An improved pyrotechnic cap capable of being activated by the radiant
energy from an adjacent flashlamp. The cap includes a plastic container
with a quantity of pyrotechnic composition hermetically sealed therein.
Receipt of the described radiant energy causes activation of the
composition whereby the cap produces an audible signal of high intensity
(e.g. 158 to 164 decibels at 25 centimeters). The improvement comprises
adding a desiccant material within the cap's container atop the
pyrotechnic composition to absorb any quantities of moisture which
might enter the container and adversely affect the cap's operability.
1. In a pyrotechnic cap for providing an audible signal of high
intensity upon receipt of energy in the form of light and/or heat
from a flashlamp wherein said cap includes a plastic container having
a pyrotechnic composition hermetically sealed therein separately
from said flashlamp, the improvement wherein said container further
includes a quantity of a nondeliquescent desiccating material therein,
said material located adjacent said pyrotechnic composition.
2. The improvement according to claim 1 wherein said desiccating
material is selected from the group consisting of activated alumina,
molecular sieves, and silica gels.
3. The improvement according to claim 1 wherein said desiccating
material is a hydrate-forming salt.
4. The improvement according to claim 4 wherein said hydrate-forming
salt is selected from the group consisting of anhydrous calcium
sulfate and magnesium sulfate.
5. The improvement according to claim 1 wherein said desiccating
material is selected from the group consisting of barium oxide,
calcium oxide, and strontium oxide.
6. The improvement according to claim 1 wherein said desiccating
material is a powder.
7. The improvement according to claim 1 wherein said desiccating
material is in pellet form.
8. The improvement according to claim 1 further including a paper
disc within said container, said desiccating material impregnated
within said disc.
CROSS-REFERENCE TO COPENDING APPLICATIONS
An application under Ser. No. 2263 was filed Jan. 10 1979. Ser.
No. 2263 entitled "Heat-Sealed Pyrotechnic Cap and Method
of Making" (Inventors: A. C. Bouchard et al), describes a method
for providing a hermetic seal in the end of a plastic cap containing
a quantity of radiant energy activated pyrotechnic material therein.
The formed cap may include a nonreactive filler located therein
separate from and atop the pyrotechnic material to serve as a support
for the sealed end.
An application under Ser. No. 2264 was also filed Jan. 10 1979.
Ser. No. 2264 entitled "Pyrotechnic Cap With Mechanically
Desensitized Composition" (Inventors: T. L. Gavenonis et al),
defines a cap wherein the pyrotechnic composition includes a quantity
of desensitizing material which serves to substantially decrease
the cap's sensitivity to ingition by mechanical impact.
An application under Ser. No. 2272 entitled "Pyrotechnic
Cap With Moisture Indicator" (Inventors: A. C. Bouchard et
al) was also filed Jan. 10 1979. In Ser. No. 2272 a pyrotechnic
cap is provided with a changing member to indicate the presence
of moisture within the cap's container.
In addition to the above, an application entitled "Flashlamp
Assembly For Providing Highly Intense Audible and Visual Signals"
(Inventors: A. C. Bourchard et al) was filed June. 6 1977 and is
now U.S. Pat. No. 4130082. U.S. Pat. No. 4130082 describes a
hermetically sealed pyrotechnic cap adapted for being activated
by the light and/or heat from a chemical flashlamp. U.S. Pat. No.
4130082 is assigned to the same assignee as the instant invention,
as are the aforementioned copending applications.
BACKGROUND OF THE INVENTION
The invention relates to pyrotechnic caps and particularly to hermetically-sealed
pyrotechnic caps capable of being activated by radiant energy in
the form of light and/or heat.
In the aforementioned U.S. Pat. No. 4103082 there is described
a unique concept in the production of substantially simultaneous,
high intensity audible and visual signals. As described in U.S.
