membrane separation activated sludge method.

However, in the conventional film, since the pore diameter is small, the turbidity can be almost removed, but there is a problem that the flow rate resistance is large and the processing amount is low. In addition, the membrane is easily clogged, and the amount of treatment is further reduced due to long-term use, which causes a problem that the frequency of membrane replacement increases, and chemical cleaning with acids, alkalis, etc. must be performed frequently, resulting in chemical resistance. There was a problem that the materials that could be used were limited from the viewpoint of sex.

As a countermeasure, for example, Patent Document 1 describes a method of imparting hydrophilicity by adding a polymer component to polyvinylidene fluoride (PVDF) in order to suppress fouling and obtain long-term water permeability of the membrane. Although it has been proposed, there is a problem that the hydrophilicizing agent falls off during use and the effect of water permeability does not continue for a long time.

Japanese Unexamined Patent Publication No. 2012-106235

The present invention has been made in view of the above background, and an object of the present invention is a filter medium for an immersion type filtration cartridge, which not only has excellent filtration performance but also has a low pressure loss and a large processing amount, and its performance is maintained for a long period of time. It is an object of the present invention to provide a filter medium for an immersion type filtration cartridge and an immersion type filtration cartridge.

As a result of diligent studies to achieve the above problems, the present inventors have made the filtration layer contain nanofibers in the filter medium for an immersion type filtration cartridge including the filtration layer, and set the Gale air permeability of the filtration layer to 20 seconds / second. We have found that by setting the content to 100 cc or less, a filter medium for an immersion type filtration cartridge having high filtration efficiency, a large amount of processing per unit time, and maintaining its performance for a long period of time can be obtained, and the present invention has been completed. ..

Thus, according to the present invention, "a filter medium for an immersion type filtration cartridge including a filtration layer, wherein the filtration layer contains nanofibers having a fiber diameter of 1000 nm or less, and the Gale air permeability of the filtration layer is 20 seconds. / 100 cc or less, a filter medium for an immersion type filtration cartridge. ”Is provided.

At that time, it is preferable that the average pore size of the filtration layer is 2.0 μm or less. Further, it is preferable that the pressure loss when the entire amount of water is filtered through a filter medium having an area of ^{140 cm 2 with a permeated water amount of 25.8 m 3} / m ^{2 / day is 10 kPa or less.} Further, it is preferable that the nanofibers are made of polyester fibers, polyphenylene sulfide fibers or polypropylene fibers. Further, it is preferable that the filtration layer further contains binder fibers. At that time, it is preferable that the single fiber fineness of the binder fiber is 1.0 dtex or less. Further, in the filtration layer, 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 fibers is 10 to 50% by weight with respect to the weight of the filtration layer. It is preferably within the range of. Further, the thickness of the filtration layer is preferably 100 μm or less. Further, it is preferable that the filtration layer is made of a wet non-woven fabric.
Further, according to the present invention, there is provided an immersion type filtration cartridge using the above-mentioned immersion type filtration cartridge filter medium.

According to the present invention, the filter medium for an immersion type filtration cartridge, the filter medium for an immersion type filtration cartridge and the immersion type filtration, which are not only excellent in filtration performance but also have a large processing amount due to a low pressure loss and the performance is maintained for a long period of time. A cartridge is obtained.

This is an example of the immersion type filtration cartridge of the present invention.

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

Here, the nanofibers referred to in the present invention have a fiber diameter of 1000 nm or less (preferably 10 to 800 nm, more preferably 200 to 750 nm). The fiber diameter is the single fiber diameter of nanofibers. If the fiber diameter is larger than 1000 nm, the filtration performance may deteriorate. On the contrary, if the fiber diameter is smaller than 10 nm, the dispersibility of the nanofibers may be lowered and the filtration performance may be lowered.

The fiber diameter can be measured by taking a cross-sectional photograph of a single fiber at a magnification of 30,000 times with a transmission electron microscope TEM. At that time, in the TEM having a length measuring function, the length measuring function can be utilized for measurement. Further, in a TEM having no length measuring function, the photograph taken may be enlarged and copied, and the measurement may be performed with a ruler after considering the scale.

