MXPA01007479A - Self regulating flexible heater - Google Patents

Abstract

The present invention relates to a self-regulating flexible heater construction (30) for producing heat when it is connected to an electrical power source, comprising: - a flexible cloth substrate (10), - a layer (12) of a material of positive temperature coefficient, and - a layer (14) of conductive material, characterized in that, the flexible fabric substrate (10) has a general density of 0.6 g / cm3 or greater, and a thermal diffusivity of 0.003 cm2 / s or

Description

FLEXIBLE SELF-REGULATING HEATER FIELD OF THE INVENTION The present invention relates to a self-regulating flexible heater construction suitable for use in automotive components, but having uses in other applications, including, but not limited to, furniture, consumer goods, materials construction and other items. The flexible heater construction is comprised of a breathable fabric substrate to which a coating of conductive material and a coating of material of positive temperature coefficient ("CTP") is applied. The conductive material is in electrical contact with a power source. The CTP material regulates the temperature of the heater. In the automotive field, the present invention can be used as a heater for seats and, to provide a non-exhaustive list of other applications, such as heater for boards, steering wheels, speed levers (for manual and automatic transmissions), mirrors, arm rests and others. BACKGROUND OF THE INVENTION In the automotive industry, heating devices with self-regulating temperature properties are used. However, these heaters are used when it is not important that the heater has flexibility. For example, These heaters are used in mirrors placed outdoors. vehicle. These heaters are printed on rigid polyester films with biaxial orientation. See, for example, US Pat. No. 4,931,627 and 4,857,711, both assigned to the assignee of the present invention. The heaters for seats of motor vehicles currently available offer inefficient operation, due to several undesirable attributes. It is known that the current heaters accumulate static electricity, which damages the controller circuit of the heater when it is discharged. Another deficiency is that the current design of heaters for seats, where the heating elements are copper wire, and this design creates several problems, in the sense that the heating is located in the area of the cables, creating an undesirable heating pattern where the areas in the vicinity of the cable are too hot, and the areas away from the cable are too cold. Furthermore, since the heating cable per se does not possess any device for regulating the temperature (i.e., the copper wire and the like are unable to detect that its temperature is too high), a sophisticated temperature controller is required to regulate the temperature of the seat heater. This creates a difficult design problem for the engineer, which could be avoided if the construction of the heater per se were self-regulating and could increase or decrease the amount of heat produced, as necessary. Furthermore, for the heating of a seat in a motor vehicle, it is evident that the construction of the seat heater must be flexible, durable and capable of withstanding the requirements of the operating environment, which include potentially debilitating effects due to prolonged exposure to heat and the flow of electricity. It would be desirable for an automotive seat heater to be designed so that a uniform amount of heat was distributed over the surface to be heated.

Similarly, it would be desirable for the seat heater to be designed in such a way that, if desired, the amount of heat supplied to a particular area could be varied, as a design parameter, so that if certain zones are considered to be more hotter than others for a given design (or colder, as the case may be), the heater could be constructed to accommodate this variation. Furthermore, since the comfort of a vehicle seat is attributable to its flexibility, it would be desirable for the construction of the seat heater to be flexible, so that its presence on the seat would complement the other flexible parts of the seat construction. It would be further desirable that the construction of the seat heater incorporate a flexible fabric layer. It would be highly advantageous if the parts of the heater could be applied to the fabric using known printing and coating techniques, which could be used to build a heater, easily, quickly and economically. In addition, application techniques such as printing or coating could be used to make uniform or variable applications of component materials, which would provide a uniform heat distribution or, if desired, variations in the amount of heat. The materials of coefficient of positive temperature (CTP) present variable electrical resistance with the temperature. As the temperature of the material increases, the electrical resistance also increases. The resistivity of the material increases so that the flow of current is reduced, limiting the flow of heat. In essence, positive temperature coefficient compositions are used to form self-regulating coatings of temperature. CTP materials are known in the art. In the U.S. Patents No. 5,206,482 and 