Method of manufacturing a colour cathode-ray tube and a colour cathode-ray tube

Abstract: The invention relates to a method of manufacturing a colour cathode-ray tube, in which in one process step a colour selection system 4 and a display window 1 having a display screen 2 are assembled. The colour selection system 4 and the display window 1 are positioned relative to one another by optimizing a test pattern displayed on the display screen 2. The adjusted position of the parts relative to one another is fixed by interconnecting the elements 7 and 8, which are connected to the parts 1, 4, by means of laser welding through the glass.

Description: The invention relates to a method of manufacturing a colour cathode-ray tube, in which in one process step two parts, namely a colour selection system and an at least substantially rectangular display window having a display screen of phosphor elements luminescing in different colours are secured to one another to form an assembly. The invention further relates to a colour cathode ray tube. DE-A-30 35 368 discloses a method of manufacturing a colour cathode-ray tube in which a colour selection system provided with primary mounting elements secured to it and a rectangular display window provided with secondary mounting elements secured to each of its corners, are secured to one another by means of the primary and secondary mounting elements. It is an object of the invention to provide a method of manufacturing a colour cathode-ray tube, in which the manufacture of the colour selection system and the display window are carried out in a readily conceivable and accurate way. To this end, a method of the type mentioned in the opening paragraph is characterized in accordance with the invention in that the two parts are secured to one another via a number of positioning elements, while prior to securing the two parts to one another the positioning elements together with one of the parts are moved over mounting elements secured to the other part, until the parts are accurately aligned relative to one another, after which the positioning elements and the mounting elements are fixedly secured to one another while maintaining this aligned position. The invention is based on the insight that if the connection elements used to secure the colour selection system to the display window are composed of two elements, i e. the mounting elements and the positioning elements, the position of the suspension means relative to the display window and the colour selection electrode can be fixed if the display window and the colour selection electrode are accurately aligned relative to one another. Due to this, the display window and the colour selection system are secured to one another in an accurate position. Consequently, the display window with the display screen the colour selection system can be produced separately in large numbers. If a random colour selection system and a random display window are joined to form an assembly and their relative position is accurately aligned, they do not belong together until they have been secured to one another in the aligned position. A preferred embodiment of a method according to the invention is characterized in that a test pattern is displayed on the display screen via the colour selection system and in that the alignment is continued until the test pattern is displayed in a desired manner. An accurate alignment of the display window relative to the colour selection system can be obtained by aligning the display window and the colour selection system relative to one another by means of a test pattern which is displayed on the display screen via the colour selection system. In practice it has been found that the accurate alignment of the display window and the colour selection system relative to one another is carried out in a simple manner in a preferred embodiment of a method according to the invention, which is characterized in that reference phosphor elements are provided at the edge of the display screen and reference apertures are provided in the colour selection system, a test pattern being displayed, by means of a lamp emitting ultraviolet light, on the reference phosphor elements at the edge of the display screen, via the reference apertures in the colour selection system, and in that the display window and the colour selection system are aligned relative to one another until the test pattern is displayed in a desired manner. The insight of the invention can also advantageously be used to secure a tube enveloping part and an assembly of a display window and a colour selection system to one another. A method of manufacturing a colour cathode-ray tube, in which in one process step two parts, namely a tube enveloping part having an edge and an assembly of a colour selection system and a display window are secured to one another, characterized in that the two parts are secured to one another via a number of positioning elements, the positioning elements together with one of the parts being moved over mounting elements secured to the other part, before securing the two parts to one another, until the parts are accurately aligned relative to one another, after which the positioning elements and the mounting elements are secured to one another while this aligned position is maintained. A further preferred embodiment of a method according to the invention is characterized in that the mounting elements and the positioning elements are made of metal and they are secured to one another by means of laser welding. In practice it has been found that due to, amongst others, the accuracy of the welds and the speed with which the welds can be formed, laser welding can suitably be used to secure the display window to the colour selection system or the enveloping part to the assembly, in the aligned position. A still further preferred embodiment of a method according to the invention is characterized in that at least one of the members to be secured to one another is at least partly made of glass, and that they are secured to one another by means of laser welding through the glass. If the desired position of the colour selection system