Pat. No. 4130082 it has been discovered that hermetically sealed
plastic caps having a pyrotechnic composition therein can be instantaneously
activated by the highly intense light and/or heat from an adjacent
flashlamp to produce an audible signal also of high intensity (e.g.
approaching 165 decibels). The preferred activating flashlamps are
those presently utilized in the photoflash products manufactured
and sold by the assignee of the instant invention under the name
MAGICUBE. As also described in U.S. Pat. No. 4130082 it is possible
to activate the sealed caps using other varieties of flashlamps
such as those which are electrically activated. One example of this
latter type are the flashlamps currently utilized in the photoflash
products manufactured and sold by the assignee of the instant invention
under the name FLIP-FLASH.
A primary use for the device in U.S. Pat. No. 4120082 is an intrusion
alarm. The device may also comprise part of an alarm system wherein
a suitable detector is used to receive the device's output and thereafter
perform an auxillary function (e.g. emit a prolonged, high intensity
signal). Quite understandably, devices such as alarm systems must
possess a high degree of reliability. Accordingly, it is essential
that the cap member which comprises an integral part of the device
must also possess a similar functioning capability.
It has been determined that the presence of moisture within the
cap, even in relatively minor quantities, can adversely affect both
the cap's reliability and the loudness of the emitted audible signal.
This moisture may enter the cap either during manufacture thereof
or subsequent to said manufacture by penetration of a defective
It is also known that water vapor is capable of permeating the
polymeric side walls of the cap's container upon prolonged exposure
of the cap to extreme conditions of high temperature and humidity.
It is believed, therefore, that a pyrotechnic cap member capable
of compensating for the presence of moisture therein to thereby
assure that the required functional reliability and loudness characteristics
of said member will be maintained would constitute a significant
advancement in the art.
OBJECTS AND SUMMARY OF THE INVENTION
It is, therefore, a primary object of the present invention to
provide a pyrotechnic cap capable of compensating for the presence
of moisture therein.
In accordance with one aspect of the invention, there is provided
an improved pyrotechnic cap which is capable of being activated
by the radiant energy from an adjacent flashlamp to in turn produce
an audible signal of high intensity. The improvement comprises adding
a desiccant within the sealed cap's plastic container adjacent the
pyrotechnic composition. The desiccant acts as a getter and prolongs
retention of the pyrotechnic composition in a dry, fully active
state, thereby benefiting both firing reliability and loudness.
BRIEF DESCRIPTION OF THE DRAWING
The drawing is an elevational view, in section, of a pyrotechnic
cap member in accordance with a preferred embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
For a better understanding of the present invention together with
other and further objects, advantages, and capabilities thereof,
reference is made to the following disclosure and appended claims
in connection with the above-described drawing.
With particular reference to the drawing, there is shown a pyrotechnic
cap member 10 which comprises a plastic container 11 which in crosssection
includes a base portion 13 at least two upstanding sides 15 and
a hermetically-sealed end portion 16. (One method of providing container
11 with a sealed end is disclosed in the copending application under
Ser. No. 2263). The plastic material for container 11 is a thermoplastic
preferably high density polyethylene. It is understood, however,
that other plastic could be used, including low density polyethylene,
polypropylene, polyvinyl chloride, polycarbonates, etc. The container
as shown is preferably cylindrical in configuration but could, of
course, assume other shapes, including rectangular, hexagonal, etc.
Cap 10 includes a quantity of pyrotechnic composition 17 which
is hermetically sealed within container 11. Examples of suitable
pyrotechnic materials for use in the invention are described in
the aforementioned U.S. Pat. No. 4130082. A preferred material
is one containing potassium chlorate, red phosphorous, manganese
dioxide, and a dispersing agent (to be further defined below). Pyrotechnic
materials known as "Armstrong's Mixtures" may also be
used with the present invention. These compositions typically include
potassium chlorate within the range of about 67 to 81 percent, phosphorous
from about 8 to 27 percent, sulfur from about 3 to 9 percent, and
precipitated chalk from about 3 to 11 percent. All of these percentages
are by weight of the material.
