Patent Publication Number: US-6043603-A

Title: Low-pressure discharge lamp having an angularly oriented support member bearing a mercury-containing coating and a getter coating

Description:
TECHNICAL FIELD 
     The invention relates to a low-pressure discharge lamp. 
     BACKGROUND ART 
     Japanese Published Application JP 6-96728 discloses a low-pressure mercury vapour discharge lamp having two essentially identical electrode frames sealed in the ends of the tubular discharge vessel. The electrode frames each have an electrode filament which is arranged transverse to the discharge vessel axis and is surrounded by an annular metal strip--a so-called ring cap. The ring axis of this annular metal strip extends parallel to the discharge vessel axis. The ring cap is assembled from two segments, of which one segment is coated with an amalgam, in particular with a mercury-titanium alloy, while the other segment is provided with a getter coating which binds the gaseous contaminants in the discharge vessel. The amount of mercury in the low-pressure discharge lamp is controlled via the length of the first segment. While the lamp is being produced, the ring caps are heated inductively with the aid of an electromagnetic radio frequency signal to a temperature of approximately 900° C. to 950° C. As a result, on the one hand the getter is activated, and on the other hand the mercury is released from the mercury alloy. The required radio frequency signal is usually generated by means of a radio frequency inductor which has an induction loop with two long legs extending parallel to one another, and which generates at the location of the ring caps an electromagnetic radio frequency field whose magnetic field extends essentially parallel to the discharge vessel axis and thus also parallel to the ring axis of the ring caps. The lamps require approximately 20 to 30 seconds to traverse this radio frequency field. Because of their dimensions, such ring caps are not suitable for low-pressure discharge lamps whose discharge vessel has an outside diameter of less than or equal to 16 mm. 
     German patent DE 26 16 577 describes a low-pressure discharge lamp, in particular a fluorescent lamp, which is provided with a mercury-containing ionizable filling inside the discharge vessel. The mercury component in the ionizable discharge medium is here approximately 5 mg to 20 mg. Since such low amounts of mercury can be dosed in the form of drops only with difficulty, the mercury is introduced into the discharge vessel with the aid of a support member which is provided with a mercury-containing coating and additionally also with a getter. The mercury-containing coating and the getter are applied to a metal strip, which is arranged parallel to the longitudinal axis of the lamp and is a component of an electrode frame of the low-pressure discharge lamp, that is to say the coated surfaces of the metal strip extend essentially in an axially parallel fashion. During production of the lamp, the metal strip is inductively heated by means of an electromagnetic radio frequency signal for approximately 20 to 30 seconds to a temperature of approximately 900° C. to 950° C. in order to release the mercury and activate the getter. 
     DISCLOSURE OF THE INVENTION 
     It is the object of the invention to provide a low-pressure discharge lamp having an improved support member which bears a mercury-containing coating and a getter coating. In particular, this support member is also to be suitable for low-pressure discharge lamps which have a mercury content of less than 10 mg and of which the outside diameter of the discharge vessel is less than or equal to 16 mm. Moreover, it is also to be possible to use the radio-frequency inductor, which is used to produce the low-pressure discharge lamps fitted with the above-described ring caps, to produce the lamps provided with the improved support member, with the result that there is no need to convert the production line. 
     The low-pressure discharge lamp according to the invention has a tubular discharge vessel which, at least in the region of its ends, has a longitudinal axis, and in whose interior one or more support members are arranged which has or have at least one first surface provided with a mercury-containing coating and at least one second surface provided with a getter coating. These surfaces, coated in such a way, of the support member or of the support members are inclined by an angle of at least 30 degrees to the longitudinal axis of the tubular discharge vessel or to the longitudinal axis of the discharge vessel ends. 
