Fiber Structures and Their Applications

Abstract

This invention provides a fiber structure with high dust retention capacity. The fiber structure comprises a coarse fiber group consisting of fibers A with a single fiber diameter exceeding 5 μm, and a fine fiber group consisting of fibers B with a single fiber diameter of 5 μm or less. The fiber structure has an interlacing region where the coarse and fine fiber groups interweave. The fiber structure is divided into 10 equal parts in the thickness direction, and regions 1 to 10 are defined from the fine fiber group side to the coarse fiber group side. The filling rates of fibers A present in regions S (representing regions 1 to 3), regions T (representing regions 4 to 7), and regions U (representing regions 8 to 10) are respectively set to SA, TA, and UA. When the filling rates of fibers B are respectively set to SB, TB, and UB, SB is the largest among SB, TB, and UB, and TA+TB > SA+SB > UA+UB.

Description

[0001] Related applications

[0002] This application claims priority based on Japanese Patent Application No. 2021-112950 and Japanese Patent Application No. 2021-112951, both filed in Japan on July 7, 2021, and the full text of both is incorporated herein by reference. Technical Field

[0003] The present invention relates to a fiber structure having an interlacing region in which coarse fiber groups and fine fiber groups are interwoven. Background Technology

[0004] Traditionally, air filters have been used to remove pollen, dust, and other particulate matter from gases. Nonwoven fabrics are commonly used as filter media in these air filters. Nonwoven fabrics, formed from fine fibers produced through processes such as meltblowing, have a high dust-collecting capacity. However, when the individual fibers constituting the fibers are made of finer fibers, the fiber density within the nonwoven fabric increases, leading to increased pressure loss.

[0005] To obtain nonwoven fabrics with low pressure loss, it is suitable for the single fibers constituting the nonwoven fabric to be coarse fibers. However, on the other hand, when the single fibers constituting the nonwoven fabric are coarse, the surface area of ​​the fibers inside the nonwoven fabric is reduced, thus reducing the collection efficiency. Thus, high collection efficiency and low pressure loss are contradictory.

[0006] To address this problem, an experiment was conducted using a fiber structure that interweaves coarse and fine fibers, thereby achieving high capture efficiency and low pressure loss.

[0007] For example, Patent Document 1 (International Publication No. 2020 / 137605) discloses a fiber structure comprising an ultrafine fiber layer extending in the planar direction and a substrate layer adjacent to the ultrafine fiber layer. The ultrafine fiber layer is composed of ultrafine fibers with a number-average fiber diameter of 5 μm or less per fiber, and the substrate layer is composed of non-ultrafine fibers with a number-average fiber diameter of 7 μm or more per fiber. In a cross-section in the thickness direction of the fiber structure, there is a mixed portion in the substrate layer where ultrafine fibers are pressed into the non-ultrafine fibers and extend in the width direction. At least a portion of the ultrafine fibers pressed into the ultrafine fiber layer reaches the far region, which divides the substrate layer into three equal parts from the ultrafine fiber layer side: a near region, a central region, and a far region.

[0008] In addition, Patent Document 2 (International Publication No. 2021 / 010178) discloses a fiber structure that integrates ultrafine fibers with a number-average fiber diameter of less than 4.5 μm and non-ultrafine fibers with a number-average fiber diameter of more than 5.5 μm, and has a protrusion on at least one surface.

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: International Publication No. 2020 / 137605

[0012] Patent Document 2: International Publication No. 2021 / 010178 Summary of the Invention

[0013] The problem that the invention aims to solve

[0014] However, in Patent Documents 1 and 2, only the initial collection efficiency and pressure loss were evaluated, and there was no record of the performance changes over time when dust collection was carried out continuously.

[0015] For long-term use as an air filter, a high dust retention capacity is required, which indicates how much dust can be captured before reaching the end of its lifespan when it can no longer be used as a filter. The fiber structures described in Patent Documents 1 and 2 have room for further improvement in terms of dust retention capacity.

[0016] Therefore, the object of the present invention is to provide a fiber structure with high dust retention capacity.

[0017] Problem Solving Methods

[0018] In order to achieve the above-mentioned objective, the inventors of the present invention conducted in-depth research and found that in a fiber structure having an interlacing region with coarse fiber groups and fine fiber groups, a fiber structure in which the filling rate of coarse fiber A and fine fiber B in the thickness direction has a specific relationship, or where the average number of melting points of the fine fiber B constituting the fine fiber group is within a specific range, can achieve a high dust retention capacity, thereby completing the present invention.

[0019] That is, the present invention can be constructed in the following ways.

[0020] [Method 1]

[0021] A fiber structure comprising a coarse fiber group consisting of fibers A with a single fiber diameter exceeding 5 μm, and a fine fiber group consisting of fibers B with a single fiber diameter of 5 μm or less, wherein the fiber structure has an interlacing region where the coarse fiber group and the fine fiber group interweave.

[0022] The aforementioned fiber structure is divided into 10 equal parts along its thickness direction, and regions 1 through 10 are designated from the fine fiber group side to the coarse fiber group side. The filling rates of fiber A in regions S (representing regions 1 through 3), regions T (representing regions 4 through 7), and regions U (representing regions 8 through 10) are designated as SA, TA, and UA, respectively. The filling rates of fiber B are designated as SB, TB, and UB, respectively.

[0023] Among SB, TB, and UB, SB is the largest.

[0024] TA+TB>SA+SB>UA+UB.

[0025] [Method 2]

[0026] According to the fiber structure described in method 1, wherein...

[0027] The average number of fusion bonding points between fibers B in the 100μm×100μm area of ​​the fiber structure is 10 or less (preferably 8 or less, more preferably 5 or less).

[0028] [Method 3]

[0029] According to the fiber structure described in method 2, wherein...

[0030] The bonding points of the aforementioned fibers B are formed by melt-blowing.

[0031] [Method 4]

[0032] A fiber structure comprising a coarse fiber group consisting of fibers A with a single fiber diameter exceeding 5 μm, and a fine fiber group consisting of fibers B with a single fiber diameter of 5 μm or less, wherein the fiber structure has an interlacing region where the coarse fiber group and the fine fiber group interweave.

[0033] The average number of fusion bonding points between the fibers B constituting the above-mentioned fine fiber group in the 100μm×100μm planar direction of the fiber structure is 1.0 or more and 10.0 or less (preferably 1.0 or more and 8.0 or less, more preferably 1.0 or more and 5.0 or less).

[0034] [Method 5]

[0035] According to the fiber structure described in method 4, wherein...

[0036] The bonding points of the aforementioned fibers B are formed by melt-blowing.

[0037] [Method 6]

[0038] The fiber structure according to method 4 or 5, wherein...

[0039] The aforementioned fiber structure is divided into 10 equal parts along its thickness direction, and regions 1 through 10 are designated from the fine fiber group side to the coarse fiber group side. The filling rates of fiber A in regions S (representing regions 1 through 3), regions T (representing regions 4 through 7), and regions U (representing regions 8 through 10) are designated as SA, TA, and UA, respectively. The filling rates of fiber B are designated as SB, TB, and UB, respectively.

[0040] Among SB, TB, and UB, SB is the largest.

[0041] TA+TB>SA+SB>UA+UB.

[0042] [Method 7]

[0043] The fiber structure according to any one of methods 1 to 6 is an aggregate of coarse fiber nonwoven fabric formed from fiber A and fine fiber nonwoven fabric formed from fiber B.

[0044] [Method 8]

[0045] The fiber structure according to any one of methods 1 to 7, wherein...

[0046] The number-average fiber diameter of the single fibers in the above-mentioned coarse fiber group is 5.5 μm or more (preferably 6.0 μm or more, more preferably 7.0 μm or more), and the number-average fiber diameter of the single fibers in the above-mentioned fine fiber group is 4.5 μm or less (preferably 4.0 μm or less, more preferably 3.0 μm or less).

[0047] [Method 9]

[0048] The fiber structure according to any one of methods 1 to 8 has a unit area weight of 15 to 180 g / m². 2 (Preferred to be 18-150g / m) 2 More preferably, 20–120 g / m 2 ).

[0049] [Method 10]

[0050] The fiber structure described according to any one of methods 1 to 9 is electrically charged.

[0051] [Method 11]

[0052] The fiber structure according to any one of methods 1 to 10 has a capture efficiency of 60% or more (preferably 70% or more, more preferably 80% or more).

[0053] [Method 12]

[0054] The fiber structure according to any one of methods 1 to 11 has a QF value of 0.10 or more (preferably 0.15 or more, more preferably 0.19 or more).

[0055] The QF value is calculated based on the capture efficiency and pressure loss using the following formula.

[0056] QF value = -ln(1 - capture efficiency (%) / 100) / pressure loss (Pa).

[0057] [Method 13]

[0058] A filter comprising a fiber structure as described in any of embodiments 1 to 12.

[0059] [Method 14]

[0060] A face mask having the filter described in method 13.

[0061] It should be noted that any combination of at least two constituent elements disclosed in the claims and / or description and / or drawings is also included in this invention. In particular, any combination of two or more claims recited in the claims is also included in this invention.

