Cylindrical filter and manufacturing method thereof

Abstract

To provide a cylindrical filter which has a low production cost, a basic filtration efficiency and filtration service life, and a manufacturing method thereof.SOLUTION: The present invention is a cylindrical filter including a filtration layer formed of a cylindrical fiber assembly, where the filtration includes layer a filtration layer B5 formed of a cylindrical fiber assembly B50 being an alternate cylindrical winding of a first fiber sheet 51 and a second sheet 52, and where in a thickness direction of the filtration layer B, the first fiber sheet and the second fiber sheet are alternately arranged, the first fiber sheet bonding via the second fiber sheet to satisfy at least one requirement of followings (a) and (b). (a) The thickness H1 of the first fiber sheet is larger than the thickness H2 of the second fiber sheet. (b) The density D1 of the first fiber sheet is larger than the density D2 of the second fiber sheet.SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] Cylindrical filters, which are made by winding a fiber assembly into a cylindrical shape, are easy to handle and are therefore widely used for filtering various liquids, such as beverages, chemicals, oils and fats, paints, and industrial cleaning water, such as cleaning water for electronic components and semiconductor products. Cylindrical filters usually have a cylindrical fiber assembly, which is manufactured by winding various fiber sheets, such as nonwoven fabrics, around a mandrel, as a filtration layer. For example, Patent Document 1 describes a cylindrical filter including a filtration layer in which a fine nonwoven fabric and a thick spunlace nonwoven fabric, which is made of constituent fibers including thermally adhesive fibers having a fineness greater than that of the constituent fibers of the fine nonwoven fabric and in which the constituent fibers are entangled with each other and at least a part of the fibers is thermally bonded, are laminated together in a state where they are not substantially thermally bonded to each other and wound into a cylindrical shape.

[0003] Another method for producing a cylindrical filter is known in which a resin is fiberized and the fiber is directly wound around a mandrel, thereby eliminating the step of forming the fiber into a sheet. For example, Patent Document 2 describes a nonwoven fabric depth filter element comprising a tubular member having a hollow interior extending axially over the entire length of the member and a filter portion consisting of a plurality of filaments substantially continuously intertwined and made of a synthetic resin material, the filter portion having a central support zone and a filtration zone, the central support zone having an inner surface forming the hollow interior and consisting of a plurality of support zone filaments having a diameter large enough to provide support for the filtration zone, the filtration zone being located radially outward of the central support zone and having at least one filtration level consisting of a plurality of filtration filaments, the filaments of the support zone and the filtration filaments being separate from each other. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2004-000851 A [Patent Document 2] Special Publication No. 8-501976 Summary of the Invention [Problem to be solved by the invention]

[0005] Patent Document 1 discloses a cylindrical filter including a filtration layer manufactured using two or more types of nonwoven fabric. In such a cylindrical filter manufactured by winding various fiber sheets, it is known that the average fiber diameter of the fibers constituting the filtration layer is gradually reduced from the inlet side (also called the primary side) of the filtrate to the outlet side (also called the secondary side) of the filtrate, or the average pore diameter of the fiber sheet constituting the filtration layer is gradually reduced from the inlet side of the filtrate to the outlet side of the filtrate, in order to increase the filtration efficiency and extend the filtration life by gradually collecting and removing foreign matter contained in the object of filtration. A cylindrical filter manufactured by such a manufacturing method is a cylindrical filter with excellent filtration efficiency and filtration life because the average fiber diameter and average pore diameter of the filtration layer are gradually reduced, but if the average fiber diameter and average pore diameter of the fiber sheet are changed in multiple stages to further improve these performances, it is necessary to prepare multiple fiber sheets with different average fiber diameters and average pore diameters, and to stop the machine once and replace the fiber sheet to be wound when changing the fiber sheet to be wound. Therefore, such cylindrical filters tend to have low productivity and high production costs. The cylindrical filter described in Patent Document 2 is produced by spinning fibers (meltblown fibers) produced by the meltblown method toward a rotating mandrel and simultaneously accumulating and winding the fibers on the mandrel surface to directly form a cylindrical filter, so that the cylindrical filter can be produced with excellent production efficiency and at low cost. However, the method of directly forming fibers produced by the meltblown method into a cylindrical shape and winding it up makes it difficult to provide differences in fiber diameter and pore diameter in the entire filter, particularly in the thickness direction of the filtration layer constituting the filter (in other words, the direction in which the object to be filtered flows from the inlet side to the outlet side).

[0006] SUMMARY OF THE PRESENT DISCLOSURE In order to solve the above-mentioned problems in the conventional art, the present invention provides a cylindrical filter having high production efficiency and therefore low production costs, and also having basic filtering efficiency and filtering life, and a method for manufacturing the same. [Means for solving the problem]

[0007] The present invention relates to a cylindrical filter including a filtration layer formed of a tubular fiber assembly, the filtration layer including a filtration layer B formed of a tubular fiber assembly B in which a first fiber sheet and a second fiber sheet are alternately wound into a cylindrical shape, the first fiber sheet and the second fiber sheet are alternately arranged in a thickness direction of the filtration layer B, and the first fiber sheet is bonded via the second fiber sheet, and the cylindrical filter satisfies at least one of the following requirements (a) and (b): (a) The thickness H1 of the first fiber sheet is greater than the thickness H2 of the second fiber sheet. (b) the density D1 of the first fiber sheet is greater than the density D2 of the second fiber sheet;

[0008] The present invention relates to a method for producing a cylindrical filter including a filtration layer formed of a cylindrical fiber aggregate, comprising a step B of: discharging a molten thermoplastic resin from an outlet hole of a spinning nozzle, and simultaneously blowing meltblown fibers stretched by a high-temperature gas flow ejected from around the outlet hole onto a surface of a rotating shaft rotating at a constant speed, while winding a first fiber sheet around the surface of the rotating shaft, and accumulating the meltblown fibers on the surface of the first fiber sheet to form a meltblown web, which is then wound around the surface, to obtain a cylindrical fiber aggregate B in which a first fiber sheet and a meltblown web are wound alternately. Effect of the Invention

[0009] The present invention can provide a cylindrical filter having high production efficiency, low production costs, and basic filtering efficiency and filtering life. Furthermore, according to the manufacturing method of the present invention, it is possible to increase the productivity of cylindrical filters having basic filtering efficiency and filtering life, and to reduce the production cost. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic partial cross-sectional perspective view of a cylindrical filter according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a partial cross-sectional view of a filtration layer B of an example of a cylindrical filter of the present invention. [Diagram 3] FIG. 1 is a schematic perspective view of an example of a cylindrical filter manufacturing apparatus used in the present invention. [Figure 4] FIG. 2 is a schematic diagram illustrating the positional relationship between filtration layers A and B of an example of a cylindrical filter of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The inventors of the present invention have conducted extensive research to solve the above-mentioned problems. Generally, regarding the performance of a cylindrical filter, if there are voids inside the filter, the amount of foreign matter that can be captured can be increased, and the filtration life is extended. In addition, by making the fibers thinner and increasing the number of fibers per unit thickness, and passing the liquid to be filtered through more fibers, finer foreign matter can be captured, and the filtration efficiency tends to be improved. Therefore, it was speculated that both the filtration life and the filtration efficiency can be improved by having these two configurations. As a result, it was found that in a cylindrical filter including a filtration layer formed of a cylindrical fiber aggregate, the filtration layer includes a filtration layer B formed of a cylindrical fiber aggregate B in which a first fiber sheet and a second fiber sheet are alternately wound into a cylindrical shape, the filtration layer B has a configuration in which the first fiber sheet and the second fiber sheet are alternately arranged in the thickness direction of the filtration layer B, the first fiber sheet is bonded via the second fiber sheet, and the filtration layer B has a configuration that satisfies at least one of the requirements (a) and (b) shown below, thereby improving both the filtration life and the filtration efficiency. (a) The thickness H1 of the first fiber sheet is greater than the thickness H2 of the second fiber sheet. (b) the density D1 of the first fiber sheet is greater than the density D2 of the second fiber sheet;

[0012] The inventors of the present invention have intensively studied the manufacture of a cylindrical filter that satisfies the above-mentioned configuration. As a result, as a cylindrical filter that satisfies the above-mentioned configuration, for example, a method is found in which meltblown fibers spun from a nozzle are discharged toward the surface of the first fiber sheet while a first fiber sheet is wound around a rotating shaft that rotates at a constant speed, and immediately after the meltblown fibers are accumulated on the surface of the first fiber sheet, the meltblown web and the first fiber sheet are wound together so that the first fiber sheet is again superimposed on the meltblown web (which becomes a second fiber sheet) made of the accumulated meltblown fibers, thereby forming a meltblown web made of the first fiber sheet and the meltblown fibers accumulated on the first fiber sheet. The inventors have found that by producing a tubular fiber aggregate B in which a meltblown web (i.e., a second fiber sheet) is laminated and integrated and continuously wound to form a tubular fiber aggregate, a cylindrical filter can be obtained that has high productivity and low production costs, includes a filtration layer formed of a tubular fiber aggregate in which fiber sheets of different thicknesses and / or densities are alternately wound, and in which a first fiber sheet having a large thickness and / or density is bonded via a second fiber sheet (meltblown web) having a small thickness and / or density, and that the cylindrical filter has basic filtration efficiency and filtration life.

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

[0014] The filtration layer includes a filtration layer B formed of a cylindrical fiber assembly B in which a first fiber sheet and a second fiber sheet are alternately wound. In the thickness direction of the filtration layer B, the first fiber sheet and the second fiber sheet are alternately arranged, and the first fiber sheet is bonded via the second fiber sheet, and (a) the thickness H1 of the first fiber sheet is greater than the thickness H2 of the second fiber sheet, and / or (b) the density D1 of the first fiber sheet is greater than the density D2 of the second fiber sheet. In this way, in the thickness direction of the filtration layer B, fiber sheets having different thicknesses and / or densities are alternately arranged and bonded to each other, so that the first fiber sheet does not collapse under pressure when a liquid passes through it, and the interlayer structure is stable, thereby exhibiting basic filtration performance, for example, a filtration life of 400 L or more and a filtration efficiency of 75.0% or more for particles with a particle size of 5.0 μm. Furthermore, by appropriately selecting the first fiber sheet, a filter layer suitable for final filtration of a liquid containing a low concentration of particles with a different physical property, for example, a liquid containing particles with a small particle size, can be obtained, and a filtration efficiency of 75% or more for particles with a particle size of 1.0 μm and a filtration life of 300 L or more can be obtained. Furthermore, by using a first fiber sheet with a large average fiber diameter, a filter layer suitable for primary filtration of a liquid containing a high concentration of particles with a large particle size can be obtained, and a filtration efficiency of 75% or more for particles with a particle size of 10 μm and a filtration life of 2000 L or more can be obtained. In this specification, the thickness and density of the fiber sheet, and the filtration life and filtration efficiency of the cylindrical filter can be measured as described in the Examples.

[0015] The ratio H1 / H2 of the thickness H1 of the first fiber sheet to the thickness H2 of the second fiber sheet is not particularly limited, but from the viewpoint of improving various filtering performances such as the filtering efficiency and filtering life of the cylindrical filter, it is preferably 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 8 or less, even more preferably 2.0 or more and 6 or less, and particularly preferably 2.0 or more and 4 or less.

[0016] From the viewpoint of improving various filtering performances of the obtained cylindrical filter, such as filtering efficiency and filtering life, the thickness H1 of the first fiber sheet is preferably 0.10 mm or more and 0.60 mm or less, more preferably 0.15 mm or more and 0.45 mm or less, even more preferably 0.18 mm or more and 0.40 mm or less, and particularly preferably 0.20 mm or more and 0.37 mm or less.

[0017] From the viewpoint of improving various filtering performances of the obtained cylindrical filter, such as filtering efficiency and filtering life, the thickness H2 of the second fiber sheet is preferably 0.04 mm or more and 0.18 mm or less, more preferably 0.06 mm or more and 0.16 mm or less, even more preferably 0.07 mm or more and 0.14 mm or less, and particularly preferably 0.075 mm or more and 0.125 mm or less.

[0018] The ratio D1 / D2 of the density D1 of the first fiber sheet to the density D2 of the second fiber sheet is not particularly limited, but from the viewpoint of improving various filtration performances of the cylindrical filter, such as the filtration efficiency and filtration life, is preferably 1.1 or more and 10.0 or less, more preferably 1.2 or more and 8.0 or less, even more preferably 1.3 or more and 6.0 or less, even more preferably 1.4 or more and 5.0 or less, and particularly preferably 1.5 or more and 4.5 or less.

[0019] The density D1 of the first fiber sheet is set to 0.03 g / cm from the viewpoint of improving various filtering performances such as filtering efficiency and filtering life of the obtained cylindrical filter. 3 More than 0.5g / cm 3 It is preferable that the concentration is 0.04 g / cm or less. 3 More than 0.4g / cm 3 More preferably, it is 0.05 g / cm or less. 3 More than 0.35g / cm 3 More preferably, it is 0.06 g / cm or less. 3 More than 0.3g / cm 3 It is particularly preferred that:

[0020] The density D2 of the second fiber sheet is set to 0.01 g / cm from the viewpoint of improving various filtering performances such as filtering efficiency and filtering life of the obtained cylindrical filter. 3 More than 0.20g / cm 3 It is preferable that the density is 0.015 g / cm or less. 3 More than 0.15g / cm 3 More preferably, it is 0.02 g / cm or less. 3 More than 0.10g / cm 3 More preferably, it is 0.025 g / cm or less. 3 More than 0.08g / cm 3 It is particularly preferred that:

[0021] The first fiber sheet has a basis weight W1 of 15 g / m from the viewpoint of improving various filtering performances such as filtering efficiency and filtering life of the obtained cylindrical filter. 2 More than 100g / m 2 It is preferable that the thickness is less than 18 g / m 2 More than 80g / m 2 More preferably, it is 20 g / m or less. 2 More than 60g / m 2 Even more preferably, it is 23 g / m or less. 2 More than 50g / m 2 It is even more preferable that the weight per unit area of ​​the fiber sheet is as follows: In this specification, the weight per unit area of ​​the fiber sheet can be measured as described in the Examples.

