Fiber mat

Abstract

To provide a fiber mat containing fine fibers and having a high strength.SOLUTION: There is provided a fiber mat that is composed of fine fibers having a thermoplastic property, and is configured in that: a first main surface is provided on one side in a thickness direction, and a second main surface is provided on the other side in the thickness direction; and the fine fibers are fused on the first main surface side and are provided so as to be releasable from a support body that supports the second main surface.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a fiber mat. [Background technology]

[0002] As a conventional method for producing a fiber sheet (fiber mat), Japanese Patent Laid-Open Publication No. 2013-076196 (Patent Document 1) discloses a method for producing a fiber sheet using a papermaking method. Specifically, the method discloses a method in which a fiber suspension in which fibers are dispersed is supplied onto a papermaking wire, and the fibers are deposited on the papermaking wire, thereby forming a fiber sheet on the papermaking wire. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-076196 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, fiber sheets such as nonwoven fabrics have been used in a wide variety of applications, including as filters, adsorbents, heat insulating materials, and even as printed wiring board materials when impregnated with epoxy resins.

[0005] The finer the fibers constituting the fiber sheet, the thinner the fiber sheet and the more suppressed thickness variation can be. Furthermore, there is a demand for improved filter performance in fiber sheets, and it is expected that fiber sheets will be produced using fine fibers in order to increase the specific surface area and reduce the pore diameter to capture small particles.

[0006] The main techniques for making fibers into sheets (mats) are the coater method and the papermaking method, but as the fibers become thinner and their specific surface area increases, the amount of solvent required to wet the fibers increases. For this reason, solvent recovery methods such as the papermaking method are more cost-effective.

[0007] When fibers with hydrogen bonds, such as pulp, are made using a papermaking method, the fibers in the formed fiber mat gain strength through hydrogen bonds by dehydrating and drying the paper after it is made.

[0008] However, in the case of chemical fibers that do not have hydrogen bonds, the only way to bond them is through entanglement between the fibers, and it is difficult to obtain sufficient strength for handling, especially for short fibers such as fine fibers. Therefore, one method of adding a binder substance to the fiber mat to give it strength is considered, but in this case, the electrical properties and heat resistance of the fiber mat deteriorate, resulting in a deterioration in the performance of the fiber mat.

[0009] Another widely used method is to use a calender to heat and pressurize the fibers to bond them together and give them strength. However, when using a calender to heat and press the fibers together, it is necessary to peel the fiber mat from the mesh or papermaking wire. When using fine, particularly ultrashort, fibers, the fiber mat does not have enough strength to withstand the peeling.

[0010] If calendering is performed without peeling, the fiber mat will become integrated with the mesh or papermaking wire, making it impossible to peel it. Also, the mesh or papermaking wire must be made of a material with a higher melting point than the fibers used to make the paper, and when using fine fibers made of a high-melting resin such as liquid crystal polymer (LCP), there are no inexpensive materials that can meet this requirement.

[0011] The present invention has been made in view of the above problems, and an object of the present invention is to provide a fiber mat containing fine fibers and having high strength. [Means for solving the problem]

[0012] A method for producing a fiber mat according to the present disclosure includes dispersing thermoplastic fine fibers in a dispersion medium and forming a mat of the dispersed fine fibers on a support. The mat-forming step includes weaving the fine fibers onto the support to form a fiber mat, and irradiating a first main surface of the fiber mat, which is located opposite to the side where the support is located, with light. In the step of irradiating the first main surface of the fiber mat with light, the fine fibers located on the first main surface side are fused together.

[0013] In the method for producing a fiber mat according to the present disclosure, the fine fibers may have a melting point higher than that of the support.

[0014] In the method for producing a fiber mat according to the present disclosure, it is preferable that pulsed light is irradiated in the light irradiating step.

[0015] In the method for producing a fiber mat according to the present disclosure, the mat-forming step may further include a step of peeling the fiber mat, the first main surface of which has been irradiated with light, from the support, and irradiating a second main surface of the fiber mat, the second main surface being located opposite to the first main surface, with light. In this case, it is preferable that the fine fibers located on the second main surface side are fused together in the step of irradiating the second main surface of the fiber mat with light.

[0016] In the method for producing a fiber mat according to the present disclosure, liquid crystal polymer powder may be used as the fine fibers.

[0017] In the fiber mat manufacturing method based on the present disclosure, it is preferable to use as the liquid crystal polymer powder short fiber particles having an aspect ratio, which is the ratio of the longitudinal length to the fiber diameter, of 10 to 500 times, and including fiber portions having an average diameter of 2 μm or less.

[0018] The fiber mat according to the present disclosure is made of thermoplastic fine fibers and has a first main surface on one side in the thickness direction. In the fiber mat, the fine fibers are fused on the first main surface side.

[0019] The fiber mat according to the present disclosure preferably has a breaking strength of 45 cN / 20 mm or more.

[0020] In the fiber mat according to the present disclosure, the fine fibers may be liquid crystal polymer powder.