At that time, when the cross-sectional shape of the single fiber is a modified cross section other than the round cross section, the diameter of the circumscribed circle of the cross section of the single fiber shall be used as the fiber diameter.

The nanofibers preferably have a fiber length of 0.4 to 1.5 mm. If the fiber length is smaller than 0.4 mm, the processability may decrease. On the contrary, if the fiber length is larger than 1.5 mm, the dispersibility may be poor, resulting in agglomerated fiber lumps, which may reduce the filtration performance and strength. 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 nanofibers is not particularly limited, and examples thereof include polyester fibers, polyphenylene sulfide fibers, polypropylene fibers, polyethylene fibers, and aliphatic polyamide fibers. Of these, polyester fibers, polyphenylene sulfide fibers, or polypropylene fibers are preferable.

Examples of the polyester forming the polyester fiber include polyethylene terephthalate (hereinafter, also referred to as "PET"), polytrimethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, and isophthalic acid and 5-, which are mainly repeating units. Aromatic dicarboxylic acids such as sulfoisophthalic acid metal salts, aliphatic dicarboxylic acids such as adipic acid and sebacic acid, hydroxycarboxylic acid condensates such as ε-caprolactone, diethylene glycol, trimethylene glycol, tetramethylene glycol, hexamethylene glycol and the like. A copolymer with a glycol component or the like is preferable. It may be a material-recycled or chemically-recycled polyester, or a polyethylene terephthalate made by using a monomer component obtained from biomass, that is, a substance derived from a living material, which is described in JP-A-2009-0916994. Further, a polyester obtained by using a catalyst containing a specific phosphorus compound and titanium compound as described in JP-A-2004-27097 and JP-A-2004-21268 may be used.

Further, the polyester fiber may be a drawn yarn, an undrawn yarn, or a semi-drawn yarn. Further, the elongation may be less than 60% or 60% or more. The polyester drawn yarn usually has an elongation of less than 60%, and the polyester undrawn yarn usually has an elongation of 60% or more.

As the polyarylene sulfide resin forming the polyphenylene sulfide (PPS) fiber, any polyarylene sulfide resin may be used as long as it belongs to the category called polyarylene sulfide resin. The polyarylene sulfide resin has, as its constituent units, for example, p-phenylene sulfide unit, m-phenylene sulfide unit, o-phenylene sulfide unit, phenylene sulfide sulfone unit, phenylene sulfide ketone unit, phenylene sulfide ether unit, diphenylene sulfide unit. , Substituent-containing phenylene sulfide unit, branched structure-containing phenylene sulfide unit, and the like. Among them, those containing 70 mol% or more, particularly 90 mol% or more of p-phenylene sulfide units are preferable, and poly (p-phenylene sulfide) is more preferable.

Further, the pophenylene sulfide fiber may be a drawn yarn, an undrawn yarn, or a semi-drawn yarn. Further, the elongation may be less than 60% or 60% or more. The polyphenylene sulfide drawn yarn usually has an elongation of less than 60%, and the polyphenylene sulfide undrawn yarn usually has an elongation of 60% or more.

The method for producing the nanofibers is not particularly limited, but the method disclosed in International Publication No. 2005/095686 Pamphlet and International Publication No. 2008/13019 Pamphlet is preferable. That is, it is composed of an island component made of a fiber-forming thermoplastic polymer and a polymer that is more soluble in an alkaline aqueous solution than the above-mentioned fiber-forming thermoplastic polymer (hereinafter, may be referred to as "easily soluble polymer"). It is preferable that the composite fiber having a sea component is subjected to an alkali weight loss process to dissolve and remove the sea component.

Here, when the dissolution rate ratio of the alkaline aqueous solution easily soluble polymer forming the sea component to the fiber-forming thermoplastic polymer forming the island component is 200 or more (preferably 300 to 3000), the island separability is good. It is preferable.

