Cylindrical filter and method for manufacturing the same

Abstract

The present invention provides a cylindrical filter and a method for manufacturing the same, which have basic filtration performance while improving filtration life or filtration accuracy. [Solution] The present invention relates to a cylindrical filter 1 including a filtration layer 4 formed of a tubular fiber assembly, wherein the filtration layer 4 includes a tubular fiber assembly A (4a) formed by winding a first fiber sheet and a second fiber sheet into a cylindrical shape, and a tubular fiber assembly B (4b) formed by winding a third fiber sheet and a fourth fiber sheet into a cylindrical shape, wherein in the thickness direction of the filtration layer 4, the first fiber sheet and the second fiber sheet are arranged alternately, the third fiber sheet and the fourth fiber sheet are arranged alternately, the first fiber sheet is bonded via the second fiber sheet, the third fiber sheet is bonded via the fourth fiber sheet, the tubular fiber assembly A (4a) is positioned on the outflow side of the material to be filtered, and the tubular fiber assembly B (4b) is positioned on the inflow side of the material to be filtered.

Description

[Technical Field]

[0001] The present invention relates to a cylindrical filter suitable for filtering fluids, particularly liquids containing foreign matter, and a method for manufacturing the same. [Background technology]

[0002] Cylindrical filters, which are made by winding a fiber aggregate into a cylindrical shape, are widely used for filtering various liquids such as beverages, pharmaceuticals, oils and fats, paints, and industrial cleaning water such as cleaning water for electronic components and semiconductor products, due to their excellent handling properties. Cylindrical filters typically have a cylindrical fiber aggregate as the filtration layer, which is manufactured by winding various fiber sheets, such as nonwoven fabrics, around a core (also called a mandrel). For example, Patent Document 1 describes a cylindrical filter that includes a filtration layer in which a fine-denier nonwoven fabric and a thick-denier spunlace nonwoven fabric, which consists of constituent fibers with a finer denier than the constituent fibers of the fine-denier nonwoven fabric, and in which the constituent fibers are intertwined and at least a portion of them are heat-bonded, are laminated and wound into a cylindrical shape without being substantially heat-bonded to each other. Furthermore, Patent Document 2 describes a cylindrical filter including a filtration layer wound around a core material, wherein the filtration layer is composed of at least three types of nonwoven fabric layers, nonwoven fabric layer A, nonwoven fabric layer B, and nonwoven fabric layer C, which are wound in a continuous manner from the inlet side of the material to be filtered, and nonwoven fabric layers A, B, and C are meltblown nonwoven fabrics, the average pore size of nonwoven fabric layer A is 15 μm or more and less than 23 μm, the average pore size of nonwoven fabric layer B is 0.62 times or more and less than 0.9 times the average pore size of nonwoven fabric layer A, and the average pore size of nonwoven fabric layer C is 0.2 times or more and less than 0.62 times the average pore size of nonwoven fabric layer A.

[0003] Another method for manufacturing tubular filters is known, which involves fiberizing a resin and directly winding the fibers onto a core, thereby eliminating the step of forming the fibers into a sheet. For example, Patent Document 3 describes a continuous method for manufacturing a generally tubular nonwoven depth filter element having an inconsistent length, comprising the steps of: providing a collection means comprising a mandrel; and simultaneously manufacturing molten first and second filament feeders, each having first and second diameters and being substantially continuous but separate, by preparing first and second filament feeders and independently controlling these first and second filament feeders, wherein the first and second filament feeders are spaced apart from each other along the rotating mandrel, and the method further comprises the steps of transporting the first and second filaments toward the rotating mandrel as flows along first and second predetermined paths, respectively; and collecting the first and second filaments around the rotating mandrel. Furthermore, Patent Document 4 describes a cylindrical filter body comprising a mass of support fibers and filter fibers, which are nonwoven meltblown fibers, wherein the filter body has at least one cylindrical layer, the support fibers define randomly formed gaps in the cylindrical layer, the filter fibers are arranged in the gaps, thereby the support fibers and filter fibers are integrally placed side by side in the cylindrical layer, the average diameter of the support fibers is 60 μm to 500 μm, and the average diameter of the filter fibers is 1 μm to 50 μm. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2004-000851 [Patent Document 2] Japanese Patent Publication No. 2013-236985 [Patent Document 3] Special Publication No. 8-501976 [Patent Document 4] Special Publication No. 11-504853 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, in the case of cylindrical filters described in Patent Documents 1 to 4, the filtration performance, such as filtration life and filtration accuracy, was sometimes inferior.

[0006] To solve the above-mentioned conventional problems, the present invention provides a cylindrical filter and a method for manufacturing the same that have improved filtration life or filtration accuracy while maintaining basic filtration performance. [Means for solving the problem]

[0007] The present invention relates to a cylindrical filter comprising a filtration layer formed of tubular fiber aggregates, wherein the filtration layer comprises a tubular fiber aggregate A formed by winding a first fiber sheet and a second fiber sheet into a cylindrical shape, and a tubular fiber aggregate B formed by winding a third fiber sheet and a fourth fiber sheet into a cylindrical shape, wherein in the thickness direction of the filtration layer, the first fiber sheet and the second fiber sheet are arranged alternately, the third fiber sheet and the fourth fiber sheet are arranged alternately, the first fiber sheet is bonded via the second fiber sheet, the third fiber sheet is bonded via the fourth fiber sheet, the tubular fiber aggregate A is positioned on the outflow side of the material to be filtered, and the tubular fiber aggregate B is positioned on the inflow side of the material to be filtered.

[0008] The present invention relates to a method for manufacturing a cylindrical filter including a filtration layer formed of a cylindrical fiber assembly, wherein molten thermoplastic resin is discharged from the discharge hole of a spinning nozzle, and at the same time, meltblown fibers A stretched by a high-temperature gas flow ejected from around the discharge hole are blown onto the surface of a rotating shaft that rotates at a constant speed, while a first fiber sheet is wound around the surface of the rotating shaft, and the meltblown fibers A are accumulated on the surface of the first fiber sheet to form a meltblown web A which is then wound, thereby forming a cylindrical fiber assembly in which the first fiber sheet and the meltblown web A are wound alternately. The present invention relates to a method for manufacturing a cylindrical filter, which includes the steps of obtaining A, and simultaneously discharging molten thermoplastic resin from the discharge hole of a spinning nozzle and blowing meltblown fibers B, which have been stretched by a high-temperature gas flow ejected from around the discharge hole, onto the surface of a rotating shaft that rotates at a constant speed, while winding a third fiber sheet around the surface of the cylindrical fiber assembly A, and accumulating the meltblown fibers B on the surface of the third fiber sheet to form a meltblown web B and winding it around, thereby obtaining a cylindrical fiber assembly B in which the third fiber sheet and the meltblown web B are wound alternately. [Effects of the Invention]

[0009] The present invention can provide a cylindrical filter that has basic filtration performance while improving filtration life or filtration accuracy. Furthermore, the manufacturing method of the present invention makes it possible to increase the productivity of cylindrical filters that have improved filtration life or filtration accuracy while maintaining basic filtration performance, and to reduce production costs. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic partially broken cross-sectional perspective view of one example of a cylindrical filter according to the present invention. [Figure 2] This is a schematic partially broken cross-sectional perspective view of one example of a cylindrical filter according to the present invention. [Figure 3] This is a schematic partially broken cross-sectional perspective view of one example of a cylindrical filter according to the present invention. [Figure 4]This is a schematic partially broken cross-sectional perspective view of one example of a cylindrical filter according to the present invention. [Figure 5] This is a schematic partial longitudinal cross-sectional view of a tubular fiber aggregate A, an example of the present invention. [Figure 6] This is a schematic partial longitudinal cross-sectional view of a tubular fiber aggregate B, an example of the present invention. [Figure 7] This is a schematic partial longitudinal cross-sectional view of a tubular fiber aggregate C, an example of the present invention. [Figure 8] This is a schematic partially exploded cross-sectional perspective view of one example of a cylindrical filter according to the present invention. [Figure 9] This is a schematic partially exploded cross-sectional perspective view of one example of a cylindrical filter according to the present invention. [Figure 10] This is a schematic partially exploded cross-sectional perspective view of one example of a cylindrical filter according to the present invention. [Figure 11] This is a schematic diagram illustrating one example of a cylindrical filter manufacturing method used in the present invention. [Figure 12] This is a schematic diagram illustrating the manufacturing process of one example of the present invention's cylindrical filter. [Figure 13] This is a schematic diagram illustrating the manufacturing process of one example of the present invention's cylindrical filter. [Modes for carrying out the invention]

[0011] The inventors of the present invention have diligently studied to solve the above-mentioned problems. As a result, they have found that by constructing the filtration layer with tubular fiber assemblies A and B arranged sequentially from the outflow side to the inflow side of the material to be filtered, forming tubular fiber assemblies A by winding alternately arranged first and second fiber sheets into a tubular shape in the thickness direction of the filtration layer, and forming tubular fiber assemblies B by winding alternately arranged third and fourth fiber sheets into a tubular shape in the thickness direction of the filtration layer, the tubular filter can have basic filtration performance while improving filtration life or filtration accuracy (also referred to as filtration efficiency). In this specification, unless otherwise specified, "outflow side" means the outflow side of the material to be filtered, and "inflow side" means the inflow side of the material to be filtered.

[0012] The inventors of the present invention have diligently studied the manufacture of a cylindrical filter that satisfies the above configuration. As a result, for example, by winding a first fiber sheet around a rotating shaft that rotates at a constant speed, and extruding meltblown fibers A spun from a nozzle toward the surface of the first fiber sheet, and immediately after accumulating them on the surface of the first fiber sheet, the first fiber sheet is again superimposed on the meltblown web (which becomes the second fiber sheet) made of the accumulated meltblown fibers, and the meltblown web and the first fiber sheet are wound together, thereby creating a cylindrical fiber assembly A in which the first fiber sheet and the meltblown web (i.e., the second fiber sheet) made of the meltblown fibers accumulated on the first fiber sheet are laminated and integrated and continuously wound, and a cylindrical fiber assembly A is produced. Similarly, a third fiber is wound around a rotating shaft that rotates at a constant speed. By continuously winding the sheet while extruding the meltblown fibers B spun from the nozzle toward the surface of the third fiber sheet and accumulating them on the surface of the third fiber sheet, and then overlapping the third fiber sheet again onto the meltblown web (which becomes the fourth fiber sheet) made of the accumulated meltblown fibers, the meltblown web and the third fiber sheet are wound together, thereby creating a tubular fiber assembly B in a laminated and integrated state. This allows for the production of a tubular fiber assembly B with high productivity and low production costs, while maintaining the above-described structure.

[0013] (Cylindrical filter) The tubular filter includes a filtration layer formed of tubular fiber aggregates. In this specification, a tubular fiber aggregate means a fiber aggregate in which fibers are assembled in a tubular shape, and the fiber sheet may be a fiber web or a nonwoven fabric.

[0014] The filtration layer includes a tubular fiber assembly A formed by alternately winding a first fiber sheet and a second fiber sheet, and a tubular fiber assembly B positioned on the inlet side of tubular fiber assembly A, formed by alternately winding a third fiber sheet and a fourth fiber sheet. In the thickness direction of the filtration layer, the first fiber sheet and the second fiber sheet are arranged alternately, and the first fiber sheet is bonded to the second fiber sheet. In the thickness direction of the filtration layer, the third fiber sheet and the fourth fiber sheet are arranged alternately, and the third fiber sheet is bonded to the fourth fiber sheet. As a result, the first and third fiber sheets do not collapse due to the pressure when liquid passes through, the interlayers are stable, and the second and fourth fiber sheets diffuse the fluid from the inlet side to the outlet side, thereby exhibiting basic filtration performance. For example, when measured by the method described in the examples, the filtration accuracy for particles with a particle size of 3.0 μm is 65% or more, and the filtration life is 100 L or more. Furthermore, filters with improved filtration lifespan of 300 L or more, improved filtration accuracy of 95% or more for particles with a particle size of 1.0 μm, and improved filtration accuracy of 60% or more for particles with a particle size of 0.5 μm can be obtained. In this specification, the filtration lifespan and filtration accuracy of the cylindrical filter can be measured as described in the examples.

[0015] The ratio H1 / H2 of the thickness of the first fiber sheet to the thickness of the second fiber sheet is not particularly limited, but from the viewpoint of improving various filtration performances such as filtration accuracy and filtration life of the cylindrical filter, it is preferable that the thickness H1 of the first fiber sheet is greater than the thickness H2 of the second fiber sheet, more preferably that H1 / H2 is 1.1 or more and 15.0 or less, even more preferably 1.3 or more and 12 or less, even more preferably 1.5 or more and 10 or less, even more preferably 1.8 or more and 9 or less, even more preferably 2.0 or more and 8 or less, and particularly preferably 2.5 or more and 7 or less. In this specification, the thickness of the fiber sheet can be measured as described in the examples.

[0016] The thickness H1 of the first fiber sheet is preferably 0.10 mm or more and 0.80 mm or less, more preferably 0.15 mm or more and 0.70 mm or less, and even more preferably 0.18 mm or more and 0.60 mm or less, from the viewpoint of improving various filtration performances such as the filtration accuracy and filtration life of the cylindrical filter.

[0017] The thickness H2 of the second fiber sheet is preferably 0.04 mm to 0.18 mm, more preferably 0.045 mm to 0.16 mm, even more preferably 0.05 mm to 0.14 mm, and particularly preferably 0.055 mm to 0.125 mm, from the viewpoint of improving various filtration performances such as the filtration accuracy and filtration life of the cylindrical filter.

[0018] The ratio D1 / D2 of the density D1 of the first fiber sheet to the density D2 of the second fiber sheet is not particularly limited, but from the viewpoint of improving various filtration performance such as the filtration accuracy and filtration life of the cylindrical filter, it is more preferably 0.4 to 10.0, even more preferably 0.5 to 8.0, even more preferably 0.6 to 6.0, even more preferably 0.7 to 5.0, even more preferably 0.8 to 4.5, especially preferably 0.85 to 4.0, and especially especially preferably 0.90 to 3.0. In this specification, the density of the fiber sheet can be measured as described in the examples.

[0019] The density D1 of the first fiber sheet is set to 0.03 g / cm³ from the perspective of improving various filtration performance aspects such as the filtration accuracy and filtration life of the cylindrical filter. 3 More than 0.50g / cm 3 Preferably, it is 0.04 g / cm³. 3 More than 0.40g / cm 3 It is more preferable that the following is the case: 0.05 g / cm³ 3 More than 0.35g / cm 3 It is even more preferable that the following is the case: 0.06 g / cm³ 3 More than 0.30g / cm 3It is particularly preferable that the following conditions are satisfied.

[0020] From the viewpoint of enhancing various filtration performances such as the filtration accuracy and filtration life of the cylindrical filter, the density D2 of the second fiber sheet is preferably 0.01 g / cm 3 or more and 0.20 g / cm 3 or less, more preferably 0.015 g / cm 3 or more and 0.15 g / cm 3 or less, even more preferably 0.02 g / cm 3 or more and 0.10 g / cm 3 or less, still more preferably 0.025 g / cm 3 or more and 0.08 g / cm 3 or less, and particularly preferably 0.025 g / cm

[0021] From the viewpoint of enhancing various filtration performances such as the filtration accuracy and filtration life of the cylindrical filter, the basis weight W1 of the first fiber sheet is preferably 15 g / m 2 or more and 100 g / m 2 or less, more preferably 18 g / m 2 or more and 80 g / m 2 or less, even more preferably 20 g / m 2 or more and 60 g / m 2 or less, still more preferably 23 g / m 2 or more and 50 g / m 2 or less. In this specification, the basis weight of the fiber sheet can be measured as described in the examples.

[0022] From the viewpoint of enhancing various filtration performances such as the filtration accuracy and filtration life of the cylindrical filter, the basis weight W2 of the second fiber sheet is preferably 2 g / m 2 or more and 16 g / m 2 or less, more preferably 3 g / m 2 or more and 14 g / m 2 or less, even more preferably 3.5 g / m 2 or more and 12 g / m 2 or less, still more preferably 4 g / m 2 or more and 10 g / m 2 or less, and particularly preferably 4 g / m

[0023] The ratio W1 / W2 of the basis weight of the first fiber sheet to the basis weight of the second fiber sheet is not particularly limited, but from the viewpoint of improving various filtration performances such as the filtration accuracy and filtration life of the cylindrical filter, it is preferably 1.1 to 50, more preferably 1.5 to 40, even more preferably 2.0 to 30, and particularly preferably 2.5 to 25.

[0024] From the viewpoint of easily achieving both filtration accuracy and filtration life of the cylindrical filter, the first fiber sheet preferably has an average fiber diameter d1 of 0.3 μm or more and 30 μm or less. From the viewpoint of achieving both filtration accuracy and filtration life of the cylindrical filter, the average fiber diameter d1 of the first fiber sheet is more preferably 0.5 μm or more, even more preferably 0.8 μm or more, and even more preferably 1.0 μm or more. Furthermore, in order to achieve both filtration accuracy and filtration life in the cylindrical filter, in particular from the viewpoint of ensuring that when the cylindrical filter is used for filtration, there are many voids inside the cylindrical filter so that the cylindrical filter does not clog in a short time and can be used for filtration for a longer time, there is no particular upper limit to the average fiber diameter d1 of the first fiber sheet, but it is more preferably 25 μm or less, even more preferably 20 μm or less, even more preferably 18 μm or less, and even more preferably 16 μm or less. In this specification, the average fiber diameter of the fiber sheet can be measured as described in the examples.

[0025] From the viewpoint of not only stably capturing and collecting smaller particles of foreign matter in the filtration layer, but also extending the filtration life of the cylindrical filter by increasing the time required for the filtration layer to become clogged, the CV value of the fiber diameter of the first fiber sheet is preferably 0.25 or more and even more preferably 0.6 or more. Furthermore, from the viewpoint of extending the filtration life of the cylindrical filter by increasing the time required for the filtration layer to become clogged, the CV value of the fiber diameter of the first fiber sheet is preferably 0.4 or more, and even more preferably 0.6 or more.

[0026] From the viewpoint of easily achieving both the filtration accuracy and filtration life of the cylindrical filter, the average fiber diameter d2 of the second fiber sheet is preferably 0.3 μm or more and 40 μm or less. From the viewpoint of achieving both the filtration accuracy and filtration life of the cylindrical filter, the average fiber diameter d2 of the second fiber sheet is more preferably 1.0 μm or more, even more preferably 1.5 μm or more, even more preferably 2.0 μm or more, even more preferably 2.5 μm or more, and particularly preferably 3.0 μm or more. Furthermore, in the cylindrical filter, from the viewpoint of achieving both filtration accuracy and filtration life, in particular, when the cylindrical filter is used for filtration, there are many voids inside the cylindrical filter, the cylindrical filter does not clog in a short time, and due to the diffusion effect present between the first fiber sheets, it can be used for filtration for a longer time, the average fiber diameter d2 of the second fiber sheet is more preferably 35 μm or less and even more preferably 30 μm or less.

[0027] From the viewpoint of increasing the filtration life of the cylindrical filter, it is preferable that the first fiber sheet and the second fiber sheet have different average fiber diameters. The ratio d1 / d2 of the average fiber diameter d1 of the first fiber sheet to the average fiber diameter d2 of the second fiber sheet is preferably 0.01 or more and 3.0 or less, more preferably 0.02 or more and 2.0 or less, even more preferably 0.03 or more and 1.8 or less, and particularly preferably 0.05 or more and 1.5 or less. Furthermore, when high-precision filtration is required, the ratio d1 / d2 of the average fiber diameter d1 of the first fiber sheet to the average fiber diameter d2 of the second fiber sheet is preferably 0.01 or more and 0.25 or less, more preferably 0.02 or more and 0.23 or less, even more preferably 0.04 or more and 0.22 or less, and even more preferably 0.06 or more and 0.20 or less.

[0028] The average pore size of the first fiber sheet is not particularly limited and can be selected considering the required filtration life for the cylindrical filter, but is preferably 0.5 μm to 80 μm, more preferably 1 μm to 70 μm, even more preferably 1.5 μm to 60 μm, and even more preferably 2.0 μm to 50 μm. Furthermore, when high-precision filtration is required, the average pore size of the first fiber sheet is preferably 0.4 μm to 7.0 μm, more preferably 0.6 μm to 6.0 μm, even more preferably 0.8 μm to 5.5 μm, and even more preferably 1.0 μm to 5.0 μm.

