Abstract:
A method of screen printing on 3D glass articles includes providing a 3D glass article having a first 3D surface with a first surface profile and a second 3D surface with a second surface profile, the first 3D surface and the second 3D surface being separated by a thickness of glass. The method includes providing a fixture having a 3D fixture surface with a fixture surface profile matching the second surface profile. The method includes providing a screen having a design, a squeegee, and an ink. The 3D glass article is supported on the fixture by mating the second 3D surface with the 3D fixture surface. The screen is positioned at a plane a distance above the first 3D surface. The ink is deposited on the screen. The squeegee is positioned at a selected orientation relative to the plane. The ink is pushed through the screen onto the first 3D surface by simultaneously contacting the squeegee with the screen, traversing the squeegee in a linear direction, maintaining the orientation of the squeegee relative to the plane, locally deflecting the screen from the plane to the first 3D surface, and locally conforming the screen to the first surface profile.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims benefit of U.S. Provisional Application No. 61/308,935 filed on 27 Feb. 2010. The disclosure of this provisional application is incorporated herein by reference. 
     
    
     FIELD 
       [0002]    The present invention relates generally to screen printing methods. More specifically, the present invention relates to a method of screen printing a design on a three-dimensional (3D) surface. 
       BACKGROUND 
       [0003]    Manufacturers of consumer electronics devices, such as laptops, tablets, and smart phones, are demanding 3D glass covers for their displays. These 3D glass covers would have printed designs on their inside surfaces. When the devices are assembled with the 3D glass covers, the printed designs would hide the innards of the devices while providing clear apertures for the displays to operate. The printed designs would be required to meet very precise specifications. For small display applications, such as smart phones, meeting these very precise specifications economically is challenging. 
         [0004]    Screen printing is a method that is widely used for printing designs on surfaces. In screen printing, a design is created on a fine mesh material called a screen. The design is created by masking off certain areas of the screen while leaving other areas open. The screen with the design is stretched on a frame. Then, a paste of ink is applied on the screen using a floodbar. A machine or operator draws a squeegee across the screen while applying a load to the squeegee. As the squeegee is drawn across the screen, ink is pushed through the open areas of the screen onto the surface. 
         [0005]    U.S. Pat. No. 6,698,345 issued to Cutcher (the &#39;345 patent) describes a method and an apparatus for screen printing on the inside surface of a curved substrate. The method includes mounting the curved substrate in a recess of a support member. The curved substrate is urged against the recess by vacuum. The inside surface of the curved substrate is brought into contact with a screen mounted on a screen mounting frame that is capable of conforming to the inside surface. The screen mounting frame has a right side, a left side, a front portion, and a rear portion. The right and left sides each have vertically movable center portions and end portions, where the center portions are each bounded by at least two hinges. The screen mounting frame is deflected by means of these movable and hinged portions. 
         [0006]    In the method of the &#39;345 patent, ink is applied to the screen while the screen is in a generally flat, horizontal position. The screen mounting frame is deflected, as described above, to substantially conform the screen to the inside surface of the curved substrate. Then, the ink is urged through the deflected screen with a squeegee. The squeegee is attached to a pendulum capable of pivotal movement. The length of the pendulum arm may be fixed or adjustable. The &#39;345 patent discloses that the method may be employed to print a pattern on the inside surface of a curved substrate where the radius of curvature is approximately 20-80 inches, measured from the pivotal mounting point of the pendulum. 
       SUMMARY 
       [0007]    In one aspect, the present invention relates to a method of screen printing on 3D glass articles. The method comprises providing a 3D glass article having a first 3D surface with a first surface profile and a second 3D surface with a second surface profile, the first 3D surface and the second 3D surface being separated by a thickness of glass. The method includes providing a fixture having a 3D fixture surface with a fixture surface profile matching the second surface profile. The method includes providing a screen having a design, a squeegee, and an ink. The method includes supporting the 3D glass article on the fixture by mating the second 3D surface with the 3D fixture surface. The method includes positioning the screen at a plane a distance above the first 3D surface. The method includes depositing the ink on the screen. The method includes positioning the squeegee at a selected orientation relative to the plane. The method includes pushing the ink through the screen onto the first 3D surface by simultaneously contacting the squeegee with the screen, traversing the squeegee in a linear direction, maintaining the orientation of the squeegee relative to the plane, locally deflecting the screen from the plane to the first 3D surface, and locally conforming the screen to the first surface profile. 