[0021] In the fiber mat based on the present disclosure, the liquid crystal polymer powder preferably includes short fiber particles having an aspect ratio, which is the ratio of the longitudinal length to the fiber diameter, of 10 to 500 times, and a fiber portion having an average diameter of 2 μm or less. [Effects of the Invention]

[0022] According to the present invention, a fiber mat containing fine fibers and having high strength can be provided. [Brief explanation of the drawings]

[0023] [Figure 1] 3 is a scanning electron microscope photograph showing an enlarged view of a first main surface of a fiber mat according to an embodiment. [Figure 2] 1 is a scanning electron microscope photograph showing a cross section in the thickness direction of a fiber mat according to an embodiment. [Figure 3] FIG. 2 is a flow chart showing a manufacturing process of a fiber mat according to an embodiment. [Figure 4] 1 is a diagram showing a matting step for matting a liquid crystal polymer powder in a fiber mat manufacturing process. FIG. [Figure 5] FIG. 10 is a diagram showing a step of irradiating the second surface of the fiber mat with light. [Figure 6] FIG. 2 is a diagram showing evaluation conditions and evaluation results in Example 1, Example 2, and a comparative example. [Figure 7]FIG. 10 is a diagram showing evaluation conditions and evaluation results in Examples 3 and 4. [Figure 8] FIG. 1 is a graph showing the breaking strength in Examples 1 to 4. DETAILED DESCRIPTION OF THE INVENTION

[0024] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following embodiments, the same or common parts are designated by the same reference numerals in the drawings, and the description thereof will not be repeated.

[0025] <Fiber mat> The fiber mat 30 according to this embodiment is composed of thermoplastic fine fibers, specifically, a liquid crystal polymer powder in which a liquid crystal polymer is finely pulverized and fibrous. The liquid crystal polymer used in the liquid crystal polymer powder is, for example, a thermotropic liquid crystal polymer. Furthermore, the liquid crystal polymer molecules have a negative thermal expansion coefficient in the axial direction of the molecular axis and a positive thermal expansion coefficient in the radial direction of the molecular axis. The liquid crystal polymer according to this embodiment does not have an amide bond.

[0026] The fiber mat 30 according to this embodiment has a plate-like shape, and has a first main surface 31 (see FIG. 4) and a second main surface 32 (see FIG. 4) that face each other in the thickness direction.

[0027] Fig. 1 is a scanning electron microscope photograph showing an enlarged view of the first main surface of a fiber mat according to an embodiment. Fig. 2 is a scanning electron microscope photograph showing a cross section in the thickness direction of a fiber mat according to an embodiment. In Fig. 2, the area surrounded by a dashed line is the first surface layer portion R1 of the fiber mat 30 located on the first main surface side.

[0028] As shown in the area surrounded by the dashed lines in Figures 1 and 2, in the fiber mat 30 according to the embodiment, the liquid crystal polymer powder is fused on the first main surface 31 side. That is, the liquid crystal polymer powder is fused in the first surface layer portion R1 of the fiber mat 30 located on the first main surface 31 side. On the other hand, the liquid crystal polymer powder is not fused in the middle layer portion R2 located closer to the center in the thickness direction than the first main surface 31 side. As a result, the fiber mat 30 has a density gradient in the thickness direction from the first main surface 31 side to the center. Specifically, the density on the first main surface 31 side in the thickness direction is higher than the density on the center side.

[0029] As will be described later, the liquid crystal polymer powder located on the second main surface 32 side may also be fused. That is, the liquid crystal polymer powder may also be fused in the second surface layer portion of the fiber mat 30 located on the second main surface 32 side.

[0030] As described above, the liquid crystal polymer powder is fused at least on the first main surface 31 side so as to have a density gradient in the thickness direction, thereby improving the strength of the fiber mat 30. When the liquid crystal polymer powder is fused on both the first main surface 31 side and the second main surface 32 side, the strength of the fiber mat 30 can be further improved.

[0031] The breaking strength of the fiber mat 30 is preferably 45 cN / 20 mm or more, more preferably 50 cN / 20 mm or more, and may further be 115 cN / 20 mm or more, or 350 cN / 20 mm or more.

[0032] The breaking strength of the fiber mat 30 can be measured using an autograph (AG-XDplus manufactured by Shimadzu Corporation) In this case, the width of the fiber mat 30 at the time of measurement is set to 20 mm.

[0033] The overall basis weight of the fiber mat 30 is approximately 30 to 40 g / m 2The overall density of the fiber mat 30 is, for example, 0.30 to 0.60 g / cm 3 and the density increases as the fused area of ​​the liquid crystal powder polymer in the thickness direction increases.

[0034] The thickness of the fiber mat 30 is approximately 50 to 100 μm, and the thickness decreases as the fused region of the liquid crystal polymer powder in the thickness direction increases.

[0035] <Film> The fiber mat 30 is pressed to be used as a film (more specifically, a liquid crystal polymer film). The liquid crystal polymer film may have a metal foil such as copper foil bonded to at least one side thereof, or may have the metal foil bonded to both sides thereof. In this case, the liquid crystal polymer film according to this embodiment can be used as a single laminate-shaped molded product, for example, as FCCL (Flexible Copper Clad Laminates), which allows circuit formation by the subtractive method.

[0036] <Method of manufacturing fiber mat> 3 is a flow diagram showing the steps of manufacturing a fiber mat. Referring to FIG. 3, the method of manufacturing a fiber mat according to this embodiment will be described.

[0037] As shown in FIG. 3, the method for manufacturing a fiber mat according to this embodiment includes a pre-process (S10) consisting of a coarse grinding process (S11), a fine grinding process (S12), a coarse particle removal process (S13), and a fiberization process (S14) in this order, and further includes a post-process (S20) following the pre-process (S10) consisting of a dispersion process (S21) and a mat-forming process (S22).

