Screen for Cathode Ray Tubes

This invention relates to a microwoven screen and will have special application to a screen which reduces glare and which suppresses static electricity and electromagnetic radiation output of a video display terminal.

Recently, there has been a rapid increase in the use of video display terminals (VDT's) and the like. It has been shown that the surface of the cathode ray tube (CRT) in a VDT reflects glare from the surrounding environment which, in many instances, causes the user to experience eye fatigue and headache. A framed mesh screen of black filaments disclosed in U.S. Pat. No. 4,253,737 has been introduced to overcome the glare problems.

A potentially more serious problem with VDT's is their tendency to generate an electrostatic field adjacent to the CRT. This problem has recently been classified as a potential health hazard. In fact, many facial rash cases among VDT operators have been reported. This is attributable to the operator becoming electrically charged in the electrostatic field of the CRT so that dust and other pollutants, such as bacteria or other irritants, of opposite charge are attracted to the operator. The dust carrying opposite charge may also be attracted to the surface of the CRT and pollute the VDT screen as a result of the induced static charge.

The risk of non-ionizing radiation in VDT screens has been debated for several years. It was reported that current levels of electromagnetic radiation which emanate from the CRT are well below the level at which the operator may become injured. However, such radiation does exist and older VDT's and those in a worsened condition most likely will produce radiation at levels which exceed the FDA standard allowed for television sets. At present, low frequency radiation is eliminated by a stainless steel (or other metal) mesh screen sandwiched between two rigid panels placed in front of the VDT screen. Due to the space between the screens and the display tubes, such devices produce Newton rings and Morie distortions. Mesh screens designed to eliminate such distortions are shown in U.S. Pat. Nos. 4,253,737 and 4,468,702.

As disclosed above, the screen of U.S. Pat. No. 4,253,737 was introduced to overcome the glare problems. The nylon screen disclosed in U.S. Pat. No. 4,468,702 is formed of a plurality of nylon yarns, some of which are electrically conductive. However, the method of making this screen is quite complicated and produces a screen where only a fraction of the warp and weft fibers of the screen are electrically conductive.

The screen of this invention is formed by treating fibers, such as nylon or polyester, in a bath which contains copper (II) sulfide and an acid. Carbon black powder may also be added to the bath. (As a result, all of the interwoven yarns of the screen are rendered conductive.) The screen is then mounted in a flexible frame which includes a rigidifying metal inner frame to assist in eliminating radiation and to secure the screen in a bent shape within the frame. A ground wire is attached to the frame prior to attaching the screen to the front surface of a VDT. By forming the screen of a series of conductive yarns, both glare and the emanation of electromagnetic radiation and static electricity from the VDT is significantly reduced.

Accordingly, it is an object of this invention to provide an improved screen which is for a video display terminal.

Another object of this invention is to provide for a VDT screen in which substantially all of the screen yarns are electrically conductive.

Another object of this invention is to provide for a VDT screen which reduces glare and effectively suppresses emanation of electromagnetic radiation and static electricity about the surface of a cathode ray tube.

Still another object of this invention is to provide for a VDT screen frame which permanently retains its shape after being bent and fitted into a VDT screen.

Another object of this invention is to provide for a VDT screen which is simple and economical to produce.

Other objects of this invention will become apparent in a reading of the following description.

FIG. 1 is a perspective view of a VDT showing the screen of this invention in use.

FIG. 2 is a front elevational view of the screen.

FIG. 3 is a rear elevational view of the screen.

FIG. 4 is a fragmentary detail view of the rear portion of the screen showing in broken line 4 of FIG. 3.

FIG. 5 is a fragmentary sectional view taken along line 5--5 of FIG. 2.

FIG. 6 is a fragmentary elevational view of the rear portion of the screen shown in broken line 6 of FIG. 2.

FIG. 7 is an exploded view of a modified screen.

FIG. 8 is a fragmentary sectional view of the modified screen.

FIG. 9 is a plan view of a non-conductive screen constructed according to the principles of this invention.

FIG. 10 is a fragmentary sectional view taken along line 10--10 of FIG. 9.

The preferred embodiments herein described are not intended to be exhaustive or to limit the invention to the precise forms disclosed. They are chosen and described to explain the principles of the invention and its application and practical use to enable others skilled in the art to utilize the invention.

Referring to the drawings, FIG. 1 depicts a static electricity and radiation elimination member 12 incorporated in a video display terminal (VDT) 8 which has a cathode ray tube (CRT) 10. Member 12 includes an electrically conductive screen 14 secured to a flexible frame 15 by conductive polymeric strip 18 (FIG. 4), and an adhesive strip 17. A ground wire 16 extends from inside CRT 10 and is attached to frame 15 by a nut 19 and bolt 20 combination.

Frame 15 includes a front frame part 15' and a rear frame part 15" as shown in FIG. 5. Frame parts 15' and 15" are joined at their end edges 9 to form frame 15. Screen 14 is formed of fibers which range from 0.002 inches to 0.0028 inches in diameter and a mesh count of 109 to 200 filaments per inch to provide mesh openings of 0.003 to 0.006 inches. As indicated in U.S. Pat. No. 4,253,737, incorporated herein by reference, screen 14 is mounted in frame 15 and maintains contact over the display surface 27 of the CRT 10 to eliminate the distortions in Newton rings and Morie patterns.

Screen 14 is formed by treating fine mesh fabric, preferably nylon or polyester, in a heated bath which contains copper (II) sulfide and an acid. Carbon black powder may be added to the bath as a catalyst. The copper sulfide is adsorbed onto the fibers to render the fibers of screen 14 electrically conductive, which allows the screen to function as a static electricity and radiation elimination device. Also, the screen 14 may be dyed with an anti-reflective color such as dark grey or black to reduce glare. The method of forming screen 14 is described in detail in U.S. Pat. No. 4,661,376 which is incorporated herein by reference.

After screen 14 has been thus formed, it is fitted into frame part 15' and secured by adhesive 17 as shown in FIG. 4. Bolt 20 is then passed through a bore 21 in frame part 15' and secured to frame part 15' in contact with screen 14 by nut 19. Frame part 15" is then secured to frame part 15' as above noted. A depression 24 in frame part 15" (FIG. 5) accommodates screw 20. This connection allows a continuous current flow between ground wire 16 and screen 14 whereby static electricity and radiation are effectively diffused.

FIGS. 7 and 8 depict a modified device 26. As shown in the drawings, device 26 includes an outer flexible frame part 28 formed of rubber, polyethylene, polyvinyl chloride or the like, which defines a concave trough part 30. A rigidifying frame part 32 of iron, aluminum, copper or other suitable metal or metal alloy is fitted restrictively in frame trough part 30. Screen 14' is then placed atop frame part 32. Screen 14' may be of the conductive fibers defined above or may be formed of non-conductive fibers such as nylon or polyester which have been dyed black, if the sole object of the screen is to reduce glare. No ground wire or securing rivet would be used in the case of device 38 which has screen 14" formed entirely of non-conductive fibers (see FIGS. 9 and 10). A frame backing part 36 of similar material to part 28 is then placed over screen 14' and the assembly secured as above described such as by rivet 34 or by gluing. Ground wire 16' extends between rivet 34 and the CRT screen as shown previously in FIG. 1. Forming frame parts 28 and 36 of flexible material allows device 26 to be bent into a shape which conforms to the shape of the VDT monitor, while frame part 32 allows the device to attain sufficient rigidity to remain in its bent shape permanently whereby the frame need not be adjusted within the VDT monitor.

It is understood that the above description does not limit the invention to the details above given but may be modified within the scope of the appended claims.