PROCESS FOR MAKING A FLEXIBLE ELECTRIC HEATER INTEGRATED IN A FABRIC

The present invention refers to a flexible electric heater integrated in a fabric and to a process for making a flexible electric heater integrated in a fabric.

In general, the present invention refers to a heater comprising heating elements intertwined with a fabric, with a surface extending substantially in a two- dimensional plane, for example a flexible heating plate or a net-type heater used in the textile field.

In particular, the present invention refers to heaters which use a particular layout for the resistive material or the resistive elements, with multiple resistive elements or mutually insulated resistive areas.

The prior art is given by patent EP-B1-1835786 dealing with a surface heating element supported by a fabric of intertwined weft and warp threads comprising at least two heating strips, each heating strip composed of a group of electrically conducting threads mutually spaced and electrically connected to a starting portion and an end portion through connecting means composed of thin plane sheets arranged spaced along a ribbon on the fabric and electrically connected to the electrically conducting threads. The distance between the adjacent electrically conducting threads and the heating strips is changed to affect the heating effect. The electrically conducting threads are designed as copper wires. The connecting means are connected to the heating strips through welding and are designed as a flexible printed circuit. The use of thin conducting threads allows obtaining a very flexible surface.

EP-B1-1835786 solves the problem of over-heating and the consequent melting of thin conducting threads due to the high resistance, both with high and with low voltage, by means of a plurality of thin conducting threads connected in parallel with a heating ribbon. In this way, the absolute resistance of the surface heating element decreases with respect the one of individual conductors. Both the lower absolute resistance and the lower produced heat allow largely doing without the danger of melting the conductors .

Moreover, the prior art is given by patent IT-B- 0001263333 dealing with an electrically conducting fabric comprising areas of non-conductive yarn intercalated with areas of yarn with metallic or carbon conductive fibers connected in series and/or in parallel through interconnections supplied with low-voltage electric current .

IT-B-0001263333 solves the problem of making an electrically conducting fabric by suitably interweaving with conductive and non-conductive yarns, in a sort of weft/warp, to allow reaching the steady state temperature without the need of using pressure welding techniques when there is heat to join the conductive threads.

Moreover, the prior art is given by patent IT-B- 0001397028, dealing with a process to obtain a heating fabric comprising a step of placing many different carbon threads arranged mutually parallel, followed by placing on the fabric at least one layer of glue of the re activating type at a pre-set temperature; therefore, bending is provided on the fabric followed by placing a first layer of threads of nickel-coated carbon and a second layer of threads made of tin-coated copper, before re-bending and hot pressing the longitudinal edges of the fabric .

Starting from this state of the art, a need is felt of further improving the operation of heating fabrics for an industrial use, above all the one dealing with producing thermal blankets.

A first problem is given by the need of removing the assembling steps which provide for gluing/welding the heating element on a matrix of non-conductive fabric.

A further problem is given by the need of simplifying the building and operating architecture of a thermal blanket in compliance with the standards in force .

Object of the present invention is solving the above prior art problems by providing a flexible electric heater integrated in a fabric lacking welded ribbons.

A further object is providing a flexible electric heater integrated in a fabric equipped with non- conductive yarns, for example, polyester, cotton or any other natural, artificial or synthetic, textile fiber, intertwined with conductive yarns of a different nature, like tin-coated copper, silver-coated copper, red copper, silver, nickel, stainless steel, conductor coated with a fabric, tinsel, conductors or semi-electric conductors for electric supply and filaments made of carbon fibers for heating the fabric.

A further object is providing a flexible electric heater integrated in a fabric designed for observing the standards dealing with electric safety of blankets, heating pads, clothing and other flexible heating electric devices for domestic use and the like, for heating a bed and a human body. A further object is making a flexible electric heater integrated in a fabric through weaving only, wherein non-conductive yarns of the fabric are the carrier structure.

The above and other objects and advantages of the invention, as will appear from the following description, are obtained with a flexible electric heater integrated in a fabric as claimed in claim 1.

Moreover, the above and other objects and advantages of the invention, as will result from the following description, are obtained with a process for making a flexible electric heater integrated in a fabric as claimed in claim 11.

Preferred embodiments and non-trivial variations of the present invention are the subject matter of the dependent claims.

It is intended that all enclosed claims are an integral part of the present description.

It will be immediately obvious that numerous variations and modifications (for example related to shape, sizes, arrangements and parts with equivalent functionality) can be made to what is described, without departing from the scope of the invention as appears from the enclosed claims.

