United States Patent 19 11 3,904.425 Young et al. (45) Sept. 9, 1975 54) ABSORPTIVE GLASS Primary Examiner-Harvey E. Behrend 75 Inventors: Robert W. Young, Woodstock, Attorney, Agent, or Firm-William C. Nealon; H. R. Conn.; Robert E. Graf, Southbridge, Berkenstock, Jr. Mass. W EXEMPLARY CLAIM 73) Assignee: American Optical Corporation, 1. A glass material having a calculated oxide composi Southbridge, Mass. tion comprising 22 Filed: June 12, 1964 21 Appl. No.: 374,811 Percent by Weight Silicon Dioxidc (SiO) 5.9 Sodium Oxide (NaO) 6.5 (52) U.S. Cl...................................... 106/52; 106/50 Potassium Oxide (KO) 6.8 (51 l Int. Cl........................................... CO3C 13/00 Calcium Oxide (CaO) 6.5 58) Field of Search................................. 106/50, 52 Antimony Trioxide (SbO) 0.4 Aluminum Oxide (AO) 4. Zinc Oxide (ZnO) 2.2 56) References Cited Titanium Dioxidc (TiO) 0.4 Manganese Dioxide (MnO) 23.4 UNITED STATES PATENTS Chromium Oxide (CrO) O.S 2,676,09 4/1954 Barnes ct al.......................... 106752 Tct O).() 2,776,900 l/1957 Duncan et al........................ 106/52 2,898,219 8/1959 Duncan ct al........................ 106/52 2,902,377 9, 1959 Duncan............ ... 106/52 a 100 micron thickness of said glass material having 3,146,2O 8/1964 Upton et al.... ... 106/52 an optical density greater than 0.25 at least for light 3,20386 8/1965 Bull et al.............................. 1 O6/52 from 0.4 to 0.6 microns wavelength. FOREIGN PATENTS OR APPLICATIONS 6 4,357 21 1961 Canada................................. 106/52 6 Claims, No Drawings 3,904,425 2 ABSORPTIVE GLASS als should have optical densities at least as high as 0.25 The field of this invention is that of glass composi in sample thickness as small as 100 microns at least for tions and the invention relates more particularly to light of wavelengths between 0.4 and 0.6 microns. Ex novel and improved absorptive glass materials. pressed another way, this means that thicknesses of In an important application of fiber optics, a great these glass materials as small as four thousandths number of very small optical fibers each having a light (.004) of an inch should be adapted to provide for at conducting glass core and a light-insulating glass clad least 75% absorption of the light from 0.4 to 0.6 mi ding are fused together in side-by-side parallel relation crons wavelength incident thereon. to each other to form a vacuum-tight faceplate for a The absorptive glass material provided by this inven cathode-ray tube. In such devices, very fine filaments tion embodies silicon dioxide (SiO2) as its major ingre of light-absorbing glass material are fused between the dient and also embodies sodium oxide (NaO) and/or optical fibers at spaced locations throughout the face potassium oxide (KO) as fluxes to aid in glass forma plate and the inner surface of the faceplate is coated tion. The glass material further embodies calcium oxide with photo-emissive phosphors or the like. In this ar (CaO) as a glass stabilizer and antimony trioxide rangement, the cathode-ray tube can form a light image 15 (SbO) to facilitate fining of the glass material. Prefer on the inner surface of the faceplate in conventional ably the glass also contains aluminum oxide (AlO3) to manner and the optical fibers can each conduct light promote durability of the glass. The glass material can from a specific part of the image to reproduce the also contain zinc oxide (ZnO) to further stabilize the image with high resolution on the outer surface of the glass and can contain titanium oxide (TiO) to help reg faceplate. The light-absorbing filaments absorb un ulate viscosity of the glass. wanted, stray light which is emitted by the tube phos phors but which is not conducted through specific opti In accordance with this invention, the glass material cal fibers, thereby to assure that the stray light is not must contain one or more colorants selected from the transmitted through the faceplate and does not wash group consisting of manganese dioxide (MnO), nick out contrast between light and dark portions of the 25 elic oxide (NiO), chromium oxide (CrO), ferric light image reproduced on the outer surface of the oxide (FeO), cobalt oxide (CoO) and cupric oxide tube. - (CuO), the quantity of the selected colorant or color It is an object of this invention to provide a glass ma ants embodied in the glass being sufficient to provide terial having very high absorptive properties for use in the glass with an optical density of 0.25 even for very forming light-absorbing filaments to be incorporated in 30 thin sheets or filaments of the glass as small as 100 mi fiber optical devices. It is