Cylindrical filter

Abstract

The present invention aims to provide a cylindrical filter in which the occurrence of fuzzing (particularly the occurrence of fuzzing resulting from the breakage of the first fiber having the smallest average fiber diameter) is prevented. [Solution] In the cylindrical filter according to the present invention, the proportion of first fibers having the smallest average fiber diameter gradually increases from one main surface to the other in the nonwoven fabric wound around the cylindrical filter. The nonwoven fabric is wound with the other main surface facing the inner circumference of the cylindrical filter. Therefore, the other main surface is not subjected to large tension. In other words, in the cylindrical filter according to the present invention, the first fibers are less likely to break, thus preventing the occurrence of fuzzing.

Description

[Technical Field]

[0001] This invention relates to a cylindrical filter that prevents the occurrence of fuzzing. [Background technology]

[0002] Conventionally, cylindrical filters made of wound nonwoven fabric have been used as filters to capture and remove particles present in fluids such as water.

[0003] As such a cylindrical filter, for example, Japanese Patent Application Publication No. 2001-96110 (Patent Document 1) addresses the problem of providing a cylindrical filter that is less prone to a decrease in filtration efficiency, with an apparent density of 0.45 to 0.6 g / cm³. 3 A cylindrical filter made by winding a heat-pressurized nonwoven fabric is disclosed. Furthermore, Patent Document 1 discloses that the heat-pressurized nonwoven fabric can be a nonwoven fabric in which fibers with a fine fiber diameter, such as meltblown fibers, and thermoplastic drawn fibers with a larger average fiber diameter are mixed together.

[0004] Furthermore, Patent Document 1 discloses the finding that a dense or coarse structure may be formed in the thickness direction of a heat-pressed nonwoven fabric by changing the ratio of thermoplastic drawn fibers in the thickness direction. However, Patent Document 1 does not disclose or suggest whether the dense structure of the wound heat-pressed nonwoven fabric should be directed toward the inner or outer circumference of a cylindrical filter.

[0005] Furthermore, Patent Document 1 describes a heat-pressed nonwoven fabric with an apparent density of 0.45 g / cm³. 3 It has been disclosed that if the value is less than the stated value, the maximum pore size of the heat-pressed nonwoven fabric increases, resulting in a decrease in filtration accuracy. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2001-96110 [Overview of the project] [Problems that the invention aims to solve]

[0007] The applicant of this application has investigated the prior art cylindrical filters described in Patent Document 1 and other documents. Specifically, the applicant has investigated cylindrical filters in which a nonwoven fabric is wound around which a first fiber having the smallest average fiber diameter and a second fiber having a larger average fiber diameter than the first fiber are composed.

[0008] However, in conventional cylindrical filters, countless fluffs sometimes occurred on the outer circumference of the nonwoven fabric wound around the cylindrical filter, due to the breakage of its constituent fibers. These fluffs were mainly caused by the breakage of the first fiber, which has the smallest average fiber diameter.

[0009] Furthermore, the cylindrical filter exhibiting the aforementioned numerous fluffing issues means that the structure of the nonwoven fabric responsible for filtration is significantly damaged. Therefore, it was considered that this cylindrical filter would have poor performance in capturing small particles.

[0010] The present invention aims to provide a cylindrical filter that prevents the occurrence of fuzzing (particularly fuzzing caused by the breakage of the first fiber having the smallest average fiber diameter). Through solving this problem, a cylindrical filter with excellent particle collection performance for small particles is provided. [Means for solving the problem]

[0011] The present invention "(Claim 1) A cylindrical filter is constructed by winding a nonwoven fabric containing a first fiber having the smallest average fiber diameter among its constituent fibers and a second fiber having a larger average fiber diameter than the first fiber, In the aforementioned nonwoven fabric, the proportion of the first fiber gradually increases from one main surface to the other main surface. The other main surface of the non-woven fabric faces the inner peripheral side of the cylindrical filter. Cylindrical filter. (Claim 2) The apparent density of the non-woven fabric is less than 0.45 g / cm 3 The cylindrical filter according to claim 1. is.

Effect of the Invention

[0012] Although the reason why the cylindrical filter according to the present invention can solve the problem has not been fully clarified, it is considered that the following effects are exhibited.

[0013] On the outer peripheral side of the cylindrical filter in the non-woven fabric wound around the cylindrical filter, as it is wound, it is stretched and receives a greater tension than the inner peripheral side of the cylindrical filter. Therefore, on the main surface of the outer peripheral side of the wound non-woven fabric, the constituent fibers of the main surface are likely to break under this tension.

[0014] At this time, if the other main surface (the main surface with a large proportion of the first fibers having a small average fiber diameter) is directed to the outer peripheral side of the cylindrical filter and the non-woven fabric is wound, the first fibers constituting the other main surface are likely to break particularly because the average fiber diameter is small. In fact, numerous fuzzes due to the breakage of the first fibers were observed on the main surface of the outer peripheral side of the cylindrical filter in the non-woven fabric.

