Abstract:
A screen printing system includes a screen made of a porous material and an adjustable variable pressure squeegee having a squeegee blade. The squeegee blade has a first edge for contacting the screen and pushing an ink medium deposited on the screen through a print area of the screen. The squeegee blade has a second edge retained in a holder. The holder has a compliant member configured to distribute a downward force applied to a point on the compliant member along a length of the squeegee blade in order to maintain contact between the first edge and the screen along the length of the squeegee blade.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a division of U.S. Pat. No. 11/712150, filed Feb. 28, 2007, under the title “Means of attaining large screen print area with new squeegee design,” the disclosure of which is hereby incorporated by reference. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    This invention was made with U.S. Government support under Cooperative Agreement 70NANB4H3036 awarded by National Institute of Standards and Technology (NIST). The Government has certain rights in this invention. 
     
    
     FIELD OF THE INVENTION 
       [0003]    The invention relates generally to squeegees for screen printing. 
       BACKGROUND OF THE INVENTION 
       [0004]    Screen printing is a printing process used to create images on a wide variety of substrates, examples of which include glasses, ceramics, metals, and fabrics. Screen printing has three main components: screen, ink, and squeegee. The screen is made of a piece of porous, finely woven fabric stretched over a wood or aluminum frame. A stencil made of impermeable material is formed on or positioned on the screen. The stencil consists of a positive of the image to be printed on a substrate. To print the image on the substrate, the screen is placed on top of the substrate and a paste of ink is applied on the screen. Then, a squeegee is drawn across the screen, whereby the squeegee pushes the ink through open areas of the screen not covered by the stencil onto the substrate. Many factors such as composition, length, angle, pressure, and speed of the squeegee blade determine the quality of the image made by the squeegee. 
         [0005]      FIG. 1  shows a standard squeegee  100  including a squeegee blade  102  that is generally rectangular in shape. The squeegee  100  further includes a generally rectangular holder  104  to which an upper edge  106  of the squeegee blade  102  is attached. The lower edge  108  of the squeegee blade  102  is the edge that will make contact with the screen in order to force ink through the screen. An operator or machine grips the holder  104  and applies downward force to the squeegee  100  to enable contact between the squeegee blade  102  and the screen. The design of the holder  104  is such that this downward force is carried only a short distance from its initial focal point. If the squeegee  100  is made long enough to cover a large print area in one continuous stroke, there is the likelihood that there would not be enough pressure along the entire length of the squeegee blade  102  to form a quality screen print. For example, the resulting screen print may have unprinted or blotchy areas. 
         [0006]    From the foregoing, there is a desire to provide a squeegee for screen printing that distributes force applied at a point on the squeegee along the entire length of the squeegee. 
       SUMMARY OF THE INVENTION 
       [0007]    In one aspect, the invention relates to an adjustable variable pressure squeegee for screen printing which comprises a holder comprising a compliant member coupled to a retainer member and a squeegee blade having an edge coupled to the retainer member. 
         [0008]    In another aspect, the invention relates to a method of screen printing which comprises placing a screen having a stenciled image thereon on a substrate, depositing ink on the screen, contacting an edge of a squeegee blade coupled to a compliant member with the screen, applying a downward force to the squeegee blade through the compliant member while drawing the squeegee blade across the screen, whereby the ink is pushed through the screen onto the substrate. 
         [0009]    Other features and advantages of the invention will be apparent from the following description and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The accompanying drawings, described below, illustrate typical embodiments of the invention and are not to be considered limiting of the scope of the invention, for the invention may admit to other equally effective embodiments. The figures are not necessarily to scale, and certain features and certain view of the figures may be shown exaggerated in scale or in schematic in the interest of clarity and conciseness. 
           [0011]      FIG. 1  depicts a prior art squeegee for screen printing. 
           [0012]      FIG. 2  depicts an adjustable variable pressure squeegee for screen printing. 
