JP6553646B2 - Filter fiber, filter and water treatment method - Google Patents

Description

Related application

  This application claims the priority of Japanese Patent Application No. 2014-265447 for which it applied on December 26, 2014 in Japan, The whole is referred as forming a part of this application by reference.

  The present invention relates to a filter fiber having water wettability despite being formed from a hydrophobic polymer, a filter including the filter fiber, and a water treatment method for treating water using the filter.

  Patent Document 1 (Japanese Patent Publication No. 2010-509099) discloses a high surface area fiber and an improved filter composite material produced therefrom. In this document, from a thermoplastic polymer (polypropylene, polyester, nylon, polyethylene, TPU, copolyester, liquid crystal polymer, etc.) and a soluble outer sheath component (polylactide, copolyester, polyvinyl alcohol or ethylene-vinyl alcohol copolymer, etc.) A composite fiber is constructed, and the outer sheath component is washed out of the composite fiber to obtain a high surface area fiber having a plurality of projections.

  Patent document 2 (Unexamined-Japanese-Patent No. 2003-129327) is disclosing the fiber which has 20 or more groove | channels on the fiber surface. In this document, as a method for producing a fiber, for example, a composite fiber in which a polyethylene terephthalate component (X component) and a copolyester (Y component) are radially combined is spun, and the Y component is dissolved and removed from the composite fiber. Is described. It is described that the obtained fiber has a brown chestnut-like cross section (see FIG. 2 of Patent Document 2), has a high surface area, high contact resistance, and good squeaking feeling.

  Patent Document 3 (Japanese Patent Laid-Open No. 2004-52161) also discloses a fiber having 20 or more grooves on the fiber surface. For example, polyethylene terephthalate is used as component X, and heat-meltable as component Y. Using a modified polyvinyl alcohol (ethylene content: 8 mol%), composite spinning is performed, and after spinning, the component Y is dissolved and removed to obtain a fiber with good squeaking feeling.

  In Patent Document 4 (Japanese Patent Laid-Open No. 2006-89851), polyethylene terephthalate (X component) and ethylene-modified polyvinyl alcohol resin (Y component) copolymerized with 8.7 mol% of ethylene are respectively divided (mandarin orange type). ) Leading to a composite spinning pack, forming an ultra-thin fiber nonwoven fabric while performing composite spinning, and then dissolving and removing most of the modified polyvinyl alcohol resin from the composite long fiber with water and drying, and then modifying polyvinyl alcohol A part of is obtaining the remaining very thin and long fiber non-woven fabric.

Special table 2010-509099 gazette JP 2003-129327 A JP 2004-52161 A JP 2006-89851 A

  Patent Document 1 does not describe a pleated shape protruding from a specific elliptical shape. Moreover, since there is a description that the outer sheath is removed by washing with a solvent, it is assumed that the outer sheath is completely removed by washing. That is, Patent Document 1 does not intend to make the surface of a high surface area fiber made of a hydrophobic polymer hydrophilic by a sheath component, and further, by making the surface hydrophilic, it is an effective filter medium as a water treatment filter. There is no suggestion that

  Although the fiber currently disclosed by patent documents 2-3 has obtained the fiber which has a groove structure on the surface by removing the polymer component Y, the main uses are the clothes use which has a feeling of creaking, and the pleat part of The tip is sharp. Therefore, the contact portions of the single fibers are engaged to form a state of association, the contact resistance between the fibers increases, and the flow resistance becomes too high for use as a water treatment filter. In addition, these documents describe that when used as a battery separator, a hydrophilic treatment is separately performed. Therefore, in this document as well, the surface of the polymer component Y is to be hydrophilized with the polymer component X. There is no intention.

  Patent Document 4 discloses that the Y component is removed from the fiber in which the X component and the Y component are combined in a radial split type. However, in this fiber, since the central part of the fiber needs to be divided, there is no technical idea that the central part of the fiber is given a specific shape and left after removal of the Y component. Therefore, there is no suggestion about a fold structure extending from the fiber center to both sides. In addition, there is a suggestion that an ultra-thin fiber non-woven fabric is constructed from the fibers from which the Y component has been removed, and this non-woven fabric is used as a liquid filter. However, such a filter structure has a large pressure loss and traps trapped particles. There is a problem that efficiency is not high.

  We ensure the form stability of the filter fiber layer when immersed in water by (i) forming the filter fiber from a hydrophobic polymer, and (ii) a specific shape for the fiber In addition to imparting, by performing specific hydrophilization on such a fiber surface, for example, in water treatment etc., it is possible to enhance the trapping property of particles to be removed and to ensure the rigidity as a fiber It was set as an issue to be solved to develop a filter fiber having a high surface area fiber form that can be

The inventors of the present invention have arrived at the present invention as a result of intensive studies to solve the above problems.
A first configuration of the present invention is a filter fiber having a plurality of pleated projections, which is composed of a hydrophobic polymer,
The cross section of the fiber is (a) an elliptical portion having a substantially elliptical shape, (b) a plurality of protrusions having rounded ends, and (c) the protrusions and the protrusions extending to both sides from the elliptical portion. It is the fiber comprised from the groove part formed between parts. A hydrophilic polymer is attached to the surface of the fiber, and the fiber surface maintains water wettability when subjected to hot water treatment at 95 ° C. 15 times. As other characteristics, this fiber may have, for example, the following characteristics singly or in combination of two or more.
The fiber has a fineness of 6 dtex or less.
The ellipse part consists of a long axis part and a short axis part, and the width of the short axis part is 3 to 30 μm.
The protrusion has a width of 0.5 to 4 μm.
The groove has a depth of 1 to 4 μm.
Here, the width of the major axis of the elliptical portion is the width (major axis) of the longest position of the straight line passing through the center of the ellipse, and the width of the minor axis is the shortest position of the straight line passing the center of the oval Means the width (minor axis) of

  In the filter fiber, the ratio of the width of the long axis portion to the width of the short axis portion is, for example, 1.1 to 6.0, preferably 1.1 to 4.0. In addition, from the viewpoint of improving the rigidity and capturing property of the fiber, the ratio of the depth of the groove and the width of the elliptical short axis (the depth of the groove / the width of the elliptical short axis) is 0.02 to 3. Is preferred.

  In the filter fiber, the protrusion may have a width of 0.5 to 4 μm, and the depth of the groove has a ratio to the width of the protrusion (the depth of the groove / the width of the protrusion) 1/1 to 4/1 may be sufficient. Furthermore, the groove may have a depth of 1 to 4 μm.

