Method for manufacturing a fibrous mat and fibrous mat

Abstract

A method for manufacturing a fiber mat includes a step of dispersing fine fibers in a dispersion medium (41) and a step of matting the dispersed fine fibers. The fine fibers have a fiber length that is smaller than a pore diameter of a papermaking wire (20). The step of matting includes a step of picking up the dispersed fine fibers to a micro-porous sheet (10) having a pore diameter that is smaller than the papermaking wire (20) and disposed on the papermaking wire (20).

Description

TECHNICAL FIELD

[0001] The present application relates to a method for manufacturing a fiber mat containing a liquid crystal polymer and a fiber mat. BACKGROUND

[0002] As a method for manufacturing a fiber sheet (fiber mat) in the related art, a method for manufacturing a fiber sheet using a papermaking method is disclosed in Japanese Patent Application Publication No. 2013-076196 (Patent Literature 1). Specifically, a fiber suspension in which fibers are dispersed is supplied to a papermaking wire, and the fibers are accumulated on the papermaking wire, thereby forming a fiber sheet on the papermaking wire.

[0003] PRIOR ART DOCUMENTS

[0004] PATENT LITERATURE

[0005] Patent Literature 1: Japanese Patent Application Publication No. 2013-076196 SUMMARY

[0006] In recent years, a fiber sheet such as a nonwoven fabric is used as a printed wiring board material containing an epoxy resin in addition to a filter, an adsorbing material, or a thermal insulation material, and is widely used.

[0007] The finer the fibers constituting the fiber sheet, the thinner the fiber sheet, and the thickness deviation can be suppressed. In addition, the fiber sheet is required to have improved filtration performance, and in order to increase the specific surface area or to capture fine substances by reducing the pore diameter, it is expected to manufacture the fiber sheet using fine fibers.

[0008] In addition to the papermaking method, a coating machine method is also used to manufacture a fiber sheet, but when fine fibers are used to manufacture a fiber sheet, the finer the fibers, the larger the specific surface area, and the more the amount of solvent required to wet the fibers increases. Therefore, a method of the solvent recovery type such as the papermaking method is advantageous in terms of cost.

[0009] However, when the papermaking method is used, commercially available papermaking wires are difficult to capture fine fibers having a fiber length of 100 μm or less. In order to capture fine fibers, a method of agglomerating fibers is also considered, but the texture of the fiber mat formed by picking up the agglomerated fibers is deteriorated.

[0010] The present application has been made in view of the above-described problems, and an object of the present application is to provide a method for manufacturing a fiber mat containing fine fibers and having a good texture and a fiber mat.

[0011] The method for manufacturing fiber felt according to this disclosure includes a step of dispersing microfibers in a dispersion medium and a step of felting the dispersed microfibers. The microfibers have a fiber length smaller than the pore size of a papermaking wire. The felting step includes a step of forming the dispersed microfibers into microporous sheets, the microporous sheets having a pore size smaller than the papermaking wire and being disposed on the papermaking wire.

[0012] In the above-described method for manufacturing fiber felt based on the present disclosure, the microfibers can be liquid crystal polymer powder.

[0013] In the above-described method for manufacturing fiber felt based on the present disclosure, the liquid crystal polymer powder preferably uses short fibrous particles with a length-to-diameter ratio of 10 to 500 times in the long side direction and including fibrous portions with an average diameter of 2 μm or less.

[0014] In the above-described method for manufacturing fiber felt based on the present disclosure, the felting process further includes a process of peeling the microporous sheet containing the dispersed microfibers from the papermaking wire.

[0015] In the above-disclosed method for manufacturing fiber felt, a fabric web with a pore size of 50 μm or less can be used as the microporous sheet.

[0016] In the above-disclosed method for manufacturing fiber felt, wet nonwoven fabric can be used as the microporous sheet.

[0017] The fiber felt disclosed herein is composed of microfibers and has a texture index of less than 100 as determined by a 3D sheet analyzer.

[0018] In the fiber felt disclosed above, the texture index can be 10 or higher.

[0019] In the fiber felt disclosed above, the microfibers can be liquid crystal polymer powder.

[0020] According to the present invention, a method for manufacturing a fiber felt containing fine fibers and of good texture, and a fiber felt can be provided. Attached Figure Description

[0021] Figure 1 This is a flowchart illustrating the manufacturing process of fiber felt.

[0022] Figure 2 This diagram illustrates the felting process in the manufacturing of fiber felt, where liquid crystal polymer powder is felted. Detailed Implementation

[0023] Hereinafter, embodiments of the present invention will be described in detail with reference to the figures. It should be noted that in the embodiments shown below, the same or common parts are labeled with the same symbols in the figures, and their descriptions will not be repeated.

