Abstract:
An apparatus and method for coating a substrate moved along a path of travel through the apparatus. A plasma source issues a plasma jet into which a first reagent is injected from a discharge orifice located upstream of the jet. A second reagent is injected into the jet from a discharge orifice located downstream of the jet. A controller is configured to regulate the flow of the first reagent according to a first set of parameters and regulate the flow of the second reagent according to a second set of parameters. As a result, the first and second reagents are applied to the substrate to form at least one layer of a coating on the substrate.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of provisional application 60/938,559 filed May 17, 2007, the entire contents of which are herein incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The present invention generally relates to a system for coating substrates. More specifically, the invention relates to a plasma coating system and method whereby the introduction of reagents is controlled to enhance the coating formed on the substrate. 
         [0004]    2. Related Technology 
         [0005]    Generally, plasma coating systems, to which the present invention is applicable, include various stations or zones connected in sequence and through which substrates are moved in a continuous series. These zones may include a load lock, a heating zone, one or more coating zones and an exit lock. In the coating zone(s) is one or more plasma sources, such as an expanding thermal plasma (ETP) source, and associated means for injecting coating reagents. During the coating process, the substrates are moved past the plasma source(s) as a coating reagent(s) is injected into a plasma jet issuing from the plasma source. As the substrates are moved through the resulting plasma plume, a coating is deposited on the surfaces of the substrates. 
         [0006]    Such prior art systems do not allow for the simultaneous application of multiple coating sub-layers on to a single side of a substrate. If multiple coating sub-layers are to be applied, the once coated substrate is passed through additional coating zones, where the additional coating sub-layers are applied. 
       SUMMARY 
       [0007]    Generally, the present invention is directed to an apparatus and method for simultaneous, dual-use of plasma sources by injecting different reagent compositions into each of the upstream and downstream sides of the plasma jet issuing from a respective plasma source. Alternatively, the reagent composition provided to both sides of the jet is the same, but the flow rates to the upstream and downstream sides are different. Different upstream and downstream reagent “recipes” can be reflected in the composite coating on the substrate, either as a blend of materials or as a gradation between two materials, depending on the injection parameters and time allowed for reagent penetration into the plasma jet before deposition onto the substrate. 
         [0008]    Generally, an apparatus according to the present invention is an in-line, continuous plasma coating system for coating substrates. In such a system, a series of substrates is continuously passed through the coating zone in a sequential (single file) order. The plasma coating system may include one plasma source or an array of plasma sources (a plasma array). The system also includes means for injecting a first coating reagent into the plasma jet issuing from the plasma source from a location upstream of the plasma source, and a means for injecting a second coating reagent into the plasma jet from a location downstream of the plasma source. The means for injecting the reagents may include manifolds, individual injectors or orifices, as are known in the art. A controller regulates the flow of the coating reagents during injection. A second set of means for injecting reagents may also be employed and controlled to deposit a coating on a second side or opposing surface of the substrate. 
         [0009]    Further features and advantages will become readily apparent from the following description, and from the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0010]      FIG. 1  is a schematic plan view of a system for coating substrates in accordance with the principles of the present invention; 
           [0011]      FIG. 2  is a schematic depiction of an end-view through the coating zone of the system of  FIG. 1 ; 
           [0012]      FIG. 3  is a schematic side-view of the coating zone seen in  FIG. 2  and as generally taken along line  3 - 3 ; 
           [0013]      FIG. 4  illustrates substrates with associated space-filling panels that may be optionally employed as the substrates are advanced through the system of  FIG. 1 ; 
           [0014]      FIG. 5A  depicts a pair of injectors for coating a substrate in accordance with one embodiment of the present invention; 
           [0015]      FIG. 5B  depicts a blended coating on the substrate produced with the injectors shown in  FIG. 5A ; 
           [0016]      FIG. 6A  depicts a pair of injectors for coating a substrate in accordance with another embodiment of the invention; 
           [0017]      FIG. 6B  depicts a multilayer coating on the substrate produced with the injectors shown in  FIG. 6A . 
       
    
    
     DETAILED DESCRIPTION  
       [0018]    Referring now to the drawings, a substrate coating system  10 , in accordance with the principles of the present invention, is schematically shown in  FIG. 1 . The substrate coating system  10  is preferably used to coat a plurality of substrates  20  in forming a plastic glazing panel. One skilled-in-the-art will recognize that the resulting plastic glazing panel may be used in many applications that require optical transparency, including but not limited to, computer displays or monitors, displays for hand-held devices (e.g., cell phones, MP3 players, etc.), lenses, automotive components (including windows, sunroofs and headlamps), motorcycle windshields, helmet visors, and windows used in non-automotive applications, such as for boats, trains, planes, and buildings. The substrates  20  (two substrates being shown) are continuously moved through the system  10 , which includes various stations or zones. Such zones may include a load lock  12 , a substrate heating zone  14 , one or more substrate coating zones  16  and an exit lock  18 , all being connected in series and in an airtight manner. The various zones may be evacuated by one or more vacuum pumps (not shown) to maintain a suitable vacuum pressure that is conducive to the coating process. 
