Tungsten Wire and Fiber Product

The present invention relates to a tungsten wire and a fiber product.

Patent Literature 1 discloses a metal fiber obtained by combining a tungsten wire having a roughened surface and an aramid fiber or a nylon-based fiber.

Compared to silver or copper, tungsten has high resistivity and high resistance. For example, in order to work tungsten into a wire and reduce resistance, it is necessary to make the wire thick. In other words, with a conventional tungsten wire, it is not possible to achieve both low resistance and narrow diameter.

In view of this, the present invention has as an object to provide a tungsten wire and a fiber product with which both low resistance and narrow diameter can be achieved.

A tungsten wire according to an aspect of the present disclosure has: a resistivity of at least 6.2 μΩ·cm and at most 6.9 μΩ·cm; and a diameter of at most 50 μm, wherein crystal grains of the tungsten wire include dislocation.

A fiber product according to an aspect of the present disclosure includes: the tungsten wire according to the above aspect.

The present invention provides a tungsten wire, and so on, with which both low resistance and narrow diameter can be achieved.

Hereinafter, a tungsten wire and a fiber product according to embodiments of the present invention will be described in detail with reference to the Drawings. It should be noted that each of the embodiments described shows a specific example of the present Invention. Therefore, numerical values, shapes, materials, elements, the arrangement and connection of the elements, steps, the processing order of the steps, etc., indicated in the following embodiments are mere examples, and thus are not intended to limit the present invention. Accordingly, among the elements described in the following embodiments, elements not recited in any independent claim are described as optional elements.

Furthermore, the figures are schematic illustrations and are not necessarily accurate depictions. Therefore, for example, the scaling, etc., in the figures is not necessarily uniform. Elements which are substantially the same have the same reference signs in the figures, and duplicate description may be omitted or simplified.

In the Written Description, terms indicating relationships between elements, terms indicating shapes of elements, and numerical ranges are expressions that refer not only to their strict meanings, but encompass a range of essentially equivalents, such as a range of deviations of a few percent.

First, the configuration of a tungsten wire and a fiber product according to the present embodiment will be described with reference to.is a schematic diagram illustrating tungsten wireand fiber products according to the present embodiment.

As illustrated in, tungsten wireis wound around winding frameand stored. Winding framemay be referred to as a bobbin, reel, spool, drum, or the like in some instances. Tungsten wirehas, for example, but not particularly limited to, a total length ranging from the order of meters, such as approximately 100 m, to the order of kilometers.

Tungsten wireillustrated incan be subjected to secondary working. That is, tungsten wireis worked to form a part of a product. The product is, for example, a fiber product that includes at least one tungsten wirehaving a predetermined length. The fiber product is a conductive fiber with conductivity of tungsten wire.

Plied yarnis illustrated inas an example of a fiber product. Plied yarnincludes tungsten wireand organic fiberthat is combined with tungsten wire.

Plied yarnis a covered yarn in which organic fiberis a core yarn and tungsten wireis a sheath yarn. Plied yarnis manufactured by, for example, extending and fixing organic fiberas the core yarn and winding tungsten wirearound organic fiberas the sheath yarn (that is, performing a covering process).

Tungsten wireis wound along an outer surface of organic fiberwith a predetermined pitch. As illustrated in, tungsten wireis wound with a gap between adjacent turns. However, the adjacent turns may be in close contact with each other. A specific configuration and a specific manufacturing method of tungsten wirewill be described later.

Organic fiberis at least one fiber selected from a group containing a synthetic fiber, a natural fiber, and a recycled fiber. Organic fiberis, for example, a synthetic fiber such as an aramid fiber, a nylon-based fiber, or a polyethylene-based fiber. As the aramid fiber, for example, a fiber manufactured using an aromatic polyamide-based resin material such as Kevlar (registered trademark) can be used. As the polyethylene-based fiber, for example, a fiber manufactured using an ultra-high-molecular-weight polyethylene such as Dyneema (registered trademark) can be used.