  In the filter fiber, the ratio of the width of the protrusion to the width of the groove (width of the protrusion / width of the groove) may be 2/1 to 20/1.

  The hydrophobic polymer is preferably polyolefin, polyamide or polyester, and more preferably the hydrophobic polymer is polypropylene.

  The hydrophilic polymer is preferably a heat-meltable and water-soluble ethylene-vinyl alcohol copolymer, and the ethylene-vinyl alcohol copolymer contains 0.1 to 20 mol% of ethylene monomer units. The ethylene-vinyl alcohol copolymer contained is preferable.

  It is preferable that the adhesion amount of the hydrophilic polymer adhering to the surface of the filter fiber is 0.5% by mass or less (vs. filter fiber). In the filter fiber in which the hydrophobic polymer is polypropylene and the hydrophilic polymer is a heat-meltable and water-soluble ethylene-vinyl alcohol copolymer, the hydrophilic polymer is attached to the fiber surface. And various surface analysis methods such as IR analysis.

  The fibers are formed from fibers formed by core-sheath type composite spinning using the hydrophobic polymer as a core layer and the hydrophilic polymer (such as a heat-meltable and water-soluble ethylene-vinyl alcohol copolymer) as a sheath layer. It is preferable that it is a fiber formed by removing a hydrophilic polymer.

  The fibers may have the shape of staple fibers or filaments.

  A second structure of the present invention is a filter comprising the filter fiber described above. In the present invention, a filter refers to an apparatus that makes it possible to remove or remove unnecessary components such as fine particles in water or components to be recovered by filtration.

  The filter is preferably a filter in which the filter fiber forms a dry or wet nonwoven fabric. As a dry-type nonwoven fabric, the nonwoven fabric formed from the fiber in which a single yarn fineness exceeds 0.5 dtex, for example, a spun bond nonwoven fabric, formed by direct spinning may be included. However, since it is disadvantageous in terms of pressure loss, it is preferable not to include an ultrafine fiber having a single yarn fineness of 0.5 dtex or less formed by a melt blown method or a nonwoven fabric composed of such a fiber.

  Preferably, the dry or wet non-woven fabric is a filter filled in a cartridge. In the present invention, the cartridge means one in which the filter is formed into a predetermined shape such as a flat plate shape or a cylindrical shape, and is accommodated in the housing.

  The filter is suitably used for water treatment.

  A third configuration of the present invention is a water treatment method for filtering water containing an object to be removed using the filter.

  In addition, any combination of at least two components disclosed in the claims and / or specification is included in the present invention. In particular, any combination of two or more of the following claims is included in the present invention.

  According to the first configuration of the present invention, the filter fiber of the first configuration is formed of a hydrophobic polymer, and a large number of pleated projections having a specific shape protruding from a specific substantially elliptical columnar portion are arranged on the fiber surface. As a result, it has rigidity as a filter fiber and high surface area. In addition, since the hydrophilic polymer is attached to the fiber surface, the fiber surface has water wettability, and for example, the water wettability is maintained even if the hot water treatment at 95 ° C. is performed 15 times. It has characteristics. Therefore, it has a preferable characteristic especially as a filter fiber for water treatment.

  According to the second configuration of the present invention, since the filter according to the second configuration is loaded with the filter fiber composed of the above-mentioned hydrophobic polymer, the filter fiber is stable even if it is immersed in water is there. Further, the filter fiber has a large number of pleated protrusions having a specific shape protruding from a specific substantially elliptical columnar part, so that the filter fiber has rigidity and a high surface area, and the filter fiber surface has water wettability. Therefore, it is suitably used as a water treatment filter.

  According to the third aspect of the present invention, by treating the water containing the particles to be filtered using the above-mentioned filter, the particles to be filtered can be efficiently removed or recovered, and water treatment with a long filtration life can be performed Can be.

The present invention will be more clearly understood from the following description of preferred embodiments with reference to the accompanying drawings. However, the embodiments and drawings are merely for illustration and description and should not be used to define the scope of the present invention. The scope of the invention is defined by the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS It is fiber sectional drawing (scanning electron micrograph: 5000 times of magnification) which shows an example of the composite fiber used in order to manufacture the filter fiber which concerns on this invention. It is a fiber sectional view (scanning electron micrograph: magnification 5000 times) showing an example of the filter fiber concerning the present invention. It is a side view (scanning electron micrograph: 5000 times of magnification) which shows the state after performing water filtration using the filter fiber which concerns on this invention. It is a graph which shows the measurement result of the surface oxygen amount of the filter fiber nonwoven fabric which concerns on this invention, and a comparison fiber nonwoven fabric. It is a photograph which shows the water wettability of the filter fiber nonwoven fabric surface concerning the present invention. It is a photograph which shows the water wettability of comparison control textiles. It is a graph which shows the relationship between the frequency | count of a hot-water process, and a water droplet absorption rate about the filter fiber nonwoven fabric and comparative control fiber nonwoven fabric which concern on this invention. It is the schematic of the filtration apparatus which measures the filtration performance of a filter fiber. It is a graph which shows the filtration performance (dust collection rate) of filter fiber.

(Filter fiber)
The first structure of the present invention is a filter fiber comprising a hydrophobic polymer and having a central portion and a plurality of fold-like projections protruding from the central portion, and is specified in the fiber cross section orthogonal to the fiber axis The hydrophilic polymer adheres to the surface of the fiber, and the fiber surface maintains water wettability when subjected to a hot water treatment at 95 ° C. 15 times. The cross section of the fiber is (a) an elliptical portion having a substantially elliptical shape, (b) a plurality of projections having rounded ends, and (c) the projections and the projections extending to both sides from the oval portion. A groove formed between the portions, and
(I) The ellipse part may be composed of a major axis part and a minor axis part, and the width of the minor axis part may be 3 to 30 μm, and / or (ii) the protrusion part may have a width of 0.5 to And / or (iii) the groove may have a depth of 1 to 4 μm.
In particular, in the cross section of the fiber, it is preferable that the elliptical portion comprises a major axis portion and a minor axis portion, and the width of the minor axis portion is 3 to 30 μm.
The filter fiber may have a fineness of 6 dtex or less, and preferably has a fineness of more than 0.5 dtex and 6 dtex or less.
Such filter fibers can be manufactured by the method described later.

