Abstract:
To date, it has been difficult to extrude precision films onto large substrates efficiently, thus, limiting the size of the substrate. One reason for the difficulty is natural sag or deflection in an extrusion head applying the film to the substrate. To counteract this deflection or sag, a crossbar has been designed that provides a substantially rigid platform to mount an extrusion head, which counteracts the deflection or sag, thus allowing for efficient extrusion of precision films over exceedingly large substrates.

Description:
TECHNICAL FIELD 
       [0001]    The invention relates generally to apparatus for the extrusion of viscous liquid onto horizontal surfaces and, more particularly, such apparatus for the application of thin film coatings to glass and similar substrate materials. 
       BACKGROUND 
       [0002]    The use of extrusion coating apparatus in the application of liquid films to glass and similar substrates is becoming increasingly common as thin-film displays (TFDs), including Liquid Crystal Displays (LCDs) and Thin Film Transistors (TFTs), rise in commercial popularity as video screens and television monitors. Such extrusion coating apparatus typically employs an extrusion head or die that is moved relative to the substrate to coat the substrate with the film material in a uniform and precisely controlled fashion. 
         [0003]    In the production of such TFDs, as well as semiconductors and other devices that use precision film applications, there has been a limitation on the overall size of the substrates because vertical deflection or sag in the extrusion head or die introduces variation and thus affects the ability to provide a generally uniform coating over a large substrate. Generally, this sag or deflection occurs because the extrusion head or die is supported on a beam that must be of relatively long length to span a large substrate. The beam cannot be supported along its length because to do so would inhibit the ability of the beam to move relative to the substrate. 
         [0004]    To date, there has not been an adequate system for precisely and controllably suspending an extrusion die or head over a substrate to provide a generally uniform coating of an extrudate. Some examples of suspension arrangements are found U.S. Pat. Nos. 3,703,880; 5,693,143; 6,942,753; and 7,169,229, and U.S. Patent Application Publication No. 3005/0103267. However, none of these applications adequately addresses the need for reduced sag or deflection in a suspension arrangement for precision extrusion applications. 
       SUMMARY 
       [0005]    A preferred embodiment of the present invention, accordingly, provides an apparatus for coating a substrate. The apparatus comprises a chuck that secures the substrate in a generally horizontal position, a shuttle secured to the crossbar adapted for relative movement between the substrate and the extrusion die, a reservoir containing a supply of the extrudate, a pump in fluid communication with the reservoir and the extrusion die that is adapted to apply work to the extrudate to move the extrudate from the reservoir to the extrusion die, a crossbar, and an extrusion die having a first and an opposite second end, the extrusion die having a length between the first and the second ends, where the extrusion die has a first predetermined deflection along at least a portion of its length and is adapted to extrude onto the substrate an extrudate at least along a portion of its length. The crossbar further includes a second predetermined deflection along at least a portion of its length, a base member having a length, a width, a first side, and an opposite second side that is secured to the extrusion die along at least a portion of its length and suspends the extrusion die above the substrate, a vertical member that extends generally perpendicular from the second side of the base member forming a T-shape, and a generally rectangular cap having a length and having a width that is less than the width of the base member, the cap extending from the vertical member that can be dimensioned to provide sufficient rigidity to the base member and vertical member in a generally horizontal direction to counteract the first predetermined deflection such that a combined predetermined deflection of the crossbar and extrusion die when secured to one another is less than the first and second predetermined deflection. 
         [0006]    In another preferred embodiment of the present invention the length of the cap is about the same length as the base member. 
         [0007]    In another preferred embodiment of the present invention, the crossbar further comprises a pair of flanges that extend generally perpendicular from the base member and perpendicular from the vertical member. 
         [0008]    In another preferred embodiment of the present invention, the vertical member further comprises a plurality of passages that extend therethrough. 
