COLOR CATHODE-RAY TUBE HAVING UNIAXIAL TENSION FOCUS MASK

Abstract: The present invention relates to a color cathode-ray tube (10) having an evacutated envelope (11) with an electron gun (26) therein for generating at least one electron beam (28). The envelope (11) further includes a faceplate panel (12) having a luminescent screen (22) with phosphor lines on an interior surface thereof. A uniaxial tension focus mask (25), having a plurality of spaced-apart first metal strands (40), is located adjacent to an effective picture area of the screen. The spacing between the first metal strands defines a plurality of slots (42) substantially parallel to the phosphor lines of the screen. Each of the first metal strands across the effective picture area of the screen has a substantially continuous first insulator layer (64) on a screen-facing side thereof. A second insulator layer (66) overlies the first insulator layer. A plurality of second metal strands (60) are oriented substantially perpendicular to the first metal strands and are bonded thereto by the second insulator layer. The first insulating layer has a coefficient of thermal expansion substantially matching, or slightly lower than, that of the first strands. The second insulating layer has a coefficient of thermal expansion that is substantially identical to that of the first insulating layer.

Description: COLOR CATHODE-RAY TUBE HAVING UNIAXIAL TENSION FOCUS MASK This invention relates to a color cathode-ray tube (CRT) and, more particularly, to a color CRT having a uniaxial tension focus mask and to the materials used in making such a mask. BACKGROUND OF THE INVENTION A conventional shadow mask type color CRT generally comprises an evacuated envelope having therein a luminescent screen with phosphor elements of three different emissive colors arranged in color groups, in a cyclic order, means for producing three convergent electron beams directed towards the screen, and a color selection structure, such as a masking plate, between the screen and the beam-producing means. The masking plate acts as a parallax barrier that shadows the screen. The differences in the convergence angles of the incident electron beams permit the transmitted portions of the beams to excite phosphor elements of the correct emissive color. A drawback of the shadow mask type CRT is that the masking plate, at the center of the screen, intercepts all but about 18 - 22 % of the beam current; that is, the masking plate is said to have a transmission of only about 18 - 22 %. Thus, the area of the apertures in the plate is about 18 - 22 % of the area of the masking plate. Since there are no focusing fields associated with the masking plate, a corresponding portion of the screen is excited by the electron beams. In order to increase the transmission of the color selection electrode without increasing the size of the excited portions of the screen, post- deflection focusing color selection structures are required. The focusing characteristics of such structures permit larger aperture openings to be utilized to obtain greater electron beam transmission than can be obtained with the conventional shadow mask. One such structure is described in Japanese Patent Publication No. SHO 39-24981, by Sony, published on Nov. 6, 1964. In that patented structure, mutually orthogonal lead wires are attached at their crossing points by insulators to provide large window openings through which the electron beams pass. One drawback of such a structure is that the cross wires offer little shielding to the insulators so that the deflected electron beams will strike and electrostatically charge the insulators. The electrostatically charged insulators will distort the paths of the electron beams passing through the window openings, causing misregister of the beams with the phosphor screen elements. Another drawback of the structure is that mechanical breakage of an insulator would permit an electrical short circuit between the crossed grid wires. Another color selection electrode focusing structure that overcomes some of the drawbacks of the above-described Japanese patent publication is described in U.S. Pat. No. 4,443,499, issued on April 17, 1984 to Lipp. The structure described in U.S. Pat. No. 4,443,499 utilizes a masking plate having a thickness of about 0.15 mm (6 mils), with a plurality of rectangular apertures therethrough, as a first electrode. Metal ridges separate the columns of apertures. The tops of the metal ridges are provided with a suitable insulating coating. A metallized coating overlies the insulating coating to form a second electrode that provides the required electron beam focusing when suitable potentials are applied to the masking plate and to the metallized coating. Alternatively, as described in U. S. Pat. No. 4,650,435, issued on Mar. 17, 1987 to Tamutus, a metal masking plate, which forms the first electrode, is etched from one surface to provide parallel trenches in which insulating material is deposited and built up to form insulating ridges. The masking plate is further processed by means of a series of photoexposure, development, and etching steps to provide apertures between the ridges of insulating material that reside on the support plate. Metallization on the tops of the insulating ridges forms the second electrode. The two U .S. Patents described above eliminate the problem of electrical short circuits between the spaced apart conductors that was a drawback in the prior Japanese structure; however, the apertured masking plates of the U.S. patents have each cross members of substantial dimension that reduce the electron beam transmission. Additionally, the thickness of the masking plates is such that deflected electrons will still impinge upon and electrostatically charge the ridges of insulating material. Thus, a need exists for a focus mask structure that overcomes the drawbacks of the prior structures. One such focus mask structure is described in copending U.S. Patent Application Serial No. 08/509,321 (RCA 87639), filed July 26, 1995, by R. W. Nosker et al. The structure described in the copending application comprises a plurality of spaced- apart first metal strands having a thickness of about 0.051 mm (2 mils) that extend across