     It is thereby ensured that the support members of the low-pressure discharge lamps according to the invention can be inductively heated sufficiently with the aid of the radio-frequency inductor normally used for inductive heating of the ring caps. During production of the lamp, the lamp ends or the discharge vessel ends traverse the electromagnetic field of the radio-frequency inductor, whose magnetic field lines at the location of the support member extend essentially parallel to the longitudinal axis of the discharge vessel or of the discharge vessel end. Since the surfaces of the support member which are provided with the getter coating and the mercury-containing coating are inclined by at least 30 degrees to the longitudinal axis of the discharge vessel end, because of its favourable orientation the electromagnetic field of the radio-frequency inductor induces in the region of these coated surfaces of the support member a comparatively high current, and thus renders it possible for these surfaces to be heated up sufficiently. The radio-frequency field achieves its optimum effect when the magnetic field lines are orientated perpendicular to the surfaces provided with the getter material and mercury-containing coating. For this reason, the surfaces, coated with the getter and with the mercury alloy, of the support members of the low-pressure discharge lamps according to the invention are advantageously arranged perpendicular to the longitudinal axis of the discharge vessel end. In the case of the particularly preferred exemplary embodiments of the invention, the support member advantageously comprises a metal plate which is coated with the getter material and with the mercury alloy. This metal plate demands less space than a ring cap and is therefore particularly suitable for low-pressure discharge lamps whose discharge vessel has only a comparatively small diameter--in particular an outside diameter of the discharge vessel which is less than or equal to 16 mm--or in the case of which the use of a ring cap is disadvantageous. Moreover, the application of the invention is suggested in the case of low-pressure discharge lamps having a comparatively low mercury content of less than 10 mg in the ionizable filling and in the case of which a liquid dosing of the mercury in the discharge vessel would be problematic. Precisely in the case of such low amounts of mercury, it is particularly important fully to release the mercury bound in the mercury-containing coating, and thus to heat up the support member optimally, with the result that the optimum mercury vapour pressure can be produced in the discharge space while the lamp is being operated. 
     In two of the preferred exemplary embodiments, the support member is advantageously constructed as an essentially flat metal plate which is aligned perpendicular to the longitudinal axis of the discharge vessel end and whose front is provided with the mercury-containing coating and whose rear is provided with the getter coating. These metal plates are advantageously welded to a lead-in wire for the electrode filament of the lamp. A simple design of the electrode frame is rendered possible thereby. In the three further exemplary embodiments, the support member is advantageously constructed as a metal plate in the shape of a U or of a V, whose U-leg or V-leg, respectively, arranged transversely or obliquely, respectively, to the longitudinal axis of the discharge vessel end are coated with the getter material and with the mercury alloy. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is explained in more detail below with the aid of a plurality of preferred exemplary embodiments. In the drawing: 
     FIG. 1 shows a schematic side view of an end of a low-pressure discharge lamp in accordance with the first exemplary embodiment of the invention, 
     FIG. 2 shows a schematic side view of the lamp end of FIG. 1, rotated by 90°, 
     FIG. 3 shows a schematic side view of an end of a low-pressure discharge lamp in accordance with the second exemplary embodiment of the invention, 
     FIG. 4 shows a schematic side view of the lamp end of FIG. 3, rotated by 90°, 
     FIG. 5 shows a schematic side view of an end of a low-pressure discharge lamp in accordance with the third exemplary embodiment of the invention, 
     FIG. 6 shows a schematic side view of the lamp end of FIG. 5, rotated by 90°, 
     FIG. 7 shows a schematic side view of an end of a low-pressure discharge lamp in accordance with the fourth exemplary embodiment of the invention, 
     FIG. 8 shows a schematic side view of an end of a low-pressure discharge lamp in accordance with the fifth exemplary embodiment of the invention, 
     FIG. 9 shows a schematic side view of the lamp end of FIG. 8, rotated by 90°. 
    
    
     The lamp according to the invention is a low-pressure mercury vapour discharge lamp, in particular a fluorescent lamp. This lamp has a tubular discharge vessel 10, 20, 30, 40, 50, which can be bar-shaped, bent in the shape of a U or also multiply bent. The two ends of the discharge vessel are sealed in a gastight fashion. An electrode frame 11, 21, 31, 41, 51 is sealed in each case with the ends of the discharge vessel 10, 20, 30, 40, 50. The electrode frames 11, 21, 31, 41, 51 each have an electrode filament 11a, 21a, 31a, 41a, 51a and two lead-in wires 11b, 11c, 21b, 21c, 31b, 31c, 41b, 41c, 51b, 51c, which are connected in an electrically conducting fashion to the ends of the electrode filament 11a, 21a, 31a, 41a, 51a. The electrode filaments 11a, 21a, 31a, 41a, 51a are arranged in the interior of the discharge vessel 10, 20, 30, 40, 50 and transverse to the longitudinal axis A--A of the end of the discharge vessel 10, 20, 30, 40, 50. The outside diameter of the discharge vessel 10, 20, 30, 40, 50 is approximately 16 mm. Fastened to one of the two electrode frames 11, 21, 31, 41, 51a is a metal plate 12, 22, 32, 42, 52 which is coated with a getter 14, 24, 34, 44, 54 and provided with a mercury-containing coating 13, 23, 33, 43, 53. The metal plates function as support members for the getter material and for the mercury-containing coating. The getter material 14, 24, 34, 44, 54 is a zircon-aluminium getter, and the mercury-containing coating 13, 23, 33, 43, 53 is a mercury-titanium alloy. The lead-in wires 11b, 11c, 21b, 21c, 31b, 31c, 41b, 41c, 51b, 51c are led out of the end of the discharge vessel 10, 20, 30, 40, 50. The amount of mercury introduced into the discharge vessel 10, 20, 30, 40, 50 with the aid of the support member is approximately 3 mg. All five exemplary embodiments agree to this extent. 