[0024] <Fiber mat>

[0025] The fiber felt of this embodiment is composed of liquid crystal polymer powder that has been micronized and fibrousized. The liquid crystal polymer used in the liquid crystal polymer powder is a thermotropic liquid crystal polymer. Furthermore, the liquid crystal polymer molecules have a negative coefficient of thermal expansion along the molecular axis and a positive coefficient of thermal expansion along the radial axis. The liquid crystal polymer of this embodiment does not contain amide bonds.

[0026] The fiber felt of this embodiment has a Formation Index of 100 or less, as measured using a 3D Formation Analyzer. It should be noted that the Formation Index of the fiber felt can be 20 or less. Alternatively, the Formation Index of the fiber felt can be 10 or more.

[0027] The 3D thin-section analyzer is manufactured by M / K Systems. The quantification of texture using this analyzer is termed the texture index. The texture index is calculated as follows.

[0028] 1) Wrap the fiber felt around the roller and irradiate the fiber felt with a light source (white light) set on the roller shaft while it is rotating.

[0029] 2) The light transmitted through the fiber felt was detected using a photodetector, and the intensity of the transmitted light at 100,000 measurement points was classified into 64 intensity levels.

[0030] 3) Calculate the texture index by multiplying the highest degree (Peak value) / number of grades (Bins value) by 1 / 100.

[0031] It should be noted that the Peak value is the number of measurement points in a histogram with 100,000 measurement points, and the Bins value is the number of bins with more than 100 points in the histogram, plus the tens digit of the degree with the largest number of points (less than 100 points), multiplied by 0.1.

[0032] The smaller the texture index, the higher the uniformity, resulting in a high-quality fiber felt. In this embodiment, by having the aforementioned texture index, both high uniformity and good texture are achieved.

[0033] <membrane>

[0034] The aforementioned fiber felt is pressed and processed to produce a film (more specifically, a liquid crystal polymer film). This liquid crystal polymer film may be bonded with a metal foil such as copper foil on at least one side, or with the aforementioned metal foil on both sides. In this case, the liquid crystal polymer film of this embodiment can serve as a laminated molded body, used for example as an FCCL (Flexible Copper Clad Laminates) capable of forming circuits using a subtractive process.

[0035] Here, when fabricating a laminated molded body with a film bonded with metal foil, generally speaking, when using a poor-quality fiber felt, the bonded metal foil will have uneven thickness. Furthermore, when forcibly making the thickness unevenness uniform by pressing both sides of the fiber felt bonded with metal foil with a rigid plate, the raw material flows from the thicker parts of the fiber felt to the thinner parts. When this raw material is an oriented material such as a liquid crystal polymer, the orientation is disrupted, for example, the in-plane coefficient of thermal expansion deviates. This results in deformation and unevenness.

[0036] On the other hand, when using the fiber felt of this embodiment to fabricate a film bonded with a metal foil, by giving the fiber felt the texture index described above, thickness unevenness of the bonded metal foil can be suppressed. Furthermore, when bonding the metal foil, as described below, the principal orientation direction of the liquid crystal polymer molecules is along the in-plane direction of the metal foil, i.e., the in-plane direction of the film. This suppresses deviations in the in-plane coefficient of thermal expansion, thereby suppressing deformation and unevenness.

[0037] <Method for manufacturing fiber felt>

[0038] Figure 1 This is a flowchart illustrating the manufacturing process of fiber felt. (See reference...) Figure 1 The manufacturing method of the fiber felt according to this embodiment will be described.

[0039] like Figure 1 As shown, the fiber felt manufacturing method of this embodiment includes a coarse crushing step (S11), a fine crushing step (S12), a coarse particle removal step (S13) and a fiberization step (S14) as a preceding step (S10), and further includes a dispersion step (S21) and a felting step (S22) as a following step (S20) after the preceding step (S10).

[0040] <Pre-process>

[0041] In the initial coarse crushing step (S12), which is the preceding step (S10), a molded article of the liquid crystal polymer is first prepared as a raw material. Examples of molded articles of the liquid crystal polymer include uniaxially oriented granular, biaxially oriented film-like, or powder-like liquid crystal polymers. From a manufacturing cost perspective, granular or powder-like liquid crystal polymers, which are less expensive than film-like liquid crystal polymers, are preferred as molded articles of the liquid crystal polymer; granular liquid crystal polymers are more preferred. In this embodiment, the molded article of the liquid crystal polymer preferably does not contain liquid crystal polymers that are directly molded into fibers by electrospinning or meltblowing. However, the molded article of the liquid crystal polymer may include liquid crystal polymers that are processed into fibers by crushing granular or powder-like liquid crystal polymers.