As the easily soluble polymer forming the sea component, polyesters having particularly good fiber forming properties, aliphatic polyamides, and polyolefins such as polyethylene and polystyrene can be mentioned as preferable examples. More specifically, polylactic acid, ultra-high molecular weight polyalkylene oxide condensing polymer, and 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 means potassium hydroxide, sodium hydroxide aqueous solution, or the like. In addition to this, as a combination of the sea component and the solution for dissolving the sea component, hydrocarbons for aliphatic polyamides such as nylon 6 and nylon 66, trichloroethylene for polystyrene and polyethylene (particularly high pressure method low density polyethylene and straight chain). Examples include hydrocarbon solvents such as hot toluene and xylene for low-density polyethylene, and hot water for polyvinyl alcohol and ethylene-modified vinyl alcohol-based polymers.

Among polyester polymers, polyethylene terephthalate having an intrinsic viscosity of 0.4 to 0.6 obtained by copolymerizing 6 to 12 mol% of 5-sodium sulfoisophthalic acid and polyethylene glycol having a molecular weight of 4000 to 12000 by 3 to 10% by weight. Polymerized polyester is preferred. Here, 5-sodium sulfoisophthalic acid contributes to the improvement of hydrophilicity and melt viscosity, and polyethylene glycol (PEG) improves the hydrophilicity. Further, the larger the molecular weight of PEG, the more hydrophilicity it is thought to be due to its higher-order structure, but the reactivity deteriorates and it becomes a blend system, which causes problems in terms of heat resistance and spinning stability. There is a risk. Further, when the copolymerization amount is 10% by weight or more, the melt viscosity may decrease.

On the other hand, examples of the poorly soluble polymer that forms the island component include polymers that finally form nanofibers, such as polyamides, polyesters, polyolefins, and polyphenylene sulfide (PPS). Specifically, in applications where mechanical strength and heat resistance are required, polyesters include polyethylene terephthalate (hereinafter, also referred to as "PET"), polytrimethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate. Aromatic dicarboxylic acids such as isophthalic acid and 5-sulfoisophthalic acid metal salt, aliphatic dicarboxylic acids such as adipic acid and sebacic acid, hydroxycarboxylic acid condensates such as ε-caprolactone, and diethylene glycol, which have these as the main repeating units. A copolymer with a glycol component such as trimethylene glycol, tetramethylene glycol, or hexamethylene glycol is preferable. Further, as the polyamides, aliphatic polyamides such as nylon 6 and nylon 66 are preferable. On the other hand, polyolefins are not easily attacked by acids and alkalis, and because of their relatively low melting point, they can be used as binder components after being taken out as ultrafine fibers. High-density polyethylene, medium-density polyethylene, high-pressure method Preferred examples include low-density polyethylene, linear low-density polyethylene, isotactic polypropylene, ethylene-propylene copolymer, and ethylene copolymer of vinyl monomer such as maleic anhydride. In particular, polyesters such as polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene terephthalate isophthalate having an isophthalic acid copolymerization rate of 20 mol% or less, polyethylene naphthalate, etc., or aliphatic polyamides such as nylon 6 and nylon 66. Since the class has heat resistance and mechanical properties due to a high melting point, it can be applied to applications requiring heat resistance and strength as compared with ultrafine fibrillated fibers made of polyvinyl alcohol / polyacrylonitrile mixed spun fibers, which is preferable. The island component is not limited to a round cross section, but may be a modified cross section such as a triangular cross section or a flat cross section.

With respect to the polymer forming the sea component and the polymer forming the island component, an organic filler, an antioxidant, and a thermal stability are required as long as they do not affect the yarn-forming property and the physical properties of the nanofiber after extraction. Additions of agents, light stabilizers, flame retardants, lubricants, antistatic agents, rust preventives, cross-linking agents, foaming agents, fluorescent agents, surface smoothing agents, surface gloss improvers, mold release improvers such as fluororesins, etc. It does not matter if it contains an agent.

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 component is as small as less than 40%, it is easy to prevent the islands from joining each other.

Preferred melt viscosity ratios (sea / island) range from 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 bonded during melt spinning, while if it exceeds 2.0 times, the viscosity difference is too large and the spinning tone is likely to decrease.

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 dissolution and removal of the sea component becomes easy, and the conversion of the island component into nanofibers becomes easy, which is preferable. Here, if the ratio of the sea component exceeds 80%, the thickness of the sea component becomes too thick, while if it is less than 20%, the amount of the sea component becomes too small, and there is a possibility that bonding between islands is likely to occur. There is.