[0062] The effects of the invention

[0063] The fiber structure according to the present invention has a high dust retention capacity, thus enabling long-term dust capture. Attached Figure Description

[0064] The invention can be more clearly understood based on the following description of preferred embodiments with reference to the accompanying drawings. However, the embodiments and drawings are for illustration and explanation only and do not limit the scope of protection of the invention. The scope of protection of the invention is determined by the appended claims. The drawings are not necessarily shown to scale and are exaggerated to illustrate the principles of the invention.

[0065] Figure 1 This is a magnified cross-sectional photograph of the fiber structure in Example 4.

[0066] Figure 2 This is a magnified photograph of the surface of the fine fiber group side of the fiber structure in Example 4.

[0067] Figure 3 This is a cross-sectional conceptual diagram used to illustrate the various regions of a fiber structure according to one embodiment of the present invention.

[0068] Symbol Explanation

[0069] A···Crude fiber A

[0070] B··· Fine fiber B

[0071] 100···Fiber Structure

[0072] 101··· Fine fiber group side

[0073] 102··· Coarse fiber group side

[0074] 1~10··· Area 1 to Area 10

[0075] S···Region S

[0076] T···Region T

[0077] U···Region U

[0078] Z···Thickness direction Detailed Implementation

[0079] The fiber structure of the present invention comprises a coarse fiber group consisting of fibers A (hereinafter, sometimes referred to as coarse fibers A) with a single fiber diameter exceeding 5 μm, and a fine fiber group consisting of fibers B (hereinafter, sometimes referred to as fine fibers B) with a single fiber diameter of 5 μm or less. The fiber structure has an interlacing region where the coarse fiber group and the fine fiber group interweave. Here, the interlacing region refers to, as... Figure 1 As shown in the elliptical frame, a portion of the fine fiber B constituting the fine fiber group intrudes into the structure of the coarse fiber group. Such a structure can be obtained by performing the cohesion treatment described later. The fiber structure of the present invention has at least a portion of an interlacing region between the coarse fiber group and the fine fiber group, unlike a laminate in which the coarse fiber group and the fine fiber group are only superimposed in the form of layers. For example, the fiber structure of the present invention may have a region where the coarse fiber group and the fine fiber group are each formed into layers and interlaced only near the interface between the two layers, or it may have a region where the coarse fiber group and the fine fiber group are not divided into separate layers but interlaced throughout the thickness direction. It should be noted that the fiber diameter of a single fiber refers to the diameter of each individual single fiber. By using the method described in the embodiments described later, the individual single fibers can be distinguished as coarse fiber A and fine fiber B using the fiber diameter of the single fiber as an indicator.

[0080] In this invention, the fiber structure is divided into 10 equal parts along its thickness direction. Regions 1 through 10 are defined from the fine fiber group side to the coarse fiber group side. Regions 1 through 3 are defined as region S, regions 4 through 7 are defined as region T, and regions 8 through 10 are defined as region U. Here, the fine fiber group side refers to the side in which, considering the distribution of fine fiber B, the filling rate of fine fiber B is higher than in other regions within the region where the fiber structure is divided into two equal parts along its thickness direction. The coarse fiber group side refers to the side opposite to the fine fiber group side.

[0081] Figure 3This is a cross-sectional conceptual diagram used to illustrate the various regions of a fiber structure in one embodiment. Figure 3 In the fiber structure 100, within a 2-equal region along the thickness direction Z, the filling rate of fine fibers B is higher in the upper region (regions 1 to 5) than in the lower region (regions 6 to 10). Therefore, the upper side of the fiber structure 100 is defined as the fine fiber group side 101, and the lower side is defined as the coarse fiber group side 102, with regions designated as region 1, region 2, ..., region 10 sequentially from the upper side. Furthermore, as... Figure 3 As shown, regions 1 to 3 correspond to region S, regions 4 to 7 correspond to region T, and regions 8 to 10 correspond to region U.

[0082] In this invention, the filling rate of coarse fiber A present in each nth region (n = 1 to 10) is defined as M. n A. The filling rate of fine fiber B is defined as M. n B. The filling rate of coarse fiber A present in the entire region from region 1 to region 10 is defined as MA, and the filling rate of fine fiber B is defined as MB. The filling rates of coarse fiber A present in regions S, T, and U are defined as SA, TA, and UA, respectively, and the filling rates of fine fiber B are defined as SB, TB, and UB, respectively. In this invention, the filling rate represents the proportion of the volume occupied by the target fiber in a given region relative to the volume of that region, and is a value measured by the method described in the embodiments described later.

[0083] For example, M1A represents the proportion of the volume occupied by coarse fiber A in region 1 relative to the total volume of region 1. 2- 3A represents the proportion of the volume occupied by coarse fiber A in regions 2 and 3 relative to the total volume of regions 2 and 3, which is equal to the average of M2A and M3A. SA represents the proportion of the volume occupied by coarse fiber A in region S relative to the total volume of region S (i.e., regions 1 to 3), which is equal to the average of M1A, M2A, and M3A.

[0084] For the fiber structure of the present invention, SB is the largest among SB, TB, and UB, and can be TA+TB>SA+SB>UA+UB. When such a fiber structure is used as a filter, the region U side can be used as the upstream side for collection. In this case, the airflow flows in from region U, passes sequentially through region U, region T, and region S, and flows out from region S. That is, such a fiber structure has a low fiber (coarse fiber A and fine fiber B) filling rate in the upstream region U, a high fiber (coarse fiber A and fine fiber B, especially coarse fiber A) filling rate in the middle region T, and a high fine fiber B filling rate in the downstream region S. The dust in the gas is a mixture of particulate matter of various particle sizes. In such a fiber structure with a specific fiber distribution, region U has a coarse structure with fewer fibers, thus enabling the collection of large-particle dust without clogging. Next, region T, due to its high fiber (especially coarse fiber A) filling rate, has a structure with smaller pores than region U. Therefore, it can capture residues of large-particle dust and gradually capture small-particle dust. Then, region S, due to the abundance of fine fibers B, has a denser structure than region T, and thus can capture small-particle dust. In this way, the aforementioned fiber structure has a gradient structure of pores that can gradually capture dust particles from large to small from the upstream side to the downstream side. Therefore, it is less prone to increased pressure loss due to clogging and can achieve a high dust retention capacity.

[0085] For the fiber structure of the present invention, from the viewpoint of preventing upstream blockage, it is preferable that the fiber filling rate of region U is low, for example, UA+UB can be 10.0% or less, preferably 8.0% or less, and more preferably 5.0% or less. As a lower limit for UA+UB, there is no particular limitation; for example, from the viewpoint of being able to capture large-particle dust to a certain extent, it can be 0.1% or more, preferably 0.5% or more.

[0086] From the viewpoint of preventing clogging in the middle region and improving collection efficiency, the fiber filling rate (TA+TB) of the fiber structure in region T of the present invention can be 6.0 to 30.0%, preferably 6.2 to 25.0%, and more preferably 6.5 to 20.0%.

[0087] For the fiber structure of the present invention, from the viewpoint of improving the collection efficiency of small-particle-size dust on the downstream side, it is preferable to have a high filling rate of fine fibers B in region S, for example, the largest M among M1B, M2B and M3B. n B can be 5.0% or more, preferably 5.5% or more, and more preferably 6.0% or more. M is the largest among M1B, M2B, and M3B. nThe upper limit of B is not particularly limited. For example, from the viewpoint of reducing pressure loss, it can be 25.0% or less, preferably 18.0% or less, and more preferably 15.0% or less.

[0088] From the viewpoint of improving dust retention capacity, the SB+UA of the fiber structure of the present invention can be 1.0 to 12.0%, preferably 2.0 to 11.5%, and more preferably 2.5 to 11.0%.

[0089] For the fiber structure of the present invention, it is preferable that coarse fibers A are present in region S on the side of the fine fiber group and that an interlacing region is present, for example, M 2-3 A can be 0.05% to 20.0%, preferably 0.08% to 15.0%, and more preferably 0.10% to 10.0%.

[0090] In the fiber structure of the present invention, the interlacing region can be regarded as a region in which both coarse fibers A and fine fibers B exist in regions 1 to 10. For example, as an interlacing region, the ratio M of the filling rate of coarse fiber A to the filling rate of fine fiber B in region n is... n A / M n B can be from 0.1 to 200. Furthermore, for the fiber structure of the present invention, it is preferable to have a wide range of interlacing regions in the thickness direction, for example, in at least two (preferably at least three, more preferably at least four) adjacent regions in regions 1 to 10, M n A / M n B is preferably 0.2 to 100, more preferably 0.5 to 80, and even more preferably 1 to 70.

[0091] For the fiber structure of the present invention, from the viewpoint of balancing high capture efficiency and low pressure loss, the fiber filling rate MA+MB of all regions from the 1st region to the 10th region can be 1.0% to 20.0%, preferably 3.0% to 18.0%, and more preferably 5.0% to 15.0%.

[0092] For the fiber structure of the present invention, the ratio of the filling rate of coarse fiber A to the filling rate of fine fiber B in the entire region from region 1 to region 10, MA / MB, can be 0.5 to 10, preferably 0.8 to 8, more preferably 1.10 to 6, and even more preferably 2.25 to 5.