         [0009]    Another preferred embodiment of the present invention also provides an apparatus for coating a substrate. The apparatus comprises a chuck that secures the substrate in a generally horizontal position, a crossbar, a shuttle secured to the crossbar adapted for relative movement between the substrate and the extrusion die, a reservoir containing a supply of the extrudate, a pump in fluid communication with the reservoir and the extrusion die that is adapted to apply work to the extrudate to move the extrudate from the reservoir to the extrusion die, and an extrusion die having a first and an opposite second end and having a length between the first and the second ends. The extrusion die has a first predetermined deflection along at least a portion of its length and is adapted to extrude onto the substrate an extrudate along an extrusion length measuring greater than about 400 mm. The crossbar includes a second predetermined deflection along at least a portion of its length, a base member having a length, a width, a first side, and an opposite second side that is secured to the extrusion die along at least a portion of its length and suspending the extrusion die above the substrate, a vertical member that extends generally perpendicular from the second side of the base member forming a T-shape, and a generally rectangular cap having a length and having a width that is less than the width of the base member that extends from the vertical member. Additionally, the base, the vertical member, the cap, and the extrusion die together can be dimensioned to have moment of inertia to have a combined deflection of less than the first and second predetermined deflections. 
         [0010]    In another preferred embodiment of the present invention, the combined deflection is less than about 10 microns. 
         [0011]    Another preferred embodiment of the present invention, a crossbar that is secured to a shuttle in extrusion apparatus for supporting an extrusion die having a first predetermined deflection is provided. The crossbar has a second predetermined deflection along at least a portion of its length. A base member is included having a length, a width, a first side, and an opposite second side, the base member being secured to the extrusion die along at least a portion of its length and suspending the extrusion die above the substrate. A vertical member is included that extends generally perpendicular from the second side of the base member forming a T-shape. Also, a generally rectangular cap is included having a length and having a width that is less than the width of the base member. The cap extends from the vertical member and is dimensioned to provide sufficient rigidity to the base member and vertical member in a generally horizontal direction to counteract the first predetermined deflection such that a combined predetermined deflection of the crossbar and extrusion die when secured to one another is less than the first and second predetermined deflections. 
         [0012]    In accordance with a preferred embodiment of the present invention, the length of the cap is about the same length as the base member. 
         [0013]    In accordance with a preferred embodiment of the present invention, the crossbar further comprises a pair of flanges that extend generally perpendicular from the base member and perpendicular from the vertical member. 
         [0014]    In accordance with a preferred embodiment of the present invention, the vertical member further comprises a plurality of passages that extend therethrough. 
         [0015]    A preferred embodiment of the present invention, accordingly, provides an apparatus for coating a substrate. A chuck secures the substrate in a generally horizontal position in the apparatus. An extrusion die having a first and an opposite second end with a length between the first and the second ends and a first predetermined deflection along at least a portion of its length is adapted to extrude onto the substrate an extrudate along an extrusion length measuring greater than about 400 mm. Supporting the extrusion die is a crossbar having a second predetermined length along at least a portion of its length, a base, a vertical member, and a cap. The base member has a length, a width, a first side, and an opposite second side, and the base member is secured to the extrusion die along at least a portion of its length, suspending the extrusion die above the substrate. The vertical member extends generally perpendicular from the second side of the base member forming a T-shape. A generally rectangular cap having a length and having a width that is less than the width of the base member extends from the vertical member. The base, the vertical member, and the cap together are dimensioned to have moment of inertia to have a combined deflection of crossbar and extrusion die that is less than the first and second predetermined deflections. A shuttle is secured to the crossbar adapted for relative movement between the substrate and the extrusion die, and a reservoir containing a supply of the extrudate is provided. A pump is in fluid communication with the reservoir and the extrusion die, where the pump is adapted to apply work to the extrudate to move the extrudate from the reservoir to the extrusion die. 
         [0016]    In accordance with a preferred embodiment of the present invention, the combined deflection is less than about 10 microns. 
         [0017]    The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
           [0019]      FIG. 1  is a perspective view of an apparatus for coating in accordance with a preferred embodiment of the present invention; 
           [0020]      FIG. 2  is an exemplary block diagram of the pumping system in accordance with a preferred embodiment of the present invention; 
           [0021]      FIG. 3  is an exploded isometric view of the crossbar and extrusion die in accordance with a preferred embodiment of the present invention; 
           [0022]      FIG. 4  is a front elevation view of the crossbar and extrusion die of  FIG. 3 ; 
           [0023]      FIG. 5  is a cross-sectional view of the crossbar and extrusion die along the section line A-A of  FIG. 4 ; and 
           [0024]      FIG. 6  is a breakout view of the cap and vertical member of the crossbar taken along the section line B-B of  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    Refer now to the drawings wherein depicted elements are, for the sake of clarity, not necessarily shown to scale and wherein like or similar elements are designated by the same reference numeral through the several views. 
