Mesh woven fabric of liquid crystal polyester yarn

Abstract

The present invention suppresses thickness rebound of mesh woven fabric due to heating. This mesh woven fabric is formed from liquid crystal polyester yarn having been subjected to a thinning treatment, wherein a thickness change rate represented by formula (I) calculated for the thickness of the mesh woven fabric before and after heat treatment at 180°C is 0%-25.0%.　(I): Δt = 100 × (t2 - t1) / t1 In formula (I), Δt is the thickness change rate, t1 is the thickness of the mesh woven fabric before the heat treatment, and t2 is the thickness of the mesh woven fabric after the heat treatment.

Description

Liquid crystal polyester yarn mesh fabric

[0001] The present invention relates to a mesh fabric made of liquid crystal polyester yarn, which has been compressed to reduce its thickness, and which can be prevented from regaining its thickness when subsequently heated.

[0002] Ion exchange membranes, reverse osmosis membranes, forward osmosis membranes, and gas separation membranes are known as polymer functional membranes with various functions. Ion exchange membranes are often required to have high durability, including high mechanical strength against various solvents and high-temperature environments. Therefore, methods have been adopted to reinforce ion exchange membranes by combining ion-permeable resins with supports made of mesh fabrics or nonwoven fabrics.

[0003] On the other hand, in order to allow ions to permeate quickly, the permeation resistance of the ion exchange membrane itself must be low, and therefore, it is desirable to make the membrane thickness as thin as possible. Therefore, it is also desirable to make the mesh fabric used as the support thinner. Among synthetic fibers, mesh fabrics using liquid crystal polyester yarns, which have a relatively small diameter, can be made thin by the liquid crystal polyester yarns themselves, but it is desirable to make the mesh fabric even thinner.

[0004] Patent Document 1 describes a method for thinning a mesh fabric by calendering or pressing.

[0005] In addition to the above-mentioned films, mesh fabrics have also been attracting attention as reinforcing materials for various components. For example, in electronic circuit boards, glass fiber mesh fabrics are used as reinforcing materials, but in high-frequency circuit boards, materials with low dielectric constants are required to prevent a decrease in signal transmission speed. Since glass fiber mesh fabrics have a high dielectric constant and are difficult to meet the performance requirements of high-frequency circuit boards, mesh fabrics using liquid crystal polyester yarns have been attracting attention as mesh fabrics with low dielectric constants (Patent Document 2).

[0006] JP 2008-74073 A JP 2014-97594 A

[0007] The inventors of the present application have found that when a mesh fabric made of liquid crystal polyester yarn is subjected to a calendering process and then a heat treatment, the mesh fabric, which has been thinned by the calendering process, regains its thickness by the subsequent heat treatment. For example, in the case of an ion exchange membrane, a heat treatment is performed when the mesh fabric, which serves as a support, and the membrane are combined to produce the membrane. Therefore, even if a mesh fabric made of liquid crystal polyester yarn is calendered, the mesh fabric will regain its thickness by the heat treatment. If such a thickness regain occurs, the effect of the calendering process will be reduced.

[0008] Mesh fabrics used as reinforcing materials for electronic circuit boards are sometimes thinned to improve resin impregnation or to reduce the thickness of the electronic circuit board. When a mesh fabric made of liquid crystal polyester yarn is used, the thinned mesh fabric can revert to its original thickness due to heating during the fabrication of the electronic circuit board or during the mounting of electronic components on the board. The reverted thickness of the mesh fabric can make it difficult to thin the electronic circuit board or can cause problems such as warping of the board or peeling of the conductive foil. Furthermore, during the manufacture of the electronic circuit board, stress can be generated at the interface between the reverted mesh fabric and the resin that shrinks during the curing reaction, potentially resulting in poor adhesion between the mesh fabric and the cured resin.

[0009] An object of the present invention is to provide a mesh fabric made of liquid crystal polyester yarn that can suppress thickness return due to heat treatment.

