Abstract:
A method for applying an abrasion resistant layer via a vacuum deposition technique to a plastic automotive window is provided. The plastic automotive window includes a plastic panel, an electroluminescent layer, and a weatherable layer. A first abrasion resistant sub-layer is then deposed on top of the weatherable layer, and a second abrasion resistant sub-layer is then applied onto the first abrasion resistant sub-layer. The deposition of the abrasion resistant sub-layers is carried out under controlled temperature conditions that reduce adhesion loss within the electroluminescent layer and maintains the electroluminescent functionality of that layer.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates generally to the field of automotive plastic windows. More specifically, it relates to a method for applying an abrasion-resistant layer to the interior and/or exterior surface of electroluminescent plastic windows. 
         [0002]    Plastic window systems are beginning to replace traditional glass windows in the automotive industry. Since plastic materials exhibit different properties than inorganic (e.g., glass) materials, various new processes for manufacturing these window systems have to be developed. One such process is the multi-step process used to manufacture the Exatec® 900 and 900 vt plastic glazing system offered by Exatec, LLC (Wixom, Mich.). This process includes (1) molding the window from a plastic resin; (2) printing an optional decoration or added functionality (e.g., defroster, etc.) layer using 3-D printing methodology; (3) applying a weatherable layer using conventional flow, dip, or spray coating techniques; and (4) applying an abrasion-resistant layer through the use of plasma enhanced chemical vapor deposition (PECVD). 
         [0003]    A key component in the manufacturing of a plastic window system comprising multiple interfacial regions between different material layers is the compatibility in both chemistry and properties that exists between the layers. A process that is developed to optimize the compatibility between two material layers may not work if one of the material layers is replaced with a different material layer. For example, in the Exatec® 900vt glazing system, the abrasion-resistant layer is optimized to exhibit optical clarity, hardness, and adhesion to both the surface of the polycarbonate window and a silicone weathering layer. However, adhesion failure occurs when another layer, such as an electroluminescent layer, is placed between the abrasion-resistant layer and the polycarbonate substrate. The observed adhesion loss occurs due to non-uniform heating across the multiple sub-layers that comprise the electroluminescent layer. Furthermore, the exposure to inert gases, such as a mixture of argon and oxygen, during the PECVD application of an abrasion-resistant layer can facilitate a loss in the properties associated with the electroluminescent layer. 
         [0004]    In view of the above, it is apparent that there is a need in the industry for a process suitable for the application of an abrasion-resistant layer to a plastic window system that comprises an electroluminescent layer without causing any adhesion loss or loss in electroluminescence. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    An object of the present invention is to provide a method for the application of an abrasion resistant layer to a plastic automotive window comprising an electroluminescent layer. Another object of the invention is to enhance the abrasion resistance of the electroluminescent automotive window through the optimized application of the abrasion-resistant layer. Yet another object of the invention is to deposit an abrasion-resistant layer while minimizing the occurrence of any adhesion loss between the various layers that comprise the electroluminescent layer, as well as maintaining the electroluminescent properties of the layer. 
         [0006]    A plastic automotive window embodying the principles of the present invention is a multi-layer glazing system, having a plastic panel, an electroluminescent layer, a weatherable layer, and an abrasion-resistant layer, among other layers. The electroluminescent layer may be encapsulated as part of the plastic panel through the use of a film insert molding (FIM) process. The weatherable layer is applied and cured under conditions (e.g., temperature, etc.) that further reduce the chance of any adhesion loss within the electroluminescent layer and prevent warpage of the plastic automotive window. The abrasion-resistant layer may comprise multiple sub-layers in order to reduce adhesion loss and deposit a layer providing a high level of abrasion resistance. The various embodiments of the present invention provide an advantageous method for the application of an abrasion-resistant layer that can be practiced when the plastic automotive window comprises an electroluminescent layer. 
         [0007]    Other objects and advantages of the present invention will become apparent upon considering the following detailed description and appended claims, and upon reference to the accompanying drawings. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  represents a fragmentary side view of an automobile incorporating a plastic automotive window, in accordance with the principles of the present invention. 
           [0009]      FIG. 2  is a schematic illustrating the various layers that comprise a plastic automotive window, in accordance with one embodiment of the present invention. 
