Nonwoven fabric, fiber product comprising same, and sheet

Abstract

A non-woven fabric characterized by having a thickness of 30.0 [mu] m or less and a toughness value of 0.50 or more, said toughness value being calculated as the integration of the specific tensile strength and the square root of the tensile elongation. The present invention relates to a nonwoven fabric having excellent mechanical properties despite being a thin film, and provides a thin film nonwoven fabric having excellent processability.

Description

Technical Field

[0001] This invention relates to thin-film nonwoven fabrics with excellent mechanical properties. Background Technology

[0002] Due to their fine and long shape, fibers have various characteristics and are therefore widely used not only in clothing but also in industrial materials. In recent years, as people's lives have become more affluent, they have demanded fiber products with higher functions.

[0003] As a way to effectively utilize fiber form, there is nonwoven fabric obtained by overlapping fibers in three dimensions and bonding them together through mechanical / chemical / thermal methods. It is a raw material characterized by a porous structure with gaps between the fibers.

[0004] As an effective way to utilize this porous structure, there are membranes that filter / separate desired substances and substrates that impregnate / support materials that cannot maintain their shape on their own. However, with the increasing demand for miniaturization, lightweighting, and high performance in products using these materials, i.e., various modules, there is also a demand for thin-film nonwoven fabrics as constituent components.

[0005] To achieve the thin-film production of nonwoven fabrics, the amount of constituent fibers per unit area, i.e., the basis weight (g / m²), needs to be reduced. 2 The method is effective, but as the amount of constituent fibers decreases, the uniformity of the nonwoven fabric deteriorates, which can easily lead to product defects. As a method to obtain nonwoven fabrics with excellent uniformity even though they are thin films, research / technology development to make the constituent fibers extremely fine is underway.

[0006] Patent document 1 proposes a technology related to thin-film nonwoven fabrics obtained by wet papermaking using ultrafine fibers as the main fibers. In microfibers with a diameter of a few μm, the number of constituent fibers increases by more than five times compared to general fibers with a diameter of tens of μm. Even in the case of fibers with a very small amount of constituent fibers, which are prone to defects caused by uniformity deterioration, the number of constituent fibers is only a few g / m. 2 The low basis weight allows for the stable production of high-quality thin-film nonwovens. Furthermore, by combining the densification of the nonwoven structure caused by the ultrafineness of the constituent fibers with the fiber reduction effect caused by the low basis weight, thin-film nonwovens with a thickness of less than 20 μm can also be obtained.

[0007] Patent document 2 proposes a technology related to wet papermaking of thin-film nonwoven fabrics using ultrafine fibers with further refined fiber microfibers as the main fibers. By using nanofibers with fiber diameters reduced to their limits, the number of fibers is increased by hundreds of times compared to fibers with a diameter of tens of μm, achieving excellent uniformity. Furthermore, through structural densification caused by ultrafine microfibers, a density of 10 g / m³ can be obtained.2 A low-basic-weight thin-film nonwoven fabric with a thickness of about 20 μm.

[0008] Patent document 3 proposes a technology related to thin-film nonwoven fabrics obtained by wet papermaking using microfibers as the main fibers and thermo-adhesive fibers as the bonding fibers. This technology involves melting the thermo-adhesive fibers during the thermal bonding process without leaving a fiber skeleton, thus firmly bonding the nanofibers that serve as the main fibers. By eliminating the coarse-diameter bonding fiber skeleton, the structural densification effect caused by the microfibers becoming ultrafine becomes significant, resulting in a density of 10 g / m³. 2 The low basis weight of approximately 10 μm enables the fabrication of ultrathin films.

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: Japanese Patent Application Publication No. 60-38193

[0012] Patent Document 2: International Publication No. 2008 / 130020

[0013] Patent Document 3: Japanese Patent Application Publication No. 2023-69101 Summary of the Invention

[0014] The problem that the invention aims to solve

[0015] Patent Document 1 utilizes the increased number of constituent fibers and denser structure resulting from the extreme fineness of the main fibers to achieve both thin-film properties and excellent uniformity in nonwoven fabrics through low-basic-weight wet papermaking. However, even with extreme fineness of the constituent fibers, the fiber diameter is at most only about half that of ordinary fibers, resulting in a limited increase in the number of fibers, which is only a few g / m². 2 Due to its low basis weight, the mechanical properties are extremely deteriorated. As a result, for thin-film nonwoven fabrics with a thickness of less than 30 μm, breakage sometimes occurs due to tension variations in the modular process or contact with other components.

[0016] Patent Document 2 aims to emphasize the effects of increasing the number of constituent fibers and densifying the structure by applying nanofibers with fiber diameters reduced to the limit in the main fibers. However, in order to produce wet nonwoven fabrics with excellent uniformity, it is necessary to uniformly disperse the nanofibers in the papermaking solution, and to suppress entanglement between nanofibers, the fiber length needs to be extremely short, less than 1 mm. Therefore, the fiber length of the main fibers that form the skeleton of the nonwoven fabric becomes extremely short, resulting in fewer joint points between fibers. The stress applied to the nonwoven fabric cannot be smoothly transferred between fibers, and the mechanical properties are sometimes lower compared to general nonwoven fabrics. In addition to low mechanical properties, fiber shedding sometimes occurs, so it is sometimes necessary to improve the processability of raw materials and the permeability of processes.

[0017] Patent Document 3, similar to Patent Document 2, applies nanofibers to the main fibers and uses thermo-adhesive fibers in the bonding fibers to form a thin-film nonwoven fabric with excellent mechanical properties. In this technology, the bonding fibers melt without leaving a fiber skeleton to form an adhesive film that firmly bonds the nanofibers together, thereby suppressing breakage caused by fiber delamination. However, because the bonding fibers block the gaps between fibers, the porosity is extremely low, around 30%, sometimes impairing the effective utilization of the porous structure of the nonwoven fabric.

[0018] As mentioned above, although there are techniques for obtaining low-basis-weight and high-quality films of wet nonwoven fabrics by incorporating various ultrafine fibers into the constituent fibers, the small amount of constituent fibers makes them prone to becoming breakage points, leading to a tendency for reduced mechanical properties and sometimes limiting applicable manufacturing processes and molding techniques. Furthermore, the low mechanical properties of film nonwoven fabrics are a significant obstacle, making it technically difficult to achieve the leaps in miniaturization, lightweighting, and high performance required for various modules by forming ultra-thin films with extremely low basis weight.

[0019] Therefore, in nonwoven fabrics with low basis weight and very little constituent fiber content, it is desirable to have nonwoven fabrics that can take into account both film and mechanical properties.

[0020] Methods for solving problems

[0021] The aforementioned task was achieved through the following means. That is, (1) A nonwoven fabric, characterized in that the thickness is 30.0 μm or less, and the toughness value calculated as the product of the specific tensile strength and the square root of the tensile elongation is 0.50 or more.

[0022] (2) The nonwoven fabric described in (1) has a porosity of 50% or more.

[0023] (3) The nonwoven fabric according to (1) or (2) above is characterized in that the bonding area of ​​the unit fiber cross-sectional area of ​​the fibers constituting the nonwoven fabric is 3.00 or more.

[0024] (4) A fiber article comprising at least a portion of the nonwoven fabric described in (1) above.

[0025] (5) A sheet wherein resin or particles are filled in the nonwoven fabric described in (1) above.

[0026] (6) A solid electrolyte sheet, wherein a solid electrolyte is filled in the nonwoven fabric described in (1) above.

[0027] The effects of the invention

[0028] This invention relates to nonwoven fabrics that, although thin films, possess excellent mechanical properties and can provide thin-film nonwoven fabrics with excellent processability. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the cross-sectional structure of a flat fiber, which is an example of the constituent fiber of the nonwoven fabric of the present invention.

[0030] Figure 2 This is a schematic diagram of the cross-sectional structure of a multilayer laminated fiber used as a raw material for flat fibers.

[0031] Figure 3 This is a schematic diagram showing the part where the main fibers and adhesive fibers are orthogonally bonded. Detailed Implementation

[0032] The present invention will now be described in detail with reference to preferred embodiments.

[0033] This invention relates to nonwoven fabrics, characterized in that, although they are thin films, they possess excellent mechanical properties. In order to achieve the purpose of this invention, it is necessary for the nonwoven fabric to be a thin film with a thickness of less than 30.0 μm, which is the first requirement of this invention.

[0034] The thickness of the nonwoven fabric mentioned here is calculated as follows.

[0035] Using a dial-type thickness gauge (PEACOCK DGN-250B, probe shape 25mm) The thickness of the nonwoven fabric of the present invention is measured in mm (with a graduation value of 0.0001 mm and a measuring force of 1.2 N or less), and the obtained value is converted to μm. The above operation is performed on one sample at any 5 positions, and the arithmetic mean of the samples is rounded to the second decimal place as the thickness of the nonwoven fabric of the present invention.