[0015] And when innumerable first fibers that bring a dense structure to the non-woven fabric break, holes are formed due to the breakage, so the cylindrical filter becomes inferior in the collection performance of particles with a small particle diameter.

[0016] On the other hand, in the cylindrical filter according to the present invention, the non-woven fabric is wound and configured with the other main surface facing the inner peripheral side of the cylindrical filter. Therefore, the other main surface does not receive a large tension. That is, in the cylindrical filter according to the present invention, the non-woven fabric is wound in a state where the first fibers are difficult to break.

[0017] Therefore, the cylindrical filter according to the present invention is a cylindrical filter in which the generation of fluff is prevented. And since the structure of the non-woven fabric responsible for filtration is prevented from being greatly damaged, it is rich in the collection performance of fine particles.

[0018] In addition, on one main surface side of the non-woven fabric constituting the cylindrical filter of the present invention, the proportion of the first fibers is small, so it has a rough structure, and on the other main surface side, the proportion of the first fibers is large, so it has a dense structure. And the non-woven fabric faces the other main surface side having a dense structure on the inner peripheral side of the cylindrical filter.

[0019] Therefore, by passing a fluid containing particles from the outer peripheral side to the inner peripheral side of the cylindrical filter,

[0020] first, particles with a large particle diameter can be collected on one main surface side having a rough structure in the non-woven fabric,

[0021] next, particles having a medium particle diameter that have not been collected can be collected inside the non-woven fabric, which becomes a dense structure in the thickness direction as the proportion of the first fibers gradually increases from one main surface to the other main surface,

[0022] finally, particles with a small particle diameter that have not been collected so far can be collected on the other main surface side having a dense structure in the non-woven fabric.

[0023] Therefore, it is a cylindrical filter rich in collection performance that can efficiently collect fine particles.

[0024] Also, due to the above-described effects being exhibited, the cylindrical filter according to the present invention has an apparent density of 0.45 g / cm 3This cylindrical filter prevents fuzzing even when it is made up of low-density nonwoven fabric, such as those with a density of less than 100%, wound around it. Furthermore, because the structure of the nonwoven fabric responsible for filtration is prevented from being significantly damaged, it has excellent particle collection performance for small particles. [Brief explanation of the drawing]

[0025] [Figure 1] This is a schematic diagram illustrating the method for manufacturing a nonwoven fabric according to the present invention. [Modes for carrying out the invention]

[0026] In this invention, various configurations can be appropriately selected, such as the following configuration. Unless otherwise specified, the various measurements described in this invention are performed under atmospheric pressure. Furthermore, the measurements are performed under a temperature of 20°C. Unless otherwise specified, the various measurement results described in this invention are obtained by measurement to a value one decimal place smaller than the desired value, and the desired value is calculated by rounding the obtained value to the nearest tenth. For example, if the desired value is to be expressed to the first decimal place, the value is obtained to the second decimal place by measurement, and the obtained second decimal place value is rounded to the nearest tenth place to calculate the value to the first decimal place, which is then used as the desired value. The upper and lower limits exemplified in this invention can be combined arbitrarily.

[0027] As the constituent fibers of the nonwoven fabric of the cylindrical filter, inorganic fibers composed of inorganic components such as glass fibers, silica fibers, and alumina fibers, or organic resin fibers can be used. Organic resin fibers include, for example, polyolefin resins (e.g., polyethylene, polypropylene, polyolefin resins with a structure in which some hydrocarbons are replaced with cyano groups or halogens such as fluorine or chlorine), polymethylpentene, styrene resins, polyvinyl alcohol resins, polyether resins (e.g., polyether ether ketone, polyacetal, modified polyphenylene ether, aromatic polyether ketone), polyester resins (e.g., polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polycarbonate, polyarylate, all aromatic polyester resins), polyimide resins, and poly These fibers are made using known organic resins such as amide-imide resins, polyamide resins (e.g., aromatic polyamide resins, aromatic polyetheramide resins, nylon resins, etc.), resins having nitrile groups (e.g., polyacrylonitrile), urethane resins, epoxy resins, polysulfone resins (e.g., polysulfone, polyethersulfone, etc.), fluororesins (e.g., polytetrafluoroethylene, polyvinylidene fluoride, etc.), cellulose resins, polybenzimidazole resins, and acrylic resins (e.g., polyacrylonitrile resins copolymerized with acrylic acid esters or methacrylic acid esters, modacryl resins copolymerized with acrylonitrile and vinyl chloride or vinylidene chloride, etc.).

[0028] To enable the creation of a cylindrical filter that is flexible, easy to wind, and less prone to fraying, it is preferable that the nonwoven fabric contains organic resin fibers as its constituent fibers, and more preferably that the nonwoven fabric consists solely of organic resin fibers.

[0029] Furthermore, the organic resin constituting the organic resin fiber may consist of either a linear polymer or a branched polymer, and may be a block copolymer or a random copolymer. Its three-dimensional structure and crystalline properties are also not particularly limited. Moreover, it may be a mixed resin containing multiple organic resins.