           [0010]      FIG. 3  is a schematic illustrating the various layers that comprise a plastic automotive window, in accordance with another embodiment of the present invention utilizing a film insert molding (FIM) process. 
           [0011]      FIG. 4  provides both a horizontal (side) view and a vertical (top) view of a part carrier and an expanding thermal plasma PECVD reactor system, in accordance with a preferred embodiment of the present invention. 
           [0012]      FIG. 5  shows a flow chart illustrating a method for depositing an abrasion resistant layer onto a plastic automotive window including an electroluminescent layer, in accordance with one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]    The following description of the preferred embodiment is merely exemplary in nature and is in no way intended to limit the invention or its application or uses. 
         [0014]    The various embodiments of the invention provide a method or process for the application of an abrasion-resistant layer to a plastic automotive window. The automotive window is a multi-layer glazing system having a plastic panel, an electroluminescent layer, a weatherable layer, and an abrasion-resistant layer. As further discussed below, the electroluminescent layer may be deposited on the surface of the plastic panel or encapsulated as part of the plastic panel through the use of a film insert molding (FIM) process. 
         [0015]      FIG. 1  shows a fragmentary side view of an automobile with a plastic automotive window  100 , in accordance with one embodiment of the present invention. While the plastic automotive window  100  may be placed at various locations on the automobile, as shown it is located between structural members A &amp; B of the automobile. The automotive window  100  includes two surfaces, namely, a first surface  10  and a second surface  20 . As used herein, the first surface  10  faces the exterior of the automobile, while the second surface  20  faces the interior of the automobile. 
         [0016]    In one embodiment of the present invention, the automotive window  100  includes a plastic panel  30  upon which an electroluminescent layer  40  is disposed so as to be oriented toward the second surface  20  of the window as shown in  FIG. 2 . In another embodiment of the present invention, the electroluminescent layer  40  is deposited on the plastic panel  30  so as to be oriented toward the first surface  10  of the window, as shown in  FIG. 3 . 
         [0017]    The electroluminescent layer  40  is a multiple-layer system that undergoes electroluminescence, e.g., emits light when an electric field is applied. The electroluminescent layer  40  may be a border or frame around part or all of the window or may be a design (such as artwork and/or words) or a solid band or lines placed as part of the frame or border or transition into or through the transparent visual area of the window. The electroluminescent layer may be deposited or printed using any technique known to those skilled in the art including, but not limited to, screen printing, ink jet printing, membrane image transfer, and mask and spray. 
         [0018]    The electroluminescent layer  40  may include several sub-layers, such as a phosphor sub-layer, a dielectric sub-layer, a conductive paste sub-layer, a decorative ink sub-layer or other sub-layer. The phosphor sub-layer is the sub-layer responsible for emitting light when an electric field is applied across it, while the dielectric sub-layers provide the necessary capacitance and the conductive paste sub-layer provides optimum heat transfer across all of the above-mentioned sub-layers. The electroluminescent layer is described in more detail in U.S. patent application Ser. No. 11/317,587 submitted on Dec. 23, 2005, entitled “Light Emissive Plastic Glazing”, the entirety of which is hereby incorporated by reference. 
         [0019]    In another embodiment of the present invention, the electroluminescent layer  40  may be encapsulated between the plastic panel  30  and a plastic film  70  by a process well known to those skilled in the art of molding as film insert molding (FIM). The film insert molding process is meant to include a series of sub-processes, including but not limited or restricted to forming the film by extrusion or other means, screen printing the electroluminescent layer  40  onto the film  70 , optionally thermoforming the film to the geometry of one mold surface, trimming the film, inserting the film into the mold cavity, and injecting a molten plastic resin that will melt bond with the plastic film  70 , and solidifying the plastic resin into the plastic panel  30  upon cooling. The screen-printing sub-process may also comprise printing additional optional sub-layers, such as graphics onto the electroluminescent layer  40 , using a dielectric ink. The thermoforming sub-process includes forming the electroluminescent layer  40  into a geometry that will properly fit in the mold&#39;s cavity. Examples of thermoforming sub-processes include, but are not limited to, vacuum forming and pressure-assisted forming. The trimming sub-process removes excess plastic film  70 , which is necessary to insure accurate insertion of the film into the injection-molding tool. Examples of trimming sub-processes include, but are not limited to, match-metal trimming, routering, and laser trimming. The injection molding sub-process includes forcing the plastic resin layer to make contact with the electroluminescent layer  40  and plastic film  70 , which are placed in a mold cavity. The molten plastic resin is shot into the mold, causing melt bonding of the plastic film  70  with the plastic panel that solidifies upon cooling the molten plastic resin. In one embodiment of the present invention, the injection-molding process is performed at a mold temperature less than about 85° C. 
