Method for manufacturing a fibrous mat and fibrous mat

Abstract

The method for manufacturing a fiber mat includes a step of dispersing fine fibers having thermoplasticity in a dispersion medium, and a step of matting the dispersed fine fibers on a support. The step of matting includes a step of forming a fiber mat (30) by picking up the fine fibers on the support, and a step of irradiating light to a first main surface (31) of the fiber mat (30) on the side opposite to the side on which the support is present. In the step of irradiating light to the first main surface (31) of the fiber mat (30), the fine fibers on the first main surface (31) side are fused.

Description

[0001] This application is a divisional application of Chinese patent application No. 202280051704.4 (the original application was entitled "Method for manufacturing fiber felt and fiber felt", and the original application was filed on March 25, 2022). Technical Field

[0002] This invention relates to a method for manufacturing fiber felt and to fiber felt itself. Background Technology

[0003] As a conventional method for manufacturing fiber sheets (fiber mats), Japanese Patent Application Publication No. 2013-076196 (Patent Document 1) discloses a method for producing fiber sheets using a papermaking process. Specifically, a fiber suspension containing dispersed fibers is supplied to a papermaking wire, causing the fibers to accumulate on the papermaking wire, thereby forming a fiber sheet on the papermaking wire.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2013-076196 Summary of the Invention

[0007] In recent years, non-woven fabrics and other fiber sheets, in addition to being used as filters, adsorbents, or heat insulation materials, have also been used as printed wiring board materials containing epoxy resin, and their applications are wide-ranging.

[0008] The finer the fibers that make up the fiber sheet, the thinner the fiber sheet, and the better it is at suppressing thickness deviations. In addition, there is a demand for improved filtration performance of fiber sheets. In order to increase the specific surface area or to capture fine substances by reducing the pore size, it is desirable to use fine fibers to manufacture fiber sheets.

[0009] As a technique for flake-forming (felt-forming) fibers, coating and papermaking are the mainstream methods. However, the finer the fibers, the larger their specific surface area, and the greater the amount of solvent required to wet them. Therefore, solvent-recovery methods like papermaking are cost-effective.

[0010] When papermaking is used to form fibers with hydrogen bonds, such as pulp, the fibers in the resulting fiber mat gain strength through hydrogen bonds by dehydration and drying after papermaking.

[0011] However, in the case of chemical fibers that do not possess hydrogen bonds, if they are bonded solely by the entanglement of fibers, especially short fibers such as microfibers, it is difficult to obtain sufficient strength for processing. Therefore, methods have been considered to give the fiber felt strength by mixing it with a binder, but in this case, the electrical properties of the fiber felt deteriorate, or its heat resistance deteriorates, resulting in a degradation of the fiber felt's performance.

[0012] Another widely used method is to use a calender to heat and press fibers together to achieve strength. However, when hot-pressing fibers using a calender, the fiber mat needs to be peeled off from a screen or papermaking wire. When using fine, and especially very short, fibers, the fiber mat lacks the strength to withstand such peeling.

[0013] If the calendering process is performed without peeling, the fiber mat becomes integrated with the screen or papermaking wire and cannot be peeled off. In addition, compared with the papermaking fibers, the screen or papermaking wire requires the use of high-melting-point materials, and there are no inexpensive materials that can match them when using microfibers of high-melting-point resins such as liquid crystal polymers (LCP).

[0014] The present invention was made in view of the problems described above, and the object of the present invention is to provide a method for manufacturing a fiber mat containing microfibers and having high strength, and the fiber mat itself.

[0015] The method for manufacturing fiber felt according to this disclosure includes a step of dispersing thermoplastic microfibers in a dispersion medium, and a step of felting the dispersed microfibers on a support. The felting step includes a step of rolling the microfibers onto the support to form a fiber felt, and a step of irradiating a first main surface of the fiber felt located on a side opposite to the side where the support is located with light. In the step of irradiating the first main surface of the fiber felt with light, the microfibers located on the first main surface side are fused together.

[0016] In the above-described method for manufacturing fiber felt based on the present disclosure, the microfibers used can have a higher melting point than the support.

[0017] In the above-described method for manufacturing fiber felt based on the present disclosure, pulsed light is preferably used in the process of performing light irradiation.

[0018] In the above-described method for manufacturing fiber felt based on this disclosure, the felting process may further include: peeling the fiber felt, on which the first main surface has been light-irradiated, from the support, and light-irradiating the second main surface of the fiber felt located on the side opposite to the side where the first main surface is located. In this case, in the process of light-irradiating the second main surface of the fiber felt, it is preferable to fuse the microfibers located on the second main surface side.

