Abstract:
An improved screen printing frame is presented that is cast from one piece of plastic material and possesses support ribs to confer additional strength to the structure. The frame is designed to be produced by a low-cost single-mold casting process and to permit the attachment of screens by adhesive means.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates to rectangular or square screen printing frames and in particular to an improvement in screen printing frame design and manufacture.  
         [0002]     Existing rectangular and square screen printing frames are intended to support the screen mesh while maintaining an even strain on the screen at all points when ink is forced through the screen. Uneven screen tension causes uneven printing of the desired image. Hence, a rigid and strong frame is required to obtain the best results, requiring strong and lightweight components.  
         [0003]     Typical screens are made out of wood or extruded aluminum hollow tubing side members with rectangular or square cross-sections. Each of these component materials has limitations. Welding the aluminum frames together is expensive and requires relatively thicker metal in the side members, thereby increasing the weight of the screen. Wooden frames must be cut and formed, then connected with fasteners and/or glue. Each frame requires a certain amount of manpower to manufacture from its component parts.  
         [0004]     A recurring problem with screen printing frames is that they need to be washed with water regularly between uses. The solid wooden frames can warp or crack after repeated washings. While aluminum does not absorb water, a pinhole in a frame weld will allow water into the hollow frame interior.  
         [0005]     Plastic frames are light-weight and low-cost, but a plastic hollow-tube frame is not strong enough to hold the tension on the silkscreen itself and still has to be cut and joined. A plastic screen with an open design and integral bracing members solves the weight and strength problem. Casting the frame in one piece is a low-cost solution.  
         [0006]     None of the prior art screen frame devices have this approach, a single-piece injection-mold or casting of rigid material. The present invention differs from the state-of-the-art devices by virtue of its low-cost manufacture, its ease of assembly with the silk screen itself, and its self-drying capability.  
       BRIEF SUMMARY OF THE INVENTION  
       [0007]     It is an object of this invention to provide a screen printing frame that is low-cost to manufacture.  
         [0008]     It is an object of this invention to provide a screen printing frame that is light-weight, strong and durable in use.  
         [0009]     It is a further object of this invention to provide a screen printing frame that is low-cost to manufacture.  
         [0010]     Further objects of this invention can be discerned by perusing the detailed description, drawings, specifications and claims of this application. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0011]     The construction and operation of the invention can be readily appreciated from inspection of the drawings that accompany this application, combined with the detailed specification to follow.  
         [0012]      FIG. 1  is a perspective drawing of the preferred embodiment of the invention.  
         [0013]      FIG. 2  is a cross-section diagram of the preferred embodiment of the invention.  
         [0014]      FIG. 3  is a cross-section of the side of the frame.  
         [0015]      FIG. 4  is side view of the invention.  
         [0016]      FIG. 5  is a perspective view of an alternative embodiment  
         [0017]      FIG. 6  is a bottom view of an alternative embodiment 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]     The invention is best described by referring to the preferred embodiment illustrated in the drawing in  FIG. 1 . Referring to  FIG. 1 , a one-piece injection-molded or cast screen printing frame (cast frame)  101  is a structure that resembles a picture frame, but the frame itself is not a solid piece of wood or a hollow metal tube. The cast frame  101  is a rectangular structure comprised of a single piece of cast material. The cast frame possesses a top edge  102 , a bottom edge  110 , an interior edge  111 , and a plurality of support ribs  103  which, in the preferred embodiment, are parallel to the top and bottom edges  102 , 110  of the cast frame  101  and perpendicular to the interior edge  111 . In other embodiments, these support ribs  103  could be cast such that they form an angle to the top and bottom edges  102 , 110 . In a particular alternate embodiment, illustrated in  FIG. 6 , the bottom edge  110  can possess bottom support ribs  115  while the sides  114  and top  102  are solid.  
         [0019]     A corner support rib  104  is placed in each corner  105  of the plastic frame  101  as shown in  FIG. 1, 2 , and  4 , and each corner support rib  104  is merged into the one-piece cast frame  101  and the support ribs  103 . The corner support ribs are perpendicular to the support ribs  103  and the top  102  and bottom edges  110 . They run from the apex of the corner  112  to the angle  113  of the interior edge  111 .  
         [0020]     The silk screen fabric  106  is fixedly attached to the top surface of the cast frame. The silk screen fabric  106  can be made from a number of different materials including polyester and metal.  
         [0021]     The cast frame  101  itself can be made of several materials, including nylon, styrene, polypropylene, or metal. Metals include aluminum. The preferred embodiment of this invention is a cast plastic frame  101  and a polyester silk screen fabric  106  with the silk screen fabric  106  attached to the frame  101  by means of adhesive.  
         [0022]     A further alternative embodiment of this invention, where the plastic used for the cast frame  101  will not hold the silk screen  106  adequately, the silk screen  106  being attached by means of adhesive, is to add an aluminum or steel liner  112  to the top edge  102  of the cast frame  101 , the liner fixedly attached to the top edge  102  of the cast frame  101  by mechanical means, by being cast into the top edge  102  when the cast frame  101  is made, or by means of adhesive, the silk screen fabric  106  then connected fixedly to the liner by means of adhesive.  
         [0023]     Another alternative embodiment of the cast frame  101  is where the frame sides  114 , inside and outside, are bowed in an outwards direction slightly to give the cast frame  101  added strength when the silk screen fabric  106  is stretched over it. The bowed shape confers strength and stability to the sides  114  when under the stress of the stretched silk screen fabric  106 .  
         [0024]     While the foregoing describes a preferred embodiment and several alternative embodiments, variation on this design and equivalent designs may be resorted to in the scope and spirit of the claimed invention.