         [0020]    The weatherable layer  50  may be applied by using any wet coating process known to those skilled in the art including, but not limited to, spray-coating, dip-coating, flow-coating, spin-coating, roll coating, and curtain coating processes. The weatherable layer  50  is deposited on to the electroluminescent layer  40 , the plastic panel  30 , and the plastic film  70  as shown in  FIGS. 2 and 3 . The application of the weatherable layer is preferably done to both the interior side  20  of the window (2 nd  surface) and the exterior side  10  of the window (1 st  surface) or to just the exterior side  10  of the window (1 st  surface). Thus, the weatherable layer on the interior side  20  of the window (2 nd  surface) is optional. 
         [0021]    The weathering layer  50  may include, but is not limited to, silicones, polyurethanes, acrylics, polyarylate, epoxies, and mixtures or copolymers thereof. The weathering layer  50  may be extruded or cast as a thin film or applied as a discrete coating. The weathering layer  50  may comprise multiple coating sub-layers, such as an acrylic primer and silicone hard-coat or a polyurethane coating, in order to enhance the protection of the plastic panel. One specific example of the weathering layer  50  comprising multiple coating sub-layers includes a combination of an acrylic primer  53  (SHP401, GE Silicones, Waterford, N.Y.) and a silicone hard-coat  56  (AS4000, GE Silicones). A variety of additives may be added to the weathering layer  50 , such as colorants (tints), Theological control agents, antioxidants, ultraviolet absorbing (UVA) molecules, and IR absorbing or reflecting pigments, among others. 
         [0022]    The plastic panel  30  and plastic film  70  may be comprised of any thermoplastic or thermoset polymeric resin. The plastic panel  30  or plastic film  70  should be substantially transparent, but may contain translucent or opaque regions, such as but not limited to an opaque frame or border. The polymeric resins may include, but are not limited to, polycarbonate, acrylic, polyarylate polyester, polysulfone, polyurethane, silicone, epoxy, polyamide, polyalkylenes, and acrylonitrile-butadiene-styrene (ABS), as well as copolymers, blends, and mixtures thereof. The preferred transparent, thermoplastic resins include, but are not limited to, polycarbonate, acrylic, polyarylate, polyester, and polysulfone, as well as copolymers and mixtures thereof. The plastic panel may further comprise various additives, such as colorants, rheological control agents, mold release agents, antioxidants, UVA molecules, and IR absorbing or reflecting pigments, among others. 
         [0023]    The abrasion resistant layer  60  comprises a combination of multiple sub-layers with the number of sub-layers being at least two. The first abrasion resistant sub-layer  63  is preferably applied on to the surface of the weatherable layer  50 . The second abrasion resistant sub-layer  66  is applied on to the surface of the first abrasion resistant sub-layer  63 . 
         [0024]    The abrasion resistant layer  60  may be comprised of aluminum oxide, barium fluoride, boron nitride, hafnium oxide, lanthanum fluoride, magnesium fluoride, magnesium oxide, scandium oxide, silicon monoxide, silicon dioxide, silicon nitride, silicon oxy-nitride, silicon oxy-carbide, hydrogenated silicon oxy-carbide, silicon carbide, tantalum oxide, titanium oxide, tin oxide, indium tin oxide, yttrium oxide, zinc oxide, zinc selenide, zinc sulfide, zirconium oxide, zirconium titanate, or a mixture or blend thereof. Preferably, the abrasion resistant layer  60  is comprised of a composition of silicon monoxide, silicon dioxide, silicon oxy-carbide, or hydrogenated silicon oxy-carbide. Thus the abrasion resistant layer  60  may be referred to as a “glass-like” coating. 
