Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND OF THE INVENTION
This invention relates to lamps wi-th a protective envelope
I coating and, more particularly, to an improved method for applying
1 such a coating on the glass envelope of a lamp. The method of the
invention is particularly useful for applying a UV curable photopolymer
as a protective coating on the exterior surface of a photoflash lamp.
A typical photoflash lamp comprises an hermetically sealed glass
envelope, a quantity of combustible material located in the envelope,
such as shredded zirconium or hafnium foil, and a combustion supporting
gas, such as oxygen, at a pressure well above one atmosphere. The lamp
B ¦ ~
. .
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.
.,~ .
.
.
Il f, - ~2~5~ ~ I
I!
-23,3~9 1 also includes an electrically or percussively activated
I primer for igniting the cornbustible m aterial to flash the
lamp. Durinq lamp flashing, the glass envelope is subject
I to sever-e thermal shock due to hot globules oF metal oxide
I impinging on the walls oF the larnp. As a result cracks
and crazes occur in the glass and, at higher internal
pressures, containment hecomes impossible. In order to
reinforce the glass envelope and improve its containment
capability, it has been common pracLice to app1y a protective
' lacquer coating on tne lamp envelope by means of a dip
process. To build up the desired coating thickness, the
glass envelope is generally dipped a number of times into
a lacquer solution containing a solvent ancl a selected
resin, typically cellulose acetate. After each dip, the
I lamp is dried to evâporate the solvent ancl leave the desire-i
coating of cellulose acetate, or whatever other plastic
, resin is employed. -
¦! In the typical solvent dipping proces for applying
~I protective coatings, a large number of photoflash lamps
¦ are loaded on a rack and then successively dipped in a solver
I solution and oven dried three or four times to build up the
i desired coating thickness. Such a process is time consumingl ¦
¦ uses a large area o-F production floor space, and involves ¦
¦ considerable hand labor, all of which adds signi-Ficantly t
I to manufac~uring costs. Further, as the lacquer solution
I includes a highly flamable so1vent, such as acetone,
¦, an inadvertent flashing of one of the lamps in either the
¦' dip bath or drying oven can ignite the solvent fumes. Tp
¦~ substantially reduce or elirninate this hazard, costly
¦, automatic extinguishing equipment must be employed. in
¦ the event of a solvent tgnition, the resulting down time and
consumption of fire extinguishing chemicals also adds to
the manufacturing costs.
Another approach to providing a more economical and
improved containing vessel is described in U.S. Patent
¦ 3,893,7g7, wherein a thermoplastic coating, such as poly-
carbonate, is vacuum formed onto the exterTor surface of
the glass envelope. The rnethod of applying the coating
, comprises: placing the glass envelope within a preformed
l~o I sleeve of the thermoplastic material; drawing a vacuum
I in the space between the thermoplastic sieeve and the glass
¦, envelope; and, sirnultaneously heating the assembly
¦~ incrementally âlong its ler)gth7 whereby the temperature
z _ _
~ I
D-20,379 ~ and vacuum cause the thermoplastic to be incrementally formed onto
the glass envelope with the interface substantially free of voids,
inclusions and the like. Although this method provides an optically
Il clear protective coating by means of a significantly faster and
I safer manufacturing process which may be easily integrated on automated
production machinery, it does present the disadvantage of requiring
prefarmed plastic sleeves which must be individually desiyned for each
Ij different lamp type, made or purchased, stocked, and fed into the
¦I production apparatus which applies the sleeves onto the envelopes.
lQ ll Further approaches toward providing improved protective coatings
¦ for lamps have related to the use of UV curable photopolymers. For
¦~ example, one prior method of coating a flashlamp with a photopolymer
comprises the following steps. First, the lamp is held vertically with
l the base up and dipped into a vat of the photopolymer at 60C and
1 extracted very slowly, the dip process taking about 45 seconds. The
wet-coated lamp is then inverted with the base down and rotated at
a speed of from one-half to four revolutions per second under a
UV lamp, the cure period taking about 30 seconds. The resulting I -
coating thickness is about 0.020". According to an alternative
method, the flashlamp, while revolving, is sprayed with the liquid
photopolymer and then transFerred directly into the ultraviolet lamp
chamber. Another known method is somewhat similar except that either
long or short stran~s of fiber glass are employed to reinforce the
¦ photopolymer coating. ;~
ll An immersion process for applying a UV cured coating on a photo-
¦¦ flash lamp is also described in a published Japanese patent application
¦¦ identified as Public Disclosure Number 52-7720 and having a publication
j date of January 21, 1977; a continuation of a continuation-in-part
!l of a corresponding U.S. application issued as U.S. Patent 4,076,489
~ on February 28~ 1978.
