Electric heating/warming fabric articles

[0002] This application is a divisional of U.S. application Ser. No. 09/468,627, filed Dec. 21, 1999, which is a continuation-part of U.S. application Ser. No. 09/296,375, filed Apr. 22, 1999, and now abandoned.

[0003] The invention relates to fabric articles which generate heat/warmth upon application of electricity.

[0004] Fabric heating/warming articles are known, e.g., in the form of electric blankets, heating and warming pads and mats, heated garments, and the like. Typically, these heating/warming articles consist of a fabric body defining one or a series of envelopes or tubular passageways into which electrical resistance heating wires or elements have been inserted. In some instances, the electric resistance heating wires are integrally incorporated into the fabric body during its formation, e.g. by weaving or knitting. Relatively flexible electric resistance heating wires or elements, e.g. in the form of a core of insulating material, e.g. yarn, about which is disposed an electrical conductive element, e.g. a helically wrapped metal wire or an extruded sheath of one or more layers of conductive plastic, have been incorporated directly into the woven or knitted structure of a fabric body.

[0005] According to one aspect of the invention, a method of forming a fabric article adapted to generate heat upon application of electrical power comprises the steps of: joining, in a continuous web, by a reverse plaiting circular knitting process, a stitch yarn and a loop yarn to form a fabric prebody, the stitch yarn forming a technical face of the fabric prebody and the loop yarn forming a technical back of the fabric prebody, the loop yarn forming in loops that overlay the stitch yarn at the technical face and the technical back of the fabric prebody, at spaced-apart intervals, incorporating into the fabric prebody as the stitch yarn an electrical resistance heating element, forming the fabric prebody into a fabric body, with the electrical resistance heating elements extending between opposite edge regions of the fabric body, and providing conductive elements for connecting the electrical resistance heating elements to a source of electrical power.

[0006] Preferred embodiments of the invention may include one or more the following additional steps: finishing at least one of the technical face and the technical back of the fabric body, in a manner avoiding damage to electrical conductivity of the electrical resistance heating elements, to form a fleece surface region, or finishing the technical is face of the fabric body, in a manner to avoid damage to electrical conductivity of the electrical resistance heating elements, to form a first fleece surface region, and finishing the technical back of the fabric body in a manner to avoid damage to electrical conductivity of the electrical resistance heating elements to form a second fleece surface region; applying, directly to the continuous web, the conductive elements for connecting the electrical resistance heating elements to a source of electrical power; incorporating into the fabric body the electrical resistance heating element in the form of a conductive yarn comprising a core of insulating material and an electrical resistance heating filament disposed generally about the core, preferably, the conductive yarn further comprises a sheath material generally surrounding the electrical resistance heating filament and the core, preferably the sheath material is formed by wrapping the electrical resistance heating filament and the core with yarn; incorporating into the fabric prebody the electrical resistance heating element in the form of a conductive yarn comprising an electrical resistance heating filament; connecting the conductive element to a source of electric power and generating heat, the source of electric power comprising alternating current or direct current, e.g. in the form of a battery, which may be mounted to the fabric article; limiting formation of loops to a central region of the fabric prebody, the central region being spaced from edge regions in the fabric body, and providing the conductive elements for connecting the electrical resistance heating elements to a source of electrical power in the edge regions of the fabric body; and/or rendering the yarns of the fabric body hydrophilic or hydrophobic.

[0007] According to another aspect of the invention, a fabric article adapted to generate heat upon application of electrical power comprises a fabric body, a plurality of spaced apart electrical resistance heating elements incorporated into the fabric body and extending generally between opposite edge regions of the fabric body, and electrical conductor elements extending generally along the opposite edge regions of the fabric body and adapted to connect the plurality of spaced apart electrical resistance heating elements to a source of electrical power.