         [0025]    The abrasion resistant layer  60  may be applied by any vacuum deposition technique known to those skilled in the art, including but not limited to plasma enhanced chemical vapor deposition (PECVD), expanding thermal plasma PECVD, ion assisted plasma deposition, magnetron sputtering, electron beam evaporation, and ion beam sputtering with PECVD being preferred and expanding thermal plasma PECVD being especially preferred. 
         [0026]    In one embodiment of the invention, the first abrasion resistant sub-layer  63  is more “organic-like” than the second abrasion-resistant sub-layer layer  66 . Although both sub-layers in this embodiment comprise a mixture of silicon, carbon, hydrogen and oxygen atoms, the first abrasion resistant sub-layer  63  comprises a greater amount of carbon and hydrogen atoms than does the second abrasion resistant sub-layer  66 . This greater amount or number of carbon and hydrogen atoms makes the first abrasion resistant sub-layer  63  more “organic-like” than the second abrasion resistant sub-layer  66  in order to enhance the adhesion between this layer and the underlying weatherable layer  50 . 
         [0027]    In one embodiment of the present invention, the second abrasion resistant sub-layer  66  is an “inorganic-like” layer that provides good abrasion resistance. The second abrasion resistant sub-layer  66  comprises more oxygen and silicon atoms, and less carbon and hydrogen atoms, as compared to first abrasion resistant sub-layer  63 , thereby providing improved or enhanced abrasion resistance. The chemical nature, as well as the number or amount of the various atoms comprising each abrasion resistant sub-layer can easily be determined by techniques, such as TEM, SIMS, and Auger that are well known to those skilled in the art of material characterization and surface analysis. 
         [0028]    In one preferred embodiment of the present invention, the abrasion-resistant layer is deposited using an expanding thermal plasma PECVD reactor system. This reactor system includes various chambers designed to preheat and apply the abrasion resistant layer  60  onto the first and second surface of an automotive window  100 . An expanding thermal plasma PECVD reactor system  200 , which is schematically depicted in  FIG. 4 , has been also explained in U.S. patent application Ser. No. 10/881,949 (filed Jun. 28, 2004 and U.S. patent application Ser. No. 11/075,343(filed Mar. 8, 2005) the entirety of which are hereby incorporated by reference. In an expanding thermal plasma PECVD process, a plasma is generated via applying a direct-current (DC) voltage to a cathode that arcs to a corresponding anode plate in an inert gas environment at pressures higher than 150 Torr, e.g., near atmospheric pressure. The near atmospheric thermal plasma then supersonically expands into a plasma treatment chamber in which the process pressure is less than that in the plasma generator, e.g., about 20 to about 100 mTorr. 
         [0029]      FIG. 4  provides both a horizontal (side) view and a vertical (top) view of a part carrier  202  and an expanding thermal plasma PECVD reactor system  200 , in accordance with one embodiment of the invention. The part carrier  202  carries a part, such as, for example, a partially manufactured plastic automotive window  100  through the reactor system. The expanding thermal plasma PECVD reactor system  200  includes a load lock chamber  204 , a preheat chamber  206 , a plurality of coating deposition chambers  208 ,  210 , and an exit lock chamber  212 . The coating deposition chambers include a chamber  208  for the deposition of the first abrasion resistant sublayer  63  and a chamber  210  for the deposition of the second abrasion resistant sublayer  66 . Additional coating deposition chambers are necessary if more than two sub-layers are used to comprise the abrasion resistant layer  60 . Each deposition chamber includes a plurality of arcs  214 ,  216 . 
         [0030]    The part carrier  202  carries the plastic automotive window  100  through the various chambers of the expanding thermal plasma PECVD reactor system  200 . The part carrier  202  first enters the load lock chamber  204 . The load lock chamber  204  includes a load lock pump that reduces the pressure in load lock chamber  204 , to create a vacuum substantially similar to the environment present in the coating deposition chambers  208 ,  210 . The part carrier  202  then moves the plastic automotive window into the preheat chamber  206 . 
         [0031]    The plastic automotive window  100  is heated in the preheat chamber  206  through the use of various heating elements. Examples of heating elements include but are not limited to infrared, microwave, resistance, and non-reactive plasma streams. In one embodiment of the invention, the preheat chamber  206  includes heating bars (resistance heating) placed along the reactor walls. After the surface of the plastic automotive window  100  is heated, the part carrier  202  moves the automotive window through the first coating deposition chamber  208 . 