         [0019]    As those skilled in the art will appreciate, the substrates themselves may be formed from a wide variety of materials. In an exemplary embodiment, the substrates  20  are made of a thermoplastic material. Such materials include, but are not limited to, polyvinylalcohol, polyvinylacetal, polyvinylacetate, polyethylene, polypropylene, polystyrene, polyamide, polyimide and polyvinylchloride. Other suitable materials for the substrates  20  include polycarbonate resins, polyestercarbonates, acrylic polymers, polyesters, polyurethanes, and the like. Further examples of materials from which the substrates  20  may be made include ceramic, glass, metal or a semiconductor. The substrates  20  may be formed by a variety of techniques, depending on the material of their construction. Such techniques include, without limitation, injection molding, cold forming, vacuum forming, extrusion, blow molding, transfer molding, compression molding, and thermal forming. Once formed, the substrates  20  may be curved or flat in shape and rigid or flexible in nature. 
         [0020]    In utilizing the system  10 , the substrates  20  are placed on a substrate carrier  24 , which may be a rack, hanger or other device. Such devices are known in the industry and, therefore, are not further described herein. The substrate carrier  24  enters the load lock  12  and, in the load lock  12  or prior thereto, is engaged by a conveyor, generally indicated by arrows  25 , that transports the carrier  24  and substrates  20  through the coating system  10 . Obviously, any means suitable for transporting the carrier  24  and substrates  20  through the coating system  10  may be employed. 
         [0021]    Once transferred into the substrate heating zone  14 , the substrates  20  are heated to a temperature suitable for coating of the substrates  20 . To achieve this, the substrate heating zone  14  includes heating units  26 , two being shown. The heating units  26  are located within or outside of, at or along the side walls of, the substrate heating zone  14  or where dictated by the overall design of the system  10 . Various types of heating units  26  may be employed and include, but are not limited to, infrared heaters, resistance heaters, non-reactive plasma jets and the like. 
         [0022]    After traveling through the substrate heating zone  14 , the substrate carrier  24  enters the substrate coating zone  16 , where a coating is deposited on the substrates  20 . Once the substrates  20  have been coated, they are then transferred to the exit lock  18 , where they are released from the coating system  10 . 
         [0023]    While a variety of coating methodologies and procedures may be employed with the present invention, as illustrated, the substrate coating zone  16  includes one or more plasma arrays  28 , such as an expanding thermal plasma (ETP) source array. The plasma arrays  28  may be arranged in pairs opposite one another in the coating zone  16 . Each plasma source  38 , as seen in  FIG. 3 , may be mounted on its own port or the plasma array  28  may be mounted to a manifold  30  located on the side walls of the substrate coating zone  16 . 
         [0024]    Each array  28  is preferably fed with an inert gas, which is heated, partially ionized and then issued from the array  28  as a series of plasma jets  32 . This is generally illustrated in  FIG. 1  as a composite plasma jet from opposed arrays  28 , into the substrate coating zone  16 . Examples of inert gases that may be utilized with the coating system  10  include, but are not limited to, argon, helium, neon and the like. 
         [0025]    A first coating reagent and a second coating reagent, one of which may be an oxidizing gas, are injected from reagent injection manifold segments  34 ,  36 , respectively. The coating reagents, injected in vapor form at a controlled rate, diffuse into the plasma jet  32 , which expands into the substrate coating zone  16  and which is directed towards the substrates  20  being conveyed therethrough. Examples of coating reagents include, but are not limited to, organosilicons such as decamethylcyclopentasiloxane (D5), vinyltrimethylsilane (VTMS), dimethyldimethoxysilane (DM DMS), octamethylcyclotetrasiloxane (D4), tetramethyldisiloxane (TMDSO), tetramethyltetravinylcyclotetrasiloxane (V-D4), hexamethyldisiloxane (HMDSO) and the like. Examples of oxidizing gases include, but are not limited to, oxygen and nitrous oxide, or any combination thereof. 
         [0026]    Referring now to  FIG. 2  and  FIG. 3 , various configurations of the system  10  involve depositing activated reagents, or, in some implementations a single reagent, on one or both sides of a substrate  20  as it advances through the coating zone  16 . The substrate  20  is heated by the heating units  26  to ensure that the substrate  20  is at a suitable temperature before entering the coating zone  16 . If needed additional heaters may be used in the coating zone  16  itself to make up for any heat loss during transit from the heating zone  14  to the coating zone  16 . 
