CA1045908A - Low temperature process for coating lamp envelopes - Google Patents
Low temperature process for coating lamp envelopesInfo
- Publication number
- CA1045908A CA1045908A CA227,911A CA227911A CA1045908A CA 1045908 A CA1045908 A CA 1045908A CA 227911 A CA227911 A CA 227911A CA 1045908 A CA1045908 A CA 1045908A
- Authority
- CA
- Canada
- Prior art keywords
- lehring
- polyethylene oxide
- alumina
- coating
- particles
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J61/00—Gas-discharge or vapour-discharge lamps
- H01J61/02—Details
- H01J61/38—Devices for influencing the colour or wavelength of the light
- H01J61/42—Devices for influencing the colour or wavelength of the light by transforming the wavelength of the light by luminescence
- H01J61/46—Devices characterised by the binder or other non-luminescent constituent of the luminescent material, e.g. for obtaining desired pouring or drying properties
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
- C09K11/02—Use of particular materials as binders, particle coatings or suspension media therefor
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Organic Chemistry (AREA)
- Luminescent Compositions (AREA)
- Formation Of Various Coating Films On Cathode Ray Tubes And Lamps (AREA)
- Paints Or Removers (AREA)
- Vessels And Coating Films For Discharge Lamps (AREA)
- Paper (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A phosphor coating process which provides for lower temperature lehring (less than about 550°C) using a polyethylene oxide binder in combination with a relatively large amount (greater than about 1% of the phosphor weight) of finely-divided alumina as an adhesion promoter, The method provides about 30% savings of fuel for the lehring.
The method can also be used to provide other coatings (such as pigments) and can be used to apply particles of which would be subject to oxidation and air at lehring tempera-tures, as the polyethylene oxide can be lehred away in a non-oxidized atmosphere.
A phosphor coating process which provides for lower temperature lehring (less than about 550°C) using a polyethylene oxide binder in combination with a relatively large amount (greater than about 1% of the phosphor weight) of finely-divided alumina as an adhesion promoter, The method provides about 30% savings of fuel for the lehring.
The method can also be used to provide other coatings (such as pigments) and can be used to apply particles of which would be subject to oxidation and air at lehring tempera-tures, as the polyethylene oxide can be lehred away in a non-oxidized atmosphere.
Description
BACKGROUND OF q~E INvEN~rIoM
This invention relates to methods for co~ti~g particles such a~ phosphors or pigment~ onto dlscharge lamp envelopes, Discharge lamp envelopes are usually coated by suspending a finely dl~ided materlal (such as a phosphor) in a liquid vehicle. The liquid ~ehicle has dissolved ~her~in an organlc binder which lmparts the proper vi~co~ity and suspending propertles to the vehicle~ mis uspension ~or so called "paint") is ~lowed o~er the lnter~or sur~ce o~ the envelope, the excegS drained, the liquid vahlcle volatilized, and the coated tube heated ~lehred) to drive of~ the binder m~terlal. Tupically the lehring is ~n an oxidizing atmosphere and the blnder material is removed by oxidl2ationO While organic solvents were widely used at one time, water vehicle systems ar~ now generally used as ~q~
. .
~ " . , . . , ~ . , . ~ , . . . .
- ., ~ ., ~ . . .. . :.
.~ . i ., . i ::
~V~ 0~
such water system~ are cheaper and sa~er. A variety o~
Na~er soluble binders have b~en used~ including methyl cellulo~e, polyacrylic acid, and ~ome hydroxy alkyl ce~lu-loses. The most widely u~ed system i~ probably hydroxy ethyl cellulose~
Hydroxyethy~ cel~ulos~ ~S typic~lly lehred at abouk 650C for approxlmately 60 seconds ~the a~orem~nttoned water soluble binderQ are all generally lehred under approxlmat~ly ~.
these same conditions). A~ these blnders are removed by pyrolysis and oxidationJ the 65~ C lehr temperature 1~
needed to reduce the res~dual carbonaceous "char" to the levsl o~ a ~ew parts per million (~allure to reduce the char to these levels results in brightne~s and lumen 108s ~n the completed lamp). me requirement for high lehring tempera-tures does present prob~ems9 howe~er, as lt dlscolors some ;:
plgments (~uch as caleium sul~ide/selenide) and requires large amounts o~ ~uel to h~at the lehring ~urnace. ~:
Prior art ¢oatings syatems hàve used ~lnely `:~ :
dl~ided particles such a~ alumina or ailica as adhesion pro~
20 moterQ. Such adhesion promoters are typlcally used in .
amounts o~ up to abouk 1/2 Or 1% o~ the phosphor welght :~
(it had generally been found that a greater amount pro~
vided no further improvement in adhaslon and reduced lamp efficiency), In U~S. Patent ~,42~,60~ issued to E~.~umont et al on ~anuary 20, 1969 is noted the addition of *inely divlded silica to promote adhasion, ~ith the comment that it can be deleterious to lamp e~fieiency.