[0042] Next, coarsely ground liquid crystal polymer is obtained by coarsely grinding the molded liquid crystal polymer. For example, coarsely ground liquid crystal polymer is obtained by coarsely grinding the molded liquid crystal polymer using a shredder. The particle size of the coarsely ground liquid crystal polymer is not particularly limited as long as it can be used as raw material for the micro-grinding process described later. The maximum particle size of the coarsely ground liquid crystal polymer is, for example, 3 mm or less.

[0043] The method for manufacturing the liquid crystal polymer film in this embodiment may not necessarily include a coarse grinding step (S11). For example, as long as the liquid crystal polymer molded article can be used as a raw material for the micro-grinding step, the liquid crystal polymer molded article can be directly used as a raw material for the micro-grinding step.

[0044] Next, in the micronization step (S12), the liquid crystal polymer is pulverized while the coarsely pulverized liquid crystal polymer is dispersed in liquid nitrogen to obtain granular micronized liquid crystal polymer. In the micronization step (S12), a medium is used to pulverize the coarsely pulverized liquid crystal polymer dispersed in liquid nitrogen. The medium is, for example, beads. In the micronization step (S12), from the viewpoint of handling liquid nitrogen, a bead mill, which has fewer technical problems, is preferred. As an apparatus that can be used in the micronization step (S12), the liquid nitrogen bead mill "LNM-08" manufactured by IMEX Corporation can be cited as an example.

[0045] In the micronization step (S12) of this embodiment, the pulverization method, in which the liquid crystal polymer is pulverized while dispersed in liquid nitrogen, differs from the existing cryogenic pulverization method. The existing cryogenic pulverization method involves pulverizing the raw material while simultaneously injecting liquid nitrogen into both the raw material and the pulverization apparatus body; however, at the moment the raw material is pulverized, most of the liquid nitrogen vaporizes. That is, in the existing cryogenic pulverization method, at the moment the raw material is pulverized, most of the raw material is not dispersed in the liquid nitrogen.

[0046] In existing cryogenic grinding methods, the heat inherent in the raw material being ground, the heat generated by the grinding device, and the heat generated by grinding the raw material cause liquid nitrogen to vaporize in a very short time. Therefore, in existing cryogenic grinding methods, the raw material being ground inside the grinding device reaches a temperature far exceeding -196°C, the boiling point of liquid nitrogen. That is, in existing cryogenic grinding methods, grinding is typically carried out at temperatures between -100°C and 0°C. Even with the maximum possible supply of liquid nitrogen, the lowest possible temperature inside the grinding device in existing cryogenic grinding methods is approximately -150°C.

[0047] Therefore, in existing cryogenic pulverization methods, for example, when pulverizing uniaxially oriented granular liquid crystal polymers or coarsely pulverized granular liquid crystal polymers, the pulverization is carried out along a plane approximately parallel to the axial direction of the liquid crystal polymer's molecular axis. Thus, fibrous liquid crystal polymers with very large aspect ratios and fiber diameters much larger than 3 μm are obtained. That is, even when pulverizing uniaxially oriented granular liquid crystal polymers or coarsely pulverized granular liquid crystal polymers in existing cryogenic pulverization methods, it is impossible to obtain the granular micro-pulverized liquid crystal polymer used in this embodiment.

[0048] In this embodiment, since the raw material is pulverized while dispersed in liquid nitrogen, it is possible to pulverize raw materials in a more cooled state compared to conventional cryogenic pulverization methods. Specifically, it is possible to pulverize raw materials at temperatures lower than -196°C, which is the boiling point of liquid nitrogen. If raw materials at temperatures below -196°C are pulverized, pulverization is achieved by repeatedly subjecting the raw material to brittle fracture. Thus, even when pulverizing uniaxially oriented liquid crystal polymers, for example, not only is fracture carried out along planes substantially parallel to the molecular axis of the liquid crystal polymer, but also along planes intersecting the aforementioned axis, thereby obtaining granular, micronized liquid crystal polymers.

[0049] Furthermore, in the micronization process (S12), the liquid crystal polymer, which has become granular through brittle fracture, is continuously impacted in a brittle state using a medium or the like in liquid nitrogen. As a result, multiple microcracks are formed in the liquid crystal polymer obtained in the micronization process (S12) from the outer surface to the interior.

[0050] The granular micronized liquid crystal polymer obtained by the micronization process (S12) has a D50 of less than 100 μm, more preferably less than 50 μm, as measured by a particle size distribution measuring device based on laser diffraction scattering. This prevents the granular micronized liquid crystal polymer from clogging the nozzle in the fiberization process described below.