[0019] In the above-described method for manufacturing fiber felt based on the present disclosure, liquid crystal polymer powder can be used as the microfiber.

[0020] In the above-described method for manufacturing fiber felt based on the present disclosure, the liquid crystal polymer powder preferably used is a liquid crystal polymer powder containing a fiber portion, wherein the fiber portion is a short fibrous particle with a length-to-diameter ratio of 10 to 500 times in the long side direction and an average diameter of 2 μm or less.

[0021] The fiber felt based on this disclosure is composed of thermoplastic microfibers and has a first main surface on one side in the thickness direction. In the aforementioned fiber felt, the microfibers are fused together on the first main surface side.

[0022] In the fiber felt based on this disclosure, the breaking strength is preferably 45 cN / 20 mm or higher.

[0023] In the fiber felt based on this disclosure, the microfibers can be liquid crystal polymer powder.

[0024] In the fiber felt based on the present disclosure, the liquid crystal polymer powder preferably includes a fiber portion, which is a short fibrous particle with a length-to-diameter ratio of 10 to 500 times in the long side direction, and an average diameter of 2 μm or less.

[0025] According to the present invention, a method for manufacturing a fiber felt containing microfibers and having high strength, and a fiber felt, can be provided. Attached Figure Description

[0026] Figure 1 This is a scanning electron microscope photograph showing the first main surface of the fiber felt in the embodiment under magnification.

[0027] Figure 2 This is a scanning electron microscope image of a cross section in the thickness direction of the fiber felt according to the embodiment.

[0028] Figure 3 This is a flowchart illustrating the manufacturing process of the fiber felt according to the embodiment.

[0029] Figure 4 This diagram illustrates the felting process in the manufacturing of fiber felt, where liquid crystal polymer powder is felted.

[0030] Figure 5 This diagram shows the process of irradiating the second side of the fiber felt with light.

[0031] Figure 6 This is a graph showing the evaluation conditions and evaluation results in Example 1, Example 2 and the comparative example.

[0032] Figure 7 This is a graph showing the evaluation conditions and evaluation results in Examples 3 and 4.

[0033] Figure 8This is a graph showing the fracture strength of Examples 1 to 4.

[0034] Symbol Explanation

[0035] 10 Microporous sheet, 15 Feed roll, 20 Paper wire, 25, 26 Conveyor roll, 30 Fiber felt, 31 First main surface, 32 Second main surface, 40 Storage section, 41 Dispersion medium, 50 Heating device, 60 Light irradiation device, 100 Paper machine. Detailed Implementation

[0036] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that in the embodiments shown below, the same or common parts are labeled with the same symbol in the drawings, and their descriptions are not repeated.

[0037] <Fiber felt>

[0038] The fiber felt 30 of this embodiment is composed of thermoplastic microfibers, specifically, of liquid crystal polymer powder that has been micronized and fibrousized. 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 coefficient of thermal expansion along the molecular axis and a positive coefficient of thermal expansion in the radial direction. The liquid crystal polymer of this embodiment does not contain amide bonds.

[0039] The fiber felt 30 of this embodiment has a plate-like shape and has first main surfaces 31 that are opposite to each other in the thickness direction (see reference). Figure 4 ) and the second main face 32 (see reference) Figure 4 ).

[0040] like Figure 1 The image shown is a scanning electron microscope photograph showing the first main surface of the fiber felt of the embodiment magnified. Figure 2 This is a scanning electron microscope image of a cross-section along the thickness direction of the fiber mat in the embodiment. It should be noted that... Figure 2 In the middle, the area surrounded by the dotted line is the first surface layer R1 of the fiber felt 30 located on the first main surface side.

[0041] like Figure 1 and Figure 2 As shown in the area enclosed by the dashed line, in the fiber felt 30 of this 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 R1 of the fiber felt 30 located on the first main surface 31 side. On the other hand, the liquid crystal polymer powder is not fused in the intermediate layer R2, which is located on the central side in the thickness direction compared to the first main surface 31 side. As a result, in the fiber felt 30, there is a density gradient in the thickness direction from the first main surface 31 side to the central portion. Specifically, in the thickness direction, the density on the first main surface 31 side is greater than the density on the central portion side.