         [0032]    In one embodiment of the present invention, the first abrasion resistant sublayer  63  and the second abrasion resistant sublayer  66  are applied in coating deposition chambers  208  and  210 , respectively. Each deposition chamber comprises an array of arcs  214 ,  216 . Each of the arcs includes a cathode plate with a centered cathode tip and an anode plate. The plasma is generated by applying a direct current voltage to the cathode plate that arcs to a corresponding anode plate in the presence of a gas or mixture of gases. Examples of gases include argon, nitrogen, ammonia, oxygen, hydrogen, or any combination thereof. The plasma is generated at pressures higher than about 150 Torr. The plasma is then emitted supersonically from the arcs  214 ,  216 , and expanded into the coating deposition chambers  208 ,  210 . In one embodiment of the present invention, the coating deposition chambers  208 ,  210  have low pressure, such as, for example, in a range of about 20 mTorr to about 100 mTorr. A reactive reagent is oxidized, decomposed, and polymerized in the plasma and deposited on the plastic automotive window  100  to form the abrasion resistant layer  60 . Examples of reactive reagents include but are not limited to, octamethylcyclotetrasiloxane (D4), tetramethyldisiloxane (TMDSO), hexamethyldisiloxane (HMDSO), or other volatile organosilicon compounds. 
         [0033]    Finally, the part carrier  202 , carrying the plastic automotive window  100  coated with the abrasion resistant layer  60 , moves into the exit lock chamber  212 . The exit lock chamber  212  includes an exit lock pump for evacuation that is similar to the one present in the load lock chamber  204 . Upon entry of the part carrier  202  into the exit lock chamber  212 , the chamber is at the same low pressure level as the coating deposition chambers  208 ,  210 . Once the part carrier  202  is inside the exit lock chamber  212 , the pressure is increased to atmospheric pressure and the part carrier is allowed to exit the expanding thermal plasma PECVD reactor system  200 . 
         [0034]    The inventors have discovered that the multiple interfaces that exist within the electroluminescent layer  40  are highly sensitive to the application of an abrasion resistant layer  60 . More specifically, upon the application of an abrasion resistant layer  60 , catastophic adhesion failure between the various interfaces within the electoluminescent layer  40  has been previously encountered. Depending upon the conditions used during the deposition of the abrasion resistant layer  60 , the adhesive failure may occur between the phosphor/dielectric sub-layers, the conductive/dielectric sublayers, or the dielectric sublayer and the plastic panel. Adhesive failure between the various interfaces within the electroluminescent layer  40  results in a substantial loss of the desired electroluminescence property. The inventors further discovered that maintaining a uniform heating profile across the multiple sub-layers of the electroluminescent layer  40  was essential to maintaining adhesion between the layers, both during and after the application of an abrasion resistant layer  60 . Uniform heating was discovered to be possible by pre-heating the plastic automotive window to a temperature between 35° C. to 65° C., preferably about 50° C. prior to the deposition of the first abrasion resistant sub-layer  63 . In the expanding thermal plasma PECVD reactor system shown in  FIG. 4 , the preheating of the plastic automotive window  100  is done in the pre-heat chamber  206  of the reactor system prior to the window entering the first coating deposition chamber  208 . 
         [0035]    The inventors have also discovered that limiting the temperature exposure of the electroluminescent layer  40  during the application and curing of the weatherable layer, or during a film insert molding process, enhances the adhesive integrity of the layer and helps to maintain the electroluminescent functionality. Thus, the application and curing of the weatherable layer should preferably be limited to a temperature of less than about 125° C. When a film insert molding (FIM) process is utilized, the temperature of the mold&#39;s surface should be maintained at a temperature not exceeding about 85° C. 
         [0036]      FIG. 5  shows a flowchart illustrating a method for depositing an abrasion resistant layer  60  onto a plastic automotive window  100  that will maintain the integrity (e.g., adhesion between sub-layers) and functionality of the electroluminescent layer  40 , in accordance with one preferred embodiment of the present invention. In step  300  a film insert molding process is utilized. In this case, the surface temperature of the mold to which the plastic film  70  and electroluminescent layer  40  is exposed should be maintained at a temperature not exceeding about 85° C. Since a film insert molding process is not always utilized, this process step  300  is optional. 