[0038] <Pre-process> In the coarse pulverization step (S12), which is the first step of the pre-processing step (S10), a liquid crystal polymer molded product is first prepared as a raw material. Examples of the liquid crystal polymer molded product include uniaxially oriented pellets, biaxially oriented films, and powdered liquid crystal polymers. From the viewpoint of production cost, pelleted or powdered liquid crystal polymers are preferred as the liquid crystal polymer molded product, as they are less expensive than film-shaped liquid crystal polymers, and pelleted liquid crystal polymers are more preferred. In this embodiment, the liquid crystal polymer molded product preferably does not include liquid crystal polymers directly molded into fibers by electrospinning or melt-blowing. However, the liquid crystal polymer molded product may include liquid crystal polymers processed into fibers by crushing pelleted or powdered liquid crystal polymers.

[0039] Next, the molded liquid crystal polymer is coarsely pulverized to obtain a coarsely pulverized liquid crystal polymer. For example, the molded liquid crystal polymer is coarsely pulverized using a cutter mill to obtain a coarsely pulverized liquid crystal polymer. The particle size of the coarsely pulverized liquid crystal polymer is not particularly limited as long as it can be used as a raw material for the fine pulverization process described below. The maximum particle size of the coarsely pulverized liquid crystal polymer is, for example, 3 mm or less.

[0040] The method for producing a liquid crystal polymer film in this embodiment does not necessarily include the coarse pulverization step (S11). For example, if the liquid crystal polymer molded product can be used as a raw material for the fine pulverization step, the liquid crystal polymer molded product may be directly used as a raw material for the fine pulverization step.

[0041] Subsequently, in the pulverization step (S12), the coarsely pulverized liquid crystal polymer is dispersed in liquid nitrogen and pulverized to obtain granular pulverized liquid crystal polymer. In the pulverization step (S12), the coarsely pulverized liquid crystal polymer dispersed in liquid nitrogen is pulverized using media. The media may be, for example, beads. In the pulverization step (S12), it is preferable to use a bead mill, which has relatively few technical problems, from the viewpoint of handling liquid nitrogen. An example of a device that can be used in the pulverization step (S12) is the "LNM-08" liquid nitrogen bead mill manufactured by Imex.

[0042] In the fine pulverization step (S12) of this embodiment, the pulverization method in which the liquid crystal polymer is dispersed in liquid nitrogen and pulverized is different from the conventional freeze pulverization method. The conventional freeze pulverization method pulverizes the raw material to be pulverized while pouring liquid nitrogen onto the raw material to be pulverized and the pulverization device body, but most of the liquid nitrogen has evaporated by the time the raw material to be pulverized is pulverized. In other words, in the conventional freeze pulverization method, most of the raw material to be pulverized is not dispersed in the liquid nitrogen by the time the raw material to be pulverized is pulverized.

[0043] In conventional freeze-pulverization, the heat of the raw material to be pulverized itself, the heat generated by the pulverizer, and the heat generated by pulverizing the raw material to be pulverized vaporize the liquid nitrogen in an extremely short time. Therefore, in conventional freeze-pulverization, the raw material being pulverized inside the pulverizer reaches a temperature much higher than the boiling point of liquid nitrogen, which is -196°C. In other words, in conventional freeze-pulverization, pulverization is carried out under conditions where the temperature inside the pulverizer is usually between -100°C and 0°C. In conventional freeze-pulverization, even when as much liquid nitrogen as possible is supplied, the temperature inside the pulverizer is at its lowest, approximately -150°C.

[0044] Therefore, in the conventional freeze-pulverization method, for example, when uniaxially oriented pellet-shaped liquid crystal polymer or coarsely pulverized pellet-shaped liquid crystal polymer is pulverized, the pulverization proceeds along a plane approximately parallel to the axial direction of the molecular axis of the liquid crystal polymer, so that a fibrous liquid crystal polymer having a very large aspect ratio and a fiber diameter much larger than 3 μm is obtained. In other words, even if uniaxially oriented pellet-shaped liquid crystal polymer or coarsely pulverized pellet-shaped liquid crystal polymer is pulverized in the conventional freeze-pulverization method, it is not possible to obtain the granular finely pulverized liquid crystal polymer used in this embodiment.

[0045] In this embodiment, the raw material to be pulverized is dispersed in liquid nitrogen and pulverized, allowing for pulverization of raw materials in a more cooled state than conventional freeze-pulverization methods. Specifically, raw materials can be pulverized at temperatures lower than -196°C, the boiling point of liquid nitrogen. When raw materials to be pulverized at temperatures lower than -196°C are pulverized, the pulverization of the raw material progresses due to repeated brittle fracture of the raw material. As a result, even when uniaxially oriented liquid crystal polymer is pulverized, for example, not only does fracture progress along a plane approximately parallel to the axial direction of the molecular axis of the liquid crystal polymer, but brittle fracture also progresses along a plane intersecting the axial direction, resulting in the production of granular pulverized liquid crystal polymer.

[0046] In the fine pulverization step (S12), the liquid crystal polymer, which has been granulated by brittle fracture in liquid nitrogen, is continuously subjected to impacts with media while in the brittle state, resulting in the formation of multiple fine cracks from the outer surface to the interior of the liquid crystal polymer obtained in the fine pulverization step (S12).

[0047] The pulverized liquid crystal polymer particles obtained in the pulverization step (S12) preferably have a D50 of 100 μm or less, more preferably 50 μm or less, as measured by a particle size distribution analyzer using a laser diffraction scattering method, which can prevent the pulverized liquid crystal polymer particles from clogging the nozzle in the fiberization step described below.