[0042] It should be noted that, as described later, the liquid crystal polymer powder located on the second main surface 32 side can also be fused together. That is, the liquid crystal polymer powder can also be fused together on the second surface layer of the fiber felt 30 located on the second main surface 32 side.

[0043] As described above, by fusing the liquid crystal polymer powder at least on the first main surface 31 side to create a density gradient in the thickness direction, the strength of the fiber felt 30 can be improved. Furthermore, by fusing the liquid crystal polymer powder on both the first main surface 31 side and the second main surface 32 side, the strength of the fiber felt 30 can be further improved.

[0044] The tensile strength of the fiber felt 30 is preferably 45 cN / 20 mm or more, more preferably 50 cN / 20 mm or more. Furthermore, the tensile strength of the fiber felt 30 can be 115 cN / 20 mm or more, or 350 cN / 20 mm or more.

[0045] The breaking strength of the fiber mat 30 can be determined using a universal testing machine (Shimadzu AG-XDplus). In this case, the width of the fiber mat 30 during the test is 20 mm.

[0046] The overall basis weight of fiber felt 30 is approximately 30–40 g / m². 2 The overall density of the fiber felt 30 is, for example, 0.30–0.60 g / cm³. 3 As the fusion region of the liquid crystal polymer powder in the thickness direction increases, the density increases.

[0047] The thickness of the fiber felt 30 is about 50 to 100 μm. As the fusion area of ​​the liquid crystal polymer powder in the thickness direction increases, the thickness decreases.

[0048] <Membrane>

[0049] The liquid crystal polymer film (more specifically, a liquid crystal polymer film) is produced by pressing the aforementioned fiber felt 30. 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 be used as a laminated molded body, for example, as an FCCL (Flexible Copper Clad Laminates) capable of forming circuits using a subtractive process.

[0050] <Method for manufacturing fiber felt>

[0051] Figure 3 This is a flowchart illustrating the manufacturing process of fiber felt. (See reference...) Figure 3 The manufacturing method of the fiber felt according to this embodiment will be described.

[0052] like Figure 3 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).

[0053] <Pre-process>

[0054] 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, and 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 contain liquid crystal polymers that are processed into fibers by crushing granular or powder-like liquid crystal polymers.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] In the micronization step (S12) of this embodiment, the pulverization method, in which the liquid crystal polymer is 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.

[0059] 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.

[0060] 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 a very large aspect ratio and fiber diameters much greater 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.

[0061] 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 occurring 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.

[0062] 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.

[0063] The granular micronized liquid crystal polymer obtained by the micronization process (S12) preferably has a D50 of 100 μm or less, more preferably 50 μm or less, 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.

[0064] 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).

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] <Subsequent Processes>

[0080] 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.

[0081] 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.

[0082] 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.

[0083] Next, in the felting process (S22), the slurry-like liquid crystal polymer powder is formed into liquid crystal polymer fiber felt by a papermaking method. In the papermaking process, the dispersion medium used in the dispersion process can be recovered and reused, enabling the manufacture of fiber felt at low cost.

[0084] Figure 4 This diagram illustrates the felting process in the manufacturing of fiber felt, where liquid crystal polymer powder is felted. (Refer to...) Figure 4 The felting process is described in detail.

[0085] like Figure 4 As shown, a paper machine 100 is used in the felting process. The paper machine 100 includes: a supply 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, a heating device 50, and a light irradiation device 60.

[0086] The papermaking wire 20 is, for example, a papermaking wire with a mesh size of about 80 to 100 mesh. That is, the papermaking wire 20 has an aperture size of about 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 disposed downstream of the conveyor roller 25. The papermaking wire 20 is conveyed by these conveyor rollers 25 and 26 to pass through the storage section 40.

[0087] The supply roller 15 supplies the microporous sheet 10 onto the papermaking wire 20. The microporous sheet 10 functions as a support for the liquid crystal polymer powder. 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.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] Furthermore, as the microporous sheet 10, for example, a material with a weight per unit area of ​​15 g / m² can be used. 2 The following is a 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.

[0093] In the conveying direction, a heating device 50 is arranged downstream of the storage section 40. The heating device 50 heats and dries the liquid crystal polymer powder 30 that has been lifted onto the microporous sheet 10. As a result, a fiber mat is formed on the microporous sheet 10.

[0094] In the conveying direction, a light irradiation device 60 is arranged downstream of the heating device 50. The light irradiation device 60 irradiates the fiber felt formed on the microporous sheet 10 with light. The light irradiation device 60 may be, for example, a flash lamp.

