Patent Application
20110297661
The present disclosure relates generally to defogging, defrosting, and/or de-icing structures.
Transparent glass or composite structures are often used for making various automotive and/or aerospace components. Such components include various transparent external parts, examples of which include windshields, mirrors, windows, backlights, headlights, and/or the like. Such transparent structures may, for example, fog up, frost, and/or become icy under certain atmospheric conditions. Such fogging, frosting, and/or icing may, in some instances, deleteriously affect visibility through the structure.
Defrosting, defogging, and de-icing structures are disclosed herein. An example of the structure includes at least one optically transparent member, at least one electrical strip extending along the at least one surface of the at least one optically transparent member; and an optically transparent composite established on at least the at least one surface of the at least one optically transparent member. The composite is in operative contact with the at least one electrical strip. The composite includes a matrix, and a predetermined amount of graphene. The predetermined amount is based upon a predetermined transparency for the structure and a predetermined thermal conductivity of the structure. Furthermore, the structure is configured such that the graphene functions as a thermal conductor for substantially uniform heating of the composite and not an electrical conductor.
Features and advantages of the present disclosure will become apparent by reference to the following detailed description and drawings, in which like reference numerals correspond to similar, though perhaps not identical, components. For the sake of brevity, reference numerals or features having a previously described function may or may not be described in connection with other drawings in which they appear.
Defrosting, defogging, and/or de-icing structures are widely used in automobiles and other vehicles during inclement weather to increase visibility and/or melt snow, frost, ice, etc. Example(s) of the defogging, defrosting and/or de-icing structure, as disclosed herein, may be used for windshields, windows (including any front, side windows and/or the rear window(s)), headlights, backlights, or other similar automotive and/or aerospace transparent or non-transparent components. In one embodiment, the structure generally includes at least one optically transparent member, and an optically transparent composite coated on at least a portion of the optically transparent member(s). Due, at least in part, to its transparency, the structure of this embodiment is aesthetically pleasing for use as an external part for a mobile vehicle (examples of which include automobiles, trucks, motorcycles, buses, motor homes, planes, helicopters, boats, trains, etc.), as well as any windows that can employ electrical sources such as points or strips which are electrically or otherwise heated for defrosting, de-icing, and/or defogging the surface of the window or other external component. In another embodiment, the structure generally includes at least one opaque member, and a composite coated on at least a portion of the opaque member(s).
The composite, whether used in a transparent embodiment or a non-transparent embodiment, includes a predetermined amount of graphene therein. The incorporation of the graphene into the composite allows the composite to substantially uniformly distribute heat delivered thereto, thereby enabling substantially homogeneous defrosting/defogging/de-icing. This is due, at least in part, to the substantially uniform distribution of the graphene throughout the matrix. The various structures are configured so that the graphene functions as a thermal conductor (as opposed to an electrical conductor), thereby enhancing the thermal conductivity of the resulting structure by at least three orders of magnitude (when compared to structures without such graphene). This enables heating of the structure without the use of Joule heating (i.e., ohmic heating or resistive heating, resulting from the passage of electrical current through a conductor). While electrical strips are used to initiate the heating of the structure disclosed herein, thermal conduction (as opposed to Joule heating) is used to transfer the heat throughout the composite. By thermal conduction, heat is conducted throughout a material based on the physical properties of the material(s) used. Graphene is capable of both electrical conduction and thermal conduction. However, in the embodiments disclosed herein, the graphene is used in an amount or is electrically isolated from a heat source such that the graphene enhances thermal conduction of the composite. This leads to substantially uniform heating of the composite and thus the structure, which in turn efficiently and quickly defogs, defrost, and/or de-ices the structure.
The enhanced thermal conductivity also enables defrosting, defogging, and/or de-icing to take place in a relatively short time frame. The quickness is due, at least in part, to the heating of the entire surface of the structure at substantially the same time, as opposed to other techniques where the structure is gradually heated through, e.g., electrical leads or wires embedded (as a grid) in the structure. The drastic reduction in time is especially advantageous.
Still further, because the composite is included as a coating adjacent to the substrate (i.e., optically transparent or opaque member), the substrate/member itself not need to include conductive materials. This is believed to decrease the manufacturing cost.