[0036] If the thickness is less than 30.0 μm, when the nonwoven fabric of the present invention is used as a diaphragm or substrate, the nonwoven fabric will not compress the space inside the module, and can meet the general requirements of miniaturization, lightweighting and high performance.

[0037] Furthermore, from this perspective, as the thickness of nonwoven fabrics decreases, the space-saving effect when applied to various modules becomes significant. If the thickness is below 15.0 μm, it is about half the thickness of general thin-film nonwoven fabrics. Even for high-performance modules such as small precision electronic devices that require higher thin-film properties, it can meet the requirements of miniaturization, lightweighting, and high performance, and can be listed as a preferred option.

[0038] Furthermore, a thickness of 8.0 μm or less is a more preferred range in this invention. Within this range, not only is the aforementioned space-saving effect further emphasized, but new effects are also achieved through the extreme thinness of the nonwoven fabric itself. That is, the bending stiffness of the nonwoven fabric is less than 1 / 50th of that of a conventional film (30 μm thick), thereby significantly softening it. When the nonwoven fabric of this invention is used as a substrate to composite with other materials, it can flexibly follow the surface shape of other materials to improve adhesion. Therefore, this is listed as a more preferred range.

[0039] Furthermore, a thickness of 5.0 μm or less is a particularly preferred range in this invention. Within this range, in addition to the significant space-saving effect, the flexural stiffness of the nonwoven fabric is less than 1 / 200th that of general-purpose film products, and it can also conform to complex shapes, thus improving its performance when used as a substrate. Additionally, if the thickness is 5.0 μm or less, when coating other materials with the nonwoven fabric of this invention as a substrate, even high-viscosity coating liquids can penetrate into the interior of the nonwoven fabric without compression due to its ultra-thin film structure. That is, it simplifies the combination with other materials, and therefore can be listed as a particularly preferred range.

[0040] On the other hand, as the thickness decreases, the nonwoven fabric becomes softer, and wrinkles and adhesion are easily generated during the manufacturing process. However, if the thickness is 0.5μm or more, there are no problems with process passability and actual use, and the purpose of this invention can be achieved.

[0041] As described above, the nonwoven fabric of the present invention, through the thickness of its ultrathin film, can not only achieve space saving as a diaphragm or substrate, but also improve the adhesion with other materials through the softness and permeability of the ultrathin film, which helps to achieve miniaturization, lightweighting and high performance of various modules.

[0042] The key to the nonwoven fabric of this invention lies in its ability to be stably manufactured without easily breaking during processing, despite being a thin film—a feat difficult to achieve with existing technologies. Mechanical properties thus become a crucial requirement. As an indicator of these mechanical properties, high toughness is a secondary requirement for the nonwoven fabric of this invention, with a toughness of 0.50 or higher.

[0043] The value of this toughness is calculated as follows.

[0044] The nonwoven fabric of the present invention is cut into specified dimensions (length 100mm × width 10mm) and tested using a tensile testing machine (e.g., Company The maximum point load (N / cm) was determined in units of UTM-III-100 under specified conditions (initial length 50 mm, specimen width 10 mm, tensile speed 100 mm / min). Five measurements were performed on samples cut in both the manufacturing direction (MD) and width direction (CD) of the nonwoven fabric. The arithmetic mean of these measurements was rounded to the third decimal place and taken as the tensile strength (N / cm) of the nonwoven fabric of this invention.

[0045] In addition, the strain under the maximum point load was measured in percentage (%). The arithmetic mean of these values ​​measured in MD and CD was rounded to the second decimal place and the result was taken as the tensile elongation (%) of the nonwoven fabric of the present invention.

[0046] It should be noted that a total of 10 specimen pieces (100mm long × 10mm wide) cut in various directions for the tensile test were weighed beforehand, and the area per unit area (m²) was calculated. 2 The weight (g) of the nonwoven fabric of the present invention is calculated by rounding the arithmetic mean of the components to two decimal places. 2 ).

[0047] Using the following formula, the specific tensile strength and toughness are calculated from the obtained tensile strength, elongation and basis weight. The third decimal place is rounded to the nearest whole number to be used as the specific tensile strength and toughness of the nonwoven fabric.

[0048] Specific tensile strength (N) m 2 / g tensile strength (N / cm) / basis weight (g / m³) 2 )

[0049] Toughness = Specific tensile strength (N) m 2 / g (cm) × Elongation at break 1 / 2 (% 1 / 2 )

[0050] The toughness referred to in this invention means the amount of tensile energy absorbed per unit of fiber in the nonwoven fabric. In the case of thin-film nonwoven fabrics, the disadvantage of being a fracture starting point due to the small amount of fiber is easily apparent. This toughness tends to be extremely reduced.

[0051] If the toughness is above 0.50, it can absorb more than twice the tensile energy of a thin-film nonwoven fabric formed from ultra-fine fibers, and is not easily broken due to tension during processing or contact with other components, thus meeting good processability requirements.

[0052] Furthermore, from this perspective, as toughness increases, the processability of nonwoven fabrics improves. If the toughness is 1.00 or higher, even in roll-to-roll processes where tension changes and friction with other components are likely to occur, the fabric is less prone to breakage and can be processed stably, thus making it a preferred option.

[0053] Furthermore, a toughness of 1.20 or higher is a more preferred range in this invention. If it is within this range, sufficient process tension can be applied during the roll-to-roll process, which can reduce wrinkles and end breakage during the process. Therefore, it can be listed as a more preferred range.

[0054] Furthermore, a toughness of 1.50 or higher is a particularly preferred range of the present invention. If it is within this range, it can sufficiently withstand the large process tension and friction applied during the high-speed roll-to-roll process, and therefore can be listed as a particularly preferred range.

[0055] Increased toughness allows for the absorption of greater tensile energy, which is desirable, but for nonwoven fabric structures where fibers are bonded together, a toughness of 4.0 or less is the practical upper limit.

[0056] As described above, the nonwoven fabric of the present invention, although a thin film, exhibits excellent mechanical properties, solving the problem of poor processability, such as breakage during processing, in existing thin film nonwoven fabrics. Furthermore, through these excellent mechanical properties, it is possible to form ultra-thin film nonwoven fabrics with extremely low basis weight, which is difficult in the prior art due to insufficient mechanical properties.

[0057] In this thin-film process, the basis weight and porosity of the constituent fibers of the nonwoven fabric have a great influence. From the viewpoint of fully utilizing the function of the porous structure while exhibiting the effects brought by the thin film, a low basis weight is preferred.

[0058] If the basis weight is 15.0 g / m 2 The following are examples of preferred materials that can fully utilize the porous structure of nonwoven fabrics and obtain thin film nonwoven fabrics with a thickness of 30.0 μm or less.

[0059] Additionally, if the basis weight is 5.0 g / m 2 The following are examples of ultrathin nonwoven fabrics with a thickness of 10.0 μm or less that utilize a porous structure, which can be formed as a more preferred range.

[0060] Furthermore, if the basis weight is 3.0 g / m 2 The following are examples of ultrathin films with a thickness of 5.0 μm or less that can be expected to improve adhesion and permeability with other materials, and can be described as particularly preferred.

[0061] It should be noted that, from the perspective of effectively utilizing the porous structure of nonwoven fabrics to achieve high functionality, a high porosity is preferred. The porosity referred to here is calculated using the following formula, rounded to the second decimal place, based on the aforementioned thickness and basis weight. It should also be noted that true density is calculated by extrapolating the material's density.

[0062] Apparent density (g / cm³) 3 ) = Basis weight (g / m 2 ) / thickness (μm)

[0063] Porosity (%) = (1 - apparent density (g / cm³)) 3 True density (g / cm³) 3 ))×100

[0064] If the porosity is above 50%, more than half of the volume can be used for filtration, separation, and impregnation of other materials. This large capacity of inter-fiber voids can be effectively utilized, making it easy to achieve a high level of functionality that other porous materials cannot reach. This can be listed as a preferred option.

[0065] Furthermore, a porosity of 55% or higher is preferred. If it is within this range, when particles, resins, etc. are impregnated in the nonwoven fabric, its high porosity allows it to carry a sufficient amount of particles and resins, and the performance of the impregnated components can be utilized even when the nonwoven fabric is used as the substrate.

[0066] Furthermore, with a porosity of 60% or more, when impregnating particles, resins, etc., it is easy to distribute the particles and resins to every corner of the nonwoven fabric. Even when processing by impregnation without applying high pressure, the performance of the impregnated components can be fully utilized. Therefore, it can be listed as a particularly preferred range.

