HK1015072B - Color crt having uniaxial tension focus mask and method of making a mask - Google Patents

Description

Color cathode ray tube having uniaxial tension focus mask and method of making the same

The present invention relates to a color Cathode Ray Tube (CRT), and more particularly, to a color CRT having a uniaxial tension focus mask and a method of manufacturing the mask.

Conventional shadow mask type color CRTs typically comprise an evacuated envelope having therein: a phosphor screen having three phosphor elements emitting light of different colors, the phosphors being arranged in a cyclic order in a color-group manner; means for generating three electron beams converging toward the phosphor screen; and a color selection structure, such as a shadow mask, positioned between the phosphor screen and the electron beam generating device. The shadow mask acts as a parallax barrier that shields the phosphor screen. The difference in convergence angles of the incident electron beams allows the transmissive portions of these electron beams to excite the phosphor elements of the correct luminescent color. One disadvantage of shadow mask CRTs is that, at the center of the screen, the shadow mask intercepts all but about 18-22% of the beam; that is, the shadow mask is considered to have only about 18-22% transmittance. Thus, the area of the apertures in the shadow mask is approximately 18-22% of the area of the shadow mask. Since there is no focus field associated with the shadow mask, the corresponding portion of the phosphor screen will be excited by the electron beam.

To increase the transmittance of the color selection electrode without increasing the size of the excited portion of the screen, a color selection structure that is focused after deflection is required. The focusing characteristics of this configuration allow the use of larger aperture sizes to achieve greater electron beam transmission than can be achieved with conventional shadow masks. Such a structure is described in Japanese patent laid-open publication Sho 39-24981, published by SONY at 11/6 in 1964. In this patented structure, mutually orthogonal leads are fixed at their intersections by insulators to provide large apertures for passage of electron beams. One disadvantage of this configuration is that the cross-leads provide little shielding for the insulator, so that the deflected electron beam will strike the insulator and electrostatically charge it. The electrostatically charged insulator will distort the path of the electron beam through the aperture such that the electron beam is misaligned with the phosphor screen unit. Another disadvantage of this structure is that mechanical breakdown of the insulator can cause electrical shorts between crossing gate lines. Another color selective electrode focusing structure that overcomes some of the disadvantages of the japanese patent publication described above is described in us patent 4443499 issued to Lipp at 17.4.4.1984. The structure described in us patent 4443499 employs a shadow mask as the first electrode, the shadow mask having a thickness of about 0.15mm (6 mils) and having a plurality of rectangular apertures therethrough. A plurality of metal strips separate the rows of holes. The top surface of the metal strip is provided with a suitable insulating coating. A metal coating overlies the insulating coating to form a second electrode that provides the desired electron beam focusing when a suitable potential is applied to the shadow mask and the metal coating. Alternatively, as described in us patent 4650435 issued to Tamutus on 3/17 1987, a metal shadow mask constituting the first electrode is etched from one surface to form a plurality of parallel trenches in which an insulating material is deposited to form insulating strips. The shadow mask is further processed through a series of exposure, development and etching steps to form a plurality of apertures between the strips of insulating material located on the support plate. The metallization (coating) of the top surface of the insulating strip constitutes the second electrode. The two U.S. patents mentioned above eliminate the problem of electrical shorts between isolated conductors, which is a disadvantage in prior japanese (patent-described) constructions; however, each cross member of the shadow mask of the us patent has a much larger size, which reduces the electron beam transmittance. In addition, the thickness of the shadow mask plate is such that the result is: the deflected electrons will still hit the strip of insulating material and electrostatically charge it. Accordingly, there is a need for a focus mask structure that overcomes these shortcomings of prior art structures.

The object of the invention is to provide a color cathode ray tube having an evacuated envelope with an electron gun for generating at least one electron beam. The envelope also includes a faceplate panel having a phosphor screen with phosphor stripes on an inner surface thereof. A uniaxial tension focus mask is disposed adjacent the effective picture area of the screen, the mask having a plurality of spaced apart first metal strips. The spacing between the first metal strips forms a plurality of slots that are substantially parallel to the phosphor lines of the screen. Each first metal strip has a substantially continuous first insulating layer on its screen-facing side across the effective picture area of the screen. A second insulating layer covers the first insulating layer. The plurality of second metal strips are oriented substantially perpendicular to the first metal strips and are bonded to the first metal strips by the second insulating layer.