[0093] For the fiber structure of the present invention, the average number of fusion bonding points between the fine fibers B in the 100μm × 100μm area of ​​the fiber structure can be more than 1.0 and less than 10.0. Here, fusion bonding refers to a state in which at least a portion of the fibers are melted and the fibers are bonded together. The number of fusion bonding points between the fine fibers B in the 100μm × 100μm area of ​​the fiber structure refers to the number of fine fibers B that can be identified in a magnified planar image of the fiber structure in the 100μm × 100μm area of ​​the fiber structure obtained by microscopy. Figure 2 The number of points where the fibers are fused together at the intersection, as shown by the circular frame. The average number of fusion points represents the average number of fusion points across a 100μm × 100μm area at five different locations in the planar direction of the fiber structure, and is a value measured using the method described in the embodiments below. It should be noted that since the number of fusion points can be confirmed in the magnified image, it includes not only the 100μm × 100μm surface of the fiber structure in the planar direction, but also the range in its thickness direction shown in the magnified image.

[0094] In fiber structures where the average number of fusion points between fine fibers B is kept to a low level, the fine fiber groups are bound together by mechanical cohesion due to less fixation based on fusion bonding. Therefore, the degrees of freedom of the fine fiber groups are increased, and the fibers are easy to move. As a result, during cohesion (described later), the fine fiber groups easily cohede with the coarse fiber groups. On the other hand, if the average number of fusion points between fine fibers B is too low, the degrees of freedom of the fine fiber groups become too high. As a result, during cohesion, the fine fiber groups may escape and disperse, or it may be difficult to interweave with the coarse fiber groups. Thus, the average number of fusion points between fine fibers B affects the relationship between the fine fiber groups and the coarse fiber groups. Alternatively, if the average number of fusion points between fine fibers B is within a certain range, the fiber structure is in a state where the fine fiber groups and coarse fiber groups easily interweave. This allows for the formation of a structure where fine fibers B remain on the fine fiber group side and the fibers are abundantly distributed in the interior region along the thickness direction, which can be considered as improving dust retention capacity. The average number of fusion points between fine fibers B is preferably 8.0 or less, and more preferably 5.0 or less.

[0095] Furthermore, the fusion bonding points of the fine fibers B can be formed by melt-blowing. As will be described later, melt-blowing is preferred from the perspective of enabling finer fibers, and is a method for manufacturing nonwoven fabrics that utilizes the self-fusion bonding properties of fibers. From the viewpoint of increasing the degree of freedom of fiber airflow, it is preferable that the average number of fusion bonding points of the fine fibers B produced by melt-blowing is within a specific range.

[0096] The fiber structure of the present invention can be an aggregate of coarse fiber nonwoven fabric (preferably meltblown nonwoven fabric or spunlace nonwoven fabric) formed from coarse fiber A and fine fiber nonwoven fabric (preferably meltblown nonwoven fabric) formed from fine fiber B.

[0097] In the fiber structure of the present invention, the fine fiber B can be a long fiber or a short fiber, and its fiber length can be 15 mm or more, preferably 20 mm or more, more preferably 30 mm or more, and even more preferably 35 mm or more. In the present invention, long fiber refers to the fiber constituting long fiber nonwoven fabric (e.g., meltblown nonwoven fabric, spunbond nonwoven fabric), which can be distinguished from short fibers that have been cut to a given fiber length and have relatively uniform fiber length.

[0098] The weight per unit area of ​​the fiber structure can be appropriately set according to the application, for example, it can be 15 to 180 g / m². 2 The optimal concentration is approximately 18–150 g / m³. 2 Approximately 20–120 g / m², more preferably 20–120 g / m² 2 Approximately. It should be noted that the weight per unit area is a value measured using the method described in the embodiments below.

[0099] Considering both high capture efficiency and low pressure loss, the apparent density of the fiber structure can be, for example, 0.005–0.30 g / cm³. 3 Approximately (e.g., 0.005–0.10 g / cm³) 3 The preferred concentration is 0.01–0.20 g / cm³. 3 Approximately (e.g., 0.01–0.08 g / cm³) 3 More preferably, it is 0.02–0.15 g / cm³. 3 Approximately (e.g., 0.02–0.07 g / cm³) 3 It should be noted that the apparent density is a value measured by the method described in the embodiments described later.

[0100] The thickness of the fiber structure can be appropriately set according to the application, for example, it can be about 0.1 to 5 mm, preferably about 0.2 to 3 mm, and more preferably about 0.3 to 1 mm. It should be noted that the thickness is a value measured by the method described in the embodiments below.

[0101] Coarse fiber A refers to all fibers in the fiber structure whose individual fiber diameter exceeds 5.0 μm. The aggregate of coarse fibers A is called a coarse fiber group. From the viewpoint of reducing pressure loss, the number-average fiber diameter of the individual fibers in the coarse fiber group can be 5.5 μm or more, preferably 6.0 μm or more, and more preferably 7.0 μm or more. There is no particular upper limit to the number-average fiber diameter of the individual fibers in the coarse fiber group. From the viewpoint of optimizing cohesion with the fine fiber group, it can be 50 μm or less, preferably 30 μm or less. The number-average fiber diameter of the individual fibers is a value measured by the method described in the examples described later.

[0102] Fine fiber B refers to all fibers in the fiber structure whose individual fiber diameter is 5.0 μm or less. An aggregate of fine fibers B is a fine fiber group. From the viewpoint of improving collection efficiency, the number-average fiber diameter of the individual fibers in the fine fiber group can be 4.5 μm or less, preferably 4.0 μm or less, and more preferably 3.0 μm or less. There is no particular limitation on the lower limit of the number-average fiber diameter of the individual fibers in the fine fiber group; from the viewpoint of processability, it can be 0.1 μm or more, preferably 0.5 μm or more.

[0103] From the viewpoint of optimizing the interweaving of the coarse fiber group and the fine fiber group, the ratio of the number-average fiber diameter of the single fiber of the fine fiber group to the number-average fiber diameter of the single fiber of the coarse fiber group, expressed as (fine fiber group) / (coarse fiber group), can be, for example, 0.05 to 0.80, preferably 0.08 to 0.50, and more preferably 0.10 to 0.35.

[0104] The coarse fiber A constituting the coarse fiber group can be selected according to its intended use, and can be any fiber from natural fibers, regenerated fibers, semi-synthetic fibers, and synthetic fibers. Specifically, examples include: natural fibers such as cotton, linen, wool, and pulp; regenerated fibers such as rayon, high-tenacity fiber, and cupro fiber; semi-synthetic fibers such as acetate and triacetate; polyolefin fibers formed from polyolefin resins such as polyethylene and polypropylene; polystyrene fibers formed from polystyrene resins such as polystyrene; polyester fibers formed from polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polypropylene terephthalate, and polylactic acid; polyamide fibers formed from polyamide resins such as polyamide 6, polyamide 66, polyamide 11, polyamide 12, polyamide 610, and polyamide 612; polycarbonate fibers formed from polycarbonate resins; polyurethane fibers formed from polyurethane resins; acrylic fibers formed from acrylic resins such as polyacrylonitrile; and various heat-resistant fibers. These fibers can be used alone or in combination of two or more.

[0105] Furthermore, the coarse fiber A can be a non-composite fiber or a composite fiber (core-sheath type composite fiber, island-type composite fiber, parallel type composite fiber, etc.). In the case of composite fibers, for example, it is preferable to use a low-melting-point resin as one component (e.g., sheath component, island component, etc.) and a high-melting-point resin as another component (e.g., core component, island component, etc.). The low-melting-point resin and the high-melting-point resin can be appropriately selected from the resins that form the above-mentioned fibers, depending on the processing temperature of the thermal bonding.

[0106] Among these fibers, polyolefin fibers, polyester fibers, acrylic fibers, heat-resistant fibers, and their composite fibers are preferred.

[0107] Heat-resistant fibers can be fibers composed of heat-resistant polymers that have structural units containing aromatic, heterocyclic, sulfur-containing, or nitrogen-containing compounds within the polymer molecule. Examples include: polyetheretherketone (PEEK) fibers, polyetherketone (PEK) fibers, polyetherketoneketone (PEKK) fibers, polyphenylene sulfide (PPS) fibers, aromatic polyamide fibers (e.g., polyamide fibers composed of aliphatic diamine units and aromatic dicarboxylic acid units), aramid fibers (para-aramid fibers, meta-aramid fibers), polyimide (PI) fibers, polyetherimide (PEI) fibers, polyamideimide fibers, amorphous polyarylate fibers, liquid crystal polyester fibers, and polyphenylene oxide fibers. Poly(phenylene oxide) (PBO) fiber, polybenzimidazole (PBI) fiber, polybenzothiazole fiber, polytetrafluoroethylene (PTFE) fiber, melamine fiber, novoloid fiber, etc. These fibers can be used alone or in combination of two or more.

[0108] Among these heat-resistant fibers, from the viewpoint of melt spinning and heat resistance, liquid crystal polyester fibers, polyetherimide fibers, polyphenylene sulfide fibers, and semi-aromatic polyamide fibers (e.g., semi-aromatic polyamide fibers with dicarboxylic acid units containing terephthalic acid units, diamine units containing 1,9-nonanediamine units and / or 2-methyl-1,8-octanediamine units) are preferred.