an effective picture area of the CRT screen. A substantially continuous first insulator layer, having a thickness about equal to that of the first metal strands, is disposed on a screen-facing side thereof. A second insulator layer is provided over the first insulator layer to facilitate bonding a plurality of second metal strands, substantially perpendicular to the first metal strands, to the first insulating layer. The second insulating layer has a thickness about one half that of the first insulating layer. SUMMARY OF THE INVENTION The present invention relates to a color cathode-ray tube having an evacuated envelope with an electron gun therein for generating at least one electron beam. The envelope further includes a faceplate panel having a luminescent screen with phosphor lines on an interior surface thereof. A uniaxial tension focus mask, having a plurality of spaced-apart first metal strands, is located adjacent to an effective picture area of the screen. The spacing between the first metal strands defines a plurality of slots substantially parallel to the phosphor lines of the screen. Each of the first metal strands, across the effective picture area of the screen, has a substantially continuous first insulator layer on a screen-facing side thereof. A second insulator layer overlies the first insulator layer. A plurality of second metal strands are oriented substantially perpendicular to the first metal strands and are bonded thereto by the second insulator layer. The first insulating layer has a coefficient of thermal expansion substantially equal to, or less than, that of the first metal strands. The second insulating layer has a coefficient of thermal expansion that is substantially identical to that of the first insulating layer. BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in greater detail, with relation to the accompanying drawings, in which: Fig. 1 (Sheet 1) is a plan view, partly in axial section, of a color CRT embodying the invention; Fig. 2 (Sheet 2) is a plan view of a uniaxial tension focus mask- frame assembly used in the CRT of Fig. 1; Fig. 3 (Sheet 2) is a front view of the mask-frame assembly taken along line 3 - 3 of Fig. 2; Fig. 4 (Sheet 3) is an enlarged section of the uniaxial tension focus mask shown within the circle 4 of Fig. 2; Fig. 5 (Sheet 3) is a section of the uniaxial tension focus mask and the luminescent screen taken along lines 5 - 5 of Fig. 4; Fig. 6 (Sheet 2) is an enlarged view of a portion of the uniaxial tension focus mask within the circle 6 of Fig. 5; and Fig. 7 (Sheet 3) is an enlarged view of another portion of the uniaxial tension focus mask within the circle 7 of Fig. 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 shows a color CRT 10 having a glass envelope 11 comprising a rectangular faceplate panel 12 and a tubular neck 14 connected by a rectangular funnel 15. The funnel has an internal conductive coating (not shown) that is in contact with, and extends from, a first anode button 16 to the neck 14. A second anode button 17, located opposite the first anode button 16, is not contacted by the conductive coating. The panel 12 comprises a cylindrical viewing faceplate 18 and a peripheral flange or sidewall 20 that is sealed to the funnel 15 by a glass frit 21. A three- color luminescent phosphor screen 22 is carried by the inner surface of the faceplate 18. The screen 22 is a line screen, shown in detail in Fig. 5, that includes a multiplicity of screen elements comprised of red-emitting, green-emitting, and blue-emitting phosphor lines, R, G, and B, respectively, arranged in triads, each triad including a phosphor line of each of the three colors. Preferably, a light absorbing matrix 23 separates the phosphor lines. A thin conductive layer 24, preferably of aluminum, overlies the screen 22 and provides means for applying a uniform first anode potential to the screen as well as for reflecting light, emitted from the phosphor elements, through the viewing faceplate 18. A cylindrical multi-apertured color selection electrode, or uniaxial tension focus mask, 25 is removably mounted, by conventional means, within the panel 12, in predetermined spaced relation to the screen 22. An electron gun 26, shown schematically by the dashed lines in Fig. 1, is centrally mounted within the neck 14 to generate and direct three inline electron beams 28, a center and two side or outer beams, along convergent paths through the mask 25 to the screen 22. The inline direction of the beams 28 is normal to the plane of the paper. The CRT of Fig. 1 is designed to be used with an external magnetic deflection yoke, such as the yoke 30, shown in the neighborhood of the funnel-to-neck junction. When activated, the yoke 30 subjects the three beams to magnetic fields that cause the beams to scan a horizontal and vertical rectangular raster over the screen 22. The uniaxial tension mask 25 is formed from a thin rectangular sheet of about 0.05 mm (2 mil) thick metal, that is shown in Fig. 2 and includes two long sides 32, 34 and two short sides 36, 38. The two long sides 32, 34 of the mask parallel the central major axis, X , of the CRT and the two short sides 36, 38 parallel the central minor axis, Y, of the CRT. The mask 25 includes an apertured portion that is adjacent to and overlies an effective picture area of the screen 22 which lies within the central dashed lines of Fig. 2 that define the perimeter of the mask 25. As shown in Fig. 4, the uniaxial tension focus mask 25 includes a plurality of elongated first metal strands 40, each having a transverse dimension, or width, of about 0.3 mm (12 mils) separated by substantially equally spaced slots 42, each having a width of about 0.55 mm (21.5 mils) that parallel the minor axis, Y, of the CRT and the phosphor lines of the screen 22. In a color CRT having a diagonal dimension of 68 cm (27V), there are about 600 of the first metal strands 40. Each of the slots 42 extends from the long side 32 of the mask to the other long side 34, not shown in Fig. 4. A frame 44, for the mask 25, is shown in Figs. 1 - 3 and includes four major members, two torsion tubes or curved members 46 and 48 and two tension arms or straight members 50 and 52. The two curved members, 46 and 48, parallel the