[0022] The second fiber sheet has a basis weight W2 of 2 g / m from the viewpoint of improving various filtering performances such as filtering efficiency and filtering life of the obtained cylindrical filter. 2 More than 15g / m 2 It is preferable that the content is less than 3 g / m 2 More than 12g / m 2 More preferably, it is 3.5 g / m or less. 2 More than 10g / m 2 More preferably, it is 4 g / m or less. 2 More than 8g / m 2 It is particularly preferred that:

[0023] 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 filtering performances such as the filtering efficiency and filtering life of the obtained cylindrical filter, it is preferably 1.1 or more and 50 or less, more preferably 1.5 or more and 40 or less, even more preferably 2.0 or more and 30 or less, and particularly preferably 2.5 or more and 25 or less.

[0024] From the viewpoint of easily achieving both the filtration efficiency and the filtration life of the cylindrical filter, the first fiber sheet preferably has an average fiber diameter d1 of, for example, 0.3 μm or more and 20 μm or less. From the viewpoint of achieving both the filtration efficiency and the 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. In addition, in order to achieve both filtration efficiency and filtration life in the cylindrical filter, particularly from the viewpoint of having many voids inside the cylindrical filter when used for filtration, preventing the cylindrical filter from clogging in a short time and allowing it to be used for filtration for a longer period of time, the average fiber diameter d1 of the first fiber sheet is more preferably 15 μm or less, even more preferably 10 μm or less, even more preferably 8 μm or less, even more preferably 6 μm or less, even more preferably 5 μm or less, even more preferably 4 μm or less, even more preferably 3.40 μm or less, and particularly preferably 3.0 μm or less. In this specification, the average fiber diameter of the fiber sheet can be measured as described in the Examples.

[0025] The first fiber sheet preferably has a fiber diameter CV value of 0.25 or more and 3.0 or less from the viewpoint that the filtration layer B not only stably captures and collects foreign matter having a smaller particle size, but also extends the filtration life of the cylindrical filter by lengthening the time required for the filtration layer B to become clogged. From the viewpoint of extending the filtration life of the cylindrical filter by lengthening the time required for the filtration layer B to become clogged, the CV value of the fiber diameter of the first fiber sheet is more preferably 0.4 or more, even more preferably 0.6 or more, and particularly preferably 0.7 or more. In addition, from the viewpoint of easily maintaining the filtration efficiency of the cylindrical filter by appropriately suppressing the variation in the fiber diameter of the first fiber sheet constituting the filtration layer B, the CV value of the fiber diameter of the first 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. In this specification, the CV value of the fiber diameter of the fiber sheet can be measured as described in the examples.

[0026] From the viewpoint of easily achieving both the filtration efficiency and the filtration life of the cylindrical filter, the second fiber sheet preferably has an average fiber diameter d2 of 0.3 μm or more and 30 μm or less. From the viewpoint of achieving both the filtration efficiency and the 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. In addition, from the viewpoint of achieving both the filtration efficiency and the filtration life of the cylindrical filter, particularly from the viewpoint of having many voids inside the cylindrical filter when used for filtration, so that the cylindrical filter does not become clogged in a short time and can be used for a longer period of time for filtration processing, the average fiber diameter d2 of the second fiber sheet is preferably 25 μm or less, more preferably 20 μm or less, particularly preferably 15 μm or less, and most preferably 12 μm or less.

[0027] From the viewpoint of increasing the filtration life of the cylindrical filter, it is preferable that the first fiber sheet and the second fiber sheet have different average fiber diameters. The ratio d1 / d2 of the average fiber diameter d1 of the first fiber sheet to the average fiber diameter d2 of the second fiber sheet is preferably 0.01 to 3.0, more preferably 0.02 to 2.0, even more preferably 0.03 to 1.8, and particularly preferably 0.05 to 1.5. 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 can be selected taking into consideration the filtration efficiency required for the resulting cylindrical filter. For example, if filtration performance is required to collect and capture particles with a particle diameter of 1.0 μm at a filtration efficiency of 75% or more, 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 0.05 or more and 1.0 or less, more preferably 0.1 or more and 0.8 or less, and particularly preferably 0.15 or more and 0.60 or less. Furthermore, if a filtration performance is required that can collect and capture particles having a particle diameter of 3.0 μm to 5.0 μm at a filtration efficiency of 75%, 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 0.15 or more and 1.0 or less, more preferably 0.20 or more and 0.8 or less, and particularly preferably 0.25 or more and 0.6 or less. Furthermore, if filtration performance is required to collect and capture particles with a particle diameter of 10.0 μm at a filtration efficiency of 75% or more, 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 0.5 or more and 3.0 or less, more preferably 0.75 or more and 2.5 or less, and particularly preferably 1.0 or more and 2.0 or less.

[0028] The average pore size of the first fiber sheet is not particularly limited, but is preferably 0.5 μm to 60 μm, and more preferably 1 μm to 50 μm. The average pore size of the first fiber sheet can be selected in consideration of the filtration efficiency required for the resulting cylindrical filter, and for example, if filtration performance is required to collect and capture particles with a particle size of 1.0 μm at a filtration efficiency of 75% or more, the average pore size of the first fiber sheet is preferably 1.2 μm to 5 μm, more preferably 1.5 μm to 3.5 μm, and even more preferably 1.8 μm to 3 μm. Furthermore, if filtration performance is required to collect and capture particles with diameters of 3.0 μm to 5.0 μm at a filtration efficiency of 75%, the average pore size of the first fiber sheet is preferably 2 μm or more and 25 μm or less, more preferably 2.5 μm or more and 20 μm or less, even more preferably 2.8 μm or more and 15 μm or less, and most preferably 2.8 μm or more and 10 μm or less. Furthermore, if a filtration performance is required that allows collection and capture of particles having a particle diameter of 10.0 μm at a filtration efficiency of 75% or more, the average pore size of the first fiber sheet is preferably 10 μm to 60 μm, more preferably 12 μm to 50 μm, and even more preferably 15 μm to 48 μm. If the average pore size of the first fiber sheet is within the above range, the filtration accuracy tends to be high.

[0029] The maximum pore size of the first fiber sheet is not particularly limited, but the maximum pore size is preferably 1 μm to 90 μm, more preferably 2 μm to 50 μm, and particularly preferably 3 μm to 40 μm. The most abundant pore size of the first fiber sheet is not particularly limited, but the most abundant pore size is preferably 1.0 μm to 40 μm, more preferably 1.0 μm to 15 μm, even more preferably 1.5 μm to 10 μm, and particularly preferably 1.8 μm to 8 μm. The minimum pore size of the first fiber sheet is not particularly limited, but the minimum pore size is preferably 0.1 μm to 20 μm, more preferably 0.5 μm to 15 μm, and particularly preferably 1 μm to 8 μm. When the maximum pore size, the most abundant pore size, and the minimum pore size of the first fiber sheet are within the above ranges, the filtration accuracy is likely to be high. If the resulting cylindrical filter is required to have a filtering performance capable of collecting and capturing particles having a particle diameter of 10.0 μm at a filtering efficiency of 75% or more, the maximum pore size of the first fiber sheet is preferably 70 μm to 100 μm, the most abundant pore size of the first fiber sheet is preferably 20 μm to 50 μm, and the minimum pore size of the first fiber sheet is preferably 10 μm to 30 μm. The average pore size, maximum pore size, most abundant pore size, and minimum pore size of the first fiber sheet can be measured using a capillary flow porometer "CFP-1200-AEXC-P" manufactured by Porous Material Inc. in accordance with JIS K 3832 (1990) (bubble point test method for microfiltration membrane elements and modules).

[0030] The air permeability of the first fiber sheet is not particularly limited and is appropriately set based on the designed filtration efficiency. For example, 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 / cm2 / second or more 20cm 3 / cm 2 / sec or less, or 3cm 3 / cm 2 / second or more 10cm 3 / cm 2 In this specification, the air permeability of the first fiber sheet can be measured in accordance with JIS L 1096 using a Frazier type testing machine.

[0031] The first fiber sheet is preferably a meltblown nonwoven fabric, and the second fiber sheet is preferably a meltblown web. The meltblown nonwoven fabric and the meltblown web can be fiber sheets with a wide fiber diameter distribution, and the CV value of the fiber diameter is likely to be 0.25 or more. In the meltblown nonwoven fabric and the meltblown web, solid matter (particles) easily passes through the inter-fiber gaps formed by fibers with a large fiber diameter, and fine particles are captured in the inter-fiber gaps formed by fibers with a small fiber diameter in the meltblown nonwoven fabric and the meltblown web. Therefore, by using a fiber assembly in which the meltblown nonwoven fabric and the meltblown web are wound alternately multiple times as a filtration layer, it is easy to obtain a filtration layer that is less likely to clog and can capture and collect fine foreign matter by fibers with a small fiber diameter.

[0032] The first fiber sheet preferably has a width of 15 mm or more and 75 mm or less, more preferably 20 mm or more and 65 mm or less, even more preferably 25 mm or more and 60 mm or less, and particularly preferably 28 mm or more and 55 mm or less. As the first fiber sheet, a nonwoven fabric having a width that satisfies the above-mentioned range can be suitably used. When the width of the first fiber sheet constituting the filtration layer B satisfies the above-mentioned range, not only the productivity is increased in the step of winding the first fiber sheet to form the filtration layer B, but also the first fiber sheet is less likely to be wrinkled when being wound, and the first fiber sheet is wound without gaps in the longitudinal direction of the cylindrical filter, making it easier to obtain a cylindrical filter with high filtration efficiency.

[0033] From the viewpoint of facilitating improvement of filtration performance, the first fiber sheet may be composed of a multi-layer fiber sheet including two or more layers of fiber sheets. When the first fiber sheet is composed of a multi-layer fiber sheet including two or more layers of fiber sheets, each of the fiber sheets constituting the multi-layer fiber sheet corresponds to the first fiber sheet and satisfies at least one of the above (a) and (b). When the first fiber sheet is composed of a multi-layer fiber sheet including two or more layers of fiber sheets, the first fiber sheets of each layer constituting the multi-layer fiber sheet may have substantially the same physical properties such as thickness, density, basis weight, average fiber diameter, and CV value of fiber diameter, or may have substantially the same physical properties in part or all different. In the multi-layer fiber sheet, from the viewpoint of productivity and maintaining filtration performance, the number of layers of fiber sheets constituting the multi-layer fiber sheet may be 6 or less, specifically 2 to 6, 2 to 5, 2 to 4, or 2 to 3. In the multi-layer fiber sheet, it is preferable that each fiber sheet is not bonded to each other from the viewpoint of productivity.

[0034] When the first fiber sheet is a multilayer fiber sheet composed of a plurality of fiber sheets, it is preferable that the thickness, density, basis weight, average fiber diameter, and CV value of fiber diameter of each fiber sheet (first fiber sheet) constituting the multilayer fiber sheet also satisfy the above-mentioned preferred ranges of the thickness, density, basis weight, average fiber diameter, and CV value of fiber diameter of the first fiber sheet. Also, when the first fiber sheet is a multilayer fiber sheet composed of a plurality of fiber sheets, each fiber sheet (first fiber sheet) constituting the multilayer fiber sheet is preferably a meltblown nonwoven fabric.

[0035] When the first fiber sheet is a multilayer fiber sheet constituted by a plurality of fiber sheets, from the viewpoint of easily improving the filtration accuracy and filtration life of the obtained cylindrical filter, it is preferable that the multilayer fiber sheet is a multilayer fiber sheet including a first fiber sheet X1 and a first fiber sheet Y1, the first fiber sheet X1 and the first fiber sheet Y1 satisfy at least one of the following requirements (r) and (s), and are wound so that the first fiber sheet X1 is located more inward than the first fiber sheet Y1. (r): The average fiber diameter dX1 of the first fiber sheet X1 is smaller than the average fiber diameter dY1 of the first fiber sheet Y1. (s): The density DX1 of the first fiber sheet X1 is greater than the density DY1 of the first fiber sheet Y1.

[0036] The average fiber diameter dX1 of the first fiber sheet X1 is not particularly limited as long as it satisfies the above-mentioned range of the average fiber diameter d1 of the first fiber sheet, but is preferably adjusted according to the filtration performance required for the obtained filtration layer B and a cylindrical filter including the same, more specifically, the degree to which foreign matter of a certain particle diameter can be collected and captured, that is, the so-called filtration accuracy. If the filtration performance required for the cylindrical filter including the filtration layer B is such that particles having a particle diameter of 1.0 μm can be collected and captured at a rate of 75% or more with a filtration efficiency of 75%, the average fiber diameter dX1 of the first fiber sheet X1 is preferably 0.3 μm to 3.3 μm, more preferably 0.5 μm to 3.0 μm, particularly preferably 0.8 μm to 2.5 μm, and most preferably 1.0 μm to 2.2 μm. If a cylindrical filter including a filtration layer B is required to have filtration performance capable of collecting and capturing particles having a particle diameter of 3.0 μm at a filtration efficiency of 75% or more, the average fiber diameter dX1 of the first fiber sheet X1 is preferably 1.5 μm or more and 4.2 μm or less, more preferably 2.0 μm or more and 3.8 μm or less, particularly preferably 2.2 μm or more and 3.6 μm or less, and most preferably 2.5 μm or more and 3.5 μm or less. If a cylindrical filter including a filtration layer B is required to have filtration performance capable of collecting and capturing particles having a particle diameter of 5.0 μm at a filtration efficiency of 75% or more, the average fiber diameter dX1 of the fiber sheet X1 is preferably 2.5 μm or more and 6.0 μm or less, more preferably 3.0 μm or more and 5.5 μm or less, particularly preferably 3.2 μm or more and 5.0 μm or less, and most preferably 3.5 μm or more and 4.8 μm or less. If a cylindrical filter including a filtration layer B is required to have filtration performance capable of collecting and capturing particles having a particle diameter of 10.0 μm at a filtration efficiency of 75% or more, the average fiber diameter dX1 of the first fiber sheet X1 is preferably 5 μm or more and 20 μm or less, more preferably 8 μm or more and 18 μm or less, particularly preferably 10 μm or more and 16 μm or less, and most preferably 12 μm or more and 15 μm or less.