The a~oramentionsd E~aumont patent also notes th~use o~ polyethylene oxide (sold under the ~r~demar~-."Polyox"
~0 ~y Union Carbide3 as a binder ~or l~mp coatingO Be~umont. ~.
note s
This invention relates to methods for co~ti~g particles such a~ phosphors or pigment~ onto dlscharge lamp envelopes, Discharge lamp envelopes are usually coated by suspending a finely dl~ided materlal (such as a phosphor) in a liquid vehicle. The liquid ~ehicle has dissolved ~her~in an organlc binder which lmparts the proper vi~co~ity and suspending propertles to the vehicle~ mis uspension ~or so called "paint") is ~lowed o~er the lnter~or sur~ce o~ the envelope, the excegS drained, the liquid vahlcle volatilized, and the coated tube heated ~lehred) to drive of~ the binder m~terlal. Tupically the lehring is ~n an oxidizing atmosphere and the blnder material is removed by oxidl2ationO While organic solvents were widely used at one time, water vehicle systems ar~ now generally used as ~q~
. .
~ " . , . . , ~ . , . ~ , . . . .
- ., ~ ., ~ . . .. . :.
.~ . i ., . i ::
~V~ 0~
such water system~ are cheaper and sa~er. A variety o~
Na~er soluble binders have b~en used~ including methyl cellulo~e, polyacrylic acid, and ~ome hydroxy alkyl ce~lu-loses. The most widely u~ed system i~ probably hydroxy ethyl cellulose~
Hydroxyethy~ cel~ulos~ ~S typic~lly lehred at abouk 650C for approxlmately 60 seconds ~the a~orem~nttoned water soluble binderQ are all generally lehred under approxlmat~ly ~.
these same conditions). A~ these blnders are removed by pyrolysis and oxidationJ the 65~ C lehr temperature 1~
needed to reduce the res~dual carbonaceous "char" to the levsl o~ a ~ew parts per million (~allure to reduce the char to these levels results in brightne~s and lumen 108s ~n the completed lamp). me requirement for high lehring tempera-tures does present prob~ems9 howe~er, as lt dlscolors some ;:
plgments (~uch as caleium sul~ide/selenide) and requires large amounts o~ ~uel to h~at the lehring ~urnace. ~:
Prior art ¢oatings syatems hàve used ~lnely `:~ :
dl~ided particles such a~ alumina or ailica as adhesion pro~
20 moterQ. Such adhesion promoters are typlcally used in .
amounts o~ up to abouk 1/2 Or 1% o~ the phosphor welght :~
(it had generally been found that a greater amount pro~
vided no further improvement in adhaslon and reduced lamp efficiency), In U~S. Patent ~,42~,60~ issued to E~.~umont et al on ~anuary 20, 1969 is noted the addition of *inely divlded silica to promote adhasion, ~ith the comment that it can be deleterious to lamp e~fieiency.
The a~oramentionsd E~aumont patent also notes th~use o~ polyethylene oxide (sold under the ~r~demar~-."Polyox"
~0 ~y Union Carbide3 as a binder ~or l~mp coatingO Be~umont. ~.
note s
-2-^, - - , , . - ................. - . - . ., :
, . , . , .~ : ,. . .... . . .
1~)45~
the adhe3ion problem with poly~thylene oxlde and adds Ba(NO~)2 ~eaumont lehrs out his temporary binder at about 600-6~5C and then rai~es the temperature to ~bout 670-810C to melt the Ba(N03)2 to obtain adequate adhesion.
SUMMARY OF I~IE INVENTION
The instant inv~ntion provides a method o~ coating of dlscharge lamp snvelopes with ~pectrum modi~ying particles (such a~ one or more pho~phors and/or pigments) and use~ an aqueous solution of polyethylene oxide in combination with a relatively large amount o~ adhesion-promoting, fin01y-d1vided alumina. The method comprlses preparing a coatlng composition compri~ing ~he spectrum mod~fying particles, the alumina par~
ticles, and an aqueous solutlon o~ polye~hylene oxideJ said solution having the viscosity o~ about 20-200 centipolses and said alumina partlcles being present in an amount such that the welght ratio o~ alumina particles to spectrum modi-~ying particle~ i8 about 0.01-0.049 coating the di~charge envelopes with the coating composltion, and lehring the ;~
coated envelope at a temperature o~ ~bout 400-550C. This method provides signi~icant savings in fuel for the lehrlng ~urnaces, the possibility of coating materials which are unstable at higher lehring terqperatures, and the possibility o~ coating particle~ which are sub~ect to oxidation in air `:~
at lehring temperatures (as the lehring can be per~ormed in a non-oxidizing atmQsphere), SCRIPTION OF THE P ~ RRED EMBODIMENT
~ It has been disco~ered that satisfactory adhesion can be obtalned u8ing a polyethylene oxide binder only if a relatively large amount o~ ~ery fine aluminum oxide (greater than about 1% o~ the phosphor weight) i~ included i~ the
, . , . , .~ : ,. . .... . . .