         [0008]    In one embodiment, the method further includes controlling traversing of the squeegee such that a change in deflection of the screen as the squeegee moves past a junction between the 3D glass article and the fixture is limited to 100 microns. 
         [0009]    In one embodiment, the step of pushing the ink is such that a design printed on the first 3D surface by pushing of the ink onto the first 3D surface has a registration resolution of +/−100 microns and a break edge resolution of +/−50 microns. 
         [0010]    In one embodiment, a difference in height between a top edge of the 3D glass article and a top surface of the fixture is in a range from 0 microns to 100 microns. 
         [0011]    In one embodiment, the step of supporting the 3D glass article includes clamping the second 3D surface to the 3D fixture surface by vacuum. 
         [0012]    In one embodiment, the step of supporting the 3D glass article includes applying an adhesive layer between the 3D surface and the 3D fixture surface. 
         [0013]    In one embodiment, the first 3D surface of the 3D glass article is concave. 
         [0014]    In one embodiment, the first 3D surface of the 3D glass article has a bottom surface, at least one side surface, and at least one corner surface joining the bottom surface to the at least one side surface. 
         [0015]    In one embodiment, an angle between the at least one side surface and the bottom surface is in a range from 90 degrees to 180 degrees measured from the bottom surface to the at least one side surface. 
         [0016]    In one embodiment, an angle between the at least one side surface and the bottom surface is in a range from 90 degrees to 135 degrees, measured from the bottom surface to the at least one side surface. 
         [0017]    In one embodiment, the at least one corner surface has a radius of curvature in a range from 1.5 mm to 10 mm. 
         [0018]    In one embodiment, the method further includes curing the ink pushed onto the first 3D surface. 
         [0019]    In one embodiment, the ink pushed onto the first 3D surface is a UV curable ink, and curing the ink includes exposing the ink to UV light. 
         [0020]    In one embodiment, the method further includes providing a further screen having a design and a further ink and repeating positioning the screen, depositing the ink, positioning the squeegee, and pushing the ink using the further screen and further ink instead of the initial screen and initial ink. 
         [0021]    In one method, the further ink is different from the initial ink. 
         [0022]    In one method, the initial ink or the further ink is provided based on one or more ink properties selected from the group consisting of reflectivity, transparency in the infrared range, transparency in the visible range, and color. 
         [0023]    In one embodiment, the color of the initial ink or further ink is selected from the group consisting of blue, grey, white, and red. 
         [0024]    In one embodiment, at least one of the screen and a blade of the squeegee has a contour that matches the first surface profile in at least one dimension. 
         [0025]    These and other aspects and embodiments of the present invention will be further described below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    The following is a description of the figures in the accompanying drawings. The figures are not necessarily to scale, and certain features and certain views of the figures may be shown exaggerated in scale or in schematic in the interest of clarity and conciseness. 
           [0027]      FIG. 1A  is a schematic of a screen having a design. 
           [0028]      FIG. 1B  is a schematic of another screen having a design. 
           [0029]      FIG. 2  is a schematic of a system for screen printing a design on a 3D surface. 
           [0030]      FIG. 3  is a perspective view of a 3D printable surface. 
           [0031]      FIG. 4  is a perspective view of another 3D printable surface. 
           [0032]      FIG. 5  is a perspective view of another 3D printable surface. 
           [0033]      FIG. 6  is a schematic of a contoured screen and contoured squeegee. 
           [0034]      FIG. 7  illustrates a step in screen printing of a design on a 3D surface. 
           [0035]      FIG. 8  illustrates another step in screen printing a design on a 3D surface. 
           [0036]      FIG. 9  illustrates another step in screen printing a design on a 3D surface. 
           [0037]      FIG. 10  shows examples of screen printed designs. 
           [0038]      FIG. 11  illustrates UV curing of a printed design. 
           [0039]      FIG. 12  illustrates a photochemistry mechanism of UV curable ink. 
       