As the mouthpiece used for melt spinning, any one can be used, such as one having a hollow pin group or a fine hole group (pinless) for forming an island component. For example, even with a spinneret in which an island component extruded from a hollow pin or a micropore and a sea component flow whose flow path is designed to fill the space 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 is taken up by a rotating roller or ejector set to a predetermined take-up speed to obtain an undrawn yarn (preferably having a birefringence Δn of 0.05 or less). .. The pick-up speed is not particularly limited, but is preferably 200 to 5000 m / min. At 200 m / min or less, productivity may decrease. Further, at 5000 m / min or more, the spinning stability may decrease.

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

For such cutting, it is preferable to cut the undrawn yarn or the drawn yarn as it is, or to make a toe bundled in units of tens to millions and cut it with a guillotine cutter or a rotary cutter.

When the sea-island type composite fiber is subjected to alkali weight loss processing to obtain nanofibers, the ratio (bath ratio) of the fiber to the alkaline solution is preferably 0.1 to 5%, more preferably 0.4 to 3%. Is preferable. If it is less than 0.1%, there is a lot of contact between the fiber and the alkaline solution, but there is a risk that processability such as drainage will be difficult. On the other hand, if it exceeds 5%, the amount of fibers is too large, so that the fibers may be entangled with each other during the alkali weight reduction process. The bath ratio is defined by the following formula.
Bath ratio (%) = (fiber mass (gr) / alkaline aqueous solution mass (gr)) × 100

The treatment time for the alkali weight loss processing is preferably 5 to 60 minutes, more preferably 10 to 30 minutes. Less than 5 minutes may result in insufficient alkali weight loss. On the other hand, if it exceeds 60 minutes, even the island component may be reduced.

Further, in the alkali weight loss processing, the alkali concentration is preferably 2% to 10%. If it is less than 2%, the alkali may be insufficient and the weight loss rate may become extremely slow. On the other hand, if it exceeds 10%, the alkali weight loss progresses too much, and the weight may be reduced to the island part.

As a method of reducing the amount of alkali, the sea-island type composite fiber is put into an alkaline solution, and after the alkali weight loss treatment is performed under a predetermined condition and for a certain period of time, it is once subjected to a neutralization step and then put into water again, and acetic acid, oxalic acid, etc. are used. A method of neutralizing and diluting with an organic acid to finally dehydrate, or an alkali weight loss treatment for a predetermined time, then neutralizing first, then injecting water to proceed with dilution and then dehydration. There are ways to do this. In the former case, since it is processed in a batch system, it can be manufactured (processed) in a small amount, but the neutralization process takes time, so the productivity is a little poor. The latter can be produced semi-continuously, but has the problem that it requires a large amount of acid-based aqueous solution during the neutralization treatment and a large amount of water for dilution. The processing equipment is not limited in any way, but from the viewpoint of preventing fiber from falling off during dehydration, the aperture 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 mesh material having a content of 50% (for example, a non-alkali hydrolyzable bag). If the aperture ratio is less than 10%, moisture escape is extremely poor, and if it exceeds 50%, fibers may fall off.

Further, after the alkali weight loss processing, a dispersant (for example, model YM-81 manufactured by Takamatsu Oil & Fat Co., Ltd.) is applied to the fiber surface in order to enhance the dispersibility of the fiber, and 0.1 to 5 with respect to the fiber weight. It is preferable to attach 0% by weight.

In the filter medium for the immersion type filtration cartridge of the present invention, the filtration layer is preferably made of a wet non-woven fabric. Compared to non-woven fabrics produced by the spunbond method, melt blow method, electrospinning method, etc., wet non-woven fabrics have less variation in properties related to filter performance such as texture, fiber diameter, and air permeability, and are superior in filtration performance. preferable.

The filtration layer preferably contains not only nanofibers but also binder fibers. At that 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. It is preferable to have.

The binder fiber is a heat-adhesive fiber. By including the binder fiber in the filtration layer, effects such as strength of the non-woven fabric, network structure, and bulk improvement due to shrinkage can be obtained. As the binder fiber, an undrawn yarn or a 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 undrawn yarn is preferably an undrawn 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. Polyethylene terephthalate and a copolymerized polyester containing the same as a main component are preferable from the viewpoint of productivity and dispersibility in water.