A somewhat critical aspect of the aforementioned UV cured coatings~
is that the shape and uniformity of thickness depends on the flow
characteristics of the photopolymer
"
-20,37 ¦~ r-esill ~s inrluencecl by the rorce oF gravity, orientation
of tlle lamp a-rter coatin~, and viscosity o-F the resin.
! Cllanges in resin viscosity resnltirl~ ~rom chclrlges in
il temperatul-e afrect both the repeatability of the shape of
, the coating ancl the uniFormity of thickness. These
¦ irreg~larities are retained once the coating is hal-dened.
In the case of UV cured coatings used to protect flashlanlps
I, from rup1:ure at the time of flashing, thin coating regions
¦I resulting from improper resin distribution can result in
!I containment failures. The comparative integrity or
¦l containment for various types of vessel constructions can
be evaluated by the use of special test lamp~, ~uch as
I described in U.S. Patent 3,955,912 assigned to the present
i assignee, which controllably induce bursting of the lamp
i upon ignition. Accordingly, such test larnps were coated
with UV cured photopolyrrlers by means of various mmersion
techniques and compared in flash tests with similar test
1amps coated in accordance with the present invention.
The results showed that the repeatable uni-formity of the
coating applied in accordance with the inven~ion provided
sigllTFicantly superior containment characteristics over the
lamps coated with the prior art immersion techniques.
SUMMARY OF THE INVENTION
Accotdingly, it is an object of this invention to
provide an improved method for applying a protective coating
on a lamp envelope.
A principa1 object of the invention is to provide an
improved method for applying an ultraviolet curable coating
¦ on a photoflash lamp which minimizes coating irregularities
pr~duced by gravity-indLIced flow or reflow of the coatiny.
These and other objects, advantages and fea~ures are
attained in accordance with the invention by a method
comprisirlg: holding the lamp with its longitudinal axis
disposed horizontally and rotating the lamp about its
longitudinal aX.is; dispensing a liguid coating material
onto the envelope of the rotating lamp from dispensing
means 70cated above the lamp; and allowing the coating on
the lamp enyelope to be cure-hardened. To assure dispensing
of the coating material frorn one end to the other of the
rotating lamp envelope, relative linear motion may be provideld
between the lamp and djspensing means, or the rotating lamp
may be held in a fixed position be70w a fixed dispening
means having a plurality of openings through which the
__1~__
!i
5~
-20,379 ~ liquid coating material is dispensed. The method is particularly useful
for applying photopolymer coatings on lamps which are substantially
cure-hardened by irradiation with a source of ultraviolet light.
. . ,
~ Rotation of the horizontally disposed lamp while coating material
is dispensed from a location above the lamp exhibits surprising
effectiveness in stabilizing the coating shape, once applied, for
periods of up to thirty seconds prior to exposure for cure-hardening.
This method is particularly efFective for overcoming the viscosity
Il characteristics encountered when using coating materials of UV curable
1l photopolymers. Uniform, repeatable coatings can be applied at
il production line speeds, and when applied to photoflash lamps, the
,¦ resulting protectively coating vessel exhibits a superior containment
i~ capability, along with excellent photometric characteristics. In
1~ addition to the above mentioned improvements in the resulting product,
lS 1ll the method of applying lamp coatings according to the invention
provides several advantages to the lamp manufacturing process. For
example, the process can be solvent free; it requires a minimum of
floor space; and it can be readily adapted to automated lamp production
~ apparatus. Further, cure time is reduced to periods oF less than a
,I minute. A hard cure is effected immediately, without the need for
warehousing to assure a complete cure.