    
    
     DETAILED DESCRIPTION 
       [0040]    In the following detailed description, numerous specific details may be set forth in order to provide a thorough understanding of embodiments of the invention. However, it will be clear to one skilled in the art when embodiments of the invention may be practiced without some or all of these specific details. In other instances, well-known features or processes may not be described in detail so as not to unnecessarily obscure the invention. In addition, like or identical reference numerals may be used to identify common or similar elements. 
         [0041]    A method is disclosed herein for screen printing a design on a printable surface of a 3D glass substrate or article. Here, a “printable surface” is the surface of the glass substrate on which the design will be printed. In one or more embodiments, the printable surface is generally concave. In one embodiment, the glass substrate has a simple-concave printable surface. In another embodiment, the glass substrate has a complex-concave printable surface. In one embodiment, the complex-concave printable surface is made of one or more side surfaces, a bottom surface, and one or more corner surfaces joining the one or more side surfaces to the bottom surface. The bottom surface could be a 2D surface or a 3D surface. In one embodiment, the one or more side surfaces are 2D surfaces. In another embodiment, the one or more side surfaces are 3D surfaces. The angle between a side surface and a bottom surface may range from 90 degrees (vertical) to 180 degrees (horizontal) in one embodiment and from 135 degrees to 180 degrees in another embodiment. The angles are measured from the bottom surface to the side surface. The corner surface is typically a curved surface and may have a radius of curvature ranging from 1.5 mm to 10 mm in one embodiment. In another embodiment, the complex-concave printable surface is contoured along two dimensions. 
         [0042]    One or more embodiments of the method described herein are suitable for screen printing on small printable surfaces, e.g., surfaces smaller than 10 inches by 10 inches, of 3D glass substrates. One or more embodiments of the method described herein can be used to apply a uniform layer of ink, typically 10 microns or less thick, on a printable surface of a 3D glass substrate with the appropriate opacity and edge definition. One or more embodiments of the method described herein can be used to print a design that meets a specification of aperture location/registration to ±100 microns, break edge (i.e., line) resolution to ±50 microns, and ink regression from the edge of less than 20 microns. 
         [0043]      FIG. 1A  is a top view of a screen  1  for screen printing a design on a printable surface of a glass substrate. Screen  1  is made of a fine mesh material. Suitable examples of mesh material for the screen include porous stainless steel, nylon, and polyester. Screen  1  has a design formed thereon. The design on the screen can be any desired design. For illustration purposes, the design shown in  FIG. 1A  is defined by a combination of the area  3  with open pores and areas  5 ,  5   a ,  5   b  with masked-off or blocked pores.  FIG. 1B  shows another screen  1   a  with a design defined by a combination of the area  6   a  with open pores and area  6   b  with masked-off or blocked pores. In a practical application, the design shown in  FIG. 1A  may be used to print a border on the printable surface. Then, the design shown in  FIG. 1B  may be used to print an insignia in the space within the border with an ink having specific characteristics, such as transparency at a specific range of wavelengths. Returning to  FIG. 1A , screen  1  will typically be slightly larger than the actual size of the 3D glass substrate to allow for flexing of the screen over the printable surface of the 3D glass substrate. The slightly larger screen will also allow for ink to be wrapped around the edge of the 3D glass substrate when the squeegee traverses across the screen to deposit ink onto the printable surface of the 3D glass substrate, as will be further described below. 
         [0044]      FIG. 2  shows a 3D glass substrate  7  mounted in a vacuum chuck  9 . The 3D glass substrate  7  may be made of any suitable glass material for the intended application. Ion-exchange, chemically-strengthened glass materials are useful for glass substrates used as glass covers of displays for consumer electronics devices. These glass materials typically have a high breaking strength. The printable surface  7   a  of the 3D glass substrate  7  has a simple-concave shape. Examples of printable surfaces having complex-concave shapes are shown in  FIGS. 3 ,  4 , and  5 . In  FIG. 3 , the printable surface  8   a  has a bottom surface  8   a   1 , a corner surface  8   a   2 , and a side surface  8   a   3 . The arrow  8   a   4  shows the direction in which a squeegee will travel relative to the printable surface  8   a  when a design is being printed on the printable surface  8   a . In  FIG. 4 , the printable surface  8   b  has a bottom surface  8   b   1 , side surfaces  8   b   2 ,  8   b   3 , and corner surfaces  8   b   4 ,  8   b   5 . The arrow  8   b   6  shows the direction in which a squeegee will travel relative to the printable surface  8   b  when a design is being printed on the printable surface  8   b . In  FIG. 5 , the printable surface  8   c  is contoured along a first dimension  8   c   1  and along a second dimension  8   c   2 . The arrow  8   c   3  shows the direction in which a squeegee will travel relative to the printable surface  8   c  when a design is being printed on the printable surface  8   c.    