[0109] The fine fiber B constituting the fine fiber group can be appropriately selected according to the preparation method, and synthetic fibers are preferred. Examples of resins constituting the synthetic fibers include: polyolefin resins, polystyrene resins, acrylic resins, polyvinyl alcohol resins, polyvinyl chloride resins, polyvinylidene chloride resins, polyurethane resins, polyester resins, polyether resins, polyamide resins, resins used to constitute the heat-resistant fibers of the aforementioned coarse fiber group, thermoplastic elastomers, etc. These resins can be used alone or in combination of two or more. The fine fiber B can be a fiber formed from the same type of resin as the coarse fiber A, or it can be a fiber formed from a different type of resin. Furthermore, from the viewpoint of trapping performance, the fine fiber B is preferably a hydrophobic fiber. Moreover, it is preferable that both the coarse fiber A and the fine fiber B are hydrophobic fibers.

[0110] From the viewpoint of forming meltblown nonwoven fabric, and from the viewpoint of melt spinning properties and heat resistance, resins such as liquid crystal polyester, polyetherimide, polyphenylene sulfide, and semi-aromatic polyamide (e.g., semi-aromatic polyamides in which the dicarboxylic acid unit includes a terephthalic acid unit, the diamine unit includes a 1,9-nonanediamine unit and / or a 2-methyl-1,8-octanediamine unit) are preferred as the resins constituting heat-resistant fibers.

[0111] The method for manufacturing the fiber structure of the present invention may include at least, for example, a step of preparing a laminate of coarse fiber nonwoven fabric and fine fiber nonwoven fabric, and a step of performing a bonding treatment on the laminate.

[0112] In the preparation process, a laminate of coarse fiber nonwoven fabric and fine fiber nonwoven fabric is prepared. The coarse fiber nonwoven fabric and fine fiber nonwoven fabric constituting the laminate can be prepared separately and laminated together, or a nonwoven fabric (e.g., coarse fiber nonwoven fabric) can be used as a support, and another nonwoven fabric (e.g., fine fiber nonwoven fabric) can be directly formed on it by deposition or other methods such as meltblowing. From the viewpoint of increasing the diversity of raw materials, it is preferable to prepare a laminate by separately preparing the coarse fiber nonwoven fabric and fine fiber nonwoven fabric and then laminating them. From the viewpoint of ensuring sufficient bonding of the coarse fiber nonwoven fabric and fine fiber nonwoven fabric in the subsequent bonding process, the laminate is preferably in a state where the two are not bonded but merely laminated together (without adhesive). In this case, for the resulting fiber structure, it is preferable that the constituent fibers of the coarse fiber nonwoven fabric and fine fiber nonwoven fabric are not fused together.

[0113] For the coarse fiber nonwoven fabric before cohesion, the number-average fiber diameter of the single fiber can be 5.5 μm or more, preferably 6.0 μm or more, and more preferably 7.0 μm or more. There is no particular upper limit to the number-average fiber diameter of the single fiber; for example, it can be 50 μm or less, preferably 30 μm or less. The coarse fiber nonwoven fabric can be mainly (e.g., 60% by weight or more) formed from coarse fibers A with a single fiber diameter exceeding 5.0 μm. As long as the coarse fibers A in the coarse fiber nonwoven fabric can be interwoven with the fine fibers B in the fine fiber nonwoven fabric, the type of coarse fiber nonwoven fabric is not particularly limited; dry nonwoven fabrics and spunbond nonwoven fabrics (e.g., meltblown nonwoven fabrics, spunbond nonwoven fabrics) are preferred. The coarse fiber nonwoven fabric can be used alone or in combination with two or more other types.

[0114] For example, in the case of dry nonwoven fabrics, a web is formed from a given fiber assembly using carding or air-jet forming. Then, the fibers are bonded together to impart practical strength to the resulting web. As bonding methods, chemical bonding (e.g., chemical adhesive), thermal bonding (e.g., thermal bonding, steam jetting), and mechanical bonding (e.g., hydroentangling, needle punching) can be used. From a simplicity perspective, hydroentangling, which utilizes water flow for bonding, is preferred.

[0115] Specifically, examples of dry nonwoven fabrics include chemically bonded nonwoven fabrics, thermally bonded nonwoven fabrics, spunlace nonwoven fabrics, steam-jet nonwoven fabrics, needle-punched nonwoven fabrics, and air-laid nonwoven fabrics. Among these, spunlace nonwoven fabrics are preferred from the viewpoint of fully bonding with fine fiber nonwoven fabrics.

[0116] The fiber length of the fibers constituting dry nonwoven fabric can be approximately 15–70 mm, preferably approximately 20–65 mm, more preferably approximately 30–60 mm, and even more preferably approximately 35–55 mm. Based on this fiber length, dry nonwoven fabric can be distinguished from wet nonwoven fabric (which typically has a fiber length of less than 10 mm).

[0117] In addition, examples of spunbond nonwovens include meltblown nonwovens and spunbond nonwovens. Among these, meltblown nonwovens are preferred because they can be adjusted to have rigidity even with low unit area weight. Meltblown nonwovens are nonwovens obtained by the meltblowing method, which generally produces fine-fiber nonwovens, but coarse-fiber nonwovens can also be obtained through specific manufacturing conditions. When meltblown nonwovens are used as coarse-fiber nonwovens, their high rigidity improves their cohesion with fine-fiber nonwovens. In order to impart rigidity to the coarse fiber group so as to facilitate interweaving with the fine fiber group, it is preferable to bring the fibers to the collection surface in a coarse state before the fibers of the meltblown fiber stream are refined, and before the fibers solidify. For example, it is preferable to increase the fiber diameter by shortening the collection distance of the meltblown fiber stream or increasing the resin viscosity, thereby extending the time until solidification. Specifically, the collection distance (the distance from the nozzle to the collection surface) can be in the range of 3 to 100 cm, preferably 5 to 80 cm, and more preferably 7 to 60 cm.

[0118] From the perspective of improving rigidity and fully integrating with fine fiber nonwoven fabric, the fibers constituting coarse fiber nonwoven fabric can be long fibers.

[0119] The unit area weight of coarse fiber nonwoven fabric can be, for example, 10-150 g / m². 2 The optimal concentration is approximately 12-130 g / m³. 2 Approximately 15–100 g / m², more preferably 15–100 g / m² 2 about.

[0120] From the viewpoint of fully integrating with the fine fiber nonwoven fabric, the coarse fiber nonwoven fabric preferably has a relatively coarse structure, and its apparent density can be, for example, 0.005–0.20 g / cm³. 3 Approximately (e.g., 0.005–0.07 g / cm³) 3 The preferred concentration is 0.01–0.15 g / cm³. 3 Approximately (e.g., 0.01–0.06 g / cm³) 3 More preferably, it is 0.02–0.10 g / cm³. 3 Approximately (e.g., 0.02–0.05 g / cm³) 3 ).

[0121] The thickness of the coarse fiber nonwoven fabric can be, for example, about 0.1 to 5 mm, preferably about 0.2 to 3 mm, and more preferably about 0.3 to 1 mm.

[0122] For the fine fiber nonwoven fabric before cohesion, the number-average fiber diameter of the single fiber can be 4.5 μm or less, preferably 4.0 μm or less, and more preferably 3.0 μm or less. The lower limit of the number-average fiber diameter of the single fiber is not particularly limited; for example, it can be 0.1 μm or more, preferably 0.5 μm or more. The fine fiber nonwoven fabric can be mainly (e.g., 60% by weight or more) formed from fine fibers B with a single fiber diameter of 5.0 μm or less.

[0123] As a fine fiber nonwoven fabric, meltblown nonwoven fabric, electrospun nonwoven fabric, nonwoven fabric obtained from split fibers (a fine fiber nonwoven fabric obtained by temporarily forming a nonwoven fabric from bundles of fibers containing different components and then splitting the fibers at the interface of different components), nonwoven fabric obtained from island fibers (a fine fiber nonwoven fabric obtained by dissolving the sea portion of a nonwoven fabric formed from island fibers), and nonwoven fabric formed from fibrillated fibers (a fine fiber nonwoven fabric obtained by applying physical impact to a temporarily formed nonwoven fabric to fibrillate the fibers), etc. From the viewpoint of ease of weaving, meltblown nonwoven fabric is preferred.

[0124] To obtain the fibrous structure of the present invention, it is preferable to use a fine-fiber nonwoven fabric with an average melt-bonding point number between the fine fibers B within a specific range. By using such a fine-fiber nonwoven fabric, it is possible to perform a bonding process with a coarse-fiber nonwoven fabric, making it easy to interweave the fine fiber group with the coarse fiber group. For example, by refining molten thermoplastic polymer extruded from a nozzle into fibers through hot air jetting, the fibers are interwoven in a high-temperature, high-speed airflow, and self-melting bonding occurs simultaneously, forming a meltblown nonwoven fabric. In the present invention, it was discovered that by adjusting the collection distance of the fiber stream based on the meltblown method, the self-melting bonding property during the period from when the extruded polymer becomes fibrous to when it reaches the collection surface can be controlled, and the average melt-bonding point number between the fine fibers B of the obtained fine-fiber nonwoven fabric can be adjusted. Specifically, by increasing the collection distance, self-melting adhesion can be suppressed. On the other hand, by shortening the collection distance, self-melting adhesion can be promoted. Although it also depends on conditions such as resin viscosity and air temperature, the collection distance (the distance from the nozzle to the collection surface) can be 35 to 90 cm, preferably 40 to 80 cm, and more preferably 40 to 70 cm.

