WIRING SHEET AND SHEET-FORM HEATER

A wiring sheet includes: a pseudo sheet structure including a plurality of conductive linear bodies arranged at intervals; a pair of electrodes; and a first power feeder provided for one of the electrodes and a second power feeder provided for the other of the electrodes, in which provided that the number of the conductive linear bodies is N, a resistance value of each conductive linear body is r, a resistance value of each electrode is R, a resistance value of each electrode between the n-th conductive linear body and the (n−1)th conductive linear body counted from a side at which the first power feeder and the second power feeder are provided is Rn, the wiring sheet satisfies all conditions represented by numerical formulae (F1) to (F3) below,  r/R≤300  (F1)  Rn≤Rn−1  (F2)  where n is an integer of 2 or more,  0<R2−RN  (F3).

TECHNICAL FIELD

The present invention relates to a wiring sheet and a sheet-shaped heater.

BACKGROUND ART

A sheet-shaped conductive member (hereinafter also referred to as a “conductive sheet”), which includes a pseudo sheet structure in which a plurality of conductive linear bodies are arranged at intervals, may be used as a component of various articles (e.g., a heat-generating body of a heater, a material of heat-generating textiles, and a protection film (anti-shattering film) for a display device).

Patent Literature 1 discloses an example of a sheet usable for a heat-generating body in a form of a conductive sheet including a pseudo sheet structure having a plurality of linear bodies arranged at intervals to extend unidirectionally. A pair of electrodes is provided at respective ends of the plurality of linear bodies to provide a wiring sheet usable as a heat-generating body.

CITATION LIST

Patent Literature 1: WO 2017/086395 A

SUMMARY OF THE INVENTION

Problem(s) to be Solved by the Invention

The electrodes used for the wiring sheet are typically provided by metallic foil or silver paste. However, in view of flexibility of electrode portions of the wiring sheet, the use of a metal wire or the like in place of the metallic foil or silver paste has been studied. On the other hand, when thin electrodes such as a metal wire are used as electrodes, a resistance value of the electrodes is relatively large. Thus, a difference in resistance value between each electrode and each linear body as a heat-generating portion is small, so that the resistance value of the electrode, which is normally supposed to be negligible, cannot be ignored. As a result, it is found that temperature variation may occur when electric current is applied to the wiring sheet for heat generation.

An object of the invention is to provide a wiring sheet and a sheet-shaped heater capable of restraining temperature variation.

Means for Solving the Problem(s)

A wiring sheet according to an aspect of the invention includes: a pseudo sheet structure including a plurality of conductive linear bodies arranged at intervals;

a pair of electrodes; and a first power feeder provided for one of the electrodes and a second power feeder provided for the other of the electrodes, in which provided that the number of the conductive linear bodies is N, a resistance value of each of the conductive linear bodies is r, a resistance value of each of the electrodes is R, a resistance value of each of the electrodes between an n-th conductive linear body and an (n−1)th conductive linear body counted from a side at which the first power feeder and the second power feeder are provided is Rn, the wiring sheet satisfies all conditions represented by numerical formulae (F1), (F2) and (F3) below.

In the numerical formula (F2), n is an integer of 2 or more.

In the wiring sheet according to the above aspect of the invention, an interval between the conductive linear bodies is preferably 20 mm or less.

It is preferable that the wiring sheet according to the above aspect of the invention further includes a base material supporting the pseudo sheet structure.

A sheet-shaped heater according to another aspect of the invention includes the wiring sheet according to the above aspect of the invention.

According to the above aspects of the invention, a wiring sheet and a sheet-shaped heater capable of restraining temperature variation can be provided.

DESCRIPTION OF EMBODIMENT(S)

First Exemplary Embodiment

Exemplary embodiment(s) of the invention will be described below with reference to the attached drawings, The scope of the invention is not limited to the disclosures of the exemplary embodiment(s). It should be noted that some parts of the drawings are enlarged or reduced in size for the convenience of description.

Wiring Sheet

As shown inFIGS.1and2, a wiring sheet100according to an exemplary embodiment includes a base material1, a pseudo sheet structure2, a resin layer3, and a pair of electrodes4. Specifically, in the wiring sheet100, the base material1, the resin layer3and the pseudo sheet structure2are laminated in this order, The pseudo sheet structure2includes a plurality of conductive linear bodies21arranged at intervals. A first power feeder51is provided on one of the electrodes4, and a second power feeder52is provided on the other of the electrodes4.

