Fiber sheet

Abstract

To provide a fiber sheet that includes ultra fine fibers, expresses elasticity with directivity, and has high tolerance to break or abrasion.SOLUTION: A fiber sheet has a first fiber layer having the median fiber diameter of 0.3 μm or more and 5 μm or less and a second fiber layer which is adjacent to the first fiber layer and has the median fiber diameter of 5 μm or more and 50 μm or less, where the first fiber layer and the second fiber layer contain a material of the same series, a material of the same series is selected from olefin-based resin, diene-based resin, and urethane-based resin and a copolymer thereof, an elongation rate in one direction of the fiber sheet is 20 or more and 100 or less, and an elongation rate in a direction orthogonal to the one direction is 0 or more and 30 or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a fibrous sheet. [Background technology]

[0002] Sheets containing fibers (hereinafter referred to as fiber sheets) include, for example, nonwoven fabrics and have various structures. For example, Patent Document 1 describes a multi-layered stretchable nonwoven fabric in which a viscous meltblown nonwoven fabric is laminated and bonded onto a non-viscous meltblown nonwoven fabric. Both of these meltblown nonwoven fabrics are made of thermoplastic elastomers and have stretch properties. Even if the multi-layered stretchable nonwoven fabric has viscous properties during production, it is designed to suppress the occurrence of sticking to production equipment without reducing the stretch properties. Patent Document 2 describes a nonwoven fabric that is mainly made of thermoplastic resin fibers and has different elongation rates in one direction and in the direction perpendicular to the one direction, which is said to eliminate the need for subsequent processing of the nonwoven fabric when it is desired to have elasticity in only one direction.

[0003] In addition to the above-mentioned general nonwoven fabrics, fiber sheets include those made by depositing ultrafine fibers (fiber diameter of 5 μm or less), which have been attracting attention in recent years. As an example of a spinning technique for uniformly manufacturing a fiber sheet made of such fine fibers, for example, electrospinning is used. Such fiber sheets containing ultrafine fibers have high adhesion to objects such as skin, and are expected to be used for various purposes in the future, and are being actively studied for industrialization. For example, the nanofiber sheet described in Patent Document 3 is shown as being attached to the skin for the purpose of cosmetic effects. In this document, a technique for controlling the rigidity of the nanofiber sheet itself and its slipperiness against the skin is described from the viewpoint of maintaining the smooth state of the nanofiber sheet itself and maintaining the ability to conceal wrinkles on the skin even if wrinkles occur on the skin surface due to changes in facial expression, etc. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 10-237752 [Patent Document 2] Japanese Patent Application Publication No. 9-279460 [Patent Document 3] Patent Publication No. 2021-54734 Summary of the Invention [Problem to be solved by the invention]

[0005] For fiber sheets containing ultrafine fibers as described in Patent Document 3, there has been a demand to impart stretchability to the sheets in order to further enhance adhesion to objects such as the skin. On the other hand, the fiber sheet is softer than conventional nonwoven fabrics due to the fineness of its constituent fibers. Therefore, the fiber sheet needs to have not only elasticity but also further improved resistance to tearing and abrasion without impairing the above-mentioned adhesion. This point is not shown in the conventional nonwoven fabrics with general fiber diameters described in Patent Documents 1 and 2.

[0006] In view of the above, the present invention relates to a fiber sheet that contains ultrafine fibers, exhibits directional stretchability, and at the same time, has high resistance to tearing and abrasion. [Means for solving the problem]

[0007] The present invention provides a fiber sheet having a first fiber layer with a median fiber diameter of 0.3 μm or more and 5 μm or less and an adjacent second fiber layer with a median fiber diameter of 5 μm or more and 50 μm or less, wherein the first fiber layer and the second fiber layer contain the same material, the same material being selected from olefin-based resins, diene-based resins, urethane-based resins and copolymers thereof, and the fiber sheet has an elongation rate of 20 to 100 in one direction and an elongation rate of 0 to 30 in a direction perpendicular to the one direction. Effect of the Invention

[0008] The fiber sheet of the present invention contains ultrafine fibers and exhibits directional stretchability while at the same time exhibiting high resistance to tearing and abrasion. [Brief description of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view that illustrates a schematic diagram of one embodiment of a fiber sheet according to the present invention. [Diagram 2] Photograph (A) is a drawing showing the first fiber layer alone pinched between fingers, and photograph (B) is a drawing showing the fiber sheet of the present invention pinched between fingers. [Diagram 3] FIG. 4 is an explanatory diagram illustrating fusion points at intersections between ultrafine fibers in the first fiber layer. [Figure 4] FIG. 4 is a photograph substituted for a drawing, showing an example of an observation image used when measuring the ratio of the number of fusion-bonded points to the number of fiber intersections. [Diagram 5] 1A and 1B are schematic diagrams showing an example in which a first fiber layer and a second fiber layer include fusion points at intersections between the fibers at the interface between the two layers, where (A) shows the state before stretching and (B) shows the stretched state. [Figure 6] 1(A) to 1(C) are explanatory views that typically show a procedure for measuring the compressive strength of a fiber sheet. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, a preferred embodiment of the fiber sheet of the present invention will be described with reference to the drawings.