[0125] From the perspective of fully integrating with coarse fiber nonwoven fabric, the unit area weight of fine fiber nonwoven fabric can be, for example, 1.0–30 g / m². 2 The optimal value is approximately 2.0–25 g / m³. 2 Approximately 3.0–20 g / m³, more preferably 3.0–20 g / m³ 2 about.

[0126] The apparent density of fine fiber nonwoven fabric can be, for example, 0.01–0.30 g / cm³. 3The optimal value is approximately 0.03–0.25 g / cm³. 3 The concentration is approximately 0.05–0.20 g / cm³, more preferably 0.05–0.20 g / cm³. 3 about.

[0127] The thickness of the fine fiber nonwoven fabric can be, for example, about 0.01 to 0.30 mm, preferably about 0.03 to 0.25 mm, and more preferably about 0.05 to 0.20 mm.

[0128] For laminated materials, from the viewpoint of ensuring sufficient bonding between the coarse fiber nonwoven fabric and the fine fiber nonwoven fabric in the subsequent bonding process, the ratio W1 / W2 of the unit area weight W1 of the coarse fiber nonwoven fabric to the unit area weight W2 of the fine fiber nonwoven fabric can be 1.2 to 8.0, preferably 1.3 to 5.0, more preferably 1.5 to 3.5, and even more preferably 1.7 to 2.5.

[0129] As a bonding process, coarse fiber nonwoven fabric and fine fiber nonwoven fabric can be bonded together by using hydroentangling, needle punching, etc. From the viewpoint of fully bonding the long fibers of the fine fiber nonwoven fabric, hydroentangling is preferred.

[0130] For example, in the hydroentangling process, a porous support is placed on which a laminate of coarse and fine nonwoven fabrics is stacked. High-pressure water (e.g., above 1 MPa) is sprayed from a nozzle with micropores. The water flow that penetrates the laminate is reflected by the support, and its energy can be used to make the fibers cohesive.

[0131] The porous support used in the hydroentangling process can be either a roller type or a flat plate type, or a combination thereof, with a flat plate type porous support being preferred. The porosity of the porous support can be, for example, 10–50%, preferably 15–40%, and more preferably about 20–30%. Furthermore, the pore diameter of the porous support can be, for example, 0.01–5.0 mm, preferably 0.05–3.0 mm, and more preferably about 0.1–1.0 mm.

[0132] The water pressure can be set appropriately according to the thickness of the stacked materials, for example, it can be 1 to 10 MPa, preferably 1.5 to 9.5 MPa, and more preferably about 2 to 9 MPa.

[0133] The nozzle used for water jetting can have an orifice diameter of, for example, about 0.05 to 0.2 mm. The spacing between the micro-orifices in the nozzle can be, for example, about 0.3 to 5.0 mm, preferably about 0.4 to 3.0 mm, and more preferably about 0.5 to 2.0 mm.

[0134] The nozzles used for water jetting can be arranged in one or more rows, for example, 1 to 5 rows. From the viewpoint of optimizing the cohesion between the coarse and fine nonwoven fabrics, 2 to 3 rows are preferred. When multiple rows of nozzles are provided, the water pressure of the water flow in each row can be different. From the viewpoint of optimizing the cohesion between the coarse and fine nonwoven fabrics, it is preferable to increase the water pressure of the water flow that contacts the laminate in the mechanical direction (MD direction).

[0135] When bonding coarse and fine nonwoven fabrics, it is preferable to place the laminate formed by combining the coarse and fine nonwoven fabrics on the aforementioned porous support, and continuously convey the laminate and the porous support together along the length direction at a certain speed, and perform the bonding process under the conditions described above. The conveying speed of the laminate can be, for example, 1.0 to 10.0 m / min, preferably 2.0 to 9.0 m / min, and more preferably about 3.0 to 8.0 m / min. By setting the conveying speed of the laminate within the above range, the bonding properties of the coarse and fine nonwoven fabrics can be optimized, further improving the dust retention capacity of the resulting fiber structure.

[0136] In addition, in the cohesion process based on hydroentangling, water can be sprayed from either the coarse fiber nonwoven side or the fine fiber nonwoven side of the laminate. From the viewpoint of fully coheding the coarse fiber nonwoven and the fine fiber nonwoven, water can be sprayed from the fine fiber nonwoven side of the laminate.

[0137] Furthermore, depending on the application, the fibrous structure can be charged to improve capture efficiency. This charging can be performed on laminates before coagulation treatment or on fibrous structures after coagulation treatment.

[0138] There are no special limitations to charging, as long as it can be charged. Examples include methods that impart charge through friction or contact, methods that irradiate with active energy rays (such as electron beams, ultraviolet rays, X-rays, etc.), methods that utilize corona discharge, plasma, or other gas discharges, methods that utilize high electric fields, and liquid charging methods that use polar solvents such as water.

[0139] In liquid charging methods, for example, a polar solvent such as water or an organic solvent (preferably water from a production point of view, such as wastewater treatment) is sprayed onto the fiber structure, either while spraying and vibrating, or while being charged or while being charged, it is drawn from one side of the fiber structure, causing the polar solvent to permeate into the fiber structure and thus charge it. The pressure of the polar solvent colliding with the fiber structure is preferably 0.1 to 5 MPa. The suction pressure from below is preferably 500 to 5000 mmH2O. The liquid charging time is preferably 0.001 to 5 seconds.

[0140] The dust retention capacity of the fiber structure of the present invention can be 4.3 mg or more, preferably 4.5 mg or more, more preferably 5.0 mg or more, and even more preferably 6.0 mg or more. A higher dust retention capacity is better, and there is no particular upper limit; for example, it can be around 30 mg. Here, dust retention capacity refers to the amount of dust captured until the pressure loss reaches twice the initial value for the fiber structure installed on a circular filter holder with an inner diameter of 110 mm, and is a value measured by the method described in the embodiments described later.

[0141] The higher the capture efficiency (initial capture efficiency) of the fiber structure of the present invention, the better. From the viewpoint of controlling the pressure loss within a suitable range, it can be, for example, 60% or more (e.g., 60% to 99.99%), preferably 70% or more, and more preferably 80% or more. Here, the capture efficiency is a value measured by the method described in the embodiments described later.

[0142] The pressure loss (initial pressure loss) of the fiber structure of the present invention can be adjusted to, for example, a range of 0 to 30 Pa, depending on the design of the fiber diameter and other parameters of the contained fibers. The pressure loss of the fiber structure can be, for example, about 0 to 20 Pa, preferably about 0 to 15 Pa, and more preferably about 1 to 14 Pa. Here, the pressure loss is a value measured by the method described in the embodiments described later.

[0143] For the fiber structure of the present invention, the QF value calculated based on the capture efficiency and pressure loss using the following formula can be, for example, 0.10 or more, preferably 0.15 or more, and more preferably 0.19 or more. A higher QF value is preferred, and there is no particular upper limit; for example, it can be around 2.00.

[0144] QF value = -ln(1 - capture efficiency (%) / 100) / pressure loss (Pa)

[0145] Such fiber structures are suitable for use as filters, particularly air filters. These filters can be used in applications such as face masks, various air conditioning applications (building air conditioning, clean rooms, painting studios, etc.), automotive applications (cabin filters, etc.), and general household appliance applications (air conditioners, air purifiers, vacuum cleaners, etc.). When using a fiber structure as a filter, the coarse fiber side can be used as the upstream side.

[0146] For example, the fiber structure of the present invention can be used as a filter sheet for a mask. The mask of the present invention only needs to have at least the fiber structure of the present invention as a covering portion covering either or both of the mouth and the bridge of the nose; for example, the fiber structure can be one layer in a multi-layer structure constituting the covering portion. Additionally, the fiber structure can be used as an intermediate sheet disposed between the exhalation side sheet and the surface side sheet constituting the mask.

[0147] It should be noted that in this invention, the mask covers at least the area around the mouth and the root of the nose (especially the nostrils), or either of these areas, regardless of whether it has a fastening part such as straps to secure it to the face. Alternatively, the mask may cover areas other than the mouth and the root of the nose. For example, as a variation, the mask of this invention may be a therapeutic mask (e.g., a nasal mask, a full-face mask, etc.) for sleep apnea syndrome, suitable for CPAP therapy for treating sleep apnea syndrome, NIPPV therapy suitable for treating ventilatory failure, etc.

[0148] Example

[0149] The present invention will now be described in more detail based on embodiments, but the present invention is not limited to these embodiments in any way. It should be noted that in the following embodiments and comparative examples, various physical properties were measured using the methods described below.

[0150] [Number-average fiber diameter of a single fiber]

[0151] The surface of the fibrous structure was observed using a scanning electron microscope. Based on the electron microscope images, fibers were randomly selected, and the fiber diameter was measured from the side of a single fiber. Fibers with a diameter greater than 5.0 μm were designated as coarse fibers A, and their number-average fiber diameters (n = 100) were calculated. Fibers with a diameter less than 5.0 μm were designated as fine fibers B, and their number-average fiber diameters (n = 100) were calculated.

[0152] [Weight per unit area and apparent density]

[0153] The unit area weight (g / m²) was determined according to section 6.2 of JIS L 191 "3 General Nonwoven Fabric Test Methods". 2 Additionally, apparent density (g / cm³) 3 It is calculated by dividing the weight per unit area by the thickness.

