RU2042988C1 - Shadow mask for cathode-ray tube - Google Patents

Abstract

FIELD: color cathode-ray tubes. SUBSTANCE: shadow mask is manufactured from alloy having following proportion of components, per cent by mass: nickel 32.0-39.0; manganese not more than 0.1; yttrium not more than 0.6; silicon not more than 0.04; aluminium not more than 0.08; phosphorus not more than 0.012; sulphur not more than 0.012; carbon not more than 0.04; iron being the balance. Surface oxide layer additionally has dispersed yttrium oxide. EFFECT: improved operational stability. 4 cl, 4 dwg, 7 tbl

Description

 The invention relates to a shadow mask with many apertures for use in a color cathode ray tube, in particular in a shadow mask made of an iron-nickel alloy that is better formed and oxidized.

The well-known shadow-masked cathode ray tube contains a vacuum flask with a screen in the form of a matrix of phosphor elements with three different radiation colors arranged in cycles, a device for creating three converging electron beams directed at the target, and a color splitting device including a perforated masking plate placed between target and beam emitting device. A masking plate obscures the target and is therefore commonly called a shadow mask. The difference in convergence angles allows each beam to hit the phosphor elements and excite them to emit the desired color. Approximately in the center of the shadow mask, the masking plate intercepts radiation fluxes, passing only about 18% i.e. the shadow mask has a throughput of about 18%. This means that the area of the holes in the masking plate is about 18% of the area of the mask. The remaining parts of each ray incident on the masking plate are not transmitted and cause the shadow mask to heat locally to a temperature of about 353 K. As a result, the shadow mask expands thermally, forming a "dome" directed towards the screen. When dome formation occurs, the color purity of the cathode ray tube deteriorates. The material from which the shadow mask is made (almost 100% of iron, similar to aluminum deoxidized steel (AK)) has a thermal expansion coefficient of about 12 x 10 ^-6 / K in the temperature range from 273 to 373 K. This material is easily subjected to dome formation.

 Modern color television receiving tubes are available mainly with a screen diameter of 25 to 27 inches diagonally and in small quantities up to 35 inches. Many of these tubes have almost flat screens, which creates the need for almost flat shadow masks with very little thermal expansion.

Invar, or iron-nickel alloy, has low thermal expandability (from ≈1 x 10 ^-6 / K to 2 x 10 ^-6 / K in the temperature range from 273 to 373 K), high elasticity and high tensile strength after annealing in comparison with ordinary iron. On an invariant shadow mask, it is very difficult to create an oxide coating with a strong bond and low reflectivity. To increase the contrast of the image, it is preferable to use dark oxide.

 In accordance with the present invention, a shadow mask for a color cathode ray tube has many holes. It is made of a sheet of iron-nickel alloy containing the following components, wt. C ≅ 0.04; Mn <0.1; Si ≅ 0.04; P ≅ 0.012; S ≅ 0.012; Ni 32-39; Al ≅ 0.08; Y ≅ 0.6; Fe the rest and impurities inevitably included in the iron-nickel alloy during its preparation. An oxide layer is formed on a sheet of an iron-nickel alloy and stabilized and bonded with yttrium oxide dispersed in the inter-slit portions along the entire lattice of the alloy sheet.

 In FIG. 1 is a partial axial sectional plan view of a color cathode ray tube in accordance with the invention; in FIG. 2, and a section of a slotted shadow mask, a plan view; in FIG. 2, b section of the shadow mask along AA; in FIG. 2, in section of a shadow mask according to BB; in FIG. 3, and a section of a shadow mask with round apertures, a plan view; in FIG. 3b cross-section of the shadow mask in BB; in FIG. 4, a, b, in the shadow mask at the stages of its manufacture, in the context.

