Core-sheath structure yarn, fabric, resin-filled fabric, and laminate for printed wiring

Abstract

To provide a material capable of forming a substrate for printed wiring having a low linear expansion coefficient, a small transmission loss and high strength.SOLUTION: The core-sheath structure yarn 1 includes a core part 2 that is a resin fiber containing at least one polymer selected from a liquid crystal polymer and a polybenzazole-based polymer, and a sheath part 3 that covers at least a part of the core part 2 and contains at least one polymer selected from the group consisting of a fluorine-based polymer, a polyether-based resin, and an olefin-based resin having 4 or more carbon atoms. The total weight of at least one polymer selected from liquid crystalline polymers and polybenzazole-based polymers in the core part 2 and at least one polymer selected from the group consisting of fluorine-based polymers, polyether-based resins, and olefin-based resins having 4 or more carbon atoms in the sheath part 3 is less than 10000m per 800g in the length direction.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a sheath-core yarn, a fabric, a resin-filled fabric, and a laminate for printed wiring. More specifically, the present disclosure relates to a sheath-core yarn, a fabric using the sheath-core yarn, a resin-filled fabric, and a laminate for printed wiring including the fabric or the resin-filled fabric. [Background technology]

[0002] It is known that a glass fiber reinforced resin substrate made by impregnating glass fibers with a fluorine-based resin, a thermosetting resin, a liquid crystal polyester, or the like is used as a substrate material for printed wiring boards of electronic device components (see Patent Documents 1 to 4). Also known as a printed wiring board is one having a polyimide layer on a metal foil (see Patent Document 5). These substrate materials and substrates for printed wiring boards have a low linear expansion coefficient and are less likely to warp in a high-temperature environment.

[0003] Also, known printed wiring boards include those having a resin layer in which ceramic fillers such as silica particles or boron nitride are added to fluorine-based resins or thermosetting resins (see Patent Document 6). By adding ceramic fillers, the linear expansion coefficient of printed wiring boards can be reduced. Furthermore, examples in which hollow particles are blended in place of ceramic fillers are also known (see Patent Document 7). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2019-541154 [Patent Document 2] Japanese Patent Application Laid-Open No. 2001-171038 [Patent Document 3] Japanese Patent Application Publication No. 2023-172651 [Patent Document 4] Japanese Patent Publication No. 2020-94111 [Patent Document 5] Japanese Patent Application Laid-Open No. 2006-159411 [Patent Document 6] Japanese Patent Application Laid-Open No. 2024-43289 [Patent Document 7] Japanese Patent Application Laid-Open No. 2013-201344 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, there has been a demand for printed wiring boards that comply with next-generation specifications known as Beyond 5G or Beyond 6G. These boards are required to have a low coefficient of linear expansion and low transmission loss in the high-frequency band.

[0006] However, conventional substrates using glass fibers have problems such as high dielectric constants and dielectric loss tangents in the high frequency band, resulting in large transmission losses. Substrates using polyimide resins have low linear expansion coefficients, but their high dielectric constants in the high frequency band and hygroscopicity result in large transmission losses. Furthermore, while fluororesins have low dielectric constants, conventional printed wiring boards laminated with metal foils have high linear expansion coefficients, which make them prone to deformations such as warping and distortion, and also result in low strength. Adding ceramic fillers to fluororesins can lower the linear expansion coefficient of the substrate and the dielectric loss tangent, but they tend to have high dielectric constants and large transmission losses. Using hollow particles instead of ceramic fillers can lower the dielectric constant, but if the hollow particles are exposed on the layer surface, they may be damaged or shed during lamination processing, or unevenness may form on the layer surface. This results in large transmission losses.

[0007] Therefore, an object of the present disclosure is to provide a material capable of forming a substrate for printed wiring having a low linear expansion coefficient, small transmission loss, and high strength. Another object of the present disclosure is to provide a laminate for printed wiring having a low linear expansion coefficient, small transmission loss, and high strength. [Means for solving the problem]

[0008] One embodiment of the present disclosure provides a core-sheath structure yarn comprising: a core that is a resin fiber containing at least one polymer selected from a liquid crystal polymer and a polybenzazole-based polymer; and a sheath that covers at least a portion of the core and contains at least one polymer selected from the group consisting of a fluoropolymer, a polyether-based resin, and an olefin-based resin having 4 or more carbon atoms, wherein the total weight of the at least one polymer selected from the liquid crystal polymer and the polybenzazole-based polymer in the core and the at least one polymer selected from the group consisting of a fluoropolymer, a polyether-based resin, and an olefin-based resin having 4 or more carbon atoms in the sheath is less than 800 g per 10,000 m in the longitudinal direction.

[0009] Liquid crystal polymers and polybenzazole-based polymers have low linear expansion coefficients, low moisture absorption, and high strength. The sheath-core yarn uses at least one polymer selected from these liquid crystal polymers and polybenzazole-based polymers as the resin fiber constituting the core, and at least one polymer selected from the group consisting of fluorine-based polymers, polyether-based resins, and olefin-based resins with a carbon number of 4 or more for the sheath. This results in a low linear expansion coefficient, low transmission loss, and high strength. Furthermore, the sheath-core yarn has a low weight of less than 800 g per 10,000 m in the longitudinal direction, resulting in a small wire diameter and low lattice point height when woven, resulting in high flatness. Therefore, the sheath-core yarn can be used to manufacture printed wiring boards with low linear expansion coefficients, low transmission loss, and high strength.

[0010] The sheath preferably contains a fluorine-based polymer and a heat-meltable resin.

[0011] The heat-meltable resin preferably contains at least one polymer selected from polyether-based resins and olefin-based resins having 4 or more carbon atoms.

[0012] The core preferably further contains a heat-fusible resin.

[0013] The liquid crystal polymer is preferably a liquid crystal polyester.

[0014] The polybenzazole polymer is preferably polyparaphenylenebenzobisoxazole.

[0015] The weight per 10,000 m in the longitudinal direction is preferably 10 to 500 g.

[0016] The proportion of the fluorine-based polymer, polyether-based resin, and olefin-based resin having 4 or more carbon atoms in the sheath is preferably 95% by mass or more.

[0017] The sheath may be in the form of a film, and may be spirally wound around the core so that one surface of the film-like sheath faces the core.

[0018] The core or sheath may be made of multifilaments.

[0019] The present disclosure also provides a fabric comprising the above-described core-sheath structure yarn.

[0020] The present disclosure also provides a resin-filled fabric in which a fabric including a core-sheath structure yarn is filled with a heat-fusible resin, The core-sheath structure yarn provides a resin-filled fabric having a core that is a resin fiber containing at least one polymer selected from a liquid crystal polymer and a polybenzazole-based polymer, and a sheath that covers at least a portion of the core and contains a fluorine-based polymer.