1~)45~
the adhe3ion problem with poly~thylene oxlde and adds Ba(NO~)2 ~eaumont lehrs out his temporary binder at about 600-6~5C and then rai~es the temperature to ~bout 670-810C to melt the Ba(N03)2 to obtain adequate adhesion.
SUMMARY OF I~IE INVENTION
The instant inv~ntion provides a method o~ coating of dlscharge lamp snvelopes with ~pectrum modi~ying particles (such a~ one or more pho~phors and/or pigments) and use~ an aqueous solution of polyethylene oxide in combination with a relatively large amount o~ adhesion-promoting, fin01y-d1vided alumina. The method comprlses preparing a coatlng composition compri~ing ~he spectrum mod~fying particles, the alumina par~
ticles, and an aqueous solutlon o~ polye~hylene oxideJ said solution having the viscosity o~ about 20-200 centipolses and said alumina partlcles being present in an amount such that the welght ratio o~ alumina particles to spectrum modi-~ying particle~ i8 about 0.01-0.049 coating the di~charge envelopes with the coating composltion, and lehring the ;~
coated envelope at a temperature o~ ~bout 400-550C. This method provides signi~icant savings in fuel for the lehrlng ~urnaces, the possibility of coating materials which are unstable at higher lehring terqperatures, and the possibility o~ coating particle~ which are sub~ect to oxidation in air `:~
at lehring temperatures (as the lehring can be per~ormed in a non-oxidizing atmQsphere), SCRIPTION OF THE P ~ RRED EMBODIMENT
~ It has been disco~ered that satisfactory adhesion can be obtalned u8ing a polyethylene oxide binder only if a relatively large amount o~ ~ery fine aluminum oxide (greater than about 1% o~ the phosphor weight) i~ included i~ the
-3-. -- -- . . . .
~V~S9~8 coatlng composition. ml8 r~sult 18 supri~lng as~ with prlor binder system8, the u~e of greater than 0.5% o~
umina had apparently nev~r further lmproved adhe~ion, It was further discov~red that lamp using the polyethylene ~ ;
and hlgh alumin~ comblnatlon produced lumen output a~ good i~ not bett~r than lamp~ uQing a hydroxysthyl c~llulose binder containing about 0.5% alumlna. Thls reæult was al80 surprislng as high alumln~ content in prior art lamps had resulted in relati~ely low e~ficiency.
Although the mechanlæm i8 not completely under ~.
stood, it is felt that a unique synerglsm occurs in thi~ ;;
system ~hat allows the usa of relatively large amountQ o~
finely divided alum~na whereas such amounts are deleterious to lamp per~ormance i9 normal binder system. This syner-gism arises because the rapid rate o~ ga~ e~olutlon in the pyrolysis o~ polyethylene oxide causes a ve~y "loose" or non-compact structure. me open nature o~ the powder layer apparently allows much greater amounts o~ alumin~ ko be added without signiflcantly increasing the scattering light ;~ :~
loss that normally prevents such high "load-up" of alumina.
I~ is considered there~ore that the combination of a rapid pyrolysis binder a~ polyethylene oxide represents a unlque situation can pro~itably utillze relatlvely large amount~ of alumina~
Poly~thylene oxide also have the ad~antage (compared :~
to hydrozyethyl cellulose) o~ being re~istant to attack by ~icro organi~ms~ me visco~ity o~ the coating composition ;~
must be accurately ~on~rolled both to maintain tha particles in suspe~6ion and to provide ~or a proper coaking thickneæs on the lamp envelopeO I~, as is comm~n in productlon pro-~04~
cessesJ the binder 30lution 1~ stored ~or ~ome period of tlme, micro-organisms will attack a binder such as hydroxy-ethyl cellulo~e and cause a dramatlc loss of vi~co~i~y (if special precaution~ are not taken). Polyethylen~ ox~de, on the other hand, is micro-blologlcally 3table and thus the diYficulties from possible micro-organism~ attack are avoided.
The most impor~an~ advantage o~ the polyethylene ~;
oxide and high alumlna system is probably the reduction in lehring temperature. Measurements have lndicated that the natural gas fired lehring ~urnaces require 30~ less of natural gas when the temperature is lowered ~rom about 650C
to about 500C. This provides a very significant sa~ings ln fuel cost. The lower temperature also allows usage of a much wider range of phosphors, Copper activated phosphors and sul~ide phosphors have generally been re~ected as unusable because of the 650C lehring, b~t can be used if lehred at about 509C, A wider ran~e o~ pigments can also be used.
The 500C lehring is also convenient ln that it is suf~icient to relieve any residual ~tress ~rom the dra~lng and cutting o~ the lamp envelopesJ but prov1des less stre~s cracking than does 650C lehring. The lower lehring temperature also min-imlzes the reaction of various phosphor~ with sodium in the glass. Zinc sllicate phosphors, ~or example, are sensitive to sodium darkening and are therefore benefited by a lower lehring temperature.