and the display window or of the assembly and the enveloping part has been obtained and if at least one of the members to be secured to one another is at least partly made of glass, the position can readily, quickly and accurately be fixed by means of laser welding through the glass. Thus, the possibility of a deviation from the desired position during the short time necessary to fix the position by the said securing operation is small. Moreover, it becomes possible to weld the metal elements to one another without excessively heating one or both elements and without softening the glass or if another way of interconnecting the elements is impossible due to objects present around the elements. A still further preferred embodiment of a method according to the invention is characterized in that the positioning elements are detachably connected to the one part. This has the advantage that if in the course of the manufacture of the cathode ray tube it is necessary to detach the colour selection system from the display window or the tube enveloping part from the assembly, the parts can subsequently be readily attached to one another again in the same position relative to one another. A further preferred embodiment of a method according to the invention is characterized in that each positioning element is provided with a cavity, and an intermediate element is arranged between each positioning element and the associated mounting element, which intermediate element lies at least partly against the positioning element and the mounting element, the intermediate element extending at least partly in the said cavity and permitting a relative movement of the parts in a direction transverse to the display window, and, in the aligned position, each intermediate element being secured to the associated positioning element and mounting element. Thus, the frame and the display screen or the tube enveloping part and the assembly can readily be positioned in three directions relative to one another. A colour cathode-ray tube comprising a colour selection system having a great number of apertures which is located opposite an at least substantially rectangular display window which is provided with a display screen having phosphor elements luminescing in different colours, and an electrode system for generating a number of electron beams, the colour selection system being aligned relative to the display window such that the apertures of the colour selection system ensure that each electron beam is incident on phosphor elements luminescing in one colour, operates satisfactorily, for example as regards colour purity, if it is characterized in accordance with the invention in that the colour selection system is connected to the display window via a number of two-part connection elements, each part of which has a surface which extends parallel to the display window, these surfaces being movable relative to one another in a common plane during the alignment and these surfaces being rigidly connected to one another in the aligned position. A few embodiments of the method according to the invention will now be described by way of example and with reference to the drawing, in which Fig. 1 is a schematic sectional view of a colour selection system and a display window, Fig. 2 is a schematic sectional view of a display window and a frame which are both provided with a metal element, Fig. 3 is a schematic sectional view of an tube enveloping part of a colour cathode-ray tube, Figs. 4 and 5 are schematic sectional views of an envelope comprising an enveloping part, a display window and a colour selection system, which are all provided with a metal element, Fig. 6 schematically shows an embodiment of a connection of two metal elements, one intermediate element being located between the two elements, Fig. 7 schematically shows an alternative embodiment of a connection of two metal elements, one intermediate element being located between the two elements, and Fig. 8 is a schematic sectional view of a colour cathode ray tube, the parts of which are interconnected by means of metal elements. In the manufacture of a colour cathode ray tube according to the invention, for example, a so-called master colour selection system is used to provide a number of display windows with a pattern of phosphor elements luminescing in one colour. A display screen of phosphor elements luminescing in different colours is obtained by providing a different pattern of phosphor elements for each colour on a display window by means of a master colour selection system. Besides, by means of a so-called master matrix a large number of colour selection systems are manufactured separately. Fig. 1 shows part of a display window 1 manufactured as described above and comprising a display screen 2. A colour selection system 4 mounted on a frame 3 and comprising a large number of apertures 5 is placed on the display window 1. Fig. 1 shows, by way of example, both a flat display window 1 and a flat colour selection system 4. It will be clear that the invention is not limited to a method of manufacturing cathode ray tubes having a flat display window, but that it also relates to cathode ray tubes having curved display windows and curved colour selection systems. The display screen 2 is further covered with an aluminium layer 40. The positioning of the display window 1 relative to the colour selection system 4 can for example be carried out by means of a test pattern which is incident on the phosphor elements of the display screen 2 through the apertures 5 of the colour selection system 4. In an embodiment of the positioning operation, the display screen 2 contains a few reference phosphor elements 41, Figure 2, at the edge, which are not covered by the aluminium layer and the colour selection system 4 contains a few reference apertures 42. By means of a lamp (not shown in Fig. 1) emitting ultraviolet light, a test pattern is displayed on the display screen 2 via the colour selection system 4. Subsequently, the colour selection system 4 and the display window 2 are moved relative to one another such that the test pattern passing through the reference apertures 42 is