Further, 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, a non-crystalline copolymer polyester is arranged in the sheath portion, and the melting point is 20 ° C. than these polymers. A core-sheath type composite fiber in which the higher other polymer is arranged in the core portion is preferable. Further, 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, even if the layer made of wet non-woven fabric (layer containing nanofibers) contains fibers that are non-binder fibers and have a finer fineness than nanofibers while helping to disperse the nanofibers and also contribute to the improvement of porosity. Good. As the fiber having a higher fineness than the nanofiber, the polyester fiber as described above having a uniform fiber diameter and good dispersibility is preferable. In addition, various fiber materials for paper can be used in a small amount and depending on the purpose. For example, wood pulp, natural pulp, synthetic pulp containing aramid or polyethylene as a main component, nylon, acrylic, vinylon, rayon and the like. Synthetic fibers or semi-synthetic fibers containing the above may be mixed and added.

The wet non-woven fabric is obtained by making paper using the above fibers using a normal long net paper machine, short net paper machine, round net paper machine, or the like, and then heat-bonding the binder fibers.

In the filtration layer thus obtained, it is important that the Gale air permeability is 20 seconds / 100 cc or less (more preferably 0.1 to 18 seconds / 100 cc). If the Gale air permeability is larger than 20 seconds / 100 cc, the pressure loss may be large and the processing amount per unit time may be small.

The conventional melt-blown non-woven fabric has a problem that the pore diameter is not uniform because the fiber diameters are not uniform, the processing amount is large, and the filtration efficiency is low. On the other hand, the membrane type filter medium has a problem that the filtration efficiency is high but the processing amount is small. Since the filter medium using nanofibers having a uniform fiber diameter according to the present invention can form a structure having a uniform pore diameter, it has a minute pore diameter and high filtration despite its small basis weight and thickness. Has efficiency. Further, by setting the Gale air permeability of the filter medium to 20 seconds / 100 cc or less, a filter medium having a small pressure loss when water is permeated and a large amount of processing per unit time can be obtained. It is considered that this is because even if the pore diameter is small, the pore diameter is uniform and there are many.

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

The support layer is preferably a low-density non-woven fabric. The density is preferably in the range of 0.1 to 0.7 g / cm ^3. If the density is ^{less than 0.1 g / cm 3} , handleability may deteriorate. On the contrary, if the density is ^{larger than 0.7 g / cm 3} , a high water treatment amount may not be obtained.

The support layer is not limited to the wet non-woven fabric, and may be a non-woven 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 the polyester fibers as described above, polyphenylene sulfide fibers, polypropylene fibers, polyethylene fibers, aliphatic polyamide fibers and the like.

In the filter medium for an immersion type membrane cartridge of the present invention, it is preferable that the filtration layer is laminated on such a support layer.

At that time, the thickness of the filtration layer is preferably 100 μm or less (preferably 5 to 90 μm). If the thickness of the filtration layer exceeds 100 μm, the amount of water treated may decrease.

Since the filter medium for an immersion type membrane cartridge of the present invention contains the above-mentioned filtration layer, it not only has excellent filtration performance, but also has a low pressure loss, a large amount of processing, and its performance is maintained for a long period of time.

Here, it is preferable that the average pore size of the filtration layer is 2.0 μm or less (more preferably 0.1 to 1.8 μm).

The initial pressure loss (pressure loss) is preferably 10 kPa or less (more preferably 0.1 to 8 kPa). However, the initial pressure loss (kPa) is defined as the pressure loss when the entire amount of water is filtered through a filter medium having an area of ^{140 cm 2 with a permeated water amount of 25.8 m 3} / m ^{2 / day.}

Next, the immersion type filtration cartridge of the present invention is an immersion type filtration cartridge made by using the above-mentioned filter medium for the immersion type filtration cartridge.

An example of such an immersion type filtration cartridge is shown in FIG. FIG. 1 is a vertical cross-sectional view of a cylindrical immersion type filtration cartridge. Activated sludge water is filtered through the filtration layer and then passes through the support layer.