[0067] Higher porosity allows for the carrying capacity of more particles and resin, which is desirable. However, for nonwoven fabrics where the structure is maintained by inter-fiber bonding, a porosity of less than 95% is a practical upper limit.

[0068] Although the nonwoven fabric of the present invention is a thin film, it exhibits excellent mechanical properties. With the main fibers forming the skeleton of the nonwoven fabric firmly and uniformly bonded together, deformation and damage to the nonwoven fabric structure relative to external forces can be suppressed, resulting in excellent dimensional stability during processing. Specifically, from the viewpoint of more firmly bonding the fibers constituting the nonwoven fabric and preventing dimensional changes in the nonwoven fabric caused by deformation or damage to the bonded areas, it is preferable that each main fiber is bonded over a large area. As an indicator, it is preferable that the bonding area per unit fiber cross-sectional area of ​​the fibers constituting the nonwoven fabric is 3.00 or more.

[0069] The bonding area per unit fiber cross-sectional area is calculated as follows.

[0070] The cross-section of the nonwoven fabric of the present invention is cut out using a razor or similar tool, and photographed using a scanning electron microscope (SEM) or similar tool at a magnification that allows observation of the cross-section of the fiber (main fiber) with its fibrous skeleton. It should be noted that the main fibers and the bonding fibers that bind them together exist mixed in the constituent fibers of the nonwoven fabric. However, the bonding fibers typically soften and flow during the manufacturing process, while the fiber skeleton deforms and disappears. Therefore, the main fibers and bonding fibers can be distinguished by the morphology of the cross-section. For the cross-section of a single main fiber present in the photographed image (refer to...),... Figure 3 Using image analysis software, the outer periphery of the cross-section is specified in μm. 2 The cross-sectional area of ​​the fiber is measured in units. This measurement is performed on 50 fibers, and the value obtained by rounding the arithmetic mean of them to the third decimal place is taken as the cross-sectional area of ​​the fiber in this invention.

[0071] Next, using the same method as above, determine the portion where the main fibers and bonding fibers (sometimes causing the fiber skeleton to disappear) are approximately orthogonal and bonded together (refer to...). Figure 3 The image is taken at a magnification that allows observation of the portion. To clearly define the contrast of the interface between the main fiber and the bonding fiber and to effectively perform the measurements described later, the fiber cross-section can be etched using an alkaline solution or similar method. In the direction perpendicular to the fiber axis of the main fiber, the length of the portion bonded between one main fiber and one bonding fiber is measured in μm using image analysis software, and this value is taken as the bonding length. In the calculation of the bonding area described in this invention, a bonding portion of the same length as the bonding length in the direction perpendicular to the fiber axis of the main fiber is considered to also be formed in the direction of the fiber axis of the main fiber, and the square of the aforementioned bonding length is taken as the bonding area in μm. 2 The bonding area is calculated per unit fiber cross-sectional area. This measurement is performed on 50 fibers, and the arithmetic mean of these fibers is rounded to the third decimal place as the bonding area of ​​the present invention. Based on the obtained fiber cross-sectional area and bonding area, the bonding area is calculated using the following formula, and the value is rounded to the third decimal place as the bonding area per unit fiber cross-sectional area of ​​the present invention.

[0072] Bonding area per unit fiber cross-sectional area = Bonding area (μm) 2 ) / fiber cross-sectional area (μm) 2 )

[0073] If the bonding area of ​​the unit fiber cross-sectional area is 3.00 or more, the main fibers that form the skeleton of the nonwoven fabric are firmly bonded over a large area by the bonding fibers. Even if an external force greater than imagined is applied due to the change in process tension, the nonwoven fabric structure will not deform and can exhibit excellent dimensional stability. This can be listed as a preferred range.

[0074] In addition, the bonding area per unit fiber cross-sectional area is more preferably 5.00 or more. If it is within this range, even if external force is concentrated on a part of the nonwoven fabric through contact with other components, the bonding point is not easily damaged, and external force can be transmitted to the whole nonwoven fabric, resulting in better dimensional stability.

[0075] Furthermore, since the bonding area per unit fiber cross-sectional area is 10.00 or more, even under the application of a sudden external force, the external force can be evenly distributed throughout the nonwoven fabric without deforming or breaking the bonding points. Therefore, it can be listed as a particularly preferred range.

[0076] A larger bonding area per unit fiber cross-sectional area results in a stronger bond, which is preferred. However, a bonding area per unit fiber cross-sectional area of ​​less than 500.00 is the practical upper limit.

[0077] As mentioned above, from the viewpoint of distributing external force evenly throughout the nonwoven fabric, in addition to the strong adhesion due to the large bonding area, the uniformity of the nonwoven fabric structure, such as the density distribution of the fibers, also has an impact. It is preferable to have a density distribution of fibers that is not visible to the naked eye, such as the absence of pinholes.

[0078] Especially in thin-film nonwoven fabrics like those of the present invention, due to the small amount of constituent fibers, regions without a single fiber, i.e., through-holes at the μm level, are formed in the thickness direction of the nonwoven fabric. Even deviations in the size of these through-holes can significantly affect the stress concentration of the nonwoven fabric. Therefore, the size of the through-holes in the nonwoven fabric is preferably uniform; specifically, the range of through-holes in the nonwoven fabric is preferably below 120 μm.

[0079] The range of the through holes in the nonwoven fabric is determined as follows.

[0080] The surface of the nonwoven fabric of the present invention was photographed using a scanning electron microscope (SEM) at a magnification that allows observation of more than 100 through-holes. It should be noted that through-holes, as referred to here, are areas where, when viewed from the surface of the nonwoven fabric, no fibers exist in the thickness direction and the area is surrounded by fibers. For the 100 through-holes present in the photographed images, the equivalent circle diameter was measured using WINROOF 2015 image analysis software manufactured by Mitani Corporation, rounded to the nearest integer in μm. The same operation was performed on 5 images, and the value obtained by subtracting the minimum equivalent circle diameter from the maximum value was taken as the range of through-holes in the present invention. It should be noted that in cases where there are no through-holes due to a large amount of constituent fibers, the range of through-holes is not calculated.

[0081] If the through-hole range of the nonwoven fabric is less than 120μm, then when an external force is applied to the nonwoven fabric, stress concentration will not occur around the large through-hole, and even the deformation of the microscopic nonwoven fabric structure will be suppressed. Therefore, it can be listed as a preferred range.

[0082] Furthermore, the through-hole range of the nonwoven fabric is more preferably 80 μm or less. Within this range, even when external forces are concentrated on a part of the nonwoven fabric due to contact with other components, the fibers around the through-holes of this size can evenly bear the external forces, resulting in superior dimensional stability. Moreover, by making the through-hole range of the nonwoven fabric 50 μm or less, even under the application of a sudden external force, the external force can be evenly distributed throughout the fabric without deformation of the nonwoven fabric structure; therefore, this range can be listed as particularly preferred.

[0083] The smaller the range of through-holes in a nonwoven fabric and the more uniform the size of the through-holes, the better. However, for nonwoven fabrics constructed by randomly laid fibers, a range of through-holes of 1 μm or more is the practical lower limit.

[0084] Furthermore, from the perspective of emphasizing good processability and high adhesion with other materials, the surface smoothness of nonwoven fabrics is preferred. As an indicator, the arithmetic mean roughness (Ra) of the nonwoven fabric surface is preferably 7.00 μm or less.

[0085] The arithmetic mean roughness (Ra) mentioned here is calculated as follows: The surface of the nonwoven fabric is observed using a laser microscope (Keeping Technology Co., Ltd., VK-X200), and the measurement is performed using analytical software (Keeping Technology Co., Ltd., VK-H1XA) according to JIS B0601:2013. This operation is performed on a single sample at any five locations, and the arithmetic mean is rounded to the third decimal place. This value is taken as the arithmetic mean roughness (Ra).

[0086] The arithmetic mean roughness (Ra) of the nonwoven fabric of the present invention is preferably 7.00 μm or less. If it is within this range, since there are no large bumps or depressions on the surface, there are no hooks on the surface, so it has good process passability, and can achieve high-quality integration by seamlessly bonding with other materials when composited.

[0087] If this view is further developed, the arithmetic mean roughness (Ra) of the nonwoven fabric surface is more preferably 5.00 μm or less, which further improves the adhesion when it is combined with other materials as a substrate, and also makes it more durable against peeling over time.

[0088] As the arithmetic mean roughness (Ra) of the nonwoven fabric surface decreases, the adhesion when combined with other materials is further improved, which is preferred. However, for nonwoven fabrics constructed by randomly laid fibers, an arithmetic mean roughness (Ra) of 0.50 μm or higher is a substantial lower limit.