major axis, X, and each other. As shown in Fig. 3, each of the straight members 50 and 52 includes two overlapped partial members or parts 54 and 56, each part having an L-shaped cross-section. The overlapped parts 54 and 56 are welded together where they are overlapped. An end of each of the parts 54 and 56 is attached to an end of one of the curved members 46 and 48. The curvature of the curved members 46 and 48 matches the cylindrical curvature of the uniaxial tension focus mask 25. The long sides 32, 34 of the uniaxial tension focus mask 25 are welded between the two curved members 46 and 48 which provide the necessary tension to the mask. Before welding to the frame 44, the mask material is pre-stressed and darkened by tensioning the mask material while heating it, in a controlled atmosphere of nitrogen and oxygen, at a temperature of about 500 °C for one hour. The frame 44 and the mask material, when welded together, comprise a uniaxial tension mask assembly. With reference to Figs. 4 and 5, a plurality of second metal strands 60, each having a diameter of about 0.025 mm (1 mil), are disposed substantially perpendicular to the first metal strands 40 and are spaced therefrom by an insulator 62 formed on the screen-facing side of each of the first metal strands. The second metal strands 60 form cross members that facilitate applying a second anode, or focusing, potential to the mask 25. The preferred material for the second metal strands is HyMu80 wire, available from Carpenter Technology, Reading, PA. The vertical spacing, or pitch, between adjacent second strands 60 is about 0.41 mm (16 mils). Unlike the cross members described in the prior art that have a substantial dimension that significantly reduces the electron beam transmission of the masking plate, the relatively thin second metal strands- 60 provide the essential focusing function to the present uniaxial focus tension mask 25 without adversely affecting the electron beam transmission thereof. The uniaxial tension focus mask 25, described herein, provides a mask transmission, at the center of the screen, of about 60 %, and requires that the second anode, or focusing, voltage, ΔV, applied to second strands 60, differs from the first anode voltage applied to the first metal strands 40 by less than about 1 kV, for a first anode voltage of about 30 kV. The insulators 62, shown in Figs. 4 and 5, are disposed substantially continuously on the screen-facing side of each of the first metal strands 40. The second metal strands 60 are bonded to the insulators 62 to electrically isolate the second metal strands 60 from the first metal strands 40. As shown in fig. 6, each of the insulators 62 is formed of at least two layers. A first insulator layer 64 is formed of a suitable material that has thermal expansion and contraction behavior matched to the material of the mask 25. Additionally, the material for the first insulator layer 64 must have a relatively low melting temperature so that it can flow, sinter and adhere to the mask strands within a temperature range of about 450 to 500° C. However, the insulator material also must be stable during the frit sealing of the CRT faceplate panel 12 to the funnel 15 that occurs at an elevated temperature of about 450 to 500° C . Additionally, the first insulator layer 64 must have a dielectric breakdown strength in excess of 4000 V/mm (100 V/mil), with bulk and surface electrical resistivties in excess of 10* 3 0 hm cm and 10^ 3 ohms/square, respectively. The first insulator layer 64 also must have adequate mechanical strength and elastic modulus, be low outgassing during processing and operation, and must retain these functional characteristics for an extended period of time within the radiative environment of the CRT. A second insulator layer 66 must be chemically, electrically, and mechanically compatible with the first insulator layer 64. The second layer 66 also must have good flow characteristics, must be stable during frit sealing of the faceplate panel 12 to the funnel 15 and must adhere well to the second strands 60. The second insulator layer 66 also seals any defects in the underlying first insulator layer 64. While only two insulator layers 64 and 66 are described, it should be evident that additional layers may be utilized, if required, as long as the layers are compatible with each other and with the underlying first metal strands 40. Suitable materials for the mask 25 include: high expansion, low carbon steels having a coefficient of thermal expansion (COE) within the range of 120 - 160 x 10 " ' /°C; an intermediate expansion alloy, such as iron-cobalt-nickel, e.g., KOVAR™ having a coefficient of thermal expansion within the range of 40 - 60 x 10 " '/°C; and a low expansion alloy, such as an iron-nickel alloy, e.g., INVAR™ having a coefficient of thermal expansion within the range of 15 - 30 x 10 " ^/°C . Suitable materials with good electrical properties that may be used for to form the first insulating layer 64 are listed in TABLE I. TABLE I MATERIAL NOMINAL NOMINAL SYSTEMS EXPANSION PROCESSING COEFFICIENT TEMPERATURE REMARKS (10-7/o (°C) Solder Glass 80 - 130 380 - 500 filler needed to (vitreous) improve heat stability & to adjust COE Solder Glass 75 - 120 400 - 550 filler needed to (devirtifying) adjust COE Conventional 30 - 130 600 - 1000 solution-chem¬ Glasses istry based (i.e., not a substantially approach to Pb-bearing system) lower process temperature, and/or adjust COE w/ filler Conventional 0 - 140 800 - 1300 same as above Glass - Ceramics Conventional 0 - 130 1000 - 2000 solution-chem¬ Ceramics istry based approach to lower process temperature, or vacuum deposition With the exception of the vitreous and devitrifying solder glasses listed in TABLE I, the other material systems have nominal processing temperatures outside of the 500°C range described above; however, these material systems may be adapted for use as first insulating layers, with the approaches outlines in the last columns of TABLE I. A devitrifying solder glass is one that melts at a specific temperature to form an insulator with substantially high crystalline content and does not remelt at the same or a lower temperature; whereas, a vitreous solder glass does not form a crystalline-glass