(Filter fiber manufacturing method)
In the filter fiber of the present invention, a hydrophobic polymer is used to form a core, and a hydrophilic polymer is extruded to form a sheath to form a core-sheath composite fiber, and after forming the composite fiber, the hydrophilic polymer of the sheath is formed. It can be obtained by dissolving and removing the hydrophilic polymer so that at least a part of the polymer remains. More specifically, in the case of forming a core-sheath type composite spun fiber, molten hydrophobicity is obtained from a nozzle capable of forming a composite fiber comprising a core having a predetermined shape and a sheath surrounding the core. The polymer is extruded to form a core, and the molten hydrophilic polymer is extruded to form a sheath to form a core-sheath composite spun fiber.

The core having a predetermined shape can be formed by using a composite spinning nozzle in which the nozzle component is adjusted to form an oval portion having a predetermined shape and a protrusion having a predetermined shape in the fiber cross section. Such a nozzle component can be appropriately selected so as to have a shape corresponding to the cross-sectional shape of the core portion.
The spinning temperature is not particularly limited as long as the polymers forming the core and the sheath can each be maintained in a molten state.

  Next, after the core-sheath type composite spun fiber is formed, the hydrophilic polymer in the sheath part is dissolved and removed within a predetermined range, so that (a) an elliptical part having a substantially elliptical shape in the fiber cross section, and (b) the above-mentioned It is composed of a plurality of protrusions with rounded tips extending from the ellipse on both sides, and (c) a groove formed between the protrusions and the protrusions. The filter fiber can be provided with a portion in which the protrusion and the groove are continuous. If necessary, the sheath may be removed after the core-sheath composite spun fiber is once formed into a predetermined shape such as a nonwoven fabric.

  The hydrophilic polymer in the sheath is removed using hot water at a predetermined temperature in accordance with the solubility of the hydrophilic polymer, but not all of the hydrophilic polymer is removed, and at least a part of the hydrophilic polymer is removed. Polymer remains in the filter fibers. For example, the temperature of the hot water may be, for example, 70 to 120 ° C., preferably about 80 to 110 ° C. Since the composite fiber has an ellipse at the core, it has high rigidity and can be treated with hot water without gradually increasing the water temperature (that is, directly combined with hot water having a predetermined temperature). Fiber).

  Also, the removal of the hydrophilic polymer may be carried out by leaving the conjugate fiber in hot water, or to the extent not removing all the hydrophilic polymer in order to shorten the time for the removal process, The composite fibers may be physically irritated in hot water (eg, by stirring). In particular, in the present invention, unlike the case of a mere ultrafine fiber, a pleated projection is formed in the core portion. Therefore, even when the removal treatment is performed in a state where physical stimulation is applied, the pleated portion is used. It is possible to leave a hydrophilic polymer.

(Core-sheath type composite spun fiber)
The core-sheath type composite spun fiber obtained after composite spinning is composed of a core composed of a hydrophobic polymer and a sheath composed of a hydrophilic polymer, and the sheath is surrounding the core. The core portion has substantially the same cross-sectional shape as the filter fiber. For example, the core of the composite spun fiber shown in FIG. 1 has substantially the same cross-sectional shape as the filter fiber shown in FIG.

  The composite ratio of the hydrophobic polymer and the hydrophilic polymer can be appropriately set as long as the composite spinning is possible. However, preferably, the hydrophobic polymer / hydrophilic property is used from the viewpoint of achieving both spinnability and sheath removability. Polymer (mass ratio) = 90/10 to 30/70, preferably about 80/20 to 40/60.

  In the core-sheath type composite spun fiber, the hydrophobic polymer constituting the core part is not particularly limited as long as it is a hydrophobic polymer having fiber forming ability, but preferably a hydrophobic polymer that can be melt-spun, for example, Polyolefin (polyethylene, polypropylene, etc.), polyester (polyethylene terephthalate, polybutylene terephthalate, etc.), polyamide (nylon 6, nylon 66, nylon 610, nylon 11, nylon 12, etc.), polyurethane (for example, thermoplastic polyurethane (TPU), etc.) And other thermoplastic hydrophobic polymers. Because it can be formed of hydrophobic polymers, the resulting filter fibers can have good durability.

  Further, the hydrophilic polymer constituting the sheath portion is not particularly limited as long as it is a hydrophilic polymer having a fiber forming ability, but preferably, an ethylene-vinyl alcohol copolymer (ethylene copolymerization ratio: 0.1 to 40) And a hydroxyl group-containing polymer such as polyvinyl alcohol and polyhydroxybutyrate. The hydrophilic polymer is preferably excellent in melt spinnability together with the hydrophobic polymer, and also excellent in removability from composite fibers (in particular, removability in hot water treatment) after spinning. From this viewpoint, an ethylene-vinyl alcohol copolymer having an ethylene copolymerization ratio of 0.1 to 20 mol%, preferably 3 to 15 mol%, achieves both melt spinnability and removability with hot water. Therefore, it is particularly preferably used as the hydrophilic polymer in the present invention. The preferred ethylene-vinyl alcohol copolymer may have, for example, a degree of saponification of 88 to 99, preferably 90 to 98. In addition, the viscosity average degree of polymerization may be, for example, 300 to 2,000, preferably 400 to 1700. The saponification degree and the viscosity average polymerization degree can be appropriately set by those skilled in the art according to the type of hydrophobic polymer constituting the core, the fineness required of the composite fiber, and the like.

  From the viewpoint of imparting water wettability to the filter fiber by removing a portion of the hydrophilic polymer from the sheath while leaving a part of the polymer in the hydrophobic polymer of the core, as a preferred combination of hydrophilic polymer and hydrophobic polymer For example, the core part / sheath part is polyolefin / ethylene-vinyl alcohol copolymer, polyester / ethylene-vinyl alcohol copolymer, polyamide / ethylene-vinyl alcohol copolymer, polyurethane / ethylene-vinyl alcohol copolymer. And so on.

In order to obtain a fiber having a fineness of, for example, 6 dtex or less, preferably a fiber having a fineness of 6 dtex or less, for example, exceeding 0.5 dtex by removing the sheath portion as described above, for example, core-sheath composite The fineness of the spun fiber may be, for example, 15 dtex or less, preferably 0.7 to 15 dtex, and more preferably 0.7 to 10 dtex.
For example, in Example 1 to be described later, a fiber having a fineness of 3.3 dtex of a core-sheath type composite spun fiber (core: 60% by mass of polypropylene; sheath: 40% by mass of ethylene-vinyl alcohol copolymer) As a result, a filter fiber having a fineness of 2.2 dtex was obtained. The fiber surface area (BET) in this case was 1.94 m ² / g. Moreover, in the result of analyzing the fiber surface after removing the sheath part by XPS analysis, since oxygen can be confirmed on the fiber surface, the hydrophilic polymer remains.