           [0013]      FIG. 3  is a diagram illustrating a method of screen printing using the squeegee depicted in  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    The invention will now be described in detail with reference to a few preferred embodiments, as illustrated in the accompanying drawings. In describing the preferred embodiments, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to one skilled in the art that the invention may be practiced without some or all of these specific details. In other instances, well-known features and/or process steps have not been described in detail so as not to unnecessarily obscure the invention. In addition, like or identical reference numerals are used to identify common or similar elements. 
         [0015]      FIG. 2  depicts an adjustable variable pressure squeegee  200  for use in screen printing. The adjustable variable pressure squeegee  200  enables quality screen prints on large areas in one continuous stroke or fewer strokes than possible with standard squeegees. With the adjustable variable pressure squeegee  200 , quality screen prints can be achieved with screen print area up to approximately three-quarters of the width of the screen. Historically, the screen print area has been limited to one-third to one-half of the width of the screen in order to achieve quality screen prints. The ability to print quality images on larger areas with screen printing would be useful in many applications, such as in fabrication of solid fuel oxide cell devices. Currently, techniques such as deposition or spray coating surface of substrates are used in printing images on large areas. Screen printing is relatively less expensive than these techniques and can be used to create images on a wide variety of substrates. 
         [0016]    The adjustable variable pressure squeegee  200  includes a squeegee blade  202  and a holder  204 . The squeegee blade  202  can be any suitable squeegee blade for screen printing. The squeegee blade  202  has a generally rectangular shape. The top edge  206  of the squeegee blade  202  is adapted for retention in the holder  204 , while the bottom edge  208  of the squeegee blade  202  is adapted for contact with a screen (not shown) for screen printing and for pushing ink through the screen onto a suitable substrate (not shown). The bottom edge  208  of the squeegee blade  202  may have any desired profile, such as square, round, single-beveled, or double-beveled. The thickness of the squeegee blade  202  can be variable. The length (L) of the squeegee blade  202  can also be variable. The length of the squeegee blade  202  can be selected to achieve quality printing of large areas in one continuous stroke or fewer strokes than possible with standard squeegees. Typically, the length of the squeegee blade  202  will be less than the width of the screen used in screen printing. The squeegee blade  202  is made of a material that is flexible and resistant to the ink used in screen printing. For example, polyurethane or other flexible, high-density plastic may be used in making the squeegee blade  202 . 
         [0017]    The holder  204  includes a retainer member  210  and a compliant member  212 . The retainer member  210  extends along the length (L) of the squeegee blade  202 . The retainer member  210  includes a base member  214 . The bottom portion of the base member  214  includes retaining element(s) for coupling with the top edge  206  of the squeegee blade  202 . In this example, the retaining elements are an array of clips  216  which engage the top edge  206  of the squeegee blade  202  on opposites sides. In alternate examples, the retaining element may be a slot or groove or channel in the bottom of the base member  214  for receiving the top edge  206  of the squeegee blade  202 . The slot or groove or channel and the top edge  206  of the squeegee blade  202  may be shaped such that they interlock. Alternatively, the retaining element may be a surface depending from the base member  214  and to which the squeegee blade  202  can be attached via screws, clamps, or other suitable attachment devices. 
         [0018]    The compliant member  212  generally has a bow-shape. The compliant member  212  includes a pyramid or stack  216  of crossbars or arms  218 . In this example, there are three levels of crossbars  218  in the pyramid  216 . The pyramid  216  generally includes at least two levels of crossbars  218  and may have more than three levels of crossbars, depending on the length of the base member  214 . Typically, a crossbar  218  at an upper level in the pyramid  216  is coupled to two crossbars  218  at a lower level in the pyramid  216 . The crossbars  218  are coupled together via flexible connections  220 , which allow the compliant member  212  to have a compliant or spring-like response when a downward force is applied to the pyramid  216 . Typically, at least a portion of the crossbars  218  in the pyramid  216 , for example, those on the sides of the pyramid  216  or the upper portion of the pyramid  216 , have a curvilinear shape, which may also be a bow-shape. All the crossbars  218  in the pyramid  216  may also have a curvilinear shape. 