[0037] The average fiber diameter dY1 of the first fiber sheet Y1 is not particularly limited as long as it satisfies the above-mentioned range of the average fiber diameter d1 of the first fiber sheet, as in the case of the first fiber sheet X1, but is preferably adjusted according to the filtering performance required for the resulting filtration layer B and a cylindrical filter including it, more specifically, the filtering accuracy, i.e., the degree to which foreign matter of a certain particle size can be collected and captured. Moreover, since the first fiber sheet Y1 is disposed upstream of the first fiber sheet X1, which has substantially the same or smaller average fiber diameter, the average fiber diameter dY1 may be larger than that of the first fiber sheet X1. Therefore, if a cylindrical filter including the filtration layer B is required to have the filtration performance to collect and capture particles having a particle diameter of 1.0 μm at a filtration efficiency of 75% or more, the average fiber diameter dY1 of the first fiber sheet Y1 is preferably 0.3 μm or more and 4.0 μm or less, more preferably 0.5 μm or more and 3.8 μm or less, particularly preferably 0.8 μm or more and 3.6 μm or less, and most preferably 1.0 μm or more and 3.5 μm or less. If a cylindrical filter including the filtration layer B is required to have the filtration performance to collect and capture particles having a particle diameter of 3.0 μm at a filtration efficiency of 75% or more, the average fiber diameter dY1 of the first fiber sheet Y1 is preferably 1.5 μm or more and 5.0 μm or less, more preferably 2.0 μm or more and 4.8 μm or less, particularly preferably 2.2 μm or more and 4.5 μm or less, and most preferably 2.5 μm or more and 4.2 μm or less. If a cylindrical filter including the filtration layer B is required to have the filtration performance to collect and capture particles having a particle diameter of 5.0 μm at a filtration efficiency of 75% or more, the average fiber diameter dY1 of the first fiber sheet Y1 is preferably from 2.5 μm to 18 μm, more preferably from 3.0 μm to 16 μm, particularly preferably from 3.2 μm to 15 μm, and most preferably from 3.5 μm to 15 μm. If a cylindrical filter including the filtration layer B is required to have the filtration performance to collect and capture particles having a particle diameter of 10.0 μm at a filtration efficiency of 75% or more, the average fiber diameter dY1 of the first fiber sheet Y1 is preferably 5 μm or more and 20 μm or less, more preferably 8 μm or more and 18 μm or less, particularly preferably 10 μm or more and 18 μm or less, and most preferably 12 μm or more and 16 μm or less.

[0038] The average fiber diameter dX1 of the first fiber sheet X1 and the average fiber diameter dY1 of the first fiber sheet Y1 may be substantially the same, or the average fiber diameter dY1 of the first fiber sheet Y1 may be larger. If the average fiber diameter dY1 of the first fiber sheet Y1 is larger than the average fiber diameter dX1 of the first fiber sheet X1, a coarse-dense structure is generated between the first fiber sheet X1 and the first fiber sheet Y1, which can further improve the filtration performance. When the first fiber sheet X1 and the first fiber sheet Y1 having different average fiber diameters are used as the first fiber sheets in the filtration layer B, the ratio dX1 / dY1 of the average fiber diameter dX1 of the first fiber sheet X to the average fiber diameter dY1 of the first fiber sheet Y1 is, from the viewpoint of improving the filtration performance, preferably 0.15 or more and less than 1, more preferably 0.2 or more and less than 1, even more preferably 0.23 or more and less than 1, and particularly preferably 0.25 or more and less than 1. If the filtration performance required for a cylindrical filter including the filtration layer B is to collect and capture particles having a particle diameter of 1.0 μm at a filtration efficiency of 75% or more, if the average fiber diameter dX1 of the first fiber sheet X1 and the average fiber diameter dY1 of the first fiber sheet Y1 are different and the difference in the average fiber diameters is too large, the filtration performance will be significantly affected. In this case, the ratio dX1 / dY1 of the average fiber diameter dX1 of the first fiber sheet X to the average fiber diameter dY1 of the first fiber sheet Y1 is preferably 0.55 or more and less than 1, more preferably 0.65 or more and 0.98 or less, and particularly preferably 0.70 or more and 0.95 or less.

[0039] From the viewpoint of improving the filtration performance, the density DX1 of the first fiber sheet X1 and the density DY1 of the first fiber sheet Y1 are set to 0.03 g / cm 3 More than 0.40g / cm 3 It is preferable that the concentration is 0.04 g / cm or less. 3 More than 0.30g / cm 3 More preferably, it is 0.05 g / cm or less. 3 More than 0.25g / cm 3 More preferably, it is 0.06 g / cm or less. 3 More than 0.20g / cm 3 It is particularly preferred that: The density DX1 of the first fiber sheet X1 and the density DY1 of the first fiber sheet Y1 are preferably adjusted depending on the filtration performance required for the resulting filtration layer B and a cylindrical filter including the same, more specifically, on the so-called filtration accuracy, that is, the degree to which foreign matter of a certain particle size can be collected and captured. Therefore, if a cylindrical filter including the filtration layer B is required to have a filtration performance capable of collecting and capturing particles having a particle diameter of 1.0 μm at a filtration efficiency of 75% or more, the density DX1 of the first fiber sheet X1 and the density DY1 of the first fiber sheet Y1 should be 0.05 / cm from the viewpoint of improving the filtration performance. 3 More than 0.22g / cm 3 It is preferable that the value is 0.06 / cm or less. 3 More than 0.20g / cm 3 More preferably, it is 0.06 g / cm or less. 3 More than 0.18g / cm 3 More preferably, it is 0.08 g / cm or less. 3 More than 0.16g / cm 3 It is particularly preferred that: In addition, if a cylindrical filter including the filtration layer B is required to have a filtration performance capable of collecting and capturing particles having a particle diameter of 3.0 μm to 10.0 μm at a filtration efficiency of 75% or more, the density DX1 of the first fiber sheet X1 and the density DY1 of the first fiber sheet Y1 should be 0.03 / cm from the viewpoint of improving the filtration performance. 3 More than 0.20g / cm 3 It is preferable that the value is 0.04 / cm or less. 3 More than 0.15g / cm 3 More preferably, it is 0.05 g / cm or less. 3 More than 0.10g / cm 3 More preferably, it is 0.06 g / cm or less. 3 More than 0.09g / cm 3 It is particularly preferred that:

[0040] In the cylindrical filter of the present invention, it is sufficient that the cylindrical filter includes the filtration layer B. The cylindrical filter may include another filtration layer upstream of the filtration layer B (in other words, on the inflow side of the filtration layer B), and the upstream side of the filtration layer B may be wound with various fabrics several times (specifically, 2 to 5 times) in order to improve the design, or the filtration layer B may not have another filtration layer upstream of it. The same is true for the downstream side of filtration layer B (in other words, the outflow side of filtration layer B), where another filtration layer may be provided downstream of filtration layer B, or filtration layer B may have a porous core material (specifically, a cylindrical porous resin molded body manufactured by injection molding or extrusion molding a thermoplastic resin) on the downstream side, or there may not be another filtration layer or core material downstream of filtration layer B. However, in the tubular filter of the present invention, from the viewpoint of not only improving various filtration performances of the tubular filter, such as the filtration efficiency and filtration life, but also increasing the productivity of the tubular filter of the present invention, it is preferable that the filtration layers in the tubular filter of the present invention include filtration layer A and filtration layer C in addition to filtration layer B, and are arranged in the order of filtration layer A, filtration layer B, and filtration layer C from the hollow portion side toward the outer periphery side of the tubular filter, from the hollow portion side.

[0041] In the filtration layer B of the cylindrical filter of the present invention, the first and second fiber sheets are preferably wound in a spiral shape in the longitudinal direction of the cylindrical filter in an overlapping state. The first and second fiber sheets are wound in a spiral shape, so that the first and second fiber sheets constituting the filtration layer B are angled with respect to the longitudinal direction of the cylindrical filter. Therefore, when a liquid containing foreign matter such as solid matter that flows in from the outside of the cylindrical filter passes through the filtration layer B, the liquid is considered to pass through the cylindrical filter obliquely along the angle of the filtration layer B, in other words, the angle between the longitudinal direction of the cylindrical filter and the direction in which the first and second fiber sheets are wound, which is generated by the first and second fiber sheets being wound in a spiral shape in an overlapping state.

[0042] The first and second fiber sheets are preferably overlapped and alternately arranged in the thickness direction, for example, by advancing 0.5 to 10 mm at a time. More preferably, they are alternately arranged in the thickness direction by advancing 1 to 5 mm at a time, particularly preferably by advancing 1 to 3 mm at a time. It is presumed that the above ranges will make the area of ​​the part through which the liquid passes wider than when the fiber sheet is not spirally wound, and thus the filtration area will be effectively utilized, contributing to high filtration efficiency. In the first fiber sheet constituting the filtration layer B, the second fiber sheet is wound between the first fiber sheets, and the cylindrical filter is provided with the filtration layer A on the downstream side thereof and the filtration layer C on the upstream side thereof in addition to the filtration layer B, so that gaps are generated between the first fiber sheets, and as a result, it is possible to suppress a sudden increase in pressure during the filtration process, which contributes to improving the filtration life.

[0043] Fig. 1 is a schematic partial cross-sectional perspective view of a cylindrical filter according to an embodiment of the present invention. As shown in Fig. 1, the cylindrical filter (1) includes a filtration layer (2) formed of a cylindrical fiber assembly, and the filtration layer (2) includes a filtration layer A (4), a filtration layer B (5), and a filtration layer C (6) that are arranged in this order from the hollow portion (3) on the inner periphery side present in the center of the cylindrical filter (1) toward the outer periphery side of the cylindrical filter (1).

[0044] Fig. 2 is a schematic partial vertical cross-sectional view of a filtration layer B according to an embodiment of the present invention. As shown in Fig. 2, the filtration layer B (5) is formed of a cylindrical fiber assembly B (50) in which a first fiber sheet (51) and a second fiber sheet (52) are alternately wound in a cylindrical shape, and the thicker first fiber sheet (51) and the thinner second fiber sheet (52) are alternately arranged in the thickness direction of the filtration layer B (5), and the first fiber sheets (51) are bonded to each other, in other words, the first fiber sheet (51) and the first fiber sheet wound one turn before the first fiber sheet are bonded to each other through the second fiber sheet (52) which is a meltblown fiber accumulated on the first fiber sheet wound one turn before.

[0045] In the filtration layer A, from the viewpoint of easily achieving both the filtration efficiency and the filtration life of the cylindrical filter, the average fiber diameter of the cylindrical fiber aggregate A is preferably 0.3 μm or more and 30 μm or less. From the viewpoint of not only achieving both the filtration efficiency and the filtration life of the cylindrical filter but also providing strength to the entire cylindrical filter, the average fiber diameter of the cylindrical fiber aggregate A is preferably 1 μm or more, and more preferably 3 μm or more. In addition, from the viewpoint of achieving both the filtration efficiency and the filtration life of the cylindrical filter, particularly from the viewpoint of having many voids inside the cylindrical filter when used for filtration, not clogging in a short time, and being able to be used for a longer period of time for filtration processing, the average fiber diameter of the cylindrical fiber aggregate A is preferably 25 μm or less, more preferably 20 μm or less, and particularly preferably 15 μm or less.

[0046] In the filtration layer A, from the viewpoint of easily achieving both the filtration efficiency and the filtration life of the cylindrical filter, the CV value of the fiber diameter of the cylindrical fiber aggregate A is preferably 0.25 or more and 1.8 or less. When the fiber diameters of the fibers constituting the filtration layer A vary, the filtration layer A becomes a cylindrical fiber aggregate containing a wide range of fibers with a thick fiber diameter and fibers with a thin fiber diameter, and many large and small inter-fiber voids are generated inside the filtration layer A, i.e., the cylindrical fiber aggregate A. Therefore, when a filtration process is performed, the ratio of the space that captures and collects foreign matter increases, and the filtration life is improved. From the viewpoint that the filtration layer A (cylindrical fiber aggregate A) becomes a filtration layer with excellent filtration life, the CV value of the fiber diameter of the cylindrical fiber aggregate A is preferably 0.30 or more, more preferably 0.33 or more, and particularly preferably 0.35 or more. In addition, the CV value of the fiber diameter of the cylindrical fiber aggregate A is preferably 1.5 or less, more preferably 1.2 or less, and particularly preferably 1.0 or less.

[0047] In the filtration layer A, the cylindrical fiber assembly A may include a fiber bundle formed by bonding a plurality of fibers in the length direction of the fibers. The presence of a fiber bundle formed by bonding a plurality of fibers in the length direction of the fibers in the filtration layer A gives the filtration layer A a structure with many voids. This not only facilitates reducing pressure losses such as airflow pressure loss and water flow pressure loss, but also makes it possible for foreign matter to be captured and collected throughout the cylindrical filter when used in a filtration process, causing clogging, and the amount of foreign matter that can be captured before the cylindrical filter becomes unusable increases, which tends to extend the filtration life.

[0048] In the filtration layer A, the tubular fiber aggregate A is not a meltblown fiber obtained by a meltblown method in which a molten thermoplastic resin is discharged from a discharge hole of a spinning nozzle and simultaneously stretched by a high-temperature gas flow ejected from the periphery of the discharge hole to form a fiber, which is then completely cooled and wound into a cylindrical shape in the form of a sheet, but is preferably a meltblown fiber directly assembled into a cylindrical shape by continuously winding the meltblown fiber discharged from the spinning nozzle while accumulating it on the surface of a rotating shaft without being completely cooled. In the filtration layer A, when the tubular fiber aggregate A is composed of meltblown fibers, the production cost is low, the fiber diameter distribution is large, and a tubular fiber aggregate having a CV value of 0.25 or more can be easily obtained. In order to directly assemble the meltblown fibers obtained by the meltblown method into a cylindrical fiber aggregate without cooling them into a sheet, a method is preferred in which a rotating shaft (also called a mandrel or core) rotating at a predetermined speed is provided on an extension line of the discharge direction of the discharge hole of the spinning nozzle, and the molten thermoplastic resin is discharged from the discharge hole while simultaneously blowing a high-temperature gas flow onto the meltblown fibers, thereby stretching the molten thermoplastic resin into a fibrous form. The meltblown fibers are then accumulated on the surface of the rotating shaft and continuously wound around the shaft to form a cylindrical fiber aggregate.