[0089] The thickness and excellent mechanical properties of the ultrathin film of the nonwoven fabric of the present invention can be effectively achieved by the shape of the constituent fibers. As the fiber (main fiber) constituting the nonwoven fabric of the present invention, it is preferable to include one or more flat fibers with a flatness of 3 or more, wherein the flatness is the value obtained by dividing the length of the long axis of the fiber cross-section by the length of the short axis.

[0090] The term "flat fiber" as used here refers to fibers with a flat cross-section, where "flat" means a shape such as rectangular or elliptical where the length of the major axis differs from the length of the minor axis. Furthermore, the degree of flatness is defined as the flatness obtained by dividing the length of the major axis by the length of the minor axis.

[0091] The flatness mentioned in this invention is calculated as follows (also refer to...) Figure 1 ).

[0092] That is, nonwoven fabric is embedded with an embedding agent such as epoxy resin, the fiber cross-section is cut using a slicer equipped with a diamond blade, and the cross-section is photographed at a magnification that allows for cross-sectional identification using a scanning electron microscope (SEM). For the cross-section of a single fiber present in the photographed image, the maximum length of the cross-section is determined using image analysis software, and this value is taken as the length of the single fiber along its major axis, rounded to three decimal places in μm. Next, the length of the line segment orthogonal to the line segment of the maximum length at the midpoint of the maximum length is measured and intersected with the fiber cross-section; this value is taken as the minor axis length of the single fiber, rounded to three decimal places in μm. Using the major axis length and the minor axis length, the flatness of the single fiber is calculated using the following formula.

[0093] Flatness = Major axis length (μm) / Minor axis length (μm)

[0094] The above measurements were performed on 100 fibers, and the flatness of each fiber was calculated. The flatness of the arithmetic mean of the fibers was rounded to the first decimal place and taken as the flatness of the present invention.

[0095] The nonwoven fabric of the present invention preferably comprises one or more flat fibers with a flatness of 3 or more. When the fibers are stacked as a nonwoven fabric, due to the anisotropic cross-sectional shape of the fibers, the cross-sectional directions of the fibers are naturally consistent, and the short axis direction of the fiber cross-section preferentially faces the thickness direction of the nonwoven fabric, promoting film formation. Furthermore, by overlapping the flat fibers with consistent cross-sectional directions, the overlapping fibers make large-area contact in the form of "surfaces," exhibiting a strong binding force that is difficult to achieve through the point contact of ordinary circular cross-section fibers.

[0096] If this viewpoint is advanced, by increasing the flatness of the flat fibers constituting the nonwoven fabric, the selective orientation effect from the cross-sectional shape and the effect of increasing the contact area become more pronounced. Therefore, by including one or more flat fibers with a flatness of 8 or more, the short axis direction of the flat cross-section is highly aligned with the thickness direction of the nonwoven fabric, significant thinning and increased contact area can be expected, and thus this can be listed as a more preferred range.

[0097] Furthermore, when the fabric contains one or more flat fibers with a flatness of 15 or more, the fibers laid out while maintaining consistent orientation have a longer length relative to the surface direction of the nonwoven fabric. This strengthens the binding force between adjacent fibers, increasing the strength of the nonwoven fabric in both the manufacturing and width directions. Furthermore, when wet papermaking is chosen as the manufacturing method for the nonwoven fabric, the anisotropy of the cross-sectional shape significantly suppresses fiber entanglement during the mixing of the papermaking solution, dramatically improving the operational stability of the papermaking process, and thus maintaining a higher level of uniformity and quality of the nonwoven fabric. Therefore, a flatness of 15 or more can be considered a particularly preferred range in this invention.

[0098] Furthermore, as the flatness of the cross-section increases, there is a tendency for bending and cracking to easily occur in the long axis direction of the cross-section when external force is applied during the processing. However, if the flatness is less than 500, there is no problem in actual use, and the purpose of the present invention can be achieved.

[0099] It should be noted that, from the viewpoint of nonwoven fabric thinning and improving adhesion with other materials, it is preferable that the short axis length of the cross-section of the above-mentioned flat fibers is short, and the short axis length of the flat fibers constituting the nonwoven fabric of the present invention is preferably 2.00 μm or less.

[0100] The shorter the short axis length of the flat fibers used in the nonwoven fabric of the present invention, the thinner the thickness occupied by a single fiber when the flat cross-section is selectively oriented. This not only makes it easier to form a thinner nonwoven fabric, but also makes the fiber itself softer in the short axis direction. Therefore, through the synergistic effect of the thinning of both the constituent fibers and the nonwoven fabric, the adhesion to other materials can be further improved.

[0101] If the short axis length of the flat fiber used in the nonwoven fabric of the present invention is less than 2.00 μm, then due to the thin thickness occupied by a single fiber, it is easy to form a nonwoven fabric with an extremely thin film. Furthermore, due to the softening of the fiber itself, the fibers can be deformed softly one by one, thereby improving the adhesion when combined with other materials.

[0102] Furthermore, if the short axis length of the flat fibers used in the nonwoven fabric of the present invention is less than 1.00 μm, then even a nonwoven fabric with a thickness of less than 10 μm, which is difficult to achieve with ordinary fibers, can be easily formed, and the fibers are significantly softened. Even a local part of the fiber cross section can follow the shape of other composite materials to form a close fit. Therefore, this can be listed as a more preferred scope of the present invention.

[0103] Furthermore, if the short axis length of the flat fibers used in the nonwoven fabric of the present invention is less than 0.70 μm, it is also possible to easily form an extremely thin film nonwoven fabric with a thickness of less than 5 μm. Moreover, since the short axis length of the flat fibers is submicron, intermolecular interactions such as van der Waals forces can play a role, and even for fine and complex morphologies, a high degree of fit can be achieved. Therefore, this can be listed as a particularly preferred range of the present invention.

[0104] On the other hand, if the short axis length of the flat fiber becomes extremely short, the fiber becomes prone to breakage during the manufacturing process. However, if the short axis length of the flat fiber is 0.05 μm or more, there is no problem in the manufacturing process or in the actual use of the nonwoven fabric. This can be cited as the lower limit of the present invention.

[0105] It should be noted that, as the fibers forming the nonwoven fabric of the present invention, flat fibers having the aforementioned flatness and short axis length are preferably used for both the main fiber and the bonding fiber. By using flat fibers in both the main fiber and the bonding fiber, the cross-sectional directions of the fibers of both sides are aligned and densely overlapped, the bonding fiber softens and flows, thereby bonding the fibers together over a large area in the form of a "surface", achieving extremely strong bonding and fixation.

[0106] Furthermore, from the viewpoint of maximizing the utilization of the porous structure of the nonwoven fabric of the present invention to achieve high functionality, it is appropriate for the shape of the fiber cross-section to be distributed within a certain range. In the flat fibers used in the nonwoven fabric of the present invention, it is preferable that there is a deviation in the short axis length.

[0107] The deviation of the minor axis length in this invention is calculated as follows: the arithmetic mean and standard deviation are calculated using the minor axis lengths of the 100 fibers measured above. The standard deviation is divided by the arithmetic mean to obtain the coefficient of variation. The coefficient of variation is expressed as a percentage and rounded to the nearest integer.

[0108] Because the short axis lengths are moderately distributed, the cross-sectional shapes of the fibers are inconsistent. Therefore, when the fibers are laid into a nonwoven fabric, each flat fiber performs a different action, resulting in more uniform dispersion. From this perspective, in the nonwoven fabric used in this invention, the deviation in the short axis length of the flat fibers is preferably 10% or more. By falling within this range, each flat fiber performs a different action during the sheeting process, preventing bias and enabling more uniform dispersion.

[0109] In addition, if the deviation of the short axis length is more than 20%, the bending behavior of the fibers in the sheeting process will also be different for each fiber. The flat fibers that are the main fibers will not easily overlap each other, and the main fibers and bonding fibers will be bonded evenly to achieve effective bonding.

[0110] If this viewpoint is pursued further, the greater the deviation in short axis length, the more uniformly the flat fibers can be dispersed. However, when external forces are applied during manufacturing processes, the flat fibers tend to break easily due to the excessively short length of the short axis. Therefore, the deviation in short axis length is preferably 50% or less, which is the practical upper limit in this invention.

[0111] In the flat fibers used in the nonwoven fabric of the present invention, in addition to the uniform dispersion effect brought about by the difference in cross-sectional area of ​​each fiber, the three-dimensional barrier effect brought about by the concavity and convexity of the outer periphery can effectively open the flat fibers supplied before the sheeting process, and easily achieve uniform dispersion of fibers in the nonwoven fabric. Therefore, the concavity and convexity of the fiber cross-section is preferably 20% or more.