[0154] [thickness]

[0155] Using a razor (FEATHER S single-blade, FEATHER Safety Razor) parallel to the thickness direction of the fiber structure or various nonwoven fabrics and perpendicular to the machine direction (MD), 10 arbitrary locations were cut using a digital microscope, and each cross-section was observed. Then, the top and bottom ends of each cut surface of the fiber structure or various nonwoven fabrics were determined, and the thickness direction distance from the top to the bottom was measured. The average value of these 10 locations was calculated, thereby determining the thickness (mm) of the fiber structure and various nonwoven fabrics.

[0156] [Fiber filling rate]

[0157] The fiber structure was cut into 2.5cm × 2.5cm pieces at five arbitrary locations along the plane, and samples were collected. Then, X-ray CT measurements were performed on each sample under the following conditions to obtain three-dimensional images.

[0158] <X-ray CT Measurement Conditions>

[0159] Measuring apparatus: Xradia 520Versa (manufactured by CARL ZEISS)

[0160] X-ray target: tungsten

[0161] X-ray source intensity: 160kV

[0162] Output: 10W

[0163] Objective lens: 4X

[0164] Shooting field of view: 1512μm

[0165] Pixel size: 1.5μm / pixel

[0166] Pixel merging: 2

[0167] Exposure time: 2 seconds / image

[0168] Number of photos taken: 3201

[0169] Filming time: 4 hours

[0170] <Image Analysis Conditions>

[0171] The following steps were followed to perform image analysis on the obtained 3D images using the image analysis software Avizo (manufactured by Thermo Fisher Scientific), thereby determining the filling rate of various fibers in each region.

[0172] For the obtained 3D image, the 3D image of the fiber structure sample was cut into 0.75mm × 0.75mm × total thickness using image analysis software, and then noise was removed using the NON-LOCAL Filter function. The NON-LOCAL Filter function was set to the following conditions.

[0173] Spatial Standard Deviation value: 5

[0174] Intensity Standard Deviation value: 0.2

[0175] Search window value: 10

[0176] Local Neighborhood value: 3

[0177] Then, binarization is performed using the Interactive Thresholding function to extract all fibers. The threshold is set to any value between 30000 and 35000 in the 65536 grayscale values.

[0178] For data obtained after noise removal through a non-local filter, the FiberTracing function is used to extract fibers with a specific diameter (coarse fiber A). The FiberTracing function is set to the following conditions.

[0179] Cylinder length value for Cylinder Correlation: any value between 2.5 and 3.5 times the fiber diameter.

[0180] Angular Sampling value: 5

[0181] Mask Cylinder Radius: Any value between fiber radius +1 and fiber radius +13

[0182] Outer Cylinder Radius: Fiber radius

[0183] Inner Cylinder Radius value: 0

[0184] Direction Coefficient value for Trace Correlation Lines: 0.45

[0185] Minimum Distance value: Any value between fiber radius and fiber diameter.

[0186] Additionally, using the Arithmetic function, fibers with a specific diameter extracted by the Fiber Tracing function are subtracted from all fibers extracted by the Interactive Thresholding function, leaving only fibers with other diameters (fine fiber B).

[0187] Using the Arithmetic function, extract the area outside all fibers extracted by the Interactive Thresholding function as voids.

[0188] Using the Regional Volume Fraction function, image data was analyzed every 7.5 μm along the thickness direction to calculate the volume ratio of coarse fiber A / fine fiber B / void in each region. Regions containing fibers of 0.1 vol% or higher were defined as areas of fiber structure and set as the measurement range.

[0189] Given that the thickness of the fiber structure measured above is L (mm), the thickness is divided into 10 equal parts so that the average thickness of each segmented region is L / 10 (mm). All regions of the fiber structure analyzed for each 7.5 μm are merged, and the cross section is divided into 10 layers with a thickness of L / 10 (mm). Among the 10 layers obtained, regions 1 to 10 are defined from the fine fiber group side to the coarse fiber group side. The filling rate of coarse fiber A and fine fiber B in each region is calculated.

[0190] Within the same fiber structure sample (2.5cm × 2.5cm), analyses were performed at 10 locations with an analytical range of 0.75mm × 0.75mm × total thickness, under the aforementioned analytical conditions, at intervals of 125μm. The results are the average values ​​of 50 points across 10 locations from all 5 samples.

[0191] Furthermore, among the 10 layers obtained, regions 1 to 10 are defined from the fine fiber group side toward the coarse fiber group side. The average filling rates of coarse fiber A and fine fiber B in region S representing regions 1 to 3, the average filling rates of coarse fiber A and fine fiber B in region T representing regions 4 to 7, and the average filling rates of coarse fiber A and fine fiber B in region U representing regions 8 to 10 are calculated respectively.

[0192] [Average Melt Point]

[0193] The fiber structure was cut into 1cm × 1cm sections along the planar direction, and samples were collected. Scanning electron microscopy was used to randomly photograph the surface of the fine fiber group side of the obtained samples within a 100μm × 100μm area. Then, the number of sites where fine fibers B were fused together was determined based on the obtained images. This was done by measuring images from five different locations within a 100μm × 100μm area along the planar direction, and the average value of these numbers was calculated. It should be noted that regarding the number of fused sites, when the same fine fibers B are fused together at multiple locations, they are counted as other sites.

[0194] [Capture efficiency, pressure loss, QF value]

[0195] The trapping performance of the fiber structures obtained in the examples and comparative examples was evaluated using an automatic filter efficiency testing device (TSI, AFT8130A). First, the test samples were mounted on a circular filter holder with an inner diameter of 110 mm, with the coarse fiber group side as the upstream side and the fine fiber group side as the downstream side. In this configuration, NaCl particles with a median mass diameter of 0.26 μm were used as test particles at a concentration of 15–20 mg / m³. 3 An airflow of 32 liters / minute and a surface velocity of 5.33 cm / second were applied to a filter holder containing the test sample for 10 seconds. The particle concentration X1 on the upstream side and the particle concentration X2 on the downstream side (after filtration) were measured using a laser particle detector. The collection efficiency was then calculated using the following formula.

[0196] Capture efficiency (%) = {(X1-X2) / X1} × 100

[0197] In addition, a differential pressure gauge was installed between the upstream and downstream sides of the filter support in the above-mentioned automatic filter efficiency detection device to measure the differential pressure (pressure loss (Pa)) when the air volume was 32 liters / minute.

[0198] Then, the QF value is calculated using the following formula based on the obtained capture efficiency and pressure loss.

[0199] QF value = -ln(1 - capture efficiency (%) / 100) / pressure loss (Pa)

[0200] [Dust retention capacity]

[0201] The trapping performance of the fiber structures obtained in the examples and comparative examples was evaluated using an automatic filter efficiency testing device (TSI, AFT8130A). First, the test samples were mounted on a circular filter holder with an inner diameter of 110 mm, with the coarse fiber group side as the upstream side and the fine fiber group side as the downstream side. In this configuration, NaCl particles with a median mass diameter of 0.26 μm were used as test particles at a concentration of 15–20 mg / m³. 3 An airflow of 32 liters / minute and a surface velocity of 5.33 cm / s were applied to a filter holder containing the test sample for 60 minutes. The collection efficiency and pressure loss were calculated every 2 minutes using the same method described above. Then, using the obtained values, the time t from the initial pressure loss to twice the pressure loss was measured. Furthermore, based on the upstream particle concentration, airflow, and collection efficiency, the particle collection weight for each 2-minute period was calculated using the following formula, and the sum up to time t was taken as the dust retention capacity.

[0202] Particle capture weight over 2 minutes = upstream particle concentration (mg / m³) 3 × air volume (liters / minute) × 0.001 (m³) 3 / L) × 2 (minutes) × Collection efficiency (%) / 100

[0203] [Example 1]

[0204] (1) Production of coarse fiber nonwoven fabric

[0205] For 100 parts by weight of polypropylene (MFR [230℃, 21.18N load] = 30g / 10min), using conventional meltblown equipment with a spinning temperature of 260℃, an air temperature of 260℃, and an air flow rate of 13Nm... 3 The fiber stream, refined by hot air, was ejected from the nozzle orifice at a rate of 0.3 g / min, a single-orifice ejection rate of 0.4 mm, an orifice diameter of 0.4 mm, and an orifice spacing of 1.5 mm. This process yielded a coarse-fiber nonwoven fabric (with a single fiber number-average diameter of 7.2 μm and a unit area weight of 20 g / m²). 2 Thickness 0.76mm, apparent density 0.03g / cm³ 3 ).

[0206] (2) Production of fine fiber nonwoven fabric

[0207] For 100 parts by weight of polypropylene (MFR [230℃, 21.18N load] = 700g / 10min), using conventional meltblown equipment, with a spinning temperature of 215℃, an air temperature of 215℃, and an air flow rate of 10Nm... 3Meltblown spinning was performed with a single-hole ejection rate of 0.036 g / hole·min, a hole diameter of 0.3 mm, a hole spacing of 0.75 mm, and a collection distance of 40 cm to obtain a fine fiber nonwoven fabric (the number average fiber diameter of a single fiber is 1.2 μm, and the unit area weight is 10 g / m²). 2 Thickness 0.10mm, apparent density 0.10g / cm³ 3 ).