[0010] The gist of the present invention is as follows. [1] A mesh fabric made of a thinning-treated liquid crystal polyester yarn, characterized in that the thickness change rate of the mesh fabric before and after heat treatment at 180°C is 0% or more and 25.0% or less, as expressed by the following formula (I): Δt = 100 × (t2 - t1) / t1 (I) In the formula (I), Δt is the thickness change rate, t1 is the thickness of the mesh fabric before the heat treatment, and t2 is the thickness of the mesh fabric after the heat treatment. [2] The mesh fabric according to [1], characterized in that it has an X-ray diffraction peak within the range of 2θ = 20 ± 2° in an X-ray diffraction method, and the half-width of the X-ray diffraction peak is 4.0° or less. [3] The mesh fabric according to [1], characterized in that the thickness of the mesh fabric is 10 μm or more and 30 μm or less. [4] The mesh fabric according to [1], characterized in that the thinning treatment is a calendering treatment. [5] A mesh fabric according to [1], characterized in that the coefficient of linear thermal expansion in both the warp and weft directions is 40 ppm / °C or less in a temperature range of 50°C to 200°C. [6] The mesh fabric according to any one of [1] to [5], characterized in that the mesh fabric is used as an ion exchange membrane support, a diaphragm support for water electrolysis, a diaphragm support for a polymer electrolyte fuel cell, a screen gauze for screen printing, a support for a circuit board, or a prepreg to be impregnated with a curable resin.

[0011] According to the present invention, when a heat treatment is performed on a mesh fabric after being thinned, the mesh fabric can be prevented from returning to its original thickness.

[0012] A liquid crystal polyester yarn mesh fabric according to an embodiment of the present invention will be described below. The mesh fabric is a fabric composed of multiple warp yarns and multiple weft yarns. In this embodiment, as will be described later, the mesh fabric is subjected to a heat treatment (hereinafter referred to as a "pre-heat treatment") before undergoing a process to reduce the thickness of the mesh fabric (hereinafter referred to as a "thinning process"), thereby preventing the thinned mesh fabric from regaining its thickness when heated. Here, the return of the mesh fabric to its original thickness means that the mesh fabric becomes thicker than the thickness immediately after the thinning process.

[0013] The threads constituting the mesh fabric are made of liquid crystal polyester (LCP). Liquid crystal polyester is a polyester that forms an anisotropic molten phase (liquid crystallinity) when melted. This property can be confirmed, for example, by placing a sample made of liquid crystal polyester on a hot stage, heating it under a nitrogen atmosphere, and observing the transmitted light through the sample under polarized light.

[0014] Examples of liquid crystal polyesters include polymers of aromatic hydroxycarboxylic acids, polymers of aromatic dicarboxylic acids and aromatic diols or aliphatic diols, and copolymers of aromatic hydroxycarboxylic acid polymers and aromatic dicarboxylic acids. Liquid crystal polyesters are classified into Type I, Type II, and Type III. Examples of aromatic hydroxycarboxylic acids include hydroxybenzoic acid, hydroxynaphthoic acid, and alkyl-, alkoxy-, and halogen-substituted aromatic hydroxycarboxylic acids. Examples of aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, diphenyldicarboxylic acid, naphthalenedicarboxylic acid, diphenyletherdicarboxylic acid, diphenoxyethanedicarboxylic acid, diphenylethanedicarboxylic acid, and alkyl-, alkoxy-, and halogen-substituted aromatic dicarboxylic acids. Examples of aromatic diols include hydroquinone, resorcinol, dioxydiphenyl, naphthalenediol, and alkyl-, alkoxy-, and halogen-substituted aromatic diols. Examples of aliphatic diols include ethylene glycol, propylene glycol, butanediol, and neopentyl glycol.

[0015] The use of the mesh fabric is not particularly limited, but it can be used, for example, as a reinforcing material (support) for ion exchange membranes or a reinforcing material (support) for electronic circuit boards. The production of ion exchange membranes includes a heating step required for combining the mesh fabric, which is a reinforcing material (support), with the membrane, and by suppressing the return of the mesh fabric to its original thickness during the heating step, the thickness of the combined membrane can be maintained thin.

[0016] Furthermore, in electronic circuit boards, the mesh fabric is heated during the curing reaction of the matrix resin and when electronic components are mounted, and if the mesh fabric serving as a reinforcing material regains its thickness, it is likely to cause warping of the board or peeling of the conductive foil laminated on the board, etc. Therefore, suppressing the regain of the mesh fabric thickness is necessary not only to achieve a thinner electronic circuit board but also to suppress the occurrence of defective electronic circuit boards.