[0112] The unevenness mentioned in this invention is measured using the following method. First, using an image of the fiber cross-section, the lengths of the line segments orthogonal to the line segments of the maximum length intersecting the fiber cross-section are measured at points where the maximum length of the cross-section is divided into 10 equal parts. The arithmetic mean and standard deviation of these 10 lengths are calculated. The standard deviation is divided by the arithmetic mean and rounded to the nearest percentage. The resulting value is taken as the unevenness of a single fiber. The same measurement is performed on 10 fiber cross-sections, and the arithmetic mean of the unevenness of the 10 fibers is taken as the unevenness of this invention. By making this unevenness 20% or more, it is easy to open flat fibers into individual strands starting from the tiny gaps between fibers, and it is easy to achieve uniform dispersion in the sheeting process.

[0113] In addition, the high roughness enables good fiber opening between flat fibers, but as a range that does not cause the load to be concentrated in a part of the cross section and cause cracking, the roughness of 50% or less can be listed as a substantial upper limit in this invention.

[0114] It should be noted that the mechanical properties of the nonwoven fabric are achieved through bridging structures based on adhesion, friction, etc., between adjacent fibers. However, since this bridging structure is a force-transferring structure existing within the nonwoven fabric through inter-fiber interaction, given the same amount of fibers in the nonwoven fabric, finer fiber diameters and longer fiber lengths promote bridging structure formation and force transmission. In other words, a higher fiber length to fiber diameter ratio promotes bridging structure formation. As an indicator, in the flat fibers used in the nonwoven fabric of this invention, a high aspect ratio (the value obtained by dividing the fiber length by the minor axis length) is appropriate.

[0115] The length and width ratios mentioned in this invention are calculated as follows.

[0116] Images of the flat fibers are taken at a magnification that allows observation of more than 10 fibers whose full length can be measured using a microscope or similar instrument. The fiber lengths of 10 randomly selected fibers from the captured images are measured. The fiber length referred to here is the length along the longitudinal direction of one fiber from the 2D image, measured in mm using image analysis software. The arithmetic mean of these fiber lengths is rounded to two decimal places and taken as the fiber length of this invention. Using this fiber length and the calculated minor axis length, the following formula, rounded to the nearest decimal, is used to determine the aspect ratio of this invention.

[0117] Aspect ratio = Fiber length (μm) / Minor axis length (μm)

[0118] In the flat fibers used in the nonwoven fabric of the present invention, the aspect ratio is preferably 1000 or more. If it is within this range, a bridging structure is sufficiently formed between the fibers, and the strength of the nonwoven fabric is improved.

[0119] Furthermore, the aspect ratio of the flat fibers used in the nonwoven fabric of the present invention is more preferably 2000 or more. If it is within this range, it not only exhibits excellent mechanical properties as a nonwoven fabric, but also results in very little fiber shedding during the manufacturing process and excellent process passability.

[0120] As described above, the nonwoven fabric of the present invention is characterized by having excellent mechanical properties despite being a thin film. As an effective application of this feature (fiber products), representative applications include filters, products for removing harmful substances, battery separators, sound-absorbing materials, etc. Other applications include cosmetics, face masks, wiping cloths, etc.; medical applications such as scaffold materials for cell culture, artificial blood vessels, blood filters, etc.; and clothing applications such as jackets, skirts, pants, underwear, etc.

[0121] In particular, when the nonwoven fabric of the present invention is used as a diaphragm or substrate to form a sheet filled with resin or particles, not only can the miniaturization, lightweighting, and high performance of the module be achieved by saving space in the substrate, but also high-quality modules can be stably manufactured by utilizing the excellent mechanical properties of the substrate. As an example, adhesive tapes made by combining the nonwoven fabric of the present invention with an adhesive, polymer electrolyte membranes composited with polymer electrolytes, and functional membranes that are composited with functional particles and thus possess self-support and flexibility can be cited.

[0122] Furthermore, by using the nonwoven fabric of the present invention as a substrate to form a sheet filled with a solid electrolyte, even for a substrate of an ultrathin film that can suppress the decrease in ionic conductivity, the solid electrolyte can be endowed with self-support and flexibility to withstand manufacturing, thereby enabling the miniaturization, lightweighting, and high performance of all-solid-state batteries.

[0123] The following describes in detail an example of a method for manufacturing nonwoven fabrics according to the present invention.

[0124] The nonwoven fabric of the present invention has the characteristic of exhibiting excellent mechanical properties despite being a thin film, and can take either long fiber or short fiber form. Among these manufacturing methods, spunbonding, meltblowing, dry methods, wet methods, etc., can all be used, and they can be combined as needed.

[0125] In various methods of manufacturing nonwoven fabrics, in order to form the thin film structure that is characteristic of the nonwoven fabric of the present invention, a wet process, namely a wet papermaking process, is suitable for producing thin film nonwoven fabrics with excellent uniformity, thereby stably forming the thin film structure that is characteristic of the present invention.

[0126] The wet papermaking method mentioned here refers to the production of nonwoven fabrics by dispersing short fibers in an aqueous medium to form a papermaking solution. Specifically, the main fibers constituting the nonwoven fabric's skeleton, along with bonding fibers that are bonded together through heat treatment, are added to water. As needed, the fibers are broken down into individual strands through dissociation and pulping. Papermaking is then performed using a papermaking solution with a uniform dispersion of various short fibers. It should be noted that the dispersibility of the papermaking solution can be adjusted by modifying the amount of short fibers added, the amount of water, and the stirring time, allowing for the creation of suitable dispersion states for various short fibers.

[0127] It should be noted that in order to suppress the aggregation of short fibers in water and to produce a uniform thin-film nonwoven fabric, a dispersant may be included.

[0128] Examples of dispersants include natural polymers, synthetic polymers, organic compounds, and inorganic compounds. For instance, additives that inhibit fiber aggregation include cationic compounds, nonionic compounds, and anionic compounds. Among these, anionic compounds are preferred from the viewpoint of electrorepulsion in an aqueous medium when the aim is to improve dispersibility. In the manufacture of this invention, the amount of dispersant added is preferably 0.001 to 10 equivalents relative to the fibers constituting the nonwoven fabric. Within this range, the fiber dispersibility can be improved without impairing the processability of wet papermaking, and the nonwoven fabric of this invention can be manufactured.

[0129] The fibers constituting the nonwoven fabric of the present invention can be fibers manufactured by conventionally known filament-making methods, but from a production point of view, fibers manufactured by effectively utilizing melt spinning methods are suitable.

[0130] When manufacturing fibers using melt spinning, the desired fibers can be obtained by extruding polymers with the desired cross-sectional shape by using spinnerets with orifices of the corresponding shape or composite spinnerets.

[0131] The polymers used in this melt spinning can be polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polypropylene terephthalate, polyolefins, polycarbonate, polyacrylate, polyamide, polylactic acid, thermoplastic polyurethane, polyphenylene sulfide, liquid crystal polyester, and their copolymers, among other polymers that can be melt-spun.

[0132] In industrial applications, nonwoven fabrics with a certain degree of heat resistance are suitable. Polyesters and polyamides, which are condensation polymers, have high melting points and are suitable for use in this invention. When used in membranes, substrates, etc., high-melting-point polyesters are preferred for compounding with other materials for heating purposes. Furthermore, in applications requiring chemical resistance as a membrane or substrate, polyphenylene sulfide (PPS) exhibits excellent heat resistance in practical use in addition to chemical resistance, and is therefore preferred.

[0133] It should be noted that the polymer used in this invention may contain various additives such as inorganic substances such as titanium dioxide, silicon dioxide, and barium oxide, carbon black, dyes, pigments, flame retardants, fluorescent whitening agents, antioxidants, or ultraviolet absorbers.

[0134] When the nonwoven fabric manufacturing method of the present invention adopts the wet papermaking method, the fiber length of various short fibers used in the papermaking solution is preferably 0.3 to 30.0 mm. If it is within this range, the dispersibility in the papermaking solution can be maintained, and a nonwoven fabric with good uniformity can be obtained.

[0135] The fiber length of short fibers can be adjusted appropriately according to their intended use. Generally speaking, as the fiber length increases, the contact length between short fibers increases, and the mechanical properties and dimensional stability of the nonwoven fabric tend to improve. However, on the other hand, during the stirring process of the fiber papermaking dosing, short fibers tend to easily entangle and agglomerate. Therefore, adjustments can be made according to the specifications of the short fibers mixed in the papermaking dosing and the desired design.

[0136] Regarding the main fibers and bonding fibers used in the nonwoven fabric of the present invention, in order to manufacture high-quality nonwoven fabrics with a uniform state of non-agglomeration of the papermaking liquor, and also with the aim of excellent mechanical properties of the nonwoven fabric and dimensional stability during the process, the fiber length is more preferably 1.0 to 10.0 mm. Further, the fiber length is particularly preferably 2.0 to 5.0 mm. Within this range, even in general papermaking equipment that generates shear forces during the process, short fibers will not agglomerate, and short fibers are less likely to get caught in the papermaking wire. Therefore, the strength improvement effect caused by the increased contact length between short fibers can be maximized, and the process throughput is more stable.

