Manufacturing method of liquid crystal polymer network

Abstract

The method for manufacturing a liquid crystal polymer network based on the present invention comprises: a slurry preparation step, which prepares a slurry comprising a dispersion medium and liquid crystal polymer fibers dispersed in the dispersion medium; a spray drying step, which sprays the slurry and dries the sprayed slurry using a drying gas; and a stacking step, which stacks the spray-dried liquid crystal polymer fibers to form a network.

Description

Technical Field

[0001] This invention relates to a method for manufacturing a liquid crystal polymer network. Background Technology

[0002] In high-frequency FPC substrates, liquid crystal polymers (LCPs) are used as the main material, but further low dielectric properties are required. For example, the addition of low-dielectric resin materials such as fluoropolymers to LCPs has been investigated. In this case, the addition of fluoropolymer powder is desirable. In addition to fluoropolymers, functional fillers are often added to LCPs to impart various functionalities.

[0003] Conventional LCP membranes are manufactured by melt extrusion. However, when fillers are mixed into LCP in melt extrusion, problems such as dispersibility, viscosity differences, gas generation or corrosion due to decomposition, and membrane perforation during stretching occur (Patent Document 3: Japanese Patent Application Publication No. 2019-65061).

[0004] A method for producing a membrane by fabricating a web of LCP fibers and pressing it to enrich it has also been considered. As a method for fabricating the web, a method of producing a wet web by fiberizing and slurrying LCP has also been proposed. Furthermore, as shown in Patent Document 2 (Japanese Patent Application Publication No. 2003-129392), a method of mixing filler is also proposed. If the LCP is made into fibers finer than those in Patent Document 2, it is possible to form a thin film by hot pressing the web containing the filler-mixed LCP.

[0005] Other methods of web making include dry methods, such as carding and air laying.

[0006] In the carding process, a carding machine or an air-flow random web forming machine is used to form a thin, continuous web from fibers cut to lengths of about 1 to 10 cm.

[0007] In air-laid web forming, pulp sheets, or short fibers (such as synthetic fibers) with a length of about 3 to 12 mm, are first dry mechanically defibered. A continuous web is then formed by depositing the defibered short fibers onto a moving metal wire mesh using air as a medium.

[0008] As another method employing airflow web forming, for example, a method for manufacturing a mesh sheet disclosed in Patent Document 1 (Japanese Patent Application Publication No. 2018-145574) is known. In this method, fibers are sieved using a rotary-driven cylindrical sieve, and the sieved fibers are then dispersed again using a rotary-driven cylindrical sieve. The dispersed fiber powder is then deposited onto a screen belt while being drawn in by a downflow pipe, thereby manufacturing a mesh sheet. It should be noted that Patent Document 1 describes fibers used in the production of the mesh sheet with an average diameter of 1 μm to 1000 μm and a length of 1 μm to 5 mm.

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: Japanese Patent Application Publication No. 2018-145574

[0012] Patent Document 2: Japanese Patent Application Publication No. 2003-129392

[0013] Patent Document 3: Japanese Patent Application Publication No. 2019-65061 Summary of the Invention

[0014] Representative methods for manufacturing LCP membranes include melt extrusion (transverse stretching) and melt extrusion (blowing). When these methods are used to composite with fluoropolymers, the temperature dependence of the melt viscosity of LCP, as a rod-shaped polymer, differs from that of typical random coil polymers. Therefore, the viscosity of LCP in the molten state is inconsistent with that of the fluoropolymer, resulting in low compatibility. Consequently, the fluoropolymer forms aggregates, making it difficult to disperse uniformly within the LCP.

[0015] One solution to this problem is the papermaking method. In the papermaking method, the material will not be in a molten state, thus preventing agglomeration of the fluoropolymer due to the difference in viscosity between the LCP and the fluoropolymer. However, because the fluoropolymer has low hydrophilicity, it cannot be suspended in a dispersion medium containing water that can disperse the fibrous material of the LCP.

[0016] It should be noted that if a dispersant such as a surfactant is added to the water, hydrophobic fibers can be dispersed in the water. However, the surfactant remains in the mesh after drying, which may have an adverse effect on the electrical properties of the mesh used in electronic components.

[0017] Furthermore, hydrophobic fibers can be pulped by incorporating a large amount of organic solvent into the dispersion medium. However, in the case of papermaking, a dilute dispersion of about 0.1% is required, thus necessitating the use of a large amount of organic solvent, which raises safety concerns and increases manufacturing costs.

[0018] On the other hand, if a dry process is used, the dispersibility of fluoropolymers in water will not be a problem. Therefore, for example, mixing LCP microfibers with fluoropolymers using air-blowing web forming methods has been considered. However, if LCP microfibers are dried, they tend to form aggregates, making it difficult to pass through a sieve or disperse in a gas.