In the exemplary embodiment, provided that the number of conductive linear bodies21is N, a resistance value of each conductive linear body21is r [Ω], a resistance value of each electrode4is R [Ω], a resistance value of the electrode4between the n-th conductive linear body21and the (n−1)th conductive linear body21counted from a side at which the first power feeder51and the second power feeder52are provided is Rn[Ω], the wiring sheet needs to satisfy all conditions represented by numerical formulae (F1), (F2) and (F3) described below,

Herein, the wording the nth conductive linear body21counted from a side at which the first power feeder51and the second power feeder52are provided” refers to one of the conductive linear bodies21, which is electrically connected to the pair of electrodes4and provided at the n-th location counted from the first power feeder51and the second power feeder52along the wiring pattern of the wiring sheet100.

In the exemplary embodiment, it is necessary that the condition represented by the numerical formula (F1) should be satisfied.

At a value of r/R exceeding 300, the resistance value of the conductive linear body21as a heat-generating portion is sufficiently larger than the resistance value of the electrode4. Thus, the resistance value of the electrode4is mostly negligible in the wiring sheet100, and the problem of temperature variation is not likely to occur.

In contrast, the problem of temperature variation is more likely to occur as the value r/R is smaller, where use of the wiring sheet100according to the exemplary embodiment is highly significant.

The value r/R may be 200 or less, or 100 or less. However, an excessively small value of r/R causes heat generation also in the electrodes4. The value r/R is thus preferably 10 or more.

In the exemplary embodiment, it is necessary that the condition represented by the numerical formula (F2) should be satisfied.

When the condition represented by the numerical formula (F2) is not satisfied, temperature variation cannot be restrained.

In the numerical formula (F2), n is an integer of 2 or more. An upper limit of n is the number N of the conductive linear bodies21.

The number N of the conductive linear bodies21is preferably 3 or more, more preferably 5 or more, and still more preferably 10 or more. The temperature variation is more likely to occur as the number of the conductive linear bodies21increases. However, the temperature variation can be restrained by the wiring sheet100according to the exemplary embodiment even when the number of the conductive linear bodies21is large. An upper limit of the number N of the conductive linear bodies21, which is not specifically limited, is, for instance,150.

In the exemplary embodiment, it is necessary that the condition represented by the numerical formula (F3) should be satisfied.

When the condition represented by the numerical formula (F3) is not satisfied, the temperature variation cannot be restrained.

In addition, in order to further restrain the temperature variation, a value R2−RNis preferably R/4N or more, more preferably R/2N or more, and still more preferably R/N or more. It should be noted that the value R2−RNdoes not exceed the value R, which is the resistance value of the electrode4.

The inventors of the invention presume that the reason why the temperature variation is restrained when all of the conditions represented by the numerical formulae (F1), (F2), and (F3) are satisfied, is as follows.

Specifically, when the condition represented by the numerical formula (F1) is satisfied, a difference between the resistance value of the conductive linear body21, which is a heat-generating portion, and the resistance value of the electrode4is small. In this case, the resistance value of the electrode4, which is normally supposed to be negligible, cannot be ignored. That is, the temperature variation may occur when electric current is applied to the wiring sheet100for heat generation. This is because the conductive linear bodies21distal to the first power feeder51and the second power feeder52are greatly affected by the resistance of the electrode4to the distal conductive linear bodies21. The inventors of the invention presume that, when electric current is applied to the wiring sheet100for heat generation, the electric current flowing in the distal conductive linear bodies21is relatively small, and consequently, the temperature of the distal conductive linear bodies21is lower than that of other conductive linear bodies21. Meanwhile, when the conditions represented by the numerical formulae (F2) and (F3) are satisfied, the resistance value Rnof the electrode4between the n-th conductive linear body21and the (n−1)th conductive linear body21decreases with increased distance from the first power feeder51and the second power feeder52. The conductive linear bodies21distal to the first power feeder51and the second power feeder52are greatly affected by the resistance of the electrode4from the power feeders to the distal conductive linear bodies21. However, this effect can be inhibited by the decrease in the resistance value Rnof the electrode4. The inventors presume that the temperature variation is restrained as described above.

The resistance values of the conductive linear body21and the electrode4can be set by any known method as appropriate, for instance, can be adjusted by changing the material, cross-sectional area, and/or length.

For instance, a cross-sectional area of the electrode4may increase with increased distance from each of the first power feeder51and the second power feeder52, as shown inFIG.1. In this configuration, the resistance value of the electrode4can decrease with increased distance from each of the first power feeder51and the second power feeder52, Further, the electrode may be formed using materials in such a manner that a material exhibiting higher electrical conductivity is used as a portion of the electrode, where the material is used, is more distanced from each of the first power feeder51and the second power feeder52.

