US3241214A - Method of making electrically heated fabric structures - Google Patents

Description

March 22, 1966 R. -A. SMITH ETAL METHOD OF MAKING ELECTRICALLY HEATED FABRIC STRUCTURES Original Filed Sept. 22. 1961 United States Patent This is a division of United States patent application Serial No. 140,082, filed September 22, 1961.

The present invention relates to the manufacture of electrically heated fabric structures, such as blankets, pads,

rugs, drapes, clothing and the like.

In the manufacture of conventional electrically heated fabric structures, as for example blankets, a grid of electrical conductors is disposed within a preformed fabric shell or envelope which is then closed, as by stitching. While efficient, conventional electric blankets have not met with wide acceptance, primarily because of appearance and high cost. Generally, the presence of the grid of electrical conductors is apparent on the blanket surface as a series of ribs, and provides for a relatively heavy or bulky construction. The high cost of such blankets can be attributed to the relatively expensive fabric from which the blanket shell is formed and to the cumbersome and time consuming task of inserting the electrical conductors within the shell itself. Accordingly, a primary object of this invention is to provide a new or generally improved and more satisfactory method for making electrically heated fabric structures.

A further object is the provision of a method for making electrically heated articles wherein an unbroken film or web of thermoplastic material is printed with a desired electric conducting circuit, and then needle-punched to project fibers from opposite sides thereof.

These and other objects and advantages of the present invention are obtained by applying, preferably by printing, an electric circuit onto an unbroken web or film followed by needle-punching a batt or web of unwoven fibers onto, the printed film to project fibers from opposite sides thereof.

The electric circuit may be printed onto a surface of the unbroken film by conventional procedures and is so arranged as to provide for uniform heating along substantially all portions of the resulting fabric or differential heating along selected areas thereof, depending upon its intended end use. In designing the electric circuit to satisfy particular heat requirements, the length or path of the circuit should be such as to minimize the cross-sectional size of the electric conductor, especially when the finished fabric is intended for use in application where fabric flexibility and drape are important considerations.

The needle-punching apparatus which is suitable for use in the practice of the present invention is of conventional construction, and includes a series of barbed needles which perforate the film, including those film areas which are printed with electric conducting materials, and concomitantly punch or drive the fibers of the batt partially through such perforations. As the needles are projected through the film, and particularly the uncoated portions thereof, the perforations or openings which are formed each include an irregular or jagged edge surface which tend to bite into or grip the fibers which have been driven into and extend through the film. During the withdrawal of the barbed needles from the film, the biting or gripping effect exerted on the punched fibers by the jagged edge surfaces of the film perforations discourage fiber movement so that the fibers project approximately to the same ice degree from opposite sides of the film base in the finished product. In most applications, however, it is preferred that a batt of fibers be applied to and punched through opposite sides of the film based to secure maximum coverage for decorative or insulating purposes.

The gripping action exerted by the jagged edge openings of the film base adapt the needle-punched fabric, and articles made therefrom, for various uses without any further treatment. However, where repeated and/ or rugged use of the resulting needle-punched fabric or article is contemplated, it is preferred that the punched fibers be more securely anchored to the film base. This may be effected by integrally bonding the projecting fibers in a base film of thermoplastic character by causing a controlled flow of the film material around and into engagement with the punched fibers. Such flow of the film material may be achieved by heating the same to within the softening range of the thermoplastic material from which the fil-rn is formed, and desirably,.subjecting either the film or the needle-punched fabric to pressure so as to encourage the flow of the film material as it assumes a softened condition. Upon setting or cooling of the softened film, the portions of the punched fibers enveloped by the thermoplastic base material are firmly embedded. Aside from the standpoint of economy and ease of manufacture, this heat-treating procedure has no detrimental effects on the printed electric circuit, the punched fibers or the film base, and avoids an undesired stiff or hard feel from being introduced into the fabric.