[0048] Next, in the coarse particle removal step (S13), coarse particles are removed from the granular pulverized liquid crystal polymer obtained in the pulverization step (S12). For example, by sieving the granular pulverized liquid crystal polymer through a mesh, granular pulverized liquid crystal polymer that falls below the sieve is obtained, and by removing the granular liquid crystal polymer that remains above the sieve, coarse particles contained in the granular pulverized liquid crystal polymer can be removed. The type of mesh can be selected appropriately, and examples of meshes include those with mesh openings of 100 μm. The mesh opening can be changed appropriately depending on the fiber length of the liquid crystal polymer powder desired. For example, a mesh with mesh openings of approximately 5 μm to 50 μm may be used. Furthermore, the method for producing a liquid crystal polymer powder according to this embodiment does not necessarily have to include the coarse particle removal step (S13).

[0049] Next, in the fiberization step (S14), the granular liquid crystal polymer is crushed using a wet high-pressure crusher to obtain a liquid crystal polymer powder. In the fiberization step (S14), the finely pulverized liquid crystal polymer is first dispersed in a dispersion medium for the fiberization step. The dispersed finely pulverized liquid crystal polymer does not need to have coarse particles removed, but it is preferable that the coarse particles have been removed. Examples of dispersion mediums for the fiberization step include water, ethanol, methanol, isopropyl alcohol, toluene, benzene, xylene, phenol, acetone, methyl ethyl ketone, diethyl ether, dimethyl ether, hexane, or mixtures thereof.

[0050] The pulverized liquid crystal polymer dispersed in the dispersion medium for the fiberization process, i.e., the pulverized liquid crystal polymer in a slurry state, is passed through a nozzle under high pressure. By passing the liquid crystal polymer through the nozzle at high pressure, shear force or collision energy due to the high-speed flow through the nozzle acts on the liquid crystal polymer, crushing the granular pulverized liquid crystal polymer, thereby promoting fiberization of the liquid crystal polymer and producing a liquid crystal polymer powder that can be used in subsequent processes. From the perspective of applying high shear force or high collision energy, it is preferable to make the nozzle diameter as small as possible without causing clogging of the pulverized liquid crystal polymer. Because the granular pulverized liquid crystal polymer in this embodiment has a relatively small particle size, the nozzle diameter of the wet high-pressure crushing device used in the fiberization process can be made small. The nozzle diameter is, for example, 0.2 mm or less.

[0051] In this embodiment, as described above, multiple fine cracks are formed in the granular pulverized liquid crystal polymer powder. Therefore, when pressurized by the wet high-pressure crushing device, the dispersion medium penetrates into the pulverized liquid crystal polymer through the fine cracks. Then, when the slurry-like pulverized liquid crystal polymer passes through the nozzle and is placed under normal pressure, the dispersion medium that penetrates into the pulverized liquid crystal polymer expands in a short time. The expansion of the dispersion medium that penetrates into the pulverized liquid crystal polymer causes destruction to progress from the inside of the pulverized liquid crystal polymer. Therefore, fiberization progresses to the inside of the pulverized liquid crystal polymer, and the liquid crystal polymer molecules are separated into domain units in which they are aligned in one direction. Thus, in the fiberization process of this embodiment, by defibrating the granular pulverized liquid crystal polymer obtained in the pulverization process of this embodiment, a liquid crystal polymer powder having a lower content of aggregates and a fine, short fiber structure can be obtained compared to liquid crystal polymer powder obtained by crushing granular liquid crystal polymer obtained by a conventional freeze-pulverization method.

[0052] In the fiberization step (S14) of this embodiment, the finely pulverized liquid crystal polymer may be crushed multiple times using a wet high-pressure crusher to obtain a liquid crystal polymer powder. The number of times of crushing using the wet high-pressure crusher is preferably small. The number of times of crushing using the wet high-pressure crusher may be, for example, 5 times or less.

[0053] The obtained liquid crystal polymer powder is used as a raw material in the subsequent steps. Here, the liquid crystal polymer powder as fine fibers will be described in detail.

[0054] The liquid crystal polymer powder contains at least a fibrous portion. The fibrous portion is a short fiber-like particle having an aspect ratio, which is the ratio of the longitudinal length to the fiber diameter, of 10 to 500 times and an average diameter of 2 μm or less. A liquid crystal polymer powder containing such fine, short fiber-like fibrous portions having an aspect ratio of 10 to 500 times and an average diameter of 2 μm or less cannot be produced by conventionally known production methods.

[0055] For example, liquid crystal polymer powder containing a fiber portion with an aspect ratio of 10 to 500 cannot be produced solely by electrospinning, a method for producing ultrafine continuous fibers. It is possible to cut continuous ultrafine liquid crystal polymer fibers produced by electrospinning into short fibers after spinning. However, there is a limit to how short such continuous ultrafine liquid crystal polymer fibers can be cut, since they have an extremely small fiber diameter and an aspect ratio that is nearly infinite. After cutting continuous ultrafine liquid crystal polymer fibers produced by electrospinning, the aspect ratio of the resulting ultrafine liquid crystal polymer fibers exceeds 500.

[0056] The average diameter of the fiber portion is the average value of the fiber diameters of the plurality of fibrous particles that make up the fiber portion. Thus, the liquid crystal polymer powder according to this embodiment contains fine fibrous particles. The fiber diameter can be measured from image data of the fibrous particles obtained when the fibrous particles are observed with a scanning electron microscope.

[0057] The aspect ratio of the fibrous portion is preferably not more than 300, more preferably not more than 100. The average diameter of the fibrous portion is preferably not more than 1 μm.