[0095] The light irradiation device 60 preferably irradiates with pulsed light. Since the pulsed light is absorbed by the surface of the fiber felt (first main surface 31), the support (microporous sheet 10) supporting the fiber felt will not deteriorate due to light irradiation. Therefore, even materials with a lower melting point than the fiber felt can be used as the support, resulting in a wide range of support options. In addition, it is possible to prevent the fiber felt from fusing to the support, thus allowing the support to be reused repeatedly. As the light irradiation device 60, the PulseForge 1300 (registered trademark) manufactured by NovaCentrix can be used.

[0096] The felting process (S21) includes a lifting process, a peeling process, a drying process, and a light irradiation 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.

[0097] Next, in the peeling process, the microporous sheet containing 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.

[0098] Next, in the drying process, the liquid crystal polymer powder scooped onto the microporous sheet 10 is heated and dried using a heating device 50. This forms a fiber mat 30 composed of liquid crystal polymer on the microporous sheet 10.

[0099] Next, in the light irradiation process, the first main surface 31 of the fiber felt 30, 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 to fuse. As a result, the strength of the fiber felt 30 is increased, allowing it to be transported to the next process without damage.

[0100] Furthermore, since the liquid crystal polymer powder is fused only on the surface layer located on the first main surface 31 side, the overall density of the fiber felt 30 is low. This ensures high air permeability and high collection efficiency.

[0101] The light-irradiated fiber felt 30 is wound by the aforementioned winding roller in the winding process, with the fiber felt 30 arranged on the microporous sheet 10.

[0102] Figure 5 This diagram illustrates the process of irradiating the second surface of the fiber mat with light. (See diagram for example.) Figure 5 As shown, the felting process may further include: peeling the fiber felt 30, whose first main surface 31 has been light-irradiated, from the microporous sheet 10, and light-irradiating the second main surface 32 of the fiber felt 30 located on the side opposite to the side where the first main surface 31 is located. In this process, the microfibers located on the second main surface 32 side are fused together by light irradiation from the light irradiation device 61. The light irradiation device 61 can be the same as the light irradiation device 60 described above. During light irradiation, the fiber felt 30 is conveyed while being irradiated.

[0103] By fusing the liquid crystal polymer powder on both sides of the first main surface 31 and the second main surface 32, the strength of the fiber felt 30 can be further improved.

[0104] In addition, when the fiber felt 30 is peeled off from the microporous sheet 10, the liquid crystal polymer powder is fused on the first main surface 31 side, and the fiber felt 30 has sufficient strength, so the fiber felt 30 can be peeled off without damage.

[0105] <Membrane Manufacturing Method>

[0106] Next, the fiber felt 30 is peeled off from the microporous sheet 10 and 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 30.

[0107] In the heat pressing process, the fiber felt 30 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, thereby enabling the inexpensive acquisition of a liquid crystal polymer film bonded with copper foil. It should be noted that, in the heat pressing process, when heating for an extended period, vacuum heat pressing of the fiber felt 30 is preferable.

[0108] 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.

[0109] 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 fiber felt 30 as a release film. Alternatively, an additional copper foil can be sandwiched between the press and the fiber felt 30 instead of the polyimide film. This allows for the production of a liquid crystal polymer film with copper foil bonded to both sides. The liquid crystal polymer film with copper foil bonded to both sides can be used as a double-sided copper-clad liquid crystal polymer (FCCL).

[0110] 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.

[0111] <Experimental Example>

[0112] The present invention will be described in more detail below with examples, but the invention is not limited thereto. In the experimental examples, fiber felts 30 of Examples 1 to 4 were prepared. The basis weight, thickness, density, and breaking strength of Examples 1 and 2 were measured, and the breaking strength of Examples 3 and 4 was measured. For breaking strength, fiber felts 30 with a width of 20 mm were prepared and measured using a universal testing machine (Shimadzu AG-XDplus).

[0113] Figure 6 This is a graph showing the evaluation conditions and evaluation results in Example 1, Example 2 and the comparative example. Figure 7 This is a graph showing the evaluation conditions and evaluation results in Examples 3 and 4. Figure 8 This is a graph showing the fracture strength of Examples 1 to 4.

[0114] (Example 1)

[0115] In Example 1, firstly, granular liquid crystal polymer, which is used as a raw material, is fed into a shredder for coarse grinding. In Example 1, a polymer with a melting point of 315°C and an absorption rate of 60% at a wavelength of 500 nm is used as the liquid crystal polymer. The coarsely ground film-like liquid crystal polymer is discharged from a discharge hole with a diameter of 3 mm provided in the shredder, thereby obtaining coarsely ground liquid crystal polymer.