[0011] As shown in FIG. 1, the fiber sheet 10 of the present invention is a laminated sheet having a first fiber layer 1 and a second fiber layer 2 adjacent thereto. The first fiber layer 1 is disposed on one surface 10T of the front and back surfaces of the fiber sheet 10, and the second fiber layer 2 is disposed on the other surface 10B opposite to the one surface 10T. The fiber sheet 10 of the present invention may further include another fiber layer in addition to the first fiber layer 1 and the second fiber layer 2. In this case, from the viewpoint of making the characteristics of the first fiber layer 1 described later work effectively and not impairing the cooperation between the first fiber layer 1 and the second fiber layer 2, it is preferable that the other fiber layer is disposed on the other surface 10B of the second fiber layer 2. That is, it is preferable that the first fiber layer 1 is disposed as the outermost layer of the fiber sheet 10.

[0012] The first fiber layer 1 contains ultrafine fibers with a median fiber diameter (P1) of 0.3 μm or more and 5 μm or less. For example, it can be formed by electrospinning. In such a first fiber layer 1, the unevenness of each fiber unit is suppressed compared to conventional fiber layers such as nonwoven fabrics due to the fineness of the fibers, and the contact area with the object (for example, the skin surface) is increased, resulting in high adhesion to the object. For this reason, it is preferable that the side of the first fiber layer 1 in the fiber sheet 10 faces the object.

[0013] The median fiber diameter (P1) of the first fiber layer 1 is preferably 5 μm or less, more preferably 3 μm or less, further preferably 2 μm or less, and particularly preferably 1 μm or less, from the viewpoint of improving adhesion to an object such as a skin surface. From the viewpoint of imparting durability to withstand repeated stretching operations, the median fiber diameter (P1) of the first fiber layer 1 is preferably 0.3 μm or more, more preferably 0.4 μm or more, and even more preferably 0.5 μm or more.

[0014] The second fiber layer 2 contains fibers with a median fiber diameter (P2) of 5 μm or more and 50 μm or less. The second fiber layer 2 has the above median fiber diameter, and thereby imparts sheet strength or rigidity to the entire fiber sheet 10 including the first fiber layer 1 and enhances resistance to tearing and abrasion without impairing the above-mentioned adhesive property of the first fiber layer 1. Such a second fiber layer 2 can be obtained by appropriately setting the median fiber diameter using a method commonly used for this type of article. For example, a nonwoven fabric obtained using a spunbond method can be mentioned.

[0015] The median fiber diameter (P2) of the second fiber layer 2 is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 25 μm or less, from the viewpoint of making the entire fiber sheet 10 thin and easy to stretch. From the viewpoint of improving resistance to tearing and abrasion, the median fiber diameter (P2) of the second fiber layer 2 is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 15 μm or more.

[0016] Furthermore, the ratio (P2 / P1) of the median fiber diameter (P2) of the second fiber diameter 2 to the median fiber diameter (P1) of the first fiber diameter 1 is preferably 1.5 or more, more preferably 10 or more, and even more preferably 20 or more, from the viewpoint of increasing the strength of the entire fiber sheet 10 while maintaining the adhesiveness of the first fiber layer 1 to the skin surface. Moreover, the ratio (P2 / P1) is preferably 170 or less, more preferably 150 or less, and even more preferably 100 or less, from the viewpoint of reducing the overall thickness of the fiber sheet and increasing the stretchability.

[0017] (Method of measuring median fiber diameter) (1) The fiber sheet 10 is peeled between the fiber layers to take out the fiber layer to be measured. This fiber layer is cut to 10 mm x 10 mm. This is attached to a sample stage for a scanning electron microscope (manufactured by Oken Shoji Co., Ltd.) via conductive carbon double-sided tape (manufactured by Oken Shoji Co., Ltd.). (2) The sample stage with the fiber layer attached is placed in a sputtering device (Ion Sputter E-1030, Hitachi High-Tech Corporation). The pressure is reduced to 6 Pa under an argon gas atmosphere, and platinum-palladium (Pt-Pd) deposition is performed. The distance between the fiber layer mounting surface and the Pt-Pd electrode is 30 mm, the deposition time is 80 seconds, and the current value during deposition is 30 mA. (3) The sample stage is placed in a scanning electron microscope (SEM) (Hitachi High-Tech Corporation, S-4300SE / N) and images are obtained in high-resolution mode (accelerating voltage: 5 kV, work distance: 10 mm, observation magnification 500x or 1000x). Images are obtained from a total of 15 locations on the same sample by changing the observation location. (4) From the observation image acquired in (3), the fiber diameter of the fiber layer is measured using image analysis software (WinRooF2015 manufactured by Mitani Shoji Co., Ltd.). From the measured fiber diameters of a total of 600 fibers, the number average diameter, the number 10% diameter (D10) (from the thin diameter side), the number 50% diameter (median diameter), and the number 90% diameter (D90) are tallied. Of these, the median diameter is taken as the representative value of the fiber diameter.