[0017] The loom for producing the mesh fabric is not particularly limited, and examples thereof include a shuttle loom, a gripper loom, a rapier loom, a water jet loom, and an air jet loom. The mesh fabric produced by the loom can be subjected to a heat treatment (heat setting).

[0018] The thickness of the mesh fabric is not particularly limited, but is preferably 10 μm or more and 30 μm or less in order to suppress the aforementioned thickness return. Furthermore, when the mesh fabric is used as a reinforcing material (support) for an ion exchange membrane, it is preferable that the permeation resistance of the membrane itself be low in order to allow ions to pass through quickly. Therefore, it is desirable to make the membrane thickness as thin as possible, and therefore it is preferable that the thickness of the mesh fabric serving as a reinforcing material (support) is also thin. Taking this into consideration, the thinner the thickness of the mesh fabric after the thinning treatment, the more preferable it is, with 30 μm or less being more preferable, and 20 μm or less being even more preferable. On the other hand, if the thickness of the mesh fabric after the thinning treatment is too thin, the strength of the mesh fabric will decrease, so the thickness of the mesh fabric is preferably 10 μm or more.

[0019] The mesh fabric of the present invention is one that prevents the return of thickness to a thinned mesh fabric, and as a method for preventing the return of thickness, a pre-heating treatment is carried out before the thinning treatment. Specifically, by exposing the mesh fabric to a high temperature of 260°C or higher before the thinning treatment, it becomes possible to prevent the return of thickness to a thinned mesh fabric when the thinned mesh fabric is subsequently heated.

[0020] As described above, the crystallinity of the liquid crystal polyester is increased by pre-heating the mesh fabric, and the subsequent thinning treatment further increases the crystallinity, making it difficult for the mesh fabric to return to its original thickness even when the thinned mesh fabric is heated.

[0021] Furthermore, by pre-heating the mesh fabric, even when the thinned mesh fabric is heated, the linear expansion coefficient of the mesh fabric in the warp and weft directions can be reduced, and dimensional change of the mesh fabric can be suppressed. As a result, when the mesh fabric of the present invention is used as a support for an electronic circuit board, warping of the electronic circuit board and peeling of the conductive foil are less likely to occur. Of the linear expansion coefficients of the mesh fabric in the warp and weft directions, the larger linear expansion coefficient is preferably 40 ppm / °C or less, more preferably 30 ppm / °C or less, and particularly preferably 20 ppm / °C or less.

[0022] The mesh fabric that has been subjected to the pre-heating treatment and then the thinning treatment has the following characteristics: Specifically, the thickness of the mesh fabric before and after the heat treatment at 180°C (hereinafter referred to as the "specific heat treatment") has a thickness change rate of 0% or more and 25.0% or less, as expressed by the following formula (1):

[0023]

[0024] In the above formula (1), Δt is the thickness change rate [%], t1 is the thickness of the mesh fabric before the specific heat treatment (180° C.), and t2 is the thickness of the mesh fabric after the specific heat treatment (180° C.). Here, when the thickness change rate Δt is a positive value, it means that the thickness of the mesh fabric increases due to the specific heat treatment (180° C.).

[0025] The crystallinity of the liquid crystal polyester yarn constituting the mesh fabric can be measured using an X-ray diffractometer (XRD). A mesh fabric that has been subjected to a pre-heating treatment and then a thinning treatment has an X-ray diffraction peak within the range of 2θ = 20 ± 2° in an X-ray diffraction method, and the half-width of the X-ray diffraction peak is 4.0° or less. The half-width of the X-ray diffraction peak is preferably 4.0° or less, more preferably 2.0° or less. If the half-width is greater than 4.0°, the thickness of the mesh fabric may easily return to its original state when the thinned mesh fabric is heated.