[0030] The constituent fibers of a nonwoven fabric may consist of one type of organic resin or inorganic component, or multiple types of organic resins or inorganic components. As a composite fiber composed of multiple types of organic resins or inorganic components, for example, the arrangement of resins in a cross-section perpendicular to the production direction of the nonwoven fabric (hereinafter sometimes referred to as the fiber cross-section or cross-section) may be a core-sheath type, sea-island type, side-by-side type, orange type, etc.

[0031] Furthermore, the constituent fibers of the nonwoven fabric may include fibers with irregular cross-sectional shapes other than those with a roughly circular or elliptical cross-section. These irregular cross-sectional fibers may have shapes such as hollow, triangular, or other polygonal shapes, Y-shapes or other alphabetical shapes, irregular shapes, multi-lobed shapes, asterisk shapes or other symbolic shapes, or shapes formed by combining multiple such shapes.

[0032] The constituent fibers of nonwoven fabrics can be obtained by known methods such as melt spinning, dry spinning, wet spinning, direct spinning (meltblown, spunbond, electrostatic spinning, etc.), methods for extracting fine fibers by removing one or more resin components from composite fibers, and methods for obtaining divided fibers by beating the fibers.

[0033] The nonwoven fabric according to the present invention includes a first fiber (hereinafter sometimes referred to as a fine fiber) having the smallest average fiber diameter as a constituent fiber, and a second fiber (hereinafter sometimes referred to as a thick fiber) having a larger average fiber diameter than the first fiber.

[0034] In this context, "fine fibers" refer to the fiber type with the smallest average fiber diameter among the constituent fibers of the nonwoven fabric, while "coarse fibers" refer to the fiber type with a larger average fiber diameter than the fine fibers. The average fiber diameter can be determined using the following method.

[0035] (How to determine the average fiber diameter) If the fiber composition used in the manufacturing process of the nonwoven fabric is known, the average fiber diameter of the fiber type is calculated from the fineness and specific gravity of the fibers used. On the other hand, if the fiber composition in the manufacturing process of the nonwoven fabric is not known, it can be determined by the following method. Prepare the nonwoven fabric that makes up the cylindrical filter. In this case, the nonwoven fabric can be prepared by removing components other than the nonwoven fabric from the cylindrical filter. Then, cut out and collect the sample from the nonwoven fabric. Next, scanning microscope images (magnification: 500x or 1000x) are taken of the exposed cross-section of the collected sample. Then, 50 fibers of the fiber species for which the average fiber diameter is to be determined are randomly selected from the scanning microscope images. Next, the fiber diameter of each of the 50 selected fibers is determined. Note that fiber diameter refers to the diameter of a circle with the same area as the fiber cross-section captured in a scanning microscope image. Finally, the arithmetic mean of the determined fiber diameters is calculated and used as the average fiber diameter for the fiber species for which the average fiber diameter is to be determined.

[0036] The average fiber diameter of the fine fibers can be adjusted as appropriate to realize a cylindrical filter with superior filtration efficiency, and is preferably 0.1 to 30 μm, more preferably 0.5 to 10 μm, more preferably 1 to 5 μm, and most preferably 1.5 to 3 μm. The average fiber diameter of the thick fibers is larger than the average fiber diameter of the fine fibers and can be adjusted as appropriate to realize a cylindrical filter with superior filtration efficiency, and is preferably 1 to 100 μm, more preferably 3 to 70 μm, and most preferably 5 to 50 μm.

[0037] The difference between the average fiber diameter of the fine fibers and the average fiber diameter of the coarse fibers is adjusted as appropriate to create a cylindrical filter with excellent collection performance. This difference is preferably 5 μm or more, more preferably 15 μm or more, and most preferably 25 μm or more. On the other hand, the upper limit can be adjusted as appropriate, but 50 μm is preferred.

[0038] Fine fibers and / or thick fibers may be short fibers cut to have a specific fiber length. The fiber length of the short fibers may be 5-120 mm, 10-100 mm, or 20-80 mm. Note that the "fiber length" of short fibers cut to have a specific fiber length refers to the fiber length measured according to JIS L1015 (2010), 8.4.1c Direct method (Method C). Alternatively, fine fibers and / or thick fibers may be continuous fibers that have not been cut to have a specific fiber length, such as fibers prepared using the direct spinning method (e.g., meltblown fibers or electrospun fibers).

[0039] In particular, it is preferable that the fine fibers constituting the nonwoven fabric are continuous fibers and the thick fibers are short fibers, as this makes it easier to prepare a nonwoven fabric in which thicker fibers penetrate between the fine fibers during the manufacturing process, and furthermore, makes it easier to prepare a nonwoven fabric having a coarser main surface and a denser main surface, thereby realizing a cylindrical filter with superior filtration efficiency.

