GB2221083A

GB2221083A - Low glare cathode ray tube

Info

Publication number: GB2221083A
Application number: GB8912140A
Authority: GB
Inventors: Yasuo Iwasaki
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 1988-06-17
Filing date: 1989-05-26
Publication date: 1990-01-24
Anticipated expiration: 2009-05-26
Also published as: KR910009663B1; GB2221083B; JPH01319232A; DE3918744A1; GB8912140D0; KR900000958A

Description

1 z FB718 LOW-GLARE CATHODE-RAY TUBE AND METHOD FOR PRODUCING THE SAME

2221083

BACKGROUND OF THE INVENTION

This invention concerns a low-glare cathode-ray tube wherein reflection of external light from the outer surface of the glass face plate is prevented, and in particular. an improved structure of the surface of the glass face plate.

Fig. 7 shows a typical cathode-ray tube 1 without lowglare treatment as known in the prior art. The outer surface of the glass face plate 2, as shown in Fig. 8, is extremely smooth. For this reason, when there is a picture being viewed on the cathode-ray tube 1, and there is for example a lamp 4 in the room being used for Illumination, the external light from the lamp 4 can be reflected Into the eyes of the viewer 3 by normal reflection from the glass face plate 2 of the tube-1 depending on their relative spatial relationships. Further, when light from the lamp strikes the glass surface almost perpendicularly, the reflection may be as much as 4%. This reflection of external light can have a serious effect on the readability of the image produced by the luminescence of the fluorescent inner surface (not shown In the figures) of the glass face plate 2 of tube 1, and if the image on the screen is viewed for long periods of time it may lead to eye fatigue which is

1.

2 FB718 also undesirable from a medical viewpoint.

For this reason, a low-glare cathode-ray tube has already been developed as shown in Fig. 9. The outer surface of the glass face plate 2 of this tube 1 has a multitude of minute prouberances 11 no larger than 1 ym as shown in Fig. 10. The external light from a lamp 4, for example, is scattered by these protuberances so that reflection from the glass is more diffuse. As the reflected image does not enter the eyes of the viewer 3, the viewer sees only the image produced by luminescence of the fluorescent surface of tube 1, which he sees accurately, and there is less eye fatigue even if the image is viewed for long periods of time. The size of these protuberances 11 is moreover chosen such that they have no effect on the resolution of the fluorescent image on thescreen.

In such a low-glare cathode-ray tube, a low-glare treatment is usually carried out after forming the glass face plate 2 and before-forming he fluorescent inner surface. To confer low-glare properties, a direct etching method is widely used.

Figs. 11A and 11B illustrate the principle of low-glare treatment of the outer surface of the glass face plate by direct etching. This treatment is carried out after the usual glass press and outer surface polishing processes. First, air or water containing carborundum or another 3 FB718 abrasive powder 6 is blasted by a nozzle 5 onto the outer surface of glass face plate 2 under certain conditions as shown in Fig. 11A, and minute defects 8 are thereby formed on the surface. Subsequently, the outer surface only of the face plate 2 Is immersed In a bath 9 of etching fluid 10 for a certain time as shown in Fig. 11B. The etching fluid 10 is usually hydrofluoric acid (HF), which has the property of dissolving glass. The defects 8 produced by the abrasive powder are thereby smoothly expanded into a multitude of minute protuberances 11 no larger than 1 pm on the outer surface of the face plate 2. as shown in Fig. 11C, which completes the low-glare treatment.

The conventional low-glare cathode-ray tube described above, however, suffered from the disadvantage that, due to the presence of a multitude of minute protuberances on the outer surface of the glass face plate 2, it was far more liable to be scratched during the manufacturing process than a conventional cathode-ray tube with a smooth outer surface. This is due to the fact that compared to a smooth surface, a surface with protuberances has a larger coefficient of friction, and is more easily scratched when it slides against other objects. These kinds of scratches, moreover, were difficult to remove later by repolishing or other methods.

4 1 FB718 SUMMARY OF THE INVENTION

This invention was conceived to solve the above problem. It aims to provide a low-glare cathode-ray tube wherein the outer surface of the glass face plate may have a multitude of minute protuberances, but is still fully resistant to surface scratching during the manufacturing process.

