Note: Descriptions are shown in the official language in which they were submitted.
CA 02294877 2004-O1-08
CONDUCTIVE PRIMER MIX
BACKGROUND OF THE INVENTION
Ammunition for small arms is typically actuated with the aid of
a primer, which initiates the principle charge in the cartridge. Typically,
these
primers have been initiated by the impact of a firing pin. With the increasing
use of electronic firing systems, development has been directed to priming
mixtures that are suitable for use in small arms, and provide the desired
combination of reliable initiation and insensitivity to stray electrical
charges.
Typically, electrically ignitable primers have been initiated by exploding
bridge wires or hot wires in combination with a semi-conductive mixture, a
pyrotechnic mix or conductive mix. Such electrically ignitable primers have
been previously used in military applications for high speed firing of large
caliber ordnance, in blasting for mining operations, for automotive crash bag
initiation and inflation, seismic guns, kiln guns and pyrotechnic displays.
However, a continuing need exists for a simple and reliable priming system
that would be suitable for small arms such as rifles, pistols and shotguns.
SUMMARY OF THE INVENTION
The present invention provides an electrically ignitable primer
mixture which is suitable for use in small arms ammunition and provides a
desirable combination of safety and reliable initiation.
Specifically, the instant invention provides an electrically
ignitable primer mixture comprising about from 30 to 40% lead styphnate;
about from 4 to 12 % antimony sulfide; about from 40 to SS% barium nitrate;
about from 4 to 8% aluminum; about from 0.5 to 2% carbon black and up to
1% binder, wherein an electrically ignitable small arms primer mixture
comprising about from 30 to 40% lead styphnate; about from 4 to 12%
antimony sulfide; about 40 to 55% barium nitrate; about from 4 to 8%
aluminum; about from 0.5 to 2% carbon black and up to about 1/% binder, and
wherein the mixture is substantially free from tetrazene.
CA 02294877 2000-O1-OS
WO 99/02470 PCT/US97/11441
2
DETAILED DESCRIPTION OF THE INVENTION
The present invention is based on the discovery that mixtures of
the indicated components, in the specified quantities, are insensitive to low
voltage initiation but at higher voltages provide reliable initiation of the
lead
styphnate which is a principal explosive component of the mixtures.
Lead styphnate should be present in a quantity of at least about
30% by weight of the formulation. In general, little additional benefit is
gained
by the incorporation of more than about 40% lead styphnate.
Antimony sulfide is used in the present formulations as a fuel. It
is used to tailor the desired shock or detonation velocity, detonation
pressure and
output temperature. In general, at least about 4% of this component should be
present, while greater than about 12% provides little additional benefit to
the
present formulations.
With the present primer mixtures, tetrazene, normally used in
primer mixtures, can be substantially eliminated. This compound is also known
as tetracene, tetrazolyl, guanyltetrazene hydrate or tetrazene-1-carboxamidine-
4-
(1-H-tetrazol-5-yl)monohydrate. In general, less than about 5% of this
component is present in the present formulations. Less than about 2% is
preferred, and the substantial absence of tetrazene is especially preferred.
Barium nitrate is present in the present formulations in a
concentration of about from 40 to SS%. The function of the barium nitrate is
as
an oxidizer. The primer mix will generally not properly ignite at
concentrations
of less than about 40% by weight, while concentrations of the barium nitrate
greater than about SS weight percent will not exhibit satisfactory explosive
2~ propagation.
The present invention is based on the discovery that aluminum
can effectively provide a secondary electrical path that assists in the
prevention
of low voltage initiation. The aluminum should be present in quantities of
about
CA 02294877 2000-O1-OS
WO 99/02470 PCT/US97/11441
3
from 4 to 8%. The aluminum used is typically in fine particulate form, having
a
particle size of about from 5 to 40 micrometers. This particle size passes a
325
mesh sieve.
The present formulations contain about from 0.5 to 2% carbon
S black. The presence of carbon black, together with the aluminum, aids in
providing secondary electrical paths to prevent or minimize low voltage
initiation. A wide variety of carbon blacks can be used in the present
invention.
Carbon blacks are crystallographically related to semiconductors. They are
usually described and categorized by their method of manufacture. For
example, lamp black is the soot formed in the glass chimney of a lamp, while
acetylene black is formed by oxygen deficient reduction of acetylene. Each
method of manufacture gives somewhat different crystalline structure to the
carbon black. Different structures are useful for specific applications. A
carbon
black used for pigment should have good light reflection characteristics,
while a
carbon black used for absorption matrix should have many small pores. An
electrically conductive carbon black also requires special characteristics,
such as
particle size and volatile content. A higher degree of electrical conductivity
is
achieved with higher surface area, higher structure, and lower volatile
content.