         [0027]    The coating zone  16  is a vacuum chamber and includes one or more plasma sources  38  (six being illustrated as a non-limiting example), on one or both sides of the coating zone  16 . The manifold segments  34 ,  36  may further be delineated as either an upstream manifold segment ( 134 ,  136 ) or a downstream manifold segment ( 234 ,  236 ) and each upstream segment  134 ,  136  is paired with a downstream segment  234 ,  236 . As used herein, the terms upstream and downstream being referenced to the location of the manifold segment relative to the plasma sources  38  and the direction of movement (designated by the arrow  40  seen in  FIG. 3 ) of the substrates  20 . Each manifold segment  34 ,  36  is associated with one or more of the plasma sources  38 . As such, one or both sides of the coating zone  16  illustrated in  FIG. 3  is provided with upstream manifold segments  134 ,  136  and downstream manifold segments  234 ,  236 . As shown in the illustrated embodiment, each side of the coating zone includes six upstream and six downstream manifold segments, although each side may include greater or fewer number of manifold segments. Segmenting the manifolds allows for individual flow switching according to a desired protocol. The various manifold segments  34 ,  36  of the coating zone  16  inject coating reagents therethrough independently of one another. 
         [0028]    As shown in  FIG. 3 , the leading edge  42  of an advancing substrate  20  first passes the upstream manifold segments  134 ,  136 , then the plasma array  28  and its individual plasma sources  38 , and finally the downstream manifold segments  234 ,  236 . Accordingly, the trailing edge  44  is the last portion of the substrate  20  to pass by the downstream manifold segments  234 ,  236 . 
         [0029]    When there are gaps or spaces between successive substrates  20  the system  10  may include features to minimize extraneous coating material being deposited on the vacuum chamber walls of the coating zone  16 . In certain implementations, as seen in  FIG. 4 , this feature may be a space-filling panel  46 , attached to the carrier  24  and/or conveyor  25  by a set of tabs  48 , closely spaced to the substrate  20  such that it is a virtual extension of the edge of the substrate  20 . Such a space-filling panel  46  is generally illustrated in  FIG. 4 . 
         [0030]    In other implementations, shown in  FIGS. 5A and 6A , rather than using manifold segments to coat the substrates  20 , one or more upstream reagent injectors  144 ,  146  and one or more downstream reagent injectors  244 ,  246 , may be associated with each plasma source  38  to deposit a coating on the substrate  20 . Control of the flow of vaporized reagents to the various injectors is accomplished in the same manner as described above with respect to the various manifolds. 
         [0031]    The above implementations are hereinafter described as being used to create a blended coating or graded coating on the substrate in a single coating zone  16 . While any of the implementations may be used to produce these coatings, the description will only describe the processes in connection with  FIGS. 5A and 6A , it being understood that manifold segments  134 ,  136 , as seen in earlier figures, could alternatively be employed. 
         [0032]    For convenience, two time characteristics are used to describe the coating process in relation to the plasma jet  32 : a) lateral mixing time I t  and b) transit time t t . Lateral mixing time I t  is characteristic of the length of time that a reagent requires to fully penetrate the plasma jet  32 . Transit time t t  is characteristic of the length of time it takes the plasma jet (with reagent(s)) to traverse the distance from the injector plane (the plane defined by the injectors  49 ), to the substrate  20 , measured along the path of the plasma jet  32 . 
         [0033]    If blending of two functional coating materials (for example, one for UV blocking and one for abrasion resistance) is desired, then the reagents for the respective materials are each independently fed to the upstream and downstream injectors  144 ,  244 , respectively. The parameters of the injectors  144 ,  244  (such as position, number, distribution, orientation, and size) and other process parameters are selected so as to promote rapid penetration of reagents towards the axis  50  of the plasma jet  32  of the respective plasma source  38 , relative to the transit time of the jet  32  with reagents to the substrate. That is the parameters of the injectors  144 ,  244  and other process parameters are selected so that I t &lt;&lt;t t . As the upstream reagent and downstream reagent are fed to the respective injectors  144 ,  244 , the reagents blend within the plasma jet  32  to produce the blended coating  52  characterized by a substantially homogeneous layer reflecting the combined coating contributions of the upstream and downstream provided reagents. Depending on the specific reagents used, functionality of the individual coating materials may or may not be preserved when blended. Such a coating may be produced by the arrangement of the injectors  144 ,  244  shown in  FIG. 5A , in which the tips of the injectors  144 ,  244  are inserted in the plasma jet  32  or near thereto. 
