CA1243723A - Electric lamp including a containment coating as part thereof - Google Patents

Abstract

ELECTRIC LAMP INCLUDING AN CONTAINMENT COATING
AS PART THEREOF

ABSTRACT
An electric lamp having an envelope, a light-source capsule mounted within the envelope and a containment coating. The containment coating, which is disposed substantially over the outer envelope, has the capability of preserving the integrity if the envelope from piercing, due to shard dispersion from the light-source capsule, in the unlikely event that the capsule should fracture. One example of the coating consists of a fluoropolymer material such as a perfuoroalkoxy resin (P.F.A.
Teflon). the containment coating is resistant to, and exhibits a high degree of tensile strength at, high temperatures and is substantially unaffected by ultraviolet radiation.

Description

37~3 D-2~,~4~

.LECTRIC LAMP INCI.UDIN& A CONTAINME~T COATING
AS PART TH~REOF

CROSS REF~RENCE TO A CO-P~NDI~G APPLICATION

In a co-pending Appllcation, having Canadian Serial No.
448,137-2 ("Electric Lamp With High Ou~er Envelope To Inner Envelope Wall Thickness Ratio,~' Peter R. Gagnon), there is defined a lamp having a relatively high outer-envelope to inner-envelope wall-thickness ratio for the purpose of substantially eliminating con~ainment failure of the lamp.

TECHNIC~L FIELD

This invention relates to electric lamps and more particularly to such lamps employing light-source capsules 15 which operate at pressures other than atmospheric. Still more particularly, this invention relates to such lamps having containment means to substantiallly ellminate the risk of a containment failure of the lamp.

BACKGROUND

The lighting industry is searching for a replacement for the Edison-type incandescent lamp which is currently the most popular type of lamp sold in the consumer market in the United States. Tungsten-halogen and arc discharge lamps, because of their superior performance characteristics, are being carefully considered by various lamp manufacturers as a replacement for the standard incandescent lamp. ~Iowever, the remote possibility of a minor dispersion of glass shards resulting ~,.

2~
D-24,44~

from a fracture of the pressurized light ~ource ~ap~ule contained within the la~p i6 a ~ub6tantial impedime~t in he path of developing a feasible replace~ant in the consumer market~ Althou~h occurrence of ~uch a fracture i~ ra~e, neverthele66 ie could present a ~afety hazard to a person or object in the immediate vicinity of the lamp (i.e., food preparation). A tung~ten-~alogen lamp or an arc diccharge lamp whic~ substantially eliminate~ the problem of shard disper6ion upon the fracture o~ the light source capsule would constitute an advancement in the art.
Method~ have been sugge~ted to improYe the ability of tungsten-halogen and arc di~charge lamp~ to with~tand a fracture of the inner light-source capsule. In one example the shard~ are re~tricted from impacting with the outer envelope through the use of a cylindrical body di~po6ed about the arc tube, U.S. Patent No. 4,281,274, i6sued July Z8, 1981 to Bechard et al. In addition, the practice of applying a coating on the outside surface of a lamp envelope to hold the glas6 piece~ together upon envelope breakage, due to an impact by an exte~nal force, i~ al60 know~ in the art. For example, Audesse et al., in United Statss Patent No. 3,715,23~, i6~ued February 6, 1973, di6clo~e~ the process of coating a lamp with a 6ilicone rubber film for the above ~entioned purpose.
It i8 believed, therefore, that an electric lamp which overcome~ the ~everal di6advantages a~sociated with the prior art devi~es mentioned above would constitute a ~ignificant advancement in the art.

DISCLOSURE OF THE INVENTION

It i~, therefore, a primary object of thi6 invention to overcome the di~advantaqe~ of the prior art device~ 6uch a~
mentioned above.