insulator. Fillers that may be used in combination with the solder glasses described in TABLE I are listed in TABLE II. TABLE II Filler Material Thermal Expansion Coefficient (IQ-7/ Q C . Beta-eucryptite - 86 Aluminum Titanate 1 9 Vitreous Silica (SiO ^ 5.5 Beta-spodumene Boron Nitride (BN) 40 Wollastonite (CaSiC 94 Quartz 120 Fluorspar 225. Cristobalite 125 (to ~225°C ) 500 (to -35000 The preferred methods for synthesizing matched expansion insulators for the three ranges of metal expansion, described above, are outlined in TABLE III. TABLE Lϋ Insulator High-Expansion Intermediate-Expansion Low-Expansion Matrix (e.g.. Steel Allov(e.g.. KOVAR™ Allov (e.g.. INVAR™) PZB, • high-expansion • intermediate-expansion • composites with PZBS, matrix as is, or matrix as is, or low expansion fillers vitreous or • composites in • composites with • accommodate devitrifying combination with intermediate and low inflection in expansion solder glass one or more of expansion fillers with small addition of systems quartz, cristobalite, cristobalite and fluorspar The processing methods for the insulators shown in TABLE I, for application to the first metal strands 40 of the mask 24, depends on the choice of the insulator. A few examples of insulator application parameters are shown in TABLE IV. ] L 1 TABLE IV Material Svstem Material Preparation Deposition Patterning Fixing devitrifying • frit molten glass w/ • spray • brush • heat solder average particle size • roller • abrade in neutral glasses < 10 μm • electro¬ • mask & or • mix & mill w/ binder phoretic strip oxidizing and solvent deposition atmosphere • dip Non-devitrifying, • frit molten glass to • spray • brush • heat in (vitreous) solder average particle size • roller • abrade neutral or glasses < 10 μm • electro- • mask & or • mix & mill w/ binder phoretic strip oxidizing and solvent • dip atmosphere Conventional • fine particle (-1000 • spray • brush • heat in glasses A or less) synthesis • roller • abrade in several • dispersion in gel or • dip • mask & atmospheric sol formats strip conditions Conventional • fine particle (-1000 • spray • brush • heat in ceramics A or less) synthesis • roller • abrade in several • dispersion in gel • dip • mask & atmospheric or sol formats strip conditions Conventional • fine particle (-1000 • spray • brush • heat in glass A or less) synthesis • roller • abrade in several ceramics • dispersion in gel or • dip • mask & atmospheric sol formats strip conditions Film deposition • sputtering targets • vacuum • abrade • not based conventional • PVD, CVD deposition • mask & always glass, ceramic, and strip required glass-ceramic Composites of the • dispersed during • as • as • heat in above systems with milling appropriate appropriate appropriate dispersed particle atomspheric Dhases conditions EXAMPLE I According to a preferred method of making the uniaxial tension focus mask 25, a first coating of an insulative, devitrifying solder glass is provided, e.g., by spraying, onto the screen-facing side of the first metal strands 40. The first metal strands, in this example, are formed of a high expansion, low carbon steel having a coefficient of thermal expansion within the range of 120 - 160 x 10"? /°C. The devitrifying solder glass may be either a PbO-ZnO-B2θ3 system, referred to in TABLE III as PZB, or a PbO-ZnO-B2θ3-Siθ2 system, referred to in TABLE III as PZBS. Each of the glass systems has a coefficient of thermal expansion of about 75 - 120 x 10" ^ /oc, depending upon the composition, in weight %, of the constituents. A suitable solvent and an acrylic binder are mixed with the devitrifying solder glass to give the first coating a modest degree of mechanical strength. Because the solder glass system has a coefficient of thermal expansion just slightly less that of the high expansion steel of the strands 40, it is not necessary to add any filler material to the solder glass system; although, one or more of the fillers quartz, fluorspar and cristobalite may be added to make the coefficients of thermal expansion of the glass and steel match exactly. In the event that it is desired to add fillers, quartz and/or flurospar may be added to comprise up to 40 %, by weight, and cristobalite may comprise less that 10 %, by weight, of the devitreous solder glass composition. The balance of the composition comprises either PZB or PZBS. The first coating has a thickness of about 0J4 mm. The frame 44, to which the first metal strands 40 are attached, is placed into an oven and the first coating is dried at a temperature of about 80 °C. After drying, the first coating is contoured so that it is shielded by the first metal strands 40 to prevent the electron beams 28, passing thought the slots 42, from impinging upon the insulator and charging it. The contouring is performed on the first coating by abrading or otherwise removing any of the solder glass material of the first coating that extends beyond the edge of the strands 40 and would be contacted by either the deflected or undeflected electron beams 28. The first coating is entirely removed from the initial and ultimate, i.e., the right and left first metal strands, hereinafter designated the first metal end strands 140, before the first coating is heated to the sealing temperature. The first metal end strands 140, which are outside of the effective picture area, subsequently will be used as busbars to address the second metal strands 60. To further ensure the electrical integrity of the uniaxial tension focus mask 25, at least one additional first metal strand 40 is removed between the first metal end strands 140 and the first metal strands 40 that overlie the effective picture area of the screen, to minimize the possibility of a short circuit. Thus, the right and left first 5 metal end strands 140, outside the effective picture area, are spaced from the first metal strands 40 that overlie the picture area by a distance of at least 1.4 mm (55 mils), which is greater than the width of the equally spaced slots 42 that separate the first metal strands 40 across the picture area. 1 0 The frame 44 with the first metal strands 40 and. the end strands 140 attached thereto (hereinafter referred to as the assembly) is placed into an oven and heated in air. The assembly