Tubular filter and method for manufacturing same

Abstract

The present invention pertains to a tubular filter 1 comprising a filtration layer 4 formed of a tubular fiber assembly. The filtration layer 4 includes a tubular fiber assembly A (4a) formed by winding a first fiber sheet 41a into a tubular shape a plurality of times. The first fiber sheet 41a has a width ranging from 15 mm to 75 mm, inclusive. The first fiber sheet 41a is spirally wound and has an overlap portion in a longitudinal direction of the tubular filter. An overlap ratio, which is indicated by a ratio of a width of the overlap portion between the first fiber sheets having a continuous winding order to the width of the first fiber sheet, is 80% to 99%, inclusive. As a result, it is possible to provide a tubular filter having improved filtration life or filtration accuracy while having basic filtration performance, and a method for manufacturing the tubular filter.

Description

Cylindrical filter and method for manufacturing the same

[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.

[0002] Cylindrical filters, which consist of fiber aggregates wound into a cylindrical shape, are widely used for filtering various liquids such as beverages, chemicals, oils and fats, paints, and industrial cleaning water for electronic components and semiconductor products, due to their ease of handling. Typically, cylindrical filters use a cylindrical fiber aggregate as the filtration layer, manufactured by winding various fiber sheets, such as nonwoven fabrics, around a core (also called a mandrel).

[0003] For example, Patent Document 1 describes a tubular filter that includes a filtration layer in which a fine-denier nonwoven fabric and a thick-denier spunlace nonwoven fabric are laminated and wound into a tubular shape, with the two fabrics being laminated in a state where they are not substantially heat-bonded to each other. The spunlace nonwoven fabric is made of constituent fibers that are thicker than the constituent fibers of the fine-denier nonwoven fabric, and the constituent fibers are intertwined with each other and at least a portion of them is heat-bonded. 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 sequence 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.

[0004] Japanese Patent Publication No. 2004-000851 Japanese Patent Publication No. 2013-236985

[0005] However, in the case of cylindrical filters described in Patent Documents 1 and 2, 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.

[0007] The present invention relates to a cylindrical filter comprising a filtration layer formed of a tubular fiber aggregate, wherein the filtration layer comprises a tubular fiber aggregate A formed by winding a first fiber sheet multiple times in a cylindrical shape, the first fiber sheet having a width of 15 mm to 75 mm, the first fiber sheet being wound in a spiral shape, and having overlapping portions in the longitudinal direction of the cylindrical filter, and the overlap rate, which is expressed as the ratio of the width of the overlapping portions between first fiber sheets that are wound in a continuous order to the width of the first fiber sheet, is 80% to 99%.

[0008] The present invention relates to a method for manufacturing a cylindrical filter including a filtration layer formed of a tubular fiber aggregate, comprising step A of spirally winding a first fiber sheet onto the surface of a rotating shaft to obtain a tubular fiber aggregate A, wherein the first fiber sheet has a width of 15 mm or more and 75 mm or less, and in step A, the first fiber sheet is wound multiple times in the longitudinal direction of the cylindrical filter so as to overlap, and the overlap rate, which is indicated by the ratio of the width of the overlapping portion between the first fiber sheets in a continuous winding order to the width of the first fiber sheet, is 80% or more and 99% or less.

[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 can increase the productivity of cylindrical filters that have basic filtration performance while improving filtration life or filtration accuracy, and reduce production costs.

[0010] This is a schematic partial fractured cross-sectional perspective view of an example of a tubular filter according to the present invention. This is a schematic partially fractured enlarged cross-sectional perspective view of an example of a tubular filter according to the present invention. This is a schematic partially fractured enlarged cross-sectional perspective view of an example of a tubular filter according to the present invention. This is a schematic partially fractured cross-sectional perspective view of an example of a tubular filter according to the present invention. This is a schematic partially fractured enlarged cross-sectional perspective view of an example of a tubular filter according to the present invention. This is a schematic partial longitudinal cross-sectional view of an example of a tubular fiber assembly A according to the present invention. This is a schematic partial longitudinal cross-sectional view of an example of a tubular fiber assembly B according to the present invention. This is a schematic partial longitudinal cross-sectional view of an example of a tubular fiber assembly C according to the present invention. This is a schematic diagram illustrating the manufacturing process of an example of a tubular filter according to the present invention. This is a schematic diagram illustrating the manufacturing process of an example of a tubular filter according to the present invention. This is a schematic diagram illustrating the manufacturing process of an example of a tubular filter according to the present 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 including a tubular fiber assembly A in the filtration layer, which is made by winding a first fiber sheet having a predetermined width multiple times in a tubular and spiral shape, and by overlapping the first fiber sheets in the longitudinal direction of the tubular filter, and by setting the overlap rate of the first fiber sheets whose winding order is continuous to a predetermined range, the tubular filter can have basic filtration performance while improving the filtration life or filtration accuracy (also called filtration efficiency).

[0012] (Cylindrical filter) The cylindrical 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.

[0013] The filtration layer includes a tubular fiber assembly A formed by winding a first fiber sheet multiple times in a cylindrical shape. The first fiber sheet has a width of 15 mm to 75 mm, preferably 20 mm to 65 mm, more preferably 25 mm to 60 mm, and even more 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 the overlap rate in the longitudinal direction of the tubular filter between the first fiber sheets, which are wound in a continuous order, can be easily adjusted to a range of 80% to 99%. In addition, it becomes easier to form winding wrinkles in the first fiber sheet along the longitudinal direction of the tubular filter. The winding wrinkles in the first fiber sheet along the longitudinal direction of the tubular filter create voids in the longitudinal direction, which can simultaneously improve filtration accuracy and filtration life. In this specification, the overlap rate in the longitudinal direction of a tubular filter between first fiber sheets whose winding order is continuous is expressed as the ratio of the width of the overlapping portion to the width of the first fiber sheet.

[0014] When the overlap rate of the first fiber sheet is 80% or more and 99% or less, the number of turns of the fiber sheet in the filter thickness direction becomes sufficiently large, making it easier to improve both filtration accuracy and filtration life simultaneously. The overlap rate of the first fiber sheet is preferably 85% or more and 98% or less, more preferably 90% or more and 97.5% or less, and even more preferably 94% or more and 97% or less.

[0015] The first fiber sheet is wound spirally multiple times. As a result, the first fiber sheet constituting the tubular fiber assembly A 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 A, the liquid passes through the tubular filter at an angle along the angle of the tubular fiber assembly A, in other words, along the angle formed by the longitudinal direction of the tubular filter and the direction in which the first fiber sheet is wound, which is created by the spiral winding of the first fiber sheet. This makes it easier to improve the filtration life and / or filtration accuracy.

[0016] The winding angle of the first fiber sheet is preferably 70 degrees or more and less than 90 degrees, more preferably 75 degrees or more and 89.9 degrees or less, even more preferably 80 degrees or more and 89.7 degrees or less, and even more preferably 85 degrees or more and 89.5 degrees or less. In this specification, the winding angle of the first fiber sheet means the angle between the longitudinal direction of the cylindrical filter and the direction in which the first fiber sheet is wound. When the winding angle of the first fiber sheet is within the above range, the area through which the liquid passes is wider 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 this specification, the winding angle of the fiber sheet can be measured as described in the examples.

[0017] The tubular fiber assembly A preferably includes a second fiber sheet arranged alternately with a first fiber sheet in the thickness direction, and the first fiber sheet is bonded via the second fiber sheet. This prevents the first fiber sheet from collapsing under pressure when liquid passes through, and the interlayers are stable, which tends to improve filtration accuracy and / or filtration life.

[0018] In the filtration layer (more specifically, the tubular fiber assembly A), it is preferable that the first fiber sheet is wound spirally with respect to the longitudinal direction of the tubular filter, overlapping with the second fiber sheet. Because the first fiber sheet is wound spirally, 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, the angle between the longitudinal direction of the tubular filter and the direction in which the first fiber sheet is wound, which is created by the spiral winding of the first fiber sheet while it is overlapping with the second fiber sheet.

[0019] 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.

[0020] The thickness H1 of the first 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. In this specification, the thickness of the fiber sheet can be measured as described in the examples.

[0021] The thickness H2 of the second fiber sheet is preferably 0.04 mm or more and 0.18 mm or less, more preferably 0.045 mm or more and 0.16 mm or less, even more preferably 0.05 mm or more and 0.14 mm or less, and particularly preferably 0.055 mm or more and 0.125 mm or less, from the viewpoint of improving various filtration performances such as the filtration accuracy and filtration life of the cylindrical filter.

[0022] 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 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.

[0023] The density D1 of the first fiber sheet is set to 0.03 g / cm³ from the viewpoint of improving various filtration performance aspects such as the filtration accuracy and filtration life of the cylindrical filter. 3 0.50g / cm or more 3 Preferably, it is 0.04 g / cm³. 3 0.40g / cm or more 3 It is more preferable that the following is the case: 0.05 g / cm³ 3 0.35g / cm or more 3 It is even more preferable that the following is the case: 0.06 g / cm³ 3 0.30g / cm or more 3The following are particularly preferred. In this specification, the density of the fiber sheet can be measured as described in the examples.

[0024] 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 from the viewpoint of enhancing various filtration performances such as the filtration accuracy and filtration life of the cylindrical filter, 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 the following.

[0025] 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 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.

[0026] The first fiber sheet preferably has a basis weight W1 of 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.

[0027] The second fiber sheet has a basis weight W2 of 2 g / m², from the perspective of improving 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 14g / m or more 2 It is more preferable that the following is the case: 3.5 g / m 2 12g / m or more 2 It is even more preferable that the following conditions apply: 4 g / m 2 10g / m or more 2 The following is particularly preferable:

[0028] The ratio W1 / W2 of the basis weight W1 of the first fiber sheet to the basis weight W2 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.

[0029] 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.

[0030] 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, it is preferable that the CV value of the fiber diameter of the first fiber sheet is 0.25 or more and even more preferable that it is 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, it is preferable that the CV value of the fiber diameter of the first fiber sheet is 0.4 or more and even more preferable that it is 0.6 or more. In addition, from the viewpoint of making it easier to maintain the filtration accuracy of the cylindrical filter by appropriately suppressing the variation in the fiber diameter of the first fiber sheet constituting the filtration layer, it is preferable that the CV value of the fiber diameter of the first fiber sheet is 2.5 or less, even more preferable that it is 2.0 or less, even more preferable that it is 1.5 or less, and particularly preferable that it is 1.2 or less. In this specification, the CV value of the fiber diameter of the fiber sheet can be measured as described in the examples.

[0031] 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 is more preferably 35 μm or less and even more preferably 30 μm or less.

[0032] 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.

[0033] 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.