[0137] In particular, in the nonwoven fabric of the present invention, by using flat fibers, it is possible to achieve both minimization of fiber diameter and maximization of fiber length, which is unattainable with conventional raw materials. As a result, even wet papermaking with extremely low basis weight can achieve very good process throughput, which is difficult to achieve in the past.

[0138] The main fiber and the bonding fiber are not limited to one type, and may contain two or more types. Depending on the application and required characteristics of the nonwoven fabric, the mixing ratio of the main fiber and the bonding fiber can be adjusted to a range of 5% to 95% by weight. It should be noted that by softening and flowing the bonding fiber, the fibers are firmly bonded together, and the mechanical properties are improved. However, the softened and flowing bonding fiber blocks the gaps between the fibers. Therefore, from the viewpoint of balancing mechanical properties and porous structure, the mixing ratio of the bonding fiber is preferably 10% to 60% by weight.

[0139] It should be noted that the softening temperature of the main fiber is preferably higher than that of the bonding fiber, and it is preferable to use a fiber with high crystallinity that has undergone sufficient crystallization. By making the main fiber a fiber with high crystallinity, and thus using the bonding fiber formed from the same polymer in an amorphous state, the main fiber does not soften and functions as a strong and tough skeleton material for the sheet, while only the bonding fiber softens and flows, thus firmly bonding the main fibers together.

[0140] Furthermore, the fiber diameter and cross-sectional shape of the main fiber and bonding fiber can be appropriately selected according to the purpose. However, by making both the main fiber and bonding fiber flat fibers, a special nonwoven fabric structure that can highly balance film-likeness and mechanical properties can be successfully formed. In particular, by using flat fibers with an flatness of 3 or more and a minor axis length of 2.00 μm or less for both the main fiber and bonding fiber, a nonwoven fabric with flat fibers overlapping in the cross-sectional direction and highly balancing film-likeness and mechanical properties can be manufactured.

[0141] The flat fibers with a flatness of 3 or higher and a short axis length of 2.00 μm or less mentioned here are sometimes difficult to manufacture stably in conventional melt spinning using nozzles with only irregularly shaped holes, because the molten polymer ejected from the nozzle is close to a circle due to surface tension.

[0142] Therefore, in this invention, it is suitable to use the following method: to form a multilayer laminated fiber by laminating multiple layers of a poorly soluble polymer and a readily soluble polymer on the cross-section of the fiber. Figure 2 Temporarily spin the fibers, dissolve and remove the easily soluble polymers from the multilayered fibers, thereby extracting the polymers. The multilayered fibers referred to here are fibers with a cross-section consisting of alternating or sequentially layered two or more polymers. The layered structure can be not only one where the layering directions are the same in the fiber cross-section, but also radial, concentric, irregularly oriented, or a combination of these layered structures.

[0143] For this multilayer laminated fiber, in order to form a laminated structure for generating stable flat fibers, it is suitable to temporarily form a cross-section in which poorly soluble polymers and readily soluble polymers are stably laminated into multiple layers, and preferably the polymers constituting the multilayer laminated fiber have high affinity.

[0144] From the above perspective, as a combination of polymers constituting the multilayered fibers of the present invention, it is suitable to use polyethylene terephthalate copolymerized with 5 mol% to 15 mol% sodium isophthalate-5-sulfonate and polyethylene glycol copolymerized with 5 wt% to 15 wt% of polyethylene glycol with a weight average molecular weight of 500 to 3000 in addition to the aforementioned sodium isophthalate-5-sulfonate, and to use polyethylene terephthalate in the poorly soluble components.

[0145] In particular, from the viewpoint of spinnability and easy solubility in low-concentration aqueous solvents, using polyesters copolymerized with polyethylene glycol and sodium isophthalate sulfonate alone or in combination as easily soluble components can stably manufacture flat fibers. From this viewpoint, combinations of the above polymers can also be listed as a more preferred way to realize the present invention.

[0146] In this invention, the substance after dissolving the easily soluble components from the multilayer laminated fibers can be directly used in wet papermaking. Alternatively, after dissolving the easily soluble components from the multilayer laminated fibers, the substances can be filtered to separate the flat fibers, washed, dried, and then redispersed in an aqueous medium for use. Furthermore, considering the high-level processing involved and the processability requirements, the pH of the medium can be adjusted by adding acids or alkalis, or it can be diluted with water before use.

[0147] The flat fibers produced by the above-mentioned multilayered fibers have a highly anisotropic cross-section with short short axis length and long long axis length. Even under a wide range of conditions from low shear to high shear, they exhibit excellent dispersibility and are not prone to entanglement between flat fibers. Therefore, they become papermaking dosings with excellent uniformity.

[0148] After diluting the stock solution for papermaking prepared from the above various short fibers to a certain concentration, a non-woven fabric is formed by dehydrating with an inclined screen, a cylinder screen, etc. As the device used in papermaking, a cylinder paper machine, a fourdrinier paper machine, an inclined short mesh paper machine, or a paper machine combining them can be cited. In the papermaking process, in addition to the dispersibility of the fibers in the stock solution for papermaking, the papermaking speed, the amount of fibers, and the amount of water medium are adjusted according to the desired basis weight, and the aggregation of fibers during drainage is controlled. The wet paper formed here undergoes drying and heat treatment processes to remove moisture and bond the fibers, thereby manufacturing the non-woven fabric of the present invention. From the perspective of being able to simultaneously implement the drying of the wet paper and the thermal bonding of the bonded fibers, the method using hot air ventilation (air through) and the method of contacting with a hot rotating roll (Yankee dryer, hot calender roll, etc.) are suitable for this drying method. The obtained non-woven fabric undergoes a hot press bonding process, and the bonded fibers are bonded more firmly, improving the mechanical properties of the non-woven fabric. From the perspective of being able to perform high-precision processing, the method using a heating press, a hot calender roll (super calender, soft calender, etc.) is suitable for this hot press bonding method.

[0149] As a method of impregnating and integrating the obtained non-woven fabric with a resin, particles, or a solid electrolyte, various coating methods such as a dip coater, a die coater, and a spray coater can be applied according to the viscosity, coating amount, and coating speed of the coating liquid of these materials.

[0150] Examples

[0151] The following examples are listed to specifically illustrate the non-woven fabric of the present invention.

[0152] The following evaluations were made on the examples and comparative examples.

[0153] A. Thickness

[0154] The thickness of the non-woven fabric was measured in mm using a dial thickness gauge DGN-250B manufactured by PEACOCK Co., Ltd. (probe shape 25 mm , graduation value 0.0001 mm, measuring force 1.2 N or less). One sample was measured at five arbitrary positions, and their arithmetic mean was converted to μm units and rounded to the second decimal place, and the obtained value was used as the thickness of the non-woven fabric.

[0155] B. Basis weight

[0156] For the machine direction (MD) and cross direction (CD) of the non-woven fabric, five specimen pieces with a length of 100 mm × width of 10 mm were cut out each, and weighed using an electronic balance GR202 manufactured by Co., Ltd. (graduation value 0.01 mg), and the weight per unit area (g / m 2Round the arithmetic mean of these samples to the second decimal place, and use the resulting value as the base weight (g / m³). 2 ).

[0157] C. Porosity

[0158] Using the thickness and basis weight of the nonwoven fabric calculated above, the porosity is obtained by rounding to the second decimal place using the following formula.

[0159] Apparent density (g / cm³) 3 ) = Basis weight (g / m 2 ) / thickness (μm)

[0160] Porosity (%) = (1 - apparent density (g / cm³)) 3 True density (g / cm³) 3 ))×100

[0161] It should be noted that the true density of polyethylene terephthalate and polyphenylene sulfide listed in the examples is 1.38 g / cm³. 3 ).

[0162] D. Toughness

[0163] Using the sample piece (100mm long × 10mm wide) cut during the calculation of the above basis weight, the method employed by [Company Name] was [Company Name]. Company-made tensile testing machine Tensile tests were conducted using UTM-III-100 at an initial length of 50 mm, a specimen width of 10 mm, and a tensile speed of 100 mm / min. The maximum point load was measured in N. Five specimens each were cut from the MD and CD plates of the nonwoven fabric. The arithmetic mean of these specimens was rounded to the third decimal place, and the calculated value was taken as the tensile strength (N / cm) of the nonwoven fabric. Additionally, the strain at the maximum point load was measured as a percentage (%). The arithmetic mean of these strains was rounded to the second decimal place, and the calculated value was taken as the tensile elongation (%) of the nonwoven fabric. Using the obtained tensile strength, elongation, and basis weight, the following formula, rounded to the third decimal place, was used to calculate the toughness of the nonwoven fabric.