[0049] The above description of the filtration layer B will not be repeated. In the tubular fiber aggregate B of the filtration layer B, the first fiber sheet is a meltblown nonwoven fabric, and the second fiber sheet is preferably a meltblown web in which meltblown fibers obtained by a meltblown method in which a molten thermoplastic resin is discharged from a discharge hole of a spinning nozzle while the first fiber sheet is wound around the tubular fiber aggregate A and is stretched to form fibers by a high-temperature gas flow ejected from the periphery of the discharge hole are directly assembled in a cylindrical shape on the surface of the first fiber sheet. In the tubular fiber aggregate B constituting the filtration layer B, if the second fiber sheet is a meltblown web directly accumulated on the surface of the first fiber sheet, the production cost is low, the fiber diameter distribution is large, and the CV value of the fiber diameter is likely to be 0.25 or more. In order to directly accumulate and continuously wind the meltblown fibers obtained by the meltblown method without cooling them, rather than first cooling them to form a sheet and then winding them into a cylindrical shape, a preferred method is to provide a rotating shaft that rotates at a predetermined speed on an extension of the discharge direction of the discharge hole of the spinning nozzle, and while winding a first fiber sheet around the rotating shaft, a molten thermoplastic resin is discharged from the discharge hole and at the same time, the meltblown fibers that have become fibrous due to being stretched by a high-temperature gas flow are accumulated in a cylindrical shape on the surface of the rotating shaft (more specifically, on the surface of the first fiber sheet that has been previously wound around the rotating shaft) and continuously wound around the rotating shaft to form a cylindrical fiber aggregate.

[0050] In the filtration layer C, from the viewpoint of achieving both the filtration efficiency and the filtration life of the cylindrical filter, particularly capturing and collecting a high proportion of foreign matter with a large particle size, the average fiber diameter of the tubular fiber aggregate C is preferably 3 μm or more and 30 μm or less. The average fiber diameter of the tubular fiber aggregate C constituting the filtration layer C is preferably 4 μm or more, more preferably 5 μm or more, and even more preferably 6 μm or more. Moreover, the average fiber diameter of the tubular fiber aggregate C constituting the filtration layer C is preferably 25 μm or less, more preferably 20 μm or less, and even more preferably 15 μm or less.

[0051] The filtration layer C is fed from the upstream side of the filtration layers A and B, that is, the fluid to be filtered contains a larger amount of foreign matter to be captured and collected. Therefore, in the filtration layer C, the fiber diameters of the fibers constituting the filtration layer C are varied, and the filtration layer C becomes a tubular fiber assembly containing both fibers with a large fiber diameter and fibers with a small fiber diameter, so that the filtration layer C has an excellent filtration life. From this viewpoint, the CV value of the fiber diameter in the tubular fiber assembly C is 0.25 or more and 2.5 or less. From the viewpoint of obtaining a tubular filter that is less likely to clog and has a long filtration life, the lower limit of the CV value of the fiber diameter of the tubular fiber assembly C is preferably 0.3 or more, more preferably 0.4 or more, and even more preferably 0.5 or more. In addition, from the viewpoint of easily obtaining a cylindrical filter having a long filtration life and stable filtration efficiency, the upper limit of the CV value of the fiber diameter of the tubular fiber aggregate C 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.

[0052] In the filtration layer C, the tubular fiber assembly C may contain a fiber bundle formed by bonding a plurality of fibers in the length direction of the fibers, similar to the tubular fiber assembly A. In the filtration layer C, similar to the filtration layer A, the presence of a fiber bundle formed by bonding a plurality of fibers in the length direction of the fibers results in the filtration layer C having a structure with many voids. This not only facilitates reducing pressure losses such as ventilation air pressure loss and water flow pressure loss, but also makes the structure with many voids such that, when used in a filtration process, foreign matter is captured and collected throughout the tubular filter, causing clogging, and the amount of foreign matter that can be captured before the tubular filter becomes unusable increases, which tends to extend the filtration life.

[0053] In the filtration layer C, the tubular fiber aggregate C is preferably a tubular aggregate directly assembled without being cooled, rather than a meltblown fiber obtained by a meltblown method in which a molten thermoplastic resin is discharged from a discharge hole of a spinning nozzle and simultaneously stretched into fibers by a high-temperature gas flow ejected from around the discharge hole, which is not cooled, formed into a sheet shape, and then wound into a cylindrical shape, as in the tubular fiber aggregate A. In the filtration layer C, when the tubular fiber aggregate C is composed of meltblown fibers, the production cost is low, and a fiber aggregate having a large fiber diameter distribution and a fiber diameter CV value of 0.25 or more can be easily obtained. In order to directly assemble the meltblown fibers obtained by the meltblown method into a cylindrical fiber aggregate without cooling them into a sheet, a preferred method is to provide a rotating shaft that rotates at a predetermined speed on an extension of the discharge direction of the discharge hole of the spinning nozzle, and while discharging a molten thermoplastic resin from the discharge hole, the meltblown fibers that have become fibrous by being stretched by a high-temperature gas flow are accumulated in a cylindrical shape on the surface of the rotating shaft (more specifically, on the surface of the tubular fiber aggregate B) while cooling to form a cylindrical fiber aggregate.

[0054] In the filtration layers constituting the cylindrical filter of the present invention, when the total mass of the filtration layers A, B and C is taken as 100 mass%, it is preferable that the content of the filtration layer A is 30 mass% or more and 70 mass% or less, the content of the filtration layer B is 15 mass% or more and 50 mass% or less, and the content of the filtration layer C is 10 mass% or more and 30 mass% or less, and it is more preferable that the content of the filtration layer A is 35 mass% or more and 65 mass% or less, the content of the filtration layer B is 18 mass% or more and 45 mass% or less, and the content of the filtration layer C is 12 mass% or more and 25 mass% or less. When the content of the filtration layer B, which mainly affects the filtration efficiency, is 15 mass% or more, preferably 18 mass% or more, the filtration efficiency is further improved. In addition, when the content of the filtration layer B is 50 mass% or less, preferably 45 mass% or less, the filtration life is also likely to be long. In addition, when the content of the filtration layer A closest to the hollow part is 70 mass% or less, preferably 65 mass% or less, the filtration life is also likely to be long. In addition, when the content of filtration layer A is 30% by mass or more, preferably 35% by mass or more, the filtration efficiency is likely to be improved. When the content of filtration layer C arranged on the outside of filtration layer B and covering filtration layer B is 10% by mass or more, preferably 12% by mass or more, the filtration efficiency is improved and stabilized, which is preferable. In addition, when the content of filtration layer C is 30% by mass or less, preferably 25% by mass or less, the proportion of filtration layer C is not too large and is an appropriate proportion, so that the filtration efficiency is improved and stabilized. In the filtration layers constituting the cylindrical filter of the present invention, when the total mass of the filtration layers A, B and C is taken as 100% by mass, the preferred contents of the filtration layers A, B and C also vary depending on the configuration of the filtration layer B, which mainly affects the filtration efficiency. That is, when the filtration layer B includes one layer of the first fiber sheet, it is preferable that the content of the filtration layer A is 50% by mass to 65% by mass, the content of the filtration layer B is 15% by mass to 40% by mass, and the content of the filtration layer C is 10% by mass to 25% by mass. When the filtration layer B includes multiple layers of the first fiber sheet, it is preferable that the content of the filtration layer A is 35% by mass to 50% by mass, the content of the filtration layer B is 25% by mass to 45% by mass, and the content of the filtration layer C is 15% by mass to 25% by mass.

[0055] In the filtration layer A, the filtration layer B (the first fiber sheet (including the first fiber sheet being a single layer or a multi-layer using a plurality of fiber sheets) and the second fiber sheet), and the filtration layer C, the type of fiber constituting each filtration layer is not particularly limited, and natural fibers, synthetic fibers, and the like can be used without any particular limitation, but fibers composed of a thermoplastic resin are preferable. 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 resin, 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; engineering plastics such as polycarbonate, polyacetal (also called polyoxymethylene resin), polystyrene, cyclic polyolefin, and polyphenylene sulfide (also called polyphenylene sulfide, 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. The polypropylene resin may be a homopolymer of propylene or a copolymer of propylene and another α-olefin. From the viewpoint of high chemical resistance such as acid resistance, base resistance, and resistance to various organic solvents when using the cylindrical filter, in the filtration layer A, the filtration layer B, and the filtration layer C, the fibers are preferably composed of polyolefin resins such as polypropylene resin, polymethylpentene resin, polybutene-1 resin, ethylene-vinyl alcohol copolymer resin, and ethylene-propylene copolymer resin, and more preferably contain at least polypropylene resin. Since polypropylene resin has a relatively high melting point among polyolefin resins, it can filter liquids at a relatively high temperature, has good chemical resistance, and is low cost.

[0056] In the filtration layer A, the filtration layer B (the first fiber sheet (including the case where the first fiber sheet is a single layer or a multi-layer using a plurality of fiber sheets) and the second fiber sheet), and the filtration layer C, it is preferable that these filtration layers are composed of fiber sheets made of synthetic fibers composed of the above-mentioned thermoplastic resin, and more preferably, they are nonwoven fabrics made of the above-mentioned thermoplastic resin. When the filtration layer A, the filtration layer B (the first fiber sheet and the second fiber sheet), and the filtration layer C are to be composed of various nonwoven fabrics made of synthetic fibers made of thermoplastic resin, the type of nonwoven fabric that can be used is not particularly limited, and may be, for example, a long fiber (for example, a fiber having a fiber length longer than 110 mm or a substantially continuous fiber) nonwoven fabric or a short fiber (for example, a fiber having a fiber length of 3 mm or more and 110 mm or less) nonwoven fabric. As the long fiber nonwoven fabric, for example, a spunbond nonwoven fabric, a meltblown nonwoven fabric obtained by a meltblowing method, a nonwoven fabric obtained by an electrospinning method (also called an electrostatic spinning method or an electrospinning method), and the like can be used. The short fiber nonwoven fabric may be one obtained by preparing a fiber web by a wet papermaking method using short fibers having a fiber length of 3 mm to 20 mm, an air-laid method (also called an air-laid method) using short fibers having a fiber length of 3 mm to 32 mm, or a carding method using short fibers having a fiber length of 24 mm to 110 mm and producing a fiber web with a carding machine, and further integrating the webs. When preparing a fiber web by a carding method, the manufacturing method is not limited, and the fiber web can be prepared by a known manufacturing method such as a parallel web, a semi-random web, a random web, a cross web, or a criss-cross web. The integration of the fiber web is carried out by one or more methods selected from bonding with an adhesive, thermal bonding (thermal bond) by softening or melting the fibers, needle punching, and high-pressure water flow treatment (spunlace). Preferably, the first fiber sheet is a nonwoven fabric composed of the above-mentioned thermoplastic resin, more preferably a meltblown nonwoven fabric composed of the above-mentioned thermoplastic resin, and the filtration layer A, the second fiber sheet, and the filtration layer C are meltblown webs composed of the above-mentioned thermoplastic resin.

[0057] The thickness of the filtration layer A may be appropriately determined depending on the use or purpose of the cylindrical filter, and is not particularly limited. For example, from the viewpoint of stabilizing the filtration efficiency and extending the filtration life, it is preferably 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 filtration layer A is represented by the difference between the outer diameter of the filtration layer A (the outer diameter of the cylindrical filter in the state of only the filtration layer A, including the diameter of the hollow part, and equivalent to the inner diameter of the filtration layer B) and the inner diameter of the filtration layer A (equivalent to the diameter of the hollow part) divided by 2.

[0058] The thickness of the filtration layer B may be appropriately determined according to the use or purpose of the cylindrical filter, and is not particularly limited. For example, from the viewpoint of maintaining the filtration life and further increasing the filtration efficiency, it is preferably 2 mm to 12 mm, more preferably 2.5 mm to 10 mm, and even more preferably 3 mm to 9 mm. Depending on the thickness of the filtration layer B, the first fiber sheet and the second fiber sheet can be wound two or more times to form a cylindrical fiber assembly B. The thickness of the filtration layer B is represented by the difference between the outer diameter of the filtration layer B (the outer diameter of the cylindrical filter in a state in which the filtration layer A and the filtration layer B are constituted, including the diameter of the hollow part, and is equivalent to the inner diameter of the filtration layer C) and the inner diameter of the filtration layer B (equivalent to the outer diameter of the filtration layer A) divided by 2.

[0059] The thickness of the filtration layer C may be appropriately determined depending on the use and purpose of the cylindrical filter, and is not particularly limited. For example, from the viewpoint of stabilizing the filtration efficiency and extending the filtration life, it is preferably 1 mm or more and 6 mm or less, more preferably 1 mm or more and 5 mm or less, and even more preferably 2 mm or more and 4.5 mm or less. The thickness of the filtration layer C is represented by the difference between the outer diameter of the filtration layer C and the inner diameter of the filtration layer C (which is equivalent to the outer diameter of the filtration layer B) divided by 2.

[0060] The filtration layer may include other members in addition to the filtration layer A, the filtration layer B, and the filtration layer C, within a range that does not impair the effects of the present invention. The other members may be disposed inside the filtration layer A and / or outside the filtration layer C. Examples of other members disposed inside the filtration layer A include cylindrical fiber molded products, thermoplastic resin perforated tubular bodies, metal perforated tubular bodies, and ceramic perforated tubular bodies. Examples of other members disposed outside the filtration layer C include nonwoven fabrics such as thermally bonded nonwoven fabrics containing thermally adhesive fibers. By winding a thermally bonded nonwoven fabric on the outside of the filtration layer C, in other words, further upstream (inlet side) than the filtration layer C, the side of the cylindrical filter becomes smooth and less fuzzed, which is not only preferable in terms of the appearance of the product, but also makes the thermally bonded nonwoven fabric form the side of the cylindrical filter, thereby reducing fiber dropout from the cylindrical filter. In the cylindrical filter of the present invention, the nonwoven fabric wound further outside the filtration layer C is not particularly limited as long as it is a thermally bonded nonwoven fabric, and may be a short fiber nonwoven fabric or a long fiber nonwoven fabric containing a core-sheath type composite fiber with a high melting point thermoplastic resin as the core component and a low melting point thermoplastic resin as the sheath component. The fineness of the thermally bonded nonwoven fabric is not particularly limited, but it may be a thermally bonded nonwoven fabric mainly containing a core-sheath type composite fiber of 1.1 dtex to 8 dtex. In the cylindrical filter of the present invention, when the thermally bonded nonwoven fabric is wound further outside the filtration layer C, the amount of winding of the thermally bonded nonwoven fabric may be 1 to 10 turns, preferably 1 to 6 turns.

[0061] From the viewpoint of satisfying basic filtering performance, the cylindrical filter preferably has a filtering efficiency of 80% or more, more preferably 90% or more, and particularly preferably 95% or more for particles having a particle size of 5.0 μm. From the viewpoint of satisfying basic filtering performance, the cylindrical filter preferably has a filtering life of 400 liters or more, more preferably 500 liters or more, even more preferably 550 liters or more, and even more preferably 580 liters or more.