[0026] Since the mesh fabric of the present invention is thinned as described above, the cross-sectional shape of the liquid crystal polyester yarn constituting the mesh fabric may be formed into a substantially elliptical shape. Here, in a cross section perpendicular to the longitudinal direction of the liquid crystal polyester yarn (warp yarn or weft yarn), the maximum yarn diameter is preferably 10 μm or more and 180 μm or less, and the minimum yarn diameter is preferably 5 μm or more and 30 μm or less. The diameters of the warp yarn and the weft yarn (maximum yarn diameter or minimum yarn diameter) may be substantially equal within a range including manufacturing tolerances, or may be different from each other within the above-mentioned range.

[0027] In addition, if the diameters of the warp and weft yarns are approximately equal, the mesh fabric can be more easily deformed isotropically than if the diameters of the warp and weft yarns were different. The yarn diameter is measured at the center of the yarn located between one intersection of the warp and weft yarns and the intersection of the warp and weft yarns adjacent to this intersection (a position equidistant from the two intersections).

[0028] The diameters of the warp and weft yarns before weaving are not particularly limited, but when a thinning treatment of the mesh fabric is required, the thinner the warp and weft yarns, the better, and the diameter of the warp and weft yarns is preferably 40 μm or less. By setting the diameter of the warp and weft yarns to 40 μm or less, the thickness of the entire mesh fabric (including the openings) can be reduced.

[0029] This makes it easier to maintain proton conduction through the openings when the mesh fabric is used as a reinforcing material (support) for the ion exchange membrane. Considering this, the smaller the diameter of the warp and weft threads, the more preferable, with 30 μm or less being more preferable, and 20 μm or less being even more preferable. On the other hand, if the diameter of the warp and weft threads is too small, the mechanical strength of the mesh fabric (thread) tends to decrease, so the diameter of the warp and weft threads is preferably 5 μm or more.

[0030] After weaving, the mesh fabric is preheated before being thinned. This preheating is preferably performed at a temperature of 260°C or higher. If the temperature is lower than 260°C, the mesh fabric may not be thinned at all, or even if it is thinned, the thickness of the mesh fabric may return to its original thickness after subsequent heating. Therefore, it is preferable to perform the preheating at 260°C or higher before the thinning process.

[0031] The mesh fabric that has been preheated at 260°C or higher after weaving is then thinned. The method of thinning is not particularly limited, but heat and pressure treatment (calendering) is preferred. The temperature for calendering is preferably 160°C or higher. If the temperature is lower than 160°C, there is a risk that the thickness of the mesh fabric will return to its original thickness due to subsequent heat treatment, even after thinning treatment. Therefore, the temperature for thinning is preferably 160°C or higher. The conditions for the pressure treatment (e.g., the load applied to the mesh fabric) can be set appropriately as long as the desired thickness of the mesh fabric can be achieved.

[0032] The number of meshes in the thinned mesh fabric is not particularly limited, and can be determined appropriately depending on the application of the mesh fabric.

[0033] The opening (OP) of the thinned mesh fabric can be 85 μm or more. The opening is the distance between two adjacent warp threads in the weft direction or the distance between two adjacent weft threads in the weft direction in the mesh fabric, and is the length of one side of an opening formed in the mesh fabric. The opening can be calculated using the following formula (2):

[0034]

[0035] In the above formula (2), OP is the opening [μm], M is the number of meshes [lines / inch], and D is the width [μm] of the warp and weft threads when viewed perpendicularly to the surface of the mesh fabric. The number of meshes M is the number of threads contained in a width of 1 inch (2.54 cm) of the mesh fabric. As shown in the above formula (2), the opening (OP) can be calculated from the number of meshes M and the thread width D.

[0036] By setting the opening to 85 μm or more, the opening of the mesh fabric can be made larger. Therefore, for example, when the mesh fabric is used as a reinforcing material (support) for an ion exchange membrane, proton conduction through the opening is more easily maintained. In consideration of this point, the larger the opening, the more preferable it is, with 100 μm or more being more preferable, and 150 μm or more being even more preferable. On the other hand, if the opening is made too large, the strength of the mesh fabric may decrease, and for example, in applications where the mesh fabric is used as an ion exchange membrane, the mesh fabric may not function as a reinforcing material (support) for the ion exchange membrane. Therefore, the opening is preferably 625 μm or less.

[0037] The open area of ​​the mesh fabric is preferably 54% or more. The open area is an index representing the area ratio of the openings in the mesh fabric, and is calculated by the following formula (3).

