Fiber structure, filter sheet and mask

Abstract

This invention provides a fiber structure with high dust retention capacity. The aforementioned fiber structure system 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 less than 5 μm, and has a complexation region where the aforementioned coarse fiber group and the aforementioned fine fiber group are complexed. The aforementioned 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 the aforementioned fibers A 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 defined as SA, TA, and UA. When the filling rates of the aforementioned fibers B are respectively defined as SB, TB, and UB, SB is the largest among SB, TB, and UB, and TA+TB>SA+SB>UA+UB.

Description

[Technical Field]

[0001] This application claims priority to Japanese Patent Application No. 2021-112950 and Japanese Patent Application No. 2021-112951 filed on July 7, 2021, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a fiber structure having a complexed region composed of coarse fiber groups and fine fiber groups. [Previous Technology]

[0003] In the past, air filters have been used to remove dust such as pollen or dust from gases. Non-woven fabrics are the most common filter material used in air filters. Non-woven fabrics made from fine fibers formed by processes such as meltblowing are particularly effective at capturing dust from gases. However, when the individual fibers constituting the fibers are made finer, the increased fiber density within the non-woven fabric leads to a problem of increased pressure loss.

[0004] In order to obtain a nonwoven fabric with low pressure loss, although the single fibers constituting the nonwoven fabric are preferably coarse fibers, on the other hand, when the single fibers constituting the nonwoven fabric are coarse, the fiber surface area inside the nonwoven fabric is reduced, thus the collection efficiency becomes a problem. Therefore, high collection efficiency and low pressure loss are contradictory.

[0005] In order to solve these problems, an attempt was made to achieve high capture efficiency and low pressure loss by using a fiber structure that combines coarse and fine fibers.

[0006] For example, Patent Document 1 (International Publication No. 2020 / 137605) discloses a fiber structure comprising an ultrafine fiber layer extending in the surface direction and a substrate layer adjacent to the aforementioned ultrafine fiber layer. The aforementioned ultrafine fiber layer is composed of ultrafine fibers with a number average fiber diameter of 5 μm or less per fiber, and the aforementioned substrate layer is composed of non-ultrafine fibers with a number average fiber diameter of 7 μm or more per fiber. On the cross-section of the aforementioned fiber structure in the thickness direction, there is a mixed portion in the aforementioned substrate layer where ultrafine fibers are squeezed into the non-ultrafine fibers and extend in the width direction. At least a portion of the ultrafine fibers squeezed from the ultrafine fiber layer reaches the far region when the substrate layer is divided into three equal parts from the side of the aforementioned ultrafine fiber layer: a near region, a central region, and a far region.

[0007] Furthermore, Patent Document 2 (International Publication No. 2021 / 010178) discloses a fiber structure in which extremely fine fibers with an average fiber diameter of 4.5 μm or less per fiber are blended together with non-extremely fine fibers with an average fiber diameter of 5.5 μm or more per fiber, and at least one surface has a protrusion. [Prior Art Documents] [Patent Documents]

[0008] Patent Document 1: International Publication No. 2020 / 137605; Patent Document 2: International Publication No. 2021 / 010178 [Summary of the Invention]

[0009] [The problem the invention aims to solve]

[0010] However, in Patent Documents 1 and 2, only the initial collection efficiency and pressure loss are evaluated, and the performance changes over time during continuous dust collection are not recorded.

[0011] In order to be used as an air filter over a long period of time, a high dust retention capacity is required, which indicates how much dust can be captured before the filter reaches its lifespan and can no longer be used as a filter. The fiber structure described in Patent Documents 1 and 2 has room for further improvement in terms of dust retention capacity.

[0012] Therefore, the object of the present invention is to provide a fiber structure with high dust retention capacity. [Means for solving the problem]

[0013] As a result of active review by the inventors of the present invention in order to achieve the aforementioned objective, they discovered that in a fiber structure having a complexed region in which coarse fiber groups and fine fiber groups are complexed, the filling rate of coarse fiber A and fine fiber B in the thickness direction has a specific relationship, and a fiber structure in which the average number of fusion points of the fine fiber B constituting the fine fiber group falls within a specific range can achieve a high dust retention capacity, thus completing the present invention.

[0014] That is, the present invention is composed of the following states. [State 1] A fiber structure comprising a coarse fiber group composed of fibers A with a single fiber diameter exceeding 5 μm and a fine fiber group composed of fibers B with a single fiber diameter of less than 5 μm, and having a complexed region in which the aforementioned coarse fiber group and the aforementioned fine fiber group are complexed. The aforementioned fiber structure is divided into 10 equal parts in the thickness direction. Regions 1 to 10 are defined from the fine fiber group side to the coarse fiber group side. The filling rates of the aforementioned fibers A 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 defined as SA, TA, and UA. When the filling rates of the aforementioned fibers B are respectively defined as SB, TB, and UB, SB is the largest among SB, TB, and UB, and TA+TB>SA+SB>UA+UB. [Sample 2] As in Sample 1, the fiber structure wherein, in a 100μm × 100μm area along the surface of the fiber structure, the average number of fusion points between fibers B is 10 or less. [Sample 3] As in Sample 2, the fusion points between the aforementioned fibers B are derived from meltblowing. [Sample 4] A fiber structure comprising a coarse fiber group composed of fibers A with a single fiber diameter exceeding 5μm and a fine fiber group composed of fibers B with a single fiber diameter of 5μm or less, and having a complexing region in which the aforementioned coarse fiber group and the aforementioned fine fiber group are complexed, wherein, in a 100μm × 100μm area along the surface of the fiber structure, the average number of fusion points between fibers B constituting the aforementioned fine fiber group 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). [Sample 5] A fiber structure as in Sample 4, wherein the fusion point of the aforementioned fibers B originates from the melt-blowing method. [Sample 6] A fiber structure as in Sample 4 or 5, wherein the aforementioned 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 the aforementioned fibers A 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 defined as SA, TA, and UA. When the filling rates of the aforementioned fibers B are respectively defined as SB, TB, and UB, SB is the largest among SB, TB, and UB, and TA+TB>SA+SB>UA+UB. [Sample 7] A fiber structure as in any of Samples 1 to 6, which is a complex of a coarse fiber nonwoven fabric formed from the aforementioned fibers A and a fine fiber nonwoven fabric formed from the aforementioned fibers B.[Sample 8] A fibrous structure of any of Samples 1 to 7, wherein the average diameter of the single fibers in the aforementioned coarse fiber group is 5.5 μm or more (preferably 6.0 μm or more, more preferably 7.0 μm or more), and the average diameter of the single fibers in the aforementioned fine fiber group is 4.5 μm or less (preferably 4.0 μm or less, more preferably 3.0 μm or less). [Sample 9] A fibrous structure of any of Samples 1 to 8, wherein the weight per unit area is 15 to 180 g / m² (preferably 18 to 150 g / m², more preferably 20 to 120 g / m²). [Sample 10] A fibrous structure of any of Samples 1 to 9, wherein it is charged. [Sample 11] A fibrous structure of any of Samples 1 to 10, wherein its capture efficiency is 60% or more (preferably 70% or more, more preferably 80% or more). [Sample 12] A fiber structure of any of Samples 1 to 11, wherein the QF value calculated by means of the capture efficiency and pressure loss according to the following formula is 0.10 or more (preferably 0.15 or more, more preferably 0.19 or more), QF value = -ln(1 - capture efficiency (%) / 100) / pressure loss (Pa). [Sample 13] A filter having a fiber structure of any of Samples 1 to 12. [Sample 14] A face mask having a filter of Sample 13.