Base Material

Examples of the base material1include a synthetic resin film, paper, metallic foil, nonwoven fabric, fabric, and glass film. The base material1can directly or indirectly support the pseudo sheet structure2. The base material1is preferably a flexible base material.

Examples of the usable flexible base material include a synthetic resin film, paper, nonwoven fabric, and fabric. The flexible base material is preferably a synthetic resin film, nonwoven fabric, or fabric, more preferably a nonwoven fabric or fabric.

Examples of the paper include high-quality paper, recycled paper, and craft paper. Examples of the nonwoven fabric include spun-bond nonwoven fabric, needle-punched nonwoven fabric, melt-blown nonwoven fabric, and spunlace nonwoven fabric. Examples of the fabric include woven fabric and knit fabric. It should be noted that the paper, nonwoven fabric, and fabric for the flexible base material are not limited to these examples,

Pseudo Sheet Structure

The pseudo sheet structure2is configured by the plurality of conductive linear bodies21arranged at intervals. The conductive linear bodies21are linear-shaped in a plan view of the wiring sheet100. The pseudo sheet structure2is configured by arraying the plurality of conductive linear bodies21in a direction intersecting an axial direction of the conductive linear bodies21.

The conductive linear bodies21may be wave-shaped in a plan view of the wiring sheet100. Specific examples of the wave-shaped conductive linear bodies21include sine-wave, circular wave, rectangular wave, triangular wave, and saw-tooth wave conductive linear bodies21. The pseudo sheet structure2with such an arrangement can restrain breakage of the conductive linear bodies21when the wiring sheet100is stretched in the axial direction of the conductive linear bodies21

A volume resistivity of the conductive linear body21is preferably in a range from 1.0×10 −9 Ω·m to 1.0×10−3Ω·m, more preferably in a range from 1.0×10−8Ω·m to 1.0×10−4Ω·m. Surface resistance of the pseudo sheet structure2is easily lowered when the volume resistivity of the conductive linear body21is within the above range.

The volume resistivity of the conductive linear body21is measured as follows. A silver paste is applied to both ends of the conductive linear bodies21and a resistance of a portion at a length of40mm from each end is measured to calculate a resistance value of the conductive linear body21. Then, a value, which is obtained by multiplying the cross-sectional area (unit: m2) of the conductive linear body21by the above resistance value, is divided by the above measured length (0.04 m) to calculate the volume resistivity of the conductive linear body21.

The cross-sectional shape of the conductive linear body21, which is not specifically limited, may be polygonal, flattened, elliptical, or circular. An elliptical shape or a circular shape is preferable in view of compatibility with the resin layer3. When the cross section of the conductive linear body21is circular, a thickness (diameter) D of the conductive linear body21(seeFIG.2) is preferably in a range from 5 μm to 75 μm. In order to restrain an increase in sheet resistance and improve heat generation efficiency and anti-insulation/breakdown properties when the wiring sheet100is used as a heat-generating body, the diameter of the conductive linear body22is more preferably in a range from 8 μm to 60 μm, and still more preferably in a range from 12 μm to 40 μm.

When the cross section of the conductive linear body21is elliptical, it is preferable that the major axis thereof is in the same range as the diameter D described above.

The diameter D of the conductive linear body21is an average of diameters measured at randomly selected five points of the conductive linear bodies21of the pseudo sheet structure2through an observation using a digital microscope.

An interval L between the conductive linear bodies21(seeFIG.2) is preferably 20 mm or less, more preferably in a range from 0.5 mm to 15 mm, and still more preferably in a range from 1 mm to 10 mm.

When the interval between the conductive linear bodies21falls within the above range, the conductive linear bodies are densely arrayed to some extent. This can enhance the performance of the wiring sheet100such as keeping the resistance of the pseudo sheet structure at a low level and providing uniform distribution in temperature rise when the wiring sheet100is used as a heat-generating body.

The interval L between the conductive linear bodies21is obtained by observing the conductive linear bodies21of the pseudo sheet structure2and measuring an interval between adjacent two of the conductive linear bodies21visually or using a digital microscope.

It should be noted that the interval between adjacent two of the conductive linear bodies21herein refers to a length between facing parts of the two conductive linear bodies21in an arraying direction of the conductive linear bodies21(seeFIG.2). When the conductive linear bodies21are arrayed at uneven intervals, the interval L is an average of all intervals between adjacent ones of the conductive linear bodies21.