[0019] In addition, short fibers smaller than 20mm are generally not allowed in carding. Short fibers smaller than 20mm can be used in air-laid spinning, but fibers with a length (length along the long side) of a few millimeters or less cannot be used.

[0020] The method described in Patent Document 1 can also use micron-sized fibers. Furthermore, compared with carding and air-laid web forming methods, the resulting web exhibits higher fiber dispersion uniformity.

[0021] However, the method described in Patent Document 1 uses a sieve mechanism in the air to screen and disperse the fibers. Therefore, when using easily charged and fine fibers such as fragmented liquid crystal polymer fibers (LCP fibers), the fibers have high cohesion, leading to clogging as the fibers fail to detach from the sieve. Furthermore, the uniformity of fiber dispersion in the mesh decreases due to the easy formation of fiber agglomerates. It should be noted that reducing the mesh size of the sieve to improve fiber dispersion uniformity further exacerbates clogging.

[0022] Furthermore, the method described in Patent Document 1 requires controlling the airflow to cause the fibers to accumulate on the screen belt. However, the smaller the fiber size, the easier it is for the fibers to aggregate, making it difficult to use airflow to evenly disperse the fibers.

[0023] Furthermore, when multiple materials are combined and used as the mesh material, different types of powders are dispersed in the air in the dry process, but the stirring force is weaker than in the wet process, making it difficult to uniformly disperse powders that are different from liquid crystal polymer fibers.

[0024] In view of the above-mentioned problems, the present invention aims to provide a method for manufacturing liquid crystal polymer networks that can be easily manufactured using fine liquid crystal polymer fibers.

[0025] In another aspect of the present invention, the objective is to provide a method for manufacturing a web composed of liquid crystal polymer fibers and a solid material different from the liquid crystal polymer fibers.

[0026] The method for manufacturing a liquid crystal polymer network based on the present invention comprises:

[0027] The slurry preparation process involves preparing a slurry comprising a dispersion medium and liquid crystal polymer fibers dispersed in the dispersion medium.

[0028] The spray drying process involves spraying the aforementioned slurry and drying it using a drying gas; and

[0029] The stacking process involves stacking the spray-dried liquid crystal polymer fibers to form a web.

[0030] According to the present invention, liquid crystal polymer networks can be easily manufactured using fine liquid crystal polymer fibers.

[0031] In another aspect of the present invention, it is possible to manufacture a web composed of liquid crystal polymer fibers and a solid material different from the liquid crystal polymer fibers. Attached Figure Description

[0032] Figure 1 This is a flowchart illustrating the manufacturing process of the liquid crystal polymer network according to an embodiment.

[0033] Figure 2 This is a schematic diagram illustrating the manufacturing process of the liquid crystal polymer network in the embodiment.

[0034] Figure 3 This is a schematic diagram illustrating the manufacturing process of the liquid crystal polymer network in the embodiment.

[0035] Figure 4 This is a schematic diagram illustrating the manufacturing process of the liquid crystal polymer network in the embodiment.

[0036] Figure 5 These are photographs taken of cross-sections of the liquid crystal polymer networks of Example 1 and Comparative Example 2.

[0037] Figure 6 This is a photograph of the dispersion in a confirmation test of a low-dispersion dispersion medium.

[0038] Figure 7 This is a cross-sectional photograph of the composite mesh from Example 2.

[0039] Figure 8 This is a cross-sectional photograph of the membrane obtained by pressing the composite mesh of Example 2.

[0040] Figure 9 This is a cross-sectional photograph of the composite mesh of Example 3.

[0041] Figure 10 This is a cross-sectional photograph of the composite mesh of Example 4.

[0042] Figure 11 This is a cross-sectional photograph of the membrane in Comparative Example 1. Detailed Implementation

[0043] The following describes a method for manufacturing a liquid crystal polymer (microfiber) web according to one embodiment of the present invention.

[0044] <<Method for Manufacturing Liquid Crystal Polymer Networks>>

[0045] like Figure 1 As shown, the method for manufacturing the liquid crystal polymer network in this embodiment includes at least a slurry preparation step (S1), a spray drying step (S2), and a stacking step (S3).

[0046] In the slurry preparation step (S1), a slurry containing a dispersion medium and liquid crystal polymer fibers dispersed in the dispersion medium is prepared.

[0047] In the spray drying process (S2), the slurry is sprayed and dried using drying gas.

[0048] In the stacking process (S3), the spray-dried liquid crystal polymer fibers are stacked to form a web.

[0049] (Liquid Crystal Polymer Network)

[0050] One embodiment of the present invention is a liquid crystal polymer mesh (LCP mesh) comprising liquid crystal polymer fibers (LCP fibers).

[0051] The LCP mesh preferably contains liquid crystal polymer fibers (LCP fibers) as the main component. It should be noted that, in this specification, "main component" refers to the component with the highest volume percentage relative to the total components. This percentage is preferably 50% to 90% by volume, more preferably 50% to 80% by volume, and even more preferably 50% to 70% by volume. The LCP mesh may consist solely of LCP fibers, or it may contain LCP fibers and other materials.