[0040] Nonwoven fabrics can be prepared using a fiber web obtained by spinning and collecting fibers using methods such as a dry method in which fibers are subjected to a carding device or air array device to entangle the fibers, a wet method in which fibers are dispersed in a dispersion medium and spun into a sheet to entangle the fibers, or a direct spinning method (meltblown method, spunbond method, electrostatic spinning method, or a method of spinning by discharging a spinning stock and a gas flow in parallel (for example, the method disclosed in Japanese Patent Publication No. 2009-287138)).

[0041] In particular, since it is easy to prepare a nonwoven fabric in which the proportion of fine fibers gradually increases from one main surface to the other, it is preferable to produce a fiber web by blowing thick short fibers onto a flow of fine fibers, which are continuous fibers spun using a direct spinning method, from one direction, thereby forming a fiber group in which fine and thick fibers are mixed, and then collecting this group.

[0042] As a specific example of the manufacturing method, we will explain using Figure 1, a schematic diagram illustrating the manufacturing method of nonwoven fabric according to the present invention. As shown in Figure 1, when the angle (θ in Figure 1: unit: °) formed by the spinning direction of the continuous fine fibers (represented by arrow a in Figure 1) and the direction in which the short, thick fibers are sprayed relative to the spinning direction (a) (represented by arrow b in Figure 1) on the side opposite to the side where gravity acts is greater than 0° and less than or equal to 90°, it is easy to manufacture a nonwoven fabric in which the proportion of fine fibers gradually increases from one main surface to the other. Note that in Figure 1, the spinning direction (a) is from the side opposite to the side where gravity acts (upward side on the paper) to the side where gravity acts (downward side on the paper). Then, a fiber web can be manufactured by collecting a group of fibers consisting of a mixture of fine and thick fibers on the side where gravity acts (downward side on the paper).

[0043] The constituent fibers of the fiber web may be entangled and integrated by means of, for example, needles or a water stream. Alternatively, if the fiber web is impregnated with binder components by immersion in a dispersion of binder particles, the constituent fibers may be bonded and integrated by the binder components through heat treatment. Or, if the nonwoven fabric contains heat-fusible fibers, the constituent fibers may be bonded and integrated by melting the heat-fusible fibers and then solidifying them. The heat treatment method can be selected as appropriate, but for example, it can be heated or heated and pressurized using a roll, heated using a heating device such as an oven dryer, far-infrared heater, dry heat dryer, or hot air dryer, or heated by irradiating with infrared rays under no pressure.

[0044] The composition of the nonwoven fabric, such as its basis weight, thickness, and apparent density, can be adjusted as appropriate.

[0045] The basis weight can be 5 to 500 g / m 2 and can be 30 to 300 g / m 2 and can be 50 to 150 g / m 2 Here, the basis weight refers to the mass per 1 m 2 of the surface (main surface) having the largest area of the object to be measured.

[0046] The thickness can be 0.1 to 50 mm, can be 0.3 to 10 mm, and can be 0.5 to 3 mm. Here, the thickness refers to the length between both main surfaces in the vertical direction when a load of 2.0 kPa is applied in the vertical direction with respect to the main surface.

[0047] The apparent density is obtained by dividing the basis weight of the non-woven fabric by the thickness, and the obtained value (unit: g / cm 3 ). For the cylindrical filter with low liquid passing resistance, the apparent density of the non-woven fabric is preferably less than 0.45 g / cm 3 , more preferably 0.40 g / cm 3 or less, still more preferably 0.30 g / cm 3 or less, and most preferably 0.20 g / cm 3 or less. On the other hand, the lower limit value can be adjusted as appropriate, but for the cylindrical filter in which the generation of fluff is prevented, it is practical and preferable that it is 0.01 g / cm 3 .

[0048] The non-woven fabric according to the present invention has a structure in which the proportion of fine fibers gradually increases from one main surface to the other main surface. By having this structure, the non-woven fabric has a rough structure on one main surface side because the proportion of fine fibers is small, and has a dense structure on the other main surface side because the proportion of fine fibers is large.

[0049] Whether the non-woven fabric has the above-described structure can be confirmed by the following method. (Method for confirming the proportion of fine fibers) (Step 1) Take a scanning microscope image (magnification: 500x or 1000x) A of one main surface A of the nonwoven fabric. (Step 2) Take a scanning microscope image (magnification: 500x or 1000x) B of the other main surface B of the nonwoven fabric. (Step 3) At the point where the thickness of the nonwoven fabric is half in the thickness direction from one main surface A to the other main surface B, the nonwoven fabric is cut in a direction parallel to main surface A to obtain a nonwoven fabric thin (a nonwoven fabric thin including main surface A). Then, a scanning microscope image (magnification: 500x or 1000x) C is taken of the newly formed main surface C (the main surface facing main surface A in the nonwoven fabric thin including one main surface A) of the obtained nonwoven fabric thin. (Step 4) Determine the ratio A of the number of fine fibers to the total number of constituent fibers visible in scanning microscope image A (i.e., the proportion of fine fibers on one main surface of the nonwoven fabric), the ratio B of the number of fine fibers to the total number of constituent fibers visible in optical microscope image B (i.e., the proportion of fine fibers on the other main surface of the nonwoven fabric), and the ratio C of the number of fine fibers to the total number of constituent fibers visible in scanning microscope image C (i.e., the proportion of fine fibers inside the nonwoven fabric). If the result of comparing the values ​​of proportions A to C is proportion B > proportion C > proportion A, then it is determined that the proportion of fine fibers in the nonwoven fabric gradually increases from one main surface A to the other main surface B. On the other hand, if the comparison of the values ​​of proportions A to C does not satisfy the condition B > C > A, then it is determined that the proportion of fine fibers in the nonwoven fabric does not gradually increase from one main surface to the other.