[0018] The first fiber layer 1 and the second fiber layer 2 contain the same material. The same material means a material whose repeating unit (monomer structure) has the same polymer structure. Specifically, the same material is selected from olefin resins, diene resins, urethane resins, and copolymers thereof. Since the first fiber layer 1 and the second fiber layer 2 contain the same material, the molecular structures of the resin components are similar to each other, and the fibers are highly compatible with each other. Therefore, the first fiber layer 1 and the second fiber layer 2 are easily fused together firmly, improving the integrity of the fiber sheet 10. The homogeneous material is selected from an olefin resin, a diene resin, a urethane resin, and copolymers thereof, and both the first fiber layer 1 and the second fiber layer 2 contain an elastomer and are thus elastic.

[0019] (Method of determining whether the first fiber layer 1 and the second fiber layer 2 contain the same material) Whether the first fiber layer 1 and the second fiber layer 2 contain the same material can be determined by peeling each fiber layer and measuring the resin composition contained in each fiber layer. The resin composition is subjected to various analyses such as nuclear magnetic resonance (NMR) analysis and infrared spectroscopy (IR) analysis, and the molecular skeleton structure and the functional group structure at the end of the molecular structure are identified based on the positions of each signal and spectrum obtained by these analyses. This identifies and specifies the type of resin contained in each fiber layer. The resin compositions specified for each fiber layer are compared to determine whether they contain the same material.

[0020] In the fiber sheet of the present invention, the first fiber layer 1 and the second fiber layer 2 adjacent to each other are both stretchable, but have high integrity. Due to this integrity, peeling is unlikely to occur at the interface between the first fiber layer 1 and the second fiber layer 2 when the fiber sheet 10 stretches. By suppressing peeling, the fiber sheet 10 as a whole has sheet strength or rigidity, and the entire sheet becomes stiff. The first fiber layer 1 is more likely to stretch together with the second fiber layer 2. This makes the fiber sheet 10 as a whole durable enough to withstand repeated stretching operations. That is, the fiber sheet 10 of the present invention is designed to stretch with the first fiber layer 1 and the second fiber layer 2 having high integrity and with the overall sheet strength or rigidity being high. Therefore, the first fiber layer 1 is less likely to twist or rub during the stretching behavior of the fiber sheet 10. In addition, shedding of the first fiber layer 1 is also suppressed. In this way, the fiber sheet 10 as a whole has improved elasticity and sheet strength, and even when elasticity is exhibited, resistance to tearing and abrasion is increased. Furthermore, the elasticity of the entire fiber sheet 10 enables the first fiber layer 1 to follow the shape and various changes (movements) of an object such as the skin surface, and can fully exhibit the above-mentioned adhesive properties even under such changes.

[0021] The fiber sheet 10 of the present invention is provided with rigidity due to the unity of the first fiber layer 1 and the second fiber layer 2, and the handling properties are improved. That is, the fiber sheet 10 has stiffness compared to a fiber sheet having only the first fiber layer 1 made of ultrafine fibers (FIGS. 2(A) and (B)), and has the effect of being easy to handle. For example, when a fiber sheet 10 is taken out from a state in which several fiber sheets 10 are stacked or from a state in which the fiber sheet 10 is stored in a packaging bag or container, etc., and used (for example, applied to the skin surface), the stiffness significantly affects the ease of taking out the fiber sheet 10. In addition, when taken out, the fiber sheet 10 of the present invention is less likely to curl up than a fiber sheet having only the first fiber layer 1 (for example, FIG. 2(A)), and the handling properties are improved. This allows the fiber sheet 10 to be neatly applied to an object such as the skin surface without wrinkles.

[0022] The above-mentioned homogeneous material is preferably an olefin-based resin from the viewpoints of improving the integrity of the first fiber layer 1 and the second fiber layer 2 and improving the stretchability of the fiber sheet 10 including them. By using an olefin-based resin, the first fiber layer 1 and the second fiber layer 2 are less likely to peel off from each other when the fiber sheet 10 is stretched. From the same viewpoint, the first fiber layer 1 preferably contains a low-crystalline olefin resin. The term "low-crystalline" means that the crystallinity is 10.5% or less, and can be measured by the following method. When the first fiber layer 1 contains a low-crystalline olefin resin, the first fiber layer 1 itself becomes easily stretchable. When the first fiber layer 1 contains a low-crystalline olefin-based resin, the mass proportion of the low-crystalline olefin-based resin in the first fiber layer 1 is preferably 70 mass% or more, more preferably 80 mass% or more, even more preferably 90 mass% or more, even more preferably 92 mass% or more, and even more preferably 94 mass% or more.

[0023] (Method for determining whether the first fiber layer 1 contains a low-crystalline olefin resin) The resin composition constituting the first fiber layer 1 is subjected to various analyses such as NMR analysis and IR analysis. Based on the signals and the positions of the spectra obtained by these analyses, the molecular skeleton structure and the functional group structure at the terminals of the molecular structure are identified. This allows the type of resin contained to be identified and specified. Next, crystallinity is measured using differential scanning calorimetry. The total heat of fusion obtained when the resin composition is heated is divided by the heat of fusion of perfect crystals. If this value is less than 10.5%, it is determined that the resin contains a low-crystalline olefin resin.

