IE44477B1 - Manufacture of electric lamps containing fluorine - Google Patents

Abstract

The invention relates to the manufacture of electric lamps containing fluorine in their gas fill. Fluorine can be accurately and conveniently introduced into an electric lamp envelope in the form of a fluorocarbon polymer. If a soluble fluorocarbon polymer, such as a degraded PTFE, is dissolved in a suitable solvent, for example a fluorinesubstituted hydrocarbon or halocarbon solvent, the resulting solution can be metered with great accuracy into the lamp envelope and the solvent subsequently evaporated. The invention avoids the difficulties otherwise inherent in dispensing accurate quantities of an extremely reactive gaseous material.

Description

The present invention relates to the manufacture of electric- lamps and, more particularly, to a method of introducing fluorine into the lamp envelopes.

In the manufacture of electric lamps having a gas 5 fill containing fluorine, more especially tungsten/fluorine incandescent lamps, it is necessary that a predetermined and carefully controlled quantity of fluorine he introduced into the lamp envelope. Halogens are conventionally introduced into lamp envelopes hy careful metering of the element as Ί0 ' such hut this is difficult in the case of fluorine owing to its gaseous state. Moreover, the necessity for accurate control is particularly important in the case of fluorine hecause of its high reactivity.

It has been proposed to introduce halogen in the form of a normally solid compound of the element, conveniently in solution in a non-polar solvent, for example as a halophosphonitrile in British Patent Specification No. 1,236,174. Other compounds are mentioned in British Patent Specification No. 1,361,224, Once again, however, there are problems with fluorine in that it is difficult to find a combination of a fluorinecontaining, low vapour pressure solid and a suitable solvent that will· facilitate the production of fluorine-containing lamps with a high degree of consistency.

We have now found that superior results can he obtained by the introduction of fluorine into a lamp envelope in the form of a soluble fluorocarbon polymer. It has further been found that particularly suitable solvents for -244477 this purpose are fluorinated organic solvents, more especially fluorinesubstituted hydrocarbon or halocarbon solvents, such as those kncwn under the Trade Marks FRECN and ARCTON.

Accordingly the invention provides a method of manufacturing an electric larrp having a gas fill containing fluorine in which the fluorine is introduced as a fluoro-carbon polymer, preferably in solution in a solvent therefor, such as a fluorinated organic solvent. The invention also embraces electric lanps containing fluorocarbon polymers as a source of fluorine for the gas fill.

The preferred fluorocarbon product is a soluble degradation product of polytetrafluoroethylene (PTEE). An exanple is the fluorinated grease sold for use as a lubricant under the Trade Mark ΚΚΪΤ0Χ (Du Pont).

This grease comprises a perfluoroalkyl polyether oil thickened with tetrafluoroethylene telcmer. Ibis substance is preferably dissolved in trichlorotrifluoroethane (C2F3C13) and the solution can be dispensed into the larcp envelopes by the technique described in British Patent Specification No. 1,236,174.

The application of the invention enables considerable inprovements in control of fluorine dosage to be achieved. For exanple, by using a gaseous fluoride, such as SFg, KFg or NF3, variations of - 50% in the fluorine dose can occur, which is quite unacceptable for other than laboratory experiments. In contrast, similar lanps dosed with a solution of fluorocarbon polymer have exhibited a fluorine dose controllable to better than - 5%. lhe lartp envelope, which may be of a high silica - 3 4 4477 content glass, for exainple fused, silica or the 96 % silica glass sold under the * Trade Mark VYCCR (Coming), is preferably provided with a protective fluorine-resistant coating. Preferred coating materials are glassy metal phosphates and arsenates, more especially aluminium and aluminium titanium phosphates, or alumina, and the formation of protective coatings of such materials, by deposition of solutions of compounds of the elements concerned followed by evaporation of the solvent and baking, is described in. Patent Specification Nos. 38743 and 52/77 respectively. Λ 12V 100W lamp, of the type commonly used in film projectors, comprises a Vycor envelope 1, in v/hich is sealed a tungsten filament 2 supported on filament tails or lead-in wires 3 and is provided with en exhaust tube A.

The lamp i.s provided with a fluoride-resistant aluminium phosphate, aluminium titanium phosphate or alumina layer (not shown) covering the inside surface of the envelope 1, the filament 2 and tails 3, as mentioned above. The lamp is then dosed with 35 Hg of the fluorocarbon polymer, as a 0.5 g/1 solution in C^F^Cl^, the solvent subsequently removed, as described in British Patent No. 1,236,174 and the lamp gasfilled in the normal manner with 3| atm. of argon, at room temperature. _Z|~ 4 4 7 7 Lamps of this type have been run at 1J.8 V, which corresponds to a temperature at the centre of the filament just below the melting point of tungsten, fusing of the centre turn occurs at about 94.5 V. Such lamps have achieved lives of 40 hours, without detectable thinning of the hottest spot at the centre of the filament, subsequent failure occurring by tungsten loss in the colder regions of the filament or tails. In comparison, similar lamps containing Brg instead of Fg fuse at Fhe centre of the filament after 20 hours operation at 13.8 V.

Claims (3)

1. Ί. An electric lamp having a gas fill containing fluorine, characterized in that the fluorine is incorporated in the form of fluorocarbon polymer. 5 2. A lamp according to claim i, characterized in that the polymer is a soluble degradation product of PIPE. 3. A lamp according to claim i or 2, characterized in that the internal surface of the envelope of the lamp and other exposed surfaces of internal components have a pro10 tective glassy coating of a metal phosphate or alumina. A. A method of manufacturing an electric lamp having a gas fill containing fluorine, characterized in that the .fluorine is introduced into the lamp envelope in the form of a fluorocarbon polymer. 15 5· A method according to claim A, characterized in that the fluorocarbon polymer is dissolved in a solvent therefor. 6. A method according to claim A or 5, characterized in that the fluorine is introduced by metering into the

2. O ' envelope a solution of a degradation product of PTFE in a fluorinated organic solvent. -64 4 4? 7. An electric lamp containing a fluorocarbon polymer to supply fluorine for the gas fill, substantial! as described, herein with reference to -she accompanying drawing.

3. 5 8. A method of making an electric lamp containing fluorine substantially as described, herein with reference to the accompanying drawing.