D-24,444 It is anot~er object of thi~ inventio~ to provide a mean~
of co~ainment for electric lamp6 whicll will ~ub~tantially eli~inate t~e po~ibility sf a ~inor ~hard di6peEsion upon fracture of a pre6~urized light ~ource ~apsule.
A urther ob~e~t of thi6 in~ention i6 to provide ~eans for containment which doe~ not detract from the ae~thetic appearance of lamps.
Another object of thi6 invention i~3 to provide mean6 for containment which will cau~e little or no 1Q6~ of luminous efficacy in lamp~ employing ~uch mean6.
Still another object of t~i6 invention i~ to overcome a 6ub~tantial impediment in the path o developing a replacement for the ~tandard incandescent lamp in the con6umer ~arket.
In accordance with one a6pect of the present invention, there i~ provided an electric lamp including a light-transmitting envelope, a pres6urized light-60urce cap6ule mounted within the envelope and containment mean6 for containing within the lamp fragment6 of glas~ re6ulting from fracture of the cap~ule. The containment means is disposed substantially over the envelope and i6 of a sub6tantially light tran~missive material. The containment mean6 has a high degree of tensile ~trength at continuous service temperatures that are 6ubstantially egual to or higher than 190 Cel~iu~.

BRIEF DESCRIPTION OF THE DRA~ING

FIG. 1 is an elevational cro66-sectional view of an embodiment of the lamp made in accordance with the teaching~ of the present invention;

D-24,444 PIG. 2 illu~trates an enlarged cro~s-~ectional vi~w o~ a portion of the la~p with a fluoropolymer contain~ent coating:
and FI~. 3 illu~trate6 an enlarged cros6-~eetion~l view of a por~ion of the lamp with a 6ilicone rubber containment coating.

. BEST MOD~ ~OR CAR~YIN~ OUT THE INVENTION

For a better understanding of the present invention, together with other and further object~, advantages, and capabilitie~ thereof, reference is made to the following di~clo6ure and appended claims taken in conjunction ~ith the above-de~cribed drawings.
As used herein, the term "light-~ource capsule" denote6: a tung~ten-halogen incandescent capsule, an arc tube of an arc discharge lamp, or any light-emitting capsule within the outer envelope of a lamp wherein the light-~ource cap~ule operate~ at a pre~sure other than atmo6pheric and the possibility of minor shard disper6ion upon fracture of the light 60urce capsule exi~ts. The light-60urce cap6ule may be either a eingle-ended or double-ended cap~ule.
The terms "contain" or "containment" as used herein mean that the containment mean~ of the lamp, ~ade in accordance with the teaching6 of the pre6ent invention, is not pierced as a result of a fracture of the inner light-~ource cap6ule. Shard~
of ~he light-source cap6ule remain within the lamp and the containment mean~ ~erves to prevent 6hard di6persion.
Referring now to ~he drawings with greater particularity, FIG. l show6 an electric lamp lO made in accordance with the ~eaching6 of the present i~vention. ~lectric lamp lO includes a light-transmissive outer envelope l2, containment ~ean~ 13 dispo~ed substantially over envelope 12 and a ba~e 14.

3'~3 D-24.qq4 _5_ Rnvelope 12, which ~a~ be for~ed of ~oda lime gla~s, has ~ body 15 and a neck 16. Lamp 10 further include6 a light-~our~e capsule 18 ~ounted ~ithin envelope 12 on a fra~e a66e~bly 24.
Light-~ource capsule 1~ which may be for~e2 of quartz or hard gla6~, ~as an en~elope 20 and a pre~6 ~eal end 22. Envelope 12 ha~ neck 16 runninq from ring 28 o brim 30. In addi~ion, containment mean~ 13 should overlap or be attached to a por~ion of base 14 to counteract the effects of ~ravity, by ~ervi~g as a pouch or ~ack, in the event that envelope 12 break6.
In one embodiment of electric lamp 10, body 15 of envelope lZ has a minimum wall thickne66, x. Envelope 20 ~a~ a maximum wall thickne~s, y, of le66 than about 0.9 millimeter. In lamp 10, the ratio of x/y, whi~h hereinafter will be referred ~o as the "~all-thickne66 ratio," is approximately equal to or greater than 3. ~hen 6uch a relation6hip exi~t6, cap~ule 18 will be de~cribed herein a~ being "thin-walled" 'with re6pect to envelope 12, and conver6ely envelope 12 will be de~crihed as being "thick~walled" with re~pect to cap6ule 18. The prescribed range of the wall-thickness ratio in6ure6 that these comparative measure~ of "thick" and "thin" will be true by a factor of approximately 3 or greater.
T~e importance of the pre6cribed range of the wall-thick~e66 ratio i6 a6 follow6. When a thin-walled capsule frac~ures into ~hard6, each shard i~ relatively thin and 25 pos6e~ses les6 ~a~6 than would be the ca6e if the cap6ule were not thin-walled. When thefie low-mass 6hards i~pact with the out~r envelope, the impact energy per colli6ion i6 reduced because energy i~ proportional to mas6. The thinner shard~
tend to ~hatter them6elve6 thereby dis~ipating colli~ion energy harmle~61y. There i6 evidence from observations that thin-walled capsules fracture into grea~er numbers of ~maller ~hards than do cap6ules with greater wall thickne66e6 under 6imilar operating conditions. The grea~er the number of 6hard~