Since the immersion type filtration cartridge uses the above-mentioned filter medium for the immersion type filtration cartridge, not only the filtration performance is excellent, but also the processing amount is large due to the low pressure loss, and the performance is maintained for a long period of time.

Next, examples and comparative examples of the present invention will be described in detail, but the present invention is not limited thereto. Each measurement item in the examples was measured by the following method.
(1) Fiber diameter Using a transmission electron microscope TEM (with a length measuring function), a cross-sectional photograph of the fiber was taken and measured at a magnification of 30,000 times. However, as the fiber diameter, the diameter of the circumscribed circle in the cross section of the single fiber was used (average value of n number 5).
(2) Fiber length With a scanning electron microscope (SEM), the sea-island type composite fiber for nanofibers before dissolution and removal of sea components was laid on the substrate, and the fiber length L was measured at a magnification of 20 to 500 (n number). Average value of 5). At that time, the fiber length L was measured by utilizing the length measuring function of the SEM.
(3) Metsuke The basis weight was measured based on JIS P8124 (method for measuring metric basis weight of paper).
(4) Thickness The thickness was measured based on JIS P8118 (method for measuring the thickness and density of paper and paperboard). The measured load was 75 g / cm ² and n = 5, and the average value was calculated.
(5) Melt viscosity The polymer after the drying process is set in an orifice set at the ruder temperature at the time of spinning, melted and held for 5 minutes, then extruded by applying a load of several levels, 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 created, and the melt viscosity when the ^{shear rate was 1000 sec -1 was read.}
(6) Average pore size Measured with a palm polo meter manufactured by PMI.
(7) Gale air permeability Performed based on JIS P8117 (paper and paperboard air permeability test method).
(8) Initial pressure loss The initial pressure loss (kPa) was defined as the pressure loss when the entire amount of water was filtered through a filter medium having an area of ^{140 cm 2 with a permeated water amount of 25.8 m 3} / m ^{2 / day.}
(9) Pressure loss after permeation of simulated liquid 1 wt% of skim milk aqueous solution was used as a simulated liquid for sludge, and the entire amount was filtered until the pressure reached 250 kPa. Then, the filter medium was immersed in a sodium hypochlorite solution (6 g / L), and ultrasonic cleaning was performed at a frequency of 45 Hz for 10 minutes. After repeating the filtration and washing of the simulated liquid 7 times, the value of the pressure loss when the entire amount of water was filtered with the ^{permeated water volume of 25.8 m 3} / m ^{2 / day was defined as the pressure loss (kPa) after the simulated liquid permeated.} ..
(10) 1 μm initial collection rate When 1 wt% of skim milk aqueous solution was used as a simulated sludge solution and the entire amount was filtered until the pressure reached 250 kPa, the 1 μm particle collection rate was determined by the difference in the number of 1 μm particles before and after filtration. (%) Was calculated.

[Example 1]
Polyethylene terephthalate having a melt viscosity at 285 ° C. of 120 Pa · sec was added to the island component, and polyethylene glycol having an average molecular weight of 4000 having a melt viscosity at 285 ° C. of 135 Pa · sec was added to the sea component in an amount of 4% by weight and 5-sodium sulfoisophthalic acid. Using modified polyethylene terephthalate copolymerized at 9 mol%, spinning was performed using a base having 400 islands at a weight ratio of sea: islands = 10:90, and the mixture was taken up at a spinning speed of 1500 m / min. The difference in alkali weight loss rate was 1000 times. This was stretched 3.9 times and then cut to 0.5 mm with a guillotine cutter to obtain a sea-island type composite fiber. This was reduced by 10% at 75 ° C. with a 4% NaOH aqueous solution to obtain nanofibers made of polyethylene terephthalate (PET) fibers having a fiber diameter of 400 nm and a cut length of 0.4 mm, which were used as main fibers.

On the other hand, as a binder fiber, an undrawn polyester fiber obtained by spinning polyethylene terephthalate by a conventional method was prepared.