[0034] 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. Furthermore, when high-precision filtration is required, the maximum pore size is preferably 1 μm to 20 μm, more preferably 2 μm to 15 μm, even more preferably 2.5 μm to 12 μm, and particularly preferably 3 μm to 10 μm. The most numerous pore size is preferably 1.0 μm to 15 μm, more preferably 1.2 μm to 10 μm, even more preferably 1.5 μm to 7 μm, and particularly preferably 2 μm to 5 μm. The minimum pore size is preferably 0.1 μm to 15 μm, more preferably 0.5 μm to 10 μm, even more preferably 0.7 μm to 7 μm, and particularly preferably 1 μm to 4 μm. In this specification, the average pore size, maximum pore size, most numerous pore size, and minimum pore size of the fiber sheet can be measured as described in the examples.

[0035] 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.

[0036] 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.

[0037] 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, the physical properties of each layer of fiber sheet constituting the multilayer fiber sheet preferably satisfy the range of physical properties of the first fiber sheet described above, such as thickness, density, basis weight, average fiber diameter, and CV value of the fiber diameter. 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 two to six, two to five, two to four, or two to three. 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.

[0038] 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 2 mm to 12 mm, more preferably 3 mm to 10 mm, and even more preferably 4 mm to 9 mm. Furthermore, as will be described later, if the filtration layer includes a tubular fiber assembly B, or a tubular fiber assembly B and a tubular fiber assembly C in addition to the tubular fiber assembly A, the thickness of the tubular fiber assembly A may be 1 mm to 6 mm, 1.5 mm to 5 mm, or 2 mm to 4.5 mm. Depending on the thickness of the tubular fiber assembly A, the tubular fiber assembly A can be formed by winding the first fiber sheet two or more times, or by winding the first fiber sheet and the second fiber sheet two or more times.

[0039] In a tubular fiber assembly A, it is preferable that the first fiber sheet is a meltblown nonwoven fabric, and the second fiber sheet is a meltblown web in which meltblown fibers obtained by the meltblown method, in which molten thermoplastic resin is discharged from the discharge hole of a spinning nozzle while the first fiber sheet is wound into a tube, and at the same time stretched by a high-temperature gas flow ejected from around the discharge hole, are directly assembled in a tubular shape on the surface of the first fiber sheet. In a tubular fiber assembly A, if the second fiber sheet is a meltblown web in which the second fiber sheet is directly accumulated on the surface of the first fiber sheet, the production cost is low 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 first 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 continuously wound onto the surface of the rotating shaft (more specifically, the core material that has been wound around the rotating shaft) in a cylindrical shape, thereby forming a cylindrical fiber aggregate.

[0040] The filtration layer preferably includes, in addition to the tubular fiber assembly A, a tubular fiber assembly B positioned on the inflow side of the tubular fiber assembly A for the material to be filtered, and comprising a third fiber sheet with a width of 15 mm to 75 mm wound multiple times in a tubular shape. The third fiber sheet is wound spirally around the outer circumference of the tubular fiber assembly A and has overlapping portions in the longitudinal direction of the tubular filter. Preferably, the overlap rate, which is the ratio of the width of the overlapping portions between the third fiber sheets that are wound in a continuous order to the width of the third fiber sheet, is 80% to 99%. This makes it easier to improve the filtration life and / or filtration accuracy.

[0041] The third fiber sheet preferably has a width of 20 mm to 65 mm, more preferably 25 mm to 60 mm, and even more 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, the productivity of the process of winding the third fiber sheet to form a tubular fiber assembly is increased, and the overlap rate of the third fiber sheets that are wound in a continuous order can be easily adjusted to a range of 80% to 99%. In addition, it becomes easier to form winding wrinkles in the third fiber sheet along the longitudinal direction of the tubular filter. The winding wrinkles in the third fiber sheet along the longitudinal direction of the tubular filter create longitudinal voids, which can simultaneously improve filtration accuracy and filtration life.

[0042] From the viewpoint of balancing filtration accuracy and filtration life, the overlap rate of the third fiber sheet is preferably 85% to 98%, more preferably 90% to 97.5%, and even more preferably 94% to 97%.

[0043] The third fiber sheet is wound spirally multiple times. As a result, 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, the liquid passes through the tubular filter at an angle along the angle of the tubular fiber assembly B, in other words, the angle formed by the longitudinal direction of the tubular filter and the direction in which the third fiber sheet is wound, which is created by the spiral winding of the third fiber sheet. This makes it easier to improve the filtration life and / or filtration accuracy.

[0044] The winding angle of the third fiber sheet is preferably 70 degrees or more and less than 90 degrees, more preferably 75 degrees or more and 89.9 degrees or less, even more preferably 80 degrees or more and 89.7 degrees or less, and even more preferably 85 degrees or more and 89.5 degrees or less. In this specification, the winding angle of the third fiber sheet means the angle between the longitudinal direction of the cylindrical filter and the direction in which the third fiber sheet is wound. It is presumed that when the winding angle of the third fiber sheet is within the above range, the area through which the liquid passes is wider than when the fiber sheet is not wound spirally, thereby allowing the filtration area to be effectively utilized and contributing to high filtration accuracy.

[0045] The tubular fiber assembly B preferably includes a fourth fiber sheet arranged alternately with a third fiber sheet in the thickness direction, and the third fiber sheet is bonded via the fourth fiber sheet. This prevents the third fiber sheet from collapsing under pressure when liquid passes through, stabilizing the interlayers and improving filtration accuracy and / or filtration life.

[0046] 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 while overlapping with the fourth 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 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, the angle between the longitudinal direction of the tubular filter and the direction in which the third fiber sheet is wound, which is created by the spiral winding of the third fiber sheet while overlapping with the fourth fiber sheet.

[0047] The third and fourth fiber sheets overlap and are 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 using the above range, the area through which the liquid passes is wider 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 voids between the third fiber sheets. As a result, a rapid pressure increase during filtration can be suppressed and is presumed to contribute to an improved filtration life.

[0048] 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.

[0049] 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.

[0050] 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, and it is preferable that H3 / H4 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.

[0051] 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 0.50g / cm or more 3 Preferably, it is 0.04 g / cm³. 3 0.40g / cm or more 3 It is more preferable that the following is the case: 0.05 g / cm³ 3 0.35g / cm or more 3 It is even more preferable that the following is the case: 0.06 g / cm³ 3 0.30g / cm or more 3 The following is particularly preferable:

[0052] 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 0.20g / cm or more 3 Preferably, it is 0.015 g / cm³. 3 0.15g / cm or more 3 It is more preferable that the following is the case: 0.02 g / cm³ 3 0.10g / cm or more 3 It is even more preferable that the following is the case: 0.025 g / cm³ 3 0.08g / cm or more 3 The following is particularly preferable:

[0053] 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.

[0054] The third fiber sheet has a basis weight W3 of 15 g / 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 More preferably, the following is 20 g / m² 2 60g / m or more 2 It is even more preferable that the following is the case: 23 g / m² 2 More than 50g / m 2 The following is even more preferable:

[0055] The fourth fiber sheet has a basis weight W4 of 2 g / m², from the perspective of improving 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 14g / m or more 2 It is more preferable that the following is the case: 3.5 g / m 2 12g / m or more 2 It is more preferable that the following is the case: 4 g / m 2 10g / m or more 2 The following is particularly preferable:

[0056] The ratio W3 / W4 of the basis weight W3 of the third fiber sheet to the basis weight W4 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.

[0057] From the viewpoint of easily achieving both the filtration accuracy and filtration life of the cylindrical filter, the average fiber diameter d3 of the third fiber sheet is preferably 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.

[0058] 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. From the viewpoint of further extending the filtration life of the cylindrical filter by increasing the time required for the filtration layer to become clogged, the fiber diameter CV value of the third fiber sheet is more preferably 0.4 or more, even more preferably 0.6 or more, and particularly preferably 0.7 or more. 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.

[0059] 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.

[0060] 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.

[0061] 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 or more and 80 μm or less, more preferably 1 μm or more and 70 μm or less, even more preferably 1.5 μm or more and 60 μm or less, and even more preferably 2.0 μm or more and 50 μm or less.

[0062] The maximum pore size of the third 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 third 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 third 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 third fiber sheet are within the above ranges, the filtration accuracy tends to be higher.

[0063] The air permeability of the third fiber sheet is not particularly limited and is appropriately set based on the designed filtration accuracy. For example, 1.5 cm 3 / cm 2 / second or more and 70 cm 3 / cm 2 / second or less, 2.0 cm 3 / cm 2 / second or more and 35 cm 3 / cm 2 / second or less, 2.5 cm 3 / cm 2 / second or more and 20 cm 3 / cm 2 / second or less, or 3 cm 3 / cm<000009​​​​​​​​​​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.

[0066] 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 0.3 or more and 2.0 or less, even more preferable that it be 0.5 or more and 1.8 or less, and even more preferable that it be 0.7 or more and 1.6 or less.

[0067] The second fiber sheet and the fourth fiber sheet may have the same density or different densities, but from the viewpoint of improving filtration life, D2 / D4 is preferably 0.1 to 10.0, more preferably 0.2 to 5.0, and even more preferably 0.25 to 4.0.

[0068] The second fiber sheet and the fourth fiber sheet may have the same basis weight or different basis weights, but from the viewpoint of improving filtration life, W2 / W4 is preferably 0.1 to 10.0, more preferably 0.2 to 5.0, and even more preferably 0.25 to 4.0.

[0069] The third fiber sheet may be composed of a multilayer fiber sheet containing two or more layers of fiber sheets. When the third 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 third 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 the individual fiber sheets are not bonded to each other.

[0070] 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 mm, more preferably 1.5 mm to 6 mm, and even more preferably 2 mm to 5 mm. Depending on the thickness of the tubular fiber assembly B, the tubular fiber assembly B can be formed by winding the third fiber sheet around it two or more times, or by winding the third fiber sheet and the fourth fiber sheet around it two or more times.

[0071] 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 (more specifically, a tubular fiber assembly A that has been wound around the rotating shaft beforehand), the meltblown fibers, which have become fibrous by being stretched by a high-temperature gas flow at the same time as being discharged from the discharge hole, are continuously wound around the rotating shaft (more specifically, a tubular fiber assembly) while accumulating them in a tubular shape on the surface of the rotating shaft (more specifically, a tubular fiber assembly A that has been wound around the rotating shaft beforehand), thereby forming a tubular fiber assembly.

[0072] The filtration layer may further include, in addition to tubular fiber assemblies A and B, a tubular fiber assembly X positioned between tubular fiber assemblies 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 assembly X.

[0073] 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 0.10 mm to 4.0 mm, even more preferably 0.15 mm to 3.0 mm, and particularly preferably 0.20 mm to 2.0 mm. In this specification, the thickness of the tubular fiber aggregate can be measured as described in the examples.

[0074] 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.

[0075] 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.

[0076] 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 on the surface of the rotating shaft without completely cooling them, thereby directly assembling the meltblown fibers into a tubular shape.