[0050] To obtain a cylindrical filter with superior filtration efficiency, it is preferable that the proportion of fine fibers gradually increases from one main surface of the nonwoven fabric to the other, and that the proportion of the fiber type with the largest average fiber diameter among the thick fibers gradually increases from the other main surface of the nonwoven fabric to the one main surface. In the method for confirming the proportion of fine fibers described above, if fine fibers are replaced with thick fibers and the results of comparing the values ​​of proportions A to C are B < C < A, then it is determined that the proportion of thick fibers gradually increases from the other main surface B to the one main surface A of the nonwoven fabric.

[0051] On the other hand, if the comparison of the values ​​of proportions A to C does not satisfy the condition B < C < A, then it is determined that the proportion of thick fibers in the nonwoven fabric does not gradually increase from one main surface to the other.

[0052] The cylindrical filter according to the present invention is constructed by winding a nonwoven fabric. The cylindrical filter is (Aspect 1) A cylindrical filter comprising a roll-shaped nonwoven fabric prepared by winding a single strip of nonwoven fabric, or, (Aspect 2) A cylindrical filter prepared by continuously winding multiple identical strip-shaped nonwoven fabrics, It can be.

[0053] In this context, "strip-shaped" refers to a rectangle where the longer side is longer than the shorter side.

[0054] Of these, the cylindrical filter shown in (Aspect 1) is preferable in order to easily provide a cylindrical filter that prevents the occurrence of fuzzing.

[0055] The nonwoven fabric wound in the cylindrical filter is wound so that the other main surface (the main surface with a dense structure due to a higher proportion of fine fibers) faces the inner circumference of the cylindrical filter. As a result, the nonwoven fabric is wound in a way that makes it difficult for the fine fibers to break, and less likely to fray. Consequently, an apparent density of 0.45 g / cm³ can be achieved to realize a cylindrical filter with low liquid permeability resistance. 3 Even at low densities, such as below zero, the filter prevents a decrease in the collection performance of small particles due to the generation of fluff. Furthermore, by passing the object to be collected from the outer circumference to the inner circumference of the cylindrical filter, small particles can be collected efficiently.

[0056] The size of the cylinder in a cylindrical filter can be adjusted as appropriate depending on the required application. The length of the cylindrical filter (axial length in the cylindrical filter) can be 100 to 1000 mm, 150 to 800 mm, or 200 to 600 mm. Furthermore, assuming that the cylindrical filter is cut perpendicular to the axial length, the outer diameter of the portion where the nonwoven fabric is wound in the cross-section can be 30 to 100 mm, 50 to 80 mm, or 60 to 70 mm. In addition, the inner diameter in the same cross-section can be 10 to 60 mm, 20 to 50 mm, or 25 to 40 mm.

[0057] Next, an example of a method for manufacturing a cylindrical filter according to the present invention will be described. Note that the configurations already described will be omitted. The method for manufacturing a cylindrical filter according to the present invention can be appropriately selected, for example, (Step 1) A step of preparing a cylindrical support having pores (hereinafter sometimes referred to as a cylindrical support), (Step 2) A step to prepare a nonwoven fabric in which fine fibers and thick fibers are included in the constituent fibers, and the proportion of fine fibers gradually increases from one main surface to the other main surface. (Step 3) The process of taking strip-shaped nonwoven fabric from the prepared nonwoven fabric, (Step 4) With the main surface of the strip-shaped nonwoven fabric that has a higher proportion of fine fibers (the other main surface) facing the inner circumference, the strip-shaped nonwoven fabric is wound from one short side to the other short side, and the strip-shaped nonwoven fabric is wound onto the cylindrical support in a rolled shape. This can be a method for manufacturing a cylindrical filter that includes the following features:

[0058] (Step 1) will be explained.

[0059] The cylindrical support used has an opening connecting the inner and outer circumferences. The size and shape of the opening, as well as the number and distribution of the openings, are adjusted as appropriate to realize a cylindrical filter that allows the desired target material to pass through.

[0060] The length of the cylindrical support (the axial length in the cylindrical support) is adjusted as appropriate to realize a cylindrical filter with the desired length. Preferably, the length of the cylindrical support is less than or equal to the length in the short side direction of the strip-shaped nonwoven fabric, in order to realize a cylindrical filter with excellent filtration efficiency due to low leakage.