         [0045]    Returning to  FIG. 2 , the 3D glass substrate  7  has a top 3D surface  7   a  and a bottom 3D surface  7   b . The 3D surfaces  7   a ,  7   b  are separated by a thickness of glass material  7   c . The top 3D surface  7   a  is the printable surface of the 3D glass substrate  7 . The vacuum chuck  9  has a 3D surface  10  defining a recess  10   a . The surface profile of the 3D surface  10  of the vacuum chuck  9  matches that of the bottom 3D surface  7   b  so that when the 3D glass substrate  7  is mounted in the vacuum chuck  9 , the 3D surface  10  mates with the bottom 3D surface  7   b . In this manner the 3D glass article is fully supported around its periphery by the vacuum chuck  9 . Cavity  11  and holes  12  are provided in the vacuum chuck  9  for applying vacuum to the bottom 3D surface  7   b . To apply the vacuum, the cavity  11  and holes  12  would need to be connected to a vacuum pump. An adhesive layer  14  may be applied between the bottom 3D surface  7   b  of the 3D glass substrate  7  and the 3D surface  10  of the vacuum chuck  9  to further secure the glass substrate  7  in the recess  10   a . The adhesive layer  14  may also provide a separation layer between the material of the vacuum chuck  9 , which may be metal, and the material of the 3D glass substrate  7 . The adhesive layer  14  is intended to be temporary and will be removed from the 3D glass substrate  7  after printing. 
         [0046]    Screen  1  is stretched on a horizontal frame  13 . The frame  13  is positioned at a plane P above the 3D glass substrate  7 . The position of the frame  13  on the plane P is adjusted such that the design on the screen  1  is precisely aligned with the printable surface  7   a  of the 3D glass substrate  7 . Fiducial on the screen  1  and vacuum chuck  9  may assist in aligning the design on the screen  1  with the printable surface  7   a . The distance D between the screen  1  and the top edge  7   d  of the 3D glass substrate  7  is one factor that may be selected to achieve high quality printing. In one embodiment, this distance is between 2 mm and 4 mm. In  FIG. 2 , the screen  1  is flat. In other embodiments, the screen may be contoured, i.e., have a 3D shape. The shape of the screen may be the same as the shape of the printable surface  7   a  in one embodiment, or the screen may be contoured to match the contour of the printable surface  7   a  in at least one dimension.  FIG. 6  shows an example of a contoured screen  16 , which may be used to print a design on a complex-concave printable surface such as shown at  8   b  in  FIG. 4 . 
         [0047]    In  FIG. 2 , a floodbar  15  and squeegee  17  are supported above the screen  1 . The floodbar  15  and squeegee  17  can linearly travel across the screen  1  by means of a suitable translation mechanism  18  (such as a linear slide) coupled to the floodbar  15  and squeegee  17 . The floodbar  15  and squeegee  17  may also each have a dedicated translation mechanism so that each can linearly travel across the screen  1  separately. The floodbar  15  and squeegee  17  are also separately extendable towards the screen  1  by means of translation mechanisms (such as piston assemblies)  20 ,  22 , respectively. The floodbar  15  can be extended to the screen  1  to spread ink over the screen  1 , and the squeegee  17  can be extended to the screen  1  to push ink through the screen  1 . The squeegee  17  may be vertical to the plane P as shown or may be at an angle to the plane P. Typically, an orientation of the squeegee  17  relative to the plane P is established and maintained during the printing process. The sides of the squeegee blade  17   a  of the squeegee  17  are flat in some embodiments. In other embodiments, the sides of the squeegee blade may be contoured to match the contour of the printable surface of a 3D glass substrate in one dimension.  FIG. 6 , for example, shows a contoured squeegee blade  24  suitable for use with the contoured screen  16 . 
         [0048]      FIGS. 7-9  show steps in screen printing a design on a 3D glass substrate. In  FIG. 7 , a roll of ink  30  is placed on the screen  1 . The ink  30  is placed at or near one end of the screen  1 . Typically, this end will not include the design to be printed on the printable surface  7   a . The floodbar  15  is lowered into close proximity with the screen  1 , while the squeegee  17  remains raised from the screen  1 . In  FIG. 8 , the floodbar  15  and squeegee  17  are translated across the screen  1 . As the floodbar  15  is translated across the screen  1 , it spreads a specific thickness of ink  30  over the portion of the screen  1  including the design. The thickness of the ink  30  spread across the screen  1  may be controlled by the gap between the floodbar  15  and the screen  1 . In  FIG. 9 , the floodbar  15  is raised from the screen  1 , and the