[0077] The filtration layer preferably includes, in addition to tubular fiber assemblies A and B, a tubular fiber assembly C positioned on the inflow side of the tubular fiber assembly B for the material to be filtered, and comprising a fifth fiber sheet with a width of 15 mm to 75 mm wound multiple times in a tubular shape. The fifth fiber sheet is wound spirally around the outer circumference of the tubular fiber assembly B and has overlapping portions in the longitudinal direction of the tubular filter. Preferably, the overlap rate, which is the ratio of the width of the overlapping portions between the fifth fiber sheets that are wound in a continuous order to the width of the fifth fiber sheet, is 80% to 99%. This makes it easier to improve the filtration life and / or filtration accuracy.

[0078] The fifth fiber sheet preferably has a width of 20 mm to 65 mm, more preferably 25 mm to 60 mm, and even more preferably 28 mm to 55 mm. 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 the overlap rate of the fifth fiber sheets that are wound in a continuous order can be easily adjusted to a range of 80% to 99%. In addition, it becomes easier to form winding wrinkles in the fifth fiber sheet along the longitudinal direction of the tubular filter. The winding wrinkles in the fifth fiber sheet along the longitudinal direction of the tubular filter create longitudinal voids, which can simultaneously improve filtration accuracy and filtration life.

[0079] The overlap rate of the fifth fiber sheet is preferably 85% to 98%, more preferably 90% to 97.5%, and even more preferably 94% to 97%, from the viewpoint of balancing filtration accuracy and filtration life.

[0080] The fifth fiber sheet is wound spirally multiple times. As a result, the fifth fiber sheet constituting the tubular fiber assembly C 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 C, the liquid passes through the tubular filter at an angle along the angle of the tubular fiber assembly C, in other words, the angle formed by the longitudinal direction of the tubular filter and the direction in which the fifth fiber sheet is wound, which is created by the spiral winding of the fifth fiber sheet. This makes it easier to improve the filtration life and / or filtration accuracy.

[0081] The winding angle of the fifth fiber sheet is preferably 70 degrees or more and less than 90 degrees, more preferably 75 degrees or more and 89.9 degrees or less, even more preferably 80 degrees or more and 89.7 degrees or less, and even more preferably 85 degrees or more and 89.5 degrees or less. In this specification, the winding angle of the fifth fiber sheet means the angle between the longitudinal direction of the cylindrical filter and the direction in which the fifth fiber sheet is wound. It is presumed that when the winding angle of the fifth fiber sheet is within the above range, the area through which the liquid passes is wider than when the fiber sheet is not wound spirally, thereby allowing the filtration area to be effectively utilized and contributing to high filtration accuracy.

[0082] The tubular fiber assembly C preferably includes a sixth fiber sheet arranged alternately with a fifth fiber sheet in the thickness direction, and the fifth fiber sheet is bonded via the sixth fiber sheet. This prevents the fifth fiber sheet from collapsing under pressure when liquid passes through, stabilizing the interlayers and improving filtration accuracy and / or filtration life.

[0083] In the filtration layer (more specifically, the tubular fiber assembly C), it is preferable that the fifth fiber sheet is wound spirally with respect to the longitudinal direction of the tubular filter while overlapping with the sixth fiber sheet. Because the fifth fiber sheet is wound spirally while overlapping with the sixth fiber sheet, 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, in other words, the angle between the longitudinal direction of the tubular filter and the direction in which the fifth fiber sheet is wound, which is created by the spiral winding of the fifth fiber sheet while overlapping with the sixth fiber sheet.

[0084] The fifth fiber sheet and the sixth 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 fifth fiber sheet constituting the cylindrical fiber assembly C, in addition to the sixth fiber sheet being wound with the fifth fiber sheet positioned between them, as described later, a core material is provided downstream and an outer layer upstream, creating voids between the fifth fiber sheets. As a result, a rapid pressure rise during filtration can be suppressed and is presumed to contribute to an improved filtration life.

[0085] The thickness H5 of the fifth 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.

[0086] 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, still 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.

[0087] The ratio H5 / H6 of the thickness H5 of the fifth fiber sheet to the thickness H6 of the sixth fiber sheet is not particularly limited. However, from the viewpoint of enhancing various filtration performances such as the filtration accuracy and filtration life of the cylindrical filter, the thickness H5 of the fifth fiber sheet is preferably larger than the thickness H6 of the sixth fiber sheet, and H5 / H6 is preferably 1.1 or more and 15.0 or less, more preferably 1.3 or more and 12 or less, still 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.

[0088] 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, still 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.

[0089] The density D6 of the sixth fiber sheet is preferably 0.01 g / cm 3 or more and 0.20 g / cm<0oo00106>or less, more preferably 0.015 g / cm 3 or more and 0.15 g / cm 3 or less, still more preferably 0.02 g / cm 30.12g / cm or more 3 It is even more preferable that the following is the case: 0.025 g / cm³ 3 0.10g / cm or more 3 The following is particularly preferable:

[0090] 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 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.

[0091] The fifth fiber sheet has a basis weight W5 of 15 g / 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 More preferably, the following is 20 g / m² 2 60g / m or more 2 It is even more preferable that the following is the case: 23 g / m² 2 More than 50g / m 2 The following is even more preferable:

[0092] The sixth fiber sheet has a basis weight of 2 g / m², with a W6 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 14g / m or more 2 It is more preferable that the following is the case: 3.5 g / m 2 12g / m or more 2 It is more preferable that the following is the case: 4 g / m 2 10g / m or more 2 The following is particularly preferable:

[0093] 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.

[0094] From the viewpoint of easily achieving both the 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 the 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 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 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.

[0095] 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. From the viewpoint of further extending the filtration life of the cylindrical filter by increasing the time required for the filtration layer to become clogged, the fiber diameter CV value of the fifth fiber sheet is more preferably 0.4 or more, even more preferably 0.6 or more, and particularly preferably 0.7 or more. 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 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.

[0096] 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.

[0097] 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.

[0098] The average pore size of the fifth 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 or more and 80 μm or less, more preferably 1 μm or more and 70 μm or less, even more preferably 1.5 μm or more and 60 μm or less, and even more preferably 2.0 μm or more and 50 μm or less.

[0099] 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.

[0100] 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 70cm 3 / cm 2 / second or less, 2.0cm 3 / cm 2 / second or more 35cm 3 / cm 2 / second or less, 2.5cm 3 / cm 2 / second or more 20cm 3 / cm 2 Less than / second, or 3cm 3 / cm 2 / second or more 10cm 3 / cm 2 It can be less than / second.

[0101] The fifth fiber sheet is preferably a meltblown nonwoven fabric, and the sixth fiber sheet is preferably 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 fifth fiber sheet, a functional nonwoven fabric having functionalities such as metal adsorption or ion exchange ability may be used.

[0102] The third fiber sheet and the fifth 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 d5 of the fifth fiber sheet is larger 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 still 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 still more preferably 1.01 or more and 3 or less.

[0103] 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 0.3 or more and 2.0 or less, even more preferable that it be 0.5 or more and 1.8 or less, and even more preferable that it be 0.7 or more and 1.6 or less.

[0104] The sixth fiber sheet and the second fiber sheet may have the same density or different densities, but from the viewpoint of improving filtration life, D6 / D2 is preferably 0.1 to 10.0, more preferably 0.2 to 5.0, and even more preferably 0.25 to 4.0. Similarly, the sixth fiber sheet and the fourth fiber sheet may have the same density or different densities, but from the viewpoint of improving filtration life, D6 / D4 is preferably 0.1 to 10.0, more preferably 0.2 to 5.0, and even more preferably 0.25 to 4.0.

[0105] The sixth fiber sheet and the second fiber sheet may have the same basis weight or different basis weight, but from the viewpoint of improving filtration life, W6 / W2 is preferably 0.1 to 10.0, more preferably 0.2 to 5.0, and even more preferably 0.25 to 4.0. Similarly, the sixth fiber sheet and the fourth fiber sheet may have the same basis weight or different basis weight, but from the viewpoint of improving filtration life, W6 / W4 is preferably 0.1 to 10.0, more preferably 0.2 to 5.0, and even more preferably 0.25 to 4.0.

[0106] The fifth fiber sheet may be composed of a multilayer fiber sheet containing two or more fiber sheets. When the fifth 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 fifth fiber sheet described above. They may all be substantially the same, some of the physical properties may be substantially the same, or they may all 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 two to six, two to five, two to four, or two to three. In a multilayer fiber sheet, from the viewpoint of productivity, it is preferable that the individual fiber sheets are not bonded to each other.

[0107] 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 7 mm, more preferably 1.5 mm to 6 mm, and even more preferably 2 mm to 5 mm. Depending on the thickness of the tubular fiber assembly C, the tubular fiber assembly C can be formed by winding the fifth fiber sheet two or more times, or by winding the fifth fiber sheet and the sixth fiber sheet two or more times.

[0108] 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 in a tubular shape around the tubular fiber assembly B, and molten thermoplastic resin is discharged from the discharge hole of a spinning nozzle while simultaneously being stretched into fibers by a high-temperature gas flow ejected from around the discharge hole, 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 (more specifically, the tubular fiber assembly B that has been wound around the rotating shaft earlier), the meltblown fibers, which have become fibrous by being stretched by a high-temperature gas flow at the same time as being discharged from the discharge hole, are continuously wound around the rotating shaft (more specifically, the fifth fiber sheet that has been wound around the rotating shaft earlier) while accumulating them in a tubular shape on the surface of the rotating shaft, thereby forming a tubular fiber assembly.

[0109] The filtration layer is positioned between tubular fiber aggregates B and C, and may further include tubular fiber aggregates R in which fibers are clustered in a tubular shape. This allows for more efficient filtration through filtration and fluid diffusion by the tubular fiber aggregates R.

[0110] 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 0.10 mm to 4.0 mm, even more preferably 0.15 mm to 3.0 mm, and particularly preferably 0.20 mm to 2.0 mm.

[0111] 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.

[0112] From the viewpoint of achieving both 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.

[0113] Preferably, the tubular fiber aggregate R is formed by continuously winding meltblown fibers obtained by the meltblown method, which involves extruding molten thermoplastic resin from the discharge hole of a spinning nozzle and simultaneously stretching it with a high-temperature gas flow ejected from around the discharge hole, into a tubular shape after the meltblown fibers have completely cooled. Rather, the meltblown fibers extruded from the spinning nozzle are continuously wound onto the surface of a rotating shaft (more specifically, a tubular fiber aggregate B) while being accumulated without completely cooling, thereby forming a tubular aggregate directly from the meltblown fibers.

[0114] 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.

[0115] 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 cylindrical fiber assembly A. The cylindrical filter may or may not have other layers, such as an outer layer, located on the inflow side of the filtration layer, more specifically on the inflow side of cylindrical fiber assembly A, cylindrical fiber assembly B, or cylindrical fiber assembly C. 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. 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.

[0116] 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.

[0117] 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. When there is 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 broadly includes fibers of both thick and thin diameters, so many large and small interfiber voids are generated 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.