Referring now to
While shown and discussed in more detail in reference to
As shown in
Referring now to
The optically transparent member 112 may be molded or otherwise manufactured into the desirable part shape. As previously mentioned, the part size and shape may correspond with the size and shape of a window, light, etc. in, for example, a mobile vehicle, a building, or another desirable application. Manufacturing the member 112 is generally accomplished prior to establishing the composite 114 thereon. For example, the optically transparent member 112 is molded or manufactured using one or more conventional processes. In instances where the member 112 is formed from a thermoset material, the member 112 may be formed using compression molding. In such instances, a mold including a desired part shape may be filled with the thermoset material and subsequently cured under compressive forces and heated to cure the material and set the part shape. When the compression molding process is complete, the optically transparent composite 114 is laminated to, or otherwise deposited on, the member 112. In instances where the member 112 is formed from a thermoplastic material, the member 112 may be formed via injection molding, extrusion molding, or the like. In one example, the thermoplastic material may be fed through an injection molding machine at a suitably high temperature (e.g., above a melting temperature of the material). The material is melted and mixed/blended while traveling through the machine. The material may then be injected into a mold having a desired part shape, and subsequently set into that part shape. When the injection molding cycle is complete, the part may be ejected from the mold and laminated with, or otherwise adhered to, the optically transparent composite 114. In still another example, the thermoplastic material may be fed through an extruder, where the material is melted and mixed/blended while traveling therethrough. It is to be understood that the shape of the die at the end of the extruder screw is in the general shape of the targeted part shape (e.g., tubular, sheet form, etc., where the die dimensions account for material expansion/contraction during thermal events). Such extrusion processes may require for the extrudate to be somewhat machined (e.g., filed, cut, etc.) prior to being casted with the optically transparent composite 114.
This embodiment of the structure 110 has two electrical strips 116 established on opposed ends E1, E2 along the periphery of the optically transparent member 112. While not shown in
In this embodiment, the composite 114 is optically transparent, and includes a matrix having graphene established therein. In a non-limiting example, the coated structure 110 includes a substantially continuous film of the composite 114. The thickness of the film generally depends, at least in part, on the product to be made, cost, the type of fillers (if any) used in the matrix, and the like. In a non-limiting example, the thickness of the film ranges from about 1 μm to about 1 mm. In another non-limiting example, the thickness of the film ranges from about 10 μm to about 250 μm. As used herein, a “substantially continuous film” refers to a layer of the composite material 114 that is molecularly continuous when laminated (or otherwise adhered) to the member 112, regardless of the amount of the surface area of the member 112 that the composite 114 layer actually covers. In other words, such continuous films do not exhibit breaks, gaps, or other spaces visually noticeable by a human eye.
The matrix may be any polymer, or sol-gel composition, or combination of polymer layer(s) on a sol-gel composition. Non-limiting examples of the polymer matrix include polycarbonates, epoxies, poly(acrylonitrile)s, transparent polyesters (such as poly(ethylene terephthalate or poly(butylene terephthalate), poly(acrylonitrile), poly(methylmethacrylate)s, and/or the like, and/or combinations thereof. In some instances, polyvinyl butyrals, polyurethanes, or polyvinyl chlorides may be used. The sol-gel compositions may be made by a sol-gel process, which is a wet-chemical method for making materials (typically a metal oxide) beginning from a chemical solution which reacts to bring forth nanosized colloidal particles (or sol). Non-limiting examples of precursors in a sol-gel composition are metal alkoxides and metal chlorides. These precursors undergo hydrolysis and polycondensation reactions, thus forming a colloid or gel which can be dried to form an essentially solid gel material. The resulting compositions have solid particles (with size ranging from 1 nm to 1 μm) dispersed in a solvent. It is to be understood that when a sol-gel composition is used, the solid particles do not deleteriously affect the desired transmissivity of the composite 114.
The matrix of the composite 114 has graphene dispersed therein. In this embodiment, since the composite 114 is in direct physical contact with the electrical strips 116, the amount of graphene incorporated is below the percolation threshold for electrical conduction. In one embodiment, the percolation threshold for graphene is about 0.1 weight % of the total composite 114 weight %. As such, in some instances, graphene present in amounts at or below this threshold is not electrically conductive, but is thermally conductive. It is to be understood that this amount of graphene also maintains the transparency of the composite 114.
It is to be understood that the threshold value may change depending upon the processing route used. For example, if a reduction-extractive dispersion method is utilized to process the graphene, the percolation threshold is at about 0.15%; if ultrasonication of expanded graphite is accomplished in a liquid medium, followed by liquid mixing with a polymer or in situ polymerization, the percolation threshold is at about 0.31%; if graphene sheets are incorporated into polycarbonate by melt blending, using a microcompounder and a small scale, conical, twin screw extruder with a recirculation channel, the percolation threshold ranges from 0.008 to 0.011 volume fraction.
“Optical transparency”, as the term is used herein to describe embodiments of the member 112 and the composite 114 of the structure 110, means the light transmittance of the corresponding structure is not below 0.75, with 1.0 being no interference with light transmittance. It is to be understood that the desired level of transparency of one structure 110 (e.g., a rear windshield) may be different from the desired level of transparency of another structure 110 (e.g., a front windshield).
It is to be understood that the graphene used in the embodiments of the composite disclosed herein may be produced via any suitable method or may be commercially obtained.