         [0026]    Referring to  FIG. 1  of the drawings, the reference numeral  100  generally depicts the coating apparatus  100  according to a preferred embodiment of the present invention. Coating apparatus  100  includes a base  102  with a rail system  104  mounted thereon. Base  102  forms a foundation along which the shuttle or transport system  106  travels for cleaning and priming of the extrusion head or die  118  (typically occurring at a utility station  112  at the periphery of base  102 ), and for conducting the coating operations of the substrate  108  (typically by traversing the die  118  over the substrate in a selected pattern). Preferably, the extrusion head or die  118  and a gauging member (not shown) are mounted to a bridge  110 , which extends generally transversely between the rails of the rail system  104 . The extrusion head  118  is preferably a linear extrusion head attached to fluid manifold preferably containing a bead forming orifice substantially as described in U.S. Pat. No. 4,696,885, titled “METHOD OF FORMING A LARGE SURFACE AREA INTEGRATED CIRCUIT.” 
         [0027]    Also, a chuck  114  is secured to the base  102  through chuck holders  116 . Chuck  114  provides support to and securely and precisely positions substrate  108  relative to base  102  and the remainder of the coating apparatus. Preferably, the chuck  114  employs a vacuum to secure or “hold down” the substrate  108  in a generally fixed horizontal position relative to the shuttle  106  during operation of the coating apparatus  100 . In a preferred embodiment of this invention, chuck holder  116  comprises a structure which will preferably support the chuck  114  principally at a plurality of points around the periphery of the chuck  114 . Correspondingly, the chuck  114  is formed (typically ground) so that it is as flat as possible as supported. Alternatively, the chuck  114  can be formed so as to selectively deform to compensate for deformation in the shuttle  106  and head  118 . 
         [0028]    In particular, a gauging member (not shown) can be implemented on the shuttle  106  to monitor and assist in “fine tuning” the gap between the dispenser or extrusion head  118  and the substrate  108  in real time during the coating operation. A height sensor as part of the gauging member (not shown) is appropriately zeroed while the head  118  is at the correct height relative to the substrate, and a correction signal is subsequently generated whenever the height deviates above or below the preset level. The height sensor typically comprises one or more non-contact laser sensors that measure the relative height above the substrate  108 , which constitutes an indirect feedback control. Alternatively, a physically contacting probe or rod can be used to supply direct feedback control. 
         [0029]    These feedback controls are used by a control system to adjust the height (“gap”) of the extrusion head  118  relative to the bridge  110 . The control system for the gauging member generally comprises computer hardware and software that convert the feedback signal into information suitable to drive the position motor(s) to move and restore the extrusion head  118  to the proper height. This process of height self-correction typically begins at the start of the coating process and continues throughout the coating process. However, it is preferable to make this adjustment only at the start of the coating process (to compensate for various thicknesses of different substrates), and to not make adjustments during the coating. 
         [0030]    In operation, the extrusion head  118  moves above the substrate  108 , which is supported by chuck  114 . During motion of the extrusion head  118 , its height can be adjusted by the gauging member and its associated control system (not shown). The travel of the shuttle  106  preferably will be at least long enough to permit the extrusion head  118  to traverse and coat the largest substrate to be placed on the apparatus  100  and to clear or traverse beyond the substrate  108  by a sufficient distance to permit the substrate  108  to be removed by external personnel or machinery. This range of travel may be reduced by providing for some movement of the substrate  108  during coating, but at some cost to precision and accuracy. The travel of the shuttle  106  preferably is long enough so that in addition to clearing the substrate  108 , the shuttle  106  will be able to gain access to utility station  112 . 