[0021] The present disclosure also provides a laminate for printed wiring comprising the fabric. [Effects of the Invention]

[0022] The core-sheath structure yarn of the present disclosure can be used to form a printed wiring board with a low linear expansion coefficient, small transmission loss, and high strength. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is an external view showing one embodiment of a sheath-core structure yarn of the present disclosure. [Figure 2] FIG. 1 is an external view showing another embodiment of a sheath-core structure yarn according to the present disclosure. [Figure 3] FIG. 1 is an external view showing another embodiment of a sheath-core structure yarn according to the present disclosure. [Figure 4] 1 is a graph showing the results of measuring the dielectric constant in Examples 1 to 4 and Comparative Examples 1 and 2. [Figure 5] 1 is a graph showing the results of the dielectric constant measured in Examples 5 to 7. [Figure 6] 1 is a graph showing the results of dielectric loss tangents measured in Examples 1 to 4 and Comparative Examples 1 and 2. [Figure 7] 1 is a graph showing the results of the dielectric loss tangent measured in Examples 5 to 7. [Figure 8] 2 is a graph showing the results of the dielectric constant and dielectric anisotropy measured in Example 1. [Figure 9] 1 is a graph showing the results of the dielectric constant and dielectric anisotropy measured in Examples 5 to 7. [Figure 10] 1 is a graph showing the results of the amount of change (in-plane direction) measured in an example. [Figure 11] 2 is a graph showing the results of the linear expansion coefficient (thickness direction) measured in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0024] [Sheath-core structure yarn] A sheath-core yarn according to one embodiment of the present disclosure includes a core portion that is a resin fiber and a sheath portion that covers at least a portion of the core portion.

[0025] <Embodiment 1> Figure 1 shows an external view of one embodiment of a sheath-core yarn according to the present disclosure. The sheath-core yarn 1 shown in Figure 1 comprises a core 2 and a sheath 3 that covers at least a portion of the core 2. The sheath 3 covers the entire surface of the core 2. Because the sheath 3 is wrapped around the core 2 without any gaps, a large amount of sheath 3 is present on the surface of the sheath-core yarn 1, which allows for a lower dielectric constant.

[0026] In Figure 1, the sheath 3 is wound spirally around the outer periphery of the core 2 in the longitudinal direction. The sheath 3 covers the core 2 with a single covering. By covering the core 2 with a covering, there is no need to use an adhesive, and it is possible to avoid a decrease in the dielectric constant caused by an adhesive. The covering may be a double covering, and the number of coverings is not particularly limited.

[0027] The sheath-core yarn 1 may be wound in either an S-winding or Z-winding manner. While the sheath 3 is tightly wound around the core 2 in FIG. 1, it may also be wound with gaps (gap winding) as shown in FIG. 2. That is, the sheath 3 may cover only a portion of the surface of the core 2. The larger the area of ​​the sheath 3 covering the core 2, the more sheath 3 is present on the surface of the sheath-core yarn 1, and the lower the dielectric constant can be. The gap D in gap winding is not particularly limited; the shorter the gap D, the larger the area of ​​the sheath 3 covering the core 2, and the lower the dielectric constant can be. The shorter the gap D, the lower the moisture absorption and the lower the transmission loss can be.

[0028] <Embodiment 2> Figure 3 shows another embodiment of a sheath-core yarn 1 according to the present disclosure. The sheath-core yarn 1 shown in Figure 3 comprises a core 2 and a sheath 3 that covers at least a portion of the core 2. The sheath 3 is film-like and is spirally wound around the core 2 with one surface of the film-like sheath 3 facing the core 2. When the sheath 3 has this structure, the sheath 3 occupies a large area of ​​the surface of the sheath-core yarn 1, and the surface is particularly flat, further reducing transmission loss.

[0029] In addition, in Figure 3, the sheath 3 is wound around the core 2 so that a small gap is formed, but it may also be wound without any gaps. If the sheath 3 is in film form, it is easier to wind it more evenly with no gaps or with only small gaps. This makes it possible to lower the dielectric constant, further reduce moisture absorption, and further reduce transmission loss. Note that gap winding may also be used even when the sheath 3 is in film form. The rest of the configuration is the same as the sheath-core structure yarn 1 shown in Figure 1.

[0030] (core) The core 2 is a core yarn, which is a resin fiber containing at least one polymer selected from a liquid crystal polymer and a polybenzazole-based polymer. That is, the core yarn constituting the core 2 contains one or both of a liquid crystal polymer and a polybenzazole-based polymer. Liquid crystal polymers and polybenzazole-based polymers have low linear expansion coefficients, low hygroscopicity, and high strength. Therefore, by using a liquid crystal polymer or a polybenzazole-based polymer as the resin constituting the core 2, the sheath-core structure yarn 1 has a low linear expansion coefficient, high strength, and low transmission loss. Furthermore, because liquid crystal polymers and polybenzazole-based polymers are more flexible than glass fibers, fabrics obtained using the sheath-core structure yarn 1 can be used in flexible printed wiring boards.

[0031] The resins constituting the core 2 may be a single liquid crystal polymer and a polybenzazole-based polymer, or two or more of each may be used. The resin fibers constituting the core 2 may also contain a resin other than the liquid crystal polymer and the polybenzazole-based polymer (e.g., a heat-fusible resin, as described below). The proportion of the liquid crystal polymer and the polybenzazole-based polymer in the resin fibers constituting the core 2 is preferably 6% by mass or more, more preferably 8% by mass or more, relative to the total amount (100% by mass) of the resin fibers. It may also be 10% by mass or more, 20% by mass or more, 30% by mass or more, 40% by mass or more, more than 50% by mass, 60% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more. The above proportion refers to the proportion of either the liquid crystal polymer or the polybenzazole-based polymer when only one of them is contained, or the sum of the proportions of both when both are contained.

[0032] The liquid crystal polymer may be a thermotropic liquid crystal polymer that exhibits liquid crystallinity in a molten state, or a lyotropic liquid crystal polymer that exhibits liquid crystallinity in a solution state. If the liquid crystal polymer is a thermotropic liquid crystal polymer, it is preferably a liquid crystal polymer that melts at a temperature of 450°C or less.

[0033] Examples of liquid crystal polymers include liquid crystal polyesters, liquid crystal polyesteramides in which an amide bond has been introduced into a liquid crystal polyester, liquid crystal polyesterethers in which an ether bond has been introduced into a liquid crystal polyester, and liquid crystal polyestercarbonates in which a carbonate bond has been introduced into a liquid crystal polyester. Liquid crystal polymers may also be polymers in which an isocyanate-derived bond, such as an imide bond, a carbodiimide bond, or an isocyanurate bond, has been introduced into an aromatic polyester or aromatic polyesteramide. Among these liquid crystal polymers, liquid crystal polyesters are preferred because of their high melting point, high strength, low linear expansion coefficient, and low dielectric loss tangent. Since the impact of energy loss is significant in the high frequency range, it is important to reduce the dielectric loss tangent. To achieve this, materials with a molecular structure that is nearly nonpolar or resins capable of immobilizing dipoles are preferred as the liquid crystal polymer. Liquid crystal polyesters, which have high crystal orientation and liquid crystal orientation, are suitable as such resins.

[0034] The polybenzazole polymer is a polymer having a benzazole skeleton, and examples thereof include polybenzoxazole (PBO), polybenzothiazole (PBT), and polybenzimidazole (PBI). Among the polybenzazole polymers, polybenzoxazole is preferred, and polyparaphenylene benzobisoxazole is more preferred. Because the impact of energy loss is significant in the high-frequency range, it is important to reduce the dielectric loss tangent. To achieve this, the liquid crystal polymer is preferably a material with a molecular structure that is nearly nonpolar or a resin that can fix dipoles. As such a resin, polybenzoxazole (particularly polyparaphenylene benzobisoxazole), which has high crystal orientation and liquid crystal orientation, is suitable.