As shown in
Referring now to
Since larger graphene loading enables the graphene to exhibit electrical conductivity, this embodiment of the structure 110′ further includes an electrical insulation layer 124 established between the electrical strips 116 and the composite 114. This layer 124 prohibits the electrical current delivered to the electrical strips 116 from conducting through to the composite 114. However, it is to be understood that the heat generated from the electric current is conducted through the layer 124, and thus effectively heats the composite 114, including the graphene therein. As such, the electrical insulation layer 124 is electrically insulating while being thermally conductive. The thickness of the electrical insulation layer 124 may be any desirable thickness as long as the insulating/conducting properties are obtained. In one example, the electrical insulation layer 124 thickness ranges from about 50 nm to about 10 μm.
Non-limiting examples of suitable materials for the electrical insulation layer 124 include silica, alumina, zirconia, magnesia, or other like films. Suitable deposition techniques for establishing the electrical insulation layer 124 include chemical or physical vapor deposition techniques, and sol-gel coating techniques.
Still other embodiments of the structure 110″, 110′″ are shown in
In
In
Referring now to
The example shown in
Referring now to
The electrical heating strip(s) 116 may be a metal wire, a sintered body of metal adhered to the member 112 or composite 114, and a paste or ink including metal printed on the member 112 or composite 114. An example of suitable metal wires includes those made of copper, which has a positive temperature coefficient. Such a strip 116 can be formed from a sintered body of metal and adhered to the window glass.
As shown in
It is to be understood that any of the electrical strip 116 configurations discussed herein may be incorporated together in any desirable geometric configuration.
For any of the examples disclosed herein, the optically transparent composite 114 may be applied to the optically transparent member 112 via lamination. In lamination, the composite 114 is applied to the member 112 by i) applying a thin film of the composite 114 to the member 112, and ii) heating the composite 114 to form a bond with the member 112. In another non-limiting example, the composite 114 is applied to the member 112 by any conventional coating techniques, such as i) casting or spraying a solution including the composite 114 on the member 112, and ii) applying heat thereto to a) evaporate the solvent in the solution, b) cure the composite 114, and c) bond the composite 114 to the member 112. In some instances, pressure may be used in addition to the heat to improve bonding and/or sealing of the composite 114 and the member 112. In other instances, the components 112, 114 are sealed with a transparent adhesive. In instances where the member 112 includes a laminate (e.g., polyvinyl butyral), the laminate may also serve as a suitable adhesive. In another example, the member 112 may include a separate adhesive that does not impede or otherwise deleteriously affect the transparency of the overall structure 110, non-limiting examples of which include a thin layer of acrylate-based adhesive material, a thin layer of epoxy material, or combinations thereof. As previously mentioned, the electrical strips 116 may be applied before or after adherence of the components 112, 114 (or 132 and 114).
To further illustrate embodiment(s) of the present disclosure, the following examples are given. It is to be understood that these examples are provided for illustrative purposes and are not to be construed as limiting the scope of embodiment(s) of the present disclosure.
Computer simulated calculations were performed for two rear vehicle windows having an optically transparent composite established thereon. Each window employs a pair of bus bars along the shorter edges of the window glass in a conventional heating strip arrangement (such as that described in Nakashima et al., U.S. Pat. No. 6,137,085). Schematic drawings of the two windows are shown in
Computer simulated calculations were performed for a rear window having an optically transparent composite coating established thereon. The window had 10 lines of printed silver paste lines, which function as electrical strips. The length of each line is 1 meter. The width of each line is 0.5 mm. The gap between each of the lines is 2.54 cm. The voltage supplied to the electrical strips is 12 volts. The surface resistivity of the rear window is 5 mΩ/(i.e., quadrature). Total resistance is equal to surface resistivity×no. of squares which is equal 0.005×1000/100.5, which in turn is equal to 1 W. Power is equal to V2/R, which, in this example, is equal to 144 watts. Power input per unit length per wire is equal to 144 watts/1 m/10 wires which is equal to 14.4 W/m/wire. Assuming a 1 mm wide conducting media composite, heat flux into the domain is 14.4 W/m/10−3 m, which is equal to 14400 W/m2. By symmetry, half of the heat flux goes upward and the other half goes downward. It is assumed for the purpose of these calculations that all of the heat is taken up by the conducting composite 114, and not by the structural elements or atmosphere. The amount of graphene included is determined by the amount of conductivity specified.
Computer simulated calculations were performed for a rear vehicle window according to the materials and dimensions described in Example 2. Temperature profiles were calculated as shown in
Computer simulated calculations were performed for a rear vehicle window according to the materials and dimensions described in Example 2. De-icing time is defined as the time it takes for the temperature at the center of the domain (x=0) to reach 273.15 K for the first time, as shown in
While several examples have been described in detail, it will be apparent to those skilled in the art that the disclosed examples may be modified. Therefore, the foregoing description is to be considered exemplary rather than limiting.