[0052] It should be noted that the composite material (material other than LCP fibers) combined with LCP can also be the main component of the LCP mesh. In this case, the ratio of the composite material to the total composition of the LCP mesh is preferably 50% to 90% by volume (10% to 50% by volume for LCP fibers), more preferably 50% to 80% by volume (20% to 50% by volume for LCP fibers), and even more preferably 50% to 70% by volume (30% to 50% by volume for LCP fibers).

[0053] It should be noted that in this specification, "web" refers to an aggregate of LCP fibers on a sheet, which are substantially unattached to each other, but may be partially attached. For example, a web illuminated by a flash lamp is also included in the term "web" as used herein.

[0054] The thickness of the LCP mesh is not particularly limited, for example, it can be 5μm to 250μm.

[0055] The LCP mesh of this embodiment can be filmized by pressing. The film can be bonded with copper foil on at least one side or on both sides. The LCP film with copper foil bonded in this way can be used as a laminated molded body, for example, as FCCL (Flexible Copper Clad Laminates) that can form circuits using a subtractive method.

[0056] (Liquid crystal polymer fiber)

[0057] Liquid crystal polymer fibers (LCP fibers) are fibrous particles (materials) containing liquid crystal polymers as the main component. There are no particular limitations on LCP fibers as long as they contain a fibrous portion. The fibrous portion can be linear or branched, etc.

[0058] The average diameter of the LCP fibers (fibrous particles) in the powdered microfibers is more preferably 2 μm or less, more preferably 1 μm or less. In addition, the average aspect ratio of the LCP fibers is preferably 10 to 500, more preferably 300 or less, and even more preferably 100 or less.

[0059] It should be noted that the average diameter and average aspect ratio of the LCP fibers contained in the LCP powder were determined by the following method.

[0060] (Determination of the average diameter and average aspect ratio of LCP fibers)

[0061] LCP powder, composed of LCP fibers used for the test, was dispersed in ethanol to prepare a slurry containing 0.01% by mass of LCP powder. The water content in the slurry was prepared to be less than 1% by mass. Then, 5–10 μL of the slurry was dropped onto a glass slide, and the slide was allowed to dry naturally. By allowing the slurry to dry naturally, the LCP powder was deposited on the glass slide.

[0062] Next, a designated area of ​​LCP powder arranged on a glass slide was observed using a scanning electron microscope, and image data of more than 100 particles (LCP fibers) constituting the LCP powder were acquired. It should be noted that the area was set according to the size of each LCP particle to ensure that the number of image data points was more than 100. Furthermore, to suppress omissions or measurement errors in the acquisition of image data for each LCP particle, the magnification of the scanning electron microscope was appropriately changed to 500x, 3000x, or 10000x while acquiring the aforementioned image data.

[0063] Next, the dimensions of the LCP fiber along its longitudinal and width directions were measured using the image data obtained above.

[0064] In the LCP fiber captured by the aforementioned image data, the direction of the straight line connecting the two ends of the longest path from one end through approximately the center of the particle to the end opposite to that end is defined as the long side direction. Furthermore, the length of the straight line connecting the two ends of the longest path is measured as the long side direction dimension.

[0065] In addition, the particle size in a direction orthogonal to the long side direction was measured at three different locations along the aforementioned long side direction of a single LCP powder particle. The average value of the dimensions measured at these three locations was taken as the width direction dimension (fiber diameter) of each LCP powder particle.

[0066] Then, the ratio of the longitudinal dimension to the fiber diameter (longitudinal dimension / fiber diameter) is calculated as the aspect ratio of the LCP fiber.

[0067] Then, the average fiber diameter measured from 100 LCP fibers was taken as the average diameter.

[0068] In addition, the average aspect ratio measured for 100 LCP fibers will be used as the mean aspect ratio.

[0069] (Liquid Crystal Polymer: LCP)

[0070] There are no particular limitations on what constitutes a liquid crystal polymer; for example, thermotropic liquid crystal polymers can be cited.

[0071] Preferably, the liquid crystal polymer does not have amide bonds. Examples of thermotropic liquid crystal polymers without amide bonds include, for example, a copolymer of p-hydroxybenzoic acid and terephthalic acid and dihydroxybiphenyl (a copolymer of p-hydroxybenzoic acid and ethylene terephthalate) with a high melting point and low CTE, referred to as type 1 liquid crystal polymers, or a copolymer of p-hydroxybenzoic acid and 2,6-hydroxynaphthoic acid with a melting point between type 1 and type 2 liquid crystal polymers, referred to as type 1.5 (or type 3).

[0072] The following describes each step of the manufacturing method of this embodiment.