[0008] Preferred embodiments of this aspect of the invention may include one or more the following additional features. The electrical conductor elements are adapted for connecting the plurality of spaced-apart electrical resistance heating elements to a power source of alternating current or to a power source of direct current, e.g., a battery, which may be mounted to the fabric body. A series of at least three of the plurality of electrical resistance heating elements are symmetrically spaced and/or a series of at least three of the plurality of electrical resistance heating elements are asymmetrically spaced. The fabric body comprises a knitted body, e.g. a reverse plaited circular knitted, or other circular knitted (such as double knitted, single jersey knitted, two-end fleece knitted, three-end fleece knitted, terry knitted or double loop knitted), warp knitted or weft knitted body, or a woven body. The fabric body comprises hydrophilic or hydrophobic material. The fabric body has a technical face formed by a stitch yarn and a technical back formed by a loop yarn. The loop yarn forms loops that overlay the stitch yarn at the technical face and the technical back of the fabric prebody. The fabric prebody has loops formed only in a center region. The fabric body has fleece formed upon at least one, and preferably both, of the technical back and the technical face. The conductive yarn is a stitch yarn. The electrical conductor elements, at least in part, are applied as an electrically conductive paste or as an electrically conductive hot melt adhesive. The electrical conductor elements may comprise a conductive wire. The conductive yarn may preferably comprise a core of insulating material, an electrical resistance heating filament disposed generally about the core, and a sheath material generally surrounding the electrical resistance heating filament and the core. Preferably, the core comprises a yarn of synthetic material, e.g. polyester; the sheath material comprises yarn, e.g. of a synthetic material, such as polyester, wrapped about the electrical resistance heating filament and the core; and the electrical resistance heating filament comprises at least one metal filament, and preferably at least three metal filaments, wrapped helically about the core, the metal filament of the electrical resistance heating filament being formed of stainless steel. The electrical resistance heating element has electrical resistance in the range of about 0.1 ohm/cm to about 500 ohm/cm. In other embodiments of the conductive yarn, the core and/or the sheath material may be omitted. The fabric body comprises first and second fabric layers, and the plurality of spaced apart electrical resistance heating/warming elements incorporated into the fabric body are disposed generally between the first and second fabric layers. The fabric body comprises a double knit fabric body and the first and second fabric layers are joined, in face-to-face relationship, by interconnecting yarns, the plurality of spaced apart electrical resistance heating/warming elements incorporated into the fabric body being positioned and spaced apart by the interconnecting yarns and joined by the conductors in a parallel circuit. The first and second fabric layers are formed separately and joined, e.g by laminating or stitching, in face-to-face relationship, with the plurality of spaced apart electrical resistance heating/warming elements incorporated into the fabric body disposed therebetween. The plurality of spaced apart electrical resistance heating/warming elements may be mounted upon a substrate, e.g. an open grid or a moisture resistant, vapor permeable barrier material, the substrate with the plurality of spaced apart electrical resistance heating/warming elements mounted thereupon being disposed between the first and second fabric layers. The plurality of spaced apart electrical resistance heating/warming elements may be mounted upon at least one opposed surface of the first and second fabric layers.

[0009] An objective of the invention is to provide electric heating/warming fabric articles, e.g. electric blankets, heating and warming pads, heated garments, etc., into which a plurality of spaced-apart electric resistance heating members, in the form of conductive yarns, are incorporated by a knitting or weaving process. The fabric body of the heating/warming article, including the incorporated electric resistance heating members, may subsequently be subjected to a fabric finishing process, e.g., one or both surfaces of. the fabric body may be napped, brushed, sanded, etc., to form fleece. In a planar structure, such as an electric heating blanket, the electric resistance heating members are connected at their ends along opposite edge regions of the planar fabric body, i.e., of the blanket, and may be powered by alternating current or direct current, including by one or more batteries mounted to the blanket.

[0010] Other features and advantages will be apparent from the following description of a presently preferred embodiment.

[0011] FIG. 1 is a perspective view of an electric heating/warming composite fabric article of the invention in the form of an electric blanket;

[0012] FIG. 2 is an end section view of the electric heating/warming composite fabric article of FIG. 1, taken at the line 2—2; and

[0013] FIG. 3 is a side section view of the electric heating/warming composite fabric article of FIG. 1, taken at the line 3—3.