[0051] Next, in the coarse particle removal step (S13), coarse particles are removed from the granular micronized liquid crystal polymer obtained in the micronization step (S12). For example, the granular micronized liquid crystal polymer is sieved through a screen to obtain the granular micronized liquid crystal polymer that passes through the screen. By removing the granular liquid crystal polymer that passes through the screen, the coarse particles contained in the granular micronized liquid crystal polymer can be removed. The type of screen can be appropriately selected; for example, a screen with a mesh size of 100 μm can be used. It should be noted that the mesh size of the screen can be appropriately changed according to the desired fiber length of the liquid crystal polymer powder. For example, a screen with a mesh size of about 5 μm to 50 μm can be used. In addition, the liquid crystal polymer powder manufacturing method of this embodiment may not necessarily include the coarse particle removal step (S13).

[0052] Next, in the fiberization step (S14), the granular liquid crystal polymer is crushed using a wet high-pressure crushing device to obtain liquid crystal polymer powder. In the fiberization step (S14), the micronized liquid crystal polymer is first dispersed in a dispersion medium for the fiberization step. The dispersed micronized liquid crystal polymer may not have coarse particles removed, but it is preferable to remove them. Examples of dispersion media for the fiberization step include water, ethanol, methanol, isopropanol, toluene, benzene, xylene, phenol, acetone, methyl ethyl ketone, diethyl ether, dimethyl ether, hexane, or mixtures thereof.

[0053] Then, the micronized liquid crystal polymer, i.e., the slurry-like micronized liquid crystal polymer, dispersed in the dispersion medium used in the fiberization process, is passed through a nozzle under high pressure. By passing through the nozzle under high pressure, the shear force or impact energy generated by the high-speed flow in the nozzle acts on the liquid crystal polymer, breaking down the granular micronized liquid crystal polymer, thereby fiberizing the liquid crystal polymer and obtaining liquid crystal polymer powder that can be used in subsequent processes. From the viewpoint of providing high shear force or high impact energy, it is preferable to minimize the nozzle diameter as much as possible to prevent clogging of the micronized liquid crystal polymer in the nozzle. In this embodiment, the particle size of the granular micronized liquid crystal polymer is small, thus allowing for a smaller nozzle diameter in the wet high-pressure crushing device used in the fiberization process. The nozzle diameter is, for example, 0.2 mm or less.

[0054] In this embodiment, as described above, multiple microcracks are formed in the granular micronized liquid crystal polymer powder. Therefore, by applying pressure in a wet high-pressure crushing device, the dispersion medium penetrates into the interior of the micronized liquid crystal polymer through the microcracks. Then, when the slurry-like micronized liquid crystal polymer passes through a nozzle under normal pressure, the dispersion medium that has penetrated into the interior of the micronized liquid crystal polymer expands within a short time. By expanding the dispersion medium that has penetrated into the interior of the micronized liquid crystal polymer, it thereby causes destruction from the interior of the micronized liquid crystal polymer. Therefore, fiberization proceeds to the interior of the micronized liquid crystal polymer, and the liquid crystal polymer molecules are separated into unidirectionally arranged structural domain units. Thus, in the fiberization process of this embodiment, by defibrating the granular micronized liquid crystal polymer obtained in the micronization process of this embodiment, a liquid crystal polymer powder with a lower content of blocky portions and consisting of fine short fibers can be obtained compared to the liquid crystal polymer powder obtained by crushing the granular liquid crystal polymer obtained by conventional cryogenic pulverization methods.

[0055] In the fiberization step (S14) of this embodiment, liquid crystal polymer powder can be obtained by repeatedly crushing the micronized liquid crystal polymer using a wet high-pressure crushing device. The number of crushing operations using the wet high-pressure crushing device is preferably small. For example, the number of crushing operations using the wet high-pressure crushing device can be 5 times or less.

[0056] The obtained liquid crystal polymer powder is used as a raw material for subsequent processes. Here, the liquid crystal polymer powder as microfibers is described in detail.

[0057] Liquid crystal polymer powders contain at least a fibrous portion. The fibrous portion refers to short, fibrous particles with an aspect ratio (length to diameter) of 10 to 500, and an average diameter of 2 μm or less. Liquid crystal polymer powders containing such fine, short, fibrous portions with an aspect ratio of 10 to 500 and an average diameter of 2 μm or less cannot be manufactured using currently known manufacturing methods.