 The rectangular color cathode ray tube 1 has a glass flask consisting of a rectangular front panel 2 (or roof) and a tubular neck 3 connected by a rectangular socket 4. Panel 2 contains a viewing screen 5 and a peripheral flange or sidewall 6, which is soldered to the socket 4. A mosaic tricolor phosphor screen 7 is placed on the inner surface of the viewing panel 5. Preferably, the screen 7 is stripe and the phosphor strips extend perpendicular to the high-frequency horizontal scan of the raster barrels (perpendicular to the plane of Fig. 1). Alternatively, the screen may be dotted. The multi-aperture color-separating electrode or shadow mask 8 is mounted with the possibility of removal by known means in a predetermined spatial arrangement to the screen 7. The shadow mask 8 is preferably a slit mask (Fig. 2A, 2B and 2C) or a circular aperture mask (Fig. 3A and 3B). A longitudinal electronic spotlight 9 is installed along the axis and inside the neck 3 and is designed to form and direct three electron beams 10 along spaced coplanar converging paths through the mask 8 to the screen 7.

 The tube 1 is designed to work with external magnetically-deflecting coils, similar to the coil 11 surrounding the neck 3 and the bell 4 at the junction. When excited, the coil 11 acts on the rays 10 by vertical and horizontal magnetic fields, which cause these rays to scan horizontally and vertically, respectively, in a rectangular raster on the screen 7. The original deflection plane (with zero deflection) is shown by the line PP passing approximately in the middle coil 11 (in fact, the curvature of the trajectories of the deflected rays in the deflection zone is not shown).

 Shadow mask 8 is made of a sheet of advanced nickel-iron alloy, which has improved formability and oxidation characteristics compared to the known Invar (Invar trademark with registration number 63,970).

 In the table. 1 shows the compositions of the proposed alloy and the known Invar alloy.

 The improved alloy has lower concentrations of manganese and silicon than the known Invar alloy, and contains aluminum. Due to this, it is assumed that the etchability and formability of the effective shadow mask have improved.

A metallurgically sufficient amount of yttrium has been added to provide fine dispersion of yttrium oxide (Y ₂ O ₃ ) in the inter-slit portions of the matrix or lattice of an improved alloy to stabilize and adhere to the surfaces of the shadow mask 8 of the subsequently formed oxide film.

 Etching tests were performed on several 4 x 4-inch alloy samples and a control sample made of aluminum deoxidized (A) steel. In the table. 2 compares the compositions of the alloys: control (AK), Invar (INV), advanced alloy (V91) with yttrium and advanced alloy (V92) without yttrium.

 Etching tests were performed by applying suitable photosensitive films 12 to opposite surfaces of the sheet 13 of the shadow mask, as shown in FIG. 4 a. Plates 14 and 15 are applied to a sheet of a shadow mask coated with photosensitive films 12. By illuminating the plates 14 and 15, the template patterns on them are printed respectively on both photosensitive films 12. Then, as shown in FIG. 4b, the parts of the films illuminated with light are removed so that the surface of the sheet 13 of the shadow mask is partially exposed. The configuration and area of the illuminated surfaces correspond to the patterns on plates 14 and 15.

The illuminated surfaces of the sheet 13 of the shadow mask are etched on both sides, and after a certain time, apertures 16 are formed (either slits or round holes). In the table. 3 shows the etching parameters. Etching temperature of about 70 ° ^C, the weight ^of the etching solution 47.2 Baume. In FIG. 4c shows the side of the sample corresponding to the side O of the shadow mask facing the electronic spotlight, the side R of the shadow mask that faces the fluorescent screen of the tube.

 In the table. 3, undercut refers to lateral erosion of the sheet of the shadow mask by photosensitive films 12. The etch coefficient is defined as the ratio of the etch depth to the amount of undercut. Materials (V91 and V92) from the improved alloy, having lower concentrations of manganese and silicon in comparison with the known Invar (INV.1) and aluminum deoxidized steel (control sample), are characterized by etching parameters comparable to those of the known Invar and aluminum deoxidized steel.

 Additional tests were carried out using six reference melts of iron-nickel alloys. The compositions of the reference alloys are shown in table. 4 and are substantially identical to each other, excluding the amount of yttrium.