[0015] Furthermore, combinations of at least two constituent elements disclosed in the claims and / or specification and / or drawings are also included in this invention. In particular, combinations of two or more claims described in the claims are also included in this invention. [Effects of the Invention]

[0016] The fiber structure according to the present invention has a high dust retention capacity, thus it can capture dust over a long period of time.

Implementation Method

[0020] 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 less than 5 μm, and has a complexing region where the coarse fiber group and the fine fiber group are complexed. The complexing region here refers to the region where a portion of the fine fiber B constituting the fine fiber group penetrates the structure of the coarse fiber group, as shown in the elliptical frame of FIG1. ​​Such structures can be obtained by performing the complexing process described later. The fiber structure of the present invention has at least a portion of a complexing 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 separately layers that merely overlap. For example, the fiber structure of the present invention may also have the coarse fiber group and the fine fiber group formed as separate layers, with the complexing region only near the interface between the two layers, or the coarse fiber group and the fine fiber group may not be divided into separate layers, but have a complexing region throughout the thickness direction. Furthermore, the fiber diameter of a single fiber refers to the diameter of each individual fiber. Using the method described in the following embodiments, each single fiber can be distinguished into coarse fiber A and fine fiber B by using the fiber diameter of the single fiber as an indicator.

[0021] 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 towards the coarse fiber group side. Regions 1 through 3 are defined as region S, regions 4 through 7 as region T, and regions 8 through 10 as region U. Here, the term "fine fiber group side" refers to the side in which, focusing on the distribution of fine fibers B, the filling rate of fine fibers 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 term "coarse fiber group side" refers to the side opposite to the fine fiber group side.

[0022] Figure 3 is a cross-sectional conceptual diagram illustrating the various regions of a fiber structure in an embodiment. In Figure 3, in the region that divides the fiber structure 100 in the thickness direction Z into two equal parts, since the filling rate of fine fibers B is greater in the lower region (regions 6 to 10) than in the upper region (regions 1 to 5), 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, and from the upper side, they are sequentially designated as region 1, region 2, ..., region 10. Moreover, as shown in Figure 3, 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.

[0023] In this invention, the filling rate of coarse fiber A present in each nth region (n=1~10) is defined as MnA, and the filling rate of fine fiber B is defined as MnB. 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 region S, region T, and region 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 refers to the volume ratio of the target fiber in a specific region relative to the volume of that region, and is a value measured by the method described in the embodiments below.

[0024] For example, M1A represents the volume ratio of coarse fiber A in region 1 relative to the volume of region 1. M2-3A represents the volume ratio of 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 volume ratio of 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.

[0025] In the fiber structure of the present invention, SB is the largest among SB, TB, and UB, and TA+TB>SA+SB>UA+UB. When these fiber structures are used as filter sheets, their region U side can be used as the upstream side for collection. In this case, the airflow flows in from region U, passes through region U, region T, and region S in sequence, and flows out from region S. That is, these fiber structures have a structure in which the filling rate of fibers (coarse fibers A and fine fibers B) is low in region U on the upstream side, the filling rate of fibers (coarse fibers A and fine fibers B, especially coarse fibers A) is high in region T on the middle side, and the filling rate of fine fibers B is high in region S on the downstream side. The dust in the gas is mixed with particulate matter of various particle sizes, but in the fiber structure with such a specific fiber distribution, since region U has a coarse structure with fewer fibers, it can capture large dust particles without causing blockage. Secondly, region T, due to its high fiber (especially coarse fiber A) filling rate, has a smaller mesh structure than region U, thus it can capture large-sized residual dust particles and successively capture small-sized dust particles. Furthermore, region S, with the highest concentration of fine fibers B, has a denser structure than region T, and therefore can capture small-sized dust particles. Thus, the aforementioned fiber structure, with its gradient structure of pores that sequentially capture dust particles from large to small from upstream to downstream, is less prone to increased pressure loss due to blockage, achieving a high dust retention capacity.

[0026] In the fiber structure of the present invention, based on the viewpoint of preventing blockage from the upstream side, it is preferable to have a lower fiber filling rate in region U. For example, UA+UB can be 10.0% or less, preferably 8.0% or less, and more preferably 5.0% or less. The lower limit of UA+UB is not particularly limited, but for example, based on 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.

[0027] The fiber structure of the present invention, based on the viewpoint of preventing blockage in the intermediate region and improving the collection efficiency, has a fiber filling rate (TA+TB) of 6.0~30.0%, preferably 6.2~25.0%, and more preferably 6.5~20.0%.

[0028] In the fiber structure of the present invention, based on the viewpoint of improving the collection efficiency of small-particle-size dust on the downstream side, it is preferable that the filling rate of fine fibers B in region S is higher. For example, the largest MnB among M1B, M2B, and M3B can be 5.0% or more, preferably 5.5% or more, and more preferably 6.0% or more. The upper limit of the largest MnB among M1B, M2B, and M3B is not particularly limited, but for example, based on 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.

[0029] The fiber structure of the present invention, based on the viewpoint of improving dust retention capacity, has SB+UA of 1.0~12.0%, preferably 2.0~11.5%, and more preferably 2.5~11.0%.

[0030] The fiber structure of the present invention preferably has a complexed region of coarse fiber A in region S on the side of the fine fiber group, for example, M2-3A can be 0.05~20.0%, more preferably 0.08~15.0%, and even more preferably 0.10~10.0%.

[0031] In the fiber structure of the present invention, the complexed region can be considered as a region in which both coarse fiber A and fine fiber B are present in the first to tenth regions. For example, as a complexed region, the ratio of the filling rate of coarse fiber A to the filling rate of fine fiber B in the nth region, MnA / MnB, can be 0.1 to 200. Furthermore, the fiber structure of the present invention preferably has complexed regions extending in the thickness direction. For example, in at least two (preferably at least three, more preferably at least four) adjacent regions in the first to tenth regions, MnA / MnB is preferably 0.2 to 100, more preferably 0.5 to 80, and even more preferably 1 to 70.

[0032] The fiber structure of the present invention, based on the viewpoint of having both high capture efficiency and low pressure loss, has a fiber filling rate MA+MB of 1.0~20.0% in all regions from the 1st region to the 10th region, preferably 3.0~18.0%, and more preferably 5.0~15.0%.

[0033] In 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 all regions from the first region to the tenth region, 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.

[0034] In the fiber structure of the present invention, the average number of fusion points between the fine fibers B in a 100μm × 100μm area in the planar direction of the fiber structure is more than 1.0 and less than 10.0. Here, fusion refers to the state in which at least a portion of the fibers melts and the fibers adhere to each other. The number of fusion points between the fine fibers B in a 100μm × 100μm area in the planar direction of the fiber structure is the number of fusion points at the intersections of the fine fibers B as shown in the circular frame in Figure 2, which can be confirmed by using a microscope in a planar enlarged image of the 100μm × 100μm area of ​​the fiber structure. The average number of fusion points represents the average number of fusion points in a 100μm × 100μm area at 5 different locations in the planar direction of the fiber structure, and is a value measured by the method described in the embodiments described later. Furthermore, since it is the number of fusion points that 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 the thickness direction shown in the magnified image.

[0035] In fiber structures where the average fusion point number of fine fibers B is suppressed to a relatively small number, the fine fiber group is less fixed due to fusion and is combined by mechanical complexation, thus increasing the degree of freedom of the fine fiber group and making the fibers easier to move. As a result, the fine fiber group is more likely to complex with the coarse fiber group during complexation, as described later. On the other hand, when the average fusion point number of fine fibers B is too small, the degree of freedom of the fine fiber group is too large. As a result, the fine fiber group disperses and escapes during complexation, or it is not easy to complex with the coarse fiber group. Thus, since the average fusion point number of fine fibers B affects the relationship between the fine fiber group and the coarse fiber group, or fiber structures where the average fusion point number of fine fibers B falls within a certain range become a state where the fine fiber group and the coarse fiber group are easy to complex, it is believed that a structure in which fine fibers B remain on the side of the fine fiber group and the fibers are more distributed in the internal region in the thickness direction can be formed, which is believed to improve the dust retention capacity. The average number of fusion points between the fine fibers B is preferably 8.0 or less, and more preferably 5.0 or less.