optimally displayed on the reference phosphor elements 41 of the display screen 2, so that the display window 2 and the colour selection system 4 are accurately aligned relative to one another. Next, the display window 1 must be secured in this aligned position to the frame 3, for example by fusing the frame 3 and the display window 1 by means of a gas flame at the location of the pasted seam 6. An alternative, simple, quick and accurate manner of fixing this aligned position is the fusing together of the display window 1 and the frame 3 by means of a laser. In this case, a laser supplies energy at the location of the pasted seam 6 (see the arrow in Fig. 1) causing the display window 1 and the frame 3 to fuse together. An accurate and solid fixation of the aligned position is obtained by providing the display window 1 with a metal mounting element 7 outside the display screen 2, as is shown in Fig. 2. At the location of its edge, the frame 3 is provided with a metal mounting element 8. The metal of which the auxiliary elements are made has a coefficient of thermal expansion which is substantially equal to the coefficient of thermal expansion of the material of which the parts are made, in the present example glass. The provision of the metal mounting element can be carried out, for example, by fusing the element into the display window 1 or by securing it to the display window 1 by means of a "solid-state" connection. A quick, clean and efficient method of securing a metal element is the securing technique which is known as thermocompression. The frame 3 and the display window 1 are placed on top of each other such that the two metal elements 7, 8 lie against one another. When the position relative to one another has been accurately adjusted by means of a test pattern, the two elements are secured to one another, for example, by means of laser welding. The laser beams used in the laser welding operation (see arrows in Fig. 2) pass through the display window 1, which is made of glass, to interconnect the two elements. In order to obtain a proper weld the laser beam must be properly focussed on the metal elements, and the energy-supply by the laser beam must be properly adjusted. In practice it has been found that by means of a pulsed Nd-YAG laser having a pulse width of 3.75 ms and an energy of 2.3 J and a wavelength of 1.06µm a proper connection can be formed, the material from which the frame 3 and the display window 1 are manufactured being undamaged or damaged to only a negligible extent. In order to secure a proper passage of the laser beams the surface of the glass of the display window must be polished. Fig. 3 shows an enveloping part 9 of a cathode-ray tube, which comprises an at least substantially rectangular edge 10 and a neck 11. The enveloping part 9, which is funnel-shaped in the present example, may be made entirely of glass or, in an alternative embodiment, it may be partly made of metal. If the cathode-ray tube is a flat (flat-type) cathode-ray tube, in which the enveloping part is box-shaped, the method according to the invention can also be used. To obtain a properly functioning display device, it is advantageous if the enveloping part and an assembly of a colour selection system and a display window are accurately aligned relative to one another before being secured to one another by means of a sealing process, the so-called "frit sealing". To position the enveloping part relative to the assembly use can be made of, for example, reference holes in the colour selection system, reference phosphor elements on the display screen and a lamp emitting ultraviolet light which is situated in the neck of the enveloping part. By means of the lamp a test pattern is displayed on the display screen and the enveloping part and the assembly are positioned relative to one another such that the test pattern passing through the reference apertures is displayed on the reference phosphor elements of the display screen in a desired manner. In the manufacture of a colour cathode-ray tube, in general, the display window is completed, i.e. it is provided with, inter alia , the display screen and an aluminium layer. Subsequently, the display window and the colour selection system are secured to one another to form an assembly, after which the assembly is placed against the enveloping part following introduction of a glass frit between them. Fig. 4 is a schematic sectional view of an envelope according to the invention, comprising an enveloping part 9, a display window 1 and a frame 3 with a flat colour selection system 4, each of which are provided with a metal element. To secure the enveloping part 9 to the assembly, it is provided on the edge 10 with a metal positioning element 18 and the assembly is provided with a metal mounting element 17. The enveloping part 9 is secured to the assembly of display window 1 and frame 3 by interconnecting the metal elements 17 and 18 by means of laser welding. The elements 7 and 17 may be joined to form one element. A simple way of positioning the parts relative to one another is described with reference to Fig. 5. Around the display screen 2, the display window 1 is provided with a metal mounting element 7 and the frame 3 is provided with a metal positioning element 8. The enveloping part 9 is provided with a metal positioning element 18 and the frame 3 is provided with a metal mounting element 19. A test pattern is optimized by positioning the frame 3 and the display window 1 relative to one another. Positioning can readily be carried out by taking each part separately and moving them relative to one another until the test pattern is displayed optimally. The adjusted position is fixed by interconnecting the element 7 and the element 8 by means of laser welding through the glass parts (see arrows Fig. 5). Subsequently, the enveloping part 9 is secured to the frame 3 by connecting the element 18 to element 19 in an aligned position. The display window 1, the frame 3 and the enveloping part 9 are finally secured to one another in a sealing process using a glass frit 20, 21. If an intermediate element 22 is located between the two elements 23, 25 as is shown in Fig. 