[0058] For example, liquid crystal polymer powder containing fiber portions with aspect ratios of 10 to 500 cannot be manufactured solely by electrospinning, a method used for manufacturing extremely fine continuous long fibers. It should be noted that it is considered that the extremely fine long liquid crystal polymer fibers, which are continuous long fibers manufactured by electrospinning, are cut into short fibers after spinning. However, there are limitations to the ability to cut such continuous long liquid crystal polymer fibers with extremely small fiber diameters and approximately infinite aspect ratios. The aspect ratio of the extremely fine long liquid crystal polymer fibers after cutting the continuous long liquid crystal polymer fibers manufactured by electrospinning exceeds 500.

[0059] The average diameter of the fibrous portion is the average of the fiber diameters of the multiple fibrous particles constituting the fibrous portion. Thus, the liquid crystal polymer powder of this embodiment contains fine fibrous particles. The fiber diameter can be determined based on image data of the fibrous particles obtained by observing them with a scanning electron microscope.

[0060] The aspect ratio of the fiber portion is preferably 300 or less, more preferably 100 or less. The average diameter of the fiber portion is preferably 1 μm or less.

[0061] The aforementioned fibrous portion can be included in the liquid crystal polymer powder as an aggregate of fibrous particles. Furthermore, the axial direction of the liquid crystal polymer molecules constituting the fibrous portion is aligned with the long side direction of the fibrous portion. It should be noted that in the manufacturing method of the fiber mat of this embodiment, since the liquid crystal polymer powder is manufactured through the aforementioned fibrous process, the multiple structural domains formed by the liquid crystal polymer molecules becoming bundles are disrupted, thereby causing the axial direction of the liquid crystal polymer molecules to be strongly oriented along the long side direction of the fibrous portion.

[0062] The liquid crystal polymer powder preferably contains substantially unfibrillated bulk portions at a content of 20% or less. Furthermore, it is more preferable that the liquid crystal polymer powder does not contain bulk portions. The content of bulk portions is evaluated by the number of bulk portions in the liquid crystal polymer powder relative to the number of aggregated portions. In this embodiment, aggregated portions with a maximum height greater than 10 μm when the liquid crystal polymer powder is placed on a plane are defined as bulk portions, and aggregated portions with a maximum height of 10 μm or less are defined as fibrous portions.

[0063] The bulk portion can be included in the liquid crystal polymer powder as an aggregated portion containing bulk particles. The bulk portion is a substantially unfibrillated liquid crystal polymer powder. The bulk portion can have a flat shape.

[0064] In this embodiment, the D50 value of the liquid crystal polymer powder, which is determined by particle size measurement using a particle size distribution measuring device based on laser diffraction scattering, can be, for example, less than 13 μm.

[0065] It should be noted that the liquid crystal polymer powder used as a raw material for subsequent processes is not limited to the liquid crystal polymer powder manufactured in the aforementioned preceding processes.

[0066] <Post-processing>

[0067] Next, the subsequent process (S20) will be explained. In the dispersion process (S21), which is the first process of the subsequent process (S20), the liquid crystal polymer powder described above is dispersed in a dispersion medium to form a slurry. Since the liquid crystal polymer powder described above is in the form of fine short fibers, the liquid crystal polymer powder can be dispersed in a high-viscosity dispersion medium, thereby enabling the manufacture of a homogeneous fiber mat.

[0068] Examples of dispersion media used in the dispersion process (S21) include water, ethanol, and mixtures thereof. By using such dispersion media, the cost of the dispersion media can be reduced, allowing for the inexpensive manufacture of fiber felt.

[0069] It should be noted that the long side 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.

[0070] Next, in the felting process (S22), the slurry-like liquid crystal polymer powder is formed into liquid crystal polymer fiber felt using a papermaking method. In the papermaking process, the dispersion medium used in the dispersion process can be recovered and reused, enabling the inexpensive manufacture of fiber felt.

[0071] Figure 2 This diagram illustrates the felting process in the manufacturing of fiber felt, where liquid crystal polymer powder is felted. (Refer to...) Figure 2 The felting process is described in detail.

[0072] like Figure 2 As shown, a paper machine 100 is used in the felting process. The paper machine 100 includes: a feed roller 15 for supplying microporous sheets 10, a winding roller (not shown) for recovering microporous sheets 10, a paper wire 20, conveying rollers 25 and 26, a storage section 40 for storing a dispersion medium 41 in which the above-mentioned liquid crystal polymer powder is dispersed, and a heating device 50.