[0118] 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.

[0119] Preferably, the tubular fiber aggregate Y is formed by continuously winding melt-blown fibers, 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, 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.

[0120] 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 a state of 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.

[0121] 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.

[0122] 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, from the viewpoint of improving the filtration life by creating variation in the fiber diameter of the fibers in the tubular fiber assembly Z, and making the outer layer a tubular fiber assembly containing both thick and thin fibers, it is preferable that the CV value of the fiber diameter in the tubular fiber assembly Z be 0.25 or more and 2.5 or less. From the viewpoint of obtaining a tubular filter that is less prone to clogging and has a long filtration life, the lower limit of the CV value of the fiber diameter of the tubular fiber assembly Z is preferably 0.3 or more, more preferably 0.4 or more, and even more preferably 0.5 or more. Furthermore, the upper limit of the CV value of the fiber diameter of the tubular fiber aggregate Z is preferably 2.0 or less, more preferably 1.4 or less, even more preferably 1.2 or less, and particularly preferably 1.0 or less, from the viewpoint of obtaining a tubular filter that has a long filtration life and exhibits stable filtration accuracy.

[0123] 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 allows foreign matter to be captured and collected throughout the 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.

[0124] 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, rather than 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, which are then cooled while accumulating them in a cylindrical shape on the surface of the rotating shaft (more specifically, on the surface of tubular fiber assembly A, tubular fiber assembly B, or tubular fiber assembly C).

[0125] 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, the thickness of the outer layer is preferably 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.

[0126] 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.

[0127] 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 68% 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.

[0128] Furthermore, in the filtration layer, when the total mass of tubular fiber aggregates A, B, C, X, and R is set to 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.

[0129] In the core material, filtration layer, and outer layer, the type of fibers constituting each layer is not particularly limited and can be used without particular limitation, 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.

[0130] 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 using 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 webs. 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 made of the aforementioned thermoplastic resin, more preferably meltblown nonwoven fabrics made 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 made of the aforementioned thermoplastic resin.

[0131] 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 inside the core material (tubular fiber assembly Y) and / or outside the outer layer (tubular fiber assembly Z). Examples of other components arranged inside the core material (tubular fiber assembly Y) include cylindrical fiber molded products, 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 the heat-bondable nonwoven fabric on the outside of the outer layer (tubular fiber assembly Z), in other words, further upstream (inflow side) than the outer layer, the side surface of the tubular filter becomes smooth and less fuzzy, which is not only preferable in terms of the appearance of the product, but the heat-bondable nonwoven fabric also forms part of the side surface of the tubular filter, which can reduce fiber shedding from the tubular filter. In a 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-adhesive nonwoven fabric, and may be a short-fiber nonwoven fabric or a long-fiber nonwoven fabric containing core-sheath type composite fibers, in which a high-melting-point thermoplastic resin is used as the core component and a low-melting-point thermoplastic resin is used as the sheath component. The fineness of the heat-adhesive nonwoven fabric is not particularly limited, but may be a heat-adhesive nonwoven fabric mainly composed of core-sheath type composite fibers of 1.1 dtex or more and 8 dtex or less. In the tubular filter of the present invention, when a heat-adhesive nonwoven fabric is wound around the outside of the outer layer, the amount of heat-adhesive nonwoven fabric wound may be 1 to 10 turns, or 1 to 6 turns.

[0132] 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.

[0133] From the viewpoint of superior long-term usability, under the measurement conditions described in the examples, the filtration life of the cylindrical 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 the cylindrical filter, or in other words, obtaining a cylindrical filter with higher filtration accuracy, the filtration accuracy for particles with a particle size of 1.0 μm is preferably 80% or more, more preferably 85% or more, and particularly preferably 90% or more. In this case, since a longer filtration life is preferable for superior long-term usability, it is preferably 300 liters or more, more preferably 350 liters or more, particularly preferably 400 liters or more, and most preferably 420 liters or more.

[0134] 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.

[0135] From the viewpoint of reliably capturing finer particles, or in other words, improving filtration accuracy, the cylindrical filter preferably has a filtration accuracy of 80% or more for particles with a particle size of 1.0 μm, more preferably 85% or more, even more preferably 87% or more, even more preferably 90% or more, and most preferably 95% or more. Furthermore, from the viewpoint of improving filtration accuracy, the cylindrical filter preferably has a filtration accuracy of 60% or more for particles with a particle size of 0.5 μm, more preferably 65% ​​or more, even more preferably 70% or more, and most preferably 80% or more. In addition, since a longer filtration life is preferable for long-term usability, the capacity is preferably 300 liters or more, more preferably 350 liters or more, most preferably 400 liters or more, and most preferably 420 liters or more.

[0136] 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.

[0137] Figure 1 is a schematic partially broken cross-sectional perspective view of one example of a cylindrical filter of the present invention. As shown in Figure 1, the cylindrical filter 1 includes a core material 3, a filtration layer 4, and an outer layer 5, which are 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).

[0138] Figure 2 is a schematic partially disassembled, enlarged cross-sectional perspective view of one example of a cylindrical filter according to the present invention. In Figure 2, a portion of the filtration layer is shown disassembled and enlarged. As shown in Figure 2, in the cylindrical fiber assembly A (4a), the first fiber sheet 41a is wound spirally multiple times around the surface of the core material 3, and the first fiber sheets 41a that are wound in a continuous order partially overlap in the longitudinal direction of the cylindrical filter 1. The first fiber sheet 41a also has winding wrinkles 6a in the longitudinal direction of the cylindrical filter 1. The first fiber sheet 41a may be a multilayer fiber sheet containing two or more fiber sheets.

[0139] Figure 3 is a schematic partially disassembled, enlarged cross-sectional perspective view of one example of a cylindrical filter according to the present invention. In Figure 3, a portion of the filtration layer is shown disassembled and enlarged. As shown in Figure 3, in the cylindrical fiber assembly B (4b), the third fiber sheet 41b is wound spirally multiple times around the surface of the cylindrical fiber assembly A (4a), and the third fiber sheets 41b that are wound in a continuous order partially overlap in the longitudinal direction of the cylindrical filter 1. The first fiber sheet 41b also has winding wrinkles 6b in the longitudinal direction of the cylindrical filter 1. The third fiber sheet 41b may be a multilayer fiber sheet containing two or more fiber sheets.

[0140] Figure 4 is a schematic partially broken cross-sectional perspective view of another example of the cylindrical filter of the present invention. As shown in Figure 4, the cylindrical filter 100 includes a core material 3, a filtration layer 40, and an outer layer 5, which are arranged in order 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 a tubular fiber assembly A (4a) and a tubular fiber assembly B (4b), as well as a tubular fiber assembly X (4x). In this embodiment, the third fiber sheet 41b is wound spirally multiple times around the surface of the tubular fiber assembly X (4x), and the third fiber sheets 41b with a continuous winding order partially overlap in the longitudinal direction of the cylindrical filter 100.

[0141] Figure 5 is a schematic partially broken cross-sectional perspective view of one example of a cylindrical filter of the present invention. As shown in Figure 5, the cylindrical filter 200 includes a core material 3, a filtration layer 240, and an outer layer 5, which are arranged in order 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).

[0142] Figure 6 is a schematic partially disassembled, enlarged cross-sectional perspective view of one example of a cylindrical filter according to the present invention. In Figure 6, a portion of the filtration layer is shown disassembled and enlarged. As shown in Figure 6, in the cylindrical fiber assembly C (4c), the fifth fiber sheet 41c is wound spirally multiple times around the surface of the cylindrical fiber assembly B (4b), and the fifth fiber sheets 41c that are wound in a continuous order partially overlap in the longitudinal direction of the cylindrical filter 200. The fifth fiber sheet 41c also has winding wrinkles 6c in the longitudinal direction of the cylindrical filter 200. The fifth fiber sheet 41c may be a multilayer fiber sheet containing two or more fiber sheets.

[0143] Figure 7 is a schematic partially broken cross-sectional perspective view of another example of a cylindrical filter of the present invention. As shown in Figure 7, 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, starting from the hollow portion 2 side located in the center of the cylindrical filter 300. The filtration layer 340 includes a tubular fiber assembly A (4a), a tubular fiber assembly B (4b), a tubular fiber assembly X (4x), and a tubular fiber assembly C (4c), in addition to a tubular fiber assembly R (4r). In this embodiment, the fifth fiber sheet 41c is wound spirally multiple times around the surface of the tubular fiber assembly B (4b), and the fifth fiber sheets 41c that are wound in a continuous order partially overlap in the longitudinal direction of the cylindrical filter 300.

[0144] Figure 8 is a schematic partial longitudinal cross-sectional view of a tubular fiber assembly A according to one example of the present invention. As shown in Figure 8, the tubular fiber assembly A (4a) is made up of first fiber sheets 41a and second fiber sheets 42a wound alternately in a tubular shape. In the thickness direction of the tubular fiber assembly A (filtration layer), the first fiber sheets 41a and second fiber sheets 42a are arranged alternately, and the first fiber sheets 41a that are wound in a continuous order, in other words, the first fiber sheet 41a and the first fiber sheet 41a wound one turn before it, are bonded together via the second fiber sheet 42a that was wound one turn before it.

[0145] Figure 9 is a schematic partial longitudinal cross-sectional view of a tubular fiber assembly B according to one example of the present invention. As shown in Figure 9, the tubular fiber assembly B (4b) is made up of a third fiber sheet 41b and a fourth fiber sheet 42b wound alternately 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 that are wound in a continuous order are bonded to each other, in other words, the third fiber sheet 41b and the third fiber sheet 41b wound one turn before it are bonded to each other via the fourth fiber sheet 42b wound one turn before it.

[0146] Figure 10 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 10, the tubular fiber assembly C (4c) is formed by alternately winding a fifth fiber sheet 41c and a sixth fiber sheet 42c 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 that are wound in a continuous order, in other words, the fifth fiber sheet 41c and the fifth fiber sheet 41c wound one turn before it, are bonded together via the sixth fiber sheet 42c wound one turn before it.

[0147] (Method for Manufacturing a Cylindrical Filter) The method for manufacturing a cylindrical filter is not particularly limited, but for example, it includes step A, in which a first fiber sheet is spirally wound around the surface of a rotating shaft to obtain a cylindrical fiber assembly A. In step A, it is preferable to wind a first fiber sheet having a width of 15 mm or more and 75 mm or less multiple times so as to overlap in the longitudinal direction of the cylindrical filter, and to wind it around the surface of the rotating shaft such that the overlap rate, which is the ratio of the width of the overlapping portion of the first fiber sheets that are consecutively wound to the width of the first fiber sheet, is 80% or more and 99% or less. In step A, the overlap rate of the first fiber sheet is preferably 85% or more and 98%, more preferably 90% or more and 97.5%, and even more preferably 94% or more and 97% or less. As the first fiber sheet, the one described in the section on cylindrical filters can be used as appropriate. Furthermore, it is preferable that the winding angle when winding the first fiber sheet be within the same range as described in the section on cylindrical filters.