(Water wettability of filter fiber)
Since the filter fiber of the present invention is used as a filter fiber for water treatment in particular, the fiber is formed from a hydrophobic polymer, but the fiber surface needs to have water wettability. For this reason, after removing the hydrophilic polymer from the core-sheath type composite spun fiber in which the hydrophobic polymer is the core and the hydrophilic polymer is the sheath, the hydrophilic polymer is slightly retained and adhered to the fiber surface after removing the hydrophilic polymer. The fiber surface maintains water wettability (water absorption) after being subjected to hot water treatment at 95 ° C. 15 times.

  About the adhesion amount of hydrophilic polymer, 99 mass% or more and less than 100 mass% of hydrophilic polymer may be removed from the core-sheath composite fiber. For example, in the filter fiber, the hydrophilic polymer may be attached in a small amount to the fiber, for example, the attached amount of the hydrophilic polymer is 0% by mass (eg, 0.001%) to the entire filter fiber. It is preferable to exceed 0.5% by mass). When the adhesion amount is too large, the hydrophilic polymer tends to come off during use as a filter. The remaining trace amount of hydrophilic polymer retains the wettability of the filter fiber over a long period of time. In the present invention, the trace amount may be an amount in which the hydrophilic polymer remains to the extent that the water wettability of the filter fiber is maintained.

  The remaining of the hydrophilic polymer (e.g. ethylene-vinyl alcohol copolymer) is considered as follows. A part of radicals at the time of polymer production (polymerization) is trapped in the polymer, and at the time of heat melting for fiber formation, a polymer in which the trapped radicals are combined to form a large molecule (including crosslinking) is formed, A small amount of this polymer having a large molecular weight is contained in the hydrophilic polymer layer of the fiber, and it remains on the fiber surface without being removed when the hydrophilic polymer is removed. And since the filter fiber has a pleated protrusion of a specific shape, when such a polymer having a large molecular weight adheres to the deep part of the groove, the hydrophilic polymer may be subjected to repeated hot water treatment. It is considered that a trace amount of adhesion is not completely removed and the water wettability of the fiber surface is maintained by this adhesion. A filter fiber obtained from a core-sheath composite spun fiber formed with a hydrophilic polymer (for example, an ethylene-vinyl alcohol copolymer having an ethylene copolymerization ratio of 0.1 to 20 mol%) as a sheath is made of hot water Since the water wettability is maintained even when the treatment is repeated 15 times or more, it is suitably used as a filter material for water treatment.

In the present invention, a hydrophilic polymer is attached to the surface of the filter fiber, and the surface of the fiber is subjected to a hydrothermal treatment at 95 ° C. for 30 minutes with a bath ratio of 1:20 to the fiber amount. It is necessary that the wettability is maintained even when the drying treatment at 60 ° C. for 10 minutes is set as one set and this treatment is carried out 15 times. If the water wettability can not be maintained in less than 15 times, the filter fiber may lose its water wettability during use and may not function as a filter fiber for a long period of time.
With regard to the presence or absence of water wettability, the absorption rate test is carried out according to JIS L 1906 water absorption rate A method (dropping method), and when the droplet absorption rate is 10 seconds or less, the water wettability (water absorption) is It can be determined that there is.

(Size and surface area of filter fiber)
In the present invention, the single fiber fineness of the filter fiber may be 6 dtex or less, for example, more than 0.5 dtex and 6 dtex or less, preferably 1 dtex to 4 dtex. A filter layer formed of fibers having too small a fineness is disadvantageous in terms of strength and is not suitable as a filter fiber because pressure loss is large. On the other hand, when the fineness is too large, the filter layer becomes coarse and it becomes difficult to filter fine particles, which is unsuitable as a filter fiber.
In addition, the surface area (BET) of the filter fiber is, for example, 0.8 to 4.0 m ² / g from the viewpoint of attaching a hydrophilic polymer to the surface of the fiber made of a hydrophobic polymer to impart water wettability. It may be 1.2 to 3.0 m ² / g.

(Cross-sectional shape of filter fiber)
The filter fiber has (a) an elliptical portion having a substantially elliptical shape, (b) a plurality of protruding portions having rounded rounded tips, and (c) the protruding portion in cross-sectional shape. And a groove formed between the protrusions. The elliptical part is preferably a solid-filled elliptical part from the viewpoint of rigidity.
The width of the minor axis of the elliptical portion may be in the range of 3 μm to 30 μm, preferably in the range of 4.0 μm to 20 μm. If the width is too narrow, the filter fibers have a flat shape, so that the density of the filter layer formed by laminating the filter fibers becomes too high, which tends to be unsuitable in terms of pressure loss. Moreover, since a fiber cross section will approximate circular when the width becomes too large, it becomes difficult to form a large number of protrusions. Further, the ratio of the major axis to the minor axis may be, for example, in the range of 1.1 to 5.0, preferably in the range of 1.1 to 4.0, and more preferably 1 It may be in the range of .5 to 4.0, more preferably in the range of 2.1 to 4.0. If the ratio is too large, the fiber shape may be flattened, which may cause the problems as described above, and if the ratio is too small, it may approach a circle, making it difficult to form many projections. .

  In the filter fiber, for example, the plurality of protrusions may protrude adjacent to each other across the groove from the ellipse, and both sides from the ellipse (upper and lower sides with the major axis of the ellipse being axisymmetric). (Both sides), preferably all around the oval. In particular, when there is a protrusion protruding from a portion within 80% centering on the short axis in the major axis width of the ellipse, the trapping property by the groove is effectively utilized by utilizing the gentle curvature of the substantially ellipse. It can be effectively used to achieve both the improvement of and the strength of the protrusion.

In the present invention, the width of the protrusion may be, for example, in the range of 0.5 to 4 μm, and preferably in the range of 1 to 3 μm. If the width is too narrow, the strength of the protrusions will be too weak and the protrusions may be chipped, which is inappropriate. On the other hand, if the width is too large, it will be difficult to place many protrusions, so it is not suitable. It is.
The number of projections per filter fiber is, for example, 5 to 50, preferably 10 to 40, more preferably 20 to 35. If the number of projections is too small, the surface area of the fiber surface is increased If the effect is not sufficient and the number of protrusions is too large, the width of one protrusion tends to be narrow, and the strength of the protrusions tends to be insufficient.

