US3893750A - Cathode-ray tube screening correction lens with a non-solarizing material - Google Patents

Abstract

Essentially, the device comprises a rigid transparent substrate, such as glass, and a nonsolarizing polymer layer, such as silicone resin, on the substrate. An effective surface is formed on the surface of the polymer layer opposite the substrate.

Description

United States Patent DAmato July 8, 1975 [54] CATHODE-RAY TUBE SCREENING 3,486,825 12/1969 Howland 350/175 NG CORRECTION LENS WITH A NON'SOLARIHNG MATERIAL Primary Examiner-Ronald L. Wibert [75] Inventor: Ralph .lames DAmato, Lancaster, Assistant ExaminerConrad Clark Pa. Attorney, Agent, or Firm-Glenn H. Bruestle; Dennis [73] Assignee: RCA Corporation, New York, NY. lrlbeck [22] Filed: May 2, 1973 [211 App]. No.: 356,454 [57] ABSTRACT [52] U S Cl 350/189. 350/175 NG Essentially, the device comprises a rigid transparent [51] 1 l3/l8. Gozb 3/04 substrate, such as glass, and a nonsolarizing polymer [58} Fieid 350/189 175 N6 layer, such as silicone resin, on the substrate. An effective surface is formed on the surface of the polymer Reierences Cited layer opposite the substrate.

UNITED STATES PATENTS 9 Claims, 6 Drawing Figures 3,279,340 [Ci/I966 Ramberg et al. 350/l89 CATI-IODE-RAY TUBE SCREENING CORRECTION LENS WITH A NON-SOLARIZING MATERIAL BACKGROUND OF THE INVENTION This invention relates to refractive devices such as optical correcting lenses for use in laying down arrays of color phosphor deposits in cathode-ray tubes.

Many cathode-ray tubes have mosaic screens or targets of different light emitting or absorbing material. For example, certain types of color television picture tubes usually include a screen comprising arrays of red, green, and blue emitting phosphor lines or dots, electron gun means for exciting the screen, and a color selection electrode e.g., an apertured sheet metal mask or a wire grill, interposed between the gun means and the screen. In one prior art process for forming each color array of phosphor lines or dots on a viewing faceplate within a tube having an apertured mask, the inner surface of the faceplate is coated with a mixture of phosphor particles adapted to emit light of one of the three colors (e.g., green). and a photosensitive binder. Light is projected from a source through the apertured mask and onto the coating so that the apertured mask functions as a photographic master. The exposed coating is subsequently developed to produce phosphor elements of the first phosphor, e.g., green emitting lines or dots. The process is repeated for the blue-emitting phosphor and red-emitting phosphor utilizing the same apertured mask but repositioning the source of light for each exposure. A more complete description of a prior art process for forming a picture tube screen can be found in U.S. Pat. No. 2,625,734 issued to Law on Jan. 20, 1953.

In exposing the screen through the mask apertures, the light source is sequentially placed in a fixed relationship with each center of deflection of each of the electron beams which later will excite the screen. Unfortunately. these deflection centers are not similarly fixed in position but rather vary in position during operation of the tube. One such variation is a shift toward the screen as the angle of deflection increases. This shift of the deflection center parallel to the tube axis causes a radial misregister of the electron impingement spots on the screen with respect to their corresponding phosphor dots established using a fixed light source.

In the case of a dot screen where three beams are subjected to dynamic convergence, an additional type of deflection center shift occurs. This additional shift is transverse ,to the tube axis and causes degrouping (e.g., an increase in size of the electron spot trios) misregister of the electron spots related to their associated phosphor dots. These and other types of misregister are dis cussed in greater detail in the following US. patents: 2,885,935 Epstein et al. and 3,282,691 Morrell et al.

In order to correct error between the position of electron beam landing and the location of a phosphor dot, the prior art has provided correcting lenses located between the light source and the tube screen which pro vide appropriate deflection of the light rays so as to locate the position of the phosphor dots at the expected landing positions on the screen of the electron beams. The design of correcting lenses for use in fabricating color television picture tubes has been described by Epstein et al in U.S. Pat. Nos. 2,817,276 and 2,885,935, by Ramberg in US. Pat. No. 3,279,340 and more recently by Yamazaki et al. in US. Pat. No.

LII

3,628,850. The lenses disclosed in the latter two patents have discontinuous surfaces that permit more accurate exposure of the screen. It becomes more difficult to form a lens out of glass as the complexity of the discontinuous surface increases. Therefore, multielement lenses, such as those shown in US. Pat. No. 3,628,850, are preferably constructed of plastics. Unfortunately, the use of most plastic lenses in color picture tube screening lighthouses has several disadvantages. Probably the greatest disadvantage is that all plastic lenses in present use decrease in ultraviolet transmission or solarize with exposure to ultraviolet radiation in the 290 to 400 namometer range, hereinafter referred to as the near range. Because of this darkenin or solarization, plastic lenses have to be replaced at frequent intervals. Another disadvantage of plastic lenses is that if they are made too thin, they will lack adequate mechanical stability.