[0061] The outer diameter of the cylindrical support used should be adjusted as appropriate to realize a cylindrical filter with the desired outer and inner diameters. Furthermore, the inner circumference of the cylindrical support is the part through which the fluid passes after the target material has been removed when using the cylindrical filter equipped with the cylindrical support. Therefore, the inner diameter of the cylindrical support should be adjusted as appropriate to realize a cylindrical filter with excellent filtration efficiency.

[0062] (Step 3) will be explained.

[0063] The size of the strip-shaped nonwoven fabric is adjusted as appropriate to realize a cylindrical filter that allows the desired material to pass through. Preferably, its length in the short-side direction is greater than or equal to the length of the cylindrical support around which it is wrapped. Furthermore, preferably, its length in the long-side direction is long enough to cover the outer circumference of the cylindrical support around which it is wrapped.

[0064] (Step 4) will be explained.

[0065] In a strip of nonwoven fabric wound around a cylindrical support in a roll-like manner, the short side on the outer circumference can be fixed by adhesion or welding to the main surface of the strip of nonwoven fabric wound around the cylindrical support.

[0066] The cylindrical filter prepared as described above may be used as is, but end plates may be provided at both ends of the cylindrical filter, another porous cylindrical structure (such as a cylindrical mesh) may be provided to cover the outer surface of the cylindrical filter, or a pre-filter may be provided on the outer surface of the cylindrical filter. The method of fixing the end plates or cylindrical structure to the cylindrical filter can be appropriately selected from common bonding methods such as bonding with a binder, double-sided tape, or by fusing the constituent fibers or using a hot melt web.

[0067] By passing a fluid containing the target material from the outer circumference to the inner circumference of a cylindrical filter, the target material contained in the fluid can be collected. In this case, if the cylindrical filter is equipped with a cylindrical support, the fluid supplied from the outer circumference of the cylindrical filter is supplied to the end of the cylindrical support through the space inside the cylindrical support via the nonwoven fabric around which it is wound. [Examples]

[0068] The present invention will be specifically described below with reference to examples, but these examples are not intended to limit the scope of the present invention.

[0069] (Preparation of a cylindrical support with porosity) A porous cylindrical support was prepared with an outer diameter of 35.0 mm, an inner diameter of 25.4 mm, and a length of 244.0 mm. The cylindrical support had multiple openings connecting the inner and outer circumferences along its entire outer surface.

[0070] (Preparation of stretched core-sheath type heat-fusible fibers A and B) The following stretched core-sheath type heat-fusible fibers A and B were prepared, each consisting of a short fiber with a polypropylene resin core (melting point 160°C) and a polyethylene resin sheath (melting point 135°C). Stretched core-sheath heat-fusible fiber A: Average fiber diameter: 30.0 μm, fiber length: 64 mm Stretched core-sheath heat-fusible fiber B: Average fiber diameter: 17.3 μm, fiber length: 37 mm

[0071] (Manufacturing methods for nonwoven fabric A, nonwoven fabric B, and nonwoven fabric B') A melt-blown nozzle piece, arranged with orifice diameters of 0.2 mm and a pitch of 0.8 mm, was heated to 320°C, and polypropylene was extruded at a rate of 0.09 g / min per orifice. Air at 340°C was then applied to the extruded polypropylene to reduce its diameter and spin it into fibers, forming a flow of polypropylene fibers (average fiber diameter: 1.5 μm, continuous fibers). Next, the polypropylene fibers and core-sheath heat-fusible fibers A were mixed by supplying them from a fiber opening machine equipped with an air nozzle and housing two fiber opening cylinders in the direction of the polypropylene fiber flow. At this time, the direction in which the core-sheath heat-fusible fibers A were sprayed (represented by arrow b in Figure 1) was 70° (θ in Figure 1: unit:°) opposite to the side where gravity acts, with respect to the flow direction of the polypropylene fibers (represented by arrow a in Figure 1), and the core-sheath heat-fusible fibers A were supplied from one direction. Then, a group of fibers was formed by mixing the two fibers, and collected on a mesh-like conveyor to form a fiber web. At this time, air was sucked out from the opposite side of the conveyor's collection surface to prevent disturbance of the fiber web. Next, the fiber web formed on the mesh conveyor was subjected to a dryer device with a temperature of 140°C, thereby fusing only the polyethylene resin, which is the sheath component of the core-sheath heat-fusible fiber A. After that, it was allowed to cool and peeled off the mesh conveyor to produce nonwoven fabric A. Furthermore, the types of fibers that make up the nonwoven fabric and the basis weight (unit: g / m²) of each fiber to be mixed are specified. 2Nonwoven fabric B used in Example 2 and nonwoven fabric B' used in Example 3 were manufactured in the same manner as the manufacturing method for nonwoven fabric A, except that the components were changed as described in the "Composition of the Strip-Shaped Nonwoven Fabric" column of Table 2.