[0035] The weight (fineness) per 10,000 m in the longitudinal direction of resin fibers containing at least one polymer selected from liquid crystal polymers and polybenzazole-based polymers is not particularly limited, but is preferably 300 dtex or less, more preferably 200 dtex or less, even more preferably 150 dtex or less, even more preferably 110 dtex or less, even more preferably 60 dtex or less, and particularly preferably 56 dtex or less. The lower the fineness, the smaller the fiber diameter, and the lower the lattice point height and higher the flatness when woven into a fabric. Therefore, by using a core with such a fineness, it is possible to produce a printed wiring board with a low linear expansion coefficient, low transmission loss, and high strength.

[0036] The weight (fineness) per 10,000 m in the longitudinal direction of the core 2 is not particularly limited, but is preferably 700 dtex or less, more preferably 650 dtex or less, and even more preferably 600 dtex or less. It may be 550 dtex or less, 500 dtex or less, 300 dtex or less, 200 dtex or less, 150 dtex or less, 110 dtex or less, 60 dtex or less, or 56 dtex or less. The lower the fineness, the smaller the wire diameter, and the lower the lattice point height and higher the flatness when woven into a fabric. Therefore, by using a core with such a fineness, it is possible to produce a printed wiring board with a low linear expansion coefficient, low transmission loss, and high strength.

[0037] The resin fiber constituting the core 2 may be a monofilament, a multifilament, or a spun yarn. Among these, a multifilament is preferred from the viewpoint that a high-strength woven fabric can be formed using a fiber with a low fineness.

[0038] The core 2 may be a twisted yarn or a non-twisted yarn. When the resin fiber constituting the core 2 is a multifilament, it may be made of at least one polymer selected from liquid crystal polymer fibers and polybenzazole polymer fibers, or may contain other fibers (for example, a heat-fusible resin described below).

[0039] The core 2 may contain a heat-fusible resin. When the core 2 contains a heat-fusible resin, the heat-fusible resin can be melted and fill the gaps in the fabric by heating the fabric formed using the core-sheath structure yarn 1. Therefore, when the fabric with filled gaps (resin-filled fabric) is used in a printed wiring board, it is possible to prevent solder from flowing and causing poor insulation when solder is used to form through-holes or circuits.

[0040] Examples of the core 2 containing a heat-fusible resin include a twisted yarn of liquid crystal polymer fibers or polybenzazole polymer fibers and heat-fusible resin fibers, and a multifilament containing these fibers.

[0041] Examples of the heat-fusible resin fibers include multifilaments, monofilaments, and film-like fibers. The multifilaments and monofilaments preferably have a fineness of 550 dtex or less. The fineness is preferably 300 dtex or more, more preferably 400 dtex or more. The film-like fibers preferably have a thickness of 50 μm or less and a width of 1 mm or less.

[0042] The proportion of liquid crystal polymer fiber and polybenzazole-based polymer fiber in the resin fibers constituting the core 2 is preferably 5% or more, more preferably 8% or more, from the viewpoint of achieving excellent linear expansion coefficient, transmission loss, and strength, and may be 10% or more, 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, 95% or more, or even 100%. The above proportion refers to the proportion of either the liquid crystal polymer or the polybenzazole-based polymer when only one of them is contained, and refers to the sum of the proportions of both when both are contained.

[0043] (Sheath) The sheath portion 3 contains at least one polymer selected from the group consisting of fluoropolymers, polyether resins, and olefin resins having 4 or more carbon atoms. Fluoropolymers, polyether resins, and olefin resins having 4 or more carbon atoms have low dielectric constants. Therefore, by using at least one polymer selected from the group consisting of fluoropolymers, polyether resins, and olefin resins having 4 or more carbon atoms for the sheath portion 3, the dielectric dissipation factor of the sheath-core yarn 1 is low, resulting in low transmission loss. Furthermore, even if at least one polymer selected from the group consisting of fluoropolymers, polyether resins, and olefin resins having 4 or more carbon atoms, which typically have a high linear expansion coefficient, is used, the linear expansion coefficient of the resulting sheath-core yarn 1 can be reduced by using a resin fiber for the core portion 2 that contains at least one polymer selected from liquid crystal polymers and polybenzazole polymers, which have a low linear expansion coefficient.

[0044] The resins constituting the sheath 3 may be a single type or a combination of two or more types of fluoropolymers, polyether resins, and olefin resins having 4 or more carbon atoms. The resins constituting the sheath 3 may also contain resins other than the fluoropolymers, polyether resins, and olefin resins having 4 or more carbon atoms. To further reduce the dielectric constant, the proportions of the fluoropolymers, polyether resins, and olefin resins having 4 or more carbon atoms in the sheath 3 are preferably greater than 50% by mass, more preferably 60% by mass or more, even more preferably 70% by mass or more, and may be 80% by mass or more or 90% by mass or more, particularly preferably 95% by mass or more, and most preferably 100% by mass, relative to the total amount (100% by mass) of the sheath. When only one type of fluoropolymer, polyether resin, and olefin resin having 4 or more carbon atoms is contained, the proportion refers to that single type. When two or more types are contained, the proportion refers to the combined proportions of those two or more types.

[0045] As the fluorine-based polymer, known or commonly used ones can be used, and examples thereof include polytetrafluoroethylene (PTFE), perfluoroalkoxyalkane (PFA), perfluoroethylenepropene copolymer (FEP), ethylene-tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-perfluorodioxole (TEE / PDD), polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), and polyvinyl fluoride (PVF).

[0046] Of the above fluorine-based polymers, polytetrafluoroethylene is particularly preferred from the viewpoint of being superior in dielectric constant, dielectric loss tangent, and strength.

[0047] The polyether resin may be a known or commonly used one, such as polycarbonate, polyphenylene ether, polysulfone, polyethersulfone, etc. Among these, polyphenylene ether (PPE) is particularly preferred from the viewpoint of being superior in dielectric constant, dielectric dissipation factor, and strength.

[0048] The olefin resin having 4 or more carbon atoms is a polymer constituted by an olefin having 4 or more carbon atoms as an essential monomer component. The olefin is not particularly limited, but examples thereof include α-olefins such as 1-butene and 4-methyl-1-pentene, and cycloolefins. That is, the olefin resin having 4 or more carbon atoms includes polyα-olefins and cycloolefin polymers containing an α-olefin having 4 or more carbon atoms as a monomer component. The number of carbon atoms in the olefin is preferably 10 or less, more preferably 8 or less.

[0049] The polyα-olefin is a polymer obtained by polymerizing an α-olefin monomer. As the polyα-olefin, poly(4-methyl-1-pentene) (PMP) is preferred. The polyα-olefin may be a homopolymer or a copolymer of one type of α-olefin.

[0050] Cycloolefin polymers (COPs) are polymers obtained by polymerizing cycloolefin monomers and have an alicyclic structure in the repeating unit of the main chain. Examples of the cycloolefin polymers include cycloolefin homopolymers made from cycloolefin monomers and cycloolefin copolymers made from copolymers of cycloolefin monomers with olefins such as ethylene.

[0051] Examples of the cycloolefin monomer include polycyclic olefins such as norbornene, methylnorbornene, dimethylnorbornene, ethylidenenorbornene, butylnorbornene, dicyclopentadiene, dihydrodicyclopentadiene, tetracyclododecene, and tricyclopentadiene; and monocyclic olefins such as cyclobutene, cyclopentene, cyclooctadiene, and cyclooctatriene.