_RIEF DESCRIPTION OF THE DRAWINGS
¦ This invention will be more fully described hereinafter in conjunc-
~ tion with the accompanying drawings, in which:
~1 FIG. 1 is an enlarged elevational view, partly in section, of an
electrically ignitable photoflash lamp having a protective coating
applied in accordance with the invention;
FIG. 2 illustrates a first method of applying a liquid coating
¦! material in accordance with the invention;
30 1l FIG. 3 is a cross-section schematically illustrating one method of
cure-hardening the lamp coating by irradiation in accordance with the
I invention; and
¦I FIG. 4 illustrates a second method of applying the liquid coating
i' material in accordance with the invention.
- 5 -
I !
2~5si
D-20,379 DESCRIPTION OF PREFERRED EMBODIMENT
The teachings of the present invention are suitable for the
application of several different types of liquid protective coating
1 materials to the exterior envelope surface of a wide variety of lamps
ll oF different sizes and shapes; however, the ihvention is particularly
advantageous as a method for applying a UV-cured photopolymer coating
on photo-flash lamps having tubular shaped envelopes with a volume of
less than one cubic centimeter. This advantage rests in the signifi- !
Il cantly improved coating uniformity which is obtained, which in turn
~ results in the superior containment capability exhibited by a small
¦ photoflash lamps coated in accordance with the invention. For purposes
i of example, the invention will be described as applied to the elec-
¦ trically ignitable, filament-type photoflash lamp illustrated in FIG. l;¦
I¦ however, it will be understood that the same principals are applicable
!¦ to high voltage or percussively ignited flashlamps.
¦ Referring to FIG. l, one embodiment of the coated lamp l is
illustrated comprising an hermetically sealed lamp envelope 2 of glass
tubing having a press 4 defining a base end thereof and an exhaust tip
l 6 defining the other end thereof. Supported by the press 4 is an
ignition means comprising a pair of lead-in wires 8 and lO extending
through and sealed into the press base. A filament l2 spans the inner
ends of the lead-in wires, and beads of primer l4 and 16 are typically
located on the inner ends of the lead-in wires 8 and l3, respectively,
at their junction with the filament. Typically, the lamp envelope 2
I has an internal diameter of less than one-half inch, and an internal
¦, volume of less than one cubic centimeter. A combustion-supporting
¦~ gas, such as oxygen, and a filamentary combustible material l8, such
as shredded zirconium or hafnium foil, is disposed within the lamp
Il envelope. Typically, the combustion-supporting gas fill is at a
~ pressure exceeding one atmosphere, with the more recent subminiature
¦ lamp types having oxygen fill pressures of up to several atmospheres.
~z~
D-20,379 As will be described in more detail hereinafter, the exterior surface
of the glass envelope 2 is covered with a protective coating comprising
a photopolymer 20.
A percussive type photoflash 1amp is described in several prior
patents of the presert assignee; For example,
fl
- 6a - I
, I
~2 ~
D-20,379 U.S. Patent No. 3,674,411. As described there;n, the percussive lamp
also includes a sea1ed glass envelope containing a filamentary
combustible material and a combustion-supporting gas; however, the
ignition means comprises a metal primer tube sealed in and extending
from one end oF the glass envelope and containing a coaxially disposed
wire anvil partially coated with a charge of fulminating material.
The high voltage type photoflash lamp is described in a number of
Il patents of the present assignee; for example, U.S. Patent 4,059,388
and 4,059,389. As described therein, each of the lamps includes a
10 I sealed glass envelope containing a filamentary combustible material
and a combustion-supporting gas; however, in the first-mentioned
patent, the ignition means comprises a mass of primer material bridging
a pair of lead in wires, one of which is enclosed in an insulating
I sleeve. In the second-mentioned patent, the ignition means includes a
15 l' pair of spaced apart lead-in wires with spherically shaped terminations;a glass frit is coated over the lead-in wires, and primer material is
coated over the frit-coated terminations. I
Il Although somewhat different in structure and operation, the fila-
!~ ment, high-voltage, and percussive lamps are similar and that in each
20 ~¦ the ignition means is attached to one end of the lamp envelope and
~I disposed in operative relationship with respect to the filamentary
¦¦ combustible material. More specifically, the ignition filament 12 ofthe flashlamp of FIG. 1 is incandesced electrically by current passing
l through the metal filament support leads 8 and 10, whereupon the
25 ¦ incandescent filament ignites the beads of primer 1~ and 16 which in
turn ignite the combustible 18 disposed within the lamp envelope to
! provide the actinic light output. Operation of the percussive-type
lamp is initiated by an impact onto the primer tube to cause deflagra-
1~ tion of the fulminating material up through the tube to ignite the
combustion material disposed within the lamp envelope. Operation of
'
Il - 7
li
~ ~2~
D-20,379 the high-voltage pulse from, e.y., a piezoelectric crystal, is
applied across the two lead-in wires, electrical breakdown of the
primer causes its deflagration which~ in turn, ignites the shredded
metallic combustible.