squeegee  17  is lowered to the screen  1 . Before lowering the squeegee  17 , the squeegee  17  is placed at a desired orientation relative to the plane P. For example, the squeegee  17  may be vertical to the plane P as shown in  FIG. 9  or may be tilted relative to the plane P. A force is applied to the squeegee  17  to deflect the screen  1  locally, vertically, and downwardly from the plane P, as shown at  1   b . The force may be applied by the translation mechanism  22 . Under the conditions described above, the squeegee  17  and floodbar  15  are translated in a linear direction across the screen  1 . The floodbar  15  is raised from the screen  1  during this translation. However, the squeegee  17  continues to deflect the screen  1  locally, vertically, and downwardly as it moves in the linear direction across the screen  1 . The height of the squeegee  17  relative to the printable surface  7   a  is adjusted as the squeegee  17  moves in the linear direction so that the screen  1  is deflected to the printable surface  7   a . A controller having information about the contour of the printable surface  7   a  along the linear direction may be used to control the translation mechanism  22  and height of the squeegee  17 . The squeegee  17  may also be spring-mounted and naturally biased towards the printable surface so that it automatically traces the contour of the printable surface  7   a  as it travels in the linear direction. In some embodiments, the allowable deflection of the screen  1  during translation of the squeegee  17  may be in a range from 0.1 mm to 5.0 mm. 
         [0049]    While the squeegee  17  is translated across the screen  1  as explained above, the ink  30  is pumped or squeezed by capillary action onto the printable surface  7   a  of the 3D glass substrate  7  in a controlled and prescribed amount, i.e., the wet ink deposited is equal to the thickness of the screen. As the squeegee  17  moves over the screen  1 , the tension of the screen material and the print gap between the screen  1  and the printable surface  7   a  helps pull the screen up away from the printable surface  7   a  (this is called snap-off), leaving the ink on the printable surface  7   a . Means for adjusting the design on the screen  1  may be provided to correct any printed image distortion from screen deflection. The printing starts at a first area of the screen not including the design, continues through a middle area of the screen including the design, and ends at a second area of the screen not including the design. This is to ensure that the squeegee traverses the entire middle area including the design. The first area and second area are at opposite ends of the middle area. A second design can be printed on the printable surface  7   a  using the same method described above. For the second printing, a different screen with the second design, or the same screen with the second design, and a different ink, or the same ink, may be used. The inks used in printing may have be selected based on one or more properties selected from reflectivity, transparency in the infrared range, transparency in the visible range, and color. In one embodiment, the color may be selected from blue, grey, white, and red. After depositing ink on the printable surface  7   a , the ink is cured. The curing method would depend on the type of ink, as will be further discussed below. 
         [0050]    Referring to  FIG. 9 , in some embodiments, the junction between the top surface  9   a  of the vacuum chuck  9  and the top edge  7   d  of the 3D glass substrate  7  is made substantially flush so as to avoid abrupt changes in the deflection of the screen  1  when the squeegee moves past this junction. In one embodiment, abrupt changes in deflection by more than 100 microns when the squeegee moves past this junction is avoided. The distance d between the top edge  7   d  and the top surface  9   a  is in a range from 0 microns to 100 microns in one embodiment, from 10 microns to 80 microns in another embodiment, and from 20 microns to 50 microns in yet another embodiment. It is generally preferable that the distance between the top edge  7   d  and the top surface  9   a  is greater than 0 microns, with the top edge  7   d  being higher than the top surface  9   a . This is so that the screen  1  can be deflected to the correct depth to start printing on the printable surface  7   a  without the screen  1  touching the top surface  9   a  of the vacuum chuck  9 . Avoiding contact between the screen  1  and vacuum chuck  9  may improve the longevity of the screen. 
         [0051]      FIG. 10  shows a set of screen printed designs on 3D glass substrates using different screen printing parameters. The inner print edge on the first two prints  40 ,  41  do not meet desired specifications, while the inner print edge on the remaining three prints  42 ,  43 ,  44  meet desired specifications.  FIG. 10  demonstrates the need for all printing conditions, such as positioning, stroke speed, squeegee pressure, print gap, and proper ink, to be defined in order for repeatable quality prints to be made. 
         [0052]    Using the method above, the criteria in Table 1 were met for printing black ink area on a printable surface of a 3D glass substrate. 
         [0000]    
       