[0052] The weight of the sheath portion 3 per 10,000 m in the longitudinal direction is not particularly limited, but is preferably 550 g or less, more preferably 450 g or less, even more preferably 300 g or less, even more preferably 250 g or less, even more preferably 150 g or less, even more preferably 110 g or less, even more preferably 60 g or less, and particularly preferably 56 g or less. The smaller the weight, the smaller the wire diameter, and the lower the lattice point height and higher flatness when woven into a fabric. Therefore, by using a sheath portion of this weight, a printed wiring board with a low linear expansion coefficient, low transmission loss, and high strength can be manufactured. Note that when the sheath portion 3 is made of fiber, the weight per 10,000 m in the longitudinal direction corresponds to the fineness [dtex] of the fiber.

[0053] When the sheath 3 is made of resin fiber, the resin fiber may be a monofilament, a multifilament, or a spun yarn. Among these, a multifilament is preferred from the viewpoint that a high-strength woven fabric can be formed using a fiber with a low fineness.

[0054] When the sheath 3 is made of resin fibers, the resin fibers may be twisted or non-twisted. When the resin fibers are multifilament, they may be made of at least one fiber selected from fluorine-based polymer fibers and cycloolefin-based polymer fibers, or may contain other fibers.

[0055] The sheath 3 preferably contains the above-mentioned heat-fusible resin. When the sheath 3 contains the heat-fusible resin, the heat-fusible resin can be melted and fill the gaps in the fabric by heating the fabric formed using the core-sheath structure yarn 1. Therefore, when the above-mentioned fabric with filled gaps (resin-filled fabric) is used in a printed wiring board, it is possible to prevent solder from flowing and causing poor insulation when solder is used to form through-holes or circuits.

[0056] Examples of sheath 3 containing a heat-fusible resin include a twisted yarn of fluoropolymer fibers and heat-fusible resin fibers, and a multifilament containing these fibers. A first sheath made of fluoropolymer fibers and a second sheath made of a heat-fusible resin may be individually wound around core 2. In this manner, multiple sheaths may be wound around core 2. The first sheath and the second sheath may be wound so that either one is closer to core 2. It is preferable to wind the first core and the second core in opposite directions, i.e., S-winding and Z-winding. When polyether resin or olefin resin with 4 or more carbon atoms, which corresponds to a heat-fusible resin, is used as the fiber constituting sheath 3, the heat-fusible resin is contained without using other fibers, and the effects of containing the heat-fusible resin can be achieved.

[0057] Examples of the heat-fusible resin fibers include multifilaments, monofilaments, and film-like fibers. The multifilaments and monofilaments preferably have a fineness of 550 dtex or less. The fineness is preferably 300 dtex or more, more preferably 400 dtex or more. The film-like fibers preferably have a thickness of 50 μm or less and a width of 1 mm or less.

[0058] The sheath 3 preferably contains at least a fluorine-based polymer, and particularly preferably contains a fluorine-based polymer and a heat-meltable resin. The heat-meltable resin preferably contains at least one polymer selected from polyether resins and olefin resins having 4 or more carbon atoms. In this configuration, the resulting fabric has even better dielectric constant, dielectric loss tangent, and strength.

[0059] The proportion of the fluoropolymer fiber, polyether resin, and olefin resin having 4 or more carbon atoms in the resin fiber is preferably 50% or more, more preferably 60% or more, and may be 70% or more, 80% or more, 90% or more, or 95% or more, and particularly preferably 100%, from the viewpoint of achieving excellent linear expansion coefficient, transmission loss, and strength. The above proportions refer to the proportion of one type of fluoropolymer, polyether resin, and olefin resin having 4 or more carbon atoms when only one type is contained, and refer to the total proportion of the two or more types when two or more types are contained.

[0060] The proportion of fluorine-based polymer fibers in the resin fibers constituting the sheath portion 3 is preferably 5% or more, more preferably 8% or more, from the viewpoint of achieving superior linear expansion coefficient, transmission loss, and strength, and may be 10% or more, 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, or 95% or more, or may be 100%.

[0061] When the sheath 3 is made of a film, the width of the film is, for example, 200 to 2000 μm, and preferably 200 to 500 μm.

[0062] As described above, the core 2 and the sheath 3 may each contain a heat-fusible resin. That is, the sheath-core yarn 1 preferably contains a heat-fusible resin. In this case, only one of the core 2 and the sheath 3 may contain a heat-fusible resin, or both may contain a heat-fusible resin.

[0063] The heat-melt resin is a resin that melts when heated and exhibits fluidity. The heat-melt resin preferably has a melting temperature lower than that of other resins (liquid crystal polymers, polybenzazole-based polymers, fluorine-based polymers, etc.) used in the core-sheath structure yarn 1. For example, the heat-melt resin preferably has a melting point or softening point of about 100 to 300°C, from the viewpoints of sufficient fluidity when heated and excellent heat resistance when used in a printed wiring board. The heat-melt resin also preferably has a dielectric constant ε of less than 3.

[0064] Examples of the heat-meltable resin include crystalline polymer materials such as polyethylene, poly(4-methyl-1-pentene), and ultra-high molecular weight polyethylene, and amorphous polymer materials such as cycloolefin polymers, polycarbonate, and polyphenylene ether. Examples of poly(4-methyl-1-pentene), cycloolefin polymers, and polyphenylene ether include those described above as being capable of being contained in the sheath 3.

[0065] The weight of the sheath-core yarn 1 per 10,000 m in the longitudinal direction is preferably less than 1,500 g, more preferably 1,400 g or less, even more preferably 1,200 g or less, even more preferably 800 g or less, even more preferably 500 g or less, even more preferably 300 g or less, even more preferably 100 g or less, and particularly preferably 90 g or less. The smaller the weight, the smaller the wire diameter, and the lower the lattice point height and flatness when made into a fabric. Therefore, using the sheath-core yarn 1, it is possible to manufacture printed wiring boards with a low linear expansion coefficient, low transmission loss, and high strength. The weight may be, for example, 10 g or more, 100 g or more, or 200 g or more. If the sheath-core yarn 1 is considered to be a fiber, the weight per 10,000 m in the longitudinal direction corresponds to the fineness [dtex].

[0066] The combined weight (fineness) of the at least one polymer selected from liquid crystal polymers and polybenzazole-based polymers in the core 2 and the at least one polymer selected from the group consisting of fluorine-based polymers, polyether-based resins, and olefin-based resins having 4 or more carbon atoms in the sheath 3 per 10,000 m in the longitudinal direction is preferably less than 800 g, more preferably 700 g or less, and even more preferably 650 g or less, and may be 600 g or less, 500 g or less, 300 g or less, 100 g or less, or 90 g or less. The smaller the weight, the smaller the wire diameter, and the lower the lattice point height and flatness when fabricated. Therefore, using the core-sheath structure yarn 1, it is possible to manufacture printed wiring boards with a low linear expansion coefficient, low transmission loss, and high strength. The weight may be, for example, 10 g or more, 100 g or more, or 200 g or more. If it is assumed that the at least one polymer selected from liquid crystal polymers and polybenzazole polymers in the core 2 and the at least one polymer selected from the group consisting of fluorine-containing polymers, polyether resins, and olefin resins having 4 or more carbon atoms in the sheath 3 correspond to fibers, the weight per 10,000 m in the longitudinal direction corresponds to the fineness [dtex]. In this specification, this fineness may also be referred to as the "fineness of the specific fiber."

