CONTRAST ENHANCING CRT FILTERS AND FUSIBLE FILTER FACEPLATES

Abstract: Filter glasses and fusible filter faceplates for use in con­ trast enhancement of cathode ray tube (CRT) signals employ­ ing P-43, P-44 and other phosphors with peak wavelengths near 546 nm or for use with green LED's have the composi­ tion in wt.%: SiO₂ 60-70 B₂O₃ 1-3 Al₂O₃ 0-1 Li₂O 1-3 Na₂O 3-10 K₂O 5-10 BaO 3-7 SrO 3-10 PbO 0-3 CeO₂ 0-3 CaO 0-10 Cr₂O₃ 0.1-3 Nd₂O₃ 0-10 CuO 0.1-1

Description: CONTRAST ENHANCING CRT FILTERS AND FUSIBLE FILTER FACEPLATES Background of the Invention This invention relates to a new glass composition useful for fabrication of contrast enhancement filters and filter glasses. Contrast enhancement filters are widely used with Phosphor P-43 CRT's to improve signal visibility at approximately 546 nm. It is preferred that such bandpass filters have narrow bandwidths and transmittance peaks at 546 nm of about 5-30t, depending on end use and user preferences. This peak wavelength lies approximately at the main emission of P-43. Various glasses meeting these requirements have becn proposed, e.g., the glass of USP 4,288,250 or Weyl, Colored Glasses, Society of Glass Technology, Sheffield, 1978, especially pp 78, 79 and 221-229, all of whose disclosures are incorporated by reference herein. However, all prior art glasses have various disadvantages. Summary of the Invention Accordingly, it is an object of this invention to provide improved contrast enhancement filters and faceplate glasses having a transjnission peak centered at about 546 nm with a narrow bandwidth. Upon further study of the specification and appended claims, further objects and advantages of this invention will become apparent to those skilled in the art. These objects have been attained by providing a glass of the following composition: wt. % Preferred SiO2 60-70 62-65 B203 1-3 1.3-1.7 Al2O3 0-1 0.3-0.7 Li2O 1-3 1-3 Na2O 3-10 4.8-6.7 K2Q 5-10 6-7 BaO 3-7 5-6 SrO 3-10 4-9.5 PbO 0-3 2-3 CeO2 0-3 0 CaO 0-10 0 Cr2O3 0.1-3 0.7-3 Nd203 0-10 0-6 CuO Ol-l 0.1-1 Optionally, there can also be included conventional refining agents in the conventional amounts, e.g., wt. % Preferred 2 0-0.4 0.2-0.4 As2O3 0-0.4 0.1-0.3 Sb2O3 0-0.4 0.2-0.4 Cl2 0-0.3 0 Na2SO4 0-0.4 0 brief Description of the Drawing Various other objects, features and attendant advantages of the present invention will be more fully appreciated as the same becomes better understood when considered in conjunction with the accompanying drawing, wherein: Figure 1 shows the transmittance spectra of two of the glass compositions of this invention. Detailed Discussion Typically, the glasses of this invention have the following properties: range Refractive Index (nD) 1.530-1.552 Peak Location (nm) 540-550 Transmittance at Peak ('1') (t) 5-30 depending on thickness Bandwidth at T/2 (nm) 20-50 CTE 20-3000C ( C-1) (90-105)X10 7 Tg( C) 450-500 Littleton Softening Point (4C) 630-700 Working Point ( C) 910-1000 The predominant ingredient, 60-70 wt. a, is SiO2. It provides the basic glass structurc, modified by other ingredients. Exceeding 70t SiO2 tends to make manufacturing difficult by increasing the viscosity. Too little silica degrades the chemical durability of the glass and may have other deleterious cffects, depending on the other ingredients. The alkali metal oxides (Li2O, Na2O, K2O) comprise 9-23E of the glass. These oxides lower the melting temperature to a convenicnt range. Excessive alkali metal oxide degrades chemical durability, a property important for efficient, trouble-free fabrication of parts from the cold glass. Too little alkali metal oxide makes the melting and forming temperatures inconveniently high. Alkaline earth metal oxides (BaO, SrO, CaO) comprise 6-278 of the glass. The alkaline earths provide a number of benefits such as increased resistance to chemical corrosion, shielding from x-rays, and a high refractive index. Excessive amounts of alkaline earths cause crystallization that spoils the transparency of the glass. The ingredients F2, C12, As2O3, Sb203 and Na2SO4, while present in only minor amounts (0-2.5 wt.%). perform an essential function, the removal of bubbles from the molten glass. These chemicals must be present in suitable amounts and combination, to produce a glass sufficiently free from bubbles to be useful. This is an art fully conventional to those of skill in glass technology. The other ingrediellta (B203 . Al2O3, and PbO), present in 1-7 wt.