~ ~37~3 D-24,44q impa~ting with the outer envelope, the more the to~al energy of the fracture will be 6pread uniformly oYer t~e outer envelope.
The ultimate result of these factors i~ that the out~r envelope ha6 the ability to contain a~ inner cap~ule fracture when She wall-thickne~s ratio i6 wit~in tbe pre6cribed range.
Con~ainment mean6 13 will preserve the integrity of the outer envelope of the la~p where the wall thicknes~ ratio is ~ot wi~hin the pre~cribed range.
In an alternative embodiment of the electric lamp, outer envelope 12 has a concave top 26 opposed to neck 16. the word "concave'~ means t~a~ the radiu6 or radii of curvature of top 26 fall~ on the exterior of envelope 12. The concave ~shape of top 26 diverts shards and energy of a fracture of eapsule 18 ~o~ard ba~e 28 where they are least likely to cause damage; in 80 doing, top 26 shatter6 many shard6 which further dissipate~
fracture energy. Top 26 also reinforces the portion of envelope 12 that lies above cap~ule 18. This re.gion of envelope 12 may require rein~orcement for two reasons. First, top 26 may be the portion of envelope 12 closest to capsule 18. Second, there is the po~sibility that capsule 18 may fracture such that the upper portion of capsule 18, i.e., the portion of capsule 18 closer to top 26, may be propelled again~t top 26. Thi~ type of ~racture may occur if envelope 20 of capsule 18 i8 fractured near pre~s seal 22. If ~uch a fracture should occur, the high pre66ure withi~ cap6ule 18 may propel the portion of capsule 18 above pres6 ~eal 2Z toward top 26. It is believed that the region of capsule 18 where envelope 20 joins pre6s seal 22 may be particularly susceptible to thermally induced fracture~ because of the ~ub~tantial temperature gradient in this region cau~ed by the high operating temperature of envelope 20 and the relatively cool operating temperature o pre~s fieal 22.

~37;~3 D-24,444 _7_ In another embodiment of the electric lamp, minimum wall thickness, z, of neck 16 is approximately equal ~o or greater than 2.5 millimeters. The extra thickness of neck 16 facililates the mounting of frame-assembly 24 on neck 16 by means of elastic and frictional forces. For a de~ailed explanation of the means for mounting frame-assembly 24 with capsule 18 thereon within envelope 12, reference is made to co-pending Canadian Patent Application having Serial No. 44~,138 1, filed 10 Pebruary 23, 198~ and assigned to ~he present assignee.
I.ight source capsule 18 oper~tes with fill pressures other than atmospheric, typically about 5 to about ZO
atmospheres. At such pressures, and where the wall thickness ratio i6 less than 3 ~i.e., the outer envelope has a wall thickness similar to a standard incandescent bulb)~ a fracture of capsule 18 would result in a dispersion of shards from the capsule that would pierce t~le outer envelope where containment means 13 was absent from tbe exterior of the electric lamp:.
Containment means 13 (see FIG. 1) includes a coating, that is disposed over envelope 12 of lamp lO, for containing fragmen~s resulting from fracture of capsule 18.
Containment coating 13 should be relatively transparent so as to allow a substant;al amount of light to pass through it. In addition, coating 13 should be resistant to degradation by high temperature and ultraviolet radiation.
According to the present invention, the containment coating material is preferably either a fluoropolymer or a sillcone rubber base material. Coating 13 can be applied to an outer envelope of any wall thickness in order to provide containment capabilities. The coating material~ used here also exhibit a high degree of tensile strength at high te~peratures.
"~
, ~