[0067] In the core-sheath structure yarn 1, the length of the sheath portion 3 (the length of one covering) relative to the length of the core portion 2 of 1 m is preferably 1.03 to 1.5 m, more preferably 1.07 to 1.3 m.

[0068] In the sheath-core yarn 1, the number of turns of the sheath portion 3 per unit length of the core portion 2 is not particularly limited, but is preferably 200 turns / m or more, and more preferably 300 turns / m or more. The greater the number of turns, the larger the surface area of ​​the sheath portion 3, which results in a smaller dielectric constant and a smaller transmission loss.

[0069] The sheath-core yarn is used as a circuit board material. Specifically, for example, a fabric can be obtained using the sheath-core yarn as a raw yarn, and the fabric can be used as a substrate material for a circuit board.

[0070] [Fabric] The fabric contains at least the sheath-core yarn. Examples of the fabric include woven fabrics containing the sheath-core yarn as a raw yarn. Examples of the woven fabric include known or conventional fabrics, such as three basic weaves (plain weave, twill weave, and satin weave), or non-crimp fabrics, such as sheets in which fiber bundles are aligned in one direction or sheets stacked at different angles, stitched to prevent unraveling. The fabric may use only the sheath-core yarn or other yarns as constituent fibers. However, from the viewpoint of achieving uniform strength and elongation of the fabric and a flatter surface, it is preferable to use only the sheath-core yarn. Furthermore, the fabric may use only one type of sheath-core yarn, or two or more types of sheath-core yarn.

[0071] The plain weave fabric includes the sheath-core yarn as at least one of the warp and weft yarns. In particular, from the viewpoints of a low coefficient of linear expansion, high strength, and low transmission loss, it is preferable to use the sheath-core yarn as the warp and weft yarns.

[0072] The fineness of the yarn used in the fabric is preferably 600 dtex or less, more preferably 500 dtex or less, even more preferably 300 dtex or less, even more preferably 200 dtex or less, even more preferably 150 dtex or less, even more preferably 110 dtex or less, even more preferably 60 dtex or less, and particularly preferably 56 dtex or less. The lower the fineness, the smaller the fiber diameter, the lower the height of the lattice points in the woven fabric and the higher the flatness, the lower the linear expansion coefficient, the smaller the transmission loss, and the higher the strength.

[0073] The fabric may be subjected to an opening treatment, which can further increase the flatness of the fabric and further reduce the transmission loss.

[0074] The fabric is preferably annealed. Annealing can relieve internal stress and reduce deformation during the production of circuit patterns when used in printed wiring boards. Furthermore, impurities that may be contained in the sheath portion of the sheath-core structure yarn can be removed by combustion. Annealing is not necessary when the heat-and-pressure treatment described below is performed. The annealing temperature is appropriately set depending on the type of resin used in the core and sheath portions of the sheath-core structure yarn. When using a crystalline polymer such as a fluorine-based polymer, liquid crystal polymer, or polybenzazole-based polymer, the temperature is preferably higher than the glass transition temperature of the polymer. When using an amorphous polymer such as a cycloolefin-based polymer, the temperature is preferably lower than the glass transition temperature of the polymer. The annealing may be performed on the core or sheath portion prior to the production of the sheath-core structure yarn, on the sheath-core structure yarn, or on the laminate for printed wiring described below. In these cases, the fabric does not need to be annealed.

[0075] The dielectric constant (ε') of the fabric at at least one point in the frequency range of 20 to 80 GHz is preferably 2.5 or less, more preferably 2.3 or less, even more preferably 2.2 or less, and particularly preferably 2.0 or less. When the dielectric constant is 2.5 or less, the dielectric constant is low and transmission loss is reduced. In particular, from the viewpoint of further reducing transmission loss in the high frequency band, the dielectric constant (ε') at a frequency of 80 GHz is preferably within the above range. Furthermore, the dielectric constant (ε') over the entire frequency range of 20 to 80 GHz is preferably within the above range.

[0076] The ratio of the maximum value of the dielectric constant (ε') to the minimum value of the dielectric constant (ε') of the fabric in the frequency range of 20 to 80 GHz [maximum value / minimum value] is preferably 1.5 or less, more preferably 1.3 or less, even more preferably 1.2 or less, and particularly preferably 1.1 or less. When the ratio is 1.5 or less, the dielectric constant is stable over a wide frequency band, and the transmission loss is less dependent on frequency.

[0077] The dielectric loss tangent (tanδ) of the fabric at at least one point in the frequency range of 20 to 80 GHz is preferably 0.0025 or less, more preferably 0.0020 or less, even more preferably 0.0015 or less, and particularly preferably 0.0010 or less. When the dielectric loss tangent is 0.0025 or less, transmission loss is further reduced. In particular, from the viewpoint of further reducing transmission loss in the high frequency band, it is preferable that the dielectric loss tangent (tanδ) at a frequency of 80 GHz is within the above range. It is also preferable that the dielectric loss tangent (tanδ) over the entire frequency range of 20 to 80 GHz is within the above range.

[0078] The ratio of the maximum value of the dielectric loss tangent (tan δ) to the minimum value of the dielectric loss tangent (tan δ) [maximum value / minimum value] of the fabric in the frequency range of 20 to 80 GHz is preferably 1.5 or less, more preferably 1.3 or less, even more preferably 1.2 or less, and particularly preferably 1.1 or less. When the ratio is 1.5 or less, the dielectric loss tangent is stable over a wide frequency band, and the transmission loss is less dependent on the frequency.

[0079] The linear expansion coefficient of the fabric at 200°C is preferably 120 ppm or less in the inner surface direction and / or thickness direction, more preferably 110 ppm or less, and even more preferably 100 ppm or less. If the linear expansion coefficient is 120 ppm or less, warping is less likely to occur during wiring formation. The linear expansion coefficient can be measured in detail by the method described in the Examples below.

[0080] When the sheath-core yarn contains the heat-fusible resin, the fabric is preferably heated while sandwiched in the thickness direction and pressed. By subjecting a fabric using the sheath-core yarn containing the heat-fusible resin to a heat-pressing treatment (hot pressing), a fabric (resin-filled fabric) can be obtained in which the heat-fusible resin fills the gaps in the fabric, including at least the core portion. By hot pressing the fabric using the sheath-core yarn in this way, the heat-fusible resin melts and fills the gaps in the fabric, allowing the woven fabric to be transformed into a film-like sheet.

[0081] When the sheath portion 3 of the sheath-core yarn 1 is made solely of a polyether resin or an olefin resin having four or more carbon atoms, which are heat-fusible resins, the sheath portion 3 of the sheath-core yarn 1 melts and flows upon heat pressing, filling the gaps in the fabric, leaving mainly the core portion 2 of the sheath-core yarn 1 as the yarn. On the other hand, when a fluoropolymer is used as the sheath portion 3 of the sheath-core yarn 1, the fluoropolymer does not melt upon heat pressing, and the structure of the sheath-core yarn 1 excluding the heat-fusible resin remains mainly as the yarn. The resin-filled fabric obtained in this manner includes a sheath-core yarn having a core that is a resin fiber containing at least one polymer selected from a liquid crystal polymer and a polybenzazole polymer, and a sheath that covers at least a portion of the core and contains a fluoropolymer.