         [0037]    At step  302 , the weatherable layer  50  is applied onto the plastic automotive window  100 . In this embodiment of the invention, the weatherable layer  50  is applied and cured at a temperature less than about 125° C. for a time period between about 30 and about 75 minutes, with less than about 60 minutes being especially preferred. This process step  302  is also considered optional in that it will enhance the integrity and functionality of the electroluminescent layer  40 , but is not as critical as the following three process steps  304 - 308 . 
         [0038]    At step  304 , the plastic automotive window  100  is preheated prior to the deposition of the first abrasion resistant sub-layer  63 . In particular, the plastic automotive window  100  is preheated to a surface temperature in the range of about 35° C. to about 65° C., with a surface temperature of about 50° C. being especially preferred. 
         [0039]    At step  306 , the first abrasion resistant sub-layer  63  is applied to the surface of the weatherable layer  50  maintaining a uniform temperature across the electroluminescent layer not exceeding about 85° C. In one preferred embodiment of the present invention, where the abrasion resistant layer  60  is deposited using an expanding thermal plasma PECVD reactor system  200 , a uniform temperature was discovered to occur when the first abrasion resistant sub-layer  63  is deposited using an arc current in a range from about 30 amps/arc to about 45 ampstarc, a reactive reagent (e.g., octamethylcyclotetrasiloxane, D4) flow in a range of about 110 standard cubic centimeter per minute (sccm) to about 140 sccm, and an oxygen flow in a range of about 250 sccm to about 350 sccm with about 37 amps/arc, a reactive reagent flow of about 125 sccm, and an oxygen flow of about 300 sccm being especially preferred. The preheat temperature, as described at step  304 , prevents the surface temperature of plastic automotive window  100  from increasing beyond about 85° C. when the first abrasion resistant sub-layer  63  is applied in step  306   
         [0040]    At step  308 , the second abrasion resistant sub-layer  66  is applied on top of the first abrasion resistant sub-layer  63  maintaining a uniform temperature across the electroluminescent layer not exceeding about 110° C. In one preferred embodiment of the present invention where the abrasion resistant layer  60  is deposited using an expanding thermal plasma PECVD reactor system, a uniform temperature was discovered to occur when the second abrasion resistant sub-layer  66  is deposited using an arc current in a range from about 30 amps/arc to about 40 amps/arc, a reactive reagent (e.g., octamethylcyclotetrasiloxane, D 4 ) flow in a range of about 110 sccm to about 140 sccm, and an oxygen flow in a range of about 700 sccm to about 900 sccm with about 34 amps/arc, a reactive reagent flow of about 125 sccm, and an oxygen flow of about 800 sccm being especially preferred. The preheat temperature, as described at step  304 , and the temperature less than about 85° C. after the deposition of the first abrasion resistant sub-layer  63  in step  306 , prevents the surface temperature of the plastic automotive window  100  from increasing beyond 110° C. when the second abrasion resistant sub-layer  66  is applied in step  308 . 
         [0041]    The various embodiments of the present invention provide an advantageous method and process for the application of an abrasion resistant layer  60  comprising at least two sub-layers  63 ,  66  to a plastic automotive window  100  comprising an electroluminescent layer  40 . The multi-layer glazing system, as described in the present invention, establishes both the adhesive integrity between the electroluminescent sub-layers and the external abrasion resistance necessary to function as a light-emitting automotive window. Furthermore, by limiting the temperature of the mold&#39;s surface in a film insert molding process, by limiting the temperature used to cure the weatherable layer, and by preheating the plastic automotive window prior to the deposition of the abrasion resistant layer  60 , the occurrence of any adhesion loss between the sub-layers of the electroluminescent layer  40  is either reduced or eliminated. 
         [0042]    While the preferred embodiments of the invention have been illustrated and described, it will be clear that the invention is not limited to these embodiments only. Numerous modifications, changes, variations, substitutions, and equivalents will be apparent to those skilled in the art, without departing from the spirit and scope of the invention, as described by the appended claims.