[0072] Nonwoven fabrics A, B, and B' prepared in this manner all contained polypropylene fibers (continuous fine fibers) and core-sheath heat-fusible fibers (short, thick fibers) as constituent fibers. Furthermore, the proportion of fine fibers gradually increased from one main surface (the main surface on which the core-sheath heat-fusible fibers were supplied) to the other main surface (the main surface on the opposite side of where the core-sheath heat-fusible fibers were supplied). Also, the proportion of the fiber species with the thickest average fiber diameter gradually increased from the other main surface (the main surface on the opposite side of where the core-sheath heat-fusible fibers were supplied) to the one main surface (the main surface on which the core-sheath heat-fusible fibers were supplied).

[0073] Furthermore, one main surface of the nonwoven fabric (the side on which the core-sheath type heat-fusible fibers were supplied) contained only thick fibers. On the other main surface of the nonwoven fabric (the side opposite to the side on which the core-sheath type heat-fusible fibers were supplied), fine and thick fibers were mixed together.

[0074] (Example 1) One strip of nonwoven fabric (long side: 3200 mm, short side: 262.5 mm) was taken from nonwoven fabric A. Then, with the other main surface of the strip-shaped nonwoven fabric, which has a higher proportion of polypropylene fibers (fine fibers), facing the inner circumference, the strip-shaped nonwoven fabric was wound around the cylindrical support in a rolled-up manner, starting from one short side to the other. At this time, the opening of the cylindrical support was covered by the strip-shaped nonwoven fabric. Furthermore, by cutting off the portions of the strip-shaped nonwoven fabric that protrude from both ends in the longitudinal direction of the cylindrical support, the length of the shorter side of the strip-shaped nonwoven fabric wrapped around the cylindrical support was made the same as the length of the cylindrical support. In addition, end plates were provided at both ends in the short-side direction of the cylindrical support and the strip-shaped nonwoven fabric wrapped around the cylindrical support, each having an opening in the center that is the same size as the inner diameter of the cylindrical support. As described above, a cylindrical filter (with an outer diameter of 62 mm in the portion where the nonwoven fabric is wound) was prepared by winding a strip of nonwoven fabric. Furthermore, only slight fuzzing, originating from the breakage of thick fibers, was observed on the main surface of the cylindrical filter on the outer periphery of the strip-shaped nonwoven fabric.

[0075] (Comparative Example 1) A cylindrical filter (outer diameter of the part around which the nonwoven fabric is wound: 62 mm) was prepared in the same manner as in Example 1, except that the other main surface of the nonwoven fabric, which has a higher proportion of polypropylene fibers (fine fibers), was oriented toward the outer periphery, and the nonwoven fabric was wound from one short side to the other short side so that it was wound around a cylindrical support in a rolled shape. Furthermore, more fluffing was observed on the outer surface of the cylindrical filter in the strip-shaped nonwoven fabric compared to Example 1. The fluffing was almost entirely due to the breakage of fine fibers.

[0076] A comparison of the cylindrical filter prepared in Example 1 and the cylindrical filter prepared in Comparative Example 1 revealed that the cylindrical filter prepared in Example 1 showed less breakage of the fibers constituting the outer main surface (one of the main surfaces) of the strip-shaped nonwoven fabric.

[0077] Furthermore, Table 1 summarizes the various physical properties of the cylindrical filter prepared in Example 1 and the various components of the strip-shaped nonwoven fabric contained within the cylindrical filter. The following evaluation methods were used to evaluate the physical properties.

[0078] (Method for evaluating filtration lifespan) Seven types of test powders (Kanto loam) specified in JIS Z8901:2006 "Test powders and test particles" were prepared. Next, these seven types of test powders (Kanto loam) were mixed with deionized water to a mass concentration of 40 ppm to prepare a test solution. The water temperature was set to 25°C. Then, the test liquid was passed through the space on the inner circumference of the cylindrical support from the outer circumference side where the strip-shaped nonwoven fabric of the cylindrical filter was exposed, at a rate of 20 liters / minute. The total volume (in liters) of the test liquid that passed through the cylindrical filter was confirmed by the time the liquid flow resistance reached 400 kPa. Furthermore, the greater the total volume of the test solution that passes through the cylindrical filter, the longer its filtration life will be.

[0079] (Method for evaluating particle collection performance) In the above-described (method for evaluating filtration life), a sample of the filtered test solution was taken after passing 50 liters of the test solution through the cylindrical filter. The particle size (in μm) and number (in particles) of particles contained in the test solution, as well as in the filtered test solution, were measured using a particle counter. The collection efficiency (in %) of particles collected by the cylindrical filter for each particle size was then calculated by substituting the obtained measurement results into the following formula. In the formula, x represents the particle size being calculated. Collection efficiency (%) = 100 × (Number of particles with particle size x μm in the test solution - Number of particles with particle size x μm in the test solution after filtration) / Number of particles with particle size x μm in the test solution Next, the collection efficiency for each particle size was checked, starting with the largest particles and progressing to the smallest particles, until the particle size at which the collection efficiency first reached 100% was identified. This identified particle size was then considered the lower limit of the particle size that the cylindrical filter could collect. Furthermore, the smaller the lower limit of the particle size that can be captured, the better the cylindrical filter is at capturing small particles.