[0073] The papermaking wire 20 has a mesh size of approximately 80 to 100 mesh. That is, the papermaking wire 20 has an aperture of approximately 150 μm to 180 μm. The papermaking wire 20 is conveyed by conveyor rollers 25 and 26 arranged in the conveying direction. The conveyor roller 26 is positioned downstream of the conveyor roller 27. The papermaking wire 20 is conveyed by these conveyor rollers 25 and 26 to pass through the storage section 40.

[0074] The supply roller 15 supplies the microporous sheet 10 onto the papermaking wire 20. The microporous sheet 10 disposed on the papermaking wire 20 is conveyed by the papermaking wire 20 to pass through the storage section 40. The microporous sheet 10 passing through the storage section 40 is peeled off from the papermaking wire 20 and wound by the winding roller.

[0075] The microporous sheet 10 has a finer mesh than the paper 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 for the trapping of fine liquid crystal polymer powder dispersed in the dispersion medium.

[0076] 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, the water filtration performance deteriorates and the dehydration time becomes longer. On the other hand, if the pore size of the microporous sheet 10 is too large, it is difficult to capture microfibers (fine liquid crystal polymer powder), resulting in a poor yield.

[0077] When selecting a microporous sheet 10 with deviations in pore size, the texture of the resulting fiber felt is affected. Therefore, when high uniformity of the fiber felt is required, it is preferable to periodically weave a mesh-like structure. That is, as the microporous sheet 10, it is preferable to use a mesh with uniform pore size and no deviation in pore position.

[0078] As the microporous sheet 10, for example, a fabric web with a pore size of 50 μm or less can be used. As the fabric web, for example, a web made of synthetic fibers such as polyester can be used.

[0079] Furthermore, the microporous sheet 10 can be made of wet-laid nonwoven fabric. This wet-laid nonwoven fabric can be made of microfibers. The microfibers are, for example, composed of synthetic fibers such as polyester. It should be noted that, as the wet-laid nonwoven fabric, a fabric with a weight per unit area of ​​15 g / m² can be used. 2 The following are examples of nonwoven fabrics.

[0080] In the conveying direction, a heating device 50 is arranged on the downstream side of the storage section 40. The heating device 50 heats the liquid crystal polymer powder 30 that has been rolled up to the microporous sheet 10 to dry it.

[0081] The felting process (S21) includes a lifting process, a peeling process, and a drying process. In the felting process (S21), firstly, the dispersed liquid crystal polymer powder is lifted onto the microporous sheet 10 by the lifting process. Specifically, the microporous sheet 10 supplied to the papermaking wire 20 is conveyed by the papermaking wire 20 and passes through the storage section 40. At this time, the liquid crystal polymer powder dispersed in the dispersion medium 41 stored in the storage section 40 is lifted onto the microporous sheet 10.

[0082] Next, in the peeling process, the microporous sheet 10, which has gathered the dispersed liquid crystal polymer powder, is peeled off from the papermaking wire 20. Specifically, the microporous sheet 10 is wound with a winding roller and conveyed in a direction different from that of the papermaking wire 20. It should be noted that the papermaking wire 20 can also be conveyed in a direction different from that of the microporous sheet 10 using a conveying roller 26.

[0083] Next, in the drying process, the liquid crystal polymer powder 30, which has been rolled up onto the microporous sheet 10, is heated and dried using a heating device 50. As a result, a fiber mat made of liquid crystal polymer is formed on the microporous sheet 10.

[0084] The microporous sheet 10 with fibrous felt is wound by the winding rollers mentioned above during the winding process.

[0085] Thus, by conveying the fiber felt together with the microporous sheet 10 while the liquid crystal polymer powder is being rolled up, the fiber felt can be transported to the next process without causing the weak and fragile fiber felt to break due to the entanglement of the microfibers.

[0086] <Membrane Manufacturing Methods>

[0087] Next, the fiber felt is peeled off from the microporous sheet 10 and then heated and pressed to obtain a liquid crystal polymer film. Through the heating and pressing process, the thickness of the liquid crystal polymer film is thinner than that of the fiber felt.

[0088] In the heat pressing process, the liquid crystal polymer fiber felt is heated and pressed together with, for example, copper foil. Thus, the heat pressing process also serves as a process for bonding the liquid crystal polymer film and the copper foil together, thereby enabling the production of a liquid crystal polymer film bonded with copper foil at low cost. It should be noted that, during prolonged heating in the heat pressing process, vacuum heat pressing of the liquid crystal polymer fiber felt is preferable.

[0089] In the heat pressing process, it is preferable to perform the heat pressing at a temperature approximately 5°C 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 approximately 5°C to 15°C lower than the aforementioned endothermic peak temperature, it is easier to sinter the liquid crystal polymers together.