It should be noted that a chemical fiber used as organic fiberis not limited to these, and other chemical fibers such as polyester, polypropylene, polyurethane, polyvinyl chloride, or acrylic can be used. Alternatively, organic fibermay be a semi-synthetic fiber or a recycled fiber. Furthermore, organic fibermay be a natural fiber such as a plant fiber or an animal fiber. For example, as organic fiber, cotton, wool, silk, hemp, rayon, or the like can be used.

It should be noted that plied yarnmay be a covered yarn that includes tungsten wireas a core yarn and organic fiberas a sheath yarn. Alternatively, plied yarnis not limited to a covered yarn and may be a doubled-and-twisted yarn.

Alternatively, plied yarnmay include a plurality of tungsten wiresrather than organic fiber. Plied yarnmay be manufactured by performing twisting processing (e.g., covering processing or doubling-and-twisting processing) on a plurality of tungsten wires. Alternatively, plied yarnmay be a plied yarn of tungsten wireand another type of metal wire such as a stainless wire.

also illustrates meshas an example of another fiber product. Meshincludes a plurality of tungsten wires. Meshis manufactured by performing weaving processing using the plurality of tungsten wiresas warp yarns and weft yarns. A weave pattern of meshis plain weave, twill weave, Dutch weave, satin weave, or the like. The weave pattern is not limited to a particular weave pattern. Meshmay be manufactured by performing knitting processing such as stockinette stitch with a predetermined gauge using the plurality of tungsten wiresas knitting yarns.

It should be noted that meshmay be manufactured by performing weaving processing or knitting processing using plied yarn. Alternatively, meshmay be formed in a three-dimensional shape. For example, meshmay form gloves, a hat, or clothes.

The fiber product such as plied yarnor meshincludes tungsten wirehaving conductivity and thus can be used in, for example, vital sensing. For example, the fiber product can sense, as an example of a vital sign, a body temperature or a pulse of a wearer. Specifically, tungsten wireincluded in the fiber product functions as terminals for sensing the vital sign. That is, tungsten wirecan detect a weak current generated by the wearer.

Alternatively, the fiber product may separately include terminals for sensing a vital sign. In this case, tungsten wirefunctions as wiring that electrically connects the terminals and a signal processing circuit.

Alternatively, the fiber product may be used for generating heat. Specifically, heat can be generated by causing current to flow through tungsten wireincluded in the fiber product.

The fiber product may be clothing including gloves, clothes, headgear such as a hat, footgear such as socks or Japanese socks, or the like. Alternatively, the fiber product may be a towel, a hand towel, a handkerchief, a blanket, a sheet, or the like.

Alternatively, the fiber product may be a non-woven fabric manufactured by performing non-woven processing using tungsten wireand organic fiberas thread materials. Alternatively, the fiber product may be tungsten wiresor plied yarnscollected in a form of a cotton pellet. Alternatively, the fiber product may be a woven fabric manufactured using an organic fiber or may be a fiber fabric such as a knitted fabric or a braided fabric into which tungsten wireis sewn (embroidery or sewing) afterward.

Subsequently, a specific configuration of tungsten wireaccording to the present embodiment will be described.

Tungsten wireis a metal wire that contains tungsten (W) as a major component. The term “major component” means that the content of a target element (here, tungsten) is greater than 50 wt %. For example, the content of tungsten contained in tungsten wireis at least 90 wt %. The content of tungsten may be at least 95 wt %, at least 99 wt %, or at least 99.9 wt %. It should be noted that the content of tungsten is a proportion of a weight of tungsten with respect to a weight of tungsten wire. Tungsten wiremay be a pure tungsten wire that is substantially 100 wt % in its content. It should be noted that the pure tungsten wire may contain inevitable impurities, which are inevitably mixed therein in the manufacture.