5,151,747 can be found exemplary disclosures related to these materials. SUMMARY OF THE INVENTION The present invention is directed to a self-regulating flexible heater, such as a heater for use in automobiles and other vehicles, in which a CTP material and conductive material is applied to a woven or non-woven fabric material constructed of natural or synthetic fibers. . A system of electric buses of a conductive material is applied on a cloth before or after coating it with a CTP material. The conductive material is applied in an interdigitating pattern that emanates from multiple bus bars. The busbars are configured in such a way that the heater provides uniform heating on the surface of the heater. The amount of heat generated can also be varied as a design parameter, so that certain regions generate more or less heat, as desired. Bus bars can be connected to the power source by a variety of interconnecting devices, such as fasteners Terminals of conductive epoxy resins, to name a few of a wide range of interconnector devices that would fall within the field of the art connoisseur. Cable connectors are attached to the terminals and the wire of the power source. Preferably, a secondary layer is applied over the heater construction, such as an adhesive layer or a breathable fabric. The breathable fabric can be such that it is breathable by virtue of the material that is used, or whatever it is - treated to be breathable, such as by needle perforations. The heating element is applied just below the outer layer of the vehicle seat, preferably as close as possible to the user. The heating element is placed on the base of the seat, or on the back of the seat, or both. Preferably, the coating of CTP material has a weight of between 3 and 9 kg per ream (ie 306 m2) and a surface resistivity of between 2 to 10 kilo-ohms measured by means of multi-measuring probes placed at a distance of 1 cm of other. More preferably, the coating of CTP material has a surface resistivity of between 3 to 8 kilo-ohms measured by means of multi-measuring probes placed at a distance of 1 cm from each other. Suitable materials for the fabric substrate include constructions of woven or non-woven fabrics of material including, but not limited to, polyesters, polyamides, polyaramides, polyimides, potetherketones, glass fibers, phenolics and carbon fibers. Regarding the fabric selection process, it was discovered that heating constructions with a general density of approximately 0.6 g / cm3 or more, and a thermal diffusivity of approximately 0.003 cm2 / s or more ensure a desirable degree of conductivity and heat flow through the fabric. This can be achieved by using multifilaments with a relatively high amount of twists per unit length. However, a high degree of twisting, or even using high denier fibers, reduces the flexibility of the fabric. Therefore, the art connoisseur can reach a balance between these properties. The heating element may comprise a coating formed from a composition of a conductive material of electrically conductive particles dispersed in a polymer matrix, and a coating of a CTP material. In the self-regulating heater of the present invention, the heating element is in thermal communication with the component to be heated, such as a car seat. Preferably, the CTP material is coated on a woven or non-woven fabric. The conductive material is applied before or after applying the CTP material. The conductive material is coated on the web in an interdigitating electrode pattern that forms an electrical bus system, which can be constructed in a variety of patterns, such as in a beveled shape (see, eg, Figure 1), in stepped form , where the sizes vary in a staggered arrangement, or in a straight or constant size over the entire construction (see, for example, Figure 3). A pattern is also possible about 33.5 to 203 grams per square meter (preferably about 125.6 grams per square meter) with a CTP material 12 as the commercially available CTP coating materials, such as a copolymer ethylene-vinyl acetate copolymer commercially available as Dupont 265. These materials are described in U.S. Pat. No. 4,857,711, incorporated herein by reference. The coating is applied at a weight of 6 kg per ream (ie 306 m2) and a surface resistivity of between 2 to 10 kilo-ohms (more preferably between 3 and 8 kilo-ohms) as measured by multi-measuring probes placed at a distance of 1 cm from each other. Before applying the conductive material, the fabric dries completely. The CTP layer 12 and the conductive layer 14 are applied as discrete layers in any order of application. The conductive material 14 can be formulated from polymeric resins such as vinyl, polyesters, acrylics and conductive materials such as a silver pigment, a copper pigment coated with silver, or plated copper pigments or solvent materials such as organic solvents, and water based solvents. that contain the conductive material. After mixing carefully, the coating is passed through a mill to effect the final dispersion. Other conductive materials can be used as interwoven conductor cables within the construction by conductive glues. Applicants of the present invention discovered that these formulations are flexible, and at the same time resist