[0029] The maximum pore size of the first fiber sheet is not particularly limited, but is preferably 1 μm to 200 μm, more preferably 2 μm to 160 μm, even more preferably 3 μm to 130 μm, and even more preferably 4 μm to 100 μm. The maximum number of pores of the first fiber sheet is not particularly limited, but is preferably 1.0 μm to 100 μm, more preferably 1.0 μm to 80 μm, even more preferably 1.5 μm to 60 μm, and particularly preferably 1.8 μm to 40 μm. The minimum pore size of the first fiber sheet is not particularly limited, but is preferably 0.1 μm to 50 μm, more preferably 0.5 μm to 30 μm, and particularly preferably 1 μm to 20 μm. When the maximum pore size, maximum number of pores, and minimum pore size of the first fiber sheet are within the above ranges, the filtration accuracy tends to be higher. In this specification, the average pore diameter, maximum pore diameter, most numerous pore diameter, and minimum pore diameter of the fiber sheet can be measured as described in the examples.

[0030] The air permeability of the first fiber sheet is not particularly limited and is set appropriately based on the filtration accuracy to be designed, for example, 1.5 cm. 3 / cm 2 / second or more 150cm 3 / cm 2 / second or less, 2.0cm 3 / cm 2 / second or more 70cm 3 / cm 2 / second or less, 2.5cm 3 / cm 2 / second or more 35cm 3 / cm 2 Less than / second, or 3cm 3 / cm 2 / second or more 20cm 3 / cm 2 It may be less than / second. In this specification, the air permeability of the fiber sheet can be measured using a Fragile type tester in accordance with JIS L 1913.

[0031] Preferably, the first fiber sheet is a meltblown nonwoven fabric, and the second fiber sheet is a meltblown web. The meltblown nonwoven fabric and meltblown web can be fiber sheets with a large distribution of fiber diameters, and the CV value of the fiber diameter tends to be 0.25 or higher. In the meltblown nonwoven fabric and meltblown web, solid matter (particles) can easily pass through the interfiber voids composed of large fiber diameters, and fine particles are captured in the interfiber voids composed of small fiber diameters. Therefore, by using a fiber aggregate in which meltblown nonwoven fabric and meltblown web are wound alternately multiple times as a filtration layer, it is easy to obtain a filtration layer that is less prone to clogging and can capture and collect fine foreign matter with the fine fiber diameters. Furthermore, a functional nonwoven fabric having functionalities such as metal adsorption or ion exchange ability may be used as the first fiber sheet.

[0032] The first fiber sheet preferably has a width of 15 mm to 75 mm, more preferably 20 mm to 65 mm, even more preferably 25 mm to 60 mm, and particularly preferably 28 mm to 55 mm. A nonwoven fabric with a width within the above range can be suitably used as the first fiber sheet. By having a width within the above range for the first fiber sheet, the productivity of the process of winding the first fiber sheet to form a tubular fiber assembly is increased, and winding creases can be formed on the first fiber sheet along the longitudinal direction of the tubular filter. Having winding creases on the first fiber sheet along the longitudinal direction of the tubular filter creates longitudinal voids, which can simultaneously improve filtration accuracy and filtration life.

[0033] The first fiber sheet may be composed of a multilayer fiber sheet containing two or more layers of fiber sheets. When the first fiber sheet is composed of a multilayer fiber sheet containing two or more layers of fiber sheets, it is preferable that the physical properties of each layer of fiber sheet constituting the multilayer fiber sheet, such as thickness, density, basis weight, average fiber diameter, and CV value of the fiber diameter, satisfy the range of physical properties of the first fiber sheet described above. All physical properties may be substantially the same, some physical properties may be substantially the same, or all physical properties may be different. In a multilayer fiber sheet, from the viewpoint of productivity and maintaining filtration performance, the number of layers of fiber sheets constituting the multilayer fiber sheet may be six or less, specifically 2 to 6, 2 to 5, 2 to 4, or 2 to 3. In a multilayer fiber sheet, from the viewpoint of productivity, it is preferable that each fiber sheet is not bonded to one another. In this specification, "multilayer fiber sheet" means that each fiber sheet constituting the multilayer fiber sheet has the same width and completely overlaps in both the width direction and the length direction.

[0034] The thickness of the tubular fiber assembly A can be determined appropriately according to the application and purpose of the tubular filter, and is not particularly limited. For example, from the viewpoint of improving filtration accuracy while maintaining filtration life, it is preferable that the thickness be 1 mm to 6 mm, more preferably 1.5 mm to 5 mm, and even more preferably 2 mm to 4.5 mm. Depending on the thickness of the tubular fiber assembly A, the first fiber sheet and the second fiber sheet can be wound around the tubular fiber assembly A two or more times to form the tubular fiber assembly A.

[0035] The ratio H3 / H4 of the thickness of the third fiber sheet to the thickness of the fourth fiber sheet is not particularly limited, but from the viewpoint of improving various filtration performances such as filtration accuracy and filtration life of the cylindrical filter, it is preferable that the thickness H3 of the third fiber sheet is greater than the thickness H4 of the fourth fiber sheet, more preferably that H3 / H4 is 1.1 or more and 15.0 or less, even more preferably that it is 1.3 or more and 12 or less, even more preferably that it is 1.5 or more and 10 or less, even more preferably that it is 1.8 or more and 9 or less, even more preferably that it is 2.0 or more and 8 or less, and particularly preferably that it is 2.5 or more and 7 or less.

[0036] The thickness H3 of the third fiber sheet is preferably 0.10 mm to 0.80 mm, more preferably 0.15 mm to 0.70 mm, and even more preferably 0.18 mm to 0.60 mm, from the viewpoint of improving various filtration performances such as the filtration accuracy and filtration life of the cylindrical filter.

[0037] The thickness H4 of the fourth fiber sheet is preferably 0.03 mm to 0.18 mm, more preferably 0.04 mm to 0.16 mm, even more preferably 0.045 mm to 0.14 mm, and particularly preferably 0.05 mm to 0.125 mm, from the viewpoint of improving various filtration performances such as the filtration accuracy and filtration life of the cylindrical filter.

[0038] The ratio D3 / D4 of the density D3 of the third fiber sheet to the density D4 of the fourth fiber sheet is not particularly limited, but from the viewpoint of improving various filtration performance such as the filtration accuracy and filtration life of the cylindrical filter, it is more preferably 0.4 to 10.0, even more preferably 0.5 to 8.0, even more preferably 0.6 to 6.0, even more preferably 0.7 to 5.0, even more preferably 0.8 to 4.5, especially preferably 0.85 to 4.0, and especially especially preferably 0.90 to 3.0.

[0039] The density D3 of the third fiber sheet is set to 0.03 g / cm³ from the perspective of improving various filtration performance aspects such as the filtration accuracy and filtration life of the cylindrical filter. 3 More than 0.50g / cm 3 Preferably, it is 0.04 g / cm³. 3 More than 0.40g / cm 3 It is more preferable that the following is the case: 0.05 g / cm³ 3 More than 0.35g / cm 3 It is even more preferable that the following is the case: 0.06 g / cm³ 3 More than 0.30g / cm 3 The following is particularly preferable:

[0040] The density D4 of the fourth fiber sheet is set to 0.01 g / cm³ from the perspective of improving various filtration performance aspects such as the filtration accuracy and filtration life of the cylindrical filter. 3 More than 0.20g / cm 3 Preferably, it is 0.015 g / cm³. 3 More than 0.15g / cm 3 It is more preferable that the following is the case: 0.02 g / cm³ 3 More than 0.10g / cm 3 It is even more preferable that the following is the case: 0.025 g / cm³ 3 More than 0.08g / cm 3 The following is particularly preferable:

[0041] The third fiber sheet has a basis weight of 15g / m², with a W3 weight designed to improve various filtration performance aspects of the cylindrical filter, such as filtration accuracy and filtration life. 2 More than 100g / m 2 Preferably, it is 18 g / m 2 More than 80g / m 2 It is more preferable that the following is the case: 20 g / m 2 More than 60g / m 2 It is even more preferable that the following conditions apply: 23 g / m² 2 More than 50g / m 2 The following is even more preferable:

[0042] The fourth fiber sheet has a basis weight of 2g / m², with a W4 weight designed to improve various filtration performance aspects of the cylindrical filter, such as filtration accuracy and filtration life. 2 More than 16g / m 2 Preferably, it is 3 g / m 2 More than 14g / m 2 It is more preferable that the following conditions be met: 3.5 g / m 2 More than 12g / m 2 It is more preferable that the following conditions apply: 4 g / m 2 More than 10g / m 2 The following is particularly preferable:

[0043] The ratio W3 / W4 of the basis weight of the third fiber sheet to the basis weight of the fourth fiber sheet is not particularly limited, but from the viewpoint of improving various filtration performances such as the filtration accuracy and filtration life of the cylindrical filter, it is preferably 1.1 to 50, more preferably 1.5 to 40, even more preferably 2.0 to 30, and particularly preferably 2.5 to 25.

[0044] From the viewpoint of easily achieving both the filtration accuracy and filtration life of the cylindrical filter, the third fiber sheet preferably has an average fiber diameter d3 of 0.3 μm or more and 30 μm or less. From the viewpoint of achieving both the filtration accuracy and filtration life of the cylindrical filter, the average fiber diameter d3 of the third fiber sheet is more preferably 0.5 μm or more, even more preferably 0.8 μm or more, and even more preferably 1.0 μm or more. Furthermore, from the viewpoint of achieving both the filtration accuracy and filtration life of the cylindrical filter, in particular, from the viewpoint of ensuring that when the cylindrical filter is used for filtration, there are many voids inside the cylindrical filter so that the cylindrical filter does not clog in a short time and can be used for filtration for a longer time, the average fiber diameter d3 of the third fiber sheet is more preferably 25 μm or less, even more preferably 20 μm or less, even more preferably 18 μm or less, and even more preferably 16 μm or less.

[0045] The third fiber sheet is preferably such that its fiber diameter CV value is 0.25 or more and 3.0 or less, from the viewpoint of not only stably capturing and collecting smaller particles of foreign matter in the filtration layer, but also extending the filtration life of the cylindrical filter by increasing the time required for the filtration layer to become clogged. More preferably, the fiber diameter CV value of the third fiber sheet is 0.4 or more, and even more preferably 0.6 or more, from the viewpoint of extending the filtration life of the cylindrical filter by increasing the time required for the filtration layer to become clogged. Furthermore, from the viewpoint of making it easier to maintain the filtration accuracy of the cylindrical filter by appropriately suppressing the variation in fiber diameter of the third fiber sheet constituting the filtration layer, the fiber diameter CV value of the third fiber sheet is more preferably 2.5 or less, even more preferably 2.0 or less, even more preferably 1.5 or less, and particularly preferably 1.2 or less.

[0046] From the viewpoint of achieving both filtration accuracy and filtration life of the tubular filter, the average fiber diameter d4 of the fourth fiber sheet is preferably 0.3 μm or more and 40 μm or less. From the viewpoint of achieving both filtration accuracy and filtration life of the tubular filter, the average fiber diameter d4 of the fourth fiber sheet is more preferably 1.0 μm or more, even more preferably 1.5 μm or more, even more preferably 2.0 μm or more, even more preferably 2.5 μm or more, and particularly preferably 3.0 μm or more. Furthermore, from the viewpoint of achieving both filtration accuracy and filtration life in the tubular filter, and in particular from the viewpoint of ensuring that there are many voids inside the tubular filter when it is used for filtration, so that the tubular filter does not clog in a short time and can be used for filtration for a longer time, the average fiber diameter d4 of the fourth fiber sheet is more preferably 35 μm or less and even more preferably 30 μm or less.

[0047] From the viewpoint of increasing the filtration life of the cylindrical filter, it is preferable that the average fiber diameters of the third fiber sheet and the fourth fiber sheet are different. The ratio d3 / d4 of the average fiber diameter d3 of the third fiber sheet to the average fiber diameter d4 of the fourth fiber sheet is preferably 0.01 or more and 3.0 or less, more preferably 0.02 or more and 2.0 or less, even more preferably 0.03 or more and 1.8 or less, and particularly preferably 0.05 or more and 1.5 or less. For example, when a balance between high-precision filtration and a long filtration life is required, the ratio d3 / d4 of the average fiber diameter d3 of the third fiber sheet to the average fiber diameter d4 of the fourth fiber sheet is preferably 0.05 or more and 0.50 or less, more preferably 0.10 or more and 0.45 or less, even more preferably 0.15 or more and 0.42 or less, and even more preferably 0.20 or more and 0.40 or less.

[0048] The average pore size of the third fiber sheet is not particularly limited and can be selected considering the filtration accuracy required for the cylindrical filter, but is preferably 0.5 μm to 80 μm, more preferably 1 μm to 70 μm, even more preferably 1.5 μm to 60 μm, and even more preferably 2.0 μm to 50 μm.

[0049] The maximum pore size of the third fiber sheet is not particularly limited, but is preferably 1 μm or more and 200 μm or less, more preferably 2 μm or more and 160 μm or less, still more preferably 3 μm or more and 130 μm or less, and even more preferably 4 μm or more and 100 μm or less. Also, the maximum pore size of the first fiber sheet is not particularly limited, but is preferably 1.0 μm or more and 100 μm or less, more preferably 1.0 μm or more and 80 μm or less, still more preferably 1.5 μm or more and 60 μm or less, and particularly preferably 1.8 μm or more and 40 μm or less. Further, the minimum pore size of the first fiber sheet is not particularly limited, but is preferably 0.1 μm or more and 50 μm or less, more preferably 0.5 μm or more and 30 μm or less, and particularly preferably 1 μm or more and 20 μm or less. When the maximum pore size, maximum pore diameter, and minimum pore size of the third fiber sheet are within the above ranges, the filtration accuracy is likely to be high.

[0050] The air permeability of the third fiber sheet is not particularly limited and is appropriately set based on the filtration accuracy to be designed. For example, 1.5 cm 3 / cm 2 / second or more and 150 cm 3 / cm 2 / second or less, 2.0 cm 3 / cm 2 / second or more and 70 cm 3 / cm 2 / second or less, 2.5 cm 3 / cm 2 / second or more and 35 cm 3 / cm 2 / second or less, or 3 cm 3 / cm 2 / second or more and 20 cm 3 / cm 2 / second or less may also be acceptable.

[0051] Preferably, the third fiber sheet is a meltblown nonwoven fabric, and the fourth fiber sheet is a meltblown web. The meltblown nonwoven fabric and meltblown web can be fiber sheets with a large distribution of fiber diameters, and the CV value of the fiber diameter tends to be 0.25 or higher. In the meltblown nonwoven fabric and meltblown web, solid matter (particles) can easily pass through the interfiber voids composed of large fiber diameters, and fine particles are captured in the interfiber voids composed of small fiber diameters. Therefore, by using a fiber aggregate in which meltblown nonwoven fabric and meltblown web are wound alternately multiple times as a filtration layer, it is easy to obtain a filtration layer that is less prone to clogging and can capture and collect fine foreign matter with the fine fiber diameters. Furthermore, as the third fiber sheet, a functional nonwoven fabric having functionalities such as metal adsorption or ion exchange ability may be used.

[0052] The third fiber sheet preferably has a width of 15 mm to 75 mm, more preferably 20 mm to 65 mm, even more preferably 25 mm to 60 mm, and particularly preferably 28 mm to 55 mm. A nonwoven fabric with a width within the above range can be suitably used as the third fiber sheet. By having a width within the above range for the third fiber sheet constituting the tubular fiber assembly B, the productivity of the process of winding the third fiber sheet to form the tubular fiber assembly B is increased, and it becomes easier to form winding creases in the third fiber sheet along the longitudinal direction of the tubular filter. The winding creases in the third fiber sheet along the longitudinal direction of the tubular filter create longitudinal voids, which simultaneously improves filtration accuracy and filtration life.

[0053] The third fiber sheet may be composed of a multilayer fiber sheet containing two or more fiber sheets, from the viewpoint of easily improving filtration performance. When the third fiber sheet is composed of a multilayer fiber sheet containing two or more fiber sheets, the physical properties of each fiber sheet in the layers constituting the multilayer fiber sheet, such as thickness, density, basis weight, average fiber diameter, and CV value of the fiber diameter, preferably satisfy the range of physical properties of the first fiber sheet described above. All physical properties may be substantially the same, some physical properties may be substantially the same, or all physical properties may be different. In a multilayer fiber sheet, from the viewpoint of productivity and maintaining filtration performance, the number of fiber sheets constituting the multilayer fiber sheet may be six or less, specifically 2 to 6, 2 to 5, 2 to 4, or 2 to 3. In a multilayer fiber sheet, from the viewpoint of productivity, it is preferable that the individual fiber sheets are not bonded to each other.

[0054] The first fiber sheet and the third fiber sheet may have the same or different average fiber diameters. However, from the viewpoint of improving filtration life and filtration accuracy, it is preferable that the average fiber diameter d3 of the third fiber sheet is greater than the average fiber diameter d1 of the first fiber sheet. More preferably, d3 / d1 is greater than 1.00 and 25 or less, even more preferably 1.001 or more and 20 or less, and even more preferably 1.005 or more and 15 or less. For example, when high-precision filtration and a long filtration life are required, the ratio d3 / d1 of the average fiber diameter d3 of the third fiber sheet to the average fiber diameter d1 of the first fiber sheet is preferably 1.10 or more and 10 or less, more preferably 1.30 or more and 7 or less, and even more preferably 1.50 or more and 4 or less.

[0055] The second fiber sheet and the fourth fiber sheet may have the same or different average fiber diameters, but from the viewpoint of improving filtration life, it is more preferable that d4 / d2 be between 0.3 and 2.0, even more preferable that it be between 0.5 and 1.8, and even more preferable that it be between 0.7 and 1.6.

[0056] The thickness of the tubular fiber assembly B can be determined appropriately according to the application and purpose of the tubular filter, and is not particularly limited. For example, from the viewpoint of improving filtration accuracy while maintaining filtration life, it is preferable that the thickness be 1 mm to 7.0 mm, more preferably 1.5 mm to 6.0 mm, and even more preferably 2 mm to 5.0 mm. Depending on the thickness of the tubular fiber assembly B, the third fiber sheet and the fourth fiber sheet can be wound around it two or more times to form the tubular fiber assembly B.

[0057] In the tubular fiber assembly B, it is preferable that the third fiber sheet is a meltblown nonwoven fabric, and the fourth fiber sheet is a meltblown web in which meltblown fibers obtained by the meltblown method, in which the third fiber sheet is wound tubularly around the tubular fiber assembly A, and molten thermoplastic resin is discharged from the discharge hole of a spinning nozzle while simultaneously being stretched by a high-temperature gas flow ejected from around the discharge hole to form fibers, are directly assembled in a tubular shape on the surface of the third fiber sheet. In the tubular fiber assembly B, if the fourth fiber sheet is a meltblown web directly accumulated on the surface of the third fiber sheet, the production cost is low, the fiber diameter distribution is large, and the CV value of the fiber diameter tends to be 0.25 or higher. Rather than cooling the meltblown fibers obtained by the meltblown method to form a sheet and then winding it into a cylinder, it is preferable to directly accumulate and continuously wind the meltblown fibers without cooling them, by providing a rotating shaft that rotates at a predetermined speed on the extension of the discharge direction of the discharge hole of the spinning nozzle, and while winding a third fiber sheet around the rotating shaft, melted thermoplastic resin is discharged from the discharge hole and at the same time stretched by a high-temperature gas flow, causing the meltblown fibers to become fibrous, which are then accumulated in a cylindrical shape on the surface of the rotating shaft (more specifically, on the surface of the third fiber sheet that was wound earlier with respect to the rotating shaft), and continuously winding the meltblown fibers to form a cylindrical fiber aggregate.

[0058] The filtration layer may further include, in addition to tubular fiber aggregates A and B, a tubular fiber aggregate X positioned between tubular fiber aggregates A and B, in which the fibers are clustered in a tubular shape. This allows for even more efficient filtration through filtration and fluid diffusion by the tubular fiber aggregate X.