[0082] The pressure and temperature during the heat pressing are appropriately set depending on the type of resin used in the core and sheath of the core-sheath structure yarn. The temperature is preferably higher than the melting point or softening point of the heat-fusible resin and lower than the glass transition temperature of the resin fiber that constitutes the core.

[0083] The dielectric constant (ε') of the resin-filled fabric at at least one point in the frequency range of 20 to 80 GHz is preferably 2.8 or less, more preferably 2.6 or less, and even more preferably 2.5 or less. When the dielectric constant is 2.8 or less, the dielectric constant is low and transmission loss is reduced. In particular, from the viewpoint of further reducing transmission loss in the high frequency band, the dielectric constant (ε') at a frequency of 80 GHz is preferably within the above range. Furthermore, the dielectric constant (ε') across the entire frequency range of 20 to 80 GHz is preferably within the above range.

[0084] The ratio of the maximum value of the dielectric constant (ε') to the minimum value of the dielectric constant (ε') of the resin-filled fabric in the frequency range of 20 to 80 GHz [maximum value / minimum value] is preferably 1.5 or less, more preferably 1.3 or less, even more preferably 1.2 or less, and particularly preferably 1.1 or less. When the ratio is 1.5 or less, the dielectric constant is stable over a wide frequency band, and the transmission loss is less dependent on frequency.

[0085] The dielectric loss tangent (tanδ) of the resin-filled fabric at at least one point in the frequency range of 20 to 80 GHz is preferably 0.0025 or less, more preferably 0.0020 or less, and even more preferably 0.0015 or less. When the dielectric loss tangent is 0.0025 or less, transmission loss is further reduced. In particular, from the viewpoint of further reducing transmission loss in the high frequency band, it is preferable that the dielectric loss tangent (tanδ) at a frequency of 80 GHz is within the above range. It is also preferable that the dielectric loss tangent (tanδ) across the entire frequency range of 20 to 80 GHz is within the above range.

[0086] The maximum height roughness of at least one surface of the resin-filled fabric is preferably 100 μm or less, more preferably 70 μm or less, and even more preferably 50 μm or less. If the maximum height roughness is 100 μm or less, when the resin-filled fabric is used in a printed wiring board, transmission loss due to surface irregularities can be reduced. Furthermore, it is preferable that the maximum height roughness of both surfaces is within the above range. The maximum height roughness can be measured by a known method.

[0087] The resin-filled fabric allows the resin to sufficiently fill gaps, further preventing poor insulation caused by solder flow during soldering to form through-holes or circuits when used in printed wiring boards. Furthermore, heat pressing provides an extremely smooth surface compared to when the fabric is impregnated with resin, significantly reducing transmission loss due to surface irregularities when the resin-filled fabric is used in printed wiring boards. Furthermore, when the core-sheath structure yarn containing the heat-fusible resin is used, the resin impregnation process can be omitted, greatly facilitating fabric processing. Furthermore, unlike multilayer materials in which various materials, such as fabrics, are layered with adhesive layers or additives interposed therebetween, the resin-filled fabric does not require the use of adhesive layers or additives. Furthermore, the resin-filled fabric can be formed into a structure with reduced anisotropy in dielectric properties not only in the in-plane direction but also in the thickness direction. Furthermore, the use of high-strength fibers with a low linear expansion coefficient as the core material results in high strength and a low linear expansion coefficient. Furthermore, since the gaps between the fibers of the resin-filled fabric are filled with a heat-melting resin, solder does not penetrate between the fibers during circuit formation, and the increased insulation prevents poor conduction and improves migration resistance, which is one of the evaluation criteria for a substrate. From the above, the resin-filled fabric is a dielectric that does not require other additives and has a high level of balance of the properties required for a substrate, such as a low dielectric constant, a low dielectric loss tangent, a low coefficient of linear expansion, high strength, and solder heat resistance.

[0088] The fabric or the resin-filled fabric can be laminated with copper foil and further multi-layered to obtain a fabric laminate. The fabric laminate is a laminate for printed wiring that can be used as a printed wiring board. The laminate for printed wiring includes at least the fabric (or the resin-filled fabric). The core-sheath yarn used in the fabric uses an organic resin as the resin that constitutes the core and sheath, so there is no need to use an adhesive when obtaining the core-sheath yarn. This makes it possible to avoid concerns that arise when using core-sheath yarn in which the core and sheath are bonded via an adhesive, such as an increase in dielectric constant due to the adhesive, an increase in transmission loss due to variations in adhesive strength, and the occurrence of anisotropy due to lamination.

[0089] The fabric used in the laminate for printed wiring may be one type or two or more types. For example, any one layer may have different warp and weft yarns, may use different fluoropolymers for the sheath (e.g., PTFE and PFA), or may have different winding methods for the sheath-core structure yarns (e.g., single covering and double covering, S-winding and Z-winding).

[0090] The sheath-core yarn of the present disclosure can be used to form a printed wiring board with a low linear expansion coefficient, small transmission loss, and high strength. Furthermore, because the sheath-core yarn of the present disclosure is made of organic fibers and has high strength, the printed wiring board is flexible and strong, and is resistant to cracking and creases.

[0091] <Circuit board> The above-mentioned fabric or the above-mentioned resin-filled fabric (particularly the above-mentioned laminate for printed wiring) can be used to manufacture the above-mentioned circuit board (printed wiring board). In the above-mentioned circuit board, the above-mentioned fabric (particularly the above-mentioned laminate for printed wiring) can be used as a substrate material in the above-mentioned circuit board.

[0092] The fabric, the resin-filled fabric, or the printed wiring laminate may be laminated to another substrate to form a substrate. For example, a circuit board can be produced by impregnating the fabric, the resin-filled fabric, or the printed wiring laminate with a thermosetting resin or a thermoplastic resin. For example, a printed wiring board can be produced by laminating a metal foil such as copper foil to the circuit board. A known or conventional adhesive can be used for the lamination. For example, a lamination target such as a prepreg may be laminated by hot pressing on the side opposite the metal foil of the fabric or the like.

[0093] The adhesive is not particularly limited and may be, for example, a polyester adhesive, an epoxy adhesive, a silicone adhesive, a polyurethane adhesive, a urea adhesive, a melamine adhesive, a phenolic resin adhesive, a vinyl acetate adhesive, a cyanoacrylate adhesive, a vinyl acetate resin adhesive, an ethylene-vinyl acetate adhesive, a polyamide adhesive, a rubber adhesive, an acrylic adhesive, or a fluorine-based adhesive. Among these, when a fluorine-based polymer is used in the sheath portion of a core-sheath structure yarn, a fluorine-based adhesive is preferred because the adhesive has excellent adhesive properties and transmission loss is less likely to increase due to the fluorine-based polymer being the same main component as the fluorine-based polymer constituting the fabric. The adhesive may be a hot-melt type or a curing type. The form of the adhesive is also not particularly limited and may be a film (sheet) or a liquid.

[0094] Furthermore, as the fluorine-based adhesive, fluorine-based polymers having a melting point lower than that of PTFE, such as hexafluoropropylene-ethylene copolymer (EFEP), tetrafluoroethylene-ethylene copolymer (ETFE), chlorotrifluoroethylene-ethylene copolymer (ECTFE), polyvinyl fluoride (PVF), tetrafluoroethylene-hexafluoropolypropylene copolymer (FEP), perfluoroalkoxy fluororesin (PFA), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), etc., can also be used. The melting point of the fluorine-based polymer is, for example, 320°C or lower, preferably 300°C or lower, more preferably 250°C or lower, and even more preferably 200°C or lower.

