Note: Descriptions are shown in the official language in which they were submitted.
~ ~34~
TRACERS, A PROCESS FOR PRODUCING SAME
AND THEIR USE FOR LABELLING EXPLOSIVES
The present invention relates to tracers,
more particularly to those for labelling explosives,
which tracers enable the identification of the mate-
rial in use with respect to its origin and composit-
ion, and possibly to the date of production as well,
by way of microanalytical methods. The invention
further relates to the process for producing said
tracers and to the use thereof, more particularly
for labelling explosives.
An increasing incidence of embezzlement and
unauthorized use of explosives has entailed a need
for means of unambigously identifying the origin,
type, and, possibly, date of production of explosi-
ves. This need has already resulted in legal regula-
tions; cf. Verordnung uber explosionsgefahrliche
Stoffe vom 26.3.1980 of the Swiss Bundesrat, article
5, sentence 3, which reads: "The explosive must con-
tain a tracer which enables its origin to be safely
determined even after an explosion. The tracer is
required to be given permission by the Central Agen-
cy, which has to take changes in the circumstances
into account"O
)9;~41
Only one such tracer has so far been offered
for sale. Said tracer is a product of the firm of
3 M, which product consists of a laminate composed
of 9 layers of a melamine resin. Various materials
such as a fluorescent pigment, dyes, and a magnetic
materials are incorporated in the 9 layers of the
melamine resin. There is to be assumed that films or
sheets are first produced, which are subsequently
crushed and ground. A product of this kind, for ex-
ample, has been described in the U.S. Patent Speci-
fication No. 4,053,433.
There has been known from the U.S. Patent
Specification No. 3,772,200 and from the correspond-
ing German Patent Specification 2 343 774 to blend
and melt into a glass composition four different
elements, mostly rare elements, mainly in the forms
of the oxides thereof, and to prepare spherical
glass micro-beads from said whole melt mix by way of
conventional methods. Though said products will
survive the explosion of the explosives, they can be
retrieved and separated from the explosion debris
only with great difficulties. An alleged improvement
has been described in the U.S. Patent Specification
No. 3,897,284, in which a non-tacky organic sub-
stance having a melting point in excess of 60C is
to be used. The improvement has been reported to
particularly reside in that the products having thus
been obtained are better compatible with an explo-
sive and do not tend to increase the sensitivity
thereof, as small glass beads do. In the examples,
extremely low molecular weight polyethylenes, par-
affin waxes or epoxy resins have been exclusively
- ~zog34~
used as the non-tacky organic substances,
since it has only been possible by using said sub-
stances to obtain a powder material after the metal
oxides have been incorporated, which powder is re-
quired to be susequently prepared. In all of the
examples, the powder material was obtained by spray
drying. However, spray drying is only applicable to
organic substances having an extremely low viscosity
at the temperatures as employed. The products having
been thus obtained, in turn, have obviously not been
usable in practice and have not led to any commer-
cial products.
Other tracers that have been processed to
give particles by aid of an potassium silicate bin-
der, and, optionally, have also been encased by a
thin polyethylene layer, have been known from the
U.S. Patent Specifications No. 4,131,064 and No.
4,197,104. In addition, attempts have been made to
obtain products having different Curie points by
adding various ferrites. Apparently, said products
also adversely affected the stability and storabi-
lity of the explosives. Furthermore, it appears that
the code to a higher or lesser degree has been
changed by the varying influences of different
temperatures in the course of the explosion, so that
an unambiguous decodification has not been possible
any more. From the U.S. Patent Specifications N.
3,961,106 and 3,967,990, there has been known to
coat the above-mentioned tracers with a thin layer
of low molecular weight polyethylene or wax in order
to increase the compatibility thereof with the ex-
plosive. Ilowever, such products apparently have also
`~34~
-- '1 --
not been capable of meeting all of the requirements
for a practical application.