therefore an important object crons thickness - at least for light from 0.4 to 0.6 mi of this invention to provide such an absorptive glass crons wavelength. Where manganese dioxide com material which can be conveniently and economically prises the sole colorant embodied in the glass, the man drawn into the form of very fine filaments of substan ganese dioxide must comprise at least about 20 percent tially uniform diameter and absorptive properties. Fur 3 5 by weight of the glass material in order to achieve the ther objects of this invention are to provide such ab minimum degree of optical density which is required. sorptive glass materials which can be conveniently However additional manganese dioxide or other color fused together with glass materials customarily embod ants can also be added for achieving greater optical ied in optical fibers; to provide such glass materials densities without adversely affecting working proper which are stable under the temperatures to which cath ties of the glass material. On the other hand, where the ode-ray tubes are subjected; and to provide such glass manganese dioxide content of the glass material com materials which are chemically unreactive with respect prises less than 20 percent by weight of the glass mate to phosphors and the like with which cathode-ray tube rial, the manganese dioxide must be supplemented by faceplates are frequently coated and which are particu other colorants in order to provide the desired optical larly adapted for absorption of light of the wavelengths density. For example, where the manganese dioxide emitted by such phosphors. It is a specific object of this content of the glass is 12 percent by weight of the glass invention to provide such absorptive glass materials material, the manganese dioxide can be supplemented which have an optical density of 0.25 or more for thick by at least 8 percent by weight of nickelic oxide alone. ness on the order of 100 microns at least for light of Similarly, where the manganese dioxide content of the wavelengths between 0.4 and 0.6 microns. Other ob 50 glass material is omitted, the manganese dioxide can be jects of this invention appear in the following detailed replaced by at least 5 percent by weight of nickelic description of preferred embodiments of this invention. oxide and at least 3.5 percent by weight of cobalt oxide. It will be understood that optical fibers employed in The various ingredients of the glass material of this in thin cathode-ray tube faceplates are ordinarily on the vention can of course be varied within certain limits so order of 25–50 microns in diameter and that the light 55 that the calculated oxide composition of this glass ma absorbing filaments fused within the fiber faceplates terial can be set forth as follows: must also be quite small in diameter and must be well dispersed throughout the faceplate if they are to be ac Percent by Weight commodated in the faceplates without adversely affect 60 ing light images transferred through the faceplate. This Silicon Dioxide (SiO,) 4() to 65 means that the absorptive properties of the glass mate Sodium Oxide (NaO) () to () Potassium Oxide (KO) () toy l() rials of this invention must be very high with respect to Calcium Oxide (CaO) 4 to 9 light of the particular wavelengths emitted by phos Antimony Trioxide (SbO) ().3 to () phors usually employed on such faceplates if the fila Aluminum Oxide (AO) () to 2 65 Zinc oxide (ZnO) () to 3 ments are to be effective in absorbing stray light emit Titanium Dioxide (TiO) () to 2 ted by the phosphors before it escapes from the face TTH--------- plates. In fact it has been found that such glass materi 3,904,425 3 4. wherein the combined content of NaO and KO equals EXAMPLE I at least 1 () percent by weight, said glass material including at least one colorant se Percent by Weight lected from the group consisting of Silicon Dic)xicle (SiO.) 5.9 5 Sociium Coxicie (NaO) 6.5 Potassium Oxide (KO) 6.8 Percent by Weight Calcium Oxide (CaO) 6.5 Antimony Trioxide (SbO) ().4 Manganese Dioxide (MnO, ) () to 32 Aluminum Oxide (AO) 1.4 Nickulic Oxide (NiO.) () to 9 Zinc Oxicic (ZnO) 2.2 Titanium Dioxide (TiO) ().4 Chromium Oxide (C.O.) () to ().5 () Ferric Oxide (FeO.) () to 9 Manganesc Dioxide (MnO) 23.4 Cobalt (xide (CoO) () to 6 Chromium Oxide (CrO) ().5 Cupric Oxide (CuO) () t 9 Total O().() wherein a content of MnO, less than 20 percent by 5' said glass having an optical density greater than 0.25 in weight is supplemented by others of said colorants for a sample sheet of glass of 100 microns thickness at least achieving an optical density of at least 0.25 in thick for light from 0.4 to O.6 microns wavelength.