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De¢- 31, 1946-
Filed Aug. l2, 1944
14 x5
Patented Dec. 31,1946
Kenneth Demb, Salem, andMalcolm L. Hayes,d
Beverly, Mass., lassignors to Sylvania Electric
. Products Inc., Salem, Mass., a corporation of
MassachusettsApplication August 12, 1944, Serial No. 549,204 `
’ sciaims., (Crim-33.5)
pear from the following description takenin con
This invention relates to a method and appa-v
nection with the accompanying drawing, and will
belparticularly pointed out in the claims.
ratus for coatingthe inner surface of fluorescent
`lamps with fluorescent material vand particularly
To'îpresent a better understanding of 'the in
vention .a specific embodiment thereof is herein
Vdescribed andv illustrated in the drawing in
yto »such a method wherein the-coating material
Áused has fast drying characteristics.
It is highly desirablethat the coating material
upon fluorescent lamps be applied evenly and to a
Figure 1 is a diagrammatic view' of _an appa
vpreek-:termined thickness. . Heretoiore it has been
ratus suitable for practicing the invention;
'considered of advantage to forego some of the ad
vantages of a rapid drying coating in the interest l0
of better quality obtainable, prior to the present
invention, by using a slower drying solvent. The
Figure 2 is an'enlarged detail view', to more
clearly vshow the structure of the tube'holding
‘Figure j?. is across _section on ’line 3'-‘-3,~ Fig
lslow drying solvent however, delayed thedrying
time and the process showed -poor production
The practice of the presentinvention permits
` The desirability
of using
M highly volatile
in the liquid material employed in coating fluores
>cent` lamps is well recognized. The art of 'suc
the use of rapid drying solvents, and produces a
fcessfully using such a material on a practical pro
high quality coating in a greatly reduced period
duction scale however, had not been successfully
present invention. With
The principles ofthe invention may be applied 20 developed prior to the and
control, the resulting
-out proper handling
to many types of lamps but are particularly
and generally in
adapted to the coating of elongated open-ended
‘eñicient in light output.
lamp tubes. The coating material is prepared
of time.
' ` The coating material is prepared by mixing to
with a‘highly volatile solvent such as acetone
gether'the desired 'iluorescent powder, a suitable
temporary binder such as nitrocellulose, and a
and is applied to the inner walls of the tubes by .
flowing it thereon at their upper ends while they
are vertically disposed. The liquid coating flows
downward wetting and coating the walls and the
surplus liquid iiows out at the bottom Where it is
collected to be used again.
volatile solvent’the major portion of which is ace
tone or other similarly volatile liquid.
_ _
The top of the, tubes. areleft openwhile the
bottom openings are restrictedin their access _to
the atmosphere by controllable means. By such
an arrangement certain natural properties of the
vapors generated by the drying process are uti
lized to control and stabilize the drying conditions
curately on a commercial scale. The lamp tubes
4 are held in a vertical position in racks 5 which
are arranged to hold a plurality of tubes. A'posi,-
within the tubes in a manner to produce a perfect
and highly eiñcient coating, as will appear more
fully hereinafter.
The principles of the invention may be applied
to the coatingfof many types of lamp envelopes.
However, the invention is herein applied -to the
'elongated type of lamp tubes which are- _open _at
Aboth ends when -the coating isapplied,v The ap
paratus illustrated in the drawing enables the
-coating operation tó be executed rapidly and ac
`tio'ning plate'ß is perforated with `>a’ number of
-holes 1 and is disposed' above a base plate 8 hav
An object of the invention is to provide means
ing apertures 9_therein situated in vertical align
for rapidly coating fluorescent lamp envelopes
with a'highly efficient light emitting coating.
ment with the apertures 1. The tubes are loaded
-into the racks by passing them through the aper- v
A further ‘object of the invention is to provide
means for utilizing theadvantages of rapid dry
turcs -1 andr projecting their end portions into
the apertures 9.
ing solvents while controlling the evaporation
Desirably the racks are so constructed that
conditions at `the coated surface in a manner
to produce a uniform layer of fluorescent mate:`
_they may be‘moved along a conveyor framework .
l lll. To feed the racks along the conveyor, a con
rial of predetermined thickness and density.
A further object of the invention is to provide
veyor drive Il is provided having lugs IZ thereon
a method of coating _the inner surface of a lamp .
tube in which the natural vaporization charac
teristics of the solvents used in the coating mate
rial are employed to condition the' coating during
‘which are positioned vto engage the racks 5 and
move them along the ways lil. A suitable power
the drying period.
communicating with a supply of liquidv I3X.