[0036] Furthermore, the fusion points of the fine fibers B can originate from the fusion of the meltblown process. As will be described later, the meltblown process can improve the fineness of the fibers, but it is a nonwoven fabric manufacturing method that utilizes the self-fusion properties of the fibers. Based on the viewpoint of increasing the degree of freedom of the fibers to airflow, the average number of fusion points of the fine fibers B produced by the meltblown process is preferably within a certain range.

[0037] The fiber structure of the present invention may be a complex of a coarse fiber nonwoven fabric (preferably meltblown nonwoven fabric or nonwoven fabric) formed by coarse fiber A and a fine fiber nonwoven fabric (preferably meltblown nonwoven fabric) formed by fine fiber B.

[0038] 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, the so-called long fiber refers to the fiber that constitutes long fiber nonwoven fabric (e.g., meltblown nonwoven fabric, spunbond nonwoven fabric), which can be distinguished from short fibers that have been cut into specific fiber lengths and whose fiber lengths are relatively consistent.

[0039] The unit area weight of the fiber structure can be appropriately set according to the application, for example, it can be about 15~180 g / m2, more preferably about 18~150 g / m2, and even more preferably about 20~120 g / m2. Furthermore, the unit area weight is a value measured by the method described in the embodiments described later.

[0040] The apparent density of the fiber structure, based on the viewpoint of combining high capture efficiency and low pressure loss, may be, for example, around 0.005~0.30 g / cm3 (e.g., 0.005~0.10 g / cm3), more preferably around 0.01~0.20 g / cm3 (e.g., 0.01~0.08 g / cm3), and even more preferably around 0.02~0.15 g / cm3 (e.g., 0.02~0.07 g / cm3). The apparent density is a value determined by the method described in the examples described later.

[0041] The thickness of the fiber structure can be appropriately set according to the application, for example, it can be about 0.1~5mm, preferably about 0.2~3mm, and even more preferably about 0.3~1mm. The thickness is a value measured using the method described in the following examples.

[0042] 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 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. The upper limit of the number average fiber diameter of the individual fibers in the coarse fiber group is not particularly limited, but from the viewpoint of optimizing the complexation 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 below.

[0043] 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. The lower limit of the number average fiber diameter of the individual fibers in the fine fiber group is not particularly limited, but from the viewpoint of processability, it can be 0.1 μm or more, preferably 0.5 μm or more.

[0044] Based on the viewpoint of optimizing the complexation of coarse fiber group and 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 (fine fiber group) / (coarse fiber group) can be, for example, 0.05~0.80, more preferably 0.08~0.50, and even more preferably 0.10~0.35.

[0045] The coarse fiber A constituting the coarse fiber group can be selected according to its intended use, and can be any of natural fibers, regenerated fibers, semi-synthetic fibers, or synthetic fibers. Specifically, examples include natural fibers such as cotton, linen, wool, and pulp; regenerated fibers such as silk, polynosic fibers, and cupra fibers; semi-synthetic fibers such as acetate and triacetate; polyolefin fibers formed from polyolefin resins such as polyethylene or polypropylene; polystyrene fibers formed from polystyrene resins such as polystyrene; and fibers formed from polyethylene terephthalate, polybutylene terephthalate, and polypropylene terephthalate. Polyester fibers formed from polyester resins such as esters 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.

[0046] 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, it is preferable to use, for example, a composite fiber in which a low-melting-point resin is used as one component (e.g., sheath component, island component, etc.) and a high-melting-point resin is used as another component (e.g., core component, island component, etc.). The low-melting-point resin and the high-melting-point resin are appropriately selected from the resins used to form the above-mentioned fibers, corresponding to the heat bonding processing temperature.

[0047] Among these fibers, polyolefin fibers, polyester fibers, acrylic fibers, heat-resistant fibers and composite fibers of the above are preferred.

[0048] Heat-resistant fibers can be fibers composed of heat-resistant polymers having units with aromatic, heterocyclic, sulfur-containing, or nitrogen-containing structures within the polymer molecule. Examples include polyether ether ketone (PEEK) fibers, polyether ketone (PEK) fibers, polyether ketone ketone (PEKK) fibers, polyphenylene sulfide (PPS) fibers, aromatic polyamide fibers (e.g., polyamide fibers composed of aliphatic diamine units and aromatic dicarboxylic acid units), arylamide fibers (para-arylamide fibers, meta-arylamide fibers), polyimide (PI) fibers, polyetherimide (PEI) fibers, polyamideimide fibers, amorphous polyacrylate fibers, liquid crystal polyester fibers, polybenzoxazole (PBO) fibers, polybenzimidazole (PBI) fibers, polybenzothiazole fibers, polytetrafluoroethylene (PTFE) fibers, melamine fibers, and novoloid fibers. These fibers can be used alone or in combination of two or more.

[0049] Among these heat-resistant fibers, based on the viewpoints of melt spinning properties and heat resistance, liquid crystal polyester fibers, polyether amide fibers, polyphenylene sulfide fibers, and semi-aromatic polyamide fibers (e.g., semi-aromatic polyamide fibers with dicarboxylic acid units including terephthalic acid units and diamine units including 1,9-nonanediamine units and / or 2-methyl-1,8-nonanediamine units) are preferred.

[0050] The fine fiber B constituting the fine fiber group can be appropriately selected according to the manufacturing method, and synthetic fibers are preferred. Examples of resins constituting 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 of heat-resistant fibers used in the above-mentioned 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 made of the same type of resin as the coarse fiber A, or it can be a fiber made of a different type of resin. Furthermore, from the viewpoint of trapping performance, the fine fiber B is preferably a hydrophobic fiber. In addition, it is preferable that both the coarse fiber A and the fine fiber B are hydrophobic fibers.

[0051] As a resin constituting heat-resistant fibers, based on the viewpoint of forming meltblown nonwoven fabric, and based on 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 whose dicarboxylic acid units include terephthalic acid units, whose diamine units include 1,9-nonanediamine units and / or 2-methyl-1,8-octanediamine units) are preferred.

[0052] The fiber structure of the present invention may include at least the steps of preparing a laminate of coarse fiber nonwoven fabric and fine fiber nonwoven fabric, and the step of performing a complexing treatment on the aforementioned laminate.

[0053] In the preparation step, 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 then overlapped to form the laminate. Alternatively, 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 deposited onto it using a melt-blowing method or similar method to form the laminate. From the viewpoint of increasing material variation, it is preferable to prepare a laminate of coarse fiber nonwoven fabric and fine fiber nonwoven fabric separately and then overlap them. In the subsequent complexing step, from the viewpoint of fully complexing the coarse fiber nonwoven fabric and fine fiber nonwoven fabric, it is preferable that the two are not bonded but only overlapped (without adhesive). In this case, the resulting fiber structure preferably does not have the constituent fibers of the coarse fiber nonwoven fabric and fine fiber nonwoven fabric fused together.

[0054] The coarse fiber nonwoven fabric before complexation has an average fiber diameter of 5.5 μm or more, preferably 6.0 μm or more, and even more preferably 7.0 μm or more. The upper limit of the average fiber diameter of the single fibers is not particularly limited; for example, it can be 50 μm or less, preferably 30 μm or less. The coarse fiber nonwoven fabric can also be mainly (e.g., 60% by weight or more) formed from coarse fibers A with a fiber diameter exceeding 5.0 μm. As long as the coarse fibers A in the coarse fiber nonwoven fabric can be complexed 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 directly bonded nonwoven fabrics (e.g., meltblown nonwoven fabrics, spunbond nonwoven fabrics) are preferable. The coarse fiber nonwoven fabric can be used alone or in combination with two or more types.