6, it becomes possible to detach and subsequently replace in the same position the positioned parts. In Fig. 6, the securing of the display window 1 to the frame 3 is described by way of example. However, the assembly can be secured to the enveloping part in a similar manner. The element 23 is secured in an aperture 26 of the frame 3 and comprises a cavity, for example in the form of a cylindrical portion 27 which is, for example, triangular in cross-section. A projection 28 engages in the element 23 to secure the intermediate element 22 to the latter. An annular metal element 25 is provided on the display window 1. The position of the display window 1 relative to the frame 3 can be adjusted by means of a test pattern. If the desired position has been obtained, the element 25 is secured to the intermediate element 22 by means of laser welding through the display window 1 (see arrows in Fig. 6). Subsequently, the frame 3 with the colour selection system can be removed from the display window 1 by separating the element 23 and the intermediate element 22 from one another. The display window 1 and the frame 3 are finally secured to one another, for example, in a sealing process using a glass frit. The glass frit 20 is provided between the frame 3 and the display window 1. On account of this, the projection 28 of intermediate element 22 does not lie against the cylindrical part 27. The glass frit 20 is softened in the sealing process, such that the projection 28 engages again against the cylindrical part 27. Owing to this, the display window 1 and the frame 3 resume the desired position relative to one another. The intermediate element 22 permits an accurate and reproducible positioning of the frame 3 relative to the display window 1. A very simple manner of positioning the frame and the display screen or the enveloping part and the assembly in three directions relative to one another is obtained by using an intermediate element which permits movement of the elements relative to one another in a direction transverse to the display window. An embodiment of such an intermediate element is described in more detail with reference to Fig. 7. Fig. 7 schematically shows a flat display window 1 comprising a display screen 6. By means of thermocompression, a metal annular mounting element 25 is provided on the display window 1 outside the display screen 6. A frame 3 on which a colour selection system (not shown in Fig. 7) is mounted is provided with an aperture 26 in which a positioning element 23 is secured. The element 23 comprises a cavity in the form of a cylindrical part which is, for example, triangular in cross-section. The intermediate element 22 is resiliently constructed and comprises a projection 28 which can be engaged in the cavity of element 23. A bidirectional positioning of the frame 3 relative to the display window 1 in the plane of the display window 1 is obtained, for example, by holding the display window 1 and the frame 3 and moving them relative to one another in the plane of the display window 1. A positioning in a direction transverse to the plane of the display window 1 is obtained by means of the intermediate element 22. The intermediate element 22 comprises an annular base 39, a conical part 40 and the projection 28. The positioning element 23 is fitted onto the projection 28. Consequently, the element 23 is clear of the annular base 39. A movement in a direction transverse to the plane of the display window 1 is obtained by moving the frame 3 up and down (see vertical arrows in Fig. 7) relative to the display window 1. As a result of the resilient deflection of the intermediate element 22 under the influence of the conical part 40, the base 39 moves relative to the annular first element 25 in a direction in the plane of the display window 1 (see horizontal arrows in Fig. 7). The distance between the frame 3 (and, hence, the colour selection system) and the display window can be varied in this way. The colour selection system and the display window are positioned relative to one another by means of a test pattern which is displayed on the display screen via the colour selection system. If the desired position is obtained, the intermediate element 22 is secured to the positioning element 23 and to the mounting element 25, for example by means of laser welding, to fix the adjusted position. Fig. 8 is a sectional view of a cathode-ray tube, the parts of which, i.e. in this example, a funnel-shaped enveloping part 9 and a frame 3, and a substantially rectangular display window 1 are secured to one another by means of metal elements 17, 18, 24 and 25 which are provided in each corner of the display window 1. To generate three electron beams 30, 31 and 32, the enveloping part 9 is provided with an electrode system 12. A substantially rectangular colour selection system 4 having a large number of apertures 5 is provided on the frame 3. The display window 1 comprises a display screen 2 having phosphor elements luminescing in different colours. The enveloping part 9, the colour selection system 4 on the frame 3 and the display screen 2 on the display window 1 are positioned relative to one another such that the apertures 5 of the colour selection system 4 ensure that each electron beam is incident on phosphor elements luminescing in one colour. Outside the display screen, each corner of the display window 1 is provided with an annular mounting element 25 and a mounting element 17. The enveloping part 9 is provided with a positioning element 18 which is secured to element 17, and the frame 3 comprises a positioning element 23 and an intermediate element 22 which is secured to the annular element 25. The enveloping part 9 and the display window 1 are sealed to one another in a vacuum-tight manner by means of a glass frit 20. Of course, the present invention is not limited to the embodiments described above, and within the scope of the invention, as defined by the claims, many variations are possible to those skilled in the art. For example, the shape of the elements to be interconnected and the material of which they are composed can be varied as long as they remain interconnectable.