is heated over a period of 30 minutes to a temperature of 300 °C and held at 300 °C for 20 minutes. Then, over a period of 20 minutes, the temperature of the oven is 1 5 increased to 460 ° C and held at that temperature for one hour to melt and crystallize the first coating to form a first insulator layer 64 on the first metal strands 40, as shown in Fig. 6. The resultant first insulator layer 64, after firing, is stable and will not remelt during frit sealing of the faceplate panel 12 to the funnel 15, and has a thickness within the 20 range of 0.5 to 0.9 mm (2 to 3.5 mils) across each of the strands 40. The preferred material for the first coating is a lead-zinc-borosilicate devitrified solder glass that melts in the range of 400 to 450 °C and is commercially available, as SCC-11, from a number of glass suppliers, including SEM-COM, Toledo, OH, and Corning Glass, Corning, NY. 25 Next, a second coating of a suitable insulative material, mixed with a solvent and a binder, is applied, e.g., by spraying, to the first insulator layer 64. Preferably, the second coating is a non-devitrifying (i.e., vitreous) solder glass having a composition of 80 wt.% PbO, 5 wt % ZnO, 14 wt.% B2O3, 0.75 wt.% Snθ2, and, optionally, 0.25 wt.% CoO. A vitreous 30 material is preferred for the second coating because, when it melts, it will fill any voids in the surface of the first insulator layer 64 without adversely affecting its electrical and mechanical characteristics, also, it , will not alter the temperature stability of the underlying first insulator layer. Alternatively, a devitrifying solder glass may be used to form the . 3 5 second coating. The second coating is applied to a thickness of about 0.025 to 0.05 mm (1 to 2 mils). The second coating is dried at a temperature of 80 °C and contoured, as previously described, to remove any excess material that could be struck by the electron beams 28. The second coating has a coefficient of thermal expansion of about 110 x IO - 7 /°C and may contain up to 40 %, by weight, of quartz and/or fluorspar and less than 10 %, by weight, of cristobalite, i.e., the same concentration of fillers that is added to the first coating. EXAMPLE II The first metal strands, in this second example, are formed of a low expansion, iron-nickel alloy, such as INVAR™, having a coefficient of thermal expansion within the range of 15 - 30 x 10"? /°C. The expansion behavior of this material up to a temperature of 100°C remains low at about 15 x 10" 7 /°C; however, there is an inflection in the expansion behavior from 160°C to 271°C, due to a magnetic phase change that increases the coefficient of thermal expansion, within this temperature range, to about 30 x 10" 7 /°C. The devitrifying solder glass used with the iron-nickel strands 40 may be either the PZB or PZBS system described above. Because each of the glass systems has a coefficient of thermal expansion of about 75 - 120 x IO" 7 /°C, depending upon the composition of the constituents, the coefficient of thermal expansion of the glass must be reduced to slightly less than, or substantially equal to, that of the iron- nickel strand material. This is achieved by including up to 40 wt. % of a low expansion filler, such as Beta-eucryptite (Li2Al2Siθ6), Aluminum Titanate (AlTiOs ), vitreous silica (Siθ2 ) or Beta-spodumene (Li2Al2Si4θ i2) to the PZB or PZBS matrix. Additionally, up to 5 wt. % of cristobalite is added to compensate for the inflection in the coefficient of thermal expansion of the iron-nickel alloy. Cristobalite has a coefficient of thermal expansion of 125 x IO" 7 C up to ~225°C and 500 x 10" 7 /°C up to ~350°C. The small amount of cristobalite added to the composite mixture provides a match between the expansion behavior of the iron- nickel alloy and the first solder glass coating. A suitable solvent and an acrylic binder are mixed with the devitrifying solder glass composite to give the first coating a modest degree of mechanical strength. The balance of the composition comprises either PZB or PZBS. The first coating has a thickness of about 0J4 mm. The frame 44, to which the first metal strands 40 are attached, is placed into an oven and the first coating is dried at a temperature of about 80 °C. After drying, the first coating is contoured so that it is shielded by the first metal strands 40 to prevent the electron beams 28, passing thought the slots 42, from impinging upon the insulator and charging it. The contouring is performed, as described in the first example, by abrading or otherwise removing any of the solder glass material of the first coating that extends beyond the edge of the strands 40 and would be contacted by either the deflected or undeflected electron beams 28. The first coating is entirely removed from the initial and ultimate, i.e., the first metal end strands 140, before the first coating is heated to the sealing temperature. The first metal end strands 140, which are outside of the effective picture area, subsequently will be used as busbars to address the second metal strands 60. To further ensure the electrical integrity of the uniaxial tension focus mask 25, at least one additional first metal strand 40 is removed between the first metal end strands 140 and the first metal strands 40 that overlie the effective picture area of the screen, to minimize the possibility of a short circuit. Thus, the right and left first metal end strands 140, outside the effective picture area, are spaced from the first metal strands 40 that overlie the picture area by a distance of at least 1.4 mm (55 mils), which is greater than the width of the equally spaced slots 42 that separate the first metal strands 40 across the picture area. The assembly comprising the frame 44 with the first metal strands 40 and the end strands 140 attached thereto is placed into an oven and heated in air. The assembly is heated over a period of 30 minutes to a temperature of 300 °C and held at 300 °C for 20 minutes. Then, over a period of 20 minutes, the temperature of the oven is increased to 460 °C and held at that temperature for one hour to melt and crystallize the first coating to form a first insulator layer 64 on the first metal strands 40, as shown in Fig. 6. The resultant first insulator layer 64, after firing, has a thickness within the range of 0.5 to 0.9 mm (2 to 3.5 mils) across each of the strands 40. Next, a second coating of a suitable insulative material, mixed with a solvent and a binder, is applied, e.g., by spraying, to the first insulator layer 64. Preferably, the second coating is a non-devitrifying (i.e., vitreous) solder glass having a composition of 80 wt.