[0055] For example, dry nonwoven fabric is formed from a specific fiber polymer by carding or air-jet laying. The resulting web is then bonded together to impart practical strength. Bonding methods include chemical bonding (e.g., chemical bonding), thermal bonding (e.g., thermal bonding, steam jetting), and mechanical bonding (e.g., nonwoven fabric, needle punching), but for simplicity, nonwoven fabrics bonded by water flow complexation are preferred.

[0056] Specifically, examples of dry-laid nonwoven fabrics include chemically bonded nonwoven fabrics, thermally bonded nonwoven fabrics, nonwoven fabrics, steam-jet nonwoven fabrics, needle-punched nonwoven fabrics, and air-laid nonwoven fabrics. Among these, nonwoven nonwoven fabrics are preferred from the viewpoint of fully complexing with fine fiber nonwoven fabrics.

[0057] The fiber length of the fibers constituting dry nonwoven fabric can be about 15 to 70 mm, preferably about 20 to 65 mm, more preferably about 30 to 60 mm, and even more preferably about 35 to 55 mm. By means of this fiber length, dry nonwoven fabric can be distinguished from wet nonwoven fabric (which usually has a fiber length of less than 10 mm).

[0058] Furthermore, examples of nonwoven fabrics that are directly bonded by spinning include meltblown nonwoven fabrics and spunbond nonwoven fabrics. Among these, meltblown nonwoven fabrics are preferred because they can be adjusted to have rigidity even with a low unit area weight. Meltblown nonwoven fabrics are nonwoven fabrics obtained by the meltblowing method. With the meltblowing method, nonwoven fabrics with fine fibers can generally be obtained, but nonwoven fabrics with coarse fibers can also be obtained with specific manufacturing conditions. When meltblown nonwoven fabrics are used as coarse fiber nonwoven fabrics, they have high rigidity, which can improve the complexing properties with fine fiber nonwoven fabrics, etc. In order to impart rigidity to the coarse fiber group so that the fine fiber group can be easily complexed, it is preferable to have the fibers reach the collection surface in a coarse state before the fibers of the fiber stream are thinned by the meltblowing method, and before the fibers are cured. For example, it is preferable to shorten the collection distance of the fiber stream by the meltblowing method, or to increase the fiber diameter by increasing the resin viscosity, thereby lengthening the time until curing. 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 even more preferably 7 to 60 cm.

[0059] The fibers constituting the coarse fiber nonwoven fabric can also be long fibers, based on the viewpoint of improving rigidity and fully complexing with the fine fiber nonwoven fabric.

[0060] The unit area weight of the coarse fiber nonwoven fabric can be, for example, about 10~150g / m2, preferably about 12~130g / m2, and even more preferably about 15~100g / m2.

[0061] Based on the viewpoint of fully complexing with fine fiber nonwoven fabric, coarse fiber nonwoven fabric preferably has a relatively coarse structure, and its apparent density may be, for example, about 0.005~0.20 g / cm3 (e.g. 0.005~0.07 g / cm3), more preferably about 0.01~0.15 g / cm3 (e.g. 0.01~0.06 g / cm3), and even more preferably about 0.02~0.10 g / cm3 (e.g. 0.02~0.05 g / cm3).

[0062] The thickness of the coarse fiber nonwoven fabric can be, for example, about 0.1~5mm, preferably about 0.2~3mm, and even more preferably about 0.3~1mm.

[0063] The number average fiber diameter of the single fiber in the nonwoven fabric before complexation 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, but for example, it can be 0.1 μm or more, preferably 0.5 μm or more. The nonwoven fabric can also be mainly (for example, 60% by weight or more) formed from fine fibers B with a single fiber diameter of 5.0 μm or less.

[0064] As a fine fiber nonwoven fabric, meltblown nonwoven fabric, electric field spun nonwoven fabric, nonwoven fabric obtained by splitting fibers (fibers formed by bundles of free different components temporarily form a nonwoven fabric, and the fine fiber nonwoven fabric obtained by splitting the fibers from the interface of different components), nonwoven fabric obtained by sea island fibers (a fine fiber nonwoven fabric obtained by dissolving the sea part of the nonwoven fabric formed by sea island fibers), and nonwoven fabric made of monofibrils (a fine fiber nonwoven fabric obtained by subjecting a temporarily formed nonwoven fabric to physical impact and monofibrilating the fibers). Based on the viewpoint of easy complexation, meltblown nonwoven fabric is preferred.

[0065] To obtain the fibrous structure of the present invention, it is preferable to use a fine fiber nonwoven fabric in which the average number of fusion points between the fine fibers B is within a specific range. By using such a fine fiber nonwoven fabric, a complexation process with a coarse fiber nonwoven fabric can be performed, making it easy to complex the fine fiber group with the coarse fiber group. For example, meltblown nonwoven fabric can be formed by refining molten thermoplastic polymer extruded from a nozzle into fibers by hot air jetting, and then allowing the fibers to complex and self-fuse in a high-temperature, high-speed airflow. In the present invention, it has been found that by adjusting the collection distance of the fiber stream using the meltblown method, the self-fusing property of the extruded polymer fiberized before reaching the collection surface can be controlled, and the average number of fusion points between the fine fibers B of the resulting fine fiber nonwoven fabric can be adjusted. Specifically, self-fusion can be suppressed by increasing the collection distance, but self-fusion can be promoted by shortening the collection distance. The collection distance (the distance from the nozzle to the collection surface) depends on conditions such as resin viscosity and air temperature, but it can be 35~90cm, preferably 40~80cm, and even more preferably 40~70cm.

[0066] Based on the viewpoint of fully complexing with coarse fiber nonwoven fabric, the unit area weight of fine fiber nonwoven fabric can be, for example, about 1.0~30g / m2, preferably about 2.0~25g / m2, and even more preferably about 3.0~20g / m2.

[0067] The apparent density of the microfiber nonwoven fabric can be, for example, about 0.01~0.30 g / cm3, preferably about 0.03~0.25 g / cm3, and even more preferably about 0.05~0.20 g / cm3.

[0068] The thickness of the microfiber nonwoven fabric can be, for example, about 0.01~0.30mm, preferably about 0.03~0.25mm, and even more preferably about 0.05~0.20mm.

[0069] In the laminated material, in the subsequent complexing step, based on the viewpoint that the coarse fiber nonwoven fabric and the fine fiber nonwoven fabric are fully complexed, the ratio W1 / W2 of the unit area weight W1 of the coarse fiber nonwoven fabric and 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.

[0070] As a complexing process, although coarse fiber nonwoven fabric and fine fiber nonwoven fabric can be complexed by using nonwoven method, needle punching method, etc., it is better to use nonwoven method from the point of view that the long fibers of fine fiber nonwoven fabric are fully complexed.

[0071] For example, in the nonwoven process, for a porous support on which a laminate of coarse fiber nonwoven fabric and fine fiber nonwoven fabric is placed, a high-pressure water flow (e.g., 1 MPa or more) is sprayed from a nozzle with micropores. The water flow that penetrates the laminate is reflected back to the support, and its energy can complex the fibers.

[0072] The porous support used in the nonwoven process can be either a roller type or a plate type, or a combination thereof, but a plate type porous support is preferred. The porosity of the porous support is, for example, 10-50%, preferably 15-40%, and more preferably about 20-30%. The pore size of the porous support is, for example, 0.01-5.0 mm, preferably 0.05-3.0 mm, and more preferably about 0.1-1.0 mm.