[0208] (3) Cohesion treatment of coarse fiber nonwoven fabric and fine fiber nonwoven fabric

[0209] Next, the coarse fiber nonwoven fabric obtained in (1) and the fine fiber nonwoven fabric obtained in (2) were stacked together. The stack was placed on a porous support (25% porosity, 0.3 mm pore size) and continuously conveyed along the length of the stack at a speed of 5.0 m / min. At the same time, two nozzles with 0.10 mm pore size orifices spaced 0.6 mm apart along the width of the stack (the distance between adjacent nozzles was 20 cm) were used. The water pressure of the high-pressure water jet from the first row of nozzles was set to 2.0 MPa and the water pressure of the high-pressure water jet from the second row of nozzles was set to 3.0 MPa. High-pressure water jets were sprayed from the side of the fine fiber nonwoven fabric to perform a bonding treatment.

[0210] Next, the fiber structure obtained by bonding coarse and fine nonwoven fibers together was subjected to electrostatic treatment using a liquid electrostatic method. Specifically, under the following conditions, water was sprayed onto one surface of the fiber structure, and then a slit-shaped suction nozzle was placed against the other surface of the fiber structure to draw in the water, thereby allowing the water to penetrate into the interior of the fiber structure. After dehydration, the structure was allowed to air dry.

[0211] Water pressure: 0.4 MPa

[0212] • Suction pressure: 2000 mmH2O

[0213] Processing time: 0.0042 seconds (speed 20m / min)

[0214] The various evaluation results of the obtained fiber structures are shown in Table 1.

[0215] [Example 2]

[0216] The coarse fiber nonwoven fabric obtained in Example 1(1) and the fine fiber nonwoven fabric obtained in Example 1(2) were stacked and placed on the porous support used in Example 1. The stack was continuously conveyed along its length at a speed of 5.0 m / min. Simultaneously, three nozzles (20 cm apart) with 0.10 mm orifices spaced 0.6 mm apart along the width of the stack were used. The water pressure of the high-pressure water jet from the first row of nozzles was set to 3.0 MPa, the water pressure of the high-pressure water jet from the second row of nozzles was set to 5.0 MPa, and the water pressure of the high-pressure water jet from the third row of nozzles was set to 10 MPa. High-pressure water jets were sprayed from the side of the fine fiber nonwoven fabric to achieve a bonding process. Next, an electrostatic treatment was performed in the same manner as in Example 1, resulting in a fiber structure formed by the interweaving of coarse and fine fiber nonwoven fabrics. Various evaluation results of the obtained fiber structure are shown in Table 1.

[0217] [Example 3]

[0218] (1) Production of coarse fiber nonwoven fabric

[0219] Using 100% by weight of polypropylene fibers (NF, manufactured by UBE Exsymo) with a single fiber average diameter of 17.5 μm and a fiber length of 51 mm as raw cotton, a semi-random web was produced using the carding method. The resulting semi-random web was then placed on a perforated drum support with an opening ratio of 25% and an aperture of 0.3 mm, and continuously conveyed along its length at a speed of 5.0 m / min while simultaneously undergoing a cohesive treatment by spraying high-pressure water from above. This produced an interwoven fiber web (nonwoven fabric). In this cohesive treatment, two nozzles with 0.10 mm apertures spaced 0.6 mm apart along the width of the web (the distance between adjacent nozzles was 20 cm) were used. The water pressure of the high-pressure water jet from the first row of nozzles was set to 3.0 MPa, and the water pressure of the high-pressure water jet from the second row of nozzles was set to 5.0 MPa. Hydroentangling was then performed, and the same cohesive treatment was further applied to the back side to obtain a coarse fiber nonwoven fabric (35 g / m²). 2 Thickness 0.42mm, apparent density 0.08g / cm³ 3 ).

[0220] (2) Production of fine fiber nonwoven fabric

[0221] For 100 parts by weight of polypropylene (MFR [230℃, 21.18N load] = 700g / 10min), meltblown spinning was performed using conventional meltblown equipment at a spinning temperature of 215℃, an air temperature of 215℃, an air flow rate of 0.4MPa, a single-hole ejection rate of 0.1g / hole·min, a hole diameter of 0.3mm, a hole spacing of 0.6mm (1 row configuration), and a collection distance of 40cm. This yielded a fine fiber nonwoven fabric (number-average fiber diameter of 2.5μm and area weight of 10g / m²). 2 Thickness 0.11mm, apparent density 0.10g / cm³ 3 ).

[0222] (3) Cohesion treatment of coarse fiber nonwoven fabric and fine fiber nonwoven fabric

[0223] Next, the coarse fiber nonwoven fabric obtained in (1) and the fine fiber nonwoven fabric obtained in (2) were laminated. This laminate was placed on the porous support used in Example 1 and continuously conveyed along the length of the laminate at a speed of 5.0 m / min. Simultaneously, a high-pressure water jet of 3.0 MPa was sprayed from the fine fiber nonwoven fabric side using a nozzle with orifices of 0.10 mm at 0.6 mm intervals along the width of the laminate to achieve a bonding process. Then, an electrostatic treatment was performed in the same manner as in Example 1, resulting in a fiber structure formed by the interweaving of coarse and fine fiber nonwoven fabrics. Various evaluation results of the obtained fiber structure are shown in Table 1.

[0224] [Example 4]

[0225] The coarse fiber nonwoven fabric obtained in Example 3(1) and the fine fiber nonwoven fabric obtained in Example 3(2) were stacked and placed on the porous support used in Example 1. The stack was continuously conveyed along its length at a speed of 5.0 m / min. Simultaneously, a high-pressure water jet of 7.0 MPa was sprayed from the fine fiber nonwoven fabric side using a nozzle with orifices of 0.10 mm at 0.6 mm intervals along the width of the stack. This process was used for bonding. Next, an electrostatic treatment was performed in the same manner as in Example 1, resulting in a fiber structure formed by the interweaving of coarse and fine fiber nonwoven fabrics. The various evaluation results of the obtained fiber structure are shown in Table 1, and enlarged cross-sectional photographs are shown in... Figure 1 A magnified photograph of the surface of the fine fiber group is shown. Figure 2 .

[0226] [Example 5]

[0227] The coarse fiber nonwoven fabric obtained in Example 3(1) and the fine fiber nonwoven fabric obtained in Example 3(2) were stacked and placed on the porous support used in Example 1. The stack was continuously conveyed along its length at a speed of 5.0 m / min. Simultaneously, three nozzles (20 cm apart) with 0.10 mm orifices spaced 0.6 mm apart along the width of the stack were used. The water pressure of the high-pressure water jet from the first row of nozzles was set to 3.0 MPa, the water pressure of the high-pressure water jet from the second row of nozzles was set to 5.0 MPa, and the water pressure of the high-pressure water jet from the third row of nozzles was set to 10 MPa. High-pressure water jets were sprayed from the side of the fine fiber nonwoven fabric to achieve a bonding process. Next, an electrostatic treatment was performed in the same manner as in Example 1, resulting in a fiber structure formed by the interweaving of coarse and fine fiber nonwoven fabrics. Various evaluation results of the obtained fiber structure are shown in Table 1.

[0228] [Example 6]

[0229] (1) Production of fine fiber nonwoven fabric

[0230] For 100 parts by weight of polypropylene (MFR [230℃, 21.18N load] = 700g / 10min), meltblown spinning was performed using conventional meltblown equipment at a spinning temperature of 215℃, an air temperature of 215℃, an air flow rate of 0.4MPa, a single-hole ejection rate of 0.1g / hole·min, a hole diameter of 0.3mm, a hole spacing of 0.6mm (1 row configuration), and a collection distance of 70cm. This yielded a fine fiber nonwoven fabric (number-average fiber diameter of 2.5μm and area weight of 10g / m²). 2 Thickness 0.11mm, apparent density 0.10g / cm³ 3 ).

[0231] (2) Cohesion treatment of coarse fiber nonwoven fabric and fine fiber nonwoven fabric

[0232] The coarse fiber nonwoven fabric obtained in Example 3(1) and the fine fiber nonwoven fabric obtained in Example 6(1) were stacked together and placed on the porous support used in Example 1. The stack was continuously conveyed along its length at a speed of 5.0 m / min. Simultaneously, a high-pressure water jet of 4.0 MPa was sprayed from the fine fiber nonwoven fabric side using a nozzle with orifices of 0.10 mm at 0.6 mm intervals along the width of the stack. This was used for cohesion treatment. Then, an electrostatic treatment was performed in the same manner as in Example 1 to obtain a fiber structure formed by the interweaving of coarse and fine fiber nonwoven fabrics. The various evaluation results of the obtained fiber structure are shown in Table 1.

[0233] [Comparative Example 1]

[0234] (1) Production of fine fiber nonwoven fabric

[0235] For 100 parts by weight of polypropylene (MFR [230℃, 21.18N load] = 700g / 10min), using conventional meltblown equipment, with a spinning temperature of 215℃, an air temperature of 215℃, and an air flow rate of 10Nm... 3 Meltblown spinning was performed with a single-hole ejection rate of 0.036 g / hole·min, a hole diameter of 0.3 mm, a hole spacing of 0.75 mm, and a collection distance of 10 cm to obtain a fine fiber nonwoven fabric (the number average fiber diameter of a single fiber is 1.2 μm, and the unit area weight is 10 g / m²). 2 Thickness 0.10mm, apparent density 0.10g / cm³ 3 ).

