Printing – Stenciling – Stencils
Reexamination Certificate
1999-11-20
2003-05-13
Evanisko, Leslie J. (Department: 2854)
Printing
Stenciling
Stencils
C101S128100, C101S128400, C038S102910
Reexamination Certificate
active
06561089
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improved method and apparatus for mounting screens on frames. More specifically, the present invention relates to improved shapes of border constructions comprising cupping features to engage frames and with improved methods of mounting screens on frames for screen printing.
2. Prior Art
The concept of putting border constructions, usually embodied as rigid or semi-rigid strips of narrow width, along the edges of screen fabric so as to better attach fabric to a frame was perhaps first described by M. Louis Courtial in French patent No. 909,651 of 1945. Although this patent addressed fabric used in furnishings, it could equally have been applied to screen fabric stretched on printing frames. Other notable innovations are described in U.S. Pat. No. 2,903,967 by H.S. Levin in 1959, U.S. Pat. No. 3,078,793 by D. Jaffa et al in 1963, U.S. Pat. No. 3,211,089 by Elmar Messerschmitt in 1965, U.S. Pat. Nos. 5,274,934 and 5,522,314 by this applicant, Eugene F. Newman, Jr., in 1994 and 1996, respectively, U.S. Pat. No. 5,379,691 by Alan and Kaino Hamu in 1995, U.S. Pat. No. 5,390,596 by Gregory Farr in 1995 and U.S. Pat. No. 5,443,003 by James Larson in 1995.
The border strips of the above inventions are described as having many shapes to engage many types of frames. Newman, Jr., Farr, and Larson describe border strips, sometimes referred to as retainers or constructions, which are shaped so as to hook or cup over edges of a frame. The Newman Jr. invention comprises means to fasten border strips to external stretchers to hook or cup the border strips in place on a rigid frame while tensioning the screen. The Newman, Jr. invention, however, suffers from the problem that without further instruction, it would seem that there is no way to mount fabric on a rigid frame to its maximum tension when the fabric is first stretched onto the frame without using spacers. Also, it would seem that it would not be possible to mount the screen at maximum tension with less than four spacers per screen. Screen printers often prefer high tension as it is generally thought that this contributes to a better print. Since the hooking or cupping of border strips over edges of a frame requires an outward movement followed by an inward movement, the final inward movement actually undoes or reduces the tension in the screen. In the initial outward movements to clear the edges of a frame, if a screen reaches maximum tension before tearing the fabric, the subsequent inward hooking movements would, of course, reduce screen tension below the maximum. By pulling the border strips outwardly, spacers could be inserted between the frame and the border strips within the cupping features of the border strips so as to expand and hold the screen on the frame at maximum tension. However, four spacers would be needed. The placement of only two spacers to achieve maximum tension, one for the width and one for the length of the frame, would cause the cupping features to extend outwardly beyond the edges of the frame. This would unhook the border strips. Therefore, four spacers, one for each edge of the frame, must be inserted to achieve maximum tension unless specific modifications are made to the border strips. The present invention teaches modifications to U.S. Pat. No. 5,274,934 for mounting screens at maximum tension without needing spacers. Furthermore, the present invention teaches that as the screen inevitably losses tension over time, the screen can be re-tensioned with only one spacer required per axis, or a total of two rather than four spacers per screen. The present invention is intended as an improvement to U.S. Pat. No. 5,274,934.
In U.S. Pat. No. 5,522,314, a method is taught for pre-stretching screen fabric on a stretcher device and attaching border strips to the stretched fabric in a pattern that bears a relationship to the shape and size of a frame. This method allows the fabric and border strips to be later re-stretched onto a prescribed frame of a certain shape and size so as to achieve a prescribed tension in the screen. This method is much faster than an earlier method as described in Farr in which fabric is stretched and attached to a frame, a very slow and labor-intensive process, before the border strips (retainers) are attached onto the fabric in a pattern. However, the Newman, Jr. invention suffers from the necessity of having to stretch the fabric twice, once in a pre-stretch to attach the border strips and again to mount the bordered screen onto the frame. If the border strips are already cupped or hooked onto edges of the frame when the border strips are attached to the stretched fabric, the need to later mount the bordered screen onto the frame is eliminated. What is missing in this earlier art is the concept of using actual screen frames as fixtures upon which to mount and position the border strips. The present invention seeks to achieve this objective.
Hamu et al describes a frame having border strips (anchors) that are inserted into channels embedded in the print-side of a frame. Hamu, like Farr, then stretches and attaches fabric to a second frame. The second frame is then placed onto the print-side of the first frame having the border strips and the stretched fabric is bonded to the border strips within the channels. In this way, the stretched fabric is transferred onto border strips already mounted in the frame. This invention suffers from the same slowness and labor-intensity of the Farr invention inasmuch as it requires that the fabric be first stretched and attached to a second frame.
On a rigid frame with no moving parts, the Hamu border strips are designed to only work in channels and must rely upon an outer wall in the channel. On such a frame there is no way to re-tension the screen and there is no way to dislodge the Hamu border strips without destroying the fabric. The Hamu invention continues on to describe a frame constructed with internal stretcher devices added to provide re-tensioning, but such a frame is very expensive to construct and the screen suffers from a continued inability to be removed from the frame without destroying the screen. The teachings of Hamu U.S. Pat. No. 5,379,691 and Newman, Jr. U.S. Pat. No. 5,522,314 can be combined, but the resulting combination would not advance the art so as the avoid the disadvantages of the Hamu frame. An objective of the present invention is to teach an improvement to the method of U.S. Pat. No. 5,522,314 that works with any simple rigid frame with edges that can be hooked or cupped over. This would be almost all existing rigid frames. The present method produces a screen that can be re-tensioned and can be removed from a frame having no moving parts without destroying the screen.
In 1997 this applicant began to make and sell screens having polypropylene border strips that are heat sealed onto the fabric. These border strips, however, differ substantially from the present invention and are inoperable with the frames of the present invention. These border strips have a unique shape as described in U.S. Pat. No. 5,957,048 by this applicant. They are designed to go inside a channel with the bonded fabric inserted into the channel on the bottom side of the border strips and wrapped around a leg portion of the border strip so as to become lodged and pressed against a wall on the inside of the channel. The bonding of the fabric is on the bottom side of the border strips facing away from the print-side of the screen and oriented upside down in relation to the printing surface of the screen. These border strips will only work in channels. Also, since the bonding surfaces of these border strips become hidden inside the channels when they are mounted on the frame, there is no way they can be bonded to the fabric when mounted on the frame. As will be seen, this is a difference that makes these screens unworkable in the present invention. Yet another consideration is that the bonding of the fabric to the border strips of U.S. Pat. No. 5,957,048 was not de
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