Abstract:
A method for providing uniform flood exposure of LED light onto large area substrates is disclosed herein. The substrates can be up to several square meters in surface area. A method for providing uniform cooling of the LEDs within the apparatus is also disclosed.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
       [0001]    This application claims priority under 35 U.S.C. §119 (e) to, and hereby incorporates by reference, U.S. Provisional Application No. 61/394,888, filed 20 Oct. 2010. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    This invention relates to substrate printing and, in particular, this invention relates to a device for curing ink being printed on a substrate. 
         [0004]    2. Background 
         [0005]    LEDs offer a potentially more efficient means of curing ink deposited on a substrate during a printing operation. This enhanced efficiency includes lower power requirement and less heat produced during use. However, the geometries of illumination emitted from LEDs needs to be sufficiently uniform to ensure that the ink being printed upon the substrate is sufficiently cured, especially over substrates having large surface areas. To the best of the inventor&#39;s knowledge, there has been no device to provide such uniform illumination on such a substrate being cured during a printing operation. 
         [0006]    There is then a need for a device to provide such uniform illumination on a substrate being cured during a printing operation. There is a particular need for such a device which could provide specific levels of uniformity of illumination. 
       SUMMARY OF THE INVENTION 
       [0007]    This invention substantially meets the aforementioned needs of the industry by providing a device for illuminating a substrate with LEDs, the device having a first plurality of first LEDs positioned in a first LED array such that said substrate is illuminated substantially uniformly by said first LEDs; means for providing electrical current to said LEDs; and means for cooling said LEDs. 
         [0008]    Also present in such device may be a second plurality of second LEDs positioned in a second LED array such that said substrate is illuminated substantially uniformly by said second LEDs. 
         [0009]    The illumination emitted from the present first or second LED array may vary less than about 5%, 2.5%, or 1% over the substrate. 
         [0010]    Further provided is a method for uniformly illuminating a substrate, comprising emitting illumination toward said substrate from a first LED array, said first LED array including a first plurality of LEDs positioned such that illumination emitted from said first LED array varies less than about 5% over the surface of said substrate. 
         [0011]    The foregoing method may further include emitting illumination toward said substrate from a second array, said second LED array including a second plurality of LEDs position such that illumination emitted from said second LED array varies less than about 5% over the surface of said substrate. 
         [0012]    Yet further provided is a method of manufacturing a device for illuminating a substrate being printed upon, comprising positioning a first plurality of first LEDs such that said illumination emitted from said first LEDs varies less than about 5%. 
         [0013]    The foregoing method may also include positioning a second plurality of second LEDs such that said illumination emitted from said second LEDs varies less than about 5%. 
         [0014]    The foregoing method may further include positioning a heat sink in contacting relation to each first and second LED. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a perspective view of one embodiment of a lamp employing a dimensional LED array of this invention. 
           [0016]      FIG. 2  is a top view of the lamp of  FIG. 1 . 
           [0017]      FIG. 3  is bottom view of the lamp of  FIG. 1 . 
           [0018]      FIG. 4  is a bottom view of the lamp of  FIG. 1  with the reflective cover removed. 
           [0019]      FIG. 5  is an exploded view of the lamp of  FIG. 1 . 
           [0020]      FIG. 6  is an isometric view of a water cooled heat sink suitable for use in this invention with LEDs mounted thereto. 
           [0021]      FIG. 7  is a top view of the water cooled heat sink of  FIG. 6 . 
           [0022]      FIG. 8  is a plan view of one embodiment of a suitable heat sink, showing coolant ports thereof. 
           [0023]      FIG. 9  is an end view of the heat sink of  FIG. 6 . 
           [0024]      FIG. 10  an end view of the heat sink of  FIG. 6  with the plugs removed. 
           [0025]      FIG. 11  is an isometric view of a distribution manifold suitable for use in this invention. 
           [0026]      FIG. 12  is a top view of the distribution manifold of  FIG. 11 . 
       
    
    
       [0027]    It is understood that the above-described figures are only illustrative of the present invention and are not contemplated to limit the scope thereof. 
       DESCRIPTION  
       [0028]    While other embodiments of the invention are possible, the following description should be understood to be an explanation of the principles of this invention. Consequently, the following description does not limit this invention to the embodiments described, but merely teaches one aspect of this invention. To achieve uniform, flood type irradiation of a substrate, a lamp head is provided that contains a two dimensional, N×M array of LEDs. The LEDs emit light out the base of the lamp head  100  shown in  FIG. 1 .  FIG. 1  shows the lamp head  100 , the electrical port  102  for providing power to the LEDs and the coolant ports  104 ,  106  that provide liquid coolant maintain the desired low junction temperature of the LEDs.  FIG. 2  is a top view of the lamp head.  FIG. 3  is a bottom view of the lamp head. 