Heating of the thermoplastic base film of the needlepunched fabric may be achieved by merely passing the same through a hot gaseous atmosphere, as provided for example by a series of resistance heating elements or infrared lamps. This procedure assures retention of the soft and fiuffy character of the punched fibers but generally requires a relatively long heating zone to obtain a desired flow of the thermoplastic base' material around the punched fibers. An alternative method is to impinge at least one side of the needle-punched fabric with a heated fluid which is under sufficient pressure to encourage flow of the thermoplastic material of the base film as it is softened. Such fluid may simply consist of a hot gas or a mixture of a heated liquid and gas, such as steam. Ho-t air alone performs the desired function and is extremely practical since it may be continuously reheated and recirculated and involves no removal or recovery problems. The temperature and pressure of the heated fluid employed will, of course, depend upon the softening temperature range of the particular thermoplastic material from which the film base is formed aswell as the character and coverage provided by the fibers punched into the film base. Generally, the punched fibers will offer some thermal insulation and thus may require that the impinging heated fluid be at a temperature Well within or even slightly above the softening temperature range of the base film.

As a still further alternative, activation of the film base may be achieved by engaging the needle-punched fabric between a pair of heated metal pressure plates of endless belts. With this procedure the needle-punched fabric is compressed while the film base is heated to within its softening temperature range so that the finished fabric presents pile surfaces which are of greater density or coverage than the initial needle-punched fabric. The temperature and pressure of the heated plates or belts will depend upon the same consideration as set forth above, in addition to the degree of fiber densification d si From the description of the invention given above it will be apparent that the film base of the needle-punched fabric must be of non-fibrous, soft, and non-brittle or pliable character so as to facilitate the formation of irregular or jagged edge openings or perforations as the barbed needles are projected therethrough without initiating tearing of the film. In effect, the films employed in the fabric of the present invention readily yield to forces applied by the barbed needles without transmitting or distributing such forces to any substantial area of the film. A variety of thermoplastic materials are presently available for providing films having the essential properties for satisfactorily practicing the invention described. Examples of such thermoplastic films include films formed of vinyl resins, such as polystyrene, polyvinyl chloride, polyvinyl chloride acetate, polyvinylidene chloride, polytetrafluoroethylene, and polyvinyl butyral, and polymeric resins, such as nylon, and including polyolefin resins, such as polyethylene and polypropylene.

Aside from the essential characteristics of the film base noted above, the particular film employed will, of course, depend upon the properties desired in the finished fabric and, as more fully described thereafter, the nature of the covering fibers. In applications where the electrically heated fabric will not normally be subjected to substantial tensions or stretching forces which might cause rupture of the printed circuit, a base film which is in an unoriented condition is satisfactory. Alternatively, such base film may be unilaterally oriented to provide a fabric which is yieldable along one restricted direction, or biaxially oriented to provide the finished fabric with substantially fixed dimensions. The thickness of the film base may be varied to satisfy strength requirements and/ or drape characteristics desired in the finished fabric. Further, from the decorative standpoint, the film may be transparent, translucent, opaque, or pigmented. When making fabrics having a sparse fabric covering or pile along one surface only, as for example for use as electrically heated floor mats or rugs, the film may be embossed with a pattern or may be roughened to impart decorative and/ or skid resistant properties to the fabric.

The fibers driven or punched into the film base may be natural fibers or synthetic fibers or various combinations of different natural and/or synthetic fibers. Suitable natural fibers include fibers such as cotton, linen, wool and silk. The synthetic fibers may be formed of thermoplastic materials, as for example from vinyl and polymeric resins heretofore noted, cellulosic fibers, such as rayon, and mineral fibers, as for example spun glass. Aside from providing fibers which offer greater resistance to electric flow than the material forming the printed electric circuit, no particular restrictions exists as to the selection of fibers for use in needle-punched fabrics in which friction alone is to be relied upon for holding the fibers in place. When it is desired to have the fibers embedded within the film base by the heat treating procedure described above, care must be exercised in selecting fibers which possess the required stability at the elevated temperatures encountered during softening of the film base. Stability as employed herein pertains not only to the material from which the fiber itself is formed, but also to any finishes, pigments, dyes or other additives applied to or incorporated within the fibers.

The properties of the fibers employed may, of course, be varied to secure desired end results. For example the surfaces of the fibers may be roughened or otherwise treated to enhance their frictional contact with the film base, they may be pigmented or dyed and may have moisture absorbent or repellent characteristics. Further, fibers of different types or colors may be punched into the film base in accordance with a predetermined pattern, or the stroke of the barbed needles of the needlepunching apparatus may be suitably adjusted to provide a pile surface in which the degree of fiber projection varies along different areas of the fabric.