A tracer will have to meet the following
standards in order to comply with all of the requi-
rements:
a) The tracer must remain unchanged in the
explosive for years. It must not act to destabilize
the explosive or change its composition.
b) The tracer must survive the explosion
and stay at the location of the explosion.
c) The tracer must be retrievable in and
separable from the other explosion debris and sus-
ceptible of being unambiguously analyzed.
d) The tracer must consist of a system
having a very high variability and, at the same
time, contain compounds which, at least in the com-
bination used, are not found in the environment.
e) The tracer must be readily and unambi-
guously analysable by microanalysis.
f) The tracer must be stable against water
and conventional solvents.
The abovementioned product of the firm of
3 M in part meets said standards, while it does,
however, due to the complicated process of its pro-
duction, substantially increase the costs the explo-
sive.
It is the object of the present invention to
provide a tracer, which meets all of the abovemen-
tioned standards set as the requirements for the use
as a tracer for explosives.
~ g3~:~
-- 5 --
It has now been found that, surprisingly,
hi.gh molecular weight synthetic materials having a
low water absorption capacity, a high specific heat
capacity, a low thermal conductivity, and a low spe-
cific gravity, more specifical.ly synthetic materials
selected from the group consisting of polyethylenes,
polypropylenes, polyamides, polycarbonates, poly-
esters, polyoxymethylenes and acrylonitrile-buta-
diene-styrene copolymers, which materials are suit-
able to thermoplastically processed, are capable of
including
a) at least 1 per cent by weight of iron
powder and/or powder of a ferromagnetic alloy and at
least two of the following groups of substances:
b) fluorescent pigments;
c) organic solvent-soluble, water-inso-
luble fluorescent materials;
d) colorant pigments;
e) sparingly soluble and heat-stable
oxides and/or salts of rarer metals;
f) oxides and/or sparingly soluble salts
of rare-earth metals in microanalytically well de-
tectable amounts;
so that a homogeneous mixture is formed to give a
tracer having excellent properties.
It is a matter of course that such synthetic
materials containing ingredients are no longer sus-
ceptible of being powderized by spray-drying, while,
however, they can be granulated and ground after the
melt has been cooled. The products having thus been
obtained meet all of the aforementioned requirements
~2Q9,3.~
6 --
set for a good tracer. The particle size of the
tracers upon grinding is preferably from 100 to
1200 ~m.
According to the present invention, it is
essential that the synthetic materials to be used
have a
high molecular weight and are thermoplastically pro-
cessable and, at the same time, have a low water
absorption capacity, a high specific heat capacity,
a low thermal conductivity, and a low specific gra-
vity.
The process for producing a tracer according
to the present invention, which tracer contains,
homogeneously mixed into a thermoplastic material,
a) at least 1 per cent by weight of iron
powder and/or powder of a ferromagnetic alloy and at
least two of the following groups of substances:
b) fluorescent pigments;
c) organic solvent-soluble, water-inso-
luble fluorescent materials;
d) .colorant pigments,
e) sparingly soluble and heat-stable
oxides and/or salts of rarer metals;
f) oxides and/or sparingly soluble salts
of rare-earth metals;
in microanalytically well detectable amounts
is characterized in that a high molecular weight
synthetic material having a low water absorption
capacity, a high specific heat capacity, a low ther-
mal conductivity, and a low specific gravity, more
specifically a synthetic material selected from the
41
-- 7
group consisting of polyethylenes, polypropylenes,
polyamides, polycarbonates, polyesters, polyoxyme-
thylenes and acrylonitrile-butadiene-styrene copoly-
mers, is used as the thermoplastically processable
material, and the substances a) to f) are introduced
into the melt thereof, followed by thorough mixing
to form a homogeneous mixture and granulating and
grinding said mixture.
The iron powder and/or powder of ferromagne-
tic alloys must be present in amounts of at least
1 % so that the tracer may be recovered from the
explosion debris by means of magnets. Generally,
amounts of from 3 to 20 % by weight are employed.