         [0019]    In general, the base  216   a  of the pyramid  216  is approximately as wide as the length of the base member  214 . In this example, the crossbars  218  at the base  216   a  of the pyramid  216  are coupled to the base member  214  and distributed along the length of the base member  214 . The manner in which the crossbars  218  are coupled to the base member  214  would depend on the material used in making the crossbars  218  and base member  214 . In general, the crossbars  218  at the base  216   a  of the pyramid  216  are not required to move relative to the base member  214  and can be attached to the base member  214  via any suitable method. As previously mentioned, the crossbars  218  in the pyramid  216  are coupled together by flexible connections  220 , which allow the ends of the crossbars  218  to pivot and/or slide where they connect to other crossbars  218 . The flexible connections  220  allow the pyramid  216  to act as a spring when a downward force is applied to the pyramid  216 , thereby maintaining contact between the squeegee blade  202  and the screen (not shown) across the length of the squeegee blade  202 . 
         [0020]    Typically, there is only one crossbar  218  at the top of the pyramid  216 . In this example, the top crossbar  218  includes a surface  222  for attachment to a handle  224 . Downward force can be applied to the pyramid  216  through the handle  224 . The handle  224  may be shaped for human use or machine use. In the latter case, for example, the handle  224  may be shaped for coupling to a carriage assembly of a screen printing machine. The handle  224  may be made of any suitable material, such as wood, plastic, or metal, and attached to the top crossbar  218   a  via any suitable attachment method. 
         [0021]      FIG. 3  is a diagram illustrating a method of screen printing using the adjustable variable pressure squeegee  200 . The method includes providing a screen assembly  300  having a screen  300   a,  typically made of a porous, finely woven fabric, such as nylon, stretched over a frame  300   b,  typically made of wood or aluminum. The method further includes producing a stencil  302  on the screen  300   a.  The stencil  302  is a positive of an image to be formed on a substrate. The stencil  302  may be produced on the screen  300   a  manually or by a photochemical process using an impermeable material, that is, a material impermeable to the screen printing ink. The method further includes placing the screen assembly  300  on a substrate  304 . The substrate can be any material that can receive ink and which is suitable for the intended application. Examples of substrate materials include glasses, ceramics, metals, and fabrics. 
         [0022]    The method further includes depositing ink  306  on the screen  300   a.  The ink would be selected based on the desired application of the ink-laid substrate. For example, to print a cathode layer of a solid fuel oxide cell device, an ink material suitable for forming a cathode layer would be used. The method further includes positioning the squeegee  200  on the screen  300   a.  A downward force is applied to the squeegee blade  202  through the compliant member  212  while drawing the squeegee blade  202  across the screen  300   a,  whereby the ink on the screen  300   a  is pushed through open areas of the screen onto the substrate  304 . The squeegee blade  202  may be drawn at an angle to the screen  300   a.  While drawing the squeegee blade  202 , the compliant member  212  acts as a spring and maintains contact between the squeegee blade  202  and the screen  300   a  across the entire length of the squeegee blade  202 . Also, the downward force applied at the top of the compliant member  212  is distributed along the length of the squeegee blade  202 . The method described above can be repeated as necessary to form a multi-layered device. 
         [0023]    The adjustable variable pressure squeegee described above enables ink to be laid uniformly on a relatively large print area through a screen. With the adjustable variable pressure squeegee described above, the screen print area can be larger than one-half the width of the screen. With the adjustable variable pressure squeegee described above, the screen print area can be up to three-quarters of the width of the screen. With the adjustable variable pressure squeegee described above, the screen print area can be in a range from one-third of the width of the screen to three-quarters of the width of the screen. With the adjustable variable pressure squeegee, the screen print area can be in a range from one-half of the width of the screen to three-quarters of the width of the screen. Screen printing is a relatively inexpensive method of applying ink to a substrate. With the adjustable variable pressure squeegee described above, large devices, such as solid fuel oxide cell devices, can be fabricated relatively inexpensively using screen printing. 
         [0024]    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.