METHOD OF MANUFACTURING A CATHODE-RAY TUBE AND A CATHODE-RAY TUBE MANUFACTURE BY MEANS OF SUCH A METHOD

Abstract: The invention relates to a method of manufacturing a cathode-ray tube which comprises a cone part 2 and a display window 1. The display window 1 and the cone part 2 are accurately positioned relative to each other, a glass frit being provided between the display window and the cone part. The positioning thus obtained is fixed by securing locating pins 22 to faces 31 and in slots 29 by means of an acrylate adhesive 23. Subsequently, the display window 1 is permanently secured to the cone part 2 by means of a sealing process.

Description: The invention relates to a method of manufacturing a cathode-ray tube, in which in a process step two parts, namely a cone part having a substantially rectangular cone edge and a substantially rectangular display window having a sealing edge are sealed to each other, both parts being positioned relative to each other and subsequently sealed to each other at the location of the sealing edge and the cone edge by means of a sealing process. The invention further relates to a cathode-ray tube manufactured by means of such a method. In the mass-production of cathode-ray tubes a number of parts, amongst others cones and display windows, are produced according to predetermined dimensions and configurations, after which a number of these parts are selected to be secured to each other. In order to obtain properly functioning cathode-ray tubes, it is necessary that the parts selected are accurately positioned relative to each other before being secured to one another. To position the parts of a cathode-ray tube use can be made of several reference systems. A commonly used reference system is described in United States Patent Specification 4.373.237. In said Specification reference surfaces are ground on the cone part of the cathode-ray tube and the display window is provided at its periphery with reference points. The display window is positioned on the cone part, the reference points of the display window and the reference surfaces of the cone part being referenced to a common reference. In this manner the display window is accurately positioned relative to the cone part. Other reference systems are described in, amongst others, German Offenlegungsschrift 2850602 and Netherlands Specifications 7909155 and 7304115 which are laid open to Public Inspection. In general the display window is sealed to the cone edge at the location of the sealing edge by means of a sealing process. To this end a glass frit is provided on the cone edge before the display window and the cone part are positioned relative to each other. After the display window has been accurately positioned on the cone part both are led through a sealing oven in which the glass frit is recrystallized in a predetermined temperature trajectory causing the display window and the cone part to be sealed to each other in a vacuum-tight manner. In the course of this sealing process temperature differences occur in the cathode-ray tube which cause tensile stresses in the cathode-ray tube. This may adversely affect the accurately adjusted positioning of the display window relative to the cone part. It is an object of the invention to provide a method of manufacturing a cathode-ray tube, by means of which the accurately adjusted positioning of the display window relative to the cone part can be retained during the sealing process. To this end, a method of the type mentioned in the opening paragraph is characterized in that after the two parts have been positioned relative to each other, this positioning is fixed temporarily prior to the sealing process by temporarily fixing the two parts together. By temporarily fixing the adjusted positioning of the display window and the cone part this positioning is retained during the sealing process. In practice it has been found that a cathode-ray tube can be accurately manufactured according to a preferred embodiment of the inventive method, which is characterized in that the temporary fixation of the positioning is obtained by securing locating pins to faces which are provided on the peripheral edge of one of the parts, each locating pin being secured in a slot which is provided on a stud present on the peripheral edge of the other part. A further preferred embodiment of a method according to the invention is characterized in that each locating pin is secured to a face and in a slot by means of an acrylate adhesive. Since an acrylate adhesive forms a proper bond in no more than a few seconds, the production time of a cathode-ray tube is hardly influenced by this readily conceivable way of fixing the adjusted positioning of the display window relative to the cone part. During the warming-up period of the sealing process the acrylate adhesive may burn, depending upon the type that is used. If this takes place before the cone part is sealed to the display window, the adjusted positioning of the display window relative to the cone part may still be adversely affected. To prevent this, a further preferred embodiment of the method according to the invention is characterized in that each locating pin is secured to a face and in a slot by means of a temperature resistant cementing agent. This cementing agent dries out completely during the warming-up period of the sealing process and immediately after the acrylate adhesive is burned it takes over the fixing of the display window and the cone part. Since the temperature resistant cementing agent dries out completely the locating pins are permanently fitted in the slot of the stud. A further preferred embodiment of the method according to the invention is