[0148] The method for manufacturing a tubular filter further includes step B, in which a third fiber sheet is spirally wound around the surface of a tubular fiber assembly A to obtain a tubular fiber assembly B. In step B, it is preferable to wind a third fiber sheet having a width of 15 mm to 75 mm multiple times around the surface of the tubular filter so as to overlap in the longitudinal direction, and to wind it multiple times around the surface of the tubular fiber assembly A such that the overlap rate, indicated by the ratio of the width of the overlapping portion of the third fiber sheets that are consecutively wound to the width of the third fiber sheet, is 80% to 99%. In step B, the overlap rate of the third fiber sheet is preferably 85% to 98%, more preferably 90% to 97.5%, and even more preferably 94% to 97%. As the third fiber sheet, those described in the section on tubular filters can be used as appropriate. Furthermore, it is preferable that the winding angle when winding the third fiber sheet be within the same range as described in the section on tubular filters.

[0149] When a tubular fiber assembly A includes a second fiber sheet arranged alternately with a first fiber sheet in the thickness direction, and the first fiber sheet is bonded via the second fiber sheet, process A is preferably carried out as follows from the viewpoint of increasing productivity and reducing production costs. 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 (which may also be a core material) that rotates at a constant speed, the first fiber sheet is wound spirally around the surface of the core material multiple times with an overlap rate within the range described above, the meltblown fibers A are accumulated on the surface of the first fiber sheet to form a meltblown web A (second fiber sheet) and wound around, and a tubular fiber assembly A is obtained in which the first fiber sheet and the meltblown web A (second fiber sheet) are wound alternately.

[0150] When a tubular fiber assembly B includes a fourth fiber sheet arranged alternately with a third fiber sheet in the thickness direction, and the third fiber sheet is bonded via the fourth fiber sheet, process B is preferably carried out as follows from the viewpoint of increasing productivity and reducing production costs. Process 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 tubular fiber assembly A (which may also be a tubular fiber assembly X) rotating at a constant speed, the third fiber sheet is wound spirally around the surface of the tubular fiber assembly A multiple times with an overlap rate within the range described above, the meltblown fibers B are accumulated on the surface of the third fiber sheet to form a meltblown web B (fourth fiber sheet) and wound around, thereby obtaining a tubular fiber assembly B in which the third fiber sheet and the meltblown web B (fourth fiber sheet) are wound alternately.

[0151] 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. There is no need to leave a gap between the first fiber sheet and the third fiber sheet, and by leaving a gap between the first fiber sheet and the second fiber sheet, a tubular fiber assembly X in which the meltblown fibers are accumulated in a tubular shape may be formed between tubular fiber assembly A and tubular fiber assembly B.

[0152] The method for manufacturing a tubular filter may further include step C, in which a fifth fiber sheet is spirally wound around the surface of a tubular fiber assembly B to obtain a tubular fiber assembly C. In step C, it is preferable to wind a fifth fiber sheet having a width of 15 mm to 75 mm multiple times around the surface of the tubular filter so as to overlap in the longitudinal direction, and to wind it multiple times around the surface of the tubular fiber assembly B such that the overlap rate, indicated by the ratio of the width of the overlapping portion of the fifth fiber sheets that are consecutively wound to the width of the fifth fiber sheet, is 80% to 99%. In step C, the overlap rate of the fifth fiber sheet is preferably 85% to 98%, more preferably 90% to 97.5%, and even more preferably 94% to 97%. As the fifth fiber sheet, those described in the section on tubular filters can be used as appropriate. Furthermore, it is preferable that the winding angle when winding the fifth fiber sheet be within the same range as described in the section on tubular filters.

[0153] When a tubular fiber assembly C includes a sixth fiber sheet arranged alternately with a fifth fiber sheet in the thickness direction, and the fifth fiber sheet is bonded via the sixth fiber sheet, process C is preferably carried out as follows from the viewpoint of increasing productivity and reducing production costs. Process C: While extruding molten thermoplastic resin from the discharge hole of a spinning nozzle and 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 tubular fiber assembly B (which may also be a tubular fiber assembly R) rotating at a constant speed, the fifth fiber sheet is wound spirally around the surface of the tubular fiber assembly B multiple times with an overlap rate within the range described above, accumulating the meltblown fibers C on the surface of the fifth fiber sheet to form a meltblown web C (sixth fiber sheet) and winding it, thereby obtaining a tubular fiber assembly C in which the fifth fiber sheet and the meltblown web C (sixth fiber sheet) are wound alternately.

[0154] 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.

[0155] The method for manufacturing a tubular filter more preferably includes at least one of the following steps Y and Z, in addition to steps A and B, or steps A, B and C, and even more preferably both. Step Y: A step before 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, and the shaft is wound while forming a meltblown web to obtain a tubular fiber assembly Y. Step Z: A step after step B or step C in which meltblown 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.

[0156] 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.

[0157] 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.

[0158] From the viewpoint of ensuring that the average fiber diameter and 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.

[0159] 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 simultaneously wind them 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 revolutions / min to 400 revolutions / min, more preferably 100 revolutions / min to 300 revolutions / min, and even more preferably 120 revolutions / min to 200 revolutions / min.

[0160] 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.

[0161] 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.

[0162] Figures 11 to 13 are schematic diagrams illustrating the manufacturing process of one example of the cylindrical filter of the present invention. The manufacturing apparatus 10 of one example of the cylindrical filter used in these manufacturing processes comprises an extruder 11, a gas heater 12, a spinning nozzle 13, and a rotating shaft 14.

[0163] 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 or higher and Tm + 200°C or lower, and more preferably Tm + 100°C or higher and Tm + 180°C or lower. If the thermoplastic resin is polypropylene resin, the melting and kneading temperature (spinning temperature) is preferably 200°C or higher and 350°C or lower, and more preferably 250°C or higher and 330°C or lower.

[0164] 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 or more and Tm + 150°C or less, more preferably Tm + 20°C or more and Tm + 100°C or less, and particularly preferably Tm + 25°C or more and Tm + 60°C or less. If the thermoplastic resin is polypropylene resin, the temperature of the heated gas is preferably 180°C or more and 260°C or less, and more preferably 185°C or more and 220°C or less. 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 or more and 0.1 MPa or less, and more preferably 0.03 MPa or more and 0.08 MPa or less.

[0165] 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 diameters. In this case, it becomes easier to obtain meltblown fibers 15 with different fiber diameters. Although only one spinning nozzle 13 is shown in the figure, two or more may be provided. Furthermore, the size and spacing of the discharge holes within a single nozzle may be changed as appropriate. In addition, conditions such as spinning temperature and discharge volume may also be changed as appropriate.

[0166] A general-purpose mandrel or the like can be used as the rotating shaft 14.

[0167] 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 (core material 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.

[0168] Next, the meltblown fibers 15 are discharged toward the surface of the first fiber sheet 41a while winding the first fiber sheet 41a spirally multiple times with an overlap rate of 80% to 99% or less onto the tubular fiber assembly Y (core material 3). By accumulating the meltblown fibers 15 on the surface of the first fiber sheet 41a and winding it, the first fiber sheet 41a and meltblown webs (not shown) made of meltblown fibers 15 are arranged alternately, forming a tubular fiber assembly A (4a) wound in a cylindrical shape. As a result, the first fiber sheet 41a is wound spirally while advancing in the longitudinal direction of the cylindrical filter by a predetermined width, for example, 0.5 to 10 mm, more preferably 0.6 to 5 mm, and particularly preferably 0.8 to 3 mm, forming a tubular fiber assembly A (4a) including the first fiber sheet 41a (overlap rate of 80% to 99%) and a second fiber sheet made of meltblown fibers 15 accumulated on its surface, thereby improving the filtration accuracy of the cylindrical filter. As shown in Figure 8, the meltblown web made of meltblown fibers accumulated on the surface of the first fiber sheet 41a becomes the second fiber sheet 42a, and adjacent first fiber sheets 41a in the thickness direction are bonded to each other via the second fiber sheet 42a positioned between them.

[0169] Simultaneously, the third fiber sheet 41b, which is placed in parallel with the first fiber sheet 41a at a predetermined interval, is wound onto the surface of the rotating shaft after the first fiber sheet has been wound around it. Meltblown fibers 15 are discharged toward the surface of the third fiber sheet 41b while winding it spirally onto the surface of the tubular fiber assembly A (4a) multiple times, with an overlap rate of 80% to 99%, thereby accumulating the meltblown fibers 15 on the surface of the third fiber sheet 41b. By winding and accumulating the meltblown fibers 15 on the surface of the third fiber sheet 41b, 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 a result, the third fiber sheet 41b is wound spirally while advancing in the longitudinal direction of the cylindrical filter by a predetermined width, 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, forming a tubular fiber assembly B (4b) including the third fiber sheet 41b and a fourth fiber sheet made of meltblown fibers 15 accumulated on its surface, thereby improving the filtration accuracy of the cylindrical filter. As shown in Figure 9, the meltblown web made of meltblown fibers 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 to each other via the fourth fiber sheet 42b positioned between them.

[0170] 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 together 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 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. Furthermore, in this case, if the first fiber sheet 41a and the third fiber sheet 41b have the same width, the same fiber composition, the same physical properties, and are of the same type of fiber sheet (e.g., nonwoven fabric), the tubular fiber assembly formed by the first fiber sheet 41a and the third fiber sheet 41b, which are arranged in parallel in the width direction, may be considered as a single tubular fiber assembly A (4a) and a tubular fiber assembly B (4b).

[0171] Next, meltblown fibers 15 are discharged toward the surface of the tubular fiber assembly B(4b), thereby accumulating and winding 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.

[0172] 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.

[0173] 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 meltblown fibers 15 are discharged toward the surface of the fifth fiber sheet 41c, which is placed in parallel with the third fiber sheet 41b at a predetermined interval, while winding it spirally onto the surface of the tubular fiber aggregate B (4b) multiple times with an overlap rate of 80% to 99%. By winding the meltblown fibers 15 onto the surface of the fifth fiber sheet 41c, the meltblown fibers 15 are accumulated on the surface of the fifth fiber sheet 41c, and at the same time the meltblown fibers 15 are accumulated on the surface of the fifth fiber sheet 41c, the meltblown web (not shown) made of meltblown fibers 15 is arranged alternately, forming a tubular fiber aggregate C (4c) that is wound in a cylindrical shape. As a result, the fifth fiber sheet 41c is wound spirally while advancing in the longitudinal direction of the cylindrical filter by a predetermined width, 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, forming a cylindrical fiber assembly C (4c) including the fifth fiber sheet 41c and a sixth fiber sheet made of meltblown fibers 15 accumulated on its surface, thereby improving the filtration accuracy of the cylindrical filter. As shown in Figure 10, the meltblown web made of meltblown fibers accumulated on the surface of the fifth fiber sheet 41c becomes the 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.