[0014] FIG. 4 is a perspective view of a segment of a circular knitting machine, and

[0015] FIGS. 5-11 are sequential views of a cylinder latch needle in a reverse plaiting circular knitting process, e.g. for use in forming an electric heating/warming composite fabric article of the invention.

[0016] FIG. 12 is a somewhat diagrammatic end section view of a preferred embodiment of a conductive yarn for an electric heating/warming fabric article of the invention, while

[0017] FIGS. 13-16 and 16A are similar views of alternative embodiments of conductive yarns for electric heating/warming fabric articles of the invention.

[0018] FIG. 17 is a somewhat diagrammatic section view of a segment of a tubular knit fabric during knitting, and

[0019] FIG. 18 is a somewhat diagrammatic perspective view of the tubular knit fabric of FIG. 17.

[0020] FIG. 19 is an end section view, similar to FIG. 2, of an electric heating/warming fabric article of the invention with fleece on both faces; FIG. 19A is similar view of an electric heating/warming fabric article of the invention, e.g., a sheet or the like, without fleece on either face; and

[0021] FIG. 20 is an enlarged, plan view of the technical face showing an alternative embodiment of a conductor element.

[0022] FIGS. 21, 22 and 23 are somewhat diagrammatic representations of other embodiments of heating/warming fabric articles of the invention, as adapted to be powered by direct current, e.g., an automobile warming or heating pad (FIG. 21), adapted to be powered from an automobile battery; and a stadium or camping blanket (FIG. 22) and a garment (FIG. 23), adapted to be powered from a battery replaceably mounted to the article.

[0023] FIG. 24 is a somewhat diagrammatic representation of another embodiment of a heating/warming fabric body of the invention, with a double knit fabric body having two, spaced-apart fabric layers joined by interconnecting yarns; and

[0024] FIG. 25 is a somewhat diagrammatic representation of yet another embodiment of a heating/warming fabric body of the invention, with two, spaced-apart fabric layers joined about electric heating/warming fabric.

[0025] Referring to FIG. 1, an electric heating/warming composite fabric article of the invention, e.g. an electric blanket 10, adapted to generate heat upon application of electrical power, consists of a fabric body 12 having a technical back 14 and a technical face 16. The fabric body 12 incorporates a plurality of spaced-apart electric resistance heating elements 18 extending between opposite edge regions 20, 21 of the fabric body.

[0026] Referring also to FIGS. 4-11, in a preferred embodiment, the fabric body 12 is formed (in a continuous web) by joining a stitch yarn 22 and a loop yarn 25 in a standard reverse plaiting circular knitting (terry knitting) process, e.g. as described in Knitting Technology, by David J. Spencer (Woodhead Publishing Limited, 2nd edition, 1996), the entire disclosure of which is incorporated herein by reference. Referring again to FIGS. 2 and 3, in the terry knitting process, the stitch yarn 22 forms the technical face 16 of the resulting fabric body and the loop yarn 25 forms the opposite technical back 14, where it is formed into loops (25, FIG. 10) extending over the stitch yarn 22. In the fabric body 12 formed by reverse plaiting circular knitting, the loop yarn 25 extends outwardly from the planes of both surfaces and, on the technical face 16, the loop yarn 25 covers the stitch yarn 22 (e.g., see FIG. 17). As a result, during napping of the opposite fabric surfaces to form a fleece, the loop yarn 25 protects the stitch yarn 22, including the conductive yarns 26 knitted into the fabric body in the stitch yarn position.

[0027] The loop yarn 25 forming the technical back 14 of the knit fabric body 12 can be made of any synthetic or natural material. The cross section and luster of the fibers or the filament may be varied, e.g., as dictated by requirements of the intended end use. The loop yarn can be a spun yarn made by any available spinning technique, or a filament yarn made by extrusion. The loop yarn denier is typically between 40 denier to 300 denier. A preferred loop yarn is a 200/100 denier T-653 Type flat polyester filament, e.g. as available commercially from E.I. duPont de Nemours and Company, Inc., of Wilmington, Del.