- 7a -
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~L~f~ .L~D~
D-20,379 ~ A number of advantages are obtained by using a photopolymer asprotective coating 20. The term "photopolymer" is underskood to
mean a radiation curable polymer. Rapid curing of such a polymer
results from any stimulus that generates free radicals. For example,
free radical initiation can be effectively provided by a source of
ultraviolet (UV) light or electron beams.
Ultraviolet light in the 185 to 400 nanometer wavelength range is
required for UV cures. UV light from commercial mercury vapor,
mercury-metal halide~ or pulsed xenon lamps is effective in the
,I required wavelength range.
Curing time with UV light can range from fractions of a second
to a minute or two depending upon the film thickness, polymer structure¦
~1 UV light intensity, and initiator type concentration. Further, the
Il curing can be effected in air, under the vacuum, or in an inert gas
ll atmosphere, such as nitrogen.
¦~ The photopolymer basically comprises prepolymers used alone or
~¦ diluted with reactive monomers. To render the material UV curable,
however, one must use a photosensitizer or photoinitiator (such as
~I benzoin ether) which will directly or indirectly give free radicals
~ when exposed to UV radiation, even at room temperature.
¦~ Examples of prepolymers include polyesters, epoxy acrylates,
acrylics, polyurethanes, thiolenes, alkenes, or any of a number of
~¦ general groups. Examples of reactive monomers include styrenes, acrylic~,
¦ and methacrylic esters, and polyfunctional monomers, such as ethylene
ll glycol diacrylate, trimethylol propane triacrylate, and pentaerythritol~
¦ tetraacrylate. The monomers also serve as viscosity reducing agents
and, as such, they aresolvents which dissolve or are miscible with
the prepolymer. Accordingly, the reactive monomers reduce the viscosity
Il of the blend to workable levels and/or impart desirable properties
il to the cured film.
Specific photopolymers we have found to be useful in coating
, photoflash lamps are thiolene based materials available from W.~.
Grace ~ Company, Maryland and identified as ~CC Blend 15 ancl ~lend
XRCP-7211. Approxirnately 99 percent by weight of these thiolene
-20,379 ~ based photopolymers comprise a blend of prepolymers, such as di- or
polyth;opolymers and di- or polyene-polymers; the balance
- ~A -
2~.~5~ `
D-20,~ of tIIe mixtllre compris~s a photoinitiatc)r, sucI~ as benzoin
j cthel- or aroIllatic ket~ne, e.g., benzophene, an(l stabilizers,
I~ which are small (luantities of free raclical scavengers.
fl Tl1e flow and viscosity ci1arac~eristics of the licluid
li photopolymer can be acIjusted by addiIlg fume~ silica to
I increase ti1e thixotropicity o~ the mixture. ~rhe increase~
viscosity enables application of a heavier coating and
reduces gravity induced runback of the wet coating prior to
; cure. The viscosity can be decreased by hea;ing, or adding
monomel-s as discussed above
¦ The photopolyrner compositions referred to above result
,i in an essentially solvent free process and solvent-free
I coating. It is to be understood, however, that the method i
¦, to be described hereinafter is equally suitabl~ for use
¦¦ with solvent-containing photopolymers.
An exarnple of a liquid photopolymer that we have found
¦ to be particularly useful for coating photoflash lamps in
I accordance with the present invention is an acrylo-urethane
¦ resin, available -Frorn the Hughson Chemical Company as
Type No. 3Q75-20 or 3254-ll, with a viscosity near 7,gOO
centipose at 25~C.