[0038]

[0039] In the above formula (3), OPA is the opening area [%], OP is the opening [μm], and D is the width [μm] of the warp yarn or weft yarn (the same as the width D shown in the above formula (2)).

[0040] By setting the opening area to 54% or more, the area ratio of the openings in the mesh fabric can be increased. Therefore, when the mesh fabric is used as a reinforcing material (support) for an ion exchange membrane, proton conduction through the openings is easily maintained. In consideration of this, the larger the opening area, the more preferable, and 70% or more is more preferable. On the other hand, if the opening area is too large, the mesh fabric will have difficulty functioning as a reinforcing material (support) for an ion exchange membrane, so the opening area is preferably 97% or less.

[0041] The weave of the mesh fabric is not particularly limited, but may be, for example, plain weave or twill weave. In order to reduce the thickness (gauze thickness) of the mesh fabric, it is preferable to use plain weave as the weave.

[0042] The warp and weft threads are preferably monofilaments. If monofilaments are used, the width (effective diameter) of the threads can be made smaller than when multifilaments are used, which makes it easier to enlarge the openings in the mesh fabric as described above.

[0043] Furthermore, since multifilaments are often formed by twisting multiple monofilaments, the external shape of the multifilament (the external shape of the cross section perpendicular to the longitudinal direction) is prone to variation depending on the position in the longitudinal direction of the yarn. On the other hand, monofilaments are less prone to variation in external shape like the multifilaments described above. Therefore, by using monofilaments as warp and weft yarns, it becomes easier to suppress variation in opening throughout the entire mesh fabric. Suppressing variation in opening makes it easier to deform the mesh fabric more isotropically.

[0044] In addition to the liquid crystal polyester described above, other materials can be combined to form warp threads and weft threads as long as the strength required for the mesh fabric is not impaired. Specifically, a thread having a core-sheath structure can be used, and for example, the liquid crystal polyester can be used as the core material and another material can be used as the sheath material.

[0045] The mesh fabric may be subjected to a surface treatment depending on the application of the mesh fabric, such as a hydrophilic treatment by plasma treatment.

[0046] The mesh fabric according to the present invention described above is suitable for use with various solvents and resins or in high-temperature environments. For example, it can be used in medical applications such as artificial skin, filtration applications, screen gauze for screen printing, membrane supports for ion-exchange resins such as chlorine-resistant reverse osmosis membranes, various structural materials, electrochemical applications, membrane supports for humidifying membranes, antifogging membranes, antistatic membranes, oxygen-removing membranes, solar cell membranes, gas barrier membranes, and various substrate supports used in electronic circuit boards. It is particularly suitable for electrochemical and electronic material applications, such as supports for electrolyte membranes and diaphragms used in solid polymer fuel cells, redox flow batteries, all-solid-state batteries, electrochemical hydrogen pumps, water electrolysis devices, alkaline water electrolysis and solid polymer electrolyte membrane-based hydrogen production devices, and chloroalkali electrolysis devices, as well as supports for electronic circuit boards.

[0047] When the mesh fabric of the present invention is used as a support for an electronic circuit board, the mesh fabric is impregnated with a resin known to those skilled in the art, such as an epoxy resin, a polyimide resin, a cyanate resin, a bismaleimide resin, a benzoxazine resin, or a polyfunctional vinyl resin, to prepare a prepreg, and the resin is then heat-cured to obtain a substrate. Here, dimensional fluctuations of the mesh fabric due to heating of the resin (such as return to thickness or an increase in the linear expansion coefficient) can be suppressed. Furthermore, although the mesh fabric of the present invention is made of a liquid crystal polyester yarn with a low dielectric constant, by selecting a resin with a low dielectric constant as the resin to be impregnated into the mesh fabric, it is possible to obtain an electronic circuit board that not only suppresses dimensional fluctuations of the mesh fabric due to heating of the resin, but also has low dielectric properties.

[0048] Examples of the present invention will be described below, but the present invention is not limited to these Examples. First, various measurement methods and processing methods in Examples 1 to 5 and Comparative Examples 1 to 4 will be described.