[0028] The stitch yarn 22 forming the technical face 16 of the knit fabric body 12 can be also made of any type of synthetic or natural material in a spun yarn or a filament yarn. The denier is typically between 50 denier to 150 denier. A preferred yarn is a 70/34 denier filament textured polyester, e.g. as available commercially from UNIFI, Inc., of Greensboro, N.C.

[0029] Referring now also to FIG. 12, and also to FIGS. 13-16, at spaced intervals during the knitting process, an electric resistance heating member 18 in the form of a conductive yarn 26 is incorporated into the fabric body 12 in place of the stitch yarn 22. Referring to FIG. 12, in a preferred embodiment, the conductive yarn 26 forming the electrical resistance heating elements 18 consists of a core 28 of insulating material, e.g. a polyester yarn, about which extends an electrical conductive element 30, e.g. three filaments 31 of stainless steel wire (e.g. 316L stainless steel) wrapped helically about the core 28, and an outer covering 32 of insulating material, e.g. polyester yarns 33 (only a few of which are suggested in the drawings) helically wrapped about the core 28 and the filaments 31 of the electrical conductive element 30. The conductive yarn 26 is available, e.g., from Bekaert Fibre Technologies, Bekaert Corporation, of Marietta, Ga., as yarn series VN14.

[0030] The number of conductive filaments in the conductive yarn, and where the filaments are located, are dependent, e.g., on the end use requirements. For example, in alternative configurations, in FIG. 13, conductive yarn 261 has four filaments 31′ wrapped about core 28′ with an outer covering 32′ of polyester yarns 33′; in FIG. 14, conductive yarn 261 has three filaments 31″ wrapped by outer covering 32″ of polyester yarns 33, without a core. Referring to FIGS. 15 and 16, in other embodiments, conductive yarns 37, 37′, respectively, are formed without an outer covering about the filaments 35, 35′, respectively, wrapped about core 34, 34′, respectively, the stitch yarn 22 and loop yarn 25 of the fabric body 12 instead serving to insulate the conductive yarns in the heating/warming fabric article. Referring to FIG. 16A, a conductive yarn 37″ without an outer cover or sheath, formed, e.g., of one or more bare filaments (one filament 35″ is shown) may also be formed without an insulating core, again, with yarn of the fabric body arranged to insulate the conductive yarns in the heating/warming fabric body. The resistance of the conductive yarn can be selected in the range, e.g., of from about 0.1 ohm/cm to about 500 ohm/cm on the basis of end use requirements of the heating/warming fabric article 10. However, conductive yarns performing outside this range can also be employed, where required. The core of the conductive yarn and the sheath material of the outer covering over the conductive filaments may be made of synthetic or natural material. The outer covering may also have the form of a sleeve, e.g. a dip-coated or extruded sleeve. Conductive yarns of different constructions suitable for use according to this invention can also be obtained from Bekaert Fibre Technologies.

[0031] In the preferred method of the invention, the fabric body 12 is formed by reverse plaiting on a circular knitting machine. This is principally a terry knit, where the loops formed by the loop yarn 25 cover the stitch yarn 22 on the technical face 16 (see FIG. 17).

[0032] The conductive yarn is incorporated into the knit fabric prebody formed on the circular knitting machine at a specific spacing or distance apart, D (FIG. 1), for uniform heating in the resulting heating/warming fabric article 10. In a fabric prebody of the invention, the spacing is typically a function, e.g., of the requirements of heating, energy consumption and heat distribution in the article to be formed. For example, the spacing of conductive yarns may be in the range of from about 0.02 inch to about 2.5 inches. However, other spacing may be employed, depending on the conditions of intended or expected use, including the resistance of the conductive yarns. The conductive yarns may be spaced symmetrically from each other, or the conductive yarns may be spaced asymmetrically, with varying spacing, as desired. Also, in a fabric body of the invention, the power consumption for each conductive yarn is generally considerably lower than in the separate heating wires of prior art devices. Asa result, the conductive yarns in a fabric body of the invention can be more closely spaced, with less susceptibility to hot spots.