From the above description of the invention, it will be apparent that the needle-punching operation has no effect on the continuity of that portion of the film base or printed circuit which extends between the punched fibers. With needle-punched fabrics which have been subjected to the heat treatment described, the continuity and strength of the fabric base are both greatly improved by the elimination of areas at which tearing may initiate and the provisions of strong bonds between punched fibers and base. The continuous and unbroken film structure of the fabric base which extends between the punched fibers performs the same functions as that of a woven or knitted base of a conventional needle-punched fabric. More important, this film structure can serve as a means for modifying or supplementing the properties imparted to the finished fabric by the fibers themselves. For example, a fabric formed by punching moisture absorbent fibers into a base film having low moisture absorption and transmission characteristics, would be soft yet strong, with the film base serving as a moisture barrier while the punched fibers facilitating air passage without substantial moisture transmission. The ability of such fabric to breathe or transmit air renders the same highly suitable for use in a variety of articles such as floor coverings, pads, bedding articles including mattress covers, blankets, etc., while the combined air transmission and moisture absorption characteristics makes such fabrics ideal for use in garments.

As a further alternative, both the fibers and base film of the needle-punched fabric may be formed of materials having low moisture absorption and transmission characteristics. A fabric of this nature would possess moisture barrier characteristics yet would exhibit the desired feel and appearance of a pile textile fabric. Such fabric may be utilized in applications where canvas is now employed and would be especially useful in the manufacture of winter garmets and foot wear.

In the accompanying drawings, illustrative of the invention:

FIGURE 1 is a diagrammatic view generally illustrating one mode of practicing the method of the present invention;

FIGURE 2 is a vertical section through a portion of the fabric base as it is subjected to the needle-punching operation;

FIGURE 3 is a bottom view of a portion of the fabric base shown in FIGURE 2;

FIGURE 4 is a side view of an apparatus for use in heat treating a needle-punched fabric of the present invention while maintaining the same under pressure;

FIGURE 5 is a side view of the non-woven fabric as made by the process in FIGURE 1; and

FIGURE 6 is a view similar to that shown in FIGURE 5 showing a needle-punched fabric after being heat treated by the apparatus in FIGURE 4.

In practicing the method of the present invention with the apparatus of FIGURE 1, a combed or carded web of fibers 15 is advanced from a source of supply over guide roll 17 and into a nip formed by rollers 19 and 21 where it is engaged with a continuous, unbroken, non-fibrous film 23 formed of thermoplastic material. As illustrated, the film 23 is provided with a series of independent printed electric circuits 25 which are applied to at least one surface thereof. The circuits 25 are formed by conventional procedures and include a thin, planar, mass or layer of electric conductive materials bonded to the film along a predetermined pattern or path for satisfying particular heat requirements. Preferably, at least the printed portion and, if desired, the entire printed surface of the film 23 may be coated or covered with a continuous film of material which is the same or similar to that from which the film 23 is formed, and more particularly a material which softens at a temperature at least equal to the softening temperature of the film 23. For the sake of simplicity and ease of description, the electric circuits 25 are illustrated as being laid along a serpentine or sinuous path with their ends terminating adjacent to each other along the same longitudinal edge of the film 23. Such L" d) circuit arrangement may be suitable, for example, in an electric blanket construction. It will be understood, however, that the materials employed in forming the electric circuits and the dimensions and arrangement or path of such circuits can be varied to satisfy the particular heat characteristics desired in the finished article.

From the rollers 19, the printed film 23 and superposed film web is passed through and into a needle-punching loom, indicated generally at 26, having a series of reciprocable barbed needles 27 which drive or punch the fibers of the web 15 through the film 23, including the printed portions thereof. Upon completion of the needle-punching operation, the resulting fabric may be collected for use, or alternatively, may be passed through a heat-treating chamber 29 where the film base 23 is softened by a heated fluid, as circulated by conduits 31, to anchor the punched fibers as more fully described hereinafter.