The low-glare cathode-ray tube In this invention is characterized by having a multitude of minute protuberances on the outer surface of the glass face plate of the tube, and a compression layer adjacent to this outer surface.

The low-glare cathode-ray tube in this invention is characterized by having a compression layer at the outer surface of the glass face plate of the tube having a multitude of minute protuberances and in the vicinity of the outer surface in the direction of the thickness. The apparent hardness of the glass surface therefore is increased, the resistance of the glass surface to scratches due to rubbing against other objects is remarkably improved, and the probability of scratches occurring is far less.

BRIEF DESCRIPTION OF DRAWING

Fig. 1 is an outline drawing of the structure of the low-glare cathoderay tube in this invention.

Fig. 2 is an enlarged sectional view of the are marked FB718 II in Fig. 1.

Fig. 3A - 3C are drawings illustrating the Ion exchange process of this Invention.

Fig. 4 is a drawing showing the principle of ion exchange.

Fig. 5 is a characteristic diagram showing the residual stress distribution In the depth direction of the glass face plate.

Fig. 6 shows the results of scratch tests on glass face plates in tabular form.

Fig. 7 is an outline drawing of the structure of a conventional cathoderay tube without low-glare treatment.

Fig. 8 is an enlarged sectional view of the area marked VIII in Fig. 7.

Fig. 9 is an outline drawing of the structure of a conventional cathoderay tube with low-glare treatment.

Fig. 10 is an enlarged sectional view-of the area marked X in Fig. 9.

Figs. 11A, 11B and 11C illustrate the principle of lowglare treatment of the outer surface of a glass face plate by direct etching.

DETAILED DESCRIPTION OF THE EMBODIMENTS

An embodiment of this invention will now be described with reference to drawings.

6 FB718 Fig. 1 is an outline drawing of the structure of the low-glare cathode- ray tube in this invention.

In the figure, a multitude of minute protuberances 11 as shown in Fig. 2 is formed on the outer surface of the glass face plate. Further, there Is a compression layer 12 extending to a depth of 0 - 50 11m in the direction of the depth of said protuberances. This compression layer 12 is produced by an ion exchange process.

Fig. 3A - 3C illustrate this ion exchange process. After a multitude of minute protuberances 11. as shown in Fig. 3A, have been formed on the outer surface of the glass face plate 2 by direct etching as in the prior art described above, the outer surface of plate 2 is immersed in an ion exchange bath 13 of molten potassium nitrate (KNO3) 15 as shown in Fig 3B. This ion exchange bath 13 is heated by a heater 14 so as to raise the temperature of the molten potassium nitrate (KN03) to approx. 4000C. By immersing the outer surface of plate 2 in the molten potassium nitrate (KN03) 15 for a period of several hours up to about 10 hours, an ion exchange process occurs, and a compression layer 12 is formed to a depth of approx. 50 jim In the direction of the depth of the minute protuberance 11 on the outer surface of plate 2 as shown in Fig. 3C. The stress distribution and depth of layer 12 depend on the ion exchanged processing time and temperature.

7 FB718 Fig. 4 shown the principle of this ion exchange process. The glass face plate 2 has an amorphous structure formed by melting raw materials which usually consist mainly of silicon dioxide (Si02), sodium oxide (Na20) and potassium oxide (K20), together with a large number of other oxides. Let us consider only sodium ions (Na+) and potassium ions M"). When the outer surface of this plate 2 is immersed in molten potassium nitrate (KNO3) at a high temperature of approx. 4000C, the ions become very active. Sodium ions (Na+) escape from the outer surface of plate 2 into the molten potassium nitrate (KN03), and potassium ions (K + from the molten nitrate enter the spaces left by the sodium ions (Na+); in other words, ion exchange occurs. However, whereas the radius of a sodium ion (Na+) is only 0.97 Angstroms, the radius of a potassium ion (C) is 1.33 Angstroms. As a result, the much larger potassium ions (C) become packed into spaces which previously contained sodium ions (Na+), and a strong compression layer 12 is thereby formed close to the outer surface of plate 2.

Fig. 5 shows the residual compression stress distribution in the depth direction of layer 12 formed on the outer surface of plate 2. It is seen that on the outer surface of the plate, the compression actually reaches 20,000 PSI, and it extends to a depth of approx. 40 Pm. The magnitude of this residual stress and its distribution In ( - 8 FB718 the depth direction depends largely, as was mentioned earlier, on the ion exchange processing conditions (temperature and time).