Other objects and features will more fully ap
'.m'eans and control not shown is provided which
enables the operator to vposition the tubes succes
sively beneath one'or more applicator nozzles I3
The nozzles I3 are or may be of well-known
vapor and air to escape. The escape of vapor
and air at the bottom of the tube sets up a slow
movement of air downward into the top. This
construction having a hand or automatic means ‘
for flowing a quantity of the coating material
onto the upper portion of the inner wall of the
air becomes saturated shortly after entering the
tubes from where'it flows downward by gravity Ul top of the tube, after which it can no longer
along the tube walls wetting and laying a coat
ing thereon. The surplus material vflows out at
the bottom end of the tubes.
To prepare the coating material a suitable fiu
orescent powder is mixed with a temporary 10
-binder and the desired quantity of solvent is add-A y
ed to give the material the correct consistency.
The type of solvent used is important. It> has
been found that acetone alone is a satisfactory
material to use but other highly volatile liquids
may be used or other solvents in combination
with acetone may also beused.
have, al drying eñect.
In the _zone in whichl
saturation is taking place the coating becomes
dried. As this portion of the tube no longer con
tributes vapor to the stream of air, the portion
immediately below it becomes the drying Zone.
. The-»drying zone thus moves smoothly down the
tube and the whole tube is dried progressively.
By varying4 the size of the adjustable opening
during the drying period, automatically or
manually, the density of coating along the length
of the tube can be controlled, and it may be
varied accordingÀ to some predetermined pattern.
The proportion of ñuorescent powder tempo
The control of the vapor at the base of the
rary binder and solvent are adjusted to produce
tubes Vmay be eiîected in any suitable manner.
the required thickness of coating, when dried 20 In the construction illustrated a pan-like con
and baked.
tainer I4 is secured to the bottom face of the
As Vis wellk known, acetone .vaporizesi very
base plate 8' of' the racks 5. The containers III
rapidly at room temperature and its vapor is
serve to .enclose all of the openings 9 in the
heavier than air. These properties are utilized
plate 8 and yalso tocatch the surplus liquid coat
to accomplish the desired end result. The whole
ing material which drains from the tubes. Ad
operation of coating Aand drying is carried out
justable openingsV IIE: are provided in the con
at ordinary room temperature. Ii no control is
tainers I4 by means of which the downward flow
exercised over the drying of the coating the
of vapor from the tubes may be regulated. The
rapid evaporation rate> causes a sharp loweringof
vapor íiow Vfrom all vof the tubes in the rack is
temperature at thel coatedzsurface. and a rela
thus controlled by a single; opening. However,
tively violent down ñow of the vapor results from
any suitable arrangement for accomplishing the
its rapid generation. If the bottom of the tubes
same result may be employed.- As shown herein
are open freely to the atmosphere the vapors
the size of the opening I5 may be adjusted by
rapidly pass downward and cause sudden drying
means of a sliding door I5, or other suitable
of the lower portions of the coating prior to
the drying of the upper portion, which, being
liquid or semi-liquid tends to ñow downward over
the dried portions causing undesirable uneven
’dense areas. The drying period under such cir
cumstances is very short but the whole operation
produces a generally unsatisfactory result. If,
however, the bottom opening of the tube> is closed
or partially closed to the flow of vapors a very
difïerent result is elîected. By closing >or par
tially closing the bottom end of the tubes and
leaving the top ends open during the drying
period a deñnite and highly beneñcial control
is exercised over the drying operation. Under
' The receptacles III are detachably secured to
the racks in any desired> manner such as by
means of bolts I'I in the plate 8 having thumb
nuts I8 thereon engaging the flange I9 upon the
upper rimv of the receptacle. To produce a
satisfactory vapor tight seal between the tubes
and the apertures 9 suitable gaskets may be pro
vided which are secured to the periphery of the
apertures and have openings to tightly receive
the tubes.V
»In brief the coating procedure may be reviewed
as follows. The liquidy coating material is first
prepared by mixing the desired type of iiuores
such conditions the solvent vapors as they are
cent powder, a suitable temporary binder such as
generated remain within thetube and in contact .
nitrocellulose, and acetone, or similar highly
volatile solvent. The proportions employed are
calculated to provide the correct viscosity and
Iiow characteristics required to produce a dried
and baked coating of the desired density and
with the coating during the drying operation.