[0073] The water pressure of the water flow can be set appropriately according to the thickness of the deposit, for example, it can be 1~10MPa, preferably 1.5~9.5MPa, and even more preferably about 2~9MPa.

[0074] The nozzle orifice diameter used for water jet spraying can be, for example, about 0.05 to 0.2 mm. The spacing between the micro-holes in the nozzle is, for example, 0.3 to 5.0 mm, preferably 0.4 to 3.0 mm, and even more preferably about 0.5 to 2.0 mm.

[0075] 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 complexation of coarse and fine nonwoven fabrics, 2 to 3 rows are preferred. When multiple rows of nozzles are set, the water pressure of each row can be different. From the viewpoint of optimizing the complexation of coarse and fine nonwoven fabrics, it is preferable to increase the water pressure of the water jet colliding with the deposited material in the mechanical direction (MD direction).

[0076] When complexing coarse fiber nonwoven fabric and fine fiber nonwoven fabric, it is preferable to place the laminate formed by overlapping the coarse fiber nonwoven fabric and the fine fiber nonwoven fabric on the aforementioned porous support, and continuously convey the laminate and the porous support together in the longitudinal direction at a constant speed while performing the complexing process under the aforementioned conditions. The conveying speed of the laminate is, for example, 1.0~10.0 m / min, preferably 2.0~9.0 m / min, and more preferably about 3.0~8.0 m / min. By setting the conveying speed of the laminate to the above range, the complexing properties of the coarse fiber nonwoven fabric and the fine fiber nonwoven fabric can be optimized, and the dust retention capacity of the resulting fibrous structure can be further improved.

[0077] Furthermore, when using the nonwoven method for complexation treatment, water can be sprayed from either the coarse fiber nonwoven fabric side or the fine fiber nonwoven fabric side of the laminate. However, based on the viewpoint of fully complexing the coarse fiber nonwoven fabric and the fine fiber nonwoven fabric, water can also be sprayed from the fine fiber nonwoven fabric side of the laminate.

[0078] Furthermore, depending on the application, electrostatic treatment of the fibrous structure can also improve the capture efficiency. Electrostatic treatment can be performed on the laminate before complexation treatment or on the fibrous structure after complexation treatment.

[0079] The charging process is not particularly limited as long as it can be charged. Examples include methods of imparting charge by friction or contact, methods of irradiating active energy lines (such as electron beams, ultraviolet rays, X-rays, etc.), methods of gas discharge by corona discharge, plasma, etc., methods of using high electric fields, and methods of hydrostatic charging using polar solvents such as water.

[0080] In the hydraulic charging method, a polar solvent, such as water or an organic solvent (preferably water from a production perspective such as wastewater treatment), is sprayed onto the fiber structure while vibrating. The solvent is then drawn from one side of the fiber structure, either after or during the charging process, allowing it to penetrate the fiber structure and become charged. The pressure at which the polar solvent impacts the fiber structure is preferably 0.1 to 5 MPa. The suction pressure from below is preferably 500 to 5000 mmH2O. The hydraulic charging process time is preferably 0.001 to 5 seconds.

[0081] 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 preferred, and the upper limit is not particularly limited, but for example, it can be around 30 mg. Here, dust retention capacity refers to the amount of dust captured before the pressure loss of the fiber structure installed on the circular filter holder with an inner diameter of 110 mm becomes twice the initial value, and is a value measured by the method described in the embodiments described later.

[0082] The capture efficiency (initial capture efficiency) of the fiber structure of the present invention is preferably high, but based on the viewpoint of controlling the pressure loss within an appropriate range, it is, 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 below.

[0083] The pressure loss (initial pressure loss) of the fiber structure of the present invention can be adjusted to a range of, for example, 0 to 30 Pa, depending on the design of the fiber diameter and other parameters of the fibers to be contained. However, 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 below.

[0084] Regarding the QF value of the fiber structure of the present invention, calculated from the collection efficiency and pressure loss according to the following formula, it is, for example, 0.10 or more, preferably 0.15 or more, and even more preferably 0.19 or more. A higher QF value is preferred, and the upper limit is not particularly limited, but it can be, for example, around 2.00. QF value = -ln(1 - collection efficiency (%) / 100) / pressure loss (Pa).

[0085] As an application of this fiber structure, it is preferably used as a filter (especially an air filter). The filter can be used as a filter for, for example, masks, various air conditioning applications (building air conditioning, clean rooms, painting rooms, etc.), automotive applications (car cabin filters, etc.), and general household appliances (air conditioners, air purifiers, vacuum cleaners, etc.). When using the fiber structure as a filter, its coarse fiber group side can be used as the upstream side.

[0086] 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 part of the mouth and the bridge of the nose of the wearer, or at least either of these. For example, the fiber structure can be one of the multiple layers constituting the covering part. Furthermore, the fiber structure can be used as an intermediate sheet disposed between the exhalation side sheet and the surface side sheet constituting the mask.

[0087] Furthermore, in this invention, a mask refers to a mask that covers at least the area around the mouth and the root of the nose (especially the nostrils), regardless of whether it has any fixing parts such as straps to the face. Furthermore, a mask may also cover parts of the body other than the area around the mouth and the root of the nose. For example, as a variation, the mask of this invention may also be a therapeutic mask for sleep apnea syndrome (e.g., a nasal mask, a full-face mask, etc.) used in CPAP therapy for treating sleep apnea syndrome, NIPPV therapy for treating incomplete ventilation, etc. [Example]

[0088] Hereinafter, the present invention will be described in more detail based on embodiments, but the present invention is not limited in any way by these embodiments. Furthermore, in the following embodiments and comparative examples, various physical properties were determined by the methods described below.

[0089] [Number-average fiber diameter of a single fiber] The surface of the fiber structure was observed using a scanning electron microscope. Fibers were randomly selected from the electron microscope images, 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 the number-average fiber diameter (n=100) was calculated. Fibers with a diameter less than 5.0 μm were designated as fine fibers B, and the number-average fiber diameter (n=100) was calculated.

[0090] [Weight per unit area and apparent density] The weight per unit area (g / m2) was determined according to section 6.2 of JIS L 1913 "General Test Methods for Nonwoven Fabrics". The apparent density (g / cm3) was calculated by dividing the weight per unit area by the thickness.

[0091] [Thickness] Using a razor ("FEATHER Razor S Blade", manufactured by FEATHER Safety Razor Co., Ltd.) to cut any 10 sections parallel to the thickness direction of the fiber structure or various nonwoven fabrics and perpendicular to the machine direction (MD), each cross-section was observed in a digital microscope photograph. Next, at each cut surface of the fiber structure or various nonwoven fabrics, the upper and lower ends were determined, the distance in the thickness direction from the upper end to the lower end was measured, and the average value of these 10 sections was calculated to determine the thickness (mm) of the fiber structure or various nonwoven fabrics.

[0092] [Fiber Filling Rate] Samples of 2.5cm × 2.5cm were cut from five arbitrary locations along the surface of the fiber structure. X-ray CT measurements were performed on each sample under the following conditions to obtain three-dimensional images. <X-ray CT Measurement Conditions> Measurement Apparatus: Xradia 520 Versa (Carl Zeiss) X-ray Target: Tungsten X-ray Source Intensity: 160kV Output: 10W Objective Lens: 4X Field of View: 1512μm Pixel Size: 1.5μm / pixel Pixel Binding: 2 Exposure Time: 2 seconds / image Number of Images: 3201 images Shooting Time: 4 hours

[0093] <Image Analysis Conditions> The obtained 3D images were analyzed using the image analysis software Avizo (manufactured by Thermo Fisher Scientific) in the following order to determine the filling rate of various fibers in each region. The obtained 3D images were cut into 0.75mm × 0.75mm × total thickness segments in the image analysis software, and then noise was removed using a NON-LOCAL filter. The NON-LOCAL filter was set to the following conditions: Spatial standard deviation: 5; Intensity standard deviation: 0.2; Search window: 10; Local neighbor value: 3. Binarization was then performed using the interaction threshold function to extract all fibers. The threshold was set to any value between 30000 and 35000 from the 65536 gray levels.