[0062] From the viewpoint of superior long-term usability, the filtration life of the cylindrical filter is more preferably 800 liters or more, further preferably 950 liters or more, and particularly preferably 1000 liters or more. On the other hand, from the viewpoint of reliably collecting finer particles, in other words, obtaining a cylindrical filter with higher filtering accuracy, the filtering efficiency 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 addition, since the longer the filtering life, the better the long-term usability, the more preferably 300 liters or more, more preferably 350 liters or more, particularly preferably 400 liters or more, and most preferably 420 liters or more.

[0063] In the cylindrical filter having a long filtration life, the first fiber sheet has an average fiber diameter d1 of preferably 2.6 μm to 10 μm, more preferably 2.8 μm to 7.0 μm, further preferably more than 3.0 μm to 6.0 μm, and particularly preferably more than 3.40 μm to 5.5 μm, which tends to lengthen the filtration life while maintaining the basic performance of the cylindrical filter.

[0064] From the viewpoint of further increasing the filtration efficiency, the filtration efficiency of the cylindrical filter for particles having a particle size of 1.0 μm is preferably 85% or more, more preferably 87% or more, even more preferably 90% or more, and particularly preferably 95% or more.

[0065] In a cylindrical filter with high filtration efficiency, the first fiber sheet has an average fiber diameter d1 of preferably 0.3 μm to 3.40 μm, more preferably 0.8 μm to 3.2 μm, further preferably 1.0 μm to 3.0 μm, and particularly preferably 1.2 μm to 3.0 μm, which makes it easy to improve the filtration efficiency while maintaining the basic performance of the cylindrical filter.

[0066] (Manufacturing method of cylindrical filter) The method for producing the cylindrical filter is not particularly limited, but from the viewpoint of increasing productivity and reducing production costs, it is preferable to include a step B in which a molten thermoplastic resin is discharged from the discharge hole of a spinning nozzle, and at the same time, a meltblown fiber stretched by a high-temperature gas flow ejected from around the discharge hole is blown onto the surface of a rotating shaft rotating at a constant speed, a first fiber sheet is wound around the surface of the rotating shaft, and the meltblown fiber is accumulated on the surface of the first fiber sheet to form a meltblown web and wound around it, thereby obtaining a cylindrical fiber aggregate B in which the first fiber sheet and the meltblown web are wound alternately. In addition to the step B, the method for producing the cylindrical filter more preferably includes at least one of the following steps A and C, and even more preferably includes both. Step A: Before step B, the meltblown fibers are sprayed onto the surface of a rotating shaft rotating at a constant speed, and a meltblown web is formed and wound to obtain a cylindrical fiber aggregate A. Step C: After step B, the meltblown fibers are blown onto the surface of a rotating shaft, and a meltblown web is formed and wound to obtain a cylindrical fiber aggregate C.

[0067] Specifically, step A may be performed until the thickness of the tubular fiber aggregate A is 5 mm or more and 15 mm or less, and then step B may be performed. Step B may be performed until the thickness of the tubular fiber aggregate B is 2 mm or more and 12 mm or less, and then step C may be performed. Step C may be performed until the thickness of the tubular fiber aggregate C is 1 mm or more and 6 mm or less.

[0068] The thermoplastic resin is not particularly limited, and it is possible to use any thermoplastic resin capable of forming the fibers of the above-mentioned filtration layer A, filtration layer B, and filtration layer C. Among them, polyolefin resins are preferred, and polypropylene resins are more preferred, from the viewpoints of cost and high chemical resistance when the cylindrical filter is used.

[0069] From the viewpoint that the average fiber diameter and the CV value of the fiber diameter of the second fiber sheet in the tubular fiber aggregate A constituting the filtration layer A, the tubular fiber aggregate C constituting the filtration layer C, and the tubular fiber aggregate B constituting the filtration layer B are likely to be in the preferred ranges described above, the discharge rate of the molten thermoplastic resin per discharge hole 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.

[0070] The rotation speed of the rotating shaft is not particularly limited as long as it is a rotation speed that can accumulate the meltblown fibers on the surface of the rotating shaft and simultaneously wind it around to form a cylindrical fiber aggregate. From the viewpoint of facilitating uniform accumulation of the meltblown fibers along the surface of the rotating shaft and facilitating the production of a cylindrical fiber aggregate with a smooth surface condition, the rotation speed is preferably 50 rpm or more and 400 rpm or less, more preferably 100 rpm or more and 300 rpm or less, and even more preferably 120 rpm or more and 200 rpm or less.

[0071] The outer diameter of the rotating shaft may be appropriately determined depending on the diameter of the hollow part of the desired cylindrical filter, and is not particularly limited, but may generally be 20 mm or more and 40 mm or less, 25 mm or more and 35 mm or less, or 26 mm or more and 32 mm or less.

[0072] The distance between the discharge hole and the surface of the rotating shaft can be appropriately adjusted depending on the desired outer diameter (thickness) of the filtration layer A and the filtration layer C, and is not particularly limited. For example, from the viewpoint of the productivity of the cylindrical filter and the fiber diameter of the fiber produced by the melt blown method in the obtained cylindrical filter, 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 fiber ejected and stretched from the discharge hole is likely to reach the surface of the rotating shaft in a molten state and while maintaining the fiber shape, and the desired fiber aggregate is likely to be obtained. In addition, when the distance from the center of the discharge hole to the surface of the rotating shaft is 30 cm or less, the fiber ejected and stretched from the discharge hole is prevented from being deviated from the direction of the rotating shaft due to the influence of the surrounding air flow, and is easily wound up on the rotating shaft, which tends to improve the productivity (production efficiency, yield) of the cylindrical filter. 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 from the discharge hole and stretched out can easily reach the surface of the rotating shaft before cooling and completely solidifying, the fibers wound around the rotating shaft can easily be thermally bonded to each other, the strength of the cylindrical filter as a whole 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. The distance from the center of the discharge hole to the surface of the rotating shaft is preferably 10 cm or more and 28 cm or less, and more preferably 12 cm or more and 25 cm or less.

[0073] 3 is a schematic explanatory diagram of an example of a cylindrical filter manufacturing apparatus used in the present invention. The manufacturing apparatus 10 includes an extruder 11, a gas heater 12, a spinning nozzle 13, and a rotating shaft 14.

[0074] A thermoplastic resin is supplied to the extruder 11 by a gear pump (not shown), and the thermoplastic resin is melt-kneaded at a predetermined temperature in the extruder 11, 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 temperature of the melt-kneading is not particularly limited as long as it is a temperature at which the thermoplastic resin can be melted, but for example, when the melting point of the thermoplastic resin is Tm, it is preferably Tm+50°C or more and Tm+200°C or less, and more preferably Tm+100°C or more and Tm+180°C or less. When the thermoplastic resin is a polypropylene resin, the temperature of the melt-kneading is preferably 200°C or more and 350°C or less, and more preferably 250°C or more and 330°C or less.

[0075] The gas heater 12 supplies the 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 the viewpoint of cost. The temperature of the heated gas may be the same as the temperature of the melt-kneading of the thermoplastic resin. For example, when 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. When the thermoplastic resin is a polypropylene resin, the temperature of the heated gas is preferably 180°C or more and 260°C or less, more preferably 185°C or more and 220°C or less. From the viewpoint of stably discharging the molten resin and reducing the variation in performance and various physical properties of the fibers produced by the melt blown 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.

[0076] The spinning nozzle 13 may be any suitable one used in the manufacture of general meltblown fibers. The spinning nozzle 13 is provided with a plurality of discharge holes for discharging a molten thermoplastic resin, and gas injection holes for blowing high-speed heated gas around each discharge hole. The diameter of the discharge holes may be, for example, 0.03 mm or more and 0.80 mm or less, 0.06 mm or more and 0.40 mm or less, or 0.10 mm or more and 0.25 mm or less. The interval between adjacent discharge holes may be 0.1 mm or more and 2.0 mm or less, 0.15 mm or more and 1.8 mm or less, or 0.2 mm or more and 1.6 mm or less. In the meltblown method, in which a molten thermoplastic resin is discharged from a discharge hole and a high-speed heated gas is blown from a gas injection hole at the same time to stretch the molten thermoplastic resin, the discharged molten thermoplastic resin is made into a fiber form and stretched at the same time, to obtain meltblown fibers 15.

[0077] A typical mandrel or the like can be used as the rotating shaft 14. The meltblown fibers 15 are accumulated in a cylindrical shape for a predetermined time on the surface of the rotating shaft 14 rotating at a constant speed to form a cylindrical fiber aggregate A (24) having a predetermined outer diameter (thickness). The cylindrical fiber aggregate A (24) may include a fiber bundle formed by bonding a plurality of meltblown fibers in the fiber length direction. In the cylindrical fiber aggregate A, the meltblown fibers are bonded to each other in the circumferential direction and thickness direction of the cylindrical filter.

[0078] Next, while winding the first fiber sheet (51) around the cylindrical fiber aggregate A (24), the meltblown fibers (15) are discharged toward the surface of the first fiber sheet (51), so that the meltblown fibers (15) are accumulated on the surface of the first fiber sheet (51) and simultaneously wound around the first fiber sheet (51), forming a cylindrically wound cylindrical fiber aggregate B (25) in which the first fiber sheet (51) and a meltblown web (not shown) made of the meltblown fibers (15) are alternately arranged. As shown in FIG. 2, the meltblown web made of the meltblown fibers (15) accumulated on the surface of the first fiber sheet (51) becomes a second fiber sheet (52) having a smaller thickness than the first fiber sheet (51), and the first fiber sheets (51) adjacent in the thickness direction are bonded via the second fiber sheet (52) arranged therebetween. A first fiber sheet (51), preferably a strip-shaped nonwoven fabric (51), is wound so as to partially overlap in the width direction, while the meltblown fibers (15) are accumulated on the surface of the first fiber sheet (51) to form a cylindrical fiber aggregate B (25).

[0079] When a multilayer fiber sheet containing two or more layers of fiber sheets (preferably a multilayer nonwoven fabric containing two or more layers of nonwoven fabric) is used as the first fiber sheet, the first fiber sheet (51) in a state in which two or more layers of fiber sheets (preferably nonwoven fabrics) are overlapped is wound around the tubular fiber aggregate A (24) while extruding meltblown fibers (15) toward the surface of the first fiber sheet (51), thereby accumulating the meltblown fibers (15) on the surface of the first fiber sheet (51) and simultaneously winding it, so that the first fiber sheet (51) and the meltblown web consisting of the meltblown fibers (15) are alternately arranged to form a tubular fiber aggregate B (25) wound into a cylindrical shape. The meltblown web consisting of the meltblown fibers (15) accumulated on the surface of the first fiber sheet (51) becomes a second fiber sheet (52) having a thickness smaller than that of the first fiber sheet (51), and the first fiber sheets (51) adjacent in the thickness direction are bonded via the second fiber sheet (52) disposed therebetween. In the multilayer fiber sheet constituting the first fiber sheet, two or more layers of fiber sheets are simply overlapped with each other and are not bonded. When the first fiber sheet is a multilayer fiber sheet including a first fiber sheet X1 and a first fiber sheet Y1, and the nonwoven fabric to become the first fiber sheet X1 and the nonwoven fabric to become the first fiber sheet Y1 satisfy at least one of the above-mentioned requirements (r) and (s), it is preferable to wind the first fiber sheet in a state in which the nonwoven fabric to become the first fiber sheet X1 and the nonwoven fabric to become the first fiber sheet Y1 are overlapped with each other so that the nonwoven fabric to become the first fiber sheet X1 is on the inner side of the nonwoven fabric to become the first fiber sheet Y1.

[0080] When the nonwoven fabric that will become the first fiber sheet is wound around the tubular fiber aggregate A, the nonwoven fabric may be wound around the tubular fiber aggregate A from two or more different positions.

[0081] FIG. 4 is a schematic diagram illustrating the positional relationship between the filtration layer A and the filtration layer B of a cylindrical filter according to an embodiment of the present invention. As shown in FIG. 4, it is preferable to form a filtration layer B (5) made of a cylindrical fiber assembly B (25) by winding a first fiber sheet, preferably a strip-shaped nonwoven fabric (51), around the cylindrical fiber assembly A (24) constituting the filtration layer A (4) so ​​that the first fiber sheet partially overlaps the strip-shaped nonwoven fabric (51) in the width direction and accumulating meltblown fibers on the surface to form a second fiber sheet (not shown). As a result, the nonwoven fabric (51) is wound around the cylindrical filter in the length direction by a predetermined width, for example, 0.5 to 10 mm, more preferably 1 to 5 mm, and particularly preferably 1 to 2 mm, to form a filtration layer B (5) made of a cylindrical fiber assembly B including the spirally overlapped nonwoven fabric (51) and the second fiber sheet made of meltblown fibers accumulated on the surface of the spirally overlapped nonwoven fabric (51), thereby improving the filtration efficiency. The second fiber sheet may include a fiber bundle formed by bonding a plurality of meltblown fibers in the fiber length direction. As shown in Fig. 4, it is preferable to wind the nonwoven fabric (51) around the cylindrical fiber aggregate A (24) constituting the filtration layer A (4) while forming wrinkles (8) obliquely in the width direction. This prevents longitudinal gaps from being generated between the nonwoven fabrics (51) constituting the filtration layer B, thereby improving both the filtration efficiency and the filtration life.

[0082] Next, the meltblown fibers (15) are discharged toward the surface of the tubular fiber aggregate B (25), so that the meltblown fibers (15) are accumulated on the surface of the tubular fiber aggregate B (25) and simultaneously wound around it. This is carried out continuously for a predetermined time to form a tubular fiber aggregate C (26) having a predetermined outer diameter. The tubular fiber aggregate C (26) may include a fiber bundle formed by bonding a plurality of meltblown fibers in the fiber length direction. In the tubular fiber aggregate C, the meltblown fibers are bonded to each other in the circumferential direction and thickness direction of the cylindrical filter.

[0083] The tubular fiber aggregate A (24), tubular fiber aggregate B (25), and tubular fiber aggregate C (26) accumulated in a cylindrical shape on the surface of the rotating shaft 14 are separated from the mandrel by moving in the direction of the arrow (16), thereby obtaining a tubular fiber aggregate (21) including the tubular fiber aggregate A (24), tubular fiber aggregate B (25), and tubular fiber aggregate C (26). Next, the tubular fiber aggregate 21 is cut to a predetermined length to obtain a cylindrical filter equipped with a filtration layer including a filtration layer A (4) made of the tubular fiber aggregate A (24), a filtration layer B (5) made of the tubular fiber aggregate B (25), and a filtration layer C (6) made of the tubular fiber aggregate C (26).