7;~3 D-24,444 Referr~ns now to ~IG. 2, one embodiment of the fluoropolymer containment coatin~ of the present ~nventlon i~
illuxtrated a6 coati~ 13A ove~ a portion of envel4pe 12. In one 6pecif~c u~e, ~oating 13A consi6ted of a ~erPluoroalkoxy re6in i.e., P.F.A. Teflon material ~"Teflonl' being a trademark of E.I. du Pont ds Nemour~ Co.). The visible ligh~
~ransmiæ~ion of thi~ coating was fou~d to be about 99~ of that of a ~lear outer envelope without such a coating. The perfluoroalkoxy resin material has a continuous ~ervi~e temperature rating of about Z63 Celsiu~, and i~ es~entially unaffected by ultraYiolet radiation. Other fluoropoly~er materialfi such as fluorinated ethylene-propylene copolymer (i.e., F.E.P. re6in~ and polychlorotrifluoroethylene (i.e., P.C.~.F.E. resin) al~o ~a~e similar containment capabilitie~
and are unaffe~ted by ultraviolet radiation, but do vaLy in 6ervice temperature rating. These ma~erial6 have a 6ervice temperature of about 190~ Celsius.
In an alternative embodiment of the fluoropolymer containment coating, the fluoropolymer coating could be applied in cnmbination with a reinforcing material to provide either improved protection or to minimize the quanti~y of coating material required. One example of such a reinforcing ~aterial consist6 of using short gla~s fiber~ ~le~ than 0.30 inch in length) mixed in suspen~ion within the fluoropolymer material.
Thi~ combination al~o has the advantage of providing inherent diffusion of the light emitted from lamp 10 where de~ired, due to t~e glas~ fibers. The thickness of ~he aforementioned fluoropolymer coating~ are normally in the range of abou~ 0.001 to 0.006 inch.
The fluoropolymer coatings of the pre6ent invention also provide lamp 10 with means for refiisting thermal shock induced fracture, a~ mig~t be caused by water droplet~ falling on t~e 3~7;~3 D-24,444 _9,_ lamp while it i~ in operation. In additio~, the coating a~ds i~ ~aking a "tamper-re6i6tant" lamp ~y reinforcing ~he outer envelope to preven~ breakage from rou~h handling or from a minor i~pact by an~external force while the la~p is i~
opera~ion. ~anufacturing ~tep~ in making ~he lamp ca~ be reduced by formulating a ~oating that can either diffu~e he light e~itted from tbe lamp (a6 in frof;ted o~ ~mo~ w~ite lamp6~ or be colored for decorative la~p purpo~e~. ~he fluoropolymer coating~ m2ntioned above can be applied by conventional technique~ 6uch as electrostatic powder coati~g, fluidized bed coating or wet 6pray coating.
Referring now to FIG. 3, one embodiment of the ~ilicone rubber containment coating of the pre~ent invention i~
illu6trated a~ coating 13B o~er a portion of outer envelope 12. The 6ilicone rubber containment coating 13B comprises coa~ing envelope 12 of lamp 10 with more ~han one layer of mate~ial. Two or more layer6 of material with differing moduli of elasticity are applied on envelope 12 of la~p 10. The combination of layer~ 13c and 13d, made of material6 having high ~13c) and low (13d) moduli of ela~ticity, provide~ a high de~ree of containment for lamp 10 due to the re6i6tance of the multi-layer system to tear propagation. Each layer of tranfiparent 6ilicone rubber i8 for~ula~ed to have a different modulu~ of elasticity. Each layer i6 applied by the proce~s of dip coating. The thickne66 of each layer i~ in the range of about 0.001 to 0.003 inch. The overall ~hickness of the ~ilicone rubber coating i~ in ~he range of a~out 0.002 to 0.006 inch. The 6ilicone rubber containment coating 13B will al~o provide containment capabilitie~ for a lamp having the wall thickness of a standard incande~cent light bulb.