The conductive linear body21, of which structure is not specifically limited, may be a linear body including a metal wire (hereinafter also referred to as a “metal wire linear body”). The metal wire is excellent in heat conductivity, electrical conductivity, handleability, and versatility. The use of the metal wire linear body as the conductive linear body21facilitates the improvement in light transmissivity while reducing the resistance value of the pseudo sheet structure2. Further, when the wiring sheet100(pseudo sheet structure2) is used as a heat-generating body, heat is easily and quickly generated. Furthermore, a small-diameter linear body as described above is easily obtainable.

It should be noted that examples of the conductive linear body21include, in addition to the metal wire linear body, a linear body including a carbon nanotube and a linear body in a form of a conductively coated yarn.

The metal wire linear body may be a linear body made of a single metal wire or a linear body provided by spinning a plurality of metal wires.

Examples of the metal wire include wires containing metals, such as copper, aluminum, tungsten, iron, molybdenum, nickel, titanium, silver, and gold, or alloys containing two or more metals (e.g., steels such as stainless steel and carbon steel, brass, phosphor bronze, zirconium-copper alloy, beryllium copper, iron nickel, Nichrome®, nickel titanium, KANTHAL®, HASTELLOYO, and rhenium tungsten). The metal wire may be plated with tin, zinc, silver, nickel, chromium, nickel-chromium alloy, solder or the like, or surface-coated with a later-described carbon material or a polymer. Especially, a wire containing one or more metals selected from tungsten, molybdenum and alloys containing tungsten and/or molybdenum is preferable in terms of providing the conductive linear bodies21with a low volume resistivity.

The metal wire may be coated with a carbon material. Coating the metal wire with a carbon material reduces metallic luster, making it easy for the metal wire to be less noticeable. Further, the metal wire coated with a carbon material is restrained from metal corrosion.

Examples of the carbon material usable for coating the metal wire include amorphous carbon (e.g., carbon black, active carbon, hard carbon, soft carbon, mesoporous carbon, and carbon fiber), graphite, fullerene, graphene, and a carbon nanotube.

The linear body including a carbon nanotube is obtained by, for instance, drawing, from an end of a carbon nanotube forest (which is a grown form provided by causing a plurality of carbon nanotubes to grow on a substrate, being oriented in a vertical direction relative to the substrate, and is also referred to as “array”), the carbon nanotubes into a sheet form, and spinning a bundle of the carbon nanotubes after drawn carbon nanotube sheets are bundled. When the carbon nanotubes are not spun, a ribbon-shaped carbon nanotube linear body is obtained. When the carbon nanotubes are spun, a yarn-shaped linear body is obtained. The ribbon-shaped carbon nanotube linear body is a linear body without a structure in which the carbon nanotubes are twisted. Alternatively, the carbon nanotube linear body can be obtained by performing, for instance, spinning from a dispersion liquid of carbon nanotubes. The production of the carbon nanotube linear body by spinning can be performed by, for instance, a method disclosed in U.S. Patent Application Publication No. 2013/0251619 (JP 2012-126635 A). The use of the yarn-shaped carbon nanotube linear body is preferable in order to obtain carbon nanotube linear bodies having a uniform diameter. The yam-shaped carbon nanotube linear body is preferably produced by spinning the carbon nanotube sheets in order to obtain carbon nanotube linear bodies with high purity. The carbon nanotube linear body may be a linear body provided by knitting two or more carbon nanotube linear bodies. Alternatively, the carbon nanotube linear body may be a linear body provided by combining a carbon nanotube and another conductive material (hereinafter also referred to as “composite linear body”),

Examples of the composite linear body include: (1) a composite linear body obtained by depositing an elemental metal or metal alloy on a surface of a forest, sheets or a bundle of carbon nanotubes, or a spun linear body through a method such as vapor deposition, ion plating, sputtering or wet plating in the process of manufacturing a carbon nanotube linear body obtained by drawing carbon nanotubes from an end of the carbon nanotube forest to form the sheets, bundling the drawn carbon nanotube sheets and then spinning the bundle of the carbon nanotubes; (2) a composite linear body in which a bundle of carbon nanotubes is spun with a linear body of an elemental metal, a linear body of a metal alloy, or a composite linear body; and (3) a composite linear body in which a carbon nanotube linear body or a composite linear body is woven with a linear body of an elemental metal, a linear body of a metal alloy, or a composite linear body. In the composite linear body of (2), metal may be supported on the carbon nanotubes when spinning the bundle of the carbon nanotubes as in the composite linear body of (1), Further, although the composite linear body of (3) is a composite linear body provided by weaving two linear bodies, the composite linear body of (3) may be provided by weaving three or more carbon nanotube linear bodies, linear bodies of an elemental metal, linear bodies of a metal alloy, or composite linear bodies, as long as at least one of a linear body of an elemental metal, a linear body of a metal alloy, or a composite linear body is contained.