The present invention will be better described by some preferred embodiments thereof, provided as a non limiting example, with reference to the enclosed drawings, in which:

Figure 1 shows a schematic view of a first embodiment of a flexible electric heater integrated in a fabric according to the present invention;

Figure 2 shows a schematic detailed view of the previous Figure;

Figure 3 shows a schematic view of a second embodiment of a flexible electric heater integrated in a fabric according to the present invention;

Figure 4 shows a schematic detailed view of the previous Figure;

Figure 5 shows an example embodiment of the flexible electric heater integrated in a fabric of Figures 1, 2; and

Figure 6 shows an example embodiment of the flexible electric heater integrated in a fabric of Figures 3, 4.

With reference to Figure 1, it is possible to note that a flexible electric heater integrated in a fabric, with a surface extending substantially in a two- dimensional plane, comprises at least one heating strip 1 approximately parallel to the weft threads and electrically connected to strips of electric conducting wires 4 arranged approximately parallel to the warp threads, next to different portions of fabric 2, 3.

Advantageously, with reference to Figure 2, such at least one heating strip 1 is composed of a plurality of electrically heating weft threads 11 intertwined with the fabric .

Moreover, each strip of electric conducting wires 4 is composed of a plurality of electrically conducting warp threads 41 intertwined with the fabric.

In particular, the plurality of electrically heating weft threads 11 is intertwined with the plurality of electrically conducting warp threads 41.

With reference to Figures 3, 4, according to a variation of the flexible electric heater integrated in a fabric, a strip of further electric conducting wires 5 approximately parallel with respect to the weft threads is composed of a plurality of electrically conducting weft threads 51 intertwined with the fabric and with the plurality of electrically conducting warp threads 41 to allow mutually connecting the strips of electric conductors 4.

The electrically heating weft threads 11 are mutually spaced by a pitch Pll, approximately included between 4 mm and 45 mm, according to design specifications .

Defining exactly the pitch between two adjacent heating weft threads, provides for allowing to determine exactly the power which is needed for obtaining a uniform and constant heating and furthermore allows to respect the temperatures which are set by the current regulations regarding safety of the products.

Each of the electrically conducting warp threads 41 and of the electrically conducting weft threads 51 is composed of strands; the formation of strands can be included from a minimum of 2 to a maximum of 46 capillaries, the section of these latter ones being included between 0.03 mm and 2 mm, according to design specifications .

An example of formation of a strand can be 20 x 0,05 mm.

The amount of the electrically conducting warp threads 41 of each electrically conducting ribbon 4, as well as the amount of the electrically conducting weft threads 51 of each strip of further electric conductors 5 depend on design specification.

According to a preferred configuration, each electrically conducting ribbon 4 is formed of a number included between 3 and 48 electrically conducting warp threads 41. In the same way, each strip of further electric conductors 5 is formed of a number included between 3 and 48 electrically conducting weft threads 51. The electrically heating weft thread 11 is of a carbon-based material, while the electrically conducting warp thread (41) and electrically conducting weft thread (51) is of at least one material between thin copper, tin-coated copper, silver-coated copper, red copper, silver, nickel, stainless steel, conductor coated with a fabric, tinsel.

With reference to Figure 2, the flexible electric heater integrated in a fabric can comprise at least one connector for the electric wiring, fastened onto the surface of the fabric to be able to supply the strips of electric conductors 4 next to at least one conducting portion of warp 42.

With reference to Figure 4, the flexible electric heater integrated in a fabric can comprise at least one connector for the electric wiring fastened onto the surface of the fabric to be able to supply the strips of electric conducting wires 4 and the strip of further electric conducting wires 5, next to at least one conducting portion of warp 42 and of weft 52.

Such at least one electric connector is composed of a receptacle adapted to house supply wires, pressure junction means, by crimping or through welding of the warp threads and/or of weft electrically conducting 41,

51. Preferably, the electric connector is connected to a cable of an electric source, in direct or alternate current, to supply the electric heater with a low voltage, included between 2 and 48 volt.

A process for making a flexible electric heater integrated in a fabric comprises a step of weaving through a loom, depending on shape and transverse sizes of the thread of weft supplied by at least one creel 13, 53, respectively of the electrically heating weft thread 11 and of the electrically conducting weft thread 51, in combination with a yarn P of the fabric.

Moreover, the process for making a flexible electric heater integrated in a fabric comprises a step of cutting the surface of fabric according to preset lines along the weft Lwe and along the warp Lwa, to allow obtaining a plurality of portions of fabric, each electrically independent .

The flexible electric heater integrated in a fabric of the present invention mainly lends itself for making blankets, heating pads, clothing and other flexible heating electric devices for household use and the like, for heating a bed or a human body, comprising arrays of electrically heating weft threads of a carbon-based material .

The carbon-based material allows exploiting the intrinsic features of flexibility and ductility, to efficiently link and twist weft and warp, optimizing the low-resistance thermal bridge, in the necessary intertwining to guarantee the electric connection between the heating weft threads made of carbon fiber and the conducting warp threads made of thin copper.

