CA1069576A

CA1069576A - Manufacture of electric lamps

Info

Publication number: CA1069576A
Application number: CA269,432A
Authority: CA
Inventors: John M. Rees; Anthony P. Downing; Christopher A. Horler
Original assignee: Imperial Chemical Industries Ltd; Thorn Electrical Industries Ltd
Current assignee: EMI Group Ltd; Imperial Chemical Industries Ltd
Priority date: 1976-01-12
Filing date: 1977-01-11
Publication date: 1980-01-08
Also published as: SE7700251L; IE44477B1; ZA77128B; BE850295A; IE44477L; GB1571195A; NL7700151A; DE2701050A1; DK11677A; LU76556A1; FR2337940B1; FR2337940A1; AU507646B2; JPS52101882A; IT1086277B; AU2126877A

Abstract

ABSTRACT OF THE DISCLOSURE:
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 fluorine-substituted 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

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The present invention relates to the manufacture of el~ectric lamps and, more particularly, to a method of introducing fluorine into the lamp envelopes.
In the manufacture of electric lamps having a gas fill containing fluorine, more especially tungsten/fluorine incandescent lamps, it is necessary that a predetermined and carefully controlled quantity of fluorine be introduced into the lamp envelope. Halogens are conventionally introduced into lamp envelopes by careful metering of the element as such but 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 because 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 halo-phosphonitrile in our United States Patent No. 3,898,500.
Other compounds are mentioned in our Canadian Patent No.
986,980 issued April 6, 1976. Once again, however, there are problems with fluorine in that it is difficult to find a combination of a fluorine-containing, 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 be 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

-2-this purpose are fluorinated organic solvents, more especially fluorine-substituted hydrocarbon or halocarbon solvents, such as those ~nown under the Trade Marks ~EON
and ARC~0~.
Accordingly the invention provides a method of manu-facturing an electric lamp having a gas fill containing flucrine in which the fluorine is introduced as a fluoro-carbon polymer, preferably in solution in a solvent therefor, such as a fluorinated organic solvent. ~he invention also embraces electric lamps containing fluorocarbon polymers as a source of fluorine for the gas fill.
~he preferred fluorocarbon product is a soluble degradation product of polytetrafluoroethylene (PTF~), sold for use as a lubricant under the ~rade Mark ERY~OX (Du Pont).
~his substance is preferably dissolved in trichlorotri-fluoroethane (C2F Cl ) and the solution can be dispensed into

3 3 United States the lamp envelopes by the technique described in~Patent No 3898500.
The application of the invention enables considerable improvements in control of fluorine dosage to be achieved.
For example, by using a gaseous fluoride, such as S~6, WF6 or NF3, variations of - 50 % in the fluorine dose can occur, whîch is quite unacceptable for other than laboratory experiments. In contrast, similar lamps dosed with a solution of fluorocarbon polymer have exhibited a fluorine dose controllable to better tha~ - 5 %.
~he lamp envelope, which may be of a high-silica . :::;, .

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.. : .. :, . ... . ,, ~ -content glass, for example fused silica or the 96% silica glass sold under the Trade Mark VYCOR (Corning), is prefer-ahly 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 our Canadian Patent No. 986,980 issued April 6, 1976.
An example of this invention will now be described with reference to the accompanying drawing, the single figure of which shows a tungsten/fluorine lamp structure:
A 12V lOOW lamp, of the type commonly used in film projectors, comprises a "Vycor" envelope l, in which is sealed a tungsten filament 2 supported on filament tails or lead-in wires 3 and is provided with an exhaust tube 4. The lamp is provided with a fluorine-resistant aluminium phosphate, aluminium titanium phosphate or alumina layer (not shown) covering the inside surface of the envelope l, the filament 2 and tails 3, as mentioned above. Th~ lamp is then dosed with 35 ~g of the fluorocarbon polymer, as a 0.5 g/l solution in C2F3C13, the solvent subsequently removed, as described in our United States Patent No. 3,898,500 and the lamp gas-filled ; in the normal manner with 3~ atm. of argon, at room temperature.

;

_4_ ~ amps of this t~ps have been run at 13~8 V, ~hich 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 14.5 V. Such lamps have achieved lives of 40 hours, without detectable thinning of the hottest spot at the centre of the fila~eLt, subsequent failure occurring b~ tungsten loss in the colder regions of the filament or tails. In comparison, similar lamps cont~ining Br2 instead of F2 fuse at the centre of the filament after 20 hours operation at 13.8 V.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In an electric lamp having an envelope, and a gas fill including fluorine in said envelope, the improve-ment which comprises:
A fluorocarbon polymer included within said envelope as a source of said fluorine.

2. An electric lamp according to claim 1 wherein the fluorocarbon polymer is a degradation product of PTFE.

3. An electric lamp according to claim 1 wherein said envelope has an internal surface coated with a protective glassy coating selected from metal phosphates and alumina.

4. In the manufacture of an electric lamp having an envelope, and a gas fill including fluorine in said envelope, the improvement which comprises:
dissolving a fluorocarbon polymer in a solvent therefor;
and metering a controlled quantity of said solution into said envelope to provide a source of said fluorine.

5. Manufacture according to claim 4 wherein said fluorocarbon polymer is dissolved in a fluorinated organic solvent.

6. Manufacture according to claim 4 wherein said solution is prepared by dissolving a soluble degradation product of PTFE in a fluorine substituted hydrocarbon or halocarbon solvent.