Due to the compressive stress In layer 12. which extends from 0---50 ym in the direction of the thickness of the minute protuberances 11 on the outer surface of plate 2, the apparent surface hardness of the glass increases. Layer 12 therefore acts as a protective layer, and even if a lowglare treatment is carried out by direct etching, therefore, the scratching of said plate 2 during the manufacturing process can be prevented.

Fig. 6 shows the results of scratching tests of the outer surface of glass face plate 2. In these tests, a pyramid needle of 900 angle was held perpendicularly to the outer surface of sample plates, the samples being run at a speed of 100 mm/minute under a constant load, and the surfaces were then examined at 100 x magnification for the presence or absence of scratches.- With sample (a). a face plate which had not received low-glare treatment, scratches were not observed up to a load of 80 g. With sample (b). a face plate which had received a low-glare treatment by the direct etching method as'described in the prior art. the critical load at which scratches could not be found decreased to 50 g. With sample (c), on the other hand, a glass face plate 2 as described in this invention which had

1 1 9 FB718 received a low-glare treatment by direct etching and additionally a strengthening treatment by the ion exchange process, the critical load at which scratches were not observed was Improved to the level of sample (a).

In the above embodiment, the formation of the compression layer 12 by the ion exchange process is carried out after the low-glare treatment of plate 2 by direct etching. The Invention is however not confined to this sequence, it being possible to carry out the low-glare treatment by direct etching after first forming the compression layer 12 by Ion exchange on the outer surface of plate 2.

In the above invention, minute protuberances are formed on the outer surface of a glass face plate, and a compression layer is formed at and adjacent to the outer surface. The apparent surface hardness of the glass is thereby increased, the probability of the outer surface of the plate being scratched in the manufacturing process Is greatly reduced, and a high quality low-glare cathode-ray tube can be obtained.

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Claims

1. A low-glare cathode ray tube having a glass face plate with an outer surface, a multitude of minute protuberances on the outer surface of the glass face plate; and a compression layer at, and adjacent to,,,this outer surface.

2. A tube according to claim 1, wherein said compression layer extends to a depth of about 0 to 50 um.

3. A tube according to claim 1 or 2, wherein said compression layer is formed by ion exchange.

4. A tube according to claim 1, 2 or 3, wherein said protuberances areformed by direct etching.

5. A tube according to anyone of claims 1 to 4, wherein said protuberances are not larger than about 1 um.

6. A tube according to claims 1 to 4, wherein the size of said protuberances is chosen such that they have no effect on the resolution of the fluorescent image on the screen.

t 11

7. A cathode-ray tube substantially as described with reference to, and as illustrated in Figure 1 or 2 of the accompanying drawings and/or with characteristics as represented in Figure 4, 5 or 6. of the accompanying drawings.

8. A method of producing a low-glare cathode-ray tube, comprising the steps of: providing a glass face plate; performing direct etching on the outer surface of the glass face plate to form a multitude of minute protuberances; and performing ion-exchange to form a compression layer adjacent to the outer surface of the glass face plate.

9. A method according to claim 8, wherein said glass face plate has an amorphous structure formed by melting raw materials which contain silicon dioxide (SiO 2 sodium oxide (Na 0) and potassium oxide (K 0); 2 and said step of ion exchange comprises immersing the outer surface of the glass face plate in an ion exchange bath of molten potassium nitrate (KNO 3 12

10. A method according to claim 8 or 9, wherein said step of ion exchange comprises immersing the outer surface of the glass face plate in an ion exchange bath of molten potassium nitrate (KNO)r at a temperature of 0 3 about 400 C for a period of several hours to 10 hours.

11. A method according to claim 8, 9 or 10, wherein said step of direct etching comprises blasting abrasive powder onto the outer surface of the glass face plate, and immersing the outer surface of the glass face plate in an etching fluid.

12. A method according to claim 11, wherein the etching fluid is hydrofluoric acid (HF).

13. A method according to claim 8 and substantially as described with reference to Figures M-3C of the accompanying drawings.

Published 1990 at The Patent office, State House. 66 71 High Holborn, London WC1R 4TP. Further copies maybe obtained from The F&tent UMce. Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Rent, Con. 1187 i