The natural tendency. for the vapors is to ¿ñow
downward since they are heavier than air. A
small regulated portion only of the vapor is per
mitted to escape from the bottom of the tubes
consequently a column of vapor automatically
accumulates in the tube. Throughout the dry
ing period therefore an atmosphere of vapo1` re
mains in the tube in contact with the coating.
If an attempt is made to restrict the flow of
_vapor by any means other than at the bottom
of the tubes a convection takes place at the tube
bottom which causes premature drying at that
point which results in an uneven coating. This
«effect is particularly noticeable in tubes of large
The process is carried out at normal room
temperature and the natural tendency is for the
solvent vapors to reach saturation pressure with
in the conñnes of the tube. Means are provided
-however to control the degree of vapor pressure
to that value which produces the most favorable
drying conditions.
This is done by regulating
an adjustable opening at the bottom of the tubes
which permits a measured amount of acetone
light emission.
The coating liquid is placed in the supply con
’rainer ISX and racks 5 containing tubes to be
coated are placed on the conveyor. The conveyor
is then manipulated to bring one or more tubes
into position under the nozzle or nozzles i3. The
ends of the nozzles are inserted in the upper ends
of the tubes and a quantity of coating liquid is
nowed onto the inner walls of the tubes by oper
ating the valve upon the nozzle I3. The liquid
iiows downward wetting and depositing a coating
on the tube walls, The surplus liquid drains
into the receptacles I4. Immediately the coating
starts to dry giving off heavy acetone fumes, some
of which is permitted to escape through the open
ing I5. The opening is so regulated that the
movement of air in the tube is restricted to the
proper rate to provide the correct drying time for
the coating. The tubes in the racks are suc
cessively coated and as they are moved along the
conveyor become dried. yThe. whole ' procedure
by the coating is dried in an atmosphere of solvent
takes place at normal room temperature and
Vapor and air regulated to a predetermined rate
Without forced air jets or vacuum devices. The
of flow.
vapor content of the exhaust air is therefore high
2. An apparatus for coating with iluorescent ma
allowing economical recovery of the solvent vapor
terial the inner walls of open ended tubular lamp
by commonly known means.
envelopes comprising a supply of liquid coating
The drainage liquid in the containers I4 is re
material having a solvent which produces a vapor
moved by detaching the containers and returning
heavier than air, an applicator nozzle connected
the liquid to the main supply or 'by a drainage
with said supply for flowing the material upon the
In a short period of time the coating is dry il) surface to be coated vapor tight means for col
lecting the surplus material which flows through
and the tubes are removed and placed in a baking
the‘tubes and means in the wall of said collect
oven to remove the temporary binder after which
ing means acting to control the downward flow
they are ready to be received by the operator who
performs the necessary operations to complete l of vapor and air during the drying period to main
the lamps.
By coating the lamps in accordance with the
principles> of the invention the total time con
tain the 'proper rate of drying within the tubes to
produce an even coating of the required density.
âäfAnv apparatus for coating with ñuorescent ma
inner walls of open ended tubular Vlamp
sumed in coating and drying is greatly reduced
envelopes comprising a supply of liquid coating
from that required when slow drying solvents are
material having a highly volatile solvent and in
used and moreover, due to the accurate control 20 which the solvent produces a vapor heavier than
which is exercised over the drying conditions a
air, an applicator nozzle connected to said sup
more uniform and efñcient coating is produced.
ply operable to ñow the material upon the surface
What we claim is:
to be coated, conveyor means for holding the tubes
1. A method of coating the inner surface of
in upright position and positioning them beneath
vertically disposed tubular ñuorescent lamp enve 25 said nozzle, means for collecting the drainage
lopes comprising the steps of preparing a liquid
from said tubes, and means for adjustably re
coating material containing fluorescent powder in
stricting the escape of solvent vapor and air from
which at least the major portion of its solvent is
the bottom ends of the tubes during the drying pe
highly volatile and in which the solvent produces
riod to restrict the rate of ñow of air through the
a vapor heavier than air, flowing the liquid onto 30 tubes to such a value that a smooth even coating
the surface to be coated, draining and collecting
of therequired density is produced.
the surplus coating liquidwhich passes complete
ly through the tubes, restricting the downward
iiow of solvent vapor and air within the tubes by
partially closing the bottomends thereof where- 35
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