Tungsten wiremay be a tungsten alloy wire formed from an alloy of tungsten and a metallic element other than tungsten. The metallic element other than tungsten is, for example, rhenium (Re), ruthenium (Ru), iridium (Ir), osmium (Os), or the like. A content of the metallic element, such as rhenium, included in the alloy (solid solution) is, for example, but not limited to, at least 0.1 wt % and at most 10 wt %. The content of the metallic element included in the alloy may be at least 0.5 wt % and at most 5 wt %. As an example, a content of rhenium is 1 wt % but may be 3 wt %.

Alternatively, tungsten wiremay be a doped tungsten wire that is doped with a predetermined element (doped element) such as potassium (K) or cerium (Ce). A content of the doped element is, for example, but not limited to, at least 0.005 wt % and at most 0.010 wt %.

Tungsten wirehas a diameter that is at most 50 μm. For example, the diameter of tungsten wiremay be at most 40 μm, at most 30 μm, at most 20 μm, or at most 10 μm. For example, the diameter of tungsten wiremay be approximately 5 μm.

Tungsten wirehas a tensile strength that is at least 2200 MPa and at most 2800 MPa. Accordingly, it is possible to ensure sufficient tensile strength for use as a fiber product, or the like.

An average width of surface crystal grains in a direction perpendicular to an axis of tungsten wireis at least 220 nm. The average width of the surface crystal grains (hereinafter, referred to as an average crystal width) is one of parameters that Indicate sizes of crystal grains included in tungsten wire. A specific method of measuring the average crystal width will be described with working examples. The average crystal width is, for example, at least 220 nm and at most 310 nm.

The average crystal width being at least 220 nm reduces a resistivity of tungsten wire. That is, when the size of the crystal grains of tungsten wireincreases, grain boundaries in tungsten wireare reduced. When current flows through tungsten wire, the grain boundaries interfere with movement of electrons, thus producing an electric resistance. In the present embodiment, it is possible to reduce the resistivity of tungsten wireby reducing the grain boundaries. Specifically, the resistivity of tungsten wireis at least 6.2 μΩ·cm and at most 6.9 μΩ·cm.

The crystal grains of tungsten wireinclude dislocations. The dislocations are linear crystallographic defects. The dislocations occur in a drawing process (wire drawing process) in the method of manufacturing tungsten wire, The occurring dislocations substantially disappear (to an extent that the dislocations cannot be observed at a predetermined magnification) when tungsten wireis subjected to heating (annealing) at a predetermined temperature (e.g., 1200° C.) or higher. In other words, tungsten wireincluding such dislocations that can be observed at the predetermined magnification means that tungsten wireis not subjected to the above-described heating at the predetermined temperature described above or higher after a final drawing process.

Furthermore, dislocations included in the crystal grains of tungsten wireincrease a secondary workability of tungsten wire. For example, when tungsten wireshaving the same diameter are compared, tungsten wireincluding dislocations has a secondary workability higher than a secondary workability of a tungsten wire including no dislocations. Specifically, tungsten wireincluding dislocations increases in flexibility (bendability) to be capable of being subjected to secondary working involving folding or bending such as twisting processing, weaving processing, or net making processing using tungsten wire. This is because propagation of force applied to tungsten wirein the secondary working is suppressed by dislocations in crystal grains, and thus occurrence of wire breakage or the like of tungsten wirecan be suppressed.

It should be noted that dislocations do not occur only by occurrence of elastic deformation. For example, dislocations do not occur only by winding tungsten wirearound winding frameto be stored as illustrated in.

As described above, tungsten wireaccording to the present embodiment can achieve both low resistance and narrow diameter. In addition, tungsten wireaccording to the present embodiment can be subjected to the secondary working such as twisting processing, thus enabling manufacture of the above-described fiber products.

Next, a method of manufacturing tungsten wireaccording to the present embodiment will be described with reference to.is a flowchart illustrating a method of manufacturing tungsten wireaccording to the present embodiment.