[0095] The adhesive side surface of the metal foil and / or the fabric (the resin-filled fabric or the laminate for printed wiring) may be subjected to a surface treatment. Examples of the surface treatment include physical and chemical surface treatments such as plasma treatment, etching treatment, and hydrophilization treatment. Such surface treatments can increase adhesive strength.

[0096] The printed wiring board has excellent electrical properties such as a low dielectric constant and a low dielectric loss tangent, and is therefore suitable for use as a high-frequency circuit board. Furthermore, by using the fabric for the circuit board, the circuit board has excellent electrical properties and mechanical strength, and is less susceptible to deformation such as warping due to a low coefficient of linear expansion. [Example]

[0097] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0098] Example 1 A sheath-core yarn was produced by using a liquid crystal polyester fiber (multifilament) with a fineness of 110 dtex as a core yarn and double covering the core yarn with a PTFE fiber (multifilament) with a fineness of 110 dtex as a sheath yarn. This sheath-core yarn was used as the warp and weft yarns to form a plain weave, producing a woven fabric. The woven fabric was annealed at 250°C to obtain the woven fabric of Example 1. The length ratio of one core yarn to one sheath yarn in the sheath-core yarn used in the above woven fabric [core yarn:sheath yarn] was 1:2.3.

[0099] Example 2 A sheath-core yarn was produced by using a liquid crystal polyester fiber (multifilament) with a fineness of 110 dtex as a core yarn and single-covering the core yarn with a PTFE fiber (multifilament) with a fineness of 110 dtex as a sheath yarn. This sheath-core yarn was used as the warp and weft yarns to form a plain weave, producing a woven fabric. The woven fabric was annealed at 250°C to obtain the woven fabric of Example 2. The length ratio of one core yarn to one sheath yarn in the sheath-core yarn used in the above woven fabric [core yarn:sheath yarn] was 1:1.15.

[0100] Example 3 A sheath-core yarn was produced by using a polyparaphenylene benzobisoxazole fiber (multifilament) having a fineness of 165 dtex, which is a PBO fiber, as a core yarn and single-covering the core yarn with a PTFE fiber (multifilament) having a fineness of 220 dtex as a sheath yarn. A plain weave was formed using this sheath-core yarn as the warp and weft yarns, producing a woven fabric. The woven fabric was annealed at 250°C to obtain the woven fabric of Example 3. The length ratio of one core yarn to one sheath yarn in the sheath-core yarn used in the fabric was 1:1.15 [core yarn:sheath yarn].

[0101] Example 4 A sheath-core yarn was produced by using a liquid crystal polyester fiber (multifilament) with a fineness of 56 dtex as a core yarn and double covering the core yarn with a PTFE fiber (multifilament) with a fineness of 55 dtex as a sheath yarn. This sheath-core yarn was used as the warp and weft yarns to form a plain weave, producing a woven fabric. The woven fabric was annealed at 250°C to obtain the woven fabric of Example 4. The length ratio of the one core yarn to the two sheath yarns in the sheath-core yarn used in the above woven fabric [core yarn:sheath yarn] was 1:2.3.

[0102] Comparative Example 1 A woven fabric was produced by forming a plain weave using liquid crystal polyester fibers (multifilament) with a fineness of 110 dtex as the warp and weft, and the woven fabric was annealed at 250°C to obtain the woven fabric of Comparative Example 1.

[0103] Comparative Example 2 A woven fabric was produced by forming a plain weave using PTFE fibers (multifilament) with a fineness of 110 dtex as the warp and weft, and the woven fabric was annealed at 250°C to obtain the woven fabric of Comparative Example 2.

[0104] Example 5 A 1 mm-wide core yarn was produced by twisting a micro-slit polycycloolefin (COP) film into a fibrous material and twisting it into a 56 dtex liquid crystal polyester fiber (multifilament fiber). A 1 mm-wide sheath yarn was produced by twisting a micro-slit COP film into a fibrous material and twisting it into a 55 dtex PTFE fiber (monofilament). The core yarn and the sheath yarn were then double-covered to produce a sheath-core yarn. This sheath-core yarn was used as the warp and weft yarns, respectively, to form a plain weave, producing a woven fabric. The above woven fabric was subjected to a heat and pressure treatment in a laminator under heat and pressure conditions of 300°C and 0.5 MPa at a feed rate of 0.2 m / min, melting the COP film and filling the gaps between the fibers of the fabric, to obtain a resin-filled woven fabric of Example 5. The length ratio of the various resin fibers in the core-sheath structure yarn used in the above woven fabric [LCP:PTFE:COP] was 1:2.3:2.3. The length of the above COP is the total length of the COP used in the core yarn and the COP used in the sheath yarn.

[0105] Example 6 A 1-mm-wide core yarn was produced by twisting micro-slit fibrous poly(4-methyl-1-pentene) (PMP) film into a 56-dtex liquid crystal polyester fiber (multifilament fiber). A 1-mm-wide sheath yarn was also produced by twisting micro-slit fibrous PMP film into a 55-dtex PTFE fiber (monofilament). The core yarn and sheath yarn were then double-covered to produce a sheath-core yarn. This sheath-core yarn was used as the warp and weft yarns, respectively, to form a plain weave, producing a woven fabric. The above-mentioned woven fabric was subjected to a heat and pressure treatment in a laminator under heat and pressure conditions of 300°C and 0.5 MPa at a feed rate of 0.2 m / min, melting the PMP film and filling the gaps between the fibers of the woven fabric, to obtain the resin-filled woven fabric of Example 6. The length ratio of the various resin fibers in the core-sheath structure yarn used in the above-mentioned woven fabric [LCP:PTFE:PMP] was 1:2.3:2.3. The length of the above-mentioned COP is the total length of the PMP used in the core yarn and the PMP used in the sheath yarn.

[0106] Example 7 A sheath-core yarn was produced by using a liquid crystal polyester fiber (multifilament) with a fineness of 55 dtex as a core yarn and double covering the core yarn with a PTFE fiber (monofilament) with a fineness of 55 dtex as a sheath yarn. This sheath-core yarn was used as the warp and weft yarns to form a plain weave, producing a woven fabric. The fabric was subjected to a heat and pressure treatment in a laminating machine under heat and pressure conditions of a temperature of 300°C and a pressure of 0.5 MPa at a feed rate of 0.2 m / min, yielding the woven fabric of Example 7. The length ratio of one core yarn to one sheath yarn in the sheath-core yarn used in the woven fabric was 1:2.3 [core yarn:sheath yarn].

[0107] <Evaluation> The core-sheath structure yarns and woven fabrics obtained in the examples and comparative examples were evaluated as follows.