[0059] The thickness of the tubular fiber aggregate X is not particularly limited, but from the viewpoint of improving various filtration performances such as the filtration accuracy and filtration life of the tubular filter, it is preferably 0.05 mm to 5.0 mm, more preferably 0.1 mm to 4.0 mm, even more preferably 0.15 mm to 3.0 mm, and particularly preferably 0.2 mm to 2.0 mm. In this specification, the thickness of the tubular fiber aggregate can be measured as described in the examples.

[0060] From the viewpoint of easily achieving both the filtration accuracy and filtration life of the tubular filter, the tubular fiber aggregate X preferably has an average fiber diameter of 2 μm to 40 μm, more preferably 5 μm to 35 μm, and even more preferably 10 μm to 30 μm. In this specification, the average fiber diameter of the tubular fiber aggregate can be measured as described in the examples.

[0061] From the viewpoint of achieving both filtration accuracy and filtration life of the tubular filter, the CV value of the fiber diameter of the tubular fiber aggregate X is preferably 0.2 to 3.0, more preferably 0.25 to 2.5, and even more preferably 0.28 to 1.5. In this specification, the CV value of the fiber diameter of the tubular fiber aggregate can be measured as described in the examples.

[0062] Preferably, the tubular fiber aggregate X is not formed by a meltblown method in which melted thermoplastic resin is extruded from the discharge hole of a spinning nozzle and simultaneously stretched into fibers by a high-temperature gas flow ejected from around the discharge hole, and then wound into a tubular shape in a sheet state after the meltblown fibers have completely cooled, but rather by continuously winding the meltblown fibers extruded from the spinning nozzle onto the surface of a rotating shaft (more specifically, tubular fiber aggregate A) while accumulating them without completely cooling, thereby directly assembling the meltblown fibers into a tubular shape.

[0063] Preferably, the filtration layer includes, in addition to tubular fiber assemblies A and B, a tubular fiber assembly C positioned on the inflow side of tubular fiber assembly B, which is formed by winding a fifth fiber sheet and a sixth fiber sheet into a tubular shape. Preferably, in the thickness direction of the filtration layer, the fifth fiber sheet and the sixth fiber sheet are arranged alternately, and the fifth fiber sheet is bonded to the sixth fiber sheet. This prevents the fifth fiber sheet from collapsing under pressure when liquid passes through, stabilizing the interlayer, and the sixth fiber sheet diffuses the fluid from the inflow side to the outflow side, making it easier to achieve basic filtration performance.

[0064] The ratio H5 / H6 of the thickness of the fifth fiber sheet to the thickness of the sixth fiber sheet is not particularly limited, but from the viewpoint of improving various filtration performances such as the filtration accuracy and filtration life of the cylindrical filter, it is preferable that the thickness H5 of the fifth fiber sheet is greater than the thickness H6 of the sixth fiber sheet, and it is preferable that H5 / H6 is 1.1 or more and 15.0 or less, more preferably 1.3 or more and 12 or less, even more preferably 1.5 or more and 10 or less, even more preferably 1.8 or more and 9 or less, even more preferably 2.0 or more and 8 or less, and particularly preferably 2.5 or more and 7 or less.

[0065] The thickness H5 of the fifth fiber sheet is preferably 0.10 mm or more and 0.80 mm or less, more preferably 0.15 mm or more and 0.70 mm or less, and even more preferably 0.18 mm or more and 0.60 mm or less from the viewpoint of enhancing various filtration performances such as the filtration accuracy and filtration life of the cylindrical filter.

[0066] The thickness H6 of the sixth fiber sheet is preferably 0.03 mm or more and 0.18 mm or less, more preferably 0.04 mm or more and 0.16 mm or less, even more preferably 0.045 mm or more and 0.14 mm or less, and particularly preferably 0.05 mm or more and 0.125 mm or less from the viewpoint of enhancing various filtration performances such as the filtration accuracy and filtration life of the cylindrical filter.

[0067] The ratio D5 / D6 of the density D5 of the fifth fiber sheet to the density D6 of the sixth fiber sheet is not particularly limited, but from the viewpoint of enhancing various filtration performances such as the filtration accuracy and filtration life of the cylindrical filter, it is more preferably 0.4 or more and 10.0 or less, even more preferably 0.5 or more and 8.0 or less, even more preferably 0.6 or more and 6.0 or less, even more preferably 0.7 or more and 5.0 or less, even more preferably 0.8 or more and 4.5 or less, particularly preferably 0.85 or more and 4.0 or less, and particularly more preferably 0.90 or more and 3.0 or less.

[0068] The density D5 of the fifth fiber sheet is preferably 0.03 g / cm 3 or more and 0.5 g / cm 3 or less, more preferably 0.04 g / cm 3 or more and 0.4 g / cm 3 or less, even more preferably 0.05 g / cm 3 or more and 0.35 g / cm 3 or less, and particularly preferably 0.06 g / cm 3 or more and 0.3 g / cm 3 or less from the viewpoint of enhancing various filtration performances such as the filtration accuracy and filtration life of the cylindrical filter.

[0069] The density D6 of the sixth fiber sheet is set to 0.01 g / cm³ from the perspective of improving various filtration performance aspects such as the filtration accuracy and filtration life of the cylindrical filter. 3 More than 0.20g / cm 3 Preferably, it is 0.015 g / cm³. 3 More than 0.15g / cm 3 It is more preferable that the following is the case: 0.02 g / cm³ 3 More than 0.12g / cm 3 It is even more preferable that the following is the case: 0.025 g / cm³ 3 More than 0.10g / cm 3 The following is particularly preferable:

[0070] The fifth fiber sheet has a basis weight of 15g / m², with the aim of improving various filtration performance aspects of the cylindrical filter, such as filtration accuracy and filtration life. 2 More than 100g / m 2 Preferably, it is 18 g / m 2 More than 80g / m 2 It is more preferable that the following is the case: 20 g / m 2 More than 60g / m 2 It is even more preferable that the following conditions apply: 23 g / m² 2 More than 50g / m 2 The following is even more preferable:

[0071] The sixth fiber sheet has a basis weight of 2g / m², with a W6 base weight, to improve various filtration performance aspects such as the filtration accuracy and filtration life of the cylindrical filter. 2 More than 16g / m 2 Preferably, it is 3 g / m 2 More than 14g / m 2 It is more preferable that the following conditions be met: 3.5 g / m 2 More than 12g / m 2 It is more preferable that the following conditions apply: 4 g / m 2 More than 10g / m 2 The following is particularly preferable:

[0072] The ratio W5 / W6 of the basis weight of the fifth fiber sheet to the basis weight of the sixth fiber sheet is not particularly limited, but from the viewpoint of improving various filtration performances such as the filtration accuracy and filtration life of the cylindrical filter, it is preferably 1.1 to 50, more preferably 1.5 to 40, even more preferably 2.0 to 30, and particularly preferably 2.5 to 25.

[0073] From the viewpoint of easily achieving both filtration accuracy and filtration life of the cylindrical filter, the fifth fiber sheet preferably has an average fiber diameter d5 of 0.3 μm or more and 30 μm or less. From the viewpoint of achieving both filtration accuracy and filtration life of the cylindrical filter, the average fiber diameter d5 of the fifth fiber sheet is more preferably 0.5 μm or more, even more preferably 0.8 μm or more, and even more preferably 1.0 μm or more. Furthermore, from the viewpoint of achieving both filtration accuracy and filtration life in the cylindrical filter, in particular, from the viewpoint of ensuring that when the cylindrical filter is used for filtration, there are many voids inside the cylindrical filter so that the cylindrical filter does not clog in a short time and can be used for filtration for a longer time, the average fiber diameter d5 of the fifth fiber sheet is more preferably 25 μm or less, even more preferably 20 μm or less, even more preferably 18 μm or less, and even more preferably 16 μm or less.

[0074] The fifth fiber sheet is preferably such that its fiber diameter CV value is 0.25 or more and 3.0 or less, from the viewpoint of not only stably capturing and collecting smaller particles of foreign matter in the filtration layer, but also extending the filtration life of the cylindrical filter by increasing the time required for the filtration layer to become clogged. More preferably, the fiber diameter CV value of the fifth fiber sheet is 0.4 or more, even more preferably 0.6 or more, and particularly preferably 0.7 or more, from the viewpoint of extending the filtration life of the cylindrical filter by increasing the time required for the filtration layer to become clogged. Furthermore, from the viewpoint of making it easier to maintain the filtration accuracy of the cylindrical filter by appropriately suppressing the variation in fiber diameter of the fifth fiber sheet constituting the filtration layer, the fiber diameter CV value of the fifth fiber sheet is preferably 2.5 or less, even more preferably 2.0 or less, even more preferably 1.5 or less, and particularly preferably 1.2 or less.

[0075] From the viewpoint of achieving both filtration accuracy and filtration life of the cylindrical filter, the average fiber diameter d6 of the sixth fiber sheet is preferably 0.3 μm or more and 40 μm or less. From the viewpoint of achieving both filtration accuracy and filtration life of the cylindrical filter, the average fiber diameter d6 of the sixth fiber sheet is more preferably 1.0 μm or more, even more preferably 1.5 μm or more, even more preferably 2.0 μm or more, even more preferably 2.5 μm or more, and particularly preferably 3.0 μm or more. Furthermore, from the viewpoint of achieving both filtration accuracy and filtration life in the cylindrical filter, and in particular from the viewpoint of ensuring that there are many voids inside the cylindrical filter when it is used for filtration, so that the cylindrical filter does not clog in a short time and can be used for filtration for a longer time, the average fiber diameter d6 of the sixth fiber sheet is more preferably 35 μm or less and even more preferably 30 μm or less.

[0076] From the viewpoint of increasing the filtration life of the cylindrical filter, it is preferable that the average fiber diameters of the fifth fiber sheet and the sixth fiber sheet are different. The ratio d5 / d6 of the average fiber diameter d5 of the fifth fiber sheet to the average fiber diameter d6 of the sixth fiber sheet is preferably 0.01 or more and 3.0 or less, more preferably 0.02 or more and 2.0 or less, even more preferably 0.03 or more and 1.8 or less, and particularly preferably 0.05 or more and 1.5 or less. For example, when high-precision filtration and a long filtration life are required, the ratio d5 / d6 of the average fiber diameter d5 of the fifth fiber sheet to the average fiber diameter d6 of the sixth fiber sheet is preferably 0.10 or more and 2.0 or less, more preferably 0.15 or more and 1.6 or less, even more preferably 0.20 or more and 1.2 or less, and even more preferably 0.25 or more and 0.80 or less.

[0077] The average pore size of the fifth fiber sheet is not particularly limited and can be selected considering the required filtration life for the cylindrical filter, but is preferably 0.5 μm to 80 μm, more preferably 1 μm to 70 μm, even more preferably 1.5 μm to 60 μm, and even more preferably 2.0 μm to 50 μm. Furthermore, if high-precision filtration is required, the average pore size of the fifth fiber sheet is preferably 0.4 μm to 7.0 μm, more preferably 0.6 μm to 6.0 μm, even more preferably 0.8 μm to 5.5 μm, and even more preferably 1.0 μm to 5.0 μm.

[0078] The maximum pore size of the fifth fiber sheet is not particularly limited, but is preferably 1 μm to 200 μm, more preferably 2 μm to 160 μm, even more preferably 3 μm to 130 μm, and even more preferably 4 μm to 100 μm. The maximum number of pores of the fifth fiber sheet is not particularly limited, but is preferably 1.0 μm to 100 μm, more preferably 1.0 μm to 80 μm, even more preferably 1.5 μm to 60 μm, and particularly preferably 1.8 μm to 40 μm. The minimum pore size of the fifth fiber sheet is not particularly limited, but is preferably 0.1 μm to 50 μm, more preferably 0.5 μm to 30 μm, and particularly preferably 1 μm to 20 μm. When the maximum pore size, maximum number of pores, and minimum pore size of the fifth fiber sheet are within the above ranges, the filtration accuracy tends to be higher.

[0079] The permeability of the fifth fiber sheet is not particularly limited and is set appropriately based on the filtration accuracy to be designed, for example, 1.5 cm. 3 / cm 2 / second or more 150cm 3 / cm 2 / second or less, 2.0cm 3 / cm 2 / second or more 70cm 3 / cm 2 / second or less, 2.5cm 3 / cm 2 / second or more 35cm 3 / cm 2 Less than / second, or 3cm 3 / cm 2 / second or more 20cm 3 / cm 2 It can be less than / second.

[0080] The fifth fiber sheet is preferably a meltblown nonwoven fabric, and the sixth fiber sheet is preferably a meltblown web. Meltblown nonwoven fabrics and meltblown webs can be fiber sheets with a large distribution of fiber diameters, and the CV value of the fiber diameter tends to be 0.25 or higher. In meltblown nonwoven fabrics and meltblown webs, solid matter (particles) can easily pass through the interfiber voids composed of large fiber diameters, and fine particles are captured in the interfiber voids composed of small fiber diameters. Therefore, by using a fiber aggregate in which meltblown nonwoven fabric and meltblown web are wound alternately multiple times as a filtration layer, it is easy to obtain a filtration layer that is less prone to clogging and can capture and collect fine foreign matter with the fine fiber diameters. Furthermore, as the fifth fiber sheet, a functional nonwoven fabric having functionalities such as metal adsorption or ion exchange ability may be used.

[0081] The fifth fiber sheet is preferably 15 mm to 75 mm wide, more preferably 20 mm to 65 mm wide, even more preferably 25 mm to 60 mm wide, and particularly preferably 28 mm to 55 mm wide. A nonwoven fabric with a width within the above range can be suitably used as the fifth fiber sheet. By having a width within the above range for the fifth fiber sheet, the productivity of the process of winding the fifth fiber sheet to form a tubular fiber assembly is increased, and winding wrinkles can be formed on the fifth fiber sheet along the longitudinal direction of the tubular filter. The winding wrinkles on the fifth fiber sheet along the longitudinal direction of the tubular filter create longitudinal voids, which can simultaneously improve filtration accuracy and filtration life.

[0082] The fifth fiber sheet may be composed of a multilayer fiber sheet containing two or more layers of fiber sheets. When the fifth fiber sheet is composed of a multilayer fiber sheet containing two or more layers of fiber sheets, it is preferable that the physical properties of each layer of fiber sheet constituting the multilayer fiber sheet, such as thickness, density, basis weight, average fiber diameter, and CV value of the fiber diameter, satisfy the range of physical properties of the fifth fiber sheet described above. All physical properties may be substantially the same, some physical properties may be substantially the same, or all physical properties may be different. In a multilayer fiber sheet, from the viewpoint of productivity and maintaining filtration performance, the number of layers of fiber sheets constituting the multilayer fiber sheet may be six or less, specifically 2 to 6, 2 to 5, 2 to 4, or 2 to 3. In a multilayer fiber sheet, from the viewpoint of productivity, it is preferable that each fiber sheet is not bonded to one another.

[0083] The average fiber diameters of the third fiber sheet and the fifth fiber sheet may be the same or different. However, from the viewpoint of improving filtration life and filtration accuracy, it is preferable that the average fiber diameter d5 of the fifth fiber sheet is greater than the average fiber diameter d3 of the third fiber sheet. More preferably, d5 / d3 is greater than 1.00 and 20 or less, even more preferably 1.005 or more and 15 or less, and even more preferably 1.01 or more and 10 or less. For example, when high-precision filtration and a long filtration life are required, the ratio d5 / d3 of the average fiber diameter d5 of the fifth fiber sheet to the average fiber diameter d3 of the third fiber sheet is preferably 1.00 or more and 10 or less, more preferably 1.005 or more and 5 or less, and even more preferably 1.01 or more and 3 or less.

[0084] The fourth fiber sheet and the sixth fiber sheet may have the same or different average fiber diameters, but from the viewpoint of improving filtration life, it is more preferable that d6 / d4 be between 0.3 and 2.0, even more preferable that it be between 0.5 and 1.8, and even more preferable that it be between 0.7 and 1.6.

[0085] The thickness of the tubular fiber assembly C can be determined appropriately according to the application and purpose of the tubular filter, and is not particularly limited. For example, from the viewpoint of improving filtration accuracy while maintaining filtration life, it is preferable that the thickness be 1 mm to 6 mm, more preferably 1.5 mm to 5 mm, and even more preferably 2 mm to 4.5 mm. Depending on the thickness of the tubular fiber assembly C, the fifth fiber sheet and the sixth fiber sheet can be wound around it two or more times to form the tubular fiber assembly C.

[0086] In the tubular fiber assembly C, it is preferable that the fifth fiber sheet is a meltblown nonwoven fabric, and the sixth fiber sheet is a meltblown web in which meltblown fibers obtained by the meltblown method, in which the fifth fiber sheet is wound tubularly around the tubular fiber assembly B, and molten thermoplastic resin is discharged from the discharge hole of a spinning nozzle while simultaneously being stretched by a high-temperature gas flow ejected from around the discharge hole to form fibers, are directly assembled in a tubular shape on the surface of the fifth fiber sheet. In the tubular fiber assembly C, if the sixth fiber sheet is a meltblown web directly accumulated on the surface of the fifth fiber sheet, the production cost is low, the fiber diameter distribution is large, and the CV value of the fiber diameter tends to be 0.25 or higher. Rather than cooling the meltblown fibers obtained by the meltblown method to form a sheet and then winding it into a cylinder, it is preferable to directly accumulate and continuously wind the meltblown fibers without cooling them, by providing a rotating shaft that rotates at a predetermined speed on the extension of the discharge direction of the discharge hole of the spinning nozzle, and while winding the fifth fiber sheet around the rotating shaft, the meltblown fibers, which have become fibrous by being stretched by a high-temperature gas flow at the same time as the molten thermoplastic resin is discharged from the discharge hole, are accumulated in a cylindrical shape on the surface of the rotating shaft (more specifically, on the surface of the fifth fiber sheet that was wound earlier with respect to the rotating shaft) and continuously winding the meltblown fibers, thereby forming a cylindrical fiber aggregate.

[0087] The filtration layer may further include a tubular fiber assembly R, which is positioned between tubular fiber assemblies B and C, and in which fibers are clustered in a tubular shape. This allows for more efficient filtration through filtration and fluid diffusion by the tubular fiber assembly R.

[0088] The thickness of the tubular fiber aggregate R is not particularly limited, but from the viewpoint of improving various filtration performances such as the filtration accuracy and filtration life of the tubular filter, it is preferably 0.05 mm to 5.0 mm, more preferably 0.1 mm to 4.0 mm, even more preferably 0.15 mm to 3.0 mm, and particularly preferably 0.2 mm to 2.0 mm.

[0089] From the viewpoint of easily achieving both the filtration accuracy and filtration life of the tubular filter, the tubular fiber aggregate R preferably has an average fiber diameter of 2 μm to 40 μm, more preferably 5 μm to 35 μm, and even more preferably 10 μm to 30 μm.

[0090] From the viewpoint of easily achieving both the filtration accuracy and filtration life of the cylindrical filter, the tubular fiber aggregate R preferably has a fiber diameter CV value of 0.2 to 3.0, more preferably 0.25 to 2.5, and even more preferably 0.3 to 1.5.

[0091] Preferably, the tubular fiber aggregate R is formed by continuously winding meltblown fibers obtained by the meltblown method, in which molten thermoplastic resin is extruded from the discharge hole of a spinning nozzle and simultaneously stretched by a high-temperature gas flow ejected from around the discharge hole to form fibers, after the meltblown fibers have completely cooled and are in a sheet state, rather than by continuously winding the meltblown fibers extruded from the spinning nozzle onto the surface of a rotating shaft (more specifically, tubular fiber aggregate A) while accumulating them without completely cooling, thereby directly assembling the meltblown fibers into a tubular shape.

[0092] In the filtration layer (more specifically, the tubular fiber assembly A), it is preferable that the first fiber sheet is spirally wound around the tubular filter in the longitudinal direction, overlapping with the second fiber sheet. Because the first fiber sheet is spirally wound, the first fiber sheet constituting the tubular fiber assembly A is angled with respect to the longitudinal direction of the tubular filter, while overlapping with the second fiber sheet. Therefore, when a liquid containing foreign matter such as solids flows in from outside the tubular filter and passes through the tubular fiber assembly A, it is considered that the liquid passes through the tubular filter at an angle along the angle of the tubular fiber assembly A, or in other words, along the winding angle between the longitudinal direction of the tubular filter and the winding direction of the first fiber sheet, which is created by the spiral winding of the first fiber sheet while it is overlapping with the second fiber sheet.