First, as illustrated in, drawing at a high working ratio is performed on a tungsten wire having a predetermined diameter (e.g., approximately 3 mm) that is thicker than a diameter set as a final diameter (S). The tungsten wire having the predetermined diameter is produced by repeatedly performing swaging processing, rolling processing, or the like on a tungsten ingot. Furthermore, the tungsten ingot is produced by performing pressing and sintering on a prepared aggregate of tungsten powder. It should be noted that, by mixing powder of the alloying element or powder of the doped element into the tungsten powder, it is possible to manufacture the tungsten alloy wire or the doped tungsten wire.

The working ratio is the percentage reduction in cross-sectional area due to the drawing. Specifically, the working ratio is a value obtained by subtracting a ratio of a cross-sectional area of the tungsten wire after the drawing with respect to the cross-sectional area of the tungsten wire before the drawing from one and is expressed in terms of a percentage. The higher the working ratio, the more an amount of reduction in the cross-sectional area by the drawing, and the lower the working ratio, the less the amount of reduction in the cross-sectional area by the drawing. That is, when tungsten wires having the same diameter are subjected to the drawing, a diameter of a tungsten wire subjected to the drawing at a high working ratio is narrower than a diameter of a tungsten wire subjected to the drawing at a low working ratio.

In Step S, the high working ratio is specifically a working ratio of at least 80%. For example, the drawing is executed at a working ratio of at least 80% and at most 95%.

The drawing is performed using one or more wire drawing dies. In the drawing process, a lubricant made of graphite dispersed in water may be used. It should be noted that annealing may be performed on the tungsten wire before first drawing. By performing the annealing, an oxide layer is formed on a surface of the tungsten wire. Accordingly, occurrence of wire breakage during drawing processing can be suppressed.

When next drawing is not final (No in S), annealing is performed on the tungsten wire (S). By performing the annealing, it is possible to suppress deterioration in workability in the drawing. A temperature of the annealing is, for example, but not limited to, a temperature at least 1000° C. and at most 1600° C. After performing the annealing, the method returns to Step S, where the drawing is performed at the high working ratio. By repeating the drawing (S) and the annealing (S), reduction of the diameter is performed until the tungsten wire has a desired diameter. In the repetition of the drawing, electrolytic polishing may be performed in a midcourse. By the electrolytic polishing, the surface of the tungsten wire can be smoothed, and thus the workability can be increased to suppress the occurrence of wire breakage during the drawing.

When next drawing is final (Yes in S), annealing is performed on the tungsten wire (S). A temperature of the annealing is a temperature at least 1200° C. and at most 1600° C. This temperature of the annealing is, for example, but not limited to, a temperature higher than the temperature of the immediately previous annealing (S).

Next, the tungsten wire after the annealing (S) is subjected to the drawing at a low working ratio (S). The low working ratio here is a working ratio lower than the working ratio in Step S. Specifically, the low working ratio is at least 20% and at most 50%. For example, the drawing is executed at a working ratio of approximately 30%. By the final drawing in Step S, dislocations are formed in crystal grains of the tungsten wire. It should be noted that, in a process after Step S, annealing at a temperature of at least 1200° C. is not performed.

If the working ratio in the final drawing is greater than 50%, the crystal grains become small, failing to reduce the resistivity. If the working ratio in the final drawing is less than 20%, dislocations are not formed in the crystal grains, failing to increase the secondary workability of tungsten wiresufficiently.

Finally, the tungsten wire after the drawing is subjected to electrolytic polishing (S). The electrolytic polishing is carried out, for example, as a result of generation of a potential difference between the tungsten wire and a counter electrode in a state in which the tungsten wire and the counter electrode are bathed into electrolyte such as aqueous sodium hydroxide. By the electrolytic polishing, the diameter of the tungsten wire is slightly reduced to be adjusted to the desired diameter. It should be noted that the electrolytic polishing (S) need not be performed.