Next, the nanofiber (60 wt%), an undrawn polyester fiber (30 wt%) having a fiber diameter of 1.2 μm and a cut length of 0.4 mm, and an undrawn polyester fiber (10 wt%) having a fiber diameter of 4.3 μm and a cut length of 3 mm. ) Was mixed and stirred, and then wet papermaking was performed with an inclined short net paper machine and dried at 140 ° C. with a Yankee dryer to obtain a wet non-woven fabric to be a filtration layer. The basis weight of the filtration layer was 20 g / m ² .

Then, a wet non-woven fabric composed of 1.7 dtex, stretched polyester fiber having a cut length of 5 mm, 1.2 dtex (60 wt%), and unstretched polyester fiber (40 wt%) having a cut length of 5 mm was used as a support layer, and the calendar heat treatment was performed at 185 ° C. Bonding with the filtration layer was carried out.

In the filter medium obtained by such a method, the thickness of the filtration layer was 19 μm. Next, when a filtration test with a simulated liquid was performed, it was found that the pressure loss after the simulated liquid permeated was equivalent to the initial pressure loss, and the water treatment amount was maintained.

[Example 2]
The same as in Example 1 except that the basis weight of the filtration layer was 10 g / m ^2.

[Example 3]
Except that the constituent fibers of the filtration layer were nanofibers (60 wt%) made of polyethylene terephthalate (PET) fibers having a fiber diameter of 700 nm and binder fibers (40 wt%) made of unstretched polyester fibers having a fiber diameter of 1.2 μm. It was the same as in Example 2.

[Example 4]
In Example 3, the same as in Example 3 except that the fiber diameter of the nanofiber was changed to 1000 nm. The filter medium obtained by such a method had an average pore diameter of 1.0 μm or more, and a collection rate of 1 μm was lower than that obtained in Example 3.

[Comparative Example 1]
In Example 3, the same as in Example 3 except that the basis weight of the filtration layer was set to 30 g / m ^2. The filter medium obtained by this method had a gullet of 20 seconds / 100 cc or more and a high initial pressure loss of 18 kPa, and was not suitable as a filter medium for an immersion type membrane cartridge.

[Comparative Example 2]
The filter medium obtained in Example 3 was subjected to calendar processing so that the average pore diameter was 1 μm or less. The filter medium obtained by this method had a gullet of 20 seconds / 100 cc or more and a high initial pressure loss of 29 kPa, and was not suitable as a filter medium for an immersion type membrane cartridge.

According to the present invention, the filter medium for an immersion type filtration cartridge, the filter medium for an immersion type filtration cartridge and the immersion type filtration, which are not only excellent in filtration performance but also have a large processing amount due to a low pressure loss and the performance is maintained for a long period of time. Cartridges are provided and their industrial value is enormous.

Claims (8)

A filter medium for an immersion type filtration cartridge including a filtration layer, wherein the filtration layer contains nanofibers having a fiber diameter of 1000 nm or less and binder fibers which are unstretched polyester fibers having a fiber diameter of 1.2 μm or less , and the filtration is performed. A filter medium for an immersion type filtration cartridge, characterized in that the Gale air permeability of the layer is 20 seconds / 100 cc or less. The filter medium for an immersion type filtration cartridge according to claim 1, wherein the filtration layer has an average pore diameter of 2.0 μm or less. The immersion type filtration cartridge according to claim 1 or 2, wherein the initial pressure loss when the entire amount of water is filtered through a filter medium having an area of 140 cm ^{2 with a permeation amount of 25.8 m 3} / m ^{2 / day is 10 kPa or less.} Filter media. The filter medium for an immersion type filtration cartridge according to any one of claims 1 to 3, wherein the nanofibers are made of polyester fiber, polyphenylene sulfide fiber, or polypropylene fiber. In the filtration layer, 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 fibers is in the range of 10 to 50% by weight with respect to the weight of the filtration layer. The filter medium for an immersion type filtration cartridge according to any one of claims 1 to 3. The filter medium for an immersion type filtration cartridge according to any one of claims 1 to 5 , wherein the filtration layer has a thickness of 100 μm or less. The filtration layer is a wet-laid nonwoven fabric, immersion type filtration cartridge filter material according to any one of claims 1 to 6. An immersion type filtration cartridge using the filter medium for the immersion type filtration cartridge according to any one of claims 1 to 7.

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