The needle-punching loom 26 operates in the conventional manner wherein the series of barbed needles 27 are reciprocated toward and through film 23 to drive the fibers of the web 15 therethrough, and then outwardly from the film 23 to permit the latter to be advanced relative to the loom itself. During the fiber-punching stroke of the loom 26, the barbed needles 27 puncture or perforate the film 23 and concomitantly drive the fibers of the web 15 partially therethrough. As best seen in FIGURES .2 and. 3, the perforations or openings 33 formed in the film 23 as the barbed needles 27 are forced therethrough .each exhibit irregular or jagged edge surfaces 35 which bite into the fibers projected through the film and snugly grip the same. As the series of barbed needles 27 are moved through their return stroke to withdraw the same from the film 23, this biting or snug gripping of the punched fibers by the jagged edge surfaces 35 of the film perforations 33 prevents the punched fibers from moving along with the barbed needles. The punched fibers are therefore locked in their projected positions and, as a result, with the method of the present invention the production of needle-punched fabrics having generally similar pile surfaces on its opposite sides may be readily achieved.

While the fibers of the needle-punched fabric formed by the above-described method may be pulled out from the film, there is sufficient locking of the fibers, however, so that the fabric is adapted for various applications without any further treatment. Where rugged and/ or repeated usage of the fabric is contemplated, the punched fibers may be more securely anchored to the film base 23. This fiber anchorage may be achieved by the use of adhesive compounds as employed in conventional needlepunched fabrics. To avoid the numerous disadvantages which are incorporated into the fabric by such adhesive compounds, the preferred procedure, in accordance with the present invention, is to soften the material from which film 23 is formed and cause the same to fiow around and into contact with the projected fibers. Once the projected fibers are embraced by the material of the film 23, the film is set so that the fibers and films form an integral structure.

Softening of the film 23 may, of course, be achieved by suitable solvents. However, in view of problems involved in solvent removal or recovery, a preferred procedure is to subject the needle-punched fabric to a heat treatment designed to elevate the temperature of the thermoplastic film 23 to within its softening range but below its melting range. This heat treatment may be achieved as shown in FIGURE 1 wherein the needlepunched fabric is passed through a chamber 29 within which a heated fluid, preferably hot air, is impinged against one surface of the fabric. The impinging hot air may be withdrawn from the chamber 29, reheated, and continuously recirculated through the conduits 31 and thus provides for an economical, simple and clean procedure. The temperature of the impinging hot air must be such as to render the film soft without actually melting the same and will depend upon such considerations as the character of the thermoplastic film 23, the coating applied to the printed circuit, and the punched fibers, the thermal insulating effect or coverage offered by the punched fibers, the period of treatment, etc. As heretofore mentioned, care must be exercised to select fibers which are stable under the elevated temperature conditions required for softening of the film 23. The pressure of the impinging hot air should be such as to encourage the flow of the softened material of the film 23 into embracing relationship about the punched fibers, yet avoid damage to the film or printed circuit.

The needle-punched fabric issuing from the chamber 29 after being subjected to the heat treatment described generally retains the soft and fluffy character of the original needle punched fabric. The punched fibers are bonded to the film 23 in the areas in which the openings 33 were first formed, with the portions of the film 23 extending between the projecting fibers still retaining an unbroken film structure. The above-described fabric possesses a soft and pleasant feel and exhibits good drape characteristics.

With the modified procedure as illustrated in FIGURE 4, however, the original needle-punched fabric may be converted into a fabric having more body, simultaneously as the fibers are anchored or embedded within the film 23. The apparatus for practicing this modified heat-treating procedure includes a pair of endless metal belts 37 which are trained over rollers 39 and 41 and driven by suitable means, not shown. As illustrated, the opposing reaches of the belts 37 pass over idler rolls 43 which cooperate with the adjacent rollers 39 to form a gradually converging entrance portion 45. Heating means 47 are positioned along the paths of the opposing reaches of the endless belts 37 for maintaining the same at a desired elevated temperature.

In operation, the original needle-punched fabric is passed into the entrance portion 45 and between the op posing reaches of the endless belts 37 which are prefer ably adjusted to exert a pressing action on the fabric as it is carried through the apparatus. The opposing reaches of the belts 37 are kept at a desired elevated temperature by the heating means 47 so as to achieve a softening of the thermoplastic material forming the film 23, and a flow of the softened material into embracing relationship about the punched fibers. The conditions of operation for this modified procedure will, in general, depend upon the same considerations as noted with regard to the heattreating method illustrated in FIGURE 1, in addition to the degree of fiber compaction desired. As diagrammatically illustrated in FIGURE 6, the fabric treated in accordance with this modified procedure possesses rather dense or compact pile surfaces as a result of the combined heating and pressing action of the endless; belts 37. The degree of fiber compaction may, of course, be varied as desired by adjusting the spacing between the opposing reaches of the belts 37.