[0033] The preferred position of the conductive yarn is in the stitch position of the circular knitted construction. The conductive yarn may then be knit symmetrically, i.e., at a specific distance apart, in each repeat, i.e., the conductive yarn can be in stitch position at any feed repeat of the circular knitting machine. Alternatively, the conductive yarns may be knit asymmetrically, with the yarns more closely or widely spaced, e.g., as desired or as appropriate to the intended product use. Again, the specific number of feeds, and the spacing of the conductive yarns, is dependent on the end use requirements.

[0034] Referring to FIGS. 17 and 18, the end regions 20, 21 may be formed as a panel 90 in the tubular knit body 92. The edge regions 20, 21 of the fabric body are preferably formed without loops, and in a manner such that the edge regions do not curl upon themselves, e.g. the edge region panel is formed by single lacoste or double lacoste knitting. The ends portions 36 (FIG. 1) of the conductive yarns 26 extending into the flat regions 20, 21 without loops are thus more easily accessible in the end regions for completing an electrical heating circuit, as described below.

[0035] The tubular knit body 92 is removed from the knitting machine and slit, e.g. along a line of stitches 94 marking the desired slit line, to create a planar fabric. Alternatively, for increased accuracy, the tubular knit body 92 may be slit on line, e.g. by a cutting edge mounted to the knitting machine.

[0036] As described above, in the fabric article 10 of the invention, spaced apart conductive yarns 18 are electrically interconnected in parallel by conductor elements 40, e.g., in a blanket, extending along the edge regions. However, during the knitting process of formation, a continuous length of conductive yarn 26′ (FIG. 18) may be inserted continuously during knitting, with the continuous length of conductive yarn only thereafter being segmented, e.g. by slitting the tubular knit body 92 (FIG. 18), into separate, spaced apart conductive yarns 26 to form the fabric article of the invention.

[0037] Preferably, the knitted fabric body 12 incorporating the electric resistance heating elements 18 in the form of the conductive yarns is next subjected to finishing. During the finishing process, the fabric body 12 may go through processes of sanding, brushing, napping, etc., to generate a fleece 38. The fleece 38 may be formed on one face of the fabric body 10 (FIG. 2), eg., on the technical back 14, in the loop yarn, or a fleece 38, 38′ may be formed on both faces of the fabric body 10′ (FIG. 19), including on the technical face 16, in the overlaying loops of the loop yarn and/or in the stitch yarn. In either case, the process of generating the fleece on the face or faces of fabric body is preferably performed in a manner to avoid damage to the conductive yarn which is part of the construction of the fabric body 12. Alternatively, referring to FIG. 19A, e.g. for the purpose of providing a fabric article in the form of a sheet 98 or the like, rather than in the form of a blanket, neither of surfaces 93, 95 may be subjected to finishing.

[0038] The fabric body may also be treated, e.g. chemically, to render the material hydrophobic or hydrophilic.

[0039] After finishing, and after the fabric body is heat set for width, the electric resistance heating elements are connected to a source of electrical power by conductors 40 in opposite edge regions 20, 21 (where, preferably, there are no loops on the surface), thereby to complete the electrical circuit. (The conductors or busses 40 may be formed on the technical back 14, as shown in FIG. 1, or they may instead be formed on the technical face 16, as seen in FIGS. 19 and 20.) Any suitable methods may be used to complete the circuit. For example, referring to FIG. 1, the conductor 40 may, at least in part, be applied in the form of a conductive paste, e.g. such as available commercially from Loctite Corporation, of Rocky Hill, Conn., or in the form of a conductive hot melt adhesive, conductive tape (with fabric or plastic base/carrier, or the like. The conductive paste or adhesive may be applied as a stripe to a surface of the fabric body 10 in electrical conductive relationship with the electrical resistance heating elements 18, and then connected to the power source. (If necessary, the conductive yarns may be exposed, e.g., the polyester covering yarn may be removed with solvent or localized heat, e.g. by laser; the covering yarn may be manually unraveled; or the fabric body 10 may be formed with a needle out in the flat regions 20, 21, thus to facilitate accessibility to each of the conductive yarns.) Alternatively, referring to FIG. 20, the conductor 40′ may consist of localized dots or regions 42 of conductive paste applied in electrical contact is with exposed portions of the electric resistance heating elements 18, with a conductive metal wire 44 disposed in electrical conductive contact with, and extending, preferably continuously, between, the localized conductive paste regions 42. The electric conductor 40′ is thereafter covered by a cloth trim or edging material 46, attached, e.g., by stitching along the edge of the fabric body 10′.