[0093] The first fiber sheet and the second fiber sheet overlap, preferably arranged alternately in the thickness direction while advancing 0.5 to 10 mm in the longitudinal direction of the cylindrical filter. More preferably, they are arranged alternately in the thickness direction while advancing 0.6 to 5 mm, and particularly preferably 0.8 to 3 mm. By using the above range, the area through which the liquid passes becomes larger than when the fiber sheet is not wound spirally, so the filtration area is effectively utilized and is presumed to contribute to high filtration accuracy. In the first fiber sheet constituting the cylindrical fiber assembly A, in addition to the second fiber sheet being wound with the first fiber sheet positioned between them, as described later, a core material is provided on the downstream side and an outer layer on the upstream side, creating voids between the first fiber sheets. As a result, a rapid pressure rise during filtration can be suppressed and is presumed to contribute to an improved filtration life.

[0094] In the filtration layer (more specifically, the tubular fiber assembly B), it is preferable that the third fiber sheet is spirally wound around the tubular filter in a manner that overlaps with the fourth fiber sheet. Because the third fiber sheet is spirally wound around the tubular fiber assembly B while overlapping with the fourth fiber sheet, the third fiber sheet constituting the tubular fiber assembly B is angled with respect to the longitudinal direction of the tubular filter. Therefore, when a liquid containing foreign matter such as solids flows in from outside the tubular filter and passes through the tubular fiber assembly B, it is considered that the liquid passes through the tubular filter at an angle along the angle of the tubular fiber assembly B, or in other words, along the winding angle between the longitudinal direction of the tubular filter and the winding direction of the third fiber sheet, which is created by the spiral winding of the third fiber sheet while overlapping with the fourth fiber sheet.

[0095] The third and fourth fiber sheets overlap, preferably arranged alternately in the thickness direction while advancing 0.5 to 10 mm in the longitudinal direction of the cylindrical filter. More preferably, they are arranged alternately in the thickness direction while advancing 0.6 to 5 mm, and particularly preferably 0.8 to 3 mm. By using the above range, the area through which the liquid passes becomes larger than when the fiber sheets are not wound spirally, so the filtration area is effectively utilized and is presumed to contribute to high filtration accuracy. In the third fiber sheets constituting the cylindrical fiber assembly B, in addition to the fourth fiber sheets being wound with the third fiber sheets positioned between them, as described later, a core material is provided on the downstream side and an outer layer on the upstream side, creating gaps between the third fiber sheets. As a result, a rapid pressure rise during filtration can be suppressed and is presumed to contribute to an improved filtration life.

[0096] In the filtration layer (more specifically, the tubular fiber assembly C), it is preferable that the fifth fiber sheet is spirally wound around the tubular filter in a manner that overlaps with the sixth fiber sheet. Because the fifth fiber sheet is spirally wound, the fifth fiber sheet constituting the tubular fiber assembly C is angled with respect to the longitudinal direction of the tubular filter while overlapping with the sixth fiber sheet. Therefore, when a liquid containing foreign matter such as solids flows in from outside the tubular filter and passes through the tubular fiber assembly C, it is considered that the liquid passes through the tubular filter at an angle along the angle of the tubular fiber assembly C, or in other words, along the winding angle between the longitudinal direction of the tubular filter and the winding direction of the fifth fiber sheet, which is created by the spiral winding of the fifth fiber sheet while it overlaps with the sixth fiber sheet.

[0097] The fifth and sixth fiber sheets overlap, preferably arranged alternately in the thickness direction, for example, advancing 0.5 to 10 mm at a time in the longitudinal direction of the cylindrical filter. More preferably, they are arranged alternately in the thickness direction, advancing 0.6 to 5 mm at a time, and particularly preferably 0.8 to 3 mm at a time. By arranging them within the above range, the area through which the liquid passes becomes larger than when the fiber sheets are not wound spirally, allowing the filtration area to be effectively utilized and contributing to high filtration accuracy. In the fifth fiber sheets constituting the cylindrical fiber assembly C, in addition to the sixth fiber sheets being wound between the fifth fiber sheets, a core material is provided downstream and an outer layer upstream, as described later. This creates gaps between the fifth fiber sheets, which suppresses a rapid pressure increase during filtration and contributes to improved filtration life.

[0098] The thickness of the filter layer can be determined appropriately according to the application and purpose of the cylindrical filter, and is not particularly limited. For example, from the viewpoint of improving filtration accuracy while maintaining filtration life, it is preferable that the thickness be 2 mm to 12 mm, more preferably 2.5 mm to 10 mm, and even more preferably 3 mm to 9 mm. The thickness of the filter layer is indicated by the value obtained by dividing the difference between the outer diameter and inner diameter of the filter layer by 2.

[0099] The cylindrical filter may or may not have a core material located on the outflow side of the filtration layer, more specifically on the outflow side of the cylindrical fiber assembly A. It may also have other layers, such as an outer layer, located on the inflow side of the filtration layer, more specifically on the inflow side of the cylindrical fiber assembly B or the cylindrical fiber assembly C, or may or may not have such layers. From the viewpoint of improving various filtration performances such as filtration accuracy and filtration life of the cylindrical filter, as well as increasing the productivity of the cylindrical filter, it is preferable that the cylindrical filter includes a core material, a filtration layer, and an outer layer arranged in order from the hollow portion on the inner circumference located in the center of the cylindrical filter toward the outer circumference of the cylindrical filter.

[0100] The core material may be a cylindrical porous resin molded body manufactured by injection molding or extrusion molding of a thermoplastic resin, but it is preferable that it be formed of a tubular fiber aggregate Y in which fibers are accumulated in a tubular shape. The average fiber diameter of the tubular fiber aggregate Y is preferably 0.3 μm or more and 30 μm or less. In order to achieve both the filtration accuracy and filtration life of the tubular filter, as well as to give strength to the entire tubular filter, it is preferable that the average fiber diameter of the tubular fiber aggregate Y is 1 μm or more, and more preferably 3 μm or more. Furthermore, in order to achieve both the filtration accuracy and filtration life of the tubular filter, in particular, in order to have many voids inside the tubular filter when used for filtration, so that the tubular filter does not clog in a short time and can be used for filtration for a longer time, it is preferable that the average fiber diameter of the tubular fiber aggregate Y is 25 μm or less, more preferably 20 μm or less, and especially preferably 15 μm or less.

[0101] In the tubular fiber assembly Y, from the viewpoint of easily achieving both filtration accuracy and filtration life of the tubular filter, the CV value of the fiber diameter is preferably 0.25 or more and 1.8 or less. Due to the variation in the fiber diameter of the fibers constituting the tubular fiber assembly Y, the tubular fiber assembly Y becomes a tubular fiber assembly that includes a wide range of fibers, from thick to thin, resulting in many large and small interfiber voids inside the core material, i.e., the tubular fiber assembly Y. Therefore, when filtration is performed, the proportion of space for capturing and collecting foreign matter increases, which is thought to improve the filtration life. From the viewpoint of further improving the filtration life of the tubular filter, the CV value of the fiber diameter of the tubular fiber assembly Y is preferably 0.30 or more, more preferably 0.33 or more, and particularly preferably 0.35 or more. Furthermore, the CV value of the fiber diameter of the tubular fiber assembly Y is preferably 1.5 or less, more preferably 1.2 or less, and particularly preferably 1.0 or less.

[0102] The tubular fiber aggregate Y may include fiber bundles formed by bonding multiple fibers together in the longitudinal direction. This results in a void-rich structure for the tubular fiber aggregate Y, which helps reduce pressure losses such as air pressure loss and water pressure loss. Furthermore, the void-rich structure of the tubular fiber aggregate Y allows foreign matter to be captured and collected throughout the entire tubular filter when used in filtration, increasing the amount of foreign matter that can be captured before clogging occurs and the tubular filter becomes unusable, thus extending the filtration life.

[0103] Preferably, the tubular fiber aggregate Y is formed by continuously winding melt-blown fibers, which are obtained by the melt-blown method in which molten thermoplastic resin is extruded from the discharge hole of a spinning nozzle and simultaneously stretched by a high-temperature gas flow ejected from around the discharge hole, into a tubular shape after the melt-blown fibers have completely cooled. Instead, the melt-blown fibers extruded from the spinning nozzle are continuously wound onto the surface of a rotating shaft while they are rotating, without completely cooling, thereby forming a tubular aggregate directly from the melt-blown fibers. When the tubular fiber aggregate Y is composed of melt-blown fibers, production costs are low, the fiber diameter distribution is large, and a tubular fiber aggregate with a fiber diameter CV value of 0.25 or higher can be easily obtained. To form a tubular fiber assembly by directly assembling meltblown fibers obtained by the meltblown method into a cylindrical shape without cooling them to form a sheet, it is preferable to provide a rotating shaft (also called a mandrel or core) that rotates at a predetermined speed on the extension of the discharge direction of the discharge hole of the spinning nozzle, and to continuously wind the meltblown fibers obtained by discharging molten thermoplastic resin from the discharge hole while simultaneously blowing a high-temperature gas stream onto it, thereby accumulating them on the surface of the rotating shaft, thereby forming a tubular fiber assembly.

[0104] The thickness of the core material (for example, a tubular fiber aggregate Y) can be determined appropriately according to the application and purpose of the tubular filter, and is not particularly limited. For example, from the viewpoint of stabilizing filtration accuracy and extending the filtration life, it is preferable that the thickness be 5 mm or more and 15 mm or less, more preferably 6 mm or more and 14 mm or less, and even more preferably 6 mm or more and 12 mm or less. The thickness of the core material can be expressed as the value obtained by dividing the difference between the outer diameter of the core material (the outer diameter of the tubular filter in the state of the core material only, including the diameter of the hollow part, and equivalent to the inner diameter of the filtration layer) and the inner diameter of the core material (equivalent to the diameter of the hollow part) by 2.

[0105] The outer layer is preferably composed of a tubular fiber aggregate Z formed by the accumulation of fibers, in order to achieve both the filtration accuracy and filtration life of the tubular filter, and in particular to capture and collect a high proportion of foreign matter with large particle sizes. The average fiber diameter of the tubular fiber aggregate Z is preferably 3 μm or more and 30 μm or less. The average fiber diameter of the tubular fiber aggregate Z is preferably 4 μm or more, more preferably 5 μm or more, and even more preferably 6 μm or more. Furthermore, the average fiber diameter of the tubular fiber aggregate Z is preferably 35 μm or less, more preferably 30 μm or less, and even more preferably 25 μm or less.

[0106] The outer layer is located upstream (inflow side) of the core material and the filtration layer, and the fluid to be filtered flows into it containing a larger amount of foreign matter that should be captured and collected. Therefore, it is preferable that the CV value of the fiber diameter in the tubular fiber assembly Z is between 0.25 and 2.5, from the viewpoint of improving filtration life by causing variation in the fiber diameter of the fibers in the tubular fiber assembly Z, resulting in the outer layer being a tubular fiber assembly containing both thick and thin fibers. The lower limit of the CV value of the fiber diameter in the tubular fiber assembly Z is preferably 0.3 or higher, more preferably 0.4 or higher, and even more preferably 0.5 or higher, from the viewpoint of obtaining a tubular filter that is less prone to clogging and has a long filtration life. The upper limit of the CV value of the fiber diameter in the tubular fiber assembly Z is preferably 2.0 or lower, more preferably 1.4 or lower, even more preferably 1.2 or lower, and particularly preferably 1.0 or lower, from the viewpoint of easily obtaining a tubular filter that has a long filtration life and exhibits stable filtration accuracy.

[0107] In the outer layer, the tubular fiber aggregate Z may contain fiber bundles formed by bonding multiple fibers together in the longitudinal direction, similar to the tubular fiber aggregate Y. In the outer layer, as with the core material, the presence of fiber bundles formed by bonding multiple fibers together in the longitudinal direction results in a structure with many voids. This not only makes it easier to reduce pressure losses such as air pressure loss and water pressure loss, but the structure with many voids also means that when used in filtration, foreign matter is captured and collected throughout the tubular filter, causing clogging and increasing the amount of foreign matter that can be captured before the tubular filter becomes unusable, thus extending the filtration life.

[0108] It is preferable that the tubular fiber aggregate Z, like the tubular fiber aggregate Y, is made of meltblown fibers obtained by the meltblown method, in which molten thermoplastic resin is extruded from the discharge hole of a spinning nozzle and simultaneously stretched by a high-temperature gas flow ejected from around the discharge hole to form fibers, and that these meltblown fibers are not cooled to form a sheet and then wound into a tube, but rather the meltblown fibers are directly assembled into a tube without cooling. When the tubular fiber aggregate Z is made of meltblown fibers, it is possible to easily obtain a fiber aggregate with low production costs, a large distribution of fiber diameters, and a fiber diameter CV value of 0.25 or more. To form a tubular fiber assembly by directly assembling meltblown fibers obtained by the meltblown method into a cylindrical shape without cooling them to form a sheet, it is preferable to provide a rotating shaft that rotates at a predetermined speed on the extension of the discharge direction of the discharge hole of the spinning nozzle, and to form a tubular fiber assembly by discharging molten thermoplastic resin from the discharge hole and simultaneously stretching it with a high-temperature gas flow, thereby forming the meltblown fibers. These meltblown fibers are then cooled while accumulating in a cylindrical shape on the surface of the rotating shaft (more specifically, on the surface of tubular fiber assembly B or tubular fiber assembly C).

[0109] The thickness of the outer layer can be determined appropriately depending on the application and purpose of the cylindrical filter, and is not particularly limited. For example, from the viewpoint of stabilizing filtration accuracy and extending the filtration life, it is preferable that the thickness be 1 mm to 6 mm, more preferably 1 mm to 5 mm, and even more preferably 2 mm to 4.5 mm. The thickness of the outer layer is expressed as the value obtained by dividing the difference between the outer diameter of the outer layer and the inner diameter of the outer layer (which is the same as the outer diameter of the filtration layer) by 2.

[0110] In a cylindrical filter, when the total mass of the core material, filter layer, and outer layer is taken as 100% by mass, it is preferable that the core material content is 20% to 70% by mass, the filter layer content is 15% to 60% by mass, and the outer layer content is 8% to 30% by mass. More preferably, the core material content is 25% to 65% by mass, the filter layer content is 18% to 58% by mass, and the outer layer content is 10% to 25% by mass. When the filter layer content, which mainly affects filtration accuracy, is 15% by mass or more, preferably 18% by mass or more, filtration accuracy is further improved. Also, when the filter layer content is 60% by mass or less, preferably 58% by mass or less, the filtration life tends to be longer. Also, when the core material content closest to the hollow part is 70% by mass or less, preferably 65% ​​by mass or less, the filtration life tends to be longer. Also, when the core material content is 20% by mass or more, preferably 25% by mass or more, filtration accuracy tends to be improved. It is preferable that the content of the outer layer, which is placed outside the filtration layer and covers it, be 8% by mass or more, preferably 10% by mass or more, as this improves and stabilizes the filtration accuracy. Furthermore, if the content of the outer layer is 30% by mass or less, preferably 25% by mass or less, the proportion of the outer layer does not become too large, resulting in an appropriate proportion, which also improves and stabilizes the filtration accuracy.

[0111] Furthermore, in the filtration layer, when the total mass of tubular fiber aggregates A, B, and X is taken as 100% by mass, it is preferable that the content of tubular fiber aggregate A is 15% to 75% by mass, the content of tubular fiber aggregate B is 25% to 85% by mass, and the content of tubular fiber aggregate X is 0% to 15% by mass. It is more preferable that the content of tubular fiber aggregate A is 18% to 80% by mass, the content of tubular fiber aggregate B is 30% to 80% by mass, and the content of tubular fiber aggregate X is 2% to 12% by mass. It is even more preferable that the content of tubular fiber aggregate A is 22% to 62% by mass, the content of tubular fiber aggregate B is 35% to 75% by mass, and the content of tubular fiber aggregate X is 3% to 10% by mass.

[0112] Furthermore, in the filtration layer, when the total mass of tubular fiber aggregates A, B, C, X, and R is taken as 100% by mass, the content of tubular fiber aggregate A is 15% to 50% by mass, the content of tubular fiber aggregate B is 15% to 50% by mass, the content of tubular fiber aggregate C is 15% to 50% by mass, the content of tubular fiber aggregate X is 1% to 10% by mass, and The content of tubular fiber aggregates R is preferably 1% by mass or more and 10% by mass or less, the content of tubular fiber aggregates A is preferably 20% by mass or more and 40% by mass or less, the content of tubular fiber aggregates B is preferably 20% by mass or more and 40% by mass or less, the content of tubular fiber aggregates C is preferably 20% by mass or more and 40% by mass or less, the content of tubular fiber aggregates X is preferably 3% by mass or more and 8% by mass or less, and the content of tubular fiber aggregates R is preferably 3% by mass or more and 8% by mass or less.

[0113] In the core material, filter layer, and outer layer, the type of fiber constituting each layer is not particularly limited and can be used without particular restriction, such as natural fibers or synthetic fibers, but it is preferable that the fibers be made of thermoplastic resin. Examples of thermoplastic resins include polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, polylactic acid, and polybutylene succinate; polyolefin resins such as polyethylene resin, isotactic, atactic, and syndiotactic polypropylene resins, polymethylpentene resin, polybutene-1 resin, ethylene-vinyl alcohol copolymer resin, and ethylene-propylene copolymer resin; polyamide resins such as nylon 6, nylon 66, nylon 11, and nylon 12; and engineering plastics such as polycarbonate, polyacetal (also called polyoxymethylene resin), polystyrene, cyclic polyolefin, and polyphenylene sulfide (also called polyphenylene sulfide or PPS). Examples of polyethylene resins include low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, and ultra-high molecular weight polyethylene. Polypropylene resin may be a homopolymer of propylene or a copolymer of propylene and other α-olefins. From the viewpoint of high chemical resistance, such as acid resistance, base resistance, and resistance to various organic solvents, when using a cylindrical filter, it is preferable that the fibers in the core material, filter layer, and outer layer be composed of polyolefin resins such as polypropylene resin, polymethylpentene resin, polybutene-1 resin, ethylene-vinyl alcohol copolymer resin, and ethylene-propylene copolymer resin, and it is even more preferable that they contain at least polypropylene resin. Since polypropylene resin has a relatively high melting point among polyolefin resins, it can filter liquids at relatively high temperatures, has good chemical resistance, and is low cost.

[0114] When a fiber sheet made of synthetic fibers composed of the thermoplastic resin is used for the core material, filter layer, and outer layer, the fiber sheet is preferably a nonwoven fabric made of the thermoplastic resin described above. The type of nonwoven fabric is not particularly limited, and may be a long-fiber nonwoven fabric (for example, a fiber with a fiber length longer than 110 mm or a substantially continuous fiber) or a short-fiber nonwoven fabric (for example, a fiber with a fiber length of 3 mm to 110 mm). As a long-fiber nonwoven fabric, for example, spunbond nonwoven fabric, meltblown nonwoven fabric obtained by the melt-blown method, or a nonwoven fabric obtained by the electrospinning method (also called electrospinning or field spinning) can be used. As a short-fiber nonwoven fabric, it may be obtained by a wet papermaking method using short fibers with a fiber length of 3 mm to 20 mm, an airlaid method using short fibers with a fiber length of 3 mm to 32 mm, or a carding method using short fibers with a fiber length of 24 mm to 110 mm, which produces a fiber web using a carding machine, and then integrating the web. When a fiber web is produced by the carding method, the manufacturing method is not limited, and the fiber web can be produced by known manufacturing methods such as parallel webs, semi-random webs, random webs, cross webs, and crisscross webs. The fiber web is integrated by one or more methods selected from bonding with adhesive, thermal bonding by softening or melting the fibers (thermal bonding), needle punching, and high-pressure water jet treatment (spunlace). Preferably, the first fiber sheet, the third fiber sheet, and the fifth fiber sheet are nonwoven fabrics composed of the aforementioned thermoplastic resin, more preferably meltblown nonwoven fabrics composed of the aforementioned thermoplastic resin, and the core material, the second fiber sheet, the fourth fiber sheet, the sixth fiber sheet, and the outer layer are meltblown webs composed of the aforementioned thermoplastic resin.