  In the present invention, in the fiber cross section, the tip of the protrusion protruding from the elliptical portion needs to be rounded (see, for example, FIG. 1). When the tip of the protrusion is not rounded but is tapered toward the tip (see FIGS. 2 and 4 of Patent Document 3), the tip tends to be damaged, which is not preferable as a filter fiber.

In the filter fiber of the present invention, the depth of the groove is, for example, in the range of 1 to 4 μm, preferably in the range of 1.5 to 3.6 μm, and more preferably in the range of 2 to 3.2 μm. It is to be in range. If the groove is too shallow, the filter fiber particles may not be sufficiently captured. By increasing the depth of the groove, the surface area of the filter fiber according to the present invention is increased, and the effect of imparting water wettability is enhanced. However, even if the groove is too deep, particles contained in the treated water Does not contribute to
The width of the groove is, for example, 0.1 μm to 2.0 μm, more preferably 0.1 to 1.0 μm, still more preferably 0.1 to 0.5 μm, particularly preferably 0.1 to 0.18 μm. It is preferable from the viewpoint of particle trapping properties.

  In addition, from the viewpoint of improving both the strength of the protrusion and good capture, the ratio of the width of the protrusion to the width of the groove (the width of the protrusion / the width of the groove) is preferably 2 / It may be in the range of 1 to 20/1, more preferably 5/1 to 15/1.

Further, the ratio of the depth of the groove to the width of the groove (the depth of the groove / the width of the groove) is preferably 1/2 to 40/1, more preferably 1/1 to 20/1. In the case where the filter fiber according to the present invention is used for a water treatment filter, water wettability is provided to improve the efficiency of the water treatment filter.
Further, the depth of the groove is, for example, the same as the width of the protrusion, and less than 4 times, and preferably 1.2 times to 3.5 times the width of the protrusion. It is preferable in terms of balance with the strength of the protruding portion.

  Moreover, it is preferable that the bottom part of the groove part between the projection parts is also rounded. When a groove part has roundness in a bottom part, the adhesiveness to the groove part of a hydrophilic polymer can be improved.

  From the viewpoint of imparting good particle trapping properties while imparting appropriate rigidity to the filter fiber, preferably the ratio of the depth of the groove and the width of the elliptical short axis (depth of the groove / width of the elliptical short axis) May be about 0.02 to about 3, more preferably about 0.1 to about 2.5, and still more preferably about 0.5 to about 1.5.

(Filter fiber non-woven fabric)
In the present invention, the filter fibers may be used directly as various shapes, for example short fibers (cut fibers) or long fibers (filaments), as long as they can be used for the filter device, or these fibers May be formed into a cloth-like shape, for example, a non-woven fabric (wet, dry, directly-bonded type such as spun bond, etc.). Of these, the filter fiber is preferably used in the form of a nonwoven fabric, and a spunbonded nonwoven fabric is particularly preferred. The nonwoven fabric may be subjected to post-processing such as embossing treatment as necessary.

The basis weight of the filter fiber nonwoven fabric is, for example, 20 to 300 g / m ² , preferably 30 to 200 g / m ² , and more preferably 40 to 100 g / m ² . If the basis weight of the nonwoven fabric is too small, the strength will be too low and it will break during processing during filter molding. In addition, when the fabric weight of the non-woven fabric is too large, a difference in tension between the inside and the outside occurs due to winding molding and the like, which causes wrinkles and the like.
The basis weight of the core-sheath type composite spun fiber non-woven fabric before removing the sheath component is, for example, 30 to 500 g / m ² , preferably 50 to 350 g / m ² , and more preferably 60 to 200 g / m ² Also good.

(Filter device)
The filter cartridge used in the present invention may be any of known filter cartridges. For example, a wound cartridge having filter fibers wound around a core material or the like, or a filter having dry or wet non-woven fabric composed of filter fibers filled in the cartridge. It may be. Specifically, exemplified are flat plate type cartridges in which a plurality of flat plate type filter units formed by arranging two rectangular filter members opposite to each other, a pleated cartridge having a structure in which filter materials are folded in a pleated shape, and the like. can do. For example, a filter medium mounted on a pleated cartridge filter is pleated, folded and folded, the filter medium is wound around a core, inserted into a cylindrical container, and used for water filtration.

(Water treatment)
By utilizing the excellent water-wettability of the filter fiber of the present invention, the filter fiber of the present invention can be suitably used as various filter materials for which hydrophilicity is required. Preferably, the filter fiber of the present invention can be suitably used as a filter material for water treatment, and specifically, water filtration (for example, such as removing or recovering the foreign matter from the water in which the foreign matter is mixed) It can be suitably used as a water treatment filter in circulation filtration of water of a pool or hot spring, or water filtration in a seawater desalination plant. FIG. 3 shows a state after the water is filtered using the filter fiber according to the present invention. It can be seen that the substance to be filtered in water is caught and collected in the groove formed between the projections of the filter fiber of the present invention and the projections.