[0108] (1) Dielectric constant and dielectric loss tangent The dielectric properties of the fabrics obtained in the examples and comparative examples (resin-filled fabrics for Examples 5 and 6) were evaluated using a system (resonance method) connecting a vector network analyzer (N5290A) to a split cylinder resonator. Both the dielectric constant and dielectric loss tangent were measured in five different frequency bands: 20 GHz, 28 GHz, 40 GHz, 60 GHz, and 80 GHz. The results are shown in Tables 1 and 2. Graphs plotting the dielectric constant versus frequency are shown in Figure 4 (Examples 1 to 4, Comparative Examples 1 and 2) and Figure 5 (Examples 5 to 7), and graphs plotting the dielectric loss tangent versus frequency are shown in Figure 6 (Examples 1 to 4, Comparative Examples 1 and 2) and Figure 7 (Examples 5 to 7).

[0109] (2) Dielectric anisotropy The dielectric anisotropy of the above-mentioned woven fabrics (resin-filled woven fabrics for Examples 5 and 6) was measured using a dielectric constant measurement system with a Fabry-Perot resonator. For the dielectric anisotropy evaluation using a Fabry-Perot resonator, a transverse plane wave known as a TEM wave was used, which has zero components in the propagation direction for both the electric and magnetic fields and oscillates perpendicular to each other. In this study, a plane wave with a vertical electric field was used. Therefore, when placing the sample, measurements were performed by aligning the fiber axis with the direction of the electric field. First, measurements were performed with the warp yarns aligned with the electric field direction, and then the sample was rotated 90° and measurements were performed with the weft yarns aligned with the electric field direction. The dielectric constant was measured within a frequency range of 110 to 170 GHz. For the woven fabric of Example 1, the dielectric constants of the warp and weft yarns are shown in Figure 8(a), and the dielectric anisotropy is shown in Figure 8(b). The dielectric constants of the warp and weft yarns in Examples 5 to 7 are shown in Figure 9(a), and the dielectric anisotropy is shown in Figure 9(b).

[0110] (3) Change (in-plane direction) For the fabrics obtained in Examples 1 and 3, and Comparative Example 2, both ends of the fabric were fixed with clamps so that the distance between the clamps was 10 mm, and the fabric was heated under the conditions described below to measure the change in length in the in-plane direction using a Seiko Instruments "TMA / SS6100." The average values ​​of the change at temperatures between 150 and 200°C are shown in Table 1. A graph plotting the change that occurred with increasing temperature is shown in Figure 10. Measurement method: TMA measurement by tension ·Load amount: 5mN Heating rate: 5℃ / min Measurement range: 50℃~300℃

[0111] (4) Linear expansion coefficient (thickness direction) For the woven fabric obtained in Example 3, a push rod (detection rod) was pressed against one side of the woven fabric using a "DIL 402 Expedis" manufactured by NETZSCH Japan, and the woven fabric was heated under the conditions described below to measure the change in length in the thickness direction, and the linear expansion coefficient was calculated from the change obtained. A graph plotting the linear expansion coefficient with increasing temperature is shown in Figure 11. Measurement method: TMA measurement by compression ·Load amount: 1N Heating rate: 5℃ / min Measurement range: RT to 400°C

[0112] (5) Presence or absence of mesh The surfaces and cross sections of the resin-filled woven fabrics obtained in Examples 5 and 6 and the woven fabric obtained in Example 7 were observed under an optical microscope. Those in which gaps were observed were evaluated as having open mesh, and those in which gaps were not observed were evaluated as having no open mesh.

[0113] (6) Flatness The surface shape of a random region was observed using a scanning electron microscope (TEM) for the resin-filled woven fabrics obtained in Examples 5 and 6 and the woven fabric obtained in Example 7. A maximum height roughness of 50 μm or less was evaluated as ◯, and a maximum height roughness of more than 100 μm was evaluated as ×.

[0114] [Table 1]

[0115] [Table 2]

[0116] As shown in Table 1, the woven fabrics of the Examples were evaluated as having lower dielectric constants and dielectric tangents, and thus smaller transmission losses, than the woven fabric of Comparative Example 1, which used only liquid crystal polymer fibers. Furthermore, the in-plane changes in Examples 1 and 3, which used the sheath-core structure yarn of the present disclosure, were smaller than the in-plane changes in Comparative Example 2, which used only PTFE fibers, and therefore the woven fabrics of the Examples, which used the sheath-core structure yarn of the present disclosure, were evaluated as having a small linear expansion coefficient. Furthermore, the woven fabrics of the Examples were evaluated as having high strength because they used high-strength core yarns as the warp and weft yarns.

[0117] 5-6, the resin-filled woven fabrics of Examples 5-6, which used a heat-fusible resin for the core-sheath yarn, had no mesh openings and had the same dielectric constant as the woven fabric of Example 7, which did not use a heat-fusible resin and had mesh openings. However, it was determined that the transmission loss was reduced due to the high flatness. It was also confirmed that the use of a heat-fusible resin did not affect the dielectric loss tangent, and the dielectric constant was maintained low. [Explanation of symbols]

[0118] 1. Core-sheath structure yarn 2 Core (core thread) 3 Sheath part (sheath thread)

Claims

1. a core portion that is a resin fiber containing at least one polymer selected from a liquid crystal polymer and a polybenzazole-based polymer; a sheath portion that covers at least a portion of the core portion and that contains at least one polymer selected from the group consisting of a fluorine-based polymer, a polyether-based resin, and an olefin-based resin having 4 or more carbon atoms; A core-sheath structure yarn, in which the total weight of the at least one polymer selected from a liquid crystal polymer and a polybenzazole-based polymer in the core portion and the at least one polymer selected from the group consisting of a fluorine-based polymer, a polyether-based resin, and an olefin-based resin having 4 or more carbon atoms in the sheath portion is less than 800 g per 10,000 m in the longitudinal direction.

2. The sheath-core yarn according to claim 1 , wherein the sheath portion contains a fluorine-containing polymer and a heat-fusible resin.

3. The sheath-core yarn according to claim 2 , wherein the heat-fusible resin contains at least one polymer selected from the group consisting of polyether-based resins and olefin-based resins having 4 or more carbon atoms.

4. The sheath-core yarn according to claim 1 , wherein the core further comprises a heat-fusible resin.

5. The core-sheath structure yarn according to claim 1, wherein the liquid crystal polymer is a liquid crystal polyester.

6. 2. The core-sheath yarn according to claim 1, wherein the polybenzazole polymer is polyparaphenylene benzobisoxazole.

7. The core-sheath structure yarn according to claim 1, wherein the weight per 10,000 m in the length direction is 10 to 500 g.

8. 2. The sheath-core yarn according to claim 1, wherein the proportion of the fluorine-based polymer, the polyether-based resin, and the olefin-based resin having 4 or more carbon atoms in the sheath portion is 95% by mass or more.

9. 2. The sheath-core yarn according to claim 1, wherein the sheath portion is film-shaped and is spirally wound around the core portion so that one surface of the film-shaped sheath portion faces the core portion.

10. The core-sheath structure yarn according to claim 1 , wherein the core or the sheath is composed of multifilaments.

11. A fabric comprising the core-sheath structure yarn according to any one of claims 1 to 10.

12. A resin-filled fabric is a fabric containing a core-sheath structure yarn filled with a heat-melting resin, The core-sheath structure yarn is a resin-filled fabric comprising a core portion which is a resin fiber containing at least one polymer selected from a liquid crystal polymer and a polybenzazole-based polymer, and a sheath portion which covers at least a portion of the core portion and contains a fluorine-based polymer.

13. A laminate for printed wiring comprising the fabric according to claim 11.

14. A laminate for printed wiring comprising the resin-filled fabric according to claim 12.

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