[0049] (Thickness Measurement) The thickness of the mesh fabric was measured as follows. The mesh fabric was cut into a piece of 5 cm x 10 cm, and the thickness was measured using a thickness measuring instrument (Model MG-4, manufactured by Protec Engineering). The thickness was measured at five different locations on the mesh fabric, and the average value of these thicknesses was taken as the thickness of the mesh fabric.

[0050] (Preheating Treatment) The mesh fabric was preheated before calendering as follows. The mesh fabric was fixed to an aluminum frame (inner diameter 13 cm x 30 cm) so as not to sag. The aluminum frame with the fixed mesh fabric was left standing in a heating furnace set at a predetermined temperature (the temperature described in Examples 1 to 5 and Comparative Examples 1 to 4 described below) for a predetermined time (the time described in Examples 1 to 5 and Comparative Examples 1 to 4 described below), thereby performing the preheating treatment. The atmosphere inside the heating furnace was air. The heat source of the heating furnace is not particularly limited, and may be near infrared rays, far infrared rays, or hot air.

[0051] (Calendering) Calendering was performed as follows: A pair of SUS rolls was heated in advance to a predetermined temperature (the calendering temperature described in Examples 1 to 5 and Comparative Examples 1 to 4 described later), and the mesh fabric was transported between the pair of SUS rolls at a transport speed of 1 m / min, thereby performing calendering.

[0052] (Measurement of Yarn Diameter) The yarn diameter of the mesh woven fabric was measured as follows. In the mesh woven fabric, the yarn diameter was measured at the center of the yarn located between one intersection of the warp and weft yarns and the intersection of the adjacent warp and weft yarns (at a position equidistant from the two intersections). In a mesh woven fabric that has been calendered, the cross section perpendicular to the longitudinal direction of the yarn is approximately elliptical. Therefore, in measuring the yarn diameter, the maximum and minimum yarn diameters were measured at the cross section perpendicular to the longitudinal direction of the yarn using an optical microscope or an electron microscope. In the mesh woven fabric, the maximum and minimum yarn diameters were measured at five different locations, and the average values ​​of the maximum and minimum yarn diameters were calculated. The average values ​​of the maximum and minimum yarn diameters (average values) were then used as the yarn diameter of the mesh woven fabric.

[0053] (Measurement of half-width) The half-width of the X-ray diffraction peak was measured as follows. The X-ray diffraction intensity of the mesh fabric was measured using an X-ray diffractometer (Rigaku XRD device, model SmartLab). Here, CuKβ rays monochromated by a CuKβ filter were used as the X-ray source, and the output was set to 40 kV and 30 mA. In addition, in the simple wide-angle (focusing method) D / teX mode, the scan conditions were 2θ: 7 to 60°, scan speed: 20 deg / min, and scan step: 0.01 deg. In the obtained X-ray diffraction profile, an X-ray diffraction peak falling within the 2θ range of 20±2° was identified, and the peak width at half the intensity of the X-ray diffraction peak was measured as the half-width.

[0054] (Measurement of Thickness Change Rate Δt) The thickness change rate Δt of the mesh woven fabric was measured as follows. The calendered mesh woven fabric was subjected to a heat treatment (specific heat treatment) at a predetermined temperature and time (the temperature and time described in Examples 1 to 5 and Comparative Examples 1 to 4 described below), and the thickness of the mesh woven fabric was measured before and after the specific heat treatment. The thickness change rate Δt was calculated based on the thickness of the mesh woven fabric before and after the specific heat treatment.

[0055] (Measurement of Linear Expansion Coefficient) The linear expansion coefficient of the mesh fabric was measured by thermomechanical analysis (TMA) under the following measurement conditions in accordance with JIS K7197 "Test method for linear expansion coefficient by thermomechanical analysis of plastics." A load was applied to the warp and weft directions of the mesh fabric to measure the linear expansion coefficient of the mesh fabric in two perpendicular thread directions (warp and weft directions). The linear expansion coefficient with the larger value in the warp and weft directions was taken as the linear expansion coefficient of the mesh fabric. Apparatus name: Thermo plus EVO2 TMA8311 (manufactured by Rigaku Corporation) Temperature range: 50°C to 200°C Heating rate: 5°C / min Load: 200mN

[0056] (Example 1) A plain weave fabric having a mesh count of 150 and woven using monofilaments made of LCP (type I LCP) with a thread diameter of 24 μm was subjected to a pre-heating treatment at 280° C. for 5 minutes, followed by calendering at 180° C. to produce a mesh fabric of Example 1. The thickness of the plain weave fabric was measured before and after calendering.