[0115] The tubular filter may include other components in addition to the core material, filtration layer, and outer layer, to the extent that it does not impede the effects of the present invention. The other components may be arranged downstream (inside) of the core material (tubular fiber assembly Y) and / or upstream (outside) of the outer layer (tubular fiber assembly Z). Examples of other components arranged inside the core material (tubular fiber assembly Y) include cylindrical fiber molded articles, perforated tubular bodies made of thermoplastic resin, perforated tubular bodies made of metal, and perforated tubular bodies made of ceramics. Examples of other components arranged outside the outer layer (tubular fiber assembly Z) include nonwoven fabrics such as heat-bondable nonwoven fabrics containing heat-bondable fibers. By winding a heat-bonded nonwoven fabric around the outside of the outer layer (tubular fiber aggregate Z), or in other words, further upstream (inflow side) than the outer layer, the side surface of the tubular filter becomes smooth and less prone to fuzzing. This is not only preferable in terms of the product's appearance, but also reduces fiber shedding from the tubular filter because the heat-bonded nonwoven fabric becomes part of the side surface of the tubular filter. In the tubular filter, the nonwoven fabric wound around the outside of the outer layer (tubular fiber aggregate Z) is not particularly limited as long as it is a heat-bonded nonwoven fabric, and may be a short-fiber nonwoven fabric or a long-fiber nonwoven fabric containing core-sheath type composite fibers with a high-melting-point thermoplastic resin as the core component and a low-melting-point thermoplastic resin as the sheath component. The fineness of the heat-bonded nonwoven fabric is not particularly limited, but may be a heat-bondable nonwoven fabric mainly composed of core-sheath type composite fibers of 1.1 dtex to 8 dtex. In the tubular filter of the present invention, when a heat-bonded nonwoven fabric is wound around the outermost part of the outer layer, the amount of heat-bonded nonwoven fabric wound around should be between 1 and 10 turns, preferably between 1 and 6 turns.

[0116] From the viewpoint of satisfying basic filtration performance, under the measurement conditions described in the examples, the cylindrical filter preferably has a filtration accuracy of over 50% for particles with a particle size of 3.0 μm, more preferably 65% ​​or more, even more preferably 75% or more, and particularly preferably 85% or more. From the viewpoint of satisfying basic filtration performance, under the measurement conditions described in the examples, the cylindrical filter preferably has a filtration life of 100 liters or more, more preferably 150 liters or more, even more preferably 250 liters or more, and even more preferably 350 liters or more.

[0117] From the viewpoint of superior long-term usability, under the measurement conditions described in the examples, the tubular filter is more preferably 800 liters or more, even more preferably 950 liters or more, and particularly preferably 1000 liters or more. On the other hand, from the viewpoint of reliably capturing finer foreign matter than a cylindrical filter, or in other words, obtaining a cylindrical filter with higher filtration accuracy, it is preferable that the filtration accuracy for particles with a particle size of 1.0 μm be 80% or higher, more preferably 85% or higher, and particularly preferable 90% or higher. Furthermore, in this case, since a longer filtration life is preferable for long-term usability, it is preferable that the filtration life be 300 liters or higher, more preferably 350 liters or higher, particularly preferable 400 liters or higher, and most preferably 420 liters or higher.

[0118] In a cylindrical filter with a long filtration life, the first fiber sheet preferably has an average fiber diameter d1 of 2.6 μm or more and 10 μm or less, more preferably 2.8 μm or more and 7.0 μm or less, even more preferably greater than 3.0 μm and 6.0 μm or less, and particularly preferably greater than 3.40 μm and 5.5 μm or less. This makes it easier to extend the filtration life while maintaining the basic performance of the cylindrical filter.

[0119] From the viewpoint of further improving filtration accuracy, the cylindrical filter is more preferably 85% or higher for particles with a particle size of 1.0 μm, even more preferably 87% or higher, even more preferably 90% or higher, and particularly preferably 95% or higher. Furthermore, from the viewpoint of further improving filtration accuracy, the cylindrical filter is more preferably 60% or higher for particles with a particle size of 0.5 μm, even more preferably 65% ​​or higher, even more preferably 70% or higher, and particularly preferably 80% or higher.

[0120] In a cylindrical filter with high filtration accuracy, the first fiber sheet preferably has an average fiber diameter d1 of 0.3 μm or more and 3.40 μm or less, more preferably 0.8 μm or more and 3.2 μm or less, even more preferably 1.0 μm or more and 3.0 μm or less, and particularly preferably 1.2 μm or more and 3.0 μm or less. This makes it easier to improve filtration accuracy while maintaining the basic performance of the cylindrical filter.

[0121] Figure 1 is a schematic partial cross-sectional perspective view of one example of a cylindrical filter according to the present invention. As shown in Figure 1, the cylindrical filter 1 includes a filter core material 3, a filtration layer 4, and an outer layer 5, arranged in order from the hollow portion 2 side toward the outer circumference of the cylindrical filter 1, starting from the hollow portion 2 side located in the center of the cylindrical filter 1. The filtration layer 4 includes a tubular fiber aggregate A (4a) and a tubular fiber aggregate B (4b).

[0122] Figure 2 is a schematic partial cross-sectional perspective view of another example of a cylindrical filter of the present invention. As shown in Figure 2, the cylindrical filter 100 includes a core material 3, a filtration layer 40, and an outer layer 5, arranged sequentially from the hollow portion 2 side toward the outer circumference of the cylindrical filter 100, starting from the hollow portion 2 side located in the center of the cylindrical filter 100. The filtration layer 40 includes tubular fiber aggregates A (4a) and B (4b), as well as an additional tubular fiber aggregate X (4x).

[0123] Figure 3 is a schematic partially broken cross-sectional perspective view of one example of a cylindrical filter of the present invention. As shown in Figure 3, the cylindrical filter 200 includes a core material 3, a filtration layer 240, and an outer layer 5, arranged sequentially from the hollow portion 2 side toward the outer circumference of the cylindrical filter 200, starting from the hollow portion 2 side located in the center of the cylindrical filter 200. The filtration layer 240 includes a tubular fiber aggregate A (4a) and a tubular fiber aggregate B (4b), as well as a tubular fiber aggregate C (4c). Includes.

[0124] Figure 4 is a schematic partially broken cross-sectional perspective view of another example of a cylindrical filter of the present invention. As shown in Figure 4, the cylindrical filter 300 includes a core material 3, a filtration layer 340, and an outer layer 5, arranged sequentially from the hollow portion 2 side toward the outer circumference of the cylindrical filter 300, from the hollow portion 2 side located in the center of the cylindrical filter 300. The filtration layer 340 includes tubular fiber aggregates A (4a), B (4b), X (4x), and C (4c), in addition to a tubular fiber aggregate R (4r).

[0125] Figure 5 is a schematic partial longitudinal cross-sectional view of one example of a tubular fiber assembly A of the present invention. As shown in Figure 5, the tubular fiber assembly A (4a) is made up of a first fiber sheet (41a) and a second fiber sheet (42a) wound alternately in a tubular shape, and in the thickness direction of the tubular fiber assembly A (filtration layer), the first fiber sheet (41a) and the second fiber sheet (42a) are arranged alternately, and the first fiber sheets (41a) are bonded to each other, in other words, the first fiber sheet (41a) and the first fiber sheet (41a) wound one turn before it are bonded to each other via the second fiber sheet (42a) wound one turn before it. The first fiber sheet 41a may be a multilayer fiber sheet containing two or more layers of fiber sheets.

[0126] Figure 6 is a schematic partial longitudinal cross-sectional view of a tubular fiber assembly B, an example of the present invention. As shown in Figure 6, the tubular fiber assembly B (4b) is formed by alternately winding a third fiber sheet (41b) and a fourth fiber sheet (42b) in a tubular shape. In the thickness direction of the tubular fiber assembly B (filtration layer), the third fiber sheet (41b) and the fourth fiber sheet (42b) are arranged alternately, and the third fiber sheets (41b) are bonded to each other, in other words, a third fiber sheet (41b) and a third fiber sheet (41b) wound one turn before it are bonded via the fourth fiber sheet (42b) wound one turn before it. The third fiber sheet 41b may be a multilayer fiber sheet containing two or more fiber sheets.

[0127] Figure 7 is a schematic partial longitudinal cross-sectional view of a tubular fiber assembly C according to one example of the present invention. As shown in Figure 7, the tubular fiber assembly C(4c) is made up of a fifth fiber sheet 41c and a sixth fiber sheet 42c that are alternately wound in a tubular shape. In the thickness direction of the tubular fiber assembly C (filtration layer), the fifth fiber sheet 41c and the sixth fiber sheet 42c are arranged alternately, and the fifth fiber sheets 41c are bonded to each other, or in other words, the fifth fiber sheet 41c and the fifth fiber sheet 41c wound one turn before it are bonded to each other via the sixth fiber sheet 42c wound one turn before it.

[0128] Figure 8 is a schematic partial cross-sectional perspective view of one example of a tubular filter according to the present invention. As shown in Figure 8, the first fiber sheet (41a) has a fold 6a in the longitudinal direction of the tubular filter 1.

[0129] Figure 9 is a schematic partial cross-sectional perspective view of one example of a tubular filter according to the present invention. As shown in Figure 9, the third fiber sheet (41b) has a fold 6b in the longitudinal direction of the tubular filter 1.

[0130] Figure 10 is a schematic partial cross-sectional perspective view of one example of a tubular filter according to the present invention. As shown in Figure 9, the fifth fiber sheet (41c) has a fold 6c in the longitudinal direction of the tubular filter 200.

[0131] (Manufacturing method for cylindrical filters) The method for manufacturing a cylindrical filter is not particularly limited, but from the viewpoint of increasing productivity and reducing production costs, it is preferable to include the following steps A and B. Process A: While extruding molten thermoplastic resin from the discharge hole of a spinning nozzle and simultaneously blowing meltblown fibers A, which have been stretched by a high-temperature gas flow ejected from around the discharge hole, onto the surface of a rotating shaft that rotates at a constant speed, a first fiber sheet is wound around the surface of the rotating shaft, and the meltblown fibers A are accumulated on the surface of the first fiber sheet to form a meltblown web A, which is then wound around the shaft to obtain a tubular fiber assembly A in which the first fiber sheet and the meltblown web A are wound alternately. Step B: While extruding molten thermoplastic resin from the discharge hole of a spinning nozzle, and simultaneously blowing meltblown fibers B, which have been stretched by a high-temperature gas flow ejected from around the discharge hole, onto the surface of a rotating shaft that rotates at a constant speed, a third fiber sheet is wound around the surface of the tubular fiber assembly A, and the meltblown fibers B are accumulated on the surface of the third fiber sheet to form a meltblown web B, and wound around, thereby obtaining a tubular fiber assembly B in which the third fiber sheet and the meltblown web B are wound alternately.

[0132] Steps A and B are preferably carried out by arranging the first fiber sheet and the third fiber sheet in parallel in the width direction, winding the first fiber sheet onto the surface of the rotating shaft, and then winding the third fiber sheet. A gap is not required between the first fiber sheet and the third fiber sheet, but by providing a gap between the first fiber sheet and the third fiber sheet, a tubular fiber assembly X in which the meltblown fibers are accumulated in a tubular shape may be formed between the tubular fiber assembly A and the tubular fiber assembly B. A multilayer fiber sheet containing two or more fiber sheets, that is, a multilayer fiber sheet made by stacking two or more fiber sheets, may be used as the first fiber sheet and / or the third fiber sheet.

[0133] The method for manufacturing a cylindrical filter may further include a step (step C) in which a fifth fiber sheet is wound around the surface of the cylindrical fiber assembly B, while simultaneously discharging molten thermoplastic resin from the discharge hole of a spinning nozzle and blowing meltblown fibers C, which have been stretched by a high-temperature gas flow ejected from around the discharge hole, onto the surface of a rotating shaft that rotates at a constant speed, and accumulating the meltblown fibers C on the surface of the fifth fiber sheet to form a meltblown web C, thereby obtaining a cylindrical fiber assembly C in which the fifth fiber sheet and the meltblown web C are wound alternately.

[0134] It is preferable that steps A, B, and C are carried out by arranging the first fiber sheet, the third fiber sheet, and the fifth fiber sheet in parallel in the width direction, winding the first fiber sheet around the surface of the rotating shaft, winding the third fiber sheet after winding the first fiber sheet, and winding the fifth fiber sheet after winding the third fiber sheet. It is not necessary to leave gaps between the first fiber sheet, the third fiber sheet, and the fifth fiber, and gaps may be left between the first fiber sheet and the second fiber sheet, and between the first fiber sheet and the second fiber sheet to form a tubular fiber assembly X in which the meltblown fibers are accumulated in a tubular shape between tubular fiber assembly A and tubular fiber assembly B, and a tubular fiber assembly R in which the meltblown fibers are accumulated in a tubular shape between tubular fiber assembly B and tubular fiber assembly C.

[0135] The method for manufacturing a cylindrical filter more preferably includes at least one of the following steps Y and Z in addition to steps A and B, or steps A, C and C, and even more preferably both. Step Y: A step prior to step A, in which melted thermoplastic resin is discharged from the discharge hole of a spinning nozzle, and at the same time, meltblown fibers stretched by a high-temperature gas flow ejected from around the discharge hole are sprayed onto the surface of a rotating shaft that rotates at a constant speed, forming a meltblown web while being wound, to obtain a tubular fiber assembly Y. Step Z: A step following Step B or Step C, in which molten thermoplastic resin is discharged from the discharge hole of a spinning nozzle, and at the same time, meltblown fibers stretched by a high-temperature gas flow ejected from around the discharge hole are sprayed onto the surface of a rotating shaft (more specifically, tubular fiber assembly B or tubular fiber assembly C), and the shaft is wound while forming a meltblown web to obtain a tubular fiber assembly Z.

[0136] Specifically, after performing step Y until the thickness of the tubular fiber aggregate Y is 5 mm or more and 15 mm or less, steps A and B, or steps A, B and C may be performed. Alternatively, steps A and B, or steps A, B and C may be performed until the thickness of the filtration layer is 2 mm or more and 12 mm or less, after which step Z may be performed. Step Z may be performed until the thickness of the tubular fiber aggregate Z is 1 mm or more and 6 mm or less.

[0137] The thermoplastic resin is not particularly limited, and any thermoplastic resin capable of constituting the core material, filter layer, and outer layer fibers described above can be used as appropriate. Among these, polyolefin resins are preferred, and polypropylene resins are more preferred, from the viewpoint of cost and high chemical resistance when using a cylindrical filter.

[0138] From the viewpoint of ensuring that the average fiber diameter and / or CV value of the fiber diameter of the tubular fiber assembly Y constituting the core material, the tubular fiber assembly Z constituting the outer layer, the second fiber sheet in the tubular fiber assembly A constituting the filtration layer, the fourth fiber sheet in the tubular fiber assembly B constituting the filtration layer, the sixth fiber sheet in the tubular fiber assembly C constituting the filtration layer, and the tubular fiber assembly X are within the above-mentioned preferred range, the discharge rate per discharge hole of the molten thermoplastic resin is preferably 0.01 g / min or more and 1 g / min or less, more preferably 0.02 g / min or more and 0.6 g / min or less, and even more preferably 0.05 g / min or more and 0.5 g / min or less.

[0139] The rotational speed of the rotating shaft is not particularly limited as long as it is a rotational speed that allows meltblown fibers to accumulate on the surface of the rotating shaft and be wound around to form a tubular fiber aggregate. However, from the viewpoint of facilitating the uniform accumulation of meltblown fibers along the surface of the rotating shaft and making it easier to obtain a tubular fiber aggregate with a smooth surface, it is preferable that the rotational speed is 50 rpm to 400 rpm, more preferably 100 rpm to 300 rpm, and even more preferably 120 rpm to 200 rpm.

[0140] The outer diameter of the rotating shaft can be appropriately determined according to the diameter of the hollow section of the desired cylindrical filter, and is not particularly limited, but is generally 20 mm to 40 mm, 25 mm to 35 mm, or 26 mm to 32 mm.

[0141] The distance from the discharge hole to the surface of the rotating shaft can be adjusted as appropriate depending on the desired core material and outer diameter (thickness) of the outer layer, and is not particularly limited. However, from the viewpoint of productivity of cylindrical filters and the fiber diameter of meltblown fibers manufactured by the meltblown method in cylindrical filters, the distance from the center of the discharge hole to the surface of the rotating shaft is preferably 8 cm or more and 30 cm or less. When the distance from the center of the discharge hole to the surface of the rotating shaft is 8 cm or more, the fibers ejected and stretched from the discharge hole can easily reach the surface of the rotating shaft in a molten state and while maintaining the shape of the fibers, making it easier to obtain the desired fiber aggregate. Furthermore, when the distance from the center of the discharge hole to the surface of the rotating shaft is 30 cm or less, the fibers ejected and stretched from the discharge hole are less likely to deviate from the direction of the rotating shaft due to the influence of the surrounding airflow, making it easier to wind them onto the rotating shaft, and thus improving the productivity (production efficiency, yield) of cylindrical filters. Furthermore, if the distance from the center of the discharge hole to the surface of the rotating shaft is 30 cm or less, the fibers ejected and stretched from the discharge hole are more likely to reach the surface of the rotating shaft before they cool and solidify completely, the fibers wound around the rotating shaft are more likely to heat-bond to each other, the overall strength of the cylindrical filter is not reduced, and deformation of the cylindrical filter due to the pressure of the liquid passing through the cylindrical filter during filtration is suppressed. Preferably, the distance from the center of the discharge hole to the surface of the rotating shaft is 10 cm or more and 28 cm or less, and more preferably 12 cm or more and 25 cm or less.

[0142] Figures 11 to 13 are schematic diagrams illustrating one example of a method for manufacturing a cylindrical filter according to the present invention. One example of a manufacturing apparatus 10 used in these manufacturing methods comprises an extruder 11, a gas heater 12, a spinning nozzle 13, and a rotating shaft 14.

[0143] A gear pump (not shown) supplies the thermoplastic resin to the extruder 11, where the thermoplastic resin is melted and kneaded at a predetermined temperature, and the resulting molten thermoplastic resin is supplied to the spinning nozzle 13. The extruder 11 may be a single-screw extruder or a twin-screw extruder. The melting and kneading temperature is not particularly limited, as long as it is a temperature at which the thermoplastic resin can be melted. For example, if the melting point of the thermoplastic resin is Tm, the melting and kneading temperature (spinning temperature) is preferably Tm+50°C to Tm+200°C, and more preferably Tm+100°C to Tm+180°C. When the thermoplastic resin is polypropylene resin, the melting and kneading temperature (spinning temperature) is preferably 200°C to 350°C, and more preferably 250°C to 330°C.

[0144] The gas heater 12 supplies heated gas to the spinning nozzle 13. The heated gas may be heated air or a heated inert gas, but heated air is preferred from a cost standpoint. The temperature of the heated gas may be equal to the temperature of the melting and kneading of the thermoplastic resin. For example, if the melting point of the thermoplastic resin is Tm, the temperature is preferably Tm+10°C to Tm+150°C, more preferably Tm+20°C to Tm+100°C, and particularly preferably Tm+25°C to Tm+60°C. If the thermoplastic resin is polypropylene resin, the temperature of the heated gas is preferably 180°C to 260°C, and more preferably 185°C to 220°C. From the viewpoint of stably extruding the molten resin and reducing variations in performance and various physical properties of the fibers produced by the meltblown method, the pressure of the heated gas is preferably, for example, 0.02 MPa to 0.1 MPa, and more preferably 0.03 MPa to 0.08 MPa.

[0145] As the spinning nozzle 13, one used for general meltblown fiber production can be used as appropriate. The spinning nozzle 13 is equipped with a plurality of discharge holes for discharging molten thermoplastic resin, and gas injection holes arranged around each discharge hole for blowing high-speed heated gas. The diameter of the discharge holes may be, for example, 0.03 mm to 0.80 mm, 0.06 mm to 0.40 mm, or 0.10 mm to 0.25 mm. The spacing between adjacent discharge holes may be 0.1 mm to 2.0 mm, 0.15 mm to 1.8 mm, or 0.2 mm to 1.6 mm. In the meltblown method, molten thermoplastic resin is discharged from the discharge holes, and at the same time, high-speed heated gas is blown from the gas injection holes to stretch the molten thermoplastic resin, thereby forming the discharged molten thermoplastic resin into fibers and simultaneously stretching them to obtain meltblown fibers 15. Multiple discharge holes may be divided into multiple groups with different hole diameters. In this case, it becomes easier to obtain meltblown fibers 15 having different fiber diameters. Although the diagram shows only one spinning nozzle 13, two or more may be provided. Furthermore, the size and spacing of the discharge holes within a single nozzle may be changed as appropriate. Additionally, conditions such as spinning temperature and discharge volume may also be changed as appropriate.