Examples of the metal for the composite linear body include elemental metals such as gold, silver, copper, iron, aluminum, nickel, chromium, tin, and zinc and alloys containing at least one of these elemental metals (e.g., a copper-nickel-phosphorus alloy, a copper-iron-phosphorus-zinc alloy).

The conductive linear body21may be a linear body in a form of a conductively coated yarn. Examples of the yarn include yarns made from resins, such as nylon and polyester, by spinning. Examples of the conductive coating include coating films of a metal, a conductive polymer, a carbon material, and the like. The conductive coating can be formed by plating, vapor deposition, or the like. The linear body in a form of a conductively coated yarn can be improved in conductivity of the linear body with flexibility of the yarn maintained. In other words, a reduction in resistance of the pseudo sheet structure2is facilitated.

Resin Layer

The resin layer3is a layer containing a resin. The resin layer3can directly or indirectly support the pseudo sheet structure2. The resin layer3is preferably a layer containing an adhesive agent. The conductive linear bodies21are easily attached to the resin layer3by an adhesive agent when the pseudo sheet structure2is formed on the resin layer3.

The resin layer3may be a layer made from a resin capable of being dried or cured. A hardness sufficient for protecting the pseudo sheet structure2is thus imparted to the resin layer3. Accordingly, the resin layer3also functions as a protection film. Further, the cured or dried resin layer3exhibits impact resistance, so that the wiring sheet100can be inhibited from being deformed by impact.

The resin layer3is preferably curable with an energy ray such as an ultraviolet ray, visible energy ray, infrared ray, or electron ray in terms of an easy curability in a short time. It should be noted that “curing with an energy ray” includes thermosetting by energy-ray heating.

Examples of the adhesive agent in the resin layer3include: a thermosetting adhesive agent that is curable by heat; a so-called heat-seal adhesive agent that is bondable by heat; and an adhesive agent that exhibits stickiness when wetted. However, in terms of easy application, the resin layer3is preferably energy-ray-curable. An energy-ray-curable resin is exemplified by a compound having at least one polymerizable double bond in a molecule, preferably an acrylate compound having a (meth)acryloyl group.

A weight average molecular weight (Mw) of the energy-ray-curable resin is preferably in a range from 100 to 30,000, more preferably in a range from 300 to 10,000.

Only one kind or two or more kinds of the energy-ray-curable resins may be contained in the adhesive agent composition. In a case where two or more kinds of the energy-ray-curable resins are contained, a combination and ratio of the energy-ray-curable resins can be selected as needed. In addition, the energy-ray-curable resin may be combined with a later-described thermoplastic resin. A combination and ratio of the energy-ray-curable resin and the thermoplastic resin can be determined as needed.

The resin layer3may be a sticky agent layer formed from a sticky agent (a pressure-sensitive adhesive agent). The sticky agent in the sticky agent layer is not particularly limited. Examples of the sticky agent include an acrylic sticky agent, a urethane sticky agent, a rubber sticky agent, a polyester sticky agent, a silicone sticky agent, and a polyvinyl ether sticky agent. Among the above, the sticky agent is preferably at least one selected from the group consisting of an acrylic sticky agent, urethane sticky agent, and rubber sticky agent, more preferably an acrylic sticky agent.

Examples of the acrylic sticky agent include a polymer including a constituent unit derived from alkyl (meth)acrylate having a linear alkyl group or a branched alkyl group (i.e., a polymer with at least alkyl (meth)acrylate polymerized) and an acrylic polymer including a constituent unit derived from a (meth)acrylate with a ring structure (i.e., a polymer with at least a (meth)acrylate with a ring structure polymerized). Herein, the “(meth)acrylate” is used as a term referring to both “acrylate” and “methacrylate”, and the same applies to other similar terms,

When the acrylic polymer is a copolymer, the form of the copolymerization is not particularly limited. The acrylic copolymer may be any of a block copolymer, a random copolymer, and a graft copolymer.

When the acrylic polymer is a copolymer, the form of the copolymerization is not particularly limited. The acrylic copolymer may be any of a block copolymer, a random copolymer, and a graft copolymer.

The acrylic copolymer may be cross-linked by a cross-linker. Examples of the cross-linker include a known epoxy cross-linker, isocyanate cross-linker, aziridine cross-linker, and metal chelate cross-linker, In cross-linking the acrylic copolymer, a hydroxyl group, a carboxyl group, or the like, which is reactive with the above cross-linkers, can be introduced into the acrylic copolymer as a functional group derived from a monomer component of the acrylic copolymer.