[0040] The completed circuit is next connected to a power source to supply electrical power to the electrical resistance heating elements for the required amount of heat generation. For example, referring to FIG. 1, an electric heating/warming fabric article 10 of the invention (an electric blanket) is adapted for connection to a source of alternating current by means of plug 50 on cord 51 for insertion in household outlet 52. Referring to FIG. 21, a warming or heating pad 60 of the invention, e.g. for an automobile seat, is adapted for connection to a source of direct current by means of plug 62 on cord 64 for insertion into the cigarette lighter or other power outlet 66 of an automobile. Referring to FIGS. 22 and 23, a stadium or camping blanket 70 and a garment 80 of the invention each includes a source of direct current, i.e. a battery pack 72, 82, respectively, e.g., as available from Polaroid Corporation, of Cambridge, Mass., replaceably mounted to the heating/warming fabric article, e.g. in a pocket 74, 84, respectively. Referring to FIG. 22, the pocket may be secured by a hook-and-loop type fastener 76. Preferably, for certification by Underwriters, Laboratory (UL®), the voltage supplied by the power source to the electrical resistance heating elements is lower than 25 volts, e.g. a Class II UL® certified transformer may be used to step down a 110 v power supply to 25 volts or under.

[0041] Other embodiments are within the invention. For example, any type of yarn may be employed.

[0042] Also, other methods of constructing fabric heating/warming articles of the invention may be employed, e.g. the yarn may be incorporated by warp knit or weft knit construction or by woven construction. Alternatively, referring to FIG. 24, the fabric body may be formed as a double knit fabric body 100, with two, separate fabric layers 102, 104 joined by interconnecting yarns 106, e.g. as described in Rock et al. U.S. Pat. No. 5,413,837, the entire disclosure of which is incorporated herein by reference. In this embodiment, conductive yarns 108 are disposed between the separate fabric layers 102, 104, e.g. by insertion during the knitting process or thereafter, and maintained apart and in position by the interconnecting yarns 106.

[0043] Referring to FIG. 25, in another embodiment of a fabric article 120 of the invention, separate fabric layers 122, 124 disposed at opposite surfaces of the fabric article 120 may be formed separately and joined together, in face-to-face engagement, in a separate operation, e.g. by laminating or stitching. In this embodiment, the heating/warming circuit 126 may be formed upon a separate substrate 128, e.g. upon an open mesh or grid, e.g. scrim, or upon a material forming a barrier that is waterproof yet vapor permeable, e.g., as described in U.S. application Ser. No. 09/298,722, filed Apr. 23, 1999, the complete disclosure of which is incorporated herein by reference, and positioned between the separate fabric layers, e.g. during the lamination process. Alternatively, the circuit may be formed upon one or both of the opposed surfaces of the separate layers, e.g as described in U.S. application Ser. No. 09/298,722, mentioned above, or as described in U.S. application Ser. No. 09/296,375, filed Apr. 22, 1999, the complete disclosure of which is incorporated herein by reference, before the layers are joined.

[0044] Also, for improved efficiency during manufacturing, busses or conductors 40 may be applied to the fabric body 12 before it is subjected to finishing. For example, the conductor 40 applied as a continuous strip of conductive paste or adhesive may be applied directly to the continuous web, either continuously, or in a predetermined intermittent pattern, e.g. using a print wheel or the like. The fabric body 12, with the conductors 40 formed thereupon, may thereafter be subjected to finishing and other steps of manufacturing.