In addition, the present invention may include the following embodiments as a filter fiber. Moreover, each characteristic described in the following embodiments may conform to each characteristic described above.
[Aspect 1]
A filter fiber comprising a plurality of pleated projections made of a hydrophobic polymer, the cross section of said fiber comprising (a) an elliptical part having a substantially elliptical shape, and (b) extending on both sides from said elliptical part A plurality of projections with rounded tips, and (c) a groove formed between the projections and the projections;
The fibers have a fineness of 6 dtex or less;
The ratio of the width of the major axis portion to the width of the minor axis portion is 1.1 to 6.0,
A filter fiber, wherein a hydrophilic polymer is attached to the surface of the fiber, and the fiber surface maintains water wettability when subjected to hot water treatment at 95 ° C. 15 times.
[Aspect 2]
A filter fiber comprising a plurality of pleated projections made of a hydrophobic polymer, the cross section of said fiber comprising (a) an elliptical part having a substantially elliptical shape, and (b) extending on both sides from said elliptical part A plurality of projections with rounded tips, and (c) a groove formed between the projections and the projections;
The fiber has a groove depth of 1 to 4 μm and a ratio of the groove depth to the width of the elliptical minor axis (the depth of the groove / the width of the elliptical minor axis) is 0.02 to 3 Yes,
A filter fiber, wherein a hydrophilic polymer is attached to the surface of the fiber, and the fiber surface maintains water wettability when subjected to hot water treatment at 95 ° C. 15 times.
[Aspect 3]
A filter fiber comprising a plurality of pleated projections made of a hydrophobic polymer, the cross section of said fiber comprising (a) an elliptical part having a substantially elliptical shape, and (b) extending on both sides from said elliptical part A plurality of projections with rounded tips, and (c) a groove formed between the projections and the projections;
The fibers have a fineness of 6 dtex or less;
A filter fiber wherein the ratio of the width of the projections to the width of the grooves (the width of the projections / the width of the grooves) is 2/1 to 20/1.
[Aspect 4]
In the filter fiber, any one of the embodiments 1 to 3, wherein the ratio of the depth of the groove to the width of the elliptical short axis (the depth of the groove / the width of the elliptical short axis) is 1/10 to 4/1. The filter fiber according to one aspect.
[Aspect 5]
The said filter fiber WHEREIN: The filter fiber as described in any one aspect of the aspects 1-4 whose ratio of the width | variety of the said long axis part and the width | variety of the said short axis part is 1.1-6.0.
[Aspect 6]
In the filter fiber, any one of the aspects 1 to 5, wherein the ratio of the depth of the groove to the width of the elliptical short axis (the depth of the groove / the width of the elliptical short axis) is 1/10 to 4/1. The filter fiber according to the embodiment.
[Aspect 7]
The filter fiber according to any one of Aspects 1 to 6, wherein in the filter fiber, the protrusion has a width of 0.5 to 4 μm, and the groove has a depth of 1 to 4 μm.
[Aspect 8]
In the filter fiber, the ratio of the width of the protrusion to the width of the groove (width of the protrusion / width of the groove) is preferably in the range of 1 to 20/1, any one of the embodiments 1 to 7 Filter fiber.
[Aspect 9]
Aspect 9. A filter fiber according to any one of aspects 1-8, wherein the hydrophobic polymer is a polyolefin, a polyamide or a polyester.
[Aspect 10]
The filter fiber according to any one of aspects 1 to 9, wherein the hydrophilic polymer is a heat-meltable water-soluble ethylene-vinyl alcohol copolymer.
[Aspect 11]
11. The filter fiber according to aspect 10, wherein the ethylene-vinyl alcohol copolymer is an ethylene-vinyl alcohol copolymer containing 0.1 to 20 mol% of ethylene monomer units.
[Aspect 12]
12. The filter fiber according to any one of aspects 1 to 11, wherein the attached amount of the hydrophilic polymer is 0.5% by mass or less (relative to filter fiber).
[Aspect 13]
The fiber is a fiber formed by removing the hydrophilic polymer from a fiber formed by core-sheath type composite spinning using the hydrophobic polymer as a core layer and the hydrophilic polymer as a sheath layer. The filter fiber according to any one of 12 embodiments.

  Hereinafter, the present invention will be described in detail by way of examples and comparative examples, but the present invention is not limited to these examples.

(Measurement of nonwoven fabric surface oxygen content by XPS analysis)
The constituent elements and bonding state of the nonwoven fabric surface were analyzed by X-ray photoelectron spectroscopy (XPS), and the surface oxygen content was calculated from the results.

<Evaluation of specific surface area of fiber (BET method)>
It evaluated using the flow method BET 1-point method specific surface area measuring apparatus (Monosorb made from Quantachrome). In the pretreatment attached to the apparatus, deaeration was performed at room temperature for 30 minutes in an N ₂ gas atmosphere. In the measurement, a mixed gas (N ₂ 30%, He 70%) was flowed in a U-shaped cell containing a sample, the sample chamber was cooled to liquid nitrogen temperature (77 K), and only N ₂ gas was adsorbed on the surface of the sample.

(Absorption rate)
Measured according to JIS L 1906 water absorption rate A method (drop method).

(Measurement of shape of filter fiber cross section)
The cross section of the filter fiber is photographed with a scanning electron microscope (magnification: 5000), and the printed image is used to determine the width of the minor axis of the elliptical portion, the ratio of the major axis to the minor axis, and the protrusion The width of the part and the depth of the groove part were measured.
Regarding the width of the protrusion, the width at a point between the tip and the root of the protrusion is measured from the above-mentioned image for 10 randomly selected protrusions, and the average value is obtained, and the protrusion is obtained. The width of the part.
The protrusions were selected basically by excluding the protrusions protruding from the long axis end, and were selected from the protrusions protruding from a portion within 80% of the center of the short axis in the major axis width.
With regard to the depth of the groove, the distance between the tip of the protrusion and the root was measured for 10 randomly selected protrusions, and the average value was obtained to obtain the depth of the groove.
With regard to the width of the groove, the width at a point between the front end and the root of the groove is measured from the above-mentioned image for 10 randomly selected grooves, and the average value is obtained. did.
The elliptical portion is the portion excluding the protrusions in the fiber cross section, and in the straight line passing through the center of the ellipse from the printed image, the location with the longest width is taken as the long axis portion and the straight line passing through the center of the ellipse The portion having the shortest width was defined as the short axis portion, and the major axis that was the width of the major axis portion and the minor axis that was the width of the minor axis portion were each calculated from the average value of ten measurement results. Here, basically, the center of the circumscribed circle of the portion excluding the protruding portion in the fiber cross section is the center of the ellipse. When the center of the circumscribed circle does not exist in a portion other than the protrusion in the fiber cross section, in the straight line passing through the center of the circumscribed circle, the portion having the shortest width is taken as the short axis portion. In the straight line passing through the center, the portion with the longest width is taken as the major axis.

[Basic weight (g / m ² )]
Measured according to JIS P 8124 “Measuring basis weight of paper”.

Example 1
Supply polypropylene (PP) and ethylene-vinyl alcohol copolymer (Kuraray Co., Ltd., ethylene copolymerization ratio: 8.7 mol%) (sometimes abbreviated as EXC) to different extruders. Core-sheath type composite spun fiber (core: polypropylene; sheath: ethylene-vinyl) which is melted and discharged from the composite fiber forming nozzle at a ratio of PP / EXC = 60/40 (mass ratio) as shown in FIG. While forming core-sheath type composite spun fibers (FIG. 1) made of alcohol copolymer (FIG. 1), they were accumulated to prepare a spunbonded fiber integrated sheet. The fineness of the core-sheath type composite spun fiber was 3.3 dtex, and the basis weight of the fiber accumulation sheet was 120 g / m ² .
Next, the non-woven fabric is immersed in hot water at 95 ° C. for 30 minutes to remove the ethylene-vinyl alcohol copolymer from the core-sheath type composite spun fiber, and a filter fiber having a cross section shown in FIG. .2 dtex) were produced. The basis weight of the spunbonded nonwoven fabric formed by hot embossing the accumulated sheet after the hot water treatment was 72 g / m ² . The fiber surface area (BET) was 1.94 m ² / g.
As a result of observing the cross section of the obtained filter fiber, the cross section of the fiber has a substantially elliptical central portion, and a protrusion protrudes from the central portion, and the tip of all the protrusions is rounded. In the elliptical shape, the width of the minor axis is 4 μm, the ratio of the major axis to the minor axis is 3.7, the number of projections is 30, the width of the projections is 1.5 μm, the width of the groove is 0. The depth of the groove portion was 3 μm, and the ratio of the groove depth to the groove width (groove depth / groove width) was 20/1. Moreover, the adhesion amount of the ethylene-vinyl alcohol copolymer from the composite spun fiber was 0.43% by mass (vs. the mass of the nonwoven fabric).