[0080] (Method for evaluating fluid flow resistance) Ion-exchanged water at a temperature of 25 degrees Celsius was passed through the space on the inner circumference of the cylindrical support from the outer circumference of the cylindrical filter where the strip-shaped nonwoven fabric is exposed, at a rate of 40 liters / minute. A differential pressure gauge was installed to measure the water pressure on the outer circumference of the cylindrical filter and the inner circumference of the cylindrical support during the flow of water. At the point when the water pressures measured by the differential pressure gauge stopped fluctuating, the difference between the water pressure on the outer circumference of the cylindrical filter and the water pressure on the inner circumference of the cylindrical filter was recorded as the water flow resistance (unit: kPa). The smaller this value, the lower the liquid flow resistance of the cylindrical filter.

[0081] [Table 1]

[0082] The cylindrical filter prepared in Example 1 has an apparent density of 0.45 g / cm³. 3 Less than (apparent density of 0.10 g / cm³) 3 Despite this, we were able to prevent particles with a diameter of 11 μm and larger particles from being present in the filtered fluid.

[0083] From the above, the cylindrical filter prepared in Example 1 is a cylindrical filter that prevents the generation of lint. Furthermore, it has excellent collection performance for small particles.

[0084] (Example 2) One strip of nonwoven fabric (long side: 3200 mm, short side: 262.5 mm) was taken from nonwoven fabric B. A cylindrical filter (with an outer diameter of the portion around which the nonwoven fabric is wound: 62 mm) was prepared in the same manner as in Example 1, except that the strip-shaped nonwoven fabric obtained in this way was used. Furthermore, on the outer surface of the cylindrical filter in the strip-shaped nonwoven fabric, only slight fuzzing, similar to that observed in Example 1, was observed, which originated from the breakage of thick fibers.

[0085] (Example 3) A strip of nonwoven fabric (long side: 3200 mm, short side: 262.5 mm) was taken from nonwoven fabric B'. A cylindrical filter (with an outer diameter of the portion around which the nonwoven fabric is wound: 62 mm) was prepared in the same manner as in Example 1, except that the strip-shaped nonwoven fabric obtained in this way was used. Furthermore, on the outer surface of the cylindrical filter in the strip-shaped nonwoven fabric, only slight fuzzing, similar to that observed in Example 1, was observed, which originated from the breakage of thick fibers.

[0086] Table 2 summarizes the physical properties of the cylindrical filters prepared in Examples 2 and 3, and the various components of the strip-shaped nonwoven fabric contained in each cylindrical filter.

[0087] Furthermore, compared to Example 1, the strip-shaped nonwoven fabrics prepared in Examples 2 and 3 were thought to have a smaller pore size distribution due to the use of core-sheath type heat-sealable fibers with a smaller average fiber diameter. Therefore, in order to more clearly determine the filtration performance of the prepared cylindrical filters, instead of the seven test powders (Kanto loam) used in Example 1, a test solution prepared using eight test powders (Kanto loam) specified in JIS Z8901:2006 "Test powders and test particles" with a higher proportion of smaller particle sizes was used.

[0088] [Table 2]

[0089] The cylindrical filter prepared in Example 2 had an apparent density of 0.45 g / cm³. 3 Less than (apparent density of 0.10 g / cm³) 3 Despite this, we were able to prevent particles with a diameter of 9 μm and larger particles from being mixed into the filtered fluid.

[0090] Furthermore, the cylindrical filter prepared in Example 3 had an apparent density of 0.45 g / cm³. 3Less than (apparent density of 0.10 g / cm³) 3 Despite this, we were able to prevent particles with a diameter of 5.5 μm and larger particles from being mixed into the filtered fluid.

[0091] From the above, the cylindrical filters prepared in Examples 2 and 3 are cylindrical filters that prevent the generation of lint. Furthermore, they have excellent collection performance for small particles. [Industrial applicability]

[0092] The present invention can be used, for example, as a cylindrical filter for filtering a material to be collected, such as a slurry. [Explanation of Symbols]

[0093] a... Spinning direction of fine fibers, which are continuous fibers b...A direction in which thicker fibers, which are short fibers, are sprayed relative to the spinning direction (a). θ···the angle that b makes with respect to a, on the opposite side from the side where gravity acts.

Claims

1. A cylindrical filter is constructed by winding a nonwoven fabric containing a first fiber having the smallest average fiber diameter and a second fiber having a larger average fiber diameter than the first fiber, In the aforementioned nonwoven fabric, the proportion of the first fiber gradually increases from one main surface to the other main surface. The other main surface of the nonwoven fabric is facing the inner circumference of the cylindrical filter. Cylindrical filter.

2. The apparent density of the aforementioned nonwoven fabric is 0.45 g / cm³. ３ A cylindrical filter according to claim 1, wherein the value is less than [value missing].

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