[0073] <Slurry preparation process: S1>

[0074] The slurry preparation step (S1) is a step of preparing a slurry (LCP slurry) containing a dispersion medium and liquid crystal polymer fibers dispersed in the dispersion medium.

[0075] In the slurry preparation process, for example, LCP slurry can be prepared by dispersing LCP fibers (fibrous particles) in powdered microfibers in a dispersion medium.

[0076] Examples of dispersion media used in the preparation of LCP slurries include water, ethanol, methanol, isopropanol, toluene, benzene, xylene, phenol, acetone, methyl ethyl ketone, diethyl ether, dimethyl ether, hexane, N,N-dimethylacetamide, tetrahydrofuran, diethylene glycol monohexyl ether, or mixtures of at least two of these. Preferred dispersion media among these are water, ethanol, or mixtures thereof (ethanol-water solutions).

[0077] It should be noted that the LCP powder used in the preparation of LCP slurry may also contain particles other than LCP fibers (particles that do not substantially contain fibrous parts, blocky particles formed by the aggregation of LCP fibers, etc.), and its content (number ratio) is preferably 20% or less.

[0078] Furthermore, the D50 (average particle size) value of the LCP powder, which is determined by particle size measurement using a particle size distribution measuring device based on laser diffraction scattering method, is preferably 13 μm or less.

[0079] In the slurry preparation process, liquid crystal polymer fibers and a solid material different from the liquid crystal polymer fibers can be dispersed in the slurry. In this case, by forming a composite containing LCP fibers and a solid material and stacking the composite, a liquid crystal polymer network with high dispersion uniformity of LCP fibers and solid material can be obtained. It should be noted that the solid material used in this case is preferably a material with high dispersibility in the dispersion medium of the slurry.

[0080] <Spray drying process: S2>

[0081] The spray drying process is a process in which slurry is sprayed and then dried using drying gas.

[0082] As a specific method for spraying slurry and drying the sprayed slurry using drying gas in the spray drying process (S2), for example, the following methods can be cited: Figure 2 As shown, the slurry is sprayed into the circulating drying gas 2 (hot air) (inside the chamber 3) using the spray device 1 and dried.

[0083] In addition, such as Figure 3 As shown, a spray drying apparatus equipped with a spray device 13 having two fluid nozzles capable of spraying two independent fluids from a first nozzle 11 and a second nozzle 12 can be used to spray dry the slurry. For example, by spraying LCP slurry from the first nozzle 11 and spraying drying gas 2 (heated N2 gas, etc.) from the second nozzle 12, the LCP slurry is spray dried into a state where micro powder composed of LCP fibers is dispersed in the chamber below the spray device 13.

[0084] In the spray drying process, solid materials (powders, fibrous materials, etc.) that are different from liquid crystal polymer fibers can be dispersed in the drying gas. In this case, by forming a composite containing LCP fibers and solid materials and stacking the composite, a liquid crystal polymer network with high dispersion uniformity of LCP fibers and solid materials can be obtained.

[0085] Here, the solid material used in conjunction with the drying gas is preferably a material with low dispersibility (low dispersibility material) contained in the dispersion medium of the LCP slurry.

[0086] It should be noted that in LCP webs, when LCP fibers are compounded with solid materials other than those used in the LCP slurry, if the solid material is highly dispersible in the dispersion medium of the LCP slurry, it can be incorporated into the LCP slurry or into the drying gas. If the solid material is poorly dispersible in the dispersion medium of the LCP slurry, it is preferable to disperse the solid material in the drying gas. This is because when a solid material with poor dispersibility in the dispersion medium is incorporated into the LCP slurry, the uniformity of dispersion of the solid material in the LCP web will decrease unless surface treatment of the material or the addition of a dispersant to the dispersion medium is performed.

[0087] For example, as a benchmark for dispersibility, 0.1% by volume of solid material is added to 50 mL of a 60% by mass aqueous solution of ethanol in a 70 mL sample vial (M-70, Kashiwagi Co., Ltd.). After shaking the sample vial by hand 10 times, it is ultrasonically treated for 1 minute using a benchtop ultrasonic cleaner "UT206" (manufactured by Sharp Corporation, oscillation frequency: 37 kHz). It should be noted that 0.1% by volume is the concentration of solid material in the pulp commonly used in wet papermaking. After standing for 1 minute, if the presence of solid material on the gas-liquid surface or bottom of the sample vial can be visually confirmed, this solid material corresponds to a low-dispersibility solid material in the dispersion medium (low-dispersibility material).

[0088] The rationale for using a 60 wt% aqueous solution of ethanol as the evaluation dispersion medium is that if the concentration of ethanol exceeds 60 wt%, the aqueous solution is considered a hazardous material, making handling in the wet papermaking process extremely difficult. Materials that cannot be dispersed in a 60 wt% aqueous solution of ethanol are difficult to composite with LCP fibers in the wet papermaking process; therefore, the dry process is considered more suitable.