[0146] A general-purpose mandrel or similar can be used as the rotating shaft 14.

[0147] In the manufacturing method 1 shown in Figure 11, first, meltblown fibers 15 are accumulated in a cylindrical shape on the surface of a rotating shaft 14 that rotates at a constant speed for a predetermined time to form a tubular fiber assembly Y (core material 3) having a predetermined outer diameter (thickness). The tubular fiber assembly Y (3) may include fiber bundles formed by bonding multiple meltblown fibers together in the longitudinal direction of the fibers. In the tubular fiber assembly Y, the meltblown fibers are bonded to each other in the circumferential direction and thickness direction of the tubular filter.

[0148] Next, while winding the first fiber sheet 41a onto the tubular fiber assembly Y(3), meltblown fibers 15 are discharged toward the surface of the first fiber sheet 41a, accumulating the meltblown fibers 15 on the surface of the first fiber sheet 41a while simultaneously winding. This causes the first fiber sheet 41a and meltblown webs (not shown) made of meltblown fibers 15 to be arranged alternately, forming a tubular fiber assembly A(4a) wound in a cylindrical shape. As shown in Figure 5, the meltblown webs made of meltblown fibers 15 accumulated on the surface of the first fiber sheet 41a become second fiber sheets 42a, and adjacent first fiber sheets 41a in the thickness direction are bonded together via the second fiber sheets 42a positioned between them. A tubular fiber aggregate A(4a) can be formed by accumulating meltblown fibers 15 on the surface of the first fiber sheet 41a, preferably a strip-shaped nonwoven fabric 41a, while spirally winding the meltblown fibers 15 so that they partially overlap in the width direction.

[0149] Simultaneously, the first fiber sheet 41a and the third fiber sheet 41b, which are placed parallel to each other in the width direction at a predetermined interval, are wound onto the surface of the rotating shaft, and then the meltblown fibers 15 are discharged toward the surface of the third fiber sheet 41b while winding the first fiber sheet onto the surface of the tubular fiber assembly A(4a). By accumulating the meltblown fibers 15 on the surface of the third fiber sheet 41b while winding, the third fiber sheet 41b and the meltblown web (not shown) made of meltblown fibers 15 are arranged alternately, forming a tubular fiber assembly B(4b) wound in a cylindrical shape. As shown in Figure 6, the meltblown web made of meltblown fibers 15 accumulated on the surface of the third fiber sheet 41b becomes the fourth fiber sheet 42b, and adjacent third fiber sheets 41b in the thickness direction are bonded together via the fourth fiber sheet 42b positioned between them. A tubular fiber aggregate B(4b) can be formed by accumulating meltblown fibers 15 on the surface of the third fiber sheet 41b, preferably a strip-shaped nonwoven fabric 41b, while spirally winding the meltblown fibers 15 so that they partially overlap in the width direction.

[0150] Furthermore, by providing a predetermined gap (for example, 10 mm to 70 mm, 20 mm to 50 mm, or 30 mm to 40 mm) between the first fiber sheet 41a and the third fiber sheet 41b, which are installed in parallel in the width direction, a tubular fiber assembly X (not shown) is formed in the thickness direction between the tubular fiber assembly A (4a) and the tubular fiber assembly B (4b), in which meltblown fibers 15 are accumulated in a tubular shape. The tubular fiber assembly X may include fiber bundles formed by bonding multiple meltblown fibers in the longitudinal direction of the fibers. In the tubular fiber assembly X, the meltblown fibers are bonded to each other in the circumferential direction and the thickness direction of the tubular filter. Note that if no gap is provided between the first fiber sheet 41a and the third fiber sheet 41b, which are installed in parallel in the width direction, tubular fiber assembly A (4a) and tubular fiber assembly B (4b) are formed, and tubular fiber assembly X is not formed.

[0151] Figure 8 is a schematic diagram illustrating the arrangement relationship between the core material and the filtration layer of one example of the present invention. As shown in Figure 8, it is preferable to form a tubular fiber assembly A(4a) by winding a first fiber sheet (preferably a strip-shaped nonwoven fabric) 41a around a tubular fiber assembly Y(3) so that they partially overlap in the width direction, and accumulating meltblown fibers on its surface to form a second fiber sheet (not shown). As a result, the first fiber sheet (preferably a strip-shaped nonwoven fabric) 41a is wound in the longitudinal direction of the tubular filter at predetermined widths, for example, 0.5 to 10 mm at a time in the direction of arrow 16, more preferably 0.6 to 5 mm at a time, and particularly preferably 0.8 to 3 mm at a time, forming a tubular fiber assembly A(4a) that includes a spirally overlapping first fiber sheet (preferably a strip-shaped nonwoven fabric) 41a and a second fiber sheet made of meltblown fibers accumulated on its surface, thereby improving the filtration accuracy of the tubular filter. The second fiber sheet may include a fiber bundle formed by bonding multiple meltblown fibers together in the longitudinal direction of the fibers. It is also preferable to wind the first fiber sheet (preferably a strip-shaped nonwoven fabric) 41a around the tubular fiber assembly Y(3) while creating winding creases 6a along the longitudinal direction of the tubular filter on the first fiber sheet (preferably a strip-shaped nonwoven fabric) 41a. As a result, as shown in Figure 8, the first fiber sheet (preferably a strip-shaped nonwoven fabric) 41a will have winding creases 6a in the longitudinal direction of the tubular filter, and no longitudinal voids will be created between the first fiber sheets (preferably a strip-shaped nonwoven fabric) 41a constituting the tubular fiber assembly A, thereby improving both filtration accuracy and filtration life simultaneously.

[0152] Figure 9 is a schematic diagram illustrating the arrangement relationship between the core material and the filtration layer of one example of the present invention. As shown in Figure 9, it is preferable to form a tubular fiber assembly A(4a) on the outside of a tubular fiber assembly Y(3), and then form a tubular fiber assembly A(4b) by winding a third fiber sheet (preferably a strip-shaped nonwoven fabric) 41b around the tubular fiber assembly A(4a) so that it partially overlaps in the width direction, and accumulating meltblown fibers on its surface to form a fourth fiber sheet (not shown). As a result, the third fiber sheet (preferably a strip-shaped nonwoven fabric) 41b is wound around the tubular filter at predetermined widths in the longitudinal direction, for example, 0.5 to 10 mm in the direction of arrow 16, more preferably 0.6 to 5 mm, and particularly preferably 0.8 to 3 mm, to form a tubular fiber assembly B(4b) including a fourth fiber sheet made of spirally overlapping third fiber sheets (preferably a strip-shaped nonwoven fabric) 41b and meltblown fibers accumulated on its surface, thereby improving the filtration accuracy of the tubular filter. The fourth fiber sheet may include fiber bundles formed by bonding multiple meltblown fibers in the longitudinal direction of the fibers. It is also preferable to wind the third fiber sheet (preferably a strip-shaped nonwoven fabric) 41b around the tubular fiber assembly A(4a) while creating winding creases 6b along the longitudinal direction of the tubular filter on the third fiber sheet 41b. As a result, as shown in Figure 9, the third fiber sheet (preferably a strip-shaped nonwoven fabric) 41b has folds 6b in the longitudinal direction of the tubular filter, preventing longitudinal voids from forming between the nonwoven fabrics 41b constituting the tubular fiber assembly B, thereby simultaneously improving filtration accuracy and filtration life.

[0153] Next, meltblown fibers 15 are discharged toward the surface of the tubular fiber assembly B(4b) to accumulate and simultaneously wind the meltblown fibers 15 onto the surface of the tubular fiber assembly B(4b). By performing this continuously for a predetermined time, a tubular fiber assembly Z(5) having a predetermined outer diameter is formed. The tubular fiber assembly Z(5) may include fiber bundles formed by bonding multiple meltblown fibers together in the longitudinal direction of the fibers. In the tubular fiber assembly Z(5), the meltblown fibers are bonded to each other in the circumferential and thickness directions of the tubular filter.

[0154] The tubular fiber aggregates Y(3), A(4a), X(not shown), B(4b), and Z(5), which are accumulated in a cylindrical shape on the surface of the rotating shaft 14, move away from the rotating shaft 14 by moving in the direction of arrow 16. Next, a tubular filter can be obtained by cutting the resulting cylindrical object to a predetermined length.

[0155] In the case of manufacturing method 2 shown in Figure 12, tubular fiber aggregates Y(3), A(4a), and B(4b) are formed in the same manner as in manufacturing method 1. Simultaneously with the formation of tubular fiber aggregate B(4b), the fifth fiber sheet 41c, which is placed in parallel with the third fiber sheet 41b at a predetermined interval, is wound onto the surface of tubular fiber aggregate B(4b) while meltblown fibers 15 are discharged toward the surface of the fifth fiber sheet 41c, accumulating the meltblown fibers 15 on the surface of the fifth fiber sheet 41c while simultaneously winding. This results in the alternating arrangement of the fifth fiber sheet 41c and meltblown webs (not shown) made of meltblown fibers 15, forming a tubular fiber aggregate C(4c) wound in a cylindrical shape. As shown in Figure 7, a meltblown web consisting of meltblown fibers 15 accumulated on the surface of a fifth fiber sheet 41c becomes a sixth fiber sheet 42c, and adjacent fifth fiber sheets 41c in the thickness direction are bonded together via the sixth fiber sheet 42c positioned between them. A tubular fiber aggregate B(4b) can be formed by accumulating meltblown fibers 15 on the surface of a third fiber sheet 41b while spirally winding a fifth fiber sheet 41c, preferably a strip-shaped nonwoven fabric 41c, so that they partially overlap in the width direction.

[0156] Furthermore, by providing a predetermined gap (for example, 10 mm to 70 mm, 20 mm to 50 mm, or 30 mm to 40 mm) between the third fiber sheet 41b and the fifth fiber sheet 41c, which are installed in parallel in the width direction, a tubular fiber assembly R (not shown) is formed in the thickness direction between the tubular fiber assembly B (4b) and the tubular fiber assembly C (4c), in which meltblown fibers 15 are accumulated in a tubular shape. The tubular fiber assembly R may include fiber bundles formed by bonding multiple meltblown fibers together in the longitudinal direction of the fibers. In the tubular fiber assembly R, the meltblown fibers are bonded to each other in the circumferential direction and the thickness direction of the tubular filter. Note that if no gap is provided between the third fiber sheet 41b and the fifth fiber sheet 41c, which are installed in parallel in the width direction, tubular fiber assemblies B (4b) and C (4c) are formed, and tubular fiber assembly R is not formed.

[0157] Next, meltblown fibers 15 are discharged toward the surface of the tubular fiber assembly C(4c), thereby accumulating and winding the meltblown fibers 15 onto the surface of the tubular fiber assembly C(4c). By performing this continuously for a predetermined time, a tubular fiber assembly Z(5) having a predetermined outer diameter is formed. The tubular fiber assembly Z(5) may include fiber bundles formed by bonding multiple meltblown fibers together in the longitudinal direction of the fibers. In the tubular fiber assembly Z(5), the meltblown fibers are bonded to each other in the circumferential and thickness directions of the tubular filter.

[0158] The tubular fiber aggregates Y(3), A(4a), X(not shown), B(4b), C(4b), R(not shown), and Z(5), which are piled up in a cylindrical shape on the surface of the rotating shaft 14, move away from the rotating shaft 14 by moving in the direction of arrow 16. Next, a tubular filter can be obtained by cutting the resulting cylindrical material to a predetermined length.

[0159] In the case of manufacturing method 3 shown in Figure 13, a cylindrical filter can be manufactured in the same manner as in manufacturing method 1, except that a multilayer fiber sheet (2-layer sheet) in which fiber sheet I and fiber sheet II are laminated is used as the first fiber sheet 41b, that is, the first layer fiber sheet (411) and the second layer fiber sheet (412) are stacked and supplied as the first fiber sheet 41b.

[0160] Cylindrical filters are suitable for various applications of removing solids from liquids and can be used to filter liquids such as pure water, drinking water, chemicals, various oils and fats, plating solutions, paint solutions, and cleaning water for the electronics industry. [Examples]

[0161] The present invention will be described in detail below with reference to examples. The present invention is not limited to the following examples.

[0162] The measurement methods used in the examples and comparative examples will be explained.

[0163] (Thickness) The thickness of the fiber sheets or tubular fiber assemblies was measured under a load of 3g. In the filtration layer, the first and second fiber sheets were measured after cutting the tubular filter longitudinally and unfolding it, peeling off tubular fiber assembly A, taking a sample of the area around which they were bonded together, and then carefully separating the first and second fiber sheets using tweezers or similar tools to avoid tearing them, after which their respective thicknesses were measured. Similarly, in the filtration layer, the third and fourth fiber sheets were measured after cutting the tubular filter longitudinally and unfolding it, peeling off tubular fiber assembly B, taking a sample of the area around which they were bonded together, and then carefully separating the third and fourth fiber sheets using tweezers or similar tools to avoid tearing them, after which their respective thicknesses were measured. Furthermore, in the filtration layer, the fifth and sixth fiber sheets were measured by cutting the cylindrical filter longitudinally and unfolding it, peeling off the cylindrical fiber assembly C, taking a sample of the combined circumference, and then carefully separating the fifth and sixth fiber sheets using tweezers or similar tools to avoid tearing them, after which the thickness of each was measured. In addition, if the first, third, or fifth fiber sheet was a multilayer fiber sheet, the multilayer fiber sheet was separated into individual single-layer fiber sheets, and then the thickness of each single-layer fiber sheet was measured.

[0164] (Inspector) The basis weight of the fiber sheets or tubular fiber assemblies was measured from the area and weight of rectangular samples taken at any size. In the filtration layer, the basis weight of the first and second fiber sheets was measured after cutting the tubular filter lengthwise, unfolding it, peeling off tubular fiber assembly A, taking a sample of one full circle where they were bonded together, and then carefully separating the first and second fiber sheets using tweezers or similar tools to avoid tearing them. Similarly, in the filtration layer, the basis weight of the third and fourth fiber sheets was measured after cutting the tubular filter lengthwise, unfolding it, peeling off tubular fiber assembly B, taking a sample of one full circle where they were bonded together, and then carefully separating the third and fourth fiber sheets using tweezers or similar tools to avoid tearing them. Furthermore, in the filtration layer, the fifth and sixth fiber sheets were measured by cutting the cylindrical filter lengthwise and unfolding it, peeling off the cylindrical fiber assembly C, taking a sample of the combined circumference, and then carefully separating the fifth and sixth fiber sheets using tweezers or similar tools to avoid tearing them, after which the basis weight of each was measured. In addition, if the first, third, or fifth fiber sheet was a multilayer fiber sheet, the multilayer fiber sheet was separated into its respective single-layer fiber sheet, and then the basis weight of each single-layer fiber sheet was measured.

[0165] (density) The density of the fiber sheet or tubular fiber aggregate was calculated based on the thickness and basis weight measured as described above. Density = Basis weight / Thickness

[0166] (Measurement of average fiber diameter and CV value of fiber diameter) The average fiber diameter and CV value of the fiber diameter of fiber aggregates (fiber sheets and tubular fiber aggregates) were determined by observing the fiber aggregates under magnification using a scanning electron microscope (Hitachi High-Technologies AMETEK Japan, model number "SU3500", acceleration voltage: 5.00kV, magnification: 200x to 400x). Ten photographs obtained were analyzed using image analysis software (ClickMeasure), and the fiber diameters of 100 arbitrarily selected fibers were measured. The arithmetic mean of these measurements was taken as the average fiber diameter. The standard deviation of the fiber diameters of these 100 arbitrarily selected fibers was then calculated as the population, and the CV value of the fiber diameter was calculated using the following formula. CV value of fiber diameter = Standard deviation of fiber diameter / Average fiber diameter

[0167] (Average pore size, maximum pore size, maximum pore size and minimum pore size) In accordance with JIS K 3832 (1990) (Test method for bubble point of precision filtration membrane elements and modules), the pore size of fiber aggregates (fiber sheets and tubular fiber aggregates) was measured using the "CFP-1200-AEXC-P" capillary flow porometer manufactured by Porous Material Inc.

[0168] (Air permeability) Measurements were taken using a Frazier type testing machine in accordance with JIS L 1913.

[0169] (Filtration accuracy) A water dispersion of test dust conforming to JIS Z 8901 (JIS Type 11 test powder [median diameter 2 μm]) was prepared to a concentration of 10 ppm and used as the test suspension. The test suspension was filtered by passing it through a cylindrical filter at a flow rate of 15 liters / minute from the outside towards the hollow part while stirring to ensure uniform concentration. The number of 0.5 μm, 1.0 μm, and 3.0 μm powders (particles) contained in the test suspension before filtration was determined. 0.5 M1 and M3 represent the number of powders (particles) with particle sizes of 0.5 μm, 1.0 μm, and 3.0 μm contained in the test suspension that passed through the cylindrical filter 1 minute after the start of filtration, respectively. 0.5 N1 and N3 were measured using a precision particle size distribution device (product name: Multisizer 4e, manufactured by Beckman Coulter, Inc.), and the filtration accuracy was determined using the following formula. • Filtration accuracy (%) for particles with a particle size of 0.5 μm = [(M 0.5 -N 0.5 ) / M 0.5 ]×100 • Filtration accuracy (%) for particles with a particle size of 1.0 μm = [(M1-N1) / M1] × 100 • Filtration accuracy (%) for particles with a particle size of 3.0 μm = [(M3-N3) / M3] × 100

[0170] (Filtration lifespan) A test suspension with a concentration of 30 ppm was prepared by dispersing a test powder conforming to JIS Z 8901 (JIS Type 11 test powder [medium diameter 2 μm]) in water. Next, the test suspension was passed through a cylindrical filter at a flow rate of 15 liters / minute, from the outer circumference to the inner hollow section, while uniformly stirring. Test powder was added every 13.5 minutes to maintain a concentration of 15 ppm. The total volume of water passed through (liters) when the water pressure required to maintain this flow rate reached 0.2 MPa was defined as the filtration life of the cylindrical filter. In Examples 7 and 8, the total volume of water passed through (liters) when the water pressure reached 0.02 MPa was defined as the filtration life of the cylindrical filter, and in Example 22, the total volume of water passed through (liters) when the water pressure reached 0.012 MPa was defined as the filtration life of the cylindrical filter.