When the resin layer3is formed from a sticky agent, the resin layer3may further contain the above-described energy-ray-curable resin in addition to the sticky agent. When the acrylic sticky agent is used as the sticky agent, a compound having a functional group reactive with the functional group derived from a monomer component of the acrylic copolymer and an energy-ray polymerizable functional group in one molecule may be used as the energy-ray-curable component. Reaction between the functional group of the compound and the functional group derived from the monomer component of the acrylic copolymer enables a side chain of the acrylic copolymer to be polymerized by energy ray irradiation. When the sticky agent is not an acrylic sticky agent, the polymer component other than the acrylic polymer may be a component whose side chain is energy-ray polymerizable.

The thermosetting resin used in the resin layer3is not particularly limited. Specific examples of the thermosetting resin include an epoxy resin, phenol resin, melamine resin, urea resin, polyester resin, urethane resin, acrylic resin, benzoxazine resin, phenoxy resin, amine compound and acid anhydride compound. One of the thermosetting resins may be used alone, or two or more thereof may be used in combination. Among the above examples, in terms of suitability for curing with an imidazole curing catalyst, it is preferable to use an epoxy resin, phenol resin, melamine resin, urea resin, amine compound and acid anhydride compound. Particularly in terms of exhibiting an excellent curability, it is preferable to use an epoxy resin, phenol resin, a mixture thereof, or a mixture of an epoxy resin and at least one selected from the group consisting of a phenol resin, melamine resin, urea resin, amine compound and acid anhydride compound.

A moisture-curable resin used in the resin layer3is not particularly limited. Examples of the moisture-curable resin include a urethane resin, which is a resin where an isocyanate group is generated by moisture, and a modified silicone resin.

When the energy-ray-curable resin or the thermosetting resin is used, a photopolymerization initiator, thermal polymerization initiator, or the like is preferably used. A cross-linking structure is formed by using the photopolymerization initiator, thermal polymerization initiator, or the like, making it possible to more firmly protect the pseudo sheet structure2.

One of the polymerization initiators may be used alone, or two or more thereof may be used in combination.

When the polymerization initiator is used for forming a cross-linking structure, a content of the polymerization initiator is preferably in a range from 0.1 parts by mass to 100 parts by mass, more preferably in a range from 1 part by mass to 100 parts by mass, and still more preferably in a range from 1 part by mass to 10 parts by mass, with respect to 100 parts by mass of the energy-ray-curable resin or the thermosetting resin.

The resin layer3is not necessarily a layer made from a curable resin composition, and may be, for instance, a layer formed from a thermoplastic resin composition. A thermoplastic resin layer can be softened by containing a solvent in the thermoplastic resin composition. With this configuration, when forming the pseudo sheet structure2on the resin layer3, attachment of the conductive linear bodies21to the resin layer3is facilitated. The thermoplastic resin layer can be dried to be solidified by volatilizing the solvent in the thermoplastic resin composition.

Examples of the solvent include an alcohol solvent, ketone solvent, ester solvent, ether solvent, hydrocarbon solvent, alkyl halide solvent, and water.

The resin layer3may contain an inorganic filler. The resin layer3containing the inorganic filler can have a further improved hardness after cured. In addition, the resin layer3containing the inorganic filler has an improved heat conductivity.

Examples of the inorganic filler include inorganic powder (e.g., powders of silica, alumina, talc, calcium carbonate, titanium white, colcothar, silicon carbide, and boron nitride), beads of spheroidized inorganic powder, single crystal fiber, and glass fiber. Among the above, a silica filler and an alumina filler are preferable as the inorganic filler. One of the inorganic fillers may be used alone, or two or more thereof may be used in combination.

The resin layer3may contain other components. Examples of other components include known additives such as an organic solvent, a flame retardant, a tackifier, an ultraviolet absorber, an antioxidant, a preservative, an antifungal agent, a plasticizer, a defoamer, and a wettability modifier.

A thickness of the resin layer3is determined as needed depending on an intended use of the wiring sheet100. For instance, in view of adhesiveness, the thickness of the resin layer3is preferably in a range from 3 μm to 150 μm, more preferably in a range from 5 μm to 100 μm.

Electrodes

The electrodes4are used for supplying electric current to the conductive linear bodies21. The electrodes4are formable using a known electrode material. Examples of the electrode material include a conductive paste (e.g., silver paste), metallic foil (e.g., copper foil), and metal wire, The electrodes4are disposed in electrical connection on both ends of the conductive linear bodies21.