Amounts of 5 to 12 % by weight have proven to be
most suitable.
In order to enable the products to be unam-
biguously coded and decoded, at least two of the
groups of substances consisting of fluorescent pig-
ments, fluorescent materials, color pigments, oxides
and/or salts of rarer metals, and oxides and/or spa-
ringly soluble salts of rare-earth metals must be
present. The more different groups of substances are
employed, the higher is the variability, and the
higher is the possibility of readily obtaining an
unambiguous assignment to producer, date of product-
ion, and composition of the explosive~ The substance
groups in the tracers according to the invention are
to be present in the following amounts to ensure
that the substances are microanalytically well de-
terminable:
1;209~
-- 8
b) Fluorescent pigments in amounts of from
0.1 to 8 % by weight and preferably from 2 to 5 % by
weight.
c) Fluorescent materials in amounts of
from 0.1 to 5 % by weight and preferably from 1 to
3 % by weight.
d) Color pigments in amounts of from 0.5
to 8 % by weight and preferably from 1 to 5 % by
weight.
e) Oxides and/or salts of rarer metals in
amounts of from 0.5 to 8 % by weight and preferably
from 1 to 5 % by weight.
f) Oxides and/or salts of rare-earth ele-
ments in amounts of from 0.5 to 5 % by weight and
preferably from 1 to 3 % by weight.
The fluorescent pigments are to be insoluble
in water and organic solvents, while the fluorescent
materials are to be insoluble in water, but soluble
in organic solvents. Both groups of substances may
thereby réadily be separated and analytically deter-
mined independently of each other. Th'e color pig-
ments, oxides and/or salts of rarer metals, and oxi-
des and/or salts of rare earth elements are to be
insoluble in water and organic solvents as well, so
that they in any case remain in the residue and may
side by side be subject to an unambiguous analytical
determination.
The various groups of substances must be
introduced into the melt of the polymers and tho-
roughly admixed in order to obtain a homogeneous
distribution thereof in the tracer according to the
~209a~ -
---d ~-
_ 9 _
invention. Mixers which effect extremely good shear-
ing and kneading have proven to serve that purpose,
while single-screw extruders are not suitable.
Double-screw extruders are suitable in the case that
they exert high shear forces. For example, the
double-screw kneader of the ZSK type made by the
firm of Werner & Pfleiderer, Stuttgart, Fed. Rep. of
Germany, is reliable. The forced circulation mixer
of the Banbury type appears to be suitable either.
The homogeneous mixtures are then granulated. The
granules are preferred to have an edge length of
from 2 to 6 mm. Said granules may be ground without
dificulties to give powders having a particle size
of from 100 to 1200 ~m. It is desirable to obtain
relatively narrow particle size distributions, as
particles having the same size will behave more uni-
formly under the conditions of the explosion than
will particles with a wide particle size distribut-
ion. If the edge length of the granules is in excess
of 6 mm, tracers having a relatively wide particle
size distribution are obtained from the grinding
procedure, which is particularly undesirable when
explosives are to be labelled. With explosives, op-
timum results have been obtained by using tracers
having particle sizes as uniform as possible within
the range of 200 to 600 ~m. If desired, those parti-
cles having particularly high and low edge lengths
may be separated by sieving, whereby a narrow parti-
cle size distribution may be obtained. Moreover, the
optimum particle size distribution may to some ex-
tent depend on the nature of the explosive to be
-- 10 --
labelled, as the tracers and the respective explosi-
ves should be mixed such as to give a mixture which
is as homogeneous as possible.