Polyethylene oxide ~s thought to break down to ethylene ox~de gas upon heating to lehring temperatur~. The ethylene oxide gas then e~capes ~rom the coating with minimal char formation, m is is in contrast to the prior art binders S~)8 which ~orm a carbQnaceous char ln the oxidatlon/pyroly~i~
which mu~t then be further oxidlzcd to r~move the res~dual carbon (the lamp output being serious affected if a~y of this re~ldual carbon i8 not removed), me ba~eout of polyethylene oxide does, ho~le~er, result in the rapid gas evolutlon which can have the un~ortun~te consequence o~
disruption of the phosphor layer re~ulting in extremely poor phosphor adherence. A variety o~ adhesion promoters were lnvestigated with varying amount of each and on~.y the relatively large percentage of flnely divlded alumlna pro~
~idad satisfactory adhesion. Among the adheslon promoters ..
which were ~ound unsatis~actory are calc~um carbonate, barium oxide, Ba(N0~)2 (whlch was not raised to its malting tempera~
ture as taught by the a~orementioned U.S, Patent 3,4249605), magnesium oxide, calcium nitrate, magnesium pho~phate, barium tungstate, barium phosphate, (NH4)2HP04 and HB03(B203)- The amount o~ these adhesl.on promoters was generally varied be~
tween 0,5 and 2.0%. The use o~ only about 0.5% 9f f~nely divided formed alumina dld not provide adequate adhesion~
At higher finely divided alumina levels (about 1~ o~ phosphor weight) maJor adhesion improvements occurred. ~t 1.5% the phosphor adhesion was comparable to the present hydroxyethyl cellulose system (wlth its approximately 0.5~ alumlna) and at 2~ alumina wlth polyethylene oxide there was excellent adherenee (better than now obtainable with hydroxyethyl cellulose), Fumed alumina with an approximatel~ 300 Angstrom particle siz~ (sold commercially under the trademark "Alon C"
by Degussa o~ West Germany) has been ~ound to be especially ~:
e~sctive. It should be noted that ~recipitated alumi~a (with : an approxi-:, " : ~
, ~
~045~0~
mately 600 Angstrom particle SiZR ) has b~en ~ound to be slgnificantly less ef~ectlve, Whether the de~ree of ef~sctivenes~ i9 dependent upon particle ~ize or i~ de-pendent upon the method Or preparation i8 not known at this time.
It has also been ~ound that good t~xture 1B best provided by dispersing the alumina ln ~ater be~ore mixing into the paint. It has also been ~ound that better per-formance is provided when the ~lexibilizers normally used in lamp coating (such as triethanolamlne or glycero~) are not used.
Tests have indicated that the ma~or portion of the polyethylene oxide can be removad by lehring ~n air Q~
400C, but that ror rapid and reasonably complete removalJ
the lehring should be per~ormed a~ about 500C, The re-moval o~ polyethylene oxide in an inert atmospher~ such as . .
nitrogen doeæ not occur to an~ signi~icant extend at 400C ~
but is almoæt completely remo~ed at about 450C~ In no .
~a~e is lehring above 550C necessary and, aæ it results in e~tremely rapid gas evolutio~9 lehring at thase higher temperatures is undesirable, .
me weight ratio:o~ alumlna particles to phosphor (or other spe¢trum modified par~cles) ls pre~erably be-tween 0.015 and 0,025, While wieght ratios as low as 0,01 can be used, the adhesion in,this range is some~hat less and some loæs o~ the phosphor coatlng can occur when the completed lamps are handed. Alumina weight o~ 0.025 to 0,04 can also be used, but such loading 1s generally unnec- ~ :
essary ror adpesion purposes, Because polyethylene oxide does require oxidation .:
during lehrlng, it can be lehred in a non-oxldizing atmosphere. This permit~ coating of a number of ~pectrum :
mod$fying par~icles which are sub~ect to oxidizing in airO -With the exception o:~ the flexiblliæer~, the ~ .
commonly u~ed additives such as wetting agents and the foaming agents are comp~tible with the polyethyl~ne oxide system, For example, ~ubble Breaker B8748~ a trademark, ~ ~ -(Balab Inc,~ can be u~ed a~ a defoaming agant and Igepal C0610~ a trademark, (GAF) can be used as the wetting agent~
me ~ollowing are speci~ic examples ~or co~ting envelopes in accordance with the present invention: ;
~XAMPLE I
In order to coat a cool white halophoæphate : ~.