[0171] (Mass ratio of cylindrical filters) When the filtration layer consists of tubular fiber aggregate A, tubular fiber aggregate X, and tubular fiber aggregate B, the measurements were taken as follows. A cylindrical filter was prepared, and the total mass of the core material, filter layer, and outer layer was first measured using an electronic balance. Next, an incision was made in the thickness direction of the cylindrical filter to prevent fibers from scattering, and the outer layer was peeled off the cylindrical filter until a third fiber sheet (specifically, nonwoven fabric) was revealed. Once the entire side surface was made of nonwoven fabric, the process of separating and recovering the outer layer was completed. The fibers that made up the outer layer that had been peeled off the cylindrical filter up to that point were collected and their mass was weighed using an electronic balance. Next, the nonwoven fabric, which is the third fiber sheet wound around the tubular filter, was peeled off. Once the nonwoven fabric had been completely removed, the tubular fiber assembly B was separated and recovered, and the mass of the nonwoven fabric and fibers constituting the tubular fiber assembly B was measured. Next, the tubular fiber assembly X was peeled off the tubular filter, taking care not to scatter the fibers, until the first fiber sheet (specifically, nonwoven fabric) was revealed. Once the entire side surface was made of nonwoven fabric, the separation and recovery of the tubular fiber assembly X was completed. The fibers that had been peeled off up to that point were collected, and their mass was weighed using an electronic balance. Next, the nonwoven fabric, which is the first fiber sheet wound around the tubular filter, was peeled off. Once the nonwoven fabric had been peeled off, the tubular fiber assembly A was separated and recovered, and the mass of the nonwoven fabric and fibers constituting the tubular fiber assembly A was measured. The mass of the core material was measured after the outer layer C and the filtration layer were removed from the cylindrical filter. Based on the measured total mass of the core material, filter layer, and outer layer, and the mass of each layer, the mass ratio of each layer was calculated. Furthermore, if a heat-bonded nonwoven fabric is wrapped around the outside of the outer layer of a cylindrical filter, the heat-bonded nonwoven fabric should be removed before measuring the total mass of the core material, filtration layer, and outer layer. When the filtration layer consists of tubular fiber aggregates A, X, B, R, and C, the measurements were taken as follows. A cylindrical filter was prepared, and the total mass of the core material, filter layer, and outer layer was first measured using an electronic balance. Next, an incision was made in the thickness direction of the cylindrical filter to prevent fibers from scattering, and the outer layer was peeled off the cylindrical filter until the fifth fiber sheet (specifically, nonwoven fabric) was revealed. Once the entire side surface was made of nonwoven fabric, the process of separating and recovering the outer layer was completed. The fibers constituting the outer layer that had been peeled off the cylindrical filter up to that point were collected and their mass was weighed using an electronic balance. Next, the nonwoven fabric, which is the fifth fiber sheet wound around the tubular filter, was peeled off. Once the nonwoven fabric had been peeled off, the tubular fiber assembly C was separated and recovered, and the mass of the nonwoven fabric and fibers constituting the tubular fiber assembly C was measured. Next, the tubular fiber aggregate R was peeled off the tubular filter, taking care not to scatter the fibers, until a third fiber sheet (specifically, nonwoven fabric) was revealed. Once the entire side surface was made of nonwoven fabric, the separation and recovery of the tubular fiber aggregate R was completed. The fibers that had been peeled off up to that point were collected, and their mass was weighed using an electronic balance. Next, the nonwoven fabric, which is the third fiber sheet wound around the tubular filter, was peeled off. Once the nonwoven fabric had been completely removed, the tubular fiber assembly B was separated and recovered, and the mass of the nonwoven fabric and fibers constituting the tubular fiber assembly B was measured. Next, the tubular fiber assembly X was peeled off the tubular filter, taking care not to scatter the fibers, until the first fiber sheet (specifically, nonwoven fabric) was revealed. Once the entire side surface was made of nonwoven fabric, the separation and recovery of the tubular fiber assembly X was completed. The fibers that had been peeled off up to that point were collected, and their mass was weighed using an electronic balance. Next, the nonwoven fabric, which is the first fiber sheet wound around the tubular filter, was peeled off. Once the nonwoven fabric had been peeled off, the tubular fiber assembly A was separated and recovered, and the mass of the nonwoven fabric and fibers constituting the tubular fiber assembly A was measured. The mass of the core material was measured after the outer layer C and the filtration layer were removed from the cylindrical filter. Based on the measured total mass of the core material, filter layer, and outer layer, and the mass of each layer, the mass ratio of each layer was calculated. Furthermore, if a heat-bonded nonwoven fabric is wrapped around the outside of the outer layer of a cylindrical filter, the heat-bonded nonwoven fabric should be removed before measuring the total mass of the core material, filtration layer, and outer layer.

[0172] (Air pressure loss) Air was introduced into a cylindrical filter, and the pressure difference (pressure loss (MPa)) between the inlet and outlet of the cylindrical filter was measured when the airflow rate was 400 liters / minute. This was defined as the airflow pressure loss.

[0173] (Example 1) A cylindrical filter was manufactured using the method shown in Figure 11. Specifically, polypropylene resin (melting point 160°C, melt flow rate conforming to JIS K 7210 (measurement temperature 230°C, load 2.16 kgf (21.18 N)) 30 g / 10 min) was melted and kneaded in an extruder at a spinning temperature of 330°C, and the molten polypropylene resin was supplied to the spinning nozzle. The mandrel 14 was positioned on the extension of the discharge direction of the discharge holes of the spinning nozzle, and the longitudinal direction of the mandrel was positioned obliquely to the row of discharge holes of the spinning nozzle. The mandrel 14 had a diameter (outer diameter) of 28 mm and a rotation speed of 150 rpm. The spinning nozzle had 300 discharge holes arranged at 1.0 mm intervals. Each discharge hole had a diameter of 0.3 mm. Molten polypropylene resin was discharged from the discharge holes at a rate of 0.25 g / min per hole. Simultaneously, heated air at a temperature of 200°C and a pressure of 0.015 MPa was blown in from gas injection holes positioned around the discharge holes to transform the molten polypropylene resin into fibers. The resulting meltblown fibers 15 were then accumulated on the surface of the front of the mandrel and continuously wound around it. This process of accumulating and winding the meltblown fibers for a predetermined time resulted in a core material 3 (thickness 9.2 mm) consisting of a tubular fiber aggregate Y. Subsequently, two 40mm wide meltblown nonwoven fabrics I are used as the first fiber sheet 41a and the third fiber sheet 41b, respectively. The first fiber sheet 41a and the third fiber sheet 41b are placed parallel to each other in the width direction (with a spacing of 30-50mm). As shown in Figure 11, the meltblown fibers are supplied to the core material 3 from the opposite direction to the direction in which the meltblown fibers are discharged from the mandrel (in other words, the direction opposite to the spinning nozzle that discharges the meltblown fibers across the mandrel). The meltblown fibers are wound spirally around the surface of the core material 3, advancing 1-2mm at a time in the direction of arrow 16, so that they partially overlap in the width direction. At the same time, the meltblown fibers 15 are discharged toward the surface of the wound meltblown nonwoven fabric I. By accumulating and simultaneously winding the meltblown fibers 15, a tubular fiber assembly A (thickness 3.1 mm) was formed in which a first fiber sheet (meltblown nonwoven fabric I) and a meltblown web (second fiber sheet) made of meltblown fibers 15 were alternately arranged in the thickness direction; a tubular fiber assembly X (thickness 0.6 mm) was placed outside tubular fiber assembly A (inflow side of the material to be filtered) and in which meltblown fibers 15 were accumulated in a tubular shape; and a tubular fiber assembly B (thickness 2.5 mm) was placed outside tubular fiber assembly X (inflow side of the material to be filtered) and in which a third fiber sheet (meltblown nonwoven fabric I) and a meltblown web (fourth fiber sheet) made of meltblown fibers 15 were alternately arranged in the thickness direction. In a tubular fiber assembly A, in the continuously wound meltblown nonwoven fabric I, meltblown fibers accumulate between adjacent meltblown nonwoven fabrics I in the thickness direction, for example, between the wound meltblown nonwoven fabric I and the meltblown nonwoven fabric I wound one turn before it, forming a meltblown web, which is a second fiber sheet. The first fiber sheets are bonded to each other, that is, the meltblown nonwoven fabric I and the meltblown nonwoven fabric I wound one turn before it, via the second fiber sheet located between them. In the tubular fiber assembly B, in the continuously wound meltblown nonwoven fabric I, meltblown fibers accumulate between adjacent meltblown nonwoven fabrics I in the thickness direction, for example, between the wound meltblown nonwoven fabric I and the meltblown nonwoven fabric I wound one turn before it, forming a meltblown web, which is the fourth fiber sheet. The third fiber sheets are bonded together, that is, the meltblown nonwoven fabric I and the meltblown nonwoven fabric I wound one turn before it, via the fourth fiber sheet located between them. The outer diameter of the cylindrical object composed of the mandrel 14, core material 3, tubular fiber assembly A (4a), tubular fiber assembly X (not shown), and tubular fiber assembly B (4b) was 64.1 mm. Subsequently, meltblown fibers 15 were continuously accumulated on the surface of the tubular fiber assembly B while winding, thereby accumulating the meltblown fibers into a tubular shape and forming an outer layer 5 (thickness: 2.8 mm) consisting of the tubular fiber assembly Z. The resulting cylindrical object was then cut to a length of 250 mm to obtain a tubular filter. The obtained cylindrical filter was disassembled into a core material, a filtration layer (cylindrical fiber assembly A, cylindrical fiber assembly X, cylindrical fiber assembly B), and an outer layer. Each was then observed under magnification of 200 to 400 times using the scanning electron microscope described above. Fiber bundles formed by the fusion of multiple fibers in the longitudinal direction were confirmed in the core material, outer layer, cylindrical fiber assembly X, the second fiber sheet contained in cylindrical fiber assembly A, and the fourth fiber sheet contained in cylindrical fiber assembly B.

[0174] (Example 2) A tubular filter was obtained in the same manner as in Example 1, except that meltblown nonwoven fabric II was used as the third fiber sheet 41b.

[0175] (Example 3) A tubular filter was obtained in the same manner as in Example 1, except that meltblown nonwoven fabric III was used as the third fiber sheet 41b.

[0176] (Example 4) A tubular filter was obtained in the same manner as in Example 1, except that a meltblown nonwoven fabric V was used as the third fiber sheet 41b.

[0177] (Example 5) A tubular filter was obtained in the same manner as in Example 1, except that meltblown nonwoven fabric II was used as the first fiber sheet 41a.

[0178] (Example 6) A tubular filter was obtained in the same manner as in Example 1, except that meltblown nonwoven fabric III was used as the first fiber sheet 41a.

[0179] (Example 7) A tubular filter was obtained in the same manner as in Example 1, except that meltblown nonwoven fabric IV was used as the first fiber sheet 41a.

[0180] (Example 8) A tubular filter was obtained in the same manner as in Example 1, except that a meltblown nonwoven fabric V was used as the first fiber sheet 41a.

[0181] (Example 9) A cylindrical filter was manufactured using the method shown in Figure 12. Specifically, polypropylene resin (melting point 160°C, melt flow rate conforming to JIS K 7210 (measurement temperature 230°C, load 2.16 kgf (21.18 N)) 30 g / 10 min) was melted and kneaded in an extruder at a spinning temperature of 330°C, and the molten polypropylene resin was supplied to the spinning nozzle. The mandrel 14 was positioned on the extension of the discharge direction of the discharge holes of the spinning nozzle, and the longitudinal direction of the mandrel was positioned obliquely to the row of discharge holes of the spinning nozzle. The mandrel 14 had a diameter (outer diameter) of 28 mm and a rotation speed of 150 rpm. The spinning nozzle had 300 discharge holes arranged at 1.0 mm intervals. Each discharge hole had a diameter of 0.3 mm. Molten polypropylene resin was discharged from the discharge holes at a rate of 0.25 g / min per hole. Simultaneously, heated air at a temperature of 200°C and a pressure of 0.015 MPa was blown in from gas injection holes positioned around the discharge holes to transform the molten polypropylene resin into fibers. The resulting meltblown fibers 15 were then accumulated on the surface of the front of the mandrel and continuously wound around it. This process of accumulating and winding the meltblown fibers for a predetermined time resulted in a core material 3 (thickness 9.2 mm) consisting of a tubular fiber aggregate Y. Subsequently, meltblown nonwoven fabrics I, II, and III, each 40 mm wide, were used as the first fiber sheet 41a, the third fiber sheet 41b, and the fifth fiber sheet 41c, respectively. The first fiber sheet 41a, the third fiber sheet 41b, and the fifth fiber sheet 41c were placed in parallel in the width direction (50 mm between the first fiber sheet 41a and the third fiber sheet 41b, and 70 mm between the third fiber sheet 41b and the fifth fiber sheet 41c). As shown in Figure 12, the meltblown fibers were discharged onto the mandrel. The meltblown fibers are supplied to the core material 3 from the opposite direction from the direction of discharge (in other words, the direction opposite to the spinning nozzle that discharges the meltblown fibers across the mandrel), and while advancing 1-2 mm at a time in the direction of arrow 16, they are wound spirally around the surface of the core material 3, and at the same time the meltblown fibers are discharged toward the surface of the wound meltblown nonwoven fabric I, and the meltblown fibers 15 are accumulated on the surface of the meltblown nonwoven fabric I while being wound, thereby forming the first fiber sheet (meltblown nonwoven fabric I) and the meltblown fibers A tubular fiber assembly A (thickness 2.4 mm) is arranged alternately in the thickness direction with meltblown webs (second fiber sheets) made of 15 fibers, a tubular fiber assembly X (thickness 0.5 mm) is placed outside of tubular fiber assembly A (inlet side of the material to be filtered) and is made up of meltblown fibers 15 arranged in a tubular shape, and a third fiber sheet (meltblown nonwoven fabric II) and a meltblown web (fourth fiber sheet) made of meltblown fibers 15 are arranged outside of tubular fiber assembly X (inlet side of the material to be filtered) in the thickness direction. A tubular fiber assembly B (3.0 mm thick) was formed by alternately arranging tubular fiber assemblies B (3.0 mm thick), a tubular fiber assembly R (0.5 mm thick) formed by the accumulation of meltblown fibers 15 in a tubular shape, and a tubular fiber assembly C (2.8 mm thick) formed by alternately arranging a fifth fiber sheet (meltblown nonwoven fabric III) and a meltblown web (sixth fiber sheet) made of meltblown fibers 15 in the thickness direction, located on the outside of tubular fiber assembly R (the inflow side of the material to be filtered). In the tubular fiber assembly A, meltblown fibers accumulate to form a meltblown web between continuously wound meltblown nonwoven fabrics I, that is, between adjacent meltblown nonwoven fabrics I in the thickness direction, for example, between a wound meltblown nonwoven fabric I and a meltblown nonwoven fabric I wound one turn before it, and this meltblown web is the second fiber sheet. The first fiber sheets, that is, the meltblown nonwoven fabric I and the meltblown nonwoven fabric I wound one turn before it, are bonded together via the second fiber sheet located between them. In the tubular fiber assembly B, meltblown fibers accumulate between continuously wound meltblown nonwoven fabrics II, that is, between adjacent meltblown nonwoven fabrics II in the thickness direction, for example, between a wound meltblown nonwoven fabric II and a meltblown nonwoven fabric II wound one turn before it, forming a meltblown web, which is the fourth fiber sheet. The third fiber sheets, that is, the meltblown nonwoven fabric II and the meltblown nonwoven fabric II wound one turn before it, are bonded together via the fourth fiber sheet located between them. In the tubular fiber assembly C, meltblown fibers accumulate between continuously wound meltblown nonwoven fabrics III, that is, between adjacent meltblown nonwoven fabrics III in the thickness direction, for example, between a wound meltblown nonwoven fabric III and a meltblown nonwoven fabric III wound one turn before it, forming a meltblown web, which is the sixth fiber sheet. The fifth fiber sheets, that is, the meltblown nonwoven fabric III and the meltblown nonwoven fabric III wound one turn before it, are bonded together via the sixth fiber sheet located between them. The cylindrical object, composed of a mandrel 14, a core material 3, tubular fiber aggregate A (4a), tubular fiber aggregate X (not shown), tubular fiber aggregate B (4b), tubular fiber aggregate R (not shown), and tubular fiber aggregate C (4c), had an outer diameter of 64.6 mm. Subsequently, meltblown fibers 15 were continuously accumulated on the surface of the tubular fiber assembly C while winding, thereby accumulating the meltblown fibers into a tubular shape and forming an outer layer 5 (thickness: 2.8 mm) consisting of the tubular fiber assembly Z. The resulting cylindrical object was then cut to a length of 250 mm to obtain a tubular filter. The obtained tubular filter was disassembled into a core material, a filtration layer (tubular fiber assembly A, tubular fiber assembly X, tubular fiber assembly B, tubular fiber assembly R, and tubular fiber assembly C), and an outer layer. Each was then observed under magnification of 200 to 400 times using the scanning electron microscope described above. Fiber bundles formed by the fusion of multiple fibers in the longitudinal direction were confirmed in the core material, outer layer, tubular fiber assembly X, the second fiber sheet contained in tubular fiber assembly A, the fourth fiber sheet contained in tubular fiber assembly B, and the sixth fiber sheet contained in tubular fiber assembly C.

[0182] (Example 10) A tubular filter was obtained in the same manner as in Example 9, except that a meltblown nonwoven fabric VI was used as the fifth fiber sheet 41c.

[0183] (Example 11) A tubular filter was obtained in the same manner as in Example 9, except that meltblown nonwoven fabric IV was used as the fifth fiber sheet 41c.

[0184] (Example 12) A tubular filter was obtained in the same manner as in Example 9, except that meltblown nonwoven fabric III was used as the third fiber sheet 41b.

[0185] (Example 13) A tubular filter was obtained in the same manner as in Example 9, except that meltblown nonwoven fabric III was used as the third fiber sheet 41b and meltblown nonwoven fabric IV was used as the fifth fiber sheet 41c.

[0186] (Example 14) A tubular filter was obtained in the same manner as in Example 9, except that meltblown nonwoven fabric III was used as the first fiber sheet 41a, meltblown nonwoven fabric VI was used as the third fiber sheet 41b, and meltblown nonwoven fabric IV was used as the fifth fiber sheet 41c.

[0187] (Example 15) A tubular filter was obtained in the same manner as in Example 9, except that meltblown nonwoven fabric III was used as the first fiber sheet 41a, meltblown nonwoven fabric IV was used as the third fiber sheet 41b, and meltblown nonwoven fabric V was used as the fifth fiber sheet 41c.

[0188] (Example 16) A tubular filter was obtained in the same manner as in Example 9, except that meltblown nonwoven fabric II was used as the first fiber sheet 41a, meltblown nonwoven fabric III was used as the third fiber sheet 41b, and meltblown nonwoven fabric IV was used as the fifth fiber sheet 41c.

[0189] (Example 17) A tubular filter was obtained in the same manner as in Example 9, except that meltblown nonwoven fabric VI was used as the first fiber sheet 41a, meltblown nonwoven fabric IV was used as the third fiber sheet 41b, and meltblown nonwoven fabric V was used as the fifth fiber sheet 41c.

[0190] (Example 18) A cylindrical filter was fabricated using the manufacturing method shown in Figure 13. Specifically, a tubular filter was obtained in the same manner as in Example 1, except that a meltblown nonwoven fabric I was used as the first fiber sheet 41a, and a multilayer fiber sheet was used as the third fiber sheet 41b, which consisted of two layers of meltblown nonwoven fabric II, i.e., two layers of meltblown nonwoven fabric II were used to form the third fiber sheet 41b.

[0191] (Example 19) A tubular filter was obtained in the same manner as in Example 18, except that a multilayer fiber sheet was used, in which meltblown nonwoven fabric III was layered as the first fiber sheet 411 and the second fiber sheet 412, that is, two sheets of meltblown nonwoven fabric III were layered and used as the third fiber sheet 41b.

[0192] (Example 20) A tubular filter was obtained in the same manner as in Example 18, except that a multilayer fiber sheet was used, in which meltblown nonwoven fabric IV was layered as the first fiber sheet 411 and the second fiber sheet 412, that is, two sheets of meltblown nonwoven fabric IV were layered and used as the third fiber sheet 41b.

[0193] (Example 21) A tubular filter was obtained in the same manner as in Example 18, except that meltblown nonwoven fabric II was used as the first fiber sheet 41a.

[0194] (Example 22) A tubular filter was obtained in the same manner as in Example 18, except that a meltblown nonwoven fabric IV was used as the first fiber sheet 41a, and a multilayer fiber sheet was used by overlapping meltblown nonwoven fabric V as the first fiber sheet 411 and the second fiber sheet 412 as the third fiber sheet 41b, that is, two meltblown nonwoven fabrics V were overlapped and used as the third fiber sheet 41b.