%, give other useful properties such as improved viscosity for forming, increased resistance to crystallization, and increased refractive index. Deviation from the specified ranges degrades one or more useful properties of the glass. The colorants (Cr203, Nd203, and CuO), which comprise 0.2-14 wt% of the glass, provide the contrast enhancing property. If too little colorant is present, the glass will not enhance the contrast of a CRT. If too much colorant is present, the glass will be too dark to permit convenient reading of the information on the screen of the CRT. The amount of each colorant is dctcrmid partly by the thickness of the glass and partly by the special needs and preferences of the user. This can be readily achieved by fully conventional Considerations, perhaps with a few Preliminary experiments. Typical examples of the transmission spectra, which describe the effect of the colorants, are given in Figure 1. For a glass which contains 2.82 wt.% of Cr203, 0.60 wt.% of CuO and no Nd2O3, and otherwise substantially corresponding to the composition of S-8005 defined herein, a 2.80 mm thick filter has a transmission maximum of 11.5% at 550 nm and with a halfwidth of 44 nm. The P-43 phosphor, which has a narrow emission band at 544 nm, is transmitted by this filter. Ambient light far from 544 nm, for example at 450 or 650 nm, is almost completely absorbed by the filter. Ambient light at wavelengths closer to the transmission maximum, for example at 525 nm, is also strongly attenuated since it passes through the filter twice: once in going from the ambient space to the CRT screen where it is diffusely reflected and a second time when the diffuselyreflected light travels through the filter toward the observer. The brightness of this scattered light can further be reduced by making the transmission band narrower. A narrower band is achieved by adding Nd2O3 to the glass. For example, glass S-8008, which has 4.95 wt.t of Nod 203 in addition to 1.72 wt.% of Cr203 and 0.54 wt.# of CuO, has a transmission band with a maximum of 12% at 544 nm and a half-width of 33 nm when 3.5 mm thick. Figure 1 shows how the presence of Nd203 has narrower the transmission band. The glasses of this invention have transmission peaks centered near 546 nm which is approximately at the main emission of P-43. Furthermorc, the faceplate crass of this invention is fusible to glasses commonly known as G-12 funnel glass and has similar or identical spectral transmittance properties. Typical G-12 glass includes glass 0120 made by Cording Class Works and class CW12 made by Wertheim. All glasses of this invention provide good x-ray absorbance properties, e.g., comparable to those of conventional clear CWF faceplate glasses such as Schott Optical S-8003. The basic difference between the properties of filters and faceplates is that the latter can be fused to G-12 funnel glass to make a CRT. Successful fusion requires that the thermal expansion coefficient be reduced from about 100 x 10 70C 1 for the filters to about 91 x 10 70C 1 for the faceplates. This decrease is achieved primarily by increasing the SiO2 content by 1-3 wt.% and decreasing the alkali metal oxide content, especially the Li2O, by 1-2t. Minor changes in some of the other ingredients which might be necessary to maintain other useful properties, of course, will also be made as is fully conventional. The various end points that define the ranges of the amounts of each ingredient can be varied, within the defined ranges, to establish narrower ranges. That is, each range defined above includes many narrower ranges within it which are part of this invention. For example, a range of 5-1Ot is given for K20. This range includes the narrower ranges 5.1-10%, 5.0-9.9t, 5.1-9.9%, 5.2-10%, etc., i.e., the narrower included ranges wherein one or both of the endpoints are varied by one or more multiples of 0.1%. Thus, the general range 5-108 also includes the narrower ranges 5.5-10%, 5.0-9.5S, 5.5-9.5t, etc., as well as the mentioned preferred ranges such as 6-7t for K2O or even narrower ranges such as 6.3-6.5%. The latter is about the smallest practical range that can be maintained with normal manufacturing procedures. The ranges of other ingredients similarly define corresponding narrower ranges. The glass of this invention can be prepared using fully conventional techniques normally employed for glasses of this type. For example, the usual raw materials corresponding to tile oxides required in tile glasses of tis invention, e.g., oxides per se, carbonates, nitrates, hydroxides, etc., are Blended into a melt in amounts corresponding to tlic amounts desired in tilQ fiiial glass. Typical melting temperatures are 1200-1400 C. Conventional crucibles or tanks, e.g., ceramic or platinum containers, can be used. The homogeneous melt is then further treated conventionally, e.g., refined, casted into molds, gradually cooled, etc. Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The following preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever. In the following examples, all temperatures are set forth uncorrected in degrees Celsius; unless otherwise indicated, all parts and percentages are by weight. Example 1 The following describes the preparation of the glass designated below as S-8005. Corresponding procedures were used to prepare the other glass compositions summarized in the following tables. Preparation of 5-8005 The following batch materials are weighed and then mixed thoroughly: Batch Material Amount (kg) supersil 160.37 B(OH)3 6.64 A1(OH)3 1.94 sodium silica fluorides 1.24 Li2CO3 15.52 Na CO 19.55 Na2NO3 3.42 K2CO3 23.91 Sr(NO3)2 47.13 Ba (CO3) 17.41 red lead oxide 6.38 sodium bichromate 14.21 black copper oxide 1.55 As2O3 0.50 Sb2O3 0.75 The mixture is placed in a container and transported to the melting facility. In this case the melting facility is a continuously operating glass tank whose interior is lined partly with standard, commercially available alumina-zirconia-silica fused-cast refractory and partly with platinum. The mixed batch is placed in the furnace a little at a time alonq with an appropriate amount (typically 0-50t) of cullet, glass unsuitable for finished parts but suitable for melting. The batch and cullet are placed on top of the molten glass within the tank at a temperature of 1200-14000C. This material melts and mixes with the other glass in the tank. A stream of molten glass is withdrawn from near the bottom of the tank. This stream flows through a platinum-lined system in which it is heated to 1400-15000C to remove gases, is stirred to increase homogeneity, and is delivered to a forming machine which produces the desired shape. The hot, rigid glass is then cooled slowly in a long furnace, a lehr, to reduce tli sain to a level suitable for cutting and grinding. This description is illustrative only and is not intended to restrict in any way the scope of this invention. It will be appreciated by anyone skilled in the art of glass making that the procedure of preparation can be varied widely and still oduce an acceptable glass. For example, the kinds and amounts of raw materials mixed can be varied, the melting facility can be an allplatinum, intermittently-operated pot, a day tank, or many other kinds of facilities, and the temperatures in the facility can be varied considerably. In all such cases, suitable glass can be made by one skilled in the art. Exemplary Glass of this Invention 1. Filters S-8005 and S-8008 Compositions in Weight Percent 5-8005 S-8008 SiO2 62.30 63.05 B203 1.45 1.50 A1203 0.50 0.50 Li2O 2.45 2.45 Na2O 6.20 6.30 K20 6.35 6.40 BaO 5.15 5.20 SrO 8.95 4.15 PbO 2.45 2.45 F2 0.30 0.30 As2O3 0.20 0.20 Sb2O3 0.30 0.30 Cr2O3 2.82 1.72 Nd203 -- CuO 0.60 0.54 100.02 100.01 Properties Refractive Index nD 1.547 Peak Location (nm) 546 546 Transmittance at Peak (#) 11.5 11.5 Bandwidth at T/2 (nm) < 45 < 35 Nominal Thickness (mm) 2.5 3.5 5-8005 S-8008 CTE20-300 C ( C-1) 101 100 Tg ( C) 463 464 Littleton Softening Point ( C) 646 645 Working Point ( C) 926 932 2. Faceplates S-8006 and S-8006W Compositions in Weight Percent S-8006 S-8006W SiO2 64.80 64.10 B203 1.50 1.45 A1203 0.50 0.50 Li2O 1.20 1.20 Na2O 5.95 5.95 K2O 6.45 6.40 BaO 5.25 5.40 SrO 9.15 5.50 PbO 2.80 2.75 F2 0.30 0.3() As2O3 0.20 0.20 Sb203 0.30 0.30 Cr203 1.34 0.91 Nd203 -- 4.90 CuO 0.27 0.20 CeO2 -- - 100.01 100.00 Properties S-8006 S-8006W Refractive Index nD 1.536 1.539 Peak Location (nm) 546 546 Transmittance at Peak 1t) 12.5 15 Bandwidth at T/2 (nm) < 45 < 35 Nominal Thickness (mm) 5.3 7.0 CTE20-300 C ( C-1) 91 92 Tg (etc) 485 478 Littleton Softening Point ( C) 677 680 Working Point ( C) 954 982 Both glasses are fusible to G-12 funnel glass. The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples. From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.