[0094] For data processed with a NON-LOCAL filter to remove noise, the fiber trace function is used to capture fibers (coarse fiber A) with a specific fiber diameter. The fiber trace function is set to the following conditions: Cylinder length value related to the cylinder: any value between 2.5 and 3.5 times the fiber diameter; Angle sampling value: 5; Mask cylinder radius value: any value between fiber radius + 1 and fiber radius + 13; Cylinder outer radius value: fiber radius; Inner cylinder radius value: 0; Direction coefficient value of the trajectory correlation line: 0.45; Minimum distance value: any value between fiber radius and fiber diameter. Furthermore, using the Arithmetic function, all fibers captured by the interaction threshold function are subtracted from the fibers with the specific fiber diameter captured by the fiber trace function, and only fibers with other fiber diameters (fine fiber B) are captured. Using the Arithmetic function, the area other than all fibers captured by the interaction threshold function is captured as a gap.

[0095] Using the regional volume fraction function, the image data is analyzed in 7.5 μm increments along the thickness direction, and the volume ratio of coarse fiber A / fine fiber B / void in each region is calculated. Regions where fibers exist at 0.1 vol% or more are defined as regions of fiber structures and are set as the measurement range. When the thickness of the fiber structure measured above is L (mm), the thickness is divided into 10 equal parts, and the thickness of the first segment is defined as L / 10 (mm). All regions of the fiber structure analyzed in each 7.5 μm increment are integrated, and the cross section is divided into 10 layers according to each L / 10 (mm) thickness. The resulting 10 layers are designated as regions 1 to 10 from the fine fiber group side to the coarse fiber group side, and the filling rate of coarse fiber A and fine fiber B in each region is calculated. Within the same fiber structure sample (2.5cm × 2.5cm), a resolution range of 0.75mm × 0.75mm × total thickness was analyzed at 125μm intervals in 10 locations under the aforementioned resolution conditions. The measurement results are the average of 50 points across 10 locations for all 5 samples. Furthermore, the 10 layers were designated as regions 1 through 10 from the fine fiber group side towards the coarse fiber group side. The average filling rates of coarse fiber A and fine fiber B in region S (representing regions 1 through 3), region T (representing regions 4 through 7), and region U (representing regions 8 through 10) were calculated.

[0096] [Average Number of Fusion Points] The fiber structure was cut into 1cm × 1cm sections in the planar direction, and samples were taken. Using a scanning electron microscope, the side surface of the fine fiber group of the obtained sample was randomly photographed within a 100μm × 100μm range. Then, from the obtained images, the number of sites where fine fibers B are fused together was determined. Images of 100μm × 100μm ranges of 5 different sites in the planar direction were measured, and the average value of these numbers was calculated. Furthermore, regarding the number of sites to be fused, when the same fine fibers B are fused together in multiple locations, these are counted as other sites.

[0097] [Capture Efficiency, Pressure Loss, QF Value] The capture 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 sample was installed 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. Using NaCl particles with a mass center diameter of 0.26 μm as test particles, the filter holder containing the test sample was circulated for 10 seconds at a particle concentration of 15-20 mg / m³, an airflow of 32 L / min, and a surface velocity of 5.33 cm / s. 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 capture efficiency was calculated using the following formula: Capture efficiency (%) = {(X1-X2) / X1} × 100

[0098] In addition, a differential pressure gauge is 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)) at an air volume of 32 liters / minute.

[0099] Next, the QF value is calculated from the obtained capture efficiency and pressure loss using the following formula: QF value = -ln(1 - capture efficiency (%) / 100) / pressure loss (Pa).

[0100] [Dust Retention Capacity] The dust collection 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 sample was installed 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. Using NaCl particles with a mass center diameter of 0.26 μm as test particles, the filter holder with the test sample was circulated for 60 minutes at a particle concentration of 15-20 mg / m³, an airflow of 32 L / min, and a surface velocity of 5.33 cm / s. The collection efficiency and pressure loss every 2 minutes were calculated using the same method as described above. Then, using the obtained values, the time t from the pressure loss at the start of the measurement to twice the pressure loss was measured. Furthermore, the particle concentration, airflow, and collection efficiency from the upstream side were used to calculate the particle collection weight every 2 minutes using the following formula, and the sum of these values ​​up to time t was defined as the dust retention capacity. Particle capture weight in 2 minutes = upstream particle concentration (mg / m3) × airflow (L / min) × 0.001 (m3 / L) × 2 (min) × capture efficiency (%) / 100

[0101] [Example 1] (1) Production of coarse fiber nonwoven fabric 100 parts by weight of polypropylene (MFR [230°C, 21.18 N load] = 30 g / 10 min) was sprayed from the nozzle hole using a general meltblown equipment with a spinning temperature of 260°C, an air temperature of 260°C, an air flow rate of 13 N m3 / min, a single hole spray rate of 0.3 g / hole·min, a hole diameter of 0.4 mm, and a hole spacing of 1.5 mm. The fiber flow refined by hot air was captured by a capture distance of 32 cm to obtain coarse fiber nonwoven fabric (average fiber diameter of single fiber is 7.2 μm, unit area weight is 20 g / m2, thickness is 0.76 mm, apparent density is 0.03 g / cm3).

[0102] (2) Production of fine fiber nonwoven fabric: 100 parts by weight of polypropylene (MFR [230℃, 21.18N load] = 700g / 10min) were melt-blown using a general meltblown equipment with a spinning temperature of 215℃, an air temperature of 215℃, an air flow rate of 10Nm3 / min, a single-hole spray rate of 0.036g / hole·min, a hole diameter of 0.3mm, a hole spacing of 0.75mm, and a collection distance of 40cm to obtain fine fiber nonwoven fabric (average fiber diameter of single fiber is 1.2μm, unit area weight is 10g / m2, thickness is 0.10mm, apparent density is 0.10g / cm3).

[0103] (3) Complexation treatment of coarse fiber nonwoven fabric and fine fiber nonwoven fabric Next, the coarse fiber nonwoven fabric obtained in (1) and the fine fiber nonwoven fabric obtained in (2) are overlapped. The laminate is placed on a porous support (open area ratio 25%, pore diameter 0.3 mm) and continuously moved along the length direction of the laminate at a speed of 5.0 m / min. At the same time, two nozzles with 0.10 mm orifices at 0.6 mm intervals along the width direction of the laminate (the distance between adjacent nozzles is 20 cm) are used. The water pressure of the high-pressure water jet from the nozzle in the first row is set to 2.0 MPa and the water pressure of the high-pressure water jet from the nozzle in the second row is set to 3.0 MPa. High-pressure water jet is sprayed from the side of the fine fiber nonwoven fabric for complexation treatment.

[0104] Subsequently, the fiber structure obtained by complexing coarse and fine nonwoven fabrics was subjected to electrostatic treatment using a hydraulic electrostatic method. Specifically, under the following conditions, water was sprayed onto one surface of the fiber structure, and water was drawn from the other surface of the fiber structure by a slit-shaped suction nozzle, thereby allowing water to penetrate into the interior of the fiber structure. After shaking off the water, the structure was allowed to dry naturally. • Water pressure: 0.4 MPa • Suction pressure: 2000 mmH2O • Processing time: 0.0042 seconds (speed 20 m / min) The various evaluation results of the obtained fiber structure are shown in Table 1.