         
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
             
             
               
                   
                 Optical density 
                 greater than or equal to 3.0 
               
               
                   
                 Thickness of print 
                 not to exceed 10 microns ± 2 microns 
               
               
                   
                 Distance of print 
                 outer edge of print can exceed by 20 
               
               
                   
                 from outer edge of 
                 microns, but no recede is allowed 
               
               
                   
                 substrate 
                   
               
               
                   
                 Surface quality of 
                 no pinholes, no deflects (such as 
               
               
                   
                 print 
                 particulate matter, impact areas, 
               
               
                   
                   
                 chips, scratches), coloration and 
               
               
                   
                   
                 finish must be uniform over entire 
               
               
                   
                   
                 print area 
               
               
                   
                 Inner print edge 
                 must meet dimensional open aperture 
               
               
                   
                   
                 size specifications with less than 30 
               
               
                   
                   
                 microns ink leakage into clear 
               
               
                   
                   
                 aperture area 
               
               
                   
               
             
          
         
       
     
         [0053]    Using the method above, the criteria in Table 2 were met for printing white/red/blue ink area on a printable surface of a 3D glass substrate. 
         [0000]    
       
         
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
             
             
               
                   
                 Optical density 
                 greater than or equal to 2.0 
               
               
                   
                 Thickness of print 
                 10 microns ± 2 microns 
               
               
                   