  The resulting spunbonded nonwoven fabric sample surface was analyzed by XPS analysis to measure the surface oxygen content. The results are shown in FIG. As a result of analyzing the fiber surface after removal of the sheath by XPS analysis, oxygen can be confirmed on the fiber surface, so that a hydrophilic polymer remains. Water drops were dropped on the obtained spunbond nonwoven fabric sample, and the spread of the water drops was observed. The result is shown in FIG. 5A. Further, the nonwoven fabric sample is immersed in hot water at 95 ° C. for 30 minutes (bath ratio: 1:20), taken out after immersion, cooled and dried (60 ° C., 10 minutes), and then again in 95 ° C. hot water. This treatment was repeated 15 times to measure the droplet absorption rate, and the results are shown in FIG.

Comparative Example 1
A spunbond non-woven fabric (weight per unit area: 80 g / m ² ) consisting of polypropylene fiber (single yarn filament: 3.3 dtex), an aqueous solution of ethylene-vinyl alcohol copolymer (ethylene copolymerization ratio: 8.7 mol%) (polymer concentration: The sample was immersed in 0.4% by mass to prepare a sample coated with 0.4% by mass (relative to the weight of filter fiber) of ethylene-vinyl alcohol copolymer.

From the results shown in FIG. 4, the presence of 25 mol% of surface oxygen is detected in the filter fiber according to the present invention (Example 1), and this surface oxygen can be treated even if the hot water treatment is repeated (25 Times) is shown to be maintained. This indicates that the ethylene-vinyl alcohol copolymer is adhered to the surface of the filter fiber. On the other hand, in the fiber of Comparative Example 1, as the hot water treatment is repeated, the amount of surface oxygen decreases, indicating that the ethylene-vinyl alcohol copolymer is likely to drop off.
From the results shown in FIG. 5A, in the filter fiber non-woven fabric of Example 1, it is observed that water is absorbed and spreads by dripping of water droplets, but in the sample of Comparative Example 1 of FIG. Since the abundance of the ethylene-vinyl alcohol copolymer was less than that in Example 1, such a phenomenon was not observed.
From the results shown in FIG. 6, in the filter fiber according to the present invention (Example 1), the absorption of water is immediately observed, whereas in the case of Comparative Example 1, as the number of times of the hydrothermal treatment increases, It has been shown that it takes time to absorb water droplets and as the number of hot water treatments increases, the detachment of the ethylene-vinyl alcohol copolymer from the fiber surface is progressing.

Example 2
The filterability of the filter fiber according to the present invention (after hot water treatment and before the formation of the non-woven fabric) is measured using an apparatus shown in FIG. 7 using micromer (latex particles) with different particle sizes [manufactured by Micromod] as evaluation dust. The test sample prepared by attaching the evaluation sample (4) to the sample holder (3) and adjusting the solid content concentration of the evaluation dust to 0.125 mg / L with a flow rate of 350 ml / min after passing 2 L of the test liquid The number of particles was evaluated by measuring the number of each particle diameter with a particle counter (manufactured by PARTICLE MEASURING SYSTEMS: MODEL LS-200). In FIG. 7, the hollow fiber filter (2) is for removing dust contained in the filter cleaning water in the filter cleaning. The dust collection efficiency was evaluated according to the following procedure.
(A) Pure water dust amount measurement: Particle number measurement [1] (for correction)
(B) Filtration path washing (c) Sample washing: particle number measurement [2] (for correction)
(D) Dust adjustment: particle number measurement [3]
(E) Filtration test: particle number measurement [4]
(F) Collection efficiency calculation Collection efficiency = 100 − ([4] − [2]) ÷ ([3] − [1]) × 100
After the step (c) and immediately before the end of the step (e), the measurement was performed with a pressure gauge installed in the apparatus shown in FIG.

  About the filter fiber (diameter: 17 micrometers, 2.2 dtex) which concerns on this invention was packed in 2 g column, dust collection performance was evaluated using evaluation dust from which a diameter differs. The results are shown in FIG.

Comparative Example 2
The dust collection performance was evaluated in the same manner as above for polypropylene fibers having a circular cross section (diameter: 3.3 μm, 0.08 dtex) as comparative fibers. The results are shown in FIG.

Comparative Example 3
Extrusion of polypropylene (PP) and ethylene-vinyl alcohol copolymer (manufactured by Kuraray Co., Ltd., ethylene copolymerization ratio: 8.7 mol%) (sometimes abbreviated as EXC) as different fibers for comparison. Core-sheath type composite spun fiber (core part: core / sheath type composite fiber) by feeding from the nozzle for composite fiber formation with 32 crimps at a ratio of PP / EXC = 60/40 (mass ratio) by supplying to the A core-sheath type composite spun fiber comprising polypropylene; sheath: ethylene-vinyl alcohol copolymer) was formed, and subjected to hot water treatment in the same manner as in Example 1 to obtain a filter fiber (fineness 3.2 dtex).
As a result of observing the cross section of the obtained filter fiber, the cross section of the fiber has a substantially elliptical central portion, and a protrusion protrudes from the central portion, and the tip of all the protrusions is rounded. In the oval shape, the width of the minor axis is 1.5 μm, the ratio of the major axis to the minor axis is 17.6, the number of projections is 32, the width of the projections is 1.3 μm, and the root of the projections The width of the portion was 1.3 μm, and the depth of the groove was 6 μm.
The dust collecting property was evaluated in the same manner as in Example 2.

Comparative Example 4
Dust collection property was evaluated in the same manner as described above for polypropylene fibers having a circular cross section (diameter: 17.5 μm, 2.2 dtex) as comparative fibers.