High molecular weight polymers, which are
thermoplastically processable and have a low water
absorption capacity, a high specific heat capacity,
a low thermal conductivity and a low specific gravi-
ty, which polymers have proven to be suitable for
the use according to the invention, especially in-
clude polyethylenes, polypropylenes, polyamides,
polycarbonates, polyesters, polyoxymethylenes, and
acrylonitrile/butadiene/styrene-copolymers. Said
polymers, without undergoing any decomposition, may
be homogeneously melt-blended with the groups of
substances which are analytically detectable. They
are as well suitable to preserve said substances
unchanged for a long period of time, thus enabling
the analytical determination thereof for the purpose
of decoding. Since the employed polymers have repro-
ducible thermal properties which may microanalyti-
cally be determined by differential thermal analy-
sis, said criteria may also be used for identificat-
ion and decodification. The molecular weight and/or
melt viscosity, respectively, of the polymer is not
critical as long as the polymer is thermoplastically
well processable and, at the same time, sufficiently
stable towards water and organic solvents at room
temperature. The high specific heat capacity and low
thermal conductivity protects the substances embed-
ded in the plastics from the action of the explosion
heat. The low specific weight allows the tracers
34~
according to the invention to be more easily separa-
ted from the explosion debris by means of liquids
having a suitable density.
The ferromagnetic particles do only serve
the purpose of separation and accumulation of the
tracers according to the invention from the explo-
sion debris, while they are not used for an analyti-
cal decodification, as has been mentioned. Iron pow-
ders having a maximum particle size of less than
60 ~lm have proven to be particularly suitable as the
ferromagnetic materials. Such iron powders having a
purity of 99.5 % are commercially available, for
example from the firm of Mannesmann-DEMAG, F.R. of
Germany, under the trade name of RZ 60. Basically,
all of the other ferromagnetic alloys may be taken
into account, in so far as they are available in the
form of powders. If said alloys contain relatively
rare alloying constituents, these may basically be
used for identification and decodification as well.
The substances which are included in the
tracers according to the invention are expected to
be stable against a short-term action of heat up to
from 200C to 300C. The fluorescent pigments to be
used may basically be any pigments that can unambi-
guously be distinguished from each other by their
fluorescence spectrum and their self-color. Examples
of suitable fluorescent pigments include the pig-
ments sold by the firm of Industrial Colours, Ltd.,
United Kingdom, under the trade names of FLARE 910
Orange, Green~ and Yellow, and the LUMILUX-C illumi-
nant pigments of the firm of Riedel-de Haën AG, Fed.
Rep. of Germany. The fluorescent materials to be
~o9~
- 12 -
used may basically be any of the fluorescent materi-
als which are soluble in organic solvents and may be
dissolved from the tracers by means of organic sol-
vents. The fluorescent materials are preferred to be
water-insoluble, so that they will not be premature-
ly dissolved from the tracers by the action of wa-
ter. Examples of suitable fluorescent materials in-
clude the products sold under the trade names of
UVITEX OB, UVITEX 127, and UVITEX OB-P by the firm
of Ciba, Switzerland, and under the trade names of
FLUOLITE XNR and FLUOLITE XMP by the firm of ICI,
United Kingdom. The color pigments to be used may be
any of the color pigments that are sufficiently in-
soluble and thermally stable and the emission spect-
rum of which is unambiguously identifiable. Suitable
color pigments are, e.g., Sicoplast Gelb 12-0190 and
Sicoplast Rot 32-0300, and, e.g., the pigments sold
~nder the trade name of Waxoline by ICI, United
Kingdom, which pigments have green, ruby-red, green,
and yellow colors.
As the sparingly soluble and heat-stable
oxides and/or salts of rarer metals, there may be
taken into account, for example, titanium dioxide,
copper oxide, zinc oxide, strontium carbonate, cad-
mium sulfide, antimony trioxide, barium sulfate,
lanthanum trioxide, and bismuth trioxide. As the
oxides and/or sparingly soluble salts of the rare-
earth metals, there are cerium(IV) oxide as well as
the other oxides and, optionally, the oxalates of
the lanthanoids, preferred to be considered. Besi-
des, sparingly soluble and heat-stable oxides and/or
salts of any metals may be used alone or in combina-
tions, if they may be unambiquously be identified by
, lZ0~
- 13 -
a microanalytical method, e.g. by X-ray fluorescence
spectrometry.