Each of the disadvantages of the prior art use of plastic lenses is overcome by the present invention. Additionally, the present invention provides a less expensive lens than lenses constructed completely out of glass.

SUMMARY OF THE INVENTION The present invention provides a refractive device such as for use in the formation of a color picture tube screen. At least a portion of the device has an effective surface thereon for changing paths of light rays passing through the device lens. The portion is constructed of a polymer that is substantially nonsolarizing when exposed to ultraviolet radiation in the 290 to 400 nanometer range.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a correcting lens embodying the present invention.

FIG. 2 is a perspective view of a second correcting lens embodying the present invention.

FIG. 3 is a cross-sectional view of a lens package in corporating the lens of FIG. 2.

FIG. 4 is a cross-sectional view of a second lens package incorporating the lens of FIG. 2.

FIG. 5 is a cross-sectional view of a third lens package incorporating the lens of FIG. 2.

FIG. 6 is a cross-sectional view of a fourth lens package incorporating the lens of FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates a refracting device or correcting lens 10 formed with a rigid transparent substrate 12. A thinner transparent nonsolarizing polymer layer 14 is uniformly attached to the substrate 12. A surface 16 of the layer 14, opposite the substrate 12, is the effective surface of the lens 10. The surface 16 is contoured to provide correction of the light path to the different areas of the screen to prevent misregister.

In a preferred embodiment, the substrate 12 is /4 inch thick optical glass of suitable quality, such as a glass manufactured by Schott Glass, Inc. designated 8K7. The transparent polymer layer 14 may be any polymer that has good ultraviolet transmission characteristics, resists solarization in the wavelength range of 290 to 400 nanometers and exhibits low shrinkage. A material that meets these criteria, and has been found to be preferable is transparent silicone resin. One silicone resin that has been found suitable for layer 14 is manufactured by Dow-Corning. Inc., and is designated R63- 489. The silicone resin layer can be any reasonable thickness, as long as it is thick enough to accomodate the irregularities of the effective surface. A thickness of I mils has been found to be satisfactory for the lens of FIG. I.

The lens 10 can be formed by any suitable construction technique. In a preferred method. a primer, such as manufactured by Dow-Corning and designated Sylgard, is first applied to the glass substrate 12. Then liq uid silicone resin, such as R63-489 is mixed with a hardener, such as that provided by Dow-Corning with the R63-4 89, and is injected into a mold between a die contoured with a reverse effective surface shape and the glass substrate. After the silicone resin has hardened, one side of it adheres to the primed glass substrate while the other side contains the effective surface. Although a primer has been used in this preferred method to ensure adhesion of the silicone resin to the substrate. adequate adhesion may be attained without use of the primer.

FIG. 2 depicts a second correcting lens 18 also formed with a rigid transparent substrate 20 and a thin transparent polymer layer 22. The effective surface 24 of this lens I8 is divided into a plurality of segments 26 each of which provide individualized optical correction for corresponding parts of the tube screen during screen formation by known photoprinting methods. The preferred materials and dimensions used to construct lens 18 are the same as those described with respect to lens I0 except that a thickness of 30 to mils is sufficient for the polymer layer since the variations from the mean surface level seldom exceed l0 mils.

Discontinuous interfaces 28 are located between each of the segments 26 of the lens 18. A portion of the light passing through the lens 18 may reflect and scatter therefrom. Therefore, it may be desirable to mask these as described in a copending application entitled Color Television Picture Tube Screening Method" by van Hekken now U.S. Pat. No. 3,782,253. Four masking techniques are shown in FIGS. 3, 4, 5 and 6. In a lens package 30, shown in FIG. 3, the lens 18 is covered with a second rigid transparent substrate 32 having an opaque pattern 34, corresponding to the discontinuity pattern, thereon. The second substrate 32 is separated from the effective surface of lens 18 by an air gap 36.

A second lens package 38 is shown in FIG. 4. In this package 38, an opaque material 40 is coated directly onto the effective surface of lens 18 at the locations of the surface discontinuities 28.

FIG. 5 shows a third lens package 42 wherein the masking pattern is a grid or grill 44 embedded in the polymer material of the layer 22.

In a fourth lens package 46, shown in FIG. 6, an opaque pattern is coated directly onto the substrate 20 before the polymer layer is applied. A preferred opaque material for the lens packages 30, 38 and 46 is graphite.