% PbO, 5 wt % ZnO, 14 wt.% B2O3, 0.75 wt.% Snθ2, and, optionally, 0.25 wt.% CoO. Alternatively, a devitrifying solder glass may be used to form the second coating. The second coating is applied to a thickness of about 0.025 to 0.05 mm ( 1 to 2 mils). The second coating is dried at a temperature of 80 ° C and contoured, as previously described, to remove any excess material that could be struck by the electron beams 28. The second coating has a coefficient of thermal expansion of about 15 - 30 x 10" 7 /°C and may contain up to 40 %, by weight, of the low expansion fillers, such as Beta- eucryptite (Li2Al2Siθ6), Aluminum Titanate (AlTiOs), vitreous silica (Siθ2) or Beta-spodumene (L12AI2S14O 1 2) and up to 5 %, by weight, of cristobalite, i.e., the same concentration of fillers that are added to the first coating. EXAMPLE III The first metal strands, in this third example, are formed of an intermediate expansion, iron-cobalt-nickel alloy, such as KOVAR™, having a coefficient of thermal expansion within the range of 40 - 60 x IO" 7 /°C . The devitrifying solder glass used with the intermediate expansion alloy strands 40 may be either the PZB or PZBS system described above. Because each of the glass systems has a coefficient of thermal expansion of about 75 - 120 x IO" 7 /°C, depending upon the composition of the constituents, the coefficient of thermal expansion of the glass must be reduced to substantially equal that of the intermediate expansion alloy strand material. This is achieved by including about 40 wt. % of suitable fillers from the group consisting of the low expansion fillers Li2Al2Siθ£, AlTi θ5 , vitreous Siθ2 and L_2Al 2 Si4θ j 2 > anc rom the group of intermediate expansion fillers consisting of Zn2SiO4, Mg2Al4Si5θ ι g, BaAl 2 Si 2 O 8 , ZnAl 2 O 4 , BN, Al 6 Si 2 O 13 , CaAl 2 Si 2 O 8 , MgSiO 3 , MgTiO 3 , Al 2 O 3 , Mg2SiO4, and CaSK^such as Beta-eucryptite O^A^SiOg), Aluminum Titanate (AIΗO5), vitreous silica (Siθ2), Beta-spodumene (Li2Al2Si4θ j2), to the PZB or PZBS matrix. A suitable solvent and an acrylic binder are mixed with the devitrifying solder glass composite to give the first coating a modest degree of mechanical strength. The balance of the composition comprises either PZB or PZBS. The first coating has a thickness of about 0J4 mm. The frame 44, to which the first metal strands 40 are attached, is placed into an oven and the first coating is dried at a temperature of about 80 °C. After drying, the first coating is contoured so that it is shielded by the first metal strands 40 to prevent the electron beams 28, passing thought the slots 42, from impinging upon the insulator and charging it. The contouring is performed, as described in the first example, by abrading or otherwise removing any of the solder glass material of the first coating that extends beyond the edge of the strands 40 and would be contacted by either the deflected or undeflected electron beams 28. The first coating is entirely removed from the initial and ultimate, i.e., the first metal end strands 140, before the first coating is heated to the sealing temperature. The first metal end strands 140, which are outside of the effective picture area, subsequently will be used as busbars to address the second metal strands 60. To further ensure the electrical integrity of the uniaxial tension focus mask 25, at least one additional first metal strand 40 is removed between the first metal end strands 140 and the first metal strands 40 that overlie the effective picture area of the screen, to minimize the possibility of a short circuit. Thus, the right and left first metal end strands 140, outside the effective picture area, are spaced from the first metal strands 40 that overlie the picture area by a distance of at least 1.4 mm (55 mils), which is greater than the width of the equally spaced slots 42 that separate the first metal strands 40 across the picture area. The assembly comprising the frame 44 with the first metal strands 40 and the end strands 140 attached thereto is placed into an oven and heated in air. The assembly is heated over a period of 30 minutes to a temperature of 300 °C and held at 300 °C for 20 minutes. Then, over a period of 20 minutes, the temperature of the oven is increased to 460 °C and held at that temperature for one hour to melt and crystallize the first coating to form a first insulator layer 64 on the first metal strands 40, as shown in Fig. 6. The resultant first insulator layer 64, after firing, has a thickness within the range of 0.5 to 0.9 mm (2 to 3.5 mils) across each of the strands 40. Next, a second coating of a suitable insulative material, mixed with a solvent and a binder, is applied, e.g., by spraying, to the first insulator layer 64. Preferably, the second coating is a non-devitrifying (i.e., vitreous) solder glass having a composition of 80 wt.% PbO, 5 wt % ZnO, 14 wt.% B2O3, 0.75 wt.% Snθ2, and, optionally, 0.25 wt.% CoO. Alternatively, a devitrifying solder glass may be used to form the second coating. The second coating is applied to a thickness of about 0.025 to 0.05 mm ( 1 to 2 mils). The second coating is dried at a temperature of 80 ° C and contoured, as previously described, to remove any excess material that could be struck by the electron beams 28. The second coating has a coefficient of thermal expansion of about 40 - 60 x IO - 7 /°C and may contain up to 40 %, by weight, of suitable fillers from the group consisting of the low expansion fillers Li2Al2SiOg, AlTiθ5, vitreous Siθ2 and Li2Al2Si4θ j 2' anc * from the group of intermediate expansion fillers consisting of Zn2SiO 4 , Mg 2 Al 4 Si 5 0 1 8 , BaAl 2 Si 2 O 8 , ZnAl 2 O 4 , BN, Al 6 Si 2 O 13 , CaAl 2 Si 2 O 8 , MgSiO 3 , MgTiO 3 , Al 2 O 3 , Mg 2 SiO 4 , and CaSiO 3 . Additional material systems, such as conventional glass systems, conventional glass-ceramic systems, conventional ceramics, deposited films, and