The tracers according to the invention are
basically suitable for labelling substances in order
to indicate their origin, composition and date of
production, if there is any serious interest to do
so. Such interest has been effective or will basic-
ally arise with respect to materials which may ad-
versely affect the safety of people. Thus, the tra-
cers according to the invention may especially be
used for the identifying powdery goods, the identi-
fiability of which as to type, producer, and date of
production is meaningful or important because of
safety requirements or criminological reasons. Said
problem has already gained a special importance in
the case of explosives. Therefore, the tracers ac-
cording to the invention are to be especially used
for labelling explosives.
Some typical embodiments of the tracers ac-
cording to the invention and the preparation thereof
are described in the following examples, to which
the present invention, however, is not limited. All
percentages therein are by weight.
- 14 -
EXAMPLE 1
15.2 kg of low-pressure polyethylene (76 %),
2.0 kg of iron powder (10 ~),
1.6 kg of fluoxescent pigment ( 8 %),
0.6 kg of cerium(IV) oxide ( 3 ~),
and 0.6 kg of antimony trioxide ( 3 %),
in the form of dry powders are charged into a fluid
mixer of the Henschel FM 7~ type, which has a volume
of 75 l and a revolution speed of 1,600 rpm, and are
mixed for 2 minutes. The mixture is filled into the
feed hopper of a twin-screw kneader of the Werner &
Pfleiderer ZSK 53 M 50*type and is homogenized with
a screw speed of 200 rpm at a mass temperature of
170C. The homogenized blend is discharged and gra-
nulated to give cylindrical granules having an edge
length of 4 mm, which granules are ground in a
grinding mill of the Pallmann PP8 type at a carrier
gas temperture of maximum 40C such as to give an
upper particle size limit of 630 ~m. The final tra-
cer has a particle size distribution ranging from 80
to 630 ~m, the average by weight value being 310 ~m.
The raw materials used were the commercially avail-
able materials set forth below:
Low pressure polyethylene powder
ELTEX A 4090 P having a particle size distribut-
ion range of from 30 to 900 ~m, a melt index
(2.16 Kp/lgOC) of 9 g/10 min and a density
(23C) of 0.953 g/cm3. ELTEX is a trade mark of
the firm of Solvay, Belgium.
* trade mark
3 ;~
.,' ~` :~.'
- lS -
Iron powder
RZ 60 having a maximum grain size of 60 ~m and a
purity of 99.5 %. RZ 60 is a trade mark of the
firm of Mannesmann-DEMAG, Fed. Rep. of Germany.
Fluorescent pigment
FLARE 910 orange 4, orange self-color. FLARE is a
trade mark of the firm of INDUSTRIAL COLOURS,
LTD., United Kingdom.
Cerium(IV) oxide
1~ A product of the firm of MERCK, Fed. Rep. of Ger-
many; purity 99.9 %.
Antimony trioxide
TIMONOX - WHITE STAR having a purity of 99 %.
TIMONOX - WHITE STAR is a trade mark of the firm
of ASSOCIATED LEAD Manufacturers, Ltd., United
Kingdom.
EXAMPLE 2
.
The following dry powdery components are
charged into a plow-type mixer of the Lodige FM 130
D type, which has a volume of 130 1 and a revolution
speed of the mixing tools of 1,000 rpm, and are mix-
ed for 4 minutes; the mixture is filled into the
feed hopper of a planetary roller extruder of the
Battenfeld-EKK PWE 100 EV* type, then homogenized
with a screw speed of 30 rpm at a mass temperature
of 145C~ discharged and granulated:
* trade mark
.~
~93~4~L
- 16 -
31.6 kg of high-pressure polyethylene (79 %),
4.0 kg of iron powder (10 %),
2.4 kg of fluorescent pigment ( 6 ~),
1.2 kg of lanthanum(III) oxide ( 3 %),
and 0.8 kg of titanium dioxide ( 2 %3.