     MODE FOR CARRYING OUT THE INVENTION 
     Illustrated in a schematic representation in FIGS. 1 and 2 is one end of a low-pressure discharge lamp in accordance with the first exemplary embodiment of the invention. The end of the discharge vessel 10 is sealed with the electrode frame 11 in the manner of a so-called plate-shaped foot seal 11d, 11f. The electrode frame 11 comprises a glass plate foot 10d, whose widened edge 11f is sealed in a gastight fashion to the end of the tubular discharge vessel 10, an electrode filament 11a, arranged transverse to the longitudinal axis A--A of the discharge vessel, and two lead-in wires 11b, 11c, which are connected in each case in an electrically conductive fashion to an end of the electrode filament 11a and are sealed in the plate foot 11d. The glass plate foot 11d is provided with an exhaust tube 11e which serves to evacuate the discharge vessel 10. Welded onto the one lead-in wire 11b is a rectangular, essentially flat metal plate 12 whose one side bears the mercury-containing coating 13, while the other side is coated with the getter 14. The metal plate 12 is aligned perpendicular to the longitudinal axis A--A, with the result that the underside, coated with the getter 14, of the metal plate 12 faces the plate foot 11d, and the upper side, provided with the mercury-containing coating, of the metal plate 12 faces the electrode filament 11a. In order to facilitate welding the metal plate 12 to the lead-in wire 11b, the metal plate 12 has on its edge a welding lug 12a bent away at right angles. 
     FIGS. 3 and 4 show an end of a low-pressure discharge lamp in accordance with the second exemplary embodiment of the invention, in a schematic representation. Here, as well, in a way completely analogous to the first exemplary embodiment, the end of the discharge vessel 20 is sealed with the electrode frame 21 in the manner of a plate-shaped foot seal 21d, 21f. The electrode frame 21 of the second exemplary embodiment does not differ from the electrode frame 11 of the first exemplary embodiment. It likewise comprises an electrode filament 21a, two lead-in wires 21b, 21c and a glass plate foot 21d which is provided with an exhaust tube 21e and whose widened edge 21f is sealed with the discharge vessel end. By contrast with the first exemplary embodiment, the second exemplary embodiment has a metal plate 22 which is bent in the shape of a U and serves as support member for the getter 24 and the mercury-containing coating 23. The base part, connecting the two U-legs, of the metal plate 22 is welded to the one lead-in wire 21b, with the result that the outsides and insides of the U-legs are aligned perpendicular to the longitudinal axis A--A of the end of the discharge vessel 20. The mercury-containing coating 23 is applied to the outside of the U-leg, facing the electrode filament 21a, of the metal plate 22, while the getter coating is applied to the outside of the other U-leg, facing the plate foot 21d, of the metal plate 12. 
     In FIGS. 5 and 6, an end of a low-pressure discharge lamp in accordance with the third exemplary embodiment of the invention is illustrated in a schematic representation. Here, as already described in the first two exemplary embodiments, the end of the discharge vessel 30 is sealed with the electrode frame 31 in the manner of a plate-shaped foot seal 31d, 31f. The electrode frame 31 of the third exemplary embodiment does not differ from the electrode frames 11, 21 of the first two exemplary embodiments. It likewise comprises an electrode filament 31a, two lead-in wires 31b, 31c and a glass plate foot 31d which is provided with an exhaust tube 31e and whose widened edge 31f is sealed with the discharge vessel end. By contrast with the first two exemplary embodiments, the third exemplary embodiment has a metal plate 32 which is bent in the shape of a V and serves as support member for the getter 34 and the mercury-containing coating 33. The V-shaped metal plate is held with the aid of a multiply bent wire 35, which is welded to a V-leg of the metal plate 32 and sealed in the glass plate foot 31d. The outer surfaces and inner surfaces of the V-legs of the metal plate 32 are aligned obliquely to the longitudinal axis A--A of the discharge vessel end. They form with it an angle of between approximately 30° and 60°. The metal plate 32 is arranged here below the electrode filament 31a, that is to say between the electrode filament 31a and the glass plate foot 31d. The mercury-containing coating 33 is applied to the outer surface, facing the electrode filament 31a, of the one V-leg, while the getter coating 34 is applied to the outer surface, facing the electrode filament 31a, of the other V-leg of the metal plate 32. 