                 Distance of outer 
                 outer edge of print cannot exceed 20 
               
               
                   
                 edge print area 
                 micron in ink leakage 
               
               
                   
                 Surface quality of 
                 no pinholes, no deflects (such as 
               
               
                   
                 print 
                 particulate matter, impact areas, 
               
               
                   
                   
                 chips, scratches), coloration and 
               
               
                   
                   
                 finish must be uniform over entire 
               
               
                   
                   
                 print area 
               
               
                   
               
             
          
         
       
     
         [0054]    Using the method above the criteria in Table 3 were met for printing smokey ink area on printable surfaces of 3D glass substrates. 
         [0000]    
       
         
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
             
             
               
                   
                 Optical density 
                 1.5 to 2.0 
               
               
                   
                 Thickness of print 
                 10 microns ± 2 microns 
               
               
                   
                 Distance of outer 
                 outer edge of print cannot exceed 20 
               
               
                   
                 edge print area 
                 micron in ink leakage 
               
               
                   
                 Surface quality in 
                 no pinholes, no defects (such as 
               
               
                   
                 print 
                 particulate matter, impact area, 
               
               
                   
                   
                 chips, scratches) 
               
               
                   
                 Scratch resistance 
                 must attain 4B rating or higher using 
               
               
                   
                   
                 ASTM D-3359 
               
               
                   
                 Light leakage 
                 no light leakage allowed 
               
               
                   
                 Environmental test 
                 must withstand 85° C./85% humidity for 
               
               
                   
                   
                 72 hours 
               
               
                   
                 Solvent reliability  
                 no hazing or ink removal with 10,000 
               
               
                   
                 test 
                 wipes 
               
               
                   
                 Lamination test 
                 no bubbles present 
               
               
                   
                 Adhesion tape test 
                 using model PA-2000 kit (for coatings 
               
               
                   
                   
                 between 2 and microns and cuts using 
               
               
                   
                   
                 6 teeth, 2 mm cutter) 
               
               
                   
                 Clear aperture 
                 using deionized water, angle needs to 
               
               
                   
                 contact angle 
                 be less than 10 degrees 
               
               
                   
               
             
          
         
       
     