In accordance with the present invention, we have
discovered a significantly improved method for providing
; an optically clear protective coating on the exterior
surface c?f the glass envelope of the lamp which minimizes
the coating irregularities produced by grav;ty-induced flow
or re-flow of the coating. As a result, the coating provide
a superior containment vessel. The method pro~ides a
significantly faster, saFer and more economical manuracturin~
process, and it may easily be integrated ireto automated
production machinery.
According to the invention, the UV-curable photopolymer
material is dispensed from above unto a horizontal, rotating
lamp. Preferably, the liquid coating material is dispensed
by means of a mechanically activated syringe which keeps
the volume flow rate cons~ant, and thus, which is independent
of the viscosity of the material. Horizoneal rotation of
the specimen stabilizes the coating shape, once applied,
for periods of up to thirty seconds prior to exposure
to ultraviolet light for curing. We have founcl that in
this rnanner uniform, repeatable coatings can be applied at
production line speeds.
One method of applying the coating in accordance with
the invention is illustrated in FIG. 2. ,he lamp l having
a glass envelope 2 is held in a horizontal position. More
I
I
D ?~/ ,79 sI-eci r ically, consj~cI- ihe longitlldinal aYis "a" passing
thrc)~ h thc bas~ oF the l~mp, forrIie~ ~y press l~, an~ the
end of th~ lam~ opp~site tlla~ base, intllis instance the
exi~ust tip 6. The lamp 1 is held with its longitudiIlal
~ axis "a" dispos~cI hori~on~ally by means of a pincer-type
holding h~acI 22 ~hich clamps th~ exterior portions of the
metallic lead-in wires 8 and 10. The head ~2 may comprise
a portion of a lathe-type mechanisrI-l which rotates the lamp
about its longitudinal axis "a". While the horizontally
disposed lamp envelope 2 is rotate(I in this manner,a
needle-type dispensing means 24, located above the larnp,
dispenses a liquicl c~ating material 20' unto the glass
envelope 2 of the rotating lamp. In this embodiment there
1, is 2 relative linear motion provided between the lamp and
` the dispensing means to cause the coating material to cover ¦
¦ the ro~ating lamp envelope from one end to the other. More ¦
particularly, in ~IG. 2, the rotating lamp 1 is shown in
a fix~d position while the dispensing means 2It above the lamp
, is moved in a 1inear path from left to right, as illustrated
¦ by the arrow. Alternatively, the dispensing means may be
¦ held in a fixed position and the roating lamp may be moved
li in a linear path with respect thereto. On the other hand,
j both thelamp and the dispensing means may be moved in
parallel but opposite directions, or in ~:he same direction
I in parallel at different speqds~
1~ ¦ In a specific application of the method illustrated in
~I`G. 2, the above-mentioned photopolymer (Hughson Chemical
¦ Company Type 3075-20~ an acrylo--urathane resin with a
i viscosity near 7,800 centipoise at 25C) was metered by
~ means of a mechanically ac~ivated syrirlge through a surgical
j needle 24 having a ~6-gau~e size and a length of 1.25
¦ inch. The dispensing end of the needle was spaced 0.2
inch from the surface of the lamp being coated. The volume
¦ flow rate was adjusted to provide approximately 0.05 cubic
¦ centimeters of resin per second. The motion Ot the needle
¦ 24 along the length of the lamp was 0.0448 inch per lamp
¦ rotation. The lamp rotation rate was 158 rpm, and flow
was terminated near the tip of the lamp. After the conclusi n
of the dispensing step, the lamp was allowed to remain
rotating for a predetermined delay period, ranging from
7 seconds to 12 seconds, prior to the step of curing the
coating by ultraviolet irradiation.
¦ Followin9 the above described coating and delay steps;
j the rotatingJ horizontal lamp 1 was exposed to UV radiation
I --10-- 1,
!
1'~ .