     FIG. 7 shows a schematic representation of an end of a low-pressure discharge lamp in accordance with the fourth exemplary embodiment of the invention. In this exemplary embodiment, the electrode frame 41 comprises an electrode filament 41a, aligned transverse to the longitudinal axis A--A of the discharge vessel end, two lead-in wires 41b, 41c and a glass bead 41d. The lead-in wires 41b, 41c are in each case connected in an electrically conducting fashion to an end of the electrode filament 41a and sealed in the glass bead 41d. The glass bead 41 [sic] lends mechanical stability to the electrode frame 41. The end of the discharge vessel 40 is sealed in a gastight fashion by means of a pinch seal 40a. The lead-in wires 41b, 41c are sealed in a gastight fashion in the pinch seal 40a and project out of the discharge vessel end. Welded onto the one lead-in wire 40b is a metal plate 42, whose one side bears the mercury-containing coating 43, while the other side is coated with the getter 44. The metal plate 42 is aligned perpendicular to the longitudinal axis A--A of the discharge vessel end, with the result that the underside, coated with the getter 44, of the metal plate 42 faces the pinch seal 40a, and the upper side, provided with the mercury-containing coating, of the metal plate 12 [sic] faces the electrode filament 41a. In order to facilitate welding the metal plate 42 to the lead-in wire 41b, the metal plate 42 has on its edge a welding lug 42a bent away at right angles. 
     FIGS. 8 and 9 show an end of a low-pressure discharge lamp in accordance with the fifth exemplary embodiment of the invention, illustrated in a schematic representation. Here, as already described in the case of the third exemplary embodiment, the end of the discharge vessel 50 is sealed with the electrode frame 51 in the manner of a plate-shaped foot seal 51d, 51f. The electrode frame 51 of the fifth exemplary embodiment does not differ from the electrode frame 31 of the third exemplary embodiment. It likewise comprises an electrode filament 51a, two lead-in wires 51b, 51c and a glass plate foot 51d which is provided with an exhaust tube 51e and whose widened edge 51f is sealed with the discharge vessel end. In a manner similar to the third exemplary embodiment, the fifth exemplary embodiment has a metal plate 52 which is bent in the shape of a V and serves as support member for the getter 54 and the mercury-containing coating 53. The V-shaped metal plate 52 is likewise held with the aid of a multiply bent wire 55, which is welded to a V-leg of the metal plate 52 and sealed in the glass plate foot 51d. The outer surfaces and inner surfaces of the V-legs of the metal plate 52 are aligned obliquely to the longitudinal axis A--A of the discharge vessel end. The aperture angle of the V-shaped metal plate 52 is between approximately 110° and 120° so that both V-legs include with the longitudinal axis A--A in each case an angle of approximately 55° to 60°. Here, however, by contrast with the third exemplary embodiment the metal plate 52 is arranged above the electrode filament 51a. The mercury-containing coating 53 is applied on the outer surface, averted from the electrode filament 51a, of the one V-leg, while the getter coating 54 is applied on the outer surface, averted from the electrode filament 51a, of the other V-leg of the metal plate 52. 
     The invention is not limited to the exemplary embodiments described in greater detail above. For example, the V-shaped metal plates of the exemplary embodiments three and five can also be fastened to a lead-in wire by means of a fastening wire. Of course, it is also possible to fasten the support bodies in accordance with the exemplary embodiments one and four, for example with the aid of a fastening wire, in the glass plate foot or in the glass bead, respectively. Moreover, instead of the mercury-titanium alloy it is also possible to use other mercury-containing alloys or compounds for the mercury-containing coating of the support member according to the invention.