         [0029]    The bottom view of  FIG. 3  shows the side of the lamp head where the light is emitted from. The LEDs  108 ,  110  can be seen. The LEDs  108 ,  110  are positioned in a rectangular N×M array. The array is covered with a flat reflective cover  112  with holes  114  cut into it to allow the light from the LEDs  108 ,  110  to shine through. The array and reflective cover  112  are also covered with a transparent material such as glass or quartz which is not shown in  FIG. 3 . 
         [0030]      FIG. 4  shows the bottom view with the reflective cover  112  removed. In  FIG. 4  the water cooled heat sinks  116  can be seen. 
         [0031]      FIG. 5  shows an exploded view of the lamp head  100 .  FIG. 5  shows the transparent cover  118  and the reflective cover  112 . It shows the frame pieces  122 ,  124  that hold the transparent cover  118  onto the housing  120 .  FIG. 5  shows the coolant tee block  126  and the distribution manifolds  128 .  FIG. 5  shows coolant fittings  130 ,  132  and tubing  134 .  FIG. 5  shows stand-offs  136  that may be used to mount the cooling assembly  138  into the housing  120 . 
         [0032]      FIG. 6  shows an isometric view of a water cooled heat sink  116  with LEDs mounted to it.  FIG. 6  shows stand-offs  140  that are used to mount the reflective cover over the array of LEDs  108 ,  110 .  FIG. 7  shows a top view of the water cooled heat sink  116  and  FIG. 8  shows a bottom view of the water cooled heat sink  116 . 
         [0033]    In  FIG. 8  coolant ports  142 ,  144  can be seen where coolant flows between the distribution manifolds  128  and the water cooled heat sink  116 .  FIG. 8  also shows bolt holes  146  that are used to fasten the water cooled heat sink  116  to the distribution manifolds  128 . 
         [0034]      FIG. 9  shows an end view of the water cooled heat sink  116  with LEDs  108 ,  110  mounted to it. It shows water passages  148  that run the length of the water cooled heat sink  116 . The water passages are plugged  150  at each end to prevent coolant from flowing anywhere but through the coolant ports  142 ,  144 . 
         [0035]      FIG. 10  shows the coolant passages  148  with the plugs  150  removed. The coolant passages  148  may contain fin features  152  that increase the rate of heat transfer into the coolant. 
         [0036]      FIG. 11  is an isometric view of a distribution manifold  128 .  FIG. 11  shows the stand-offs  136  that are used to mount the housing  120  to the cooling assembly  138 .  FIG. 11  shows coolant ports  154 ,  156  that supply the manifold. The distribution manifold contains to two passages  158 ,  160  that can act as either the supply or return for the water cooled heat sinks. These passages  158 ,  160  run the length of the distribution manifold  128  and are plugged  162  at each end. 
         [0037]      FIG. 12  shows a top view of the distribution manifold  128 .  FIG. 13  shows a bottom view of the distribution manifold  128 .  FIG. 13  shows coolant ports  164 ,  166  that mate with the corresponding coolant ports  142 ,  144  in the water cooled heat sinks  116 .  FIG. 13  also shows o-rings  168  that seal the connection between the coolant ports  142 ,  144  and the coolant ports  164 ,  166 . 
         [0038]    The N×M array can be constructed such that the pitch in one direction is the same as the pitch in the other or the two pitches can be different where the pitch is the spacing between LEDs in the array. The array could be constructed such that N equals M where N and M are the number of LEDs in each direction. To achieve uniform irradiation of the substrate, e.g., variation intensity varying no more than about 5%, 2.5%, or 1%, the base of the lamp head must be oriented parallel to the substrate and positioned such that the distance between the base of the lamp head and the substrate is larger than the greatest of the LED pitches within the array. It is also possible to interlace two different LED arrays within one lamp such as is shown in  FIG. 3  where LED  108  makes up un array, and LED  110  makes up another array. For example, in  FIG. 3 , LEDs  108  are positioned in a 3×6 array and LEDs  110  are positioned in a 3×3 array. By way of illustration and not limitation, it has been determined that a 1.2 square meter lamp of this invention has been capable of uniformly illuminating a 1.0 square meter substrate. In this instance, a lamp having an area of positioned LEDs, which is 120% of the substrate surface area emitted such uniform illumination. 
         [0039]    To achieve uniform cooling of the LEDs liquid coolant can be supplied into either of the coolant ports  104 ,  106 . For an example, coolant port  104  is chosen as the supply. Then coolant port  106  will be the return. Coolant flows into coolant port  104  and then into the coolant tee block  126  where it is divided and half of the coolant flows into one distribution manifold  128  and the other half flows into the other distribution manifold  128 . The coolant is divided again inside of the distribution manifolds such that one sixth of the coolant flows into each water cooled heat sink  116 . The coolant is supplied to each water cooled heat sink  116  such that it flows anti parallel through the fined water passages  148 . This provides a uniform average heat sink temperature across the LEDs. 
         [0040]    Because numerous modifications of this invention may be made without departing from the spirit thereof, the scope of the invention is not to be limited to the embodiments illustrated and described. Rather, the scope of the invention is to be determined by the appended claims and their equivalents.