composites of these systems, that are listed in TABLE III, also may be utilized as suitable insulator coatings for the metal strands 40 of the mask 25. The methods for preparing, depositing, patterning and fixing, i.e., sintering or heat treating, these material systems are summarized in TABLE III, and are suitably specific to permit one having ordinary skill in the art to form insulator coatings therefrom. As shown in Figs. 4, 5 and 7, a thick coating of a devitrifying solder glass containing silver, to render it conductive, is provided on the screen- facing side of the left and right first metal end strands 140. A conductive lead 65, formed from a short length of nickel wire, is embedded into the conductive solder glass on one of the first metal end strands. Then, the assembly, having the dried and contoured second coating overlying the first insulator layer 64, has the second metal strands 60 applied thereto so that the second metal strands overlie the second coating of insulative material and are substantially perpendicular to the first metal strands 40. The second metal strands 60 are applied using a winding fixture, not shown, that accurately maintains the desired spacing of about 0.41 mm between the adjacent second metal strands. The second metal strands 60 also contact the conductive solder glass on the first metal end strands 140. Alternatively, the conductive solder glass can be applied at the junction between the second metal strands 60 and the first metal end strands 140 during, or after, the winding operation. Next, the assembly, including the winding fixture, is heated for 7 hours to a temperature of 460 °C to melt the second coating of insulative material, as well as the conductive solder glass, to bond the second metal strands 60 within both a second insulator layer 66 and a glass conductor layer 68. The second insulator layer 66, has a thickness, after sealing, of about 0.013 to 0.025 mm (0.5 to 1 mil). The height of the glass conductor layer 68 is not critical, but should be sufficiently thick to firmly anchor the second metal strands 60 and the conductive lead 65 therein. The portions of the second metal strands 60 extending beyond the glass conductor layer 68 are trimmed to free the assembly from the winding fixture. As shown in Fig. 4, the first metal end strands 140 are severed at the ends adjacent to the long side or top portion 32. The strands 140 are similarly severed adjacent to the long side or bottom portion 34, not shown in Fig. 4, of the mask 25 to provide gaps of about 0.4 mm (15 mils) therebetween that will electrically isolate the first metal end strands 140. The first metal end strands 140 form busbars that permit a second anode voltage to be applied to the second metal strands 60 when the conductive lead 65, embedded in the glass conductor layer 68, is connected to the second anode button 17.

Claims: CLAIMS 1. A color cathode-ray tube (10) comprising an evacuated envelope (11) having therein an electron gun (26) for generating at least one 5 electron beam (28), a faceplate panel (12) having a luminescent screen (22) with phosphor lines on an interior surface thereof, and a uniaxial tension focus mask (25) having a plurality of spaced-apart first metal strands (40) which are adjacent to an effective picture area of said screen and define a plurality of slots (42) substantially parallel to said phosphor 1 0 lines, each of said first metal strands across said effective picture area having a substantially continuous insulator (62) on a screen-facing side thereof, said insulator comprising more than one insulator layer (64,66), and a plurality of second metal strands (60) oriented substantially perpendicular to said first metal strands, said second metal strands being 1 5 bonded to said insulator, wherein said insulator (62) comprises a first insulator layer (64) having a coefficient of thermal expansion substantially matching, or slightly lower than, the coefficient of thermal expansion of said first metal strands (40), and a second insulator layer (66) having a coefficient of thermal 20 expansion substantially equal to the coefficient of thermal expansion of said first insulator layer. 2. A color cathode-ray tube (10) comprising an evacuated envelope (11) having therein an electron gun (26) for generating three electron 25 beams (28), a faceplate panel (12) having a luminescent screen (22) with phosphor lines on an interior surface thereof, and a uniaxial tension focus mask (25) in proximity to said screen, said tension focus mask having two long sides (32,34) with a plurality of transversely spaced-apart first metal strands (40) extending therebetween, the space between adjacent 3 0 first metal strands defining substantially equally spaced slots (42) parallel to said phosphor lines of said screen, said long sides of said mask being secured to a substantially rectangular frame (44) having two long sides and two short sides, each of said first metal strands across an effective picture area of said screen having a substantially continuous , 3 5 first insulator layer (64) on a screen-facing side thereof, a second insulator layer (66) overlying said first insulator layer, and a plurality of second metal strands (60) oriented substantially perpendicular to said first metal strands, said second metal strands being bonded by said second insulator layer, wherein said first insulator layer (64) has a coefficient of thermal expansion substantially matching, or slightly lower than, the coefficient of thermal expansion of said first metal strands (40), and said second insulator layer (66) has a coefficient of thermal expansion substantially equal to the coefficient of thermal expansion of said first insulator layer. 3. The cathode-ray tube (10) as described in claim 2, wherein said first metal strands (40) have a coefficient of thermal expansion within the range of 15 - 160 x IO" 7 /°C . 4. The cathode-ray tube (10) as described in claim 2, wherein said first insulator layer (64) has a coefficient of thermal expansion within the range of 0 - 140 x 10" 7 /°C . 5. The cathode-ray tube (10) as described in claim 2 wherein said first metal strands (40) comprise a low carbon steel having a coefficient of thermal expansion within the range of 120 - 160 x 10" /°C . 