[0024] From the viewpoint of enhancing the integrity of the first fiber layer 1 and the second fiber layer 2 and enhancing the stretchability of the fiber sheet 10 including these, specific examples of the above-mentioned homogeneous material include the following. That is, examples of olefin resins include polypropylene (hereinafter referred to as PP) and polyethylene. Examples of low-crystalline olefin resins include α-olefins, such as polypropylene with controlled stereoregularity (polypropylene polymerized with controlled stereoregularity using a metallocene catalyst). Examples of the diene resin include polybutadiene and polyisoprene. The urethane resin includes polyurethane. Copolymers of olefin resins, diene resins, and urethane resins include ethylene-propylene copolymers, ethylene-1-butene copolymers, ethylene-1-octene copolymers, propylene-1-butene copolymers, propylene-1-octene copolymers, ethylene-isoprene copolymers, ethylene-butadiene copolymers, propylene-isoprene copolymers, propylene-butadiene copolymers, ethylene-propylene-isoprene copolymers, and ethylene-propylene-butadiene copolymers.

[0025] In the fiber sheet 10, in a structure in which the first fiber layer 1 and the second fiber layer are both integrated and have elasticity, the elongation rate in one direction Y (also called Y direction) in the planar direction is preferably 20 to 100, and the elongation rate in a direction X (also called X direction) perpendicular to the one direction is preferably 0 to 30. The difference in elongation rate between these two mutually perpendicular directions gives the fiber sheet 10 directional elasticity. The one direction Y and the direction X perpendicular to the one direction Y are appropriately determined depending on the intended use of the fiber sheet 10. For example, the longitudinal direction of the fiber sheet 10 may be the one direction Y, and the width direction may be the direction X perpendicular to the one direction Y. In this case, it is preferable that the longitudinal direction of the fiber sheet 10 is aligned with the elasticity direction required for the article to which it is applied.

[0026] (Method of measuring elongation rate) The above-mentioned elongation percentage of the fiber sheet 10 refers to the elongation of a test piece having a width of 20 mm and a length of 70 mm, fixed with a gripping distance of 50 mm, when a tensile load of 1.2 N is applied, expressed as a percentage (%) of the gripping distance of 50 mm. More specifically, the length between the grips of the test piece before the elongation test is taken as L0, and the length between the grips of the test piece at the time of breaking elongation is taken as LB, and the elongation percentage (%) can be calculated as 100×(LB−L0) / L0. The measurement is performed along any two mutually perpendicular directions in the sheet plane of the fiber sheet 10, for example, along the longitudinal direction and the width direction perpendicular to the longitudinal direction.

[0027] The fiber sheet 10 has directional elasticity due to the difference in elongation rate, and the elasticity can be appropriately controlled according to the intended use, reducing excessive stretching in directions where elasticity is not required and reducing excessive loads associated with stretching, thereby more effectively preventing twisting, abrasion, and tearing of the first fiber layer 1. For example, when the fiber sheet 10 is made into a glove, it is preferable that the stretchability in the length direction of the fingers is large and the stretchability in the width direction perpendicular to the length direction is small, which makes it possible to provide a glove that fits closely to the tips of the fingers and webs of the user. On the other hand, when the fiber sheet 10 is made into gloves, it is also preferable to make the stretchability small in the length direction of the fingers and large in the width direction perpendicular to the length direction. This makes it possible to provide gloves that have a high adhesion according to the thickness of the user's fingers when wearing the gloves made of the fiber sheet 10.

[0028] As described above, the fiber sheet 10 of the present invention contains ultrafine fibers and exhibits directional stretchability while at the same time exhibiting high resistance to tearing and abrasion.

[0029] From the viewpoint of further enhancing the above-mentioned effects, the elongation percentage (T1) of the fiber sheet 10 in one direction Y is preferably 20% or more, more preferably 25% or more, and even more preferably 30% or more. From the viewpoint of processing the fiber sheet into a desired shape and attaching it, the elongation percentage (T1) is preferably 100% or less, more preferably 80% or less, and even more preferably 60% or less. The elongation percentage (T2) of the fiber sheet 10 in a direction X perpendicular to the direction Y is preferably 0% or more from the viewpoint of continuously transporting the fiber sheet. From the viewpoint of continuously transporting the fiber sheet, the elongation (T2) is preferably 30% or less, more preferably 25% or less, and even more preferably 20% or less.

[0030] The absolute value |T1-T2| of the difference between the elongation percentage (T1) of the fiber sheet 10 in one direction Y and the elongation percentage (T2) of the fiber sheet 10 in the direction X perpendicular to the one direction Y is preferably 0 or more, more preferably 10 or more, and even more preferably 20 or more, from the viewpoint of clarifying the directionality of the elasticity of the fiber sheet 10 and more effectively suppressing twisting, abrasion, and tearing of the first fiber layer 1. From the viewpoint of improving the fit of the fiber sheet to an object such as the skin, the absolute value of the difference |T1-T2| is preferably equal to or less than 70, more preferably equal to or less than 60, and even more preferably equal to or less than 50. Thereby, for example, when the fiber sheet 10 is applied to gloves, the elongation rates in two perpendicular directions in the gloves can be balanced to make the gloves easier to put on.