7;~3 20040 ~~-E~ .
~ oraa~ce ~i h o~e e~bo~ent o~ ~e ~ra6~t ~en~ionO
the e~terior of ~n A 19 bulbo ~onta~ni~q ~ T-4 ~ze tun~sten-~alo~en cap~le, ~ade o alumino611i~ate or hara gla~
~a~erial, ~t about 10 atmo~phere~ ~reæ~urer wa~ ~oat~d wi~h a 0.005 i~h ~ k coa~ing of per~luoroal~oxy resi~. S~e ~oat~ng reliably contained ~e glass ~raymen~6 of ~e purpo~ely fr~c~ured T-4 ~ize haloqen capsule. Vi~ible liqht tran~mis~ion of thi~ coating wa~ ~ou~d to be abou~ 99~ of tha~ of a lamp with a ~lear envelope or bul~. Th~ perfluoroalkoxy resin had a continuou6 6er~ice temperature rating of about 260~ Cel6iu~.
I~ accordance with another e~bodiment of the pre~ent invention, an outer envelope of the lamp wa~ ~ormed from 6oda-lime gla66 with a concave top. The envelope had a minimum wall t~ickne6~ of about 1.9 ~ imeterB. The T-~l 6ize tung6ten-halogen cap6ule ~ithin the lamp, which was ~ade of alumi~o6ilicate gla6~, was at 10 atmo6phere6 pres6ure and had a volume of about two cubic centimeter~. The perfluroalkoxy resin coating on the outer envelope was about O.OOl inc~ in t~ic~nes6. The coating here reliably ~ontained the glax~
ragment~ of the purpo~ely ~ractured halogen cap~ule.
In accordance with 6till anot~er embodi~ent of the pre~ent invention, an A-l9 bulb containing a T-4 ~ize tung6ten-halogen capsule at about lO atmo6phere~ pre6~ure wa6 coa~ed ~it~ an overall 0.006 i~ch thic~ layer of 6ilicone rubber mate~ial.
The ~oating was compri6ed of two layer6 of ~ilicone rubber ~aterialO each layer having a difering moduli of ela~ticity.
One layer ~ad a high modulus of ela~ticity and ~he other had a low ~odulu~ cf ela~icity. The layer6 ~ere applied by the proce~6 of dip ~oati~g. ~e coa~i~g here reliably co~tained t~e glas6 fragment6 of the purposely fractured halogen capsule.

~437Z3 D-24,4~4 --11~
Thu~, there ha been shown and de~cribe~ an improved cont2inment ~eans for containi~g frag~ents of gl~66 within a lamp re6ul~ing from t~ fra~ture cf a light ~ource capsule within the lamp. The contain~ent means consi6t~ of a coating of eit~er a fluoropolymer material or ~ 6ilicone rubber material that i~ difipv6ed over the outer envelope of the lamp and is of a 6ubstantially light-tran~mi~sive material. The coating~ al~o exhibit a hig~ degree of tensile strength at high temperature~. The coating ~hould be re~istant ~o hi~h temperature~ (about 190 Cel6ius or higher) and be unaffected by ultraviolet radia~ion.
~ hile there have been shown what are at present con6idered to be the preferred embodiments of the invention, it ~ill be appa~ent to those skilled in the art that variou6 change~ and modification~ can be made herein without departi.ng from the scope of the invention as defined in the appended claims.

Claims (6)

1. WHAT IS CLAIMED IS:
   
   --1. An electric lamp comprising:
   (a) a light-transmissive outer envelope;
   (b) a pressurized light-source capsule mounted within said outer envelope;
   (c) a light-transmissive coating adhering to the outside surface of said outer envelope, said coating including perfluoroalkoxy resin; and (d) means for structurally and electrically completing said lamp.
2. 2. A lamp as described in Claim 1 wherein said light-source capsule is a tungsten-halogen light-source capsule.
3. 3. A lamp as described in Claim 1 wherein said light-source capsule is an arc tube of an arc discharge lamp.
4. 4. An electric lamp comprising:
   (a) a light-transmissive outer envelope;
   (b) a pressurized light-source capsule mounted within said outer envelope;
   (c) a light-transmissive coating adhering to the outside surface of said outer envelope, said coating including a fluoropolymer material selected from the group consisting of fluorinated ethylene-propylene copolymer resin and polychlorotrifluoroethylene resin; and (d) means for structurally and electrically completing said lamp.
5. 5. A lamp as described in Claim 4 wherein said light-source capsule is a tungsten-halogen light-source capsule.
6. 6. A lamp as described in Claim 4 wherein said light-source capsule is an arc tube of an arc discharge lamp.--