Note: Descriptions are shown in the official language in which they were submitted.
5~3
-- 1 LD 776~ii
PHOTOFLASH LAMP PRIMER M~TERIAI,
BACKGROUND OF THE INVE21TI ()N
._
This invention relates in general to miniatura
photo~lash lamps oE the all-glass type, and more particu-
larly to those of the so-called electrical-i.gnition type
ignited with a 1~5 vol-t dry cell.- Such photoflash lamps
in general comprise a he:.metically sealed light-trans-
mitting envelope usually made of soft glass which contains
a combustion-supporting ga5 such as oxygen at about five
or seven atmospheres, together with a filling o suitable
light-producing combustible material such as shredded foil
o zixconium, for example~ to produce a high intensity flash
o actinic light. A stem press ~ase is located at one end
o~ the lamp envelope to form a hermetic seal with a pair of
~ electrical lead-in w.ires having a refractory metal resistance
filament connected therebetween. In such electrical~ignition
type photoflash lamps now being used, the inner ends of these
wires are coated with a charge oE heat-sen~itive primer
material so that when electrical current is passed through
the resistant ~ilament, there will be deElagration o the
primer material cau~ing the shredded combustible foil in
the lamp envelope to burn rapidly with incandescence. Two
lamps of this general type in current manuacture with soft
glass ~or ~lashcube-type product applications and called
AG-l or AG-3, are more particularly described in IJ.S. Patent
3,506,385, assigned to the assi~nee o~ the present invention.
- ~ - LD 7766
A primer ignition material for use with a high-
voltage type flash lamp which can be deposited from an
a~ueous coa~ing composition is disclosed in UOS. Patent
3~972,673, also assigned to the present assignee~ Said
ignition pri~er material includes a combustion-supporting
oxide to provide an additional oxygen ~ource in the primer
material which is readily available for combustion of the
primer fuel when the primer mixture is ignited~ Preferred
combustion supporting oxides are cobalt oxide, barium
chromateJ iron oxide ana higher oxides of nickel which
are easily reduced by zirconium fuel in the primer mîxture
to lower non-conducting oxides but which resist further
dissociation forming conductive residues after the lamp
has been flashed. Where formation of such conductive
residues is not objection~ble, however, still other metal
oxides are disclosed which can be reduced by the fuel
metal upon primer ignition including copper oxide, lead
oxide, tin oxide, titanium oxide, and zinc oxide as well
as still oth~rs. Utilization of said combustion supporting
oxide~ in this type primer ignition matexial enhances
reliable ignition of the overall high voltage flash lamp
to produce th~ desired light output in a relatively short
time period.
A comparison o the ignition characteristics
for such flash lamp between primer materials applied from
an aqueous suspension as compared with the sama primer
materials applied from organic liquid suspension finds
the latter primers to ignite more rapidly which is desirable.
Since the relative speed of primer ignition influences the
rate at which light i9 generated by the flash lamp, it
follows that such water-based primer materials could
prove too slow to ignite for acceptable use although
safer to handle in lamp manufacture than primer materi~ls
applied from organic liquid suspen~ion. It is a desirab1e
objective, therefore, to improve the speed of ignition for
- 3 - LD 7766
prim~r materials which can be applied from an aqueous
liquid suspension~ ,
It is another desirable objective to improve
the stability of primer materials used in said flash
lamps so that the flash lamps are less prone -to prematur~
ignition from either mechanical vibration or electros~atic
charges.
SUMMARY OF THE INVENTION
_.
An improved primer material has now been
discovered which can be applied reliably as a coating for
the lead-in conductors of an electrical-ignition flashcube
type flash lamp from a water-based suspension having none
o the foregoing drawbacks. Specifically, it has been
ound tha~ incorporation of a hygroscopic agent ;n the
aqueous suspension of said primer material provides a
dried product con~a.ining sa.id additive which ignites more
rapidly and is also less prone to premature ignition than
when a primer material no~ containing said addi-tive has
been deposited from an organic liquid suspension. The
primer material havi~g the desired characteristics compxise~
a mixture of powdered zirconium fuel, a polymer binder, an
oxidizer for said fuel selected from an alkali metal chlorate
ox pe~chlorate compound, a com~ustion-supporting oxide, and
said hygroscopic additive. In its preferred embodiments,
the primer material utilizes a combustion-supporting oxide
selected from cobalt oxide, barium chromate, 'ron oxide,
and higher oxides of nickel to avoid any electrical short-
circuited condition in the lamp ater Elashing created by
a conductive primer residue. An alkali metal chlorate
compound is also preferred as the oxidizer in the present
primer material by xeason of being water-soluble to provide
more uniform distribution in the dri.ed primer ignition mass
than an alkali metal perchlorate compound which is les~
water-soluble. In said preferred dried primer mixtures,
the proportion of oxidizer is approxi.mately 4-12% by
35~
4 - LD 7766
weight with the hygroscopic agent also being present in
the same weight range (4-12%). Polyvinyl alcohol and
polyvinyl pyrrolidone are preferred organîc binders ~or
the aqueous coating composition since both provide a
S tough and adherent coating of the dried primer mass in
the flash lamp.
A suitable hygroscopic agent can be selected
from a wide variety of known materials which absorb water
without becoming liquified. More particularly, said
hygroscopic additive must be capable of preferentially
absorbing mois~ure from the fuel and oxidizer constituents
in the deposited mixture after drying to enhance ~he speed
of primer igni~ion. Rnown hygroscopic addi~ives include
such diverse materials as cobaltous cobaltic cyanide,
boric oxide, and calcium sulfate which all can be
distributed uniformly in the present aqueous primer
suspensions ei-~her as a powdered solid or dissolvsd in
said suspensions~ The preferred hygroscopic additive is
cobaltous cobaltic cyanide since said material may provide
a source of combustion supportin~ oxide when the primer is
ignited and thereby support more thorough and rapid combustion.