pho~phor~ a ~tock solution of 8.o grams of pol~ethylene oxide is dissol~ed in 1 liter o~ deionized water. The dissolved 801ut~0n iS then passed through a mixed bed ~;
polystyrene ion exchanger sys~em in order to remove the impurities ~rom the solu~ion. About 1.4 gram of ~umed alumlnum oxid~ is dispersed in ~pproxima~el~ 10 CCI9 of dionized ~later and this dls~ersion is added to about lQ0 cc's of the purified polyethylene oxide ~olution~ Approxi-; mately 0,04 grams of wettlng agent and 0~04 grams o~ de-~oaming agent i8 then added and then 70 grams o~ cool white halophosphate phos~hor is stirr6d into the ~oregoing to form the paint. The resulting paint i~ then flowed -over a fluorescent lamp envelope in the usual manner to provide such a thick~ess that about 7 gr~ms of phosphor is deposited ~n a 40W T12 bulb, A~ter coatingJ the en~
velope i~ dried to remove the water and then lehred by ~ ~-heating to a temperature of approxima~ely 500C ~or about ,, -o-1~45911 ~ - :
1 minute ln ord~r to completely volatiliz~ the re~idual polyethylene oxide binder materlal.
In the foregoing pai~t, the amount o~ fum~d alumlnum oxlde can be varled between approximately 007 grams and 2.8 grams~ and is pre~erably between 1JO5-1~75 grams, Th8 wetting agent can be ~dded in amounts up to 1 gram and the defoamer ca~ b~ added in amountB up ~o about 0.5 grams. me amount o* phosphor can also be varied be~
t~rean 10 and 100 grams ~thus providing one method o~ ~ary-ing ~he thickne~s of the phosphor coatlng on the lamp en-velope~. Viscosltles of about 20-200 centipoises are gen~
erally desired for coating paints. A~ known in the art~ ~ -the viscoslty can be ad~usted by varying either the amount or melecular welght of the blnder, EXAMPLE II
In order to coat calcium tungstate phosphor, 1.0 grams of polyethylene oxide is completely dissolved in 100 cc's of deionized water. Approxlmately 1.75 grams of fumed alumlna is dispersed in ~pproximately 5 cc'æ of deioniæed water and added to the polyethylene oxide solu~ion. Approx~- ;
mately 70 grams of finely divided calcium tungstate phosphor is then suspended therein, The coa~n~ composi~ion is then coated on the discharge lamp envelope in the usual manner.
me coa~ed envelope is then lehrad ~or approximately 1 min~
ute and about 450-550C.
EXAMPLE III
In order to coat a pigment onto a ~luorescent lamp envelope, 0.44 gram of polyethylene oxide is dissol~ed in 55 cc's of deionized water. About 0,4 gram~ o~ ~inely divided ;-~
_g_ ~ 59~
alumlna is dispersed ln 44 cc o* deioniz~d water which 1 then rnixed with the polyethylene oxide solution, Approxi~
mately 20 grams of c~dmium sulfide/3elenide pigment and .04 gram of wetting agent are then added, me pigment suspension ls then coated on a discharge lamp en~elope in the normal manner and the coated envelope is ~ehred at a temperature o~ approxlmately 50QCo As illustratsd by the ~oreeoinæ examples, poly- ~.
ethylene oxide binder coatlng ~olutions contalnlng finely :~.
10 divided alumina (ln amount~ o~ greater than about l~ o~ the -pho~phor weight) can be coat~d in the normal manner and lehred at less th~n 550C. The ~low propertie~ o~ thls c~ating composition are as good or bettsr than hydroxy ethyl cellulose tand generally somewhat better than hydroxy propyl methyl cellulose) with the lower molecular weight variet~es of polyethylene oxide having slightly better flow ::~
properties than the somewh~t higher molecular weight poly-ethylene oxide paints, The vl~osity o~ the coated com~
position can be adjusted by the one skilled in the art ~:.
in the normal manner, with the lower molecular welght polyethylene oxide requiring the slightly higher number o~ grams per liter o~ water to provide a desired viscosity.
It has been found that molecular welght~ in the range o~ :
abou~ 300~000 to 400~000 provide v2ry good per~ormance.
--10-- ~,
~V~S9~8 coatlng composition. ml8 r~sult 18 supri~lng as~ with prlor binder system8, the u~e of greater than 0.5% o~
umina had apparently nev~r further lmproved adhe~ion, It was further discov~red that lamp using the polyethylene ~ ;
and hlgh alumin~ comblnatlon produced lumen output a~ good i~ not bett~r than lamp~ uQing a hydroxysthyl c~llulose binder containing about 0.5% alumlna. Thls reæult was al80 surprislng as high alumln~ content in prior art lamps had resulted in relati~ely low e~ficiency.
Although the mechanlæm i8 not completely under ~.
stood, it is felt that a unique synerglsm occurs in thi~ ;;
system ~hat allows the usa of relatively large amountQ o~
finely divided alum~na whereas such amounts are deleterious to lamp per~ormance i9 normal binder system. This syner-gism arises because the rapid rate o~ ga~ e~olutlon in the pyrolysis o~ polyethylene oxide causes a ve~y "loose" or non-compact structure. me open nature o~ the powder layer apparently allows much greater amounts o~ alumin~ ko be added without signiflcantly increasing the scattering light ;~ :~
loss that normally prevents such high "load-up" of alumina.