D-20,379 ~ having a peak wavelength near 313 nanometers generated by ten fluorescent
lamps 26 (GTE Sylvania Incorporated Type F6T55 having an internal
coating of No. 2021 Phospnor) arranged in a cylindrical fashion, as
schematically illustrated in the cross-section of FIG. 3. Curing of
the resin took place in nitrogen at a distance of 2 inches From the
sources 26 in forty seconds. For example, in FIG. 3 the circular
ll dashed-line 28 represents the position of the quartz tubing that may be i
'f used to provide the nitrogen purged container within which lamp 1 is
Il held. The solid circular line 30 at the outer periphery represents
1O fl the cylindrical internal reflective housing containing the UV sources. f
The cured coating products by this method measured 0.023 inch in
thickness.
Il Subsequent to the curing step and post-cure cooling, a lubricant
¦I may be applied, such as by spraying, over the coating 20. This also
ll functions as an antistàtic agent. Suitable lubricant materials include
; li Dow Corning type DC 230, which is a silicone in textile spirits, and
f Dupont products such as the aqueous Duponol* (a sodium lauryl sulfate),
Merpol* (a long chain alcohol-ethylene oxide condensate), and ~elec*
(an alcohol phosphate).
,~ Coatings produced according to the invention are more uniform
in thickness than that provided by the previously described prior art
¦I techniques. This in turn provides reliable coating perFormance with
¦¦ regard to preventing rupture at the time of flashing. For example,
¦I this is particularly illustrated by Table I, below which illustrates
~ the comparative containment capabilities of lamp coatings applied by
~I different techniques, along with a comparative indication of the
¦¦ coa~ing irregularity. The lamps employed in obtaining the flash testing
data of Table I were of the type described in U.S. Patent 3,955,912,
I, which are particularly designed to controllably induce bursting of
1I the lamp upon ignition. In the first test (Test-l), the test lamp
fl specimens, once dipped according to the indicated prior art technique,
,i .
Il * Trademark of E.I. Du Pont De Nemours & Co.
~, ,
~,~ , _ 1 1
D-20,379 were immediately exposed to UV radiation while the tip remained down.
The cured coatings were irregular and thin in the press area 4. The
thin area failed to provide adequate protection -Frorn rupture at the
time of flashing. Test lamps similarly dippecl, bu-t remaining tip
I down for periods exceeding 2 to 3 seconds before curing tip down,
produced even more irregular coatings, resulting in higher coating
failures.
llA -
3L5S
1' ~
D-20,3,J In a seconcl test (Tes~-2), test larnps were sirnilarly n coated but were inverted immcdiately ~fter dipping,
pcrmilLi n9 t he resin to re~istrib-Ite (reflow) over the
lclInp prior to curin9. The amo~nt of time allow~d for reFlow ¦
5,~ affected the uniForInity of tile coatin~ tickness as well.
. The longer tne reflow time the more non-uniforrn the coating. I
The third test (Test-3) illustrates the results i
achieved with rest larnp.s coatecl in accordance with the I
present invention~ The significant improvement in
10. containment and the uniformity of coating thickness is
evident.
I TABLE I
I Coating Difference in
Failures Coating
~ ~lo. of Causi ng Thickness I
Test Description Lamps Rupt1Ire Lamp End-to-Enid
I Test-l Immerslon coat, 10 80% 33%
tip~down cure
I Test-2 Irnmersion coat, 52 23% 13%
I tip-up cure--
! preceded by
2-sec. reflow .
j Test-3 horizontal 48 t5% ~3%
I rotating coat
¦ ~ollowed by ~ I
: ~ delay of up to
: I 12 seconds prior
to UV cure . I
The followingTable 2 relates to flash testing with
3 ¦ regular production lamps. In Test-4, the regular lamps
: . were coated according to the invention and exposed to UV
I radiation within a 12 second delay period after conclusion
: ' of the step during which the coating was dispensed. Test-5
¦~ provides a control group and relates to uncoated lamps oF
35 ¦ the same type.
: . .
TABLE 2_
. Coating DiFference in
Failures Coati ng .
No.. of Causing Thickness
Test Description Lamps Rupture Lamp End-to-En d
_ . .... , . . _ I
Test-4 Less than 12 sec. 29 C~ - 2~
j stabilize.before .