         [0055]    The image design chosen for a particular pattern is influenced by the screen material and the diameter of the material. The emulsion and the thickness of the screen material factor into the amount of ink deposited onto the substrate surface. When screen printing on a 3D glass substrate, flexure is important to maintain ink thickness. This is another reason for the glass substrate being fully supported by the vacuum chuck. The tightness of the weave of the screen material and the bias angle at which the weave of the material is stretched for optimal tension affect the quality of the fine line edge of the substrate. In some embodiments, a screen mesh 355-34P 22.5° bias E11 emulsion 10-12 microns thick has been found to be satisfactory. 
         [0056]    Squeegees, though simple, are important factors in printing success. Hardness, shape, edge quality, and angle allow the ink to transfer through the screen in a proper manner onto the substrate surface. Squeegee selection has to address abrasion, cut, and solvent resistance, be free from additives for the ink and application chosen. Squeegee/ink combination have to be tested for swelling or softening, which demonstrates an incompatibility between the two components. In one or more embodiments, a squeegee made from polyurethane with a durometer of 70-75 Shore A (medium hardness) with an angle of 60° was chosen for printing. The blade of the squeegee needs to be rigid enough to transfer ink through the screen, but should also be soft enough to adapt to the contour of the screen and substrate. A 70 Shore A durometer blade has performed satisfactorily in terms of rigidity and softness. 
         [0057]    The ink used in printing a design on the printable surface will be selected based on the glass material and to achieve good adherence. The ink can be selected from thermally curable ink, UV (ultraviolet) curable ink, or ink comprised of a UV/solvent system. Thermally curable inks have been used for printing on glass. As will be explained below, when the material of the glass is an ion exchanged, chemically strengthened glass, a UV curable ink may offer advantages over a thermally curable ink. The ink used in printing may be optimized to maximize adhesive to the printable surface. For a UV curable ink, the ink is cured using a UV lamp radiation system. In mass manufacturing, a tunnel UV curing system may be used for high throughput. Some UV curable inks come with an ink base and a catalyst to be mixed prior to use. Other UV curable inks come with the catalyst already premixed into the ink base. Solvent can also be added to the UV curable ink to modulate the viscosity to an optimum level, but the addition of volatile component to the ink would negate some of the advantages of the UV curable ink and significantly limit shelf life of the mixture. 
         [0058]    By definition, thermally curable ink is cured by baking at high temperatures, generally between 80° C. and 180° C. The typical baking time is 30 to 60 minutes, which results in low throughput, a large number of Work-in-Progress (parts) in the production process, and significant floor space and capital investment dedicated to the thermal curing equipment. Furthermore, solvent and other volatile hazardous and flammable materials are vaporized from the ink base during the thermal cure, causing complications and additional expenses in environmental controls and effluent treatment. Solvents and other volatile materials also evaporate from the ink base at room temperature during the printing process, causing the ink to become increasingly viscous during printing and introduce variability into the process. Dried ink tends to clog screen openings, causing “pin hole” defects, and if hardened over time, become very difficult to clean with solvents. Most thermally curable inks can only be printed for 1 to 4 hours before becoming too viscous for the optimal printing process. 
         [0059]    UV curable inks, on the other hand, are cured in the presence of UV light. The ink curing process is a photochemical reaction, with UV-sensitive monomers cross-linking under UV radiation, resulting in hardening of the ink and solid adhesion on glass surface. Inks of different color have different absorption and transmittance characteristics. UV curable inks with lower absorption rate and higher transmittance require comparatively less energy to cure, and cure more easily. Black ink&#39;s absorption in the UV range is usually higher, and thus cures more slowly. For white inks, the high reflectivity also results in longer curing cycles. In general, UV wavelength absorption decreases with increasing wavelength of the ink color, i.e., black&gt;purple&gt;blue&gt;green&gt;yellow&gt;red. The UV curing process completes within a few seconds, occurs at relatively low temperatures, and is thus more efficient compared to the high temperature cure of the thermally curable inks. The volatile materials content in this class of ink is negligible without significant amount of hazardous and combustible solvents vaporized during the curing process. The lack of volatile compounds also results in very stable ink viscosity and fluidics over very long printing runs, ranging from 6 hours to multiple days. There is little dried ink flakes to block screen openings, and residual ink is easily washed off by screen cleaning solvents. When optimized for specific glass substrates, the UV curable ink performs similarly to or better than the thermally curable inks in the following aspects: optical density, cured ink layer thickness profile, adhesion reliability test (thermal cycle, thermal shock, high temperature, high humidity, salt vapor test), defect, and yield. 
         [0060]    After depositing UV curable ink on the glass substrate, the glass substrate is exposed to UV light to cure the ink. A suitable arrangement is shown in  FIG. 11 , where the glass substrate  7  with the printed design is mounted on a movable platform  19  positioned below a UV source  21 . A filter  23  may be disposed between the UV source and substrate to filter out wavelengths of the UV light not needed in curing the ink. Cooling air  26  may be circulated around the filter  23  and substrate  7  during the curing process.  FIG. 11  shows the photochemistry mechanism of UV curable ink. The UV curable ink before exposure to UV light is shown at  25 . R represents resins, and the dots represent photoinitiators. At  27 , the UV curable ink is exposed to UV light. The photoinitiators absorb UV light and are thereby raised to an excitation state. In this excited state, the photoinitiators photolyze or degrade into free radicals. These free radicals become the initiating species that cause rapid polymerization of the resins. At  29 , a chain reaction starts with the resins being attracted by radicals. At  31 , free radical polymerization and cross-linking of the resins occur. At  33 , the chain reaction is complete and a final solid structure is shown. 
         [0061]    While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.