[0031] The directionality of the elasticity of the fiber sheet 10 is determined mainly by the second fiber layer 2 rather than the first fiber layer 1. The first fiber layer 1 contains the ultrafine fibers described above, and is formed by directly spinning and depositing a resin solution or a resin melt using, for example, an electrospinning method, so that it is difficult to form a directionality of elasticity. Therefore, it is preferable to give the directionality of elasticity of the fiber sheet 10 mainly by the second fiber layer 2. In addition, since the directionality of elasticity of the fiber sheet 10 is determined mainly by the second fiber layer 2, it is possible to suitably control the second fiber layer 2 to stop stretching before the first fiber layer 1 breaks when the fiber sheet 10 is stretched. The directionality of elasticity of the second fiber layer 2 can be determined, for example, by stretching in the conveying direction and cooling and solidifying during the conveying process, to form a second fiber layer that does not have elasticity in the conveying direction but has elasticity in the perpendicular direction.

[0032] From the viewpoint of further increasing the strength of the first fiber layer 1 itself in the fiber sheet 10, the ratio of the number of fusion points (for example, the enclosed areas with symbols D4, D14, and D1 in FIG. 4) to the number of fiber intersections in a field of view of 0.128 mm×0.096 mm in the SEM image of the first fiber layer 1 is preferably 50% or more, more preferably 70% or more. As a result, each of the ultrafine fibers in the first fiber layer 1 is fixed at the intersections, increasing the strength. That is, the integrity of the first fiber layer 1 itself is strengthened. For example, when the surface of the first fiber layer 1 on one side 10T of the fiber sheet 10 is traced with a finger, the fibers are less likely to fluff, and fiber dropout is suppressed. In addition, since the bonding area is suppressed at the fusion points at the fiber intersections, the excessive increase in the rigidity of the first fiber layer 1 itself is suppressed compared to surface fusion, and softness is maintained, and the above-mentioned adhesive property is easily expressed.

[0033] (The ratio of the number of fusion points to the number of fiber intersections) The same operations as those in (1), (2), and (3) in the above section (Method of measuring median fiber diameter) are performed to obtain SEM observation images of the fiber layer to be measured at a magnification of 1000 times. The same sample is measured at a total of five locations by changing the observation location. A total of five observation images are obtained by focusing on the sample surface side for each location. The image quality is 0.128 mm in width and 0.096 mm in height. From the obtained observation images, the fiber intersections are marked using image analysis software (WinRooF2015 made by Mitani Shoji Co., Ltd.), and the number of fusion points at the fiber intersections is recorded. The ratio of the number of fusion points to the total number of fiber intersections is calculated using the following formula (I). This evaluation is performed by two people, an observer and a recorder. The number of fiber intersections is tallied by the observer's manual marking process on the above image analysis software. Regarding the fusion points, the recorder tallies the fiber intersections that the observer has determined to be fusion points according to the definition of fusion points below. Percentage of fusion points [%] = Number of fusion points / Total number of fiber intersections × 100 (Formula (I)) The fiber intersections and the fusion points of the fiber intersections are defined as follows. (Fiber intersection) In the SEM observation image of the fiber layer to be measured, the image itself is enlarged three times (300%) on a 410 mm × 260 mm monitor. In this case, a focused image is selected within a range in which the width between the boundaries of the fiber shape (fiber width confirmed in the observation image) does not exceed 1 mm. The fiber intersections are defined as the points where they cross, or the points where they do not cross but are in contact (contact), or the points where one fiber branches off in the middle (e.g., the boxed areas D4, D14, and D1 in Figure 4). If two or more fibers shown in the image are in contact with each other in the whole or part of the image capture area over the longitudinal direction to form a fiber bundle, these are also defined as fiber intersections (e.g., the boxed area D5 in Figure 4). For example, if there is a point in the observation image where four fibers are lined up without any gaps, the number of fiber intersections is determined to be three. In addition, due to the characteristics of the fiber layer, there is a depth due to the thickness of the fiber layer on the side closer to the detector (surface side in the specimen thickness direction) and the side farther away (sample stage side in the specimen thickness direction) in SEM observation. Therefore, even if the fibers appear to cross in the observation image, they may not be in contact with each other. As described above, when the image itself is enlarged three times (300%) on a 410 mm x 260 mm monitor, multiple fibers that are in focus within a range where the width of the boundary line of the fiber shape does not exceed 1 mm are considered to be in the same positional relationship in the thickness direction (depth) of the specimen. The intersections of the fibers selected in this way are considered to be fiber intersections according to the above definition. (Fusion points at fiber intersections) Among the intersections defined above, (i) a point where the boundary line between two or more fibers related at the intersection is not clearly visible (e.g., the area enclosed by reference symbol D4 in FIG. 4), and (ii) a point where the width between the boundary lines of one or more fibers related at the intersection is wider than the width between the boundary lines at the other points (e.g., the area enclosed by reference symbol D16 in FIG. 4) are defined as fusion points at fiber intersections. When the sheet is in a laminated state, the fiber layers are peeled off, and the fiber layer to be measured is taken out and subjected to the above operation.