cracking by supporting a load or by stretching. The conductive material 14 is preferably applied in an interdigitating pattern (see Figure 1) by a mask printing method, and then dried completely, thereby forming an electric bus system. Other methods may be used to apply the conductive material, including spraying, stretch applications, grid printing or other printing methods that provide a uniform coating. The conductive material is printed on electrode patterns that are interdigitated. Each electrode of the pattern is in electrical contact with one of the multiple busbars 16 and 18, with adjacent electrodes alternating their connections between the busbars 16 and 18. The busbars are configured in a tapered bevel arrangement. That is, the width of the bus bars gradually decreases from the terminal end (20.22) to the free end (24.26). This ensures that the electrical resistance created by the bus bars will create a heating effect that is essentially equal to that created by the heating zones. The connoisseur of the electrical characteristics of the CTP material, the conductive material and the temperature requirements can design easily heating zones of various sizes and shapes with variable bus sizes that can supply varying amounts of heat over the heating zone. Accordingly, the entire substrate, from the center to the periphery, including the zones below the bus bars, will be heated as desired essentially without cold zones. It should be noted that although the connections to the heater construction are placed on its edges, other configurations are possible, such as making connections from inside the construction, or a combination of connections on the edges and on the inside. The heater construction can be varied by varying the separation of the smaller buses. That is, the connoisseur of the technique will easily appreciate that by doing so the current is varied at any given place in the construction. Figure 2 shows a circuit diagram for a self-regulating flexible heater design in accordance with the present invention that provides a multiple watt heater. As shown in this design, high or low heaters are possible where current flows from common or high bus arrangements, or a common or low bus layout. Other combinations are possible based on other terminal connections. The terminals 20 and 22 are attached to the bars buses and are in communication with a power source (not shown). The terminals may be attached to busbars 16 and 18 by fasteners or any other device that allows an electrical contact to be formed. A secondary protective layer, such as an encapsulating layer, can be laminated on the heating assembly 30. When a voltage is applied across the terminals and the electrode arrangement, depending on the ambient temperature and electrical characteristics of the CTP material, current will flow through the CTP material between the electrodes, generating heat in each heating zone. The flow of current and the heating effect of the CTP material depends on its temperature, which will change when the ambient temperature changes and, at a predetermined temperature of the CTP material, the resistivity of the material will increase causing the material not to conduct current, thereby Heating zones will not generate more heat, or will produce a very small amount of heat due to significantly reduced current flow. Accordingly, it can be appreciated that the heater is self-regulating in accordance with the surrounding ambient temperature. Figure 3 shows an alternative arrangement in which the width of the bus bars is a combination of a section where the size remains constant near the free end (24.26) and a beveled section where the bars Buses gradually decrease in size when moving away from the terminal end (20,22). The skilled artisan will readily appreciate that placing a safety switch in the terminals will prevent conditions in which the heat generated exceeds the upper limit that was set in the design of the heater. The switch can be a simple on / off switch that allows the user to turn off the current flowing through the heater. Example 1 The thermal diffusivity of five samples of coated polyester fabric was determined. The samples, identified from 1 to 5, differed in terms of whether they were woven or non-woven and, if woven, in the warp yarn, number of yarns per unit length extremes per unit length, number of filaments in the warps and twists per unit length in the threads. These fabrics were presented as strips of coated fabrics approximately 500 mm long ppr 70 mm wide. 12.7 mm diameter samples of the strips were cut out to test them. The thermal diffusivity of the samples was measured ° and 100 ° using a laser flash method, using a Holometrix Microflash instrument available from Holomet :: Lx Micromet. This instrument and method conform to ASTM E1461-92, "Conventional test method for thermal diffusivity of solids by flash method". The results of the tests are given after the description of the experimental procedure. The thermal diffusivity is related to the thermal conductivity of the stable state by means of the equation: D: "where D is the thermal diffusivity," is the thermal conductivity, Cp is the specific heat and p is the density.Diffusivity is a measure of the speed with