[0058] The fiber portion may be contained in the liquid crystal polymer powder as an aggregate portion formed by aggregation of fibrous particles. Furthermore, the axial direction of the liquid crystal polymer molecules constituting the fiber portion and the longitudinal direction of the fiber portion are aligned with each other. In the method for producing a fiber mat according to this embodiment, the liquid crystal polymer powder is produced through the fiberization step described above, and therefore, destruction occurs between multiple domains formed by bundling the liquid crystal polymer molecules, resulting in the axial direction of the liquid crystal polymer molecules being strongly oriented along the longitudinal direction of the fiber portion.

[0059] The liquid crystal polymer powder preferably contains substantially non-fibrous aggregates at a content of 20% or less. Furthermore, the liquid crystal polymer powder more preferably does not contain aggregates. The aggregate content is evaluated by the number of aggregates relative to the number of aggregates contained in the liquid crystal polymer powder. In this embodiment, when the liquid crystal polymer powder is placed on a flat surface, aggregates having a maximum height of more than 10 μm are aggregates, and aggregates having a maximum height of 10 μm or less are fibrous.

[0060] The lump portion may be contained in the liquid crystal polymer powder as an aggregate portion containing lump particles. The lump portion is a liquid crystal polymer powder that is substantially not fibrous. The lump portion may have a flat outer shape.

[0061] In this embodiment, the liquid crystal polymer powder can have a D50 value of, for example, 13 μm or less, as measured by particle size measurement using a particle size distribution measuring device based on a laser diffraction scattering method.

[0062] The liquid crystal polymer powder used as a raw material in the subsequent process is not limited to that produced in the preceding process.

[0063] <Post-process> Next, the post-process (S20) will be described. In the dispersion process (S21), which is the first process of the post-process (S20), the liquid crystal polymer powder is dispersed in a dispersion medium to form a slurry. Because the liquid crystal polymer powder in the form of fine short fibers is used, the liquid crystal polymer powder can be dispersed in a highly viscous dispersion medium, and thus a homogeneous fiber mat can be produced.

[0064] The dispersion medium used in the dispersion step (S21) may be water, ethanol, a mixture thereof, etc. By using such a dispersion medium, the cost of the dispersion medium can be reduced, and the fiber mat can be produced inexpensively.

[0065] It is believed that the longitudinal direction of the fiber portion in the liquid crystal polymer powder dispersed in the dispersion medium is not oriented in a specific direction in the dispersion medium.

[0066] Next, in the mat-forming step (S22), the slurry liquid crystal polymer powder is formed into a liquid crystal polymer fiber mat by a papermaking method. In the papermaking method, the dispersion medium used in the dispersion step can be recovered and reused, allowing the fiber mat to be produced inexpensively.

[0067] 4 is a diagram showing a matting step for matting the liquid crystal polymer powder in the fiber mat manufacturing process. Details of the matting step will be described with reference to FIG.

[0068] 4, the mat-forming step uses a papermaking machine 100. The papermaking machine 100 includes a supply roller 15 that supplies the microporous sheet 10, a take-up roller (not shown) that collects the microporous sheet 10, a papermaking wire 20, transport rollers 25 and 26, a storage section 40 that stores a dispersion medium 41 in which the liquid crystalline polymer powder is dispersed, a heating device 50, and a light irradiation device 60.

[0069] The papermaking wire 20 is a papermaking mesh of, for example, about 80 to 100 mesh. That is, the papermaking wire 20 has a pore size of about 150 μm to 180 μm. The papermaking wire 20 is transported by transport rollers 25 and 26 arranged in the transport direction. The transport roller 26 is disposed downstream of the transport roller 25. The papermaking wire 20 is transported by these transport rollers 25 and 26 so as to pass through the storage section 40.

[0070] A supply roller 15 supplies the microporous sheet 10 onto the papermaking wire 20. The microporous sheet 10 functions as a support for the liquid crystalline polymer powder. The microporous sheet 10 placed on the papermaking wire 20 is transported by the papermaking wire 20 to pass through a storage section 40. After passing through the storage section 40, the microporous sheet 10 is peeled off from the papermaking wire 20 and taken up by a take-up roller.

[0071] The microporous sheet 10 has a mesh that is finer than the papermaking wire 20. The microporous sheet 10 preferably has a mesh size of approximately 157 mesh or more. That is, the microporous sheet 10 preferably has a pore size of approximately 100 μm or less. This allows the fine liquid crystal polymer powder dispersed in the dispersion medium to be collected.

[0072] More preferably, the microporous sheet 10 has a pore size of about 5 μm to 50 μm. If the pore size of the microporous sheet 10 is too small, drainage will be poor and dehydration will take a long time. On the other hand, if the pore size of the microporous sheet 10 is too large, it will be difficult to collect the fine fibers (fine liquid crystal polymer powder), resulting in a low yield.

[0073] If a microporous sheet 10 is selected that has variations in pore size, this will affect the texture of the formed fiber mat, so if high uniformity is required for the fiber mat, a mesh that is periodically woven in a reticulated pattern is preferred. In other words, it is preferable to use a mesh for the microporous sheet 10 that has uniform pore size and no bias in the location of the pores.

[0074] For example, a woven mesh with a pore size of 50 μm or less can be used as the microporous sheet 10. The woven mesh can be made of synthetic fibers such as polyester.

[0075] The microporous sheet 10 may have a basis weight of 15 g / m. 2 The following wet-laid nonwoven fabrics may be used. As the wet-laid nonwoven fabric, those made of microfibers may be used. The microfibers may be made of synthetic fibers such as polyester.