As an alternate embodiment, it may be desirable to use a pyrotechnic
mixture which emits a "whistling" or similar sound. Such
materials are well known in the art and may contain potassium chlorate,
potassium perchlorate, potassium nitrate, red gum, gallic acid,
potassium picrate, potassium benzoate, potassium dinitrophenate
and sodium salicylate. These formulations are shown on pages 376
and 377 of the book entitled "Military and Civilian Pyrotechnics"
by Dr. Herbert Ellern, copyright 1968 by The Chemical Publishing
Co., Inc. The aforementioned "Armstrong's Mixtures" are
defined on page 353 of this text.
The above nonwhistling materials assure an audible signal of high
intensity when the cap is activated by the energy from an adjacent
flashlamp. By high intensity is meant an output of above 85 decibels
measured at a distance of 25 centimeters. The preferred range when
cap 10 is utilized in the aforedescribed invention is from about
158 to about 164 decibels at this distance.
For toxicity consideration, compostions including red phosphorous
and potassium chlorate are preferred. One disadvantage of red phosphorous,
however, is that it possesses a tendency to prematurely degrade
when in the presence of even minor quantities of moisture, particularly
in the presence of traces of degradation-catalyzing metals such
as iron and copper. These metals may be found in even the most purified
commercial grades of red phosphorous. The end result of such degradation
is that the cap's ability to be activated by absorbed radiant energy,
as well as the rate of burning of the member upon said activation,
is adversely affected. Burning rate, in turn, affects the level
and uniformity of the generated audible signal. Furthermore, the
presence of excessive amounts of moisture can result in the cap
becoming totally inoperable for the purpose defined.
The present invention substantially eliminates the above deleterious
effects. It has been found, quite unexpectedly, that the addition
of a quantity of desiccating material 19 to the cap before sealing
the plastic container substantially enhances the operability of
the finished product by improving the cap's reliability and assuring
uniformity of loudness of the emitted signal. And these features
are provided without an adverse affect on the cap's ability to respond
to the activating radiant energy. Material 19 is located above the
pyrotechnic composition and adjacent thereto. As such, material
19 is also located immediately adjacent the cap's sealed end 16.
It is important that desiccant material 19 be nondeliquescent;
that is, it must not gradually dissolve or become liquid as a result
of its attraction and absorption of moisture. Accordingly, a material
such as calcium chloride would not prove suitable.
The preferred desiccant for use in the instant invention is a material
having a high internal absorbing surface area. Of these, the most
preferred is activated alumina. To caps containing approximately
eleven milligrams of one of the above pyrotechnic compositions,
quantities ranging from about 1 to 20 milligrams of activated alumina
powder were added prior to cap sealing. Other suitable materials
of the above variety include silica gel and molecular sieves, both
preferably, in powdered form. A preferred molecular sieve may be
purchased from the Union Carbide Corporation, New York, N.Y. under
the product number 3A. This material is available in powder form
(600 mesh) and as pellets (0.0625 and 0.125 diameter).
It is further possible in the invention to use hydrate-forming
salts as the desiccant. Of these, anhydrous calcium sulfate and
magnesium sulfate are preferred. Reactive desiccants which undergo
chemical reaction with moisture may be used. Suitable examples include
the oxides of calcium, strontium, and barium.
The desiccant may be incorporated within cap member 10 in the form
of a powder (as described) or a pellet. It is also possible to utilize
a disc of desiccant-impregnated paper. In either event, the desiccant
is added to the cap after the pyrotechnic composition has been deposited
therein. This composition is usually deposited in slurry form and
thereafter dried. Understandably, the desiccant would not be added
until the pyrotechnic composition had assumed a completely dry state.
There has thus been described a substantially improved pyrotechnic
cap capable of being activated by the intense light from an adjacent
flash-lamp. The improvement constitutes the addition of a desiccating
material to the cap's container adjacent the desired pyrotechnic
composition. The addition of such material substantially assures
prevention of pyrotechnic composition degradation in high humidity
environments without adversely affecting the degree of uniformity
of the cap's audible signal. The desiccant material also does not
adversely affect the ability of the sealed cap to receive the requisite,
activating radiant energy.
While there have been shown and described what are at present considered
the preferred embodiments of the invention, it will be obvious to
those skilled in the art that various changes and modifications
may be made therein without departing from the scope of the invention
as defined by the appended claims.