Higher surface area is attained by forming a particle with many pores, and
higher structure means that the carbon particles are aggregated to a
significant
extent. A lower volatile content results in fewer chemisorbed oxygen complexes
on the surface of the particles. This chemisorbed oxygen can act as an
insulator
making the carbon black less conductive. A volatile content of less than about
5%, and especially less than about 2%, is preferred.
The degree to which the carbon black is electrically conductive
also depends on the network formed by the carbon atom aggregates in their
surrounding matrix. The electron path flow is facilitated by aggregate contact
and small separation distances between aggregates. The more contact between
CA 02294877 2000-O1-OS
WO 99/02470 PCT/US97/11441
4
aggregates, the closer the aggregates are, the better the electron flow.
Furnace
black is preferred in the present invention. Acetylene blacks used in large
caliber military electric primers generally lack the electrical
characteristics
required by small arms firing systems. Pigment carbon blacks typically lack
the
conductivity required for small arm primers. The particle size of the carbon
black is preferably about from 10 to 30 nanometers. The surface area of a
carbon black is typically measured as nitrogen surface area, according to
ASTM-D-3037. Nitrogen surface areas of greater than about 1000 m2/g have
been found to be satisfactory. A particularly preferred carbon black is that
having a nitrogen surface area of about 1475 rn2/g.
The primer composition of the present invention can further
contain up to about 1 % binder to minimize dusting. Typically, at least about
0.5% by weight is used. Binders which can be used can be selected from a
variety of gums, such as gum arabics, and particularly gum arabic (acacia), as
well as polyvinyl alcohol with guar gum. However, gum arabic has been found
to be particularly satisfactory. The particular binder used will be selected
for
maximum compatibility with the explosive formulation prepared.
The indicated components can be combined by the use of
standard low shear mixers, using customary techniques for blending explosives.
With these techniques, the explosive components are generally blended first,
followed by the fuels, and finally the oxidizer components.
The primer mixtures of the present invention generally initiate at
a direct current of 100 volts or less. The mixtures exhibit reduced impact
sensitivity compared to normal primer mixtures, primarily resulting from the
reduction or elimination of tetrazene from the mixture. The present invention
is
further illustrated by the following specific examples, in which parts and
percentages are by weight unless otherwise indicated.
CA 02294877 2000-O1-OS
WO 99/02470 PCT/US97/11441
EXAMPLES 1- 4 AND COMPARATIVE EXAMPLE A
Primer mixtures were formulated from the components and in the
quantities indicated in Table I. These formulations were evaluated using a
computer data base to determine the characteristics for optimum initiations of
propellant, approximating a standard percussion priming mixture. The results
are summarized in the table, together with parallel calculations for
Comparative
Example A, which is a lead styphnate primer mix currently used in the
commercial production of percussion primers.
CA 02294877 2000-O1-OS
WO 99/02470 PCT/US97/11441
6
a
a~ o
a
G
~"
~
~
N
,o o
.
o
v
N
M M 01
M .-Nr ~ ~ t~ O O C~ V1 ~ N
4 .-r
a
~o°or°NOv
M N ~ M O~ 00
!t M N O N V7 .-i p ~ ~ N . ~-~
..r
H
O~V~10~ON
M ~ \G .--a ....~
M M 00 O i0 V~ "' O v7 M N .-.
H
M O N O ~p
eIWO .-r l~ ..r
O M o0 O .-r
N c'M~1 .M.~ p ~ ~ ~-r p N ~ N ~'
N O ~O ~O l~
O O O ~D
O 00 00 p .r
~ O ~t n .-~ p h ~ N "',"
~t' .
O _
~
r
g
~
r- .SE ' ~'' r.~.per,
>,
t3'
~
O
' . a
~
.b ~ ~ T! O '
.... w ~ f~ w
oHw
a ~ ~~ y~~' ~ ,'~ ~~
~ ~
o.o
, . o
~
W ~ ~
a H ~ c7 U v A ~
m ~
~
CA 02294877 2000-O1-OS
WO 99/02470 PCT/US97/11441
7
The primer mix of Example 4 was tested ballistically in two
metal primer cartridges. In the design used in Example 4A, the conduction path
was from a conductive center post through the mix and into the side wall of
the
S primer cup, which was attached to ground. In the second design, used in
Example 4B, the conduction path was from the primer cup through the mix and
into an annular post which was attached to ground. The ballistic results of
firing
this mix are as follows:
Loaded in 22-250 REM SS gr PSP 4A 4B
Velocity, ambient (fps) 3,564 3,599 Spec: 3,650fps+/-35
Pressure, ambient (psi) 57,400 58,300 Spec: 60,000 psi
maximum