Examples of metal of the metallic foil or metal wire include metals such as copper, aluminum, tungsten, iron, molybdenum, nickel, titanium, silver, and gold and alloys containing two or more metals (e.g., steels such as stainless steel and carbon steel, brass, phosphor bronze, zirconium-copper alloy, beryllium copper, iron nickel, Nichrome®, nickel titanium, KANTHAL®, HASTELLOYO, and rhenium tungsten). The metallic foil or metal wire may be plated with tin, zinc, silver, nickel, chromium, nickel-chromium alloy, solder, or the like. Especially, metal containing at least one selected from copper, silver, and an alloy containing copper and/or silver is preferable in view of metal having a low volume resistivity.

The width of electrodes4may be larger with increased distance from the first power feeder51and the second power feeder52, as shown inFIG.1.

In this case, an average width of the electrode4is, in a plan view of the pseudo sheet structure2, preferably 100 mm or less, more preferably 10 mm or less, and still more preferably 100 μm or less. The temperature variation is more likely to occur as the width of the electrode4decreases. However, even when the width of the electrode4is small, the wiring sheet100according to the exemplary embodiment can restrain the temperature variation.

A ratio of resistance values between the electrode4and the pseudo sheet structure2(i.e., the resistance value of the electrode4/the resistance value of the pseudo sheet structure2) is preferably in a range from 0.0001 to 0.3, and more preferably in a range from 0.0005 to 0.1. The ratio of the resistance values between the electrode and the pseudo sheet structure2can be calculated from “the resistance value of the electrode4/the resistance value of the pseudo sheet structure2.” At a ratio of the resistance values falling within this range, when the wiring sheet100is used as a heat-generating body, abnormal heat generation at the electrodes are restrained. When the pseudo sheet structure2is used as a sheet-shaped heater, heat is generated only in the pseudo sheet structure2, thereby providing a sheet-shaped heater with excellent heat generation efficiency.

The resistance values of the electrode4and the pseudo sheet structure2can be measured using a tester. First, the resistance value of the electrode4is measured and the resistance value of the pseudo sheet structure2attached with the electrodes4is measured. Subsequently, the respective resistance values of the electrode4and the pseudo sheet structure2are calculated by subtracting the measurement value of the electrode4from the resistance value of the pseudo sheet structure2attached with the electrodes.

Power Feeder

The first power feeder51and the second power feeder52are configured to apply voltage to the wiring sheet100. When the electrodes4are exposed to be electrically connectable, any part of the electrodes4may function as the first power feeder51or the second power feeder52.

Alternatively, for the convenience of connection of a power source (not shown) to the electrodes4, the first power feeder51and the second power feeder52may be separately provided, In this case, the material for the first power feeder51and the second power feeder52may be the same as the material for the electrodes4. Further, when the electrodes4are covered with an insulation material for preventing a short circuit and the like, the first power feeder51and the second power feeder52may be provided by removing a part of the insulation material.

Method for Manufacturing Wiring Sheet

A method for manufacturing the wiring sheet100according to the exemplary embodiment is not specifically limited. The wiring sheet100can be manufactured, for instance, by a process described below.

First, the base material1is coated with a composition for forming the resin layer3to form a coating film. Subsequently, the coating film is dried to form the resin layer3, Then, the conductive linear bodies21are arrayed on the resin layer3to form the pseudo sheet structure2. For instance, a drum member is rotated while the resin layer3attached with the base material1is disposed on an outer circumferential surface of the drum member, and the conductive linear bodies21are spirally wound on the resin layer3during the rotation of the drum member. After that, a bundle of the conductive linear bodies21spirally wound is cut along an axial direction of the drum member, resulting in the pseudo sheet structure2arranged on the resin layer3. The resin layer3attached with the base material1, on which the pseudo sheet structure2is formed, is taken off the drum member, thereby obtaining a sheet-shaped conductive member. According to this method, the interval L between adjacent ones of the conductive linear bodies21of the pseudo sheet structure2is easily adjusted by, for instance, moving a feeder of the conductive linear bodies21along a direction parallel with an axis of the drum member while turning the drum member.

Next, the electrodes4are attached to respective ends of the conductive linear bodies21of the pseudo sheet structure2of the sheet-shaped conductive member. Then, the first power feeder51and the second power feeder52are provided to produce the wiring sheet100.

Advantages of First Exemplary Embodiment

The following advantages can be achieved by the exemplary embodiment.

(1) According to the exemplary embodiment, by satisfying the conditions represented by the numerical formulae (F2) and (F3), the cross-sectional area of the electrode4increases with increased distance from each of the first power feeder51and the second power feeder52. This can inhibit the temperature variation in the wiring sheet100.
(2) In the exemplary embodiment, the width of the electrode4increases with increased distance from each of the first power feeder51and the second power feeder52, so that the cross-sectional area of the electrode4can increase with increased distance from each of the first power feeder51and the second power feeder52.
(3) The wiring sheet100according to the exemplary embodiment, which can restrain the temperature variation, is suitably usable as a sheet-shaped heater.

