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United States Patent  [ii] Patent Number: 4,879,451
Gart  Date of Patent: Nov. 7,1989
U.S. Patent Nov. 7,1989 Sheet 1 of 2 4,879,451
 LASER CUT VIDEO DISPLAY TERMINAL FILTER SCREEN
 Inventor: Mark Gart, Novato, Calif.
 Assignee: Sun-Flex Company, Inc., Novato, Calif.
 Appl. No.: 219,537
 Filed: Jul. 14,1988
 Int. CI.4 B23K 26/18
 U.S. CI 219/121.69; 219/121.71
 Field of Search 219/121.6, 121.85, 121.68,
219/121.69, 121.7, 121.71, 54.78, 121.79, 121.82, 121.8; 358/252
 References Cited
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Materials Processing with Excimer Lasers, by Darcy Poulin, et al., presented at ICALEO '87 Nov. 11, 1987.
Primary Examiner—C. L. Albritton
Attorney, Agent, or Firm—Townsend & Townsend
A filter screen for a video display terminal is formed by ablating a sheet of plastic material with an excimer laser beam to produce desired apertures in the sheet spaced by webs of the sheet material. The filter screen formed in this manner can produce clean cut apertures in the sheet material and the retained material or webs between the apertures can be reduced to small dimensions because of the control of the laser beam. The sheet material can be coated for optical reflection control and for radiation control either before or after formation as the filter screen. The filter screen and the method for its formation is disclosed.
10 Claims, 2 Drawing Sheets
U.S. Patent Nov. 7,1989 Sheet 2 of 2 4,879,451
LASER CUT VIDEO DISPLAY TERMINAL FILTER SCREEN
FIELD OF THE INVENTION 5
This invention relates generally to the formation of a filter screen for a display surface as used in a video display terminal wherein the filter screen is used to reduce or eliminate radiation of electromagnetic and static electricity from within the terminal and to reduce 10 or eliminate the surface glare caused by reflection of background lighting near and around the face of the display surface. More particularly, the invention relates to a method and apparatus for the production of such filter screens from a continuous sheet of material by ^ laser beam cutting of the material.
BACKGROUND OF THE INVENTION
Video display terminals are now commonplace as a result of the rapid increase in the use of computers and 20 the like. The usual display surface of such a terminal is a cathode ray tube but other possible display surfaces include light emitting diodes (LED), liquid crystal diodes (LCD) or plasma display devices. Since the display surface of a terminal is usually relatively dark, it 25 serves to reflect glare from the surrounding environment, hence reading of the information on the display surface can be difficult. This glare problem was to a large extent overcome by the addition of a glare filter as described in U.S. Pat. No. 4,253,737 issued to Patrick 30 Brennan and Eric Thomson.
An equally and possibly more serious problem is the radiation of electromagnetic energy from the area of the display surface and the generation of static electrical field adjacent to the surface. Electromagnetic radiation 35 is more likely to occur with the use of a cathode ray tube as a display surface; however static electrical fields can exist with other forms of display surfaces. While a good deal of attention has been directed toward the suppression of electromagnetic radiation, it has not been 40 completely eliminated from unshielded cathode ray tubes and other display devices. Throughout this specification the display surface of the video display terminal will be most usually referred to as a cathode ray tube; however, it should be understood that the present in- 45 vention is applicable to any form of display surface where glare and radiation can occur.
Currently electromagnetic radiation from the face of a cathode ray tube is reduced by the use of a conductive filter screen placed in front of the tube. The filter screen 50 is connected electrically to the system ground of the cathode ray tube to conduct the radiation and any generated static electrical fields to the system ground and thus to reduce or eliminate the radiation from the face of the tube. These filter screens have also been formed 55 or coated with glare reducing materials to reduce the reflection of surrounding light from the face of the tube.
Filter screens of the prior art type have been formed from woven fine yarn, wires or fibers to produce a mesh fabric of those fibers. The fabric is then cut and framed 60 to the desired size and coated or impregnated with conductive and nonreflective materials as desired to form the filter screen for the face of a cathode ray tube. The fibers of the fabric should have a diameter in the 30 to 80 micron range, depending on whether the applica- 65 tion is for color or black and white terminals. The color terminals have a finer dot pattern or pixcel dot size on the face of the cathode ray tube and therefore require a
mesh designed for color displays and a more critical orientation of the fabric with respect to the face of the cathode ray tube. Typically the mesh needed for a display terminal filter screen is formed from fibers in the range of 0.001 inches (0.00254 centimeters) to 0.003 inches (0.00762 centimeters) diameter and a thread count of 75 to 300 fibers per inch. The limitation on the thread count of the mesh material is the limitation on the ability to form fibers of a smaller diameter, and the utility of the mesh for display terminal filter screens is the spacing between apertures in the mesh; that spacing being limited by the fiber size. The mesh formed by these fibers is typically then coated with a conductive coating and an anti-reflective color coating is then applied.
The production of mesh materials to the above specifications has been difficult and the cost of producing filter screens of such materials has been expensive. A method for forming suitable and desirable screen materials for the purpose above described at an increased rate and at a reduced cost has been needed.
SUMMARY OF THE PRESENT INVENTION
The present invention is directed to a method and apparatus for the formation of filter screen material that can be conductive for electromagnetic and static radiation and non-reflective for glare reduction. It is the object of the present invention to form the filter screen by ablating materials from a continuous film of material with the use of an excimer laser. Ablation, as used in this specification, is intended to mean the complete removal of material as by decomposition of the material through the introduction of laser energy in the ultraviolet range.
In a paper delivered at the ICALEO '87, Nov. 11. 1987 titled MATERIALS PROCESSING WITH EXCIMER LASERS by Darcy Poulin, John Reid and Thomas Znotins, the use of excimer lasers has been described. As stated in that paper, the use of lasers in materials processing applications has evolved to the point where high power lasers have been commonplace in many industries. Applications include the cutting, welding and drilling of metals, the scribing of ceramics, the cutting of plastics and composites, and the marking of a wide variety of materials and finished products. Common to many of these applications is a thermal mechanism whereby the laser radiation heats the materials so as to cause melting, evaporation or vaporization. Those thermal mechanisms limit the capability of many lasers in processing applications. In some cases, as in the cutting or drilling of plastics or polymers, unwanted flow of melted material can substantially degrade the edge quality or limit the minimum thickness which can be processed. It has been suggested that excimer lasers offer the potential for greatly extending the capabilities of laser based processing.
An advantage of excimer lasers for materials processing applications is their ultraviolet output. If particular, it has been demonstrated that the short pulses of UV radiation from an excimer laser can ablate organic materials very cleanly, leaving well defined edges and resulting in minimal damage to the surrounding unexposed material.
It is the object of the present invention to apply the capabilities of excimer lasers to the formation of a filter screen for use with a cathode ray tube as is employed in video display terminals.