Comparative Example 5
As comparative fibers, polypropylene (PP) and polylactic acid (PLA) are supplied to different extruders and melted, and the composite of Example 1 is produced at a ratio of PP / PLA = 60/40 (mass ratio). The mixture is discharged from a fiber-forming nozzle to form a core-sheath composite fiber comprising core-sheath composite fiber (core: polypropylene; sheath: polylactic acid) in 10% sodium hydroxide at 80 ° C. The polylactic acid component was removed by dipping to obtain filter fibers (fineness: 2.2 dtex). When the obtained fiber was subjected to hot water treatment at 95 ° C. 15 times, the wettability was not maintained.
The obtained filter fiber cross section had the same shape as in Example 1, and the dust collecting property was evaluated in the same manner as in Example 2.
The results obtained in Example 2 and Comparative Examples 2 to 5 are shown in Table 1.

  As shown in Table 1, Example 2 has a pleated protrusion protruding from an elliptical columnar part having a predetermined shape, and also has water wettability derived from a hydrophilic polymer. In addition to exhibiting dust collection efficiency, it is possible to maintain the pressure at the time of passing a fluid at a low value. That is, in Example 2, not only the initial pressure has a low value of 15 Kpa, but also the post-evaluation pressure at the end of the filtration test can be maintained at a low pressure of 20 Kpa.

  On the other hand, in Comparative Example 2, the degree of ultrafineness of the filter fiber of Example 2 is about 1/30, which is advantageous in terms of collecting property. However, since the filter fiber of Comparative Example 2 has an extremely fine degree and does not have water wettability, the initial pressure in the filtration test is an extremely high pressure of 55 Kpa. At the end of the filtration test, the pressure is further increased, and the post-evaluation pressure shows an extremely high value of 85 Kpa.

  In Comparative Example 3, although it is derived from a hydrophilic polymer and has water wettability, the fiber does not have the predetermined shape defined in the present invention, and thus exhibits satisfactory characteristics in terms of collection. The initial pressure in the filtration test is 30 Kpa, which is twice as high as that in Example 2. At the end of the filtration test, the pressure is further increased, and the post-evaluation pressure shows 45 Kpa, a value twice as high as that of the example.

  In Comparative Example 4, the fineness is about the same as that of the filter fiber of Example 2, but the cross-sectional shape is a round cross-section, and because it does not have water wettability, the collection efficiency is extremely 0.1% or less The value is low.

  In Comparative Example 5, although the fibers have a predetermined shape defined in the present invention, the collection efficiency is inferior to that of Example 2 because it is derived from the hydrophilic polymer and does not have water wettability. Not only that, the initial pressure in the filtration test is 25 Kpa, which is higher than the end of the filtration test in Example 2. At the end of the filtration test, the pressure was further increased, and the post-evaluation pressure was 30 Kpa, 1.5 times higher than Example 2.

  Although the filter fiber of the present invention is formed from a hydrophobic polymer, the surface has many pleated projections, a high surface area, and the surface has water wettability, so that the water treatment is particularly effective. Since it is useful as a filter fiber, it has industrial applicability.

  Although the preferred embodiments of the present invention have been described above by way of example, those skilled in the art can make various modifications, additions and substitutions without departing from the scope and spirit of the present invention disclosed in the claims. It will be understandable. Accordingly, such changes and modifications are to be construed as being within the scope of the invention as defined by the claims.

1 3-way cock 2 0.04 μm hollow fiber filter 3 sample holder 4 evaluation sample

Claims (15)

A filter fiber comprising a plurality of pleated projections made of a hydrophobic polymer, the cross section of said fiber comprising (a) an elliptical part having a substantially elliptical shape, and (b) extending on both sides from said elliptical part A plurality of projections with rounded tips, and (c) a groove formed between the projections and the projections;
The fibers have a fineness of 6 dtex or less;
The ellipse part is composed of a long axis part and a short axis part, and the ratio of the width of the long axis part to the width of the short axis part is 1.5 to 6.0, and the width of the short axis part is 3 to 30 μm,
A hydrophilic polymer is attached to the surface of the fiber, and the fiber surface is subjected to hot water treatment at 95 ° C. (bath ratio 1:20 with respect to the amount of fiber, 95 ° C. for 30 minutes). The filter fiber in which the water wettability is maintained when the treatment of performing drying treatment at 60 ° C. for 10 minutes is performed 15 times after the treatment . The filter fiber according to claim 1, wherein the filter fiber has a surface area (BET) of 0.8 to 4.0 m ² / g .   3. The filter fiber according to claim 1, wherein a ratio of the depth of the groove portion to the width of the elliptical short axis portion (depth of the groove portion / width of the elliptical short axis portion) is 0.02 to 3 in the filter fiber. .   In the filter fiber, the protrusion has a width of 0.5 to 4 μm, and the depth of the groove is a ratio of the width of the protrusion (the depth of the groove / the width of the protrusion) to 1/1. The filter fiber according to any one of claims 1 to 3, which is ~ 4/1.   In the said filter fiber, ratio (width | variety of a projection part / width | variety of a groove part) of the width | variety of a projection part and the width | variety of the said groove part is 2/1-20/1, Any one of Claims 1-4. Filter fiber as described in.   The filter fiber according to claim 1 or 2, wherein the hydrophobic polymer is polyolefin, polyamide or polyester.   The filter fiber according to any one of claims 1 to 6, wherein the hydrophilic polymer is a heat-meltable water-soluble ethylene-vinyl alcohol copolymer.   The filter fiber according to claim 7, wherein the ethylene-vinyl alcohol copolymer is an ethylene-vinyl alcohol copolymer containing 0.1 to 20 mol% of ethylene monomer units.   The filter fiber according to any one of claims 1 to 8, wherein the attached amount of the hydrophilic polymer is 0.5% by mass or less (relative to the filter fiber).   2. The fiber is a fiber formed by removing the hydrophilic polymer from a fiber formed by core-sheath composite spinning using the hydrophobic polymer as a core layer and the hydrophilic polymer as a sheath layer. The filter fiber as described in any one of -9.   A filter comprising the filter fiber according to any one of the preceding claims.   The filter according to claim 11, wherein the filter fiber forms a dry or wet nonwoven fabric.   The filter according to claim 12, wherein the dry or wet non-woven fabric is filled in a cartridge.   14. A filter according to any one of the claims 11-13, for use in water treatment.   The processing method of the water which filters the water containing a to-be-removed object using the filter as described in any one of Claims 11-14.

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