[0034] The fiber sheet 10 has the above-mentioned elasticity, while maintaining the integrity of the first fiber layer 1 and the second fiber layer 2, and has high strength. This strength is indicated as breaking strength. In relation to the above-mentioned elasticity and the relationship with the resistance of the first fiber layer 1 to abrasion and tearing during the elastic behavior, the breaking strength is preferably set to the following range in the two directions X and Y showing the above-mentioned elongation. The breaking strength in the Y direction is preferably 1 N / 20 mm or more, more preferably 2 N / 20 mm or more, and even more preferably 2.5 N / 20 mm or more, from the viewpoint of obtaining resistance to elongation. The breaking strength in the X direction is preferably 1 N / 20 mm or more, more preferably 3 N / 20 mm or more, and even more preferably 5 N / 20 mm or more, from the viewpoint of facilitating transport of the fiber sheet.

[0035] (Method of measuring breaking strength of fiber sheet 10) The breaking strength of the fiber sheet 10 is measured by fixing a test piece 20 mm wide and 70 mm long with a gripping distance of 50 mm and stretching it at a tensile speed of 300 mm / min, and measuring the maximum load until the test piece breaks. The measurement temperature is 23°C.

[0036] In the fiber sheet 10, it is preferable that the fibers of the first fiber layer 1 and the second fiber layer 2 at the interface between them are fused to each other from the viewpoint of improving the integrity of the fiber sheet 10 (for example, fused points 32 in FIG. 5(A)). It is also preferable that the fibers at the interface are bonded to each other at fused points at the intersections of the fibers while maintaining their fiber shapes, in order to prevent the rigidity of the fiber sheet 10 from becoming excessively high. The fusion means that the resin components contained in the first fiber layer 1 and the second fiber layer 2 are melted by heat and bonded (thermal bonding, etc.). Since the first fiber layer 1 and the second fiber layer 2 contain the same material with high compatibility as described above, the fusion at the interface becomes stronger. This further improves the integrity of the first fiber layer 1 and the second fiber layer 2 while maintaining the softness and adhesion to the skin surface, etc., on one surface side 10T of the first fiber layer 1 itself. In particular, during the expansion and contraction behavior of the fiber sheet 10, peeling at the interface between the first fiber layer 1 and the second fiber layer 2 can be more effectively suppressed, and the followability of both layers becomes better (for example, Fig. 5 (A) to (B)). By suppressing peeling, it is possible to more effectively prevent twisting, wrinkles, abrasion, and tearing of the first fiber layer 1 caused by peeling. In addition, further improvement in integrity improves the above-mentioned handleability of the fiber sheet 10.

[0037] From the viewpoint of further improving the above-mentioned action, the fusion strength at the interface is preferably 0.01 N / 20 mm or more, more preferably 0.1 N / 20 mm or more, and even more preferably 0.2 N / 20 mm or more. Furthermore, the strength of the fusion at the interface is practically 10N / 20mm or less.

[0038] (Method of measuring fusion strength at the interface between the first fiber layer and the second fiber layer 2) It is measured by the following means. An adhesive tape is applied to the surface of the first fiber layer 1 of the fiber sheet, and the tape is T-peeled using a tensile tester. This allows the strength of fusion between the fibers of the first fiber layer 1 and the second fiber layer 2 at the interface between the two layers to be measured. The greater the number of fusion points at the interface between the first fiber layer and the second fiber layer, the greater the resistance to T-peel. An adhesive tape (adhesive strength: 4.4 N / 10 mm) is applied to the surface side of the first fiber layer 1, and a test piece 20 mm wide and 100 mm long is prepared. The end of the tape on the longitudinal side is peeled off, and the end of the tape and the fiber sheet are pulled with a gripping distance of 50 mm and a pulling speed of 100 mm / min, and the test force at which the tape peels off from the fiber sheet is measured. Of the test forces obtained, the average value of the test forces where the gripping tool travels a distance of 30 mm or more and 80 mm or less from the initial position is taken as the strength of the fusion, i.e., the fusion force.