[0089] Examples of low-dispersibility materials include perfluoroalkoxyalkane (PFA), polytetrafluoroethylene (PTFE), FEP (Teflon: registered trademark), cyclic olefin polymers (COP / COC), polyphenylene ether (PPE), syndiotactic polystyrene (SPS), polyether ether ketone (PEEK), bismaleimide, polynorbornene (PNB), and hydrocarbon polymer materials. The types of compounds equivalent to these low-dispersibility materials can vary depending on the type of dispersion medium in the LCP slurry.

[0090] It should be noted that, as an example, experiments have confirmed that perfluoroalkoxyalkane (PFA) with an average particle size (D50) of 2 μm and polytetrafluoroethylene (PTFE) with an average particle size of 4 μm are equivalent to low-dispersibility materials based on the above benchmark in an aqueous ethanol solution containing 60% by mass of ethanol as the dispersion medium. Figure 6 The above-mentioned low-dispersibility dispersion medium was confirmed in a validation test (after standing for 1 minute) using PFA ( Figure 6 (a) and PTFE ( Figure 6 Photograph of the dispersion in (b)).

[0091] In the spray drying process, the drying gas can be reused. When the drying gas is N2 or similar, reusing the drying gas can reduce environmental and cost burdens.

[0092] <Stacking process: S3>

[0093] The stacking process is a process of stacking spray-dried liquid crystal polymer fibers to form a web.

[0094] For example, such as Figure 4 As shown, LCP fiber micro-powder 4, which is dispersed in the gas in the chamber 3 by the spray drying process, is drawn from below the screen 6 (conveyor screen) and deposited on the screen 6. This results in deposit 5.

[0095] In this way, by preventing the LCP fibers in a less agglomerated state after spray drying from re-agglomerating and piling up, an LCP network with high dispersion uniformity of LCP fibers can be obtained.

[0096] As a specific method for producing an LCP web from the deposit 5, one example is to subject the LCP fiber deposit to instantaneous heat treatment using a flash lamp or similar method. By using such instantaneous heat treatment to fix the LCP fibers together, an LCP web can be produced. It should be noted that by fixing the LCP fibers together using a method that does not apply pressure to the deposit, a large-volume (high porosity) LCP web can be obtained. Such a large-volume LCP web is difficult to obtain using conventional manufacturing methods (especially wet methods such as papermaking).

[0097] The method for making LCP mesh from the stockpile 5 is not particularly limited. Depending on the intended use of the LCP mesh, the strength of the web can be increased to a level where it can be peeled off from the mesh by slightly heating or pressurizing the stockpile 5. Alternatively, LCP mesh can be made by fixing LCP fibers together with adhesives or the like.

[0098] It should be noted that the obtained LCP mesh can be further applied to other processes such as pressing and winding as needed.

[0099] According to the manufacturing method of this embodiment described above, even when using fine liquid crystal polymer fibers, liquid crystal polymer mesh can be easily manufactured. This is because the manufacturing method of this embodiment does not cause the fine LCP fibers to scatter as in the dry method, and it is less prone to the problems of clogging and airflow control of fine LCP fibers as described in Patent Document 1.

[0100] Furthermore, fine fibers like LCP fibers, which are easily charged, tend to aggregate and form aggregates. In conventional dry processes, it is difficult to de-fibrillate these LCP fiber aggregates and achieve sufficient dispersion of the LCP fibers in an airflow. In contrast, by controlling the wettability and agitating the slurry, LCP fibers can be fully dispersed. Moreover, by spray-drying the well-dispersed slurry, the dried LCP fiber powder can be well dispersed in the gas, and an LCP web can be fabricated from the aggregate maintaining this dispersion. Therefore, regardless of the size or charge of the LCP fibers, a highly uniformly dispersed LCP web can be obtained.

[0101] Furthermore, in the manufacturing method of this embodiment, by spray-drying the pulp of LCP fibers with a high concentration compared to the papermaking method and directly stacking the LCP fibers (uncaptured) dispersed in the gas phase, the amount of solvent used can be reduced to about 1 / 10 compared to the papermaking method.

[0102] <Preparation Method of Liquid Crystal Polymer Powder>

[0103] The following describes the detailed manufacturing method of a liquid crystal polymer powder used in the above-described slurry preparation process. This liquid crystal polymer powder can be manufactured, for example, by sequentially performing the following coarse grinding, fine grinding, coarse particle removal, and fibrosis processes.

[0104] The shapes of raw materials (LCP raw materials) made of liquid crystal polymers used in the production of liquid crystal polymer powders include, for example, biaxially oriented films or webs, uniaxially oriented particles, and powders. The LCPs constituting LCP raw materials are the same as those constituting the aforementioned LCP fibers.

[0105] (Coarse grinding process)

[0106] In the coarse grinding process, the LCP raw material is coarsely ground. For example, the LCP raw material is coarsely ground using a shredder. The size of the coarsely ground LCP particles is not particularly limited, as long as they can be used as raw materials for the micro-grinding process described later. The maximum particle size of the coarsely ground LCP particles is, for example, 3 mm or less.