The invention will now be described in more detail with reference to the accompanying drawings, in which:

fig. 1 (first page) is a plan view, partly in axial section, of a color CRT embodying the present invention;

fig. 2 (second page) is a plan view of a single axis tension focus mask-frame assembly for use in the CRT of fig. 1;

fig. 3 (second page) is a front view of the mask-frame assembly taken along line 3-3 in fig. 2;

figure 4 (third page) is an enlarged view of the uniaxial tension focus mask shown within ring 4 in figure 2;

FIG. 5 (third page) is a cross-sectional view of the uniaxial tension focus mask and phosphor screen taken along line 5-5 in FIG. 4;

fig. 6 (second page) is an enlarged schematic view of a portion of the uniaxial tension focus mask within ring 6 of fig. 5;

figure 7 (third page) is an enlarged schematic view of another portion of the uniaxial tension focus mask within ring 7 of figure 5.

Fig. 1 shows a color CRT10 having a glass envelope 11 comprising a rectangular faceplate panel (faceplate panel)12 and a tubular neck 14, the faceplate panel 12 and neck 14 being connected by a rectangular funnel 15. The cone has an inner conductive coating (not shown) that contacts the first anode button (anodebutton)16 and extends therefrom to the neck 14. A second anode button 17 disposed opposite the first anode button 16 is not in contact with this conductive coating. The panel 12 includes a cylindrical viewing panel 18 and a peripheral edge or sidewall 20 that is sealed to the cone 15 by a frit 21. A three-color phosphor screen 22 is carried by the inner surface of the faceplate panel 18. The screen 22 is a striped screen, as shown in detail in fig. 5, which includes a plurality of screen cells comprised of phosphor stripes R, G and B that emit red, green, and blue light, respectively, the phosphor stripes being arranged in triads, each triad including a phosphor stripe for each of the three colors. Preferably, a light absorbing matrix 23 separates the phosphor stripes. The entire array of phosphor screen elements and light absorbing matrix 23 that a viewer can observe during operation of the CRT is referred to as the active image area. A thin conductive layer 24, preferably formed of aluminum, covers the screen 22 to provide a means for applying a uniform first anode potential to the screen and for reflecting light emitted from the phosphor elements through the faceplate 18. A cylindrical porous color selection electrode or uniaxial tension focus mask 25 is removably mounted in the faceplate panel 12 by conventional means and at a predetermined spacing relative to the screen 22. An electron gun 26, shown schematically by dashed lines in fig. 1, is centrally mounted within the neck 14 for generating three inline electron beams 28, a center beam and two side or outer beams, and directing the three beams along convergent paths through the mask 25 to the screen 22. The in-line arrangement of the electron beams 28 is oriented perpendicular to the plane of the paper.

The CRT of fig. 1 is intended to be used with an external magnetic deflection yoke, such as yoke 30 shown adjacent the cone-neck junction. When energized, the yoke 30 subjects the three beams to magnetic fields that cause the beams to scan a horizontal and vertical rectangular raster across the screen 22. The uniaxial tension mask 25 is preferably made from a thin rectangular sheet of about 0.05mm (2 mil) thick mild steel, as shown in figure 2, which includes two long sides 32, 34 and two short sides 36, 38. The two long sides 32, 34 of the mask are parallel to the long central axis X of the CRT and the two short sides 36, 38 are parallel to the short central axis Y of the CRT. This steel has the following composition (about by weight): 0.005% carbon, 0.01% silicon, 0.12% phosphorus, 0.43% manganese and 0.007% sulfur. The mask material preferably has an ASTM (American Standard for testing materials) particle size in the range of 9-10.