[0174] 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 the 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 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. Furthermore, in this case, if the third fiber sheet 41b and the fifth fiber sheet 41c have the same width, the same fiber composition, the same physical properties, and are the same type of fiber sheet (e.g., nonwoven fabric), the tubular fiber assembly formed by the third fiber sheet 41b and the fifth fiber sheet 41c, which are arranged in parallel in the width direction, may be considered as a single tubular fiber assembly B (4b) and a tubular fiber assembly C (4c).

[0175] 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.

[0176] The tubular fiber aggregates Y(3), A(4a), X(not shown), B(4b), C(4b), R(not shown), 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 cylindrical filter can be obtained by cutting the resulting cylindrical object to a predetermined length.

[0177] 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 (two-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 fiber sheet (411) and the second fiber sheet (412) are stacked and supplied as the first fiber sheet 41b.

[0178] 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.

[0179] The present invention will be described in detail below with reference to examples. The present invention is not limited to the following examples.

[0180] The measurement methods used in the examples and comparative examples will be explained.

[0181] (Thickness) The thickness of the fiber aggregate (fiber sheet or tubular fiber aggregate) was measured under a load of 3g. In the filtration layer, the first fiber sheet and the second fiber sheet were measured after cutting the tubular filter longitudinally and unfolding it, peeling off the tubular fiber aggregate 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, and then measuring the thickness of each. In the filtration layer, the third fiber sheet and the fourth fiber sheet were measured after cutting the tubular filter longitudinally and unfolding it, peeling off the tubular fiber aggregate 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, and then measuring the thickness of each. 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 area around where they were bonded together, 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 its respective single-layer fiber sheet, and then the thickness of each was measured.

[0182] (Balance) The basis weight of the fiber aggregate (fiber sheet or tubular fiber aggregate) was measured from the area and weight of a rectangular sample taken at any size. In the filtration layer, the basis weight of the first fiber sheet and the second fiber sheet was measured after cutting the tubular filter lengthwise and unfolding it, peeling off the tubular fiber aggregate A, taking a sample of one full circle where they were bonded together, and then carefully separating the first and second fiber sheets with tweezers or similar tools to avoid tearing them. In the filtration layer, the basis weight of the third fiber sheet and the fourth fiber sheet was measured after cutting the tubular filter lengthwise and unfolding it, peeling off the tubular fiber aggregate B, taking a sample of one full circle where they were bonded together, and then carefully separating the third and fourth fiber sheets with 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 longitudinally and unfolding it, peeling off the cylindrical fiber assembly C, taking a sample of the area around where they were bonded together, 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 was measured.

[0183] (Density) The density of the fiber aggregate (fiber sheet or tubular fiber aggregate) was calculated based on the thickness and basis weight measured as described above. Density = basis weight / thickness

[0184] (Measurement of Average Fiber Diameter and CV Value of Fiber Diameter) The average fiber diameter and CV value of the fiber diameter of the fiber aggregate (fiber sheet or tubular fiber aggregate) were determined by observing the fiber aggregate 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

[0185] (Average pore size, maximum pore size, most numerous 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 capillary flow porometer "CFP-1200-AEXC-P" manufactured by Porous Material Inc.

[0186] (Air permeability) Measured using a Frazier type testing machine in accordance with JIS L 1913.

[0187] (Filtration accuracy) A water dispersion of test dust conforming to JIS Z 8901 (JIS Type 11 test powder [median diameter 2 μm]) adjusted to a concentration of 10 ppm was used as the test suspension. The test suspension was passed through a cylindrical filter at a flow rate of 15 liters / min from the outside towards the hollow part while stirring to ensure uniform concentration, and the number of 0.5 μm, 1.0 μm, and 3.0 μm powders (particles) contained in the test suspension before filtration was measured. 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 one 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

[0188] (Filtration Life) 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 [median 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 part while uniformly stirring. The test powder was added every 13.5 minutes to maintain a concentration of 15 ppm, and 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.

[0189] (Overlap rate of fiber sheets) In the tubular fiber assembly A of the tubular filter, the overlap rate of the first fiber sheet is expressed by the following formula, where x1 is the pitch interval obtained by dividing the number of turns in the longitudinal direction of the surface measured by dividing the filter into the total length of the filter, and y1 is the width of the fiber sheet used. Overlap rate of the first fiber sheet (%) = 100 × (y1 - x1) / y1 Furthermore, in the tubular fiber assembly B of the tubular filter, the overlap rate of the third fiber sheet is expressed by the following formula, where x3 is the pitch interval obtained by dividing the number of turns in the longitudinal direction of the surface measured by dividing the filter into the total length of the filter, and y3 is the width of the fiber sheet used. The overlap rate (%) of the third fiber sheet is 100 × (y³ - x³) / y³. Furthermore, in the tubular fiber assembly C of the tubular filter, the overlap rate of the fifth fiber sheet is expressed by the following formula, where x₅ is the pitch interval obtained by dividing the number of turns in the longitudinal direction of the surface measured by dividing the filter into the total length of the filter, and y₅ is the width of the fiber sheet used: Overlap rate (%) of the fifth fiber sheet = 100 × (y₅ - x₅) / y₅

[0190] (Wrapping angle of fiber sheets) In the tubular fiber assembly A of the tubular filter, the wrapping angle of the first fiber sheet was calculated by creating a right triangle with x1 as the base and z1 as the height, where x1 is the base and z1 is the height, and the angle between x1 and z1 is a right angle, and the angle θ1 that satisfies the following equation: tanθ1 = z1 / x1. In addition, in the tubular fiber assembly B of the tubular filter, the wrapping angle of the third fiber sheet was calculated by creating a right triangle with x3 as the base and z3 as the height, where x3 is the base and z3 is the height, and the angle between x3 and z3 is a right angle, and the angle θ3 that satisfies the following equation. tanθ3 = z3 / x3 Furthermore, in the tubular fiber assembly C of the tubular filter, the winding angle of the fifth fiber sheet was calculated by creating a right-angled triangle with x5 as the base and z5 as the height, where x5 is the pitch spacing of the fifth fiber sheet and z5 is the length required to wind the fiber sheet once. The angle θ5 satisfying the following equation was calculated: tanθ5 = z5 / x5

[0191] (Mass Ratio of Cylindrical Filters) A cylindrical filter was prepared, and first, the total mass of the core material, filtration layer, and outer layer was measured using an electronic balance. When the filtration layer consisted of cylindrical fiber aggregate A and cylindrical fiber aggregate B, the measurement was performed as follows. Next, an incision was made in the thickness direction of the cylindrical filter, and the outer layer was peeled off the cylindrical filter to prevent fibers from scattering. When the third fiber sheet (specifically, nonwoven fabric) was revealed and the entire side surface was made of nonwoven fabric, the process of separating and recovering the outer layer was completed, and the fibers constituting the outer layer that had been peeled off the cylindrical filter were collected and weighed using an electronic balance. Next, the nonwoven fabric, which is the third fiber sheet wound around the cylindrical filter, was peeled off, and when the nonwoven fabric had been completely peeled off, the process of separating and recovering cylindrical fiber aggregate B was completed, and the mass of the nonwoven fabric and fibers constituting cylindrical fiber aggregate B was measured. Next, the tubular fiber assembly X was peeled from the tubular filter, taking care not to scatter the fibers. When the first fiber sheet (specifically, nonwoven fabric) was revealed and the entire side surface was made of nonwoven fabric, the separation and recovery of the tubular fiber assembly X was completed. The fibers constituting the tubular fiber assembly X 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 completely peeled off, the separation and recovery of the tubular fiber assembly A was completed, and the mass of the nonwoven fabric and fibers constituting the tubular fiber assembly A was measured. The remaining portion after peeling off the outer layer C and the filtration layer from the tubular filter was used as the core material, and its mass was measured. Based on the total mass of the measured core material, filtration layer, and outer layer, and the mass of each layer, the mass ratio of each layer was calculated. If a heat-bonded nonwoven fabric was further wrapped around the outside of the outer layer of the tubular filter, the heat-bonded nonwoven fabric was 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, B, and C, the measurements were taken as follows.Next, an incision was made in the thickness direction of the tubular filter to prevent fibers from scattering, and the outer layer was peeled off the tubular filter until the fifth fiber sheet (specifically, nonwoven fabric) was revealed, and when 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 tubular 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, and when the nonwoven fabric had been completely peeled off, the process of separating and recovering the tubular fiber assembly C was completed, and the mass of the nonwoven fabric and fibers constituting the tubular fiber assembly C was measured. Next, the tubular fiber assembly R was peeled off the tubular filter to prevent fibers from scattering, and when the third fiber sheet (specifically, nonwoven fabric) was revealed, and when the entire side surface was made of nonwoven fabric, the process of separating and recovering the tubular fiber assembly R was completed. The fibers constituting the tubular fiber assembly R 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 cylindrical filter, was peeled off. Once the nonwoven fabric had been completely peeled off, the separation and recovery of the cylindrical fiber assembly B was completed, and the mass of the nonwoven fabric and fibers constituting the cylindrical fiber assembly B was measured. Next, the cylindrical fiber assembly X was peeled off from the cylindrical filter, taking care not to scatter the fibers, until the first fiber sheet (specifically the nonwoven fabric) was revealed. Once the entire side surface was made of nonwoven fabric, the separation and recovery of the cylindrical fiber assembly X was completed, and the fibers constituting the cylindrical fiber assembly X 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 cylindrical filter, was peeled off. Once the nonwoven fabric had been completely peeled off, the separation and recovery of the cylindrical fiber assembly A was completed, and the mass of the nonwoven fabric and fibers constituting the cylindrical fiber assembly A was measured. The mass of the core material was measured from the portion remaining after the outer layer C and the filtration layer had been peeled off from the cylindrical filter. The mass ratio of each layer was calculated based on the measured total mass of the core material, filter layer, and outer layer, and the mass of each layer. If a heat-bonded nonwoven fabric is wrapped around the outside of the outer layer of a cylindrical filter, the heat-bonded nonwoven fabric was removed before measuring the total mass of the core material, filter layer, and outer layer.

[0192] (Airflow 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 when the airflow rate was 400 liters / minute was measured and defined as the airflow pressure loss.