[0107] It should be noted that a coarse grinding process is not necessarily required. For example, as long as the LCP raw material can be used as a raw material for the micro-grinding process, it can be used directly as a raw material for the micro-grinding process.

[0108] (Micro-pulverization process)

[0109] In the micronization process, the LCP raw material (after the coarse grinding process) is pulverized in a state of dispersion in liquid nitrogen to obtain granular micronized liquid crystal polymer (micronized LCP).

[0110] In the micronization process, it is preferable to use a medium to pulverize the LCP raw material dispersed in liquid nitrogen. The medium is, for example, beads. From the viewpoint of handling liquid nitrogen, a bead mill, which presents fewer technical problems, is preferred in the micronization process of this embodiment. For example, the liquid nitrogen bead mill "LNM-08" manufactured by IMEX Corporation can be cited as an example of an apparatus that can be used in the micronization process.

[0111] The granular micronized LCP obtained from the micronization process preferably has a D50 of less than 50 μm, as measured using a particle size distribution measuring device based on laser diffraction scattering. This prevents the granular micronized LCP from clogging the nozzles in the fiberization process described below.

[0112] (Coarse particle removal process)

[0113] Next, in the coarse particle removal process, coarse particles are removed from the granular micronized LCP obtained in the above-mentioned micronization process. For example, the granular micronized LCP can be sieved through a screen to obtain the granular micronized LCP that passes through the screen, and the coarse particles contained in the granular micronized LCP are removed by removing the granular liquid crystal polymer on the screen. The type of screen can be appropriately selected; for example, a screen with a mesh size of 53 μm can be used. It should be noted that the coarse particle removal process is not necessarily required.

[0114] (Fiberization process)

[0115] Next, in the fiberization process, the granular liquid crystal polymer is crushed using a wet high-pressure crushing device to obtain liquid crystal polymer powder. In the fiberization process, the micronized LCP is first dispersed in a dispersion medium for the fiberization process. The dispersed micronized LCP may not have coarse particles removed, but it is preferable to remove them. Examples of dispersion media for the fiberization process include water, ethanol, methanol, isopropanol, toluene, benzene, xylene, phenol, acetone, methyl ethyl ketone, diethyl ether, dimethyl ether, hexane, or mixtures thereof. The dispersion medium used in this fiberization process is preferably the same as the dispersion medium for the LCP slurry described above.

[0116] Then, the micronized LCP, dispersed in the dispersion medium of the fiberization process, i.e., the paste-like or slurry-like micronized LCP, is passed through a nozzle under high pressure. By passing through the nozzle under high pressure, the shear force or impact energy based on high-speed flow in the nozzle acts on the liquid crystal polymer, breaking up the granular micronized LCP, thereby fiberizing the liquid crystal polymer and obtaining a liquid crystal polymer powder composed of fine LCP fibers. From the viewpoint of imparting high shear force or high impact energy, the nozzle diameter is preferably minimized to prevent clogging of the micronized LCP in the nozzle. Since the granular micronized LCP has a small particle size, the nozzle diameter of the wet high-pressure crushing device used in the fiberization process can be reduced. For example, the nozzle diameter is 0.2 mm or less.

[0117] As explained above, the granular micro-pulverized LCP has multiple micro-cracks. Therefore, by applying pressure with a wet high-pressure crushing device, the dispersion medium penetrates into the interior of the micro-pulverized LCP through these micro-cracks. Furthermore, when the paste-like or slurry-like micro-pulverized LCP is placed under normal pressure through a nozzle, the dispersion medium that has penetrated into the interior of the micro-pulverized LCP expands within a short period of time. This expansion of the dispersion medium inside the micro-pulverized LCP causes destruction from within. Therefore, fiberization proceeds into the interior of the micro-pulverized LCP, 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 micro-pulverized LCP obtained in the micro-pulverization process of this embodiment, a liquid crystal polymer powder with a lower content of bulk particles and composed of fine LCP fibers can be obtained compared to the liquid crystal polymer powder obtained by crushing granular liquid crystal polymer obtained by conventional freeze-pulverization methods.

[0118] It should be noted that in the fiberization process of this embodiment, liquid crystal polymer powder can be obtained by repeatedly crushing the micronized LCP using a wet high-pressure crushing device. However, from the viewpoint of manufacturing efficiency, the number of crushing operations using a wet high-pressure crushing device is preferably small, for example, 5 times or less.

[0119] Example

[0120] The present invention will be described in more detail below with reference to specific embodiments, but the present invention is not limited to these embodiments.

[0121] <Example 1>

[0122] (Slurry preparation process: S1)

[0123] First, an LCP film with biaxial molecular orientation in the planar direction (melting point: 315℃, thickness: 250μm) was prepared as the LCP raw material. The LCP material was a copolymer of p-hydroxybenzoic acid and 4,6-hydroxynaphthoic acid.