The cylindrical granules thus obtained, which have
an edge length of 3 mm, are ground according to
examp]e 1 to have a final fineness of from 80 to
630 ~m.
The commercially available types of raw
materials as set forth below were used:
High-pressure polyethylene powder
Coathylene HO 2454, based on Lotrene IYD 0707,
having a particle size distribution range of from
80 to 630 ~m, a melt index (2.16 Kp/190C) of
7 g/10 min and a density (23C) o~ 0.924 g/cm3.
Coathylene is a trade name of the firm of Plast-
Labor SA, Switzerland, and Lotrene is a trade
name of the firm of CdF, France.
Iron powder
Corresponds to that of Example 1.
Fluorescent pigment
FLARE 910 yellow 27, yellow self-color. Supplier
as in Example 1.
Lanthanum(III) oxide
A product of the firm of MERCK, Fed. Rep. of Ger-
many; purity 99.9 ~.
~D9;~ !
Titanium dioxide
Kronos CL 220, having a purity of 92.5 %. Kronos
is a trade name of the firm of Kronos-Titan GmbH,
Fed. Rep. of Germany.
EXAMPLE 3
According to the process described in examp-
le, with the exception that the mass temperature in
the extruder is 195C, cylindrical granules having
an edge length of 5 mm are produced and ground to
have a final fineness of from 80 to 630 ~m according
to the procedure of example 1 from the following dry
powdery components:
15.4 kg of polypropylene (77 %),
2.0 kg of iron powder (10
1.4 kg of fluorescent pigment ( 7 %),
0.6 kg of yttrium(III) oxide
and 0.6 kg of zinc oxide
Polypropylene powder
Moplen FL V 20 having a particle size distribut-
ion range of from 40 to 450 ~m, a melt index
(2.16 Kp/190C) of 16 g/10 min and a density
(23C) of 0.90 g/cm3. Moplen is a trade name of
the firm of Montedison, Italy.
Iron powder
Corresponds to that of Example 1.
~20g~
- 18 -
Fluorescent pigment
FLARE 910 green 8, green self-color. Supplier as
in Example 1.
Yttrium(III) oxide
A product of the firm of MERCK, Fed. Rep. of Ger-
many; purity 99.9 %.
Zinc oxide
A product of the firm of Lehmann & Vos5, Fed.
Rep. of Germany; purity 99 %.
EXAMPLE 4
In an analogous manner to that of example 1,
the following components were blended, homogenized,
granulated and ground:
16.6 kg of high-pressure polyethylene (83 %),
2.0 kg of iron powder (10 %),
0.2 kg of fluorescent material ( 1 %),
0.6 kg of color pigment ( 3 %),
and 0.6 kg of strontium stearate ( 3 %).
The commercially available types of raw
materials as set forth below were used:
High-pressure polyethylene powder
as in Example 2.
Iron powder
as in Example 1.
læ~a34~
-- 19 --
Fluorescent material
Uvitex OB, no self-color, but blue fluorescence
at 435 nm (maximum wavelength). Uvitex is a brand
name of the firm of Ciba-Geigy AG, Switzerland.
Color pigment
Sicoplast-Gelb 12-0190 having yellow self-color,
comprising cadmium-zinc sulfide. Sicoplast is a
brand name of the firm of BASF, Fed. Rep. of Ger-
many.
Strontium stearate
A product of the firm of Barlocher AG, Fed. Rep.
of Germany; purity 98 %).
EXAMPLE 5
Tracers obtained according to the preceding
examples 1 through 4 in amounts of 0.05 to 1 % by
weight were mixed with explosives. The tracers were
accumulated from the debris of test explosions by
means of magnets. The mixture of tracers and other
ferromagnetic debris components was separated by
means of aqueous salt solutions having different
densities. The fraction which exclusively contained
the tracers were analyzed for the respective compo-
nents thereof. It was readily possible to distin-
guish the various tracer substances from each other
and, thus, to identify the used explosive.