[0057] For the mesh fabric of this example, the half-width of the X-ray diffraction peak in the 2θ range of 20±2° was measured by X-ray diffraction measurement as described above. In addition, to verify the change in thickness (thickness return) when the mesh fabric was heated, the mesh fabric was subjected to a heat treatment (specific heat treatment) at 180° C. for 10 minutes, and the thickness of the mesh fabric before and after the specific heat treatment was measured, and the thickness change rate Δt was calculated.

[0058] (Example 2) A mesh fabric of Example 2 was produced under the same conditions as Example 1, except that the temperature of the pre-heating treatment was set to 290°C. The thickness and half-width of the mesh fabric of this example were measured before and after calendering. In addition, the mesh fabric of this example was subjected to a heat treatment (specific heat treatment) at 180°C for 10 minutes, and the thickness change rate Δt was calculated. The linear expansion coefficient of the mesh fabric was 32 ppm / °C.

[0059] (Example 3) A mesh fabric of Example 3 was produced under the same conditions as Example 1, except that the temperature of the pre-heating treatment was 300°C. The thickness and half-width of the mesh fabric of this example were measured before and after calendering. The mesh fabric of this example was also subjected to a heat treatment (specific heat treatment) at 180°C for 10 minutes, and the thickness change rate Δt was calculated. The linear expansion coefficient of the mesh fabric was 18 ppm / °C.

[0060] Example 4 A mesh fabric of Example 4 was produced under the same conditions as Example 1, except that the pre-heating temperature was 260°C, the heating time was 10 minutes, and the calendering temperature was 160°C. The thickness and half-width of the mesh fabric of this example were measured before and after calendering. In addition, the mesh fabric of this example was subjected to a heat treatment (specific heat treatment) at 180°C for 10 minutes, and the thickness change rate Δt was calculated.

[0061] Example 5 A plain weave fabric having a mesh count of 330 and woven using monofilaments made of LCP (type II LCP) with a thread diameter of 23 μm was subjected to a pre-heating treatment at 290°C for 5 minutes, followed by calendering at 180°C to produce a mesh fabric of Example 5. The thickness and half-width of the mesh fabric were measured before and after calendering. The mesh fabric of Example 5 was also subjected to a heat treatment (specific heat treatment) at 180°C for 10 minutes to calculate the thickness change rate Δt. The linear expansion coefficient of the mesh fabric was 18 ppm / °C.

[0062] (Comparative Example 1) A mesh fabric of Comparative Example 1 was produced under the same conditions as in Example 1, except that calendering was performed at 30°C without prior heating. The thickness and half-width of the mesh fabric of this comparative example were measured before and after calendering. In addition, the mesh fabric of this comparative example was subjected to a heat treatment (specific heat treatment) at 180°C for 10 minutes, and the thickness change rate Δt was calculated.

[0063] (Comparative Example 2) A mesh fabric of Comparative Example 2 was produced under the same conditions as in Example 1, except that calendering was performed at 190°C without prior heating. The thickness and half-width of the mesh fabric of this comparative example were measured before and after calendering. In addition, the mesh fabric of this comparative example was subjected to a heat treatment (specific heat treatment) at 180°C for 10 minutes, and the thickness change rate Δt was calculated.

[0064] (Comparative Example 3) A mesh fabric of Comparative Example 3 was produced under the same conditions as in Example 1, except that a pre-heating treatment was performed at 280°C for 5 minutes, followed by calendering at 35°C. The thickness and half-width of the mesh fabric of this comparative example were measured before and after calendering. In addition, the mesh fabric of this comparative example was subjected to a heat treatment (specific heat treatment) at 180°C for 10 minutes, and the thickness change rate Δt was calculated.