[0195] (Comparative Example 1) Card web (basis weight: 25.5 g / m²) manufactured using a parallel carding machine consisting solely of core-sheath type composite fibers (average fiber diameter: 18.36 μm, fiber length: 51 mm) in which the core component is polypropylene resin and the sheath component is high-density polyethylene resin, and the core and sheath components are arranged concentrically. 2A water jet was prepared, and a high-pressure water jet (water pressure 2 MPa) was sprayed onto the card web once on the surface and once on the back to perform a water jet entanglement treatment. Next, after drying with hot air at 120°C, the material was heated with hot air at 140°C, melting the sheath component of the core-sheath type composite fiber, and continuously wound onto a 30 mm diameter iron core until the outer diameter reached 55 mm to produce a tubular fiber aggregate I. Next, a parallel card web (basis weight: 25.5 g / m²) consisting only of the same core-sheath type composite fibers used in the fabrication of tubular fiber aggregate I was prepared. 2 A nonwoven fabric (I) was prepared, and a high-pressure water stream (water pressure 2 MPa) was sprayed once on the surface and once on the back to perform a water entanglement treatment. Next, it was dried with hot air at 110°C, and then heated with hot air at 140°C to melt the sheath component, thereby heat-bonding the intersections of the fibers to create a heat-bonded nonwoven fabric I (basis weight: 25.5 g / m²). 2 Thickness: 0.33mm, Density: 0.078g / cm³ 3 ) was obtained. The tip of the heat-bonded nonwoven fabric I is pressed against the outer surface of the tubular fiber aggregate I obtained above using a metal spatula heated to 140°C to heat-press it. Then, the tubular fiber aggregate is rotated to begin winding the heat-bonded nonwoven fabric I. After winding the heat-bonded nonwoven fabric I twice, meltblown nonwoven fabric (consisting only of single polypropylene fibers, average fiber diameter: 2.01 μm, basis weight: 64.0 g / m²) is applied. 2 Thickness: 0.9 mm, Air permeability: 8.5 cm² measured using a Fragile type testing machine in accordance with JIS L 1913. 3 / cm 2 The heat-bonded nonwoven fabric I was wrapped around the heat-bonded nonwoven fabric I three times while the heat-bonded nonwoven fabric I was supplied with the melt-blown nonwoven fabric I in an overlapping state (however, the heat-bonded nonwoven fabric I and the melt-blown nonwoven fabric were not bonded together in the overlapping state), thereby forming a tubular fiber aggregate II. Next, only the heat-bonded nonwoven fabric I was wound around the surface of the tubular fiber aggregate II again until the outer diameter reached 65 mm. A heating element (surface temperature 140°C), with 1 mm wide metal flanges planted at 10 mm intervals on a metal rod surface, was pressed against the outer surface of the outermost heat-bonded nonwoven fabric I. By melting the sheath component, which is the low-melting-point component of the heat-bonded fibers that are in contact with the metal flanges, the material was bonded and molded to prevent peeling, thus creating a tubular filter.

[0196] (Comparative Example 2) Card web (basis weight: 25.5 g / m²) manufactured using a parallel carding machine consisting solely of core-sheath type composite fibers (average fiber diameter: 18.36 μm, fiber length: 51 mm) in which the core component is polypropylene resin and the sheath component is high-density polyethylene resin, and the core and sheath components are arranged concentrically. 2 A water jet was prepared, and a high-pressure water jet (water pressure 2 MPa) was sprayed onto the card web once on the surface and once on the back to perform a water jet entanglement treatment. Next, after drying with hot air at 120°C, the material was heated with hot air at 140°C, melting the sheath component of the core-sheath type composite fiber, and continuously wound onto a 30 mm diameter iron core until the outer diameter reached 42 mm to produce a tubular fiber aggregate III. To the tubular fiber aggregate III obtained above, meltblown nonwoven fabric J (consisting only of single polypropylene fibers, average fiber diameter: 2.01 μm, basis weight: 64.0 g / m²) was added. 2 Thickness: 0.9 mm, Air permeability: 8.5 cm² measured using a Fragile type testing machine in accordance with JIS L 1913. 3 / cm 2 ( / second) 500cm, Meltblown nonwoven fabric K (consisting only of single polypropylene fibers, average fiber diameter: 3.12μm, basis weight: 32.0g / m²) 2 Thickness: 0.4 mm, Air permeability measured using a Fragile type testing machine in accordance with JIS L 1913: 22.3 cm² 3 / cm 2 ( / second) 200cm, Meltblown nonwoven fabric L (consisting only of single polypropylene fibers, average fiber diameter: 5.94μm, basis weight: 31.5g / m²) 2 Thickness: 0.34 mm, Air permeability measured using a Fragile type testing machine in accordance with JIS L 1913: 41.2 cm² 3 / cm 2They were continuously wound in the order of 75 cm at (per second). After the winding of the non-woven fabric for the filter layer was completed, a support non-woven fabric was wound around the periphery of the filter layer until the winding diameter (outer diameter of the cylindrical filter) reached about 62 to 68 mm, and the ends were lightly heat-bonded at the end of winding. After cutting 5 cm from each of the both ends of the obtained cylindrical filter, it was cut every 25 cm to obtain a cylindrical filter.

[0197] In the examples and comparative examples, the average fiber diameter, CV value of the fiber diameter, thickness, basis weight, density, minimum pore diameter, maximum pore diameter, average pore diameter, and maximum pore diameter of the melt-blown non-woven fabrics I to VI used as the first fiber sheet, the third fiber sheet, and the fifth fiber sheet were measured as described above.Alsothe average fiber diameter, thickness, basis weight, and density of the second fiber sheet, the fourth fiber sheet, and the sixth fiber sheet were measured in the examples and comparative examples. Also, in the examples and comparative examples, the mass ratios of the core material, the cylindrical fiber aggregate A, the cylindrical fiber aggregate X, the cylindrical fiber aggregate B, the cylindrical fiber aggregate R, the cylindrical fiber aggregate C, and the outer layer were measured as described above. Also, in the examples and comparative examples, the filtration performance of the cylindrical filter was measured as described above. The results are shown in Tables 1 to 13 below.

[0198]

Table 1

[0199]

Table 2

[0200]

Table 3

[0201]

Table 4

[0202]

Table 5

[0203] Table 6

[0204] Table 7

[0205] Table 8

[0206] Table 9

[0207] Table 10

[0208] Table 11

[0209] Table 12

[0210] Table 13

[0211] As can be seen from Tables 1 to 13 above, the tubular filters of Examples 1 to 22 had a filtration accuracy of over 50% for particles with a particle size of 3.0 μm, and in particular, the tubular filters of Examples 1 to 21 had a filtration accuracy of over 65% for particles with a particle size of 3.0 μm and a filtration life of over 100 L, demonstrating basic filtration performance. Furthermore, the tubular filters of Examples 1 to 5, 10 to 13, 16, and 18 to 21 showed improved filtration accuracy compared to the tubular filters of Comparative Examples 1 and 2. Specifically, the tubular filters of Examples 1 to 5, 10, 13, 16, and 18 to 21 showed improved filtration accuracy for particles with a particle size of 1.0 μm compared to the tubular filters of Comparative Examples 1 and 2, and the tubular filters of Examples 1 to 4, 10 to 13, 16, and 18 to 21 showed improved filtration accuracy for particles with a particle size of 0.5 μm compared to the tubular filters of Comparative Examples 1 and 2. Furthermore, the cylindrical filters of Examples 6-9, 14, 15, and 17 showed improved filtration life compared to the cylindrical filters of Comparative Examples 1 and 2.

[0212] As can be seen from the comparison of Examples 1 to 3, the filtration life was improved when the average fiber diameter of the third fiber sheet constituting the tubular fiber assembly B on the inlet side (upstream side) of the material to be filtered was greater than the average fiber diameter of the first fiber sheet constituting the tubular fiber assembly A on the outlet side (downstream side) of the material to be filtered, and the ratio between them was 3 or less. Furthermore, as can be seen from the comparison between Example 1 and Examples 5-8, when using fiber sheets (specifically meltblown nonwoven fabrics) with similar average fiber diameter and CV values ​​for fiber diameter as the first and third fiber sheets, the larger the average fiber diameter, the better the filtration life. A comparison of Examples 9 to 17 shows that even when the first fiber sheet has a small average fiber diameter, the filtration accuracy and filtration life change depending on the selection of the third and fifth fiber sheets. A comparison of Examples 18-22 shows that when the average fiber diameter ratio of the first fiber sheet to the third and fifth fiber sheets is approximately 3, both filtration accuracy and filtration life are improved. For other combinations, under the measurement conditions used here, only one of either filtration accuracy or filtration life is improved.

[0213] The present invention is not particularly limited, but includes, for example, the following embodiments. [1] A cylindrical filter comprising a filtration layer formed of a tubular fiber aggregate, The filtration layer includes a tubular fiber assembly A formed by winding a first fiber sheet and a second fiber sheet into a cylindrical shape, and a tubular fiber assembly B formed by winding a third fiber sheet and a fourth fiber sheet into a cylindrical shape. In the thickness direction of the filtration layer, the first fiber sheet and the second fiber sheet are arranged alternately, and the third fiber sheet and the fourth fiber sheet are arranged alternately. The first fiber sheet is bonded via the second fiber sheet. The third fiber sheet is bonded via the fourth fiber sheet. A cylindrical filter in which a cylindrical fiber assembly A is positioned on the outflow side of the material to be filtered, and a cylindrical fiber assembly B is positioned on the inflow side of the material to be filtered. [2] The tubular filter according to [1], wherein the filtration layer is disposed between tubular fiber aggregate A and tubular fiber aggregate B and further comprises a tubular fiber aggregate X formed by the accumulation of fibers. [3] A cylindrical filter according to [1] or [2], wherein the thickness H1 of the first fiber sheet is greater than the thickness H2 of the second fiber sheet, and / or the density D1 of the first fiber sheet is greater than the density D2 of the second fiber sheet. [4] A cylindrical filter according to any one of [1] to [3], wherein the thickness H3 of the third fiber sheet is greater than the thickness H4 of the fourth fiber sheet, and / or the density D3 of the third fiber sheet is greater than the density D4 of the fourth fiber sheet. [5] A cylindrical filter according to any one of [1] to [4], wherein the width of the first fiber sheet and / or the width of the third fiber sheet is 15 mm or more and 75 mm or less. [6] A tubular filter according to any one of [1] to [5], wherein the first fiber sheet and / or the third fiber sheet have creases in the longitudinal direction of the tubular filter. [7] A tubular filter according to any one of [1] to [6], wherein the first fiber sheet and the third fiber sheet are meltblown nonwoven fabrics, and the second fiber sheet and the fourth fiber sheet are meltblown webs. [8] The tubular fiber aggregate X is formed by the accumulation of meltblown fibers, as described in [2], for the tubular filter. [9] The filtration layer is positioned on the inflow side of the tubular fiber assembly B to be filtered, and includes a tubular fiber assembly C in which a fifth fiber sheet and a sixth fiber sheet are wound in a tubular shape. In the thickness direction of the filtration layer, the fifth fiber sheet and the sixth fiber sheet are arranged alternately, and the fifth fiber sheet is bonded via the sixth fiber sheet, as described in any of [1] to [8].

[10] A tubular fiber assembly B, wherein the third fiber sheet is a multilayer fiber sheet containing two or more fiber sheets, as described in any of [1] to [9].

[11] A tubular fiber assembly A, wherein the first fiber sheet is a multilayer fiber sheet containing two or more fiber sheets, as described in any of [1] to

[10] .

[12] The tubular filter according to claim 9, wherein in the tubular fiber assembly C, the fifth fiber sheet is a multilayer fiber sheet comprising two or more fiber sheets.

[13] A method for manufacturing a cylindrical filter including a filtration layer formed of a tubular fiber aggregate, A process to obtain a tubular fiber assembly A in which the first fiber sheet and the meltblown web A are wound alternately, and the first fiber sheet is wound around the surface of the rotating shaft, while simultaneously extruding molten thermoplastic resin from the discharge hole of a spinning nozzle and blowing the meltblown fibers A, which have been stretched by a high-temperature gas flow ejected from around the discharge hole, onto the surface of a rotating shaft that rotates at a constant speed, and accumulating the meltblown fibers A on the surface of the first fiber sheet to form a meltblown web A and winding it around, and A method for manufacturing a cylindrical filter, comprising the steps of: discharging molten thermoplastic resin from the discharge hole of a spinning nozzle; simultaneously blowing meltblown fibers B, which have been stretched by a high-temperature gas flow ejected from around the discharge hole, onto the surface of a rotating shaft that rotates at a constant speed; winding a third fiber sheet onto the surface of the cylindrical fiber assembly A; and accumulating the meltblown fibers B on the surface of the third fiber sheet to form a meltblown web B, thereby obtaining a cylindrical fiber assembly B in which the third fiber sheet and the meltblown web B are wound alternately.

[14] A method for manufacturing a cylindrical filter according to

[13] , wherein a first fiber sheet and a third fiber sheet are arranged in parallel, and the first fiber sheet is wound around the surface of the rotating shaft, and then the third fiber sheet is wound around it.

[15] A method for manufacturing a tubular filter according to

[13] or

[14] , further comprising the steps of: discharging molten thermoplastic resin from the discharge hole of a spinning nozzle; simultaneously blowing meltblown fibers C, which have been stretched by a high-temperature gas flow ejected from around the discharge hole, onto the surface of a rotating shaft that rotates at a constant speed; winding a fifth fiber sheet onto the surface of the tubular fiber assembly B; and accumulating the meltblown fibers C on the surface of the fifth fiber sheet to form a meltblown web C, thereby obtaining a tubular fiber assembly C in which the fifth fiber sheet and the meltblown web C are wound alternately.

[16] A method for manufacturing a tubular filter according to any one of

[13] to

[15] , wherein in the step of obtaining a tubular fiber aggregate B, a multilayer fiber sheet containing two or more fiber sheets is used as the third fiber sheet.

[17] A method for manufacturing a tubular filter according to any one of

[13] to

[16] , wherein in the step of obtaining a tubular fiber aggregate A, a multilayer fiber sheet containing two or more fiber sheets is used as the first fiber sheet.

[18] The method for manufacturing a cylindrical filter according to

[15] , wherein in step C, a multilayer fiber sheet containing two or more fiber sheets is used as the fifth fiber sheet. [Industrial applicability]

[0214] The cylindrical filter of the present invention can be suitably used for filtering liquids such as beverages, pharmaceuticals, oils and fats, paints, and industrial cleaning water such as cleaning water for electronic components and semiconductor products. [Explanation of Symbols]

[0215] 1, 100, 200, 300 cylindrical filters 2 Hollow part 3. Core material (tubular fiber aggregate Y) 4, 40, 240, 340 filtration layers 4a Tubular fiber aggregate A 4b Tubular fiber aggregate B 4c Tubular fiber aggregate C 4x tubular fiber aggregate X 4r tubular fiber aggregate R 5 Outer layer 6a, 6b Rolled creases 10. Manufacturing apparatus for cylindrical filters 11 Extruder 12 Gas heaters 13 Spinning nozzle 14 Rotation axis 14a center shaft 14b Outer shaft 15 Meltblown Fibers 16 Arrows 41a First fiber sheet (strip-shaped nonwoven fabric) 42a Second fiber sheet 41b Third type of fiber sheet (strip-shaped nonwoven fabric) 42b Fourth fiber sheet 41c Fifth type fiber sheet (strip-shaped nonwoven fabric) 42c Sixth Fiber Sheet

Claims

1. A cylindrical filter comprising a filtration layer formed of a tubular fiber aggregate, The filtration layer includes a tubular fiber assembly A formed by winding a first fiber sheet and a second fiber sheet into a cylindrical shape, and a tubular fiber assembly B formed by winding a third fiber sheet and a fourth fiber sheet into a cylindrical shape. In the thickness direction of the filtration layer, the first fiber sheet and the second fiber sheet are arranged alternately, and the third fiber sheet and the fourth fiber sheet are arranged alternately. The first fiber sheet is bonded via the second fiber sheet. The third fiber sheet is bonded via the fourth fiber sheet. A cylindrical filter in which a cylindrical fiber assembly A is positioned on the outflow side of the material to be filtered, and a cylindrical fiber assembly B is positioned on the inflow side of the material to be filtered.

2. The tubular filter according to claim 1, wherein the filtration layer further includes a tubular fiber assembly X formed by the accumulation of fibers, which is disposed between a tubular fiber assembly A and a tubular fiber assembly B.

3. The cylindrical filter according to claim 1, wherein the thickness H1 of the first fiber sheet is greater than the thickness H2 of the second fiber sheet, and / or the density D1 of the first fiber sheet is greater than the density D2 of the second fiber sheet.

4. The cylindrical filter according to claim 1, wherein the thickness H3 of the third fiber sheet is greater than the thickness H4 of the fourth fiber sheet, and / or the density D3 of the third fiber sheet is greater than the density D4 of the fourth fiber sheet.

5. The cylindrical filter according to claim 1, wherein the width of the first fiber sheet and / or the width of the third fiber sheet is 15 mm or more and 75 mm or less.

6. The cylindrical filter according to claim 1, wherein the first fiber sheet and / or the third fiber sheet have folds in the longitudinal direction of the cylindrical filter.

7. The tubular filter according to claim 1, wherein the first fiber sheet and the third fiber sheet are meltblown nonwoven fabrics, and the second fiber sheet and the fourth fiber sheet are meltblown webs.

8. The tubular filter according to claim 2, wherein the tubular fiber aggregate X is formed by the accumulation of meltblown fibers.

9. The filtration layer is positioned on the inflow side of the tubular fiber assembly B to be filtered, and includes a tubular fiber assembly C in which a fifth fiber sheet and a sixth fiber sheet are wound in a tubular shape. The cylindrical filter according to claim 1, wherein in the thickness direction of the filtration layer, the fifth fiber sheet and the sixth fiber sheet are arranged alternately, and the fifth fiber sheet is bonded to the sixth fiber sheet.

10. The cylindrical filter according to claim 1, wherein in the tubular fiber assembly B, the third fiber sheet is a multilayer fiber sheet comprising two or more fiber sheets.

11. The cylindrical filter according to claim 1, wherein in the tubular fiber assembly A, the first fiber sheet is a multilayer fiber sheet comprising two or more fiber sheets.

12. The tubular filter according to claim 9, wherein in the tubular fiber assembly C, the fifth fiber sheet is a multilayer fiber sheet comprising two or more fiber sheets.

13. A method for manufacturing a cylindrical filter including a filtration layer formed of a tubular fiber aggregate, A process to obtain a tubular fiber assembly A in which the first fiber sheet and the meltblown web A are wound alternately, and the first fiber sheet and the meltblown web A are wound alternately, by extruding molten thermoplastic resin from the discharge hole of a spinning nozzle and simultaneously blowing the meltblown fibers A, which have been stretched by a high-temperature gas flow ejected from around the discharge hole, onto the surface of a rotating shaft that rotates at a constant speed, and accumulating the meltblown fibers A on the surface of the first fiber sheet to form a meltblown web A and winding it around, and A method for manufacturing a cylindrical filter, comprising the steps of: discharging molten thermoplastic resin from the discharge hole of a spinning nozzle; simultaneously blowing meltblown fibers B, which have been stretched by a high-temperature gas flow ejected from around the discharge hole, onto the surface of a rotating shaft that rotates at a constant speed; winding a third fiber sheet onto the surface of the cylindrical fiber assembly A; and accumulating the meltblown fibers B on the surface of the third fiber sheet to form a meltblown web B, thereby obtaining a cylindrical fiber assembly B in which the third fiber sheet and the meltblown web B are wound alternately.

14. A method for manufacturing a cylindrical filter according to claim 13, wherein a first fiber sheet and a third fiber sheet are arranged in parallel, and the first fiber sheet is wound around the surface of the rotating shaft, and then the third fiber sheet is wound around it.

15. A method for manufacturing a cylindrical filter according to claim 13, further comprising the steps of: discharging molten thermoplastic resin from the discharge hole of a spinning nozzle; simultaneously blowing meltblown fibers C, which have been stretched by a high-temperature gas flow ejected from around the discharge hole, onto the surface of a rotating shaft that rotates at a constant speed; winding a fifth fiber sheet around the surface of the cylindrical fiber assembly B; and accumulating the meltblown fibers C on the surface of the fifth fiber sheet to form a meltblown web C, thereby obtaining a cylindrical fiber assembly C in which the fifth fiber sheet and the meltblown web C are wound alternately.

16. A method for manufacturing a tubular filter according to claim 13, wherein in the step of obtaining a tubular fiber aggregate B, a multilayer fiber sheet containing two or more fiber sheets is used as the third fiber sheet.

17. A method for manufacturing a tubular filter according to claim 13, wherein in the step of obtaining a tubular fiber aggregate A, a multilayer fiber sheet containing two or more fiber sheets is used as the first fiber sheet.

18. The method for manufacturing a cylindrical filter according to claim 15, wherein in step C, a multilayer fiber sheet containing two or more fiber sheets is used as the fifth fiber sheet.

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