[0164] Specific tensile strength (N) m 2 / g tensile strength (N / cm) / basis weight (g / m³) 2 )

[0165] Toughness = Specific tensile strength (N) m 2 / g (cm) × Elongation at break1 / 2 (% 1 / 2 )

[0166] E. Bonding area per unit fiber cross-sectional area

[0167] The cross-section of the nonwoven fabric is cut out using a razor or similar tool, utilizing Hitachi, Inc. The company's S-5500 scanning electron microscope (SEM) was used to take images at a magnification that allows observation of the cross-section of the fiber (main fiber) with its fibrous skeleton. For the cross-section of a single main fiber present in the captured images, the outer periphery of the cross-section was specified using WINROOF 2015 image analysis software manufactured by Mitani Corporation, and measured in μm. 2 The cross-sectional area of ​​the fibers was measured in units. This measurement was performed on 50 fibers, and their arithmetic mean was rounded to the third decimal place. The calculated value was taken as the fiber cross-sectional area. Using the same method, the portion where the main fiber and the bonding fiber (sometimes with the fiber skeleton disappearing) were bonded approximately orthogonally was determined, and photographed at a magnification that allowed observation of this portion. In the direction perpendicular to the fiber axis of the main fiber, the length of the portion bonded between one main fiber and one bonding fiber was measured in μm using the aforementioned image analysis software, and this value was taken as the bonding length. Bonded portions of the same length as the bonding length in the direction perpendicular to the fiber axis of the main fiber were considered to also form in the direction of the fiber axis of the main fiber, and the square of this bonding length was taken as the bonding area in μm. 2 The value is calculated per unit. This measurement is performed on 50 fibers, and their arithmetic mean is rounded to the third decimal place. This value is then used as the bonded area. Using the obtained fiber cross-sectional area and bonded area, the following formula, rounded to the third decimal place, is used as the bonded area per unit fiber cross-sectional area. It should be noted that in the constituent fibers of nonwoven fabrics, the main fibers and bonded fibers coexist; the main fibers are determined by the degree of deformation of the fiber skeleton.

[0168] Bonding area per unit fiber cross-sectional area = Bonding area (μm) 2 ) / fiber cross-sectional area (μm) 2 )

[0169] F. Range of through holes

[0170] The surface of the nonwoven fabric was photographed using a scanning electron microscope (SEM) at a magnification that allowed for the observation of more than 100 through-holes. For each of the 100 through-holes identified in the images, the equivalent circle diameter was determined using Winroof 2015 image analysis software manufactured by Mitani Corporation, rounded to the nearest integer in μm. The same procedure was performed on five images, and the range of the through-holes was determined by subtracting the minimum equivalent circle diameter from the maximum value.

[0171] G. Arithmetic mean roughness (Ra)

[0172] Utilization Co., Ltd. The surface of the nonwoven fabric was observed using a VK-X200 laser microscope manufactured by the company. The arithmetic mean roughness was measured using the company's VK-H1XA analytical software according to JIS B 0601:2013. The arithmetic mean calculated at any 5 locations was rounded to the third decimal place, and the resulting value was taken as the arithmetic mean roughness (Ra).

[0173] H. Flatness, major axis length, and minor axis length of flat fibers

[0174] Nonwoven fabrics were embedded with embedding agents such as epoxy resin. The fiber cross-sections were cut using a slicing machine equipped with a diamond blade, and the cross-sections were photographed using a scanning electron microscope (SEM) at a magnification sufficient to identify the cross-sections. For the cross-sections of individual fibers present in the images, the maximum length of the cross-section of each fiber was measured using WINROOF 2015 image analysis software manufactured by Mitani Corporation. This value was taken as the major axis length of the fiber and rounded to three decimal places in μm. The length of the line segment orthogonal to the line segment of the maximum length at the midpoint of the maximum length was measured and intersected with the fiber cross-section. This value was taken as the minor axis length of the fiber and rounded to three decimal places in μm. Using the major and minor axis lengths, the flatness of the single fiber was calculated using the following formula.

[0175] Flatness = Major axis length (μm) / Minor axis length (μm)

[0176] The above measurements were performed on 100 fibers to calculate the major axis length, minor axis length, and flatness of each fiber. The arithmetic mean of the major axis length and minor axis length of each fiber was rounded to the third decimal place as the major axis length and minor axis length, and the arithmetic mean of the flatness of each fiber was rounded to the third decimal place as the flatness.

[0177] I. Deviation in minor axis length, concavity / convexity

[0178] The standard deviation is calculated from the short axis length of the 100 fibers measured above. The standard deviation is divided by the arithmetic mean to obtain the coefficient of variation. The coefficient of variation is rounded to the nearest percent to calculate the deviation of the short axis length.

[0179] In addition, using the fiber cross-section images captured above, the lengths of the portions intersecting the fiber cross-sections in straight lines orthogonal to the line segment of the maximum length were measured at points where the maximum length of the cross-section was divided into 10 equal parts. The arithmetic mean and standard deviation of the lengths at these 10 locations were calculated. The standard deviation was divided by the mean and rounded to the nearest percentage, and the resulting value was taken as the roughness of a single fiber. The same measurements were performed on 10 fiber cross-sections, and the arithmetic mean of the roughness of the 10 single fibers was used as the roughness.

[0180] J. Fiber length, aspect ratio

[0181] Utilization Co., Ltd. The company's VHX-2000 microscope was used to observe the surface of nonwoven fabrics, capturing images at a magnification that allowed for the observation of at least 10 fibers capable of full-length measurement. The length of the fiber axis of any 10 fibers randomly selected from the captured images was measured in mm, up to one decimal place. The arithmetic mean of the measurements from these 10 images, rounded to the second decimal place, was taken as the fiber length. Using this fiber length and the calculated minor axis length, the aspect ratio was calculated using the following formula, rounded to the nearest decimal.

[0182] Aspect ratio = Fiber length (μm) / Length of minor axis (μm)

[0183] K. Uniformity

[0184] The uniformity of the nonwoven fabric cut into 250mm×250mm pieces was evaluated by visual observation and was assessed on a three-level scale.

[0185] A: No (invisible) fibrous clumps, good consistency and uniformity.

[0186] B: Although the fiber clumps cannot be visually identified, the concentration can be visually determined.

[0187] C: You can visually distinguish the concentration and fiber clumps.

[0188] L. Fit

[0189] Nonwoven fabric sample pieces with a length of 10mm and a width of 10mm were placed on the skin surface, a drop of water was added with a dropper and visual observation was performed as an indicator of the tightness of the fit. The tightness of the fit to the skin was evaluated in three grades.

[0190] A: The sample sheet is even completely enclosed in the skin folds, making it impossible to see the sample sheet.

[0191] B: The sample floats in the skin folds, allowing for visual identification of the sample.

[0192] C: The sample piece floats up as a whole, making it easy to see clearly.

[0193] [Example 1]

[0194] Component A uses polyethylene terephthalate (PET), and component B uses polyethylene terephthalate (SSIA-PEG copolymer PET) copolymerized with 8.0 mol% sodium isophthalate-5-sulfonate and 9 wt% polyethylene glycol to form... Figure 2 The two polymers, as shown, were discharged in a composite configuration where they were alternately stacked in one direction in multiple layers. Undrawn filaments with a single fiber fineness of 2.8 dtex were collected. Furthermore, the undrawn filaments were drawn to obtain drawn filaments with a single fiber fineness of 1.2 dtex.

[0195] The obtained multilayer laminated fibers were processed by cutting the undrawn and drawn filaments to a length of 3.0 mm. The undrawn filaments were immersed in a 1% (w / w) sodium hydroxide aqueous solution (bath ratio 1 / 100) heated to 70°C for 60 minutes, and the drawn filaments were immersed in a 1% (w / w) sodium hydroxide aqueous solution (bath ratio 1 / 100) heated to 90°C for 30 minutes to dissolve and remove component B, thereby obtaining... Figure 1 The cross-section shown is a flat fiber with a flat shape.

[0196] Crystallized flat fibers obtained from drawn yarns are used as the main fibers, and amorphous flat fibers obtained from undrawn yarns are used as the bonding fibers. The raw materials are added to water with a mixing ratio of 70% by weight for the main fibers and 30% by weight for the bonding fibers, and a papermaking liquor with a fiber concentration of 0.25% by weight is prepared.

[0197] Using this papermaking solution, and employing a square sheeter (250mm square) manufactured by Kumagai Riki Kogyo Co., Ltd., the basis weight was 3.0 g / m³. 2 The paper is made using the same method, dried and heat-treated using a rotary dryer of the same company set to 120℃, and then subjected to a process using a dryer set to 200℃ × 10MPa. A heating press was used to perform hot pressing for 1 minute to obtain a nonwoven fabric.