I~ is considered there~ore that the combination of a rapid pyrolysis binder a~ polyethylene oxide represents a unlque situation can pro~itably utillze relatlvely large amount~ of alumina~
Poly~thylene oxide also have the ad~antage (compared :~
to hydrozyethyl cellulose) o~ being re~istant to attack by ~icro organi~ms~ me visco~ity o~ the coating composition ;~
must be accurately ~on~rolled both to maintain tha particles in suspe~6ion and to provide ~or a proper coaking thickneæs on the lamp envelopeO I~, as is comm~n in productlon pro-~04~
cessesJ the binder 30lution 1~ stored ~or ~ome period of tlme, micro-organisms will attack a binder such as hydroxy-ethyl cellulo~e and cause a dramatlc loss of vi~co~i~y (if special precaution~ are not taken). Polyethylen~ ox~de, on the other hand, is micro-blologlcally 3table and thus the diYficulties from possible micro-organism~ attack are avoided.
The most impor~an~ advantage o~ the polyethylene ~;
oxide and high alumlna system is probably the reduction in lehring temperature. Measurements have lndicated that the natural gas fired lehring ~urnaces require 30~ less of natural gas when the temperature is lowered ~rom about 650C
to about 500C. This provides a very significant sa~ings ln fuel cost. The lower temperature also allows usage of a much wider range of phosphors, Copper activated phosphors and sul~ide phosphors have generally been re~ected as unusable because of the 650C lehring, b~t can be used if lehred at about 509C, A wider ran~e o~ pigments can also be used.
The 500C lehring is also convenient ln that it is suf~icient to relieve any residual ~tress ~rom the dra~lng and cutting o~ the lamp envelopesJ but prov1des less stre~s cracking than does 650C lehring. The lower lehring temperature also min-imlzes the reaction of various phosphor~ with sodium in the glass. Zinc sllicate phosphors, ~or example, are sensitive to sodium darkening and are therefore benefited by a lower lehring temperature.
Polyethylene oxide ~s thought to break down to ethylene ox~de gas upon heating to lehring temperatur~. The ethylene oxide gas then e~capes ~rom the coating with minimal char formation, m is is in contrast to the prior art binders S~)8 which ~orm a carbQnaceous char ln the oxidatlon/pyroly~i~
which mu~t then be further oxidlzcd to r~move the res~dual carbon (the lamp output being serious affected if a~y of this re~ldual carbon i8 not removed), me ba~eout of polyethylene oxide does, ho~le~er, result in the rapid gas evolutlon which can have the un~ortun~te consequence o~
disruption of the phosphor layer re~ulting in extremely poor phosphor adherence. A variety o~ adhesion promoters were lnvestigated with varying amount of each and on~.y the relatively large percentage of flnely divlded alumlna pro~
~idad satisfactory adhesion. Among the adheslon promoters ..
which were ~ound unsatis~actory are calc~um carbonate, barium oxide, Ba(N0~)2 (whlch was not raised to its malting tempera~
ture as taught by the a~orementioned U.S, Patent 3,4249605), magnesium oxide, calcium nitrate, magnesium pho~phate, barium tungstate, barium phosphate, (NH4)2HP04 and HB03(B203)- The amount o~ these adhesl.on promoters was generally varied be~
tween 0,5 and 2.0%. The use o~ only about 0.5% 9f f~nely divided formed alumina dld not provide adequate adhesion~
At higher finely divided alumina levels (about 1~ o~ phosphor weight) maJor adhesion improvements occurred. ~t 1.5% the phosphor adhesion was comparable to the present hydroxyethyl cellulose system (wlth its approximately 0.5~ alumlna) and at 2~ alumina wlth polyethylene oxide there was excellent adherenee (better than now obtainable with hydroxyethyl cellulose), Fumed alumina with an approximatel~ 300 Angstrom particle siz~ (sold commercially under the trademark "Alon C"
by Degussa o~ West Germany) has been ~ound to be especially ~:
e~sctive. It should be noted that ~recipitated alumi~a (with : an approxi-:, " : ~
, ~
~045~0~
mately 600 Angstrom particle SiZR ) has b~en ~ound to be slgnificantly less ef~ectlve, Whether the de~ree of ef~sctivenes~ i9 dependent upon particle ~ize or i~ de-pendent upon the method Or preparation i8 not known at this time.
It has also been ~ound that good t~xture 1B best provided by dispersing the alumina ln ~ater be~ore mixing into the paint. It has also been ~ound that better per-formance is provided when the ~lexibilizers normally used in lamp coating (such as triethanolamlne or glycero~) are not used.
Tests have indicated that the ma~or portion of the polyethylene oxide can be removad by lehring ~n air Q~
400C, but that ror rapid and reasonably complete removalJ
the lehring should be per~ormed a~ about 500C, The re-moval o~ polyethylene oxide in an inert atmospher~ such as . .
nitrogen doeæ not occur to an~ signi~icant extend at 400C ~
but is almoæt completely remo~ed at about 450C~ In no .