[0084] Cylindrical filters are suitable for various applications in which solid matter is removed from liquids, and can be used to filter liquids such as pure water, drinking water, chemical solutions, various oils and fats, plating solutions, paint solutions, and cleaning water for the electronics industry. EXAMPLES

[0085] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0086] The measurement methods used in the examples and comparative examples will be described below.

[0087] (Thickness) The thickness of the fiber sheet was measured under a load of 3 g. For the filtration layer B, the first fiber sheet and the second fiber sheet were cut in the lengthwise direction of the filter, spread out, and then the filtration layer A was peeled off. One circumference of the bonded sheets was sampled, and the first fiber sheet and the second fiber sheet were peeled off with tweezers or the like carefully not to tear them, and then the thickness of each was measured.

[0088] (Met) The basis weight of the fiber sheet was measured from the area and weight of a rectangular sample of any size. For the filtration layer B, the first fiber sheet and the second fiber sheet were sampled by cutting the filter lengthwise and unfolding it, peeling off the filtration layer A, and then peeling off the first fiber sheet and the second fiber sheet with tweezers or the like to avoid tearing them, and the basis weight of each was measured.

[0089] (density) The density of the fiber sheet was calculated based on the thickness and basis weight measured as described above. Density = basis weight / thickness

[0090] (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 assembly were measured by magnifying and observing the fiber assembly with a scanning electron microscope (Hitachi High-Technologies Ametech Japan, model number "SU3500", accelerating voltage: 5.00 kV, magnification: 200 to 400 times), and analyzing the obtained photographs of 10 locations with image analysis software (ClickMeasure). The fiber diameters of 100 randomly selected fibers were measured, and the arithmetic average value was taken as the average fiber diameter. The standard deviation was then calculated using the fiber diameters of the 100 randomly selected fibers 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

[0091] (Average pore size, maximum pore size, maximum pore size, and minimum pore size) The pore size of the fiber assembly was measured using a capillary flow porometer "CFP-1200-AEXC-P" manufactured by Porous Material Inc. in accordance with JIS K 3832 (1990) (bubble point test method for microfiltration membrane elements and modules).

[0092] (filtration efficiency) A water dispersion of test dust conforming to JIS Z 8901 (a mixture of JIS 11 type [median diameter 2 μm] and JIS 8 type [median diameter 6.6 to 8.6 μm] in a 1:1 mass ratio) adjusted to a concentration of 30 ppm was used as the test suspension, and the test suspension was filtered from the outside of the cartridge filter toward the hollow part at a flow rate of 15 liters / min while stirring to make the concentration uniform, and the number of powders (particles) of 1.0 μm, 3.0 μm, 5.0 μm and 10.0 μm contained in the test suspension before filtration treatment, M1μ m , M3μ m , M5μ m , M 10 μ m and the number of particles with particle sizes of 1.0 μm, 3.0 μm, 5.0 μm, and 10.0 μm contained in the test suspension that passed through the cylindrical filter one minute after the start of filtration, N1μ m , N3μ m , N5μ m , and N 10 μ m was measured using a precision particle size distribution device (product name: Multisizer 4e, manufactured by Beckman Coulter, Inc.), and the filtration efficiency was calculated using the following formula. · Filtration efficiency (%) of particles with a diameter of 1.0 μm = ((M1μ m -N1μ m ) / M1μ m ) x 100 · Filtration efficiency (%) of particles with a diameter of 3.0 μm = ((M3μ m -N1μ m ) / M3μ m ) x 100 · Filtration efficiency (%) of particles with a diameter of 5.0 μm = ((M5μ m -N5μ m ) / M5μ m ) x 100 Filtration efficiency (%) of particles with a diameter of 10.0 μm = ((M 10 μ m -N 10 μ m ) / M 10 μ m ) x 100

[0093] (Filter life) A test powder conforming to JIS Z 8901 (JIS type 8 test powder and JIS type 11 test powder were prepared and mixed in a mass ratio of 1:1) was dispersed in water to prepare a test suspension with a concentration of 30 ppm. Next, the test suspension was passed through the cylindrical filter from the outer periphery to the inner hollow portion at a flow rate of 15 liters / min while being uniformly stirred, and the total amount of water passing (liters) when the water passing pressure required to maintain this flow rate reached 0.2 MPa was taken as the filtration life of the cylindrical filter.

[0094] (Mass ratio of filtration layer) A cylindrical filter was prepared, and the total mass of the filtration layers A, B, and C was measured with an electronic balance. Next, the filtration layer of the cylindrical filter was cut in the thickness direction, and the filtration layer C was peeled off from the cylindrical filter so that the fibers would not scatter. When the first fiber sheet (specifically, nonwoven fabric) appeared and the sides were all nonwoven fabric, the work of separating and recovering the filtration layer C was completed, and the fibers constituting the filtration layer C peeled off from the cylindrical filter up to that point were collected and their mass was weighed with an electronic balance. Next, the nonwoven fabric wound around the cylindrical filter was peeled off, and when all the nonwoven fabric was peeled off, the work of separating and recovering the filtration layer B was completed, and the mass of the nonwoven fabric and fibers constituting the filtration layer B was measured. The part remaining after peeling off the filtration layer C and the filtration layer B from the cylindrical filter was set as the filtration layer A and its mass was measured. Based on the measured total mass of the filtration layers A, B, and C and the mass of each filtration layer, the mass ratios of the filtration layers A, B, and C were calculated. When a thermally bonded nonwoven fabric is further wound around the outside of filtration layer C in the cylindrical filter, the thermally bonded nonwoven fabric is removed before measuring the total mass of filtration layers A, B, and C.

[0095] (Ventilation pressure loss) Air was allowed to flow into the 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 / min was measured, and this was taken as the airflow pressure loss.

[0096] Example 1 A cylindrical filter was produced using the manufacturing apparatus shown in FIG. 3. Specifically, polypropylene resin (melting point 160°C, melt flow rate according 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 was positioned on an extension line of the discharge direction of the discharge hole of the spinning nozzle, and the longitudinal direction of the mandrel was arranged so as to be oblique to the row of multiple discharge holes of the spinning nozzle. The mandrel 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. The diameter of each nozzle hole was 0.3 mm, and the molten thermoplastic resin was discharged from the nozzle holes so that the discharge rate per nozzle was 0.25 g / min. At the same time, heated air at a temperature of 200°C and a pressure of 0.015 MPa was blown from the gas injection holes arranged around the nozzle holes to turn the molten thermoplastic resin into a fiber form, and the meltblown fiber obtained by stretching the fiber was accumulated on the surface of the front stage of the mandrel and was continuously wound around the mandrel. By continuing this for a predetermined time, the meltblown fiber was accumulated and wound around the mandrel to obtain a cylindrical fiber aggregate A. The outer diameter of the cylindrical object consisting of the hollow part (the diameter of the hollow part is the same as the outer diameter of the mandrel) and the cylindrical fiber aggregate A was 50 mm. Thereafter, a meltblown nonwoven fabric (a commercially available meltblown nonwoven fabric consisting of a single fiber of polypropylene resin, with an average fiber diameter of 2.02 μm and a basis weight of 30.4 g / m) was formed. 2 , thickness 0.27 mm, air permeability measured using a Frazier type tester according to JIS L 1096 is 4.0 cm 3 / cm 2 / sec, hereinafter also referred to as MB nonwoven fabric 1.) was slit to a width of 30 mm and inserted into tubular fiber assembly A from the opposite direction to the direction in which the meltblown fibers were discharged onto the mandrel (in other words, from the direction opposite to the spinning nozzle that discharges the meltblown fibers across the mandrel), and while advancing by 1 to 2 mm at a time, was wound around the surface of tubular fiber assembly A so as to overlap in a spiral shape, and at the same time, meltblown fibers were discharged toward the surface of the wound MB nonwoven fabric 1, and the meltblown fibers were accumulated on the surface of MB nonwoven fabric 1 and wound around it at the same time, thereby obtaining a tubular fiber assembly B in which MB nonwoven fabric 1 and a meltblown web made of meltblown fibers were arranged alternately in the thickness direction. In the cylindrical fiber assembly B, the MB nonwoven fabric 1 is the first fiber sheet, and in the continuously wound MB nonwoven fabric 1, meltblown fibers are accumulated between adjacent MB nonwoven fabrics 1 in the thickness direction, for example, between the wound MB nonwoven fabric 1 and the MB nonwoven fabric 1 wound one turn before the MB nonwoven fabric 1, to form a meltblown web, and the meltblown web is the second fiber sheet. The first fiber sheets, i.e., the MB nonwoven fabric 1 and the MB nonwoven fabric 1 wound one turn before the MB nonwoven fabric 1, are bonded to each other via the second fiber sheet present between them. The outer diameter of the cylindrical object composed of the mandrel, the cylindrical fiber assembly A, and the cylindrical fiber assembly B was 57 mm. Thereafter, the meltblown fibers were continuously accumulated on the surface of the cylindrical fiber aggregate B and wound around it to accumulate the meltblown fibers in a cylindrical shape, forming a cylindrical fiber aggregate C. A cylindrical fiber aggregate (outer diameter 65 mm) consisting of the cylindrical fiber aggregate A, the cylindrical fiber aggregate B, and the cylindrical fiber aggregate C was obtained. Next, the cylindrical fiber aggregate was cut to a length of 250 mm to obtain a cylindrical filter equipped with a filtration layer including a filtration layer A (thickness of filtration layer A: 11 mm) consisting of the cylindrical fiber aggregate A, a filtration layer B (thickness of filtration layer B: 3.5 mm) consisting of the cylindrical fiber aggregate B, and a filtration layer C (thickness of filtration layer C: 4 mm) consisting of the cylindrical fiber aggregate C.The obtained cylindrical filter was disassembled into filtration layers A, B, and C, and each filtration layer was observed at 200 to 400 times magnification using the scanning electron microscope. As a result, fiber bundles formed by a plurality of fibers fused in the longitudinal direction were confirmed in filtration layer A (cylindrical fiber aggregate A), filtration layer C (cylindrical fiber aggregate C), and the second fiber sheet contained in filtration layer B.

[0097] Example 2 A cylindrical filter was obtained in the same manner as in Example 1, except that MB nonwoven fabric 1 having a width of 40 mm was used instead of MB nonwoven fabric 1 having a width of 30 mm.

[0098] Example 3 A cylindrical filter was obtained in the same manner as in Example 1, except that MB nonwoven fabric 1 having a width of 50 mm was used instead of MB nonwoven fabric 1 having a width of 30 mm.

[0099] Example 4 Instead of the 30 mm wide MB nonwoven fabric 1, a 30 mm wide meltblown nonwoven fabric (a commercially available meltblown nonwoven fabric consisting of a single fiber of polypropylene resin, with an average fiber diameter of 2.43 μm and a basis weight of 30.0 g / m) was used. 2 , thickness 0.36 mm, air permeability measured using a Frazier type tester according to JIS L 1096 is 5.0 cm 3 / cm 2 / sec, hereinafter also referred to as MB nonwoven fabric 2. A cylindrical filter was obtained in the same manner as in Example 1, except that MB nonwoven fabric 2 was used.

[0100] Example 5 A cylindrical filter was obtained in the same manner as in Example 1, except that the mandrel was positioned so that its longitudinal direction was parallel to the row of multiple outlet holes of the spinning nozzle, and that MB nonwoven fabric 2 having a width of 40 mm was used instead of MB nonwoven fabric 1 having a width of 30 mm.

[0101] Example 6 A cylindrical filter was obtained in the same manner as in Example 1, except that MB nonwoven fabric 2 having a width of 50 mm was used instead of MB nonwoven fabric 1 having a width of 30 mm.

[0102] Example 7 Instead of the 30 mm wide MB nonwoven fabric 1, a 30 mm wide meltblown nonwoven fabric (a commercially available meltblown nonwoven fabric consisting of a single fiber of polypropylene resin, with an average fiber diameter of 3.90 μm and a basis weight of 30.0 g / m) was used. 2 , thickness 0.36 mm, air permeability measured using a Frazier type tester in accordance with JIS L 1096 is 65.2 cm 3 / cm 2 / sec, hereinafter also referred to as MB nonwoven fabric 3. A cylindrical filter was obtained in the same manner as in Example 1, except that the MB nonwoven fabric 3 was used.

[0103] Example 8 The mandrel was arranged so that its central axis was parallel to the row of multiple discharge holes of the spinning nozzle. Instead of the 30 mm-wide MB nonwoven fabric 1, a 30 mm-wide meltblown nonwoven fabric (a commercially available meltblown nonwoven fabric made of a single fiber of polypropylene resin, with an average fiber diameter of 3.44 μm and a basis weight of 30.0 g / m) was used. 2 , thickness 0.40 mm, air permeability measured using a Frazier type tester according to JIS L 1096 is 28.0 cm 3 / cm 2 / sec, hereinafter also referred to as MB nonwoven fabric 4. A cylindrical filter was obtained in the same manner as in Example 1, except that a nonwoven fabric having a molecular weight of 1000 g / s and a molecular weight of 1000 g / s were used.

[0104] Example 9 A cylindrical filter was obtained in the same manner as in Example 1, except that MB nonwoven fabric 4 having a width of 40 mm was used instead of MB nonwoven fabric 1 having a width of 30 mm.

[0105] Example 10 A cylindrical filter was obtained in the same manner as in Example 1, except that MB nonwoven fabric 4 having a width of 50 mm was used instead of MB nonwoven fabric 1 having a width of 30 mm.

[0106] Example 11 A cylindrical filter was obtained in the same manner as in Example 1, except that MB nonwoven fabric 4 having a width of 70 mm was used instead of MB nonwoven fabric 1 having a width of 30 mm.

[0107] Example 12 A cylindrical filter was obtained in the same manner as in Example 1, except that MB nonwoven fabric 3 having a width of 40 mm was used instead of MB nonwoven fabric 1 having a width of 30 mm.

[0108] (Example 13) A cylindrical filter was obtained in the same manner as in Example 1, except that MB nonwoven fabric 5 having a width of 40 mm was used instead of MB nonwoven fabric 1 having a width of 30 mm.

[0109] Example 14 A cylindrical filter was obtained in the same manner as in Example 1, except that instead of the 30 mm wide MB nonwoven fabric 1, two 40 mm wide MB nonwoven fabrics 1 were used stacked together, and the thickness of filtration layer A made of tubular fiber aggregate A was 9.3 mm, the thickness of filtration layer B made of tubular fiber aggregate B was 6.4 mm, and the thickness of filtration layer C made of tubular fiber aggregate C was 3.2 mm.