A further advantage in the use of carbon fibers is being able to exploit features such as: resistance to oxidation and humidity; absence of thermal inertia and thermal dilatations; high capability of storing and diffusing heat; resistance to oxidation; durability in time; structural flexibility; efficient heating transient to allow quickly reaching the steady state temperature.

Normally, such electrically heating weft threads are carbon yarns IK, 3K, 6K, 12K, whose roving or yarn is composed of 1000, 3000, 6000, 12000 filaments.

Each electrically heating weft thread made of carbon fiber is unwound from a respective creel and inserted through the warp of the fabric through the same inserting means of the weft, for example a pliers, of the multi weft loom. In so making, a contact is ensured for the conducting warp threads intertwined with respect to the weft thread made of carbon fibers, without the risk of etching or cutting the carbon fibers. At the same time, the thereby obtained intersection between the conducting threads and the carbon yarns ensures the electric connection through an adequate abutment action of the loom. On the sides of each conducting band, a warp density is obtained with a higher value, to stabilize and guarantee a good connection and a good conductibility under different use situations. Furthermore, the said higher density of the wrap allows to avoid the generation of so-called hot spots, i.e. spots in which the temperature is higher than in the surrounding area.

A further parameter to be taken into account to comply with steady state thermal conditions is given by the mutual distance of the copper threads, both of weft and of warp, and of the heating threads made of carbon fibers .

According to a preferred configuration, a flexible electric heater integrated in a fabric is obtained through weaving through a beam of polyester yarn or other textile fiber whose height ranges from 1200 mm to 3200 mm, cloth rollers of yarn of conducting warp whose number ranges from 2 to 28, suitably arranged depending on design specifications.

The final cut of the patch ensures the electric continuity and the electric supply is ensured through electric wiring and a connector fastened to the fabric and connected to the copper threads .

According to a further embodiment the flexible electric heater may be combined with one or more other layers of fabrics.

The said flexible electric heater may be realized according to one or more of the preceding combinations or embodiments .

The said flexible electric heater is provided as an intermediate layer sandwiched in between of two or more outer layers.

According to a further embodiment the flexible heating element is provided of two layers which are generated and interlinked during the same weaving process .

Particularly the said flexible heating element comprises a three-dimensional fabric comprising two fabric layers which are interconnected by transverse threads, the two layers forming a chamber between them.

In a variant embodiment the electric conductive threads and the heating threads, i.e. the electric conductive yarn or fibers and/or the electric heating yarn or fibers are simply housed inside the two layers forming the three-dimensional fabric, the transverse yarn providing for keeping in position the heating threads avoiding short-circuits due to two heating threads coming into contact.

In a further variant embodiment, the said the electric conductive threads and the heating threads, i.e. the electric conductive yarn or fibers and/or the electric heating yarn or fibers are intertwined with the two layers and the transverse yarn of the three- dimensional fabric in a similar way as in the embodiments of figures 1 to 6.

The last embodiments allows to produce in a one step weaving process heating pads or covers which currently needs to laminate or fix a flexible heating blanket to other fabric layers such as a sandwiched pad or similar.

In the case of the said last embodiment the pad or the heating cover is produced during the weaving of the three-dimensional fabric.

According to an embodiment the said three- dimensional fabric is obtained by using a jacquard weaving apparatus .

According to still a further embodiment which can be provided in combination with any of the above disclosed embodiments or variants, the heating thread is protected by means of a sort of housing tube extending parallel to the extension of the heating thread and generating a housing chamber for the said heating thread.

According to an embodiment of the above general embodiment, the housing chambers are obtained by separating for a certain time of the fabric. Due to this technology tubes are generated within the thickness of the fabric, the tubes having about 2mm of diameter.

In detail the method provides for the following steps :

- generating of two layers during weaving;

inserting the heating yarn inside the said two layers in a chamber provided exclusively for one or a group of heating threads.

In order to produce such kind of fabrics, there is the need of dividing the wrap in two equal parts and doubling the number of the weft pro cm in order to produce two new layers which provides for housing chambers for the heating threads. Each housing chambers isolates the heating and/or electric conducing threads from the environment and from the other yarns avoiding thus short circuits due to thiolation of the heating or conducting thread.

The final result consists in the fact that the heating threads is secured inside the housing chamber which is formed automatically during the weaving phase and at the same time strengthening the fabric against mechanical stresses.

The effect obtained is the one of protecting the heating threads made of carbon in the housing tunnels. According to man example the structure of the fabric is composed of 64 threads of the warp and of 16,5 weft for each cm. At the housing tunnels the two layers of fabric are formed each one of 32 threads and of 16,5 weft.