Second Exemplary Embodiment

Next, a second exemplary embodiment of the invention will be described below with reference to the attached drawings.

As shown inFIG.3, a wiring sheet100A according to the exemplary embodiment includes the base material1, the pseudo sheet structure2, the resin layer3, and a pair of electrodes4A. The pseudo sheet structure2includes a plurality of conductive linear bodies21arranged at intervals. The first power feeder51is provided on one of the electrodes4A, and the second power feeder52is provided on the other of the electrodes4A.

It should be noted that the second exemplary embodiment is similar to the first exemplary embodiment except for the electrodes4A. Thus, description will be focused on the electrodes4A, and the description common to the first exemplary embodiment will be omitted.

The electrodes4A of the exemplary embodiment each include a plurality of metal wires, as shown inFIG.3. The metal wires have different lengths. In the electrodes4A, the number of the metal wires increases with increased distance from the first power feeder51and the second power feeder52. In each electrode4A, the metal wires are electrically connected with each other. In this case, an effect of contact resistance between the metal wires is negligible. With this configuration, a cross-sectional area of the electrode4A can increase with increased distance from each of the first power feeder51and the second power feeder52.

Advantages of Second Exemplary Embodiment

According to the exemplary embodiment, the following advantage (4) can be achieved in addition to the advantages (1) and (3) in the first exemplary embodiment.

(4) In the exemplary embodiment, the number of the metal wires forming the electrode4A increases with increased distance from each of the first power feeder51and the second power feeder52, so that the cross-sectional area of the electrode4A can increase with increased distance from each of the first power feeder51and the second power feeder52.

Modifications of Exemplary Embodiment(s)

The scope of the invention is not limited to the above exemplary embodiments, and modifications, improvements, etc. are included within the scope of the invention as long as they are compatible with an object of the invention.

For instance, the wiring sheet100includes the base material1in the above exemplary embodiment. The invention, however ; is not limited thereto. As an example, the wiring sheet100may not include the base material1. In such a case, the wiring sheet100is usable by being attached to an adherend through the resin layer3.

The wiring sheet100includes the resin layer3in the above exemplary embodiment. The invention, however, is not limited thereto. As an example, the wiring sheet100may not include the resin layer3. In such a case, a knitted fabric may be used as the base material1and the pseudo sheet structure2may be formed by weaving the conductive linear bodies21into the base material1.

Confirmation of Advantages

Power consumption distribution was analyzed as described below in order to confirm that the exemplary embodiment provided a wiring sheet capable of restraining the temperature variation.

In analyzing the power consumption distribution, the wiring sheet according to the exemplary embodiment was applied to a ladder-shaped circuit diagram for analysis of the power consumption distribution in the circuit.

In Example 1, the number N of the conductive linear bodies21was30, the resistance value r of each conductive linear body21was 25,070 [mΩ], the resistance value R of each electrode4was 148 [mΩ], the resistance value R2of the electrode4between the second conductive linear body21and the first conductive linear body21counted from the side at which the first power feeder51and the second power feeder52were provided was 10.21 [mΩ], and the resistance value R30of the electrode4between the30th conductive linear body21and the29th conductive linear body21counted from the side at which the first power feeder51and the second power feeder52were provided was 0 [mΩ], It should be noted that the values R3to R29([mΩ]) were gradually decreased from the value R2to the value R30at a constant change rate (approximately 0.36 [mΩ] between adjacent conductive linear bodies on the electrodes).

Power consumption distribution from the first conductive linear body21to the conductive linear body21when electric current was applied to the above circuit was analyzed. It should be noted that each conductive linear body21was numbered and the n-th conductive linear body21was numbered n.FIG.4shows the obtained results. It should be noted that power consumption is a relative value assuming that an electric current of a power source is defined as 1.

In Example 2, the power consumption distribution was analyzed in the same manner as in Example 1 except that the values R2to R30were not changed. It should be noted that the values R2to R30are each 10.21 [mΩ].FIG.4shows the obtained results.

In addition, maximum power consumption, minimum power consumption and average power consumption were determined from the obtained power consumption distribution to calculate an electric power variation (unit: ±%) using a formula below.

It has been found that Example 1 has an electric power variation of ±35%, which is lower than ±47% in Example 2. Presumably, the smaller the electric power variation is, the more temperature variation is restrained.

EXPLANATION OF CODE(S)