[0110] Example 15 A cylindrical filter was obtained in the same manner as in Example 1, except that, instead of the 30 mm wide MB nonwoven fabric 1, one sheet of 40 mm wide MB nonwoven fabric 1 and one sheet of 40 mm wide MB nonwoven fabric 2 were used in a stacked state, and the MB nonwoven fabric 1 was wound so that it was on the inside of the MB nonwoven fabric 2, so that the thickness of filtration layer A made of tubular fiber aggregate A was 8.2 mm, the thickness of filtration layer B made of tubular fiber aggregate B was 6.9 mm, and the thickness of filtration layer C made of tubular fiber aggregate C was 3.0 mm.

[0111] (Example 16) A cylindrical filter was obtained in the same manner as in Example 1, except that, instead of the 30 mm wide MB nonwoven fabric 1, one sheet of 40 mm wide MB nonwoven fabric 1 and one sheet of 40 mm wide MB nonwoven fabric 4 were used in a stacked state, and the MB nonwoven fabric 1 was wound so that it was on the inside of the MB nonwoven fabric 4, so that the thickness of filtration layer A made of tubular fiber aggregate A was 7.8 mm, the thickness of filtration layer B made of tubular fiber aggregate B was 8.0 mm, and the thickness of filtration layer C made of tubular fiber aggregate C was 2.9 mm.

[0112] (Example 17) A cylindrical filter was obtained in the same manner as in Example 1, except that instead of the 30 mm wide MB nonwoven fabric 1, two 40 mm wide MB nonwoven fabrics 2 were used stacked together, and the thickness of filtration layer A made of tubular fiber aggregate A was 9.4 mm, the thickness of filtration layer B made of tubular fiber aggregate B was 5.2 mm, and the thickness of filtration layer C made of tubular fiber aggregate C was 3.7 mm.

[0113] (Example 18) A cylindrical filter was obtained in the same manner as in Example 1, except that, instead of the 30 mm wide MB nonwoven fabric 1, one sheet of 40 mm wide MB nonwoven fabric 2 and one sheet of 40 mm wide MB nonwoven fabric 4 were used in a stacked state, and the MB nonwoven fabric 2 was wound so that it was on the inside of the MB nonwoven fabric 4, so that the thickness of filtration layer A made of tubular fiber aggregate A was 8.1 mm, the thickness of filtration layer B made of tubular fiber aggregate B was 6.1 mm, and the thickness of filtration layer C made of tubular fiber aggregate C was 3.7 mm.

[0114] (Example 19) A cylindrical filter was obtained in the same manner as in Example 1, except that instead of the 30 mm wide MB nonwoven fabric 1, two 40 mm wide MB nonwoven fabrics 4 were used in a stacked state, and the thickness of filtration layer A made of tubular fiber aggregate A was 8.1 mm, the thickness of filtration layer B made of tubular fiber aggregate B was 7.6 mm, and the thickness of filtration layer C made of tubular fiber aggregate C was 3.2 mm.

[0115] (Example 20) A cylindrical filter was obtained in the same manner as in Example 1, except that, instead of the 30 mm wide MB nonwoven fabric 1, one 40 mm wide MB nonwoven fabric 4 and one 40 mm wide MB nonwoven fabric 3 were used in a stacked state and wound so that the MB nonwoven fabric 4 was on the inside of the MB nonwoven fabric 3, so that the thickness of filtration layer A made of tubular fiber aggregate A was 8.4 mm, the thickness of filtration layer B made of tubular fiber aggregate B was 6.3 mm, and the thickness of filtration layer C made of tubular fiber aggregate C was 3.3 mm.

[0116] Example 21 A cylindrical filter was obtained in the same manner as in Example 1, except that instead of the 30 mm wide MB nonwoven fabric 1, two 40 mm wide MB nonwoven fabrics 3 were used stacked together, and the thickness of filtration layer A made of tubular fiber aggregate A was 8.4 mm, the thickness of filtration layer B made of tubular fiber aggregate B was 6.2 mm, and the thickness of filtration layer C made of tubular fiber aggregate C was 3.5 mm.

[0117] Example 22 A cylindrical filter was obtained in the same manner as in Example 1, except that, instead of the 30 mm wide MB nonwoven fabric 1, one 40 mm wide MB nonwoven fabric 3 and one 40 mm wide MB nonwoven fabric 5 were used in a stacked state, and the MB nonwoven fabric 3 was wound so that it was on the inside of the MB nonwoven fabric 5, so that the thickness of filtration layer A made of tubular fiber aggregate A was 8.3 mm, the thickness of filtration layer B made of tubular fiber aggregate B was 7.3 mm, and the thickness of filtration layer C made of tubular fiber aggregate C was 3.0 mm.

[0118] (Example 23) A cylindrical filter was obtained in the same manner as in Example 1, except that instead of the 30 mm wide MB nonwoven fabric 1, two 40 mm wide MB nonwoven fabrics 5 were used in a stacked state, and the thickness of filtration layer A made of tubular fiber aggregate A was 7.8 mm, the thickness of filtration layer B made of tubular fiber aggregate B was 7.3 mm, and the thickness of filtration layer C made of tubular fiber aggregate C was 3.3 mm.

[0119] Comparative Example 1 A cylindrical filter was obtained in the same manner as in Example 1, except that the tubular fiber aggregate A was continued to be formed, and the meltblown fiber was wound around it until the outer diameter of the tubular fiber aggregate A reached 65 mm, and the tubular fiber aggregate B and the tubular fiber aggregate C were not formed.

[0120] Comparative Example 2 The card web (basis weight: 25.5 g / m) produced by a parallel carding machine is composed only of core-sheath 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 the sheath component are arranged concentrically. 2) was prepared, and a high-pressure water stream (water pressure 2 MPa) was sprayed once on the front side and once on the back side of the card web to perform a hydroentanglement treatment. The card web was then dried with hot air at 120°C and heated with hot air at 140°C to melt the sheath component of the core-sheath composite fibers, while continuously winding the fibers around an iron core with a diameter of 30 mm until the outer diameter reached 55 mm, thereby producing a cylindrical fiber aggregate I. Next, a parallel card web (basis weight: 25.5 g / m) consisting of only the same core-sheath type composite fiber as that used in the preparation of the cylindrical fiber aggregate I was prepared. 2 A high-pressure water jet (water pressure 2 MPa) was sprayed once on the front side and once on the back side to perform a hydroentanglement treatment. Then, after drying with hot air at 110°C, it was heated with hot air at 140°C to melt the sheath component and thermally bond the intersections of the fibers to form a thermally bonded nonwoven fabric I (basis weight: 25.5 g / m 2 , Thickness: 0.33mm, Density: 0.078g / cm 3 ) was obtained. The tip of the thermally bonded nonwoven fabric I was pressed against the outer surface of the cylindrical fiber assembly I obtained above with a metal spatula heated to 140°C to thermally press the fabric, and then the cylindrical fiber assembly was rotated to start winding the thermally bonded nonwoven fabric I. After wrapping the thermally bonded nonwoven fabric I around twice, a meltblown nonwoven fabric (made of a single fiber of polypropylene resin, average fiber diameter: 2.01 μm, basis weight: 64.0 g / m) was formed. 2 , Thickness: 0.9mm, Air permeability measured using a Frazier type tester according to JIS L1096: 8.5cm 3 / cm 2 / sec) was supplied in a state where it was overlapped under the thermally bonded nonwoven fabric I (however, the thermally bonded nonwoven fabric I and the meltblown nonwoven fabric were not bonded in the overlapping state), and was wound three times around the thermally bonded nonwoven fabric I to form a cylindrical fiber aggregate II. Next, only the thermally bonded nonwoven fabric I was wrapped around the surface of the tubular fiber aggregate II again until the outer diameter became 65 mm. A heating body (surface temperature 140°C) consisting of a metal rod surface with 1 mm wide metal flanges implanted at 10 mm intervals was pressed against the outer surface of the outermost thermally bonded nonwoven fabric I, melting the sheath component, which is a low-melting point component of the thermally bondable fiber abutted against the metal flange, thereby bonding the fabric together and forming it so that it would not peel off, thereby producing a cylindrical filter.

[0121] Comparative Example 3 A tubular fiber assembly I and a thermally bonded nonwoven fabric I were prepared in the same manner as in Comparative Example 2. A cylindrical filter was produced in the same manner as in Comparative Example 2, except that no meltblown nonwoven fabric was used and only the thermally bonded nonwoven fabric I was wound around the cylindrical fiber aggregate I.

[0122] In the examples and comparative examples, the average fiber diameter, CV value of fiber diameter, thickness, basis weight and density of the first and second fiber sheets in the fiber assembly forming the filtration layer B, the average fiber diameter and CV value of fiber diameter of the fiber assemblies forming the filtration layer A and the filtration layer C, and the mass ratio of the filtration layer were measured as described above. The results are shown in Tables 1 to 3, 5 and 6 below. In the examples and comparative examples, the filtration performance of the cylindrical filter was measured as described above. The results are shown in Tables 4 and 7 below.

[0123] [Table 1]

[0124] [Table 2]

[0125] [Table 3]

[0126] [Table 4]

[0127] [Table 5]

[0128] [Table 6]

[0129] [Table 7]

[0130] As can be seen from Tables 1 to 7 above, the cylindrical filters of the embodiments have a filtration efficiency of 75.0% or more for particles with a particle size of 5.0 μm and a filtration life of 400 liters or more, a filtration efficiency of 80% or more for particles with a particle size of 1.0 μm and a filtration life of 300 L or more, and a filtration efficiency of 80% or more for particles with a particle size of 10 μm and a filtration life of 2000 L or more, thereby having basic filtration efficiency and filtration life.

[0131] On the other hand, the cylindrical filter of Comparative Example 1, in which the filtration layer is made of only a fiber aggregate in which meltblown fibers are accumulated and does not include a filtration layer in which fiber sheets of different thicknesses or densities are alternately wound, has poor filtration performance, the filtration efficiency for particles with a particle size of 5.0 μm is less than 75.0%, and the filtration life could not be measured. The cylindrical filter of Comparative Example 2, in which a thermally bonded nonwoven fabric and a meltblown nonwoven fabric are used for the filtration layer, has a filtration layer in which meltblown nonwoven fabrics and thermally bonded nonwoven fabrics with different thicknesses are alternately arranged in the thickness direction of the cylindrical filter, but the meltblown nonwoven fabric is not bonded via the thermally bonded nonwoven fabric, the filtration life was less than 400 L, and it was difficult to exhibit basic filtration performance. The cylindrical filter of Comparative Example 3 does not have a filtration layer in which fiber sheets of different thicknesses or densities are alternately arranged, and the filtration efficiency for particles with a particle size of 5.0 μm is less than 75.0%, and it was difficult to exhibit basic filtration performance.

[0132] As can be seen from the comparison between Example 2 and Examples 14 to 16, Examples 14 to 16, which used a multilayer fiber sheet as the first fiber sheet, had improved filtration efficiency for particles with a particle size of 1.0 μm. Also, Examples 15 and 16, in which a multilayer fiber sheet (two-layer fiber sheet) consisting of a first fiber sheet X1 and a first fiber sheet Y1 having different average fiber diameters or densities as the first fiber sheet is wound so that the first fiber sheet X1 having a smaller average fiber diameter or higher density is located inside the first fiber sheet Y1, have a longer filtration life than Example 14, which used a multilayer fiber sheet (two-layer fiber sheet) consisting of a first fiber sheet X1 and a first fiber sheet Y1 having the same average fiber diameter and density as the first fiber sheet, and can be used depending on the application of the filter, etc. As can be seen from the comparison of Example 5 with Examples 17 and 18, Examples 17 and 18, which used a multilayer fiber sheet as the first fiber sheet, had improved filtration efficiency for particles with a particle size of 1.0 μm. Furthermore, Example 18, in which a multilayer fiber sheet (two-layer fiber sheet) consisting of a first fiber sheet X1 and a first fiber sheet Y1 having different average fiber diameters or densities as the first fiber sheet was wound so that the first fiber sheet X1 having a smaller average fiber diameter or higher density was on the inner side than the first fiber sheet Y1, had a longer filtration life than Example 17, which used a multilayer fiber sheet (two-layer fiber sheet) consisting of a first fiber sheet X1 and a first fiber sheet Y1 having the same average fiber diameter as the first fiber sheet. Furthermore, compared to Examples 14 to 16 in which the average fiber diameter of the first fiber sheet was small, Examples 17 and 18 in which the average fiber diameter of the first fiber sheet was large tended to have inferior filtration efficiency, but had lower ventilation pressure loss and longer filtration life. Furthermore, Examples 19 and 20, in which the first fiber sheet has a larger average fiber diameter than Examples 14 to 18, have a higher filtration efficiency for particles with a particle diameter of 3.0 μm and a longer filtration life than Examples 14 to 18, and are therefore suitable for blocking particles with a size of 3.0 μm or more while ignoring small particles. Furthermore, by increasing the average fiber diameter of the first fiber sheet Y1, emphasis can be placed on the filtration life. Furthermore, Examples 21 and 22, in which the first fiber sheet has a larger average fiber diameter than Examples 14 to 20, have high filtration efficiency for particles with a particle size of 5.0 μm, and are suitable for blocking particles of this size. Furthermore, Example 23, in which the average fiber diameter of the first fiber sheet is larger than those of Examples 14 to 22, has a high filtration efficiency for particles with a particle size of 10.0 μm and a long filtration life, and is therefore preferable as a filter to be used when the filtrate contains a large amount of foreign matter or the foreign matter is large in size.

[0133] The present invention is not particularly limited, but includes, for example, the following embodiments.