[0124] The LCP raw material was coarsely ground using a shredder (IKA, MF10). The coarsely ground LCP was then passed through a 3mm mesh screen located at the outlet of the shredder, thus obtaining coarsely ground LCP.

[0125] Next, the coarsely ground LCP was micronized using a liquid nitrogen bead mill (IMEX, LNM-08, container capacity: 0.8L). Specifically, 500 mL of media and 30 g of coarsely ground LCP were added to the container and milled at 2000 rpm for 120 minutes. Zirconia (ZrO2) beads with a diameter of 5 mm were used as the media. It should be noted that in the liquid nitrogen bead mill, the coarsely ground LCP was wet-milled while dispersed in liquid nitrogen. Thus, by pulverizing the coarsely ground LCP using a liquid nitrogen bead mill, granular micronized LCP was obtained.

[0126] The particle size distribution of the micronized LCP was determined. In the particle size determination, the micronized LCP dispersed in the dispersion medium was subjected to ultrasonic treatment for 10 seconds, and then the particle size distribution was measured in a particle size distribution measuring device based on laser diffraction scattering (Horiba Manufacturing Co., Ltd., LA-950). It should be noted that Ekinen (registered trademark, Japan Alcohol Trading Co., Ltd.) was used as the dispersion medium, with ethanol as the main solvent. The measured D50 value of the micronized LCP was 23 μm.

[0127] Next, the dispersion of micronized LCP in Ekinen was sieved through a 53 μm mesh sieve to remove coarse particles from the micronized LCP, and the micronized LCP that passed through the sieve was recovered. The yield of micronized LCP based on the removal of coarse particles was 85% by mass.

[0128] Next, the micronized LCP, from which coarse particles have been removed, was dispersed in a 20% by mass aqueous ethanol solution. The ethanol slurry containing the micronized LCP was repeatedly pulverized five times using a wet high-pressure pulverizer at a nozzle diameter of 0.18 mm and a pressure of 200 MPa, thereby fiberizing the slurry. A high-pressure disperser (SUGINO MACHINE StarBurst Labo) was used as the wet high-pressure pulverizer. This yielded a slurry of LCP powder (LCP fibers) dispersed in an aqueous ethanol solution. This slurry was further diluted with an aqueous ethanol solution (ethanol concentration: 50% by mass) to a LCP concentration of 1% by mass. This prepared the LCP slurry used in the following spray drying process.

[0129] (Spray drying process: S2)

[0130] The LCP slurry prepared as described above is spray-dried. Specifically, using... Figure 3 The spray drying apparatus shown is equipped with a spray device 13 having two-fluid nozzles capable of spraying two independent fluids using a first nozzle 11 and a second nozzle 12. That is, by spraying LCP slurry through the first nozzle 11 and spraying N2 gas heated to 180°C as a drying gas through the second nozzle 12, the LCP slurry is sprayed and dried into a state in which micro powder composed of LCP fibers is dispersed in the chamber below the spray device 13.

[0131] (Stacking process: S3)

[0132] A 11μm mesh screen (manufactured by Clever Co., Ltd.) is installed 40cm below the spray device 13. Suction is performed from below the screen, causing the micro-powder composed of LCP fibers dispersed in the chamber to accumulate on the screen. After a predetermined amount of LCP fibers has accumulated, the screen is removed (see reference). Figure 4 ).

[0133] The LCP fiber deposits removed from the screen were heat-treated using a flash lamp. To obtain sufficient strength for peeling from the screen, the surface portion of the LCP fibers was fixed together, thereby creating an LCP mesh. The resulting LCP mesh was then peeled from the screen to obtain the LCP mesh of Example 1. It should be noted that the thickness of the obtained LCP mesh was approximately 100 μm. Figure 5 ).

[0134] <Example 2>

[0135] The same slurry as in Example 1 was sprayed under the same conditions. This time, in the spray drying process, PFA particles with an average particle size (D50) of 2 μm were dispersed in the drying gas to achieve a concentration of 30% by volume. Otherwise, an LCP mesh was prepared in the same manner as in Example 1. The resulting composite mesh showed good dispersibility of PFA (see [reference]). Figure 7 It should be noted that... Figure 7 This is a cross-sectional photograph of the composite mesh in Example 2. Figure 7 The shaded portion indicated by the diagonal line represents PFA. The membrane obtained by enriching this mesh (after pressure) is compared with Comparative Example 1 described later. Figure 11 Compared to other methods, PFA also shows good dispersibility (see reference). Figure 8 ). Figure 8 This is a cross-sectional photograph of the membrane mentioned above.