[0039] The fusion points at the fiber intersections in the first fiber layer 1 and the fusion points between the fibers at the interface between the first fiber layer 1 and the second fiber layer 2 are easily formed when the first fiber layer and the second fiber layer contain the same material as described above. They can be formed as follows. On the surface of the second fiber layer 2, a resin solution or resin melt using the same material as described above is discharged from a nozzle by, for example, an electrospinning method. The spun fibers (constituent fibers of the first fiber layer 1) formed by the discharge are collected on the second fiber layer 2 in a state of high temperature and fluidity. As a result, the spun fibers can be collected in a state in which they are fused at the intersections, and the spun fibers and the fibers of the second fiber layer 2 are integrated in a fused state. By collecting such spun fibers, the first fiber layer 1 is formed, which forms a network having fusion points at the fiber intersections described above. At the same time, fusion points can be formed between the fibers of the first fiber layer 1 and the second fiber layer 2 at the interface between them. The temperature at which the spun fibers are made to have fluidity is appropriately set depending on the resin raw material used. For example, when a low-crystallinity PP resin is used as the resin raw material of the first fiber layer 1, it is preferable to collect the spun fibers in a range of 40°C to 70°C at which the resin changes to a rubber state. In addition, it is preferable to heat and maintain such a temperature for the second fiber layer 2, which serves as a receiver for the collected fibers. In addition to the above-mentioned methods, the above-mentioned fusion points can also be formed by heat sealing. From the viewpoint of preventing the thermal shrinkage of the elastomer of the fiber and the film formation due to the melting of the resin, as described above, fusion during spinning, which requires less time and fewer exposures to heat, is more preferable.

[0040] In the fiber sheet 10, the basis weight of the first fiber layer 1 is 1 g / m 2More than 8g / m 2 The following is preferred. By having the basis weight of the first fiber layer 1 within this range, the first fiber layer 1 can maintain the aforementioned softness, adhesion to the skin surface, etc., and uniformity of the formulation liquid film accompanied by capillary force, and can be made strong without impairing these properties. Furthermore, in a first fiber layer 1 whose basis weight is suppressed within the above range, the number of ultrafine fibers with the aforementioned median fiber diameter is reduced accordingly, and the number of fiber voids is also reduced. This suppresses light scattering due to the presence of the fiber voids, and makes the first fiber layer 1 more transparent. From the viewpoint of increasing the capillary force and the strength, the basis weight of the first fiber layer 1 is set to 1 g / m 2 More than 1.5 g / m is preferable. 2 More preferably, 2 g / m 2 The above is more preferable. From the viewpoint of further improving the softness and adhesion to the skin surface, the basis weight of the first fiber layer 1 is set to 8 g / m 2 Less than 6 g / m is preferable. 2 Less than 5 g / m is more preferable. 2 The following is even more preferred:

[0041] In the fiber sheet 10, the basis weight of the second fiber layer 2 is 8 g / m 2 More than 50g / m 2 The following is preferred. When the basis weight of the second fiber layer 2 is within this range, the strength of the entire fiber sheet 10 can be further increased, and resistance to tearing and abrasion can be further improved. In addition, in the second fiber layer 2 having a basis weight within the above range, the number of fibers having the above-mentioned median fiber diameter is reduced. In order to further increase the strength of the entire fiber sheet 10, the basis weight of the second fiber layer 2 is set to 8 g / m 2 More than 15g / m is preferable. 2 More preferably, 20 g / m 2 The above is more preferable. In order to maintain the softness and adhesion to the skin surface of the first fiber layer 1, the basis weight of the second fiber layer 2 is set to 50 g / m 2 Less than 40 g / m is preferable. 2 Less than 30 g / m is more preferable. 2 The following is even more preferred:

[0042] Such a fiber sheet 10 can be used in various articles. For example, it can be used in bandages, dressings, cylindrical objects, gloves, etc., which are used by contacting the skin surface. Specific examples of the cylindrical objects include supports, finger cots, etc. In such an article, it is preferable that the fiber sheet 10 has unidirectional stretchability, that is, the fiber sheet 10 is preferably applied to the article so as to stretch along the stretch direction of the unidirectional Y direction. The "elasticity in one direction" refers to the direction in which the difference in elongation between two mutually perpendicular directions, measured by applying a load of 1.2 N to a sample based on the above-mentioned (method of measuring elongation), is 20% or more and the elongation is large. In the fiber sheet 10, the two mutually perpendicular directions are the one direction Y and the direction X perpendicular to the one direction Y. EXAMPLES

[0043] The present invention will be described in more detail below based on examples, but the present invention is not limited thereto. In the examples, "parts" and "%" expressing mass are all based on mass unless otherwise specified. "←" means that the content is the same as the column to the left. "-" means that there is no value or the like corresponding to that item.

[0044] Example 1 The second fiber layer 2 having the median fiber diameter and basis weight shown in Table 1 was formed by the spunbond method using the resin raw material PP. A resin melt was prepared using the resin raw material PP, and spun by electrospinning. At that time, the space between the spinning nozzle and the collector was heated to 40°C or higher by hot air ejected from around the spinning nozzle, and the spun fibers were collected on the second fiber layer 2 in a fluid state. The distance between the nozzle and the collector was 300 mm. In this way, the first fiber layer 1 was formed with the median fiber diameter and basis weight shown in Table 1. By the above-mentioned production method, fusion points were formed at the fiber intersections in the first fiber layer 1, and fusion points were formed between the fibers of the first fiber layer 1 and the second fiber layer 2 at the interface between the two layers. This resulted in the production of a stretchable fiber sheet sample of Example 1 in which the first fiber layer 1 and the second fiber layer 2 were firmly integrated. The fiber sheet sample of Example 1 thus obtained was cut out into a rectangle measuring 100 mm in the machine direction (MD) during the production of the long second fiber layer 2 and 20 mm in the cross direction (CD) perpendicular to the MD. In other words, the MD and CD directions correspond to the above-mentioned direction X and direction Y. In the obtained fiber sheet sample, the difference between the elongation percentage in the MD direction and the elongation percentage in the CD direction was 25 percentage points, as shown in Table 1. That is, the directionality of the stretchability in Example 1 was in the MD direction.