[0090] Furthermore, in the heat pressing process, a polyimide film, a PTFE film, or a composite sheet made of reinforcing materials such as glass fiber fabric and heat-resistant resin can be sandwiched between the press and the liquid crystal polymer fiber felt as a release film. Alternatively, an additional copper foil can be sandwiched between the press and the liquid crystal polymer fiber felt instead of the polyimide film. This allows for the production of a liquid crystal polymer film with copper foil bonded to both sides. This liquid crystal polymer film with copper foil bonded to both sides can be used as a double-sided copper-clad liquid crystal polymer (FCCL).

[0091] By heating and pressing, the fibrous portions of the liquid crystal polymer powder in the fiber felt, particularly those with a long side along the thickness direction of the fiber felt, are heated while being pushed toward the in-plane direction of the copper foil. Since the liquid crystal polymer constituting the liquid crystal polymer powder has molecular axial direction along the long side of the fibrous portion, the molecular axial direction of the liquid crystal polymer is also pushed toward the in-plane direction of the copper foil.

[0092] Therefore, in the formed liquid crystal polymer film, the main orientation direction of the liquid crystal polymer molecules is along the in-plane direction of the copper foil, that is, the in-plane direction of the liquid crystal polymer film. The axial direction of the molecules in the bulk portions is random, and depending on the proportion of bulk portions contained in the liquid crystal polymer film, there are portions where the axial direction of the liquid crystal polymer molecules is oriented towards the thickness direction of the liquid crystal polymer film.

[0093] Specifically, in the in-plane direction of the liquid crystal polymer film, there are regions where the axial direction of the liquid crystal polymer molecules is more likely to be towards the thickness direction of the liquid crystal polymer film, and regions where the axial direction of the liquid crystal polymer molecules is more likely to be towards the in-plane direction. More specifically, apart from the molecules constituting the bulk portion, the axial directions of the molecules constituting the liquid crystal polymer are oriented along the in-plane direction of the liquid crystal polymer film in the thickness direction.

[0094] Furthermore, the liquid crystal polymer powder in the fiber felt sometimes bonds together while the fibers are intertwined. Thus, the liquid crystal polymer in the liquid crystal polymer film has a structure in which the molecules are intertwined. In addition, since the surface area of ​​the aforementioned fiber portion is larger than that of a spherical liquid crystal polymer having the same volume, the bonding area when the liquid crystal polymer powder bonds together also increases through the heat pressing process. Therefore, the toughness and folding resistance of the liquid crystal polymer film of this embodiment are improved.

[0095] It should be noted that, if necessary, the metal foil bonded to the liquid crystal polymer film can be removed by etching or the like. This yields a liquid crystal polymer film of monomers without the bonded metal foil.

[0096] <Experimental Example>

[0097] The present invention will now be described in more detail with reference to examples and comparative examples, but the invention is not limited to these examples. In the experimental examples, fiber mats of Examples 1 and 2 were prepared, and their texture index was determined using a 3D sheet analyzer manufactured by M / K Systems. In Comparative Example 1, an attempt was made to produce fiber mats, but it could not be produced as described below.

[0098] (Example 1)

[0099] In Example 1, firstly, granular liquid crystal polymer, which is used as a raw material, is fed into a shredder for coarse grinding. The melting point of the liquid crystal polymer used in Example 1 is 315°C. The coarsely ground film-like liquid crystal polymer is discharged from a 3mm diameter discharge hole provided in the shredder, thereby obtaining coarsely ground liquid crystal polymer.

[0100] Next, the coarsely pulverized liquid crystal polymer was micronized using a liquid nitrogen bead mill (IMEX, LNM-08). In the liquid nitrogen bead mill, a 0.8L container was used, 5mm diameter zirconia beads were used as the grinding medium, and 500mL of medium was added. 30g of the coarsely pulverized liquid crystal polymer was added, and the milling process was carried out at 2000rpm for 120 minutes. In the liquid nitrogen bead mill, the coarsely pulverized liquid crystal polymer was dispersed in liquid nitrogen for wet milling. Thus, by pulverizing the coarsely pulverized liquid crystal polymer using a liquid nitrogen bead mill, granular micronized liquid crystal polymer was obtained.

[0101] Next, the micronized liquid crystal polymer was wet-classified using a 100μm mesh sieve to remove coarse particles and recover the micronized liquid crystal polymer that had passed through the sieve. It should be noted that a 100μm mesh sieve was used in Example 1, but a sieve with a smaller mesh size can also be used for classification.

