Display tube with deflection unit mounted on said tube

Abstract: Display tube (1) with a deflection unit (4) which is mounted on said tube and comprises a funnel-shaped coil support (5). After the optimum position of the deflection unit has been set with respect to the display tube, the coil support is fixedly secured to the envelope of the display tube. A shrink sleeve (13) which is partly shrunk around the narrow end of the coil support and partly around the envelope of the tube is used for fixation.

Description: The invention relates to a display tube with a deflection unit which is mounted on said tube and comprises a coil support, said deflection unit being fixedly secured to the envelope of the display tube by means of a shrink sleeve comprising an annular body of a synthetic material which shrinks upon heating, one end of the annular body being shrunk around one end of the coil support and the other end of the annular body being shrunk around the envelope of the display tube. It is known that in display tubes of the type used for TV receivers and monitors a deflection unit is slid on the neck of the display tube after its assembly, which deflection unit is supported by the funnel-shaped portion of the envelope of the display tube. In practice, the rear end of the coil support of the deflection unit is fixedly secured to the glass neck of the display tube by means of a metal clamping strap. For a good performance it is generally necessary to set the correct operational position of each deflection unit with respect to its display tube in advance, notably by moving in the axial direction, by tilting, and/or by rotating about its longitudinal axis so as to optimally adjust given parameters such as colour purity, convergence and the position of the grid with respect to the display screen. In this connection it is desirable to use easy-assembly techniques for fixing the deflection unit on the neck, i.e. techniques which require a small number of components, are preferably not time-consuming and can preferably be automated without this being at the expense of the mechanical specifications (such as resistance to drop tests). It is an object of the invention to provide a display tube with a deflection unit in which an easy-assembly fixation of the deflection unit is inherent. This object is achieved in that the annular body (13) is provided on its inner surface with a thin layer of an adhesive bonding material. The use of an annular body (or sleeve) of a synthetic material which shrinks under the influence of applying thermal energy (known as shrink sleeve) for the purpose of fixing renders a clamping strap with a bolt and the associated time-consuming operation of tightening the bold redundant. This tightening operation cannot be automated. Moreover, the use of a shrink sleeve leads to less neck breakage, while nevertheless mechanical requirements such as resistance to drop tests and satisfactory long-term fixation are satisfied. In this respect deflection units glued onto the neck or secured by means of rubber constructions are not satisfactory. However, it is possible to choose such a material for the shrink sleeve that when setting the correct position of the deflection unit the shrink sleeve has such a flexibility that it does not impede setting. By applying thermal energy and subsequently cooling, the shrink sleeve shrinks tightly around the envelope of the display tube and the end of the coil support so that it retains the setting of the deflection unit. The material of the annular body may be selected from a plurality of known synthetic materials which are suitable for forming objects which shrink when thermal energy is applied to them. Suitable materials are, inter alia, thermoplastic synthetic materials such as polyolefins, polyvinylidene fluoride, polythene, soft PVC. The invention also relates to a method of mounting a deflection unit (4), including a deflection coil support (5), on a display tube (1), said method comprising the steps of: a. placing the deflection unit (4) on the tube (1); b. placing an annular body (13) of a heat-shrinkable synthetic material by disposing a first end of said annular body (13) around an end (12) of the coil support and by disposing a second end of said member around a portion (3) of the tube (1); c. disposing a thin layer of an adhesive bonding material on the inner surface of the annular body (13) before placing it; d. adjusting the deflection unit to a selected operational position and orientation relative to the tube; e. heating the annular body (13) until respective portions of said body shrink around said end (12) of the coil support (5) and around said portion (3) of the tube (1), thereby bonding the coil support (5) to the tube (1). It is noted that it is known per se from RD-A-314072 to use a tubing of heat shrinkable material for the connection of a deflection unit to a display tube. This document, however, does not discloses the use of an adhesive layer interposed between the tubing and the deflection unit in order to enhance the connection nor does it disclose to set the deflection unit in its desired position while the shrink sleeve has already been applied. Below, the invention will be described in greater detail with reference to a specific embodiment and an associated drawing in which Fig. 1 shows a display tube with a deflection unit according to the invention. Fig. 1 shows a display tube 1 having a funnel-shaped portion (cone) 2 and a neck 3. A deflection unit 4 with a coil support 5 of, for example, synthetic material supporting a pair of field deflection coils 6, 6′, a pair of line deflection coil 7, 7′ and a yoke ring 8 is arranged on the envelope 9 of the display tube and its front end 10 is supported by the funnel-shaped portion 2. Adjusting members such as bolts or pins 11, 12 may be used, for example, for supporting the front end in the correct position. After it has been slid on the neck 3, the deflection unit 4 is set to its optimum position with respect to the display tube 1. When setting the correct position, use can be made of a match head with grippers. To retain the optimum position, use is made of an annular body 13 of a material which shrinks when thermal energy is applied to it (commonly known as shrink sleeve) and one end of which is shrunk around the rear end 12 of the coil support 5 and the other end of which is shrunk around the neck 3. The shrink sleeve may be, for example, cylindrical, having a constant diameter, or bottle-shaped with a wider end surrounding the coil support 5 and a narrower end surrounding the neck 3. The shrink sleeve 13 may have a thickness ranging between, for example several tenths of millimetres to one or several millimetres and a length of 1 to 5 cm with a diameter of one to several centimetres. The material of the shrink sleeve may be chosen from a plurality of known thermoplastic synthetic materials. When the shrink sleeve 13 is being formed, it is subjected to a stretching process in the heated state and is subsequently cooled to make it suitable for a process in which it reassumes its original shape when thermal energy is applied. In its stretched shape the shrink sleeve 13 is arranged on the rear end of the coil support 5 and on the adjacent part of the neck 3. After the position of the deflection unit 4 is set optimally, thermal energy is applied to the shrink sleeve 13. (A practical form of supplying energy is the use of IR radiators or a hot-air gun.) The supply of thermal energy may already be started when the desired position is being set. By supplying thermal energy, the shrink sleeve attempts to reassume its original shape. The shrink sleeve then shrinks tightly around the coil support and the neck and the optimum position of the deflection unit 4 is fixed. The display tube with the deflection unit can therefore be removed from the aligning apparatus a very short time after it has been aligned and the optimum setting can be fixed fully automatically. Fixation of the rear end of the coil support on the neck of the display tube by means of a shrink sleeve has been described in the foregoing. Alternatively, the display screen-facing front end of the coil support can be fixed on the cone of the display tube by means of a shrink sleeve. Adjusting members, such as the adjusting members 11 and 12 may then be dispensed with. If necessary, the two ends may be fixed simultaneously in this manner. A shrink sleeve is manufactured, for example, by crosslinking the material of an extruded flexible tube of a polymer material by means of β radiation and by subsequently heating and stretching it. The sleeve is cooled in its stretched state so that the stretched shape is maintained. In this state the sleeve is sold to the "consumer". The material which is still under tensile stress will attempt to reassume its original shape ( i.e. the shape actually formed by means of a chemical reaction (crosslinking)) after it has been reheated to a temperature above its softening point. The latter operation is carried out by the customer, in this case the manufacturer of the display tube, when the deflection unit is fixed on the tube. Within the scope of the invention it may be practical to provide at least one end of the coil support with a shrink sleeve projecting beyond this end, before the coil support is placed on a display tube. The shrink sleeve may be secured in its non-shrink state to the coil support and shrunk onto this support (during or after setting the position of the coil support on the display tube), or it may be secured already in its shrunk state to the coil support. It has proven to enhance the mechanical strength of the connection if the sleeve before it is placed is provided on its inner surface with a thin layer of a bonding material (an adhesive).