         [0034]    If, on the other hand, a transition from one functional coating material to the other is desired, then reagents for the respective materials are again each independently fed to one of the upstream and downstream manifolds. However, the parameters of the injectors  144 ,  244  and other process parameters are selected to promote slow penetration of reagents into the plasma jet  32 , relative to the transit time of the jet with reagents to the substrate; that is I t &gt;&gt;t t . Coating sub-layers deposited by the upstream and downstream halves of the jet  32  will tend to reflect the respective reagents fed via the upstream and downstream injectors  144 ,  244 . The resulting composite coating  54  on a substrate scanned or moved past the jet  32  will reflect a transition from the coating sub-layer formed by the upstream reagent to the coating sub-layer formed by the downstream reagent. Such a multilayer coating  54  may be produced by the arrangement of the injectors  144 ,  244  shown in  FIG. 6A , in which the tips of the injectors are spaced from, and not inserted into, the plasma jet  32 . That is, the parameters of the upstream and downstream injectors  144 ,  244  and other process parameters are selected to promote incomplete mixing and a separation of upstream reagent and downstream reagent within the plasma jet  32 . The multilayer coating  54  ( FIG. 6B ) is characterized by two sub-layers  56 ,  58  and an intervening transition zone  60 . The sub-layer  56  closest to and the sub-layer  58  furthest from the substrate  20  reflect, respectively, the dominance of the individual coating contributions of the upstream and downstream reagents. 
         [0035]    The arrangement shown in  FIG. 6A  can be used to produce various types of multilayer coatings  54 . In some implementations, the upstream and downstream injectors  144 ,  244  may share the same reagent sources, but the flow rates to the upstream and downstream injectors may be different. For example, one set of injectors may be supplied with D 4  at one flow rate and the other set of injectors may be supplied with D 4  at another flow rate. In other implementations, different reagents may be supplied to the upstream and downstream injectors  144 ,  244  from different sources  62 ,  64 . 
         [0036]    In a particular implementation, the transition between the first and second sub-layers  56 ,  58  of an abrasion-resistant coating can be such that significantly unbalanced thicknesses of the sub-layers result. For example, the thickness of the first sub-layer  56  may be reduced while the thickness of the second sub-layer  58  is increased, which improves abrasion-resistance without compromising water immersion performance, and without reducing throughput through the system  10 . 
         [0037]    In another implementation, the upstream injector  144  is employed to deposit an interface layer (IL) as the first sub-layer  56  to secure adhesion of the subsequent abrasion-resistant layer (the second sub-layer  58 ) to certain substrates  20  (for example, polycarbonate substrates). In one case, the IL is formed from the same organosilicon reagent used for the abrasion-resistant layer, but the oxidizing reagent flow associated therewith is relatively low or absent. 
         [0038]    In another implementation, the upstream injector  144  is employed to deposit an IL first sub-layer  56 , but the reagent differs from that used for the abrasion-resistant layer of the second sub-layer  58 . In this case, separate sources ( 62 ,  64 ) are employed for the upstream and downstream injectors  144 ,  244 . 
         [0039]    In a further implementation, one of the injectors  144 ,  244  may be employed to deposit a UV blocking sub-layer (for example, TiO 2 ). In particular, the upstream and downstream injectors  144 ,  244  deposit an IL and a UV layer, respectively. An additional coating zone  16  can then be used to deposit an abrasion-resistant layer, as either one layer or two sub-layers. Alternatively, the upstream and downstream injectors  144 ,  244  in the first coating zone  16  deposit a UV layer as a first sub-layer  56  and an abrasion-resistant layer as a second sub-layer  58 , and then a second coating zone  16  is used to complete deposition of the abrasion-resistant layer through further sub-layers. 
         [0040]    In yet another implementation, the upstream injector  144  deposits a sub-layer of an abrasion-resistant layer, while the downstream injector  244  deposits a modified version of that sub-layer, tailored to provide a desired surface character, such as water-repelling or self-cleaning behavior, while preserving abrasion-resistance. 
         [0041]    In any of the implementations, coatings may be produced as blends instead of as a gradation of sub-layers, with the use of the arrangement of the injectors  144 ,  244  shown in  FIG. 5A . Additionally, more than one reagent may be supplied to each injector  144 ,  244 . Another set of one or more injectors may be associated with each plasma source  38 . These additional injectors may receive another reagent that is different from the reagents supplied to the injectors  144 ,  244 . Alternatively, the additional injectors may receive a reagent that is the same as that supplied to one or both injectors  144 ,  244 . 
         [0042]    As seen in  FIGS. 5A and 6A , the system  10  further includes a controller  66  that directs the upstream and downstream injectors  144 ,  244 , such that the injectors can operate independently of one another. The sources  62 ,  64  provide the coating reagents in vapor form and, in doing so, may utilize pressurized coating reagent reservoirs and mass flow controllers. The controller  66  regulates the flow of the coating reagent to the individual injectors via the mass flow controllers. 
         [0043]    As a person skilled in the art will readily appreciate, the above description is meant as an illustration of implementation of the principles of this invention. This description is not intended to limit the scope or application of this invention in that the invention is susceptible to modification, variation and change, without departing from spirit of this invention, as defined in the following claims.