[0193] (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 a 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 multiple 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 discharge 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 arranged around the discharge holes to convert 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 was continued for a predetermined time to obtain a core material 3 (thickness 9.2 mm) consisting of a tubular fiber aggregate Y.Subsequently, two 40 mm 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 to 50 mm). 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 toward the mandrel (in other words, the direction opposite to the spinning nozzle that discharges the meltblown fibers across the mandrel). While advancing 1 to 2 mm at a time in the direction of arrow 16, the meltblown fibers 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 are formed on the surface of the meltblown nonwoven fabric I. By accumulating and simultaneously winding the 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 tubular fiber assembly A, the first fiber sheet (meltblown nonwoven fabric I) is spirally wound around the surface of core material 3 such that the overlap rate is 95.6% in the longitudinal direction of the tubular filter (similar to the longitudinal direction of the mandrel) and the winding angle of the first fiber sheet is 89.4 degrees. In tubular fiber assembly B, the third fiber sheet (meltblown nonwoven fabric I) is spirally wound around the surface of tubular fiber assembly A (more specifically, tubular fiber assembly X) such that the overlap rate is 95.6% in the longitudinal direction of the tubular filter (similar to the longitudinal direction of the mandrel) and the winding angle of the third fiber sheet is 89.4 degrees.In the tubular fiber assembly A, meltblown fibers accumulate 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, forming a meltblown web, which is a 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 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, forming a meltblown web, which is the fourth fiber sheet. The third 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 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 tubular fiber assembly B while winding to form a tubular structure, creating an outer layer 5 (thickness: 2.8 mm) made of 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), and an outer layer. Each was 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, and the fourth fiber sheet contained in tubular fiber assembly B.

[0194] (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.

[0195] (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.

[0196] (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.

[0197] (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.

[0198] (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.

[0199] (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.

[0200] (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.

[0201] (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 melt-kneaded in an extruder at a spinning temperature of 330°C, and the molten polypropylene resin was supplied to a 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 multiple 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 discharge 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 arranged around the discharge holes to convert 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 was continued for a predetermined time to obtain 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 to 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 fibers 15, a tubular fiber assembly X (thickness 0.5 mm) is placed outside the tubular fiber assembly A (inflow 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 up of meltblown fibers 15 are arranged outside the tubular fiber assembly X (inflow side of the material to be filtered) in the thickness direction. A tubular fiber assembly B (3.0 mm thick) is formed by alternately arranging tubular fiber assemblies B (3.0 mm thick), a tubular fiber assembly R (0.5 mm thick) is placed outside tubular fiber assembly B (on the inflow side of the material to be filtered) and is formed by the accumulation of meltblown fibers 15 in a tubular shape, and a tubular fiber assembly C (2.8 mm thick) is placed outside tubular fiber assembly R (on the inflow side of the material to be filtered) and is 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.In tubular fiber assembly A, the first fiber sheet (meltblown nonwoven fabric I) is spirally wound around the surface of core material 3 such that the overlap rate is 96.6% in the longitudinal direction of the tubular filter (same as the longitudinal direction of the mandrel) and the winding angle of the first fiber sheet is 89.3 degrees. In tubular fiber assembly B, the third fiber sheet (meltblown nonwoven fabric II) is wound around the surface of core material 3 such that the overlap rate is 94.8% in the longitudinal direction of the tubular filter (same as the longitudinal direction of the mandrel). Furthermore, the third fiber sheet was spirally wound around the surface of tubular fiber assembly A (more specifically, tubular fiber assembly X) such that the winding angle of the third fiber sheet was 89.3 degrees, and in tubular fiber assembly C, the fifth fiber sheet (meltblown nonwoven fabric III) was spirally wound around the surface of tubular fiber assembly B (more specifically, tubular fiber assembly R) such that the overlap rate in the longitudinal direction of the tubular filter (similar to the longitudinal direction of the mandrel) was 94.8%, and the winding angle of the fifth fiber sheet was 89.3 degrees. In the tubular fiber assembly A, meltblown fibers accumulate 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, forming a meltblown web, which is a 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 aggregate 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, and this meltblown web is the fourth fiber sheet.Furthermore, the third fiber sheets, namely meltblown nonwoven fabric II and meltblown nonwoven fabric II wound one turn before it, are bonded together via a fourth fiber sheet located between them. In the tubular fiber assembly C, meltblown fibers accumulate between continuously wound meltblown nonwoven fabric III, namely between adjacent meltblown nonwoven fabric 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. Furthermore, the fifth fiber sheets, namely meltblown nonwoven fabric III and meltblown nonwoven fabric III wound one turn before it, are bonded together via a sixth fiber sheet located between them. The cylindrical object, composed of a mandrel 14, a core material 3, a tubular fiber assembly A (4a), a tubular fiber assembly X (not shown), a tubular fiber assembly B (4b), a tubular fiber assembly R (not shown), and a tubular fiber assembly 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 to form a tubular structure, creating an outer layer 5 (thickness: 2.8 mm) made of a 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, cylindrical fiber assembly R, and cylindrical 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. As a result, 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, the fourth fiber sheet contained in cylindrical fiber assembly B, and the sixth fiber sheet contained in cylindrical fiber assembly C.

[0202] (Example 10) A tubular filter was obtained in the same manner as in Example 9, except that meltblown nonwoven fabric VI was used as the fifth fiber sheet 41c.

[0203] (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.

[0204] (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.

[0205] (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.

[0206] (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.

[0207] (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.

[0208] (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.

[0209] (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.

[0210] (Example 18) A tubular filter was manufactured using the manufacturing method shown in Figure 13. Specifically, 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. Otherwise, a tubular filter was obtained in the same manner as in Example 1.

[0211] (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.

[0212] (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 meltblown nonwoven fabric IVs were layered and used as the third fiber sheet 41b.

[0213] (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.

[0214] (Example 22) A tubular filter was obtained in the same manner as in Example 18, except that 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 fabric V sheets were overlapped and used as the third fiber sheet 41b.

[0215] (Comparative Example 1) A card web (basis weight: 25.5 g / m²) manufactured using a parallel card machine consisting only 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 component and sheath component are arranged concentrically. 2 A card web was prepared, and a high-pressure water stream (water pressure 2 MPa) was sprayed onto the card web once on the surface and once on the back to perform a water entanglement treatment. Next, after drying with hot air at 120°C, it 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 assembly I. Next, a parallel card web (basis weight: 25.5 g / m²) made only of the same core-sheath type composite fiber used in the production of tubular fiber assembly 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: 0.33 mm, Density: 0.078 g / cm³ 3 A tubular fiber aggregate I was obtained. The tip of the heat-bonded nonwoven fabric I was 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, and then the winding of the heat-bonded nonwoven fabric I was started by rotating the tubular fiber aggregate. After winding the heat-bonded nonwoven fabric I twice, a meltblown nonwoven fabric (consisting only of single polypropylene fibers, average fiber diameter: 2.01 μm, basis weight: 64.0 g / m²) was obtained. 2 Thickness: 0.9 mm, Air permeability measured using a Fragile type testing machine in accordance with JIS L1096: 8.5 cm 3 / cm 2A tubular fiber assembly II was formed by supplying (at a rate of 0.7 / second) to the underside of the heat-bonded nonwoven fabric I (however, the heat-bonded nonwoven fabric I and the meltblown nonwoven fabric were not bonded together in the overlapping state) and wrapping them around the heat-bonded nonwoven fabric I three times. Next, the heat-bonded nonwoven fabric I was wound around the surface of the tubular fiber assembly II again until the outer diameter reached 65 mm. A heating element (surface temperature 140°C), with a metal rod surface and metal flanges with a width of 1 mm implanted at 10 mm intervals, 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-bondable fibers that are in contact with the metal flanges, the fibers were bonded and molded to prevent peeling, thereby creating a tubular filter.

[0216] (Comparative Example 2) A card web (basis weight: 25.5 g / m²) manufactured using a parallel card machine consisting only 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 component and sheath component are arranged concentrically. 2 A sheet of material was prepared, and a high-pressure water stream (water pressure 2 MPa) was sprayed onto the card web once on the surface and once on the back to perform a water entanglement treatment. Next, after drying with hot air at 120°C, it 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 assembly III. Meltblown nonwoven fabric J (consisting only of single polypropylene resin fibers, average fiber diameter: 2.01 μm, basis weight: 64.0 g / m²) was applied to the tubular fiber assembly III obtained above. 2 Thickness: 0.9 mm, Air permeability measured using a Fragile type testing machine in accordance with JIS L 1913: 8.5 cm 3 / cm 2 (at 500 cm / second), meltblown nonwoven fabric K (consisting only of single polypropylene fibers, average fiber diameter: 3.12 μm, basis weight: 32.0 g / m²) 2 Thickness: 0.4 mm, Air permeability measured using a Fragile type testing machine in accordance with JIS L 1913: 22.3 cm 3 / cm 2( / second) at 200 cm, meltblown nonwoven fabric L (consisting only of single polypropylene fibers, average fiber diameter: 5.94 μm, basis weight: 31.5 g / 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 2 The nonwoven fabric for the filtration layer was wound continuously in 75 cm increments (at 1 / second). After winding the nonwoven fabric for the filtration layer was complete, the supporting nonwoven fabric was wound around the filtration layer until the winding diameter (outer diameter of the cylindrical filter) was approximately 62-68 mm, and the ends were lightly heat-sealed at the end of the winding. After cutting off 5 cm from each end of the obtained cylindrical filter, it was cut into 25 cm sections to obtain cylindrical filters.

[0217] In the examples and comparative examples, the average fiber diameter, CV value of the fiber diameter, thickness, basis weight and density, minimum pore diameter, maximum pore diameter, average pore diameter, maximum pore diameter and air permeability of the meltblown nonwoven fabrics I to VI used as the first, third, and fifth fiber sheets were measured as described above. In addition, in the examples and comparative examples, the average fiber diameter, thickness, basis weight and density of the second, fourth, and sixth fiber sheets were measured. In addition, in the examples and comparative examples, the overlap rate and winding angle of the first, third, and fifth fiber sheets were measured as described above. In addition, in the examples and comparative examples, the mass ratio of the core material, tubular fiber assembly A, tubular fiber assembly X, tubular fiber assembly B, tubular fiber assembly R, tubular fiber assembly C, and outer layer were measured as described above. In addition, in the examples and comparative examples, the filtration performance of the tubular filter was measured as described above. The results are shown in Tables 1 to 13 below.

[0218]

[0219]

[0220]

[0221]

[0222]

[0223]

[0224]

[0225]

[0226]

[0227]

[0228]

[0229]

[0230]

[0231] As can be seen from Table 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 65% or more for particles with a particle size of 3.0 μm and a filtration life of 100 L or more, 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.

[0232] From a comparison of Examples 1 to 3, it can be seen that if 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 is 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 is 3 or less, the filtration life is improved. Also, from a comparison of Examples 1 and 5 to 8, it can be seen that when fiber sheets (specifically meltblown nonwoven fabrics) with similar average fiber diameters and CV values ​​of fiber diameter are used as the first and third fiber sheets, the larger the average fiber diameter, the better the filtration life. From a comparison of Examples 9 to 17, it can be seen that even if a first fiber sheet with a small average fiber diameter is used, the filtration accuracy and filtration life change depending on the selection of the third and fifth fiber sheets. From a comparison of Examples 18 to 22, it can be seen that when the ratio of the average fiber diameters of the first fiber sheet to the third and fifth fiber sheets is approximately 3, both the filtration accuracy and filtration life are improved. In other combinations, it was found that only one of either filtration accuracy or filtration life improved under the measurement conditions used in this study.