[0076] The heating device 50 is disposed downstream of the storage section 40 in the conveying direction. The heating device 50 heats and dries the liquid crystalline polymer powder 30 that has been woven onto the microporous sheet 10. As a result, a fiber mat is formed on the microporous sheet 10.

[0077] The light irradiation device 60 is disposed downstream of the heating device 50 in the conveying direction. The light irradiation device 60 irradiates light toward the fiber mat formed on the microporous sheet 10. The light irradiation device 60 may be, for example, a flash lamp.

[0078] The light irradiation device 60 preferably irradiates pulsed light. Because the pulsed light is absorbed by the surface (first main surface 31) of the fiber mat, the support (microporous sheet 10) that supports the fiber mat is not deteriorated by light irradiation. Therefore, materials with a lower melting point than the fiber mat can be used as the support, widening the range of support options. Furthermore, since the fiber mat can be prevented from fusing to the support, the support can be reused. As the light irradiation device 60, PulseForge (registered trademark) 1300 manufactured by NovaCentrix can be used.

[0079] The mat-forming step (S21) includes a paper-making step, a peeling step, a drying step, and a light irradiation step. In the mat-forming step (S21), first, in the paper-making step, the dispersed liquid crystal polymer powder is papered into the microporous sheet 10. Specifically, the microporous sheet 10 supplied onto the papermaking wire 20 is transported by the papermaking wire 20 and passed through the storage unit 40. At this time, the liquid crystal polymer powder dispersed in the dispersion medium 41 stored in the storage unit 40 is papered into the microporous sheet 10.

[0080] Next, in a peeling step, the microporous sheet formed by weaving the dispersed liquid crystal polymer powder is peeled off from the papermaking wire 20. Specifically, the microporous sheet 10 is wound up on a winding roller, thereby transporting the microporous sheet 10 in a direction different from that of the papermaking wire 20. The papermaking wire 20 may also be transported in a direction different from that of the microporous sheet 10 by a transport roller 26.

[0081] Next, in the drying step, the liquid crystalline polymer powder that has been laid on the microporous sheet 10 is heated and dried by a heater 50. As a result, a fiber mat 30 made of the liquid crystalline polymer is formed on the microporous sheet 10.

[0082] Next, in the light irradiation step, the first main surface 31 of the fiber mat 30, which is located on the side opposite to the side where the microporous sheet 10 is located, is irradiated with light. This causes the liquid crystal polymer powder located on the first main surface 31 side to fuse together. As a result, the strength of the fiber mat 30 is improved, and the fiber mat 30 can be carried to the next step without being damaged.

[0083] Furthermore, since only the liquid crystal polymer powder located in the surface layer on the first main surface 31 side is fused, the density of the entire fiber mat 30 is low, thereby ensuring high breathability and high collection efficiency.

[0084] After the light irradiation, the fiber mat 30 is placed on the microporous sheet 10 and then wound up by the winding roller in the winding step.

[0085] Fig. 5 is a diagram showing a step of irradiating the second surface of the fiber mat with light. As shown in Fig. 5, the mat-forming step may further include a step of peeling the fiber mat 30, whose first main surface 31 has been irradiated with light, from the microporous sheet 10, and irradiating the second main surface 32 of the fiber mat 30, which is located opposite the side where the first main surface 31 is located, with light. In this step, the fine fibers located on the second main surface 32 side are fused together by light irradiation from a light irradiation device 61. The light irradiation device 61 may be the same as the light irradiation device 60 described above. During light irradiation, the fiber mat 30 is irradiated while being transported.

[0086] When the liquid crystal polymer powder is fused on both the first main surface 31 side and the second main surface 32 side, the strength of the fiber mat 30 can be further improved.

[0087] Furthermore, when peeling the fiber mat 30 from the microporous sheet 10, the liquid crystal polymer powder is fused on the first main surface 31 side, and the fiber mat 30 has sufficient strength, so the fiber mat 30 can be peeled off without being damaged.

[0088] <Film manufacturing method> Next, the fiber mat 30 is peeled from the microporous sheet 10, and the fiber mat 30 is hot-pressed to obtain a liquid crystal polymer film. The thickness of the liquid crystal polymer film becomes thinner than that of the fiber mat 30 through the hot-pressing process.

[0089] In the heat-pressing step, the fiber mat 30 is heat-pressed together with, for example, copper foil. This heat-pressing step also serves as a step of bonding the liquid crystal polymer film and the copper foil together, making it possible to inexpensively obtain a liquid crystal polymer film with the copper foil bonded to it. Note that, if heating is required for a long period of time in the heat-pressing step, it is preferable to vacuum heat-press the fiber mat 30.

[0090] In the heat pressing step, the heat pressing is preferably performed at a temperature about 5 to 15°C lower than the melting point of the liquid crystal polymer constituting the liquid crystal polymer powder. If the heat pressing is performed at a temperature about 5 to 15°C lower than the endothermic peak temperature, sintering of the liquid crystal polymers with each other tends to proceed.

[0091] In the heat-pressing step, a release film such as a polyimide film, a PTFE film, or a composite sheet made of a reinforcing material such as glass fiber fabric and a heat-resistant resin may be sandwiched between the press used in the heat-pressing step and the fiber mat 30. Alternatively, instead of a polyimide film, an additional copper foil may be sandwiched between the press and the fiber mat 30. This allows a liquid crystal polymer film with copper foil bonded to both sides to be obtained. The liquid crystal polymer film with copper foil bonded to both sides can be used as a double-sided copper-clad FCCL.