[0134] [1] A cylindrical filter including a filtration layer formed of a cylindrical fiber assembly, The filtration layer includes a filtration layer B formed of a cylindrical fiber assembly B in which a first fiber sheet and a second fiber sheet are alternately wound into a cylindrical shape, the first fiber sheets and the second fiber sheets are alternately arranged in a thickness direction of the filtration layer B, and the first fiber sheets are bonded to each other via the second fiber sheets; A cylindrical filter that satisfies at least one of the following requirements (a) and (b): (a) The thickness H1 of the first fiber sheet is greater than the thickness H2 of the second fiber sheet. (b) the density D1 of the first fiber sheet is greater than the density D2 of the second fiber sheet; [2] The cylindrical filter according to [1], wherein a ratio H1 / H2 of a thickness H1 of the first fiber sheet to a thickness H2 of the second fiber sheet is 1.1 or more and 15.0 or less. [3] The cylindrical filter according to [1] or [2], wherein a ratio D1 / D2 of a density D1 of the first fiber sheet to a density D2 of the second fiber sheet is 1.1 or more and 10.0 or less. [4] The cylindrical filter according to any one of [1] to [3], wherein the first fiber sheet has a width of 15 mm or more and 70 mm or less. [5] The cylindrical filter according to any one of [1] to [4], wherein the first fiber sheet has an average fiber diameter d1 of 0.3 μm or more and 20 μm or less. [6] The first fiber sheet has a basis weight W1 of 15 g / m 2 More than 100g / m 2 The cylindrical filter according to any one of [1] to [5] below. [7] The cylindrical filter according to any one of [1] to [6], wherein the second fiber sheet has an average fiber diameter d2 of 0.3 μm or more and 30 μm or less. [8] The second fiber sheet has a basis weight W2 of 2 g / m 2 More than 15g / m 2 The cylindrical filter according to any one of [1] to [7] below. [9] The cylindrical filter according to any one of [1] to [8], wherein a 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 0.01 or more and 2.0 or less.

[10] The cylindrical filter according to any one of [1] to [9], wherein a ratio W1 / W2 of the basis weight W1 of the first fiber sheet to the basis weight W2 of the second fiber sheet is 1.1 or more and 50 or less.

[11] The cylindrical filter according to any one of [1] to

[10] , wherein the first fiber sheet is a multilayer fiber sheet including two or more layers of fiber sheets.

[12] The cylindrical filter according to

[11] , wherein in the multilayer fiber sheet, each fiber sheet has substantially the same average fiber diameter and density.

[13] The cylindrical filter according to

[11] , wherein the multilayer fiber sheet includes a fiber sheet X1 and a fiber sheet Y1, the fiber sheets X1 and Y1 satisfy at least one of the following requirements (r) and (s), and the fiber sheet X1 is wound so as to be located more inward than the fiber sheet Y1: (r): The average fiber diameter of the fiber sheet X1 is smaller than the average fiber diameter of the fiber sheet Y1. (s): The density of fiber sheet X1 is greater than the density of fiber sheet Y1

[14] The cylindrical filter according to any one of [1] to

[13] , wherein the first fiber sheet is a meltblown nonwoven fabric and the second fiber sheet is a meltblown web.

[15] The filtration layer includes, in addition to the filtration layer B, a filtration layer A and a filtration layer C; The cylindrical filter according to any one of [1] to

[14] , wherein a filtration layer A, a filtration layer B, and a filtration layer C are arranged in this order from the hollow portion side toward the outer periphery side of the cylindrical filter from the hollow portion side present in the center of the cylindrical filter.

[16] The filtration layer A is formed of a cylindrical fiber assembly A having an average fiber diameter of 0.3 μm or more and 30 μm or less and a CV value of the fiber diameter of 0.25 or more and 1.0 or less; and The filtration layer C is formed of a tubular fiber assembly C having an average fiber diameter of 3 μm or more and 30 μm or less and a CV value of the fiber diameter of 0.25 or more and 2.5 or less.

[17] The cylindrical filter according to

[15] or

[16] , wherein, when the total mass of the filtration layer A, the filtration layer B, and the filtration layer C is taken as 100 mass%, the content of the filtration layer A is 30 mass% or more and 70 mass% or less, the content of the filtration layer B is 15 mass% or more and 50 mass% or less, and the content of the filtration layer C is 10 mass% or more and 30 mass% or less.

[18] The cylindrical filter according to any one of

[15] to

[17] , wherein the first fiber sheet has an average fiber diameter of 0.3 μm or more and 3.40 μm or less, and a CV value of the fiber diameter of 0.25 or more and 3.0 or less.

[19] The cylindrical filter according to any one of

[15] to

[18] , wherein the first fiber sheet has an average fiber diameter greater than 3.40 μm and equal to or less than 10 μm, and a CV value of the fiber diameter of 0.25 or more and 3.0 or less.

[20] A method for producing a cylindrical filter including a filtration layer formed of a cylindrical fiber assembly, comprising: The method for producing a cylindrical filter includes a step B of winding a first fiber sheet around the surface of a rotating shaft rotating at a constant speed while discharging a molten thermoplastic resin from the discharge holes of a spinning nozzle and simultaneously blowing meltblown fibers stretched by a high-temperature gas flow ejected from around the discharge holes onto the surface of the rotating shaft, and accumulating the meltblown fibers on the surface of the first fiber sheet to form a meltblown web, which is then wound around the surface to obtain a cylindrical fiber aggregate B in which the first fiber sheet and the meltblown web are wound alternately.

[21] A method for producing the cylindrical filter according to

[20] , comprising, in addition to step B, at least one step selected from the following steps A and C: Step A: before step B, a step of spraying only the meltblown fibers onto the surface of a rotating shaft rotating at a constant speed, forming a meltblown web and winding it to obtain a cylindrical fiber aggregate A. Step C: After step B, the meltblown fibers alone are blown onto the surface of a rotating shaft, and a meltblown web is formed and wound to obtain a cylindrical fiber aggregate C.

[22] The method for producing a cylindrical filter according to

[21] , wherein step A is carried out until the thickness of the cylindrical fiber aggregate A becomes 8 mm or more and 15 mm or less, and then step B is carried out.

[23] The method for producing a cylindrical filter according to

[21] or

[22] , wherein step B is carried out until the thickness of the cylindrical fiber aggregate B becomes 2 mm or more and 8 mm or less, and then step C is carried out.

[24] The method for producing a cylindrical filter according to any one of

[20] to

[23] , wherein the first fiber sheet is a multilayer fiber sheet including a first fiber sheet X1 and a first fiber sheet Y1, and the first fiber sheet X1 and the first fiber sheet Y1 satisfy at least one of the following requirements (r) and (s), and in step B, the first fiber sheet X1 and the first fiber sheet Y1 are superimposed on each other and wound so that the first fiber sheet X1 is located on the inner side of the first fiber sheet Y1. (r): The average fiber diameter dX1 of the first fiber sheet X1 is smaller than the average fiber diameter dY1 of the first fiber sheet Y1. (s): The density DX1 of the first fiber sheet X1 is greater than the density DY1 of the first fiber sheet Y1. [Industrial Applicability]

[0135] The cylindrical filter of the present invention can be suitably used for filtering liquids such as beverages, chemical solutions, oils and fats, paints, and industrial cleaning water such as cleaning water for electronic parts and semiconductor products. [Explanation of symbols]

[0136] 1 Cylindrical filter 2. Filtration layer 3 Hollow part 4. Filtration layer A 5 Filtration layer B 6 Filtration layer C 51 First fiber sheet (strip-shaped nonwoven fabric) 52 Second fiber sheet 8 wrinkles 10. Cylindrical filter manufacturing equipment 11 Extruder 12 Gas heater 13 Spinning nozzle 14 Rotational Axis 14a center shaft 14b Outer shaft 15 Meltblown Fibers 16 Arrow 21 Cylindrical fiber assembly 24 Cylindrical fiber assembly A 25, 50 Cylindrical fiber assembly B 26 Cylindrical fiber assembly C

Claims

1. A cylindrical filter including a filtration layer formed of a cylindrical fiber assembly, The filtration layer includes a filtration layer B formed of a cylindrical fiber assembly B in which a first fiber sheet and a second fiber sheet are alternately wound into a cylindrical shape, the first fibrous sheets and the second fibrous sheets are alternately arranged in a thickness direction of the filtration layer B, and the first fibrous sheets are bonded to each other via the second fibrous sheets; A cylindrical filter that satisfies at least one of the following requirements (a) and (b): (a) The thickness H1 of the first fiber sheet is greater than the thickness H2 of the second fiber sheet. (b) the density D1 of the first fiber sheet is greater than the density D2 of the second fiber sheet;

2. 2. The cylindrical filter according to claim 1, wherein a ratio H1 / H2 of a thickness H1 of the first fiber sheet to a thickness H2 of the second fiber sheet is 1.1 or more and 15.0 or less.

3. 2. The cylindrical filter according to claim 1, wherein a ratio D1 / D2 of a density D1 of the first fiber sheet to a density D2 of the second fiber sheet is 1.1 or more and 10.0 or less.

4. 2. The cylindrical filter according to claim 1, wherein the first fiber sheet has a width of 15 mm or more and 70 mm or less.

5. 2. The cylindrical filter according to claim 1, wherein the first fiber sheet has an average fiber diameter d1 of 0.3 μm or more and 20 μm or less.

6. The first fiber sheet has a basis weight W1 of 15 g / m 2 More than 100g / m 2 2. The cylindrical filter of claim 1, wherein:

7. 2. The cylindrical filter according to claim 1, wherein the second fiber sheet has an average fiber diameter d2 of 0.3 μm or more and 30 μm or less.

8. The second fiber sheet has a basis weight W2 of 2 g / m 2 15g / m or more 2 2. The cylindrical filter of claim 1, wherein:

9. 2. The cylindrical filter according to claim 1, wherein a ratio d1 / d2 of an average fiber diameter d1 of the first fiber sheet to an average fiber diameter d2 of the second fiber sheet is 0.01 or more and 2.0 or less.

10. 2. The cylindrical filter according to claim 1, wherein a ratio W1 / W2 of a basis weight W1 of the first fiber sheet to a basis weight W2 of the second fiber sheet is 1.1 or more and 50 or less.

11. 2. The cylindrical filter according to claim 1, wherein the first fiber sheet is a multi-layer fiber sheet including two or more layers of fiber sheets.

12. 12. The cylindrical filter according to claim 11, wherein each of the multi-layered fiber sheets has substantially the same average fiber diameter and density.

13. The multilayer fiber sheet includes a first fiber sheet X1 and a first fiber sheet Y1, and the first fiber sheet X1 and the first fiber sheet Y1 satisfy at least one of the following requirements (r) and (s): The cylindrical filter according to claim 11, wherein the first fiber sheet X1 is wound so as to be located more inward than the first fiber sheet Y1. (r): the average fiber diameter dX1 of the first fiber sheet X1 is smaller than the average fiber diameter dY1 of the first fiber sheet Y1 (s): the density DX1 of the first fiber sheet X1 is greater than the density DY1 of the first fiber sheet Y1

14. 2. The cylindrical filter of claim 1, wherein the first fibrous sheet is a meltblown nonwoven fabric and the second fibrous sheet is a meltblown web.

15. The filtration layer includes a filtration layer A and a filtration layer C in addition to a filtration layer B, The cylindrical filter according to any one of claims 1 to 14, wherein a filtration layer A, a filtration layer B, and a filtration layer C are arranged in this order from the hollow portion side toward the outer periphery side of the cylindrical filter from the inner periphery side hollow portion present in the center of the cylindrical filter.

16. The filtration layer A is formed of a cylindrical fiber assembly A having an average fiber diameter of 0.3 μm or more and 30 μm or less and a CV value of the fiber diameter of 0.25 or more and 1.0 or less; and 16. The cylindrical filter according to claim 15, wherein the filtration layer C is formed of a cylindrical fiber assembly C having an average fiber diameter of 3 μm or more and 30 μm or less and a CV value of the fiber diameter of 0.25 or more and 2.5 or less.

17. 16. The cylindrical filter according to claim 15, wherein, when the total mass of the filtration layer A, the filtration layer B, and the filtration layer C is 100 mass%, the content of the filtration layer A is 30 mass% or more and 70 mass% or less, the content of the filtration layer B is 15 mass% or more and 50 mass% or less, and the content of the filtration layer C is 10 mass% or more and 30 mass% or less.

18. 16. The cylindrical filter according to claim 15, wherein the first fiber sheet has an average fiber diameter of 0.3 μm or more and 3.40 μm or less, and a CV value of the fiber diameter of 0.25 or more and 3.0 or less.

19. 16. The cylindrical filter according to claim 15, wherein the first fiber sheet has an average fiber diameter of more than 3.40 μm and not more than 10 μm, and a CV value of the fiber diameter of 0.25 or more and 3.0 or less.

20. A method for producing a cylindrical filter including a filtration layer formed of a cylindrical fiber assembly, comprising the steps of: A method for manufacturing a cylindrical filter includes a step B of winding a first fiber sheet around the surface of a rotating shaft rotating at a constant speed while discharging a molten thermoplastic resin from an outlet hole of a spinning nozzle and simultaneously blowing meltblown fibers stretched by a high-temperature gas flow ejected from around the outlet hole onto the surface of the rotating shaft, and accumulating the meltblown fibers on the surface of the first fiber sheet to form a meltblown web, which is then wound around the surface, thereby obtaining a cylindrical fiber aggregate B in which a first fiber sheet and a meltblown web are wound alternately.

21. The method for producing a cylindrical filter according to claim 20, comprising, in addition to step B, at least one step selected from the following steps A and C: Step A: Before the step B, only the meltblown fibers are sprayed onto the surface of a rotating shaft rotating at a constant speed, and a meltblown web is formed and wound to obtain a cylindrical fiber aggregate A. Step C: After step B, only the meltblown fibers are sprayed onto the surface of a rotating shaft, and a meltblown web is formed and wound to obtain a cylindrical fiber aggregate C.

22. The method for producing a cylindrical filter according to claim 21, wherein step A is carried out until the thickness of the cylindrical fiber aggregate A becomes 8 mm or more and 15 mm or less, and then step B is carried out.

23. The method for producing a cylindrical filter according to claim 21, wherein step B is carried out until the thickness of the cylindrical fiber aggregate B becomes 2 mm or more and 8 mm or less, and then step C is carried out.

24. 22. The method for producing a cylindrical filter according to claim 20 or 21, wherein the first fiber sheet is a multilayer fiber sheet including a first fiber sheet X1 and a first fiber sheet Y1, and the first fiber sheet X1 and the first fiber sheet Y1 satisfy at least one of the following requirements (r) and (s), and in step B, the first fiber sheet X1 and the first fiber sheet Y1 are wound in a superimposed state such that the first fiber sheet X1 is positioned more inward than the first fiber sheet Y1. (r): the average fiber diameter dX1 of the first fiber sheet X1 is smaller than the average fiber diameter dY1 of the first fiber sheet Y1 (s): the density DX1 of the first fiber sheet X1 is greater than the density DY1 of the first fiber sheet Y1

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