To provide for a uniform heating and pressing of the needle-punched fabric, the belts 37 are preferably in the form of endless sheets having continuous or unbroken surfaces. It will of course be apparent that the belts 37 may be in the form of endless screens of fine mesh, in which case the heating means 47 may supply hot air. Alternatively, the belts 37 may be formed with projecting portions or openings so that the needle-punched fabric may be embossed with a desired pattern during the heattreating stage.

The resulting needle-punched fabric, with or without being subjected to the heat treatment described above, is then severed between the independent elctric circuits 25, as indicated by the broken lines 49, to provide a series of individual units. An electric supply cord, preferably including a step-down transformer, is then connected to the ends of the printed circuit in a conventional manner to Complete the manufacture of the electrically heated structure which may be, for example, an electric blanket. Since only a single film is employed, the finished article is light in weight and of less bulk than corresponding conventional structures. Further, a thin layer of electrically conductive materials required for providing a desired heating circuit does not detract from the appearance of the finished article nor add substantial weight thereto.

While the method of making the electrically heated structure has been described as involving the needlepunching of only one web of carded fibers onto the film 23, it will of course be apparent that such fiber webs may be needled onto opposite surfaces of the film 23 Without departing from the spirit and scope of the invention.

It is to be understood that changes and variations may be made without departing from the spirit and scope of the invention as defined in the appended claims.

We claim:

1. A method of making an electrically heated fabric structure including the steps of depositing a thin layer of electrically conductive material along a predetermined path on at least one surface of an unbroken, non-fibrous, thermoplastic, polymeric film and adhering the same thereto, disposing a batt of fibers onto said film, and projecting the fibers of said batt into and partially through said film, including the portions thereof onto which the electrically conducting material has been deposited and adhered.

2. A method as described in claim 1 wherein said electrically conductive material is printed onto said film and wherein said fibers are projected through said film by a plurality of barbed needles which form openings in said film having jagged edge surfaces for gripping the fibers projected therethrough.

3. A method of making an electrically heated fabric structure including the steps of depositing a thin layer of electrically conductive material along a predetermined path on at least one surface of an unbroken, non-fibrous, thermoplastic, polymeric film and adhering the same thereto, disposing a batt of fibers onto said film, needle-punching the batt of fibers onto said film including the portions thereof onto which the electrically conducted material has been deposited and adhered, effecting a controlled flow of the film material around and into engagement with the needle-punched fibers, and setting the film material to anchor said fibers to said film.

4. A method as defined in claim 3 wherein said controlled flow of film material is effected by heating the same to within its softening temperature range.

5. A method of making an electrically heated fabric structure including the steps of printing a thin layer of electrically conductive material along a continuous path onto at least one side of a non-fibrous, thermoplastic, polymeric film and projecting fibers into the film through the printed and unprinted portions thereof, the portions of the film extending between said fibers remaining in continuous and unbroken construction.

References Cited by the Examiner UNITED STATES PATENTS 2,619,580 11/1952 Pontiere 219-528 2,724,674 11/ 1955 Pritkin.

2,745,942 5/1956 Cohen 219528 2,951,278 9/1960 Hoffman 151154XR 2,955,351 10/ 1960 McCreadie.

3,010,180 11/1961 Hoffman 161154XR FOREIGN PATENTS 607,656 9/1948 Great Britain.

EARL M. BERGERT, Primary Examiner.

Claims (1)

1. 3. A METHOD OF MAKING AN ELECTRICALLY HEATED FABRIC STRUCTURE INCLUDING THE STEPS OF DEPOSITING A THIN LAYER OF ELECTRICALLY CONDUCTIVE MATERIAL ALONG A PREDETERMINED PATH ON AT LEAST ONE SURFACE OF AN UNBROKEN, NON-FIBROUS, THERMOPLASTIC, POLYMERIC FILM AND ADHERING THE SAME THERETO, DISPOSING A BATT OF FIBERS ONTO SAID FILM, NEEDLE-PUNCHING THE BATT OF FIBERS ONTO SAID FILM INCLUDING THE PORTIONS THEREOF ONTO WHICH THE ELECTRICALLY CONDUCTED MATERIAL HAS

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