[0105] [Example 2] The coarse fiber nonwoven fabric obtained in Example 1 (1) and the fine fiber nonwoven fabric obtained in Example 1 (2) were overlapped and placed on the porous support used in Example 1. The fabric was continuously moved along the length of the laminate at a speed of 5.0 m / min. At the same time, three nozzles (with 0.10 mm orifices at 0.6 mm intervals along the width of the laminate) 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 for complexation treatment. Then, the same electrostatic treatment as in Example 1 was performed to obtain a fiber structure formed by complexing coarse fiber nonwoven fabric and fine fiber nonwoven fabric. The various evaluation results of the obtained fiber structure are shown in Table 1.

[0106] [Example 3] (1) Production of coarse fiber nonwoven fabric: 100% by weight of polypropylene fiber (NF, manufactured by Ube Exemo Co., Ltd.) with an average fiber diameter of 17.5 μm and a fiber length of 51 mm was used as raw cotton, and a semi-random web was made using the carding method. Next, the obtained semi-random web was placed on a perforated roller support with an opening ratio of 25% and an aperture of 0.3 mm, and continuously conveyed along the length direction at a speed of 5.0 m / min, while simultaneously being complexed by high-pressure water jets sprayed from above. In this way, a complexed fiber web (nonwoven fabric) was manufactured. In this complexing process, two nozzles with 0.10mm orifices spaced 0.6mm apart along the width of the mesh (the distance between adjacent nozzles is 20cm) are used. The water pressure of the high-pressure water jet from the first row of nozzles is set to 3.0MPa, and the water pressure of the high-pressure water jet from the second row of nozzles is set to 5.0MPa for nonwoven processing. Then, the same complexing process is performed on the back side to obtain a coarse fiber nonwoven fabric (unit area weight 35g / m2, thickness 0.42mm, apparent density 0.08g / cm3).

[0107] (2) Production of fine fiber nonwoven fabric: 100 parts by weight of polypropylene (MFR [230℃, 21.18N load] = 700g / 10min) were melt-blown using general meltblown equipment with spinning temperature of 215℃, air temperature of 215℃, air volume of 0.4MPa, single-hole spray rate of 0.1g / hole‧min, hole diameter of 0.3mm, hole spacing of 0.6mm (1 row configuration), and collection distance of 40cm to obtain fine fiber nonwoven fabric (average fiber diameter of single fiber is 2.5μm, unit area weight is 10g / m2, thickness is 0.11mm, apparent density is 0.10g / cm3).

[0108] (3) Complexation treatment of coarse and fine nonwoven fabrics Next, the coarse nonwoven fabric obtained in (1) and the fine nonwoven fabric obtained in (2) were overlapped. The laminate was placed on the porous support used in Example 1 and continuously moved along the length of the laminate at a speed of 5.0 m / min. At the same time, a high-pressure water jet of 3.0 MPa was sprayed from the side of the fine nonwoven fabric using a nozzle with orifices of 0.10 mm at 0.6 mm intervals along the width of the laminate. Then, the same electrostatic treatment as in Example 1 was performed to obtain a fiber structure formed by the complexation of coarse and fine nonwoven fabrics. The various evaluation results of the obtained fiber structure are shown in Table 1.

[0109] [Example 4] The coarse fiber nonwoven fabric obtained in Example 3(1) and the fine fiber nonwoven fabric obtained in Example 3(2) were overlapped and placed on the porous support used in Example 1. The layers were continuously moved along the length of the laminate at a speed of 5.0 m / min. At the same time, a high-pressure water jet of 7.0 MPa was sprayed from the side of the fine fiber nonwoven fabric using a nozzle with orifices of 0.10 mm at 0.6 mm intervals along the width of the laminate to perform a complexation treatment. Then, the same electrostatic treatment as in Example 1 was performed to obtain a fiber structure formed by complexing the coarse fiber nonwoven fabric and the fine fiber nonwoven fabric. The various evaluation results of the obtained fiber structure are shown in Table 1, the magnified cross-sectional photograph is shown in Figure 1, and the magnified surface photograph of the fine fiber group side is shown in Figure 2.

[0110] [Example 5] The coarse fiber nonwoven fabric obtained in Example 3(1) and the fine fiber nonwoven fabric obtained in Example 3(2) were overlapped and placed on the porous support used in Example 1. The fabric was continuously moved along the length of the laminate at a speed of 5.0 m / min. At the same time, three nozzles (with 0.10 mm orifices at 0.6 mm intervals along the width of the laminate) 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 for complexation treatment. Then, the same electrostatic treatment as in Example 1 was performed to obtain a fiber structure formed by complexing coarse fiber nonwoven fabric and fine fiber nonwoven fabric. The various evaluation results of the obtained fiber structure are shown in Table 1.

[0111] [Example 6] (1) Preparation of fine fiber nonwoven fabric 100 parts by weight of polypropylene (MFR [230°C, 21.18N load] = 700g / 10min) were melt-blown using a general meltblown equipment with a spinning temperature of 215°C, an air temperature of 215°C, an air volume 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 to obtain a fine fiber nonwoven fabric (average fiber diameter of single fiber is 2.5μm, unit area weight is 10g / m2, thickness is 0.11mm, apparent density is 0.10g / cm3).

[0112] (2) Complexation treatment of coarse fiber nonwoven fabric and fine fiber nonwoven fabric: The coarse fiber nonwoven fabric obtained in Example 3 (1) and the fine fiber nonwoven fabric obtained in Example 6 (1) were overlapped and placed on the porous support used in Example 1. The layers were continuously moved along the length of the laminate at a speed of 5.0 m / min. At the same time, a high-pressure water jet of 4.0 MPa was sprayed from the side of the fine fiber nonwoven fabric using a nozzle with orifices of 0.10 mm at 0.6 mm intervals along the width of the laminate. Then, the same electrostatic treatment as in Example 1 was performed to obtain a fiber structure formed by complexing coarse fiber nonwoven fabric and fine fiber nonwoven fabric. The various evaluation results of the obtained fiber structure are shown in Table 1.

[0113] [Comparative Example 1] (1) Production of fine fiber nonwoven fabric 100 parts by weight of polypropylene (MFR [230°C, 21.18 N load] = 700 g / 10 min) were melt-blown using a general meltblown equipment with a spinning temperature of 215°C, an air temperature of 215°C, an air flow rate of 10 N m3 / min, 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 (average fiber diameter of single fiber 1.2 μm, unit area weight of 10 g / m2, thickness of 0.10 mm, apparent density of 0.10 g / cm3).

[0114] (2) Complexation treatment of coarse fiber nonwoven fabric and fine fiber nonwoven fabric The coarse fiber nonwoven fabric obtained in Example 1 (1) and the fine fiber nonwoven fabric obtained in Comparative Example 1 (1) were overlapped and placed on the porous support used in Example 1. The fabric was continuously conveyed along the length of the laminate at a speed of 5.0 m / min. At the same time, two nozzles with orifices of 0.10 mm in diameter were used along the width of the laminate (the distance between adjacent nozzles was 20 cm). The water pressure of the high-pressure water jet sprayed from the nozzle in the first row was set to 2.0 MPa and the water pressure of the high-pressure water jet sprayed from the nozzle in the second row was set to 3.0 MPa. The high-pressure water jet was sprayed from the coarse fiber nonwoven fabric side for complexation treatment. Then, the same electrostatic treatment as in Example 1 was performed to obtain a fiber structure formed by complexing coarse fiber nonwoven fabric and fine fiber nonwoven fabric. The various evaluation results of the obtained fiber structure are shown in Table 1.