characterized in that two studs, having one slot each, and two faces respectively are provided on the peripheral edge of one of the long sides of the substantially rectangular parts, and in that one stud, having one slot, and one face respectively are provided on the peripheral edge of one of the short sides of the substantially rectangular parts. In practice it has been found that three locating pins are sufficient to fix the accurate positioning of the two parts relative to each other. A cathode-ray tube manufactured by means of the method according to the invention exhibits an accurate positioning of the display window relative to the cone part and operates satisfactorily. The invention will now be explained in more detail by means of several exemplary embodiments and with reference to the drawings, in which Figure 1 is a sectional view of a cathode-ray tube; Figure 2 shows a cone having studs provided with a slot, according to the invention; Figure 3 shows a display window having faces, according to the invention; Figure 4 shows a part of a cone and a display window which are positioned relative to each other; Figure 5 shows one way of fixing the position of the display window relative to the cone by means of pins, according to the invention; and Figure 6 shows a different way of fixing the position of the display window relative to the cone by means of pins, according to the invention. The cathode-ray tube shown in a horizontal sectional view in Figure 1 contains an envelope consisting of a substantially rectangular display window 1, and a cone part 2 having a substantially rectangular cone edge 16 and a neck 3. In the neck 3 there is provided an electrode system 4 having three electron guns for generating three electron beams 5, 6 and 7. The electron beams are generated in one plane (in this case the plane of the drawing), and they are focused on a picture screen 8 which is provided on the inside of the display window 1, which picture screen consists of a large number of phosphor elements which are coated with an aluminium layer 20 and which emit red, green and blue light. The phosphor elements may be in the form of, for example, strips or dots. By way of example the invention will be further described by means of strip-like elements whose longitudinal direction is perpendicular to the plane through the electron guns (in this case the plane of the drawing). On their way to the picture screen 8 the electron beams 5, 6 and 7 are deflected across the picture screen 8 by means of a number of deflection coils 9 which are coaxially arranged about the axis of the tube, the beams passing a shadow mask 10 consisting of a metal plate with apertures 11, the longitudinal direction of which is parallel to the phosphor elements of the picture screen 8. The three electron beams 5, 6 and 7 pass through the apertures 11 at a small angle with one another, and consequently, are incident on only one colour each. The shadow mask 10 is secured to a framework 12 which is suspended in the cathode-ray tube from the upright edge 14 of the display window is provided with an edge 15, the so-called sealing edge. To obtain a properly functioning cathode-ray tube, the cone part 2 and the display window 1, which are generally manufactured separately, should be properly positioned relative to each other before sealing them to each other in a sealing process. In the manufacture of a cathode-ray tube it is customary to complete the display window 1, i.e. it is provided with, amongst others, the picture screen 8, the aluminium layer 20, the suspension means 13 and the shadow mask 10. The display window 1 is then positioned against the cone part 2 with an intermediate glass frit 17, such that the sealing edge 15 lies against the cone edge 16. Before sealing the display window 1 to the cone part 2, these two parts must be accurately positioned relative to each other. This positioning of the two parts relative to each other can be carried out in various known ways, one of them being described in, United States Patent Specification 4.373.237. When both parts have been accurately positioned relative to each other, they are led through a sealing oven and are sealed to each other by means of a well-known sealing process. The invention provides a method of manufacturing a cathode-ray tube, in which the adjusted accurate positioning is retained during the sealing process, and of which method a description is given by means of an example with reference to the Figures 2 up to and including 6. The cone part 2 is provided with a number of studs 18, 28 and 38 which are each provided with a slot 19, 29 and 39, respectively, as is shown in perspective in Figure 2. The studs 18, 28 and 38 may be made separately of a material having a coefficient of thermal expansion which is substantially equal to that of the cone part 2. The studs 18, 28 and 38 may, however, also be pressed together with the cone part 2. The upright edge 14 of the display window 1 comprises faces 21, 31 and 41 as shown in Figure 3. These faces can simply be plain portions of the upright edge 14 of the window 1. Two studs 18 and 28, each having a slot 19 and 29, respectively, are provided on the peripheral edge of a long side 25 of the substantially rectangular cone edge 16, and one stud 38 having a slot 39 is provided on the peripheral edge of the short side 26 of the cone edge 16. Analogously, the periphery of the upright edge 14 comprises three faces 21, 31, 41 such that the faces 21, 31 and 41 and the studs 18, 28 and 38 are juxtaposed when the cone part 2 is accurately positioned relative to the display window 1, as is shown in Figure 4 for the face 31 and the corresponding stud 28. For the sake of clarity