which a body can change its temperature, increases with the ability of a body to conduct heat (?) and decreases with the amount of heat necessary to change the temperature of a body (Cp.) The three magnitudes of the right side of the equation (1), as well as thermal diffusivity, can be functions of temperature.The measurement of the thermal diffusivity of a material is usually done by rapidly heating one side of a sample, and measuring the temperature rise curve on the opposite side. The time it takes for the heat to travel through the sample and cause the temperature to rise at the back end can be used to measure the diffusivity of the plane and calculate the thermal conductivity of the plane if the density and the specific heat. - Direct plane method and analysis The sample is a disk with a diameter of 12.7 mm and a thickness that varies from 0.1 to 3 mm. With the Holometrix Thermoflash 2200 laser flash system, the sample disk is aligned between a neodynium crystal laser (1.06 μm wavelength, 330μs pulse width) and an indium antimonide IR (InSb) detector in a tantalum tube furnace. A type C thermocouple in contact with the sample controls the sample and its environment at any temperature between 20 and 2,000 ° C. Once the sample is stabilized at the desired temperature, the laser is fired several times over a period of several minutes, and the necessary data are recorded for each "shot" of the laser. The energy of the laser beam collides with, and is absorbed by, the front surface of the sample, causing a pulse of heat to travel through the thickness of the sample. The resulting temperature increase in the sample is rather reduced, varying between 0.5 and 2CC. This temperature rise is maintained in the optimum range by adjustable filters between the laser and the oven. A lens focuses the image of the back surface of the sample on the detector, and the temperature increase signal is amplified and recorded against time with a high-speed A / D converter. Conductivity The thermal conductivity of the sample ßon Equation (1) can be calculated, after measuring the diffusivity as described above, and with measurements of the specific heat and general density of the sample. The general density is usually calculated from the mass and volume of the sample (calculated from the dimensions that were measured.) Test results The measured values of thickness, density and thermal diffusivity are shown in Table 1. they were not corrected for thermal expansion The samples were coated with approximately 5 μm of graphite for thermal diffusivity tests The second column to the right of Table 1 presents the standard deviation as a percentage of the average diffusivity of the five to ten "shots "Laser taken from each data point." The density values were estimated at an accuracy of ± 5%. TABLE 1 Thermal diffusivity results with laser flash Note: the thermal diffusivities are an average of 5 readings. Example 2 The five polyester test samples discussed in Example 1 were tested to determine if they would be broken by subjecting them to a prolonged period of operation. The samples were coated with CTP material. After drying, a silver pigment was applied on the CTP material. These self-regulating flexible heater constructions were subjected to a 12 volt DV potential for a prolonged and continuous period. The heat continued to increase in the buildings until a stable state was obtained in constructions 1 and 3. These constructions showed sufficient resistance to heat. Constructions 2, 4 and 5 were destroyed before reaching the steady state. That is, the "failed" heater constructions were burned during the tests as a result of the heat generated during the operation of the heater. It is noted that the fabrics that approved the test had a density of at least 0.6 g / cm3 or more, and a thermal diffusivity of at least 0.003 cm2 / s. Thermal diffusivity results with laser flash ^ Note: the thermal diffusivities are an average of 5 readings. Regarding the fabric selection process, it was discovered that heater constructions with a density of approximately 0.6 g / cm3 or more, and a thermal diffusivity of at least 0.003 cm2 / s ensure a desirable degree of conductivity and heat flow. through the cloth. This can be achieved by using multifilaments with a relatively high amount of twists per unit length. However, a high degree of twisting, or even using high denier fibers, reduces the flexibility of the fabrics. Accordingly, the artisan can achieve a balance between these properties. Although described in its preferred embodiment as a car seat heater, it should be understood that the self-regulating flexible heater construction of the present invention is suitable for use not only in automotive components but also in other applications, including, but not limited to, furniture , consumer items, construction materials and other items. Accordingly, the present disclosure should be read as a context for the present invention, and not as a limitation of the field to be used. Having described the preferred construction of the present invention, those skilled in the art benefiting from the description will be able to invent other modifications, and such modifications are considered within the scope of the appended claims.