The shadow mask 25 includes an apertured portion adjacent to and overlying a corresponding active image area of the screen 22, which area is within the central dashed line of fig. 2, which lines define the periphery of the shadow mask 25. As shown in fig. 4, the uniaxial tension focus mask 25 includes a plurality of elongated first metal strips 40 each having a transverse dimension or width of about 0.3mm (12 mils), separated by substantially equally spaced slots 42, each slot having a width of about 0.55mm (21.5 mils), the first metal strips 40 being parallel to the short axis Y of the CRT and the phosphor stripes of the screen 22. Each aperture 42 corresponds to a triad in the active image of the screen 22. In a color CRT having a diagonal dimension of 68cm (27 inches), there are about 600 first metal strips 40. Each slot 42 extends from one long side 32 of the mask to the other long side 34 (not shown in fig. 4). Any pair of adjacent split first metal strips 40 define a slot 42 and a plurality of adjacent split first metal strips 40 define a plurality of slots 42 of the single axis tension focus mask 25. The slot 42 is substantially parallel to the phosphor strip. A frame 44 for the shadow mask 25 is shown in fig. 1-3 and includes four main components, namely two torsion tubes or curved components 46 and 48 and two tension arms or straight components 50 and 52. The two curved members 46 and 48 are parallel to the long axis X and to each other. As shown in FIG. 3, each straight section 50 and 52 includes two overlapping half sections or portions 54 and 56, each having an L-shaped cross-section. The overlapping portions 54 and 56 are welded together where they overlap. One end of each portion 54 and 56 is connected to one end of one of the curved members 46 and 48. The curvature of the curved sections 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 two curved sections 46 and 48, which provide the tension required for the mask. The mask material is pre-stretched and blackened prior to welding to the frame 44 by stretching the mask material while heating, the stretching being performed in a controlled atmosphere of nitrogen and oxygen at a temperature of about 500 c for 1 hour. When welded together, the frame 44 and mask material form a single axis tension mask assembly.

Referring to fig. 4 and 5, a plurality of second metal stripes 60, each having a diameter of about 0.025mm (1 mil), are disposed substantially perpendicular to first metal stripes 40 and are separated from the first metal stripes by an insulator 62, the insulator 62 being formed on the screen-facing side of each first metal stripe. The second metal strips 60 form cross members that facilitate the application of a second anode or focus potential to the shadow mask 25. A preferred material for the second metal strip is HyMu80 wire, which is available from Carpenter technology, Reading, PA. The vertical spacing or pitch between adjacent second metal strips 60 is about 0.41mm (16 mils). Unlike the prior art cross-members described as having large dimensions that significantly reduce the electron beam transmission of the shadow mask, the thinner second metal strips 60 provide the necessary focusing function for the uniaxial tension focus mask 25 of the present invention without adversely affecting its electron beam transmission. The uniaxial tension focus mask 25 described herein provides a mask transmission of about 60% at the center of the screen and requires such voltage settings: the second anode or focus voltage av applied to the second metal strip 60 is different from the first anode voltage applied to the first metal strip 40, which is about 1kV less for a first anode voltage of about 30 kV.

As shown in fig. 4 and 5, the insulator 62 is disposed substantially continuously on the screen-facing side of each first metal bar 40. Second metal strip 60 is bonded to insulator 62 to electrically insulate second metal strip 60 from first metal strip 40.