[0198] Although the resulting nonwoven fabric is an ultrathin film with a thickness of 5.3 μm, it exhibits extremely high toughness (2.09), excellent processability, and a porosity of 58.3%, forming a sufficiently porous structure. It should be noted that the nonwoven fabric lacks fiber clumps, varying density, and exhibits excellent uniformity. In the cross-section of the nonwoven fabric, the cross-sectional direction of the flat fibers is highly consistent, with fibers contacting each other on a surface basis. The bonding area per unit fiber cross-sectional area is 15.23, indicating strong adhesion over a large area. The pores on the surface of the nonwoven fabric range from 46 μm, forming uniformly sized pores. Furthermore, the Ra value is 4.43 μm, indicating an extremely smooth surface. Adhesion was evaluated, and the results showed that the nonwoven fabric even adheres tightly to skin folds, making it difficult to see, demonstrating excellent adhesion. The results are shown in Table 1.

[0199] [Examples 2 and 3]

[0200] The basis weight of the nonwoven fabric was changed to 2.0 g / m². 2 (Example 2), 1.0 g / m 2 (Example 3), except that all are carried out in the same manner as Example 1.

[0201] The resulting nonwoven fabric, like that of Example 1, has a highly consistent cross-sectional direction of flat fibers, with the fibers in "surface" contact and firmly bonded over a large area. The evaluation results of these nonwoven fabrics are shown in Table 1. As the basis weight decreases, the thickness decreases, achieving a leap forward in ultra-thin film production that was previously unattainable. Furthermore, while the toughness tends to decrease with decreasing basis weight, the processability remains good.

[0202] [Examples 4 and 5]

[0203] The basis weight of the nonwoven fabric was changed to 10.0 g / m². 2 (Example 4), 15.0 g / m 2 (Example 5), except that all are carried out in the same manner as Example 1.

[0204] The resulting nonwoven fabric, like that of Example 1, has a highly consistent cross-sectional direction of flat fibers, with the fibers firmly bonded together over a large area. The evaluation results of these nonwoven fabrics are shown in Table 1. With increasing basis weight, the thickness increases, and there is a tendency for the adhesion to other raw materials to deteriorate. Furthermore, the toughness is as high as that of Example 1, and the processability is excellent. The results are shown in Table 1.

[0205] [Examples 6 and 7]

[0206] The mixing ratio of the main fiber and the bonding fiber was changed to 50:50 wt% (Example 6) and 90:10 wt% (Example 7), and all other procedures were carried out in the same manner as in Example 1.

[0207] The resulting nonwoven fabric, like that of Example 1, has a highly consistent cross-sectional direction of flat fibers, with the fibers firmly bonded together over a large area. The evaluation results of these nonwoven fabrics are shown in Table 1. As the mixing ratio of the bonding fibers increases, the thickness of the nonwoven fabric decreases, the porosity decreases, and on the other hand, an increase in toughness is observed. It should be noted that, within the scope of the examples, both film and mechanical properties are adequately considered even when increasing or decreasing the mixing ratio of the bonding fibers. The results are shown in Table 1.

[0208] [Table 1]

[0209] [Example 8]

[0210] The pressure during heating and pressurization was changed to 1 MPa, and otherwise the same procedure was followed as in Example 1.

[0211] The resulting nonwoven fabric, like that of Example 1, has a high degree of uniformity in the cross-sectional direction of the flat fibers, and the fibers are firmly bonded together over a large area, but the spacing between the fibers tends to be slightly coarser. The evaluation results of these nonwoven fabrics are shown in Table 1. By reducing the hot-pressing pressure, the thickness of the nonwoven fabric increases, the porosity increases, and the bonding between the fibers weakens, resulting in reduced toughness, but the processability remains excellent. The results are shown in Table 2.

[0212] [Comparative Example 1]

[0213] As the fibers constituting the nonwoven fabric, the main fibers used were drawn PET yarns with a circular cross-section (fiber diameter 3.10 μm), and the bonding fibers used were undrawn PET yarns with a circular cross-section (fiber diameter 4.30 μm). Otherwise, all were carried out in the same manner as in Example 1.

[0214] The evaluation results are shown in Table 2. The use of circular cross-section fibers in both the main fiber and the bonding fiber indicates a tendency for increased thickness and higher porosity. Furthermore, the toughness is extremely low at 0.18, meaning even minor tension during processing can cause deformation or breakage of the nonwoven fabric, indicating poor processability. The surface of the nonwoven fabric also shows significant unevenness in density and poor uniformity. Observation of the nonwoven fabric's cross-section reveals that the fibers contact each other at points with a small area, significantly reducing the bonding area per unit fiber cross-sectional area. Additionally, the increased Ra value indicates decreased adhesion.

[0215] [Comparative Example 2]

[0216] As the fibers constituting the nonwoven fabric, the bonding fibers use PET core-sheath filaments with a circular cross-section (fiber diameter 10.50 μm) and a basis weight of 60 g / m². 2 The paper was made in the same manner as in Comparative Example 1, and hot-pressed at 200°C × 10MPa for 1 minute.

[0217] The evaluation results are shown in Table 2. Due to the significant increase in the amount of constituent fibers, defects are difficult to notice, and the toughness is 1.27, which is excellent. However, the thickness is too large at 87.0 μm, which cannot balance mechanical properties and film properties. Because the nonwoven fabric is very thick, the adhesion is also extremely low.

[0218] [Examples 9 and 10]

[0219] Various modifications were made to the flatness and short axis length of the flat fibers constituting the nonwoven fabric; otherwise, all were carried out in the same manner as in Example 1 (Examples 9 and 10). It should be noted that the flatness and short axis length were changed by altering the number of layers of the multilayered fibers used to make the flat fibers.

[0220] The resulting nonwoven fabrics exhibited a consistent cross-sectional orientation of flat fibers, with the fibers bonded together over a large area, although the uniformity of the cross-sectional orientation was slightly inconsistent. Evaluation results for these nonwoven fabrics are shown in Table 2. With decreasing flatness and increasing minor axis length, a tendency was observed for the nonwoven fabric to become thicker and more porous. On the other hand, with decreasing flatness and increasing minor axis length, toughness decreased and processability deteriorated, but not to the point of causing fatal problems like breakage. In the cross-section of the nonwoven fabric, with decreasing flatness and increasing minor axis length, there was a tendency for surface contact to weaken and become point contact, resulting in a decrease in the bonded area per unit fiber cross-sectional area. Furthermore, with increasing Ra, surface smoothness tended to deteriorate slightly, and a decrease in adhesion was also observed.

[0221] [Examples 11 and 12]

[0222] The deviation of the short axis length of the flat fibers constituting the nonwoven fabric was changed (Example 11) and the unevenness (Example 12), but otherwise, it was implemented in the same way as in Example 1. It should be noted that the deviation of the short axis length and the unevenness were changed by changing the flow path shape of the nozzle of the multilayer laminated fibers that are the raw material for manufacturing flat fibers.

[0223] The resulting nonwoven fabric, like that of Example 1, has flat fibers with the same cross-sectional direction, and the fibers are firmly bonded together over a large area. The evaluation results of these nonwoven fabrics are shown in Table 2. Due to deviations in short axis length or reduced unevenness, the visual uniformity of the nonwoven fabrics is slightly more noticeable, and the uniformity tends to deteriorate. Although the bonded area per unit fiber cross-sectional area is the same as in Example 1, a tendency for reduced toughness is observed due to the slightly deteriorated uniformity.

[0224] [Table 2]

[0225] Explanation of symbols

[0226] 1: Flat fibers

[0227] 2: Minor axis length

[0228] 3: Major axis length

[0229] 4: Multilayer laminated fibers

[0230] 5: A component

[0231] 6: Component B

[0232] 7: Main fiber

[0233] 8: Adhesive fibers

[0234] 9: Adhesion area

[0235] 10: Fiber cross-sectional area.

Claims

1. A nonwoven fabric, characterized in that, For thicknesses of 30.0 μm or less, the toughness value calculated as the product of the square root of the specific tensile strength and tensile elongation is 0.50 or higher.

2. The nonwoven fabric according to claim 1 has a porosity of 50% or more.

3. The nonwoven fabric according to claim 1 or 2, characterized in that, The bonding area per unit fiber cross-sectional area of ​​the fibers constituting the nonwoven fabric is 3.00 or more.

4. A fiber article comprising at least a portion of the nonwoven fabric as described in claim 1.

5. A type of sheet, wherein, The nonwoven fabric of claim 1 is filled with resin or particles.

6. A solid electrolyte sheet, wherein, The nonwoven fabric of claim 1 is filled with a solid electrolyte.

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