All of the foregoing device embodiments have included a rigid substrate and polymer layer. Such construction takes advantage of the fact that relatively inexpensive materials that are dimensionally stable and readily finished to desired optical requirements, such as glasses, can be used to support thinlayers of a relatively expensive nonsolarizing polymer. Therefore, the overall cost of a lens so constructed can be significantly less than a lens constructed entirely of the nonsolarizing lens material. i

It should be recognized that heretofore no plastic or polymer lens for screening of color television picture tube screens has ever been constructed that is substantially nonsolarizing when exposed to ultraviolet radiation in the 290 to 400 nanometer range. The present invention provides the art with nonglass lenses that will not solarize to the extent that they require frequent replacement. Therefore, the present invention can significantly reduce the cost of producing color television picture tubes.

Although the term lens has been used in describing the prior art and the preferred embodiments, it is to be understood that such term has been in long use in the television screening art to describe refractive devices that change or correct paths of light rays but do not provide focusing. It also should be noted that for various reasons known in the art, light ray path correction may not be made to exactly correspond to the path an electron beam will take in striking the screen. For ex ample, in a compromise to compensate for mask doming caused by heat expansion, it may be desirable to provide slight misregister. Therefore, the correction lens may provide light path corrections to parts of the screen to substantially, but not exactly, correspond them to the paths electron beams will take.

I claim:

1. A refractive device for correcting the paths oflight rays in the formation of a color television picture tube screen comprising,

at least a portion of said device having an effective surface thereon for correcting paths of light rays passing therethrough during formation of said screen to substantially correspond to paths electron beams will take in striking the screen in a completed tube, said portion being a silicone resin that is substantially nonsolarizing when exposed to ultraviolet radiation in the range of 290 to 400 nanometers, and

a rigid transparent substrate for supporting said portion.

2. The device as defined in claim 1, wherein said effective surface is a continuously contoured surface.

3. The device as defined in claim 1, wherein said effective surface has at least one surface discontinuity.

4. The device as defined in claim 3, including a mask grid embedded in said portion and aligned with said discontinuity.

5. The device as defined in claim I, wherein said effective surface has at least one surface discontinuity and said substrate includes a mask pattern on a surface thereof, said mask pattern aligned with said discontinuity.

6. A refractive device for correcting the paths of light rays in the formation of a color television picture tube screen comprising,

a rigid transparent substrate,

a transparent silicone resin layer uniformly attached to said substrate, said silicone resin being a material having good ultraviolet transmission characteristics and being resistant to solarization in the ultraviolet wavelength range of 290 to 400 nanometers of color television picture tube screening devices, said silicone resin layer having an effective surface thereon for correcting paths of light rays passing therethrough during formation of said screen to 6 substantially correspond to paths electron beams 8. The device as defined in claim 6, wherein thickwill take in striking the screen in a completed tube. mess f said polymer layer is less than o mils 7. The device as defined in claim 6, wherein the sili- The device as defined in Claim 8 whgrein thick cone resin has ultraviolet transmission characteristics and solarization resistance similar to a silicone resin manufactured by DowwCorning, Inc. and designated R63-489.

ness of said polymer layer is within the range of 30 to 40 mils.

Claims (9)

1. A refractive device for correcting the paths of light rays in the formation of a color television picture tube screen comprising, at least a portion of said device having an effective surface thereon for correcting paths of light rays passing therethrough during formation of said screen to substantially correspond to paths electron beams will take in striking the screen in a completed tube, said portion being a silicone resin that is substantially nonsolarizing when exposed to ultraviolet radiation in the range of 290 to 400 nanometers, and a rigid transparent substrate for supporting said portion.

2. The device as defined in claim 1, wherein said effective surface is a continuously contoured surface.

3. The device as defined in claim 1, wherein said effective surface has at least one surface discontinuity.

4. The device as defined in claim 3, including a mask grid embedded in said portion and aligned with said discontinuity.

5. The device as defined in claim 1, wherein said effective surface has at least one surface discontinuity and said substrate includes a mask pattern on a surface thereof, said mask pattern aligned with said discontinuity.

6. A refractive device for correcting the paths of light rays in the formation of a color television picture tube screen comprising, a rigid transparent substrate, a transparent silicone resin layer uniformly attached to said substrate, said silicone resin being a material having good ultraviolet transmission characteristics and being resistant to solarization in the ultraviolet wavelength range of 290 to 400 nanometers of color television picture tube screening devices, said silicone resin layer having an effective surface thereon for correcting paths of light rays passing therethrough during formation of said screen to substantially correspond to paths electron beams will take in striking the screen in a completed tube.

7. The device as defined in claim 6, wherein the silicone resin has ultraviolet transmission characteristics and solarization resistance similar to a silicone resin manufactured by Dow-Corning, Inc. and designated R63-489,

8. The device as defined in claim 6, wherein thickness of said polymer layer is less than 100 mils.

9. The device as defined in claim 8, wherein thickness of said polymer layer is within the range of 30 to 40 mils.

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