The method of making the uniaxial tension focus mask 25 includes providing a first coating of an insulating devitrifying solder glass on the screen-facing side of the first metal strip 40, such as by spray coating. A suitable solvent and an acrylic binder are mixed with the devitrifying solder glass to provide the first coating with a moderate mechanical strength. The thickness of the first coating is about 0.14 mm. The frame 44 with the first metal strip 40 mounted thereon is placed in an oven and the first coating is dried at a temperature of about 80 c. Devitrifying solder glasses are glasses that melt at a particular temperature to form a crystalline glass insulator. The crystallized glass insulator formed is stable and will not melt again when heated again to the same temperature. After drying, the first coating is shaped such that it is shielded by the first metal strip 40 to prevent the electron beam 28 passing through the slot 42 from striking the insulator and charging it. The forming process is realized on the first coating layer in such a way that: any solder glass material of the first coating that extends beyond the edge of the metal strip 40 and will be touched by the deflected or undeflected electron beam 28 is removed by abrasion or otherwise. The first coating is completely removed from the first starting and last, i.e., right and left, first metal strips (hereinafter referred to as first metal end strips 140) before the first coating is heated to the sealing temperature. The first metal end bars 140, which are outside the active picture area, will then be used as bus lines to address the second metal bars 60. To further ensure the overall electrical characteristics of the uniaxial tension focus mask 25, at least one of the remaining first metal strips 40 is removed between the first metal end bar 140 and the first metal strip 40 covering the active picture area of the screen to minimize the possibility of shorting. Thus, the right and left first metal end strips 140, which are outside the active image area, are spaced from the first metal strip 40 overlying the image area by a distance of at least 1.4mm (55 mils), which is greater than the width of the equally spaced slots 42, which slots 42 separate the first metal strip 40 across the image area.

The frame 44 (hereinafter referred to as an assembly) with the first metal strip 40 and the end strip 140 mounted thereon is placed in an oven and heated in air. The assembly was heated to a temperature of 300 ℃ over a period of 30 minutes and held at 300 ℃ for 20 minutes. Thereafter, the temperature of the oven is raised to 460 ℃ for a period of 20 minutes and held at that temperature for 1 hour to cause the first coating to melt and crystallize to form a first insulating layer 64 on the first metal strip 40, as shown in fig. 6. After firing, the thickness of the first insulating layer 64 ultimately formed on each metal strip 40 is in the range of 0.5-0.9mm (2-3.5 mils). A preferred material for the first coating is lead-zinc-borosilicate devitrifying solder glass, which melts in the temperature range of 400-450 ℃ and is commercially available from a number of glass suppliers including SEM-COM (To1edo, OH) and Corning glass (Corning, NY) under the model SCC-11.

Next, a second layer of a suitable insulating material mixed with a solvent is applied to the first insulating layer 64, for example by spraying. The second coating is preferably an amorphous (i.e., transparent) solder glass having the composition: 80% by weight of PbO, 5% by weight of ZnO, 14% by weight of B₂O₃0.75% by weight of SnO₂And optionally 0.25 wt.% CoO. A transparent material is preferred for the second coating layer because when it melts it will fill the first insulationAny voids in the surface of the insulating layer 64 while not adversely affecting the electrical and mechanical properties of the first insulating layer. Alternatively, the second coating layer may be formed using a devitrifying solder glass. The second coating is applied at a thickness of about 0.025 to 0.05mm (1 to 2 mils). The second coating is dried at a temperature of 80 c and shaped in the manner previously described to remove any excess material that may be impacted by the electron beam 28.

As shown in fig. 4, 5 and 7, the screen-facing sides of the left and right first metal end bars 140 are provided with a thick coating of a silver-containing devitrifying solder glass to render it electrically conductive. A conductive lead 65, comprised of a short length of nickel wire, is embedded in the conductive solder glass on one of the first metal end bars. The assembly with the dried and formed second coating overlying the first insulating layer 64 then has the second metal strip 60 adhered thereto such that it overlies the second coating of insulating material and is substantially perpendicular to the first metal strip 40. The second metal strips 60 are added using a winding fixture (not shown) so that the desired spacing of about 0.41mm between adjacent second metal strips can be accurately maintained. The second metal strip 60 also contacts the conductive solder glass on the first metal end strip 140. Alternatively, conductive solder glass may be applied to the joint between the second metal strip 60 and the first metal end strip 140 during or after the winding operation. Next, the assembly including the winding fixture was heated at 460 ℃ for 7 hours to melt the second coating of insulating material and the conductive solder glass, thereby encapsulating the second metal strip 60 within the second insulating layer 66 and the glass conductor layer 68. The second insulating layer 66 has a thickness of about 0.013-0.025mm (0.5-1 mil) after melt sealing. The height of the glass conductor layer 68 is not important but should be thick enough to securely bond the second metal strip 60 and the conductive leads 65 therein. The portion of the second metal strip 60 that extends beyond the glass conductor layer 68 is cut away to protect the assembly from the winding fixture.