BRIEF DESCRIPTION OF THE DRAWING
In the accompanying drawing, the single figure
represents a cross section view partly in elevation of a
preferred flash lamp utilizing the present invention~
DESCRIPT~ON OF THE PRRFERRED EMBODIMENTS
A preferred flash lamp construction is depicted
compr.ising a glass bulb or envelope 1 which is shown may
be formed of a short lengthened glass tubing, for example,
about 0.340 inch outside diameter which is constricted and
rounded off at one end as indicated at 2 and closed off
thereof by an exhaust tube 3 and is ~ormed at the other
or base end 4 with a stem press base. A flashcube type
lamp having this general conEigurat.ion and in commercial
production is the previously rPferenced AG-l which
- 5 - LD 7766
produces approximately 7,000 lumen-seconds light output
for a 1.1 cubic centimeter internal volume The lead-in
wires 6 are sealed in opposi-te corners 7 of the stem press
base which provides a longer path length of the in-leads
through the lamp envelope and less likelihood o~ leakage
or loss o a hermetic seal~ The glass and metal in-lead
compositions ~or said flash lamp are dictated by the
desired ligh~ output characteristics and some high
performance flash lamps utilize a borosilicate glass in
combination with alloy in-leads of iron, nickel, and
cobalt. The inner ends of said in-leads axe coated with
the primer material 8 and have an electrical filament 9
connected therebetween. This filament is a re~ractory
metal such as tungsten or a tungsten alloy. A quantity
of ~ilamentary combustible material 10 such as a shredded
foil of zirconium or hafnium, for example, is distributed
within the interior space of the envelope 1 which also
contains a ~illin~ of a suitable combustion supporting
gas such as o~ygen, generally a-t high pressures in excess
of several atmospheres.
The solid coating of primer material in the above
embodiment is applied to the lead-in conductors from an
aqueous suspension of the present invention in various
known ways. For example, the in-lead members can be
dipped into the aqueous slurry followed by drying in air
or wi-th heat to remove the liquid and form a solid adherent
coating having the desired characteristics above de~cribed.
Alterna~.ely, the aqueous slurry can be sprayed on the in-lead
members and thareafter processed to provide a solid coating
exhibi~ing comparable performance.
AS an example of a suitable aqueous coating
composition, there is initially prepared the fuel portion
of said primer mixture as an aqueous suspension containing
80 parts milled zirconium, 10 parts barium chromate, 10
parts cobalt oxide, 5 parts cobaltous cohaltic cyanide,
3s~
~ 6 ~ I,D 7766
and ~ pa:rts polyvinyl pyrrolidone binder. To said aqueous
fuel suspension there is added with mixing an aqueous
oxidizer solution of sodium chlorate in various amounts
so that the dried primer ml~ture cont~ins from 4-12
percent ox.idi~er by weight. ~ solid coating of sa.id
primer material .is applied to both in-leads of the above
type lamp construction in the conventional manner.
Performance tests were conducted on -the above
described flash lamp embodiments to evaluate the
effectiveness of the hygroscopic additive in providing
light output improvement. Spec.iicallyt flash lamps
utilizing a water~based primer containing said hygroscopic
~dditive were ~lashed for comparison with flash lamp
performance when said additive was not used and :~urther
compared with flash lamp performance when the same la-tter
primer solids had been deposlted from a conventi.onal
organic liquid suspension. Sample lo-ts o~ 50 lamps were
flashed duriny said performance tests by application of
an electrical pulse of 1.5 volts and 0.8 ampere during a
~0 0.7 second time interval. The sample lot of flash lamps
using primer not containlng said hygroscopic additive
and deposited ~rom an amyl aceta-te liquid susper.sion
demonstrated a 76% flashabili-ty rate. The flashability
rate of :Lamps utilizing the water-based primer suspensions
is reported in the table below for various oxidizer
levels in the primer mixture.
Flashahility o~ Flashability of
Oxiclizer Content Primer with 5% Primer without
(B~ We.ight) _ Additive (By Weight~ Additive
5% 96% 78%
7~ 84% 72%
9~ ~2~ 72~
'rhe above tes-t results demonstrate an average increase in
lamp flashability from 74% to 91% at the indicated test
condi.tions when said water-based primer materials contain
ci8
- 7 - I.D 7766
cobaltic cobaltous cyanide addi-tive, Further observations
conducted during flash lamp manufacture with said water-
based primers indicated a significant reduction in
premature flashing from mechanical vibration and elec-tro-
static discharge as compared with lamp manufactura usingsaid conven-tional amyl acetate primer suspension.
It follows from the foregoing disclosure that
various changes and modifications may be made in the
above described improved primer material without departing
from ~he spirit and scope of the invention. For example,
it will be apparent that other fuel compositions can be
employed in said primer mixture, such as red phosphorus
to still provide comparable electrical ignition charac-
teristics. Additionally, it is contemplated to vary the
weight proportions of the specific cons-tituents in the
primer mix-ture above specifically disclosed depending
upon the performance requirements desired in a particular
flash lamp construction with respect to light OUtpllt level
and flash duration, Consequentlyl it is intended to limit
the presen~ invention, therefore, only by the scope of the
following claims.