[0102] Next, the micronized liquid crystal polymer, from which coarse particles have been removed, was dispersed in a 20 wt% aqueous ethanol solution. Using a wet high-pressure crushing apparatus, the ethanol slurry containing the micronized liquid crystal polymer was repeatedly crushed five times under conditions of a nozzle diameter of 0.2 mm and a pressure of 200 MPa, thereby achieving fiberization. The wet high-pressure crushing apparatus used was a Star Burst HJP-25060 manufactured by SUGINO MACHINE. This yielded a liquid crystal polymer powder dispersed in an aqueous ethanol solution.

[0103] Next, the necessary amounts of water and ethanol were added to prepare a solution containing 2.2 g of liquid crystal polymer powder relative to 30 L of a 50 wt% ethanol aqueous solution. This slurry-like liquid crystal polymer powder was then formed into fiber mats using a papermaking process. A square sheet forming machine 2555 manufactured by Kumagai Riki Co., Ltd. was used as the papermaking machine to form the liquid crystal polymer powder dispersed in the dispersion medium onto a microporous sheet of a polyester mesh with a pore size of 11 μm.

[0104] Next, the fiber mat is dried at 100°C using a hot air dryer, forming it on a microporous sheet. The surface area weight of the fiber mat is 35 g / m². 2 about.

[0105] Two fiber mats of Example 1 were prepared, with texture indices of 100 or less, specifically 98.4 and 77.2, respectively. It was confirmed that the fiber mat of Example 1 contained fine fibers and had a particularly good texture.

[0106] (Example 2)

[0107] In Example 2, a wet nonwoven fabric composed of polyester microfibers with a unit area weight of 35 g / m² was used as the microporous sheet. 2 The microporous sheets are on the left and right. Except as described above, the fiber mat is obtained in essentially the same manner as in Example 1.

[0108] Two fiber mats of Example 2 were prepared, with texture indices of 10 or higher, specifically 15.6 and 11.7 respectively. Although the texture of Example 2 was lower than that of Example 1, a fiber mat containing fine fibers and with good texture was obtained.

[0109] (Comparative Example 1)

[0110] In Comparative Example 1, liquid crystal polymer powder dispersed in a dispersion medium was transferred onto a papermaking wire without using a microporous sheet. The papermaking wire used was an LTT-9FE manufactured by NIPPON FILCON.

[0111] Since no microporous sheet was used in Comparative Example 1, most of the liquid crystal polymer powder passed through the pores of the papermaking wire and could not form a fiber mat.

[0112] In the above embodiments and examples, the case where the microfiber is liquid crystal polymer powder has been described, but the microfiber is not limited to liquid crystal polymer powder. As described above, as long as the fiber length is smaller than the pore size of the papermaking wire 20, organic fibers with organic matter as the main component can also be appropriately used as microfibers.

[0113] The above description of all embodiments and examples of this invention is illustrative and not restrictive. The scope of this invention is indicated by the scope of the claims, including all modifications within the scope and meaning of the same claims.

[0114] Symbol Explanation

[0115] 10 Microporous sheet, 15 Feed roll, 20 Paper wire, 25, 26 Conveyor roll, 30 Liquid crystal polymer powder, 40 Storage section, 41 Dispersion medium, 50 Heating device, 100 Paper machine.

Claims

1. A method for manufacturing fiber felt, comprising: The process of dispersing microfibers in a dispersion medium, and The process of felting the dispersed microfibers; The microfibers have a fiber length smaller than the pore size of the papermaking wire. The felting process includes the step of forming the dispersed microfibers into microporous sheets, the microporous sheets having pore sizes smaller than the papermaking wire and being disposed on the papermaking wire. The microfibers are liquid crystal polymer powder. The liquid crystal polymer powder used is a short fibrous particle with a length-to-diameter ratio of 10 to 500 times, and includes a fibrous portion with an average diameter of 2 μm or less.

2. The method for manufacturing fiber felt according to claim 1, wherein, The felting process further includes the step of peeling the microporous sheet, which has been scooped up and dispersed microfibers, from the papermaking wire.

3. The method for manufacturing fiber felt according to claim 1 or 2, wherein, As the microporous sheet, a fabric mesh with a pore size of less than 100 μm is used.

4. The method for manufacturing fiber felt according to claim 1 or 2, wherein, The microporous sheet is made of wet nonwoven fabric.

5. A fiber felt composed of fine fibers, The microfibers are liquid crystal polymer powder. The liquid crystal polymer powder used is a short fibrous particle with a length-to-diameter ratio (length to diameter) of 10 to 500 times, and includes a fibrous portion with an average diameter of 2 μm or less. The texture index, as determined using a 3D thin-film analyzer, is below 100.

6. The fiber felt according to claim 5, wherein, The texture index is 10 or higher.

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