Claims: A display tube (1) with a deflection unit (4) which is mounted on said tube and comprises a coil support (5), said deflection unit (4) being fixedly secured to the envelope of the display tube (1) by means of a shrink sleeve comprising an annular body (13) of a synthetic material which shrinks upon heating, one end of the annular body being shrunk around one end (12) of the coil support (5) and the other end of the annular body being shrunk around the envelope of the display tube, characterized in that the annular body (13) is provided on its inner surface with a thin layer of an adhesive bonding material. A method of mounting a deflection unit (4), including a deflection coil support (5), on a display tube (1), said method comprising the steps of: a. placing the deflection unit (4) on the tube (1); b. placing an annular body (13) of a heat-shrinkable synthetic material by disposing a first end of said annular body (13) around an end (12) of the coil support and by disposing a second end of said member around a portion (3) of the tube (1); c. disposing a thin layer of an adhesive bonding material on the inner surface of the annular body (13) before placing it; d. adjusting the deflection unit to a selected operational position and orientation relative to the tube; e. heating the annular body (13) until respective portions of said body shrink around said end (12) of the coil support (5) and around said portion (3) of the tube (1), thereby bonding the coil support (5) to the tube (1). A method as in claim 2 where the heat-shrinkable synthetic material comprises a thermoplastic synthetic material selected from the group of polyolefin, polyvinylidene fluoride, polythene and soft PVC. A method as in claim 2 where the annular body (13) has a substantially cylindrical shape before the shrinking step is carried out. A method as in claim 2 where, before the shrinking step is carried out, the annular body (13) has a bottle shape, the first end of said member having a different diameter than the second end of said member. A method as in claim 2 where the first end of the annular body (13) is disposed around the end (12) of the coil support before the deflection unit (4) is placed on the tube (1). A method as in claim 2 where the heating step is performed during the adjusting step.

Inventors: FLEUREN PETRUS ANTONIUS MARIA, STRIJBOS PETRUS ANTONIUS WILHE, VAN DE HEI GERARDUS MARTINUS M, FLEUREN, PETRUS ANTONIUS MARIA, STRIJBOS, PETRUS ANTONIUS WILHEMUS, VAN DE HEI, GERARDUS MARTINUS MARIA
Applicants: PHILIPS ELECTRONICS NV, PHILIPS ELECTRONICS N.V.
Application year: 1992
Main classification: H01J29
IPC codes: H01J29