Claims: WHAT IS CLAIMED IS: 1. A glass consisting essentially of: wt.% SiO2 60-70 B203 1-3 A1203 0-1 Li2 0 1-3 Na2O 3-10 K2O 5-10 BaO 3-7 SrO PbO 0-3 CeO2 0-3 CaO 0-10 Cr203 0.1-3 Nd2O3 0-10 CuO 0l-l 2. A glass of claim 1 consisting essentially of wt. 8 SiO2 62-65 B2O3 1.3-1.7 Al2O3 0.3-0.7 Li2O 1-3 Na20 4.8-6.7 K20 6-7 BaO 5-6 SrO 4-9.5 PbO 2-3 Cr2O3 0.7-3 Nd2O3 0-6 CuO 0.1-1 3. A glass of claim 1 further consisting essentially of wt. % F2 0-0.4 As2O3 0-0.4 Sb2O3 0-0.4 C12 0-0.3 Na2S 4 0-0.4 4. A glass of claim 2 further consisting essentially of wt. % F2 0-0.4 As2O3 0-0.4 Sb203 0-0.4 Cl2 0-0.3 Na2S 4 0-0.4 5. A glass of claim 1 further consisting essentially of wt. % F2 0.2-0.4 As2O3 0.1-0.3 Sb2O3 0.2-0.4 6. A glass of claim 2 further consisting essentially of wt. % F2 0.2-0.4 As203 0.1-0.3 Sb2O3 0.2-0.4 7. A glass of claim 1 having the following properties: range Refractive Index (nD) 1.530-1.552 Peak Location (nm) 540-550 Transmittance at Peak (T) (%) 5-30 depending on thickness Bandwidth at T/2 (nm) 20-50 CTE 20-300 C ( C-1) (90-105)X10-7 Tg( C) 450-500 Littleton Softening Point ( C) 630-700 Working Point ( C) 910-1000 8. A glass of claim 2 having the following properties: range Refractive Index (nod) 1.530-1.552 Peak Location (nm) 540-550 Transmittance at Peak (T) (%) 5-30 depending on thickness Bandwidth at T/2 (nm) 20-50 CTE 20-300 C ( C-1) (90-105)X10-7 Tg( C) 450-500 Littleton Softening Point ( C) 630-700 Working Point ( C) 910-1000 9. A glass of claim 1 useful to make CRT faceplates wherein the thermal expansion coefficient of the glass is about 91 x 10 70C 1. 10. A glass of claim 1 useful to make filters wherein the thermal expansion coefficient of the glass is about 100 x 10-7 C-1. 11. A glass of claim 1 useful as a filter, consisting essentially of about the following amounts of ingredients in wt.%: SiO2 62.30 B203 1.45 A1203 0.50 Li2O 2.45 Na2O 6.20 K20 6.35 BaO 5.15 SrO 8.95 PbO 2.45 F2 0.30 As203 0.20 Sb203 0.30 Cr203 2.82 CuO 0.60 12. A glass of claim 1 useful as a filter, consisting essentially of about the following amounts of ingredients in wt.%: SiO2 63.05 B203 1.50 A12O3 0.50 Li2O 2.45 Na2O 6.30 K20 6.40 BaO 5.20 SrO 4.15 PbO 2.45 F2 0.30 As2O3 0.20 Sb2O3 0.30 Cr203 1.72 Nd2O3 4.95 CuO 0.54 13. A glass of claim 1 useful as a faceplate consisting essentially of about the following amounts of ingredients in wt.%: SiO2 64.80 B2O3 1.50 Al2O3 0.50 Li2O 1.20 Na2O 5.95 K2O 6.45 BaO 5.25 SrO 9.15 PbO 2.80 F2 0.30 As2O3 0.20 Sb203 0.30 Cr2O3 1.34 CuO 0.27 14. A glass of claim 1 useful as a filter, consisting essentially of about the following amounts of ingredients in wt.%: SiO2 64.10 B203 1.45 A1203 0.50 Li2O 1.20 Na2O 5.95 K20 6.40 BaO 5.40 SrO 5.50 PbO 2.75 F2 0.30 As2O3 0.20 Sb2O3 0.30 Cr2O3 0.91 Nd2O3 4.90 CuO 0.2(0 15. In an enhancement contrast filter, the improvement wherein the filter comprises the glass of claim 1. 16. In a CRT faceplate, the improvement wherein the faceplate comprises the glass of claim 1.

Inventors: KASSNER, REINHARD, MADER, KARL-HEINZ
Applicants: SCHOTT GLASS TECHNOLOGIES, INC.
Application year: 1984
Main classification: C03C3
IPC codes: C03C4, H01J29, C03C3