6. The cathode-ray tube (10) as described in claim 5, wherein said first insulator layer (64) comprises a devitrified solder glass matrix, having a coefficient of thermal expansion within the range of 75 - 120 x 10" 7 /°C, said matrix being selected from the group consisting of PbO-ZnO- B2O3 and PbO-ZnO-B2θ3-Siθ2 . 7. The cathode-ray tube (10) as described in claim 6, wherein said first insulator layer (64) comprises a composite material including said devitrified solder glass matrix and a filler selected from the group consisting of cristobalite, flourspar and quartz, said cristobalite comprising not more than 10 wt.%, at least one of said fluorspar and quartz comprising 40 wt.%, and said devitrified solder glass matrix comprising the balance of said composite material. 8. The cathode-ray tube (10) as described in claim 2, wherein said first metal strands (40) comprise a low expansion iron-nickel alloy having a coefficient of thermal expansion within the range of 15 - 30 x 10 "7 /°C . 9. The cathode-ray tube (10) as described in claim 8, wherein said first insulator layer (64) comprises a composite material consisting of a devitrified solder glass matrix, having a coefficient of thermal expansion within the range of 75 - 120 x 10" 7 /°C, said matrix being selected from the group consisting of PbO-ZnO-B2θ3 and PbO-ZnO-B2θ3-Siθ2 , and at least two fillers to lower the coefficient of thermal expansion within the range of 10 - 25 x 10 "7 /°C, one of said fillers having a low coefficient of thermal expansion and the other having a high coefficient of thermal expansion with an inflection occurring at a temperature at which said iron-nickel alloy undergoes an inflection due to magnetic transitions. 10. The cathode-ray tube (10) as described in claim 9, wherein said filler a said low coefficient of thermal expansion is selected from the group consisting of Li2Al2SiO£, AIΗO5, vitreous SK>2 and Li2Al2Si4θ i 2, and said filler having a high coefficient of thermal expansion comprises cristobalite. 11. The cathode-ray tube (10) as described in claim 10, wherein said filler having a low coefficient of thermal expansion comprises up to 40 wt. % of said composition material, said cristobalite comprises up to 5 wt. %, and said matrix of devitrifying solder glass comprises the balance. 12. The cathode-ray tube (10) as described in claim 2, wherein said first metal strands (40) comprise an intermediate expansion alloy having a coefficient of thermal expansion within the range of 40 - 60 x 13. The cathode-ray tube (10) as described in claim 12, wherein said first insulator layer (64) comprises a composite material consisting of a devitrified solder glass matrix, having a coefficient of thermal expansion within the range of 75 - 120 x 10 "7 /°C, said matrix being selected from the group consisting of PbO-ZnO-B2θ3 and PbO-ZnO-B2C»3-SiO2 , and at least one filler to lower the coefficient of thermal expansion within the range of 40 - 60 x 10" 7 /°C, said filler having a low or intermediate coefficient of thermal expansion. 14. The cathode-ray tube (10) as described in claim 13, wherein said filler is selected from the group of low expansion fillers consisting of Li2Al2Siθ6, AlTiθ5, vitreous Siθ2 and Li2Al2Si4θ i 2, and from the group of intermediate expansion fillers consisting of Zn2Siθ4, Mg2Al4Si5θ j 8 , BaAl 2 Si 2 O 8 , ZnAl 2 0 4 , BN, Al 6 Si 2 0 13 , CaAl 2 Si 2 0 8 , MgSi0 3 , MgTi0 3 , Al 2 O 3 , M g 2S iO4, and CaSiθ3 , said filler comprising up to 40 wt. % of said composite material of said first insulator layer (64). 15. The cathode-ray tube (10) as described in claim 2, wherein said second insulator layer (66) comprises a vitreous solder glass consisting essentially of PbO-ZnO-B2C»3-SnO2 and, optionally, CoO. 16. The cathode-ray tube (10) as described in claim 9, wherein said second insulator layer (66) comprises a vitreous solder glass matrix having a composition comprising 80 wt.% PbO, 5 wt.% ZnO, 14 wt.% B2O3, 0.75 wt.% Snθ2, and optionally, 0.25 wt.% CoO, with a coefficient of thermal expansion of about 110 x 10" 7 /°C, and at least two fillers to lower the coefficient of thermal expansion within the range of 10 - 25 x 10" 7 /°C, one of said fillers having a low coefficient of thermal expansion and the other having a high coefficient of thermal expansion with an inflection occurring at a temperature at which said iron-nickel alloy undergoes an inflection due to magnetic transitions. 17. The cathode-ray tube (10) as described in claim 16, wherein said filler a said low coefficient of thermal expansion is selected from the group consisting of Li2Al2SiO6, AlTiU5, vitreous Siθ2 and Li2Al2Si4θ i 2, and said filler having a high coefficient of thermal expansion with an inflection comprises cristobalite. 18. The cathode-ray tube (10) as described in claim 17, wherein said filler a said low coefficient of thermal expansion comprises up to 40 wt.% of said second insulator layer (66), said cristobalite comprises up to 5 wt.%, and said vitreous solder glass matrix comprises the balance. 19. The cathode-ray tube (10) as described in claim 8, wherein said second insulator layer (66) comprises a vitreous solder glass matrix having a composition comprising 80 wt.% PbO, 5 wt.% ZnO, 14 wt.% B2O3, 0.75 wt.% SnO 2 , and optionally, 0.25 wt.% CoO, with a coefficient of thermal expansion of about 110 x 10 "7 /°C, and at least one filler to lower the coefficient of thermal expansion within the range of 40- 60 x 10" 7 /°C , said fillers having a low or intermediate coefficient of thermal expansion. 20. The cathode-ray tube (10) as described in claim 19, wherein said filler is selected from the group of low expansion fillers consisting of Li2Al2SiOg, AlTiθ5, vitreous Siθ2 and L12AI2S14O 12, and from the group of intermediate expansion fillers consisting of Zn2SiO4, Mg2Al4Si5θ j 8 , BaAl 2 Si 2 O 8 , ZnAl 2 O 4 , BN, Al 6 Si 2 O 13 , CaAl 2 Si O 8 , MgSiO 3 , MgTiO 3 , Al 2 O 3 , Mg2Siθ4, and CaSiθ3, said filler comprising up to 40 wt.% of said second insulator layer (66).

Inventors: CHERUKURI SATYAM CHOUDARY, CHERUKURI, SATYAM, CHOUDARY
Applicants: RCA THOMSON LICENSING CORP, RCA THOMSON LICENSING CORPORATION
Application year: 1996
Main classification: H01J29
IPC codes: H01J9, H01J29