[0136] <Example 3>

[0137] The PFA particle powder was replaced with PTFE, and the composite mesh was prepared in the same manner as in Example 2. The composite mesh assembled under these conditions showed good dispersibility of PTFE (see [reference]). Figure 9 It should be noted that... Figure 9 This is a cross-sectional photograph of the composite mesh in Example 3. Figure 9 The shaded area indicated by the diagonal lines is PTFE.

[0138] <Example 4>

[0139] PFA, which had undergone hydrophilic treatment of the slurry from Example 1, was added to a concentration of 30% by volume and then spray-dried to form a web. The composite web formed under these conditions exhibited good dispersibility of PFA (see reference). Figure 10 It should be noted that... Figure 10 This is a cross-sectional photograph of the composite mesh in Example 4. Figure 10 The shaded area indicated by the diagonal lines is PFA.

[0140] As a hydrophilic treatment, surface treatment was performed using a powder plasma treatment apparatus manufactured by Kai Semiconductor Co., Ltd. until the PFA was mixed and dispersed with an aqueous solution. It should be noted that the aforementioned powder plasma treatment apparatus is an apparatus for performing atmospheric pressure plasma treatment in a liquid, and is a dielectric barrier discharge plasma apparatus using water as the dielectric. This yields a dispersion of PFA after hydrophilic treatment.

[0141] <Example 5>

[0142] The PFA particles were replaced with polynorbornene powder, and the composite mesh was prepared in the same manner as in Example 2. The composite mesh assembled under these conditions showed good dispersibility of polynorbornene.

[0143] <Comparative Example 1>

[0144] The cross-sectional state of the film obtained by melt extrusion molding of LCP and PFA is shown below. Figure 11 This demonstrates the strong cohesion of PFA.

[0145] <Comparative Example 2>

[0146] The LCP pulp, prepared in the same manner as in Example 1, was diluted to a concentration of 0.1% by mass using an aqueous ethanol solution (ethanol concentration: 50% by mass). The diluted LCP pulp was then used to produce the LCP wire of Comparative Example 2 using a square papermaking method (wet process).

[0147] <Comparative Example 3>

[0148] An attempt was made to recover LCP fibers generated by spraying in the same manner as in Example 1 and to sieve them using a 150 μm mesh sieve (SANPO made) to allow them to accumulate and form a mesh. However, the LCP fibers agglomerated and could not pass through the sieve, making it impossible to produce an LCP mesh.

[0149] [Observations on the LCP Network]

[0150] After filling the LCP web obtained in Example 1 and Comparative Example 2 with resin, the resin was cured to prepare an observation sample. The sample was then ground to create a cross-section (a surface parallel to the thickness direction). The ground cross-section was further processed by CP (chemical polishing) and observed using a scanning microscope.

[0151] Figure 5 These are photographs (scanning electron microscope images) taken of cross-sections (planes parallel to the thickness direction of the mesh) of the LCP meshes of Example 1 (upper side) and Comparative Example 2 (lower side). It should be noted that... Figure 5 The values ​​on the photograph represent the magnification of the microscope. According to... Figure 5 As can be seen from the photographs, Example 1 was able to produce a web with high uniformity of LCP fiber dispersion. Furthermore, it can be seen that the LCP web of Example 1 has a larger volume (higher porosity) compared to the LCP web of Comparative Example 2 produced using the papermaking method.

[0152] In the description of the above embodiments, the combinable components can also be combined with each other.

[0153] The embodiments and examples disclosed herein should be considered illustrative rather than restrictive in all respects. The scope of the invention is indicated by the scope of the claims and not by the foregoing description, and is intended to include all modifications within the meaning and scope equivalent to the scope of the claims.

[0154] Symbol Explanation

[0155] 1. 13 Spraying device, 11 Nozzle 1, 12 Nozzle 2, 2 Drying gas, 3 Chamber, 4 Micro powder of LCP fiber, 5 Accumulation material, 6 Mesh screen.

Claims

1. A method for manufacturing a liquid crystal polymer network, comprising: The slurry preparation process involves preparing a slurry comprising a dispersion medium and liquid crystal polymer fibers dispersed in the dispersion medium. The spray drying process involves spraying the slurry and drying it with a drying gas. The stacking process involves stacking the spray-dried liquid crystal polymer fibers to form a web; In the spray drying process, a solid material different from the liquid crystal polymer fiber is dispersed in the drying gas.

2. The manufacturing method according to claim 1, wherein, The average fiber diameter of the liquid crystal polymer fiber is less than 2 μm. The average aspect ratio of the liquid crystal polymer fiber is 10 to 500.

3. The manufacturing method according to claim 1, wherein, The solid material comprises a material with low dispersibility to the dispersion medium in the slurry.

4. The manufacturing method according to claim 1, wherein, In the slurry preparation process, the liquid crystal polymer fiber and a solid material different from the liquid crystal polymer fiber are dispersed in the slurry.

5. The manufacturing method according to any one of claims 1 to 4, wherein, In the spray drying process, the drying gas is reused.

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