~a~e is lehring above 550C necessary and, aæ it results in e~tremely rapid gas evolutio~9 lehring at thase higher temperatures is undesirable, .
me weight ratio:o~ alumlna particles to phosphor (or other spe¢trum modified par~cles) ls pre~erably be-tween 0.015 and 0,025, While wieght ratios as low as 0,01 can be used, the adhesion in,this range is some~hat less and some loæs o~ the phosphor coatlng can occur when the completed lamps are handed. Alumina weight o~ 0.025 to 0,04 can also be used, but such loading 1s generally unnec- ~ :
essary ror adpesion purposes, Because polyethylene oxide does require oxidation .:
during lehrlng, it can be lehred in a non-oxldizing atmosphere. This permit~ coating of a number of ~pectrum :
mod$fying par~icles which are sub~ect to oxidizing in airO -With the exception o:~ the flexiblliæer~, the ~ .
commonly u~ed additives such as wetting agents and the foaming agents are comp~tible with the polyethyl~ne oxide system, For example, ~ubble Breaker B8748~ a trademark, ~ ~ -(Balab Inc,~ can be u~ed a~ a defoaming agant and Igepal C0610~ a trademark, (GAF) can be used as the wetting agent~
me ~ollowing are speci~ic examples ~or co~ting envelopes in accordance with the present invention: ;
~XAMPLE I
In order to coat a cool white halophoæphate : ~.
pho~phor~ a ~tock solution of 8.o grams of pol~ethylene oxide is dissol~ed in 1 liter o~ deionized water. The dissolved 801ut~0n iS then passed through a mixed bed ~;
polystyrene ion exchanger sys~em in order to remove the impurities ~rom the solu~ion. About 1.4 gram of ~umed alumlnum oxid~ is dispersed in ~pproxima~el~ 10 CCI9 of dionized ~later and this dls~ersion is added to about lQ0 cc's of the purified polyethylene oxide ~olution~ Approxi-; mately 0,04 grams of wettlng agent and 0~04 grams o~ de-~oaming agent i8 then added and then 70 grams o~ cool white halophosphate phos~hor is stirr6d into the ~oregoing to form the paint. The resulting paint i~ then flowed -over a fluorescent lamp envelope in the usual manner to provide such a thick~ess that about 7 gr~ms of phosphor is deposited ~n a 40W T12 bulb, A~ter coatingJ the en~
velope i~ dried to remove the water and then lehred by ~ ~-heating to a temperature of approxima~ely 500C ~or about ,, -o-1~45911 ~ - :
1 minute ln ord~r to completely volatiliz~ the re~idual polyethylene oxide binder materlal.
In the foregoing pai~t, the amount o~ fum~d alumlnum oxlde can be varled between approximately 007 grams and 2.8 grams~ and is pre~erably between 1JO5-1~75 grams, Th8 wetting agent can be ~dded in amounts up to 1 gram and the defoamer ca~ b~ added in amountB up ~o about 0.5 grams. me amount o* phosphor can also be varied be~
t~rean 10 and 100 grams ~thus providing one method o~ ~ary-ing ~he thickne~s of the phosphor coatlng on the lamp en-velope~. Viscosltles of about 20-200 centipoises are gen~
erally desired for coating paints. A~ known in the art~ ~ -the viscoslty can be ad~usted by varying either the amount or melecular welght of the blnder, EXAMPLE II
In order to coat calcium tungstate phosphor, 1.0 grams of polyethylene oxide is completely dissolved in 100 cc's of deionized water. Approxlmately 1.75 grams of fumed alumlna is dispersed in ~pproximately 5 cc'æ of deioniæed water and added to the polyethylene oxide solu~ion. Approx~- ;
mately 70 grams of finely divided calcium tungstate phosphor is then suspended therein, The coa~n~ composi~ion is then coated on the discharge lamp envelope in the usual manner.
me coa~ed envelope is then lehrad ~or approximately 1 min~
ute and about 450-550C.
EXAMPLE III
In order to coat a pigment onto a ~luorescent lamp envelope, 0.44 gram of polyethylene oxide is dissol~ed in 55 cc's of deionized water. About 0,4 gram~ o~ ~inely divided ;-~
_g_ ~ 59~
alumlna is dispersed ln 44 cc o* deioniz~d water which 1 then rnixed with the polyethylene oxide solution, Approxi~
mately 20 grams of c~dmium sulfide/3elenide pigment and .04 gram of wetting agent are then added, me pigment suspension ls then coated on a discharge lamp en~elope in the normal manner and the coated envelope is ~ehred at a temperature o~ approxlmately 50QCo As illustratsd by the ~oreeoinæ examples, poly- ~.
ethylene oxide binder coatlng ~olutions contalnlng finely :~.