Claims: A method of manufacturing a colour cathode-ray tube in which a colour selection system (4) provided with primary mounting elements (8;24) secured to it and a substantially rectangular display window (1), carrying a display screen (2) of phosphor elements luminescing in different colours, provided with secondary mounting elements (7;25) secured to each of its corners, are secured to one another by means of said primary- and secondary mounting elements (7,8,24,25) to form an assembly characterized in that the colour selection system (4) and the display window (1) are brought together such that the primary mounting elements (8;24) adjoin the secondary mounting elements (7;25), in that the colour selection system (4) and the display window (1) are accurately aligned with respect to each other by moving the colour selection system (4) and the display window (1) relative to each other in a plane substantially parallel to the display screen (2) and in that the primary mounting elements (8;24) and the secondary mounting elements (7;25) are rigidly secured to one another, while maintaining the colour selection system (4) and the display screen (1) in their aligned position. A method as claimed in claim 1 characterized in that during said alignment step a test pattern is displayed on the display screen (2) via the colour selection system (4) and in that the colour selection system (4) and the display window (1) are moved relative to one another until the test pattern is displayed in the desired manner. A method as claimed in claim 2 characterized in that reference phosphor elements (41) are provided at the edge of the display screen (2) and reference apertures (42) are formed in the colour selection system (4), in that the colour selection system (4) is exposed to a lamp emitting ultraviolet light and in that the colour selection system (4) and the display window (1) are aligned such that the reference phosphor elements (41) are irradiated by said ultraviolet light through the reference apertures (42). A method as claimed in claim 1, 2 or 3 characterized in that the primary mounting elements (8,24) and the secondary mounting elements (7,25) are rigidly secured to one another by means of laser welding. A method as claimed in claim 4 characterized in that at least one of the colour selection system (4) and the display window (1) is made of glass at least at the parts where the mounting elements (8,24,7,25) are secured to it and in that the mounting elements (8,24,7,25) are exposed to a laser beam passing through said glass. A colour cathode ray tube comprising an electrode system (12) for generating a number of electron beams (30-32) and a colour selection system (4) located opposite to a display window (1) which carries a display screen (2) consisting of phosphor elements luminescing in different colours, in which the colour selection system is provided with a number of primary mounting elements (8,24) and the display window is provided with corresponding secondary mounting elements (7,25) and in which the colour selection system (4) and the display window (1) are secured to one another by means of a rigid connection between said primary and secondary mounting elements (7,8,24,25) characterized in that the primary and secondary mounting elements engage with each other in a common connection plane which is substantially parallel to the display screen (1) in a manner which permits a relative alignment of the colour selection system and the display window in a direction substantially parallel to the display screen as long as the primary mounting elements and the associated secondary mounting elements are not rigidly connected to one another. A colour cathode ray tube as claimed in claim 6 characterized in that the colour selection system (4) and the display window (1) are detachably connected to one another. A colour cathode ray tube as claimed in claim 7 characterized in that either the primary or the secondary mounting elements comprise two detachable parts (22,23) one of said parts (23) comprising a cavity (27) and the other part (22) comprising a projection (28) mating with said cavity (27).

Inventors: VAN DEN BROEK ADRIANUS PETRUS, VAN DEN BROEK, ADRIANUS PETRUS
Applicants: PHILIPS ELECTRONICS NV, PHILIPS ELECTRONICS N.V.
Application year: 1989
Main classification: H01J9
IPC codes: H01J29, H01J9