[0065] Comparative Example 4 A mesh fabric of Comparative Example 4 was produced under the same conditions as in Example 1, except that a plain weave fabric woven using monofilaments made of PPS (polyphenylene sulfite) with a thread diameter of 35 μm and having a mesh count of 120 was subjected to calendering at 160°C without pre-heating. The thickness and half-width of the mesh fabric of this comparative example were measured before and after calendering. The mesh fabric of this comparative example was also subjected to a heat treatment (specific heat treatment) at 180°C for 10 minutes, and the thickness change rate Δt was calculated.

[0066] For the above-mentioned Examples 1 to 5 and Comparative Examples 1 to 4, the manufacturing conditions of the mesh fabrics and the measurement / calculation results are shown in Table 1 below.

[0067]

[0068] In Comparative Examples 1 and 2, calendering was performed without pre-heating, but the half-width was 4.0° or more and the thickness change rate Δt significantly exceeded 25.0%. On the other hand, in Examples 1 to 5, pre-heating (260°C or higher) was performed before calendering, and calendering was performed at a predetermined temperature (160°C) or higher, resulting in a half-width of 4.0° or less and a thickness change rate Δt of 25.0% or less. From this, it was found that the mesh fabrics of Examples 1 to 5 could suppress thickness return due to heating.

[0069] Furthermore, as shown in Examples 2, 3 and 5, the linear expansion coefficient of the mesh fabric was 40 ppm / ° C. or less, and it was found that the mesh fabric could be used satisfactorily as a support for an electronic circuit board.

[0070] As shown in Comparative Example 3, even when a pre-heating treatment similar to that in Example 1 was performed before calendaring, when the temperature during calendaring was lower than the predetermined temperature (160 °C), the half-width was 4.0 ° or more, and the thickness change rate Δt significantly exceeded 25.0%. Furthermore, as shown in Comparative Example 4, in a mesh fabric using filaments made of polyphenylene sulfite (PPS), a crystalline thermoplastic resin, the thickness change rate Δt was 25.0% or less even without pre-heating before calendaring. Therefore, when using LCP filaments, the significance of pre-heating before calendaring was recognized. Furthermore, according to Examples 1 to 5, regardless of the type of LCP (type I or type II), pre-heating before calendaring allowed the thickness change rate Δt to be 25.0% or less.

[0071] Although the mechanism by which the thickness return phenomenon occurs only in mesh fabrics made of LCP filaments is unclear, it is believed that the crystallization behavior of the LCP is deeply involved, since when the half-width is 4.0° or less, the thickness change rate Δt becomes 25.0% or less, and the thickness return phenomenon is suppressed. Furthermore, it is believed that the crystallinity of the LCP is improved by performing a pre-heating treatment before calendering, and that performing calendering at a predetermined temperature (160°C or higher) makes it possible to thin the mesh fabric without destroying the crystallinity of the LCP.

Claims

1. A mesh fabric made of thinning-treated liquid crystal polyester yarn, characterized in that the thickness of the mesh fabric before and after heat treatment at 180°C has a thickness change rate of 0% or more and 25.0% or less, as expressed by the following formula (I): Δt = 100 × (t2 - t1) / t1 (I) In the above formula (I), Δt is the thickness change rate, t1 is the thickness of the mesh fabric before the heat treatment, and t2 is the thickness of the mesh fabric after the heat treatment.

2. The mesh fabric according to claim 1, characterized in that it has an X-ray diffraction peak within the range of 2θ=20±2° in X-ray diffraction analysis, and the half-value width of the X-ray diffraction peak is 4.0° or less.

3. The mesh fabric according to claim 1, wherein the thickness of the mesh fabric is 10 μm or more and 30 μm or less.

4. The mesh fabric according to claim 1, wherein the thinning treatment is a calendaring treatment.

5. A mesh fabric as described in claim 1, characterized in that the coefficient of linear thermal expansion in both the warp and weft directions is 40 ppm / °C or less in the temperature range of 50°C to 200°C.

6. The mesh fabric according to any one of claims 1 to 5, characterized in that the mesh fabric is used as an ion exchange membrane support, a diaphragm support for water electrolysis, a diaphragm support for a polymer electrolyte fuel cell, a screen gauze for screen printing, a support for a circuit board, or a prepreg to be impregnated with a curable resin.

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