10 divided alumina (ln amount~ o~ greater than about l~ o~ the -pho~phor weight) can be coat~d in the normal manner and lehred at less th~n 550C. The ~low propertie~ o~ thls c~ating composition are as good or bettsr than hydroxy ethyl cellulose tand generally somewhat better than hydroxy propyl methyl cellulose) with the lower molecular weight variet~es of polyethylene oxide having slightly better flow ::~
properties than the somewh~t higher molecular weight poly-ethylene oxide paints, The vl~osity o~ the coated com~
position can be adjusted by the one skilled in the art ~:.
in the normal manner, with the lower molecular welght polyethylene oxide requiring the slightly higher number o~ grams per liter o~ water to provide a desired viscosity.
It has been found that molecular welght~ in the range o~ :
abou~ 300~000 to 400~000 provide v2ry good per~ormance.
--10-- ~,
Claims (3)
1. The method of coating of a discharge lamp envelope with a layer of finely divided spectrum modifying particles using a polyethylene oxide binder together with finely divided alumina as an adhesion promoter, which method comprises:
(a) preparing a coating composition comprising said spectrum modifying particles, said alumina particles, and an aqueous solution of polyethylene oxide having a viscosity of about 20-200 centipoises, said alumina par-ticles being present in an amount such that the weight ratio of alumina particles to spectrum modifying particles is between 0.015 and 0.025;
(b) coating said discharge lamp envelope with said coating composition; and (c) lehring said coated envelope at a tempera-ture of about 400-500°C.
(a) preparing a coating composition comprising said spectrum modifying particles, said alumina particles, and an aqueous solution of polyethylene oxide having a viscosity of about 20-200 centipoises, said alumina par-ticles being present in an amount such that the weight ratio of alumina particles to spectrum modifying particles is between 0.015 and 0.025;
(b) coating said discharge lamp envelope with said coating composition; and (c) lehring said coated envelope at a tempera-ture of about 400-500°C.
2. The method of claim 1, wherein said lehring temperature is between 450°C and 500°C.
3. The method of claim 1, wherein said spectrum modifying particles are subject to oxidation in air at lehring temperatures and said lehring is performed in a non-oxidizing atmosphere.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US47880774A | 1974-06-12 | 1974-06-12 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1045908A true CA1045908A (en) | 1979-01-09 |
Family
ID=23901431
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA227,911A Expired CA1045908A (en) | 1974-06-12 | 1975-05-28 | Low temperature process for coating lamp envelopes |
Country Status (7)
| Country | Link |
|---|---|
| JP (1) | JPS518782A (en) |
| CA (1) | CA1045908A (en) |
| DE (1) | DE2526281A1 (en) |
| GB (1) | GB1441900A (en) |
| MY (1) | MY7700180A (en) |
| NL (1) | NL7506340A (en) |
| PL (1) | PL96170B1 (en) |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS55121250A (en) | 1979-03-12 | 1980-09-18 | Mitsubishi Electric Corp | Fluorescence |
| US4308186A (en) | 1980-07-07 | 1981-12-29 | North American Philips Corporation | Reflector coating composition for fluorescent lamps |
| US5858277A (en) * | 1992-12-23 | 1999-01-12 | Osram Sylvania Inc. | Aqueous phosphor coating suspension for lamps |
| DE4305520C1 (en) * | 1993-02-17 | 1994-06-01 | Prolux Maschinenbau Gmbh | Aq. suspension for coating inside of complex lamp discharge vessel - contains water-soluble adduct of polyethylene oxide and ammonium polyacrylate as binder, giving good thixotropic flow, drying and dispersion |
| DE4309408A1 (en) * | 1993-03-19 | 1994-09-22 | Prolux Maschinenbau Gmbh | Suspension for the internal coating of glass vessels, especially lamp discharge vessels of complicated geometric shape, and method for the interior coating of the glass vessels |
| US8622053B2 (en) | 2009-03-16 | 2014-01-07 | Planika Sp. Z O.O. | Burner and method of its operation |
-
1975
- 1975-05-23 GB GB2284875A patent/GB1441900A/en not_active Expired
- 1975-05-28 CA CA227,911A patent/CA1045908A/en not_active Expired
- 1975-05-29 NL NL7506340A patent/NL7506340A/en not_active Application Discontinuation
- 1975-06-12 JP JP7025775A patent/JPS518782A/en active Granted
- 1975-06-12 PL PL18115675A patent/PL96170B1/en unknown
- 1975-06-12 DE DE19752526281 patent/DE2526281A1/en not_active Ceased
-
1977
- 1977-12-30 MY MY7700180A patent/MY7700180A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| DE2526281A1 (en) | 1976-01-02 |
| GB1441900A (en) | 1976-07-07 |
| JPS53871B2 (en) | 1978-01-12 |
| JPS518782A (en) | 1976-01-23 |
| PL96170B1 (en) | 1977-12-31 |
| MY7700180A (en) | 1977-12-31 |
| NL7506340A (en) | 1975-12-16 |
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