[0116] 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.

[0117] 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.

[0118] Next, the micronized liquid crystal polymer, from which coarse particles have been removed, was dispersed in a 20 wt% aqueous ethanol solution. The ethanol slurry containing the micronized liquid crystal polymer was repeatedly crushed five times using a wet high-pressure crusher at a nozzle diameter of 0.2 mm and a pressure of 200 MPa, thereby achieving fiberization. A StarBurst HJP-25060 manufactured by SUGINO MACHINE was used as the wet high-pressure crusher. This yielded a liquid crystal polymer powder dispersed in an aqueous ethanol solution.

[0119] 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 mat 30 using a papermaking process. As a papermaking machine, a square sheet forming machine 2555 manufactured by Kumagai Riki Co., Ltd. was used to form the liquid crystal polymer powder dispersed in the dispersion medium onto a microporous sheet of polyester wire with a pore size of 11 μm.

[0120] Next, the fiber felt 30 was dried at 100°C using a hot air dryer, forming it on a microporous sheet. The area weight of the fiber felt 30 was 35 g / m². 2 about.

[0121] Next, multiple fiber mats 30 were prepared, and the voltage conditions of the light irradiation device (PulseForge 1300 manufactured by NovaCentrix, a registered trademark) were changed to irradiate the first principal surface 31 of each fiber mat 30. The voltages were 230V, 250V, and 270V, and the pulse length was 3.5ms.

[0122] The fiber felt 30, which had been exposed to light under such conditions, was peeled off from the microporous sheet, and the basis weight, thickness, density, and breaking strength of the fiber felt 30 of Example 1 were determined using a thickness measuring instrument (digital linear gauge DG-525H (manufactured by Ono Seiki Co., Ltd.)), a density measuring device, or by performing a tensile test.

[0123] In Example 1, the basis weight, thickness, density, and tensile strength of the felt irradiated with 230V were 33.9 g / m³. 2 95.3μm, 0.36g / cm 3 50cN / 20mm.

[0124] In Example 1, the basis weight, thickness, density, and tensile strength of the felt irradiated with 250V were 34.2 g / m³. 2 84.1μm, 0.41g / cm 3 130cN / 20mm.

[0125] In Example 1, the basis weight, thickness, density, and tensile strength of the felt irradiated with 270V were 34 g / m³. 2 79.2μm, 0.43g / cm 3 350cN / 20mm.

[0126] (Example 2)

[0127] In Example 2, the fiber felt 30 was fabricated in substantially the same manner as in Example 1, and the second main surface 32, located on the side opposite to the first main surface 31, was irradiated with light using the same energy as in Example 1. That is, in Example 2, after the fiber felt 30, on which the first main surface 31 had already been irradiated, was peeled from the microporous sheet, the second main surface 32 was further irradiated with light. The voltage of the NovaCentrix PulseForge (registered trademark) 1300 used for irradiating the second main surface 32 was the same as in Example 1: 230V, 250V, and 270V, with a pulse length of 3.5ms. In the fiber felt 30 of Example 2, the basis weight, thickness, density, and breaking strength were also measured in the same manner as in Example 1.

[0128] In Example 2, the basis weight, thickness, density, and tensile strength of the felt irradiated with 230V on both the first main surface 31 and the second main surface 32 were 33.9 g / m². 2 92.8μm, 0.37g / cm 3 120cN / 20mm.

[0129] In Example 2, the basis weight, thickness, density, and tensile strength of the felt that was irradiated with light at 250V on both the first main surface 31 and the second main surface 32 were 34.2 g / m².2 78.5μm, 0.44g / cm 3 380cN / 20mm.

[0130] In Example 2, the basis weight, thickness, density, and tensile strength of the felt irradiated with 270V on both the first main surface 31 and the second main surface 32 were 34 g / m². 2 65μm, 0.52g / cm 3 720cN / 20mm.

[0131] (Comparative example)

[0132] The comparative example differs from Example 1 in that the light irradiation process is omitted in the felting process. That is, the fiber felt of the comparative example, compared with the fiber felt 30 of Example 1, did not have its surface (first main surface) light-irradiated, and the fibers on the surface did not melt.

[0133] In this case, the basis weight, thickness, density, and tensile strength of the felt are 34.2 g / m². 2 105.2μm, 0.33g / cm 3 19.8cN / 20mm.