Claims (24)

1. CLAIMS ¿.I. A self-regulating flexible heater construction for producing heat when connected to an electrical power source, comprising: a flexible cloth substrate; a layer of material of positive temperature coefficient; and a layer of conductive material.
2. 2. The heater of claim 1, wherein the substrate is a woven or non-woven fabric.
3. The heater of claim 1, wherein the layer of conductive material is applied to the material layer of positive temperature coefficient in an interdigitated pattern.
4. The heater of claim 1, wherein the positive temperature coefficient material layer is applied to the layer of conductive material in an interdigitated pattern.
5. 5. The heater of claim 1, wherein the density of the fabric is from 33.5 to 203 grams per square meter.
6. 6. The heater of claim 1, wherein the CTP material is comprised of a polyolefin resin.
7. 7. The heater of claim 1, wherein the coating of CTP material has a weight of between 3 and 9 kg per ream.
8. 8. The heater of claim 1, wherein the The positive temperature coefficient material has a surface resistivity of between 2 to 10 kilo-ohms measured by means of multi-measuring probes placed at a distance of 1 cm from each other.
9. 9. The heater of claim 1, wherein the positive temperature coefficient material has a surface resistivity of between 3 to 8 kilo-ohms measured by multi-measuring probes positioned at a distance of 1 cm from each other.
10. The heater of claim 1, wherein the conductive material is formulated with a polymeric resin blend selected from the group consisting of vinyl, polyesters, acrylics and a conductive material selected from the group consisting of silver pigment, a copper pigment coated with silver, or copper-plated pigments.
11. The heater of claim 1, wherein the conductive material is formulated from a mixture of solvent materials selected from the group consisting of organic solvents and water-based solvents, and a conductive material selected from the group consisting of silver pigment, a copper pigment coated with silver, or plated copper pigments.
12. The heater of claim 1, wherein the conductive material is constructed of conductive wires fixed within the construction by glues drivers ^
13. 13. The heater of claim 1, wherein the first and second layers are applied to the substrate by mask printing, spraying, drawing, grid printing or any other printing method capable of providing a uniform coating.
14. 14. The heater of claim 1, further comprised by a plurality of bus bars. in electrical contact with the conductive material and a source of electrical power.
15. 15. The heater of claim 14, wherein the bus bars have a width dimension and a length dimension, and wherein the width decreases over at least a portion of its length.
16. 16. The heater of claim 14, wherein the bus bars have a width dimension and a length dimension, and where the width remains constant over cuct less a portion of its length.
17. The heater of claim 14, wherein the busbars have a width dimension and a length dimension, and at least one vacuum at a preselected location over its length.
18. The heater of claim 14, wherein the bus bars have a width dimension and a length dimension, and where the width dimension increases stepwise on at least a portion of its length.-
19. 19. The heater of claim 14, wherein the separation of the buses varies over the heater.
20. 20. The heater of claim 1, further comprising a top layer of secondary breathable or non-woven fabric., laminated or stitched, comprised of natural or synthetic fibers that cover the heater.
21. The heater of claim 20, wherein the overcoat is an encapsulating coating, which may be a flame retardant coating, which is applied over the elements of the heater.
22. 22. The heater of claim 1, wherein the heater is incorporated within the construction of a car seat.
23. The heater of claim 1, wherein the heater has a multiple bus design providing high and low current positions, comprised of at least one common bus, a low current position bus and a high current position bus , where the current flows from the common bus to the high current position bus, or from the common bus to the low current position bus.
24. 24. A self-regulating flexible heater construction to produce heat when connected to a source electric power, comprising: a flexible cloth substrate, - a material layer of positive temperature coefficient; and a layer of conductive material, wherein the composition of the seat heater has a density of about 0.6 g / cm3 or more, and a thermal diffusivity of about 0.003 cm2 / s or more.