Figure 4 does not show the glass frit present between the display window 1 and the cone part 2. In practice it has been found that the accurate positioning can suitably be fixed by securing three locating pins to the faces and in the slots, as is shown in Figure 5 for one locating pin 22 on the face 31 and in the corresponding slot 29. The locating pin 22 is, for example, a metal rod whose coefficient of thermal expansion is equal to that of the glass from which the display window 1 is made. A suitable metal is, for example, a Cr-Fe alloy containing 28 % of Cr. Preferably, the locating pin 22 is secured to the face 31 and in the slot 29 by means of a drop of acrylate adhesive 23, such that the accurately adjusted positioning of the display window 1 relative to the cone part 2 is fixed after no more than a few seconds. Once the relative positioning has been fixed, the cathode-ray tube can be led through a sealing oven. A commonly known sealing process which consists of a number of temperature trajectories makes sure that the display window is permanently sealed to the cone part by means of a glass frit. During the warming-up stage of this sealing process the acrylate adhesive may burn, depending upon the type used, for securing the locating pins. This might adversely affect the accurately adjusted positioning. To avoid this, the locating pin 22′ is preferably embedded in a temperature resistant cement 24 after it has been secured to the display window 1′ and the cone part 2′ by means of an acrylate adhesive 23′, which temperature resistant cement 24 dries out completely during the warming-up stage of the sealing process and takes over the fixing of the display window 1 and the cone part 2 immediately after the acrylate adhesive 23′ has burned, as is shown in Figure 6. When, for example, Loctite Cyanoacrylate 496 (Trade mark) is used as an acrylate adhesive a suitable temperature resistant cement is, for example, Aremco 571 A+B (Trade mark). After the display window and the cone part have been permanently secured to each other the locating pins and the studs are no longer required and may be removed by grinding. In order to protect a cathode-ray tube against implosion a clamping strip is usually provided around it at the location where the display window and the cone part are secured to each other. The locating pin may have several shapes, for example, a straight rod 22 as is shown in Figure 5 or like locating pin 22′ shown in Figure 6 it may have an eccentric portion. One end 50 of a locating pin having an eccentric portion, as is shown in Figure 6, is introduced into the slot. By rotating the pin, the end 51 of the locating pin is made to lie against the face. Dependent upon the type of clamping strip used as a protection against implosion, the locating pins can be fixed such that they do not have to be removed after the display window has been permanently secured to the cone part. It will be obvious that the present invention is not limited to the above-described embodiments, but that within the scope of the claims many variations are possible to those skilled in the art. For example, it is alternatively possible to secure the studs with the slots to the display window and to secure the faces to the cone part, and it is possible to vary the number of locating pins used.

Claims: A method of manufacturing a cathode-ray tube, in which in a process step two parts, namely a cone part having a substantially rectangular cone edge and a substantially rectangular display window having a sealing edge are sealed to each other, both parts being positioned relative to each other and subsequently sealed to each other at the location of the sealing edge and the cone edge by means of a sealing process, characterized in that after both parts have been positioned relative to each other this positioning is fixed temporarily prior to the sealing process by temporarily fixing the two parts together. A method as claimed in Claim 1, characterized in that the temporary fixation of the positioning is obtained by securing locating pins to faces which are provided on the peripheral edge of one of the parts, each locating pin being secured in a slot which is provided on a stud present on the peripheral edge of the other part. A method as claimed in Claim 2, characterized in that each locating pin is secured to a face and in a slot by means of an acrylate adhesive. A method as claimed in Claim 2 or 3, characterized in that each locating pin is secured to a face and in a slot by means of a temperature resistant cement. A method as claimed in Claim 2, 3 or 4, characterized in that two studs, having one slot each, and two faces, respectively, are provided on the peripheral edge of one of the long sides of the substantially rectangular parts, and in that one stud, having one slot, and one face respectively are provided on the peripheral edge of one of the short sides of the substantially rectangular parts. A cathode-ray tube manufactured by means of the method as claimed in Claim 1, 2, 3, 4 or 5. A cathode-ray tube containing two parts which are sealed to each other by means of a sealing process, namely a cone part having a substantially rectangular edge and a substantially rectangular display window having a sealing edge, characterized in that the cathode-ray tube is provided with locating pins which are secured in slots of studs which are provided on the peripheral edge of one of the parts and which locating pins are secured to faces which are provided on the peripheral edge of the other part.

Inventors: VAN DER AVOORT, HENRICUS JOZEF MARIA
Applicants: N.V. PHILIPS' GLOEILAMPENFABRIEKEN
Application year: 1988
Main classification: H01J9
IPC codes: H01J9, H01J29