         [0031]    To reduce the system footprint and to improve coating performance, particularly on the leading edge of a substrate  108  (starting point for the coating operation), substrate  108  is located as close as possible to utility station  112 . Preferably, shuttle  106  carries the bridge  110  and the extrusion head  118  to the utility station  112  for head cleaning and for priming of the bead either before or during the loading of the substrate  108 . The shuttle  106  then carries the bridge  110  and the extrusion head  118  to the near edge of the substrate  108  (the side closest to the station  112 ) so that coating of the substrate  108  may begin. Extrusion is accomplished by moving an extrudate (such as color filter resist and photoresist) with a pump (not shown) from a reservoir (not shown) to the extrusion die  118 . The shuttle  106  then carries the extrusion head  118  across the substrate at a carefully monitored and predetermined rate, preferably under computer control, while the extrusion head  118  dispenses coating material at a controlled rate onto the substrate  108 . Once the shuttle  106  has traveled to a point where the extrusion head  118  has coated the entire substrate  108  or that portion to be coated, extrudate flow to the extrusion head  118  is discontinued. 
         [0032]    It should also be appreciated that there is no limitation that the present invention coat the entire surface of the substrate  108 . For example, the motion of the head  118  may be stopped at some point prior to fully coating a substrate  108  where only a portion of the substrate  108  is desired to be coated. 
         [0033]    In order to extrude the extrudate through the die  118 , pumping system  200  depicted in  FIG. 2  is employed. Preferably, pumping system  200  employs components mounted on bridge  110  (namely, extrusion head  118 , valves  210 , an optional intermediate reservoir  212 , and pump  214 ) and a pumping station  202  (which is located in the utility station  112 ). Pumping station  202  comprises a source reservoir  204 , a drain reservoir  206 , and pumps  208 . Pumps  208  perform mechanical work on the extrudate in the pumping system  200  to move the source extrudate from the source reservoir  204  to the bridge  110  and to move excess or drain extrudate from bridge  110  to the drain reservoir  206 . When extrudate is moved from the source reservoir  204 , the extrudate is optionally moved to an intermediate reservoir for temporary storage. From the intermediate reservoir  212 , pump  214  performs mechanical work on the extrudate to move the extrudate from the intermediate reservoir  212  to the extrusion die  118 . Excess or drain extrudate can then be moved directly from the extrusion head  118  to the pumping station  202 . Additionally, along the entire system  200 , a number of values  210  can be used to control the flow of extrudate. 
         [0034]    Included with the bridge  110 , which cannot readily be seen in  FIG. 1 , is a crossbar  300 . Crossbar  300  and extrusion head  118  can be seen in greater detail in  FIGS. 3 through 6 . Preferably, the crossbar  300  is secured to the shuttle  106  and suspended in a position that is generally parallel to the substrate. The crossbar  300  provides structural support for the extrusion head  118  as it pass over the substrates. This particular crossbar typically is used for substrates having a width greater than 400 mm. 
         [0035]    In particular, the crossbar  300  according to a preferred embodiment of the present invention is designed to reduce the sag or deflection in the extrusion head  118 . Generally, the extrusion head  118  has been (and still is) suspended from either end. Because of gravitational effects and because the dispensing head  118  is not an infinitely rigid material, the dispensing head  118  sags or has vertical deflection. This deflection typically reaches a maximum at the center of the suspension, which can be as much as 100 microns depending on the overall length of the dispensing head. Such a deviation can adversely affect the ability to provide a generally uniform coat (typically less than 1 micron difference in height across the entire substrate). To accomplish this, the crossbar  300  is comprised of several components: a base or base member  302 , a vertical member  304 , a cap  306 , and flanges  310 . For example, these pieces can all be formed from or machined from a block of either AISI 304 stainless steel or AA  606 ′-T6 aluminum. 
         [0036]    The two most apparent and easily viewable components are the base  302  and the vertical member  304 . The base  302  is a generally rectangular member and is typically suspended over (generally parallel to) the substrate  108 , with its flat surface parallel to the substrate. As can be seen in  FIGS. 3 through 6 , the extrusion head or die  118  is bolted to the base member  302 . Extending perpendicular from approximately the center of the base  302  (opposite the extrusion head  118 ) is the vertical member  304 . These two members  302  and  304  together form an inverted T-shaped beam. 