[0233] 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 assembly, wherein the filtration layer comprises a tubular fiber assembly A obtained by winding a first fiber sheet multiple times in a cylindrical shape, the first fiber sheet having a width of 15 mm or more and 75 mm or less, the first fiber sheet being wound in a spiral manner and having overlapping portions in the longitudinal direction of the cylindrical filter, and the overlap rate, which is indicated by the ratio of the width of the overlapping portions between first fiber sheets that are wound in a continuous order to the width of the first fiber sheet, is 80% or more and 99% or less. [2] The cylindrical filter according to [1], wherein the winding angle of the first fiber sheet is 70 degrees or more and less than 90 degrees. [3] The filtration layer is arranged on the inflow side of the tubular fiber assembly A and includes a tubular fiber assembly B formed by winding a third fiber sheet multiple times in a tubular shape, wherein the third fiber sheet has a width of 15 mm to 75 mm, the third fiber sheet is wound spirally around the outer circumference of the tubular fiber assembly A and has overlapping portions in the longitudinal direction of the tubular filter, and the overlap rate, indicated by the ratio of the width of the overlapping portions between the third fiber sheets that are wound in a continuous order to the width of the third fiber sheet, is 80% to 99%, as described in [1] or [2]. [4] The tubular fiber assembly A includes a second fiber sheet that is arranged alternately with the first fiber sheet in the thickness direction, as described in any of [1] to [3]. [5] The tubular fiber assembly A is bonded to the first fiber sheet via the second fiber sheet, as described in [4]. [6] The tubular filter according to [3], wherein the tubular fiber assembly B includes a fourth fiber sheet that is alternately arranged with the third fiber sheet in the thickness direction. [7] The tubular filter according to [6], wherein the third fiber sheet is bonded to the tubular fiber assembly B via the fourth fiber sheet.[8] The filtration layer is located on the inlet side of the tubular fiber assembly B and includes a tubular fiber assembly C formed by winding a fifth fiber sheet multiple times in a tubular shape, wherein the fifth fiber sheet has a width of 15 mm to 75 mm, the fifth fiber sheet is spirally wound around the outer circumference of the tubular fiber assembly B and has overlapping portions in the longitudinal direction of the tubular filter, and the overlap rate, indicated by the ratio of the width of the overlapping portions between the fifth fiber sheets that are wound in a continuous order to the width of the fifth fiber sheet, is 80% to 99%. This is the tubular filter according to [3], [6], or [7]. [9] The tubular filter according to [8], wherein the tubular fiber assembly C includes a sixth fiber sheet that is alternately arranged with the fifth fiber sheet in the thickness direction.

[10] The tubular filter according to [9], wherein the fifth fiber sheet is bonded to the tubular fiber assembly C via the sixth fiber sheet.

[11] A tubular fiber assembly B, wherein the third fiber sheet is a multilayer fiber sheet containing two or more fiber sheets, as described in [3] and any of [6] to

[10] .

[12] 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

[11] .

[13] A tubular fiber assembly C, wherein the fifth fiber sheet is a multilayer fiber sheet containing two or more fiber sheets, as described in any of [8] to

[10] .

[14] A method for manufacturing a cylindrical filter including a filtration layer formed of a cylindrical fiber aggregate, comprising step A of spirally winding a first fiber sheet onto the surface of a rotating shaft to obtain a cylindrical fiber aggregate A, wherein the first fiber sheet has a width of 15 mm or more and 75 mm or less, is wound multiple times so as to overlap, and the overlap rate, which is indicated by the ratio of the width of the overlap portion between the first fiber sheets in a continuous winding order to the width of the first fiber sheet, is 80% or more and 99% or less.

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

[14] , comprising step B of spirally winding a third fiber sheet onto the surface of a tubular fiber assembly A to obtain a tubular fiber assembly B, wherein the third fiber sheet has a width of 15 mm or more and 75 mm or less, and in step B, the third fiber sheet is wound multiple times in the longitudinal direction of the tubular filter so as to overlap, and the overlap rate, which is indicated by the ratio of the width of the overlap portion of the third fiber sheets that are consecutively wound to the width of the third fiber sheet, is 80% or more and 99% or less.

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

[15] , comprising step C of spirally winding a fifth fiber sheet onto the surface of a tubular fiber assembly B to obtain a tubular fiber assembly C, wherein the fifth fiber sheet has a width of 15 mm or more and 75 mm or less, and in step C, the fifth fiber sheet is wound multiple times in the longitudinal direction of the tubular filter so as to overlap, and the overlap rate, which is indicated by the ratio of the width of the overlap portion of the fifth fiber sheets that are wound in a continuous order to the width of the fifth fiber sheet, is 80% or more and 99% or less.

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

[15] or

[16] , wherein in step B, a multilayer fiber sheet containing two or more fiber sheets is used as the third fiber sheet.

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

[14] to

[17] , wherein in step A, a multilayer fiber sheet containing two or more fiber sheets is used as the first fiber sheet.

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

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

[0234] 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.

[0235] 1, 100, 200, 300 Cylindrical filter 2 Hollow section 3 Core material (cylindrical fiber aggregate Y) 4, 40, 240, 340 Filtration layer 4a Cylindrical fiber aggregate A 4b Cylindrical fiber aggregate B 4c Cylindrical fiber aggregate C 4x Cylindrical fiber aggregate X 4r Cylindrical fiber aggregate R 5 Outer layer 6a, 6b Wrinkles 10 Manufacturing apparatus for cylindrical filters 11 Extruder 12 Gas heater 13 Spinning nozzle 14 Rotating shaft 14a Inner shaft 14b Outer shaft 15 Meltblown fiber 16 Arrow 41a First fiber sheet (strip-shaped nonwoven fabric) 42a Second fiber sheet 41b Third fiber sheet (strip-shaped nonwoven fabric) 42b Fourth fiber sheet 41c Fifth 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, wherein the filtration layer comprises a tubular fiber aggregate A formed by winding a first fiber sheet multiple times in a cylindrical shape, the first fiber sheet having a width of 15 mm to 75 mm, the first fiber sheet being wound spirally and having overlapping portions in the longitudinal direction of the cylindrical filter, and the overlap rate, which is expressed as the ratio of the width of the overlapping portions between first fiber sheets that are wound in a continuous order to the width of the first fiber sheet, is 80% to 99%.

2. The cylindrical filter according to claim 1, wherein the winding angle of the first fiber sheet is 70 degrees or more and less than 90 degrees.

3. The filtration layer is arranged on the inflow side of the tubular fiber assembly A to be filtered, and includes a tubular fiber assembly B formed by winding a third fiber sheet multiple times in a tubular shape, wherein the third fiber sheet has a width of 15 mm or more and 75 mm or less, the third fiber sheet is wound spirally around the outer circumference of the tubular fiber assembly A, and has overlapping portions in the longitudinal direction of the tubular filter, and the overlap rate, which is expressed as the ratio of the width of the overlapping portions between the third fiber sheets that are wound in a continuous order to the width of the third fiber sheet, is 80% or more and 99% or less, as described in claim 1.

4. The cylindrical filter according to claim 1, wherein the cylindrical fiber assembly A includes a second fiber sheet that is alternately arranged with a first fiber sheet in the thickness direction.

5. The cylindrical filter according to claim 4, wherein in the tubular fiber assembly A, a first fiber sheet is bonded via a second fiber sheet.

6. The cylindrical filter according to claim 3, wherein the tubular fiber assembly B includes a fourth fiber sheet that is alternately arranged with a third fiber sheet in the thickness direction.

7. The tubular filter according to claim 6, wherein in the tubular fiber assembly B, a third fiber sheet is bonded via a fourth fiber sheet.

8. The filtration layer is arranged 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 is wound multiple times in a tubular shape, the fifth fiber sheet having a width of 15 mm or more and 75 mm or less, the fifth fiber sheet being wound spirally around the outer circumference of the tubular fiber assembly B, having overlapping portions in the longitudinal direction of the tubular filter, and the overlap rate, which is expressed as the ratio of the width of the overlapping portions between the fifth fiber sheets that are wound in a continuous order to the width of the fifth fiber sheet, is 80% or more and 99% or less, as described in claim 3.

9. The cylindrical filter according to claim 8, wherein the tubular fiber aggregate C includes a sixth fiber sheet that is alternately arranged with a fifth fiber sheet in the thickness direction.

10. The tubular filter according to claim 9, wherein in the tubular fiber assembly C, a fifth fiber sheet is bonded via a sixth fiber sheet.

11. The tubular filter according to claim 3, wherein in the tubular fiber assembly B, the third fiber sheet is a multilayer fiber sheet comprising two or more fiber sheets.

12. The tubular 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.

13. The tubular filter according to claim 8, wherein in the tubular fiber assembly C, the fifth fiber sheet is a multilayer fiber sheet comprising two or more fiber sheets.

14. A method for manufacturing a cylindrical filter including a filtration layer formed of a tubular fiber aggregate, comprising step A of spirally winding a first fiber sheet around the surface of a rotating shaft to obtain a tubular fiber aggregate A, wherein the first fiber sheet has a width of 15 mm or more and 75 mm or less, and in step A, the first fiber sheet is wound multiple times in the longitudinal direction of the cylindrical filter so as to overlap, and the overlap rate, which is indicated by the ratio of the width of the overlapping portion between the first fiber sheets in a continuous winding order to the width of the first fiber sheet, is 80% or more and 99% or less.

15. A method for manufacturing a tubular filter according to claim 14, comprising step B of spirally winding a third fiber sheet onto the surface of a tubular fiber assembly A to obtain a tubular fiber assembly B, wherein the third fiber sheet has a width of 15 mm or more and 75 mm or less, and in step B, the third fiber sheet is wound multiple times in the longitudinal direction of the tubular filter so as to overlap, and the overlap rate, which is indicated by the ratio of the width of the overlapping portion of the third fiber sheets that are wound in a continuous order to the width of the third fiber sheet, is 80% or more and 99% or less.

16. A method for manufacturing a tubular filter according to claim 15, comprising step C of spirally winding a fifth fiber sheet onto the surface of a tubular fiber assembly B to obtain a tubular fiber assembly C, wherein the fifth fiber sheet has a width of 15 mm or more and 75 mm or less, and in step C, the fifth fiber sheet is wound multiple times in the longitudinal direction of the tubular filter so as to overlap, and the overlap rate, which is indicated by the ratio of the width of the overlapping portion between the fifth fiber sheets that are wound in a continuous order to the width of the fifth fiber sheet, is 80% or more and 99% or less.

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

18. The method for manufacturing a cylindrical filter according to claim 14, wherein in step A, a multilayer fiber sheet containing two or more fiber sheets is used as the first fiber sheet.

19. The method for manufacturing a cylindrical filter according to claim 16, 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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