[0115] [Comparative Example 2] (1) Production of fine fiber nonwoven fabric 100 parts by weight of polypropylene (MFR [230°C, 21.18 N load] = 700 g / 10 min) were melt-blown using a general meltblown equipment with a spinning temperature of 215°C, an air temperature of 215°C, an air volume of 0.4 MPa, a single-hole ejection rate of 0.1 g / hole‧min, a hole diameter of 0.3 mm, a hole spacing of 0.6 mm (1 row configuration), and a collection distance of 30 cm to obtain a fine fiber nonwoven fabric (average fiber diameter of single fiber is 2.5 μm, unit area weight is 10 g / m2, thickness is 0.11 mm, apparent density is 0.10 g / cm3).

[0116] (2) Complexation treatment of coarse fiber nonwoven fabric and fine fiber nonwoven fabric The coarse fiber nonwoven fabric obtained in Example 3 (1) and the fine fiber nonwoven fabric obtained in Comparative Example 2 (1) were overlapped and placed on the porous support used in Example 1. The layers were continuously moved along the length of the laminate at a speed of 5.0 m / min. At the same time, a high-pressure water jet of 3.0 MPa was sprayed from the side of the fine fiber nonwoven fabric using a nozzle with orifices of 0.10 mm at 0.6 mm intervals along the width of the laminate. Then, the same electrostatic treatment as in Example 1 was performed to obtain a fiber structure formed by complexing coarse fiber nonwoven fabric and fine fiber nonwoven fabric. The various evaluation results of the obtained fiber structure are shown in Table 1.

[0117] [Comparative Example 3] (1) Production of fine fiber nonwoven fabric 100 parts by weight of polypropylene (MFR [230°C, 21.18 N load] = 700 g / 10 min) were melt-blown using a general meltblown equipment with a spinning temperature of 215°C, an air temperature of 215°C, an air volume of 0.4 MPa, a single-hole ejection rate of 0.1 g / hole‧min, a hole diameter of 0.3 mm, a hole spacing of 0.6 mm (1 row configuration), and a collection distance of 100 cm to obtain a fine fiber nonwoven fabric (average fiber diameter of single fiber is 2.5 μm, unit area weight is 10 g / m2, thickness is 0.11 mm, apparent density is 0.10 g / cm3).

[0118] (2) Complexation treatment of coarse fiber nonwoven fabric and fine fiber nonwoven fabric The coarse fiber nonwoven fabric obtained in Example 3(1) and the fine fiber nonwoven fabric obtained in Comparative Example 3(1) were overlapped and placed on the porous support used in Example 1. The layers were continuously moved along the length of the laminate at a speed of 5.0 m / min. At the same time, a high-pressure water jet of 4.0 MPa was sprayed from the side of the fine fiber nonwoven fabric using a nozzle with orifices of 0.10 mm at 0.6 mm intervals along the width of the laminate. Then, the same electrostatic treatment as in Example 1 was performed to obtain a fiber structure formed by complexing coarse fiber nonwoven fabric and fine fiber nonwoven fabric. The various evaluation results of the obtained fiber structure are shown in Table 1.

[0119]

[0120] As shown in Table 1, Comparative Examples 1 to 3 have a fiber filling rate relationship of SA+SB>TA+TB>UA+UB in regions S, T and U. The filling rates of coarse fiber A and fine fiber B have no specific relationship, and the average number of fusion points of fine fiber B is not within a specific range, resulting in low dust retention capacity.

[0121] On the other hand, in Examples 1 and 2, SB is the largest among SB, TB, and UB, exhibiting a specific relationship of TA+TB>SA+SB>UA+UB, and the average number of fusion points of the fine fibers B is within a specific range. Although these fiber structures are manufactured using coarse fiber nonwoven fabric and fine fiber nonwoven fabric with the same average fiber diameter as Comparative Example 1, their dust retention capacity is more than 1.4 times higher than that of Comparative Example 1.

[0122] Similarly, in Examples 3-6, the coarse fibers A and fine fibers B in each region have a specific distribution, and the average number of fusion points of the fine fibers B is within a specific range. Although these fiber structures are manufactured using coarse and fine fiber nonwoven fabrics with the same average fiber diameter as Comparative Examples 2 and 3, their dust retention capacity is more than 1.5 times higher than that of Comparative Examples 2 and 3. [Industrial Applicability]

[0123] The fiber structure of the present invention has a high dust retention capacity and a long lifespan, and therefore can be appropriately used as various filter sheets (especially air filter sheets, bag filter sheets, liquid filter sheets, etc.). For example, it can be used as a filter sheet for masks, various air conditioning applications (building air conditioning, clean rooms, painting rooms, etc.), automotive industry applications (car cabin filter sheets, etc.), and general household appliances (air conditioners, air purifiers, vacuum cleaners, etc.).

[0124] As described above, although the preferred embodiments of the present invention have been described, various additions, changes or deletions may be made without departing from the spirit of the present invention, and such additions, changes or deletions are also included within the scope of the present invention. [Simplified Explanation of the Diagram]

[0018] The present invention will become clearer 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 should not be used to determine the scope of the invention. The scope of the invention is determined by the appended claims. The drawings are not necessarily shown at a fixed scale and may be exaggerated to illustrate the principles of the invention. [Figure 1] is an enlarged cross-sectional photograph of the fiber structure of Embodiment 4. [Figure 2] is an enlarged surface photograph of the fine fiber group side of the fiber structure of Embodiment 4. [Figure 3] is a cross-sectional conceptual diagram illustrating various regions of the fiber structure of one embodiment of the present invention.

Claims

1. A fiber structure comprising a coarse fiber group composed of fibers A with a single fiber diameter exceeding 5 μm and a fine fiber group composed of fibers B with a single fiber diameter of 5 μm or less, and having a complexation region in which the aforementioned coarse fiber group and the aforementioned fine fiber group are complexed, wherein the fiber structure is divided into 10 equal parts in the thickness direction, and regions 1 to 10 are designated from the fine fiber group side to the coarse fiber group side. The filling rates of the aforementioned fibers A 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 designated as SA, TA, and UA. When the filling rates of the aforementioned fibers B are respectively designated as SB, TB, and UB, SB is the largest among SB, TB, and UB, and the order is TA+TB>SA+SB>UA+UB. Furthermore, within a 100μm×100μm area along the surface of the fiber structure, the average number of fusion points between fibers B constituting the aforementioned fine fiber group is more than 1.0 and less than 10.

0.

2. The fiber structure as claimed in claim 1, wherein the fusion points of the aforementioned fibers B are derived from the melt-blowing method.

3. The fiber structure as claimed in claim 1 or 2 is a complex of a coarse fiber nonwoven fabric formed from the aforementioned fiber A and a fine fiber nonwoven fabric formed from the aforementioned fiber B.

4. The fiber structure as claimed in claim 1 or 2, wherein the average fiber diameter of the number of individual fibers in the aforementioned coarse fiber group is 5.5 μm or more, and the average fiber diameter of the number of individual fibers in the aforementioned fine fiber group is 4.5 μm or less.

5. The fiber structure as requested in item 1 or 2, wherein the unit area weight is 15~180g / m2.

6. The fiber structure as requested in item 1 or 2 is electrically charged.

7. The fiber structure of request item 1 or 2 has a capture efficiency of 60% or more.

8. For the fiber structure of claim 1 or 2, wherein the QF value calculated by means of the collection efficiency and pressure loss according to the following formula is 0.10 or more, QF value = -ln(1 - collection efficiency (%) / 100) / pressure loss (Pa).

9. A filter having a fibrous structure as claimed in any one of claims 1 to 8.

10. A face mask having a filter as described in claim 9.

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