         [0037]    The combination of the base  302  and vertical member  304 , though, generally do not provide sufficient rigidity without being overly large or heavy. As the base  302  and vertical member  304  are suspended over the substrate  108 , the bottom of the base  302  (side facing the extrusion head  118 ) and the extrusion head  118  are in tension while the upper end of the vertical member  304  is in compression. Thus, to provide additional rigidity to the base  302  and vertical member  304 , a generally rectangular cap  306  extends from the upper end of the vertical member  304 . This cap  304  provides rigidity in the horizontal direction, directly counteracting the compression occurring in the upper end of the vertical member  304 . This additional rigidity in the horizontal direction, in turn, counteracts the natural sag or deflection in the extrusion head  118 , allowing for there to be a relatively small and acceptable deflection across the length of the extrusion head  118 . 
         [0038]    The cap  306  is narrower in its minor dimension than base  302 . In the case where the base  302  and the cap  306  have roughly equivalent lengths and widths, the crossbar  300  takes the form of an I-beam. For applications such as extrusion for LCDs, semiconductors, and other thin film applications, the conventional I-beam cross section has excess weight in the upper region that can reintroduce sag or deflection, despite the increased rigidity of the shape. Thus, one feature of a preferred embodiment of the present invention is to maintain a width “w” of the cap  306  that is less than the width “W” of the base  302 . Additionally, under some circumstances, the cap  306  can have a length “l” that is less than the length “L” of either the base  302  and/or vertical member  304 . Generally, the cross-section of the combined base  302 , vertical member  304  and cap  306  is selected or dimensioned to have a maximum deflection of less than about 10 microns along the extrusion length and is specifically adjusted for each given length and for each cross-section of the extrusion head (such as extrusion head  118 ) for which the base  302  is secured. 
         [0039]    An exemplary application of a crossbar  300  according to a preferred embodiment of the present invention in conjunction with an extrusion head  118  having an extrusion length (the length over which the extrusion head  118  is able to apply a film of an extrudate) of greater than about 400 mm (or about 16 inches) is as follows. Assuming a crossbar made of AISI 304 stainless steel having a density of about 0.254 lbs/in 3 , a length of about 95 inches, and a weight of about 691.3 lbs (which includes the extrusion head  118 ), the moment of inertia (which includes the extrusion head  118 ) is chosen to be 1049 in 4  by varying the heights and widths of the base  302 , vertical member  304 , and cap  306 . Preferably, for this example, the width of the base member  302  (D 1 ), the height of the base member  302  (D 2 ), the radii of curvature of the joints between the vertical member  304  and base member  302  (D 3 ), the radii of curvature of the joints between the vertical member  304  and the cap  306  (D 4 ), the width of the vertical member  304  (D 5 ), the width of the cap  306  (D 6 ), the height of the cap (D 7 ) and the overall height (D 8 ) are chosen to be about 7 inches, about 0.480 inches, about 0.250 inches, about 0.250 inches, about 1 inch, about 2.5 inches, and about 18 inches, respectively. Individually, the deflection of the crossbar  300  (by itself and under its own weight) is about 12.4 microns, while the deflection of the extrusion head  118  is about 100 microns. However, when combined the overall deflection is markedly diminished to about 6.44372 microns (in a “worst case scenario”). The overall maximum deflection of the crossbar  300  and extrusion head  118  would be typically be about 60% of the “worst case” deflection or about 3.86623 microns. 
         [0040]    In addition to the base  302 , vertical member  304 , and cap  306 , several other features are provided on the crossbar  300 . As can be seen in  FIGS. 3 through 6 , there are a pair of flanges  308  near each end of crossbar  300 . These flanges  308 , too, are generally rectangular and extend perpendicular from the base  302  and vertical member  304 . Additionally, through the flanges  308  and the vertical member  302 , there are also a number of portals  310 . These portals  310  allow wiring, pneumatic lines, and hydraulic lines to be passed through. 
         [0041]    Having thus described the present invention by reference to certain of its preferred embodiments, it is noted that the embodiments disclosed are illustrative rather than limiting in nature and that a wide range of variations, modifications, changes, and substitutions are contemplated in the foregoing disclosure and, in some instances, some features of the present invention may be employed without a corresponding use of the other features. Many such variations and modifications may be considered obvious and desirable by those skilled in the art based upon a review of the foregoing description of preferred embodiments. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.