[0092] If necessary, the metal foil bonded to the liquid crystal polymer film may be removed by etching, etc. This provides a liquid crystal polymer film free of any metal foil bonded thereto.

[0093] <Experimental Example> The present invention will be described in more detail below with reference to examples, but is not limited to these. In the experimental examples, fiber mats 30 according to Examples 1 to 4 were prepared, and the basis weight, thickness, density, and breaking strength were measured for Examples 1 and 2, and the breaking strength was measured for Examples 3 and 4. The breaking strength was measured using an autograph (AG-XDplus, manufactured by Shimadzu Corporation) for a fiber mat 30 having a width of 20 mm.

[0094] Fig. 6 is a diagram showing the evaluation conditions and evaluation results in Examples 1 and 2 and Comparative Example. Fig. 7 is a diagram showing the evaluation conditions and evaluation results in Examples 3 and 4. Fig. 8 is a diagram showing the breaking strength in Examples 1 to 4.

[0095] Example 1 In Example 1, first, pellet-shaped liquid crystal polymer was introduced into a cutter mill device as a raw material liquid crystal polymer molding and coarsely pulverized. In Example 1, the liquid crystal polymer used had a melting point of 315°C and an absorptivity of 60% at a wavelength of 500 nm. The coarsely pulverized film-shaped liquid crystal polymer was discharged from a 3 mm diameter discharge hole provided in the cutter mill device to obtain a coarsely pulverized liquid crystal polymer.

[0096] Next, the coarsely pulverized liquid crystal polymer was finely pulverized in a liquid nitrogen bead mill (LNM-08, manufactured by Imex Co., Ltd.). In the liquid nitrogen bead mill, the vessel volume was 0.8 L, zirconia beads with a diameter of 5 mm were used as media, the amount of media charged was 500 mL, 30 g of coarsely pulverized liquid crystal polymer was charged, and the pulverization process was carried out for 120 minutes at a rotation speed of 2000 rpm. In the liquid nitrogen bead mill, the coarsely pulverized liquid crystal polymer was dispersed in liquid nitrogen and subjected to a wet pulverization process. In this way, by pulverizing the coarsely pulverized liquid crystal polymer in the liquid nitrogen bead mill, a granular finely pulverized liquid crystal polymer was obtained.

[0097] Next, the finely pulverized liquid crystal polymer was wet classified using a mesh with a mesh size of 100 μm to remove coarse particles contained in the finely pulverized liquid crystal polymer, and the finely pulverized liquid crystal polymer that passed through the mesh was collected. In Example 1, a mesh with a mesh size of 100 μm was used, but classification may also be performed using a mesh with a smaller mesh size.

[0098] Next, the finely pulverized liquid crystal polymer from which the coarse particles had been removed was dispersed in a 20 wt% aqueous ethanol solution. The ethanol slurry containing the finely pulverized liquid crystal polymer was crushed five times using a wet high-pressure crusher under conditions of a nozzle diameter of 0.2 mm and a pressure of 200 MPa to produce fibers. The wet high-pressure crusher used was a Starburst HJP-25060 manufactured by Sugino Machine. This resulted in a liquid crystal polymer powder dispersed in the aqueous ethanol solution.

[0099] Next, the required amount of water and ethanol was added to 30 L of 50 wt% ethanol aqueous solution to prepare 2.2 g of liquid crystal polymer powder, and the resulting slurry liquid crystal polymer powder was formed into a fiber mat 30 by a papermaking method. A square sheet machine 2555 manufactured by Kumagai Riki Co., Ltd. was used as the papermaking machine, and the liquid crystal polymer powder dispersed in the dispersion medium was papered onto a microporous sheet of polyester mesh with a pore size of 11 μm.

[0100] Subsequently, the fiber mat 30 was formed into a microporous sheet by heating and drying at a temperature of 100°C using a hot air dryer. The fiber mat 30 had a basis weight of 35 g / m 2 That was about it.

[0101] Next, multiple fiber mats 30 were prepared, and the first main surface 31 of each fiber mat 30 was irradiated with light under different voltage conditions using a light irradiation device (NovaCentrix PulseForge (registered trademark) 1300). The voltages were 230 V, 250 V, and 270 V, and the pulse length was 3.5 ms.

[0102] The fiber mat 30 irradiated with light under these conditions was peeled off from the microporous sheet, and the basis weight, thickness, density, and breaking strength of the fiber mat 30 of Example 1 were measured using a thickness measuring device (digital linear gauge DG-525H (manufactured by Ono Seiki Co., Ltd.)), a density measuring device, or by conducting a tensile test, etc.

[0103] In Example 1, the basis weight, thickness, density and breaking strength of the mat irradiated with light at 230 V were 33.9 g / m 2 , 95.3 μm, 0.36 g / cm 3 , 50cN / 20mm.

[0104] In Example 1, the basis weight, thickness, density and breaking strength of the mat irradiated with light at 250 V were 34.2 g / m 2 , 84.1 μm, 0.41 g / cm 3 , 130cN / 20mm.

[0105] In Example 1, the basis weight, thickness, density and breaking strength of the mat irradiated with light at 270 V were 34 g / m 2 , 79.2 μm, 0.43 g / cm 3 , 350cN / 20mm.