[0236] (2) Cohesion treatment of coarse fiber nonwoven fabric and fine fiber nonwoven fabric

[0237] The coarse fiber nonwoven fabric obtained in Example 1 (1) and the fine fiber nonwoven fabric obtained in Comparative Example 1 (1) were stacked together and placed on the porous support used in Example 1. The stack was continuously conveyed along its length at a speed of 5.0 m / min. Simultaneously, two nozzles (with orifices of 0.10 mm diameter spaced 0.6 mm apart along the width of the stack, and a distance of 20 cm between adjacent nozzles) were used to spray high-pressure water from the first row of nozzles at a pressure of 2.0 MPa and from the second row of nozzles at a pressure of 3.0 MPa. High-pressure water was sprayed from the coarse fiber nonwoven fabric side to achieve a bonding treatment. Then, an electrostatic treatment was performed in the same manner as in Example 1 to obtain a fiber structure formed by the interweaving of coarse and fine fiber nonwoven fabrics. The various evaluation results of the obtained fiber structure are shown in Table 1.

[0238] [Comparative Example 2]

[0239] (1) Production of fine fiber nonwoven fabric

[0240] For 100 parts by weight of polypropylene (MFR [230℃, 21.18N load] = 700g / 10min), meltblown spinning was performed using conventional meltblown equipment at a spinning temperature of 215℃, an air temperature of 215℃, an air flow rate of 0.4MPa, a single-hole ejection rate of 0.1g / hole·min, a hole diameter of 0.3mm, a hole spacing of 0.6mm (1 row configuration), and a collection distance of 30cm. This yielded a fine fiber nonwoven fabric (number-average fiber diameter of 2.5μm and area weight of 10g / m²). 2 Thickness 0.11mm, apparent density 0.10g / cm³ 3 ).

[0241] (2) Cohesion treatment of coarse fiber nonwoven fabric and fine fiber nonwoven fabric

[0242] The coarse fiber nonwoven fabric obtained in Example 3(1) and the fine fiber nonwoven fabric obtained in Comparative Example 2(1) were stacked together and placed on the porous support used in Example 1. The stack was continuously conveyed along its length at a speed of 5.0 m / min. Simultaneously, a high-pressure water jet of 3.0 MPa was sprayed from the fine fiber nonwoven fabric side using a nozzle with orifices of 0.10 mm at 0.6 mm intervals along the width of the stack. This was used for cohesion treatment. Next, an electrostatic treatment was performed in the same manner as in Example 1 to obtain a fiber structure formed by the interweaving of coarse and fine fiber nonwoven fabrics. The various evaluation results of the obtained fiber structure are shown in Table 1.

[0243] [Comparative Example 3]

[0244] (1) Production of fine fiber nonwoven fabric

[0245] For 100 parts by weight of polypropylene (MFR [230℃, 21.18N load] = 700g / 10min), meltblown spinning was performed using conventional meltblown equipment at a spinning temperature of 215℃, an air temperature of 215℃, an air flow rate of 0.4MPa, a single-hole ejection rate of 0.1g / hole·min, a hole diameter of 0.3mm, a hole spacing of 0.6mm (1 row configuration), and a collection distance of 100cm. This yielded a fine fiber nonwoven fabric (number-average fiber diameter of 2.5μm and area weight of 10g / m²). 2 Thickness 0.11mm, apparent density 0.10g / cm³ 3 ).

[0246] (2) Cohesion treatment of coarse fiber nonwoven fabric and fine fiber nonwoven fabric

[0247] The coarse fiber nonwoven fabric obtained in Example 3(1) and the fine fiber nonwoven fabric obtained in Comparative Example 3(1) were stacked together and placed on the porous support used in Example 1. The stack was continuously conveyed along its length at a speed of 5.0 m / min. Simultaneously, a high-pressure water jet of 4.0 MPa was sprayed from the fine fiber nonwoven fabric side using a nozzle with orifices of 0.10 mm at 0.6 mm intervals along the width of the stack. This was used for bonding treatment. Then, an electrostatic treatment was performed in the same manner as in Example 1 to obtain a fiber structure formed by the interweaving of coarse and fine fiber nonwoven fabrics. The various evaluation results of the obtained fiber structure are shown in Table 1.

[0248]

[0249] As shown in Table 1, in Comparative Examples 1 to 3, the fiber filling rates of regions S, T and U have the relationship SA+SB>TA+TB>UA+UB. The filling rates of coarse fiber A and fine fiber B do not have a specific relationship. In addition, the average number of melting points of fine fiber B is not within a specific range, and the dust retention capacity is low.

[0250] On the other hand, in Examples 1 and 2, SB is the largest among SB, TB, and UB, and there is a specific relationship of TA+TB>SA+SB>UA+UB. In addition, the average number of melt-bonding points of the fine fibers B is within a specific range. Although these fiber structures were manufactured using coarse fiber nonwoven fabric and fine fiber nonwoven fabric with the same average fiber diameter as Comparative Example 1, the dust retention capacity is more than 1.4 times higher than that of Comparative Example 1.

[0251] Similarly, in Examples 3-6, coarse fibers A and fine fibers B have specific distributions in each region, and the average number of melt-bonding points of fine fibers B is within a specific range. Although these fiber structures were manufactured using coarse fiber nonwoven fabric and fine fiber nonwoven fabric with the same average fiber diameter as Comparative Examples 2 and 3, their dust retention capacity was more than 1.5 times higher than that of Comparative Examples 2 and 3.

[0252] Industrial applicability

[0253] The fiber structure of this invention has a high dust retention capacity and a long lifespan, and therefore can be suitable for use as various filters (especially air filters, bag filters, liquid filters, etc.). For example, it can be used as a filter in masks, various air conditioning applications (building air conditioning, clean rooms, painting rooms, etc.), automotive industry applications (cabin filters, etc.), and general household appliance applications (air conditioners, air purifiers, vacuum cleaners, etc.).

[0254] As described above, preferred embodiments of the present invention have been explained, but various additions, modifications or deletions may be made without departing from the spirit of the present invention, and these are also included within the scope of the present invention.

Claims

1. A fiber structure comprising a coarse fiber group consisting of fibers A with a single fiber diameter exceeding 5 μm, and a fine fiber group consisting of fibers B with a single fiber diameter of less than 5 μm, the fiber structure having an interlacing region where the coarse fiber group and the fine fiber group are interwoven. The fiber structure is divided into 10 equal parts along its thickness direction, and regions 1 through 10 are defined from the fine fiber group side to the coarse fiber group side. The filling rates of fiber A in regions S (representing regions 1 through 3), regions T (representing regions 4 through 7), and regions U (representing regions 8 through 10) are set to SA, TA, and UA, respectively. The filling rates of fiber B are set to SB, TB, and UB, respectively. Among SB, TB, and UB, SB is the largest. TA+TB>SA+SB>UA+UB.

2. The fiber structure according to claim 1, wherein, The average number of fusion bonding points between fibers B in a 100μm×100μm area along the surface of the fiber structure is less than 10.

3. The fiber structure according to claim 2, wherein, The bonding points of the fibers B to each other are formed by melt-blowing.

4. A fiber structure comprising a coarse fiber group consisting of fibers A with a single fiber diameter exceeding 5 μm, and a fine fiber group consisting of fibers B with a single fiber diameter of less than 5 μm, the fiber structure having an interlacing region where the coarse fiber group and the fine fiber group are interwoven. The average number of fusion bonding points between the fibers B constituting the fine fiber group in the 100μm×100μm area of ​​the fiber structure is more than 1.0 and less than 10.

0.

5. The fiber structure according to claim 4, wherein, The bonding points of the fibers B to each other are formed by melt-blowing.

6. The fiber structure according to claim 4, wherein, The fiber structure is divided into 10 equal parts along its thickness direction, and regions 1 through 10 are defined from the fine fiber group side to the coarse fiber group side. The filling rates of fiber A in regions S (representing regions 1 through 3), regions T (representing regions 4 through 7), and regions U (representing regions 8 through 10) are set to SA, TA, and UA, respectively. The filling rates of fiber B are set to SB, TB, and UB, respectively. Among SB, TB, and UB, SB is the largest. TA+TB>SA+SB>UA+UB.

7. The fiber structure according to any one of claims 1 to 6, wherein it is an aggregate of coarse fiber nonwoven fabric formed from said fiber A and fine fiber nonwoven fabric formed from said fiber B.

8. The fiber structure according to any one of claims 1 to 6, wherein, The number-average fiber diameter of the single fiber in the coarse fiber group is 5.5 μm or more, and the number-average fiber diameter of the single fiber in the fine fiber group is 4.5 μm or less.

9. The fiber structure according to any one of claims 1 to 6, wherein the weight per unit area is 15 to 180 g / m². 2 .

10. The fiber structure according to any one of claims 1 to 6, wherein it is electrically charged.

11. The fiber structure according to any one of claims 1 to 6, wherein the capture efficiency is 60% or more.

12. The fiber structure according to any one of claims 1 to 6, wherein the QF value is 0.10 or higher. The QF value is calculated based on the capture efficiency and pressure loss using the following formula. QF value = -ln(1 - capture efficiency (%) / 100) / pressure loss (Pa).

13. A filter comprising the fiber structure according to any one of claims 1 to 12.

14. A face mask comprising the filter of claim 13.

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