[0045] Example 2 A fibrous sheet sample of Example 2 was prepared in the same manner as in Example 1, except that the basis weight of the first fibrous layer 1 was as shown in Table 1.

[0046] Comparative Example 1 The first fiber layer 1 produced in Example 1 was used alone as a fiber sheet sample of Comparative Example 1.

[0047] Comparative Example 2 The second fiber layer 2 produced in Example 1 was used alone to prepare a fiber sheet sample of Comparative Example 2.

[0048] The following tests were carried out on the fiber sheet samples of each of the Examples and Comparative Examples. (1) Elongation rate (under 1.2N load) Based on the above-mentioned (Method of measuring elongation), the elongation of each fiber sheet sample was measured under a load of 1.2 N. The elongation was measured in two directions of each fiber sheet sample, the MD direction and the width direction perpendicular to the MD direction. (2) Breaking strength The measurement was performed based on the above-mentioned (Method of Measuring the Breaking Strength of the Fiber Sheet 10). (3) Fusion strength The measurement was performed based on the above-mentioned (method of measuring the fusion strength at the interface between the first fiber layer 1 and the second fiber layer 2). (4) Compressive strength Ten test pieces S, each 20 mm wide and 100 mm long, were stacked together, with both ends S1 and S2 overlapping by 20 mm to create a ring-shaped test piece Q (Figs. 6(A) and (B)). S1 and S2 were fixed in place using a stapler or similar tool. A compression test was performed on the width direction X of the test piece Q using two flat plates W1 and W2, each 30 mm or larger in diameter, at a compression speed of 10 mm / min (Fig. 6(C)). The maximum compression load in the compression test was recorded as the compression strength. The higher the compression strength, the higher the rigidity of the sheet and the better the sheet's handleability.

[0049] [Table 1]

[0050] In Comparative Example 1, the elongation percentage could not be measured because the breaking strength of the fiber sheet was 1.2 N or less. In other words, when a load of about 1.2 N was applied, the sheet broke and could not maintain its elongation. In contrast, in Examples 1 and 2, the elongation percentages were as shown in Table 1, and stretchability was exhibited. Moreover, Examples 1 and 2 both had higher breaking strength than Comparative Example 1. Therefore, it is understood that Examples 1 and 2 have higher resistance to breaking than Comparative Example 1. Moreover, it is understood that Examples 1 and 2 have a fusion strength between the first and second fiber layers, which results in high resistance to abrasion. In addition, Examples 1 and 2 both had higher compressive strength than Comparative Examples 1 and 2. This, together with the fact that they had an integrated laminate structure with the above-mentioned fusion strength, shows that Examples 1 and 2 had better handleability than Comparative Example 1, which had only the first fiber layer 1, and Comparative Example 2, which had only the second fiber layer 2. From the above, it was found that the fiber sheet of the present invention exhibits stretchability and at the same time has high resistance to tearing and abrasion. In addition, it was found that the fiber sheet of the present invention also has excellent handleability. [Explanation of symbols]

[0051] 1. First fiber layer 2 Second fiber layer 10 Fiber sheet

Claims

1. A fiber sheet having a first fiber layer having a median fiber diameter of 0.3 μm or more and 5 μm or less and a second fiber layer adjacent thereto having a median fiber diameter of 5 μm or more and 50 μm or less, the first fiber layer and the second fiber layer contain the same material, and the same material is selected from an olefin resin, a diene resin, a urethane resin, and a copolymer thereof; The fiber sheet has an elongation percentage of 20 to 100 in one direction and an elongation percentage of 0 to 30 in a direction perpendicular to the one direction.

2. the identical material is an olefin-based resin, The fibrous sheet according to claim 1 , wherein the first fibrous layer contains a low-crystalline olefin-based resin.

3. 3. The fiber sheet according to claim 1, wherein the first fiber layer has a ratio of fusion points to fiber intersection points in a 0.128 mm x 0.096 mm field of view of a scanning electron microscope image of 50% or more.

4. The first fiber layer has a basis weight of 1 g / m ２ 8g / m or more ２ 3. The fiber sheet according to claim 1, wherein:

5. The second fiber layer has a basis weight of 8 g / m ２ 50g / m or more ２ 3. The fiber sheet according to claim 1, wherein:

6. 3. An adhesive bandage, a dressing, a cylindrical body, or a glove comprising the fiber sheet according to claim 1 or 2.

7. 7. The adhesive bandage, dressing, cylindrical body or glove according to claim 6, which has unidirectional stretchability.

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