[0106] Example 2 In Example 2, a fiber mat 30 was prepared in substantially the same manner as in Example 1, and the second main surface 32, located on the opposite side to the first main surface 31, was also irradiated with light at the same energy level as in Example 1. That is, in Example 2, after the fiber mat 30 had been irradiated with light on the first main surface 31 and was peeled off from the microporous sheet, the second main surface 32 was further irradiated with light. The voltages of the light irradiator (NovaCentrix PulseForge (registered trademark) 1300) when irradiating the second main surface 32 with light were 230 V, 250 V, and 270 V, respectively, and the pulse length was 3.5 ms, similar to Example 1. The basis weight, thickness, density, and breaking strength of the fiber mat 30 according to Example 2 were also measured in the same manner as in Example 1.

[0107] In Example 2, the basis weight, thickness, density, and breaking strength of the mat in which both the first main surface 31 and the second main surface 32 were irradiated with light at 230 V were 33.9 g / m 2 , 92.8 μm, 0.37 g / cm 3 , 120cN / 20mm.

[0108] In Example 2, the basis weight, thickness, density, and breaking strength of the mat in which both the first main surface 31 and the second main surface 32 were irradiated with light at 250 V were 34.2 g / m 2 , 78.5 μm, 0.44 g / cm 3 , 380cN / 20mm.

[0109] In Example 2, the basis weight, thickness, density, and breaking strength of the mat in which both the first main surface 31 and the second main surface 32 were irradiated with light at 270 V were 34 g / m 2 , 65μm, 0.52g / cm 3 , 720cN / 20mm.

[0110] (Comparative Example) The comparative example differs from Example 1 in that the light irradiation step is omitted in the matting step. That is, the fiber mat of the comparative example is not irradiated with light on the surface (first main surface) as compared with the fiber mat 30 of Example 1, and the fibers on the surface are not melted.

[0111] In this case, the basis weight, thickness, density and breaking strength of the mat are 34.2 g / m 2 , 105.2 μm, 0.33 g / cm 3 , 19.8cN / 20mm.

[0112] Example 3 In Example 3, the liquid crystal polymer used had a melting point of 315° C. and an absorptivity of 70% at a wavelength of 500 nm. Except for the above, the fiber mat 30 was obtained in substantially the same manner as in Example 1.

[0113] In Example 3, the breaking strengths of the mats irradiated with light at 230 V, 250 V, and 270 V were 400 cN / 20 mm, 830 cN / 20 mm, and 1720 cN / 20 mm, respectively.

[0114] Example 4 In Example 4, the liquid crystal polymer used had a melting point of 315° C. and an absorptivity of 70% at a wavelength of 500 nm. Except for the above, the fiber mat 30 was obtained in substantially the same manner as in Example 2.

[0115] In Example 4, the breaking strengths of the mats irradiated with light at 230 V, 250 V, and 270 V were 930 cN / 20 mm, 1690 cN / 20 mm, and 2410 cN / 20 mm, respectively.

[0116] As described above, it was confirmed that each fiber mat 30 in Examples 1 to 4 had sufficient strength (breaking strength) compared to the comparative example. It was also confirmed that by increasing the voltage during light irradiation, the amount of fused liquid crystal polymer powder increased, and although the thickness decreased, the density and breaking strength increased.

[0117] Furthermore, it was confirmed that the breaking strength was further increased by irradiating the second main surface 32 with light in addition to the first main surface 31, as in Examples 2 and 4. In addition, by comparing Examples 1 and 2 with Examples 3 and 4, it was confirmed that the breaking strength was further increased by using a liquid crystal polymer powder with high absorptivity.

[0118] <Other variations> In the above-described embodiments and examples, the fine fibers are liquid crystal polymer powder, but the fine fibers are not limited to liquid crystal polymer powder. As described above, chemical fibers without hydrogen bonds may be used as the fine fibers as long as they have thermoplasticity.

[0119] In the above-described embodiment and examples, the support for drawing up the fine fibers is a microporous sheet, but this is not limiting. The microporous sheet may be omitted, and the papermaking wire 20 may be used as the support. In this case, the fine fibers may have a fiber length greater than the pore diameter of the papermaking wire 20, and may have a fiber length of 200 μm or less. Furthermore, the fine fibers may have a fiber length of 1 mm or less.

[0120] The above-described embodiments and examples of the present invention are illustrative in all respects and are not restrictive. The scope of the present invention is defined by the claims, and includes all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0121] 10 Microporous sheet, 15 Supply roller, 20 Papermaking wire, 25, 26 Conveying rollers, 30 Fiber mat, 31 First main surface, 32 Second main surface, 40 Reservoir, 41 Dispersion medium, 50 Heating device, 60 Light irradiation device, 100 Papermaking machine.

Claims

1. It is made up of fine thermoplastic fibers, a first main surface on one side in a thickness direction and a second main surface on the other side in the thickness direction; The fine fibers are fused on the first main surface side, A fiber mat provided so as to be releasable from a support supporting the second main surface.

2. In the thickness direction, a density gradient is formed from the first main surface side to the center side of the fiber mat, the density on the first main surface side is higher than the density on the central portion side, The overall density of the fiber mat is 0.30 to 0.52 g / cm ３ 2. The fiber mat of claim 1, wherein:

3. 3. The fiber mat according to claim 1, wherein the breaking strength is 45 cN / 20 mm or more.

4. The fiber mat according to claim 1 , wherein the fine fibers are liquid crystal polymer powder.

5. The fiber mat described in claim 4, wherein the liquid crystal polymer powder is short fiber particles having an aspect ratio, which is the ratio of the longitudinal length to the fiber diameter, of 10 to 500 times and includes fiber portions having an average diameter of 2 μm or less.

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