~ exposure
1~5 I Test-5 Uncoated lamps lO 1U0% Not Applicable
¦ of same type
I
The foregoing tables therefore clearly illustrate the
effectiveness of the coating method of the invention in
preventing rupture at the time of Flashing. Further, as
(
D-20,3-j~ evideIlt from Table 2, the preferrecI clelay tirnes bet~een
j the conclusion of resin cIispensirl~ and the begirlning of UV
¦ curing are less than 12 seconds.
~ An alternative emboclimellt for disperlsing the liquid
I coating material 20' is illustrated in FIG. 4 In this
instance, there is n~ relativ~ linear motion between the
dispensing means and the rotating lamp. More specifically,
as illustrated, the overheacl dispensing means 32 is fixed
~ and provided with a plurality of openings, or needle
ori-fices 33, through which the liquid coating rnaterial 20'
is dispensed onto the exterior surface of lamp 1, which is
held in a fixed position while being rotated about its
I longitudinal axis "a" under the dispensing means 32. A
j sufficient number of needle oriFices 33 are provided and
I arranged so as to cause the dispensed coating material 20'
¦ to cover the rotating lamp envelope from one end to another,
as illustrated
I Variations of the above-described coating application
¦ technique have been tested and provecl to be effective.
I For example~ the opening size of each o~ the circular
I~ ori~ice no~zles may range from l~ x 10 6 square inches
¦I to 5 x 10 3 square inches. Further, rectangular orifice
li nozzles may be employed. The lamp rotation speed may be
at a fjxed rate selected from a range oF 24 to 300 rpm. I
1 25 I In the case where there is relative linear motion between
the lamp and the dispensing means, the traverse speeds
may range from 0.010 inch to 0.125 inch per lamp revolu~iorl.
Anothe r preferred coating material is an epoxy-urethane
' type UV-cure resin. The traverse direction is not 1imited
, to that shown in FIG. 2 but may travel from the tip of the
¦1 lamp toward the press 4.
Other modifications of the basic method include the use
of elliptical or other orifice shapes. A plurality of
I needles, or nozzles, all of the same slze and shape or
; 35 with combinations of various sizes and shapes may be used.
A vari~ble ro~ation speed or an oscillating motion may be
employed during resin application.
Further, it may be quite desirable to provide a
¦ rotatton o~ the lamp during irradiation (the curing step)
I which is at a substantially diFferent speed than the
rotation or the lamp under the dispensing means. Variable
I or intermittent rotation may be employed during exposure
I'
i'. ' .
~-20,37~ ¦, to UV radiat;on. The steps of tne rnethod rnay be repeated
¦l to build up a precl~ternlined Final coating thickness. Other
II types of UV sources may be employed wherein the spectrum
! and power density are commensurate with the curing require
¦, mer-ts of given UV-cure resins, or a combinationoF UV sources
II with differincJ UV emission may be used to provide a similar
!~ effect. Another particularly desirable -feature for providing
improved viscosity control is to employ heated or chilled
1 coating dispensers for preconclitioning the resin to facilitate
1 dispensing. Prior to the curing step, the delay period
t step may include the use of racliant energy for facilitating ;
distribution of the coating applied by the dispensing
means to thereby provide a smooth uniform coatin~ of the
¦ photopolymer on the surface of the glass envelope. Forced
¦ air or a mechanical blade may also be employed to assist
in distribution of the applied coating. In certain instances
it may ~e desirable during the curing phase to partially ¦
I cure the lamp while in a horizontal position followed
¦¦ by additional cure of the lamp coating in a non-hori~ontal
position.
Regarding the various type resins that may be employed,
the viscosities may range from 250 centipose to 106
¦ centipose at 25C. Heating or chilling of the dispel,ser
may then be employed to provide a viscosity at the
~5 application temperature of between 4000 and 7000 centipoise.
Although the invention has been described with respect
to specific embodiments, it will be appreciated that
modifications and changes may be made by those skilled in
I the art without departing from the true spirit and scope
¦ o~ the invention. For example, the described coating method
is also applicable to spherical or bulb shaped lamps, other l ~-
than tubular, associated with other lightin~ applications,
such as incandescent, fluorescent, and other types of arc
l discharge lamps. Further, the method is not lim7ted to
¦ the application ofphotopolymer coatings but may be also
employed with air-cure, moisture-cure, heat~cure, or hot
m-lt type co tings.
.