The first metal end bar 140 is cut at its ends adjacent the long side or top 32 (as shown in fig. 4) and the long side or bottom 34 (not shown) of the mask 25 to provide a gap of about 0.4mm (15 mils) therebetween that will electrically isolate the first metal end bar 140, thereby forming (the first metal end bar) bus lines that allow a second anode voltage to be applied to the second metal bar 60 when the conductive lead 65 embedded in the glass conductor layer 68 is connected to the second anode button 17.

Claims (11)

1. A color cathode ray tube (10) comprising an evacuated envelope (11) having therein: an electron gun (26) for generating at least one electron beam (28); a faceplate panel (12) having a phosphor screen (22) with phosphor stripes on an inner surface thereof; and a uniaxial tension focus mask (25), wherein said mask has a plurality of spaced first metal strips (40) adjacent an active image area of said screen and defining a plurality of slots (42) substantially parallel to said phosphor strips across said active image area, each of said first metal strips having a substantially continuous first insulating layer (64) on a screen-facing side thereof, a second insulating layer (66) overlying and thinner than said first insulating layer, a plurality of second metal strips (60) oriented substantially perpendicular to said first metal strips, said second metal strips being bonded by said second insulating layer.

2. The color cathode ray tube (10) of claim 1 wherein said tension focus mask (25) has two long sides (32, 34) between which said plurality of spaced apart first metal strips (40) extend, said long sides of said mask being secured to a substantially rectangular frame (44) having two long sides and two short sides.

3. The cathode ray tube (10) of claim 2, wherein the first insulating layer (64) is a devitrifying solder glass.

4. The cathode ray tube (10) of claim 3, wherein the devitrifying solder glass is shaped such that it is shielded from impingement by the electron beam (28) by the first metal strip (40).

5. The cathode ray tube (10) of claim 4, wherein the second insulating layer (66) is a solder glass.

6. The cathode ray tube (10) of claim 5, wherein said solder glass is shaped such that it is shielded from impingement by said electron beam (28) by said first metal strip (40).

7. The cathode ray tube (10) of claim 5, wherein the solder glass is transparent.

8. The cathode ray tube (10) of claim 5, wherein the solder glass is devitrifying.

9. A method of manufacturing a uniaxial tension focus mask (25) for a color cathode ray tube (10) including an electron gun (26) for generating three electron beams (28) and directing the beams through slots (42) in the uniaxial tension focus mask to impinge on a phosphor screen (22), wherein said method comprises the steps of:

securing a uniaxial tension mask (25) to a substantially rectangular frame (44) having two long sides and two short sides, said uniaxial tension mask having two long sides (32, 34) with a plurality of laterally spaced first metal strips (40) extending therebetween, the spaces between adjacent first metal strips defining parallel slot apertures (42), said long sides of said mask being attached to said long sides of said frame, said frame applying tension to said first metal strips of said mask;

forming an insulator (62) on the screen-facing side of said first metal strands across an effective image area of said screen, said insulator being substantially continuous over each of said first metal strands and comprising a first insulator layer (64) and a second insulator layer (66) overlying said first insulator layer and being thinner than the first insulator layer; and

providing a plurality of second metal cross bars (60) secured to the second layer.

10. The method of claim 9, wherein the first insulating layer (64) is formed as follows:

disposing a first coating of a suitable insulating material on each of said discrete first metal strips (40) across said effective image area of said screen;

shaping said first coating of insulating material in such a way as to remove from each metal strip any insulating material that may be struck by said electron beam (28) so as to avoid charging thereof; and

heating the first coating layer of the insulating material.

11. A method according to claim 10, wherein the step of mounting said cross-bars (60) comprises the sub-steps of:

applying a second coating of a suitable insulating material over said first insulating layer (64);

shaping said second coating of said insulating material in such a way as to remove any said second coating of said insulating material that may be impinged by said electron beam (28) so as to avoid charging thereof; and

after the cross bars are positioned, the second coating of insulating material is heated to form a second layer of insulation (66) which bonds the cross bars together.