[0134] (Example 3)

[0135] In Example 3, a polymer with a melting point of 315°C and an absorption rate of 70% at a wavelength of 500 nm was used as the liquid crystal polymer. For other parameters, fiber mat 30 was obtained in approximately the same manner as in Example 1.

[0136] In Example 3, the breaking strengths of the felts irradiated with light at 230V, 250V, and 270V were 400cN / 20mm, 830cN / 20mm, and 1720cN / 20mm, respectively.

[0137] (Example 4)

[0138] In Example 4, a polymer with a melting point of 315°C and an absorption rate of 70% at a wavelength of 500 nm was used as the liquid crystal polymer. For other parameters, fiber mat 30 was obtained in approximately the same manner as in Example 2.

[0139] In Example 4, the breaking strengths of the felts irradiated with light at 230V, 250V, and 270V were 930cN / 20mm, 1690cN / 20mm, and 2410cN / 20mm, respectively.

[0140] As described above, it was confirmed that each of Examples 1-4, compared to the comparative example, had sufficient strength (breaking strength). Furthermore, it was confirmed that by increasing the voltage during light irradiation, the amount of fused liquid crystal polymer powder increased, resulting in a thinner thickness but increased density and breaking strength.

[0141] Furthermore, it was confirmed that by irradiating the second main surface 32 side in addition to the first main surface 31 side with light, as in Examples 2 and 4, the fracture strength was further increased. Moreover, comparing Examples 1 and 2 with Examples 3 and 4, it was confirmed that by using liquid crystal polymer powder with high absorption rate, the fracture strength was further increased.

[0142] <Other variations>

[0143] In the above embodiments and examples, the case where the microfiber is liquid crystal polymer powder has been described as an example, but the microfiber is not limited to liquid crystal polymer powder. As described above, as long as it is thermoplastic, chemical fibers without hydrogen bonds can also be used as microfibers.

[0144] In the above embodiments and examples, the case where the support for picking up the microfibers is a microporous sheet has been described, but it is not limited to this. The microporous sheet can be omitted, and the papermaking wire 20 can be used as the support. In this case, as the microfiber, microfibers with a fiber length larger than the pore size of the papermaking wire 20 can be used, and the fiber length can be 200 μm or less. Furthermore, microfibers with a fiber length of 1 mm or less can be used.

[0145] 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.

Claims

1. A fiber felt composed of thermoplastic microfibers, It has a first main surface on one side of the thickness direction and a second main surface on the other side of the thickness direction. The density on the first main surface side is higher than the density on the central portion side in the thickness direction. The fiber felt is configured to be peelable from the support supporting the second main surface.

2. The fiber felt according to claim 1, wherein, In the thickness direction, there is a density gradient from the first main surface side to the central portion side of the fiber felt. The overall density of the fiber felt is 0.30–0.60 g / cm³. 3 .

3. A method for manufacturing fiber felt, the method for manufacturing fiber felt according to claim 1, comprising: The process of dispersing the thermoplastic microfibers in a dispersion medium, and The process of felting the dispersed microfibers on a support; The felting process includes: The process of forming a fiber felt by shoveling the microfibers onto the support body, and the process of irradiating the first main surface of the fiber felt located on the side opposite to the side where the support body is located with light. In the process of irradiating the first main surface of the fiber felt with light, the microfibers located only on the first main surface side are fused together.

4. The method for manufacturing fiber felt according to claim 3, wherein, The microfibers used are those with a higher melting point than the support.

5. The method for manufacturing fiber felt according to claim 3 or 4, wherein, In the process of irradiating light, pulsed light is irradiated.

6. The method for manufacturing fiber felt according to any one of claims 3 to 5, wherein, The felting process further includes: peeling the fiber felt, which has been light-irradiated on the first main surface, from the support, and light-irradiating the second main surface of the fiber felt located on the side opposite to the side where the first main surface is located. In the process of irradiating the second main surface of the fiber felt with light, the microfibers located on the second main surface side are fused together.

7. The method for manufacturing fiber felt according to any one of claims 3 to 6, wherein, Liquid crystal polymer powder is used as the microfiber.

8. The method for manufacturing fiber felt according to claim 7, wherein, As the liquid crystal polymer powder, a liquid crystal polymer powder containing a fibrous portion is used. The fibrous portion is a short fibrous particle with a length-to-diameter ratio of 10 to 500 times and an average diameter of 2 μm or less.

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