Both yttrium-containing samples (V63-V66) and yttrium-free samples (V61 and V62) were tested for formability by evaluating the elastic aftereffect of the samples in the form of strips 0.15 mm thick. Elastic effect was measured for cold rolled samples and for samples annealed at 860 ° ^C. Tests were performed by clamping one end of the strip and the free end 90 ^of the displacement. Then the strip was released and the angular displacement from the release point was measured. In most cases, measurements were performed for three samples, and then the results were averaged. The test results are summarized in table. 5 and 6.

 The elastic consequence of yttrium-containing samples (V61-V66) was compared with that of yttrium-free samples (V61-V62). As expected, annealing usually reduced the elastic aftereffect of both yttrium-containing and non-yttrium-containing samples.

Additional tests were carried out to determine the oxidation characteristics of alloy samples and a control sample deoxidized with aluminum. All samples were steam blackened by steaming at a temperature of ^about 600 C to form an oxide film. The thickness of the oxide film is measured by peak values, and all samples had areas without visible oxidation. About 1.5 microns are read in the desired oxide film thickness. Too thick oxide layers tend to peel and form particles, while very thin oxide films degrade image contrast. The oxidation tests are summarized in table. 7. Therefore, to obtain an oxide film of about 1.5 microns, one should either lower the temperature or use an atmosphere of natural gas.

The peak thickness of the oxide film on aluminum deoxidized steel is almost three times greater than that on samples of iron-nickel alloys. The surface roughness of any sample was about 0.5 microns. Additional alloy samples were electrolytically polished to create a substantially smooth surface (0 microns). Electropolished alloy samples were steam blackened at a temperature of 600 ^{° C} and again carried metering of oxide film thickness. The electropolished yttrium-containing samples (V63-V66) had an oxide thickness of 1.32 to 1.44 microns, which is considered satisfactory; however, the yttrium-free electropolished sample V61 had a peak oxide film thickness of only 0.47 microns and the yttrium-free electropolished sample V62 did not have a measurable oxide coating on the electrolytically polished surface. The electro-polished yttrium-containing alloy samples had an almost (three times as large) peak oxide film thickness as the yttrium-free electro-polished alloy samples. The oxide film formed on yttrium-containing alloy samples consists mainly of meghemite and magnetite, and to a lesser extent of hematite and yttrium oxide. It is assumed that, in yttrium-containing alloy samples, the oxide film is stabilized and adheres to the surface of the samples by yttrium oxide (Y ₂ O ₃ ), which is dispersed in the interstitial regions along the lattice of the alloy sheet. Based on the test results, a preferred yttrium content in the range of 0.1 to 02 wt.

Claims (4)

 1. SHADOW MASK FOR COLORED ELECTRON BEAM TUBES, made in the form of a metal sheet with many apertures of an alloy containing iron, nickel, carbon, manganese, silicon, phosphorus, sulfur, and with a surface oxide layer based on iron oxides, characterized in that the alloy composition additionally contains aluminum and yttrium in the following ratio of components, wt. Nickel 32 39
Manganese Not more than 0.1
Yttrium Not more than 0.6
Silicon Not more than 0.04
Aluminum Not more than 0.08
Phosphorus Not more than 0.012
Sulfur Not more than 0.012
Carbon Not more than 0.04
Iron Else
and the oxide layer further comprises dispersed yttrium oxide.  2. The mask according to claim 1, characterized in that the nickel content in the alloy is selected from the ratio, wt. 34.5 <Ni <37.5,
and the yttrium content in the oxide layer is selected from the ratio, wt.  0 <Y ≅ 0.5.  3. The mask according to claim 1, characterized in that the nickel content in the alloy is selected from the ratio, wt. 34.5 <Ni <37.5,
and the yttrium content in the oxide layer is selected from the ratio, wt.  0.1 <Y <0.2. 4. The mask according to claims 1, 2 or 3, characterized in that the oxide layer contains γ = Fe ₂ O ₃ , Fe ₃ O ₄ , α = Fe ₂ O ₃ and Y ₂ O ₃
in the following ratio of components, wt. (γ = Fe ₂ O ₃ + Fe ₃ O ₄ ) <(α = Fe ₂ O ₃ + Y ₂ O ₃ ),

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